Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C5/00—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms
  • C07C5/22—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms by isomerisation
  • C07C5/27—Rearrangement of carbon atoms in the hydrocarbon skeleton
  • C07C5/2702—Catalytic processes not covered by C07C5/2732 - C07C5/31; Catalytic processes covered by both C07C5/2732 and C07C5/277 simultaneously
  • C07C5/2724—Catalytic processes not covered by C07C5/2732 - C07C5/31; Catalytic processes covered by both C07C5/2732 and C07C5/277 simultaneously with metals
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C2523/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group C07C2521/00
  • C07C2523/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group C07C2521/00 of noble metals
  • C07C2523/40—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group C07C2521/00 of noble metals of the platinum group metals
  • C07C2523/42—Platinum
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C2529/00—Catalysts comprising molecular sieves
  • C07C2529/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites, pillared clays
  • C07C2529/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
  • C07C2529/70—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of types characterised by their specific structure not provided for in groups C07C2529/08 - C07C2529/65
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C2529/00—Catalysts comprising molecular sieves
  • C07C2529/82—Phosphates
  • C07C2529/83—Aluminophosphates (APO compounds)
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C2529/00—Catalysts comprising molecular sieves
  • C07C2529/82—Phosphates
  • C07C2529/84—Aluminophosphates containing other elements, e.g. metals, boron
  • C07C2529/85—Silicoaluminophosphates (SAPO compounds)

Definitions

• This invention relates to a process for isomerization of alkylaromatics.
• the xylenes i.e., para-xylene, metaxylene and orthoxylene, are important intermediates which find wide and varied application in chemical synthesis.
• Para- xylene upon oxidation yields terephthalic acid which is used in the manufacture of synthetic textile fibers and resins.
• Metaxylene is used in the manufacture of plasticizers, azo dyes, wood preservers, etc.
• Orthoxylene is feedstock for phthalic anhydride production.
• Xylene isomers from catalytic reforming or other sources generally do not match demand proportions as chemical intermediates, and further contain ethylbenzene which is difficult to separate or convert.
• Para-xylene amounts to only 20-25% of a typical C 8 aromatics stream.
• Combining xylene-recovery, such as adsorption for para-xylene recovery, with isomerization can effect adjustment in the additional quantity of the desired isomer. Isomerization converts a non- equilibrium mixture of the xylene isomers which is lean in desired components to a mixture approaching equilibrium concentrations.
• Ethylbenzene is not easily isomerized to xylenes, but it normally must be reacted because separation from the xylenes by superfractionation or adsorption is very expensive.
• Modern approaches to C 8 aromatics isomerization include reaction of the ethylbenzene in the presence of a solid acid catalyst with a hydrogenation-dehydrogenation function to effect hydrogenation to a naphthene intermediate followed by dehydrogenation to form a xylene mixture.
• Another approach is to convert ethylbenzene via dealkylation to form principally benzene while isomerizing xylenes to a near-equilibrium mixture.
• the former approach enhances xylene yield by forming xylenes from ethylbenzene, but the latter approach commonly effects higher ethylbenzene conversion and thus lowers the quantity of recycle to the para-xylene recovery unit with a concomitant reduction in processing cost.
• the latter approach also yields a high-quality benzene product.
• US-A-4,300,013, discloses the addition of large quantities of water (0.05-1.0 wt.%) in an alkylbenzene isomerization process based on zeolite FU-1.
• US-A-4,723,050 also discloses the supply of large quantities of water (0.1-10 wt.%) to an isomerization process based on the idea that steam is believed to reduce catalyst coking due to sulfur.
• U.K. Patent Specification 1 ,255,459 discloses steam addition in an amount ranging from 100 to 1500 ppm for an xylene isomerization process.
• Hart et al. discloses ethylbenzene isomerization to xylenes through naphthenes using a catalyst based on an acidic refractory oxide containing a mixture of silica and alumina.
• Also disclosed is the use of zeolitic aluminosilicates such as faujasite (FAU).
• German Patent DD-219,183 discloses a mordenite (MOR) based catalyst contacted with NH3, where the selectivity of ethylbenzene isomerization is improved by the addition of 500 to 800 ppm water in the initial reaction period up to a running time of 300 hours followed by reduction of the water content to the range of 10 to 50 ppm.
