Enzymatic Synthesis of Dipalmitin in Supercritical Carbon Dioxide and Mechanism Study

Dipalmitin was enzymatically synthesized from palmitic acid and glycerol in supercritical carbon dioxide (scCO(2)), and optimum reaction conditions were determined. An organic solvent (tert-butanol) system was also investigated, but the highest conversion of palmitic acid (81%) and highest yield of dipalmitin (69.44%) were obtained in scCO(2) with an extremely low enzyme concentration, 0.34 g/L, the volumetric concentration of enzyme in scCO(2). The immobilized enzyme showed excellent operational stability in scCO(2) under the experimental conditions. A phase behavior study indicated that the difference in solubilities of the products in scCO(2) resulted in an improved selectivity for dipalmitin. A phase transfer model was designed to illustrate the reaction process in scCO(2). The enzyme kinetic parameters in the scCO(2) system and tert-butanol solvent system were also evaluated using a ping-pong Bi-Bi mechanism with inhibition, and palmitic acid in scCO(2) was to have the lowest inhibition (K-B/K-iB = 4.356), which is due to the low viscosity and high diffusivity of scCO(2).