Monitoring the transesterification reaction of castor oil and methanol by ultraviolet visible spectroscopy

This study investigated the kinetics of transesterification of castor oil with methanol by absorbance measurement using ultraviolet-visible (UV-Vis) spectroscopy. The transesterification reaction was carried out at determined optimum reaction conditions of catalyst concentration of 1.0?wt.% KOH, temperature of 50?C and methanol-to-oil molar ratio of 9:1. The progress of the reaction was monitored by measuring the absorbance of the reaction mixture at intervals for 1 h using a UV-Vis spectrophotometer at a wavelength of 700?nm. Concentration of glycerol formed during the reaction was calculated from the measured absorbance of the reaction mixture. First-, second- and third-order reaction kinetic models with respect to castor oil were used to analyze the kinetic data by the integral method. Based on the correlation coefficient (R-2) of the models tested, the second-order kinetic model best described the reaction, with a reaction rate constant of 7.221?L/mol.min at 50?C. Activation energy for the reaction was calculated to be 38.33?kJ/mol with a collision frequency factor of 176.708 m(3)/mol.s. There was a high degree of correlation between the experimental and the model rate constant values with R-2 of . It was concluded that the progress of the transesterification reaction for biodiesel production can be monitored by absorbance measurement.