GB1602460A - Process for the alkylation of aromatic hydrocarbons - Google Patents

Description

(54) PROCESS FOR THE ALKYLATION OF AROMATIC HYDROCARBONS (71) We. UOP INC, a corporation organized under the laws of the State of Delaware United States of America, of Ten UOP Plaza, Algonquin & Mt. Prospect Roads, Des Plaines. Illinois. United States of America. do hereby declare the invention, for which we pray that a Patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following Statement: The present invention relates to an improved process for the alkylation of an aromatic hydrocarbon in the presence of a catalyst system comprising a titanium tetrahalide selected from the tetrachloride and the tetrafluoride.

The invention will be described particularly with reference to the synthesis of cumene by alkvlation of benzene with propylene in the presence of the catalyst, but it is not limited to this feed stock.

There has been extensive work done with Ti catalysts, though most work occurred in conjunction with studies of Ziegler-Natta catalysts. The closest prior art known includes U.S. Patent 2.381.481 U.S. Patent 2.951,885. U.S. Patent 2,965,686 and U.S. Patent 3.153.634.

According to the present invention there is provided a process for the alkylation of an aromatic hydrocarbon comprising contacting the aromatic hydrocarbon with an alkylating agent at aromatic hydrocarbon alkylation conditions in the presence of a catalyst system prepared by contacting titanium tetrachloride and/or titanium tetrafluoride composited with a Group III-A metal oxide support containing surface hydroxyl groups, and recovering an alkylated aromatic hydrocarbon product.

Specific examples of Group III-A metal oxides which possess surface hydroxyl groups and which also possess a relatively high surface area are alumina, gallium oxide, indium oxide, and thallium oxide. Of these compounds, the preferred substrate is alumina, and especially low density. high surface area aluminas such as gamma-alumina or eta-alumina.

The apparent bulk density of the alumina may range from 0.3 to 0.7 g/cmi or higher with a surface area ranging from 1 to 5()0 m/g. The alumina may have any desired shape, for example spheroidal particles of alumina. A commercial gamma-alumina may be used as the support. However. as this material may contain excessive water, it is preferably subjected to a predrying step by heating to a temperature in the range of from 400 to 55() C under an inert gas or hydrogen flow for a period of 1 to 8 hours.

To composite titanium tetrachloride with the support. preferably the predried gammaalumina support. a gas mixture of nitrogen and titanium tetrachloride which has been prepared by bubbling nitrogen gas through the liquid titanium tetrachloride at room temperature may be passed over the gamma-alumina at temperatures of 20 to 4()() C.

Thereafter the temperature is increased. e.g. to 55() C or more. The passage of the nitrogen-titanium tetrachloride mixture over the alumina is suitably effected for 0.5 to 10 hours or more. It is preferred to pass the titanium tetrachloride or the gaseous mixture over the support at a temperature of 25 to 1350 C. The temperature is generally then raised, e.g. to 25()0C or another desired temperature. either gradually or in a series of steps. The preferred temperature for the heat treatment of this resulting composite is from 135 to 55() C. It is preferred that the temperature which is used in the treatment of the composite be equal to. or higher than. the aromatic hydrocarbon conversion temperature. Thereafter the temperature may be maintained at this point and a stream of nitrogen passed over the catalyst composite. e.g. for an additional I to 1() hours. The finished catalyst is then sealed under an inert atmosphere such as argon, helium or nitrogen prior to being used.

Alternatively, the titanium tetrachloride catalyst may be prepared by forming a solution of titanium tetrachloride in a polar, non-aqueous organic solvent and impregnating the alumina. The impregnated alumina is then treated under a nitrogen flow at temperatures in the range hereinbefore set forth.

It is also within the scope of this invention that one or more promoters may be added to the catalyst system, selected from the metals of Group VIB (i.e. chromium, molybdenum, tungsten) or Group VIII of the Periodic Table.

