MXPA06007561A - Process and catalyst for c8 alkylaromatic isomerization - Google Patents

Abstract

A process for isomerizing ethylbenzene into xylenes such as para-xylene using a zeolitic catalyst system based on MTW-type zeolite is disclosed. Preferably the two metals are platinum and tin. The invention obtains a stable and improved yield of xylenes such as para-xylene without excess benzene production by dealkylation. The zeolitic silica-to-alumina ratio ranges from 20 to 45. Use of MTW substantially free of mordenite improves yields and integrated aromatics complex economics by reducing undesirable aromatic ring-loss reactions.

Description

PROCESS AND CATALYST FOR ISOMERIZATION OF C8-ALKYLAROMETHICS BACKGROUND OF THE INVENTION The present invention relates to the catalytic conversion of hydrocarbons, and more specifically to the use of a catalyst system comprising MTW-type zeolites essentially free of mordenite, in a conversion process of hydrocarbons, and even more specifically to a process of isomerization of aromatics to convert ethylbenzene to xylene with a catalyst which preferably contains platinum and tin. The xylenes, para-xylenes, meta-xylenes and ortho-xylenes are important intermediaries that have wide and varied applications in the guímica synthesis. Para-xylene upon oxidation produces terephthalic acid which is used in the manufacture of synthetic textile fibers and resins. Meta-xylene is used in the use of plasticizers, azo dyes, wood preservers, and so on. Ortho-xylene is a feedstock for the production of italic anhydride. The xylene isomers for catalytic reforming or other sources generally do not meet the proportions of the demand as guialic intermediates and also comprise ethylbenzene, which is difficult to separate or convert. In particular, para-xylene is an important guiding intermediate with a rapidly growing demand, although only 20 to 25% of a typical stream of C8 aromatics. The adjustment of the ratio of isomers to demand can be effected by combining the recovery of xylene isomers, such as adsorption for the recovery of para-xylene with isomerization to produce an additional amount of the desired isomer. The isomerization converts a mixture out of equilibrium of the xylene isomers, which is lean in the desired xylene isomer, to a mixture which tends to equilibrium concentrations. Various catalysts and processes have been developed to effect the isomerization of xylene. In selecting the appropriate technology, it is desirable to perform the isomerization process as close to equilibrium as practical, in order to maximize the performance of para-xylene; however, with this a greater loss of cyclic Cs is associated, due to secondary reactions. The approach to the eguilíbrio that is used is an optimized compromise between a high loss of cyclic Cs to a high conversion (that is, a great approach to the equilibrium) and high utility costs due to the high recycling rate of non-converted Cs aromatics. Accordingly, the catalysts are evaluated based on a favorable balance of activity, selectivity and stability.

U.S. Pat. 4,899,012 discloses an isomerization process of algayl-aromatics based on a catalyst system of bimetallic pentacil zeolites which also produces benzene. U.S. Pat. 4,962,258 discloses a process for the isomerization of phase-separated xylene on crystalline silicate and gallium-containing molecular filters, as an improvement over the aluminosilicate zeolites ZSM-5, ZSM-12 (type MTW) and ZSM-21 as disclosed in U.S. Pat. 3,856,871. The '258 patent relates to borosilicate works, as exemplified in U.S. Pat. 4,268,420, and with zeolites of the large pore type, such as faujasite or mordenite. U.S. Pat. 5,744,673 discloses an isomerization process using zeolite beta, and exemplifies the use of gas phase conditions with hydrogen. U.S. Pat. 5,898,090 discloses an isomerization process using molecular filters of crystalline silicoaluminophosphate. U.S. Pat. 6,465,705 discloses a mordenite catalyst for isomerization of aromatics, which is modified with an element of the IUPAC III group. The catalysts for the isomerization of Cs aromatics are generally classified by the manner of processing ethylbenzene associated with the xylene isomers. It is not easy to isomerize ethylbenzene to xylenes, aungue usually becomes the isomerization unit because the separation of the xylenes by superfractionation or adsorption is extremely costly. A widely used term is "to desalicate ethylbenzene to form mainly benzene, while isomerizing xylenes to a mixture almost in equilibrium." An alternative approach is to react ethylbenzene to form a mixture of xylenes by converting to, and