Comparative absorption factor (CAF) for screening ionic liquids to capture CO2 in biogas, natural gas, and shale gas: Effect of operating conditions

Upgrading clean energy fuels, such as biogas, natural gas, and shale gas, requires the capture of CO 2 to enhance their heating value. Ionic liquids (ILs) are promising absorbents for this purpose, but the vast number of available ILs necessitates an efficient screening method. The Comparative Absorption Factor ( CAF ) developed in our previous study can estimate the total annual cost ( TAC ) of CO 2 capture from biogas, which is a key advantage over alternative screening methods. However, CAF does not consider the effects of operating conditions such as CO 2 concentration, pressure, and temperature. To address this limitation, a modified CAF ( CAF modified ) that incorporates these factors was proposed. Given the linear relationship between the original CAF and TAC , three representative ILs ([C 10 mpy][DCA], [C 1 mim][tfo], and [C 1 py][tfo]) were selected from 490 ILs based on their melting point, viscosity, and original CAF values. Subsequently, process simulations for these ILs were conducted using Aspen Plus, considering a wider range of operating conditions: CO 2 concentrations of 30–50 vol%, temperatures of 303.15–318.15 K, and pressures of 7–15 bar. These simulations were used to determine the Aspen Plus-derived TAC , which served as the basis for proposing CAF modified . Finally, data for Aspen Plus-derived TAC from the previous study and for 6 additional ILs over a broad range of operating conditions were used to compare with the TAC values estimated by CAF modified . The results showed an average relative deviation of 16%, indicating that CAF modified is effective for screening ILs for CO 2 capture under varying operating conditions.