• MOR mordenite
• alkyl benzene isomerization process based on fluorided variations of amorphous aluminas or silica/aluminas optionally containing alkali or alkaline earth metals in the presence of steam in the range of 0.005 to 1.0 wt%.
• US-A-4,431 ,857 discloses the use of crystalline borosilicate (AMS-1 B) impregnated with molybdenum and the use of water addition to favor A 10 formation via a disproportionation mechanism.
• AMS-1 B crystalline borosilicate
• US-A-5,773,679 discloses the co-feeding of water during the initial operation of selectivated ZSM type zeolites for hydrocarbon conversion, and the use of silicon treated ZSM-5 for toluene disproportionation in particular.
• the effect of this zeolite treatment is to increase para-selectivity of the catalyst by decreasing the yield of xylenes, with the total xylenes decreasing a greater amount than the para-isomer such that the relative ratio of para-xylene increases, and with the resultant balance showing increased yield of benzene. No effect on ethylbenzene conversion is shown.
• This invention is based on the discovery that injection of trace amounts of water or a water producing compound into the reactor zone of a C 8 aromatics isomerization process results in a surprising improvement in ethylbenzene conversion and para-xylene yield at given reactor temperatures, along with improved catalyst stability.
• a broad embodiment of the present invention is a process for the upgrading of a nonequilibrium C 8 aromatics feed mixture wherein water or a water forming compound is supplied continuously or intermittently to a reaction zone containing a catalyst comprising either a non-zeolitic molecular sieve or a pentasil zeolitic aluminosilicate in order to increase xylenes isomerization and ethylbenzene conversion at a given temperature.
• the catalyst further comprises at least one platinum-group metal component, and an inorganic-oxide binder.
• the equivalent water provided to the reaction zone corresponds to 75 to 750 mass ppm, or preferably corresponds to 100 to 500 mass ppm.
• a feedstock to the present process comprises alkylaromatic hydrocarbons of the general formula C 6 H (6 - n) R n , where n is an integer from 2 to 5 and R is CH 3> C 2 H 5 , C 3 H 7 , or C 4 H 9 , in any combination and including all the isomers thereof.
• Preferred isomerizable alkylaromatic hydrocarbons include the xylene isomers in admixture with ethylbenzene as a nonequilibrium mixture.
• the present process effects conversion of C 2 H 5 , C 3 H 7 , and higher R groups on aromatic rings via dealkylation in conjunction with isomerization of methyl side chains on aromatic rings to approach a near-equilibrium isomer distribution in the aromatics product from the process.
• the alkylaromatic hydrocarbon feedstock may be utilized as found in selected fractions from various refinery petroleum streams, e.g., as recovered from catalytic reformate by fractionation or solvent extraction, produced as a byproduct of pyrolysis of petroleum distillates to obtain principally light olefins, or recovered from cracking of heavy petroleum fractions principally to gasoline-range products.
• An especially preferred feedstock is the raffinate after recovery of one or more valuable C 8 aromatic isomers, e.g., the recovery of para-xylene by adsorption or crystallization and/or the recovery of orthoxylene by fractionation.
• the feedstock will be substantially sulfur-free, generally containing less than 1 mass ppm sulfur due to prior catalytic processing.
• the isomerizable aromatic hydrocarbons which are converted in the process of this invention need not be concentrated.
• an alkylaromatic hydrocarbon feedstock preferably in admixture with hydrogen
• a catalyst of the type hereinafter described in a reaction zone is contacted with a catalyst of the type hereinafter described in a reaction zone.
• Contacting may be effected using the catalyst in a fixed-bed system, a moving-bed system, a fluidized-bed system, or in a batch-type operation.
• a fixed-bed system In view of the danger of attrition loss of the valuable catalyst and of operational advantages, it is preferred to use a fixed-bed system.
• a hydrogen-rich gas and the feedstock are preheated by suitable heating means to the desired reaction temperature and the combined reactants then pass into a reaction zone containing a fixed bed of the catalyst.
• the reaction zone may be one or more separate reactors with suitable means therebetween to ensure that the desired isomerization temperature is maintained at the entrance to each reactor. It is to be noted that the reactants may be contacted with the catalyst bed in either upward, downward, or radial-flow fashion, and that the reactants may be in the liquid phase, a mixed liquid-vapor phase, or a vapor phase when contacted with the catalyst.
