Patent Publication Number: US-2012024754-A1

Title: Multi-stage reforming process with final stage catalyst regeneration

Description:
RELATED APPLICATION 
     This application claims priority to U.S. patent application Ser. No. 12/134,153, filed Jun. 5, 2008. This application claims priority to and benefits from the foregoing, the disclosure of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a multistage reforming process with minimized down time during final stage catalyst regeneration. The process uses a medium pore molecular sieve catalyst in the final stage to enable fast regeneration without a halogenation step. 
     BACKGROUND OF THE INVENTION 
     Catalytic reforming is one of the basic petroleum refining processes for upgrading light hydrocarbon feedstocks, frequently referred to as naphtha feedstocks. 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 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. Dealkylation and hydrocracking are generally undesirable due to the low value of the resulting light hydrocarbon products. 
     Catalysts commonly used in commercial reforming reactions often include a Group VIII metal, such as platinum or palladium, or a Group VIII metal plus a second catalytic metal, which acts as a promoter. Examples of metals useful as promoters include rhenium, tin, tungsten, germanium, cobalt, nickel, rhodium, ruthenium, iridium or combinations thereof. The catalytic metal or metals may be dispersed on a support such as alumina, silica, or silica-alumina. Typically, a halogen such as chlorine is incorporated on the support to add acid functionality. In addition to Group VIII metals, other reforming catalysts include aluminosilicate zeolite catalysts. For example, U.S. Pat. Nos. 3,761,389, 3,756,942 and 3,760,024 teach aromatization of a hydrocarbon fraction with a ZSM-5 type zeolite catalyst. U.S. Pat. No. 4,927,525 discloses catalytic reforming processes with beta zeolite catalysts containing a noble metal and an alkali metal. Other reforming catalysts include other molecular sieves such as borosilicates and silicoaluminophosphates, layered crystalline clay-type phyllosilicates, and amorphous clays. 
     In addition to selection of catalysts for reforming, various processes for reforming a naphtha feedstock in one or more process steps to produce higher value reformate products are known in the art. U.S. Pat. No. 3,415,737 teaches a process for reforming naphtha under conventional mild reforming conditions with a platinum-rhenium-chloride reforming catalyst to increase the aromatics content and octane number of the naphtha. In U.S. Pat. No. 3,770,614 there is disclosed a process in which a reformate is fractionated and the light reformate fraction (C6 fraction) passed over a ZSM-5-type zeolite to increase aromatic content of the product. U.S. Pat. No. 3,950,241 discloses a process for upgrading naphtha by separating it into low- and high-boiling fractions, reforming the low-boiling fraction, combining the high-boiling naphtha with the reformate, and contacting the combined fractions with a ZSM-5-type catalyst. U.S. Pat. No. 4,181,599 discloses a process for reforming naphtha comprising separating the naphtha into heavy and light fractions and reforming and isomerizing the naphtha fractions. U.S. Pat. No. 4,190,519 teaches a process for upgrading a naphtha-boiling-range hydrocarbon which comprises separating the naphtha feedstock into a light naphtha fraction containing C6 paraffins and lower-boiling hydrocarbons and a heavy naphtha fraction containing higher-boiling hydrocarbons, reforming the heavy naphtha fraction and passing at least a portion of the reformate together with the light naphtha fraction over a zeolite catalyst to produce an aromatics-enriched effluent. Different catalysts may be employed in different process steps during the reforming of naphtha feedstocks as described in U.S. Pat. No. 4,627,909, U.S. Pat. No. 4,443,326, U.S. Pat. No. 4,764,267, U.S. Pat. No. 5,073,250, U.S. Pat. No. 5,169,813, U.S. Pat. No. 5,171,691, U.S. Pat. No. 5,182,012, U.S. Pat. No. 5,358,631, U.S. Pat. No. 5,376,259 and U.S. Pat. No. 5,407,558, for example. 
     Even with the advances in naphtha reforming catalysts and processes, a need still exists to develop new and improved reforming methods to provide higher liquid yield, improve hydrogen production, and minimize the formation of less valuable low molecule weight (C 1 -C 4 ) products. It has been discovered that interstage feed separation in a staged reforming process and lower pressure in the final stage of a multistage reforming process can improve the RON (Research Octane Number), aromatics content, C 5 + liquid yield, hydrogen production, and catalyst life. 
     SUMMARY OF THE INVENTION 
     The present invention is based on the discovery that in a multi-stage reforming process, the yield of hydrocarbon product and hydrogen can be optimized by increasing the severity of the penultimate stage during regeneration of the final stage catalyst. During regeneration of the final stage catalyst, the RON of the effluent from the penultimate stage can meet the target RON of the hydrocarbon product by temporarily increasing the severity of the penultimate stage reaction conditions. Due to fast regeneration times of the final stage catalyst, the lifetime of the penultimate stage catalyst is minimally affected by the increased reaction severity. 
     The present invention relates to processes for catalytically reforming a naphtha feed to produce a product reformate in a multistage reforming operation. The reforming process includes providing a naphtha to a multi-stage reforming system that includes a penultimate reforming stage containing a first reforming catalyst and a final reforming stage containing a second reforming catalyst; contacting the naphtha at a first reforming temperature with the first reforming catalyst and producing a penultimate effluent; contacting at least a portion of the penultimate effluent at a second reforming temperature with the second reforming catalyst and producing a final reformate having an RON of greater than 90; and regenerating the second reforming catalyst in the final reforming stage while reforming the naphtha in the penultimate reforming stage and producing a third reformate from the penultimate reforming stage that has an RON of at least 90. 
     In embodiments, the first reforming catalyst includes platinum and rhenium on an alumina support. In embodiments, the second reforming catalyst includes silicalite having a silica to alumina molar ratio of at least 200, a crystallite size of less than 10 microns and an alkali content of less than 5,000 ppm. 
     In embodiments, the step of regenerating the second reforming catalyst includes ceasing the flow of intermediate reformate to the final reforming stage; increasing the reforming temperature in the penultimate reforming stage by at least 5° F. (2.8° C.) to produce a third reformate having an RON of at least 90; and regenerating the second reforming catalyst in the final reforming stage. In further embodiments, the step of regenerating the second reforming catalyst includes passing a nitrogen containing stream through the second reforming stage to remove at least a portion of the naphtha container therein; passing an oxygen containing stream through the final reforming stage to remove at least a portion of the carbon deposited on the second reforming catalyst contained within the final reforming stage; passing a nitrogen containing stream through the second reforming catalyst to remove at least a portion of the oxygen contained therein; reducing the temperature of the second reforming catalyst within the final reforming stage to a temperature of less than the second reforming temperature; introducing at least a portion of the penultimate effluent to the final reforming stage; and increasing the temperature of the second reforming catalyst to a temperature in the range of 800° F. to 1100° F. (427° C.-593° C.). In further embodiments, the step of regenerating the second reforming catalyst includes reducing the reforming temperature in the penultimate reforming stage by at least 5° F. (2.8° C.). 
     Other aspects, features and advantages will be apparent from the description of the embodiments thereof and from the claims. 
    
    
     
