Theoretical Analysis of Biodiesel Production Under High Temperature and Pressure Conditions

Typically, biodiesel is synthesized by the transesterification of vegetable oil in heterogeneous fashion, i.e. in multiple liquid phases since the reactants, methanol and vegetable oil, are immiscible. In this work, we propose that the synthesis of fatty acid methyl esters (FAME), which after purification become biodiesel, take place in a solution where methanol, vegetable oil, and FAME are all homogeneously dissolved. Carrying out the reaction scheme in this manner eliminates any mass transfer effects between the oil and methanol phases. In addition, the overall reaction rate is further enhanced by the gravity based removal of the glycerol final product from the reaction mixture. The proposed process is modeled as a multiphase reactor with three phases (vapor, FAME, glycerol) in equilibrium with each other. Reactions are only considered to be carried out in the FAME phase. The mathematical model constitutes a Differential-Algebraic-Equation (DAE) problem that is solved through the implementation of a hybrid Runge-Kutta/Newton-Raphson solver. Several temperature and pressure conditions are considered to explore the operational characteristics of this process. Comparisons with the original heterogeneous biodiesel production process are carried out.