Application of ionic liquids in CO₂ capture, sequestration, and conversion: A comprehensive review

The substantial rise in greenhouse gas emissions, especially carbon dioxide (CO₂), is causing global warming, sea level rise, and climate change. This situation has prompted a search for effective and environmentally friendly carbon capture, utilization, and storage (CCUS) methods, which are emerging as significant solutions with the potential to reduce CO₂ emissions on a large scale. However, the current methods of CO₂ capture, which are primarily based on absorption techniques, face significant challenges. This involves limited CO₂ capture capacity, degradation of expensive reagents, thermal instability, and high costs associated with separation and purification during the CO₂ capture process, along with the need for energy input for carbon conversion and utilization. In response to these challenges, the application of ionic liquids (ILs) for CO₂ capture has gained increasing interest among scientists. These ILs are characterized by low vaporization, low flammability, high designability, and non-corrosive properties, which make them a viable alternative to traditional CO₂ capture, conversion, and sequestration processes. Hence, the present review offers a comprehensive overview of the fundamental properties of ILs, as well as examining their role in CO₂ capture and conversion, and their applications in enhanced oil recovery (EOR). It examines how the ILs facilitate CO₂ capture through both physical and chemical absorption mechanisms, and explores the influence of the IL structure, particularly the anionic component, on CO₂ solubility. In addition, it explores the use of IL membranes for cost-effective CO₂ separation, and the applications of ILs for reducing the interfacial tension and altering the rock wettability in EOR processes. It highlights how the viscosity of ILs can be chemically tuned to control the CO₂ mobility in sequestration sites, which is an essential feature for enhancing the security and efficiency of carbon capture and storage (CCS) processes. The review also investigates the transformative character of ILs in the catalytic conversion of CO₂. Specifically, the ILs are characterized by their adaptability and capacity to stabilize reactive intermediates, and are therefore emerging as strong solvents and co-catalysts in the transformation of CO₂ into various important materials, including carbonates, fuels, polymers, and diverse organic compounds. Overall, the review highlights the recent findings and emphasizes the significant potential of ILs in revolutionizing CO₂ capture, conversion, and sequestration. These processes not only reduce CO₂ emissions, but also contribute to the valorization of CO₂ as a feedstock for value-added products. Finally, the review underscores the necessity for further research and development in order to optimize the ILs for practical applications in addressing global greenhouse gas emissions, while also considering their environmental and health impacts.