Production of monoolein from oleic acid and glycerol in supercritical carbon dioxide media: A kinetic approach

Esterification of free fatty acids (FFA) with glycerol in supercritical carbon dioxide (SC-CO2) media to produce designer monoacylglycerols (MAG) for food, cosmetic, and pharmaceutical industries, was conducted to elucidate the reaction kinetics and provide the reaction mechanism. Reactions were conducted in SC-CO2 at 10–30 MPa, 170–250 °C in a batch stirred reactor using an anhydrous glycerol to oleic acid initial molar ratio (gly/oleic) of 10:1, 1:1 and 1:2 and in supercritical nitrogen at 10 MPa and 250 °C using 10:1 gly/oleic. Samples were collected as a function of time and MAG, diacylglycerol, triacylglycerol and FFA concentrations were determined using thin layer chromatography–flame ionization detection. The rate of MAG formation at 50% of equilibrium concentrations (Rate-50%) increased significantly (p ≤ 0.05) with temperature but was not affected by pressure or supercritical media (p > 0.05). Rate-50% values for 10:1 and 1:1 gly/oleic were similar (p > 0.05) but higher (p ≤ 0.05) than that for 1:2 gly/oleic. Equilibrium concentration of MAG significantly (p ≤ 0.05) decreased with decreased initial glycerol concentration. The calculated rate constants provided a better understanding of the mechanism and are essential for optimal process design.