Patent Publication Number: US-2023151284-A1

Title: Systems and processes integrating steam cracking with dual catalyst metathesis for producing olefins

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a continuation of co-pending U.S. patent application Ser. No. 16/830,759, filed on Mar. 26, 2020 and entitled “Systems and Processes Integrating Steam Cracking with Dual Catalyst Metathesis for Producing Olefins,” the entire contents of which is incorporated by reference in the present disclosure. 
    
    
     TECHNICAL FIELD 
     Embodiments of the present disclosure generally relate to systems and processes for producing olefins from hydrocarbon feed compositions, in particular, systems and processes integrating steam cracking systems and dual catalyst metathesis systems for producing olefins. 
     BACKGROUND 
     Ethylene, propene, butene, butadiene, and aromatics compounds such as benzene, toluene and xylenes are basic intermediates for the petrochemical industry. These compounds can be produced through steam cracking (thermal cracking or steam pyrolysis) of petroleum gases and distillates such as naphtha, kerosene, or even gas oil. These compounds are also produced through refinery fluidized catalytic cracking (FCC) process where classical heavy feedstocks such as gas oils or residues are converted. Typical steam cracking feedstocks range from hydrocracked bottoms to heavy feed fractions such as vacuum gas oil and atmospheric residue; however, these feedstocks are limited. 
     The worldwide increasing demand for light olefins remains a major challenge for many integrated refineries. In particular, the production of some valuable light olefins such as ethylene, propene, and butene has attracted increased attention as purified olefin streams are considered the building blocks for polymer synthesis. The production of light olefins depends on several process variables, such as the feed type, operating conditions, and the type of catalyst. Despite the options available for producing a greater yield of propene and light olefins, intense research activity in this field is still being conducted. 
     SUMMARY 
     Steam cracking units can be used to convert hydrocarbon feed streams to light olefins, such as ethylene and propene. However, steam cracking systems can produce substantial amounts of C4+ compounds, such as mixed butenes (1-butene, trans-2-butene, cis-2-butene, isobutene) butane, and isobutane, isobutene, and 1,3-butadiene, as well as pentene, aromatic compounds, and other C5+ hydrocarbons. Production of these larger hydrocarbons may reduce the selectivity and yield of propene, ethylene, or both, from the steam cracking system. Accordingly, ongoing needs exist for processes and systems for producing olefins, such as propene and ethylene, from hydrocarbon feedstocks at greater selectivity and yield of propene, ethylene, or both, compared to commercially available steam cracking processes. Additionally, ongoing needs exist for processes and systems for producing olefins, such as propene and ethylene, from a broader spectrum of hydrocarbon feedstocks, such as feedstocks including naphtha streams or gas condensate streams. 
     The systems and processes of the present disclosure include a steam cracking system integrated with a metathesis system downstream of the steam cracking system. The steam cracking system may be operable to contact the hydrocarbon feed, such as a naphtha or gas condensate feed, with steam at a temperature sufficient to cause the hydrocarbons in the naphtha or gas condensate to undergo steam cracking (steam pyrolysis) to produce olefins, such as ethylene, propene, mixed butenes, and other C4+ compounds. A cracking C4 effluent from the steam cracking system may be selectively hydrogenated to convert 1,3-butadiene to mixed butenes and then subjected to an isobutene removal unit to remove isobutene to produce a metathesis feed comprising normal butenes. The metathesis system is a dual catalyst metathesis system comprising at least a metathesis catalyst and a cracking catalyst. The metathesis feed may be passed to a metathesis system comprising the metathesis catalyst disposed in a metathesis reaction zone and the cracking catalyst disposed in a cracking reaction zone downstream of the metathesis reaction zone. The metathesis system may be operable to convert at least a portion of the normal butenes in the metathesis feed to ethylene, propene, or both. Contact of C5+ olefins produced during metathesis with the cracking catalyst may convert at least a portion of these C5+ olefins to additional ethylene, propene, or both, which may further increase the ethylene and propene yield and selectivity of the systems and processes of the present disclosure. 
     According to one or more aspects of the present disclosure, a process for producing olefins may include contacting a hydrocarbon feed with at least steam at a temperature of from 700° C. to 900° C. The contacting may cause at least a portion of the hydrocarbon feed to undergo steam cracking to form a cracking reaction effluent comprising at least butenes. The process may further include separating the cracking reaction effluent to produce at least a cracking C4 effluent that includes at least normal butenes, isobutene, and 1,3-butadiene. The process may further include subjecting the cracking C4 effluent to selective hydrogenation to produce a hydrogenation effluent. Selective hydrogenation may cause at least a portion of the 1,3-butadiene in the cracking C4 effluent to react to form normal butenes. The process may further include removing isobutene from the hydrogenation effluent to produce a metathesis feed comprising at least normal butenes and contacting at least a portion of the metathesis feed with a metathesis catalyst and a cracking catalyst directly downstream of the metathesis catalyst to produce a metathesis reaction effluent. Contacting the metathesis feed with the metathesis catalyst may cause metathesis of normal butenes to produce at least ethylene, propene, and C5+ olefins, and contacting with the cracking catalyst may cause at least a portion of the C5+ olefins produced through metathesis to undergo cracking reactions to produce propene, ethylene, or both. The metathesis reaction effluent may include at least ethylene, propene, or both. 
     According to one or more other aspects of the present disclosure, a process for producing olefins may include contacting a hydrocarbon feed with steam in a steam cracking system at a temperature sufficient to produce a cracking reaction effluent and separating the cracking reaction effluent to produce at least a cracking C4 effluent comprising normal butenes, isobutene, and 1,3-butadiene. The process may further include subjecting the cracking C4 effluent to selective hydrogenation in a selective hydrogenation unit to produce a hydrogenation effluent. Selective hydrogenation may cause at least a portion of the 1,3-butadiene in the cracking C4 effluent to react to form normal butenes. The process may further include passing the hydrogenation effluent to an isobutene removal unit, removing isobutene from the hydrogenation effluent in the isobutene removal unit to produce at least a metathesis feed comprising normal butenes, passing at least a portion of the metathesis feed to a metathesis system comprising a metathesis catalyst and a cracking catalyst directly downstream of the metathesis catalyst, and contacting the portion of the metathesis feed with the metathesis catalyst and the cracking catalyst to produce a metathesis reaction effluent. Contacting with the metathesis catalyst may cause metathesis of normal butenes in the metathesis feed to produce at least ethylene, propene, and C5+ olefins, and contacting with the cracking catalyst may cause at least a portion of the C5+ olefins produced through metathesis to undergo cracking reactions to produce ethylene, propene, or both. The metathesis reaction effluent may comprise at least ethylene, propene, or both. 
     According to still other aspects of the present disclosure, a system for producing olefins may include a steam cracking system that may be operable to contact a hydrocarbon feed with steam at a temperature of from 700° C. to 900° C. to produce at least a cracking C4 effluent comprising normal butenes, isobutene, and 1,3-butadiene. The system may include a selective hydrogenation unit downstream of the steam cracking system. The selective hydrogenation unit may be operable to convert 1,3-butadiene in the cracking C4 effluent from the steam cracking system to normal butenes. The system may further include an isobutene removal unit downstream of the selective hydrogenation unit and a metathesis system downstream of the isobutene removal unit. The metathesis system may comprise a metathesis reaction zone comprising a metathesis catalyst and a cracking reaction zone comprising a cracking catalyst. The cracking reaction zone may be disposed directly downstream of the metathesis reaction zone. 
     Additional features and advantages of the present disclosure will be set forth in the detailed description that follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the described subject matter, including the detailed description that follows, the claims, as well as the appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following detailed description of specific aspects of the present disclosure can be best understood when read in conjunction with the following drawings, in which like structure is indicated with like reference numerals and in which: 
         FIG.  1    schematically depicts a process flow diagram for a system for producing olefins, according to one or more embodiments shown and described in the present disclosure; 
         FIG.  2    schematically depicts a process flow diagram for a steam cracking system of the system for producing olefins of  FIG.  1   , according to one or more embodiments shown and described in the present disclosure; 
         FIG.  3    schematically depicts a process flow diagram of an isobutene removal unit of the system of  FIG.  1   , according to one or more embodiments shown and described in the present disclosure; 
         FIG.  4    schematically depicts a process flow diagram of another system for producing olefins, according to one or more embodiments shown and described in the present disclosure; 
         FIG.  5    schematically depicts a process flow diagram of still another system for producing olefins, according to one or more embodiments shown and described in the present disclosure; and 
         FIG.  6    schematically depicts a process flow diagram of a system for producing olefins modeled in the Examples section, according to one or more embodiments shown and described in the present disclosure. 
     
    
    
     For purposes of describing the simplified schematic illustrations and descriptions in  FIGS.  1 - 6   , the numerous valves, temperature sensors, flow meters, pressure regulators, electronic controllers, pumps, heat exchangers, and the like that may be employed and well known to those of ordinary skill in the art of certain chemical processing operations may not be depicted. Further, accompanying components that are often included in typical chemical processing operations, such as valves, pipes, pumps, agitators, heat exchangers, condensers, boilers, instrumentation, internal vessel structures, or other subsystems may not be depicted. Though not depicted, it should be understood that these components are within the spirit and scope of the present embodiments disclosed. However, operational components, such as those described in the present disclosure, may be added to the embodiments described in this disclosure. 
     Arrows in the drawings refer to process streams. However, the arrows may equivalently refer to transfer lines, such as pipes or conduits, which may serve to transfer process streams between two or more system components. Additionally, arrows that connect to system components may define inlets or outlets in each given system component. The arrow direction corresponds generally with the major direction of movement of the materials of the stream contained within the physical transfer line signified by the arrow. Furthermore, arrows which do not connect two or more system components may signify a product stream which exits the depicted system component or a system inlet stream which enters the depicted system or system component. 
     Additionally, arrows in the drawings may schematically depict process steps of transporting a stream or composition from one system component to another system component. For example, an arrow from one system component pointing to another system component may represent “passing” a stream or composition to another system component, which may include the contents of a process stream “exiting” or being “removed” from one system component and “introducing” the contents of that product stream to another system component. 
     Reference will now be made in greater detail to various aspects of the present disclosure, some aspects of which are illustrated in the accompanying drawings. 
     DETAILED DESCRIPTION 
     The present disclosure is directed to systems and processes for producing olefins from a hydrocarbon feed, such as a naphtha feed or a gas condensate feed. Referring to  FIG.  1   , one embodiment of a system  100  for producing olefins is depicted. Referring to  FIG.  1   , the system  100  includes a steam cracking system  110 , a selective hydrogenation unit  130  disposed downstream of the steam cracking system  110 , isobutene removal unit  150  disposed downstream of the selective hydrogenation unit  130 , and a metathesis system  160  disposed downstream of the isobutene removal unit  150 . The steam cracking system  110  may be operable to contact the hydrocarbon feed  102  with steam at reaction temperatures sufficient to conduct steam cracking of the hydrocarbon feed  102 , such as temperatures from 700° C. to 900° C. The selective hydrogenation unit  130  may be operable to convert 1,3-butadiene in a cracking C4 effluent  122  from the steam cracking system  110  to normal butenes to produce a hydrogenation effluent  134 . The isobutene removal unit  150  may be operable to remove isobutene from the hydrogenation effluent  134  to produce a metathesis feed  158 . The metathesis system  160  may include a metathesis reaction zone  172  comprising a metathesis catalyst and a cracking reaction zone  174  comprising a cracking catalyst, the cracking reaction zone  174  disposed directly downstream of the metathesis reaction zone  172 . 
     Referring to  FIGS.  1  and  2   , processes for producing olefins using the systems  100  described in the present disclosure may include contacting the hydrocarbon feed  102  with steam in the steam cracking system  110  at a temperature sufficient to produce the cracking reaction effluent  117  ( FIG.  2   ) and separating the cracking reaction effluent  117  in the cracking effluent separation system  120  ( FIG.  2   ) to produce at least the cracking C4 effluent  122  comprising normal butenes, isobutene, and 1,3-butadiene. The processes may further include subjecting the cracking C4 effluent  122  to selective hydrogenation in the selective hydrogenation unit  130  to produce the hydrogenation effluent  134 . Selective hydrogenation may cause at least a portion of the 1,3-butadiene in the cracking C4 effluent  122  to react to form normal butenes. The processes may further include passing the hydrogenation effluent  134  to the isobutene removal unit  150  downstream of the selective hydrogenation unit  130  and removing isobutene from the hydrogenation effluent  134  in the isobutene removal unit  150  to produce a metathesis feed  158  comprising normal butenes. The processes may further include passing at least a portion of the metathesis feed  158  to the metathesis system  160  comprising the metathesis catalyst and the cracking catalyst directly downstream of the metathesis catalyst and contacting the portion of the metathesis feed  158  with the metathesis catalyst and the cracking catalyst to produce a metathesis reaction effluent  176 . Contacting with the metathesis catalyst may cause metathesis of normal butenes in the metathesis feed  158  to produce at least ethylene, propene, and C5+ olefins, and contacting with the cracking catalyst may cause at least a portion of the C5+ olefins produced through metathesis to undergo cracking reactions to produce additional ethylene, propene, or both. The metathesis reaction effluent  176  may include at least ethylene, propene, or both. The systems and processes of the present disclosure may increase the yield of propene, ethylene, or both, from steam cracking of hydrocarbon feeds  102  that include naphtha and gas condensates. 
     The term “or”, as used in the present disclosure, is inclusive; more specifically, the phrase “A or B” means “A, B, or both A and B.” Exclusive “or” is designated in the present disclosure by terms such as “either A or B” and “one of A or B,” for example. 
     The indefinite articles “a” and “an” are employed to describe elements and components of the present disclosure. The use of these articles means that one or at least one of these elements or components is present. Although these articles are conventionally employed to signify that the modified noun is a singular noun, as used herein the articles “a” and “an” also include the plural, unless otherwise stated in specific instances. Similarly, the definite article “the”, as used in the present disclosure, also signifies that the modified noun may be singular or plural, again unless otherwise stated in specific instances. 
     As used throughout the present disclosure, the terms “upstream” and “downstream” refer to the positioning of components or units of the system  100  relative to a direction of flow of materials through the system  100 . For example, a first component may be considered “upstream” of a second component if materials flowing through the system  100  encounter the first component before encountering the second component. Likewise, the second component is considered “downstream” of the first component if the materials flowing through the system  100  encounter the first component before encountering the second component. 
     As used in the present disclosure, reciting that a stream is passed “directly” from an upstream component to a downstream component may refer to passing the stream from the upstream component to the downstream component without passing the stream through an intervening unit operation operable to change the composition or characteristics of the stream. Intervening unit operations can include reactors and separation units but are not generally intended to include ancillary equipment, such as but not limited to heat exchangers, valves, pumps, sensors, or other process equipment required for operation of a chemical process. 
     As used in the present disclosure, the term “fluid” may be used to refer to a flowable composition that includes gases, liquids, or a combination of these. 
     As used throughout the present disclosure, a “reactor” refers to a vessel in which one or more chemical reactions may occur between one or more reactants, optionally, in the presence of one or more catalysts. For example, a reactor may include a tank or tubular reactor configured to operate as a batch reactor, a continuous stirred-tank reactor (CSTR), a plug flow reactor, a packed bed reactor, a fluidized bed reactor, continuous fluidized bed reactor, a riser reactor, downer reactor, or other type of reactor. One or more “reaction zones” may be disposed in a reactor. As used in this disclosure, a “reaction zone” may refer to a region where a particular reaction takes place in a reactor. For example, a packed bed reactor with multiple catalyst beds may have multiple reaction zones, where each reaction zone is defined by the region occupied by one of the catalyst beds. In another non-limiting example, a multi-stage catalyst reaction system may include multiple reactors, and each reactor may define a separate “reaction zone.” 
     As used throughout the present disclosure, the terms “separation unit” and “separator” may be interchangeable and may refer to any separation device that at least partially separates one or more chemicals that are mixed in a process stream from one another. For example, a separation unit may selectively separate differing chemical species from one another, forming one or more chemical fractions. Examples of separation units include, without limitation, distillation columns, flash drums, knock-out drums, knock-out pots, centrifuges, cyclones, filtration devices, traps, scrubbers, expansion devices, adsorption units, membrane separation units, thin film evaporators, solvent extraction devices, and the like. As used throughout the present disclosure, the term “separation system” may refer to a system that includes one or a plurality of separation units, which may be operated in series, parallel, or both. 
     It should be understood that separation units and separation systems described in this disclosure may not completely separate all of one chemical constituent from all of another chemical constituent. It should be understood that the separation units and separation systems described in this disclosure “at least partially” separate different chemical components from one another, and that even if not explicitly stated, it should be understood that separation may include only partial separation. As used in this disclosure, one or more chemical constituents may be “separated” from a process stream to form a new process stream. Generally, a process stream may enter a separation unit and be divided, or separated, into two or more process streams of different compositions. A process stream passed out of a separation unit or separation system may be designated using the name of a certain compound or class of compounds present in the process stream and may be considered to include a greater proportion of that certain compound or class of compounds relative to other streams passed out of the separation unit or separation system. It is understood, however, that the other streams passed out of the separation unit or separation system may also include some amounts of the certain compound or class of compounds. 
     As used throughout the present disclosure, the term “residence time” may refer to the amount of time that the reactants are maintained in contact with each other or, optionally, with a catalyst at reaction conditions, such as at the reaction temperature, in a reaction system. 
     As used throughout the present disclosure, the term “effluent” may refer to a stream that exits a system component such as a separation unit, a reactor, or reaction zone, following a particular reaction or separation, and generally has a different composition (at least proportionally) from the stream that entered the separation unit, reactor, or reaction zone. 
     As used throughout the present disclosure, a “catalyst” may refer to any substance that increases the rate of a specific chemical reaction. Catalysts described in this disclosure may be utilized to promote various reactions, such as, but not limited to, cracking reactions, metathesis reactions, isomerization reactions, hydrogenation reactions, etherification reactions, or other chemical reactions. 
     As used in this disclosure, “cracking” may generally refer to a chemical reaction where a molecule having carbon to carbon bonds is broken into more than one molecule by the breaking of one or more of the carbon to carbon bonds, or is converted from a compound which includes a cyclic moiety, such as a cycloalkane, cycloalkene, naphthalene, an aromatic or the like, to a compound which does not include a cyclic moiety or contains fewer cyclic moieties than prior to cracking. 
     It should further be understood that streams may be named for the components of the stream, and the component for which the stream is named may be the major component of the stream (such as comprising from 50 weight percent (wt. %), from 70 wt. %, from 90 wt. %, from 95 wt. %, from 99 wt. %, from 99.5 wt. %, or even from 99.9 wt. % of the contents of the stream to 100 wt. % of the contents of the stream). It should also be understood that components of a stream are disclosed as passing from one system component to another when a stream comprising that component is disclosed as passing from that system component to another. For example, a disclosed “steam cracking C4 effluent” passing from a first system component to a second system component should be understood to equivalently disclose the “steam cracking C4 effluent” passing from a first system component to a second system component. 
     As used in the present disclosure, the terms “butenes” or “mixed butenes” may be used interchangeably and may refer to combinations of one or a plurality of isobutene, 1-butene, trans-2-butene, or cis-2-butene. As used in the present disclosure, the term “normal butenes” may refer to a combination of one or a plurality of 1-butene, trans-2-butene, or cis-2-butene. 
     As used in the present disclosure, the term “C4” may be used to refer to compounds having 4 carbon atoms, and the term “C5+” may be used to refer to compounds having 5 or more than 5 carbon atoms. 
     Referring again to  FIG.  1   , the system  100  for producing olefins, such as but not limited to propene and ethylene, may include the steam cracking system  110 , the selective hydrogenation unit  130  downstream of the steam cracking system  110 , the isobutene removal unit  150  downstream of the selective hydrogenation unit  130 , and the metathesis system  160  downstream of the isobutene removal unit  150 . The steam cracking system  110  may be operable to contact the hydrocarbon feed  102  with steam under reaction conditions sufficient to cause at least a portion of the hydrocarbon feed  102  to undergo thermal cracking reactions to produce olefins, such as but not limited to ethylene, propene, butenes, or combinations of these. 
     The hydrocarbon feed  102  may include a mixture of hydrocarbon materials. The hydrocarbon materials of the hydrocarbon feed  102  may include hydrocarbons derived from crude oil. As used in this disclosure, the term “crude oil” may be understood to mean a mixture of petroleum liquids and gases, including impurities such as sulfur-containing compounds, nitrogen-containing compounds and metal compounds, as distinguished from fractions of crude oil. The hydrocarbon feed  102  may include, but may not be limited to, crude oil, vacuum residue, tar sands, bitumen, atmospheric residue, vacuum gas oils, demetalized oils, naphtha streams, gas condensate streams, or combinations of these materials. The hydrocarbon feed stream  102  may include one or a plurality of non-hydrocarbon constituents, such as one or more heavy metals, sulphur compounds, nitrogen compounds, inorganic components, or other non-hydrocarbon compounds. In embodiments, the hydrocarbon feed  102  may be pretreated to remove the non-hydrocarbon constituents and other contaminants. The hydrocarbon feed  102  may be a naphtha stream, a gas condensate stream, or a combination of these. As used in the present disclosure, the term “naphtha” may refer to an intermediate hydrocarbon composition derived from crude oil refining and having a boiling point temperature of from 35° C. to 200° C. Naphtha streams may include paraffinic, naphthenic, and aromatic hydrocarbons having from 4 to 11 carbon atoms. In embodiments, the hydrocarbon feed  102  may be a naphtha stream comprising an Arab Extra Light (AXL) feedstock. 
     As used in the present disclosure, the term “gas condensate” may refer to a mixture of liquid hydrocarbons having a specific gravity of from 0.5 to 0.8 and derived from raw natural gas produced from natural gas fields. Gas condensates may include paraffinic hydrocarbons having from 3 to 12 carbon atoms and lesser amounts of naphthenic and aromatic compounds compared to naphtha streams. Hydrocarbons with greater than 12 carbon atoms may also be present. The gas condensate may include at least 70 wt. %, at least 75 wt. %, or even at least 80 wt. % hydrocarbons having a boiling point temperatures less than 265° C. The gas condensates may include greater boiling hydrocarbons recovered from raw natural gas as a condensate in a natural gas processing plant. In embodiments, the gas condensate may be a Khuff gas condensate (KGC) recovered from natural gas extracted from the Khuff reservoir in Saudi Arabia. Table 1 provides boiling point profile data for Khuff gas condensate. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Boiling Point Temperature Profile for Khuff Gas Condensate 
               