At least 0.5 weight percent titanium, on an elemental basis, is believed necessary in the catalyst system for a significant amount of reaction to occur. The practical upper limit on titanium is 20 wt. % of the catalyst system.

In preparing the titanium tetrafluoride catalyst, either of two different catalyst preparation techniques may be used, sublimation and impregnation.

Sublimation techniques may involve passing TiCl4 vapor over alumina having surface hydroxyl groups at a temperature of 20 to 4000C for 1 to 10 hours, or subliming TiF4 in a carrier gas and contacting the gas and TiF4 with the support at a temperature of 284 to 7000C.

In one sublimation procedure titanium tetrafluoride may be placed on top of a bed of gamma-alumina. Preferably the support is predried, provided that the predrying does not remove the surface hydroxyl groups. The titanium tetrafluoride and alumina should be maintained in a dry, inert atmosphere after drying. While passing nitrogen downflow over the mixture of alumina and titanium tetrafluoride, the temperature is slowly increased to a temperature above (preferably slightly above) the sublimation temperature of titanium tetrafluoride, then the temperature is progressively increased to elevated temperatures.

This thermal treatment step is preferably carried out at 250 to 350" C for one-half to two hours, followed by treatment at 400 to 6000 C for one to ten hours.

Another way to prepare catalyst for use in the present invention is to impregnate the Group III-A metal oxide with a solution containing a compound which will decompose to form titanium tetrafluoride upon heating in an inert atmosphere while not converting TiF4 to lower valence Ti compound. A preferred titanium tetrafluoride impregnating solution consists of an organic or aqueous solution of TiF4 or an aqueous solution of M2TiF6, where M equals H, Li, Na, or K. In all impregnating methods it is preferred to contact the metal oxide with impregnating solution at room temperature and then progressively increase the temperature to evaporate the solution. The catalyst is then preferably thermally treated at 100 to 200"C for one-half to two hours and then at 250 to 350" C for one-half to two hours and then at 400 to 600" C for one to ten hours under an inert atmosphere.

The impregnation of the titanium compounds onto the Group III-A metal oxide is preferred. because it is possible to vary over a wide range the concentration of titanium compound in the finished catalyst system.

The ratios of reactants and other reaction conditions when alkylating benzene with propylene may be basically those well known in the art. The pressure may range from 1 to 100 atmospheres. or even higher, but should be high enough to ensure a liquid phase. The preferred pressure is 20 to 60 atm. with optimum pressure being about 35 atm.

The temperature may range between ambient and 250"C. Preferred temperatures are 100 to 200"C.

The catalyst may be disposed in a reactor vessel as a fixed, fluidized or moving bed of catalyst. The reactants may contact the catalyst in upflow. downflow or crossflow fashion, though upflow of reactants over a fixed bed of catalyst is preferred.

The liquid hourly space velocity in the reactor may range from 0.1 to 20. However. higher LHSV is possible depending on the desired conversion level of propylene.

Example I This example shows how to make a catalyst via a sublimation technique. About 200 ml of gamma-alumina in the form of 1.6 mm spheres, prepared by the well known oil method, was dried at 550" C for 300 minutes under H2 flow. The apparent bulk density was 0.52 g/cc.

The H2 flow was replaced with N2 flow and the alumina cooled to room temperature. About 30 grams of TiF4 was placed on top of the predried alumina. Temperature was slowly increased to 310 C while maintaining a downflow of N2 over the alumina. This temperature was maintained for 90 minutes. Temperature was then increased to 350"C for 15 minutes, then to 4000 C for 30 minutes.

Example II This example shows how to make an impregnated catalyst of the present invention.

Gamma-alumina was impregnated with aqueous TiF4, solution. The solution was prepared by dissolving H2TiF6 in deionized water. The alumina and impregnating solution were cold rolled in a rotating steam drier, then steam was turned on to evaporate the solution. These catalysts were then given further thermal treatments under N2 flow. In one instance, a Cr promoter was added to the catalyst by dissolving Cr03 in the impregnating solution. Details of the preparation of these catalysts are shown in Table I. There were catalyst A, B, and C.

