Synthesis of Polyglycerol under Superbasic Conditions to Reduce the Severity of the Reaction Conditions

The increasing biodiesel production in Indonesia will affect the supply of glycerol because it is a by-product of the transesterification reaction. Abundant glycerol can provide added value if further processed into higher-value products such as polyglycerol. Polyglycerol is made from the polymerization of glycerol with the help of an alkaline catalyst, such as KOH, but the temperature and reaction time used are very high and long. Therefore, this study aims to increase the conversion of glycerol by adding DMSO to the glycerol and KOH solution to increase the basicity of the mixture, increase the polymerization rate, and decrease the temperature and reaction time. The conversion of glycerol to polyglycerol with the addition of 10 mL DMSO to the KOH and glycerol mixture, giving a DMSO to KOH-glycerol volume ratio of 1:5, with a reaction time of 2 hours and a reaction temperature of 140-150°C was 77%, compared to without the addition of KOH which required a reaction time of 8 hours and a reaction temperature of 260-280 °C resulting in a glycerol conversion of 99%. Adding DMSO, with constant KOH-glycerol volume, affects the polymerization reaction because compared to adding 5 mL DMSO (volume ratio of 1:10), the resulting glycerol conversion is 16%. For the effect of reaction time on the results of glycerol polymerization, 5 mL DMSO shows that the longer the time, the more polyglycerol formed can depolymerize into short-chain oligomers or back into glycerol. The optimum reaction time for 5 mL DMSO is 6 hours because the glycerol conversion is 63%, producing diglycerol and triglycerol with 30% and 17% selectivities, respectively.