GB892766A - Improvements in or relating to the production of aromatic acids - Google Patents

Abstract

In a process for the oxidation with molecular oxygen, of an aliphatic-substituted aromatic compound or a fused-ring aromatic compound, dissolved in an inert solvent and in the presence of a heavy metal oxidation-catalyst, advantageously promoted by bromine or bromide ions, the oxidation-product is submitted to distillation to separate the inert solvent and, if desired, part of the aromatic acid product, and the distillation-bottoms are extracted with water or a lower aliphatic or naphthenic monocarboxylic acid in order to separate tar-like by-products from the catalyst so that the latter may be reused in the oxidation reaction. The extraction is preferably carried out with between 3 and 50 volumes of solvent per volume of bottoms, and at a temperature between 50 DEG C. and 150 DEG C. In some cases, the catalyst extract may be used in the oxidation; in other cases the catalyst is separated from the extract so that the catalyst alone may be recycled. In an example, a reaction-mixture from the air-oxidation of mixed petroleum xylenes in acetic acid and in the presence of a bromine-promoted manganese and cobalt acetate catalyst, is cooled and filtered, whereby a filter-cake comprising ortho-, iso-, and terephthalic acids is obtained. The filtrate is distilled at atmospheric pressure to remove acetic acid and water-of-oxidation, leaving a solid residue which contains catalyst, benzoic acid, toluic acids and phthalic acids. This residue is distilled under an absolute pressure of 40 mm. to remove benzoic acid and some of the orthophthalic acid (as anhydride). The distillation-bottoms is divided into two portions. One portion is pulverized and extracted with hot water; and the other portion is pulverized and extracted with hot acetic acid. Both extracts are filtered and evaporated to dryness whereby two pale-coloured solids are obtained, which are found to contain over 90% of the catalyst in the distillation-bottoms but only minor proportions of tar-like oxidation by-products. Both extracts are suitable for recycling to a subsequent oxidation step. A list of aromatic compounds which may be oxidized according to the process of the invention is given in the Specification; also a list of catalysts, which includes nickel, chromium, vanadium, molybdenum, tungsten, tin, neodymium and cerium.