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

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, 10 MPa; reaction time, 3.5 h. 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.