WO1993002027A1

WO1993002027A1 - Process for extending the life of alkylation catalysts

Info

Publication number: WO1993002027A1
Application number: PCT/US1992/002877
Authority: WO
Inventors: Ali Mohammad Khonsari; John Earle Paustian; George Dan Suciu
Original assignee: Abb Lummus Crest Inc.
Priority date: 1991-07-18
Filing date: 1992-04-06
Publication date: 1993-02-04
Also published as: AU2002292A; MX9202524A; CN1068809A

Abstract

An improvement in a process for the alkylation of at least one aromatic (e.g. benzene) with at least one olefin to produce at least one monoalkylaromatic in a reaction zone in the presence of an alkylation catalyst. The improvement comprises admixing with at least one aromatic and at least one olefin an additive selected from the group consisting of alcohols and water. The addition of an alcohol or water to the feed results in increased catalyst life, and enables one to conduct alkylation reactions at lower aromatic-to-olefin mole ratios.

Description

PROCESS FOR EXTENDING THE LIFE OF ALKYLATION CATALYSTS

This invention relates to extending the life of ah alkylation catalyst, such as, for example, a zeolite alkylation catalyst. More particularly, this invention relates to a process for extending the life of an alkylation catalyst employed in the alkylation of aromatics with olefin to produce alkylaromatics.

In an alkylation reaction, an aromatic compound (for example, benzene, napthalene, or tetralin) and a olefin (for example, ethylene, propylene, or butylene) are reacted in an alkylation reactor under catalytic conversion conditions, in the presence of an alkylation catalyst, to produce alkylaromatics. For example, benzene may be reacted with ethylene or propylene to produce ethylbenzene or cumene, respectively. The reactor contains one or more beds of alkylation catalyst. The catalyst may be a zeolite catalyst or other type of alkylation catalyst.

The alkylation may be carried out in the liquid phase, the vapor phase, or a mixed vapor-liquid phase. Because such alkylation reactions are very exothermic, one can maintain the operating temperatures most favorably by providing for heat removing capabilities within the catalyst bed or by performing the reaction in a staged manner and provide for adequate cooling between the stages. Such an adiabatic method of operation is preferable. In order to limit the temperature increase in each reaction stage, one uses an excess of aromatics over the olefin, and one may limit the amount of olefin introduced into the reaction mixture in each of the reactor stages when multiple stages are employed. Also, the excess of aromatics will reduce the amount of undesirable polyalkyl aromatics formed in each reaction stage. For example, in the manufacture of alkylbenzene (eg., ethylbenzene or cumene), one may use an overall molar ratio of benzene to olefin of from about 5:1 to about 6:1. If multiple reaction stages are employed, the ethylene may be added in separate portions to each reaction stage. Cooling may be provided after each stage, following the conversion of each portion of the olefin. Preferably, the olefin is divided in equal parts between the stages. Under catalytic conversion conditions, the reaction is very fast, and only a thin layer of the catalyst bed is able to convert the olefin completely.

As the time on-stream of each bed of catalyst increases, deactivation of catalyst gradually takes place. Deactivation of catalyst is accompanied by a displacement of the zone in which the reaction takes place along the catalyst bed. After the reaction zone is displaced completely along the length of the catalyst bed, the catalyst is regenerated. The faster the rate of displacement of the peak temperature, the more frequent the need will be for regenerating or replacing catalyst in the bed. The rate of catalyst deactivation is proportional, in otherwise constant conditions to the rate of alkylbenzene production. The rate of catalyst deactivation also increases with decreasing benzene-to-olefin ratios. At low benzene-to-olefin ratios, some of the olefins may oligomerize and form other olefins of high molecular weight. These olefins may alkylate benzene rings to form alkylates with long side chains. In addition, the selectivity to polyalkylbenzenes, such as dialkyl, trialkyl, and tetraalkyl benzenes, increases as benzene-to-olefin ratios decrease. In general, the rate of catalyst deactivation increases with increased concentrations of heavy alkylbenzenes and polyalkylbenzenes. These heavy products adsorb preferentially on the active sites of the catalyst, will polymerize and will not be desorbed from the catalyst any more. The catalyst thus becomes deactivated.

