Abstract:
This invention is directed to middle distillate production (e.g., diesel and kerosene products) by means of a reactor hydroprocessing system using two or more reactors (or a single reactor vessel having two or more stages, each stage containing one or more reaction zones). Hydrocracking is preferably performed in the initial reactor, and hydrotreating (and/or further hydrocracking) is preferably performed in the subsequent reactor vessel or stages within a single vessel. Reaction stages are effectively segregated to avoid recracking of products, to dramatically reduce hydrogen consumption in saturating the bottoms product and to carry out aromatic saturation of middle distillates in a clean low-temperature environment.

Description:
[0001]    This application is a continuation-in-part of copending application, Ser. No. 09/227,783, filed Jan. 8, 1999. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention is directed to middle distillate production (e.g., diesel and kerosene products) by means of a reactor hydroprocessing system using two or more reactors (or a single reactor vessel having two or more stages, each stage containing one or more reaction zones). Product effluents are effectively segregated to avoid recracking of products, to dramatically reduce hydrogen consumption in saturating the bottoms product, and to carry out aromatic saturation of middle distillates in a clean low-temperature environment.  
         BACKGROUND OF THE INVENTION  
         [0003]    In an SSOT (single-stage once-through) environment, all the products of the reaction from each zone of a reactor are forced to pass over following zones in a cascade mode. Operating conditions of the reactor are dictated by the need for deep denitrification and subsequent conversion in a harsh ammonia and hydrogen sulfide-rich environment. Temperatures tend to be higher, favoring hydrocracking, and are not optimal for aromatic saturation. Recracking occurs in the lower beds, leading to destruction of valuable diesel and jet range material to naphtha and lighter material. Since there is no subsequent reactor stage available, all products must be hydrogenated in the same reactor system. The biggest source of hydrogen loss is the oversaturation of the unconverted oil destined for the FCC unit.  
           [0004]    The parent application was concerned with a single stage process (employing more than one reaction zone, preferably in a single reactor vessel) for hydroconverting dissimilar refinery streams using a single hydrogen source. It disclosed a method for hydroprocessing two refinery streams using a single hydrogen supply and a single hydrogen recovery system. It further disclosed a method for hydrocracking a refinery stream and hydrotreating a second refinery stream in a common reactor and with a common hydrogen feed supply in which the feed to the hydrocracking zone was not poisoned with contaminants present in the feed to the hydrotreating reaction zone. Furthermore, the parent application was directed to hydroprocessing two or more dissimilar refinery streams in an integrated hydroconversion process while maintaining good catalyst life and high yields of the desired products, particularly distillate range refinery products. Such dissimilar refinery streams might originate from different refinery processes, such as a VGO, derived from the effluent of a VGO hydrotreater, which contains relatively few catalyst contaminants and/or aromatics, and an FCC cycle oil or straight run diesel, which contains substantial amounts of aromatic compounds.  
           [0005]    Publications concerned with methods for using a single hydrogen loop in a two-stage reaction process have been disclosed in the parent application. The instant invention is further concerned with effectively segregating reaction stages in order to avoid recracking of products. Segregation may be done using two separate fractionation columns or a single fractionation column in which reaction stages are separated by the use of a baffle. The article, “Divided-wall columns novel distillation concept” ( Process Technology , Autumn, 2000), discloses the use of divided wall columns in benzene removal processes.  
           [0006]    WO 97/23584 discloses an integrated hydroprocessing scheme involving a hydrocracking stage and a subsequent dewaxing stage for the production of lubricants, as well as naphtha and middle distillates. (The instant invention is directed to hydrocracking and hydrotreating of middle distillates). The bottoms streams, and optionally other streams from each stage, are maintained separately from one another during processing. Dewaxing may occur using either hydroisomerization catalysts, shape-selective catalysts, or both in series. One embodiment employs a baffle in the flash zone of a fractionator to separate bottoms streams from each other. Alternately, the effluent from the hydrocracking stage may be processed separately from the effluent from the dewaxing stage. The bottoms fraction from the dewaxing stage may be recycled back to the hydrocracking stage for further processing or used as a lube base stock.  