TABLE I IMPREGNATION THERMAL TREATMENT (All With 2000 cc/min N2 Flow) Impreg. Solution Catalyst Alumina 60%H2TiF6 Volume Cold Roll First Second Third Fourth cc g cc cc minutes C/hours C/hours C/hours C/hours A 200 12.44 7.55 250 60 150/1 200/1.25 300/1 500/5 B 125 6.0 4.0 125 30 150/1 200/1 300/1 350/3.25 C 300 16.5 10.0 300 30 140/1 300/1.5 500/3 - / Note: Catalyst A also contained Cr added by dissolving 5.15 g CrO3 to the impregnating solution Example III The catalysts were tested in a laboratory scale plant. The reaction studied was alkylation of benzene with propylene. The catalyst was maintained as a fixed bed, of 50 cc volume.

The reactants were passed upflow over the catalyst bed. Benzene was dried by circulating it over high surface area sodium. Pure propylene was dried by passing it over type 4-A molecular sieves. The dried benzene and propylene were mixed together and then charged to the reactor. The reactions were all carried out at 120 to 2450C, 1 to 4.2 LHSV, and 25 to 55 atmospheres pressure. The reactor was started up full of liquid benzene and then the mixture of propylene and benzene added. It is believed that if propylene alone is charged, or even propylene and benzene charged simultaneously, high molecular weight polymer may form.

Reaction conditions and test results are reported in Table II. Conversion (C) refers to conversion of propylene in the feed, while selectivity (S) refers to moles of cumene produced per mole of propylene reacted, expressed as mole percent. Productivity (P) refers to weight percent cumene in product.

TABLE II: SUMMARY OF RESULT Catalyst Reaction Conditions T( C) P(atm) Bz/C3= LHSV C S P B 120 55 6.24 1.1 72.1 59.2 69.1 B 150 55 6.00 2.0 80.3 62.3 72.4 B 150 35 4.6 0.9 84.2 57.5 67.4 B 150 55 7.5 2.0 78.6 74.6 77.2 C 120 35 4.68 1.1 95.5 62.1 71.0 C 150 25 4.84 2.9 81.7 61.7 71.0 C 150 25 7.85 2.0 93.0 69.6 77.6 C 150 35 5.03 1.0 95.0 60.7 70.0 C 120 25 5.20 2.1 96.3 60.6 70.2 Because of poor weight recoveries experienced when testing catalyst A, the results obtained with catalyst A are not recorded in Table II. However, the products obtained were analyzed. and it is believed that the analysis of products gives a good indication of the catalyst system's performance. Table Ill provides a comparison of the product streams produced by the different titanium tetrafluoride catalysts. From these data it can be observed that the catalyst containing chromium promoter is very selective for the production of cumene.

TABLE III Comparison of Various Supported Titanium Tetrafluoride Catalysts CATALYST A B C Hours of Operation 70 190 140 Analysis of product Benzene % by volume 5.5 74.2 79.2 Toluene Tr Cumene % by volume 32.9 18.0 12.8 n-Propylbenzene % by volume 0.1 1.4-Dimethyl 2-Ethylbenzene No by volume 6.1 Dipropylbenzene % by volume 6.7 5.1 Tripropylbenzene % by volume 1.0 1.1 Reaction Conditions T( C) 245 150 150 P(atm) 55 35 35 CH,/CH, 2.6 5.0 5.3 LHSV 4.2 1.0 2.1 Based on these studies it is believed that the important factor in the thermal treating steps is the temperature, rather than the total time, as long as the total period for thermal treatment is reasonably long, around five or six hours. It is believed that the activity of the catalyst is effected by the thermal treatment temperatures because the desorption of water molecules from the catalyst surface may require higher temperature than certain initial temperatures. Water can compete for active sites with the reactants, thus water is to some extent a catalyst poison. However, if catalyst deactivation occurs due to water adsorption, the catalyst can be regenerated by appropriate further thermal treatment under inert gas flow. Any regenerative thermal treatments, in that heating which is too rapid or too high a temperature, may cause hydrolysis of the TiF4 component on the catalyst, which would reduce catalyst activity.

