DOI: https://doi.org/10.55373/mjchem.v26i5.315

Keywords: Fatty acid methyl ester; Bentonite; waste cooking oil; reusability

Abstract

Fatty acid methyl ester, also known as biodiesel, is a sustainable and clean-burning fuel that can be a substitute for conventional diesel. However, the production of biodiesel requires higher costs compared to conventional diesel. The cost of production can be reduced by using waste cooking oil (WCO) as feedstock. In this study, biodiesel production was carried out via transesterification using WCO as feedstock, and potassium hydroxide (KOH)/bentonite catalyst was used as a heterogeneous catalyst. Different molar ratios of KOH/bentonite catalysts (1:2, 1:3, 1:4, 1:5, and 1:6) were prepared by the impregnation of bentonite with KOH at 60 °C for 6 h. Both raw bentonite and KOH/bentonite catalyst were characterized using thermogravimetric analysis (TGA), Brunauer-Emmett-Teller (BET) surface analysis, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). The decrease of BET surface area in raw bentonite and KOH/bentonite catalyst and the presence of potassium oxide phase in the XRD pattern showed that KOH was successfully impregnated into the pores of bentonite. Moreover, SEM analysis indicated that the granular size of KOH/bentonite was higher than raw bentonite due to aggregation. A high free fatty acid (FFA) conversion of 27.55% was obtained at an optimum molar ratio of KOH/bentonite of 1:5 under the reaction parameters of methanol-to-oil molar ratio of 6:1, reaction temperature of 60 °C, catalyst concentration of 3 wt.%, and reaction time of 3 h. The reusability test determined that the performance of the KOH/bentonite catalyst decreased from 27.55% to 13.73% in FFA conversion. This research reveals that KOH/bentonite catalyst has great potential to produce biodiesel using of WCO as feedstock.