Semi-clathrate hydrate based carbon dioxide capture and separation techniques

● Structural and thermodynamical properties of semi-clathrate hydrate are summarized.● Properties of quaternary salts and gas mixture hydrate are summarized.● Challenges persist in the application of semi-clathrate hydrates for carbon capture and separation.CO2 is considered as the main contributor to global warming, and hydrate enclathration is an efficient way for carbon capture and separation (CCS). Semi-clathrate hydrate (SCH) is a type of clathrate hydrate capable of encaging CO2 molecules under mild temperature and pressure conditions. SCH has numerous unique advantages, including high thermal stability, selective absorption of gas molecules with proper size and recyclable, making it a promising candidate for CCS. While SCH based CCS technology is in the developing stage and great efforts have to be conducted to improve the performance that is determined by their thermodynamical and structural properties. This review summarizes and compares the thermodynamic and structural properties of SCH and quaternary salt hydrates with gas mixtures to be captured and separated. Based on the description of the physical properties of SCH and hydrate of quaternary salts with gas mixture, the CO2 capture and separation from fuel gas, flue gas and biogas with SCH are reviewed. The review focuses on the use of tetra-n-butyl ammonium halide and tetra-n-butyl phosphonium halide, which are the current application hotspots. This review aims to provide guidance for the future applications of SCH.