JP2006513252A - Process for activation of alkylated aromatic isomerization catalysts with water - Google Patents

Abstract

An improved process for ethylbenzene and xylene isomerization in an unbalanced mixture of xylene and ethylbenzene is disclosed. By adding a trace amount of water to the reaction zone, equilibrium isomerization could be achieved at lower temperatures, where the benefits of reduced losses and improved catalyst life could be realized.

Description

  The present invention relates to a process for the isomerization of alkylated aromatic compounds, and in particular to an improved process for the isomerization of ethylbenzene and xylene in an unbalanced mixture of xylene and ethylbenzene.

  Xylenes, i.e. para-xylene, meta-xylene and ortho-xylene are important intermediate products that provide a wide variety of uses in chemical synthesis. When paraxylene is oxidized, it produces terephthalic acid which is used in the production of synthetic textile fibers. Metaxylene is used in plasticizers, azo dyes, wood preservatives and the like. Ortho-xylene is a feedstock for producing phthalic anhydride.

Xylene isomers from catalytic reforming and other sources generally contain ethylbenzene which is not commensurate with the demand ratio as a chemical intermediate and is difficult to separate or convert. The amount of para-xylene is only 20-25% of the typical C ₈ aromatics stream. By combining xylene recovery and isomerization, such as adsorption for para-xylene recovery, additional amounts of the desired isomer can be adjusted. Isomerization converts a non-equilibrium mixture of xylene isomers lacking the desired components into a mixture close to the equilibrium concentration.

Further approaches how to balance C ₈ aromatic isomers in an isomerization process, C ₈ aromatics is related to more loss to other hydrocarbons. By approaching equilibrium, the amount of reuse for paraxylene recovery is minimized, thus reducing investment and equipment operating costs. Less loss of C ₈ aromatics reduces the required feedstock and increases the proportion of higher value products. The ability of the isomerization process is determined primarily by interaction of conversion C ₈ aromatics losses and catalyst stability. In general, the higher the temperature, the greater the loss to by-products and the faster the catalyst deactivation, so the operating temperature required to achieve a given conversion is an indicator of such capability.

Ethylbenzene does not readily isomerize to xylene, but separation from xylene by hyperfractionation or adsorption is extremely expensive and usually ethylbenzene must be reacted. The modern method for isomerization of C ₈ aromatics involves the reaction of ethylbenzene with hydrogenation / dehydrogenation in the presence of a solid acid catalyst to hydrogenate the naphthene intermediate, followed by dehydrogenation. For example, a method of forming a xylene mixture. Another method is to convert ethylbenzene via dealkylation to form primarily benzene, while isomerizing xylene to an approximate equilibrium mixture. The former method increases the yield of xylene by forming xylene from ethylbenzene, while the latter method typically results in higher ethylbenzene conversion, thus reducing the amount recycled to the paraxylene recovery unit. Concomitantly reduce processing costs. The latter method also produces a high quality benzene product.

  In the isomerization technology for the combination scheme, where the isomerization process is disclosed in the context of product recovery technology, there is a strong suggestion that the isomerization feed is in the dry state. U.S. Pat. No. 3,856,872, U.S. Pat. No. 4,218,573 and ref. 31,782 disclose various flow schemes such as a crystallizer that provides a feed to the isomerization process. It is well known in the art that crystallizers that recover para-xylene must be dry operation and, therefore, the raffinate from the crystallizer to the isomerization process is in the dry state. U.S. Pat. No. 4,584,423 discloses pre-fractionation and crystallization prior to isomerization, and either process will remove moisture from the isomerization feed.

  In contrast, US Pat. No. 4,300,013 discloses the addition of large amounts of water (0.05-1.0% by weight) in an alkylbenzene isomerization process based on zeolite FU-1. US Pat. No. 4,723,050 also discloses that steam supplies a large amount of water (0.1-10 wt%) to the isomerization process based on the idea of reducing the catalyst coking by sulfur.

  British Patent 1,255,259 discloses the addition of water vapor in the range of 100 to 1500 ppm to the xylene isomerization process. Hart et al. Disclose the isomerization of ethylbenzene to xylene via naphthene using a catalyst based on an acid refractory oxide containing a mixture of silica and alumina. It also discloses the use of zeolitic aluminosilicates such as faujasite (FAU).

  German Patent DD-219,183 (Doms et al.) Discloses contacting a catalyst based on mordenite (MOR) with NH3, where 500 to 800 ppm from the beginning of the reaction run to 300 hours. The selectivity of ethylbenzene isomerization is improved by adding a small amount of water and then reducing the water content to the range of 10 to 50 ppm.