       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 
     In the present process, a naphtha boiling range feedstock is processed in a multi-stage reforming process, in which said process involves at least a penultimate stage for reforming the naphtha feedstock to produce a penultimate effluent and a final stage for further reforming a portion of the penultimate effluent. The reforming process is operated at conditions and with catalysts selected for conducting dehydrocyclization, isomerization and dehydrogenation reactions of paraffins thus converting low octane normal paraffins and cycloparaffins into high octane materials. In this way, a product having increased octane and/or containing an increased amount of aromatics is produced. In preferred embodiments, the multi-stage reforming process is operated at conditions and with one or more catalysts for producing a net positive quantity of hydrogen. It is a further object of the invention to provide for a regeneration step during which the final stage catalyst is regenerated while reformate product of a target RON is produced by temporarily increasing the severity of the penultimate stage such that the effluent of the penultimate stage comprises reformate of the target RON. 
     The multi-stage reforming process of the invention comprises passing a refinery stream through at least two reforming stages in series. In general, each reforming stage is characterized by one or more reforming reactor vessels, each containing a catalyst and maintained at reforming reaction conditions. The product from each stage before the final stage is passed, at least in part, to the succeeding stage in the multi-stage process. The temperature of the product from each stage which is passed to a succeeding stage may be increased or decreased to meet the particular needs of the process. Likewise, the pressure of the product which is passed to a succeeding stage before the final stage may be increased or decreased. Preferably the final stage is run at a lower pressure than the penultimate stage. 
     The present invention is based in part on the discovery that selective reforming of C5-C8 paraffins in a separate or additional reforming stage provides improved performance of the overall reforming process. Thus, a penultimate reforming stage using a conventional reforming catalyst is operated at relatively low severity, since it is not required to reach the high octane levels normally desired for a naphtha fuel or fuel blend stock. While not being bound to any theory, we believe that under these conditions the reforming catalyst of the penultimate stage catalyzes the more facile reactions, such as cyclohexane and alkycyclohexane dehydrogenation, while keeping hydrocracking to a minimum. Generally, a conventional catalyst used to dehydrocyclize paraffins under more severe conditions produces higher quantities of light C1-C4 gases, on account of the catalyst being somewhat unselective for dehydrocyclization. With the present invention, however, an intermediate reformate comprising at least 70 vol. % C5-C8 hydrocarbons from a penultimate reforming stage is passed to a final reforming stage containing the same or a different reforming catalyst as the penultimate stage. The C9+ fraction from the penultimate stage has higher octane than the C5-C8 fraction, and is not further reformed in the final stage, thus preventing any unwanted dealkyation or cracking of the C9+ hydrocarbons. In a preferred embodiment the final stage is run at a lower pressure than the penultimate stage. We believe that running the final stage at a lower pressure than the penultimate stage leads to improvements including one or more of the following characteristics—1) increased yield of C5+ liquid products, 2) minimized unwanted hydrocracking/dealkylation reactions, and 3) increased hydrogen production. Lower pressure of the final stage can, in some cases, lead to higher catalyst fouling rates depending on the type of catalyst used; however, in situ catalyst regeneration of the final stage catalyst can be used to maintain catalyst activity. While the final stage catalyst is being regenerated, the severity of the penultimate stage can be temporarily increased to meet octane targets for the total blended reformate which would otherwise be achieved with both the penultimate and final stages operating. Consequently, the performance characteristics of the penultimate and final stage reactors provide complementary benefits, resulting in an overall process which produces a high octane product at an improved C5+ liquid yield and improved hydrogen production. 
     While the discussion which follows relates at times, for convenience, to operation of penultimate and final reforming stages, the principles of the invention are applicable as between any two successive stages and can be applied to several sequentially connected stages. In essence then, the term final stage as used herein does not necessarily indicate the last stage if there are three or more stages, but rather indicates a succeeding stage which follows a preceding (often referred to for convenience as “penultimate”) stage. 
     As disclosed herein, boiling point temperatures are based on 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. 
     As disclosed herein, Research Octane Number (RON) is determined using the method described in ASTM D2699. 
     Unless otherwise specified, as used herein, feed rate to a catalytic reaction zone is reported as the volume of feed per volume of catalyst per hour. The feed rate as disclosed herein is reported in reciprocal hours (i.e. hr-1) which is also referred to as liquid hourly space velocity (LHSV). 
     As used herein, a C 4 − stream comprises a high proportion of hydrocarbons with 4 or fewer carbon atoms per molecule. Likewise, a C 5 + stream comprises a high proportion of hydrocarbons with 5 or more carbon atoms per molecule. It will be recognized by those of skill in the art that hydrocarbon streams in refinery processes are generally separated by boiling range using a distillation process. As such, the C 4 − stream would be expected to contain a small quantity of C 5 , C 6  and even C 7  molecules. However, a typical distillation would be designed and operated such that at least about 70% by volume of a C 4 − stream would contain molecules having 4 carbon atoms or fewer per molecule. Thus, at least about 70 vol % of a C 4 − stream boils in the C 4 − boiling range. As used herein, C 5 +, C 6 -C 8 , C 9 + and other hydrocarbon fractions identified by carbon number ranges would be interpreted likewise. In embodiments, the naphtha that is provided to the multi-stage reforming system has an RON of less than 80 or less than 75. 
     As used herein, the multi-stage reforming system includes at least two reaction stages, a first (i.e. penultimate) containing a first reforming catalyst and a second (i.e. final) containing a second reforming catalyst. Included in the reforming system are the necessary heaters and furnaces, valves, piping and associated hardware, and fractionation zones that are necessary for successful operation of the reforming system. 
     The term “silica to alumina ratio” refers to the molar ratio of silicon oxide (SiO2) to aluminum oxide (Al 2 O 3 ). 
     As used herein the term “molecular sieve” refers to a crystalline material containing pores, cavities, or interstitial spaces of a uniform size in which molecules small enough to pass through the pores, cavities, or interstitial spaces are adsorbed while larger molecules are not. Examples of molecular sieves include zeolites and non-zeolitic molecular sieves such as zeolite analogs including, but not limited to, SAPOs (silicoaluminophosphates), MeAPOs (metalloaluminophosphates), AlPO4, and ELAPOs (nonmetal substituted aluminophosphate families). 
     When used in this disclosure, the Periodic Table of the Elements referred to is the CAS version published by the Chemical Abstract Service in the Handbook of Chemistry and Physics, 72nd edition (1991-1992). 
     As used herein, naphtha is a distillate hydrocarbonaceous fraction boiling within the range of from 50° (10° C.) to 550° F. (288° C.). In some embodiments, naphtha boils within the range of 70° (21° C.) to 450° F. (232° C.) or within the range of 80° (27° C.) to 400° F. (204° C.) or even within the range of 90° (32° C.) to 360° F. (182° C.). In some embodiments, at least 85 vol % of naphtha boils within the range of from 50° (10° C.) to 550° F. (288° C.) or within the range of from 70° (21° C.) to 450° F. (232° C.). In embodiments, at least 85 vol % of naphtha is in the C4-C12 range, or in the C5-C11 range, or in the C6-C10 range. Naphtha can include, for example, straight run naphthas, paraffinic raffinates from aromatic extraction or adsorption, C6-C10 paraffin-rich 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. 
     The reforming catalyst used in the penultimate reforming stage may be any catalyst known to have catalytic reforming activity. In one embodiment, the penultimate stage catalyst comprises a Group VIII metal disposed on an oxide support. Examples of Group VIII metals include platinum and palladium. The catalyst may further comprise a promoter, such as rhenium, tin, tungsten, germanium, cobalt, nickel, iridium, rhodium, ruthenium, or combinations thereof. In some such embodiments, the promoter metal is rhenium or tin. 
     The above mentioned metals can be disposed on a support comprising one or more of (1) a refractory inorganic oxide such as alumina, silica, titania, magnesia, zirconia, chromia, thoria, boria or mixtures thereof; (2) a synthetically prepared or naturally occurring clay or silicate, which may be acid-treated; (3) a crystalline zeolitic aluminosilicate, either naturally occurring or synthetically prepared such as FAU, MEL, MFI, MOR, MTW (IUPAC Commission on Zeolite Nomenclature), in hydrogen form or in a form which has been exchanged with metal cations; (4) a spinel such as MgAl 2 O 4 , FeAl 2 O 4 , ZnAl 2 O 4 , CaAl 2 O 4 ; (5) a silicoaluminophosphate; and (6) combinations of materials from one or more of these groups. The refractory support of the reforming catalyst preferably comprises an inorganic oxide, more preferably alumina. In embodiments, the reforming catalyst used in the penultimate reforming stage includes platinum on an alumina-containing support. 
     Halogen may be incorporated into the catalyst by combining it with a source of halogen such as alkali or alkaline earth chlorides, fluorides, iodides or bromides. Other halogen sources include compounds such as hydrogen halide, e.g., hydrogen chloride, and ammonium halides, e.g., ammonium chloride. The preferred halogen source is a source of chlorine. The amount of halogen source combined with the catalyst should be such that the catalyst contains from about 0.1 to 3 wt % halogen, more preferably from about 0.2 to about 1.5 wt % halogen, and most preferably between 0.5 to 1.5 wt % halogen. 
     The catalyst, if it includes a promoter metal, suitably includes sufficient promoter metal to provide a promoter to platinum ratio between 0.5:1 and 10:1, more preferably between 1:1 and 6:1, most preferably between 2:1 and 5:1. The precise conditions, compounds, and procedures for catalyst manufacture are known to those persons skilled in the art. Some examples of conventional catalysts are shown in U.S. Pat. Nos. 3,631,216; 3,415,737; and 4,511,746, which are hereby incorporated by reference in their entireties. 
     The reforming catalyst in the penultimate stage and final stage may be employed in the form of pills, pellets, granules, broken fragments, or various special shapes, disposed as a fixed bed within a reaction zone, and the charging stock may be passed through in the liquid, vapor, or mixed phase, and in either upward, downward or radial flow. Alternatively, the reforming catalysts 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 are preferred due to less catalyst attrition and other operational advantages. In a fixed bed system, the feed is 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 with suitable means to maintain the desired temperature at the reactor entrance. The temperature must be maintained because reforming reactions are typically endothermic in nature. 
