GB1152577A - Purification of Aromatic Polycarboxylic Acids. - Google Patents

Abstract

1,152,577. Purification of aromatic polycarboxylic acids. STANDARD OIL CO. 16 May, 1966 [17 May, 1965], No. 21656/66. Addition to 994,769. Heading C2C. An aromatic polycarboxylic acid containing undesirable aldehyde and other impurities is purified by a process which comprises contacting a solution of the impure acid in demineralized water in the liquid phase at an elevated temperature and pressure and in the presence of H 2 with a Pd-containing catalyst under mild hydrogenation conditions, and recovering purified acid. The aromatic polycarboxylic acid may be obtained by liquid phase catalytic oxidation of polyalkyl aromatic hydrocarbons. Specified polycarboxylic acids which may be purified are terephthalic, isophthalic, trimesic, trimellitic, mellitic and naphthalene dicarboxylic acids. The hydrogenation is suitably carried out at a temperature in the range of about 450-600‹ F., in an inert polar solvent either as a batch process under static conditions or as a continuous process maintaining a concurrent or countercurrent flow of H 2 through the catalyst chamber. A sufficient pressure may be maintained in a reactor by using a mixture of H 2 and an inert gas, e.g. N 2 . The product may be obtained from the reaction mixture by filtering and crystallizing from the filtrate. A process is described with reference to the accompanying drawings (not shown) for the preparation of terephthalic acid. Examples are given for the production of terephthalic acid showing the effect of using water of varying purity.