Patent Publication Number: US-2012024752-A1

Title: Multi-Stage Hydroprocessing for the Production of High Octane Naphtha

Description:
FIELD OF THE INVENTION 
     The present invention provides a multi-stage integrated process for the production of high octane naphtha from a hydrocarbonaceous feedstock. 
     BACKGROUND 
     Different processes exist for upgrading hydrocarbonaceous feedstocks. As the demand for transportation fuels such as gasoline, diesel, and jet fuel grows, processes for upgrading low grade distillates and residuum are becoming increasingly important. Hydroprocessing reactions such as hydrotreating, hydrocracking, and reforming use catalysts to upgrade various feedstocks. Because heteroatoms can damage hydrocracking and/or reforming catalysts they are generally removed prior to hydrocracking and/or reforming by hydrotreating. Hydrotreating removes nitrogen, sulfur, and other impurities in hydrocarbon feedstocks. Subsequently, these feedstocks can be used in other refinery processes such as hydrocracking and reforming. In hydrocracking, heavy feedstocks including low grade distillates and gas oils with high molecular weights are converted to lower molecular weight effluents such as naphthas. Large amounts of hydrogen are consumed in typical hydrocracking processes. Reforming is used for upgrading light hydrocarbon feedstocks such as naphthas. Products from catalytic reforming can include high octane gasoline useful as automobile fuel, aromatics (for example benzene, toluene, xylenes and ethylbenzene), and/or hydrogen. Reactions typically involved in catalytic reforming include dehydrocyclization, isomerization and dehydrogenation of naphtha range hydrocarbons, with dehydrocyclization and dehydrogenation of linear and slightly branched alkanes and dehydrogenation of cycloparaffins leading to the production of aromatics. 
     Many refinery processes use a combination of hydroprocessing reactions to upgrade heavy feedstocks. For example, in an initial stage, the feedstock can be hydrotreated to reduce the amount of heteroatoms which can have a deleterious effect on downstream hydrocracking and/or reforming catalysts. The multistage process can use a common hydrogen supply system as disclosed in, for example, U.S. Pat. No. 5,009,768. Other U.S. patents which are directed to multistage hydroprocessing within a single high pressure hydrogen loop include, for example, U.S. Pat. No. 6,797,154. In this patent high conversion of heavy gas oils and the production of high quality middle distillate products are possible in a single high-pressure loop with reaction stages operating at different pressure and conversion levels. The flexibility offered is great and allows the refiner to avoid decreases in product quality while at the same time minimizing capital cost. Feeds with varying boiling ranges are introduced at different sections of the process, thereby minimizing the consumption of hydrogen and reducing capital investment. 
     U.S. Pat. No. 6,787,025 also discloses multi-stage hydroprocessing for the production of middle distillates. A major benefit of this invention is the potential for simultaneously upgrading difficult cracked stocks such as Light Cycle Oil, Light Coker Gas Oil, Visbroken Gas Oil, and/or Straight-Run Atmospheric Gas Oils utilizing the high-pressure environment required for mild hydrocracking. 
     U.S. Pat. No. 7,238,277 provides very high to total conversion of heavy oils to products in a single high-pressure loop, using multiple reaction stages. The second stage or subsequent stages may be a combination of co-current and counter-current operation. The benefits of this invention include conversion of feed to useful products at reduced operating pressures using lower catalyst volumes. Lower hydrogen consumption also results. 
     U.S. Publication 20050103682 relates to a multi-stage process for hydroprocessing gas oils. Preferably, each stage possesses at least one hydrocracking zone. The second stage and any subsequent stages possess an environment having a low heteroatom content. Light products, such as naphtha, kerosene and diesel, may be recycled from fractionation (along with light products from other sources) to the second stage (or a subsequent stage) in order to produce a larger yield of lighter products, such as gas and naphtha. Pressure in the zone or zones subsequent to the initial zone is from 500 to 1000 psig lower than the pressure in the initial zone, in order to provide cost savings and minimize overcracking. 
     Catalytic reforming is a well-known refinery process for upgrading light hydrocarbon feedstocks, frequently referred to as naphtha feedstocks. Products from catalytic reforming can include high octane gasoline, useful as automobile fuel, and/or aromatics, such as benzene and toluene, useful as chemicals. Reactions typically involved in catalytic reforming include dehydrocyclization, isomerization and dehydrogenation. Dehydrocyclization is a well known reaction wherein alkanes are converted to aromatics. For example, hexane may be dehydrocyclized to benzene. Thus, reforming typically includes dehydrocyclization. However, dehydrocyclization or aromatization of alkanes can be directed more narrowly than reforming. 
     Even with the advances in hydroprocessing catalysts and processes, a need still exists to develop new and improved methods to provide high liquid yield of valuable gasoline, diesel, and jet fuel products, improve hydrogen production, and minimize the formation of less valuable low molecule weight (C 1 -C 4 ) products. Thus, further improvements for reducing refinery operating costs by maximizing the production of valuable high octane products from low grade feedstocks and minimizing the amount of hydrogen needed during the hydroprocessing reactions are desirable. 
     SUMMARY OF THE INVENTION 
     Accordingly, a process is provided for producing high octane naphtha, including (a) isolating a hydrocracked naphtha from a hydrocracking reaction zone effluent; (b) providing at least a portion of the hydrocracked naphtha to a reforming reaction zone containing a reforming catalyst containing a silicate having a silica to alumina molar ratio of at least 200, and a crystallite size of less than 10 microns; (c) contacting the at least a portion of the hydrocracked naphtha with the reforming catalyst at reforming reaction conditions and producing a hydrogen-rich stream and a reformed naphtha; and (d) passing the hydrogen-rich stream to the hydrocracking reaction zone. 
     In embodiments, the hydrocracked naphtha contains at least 70 wt % C 4  to C 10  hydrocarbons, and has an octane of less than 90. In embodiments, the reformed naphtha includes at least 70 wt % C 5  to C 9  hydrocarbons, and has an octane of greater than 95. 
     In embodiments, at least a portion of the hydrocracked naphtha and at least a portion of the reformed naphtha are blended as a combined naphtha, to be used as a fuel or fuel blendstock. 