     The actual reforming conditions in the penultimate stage will depend, at least in part, on the feed used, whether highly aromatic, paraffinic or naphthenic and upon the desired octane rating of the product and the desired hydrogen production. 
     The penultimate stage is maintained at relatively mild reaction conditions, so as to inhibit the cracking of the stream being upgraded, and to increase the useful lifetime of the catalyst in the penultimate stage. The naphtha boiling range feedstock to be upgraded in the penultimate stage contacts the penultimate stage catalyst at reaction conditions, which conditions include a temperature in the range from about 800° F. (427° C.) to about 1100° F. (593° C.), a pressure in the range from about 70 psig (482 kPa) to about 400 psig (2760 kPa), and a feed rate in the range of from about 0.5 LHSV to about 5 LHSV. In some embodiments, the pressure in the penultimate stage is in the range from about 200 psig (1380 kPa) to about 400 psig (2760 kPa). 
     The effluent from the penultimate stage is an upgraded product, in that the RON has been increased during reaction in the penultimate stage as compared to the RON of the naphtha feedstock. The penultimate stage effluent comprises hydrocarbons and hydrogen generated during reaction in the penultimate stage and at least some of the hydrogen, if any, which is added to the feed upstream of the penultimate stage. The effluent hydrocarbons may be characterized as a mixture of C4− hydrocarbons and C5+ hydrocarbons, the distinction relating to the molecular weight of the hydrocarbons in each group. In embodiments, the C5+ hydrocarbons in the effluent have a combined RON of at least 85. 
     The effluent from the penultimate stage (otherwise termed the “penultimate effluent”) comprises C5+ hydrocarbons which are separated into at least an intermediate reformate and a heavy reformate. The effluent further comprises hydrogen and C4− hydrocarbons. In some embodiments, a hydrogen-rich stream is separated from the effluent in a preliminary separation step, using, for example, a high pressure separator or other flash zone. C 4 − hydrocarbons in the effluent may also be separated in a preliminary separation, either along with the hydrogen or in a subsequent flash zone. The intermediate reformate is characterized as having a lower mid-boiling point than that of the heavy reformate. In some embodiments, the intermediate reformate boils in the range from about 70° F. (21° C.) to about 280° F. (138° C.). In some such embodiments, the intermediate reformate comprises at least 70 vol % C5-C8 hydrocarbons. In some embodiments, the intermediate reformate boils in the range from about 100° F. (38° C.) to about 280° F. (138° C.). In some such embodiments, the intermediate reformate comprises at least 70 vol % C6-C8 hydrocarbons. In some embodiments, the intermediate reformate boils in the range from about 100° F. (38° C.) to about 230° F. (110° C.). In some such embodiments, the intermediate reformate comprises at least 70 vol % C 6 -C 7  hydrocarbons. Recovery of an intermediate reformate fraction may be accompanied by the further recovery of a largely C5 light reformate fraction. The light reformate is characterized as having a lower mid-boiling point than that of the intermediate reformate. In some embodiments, the light reformate fraction boils in the range from about 70° F. (21° C.) to about 140° F. (60° C.). In some such embodiments, the light reformate fraction comprises at least 70 vol % C5 hydrocarbons. The heavy reformate that is produced during separation of the upgraded product boils in the range of about 220° F. (14° C.) and higher. In some such embodiments, the heavy reformate comprises at least 70 vol % C9+ hydrocarbons. 
     The RON of the intermediate reformate is indicative of the mild reforming conditions in the penultimate stage. As such, the intermediate reformate typically has an RON within the range of about 65 to 90. In one embodiment the intermediate reformate has a RON of 70 to 90. In a further embodiment the intermediate reformate has an RON within the range of 70 to 85. 
     The reforming catalyst used in the final stage may be any catalyst known to have catalytic reforming activity. Catalysts described above for the penultimate stage can be used in the final stage. Examples of catalysts useful in the final stage include: (1) molecular sieves such as zeolites, borosilicates, and silicoaluminophosphates; (2) amorphous Group VIII metal catalysts with an optional promoter metal selected from the group consisting of a non-platinum Group VIII metal, e.g. rhenium, germanium, tin, lead, gallium, indium, and mixtures thereof; and (3) additional catalysts comprising acid catalysts and clays. The final stage catalyst may include a single catalyst or a mixture of more than one of the above catalysts. In an embodiment the final stage catalyst comprises a zeolite and a group VIII metal. In another embodiment the final stage catalyst is a platinum rhenium catalyst supported on alumina. 
     Molecular sieves particularly useful in the practice of the present invention include zeolites, zeolite analogs, and nonzeolitic molecular sieves. By “zeolite analog” it is meant that a portion of the silicon and/or aluminum atoms in the zeolite are replaced with other tetrahedrally coordinated atoms such as germanium, boron, titanium, phosphorus, gallium, zinc, iron, or mixtures thereof. The term “nonzeolitic molecular sieve” as used herein refers to molecular sieves whose frameworks are not formed of substantially only silicon and aluminum atoms in tetrahedral coordination with oxygen atoms. Zeolites, zeolite analogs, and nonzeolitic molecular sieves can be broadly described as crystalline microporous molecular sieves that possess three-dimensional frameworks composed of tetrahedral units (TO4/2, T=Si, Al, or other tetrahedrally coordinated atom) linked through oxygen atoms. Depending on the identity of the T atoms in the zeolite, zeolite analog, or nonzeolitic molecular sieve the properties of the material are affected. For example, the presence of aluminum in a zeolite introduces a negative charge in the zeolite framework and affects the acidity and activity of the zeolite as a reforming catalyst. The Si/Al ratio in zeolites can vary from about 1 to infinity. The lower limit arises from the avoidance of neighboring tetrahedral units with negative charges (Al—O—Al). It is generally accepted that the linking of two AlO 4  tetrahedra is energetically unfavorable enough to preclude such occurrences. Negative charges in a zeolite, zeolite analog, or nonzeolitic molecular sieve framework are compensated by extraframework cations such as protons and alkali cations. The properties of zeolites, zeolite analog, or nonzeolitic molecular sieve can be altered through exchange of these extraframework cations with other positively charged species. The type of cations present in the zeolite, zeolite analog, or nonzeolitic molecular sieve framework help determine the acidity of the molecular sieve. 
     Strong acidity in the molecular sieve can be undesirable for catalytic reforming because it promotes cracking, resulting in lower selectivity. To reduce acidity, the molecular sieve preferably contains an alkali metal and/or an alkaline earth metal. The alkali or alkaline earth metals are preferably incorporated into the catalyst during or after synthesis of the molecular sieve. Preferably, at least 90% of the acid sites are neutralized by introduction of the metals, more preferably at least 95%, most preferably at least 99%. In one embodiment, the intermediate pore molecular sieve has less than 5,000 ppm alkali. Such intermediate pore silicate molecular sieves are disclosed, for example, in U.S. Pat. No. 4,061,724 and in U.S. Pat. No. 5,182,012. These patents are incorporated herein by reference, particularly with respect to the description, preparation and analysis of silicates having a specified silica to alumina molar ratio, having a specified crystallite size, having a specified crystallinity, and having a specified alkali content. 
     Prior art techniques have resulted in the formation of a great variety of synthetic zeolites. Many of the zeolites have come to be designated by letter or other convenient symbol, as illustrated by zeolite Z (U.S. Pat. No. 2,882,243); zeolite X (U.S. Pat. No. 2,882,244); zeolite Y (U.S. Pat. No. 3,130,007); zeolite ZK-5 (U.S. Pat. No. 3,247,195); zeolite ZK-4 (U.S. Pat. No. 3,314,752); zeolite ZSM-5 (U.S. Pat. No. 3,702,886); zeolite ZSM-11 (U.S. Pat. No. 3,709,979); zeolite ZSM-12 (U.S. Pat. No. 3,832,449); zeolite ZSM-20 (U.S. Pat. No. 3,972,983); zeolite ZSM-35 (U.S. Pat. No. 4,016,245); and zeolite ZSM-23 (U.S. Pat. No. 4,076,842). Zeolite Beta is described in U.S. Pat. No. 3,308,069 and RE 28,341 both to Wadlinger, and reference is made to these patents for a general description of zeolite Beta. The zeolite Beta of Wadlinger is described as having a silica-to-alumina ratio going from 10 to 100 and possibly as high as 150. Highly silicious zeolite Beta described as having silica-to-alumina ratios within the range of 20-1000 is disclosed in Valyocsik et al, U.S. Pat. No. 4,923,690. 
     In addition to cation-exchange, the catalytic properties of the zeolitic molecular sieve can be altered by isomorphous substitution of at least some of the tetrahedral atoms to make zeolite analogs or nonzeolitic molecular sieves wherein a portion or all of the silicon or aluminum atoms of the zeolite framework are replaced with, for example, germanium, titanium, boron, phosphorus, gallium, iron, or zinc. The use of these different elements in zeolite synthesis has often led to materials with novel topologies or to materials with properties that are very different from their aluminosilicate (zeolite) counterparts which have equivalent framework topologies. For example, the aluminosilicate zeolite RHO cannot currently be synthesized with a Si/Al ratio much below 3. However, the aluminogermanate and gallosilicate analogues of zeolite RHO can be made with a Ge/Al ratio and a Si/Ga ratio of 1.0 and 1.3 respectively. The cation-exchange capacities of these RHO materials are therefore very different. Aluminophosphate and gallophosphate analogues of zeolites are other example of molecular sieves based on replacement of silicon with other atoms. These materials are usually composed of strictly alternating AlO 4  (or GaO 4 ) and PO4 tetrahedral units, but they can be altered by isomorphous substitution of silicon, magnesium, beryllium, or transition metal ions. 
     Molecular sieves have uniformly sized pores (3 to 10 Å) which are determined by their unique crystal structures. The pores in zeolites and zeolite analogs are often classified as small (8 T atoms), medium (10 T atoms), large (12 T atoms), or extra-large (≧14 T atoms) according to the number of tetrahedral atoms that surround the pore apertures. Zeolite A (LTA) and zeolite Rho are examples of molecular sieves with small pores delimited by 8-membered rings, wherein the pore aperture measures about 4.1 Å, while zeolite X (FAU) and zeolite Beta are examples of zeolites with large pores delimited by 12-membered rings wherein the pore aperture measures about 7.4 Å. While the final stage catalyst can comprise large pore molecular sieves such as zeolite X, in a preferred embodiment the final stage catalyst comprises a medium pore 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 molecular sieve is in the calcined form. Shape selective medium pore molecular sieves used in some embodiments of the practice of the present invention have generally 1-, 2-, or 3-dimensional channel structures, with the pores characterized as being 9 or 10-ring structures. 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 molecular sieves include ZSM-5, ZSM-11, ZSM-22, ZSM-23, ZSM-35, ZSM-38, ZSM-48, ZSM-57, MCM-22, SSZ-20, SSZ-25, SSZ-32, SSZ-35, SSZ-37, SSZ-44, SSZ-45, SSZ-47, SSZ-57, 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. 
