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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.

The current research work represents solvent free enzymatic synthesis of fatty acid ethyl ester; ethyl laurate. Immobilized lipase Fermase CALB™10,000 was used for the synthesis of ethyl laurate from ethanol and lauric acid. The influence of process parameters such as catalyst loading, speed of agitation, mole ratio, molecular sieves and temperature were studied. Fermase CALB™10,000 offered a conversion of 92.46 % at 60 °C in 4 h at optimized condition. The experimental data was best fitted by the Random Bi-Bi model with inhibition of both the substrates i.e. lauric acid and ethanol. The following kinetic parameters were retrieved from the model: V = 1.243 × 10 mmol/min/g enzyme; K = 0.1283 mmol; K = 8.51 mmol; K = 5.098 mmol; and SSE = 0.0142. The activation energy for the enzymatic esterification was also determined and calculated to be 28.49 kJ/mol. A maximum conversion of 71 % was obtained after 5 successive reuse of Fermase CALB™10,000 lipase.

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IntroductionNowadays, there is a huge demand for the synthesis of sustainable products from natural resources. It is equally of major concern to investigate natural raw resources to feature the bio-based lubricants 1, 2 . In recent years, the bio-lubricants have been used widely in the industrial sectors because of their distinctive harmfulness and biodegradable nature. The ethylhexyl esters are oily in nature and therefore regularly used in the beautifying formulations as an oil component and as a solvent for active substances 3 . It is popularly used in the formulations of skincare products and eye makeup. With the consistently developing interest for bio-lubricants in various industries like food, pharmaceuticals, and cosmetics, different chemical and enzymatic methods have been evolved for the synthesis of fatty acid ethylhexyl esters 4,5 .Several lubricants were obtained from vegetable oils, waste cooking oils and their methyl esters. Zheng et al. developed 2-ethylhexyl palmitate by transesterification method by using powdered potassium carbonate as a catalyst 5 . But this method requires a high temperature of 180 . Hence, enzyme catalyzed production of bio-lubricant is in high demand, as enzymatic synthesis requires ambient conditions. Recently, enzymatic synthesis of 2-ethylhexyl oleate by transesterification of 2-ethylhexanol and biodiesel was reported by Kleinaitė et al. 6 . Habib et al. discussed the transesterification of palm oil methyl ester with 2-ethylhexanol 7 . Richetti et al.