Abstract
Biodiesel is produced through the process of transesterification of different edible and non-edible oils and animal fats. The process takes place either in the presence of a homogeneous or heterogeneous catalyst. A suitable catalyst is selected based on the amount of free fatty acid (FFA) content present in the oil. The major difference between homogeneous and heterogeneous catalysts is that the homogeneous catalysts are insensitive to the amount of free fatty acids present in the oil. Also, homogeneous catalysts are toxic, highly flammable, and corrosive. Besides, the use of homogeneous catalysts produces soaps as a by-product and a bulk of wastewater which requires additional pretreatment methods and expenses for proper disposal. The research on the biodiesel synthesis in the presence of heterogeneous catalysts (carbon-based catalysts) is continuously studied to achieve a suitable process to produce biodiesel and to improve fuel quality on an industrial scale. Heterogeneous catalysts have great significance in the biodiesel production because of their simple and less expensive manufacturing process, ease of separation, and high reusability. They can be prepared easily by functionalizing the carbon surface with acid or base. Carbon-based catalysts have a high surface area and porosity that can enhance the rate of the esterification/transesterification process. Also, solid acid catalysts can convert the low-quality feedstocks to biodiesel in the presence of active acidic sites. Besides, carbon-based catalysts can be produced through waste e.g. sugarcane bagasse and their use make the production of biodiesel “Greener” one. This review paper is mainly based on the utilization of different catalysts derived from waste biomass in the biodiesel. Under optimum conditions biodiesel (FAME) yields 90%–99% were reported in the literature.
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•Biodiesel synthesis using waste cooking oil is reviewed.•Issues with the currently employed catalysts are reported.•Application of sugar bagasse for renewable catalyst has been discussed.•Carbon and CaO based functionalized catalysts for biodiesel synthesis are discussed.