• Operating conditions in the reaction zone include a temperature in the range from 0° to 600°C and a pressure from atmospheric to 5 MPa. Preferably, a temperature range of 300° to 500°C and a pressure range of 1 to 50 atmospheres is employed.
• the liquid hourly hydrocarbon space velocity of the feedstock relative to the volume of catalyst is from 0.1 to 30 hr-1 , and most preferably at 0.5 to 15 hr 1 .
• the hydrocarbon is passed into the reaction zone preferably in admixture with a gaseous hydrogen-containing stream at a hydrogen-to- hydrocarbon mole ratio of from 0.5:1 to 15:1 or more, and preferably a ratio of from 0.5 to 10.
• Other inert diluents such as nitrogen, argon, methane, ethane, and the like may be present.
• trace quantities of water are supplied to the reaction zone of the present process. Trace quantities generally will amount to no more than the water of saturation of the alkylaromatic feedstock, or typically up to 750 mass ppm (parts per million) relative to the alkylaromatic hydrocarbons; since above this level, water is believed to affect the hydrothermal stability of the molecular-sieve catalyst. At least 75 mass ppm of water must be supplied to have a significant effect on the process, and the most effective range of trace quantities is from 100 to 500 mass ppm relative to the alkylaromatic hydrocarbons.
• the water may be injected into the alkylaromatic feedstock or into the combined reactants to the reaction zone.
• the water source is continuously provided at the typical operating conditions in the reaction zone. Alternatively, the water source is provided intermittently.
• the water source can be stopped or provided in various amounts depending on the performance required from the catalyst system in the reaction zone.
• One measure of catalyst performance is weighted average bed temperature (WABT).
• WABT weighted average bed temperature
• WABT becomes too high it can begin to become a limiting control variable based on equipment constraints such as heater duty. Therefore intermittent water injection in the range provided herein above can allow for an extra WABT operating margin to improve the operating cycle of a temperature constrained reactor.
• the amount and effectiveness of the trace water will vary. Water already present in the feed as received from the feed source will also periodically require some adjustment to the amount of additional trace water supplied to the reaction zone.
• the reactor effluent will be condensed with the hydrogen and light hydrocarbon components removed therefrom by flash separation.
• the condensed liquid product is then subjected to a fractionation procedure to further purify the desired liquid product.
• Valuable high-purity benzene can be recovered from the light liquid product.
• a liquid C 8 aromatics product is processed to selectively recover the para-xylene isomer.
• Recovery of para-xylene can be performed by crystallization methods or most preferably by selective adsorption using crystalline aluminosilicates.
• the raffinate remaining after recovery of the desired xylene isomers may be returned to the isomerization reactor section.
• a component of the catalyst of the present invention is at least one non- zeolitic molecular sieve, usually denoted as "NZMS” and defined in the instant invention to include molecular sieves containing framework tetrahedral units (TO 2 ) of aluminum (AIO 2 ) and phosphorus (PO 2 ) in the form of aluminophosphates as disclosed in US-A-4,310,440.
• NZMS also includes molecular sieves containing at least one additional element (EL) as a framework tetrahedral unit (ELO 2 ).
• NZMS includes the "SAPO” molecular sieves of US-A-4 ,440,871 , "ELAPSO” molecular sieves as disclosed in US-A-4,793,984 and "MeAPO", “FAPO”, “TAPO” and “MAPO” molecular sieves, as hereinafter described.
• Crystalline metal aluminophosphates (MeAPOs where "Me” is at least one of Mg, Mn, Co and Zn) are disclosed in US-A- 4,567,029, crystalline ferroaluminophosphates (FAPOs) are disclosed in US-A-4,554,143, titanium aluminophosphates (TAPOs) are disclosed in US-A-4,500,651 , MAPO metal aluminophosphates wherein M is As, Be, B, Cr, Ga, Ge, Li or V are disclosed in US-A-4,686,093, and binary metal aluminophosphates are described in Canadian Patent 1 ,241 ,943.
• ELAPSO molecular sieves also are disclosed in patents drawn to species thereof, including but not limited to GaAPSO as disclosed in US-A-4,735,806, BeAPSO as disclosed in US-A-4,737,353, CrAPSO as disclosed in US-A-4,738,837, CoAPSO as disclosed in US-A-4,744,970, MgAPSO as disclosed in US-A-4,758,419 and MnAPSO as disclosed in US-A-4,793,833.
