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The current paper exemplifies the application of ultrasound technology to enzymatic synthesis of a cosmetic emollient ester, cetyl oleate. Fermase CALB™10000, a commercial Candida antarctica lipase B was used as a catalyst to accomplish the ultrasound supported synthesis. Multiple process parameters like reaction time, temperature, enzyme dose, alcohol to acid molar ratio, ultrasound power, frequency and speed of agitation were optimised. Maximum conversion of ∼95.96% was discerned at optimum conditions, i.e., 60°C temperature, 5% enzyme dose, 2:1 alcohol:acid ratio, 60 W ultrasound power, 25 kHz ultrasound frequency, 80% duty cycle and 80 rpm speed of agitation after purification steps. It was observed that the reaction reached equilibrium in a short duration of 30 min under the optimised conditions. This was considerably lesser than the time required for attaining equilibrium in conventional mechanical stirring method which was over 2h. Bisubstrate kinetic models like random bi-bi, ping pong bi-bi and ordered bi-bi were applied to the experimental data to determine initial rates and other kinetic parameters. Ordered bi-bi model showed the best fit with kinetic parameters, Vmax=0.029 M/min/gcatalyst, KA=0.00001 M, KB=4.8002 M, KiA=0.00014 M, KiB=3.7914 M & SSE=0.00022 for enzymatic cetyl oleate synthesis under ultrasound irradiation with inhibition by both acid and alcohol at high concentrations.

This work exhibits the implementation of ultrasound technology in solvent-free synthesis study of n-butyl palmitate using Fermase CALB™10000. Sequential experimental design study was instrumental in determining the most significant process variables. The effect of acid-alcohol molar ratio, enzyme dose, temperature, power and duty cycle on the reaction kinetics was studied. Highest conversion of ~ 96.6% was observed in 50 min at 1:1 molar ratio of palmitic acid to n-butanol, 70 °C temperature, 4% w/w enzyme loading, 40 W power, 70% duty cycle, 25 kHz frequency and 100 rpm speed of impeller. Ping-pong bisubstrate model showed the best fit with kinetic parameters, V = 21.88 M/min/g catalyst, K = 0.011 M, K = 8.74M, K = 0.014M, K = 0.00036M and SSE = 0.0000193. Ultrasound reduced the reaction time by over 70%. The enzyme was reusable for four successive cycles after which it showed decline in conversion.

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