KR100248667B1 - Shape selective hydrocarbon conversion - Google Patents

Abstract

The present invention relates to a method of shape-selective hydrocarbon conversion, such as disproportionation of toluene, comprising contacting a reaction stream with a preselected catalytic molecular sieve by coagulating the organosilicon compound under conversion conditions.

Description

Method of Conversion of Shape-Selective Hydrocarbons

The present invention relates to the conversion of shape-selective hydrocarbons, for example the selective preparation of para-substituted aromatic compounds, in particular the selective disproportionation of toluene for producing para-xylene.

The term 'shape-selective catalyst' describes the selectivity of an unexpected catalyst in a zeolite. The principle behind shape-selective catalysts has been widely reconsidered and is described in N.Y. Chen, W.E. Garwood and F.G. For example, Dwyer's "Shape selective Catalysis in Industrial Applications, 36, Marcel Dekker, Inc. (1989). In the pores of zeolites, isomerization of paraffins, isomerization of olefin backbones and double bonds, oligomerization and aromatic disproportionation. Hydrocarbon conversion reactions, such as alkylation or transalkylation reactions, are governed by constraionts by channel size The choice of reactants occurs when the feedstock fraction is larger than the pores of the zeolite that must be understood to react; On the other hand, if some of the product does not pass through the channel of the zeolite, the product selection occurs, the distribution of the product is also altered by the transition state selectivity, and some reactions are too prone to occur in the reaction transition state inside the zeolite pores or cages. The reaction cannot occur because other types of selectivity The dimension is caused by the configurational diffusion of molecules in close proximity to the zeolite pore system Small changes in the molecular or zeolite pores result in large diffusion changes resulting in different product distributions. An example is a catalyst that selectively disproportionates toluene into para-xyl.

Para-xylene is Chen. et al., J. Amer. Chem. Sec. Metallurgical toluene with methanol as described in 1979, 101, 6783, or by Pines, "The Chemistry of Catalytic Hydrocarbon Conversions", Academic Press. N. Y., 1981, p. It can be prepared by disproportionating toluene as described in 72. Such methods typically produce a mixture comprising para-xylene, ortho-xylene, and meta-xylene. Depending on the para-selectivity of the catalyst and the reaction conditions, different percentages of para-xylene are obtained. The yield, ie the amount of feedstock actually converted to xylene, is also affected by the catalyst and reaction conditions.

The methylation reaction of toluene, which is already known, typically provides many by-products represented by the formula:

Thermodynamic equilibrium for toluene conversion to the indicated product

Non-MTPX

184.27 g (2 mol toluene)

Yield = Selectivity × Conversion Rate = (100 × 9.64 / 101.35) × 0.55 = 5.23 weight%

Para-xylene yield = 100 × 9.64 / 184.27 = 5.23 weight%

Para-Xylene Purity (Para-Xylene / Total C ₈ 's) = 21.45 wt%

One way to improve the para-selectivity of zeolite catalysts is to modify the catalyst by treatment with a selection agent. Various silicone compounds have been used in reforming to improve the selectivity of the catalyst in hydrocarbon conversion processes. For example, US Pat. Nos. 4,145,315, 4,127,616 and 4,090981 describe the use of silicone compounds dissolved in organic solvents to treat zeolites. US Pat. Nos. 4,465,886 and 4,477,583 describe the use of an aqueous emulsion of silicone to treat zeolites. U.S. Patent Nos. 4,950,835 and 4,927,979 describe the use of alkoxysilanes carried by gas or organic solvent to treat zeolites. U.S. Patent Nos. 4,100,215 and 3,698157 describe the use of silanes in hydrocarbons such as pyridine, ethers to treat zeolites. Such modification methods are known in the art to be carried out after agglomeration of zeolites.

Some of these catalyst reforming methods, for example US Pat. Nos. 4,477,583 and 4,127,616, are successful in obtaining para-selectivity, i.e., at least about 90% of para-xylene / total xylene, but conversion of toluene Only about 10%, yield is less than about 9%, ie 10% x 90%, commercially unacceptable. Such preparations also produce significant amounts of ortho-xylene and meta-xylene, thus requiring expensive separation methods for separating para-xylene from other isomers.