            
           
           
               
               
               
               
            
               
                   
                   
                 Cummulative 
                   
               
               
                 Boiling Point (BP) 
                 Weight 
                 Weight 
                 Volume 
               
               
                 Temperature Range 
                 Percent 
                 Percent 
                 Percent 
               
            
           
           
               
               
               
               
               
            
               
                 Initial BP (° C.) 
                 Final BP (° C.) 
                 wt. % 
                 wt. % 
                 vol. % 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 C5 (35) 
                 70 
                 12.9 
                 12.9 
                 15.36 
               
               
                 70 
                 185 
                 47.32 
                 60.22 
                 48.15 
               
               
                 185 
                 265 
                 19.9 
                 80.12 
                 18.79 
               
               
                 265 
                 345 
                 12.14 
                 92.26 
                 10.99 
               
               
                 345 
                 460 
                 6.87 
                 99.13 
                 6.04 
               
               
                 460 
                 565 
                 0.29 
                 99.42 
                 0.25 
               
               
                 565 
                 1000 
                 0.56 
                 99.98 
                 0.41 
               
               
                   
               
            
           
         
       
     
     In one or more embodiments, one or more supplemental feed streams (not shown) may be added to the hydrocarbon feed  102  prior to introducing the hydrocarbon feed  102  to the steam cracking system  110  or introduced independently to the steam cracking system  110  in addition to the hydrocarbon feed  102 . For example, the hydrocarbon feed  102  may include a naphtha stream, a gas condensate, or a combination of these, and a supplemental stream, such as one or a plurality of a vacuum residue, atmospheric residue, vacuum gas oils, demetalized oils, or other hydrocarbon streams, or combinations of these materials, may be combined with the hydrocarbon feed  102  upstream of the steam cracking system  110  or introduced independently to the steam cracking system  110 . 
     Referring now to  FIG.  2   , the steam cracking system  110  is schematically depicted. The steam cracking system  110  may include a steam cracking reactor  111  and a cracking effluent separation system  120  disposed downstream of the steam cracking reactor  111 . The steam cracking system  110  may additionally include a heat exchanger  116  disposed between the steam cracking reactor  111  and the cracking effluent separation system  120 . The steam cracking reactor  111  may be operable to heat the hydrocarbon feed  102  and contact the hydrocarbon feed  102  with steam  104  at a reaction temperature sufficient to cause at least a portion of the hydrocarbons in the hydrocarbon feed  102  to undergo thermal cracking to produce a cracking reaction effluent  117  comprising olefins. 
     The hydrocarbon feed  102  and steam  104  may be passed directly to the steam cracking reactor  111 . Other hydrocarbon containing streams, such as hydrotreated effluent  142 , may also be passed to the steam cracking reactor  111 , as will be described subsequently in this disclosure. The steam cracking reactor  111  may include a convection zone  112  and a pyrolysis zone  114  downstream of the convection zone  112 . At least the hydrocarbon feed  102  and the steam  104  may pass into the convection zone  112 . The flowrate of steam  104  passed into the convection zone  112  may be sufficient to conduct steam pyrolysis in the pyrolysis zone  114  downstream of the convection zone  112 . The flowrate of steam  104  into the convection zone  112  may be sufficient to maintain a mass ratio of steam to hydrocarbons in the steam cracking reactor  111  of from 0.3:1 to 2:1. In the convection zone  112 , the hydrocarbon feed  102  (and any other hydrocarbon streams passed to the convection zone  112 ) may be pre-heated to a pre-heat temperature. The pre-heat temperature of the convection zone  112  may be from 400 degrees Celsius (° C.) to 650° C. 
     The contents present in the convection zone  112  (at least the hydrocarbon feed  102  and the steam  104 ) may be passed to the pyrolysis zone  114  downstream of the convection zone  112 . In the pyrolysis zone  114 , at least the hydrocarbon feed  102  and any other hydrocarbons introduced to the steam cracking reactor  111  may be contacted with the steam  104  at reaction conditions sufficient to cause at least a portion of the hydrocarbons to undergo steam cracking (also known as steam pyrolysis) to produce a pyrolysis zone effluent  115 . The pyrolysis zone  114  may operate at a temperature of from 700° C. to 900° C. The pyrolysis zone  114  may operate with a residence time of from 0.05 seconds to 2 seconds, where the residence time is the duration of time that the hydrocarbons are in contact with the steam at the reaction temperature of from 700° C. to 900° C. The mass ratio of steam  104  to hydrocarbons in the pyrolysis zone  114  may be from about 0.3:1 to about 2:1. 
     The pyrolysis zone effluent  115  may exit the pyrolysis zone  114  of the steam cracking reactor  111  and may be passed through a heat exchanger  116  downstream of the steam cracking reactor  111 . In the heat exchanger  116 , a process fluid  118 , such as water, pyrolysis fuel oil, or other process stream, may cool the pyrolysis zone effluent  115  to form the cracking reaction effluent  117 . The cracking reaction effluent  117  may include a mixture of cracked hydrocarbon-based materials which may be separated into one or more petrochemical products included in one or more system product streams. For example, the cracking reaction effluent  117  may include at least mixed butenes (1-butene, trans-2-butene, cis-2-butene, isobutene, or combinations of these). The cracking reaction effluent  117  may also include other olefins, such as but not limited to ethylene, propylene, 1,3-butadiene, C5+ olefins, or combinations of these; light gases, such as but not limited to methane, hydrogen, and steam; saturated hydrocarbons, such as but not limited to ethane, propane, butane, isobutane, C5+ alkanes, or combinations of these; and aromatic compounds, such as but not limited to benzene, toluene, ethylbenzene, xylenes, or other aromatic compounds. 
     Referring again to  FIG.  2   , the cracking reaction effluent  117  may be passed to the cracking effluent separation system  120 . As previously discussed, the cracking reaction effluent  117  may include a mixture of cracked hydrocarbon materials. In particular, the cracking reaction effluent  117  may include at least ethylene, propene, and one or a plurality of C4 compounds, such as but not limited to mixed butenes (1-butene, trans-2 butene, cis-2-butene, isobutene). The cracking reaction effluent  117  may also include one or a plurality of fuel gas, fuel oil, pyrolysis gas, gasoline, dienes such as 1,3-butadiene or propadiene, methane, ethane, propane, butane, pentane, other C5+ hydrocarbons, light cycle oil (LCO, 216-343° C.), heavy cycle oil (HCO, &gt;343° C.), other compounds, or combinations of these. The cracking reaction effluent  117  may also include other gases from the steam cracking reactor  111 , such as steam introduced to the steam cracking reactor  111  or other gases passing through or generated in the steam cracking reactor  111 . In embodiments, the cracking reaction effluent  117  may include at least fuel gas, ethylene, propene, normal butenes, isobutene, 1,3-butadiene, n-butane, fuel oil, and pyrolysis gas. 
     The cracking effluent separation system  120  may be fluidly coupled to the steam cracking reactor  111  such that the cracking reaction effluent  117  may be passed directly from the steam cracking reactor  111  to the cracking effluent separation system  120 . The cracking effluent separation system  120  may be operable to separate the cracking reaction effluent  117  into a plurality of cracking effluent streams that include at least a cracking C4 effluent  122 . The cracking effluent separation system  120  may include one or a plurality of separation units operable to separate the cracking reaction effluent  117  into a plurality of cracking effluents. Separation units may include, but are not limited to, flash drums, high-pressure separators, distillation units, fractional distillation units, condensing units, strippers, quench units, debutanizers, depropanizers, de-ethanizers, or combinations of these. In one or more embodiments, the cracking effluent separation system  120  may include a fractional distillation unit operable to separate the cracking reaction effluent  117  to produce at least the cracking C4 effluent  122 . The cracking C4 effluent  122  may include one or a plurality of n-butane, isobutane, 1,3-butadiene, normal butenes (1-butene, trans-2-butene, cis-2-butene), isobutene, or combinations of these. The cracking C4 effluent  122  may also include small amounts of one or more other compounds present in the cracking reaction effluent  117 . The cracking C4 effluent  122  may include at least 90%, at least 95%, at least 98%, or even at least 99% by weight of the C4 compounds from the cracking reaction effluent  117 . The cracking C4 effluent  122  may include at least 90%, at least 95%, at least 98%, or even at least 99% by weight of the normal butenes from the cracking reaction effluent  117 . 
     The cracking effluent separation system  120  may also be operable to separate the cracking reaction effluent  117  into a greater boiling temperature effluent  124  ( FIG.  1   ), a cracking propene effluent  126 , a cracking ethylene effluent  128 , a lesser molecular weight gas effluent  129 , or combinations of these. The greater boiling temperature effluent  124  may include constituents of the cracking reaction effluent  117  having a boiling point temperature greater than the boiling point temperatures of the constituents of the cracking C4 effluent  122 . The greater boiling temperature effluent  124  may include one or a plurality of fuel oil, pyrolysis gas, gasoline, pentane, other C5+ hydrocarbons, light cycle oil (LCO, having a boiling point temperature of 216° C. to 343° C.), heavy cycle oil (HCO, having a boiling point temperature of greater than 343° C.), other compounds, or combinations of these. The greater boiling temperature effluent  124  may also include small amounts of C4 hydrocarbons not separated into the cracking C4 effluent  122 . In embodiments, the greater boiling temperature effluent  124  may include at least fuel oil and pyrolysis gas. The cracking effluent separation system  120  may be further operable to separate the greater boiling temperature effluent  124  into fuel oil  123  and pyrolysis gas  125 . 
     The cracking propene effluent  126  may include propene as a primary component. The cracking propene effluent  126  may include at least 90%, at least 95%, at least 98%, or even at least 99% by weight of the propene from the cracking reaction effluent  117 . The cracking ethylene effluent  128  may include ethylene as a primary component. The cracking ethylene effluent  128  may include at least 90%, at least 95%, at least 98%, or even at least 99% by weight of the ethylene from the cracking reaction effluent  117 . The lesser molecular weight gas effluent  129  may include other lesser boiling gases from the cracking reaction effluent  117 , such as but not limited to fuel gases such as methane and hydrogen; inert gases such as nitrogen; or other gases having a boiling point temperature less than the boiling point temperatures of ethylene and propene. One or a plurality of the greater boiling temperature effluent  124 , fuel oil  123 , pyrolysis gas  125 , cracking propene effluent  126 , cracking ethylene effluent  128 , lesser molecular weight gas effluent  129 , or combinations of these may be passed to one or more additional downstream unit operations for further processing. Steam may also be recovered from the cracking reaction effluent  117 . 
     Referring again to  FIG.  1   , the cracking C4 effluent  122  may be passed to the selective hydrogenation unit  130  disposed downstream of the steam cracking system  110 . The selective hydrogenation unit  130  may be fluidly coupled to an outlet of the cracking effluent separation system  120  so that the cracking C4 effluent  122  can be passed directly from the cracking effluent separation system  120  to the selective hydrogenation unit  130 . As previously discussed, the cracking C4 effluent  122  may include 1,3-butadiene, which may produce unwanted metathesis products when contacted with the metathesis catalyst in the metathesis system  160  downstream of the steam cracking system  110 . In embodiments, the cracking C4 effluent  122  may include up to 60 wt. % 1,3-butadiene, such as from 1 wt. % to 60 wt. %, or from 10 wt. % to 50 wt. % 1,3-butadiene, based on the total weight of the cracking C4 effluent  122 . 
     The selective hydrogenation unit  130  may be a selective butadiene hydrogenation unit operable to react at least a portion of the 1,3-butadiene in the cracking C4 effluent  122  to form normal butenes, such as 1-butene, trans-2-butene, cis-2-butene, or combinations of these. Converting the 1,3-butadiene to normal butenes may increase the yield of propene and ethylene from the system  100  by providing a greater amount of normal butenes for metathesis to propene and ethylene in the metathesis system  160  downstream of the selective hydrogenation unit  130 . The selective hydrogenation unit  130  may be selective for hydrogenating 1,3-butadiene relative to hydrogenation of normal butenes so that the 1,3-butadiene can be hydrogenated to normal butenes without further hydrogenation of the normal butenes produced to n-butane or substantial hydrogenation of the normal butenes from the cracking C4 effluent  122  to n-butane. The selective hydrogenation unit may be operable to convert greater than or equal to 90% by weight, greater than or equal to 93% by weight, or even greater than or equal to 95% by weight of the 1,3-butadiene present in the cracking C4 effluent  122  to 1-butene and 2-butene. The selectivity for 1-butene and 2-butene can be tuned by carbon monoxide injection as further discussed subsequently in the present disclosure. 
     The selective hydrogenation unit  130  may include one or a plurality of hydrogenation reactors, such as 1, 2, 3, or more than 3 hydrogenation reactors. When the selective hydrogenation unit  130  includes a plurality of hydrogenation reactors, the hydrogenation reactors may be operated in series or in parallel. In embodiments, the selective hydrogenation unit  130  may include two or more hydrogenation reactors to achieve more than 99% conversion of 1,3-butadiene. Each of the hydrogenation reactors of the selective hydrogenation unit  130  may include at least one hydrogenation reaction zone comprising a selective hydrogenation catalyst. Each of the hydrogenation reactors of the selective hydrogenation unit  130  may be a fixed bed reactor comprising the selective hydrogenation catalyst. 
     The selective hydrogenation catalyst may include a catalytic metal supported on an alumina catalyst support. The catalytic metal may include one or more metals in Groups 8-11 of the International Union of Pure and Applied Chemistry (IUPAC) periodic table of elements (IUPAC periodic table). For example, the catalytic metal of the selective hydrogenation catalyst may include one or more of platinum, rhodium, palladium, ruthenium, cobalt, nickel, copper, or combinations of these metals. The selective hydrogenation catalyst may include from 0.3 wt. % to 0.5 wt. % catalytic metal based on the total weight of the selective hydrogenation catalyst. 
     Referring again to  FIG.  1   , in operation, the cracking C4 effluent  122  may be passed to the selective hydrogenation unit  130 , in which the cracking C4 effluent  122  may be contacted with hydrogen in the presence of the selective hydrogenation catalyst. The hydrogen may be provided by hydrogen stream  132 , which may be introduced to one or more of the hydrogenation reactors of the selective hydrogenation unit  130  or combined with the cracking C4 effluent  122  upstream of the selective hydrogenation unit  130 . The cracking C4 effluent  122  may be contacted with hydrogen in the presence of the selective hydrogenation catalyst at a hydrogenation reaction temperature of from 50° C. to 100° C. and a hydrogenation reaction pressure of from 965 kilopascals (kPa) to 2758 kPa, such as from 1500 kPa to 2500 kPa. The hydrogenation reactors of the selective hydrogenation unit  130  may be operated at a weight hourly space velocity (WHSV) of from 2 per hour to 4 per hour. Contacting the cracking C4 effluent  122  with hydrogen in the presence of the selective hydrogenation catalyst may cause at least a portion of the 1,3-butadiene to undergo selective hydrogenation to produce a hydrogenation effluent  134 . The hydrogenation effluent  134  may have a concentration of 1,3-butadiene less than a concentration of 1,3-butadiene in the cracking C4 effluent  122 . In embodiments, the hydrogenation effluent  134  may have a greater concentration of one or more of 1-butene, trans-2-butene, or cis-2-butene compared to the concentration of these constituents in the cracking C4 effluent  122 . The conversion rate of 1,3-butadiene to normal butenes may be greater than or equal to 90% by weight of the 1,3-butadiene in the cracking C4 effluent  122 , such as greater than or equal to 93%, greater than or equal to 94%, or even greater than or equal to 95% by weight of the 1,3-butadiene from the cracking C4 effluent  122 . 
     In embodiments, the selective hydrogenation unit  130  can include three reactor stages, such as three hydrogenation reactors, in series. The first two hydrogenation reactors can convert the 1,3-butadiene present in the cracking C4 effluent  122  to 1-butene, cis-2-butene, trans-2-butene, or combinations of these. The first two hydrogenation reactors can include the selective hydrogenation catalyst, such as palladium supported on alumina. The selective hydrogenation catalyst can be the same for the first two hydrogenation reactors. The hydrogen stream  132  can be combined with the cracking C4 effluent  122  upstream of the first hydrogenation reactor of the selective hydrogenation unit  130 . The third hydrogenation reactor may also include a selective hydrogenation catalyst, which may be the same as or different from the selective hydrogenation catalyst in the first two hydrogenation reactors. The hydrogenation effluent  134  may be passed out of the selective hydrogenation unit  130  to downstream operations, such as the isobutene removal unit  150 . 
     As previously discussed, the cracking C4 effluent  112  from the steam cracking system  110  may include isobutene, which may have a negative impact on the propene selectivity and yield of the system  100 . Isobutene may undergo cross-metathesis with 1-butene or 2-butene. Cross-metathesis between isobutene and 2-butene produces propene and 2-methyl-2-butene, which is productive for producing propene. However, cross-metathesis between isobutene and 1-butene produces ethylene and 2-methy-2-pentene with no propene produced. Therefore, the presence of isobutene in the metathesis feed  142  may operate to reduce the selectivity and yield of propene from the system  100 . 
     Referring again to  FIG.  1   , to increase the selectivity and yield of propene, the system  100  may include the isobutene removal unit  150  disposed downstream of the selective hydrogenation unit  130 . The isobutene removal unit  150  may be disposed between the selective hydrogenation unit  130  and the metathesis system  160  such that the isobutene removal unit  150  is downstream of the selective hydrogenation unit  130  and the metathesis system  160  is downstream of the isobutene removal unit  150 . The hydrogenation effluent  134  may be passed directly from the selective hydrogenation unit  130  to the isobutene removal unit  150 . The isobutene removal unit  150  may be operable to receive the hydrogenation effluent  134  from the selective hydrogenation unit  130  and remove isobutene from the hydrogenation effluent  134  to produce the metathesis feed  158 , which may have a decreased concentration of isobutene compared to the hydrogenation effluent  134 . 
     Referring to  FIG.  3   , the isobutene removal unit  150  may include a methyl-tert-butyl ether reactor  200  (MTBE reactor  200 ), which may be operable to convert at least a portion of the isobutene to methyl-tert-butyl ether (MTBE). The isobutene removal unit  150  may also include an MTBE separation system  210  disposed downstream of the MTBE reactor  200 . MTBE reactor  200  may include a cation exchange resin or an acid catalyst. The MTBE reactor  200  may be operable to contact the hydrogenation effluent  134  and methanol from a methanol feed  156  in the presence of the cation exchange resin or acid catalyst at reaction conditions sufficient to convert at least a portion of the isobutene in the hydrogenation effluent  134  to MTBE. The MTBE reactor  200  may be maintained at a temperature of from 35° C. to 100° C. Contacting the hydrogenation effluent  134  with the methanol in the presence of the cation exchange resin or acid catalyst in the MTBE reactor  200  may cause at least a portion of the isobutene in the hydrogenation effluent  134  to undergo etherification to produce MTBE. 
     An MTBE reactor effluent  202 , which may include at least the MTBE, excess methanol, and the unreacted constituents of the hydrogenation effluent  134 , may be passed to the MTBE separation system  210  downstream of the MTBE reactor  200 . The MTBE reactor effluent  202  may include a concentration of isobutene less than the concentration of isobutene in the hydrogenation effluent  134 . The MTBE separation system  210  may include one or a plurality of separation units operable to separate the MTBE reactor effluent  202  into at least the metathesis feed  158  and an MTBE effluent  152 . The metathesis feed  158  and the MTBE effluent  152  may comprise at least 95 percent by weight of the constituents of the MTBE reactor effluent  202 . The MTBE effluent  152  may include at least 80%, at least 90%, at least 95%, or even at least 98% of the MTBE produced in the MTBE reactor  200 . The metathesis feed  158  may include at least 90%, at least 95%, at least 98%, or even at least 99% of the normal butenes from the hydrogenation effluent  134 . In embodiments, the MTBE separation system  210  may be operable to produce a methanol effluent  157  comprising at least a portion of the excess methanol from the MTBE reaction, which may be recycled back to the MTBE reactor  200 . Referring again to  FIG.  1   , the metathesis feed  158  may be passed to the metathesis system  160  disposed downstream of the isobutene removal unit  150 . The MTBE effluent  152  may be passed out of the system  100  to one or more downstream unit operations for further processing. The MTBE from the MTBE effluent  152  may be recovered and sold as a product or as an intermediate chemical for use in chemical processing operations. 
     Referring again to  FIG.  3   , in embodiments, the isobutene removal unit  150  may include an MTBE catalytic cracking unit  220  disposed downstream of the MTBE separation system  210 . The MTBE catalytic cracking unit  220  may be operable to receive at least a portion of the MTBE effluent  152  and contact the portion of the MTBE effluent  152  with a cracking catalyst under conditions sufficient to convert the MTBE back into isobutene. The MTBE catalytic cracking unit  220  may be a fixed bed reactor comprising an MTBE cracking reaction zone that includes the cracking catalyst. The cracking catalyst may be any catalyst capable of catalyzing the cracking of MTBE back to isobutene. The cracking catalyst may be a zeolite. In embodiments, the cracking catalyst may be a structured zeolite, such as MFI or BEA structured zeolite, for example. The cracking catalyst may be an MCM-41 catalyst or an SBA-15 catalyst. In embodiments, the cracking catalyst may be an MFI structured silica-containing catalyst. Contacting the portion of the MTBE effluent  152  with the cracking catalyst in the MTBE catalytic cracking unit  220  may cause the MTBE in the MTBE effluent  152  to undergo catalytic cracking to produce an isobutene effluent  154 . 
     Referring again to  FIG.  1   , the isobutene effluent  154  may be passed to a hydrotreating unit  140 , in which the isobutene in the isobutene effluent  154  may be saturated before being passed back to the steam cracking system  110  as part of the hydrotreated effluent  142 . The hydrotreating unit  140  and operation of the hydrotreating unit  140  to saturate isobutene and C5+ olefins from the metathesis system  160  will be discussed in further detail subsequently in this disclosure. Thus, cracking at least a portion of the MTBE effluent  152  back to isobutene, saturating the isobutene effluent  154  in the hydrotreating unit  140 , and passing the resulting hydrocarbon compounds back to the steam cracking system  110  may increase the overall conversion and propene selectivity and yield of the system  100  compared to removing all of the MTBE effluent  152  from the system  100 . 
     Referring again to  FIG.  1   , the system  100  includes the metathesis system  160  disposed downstream of the isobutene removal unit  150 . The metathesis system  160  may be operable to contact the metathesis feed  158  with at least a metathesis catalyst in a metathesis reactor  170  to produce a metathesis reaction effluent  176  comprising one or more olefins, such as but not limited to ethylene, propene, pentene, or combinations of these. The metathesis system  160  may be operable to contact the metathesis feed  158  with a multiple catalyst system comprising a metathesis catalyst and a cracking catalyst downstream of the metathesis catalyst to produce the metathesis reaction effluent. The metathesis system  160  may also be operable to separate the metathesis reaction effluent  176  into one or more metathesis effluent streams. 
     Referring again to  FIG.  1   , the metathesis system  160  may include at least one metathesis reactor  170  and a metathesis effluent separation system  180  downstream of the metathesis reactor  170 . In embodiments, the metathesis system  160  may also include a metathesis feed treatment unit (not shown), which may be operable to remove impurities from the metathesis feed  158 . The metathesis feed treatment unit may include one or more catalysts and may remove impurities such as, but not limited to, butadiene and other dienes, oxygenates such as carbonyls and alcohols, sulfur compounds, water, other impurities, or combinations of these. 
     The metathesis reactor  170  may be operable to receive the metathesis feed  158  (treated or not treated) and contact the metathesis feed  158  with at least the metathesis catalyst. Contacting the metathesis feed  158  with the metathesis catalyst may cause at least a portion of the mixed butenes from the metathesis feed  158  to undergo at least a metathesis reaction to produce a metathesis reaction effluent  176  that includes one or more metathesis reaction products. The metathesis reactor  170  may also be operable to contact the metathesis feed  158  with the metathesis catalyst and a cracking catalyst downstream of the metathesis catalyst. The metathesis effluent separation system  180  may be operable to receive the metathesis reaction effluent  176  from the metathesis reactor  170  and separate the metathesis reaction effluent  176  into one or a plurality of metathesis effluent streams. Alternatively, the metathesis reaction effluent  176  and the cracking reaction effluent  117  may be passed to a single separation system, such as but not limited to a combined separation system  300  ( FIG.  5   ). 
     As used throughout the present disclosure, “metathesis” refers to an organic reaction that involves the redistribution of fragments of alkenes by the scission and regeneration of carbon-carbon double bonds. As used throughout the present disclosure, a “metathesis catalyst” may refer to a catalyst that promotes the metathesis reaction of alkenes to form other alkenes. Contact of butenes with a metathesis catalyst may result in conversion of 2-butene to 1-butene or conversion of 1-butene to 2-butene through “self-metathesis,” which is shown in Chemical Reaction 1 (RXN 1). Self-metathesis of 2-butene to 1-butene and 1-butene to 2-butene by the metathesis catalyst may be an equilibrium reaction as denoted by the bi-directional arrows with single heads in RXN 1. 
     