converting, naphthenes in the presence of a solid acid catalyst with a hydrogenation-dehydrogenation function The first lead usually produces a higher conversion of ethylbenzene, thereby reducing the amount of recycling to the para-xylene recovery unit and the processing costs concomitants, but the second approach increases the yield of xylenes, by forming xylenes from ethylbenzene.A process and catalyst composite material that increases the conversion based on the second approach, ie, obtain an isomerization of ethylbenzenes to xylenes with high conversion , would significantly improve the production economy No xylenes. SUMMARY OF INVENTION A principal object A of the present invention to provide a process for the isomerization of hydrocarbons alguiloaromáticos. More specifically, the process of the present invention is directed to a lysed phase isomerization for aromatic hydrocarbons Cs on a zeolitic catalyst of MTW type, in order to obtain higher yields of the desired xylene isomers. The present invention is based on the discovery that a catalyst system comprising platinum and tin, on an MTW type zeolite essentially free of mordenite with a binder, has a better conversion and selectivity in the isomerization of Cs aromatics, and at the same time minimizes the undesirable formation of benzene. Accordingly, the present invention is directed to a process for the isomerization of allyloaromatics which comprises placing a hydrocarbon feed stream rich in C8 aromatics comprising ethylbenzene, and less than the amount of xylenes equilibrium, in contact with a catalyst which has a MTW zeolite and an element of the platinum group and an element of group IV (IUPAC 14) of the periodic table [see Cotton and Wilkinson, Advanced Inorganic Chemistry, John Wiley & Sons (5th edition, 1988), which is preferably tin.Preferably, the catalyst comprises an MTW zeolite essentially free of mordenite, preferably with a silica to alumina ratio of less than 45, under isomerization conditions, to obtain a product having an higher xylene content than the feed load.

DETAILED DESCRIPTION OF THE INVENTION The feed charges to the aromatic isomerization process of the present invention comprise isomerizable algayl aromatic hydrocarbons with the general formula C6H (6-n) Rn, where n is an integer between 2 and 5, and R is CH3 , C2H5, C3H7 or C4H9, in any combination and including the isomers thereof. Suitable alkylaryl-aromatic hydrocarbons include, for example, but without limiting the invention, ortho-xylenes, meta-xylenes, paraxylenes, ethylbenzenes, ethyl toluenes, tri-methylbenzenes, di-ethylbenzenes, tri-ethylbenzenes, methylpropylbenzenes, ethylpropylbenzenes, diisopropylbenzenes and mixtures of these. A particularly preferred application of the catalyst system of the present invention is the isomerization of a C8 aromatic mixture containing ethylbenzene and xylene. Generally the mixture will have an ethylbenzene content of between 1 and 50% by weight, an orthoxylene content of 0 and 35% by weight, a meta-xylene content of 20 and 95% by weight, and a content of para-xylene between 0 and 30% of the weight. The aforementioned aromatic Cs are a mixture outside equilibrium, that is, at least one C8 aromatic isomer is present in a concentration which essentially differs from the concentration in equilibrium to isomerization conditions. Generally, the mixture which is not in equilibrium is prepared to extract para-, ortho- and meta-xylenes from a new Cs aromatic mixture obtained from an aromatics production process. The algiloaromatic hydrocarbons can be used in the present invention as they are in appropriate fractions of various petroleum refinery streams, ie, as certain fractions in the boiling range obtained by the selective fractionation and distillation of catalytically fissured or reformed hydrocarbons. The concentration of isomerizable aromatic hydrocarbons is optional; the process of the present invention allows the isomerization of algeoaromatic containing streams with a catalytic reforming, with or without the subsequent extraction of aromatics, to produce specific xylene isomers, and particularly to produce para-xylene. A stream of Cs aromatics to the present process may contain non-aromatic hydrocarbons, ie naphthenes and paraffins in an amount of up to 30% by weight. Preferably, the isomerizable hydrocarbons contain essentially aromatics, to ensure pure products from the downstream recovery process. In addition, a C8 aromatic stream rich in undesirable ethylbenzene can be supplied so that it can be converted to xylenes or other non-C8 compounds, in order to further concentrate the desired xylene species.

