Study of reversible kinetic models for alkali-catalyzed Jatropha curcas transesterification

Abstract

Biodiesel is a promising alternative to diesel fuel because of its renewable feedstocks and potential environmental benefits. Chemically, biodiesel is monoalkyl esters of long-chain fatty acids, which fall in the carbon range of C12–C22. It has similar properties as mineral diesel. Transesterification process is a chemical transformation of triglycerides to biodiesel. Experimental studies of alkali-catalyzed transesterification of nonedible feedstock, Jatropha curcas, to produce Jatropha methyl esters (biodiesel) in a batch reactor are reported. The effects of operating conditions, temperatures (30–60 °C), and stirring rates (750 and 300 rpm), at constant concentration of catalyst (0.5 % w/w of oil) and constant molar ratio of methanol to oil (6:1), on product yields were investigated. The equilibrium conversions of triglycerides to biodiesel were achieved in approximately 40 min for all the experiments conducted and were observed in the range of 43–80 %. The conversion values were observed to increase with the increase in temperature and stirring rate. The main thrust of the present work was to model the kinetics and to simulate alkali-catalyzed transesterification process. Reversible kinetic models for overall transesterification reaction were applied on experimentally obtained conversion data. The model parameters were optimized. The optimal equilibrium rate constant obtained from systematic approaches was found to increase with the increase in temperature and stirring rate. It was concluded that the overall alkali-catalyzed transesterification reaction of Jatropha curcas is a reversible endothermic reaction. Characterization of feedstock oil and biodiesel produced had revealed significant changes in the physical properties during transesterification.