Production of biodiesel from castor oil using sub and supercritical ethanol: Effect of sodium hydroxide on the ethyl ester production

The biodiesel obtained by the reaction of castor oil with ethanol under sub and supercritical condition (200–350 °C at endogenous pressure) using small amounts of sodium hydroxide (NaOH) as catalyst was studied. The influence of the operating variables such as temperature, reaction time, ethanol:oil molar ratio and catalyst concentration (when used) on the reaction yield was evaluated using a statistical design of experiments along with the surface response methodology for both the catalytic and non-catalytic processes. It was observed that using only 0.1% wt of NaOH for the catalytic process, amount smaller than the necessary to neutralize the castor oil, it was possible to obtain high yields. The maximum ethyl ester yield reached was 98.9% for the catalytic process and 56.2% for the non-catalytic process. Additionally, the reaction kinetic was determined and it was found that a pseudo first order model represents the overall reaction. Activation energies were calculated from the Arrhenius equation for both processes.