Patent Publication Number: US-8993824-B2

Title: Fluid catalytic cracking process

Description:
FIELD OF THE INVENTION 
     This invention generally relates to a fluid catalytic cracking process. 
     DESCRIPTION OF THE RELATED ART 
     Catalytic cracking can create a variety of products from larger hydrocarbons. Often, a feed of a heavier hydrocarbon, such as a vacuum gas oil, is provided to a catalytic cracking reactor, such as a fluid catalytic cracking reactor. Various products may be produced from such a system, including a gasoline product and/or a light product such as propene and/or ethene. 
     In such systems, a single reactor or a dual reactor can be utilized. Although additional capital costs may be incurred by using a dual reactor system, one of the reactors can be operated to tailor conditions for maximizing products, such as light olefins including propene and/or ethene. 
     In such dual reactor systems, high yields of butene, such as about 70-about 150%, or even about 100-about 300%, by weight, based on propene yield, can occur during cracking of either light cracked naphtha or polymer naphtha. Yields may be especially high for polymer naphtha because the naphtha is almost entirely composed of dimers and trimers of butene. Generally, this is undesirable as, historically, propene has been a more valuable product than butene. As a consequence, there is a desire to improve the selectivity of such feeds and dual reactor systems to produce propene. 
     SUMMARY OF THE INVENTION 
     One exemplary embodiment can be a process for fluid catalytic cracking. The process may include providing a first feed having a boiling point of about 180-about 800° C. to a first riser reactor, and providing a second feed having first and second parts to a second reactor. Typically, the first part includes one or more C5-C12 hydrocarbons and a second part includes one or more C4-C5 hydrocarbons. Generally, an effective amount of the second part is combined with the first part to maximize production of propene. 
     Another exemplary embodiment may be a process for fluid catalytic cracking. The process can include providing at least one of a gas oil, a vacuum gas oil, an atmospheric gas oil, a coker gas oil, a hydrotreated gas oil, a hydrocracker unconverted oil, and an atmospheric residue to a first riser reactor, and providing a light cracked naphtha and/or a polymer naphtha combined with an effective amount of at least one C4 and C5 hydrocarbon to a second riser reactor to maximize production of propene. 
     Yet another exemplary embodiment can be a process for fluid catalytic cracking. The process may include providing at least one of a gas oil, a vacuum gas oil, an atmospheric gas oil, a coker gas oil, a hydrotreated gas oil, a hydrocracker unconverted oil, and an atmospheric residue to a first riser reactor operating at a temperature of about 150-about 580° C., providing a light cracked naphtha and/or a polymer naphtha combined with an effective amount of at least one C4 and C5 hydrocarbon to a second riser reactor operating at a temperature of about 425-about 630° C. to maximize production of propene, providing a catalyst to at least one of the first and second riser reactors, and regenerating the catalyst in a regeneration zone. 
     The embodiments disclosed herein add one or more C4-C5 hydrocarbons, preferably one or more C4 and C5 alkenes, which can shift the reaction equilibrium to produce more propene. By including, e.g., butene in a feed including a naphtha, light cracked naphtha, or polygas to e.g., a second riser, propene selectivity can be enhanced and overall recycle rates and gas yields may be minimized. 
     DEFINITIONS 
     As used herein, the term “stream” can include various hydrocarbon molecules, such as straight-chain, branched, or cyclic alkanes, alkenes, alkadienes, and alkynes, and optionally other substances, such as gases, e.g., hydrogen, or impurities, such as heavy metals, and sulfur and nitrogen compounds. The stream can also include aromatic and non-aromatic hydrocarbons. Moreover, the hydrocarbon molecules may be abbreviated C1, C2, C3 . . . Cn where “n” represents the number of carbon atoms in the one or more hydrocarbon molecules. 
     As used herein, the term “zone” can refer to an area including one or more equipment items and/or one or more sub-zones. Equipment items can include one or more reactors or reactor vessels, heaters, exchangers, pipes, pumps, compressors, and controllers. Additionally, an equipment item, such as a reactor, dryer, or vessel, can further include one or more zones or sub-zones. 
     As used herein, the term “rich” can mean an amount of generally at least about 50%, and preferably about 70%, by mole, of a compound or class of compounds in a stream. 
     As used herein, the term “substantially” can mean an amount of generally at least about 80%, preferably about 90%, and optimally about 99%, by mole, of a compound or class of compounds in a stream. 
     As used herein, the terms “alkane”, “paraffin”, and “saturate” may be used interchangeably. 
     As used herein, the terms “alkene” and “olefin” may be used interchangeably. 
     As used herein, the term “butene” can include but-1-ene, cis-2-butene, trans-2-butene, and/or 2-methylpropene. 
     As used herein, the term “pentene” can include 1-pentene, cis-2-pentene, trans-2-pentene, 2-methylbut-1-ene, 3-methylbut-1-ene, and/or 2-methylbut-2-ene. 
     As used herein, the term “light cracked naphtha” may be abbreviated “LCN”. 
