MULTI-STAGE REFORMING PROCESS

Abstract: A multi-stage reforming process is described in which a conventional reforming catalyst (12) is used upstream of an intermediate pore size crystalline silicate containing a Group VIII metal (14). The conventional catalyst is operated at typical reforming conditions and the crystalline silicate is operated at lower pressures. At least a portion of the hydrogen and substantially all of the hydrogen sulfide present is removed (18) from the penultimate stage reformate before it is used in the feed to the final stage.

Description: MULTI-STAGE REFORMING PROCESS Background Of The Invention The present invention is a multi-stage reforming process for upgrading a hydrocarbon feed and increasing its octane rating. More specifically, two catalysts are used in sequential operation to reform a naphtha hydrocarbon feed. Catalytic reforming is well known in the petroleum industry and refers to the treatment of naphtha fractions to improve their octane rating. There are at least three important hydrocarbon . reactions that occur during reforming operation. These include: 1) dehydrogenation of cyclohexanes to aromatics; 2) dehydroisomerization of alkylcyclopentanes to aromatics; and 3) dehydrocyclization of acyclic hydrocarbons to aromatics. A number of other reactions also occur, including the following: alkylbenzene dealkylation, paraffin isomerization, aromatic disproportionation and hydrocracking reactions which produce light gaseous hydrocarbons, e.g., methane, ethane, propane and butane. Hydrocracking reactions are to be particularly minimized during reforming as they decrease both the product yield in the gasoline boiling range and the product yield of hydrogen. Naphthene dehydrogenation to aromatics is the most thermodynamically favorable aromatization reaction at reforming conditions. It yields higher ratios of aromatic product/nonaromatic reactant than the dehydrocyclization or dehydroisomerization reactions at a given reaction temperature and pressure. Moreover, it is also the fastest of the three aromatization reactions. Consequently, the selectivity for naphthene dehydrogenation is generally higher than that for the other two aromatization reactions . Benzene, alkylbenzenes, and hydrogen are important products of catalytic reforming. The aromatic hydrocarbons are valuable because they increase the gasoline octane number and because they can be used in the synthesis of other chemicals. The hydrogen is useful elsewhere in the refinery, for such tasks as: processing of high boiling feedstreams; removing heteroatoms; and other reforming operations . The demand for high octane gasoline has stimulated extensive research for developing improved reforming catalysts and catalytic reforming processes. Successful reforming catalysts must be selective for high octane aromatic hydrocarbons without producing low yields or light gaseous hydrocarbons and sufficiently active to produce a certain quality product without an excessively high reaction temperature. Additionally, the catalysts should: be stable to retain their activity and selectivity characteristics during prolonged periods of operation; permit frequent regeneration without loss of performance; and be tolerant to common catalyst poisons, such as sulfur. Catalysts comprising platinum supported on alumina are well known and widely used for naphtha reforming. However, other reforming catalysts typically contain a catalytic metal such as platinum, disposed on silica, silica/alumina, boria/silica, large pore zeolites, and a plethora of other natural and manmade crystalline silicates. One example of a crystalline silicate useful in reforming hydrocarbons is ZSM-5, particularly ZSM-5 which has a high silica:alumina (Si0 2 :A10 3 ) ratio and is sometimes referred to as silicalite. Examples of its methods of manufacture are shown in: Dwyer, et al., S UB STIT UTESHEE U.S. Patents Nos . 3,941,871, issued March 2, 1976 and 4,441,991, issued April 10, 1984; and Derouane, et al., EPO Application No. 186,479, published February 7, 1986, al-l of which are incorporated by reference in their entirety. Currently, conventional catalytic reforming processes must operate at higher severity to produce higher octane products because lead can no longer be added to boost octane in gasolines. High severity operations produce high octane gasolines, but at the expense of liquid yield and reformer run length. Thus, it is advantageous to develop a process which can produce a high octane gasoline while retaining a high liquid yield and run length. In accordance with the present invention a combination process is set forth which offers the flexibility needed to achieve this result. The art contains combination reforming processes in which a hydrocarbon feed is converted with one or more different types of conversion catalysts. For example, U.S. Patents Nos. 4,440,628, 4,436,612 and 4,425,222 show two-stage reforming with platinum and rhenium on chlorided alumina catalysts . U.S. Patents Nos. 4,636,298 and 4,645,586 disclose two-stage processes using a conventional bifunctional catalyst (e.g., platinum/rhenium on alumina) ahead of a monofunctional catalyst (e.g., platinum on L zeolite). U.S. Patent No. 4,190,519 shows a two- stage system for aromatics production using two different catalysts. They are platinum and rhenium on chlorided alumina and ZSM-5 in the H-form without a Group VIII metal. U.S. Patent No. 4,443,326 discloses reforming using a large pore zeolite having a Group VIII metal and then cracking low octane components in the reformate using an intermediate pore zeolite without Group VIII metal. U.S. Patent No. 4,370,219 discloses cracking low octane components to C 3 -C 4 olefins, followed by olefin oligomerization using ZSM-5. U.S. Patent No. 4,292,167 discloses reforming using a conventional noble metal reforming catalyst followed by shape selective cracking of reformate using ZSM-5 and then reforming again. U.S. Patent No. 4,211,886 discloses a two-stage process wherein the first stage reforms a feed to produce aromatics and the final stage isomerizes and dealkylates the reformate using ZSM-5. U.S. Patent No. 4,162,212 discloses a parallel process for reforming and isomerization using ZSM-5. Australian Patent Application 65624/86 discloses a two-stage system for upgrading a hydrocarbon feedstock. A conventional reforming catalyst. is used in sequence with a ZSM-5 type zeolite containing a metal from Groups IIB or IIIA (such as gallium or beryllium) . The ZSM-5 type catalyst is acidic and makes aromatics by forming C 3 +C 4 olefins and then combining them. However, even with the combination processes listed above, there is still a need for a process which will reform hydrocarbons to a high octane number while maintaining a correspondingly high liquid yield. That need has now been satisfied by the invention which is discussed below. Brief Description Of Drawing The invention will be better understood by reference to the drawing which schematically represents a process in accordance with the embodiments of the invention. Summary Of Invention According to the present invention a staged process is provided for