GB816420A - Process for producing aromatic monocarboxylic acids - Google Patents

Abstract

The invention comprises a process for the production of aromatic monocarboxylic acids by the catalytic oxidation of cumene or an aromatic hydrocarbon having the formula <FORM:0816420/IV (b)/1> where n=1-5, x=0-4, x not being more than 1 when n exceeds 1, the oxidation being conducted in a reactor, from which is obtained an effluent comprising the desired acid, undesired by-product and unoxidized hydrocarbon, the steps comprising contacting the effluent with an aqueous solvent having a pH of 5-9, thus to form a first aqueous phase, and a first organic phase, separating these phases, contacting at least a portion of the first organic phase with a second aqueous solvent having a pH of at least 10, separating the second organic and aqueous phases so formed, returning the second organic phase and the remainder, if any, of the first organic phase to the reactor as part of the aromatic hydrocarbon fed thereto, and recovering aromatic monocarboxylic acid from the first aqueous phase. A third or half of the reactor effluent is preferably subjected to the second extraction step, the remainder being directly recycled to the reactor after the first extraction step. Suitable solvents which may be used in the first extraction are solutions of alkali metal carbonates, bicarbonates, or hydroxides, especially sodium bicarbonate, and the amount of aqueous solvent used for the first extraction should be enough to neutralize and dissolve all the monocarboxylic acid in the reactor effluent being treated. The aqueous solvent used in the second extractor is preferably sodium hydroxide. The process may be carried out batchwise or continuously and the two extractor units should be effective liquid-liquid contactors, preferably adapted for countercurrent flow. Examples are given of the oxidation of o-xylene and p-tert.-butyl toluene in the presence of cobaltous 2-ethyl hexoate, to toluic and p-tert.-butyl benzoic acid respectively. Other starting materials specified are m- and p-xylenes, tri- and tetra-methylbenzenes, cymene, tert.-amyl toluenes and tert.-butyl toluenes.