Glycerol conversion to lactic acid with sodium hydroxide as a homogeneous catalyst in a fed-batch reactor

Abstract

This study investigated a fed-batch process for glycerol conversion to lactic acid with sodium hydroxide (NaOH) as homogeneous catalyst, with the aim to reduce the corrosiveness of catalyst to reactor. At the optimal conditions of the fed-batch process (1.1 M initial glycerol concentration, reaction time of 220 min, reaction temperature of 300 °C, NaOH concentration around 0.2 M), lactic acid yield reached 82 mol%, with 93 mol% of glycerol conversion. A first order kinetic model in the fed-batch conversion of glycerol was developed and validated under different process conditions. The corrosiveness to stainless steel reactor in glycerol conversion in the fed-batch process, measured as Fe3+ at the end of reaction, decreased from 9.5 to 1.5 ppm Fe3+ when compared to a batch process using a homogeneous 1.25 M NaOH as catalyst. Application of the fed-batch reactor in the crude glycerol conversion reached the maximum lactic acid yield of 72.9 mol% with 92.4 mol% glycerol conversion, but high soap content in crude glycerol has negative effects on both lactic acid yield and glycerol conversion.