reforming hydrocarbons. It comprises contacting a hydrocarbon feed with a conventional reforming catalyst in a penultimate reforming zone under reforming conditions to produce a reformate, separating at least some of the hydrogen from the penultimate reforming zone along with any hydrogen sulfide present from the reformate to provide a hydrogen content substantially reduced and substantially hydrogen sulfide free reformate hydrocarbon fraction and contacting the reformate hydrocarbon fraction with a final catalyst which comprises a Group VIII metal on a nonacidic intermediate pore size crystalline silicate in a final reforming zone. The crystalline silicate catalyst is contacted with the reformate hydrocarbon fraction at a temperature between 550 and 1200#F, a space velocity between 0.1 and 20 LHSV and a pressure between 0 and about 100 psig. Preferably, the crystalline silicate is silicalite. Among other factors, the present invention is based on the discovery that the multi-stage sequential process of the invention, using a conventional reforming catalyst and a silicalite catalyst under specified conditions, produces a relatively high octane product at a relatively high liquid yield. The combined high octane and high C 5 + liquid yield from this multi-stage process is greater than the combined octane and liquid yield for either of the two individual catalysts. These advantages are believed to result from a combination of the conventional catalyst's ability to selectively catalyze cyclohexane dehydrogenation, alkylcyclo- hexane dehydrogenation and alkylcyclopentane dehydroisomerization, and the silicalite catalyst's ability to selectively catalyze paraffin dehydro- cyclization. In accordance with an embodiment of the invention it is not necessary to contact the platinu /silicalite catalyst in the final stage with recycle hydrogen. In this embodiment the absence of added hydrogen favors aromatics production and relative activity which increases liquid yield at a given octane. In accordance with another embodiment of the invention some hydrogen is recycled. This increases catalyst life and allows some heat to be returned to the catalyst beds. A specific embodiment of the present invention comprises contacting a catalyst, which comprises between 0.1 and 2.5 weight percent platinum, 0.1 and 5.0 weight percent rhenium and 0.5 and 1.5 weight percent chloride on alumina, the ratio of rhenium to platinum being between 1 : 1 and 6:1, in a penultimate reforming zone with a feed having less than 1 ppm sulfur, at a temperature between 800 and 1100'F, a liquid hourly space velocity (LHSV) between 0.5 and 6, a pressure between 50 and 500 psig, and a hydrocarbon recycle ratio between 1 and 20 H 2 /HC, to form a reformate; separating at least a portion of the gaseous hydrogen along with hydrogen sulfide from the reformate to form a hydrogen content substantially reduced and substantially hydrogen sulfide free reformate hydrocarbon fraction; and contacting the reformate hydrocarbon fraction in a final reforming zone with a catalyst which comprises between 0.1 weight percent to 2.5 weight percent platinum on silicalite and an alkali or alkaline earth metal, at a temperature between 700 and 1100"F, a space velocity between 0.3 and 5 LHSV and a pressure between 15 and 75 psig. Detailed Description Of The Invention The present invention is a multi-stage process shown generally as 10 in the drawing which uses a conventional reforming catalyst in the penultimate stage or zone 12 and an intermediate pore size crystalline silicate catalyst in the final stage or zone 14. It should be noted that while only two reforming zones, 12 and 14, are illustrated, additional reforming zones can precede the penultimate zone 12. A hydrocarbon feed is introduced via line 16 to the penultimate reforming zone 12 where it is contacted with the conventional reforming catalyst in the penultimate reforming zone at less severe conditions than those needed to produce a reformate of the desired octane of the overall process. At least a portion of the hydrogen and substantially all of the hydrogen sulfide are separated by a separator 18 from the reformate exiting the penultimate zone 12 via line 20. The remaining reformate C 5 + hydrocarbon fraction is introduced via line 22 and is upgraded to the desired octane rating in the final stage 14. The reformate from the penultimate stage 12 is upgraded in the final reforming stage 14 at low pressure. The multi¬ stage process produces a relatively high octane product at a relatively high liquid yield. Conventional Catalyst (Penultimate Reforming Zone 12) The conventional reforming catalyst used in the penultimate reforming zone 12 comprises a Group VIII metal, more preferably a noble metal, most preferably platinum. Preferably, the conventional reforming catalyst also comprises a promoter metal, such as rhenium, tin, germanium, cobalt, nickel, iridium, rhodium, ruthenium, or combinations thereof. More preferably, the promoter metal is rhenium or tin. These metals are disposed on a support. Preferable supports include alumina, silica/alumina, silica, natural or man-made zeolites. More preferably, the support is alumina. The catalyst may also include between 0.1 and 3 weight percent chloride, more preferably between 0.5 and 1.5 weight percent chloride. 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. Patents Nos. 3,631,216; 3,415,737; and 4,511,746, which are hereby incorporated by reference in their entireties. Crystalline Silicates (Final Reforming Zone 14) The final stage catalyst of the present process comprises an intermediate pore size crystalline silicate. By "intermediate pore size", as used herein, is meant an effective pore aperture in the range of about 5 to 6.5P when the molecular sieve is in the H-form. Molecular sieves having pore apertures in this range tend to have unique molecular sieving characteristics. Unlike small pore zeolites such as erionite and chabazite, they will allow hydrocarbons having some branching into the molecular sieve void spaces. Unlike larger pore zeolites such as the faujasites and mordenites, they can differentiate between n-alkanes and slightly branched alkanes on the one hand and larger branched alkanes having, for example, quaternary carbon atoms. The effective pore size of the molecular sieves can be measured using standard adsorption techniques and hydrocarbonaceous compounds of known minimum kinetic diameters. See Breck, Zeolite Molecular Sieves, 1974 (especially Chapter 8) and Anderson, et al., J. Catalysis 58, 114 (1979), both of which are incorporated by reference. Intermediate pore size molecular sieves in the H-form will typically admit molecules having kinetic diameters of 5.0 to 6.5P with little hindrance. Examples of such compounds (and their kinetic diameters in P) are: n-hexane (4.3), 3-methylpentane (5.5), benzene (5.85), and toluene (5.8). Compounds having kinetic diameters of . about 6 to 6.5P can be admitted into the pores, depending on the particular sieve, but do. not penetrate as quickly and in some cases are effectively excluded. Compounds having kinetic diameters in the range of 6 to 6.5P include: cyclohexane (6.0), 2, 3-dimethylbutane (6.1), 2 ,2-dimethylbutane (6.2), m-xylene (6.1) and 1,2, 3,4-tetramethylbenzene (6.4). Generally, compounds having kinetic diameters of greater than about 6.5P do not penetrate the pore apertures and thus are not absorbed into the interior of the molecular sieve lattice. Examples of such larger compounds include: o-xylene (6.8), hexamethylbenzene (7.1), 1, 3, 5-trimethylbenzene (7.5), and tributylamine (8.1). The preferred effective pore size range is from about 5.3 to about 6.2P. Among the materials falling within this range are the crystalline silica polymorph, silicalite, RE 29,948 organosilicates, and the chromia silicate CZM. In performing adsorption measurements to determine pore size, standard techniques are used. It is convenient to consider a particular molecule as SUBSTI TU excluded if it does not reach at least 95% of its equilibrium adsorption value on the zeolite in less than about 10 minutes (p/po = 0.5; 25'C.) . By "crystalline silica polymorphs", as used herein, is meant materials having very low aluminum contents (or high silica:alumina mole ratios) . Aluminum contents of these materials are generally less than about 4000 ppm, preferably less than about 2000 ppm, more preferably less than about 1000 ppm. Intermediate pore size crystalline silica polymorphs useful in the present invention include silicalite, as disclosed in U.S. Patent No. 4,061,724, and the "RE 29,948 organosilicates", disclosed in RE 29,948, both of which are incorporated by reference. The essentially alumina- free chromia silicate, CZM, is disclosed in Serial No. 160,618, Miller, filed June 28, 1980, incorporated by reference. Intermediate pore size zeolites include materials such as CZH-5 and members of the ZSM series, e.g., ZSM-5, ZSM-11, ZSM-12, ZSM-21, ZSM- 22, ZSM-23, ZSM-35, and ZSM-38. ZSM-5 is described in U.S Patents Nos. 3,702,886, Re. 29,948 and 3,770,614; ZSM-11 is described in U.S. Patent No. 3,709,979 (See also, Bibby, et al., Nature, 280, 664- 665 (August 23, 1980) which reports the preparation of a crystalline silicate called "silicalite-2" ) ; ZSM-12 is described in U.S. Patent No. 3,832,449; ZSM-21 and ZSM-38 are described in U.S. Patent No. 3,948,758; ZSM-22 is described in U.S. Patents Nos. 4,481,177 and 4,556,477; ZSM-23 is described in U.S. Patent No. 4,076,842; ZSM-35 is described in U.S. Patent No. 4,016,245; ZSM-38 is described in U. S. Patent No. 4,046,859; ZSM-48 is described in U. S. Patent No. 4,397,827 and CZH-5 is disclosed in Serial No. 166,863, Hickson, filed July 7, 1980. All of these patents, publications and specifications which have not previously already been incorporated herein by reference are hereby so incorporated. The intermediate pore size zeolites can include "crystalline admixtures" which are thought to be the result of faults occurring within the crystal or crystallite area during the synthesis of the zeolites. The "crystalline admixtures" are themselves zeolites but have characteristics in common, in a uniform or nonuniform manner, to what the literature reports as distinct zeolites. Examples of crystalline admixtures of ZSM-5 and ZSM- 11 are disclosed and claimed in U.S. Patent No. 4,229,424, Kokotailo, October 21, 1980 (incorporated by reference) . The crystalline admixtures are themselves intermediate pore size zeolites and are not to be confused with physical admixtures of zeolites in which distinct crystals or crystallites of different zeolites are physically present in the same catalyst or hydrothermal reaction mixture. Additionally, zeolites SSZ-20 and SSZ-23 are preferred catalysts. SSZ-20 is disclosed in U.S. Patent No. 4,483,835, and SSZ-23 is disclosed in U.S. Patent No. 4,859,442, both of which are incorporated herein by reference. "Crystalline silicate" as used herein refers to silicates having a rigid, three-dimensional network of Si0 4 tetrahedra in which the tetrahedra are crosslinked by the sharing of oxygen atoms. Preferably, the crystalline silicates are non-acidic and substantially alumina-free, but they may contain minor amounts of alumina resulting from impurities in the starting materials or contamination of the reaction vessels. The preferred intermediate pore size crystalline silicate is silicalite, examples of which are disclosed in the U.S. Patent No. 4,061,724 and U.S. Patent No. Re. 29,948. The silica: alumina molar ratio of the crystalline silicates of the present invention are preferably greater than about 200:1, more preferably greater than about 500:1 and most preferably greater than about 1000:1. The crystalline silicates also preferably have specific gravities, in the calcined form, between about 1.50 and about 2.10 g/cc and a refractive index between about 1.3 and about 1.5. The crystalline silicate may be in the form of a borosilicate, where boron replaces at least a portion of the aluminum of the more typical aluminosilicate form of the silicate. Borosilicates are described in U.S. Patent Nos. 4,268,420; 4,269,813; 4,327,236 to Klotz, the disclosures of which patents are incorporated herein, particularly that disclosures related to borosilicate preparation. In the borosilicate, the preferred crystalline structure is that of ZSM-5, in terms of X-ray diffraction pattern. Boron in the ZSM-5 type borosilicates takes the place of aluminum that is present in the more typical ZSM-5 crystalline aluminosilicate structures. Borosilicates contain boron in place of aluminum, but generally there are some trace amounts of aluminum present in crystalline borosilicates. Still further crystalline silicates which can be used in the present invention are iron silicates and gallium silicates. Borosilicates and aluminosilicates are the more preferred silicates for use in the present invention. Aluminosilicates are the most preferred. The following sets forth the relevant details and methods of manufacture for the preferred catalyst. As noted above, crystalline silicates which can be used in the process of the present invention have been reported in the literature. As synthesized, silicalite (U.S. Patent No. 4,061,724) has a specific gravity at 77"F of 1.99 % 0.05 g/cc as SUBSTITUTE SHEET measured by water displacement. In the calcined form (1112 * F in air for one hour), silicalite has a specific gravity of 1.70 % 0.05 g/cc. With respect to the mean refractive index of silicalite crystals, values obtained by measurement of the as synthesized form and the calcined form ( 1112 °F in air for one hour) are, 1.48 % 0.01 and 1.39 % 0.01, respectively. The X-ray powder diffraction pattern of silicalite (1112'F calcination in air for one hour) has six strongest lines (i.e. , interplanar spacings). They are set forth in Table A ("S"-strong, and "VS"- very strong) : Table B shows the X-ray powder diffraction pattern of a typical silicalite composition containing 51.9 moles of Si0 2 per mole of tetrapropylammonium oxide (TPA) 2 0, prepared according to the method of U.S. Patent No. 4,061,724, and calcined in air at 1112'F for one hour. Silicalite crystals in both the "as synthesized" and calcined forms are generally orthorhombic and have the following unit cell parameters, in Angstroms: a = 20.05, b = 19.86, c = 13.36 (all values % 0.1 Angstrom). The pore diameter of silicalite is about 6P and its pore volume is 0.18 cc/gram as determined by adsorption. Silicalite adsorbs neopentane (6.2P kinetic diameter) slowly at ambient room temperature. The uniform pore structure imparts size-selective molecular sieve properties to the composition, and the pore size permits separation of p-xylene from o-xylene, m-xylene and ethylbenzene as well as separations of compounds having quaternary carbon atoms from those having carbon-to-carbon linkages of lower value (e.g., normal and slightly branched paraffins) . The crystalline silicates of U.S. Patent No. Re. 29,948 are disclosed as having a composition, in the anhydrous state: 0.9 % 0.2 [xR g O + (1 - x)M 2/n 0]: <.005 A1 2 0 3 :>1 Si0 2 where M is a metal, other than a metal of Group IIIA, n is the valence of said metal, R is an alkyl ammonium radical and x is a number greater than 0 but not exceeding 1. The crystalline silicate is characterized by the X-ray diffraction pattern of Table C. The following discloses crystalline silicates that are related to silicalite. The crystalline silicate polymorph of U.S. Patent No. 4,073,865 is disclosed as having a specific gravity of 1.70 % 0.05 g/cc and a mean refractive index of 1.39 % 0.01 after calcination in air at 600'C, as prepared by a hydrothermal process in which fluoride anions are included in the reaction mixture. The crystals, which can be as large as 200 microns, exhibit a substantial absence of infrared adsorption in the hydroxyl-stretching region and also exhibit an exceptional degree of hydrophobicity. They exhibit the X-ray diffraction pattern of Table D. SUBSTITUTE SHEET The literature also describes other intermediate pore size crystalline silicates and their method of preparation. For example, silicalite-2 is described in Nature, August, 1979 and is totally incorporated by reference. The Nature article discloses the method of preparing silicalite-2 and shows that the major differences between the patterns of silicalite and silicalite-2 are that peaks at 9.06, 13.9, 15.5, 16.5, 20.8, 21.7, 22.1, 24.4, 26.6 and 27.0 degrees 2R (CuK alpha radiation) in the silicalite X-ray diffraction pattern are absent from the silicalite-2 pattern. Also, peaks at 8.8, 14.8, 17.6, 23.1, 23.9 and 29.9 degrees are singlets in the silicalite-2 pattern rather than doublets as in the silicalite pattern. These differences are reported as being the same as those found between the diffraction patterns of the aluminosilicalites, orthorho bic ZSM-5 and tetragonal ZSM-11. Unit cell dimensions reported as calculated on the assumption of tetragonal symmetry for silicalite-2 are (in Angstroms) a = 20.04; b = 20.04; c = 13.38. The measured densities and refractive indices of silicalite-2 and its precursor are reported as 1.82 and 1.98 g/cc and 1.41 and 1.48 respectively. It is envisioned that the definition of silicalite includes these variants and others which may function as described by the present invention even though there are differences in such things as X-ray diffraction pattern or refractive index. Preparation of Intermediate Pore Size Crystalline Silicates The preparation of crystalline silicates of the present invention generally involves the hydrothermal crystallization of a reaction mixture comprising water, a source of silica and an organic templating compound at a pH of 10 to 14. Representative templating moieties include quaternary cations such as XR 4 where X is phosphorous or nitrogen and R is an alkyl radical containing from 2 to 6 carbon atoms, e.g., tetrapropylammonium hydroxide (TPA-OH) or halide, as well as alkyl hydroxyalkyl compounds, organic amines and diamines, and heterocycles such as pyrrolidine. When the organic templating compound (i.e. , TPA-OH) is provided to the system in the hydroxide form in sufficient quantity to establish a basicity equivalent to the pH of 10 to 14, the reaction mixture need contain only water and a reactive form of silica as additional ingredients. In those cases in which the pH must be increased to above 10, ammonium hydroxide or alkali metal hydroxides can be suitably employed for that purpose, particularly, the hydroxides of lithium, sodium and potassium. The ratio R + /(R + + M + ), where R + is the concentration of organic templating cation and M + is the concentration of alkali metal cation, is preferably between 0.7 and 0.98, more preferably between 0.8 and 0.98, most preferably between 0.85 and 0.98. The source of silica in the reaction mixture can by wholly, or in part, alkali metal silicate but should not be employed in amounts greater than that which would change the molar ratio of alkali metal to organic templating compound set forth above. Other silica sources include solid reactive amorphous silica, e.g., fume silica, silica sols, silica gel, and organic orthosilicates. One commercial silica source is Ludox AS-30 available from DuPont. Aluminum is easily incorporated as an impurity into the crystalline silicate. Accordingly, care should be exercised in selecting the silica source to minimize alumina uptake. Commercially available silica sols can typically contain between 500 and 700 ppm A1 2 0 3 , whereas fumed silica can contain between 80 and 2000 ppm of A1 2 0 3 impurity. As explained above, the silica to alumina molar ratio in the crystalline silicate is preferably greater than 200:1, more preferably greater than 500:1, most preferably greater than 1000:1. Aluminum in the synthesis contributes acidity to the catalyst, which is undesirable. The quantity of silica in the reaction system is preferably between about 1 and 10 moles Si0 2 per mole-ion of the organic templating compound. Water should be generally present in an amount between 20 and 700 mole per mole-ion of the quaternary cation. The reaction preferably occurs in an aluminum-free reaction vessel which is resistant to alkali or base attack, e.g., Teflon. Strong catalyst acidity is undesirable because it promotes cracking which results in lower selectivity. To reduce acidity the catalyst 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 silicalite synthesis. Preferably, at least 90% of the acid sites are neutralized by introduction of the metals, more preferably at least 95%, most preferably 100%. Crystalline silicates are conventionally synthesized largely in the sodium or potassium form. These cations are exchangeable, so that a given silicalite can be used to obtain silicalites containing other cations, such as alkaline earth metals or other alkali metals, by subjecting the silicalite to ion exchange treatment in an aqueous solution of the appropriate salts . The preferred alkali and/or alkaline earth metals are: lithium, sodium, potassium, rubidium, cesium, strontium and barium, more preferred metals are: sodium, potassium, rubidium and cesium. To determine whether a zeolite is non- acidic, the following test may be conducted. An aliquot of catalyst,. 