A novel binary solid-liquid biphasic functionalized ionic liquids for efficient CO2 capture: Reversible polarity and low energy penalty

Ionic liquids (ILs) solid-liquid biphasic solvents for CO2 capture have the advantages of high CO2 loading and low energy consumption, and their phase change behavior was regulated via phase separation agents. However, phase separator agents exhibit bottlenecks in terms of volatility loss and high-rich phase viscosity. A novel "reversible polarity" functionalized ionic liquids (isophorone diamine-imidazole, [IPDAH][Im]) was innovatively proposed in this work, which featured solid-liquid phase change behavior upon CO2 absorption in water in the absence of a phase separation agent. After saturated absorption, CO2 products were enriched into the lower phase and precipitated as a white crystalline powder with 91 % of the total CO2 loading (1.15 mol mol-1) but only 60 % of the total volume. Products after thermal desorption (393.15 K), maintaining 80 % of its initial loading after the sixth regeneration cycle. Based on the results of experimental characterization and theoretical calculation, [IPDAH][Im] possessed reversible polarity, and its initial polarity was consistent with that of water. After absorption, [IPDAH][Im] interacted with CO2 to form products whose polarity diminishes, resulting in the associated phase transition; after desorption, the high polarity is restored. The products existed as ion pairs (ILsCOO- -ILsH+), as evidenced by strong van der Waals interaction, and electrostatic attraction. Strong hydrogen bonding forces between the products and the Hansen solubility parameter, as well as the high lattice energy, led to the self-agglomeration formation of the products in water, resulting in the development of a solid powder product. The heat duty of [IPDAH][Im]-H2O was 1.23 GJ ton- 1 CO2, which was approximately 67 % less than that of monoethanolamine (MEA; 3.77 GJ ton- 1 CO2), signifying a major potential for application in CO2 capture.