(190d) Using Ethanol in Continuous Biodiesel Production with Trace Catalyst and CO2 Co-Solvent

The continuous biodiesel production process under sub and super-critical conditions using a trace amount of potassium hydroxide (KOH) as a catalyst have been studied. In addition, CO₂ was added as a co-solvent to reduce the reaction time and increase biodiesel yield. The proposed procedure enables simultaneous transesterification and esterification of triglycerides and free fatty acid (FFA), respectively. The shorter reaction time and milder reaction conditions may reduce energy consumption due to simplification of the separation and purification steps. The process variables, including reaction temperature, ethanol to oil molar ratio, catalyst amount, and process pressure were systematically optimized. The highest biodiesel yield (98.12%) was obtained after 25 minutes reaction time using only 0.11% wt. of KOH and 20:1 ethanol to oil ratio. The process optimum temperature and pressure were 240 °C and 120 bars, respectively. The proposed kinetic model suggested a first order reaction with an activation energy of 19.5 kJ.mol^-1 and a reaction rate constant of 0.0398/min^-1. The thermodynamic parameter values including enthalpy, entropy and Gibbs free energy for this process were calculated as 15.05 kJ.mol^-1, -0.27 kJ.mol^-1 and 153.6 kJ.mol^-1 at 240 °C, respectively.