  Other disclosures of this technology include US Pat. No. 3,381,048 and US Pat. No. 3,898,297, both of which are based on an amorphous catalyst system. Lovell et al., A platinum-alumina-halogen catalyst system with controlled process conditions such that the water content is about 20 to 200 ppm by weight during the reaction and 0.3 to 2.0% by weight wet during regeneration. Discloses a xylene isomerization process. Sampson et al. Optionally alkylbenzene isomers based on amorphous alumina or fluorinated variants of silica / alumina containing alkali or alkaline earth metals in the presence of water vapor in the range of 0.005 to 1.0 wt%. Disclosure process.

U.S. Patent No. 4,431,857, the use of crystalline borosilicate impregnated molybdenum (AMS-1B), and use of the addition of favors water A ₁₀ formed via a disproportionation method is disclosed Has been.

  US Pat. No. 5,773,679 describes the co-feeding of water during the initial operation of a selected ZSM-type zeolite for hydrocarbon conversion, and silicon treated ZSM specifically for toluene disproportionation. -5 is disclosed. The effect of this zeolite treatment is to increase the para-selectivity of the catalyst by reducing the yield of xylene, so that the total amount of xylene is higher than the para isomer so that the relative proportion of para-xylene is increased. The reduced and resulting balance indicates an increase in benzene yield. No effect on ethylbenzene conversion is shown.

  In order to improve or reactivate the catalyst performance while maintaining the presence of hydrocarbon feedstock in the system, a small amount of water injection is performed between the alkylated aromatic compound isomerization conditions on the non-zeolite molecular sieve containing the catalyst. The prior art does not suggest anything to use. Further, the use of selected pentasil-type zeolitic aluminosilicates that are not silicon-selective and contain a catalyst that promotes the advantageous ethylbenzene conversion by continuous or intermittent water injection. The need for improvement is also addressed in the present invention.

Summary of the Invention

  In summary, one object of the present invention is to provide an improved process for xylene isomerization and ethylbenzene conversion.

The present invention provides a surprising improvement in ethylbenzene conversion and paraxylene yield at a given reactor temperature when a small amount of water or water-generating compound is injected into the reactor zone of a C ₈ aromatics isomerization process. It is based on the discovery that it will be brought together with the improvement of computerization.

One broad embodiment of the present invention is a process for the upgrading of unbalanced C ₈ aromatics feed mixture, where, increases the isomerization and conversion of ethylbenzene and xylene in a given reactor temperature For this purpose, water or a water-forming compound is fed continuously or intermittently to a reaction zone containing a catalyst composed of either a non-zeolitic molecular sieve or a pentasil-type zeolitic aluminosilicate.

  In one particular embodiment, the catalyst is further comprised of at least one platinum group metal component and an inorganic oxide binder. The equivalent of water fed to the reaction zone corresponds to 75 to 750 ppm by weight, or preferably 100 to 500 ppm by weight.

The feedstock to the process is composed of alkylated aromatic hydrocarbons represented by the general formula C ₆ H _(6-n) R _n , where n is an integer from 2 to 5 and R is CH ₃ , Any combination of C ₂ H ₅ , C ₃ H ₇ , or C ₄ H ₉ and any isomers thereof. Preferred isomerizable alkylated aromatic hydrocarbons include xylene isomers mixed with ethylbenzene as a non-equilibrium mixture.

This process achieves the conversion of C ₂ H ₅ , C ₃ H ₇ and higher R groups on the aromatic ring via dealkylation in conjunction with isomerization of the methyl side chain on the aromatic ring. Approaching the approximate equilibrium isomer distribution in aromatic products from the process.

The alkylated aromatic hydrocarbon feedstock can be recovered from the catalyst reformate, for example, by fractional distillation or solvent extraction, as seen in selected fractions from various refined petroleum streams, or mainly light olefins. It can be used as a by-product from the pyrolysis of petroleum distillates to obtain, or it can be recovered from the pyrolysis of heavy oil fractions mainly into gasoline products. Particularly preferred feedstocks, the recovery of one or more useful C ₈ aromatic isomers, for example, in the raffinate after performing the recovery of o-xylene by recovering and / or fractionation of para-xylene by adsorption or crystallization . Typically, the feedstock is substantially free of sulfur and generally contains less than 1 ppm by weight of sulfur by prior catalyst treatment. The isomerizable aromatic hydrocarbons converted in the process of the present invention need not be concentrated. By increasing the yield of useful petrochemical intermediates from streams that otherwise have value as fuel, the profitability of such petrochemical operations can be increased.