• a particular member of a class is generally referred to as a "-n” species wherein "n” is an integer, e.g., SAPO-11 , MeAPO-11 and ELAPSO-31.
• the preferred elliptical-pore crystalline non-zeolitic molecular sieves are one or more of the AEL framework types, especially SAPO- 11 , or one or more of the ATO framework types, especially MAPSO-31 , according to the "Atlas of Zeolite Structure Types" (Butterworth-Heineman, Boston, Mass., 3 rd ed. 1992).
• the mole fractions of the NZMSs are defined as compositional values which are plotted in phase diagrams in each of the identified patents or published applications.
• the silicoaluminophosphate molecular sieve SAPO-11 having respective maximum and minimum crystallographic free diameters of 6.3 and 3.9 A and resulting maximum/minimum ratio of 1.6+, is especially preferred.
• the silicoaluminophosphate molecular sieves are disclosed as microporous crystalline silicoalumino-phosphates, having a three-dimensional microporous framework structure of PO 2 + , AIO 2 " and Si0 2 tetrahedral units, and whose essential empirical chemical composition on an anhydrous basis is:
• R represents at least one organic templating agent present in the intracrystalline pore system
• m represents the moles of “R” present per mole of (Si x Al y P z )O 2 and has a value of from 0.02 to 0.3
• x, "y” and “z” represent, respectively, the mole fractions of silicon, aluminum and phosphorus present in the oxide moiety, said mole fractions being within the compositional area bounded by points A, B, C, D and E on the ternary diagram which is FIG. 1 of US-A- 4,440,871 , and represent the following values for "x", "y” and "z”: Mole Fraction
• SAPO silicoaluminophosphat.es are generally referred to therein as "SAPO” as a class, or as “SAPO-n” wherein “n” is an integer denoting a particular SAPO such as SAPO-11 , SAPO-31 , SAPO-40 and SAPO-41.
• a preferred SAPO-11 for use in the present invention is condensed-silica SAPO-11 denoted as SM-3 and prepared in accordance with the teachings of US- A-5,158,665.
• SM-3 comprises a P 2 0 5 -to-alumina mole ratio at the surface of the silicoaluminophosphate of 0.80 or less, preferably from 0.80 to 0.55; a P 2 O 5 -to- alumina mole ratio in the bulk of the SAPO of 0.96 or greater, preferably from 0.96 to 1 ; and a silica-to-alumina mole ratio at the surface which is greater than in the bulk of the SAPO.
• the SM-3 has a composition in terms of mole ratios of oxides on an anhydrous basis of:
• R represents at least one organic templating agent present in the intracrystalline pore system
• m represents the moles of "R” present and has a value such that there are from 0.02 to 2 moles of "R” per mole of alumina
• n has a value of from 0.96 to 1.1 and preferably 0.96 to 1
• q has a value of from 0.1 to 4 and preferably 0.1 to 1.
• US-A-4,943,424 is also incorporated herein by reference for its teachings with respect to preparation and properties of the preferred SM-3.
• the alternative preferred crystalline non-zeolitic molecular sieves are one or more of the ATO framework types according to the "Atlas of Zeolite Structure Types".
• MgAPSO sieves have a framework structure of Mg0 2 '2 , AIO 2 " , P0 2 + , and Si0 2 tetrahedral units having an empirical chemical composition on an anhydrous basis expressed by the formula:
• the MgAPSO-31 molecular sieve preferably has a framework magnesium content of from 0.003 to 0.035 mole fraction, consistent with the teachings of US- A-5,240,891.
• the present invention is drawn to a process for use in isomerization of C8 aromatics comprising a non-zeolitic molecular-sieve or zeolitic aluminosilicate catalyst.
• a component of this catalyst of the present invention preferably comprises at least one pentasil zeolitic aluminosilicate medium-pore molecular sieve.
• Intermediate-pore crystalline molecular sieves have pore sizes between 0.4 nm and 0.8 nm, especially 0.6 nm.
• crystalline molecular sieves having pores between 5 and 6.5 A are defined as “medium-pore” molecular sieves.
