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

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 °C (the corresponding pressure was 25 and 26 bar). The experimental data were simulated using ASPENplus® and UniSim® 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 < 270 °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 > 270 °C at 200 bar) the initially high reaction rate is limited at high conversion levels due to increasing extent of reversible reaction.

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► The VL equilibrium and phase distribution of ethanol and triolein were investigated.
► The experimental data were compared with calculation obtained using ASPENplus® and UniSim® software.
► Modelling results obtained using RK-Aspen EOS were found to correlate well with the experimental data.
► The predicted and experimental data were in excellent agreement for all analysed ethanol to oil molar ratio.
► The phase equilibrium plays an important role in the reaction mechanism and kinetics of ethanolysis under high p,T conditions.