WO1994013603A1

WO1994013603A1 - Production of ethylbenzene

Info

Publication number: WO1994013603A1
Application number: PCT/US1993/011992
Authority: WO
Inventors: Jeevan Sahib Abichandani; Lloyd Lee Breckenridge; Chaya Rao Venkat
Original assignee: Mobil Oil Corporation
Priority date: 1992-12-16
Filing date: 1993-12-09
Publication date: 1994-06-23
Also published as: AU5746294A

Abstract

There is provided a process for producing ethylbenzene, wherein benzene is alkylated with ethylene in a vapor phase reaction over a catalyst comprising ZSM-5. Diethylbenzene byproduct from the vapor phase alkylation reaction is separated from the ethylbenzene product and reacted with benzene in a liquid phase transalkylation reaction to produce more ethylbenzene. The catalyst of the liquid phase transalkylation reaction may comprise a zeolite, such as zeolite beta. The combined ethylbenzene product from the vapor phase alkylation reaction and from the liquid phase transalkylation reaction has a low xylene impurity level of less than 1000 ppm.

Description

PRODϋCTION OF ETHYLBENZENE

This invention relates to a process for the production of ethylbenzene.

Ethylbenzene is a valuable commodity chemical which is currently used on a large scale industrially for the production of styrene monomer. Ethylbenzene may be produced by a number of different chemical processes but one process which has achieved a significant degree of commercial success is the vapor phase alkylation of benzene with ethylene in the presence of a solid, acidic ZSM-5 zeolite catalyst. In the production of ethylbenzene by this process, ethylene is used as the alkylating agent and is reacted with benzene in the presence of the catalyst at temperatures which vary between the critical temperature of benzene up to 900°F (about 480°C) at the reactor inlet. The reactor bed temperature may be as much as 150°F (about 85°C) above the reactor inlet temperature and typical temperatures for the benzene/ethylene reaction vary from 600° to 900°F (315° to 480°C) , but are usually maintained above about 700°F. (about 370°C.) in order to keep the content of the more highly alkylated benzenes such as diethylbenzene at an acceptably low level. Pressures typically vary from atmospheric to 3000 psig (100 to 20800 kPa) with a molar ratio of benzene to ethylene from 1:1 to 25:1, usually about 5:1 (benzene: ethylene) . Space velocity in the reaction is high, usually in the range of 1 to 6, typically 2 to 5, HSV based on the ethylene flow, with the benzene space velocity varying accordingly, in proportion to the ratio of the reactants. The products of the reaction include ethylbenzene which is obtained in increasing proportions as temperature increases together with various polyethylbenzenes, principally diethylbenzene (DEB) . Under favorable operating conditions on the industrial scale, an ethylene conversion in excess of 99.8 weight percent may be obtained at the start of the cycle. In the commercial operation of this process, the polyalkylated benzenes, including both polymethylated and polyethylated benzenes are recycled to the alkylation reactor in which the reaction between the benzene and the ethylene takes place. By recycling the by-products to the alkylation reaction, increased conversion is obtained as the polyethylated benzenes (PEB) are converted to ethylbenzene (EB) . In addition, the presence of the PEB during the alkylation reaction reduces formation of these species through equilibration of the components because at a given feed composition and under specific operating conditions, the PEB recycle will reach equilibrium at a certain level. This commercial process is known as the Mobil/Badger process and is described in more detail in an article by Francis G. Dwyer, entitled "Mobil/Badger Ethylbenzene Process-Chemistry and Catalytic Implications", appearing on pages 39-50 of a book entitled Catalysis of Organic Reactions, edited by William R. Moser, Marcel Dekker, Inc., 1981.

Ethylbenzene production processes are described in U.S. Patents Nos. 3,751,504 (Keown) , 4,547,605 (Kresge) , and 4,016,218 (Haag) . The process described in U.S. 3,751,504 is of particular note since it includes a separate, ZSM-5 catalysed vapor phase transalkylation step in the recycle loop which is effective for converting a significant proportion of the more highly alkylated products to the desired ethylbenzene product. Other processes for the production of ethylbenzene are disclosed in U. S. Patents Nos. 4,169,11 (Wight) and 4,459,426 (Inwood) , in both of which a preference for large pore size zeolites such as zeolite Y is expressed, in distinction to the intermediate pore size zeolites used in the processes described in the Keown, Kresge and Haag patents. U.S. Patent No. 3,755,483 (Burress) describes a process for the production of ethylbenzene using zeolite ZSM-12 as the alkylation catalyst. According to the present invention, there is provided a process for the production of ethylbenzene with a low level of xylene impurity, said process comprising the steps of:

