GB890387A - Improvements in the production of terephthalic acid - Google Patents

Abstract

Terephthalic acid is prepared by oxidising p-xylene with a gas containing molecular oxygen at elevated temperature in the presence of an oxidation catalyst and in the presence of at least 5% by weight of dimethyl terephthalate with reference to the weight of the mixture to be oxidised and at a temperature above the melting point of the diester. The reaction is preferably carried out by passing oxygen through the mixture at 140 DEG C.-200 DEG C. using about 20%-50% of the diester which is said to act as an oxidation promoter and to bring about oxidation to terephthalic acid in one step. The starting material may be pure p-xylene, commercial crude xylene or xylene mixed with partial oxidation products, e.g. tolualdehyde, toluic acid, terephthalaldehydic acid or esters of the acids with alkanols of 1 to 4 carbon atoms. The catalyst may be a copper, cobalt, manganese or cerium salt of a higher aliphatic acid or hydrobromic acid and may be dissolved in the xylene. A lower alkanol, particularly methanol, may be introduced into the oxidation zone during the oxidation in amounts of 0.5% to 5% by weight based on the mixture to be oxidised. The oxidation may be carried out batchwise or continuously at normal or elevated pressures. The product, which may contain some p-toluic acid may be esterified with methanol under increased pressure in a known manner. Examples are given. Specification 623,826 is referred to.