       
         
         
             
             
         
       
     
     Contact of a mixture of normal butenes (1-butene, trans-2-butene, cis-2-butene, or combinations of these) with the metathesis catalyst may also result in cross-metathesis of 1-butene and 2-butene. As used in the present disclosure, the term “2-butene” may refer to trans-2-butene, cis-2-butene, or a mixture of these. Cross-metathesis between 1-butene and 2-butene may be achieved with the metathesis catalyst as shown in Chemical Reaction 2 (RXN 2). In the case of cross-metathesis of 2-butene and 1-butene, the redistribution of these carbon-carbon double bonds through metathesis may produce propene and C 5 -C 6  olefins. 
     
       
         
         
             
             
         
       
     
     Further, as shown in the following Chemical Reaction 3 (RXN 3), “catalytic cracking” may refer to catalytic conversion of C 4 -C 6  alkenes to propene and other alkanes, alkenes, or alkanes and alkenes, for example, C 1 -C 2  alkenes (propene, ethylene, or both). Catalytic conversion of C4-C6 alkenes to propene and other alkanes, alkenes, or alkanes and alkenes may further increase the yield of propene and ethylene from the metathesis system  160 . 
     
       
         
         
             
             
         
       
     
     Referring to Chemical Reactions RXN 1-RXN 3, the metathesis and cracking reactions are not limited to these reactants and products; however, Chemical Reactions RXN 1-RXN 3 provide a simplified illustration of the reaction methodology. 
     The metathesis feed  158  passed to the metathesis system  160  may be any composition or stream comprising butenes, such as 1-butene, cis-2-butene, trans-2-butene, or combinations of these isomers of butene. The metathesis feed  158  may also include other C4 hydrocarbons, such as n-butane, iso-butane, or combinations of these. The metathesis feed  158  may also include any 1,3-butadiene or isobutene not reacted in the selective hydrogenation unit  130  or the isobutene removal unit  150 , respectively. The metathesis feed  158  may include at least a portion of the cracking C4 effluent  122  from the steam cracking system  110 . In embodiments, the metathesis feed  158  may be passed directly from the isobutene removal unit  150 , such as the MTBE separation system  210 , to the metathesis system  160 . 
     The metathesis feed  158  may include from 10 weight percent (wt. %) to 70 wt. %, from 10 wt. % to 60 wt. %, from 10 wt. % to 50 wt. %, from 20 wt. % to 70 wt. %, from 20 wt. % to 60 wt. %, or from 20 wt. % to 50 wt. % 2-butene based on the total weight of the metathesis feed  158 . The metathesis feed  158  may include from 5 wt. % to 70 wt. %, from 5 wt. % to 60 wt. %, from 10 wt. % to 70 wt. %, from 10 wt. % to 60 w. %, from 10 wt. % to 50 wt. %, from 15 wt. % to 70 wt. %, from 15 wt. % to 60 wt. %, or from 15 wt. % to 50 wt. % 1-butene based on the total weight of the metathesis feed  158 . The metathesis feed  158  may include from 5 wt. % to 30 wt. % or 10 wt. % to 25 wt. % n-butane based on the total weight of the metathesis feed  158 . The metathesis feed  158  may include at least 90%, at least 95%, at least 98%, or even at least 99% of the normal butenes from the cracking reaction effluent  117 . 
     In embodiments, the metathesis feed  158  may be substantially free of ethylene. As used in the present disclosure, the term “substantially free” of a component means less than 1 weight percent (wt. %) of that component in a particular portion of a catalyst, stream, or reaction zone. As a non-limiting example, a metathesis feed  158  that is substantially free of ethylene, may have less than 1 wt. % of ethylene based on the total weight of the metathesis feed  158 . The metathesis feed  158  may be substantially free of propene. In embodiments, the metathesis feed  158  may be substantially free of isobutene. In embodiments, the metathesis feed  158  may have less than 1.0 wt. % isobutene, or even less than 0.1 wt. % of isobutene, based on the total weight of the metathesis feed  158 . In embodiments, the metathesis feed  158  may be substantially free of 1,3-butadiene. In embodiments, the metathesis feed  158  may have less than 1 wt. %, or even less than 0.1 wt. % 1,3-butadiene based on the total weight of the metathesis feed  158 . 
     Referring again to  FIG.  1   , the metathesis reactor  170  may include one or a plurality of reaction zones, such as but not limited to, a metathesis reaction zone  172 , a cracking reaction zone  174 , or a combination of both. The metathesis reactor  170  may include at least one fixed bed reactor operated in an upflow or a downflow configuration. Although depicted as a fixed bed reactor, the metathesis reactor  170  may be any other type of reactor suitable for conducting a metathesis reaction. In one or more embodiments, the metathesis reactor  170  may include a plurality of metathesis reactors operated in series or in parallel. The metathesis reactor  170  may include a plurality of catalyst beds, where each of the catalyst beds may be a separate reaction zone. Two or more of the plurality of catalyst beds or reaction zones may be disposed in a single reactor. In embodiments, metathesis reactor  170  may include a single reactor having the metathesis reaction zone  172  comprising the metathesis catalyst and the cracking reaction zone  174  comprising the cracking catalyst and disposed downstream of the metathesis reaction zone  172 . 
     In embodiments, the metathesis reactor  170  may include a plurality of catalyst beds or reaction zones where at least one of the catalyst beds or reaction zones is disposed in a separate reactor from the other of the plurality of catalyst beds or reactions zones. For example, the metathesis reactor  170  may include a first reactor (not shown) comprising the metathesis reaction zone  172  having the metathesis catalyst and a second reactor (not shown) disposed downstream of the first reactor and comprising the cracking reaction zone  174  that includes the cracking catalyst. The first reactor and the second reactor may be fluidly coupled by a conduit extending directly from the first reactor to the second reactor. The conduit may fluidly couple the first reactor and the second reactor in series. 
     The metathesis reactor  170  may be operable to contact the metathesis feed  158  with one or a plurality of catalysts, such as but not limited to the metathesis catalyst, the cracking catalyst, or both. In embodiments, the metathesis reactor  170  may include the metathesis reaction zone  172  and the cracking reaction zone  174  downstream of the metathesis reaction zone  172 . The metathesis reaction zone  172  may include the metathesis catalyst, and the cracking reaction zone  174  may include the cracking catalyst. The metathesis feed  158  introduced to the metathesis reactor  170  may encounter the metathesis catalyst in the metathesis reaction zone  172  before encountering the cracking catalyst in the cracking reaction zone  174 . 
     Contacting of the metathesis feed  158  with the metathesis catalyst may cause at least a portion of the butene in the metathesis feed  158  to undergo a metathesis reaction to produce olefins, such as ethylene, propene, or both. The metathesis catalyst may be any catalyst operable to promote cross-metathesis of butenes to produce propene. The metathesis catalyst may be a particulate catalyst that includes a metal oxide disposed on the surfaces of a catalyst support material. The catalyst support material may be mesoporous silica catalyst support or a mesoporous silica-alumina catalyst support, such as but not limited to one or more molecular sieves or zeolites. As used in the present disclosure, “mesoporous” refers to a material having an average pore size of greater than 2 nanometers and less than 50 nanometers. The mesoporous silica catalyst support may include alumina or may be substantially free of alumina. As a non-limiting example, a mesoporous silica catalyst support that is substantially free of alumina may have less than 1 wt. % alumina. 
     The metathesis catalyst may include one or a plurality of metal oxides incorporated into the catalyst support material or deposited onto the surfaces of the catalyst support material. The metal oxide may include one or more oxides of a metal from Groups 6-10 of the IUPAC periodic table. As non-limiting examples, the metal oxide may include one or more oxides of molybdenum, rhenium, tungsten, or any combination of these. In one or more embodiments, the metal oxide of the metathesis catalyst may be tungsten oxide (WO 3 ). It is contemplated that various amounts of the metal oxide may be impregnated into the mesoporous silica catalyst support. For example and not by way of limitation, the weight percentage (wt. %) of metal oxide, for example WO 3 , in the metathesis catalyst may be from 1 wt. % to 30 wt. %, such as from 5 wt. % to 25 wt. %, or even from 8 wt. % to 20 wt. % based on the total weight of the metathesis catalyst. The metal oxides may be incorporated into the catalyst support material through co-precipitation, methods, sol-gel methods, or other methods. Alternatively or additionally, the metal oxide may be deposited onto the outer surfaces and pore surfaces of the catalyst support material through any type of impregnation or deposition process, such as but not limited to wet impregnation, vapor deposition, or other suitable method. The amount of metal oxide impregnated onto the catalyst support material of the metathesis catalyst may be verified using inductively coupled plasma (ICP) mass spectrometer or an x-ray fluorescence (XRF) spectrometer to determine the amount of tungsten in a sample of the mesoporous silica catalyst support impregnated with tungsten oxide. 
     The average pore size of the metathesis catalyst may be obtained from the average surface area and pore size distribution, which are determined using the Brunauer-Emmett-Teller (BET) method according to standard test methods known in the art. Average pore size is generally determined as a pore diameter or pore radius based on the assumption of cylindrical shaped pores. However, it is understood that metathesis catalysts described in this disclosure may have actual shapes that are cylindrical or other shapes, such as, but not limited to, conical, square, slit-shaped, or other irregular shaped pores or combinations of these. The metathesis catalyst may have a relative pore volume per weight of material of at least 0.6 cubic centimeters per gram (cm 3 /g), such as from 0.6 cm 3 /g to 2.5 cm 3 /g or even from 0.7 cm 3 /g to 1.5 cm 3 /g. The metathesis catalyst may have a surface area per unit weight of the metathesis catalyst of from 200 meters squared per gram (m 2 /g) to 600 m 2 /g, such as from 225 m 2 /g to 350 m 2 /g, or even from 250 m 2 /g to 325 m 2 /g. The metathesis catalyst may have a mean particle size of from 20 nanometers (nm) to 200 nm, such as from 50 nm to 150 nm. The metathesis catalyst may have a mean particle size distribution of from 100 angstroms (Å) to 300 A. The mean particle size and mean particle size distribution can be measured using a particle size analyzer, such as a Nanopartica™ series particle size analyzer from Horiba Scientific Company, which measures the size of single particles dispersed in water using ultraviolet (UV) light. 
     The metathesis catalyst may have a total acidity from 0.001 millimole/gram (mmol/g) to 0.5 mmol/g, from 0.01 mmol/g to 0.5 mmol/g, from 0.1 mmol/g to 0.5 mmol/g, from 0.3 mmol/g to 0.5 mmol/g, from 0.4 mmol/g to 0.5 mmol/g, from 0.001 mmol/g to 4 mmol/g, or from 0.001 mmol/g to 0.3 mmol/g. The acidity of the metathesis catalyst may be generally maintained at or less than 0.5 mmol/g to produce a greater propene selectivity for the multiple-stage catalyst system and to reduce production of byproducts, such as aromatics. Increasing acidity may increase the overall butene conversion; however, this increased conversion may lead to decreased propene selectivity and increased production of aromatic byproducts, which may lead to catalyst coking and deactivation. 
     Contact of the metathesis feed  158  with the metathesis catalyst in the metathesis reaction zone  172  may produce a metathesis reaction zone product that may include propene and other alkanes and alkenes, such as ethylene and C5+ olefins, for example. The metathesis reaction zone product may also include unreacted butenes, such as cis-2-butene, trans-2-butene, 1-butene, or combinations of two or more of these butenes. The metathesis catalyst may also promote self-metathesis of 2-butene to 1-butene, or 1-butene to 2-butene, in the metathesis reaction zone  172 . 
     Referring again to  FIG.  1   , the metathesis reaction zone product may pass into contact with the cracking catalyst in the cracking reaction zone  174  downstream of the metathesis reaction zone  172 . The cracking reaction zone  174  may include the cracking catalyst capable of converting at least a portion of the unreacted normal butenes and the produced C5+ olefins in the metathesis reaction zone product stream, to lighter olefins, such as ethylene and propene. Contact of the metathesis reaction zone product with the cracking catalyst in the cracking reaction zone  174  may cause at least a portion of the C5+ olefins produced in the metathesis reaction zone  172  to undergo catalytic cracking to produce at least ethylene, propene, or combinations of these. 
     The cracking catalyst may be any catalyst capable of catalyzing the cracking of C5+ olefins to produce additional propene, ethylene, or both. The cracking catalyst may be a zeolite. In embodiments, the cracking catalyst may be a structured zeolite, such as MFI or BEA structured zeolite, for example. The cracking catalyst may be an MCM-41 catalyst or an SBA-15 catalyst. The cracking catalyst may be an MFI structured silica-containing catalyst. For example, the MFI structured silica-containing catalyst may include MFI structured aluminosilicate zeolite catalysts or MFI structured silica catalysts that do not contain alumina or are substantially free of alumina, such as having less than 0.01 wt. % alumina based on the total weight of the catalyst. The cracking catalyst may be a WI structured silica-containing catalyst may include other impregnated metal oxides in addition to or as an alternative to alumina. The cracking catalyst may include one or more of metal oxides of metals from Groups 6-10 of the IUPAC Periodic Table, more specifically, metal oxides of molybdenum, rhenium, tungsten, titanium, or combinations of these. It should be understood that the cracking catalyst may include a combination of multiple zeolites, such as zeolite particles which include multiple types of zeolites, or a mixture of zeolite particles where particles include different zeolites. The cracking catalyst may be an MFI structured aluminosilicate zeolite catalyst may have a molar ratio of silica to alumina of from 5 to 5000. Various suitable commercial embodiments of cracking catalyst comprising WI structured aluminosilicate zeolites are contemplated, for example, ZSM-5 zeolites such as MFI-280 produced by Zeolyst International or MFI-2000 produced by Saudi Aramco. Various suitable commercial embodiments are also contemplated for the alumina free MFI structured silica-containing catalysts. One such example is Silicalite-1 produced by Saudi Aramco. 
     The cracking catalyst may have an average pore size of from 1.5 nm to 3 nm, or from 1.5 nm to 2.5 nm. The cracking catalyst may have an average relative pore volume per weight of material of from 0.1 cm 3 /g to 0.3 cm 3 /g, or from 0.15 cm 3 /g to 0.25 cm 3 /g. The cracking catalyst may have an average surface area of from 300 m 2 /g to 425 m 2 /g, or from 340 m 2 /g to 410 m 2 /g. The cracking catalyst may have an individual crystal size of from 10 microns to 40 microns, from 15 microns to 40 microns, or from 20 microns to 30 microns. The cracking catalyst may have a total acidity of from 0.001 mmol/g to 0.1 mmol/g, or from 0.01 mmol/g to 0.08 mmol/g. The acidity may be maintained at or less than 0.1 mmol/g to reduce production of byproducts, such as aromatic compounds. Increasing acidity may increase the amount of cracking; however, this increased cracking may also lead to less selectivity and increased production of aromatic hydrocarbon byproducts, which may lead to catalyst coking and deactivation. In some cases, the cracking catalyst may be modified with an acidity modifier to adjust the level of acidity in the cracking catalyst. Examples of acidity modifiers may include, but are not limited to, rare earth modifiers, phosphorus modifiers, potassium modifiers, or combinations of each. Alternatively, the cracking catalysts may be substantially free of acidity modifiers, such as those selected from rare earth modifiers, phosphorus modifiers, potassium modifiers, or combinations of each. 
     The metathesis reactor  170  may optionally include an isomerization zone (not shown) having an isomerization catalyst. The isomerization zone may be disposed upstream of the metathesis reaction zones  172  and the cracking reaction zone  174 . In embodiments, the isomerization zone may be in a separate reactor upstream of the metathesis reactor  170  and fluidly coupled to the metathesis reactor  170  such that the isomerization reaction products pass directly from the isomerization reaction zone to the metathesis reaction zone  172 . In some embodiments, the isomerization reaction zone may be disposed within the metathesis reactor  170  and upstream of the metathesis reaction zone  172 . The isomerization catalyst may be any catalyst that may promote equilibration of the isomerization reaction of 2-butene in the metathesis feed  158  to 1-butene. In embodiments, the isomerization catalyst may be magnesium oxide (MgO). 
     Referring again to  FIG.  1   , the metathesis feed  158  may be contacted with metathesis catalyst or the metathesis catalyst and the cracking catalyst in the metathesis reactor  170  under conditions sufficient to promote the cross-metathesis of at least a portion of the mixed butenes in the metathesis feed  158  to produce at least propene, ethylene, or both. The metathesis feed  158  may be contacted with the metathesis catalyst or the metathesis catalyst and cracking catalyst at a gas hourly space velocity (GHSV) of from 10 per hour (h −1 ) to 10,000 h −1 , such as from 100 h −1  to 5000 h −1 , or from 300 h−1 to 2500 h−1. The metathesis feed  158  may be contacted with the metathesis catalyst or the metathesis catalyst and cracking catalyst in the metathesis reactor  170  at a temperature of from 200° C. to 600° C., such as from 300° C. to 550° C., or even from 350° C. to 500° C. The metathesis feed  158  may be contacted with the metathesis catalyst or the metathesis catalyst and cracking catalyst in the metathesis reactor  170  at a pressure of from 1 bar to 30 bar or from 2 bar to 20 bar. In embodiments, the metathesis feed  158  may be contacted with the metathesis catalyst or the metathesis catalyst and cracking catalyst in the metathesis reactor  170  at atmospheric pressure. 
     Contact of the metathesis feed  158  with the metathesis catalyst in the metathesis reaction zone  172  may cause at least a portion of the butenes (1-butene, trans-2-butene, cis-2-butene) to undergo metathesis to produce a metathesis reaction zone product stream that includes at least propene. The metathesis reaction zone product stream may additionally include C5+ olefins, ethylene, butenes, or combinations of these. The metathesis reaction zone product stream may be passed directly into contact with the cracking catalyst in the cracking reaction zone  174 . Contact of metathesis reaction zone product stream with the cracking catalyst in the cracking reaction zone  174  may cause at least a portion of the C5+ olefins to undergo catalytic cracking reactions to produce the metathesis reaction effluent  176 , which may have a greater concentration of propene compared to the metathesis reaction zone product stream prior to contacting with the cracking catalyst. 
     The metathesis reaction effluent  176  may be passed out of the metathesis reactor  170 . In addition, the metathesis reaction effluent  176  may include one or more of ethylene, unreacted normal butenes, fuel gas, propane, isobutane, n-butane, isobutene, 1,3-butadiene, and C5+ compounds. At least a portion of the propane, n-butane, isobutane, isobutene, and 1,3-butadiene in the metathesis reaction effluent  176  may be constituents from the metathesis feed  158  that pass through the metathesis reactor  170  without undergoing reaction to form olefins. The ethylene and certain C5+ compounds, such as but not limited to pentene or hexene, may be produced in the metathesis reactor  170  through the metathesis reactions. At least a portion of the C5+ olefins may be converted to propene, ethylene, or olefins through contact with the cracking catalyst. 
     Referring again to  FIG.  1   , the metathesis reaction effluent  176  may be passed from the metathesis reactor  170  to the metathesis effluent separation system  180 . The metathesis effluent separation system  180  may be fluidly coupled to the metathesis reactor  170  so that the metathesis reaction effluent  176  can be passed directly from the metathesis reactor  170  to the metathesis effluent separation system  180  without passing the metathesis reaction effluent  176  through any intervening unit operations, such as a reactor. The metathesis effluent separation system  180  may include one or a plurality of separators operable to separate the metathesis reaction effluent  176  into at least a metathesis C5+ effluent  184  and at least one other olefin-containing effluent, which may include at least one of ethylene, propene, normal butenes, or combinations of these. The metathesis C5+ effluent  184  and the at least one other olefin-containing effluent may comprise at least 95 percent by weight of the constituents of the metathesis reaction effluent  176 . The metathesis effluent separation system  180  may be operable to separate the metathesis reaction effluent  176  into a metathesis C4 effluent  182 , a metathesis C5+ effluent  184 , a metathesis propene effluent  186 , and a metathesis ethylene effluent  188 . The metathesis C4 effluent  182 , metathesis C5+ effluent  184 , metathesis propene effluent  186 , and metathesis ethylene effluent  188 , combined, may include at least 95 percent, at least 98 percent, or even at least 99 percent by weight of the constituents of the metathesis reaction effluent  176 . The separation units of the metathesis effluent separation system  180  may include, but are not limited to, flash drums, high-pressure separators, distillation units, fractional distillation units, membrane separation units, or combinations of these. One or more of the metathesis C4 effluent  182 , metathesis C5+ effluent  184 , the metathesis propene effluent  186 , the metathesis ethylene effluent  188  may be passed to one or more downstream unit operations for further processing. 
     Referring again to  FIG.  1   , at least a portion of the metathesis C5+ effluent  184  may be passed from the metathesis system  160  back to the steam cracking system  110  for further conversion of C5+ compounds to ethylene, propene, or both. The portion of the metathesis C5+ effluent  184  may be passed through metathesis C5+ recycle  185  to a hydrotreating unit  140  disposed between the metathesis effluent separation system  180  and the steam cracking system  110 . The system  100  may include the metathesis C5+ recycle  185  fluidly coupled to the metathesis system  160 , such as to the metathesis effluent separation system  180 , and to the hydrotreating unit  140 . The metathesis C5+ recycle  185  may be operable to pass at least a portion of the metathesis C5+ effluent  184  from the metathesis system  160  to the hydrotreating unit  140  and ultimately back to the steam cracking system  110 . 
     The hydrotreating unit  140  may be operable to receive the metathesis C5+ recycle  185 , and optionally the isobutene effluent  154  from the isobutene removal unit  150 , and contact the metathesis C5+ recycle  185 , the isobutene effluent  154 , or both with one or a plurality of hydrotreating catalysts under reaction conditions sufficient to saturate the olefins in the metathesis C5+ recycle  185 , the isobutene effluent  154 , or both to produce a hydrotreated effluent  142 . The hydrotreating unit  140  may include one or a plurality of fixed bed reactors comprising one or more hydrotreating catalysts. The hydrotreating catalyst may be a catalyst capable of saturating isobutene and C5+ olefins to produce saturated hydrocarbons that can be subjected to steam cracking. Hydrotreating catalysts may include, but are not limited to hydrodesulfurization catalysts, hydrodemetalization catalysts, hydrodenitrogenation catalysts, hydrodearomatization catalysts, hydrocracking catalysts, or combinations of these. The hydrotreating catalysts may comprise one or more metal catalysts selected from the metallic elements in Groups 5, 6, 8, 9, or 10 of the IUPAC periodic table, such as, but not limited to, molybdenum, nickel, cobalt, and tungsten. The metals of the catalysts may be supported on a support. Support materials may include alumina or silica-alumina support materials. In embodiments, the support material may be a zeolite, such as a mesoporous zeolite support. The hydrotreating unit  140  may be operated at a temperature of from 300° C. to 450° C. and at a pressure of from 30 bars (3,000 kilopascals (kPa)) to 200 bars (20,000 kPa), such as from 30 bars (3,000 kPa) to 180 bars (18,000 kPa). The hydrotreating unit  140  may operate with a liquid hour space velocity (LHSV) of from 0.1 per hour (hr −1 ) to 10 hr −1 , such as from 0.2 hr −1  to 10 hr −1 . 
     The hydrotreated effluent  142  may be passed from the hydrotreating unit  140  to the steam cracking system  110  in which the hydrotreated effluent  142  can be contacted with steam at the temperature sufficient to cause at least a portion of hydrocarbons in the hydrotreated effluent  142  to undergo thermal cracking to produce olefins, such as ethylene, propene, and butene. The hydrotreated effluent  142  may be passed directly from the hydrotreating unit  140  to the steam cracking system  110 , or the hydrotreated effluent  142  may be combined with the hydrocarbon feed  102  upstream of the steam cracking system  110  to produce a combined feed to the steam cracking system  110 . 
     Contacting the saturated hydrocarbon compounds of the hydrotreated effluent  142  with steam at the temperatures of 700° C. to 900° C. in the pyrolysis zone  114  of the steam cracking reactor  111  may cause at least a portion of the saturated hydrocarbon compounds from the hydrotreated effluent  142  to undergo thermal cracking to produce olefins, such as ethylene, propene, and butene, and other C4− compounds. The additional conversion of at least a portion of the hydrocarbons from the hydrotreated effluent  142  may increase the overall conversion of the system  100  for producing olefins, such as ethylene and propene. Some portions of the hydrocarbon compounds in the hydrotreated effluent  142  may undergo cracking in the steam cracking system  110  to produce propene or ethylene, which may be passed out of the steam cracking system  110  in the cracking propene effluent  126  and the cracking ethylene effluent  128 , respectively. Additionally, other portions of the hydrocarbon compounds from the hydrotreated effluent  142  may be converted to butenes in the steam cracking system  110 . The butenes produced from cracking the portion of the hydrotreated effluent  142  may be passed downstream to the selective hydrogenation unit  130 , the isobutene removal unit  150 , and the metathesis system  160  for further conversion of normal butenes to ethylene and propene through metathesis. Thus, passing the hydrotreated effluent  142 , which includes hydrocarbons resulting from hydrotreating C5+ olefins from the metathesis C5+ recycle  185 , isobutene from the isobutene effluent  154 , or both, back to the steam cracking system  110  may increase the overall conversion of the hydrocarbon feed  102  and the overall yield of propene for the system  100 . 
     Referring again to  FIG.  1   , the metathesis C4 effluent  182  may include one or more of n-butane, isobutane, unreacted normal butenes, 1,3-butadiene, isobutene, or combinations of these. The metathesis C4 effluent  182  may also include other compounds having boiling point temperatures in the range of the C4 compounds of the metathesis C4 effluent  182 , such as boiling point temperatures greater than the boiling point temperature of propene and less than the boiling point temperatures of the metathesis C5+ effluent  184 . The metathesis C4 effluent  182  may be passed to one or a plurality of downstream unit operations (not shown) for further processing. 
