Statistical Study on Lipase-Catalyzed Synthesis of Biodiesel from Castor Oil using Response Surface Methodology

The production of fatty acid methyl esters (biodiesel) from crude castor oil using n-hexane as a solvent and commercial immobilized lipase, Nozozym 435, as catalyst was carried out in the present study. To this purpose, a response surface methodology (RSM), in the form of central composite rotatable design (CCRD), was adopted considering the following variables: the amount of enzyme (2-6 wt/wt%), molar ratio of methanol to castor oil (3:1 to 7:1), temperature (30-50 ºC) and reaction time (12-48 h). The influence of these factors on the biodiesel production yield was evaluated using second-order polynomial multiple regression model. Analysis of variance showed a high coefficient of determination value of 0.99, thus ensuring a satisfactory adjustment of the regression model with the experimental data. The empirical model predicted the maximum conversion of 97.9 % at the enzyme loading of 5 wt/wt%, methanol/oil molar ratio of 6:1, reaction temperature of 42 ºC, and reaction time of 39 h. The experimental conversion at optimum reaction conditions were obtained as 98.0%.