KR100290970B1 - Method for producing ethyl toluene - Google Patents

Abstract

The present invention relates to a process for preparing an ethyltoluene isomeric mixture comprising a high content of meta isomers and a very low amount of ortho isomers by ethylating toluene in the presence of a ZSM-5 catalyst having controlled acidity and diffusibility. The weight ratio of meta isomers and para isomers in the product is at least 1: 1, preferably at least 1.2: 1, and the content of ortho isomers is maintained at 1.5% by weight or less, preferably 0.5% by weight or less. In addition, polymerization-improved vinyl toluene can be prepared by dehydrogenating the ethyltoluene product.

Description

Method for producing ethyl toluene

The present invention relates to the preparation of ethyltoluene, more specifically to a process for preparing a mixture of ethyltoluene isomers containing a high content of meta isomers and very small amounts of ortho isomers.

Vinyl toluene is an important industrial chemical used to make polymers. For some purposes, it is desired to produce vinyl toluene having a relatively high meta isomer (m-methyl styrene) content of 50 to 70% relative to the total content of vinyl toluene. At the same time, very small amounts of ortho isomers (o-methyl styrene) are desired because they act as chain stoppers in the polymerization reaction. Usually, in the case of commercially acceptable materials, the maximum content of ortho isomers should be maintained at 1.5%, preferably at most 1% or at most 0.5%.

Vinyl toluene is prepared by dehydrogenation of ethyltoluene and the isomer ratio of the vinyl toluene product depends entirely on the isomer ratio of the ethyltoluene precursor. Thus, ethyltoluene should typically comprise from 50 to 70% meta isomers, up to 1% of ortho isomers and the remaining para isomers.

Ethyltoluene can be prepared by ethylating toluene in the presence of an acid catalyst. For this purpose, heterogeneous zeolite catalysts and catalysts of Lewis acids such as aluminum chloride are used. Homogeneous Lewis acid catalysts, such as aluminum trichloride, are effective in producing ethyltoluene products in which the proportion of isomers is relatively close to the equilibrium ratio of para 31.5%, meta 50.2% and ortho 18.3% by ethylating toluene under relatively mild conditions. . For example, US Pat. No. 4,143,084 to Kaeding (Example 13) discloses ethyltoluene having a p-isomer: m-isomer: o-isomer ratio of 27:60:13 by ethylating toluene in the presence of aluminum chloride. A method of making is disclosed. This ethyltoluene product contains the necessary amount of meta isomers, but the ortho isomer is present in excess.

Zeolites with medium size pores, such as ZSM-5, can be used to promote ethylation of toluene, usually at temperatures ranging from 500 to 850 ° F. (260 to 455 ° C.). The proportion of isomers of the product depends on the specific formation selectivity of the zeolite component of the catalyst. When used in hydrogen form without modifying ZSM-5, the ethyltoluene product has a proportion of isomers that are relatively close to equilibrium. An example of this is disclosed in US Pat. No. 4,086,287, which shows that an ortho isomer is present in excess, although Example 3 of this patent yields a meta content of about 60%.

In addition, by modifying the zeolite catalysts, the selectivity to para isomers can be greatly increased above the equilibrium level. For example, by increasing the size of the crystals of ZSM-5, the ratio of para isomers to meta isomers can be greatly increased corresponding to the loss of ortho isomers. U.S. Patent 4,086,287 (Example 4) describes that when using a large crystalline ZSM-5 catalyst, a low ortho content of about 1.6% and a meta content of about 65% can be obtained. However, even in this case, the content of the ortho isomer is present in excess. High temperatures and relatively slow space velocities further increase the content of meta isomers and further reduce the content of ortho isomers (US Pat. No. 4,086,287 (Example 4)). However, for commercial processes, faster space velocities are preferred because more and more product can be produced from Example 4 and in units of a given size. However, there is no suggestion that yielding preferred isomer ratios at higher space velocities.

By appropriately adjusting the diffusion properties of the zeolites, the content of ortho isomers can be adequately reduced in small quantities, but this involves a major increase in the selectivity to the para isomers such that the process becomes very regioselectivty. . When ZSM-5 is modified with magnesium, phosphorus or boron, the content of ortho isomers can be reduced to almost zero, but in this case the selectivity to para isomers becomes very high, so that the para isomers and meta isomers of the ethyl toluene product The desired balance is not achieved. Such a method is disclosed in US Pat. Nos. 4,086,287 and 4,143,084.