     As used herein, the term “fluid catalytic cracking” may be abbreviated “FCC”. 
     As used herein, the term “dry gases” may include hydrogen, hydrogen sulfide, methane, ethane, and ethene, and can be abbreviated “DG”. 
     As used herein, the term “weight percent” may be abbreviated “wt. %”. 
     As used herein, the term “riser reactor” generally means a reactor used in a fluid catalytic cracking process that can include a riser and a reaction vessel. Usually, such a reactor has catalyst provided at a bottom of a riser and the catalyst proceeds to a reaction vessel having a mechanism for separating the catalyst from a hydrocarbon. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic depiction of an exemplary fluid catalytic cracking zone. 
         FIG. 2  is a graphical depiction of the net yield weight percent based on total feed versus weight percent of butenes in alkenes for three exemplary feeds. 
         FIG. 3  is a graphical depiction of selectivity yield based on conversion versus weight percent butenes in alkenes for three exemplary feeds. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , an exemplary fluid catalytic cracking zone  100  can include a first riser reactor  160 , a second riser reactor  260 , and a regeneration zone  300 . An exemplary dual riser system is disclosed in, e.g., US 2010/0236980. 
     The first riser reactor  160  can include a riser  170  terminating in a reaction vessel  180 . Usually, the first riser reactor  160  can further include a stripper zone  130  including one or more baffles and an internal shell  150 . The second riser reactor  260  can include a riser  270  terminating in a reaction vessel  280 . Typically, the second riser reactor  260  can also include a stripping zone  284 . 
     Usually, a first feed  120  having a boiling point of about 180-about 800° C., typically a boiling point no less than about 350° C., is provided above a fluidizing gas  110  in the riser  170 . These fluids and catalyst can rise within the riser  170  to the reaction vessel  180 . Generally, the reactants and catalysts can be separated by one or more swirl arms with the product gases rising within the reaction vessel  180  to exit as a product stream  190  and the catalyst dropping. A portion of the catalyst can be provided via a first catalyst line  154  to the regeneration zone  300 , and another portion passing through a line  156  may be provided at the base of the riser  170  to maximize the ratio of catalyst to oil. Usually, the first riser reactor  160  operates at a temperature of about 450-about 600° C. and processes heavy hydrocarbons, e.g., those feeds boiling at no less than about 350° C. 
     The second riser reactor  260  can receive a second feed  220  that can include at least about 20%, by weight, one or more C4 hydrocarbons, preferably one or more C4-C5 alkenes, such as butene. Preferably, at least about 30%, by weight, of the one or more C4-C5 alkenes, such as butene, are provided based on the weight of the second feed  220 . Desirably, the second feed has about 30-about 80%, by weight, of one or more butenes based on the amount of the one or more alkenes in the second feed  220 . The second feed  220  can include a first part  230  and a second part  240 . The first part  230  can include a naphtha having one or more C5-C12 hydrocarbons, and typically can include a light cracked naphtha, which can include at least one C5-C7 hydrocarbon, and/or a polymer naphtha, which can include at least one C8-C12 hydrocarbon. 
     The second part  240  can include one or more C4-C5 hydrocarbons, typically one or more C4-C5 alkenes, such as at least one of butene and pentene. Generally, an effective amount of the second part  240  is combined with the first part  230  to maximize the production of propene by changing the reaction equilibrium by providing, e.g., butene and/or pentene, which can be products of the reaction. Although not wanting to be bound by theory, butene and/or pentene in the feed shifts the reaction from producing these compounds to producing more of other compounds, e.g., propene. 
     The second feed  220  can be provided above a fluidizing stream  210  to enable the reactants to react within the riser  270 . The catalyst and products may rise to a separating device, such as swirl arms, with the catalyst dropping within the reaction vessel  280  and the gases rising and exiting as a second product stream  290 . The catalyst can be provided via a line  244  to a regenerator  320  in the regeneration zone  300  with another portion traveling via a line  256  to the base of the riser  270 . Similarly as discussed above, this catalyst from the reaction vessel  280  may maximize the ratio of catalyst to oil. Typically, the reaction vessel  280  can eliminate the net production of butene with respect to the feed  220  for the second riser reactor  260 . Usually, the second riser reactor  260  operates at a temperature of about 425-about 630° C., and at a temperature greater than the first riser reactor  160 . 
     The regeneration zone  300  can include the regeneration vessel  320  that may receive spent catalyst via lines  154  and  244 , and provides regenerated catalyst via a line  158  to the base of the first riser  170  and via the line  330  to the base of the second riser  270 . Usually, the regenerator  320  may receive make-up catalyst through a line  152  and equilibrium catalyst may be withdrawn via a line  184  to maintain catalyst activity. Typically, the regeneration vessel  320  may be operated at about 650-about 800° C. Generally, a flue gas  310  can exit the regeneration vessel  320 . Exemplary regeneration vessels are disclosed in, e.g., U.S. Pat. No. 7,312,370 and U.S. Pat. No. 7,247,233. 
