Optimization, fuel characterization, and economic assessment of biodiesel production from watermelon seed oil using a kaolin‐based zeolite catalyst

Abstract

Abstract Background Watermelon seeds are an underutilised agricultural by‐product with potential for biodiesel production, while locally available kaolin provides a low‐cost precursor for heterogeneous catalysts. This study investigated biodiesel production from watermelon seed oil (WMSO) using a kaolin‐based zeolite catalyst, integrating process optimisation, fuel characterisation and a screening economic assessment in the Nigerian context. Results Response surface methodology based on central composite design gave a maximum experimental biodiesel yield of 92.43%, compared with a predicted value of 92.59%, at a methanol‐to‐oil molar ratio of 7.5:1, catalyst loading of 0.75 wt%, 65 °C and 105 min. The quadratic model showed a strong fit ( R 2 = 0.9955). The biodiesel exhibited a kinematic viscosity of 4.4 mm 2 /s, cetane number of 62.4, flash point of 156 °C, free fatty acid content of 0.37%, and acid value of 0.74 mg KOH g −1 . The base‐case economic screening gave a contribution margin of ₦624.93 L −1 . Biodiesel selling price exerted the greatest sensitivity (±50.57%), followed by methanol cost (±18.72%) and feedstock cost (±11.8%). Conclusion The results demonstrate that watermelon seed oil and kaolin‐based zeolite constitute a promising feedstock‐catalyst system for sustainable biodiesel production under moderate conditions, with strong potential for further process refinement and scale‐up. The integrated process and economic assessment identify product price, methanol cost, and practical feedstock recovery as the principal determinants of scale‐up potential, while further purification, catalyst reuse, engine‐level testing, and full techno‐economic studies are required to establish commercial viability. © 2026 Society of Chemical Industry (SCI).