Typical separation methods usually involve fractional crystallization or absorption separation of para-xylene at high cost from circulating xylene isomers. The xylene isomerization unit therefore requires further conversion of the circulated xylene isomers into the equilibrium mixture containing para-xylene.

Those skilled in the art know that the cost of the separation method is proportional to the desired degree of separation. Therefore, significant cost savings are achieved by improving selectivity to para-isomers while maintaining commercially acceptable conversion levels.

Therefore, it is highly desirable to provide a method for producing para-xylene from toluene with high selectivity while maintaining commercially acceptable conversion levels. It is also highly desirable to effectively and economically select the catalysts used.

Accordingly, one object of the present invention relates to a catalyst containing a crystalline molecular sieve having a Constraints index of 1-12, which catalyst aggregates a mixture containing a crystalline molecular sieve and an organosilicon compound. And then preselected by calcining the prepared aggregates.

In another aspect, an object of the present invention is to provide a method of shape-selective hydrocarbon conversion, for example, a hydrocarbon feedstock having a bond index of 1-12 and agglomerating a mixture containing crystalline molecular sieves and organosilicon compounds and then thereafter. A method of para-selective disproportionation of toluene, which involves contacting a catalyst containing crystalline molecular sieves preselected by calcining aggregates.

The present invention is useful for shape-selective hydrocarbon conversion methods, for example for the conversion of various aromatics of C _6-12 , for example toluene and benzene, to commercially useful para-substituted benzenes, for example para-xylene. Do.

The molecular sieves used in the process according to the invention comprise medium sized pore zeolites. Such mesoporous zeolites have a bond index of 1-12. The method of determining the bond index is fully described in US Pat. No. 4,016,218. Molecular sieves that follow a specific value of the bond index for medium pore zeolites are described, for example, in US Pat. Nos. 3,702,886 and Re. Nos. 29,949, 3,709,979, 3,832,449, 4,556,447, 4,076,842, 4,016,245, 4,397,827, 4,650,655, 3,308,069, Re. ZXM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM-48, ZSM-50, MCM-22 and Zeolite Beta as described in US Pat. No. 28,341 and EP 127,399 Included. Such zeolites can be prepared with varying silica: alumina ratios in the range of 12: 1 or greater. Preferred molecular sieves include ZSM-5, ZSM-11, ZSM-12, ZSM-35 and MCM-22. Particularly preferred molecular sieve is ZSM-5.

In the present invention, the catalyst preferably has a silica-alumina ratio of less than 100, preferably of 20-80 and an alpha value of at least 100, for example an alpha value of 150-2000. The alpha value represents the catalytic cracking activity of the catalyst relative to the standard catalyst and gives a relative rate constant (catalyst volume-end normal hexane conversion rate per unit time). This is based on the activity of the amorphous silica-alumina decomposition catalyst with alpha = (1 rate constant = 0.016 sec ⁻¹ ). Alpha tests are described in US Pat. No. 3,354,078 and The Journal of Catalysts, Vol. 4, pp. 522-529 (August 1965): Vol., (6, P. 278 (1966): and Vol. 61), p. 395 (1980).

In the synthesis of zeolites, the reaction mixture generally contains a silicon oxide, optionally an aluminum source, a templating agent which is a nitrogen containing organic compound, and an alkaline aqueous medium.

Silicon oxide can be supplied from known raw materials, for example silicates, silica hydrosols, precipitated silica hydrosols, precipitated silicas, for example Hi-Sil, silica gel, silicic acid. . Aluminum oxide can only be supplied as an impurity in other reactants, for example silica raw materials.