0.1 - 0.5g, is mixed with Ig of acid-washed and neutralized alundum and packed in a HEET 3/16 inch stainless steel reactor tube with the remaining space filled with alundum. The reactor contents are calcined for one hour at 450 'C. The reactor is then placed in a clam-shell furnace and the reactor outlet is connected to the inlet of a gas chromatograph. The inlet is connected to the carrier gas line of the gas chromatograph. The reactor temperature is set at 427 'C. Pulses of n- decane, 0.04 microliter each, are injected through a septum above the reactor and reaction products are determined by standard gas chromatographic analysis. Blank runs with alundum should show no conversion under the experimental conditions, nor should a 100% Catapal alumina catalyst. A pseudo-first-order, cracking rate constant, k, is calculated using the formula: k = 1 In 1 1 - x where A is the weight of zeolite in grams and x is the fractional conversion to products boiling below decane. The catalyst is substantially free of acidity when the value of In k is less than about - 3.8. The catalyst is low in acidity if In k is less than about -2.3. The crystalline silicate is preferably bound with a matrix or porous matrix. The terms "matrix" and "porous matrix" include inorganic compositions with which the silicate can be combined, dispersed, or otherwise intimately admixed. Preferably, the matrix is not catalytically active in a hydrocarbon cracking sense, i.e., is substantially free of acid sites. The matrix porosity can either be inherent or it can be caused by a mechanical or chemical means. Satisfactory matrices include diatomaceous earth and inorganic oxides. Preferred inorganic oxides include alumina, silica, naturally occurring and conventionally processed clays, for example bentonite, kaolin, sepiolite, attapulgite and halloysite. Compositing the crystalline silicate with an inorganic oxide matrix can be achieved by any suitable known method wherein the silicate is intimately admixed with the oxide while the latter is in a hydrous state (for example, as a hydrous salt, hydrogel, wet gelatinous precipitate, or in a dried state, or combinations thereof) . A convenient method is to prepare a hydrous mono or plural oxide gel or cogel using an aqueous solution of a salt or mixture of salts (for example aluminum and sodium silicate) . Ammonium hydroxide carbonate (or a similar base) is added to the solution in an amount sufficient to precipitate the oxides in hydrous form. Then, the precipitate is washed to remove most of any water soluble salts and it is thoroughly admixed with the silicate which is in a finely divided state. Water or a lubricating agent can be added in an amount sufficient to facilitate shaping of the mix (as by extrusion) . The preferred crystalline silicate is silicalite. Assuming that the only crystalline phase in the silicalite preparation is silicalite, the silicalite preferably has a percent crystallinity of at least 80%, more preferably at least 90%, most preferably 95%. To determine percent crystallinity, an X-ray diffraction (XRD) pattern of the silicalite is made and the area under the 8 major peaks is measured in the angle interval between 20.5 and 25.0 degrees. Once the area under the curve is calculated, it is compared with the area under the curve for a 100% crystalline standard for silicalite. Group VIII Metals The catalysts useful in either stage of the SUBSTITUTE SHEET present invention 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 particularly platinum. The preferred percentage of the Group VIII metal, such as platinum, in the catalysts is between 0.1 weight percent and 5 weight percent, more preferably from 0.1 weight percent to 2.5 weight percent. Group VIII metals are preferably introduced into the catalyst by impregnation, occlusion, or exchange in an aqueous solution of an appropriate salt. When it is desired to introduce two Group VIII metals into the catalysts, the operation may be carried out simultaneously or sequentially. Preferably, the Group VIII metal is finely dispersed within, and on, the catalysts. By way of example, platinum can be introduced by impregnation with an aqueous solution of tetraammineplatinum (II) nitrate, tetraamine- platinum (II) chloride, tetraammineplatinum (II) hydroxide, chloroplatiniσ acid or dinitrodiaminoplatinum. In an ion exchange process, platinum can be introduced by using cationic platinum complexes such as tetraammineplatinum (II) chloride. Platinum may be occluded into the catalyst by introducing a platinum complex into the synthesis mixture. After the desired metal or metals have been introduced, the catalysts are preferably treated in air, or air diluted with an inert gas, and reduced in hydrogen. Catalysts containing platinum are typically subjected to halogen or halide treatments to achieve or maintain a uniform metal dispersion. Typically, the halide is a chloride compound. The conventional catalysts can be subjected to similar treatments. The preferred crystalline silicate catalyst was not subjected to this treatment so as to keep its acidity low, thereby keeping undesirable side reactions which keeps C 4 - products to a minimum. Other metals can be added to the penultimate stage catalyst as promoters. These metals are preferably selected from Groups VIIB, IVA, IB or VIB. More preferably, the additional metals may include: rhenium, tin, gold, germanium, iridium, or chromium. Preferably, the promoter metal comprises between 0.1 and 10 weight percent of the catalyst, more preferably between 0.1 and 5.0 weight percent of the catalyst. Reforming and Dehydrocyclizing Both catalysts 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 therethrough in the liquid, vapor, or mixed phase, and in either upward, downward or radial flow. Alternatively, they can be used in moving beds, or in fluidized-solid processes, in which the charging stock is passed upward through a turbulent bed of finely divided catalyst. However, a fixed bed system or a dense-phase moving bed system are preferred due to catalyst attrition losses 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 reformer feed entering the penultimate stage 12 of the multi-stage process 10 via line 16 is preferably a naphtha fraction boiling within the range of 70 to 550 "F and preferably from 120 to 400"F. This can include, for example, straight run naphthas, paraffinic raffinates from aromatic extraction or adsorption, and C 6 -C 10 paraffin-rich f eds, as well as paraffin-containing naphtha products from other refinery processes, such as hydrocracking or conventional reforming. The reformate from the penultimate stage 12 is separated by separator 18 into a hydrogen/hydrogen sulfide containing fraction (which usually includes C,-C 5 hydrocarbons) which exits separator 18 via line 24 and a hydrocarbon fraction (generally C 5 + ) which exits separator 18 via line 22. The hydrocarbon fraction serves as the feed to the final stage 14 although additional feeds such as light straight run and pen-hex feeds (C 5 and C 6 ) can be added. Usually, the hydrogen/hydrogen sulfide containing fraction is recycled to the penultimate stage 12 thereby reducing heating requirements. A low sulfur feed is especially preferred in the present process. The feed preferably contains less than 5 ppm, more preferably less than 1 ppm, and most preferably less than 0.1 ppm sulfur. In the