In accordance with the process of the present invention, a feed mixture of algao-aromatic hydrocarbons, preferably mixed with hydrogen, is placed in contact with a catalyst of the type described below, in an isomerization zone of algao-aromatic hydrocarbons. This contact can be made using the catalyst in a fixed bed system, a moving bed system, a fluidized bed system or in a batch operation. In view of the danger of wear loss of valuable catalyst, and due to a simpler operation, it is preferred to use a fixed bed system. In this system, a hydrogen-rich gas and the feed mixture are preheated by a suitable heating device up to the desired reaction temperature, and then it is passed to an isomerization zone containing a fixed bed of catalyst. The conversion zone may be one or more separate reactors with suitable devices therebetween, to ensure that the desired isomerization temperature is maintained at the entrance of each zone. The reagents can be put in contact with the catalyst bed, whether in an upward, downward or radial flow, and the reagents can be in the liquefied phase, in the vapor-vapor mixed phase, or in the vapor phase, when in contact with the catalyst. . The algiloaromatic feed mixture, preferably a mixture of aromatic Cs out of equilibrium, is contacted with the isomerization catalyst under suitable isomerization conditions of algiloaromatics. These conditions comprise a temperature between 0 and 600 ° C or more, and preferably in the range between 300 and 500 ° C. The absolute pressure is generally between 1 to 100 atmospheres, preferably less than 50 atmospheres. The isomerization zone contains sufficient catalyst to provide an hourly space velocity with respect to the hydrocarbon feed mixture of between 0.1 to 30 hr, and preferably 0.5 to 10 hr. Optimally, the hydrocarbon feed mixture is reacted in a mixture with hydrogen at a hydrogen / hydrocarbon molar ratio of between 0.5: 1 and 25: 1 or more. Other inert diluents such as nitrogen, argon and light hydrocarbons may be present. The reaction proceeds by the mechanism, described above, of isomerizing xylenes while ethylbenzene is reacted to form a xylene mixture by conversion to, and reconversion of, naphthenes. In this way the yield of xylenes in the product is increased, forming xylenes from ethylbenzene. Thus, the loss of Cs aromatics through the reaction is low: typically less than 4% of the weight per step of Cs aromatics in the feed to the reactor, preferably not more than 3.5% by weight and more preferably less than 3% by weight . The particular molecule used to recover an isomerized product from the effluent of the reactors of the isomerization zone is not considered as critical to the present invention, and any effective recovery system known in the art can be used. Typically, the liquefied product is fractionated to remove light or heavy by-products to obtain the isomerized product. Heavy by-products include A? 0 compounds such as dimethylethylbenzene. In some instances, certain species of products such as ortho-xylene or dimethylethylbenzene may be recovered from the isomerized product by selective fractionation. Generally the product of the aromatic isomerization Cs is processed to selectively recover the para-xylene isomer, optionally by crystallization. Selective adsorption is preferred using crystalline aluminosilicates in accordance with U.S. Pat. 3,201,491. Improvements and alternatives in the preferred adsorption recovery process are described in U.S. Pat. 3,626,020, 3,696,107, 4,039,599, 4,184,943, 4,381,419 and 4,402,832, incorporated herein by reference. An essential component of the catalyst of the present invention is at least one MTW type zeolitic molecular filter, also characterized as "ZSM-12 low in silica" and defined in the present invention to include molecular filters with a ratio of silica to alumina of less of 45, preferably 20 to 40. Preferably, the MTW type zeolite is essentially free of mordenite, which is defined herein as an MTW component containing less than 20% by weight of mordenite impurities, preferably less than 10% of weight, and more preferably less than 5% of the weight of mordenite, which is approximately the lower level of detectability using most of the characterization methods in the art, as X-ray diffraction crystallography. Applicants discovered surprisingly that a new and unique property in their type of MTW type zeolite is that when the ratio of silica to alumina is reduced, and the concomitant phase of mordenite is avoided in low conditions In silica, a catalyst compound with excellent properties for low losses of aromatic rings is produced by converting ethylbenzene to para-xylene under minimal benzene conditions. The preparation of MTW-type zeolites by crystallizing a mixture comprising