GB2090281A - Para-selective Methylation of Ethylbenzene - Google Patents

Abstract

Ethylbenzene is contacted under conversion conditions, with a methylating agent eg methyl alcohol methyl halide, dimethylsulphide or dimethyl ether in the presence of a catalyst comprising a crystalline aluminosilicate zeolite, which zeolite is characterized by an activity, in terms of alpha value of between about 0.2 and about 5000, a xylene sorption capacity greater than 1 gram/100 grams of zeolite and an ortho xylene sorption time for 30 percent of said capacity of greater than 10 minutes, said sorption capacity and sorption time being measured at 120 DEG C and a xylene pressure of 4.5+/-0.8 mm of mercury, said crystalline aluminosilicate zeolite having a silica to alumina ratio of at least about 12 and a constraint index within the approximate range of 1 to 12 to yield a resulting product containing ethyl toluene isomers, based on the total amount of ethyl toluene produced, of at least 85 weight percent of the para isomer, 1 to 15 weight percent of the meta isomer, and 1 to 0 weight percent of the ortho isomer.

Description

SPECIFICATION Para-selective Methylation of Ethylbenzene This invention relates to a process for reacting ethylbenzene with a methylating agent in the presence of a particular crystalline zeolite catalyst to produce an ethyltoluene isomer mixture with a high proportion of the product in the para-isomeric form. The catalyst is a crystalline zeolite characterized by a high silica:alumina ratio, an activity, in terms of alpha value, of between 0.2 and 5000, and a constraint index of about 1 to 12. The ethyl toluene isomer mixture produced can be dehydrogenated by conventional techniques to obtain a mixture of the corresponding methyl styrene isomers which are suitable for polymerization alone or with other unsaturated monomers to obtain valuable polymers.

Compared to a conventional thermodynamic equilibrium alkylated benzene mixture, the process described herein affords a product of which para-isomer predominates. The improved yield of greater than 50 percent of the total isomer production compared with the lower equilibrium concentration reduces the cost of production and the cost of separation of para-alkylhalobenzenes from meta and ortho isomers. The method of this invention is capable of producing isomeric mixtures containing 85 percent or more of para-ethyl toluene, and corresponding lower than usual amounts of the meta and ortho isomer, e.g., 1-15 percent and 1-0 percent respectively.Preferably catalyst and conditions are selected so that the product contains at least 90 percent of the para isomer, 1 0-1 percent of the meta isomer and less than 1 percent of the other isomer.

The reactants are brought into contact, under conversion conditions, with a bed of particulate catalyst containing a crystalline zeolite having: (1) an activity, in terms of alpha value, of between about 0.2 and about 5,000; (2) a xylene sorption capacity greater than 1 gram/l 00 grams of zeolite; and (3) an ortho-xylene sorption time of greater than 10 minutes for 30 percent of said capacity, where the sorption capacity and sorption time are measured at 1 200C and a xylene pressure of 4.5+0.8 mm of mercury.

The alpha value reflects the relative activity of the catalyst with respect to a high activity silicaalumina cracking catalyst. To determine the alpha value as such term is used herein, n-hexane conversion is determined at about 10000 F. Conversion may be varied by changing space velocity such that a conversion level of 10 to 60 percent of n-hexane is obtained and converted to a rate constant per unit volume of zeolite and compared with that of silica-alumina catalyst which is normalized to a reference activity of 10000 F. Catalytic activity of the catalysts is expressed as multiples of this standard, i.e., the silica-alumina standard. The silica-alumina reference catalyst contains about 10 weight percent Al203 and remainder SiO2.This method of determining alpha, modified as described above, is more fully described in the Journal of Catalysis, Vol. VI, Pages 278-287, 1 966.

The measurement of hydrocarbon sorption capacities and rates are conveniently carried out gravimetrically in a thermal balance. Zeolites having an equilibrium sorption capacity for xylene of at least 1 gram per 100 grams of zeolite measured at 1 200C and a xylene pressure of 4.5+0.8 mm of mercury are preferred. In sorption capacity tests para, meta, ortho or mixtures thereof may be employed. Preferably para-xylene is used for capacity test purposes, since this isomer reaches equilibrium within the shortest time. An ortho-xylene sorption time for 30 percent of said capacity of greater than 10 minutes (at the same conditions of temperatures and pressure) is desired in order to achieve highly selective production of ethyl toluene.