U.S. Patent No. 4,489,214 (Butler) discloses a process for producing ethyltoluene using a catalytic material called "silicalite", known as a highly siliceous zeolite ZSM-5 (Fyfe et al., "Resolving crystallographically distinct sites in silicalite and ZSM-5 by solid state NMR ”] (Nature 296, 530 (1982)) and Olson, DH et al., J. Catalysis (61, 390-396 (1980)).

Therefore, in summary it remains a problem that ethyl toluene having a relatively high content of meta isomers and a low content of ortho isomers of up to 1.5%, preferably up to 0.5%, still remains.

The inventors have come to focus on a process for producing ethyltoluene having relatively high meta isomers and low ortho isomers. The weight ratio of meta isomer to para isomer of the product is at least 1.1 (m-: p-), preferably at least 1.5: 1, and the content of ortho isomers in any case does not exceed 1.5% and is usually 1% or less. to be. This is achieved by the appropriate choice of catalyst and processing inhibitor in the reaction.

The ethyltoluene product is prepared by ethylating toluene in the presence of an aluminosilicate zeolite catalyst of moderately sized pore size produced by steaming. The reaction is typically 700 to 900 ° F. (370 to 480 ° C.) with a ratio of toluene: ethylene of about 2: 1 to 20: 1 and a space velocity (WHSV) of about 10 to 40 based on the toluene feedstock. Is carried out at a temperature of.

In the process of the invention, toluene is reacted with ethylene in the presence of a steamed aluminosilicate zeolite catalyst of medium pore size. The purpose of the process is to produce an ethyltoluene product having a high content of meta isomers and a very small amount of ortho isomers. The weight ratio of meta isomer: para isomer of the product is 1: 1 or more (equivalent to 50% by weight or more meta isomer based on ortho free state), preferably 1.2: 1 or more (based on ortho free state) Meta isomer of at least 55% by weight). In all cases, however, the maximum content of ortho isomers should be maintained at 1.5% by weight, preferably at most 1% by weight, or when the ethyltoluene product is intended for use in the polymerized reaction grade vinyl toluene. It is better that it is 0.5 weight%.

When toluene is reacted with ethylene in the presence of a form-selective heterogeneous catalyst such as ZSM-5, the initial product is likely para toluene, which is progressively meta-isomer and then ortho-isomer as the contact with the acidic catalyst is continued. Is switched to. As the reaction intensifies, the equilibrium shift is accelerated accordingly, making it difficult to produce products containing relatively large amounts of metaisomers, while at the same time retaining very small amounts of ortho isomers. Typically, as described in Kaeding, supra, U.S. Patent No. 4,143,084, when meta-isomers are produced, the shape selectivity of the catalysts is highly regioselective with respect to the para-isomers, in which case insufficient amounts of meta-isomers are produced. If not modified to a degree, the composition of the reaction product entails increasing the amount of ortho isomers as it moves to equilibrium in the presence of the catalyst.

In the process of the present invention, however, the acidity and selectivity of the catalyst are simultaneously modified and used together with the selected reaction factors to produce an ethyltoluene product having the desired isomer distribution. In addition to providing the desired product with very small amounts of ortho and high meta isomers, the process maintains a sufficient contact time (inverse of space velocity) to shift the composition of the desired product ethyltoluene to the desired isomer distribution. By suppressing the disproportionation reaction by controlling the activity of, the proportion of ethylbenzene by-products produced by the disproportionation reaction of the toluene feedstock is reduced.

The catalyst includes aluminosilicate zeolite ZSM-5 as an essential catalyst component. Such zeolites, i.e. the zeolites of medium pore size, provide a sufficient strength to the catalyst by using a binder such as alumina as a substrate, and it is preferable to avoid the influence of the binder on the desired low acidic material. ZSM-5 should have a crystal size larger than 1 μm, preferably about 1.5 μm or more, such as 2 μm, to provide the desired diffusion properties. ZSM-5 of this crystal size can be easily prepared by the prior art using a substituted ammonium agent, for example, tetrapropylammonium cation and trimethylammonium cation. As disclosed in US Pat. No. 4,375,458 (Dwyer), which is incorporated herein by reference.