     The crystallite size of the molecular sieve can vary depending on preparation conditions and may be tuned depending on the desired product and reactor conditions in the final stage of the reforming process. By way of illustration only, in the medium pore zeolite ZSM-5, manipulating crystal size in order to change the selectivity of the catalyst has been described in U.S. Pat. No. 4,517,402 which is incorporated herein by reference. Additional references disclosing ZSM-5 are provided in U.S. Pat. No. 4,401,555 to Miller, hereby incorporated by reference in its entirety and in U.S. Pat. No. 5,407,558. In one embodiment, the final stage catalyst is a high silica to alumina ZSM-5 having a silica to alumina molar ratio of at least 40:1, preferably at least 200:1 and more preferably at least 500:1. In an embodiment the final stage catalyst is high silica to alumina ZSM-5 with a small crystallite size wherein the crystallite size less than 10 microns, more preferably less than 5 microns, and most preferably less than 1 micron. 
     Other molecular sieves which can be used in the final reforming stage 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 such as CZH-5 disclosed in Ser. No. 166,863 of Hickson, filed Jul. 7, 1980 and incorporated herein by reference. 
     SSZ-20 is disclosed in U.S. Pat. No. 4,483,835, and SSZ-23 is disclosed in U.S. Pat. No. 4,859,442, both of which are incorporated herein by reference. 
     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 Pat. 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. 
     Other zeolites useful in the practice of the present invention include, but are not limited to: Y zeolite, mordenite, offretite, omega, ferrierite, heulandite, SSZ-24, SSZ-25, SSZ-26, SSZ-31, SSZ-32, SSZ-33, SSZ-35, SSZ-37, SSZ-42, SSZ-44, EU-1, NU-86, NU-87, UTD-1, MCM-22, MCM-36, MCM-56, and mixtures thereof. 
     Examples of zeolite analogs useful in the process of the invention include borosilicates, where boron replaces at least a portion of the aluminum of the zeolitic form of the material. Examples of borosilicates are described in U.S. Pat. Nos. 4,268,420; 4,269,813; 4,327,236 to Klotz, the disclosures of which patents are incorporated herein. 
     Silicoaluminophosphates (SAPOs) are an example of nonzeolitic molecular sieves useful in the practice of the present invention. SAPOs comprise a molecular framework of corner-sharing [SiO4] tetrahedra, [AlO 4 ] tetrahedra and [PO 4 ] tetrahedra linked by oxygen atoms. By varying the ratio of P/Al and Si/Al the acidity of the SAPO can be modified to minimize unwanted hydrocracking and maximize advantageous isomerization reactions. Preferred molar ratios of P/Al are from about 0.75 to 1.3 and preferred molar ratios of Si/Al are from about 0.08 to 0.5. Examples of a silicoaluminophosphate useful to the present invention include SAPO-11, SAPO-31, and SAPO-41, which are also disclosed in detail in U.S. Pat. No. 5,135,638. 
     The molecular sieves optionally include an amorphous support or binder such as amorphous alumina or amorphous silica. Other examples of amorphous supports are selected from the group consisting of alumina, silica, titania, vanadia, chromia, zirconia, and mixtures thereof. Other supports such as naturally occurring or synthetic clays including, but not limited to, bentonite, kaolin, sepiolite, attapulgite, and hallyosite can be used in the process of this invention. The support may make up to 80% by weight of the catalyst. 
     The molecular sieve catalysts according to the present invention may also contain one or more Group VIII metals, e.g., nickel, ruthenium, rhodium, palladium, iridium or platinum. The preferred Group VIII metals are iridium, palladium, and platinum. Most preferred is platinum due to its high selectivity with regard to dehydrocyclization and stability under the dehydrocyclization reaction conditions. The preferred percentage of the Group VIII metals, such as platinum, in the catalyst is between 0.1 wt. % and 5 wt. %, more preferably from 0.3 wt. % to 2.5 wt. %. 
     Examples of amorphous Group VIII metal catalysts include those detailed in “penultimate zone catalyst” above. Suitable catalysts for the final stage include platinum-containing amorphous reforming catalysts which optionally contain a promoter metal selected from the group consisting of a non-platinum Group VIII metal, e.g. rhenium, germanium, tin, lead, gallium, indium, and mixtures thereof. The platinum may exist within the catalyst as a compound such as the oxide, sulfide, halide, oxyhalide, in chemical combination with one or more other ingredients of the catalytic composite, or as an elemental metal. Preferably, substantially all of the platinum exists in the catalytic composite in a reduced state. The preferred platinum component generally comprises from about 0.01 wt. % to 2 wt. % of the catalytic composite, preferably 0.05 to 1 wt. %, calculated on an elemental basis. 
     The catalyst can also include a binder material. Binders include inorganic oxide supports such as alumina, silica, silica-alumina, titania, vanadia, chromia, zirconia, clays, zeolites, non-zeolitic molecular sieves, and mixtures thereof. The binder may make up to 80% by weight of the catalyst. 
     Any conventional impregnation, mulling, ion exchange or other known methods for adding the metals to the binder may be used. The Group VIII noble metals may be introduced into the amorphous binder by, for example, ion exchange, impregnation, carbonyl decomposition, adsorption from the gaseous phase, introduction during synthesis, and adsorption of metal vapor. The preferred technique is ion exchange or impregnation by the so-called incipient witness method. Preparations of such catalysts are taught, e.g., in U.S. Pat. Nos. 3,415,737; 4,636,298; and 4,645,586, the disclosures of which are incorporated herein by references. 
     The catalyst optionally contains a halogen component. The halogen component may be either fluorine, chlorine, bromine, iodine or mixtures thereof. Chlorine is the preferred halogen component. The halogen component is generally present in a combined state with the inorganic-oxide support. The halogen component is preferably well dispersed throughout the catalyst and may comprise from more than 0.2 wt. % to about 15 wt. %, calculated on an elemental basis, of the final catalyst. 
     Conventional acid catalysts such as solid acid catalyst including, but not limited to, acidic clays and acidic zeolites may also be used in the practice of the present invention as a final stage catalyst or as a component of the final stage catalyst. The zeolite molecular sieves discussed above with protons as counterions in the anionic zeolite framework are examples of solid acid catalysts. MCM-22 is an example of a layered aluminosilicate clay which can act as a solid acid. 
     The final stage catalyst may comprise acidic or non acidic phyllosilicate clay compositions derived from the smectites such as those described in U.S. Pat. Nos. 4,248,739 and 5,414,185. Final stage catalysts may comprise any natural or synthetic clays having a lamellar structure, examples of which include, but are not limited to, bentonite, montmorillonite, berdellite, hectorite, vermiculite and the like. Layered clays can be delaminated or pillared to produce high surface area materials with a majority of their active sites or cations exposed at the crystal surface. 
     The clays may further comprise active metals such as Group VIII metals, preferably platinum or palladium. The clays mentioned above may be used alone or admixed with inorganic oxide matrix components such as silica, alumina, silica-alumina, hydrogels and other clays. The clays may be any suitable size or shape as to ensure good contact with the reactants. Examples include powder, pellets, granules, extrudates, and spheres. 
     The final stage 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 final stage catalyst comprises at least one medium pore molecular sieve. 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. In embodiments, the medium pore molecular sieve 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. 
     A type of ZSM-5 that is useful includes a silicate having a form of ZSM-5 with a molar ratio of SiO2/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. A type of ZSM-5 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. A type of ZSM-5 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 C5+ liquid product. To reduce acidity, a type of ZSM-5 that contains an alkali metal and/or an alkaline earth metal is useful for reforming the hydrocracked naphtha. The alkali or alkaline earth metals 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 metals. In one embodiment, the medium pore molecular sieve contains less than 5,000 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 silica to alumina molar ratios, having a specified crystallite size, having a specified crystallinity and having a specified alkali content. 
     Other medium pore molecular sieves that are useful for reforming include high silica to alumina mole ratio types of ZSM-11 and crystalline borosilicates. ZSM-11 is more particularly described in U.S. Pat. No. 3,709,979, the entire contents of which are incorporated herein by reference. The crystalline molecular sieve 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 molecular sieve. Borosilicate molecular sieves are described in U.S. Pat. Nos. 4,268,420; 4,269,813; 4,327,236 to Klotz, the disclosures of which patents are incorporated herein, particularly those disclosures related to borosilicate preparation. 
     The final stage 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 final stage 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 forming the final stage catalyst, the crystalline molecular sieve is preferably bound with a matrix. The matrix is not catalytically active for reforming or other hydrocarbon conversion. Satisfactory matrices include inorganic oxides, including alumina, silica, naturally occurring and conventionally processed clays, such as bentonite, kaolin, sepiolite, attapulgite and halloysite. Such materials have few, if any, acid sites and therefore have little or no cracking activity. 
     Reaction conditions in the final reforming stage are specified to effectively utilize the particular performance advantages of the catalyst used in the stage. Preferably the reaction pressure of the final reforming stage is less than the pressure in the penultimate stage. Low pressure in the final stage may lead to increased catalyst fouling. However, as the process of the invention requires at least two stages—a penultimate and a final stage—catalyst regeneration in the final stage reactor can occur as needed to maintain high catalyst activity in the final stage. For example, as naphtha reforming is taking place in the penultimate reactor, catalyst regeneration can take place in the final reactor. While the final stage catalyst is being regenerated, the severity of the penultimate stage can be temporarily increased to meet RON targets for the total blended reformate which would otherwise be achieved with both the penultimate and final stages in operation. Operating the final reforming stage at a lower relative pressure than the penultimate stage minimizes the formation of light (C 4 −) products while increasing the yield of high octane naphtha and overall liquid yield in the two stage process of the invention. Because the penultimate stage is operated at relatively mild conditions, catalyst life in that stage is lengthened while giving good yields of desired high octane products. 
     The naphtha feed to the final stage is the intermediate reformate which is separated from the effluent of the penultimate stage. In the process, the intermediate reformate contacts the catalyst in the final stage at reforming reaction conditions, which reaction conditions include a temperature in the range from about 800° F. to about 1100° F. (427° C. to 593° C.), a pressure in the range from about 40 psig to about 400 psig (276 kPa to 2760 kPa) to and a feed rate in the range of from about 0.5 LHSV to about 5 LHSV. In some embodiments, the pressure in the final reforming stage is less than 100 psig (690 kPa). Preferably the pressure in the final reforming stage is from about 40 psig (276 kPa) to about 200 psig (1380 kPa), and more preferably from about 40 psig (276 kPa) to about 100 psig (690 kPa). Hydrogen is preferably added as an additional feed to the final reforming stage, but it is not required. In embodiments, hydrogen added with the feed is recovered from the process and is recycled to the final stage. 
