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

ABSTRACT

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 (R²) 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 m³/mol.s. There was a high degree of correlation between the experimental and the model rate constant values with R² of $0.9785$. It was concluded that the progress of the transesterification reaction for biodiesel production can be monitored by absorbance measurement.

KEYWORDS:

• Biodiesel
• transesterification
• kinetics
• absorbance
• glycerol

Acknowledgements

The authors would like to thank the Department of Chemical Engineering, University of Benin, Nigeria, for providing the necessary facilities for carrying out this study.

Disclosure statement

No potential conflict of interest was reported by the authors.