Disproportionation of Toluene to Produce Benzene and <i>p</i>-Xylene – A Review

Abstract

An increasing demand for benzene and xylenes as raw materials for polyester fibres and synthetic resins in the recent past has stimulated newer developments in converting toluene to benzene and xylenes. Among the xylenes, <i>p</i>-xylene is of considerable importance as raw material for terephthalic acid and dimethyl terephthalate manufacture, required for polyester fibre and for the synthesis of vitamins and other pharmaceuticals. The paper reviews the activity and selectivity (towards <i>p</i>-xylene production) of various catalysts viz., amorphous SiO₂/Al₂O₃, X- and Y-zeolites, mordenite, faujasite, HZSM-5 in its unmodified, modified, as

well as ion exchange forms. The effects of preparation method of the catalysts, surface acidity, shape selectivity, and crystal size of the zeolites as well as temperature, pressure, and carrier gas on the activity and selectivity for <i>p</i>-xylene is discussed here. The performance of perovskite based oxides as prospective catalyst is also explored.