     In embodiments, reformer reaction conditions include a pressure in the range of between 0 psig and 250 psig, a temperature in the range of between 600° and 1100° F. and a liquid feed rate in the range of between 0.1 and 20 hr −1 . 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of one embodiment of the invention. 
         FIG. 2  is a schematic diagram of a second embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
     The upgrading process integrates two upgrading zones. A first upgrading zone produces a hydrocracked naphtha which is upgraded in a second zone. The second upgrading zone in turn produces a hydrogen-rich stream that is used in the first upgrading zone. The first upgrading zone reduces the molecular weight of a hydrocarbonaceous feed. A fuel intermediate isolated from the effluent from the first upgrading zone is reformed in the second zone to produce a fuel or fuel-blending component. In embodiments, the catalyst employed in the reforming zone is an intermediate pore size crystalline molecular sieve having a crystalline framework characterized by a range of silica to alumina ratios. In embodiments the intermediate pore size molecular sieve is further characterized by a X-ray diffraction pattern. In embodiment, the intermediate pore size molecular sieve is further characterized by an alkali content. In embodiments, the intermediate pore size molecular sieve is further characterized by a crystallite size range. 
     The process involves using an integrated petroleum upgrading system for producing a high octane naphtha blend component. The system involves a hydrocracking reaction zone for producing a naphtha product and a reforming zone for upgrading the naphtha product and for producing a hydrogen-rich stream for use in the hydrocracking reaction zone. In hydrocracking reactions the molecular weight of the feedstock is greater than the molecular weight of the effluent produced due to bond cleavage reactions which occur during hydrocracking Hydrogen is a necessary component of hydrocracking reactions, both to protect the hydrocracking catalysts from premature fouling and to provide the hydrogen needed for the cracked, hydrogenated and/or heteroatom reduced reaction products. 
     DEFINITIONS 
     The following terms will be used throughout the specification and will have the following meanings unless otherwise indicated. 
     As used herein, the terms “hydrocarbon” or “hydrocarbonaceous” or “petroleum” are used interchangeably to refer to carbonaceous material originating from crude oil, natural gas or biological processes. 
     As used herein “Group VIB” or “Group VIB metal” refers to one or more metals, or compounds thereof, selected from Group VIB of the Chemical Abstract Services Periodic Table. The Chemical Abstract Services Periodic Table may be found, for example, behind the front cover of CRC Handbook of Chemistry and Physics, 81 st  Edition, 2000-2001. 
     As used herein “Group VIII” or “Group VIII metal” refers to one or more metals, or compounds thereof, selected from Group VIII of the Chemical Abstract Services Periodic Table. 
     Hydrocracking is a chemical reaction of liquid feed materials, including hydrocarbons, petroleum and other biologically derived material, in the presence of hydrogen and one or more catalysts, resulting in product molecules having reduced molecular weight relative to that of the liquid feed materials. Additional reactions, including olefin and aromatic saturation and heteroatom (including oxygen, nitrogen, sulfur and halogen) removal may also occur during hydrocracking. 
     Reforming is a chemical reaction of liquid feed materials, including hydrocarbons, petroleum and other biological derived material, in the presence of one or more catalysts, resulting in product molecules such as automobile fuel, aromatics (for example benzene, toluene, xylenes and ethylbenzene), and/or hydrogen. Reactions typically involved in catalytic reforming include dehydrocylization, isomerization and dehydrogenation of naphtha range hydrocarbons, with dehydrocyclization and dehydrogenation of linear and slightly branched alkanes and dehydrogenation of cycloparaffins leading to the production of aromatics. 
     As used herein, a paraffin refers to a non-cyclic, linear or branched saturated hydrocarbon. For example, a C 8  paraffin is a non-cyclic, linear or branched hydrocarbon having 8 carbon atoms per molecule. Normal octane, methylheptanes, dimethylhexanes, trimethylpentanes are examples of C 8  paraffins. A paraffin-containing feed comprises non-cyclic saturated hydrocarbons, such as normal paraffins, isoparaffins, and mixtures thereof. 
     As used herein, a naphthene is a type of alkane having one or more rings of carbon atoms in its chemical structure. In embodiments, the naphthene is a cyclic, non-aromatic hydrocarbon. In some such embodiments, the naphthene is saturated. In some such embodiments, the naphthene is a cyclic, non-aromatic, saturated hydrocarbon having in the range of 5 to 8 carbon atoms in the cycle structure. 
     As used herein, naphtha is a distillate hydrocarbonaceous fraction boiling within the range of from 50° to 550° F. In some embodiments, naphtha boils within the range of 70° to 450° F., and more typically within the range of 80° to 400° F., and often within the range of 90° to 360° F. In some embodiments, at least 85 vol. % of naphtha boils within the range of from 50° to 550° F., and more typically within the range of from 70° to 450° F. In embodiments, at least 85 vol. % of naphtha is in the C 4 -C 12  range, and more typically in the C 5 -C 11  range, and often in the C 6 -C 10  range. Naphtha can include, for example, straight run naphthas, paraffinic raffinates from aromatic extraction or adsorption, C 6 -C 10  paraffin containing feeds, bioderived naphtha, naphtha from hydrocarbon synthesis processes, including Fischer Tropsch and methanol synthesis processes, as well as naphtha from other refinery processes, such as hydrocracking or conventional reforming. 
     As disclosed herein, boiling point temperatures are based on the ASTM D-2887 standard test method for boiling range distribution of petroleum fractions by gas chromatography, unless otherwise indicated. The mid-boiling point is defined as the 50% by volume boiling temperature, based on an ASTM D-2887 simulated distillation. 
     As disclosed herein, carbon number values (i.e. C 5 , C 6 , C 8 , C 9  and the like) of hydrocarbons may be determined by standard gas chromatography methods. 
     Unless otherwise specified, liquid feed rate to a catalytic reaction zone is reported as the volume of feed per hour per volume of catalyst. In effect, the feed rate as disclosed herein, referred to as liquid hourly space velocity (LHSV), is reported in reciprocal hours (i.e. hr −1 ). 
     The term “silica to alumina ratio” refers to the molar ratio of silicon oxide (SiO 2 ) to aluminum oxide (Al 2 O 3 ). ICP analysis may be used to determine silica to alumina ratio. 