It has been found that zeolites exhibiting very high selectivity for para-ethyltoluene production require a long time to sorb o-xylene in an amount of 30 percent of total xylene sorption capacity. For those materials it is more convenient to determine the sorption time for a lower extent of sorption, such as 5%, 10% or 20% of capacity, and to estimate the 30 percent of sorption time by calculation.

The crystalline zeolites utilized herein are typically members of a unique class of zeolitic materials, which exhibit selective properties. Although these zeolites have unusually low alumina contents, i.e., high silica to alumina mole ratios, they are very active even when the silica to alumina mole ratio exceeds 30. The activity is surprising since catalytic activity is generally attributed to framework aluminum atoms and/or cations associated with these aluminum atoms. These zeolites retain their crystallinity for long periods in spite of the presence of steam at high temperatures which induces irreversible collapse of the framework of other zeolites, e.g., of the X and A type. Furthermore, carbonaceous deposits, when formed, may be removed by burning at higher than usual temperatures to restore activity.These zeolites, used as catalysts, generally have low coke-forming activity and may be kept on stream for long periods of time between regenerations.

An important characteristic of the crystal structure of this class of zeolites is the selective constrained access to and egress from the intracrystalline free space provided to certain molecules by virtue of having an effective pore size intermediate between the small pore Line A and the large pore Line X. The pore windows of the structure are of about a size such as would be provided by 10 membered rings of silicon atoms interconnected by oxygen atoms. These rings are formed by the regular deposition of the tetrahedra making up the anionic framework of the crystalline zeolite, the oxygen atoms themselves being bonded to the silicon (or aluminum, etc.) atoms at the centers of the tetrahedra.

The silica to alumina mole ratio represents the ratio in the rigid anionic framework of the zeolite crystal and excludes aluminum in the binder or in cationic or other form within the channels. Although zeolites with a silica to alumina ratio of at least 12 are useful it is preferred in the present invention to use zeolites having higher silica/alumina ratios of at least about 30. Typical ZSM-5 catalysts employed herein have a ratio of about 70:1 to 90:1. In addition, zeolites as otherwise characterized herein but which are substantially free of aluminum, i.e., having silica to alumina mole ratios of 1,600 and higher, are found to be useful and even preferable in some instances. Such "high silica" zeolites are intended to be included within this description.

Rather than attempt to judge from crystal structure whether or not a zeolite possesses the necessary constrained access to molecules of larger cross-section than normal paraffins, a simple determination of the "Constraint Index," as herein defined, may be made by passing continuously a mixture of an equal weight of normal hexane and 3-methylpentane over a sample of zeolite at atmospheric pressure according to the following procedure. A sample of the zeolite, in the form of pellets or extrudate, is crushed to a particle size about that of coarse sand and mounted in a glass tube.

Prior to testing, the zeolite is treated with a stream of air at 5400C for at least 1 5 minutes. The zeolite is then flushed with helium and the temperature is adjusted between 2900C and 51 00C to give an overall conversion of between 10% and 60%. The mixture of hydrocarbons is passed at 1 liquid hourly space velocity (i.e., 1 volume of liquid hydrocarbon per volume of zeolite per hour) over the zeolite with a helium dilution to give a helium to (total) hydrocarbon mole ratio of 4:1. After 20 minutes on stream, a sample of the effluent is taken and analyzed, most conveniently by gas chromatography, to determine the fraction remaining unchanged for each of the two hydrocarbons.

While the above experimental procedure will enable one to achieve the desired overall conversion of 10 to 60% for most zeolite samples and represents preferred conditions, it may occasionally be necessary to use somewhat more severe conditions for samples of very low activity, such as those having an exceptionally high silica to alumina mole ratio. In those instances, a temperature of up to about 540cm and a liquid hourly space velocity of less than one, such as 0.1 or less, can be employed in order to achieve a minimum total conversion of about 10%.

The "Constraint Index" is calculated as follows: logaO (fraction of hexane remaining) Constraint Index log10 (fraction of 3-methylpentane remaining) The Constraint Index approximates the ratio of the cracking rate constants for the two hydrocarbons. Zeolites suitable for the present invention are those having a Constraint index of 1 to 12.

