Research on influencing factors and mechanism of CO2 absorption by poly-amino-based ionic liquids

• Water content of poly-amino-based ionic liquids (ILs) had the most significant impact on CO2 absorption.
• CO2 absorption of [TETAH]+[BF4]− increased to 2.04 mol-CO2/mol-IL from 0.96 when water content varied from 0% to 40%.
• Results of FT-IR and 13CNMR indicated that CO2 reacted with NH2 and NH in [TETAH]+ [BF4]− and formed carbamate.
• CO2 reacted with H2O and released H+, thus enhancing the absorption of CO2.

Ionic liquids (ILs) are varieties of green solvents that can capture CO2 effectively. In this research, five synthesized amino ILs were evaluated for their CO2 absorption performance. Experimental results showed that more amino groups in ILs led to higher CO2 absorption capacities. For factors such as temperature, gas flow rate, and water content, water content had the most significant impact on the capacity to absorb CO2. A CO2 absorption capacity of 0.96 mol-CO2/mol-IL was achieved with [TETAH]+[BF4]−, with the IL containing 0% water and a gas flow rate of 100 ml/min at 293 K. However, when the water content of [TETAH]+[BF4]− reached 40%, CO2 absorption capacity increased to as high as 2.04 mol-CO2/mol-IL. Also, the CO2 absorption capacity of [TETAH]+[BF4]− increased rapidly with temperature in the range of 283–333 K, but decreased at temperatures greater than 333 K. According to the absorption–desorption recycling experiment of IL 3#, the regeneration rates of ILs increase with water content from 0% to 40%, while raising temperature does not improve regeneration rates. The FT-IR, 13CNMR, pH and conductivity characterization results indicate that CO2 reacted with NH2 and NH in [TETAH]+[BF4]− and formed carbamate. Simultaneously, CO2 reacted with H2O and released H+, thus enhancing the absorption of CO2. This has important implications for various projects.