Reaction Characteristics of Glycerol Pretreatment of Bio-oil with Calcium Hydroxide for Biodiesel Production

Abstract

Glycerol pretreatment of bio-oil has been found to be effective for producing rapid ethanolysis, which is of great usefulness in biodiesel production for sub-Saharan regions such as Malawi. However, the reaction characteristics of glycerolysis have not been elucidated, so design of a novel biodiesel production process has been hindered. In this study, the overall thermodynamic reaction properties were evaluated and the reaction kinetics were determined. Pre-mixtures of groundnut (Arachis hypogaea) oil feedstock, glycerol (GL), and calcium hydroxide (Ca(OH)₂) were prepared in a 300-mL flat-base round flask reactor and heated at different temperatures and for different times. The results showed that thermal pretreatment at 180°C for 5 h significantly enhanced triglyceride (TG) decomposition and initial diglyceride (DG) and monoglyceride (MG) concentrations as reactive intermediates for ethanolysis. The change in enthalpy, entropy and Gibbs free energy were determined, which led to the determination of the reaction equilibrium. First-order kinetics for glycerolysis of TG and MG expressed the concentration change of the reactants and products well. The reaction parameters including activation energy are reported in this paper.