     Additionally or alternatively, the metathesis C4 effluent  182  may be recycled back to the metathesis reactor  170  of the metathesis system  160  for further conversion of a portion of the normal butenes in the metathesis C4 effluent  182  to ethylene and propene. The at least a portion of the metathesis C4 effluent  182  may be passed from the metathesis effluent separation system  180  directly back to the metathesis reactor  170  or may be combined with the metathesis feed  158  upstream of the metathesis reactor  170  to produce a combined metathesis feed stream. The system  100  may include a metathesis C4 effluent recycle  183 , which may be fluidly coupled to an outlet of the metathesis effluent separation system  180  and an inlet of the metathesis reactor  170 . The metathesis C4 effluent recycle  183  may be operable to transfer at least a portion of the metathesis C4 effluent  182  from the metathesis effluent separation system  180  back to the metathesis reactor  170  and into contact with the metathesis catalyst or the metathesis catalyst and cracking catalyst in the metathesis reactor  170 . 
     Passing the metathesis C4 effluent  182  back to the metathesis reactor  170  and contacting the metathesis C4 effluent  182  with the metathesis catalyst or the metathesis catalyst and cracking catalyst in the metathesis reactor  170  may further increase the overall conversion and yield of ethylene and propene of the system  100 . Contacting at least a portion of the metathesis C4 effluent  182  with the metathesis catalyst or metathesis catalyst and cracking catalyst in the metathesis reactor  170  may cause at least a portion of the normal butenes in the metathesis C4 effluent  182  to undergo metathesis reactions to produce olefins, such as ethylene, propene, or both. Thus, recycling the metathesis C4 effluent  182  back to the metathesis reactor  170  may increase the overall conversion and yield of propene from the system  100 . Recycling the metathesis C4 effluent  182  back to the metathesis reactor  170  may also increase the yield of ethylene from the system  100 . 
     Referring again to  FIG.  1   , the metathesis C4 effluent  182  passed out of the metathesis system  160  may include isobutene produced in or passed through the metathesis system  160 . In embodiments, at least a portion of the metathesis C4 effluent  182  may be passed back to the isobutene removal unit  150  so that at least a portion of the isobutene in the metathesis C4 effluent  182  can be removed through reaction with methanol to produce MTBE. The portion of the metathesis C4 effluent  182  may be passed back to the isobutene removal unit  150  as the metathesis C4 effluent recycle  183 . The metathesis C4 effluent recycle  183  may be passed directly to the isobutene removal unit  150 , such as directly to the MTBE reactor  200  of the isobutene removal unit  150 , or may be combined with the hydrogenation effluent  134  upstream of the isobutene removal unit  150 . Recycling at least a portion of the metathesis C4 effluent  182  back to the isobutene removal unit  150  as the metathesis C4 effluent recycle  183  may further increase the selectivity and yield of propene for the system  100  by removing isobutene from the metathesis C4 effluent  182  before passing it back to the metathesis system  160 . 
     Referring again to  FIG.  1   , in embodiments, the metathesis C4 effluent  182  passed out of the metathesis system  160  may include 1,3-butadiene or other dienes produced in or passed through the metathesis system  160 . In embodiments, at least a portion of the metathesis C4 effluent  182  may be passed back to the selective hydrogenation unit  130  so that at least a portion of the 1,3-butadiene in the metathesis C4 effluent  182  can be removed through selective hydrogenation in the selective hydrogenation unit  130 . The portion of the metathesis C4 effluent  182  may be passed back to the selective hydrogenation unit  130  as the metathesis C4 effluent recycle  183 . The metathesis C4 effluent recycle  183  may be passed directly to the selective hydrogenation unit  130  or may be combined with the cracking C4 effluent  122  upstream of the selective hydrogenation unit  130 . Recycling at least a portion of the metathesis C4 effluent  182  back to the selective hydrogenation unit  130  as the metathesis C4 effluent recycle  183  may further increase the selectivity and yield of propene for the system  100  by removing 1,3-butadiene from the metathesis C4 effluent  182  before passing it along to the isobutene removal unit  150  and the metathesis system  160  downstream of the isobutene removal unit  150 . 
     Referring to  FIG.  1   , the metathesis propene effluent  186  and the metathesis ethylene effluent  188  may be passed to one or more downstream unit operations for further processing, such as but not limited to purification or polymerization processes. The metathesis propene effluent  186  may be combined with the cracking propene effluent  126  from the steam cracking system  110  to form a combined propene effluent passed out of the system  100 . Likewise, the metathesis ethylene effluent  188  may be combined with the cracking ethylene effluent  128  to form a combined ethylene effluent passed out of the system  100 . The combined propene effluent and the combined ethylene effluent of the system  100  may be passed independently to downstream operations for further processing. 
     In embodiments, the metathesis ethylene effluent  188  may not be passed back to the metathesis reactor  170  and no supplemental ethylene may be introduced or passed to the metathesis reactor  170 . Ethylene itself can be a useful intermediate for producing other chemical products, such as polyethylene and other polymers. Thus, the metathesis reactor  170  may be operated in the absence of any supplemental ethylene introduced to the metathesis reactor  170  and the only ethylene present in the metathesis reactor  170  may be any residual ethylene incidentally remaining in the metathesis feed  158  passed to the metathesis system  160  or ethylene produced in the metathesis reactor  170  through cross-metathesis of 1-butene and 2-butene. 
     Referring now to  FIG.  4   , in embodiments, ethylene produced through metathesis of butene in the metathesis system  160  may be recycled back to the metathesis system  160  as a reactant. In the metathesis system  160 , the ethylene may react with 2-butene in the presence of the metathesis catalyst to produce propene. The system  100  depicted in  FIG.  4    may include the steam cracking system  110 , the selective hydrogenation unit  130 , and the isobutene removal unit  150  previously described in the present disclosure. When ethylene is recycled back to the metathesis system  160 , the metathesis system  160  may include the metathesis reactor  170  and a supplemental metathesis reactor  190 , which may be operated in parallel with the metathesis reactor  170 . The metathesis reactor  170  may include the metathesis reaction zone  172  with the metathesis catalyst and the cracking reaction zone  174  with the cracking catalyst downstream of the metathesis reaction zone  172 , as previously discussed. The metathesis reactor  170  may have any of the features, catalysts, or operating conditions previously described in the present disclosure for the metathesis reactor  170 . The metathesis reactor  170  may include one or a plurality of reaction vessels in series or in parallel. 
     Referring again to  FIG.  4   , the supplemental metathesis reactor  190  may include at least one metathesis reaction zone  192  comprising a supplemental metathesis catalyst. The supplemental metathesis catalyst in the supplemental metathesis reactor  190  may be the same as or different from the metathesis catalyst in the metathesis reaction zone  172  of the metathesis reactor  170 . The supplemental metathesis catalyst in the supplemental metathesis reactor  190  may have any of features, compositions, or characteristics previously described in the present disclosure for the metathesis catalyst. The supplemental metathesis reactor  190  may include one reactor or a plurality of reactors arranged and operated in series or in parallel. In embodiments, the supplemental metathesis reactor  190  may not include a cracking catalyst. In embodiments, the supplemental metathesis reactor  190  may include an isomerization catalyst operable to isomerize 1-butene to 2-butene or 2-butene to 1-butene. 
     Referring to  FIG.  4   , a first portion  158   a  of the metathesis feed  158  may be directed to the metathesis reactor  170  and a second portion  158   b  of the metathesis feed  158  may be directed to the supplemental metathesis reactor  190 . The first portion  158   a  of the metathesis feed  158  may be contacted with the metathesis catalyst in the metathesis reaction zone  172  and the cracking catalyst in the cracking reaction zone  174  to produce the metathesis reaction effluent  176 . The second portion  158   b  of the metathesis feed  158  may be passed to the supplemental metathesis reactor  190 . At least a portion of the metathesis ethylene effluent  188  may also be passed to the supplemental metathesis reactor  190  through a metathesis ethylene recycle  189 . The metathesis ethylene recycle  189  may be operable to pass at least a portion of the metathesis ethylene effluent  188  from the metathesis effluent separation system  180  back to the supplemental metathesis reactor  190 . The metathesis ethylene recycle  189  may be combined with the second portion  158   b  of the metathesis feed  158  upstream of the supplemental metathesis reactor  190  or may be passed to the supplemental metathesis reactor  190  independent of the second portion  158   b  of the metathesis feed  158 . A supplemental ethylene stream, ethylene from the cracking ethylene effluent  128 , or both, may also be passed to the supplemental metathesis reactor  190 . 
     Referring again to  FIG.  4   , the second portion  158   b  of the metathesis feed  158  and ethylene from the metathesis ethylene recycle  189  may be combined in the supplemental metathesis reactor  190  and contacted with the supplemental metathesis catalyst in the metathesis reaction zone  192 . Contact between the ethylene and 2-butene (trans-2-butene, cis-2-butene, or both) in the presence of the supplemental metathesis catalyst in the metathesis reaction zone  192  may cause cross-metathesis between at least a portion of ethylene and at least a portion of the 2-butenes to produce propene. Cross-metathesis between 1-butene and 2-butene to produce propene and pentene and other metathesis reactions may also occur in the supplemental metathesis reactor  190 . A supplemental metathesis reaction effluent  196  may be passed out of the supplemental metathesis reactor  190 . The supplemental metathesis reaction effluent  196  may include the propene, ethylene, and C5+ olefins produced through the various cross-metathesis reactions occurring in the supplemental metathesis reactor  190 , unreacted ethylene, and unreacted C4 constituents from the second portion  158   b  of the metathesis feed  158 . 
     Recycling at least a portion of the metathesis ethylene effluent  188  back to the metathesis system  160 , such as back to the supplemental metathesis reactor  190 , through the metathesis ethylene recycle  189  may operate to shift the system  100  towards greater yield of propene relative to ethylene compared to operation of the system  100  without recycling the metathesis ethylene effluent  188  back to the metathesis system  160 . Thus, recycling at least a portion of the metathesis ethylene effluent  188  back to the metathesis system  160  may further increase the selectivity and yield of propene from the system  100 . 
     Referring again to  FIG.  4   , the metathesis reaction effluent  176  and the supplemental metathesis reaction effluent  196  may be passed to the metathesis effluent separation system  180 . The metathesis reaction effluent  176  and the supplemental metathesis reaction effluent  196  may be passed individually to the metathesis effluent separation system  180  or may be combined upstream of the metathesis effluent separation system  180 . As previously discussed, the metathesis effluent separation system  180  may be operable to separate the metathesis reaction effluents into a plurality of effluent streams, such as but not limited to the metathesis C4 effluent  182 , the metathesis C5+ effluent  184 , the metathesis propene effluent  186 , and the metathesis ethylene effluent  188 . As previously discussed, at least a portion of the metathesis C5+ effluent  184  may be passed back to the steam cracking system  110  through the metathesis C5+ recycle  185 , and at least a portion of the metathesis C4 effluent  182  may be passed back to the selective hydrogenation unit  130 , the isobutene removal unit  150 , or the metathesis system  160 , as previously discussed. 
     Referring now to  FIG.  5   , the system  100  may not include the metathesis effluent separation system  180 . Instead, the system  100  may include a combined separation system  300 , and the metathesis reaction effluent  176  and the cracking reaction effluent  117  may both be passed to the combined separation system  300 . In  FIG.  5   , the steam cracking reactor  111 , the selective hydrogenation unit  130 , the isobutene removal unit  150 , and the metathesis reactor  170  may have any of the features or characteristics previously described for these unit operations. The metathesis reaction effluent  176  and the cracking reaction effluent  117  may be passed separately and independently to the combined separation system  300  or may be combined upstream of the combined separation system  300 . The combined separation system  300  may include one or a plurality of separation units in series or in parallel. The combined separation system  300  may be operable to separate the metathesis reaction effluent  176  and the cracking reaction effluent  117  into at least a C4 stream  312 , a greater boiling effluent  314 , a system propene effluent  316 , a system ethylene effluent  318 , and a lesser-molecular weight gas effluent  319 . The metathesis reaction effluent  176  may be passed directly from the metathesis reactor  170  to the combined separation system  300 . 
     The metathesis reaction effluent  176  may include isobutene produced in the metathesis reactor  170 . This isobutene may pass out of the combined separation system  300  in the C4 stream  312 . The C4 stream  312  may be passed from the combined separation system  300  to the selective hydrogenation unit  130  and the isobutene removal unit  150  for removal of 1,3-butadiene and isobutene, respectively. The greater boiling effluent  314 , the system propene effluent  316 , the system ethylene effluent  318 , and the lesser-molecular weight gas effluent  319  may each be passed out of the combined separation system  300  and out of the system  100  to one or more downstream unit operations for further processing. The combined separation system  300  may also be used in the system  100  in which the ethylene is recycled back to the metathesis system  160  as shown in  FIG.  4   . The system ethylene effluent  318  may then be passed to the supplemental metathesis reactor  190  ( FIG.  4   ), and both the metathesis reaction effluent  176  and the supplemental metathesis reaction effluent  196  ( FIG.  4   ) can be passed to the combined separation system  300 . 
     Referring again to  FIG.  1   , processes for producing olefins may be conducted using the systems  100  of the present disclosure, which may include at least the steam cracking system  110 , the selective hydrogenation unit  130 , the isobutene removal unit  150 , and the metathesis system  160  as previously described in the present disclosure. Processes for producing olefins may include contacting the hydrocarbon feed  102  with steam in the steam cracking system  110  at a temperature sufficient to produce the cracking reaction effluent  117  ( FIG.  2   ) and separating the cracking reaction effluent  117  in the cracking effluent separation system  120  ( FIG.  2   ) to produce at least the cracking C4 effluent  122  comprising normal butenes, isobutene, and 1,3-butadiene. The steam cracking system  110  may have any of the features, characteristics, or operating conditions previously described in the present disclosure for steam cracking system  110 . Referring again to  FIG.  1   , the processes may further include subjecting the cracking C4 effluent  122  to selective hydrogenation in the selective hydrogenation unit  130  to produce the hydrogenation effluent  134 . Selective hydrogenation may cause at least a portion of the 1,3-butadiene in the cracking C4 effluent  122  to react to form normal butenes. The selective hydrogenation unit  130  may have any of the features, characteristics, or operating conditions previously described in the present disclosure for selective hydrogenation unit  130 . The processes may further include passing the hydrogenation effluent  134  to the isobutene removal unit  150  downstream of the selective hydrogenation unit  130  and removing isobutene from the hydrogenation effluent  134  in the isobutene removal unit  150  to produce at least a metathesis feed  158  comprising normal butenes. The isobutene removal unit  150  may have any of the features, characteristics, or operating conditions previously described in the present disclosure for isobutene removal unit  150 . The processes may further include passing at least a portion of the metathesis feed  158  to the metathesis system  160  comprising a metathesis catalyst and a cracking catalyst directly downstream of the metathesis catalyst and contacting the portion of the metathesis feed  158  with the metathesis catalyst and the cracking catalyst to produce a metathesis reaction effluent  176 . The metathesis system  160  may have any of the features, characteristics, or operating conditions previously described in the present disclosure for metathesis system  160 . Contacting with the metathesis catalyst may cause metathesis of normal butenes in the metathesis feed  158  to produce at least ethylene, propene, and C5+ olefins, and contacting with the cracking catalyst may cause at least a portion of the C5+ olefins produced through metathesis to undergo cracking reactions to produce ethylene, propene, or both. The metathesis reaction effluent may include at least ethylene, propene, or both. The hydrocarbon feed  102  may include a naphtha stream, a gas condensate stream, or both. 
     As previously discussed, the metathesis system  160  may include a metathesis reactor  170  having the metathesis reaction zone  172  comprising the metathesis catalyst and the cracking reaction zone  174  comprising the cracking catalyst, where the cracking reaction zone  174  is directly downstream of the metathesis reaction zone  172 . The processes may further include passing at least a portion of the metathesis feed  158  through the metathesis reaction zone  172  and the cracking reaction zone  174  downstream of the metathesis reaction zone  172 . Contacting the metathesis feed  158  with the metathesis catalyst in the metathesis reaction zone  172  may cause at least a portion of the normal butenes in the metathesis feed  158  to undergo metathesis to produce at least propene and C5+ olefins. Contacting the resulting C5+ olefins with the cracking catalyst in the cracking reaction zone  174  may cause at least a portion of the C5+ olefins to undergo catalytic cracking to produce at least one of ethylene, propene, or both. In embodiments, the cracking catalyst may be in contact with the metathesis catalyst. In other embodiments, the metathesis reaction zone  172  may be disposed in a first reactor, the cracking reaction zone  174  may be disposed in a second reactor directly downstream of the first reactor, and a conduit may fluidly couple the second reactor to the first reactor. The metathesis catalyst may have any of the features or compositions previously described in the present disclosure for the metathesis catalyst. In embodiments, the metathesis catalyst may be at least one metal oxide deposited on the surfaces of a mesoporous silica catalyst support or a mesoporous silica-alumina catalyst support. The cracking catalyst may have any of the features or compositions previously described in the present disclosure for the cracking catalyst. In embodiments, the cracking catalyst may be an MFI structured silica-containing catalyst. 
     Referring again to  FIG.  1   , the processes may further include separating the metathesis reaction effluent  176  into the metathesis C4 effluent  182 , the metathesis C5+ effluent  184 , the metathesis propene effluent  186 , and the metathesis ethylene effluent  188 . The processes may further include passing at least a portion of the metathesis C5+ effluent  184  back to the steam cracking system  110 . Passing the at least a portion of the metathesis C5+ effluent  184  back to the steam cracking system  110  may include hydrotreating the portion of the metathesis C5+ effluent  184  in the hydrotreating unit  140  to produce the hydrotreated effluent  142  and passing the hydrotreated effluent  142  back to the steam cracking system  110 . The hydrotreating unit  140  may have any of the features, characteristics, or operating conditions previous described in the present disclosure for the hydrotreating unit  140 . The processes may further include contacting the hydrotreated effluent  142  with steam at the temperature of from 700° C. to 900° C. in the steam cracking system  110 , where the contacting causes at least a portion of the hydrotreated effluent  142  to undergo steam cracking. The processes may further include passing at least a portion of the metathesis C4 effluent  182  back to the metathesis system  160 , the isobutene removal unit  150 , or the selective hydrogenation unit  130 . The metathesis ethylene effluent  188  may be passed back to the metathesis system  160 . In embodiments, the metathesis ethylene effluent  188  may not be passed back to the metathesis system  160  and no supplemental ethylene may be introduced to the metathesis system  160 . 
     Referring to  FIG.  4   , as previously discussed, the processes may include passing the metathesis ethylene effluent  188  back to the metathesis system  160 . The metathesis system  160  may include the metathesis reactor  170  comprising the metathesis reaction zone  172  having the metathesis catalyst and the cracking reaction zone  174  downstream of the metathesis reaction zone  172  and having the cracking catalyst. The metathesis system  160  may further include the supplemental metathesis reactor  190  comprising the supplemental metathesis catalyst. The supplemental metathesis reactor  190  may be operated in parallel with the metathesis reactor  170 . The processes may include contacting a first portion  158   a  of the metathesis feed  158  with the metathesis catalyst and the cracking catalyst in the metathesis reactor  170  to produce the metathesis reaction effluent  176  and contacting a second portion  158   b  of the metathesis feed  158  and the portion of the metathesis ethylene effluent  188  with the supplemental metathesis catalyst in the supplemental metathesis reactor  190  to produce the supplemental metathesis reaction effluent  196 . 
     Referring again to  FIG.  1   , subjecting the cracking C4 effluent  122  to selective hydrogenation may include contacting the cracking C4 effluent  122  with hydrogen from hydrogen stream  132  in the presence of a selective hydrogenation catalyst in the selective hydrogenation unit  130  at reaction conditions sufficient to cause at least a portion of the 1,3-butadiene in the steam cracking C4 effluent  122  to undergo a hydrogenation reaction to produce a hydrogenation effluent  134  having a concentration of 1,3-butadiene less than a concentration of 1,3-butadiene in the cracking C4 effluent. The hydrogenation effluent  134  may have a greater concentration of normal butenes compared to the concentration of normal butenes in the cracking C4 effluent  122 . 
     Referring to  FIG.  3   , removing isobutene from the hydrogenation effluent  134  may include contacting the hydrogenation effluent with methanol  156  in the MTBE reactor  200  of the isobutene removal unit  150  under reaction conditions sufficient to convert at least a portion of isobutene in the hydrogenation effluent  134  to methyl-tert-butyl ether to produce the MTBE reactor effluent  202 . The processes may further include separating the MTBE reactor effluent  202  into at least the MTBE effluent  152  and the metathesis feed  158 , which may include normal butenes. The processes may further include recovering at least a portion of the methyl-tert-butyl ether from the MTBE effluent  152 . Referring to  FIGS.  1  and  3   , in embodiments, the processes may include passing at least a portion of the MTBE effluent  152  back to the steam cracking system  110 . Passing the portion of the MTBE effluent  152  back to the steam cracking system may include contacting the MTBE effluent  152  with a cracking catalyst under conditions sufficient to produce an isobutene effluent  154 , where the contacting with the cracking catalyst may cause at least a portion of the methyl-tert-butyl ether in the MTBE effluent  152  to react to form isobutene. The cracking catalyst may have any of the features or compositions previously described in the present disclosure for cracking catalysts. The processes may further include passing the isobutene effluent  154  back to the steam cracking system  110 . The processes may further include passing the isobutene effluent  154  to the hydrotreating unit  140  and contacting the isobutene effluent  154  with one or more hydrotreating catalysts at reaction conditions sufficient to saturate the isobutene in the isobutene effluent  154 . The isobutene effluent  154  may be passed independently to hydrotreating unit  140  or may be combined with the metathesis C5+ recycle  185  upstream of the hydrotreating unit  140 . 
     Referring now to  FIG.  2   , the processes further include separating the cracking reaction effluent  117  to produce the cracking C4 effluent  122  comprising butenes, and one or more of the fuel oil  123 , the pyrolysis gas  125 , the cracking propene effluent  126 , the cracking ethylene effluent  128 , the lesser molecular weight gas  129 , or combinations of these. Separating the cracking reaction effluent  117  may include passing the cracking reaction effluent  117  to the cracking effluent separation system  120  that may include one or a plurality of separators operable to separate the cracking reaction effluent  117  into the cracking C4 effluent  122  and at least one of the fuel oil  123 , the pyrolysis gas  125 , the cracking propene effluent  126 , the cracking ethylene effluent  128 , the lesser molecular weight gas  129 , or combinations of these. The processes may include contacting the hydrocarbon feed  102  with the steam  104  in the pyrolysis zone  114  of the steam cracking reactor  111  at a temperature of from 700° C. to 900° C., for a residence time of from 0.05 seconds to 2 seconds, and at a mass ratio of steam to hydrocarbon of from 0.3:1 to 2:1. The processes may further include preheating the hydrocarbon feed  102  in the convection zone  112  of the steam cracking reactor  111 . 
     Referring now to  FIG.  5   , in embodiments, the processes may include passing the cracking reaction effluent  117  and the metathesis reaction effluent  176  to a combined separation system  300 . The cracking reaction effluent  117  and the metathesis reaction effluent  176  may be passed independently to the combined separation system  300  or may be combined upstream of the combined separation system  300 . The combined separation system  300  may include one or more separation units and may be operable to separate the cracking reaction effluent  117  and the metathesis reaction effluent  176  into a C4 effluent  312  and at least one of the greater boiling effluent  314 , the system propene effluent  316 , the system ethylene effluent  318 , the lesser-molecular weight gas effluent  319 , or combinations of these. The greater boiling effluent  314  may be further separated into one or more of a fuel oil stream, a pyrolysis gas stream, or other greater boiling stream. 
     The systems and processes of the present disclosure may be employed to produce olefins, such as ethylene and propene, from hydrocarbon feeds, such as naphtha and gas condensate streams. The ethylene and propene produced by the systems and processes of the present disclosure may be used as intermediates in various chemical processes to produce further chemical products. As a non-limiting example, the ethylene and propene may be introduced to a polymerization process to make polymer materials, such as but not limited to polyethylene-based polymers, polypropene-based polymers, or combinations of these. Ethylene and propene may also be used as reactants in various other reactions, such as but not limited to, oxidation, alkylation, oligomerization, hydration, to produce chemical products. Other uses of the ethylene and propene produced by the systems and processes of the present disclosure are also contemplated. 
     EXAMPLES 
     The following non-limiting examples illustrate one or more features of the present disclosure. 
     Example 1: Cracking Reaction Products from Steam Cracking of a Naphtha Feed 
     In Example 1, the composition of the cracking reaction product resulting from steam cracking a naphtha feed in a steam cracking reactor was modeled. The naphtha feed was an Arab Extra Light (AXL) naphtha stream produced by Saudi Arabian Oil Company. Properties and characteristics of the AXL naphtha stream for example 1 are provided in Table 2. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Properties and Characteristics for AXL Naphtha Feed 
               