  According to the process of the present invention, an alkylated aromatic hydrocarbon feed, preferably mixed with hydrogen, is contacted in a reaction zone with a catalyst of the type described below. Contact can be achieved using the catalyst in a fixed bed system, moving bed system, fluidized bed system or batch operation. Considering the risk of depletion of useful catalyst and operational advantages, it is preferable to use a fixed bed system. In this system, the hydrogen-rich gas and feed are preheated to the desired reaction temperature by suitable heating means, and then the mixed reactants are sent to a reaction zone containing a fixed bed of catalyst. Send it in. The reaction zone is one or more individual reactors, with appropriate means between the reactors to ensure that the desired isomerization temperature is maintained at the inlet of each reactor. The reactant is brought into contact with the catalyst either upwardly, downwardly or in a radial flow manner, and when the reactant is brought into contact with the catalyst, any of a liquid layer, a liquid-gas mixed phase, or a gas phase is brought about. But you can.

The operating conditions of the reaction zone include a temperature ranging from 0 ° C. to 600 ° C. and a pressure from atmospheric pressure to 5 MPa. Preferably, a temperature range of 300 ° C. to 500 ° C. and a pressure range of 1 to 50 atmospheres are used. The liquid hourly space velocity of the feed relative to the catalyst volume is from 0.1 to 30 hours- ¹ , most preferably from 0.5 to 15 hours- ¹ . The hydrocarbon is preferably mixed with a stream containing hydrogen gas and fed into the reaction zone at a molar ratio of hydrogen to hydrocarbon of from 0.5: 1 to 15: 1 or more, preferably from 0.5 to 10. Other inert diluents such as nitrogen, argon, methane, ethane may be present.

  It is a very important aspect of the present invention that a trace amount of water is fed into the reaction zone of the process. A trace amount is generally an amount that does not exceed the saturated water of the alkylated aromatic feedstock, usually up to 750 ppm by weight (parts per million) relative to the alkylated aromatic hydrocarbon, If this level is exceeded, water is thought to affect the hydrothermal stability of the molecular sieve catalyst. At least 75 ppm by weight of water must be supplied to significantly affect the above process, and the most effective range of traces is 100 to 500 ppm by weight for alkylated aromatic hydrocarbons . The water can be injected into the alkylated aromatic feed or mixed reactant to the reaction zone. Alternatively, the water may be supplied as water vapor in a stream containing hydrogen.

  As will be apparent to those skilled in the art, in addition to water itself, other compounds can be injected into a location that effectively forms water when such compounds are fed into the reaction zone. While not intending to limit the invention, examples of water source compounds that form water during the reaction include alcohols, ethers, esters and the like. One preferred water source compound is methanol.

  The water source is continuously fed at the typical operating conditions of the reaction zone. Alternatively, the water supply source is supplied intermittently. The water source is stopped or provided in various amounts depending on the capacity required from the reaction zone catalyst system. One measure of catalytic capacity is the weighted average bed temperature (WABT). If the catalyst acts to achieve a certain conversion of ethylbenzene, it will gradually deactivate as a result, requiring adjustment of WABT for complementation. If the WABT becomes too high, it may begin to become a limited control variable based on equipment constraints such as heater load. Thus, by intermittently supplying water within the range provided herein above, additional WABT operation margins are possible and the operating cycle of the reactor with temperature constraints is improved. Depending on the nature of the feed mixture and the type and conditions of the catalyst, the amount and effect of trace amounts of water will vary. The water received from the feed source and already present in the feed will also require periodic adjustments in the amount of additional trace water supplied to the reaction zone.

The specific product recovery procedure used is not considered critical to the present invention. Any recovery procedure known in the art can be used. Typically, the reactor process liquid is concentrated with hydrogen and light hydrocarbon components removed therefrom by flash separation. The concentrated liquid product is then subjected to fractional distillation treatment to further purify the desired liquid product. Useful high purity benzene can be recovered from the light liquid product. In some instances, it may be desirable to recover certain product species such as orthoxylene by more stringent fractionation. In most instances, the liquid C ₈ aromatic product is subjected to processing and the paraxylene isomer is selectively recovered. The recovery of para-xylene can be carried out by crystallization methods or most preferably by selective adsorption using crystalline aluminosilicates. The raffinate remaining after recovery of the desired xylene isomer can be returned to the isomerization reactor section.