         SUMMARY OF THE INVENTION  
         [0007]    This invention is directed to middle distillate production (e.g., diesel and kerosene products) by means of a reactor hydroprocessing system using two or more reactors (or a single reactor vessel having two or more stages, each stage containing one or more reaction zones). Hydrocracking is preferably performed in the initial reactor, and hydrotreating (and/or further hydrocracking) is preferably performed in a subsequent reactor or reactors. Reaction effluents are effectively segregated to avoid recracking of products, in order to dramatically reduce hydrogen consumption in saturating the bottoms product and to carry out aromatic saturation of middle distillates in a clean low-temperature environment.  
           [0008]    The quality of the products from the different reactors (or stages) can be distinctly different, and this invention keeps them segregated for specialized use or marketing. The preferred means of separation is by using separate fractionators or distillation columns, although, in an alternate configuration, a single fractionator having a baffle may be used. The latter configuration results in decreased modification expense.  
           [0009]    In the instant invention, when hydrotreating is desired, feed may be hydrotreated at relatively high space velocities and low hydrogen-to-oil ratio. Conditions will be suitable for deep hydrodesulfurization, hydrodenitrification and low conversion. Intermediate flash zones and rough fractionation segregates the lighter product effluent from the first reactor from the bottoms.  
           [0010]    FCC feed essentially consists of unconverted oil from the first reactor. The remainder of the unconverted oil is extinction cracked to diesel in a clean second stage reactor operating under typical second stage hydrocracking conditions. The last bed of the second stage reactor is used to “post-treat” the small quantity of distillates formed in the first stage.  
           [0011]    The operating conditions in the second reactor (or stage) of a two-reactor (or two-stage) hydroprocessing system (moderate temperature, high partial pressure hydrogen, low partial pressure nitrogen, and low partial pressure H 2 S) are very favorable for aromatic saturation. Therefore, injection of middle distillates or other stocks needing saturation into the bottom beds and processing over treating catalyst (the second-stage cracking catalyst being upstream or mostly upstream of the point of injection) provides a low cost means to upgrade these stocks. The injected stocks might be straight run kerosene or diesel, cracked stocks such as coker gas oils or FCC cycle oils, or could even be first stage middle distillates in cases where first stage conditions hinder the attainment of what are sometimes very stringent product specifications (e.g., smoke point, cetane number). This scheme can also be used for very deep hydrodesulfurization. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 illustrates a preferred embodiment of the instant invention. Two reactor vessels, each vessel having more than one reaction zone. The effluent from the reactors are maintained separately from each other. Separate flash drums and fractionators are employed.  
         [0013]    [0013]FIG. 2 illustrates another embodiment of the invention, whereby reactor effluents are separated by the use of a single fractionator having a baffle, rather than two fractionators.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]    Feeds  
         [0015]    One suitable feed to the first reactor is a VGO having a boiling point range starting at a temperature above 500° F. (260° C.), usually within the temperature range of 500-100° F. (260-593° C.). A refinery stream wherein 75 vol. % of the refinery stream boils within the temperature range 650-1050° F. is an example feedstock for the feed to the first reactor. The first refinery stream may contain nitrogen, usually present as organonitrogen compounds, in amounts greater than 1 ppm. Preferred feed streams to the first reactor contain less than about 200 ppm nitrogen and less than 0.25 wt. % sulfur, though feeds with higher levels of nitrogen and sulfur, including those containing up to 0.5 wt. % and higher nitrogen and up to 2 wt. % sulfur and higher may be treated in the present process. The first refinery stream is also preferably a low aromatic stream, including multi-ring aromatics and asphaltenes. Suitable first refinery streams contain less than about 500 ppm asphaltenes, preferably less than about 200 ppm asphaltenes, and more preferably less than about 100 ppm asphaltenes. Example streams include light gas oil, heavy gas oil, straight run gas oil, deasphalted oil, and the like. The first refinery stream may have been processed, e.g., by hydrotreating, prior to the present process to reduce or substantially eliminate its heteroatom content. The first refinery stream may comprise recycle components.  