            
           
           
               
               
               
               
            
               
                 Property 
                 Value 
                 Units 
                 Test Method 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 API Specific Gravity (SG) 
                 0.7089 
                 None 
                 ASTM D1298 
               
               
                 Initial Boiling Point (IBP) 
                 167.2 
                 ° C. 
                 ASTM D86 
               
               
                 50% Boiling Point 
                 212.9 
                 ° C. 
                 ASTM D86 
               
               
                 95% Boiling Point 
                 265.5 
                 ° C. 
                 ASTM D86 
               
               
                 Paraffins by Volume 
                 42.6 
                 Volume % 
                 ASTM D8017 
               
               
                 Isoparaffins by Volume 
                 28.1 
                 Volume % 
                 ASTM D8017 
               
               
                 Naphthenes by Volume 
                 26.8 
                 Volume % 
                 ASTM D8017 
               
               
                 Aromatics by Volume 
                 2.5 
                 Volume % 
                 ASTM D8017 
               
               
                   
               
            
           
         
       
     
     The steam cracking reactor was modeled using AspenPlus® 9 chemical process modeling software (AspenTech). Contact of the naphtha feed with steam at the reaction conditions produced a cracking reaction product having the composition in Table 3, which is provided in weight percent (wt. %) and in kilotons per anum (KTA). 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Cracking reaction products from steam 
               
               
                 cracking of a naphtha feed of Example 1 
               
            
           
           
               
               
            
               
                   
                 Feed 
               
               
                   
                 Cracking Reaction Product from Naphtha Feed 
               
            
           
           
               
               
               
            
               
                 Product Yields 
                 wt. % 
                 KTA 
               
               
                   
               
            
           
           
               
               
               
            
               
                 Hydrogen 
                 0.9 
                 9 
               
               
                 Methane 
                 10.9 
                 109 
               
               
                 Ethylene 
                 26.9 
                 269 
               
               
                 Propene 
                 15.7 
                 157 
               
               
                 Propane 
                 0.0 
                 0 
               
               
                 Mixed C4 Compounds 
                 12.3 
                 123 
               
               
                 Pyrolysis Gas 
                 24.2 
                 242 
               
               
                 Fuel oil 
                 9.0 
                 90 
               
               
                 Total 
                 100 
                 1000 
               
               
                   
               
            
           
         
       
     
     Example 2: Cracking Reaction Products from Steam Cracking of a Gas Condensate Feed 
     In Example 2, the composition of the cracking reaction products resulting from steam cracking a gas condensate feed were modeled. The gas condensate feed was a gas condensate produced from the Khuff reservoirs in Saudi Arabia (Khuff gas condensate or KGC) and having the composition provided in Table 1. The steam cracking reactor was modeled using AspenPlus® 9 chemical process modeling software (AspenTech). Contact of the gas condensate feed with steam at the reaction conditions produced a cracking reaction product having the composition in Table 4, which provided in weight percent (wt. %) and in tons. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Cracking reaction products from high-severity fluidized catalytic 
               
               
                 cracking of a Khuff gas condensate feed for Example 2 
               
            
           
           
               
               
               
            
               
                   
                 Feed 
                   
               
               
                   
                 Cracking Reaction Product 
               
               
                   
                 from Gas Condensate Feed 
               
            
           
           
               
               
               
               
            
               
                   
                 Product Yields 
                 wt. % 
                 KTA 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Hydrogen 
                 2.1 
                 21 
               
               
                   
                 Methane 
                 10.9 
                 109 
               
               
                   
                 Ethylene 
                 27.8 
                 278 
               
               
                   
                 Propene 
                 14.5 
                 145 
               
               
                   
                 Propane 
                 0.0 
                 0 
               
               
                   
                 Mixed C4 Compounds 
                 9.5 
                 95 
               
               
                   
                 Pyrolysis Gas 
                 17.3 
                 173 
               
               
                   
                 Fuel Oil 
                 17.9 
                 179 
               
               
                   
                 Total 
                 100 
                 1000 
               
               
                   
                   
               
            
           
         
       