a source of alumina, a source of silica and a quenching agent, uses methods well known in the art. In particular, U.S. Pat. 3,832,449 discloses a MTW-type zeolite utilizing tetraalgammonium cations. U.S. Pat. 4,452,769 and 4,537,758 use a methyltriethylammonium cation to prepare a highly siliceous MTW type zeolite. U.S. Pat. No. 6,652,832 uses a cation of N, N-dimethylhexamethyleneimine as a quencher, to produce a MTW type zeolite with a low proportion of silica versus alumina, and without MFI impurities. Preferably, high purity crystals are used as cores for subsequent batches. The MTW type zeolite is preferably composed with a binder for convenient formation of catalyst particles. The proportion of zeolite in it is from 1 to 90% by weight, and preferably 2 to 20% by weight, where the remainder is different from the metals, and the other components discussed herein are the binder component. As previously mentioned, zeolite will generally be used in combination with a refractory inorganic oxide binder. The binder must be an adsorptive and porous support that has a surface area of between 25 to 500 m2 / g. It is intended to include in the scope of the present invention binder materials which have traditionally been used in hydrocarbon conversion catalysts such as: (1) refractory inorganic oxides such as alumina, titania, zirconia, chromia, zinc oxide, magnesia, chromia-alumina, alumina-boria, silica-zirconia, phosphorus-alumina, etcetera; (2) ceramics, porcelain, bauxite; (3) silica or silica gel, silica carbide, clays and silicates, including those of synthetic preparation and of natural occurrence, which may or may not be treated with acid, for example attapulgite clay, diatomaceous earth, Fuller's earth, kaolin, kieselguhr, etcetera; (4) crystalline zeolitic aluminosilicates, either naturally occurring or synthetically prepared, such as FAU, MEL, MFI, MOR, MTW (IUPAC Commission for the nomenclature of zeolites), in hydrogenated form or in an exchanged form with metal cations; (5) spinels such as MgAl204, FeAl204, ZnAl204, CaAl20, and other similar compounds that have the formula MOAI2O3, where M is a metal with valence 2; (6) material combinations of one or more of these groups. A preferred refractory inorganic oxide for use in the present invention is alumina. Suitable alumina materials are crystalline aluminas known as gamma-, eta-, and theta-alumina, where gamma- or eta-alumina give the best results. One form for the catalyst compound is an extrudate. The already known extrusion method generally involves mixing the molecular filter optionally with the binder and a suitable peptizing agent to form a homogeneous mass or thick paste with the correct moisture content, to allow the formation of extrudates with acceptable integrity to resist direct calcination . The extrudability is determined from an analysis of the moisture content of the dough, where a moisture content in the range of between 30 to 50% by weight is preferred. The mass is then extruded through a die with multiple perforations, and the extrudate is cut into noodles to form particles in accordance with techniques well known in the art. A multitude of different forms of extrudates are possible, including, without limitation, cylinders, trefoils, cufflinks and symmetric and asymmetric polylobates. It is also within the scope of the present invention that extrudates can be formed to any desired shape, such as spheres, by marumerization or any other form known in the art. An alternative form of the composite material is a continuous manufacturing sphere by the oil drip method already known. The preparation of spheres bonded with alumina generally involves placing a mixture of molecular filter, alumina sol and gelling agent in an oil bath maintained at elevated temperatures. Alternatively, the gelation of a silica hydrosol can be effected using the oil drip method. A method for gelling this mixture involves combining a gelling agent with a mixture, and then dispersing the resulting combined mixture in a bath or oil tower heated at elevated temperatures until the gelation occurs, with the consequent formation of spheroidal particles. The gelling agents which can be used in this process are hexamethylene tetraamine, urea or mixtures thereof. The gelling agents release ammonia at elevated temperatures, which fixes or converts the hydrosol spheres into hydrogel spheres. The spheres of the oil bath are then continuously extracted, and typically subjected to specific oil curing treatments and an ammonia solution, to improve their physical characteristics. Preferably, the resulting compounds are then washed and dried at a relatively low temperature of between 50 and 200 ° C, and subjected to a calcination procedure at a temperature of between 450 and 