• pentasil of the preferred pentasil zeolite component is used to describe a class of shape-selective zeolites. This class of zeolites is typically characterized by a silica/alumina mole ratio of at least 12. Descriptions of the pentasils may be found in US-A-4, 159,282; US-A-4, 163,018; and US-A- 4,278,565. Of the pentasil zeolites, the preferred ones are MFI, MEL, MTW, MTT and FER (IUPAC Commission on Zeolite Nomenclature), with MFI-type zeolites, often identified as ZSM-5, being particularly preferred.
• the pentasil be in the hydrogen form. Conversion of an alkali metal form pentasil to the hydrogen form may be performed by treatment with an aqueous solution of a mineral acid. Alternatively, hydrogen ions can be incorporated into the pentasil by ion exchange with ammonium hydroxide followed by calcination.
• the particular pentasil selected may be a gallosilicate.
• Gallosilicates have essentially the same structure as the preferred zeolites described hereinabove, except that all or part of the aluminum atoms in the aluminosilicate crystal framework are replaced by gallium atoms.
• the gallium content for this particular type of pentasil expressed as mole ratios of SiO 2 to Ga 2 O 3 , ranges from 20:1 to 400:1 or more.
• the non-zeolitic molecular sieve and the zeolitic aluminosilicate each preferably are composited with a binder for convenient formation of catalyst particles.
• the proportion of NZMS in the first catalyst is 5 to 90 mass-% , preferably 10 to 80 mass-%, the remainder other than metal and other components discussed herein being the binder component.
• the relative proportion of zeolite in the second catalyst may range from 5 to 99 mass-%, with 10 to 90 mass-% being preferred.
• a catalytic composition can combine one or more NZMSs with each other or with crystalline zeolitic aluminosilicates.
• Catalysts containing the more non-zeolitic molecular sieves and zeolitic aluminosilicates may be contained in separate reactors, arranged sequentially in the same reactor, mixed physically, or composited on the same particle.
• binder utilized in the present invention should be a porous, adsorptive, high-surface area support having a surface area of 25 to 500 m 2 /g.
• binder materials which may be used in dual-functional hydrocarbon conversion catalysts include: (1) silica or silica gel, silicon carbide, clays and silicates including those synthetically prepared and naturally occurring, which may or may not be acid treated, such as, attapulgus clay, diatomaceous earth, fuller's earth, kaolin, kieselguhr, etc.; (2) ceramics, porcelain, bauxite; (3) refractory inorganic oxides such as alumina, titanium dioxide, zirconium dioxide, chromium oxide, zinc oxide, magnesia, thoria, boria, silica-alumina, silica-magnesia, chromia-alumina, alumina- boria, silica-zirconia, zirconia-alumina, etc.; and (4) combinations of
• Preferred binders are refractory inorganic oxides, such as a binder comprising alumina.
• Suitable aluminas are the crystalline aluminas known as the gamma-, eta-, and theta-aluminas, with gamma- alumina as the preferred form.
• the alumina binder may contain minor proportions of other well known refractory inorganic oxides such as silica, zirconia, magnesia, etc.; good results may be obtained with a binder containing from 90 to 99 mass-% alumina and from 1 to 10 mass-% zirconia.
• a preferred binder or matrix component is a phosphorus-containing alumina component.
• the phosphorus may be incorporated in any acceptable manner known in the art.
• US-A-4,629,717 describes one method of preparing such alumina phosphate.
• the preferred alumina binder is uniform in composition.
• the alumina may be activated prior to use by one or more treatments including drying, calcination, steaming, etc., and it may be in a form known as activated alumina, activated alumina of commerce, porous alumina, alumina gel, etc.
• An alternative preferred binder is a form of amorphous silica.
• the preferred amorphous silica is a synthetic, white, amorphous silica (silicon dioxide) powder which is classified as wet-process, hydrated silica.
• the BET surface area of the silica is in the range from 120 to 160 m 2 /g.
• Nonacidic amorphous silica binder is especially preferred e.g., that the pH of a 5% water suspension be 7 or above.
• the catalyst of the present invention may be composited and shaped into any useful form such as spheres, pills, cakes, extrudates, powders, granules, tablets, etc., and utilized in any desired size. These shapes may be prepared by spray drying, tabletting, spherizing, extrusion, and nodulizing.
• a preferred shape for the catalyst composite is the extrudate.
• the extrudates may be further shaped to any desired form, such as spheres.
