Study On Synthesis And Purification Of Optically Pure L-Lactide

Polylactide has attracted much attention due to its biodegradability, compatibility. However, its applications is restricted by its high price. Since lactide is an indispensable material to prepare polylactide, reducing its cost will greatly extend application.In this paper, the purpose of the study planned to prepare optically pure L-lactide and raise its yield, explored the optimal conditions of synthesizing L-lactideWith L-lactic acid as raw material, improved the technical route of synthesis, used the dimethylbenzene as azeotropic solvent in order to resolve the problem of dehydration during the course of polycondensation, avoided fell press process as ever literature. During the single factor experiment, effects of catalyst type, different ratio of composite catalyst, quantity of catalyst, time of polycondensation reaction, temperature of pyrolysis as well as pressure of pyrolysis were studied on yield of lactide; The contrast experiment between the method of azeotropic solvent and decompression was studied; Improved the method of purification, the structure of lactide was characterized by the melting point, IR, UV, Digital Automatic Polarimeter and HPLC.The results of research indicated that: get the most optimized condition, with Zn(OAc)2/Sn(Oct)2=1:2 as the composite catalyst and the quality of catalyst was 1% of the lactic acid, the dehydrated temperature was 140-160℃, the time of polycondensation reaction was 4h, the temperature of pyrolysis was 240-260℃, the pressure of pyrolysis was 2Pa, The best yield of L-lactide was 88.08%; In contrast with the method of decompression, the method of azeotropic solvent has its obvious superiority and innovation and has opened up a new path for the industrial production of L-lactide; the L-lactide of the ultimate total yield of 70.66%, optical purity of 99% was received via the purification.