         [0016]    The first reaction step removes nitrogen and sulfur from the first refinery stream in the first reaction zone and effects a boiling range conversion, so that the liquid portion of the first reaction zone effluent has a normal boiling range below the normal boiling point range of the first refinery feedstock. By “normal” is meant a boiling point or boiling range based on a distillation at one atmosphere pressure. Unless otherwise specified, all distillation temperatures listed herein refer to normal boiling point and normal boiling range temperatures. The process in the first reaction zone may be controlled to a certain cracking conversion or to a desired product sulfur level or nitrogen level or both. Conversion is generally related to a reference temperature, such as, for example, the minimum boiling point temperature of the hydrocracker feedstock. The extent of conversion relates to the percentage of feed boiling above the reference temperature which is converted to products boiling below the reference temperature.  
         [0017]    The effluent from the first reactor vessel, which has been processed over one or more zones containing a hydroprocessing catalyst or catalysts, includes normally liquid phase components, e.g., reaction products and unreacted components of the first refinery stream, and normally gaseous phase components, e.g., gaseous reaction products and unreacted hydrogen. In the process, the first reactor is maintained at conditions sufficient to effect a boiling range conversion of the first refinery stream of at least about 25%, based on a 650° F. reference temperature. Thus, at least 25% by volume of the components in the first refinery stream which boil above about 650° F. are converted in the first reactor to components which boil below about 650° F. Operating at conversion levels as high as 100% is also within the scope of the invention. Example boiling range conversions are in the range of from about 30% to 90% or of from about 40% to 80%. The first reactor effluent is further decreased in nitrogen and sulfur content, with at least about 50% of the nitrogen containing molecules in the first refinery stream being converted in the first reactor. Preferably, the normally liquid products present in the first reactor effluent contain less than about 1000 ppm sulfur and less than about 200 ppm nitrogen, more preferably less than about 250 ppm sulfur and about 100 ppm nitrogen.  
         [0018]    Examples of streams to the second reactor which are suitable for treating in the present process include straight run vacuum gas oils, including straight run diesel fractions, from crude distillation, atmospheric tower bottoms, or synthetic cracked materials such as coker gas oil, light cycle oil or heavy cycle oil.  
         [0019]    The feed to the second reactor has a boiling point range generally lower than the first refinery stream. A substantial portion of the second refinery stream has a normal boiling point in the middle distillate range, so that cracking to achieve boiling point reduction is not necessary. Thus, at least about 75 vol. % of a suitable feed to the second reactor has a normal boiling point temperature of less than about 1000° F. A refinery stream with at least about 75% v/v of its components having a normal boiling point temperature within the range of 250° F.-700° F. in an example of a preferred stream to the second reactor. A refinery stream with at least about 75 vol. % of its components having a normal boiling point temperature within the range of 250° F.-700° F. is another example of a preferred stream to a second reactor. The process is particularly suited for treating middle distillate streams which are not suitable for high quality fuels. For example, the process is suitable for treating a stream to the second reactor which contains high amounts of nitrogen and/or high amounts of aromatics, including streams which contain up to 90% aromatics and higher.  
         [0020]    Catalysts  
         [0021]    Each of the reactor vessels may contain one or more catalysts. If more than one distinct catalyst is present in either of the reactors, the catalysts may be blended or be present as distinct layers, creating multiple reaction zones. Layered catalyst systems are taught, for example, in U.S. Pat. No. 4,990,243, the disclosure of which is incorporated herein by reference for all purposes. Hydrocracking catalysts useful for the first reaction zone are well known. In general, the hydrocracking catalyst comprises a cracking component and a hydrogenation component on an oxide support material or binder. The cracking component may include an amorphous cracking component and/or a zeolite, such as a Y-type zeolite, an ultrastable Y type zeolite, or a dealuminated zeolite. A suitable amorphous cracking component is silica-alumina.  
