Post-combustion CO2 capture by coupling [emim] cation based ionic liquids with a membrane contactor; Pseudo-steady-state approach

Abstract

This study demonstrates the coupling of Ionic liquids (ILs) with a membrane contactor for post-combustion CO2 capture at moderate pressures and temperatures. ILs 1-ethyl-3-methylimidazolium methyl sulfate([emim][MeSO4]), 1-ethyl-3-methylimidazolium dicyanamide([emim][DCA]), 1-ethyl-3-methylimidazolium ethyl sulfate([emim][EtSO4]) and 1-ethyl-3-methylimidazolium acetate ([emim][Ac]) were selected due to their high thermal stability, moderate viscosity and surface tension, as well as high CO2 solubility. No wetting conditions were confirmed for the polypropylene membrane by measuring contact angle, liquid entry pressure (LEP) and SEM of fiber surface before and after the operation. ILs were recirculated in the setup until reaching pseudo-steady-state. All four ILs were able to capture a substantial amount of CO2 during the specified operation time. Initially, very high values of CO2 mass transfer flux and experimental overall mass transfer coefficient were obtained which further decreased with operation time and reached a nearly constant value at pseudo-steady-state. Effect of CO2 loading of the ILs and temperature on enhancement factor and first order rate constant were evaluated. The absorption behavior and kinetics were strongly influenced by the CO2 concentration in the ILs, which divides the absorption process in two steps; an initial faster absorption at the gas-liquid interface and later slower absorption in the bulk of the IL. Finally, a pseudo-steady-state modelling approach was implemented and validated.