(a) alkylating benzene with ethylene in the presence of a catalyst comprising ZSM-5 under vapor phase conditions, said vapor phase conditions being sufficient to produce ethylbenzene and diethylbenzene;

(b) separating said diethylbenzene from said ethylbenzene produced in step (a) ;

(c) transalkylating said diethylbenzene from step (b) with benzene in the presence of a catalyst comprising a zeolite under liquid phase conditions, said liquid phase conditions being sufficient to produce ethylbenzene; and

(d) combining the ethylbenzene produced in step (a) with the ethylbenzene produced in step (c) , wherein the combined ethylbenzene product of step (d) contains less than 1000 ppm xylene impurity.

The catalyst in the present vapor phase alkylation reaction comprises zeolite ZSM-5. ZSM-5 is described in U.S. Patent No. 3,702,886. The use of ZSM-5 as a catalyst in the vapor phase alkylation of benzene with ethylene is described in the aforementioned U.S. Patent No. 3,751,504.

The catalyst in the present liquid phase transalkylation reaction comprises a zeolite, preferably a large pore zeolite, such as zeolite Y and, especially, zeolite beta. Zeolite beta is described in U.S. Patent No. 3,308,069. The use of zeolite beta as a catalyst in the liquid phase transalkylation of diethylbenzene with benzene is described in U.S. Patent No. 4,891,458.

The present process can be carried out at high ethylene conversion to produce an ethylbenzene product with very low content of impurities such as xylenes, cumene, butylbenzene and heavy aromatic residues including the more highly alkylated benzenes. The xylene level of the product is notably low at less than about 1000 ppm, which is an important advantage commercially. By adjusting process parameters in a suitable manner, it is possible to obtain a xylene level of the product of less than 800 ppm, even less than 500 ppm, without taking any measures to remove xylene from the product.

Each of the zeolite catalysts used in the process of the invention may be composited with another material which is resistant to the temperatures and other conditions employed in the process. Such materials include active and inactive materials and synthetic or naturally occurring zeolites as well as inorganic materials such as clays and/or oxides such as alumina, silica, silica- alumina, zirconia, titania, magnesia or mixtures of these and other oxides. The latter may be either naturally occurring or in the form of gelatinous precipitates or gels including mixtures of silica and metal oxides. Clays may also be included with the oxide type binders to modify the mechanical properties of the catalyst or to assist in its manufacture. Use of a material in conjunction with the zeolite, i.e., combined therewith or present during its synthesis, which itself is catalytically active may change the conversion and/or selectivity of the catalyst. Inactive materials suitably serve as diluents to control the amount of conversion so that products can be obtained economically and orderly without employing other means for controlling the rate of reaction. These materials may be incorporated into naturally occurring clays, e.g., bentonite and kaolin, to improve the crush strength of the catalyst under commercial operating conditions and function as binders or matrices for the catalyst. The relative proportions of zeolite and inorganic oxide matrix vary widely, with the zeolite content typically ranging from 1 to 90 percent by weight and more usually, particularly when the composite is prepared in the form of beads, in the range of 2 to 80 weight percent of the composite.

