GB808118A - A process for the preparation of benzene dicarboxylic acids - Google Patents

Abstract

Catalyst compositions for use in the preparation of benzene dicarboxylic acids, e.g. terephthalic acid, by oxidation of di-alkyl benzenes (see Group IV (b)), comprise both cobalt and cerium. Cobalt and cerium oxides may be used; also the chlorides, nitrates or sulphates; but salts of organic acids, which are soluble in the reaction mixture, are preferred. The acetates, salicylates, butyrates, octoates, toluates and propionates are specified. Also chelate complexes of cobalt and cerium with diketones, such as cobalt isovalerylacetonate and cobalt acetoacetonate. When oxidizing di-isopropyl benzene to terephthalic acid, the catalyst is preferably employed in an amount ranging from about 0.01 to about 5 per cent by weight of the aromatic charge calculated as metallic cobalt or cerium. The ratio of cobalt to cerium in the zone is preferably in the range of from about 1 : 4 to about 4 : 1. The examples relate to the use of cobalt acetate and cerium acetate, and of cobalt p-octylbenzoate and cerium naphthenate.ALSO:Benzene dicarboxylic acids are prepared by catalytic oxidation of a di-alkyl benzene, or a partial oxidation product thereof, with gaseous oxygen, the oxidation being carried out in an organic solvent, at a temperature between 60 DEG and 300 DEG C. and in the presence of a catalyst composition comprising both cobalt and cerium. Suitable starting materials are the alkyl benzenes wherein the alkyl groups are methyl, ethyl, propyl, isopropyl, butyl or octyl groups. Other suitable starting materials are alkyl benzoic acids, alkyl acetophenones, diacetyl benzenes and acetyl benzoic acids. Terephthalic acid may be prepared by the oxidation of p-diisopropyl benzene, p-diacetyl benzene, p-ethyl toluene or p-methylacetophenone. Preferred solvents are acetic, propionic, valeric, n-caproic and n-heptoic acids, or a mixture of such acids. Other suitable solvents are glutaric acid, chlorobenzene, benzene, carbon tetrachloride and tetrachloroethane. The catalyst may comprise the oxides of cobalt and cerium; the chlorides, nitrates or sulphates of the metals may also be used. It is preferred, however, to use metallic compounds which are soluble in the reaction mixture, e.g. the acetates, salicylates, butyrates, octoates, toluates and propionates. Chelate complexes of the metals with diketones may also be used, e.g. cobalt isovalerylacetonate, and cobalt acetoacetonate. The water-content of the reaction zone should be maintained below the amount which would cause the formation of a separate aqueous phase. Thus a portion of the reaction mixture may be withdrawn intermittently or continuously from the reaction zone and the water content thereof adjusted before its return to the reaction zone. Water may also be removed from the reaction zone by vapour-entrainment in part of the solvent; the vapour is condensed, the solvent is recovered from the condensate and recycled to the reaction zone. In examples (1) and (2) terephthalic acid is prepared by passing air through p-di-isopropyl benzene dissolved in acetic acid using a mixture of cobalt acetate and cerium acetate as catalyst, the temperature of the reactor being maintained at 165 DEG C. and the pressure at 30 atmospheres. In Example (4) terephthalic acid is prepared by the oxidation of p-ethyl toluene dissolved in acetic acid using a mixture of cobalt-p-octylbenzoate and cerium naphthenate as catalyst. Ammonium cerium nitrate may be used in place of cerium naphthenate. In Example (5) terephthalic acid is prepared from p-methylacetophenone.