One component of the catalyst according to the present invention, usually labeled “NZMS”, is an aluminum (AlO ₂ ) and phosphorus (PO ₂ ) form of aluminophosphate as disclosed in US Pat. No. 4,310,440. It is at least one non-zeolite molecular sieve as defined in the present invention as including a molecular sieve containing framework tetrahedral units (TO ₂ ) and the like. “NZMS” also includes a molecular sieve containing at least one additional element (EL) as a framework tetrahedral unit (ELO ₂ ). NZMS includes SAPO molecular sieve according to U.S. Pat.No. 4,440,871, ELAPSO molecular sieve as disclosed in U.S. Pat.No. 4,793,984, and MeAPO, FAPO as described below. ”,“ TAPO ”, and“ MAPO ”molecular sieves. Crystalline metal aluminophosphates (MeAPO where “Me” is at least one of Mg, Mn, Co and Zn) are disclosed in US Pat. No. 4,567,029, where crystalline ferroaluminophosphates ( FAPO) is disclosed in US Pat. No. 4,554,143, and titanium aluminophosphate (TAPO) is disclosed in US Pat. No. 4,500,651. MAPO metal aluminophosphates where M is As, Be, B, Cr, Ga, Ge, Li or V are disclosed in U.S. Pat.No. 4,686,093, and bimetallic aluminophosphates are disclosed in Canadian Patent No. This is disclosed in US Pat. No. 1,241,943. ELAPSO molecular sieves are also GaAPSO as disclosed in US Pat. No. 4,735,806, BeAPSO as disclosed in US Pat. No. 4,737,353, as disclosed in US Pat. No. 4,738,837. CrAPSO, CoAPSO as disclosed in US Pat. No. 4,744,970, MgAPSO as disclosed in US Pat. No. 4,758,419, and as disclosed in US Pat. No. 4,793,833 Although disclosed in patents in which such species are described, such as MnAPSO, it is not so limited. One type of specific member is commonly referred to as the “-n” species, where “n” is an integer, such as SAPO-11, MeAPO-11, and ELAPSO-31. Preferred oval hole crystalline non-zeolitic molecular sieves, "Atlas of Zeolite Structure Types" (Butterworth-Heineman, Boston, Mass., 3 rd ed. 1992) according to one or more of AEL framework types, especially SAPO-11 Or one or more ATO framework types, in particular MAPSO-31.

  In the following discussion of preferred NZMS, the NZMS mole fraction is defined as the composition value plotted in the respective phase diagram of the referenced patent or published application.

Silico-aluminophosphate molecular sieve SAPO-11 is particularly preferred, with maximum and minimum crystal free diameters of 6.3 and 3.9 mm, respectively, resulting in a maximum / minimum ratio of 1.6+. The silico-aluminophosphate molecular sieve is disclosed as a microporous crystalline silico-aluminophosphate, having a three-dimensional microporous framework structure of tetrahedral units of PO ₂ ⁺ , AlO ₂ ⁻ and SiO ₂ , And its essential experimental chemical formula on an anhydrous basis is:
_{mR: (Si x Al y P} z) O 2
And a, wherein "R" represents at least one organic templating agent present in the intracrystalline pore system: "m" are present in the per mole _{(Si x Al y P z)} O 2 Represents the mole of “R”, with values from 0.02 to 0.3: “x”, “y” and “z” represent the mole fraction of silicon, aluminum and phosphorus present in the oxide fraction, respectively. And the molar fraction is the same as that of FIG. 1 disclosed in US Pat. No. 4,470,871, and represents the following values for “x”, “y”, and “z” on a three-dimensional diagram: It is in a composition region surrounded by points A, B, C, D and E.

  Silicoaluminosilicate is commonly referred to herein as “SAPO” or “SAPO-n”, where “n” refers to SAPO-11, SAPO-31, SAPO-40 and SAPO-41. It is an integer that indicates a specific SAPO.

A preferred SAPO-11 for use in the present invention is concentrated silica SAPO-11, designated SM-3, prepared according to the teachings of US Pat. No. 5,158,665. SM-3 is silicoaluminophosphates molar ratio of P ₂ O ₅ to alumina in silicate surface 0.80 or less, preferably from 0.80 to 0.55; the molar ratio of P ₂ O ₅ to alumina in the SAPO a mass is 0.96 or more , Preferably 0.96 to 1.0; and the silica to alumina molar ratio at the surface is greater than in the bulk SAPO. Preferably, SM-3 has a composition in the form of a molar ratio of oxides on an anhydrous basis:
mR: Al ₂ O ₃ : nP ₂ O ₅ : qSiO ₂
Where “R” represents at least one organic templating agent present in the intracrystalline pore system: “m” represents the moles of “R” present and “R” per mole of alumina. Has a value such that n is present from 0.02 to 2 moles: n has a value from 0.96 to 1.1, preferably from 0.96 to 1; and q is from 0.1 to 4, preferably from 0.1 to 1 Has the value of US Pat. No. 4,943,424 (Miller) is also incorporated herein by reference for its teachings on the preparation and properties of preferred SM-3.