700 ° C for a period of 1 to 20 hours. . The catalysts of the present invention also comprise a metal of the platinum group, including one or more of platinum, palladium, rhodium, ruthenium, osmium and iridium. The preferred metal of the platinum group is platinum. The metal component of the platinum group may exist in the final catalyst compound as a compound such as oxide, sulfide, halide, oxysulfide, etc., or as the elemental metal or in combination with one or more ingredients of the catalyst compound. It is thought that the best results are obtained when essentially all the metal component of the platinum group exists in reduced state. This component may be present in the final catalyst compound in any amount that is catalytically effective; the metal of the platinum group generally comprises from 0.1 to 2% of the weight of the final catalyst, calculated with an elemental base. Excellent results are obtained when the catalyst contains from 0.05 to 1% of the weight of the platinum. The metal component of the platinum group can be incorporated into the catalyst composite in any suitable manner. A method for preparing the catalyst involves the use of a water-soluble and unfolding compound of a metal of the platinum group, to impregnate the calcined filter / binder composite material. Alternatively, a metal compound of the platinum group can be added at the time of making the filter / binder composite. Metal complexes of platinum groups can be used to impregnate solutions, co-extruded with the filter and binder, or chloroplatinic acid, chloropalladic acid, ammonia chloroplatinate, bromoplatinic acid, platinum trichloride, hydrated platinum tetrachloride, platinum dichlorocarbonyl, tetramine tetramine chloride, dinitrodiamino platinum, sodium (II) tetranitroplatinate, palladium chloride, palladium nitrate, palladium sulfate, diaminopalladium (II) hydroxide, tetraminepalladium (II) chloride, and the like.

Another essential ingredient of the catalyst of the present invention is a metal component of the IVA group (IUPAC 14). Of the metals of the IVA group (IUPAC 14), tin and germanium, and especially tin, are preferred. This component can be present as elemental metal, as a guimic compound such as oxide, sulfide, halide, oxychloride, etc., or as a physical or guímica combination, with the porous carrier material and other components of the catalyst. Preferably, there is a substantial portion of the group IVA metal (IUPAC 14) in the finished catalyst, in a state of oxidation higher than that of the elemental metal. The metallic component of the IVA group (IUPAC 14) is optimally used in sufficient quantity to produce a final catalyst containing 0.01 to 5% of the weight of metal, calculated on elemental basis, and the best results are obtained at a level between 0.1 and 2% of the weight of metal. Another essential ingredient of the catalyst of the present invention is a metallic component of the VAT group (IUPAC 14). Of the metals of the IVA group (IUPAC 14), germanium and tin are preferred, and tin is especially preferred. This component can be present as an elemental metal, as a gum compound such as oxide, sulfide, halide, oxychloride, etc., or as a physical or guímica combination with the porous carrier material and other components of the catalyst. Preferably, a substantial portion of the group IVA metal (IUPAC 14) exists in the finished catalyst in an oxidation state above the elemental metal. The metal component of the IVA group (IUPAC 14) is optionally used in an amount sufficient to produce a final catalyst containing 0.01 to 5% of the weight of metal, calculated on an elemental basis, where the best results are obtained at a level of between 0.1 and 2% of the weight of the metal. The component of the IVA group (IUPAC 14) can be incorporated into the catalyst metal in any suitable way to obtain a homogeneous dispersion, such as co-precipitation with the porous carrier material, exchange of ions with the carrier material or by impregnation of the carrier material. any stage of preparation. A method of incorporating the metal component of the VAT group (IUPAC 14) to the catalyst composite material involves the use of a soluble and unfolding compound of a metal of the IVA group (IUPAC 14), to impregnate and disperse the metal throughout the porous carrier material. The metal component of the IVA group (IUPAC 14) can be impregnated before, simultaneously with, or after adding the other components to the carrier material. Accordingly, the metal component of the IVA group (IUPAC 14) can be added to the carrier material by mixing the latter in an aqueous solution of suitable metal salt or soluble compound such as tin bromide, tin chloride, stannic chloride, stannic chloride pentahydrate, germanium oxide, germanium