GB993223A - A method of isomerizing alkyl aromatic compounds - Google Patents

Abstract

A non-equilibrium mixture of alkyl aromatic compounds is isomerized to near equilibrium concentration by contacting a hydrocarbon charge stock containing a mixture of close boiling isomeric alkyl aromatic compounds having 1 to 4 carbon atoms in each alkyl group in the presence of substantially dry hydrogen with a reduced acidic carrier-based platinum group metal catalyst at a total pressure of 100 to 500 p.s.i.g., a hydrogen partial pressure of 50 to 225 p.s.i.g., a weight hourly space velocity of 0.5 to 5, a ratio of 5 to 20 mols. of hydrogen per mol. of hydrocarbon charge stock, and a temperature of 750 DEG to 950 DEG F., the nitrogen content of the total feed entering the reaction system being maintained below that sufficient to provide 15 parts of ammonia per million parts by volume of total effluent. The water content of the total feed entering the reaction is maintained below 50 parts of water per million parts by volume of total feed in the vapour phase and the water content of effluent is maintained below 50 parts of water per million parts by volume of total effluent. Starting materials used may be of the benzene or naphthalene series e.g. a C8 fraction containing 1 to 30 vol. per cent ethylbenzene, 1 to 30 volume per cent o-xylene, 10 to 30 vol. per cent p-xylene and 40 to 88 vol. per cent m-xylene. The catalyst consists essentially of 0.1 to 2.0% by weight of a platinum group metal e.g. platinum palladium, rhodium and iridium. supported on alumina or magnesia containing at least one acidic component e.g. silica, boria, zirconia or mixtures thereof. Pure hydrogen i.e. that from a palladium type diffusion unit, can be employed for the reaction and ammonia can be removed by conventional means e.g. by passing through copper chloride. Specifications 735,390, 837,907 and 951,344 are referred to.