GB806632A - Manufacture of terephthalic acid and potassium salt thereof - Google Patents

Abstract

Di-potassium terephthalate is prepared by heating di-potassium phthalate at temperatures between 300 DEG and 330 DEG C. in an inert atmosphere in the presence of an inert high boiling organic liquid or a salt or a mixture of salts which ensures fluidity of the contents of the reaction vessel at the temperature employed. Inert organic liquids mentioned are diphenyl or diphenyl ether or mixtures thereof or dimethyl phthalate. The salts which may be used are alkali-metal acetates or di-lithium or di-sodium phthalates or mixtures thereof. Inert gases mentioned are nitrogen and carbon dioxide and mixtures thereof. Inert materials such as metal turnings may also be present in the reaction mixture. The potassium phthalate may be replaced by a mixture of phthalic acid and potassium carbonate. Terephthalic acid may be isolated by cooling the reaction mixture, dissolving the solid product obtained in water, filtering the solution and acidifying the filtrate with an inorganic acid to precipitate terephthalic acid or a mixture thereof with phthalic acid. Phthalic acid may be removed from the mixture by treatment with boiling water. In examples, terephthalic acid is obtained from di-potassium terephthalate prepared by heating the following mixtures with stirring under pressure of carbon dioxide: (1) and (2) di-potassium and di-lithium phthalates; and (3) di-potassium, di-lithium and di-sodium phthalates. In the Provisional Specification, di-potassium phthalate is heated under conditions which ensure fluidity of the contents of the reaction vessel at temperatures up to 450 DEG C. The salts used to attain fluidity also include lithium and potassium chlorides.