Calculating the thermodynamic characteristics and chemical equilibrium of the stepwise transesterification of triolein using supercritical lower alcohols

A comparative study of triolein transesterification using three individual supercritical alcohols (methanol, ethanol, and isopropanol) was performed using thermodynamic analysis. The correlative properties were calculated for all components, including boiling point, critical parameters, acentric factor, enthalpy, entropy, and constant-pressure heat capacity. Chemical equilibria of the three reaction systems were discussed and diagrams of reaction enthalpy, Gibbs free energy and the chemical equilibrium constant as a function of temperature were constructed for the temperature range from 300 to 700 K. The results illustrated that, in the supercritical state, the triolein transesterification reaction proceeds primarily with methanol under the proper reaction conditions, but rarely occurs with ethanol or isopropanol. This observation was consistent with the experimental results reported in literature. This study provides a reliable method for analyzing analogous reaction systems for biodiesel synthesis with supercritical fluids.