         [0022]    The hydrogenation component of the catalyst particles is selected from those elements known to provide catalytic hydrogenation activity. At least one metal component selected from the Group VIII elements and/or from the Group VI elements is generally chosen. Group V elements include chromium, molybdenum and tungsten. Group VIII elements include iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium and platinum. The amount(s) of hydrogenation component(s) in the catalyst suitably range from about 0.5% to about 10% by weight of Group VIII metal component(s) and from about 5% to about 25% by weight of Group VI metal component(s), calculated as metal oxide(s) per 100 parts by weight of total catalyst, where the percentages by weight are based on the weight of the catalyst before sulfiding. The hydrogenation components in the catalyst may be in the oxidic and/or the sulphidic form. If a combination of at least a Group VI and a Group VIII metal component is present as (mixed) oxides, it will be subjected to a sulfiding treatment prior to proper use in hydrocracking. Suitably, the catalyst comprises one or more components of nickel and/or cobalt and one or more components of molybdenum and/or tungsten or one or more components of platinum and/or palladium. Catalysts containing nickel and molybdenum, nickel and tungsten, platinum and/or palladium are particularly preferred.  
         [0023]    The hydrocracking catalyst particles of this invention may be prepared by blending, or co-mulling, active sources of hydrogenation metals with a binder. Examples of suitable binders include silica, alumina, clays, zirconia, titania, magnesia and silica-alumina. Preference is given to the use of alumina as binder. Other components, such as phosphorous, may be added as desired to tailor the treatment prior to proper use in hydrocracking. Suitably, the catalyst comprises one or more components of nickel and/or cobalt and one or more components of molybdenum and/or tungsten or one or more components of platinum and/or palladium. Catalysts containing nickel and molybdenum, nickel and tungsten, platinum and/or palladium are particularly preferred.  
         [0024]    The second reactor contains hydrotreating catalyst in at least one zone, which is maintained at hydrotreating conditions. Hydrotreating catalysts are suitable for hydroconversion of feedstocks containing high amounts of sulfur, nitrogen and/or aromatic-containing molecules. It is a feature of the present invention that hydrotreating may be used to treat feedstocks containing asphaltenic contaminants which would otherwise adversely affect the catalytic performance or life of the hydrocracking catalysts. The hydrotreating catalysts are selected for removing these contaminants to low values. Such catalysts generally contain at least one metal component selected from Group VIII and/or at least one metal component selected from the Group VI elements. Group VI elements include chromium, molybdenum and tungsten. Group VIII elements include iron, cobalt and nickel.  
         [0025]    While the noble metals, especially palladium and/or platinum, may be included, alone or in combination with other elements, in the hydrotreating catalyst, use of the noble metals as a hydrogenation component is not preferred. The amount(s) of hydrogenation component(s) in the catalyst suitably range from about 0.5% to about 10% by weight of Group VIII metal component(s) and from about 5% to about 25% by weight of Group VI metal component(s), calculated as metal oxide(s) per 100 parts by weight of total catalyst, where the percentages by weight are based on the weight of the catalyst before sulfiding. The hydrogenation components in the catalyst may be in the oxidic and/or the sulphidic form. If a combination of at least a Group VI and a Group VIII metal component is present as (mixed) oxides, it will be subjected to a sulfiding treatment prior to proper use in hydrocracking. Suitably, the catalyst comprises one or more components of nickel and/or cobalt and one or more components of molybdenum and/or tungsten. Catalysts containing cobalt and molybdenum are particularly preferred.  
         [0026]    The hydrotreating catalyst particles of this invention are suitably prepared by blending, or co-mulling, active sources of hydrogenation metals with a binder. Examples of suitable binders include silica, alumina, clays, zirconia, titania, magnesia and silica-alumina. Preference is given to the use of alumina as binder. Other components, such as phosphorous, may be added as desired to tailor the catalyst particles for a desired application. The blended components are then shaped, such as by extrusion, dried and calcined at temperatures up to 1200° F. (649° C.) to produce the finished catalyst particles. In the alternative, equally suitable methods of preparing the amorphous catalyst particles include preparing oxide binder particles, such as by extrusion, drying and calcining, followed by depositing the hydrogenation metals on the oxide particles using methods such as impregnation. The catalyst particles, containing the hydrogenation metals, are then further dried and calcined prior to use as a hydrotreating catalyst.  
