Cleaner biodiesel production from waste oils (cooking/vegetable/frying): Advances in catalytic strategies

The decline in diesel fuel availability and its associated pollution have necessitated the exploration of alternative energy sources, with biodiesel emerging as a prominent contender due to its similar combustion properties to diesel. Fatty acid methyl ester (biodiesel) is a favorable renewable energy source, particularly as global fossil fuel reserves diminish. However, producing biodiesel from fresh edible vegetable oil using homogeneous catalysts presents significant ethical and economic challenges, including food competition and environmental concerns such as wastewater generation and the inability to reuse catalysts. Utilizing low-grade feedstocks like waste cooking oil (WCO), waste frying oil (WFO), and waste vegetable oil (WVO) offers a viable alternative; however, these feedstocks often contain high levels of water and free fatty acids (FFA), complicating the production process. Heterogeneous catalysis presents a promising solution to these challenges, with solid acid catalysts capable of conducting transesterification and esterification simultaneously, even in the presence of high FFA. This review discusses the production of biodiesel from waste vegetable oils using both homogeneous and heterogeneous catalysts, highlighting the superiority of solid acid catalysts for low-quality feedstocks. Characterization of sulfated nano-titanium oxide (Ti(SO4)O) and TiO2 catalysts is conducted using XRD, FT-IR, SEM, and TEM analyses. Notably, a biodiesel yield of approximately 97 % can be achieved using Ti(SO4)O as a solid acid catalyst at 75 degrees C within three hours, demonstrating its potential for sustainable biodiesel production.