Although water is discussed above as a catalyst poison, the titanium tetrafluoride catalyst system of the present invention is much less susceptible to attack by water than are corresponding titanium tetrachloride catalysts. For some reason, not yet fully understood, the fluoride is held much more tenaciously by the support than the corresponding chloride compounds.

The catalyst which contained a chromium compound in addition to TiF4 showed superior selectivity to cumene when compared to non-promoted TiF4 catalysts. It is not understood why the addition of Cr promoter is beneficial. The reaction may be more selective, but it is also possible that a certain amount of transalkylation also occurs.

The catalyst of the present invention also seems to be more stable than prior art catalyst.

The stability of a catalyst is technically very important. The Ti fluoride catalyst is very stable compared with the titanium chloride. The titanium catalyst is reasonably stable to air. A high water content in the feed or too long exposure to air will reduce catalyst activity.

However, it is possible to restore the catalyst activity by simply passing dry inert gas on the catalyst at elevated temperatures.

Example IV In this example a catalyst was prepared by predrying 125 cc of gamma-alumina at a temperature of 550" C for a period of six hours under a flow of 2000 cc/min. nitrogen gas.

Thereafter a gaseous mixture of nitrogen and titanium tetrachloride which was prepared by bubbling nitrogen gas through liquid titanium tetrachloride was passed over the gamma-alumina at a temperature of 75" C for a period of 40 minutes. The flow rate of nitrogen was 2000 cc/min. At the end of this time, the temperature was increased to 250 C while maintaining the nitrogen-titanium tetrachloride vapor flow over the gamma-alumina.

The nitrogen-titanium tetrachoride flow was discontinued and the catalyst composite was treated with a nitrogen flow for a period of 4.4 hours while maintaining the temperature at 250 C. At the end of this period, the catalyst was analyzed and found to contain 2.17% titanium and 4.86% chorine.

The reaction contemplated is alkylation of benzene with propylene. Catalyst is maintained as a fixed bed, of 50 cc volume. Reactants are passed upflow over the catalyst bed. Benzene is dried by circulating it over high surface area sodium. Pure propylene is dried by passing it over type 4-A molecular sieves. Benzene and propylene are mixed together and charged to the reactor. The reaction is carried out at 120 to 245 C, 1 to 3 LHSV and at 25 to 55 atmospheres pressure. The reactor is started up full of liquid benzene and then the mixture of propylene and benzene added. It is believed that if propylene alone is charged, or even propylene and benzene charged simultaneously, high molecular weight polymer may form. Using the conditions indicated above, a good yield of cumene is obtained.

While the invention has been described with emphasis upon propylene as alkylating agent, any other alkylating agent conventionally used for alkylation of aromatic hydrocarbons may be employed. Olefins are preferred alkylating agents, particularly preferred being ethylene, propylene and any of the C8 to C18 olefins. Benzene, toluene, ethylbenzene and xylene are the preferred aromatic hydrocarbons.

Claims (19)

WHAT WE CLAIM IS:

1. A process for the alkylation of an aromatic hydrocarbon comprising contacting the aromatic hydrocarbon with an alkylating agent at aromatic hydrocarbon alkylation conditions in the presence of a catalyst system prepared by contacting titanium tetrachloride or titanium tetrafluoride with a Group III-A metal oxide support containing surface hydroxyl groups, and recovering an alkylated aromatic hydrocarbon product.

2. A process as claimed in claim 1 wherein the catalyst system comprises titanium tetrachloride and an alumina support and is prepared by passing TiCI4 vapor over alumina having surface hydroxyl groups at a temperature of 20 to 400"C. for 1 to 10 hours.

