Esters purification process

摘要

Alkyl and oxa-alkyl diesters of dicarboxylic acids are decolourized by treating with ozone and thereafter washing the treated ester with alkali. Esters which may be treated include the diesters of dicarboxylic acids, such as phthalic acid, pimelic acid, sebacic acid, oxalic acid and tartaric acid, with saturated aliphatic alcohols such as those having four or more carbon atoms, e.g. butanols, octanols, nonanols, and decanols, and the alcohols containing ether linkages such as butoxyethyl phthalate and di-2-ethylhexyl phthalate and the diester of a mixture of C9-C7 oxo alcohols with phthalic acid. The ozone used may be employed as ozonized air or ozonized oxygen. The decolourization takes place more rapidly at elevated temperature but temperatures above 100 DEG C. are not so efficient owing to the decomposition of the ozone. After treating with ozone, the ester is washed with aqueous alkali, suitable alkalies being the hydroxides of sodium and potassium. The concentration of alkali is desirably within the range of 1 to 20 per cent by weight, 10 per cent by weight being preferred. The washing may be effected at 20-100 DEG C. The ratio of ester to aqueous alkali is desirably within the range 20:1 to 5:1 volume/volume, a ratio of 10:1 being preferred. The ester may then be washed with water at 20-100 DEG C., the ratio of ester to water being within the range 6:1 to 2:1 volume/volume, a ratio of 4:1 being preferred. The ester may then be dried by any suitable method, such as chemical drying or heating in vacuo on a water-bath followed by filtration. The treatment with ozone may be combined with further purification processes. The crude ester may be washed with aqueous alkali before treating with ozone and passed through a tower containing activated carbon after the ozone treatment. The product may be further treated with ozone to reduce the colour still further. The ester may also be treated with steam after being washed with alkali to remove traces of free alcohols. Detailed examples describe the treatment of the phthalates of a mixture of C7-C9 oxo alcohols and 2-ethyl hexanol, dioctyl sebacate, and methyl glycol phthalate. The Provisional Specification refers also to the purification of esters such as di-2-ethyl-hexyl phthalate by treatment with ozone followed by washing with water, without washing with alkali.