     
     Example 3: Integrated Steam Cracking and Metathesis Process for Naphtha Feed 
     In Example 3, the system  100  of  FIG.  6    integrating a steam cracking system  110  with a metathesis system  160  for upgrading a hydrocarbon feed  400  comprising naphtha to ethylene and propylene is modeled. A combination of AspenPlus® 9 chemical process modeling software (AspenTech) and bench scale reactor testing is used to model the system  100 , which includes the steam cracking system  110 , the selective hydrogenation unit  130  downstream of the steam cracking system  110 , the isobutene removal unit  150  downstream of the selective hydrogenation unit  130 , and the metathesis system downstream of the isobutene removal unit  150 . The naphtha for the hydrocarbon feed is the AXL naphtha stream from Table 2. 
     Referring to  FIG.  6   , the steam cracking system  110  is operated at a temperature of the convection zone of 565° C. The outlet of the furnace of the steam cracking system was set to 825° C. and 25 pounds per square inch absolute (psia) (172 kPa). The mass balance for the steam cracking system  110  is provided in Table 5. The cracking reaction effluent is separated into a lesser molecular weight gas  401 , a cracking ethylene effluent  402 , a cracking propene effluent  403 , a cracking C4 effluent  404 , a pyrolysis gas  415 , and a fuel oil  416 . Separation of the cracking reaction effluent into the various effluent streams is assumed to be 100%. The cracking C4 effluent  404  is passed to the selective hydrogenation unit  130 . Hydrogen is also passed to the selective hydrogenation unit  130  by way of hydrogen stream  420 , and the weight ratio of hydrogen to 1,3-butadiene in the selective hydrogenation unit  130  is set to 2.2. The conversion of 1,3-butadiene in the selective hydrogenation unit  130  is set to 100% conversion of 1,3-butadiene to normal butenes (1-butene, trans-2-butene, cis-2-butene). The mass balance for the selective hydrogenation unit  130  is provided in Table 5. 
     A hydrogenation effluent  405  is passed from the selective hydrogenation unit  130  to the isobutene removal unit  150 . Methanol  406  is also passed to the isobutene removal unit  150 . The amount of methanol  406  is 12 wt. % based on the total mass flow rate of the hydrogenation effluent  405  and the methanol  406 . The conversion of isobutene to MTBE in the isobutene removal unit  150  is set to 100% conversion and the separation of MTBE  408  from the metathesis feed  407  is assumed to be 100% efficient. The mass balance for the isobutene removal unit  150  is provided in Table 5. 
     The metathesis system  160  includes a metathesis reaction zone comprising a metathesis catalyst and a cracking reaction zone downstream of the metathesis reaction zone and comprising a cracking catalyst. The metathesis system  160  was tested using a bench scale reactor having the metathesis catalyst in the metathesis reaction zone and the cracking catalyst in the cracking reaction zone downstream of the metathesis reaction zone. The feed to the bench scale metathesis reactor was synthesize using the composition modeled for the metathesis feed  407  and provided below in Table 6. In particular, the metathesis feed included 55.6 wt. % 1-butene, 32.7 wt. % 2-butene, 5.6 wt. % n-butane, and 3.7 wt. % isobutane based on the total weight of the metathesis feed. The metathesis reaction effluent was analyzed to determine the composition. The metathesis system  160  produced a total conversion of butene of 80% with a propylene selectivity of 46% and an ethylene selectivity of 14.5%. The metathesis reaction effluent is separated into a metathesis ethylene effluent  409 , a metathesis propene effluent  410 , a metathesis C4 effluent  411 , and a metathesis C5+ effluent  414 . Separation of the metathesis reaction effluent into the various effluents  409 ,  410 ,  411 , and  414  is assumed to be 100% efficient. The mass balance for the metathesis system  160  is provided in Table 5. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Mass Balance Information for Modeling the Unit  
               
               
                 Operations of FIG. 6 for Example 3. 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 Selective 
                   
                   
               
               
                   
                 Steam Cracking 
                 Hydrogenation 
                 Isobutene 
                 Metathesis 
               
               
                 Yields 
                 System 
                 Unit 
                 Removal Unit 
                 System 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Feed 
                 wt. % 
                 KTA 
                 wt. % 
                 KTA 
                 wt. % 
                 KTA 
                 wt. % 
                 KTA 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 AXL 
                 100 
                 1000 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Hydrogen 
                 — 
                 — 
                 4 
                 5 
                   
                   
                 2 
                 2 
               
               
                 Cracking C4 Eff 
                 — 
                 — 
                 96 
                 123 
                 — 
                 — 
                 — 
                 — 
               
               
                 Hydrogenation Eff. 
                 — 
                 — 
                 — 
                 — 
                 88 
                 128 
                 — 
                 — 
               
               
                 Methanol 
                 — 
                 — 
                 — 
                 — 
                 12 
                 17 
                 — 
                 — 
               
               
                 Metathesis Feed 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 98 
                 95 
               
               
                 Total Feed 
                 100 
                 1000 
                 100 
                 128 
                 100 
                 140 
                 100 
                 98 
               
            
           
           
               
            
               
                 Component Yields in Effluent 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Off-gas 
                 NA 
                 NA 
                 NA 
                 NA 
                 NA 
                 NA 
                 1 
                 1 
               
               
                 Hydrogen 
                 1 
                 9 
                 2 
                 2 
                 2 
                 2 
                 2 
                 2 
               
               
                 Methane 
                 11 
                 109 
                 0 
                 0 
                 0 
                 0 
                 NA 
                 NA 
               
               
                 Ethylene 
                 27 
                 269 
                 0 
                 0 
                 0 
                 0 
                 13 
                 13 
               
               
                 Propylene 
                 16 
                 157 
                 0 
                 0 
                 0 
                 0 
                 38 
                 37 
               
               
                 1,3-butadiene 
                 12 
                 123 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 Isobutene 
                   
                   
                 24 
                 30 
                 0 
                 0 
                 11 
                 11 
               
               
                 1-Butene 
                   
                   
                 43 
                 54 
                 38 
                 53 
                 6 
                 5 
               
               
                 2-Butene 
                   
                   
                 25 
                 32 
                 22 
                 31 
                 12 
                 12 
               
               
                 n-Butane 
                   
                   
                 4 
                 5 
                 4 
                 5 
                 5 
                 5 
               
               
                 Isobutane 
                   
                   
                 3 
                 4 
                 2 
                 4 
                 4 
                 4 
               
               
                 MTBE 
                 NA 
                 N/A 
                 NA 
                 NA 
                 32 
                 46 
                 NA 
                 0 
               
               
                 C5+ 
                 NA 
                 NA 
                 0 
                 0 
                 0 
                 0 
                 6 
                 5 
               
               
                 Pyrolysis Gas 
                 24 
                 242 
                 NA 
                 NA 
                 NA 
                 NA 
                 NA 
                 NA 
               
               
                 Fuel Oil 
                 9 
                 90 
                 NA 
                 NA 
                 NA 
                 NA 
                 NA 
                 NA 
               
               
                 Total Yield 
                 100 
                 1000 
                 100 
                 128 
                 100 
                 145 
                 100 
                 98 
               
               
                   
               
               
                 KTA stands for kilotons per annum. 
               
               
                 Weight percent (wt. %) for the feed to each unit operation is based on the total weight of all feed streams introduced to that unit operation. 
               
               
                 Weight percent (wt. %) for the Component Yields in Effluent from one of the unit operations are based on the total weight of the effluent passed out of that unit operation. 
               
            
           
         
       
     
     The metathesis ethylene effluent  409  is combined with the cracking ethylene effluent  402  to produce a system ethylene effluent  412 . The metathesis propene effluent  410  is combined with the cracking propene effluent  403  to produce a system propene effluent. The metathesis C5+ effluent  414  is combined with the fuel oil effluent  417  from the steam cracking system  110  to produce a system fuel oil effluent  419 . The modeling data for the system  100  of  FIG.  6    with the naphtha hydrocarbon feed is provided in Table 6. 
     
       
         
           
               
             
               
                 TABLE 6 
               
               
                   
               
               
                 Modeling Data for System of FIG. 6 with the  
               
               
                 AXL Naphtha Feed According to Example 3. 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Stream # 
                 400 
                 401 
                 402 
                 403 
                 404 
                 420 
                 405 
                 406 
                 407 
                 408 
               
               
                 Units 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
               
               
                   
               
               
                 AXL 
                 1000 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Hydrogen 
                 — 
                 — 
                 — 
                 — 
                 — 
                 4.6 
                 2.4 
                 — 
                 2 
                 — 
               
               
                 Fuel Gas 
                 — 
                 118.3 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Methanol 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 17.0 
                 — 
                 — 
               
               
                 MTBE 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 47.1 
               
               
                 Ethylene 
                 — 
                 — 
                 269 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Propene 
                 — 
                 — 
                 — 
                 156.9 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Butadiene 
                 — 
                 — 
                 — 
                 — 
                 57.0 
                 — 
                 0.0 
                 — 
                 — 
                 — 
               
               
                 Isobutene 
                 — 
                 — 
                 — 
                 — 
                 29.5 
                 — 
                 30.1 
                 — 
                 — 
                 — 
               
               
                 1-Butene 
                 — 
                 — 
                 — 
                 — 
                 18.2 
                 — 
                 54.4 
                 — 
                 54.4 
                 — 
               
               
                 2-Butene 
                 — 
                 — 
                 — 
                 — 
                 9.6 
                 — 
                 32.0 
                 — 
                 32.0 
                 — 
               
               
                 n-Butane 
                 — 
                 — 
                 — 
                 — 
                 5.4 
                 — 
                 5.5 
                 — 
                 5.5 
                 — 
               
               
                 Isobutane 
                 — 
                 — 
                 — 
                 — 
                 3.5 
                 — 
                 3.6 
                 — 
                 3.6 
                 — 
               
               
                 Pyrolysis 
                 — 
                 — 
                 — 
                 — 
                 0.1 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Gas 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Fuel Oil 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Total 
                 1000 
                 118.3 
                 269 
                 156.9 
                 123.4 
                 4.6 
                 128.0 
                 17.0 
                 97.9 
                 47.1 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 Stream # 
                 409 
                 410 
                 411 
                 412 
                 413 
                 414 
                 415 
                 417 
                 419 
               
               
                 Units 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
               
               
                   
               
               
                 AXL 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Hydrogen 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Fuel Gas 
                 — 
                 — 
                 3.6 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Methanol 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 MTBE 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Ethylene 
                 13.5 
                 — 
                 — 
                 282.5 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Propene 
                 — 
                 37.9 
                 — 
                 — 
                 194.8 
                 — 
                 — 
                 — 
                 — 
               
               
                 Butadiene 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Isobutene 
                 — 
                 — 
                 11.0 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 1-Butene 
                 — 
                 — 
                 5.5 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 2-Butene 
                 — 
                 — 
                 11.8 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 n-Butane 
                 — 
                 — 
                 5.5 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Isobutane 
                 — 
                 — 
                 3.6 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Pyrolysis 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 242.4 
                 — 
                 — 
               
               
                 Gas 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Fuel Oil 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 90.0 
                 95.5 
               
               
                 Total 
                 13.5 
                 37.9 
                 41.1 
                 282.5 
                 194.8 
                 5.5 
                 242.4 
                 90.0 
                 95.5 
               
               
                   
               
            
           
         
       
     
     As shown in Table 6, the system  100  with the dual catalyst metathesis system  160  integrated with the steam cracking system  110  produces a total of 282.5 KTA ethylene and 194.8 KTA propene. The production of 282.5 KTA ethylene from system  100  represents a greater than 5% increase in the production of ethylene compared to steam cracking by itself (Table 3), and the production of 194.8 KTA propene from system  100  represents a 24% increase in the product of propene compared to steam cracking by itself (Table 3). 
     Example 4: Integrated Steam Cracking and Metathesis Process for Gas Condensate Feed 
     In Example 4, the system  100  of  FIG.  6    integrating a steam cracking system  110  with a metathesis system  160  for upgrading a hydrocarbon feed  400  comprising a gas condensate to ethylene and propylene is modeled. AspenPlus® 9 chemical process modeling software (AspenTech) is used to model the steam cracking system  110 , selective hydrogenation unit  130 , and isobutene removal unit  150  of system  100  according to the description previously provided in Example 3. The gas condensate for the hydrocarbon feed  400  is Khuff gas condensate recovered from natural gas extracted from the Khuff reservoir in Saudi Arabia. Characteristics for the Khuff gas condensate for Example 4 are provided in Table 1. 
     The metathesis system  160  was tested using a bench scale reactor having the metathesis catalyst in the metathesis reaction zone and the cracking catalyst in the cracking reaction zone downstream of the metathesis reaction zone. The feed to the bench scale metathesis reactor was synthesized using the composition modeled for the metathesis feed  407  and provided below in Table 8. In particular, the metathesis feed included 55.7 wt. % 1-butene, 32.9 wt. % 2-butene, 5.2 wt. % n-butane, and 3.4 wt. % isobutane based on the total weight of the metathesis feed. The metathesis reaction effluent was analyzed to determine the composition. The mass balance information for the steam cracking system  110 , selective hydrogenation unit  130 , isobutene removal unit  150 , and metathesis system based on using the Khuff gas condensate for the hydrocarbon feed  400  is provided in Table 7. 
     
       
         
           
               
             
               
                 TABLE 7 
               
             
            
               
                   
               
               
                 Mass Balance Information for Modeling the Unit  
               
               
                 Operations of FIG. 6 for Example 4 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 Selective 
                   
                   
               
               
                   
                 Steam Cracking 
                 Hydrogenation 
                 Isobutene 
                 Metathesis 
               
               
                 Yields 
                 System 
                 Unit 
                 Removal Unit 
                 System 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Feed 
                 wt. % 
                 KTA 
                 wt. % 
                 KTA 
                 wt. % 
                 KTA 
                 wt. % 
                 KTA 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 KGC 
                 100 
                 1000 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Hydrogen 
                 — 
                 — 
                 4 
                 4 
                 — 
                 — 
                 3 
                 2 
               
               
                 Cracking C4 Eff 
                 — 
                 — 
                 96 
                 95 
                 — 
                 — 
                 — 
                 — 
               
               
                 Hydrogenation 
                 — 
                 — 
                 — 
                 — 
                 89 
                 99 
                 — 
                 — 
               
               
                 Eff. 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Methanol 
                 — 
                 — 
                 — 
                 — 
                 11 
                 12 
                 — 
                 — 
               
               
                 Metathesis Feed 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 97 
                 75 
               
               
                 Total Feed 
                 100 
                 1000 
                 100 
                 99 
                 100 
                 107 
                 100 
                 77 
               
            
           
           
               
            
               
                 Component Yields in Effluent 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Off-gas 
                 NA 
                 NA 
                 NA 
                 NA 
                 NA 
                 NA 
                 1 
                 1 
               
               
                 Hydrogen 
                 2.1 
                 21 
                 2.2 
                 2.2 
                 1.9 
                 2.2 
                 3 
                 2.2 
               
               
                 Methane 
                 10.9 
                 109 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 Ethylene 
                 27.8 
                 278 
                 0 
                 0 
                 0 
                 0 
                 14 
                 11 
               
               
                 Propylene 
                 14.5 
                 145 
                 0 
                 0 
                 0 
                 0 
                 39 
                 30 
               
               
                 1,3-butadiene 
                 9.5 
                 95 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 Isobutene 
                   
                   
                 22 
                 22 
                 0 
                 0 
                 11 
                 9 
               
               
                 1-Butene 
                   
                   
                 43 
                 43 
                 39 
                 43 
                 6 
                 4 
               
               
                 2-Butene 
                   
                   
                 26 
                 25 
                 23 
                 25 
                 12 
                 9 
               
               
                 n-Butane 
                   
                   
                 4 
                 4 
                 4 
                 4 
                 5 
                 4 
               
               
                 Isobutane 
                   
                   
                 3 
                 3 
                 2 
                 3 
                 3 
                 3 
               
               
                 MTBE 
                 NA 
                 NA 
                 NA 
                 NA 
                 31 
                 34 
                 0 
                 0 
               
               
                 C5+ 
                 NA 
                 NA 
                 0 
                 0 
                 0 
                 0 
                 6 
                 4 
               
               
                 Pyrolysis Gas 
                 17.3 
                 173 
                 NA 
                 NA 
                 NA 
                 NA 
                 NA 
                 NA 
               
               
                 Fuel Oil 
                 17.9 
                 179 
                 NA 
                 NA 
                 NA 
                 111 
                 NA 
                 NA 
               
               
                 Total Yield 
                 100 
                 1000 
                 100 
                 99 
                 100 
                 111 
                 100 
                 77 
               
               
                   
               
               
                 KTA stands for kilotons per annum. 
               
               
                 Weight percent (wt. %) for the feed to each unit operation is based on the total weight of all feed streams introduced to that unit operation. 
               
               
                 Weight percent (wt. %) for the Component Yields in Effluent from one of the unit operations are based on the total weight of the effluent passed out of that unit operation. 
               
            
           
         
       
     
     As described previously in Example 3, the metathesis ethylene effluent  409  is combined with the cracking ethylene effluent  402  to produce a system ethylene effluent  412 . The metathesis propene effluent  410  is combined with the cracking propene effluent  403  to produce a system propene effluent. The metathesis C5+ effluent  414  is combined with the fuel oil effluent  417  from the steam cracking system  110  to produce a system fuel oil effluent  419 . The modeling data for the system  100  of  FIG.  6    with the Khuff gas condensate for the hydrocarbon feed is provided in Table 8. 
     
       
         
           
               
             
               
                 TABLE 8 
               
               
                   
               
               
                 Modeling Data for System of FIG. 6 with Khuff Gas  
               
               
                 Condensate (KGC) Feed According to Example 4. 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Stream # 
                 400 
                 401 
                 402 
                 403 
                 404 
                 420 
                 405 
                 406 
                 407 
                 408 
               
               
                 Units 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
               
               
                   
               
               
                 KGC 
                 1000 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Hydrogen 
                 — 
                 — 
                 — 
                 — 
                 — 
                 3.8 
                 2.2 
                 — 
                 2 
                 — 
               
               
                 Fuel Gas 
                 — 
                 130.2 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Methanol 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 12.4 
                 — 
                 — 
               
               
                 MTBE 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 34 
               
               
                 Ethylene 
                 — 
                 — 
                 278.4 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Propene 
                 — 
                 — 
                 — 
                 145.2 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Butadiene 
                 — 
                 — 
                 — 
                 — 
                 46.7 
                 — 
                 0.0 
                 — 
                 — 
                 — 
               
               
                 Isobutene 
                 — 
                 — 
                 — 
                 — 
                 21.5 
                 — 
                 21.9 
                 — 
                 — 
                 — 
               
               
                 1-Butene 
                 — 
                 — 
                 — 
                 — 
                 13.2 
                 — 
                 42.8 
                 — 
                 42.8 
                 — 
               
               
                 2-Butene 
                 — 
                 — 
                 — 
                 — 
                 7.0 
                 — 
                 25.3 
                 — 
                 25.3 
                 — 
               
               
                 n-Butane 
                 — 
                 — 
                 — 
                 — 
                 3.9 
                 — 
                 4.0 
                 — 
                 4.0 
                 — 
               
               
                 Isobutane 
                 — 
                 — 
                 — 
                 — 
                 2.6 
                 — 
                 2.6 
                 — 
                 2.6 
                 — 
               
               
                 Pyrolysis 
                 — 
                 — 
                 — 
                 — 
                 0.1 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Gas 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Fuel Oil 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Total 
                 1000 
                 130.2 
                 278.4 
                 145.2 
                 95.0 
                 3.8 
                 98.8 
                 12.4 
                 76.9 
                 34.2 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 Stream # 
                 409 
                 410 
                 411 
                 412 
                 413 
                 414 
                 415 
                 417 
                 419 
               
               
                 Units 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
               
               
                   
               
               
                 KGC 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Hydrogen 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Fuel Gas 
                 — 
                 — 
                 3.1 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Methanol 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 MTBE 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Ethylene 
                 10.6 
                 — 
                 — 
                 289.0 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Propene 
                 — 
                 29.9 
                 — 
                 — 
                 175.1 
                 — 
                 — 
                 — 
                 — 
               
               
                 Butadiene 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Isobutene 
                 — 
                 — 
                 8.7 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 1-Butene 
                 — 
                 — 
                 4.4 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 2-Butene 
                 — 
                 — 
                 9.3 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 n-Butane 
                 — 
                 — 
                 4.0 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Isobutane 
                 — 
                 — 
                 2.6 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Pyrolysis 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 172.7 
                 — 
                 — 
               
               
                 Gas 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Fuel Oil 
                 — 
                 — 
                 — 
                 — 
                 — 
                 4.3 
                 — 
                 178.6 
                 182.9 
               
               
                 Total 
                 10.6 
                 29.9 
                 32.0 
                 289.0 
                 175.1 
                 4.3 
                 172.7 
                 178.6 
                 182.9 
               
               
                   
               
            
           
         
       
     
     As shown in Table 8, for processing the Khuff gas condensate, the system  100  with the dual catalyst metathesis system  160  integrated with the steam cracking system  110  produces a total of 289.0 KTA ethylene and 175.1 KTA propene. The production of 289.0 KTA ethylene from system  100  represents a 4% increase in the production of ethylene compared to steam cracking by itself (Table 4), and the production of 175.1 KTA propene from system  100  represents a 20% increase in the product of propene compared to steam cracking by itself. 
     Example 5: Integrated Steam Cracking and Metathesis Process for Naphtha Feed: Single Catalyst Metathesis System 
     In Example 5, the system  100  of  FIG.  6    integrating a steam cracking system  110  with a metathesis system  160  for upgrading a hydrocarbon feed  400  comprising naphtha to ethylene and propylene is modeled with a metathesis system that include the metathesis catalyst only and does not include the cracking catalyst. The naphtha for the hydrocarbon feed for Example 5 is the AXL naphtha stream from Table 2. In Example 5, the steam cracking system  110 , selective hydrogenation unit  130 , and isobutene removal unit  150  are modeled using the same conditions and assumptions described in relation to Example 3. 
     The metathesis system  160  for Example 5 includes only the metathesis reaction zone comprising the metathesis catalyst and does not include the cracking catalyst. The metathesis system was tested using a bench scale reactor having the metathesis catalyst only. The feed to the bench scale metathesis reactor was synthesized using the composition modeled for the metathesis feed  407  and provided below in Table 10. In particular, the metathesis feed included 55.6 wt. % 1-butene, 32.7 wt. % 2-butene, 5.6 wt. % n-butane, and 3.7 wt. % isobutane based on the total weight of the metathesis feed. The metathesis reaction effluent was analyzed to determine the composition. The metathesis system  160  produced a total conversion of butene of 80% with a propylene selectivity of 46% and an ethylene selectivity of 14.5%. The metathesis reaction effluent is separated into a metathesis ethylene effluent  409 , a metathesis propene effluent  410 , a metathesis C4 effluent  411 , and a metathesis C5+ effluent  414 . Separation of the metathesis reaction effluent into the various effluents  409 ,  410 ,  411 , and  414  is assumed to be 100% efficient. The mass balances for each of the steam cracking system  110 , the selective hydrogenation unit  130 , the isobutene removal unit  150 , and the metathesis system  160  for Example 5 are provided in Table 9. 
     