Another preferred crystalline non-zeolite molecular sieve is one or more ATO framework types according to “Atlas of Zeolite Structure Types”. The MgAPSO-31 molecular sieve disclosed in US Pat. No. 4,758,419 having a crystal free diameter of 5.4 mm is particularly preferred. MgAPSO molecular sieve has a framework structure of MgO ₂ ⁻² , AlO ₂ ⁻ , PO ₂ ⁺ and SiO ₂ tetrahedral units, and an experimental chemical formula on an anhydrous basis:
mR: (Mg _w Al _x P _y Si _z ) O ₂
Where “R” represents at least one organic templating agent present in the intracrystalline pore system: “m” per mole (Mg _w Al _x P _y Si _z ) O ₂ Represents the molar amount of “R” present and has a value from 0 to 0.3; and “w”, “x”, “y” and “z” are the elements present as tetrahedral oxides, respectively. Represents the molar fraction of magnesium, aluminum, phosphorus and silicon. The molar fractions “w”, “x”, “y” and “z” are generally defined as having limited composition values or within the following points.

  The MgAPSO-31 molecular sieve preferably has a framework magnesium content of 0.003 to 0.035 mole fraction consistent with the teachings of US Pat. No. 5,240,891.

As already mentioned, the present invention describes a process used for the isomerization of C ₈ aromatics composed of non-zeolitic molecular sieves or zeolitic aluminosilicate catalysts. Although preferred NZMS catalyst embodiments have been described above, a description of another pentasil-type zeolitic aluminosilicate catalyst embodiment is as follows. One component of this catalyst according to the invention is preferably composed of at least one pentasil-type zeolitic aluminosilicate mesoporous molecular sieve. The term “intermediate pore” is intermediate between what is recognized in the art as “large pores” and “small pores” and is determined by standard weight adsorption techniques in the technical field of crystalline molecular sieves referenced. This is the size of the hole, published in “New Developments in Zeolite Science and Technology” Proceedings of the 7th International Zeolite Conference, edited by Y. Murakami, A. Iijima and JW Ward, pages 103-112 (1986). See also “Aluminophosphate Molecular Sieves and the Periodic Table” by Flanigen et al. Mesoporous crystalline molecular sieves have a pore size between 0.4 nm and 0.8 nm, in particular 0.6 nm. For the purposes of the present invention, a crystalline molecular sieve having a pore between 5 and 6.5 mm is defined as an “medium pore” molecular sieve.

  The term “pentacil” in the preferred pentasil-type zeolite component is used to represent one type of shape selective zeolite. This type of zeolite is generally characterized by a silicon / alumina molar ratio of at least 12. A description of pentasil can be found in US Pat. No. 4,159,282; US Pat. No. 4,163,018; and US Pat. No. 4,278,565. Among the pentasil-type zeolites, preferred are MFI, MEL, MTW, MTT and FER (IUPAC Commission on Zeolite Nomenclature), and MFI-type zeolite, often referred to as ZSM-5, is particularly preferred. It is one preferred embodiment of the present invention that the pentasil is in the form of hydrogen. Conversion of the alkali metal pentasil to the hydrogen form can be performed by treatment with an aqueous inorganic acid solution. Alternatively, hydrogen ions can be incorporated into pentasil by ion exchange with ammonium hydroxide and then calcined.

It is also within the scope of the present invention that the particular pentasil selected is gallosilicate. Gallosilicate has essentially the same structure as the preferred zeolite described above, except that in the aluminosilicate crystal framework all or part of the aluminum atoms are replaced by gallium atoms. The gallium content of this particular type of pentasil, expressed as the molar ratio of SiO ₂ to Ga ₂ O ₃ , ranges from 20: 1 to 400: 1 or more.

  Each of the non-zeolitic molecular sieve and the zeolitic aluminosilicate is preferably combined with a binder to conveniently form catalyst particles. The proportion of NZMS in the first catalyst is 5 to 90% by weight, preferably 10 to 80% by weight, with the remainder other than the metals and other components discussed here being the binder component. The proportion of zeolite in the second catalyst is in the range of 5 to 99% by weight, preferably 10 to 90% by weight.

  It is within the scope of the present invention that the catalyst composition can be combined with one or more NZMSs with each other or with a crystalline zeolitic aluminosilicate. Catalysts containing multiple non-zeolitic molecular sieves and zeolitic aluminosilicates can be placed into individual reactors, sequentially into the same reactor, physically mixed, or combined into the same particles .

