Synthesis of Racemic Lactide Using Glycerol By-product from Biodiesel Fuel Production Process as Feedstock

Abstract

To reduce CO2 emission, the utilization of biodiesel fuel (BDF) has expanded worldwide last decade. Accordingly, more and more glycerol that is a by-product of the BDF production process is discharged, and an effective conversion of glycerol into valuable substances has been desired. In this article, we describe a study of conversion from glycerol into racemic lactide which is to be a monomer of stereoblock poly(lactic acid) (sb-PLA) by using an achiral homosalen–aluminum complex as a polymerization catalyst. This sb-PLA is semi-crystalline and has high melting point (up to 210°C). The glycerol was first converted into racemic lactic acid by hydrothermal reaction with an alkaline catalyst under the following conditions: temperature, 300°C; pressure, 10MPa; reaction time, 3.5h. The conversion of glycerol into lactic acid was 62.5%. The racemic lactic acid was then converted into the mixture of lactide isomers, followed by purification process to afford racemic lactide (rac-LA). Purity of the obtained rac-LA was more than 99%. It demonstrates that glycerol can be a good feedstock of rac-LA for the first time.