GB843698A - Production of aromatic carboxylic acids - Google Patents

Abstract

The invention comprises a process for the production of aromatic carboxylic acids, by the oxidation of alkyl-substituted aromatic compounds, in a liquid medium which is stable under the oxidation conditions used, by means of molecular oxygen in the presence of bromine or a bromine containing substance and, if desired in the presence of an oxidation catalyst, wherein the bromine is recovered from the off gases and water which are removed from the reaction vessel, and if desired re-used in a further oxidation process. Any further additional bromine required in order to maintain the desired bromine content of the reaction mixture may be added at any time. The bromine may be recovered by passing the off-gases and the water removed from the reaction vessel to an alkaline scrubbing tower or towers, treating the contents of the tower with chlorine and then cooling to condense the liberated bromine. The oxidation may be carried out at atmospheric or superatmospheric pressure and at an elevated temperature. The bromine may be used as such or e.g. as hydrogen bromide, A metallic bromide or an organic bromide. The bromide is preferably present in an ionic form. The liquid medium may be provided by acetic, propionic or benzoic acid. Suitable oxidation catalysts which may be present are metals, metal oxides or metal salts e.g. manganese and/or cobalt bromide, or manganese and/or cobalt acetate. In the latter case hydrogen, sodium ammonium an alkyl or an aryl-alkyl bromide should also be present. An example is given of the oxidation of p-xylene to terephthalic acid, wherein the bromine is recovered is recycled to p-xylene feed. Specification 833,438 is referred to.