Biodiesel Production from Castor Oil: Optimization of Alkaline Ethanolysis

Abstract

This work presents the biodiesel production from castor oil with bioethanol from sugar cane (also called here ethanol) in presence of sodium ethoxide and sodium hydroxide as catalysts. The studied variables were reaction temperature, catalyst concentration, and ethanol:castor oil molar ratio. The experimental design was used in the optimization process because this methodology permitted a careful evaluation of the process variables. A model describing the biodiesel conversion in terms of reaction temperature, molar ratio ethanol:castor oil was identified. The experimental design shows the catalyst concentration as the most important variable and the model obtained predicts the ethyl ester concentration as function of the reaction temperature, the ethanol:castor oil molar ratio and the catalyst concentration. A conversion of 99%wt of ethyl ester was obtained at 30 °C, with mechanic stirrer, 1 %wt of sodium ethoxyde, ethanol:castor oil molar ratio of 16:1 and at 30 min of reaction. The kinetic study of the transesterification reaction was carried out, and the apparatus used for the experiment was a 1 L jacketed reactor, equipped with a variable speed agitator. The study was based on the overall transesterification reaction. In the kinetic study, the temperature of the reactor was controlled and maintained at 30, 40, 50, and 70 °C. The results from the experiments demonstrate that the kinetically controlled region follows a first-order mechanism for the forward reaction. The castor oil molecular weight was determined using the vapor pressure osmometry technique (VPO). The results showed that VPO technique is a robust alternative methodology for determining vegetable oil molecular weight presenting lower cost than gas chromatography analysis (GC).