By steaming the zeolite raw material to reduce the occurrence of side reactions such as toluene disproportionation, the zeolite activity is maintained at relatively low controlled levels. The acid activity of the catalyst should be maintained at an alpha value of 1 to 80, preferably 1 to 50. It has been found that good results are obtained when the alpha value is about 30.

The alpha value is an approximate indicator of the catalytic cracking activity of the catalyst compared to the standard catalyst. The alpha test provides the relative rate constants (unit time and conversion of n-hexane per volume of catalyst) of the test catalyst relative to the standard catalyst, given an alpha value of 1 (rate constant = 0.016 / sec). Such alpha tests are shown in US Pat. No. 3,354,078 and J. Catalysis (4, 527 (1965); 6, 278 (1966); and 61, 395 (1980)), which describe the test. It is hereby incorporated by reference. The experimental conditions of the test used to determine the alpha value referred to herein are described in J. Catalysis (61, 395 (1980)), which includes a variable flow rate and a constant temperature of 538 ° C.

It has been found that producing the desired acidic activity by steam treatment is an essential feature of the process. In other words, when using a highly siliceous low activity zeolite, an ethyltoluene product having the desired high meta metaisomer cannot be produced. Typically, a silica to alumina ratio of about 70: 1 in the zeolite prior to steaming up to the final alpha value will provide good results for the final catalyst.

The reaction of the present invention is carried out by passing together toluene and ethylene over a ZSM-5 catalyst at a temperature in the range of about 500 to about 850 ° F. (about 260 to 455 ° C.). The contact time (inverse of the space velocity) maintains the content of the ortho isomer at a necessary low level while at the same time allowing the composition of the product to shift to provide the desired content of the metaisomer. Since both reaction temperature and contact time are related to the severity of the overall reaction, there is a trade-off between temperature and knot velocity, and decreasing the space velocity increases the content of meta- and ortho-isomers. Typically, the temperature is about 750-850 ° F. (about 400-455 ° C.) and the space velocity is 10-40 WHSV for the toluene feedstock.

Relatively fast space velocities are important In commercial processes, faster space velocities allow for the production of larger amounts of product on a scale basis. In addition, it was found that space velocity also contributes to the production of mixtures containing large amounts of meta isomers and very small amounts of ortho isomers.

In this reaction, the pressure is not critical and in some cases higher pressures may be used, but for economic reasons it is carried out at a suitable low pressure, typically about 500 psig (about 3550 KPa, absolute pressure) or less. Is convenient. The ratio of toluene to ethylene is preferably relatively high in order to ensure high selectivity of ethylene over ethyltoluene. Typically, the ratio of toluene to ethylene is from 2: 1 to about 30: 1, in most cases from 10: 1 to 20: 1 (molar ratio).

Three different ZSM-5 / alumina catalysts were tested for ethylating toluene. The catalyst used is as follows:

Catalyst A: ZSM-5 without steam treatment, crystal size> 1 μm, 358 alpha

Catalyst B: Steam-treated ZSM-5, Crystal size> 1 μm, 70 alpha

Catalyst C: ZSM-5 vaporized, crystal size> 1 mu m, 30 alpha.

Toluene and ethylene were passed over the catalyst at a pressure of 150 psig (1130 KPa, absolute pressure) at a temperature of 810-835 F (432-446 C). The space velocity based on the feedstock of toluene was 130 WHSV. A molar ratio of toluene to ethylene was used as 16. The results are summarized in Table 1 below.

TABLE 1

^* Reactor inlet

Example 2

The vaporized ZSM-5 30 alpha catalyst (catalyst C) was used to investigate the effect (reaction time, temperature) on the severity of the reaction. Toluene was ethylated at a temperature of 760 to about 790 ° F. (404 to 421 ° C.) (reactor inlet). The space velocity based on the feedstock of toluene ranged from 20 to 130 (WHSV). The molar ratio of toluene to ethylene was used at 7 or 16 under a pressure of 150 psig. No hydrogen was added at all. The results are summarized in Table 2 below.

TABLE 2

^* Reactor inlet

The results in Table 3 show that as the contact time increases (as the space velocity figure decreases) the production rate of meta isomers increases, but it is accompanied by an increase in the content of undesirable ortho isomers. By selecting the intensity of the reaction, it is possible to obtain a high content of meta isomers while maintaining the ortho isomer at 0.5% or less.