3. A process as claimed in claim 1 wherein the catalyst system comprises titanium tetrafluoride and is prepared by impregnating the support with TiF4 and drying in an inert atmosphere at 100" to 600 C.

4. A process as claimed in claim 3 wherein the support is impregnated with TiF4 by means of an impregnating solution selected from aqueous solutions of TiF4, polar organic solvent solutions of TiF4 and aqueous solutions of M2TiF6 where M is H, Li, Na or K.

5. A process as claimed in claim 3 wherein the impregnated support is given a thermal treatment at 100 to 200"C. for one-half to two hours, then at 250 to 350"C. for one-half to two hours, and then at 400 to 600"C. for one to 10 hours.

6. A process as claimed in claim 1 wherein the catalyst system comprises titanium tetrafluoride and is prepared by subliming TiF4 in a carrier gas and contacting the gas and TiF4 with the support at a temperature of 284 to 700"C.

7. A process as claimed in claim 2 or 6 wherein the support containing titanium tetrahalide is given a thermal treatment at 250 to 350"C for one-half to two hours, and then at 400 to 600"C for one to 10 hours.

8. A process as claimed in any of claims 1 to 7 wherein the catalyst system contains, on an elemental basis. 0.5 to 20 weight percent titanium.

9. A process as claimed in any of claims 1 to 8 wherein the catalyst support is an eta-alumina or a gamma-alumina which has been predried by heating to from 400 to 500"C under an inert gas or hydrogen flow.

10. A process as claimed in claim 9 as appendent to claim 1 wherein the catalyst system is obtained by passing a gas mixture of nitrogen and titanium tetrachloride over a predried gamma-alumina at from 25 to 1350C for-at least 0.5 hour, then increasing the temperature gradually or in a series of steps to a temperature not less than the temperature used in the alkylation reaction and passing nitrogen over the catalyst composite, whereupon it is sealed under an inert atmosphere until use.

11. A process as claimed in claim 1 wherein the catalyst system is prepared by forming a solution of titanium tetrachloride in a non-aqueous polar organic solvent and impregnating alumina with the solution followed by increasing the temperature gradually or in a series of steps to a temperature not less than the temperature used in the alkylation reaction and passing nitrogen over the catalyst composite, whereupon it is sealed under an inert atmosphere until use.

12. A process as claimed in claim 6 wherein the catalyst system is obtained by placing titanium tetrafluoride on top of a bed of predried gamma-alumina still containing surface hydroxyl groups and passing nitrogen downflow over the mixture whilst raising the temperature to a value above the sublimation temperature of titanium tetrafluoride and then progressively to higher temperatures, the treatment being carried out at 250 to 3500C for 0.5 to 2 hours and at 400 to 600"C for 1 to 10 hours.

13. A process as claimed in any of the claims 1 to 12 wherein the aromatic hydrocarbon is benzene, toluene, ethylbenzene or xylene.

14. A process as claimed in any of the claims 1 to 13 wherein the alkylating agent is ethylene, propylene or one or more C8 to C18 olefins.

15. A process as claimed in claim 14 wherein benzene is alkylated with propylene at conditions including a pressure of from 1 to 100 atmospheres, a temperature of from ambient to 250"C and a liquid hourly space velocity of from 0.1 to 20.

16. A process as claimed in any of the claims 13 to 15 wherein the reactants are passed in upflow over a fixed bed of the catalyst.

17. A process as claimed in any of the claims 1 to 16 wherein the catalyst contains a promoter element from Group VIB or Group VIII of the Periodic Table.

18. A process as claimed in any of claims 1 to 17 wherein a catalyst system substantially as hereinbefore described in any of the foregoing Examples I, II and IV is used.

19. An alkylated aromatic hydrocarbon when manufactured by a process as claimed in any of the claims 1 to 18.