Emerging Roles of Ionic Liquids in Biodiesel: A Review on Catalysis, Process Design, and Recyclability
Jai Ganesh Ramajayam, Priyaranjan Samal, Mangesh Varadarajulu Lakshmipathy, P. Tamizhdurai, G. Murali, Tinku Baidya, Krishna Kumar Yadav, Javed Khan Bhutto, Maha Awjan Alreshidi, Hadi Hakami
Abstract
Ionic liquids (ILs) are distinctive salts that persist in liquid form at relatively lower temperatures and exhibit remarkable physicochemical properties like high thermal stability, low volatility, and tunable solubility. These characteristics have driven their expanding application across academic research and industrial processes. The ability to engineer specific cation–anion assemblies enables precise tuning of IL properties, making them particularly attractive for biodiesel synthesis. The present study explores the innovative use of ILs as catalysts and solvents for the production of biodiesel, emphasizing how the strategic choice of cationic and anionic constituents impacts critical properties like viscosity, melting point, and thermal stability, thereby influencing catalytic performance and reaction efficiency. The catalytic roles of both acidic and basic ILs are explored in detail, including advancements in microwave-assisted and photocatalytic processes that have demonstrated high conversion efficiencies and robust reusability. The review further examines the application of deep eutectic solvents (DES), a family of solvents derived from ionic liquids, in biodiesel production. Kinetic and mechanistic studies are discussed to illustrate how ILs enhance reaction pathways, reduce activation energies, and stabilize the intermediate species. The integration of computational tools and machine learning models for process parameter optimization is also examined, showcasing promising directions for improving the cost efficiency and sustainability. Additionally, various IL recovery and reuse strategies like distillation, aqueous two-phase extraction, liquid–liquid extraction, membrane separation, magnetic separation, and adsorption are analyzed for their feasibility along with environmental impact. Overall, this review presents a comprehensive assessment of IL-assisted biodiesel production and highlights its transformative potential in advancing green fuel technologies.