case of a feed which is not already low in sulfur, acceptable levels can be reached by hydrotreating the feed in a presaturation zone with a hydrotreating catalyst which is resistant to sulfur poisoning. An example of a suitable catalyst for this hydrotreating process is an alumina-containing support and a minor catalytic proportion of molybdenum oxide, cobalt oxide and/or nickel oxide. A Group VIII metal (such as platinum) on alumina can also be used as the hydrotreating catalyst. A sulfur sorber is preferably placed downstream of the hydrotreating catalyst, but upstream of the penultimate or final reforming catalysts. It may also be advantageous to place an additional sulfur sorber between the penultimate and final reforming catalysts . Examples of sulfur sorbers are alkali or alkaline earth metals or Group VIII metals, e.g., Cu, Ni, on porous refractory inorganic oxides such as zinc oxide, etc. It is also preferable to limit the nitrogen level in the feed to the penultimate reforming catalyst to less than 10 ppm nitrogen, or more preferably less than 1 ppm. Preferably, water in the feed is limited to less than 100 ppm H 2 0, more preferably less than about 10 ppm H 2 0. Catalysts and processes which are suitable for these purposes are known to those skilled in the art. In the penultimate reforming stage 12 the conventional catalyst upgrades the feed. Although dependent on the feed RON (Research Octane Number), the RON of the C 5 + hydrocarbon fraction of the penultimate stage reformate is typically between 80 and 96 RON. Typically, the feed is heated by contact with a feed effluent heat exchanger (not illustrated) before entering the penultimate reforming stage. The temperature is preferably between 500° and 1200'F, more preferably between 800" and 1100'F. The heated feed contacts the conventional catalyst at pressures between 50 psig and 1000 psig, more preferably, between 50 psig and 500 psig, and most preferably between 50 and 300 psig. The liquid hourly space velocity (LHSV) is preferably between 0.2 and 20, more preferably between 0.5 and 6. The H 2 /HC ratio is preferably between 1 and 20, more preferably between 1 and 10, most preferably between 2 and 6. The actual reforming conditions for both catalysts will depend largely on the feed used, whether highly aromatic, paraffinic or naphthenic and upon the desired octane rating of the product. After the feed has been partially reformed in the penultimate stage 12, at least a portion of the hydrogen and substantially all of the hydrogen sulfide present is separated from the liquid product. This can be accomplished by the separator 18 which can be, for example, a liquifier. As previously stated, it may be desirable or necessary to add a sulfur sorber to assure that the feed to the final reforming zone 14 is substantially sulfur free. The partially reformed product (generally C 5 + ) can be reheated and is passed to a final reforming stage 14. The final stage 14 contains the intermediate pore size crystalline silicate catalyst. In the final stage 14 the reformate is ■ further upgraded to a higher RON. The pressure in the final stage 14 is preferably between 0 psig and 200 psig, more preferably between 0 and 100 psig, and most preferably between 15 psig and 75 psig. The liquid hourly space velocity (LHSV) is preferably between about 0.1 to about 10 hr. "1 more preferably between 0.3 and 5 hr. "1 . The temperature is preferably between about 550 °F and about 1200 °F, more preferably between 700'F and 1100'F. As is well known to those skilled in the dehydrocyclization art, the initial selection of the temperature (for either catalyst) is determined primarily by the desired conversion level of the acyclic hydrocarbon (considering the characteristics of the feed and of the catalyst) . Thereafter, to provide a relatively constant value for conversion, the temperature is slowly increased during the run to compensate for any deactivation that occurs. In accordance with one embodiment of the present invention the recycle H 2 /HC mole ratio in the final stage 14 is between 0 and 3, preferably between 0 and about 1. In a preferred mode the final stage 14 is operated in the absence of recycle hydrogen. The absence of recycle hydrogen favors S UBSTITUTESHEET aromatics formation and increases liquid yield at a given octane by decreasing hydrocracking which is favored by high hydrogen partial pressures. In accordance with another embodiment of the invention hydrogen is recycled via dashed line 26 from the final stage reformate to the final stage 14 in any desired amount. In such an instance the hydrogen is, however, substantially sulfide free and does not come from the reformate from the penultimate stage 12. This mode of operation serves to increase catalyst life. To insure relatively long catalyst life between regenerations of the final stage catalyst it is important that the feed to the final stage be quite low in sulfur (including sulfur introduced with recycle hydrogen) . Generally no more than about 2 ppm, preferably no more than about 1 ppm and more preferably no more than about 0.1 ppm sulfur should be in the final stage feed. For sulfur sensitive catalysts the sulfur should be no more than about 0.02 ppm in the final stage, whether introduced with the feed or recycle hydrogen. Since the feed to the penultimate stage 12 can have a higher sulfur content it is important to use the separator 18 and to exclude the hydrogen and hydrogen sulfide containing fraction exiting the separator 18 from the final stage 14. After the product is removed from the final stage 14, it can be passed to a distillation section (not shown) to separate out the more desired products (e.g., high octane blend stocks, aromatics rich stock) . The relative amounts of each catalyst may be different. The conventional catalyst that is used in the penultimate stage 12 may be between 10 and 90 volume percent of the total catalyst, preferably between 25 and 75 volume percent. The silicalite catalyst used in the final stage 14 may comprise between 10 and 90 volume percent of the total catalyst, more preferably between 25 and 75 volume percent. After a period of operation a catalyst can become deactivated by sulfur or coke. Coke and some sulfur can be removed by contacting the catalyst with an oxygen-containing gas at an elevated temperature. If the Group VIII metal(s) has agglomerated, then it can be redispersed by contacting the catalyst with a chlorine-containing gas under conditions effective to redisperse the metal(s). The method of regenerating the catalyst will depend on whether there is a fixed bed, moving bed, or fluidized bed operation. Regeneration methods and conditions are well known in the art. An example of an oxychlorination regeneration procedure is shown in U.S. Patent No. 4,855,269 which is hereby incorporated by reference in its entirety. An example of a sulfur removal procedure is shown in U.S. Patent No. 4,851,380 which is hereby incorporated by reference in its entirety. Without wishing to be bound by theory, it is believed that the octane advantage of this process comes from the conventional reforming catalyst's ability to convert the