     The catalyst can be a single catalyst or a mixture of different catalysts. Usually, the catalyst includes two components or catalysts, namely a first component or catalyst, and a second component or catalyst. Such a catalyst mixture is disclosed in, e.g., U.S. Pat. No. 7,312,370. 
     Generally, the first catalyst may include any of the catalysts that are used in the art of FCC, such as an active amorphous clay-type catalyst and/or a high activity, crystalline molecular sieve. Zeolites may be used as molecular sieves in FCC processes. Preferably, the first catalyst includes a large pore zeolite, such as a Y-type zeolite, an active alumina material, a binder material, including either silica or alumina, and an inert filler such as kaolin. 
     Typically, the zeolitic molecular sieves appropriate for the first catalyst have a large average pore size. Usually, molecular sieves with a large pore size have pores with openings of greater than about 0.7 nm in effective diameter defined by greater than about 10, and typically about 12, member rings. Pore Size Indices of large pores can be above about 31. Suitable large pore zeolite components may include synthetic zeolites such as X and Y zeolites, mordenite and faujasite. A portion of the first catalyst, such as the zeolite, can have any suitable amount of a rare earth metal or rare earth metal oxide. 
     The second catalyst may include a medium or smaller pore zeolite catalyst, such as an MFI zeolite, as exemplified by at least one of ZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38, ZSM-48, and other similar materials. Other suitable medium or smaller pore zeolites include ferrierite, and erionite. Preferably, the second catalyst has the medium or smaller pore zeolite dispersed on a matrix including a binder material such as silica or alumina and an inert filler material such as kaolin. The second catalyst may also include some other active material such as Beta zeolite. These compositions may have a crystalline zeolite content of about 10-about 50 wt. % or more, and a matrix material content of about 50-about 90 wt. %. Components containing about 40 wt. % crystalline zeolite material are preferred, and those with greater crystalline zeolite content may be used. Generally, medium and smaller pore zeolites are characterized by having an effective pore opening diameter of less than or equal to about 0.7 nm, rings of about 10 or fewer members, and a Pore Size Index of less than about 31. 
     In the embodiments disclosed herein, the selectivity of propene may be enhanced by feeding butene and/or pentene, preferably butene, to a naphtha cracking riser. Although not wanting to be bound by theory, co-feeding butene and/or pentene with a light cracked naphtha and/or polymer naphtha may shift equilibrium of reaction to the production of propene, and hence improve propene selectivity. 
     ILLUSTRATIVE EMBODIMENTS 
     The following examples are intended to further illustrate the subject catalyst. These illustrations of embodiments of the invention are not meant to limit the claims of this invention to the particular details of these examples. These examples are based on engineering calculations and actual operating experience with similar processes. 
     In the following examples, three feeds are provided to a pilot plant. The feeds are an LCN having 30%, by weight, alkenes, based on the weight of the LCN (abbreviated “F1”), one or more C4 hydrocarbons having 59%, by weight, alkenes, based on the weight of the one or more C4 hydrocarbons (abbreviated “F2”), and a 50/50% blend of F1 and F2 with 45%, by weight, alkenes, based on the weight of the blend (abbreviated “F3”). Moreover, F1 may also have 3.2%, by weight, one or more butenes in alkenes, F2 can also have 100%, by weight, one or more butenes in alkenes, and F3 may also have 66.8%, by weight, of one or more butenes in alkenes. The pilot plant utilizes a blend of large and medium pore zeolite catalysts. The blend consists 75%, by weight, commercial high propene FCC catalyst deactivated to commercial activity by steaming for 7 hours at 774° C. and 25%, by weight, of a commercial 40%, by weight, ZSM-5 additive, steamed for 24 hours at 774° C. The final catalyst mixture contains about 14%, by weight, ZSM-5 based on the phosphorus content. The pilot plant having an isothermal riser reactor is operated at a temperature of 566° C., a riser pressure of 270 kPa, a feed partial pressure of 140 kPa, and a weight ratio of catalyst to oil of 8:1-12:1. 
     The amount of alkanes, dry gases (DG), propene, butene, pentene, and C6-C12 alkenes products having the formula C n H 2n  where n is the carbon number of the alkene are measured using a combination of methods. The gaseous products are analyzed by a multi-column refinery gas analyzer with thermal-conductivity and flame-ionization detectors. Liquid products are measured by a gas chromatograph utilizing analyzer software and the gasoline specification is determined by analysis with a capillary gas chromatography with a flame-ionization detector. For DG and propene, there are no measurable amounts of these components in the feed. The weight percent (sum may not total 100% due to rounding) of components for the feeds and respective products is depicted in the table below: 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 F1 
                 F2 
                 F3 
               