• An alternative preferred shape of the subject catalyst is a sphere, advantageously manufactured by the oil drop method which comprises forming a hydrosol of the desired inorganic oxide binder.
• Alumina hydrosol is preferably prepared by reacting aluminum metal with hydrochloric acid. The molecular sieve is then uniformly dispersed in the hydrosol. This resultant zeolite-containing hydrosol is then commingled with a suitable gelling agent and is dispersed as droplets into an oil bath maintained at elevated temperatures.
• the lead component may be added to the mixture prior to forming the droplets and either before, after, or simultaneously with the pentasil. The droplets of the mixture remain in the oil bath until they set and form hydrogel spheres.
• the zeolitic aluminosilicate catalyst optimally is subjected to steaming to tailor its acid activity.
• the steaming may be effected at any stage of the zeolite treatment, but usually is carried out on the composite of zeolite and binder prior to incorporation of the platinum-group metal.
• Steaming conditions comprise a water concentration of 5 to 100 volume-%, pressure of from 100 kPa to 2 MPa, and temperature of between 600° and 1200°C.
• the steaming should be carried out for a period of at least one hour, and periods of 6 to 48 hours are preferred.
• the composite may be washed with one or more of a solution of ammonium nitrate, a mineral acid, and/or water.
• Another component of the present invention is one or more of the platinum- group metals, selected from platinum, palladium, rhodium, ruthenium, osmium, and iridium.
• the preferred platinum-group metal component is platinum, with palladium being the next preferred metal.
• the platinum-group metal component may exist within the final catalyst composite as a compound such as an oxide, sulfide, halide, oxysulfide, etc., or as an elemental metal or in combination with one or more other ingredients of the catalyst. It is believed that the best results are obtained when substantially all the platinum-group metal component exists in a reduced state.
• the platinum-group metal component generally comprises from 0.01 to 2 mass % of the final catalytic composite, calculated on an elemental basis. Most preferably, the catalyst contains from 0.05 to 1 mass % platinum.
• the platinum-group-metal component may be incorporated into the catalyst composite in any suitable manner.
• One method of preparing the catalyst involves the utilization of a water-soluble, decomposable compound of a platinum-group metal to impregnate the calcined sieve/binder composite.
• a platinum-group metal compound may be added at the time of compositing the sieve component and binder.
• platinum-group metals which may be employed in impregnating solutions, co-extruded with the sieve and binder, or added by other known methods include chloroplatinic acid, chloropalladic acid, ammonium chloroplatinate, bromoplatinic acid, platinum trichloride, platinum tetrachloride hydrate, platinum dichlorocarbonyl dichloride, tetramine platinic chloride, dinitrodiaminoplatinum, sodium tetranitroplatinate (II), palladium chloride, palladium nitrate, palladium sulfate, diamminepalladium (II) hydroxide, tetramminepalladium (II) chloride, and the like.
• the platinum-group metal component is concentrated on the binder component of the catalyst.
• the present catalyst composites may contain other metal components known to modify the effect of the platinum-group metal component.
• metal modifiers may include rhenium, tin, germanium, lead, cobalt, nickel, indium, gallium, zinc, uranium, dysprosium, thallium, and mixtures thereof. Catalytically effective amounts of such metal modifiers may be incorporated into the catalyst by any means known in the art to effect a homogeneous or stratified distribution.
• the optional metal modifier group component generally comprises from 0.01 to 5.0 mass % of the final catalytic composite.
• the catalyst of the present invention may contain a halogen component, comprising either fluorine, chlorine, bromine or iodine or mixtures thereof, with chlorine being preferred.
• a halogen component comprising either fluorine, chlorine, bromine or iodine or mixtures thereof, with chlorine being preferred.
• the catalyst contains no added halogen other than that associated with other catalyst components.
• the catalyst composite is dried at a temperature of from 100° to 320°C for a period of from 2 to 24 or more hours and, usually, calcined at a temperature of from 400° to 650°C in an air atmosphere for a period of from 0.1 to 10 hours until the metallic compounds present are converted substantially to the oxide form.
• the optional halogen component may be adjusted by including a halogen or halogen-containing compound in the air atmosphere to result in a final composite that contains from 0.1 to 2.0 mass % halogen, calculated on an elemental basis.
• the resultant calcined composites optimally are subjected to a substantially water-free reduction step to insure a uniform and finely divided dispersion of the optional metallic components.