Temperature also has an effect upon catalyst activity. At temperatures below the optimal range, a larger selectivity to polyalkylbenzenes will result, thus producing a greater deactivation rate. At temperatures above the optimal range, cracking of polyalkylbenzenes can take place and reactive species which are able to produce polymers and other high-boiling materials will accelerate the rate of deactivation of the catalyst.

The deactivation rate can be quantified as an "activity parameter", or AP. The activity parameter is calculated by dividing the mass of alkylbenzene produced during a certain time span by the mass of catalyst which has deactivated in the process, during the same length of time. Catalysts which have a relatively high AP value have a longer life before replacement or regeneration is needed. Catalysts which have a relatively low AP value require more frequent regenerations, which are usually accompanied by production loss and/or additional costs. It has also been found that catalysts, which when fresh have a high AP value, will have a much smaller AP value after regeneration; i.e., after regeneration, the catalyst will deactivate much faster than before regeneration. Such phenomena are undesirable because they increase the operating costs and reduce the ability to predict catalyst performance.

It is therefore an object of the present invention to provide an improved alkylation process whereby the catalyst life is extended.

In accordance with an aspect of the present invention, there is provided an improvement in a process for the alkylation of at least one aromatic with at least one olefin to produce at least one monoalkylaromatic in a reaction zone in the presence of an alkylation catalyst. The improvement comprises admixing with the at least one aromatic and the at least one olefin an additive selected from the group consisting of alcohols and water.

Aromatics which may be alkylated include, but are not limited to, benzene, naphthalenes, and tetralins. Olefins which may be employed to alkylate the aromatic compounds include, but are not limited to, ethylene, propylene, butene, and mixtures thereof. In one embodiment the at least one aromatic is benzene. Representative examples of alkylation reactions which may be conducted in accordance with the present invention include the alkylation of benzene with ethylene to produce ethylbenzene, an,d the alkylation of benzene with propylene to produce cumene.

In one embodiment, the alkylation may take place at an aromatic-to-olefin molar ratio of from about 3:1 to about 30:1, preferably from about 5:1 to about 6:1.

In one embodiment, the additive is water. Preferably, the water is present in an amount of at least 100 ppm based on the benzene feed, more preferably from about 200 ppm to about 1,500 ppm, still more preferably from about 300 ppm to about 1,000 ppm, and most preferably from about 400 ppm to about 800 ppm, all based on the benzene feed. The exact amount of the water added depends upon the aromatic-to-olefin ratio employed and the nature and state of the alkylation catalyst.

In accordance with another embodiment, the additive may be an alcohol. Although any type of alcohol (eg. , mono- or dihydro alcohols, phenols, ethanols) may be employed, it is preferred, however, to use an alcohol which will not increase the number of impurities or by-products in the reactor effluent. For example, if one is alkylating benzene with ethylene to produce ethylbenzene, the alcohol added to the feed preferably is ethanol. If one is alkylating benzene with propylene to produce cumene, the preferred alcohol is isopropanol. In cases where the desired alkylate is not necessarily one pure compound, mixtures of alcohols may be used as additives.

The alcohol should be present in an amount effective to extend the life of the catalyst; however, the amount of alcohol present in the feed should not be present in amounts which would result in the formation of undesirable quantities of water as a reaction by-product, or be present in an amount which could suppress the rate of the alkylation reaction. Preferably, the alcohol may be present in amount of from about 1 mole % to about 10 mole % based on the amount of olefin employed, or from about 0.2 wt. % to about 0.5 wt. % based on the weight of benzene.

The alkylation may be carried out in the liquid phase, the vapor phase, or a mixed vapor-liquid phase. The alkylation may be carried out at a temperature of from about 250°F to about 900°F, preferably from about 350°F to about 600°F, at a pressure of from about 150 psig to about 2,000 psig, preferably from about 250 psig to about 1,000 psig, and at a total WHSV from about 2 to about 1,000 hr. preferably from about 4 to about 100 hr.^~ . WHSV means Weight Hourly Space Velocity, and is expressed as mass of feed per unit mass of catalyst, or hr, -1.

The alkylation catalyst which may be employed preferably is a zeolite catalyst. The zeolite catalyst, in one embodiment, is free of hydrogenating metals. Zeolite catalysts which may be employed include zeolite X, zeolite Y, zeolite L, zeolite-Beta, ZSM-5, Omega zeolites, mordenite, and chabazite. In one embodiment, the zeolite may be zeolite Y or zeolite-Beta. Preferably, the zeolites are in acidic form.

