GB788276A - A process for the purification of phthalic acids - Google Patents

Abstract

Phthalic acids are purified by treating the salt of the phthalic acid with an adsorbent material or an ion exchanger. Suitable salts are those of alkali metals or ammonia, and suitable adsorbents are e.g. active carbon or activated aluminium hydroxide. The crude acids purified may be those which have been prepared by the oxidation of a dialkyl benzene with an oxygen containing gas in the presence of a heavy metal compound, e.g. cobalt and manganese acetate, as catalyst, and which have been washed one or more times with water. Crude acid so obtained is treated with an aqueous solution of a base, the amount of base being equivalent stoichiometrically to the amount of phthalic acid in the crude acid. After the treatment of the phthalate solution with the adsorbent or the ion exchanger the solution is separated therefrom. If an adsorbent is used this is separated by filtration, while when an ion exchanger is used the purification may be carried out continuously by passing the solution through a column filled with the ion exchanger, a clear liquid being immediately drawn off. The phthalate may then be crystallized, separated from the solution and dissolved again in water, after which the phthalic acid is recovered e.g. by acidifying the phthalate solution preferably with the exact amount of acid required, or by hydrolytic decomposition, or by thermal decomposition. Specification 767,463 is referred to.