The raw material of the nitrogen-containing organic cation, of course, depends on the particular zeolite product made by crystallization from the reaction mixture, but can be a primary, secondary or tertiary amine or quaternary ammonium compound. Examples of non-limiting quaternary ammonium compounds include tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium, diethylammonium, triethylammonium, dibenzylammonium, dibenzyldimethylammonium, dibenzyldiethylammonium, benzyltrimethyl Salts of ammonium and chlorine. Non-limiting examples of amines useful herein include trimethylamine, triethylamine, tripropylamine, ethylenediamine, propanediamine, butanediamine, pentanediamine, hexanediamine, methylamine, ethylamine, propylamine, butylamine, dimethylamine, Diethylamine, dipropylamine, benzylamine, aniline, pyridine, piperidine and pyrrolidine.

Sources of oxides of alkali or alkaline earth metals are, for example, sodium, lithium, calcium, magnesium, cesium or potassium hydroxides, halides (eg chlorides and bromide), sulfates, nitrates, acetates, silicates, aluminas Salts of nates, phosphates and carboxylic acids.

After crystallization of the zeolite, the organic cations are generally removed by calcination or by other methods known in the art, and alkali metals or alkaline earth metals generally form intermediates of ammonium ion exchangers and calcinate the ammonium form to hydrogen form. Make and remove.

After crystallization, zeolite crystals that can be used in commercial processes are generally made in the form of aggregates to improve the strength and resistance to attrition. Various methods are used to aggregate the zeolite crystals. Such methods include, for example, spray drying to microspheres that can be extruded and fluidized into pellets or beads, or hot pressing zeolite crystals into aggregates. .

In the present invention, a zeolite molecular sieve catalyst modified with silicon is prepared by mixing zeolite crystals with an organic silicon compound and optionally a binder, agglomerating the mixture, and then calcining the aggregate. Calcination is conveniently carried out at a temperature of at least 300 ° C., but at a rate of 0.2 to 5 ° C./min, under a coral containing atmosphere, preferably air, but at a temperature at which the crystallinity is inversely affected. Typically such temperatures are below 600 ° C. Preferably the calcination temperature is in the range of about 350 to 550 ° C. The product is usually maintained at the calcination temperature for 1 to 24 hours.

Zeolite crystals can be introduced into the mixture in the form as synthesized, and alkali metal or alkaline earth metal ions remaining in the zeolite structure from crystallization of organic templates and reaction mixtures are known in the art after crystals aggregate. Can be removed in a conventional manner.

The organosilicon compound is added to the mixture in aqueous form, for example in the form of an emulsion, solution, or aerosol, which may be stabilized by a surfactant. Useful surfactants include, for example, ethers of polyoxyethylene-octylphenol.

Organosilicon compounds include silanes such as alkylsilanes, arylsilanes, alkylarylsilanes, alkoxysilanes, aryloxysilanes, oxyethylenesilanes, alkylaryloxysilanes, siloxanes and polysiloxanes having alkyl and / or aryl and / or glycol groups do. Alkyl is meant to include from 1 to 12 carbons. Aryl is intended to represent those containing 6 to 10 carbons. The organosilicon compound also includes the silicon compound described below (which may also be used for trim selectivity). Preferred are siloxanes such as phenyl-methylpolysiloxanes.

In the shape-selective hydrocarbon conversion process according to the invention, suitable molecular sieves can be aggregated or extruded together with a support or a binder, for example a porous inorganic oxide support or a clay binder. Silica is the preferred binder, but non-limiting examples of such other binders include alumina, zirconia, magnesia, toria, titania. Boria and combinations thereof are included and are generally in the form of dry inorganic oxide gels or gelatinous precipitates. Suitable clay materials include, for example, bentonite and kieselguhr. The relative proportion of the appropriate crystalline molecular sieve relative to the total composition of the catalyst and binder or support may be 30 to 90% by weight of the composition, preferably 50-80% by weight. The composition is an extrudate, bead, pellet. (Tablet) or fluidizable microspheres.