tetrachloride; or lead nitrate, lead acetate, lead chlorate and similar compounds. The use of chlorinated metal compounds of the group IVA (IUPAC 14) such as tin chloride, germanium tetrachloride or lead chlorate is particularly preferable, since it facilitates the incorporation of the metal component, and at least a minor amount of the preferred halogen component in one step When combined with hydrogen chloride during the alumina peptization step, especially preferred as described above, a homogeneous dispersion of the metal component of the IVA group (IUPAC 14) according to the present invention is obtained. In an alternative method, organic metal compounds such as trimethyltin chloride, and dimethyltin bichloride are incorporated into the catalyst during peptization of the inorganic oxide binder, and more preferably during the peptization of alumina with hydrogen chloride or nitric acid. It is within the scope of the present invention that the catalyst compounds may also contain other traditional metal components. These metal modifiers may include rhenium, cobalt, niguel, indium, gallium, zinc, uranium, dysprosium, thallium and mixtures thereof. Catalytically effective amounts of these metal modifiers can be integrated into the catalysts by any means known in the art, to effect a homogeneous or stratified distribution. The catalysts of the present invention may contain a halogen component, which comprises fluorine, chlorine, bromine or iodine, or mixtures thereof, where chlorine is especially preferred. However, preferably the catalyst does not contain added halogens in addition to those associated with other catalyst components. The catalyst compound is dried at a temperature of between 1000 and 320 ° C for a period of between 2 and 24 hours or more and, generally, is calcined at a temperature between 400 and 600 ° C in an air atmosphere, during a period of time. period between 0.1 and 10 hours until the metal compounds present are converted essentially to the oxidized form. If desired, the optional halogen component can be adjusted by including in the air atmosphere a halogen or halogen-containing compound. Optimally, the resulting calcined compounds are subjected to a reduction step essentially without water, to ensure uniform and finely divided dispersion of the optional metal components. Optionally, reduction can be effected in the process form of the present invention. Preferably, essentially pure and dry hydrogen (ie, less than 20 vol ppm H20) is used as the reducing agent in this step. The reducing agent is contacted with the catalyst at conditions which include a temperature of between 200 and 650 ° C for a period of between 0.5 and 10 hours, effective to reduce essentially all the metal component of group VIII to the metallic state. In some cases, the resulting reduced catalyst compound can also be beneficially subjected to presulfurization by a method known in the art, such as with clean H2S at room temperature, to be incorporated into the catalyst composite with 0.05 to 1.0% of the weight of sulfur, calculated on the basis of elementary. EXAMPLES The following examples are presented only to illustrate certain specific aspects of the present invention, and should not be construed as limiting the scope of the present invention as set forth in the claims. Within the spirit of the present invention there are many other possible variations, as will be recognized by those skilled in the art. Example I Samples of catalysts comprising zeolites were prepared for a comparative pilot plant test. First a catalyst A was prepared to represent a catalyst of the prior art, to be used in a process of isomerization of ethylbenzene to para-xylene with minimal benzene formation. Catalyst A contained silicoaluminophosphate SM-3 prepared in accordance with the disclosures of U.S. Pat. 4,943,424, and had characteristics as disclosed in the "424 patent. Following the disclosures of US Patent 5,898,090, catalyst A was mixed with alumina and tetramine tetramine chloride at a platinum level of 0.4% by weight in elemental base The composite material comprised 60% by weight of SM-3 and 40% by weight of alumina, and when the catalyst was calcined and reduced, the product was set as catalyst A. Example II Catalysts containing zeolite were prepared MTW type prepared in accordance with US patent 4,452,769, but achieving various amounts of mordenite impurities.Add to a solution of 0. 