The invention will now be described with respect to the following examples; however, the scope of the present invention is not intended to be limited thereby.

For the following examples, unless otherwise noted, the following conditions are employed:

The alkylation reactor which is employed consists of a 1" (inner diameter) steel tube packed with catalyst over a length of 20" and is provided with an axially-placed traveling thermocouple. The reactor is placed within a thick layer of insulation so that it operates in an adiabatic mode. Benzene is fed by a metering pump through a preheater into the lower end of the reactor. Ethylene is metered by a mass flow controller and is mixed with the benzene before the benzene enters the preheater. The reaction mixture leaving through the top of the reactor passes through the cooler and a back pressure regulator, and is collected in a storage tank. In each of two equal reactor stages, the benzene and ethylene are reacted in each stage at a benzene to ethylene (B/E) molar ratio of 12/1. The overall B/E molar ratio, therefore, is 6/1. The preheat temperature is adjusted so that the peak temperature obtained in each reactor stage is from about 475°F to about 485°F. The pressure in the system is maintained at from about 550 psig to about 600 psig. The position of the peak temperature is determined from plots of the temperature profile as measured by the axial thermocouple.

Example 1

The catalyst consists of a commercial zeolite, designated as zeolite "A", shaped as an extrudate with diameter of 1/16" and length of approximately 1/4" . In operating the reactor system for 840 hours, a displacement of the peak temperature of 1.35" was measured.

Based on the flow rate of ethylene, one can calculate the amount of ethylbenzene (EB) produced. The weight of the catalyst contained in the reactor volume limited by the positions of the peak temperature at the beginning and the end of the same time interval, was deactivated. Using these values one calculates an activity parameter of 14,000 kgEB/kg catalyst deactivated. The change in position of the peak temperature with time for this catalyst is depicted in Figure 1.

Example 2 Another commercial zeolite, designated as zeolite "B", was tested in an adiabatic experimental unit in conditions as described above. An activity parameter of 6,000 kgEB/kg catalyst was obtained. The change in position of the peak temperature with time for this catalyst is depicted in Figure 2.

Example 3 A sample of Zeolite "A", after it had been deactivated in performing alkylation of benzene to ethylbenzene, was regenerated as known in the art by selectively combusting the heavy organic materials deposited on it. The regenerated catalyst was used in an adiabatic alkylation in the conditions described above. An activity parameter of 1,100 kgEB/kg catalyst was obtained. The change in position of the peak temperature with time is presented in Figure 3.

Example 4

A sample of Zeolite "A" was treated as in Example 3 with the exception that the benzene contained 0.2wt% ethanol dissolved therein. This ethanol is equivalent to 5% of the ethylene fed to the reactor. The rest of the required ethylene was fed as gas which was dissolved in the benzene feed as described above. The change in position of the peak temperature with time is shown in Figure 4. From this one calculates an activity parameter of 32,700 kgEB/kg catalyst. If the addition of ethanol were stopped, the deactivation rate of the catalyst increased immediately, as indicated by the curve of Figure 4 at times greater than 168 hrs. This example shows that the beneficial impact of the ethanol addition is lost if the addition is interrupted.

Example 5

The same catalyst and reaction conditions, as described in Example 1 were used, with the exception that in the benzene feed line a liquid-liquid contacting vessel was provided in order to achieve the saturation of the benzene stream with water. The vessel contained a layer of water through which the benzene feed passed as small drops. The benzene phase accumulating at the top of the water layer was saturated with water. It was further mixed with ethylene, preheated and fed to the reactor as above. Samples of the reactor effluent showed concentrations of 500-650 ppm water which correspond to approximately 80-90% of the saturation concentration at the contacting temperature (20-25°C) . The displacement of the position of the peak temperature within the bed during 540 hours of testing is indicated in Figure 5. For this test one calculates an activity parameter (AP) of 39,800 kgEB/kg catalyst. This test shows that water fed to the reactor in the amounts indicated can significantly increase the stability of the catalyst as expressed by the increased value of AP. In a separate test, the above conditions were repeated with the exception that the amount of water fed to the reactor was approximately 200 ppm. A minimal effect on the catalyst deactivation rate was obtained.

