New polyalkylated imidazoles tailored for carbon dioxide capture

Aqueous polyalkylated imidazoles have gained interest as potential CO2 capture solvents due to their high oxidative stability and low vapor pressures compared to traditional amines. In this work, 21 aqueous solutions of polyalkylatedimidazoles were screened as absorbents for CO2 capture and four solvent candidates were further characterized by measuring the vapor-liquid equilibria and the heat of absorption of CO2. The pKa values of the imidazoles were measured and a positive correlation between the absorption capacity and pKa of polyalkylated imidazoles was found. Increasing the pKa of imidazoles to 9 by alkylation improved the CO2 absorption capacity significantly. Based on the equilibrium experiments, the cyclic capacities of the selected solvents varied from 0.8 to 2 mol CO2/kg solvent. Furthermore, the heat of absorption of CO2 of the studied imidazoles was lower compared to primary amines. In general, the tested polyalkylated imidazoles are more feasible for processes with partial pressures of CO2 above 50 kPa. Trimethylimidazole that forms bicarbonate precipitate might be applicable for post combustion CO2 capture as a high cyclic capacity is obtained even at CO2 partial pressures around 10 kPa. The present study gives new important knowledge of the absorption properties of polyalkylated imidazoles.