Constraint Index (Cl) values for some typical materials are: Zeolite Type C.l, ZSM-4 0.5 ZSM-5 8.3 ZSM-11 8.7 ZSM-12 2.0 ZSM-23 9.1 ZSM-35 4.5 ZSM-38 2.0 ZSM-48 3.4 TMA Offretite 3.7 Clinoptilolite 3.4 Beta 0.6 H-Zeolon (Mordenite) 0.4 REY 0.4 Erionite 38 Constraint Index seems to vary somewhat with severity of operation (conversion) and the presence or absence of binders. Likewise, other variables such as crystal size of the zeolite, the presence of occluded contaminants, etc., may affect the constraint index. Therefore, it will be appreciated that it may be possible to so select test conditions as to establish more than one value in the range of 1 to 12 for the Constraint Index of a particular zeolite. Such a zeolite exhibits the constrained access as herein defined and is to be regarded as having a Constraint Index in the range of 1 to 1 2. Also contemplated herein as having a Constraint Index in the range of 1 to 1 2 and therefore within the scope of the defined novel class of highly siliceous zeolites are those zeolites which,when tested under two or more sets of conditions within the above-specified ranges of temperature and conversion, produce a value of the Constraint Index slightly less than 1, e.g., 0.9, or somewhat greater than 12, e.g., 14 or 1 5, with at least one other value within the range of 1 to 12. Thus, it should be understood that the Constraint Index value as used herein is an inclusive rather than an exclusive value.

That is, a crystalline zeolite when identified by any combination of conditions within the testing definition set forth herein as having a Constraint Index in the range of 1 to 12 is intended to be included in the instant novel zeolite definition whether or not the same identical zeolite, when tested under other of the defined conditions, may give a Constraint Index value outside of the range of 1 to 12.

The class of zeolites defined herein is exemplified by ZSM-5, ZSM-1 1 , ZSM-1 2, ZSM-23, ZSM35, ZSM-38, ZSM-48 and other similar materials.

ZSM-5 is described in greater detail in U.S. Patent No. 3,702,886 and No. 3,941,871. ZSM-1 1 is described in U.S. Patent No. 3,709,979. ZSM-23 is described in U.S. Patent 4,016,245. ZSM-38 is more particularly described in U.S. Patent No. 4,046,859. The description of these catalysts, their preparation and specified X-ray diffraction pattern thereof, is incorporated herein by reference to the above-identified patents.

ZSM-48 can be identified, in terms of anhydrous oxides per 100 moles of silica, as follows: (0--1 5)RN: (0--1.5)MO: (0-2)A1203: (100)Si02 wherein M is at least one cation having a valence n; and RN is a C1-C20 organic compound having at least one amine functional group of pK > 7.

The ZSM-48 can be prepared from a reaction mixture containing a source of silica, water, RN, an alkali metal oxide (e.g., sodium) and optisnaliy alumina. The reaction mixture should have a composition, in terms of mole ratios of oxides, falling within the following ranges.

Reactants Broad Preferred A120WSi02 = O to 0.02 0 to 0.01 Na/SiO2 = 0 to 2 0.1 to 1.0 RN/SiO2 = 0.01 to 2.0 0.05 to 1.0 OH-/SiO2 = O to 0.25 0 to 0.1 H2O/SiO2 =10 to 100 20 to 70 H+(added)/Sio2 = O to 0.2 0 to 0.05 wherein RN is a C2-C20 organic compound having amine functional group of pK > 7 The mixture is maintained at 80-2500C until crystals of the material are formed. H+(added) is moles acid added in excess of the moles of hydroxide added. In calculating H+(added) and OH values, the term acid (H+) includes both hydronium ion, whether free or coordinated, and aluminum.Thus alumum sulfate, for example, would be considered a mixture of aluminum oxide, sulfuric acid, and water. An amine hydrochloride would be a mixture of amine and HCI. In preparing the highly siliceous form of ZSM-48, no alumina is added. Thus, the only aluminum present occurs as an impurity in the reactants.

Preferably, crystallization is carried out under pressure in an autoclave or static bomb reactor, at 800C to 2500C. Thereafter, the crystals are separated from the liquid and recovered. The composition can be prepared utilizing materials which supply the appropriate oxide. Such compositions include sodium silicate, silica hydrosol, silica gel, silicic acid, RN, sodium hydroxide, sodium chloride, aluminumsulfate, sodium aluminate, aluminum oxide, or aluminum itself.RN is a C1-C20 organic compound containing at least one amine functional group of pKa > 7 as defined above, and includes such compounds as C3C1, primary, secondary, and tertiary amines, cyclic amine (such as piperidine, pyrrolidine and piperazine), and polyamines such as NH2CnH2nNH2 wherein n is 4-12.

