Lipase catalysed synthesis of cetyl oleate using ultrasound: Optimisation and kinetic studies

•Ultrasound assisted enzymatic synthesis of cetyl oleate in a solvent free system was performed.•Various experimental parameters were studied and optimised to get maximum conversion.•Maximum yield of 95.96±0.33% was obtained in only 30min.•Ultrasonication gave a reduction of about 75% in the time required for cetyl oleate synthesis.•Ordered bi–bi model showed the best fit with experimental data. 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, 60W ultrasound power, 25kHz ultrasound frequency, 80% duty cycle and 80rpm speed of agitation after purification steps. It was observed that the reaction reached equilibrium in a short duration of 30min 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=0.029M/min/gcatalyst, KA=0.00001M, KB=4.8002M, KiA=0.00014M, KiB=3.7914M & SSE=0.00022 for enzymatic cetyl oleate synthesis under ultrasound irradiation with inhibition by both acid and alcohol at high concentrations.