               
                   
                 Weight 
                 Weight 
                 Weight 
               
               
                   
                 Percent 
                 Percent 
                 Percent 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Component 
                 Feed 
                 Product 
                 Feed 
                 Product 
                 Feed 
                 Product 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 DG 
                 0 
                 2.5 
                 0 
                 2.0 
                 0 
                 1.7 
               
               
                 Propene 
                 0 
                 10.4 
                 0 
                 12.4 
                 0 
                 10.3 
               
               
                 Butene 
                 1.0 
                 8.4 
                 59.2 
                 31.7 
                 30.1 
                 21.2 
               
               
                 Pentene 
                 12.9 
                 6.0 
                 0 
                 8.6 
                 6.4 
                 8.4 
               
               
                 C6-C12 Alkenes 
                 17.1 
                 4.1 
                 0 
                 0 
                 8.6 
                 6.1 
               
               
                 Dienes and Cyclic 
                 4.4 
                 1.7 
                 0 
                 0.1 
                 2.2 
                 2.4 
               
               
                 Alkenes 
               
               
                 Aromatics 
                 22.4 
                 25.0 
                 0 
                 0 
                 11.2 
                 11.1 
               
               
                 Alkanes 
                 42.3 
                 39.8 
                 40.8 
                 45 
                 41.5 
                 37.7 
               
               
                 Cycle Oils Plus 
                 0 
                 2.1 
                 0 
                 0.3 
                 0 
                 1.1 
               
               
                 Coke 
               
               
                   
               
            
           
         
       
     
     The net yield is determined by measuring and calculating the weight percent in the feed and product and subtracting, respectively, the weight percent of the feed from the weight percent of product for respectively, DG, propene, butene, pentene, and C6-C12 alkenes. As an example, the net yield for DG of F1 can be calculated:
 
2.5%=2.5%−0%
 
     The total converted alkenes and alkanes are calculated by summing only converted components, in other words, only those having negative yields. As an example for F1, the total converted alkenes and alkanes (except for dienes and cyclic alkenes) can expressed as weight percent and calculated as:
 
−22.4%=(6.0−12.9)%+(4.1−17.1)%+(39.8−42.3)%
 
For these feeds, the following net yields are obtained expressed as percentages and depicted in the table below:
 
     
       
         
           
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 Net Yield Expressed as Weight Percent Based 
               
               
                   
                 on Total Feed (Negative Values Denote Conversion) 
               
            
           
           
               
               
               
               
            
               
                   
                 F1 3.2%, 
                 F2 100%, 
                 F3 66.8%, 
               
               
                   
                 By Weight, 
                 By Weight, 
                 By Weight, 
               
               
                   
                 Butenes 
                 Butenes 
                 Butenes 
               
               
                   
                 in Alkenes 
                 in Alkenes 
                 in Alkenes 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                 DG 
                 2.5 
                 2.0 
                 1.7 
               
