A novel biphasic solvent of amino-functionalized ionic liquid for CO2 capture: High efficiency and regenerability

Due to its great potential of energy consumption saving, the biphasic solvent has attracted more and more attention. In the present work, an efficient absorbent of amino-functionalized ionic liquids (AFILs) was dissolved in ethanol-water solvent to form a novel biphasic solvent for CO2 capture. When the concentration of triethylenetetramine L-lysine ([TETAH][Lys]) was 0.5 mol/L and the volume ratio of ethanol-water solvent was 4:6, the [TETAH][Lys] solution separated into two phases after CO2 absorption. Under the optimal conditions, the volume of the CO2-rich phase was about one third of the total volume of the mixture, which meant that only one third of the solution needed to be regenerated and the energy consumption could be greatly reduced. Meanwhile, the loading of the CO2-rich phase contributed about 93% of the total loading of the solution, and its viscosity was only 27.95 mPa s. The regeneration efficiency of the solvent after the 5th absorption-desorption cycle still kept at 91.3%. Based on the experimental and C-13 NMR analysis results, the reaction and phase change mechanisms of CO2 capture into the [TETAH][Lys]-ethanol- water solution were clarified. CO2 absorption into [TETAH][Lys] firstly formed carbamate, which would further hydrolyze to HCO3-/CO32- and react with ethanol to form the ethyl carbonate. Due to the limited solubility of these absorption products in ethanol, as well as the good solubility in H2O, the products transferred to the lower phase while the ethanol stayed in the upper phase in the biphasic system.