The binder used in the present invention must be a porous, adsorptive, high surface area support having a surface area of 25 to 500 m ² / g. Examples of binder materials that can be used in dual function hydrocarbon conversion catalysts include: (1) silicon or silica gels, including artificially prepared and naturally occurring, silicon carbide, clay, and Silicates; they may or may not be acid treated, such as attapulgite, diatomaceous earth, fuller's earth, kaolin, porous diatomaceous earth: (2) Ceramics, porcelain, bauxite: (3) Alumina, titanium dioxide , Heat-resistant inorganic oxides such as zirconium oxide, chromium oxide, zinc oxide, magnesia, tria, boria, silica-alumina, silica-magnesia, chromia-alumina, alumina-boria, silica-zirconia, zirconia-alumina, and 4) A combination of one or more substances from one or more of these groups. A preferred binder is a refractory inorganic oxide such as a binder composed of alumina. The preferred alumina is crystalline alumina, known as gamma-, eta-, and theta-alumina, with a preferred shape being gamma-alumina. The alumina binder may contain other known heat resistant inorganic oxides such as silica, zirconia, magnesia, etc. in small proportions. Good results can be obtained with binders containing 90 to 99% by weight of alumina and 1 to 10% by weight of zirconia. A preferred binder or matrix component is a phosphorus-containing alumina component. The phosphorus can be incorporated by any acceptable method known in the art. U.S. Pat. No. 4,629,717 describes one method for preparing such alumina phosphate.

  Preferred alumina binders are uniform in composition. Prior to use, the alumina can be activated by one or more treatments such as drying, firing, steaming, etc., the alumina being activated alumina, industrial activated alumina, porous alumina, alumina gel, etc. It takes a well-known shape.

Another preferred binder takes the form of amorphous silica. Preferred amorphous silica is amorphous silica (silicon dioxide) powder, silicic acid, classified as synthetic, white, wet-process. Preferably, the silica has a BET surface area in the range of 120 to 160 m ² / g. It is particularly preferred that the non-acidic amorphous silica binder has, for example, a 5% suspension pH of 7 or higher.

  The catalyst according to the present invention can be compounded and molded into any useful shape such as spheres, pills, cakes, extrudates, powders, granules, tablets, etc., and can be used in any desired size. These shapes can be prepared by spray drying, tableting, spheronization, extrusion and nodulation. A preferable shape of the catalyst composite is an extruded product. The extruded product can be further shaped into any desired shape, such as a sphere.

  Another preferred form of the catalyst is a sphere, suitably produced by an oil droplet process that consists of forming a desired inorganic oxide binder hydrosol. The alumina hydrosol is preferably prepared by reacting aluminum metal with hydrochloric acid. Subsequently, the molecular sieve is uniformly dispersed in the hydrosol. The resulting zeolite-containing hydrosol is then mixed with a suitable gelling agent and dispersed as droplets in an oil bath maintained at an elevated temperature. The lead component can be added to the mixture before droplet formation and before, after or simultaneously with pentasil. The droplets of the mixture remain in the oil bath until the hydrogel spheres are trimmed and shaped.

  The zeolitic aluminosilicate catalyst is preferably subjected to steam treatment to adjust its acid activity. Steam treatment may be performed at any stage of the zeolite treatment, but is usually performed on the zeolite and binder composite prior to incorporation of the platinum group metal. Steam treatment conditions include water concentrations from 5 to 100% by volume, pressures from 100 kPa to 2 MPa, and temperatures between 600 ° C and 1200 ° C. The steaming should be performed for at least 1 hour, preferably 6 to 48 hours. Instead of, or in addition to, steaming, the composite can be washed with one or more of ammonium nitrate solution, inorganic acid and / or water.

  Another component of the present invention is one or more platinum group metals selected from platinum, palladium, rhodium, ruthenium, osmium and iridium. A preferred platinum group metal component is platinum, with palladium being the next preferred metal. The platinum group metal component is included in the final catalyst composite as a compound such as an oxide, sulfide, halide, sulfide, etc., or as an elemental metal, or in combination with one or more other inclusions of the catalyst. Can exist. Best results are believed to be obtained when substantially all of the platinum group metal component is present in the reduced state. The platinum group metal component is generally composed of 0.01 to 2% by mass of the final catalyst composite in terms of element base. More preferably, the catalyst contains 0.05 to 1% by weight of platinum.