     As used herein, the value for octane refers to the research octane number (RON), as determined by ASTM D2699. 
     As used herein, the quantity of pressure in units of psig (pounds per square inch gauge) is reported as “gauge” pressure, i.e. the absolute pressure minus the ambient pressure, unless otherwise indicated. The quantity of pressure in units of either psi (pounds per square inch) or kPa (kilopascals) is reported as absolute pressure, unless otherwise indicated. 
     As used herein “penultimate stage” does not refer necessarily to the second to last stage in a multistage reforming process but rather refers to a stage preceding at least one additional stage. As used herein “final stage” does not refer necessarily to the last stage of a multi stage reforming process but rather refers to the stage after a penultimate stage. 
     The equilibrium reaction for the conversion of toluene to xylene and benzene products normally yields about 24 wt. % para-xylene (PX), about 54 wt. % meta-xylene (MX), and about 22 wt. % ortho-xylene (OX) among xylenes. For a more complete description of equilibrium product distributions for xylene isomerization see R. D. Chirico and W. V. Steele, “Thermodynamic Equilibria in xylene isomerization. 5. Xylene isomerization equilibria from thermodynamic studies and reconciliation of calculated and experimental product distributions”,  Journal of Chemical Engineering Data,  1997, 42 (4), 784-790, herein incorporated by reference in its entirety. 
     The catalysts employed in the process of the invention may be employed in the form of pills, pellets, granules, cylinders, extrudates, broken fragments, or various special shapes, disposed as a fixed bed within a reaction zone, and the charging stock may be passed there through in the liquid, vapor, or mixed phase, and in either upward, downward or radial flow. Alternatively, they can be used in moving beds or in fluidized-solid processes, in which the charging stock is passed upward through a turbulent bed of finely divided catalyst. However, a fixed bed system or a dense-phase moving bed system often result in lower catalyst attrition losses and other operational advantages. In a fixed bed system, the feed can be preheated (by any suitable heating means) to the desired reaction temperature and then passed into a reaction zone containing a fixed bed of the catalyst. This reaction zone may be one or more separate reactors. 
     Hydrocracking 
     The hydrocracking reaction zone is maintained at conditions sufficient to effect a boiling range conversion of the hydrocarbonaceous feed to the hydrocracking reaction zone, so that the liquid hydrocrackate recovered from the hydrocracking reaction zone has a normal boiling point range below the boiling point range of the feed. The hydrocracking step reduces the size of the hydrocarbon molecules, hydrogenates olefin bonds, hydrogenates aromatics, and removes traces of heteroatoms resulting in an improvement in fuel or base oil product quality. 
     The hydrocracking catalyst generally comprises a cracking component, a hydrogenation component and a binder. Such catalysts are well known in the art. The cracking component may include an amorphous silica/alumina phase and/or a zeolite, such as a Y-type or USY zeolite. If present, the zeolite is at least about 1 percent by weight based on the total weight of the catalyst. A zeolite containing hydrocracking catalyst generally contains in the range of from 1 wt. % to 99 wt. % zeolite, and more typically in the range of 2 wt. % to 70 wt. % zeolite. Actual zeolite amounts will, of course be adjusted to meet catalytic performance requirements. The binder is generally silica or alumina. The hydrogenation component will be a Group VI, Group VII, or Group VIII metal or oxides or sulfides thereof, preferably one or more of molybdenum, tungsten, cobalt, or nickel, or the sulfides or oxides thereof. If present in the catalyst, these hydrogenation components generally make up from about 5% to about 40% by weight of the catalyst. Alternatively, platinum group metals, especially platinum and/or palladium, may be present as the hydrogenation component, either alone or in combination with the base metal hydrogenation components molybdenum, tungsten, cobalt, or nickel. If present, the platinum group metals will generally make up from about 0.1% to about 2% by weight of the catalyst. 
     The process of the invention can employ a wide variety of hydrocarbonaceous feedstocks from many different sources, such as crude oil, virgin petroleum fractions, recycle petroleum fractions, shale oil, liquefied coal, tar sand oil, synthetic paraffins from normal alphaolefin, recycled plastic feedstocks, petroleum distillates, solvent-deasphalted petroleum residua, shale oils, coal tar distillates, hydrocarbon feedstocks derived from plant, animal, and/or algal sources, and combinations thereof. Other feedstocks that can be used in the process of the invention include synthetic feeds, such as those derived from a Fischer Tropsch processes. Other suitable feedstocks include those heavy distillates normally defined as heavy straight-run gas oils and heavy cracked cycle oils, as well as conventional fluid catalytic cracking feed and portions thereof. In general, the feed can be any carbon containing feedstock susceptible to hydroprocessing catalytic reactions, particularly hydrocracking and/or reforming reactions. A suitable liquid hydrocracker feedstock is a vacuum gas oil boiling in a temperature range above about 450° F. (232° C.) and more typically within the temperature range of 550°-1100° F. (288-593° C.). In embodiments, at least 50 wt. % of the hydrocarbonaceous feedstock boils above 550° F. (288° C.). The term liquid refers to hydrocarbons, which are liquid at ambient conditions. 
     The liquid hydrocracker feedstock, which may be used in the instant invention, contains impurities such as nitrogen and sulfur, at least some of which are removed from the hydrocarbonaceous feedstock in the hydrocracking zone. Nitrogen impurities present in the hydrocarbonaceous feedstock may be present as organonitrogen compounds, in amounts greater than 1 ppm. Sulfur impurities may also be present. Feeds with high levels of nitrogen and sulfur, including those containing up to 0.5 wt % (and higher) nitrogen and up to 2 wt % and higher sulfur may be treated in the present process. However, feedstocks which are high in asphaltenes and metals will usually require some kind of prior treatment, such as in a hydrotreating operation, before they are suitable for use as a feedstock for the hydrocracking process step. A suitable liquid hydrocarbon feedstock generally contains less than about 500 ppm asphaltenes, more typically less than about 200 ppm asphaltenes, and often less than about 100 ppm asphaltenes. 
