GB865677A - Purification of phenol - Google Patents

Abstract

A process for the purification of phenol derived from cumene and containing colour forming impurities including aliphatic a -hydroxy carbonyl compounds comprises subjecting the impure phenol at an elevated temperature to conditions which will cause the substantially complete condensation of the aliphatic a -hydroxy carbonyl compounds with phenol to form benzofurans and separating the phenol substantially completely from the benzofurans. The condensation of the a -hydroxy carbonyl condensation of the a -hydroxy carbonyl compounds with phenol may be carried out by heating the phenol in liquid or vapour phase at atmospheric, reduced or elevated pressures and optionally in the presence condensation catalysts such as activated alumina, aluminium silicate e.g. acid-or alkali-treated pumice or porcelain, acidic or basic ion exchange resins, mineral acids e.g. sulphuric and phosphoric acid, especially in the presence of iron, strong organic acids, e.g. p-toluene sulphonic acid and surface active earths e.g. montmorillonites such as fuller's earth, bentonite and attapulgite which may be acid-activated or alkali or heattreated. In the liquid phase treatment activated charcoal or metal halides of the Friedel-Crafts type and sulphates of the same metals e.g. aluminium ferric, nickel and zinc chlorides, aluminium, ferric and nickel sulphates or boron trifluoride maye be employed as catalyst. The vapour phase treatment may be carried out by passing the vaporised phenol through a tube which may be packed with catalyst. The liquid phase treatment may be carried out batchwise or continuously. The separation of the phenol from the benzofurans and other impurities is carried out by neutralisation of the phenol with an alkali followed by extraction of the benzofurans with a solvent or by steam distillation or by extractive distillation in the presence of a suitable solvent and preferably by extractive distillation in the presence of water, benzofurans being removed overhead. The aqueous phenol may be subjected to dehydration and fractional distillation. The tendency for the phenol to form coloured products on sulphonation and chlorination is shown to be substantially reduced after purification. Examples are furnished in which crude phenol obtained from cumene by oxidatation and an acid-cleavage of the hydroperoxides formed, is purified.