The original cations can be subsequently replaced, at least in part, by calcination and/or ion exchange with another cation. Thus, the original cations are exchanged into a hydrogen or hydrogen ion precursor form or a form in which the original cation has been replaced by a metal of Groups II through VIII of the Periodic Table. Thus, for example, it is contemplated to exchange the original cations with ammonium ions or with hydronium ions. Catalytically active forms of these would include, in particular, hydrogen, rare earth metals, aluminum, manganese and other metals of Groups II and VIII of the Periodic Table.

The crystalline zeolites employed herein may be modified prior to use by combining therewith a small amount, generally in the range of about 0.5 to about 40 weight percent, preferably of a difficultly reducible oxide, such as the oxides of phosphorus, magnesium or antimony. Modification of the zeolite with the desired materials can readily be effected by contacting the zeolite with a solution of an appropriate compound of the element to be introduced, followed by drying and calcining to convert the compound to its oxide form.

Representative modifying materials which may be used are disclosed in U.S. Patent No. 4,143,084, along with a description of catalyst preparation. These include incorporation of magnesium, phosphorus, antimony and boron to the zeolite structure. Phosphorus-modified zeolites may contain as little as 0.5% P. Preferably 0.7 to 1 5% P is employed for such catalysts. Magnesium may be employed in smaller amounts; however, best results are obtained with a 1 to 15% Mg on the treated ZSM-5 type zeolites. SB203 in the amount of 6 to 40% in the composite catalyst may be incorporated, preferably between about 10 and 35%.

In some instances, it may be desirable to modify the crystalline aluminosilicate zeolite by combining therewith two or more of the specified oxides. Thus, the zeolite may be modified by combination therewith of oxides of phosphorus and boron, oxides of phosphorus and magnesium or oxides of magnesium and boron. When such modification technique is employed, the oxides may be deposited on the zeolite either sequentially or from a solution containing suitable compounds of the elements, the oxides of which are to be combined with the zeolite. The amounts of oxides present in such instances are in the same range as specified above for the individual oxides, with the overall added oxide content being between about 0.5 and about 40 weight percent.

Still another modifying treatment entails steaming of the zeolite by contact with an atmosphere containing from about 5 to about 1 00 percent steam at a temperature of from about 250 to about 10000C for a period of between about 0.25 and about 100 hours and under pressures ranging from sub-atmospheric to several hundred atmospheres to reduce the alpha value thereof to less than 500 and preferably less approximate than 20 but greater than zero.

In addition to the modified ZSM-5 and ZSM-23 catalysts, other selective crystalline zeolites include modified ZSM-1 1, ZSM-48, ZSM-35. In general these catalysts show reduced o-xylene diffusivity and relatively higher p-xylene diffusivity, as measured by xylene sorption capacity and rate of sorption for the particular isomer.

Methanol is a preferred methylating agent. Other methylating agents such as methylchloride, methylbromide, dimethylether or dimethylsulfide may be used. The compound containing the methyl moiety may dissociate thermally or by acid catalysis to form the methylating material. Methylation is generally conducted at a temperature of between about 2500C and 6000C at a pressure of between about 0.1 and about 100 atmospheres utilizing a weight feed hourly space velocity (WHSV) of between 0.1 and about 100. The WHSV is based upon the weight of the catalyst composition, i.e., total weight of catalyst and binder therefor. The molar feed ratio of ethylbenzene/methylating agent is generally between about 1 and about 1 0.

The invention is illustrated by the following examples in which parts are by weight and units are metric unless otherwise stated.

Example 1 This example illustrates the preparation of a phosphorus modified zeolite catalyst (PZSM-5) suitable for use in this invention.

Ten grams of pelletized large crystal HZSM-5 was treated with 3.25 grams of 85% phosphoric acid by dissolving the phosphoric acid in 1 50 ml methyl alcohol and refluxing the mixture containing catalyst overnight in a nitrogen atmosphere. Solvent was removed at a temperature of 90 to 1000C and 17.90 grams of a solid was recovered. The solid was then heated in an oven in air for three hours at a temperature of 1 500 C. The sample, which weighed 12.20 grams after heating at 1 500C was further heated in a furnace, in air, for four hours to give a final weight of 11.85 grams.