  The platinum group metal component may be incorporated into the catalyst composite by any suitable method. One method of preparing the catalyst includes impregnating the calcined sieve / binder composite with a water-soluble decomposable composite of a platinum group metal. Alternatively, the platinum group metal composite may be added at the time of combining the sieve component and the binder. Platinum group metal composites used in impregnation solutions and coextruded with sieves or binders or added by other well known methods include chloroplatinic acid, chloropalladate, ammonium chloroplatinate, platinum bromide Acid, platinum trichloride, platinum hydroxide tetrachloride, platinum dichlorocarbonyl dichloride, tetraamine platinum chloride, dinitrodiamine platinum, sodium tetranitroplatinate (II), palladium chloride, palladium nitrate, palladium sulfate, diamine palladium hydroxide (II) And tetraamine palladium (II) chloride. Preferably, the platinum group metal component is concentrated in the binder component of the catalyst.

  The present catalyst composite may contain other known metal components in order to adjust the effect of the platinum group metal component. Such metal polymerization modifiers include rhenium, tin, germanium, lead, cobalt, nickel, indium, gallium, zinc, uranium, dysprosium, thallium, and mixtures thereof. A catalytically effective amount of such a metal polymerization modifier can be incorporated into the catalyst by any means well known in the art to achieve a homogeneous or layered distribution. The optional metal polymerization modifier group components are generally comprised of 0.01 to 5.0 wt% final catalyst composite.

  The catalyst according to the present invention may contain a halogen element component composed of any of fluorine, chlorine, bromine or iodine, or a mixture thereof, with chlorine being preferred. Preferably, however, the catalyst does not contain added halogens other than those associated with other catalyst components.

  The catalyst composite is dried at a temperature of 100 ° C. to 320 ° C. for 2 to 24 hours or longer and is usually present in an air atmosphere at a temperature of 400 ° C. to 650 ° C. for 0.1 to 10 hours. Baking until the metal component is substantially converted to the oxide form. Optional halogen component is prepared by including halogen or halogen-containing component in air atmosphere, and as a result, the final composite contains 0.1 to 2.0 mass% halogen in terms of element base become.

The resulting fired composite is preferably subjected to a reduction step that is substantially free of water, ensuring that the optional metal component is finely divided and uniformly dispersed. As an option, the reduction can be carried out in a process apparatus according to the invention. Substantially pure and dry hydrogen (ie, less than 20 ppm by volume of H ₂ O) is preferably used as the reducing agent in this step. The reducing agent is in contact with the catalyst at conditions such as a temperature from 200 ° C. to 650 ° C. and a time from 0.5 to 10 hours, which is effective to reduce substantially all Group VIII metal components to the metallic state. Be made. In some cases, the resulting reduced catalyst composite is suitably subjected to presulfidation, and 0.05 to 1.0 weight percent sulfur, converted on an element basis, can also be incorporated into the catalyst composite.

In order to illustrate the advantages of the present invention, catalyst (X) was prepared according to the procedure described above. MFI zeolite was added to the alumina sol solution and the metal aluminum was prepared by digestion with hydrochloric acid in an amount sufficient to yield a zeolite content of 11% by weight of the final catalyst. A second solution, hexamethylenetetramine (HMT), was prepared and added to the zeolite / alumina sol mixture to obtain a homogeneous mixture. The mixture was then dispersed as droplets in an oil bath maintained at 93 ° C. The droplet remained in the oil bath at 150 ° C until the hydrogel spheres were trimmed and shaped. The spheres were removed from the oil bath, washed with 0.5% ammonia / water solution, air dried and fired at 650 ° C. The fired spheres were then co-impregnated with platinum and lead using a solution of chloroplatinic acid, lead nitrate, and 2% by weight hydrochloric acid. The impregnated spheres were oxidized, conditioned at 525 ° C., subjected to a reducing atmosphere of H ₂ at 565 ° C. and sulfided with H ₂ S to produce 0.07 wt% sulfur on the catalyst. The final catalyst consisted essentially of 11% by weight MFI zeolite, 0.21% by weight platinum, 0.67% by weight lead, and 0.78% by weight chlorine, the remainder being an alumina binder.

The catalyst (X) of Example 1 was evaluated for upgrading C ₈ aromatics in an experimental plant. The feed composition was generally as follows in mass%.

The feed was prepared by diffusing in a rectifying column and storing under a dry (<1 ppm H ₂ O) nitrogen blanket. The operating conditions in the experimental plant were a temperature range of 390 ° C. to 450 ° C., a liquid hourly space velocity of 4 hours ⁻¹ , and a hydrogen gas to hydrocarbon feedstock molar ratio of 3 to 5. The pressure was 4 to 11 atmospheres (standard), limiting the formation of C ₈ naphthene as the temperature changed.