Example 3

Toluene was ethylated on the steamed 30 alpha ZSM-5 catalyst while feeding hydrogen together at a total pressure of 250 psig (blank KPa, absolute pressure) (reactor inlet). The results are summarized in Table 3 below.

The results show that the hydrogen supplied together does not significantly affect the distribution of ethyltoluene isomers (compare Table 2 above) but slightly reduces disproportionation activity. However, in this study a relatively long contact time was used, where the content of undesirable ortho ethyltoluene could exceed acceptable levels when working at higher severity.

TABLE 3

^* Reactor inlet

Example 4

Three operations were performed using ZSM-5, a highly siliceous, low alpha value (alpha = 16) and crystal size 2 μm. The reaction was carried out at higher temperatures where the temperature of the reactor inlet was varied in the range from 820 to 850 ° F. (438 to 455 ° C.) to compensate for the low acidity of the catalyst. The reaction was carried out with a molar ratio of toluene to ethylene of 16: 1 in the absence of hydrogen. The space velocity was 60 to 130 and was changed inversely with respect to temperature. The results are summarized in Table 4 below.

TABLE 4

^* Reactor inlet

The results in Table 4 show that when a highly siliceous zeolite is used, a low content of ortho isomers can be obtained in the product, but at the same time it is not possible to obtain adequately padded content for metaisomers.

Example 5

Two ZSM-5 catalysts were used to investigate the effect of ZSM-5 crystal size. The first catalyst (catalyst D) has an alpha value of 50, a zeolite crystal size of 0.05 μm or less, a second catalyst (catalyst E) has an alpha value of 18 and a crystal size of 0.1 to 1 μm. The two catalysts were used to ethylate toluene at a temperature of about 780 to 860 ° F. (about 415 to 460 ° C.) under a pressure of 150 psig (1135 KPa) in the absence of hydrogen. The results for catalysts D and E are summarized in each of Tables 5 and 6 below.

TABLE 5

^* Reactor inlet

TABLE 6

^* Reactor inlet

The results show that the crystal size of the zeolite component of the catalyst affects the isomer distribution of the ethyltoluene product. The smaller acidic low acid ZSM-5 catalyst was not able to obtain the low content ortho isomers that could be obtained using the larger acidic acid catalysts of Example 1 (catalysts B and C) under comparable conditions.

Example 6

A steamed ZSM-5 catalyst with an alpha value of about 30 was used to investigate the effect of increasing space velocity on the proportion of metaisomers in the product.

The four cases reported in Table 7 show the results obtained at four different times on stream (OS) in a two-bed mode of operation at temperatures in the range of 775 to 800 ° F. The space velocity of the reactants recorded with WHSV toluene was varied from about 15 to about 42 to obtain the results shown in Table 7 below.

TABLE 7

The results show that as the space velocity increases, the proportion of meta isomers in the product decreases. At the same time, the proportion of ortho isomers decreases. Therefore, an increase in space velocity has the effect of shifting the composition of the isomeric mixture away from the equilibrium value, while a decrease in space velocity will generate a tendency to reach equilibrium. The content of ortho isomers in the product tends to increase with meta isomers at gradually decreasing space velocities.

Claims (8)

Toluene was converted into ethylene in the presence of a catalyst having a crystal size exceeding 1 μm and containing ZSM-5 steamed to a alpha value of 1 to 80 at a temperature of 700 to 900 ° F. and a space velocity of 10 to 40 WHSV for the toluene feedstock. Ethylation to produce a reaction product consisting of a mixture of ethyltoluene isomers having a weight ratio of meta isomers to para isomers of at least 1: 1 and an ortho isomer content of 1.5 wt% or less, characterized in that the high content of meta isomers and trace amounts Process for the preparation of ethyltoluene isomer mixture consisting of ortho isomers. The method of claim 1, wherein the weight ratio of meta isomer to para isomer in the ethyltoluene isomer mixture is at least 1.2: 1. The method of claim 1 wherein the content of ortho isomers in the ethyltoluene isomer mixture is 1 wt% or less. The method of claim 1, wherein the content of ortho isomers in the ethyltoluene isomer mixture is 0.5 wt% or less. The method of claim 1, wherein the ZSM-5 has a crystal size of at least 2 μm. The method of claim 1 wherein the alpha value of the catalyst is 1-50. The method of claim 5, wherein the alpha value of the catalyst is 1-40. The method of claim 1 wherein the toluene is reacted with ethylene at a temperature of 750 to 850 ° F.