Product Selectivity and Optimization of Lipase-Catalyzed 1,3-Propylene Glycol Esters by Mixture Design and RSM

Propylene glycol mono- (PGM) and diesters (PGD) are widely used as emulsifiers in food and pharmaceutical industry. Solvent engineering was applied to determine the optimum solvent mixtures for the lipase-catalyzed synthesis of 1,3-PGM and 1,3-PGD. After 24 h reaction, the results showed that the molar production of 1,3-PGM was 75% under pure 2M2B (2-methyl-2-butanol) system, whereas 1,3-PGD was preferred to produce in binary mixture system (n-hexane: octane 1:1) with 55% of molar production. Furthermore, the reaction parameters that affect esterification of 1,3-PGD using oleic acid as acyl donor in optimum cosolvent environment were evaluated by response surface methodology (RSM). The reaction temperature and reaction time were the most important parameters. Based on a ridge max analysis, the optimum conditions for 1,3-PGD synthesis were predicted to consist of a reaction time of 40.6 min, a temperature of 59 °C, an enzyme amount of 70.4%, a substrate molar ratio (1,3-propylene glycol/oleic acid) of 1:2.7 and an enzyme pretreatment pH of 6.4 on percentage of molar production of 1,3-PGD of 43.3 ± 4.2%.