     According to one embodiment, the hydrocarbonaceous feedstock is placed in contact with the hydrocracking catalyst in the presence of hydrogen, usually in a fixed bed reactor in the hydrocracking reaction zone. The conditions of the hydrocracking reaction zone may vary according to the nature of the feed, the intended quality of the products, and the particular facilities of each refinery. Hydrocracking reaction conditions include, for example, a reaction temperature within the range of 450° F. to 900° F. (232° C.-482° C.), and typically a reaction temperature in the range of 650° F. to 850° F. (343° C.-454° C.); a reaction pressure within the range of 500 to 5000 psig (3.5-34.5 MPa), and typically a reaction pressure in the range of 1500-3500 psig (10.4-24.2 MPa); a liquid reactant feed rate, in terms of liquid hourly space velocity (LHSV) within the range of 0.1 to 15 hr −1  (v/v), typically in the range of 0.25 to 2.5 hr −1 ; and hydrogen feed rate, in terms of H 2 /hydrocarbon ratio, is within the range of 500 to 5000 standard cubic feet per barrel of liquid hydrocarbon feed (89.1-445 m 3  H 2 /m 3  feed). The hydrocrackate is then separated into various boiling range fractions. The separation is typically conducted by fractional distillation preceded by one or more vapor-liquid separators to remove hydrogen and/or other tail gases. 
     In some situations, the hydrocracking reaction conditions are established to achieve a target conversion of the hydrocarbonaceous feedstock within the hydrocracking reaction zone. For example, the hydrocracking reaction conditions may be set to achieve a conversion of greater than 30%. As an example, the target conversion may be greater than 40% or 50% or even 60%. As used herein, conversion is based on 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. 
     The hydrocracking reaction zone that contains the hydrocracking catalyst may be contained within a single reactor vessel, or it may be contained in two or more reactor vessels, connected together in fluid communication in a serial arrangement. In embodiments, hydrogen and the hydrocarbonaceous feed are provided to the hydrocracking reaction zone in combination. Additional hydrogen may be provided at various locations along the length of the reaction zone to maintain an adequate hydrogen supply to the zone. Furthermore, relatively cool hydrogen added along the length of the reactor may serve to absorb some of the heat energy within the zone, and help to maintain a relatively constant temperature profile during the exothermic reactions occurring in the reaction zone. 
     Catalysts within the hydrocracking reaction zone may be of a single type. In embodiments, multiple catalyst types may be blended in the reaction zone, or they may be layered in separate catalyst layers to provide a specific catalytic function that provides improved operation or improved product properties. The catalyst may be present in the reaction zone in a fixed bed configuration, with the hydrocarbonaceous feed passing either upward or downward through the zone. In embodiments, the hydrocarbonaceous feed passes co-currently with the hydrogen feed within the zone. In other embodiments, the hydrocarbonaceous feed passes countercurrent to the hydrogen feed within the zone. 
     The effluent from the hydrocracking reaction zone is the total of materials passing from the hydrocracking reaction zone, and generally includes normally liquid hydrocarbonaceous materials, normally gas phase hydrocarbonaceous reaction products, one or more of H 2 S, NH 3  and H 2 O from reaction of heteroatoms with hydrogen in the reaction zone and unreacted hydrogen. 
     In general, the hydrocracking reaction zone effluent is first processed to recover at least a portion of the unreacted hydrogen in one or more initial separation steps, using flash separation or fractional distillation processes. These initial separation steps are well known, and their design and operation are dictated by the specific process requirements. The flash separation steps are usually operated at a pressure within the range of from ambient pressure up to the pressure of the hydrocracking reaction zone, and at a temperature within the range of 100° F. up to the hydrocracking reaction zone temperature. 
     At least a portion of the effluent from the hydrocracking reaction zone is separated by means of fractional distillation into various fractions based on the initial and final boiling points of the components. In embodiments, the separation is conducted in an atmospheric distillation column, operated at a pressure of roughly equal to or slightly above ambient pressures, including a pressure from 0 psig to 100 psig. Distillate fractions from an atmospheric column may include one or more of C 4 − fractions, C 5 -C 8  fraction, and one or more C 9 + fractions, with each fraction being distinguished by a unique boiling point range. Such atmospheric distillation processes are well known. In embodiments, the bottoms fraction from the atmospheric distillation is further separated in a vacuum distillation column, operated at subatmospheric pressure. Distillate fractions from vacuum distillation include one or more vacuum gas oil fractions, boiling within a range of from approximately 500°-1100° F. In general, a distillate fraction recovered from the distillation is in the vapor phase at the conditions of the distillation but in the liquid phase at ambient conditions; a gaseous overhead fraction recovered from the distillation is in the vapor phase at the conditions of the distillation and also in the vapor phase at ambient conditions; and a bottoms fraction recovered from the distillation remains in the liquid phase at the conditions of the distillation. 
     In embodiments, the C 8  containing paraffin feedstock is a hydrocracked naphtha. An exemplary hydrocracked naphtha that is useful in the process is recovered from the atmospheric distillation of at least a portion of the effluent from the hydrocracking reaction zone. Exemplary hydrocracked naphthas that are recovered from atmospheric distillation generally have a normal boiling point range within the range of from 50° to 550° F. and more typically within the range of from 70° to 450° F. The distillation may be generally operated to produce a naphtha stream comprising at least 60 wt. % C 4  to C 10  hydrocarbons, more typically at least 70 wt. % C 4  to C 10  hydrocarbons, and often at least 80 wt. % C 4  to C 10  hydrocarbons. In embodiments, the distillation may be generally operated to produce a naphtha stream comprising at least 60 wt. % C 5  to C 9  hydrocarbons, more typically at least 70 wt. % C 5  to C 9  hydrocarbons and often at least 80 wt. % C 5  to C 9  hydrocarbons. In embodiments, the distillation may be generally operated to produce a naphtha stream comprising at least 60 wt. % C 6  to C 8  hydrocarbons, more typically at least 70 wt. % C 6  to C 8  hydrocarbons, and often at least 80 wt. % wt. % C 6  to C 8  hydrocarbons. 
