Energy efficient CO2 capture in dual functionalized ionic liquids and N-methyldiethanolamine solvent blend system at elevated pressures: Interaction mechanism and heat duties

Abstract

In this study, three lab synthesized dual functionalized ionic liquids (DFILs) were utilized as promoters to improve the CO2 absorption performance of methyl diethanolamine (MDEA) absorbent under elevated pressures of 2–7 bar. Initially, 5 wt% DFILs containing polyamine cations (triethylenetetramine and diethylenetriamine) and cyclic amine anions (piperazine and imidazole) were blended with 20 wt% MDEA and their physical and chemical properties were examined. The pKa value at 303 K of the blend of [TETAH][Pz] + MDEA is found to be 9.83, which is nearly equal to the industrial 30 wt% monoethanolamine (MEA) solution. The CO2 absorption performance at different temperatures and pressures demonstrated that the blending of 5 wt% DFILs into aqueous MDEA significantly altered both the absorption rate and loading. The percentage loading showed a significant 22% increase in the [TETAH][Pz] promoted aqueous MDEA blend. This is attributed to the high amount of carbamate and bicarbonate formation in the DFILs blended aqueous MDEA as revealed by 13C NMR results. These results were possible due to the highly reactive piperazine anion being a crucial factor in the significant performance of the [TETAH][Pz] blend system. Further, when the regeneration heat duty of all these absorbents was calculated, it was found that MDEA and DFILs blended MDEA absorbents consumed 25.36% and 33.34–22.79% less energy than industrial MEA, respectively along with a low absorbent loss during regeneration thus, [TETAH][Pz] and [TETAH][Im] are potential promoters in an aqueous MDEA solvent system for pressurized capture of carbon dioxide.