The stability of the catalysts used in the present process may be increased by steaming. U.S. Patent NOS. 4,663,492; 4,594,146; 4,522,929; and 4,429,176, describe conditions for the steam stabilization of zeolite catalysts which can be utilized to steam-stabilize the catalyst. The steam stabilization conditions typically include contacting the catalyst with, e.g., 5-100% steam at a temperature of at least about 300°C (e.g., 300-650°C) for at least one hour (e.g., 1-200 hours) at a pressure of 100-2,500 kPa. In a more particular embodiment, the catalyst can be made to undergo steaming with 75-100% steam at 315°-500°C and atmospheric pressure for 2-25 hours. The steaming of the catalyst can take place under conditions sufficient to initially increase the Alpha Value of the catalyst and produce a steamed catalyst having an enhanced Alpha Value. If desired, steaming can be continued to subsequently reduce the Alpha Value from the higher Alpha Value to an Alpha Value which is substantially the same as, or lower than, the Alpha Value of the unsteamed catalyst. The alkylation reaction between the benzene and the ethylene requires the alkylation catalyst to possess acidic activity and for this reason the catalyst will normally have a relatively high Alpha Value. Alpha Values of at least about 10 e.g. 40 or higher are typical, and Alpha Values above 100 have been demonstrated as useful in this process. A zeolite Alpha Value is an approximate indication of the catalytic cracking (acidic) activity of the catalyst compared to a standard catalyst and it gives a relative rate constant based on the activity of a highly active silica-alumina cracking catalyst taken as an Alpha of 1 (Rate Constant = 0.016 sec ~ ). The Alpha Test is described in U.S. Patent 3,354,078, in the Journal of Catalysis. Vol. 4, p. 527 (1965); Vol. 6, p. 278 (1966); and Vol. 61, p. 395 (1980). The experimental conditions of the tests may include a constant temperature of 538°C and a variable flow rate as described in detail in the Journal of Catalysis. Vol. 61, p. 395. Excessive activity may lead to the production of undesired quantities of xylenes by secondary reactions and for this reason, Alpha Values of 10 to 100 will normally be adequate although higher Alpha Values, e.g. 100 to 500, may be employed. The alkylation reaction is carried out at elevated temperatures in the vapor phase. Suitable conditions can be selected by reference to the phase diagram for benzene. In the vapor phase reaction, the conditions are selected to maintain the benzene in the vapor phase, for example, with a reactor inlet temperature which is above the temperature required to maintain the benzene in the vapor phase at the selected pressure, with a preferred maximum of about 900°F (about 480°C) . Because the reaction is exothermic, the reactor bed temperature will be higher than the reactor inlet temperatures, typically by as much as about 150°F (about 85°C) but generally it is preferred to control the exotherm to a maximum of about 100°F (55°C). In most cases, the reaction temperature will be from 300°F (about 150°C) to 950°F (510°C) with the yield of ethylbenzene increasing with increasing temperatures. Normally, a temperature of at least 500^βF (about 260°C) will be used. Because the yield of PEB and certain other by¬ products usually decreases with increasing temperature, higher temperatures toward 900°F (about 480°C) would be preferred, although a disadvantage of these higher temperatures is that the yield of xylenes would be increased. The weight ratio of ethylbenzene to diethylbenzene produced in the vapor phase alkylation step (a) may be from about 2 to about 30.

Pressures during the vapor phase alkylation step typically are between atmospheric and about 3000 psig (100 to 20875 kPa) but preferably do not exceed 1000 psig (about 7000 kPa) . Relatively low pressures, for example, 50 or 100 psig (445 or 790 kPa) , sufficient to maintain the desired flow rates through the reaction bed, will normally be satisfactory. The reaction is preferably carried out in the absence of hydrogen and accordingly the prevailing pressures are usually those of the reactant species. In a typical low pressure vapor phase operation, the temperature will be from 600 to 900°F (315 to 480°C) with the pressure from 50 to 500 psig (450 to 3550 kPa) , usually 200 to 500 psig (1480 to 3550 kPa) . The space velocity may be from 0.1 to 10 WHSV, based on the ethylene feed, but is usually maintained at a relatively high value e.g. 1 to 10 WHSV, typically between 1 to 6 WHSV, based on the ethylene, for the gas phase reaction. The ratio of the benzene to the ethylene in the alkylation reactor is typically from 1:1 to 30:1 molar, normally 5:1 to 20:1 molar and in most cases 5:1 to 10:1 molar.

The use of temperatures significantly above 950^βF (510^βC) is undesirable because at these high temperatures, a number of undesirable reactions occur. The reactants and the alkylated products undergo degradation resulting in the loss of the desired products as well as the reactants and in addition, undesirable residues may be formed from other side reactions. The ethylene which functions as the alkylating agent will tend to polymerize with itself, especially at high pressures or with other reactants to form resinous compounds within the reaction zone. These resinous compounds together with the degradation products may lead to the formation of coke-like deposits on the active surfaces of the catalyst which will rapidly inhibit the high activity necessary in the catalyst for acceptable conversion rates. The use of temperatures below 900°F (480°C) will normally enable these problems to be maintained within acceptable bounds. The alkylation process can be carried out as a batch-type, semi-continuous or continuous operation utilizing a fixed, fluidized or moving bed catalyst system. The process is, however, preferably operated in the general manner described in U.S. Patent No. 3,751,504 (Keown).