• the reduction optionally may be effected in the process equipment of the present invention.
• Substantially pure and dry hydrogen i.e., less than 20 vol. ppm H2O
• the reducing agent contacts the catalyst at conditions, including a temperature of from 200° to 650°C and for a period of from 0.5 to 10 hours, effective to reduce substantially all of the Group VIII metal component to the metallic state.
• the resulting reduced catalyst composite may also be beneficially subjected to presulfiding to incorporate in the catalyst composite from 0.05 to 1.0 mass-% sulfur calculated on an elemental basis.
• a catalyst (X) was prepared in accordance with the procedures described hereinabove in order to illustrate the advantages of the present invention.
• MFI zeolite was added to an alumina sol solution, prepared by digesting metallic aluminum in hydrochloric acid, in an amount sufficient to yield a zeolite content in the finished catalyst of 11 mass %.
• a second solution of hexamethylenetetramine (HMT) was prepared and added to the zeolite/alumina sol mixture to give a homogeneous admixture. This admixture was then dispersed as droplets into an oil bath maintained at 93°C. The droplets remained in the oil bath at 150°C until they set and formed hydrogel spheres.
• the catalyst X of Example 1 was evaluated for upgrading of C 8 aromatics in a pilot plant.
• the feedstock composition was approximately as follows in mass %:
• Feedstock was prepared by stripping in a fractionator and storing under a dry ( ⁇ 1 ppm H20) nitrogen blanket. Pilot-plant operating conditions comprised a temperature range of 390°-450°C, a liquid hourly space velocity of 4 hr " ⁇ and a molar ratio of hydrogen gas to hydrocarbon feedstock of 3 to 5. Pressure was varied from 4 to 1 atmospheres (gauge) to limit formation of C 8 naphthenes as temperature was varied.
• the feedstock was processed in the pilot plant over a range of temperatures, varying pressure as described.
• the temperature survey on fresh catalyst was performed on a dry feedstock without water addition at a gas-to- hydrocarbon ratio of 3.
• a subsequent test at low temperature showed severe deactivation, and the testing at dry conditions was discontinued. Trace quantities of water were added to the reactor feed to determine effect on catalyst performance.
• the initial test and temperature survey showed improved results over even the fresh catalyst, and a one-week stability test at 435°C confirmed catalyst stability with trace water addition.
• Figure I is a plot of the product ratio of para-xylene in total xylenes against reactor temperature.
• Figure II shows ethylbenzene conversion as a function of reactor temperature.
• Performance of the deactivated catalyst with trace water addition shows a significant benefit over the dry operation, and even over fresh catalyst at higher temperatures. Comparing the dry test (broken line between high temperature on fresh catalyst and return to low temperature) with the test based on water addition, the provision of trace quantities of water on average lowered the temperature required to achieve a given para-xylene yield by 15-20°C, or alternatively improved the para-xylene content of the xylenes by nearly 3%. Ethylbenzene conversion was increased by 8-20% at the same temperature.
• a second catalyst (Y) was prepared in accordance with the procedures described hereinabove in order to illustrate the advantages of the present invention where water injection is provided intermittently.
• SM-3 silicoaluminophosphate was prepared in accordance with the teachings of US-A- 4,943,424.
• the SM-3 was composited with alumina and tetramine platinic chloride.
• the composite comprised 60 mass-% SM-3 and 40 mass-% alumina.
• Tetramine platinic chloride was incorporated into the composition to effect a platinum level of 0.28 mass-% on an elemental basis, and the catalyst was calcined and reduced.
• This catalyst was tested in a pilot plant flow reactor processing a non- equilibrium C 8 -aromatic feed mixture having the following approximate composition in mass-%:
• This feed was contacted with 100 cc of catalyst at a liquid hourly space velocity of 3.0 and a hydrogen/hydrocarbon mole ratio of 4.
• Reactor temperature was adjusted to maintain a favorable conversion level. Conversion is expressed as the disappearance per pass of ethylbenzene. C 8 aromatic loss is primarily to benzene and toluene, with smaller amounts to light gases being produced.
• the feed containing initial low water at 25 mass-ppm up for the initial part of the experiment. Points 1a and 1 b indicate the gradual decline in catalyst performance. The water was then increased to 300 mass-ppm for the middle part. Point 2 indicates the effect of water addition on improving catalyst performance.

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