Method for the manufacture of a polyhydroxy-carboxylic acid

摘要

Disclosed is a method to prepare a polylactic acid comprising the steps of performing a ring opening polymerization using a catalyst and either a catalyst killer compound or an endcapping additive to obtain a raw polylactic acid of MW greater than 10,000 g/mol, purifying the raw polylactic acid by removing and separating low boiling compounds comprising lactide and impurities from the raw polylactic acid by devolatization of the low boiling compounds as a gas phase stream, and purifying the lactide from the devolatization and removing the impurities from the gas phase stream of evaporated low boiling compounds by means of crystallization by desublimation from the gas phase, wherein the lactide is purified and the removed impurities include a catalyst residue and a compound containing at least one hydroxyl group such that the purified lactide is then polymerized by feeding it back into the ring opening polymerization. The invention further relates to an apparatus for carrying out the method comprising a polymerization reactor for performing a ring opening polymerization to obtain a raw polylactic acid, a devolatization apparatus for separating low boiling compounds comprising lactide and impurities from a raw polylactic acid, and a crystallization apparatus for purifying a lactide and removing impurities by means of a desublimation and a crystallization in the same crystallization apparatus.

主权项

1. An apparatus for preparing polylactic acid, comprising:
a polymerization reactor adapted for performing a ring opening polymerization to obtain a raw polylactic acid having a Mw of at least 20,000 g/mol, a devolatization apparatus adapted for separating low boiling compounds comprising lactide and impurities from the raw polylactic acid having a Mw of at least 20,000 g/mol, a crystallization apparatus for purifying lactide from the low boiling compounds separated in the devolatization apparatus and removing impurities by means of a desublimation and a crystallization in the same crystallization apparatus, and a recycle line connecting the crystallization apparatus and the polymerization reactor for recycling purified lactide from the crystallization apparatus back into the polymerization reactor wherein:
lactide and a raw polylactic acid having a Mw of at least 20,000 g/mol are present in the polymerization reactor,a ring opening polymerization reaction of lactide to form polylactic acid having a Mw of at least 20,000 g/mol is occurring within the polymerization reactor, andpurified lactide from the crystallization apparatus is present in the recycle line.