Optimization of the used sunflower oil methanolysis catalyzed by hazelnut shell ash

Abstract

The methanolysis of used sunflower oil catalyzed by hazelnut shell ash was studied to evaluate the statistical significance of the process factors, i.e., the initial methanol-to-oil molar ratio, the catalyst amount, and the reaction time on fatty acid methyl ester (FAME) content and to determine their optimal values ensuring the highest FAME content. The reaction was conducted in a batch reactor at the methanol-to-oil molar ratios of 6:1-18:1, the catalyst amounts of 1-5% (of the oil weight), and the reaction time of 10-50 min. Furthermore, statistical modeling and optimization were performed using a modified second-order polynomial model developed by the response surface methodology in combination with a 33 factorial design with three central points. The analysis of variance showed that all three factors, the two-parameter interaction of the catalyst amount and the reaction time, as well as the quadratic term of the reaction time, had a statistically significant effect on FAME content. The optimum conditions were found to be the methanol-to-oil molar ratio of 10.34:1, the catalyst amount of 5%, and the reaction time of 34 min. The predicted value of FAME content was 99.63%, which agreed well with the experimentally determined FAME content (97.15%).