  The feedstock was processed at various pressures at various temperatures in the experimental plant as described. A temperature test on the fresh catalyst was performed on the dry feed with a gas to hydrocarbon ratio of 3 without adding water. The next low temperature test showed significant deactivation and the dry test was discontinued. A small amount of water was added to the reactor feed to determine the effect on catalytic performance. Initial tests and temperature tests showed that even a fresh catalyst improved the effect, and a stability test at 435 ° C. for 1 week confirmed the stability of the catalyst with the addition of trace water.

  The results of the temperature test and the individual data points are shown in FIGS. FIG. 1 is a plot of para-xylene product ratio and reaction temperature in total xylene. FIG. 2 shows ethylbenzene conversion as a function of reactor temperature.

  The deactivated catalytic capacity with the addition of trace amounts of water shows the significant advantages of dry operation, as well as fresh catalyst at higher temperatures. Comparing the dry experiment (dashed line between high temperature and low temperature for fresh catalyst) with the experiment based on the addition of water, the temperature required to achieve a given paraxylene yield by supplying a trace amount of water is On average, it decreased by 15-20 ° C, or the paraxylene content in xylene increased by nearly 3%. Ethylbenzene conversion increased by 8 to 20% at the same temperature.

  In order to illustrate the advantage of the present invention of intermittently supplying water, a second catalyst (Y) was prepared according to the procedure described above. SM-3 silicoaluminophosphate was prepared according to the teachings of US Pat. No. 4,943,424. The SM-3 was complexed with alumina and tetramine platinum chloride. The composite contained 60 wt% SM-3 and 40 wt% alumina. Tetramine platinum chloride was incorporated into the composite to achieve a platinum level of 0.28 wt% on an element basis and the catalyst was calcined and reduced.

The catalyst was tested in a flow reactor experiments plant processing non-equilibrium C ₈ aromatic feedstock mixture having the following approximate composition in mass%.

This feed was contacted with 100 cc of catalyst with a liquid hourly space velocity of 3.0 and a hydrogen / hydrocarbon molar ratio of 4 per hour. The reactor temperature was adjusted to maintain an advantageous conversion level. Conversion is expressed as the disappearance per pass of ethylbenzene. The loss of C ₈ aromatics is mainly due to benzene and toluene, and the smaller loss is due to the light gas produced. A feedstock initially containing a low water content of 25 ppm by weight is convenient for the first part of the experiment. Points 1a and 1b indicate a gradual decrease in catalytic ability. The moisture was then increased to 300 ppm by weight for the middle part of the experiment. Point 2 shows the effect of the addition of water on the catalytic performance. In the final part of the experiment, moisture returns to the initial level. Point 3 shows the regeneration of the catalyst and the return to the initial fresh catalytic capacity. The above results can be summarized as follows.

It is a figure which compares the product ratio of paraxylene in total xylene, and reaction temperature when ethylbenzene is converted together with isomerization of xylene with and without a small amount of water supplied to the reaction zone. . It is a figure which compares the ethylbenzene dealkylation as an effect | action of temperature, and shows the effect of addition of a trace amount of water.

Claims (8)

A process for the isomerization of an unbalanced alkylated aromatic feedstock of xylene and ethylbenzene,
The process comprises feeding the feedstock;
0.1 to 2% by weight of at least one platinum group component,
An inorganic oxide binder, and at least one non-zeolite molecular sieve, or at least one pe selected from the group consisting of 5 to 90% by weight of MFI, MEL, MTW, MTT and FER, and mixtures thereof. Comprising a step of contacting a catalyst composed of a third component composed of tantacil-type zeolitic aluminosilicate, and a trace amount selected from the group consisting of water, water-forming precursors and mixtures thereof The water source is operated at isomerization conditions to produce an approximate equilibrium product of xylene in an amount equivalent to 75 to 750 ppm by weight of water equivalent to an alkylated aromatic feedstock A process characterized by being added to the reactor zone.   The process of claim 1, wherein the water source is added intermittently.   The process of claim 1, wherein the feedstock is substantially free of sulfur.   The process of claim 1, wherein the water source supplies 100 to 500 ppm by weight of water to the feedstock.   The process according to claim 1, wherein the zeolitic aluminosilicate is MFI.   The process of claim 1, wherein the non-zeolite molecular sieve is a crystalline SAPO-11 molecular sieve or a MgAPSO-31 molecular sieve.   The process of claim 1, wherein the non-zeolite molecular sieve is an aluminophosphate molecular sieve. The process of claim 1 further comprising the step of adding hydrogen in an amount of 0.5 to 10 moles per mole of feedstock.

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