     Depending on the particular process, the effluent from the final reforming stage may contain light (i.e. C 4 − products and/or hydrogen) products which may be removed from the reformate prior to further processing or blending to make a fuel product. The C 5 + reformate, herein referred to as the final reformate, which is produced in the final reforming stage has an increased RON relative to that of the intermediate reformate which is the feed to the final reforming stage. Preferably, at least 75 vol % of the final reformate boils in the C 5 + range. The final reformate may be used as a fuel or a fuel component by blending with other hydrocarbons. In embodiments, the RON of the final reformate is 80 or higher, or 90 or higher, or 95 or higher. 
     The reformate is useful as a fuel or as a blend stock for a fuel. In some embodiments, at least a portion of the reformate from the final reforming stage is blended with at least a portion of the heavy reformate, which is recovered from the penultimate reforming stage; the blend may be used as a fuel or as a blend stock for a fuel. 
     Depending on the particular process, the effluent (otherwise termed the “final effluent”) from the final reforming stage may contain light (i.e. C 4 − products and/or hydrogen) products which may be removed from the reformate in a final separation step prior to further processing for blending or use as a fuel. A hydrogen-rich stream may be separated from the effluent prior to the separation step, using, for example, a high pressure separator or other flash zone. C 4 − hydrocarbons in the effluent may also be separated in a preliminary flash zone, either along with the hydrogen or in a subsequent flash zone. The reformate which is produced in the final reforming stage has an increased RON relative to that of the intermediate reformate which is the feed to the final reforming stage. In embodiments, the RON of the final reformate is greater than 90 or at least 95, or at least 98. In some embodiments, the final reformate boils in the range from about 70° F. (21° C.) to about 280° F. (138° C.). In some such embodiments, the final reformate comprises at least 70 vol % C 5 -C 8  hydrocarbons. In some embodiments, the final reformate boils in the range from about 100° F. (38° C.) to about 280° F. (138° C.). In some such embodiments, the final reformate comprises at least 70 vol % C 6 -C 8  hydrocarbons. In some embodiments, the final reformate boils in the range from about 100° F. (38° C.) to about 230° F. (110° C.). In some such embodiments, the final reformate comprises at least 70 vol % C 6 -C 7  hydrocarbons. In addition to the final reformate stream, a final light stream may also be recovered from the final effluent. In such cases, the final light stream boils in the range of about 70° (21° C.) to about 140° F. (60° C.). In some such embodiments, the final light stream comprises at least 70 vol % C 5  hydrocarbons. 
     The reformate is useful as a fuel or as a blend stock for a fuel. In some embodiments, at least a portion of the reformate from the final reforming stage is blended with at least a portion of the heavy reformate, which is recovered from the penultimate reforming stage; the blend may be used as a fuel or as a blend stock for a fuel. 
     The gradual accumulation of coke and other deactivating carbonaceous deposits on the catalyst will eventually reduce the activity and/or selectivity of the catalyst. Typically, catalyst regeneration becomes desirable when from about 0.5 to about 5.0 wt. % or more of carbonaceous deposits are laid down upon the catalyst. At this point, it is typically necessary to take the hydrocarbon feedstream out of contact with the catalyst and purge the hydrocarbon conversion zone with a suitable gas stream. Catalyst regeneration can then performed either by unloading the catalyst from the conversion zone and regenerating in a separate vessel or facility or performing regeneration in-situ. Alternatively, the catalyst may be continuously withdrawn from the reactor for regeneration in a separate vessel, to be returned to the reactor as in a Continuous Catalytic Reformer. Preferably, the catalyst is regenerated in situ. 
     Various regeneration procedures are known in the art. Generally, the temperature of the final stage catalyst is gradually lowered to below the temperature of regeneration. The final stage reformer is taken offline, for example by the use of a valve. The penultimate reformer continues to operate at reforming reaction conditions, and to produce both a hydrocarbon product of the desired RON as well as hydrogen while the final stage is bypassed. However, reforming severity in the penultimate stage is increased so that the intermediate reformate has an RON of at least 90 or at least 95 or even at least 98. In embodiments, the reforming temperature in the penultimate stage is increased by at least 5° F. (2.8° C.), or by at least 10° F. (5.6° C.) or even by at least 15° F. (8.3° C.) while regenerating the final stage catalyst. In embodiments, the reforming pressure in the penultimate stage is decreased by at least 10 psig (69 kPa), or at least 20 psig (138 kPa) or even at least 30 psig (207 kPa) while regenerating the final stage catalyst. During regeneration, the intermediate reformate bypasses the final stage, and to be used, for example, as a fuel or fuel blendstock. Likewise, hydrogen which is recovered from the penultimate stage bypasses the final stage, to be used, for example, in other refinery processes. 
     The final stage catalyst is then regenerated by depressurizing the final stage reactor, purging the final stage reactor with nitrogen, and then introducing a low level of oxygen, generally between 0.1 to 2%, and preferably between 0.5 to 1%. The temperature of the final stage is raised to initiate a carbon burn to remove coke deposits. During catalyst regeneration, the coked catalyst is contacted with a predetermined amount of molecular oxygen. A desired portion of the coke is burned off the catalyst, restoring catalyst activity. Flue gas formed by combustion of coke in the catalyst regenerator may be treated for removal of particulates and conversion of carbon monoxide, after which it is normally discharged into the atmosphere. After the carbon burn the final stage reactor is purged with nitrogen, the temperature is reduced to below the start of run temperature, and the final stage is put back on-line, i.e. the effluent of the penultimate stage now flows through the final stage. The temperature of the final stage is gradually raised to run temperature while the temperature of the penultimate stage is gradually lowered so as to maintain the desired RON of the final product coming off of the final stage reactor. In accordance with the invention, the final stage catalyst does not undergo chloriding or other halogen treatment during regeneration. Preferably, the final stage catalyst comprises a medium pore zeolite and at least one noble metal. In an embodiment the final stage catalyst comprises ZSM-5, ZSM-11, and mixtures thereof. It is an object of the invention to minimize the amount of time the multi-stage reforming process is run without the final stage due to catalyst regeneration. It has been found that avoiding a chloriding step during regeneration of the final stage catalyst minimizes the time the multi stage reforming process is run without the final stage reactor during final stage catalyst regeneration. 
     The regeneration is performed in a halogen-free environment. By halogen-free, it is meant that chlorine, fluorine, bromine, or iodine or their compounds including for example, hydrogen chloride, carbon tetrachloride, ethylene dichloride, propylene dichloride, are not added at anytime during the catalyst regeneration process. Halogen free methods to regenerate reforming catalysts are known in the art. For example, U.S. Pat. No. 5,155,075 discloses a process for regenerating a medium pore zeolite catalyst and is herein incorporated by reference in its entirety. Regeneration of coked catalyst may be effected by any of several procedures. The catalyst may be removed from the reactor of the regeneration treatment to remove carbonaceous deposits or the catalyst may be regenerated in-situ in the reactor. For example, the final stage reformer unit may be operatively connected with a source of oxidizing gas at elevated temperature. The catalyst is regenerated by burning off coke, producing CO 2  and H 2 O. Reactor effluent can be cooled in a feed/effluent exchanger and/or in an air cooler. Final cooling can occur in a trim cooler. The effluent then enters a separator. Gas is released from the separator to maintain system pressure through pressure-response venting. By the time it reaches the separator, water vapor formed during the burn has condensed and is separated from the recycle gas. Because water vapor at high temperatures may damage the catalyst, a relatively low separator temperature is generally maintained in order to minimize the H 2 O partial pressure in the recycle gas returning to the reactor. In an embodiment the separator temperature can be between about 20°-90° C., preferably between about 30°-70° C., and most preferably between about 40°-50° C. at 800 kPa pressure. 
     In a typical regeneration process, the final stage reactor is brought up to pressure with an inert gas, preferably nitrogen. The reactor inlet temperature is gradually decreased to a temperature of from 140° C. to no more than about 420° C. Oxygen is then introduced into the reactor. The oxygen is typically derived from air and an inert gas serves as a diluent, such that oxygen concentration is from about 21 mole % oxygen to a lower limit of about 0.1 mole % oxygen. Higher levels of oxygen may be used in methods where oxygen is supplied in a more pure form such as from cylinders or other containing means. Typical inert gases useful in the carbon burn step may include nitrogen, helium, carbon dioxide, and like gases or any mixture thereof; nitrogen being preferred. The regeneration gases should be substantially sulfur-free as they enter the reactor, and preferably contain less than 100 part per million by volume water. Because the oxygen content determines the rate of burn, it is desirable to keep the oxygen content low so as not to damage the catalyst by overheating and causing metal agglomeration, while still conducting the carbon burn step in a manner that is both quick and effective. In an embodiment, the oxygen level in the inlet to the regeneration vessel is between 0.2 to 4.0 mole % In another embodiment, air or oxygen is injected at a controlled rate to give a maximum oxygen concentration of between about 0.1% and up to about 2%, preferably between about 0.25% and up to about 1%, and most preferably between about 0.5% and up to about 0.7% at the reactor inlet. The temperature is then increased to facilitate coke removal through a “burn.” As burning begins, a temperature rise of about 85° C. is generally observed. As the burn dies off the inlet temperature is raised to and maintain at about 455° C. The pressure of the reactor can vary, but generally, a pressure sufficient to maintain the flow of the gaseous oxygen containing mixture through the catalyst zone is selected. Generally, pressures can range from between about 1.0 to 50.0 atmospheres and preferably from about 2 to about 15 atmospheres. A gas hourly space velocity of about 100 to about 10,000 per hour, with a preferred value of about 500 to about 5,000 per hour is generally used, although this can vary depending on the catalyst and amount of coking. 
