Continuous Production of Biodiesel from Vegetable Oil Using Supercritical Ethanol/carbon Dioxide Mixtures

Biodiesel production is worthy of continued study and optimization of production procedures because of its environmentally beneficial attributes and its renewable nature. Transesterification of triglycerides using supercritical ethanol on ionexchange resin catalyst was investigated to study the ethyl ester conversion process. The reaction parameters investigated were the reaction time, pressure and temperature at a constant molar ratio (alcohol to triglycerides), and their effect on the biodiesel formation. Addition of a co-solvent, supercritical CO2 (critical point at 31 °C and 7.3 MPa), increased the rate of the supercritical ethanol transesterification reaction, making it possible to obtain high biodiesel yields at less harsh temperature conditions. The experiments were conducted at temperatures of 150 – 200 oC, pressure from 150 to 250 bar and reaction times from 2 to 10 min, and molar ratios of ethanol to vegetable oil from 20 to 45. The evolution of the process was followed by gas chromatography, determining the concentration of the ethyl esters at different reaction times. Results showed that ethyl esters obtained in the continuous fixed bed reactor under supercritical conditions can achieve 80% yield of biodiesel at reaction time of 4 minutes