Patent ID: 6310218
Filing Date: 2001-10-30
Classification: C07D

Abstract:
A solvent-free method for the purification of a non-eutectic lactide mixture derived from the depolymerizaton of lactic acid oligomers comprising by weight a major amount of one lactide isomer and a minor amount of at least one other lactide isomer and acidic and other impurities comprising the steps:(1) melting the lactide mixture;(2) cooling the molten lactide mixture to the freeze point or slightly below the freeze point of the lactide mixture to effect partial crystallization of the mixture and formation of a solid phase having a higher content than the molten mixture of the major isomer and a lower content of the minor isomer(s) and acidic and other impurities;(3) separating the solid phase from the liquid phase;(4) forming an additional molten mixture by melting the separated solid phase; and(5) repeating steps (2)-(4) with the additional molten mixture until a predetermined degree of putity is obtained in the separated solid phase.