     When the main burn is completed, as evidenced by no temperature rise across the catalyst bed, the temperature is raised over 500° C. and the O 2  content can be raised. In an embodiment the O 2  content is raised to at least 3%, preferably at least 4%, and more preferably at least 5%. This condition is held at least one hour (or until all evidence of burning has ceased). Generally, the regeneration process continues for a sufficient period of time such that the aromatization activity is restored to within 20° F. (11° C.) of the aromatization activity the catalyst possessed at the start of the previous run cycle. By the term “aromatization activity” we mean the extrapolated start of run temperature where the run conditions and the feed as well as the aromatics yield are substantially the same as in the previous run cycle. The platinum on the catalyst remains sufficiently dispersed on the support to allow for an activity change of not more than 10° C. upon termination of the regeneration procedure, and return of the catalyst to hydrocarbon conversion service. Thus, the catalyst aromatization activity is based upon the temperature needed to achieve a desired constant aromatics production. Regeneration by the process of the present invention results in a catalyst which has an aromatization activity, as defined above, which is within 10° C. of the temperature needed in the previous run to achieve the same constant aromatics production. 
     When the regeneration is complete, the temperature is reduced, generally to less than 500° C., and the system purged free of O 2  with an inert gas, preferably nitrogen to displace the oxygen and any water therefrom. The exit gas is easily monitored to determine when the catalyst zone is substantially free of oxygen and water. After the carbon burn-off and purge, the catalyst is activated by treatment with hydrogen. In the initial reduction step, the catalyst is contacted with a hydrogen containing stream at a temperature of from about 150° C. to about 380° C. for a period of at least of about 0.1 to about 10.0 hours. Preferred conditions for the reduction step are from about 200° C. to about 320° C. for a period from about 0.1 to about 2.0 hours. The pressure and gas rates utilized in the reduction step are preferably very similar to those above described in the carbon burn step. Following the initial reduction, the catalyst may be further reduced and dried by circulating a mixture of inert gas and hydrogen while raising the temperature to between 480° and 540° C. In the reduction step, metallic components are returned to their elemental state and the resulting regenerated catalyst possesses activity, and selectivity characteristics quite similar to those occurring in a fresh catalyst. 
     After completing the reduction step, the temperature is lowered to 450° C. or less. The reforming process in which the catalyst is employed may be resumed by charging the hydrocarbon feedstream to the catalyst zone and adjusting the reaction conditions to achieve the desired conversion and product yields. The reactor is brought up to reaction pressure and the temperature decreased to below the reaction temperature during the multi-stage reforming process. The final stage reactor is put back online, i.e. at least a portion of the effluent from the penultimate reactor flows through the final stage reactor to produce a hydrocarbon product of the desired RON. 
     In order to avoid a metal re-dispersion step, the ultimate temperature in the carbon burn regeneration procedure is generally less than 415° C., and preferably between 315° C. to 400° C. This procedure allows the catalyst to be restored to an activity very close to that of the fresh catalyst, without noble metal agglomeration which would require a metal re-dispersion step. It is further preferred the carbon burn be initiated at a temperature of less than about 260° C. and further that the recycle gas be dried to achieve a water concentration in the recycle gas of less than 100 ppm water, prior to the recycle gas entering the reforming reactor train. 
     Reference is now made to an embodiment of the invention illustrated in  FIG. 1 . A naphtha boiling range fraction  5  which boils within the range of 50° F. (10° C.) to 550° F. (288° C.) passes into the reaction stage  10  at a feed rate in the range of about 0.5 hr −1  to about 5 hr −1  LHSV. Reaction conditions in the reforming stage  10  include a temperature in the range from about 800° F. (427° C.) to about 1100° F. (593° C.) and a total pressure in the range of greater than 70 psig (483 kPa) to about 400 psig (2760 kPa). 
     The effluent  11  from the penultimate stage is an upgraded product, in that the RON has been increased during reaction in the penultimate stage  10 . The penultimate stage effluent  11  comprises hydrocarbons and hydrogen generated during reaction in the penultimate stage and at least some of the hydrogen (if any) added to the feed upstream of the penultimate stage. In the embodiment illustrated in  FIG. 1 , the effluent is separated in separation zone  20  into a hydrogen-rich stream  21 , a C 4 − stream  22 , an intermediate reformate  26  and a heavy reformate  26 . In embodiments, this separation occurs in a single separation zone. In other embodiments, this separation is done in sequential zones, with the hydrogen, and optionally the C 4 − stream, separated in one or more preliminary separation zones prior to the separation of the intermediate reformate  25  and the heavy reformate  26 . 
     In the embodiment illustrated in  FIG. 1 , the intermediate reformate  25  comprises a substantial amount of the C 5 -C 8  hydrocarbons contained in the effluent, with smaller quantities of C 4  and C 9  hydrocarbons. At least a portion of intermediate reformate  25  is passed to final reforming stage  30 . Heavy reformate  26  contains a substantial amount of the C 9 + hydrocarbons contained in the effluent  11 , and has an RON of greater than 98, preferably greater than 100. 
     Intermediate reformate  25  is passed to final reforming stage  30  for contact with a catalyst comprising platinum and at least one medium pore molecular sieve, at reaction conditions which include a temperature in the range from about 800° F. (427° C.) to about 1100° F. (593° C.) and a pressure in the range from about 50 psig (345 kPa) to about 250 psig (1725 kPa). 
     Effluent  31  from the final reforming stage is separated in separation zone  40 , yielding at least a hydrogen-rich stream  41 , a C 4 − stream  42 , and a final reformate stream  45 . In embodiments, the final reformate stream boils in the C 5 + boiling range. As described above, this separation may take place in one, or multiple, separation zones, depending on the specific requirements of a particular process. In an embodiment, the final reformate stream  45  may be further combined with the heavy reformate  26  before further processing or use as a fuel or fuel blend stock. Hydrogen-rich stream  41  is combined with hydrogen-rich stream  21  before using in other refinery processes, and C 4 − stream  42  is combined with C 4 − stream  22 . 
     Reference is now made to an embodiment of the invention illustrated in  FIG. 2 . A naphtha boiling range fraction  5  which boils within the range of 50° F. (10° C.) to 550° F. (288° C.) passes into the reaction stage  10  at a feed rate in the range of about 0.5 hr −1  to about 5 hr −1  LHSV. Reaction conditions in the reforming stage  10  include a temperature in the range from about 800° F. (427°/c) to about 1100° F. (593° C.) and a total pressure in the range of greater than 70 psig (483 kPa) to about 400 psig (2760 kPa). 
     The effluent  11  from the penultimate stage is an upgraded product, in that the RON has been increased during reaction in the penultimate stage  10 . The penultimate stage effluent  11  comprises hydrocarbons and hydrogen generated during reaction in the penultimate stage and at least some of the hydrogen (if any) added to the feed upstream of the penultimate stage. In the embodiment illustrated in  FIG. 2 , the effluent is separated in separation zone  20  into a hydrogen-rich stream  21 , a C 4 − stream  22 , a light reformate  23 , an intermediate reformate  24  and a heavy reformate  26 . In embodiments, this separation occurs in a single separation zone. In other embodiments, this separation is done in sequential zones, with the hydrogen, and optionally the C 4 − stream, separated in one or more preliminary separation zones prior to the separation of the light reformate  23 , the intermediate reformate  24  and the heavy reformate  26 . 
     In the embodiment illustrated in  FIG. 2 , the light reformate  23  comprises a substantial amount of the C 5  hydrocarbons contained in the effluent, with smaller quantities of C 4  and C 6  hydrocarbons. The intermediate stream comprises a substantial portion of the C 6 -C 8  hydrocarbons contained in the effluent; the heavy reformate  26  contains a substantial amount of the C 9 + hydrocarbons contained in the effluent  11 . Intermediate reformate  24  is passed to final reforming stage  30  at a feed rate in the range of from about 0.5 hr −1  to about 5 hr −1  LHSV, for contact with a catalyst comprising platinum and at least one medium pore molecular sieve, at reaction conditions which include a temperature in the range from about 800° F. (427° C.) to about 1100° F. (593° C.) and a pressure in the range from about 50 psig (345 kPa) to about 250 psig (1725 kPa). During regeneration of the final stage catalyst, the severity of the penultimate stage can be increased to increase the RON of the intermediate reformate. The RON of the intermediate under increased severity of the penultimate stage (i.e. increased temperature and/or pressure) would meet the target RON of the final reformate stream. 
     Effluent  31  from the final reforming stage is separated in separation zone  40 , yielding at least a hydrogen-rich stream  41 , a C 4 − stream  42 , a final C 5  stream  43  and a final reformate stream  44 . In embodiments, the final reformate stream boils in the C 6 + boiling range. As described above, this separation may take place in one, or multiple, separation zones, depending on the specific requirements of a particular process. As shown in the embodiment illustrated in  FIG. 2 , the final reformate stream  44  is further combined with the heavy reformate  26  before further processing or use as a fuel or fuel blend stock, hydrogen-rich stream  41  is combined with hydrogen-rich stream  21  before using in other refinery processes, C 4 − stream  42  is combined with C 4 − stream  22  and final C 5  stream  43  is combined with C 5  stream  23 . 
     The following examples are presented to exemplify embodiments of the invention but are not intended to limit the invention to the specific embodiments set forth. Unless indicated to the contrary, all parts and percentages are by weight. All numerical values are approximate. When numerical ranges are given, it should be understood that embodiments outside the stated ranges may still fall within the scope of the invention. Specific details described in each example should not be construed as necessary features of the invention. 
     EXAMPLES 
     In the following examples, the RON values are calculated values, based on RON blending correlations applied to a composition analysis using gas chromatography. The method was calibrated to achieve a difference between measured RON values, determined by ASTM D2699, and calculated RON values of within ±0.8. 
     Example 1 
     A naphtha feed, with an API of 54.8 (0.76 g/cm 3 ), RON of 53.3 and an ASTM D-2887 simulated distillation shown in Table 1 was reformed in a penultimate stage using a commercial reforming catalyst comprising platinum with a rhenium promoter on an alumina support. The catalyst contained about 0.3 wt. % platinum, and about 0.6 wt. % rhenium on an extruded alumina support. Reaction conditions included a temperature of 840° F., a pressure of 200 psig, a 5:1 molar ratio of hydrogen to hydrocarbon and a feed rate of 1.43 hr −1  LHSV. The C 5 + liquid yield was 92.7 wt %. The hydrogen production was 975 standard cubic feet per barrel feed (0.16 m 3  H 2 /liter oil). 
     This C 5 + liquid product (penultimate effluent) collected from the penultimate stage had an API of 46.6 (0.79 g/cm 3 ), an RON of 89 and an ASTM D-2887 simulated distillation as given in Table 2. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Simulated Distillation of naphtha feed 
               