       
         
           
               
             
               
                 TABLE 9 
               
             
            
               
                   
               
               
                 Mass Balance Information for Modeling the Unit  
               
               
                 Operations of FIG. 6 for Example 5 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 Selective 
                   
                   
               
               
                   
                 Steam Cracking 
                 Hydrogenation 
                 Isobutene 
                 Metathesis 
               
               
                 Yields 
                 System 
                 Unit 
                 Removal Unit 
                 System 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Feed 
                 wt. % 
                 KTA 
                 wt. % 
                 KTA 
                 wt. % 
                 KTA 
                 wt. % 
                 KTA 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 AXL 
                 100 
                 1000 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Hydrogen 
                 — 
                 — 
                 4 
                 5 
                   
                   
                 2 
                 2 
               
               
                 Cracking C4 Eff 
                 — 
                 — 
                 96 
                 123 
                 — 
                 — 
                 — 
                 — 
               
               
                 Hydrogenation Eff. 
                 — 
                 — 
                 — 
                 — 
                 88 
                 128 
                 — 
                 — 
               
               
                 Methanol 
                 — 
                 — 
                 — 
                 — 
                 12 
                 17 
                 — 
                 — 
               
               
                 Metathesis Feed 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 98 
                 95 
               
               
                 Total Feed 
                 100 
                 1000 
                 100 
                 128 
                 100 
                 140 
                 100 
                 98 
               
            
           
           
               
            
               
                 Component Yields in Effluent 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Off-gas 
                 NA 
                 NA 
                 NA 
                 NA 
                 NA 
                 NA 
                 1 
                 1 
               
               
                 Hydrogen 
                 0.9 
                 9 
                 2.0 
                 2.5 
                 1.7 
                 2.4 
                 2 
                 2.4 
               
               
                 Methane 
                 10.9 
                 109 
                 0 
                 0 
                 0 
                 0 
                 NA 
                 NA 
               
               
                 Ethylene 
                 26.9 
                 269 
                 0 
                 0 
                 0 
                 0 
                 4 
                 4 
               
               
                 Propylene 
                 15.7 
                 157 
                 0 
                 0 
                 0 
                 0 
                 24 
                 23 
               
               
                 1,3-butadiene 
                 12.3 
                 123 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 Isobutene 
                   
                   
                 23 
                 30 
                 0 
                 0 
                 2 
                 2 
               
               
                 1-Butene 
                   
                   
                 42 
                 54 
                 38 
                 54 
                 11 
                 10 
               
               
                 2-Butene 
                   
                   
                 25 
                 32 
                 22 
                 32 
                 26 
                 25 
               
               
                 n-Butane 
                   
                   
                 4 
                 5 
                 4 
                 5 
                 6 
                 5 
               
               
                 Isobutane 
                   
                   
                 3 
                 4 
                 2 
                 4 
                 4 
                 4 
               
               
                 MTBE 
                 NA 
                 N/A 
                 NA 
                 NA 
                 32 
                 47 
                 0 
                 0 
               
               
                 C5+ 
                 NA 
                 NA 
                 0 
                 0 
                 0 
                 0 
                 21 
                 20 
               
               
                 Pyrolysis Gas 
                 24.2 
                 242 
                 NA 
                 NA 
                 NA 
                 NA 
                 NA 
                 NA 
               
               
                 Fuel Oil 
                 9 
                 90 
                 NA 
                 NA 
                 NA 
                 NA 
                 NA 
                 NA 
               
               
                 Total Yield 
                 100 
                 1000 
                 100 
                 128 
                 1 
                 145 
                 100 
                 98 
               
               
                   
               
               
                 KTA stands for kilotons per annum. 
               
               
                 Weight percent (wt. %) for the feed to each unit operation is based on the total weight of all feed streams introduced to that unit operation. 
               
               
                 Weight percent (wt. %) for the Component Yields in Effluent from one of the unit operations are based on the total weight of the effluent passed out of that unit operation. 
               
            
           
         
       
     
     The metathesis ethylene effluent  409  is combined with the cracking ethylene effluent  402  to produce a system ethylene effluent  412 . The metathesis propene effluent  410  is combined with the cracking propene effluent  403  to produce a system propene effluent. The metathesis C5+ effluent  414  is combined with the fuel oil effluent  417  from the steam cracking system  110  to produce a system fuel oil effluent  419 . The modeling data for the system  100  of  FIG.  6    with the naphtha hydrocarbon feed according to Example 5 is provided in Table 10. 
     
       
         
           
               
             
               
                 TABLE 10 
               
               
                   
               
               
                 Modeling Data for System of FIG. 6 with the AXL  
               
               
                 Naphtha Feed According to Example 5. 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Stream # 
                 400 
                 401 
                 402 
                 403 
                 404 
                 420 
                 405 
                 406 
                 407 
                 408 
               
               
                 Units 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
               
               
                   
               
               
                 AXL 
                 1000 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Hydrogen 
                 — 
                 — 
                 — 
                 — 
                 — 
                 4.6 
                 2.5 
                 — 
                 2 
                 — 
               
               
                 Fuel Gas 
                 — 
                 118.3 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Methanol 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 17.0 
                 — 
                 — 
               
               
                 MTBE 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 47.1 
               
               
                 Ethylene 
                 — 
                 269 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Propene 
                 — 
                 — 
                 — 
                 156.9 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Butadiene 
                 — 
                 — 
                 — 
                 — 
                 57.0 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Isobutene 
                 — 
                 — 
                 — 
                 — 
                 29.5 
                 — 
                 30.1 
                 — 
                 — 
                 — 
               
               
                 1-Butene 
                 — 
                 — 
                 — 
                 — 
                 18.2 
                 — 
                 54.3 
                 — 
                 54.4 
                 — 
               
               
                 2-Butene 
                 — 
                 — 
                 — 
                 — 
                 9.6 
                 — 
                 31.9 
                 — 
                 32.0 
                 — 
               
               
                 n-Butane 
                 — 
                 — 
                 — 
                 — 
                 5.4 
                 — 
                 5.5 
                 — 
                 5.5 
                 — 
               
               
                 Isobutane 
                 — 
                 — 
                 — 
                 — 
                 3.5 
                 — 
                 3.6 
                 — 
                 3.6 
                 — 
               
               
                 Pyrolysis Gas 
                 — 
                 — 
                 — 
                 — 
                 0.1 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Fuel Oil 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Total 
                 1000 
                 118.3 
                 269 
                 156.9 
                 123.4 
                 4.6 
                 127.9 
                 17.0 
                 97.9 
                 47.1 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 Stream # 
                 409 
                 410 
                 411 
                 412 
                 413 
                 414 
                 415 
                 417 
                 419 
               
               
                 Units 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
               
               
                   
               
               
                 AXL 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Fuel Gas 
                 — 
                 — 
                 3.8 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Methanol 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 MTBE 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Ethylene 
                 3.8 
                 — 
                 — 
                 272.8 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Propene 
                 — 
                 23.2 
                 — 
                 — 
                 180.1 
                 — 
                 — 
                 — 
                 — 
               
               
                 Butadiene 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Isobutene 
                 — 
                 — 
                 2.1 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 1-Butene 
                 — 
                 — 
                 10.5 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 2-Butene 
                 — 
                 — 
                 25.1 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 n-Butane 
                 — 
                 — 
                 5.5 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Isobutane 
                 — 
                 — 
                 3.6 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Pyrolysis Gas 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 242.4 
                 — 
                 — 
               
               
                 Fuel Oil 
                 — 
                 — 
                 — 
                 — 
                 — 
                 20.4 
                   
                 90.0 
                 110.5 
               
               
                 Total 
                 3.8 
                 23.2 
                 50.5 
                 272.8 
                 180.1 
                 20.4 
                 242.4 
                 90.0 
                 110.5 
               
               
                   
               
            
           
         
       
     
     As shown in Table 10, the system  100  with the single catalyst metathesis system integrated with the steam cracking system  110  according to Example 5 produces a total of 272.8 KTA ethylene and 180.1 KTA propene. The production ethylene in Example 5 was 3% less compared to the ethylene produced in Example 3 with the two-catalyst metathesis system integrated with the steam cracking system  110 . The production of propene in Example 5 was 7.4% less compared to the propene produced in Example 3. Thus, comparison of Example 3 and Example 5 demonstrates that integrating the steam cracking system  110  with the dual catalyst metathesis system with the metathesis catalyst and cracking catalyst, as in Example 3, can increase the selectivity and yield of propene and ethylene from the process. 
     Example 6: Integrated Steam Cracking and Metathesis Process for Gas Condensate Feed: Single Catalyst Metathesis System 
     In Example 6, the system  100  of  FIG.  6    integrating a steam cracking system  110  with a metathesis system  160  for upgrading a hydrocarbon feed  400  comprising gas condensate feed to ethylene and propylene is modeled with a metathesis system that includes the metathesis catalyst only and does not include the cracking catalyst. The gas condensate feed for the hydrocarbon feed  400  is the Khuff gas condensate provided in Table 1. In Example 6, the steam cracking system  110 , selective hydrogenation unit  130 , and isobutene removal unit  150  are modeled using the same conditions and assumptions described in relation to Example 4. 
     The metathesis system  160  was tested using a bench scale reactor having the metathesis catalyst in the metathesis reaction zone and the cracking catalyst in the cracking reaction zone downstream of the metathesis reaction zone. The feed to the bench scale metathesis reactor was synthesized using the composition modeled for the metathesis feed  407  and provided below in Table 8. In particular, the metathesis feed included 55.7 wt. % 1-butene, 32.9 wt. % 2-butene, 5.2 wt. % n-butane, and 3.4 wt. % isobutane based on the total weight of the metathesis feed. The metathesis reaction effluent was analyzed to determine the composition. The metathesis reaction effluent is separated into a metathesis ethylene effluent  409 , a metathesis propene effluent  410 , a metathesis C4 effluent  411 , and a metathesis C5+ effluent  414 . Separation of the metathesis reaction effluent into the various effluents  409 ,  410 ,  411 , and  414  is assumed to be 100% efficient. The mass balances for each of the steam cracking system  110 , the selective hydrogenation unit  130 , the isobutene removal unit  150 , and the metathesis system  160  for Example 6 are provided in Table 11. 
     
       
         
           
               
             
               
                 TABLE 11 
               
             
            
               
                   
               
               
                 Mass Balance Information for Modeling the Unit  
               
               
                 Operations of FIG. 6 for Example 6 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 Selective 
                   
                   
               
               
                   
                 Steam Cracking 
                 Hydrogenation 
                 Isobutene 
                 Metathesis 
               
               
                 Yields 
                 System 
                 Unit 
                 Removal Unit 
                 System 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Feed 
                 wt. % 
                 KTA 
                 wt. % 
                 KTA 
                 wt. % 
                 KTA 
                 wt. % 
                 KTA 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 KGC 
                 100 
                 1000 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Hydrogen 
                 — 
                 — 
                 4 
                 4 
                 — 
                 — 
                 3 
                 2 
               
               
                 Cracking C4 Eff 
                 — 
                 — 
                 96 
                 95 
                 — 
                 — 
                 — 
                 — 
               
               
                 Hydrogenation Eff. 
                 — 
                 — 
                 — 
                 — 
                 89 
                 99 
                 — 
                 — 
               
               
                 Methanol 
                 — 
                 — 
                 — 
                 — 
                 11 
                 12 
                 — 
                 — 
               
               
                 Metathesis Feed 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 97 
                 75 
               
               
                 Total Feed 
                 100 
                 1000 
                 100 
                 99 
                 100 
                 107 
                 100 
                 77 
               
            
           
           
               
            
               
                 Component Yields in Effluent 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Off-gas 
                 NA 
                 NA 
                 NA 
                 NA 
                 NA 
                 NA 
                 1 
                 1 
               
               
                 Hydrogen 
                 2.1 
                 21 
                 2.2 
                 2.2 
                 1.9 
                 2.2 
                 3 
                 2.2 
               
               
                 Methane 
                 10.9 
                 109 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 Ethylene 
                 27.8 
                 278 
                 0 
                 0 
                 0 
                 0 
                 4 
                 3 
               
               
                 Propylene 
                 14.5 
                 145 
                 0 
                 0 
                 0 
                 0 
                 24 
                 18 
               
               
                 1,3-butadiene 
                 9.5 
                 95 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 Isobutene 
                   
                   
                 22 
                 22 
                 0 
                 0 
                 2 
                 2 
               
               
                 1-Butene 
                   
                   
                 43 
                 43 
                 39 
                 43 
                 11 
                 8 
               
               
                 2-Butene 
                   
                   
                 26 
                 25 
                 23 
                 25 
                 26 
                 20 
               
               
                 n-Butane 
                   
                   
                 4 
                 4 
                 4 
                 4 
                 5 
                 4 
               
               
                 Isobutane 
                   
                   
                 3 
                 3 
                 2 
                 3 
                 3 
                 3 
               
               
                 MTBE 
                 NA 
                 NA 
                 NA 
                 NA 
                 31 
                 34 
                 0 
                 0 
               
               
                 C5+ 
                 NA 
                 NA 
                 0 
                 0 
                 0 
                 0 
                 21 
                 16 
               
               
                 Pyrolysis Gas 
                 17.3 
                 173 
                 NA 
                 NA 
                 NA 
                 NA 
                 NA 
                 NA 
               
               
                 Fuel Oil 
                 17.9 
                 179 
                 NA 
                 NA 
                 NA 
                 NA 
                 NA 
                 NA 
               
               
                 Total Yield 
                 100 
                 1000 
                 100 
                 99 
                 100 
                 111 
                 100 
                 77 
               
               
                   
               
               
                 KTA stands for kilotons per annum. 
               
               
                 Weight percent (wt. %) for the feed to each unit operation is based on the total weight of all feed streams introduced to that unit operation. 
               
               
                 Weight percent (wt. %) for the Component Yields in Effluent from one of the unit operations are based on the total weight of the effluent passed out of that unit operation. 
               
            
           
         
       
     
     As described previously in Examples 2-5, the metathesis ethylene effluent  409  is combined with the cracking ethylene effluent  402  to produce a system ethylene effluent  412 . The metathesis propene effluent  410  is combined with the cracking propene effluent  403  to produce a system propene effluent. The metathesis C5+ effluent  414  is combined with the fuel oil effluent  417  from the steam cracking system  110  to produce a system fuel oil effluent  419 . The modeling data for the system  100  of  FIG.  6    with the Khuff gas condensate for the hydrocarbon feed according to Example 6 is provided in Table 12. 
     
       
         
           
               
             
               
                 TABLE 12 
               
               
                   
               
               
                 Modeling Data for the System of FIG. 6  
               
               
                 with Khuff Gas Condensate (KGC) Feed. 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Stream # 
                 400 
                 401 
                 402 
                 403 
                 404 
                 420 
                 405 
                 406 
                 407 
                 408 
               
               
                 Units 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
               
               
                   
               
               
                 KGC 
                 1000 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Hydrogen 
                 — 
                 — 
                 — 
                 — 
                 — 
                 3.8 
                 2.2 
                 — 
                 2.2 
                 — 
               
               
                 Fuel Gas 
                 — 
                 130.2 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Methanol 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 12.4 
                 — 
                 — 
               
               
                 MTBE 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 34.2 
               
               
                 Ethylene 
                 — 
                 — 
                 278.4 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Propene 
                 — 
                 — 
                 — 
                 145.2 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Butadiene 
                 — 
                 — 
                 — 
                 — 
                 46.7 
                 — 
                 0.0 
                 — 
                 — 
                 — 
               
               
                 Isobutene 
                 — 
                 — 
                 — 
                 — 
                 21.5 
                 — 
                 21.9 
                 — 
                 — 
                 — 
               
               
                 1-Butene 
                 — 
                 — 
                 — 
                 — 
                 13.2 
                 — 
                 42.8 
                 — 
                 42.8 
                 — 
               
               
                 2-Butene 
                 — 
                 — 
                 — 
                 — 
                 7.0 
                 — 
                 25.3 
                 — 
                 25.3 
                 — 
               
               
                 n-Butane 
                 — 
                 — 
                 — 
                 — 
                 3.9 
                 — 
                 4.0 
                 — 
                 4.0 
                 — 
               
               
                 Isobutane 
                 — 
                 — 
                 — 
                 — 
                 2.6 
                 — 
                 2.6 
                 — 
                 2.6 
                 — 
               
               
                 Pyrolysis Gas 
                 — 
                 — 
                 — 
                 — 
                 0.1 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Fuel Oil 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Total 
                 1000 
                 130.2 
                 278.4 
                 145.2 
                 95.0 
                 3.8 
                 98.8 
                 12.4 
                 76.9 
                 34.2 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 Stream # 
                 409 
                 410 
                 411 
                 412 
                 413 
                 414 
                 415 
                 417 
                 419 
               
               
                 Units 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
                 KTA 
               
               
                   
               
               
                 KGC 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Hydrogen 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Fuel Gas 
                 — 
                 — 
                 3.2 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Methanol 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 MTBE 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Ethylene 
                 3.0 
                 — 
                 — 
                 281.4 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Propene 
                 — 
                 18.2 
                 — 
                 — 
                 163.4 
                 — 
                 — 
                 — 
                 — 
               
               
                 Butadiene 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Isobutene 
                 — 
                 — 
                 1.7 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 1-Butene 
                 — 
                 — 
                 8.2 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 2-Butene 
                 — 
                 — 
                 19.8 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 n-Butane 
                 — 
                 — 
                 4.0 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Isobutane 
                 — 
                 — 
                 2.6 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Pyrolysis 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 172.7 
                 — 
                 — 
               
               
                 Gas 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Fuel Oil 
                 — 
                 — 
                 — 
                 — 
                 — 
                 16.1 
                 — 
                 178.6 
                 194.7 
               
               
                 Total 
                 3.0 
                 18.2 
                 39.5 
                 281.4 
                 163.4 
                 16.1 
                 172.7 
                 178.6 
                 194.7 
               
               
                   
               
            
           
         
       
     
