Lipase-catalyzed Production of Biodiesel from High Acid Value Waste Oil Using Ultrasonic Assistant

Biodiesel fuel produced by the enzyme-catalyzed esterification and transesterification of high acid value waste oil using ultrasonic assistant was explored. Propyl oleate, a biodiesel converted from high acid value waste oil and 1-proponal, was catalyzed with immobilized lipases from Candida Antarctica and Aspergillus oryzae under the conditions of ultrasonic assistant. Commercial immobilized lipase Novozym 435 from C. antarctica was utilized as a biocatalyst for catalyzing high acid value waste oil and 1-proponal by esterification and transesterification to propyl oleate under the conditions of ultrasonic assistant. Various conditions such as the amounts of lipases, initiatory molar ratio of propanol to oil, and frequency and power of ultrasonic assistant were investigated and optimized. It is revealed that the enzymatic activity of Novozym435 is enhanced and, in particular, enzyme-catalyzed transesterification activity is obviously enhanced under the conditions of ultrasonic assistant. Low frequency and mild energy ultrasonic assistant is a key factor for enhancing enzymatic activity, emulsifying oil-propanol system, and accelerating the speed of diffusion in the system. Under the optimal ultrasonic assistant reaction conditions, such as 8% oil quantity of Novozym435, the initiatory molar ratio of propanol to oil 3:1, the frequency of ultrasonic assistant 28 kHz, the power of ultrasonic assistant 100 W, and the temperature of water batch 40-45 °C, the conversion ratio of 94.86% to propyl oleate is achieved in 50 mins, which is very high in comparison with the highest conversion ratio of 84.43% to propyl oleate under the conventional mechanical agitation conditions. Furthermore, it is demonstrated that various short chain linear and branched alcohols (C1-C5) show high conversion ratio to fatty acid alkyl esters (biodiesel) under the optimal ultrasonic assistant reaction conditions. On the other hand, ultrasonic energy is propitious to reduce the rate of adsorption during the production of propyl oleate, by-product glycerol, and other emplastics in the system on the surface of immobilized lipase Novzym435, and recyclable Novozym435 has the characteristics of clean appearances, well decentralizations, no agglomeration, easy washing and well operational stability.