Enhancement in synthesis of ethyl laurate catalyzed by fermase by combined effect of ultrasound and stage wise addition of ethanol

Abstract

The current work focuses on the intensification of fermase catalysed synthesis of ethyl laurate from ethanol and lauric acid in a solvent free condition with ultrasound and stage wise ethanol addition. The effect of molar ratio, stepwise addition of ethanol, catalyst loading, speed of agitation, temperature, ultrasound power and duty cycle was systematically studied. The optimal conditions were found as 1:2 lauric acid:ethanol mole ratio, 2% enzyme loading, 50 °C temperature, 40 min reaction time, 100 W power with 50% duty cycle. The highest conversion of 96.87% was obtained for stage wise addition of ethanol in presence of ultrasound and mechanical stirring. Thermodynamic study showed decrease in the value of enthalpy (ΔH), entropy (ΔS), free energy (ΔG) and activation energy (E) for ultrasound with stirring than that of ultrasound alone and conventional stirring. The thermodynamic study reveals that the combination of ultrasound and stirring is more effective as contrasted the ultrasound without stirring and mechanical stirring method. Application of ultrasound irradiation significantly decreased the time of reaction process when equated with mechanical stirring method. Under optimized conditions, the continuous use of fermase enzyme for repetitive cycles causes loss in percentage conversion of the reaction.