naphthenes to aromatics and the silicalite catalyst's ability to selectivity convert C 6 -C 8 paraffins (in particular n-paraffins) to aromatics at low hydrogen pressure. It is believed to be best to operate the conventional reforming catalyst at low to moderate severity conditions which can produce a reformate having between about 85 and about 96 RON (depending on the feed) . Under these conditions the conventional catalyst catalyzes the easier reactions, such as cyclohexane and alkycyclohexane dehydrogenation, and keeps hydrocracking to a minimum. The penultimate stage conventional reforming catalyst also serves to T reduce the sulfur level as it converts most organic sulfur compounds to hydrogen sulfide which can then be removed along with the hydrogen. Generally, when the conventional catalyst is used to dehydrocyclize paraffins under more severe conditions more light gases are produced (i.e., the catalyst is not very selective for dehydrocyclization) . With the present invention, however, the partially reformed feed from the conventional catalyst, after hydrogen and hydrogen sulfide are removed, is passed to the silicalite catalyst which is more selective in dehydrocyclizing paraffins. Consequently, the catalysts are complimentary by their selectivities for different reactions and the entire process produces a high octane product at a relatively high liquid yield. The present invention will be more fully understood by reference to the following examples . They are intended to be purely exemplary and are not intended to limit the scope of the invention in any way. Example 1 Conventional Catalyst A 2:1 rhenium to platinum catalyst was prepared beginning with the following solutions: a chloroplatinic acid solution containing 1.20 g of Pt as metal; a perrhenic acid solution containing 2.40 g of Re as metal; and HC1 containing 5.36 g of chloride. These solutions were added together and diluted to a total volume of 340 ml with deionized water. The combined solution was slowly added, with shaking, to a flask containing 400.0 g of calcined alumina extrudate. The impregnated alumina was allowed to stand for 16 hours, dried for 2 hours at 250 * F and then calcined for 2 hours at 950 * F in flowing, dry air. The resulting catalyst comprised 0.30 weight percent Pt, 0.60 weight percent Re, and 1.2 percent Cl. The catalyst exhibited a bulk density of approximately 0.622 g/cc, a pore volume of approximately 0.68 cc/g, and a nitrogen surface area that was approximately 200 m 2 /g. Example 2 Silicalite Catalyst A Pt-impregnated silicalite catalyst was prepared as follows: NaN0 3 , 8.4 g, and 40 g of EDTA were mixed into 80 ml of distilled water. Eight . hundred (800) g of a 25% aqueous solution of TPA-OH were added and the resulting solution was mixed well for 15 minutes. Six hundred forty (640) g of Ludox AS-30 were added and mixed in with rapid stirring for 15 minutes. The pH of the mixture was 13.1. The mixture was poured into a Teflon bottle and kept at 100"C for 7 days. The resulting product was filtered and then dried overnight in a vacuum oven at 120 'C. Then it was calcined for 8 hours at 566 "C in air. The percent silicalite was 100% as measured by XRD analysis. The product had an average crystallite size of about one micron in diameter (roughly spherical). Then the product was impregnated with 0.8 weight percent platinum by the pore-fill method using an aqueous solution of Pt(NH 3 ) 4 (N0 3 ) 2 . The catalyst was dried overnight in a vacuum oven at 120#C and calcined in dry air for 4 hours at 240 'C, 4 hours at 288 "C, 4 hours at 371 'C and 4 hours at 427'C. This catalyst was exchanged once with a 5 weight percent aqueous solution of KN0 3 at 82 'C for 2 hours. Then it was filtered, washed with distilled water, and dried overnight in a vacuum oven at 120°C. The catalyst was calcined in dry air for 4 hours at 204 * C and 4 hours at 288 * C. The K + level of the SUBSTITUTE SHEET catalyst was approximately 0.69 weight percent. Na + was 239 ppm. Example 3 Reforming With The Conventional Catalyst Under More Severe Conditions A commercially produced conventional platinum and rhenium on alumina reforming catalyst similar to that of Example 1 but made on a commercial scale was used to reform hydrocarbons . A hydrocarbon feed comprising a full boiling range naphtha was contacted with the catalyst at 200 psig, a H 2 /HC recycle ratio of 3, and a space velocity of 2 LHSV. The catalyst average temperature was 920.°F. The product RON was 98.5 and the C 5 + liquid yield was 76 LV%. Example 4 Reforming With The Conventional Catalyst and the Silicalite Catalyst Under Less Severe Conditions Without Recycle Hydrogen A commercially produced conventional platinum and rhenium on alumina reforming catalyst was used to reform the same feed as in Example 3 under the following less severe conditions: 200 psig, 3H 2 /HC recycle ratio, and 3 LHSV. The catalyst average temperature was 890 * F. The product RON was 91.4 and the C 5 + liquid yield was 83 LV% . The C 5 + reformate from the conventional catalyst (after separation from the hydrogen/hydrogen sulfide fraction) was contacted with the silicalite catalyst of Example 2 at 50 psig, 0 H 2 /HC recycle ratio, and 1.5 LHSV. The catalyst average temperature was 840"F. The product RON was 101.6 and the C 5 + liquid yield was 91 LV% of the yield from the penultimate stage. The results of. Example 4 are shown in Table 1. Catalyst RON C 5 +, LV% Yields: H 2 , SCF/B 1170 1243 C 1# SCF/B 150 265 C 2 , SCF/B 104 80 C 3 , SCF/B 103 65 C 4 , LV% 7.3 5.4 It is evident that a higher RON is achieved with a comparable C 5 + liquid volume yield by the combination process over the single conventional catalyst. Example 5 Reforming With The Conventional Catalyst and the Silicalite Catalyst Under Less Severe Conditions With Recycle Hydrogen Another full boiling range naphtha was reformed over the catalyst of Example 1 to produce a reformate with a 90.7 RON and sulfur content less than 0.1 ppm. This reformate was then reformed further over a Pt/silicalite catalyst similar to that of Example 2 except that there was no K + -exchange and the final Na + level was 0.96 wt.%. Run conditions were 50 psig pressure, a LHSV of 1.0, and a H 2 /HC ratio of 1.0. At 790°F, a 101.5 RON product was made with a 92 wt.% C 5 + yield in the final stage. This example demonstrates increased C 5 + RON product with substantially equal yield and with added recycle hydrogen. Example 6 Reforming With The Conventional Catalyst and the Silicalite Catalyst Without Use Of Separator To Remove Hydroσen To illustrate the importance of removing sulfur ahead of the final stage catalyst, H 2 S, at a S/Pt mole ratio of 0.5, was injected into the H stream ahead of the Pt/silicalite catalyst of Example 5 and using the feed of Example 5 to the penultimate reforming stage. A 101.5 RON product subsequently could not be produced even at a catalyst temperature of 980°F. SUBSTITUTE SHEET While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modification, and this application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth, and as fall within the scope of the invention and the limits of the appended claims .

