Utilizing cashew nut shell liquid for the sustainable production of biodiesel: A comprehensive review

Biodiesel has proven to be better in terms of emission and engine performance when compared to diesel. The reason for this can be attributed to the fact that they are environmentally friendly and combust well in diesel engines. Implementing the use of Cashew Nut Shell Liquid (CNSL) for biodiesel production on a commercial scale has the potential to be profitable as the feedstock is a waste. The environmental concern associated with improper waste disposal and combustion of fossil fuel for energy production is a huge issue that is ravaging most developing regions of the world. Providing research-based solutions to these problems is expedient and meets major sustainable development goals. The waste-to-fuel technique has proven to be an effective tool that can be harnessed in ending these concerns. Hence, improving the efficiency of wastes used as feedstock to produce clean fuel is pivotal to building a sustainable environment. CNSL is inexpensive and using it as fuel can help mitigate the environmental effects of improper waste disposal in cashew processing factories. CNSL is obtained from cashew nuts through different methods, including mechanical extraction, thermal extraction and solvent extraction. This paper reviews the state of research on the utilization of cashew nut shell liquid biodiesel (CNSLBD) in diesel engines. Further research gaps that need to be addressed for this fuel to be more efficient were also mentioned. This work weighs the potential of this fuel as a good alternative energy source. Performance parameters such as brake thermal efficiency (BTE) and brake specific fuel consumption (BSFC) were considered in this review. This article established that CNSLBD gives a BTE as low as 12.3% and as high as 25.7% depending on the experimental conditions involved. It gives high BSFC and low HC, CO and CO₂ emissions. It produces high NO_X emission, but this can be reduced with techniques like Exhaust Gas Recirculation and blending the fuel with other additives. The main problem with CNSLBD is its high density and viscosity. However, this can be fixed by blending the fuel with another low viscous fuel. The ideal mix ratio for CNSLBD blends is 80% diesel: 20% CNSL. This work also established that the yield of CNSLBD during transesterification can be increased through ultrasonication. Finally, CNSLBD can be said to be a promising alternative fuel that has the potential to benefit both cashew nut companies and the energy industry.