         [0027]    Operating Conditions  
         [0028]    Reaction conditions in the first reactor include a reaction temperature between about 250° C. and about 500° C. (482° F.-932° F.), pressures from about 3.5 MPa to about 24.2 MPa (500-3,500 psi), and a feed rate (vol oil/vol cat h) from about 0.1 to about 20 hr −1 . Hydrogen circulation rates are generally in the range from about 350 std liters H 2 /kg oil to 1780 std liters H 2 /kg oil (2,310-11,750 standard cubic feet per barrel). Preferred reaction temperatures range from about 340° C. to about 455° C. (644° F.-851° F.). Preferred total reaction pressures range from about 7.0 MPa to about 20.7 MPa (1,000-3,000 psi). With the preferred catalyst system, it has been found that preferred process conditions include contacting a petroleum feedstock with hydrogen under hydrocracking conditions comprising a pressure of about 13.8 MPa to about 20.7 MPa (2,000-3000 psi), a gas to oil ratio between about 379-909 std liters H 2 /kg oil (2,500-6,000 scf/bbl), a LHSV of between about 0.5-1.5 hr −1 , and a temperature in the range of 360° C. to 427° C. (680° F.-800° F.).  
         [0029]    The second reactor contains at least one zone which is maintained at conditions sufficient to remove at least a portion of the nitrogen compounds and at least a portion of the aromatic compounds from the feed to the second reactor. In the preferred embodiment, there are at least two reaction zones which are in liquid and vapor communication with each other. The pressure and the temperature in the second reaction zone are substantially the same as the pressure and the temperature in the first reaction zone. A small pressure decrease may occur, depending on the pressure drop across the reaction zones and through the interstage region. The second reaction zone will operate at approximately the same temperature as the first reaction zone, except for possible temperature gradients resulting from exothermic heating within the reaction zones, moderated by the addition of relatively cooler streams into the one or more reaction zones or into the interstage region. Feed rate of the reactant liquid stream through the reaction zones will be in the region of 0.1 to 20 hr −1  liquid hourly space velocity. Feed rate through second reaction zone will be increased relative to the feed rate through first reaction zone by the amount of liquid feed in second refinery stream and will also be in the region of 0.1 to 20 hr −1  liquid hourly space velocity. These process conditions selected for the first reaction zone may be considered to be more severe than those conditions normally selected for a hydrotreating process.  
         [0030]    Hydroprocessing conditions in the second reactor may provide either hydrotreating or further hydrocracking depending on the feed and the desired characteristics of the effluent. If hydrocracking is occurring, the reaction temperature is typically between about 250° C. and about 500° C. (482° F.-932° F.), pressures from about 3.5 MPa to about 24.2 MPa (500-3,500 psi), and a feed rate (vol oil/vol cat h) from about 0.1 to about 20 hr −1 . Hydrogen circulation rates are generally in the range from about 350 std liters H 2 /kg oil to 1780 std liters H 2 /kg oil (2,310-11,750 standard cubic feet per barrel). Preferred reaction temperatures range from about 340° C. to about 455° C. (644° F.-851° F.). Preferred total reaction pressures range from about 7.0 MPa to about 20.7 MPa (1,000-3,000 psi). U.S. Pat. No. 4,435,275 further describes the conditions employed in a process for producing low sulfur distillates by operating the hydrotreating-hydrocracking process without interstage separation and at relatively low pressures, typically below about 7,000 kPa (about 1,000 psig).  
         [0031]    The process of the instant invention is especially useful in the production of middle distillate fractions boiling in the range of about 250° F.-700° F. (121° C.-371° C.). By a middle distillate fraction having a boiling range of about 250° F.-700° F. is meant that at least 75 vol. %, preferably 85 vol. %, of the components of the middle distillate have a normal boiling point of greater than about 250° F. and furthermore that at least about 75 vol. %, preferably 85 vol. %, of the components of the middle distillate have a normal boiling point of less than 700 20  F. The term “middle distillate” is intended to include the diesel, jet fuel and kerosene boiling range fractions. The kerosene or jet fuel boiling point range is intended to refer to a temperature range of about 280° F.-525° F. (138° C.-274° C.), and the term “diesel boiling range” is intended to refer to hydrocarbon boiling points of about 250° F.-700° F. (121° C.-371° C.). Gasoline or naphtha is normally the C 5  to 400° F. (204° C.) endpoint fraction of available hydrocarbons. The boiling point ranges of the various product fractions recovered in any particular refinery will vary with such factors as the characteristics of the crude oil source, refinery local markets, product prices, etc.  
       DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0032]    Reference is now made to FIGS. 1 and 2, which disclose preferred embodiments of the invention. Not included in the figures are the various pieces of auxiliary equipment such as heat exchangers, condensers, pumps and compressors, which, of course, would be necessary for a complete processing scheme and which would be known and used by those skilled in the art.  
         [0033]    [0033]FIG. 1 illustrates two downflow reactor vessels  30  and  31 , each containing at least two vertically aligned reaction zones. The first reaction zone  39 , found in reactor vessel  31 , is for cracking a first refinery stream  8 . The second reaction zone  41  of reactor vessel  31  is an additional hydroprocessing zone  41  for additional upgrading. The severity of the upgrading will depend upon the characteristics desired of the reactor effluent.  
         [0034]    The first reaction zone  22  of reactor vessel  30  is for cracking a second refinery stream  79 . The second reaction zone  26  is for removing nitrogen-containing and aromatic molecules from a second refinery stream  78 .  
         [0035]    In either of the reactor vessels  30  and  31 , suitable volumetric ratio of the catalyst volume in the first reaction zone to the catalyst volume in the second reaction zone encompasses a broad range, depending on the ratio of the first refinery stream to the second refinery stream. Typical ratios generally lie between 20:1 and 1:20. A preferred volumetric range is between 10:1 and 1:10. A more preferred volumetric ratio is between 5:1 and 1:2.  
         [0036]    In the integrated process, a first refinery stream  2  is combined with a hydrogen-rich gaseous stream  6  to form a first feedstock  8 , passed to first reaction zone  39  contained within reactor vessel  31 . Hydrogen-rich gaseous stream  69  contains greater than 50% hydrogen, the remainder being varying amounts of light gases, including hydrocarbon gases. The hydrogen-rich gaseous stream  69  shown in the drawing is primarily recycle hydrogen. While the use of a recycle hydrogen stream is generally preferred for economic reasons, it is not required. First feedstock  8  may be heated in one or more exchangers, such as exchanger  15 , and one or more heaters, such as heater  43 , before being introduced to first reaction zone  22 .  
         [0037]    Interstage region  21  is a region in the reactor vessel which contains means for mixing and redistributing liquids and gases from the reaction zone above before they are introduced into the reaction zone below. Such mixing and redistribution improves reaction efficiency and reduces the chances of thermal gradients or hot spots in the reaction zone below. Additional streams, including an additional hydrogen stream  35 , may also be introduced into the reactor vessel in the interstage region. Hydrogen may also be added as a quench stream through lines  33  and  37  for cooling the first and the second reaction zones, respectively. Streams  33 ,  35  and  37  are branches of stream  23 .  
         [0038]    The effluent of reactor  31  exits the reaction zone  41  through line  75  and is cooled in exchanger  15 . The effluent  75  proceeds to separation zone  47 . Separation zone  47  represents one or more process units known in the art for separating normally liquid products from normally gaseous products in the reaction effluent  75 , and thus preparing a liquid stream  51  and a purified hydrogen stream  49 . An example separation scheme for a hydroconversion process is taught in U.S. Pat. No. 5,082,551, the entire disclosure of which is incorporated herein by reference for all purposes. In the example embodiment of FIG. 1, effluent  75  is separated in separation zone  47  to form second hydrogen-rich gaseous stream  49  and liquid stream  51 . Separation zone  47  may include means for contacting a gaseous component of the reaction effluent  75  with a solution, such as an alkaline aqueous solution, for removing contaminants such as hydrogen sulfide and ammonia which may be generated in the reaction zones and may be present in reaction effluent  75 . The second hydrogen-rich gaseous stream is preferably recovered from the separation zone at a temperature in the range of 100° F.-300° F., or 100° F.-200° F. Purified hydrogen stream  49 , the second hydrogen-rich gaseous stream recovered from separation zone  47 , is recompressed, along with hydrogen from separation zone  36 , through compressor  68  and passed as recycle to one or both of the reactors (see streams  33 ,  35  and  36 , or  72 ,  66  and  74 ) and as a quench stream for cooling the reaction zones. Such uses of hydrogen are well known in the art.  