Claims: Claims That Which Is Claimed Is: 1. A staged reforming process, comprising: contacting a hydrocarbon feed with a conventional reforming catalyst in a penultimate reforming zone under reforming conditions to produce a reformate; separating some or all of the hydrogen along with any hydrogen sulfide present from the reformate to provide a hydrogen containing fraction and a substantially hydrogen content reduced and substantially hydrogen sulfide-free reformate fraction; and contacting the reformate fraction with a final catalyst which comprises a Group VIII metal on a non-acidic intermediate pore size crystalline silicate in a final reforming zone, under reforming conditions without substantial hydrocracking, the reforming conditions comprising a temperature between 550 and 1200°F, a space velocity between 0.1 and 20 LHSV and a pressure between 0 and 200 psig. 2. A staged reforming process as set forth in claim 1, wherein the reforming conditions in the final reforming zone include a hydrogen recycle ratio between 0 and 1 H 2 /HC. 3. A staged reforming process in accordance with claim 2, wherein the final catalyst is silicalite. 4. A staged reforming process in accordance with claim 3, further including: recycling the hydrogen containing fraction to the penultimate reaction zone. SUBSTITUTESHEET 5. A staged reforming process in accordance with claim 3, wherein the penultimate reforming catalyst is contacted with the feed at a temperature between 500 and 1200 °F, a pressure between 50 and 1000 psig, a space velocity between 0.2 and 20 LHSV, and a hydrogen recycle ratio between 1 and 20 H 2 /HC; and the final reforming catalyst is contacted with the reformate at a temperature between 700 and 1100'F, a pressure between 0 and 100 psig, a space velocity between 0.3 and 5 LHSV, and a hydrogen recycle ratio of zero. 6. A staged reforming process in accordance with claim 3, wherein the feed is partially reformed to between 85 and 96 RON by the penultimate reforming catalyst and then further upgraded by the final reforming catalyst. 7. A staged reforming process in accordance with claim 5, wherein the penultimate reforming catalyst comprises a Group VIII metal and a promoter on a porous refractory inorganic oxide support. 8. A staged reforming process in accordance with claim 3, wherein the feed has less than 10 ppm sulfur. 9. A staged reforming process in accordance with claim 3, wherein the feed has less than 1 ppm sulfur. 10. A staged reforming process in accordance with claim 3, wherein the feed has less than 0.1 ppm sulfur. 11. A staged reforming process in accordance with claim 3, wherein the silicalite reforming catalyst further comprises an alkali or alkaline earth metal. 12. A staged reforming process in accordance with claim 1, wherein the penultimate catalyst comprises platinum and rhenium on chlorided alumina and the final catalyst comprises platinum on silicalite which contains an alkali or alkaline earth metal. 13. A staged reforming process in accordance with claim 1, wherein the final catalyst is silicalite. 14. A staged reforming process in accordance with claim 13, further including: recycling the hydrogen containing fraction to the penultimate reaction zone. 15. A staged reforming process in accordance with claim 13, wherein the penultimate reforming catalyst is contacted with the feed at a temperature between 500 and 1200°F, a pressure between 50 and 1000 psig, a space velocity between 0.2 and 10 LHSV, and a hydrogen recycle ratio between 1 and 20 H 2 /HC; and the final reforming catalyst is contacted with the reformate at a temperature between 700 and 1100'F, a pressure between 0 and 100 psig, a space velocity between 0.3 and 5 LHSV, and a hydrogen recycle ratio of zero. SU BSTITUTESHEET 16. A staged reforming process in accordance with claim 13, wherein the feed is partially reformed to between 85 and 96 RON by the penultimate reforming catalyst and then further upgraded by the final reforming catalyst. 17. A staged reforming process in accordance with claim 14, wherein the penultimate reforming catalyst comprises a Group VIII metal and a promoter on a porous refractory inorganic oxide support. 18. A staged reforming process in accordance with claim 14, wherein the feed has less than 10 ppm sulfur. 19. A staged reforming process in accordance with claim 13, wherein the feed has less than 1 ppm sulfur. 20. A staged reforming process in accordance with claim 13, wherein the feed has less than 0.1 ppm sulfur. 21. A staged reforming process in accordance with claim 13, wherein the silicalite reforming catalyst further comprises an alkali or alkaline earth metal. SUBSTITUTE SHEET 22. A staged reforming process comprising: contacting a penultimate catalyst with a feed having less than 1 ppm sulfur at a temperature between 800 and 1100'F, a space velocity between 0.5 and 6 LHSV, a pressure between 50 and 500 psig, and a hydrogen recycle ratio between 1 and 20 H 2 /HC, to form a reformate, the penultimate catalyst comprises between 0.1 nd 2.5 weight percent platinum, between 0.1 and 5.0 weight percent rhenium, and between 0.5 and 1.5 weight percent chloride on alumina, the ratio of rhenium to platinum being in the range from 1: 1 to 6:1; separating the reformate into a gaseous hydrogen fraction and a hydrocarbon fraction; and contacting the hydrocarbon fraction with a final catalyst at a temperature between 700 and 1000'F, a space velocity between 0.3 and 5 LHSV, a pressure between 15 and 75 psig in the absence of recycle hydrogen, the final catalyst comprising between 0.1 and 2.5 weight percent platinum on silicalite and an alkali or alkaline earth metal. 23. A staged reforming process in accordance with claim 22, further comprising separating H 2 S out with the hydrogen. SUBSTITUTE SHEET

Inventors: HOLTERMANN DENNIS L, JACOBSON ROBERT L, MILLER STEPHEN J, MULASKEY BERNARD F, HOLTERMANN, DENNIS, L., JACOBSON, ROBERT, L., MILLER, STEPHEN, J., MULASKEY, BERNARD, F.
Applicants: CHEVRON RES & TECH, CHEVRON RESEARCH AND TECHNOLOGY COMPANY
Application year: 1991
Main classification: C10G35
IPC codes: C10G35, C10G59