Example 6 The reactor system and procedures described in Example 2, were employed. A different zeolite catalyst, designated as zeolite "C", had essentially the same shape and size as zeolite "A". Its acidity, however, was higher. The curve of Figure 6 presents the change of the position of the peak temperature with time on stream. Up to 100 hours no water was introduced in the system. After that time, the water-benzene contactor, as described in Example 5, was employed. The immediate effect of water addition on the stability of the zeolite catalyst is proven by the lower slope of the curve depicting the displacement of the position of the peak temperature in time.

Example 7 The same reactor system and operating conditions as those in Example 1 were used. This run tested whether the addition of water and/or ethanol could stabilize the performance of the catalyst at lower B/E values than those practiced in the previous examples. In each stage, a B/E ratio of 10/1 was used; i.e., B/E = 5/1 overall. The position of the peak temperature at various times on-stream is indicated in Figure 7. The run was started with dry benzene. For the first 90 hours of operation, the activity parameter was 350kg EB/kg catalyst. After 90 hours on-stream, 0.4wt% ethanol was admixed with the benzene feed. The alkylator effluent contained 1000 ppm H-0. For the period during which the ethanol addition occurred, one calculates an activity parameter of 13,700 kgEB/kg catalyst. This example shows that the beneficial effect of the ethanol and/or the water produced by the reaction of ethanol with benzene on the catalyst deactivation rate is also maintained when the ethylene concentration in the feed is higher than in the previous examples.

Advantages of the present invention include the ability to obtain longer operation times for the reactor system between catalyst regenerations, due to the decrease in the rate of deactivation of the catalyst. Also, smaller volumes of catalyst may be employed for the same plant capacity. In addition, by reducing the rate of catalyst deactivation at increased concentrations of olefin in the feed, the reactor can operate at higher alkylbenzene concentrations in the effluent, and therefore, smaller reactors may be employed for a given capacity.

It is to be understood, however, that the scope of the present invention is not to be limited to the specific embodiments described above. The invention may be practiced other than as particularly described and still be within the scope of the accompanying claims.

Claims

WHAT IS CLAIMED IS:

1. In a process for the alkylation of at least one aromatic with at least one olefin to produce at least one monoalkylaromatic, in a reaction zone in the presence of an alkylation catalyst, the improvement comprising: admixing with said at least one aromatic and said at least one olefin an additive selected from the group consisting of alcohols and water.

2. The process of Claim 1 wherein said additive is water.

3. The process of Claim 2 wherein said water is present in an amount of at least 100 ppm.

4. The process of Claim 3 wherein said water is present in an amount of from about 200 ppm to about 1,000 ppm.

5. The process of Claim 4 wherein said water is present in an amount of from about 300 ppm to about 900 ppm.

6. The process of Claim 5 wherein said water is present in an amount of from about 400 ppm to about 800 ppm.

7. The process of Claim 1 wherein said additive is an alcohol.

8. The process of Claim 1 wherein said at least one aromatic is benzene.

9. The process of Claim 1 wherein said at least one aromatic is alkylated with said at least one olefin at an aromatic-to-olefin molar ratio of from about 3:1 to about 30:1.

10. The process of Claim 9 wherein said at least one aromatic is alkylated with said at least one olefin at an aromatic-to-olefin molar ratio of from about 5:1 to about 6:1.

11. The process of Claim 8 wherein the the at least one olefin is ethylene.

12. The process of Claim 11 wherein the at least one olefin is propylene.

13. The process of Claim 11 wherein the at least one monoalkylaromatic is ethylbenzene.

14. The process of Claim 8 wherein the at least one monoalkylaromatic is cumene.

15. The process of Claim 8 wherein the additive is an alcohol.

16. The process of Claim 15 wherein said alcohol is present in an amount of from about 0.2wt.% to about 0.5wt.% based upon the weight of benzene.

17. The process of Claim 15 wherein the olefin is ethylene and the alcohol is ethanol.

18. The process of Claim 15 wherein the olefin is propylene and the alcohol is isopropanol.

19. The process of Claim 1 wherein said alkylation catalyst is a zeolite catalyst.