| 摘要 |
<p>Esters of terephthalic and isophthalic acids, or a mixture of these esters, are purified by contacting the ester in the liquid phase, preferably at a temperature of from 140 DEG to 220 DEG C., with oxygen or gases containing oxygen in the presence of a small proportion (e.g. 0.1 to 0.5% by weight) of copper or manganese compounds or a mixture thereof, the time of treatment being less than 5 hours when the temperature is more than 200 DEG C. The ester is preferably treated in the molten state; but an inert solvent may be employed, if necessary, in order to obtain the liquid phase. A cobalt compound may be present in addition to the copper and/or manganese compounds. The metal compounds are removed, after the treatment, by water-washing, or by crystallizing or distilling the ester. In an example, dimethyl terephthalate, obtained by esterifying the acid produced by the oxidation of p-di-isopropyl benzene with air in the presence of cobalt and manganese compounds in an acetic acid medium, is distilled; and the white distillate, which contained 750 p.p.m. of the methyl ester of p-acetyl benzoic acid, is then treated, in the molten state, at 170 DEG C., with oxygen for 1 hour in the presence of 0.5% by weight of manganese acetate. The oxygen was passed through the molten ester at the rate of 3 litres per hour. The ester was then rectified. The product contained only 25 p.p.m. of p-acetyl benzoic acid ester: and it could be heated for 5 hours at 200 DEG C. without turning brown.</p> |