            
           
           
               
               
               
            
               
                   
                   
                 Temperature, 
               
               
                   
                 Vol % 
                 ° F. (° C.) 
               
               
                   
                   
               
               
                   
                 IBP 
                 182 (83)  
               
               
                   
                 10 
                 199 (93)  
               
               
                   
                 30 
                 227 (108) 
               
               
                   
                 50 
                 258 (126) 
               
               
                   
                 70 
                 291 (144) 
               
               
                   
                 90 
                 336 (169) 
               
               
                   
                 EP 
                 386 (197) 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Simulated Distillation of the C5+ liquid product 
               
               
                 from the penultimate stage (penultimate effluent) 
               
            
           
           
               
               
               
            
               
                   
                   
                 Temperature, 
               
               
                   
                 Vol % 
                 ° F. (° C.) 
               
               
                   
                   
               
               
                   
                 IBP 
                 165 (74)  
               
               
                   
                 10 
                 189 (87)  
               
               
                   
                 30 
                 234 (112) 
               
               
                   
                 50 
                 257 (125) 
               
               
                   
                 70 
                 289 (143) 
               
               
                   
                 90 
                 336 (169) 
               
               
                   
                 EP 
                 411 (211) 
               
               
                   
                   
               
            
           
         
       
     
     Example 2 
     The C5+ liquid product from Example 1 was distilled into an intermediate reformate and a heavy reformate. The intermediate reformate was found to represent 80 vol % of the C5+ liquid product from Example 1. The intermediate reformate, had an API of 55.7 (0.76 g/cm3), an RON of 85 and an ASTM D-2887 simulated distillation as shown in Table 3, and was used as feed in a final reforming stage in Examples 3-6. The heavy reformate was found to represent 20 vol. % of the C5+ liquid product from Example 1. The heavy reformate had an API of 28.9 (0.88 g/cm3) and an RON of 105, and is further described in Table 4. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Simulated Distillation of intermediate reformate 
               
            
           
           
               
               
               
            
               
                   
                   
                 Temperature, 
               
               
                   
                 Vol % 
                 ° F. (° C.) 
               