Geometry selective transition

Selective flocculated molecular sieves according to the present invention generally include a decomposition reaction involving dewaxing of a hydrocarbon feedstock; Isomerization of alkyl aromatics; Oligomerization of olefins to prepare gasoline, oligomerization of distillates, lubricants or chemicals; Transalkylation of aromatics; Alkylation of aromatics; It is useful for shape-selective hydrocarbon conversion methods such as conversion of oxygenates to hydrocarbons, rearrangement of oxygenates, and conversion of light paraffins and olefins to aromatics.

In general, the contact conversion conditions on the catalyst containing the modified zeolite include a temperature of 100 to 760 ° C., a pressure of 10 to 20,000 kPa (0.1 to 200 atm) and a weight hourly space velocity of 0.08 to 2000 hr ⁻¹ . (WHSV) and a hydrogen / organic (ie hydrocarbon) compound ratio of 0 to 100.

The catalysts according to the invention have been tried in particular for use in the transalkylation or disproportionation of toluene for the production of para-xylene, which methods will be described here as representative examples of shape-selective conversion on the present catalysts.

Toluene Disproportionation

The reaction conditions intended for toluene disproportionation here are in the temperature range of 350 to 540 ° C, preferably at least 400 ° C; A pressure of 100 to 34,500 kPa (0 to 5000 psig), preferably a pressure of 790 to 7000 kPa (100 to 1000 psig); A molar ratio of hydrogen to hydrocarbon of 0.1 to 20, preferably 2 to 4; It has a WHSV of 0.1 to 20 hr ⁻¹ , preferably 2 to 4 hr ⁻¹ .

The toluene feedstock preferably contains 50% to 100%, more preferably at least about 80% or more of toluene. Other compounds such as benzene, xylene, and trimethylbenzene may also be present in the toluene feedstock without adversely affecting the present invention. The toluene feedstock can also be dried in a manner that minimizes the moisture entering the reaction zone, if necessary. There are many methods known in the art that are suitable for drying the toluene feedstock for the process of the present invention. Such methods include passing through a suitable desiccant, such as silica gel, activated alumina, molecular sieve or other suitable material or using a liquid feed molar dryer.

Usually a single pass conversion of the toluene stream produces a product containing dimethylbenzene, ortho-, methane- and para-xylene, with alkyl groups at all positions. Xylene is also known to produce undesired ethylbenzene (EB) during the reaction according to the following scheme;

In the past, the purity of para-xylene for all C ₈ products has been limited to less than 90% when isomerization is allowed in single pass methods. This efficiency is somewhat reduced by the production of ethylbenzene.

However, the present invention provides a high efficiency conversion by reducing the production of ortho- and meta-isomers in favor of the desired para-isomers. The product stream produced by the process has a para-xylene purity of at least 90%. For example, the ortho-xylene isomer can be reduced to about 0.5% or less of the total xylene content, and the meta-xylene isomer to less than about 5%. Moreover, when the reaction system is properly treated, the amount of ethylbenzene can be reduced to less than about 0.3% relative to the C ₈ product, for example by depositing platinum in the molecular sieve.

As described in detail herein, the present invention provides a conversion of at least about 15%, preferably at least about 25-25%, and at least 90%, preferably at least 95%, most preferably at least about 99% Provided is a method of obtaining para-xylene in celine purity.

Therefore, high para-xylene purity can be obtained as a commercially acceptable conversion rate compared to the methods described above. Thus, the present invention can significantly reduce the aforementioned process costs due to separating undesired by-products. Prior art toluene disproportionation methods typically require expensive secondary and tertiary treatment sequences to achieve this efficiency.

Preferably, the toluene disproportionation method of the present invention further comprises the step of further selecting the zeolite catalyst in situ in addition to the preselection to the coagulation course of the catalyst in the external system. Further in situ, referred to herein as 'trim selectivity', allows the catalyst to be reacted with toluene, a selector until the desired para-xylene selectivity, eg 90% or 95%, is achieved under reaction conditions. And simultaneously contacting with hydrogen, and then stopping the supply of the selector. The trim selector is preferably a silicone containing compound, more preferably a silicone containing compound according to the following general formula:

Wherein R ₁ is hydrogen, fluorine, hydroxy, alkyl, aryl, alkylaryl or fluoro-alkyl. Hydrocarbon substituents generally have 1 to 10 carbon atoms and are preferably methyl or ethyl groups.