Example 2 An ethylbenzene/methanol mixture (2:1 mole ratio) was passed over a PZSM-5 catalyst prepared in Example 1 at 5500C, at a feed rate of 6.6 ml of feed per gram of catalyst per hour. The product was rich in ethyltoluenes. The ethyltoluene fraction contain 95% of the para isomer and is described in detail in Table I.

A mixture of toluene/ethylene (2:1 molar ratio) was passed over the same catalyst (6.6 ml toluene/gram catalyst/hr) at 5500 C. Ethyltoluenes were produced (1.5% of product) which contained 95% of the para isomer. Thus the same selectivity to para isomer (in ethyltoluenes) is achieved starting from either toluene or ethylbenzene. A lower activity catalyst can be used, however, when ethylbdnzene is the starting material.

Table 1

Product Composition, % Para/Meta/Ortho Light ends 0.44 Benzene 2.01 Toluene 3.88 Ethylbenzene 67.18 para xylene 4.14 meta xylene 0.33 5 90.0/7.2/2.8 ortho xylene 0.13 Styrene 0.96 paraethyltoluene 1 8.40 metaethyltoluene 0.84 95.0/4.3/0.7 orthoethyltoluene 0.1 3 Cc+ 1.44

Claims (14)

Claims

1. Process for methylating ethylbenzene which comprises contacting ethylbenzene, under conversion conditions, with a methylating agent in the presence of a catalyst comprising a crystalline aluminosilicate zeolite, which zeolite is characterized by an activity, in terms of alpha value of between about 0.2 and about 5000, a xylene sorption capacity greater than 1 gram/1 00 grams of zeolite and an ortho xylene sorption time for 30 percent of said capacity of greater than 10 minutes, said sorption capacity and sorption time being measured at 1200C and a xylene pressure of 4.5+0.8 mm of mercury, said crystalline aluminosilicate zeolite having a silica to alumina ratio of at least about 12 and a constraint index within the approximate range of 1 to 12 to yield a resulting product containing ethyl toluene isomers, based on the total amount of ethyl toluene produced, of at least 85 weight percent of the para isomer, 1 to 15 weight percent of the meta isomer, and 1 to 0 weight percent of the ortho isomer.

2. The process of Claim 1 wherein the methylating agent is methylchloride, methylbromide, dimethylether, methylcarbonate or dimethylsulfide.

3. The process of Claim 1 wherein the methylating agent is methanol.

4. The process of Claim 1 wherein said conversion conditions include a temperature between about 250 and about 6000C, a pressure between about 0.1 and about 100 atmospheres utilizing a feed weight hourly space velocity between about 0.1 and about 100 and a molar feed ratio of ethylbenzene/methylating agent between about 1 and about 10.

5. The process of Claim 1 wherein the crystalline alumino- silicate zeolite has undergone prior modification by combining therewith hetween about 0.5 and about 40 weight percent of at least one oxide selected from the group consisting of the oxides of phosphorus, antimony, boron and magnesium.

6. The process of Claim 1 wherein the crystalline aluminosilicate zeolite has undergone prior modification by combining therewith between about 1 and about 25 weight percent of an oxide of phosphorus.

7. The process of Claim 1 wherein the crystalline aluminosilicate zeolite has undergone prior modification by combining therewith between about 1 and about 25 weight percent of an oxide of magnesium.

8. The process of Claim 1 wherein the crystalline aluminosilicate zeolite has undergone prior modification by combining therewith between about 1 and about 20 weight percent of an oxide of boron.

9. The process of Claim 1 wherein the crystalline aluminosilicate zeolite has undergone prior modification by combining therewith between about 6 and about 40 weight percent of an oxide of antimony.

10. The process of Claim 1 wherein the crystalline aluminosilicate zeolite has undergone prior modification by steaming at a temperature between about 2500 and 1 0000C for a period of between about 0.5 and about 100 hours.

11. The process of Claim 10 wherein the steamed catalyst has deposited thereon between about 2 and about 75 weight percent of coke thereon.

12. The process of Claim 1 wherein the crystalline aluminosilicate zeolite has undergone prior modification by precoking to deposit between about 2 and about 75 weight percent of coke thereon.

1 3. The process of Claim 1 wherein said crystalline aluminosilicate zeolite is ZSM-5.

14. The process of Claim 1 3 wherein said ZSM-5 is admixed with a binder therefor.

1 5. The process of Claim 1 wherein said crystalline aluminosilicate zeolite is admixed with a binder therefor.