Chemistry of hydrocarbon compounds – Aromatic compound synthesis – By isomerization
Patent
1984-05-31
1986-01-28
Doll, John
Chemistry of hydrocarbon compounds
Aromatic compound synthesis
By isomerization
585665, 585670, 585482, C07C 522, C07C 523, C07C 525
Patent
active
045673136
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for isomerizing alkylbenzenes, in particular xylenes, in the presence of a solid (heterogeneous) catalyst.
Aromatic C.sub.8 -fractions from petrochemical industrial plants and petroleum refineries will as a rule contain the three xylene-isomers in proportions which approximately are 18 percent ortho-xylene, 58 percent meta-xylene and 24 percent para-xylene. Meta-xylene is a substantially less demanded product than ortho- and para-xylene which i.a. constitute basic materials for important products such as phtalic acid anhydride and terephthalic acid. Consequently, conversion of meta-xylene to ortho- and para-xylene represents an important industrial process.
A previously well known and applied process for isomerization of xylenes relates to the use of a catalyst which is based on platinum deposited on the mixed oxide compound SiO.sub.2 /Al.sub.2 O.sub.3. The process runs at temperatures from 420.degree. to 480.degree. C. and at pressures from 10 to 20 atm. The feed has a hydrogen/hydrocarbon ratio of approximately 10, and may contain up to 45 percent ethylbenzene.
In another previously known and applied xylene isomerization process a catalyst with platinum on Al.sub.2 O.sub.3 is used. The conditions in this process are approximately as given above, except for a somewhat lower hydrogen consumption, and the feed may contain from 10 to 15 percent ethylbenzene.
More processes of similar types are utilized for isomerizing xylene. A common feature of these industrial processes is that they concern application of catalysts which comprise metal on supports, often platinum on Al.sub.2 O.sub.3 or platinum on SiO.sub.2 /Al.sub.2 O.sub.3.
In still another applied process for isomerizing xylene a zeolite catalyst containing rare earth metals is used. The process is a liquid phase process that runs at temperatures from 200.degree. to 600.degree. C. and at a pressure of 22 atm., and with 20 percent toluene in the feed.
In the patent literature isomerization of xylene by means of catalyst systems with platinum deposited on Al.sub.2 O.sub.3 has been described (U.S. Pat. No. 4,179,581), systems with fluorided Al.sub.2 O.sub.3 (U.S. Pat. No. 3,898,297). Catalyst systems with nickel deposited on Al.sub.2 O.sub.3 and other oxide supports have also been described. Additionally, there are patent specifications relating to isomerization of xylene in the presence of different synthetic zeolite catalysts, as well as special liquid phase systems, for instance with HF/BF.sub.3.
Conversion of meta-xylene to ortho-xylene and para-xylene is a monomolecular reaction which is assumed to go via 1,2-shifts of methyl groups. This reaction is independent of the pressure. On the contrary, bireactions, like e.g. disproportionation of xylene, are bimolecular reactions and are promoted by high pressure. These reactions consume more energy, and are more predominant at higher temperatures. Previously known processes applied industrially for isomerizing xylene are encumbered with the drawback that they are operated at relatively high pressures and temperatures, and thus yield unwanted by-products.
An object of the present invention is to provide a catalytic process for isomerizing alkylbenzenes at moderate pressures and temperatures in order to enhance the selectivity.
This object has been obtained by the method according to the invention, which method is based on the application of a heterogeneous catalyst which comprises an inorganic oxide support containing at least one mixed oxide compound of SiO.sub.2 and Al.sub.2 O.sub.3 in any proportion, and which is characterized in that the isomerization is performed at a temperature between 150.degree. and 300.degree. C. and under a pressure ranging from about atmospheric to a few atmospheres in the presence of a catalyst having been produced by reaction of the support with an aluminum alkyl compound of the type AlR.sub.y X.sub.3-y, wherein R=CH.sub.3, C.sub.2 H.sub.5 or C.sub.3 H.sub.7, y=1 or 2 and X=Cl. The improved effect of the catalyst containing a mixed oxi
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Blindheim Ulf
Haegh Gerd S.
Nilsen Bjorn P.
Doll John
Pak Chung K.
Sentralinstitutt for Industriell Forskning
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