A Novel Intercooling Carbon Dioxide Capture Process Using Ionic Liquids with Ultra-low Energy Consumption

This study focuses on the use of ionic liquids as solvents for carbon dioxide capture due to their low energy demand. We screened an ideal ionic liquid, 1-ethyl-3-methylimidazolium bis[trifluoromethylsulfonyl]imide ([emim][Tf2N]), based on its excellent absorption capacity and low viscosity. We performed thermodynamic modeling of the gas-liquid phase equilibrium to lay the foundation for process simulation. A basic process was designed for benchmarking performance, and various cases were compared by adjusting key operating parameters such as pressure and temperature. The results showed that the lowest specific capture energy achieved was 1.12 GJ/t at 20 bar and 5 °C. However, further improvements in energy performance were constrained by reduced absorption capacity and increased viscosity resulting from lower operating pressures and temperatures. To address these constraints, we proposed a novel process that optimized the temperature profile in the absorption column by dividing it into two sections with intercooling. This approach did not require significant changes to the base case but offered multidimensional benefits, including reduced energy demand and associated equipment costs. The specific capture energy was further reduced to 1.04 GJ/t. Economic analysis indicated that the capture cost at a production scale of 13.7 kt/a was 206 $/t but had the potential to be reduced to 82 $/t. The costs associated with compressors were found to be the major contributors to both equipment and capture costs. The proposed novel process demonstrates promising benefits and highlights the importance of further investigation into low-pressure operation.