     As shown in Table 12, the system  100  with the single catalyst metathesis system integrated with the steam cracking system  110  for processing Khuff gas condensate according to Example 6 produces a total of 281.4 KTA ethylene and 163.4 KTA propene. The production of ethylene in Example 6 was 2.6% less compared to the ethylene produced in Example 4 with the two-catalyst metathesis system integrated with the steam cracking system  110 . The production of propene in Example 6 was 6.5% less compared to the propene produced in Example 4. Thus, comparison of Example 4 and Example 6 demonstrates that, for gas condensate feeds, integrating the steam cracking system  110  with the dual catalyst metathesis system with the metathesis catalyst and cracking catalyst, as in Example 4, can increase the selectivity and yield of propene and ethylene from the process. 
     A first aspect of the present disclosure may include a process for producing olefins. The process may include contacting a hydrocarbon feed with at least steam at a temperature of from 700° C. to 900° C. The contacting may cause at least a portion of the hydrocarbon feed to undergo steam cracking to form a cracking reaction effluent comprising at least butenes. The process may further include separating the cracking reaction effluent to produce at least a cracking C4 effluent that includes at least normal butenes, isobutene, and 1,3-butadiene. The process may further include subjecting the cracking C4 effluent to selective hydrogenation to produce a hydrogenation effluent. Selective hydrogenation may cause at least a portion of the 1,3-butadiene in the cracking C4 effluent to react to form normal butenes. The process may further include removing isobutene from the hydrogenation effluent to produce a metathesis feed comprising at least normal butenes and contacting at least a portion of the metathesis feed with a metathesis catalyst and a cracking catalyst directly downstream of the metathesis catalyst to produce a metathesis reaction effluent. Contacting the metathesis feed with the metathesis catalyst may cause metathesis of normal butenes to produce at least ethylene, propene, and C5+ olefins, and contacting with the cracking catalyst may cause at least a portion of the C5+ olefins produced through metathesis to undergo cracking reactions to produce propene, ethylene, or both. The metathesis reaction effluent may include at least ethylene, propene, or both. 
     A second aspect of the present disclosure may include the first aspect, in which the hydrocarbon feed may comprise naphtha, a gas condensate, or both. 
     A third aspect of the present disclosure may include any one of the first or second aspects, further comprising separating the metathesis reaction effluent into a metathesis C5+ effluent and at least one olefin-containing effluent. The olefin-containing effluent may comprise at least one of ethylene, propylene, or normal butenes. The process may further include passing the metathesis C5+ effluent back into contact with the hydrocarbon feed and steam at the temperature of from 700° C. to 900° C., where contacting may cause at least a portion of the metathesis C5+ effluent to undergo steam cracking. 
     A fourth aspect of the present disclosure may include the third aspect, in which passing the metathesis C5+ effluent back into contact with the hydrocarbon feed and steam may comprise hydrotreating the metathesis C5+ effluent to produce a hydrotreated effluent and passing the hydrotreated effluent into contact with the hydrocarbon feed and steam at the temperature of from 700° C. to 900° C. The contacting of the hydrotreated effluent with the hydrocarbon feed and steam may cause at least a portion of the hydrotreated effluent to undergo steam cracking. 
     A fifth aspect of the present disclosure may include any one of the first through fourth aspects, comprising separating the metathesis reaction effluent into a metathesis C5+ effluent, a metathesis C4 effluent, a metathesis propene effluent, and a metathesis ethylene effluent. 
     A sixth aspect of the present disclosure may include the fifth aspect, further comprising, after separating, passing at least a portion of the metathesis C4 effluent back into contact with the metathesis catalyst, where contact may cause further metathesis of normal butenes in the metathesis C4 effluent to produce the metathesis reaction effluent. 
     A seventh aspect of the present disclosure may include the fifth aspect, further comprising passing at least a portion of the metathesis C4 effluent into contact with the cracking C4 effluent, hydrogen, and a selective hydrogenation catalyst and contacting the portion of the metathesis C4 effluent with the hydrogen in the presence of the selective hydrogenation catalyst, where contacting may cause at least a portion of 1,3-butadiene in the portion of the metathesis C4 effluent to undergo a selective hydrogenation reaction. 
     An eighth aspect of the present disclosure may include any one of the fifth through seventh aspects, further comprising passing at least a portion of the metathesis ethylene effluent back into contact with the metathesis catalyst. 
     A ninth aspect of the present disclosure may include any one of the fifth through seventh aspects, in which the metathesis ethylene effluent may not be passed back into contact with the metathesis catalyst and no supplemental ethylene is introduced into contact with the metathesis catalyst. 
     A tenth aspect of the present disclosure may include any one of the first through ninth aspects, in which subjecting the cracking C4 effluent to selective hydrogenation may comprise contacting the cracking C4 effluent with hydrogen in the presence of a selective hydrogenation catalyst under conditions sufficient to cause at least a portion of the 1,3-butadiene in the cracking C4 effluent to undergo hydrogenation to produce a hydrogenation effluent comprising a greater concentration of normal butenes compared to the concentration of normal butenes in the cracking C4 effluent. 
     An eleventh aspect of the present disclosure may include the tenth aspect, in which the hydrogenation effluent may have a concentration of 1,3-butadiene less than a concentration of 1,3-butadiene in the cracking C4 effluent. 
     A twelfth aspect of the present disclosure may include any one of the first through eleventh aspects, in which removing isobutene may comprise contacting the hydrogenation effluent with methanol under reaction conditions sufficient to convert at least a portion of the isobutene in the hydrogenated C4 effluent to methyl tert-butyl ether to produce an MTBE reaction product and separating at least a portion of the methyl tert-butyl ether from the MTBE reaction product to produce an MTBE effluent comprising the methyl tert-butyl ether and the metathesis feed comprising butene. 
     A thirteenth aspect of the present disclosure may include the twelfth aspect, further comprising recovering at least a portion of the methyl-tert-butyl ether from the MTBE effluent. 
     A fourteenth aspect of the present disclosure may include the twelfth or thirteenth aspects, further comprising passing at least a portion of the MTBE effluent back into the hydrocarbon feed and subjecting the portion of the MTBE effluent to steam cracking. 
     A fifteenth aspect of the present disclosure may include the fourteenth aspect, further comprising contacting the MTBE effluent with a cracking catalyst under conditions sufficient to produce an isobutene effluent, where the contacting may cause at least a portion of the methyl tert-butyl ether in the MTBE effluent to react to form isobutene. The process may further include passing the isobutene effluent back into the hydrocarbon feed and subjecting the isobutene effluent to steam cracking. 
     A sixteenth aspect of the present disclosure may include any one of the first through fifteenth aspects, comprising separating the cracking reaction effluent into at least the cracking C4 effluent, a cracking ethylene effluent, a cracking propylene effluent, a pyrolysis gas effluent, a fuel gas effluent, and a lesser molecular weight gas effluent. 
     A seventeenth aspect of the present disclosure may include any one of the first through sixteenth aspects, comprising contacting the hydrocarbon feed with the steam at the temperature of from 700° C. to 900° C. for a residence time of from 0.05 seconds to 2 seconds and at a mass ratio of steam to hydrocarbon of from 0.3:1 to 2:1. 
     An eighteenth aspect of the present disclosure may include a process for producing olefins, the process including contacting a hydrocarbon feed with steam in a steam cracking system at a temperature sufficient to produce a cracking reaction effluent and separating the cracking reaction effluent to produce at least a cracking C4 effluent comprising normal butenes, isobutene, and 1,3-butadiene. The process may further include subjecting the cracking C4 effluent to selective hydrogenation in a selective hydrogenation unit to produce a hydrogenation effluent. Selective hydrogenation may cause at least a portion of the 1,3-butadiene in the cracking C4 effluent to react to form normal butenes. The process may further include passing the hydrogenation effluent to an isobutene removal unit, removing isobutene from the hydrogenation effluent in the isobutene removal unit to produce at least a metathesis feed comprising normal butenes, passing at least a portion of the metathesis feed to a metathesis system comprising a metathesis catalyst and a cracking catalyst directly downstream of the metathesis catalyst, and contacting the portion of the metathesis feed with the metathesis catalyst and the cracking catalyst to produce a metathesis reaction effluent. Contacting with the metathesis catalyst may cause metathesis of normal butenes in the metathesis feed to produce at least ethylene, propene, and C5+ olefins, and contacting with the cracking catalyst may cause at least a portion of the C5+ olefins produced through metathesis to undergo cracking reactions to produce ethylene, propene, or both. The metathesis reaction effluent may comprise at least ethylene, propene, or both. 
     A nineteenth aspect of the present disclosure may include the eighteenth aspect, in which the hydrocarbon feed may comprise a naphtha stream, a gas condensate stream, or both. 
     A twentieth aspect of the present disclosure may include either one of the eighteenth or nineteenth aspects, in which the metathesis system may comprise a metathesis reaction zone comprising the metathesis catalyst and a cracking reaction zone comprising the cracking catalyst, and the cracking reaction zone may be directly downstream of the metathesis reaction zone. 
     A twenty-first aspect of the present disclosure may include the twentieth aspect, comprising passing at least a portion of the metathesis feed through the metathesis reaction zone and the cracking reaction zone downstream of the metathesis reaction zone. Contacting the metathesis feed with the metathesis catalyst in the metathesis reaction zone may cause at least a portion of the normal butenes in the metathesis feed to undergo metathesis to produce at least propene and C5+ olefins, and contacting the C5+ olefins with the cracking catalyst in the cracking reaction zone may cause at least a portion of the C5+ olefins to undergo catalytic cracking to produce at least one of ethylene, propene, or both. 
     A twenty-second aspect of the present disclosure may include either one of the twentieth or twenty-first aspects, where the cracking catalyst may be in contact with the metathesis catalyst. 
     A twenty-third aspect of the present disclosure may include either one of the twentieth or twenty-first aspects, where the metathesis reaction zone may be in a first reactor, the cracking reaction zone may be in a second reactor directly downstream of the first reactor, and a conduit may fluidly couple the second reactor to the first reactor. 
     A twenty-fourth aspect of the present disclosure may include any one of the eighteenth through twenty-third aspects, in which the metathesis catalyst may comprise a least one metal oxide deposited on surfaces of a mesoporous silica catalyst support or a mesoporous silica-alumina catalyst support. 
     A twenty-fifth aspect of the present disclosure may include any one of the eighteenth through twenty-fourth aspects, in which the cracking catalyst may comprise an MFI structured silica-containing catalyst. 
     A twenty-sixth aspect of the present disclosure may include any one of the eighteenth through twenty-fifth aspects, comprising separating the metathesis reaction effluent into a metathesis ethylene effluent, a metathesis propene effluent, a metathesis C4 effluent, and a metathesis C5+ effluent. 
     A twenty-seventh aspect of the present disclosure may include the twenty-sixth aspect, further comprising passing at least a portion of the metathesis C5+ effluent back to the steam cracking system. 
     A twenty-eighth aspect of the present disclosure may include the twenty-seventh aspect, where passing the at least a portion of the metathesis C5+ effluent back to the steam cracking system may comprise hydrotreating the portion of the metathesis C5+ effluent to produce a hydrotreated effluent, passing the hydrotreated effluent back to the steam cracking system, and contacting the hydrotreated effluent with steam at the temperature of from 700° C. to 900° C. in the steam cracking system, where contacting causes at least a portion of the hydrotreated effluent to undergo steam cracking. 
     A twenty-ninth aspect of the present disclosure may include any one of the twenty-sixth through twenty-eighth aspects, further comprising passing at least a portion of the metathesis C4 effluent back to the metathesis system, the isobutene removal unit, or the selective hydrogenation unit. 
     A thirtieth aspect of the present disclosure may include any one of the eighteenth through twenty-ninth aspects, further comprising passing at least a portion of the metathesis ethylene effluent back to the metathesis system. 
     A thirty-first aspect of the present disclosure may include any one of the eighteenth through thirtieth aspects, in which the metathesis system may comprise a metathesis reactor comprising a metathesis reaction zone having the metathesis catalyst and a cracking reaction zone downstream of the metathesis reaction zone and having a cracking catalyst and a supplemental metathesis reactor comprising a supplemental metathesis catalyst. The supplemental metathesis reactor may be operated in parallel with the metathesis reactor. The process may further comprise contacting a first portion of the metathesis feed with the metathesis catalyst and the cracking catalyst in the metathesis reactor to produce the metathesis reaction effluent and contacting a second portion of the metathesis feed and a portion of the metathesis ethylene effluent with the supplemental metathesis catalyst in the supplemental metathesis reactor to produce a supplemental metathesis reaction effluent. 
     A thirty-second aspect of the present disclosure may include any one of the eighteenth through twenty-ninth aspects, where the metathesis ethylene effluent may not be passed to the metathesis system and no supplemental ethylene may be introduced to the metathesis system. 
     A thirty-third aspect of the present disclosure may include any one of the eighteenth through thirty-second aspects, in which the selective hydrogenation unit may be downstream of the steam cracking system, the isobutene removal unit may be downstream of the selective hydrogenation unit, and the metathesis system may be downstream of the isobutene removal unit. 
     A thirty-fourth aspect of the present disclosure may include any one of the eighteenth through thirty-third aspects, where subjecting the cracking C4 effluent to selective hydrogenation may comprise contacting the cracking C4 effluent with hydrogen in the presence of a selective hydrogenation catalyst in the selective hydrogenation unit at reaction conditions sufficient to cause at least a portion of the 1,3-butadiene in the steam cracking C4 effluent to undergo a hydrogenation reaction to produce a hydrogenation effluent having a concentration of 1,3-butadiene less than a concentration of 1,3-butadiene in the cracking C4 effluent. 
     A thirty-fifth aspect of the present disclosure may include any one of the eighteenth through thirty-fourth aspects, where removing isobutene from the hydrogenation effluent may comprise contacting the hydrogenation effluent with methanol in an MTBE reactor of the isobutene removal unit under reaction conditions sufficient to convert at least a portion of isobutene in the hydrogenation effluent to methyl tert-butyl ether to produce an MTBE reaction product and separating the MTBE reaction product into at least an MTBE effluent and the metathesis feed, the metathesis feed comprising normal butenes. 
     A thirty-sixth aspect of the present disclosure may include the thirty-fifth aspect, further comprising recovering at least a portion of the methyl-tert-butyl ether from the MTBE effluent. 
     A thirty-seventh aspect of the present disclosure may include any one of the thirty-fifth or thirty-sixth aspects, further comprising passing at least a portion of the MTBE effluent back to the steam cracking system. 
     A thirty-eighth aspect of the present disclosure may include the thirty-seventh aspect, further comprising contacting the MTBE effluent with a cracking catalyst under conditions sufficient to produce an isobutene effluent, where the contacting may cause at least a portion of the methyl-tert-butyl ether in the MTBE effluent to react to form isobutene. The process may further include passing the isobutene effluent back to the steam cracking system and contacting the isobutene effluent with steam at the temperature of from 700° C. to 900° C. in the steam cracking system, where contacting may cause at least a portion of the isobutene effluent to undergo steam cracking. 
     A thirty-ninth aspect of the present disclosure may include any one of the eighteenth through thirty-eighth aspects, comprising separating the cracking reaction effluent to produce the cracking C4 effluent comprising butenes, and one or more of a cracking ethylene effluent, a cracking propene effluent, a fuel oil, a pyrolysis gas, a lesser-molecular weight gas, or combinations of these. 
     A fortieth aspect of the present disclosure may include the thirty-ninth aspect, in which separating the cracking reaction effluent may comprise passing the cracking reaction effluent to a cracking effluent separation system comprising one or a plurality of separators operable to separate the cracking reaction effluent into the cracking C4 effluent and at least one of the cracking propene effluent, the cracking ethylene effluent, the lesser-molecular weight gas effluent, the fuel oil, the pyrolysis gas, or combinations of these. 
     A forty-first aspect of the present disclosure may include any one of the eighteenth through fortieth aspects, comprising contacting the hydrocarbon feed with the steam in a pyrolysis zone of the steam cracking system at a temperature of from 700° C. to 900° C., for a residence time of from 0.05 seconds to 2 seconds, and at a mass ratio of steam to hydrocarbon of from 0.3:1 to 2:1. 
     A forty-second aspect of the present disclosure may include a system for producing olefins. The system may include a steam cracking system that may be operable to contact a hydrocarbon feed with steam at a temperature of from 700° C. to 900° C. to produce at least a cracking C4 effluent comprising normal butenes, isobutene, and 1,3-butadiene. The system may include a selective hydrogenation unit downstream of the steam cracking system. The selective hydrogenation unit may be operable to convert 1,3-butadiene in the cracking C4 effluent from the steam cracking system to normal butenes. The system may further include an isobutene removal unit downstream of the selective hydrogenation unit and a metathesis system downstream of the isobutene removal unit. The metathesis system may comprise a metathesis reaction zone comprising a metathesis catalyst and a cracking reaction zone comprising a cracking catalyst. The cracking reaction zone may be disposed directly downstream of the metathesis reaction zone. 
     A forty-third aspect of the present disclosure may include the forty-second aspect, where the metathesis system may comprise at least one metathesis reactor operable to contact a metathesis feed from the isobutene removal unit with the metathesis catalyst in the metathesis reaction zone and then the cracking catalyst in the cracking reaction zone. 
     A forty-fourth aspect of the present disclosure may include either one of the forty-second or forty-third aspects, where the cracking catalyst may be in contact with the metathesis catalyst. 
     A forty-fifth aspect of the present disclosure may include either one of the forty-second or forty-third aspects, where the metathesis reaction zone may be in a first reactor, the cracking reaction zone may be in a second reactor directly downstream of the first reactor, and a conduit may fluidly couple the second reactor to the first reactor. 
     A forty-sixth aspect of the present disclosure may include any one of the forty-second through forty-fifth aspects, in which the metathesis catalyst may comprise a least one metal oxide supported on a mesoporous silica catalyst support or a mesoporous silica-alumina catalyst support. 
     A forty-seventh aspect of the present disclosure may include any one of the forty-second through forty-sixth aspects, in which the cracking catalyst may comprise an MFI structured silica-containing catalyst. 
     A forty-eighth aspect of the present disclosure may include any one of the forty-second through forty-seventh aspects, in which the metathesis system further comprises a metathesis effluent separation system that may be operable to separate a metathesis reaction effluent into at least a metathesis ethylene effluent, a metathesis propene effluent, a metathesis C4 effluent, and a metathesis C5+ effluent. 
     A forty-ninth aspect of the present disclosure may include the forty-eighth aspect, further comprising a metathesis C5+ recycle operable to pass at least a portion of the metathesis C5+ effluent back to the steam cracking system. 
     A fiftieth aspect of the present disclosure may include the forty-ninth aspect, further comprising a hydrotreating unit downstream of the metathesis effluent separation system and upstream of the steam cracking system, the hydrotreating unit operable to hydrotreat the portion of the metathesis C5+ effluent in the metathesis C5+ recycle to produce a hydrotreated effluent. 
     A fifty-first aspect of the present disclosure may include any one of the forty-eighth through fiftieth aspects, further comprising a metathesis C4 effluent recycle operable to pass at least a portion of the metathesis C4 effluent from the metathesis effluent separation system back to the metathesis system, the isobutene removal unit, or the selective hydrogenation unit. 
     A fifty-second aspect of the present disclosure may include any one of the forty-eighth through fifty-first aspects, in which the metathesis system may further comprise a supplemental metathesis reactor comprising a supplemental metathesis catalyst and a metathesis ethylene recycle operable to pass at least a portion of the metathesis ethylene effluent to the supplemental metathesis reactor. 
     A fifty-third aspect of the present disclosure may include any one of the forty-second through fifty-second aspects, in which the selective hydrogenation unit may comprise one or a plurality of selective hydrogenation reactors, each of which comprises a selective hydrogenation catalyst. The selective hydrogenation unit may be operable to contact the cracking C4 effluent with hydrogen in the presence of the selective hydrogenation catalyst at reaction conditions sufficient to convert at least a portion of the 1,3-butadiene in the cracking C4 effluent to normal butenes. 
     A fifty-fourth aspect of the present disclosure may include any one of the forty-second through fifty-third aspects, in which the isobutene removal unit may comprise an MTBE reactor operable to contact a hydrogenation effluent from the selective hydrogenation unit with methanol at reaction conditions sufficient to convert at least a portion of the isobutene to methyl tert-butyl ether and an MTBE effluent separation system operable to separate an MTBE reactor effluent from the MTBE reactor into at least a metathesis feed and an MTBE effluent. 
     A fifty-fifth aspect of the present disclosure may include the fifty-fourth aspect, in which the isobutene removal unit may further comprise an MTBE cracking unit downstream of the MTBE effluent separation system, the MTBE cracking unit operable to contact at least a portion of the MTBE effluent with a cracking catalyst to convert at least a portion of the methyl tert-butyl ether in the MTBE effluent back to isobutene. 
     A fifty-sixth aspect of the present disclosure may include any one of the forty-second through fifty-fifth aspects, in which the steam cracking system comprises a cracking effluent separation unit comprising one or a plurality of separators operable to separate a cracking reaction effluent into a cracking C4 effluent and at least one other cracking effluent. 
     A fifty-seventh aspect of the present disclosure may include any one of the forty-second through fifty-sixth aspects, further comprising a combined separation system operable to separate a cracking reaction effluent from a steam cracking reactor of the steam cracking system and a metathesis reaction effluent from the metathesis system into at least a C4 stream, a system propene effluent, and a system ethylene effluent. 
     It should now be understood that various aspects of the systems and processes for producing olefins that include high-severity fluidized catalytic cracking integrated with metathesis are described and such aspects may be utilized in conjunction with various other aspects. 
     Throughout this disclosure ranges are provided for various processing parameters and operating conditions for the systems and processes for producing olefins and the compositions of various streams and mixtures. It will be appreciated that when one or more explicit ranges are provided the individual values and the sub-ranges formed within the range are also intended to be provided as providing an explicit listing of all possible combinations is prohibitive. For example, a provided range of 1-10 also includes the individual values, such as 1, 2, 3, 4.2, and 6.8, as well as all the ranges that may be formed within the provided bounds, such as 1-8, 2-4, 6-9, and 1.3-5.6. 
     It is noted that recitations herein of “at least one” component, element, etc., should not be used to create an inference that the alternative use of the articles “a” or “an” should be limited to a single component, element, etc. 
     It should be apparent to those skilled in the art that various modifications and variations can be made to the described embodiments without departing from the spirit and scope of the claimed subject matter. Thus, it is intended that the specification cover the modifications and variations of the various described embodiments provided such modifications and variations come within the scope of the appended claims and their equivalents.