Kinetics of free fatty acid esterification in used cooking oil using hypercrosslinked exchange resin as catalyst

A kinetic study of free fatty acid esterification was carried out using Purolite D5081 as a catalyst. Esterification reaction was carried out using 1.25% (w/w) catalyst loading, 6:1 methanol to oil feed mole ratio, 350 rpm stirring speed and reaction temperatures ranging from 323 - 335 K. The experimental data from the esterification reaction were fitted to three kinetic models: Pseudo Homogeneous (PH), Eley-Rideal(ER) and Langmuir-Hinshelwood-Hougen-Watson (LHHW) models. A built-in ODE45 solver in MATLAB 7.0 was used to numerically integrate the differential molar balances describing the concentration of FFA in the system. The influence of temperature on the kinetic constants was determined by fitting the results to the Arrhenius equation. Experimental data were successfully fitted by the PH model and a good agreement between the experimental and the calculated moles of FFA were observed for all the experimental data points. The activation energies for the esterification and hydrolysis reactions were found to be 53 and 107 kJ/mol, respectively. These results proved that the hydrolysis reverse reaction requires more energy to occur as compared to esterification reaction, hence validated the proposed model