The phase equilibrium of triglycerides and ethanol at high pressure and temperature: The influence on kinetics of ethanolysis

Abstract

Biodiesel synthesis by ethanolysis of triglycerides conducted under high pressure and at elevated temperature can lead to high levels of conversion and biodiesel yield over short reaction time. The vapour-liquid or vapour-liquid-liquid equilibrium and phase distribution of ethanol and triolein were investigated in order to determine the range of pressure and temperature required for high oil conversion. The phase equilibrium of the triolein and ethanol mixture (1:40 and 1:26 molar ratio of triolein to ethanol) was monitored in a view cell in order to determine the phase transition during heating of mixture up to 195 degrees C (the corresponding pressure was 25 and 26 bar). The experimental data were simulated using ASPENplus (R) and UniSim (R) software and results obtained using RK-Aspen EOS were found to correlate well with the experimental data. Simulation results show the important influence of the phase equilibrium on the reaction mechanism and overall kinetics under subcritical conditions (T lt 270 degrees C at 200 bar) since the two liquid phases exist at the beginning of reaction, thereby limiting the contact between the reactants. In case of single reaction phase (T gt 270 degrees C at 200 bar) the initially high reaction rate is limited at high conversion levels due to increasing extent of reversible reaction.