               
                 Propene 
                 10.4 
                 12.4 
                 10.3 
               
               
                 Butene 
                 7.4 
                 −27.5 
                 −8.9 
               
               
                 Pentene 
                 −6.9 
                 8.6 
                 1.9 
               
               
                 C6-C12 Alkenes 
                 −13 
                 0.0 
                 −2.4 
               
               
                 Alkanes 
                 −2.5 
                 4.2 
                 −3.9 
               
               
                 Cycle Oil Plus Coke 
                 2.1 
                 0.3 
                 1.1 
               
               
                 Total Converted 
                 −22.4 
                 −27.5 
                 −15.2 
               
               
                 Alkenes and 
               
               
                 Alkanes 
               
               
                   
               
            
           
         
       
     
     The ratio of selectivity yield divided by conversion can be calculated by dividing the net yield for, respectively, DG, propene, butene, pentene, and C6-C12 alkenes by the total converted alkenes and alkanes, as depicted in the last row of Table 2, and multiplying by a negative 100%. The net yield of alkanes is determined by subtracting the weight percent of alkanes in feed (F1, F2, and F3) from respective alkanes in the products for F1, F2, and F3. As an example, the ratio, which may be referred to as the “net selectivity ratio”, can be calculated for DG of F1 can be calculated as:
 
11%=−100*(2.5%/−22.4%)
 
The ratios are depicted as percentages of the converted alkenes in the table below:
 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 3 
               
             
            
               
                   
                   
               
               
                   
                 Selectivity Yield/Conversion Expressed 
                   
               
               
                   
                 as Weight Percent 
               
            
           
           
               
               
               
               
            
               
                   
                 F1 3.2%, 
                 F2 100%, 
                 F3 66.8%, 
               
               
                   
                 By Weight, 
                 By Weight, 
                 By Weight, 
               
               
                   
                 Butenes 
                 Butenes 
                 Butenes 
               
               
                   
                 in Alkenes 
                 in Alkenes 
                 in Alkenes 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                 DG 
                 11% 
                  7% 
                 11% 
               
               
                 Propene 
                 46% 
                 45% 
                 68% 
               
               
                 Butene 
                 33% 
                 −100%  
                 −59%  
               
               
                 Pentene 
                 −31%  
                 31% 
                 13% 
               
               
                 C6-C12 Alkenes 
                 −58%  
                  0% 
                 −16%  
               
               
                   
               
            
           
         
       
     
     Referring to  FIG. 2 , generally about 10-13%, by weight, propene yield is obtained for all three feeds. Moreover, the net yields of alkenes by carbon number as well as DG are plotted against the butene content of the feed alkenes. As depicted, negative numbers represent conversion of feed into products. With only F1 the butene yield is about 70%, by weight, of the propene yield, which limits propene selectivity and increases recycle costs. By including butene in the feed, net production of butene can be reduced or eliminated and, as depicted by feeds F2 and F3, butene can even be converted. 
     The yield for a component of F2 or F3 can be calculated by subtracting a quotient (F2/F1 or F3/F1) of a net yield of a component from one, and multiplying by 100%. As an example, the dry gas (DG) yield for F2 is calculated as follows:
 
20%=100%*(1−2.0%/2.5%)
 
     As a consequence, the dry gas (DG) yields are reduced by 20% and 32%, by weight, for, respectively, F2 and F3 feeds as compared to the F1 feed. Referring to the tables above, cycle oils and coke yields are, respectively, 86% and 48%, by weight, lower for F2 and F3, respectively, as compared to the F1 feed. 
     Referring to  FIG. 3 , the net selectivity ratios from Table 3 are plotted against the percentage of butenes in the feed alkenes. For F3, the propene net selectivity ratio is highest at about 68%, by weight, of converted alkenes and alkanes. For F1, at 3.2%, by weight, the propene net selectivity ratio is diminished to 46%, by weight, of converted alkenes and alkanes with a butene net selectivity ratio of 33%, by weight, and for F2, the propene net selectivity ratio is diminished to 45%, by weight, of converted alkenes and alkanes. Although not wanting to be bound by theory, it is believed that the propene net selectivity ratio is highest at about 30-about 80%, by weight, one or more butenes in one or more alkenes because butene and pentene should both show net conversion. By maximizing propene selectivity, overall recycle and gas, and coke and cycle oil yields can be minimized for a given target of propene yield. Thus, while F3 may produce slightly less propene on a give pass, F3 can exhibit higher selectivity, and thus results in the production of less by-products. 
     Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever. 
     In the foregoing, all temperatures are set forth in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated. 
     From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.