Advancing biodiesel production: A review of feedstocks, geopolymer catalysis, and applications of machine learning

The increasing global demand for energy and environmental issues have heightened interest in biodiesel as a sustainable alternative to fossil fuels. This review assesses biodiesel production, emphasising feedstock evolution, catalyst development, and optimisation strategies, including machine learning. It highlights the transition from edible oils to fourth-generation, genetically engineered organisms, underscoring the preference for waste-derived feedstocks due to their sustainability and cost-effectiveness. Various production methods, particularly transesterification,/ are evaluated, with a focus on their advantages and limitations. Feedstocks have advanced through four generations, with waste-derived options becoming increasingly prominent. The review examines various catalyst types, homogeneous, heterogeneous, and enzymatic, highlighting geopolymers as a novel, eco-friendly choice due to their thermal stability and affordability from waste materials. Optimisation techniques, such as response surface methodology (RSM) and machine learning, are discussed for their potential in improving and predicting yields, as well as reducing costs. Key challenges include scaling advanced feedstocks and overcoming emerging limitations in catalysts. The review identifies critical knowledge gaps and advocates for interdisciplinary research to enhance feedstock utilisation, catalyst innovation, and process modelling. Geopolymer catalysts have been reported to yield biodiesel at up to 99.2% and exhibit typical reusability of up to five cycles. ML models used in related studies have reported R² values of up to 0.997 in the best cases. This review uniquely integrates feedstock evolution, geopolymer catalysis and ML-driven process modelling to identify synergistic routes to scalable, low-cost biodiesel production. Future efforts should prioritise integrating green materials and intelligent systems to boost the commercial viability and environmental benefits of biodiesel production. The future of biodiesel integrates green chemistry, intelligent modelling, and circular economy principles, contributing to several UN Sustainable Development Goals by promoting renewable fuels (SDG7), advancing production technologies (SDG9), utilising waste feedstocks (SDG12), and reducing greenhouse gas emissions (SDG13).