R ₂ is selected from the same group as R ₁ , n is an integer of 2 or more, and is generally in the range of 3 to 1000.

The molecular weight of the silicone compound used is generally between 80 and 20,000, preferably between 150 and 10,000. Representative silicone compounds include dimethylsilicone, diethylsilicone, phenylmethylsilicone, methylhydrogensilicon, ethylhydrogensilicon, phenylhydrogensilicon, methylethylsilicon, phenylethylsilicone, diphenylsilicone, methyltrifluoropropylsilicone, ethyltrifluoro Propylsilicone, polydimethylsilicone, tetrachlorophenylmethylsilicone, tetrachlorophenylethyl silicone, tetrachlorophenylhydrogensilicon, tetrachlorophenylphenylsilicone, methylvinylsilicone and ethylvinylsilicone. The silicone compound need not be linear and may be a cyclic compound such as hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, hexaphenylcyclotrisiloxane and octaphenylcyclotetrasiloxane. Mixtures of these compounds as well as silicone compounds with other functional groups can also be used. Other silicone containing compounds such as silanes and siloxanes may also be used.

Preferably, the kinetic diameter of the silicon preselective compound added in the trim selector of para-xylene and the agglomeration of the zeolite is such that the zeolite is larger than the pore diameter to avoid a decrease in the internal activity of the catalyst. The reaction conditions of the trim selectivity step are generally temperatures of 350-540 ° C. and pressures of 100 to 34500 k kPa (atmospheric pressure—5000 psig). The feedstock supplied to the system has a speed of 0.1-20 WHSV. Hydrogen is supplied at a molar ratio of hydrogen to hydrocarbon of 0.1-20. The trim selector is preferably supplied in an amount of 0.1% to 50% relative to toluene, depending on the amount of selector used, but the trim selector is preferably 50-300 hours, most preferably 170 hours or less. Continues.

While not wishing to be bound by theory, it is believed that the advantages of the present invention are achieved by increasing the tortuosity of the catalyst while increasing the acid site of the outer surface of the catalyst while making the reactants substantially inaccessible. . Acid sites present on the outer surface of the catalyst are believed to isomerize the para-xylene present in the catalyst pores to equilibrium levels with the other two isomers, thereby reducing the amount of para-xylene in xylene to only about 24%. By reducing the use of these acid sites by para-xylene present in the catalyst pores, relatively high levels of para-xylene can be maintained. It is contemplated that the trim selector of the present invention chemically modifies the mentioned acid sites such that para-xylene is not available by blocking or modifying these external acid sites.

The catalyst can be further modified to reduce the amount of unwanted byproducts, especially ethylbenzene. In the context of the art, standard disproportionation reactor effluents typically contain 0.5% ethylbenzene byproduct. By distilling the reaction product, the level of ethylbenzene in the C ₈ fraction is often increased to 3-4%. This level of ethyl benzene is not acceptable for polymer grade para-xylene because ethylbenzene in the C ₈ product seriously degrades the fiber produced from the para-xylene product if not removed. In conclusion, the content of ethylbenzene should be kept quiet. The specification of ethylbenzene in the C ₈ product was determined by industry to less than 0.3%. Ethylbenzene can be removed in significant amounts by isomerization or superfractionation methods. Removal of ethylbenzene by conventional isomerization is not practical for the present invention because the xylene stream of the present invention contains at least 90% of para-xylene, and also the amount of para-xylene in the present xylene stream is equilibrated to xylene. And isomerized to about 24%. Second fractionation, another removal of ethylbenzene, is known in the art to require very high cost.

