EMPIRICAL MODELING OF KINETICS OF TRANSESTERIFICATION AND COLD FLOW PROPERTIES OF USED SOYA OIL BIODIESEL

Abstract

This research work focused on empirical modeling of kinetics of transesterification and cold flow properties of homogeneous catalyzed used soya oil fatty acid methyl ester (USOFAME]. Used soya oil (USO) was prepared by frying food (yam, potato plantain etc) with virgin soya oil for a total of 72 hours [1]. The oil was characterized based on American Society for Testing and Materials (ASTM) method. The fatty acid profile of used soya oil was analyzed using gas chromatography mass spectroscopy (GC MS) while the functional groups of the triglyceride were determined using Fourier transform infrared spectroscopy (FTIR). The oil was pretreated to reduce the free fatty acid level below 1% and then transesterified using methanol in the presence of sodium hydroxide catalyst. The fuel properties of the USOFAME produced were determined based on ASTM standards. Kinetic experiments were conducted in batches at different temperatures of 450C, 550C and 650C. Application of rate laws to the three-step reversible reaction scheme of transesterification yielded a series of ordinary differential equations (ODEs) solved with polymath 5.1 software to give the forward and reverse rate constants k1,k2, k3, k4, k5 and k6 from which the rate limiting step (RLS) and activation energy (∆E) were derived. The cold flow properties, cloud point (CP), cold filter plugging point (CFPP) and pour point (PP) were determined experimentally for different blends of biodiesel with #2 diesel, at a percentage volume ratio of biodiesel to diesel 0, 20, 40, 60, 80, and 100. The values obtained for CP, CFPP, and PP were plotted against the biodiesel fraction in the blends. Least square regression of the data of the plots were tested on linear, quadratic and polynomial models using Microsoft excel. The fuel properties of the USOFAME which is within the ASTM standards were determined as acid value 0.4mgKOH/g, density 863mm2/s, kinematic viscosity 4.60mm2/s, flash point 1620C, cetane number 61.00, calorific value 40.06MJ/Kg, pour point -40C, cold filter plugging point -2.80C, cloud point 00C, iodine value 30.60gI2/100g. Kinetic modeling of transesterification of USOFAME shows that the forward rate constants K1, K2, and K3 are greater than those of the reverse reaction k2, k4, k6, imply that the forward reaction dominates while the reverse reaction could be neglected. The rate constant k1 for triglyceride conversion to diglyceride is the least among the forward rate constants at 450C, 550C and650C imply that this step is the rate limiting step (RLS). Application of least square regression analysis of Microsoft excel on the data of variation of cold flow properties with biodiesel fraction, revealed polynomial model to be the best fitting equation.