The environmentally sustainable production of biodiesel is important for providing both a renewable alternative transportation fuel as well as a fuel for power generation using diesel engines. This research evaluates the use of inexpensive catalysts derived from waste materials for converting triglycerides in seed oils into biodiesel composed of fatty acid methyl esters. The performance of CaO catalysts derived from the shells of oysters, mussels, lobsters, and chicken eggs was investigated. The shell-derived powders were calcined with and without the addition of zinc nitrate at 700–1000 °C for 4 h to yield CaO whereas the CaO-ZnO mixed catalyst were prepared by wet impregnation followed by calcination at 700 °C. The catalysts were characterized by XRF, XRD, TGA, SEM, FTIR and GC-MS. The CaO-ZnO catalysts showed slightly better conversion efficiency compared to CaO catalysts for the transesterification of canola oil. The mixed CaO-ZnO catalysts derived mainly from oyster shells showed the highest catalytic activity with >90% biodiesel yield at a 9:1 methanol-to-oil mole ratio within 10 min of ultrasonication. The reduction of toxicant emission from the generator is 43% and 60% for SO₂, 11% and 26% for CO, were observed for the biodiesel blending levels of B20 and B40, respectively.

Wax deposition, driven by the crystallization of long-chain n-alkanes, poses severe challenges across industries such as petroleum, oil and natural gas, food processing, and chemical manufacturing. This phenomenon compromises flow efficiency, increases energy demands, and necessitates costly maintenance interventions. Wax inhibitors, designed to mitigate these issues, operate by altering wax crystallization, aggregation, and adhesion over the pipelines. Classic wax inhibitors, comprising synthetic polymers and natural compounds, have been widely utilized due to their established efficiency and scalability. However, synthetic inhibitors face environmental concerns, while natural inhibitors exhibit reduced performance under extreme conditions. The advent of nano-based wax inhibitors has revolutionized wax management strategies. These advanced materials, including nanoparticles, nanoemulsions, and nanocomposites, leverage their high surface area and tunable interfacial properties to enhance efficiency, particularly in harsh environments. While offering superior performance, nano-based inhibitors are constrained by high production costs, scalability challenges, and potential environmental risks. In parallel, the development of “green” wax inhibitors derived from renewable resources such as vegetable oils addresses sustainability demands. These eco-friendly formulations introduce functionalities that reinforce inhibitory interactions with wax crystals, enabling effective deposition control while reducing reliance on synthetic components. This review provides a comprehensive analysis of the mechanisms, applications, and comparative performance of classic and nano-based wax inhibitors. It highlights the growing integration of sustainable and hybrid approaches that combine the reliability of classic inhibitors with the advanced capabilities of nano-based systems. Future directions emphasize the need for cost-effective, eco-friendly solutions through innovations in material science, computational modeling, and biotechnology.