A review on the chemical and physical characteristics of biodiesels produced from animal fat waste

Biodiesel is a promising and eco-friendly energy resource that can substitute conventional diesel. It can be derived from both plant and animal-based feedstocks. Animal fat waste (AFW) is oil-rich material that can serve as a viable and affordable feedstock for biodiesel fuel. However, the characteristics of biodiesel synthesized from AFW raise important concerns. This review highlights the chemical composition of animal-based oils, which typically contain higher proportions of saturated fatty acids (SFAs) and monounsaturated fatty acids (MUFAs), and smaller proportions of polyunsaturated fatty acids (PUFAs). These compositional features strongly influence the physicochemical properties of biodiesel. The review further categories these properties into physical, cold-flow, thermal performance, and chemical stability properties. Animal fat-derived biodiesels generally exhibit favorable thermal and stability properties like the high cetane number, heating value, and flash point. Conversely, their poor cold-flow properties remain a major drawback which require improvement through techniques such as winterization, blending, and the use of cold-flow improvers (CFIs). Nonetheless, the applications of AFW in the biofuel industry have favorable implications that foster sustainability by supporting the waste-to-energy (WTE) principle and producing eco-friendly fuels that comply with standards.