In order to avoid the need to remove downstream ethylbenzene, the level of ethylbenzene by-products is advantageously reduced by imparting a hydrogenation-dehydrogenation function, such as adding metal compounds such as platinum to the catalyst. Platinum is the preferred metal, but other metals may be used, such as palladium, nickel, copper, cobalt, molybdenum, rhodium, ruthenium, silver, gold, mercury, osmium, iron, zinc, cadmium, and mixtures thereof. . The metal may be added by cation exchange in an amount of about 0.01% -2%, typically about 0.5%. The metal must be able to enter the pores of the catalyst to remain in the subsequent calcination step. For example, a catalyst modified with platinum can be prepared by first adding the catalyst to the ammonium nitrate solution to convert the catalyst into ammonium form. The catalyst is then contacted with aqueous tetraamine nitrate (II) solution. The metallic compound advantageously enters the pores of the catalyst. The catalyst is then filtered off, washed with water and then calcined at a temperature of about 250 to 500 ° C.

The effluent is separated and distilled to separate the desired product, para-xylene, and other by-products.

By the present invention, toluene can be converted to an aromatic concentrate of about 99% para-xylene based on high values, for example total C ₈ product. In a representative embodiment of the method, the optimal toluene conversion was found to be 20-25% by weight at a para-xylene purity of 90-99%.

The invention is illustrated by the following non-limiting examples:

15.57 g of distilled water in a 150 cc beaker was added 1.01 g of 50% sodium hydroxide solution and 2.20 g of dimethyl silicone modified with oxyethylene groups to give water solubility at 38 ° C. To this solution was added a mixture of 10.85 g of as-synthesized ZSM-5 and 5.85 g of hydrous amorphous silica with stirring. The resulting dry paysheet was made into a 1.6 mm (1/16 inch) size extrudate using a hand extruder. Drying at 120 ° C. for 2 hours gave 12.91 g of product.

Example 2

An emulsion was made by adding a mixture of 1.03 g of 50% sodium hydroxide solution, 4.06 g of phenylmethylpolysiloxane and 0.79 g of iso-octylphenoxypolyethoxyethanol surfactant to 15.58 g of distilled water in a 150 cc beaker. To this solution was added a mixture of 10.85 g of as-synthesized ZSM-5 and 5.85 g of hydrous amorphous silica (HiSil, PPG Industries, Inc.) with stirring. The resulting dry paste was made into an extrudate of size 1.6 mm (1/6 inch) using a manual extruder. Drying at 120 ° C. for 2 hours gave 13.49 g of product.

Claims (8)

Agglomerates a mixture containing a crystalline molecular sieve and an organosilicon compound, and then calcinates the agglomerate to contain a crystalline molecular sieve having a Constraint Index of 1 to 12 preselected. One catalyst. The catalyst of claim 1 wherein the organosilicon compound is selected from silicones, silanes, alkoxysilanes, siloxanes, and polysiloxanes. The catalyst according to claim 1 or 2, further comprising a hydrogenated / dehydrogenated metal. Characterized by preparing a mixture containing a crystalline molecular sieve material having a bond index of 1 to 12 and an organic silicon compound such that the molecular sieve / organic silicon compound weight ratio is 1/10 to 100/1, and coagulating the mixture. To preselectively select the catalytic molecular sieve. 5. The method of claim 4, wherein the preselected catalytic molecular sieve is contacted twice with a mixture containing a secondary silicon source which is a selector of toluene and para-xylene under reaction conditions for converting toluene to xylene for at least 1 hour. Further comprising obtaining a modified catalyst. Agglomerating the mixture containing the crystalline molecular sieve and the organosilicon compound and calcining the resulting agglomerate, thereby contacting the hydrocarbon with the catalyst containing the crystalline molecular sieve having a preselected bond index of 1-12. Shape-selective hydrocarbon conversion method. The method of claim 6, wherein the shape-selective hydrocarbon conversion method selectively disproportionates toluene to para-xylene. The disproportionation reaction according to claim 7, wherein the disproportionation reaction is carried out under conditions of a temperature of 350 ° C to 540 ° C, a pressure of 100 to 34500 kPa (atmospheric pressure to 5000 psig), a WHSV of 0.1 to 20, and a hydrogen to hydrocarbon molar ratio of 0.1 to 20 How to be.