Abstract
The catalytic behavior of K/Fe catalyst in biodiesel synthesis by ethanolic transesterification of sunflower vegetable oil was investigated. The catalysts were prepared according to the conventional precipitation, impregnation, and calcination methods. The catalysts were characterized by X-ray diffraction (XRD), FT-IR spectroscopy, thermogravimetric analysis (TGA), and Hammett-Benzoic acid indicator titration. Catalytic tests for biodiesel production revealed an excellent activity of the K/Fe3-800 catalyst, which is consistent with the number of basic sites (1.50 mmol/g) in bulk. Potassium polyferrite phases K1.55Fe11O17/K2Fe10O16 as basic active sites on the catalyst surface were generated, increasing the catalytic ability for biodiesel synthesis. The optimum conditions for transesterification reaction were catalyst amount of 5%, ethanol-to-oil molar ratio of 9:1, reaction temperature of 70 °C, and reaction time of 45 min. The maximum conversion of oil to ethyl esters reached 98.2%. The catalyst can tolerate free fatty acid and moisture up to 0.5% and 1%, respectively. K/Fe3-800 catalyst was successfully reused at least three times without post-treatment, and the obtained yield was higher than 92.3%. The XRD and TGA characterizations showed that poisoning of the active sites and pore fouling are the main reasons for the K/Fe3-800 deactivation. This finding indicates that the potassium loading on iron oxide catalysts provides valuable advantages such as low reaction time, easy recovery, and reuse in the transesterification reaction of sunflower oil.