4 grams of sodium hydroxide in 9 grams of distilled water 0.078 g of aluminum hydroxide hydrated, and stirred until dissolved.A second solution of 1.96 grams of methyltriethylammonium halide (MTEA-C1) was prepared.; note that the chlorinated form was used instead of the bromide form) in 9 grams of distilled water, and stirred until dissolved. Then both solutions were agitated together until homogenized. Then 3 grams of precipitated silica were added, and then stirred for one hour at room temperature and sealed in a Teflon-coated autoclave for 8 days at 150 ° C. MTW type zeolite was recovered after cooling, filtering and washing with distilled water. After drying, a product of 5Na20 was obtained: 1.25Al203: 50Si02: 1000H20: 10 (MTEA-Cl) with a BET 454 m2 / g. X-ray diffraction analysis indicated that the product was 100% by weight of MTW type zeolite. To form the catalyst b, a composite material of 10% by weight with 90% by weight of alumina was prepared to form catalyst particles in an extruded form. The particles were then impregnated with metal using a chloroplatinic acid solution. Upon completion of the impregnation, the catalyst was dried, oxidized, reduced and sulfided to produce a catalyst containing 0.3% by weight of platinum and 0.1% by weight of sulfur. The finished catalyst was etched as catalyst B. Example III The isomerization of ethylbenzene to para-xylene from catalysts A and B was evaluated, using a pilot plant flow reactor which processed an aromatic mixture Cs out of equilibrium with the following appropriate composition in% of weight: Toluene 0.2 Non-aromatic C8 8.3 Ethylbenzene 26.8 Para-xylene 0.9 Meta-xylene 42.4 Ortho-xylene 21.0 Cg + non-aromatic 0.4 This mixture was placed in contact with a catalyst at a pressure of 620 kPa, an hourly hourly speed 3, and a hgen / hcarbon molar ratio of 4. The reactor temperature was adjusted to effect a favorable conversion level. The conversion is expressed as the disappearance per step of ethylbenzene, and the loss of C8 aromatic rings is mainly due to benzene and toluene, and smaller amounts of light gases are produced. The results were the following: Catalyst A B Temperature C 386 371 p-xylene / xylenes 22. 5 22. 3 Conversion EB,% of weight 31 38 Benzene yield,% of weight 0. 25 0. 10 Loss of rings C8 2. 5 2. Accordingly, catalyst B showed a better conversion of ethylbenzene, reducing the production of undesirable benzene compared to catalyst A of the prior art. Note that the "loss of C8 ring" is in molar percentage defined as "(1-naphthene C8 and aromatics in the product) / (naphthene Cs and aromatics in the feed)) * 100", which represent material to be circulated to another unit in a complex of aromatics. This circulation is expensive, and a low amount of C8 ring loss is a favorable feature of the catalyst of the present invention. Example IV Similarly, additional batches of MTW type zeolite were prepared according to the procedure described in Example II above. However, due to variations in the agitated and crystal nuclei, as well as other inhomogeneous effects in the containers used, it was found that the resulting iotes had different amounts of impurities with a ratio of silica to alumina of 34. It was determined The impurities were from the mordenite type zeolite using X-ray diffraction methods. To understand the effect of the impurity, several samples were obtained and catalysts were formed with them. Catalyst C was prepared with the same material as catalyst B, with 100% by weight of MTW. Catalyst D was prepared with a zeolitic composite comprising 90% by weight of MTW and 10% by weight of mordenite. Catalyst E was prepared with a zeolitic composite comprising 80% by weight of MTW and 20% by weight of mordenite. Finally, catalyst F was prepared with a zeolitic composite comprising 50% by weight of MTW and 50% by weight of mordenite to illustrate a catalyst with substantial mordenite impurities and therefore was not considered as a catalyst within the scope of the present invention. With the catalysts C to F, extruded particles were formed using 5% of the weight of the zeolitic composite above., 95% by weight of alumina binder. The particles were then impregnated with metal using a solution of chloroplatinic acid. Upon completion of the impregnation, the catalysts were dried, oxidized, reduced and sulphided to produce catalysts containing 0.3% by weight of platinum and 0.1% by weight of sulfur. The finished catalysts were respectively ethylated as catalysts C to F. Example V The loss of C8 aromatic rings from catalysts C to F was evaluated using a pilot plant flow reactor, which processed a Cs aromatic feed out of equilibrium, with the following approximate composition in% weight: Non-aromatic C8 7 Ethylbenzene 16 Para-xylene <; 1 Meta-xylene 52 Ortho-xylene 25 This feed was contacted with a catalyst at a pressure of 620 kPa, an hourly space velocity of 4, and a hydrogen / hydrocarbon molar ratio of 4. The temperature of the catalyst was adjusted. reactor at between 370 and 375 ° C to effect a favorable conversion level of ethylbenzene. The results were the following: Catalyst C D