Optimizing Catalyst Free-Biodiesel Production with Super-Critical Ethanol and CO2 Co-Solvent Using Response Surface Methodology

ABSTRACT

Fossil-based methanol production for biodiesel generation is not considered renewable compared to biodiesel produced from ethanol generated from agricultural biomass via fermentation. In this study, biodiesel production from corn oil using super-critical ethanol and CO₂ as a co-solvent is investigated under reaction conditions of 250-350 °C/17MPa with a residence time of 10-30 minute and ethanol to oil ratio of 15-35. Furthermore, the co-solvent pressure was varied between 10-50 bars. In this study, response surface methodology was used to identify the optimum values for biodiesel transesterification yield. Results identified the controlling factors as the reaction temperature, reaction time, CO₂ pressure plus second order effects including the temperature with reaction time for biodiesel yield. The highest biodiesel yield of 94% was achieved at 275 °C, 20:1 ethanol to oil ratio, and co-solvent pressure of 40 bar for 25-minute reaction time. The order of significance for reaction parameters for biodiesel yield was reaction time > CO₂ pressure > reaction temperature. The process R² and adjusted R² were 0.96 and 0.92 respectively.