CA1075268A - Process for the conversion of aromatic hydrocarbons - Google Patents

Abstract

ABSTRACT

A process for the conversion of aromatic hydrocarbons is disclosed which is especially useful for reaction of an alkylating agent, preferably propylene, with an aromatic hydrocarbon. Novel feature is use of a catalyst system comprising TiCl4 and a Group III-A metal oxide.

Description

1~75Z68 .

PROCESS FOR THE CONVERSION
D~ A~ D~ DG~

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 alkylation of benzene with propylene in the presence of the catalyst.
There has been extensive work done with Ti catalysts, though most work occurred in ccnjunction 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.
Accordingly, the present invention provides 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 comprising a titanium tetrahalide selected from the tetrachloride and the tetrafluoride com-posited with a Group III-A metal oxide support con~aining surface hydroxyl groups, and recovering an alkylated aromatic hydrocarbon product The catalyst used thus comprises titanium tetrachloride or tetrafluoride impregnated on a, preferably activated, Group III-A metal oxide which possesses surface hydroxyl groups. Specific examples of these 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 bull( density of the alumina may range from about 0.3 to about 0.7 glcm3 or higher with a surface area ranging from about .
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1 to about 500 m /9. The alumina may have any desired shape, for example spheroidal particles of alumina. A commercial gamma-alumina may be used as the support. However, since this material may contain excessive water, it is preferably subjected to a predrying step by heating to a temperature in the range of from about 400 to about 500 C under an inert gas or hydrogen flow for a period of about 1 to about 8 hours.
To composite titanium tetrachloride with the preferred, predried gamma-alumina 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 is passed over the gamma-alumina at temperatures of 25 to 135 C. Thereafter the temperature is increased to 550 C or more. The passage of the nitrogen-titanium tetrachloride mixture over the alumina is effected about 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 about 25 to about 135 C. The temperature is then raised to 250 or a desired temperature, either gradually or in a series of steps. The preferred temperature for the heat treatment of this resulting composite is from about 135 to about 550 C. It is preferred that the temperature which is used in the treat-ment of the composite be e~ual to, or higher than, the aromatic hydro-carbon conversion temperature. Thereafter the temperature is maintained at this point and a stream of nitrogen is passed over the catalyst com-posite for an additional 1 to 10 hours. The finished catalyst is then sealed under an inert atmosphere such as argon, helium, nitrogen, etc., 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 impreg-- .
.

nated 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 or Group VIII of the Periodic Table.
At least about 0.5 weight percent titanium, on an elemental basis, is believed necessary for a significant amount of reaction to occur. The upper limit on titanium is believed to ba about 20 wt. %.
In preparing the titanium tetrafluoride catalyst, either of two different catalyst preparation techniques may be used, sublimation and impregnation.
In one sublimation procedure titanium tetrafluoride may be placed on top of a bed of gamma-alumina. Preferably the support is predried. 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 slightly above the sublimation temperature of titanium tetrafluoride, then the tempera-ture is progressively increased to elevated temperatures. This thermal pretreatment step is preferably 250 to 350 C for one-half to two hours, followed by treatment at 400 to 600 C for one to ten hours.
¦ Another way to prepare catalyst for use in the present in-¦ vention 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

-3-~07SZ68 impregnating methods it is preferred to contact the metal oxide wi~h impregnating solution at room temperature and then progressively increase the temperature to evaporate the solution. The catalyst is then pre-ferably 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 reac.tants and other reaction conditions when alkylating benzene with propylene are basically those well known in the art. Pressures may range from 1 to 100 atmospheres, or even hîgher, but high enough to have liquid phase. Preferred pressure is 20 to 60 atm, with optimum pressure being about 35 atm Temperature may range between amb;ent and 2~0 C. Preferred temperatures are about 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.
2~ EXAMPLE I
t 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 drop method, was dried at 550 C for

-4-300 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 400 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 thén given further thermal treatments under N2 flow. In one instance, a Cr promoter was added to the catalyst by dissolv-ing CrO3 in the impregnating solution. Details of the preparation of these catalysts are shown in Table I. There were catalysts A, B, and C.