The present liquid phase transalkylation step may be carried out at a temperature in the range of 250 to 600°F (120 to 315°C) and a pressure in the range 300 to 900 psig (2170 to 6310 kPa) . A possible combination of temperature and pressure within these ranges involves the use of high temperatures, such as from 460 to 600°F (238 to 315°C), e.g., about 500°F (260°C) , and high pressures, such as from 650 to 900 psig (4580 to 6310 kPa) , e.g., about 700 psig (4930 kPa) . The molar ratio of benzene to diethylbenzene in the liquid phase transalkylation step may be from 1:1 to 50:1. The liquid phase transalkylation step may be carried out at a weight hourly space velocity of 1 to 50, based upon the weight of the total liquid feed to the reactor. Relatively high weight hourly space velocities within this range, such as from 20 to 30, e.g., about 25, may be used, especially when the above-mentioned combination of high temperatures and pressures are employed.

It will be understood that the hydrocarbon feed to the transalkylation step may comprise other hydrocarbons in addition to benzene and diethylbenzenes. These hydrocarbons include byproducts from the vapor phase alkylation step which are carried over along with diethylbenzenes when diethylbenzenes are removed from the ethylbenzene product from the vapor phase alkylation step. These other hydrocarbons may include cumene, butylbenzenes and other polyethylbenzenes, such as triethylbenzenes. To the extent that other polyethylbenzenes, such as triethylbenzenes, are included in the feed to the transalkylation step, these other polyalkylbenzenes can contribute to the yield of ethylbenzene products obtained via transalkylation reactions of the polyethylbenzenes with benzene.

EXAMPLE Based on data derived from actual vapor phase alkylations of benzene with ethylene, coupled with data derived from an actual liquid phase transalkylation, a simulated overall reaction is summarized as follows: Gas Phase Alkylation Reactor with ZSM-5 Catalyst Operating pressure, psig

Reactor inlet temperature, °F(°C) Overall BZ/C- = ratio, wt. Ethylene WHSV

Ethylene conversion, wt.% PEB/EB ratio, wt.

Xylenes/EB, wt. ppm

Liquid Phase Transalkylation Reactor With Zeolite Beta Catalyst

Operating pressure, psig 500 (3550 kPa) Reactor inlet temperature, °F(°C) 500 ( 260) BZ/PEB, Wt. 3

WHSV, total feed 20

DEB conversion, wt.% 57

C₉ BZ conversion, wt.% 9 C₁₀ BZ conversion, wt.% 20 Xylenes/EB, wt. ppm

Overall System

EB made in alkylator, % of total 80 EB made in transalkylator, % of total 20

Xylenes/total EB, wt. ppm 640

Lights/total EB, wt% 1.3

Heavy Residue/Total EB, wt.% 0.5

Claims

Clai s :

1. A process for the production of ethylbenzene with a low level of xylene impurity, said process comprising the steps of: (a) alkylating benzene with ethylene in the presence of a catalyst comprising ZSM-5 under vapor phase conditions, said vapor phase conditions being sufficient to produce ethylbenzene and diethylbenzene; (b) separating said diethylbenzene from said ethylbenzene produced in step (a) ;

2. A process according to claim 1, wherein the zeolite in the catalyst of the liquid phase transalkylation step (c) is zeolite Y or zeolite beta.

3. A process according to claim 1, wherein the zeolite in the catalyst of the liquid phase transalkylation step (c) is zeolite beta.

4. A process according to claim 1, wherein the molar ratio of benzene to ethylene in the vapor phase alkylation step (a) is greater than or equal to 1 and wherein the percentage of ethylene converted in step (a) is at least 95%.

5. A process according to claim 1, wherein the weight ratio of ethylbenzene to diethylbenzene produced in vapor phase alkylation step (a) is from 2 to 30.

6. A process according to claim 1, wherein the liquid phase transalkylation step (c) is carried out at a temperature in the range 250 to 600°F (120 to 315°C) and a pressure in the range 300 to 900 psig (2170 to 6310 kPa) .

7. A process according to claim 6, wherein the molar ratio of benzene to diethylbenzene in the liquid phase transalkylation step (c) is 1:1 to 50:1.

8. A process according to claim 7, wherein the liquid phase transalkylation step (c) is carried out at a weight hourly space velocity of 1 to 50, based upon the weight of the total liquid feed to the transalkylation step (c) .

9. A process according to claim 1, wherein the vapor phase alkylation step (a) is carried out at a pressure from 50 to 500 psig (450 to 3550 kPa) and at a temperature from 600 to 800°F (315 to 480°C) .

10. A process according to claim 1, wherein the molar ratio of benzene to ethylene in step (a) is from 1:1 to 30:1, based on the total feed to the reactor.