     In an embodiment, the hydrocracked naphtha generally contains at least about 5 wt. % paraffinic C 8  hydrocarbons, more typically at least about 10 wt. % paraffinic C 8  hydrocarbons, and often at least about 12 wt. % paraffinic C 8  hydrocarbons, or at least about 15 wt. % paraffinic C 8  hydrocarbons. In a separate embodiment, the hydrocracked naphtha generally contains at least about 40 wt. % paraffinic C 8  hydrocarbons, more typically at least about 50 wt. % paraffinic C 8  hydrocarbons and often at least about 60 wt. % paraffinic C 8  hydrocarbons. Tailoring the hydrocracked naphtha to yield a desired paraffinic C 8  hydrocarbon content is achieved, at least in part, by selection of the distillation design and operating parameters. 
     In embodiments, the hydrocracked naphtha contains less than 10 wt. % aromatics, more typically less than 5 wt. % aromatics, and often less than 2 wt. % aromatics. In embodiments, the hydrocracked naphtha contains less than 1000 ppm sulfur, more typically less than 100 ppm sulfur, and often less than 10 ppm sulfur and even less than 1 ppm sulfur. In embodiments, the hydrocracked naphtha contains less than 1000 ppm nitrogen, more typically less than 100 ppm nitrogen, and often less than 10 ppm nitrogen and even less than 1 ppm nitrogen. In embodiments, the hydrocracked naphtha has an octane number of less than 90, more typically less than 85, often less than 80, and even less than 75. 
     Reforming 
     At least a portion of the hydrocracked naphtha is upgraded in a reforming reaction zone to a reformed naphtha. In embodiments, the entire hydrocracked naphtha is upgraded in this way. In the process, at least a portion of the hydrocracked naphtha is contacted in a reforming reaction zone with a reforming catalyst comprising a silicate having a silica to alumina ratio of at least 200, a crystallite size of less than 10 microns and an alkali content of less than 5000 ppm at reforming conditions to produce a hydrogen-rich stream and a reformed naphtha. 
     The reforming catalyst is selected to provide a high selectivity for the production of aromatic compounds at a reduced pressure, which increases the selectivity of C 6  to C 8  paraffin dehydrocyclization while maintaining low catalyst fouling rates. In embodiments, the reforming catalyst comprises at least one medium pore zeolite. The molecular sieve is a porous inorganic oxide characterized by a crystalline structure which provides pores of a specified geometry, depending on the particular structure of each molecular sieve. The phrase “medium pore” as used herein means having a crystallographic free diameter in the range of from about 3.9 to about 7.1 Angstrom when the porous inorganic oxide is in the calcined form. The crystallographic free diameters of the channels of molecular sieves are published in the “Atlas of Zeolite Framework Types”, Fifth Revised Edition, 2001, by Ch. Baerlocher, W. M. Meier, and D. H. Olson, Elsevier, pp 10-15, which is incorporated herein by reference. Non-limiting examples of medium pore zeolites include ZSM-5, ZSM-11, ZSM-22, ZSM-23, ZSM-35, ZSM-38, ZSM-48 MCM-22, SSZ-20, SSZ-25, SSZ-32, SSZ-35, SSZ-37, SSZ-44, SSZ-45, SSZ-47, SSZ-58, SSZ-74, SUZ-4, EU-1, NU-85, NU-87, NU-88, IM-5, TNU-9, ESR-10, TNU-10 and combinations thereof. In embodiments, the medium pore zeolite is a zeolite, which is a crystalline material that possess three-dimensional frameworks composed of tetrahedral units (TO 4/2 , T=Si, Al, or other tetrahedrally coordinated atom) linked through oxygen atoms. An medium pore zeolite that is useful in the present process includes ZSM-5. Various references disclosing ZSM-5 are provided in U.S. Pat. No. 4,401,555 to Miller. Additional disclosure on the preparation and properties of high silica ZSM-5 may be found, for example, in U.S. Pat. No. 5,407,558 and U.S. Pat. No. 5,376,259. 
     In embodiments, the reforming catalyst includes a silicate having a form of ZSM-5 with a molar ratio of SiO 2 /M 2 O 3  of at least 40:1, or at least 200:1 or at least 500:1, or even at least 1000:1, where M is selected from Al, B, or Ga. In embodiments, the ZSM-5 has a silica to alumina molar ratio of at least 40:1, or at least 200:1, or at least 500:1, or even at least 1000:1. The silicate that is useful further is characterized as having a crystallite size of less than 10 μm, or less than 5 μm or even less than 1 μm. Methods for determining crystallite size, using, for example Scanning Electron Microscopy, are well known. The silicate that is useful is further characterized as having at least 80% crystallinity, or at least 90% crystallinity, or at least 95% crystallinity. Methods for determining crystallinity, using, for example, X-ray Diffraction, are well known. 
     Strong acidity is undesirable in the catalyst because it promotes cracking, resulting in lower selectivity to C 5 + liquid product. To reduce acidity, a silicate that contains alkali metal and/or alkaline earth metal cations is useful for reforming the naphtha. The alkali or alkaline earth cations may be incorporated into the catalyst during or after synthesis of the molecular sieve. Suitable molecular sieves are characterized by having at least 90% of the acid sites, or at least 95% of the acid sites, or at least 99% of the acid sites being neutralized by introduction of the alkali or alkaline earth cations. In one embodiment, the medium pore zeolite contains less than 5000 ppm alkali. Such molecular sieves are disclosed, for example, in U.S. Pat. No. 4,061,724, in U.S. Pat. No. 5,182,012 and in U.S. Pat. No. 5,169,813. These patents are incorporated herein by reference, particularly with respect to the description, preparation and analysis of molecular sieves having the specified molar silica to alumina molar ratios, having a specified crystallite size, having a specified crystallinity and having a specified alkali and/or alkaline earth content. 
     In embodiments, the silicate is a ZSM-5 type medium pore zeolite. In some such embodiments, the silicate is silicalite, a very high ratio silica to alumina form of ZSM-5. In embodiments, the silicalite has a silica to alumina molar ratio of at least 40:1, or at least 200:1, or at least 500:1, or even at least 1000:1. Various references disclosing silicalite and ZSM-5 are provided in U.S. Pat. No. 4,401,555 to Miller and U.S. Pat. No. 6,063,723 to Miller. These references include the aforesaid U.S. Pat. No. 4,061,724 to Grose et al.; U.S. Pat. Reissue No. 29,948 to Dwyer et al.; Flanigen et al., Nature, 271, 512-516 (Feb. 9, 1978) which discusses the physical and adsorption characteristics of silicalite; and Anderson et al., J. Catalysis 58, 114-130 (1979) which discloses catalytic reactions and sorption measurements carried out on ZSM-5 and silicalite. The disclosures of these publications are incorporated herein by reference. 
