Optimization of Lipase-Catalyzed Synthesis of Cetyl Octanoate in Supercritical Carbon Dioxide

Cetyl octanoate, a wax ester of 24 carbons, is widely used in the cosmetic industry as a base oil. The current work focuses on lipase-catalyzed synthesis of cetyl octanoate in supercritical carbon dioxide (SC-CO2) by esterification of cetyl alcohol and octanoic acid. Three immobilized lipases were screened, and 15 reaction conditions were tested in order to find the combination for maximal yield. The results showed that Novozym® 435 was the best catalyst for the synthesis, and a reaction time of 20 min was adequate for a maximal yield. Response surface methodology (RSM) with a 3-factor-3-level Box-Behnken design was employed to evaluate the effects of synthesis parameters, including reaction temperature (35–75 °C), pressure (8.27–12.41 MPa), and enzyme amount (5–15% wt of cetyl alcohol). A model for the synthesis was developed and the optimum conditions could be predicted to be reaction pressure of 10.22 MPa, reaction temperature of 63.70 °C, and enzyme amount of 11.20%. An experiment was performed under this optimum condition and a yield of 99.5% was obtained. This experimental yield correlated well with the predicted value of yield (97.6%). We concluded that, in a SC-CO2 system, nearly 100% molar conversion of cetyl octanoate could be obtained by immobilized Novozym® 435 in a short reaction time (20 min) under the predicted optimal conditions.