               
                   
                   
               
               
                   
                 IBP 
                 168 (76)  
               
               
                   
                 10 
                 190 (88)  
               
               
                   
                 30 
                 235 (113) 
               
               
                   
                 50 
                 240 (116) 
               
               
                   
                 70 
                 284 (140) 
               
               
                   
                 90 
                 296 (147) 
               
               
                   
                 EP 
                 336 (169) 
               
               
                   
                   
               
            
           
         
       
     
     Example 3 
     The intermediate reformate produced in Example 2 was used as feed to the final reforming stage which used a ZSM-5 zeolite based catalyst composited with 35% alumina binder material. The ZSM-5 had a SiO 2 /Al 2 O 3  molar ratio of ˜2000 and was ion exchanged to the ammonium form before incorporating in a 65% zeolite/35% alumina extrudate. The extrudate was impregnated with 0.8% Pt, 0.3% Na, and 0.3% Mg by an incipient wetness procedure to make the final catalyst. The reaction conditions and experimental results are listed in Tables 4 and 5. 
     Example 4 
     A product which was produced in the final stage reforming of the intermediate reformate in Example 3 was blended with the heavy reformate (Example 2) which was not subjected to the final stage reforming. The total RON of C 5 +, total C 5 + yield and total H 2  production of the blended final product are given in Table 4 based on using the total C 5 + penultimate effluent as feed (which is distilled into intermediate reformate and heavy reformate in Example 2). The results are compared to those obtained from Comparative Example 1 where the total C 5 + product was produced from the total C 5 + penultimate effluent as feed, without distillation into an intermediate and heavy reformate. 
     Example 5 
     The intermediate reformate produced in Example 2 was contacted with the platinum/rhenium on alumina based catalyst described in Example 1 in a final reforming stage. The reaction conditions and experimental results are listed in Table 5 and compared with Example 3. 
     Example 6 
     The intermediate reformate produced in Example 2 is contacted with the platinum/rhenium on alumina based catalyst described in Example 1 in a final reforming stage wherein the final reforming stage pressure is less than 200 psig (1380 kPa). The final reforming stage is run at the same temperatures, LHSV, and hydrogen to hydrocarbon ratio as in Example 5. The C 5 + liquid yield for Example 6 is higher than the C 5 + liquid yield for Example 5 at the same or similar RON. The higher C 5 + liquid yield of Example 6 as compared to Example 5 illustrates the benefits of running the final stage at a lower pressure than the penultimate stage with a platinum/rhenium on alumina catalyst. 
     Comparative Example 1 
     The total C 5 + product produced in Example 1, without distillation into an intermediate and heavy reformate, was contacted with the ZSM-5 based catalyst of Example 3 in a final reforming stage at 930° F. (499° C.), 80 psig (550 kPa), 2:1 molar ratio of hydrogen to hydrocarbon and 1.5 hr −1  LHSV feed rate. The C 5 + liquid yield was 89.9 wt. % and RON of the C 5 + liquid product from the final reforming stage was 97.4. The hydrogen production was 190 standard cubic feet per barrel feed. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Comparison of results from Example 4 and Comparative Example 1 
               
            
           
           
               
               
               
            
               
                   
                 Example 4 
                 Comparative 
               
            
           
           
               
               
               
               
            
               
                   
                 Example 3 
                 Example 2 
                 Example 1 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                 Feedstock 
                 Intermediate 
                 Heavy 
                 Total C 5 + 
               
               
                   
                 reformate 
                 reformate 
                 penultimate 
               
               
                   
                 (Example 2, 
                 (Example 2, 
                 effluent 
               
               
                   
                 Table 3) 
                 Table 3) 
                 (Example 1, 
               
               
                   
                   
                   
                 Table 2) 
               
               
                 Catalyst 
                 Pt/Na/Mg/ZSM-5 
                 Not subjected 
                 Pt/Na/Mg/ZSM-5 
               
               
                   
                 with alumina 
                 to the final 
                 with alumina 
               
               
                   
                 binder 
                 stage 
                 binder 
               
               
                   
                   
                 reforming 
               
               
                 Temperature, ° F. 
                 900       
                 — 
                 930       
               
               
                 Pressure, psig 
                 80       
                 — 
                 80       
               
               
                 LHSV, hr −1   
                 1.5   
                 — 
                 1.5   
               
               
                 Molar 
                 2:1 
                 — 
                 2:1 
               
               
                 H 2 /hydrocarbon 
               
               
                 Ratio 
               
               
                 RON of C 5 + 
                 97.0  (1)   
                 105  (2)   
                 97.4  (3)   
               
               
                 C 5 + Yield, wt % 
                 92.7  (1)   
                 100  (2)   
                 89.9  (3)   
               
               
                 H 2  Yield, scf/bbl 
                 300  (1)    
                 — 
                 190  (3)    
               
               
                 feed 
               
               
                 Total RON of C 5 + 
                 98.7  (4)   
                   97.4  (3)   
               
               
                 Total C 5 + Yield, wt % 
                 94.2  (4)   
                   89.9  (3)   
               
               
                 Total H 2  Yield, 
                 240  (4)    
                 190  (3)   
               
               
                 scf/bbl feed 
               
               
                   
               
               
                 Notes to Table 4: 
               
               
                   (1)  For Example 3: RON of C 5 +, C 5 + yield and H 2  production of the product are given based on the intermediate reformate as feed. 
               
               
                   (2)  For Example 2: RON of C 5 + and C 5 + yield are given based on the heavy reformate which is not subjected to the final stage reforming. 
               
               
                   (3)  For Comparative Example 1: RON of C 5 +, C 5 + yield and H 2  production of the product are given based on the total C 5 + penultimate effluent as feed. 
               
               
                   (4)  For Example 4: Total RON of C 5 +, total C 5 + yield and total H 2  production are given based on the total C 5 + penultimate effluent as feed (which is distilled into intermediate reformate and heavy reformate in Example 2). The final product of Example 4 consists of a blend of (i) the product from the final stage reforming of the intermediate reformate and (ii) the heavy reformate which is not subjected to the final stage reforming. 
               
            
           
         
       
     
     Table 4 demonstrates the benefits of the present invention when using the intermediate reformate as the feedstock at lower reaction temperature (900° F. vs. 930° F.) (482° C. vs/499° C.) by showing improved hydrogen yield, higher C 5 + liquid yield and higher RON versus the full boiling range C 5 + feedstock. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Comparison of results from Example 3 and Example 5 
               
            
           
           
               
               
               
            
               
                   
                 Example 3 
                 Example 5 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                 Catalyst 
                 Pt/Na/Mg/ZSM-5 
                 Pt/Re with alumina binder 
               
               
                   
                 with alumina binder 
               
            
           
           
               
               
               
               
               
            
               
                 Feedstock 
                 Intermediate 
                 Intermediate 
                 Intermediate 
                 Intermediate 
               
               
                   
                 reformate 
                 reformate 
                 reformate 
                 reformate 
               
               
                   
                 (Example 2) 
                 (Example 2) 
                 (Example 2) 
                 (Example 2) 
               
               
                 Temperature, ° F. (° C.) 
                 900 (482) 
                 950 (510) 
                 910 (488)  
                 940 (504) 
               
               
                 Pressure, psig (kPa) 
                  80 (552) 
                  80 (552) 
                 200 (1380) 
                 (1380) 
               
               
                 LHSV, hr −1   
                 1.5 
                 1.5 
                 1.5 
                 1.5 
               
               
                 Molar H 2 /hydrocarbon 
                 2:1 
                 2:1 
                 5:1 
                 5:1 
               
               
                 Ratio 
               
               
                 RON of C 5 + 
                 97.0 
                 100.6 
                 96.9 
                 101.8 
               
               
                 C 5 + Yield, wt % 
                 92.7 
                 88.4 
                 88.9 
                 85.2 
               
               
                 H 2  Yield, scf/bbl feed 
                 300 
                 430 
                 130 
                 175 
               
               
                   
               
            
           
         
       
     
     Table 5 demonstrates a preferred embodiment of the present invention, wherein the pressure of the final stage reactor is lower than the pressure in the penultimate stage Improvements at the lower pressure with the ZSM-5 based catalyst in terms of C5+ yield and hydrogen production at similar C5+RON are seen versus the Pt/Re catalyst at higher pressure.