     Other zeolites which can be used in the process of the present invention include those as listed in U.S. Pat. No. 4,835,336; namely: ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM-38, ZSM-48, and other similar materials. 
     ZSM-5 is more particularly described in U.S. Pat. No. 3,702,886 and U.S. Pat. Re. 29,948, the entire contents of which are incorporated herein by reference. 
     ZSM-11 is more particularly described in U.S. Pat. No. 3,709,979 the entire contents of which are incorporated herein by reference. 
     ZSM-12 is more particularly described in U.S. Pat. No. 3,832,449, the entire contents of which are incorporated herein by reference. 
     ZSM-22 is more particularly described in U.S. Pat. Nos. 4,481,177, 4,556,477 and European Patent No. 102,716, the entire contents of each being expressly incorporated herein by reference. 
     ZSM-23 is more particularly described in U.S. Pat. No. 4,076,842, the entire contents of which are incorporated herein by reference. 
     ZSM-35 is more particularly described in U.S. Pat. No. 4,016,245, the entire contents of which are incorporated herein by reference. 
     ZSM-38 is more particularly described in U.S. Pat. No. 4,046,859, the entire contents of which are incorporated herein by reference. 
     ZSM-48 is more particularly described in U.S. Pat. No. 4,397,827 the entire contents of which are incorporated herein by reference. 
     In embodiments, the crystalline silicate may be in the form of a borosilicate, where boron replaces at least a portion of the aluminum of the more typical aluminosilicate form of the silicate. Borosilicates are described in U.S. Pat. Nos. 4,268,420; 4,269,813; and 4,327,236 to Klotz, the disclosures of which patents are incorporated herein, particularly that disclosure related to borosilicate preparation. In a suitable borosilicate, the crystalline structure is that of ZSM-5, in terms of X-ray diffraction pattern. Boron in the ZSM-5 type borosilicates takes the place of aluminum that is present in the more typical ZSM-5 crystalline aluminosilicate structures. Borosilicates contain boron in place of aluminum, but generally there is some trace amounts of aluminum present in crystalline borosilicates. 
     Still further crystalline silicates which can be used in the present invention are ferrosilicates, as disclosed for example in U.S. Pat. No. 4,238,318, gallosilicates, as disclosed for example in U.S. Pat. No. 4,636,483, and chromosilicates, as disclosed for example in U.S. Pat. No. 4,299,808. 
     The reforming catalyst further contains one or more Group VIII metals, e.g., nickel, ruthenium, rhodium, palladium, iridium or platinum. In embodiments, the Group VIII metals include iridium, palladium, platinum or a combination thereof. These metals are more selective with regard to dehydrocyclization and are also more stable under the dehydrocyclization reaction conditions than other Group VIII metals. When employed in the reforming catalyst, these metals are generally present in the range of between 0.1 wt. % and 5 wt. % or between 0.3 wt. % to 2.5 wt. %. The catalyst may further comprise a promoter, such as rhenium, tin, germanium, cobalt, nickel, iridium, tungsten, rhodium, ruthenium, or combinations thereof. In an illustrative embodiment, the catalyst comprises in the range of 0.1 wt. % to 1 wt. % platinum and in the range of 0.1 wt. % to 1 wt. % rhenium. 
     In forming the reforming catalyst, the crystalline molecular sieve is preferably bound with a matrix. Satisfactory matrices include inorganic oxides, including alumina, silica, naturally occurring and conventionally processed clays, such as bentonite, kaolin, sepiolite, attapulgite and halloysite. 
     Reforming reaction conditions employed in the reforming reaction zone will depend, at least in part, on the characteristics of the naphtha feed, whether highly aromatic, paraffinic or naphthenic. Reaction conditions of temperature, pressure, hydrocarbon to hydrogen ratio, and LHSV can be tuned in order to maximize production of reformate products of a desired octane, depending at least in part on the particular performance advantages of the reforming catalyst. In the process, the hydrocracked naphtha fraction is contacted with reforming catalyst in the reforming reaction zone at reforming reaction conditions. In embodiments, reforming reaction conditions include a pressure in the range of between 0 psig (0 kPa) and 250 psig (1720 kPa). In some cases pressure range is between 0 psig (0 kPa) and 100 psig (689 kPa), and in some cases is between 25 psig (172 kPa) and 75 psig (517 kPa). In embodiments, reforming reaction conditions include a liquid hourly space velocity (LHSV) in the range of between 0.1 and 20 hr −1 , and in some cases in the range of between 0.3 and 5 hr −1 . In embodiments, reforming conditions include a temperature in the range of between 600° F. (316° C.) and 1100° F. (593° C.), and in some cases in the range of between 640° F. (338° C.) and 1050° F. (566° C.). Hydrogen may be added as an additional feed to the final reforming zone, but it is not required. In embodiments, reforming reaction conditions include conditions to maintain a molar H 2 /hydrocarbon ratio in the range of 1:1 to 10:1. A molar H 2 /hydrocarbon ratio in the range of 1:1 to 4:1 is exemplary. 
     The naphtha stream is contacted in a reforming reaction zone with a reforming catalyst to produce a hydrogen-rich stream and reformed naphtha. Additional C 5 − liquids and gases, including additional C 4 − liquids and gases, may also be produced. In embodiments, these lighter reaction products are separated from the reformed naphtha in a fractionation unit, using, for example a flash separation zone or a multi-stage distillation unit. The reformed naphtha has an increased octane relative to that of the hydrocracked naphtha, such as, for example, an octane of at least 90, or at least 95, or at least 98. The reformed naphtha further boils in the gasoline range, such as, for example, having a normal boiling point range within the range of from 70° F. (21° C.) to 280° F. (138° C.), or in the range of from 100° F. (38° C.) to 260° F. (127° C.), or in the range of 100° F. (38° C.) to 230° F. (110° C.). 
