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Biodiesel is an intensively researched alternative fuel to fossil diesels. Since biodiesel is more prone to oxidation compared to fossil diesels, the use of antioxidants, both synthetic and more recently, natural ones, is necessary to enhance its oxidation stability. This review aims to provide insights into the use of natural additives versus synthetic ones in biodiesel. Natural antioxidants, which are usually presented in the form of plant extracts, consist of multiple phytochemicals which might have synergistic effects when used. This complexity has resulted in the lack of studies compared to synthetic antioxidants. Moreover, the oxidation mechanisms of these antioxidants remain unexplored. Their environmental impacts upon biodiesel combustion and emissions are yet to be elucidated. Moving forward, purification and profiling of natural antioxidants are recommended to set guidelines for manufacturers and end-users, while kinetics and thermodynamics studies will aid in understanding the oxidation pathways of the antioxidants. Furthermore, life cycle assessment (LCA) and exergy study on the doped biodiesel will enable enhanced understanding of their environmental impacts.
Lau et al. (Fri,) studied this question.