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107S'~68 EXAMPLE III
The catalysts were tested in a laboratory scale plant. The reaction studied was alkylation of benzene with propylene. 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. Benzene and propylene were mixed together and then charged to the reactor. The reactions were all carried out at 120 to 245 C, 1 to 3 LHSV, and at 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 perc-nt cumene in product.

~075Z68 TABLE II: SUMMARY OF RESULT

Catalyst Reaction Conditions _(_ C? P(atm) BZ/C3- LHSV C S p B 120 55 6.24 1.1 72.1 59.2 69.1 " 150 " 6.00 2.0 80.3 62.3 72.4 " 150 35 4.6 0.9 84.2 57.5 67.4 " 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 " 150 25 4.84 2.9 81.7 61.7 71.0 " 150 25 7.85 2.0 93.0 69.6 77.6 " 150 35 5.03 1.0 95.0 60.7 70.0 " 120 25 5.20 2.1 96.3 60.6 70.2 1075Z~i8 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 be-lieved that the analysis of products gives a good indication of the catalyst system's performance. Table IIlprovides 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.

::i : . , _ 9 _ TABLE III
Comparison o-f Various Supported Titanium Tetraf1uoride Catalysts.

CATALY_ A B C
Hours of Operation 70 190 140 Benzene 5.5 74.2 79.2 Toluene Tr Cumene 32.9 18.0 12.8 n-Propylbenzene 0.1 1.4-Dimethyl-2-Ethylbenzene 6.1 Dipropylbenzene 6.7 5.1 Tripropylbenzene 1.0 1.1 Reaction Condition T(C) 245 150 150 P(atm) 55 35 35 C6H6/C3H6 2.6 5.0 5.3 LHSV 4.2 1.0 2.1 ~0752~8 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 treat-ments, in that heating which is too repid, or too high a temperature, may cause hydrolysis of the TiF4 component on the catalys~, 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 ~5 that a certain amount o~ transalkylation also occurs.
The catalyst of the present invention is also believed more stable than prior art catalyst. The stability of a catalyst is technically very important. Ti fluoride is very stable compared with the titanium iO752~;8 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 pass1ng 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 ~ while maintaining the nitrogen-titanium tetrachloride vapor flow over the gamma-alumina. The nitrogen-titanium tetrachloride flow was disco~tinued and the catalys~ composite was treated with a nitrogen flow for a period of 4.4 hours while main-taining the temperature at 250 C. At eht end of this period, the catalyst was analyzed and found to contain 2.17~ +itanium and 4.~% chlorirle.
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, l 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 10752~;8 molecular weight polymer may form. Using the conditions indicated above, a good yield of cumene is obtained.
While the ;nvention has been described with emphasis upon ~ -s propylene ~ alkylating agent, any other alkylating agent conventionally used for alkylation of aromatic hydrocarbons may be employed. Olefins are preferred alkylating agents, particu1arly preferred being ethylene, propylene and any of the C8 to C18 olefins.

Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

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 comprising a titanium tetrahalide selected from the tetrachloride and the tetrafluoride composited with a Group III-A metal oxide support containing surface hydroxyl groups, and recovering an alkylated aromatic hydrocarbon product.

2. Process of claim 1, wherein the catalyst system comprises titanium tetrachloride and alumina prepared by passing TiCl4 vapor over activated alumina having surface hydrogel groups at a temperature of 20° to 400°C. for 1 to 10 hours.

3. Process of 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. The process of claim 3 wherein the impregnating solution used is selected from the group of an aqueous solution of TiF4, polar organic solvent solutions of TiF4, and aqueous solutions of M2TiF6 where M is H, Li, Na or K.

5. Process of 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.

6. The process of any of the claims 1 to 3 wherein the catalyst is given a thermal pre-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.

7. The process of any of the claims 1 to 3 wherein the catalyst contains, on an elemental basis, about 0.5 to 20 weight percent titanium.

8. The process of any of the Claims 1 to 3 wherein the aromatic hydrocarbon is selected from the group consisting of benzene, toluene, ethylbenzene and xylene.

9. The process of Claim 1 wherein the alkylating agent is an olefin sleected from ethylene, propylene and the C8 to C18 olefins.

10. Process of Claim 9, 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.