     In some aspects, the reformed naphtha comprises at least 60 wt % or at least 70 wt % or at least 80 wt % C 4  to C 10  hydrocarbons. In some of these situations, the reformed naphtha comprises at least 60 wt % or at least 70 wt % or at least 80 wt % wt % C 5  to C 9  hydrocarbons. In some of these situations, the reformed naphtha comprises at least 60 wt % or at least 70 wt % or at least 80 wt % wt % C 6  to C 8  hydrocarbons. In embodiments, the reformed hydrocracked naphtha contains in the range of 1% to 40% aromatics, or in the range of 5% to 30% aromatics. In embodiments, the reformed naphtha contains less than 1000 ppm sulfur, or less than 100 ppm sulfur or less than 10 ppm sulfur or even less than 1 ppm sulfur. In embodiments, the reformed naphtha contains less than 1000 ppm nitrogen, or less than 100 ppm nitrogen or less than 10 ppm nitrogen or even less than 1 ppm nitrogen. 
     The reformed naphtha is useful as a fuel or as a blend stock for a fuel. In some embodiments, at least a portion of the final reformate from the final reforming zone is blended with at least a portion of the heavy stream, which is recovered from the penultimate zone; the blend may be used as a fuel or as a blend stock for a fuel. In embodiments, a portion of the hydrocracked naphtha is caused to bypass the reformer reaction zone, and is combined with at least a portion of the reformed naphtha. 
     A combined naphtha is prepared by combining a portion of the hydrcarcked naphtha with a portion of the reformed naphtha. For example, the combined naphtha is suitable for use as a fuel or fuel blendstock, such as gasoline or a gasoline blend stock. In embodiments, the combined naphtha has an octane of greater than 90. Exemplary combined naphthas have an octane of greater than 91, or greater than 92, or greater than 93, or greater than 94, or even greater than 95. 
     In embodiments, the integrated process for producing high octane naphtha comprises: (a) isolating a hydrocracked naphtha from a hydrocracking reaction zone effluent; (b) providing a first portion of the hydrocracked naphtha to a reforming reaction zone containing a reforming catalyst that comprises a silicate having a silica to alumina molar ratio of at least 200, and a crystallite size of less than 10 microns; (c) contacting the first portion of the hydrocracked naphtha with the reforming catalyst at reforming reaction conditions and producing a hydrogen-rich stream and a reformed naphtha; (d) passing the hydrogen-rich stream to the hydrocracking reaction zone; and (e) combining the reformed naphtha with a second portion of the hydrocracked naphtha to form a combined naphtha having an octane of greater than 90. In some such embodiments, a portion of the hydrocracked naphtha is provided to the reforming reaction zone; the remainder of the hydrocracked naphtha is combined with the reformed naphtha to form the combined naphtha. 
     At least a portion of the hydrogen that is isolated from the reforming reaction zone is passed as at least a portion of the hydrogen feed to the hydrocracking reaction zone. The hydrogen-rich stream may be isolated from the liquid products recovered from the reforming reaction zone in a high pressure separator or other flash zone. Any C 4 — hydrocarbons in the effluent from the reforming reaction zone may also be isolated in a flash zone, either along with the hydrogen or in a subsequent flash zone. Depending on the type of feed to the reforming reaction zone, a stream having a boiling point that is relatively higher than that of the final reformate may further be isolated from the reforming reaction zone effluent. 
     Reference is now made to embodiments of the invention illustrated in  FIG. 1 . The integrated process includes a hydrocracking reaction zone and a reforming reaction zone, operating in combination to improve operational efficiency and product quality. In the integrated process, a hydrocarbonaceous feedstock  12  is supplied to a first hydrocracking reaction zone  10 . Separating at least a portion of the hydrocracking reaction zone effluent  16  yields at least recycle hydrogen  22  and naphtha  26 . The naphtha is passed to reforming reaction zone  40  for increasing the octane of the naphtha and for producing reformer hydrogen  42 , which is used as one of the sources of hydrogen feed to the hydrocracking reaction zone. Reformed naphtha  44  having increased octane is available, for example, as a fuel or fuel blendstock, a petrochemical feedstock or a refinery feedstock. 
     A detailed description of the present invention is made with reference to specific embodiments thereof as illustrated in the appended drawings. The drawings depict only typical embodiments of the invention and therefore are not to be considered to be limiting of its scope. 
     In the embodiment illustrated in  FIG. 1 , a hydrocarbonaceous feedstock  112  boiling in a temperature range of above about 450° F. (232° C.) is passed to a hydrocracking reaction zone  110  and is contacted with a hydrocracking catalyst in the presence of hydrogen. The reaction zone  110  may contain one or more beds of the same or different catalyst. Process conditions in the hydrocracking reaction zone include a temperature from about 450° F. to about 900° F., a pressure from about 500 psig to about 5000 psig, a liquid feed rate of from about 0.1 to about 15 hr −1 , and a hydrogen circulation rate from about 500 to about 5,000 standard cubic feet per barrel. Hydrogen passed to the hydrocracking reaction zone  110  is a combination of fresh hydrogen feed  114 , recycle hydrogen  121  and reformer hydrogen  142 . 
     Hydrocracking reaction zone effluent  116  is passed to separation zone  120  for isolation of hydrocracked naphtha  123 . In embodiments, additional streams may be produced during the separation process, including recycle hydrogen  122 , one or more light distillates  123 , one or more heavy distillates  126  and a bottoms stream  127 . In embodiments, the one or more light distillates include C 4 − hydrocarbons. In embodiments, the one or more heavy distillates include C 9 + hydrocarbons. Exemplary heavy distillates include C 10 + hydrocarbons or C 11 + hydrocarbons, or C 12 + hydrocarbons. 
     Isolation of the various fractions from the hydrocracking reaction zone effluent generally takes place in one or more single and/or multiple stage fractional distillation units. In embodiments, isolation of the hydrocracked naphtha and production of the additional streams occur in a single separation zone using a fractionator, such as a multiple stage distillation column. In other embodiments, this separation is done in sequential zones, with the hydrogen, and optionally one or more light distillates being separated in one or more preliminary separation zones, for example in single stage flash separation zones, prior to the isolation of the hydrocracked naphtha  123 , the one or more heavy distillates  126  and the bottoms stream  127 . 
