Sustainable Production and Comparison of Biodiesel from Non-Edible Seeds: Neem and Almond Oils

The increasing global energy crisis and the ongoing environmental degradation have heightened the urgency for the development of alternative and sustainable fuel sources. This research examines the feasibility of utilising neem (Azadirachta indica) and almond (Terminalia catappa) seed oils—both non-edible and abundantly accessible in tropical areas—as effective feedstocks for biodiesel synthesis. Biodiesel was synthesised and characterised through Soxhlet extraction and a two-stage transesterification process, adhering to ASTM D6751 and EN 14214 standards. The assessment included various physicochemical properties such as kinematic viscosity, density, cetane number, calorific value, and acid value, in addition to an evaluation of cold flow properties and sulphur content. Advanced spectroscopic and microscopic techniques— FTIR, XRD, and SEM—were utilised to examine the structural characteristics and surface morphology of the biodiesel and catalysts produced from agricultural waste materials, including eggshells and fish bones. The findings indicated that neem biodiesel demonstrated a higher cetane number of 58.13 and an energy content of 40.15 MJ/kg. In contrast, almond biodiesel presented better cold flow properties and a lower acid value. Both biodiesels conformed to international standards, underscoring their viability for local and industrial energy applications. The study highlights the practicality of transforming non-edible biomass into clean fuel, enhancing energy security, promoting environmental sustainability, and optimising waste utilisation in emerging economies. Future work should focus on extensive validation efforts, prolonged engine testing, and the advancement of catalyst technologies to optimise process economics and efficiency.