Method of recovering adipic acid and 6-hydroxycaproic acid from waste solution of alkali metal salts of organic acids coming from the process of cyclohexane oxidation

摘要

A method of recovering adipic acid and 6-hydroxycaproic acid from the waste solution of alkali metal salts of organic acids coming from the process of cyclohexane oxidation, which comprises:(i)basifying the reaction mixture coming from cyclohexane oxidation with an aqueous solution of an alkali-metal base so that the organic acids essentially comprising adipic acid and 6-hydroxycaproic acid therein, are saponified, extracting the formed alkali metal salts of organic acids from the mixture with water, then acidifying the aqueous extract comprising the alkali metal salts of organic acids to a pH value of 3 or lower with an aqueous solution of a protic inorganic acid, as a result, said aqueous extract is separated into an oily layer and an aqueous layer;(ii) extracting the organic acid from said oily layer obtained from the step(i) with an aqueous solution of a protic inorganic acid, to obtain an aqueous extract;(iii) extracting the organic acid from the aqueous layer obtained from the step (i) with an organic solvent selected from alcohols, ketones, esters or the mixtures thereof, to obtain an oily extract;(iv) extracting the organic acid from the aqueous extract obtained from the step(ii) with an organic solvent selected from alcohols, ketones, esters or mixtures thereof, to obtain an oily extract; and(v) combining and distilling the oily extracts obtained from the steps (iii) and (iv), to recover the organic acid essentially comprising adipic acid and 6-hydroxycaproic acid. Useful organic acids such as adipic acid and 6-hydroxycaproic acid can be recovered efficiently in the present invention. Besides, the waste oily layer coming from the process of recovering the useful organic acids has the reduced content of alkali metal ions and hence can be used as a fuel for a boiler or a combustion system. In addition, the quality of the by-produced crystals of alkali metal salts of inorganic acid can be improved.