     In some situations, at least a portion of the bottoms stream  127  is recovered as heavy product  128 . In embodiments, at least 10 wt. % of the bottoms stream is recovered as heavy product  128 . In an exemplary process, at least 50 wt. % of the bottoms stream is recovered as heavy product  128 . In an exemplary process, 100 wt. % of the bottoms stream is recovered as heavy product  128 . Depending on the type of hydrocarbonaceous feedstock and the hydrocracking reaction conditions in a particular application, bottoms stream  127  is suitable as a lubricant base stock or a similar product or as a feedstock for additional processing, using, for example one or more of hydroisomerization and hydrotreating and hydrofinishing to prepare the lubricant oil base stock. 
     In some situations, at least a portion of the bottoms stream  127  is passed as recycle  129  to hydrocracking reaction zone  110 . In embodiments, at least 10 wt. % of the bottoms stream  127  is passed as recycle  129  to the hydrocracking reaction zone. In an exemplary process, at least 50 wt. % of the bottoms stream  127  is passed as recycle  129  to the hydrocracking reaction zone. In an exemplary process, 100 wt. % of the bottoms stream  127  is passed as recycle  129  to the hydrocracking reaction zone. 
     In the process, hydrocracked naphtha  123  is provided, with additional heating as needed to raise the temperature to reforming temperature, to reforming reaction zone  140  for contacting at reforming reaction conditions over a catalyst that includes a silicate having a silica to alumina molar ratio of at least 200 and a crystallite size of less than 10 microns. In embodiments, the silicate further has an alkali content of less than 5000 ppm. In general, reformer hydrogen  142 , C 4 − hydrocarbons  146  and reformed naphtha  144  are recovered during reforming of the hydrocracked naphtha  123  and any subsequent fractional separation process. In embodiments, reformed naphtha  144  has an octane (RON) of greater than 90. An exemplary reformed naphtha has an octane of greater than 92 or greater than 95 or even greater than 98. The reformed naphtha can be used as a fuel such as gasoline, diesel, or jet fuel depending on the desired application. The reformed naphtha can also, or in the alternative, be a component in a blended fuel stock. 
     In embodiments, at least a portion of hydrocracked naphtha  123  is combined with at least a portion of reformed naphtha  144  to form combined naphtha  146 . The fraction of hydrocracked naphtha  123  that bypasses reforming reaction zone  140  can cover a wide range, from as low as 0 wt. % to as high as 95 wt. % of the hydrocracked naphtha  123 . 
     In addition, reformer hydrogen  142 , a hydrogen-rich stream containing greater than 95 vol. %, that is produced during the reforming reaction is recycled to the hydrocracking reaction zone  110 . The generation of hydrogen by the process of the invention provides an economic benefit by minimizing the additional hydrogen needed for the hydrocracking reaction zone. 
     In the embodiment illustrated in  FIG. 2 , a hydrocarbonaceous feedstock  212  boiling in a temperature range of above about 450° F. (232° C.) is passed to a first hydrocracking reaction zone  210  and is contacted with a hydrocracking catalyst in the presence of hydrogen. The reaction zone  210  may contain one or more beds of the same or different catalyst. Process conditions in the first hydrocracking reaction zone include a temperature from about 450° F. to about 900° F., a pressure from about 500 psig to about 5000 psig, a liquid feed rate from about 0.1 to about 15 hr −1 , and a hydrogen circulation rate from about 500 to about 5,000 standard cubic feet per barrel. Hydrogen passed to the hydrocracking reaction zone  210  is a combination of fresh hydrogen feed  214 , recycle hydrogen  222  and reformer hydrogen  242 . 
     First zone effluent  216  is passed to separation zone  220  for isolation of hydrocracked naphtha  225 . In embodiments, additional streams may be produced during the separation process, including recycle hydrogen  222 , one or more light distillates  224 , one or more heavy distillates  228  and a bottoms stream  229 . In embodiments, the one or more light distillates include C 4 − hydrocarbons. In embodiments, the one or more heavy distillates include C 9 + hydrocarbons. Exemplary heavy distillates include C 10 + hydrocarbons or C 11 + hydrocarbons, or C 12 + hydrocarbons. 
     Isolation of the various fractions from the hydrocracking reaction zone effluent generally takes place in one or more single and/or multiple stage fractional distillation units. In embodiments, isolation of the hydrocracked naphtha and production of the additional streams occur in a single separation zone using a fractionator, such as a multiple stage distillation column. In other embodiments, this separation is done in sequential zones, with the hydrogen, and optionally one or more light distillates being separated in one or more preliminary separation zones, for example in single stage flash separation zones, prior to the isolation of the hydrocracked naphtha  225 , the one or more heavy distillates  228  and the bottoms stream  229 . 
     At least a portion of the bottoms stream  229  is passed to a second hydrocracking reaction zone  230  for additional hydrocracking The second reaction zone  230  may contain one or more beds of the same or different catalyst. Furthermore, the catalyst(s) in the second reaction zone  230  may be the same as or different from the catalyst(s) in the first reaction zone  210 . In embodiments, at least a portion of second zone effluent  232  is returned as hydrocracked recycle  234  to separation zone  220 . Depending on the particular application, from as little as 0 wt. % to as much as 100 wt. % of second zone effluent  232  is recycled; the remaining bottoms product  236  is recovered for use elsewhere. 
     In the process, hydrocracked naphtha  225  is passed, with additional heating as needed to raise the temperature to reforming temperature, to reforming reaction zone  240  for contacting at reforming reaction conditions over a catalyst comprising a silicate having a silica to alumina ratio of at least about 40:1. Reformed naphtha  244  that is produced by the reforming reactions in zone  240  has an octane (RON) of greater than 90. An exemplary reformed naphtha has an octane of greater than 92 or greater than 95 or even greater than 98. The reformed naphtha can be used as a fuel such as gasoline, diesel, or jet fuel depending on the desired application. The reformed naphtha can be a component in a blended fuel stock. 
     Notwithstanding that the present invention has been described above in terms of alternative embodiments, it is anticipated that still other alterations, modifications and applications will become apparent to those skilled in the art after having read this disclosure. It is therefore intended that such disclosure be considered illustrative and not limiting, and that the appended claims be interpreted to include all such applications, alterations, modifications and embodiments as fall within the true spirit and scope of the invention.