Enzymatic synthesis of biodiesel from palm oil assisted by microwave irradiation

Optimal conditions for enzymatic synthesis of biodiesel from palm oil and ethanol were determined with lipase from Pseudomonas fluorescens immobilized on epoxy polysiloxane-polyvinyl alcohol hybrid composite under a microwave heating system. The main goal was to reduce the reaction time preliminarily established by a process of conventional heating. A full factorial design assessed the influence of ethanol-to-palm oil (8:1-16:1) molar ratio and temperature (43-57 °C) on the transesterification yield. Microwave irradiations varying from 8 to 15 W were set up according to reaction temperature. Under optimal conditions (8:1 ethanol-to-oil molar ratio at 43 °C), 97.56 % of the fatty acids present in the palm oil were converted into ethyl esters in a 12-h reaction, corresponding to a productivity of 64.2 mg ethyl esters g⁻¹ h⁻¹. This represents a sixfold increase from the process carried out under conventional heating, thus proving to be a potential tool for enhancing biochemical modification of oils and fats. In general, advantages of the new process include: (1) microwaves speed up the enzyme-catalyzed reactions; (2) there are no destructive effects on the enzyme properties, such as stability and substrate specificity, and (3) the microwave assistance allows the entire reaction volume to be heated uniformly. These bring benefits of a low energy demand and a faster conversion of palm oil into biodiesel.