PROCESS AND APPARATUS FOR RECOVERING LACTIDE FROM POLYLACTIDE OR GLYCOLIDE FROM POLYGLYCOLIDE

摘要

Recovering lactide from polylactide (PLA) or glycolide from polyglycolide (PGA), comprises (a) reacting PLA or PGA with a hydrolyzing medium into a melt, and hydrolytically reducing the melt into PLA-oligomers having a number average molecular weight of 162-10000 g/mole; or hydrolytically reducing the melt into PGA-oligomers having a number average molecular weight of 134-10000 g/mole, and (b) subjecting the PLA- or PGA-oligomers to a cyclizing depolymerization to obtain lactide or glycolide. Recovering lactide from polylactide (PLA) or glycolide from polyglycolide (PGA), comprises (a) reacting PLA or PGA with a hydrolyzing medium into a melt, and hydrolytically reducing the melt into PLA-oligomers having a number average molecular weight of 162-10000 g/mole (measured by acid-base-titration of the carboxyl groups); or hydrolytically reducing the melt into PGA-oligomers having a number average molecular weight of 134-10000 g/mole (measured by acid-base-titration of the carboxyl groups), and (b) subjecting the PLA- or PGA-oligomers to a cyclizing depolymerization to obtain lactide or glycolide. Independent claims are also included for: (1) preparing the PLA or PGA, comprising converting the lactide or glycolide in to PLA or PGA by carrying out a ring-opening polymerization of lactide or glycolide, where at least one portion or the entire amount of the used lactide or glycolide is prepared by the above mentioned method; (2) an apparatus for continuously recovering lactide from PLA or glycolide from PGA, comprising (a1) a device for melting PLA or PGA and/or a device for supplying the PLA- or PGA-melt, (a2) a hydrolyzing device arranged downstream of the device for melting PLA or PGA and/or a device for supplying the PLA- or PGA-melt, for carrying out a partial hydrolysis of the PLA- or PGA-melt into PLA- or PGA-oligomers, and (a3) a depolymerisation reactor arranged downstream of the hydrolyzing device; and (3) a device for preparing PLA or PGA by ring opening polymerization of lactide or glycolide, comprising the above mentioned apparatus for continuously recovering lactide from PLA-waste or glycolide from PGA-waste, and a downstream ring-opening polymerization unit.