Patent ID: 8404868

Claim:
A method of purifying a cyclic ester, comprising, sequentially: (Step 1) subjecting a co-distillated liquid comprising a cyclic ester produced by heating depolymerization of a hydroxycarboxylic acid oligomer in the presence of a depolymerization solvent and the depolymerization solvent to liquid-liquid separation separating the co-distillated liquid into a depolymerization solvent phase and a cyclic ester phase containing the depolymerization solvent; (Step 2) mixing the resultant cyclic ester phase containing the depolymerization solvent with an organic solvent for washing which is mutually soluble with the depolymerization solvent and has a lower boiling point than the cyclic ester; and subjecting the resultant mixture liquid to liquid-liquid separation into an organic solvent phase containing the depolymerization solvent and a cyclic ester phase containing the organic solvent; and (Step 3) evaporating the organic solvent from the cyclic ester phase containing the organic solvent to recover the cyclic ester having a reduced amount of the depolymerization solvent.