GB637595A - Demethylation of methylbenzenes - Google Patents

Abstract

Methylbenzenes are demethylated by contacting with activated alumina at 800 DEG F. upwards, preferably 1000-1200 DEG F., and under a partial pressure of hydrogen of at least 100 p.s.i.g. Toluene, xylenes, and trimethyl benzenes such as mesitylene are specified feedstocks, also mixtures such as toluene and xylene or fractions containing one or more of the reactants. In general, the hydrogen partial pressure is 100-3000, preferably above 500 p.s.i. Preferably the molar ratio of hydrogen to methyl benzenes is at least 2 : 1, especially 4 to 10 : 1 or more. The contact time is correlated with hydrogen partial pressure, temperature, and catalyst activity and is generally below 50 secs. Space velocities are usually 0.2-5, preferably 0.6-1.0. Aluminas of high specific surface areas are preferred. Commercial activated aluminas are generally dried, e.g. at 1050 DEG F. for 2 1/2 hours, before use. Aluminium oxide hydrate may be calcined to give a dehydrated oxide substantially in the gamma form. Preferably, alumina is the sole catalyst and is used at 1050-1200 DEG F. Hydrogen halide, e.g. 1-6 mol. per cent of the reaction mixture may, however, be present when preferred temperatures are 900-1100 DEG F. Comparative figures are given for conversions of toluene, xylenes, and a crude 329-380 DEG F. fraction using activated alumina catalysts and Cr2O3-Al2O3, SiO2-Al2O3 or silica gel.