         [0039]    Liquid stream  51  is further separated in distillation zone  71  to produce overhead stream  73 , distillate fractions  76  and  77 , and bottoms product  80 . A preferred distillate product has a boiling point range within the temperature range 250° F.-700° F. A gasoline or naphtha fraction having a boiling point range within the temperature range C 5 -400° F. is also desirable. At least a portion of one or more distillate fractions or bottoms fractions recovered from distillation zone  71  may be recycled to the first reaction vessel. Recycle of stream  80  is preferred.  
         [0040]    Stream  80  may be combined with stream  50 , the effluent from fractionator  70 , and heated in exchanger  10 . Stream  80  is combined with hydrogen rich gas stream  27 , further heated in heater  20 , and combined with hydrogen-rich gas stream  79  to form a second feedstock  81 , passed to first reaction zone  22  contained within reactor vessel  30 . Hydrogen-rich gaseous stream  27  contains greater than 50% hydrogen, the remainder being varying amounts of light gases, including hydrocarbon gases. The hydrogen-rich gaseous stream  27  shown in the drawing is primarily recycle hydrogen. In the process, distillate stream  78  is combined with optional hydrogen stream  64  forming combined feedstock  66 , and is further combined with the total first reaction zone effluent  38  from the first reaction zone  22  to form second feedstock  39  for passage through the second reaction zone. In the embodiment shown in the drawing in FIG. 1, the combination of the two streams takes place in interstage region  24 . Optional hydrogen stream  64  is shown originating as a portion of recycle hydrogen stream  79 . Alternatively, optional hydrogen stream  64  may be a fresh hydrogen stream, originating from hydrogen sources external to the present process.  
         [0041]    The second feedstock  39 , comprising combined stream  66  and first reaction zone effluent  38 , is passed to a second reaction zone  26 . The second reaction zone  26  contains at least one bed of catalyst, such as hydrotreating catalyst, which is maintained at conditions sufficient for converting at least a portion of the nitrogen compounds and at least a portion of the aromatic compounds in the second feedstock.  
         [0042]    Effluent from reactor  30 , stream  28 , may be cooled in heat exchanger  10 . Stream  28  is further separated into at least one distillate fraction and a second hydrogen-rich gaseous stream  41  in separation zone  36 , preparing a liquid stream  42  and a purified hydrogen stream  41 . Hydrogen-rich stream  41  is preferably recovered from the separation zone at a temperature in the range of 100° F.-300° F., or 100° F.-200° F. Stream  41  is recompressed through compressor  68  and passed as recycle to one or more of the reaction zones and as a quench stream (streams  72 ,  66  and  74 ) for cooling the reaction zones. Such uses of hydrogen are well known in the art.  
         [0043]    Liquid stream  42  is further separated in distillation zone  70  to produce overhead stream  44 , distillate fractions  46  and  48 , and bottoms product  50 . A preferred distillate product has a boiling point range within the temperature range 250° F.-700° F. A gasoline or naphtha fraction having a boiling point range within the temperature range C 5 -400° F. is also desirable. At least a portion of one or more distillate fractions or bottoms fractions recovered from distillation zone  70  may be recycled to the second reactor  30 . Recycle of bottoms fraction  70  is preferred.  
         [0044]    It is a feature of the present invention that the effluents of the first reaction vessel  31  and the second reactor vessel  30  are maintained separately. None of stream  80  is recycled to the first reaction vessel  31 , in order to prevent overcracking of the second refinery stream components. Accordingly, all of the converted second refinery stream present in the effluent of reactor  30  is recovered as a distillate fraction for use elsewhere, most being recovered as either a light gas, naphtha or middle distillate fuel.  
         [0045]    [0045]FIG. 2 illustrates a flow scheme identical to FIG. 1, except that separate fractionators  70  and  71  are replaced by a single fractionator  82  having a baffle  83 . The fractionator is divided by the baffle into sections  70  and  71  which are comparable to fractionators  70  and  71  in FIG. 1.