GB712980A - Improvements in and relating to the de-alkylation of aromatic hydrocarbons - Google Patents

Abstract

De-alkylation of monocyclic aromatic hydrocarbons is effected by treating a feed consisting substantially of one or more alkyl-substituted monocyclic aromatic hydrocarbons at 500-600 DEG , preferably 540-570 DEG C. and above 100, preferably 200-300, atmospheres with hydrogen in the presence of a catalyst consisting of silica, a mixture of silica and alumina, alumina pretreated with silicon tetrafluoride or an aluminium silicate which has not undergone a swelling treatment with a liquid swelling agent. While alkyl groups such as ethyl and propyl may be removed, the process is particularly suitable for methyl groups, e.g. in toluene, xylenes, and trimethylbenzenes. Products obtained from petroleum products and from coal or coal tar may also be treated. The catalysts may include hydrogenating metals or their compounds, e.g. platinum and oxides of molybdenum, tungsten, and manganese, when the sulphur content of the hydrocarbon is at the same time reduced, and silicon tetrafluoride. In the latter case, periodic additions are desirable. Batch or continuous operation is used. Catalyst may be regenerated by treating with oxygen-containing gas and/or steam. Examples describe the conversion of xylenes to benzene and toluene at 550 DEG C. and 250-260 atmospheres, the catalysts being: silica-alumina made by impregnating silica gel granules with aluminium nitrate and calcining at 400 DEG C. or precipitating aluminium nitrate and sodium silicate from solution with ammonia, extruding, and calcining; "Superfiltrol," an aluminium silicate earth; g -alumina dried at 450 DEG C. and saturated with silicon tetrafluoride and, optionally, impregnated with ammonium orthomolybdate to give 1 per cent MoO3 in the calcined product. Specifications 637,595 and 712,981 are referred to.