E F p-xylene / xylenes 22.3 22.3 22.3 22.3 Loss of ring C8 2.6 3.3 3.6 5.4 Accordingly, catalyst C showed minimal ring loss, and catalysts D to F illustrate that ring loss in molar percentage increased with the level of mordenite impurities. This circulation is expensive, and a low ring loss Cs is a favorable feature of the catalysts of the present invention which contain a MTW type zeolite essentially free of mordenite impurities. Example VI Catalyst G was prepared to illustrate a bimetal catalyst of the present invention. Catalyst G was prepared with the same zeolitic material as catalyst B, 100% by weight of MTW type zeolite, and formed into extruded particles using 5% by weight of zeolitic material and 95% by weight of alumina binder. The particles were then impregnated with metal using a first aqueous solution of tin chloride in an impregnation vessel by evaporation and cold rolling for one hour, and then steam dried. The base impregnated with tin was calcined at 550 ° C in air for 2 hours. Then a second aqueous impregnation of platinum was made with chloroplatinic acid, and similarly cold rolled for one hour and steam dried. The catalyst was then oxidized and reduced to produce a finished catalyst containing 0.3% by weight of platinum 0.1% by weight of tin, which was labeled as catalyst G. Example VII The isomerization stability of ethylbenzene was evaluated. to para-xylene of catalysts B and G, using a pilot plant flow reactor which processed an aromatic mixture Cs out of equilibrium with the same approximate composition as Example III above. This feed was contacted with a catalyst at a pressure of 690 kPa, a weighted hourly space velocity of 9.5, and a hydrogen / hydrocarbon molar ratio of 4. The reactor temperature was set at 385 ° C, and the conversion will decline over time. The results showed that catalyst G had an initial conversion of less than 5% by weight of ethylbenzene compared to catalyst B, but catalyst G had a deactivation rate of only two thirds of catalyst B. The rate of deactivation based on the ethylbenzene conversion decline index, with respect to the time under the test conditions described above. When a second comparative test was performed at the same conditions described above, except that a weighted hourly space velocity of 3 was used, the conversion of ethylbenzene from catalyst G exceeded the performance of catalyst B after 130 hours in the stream. Accordingly, catalyst G showed that superior stability, in terms of reduced deactivation, provides a long-term value for the isomerization of ethylbenzene to xylenes, and that higher yields occur when the conversion is averaged over a prolonged period. In addition, it should be noted that the performance of the catalyst in terms of loss of C8 ring was eguivalent between catalyst B and catalyst G.

Claims (9)

1. CLAIMS 1. A catalyst for the stable isomerization of ethylbenzene to xylenes, with minimal loss of C8 ring, where the catalyst comprises 0.1 to 2% by weight of a component of the platinum group calculated on elemental basis, 1 to 90% by weight of an MTW-type zeolite component essentially free of mordenite with a molar ratio of silica versus alumina of 45 or less, and an inorganic oxide binder component.
2. 2. The catalyst of claim 1, which further comprises 0.01 of 5% of the weight of a component of the IVA group (IUPAC 14), calculated on an elemental basis.
3. 3. The catalyst of claim 2, wherein the component of the IVA group (IUPAC 14) is tin.
4. 4. The catalyst of claims 1 or 2, which further comprise 0.05 of 1.0% of the weight of sulfur.
5. The catalyst of claims 1 or 2, wherein the MTW-type zeolite component is present in an amount of between 2% by weight to 20% by weight.
6. The catalyst of claims 1 or 2, wherein the MTW type zeolite component has a ratio of silica to alumina of between 20 and 40.
7. The catalyst of claims 1 or 2, wherein the binder component of inorganic oxide comprises one or more of alumina and silica.
8. 8. The catalyst of claims 1 or 2, wherein the MTW-type zeolite component comprises at most 20% of the weight of mordenite.
9. 9. A process for the isomerization of a feed mixture of xylenes and ethylbenzene, which comprises placing the feed mixture, in the presence of hydrogen in an isomerization zone in contact with the catalyst of claims 1 or 2 under isomerization conditions, which comprises a temperature of between 300 and 500 OC, a pressure of between 1 to 50 atmospheres, a liquid hourly space velocity between 0.5 and 10 hr "1 and a molar ratio of hydrogen against hydrocarbons of between 0.5: 1 and 25: 1 , to obtain an isomerized product comprising a greater proportion of xylenes than in the feed mixture, with a loss of C8 aromatic rings with respect to the feed mixture of not more than 4 mol%.