Chemical kinetics of a two-step transesterification of dyacrodes edulis seed oil using acid-alkali catalyst

A chemical kinetic model for acid-alkali catalyzed methanolysis of high free fatty acid (FFA) underutilized African pear seed oil (APSO) is presented for the first time. A two-step: esterification followed by transesterification in a stirred batch reactor was carried out over 100 min, at 55–65 °C temperature range. Physico-chemical properties of the methyl ester was determined and discussed in accordance with relevant international methods and specifications. Composition of the reaction mixtures were determined using GC-FID and Karl Fischer titration methods. Integrated Gauss-Jordan elimination method on 4.03 GNU Octave software, 2016 version was efficient, simple and a fast approach in determining the rate constants. Rate constants of the forward and backward reactions of esterification were 0.732, 1.255, 2.031 and 0.549, 0.845, 1.421 L/g min respectively while those of the forward and backward reactions of the triglycerides, diglycerides and monoglycerides hydrolysis were 0.442, 0.0476 and 0.0493; 0.0476, 0.0851, and 0.1347; 0.1049, 0.2010 and 0.3319 and 0.0241, 0.0430 and 0.0597; 0.0113, 0.2172 and 0.2540; 0.0517, 0.1011 and 0.1570 L/g min respectively. Activation energy of the forward and backward esterification and transesterification reactions respectively were higher than the reverse reactions which indicates that the formation of free fatty acid (FFA), triglycerides and diglycerides were faster. Rates of reactions were found to increase with temperature and mixing rate (200, 400 and 800 rpm). The hydrolysis of monoglycerides to diglycerides, diglycerides to triglycerides and triglycerides to diglycerides at 55 °C, 60 °C and 65 °C respectively were ascertained as the rate determining steps.