Phase Change\nand Reaction Mechanism of [TEPAH][Lys]-1-propanol‑H<sub>2</sub>O in Carbon Dioxide Capture

Conventional amino-functionalized ionic liquids (AFILs)\nare known\nto exhibit high viscosity and difficulties in regeneration. To address\nthese challenges, this study proposes a potential solution: the formation\nof phase change absorbents through the combination with other solvents.\nThe [TEPAH][Lys] was dissolved in a specific ratio of 1-propanol–water\nsolution to form a [TEPAH][Lys]-1-propanol–H<sub>2</sub>O phase\nchange absorbent. At an absorption temperature of 30 °C, when\nthe concentration of [TEPAH][Lys] is 0.5 mol/L and the volume ratio\nof 1-propanol to water is 6:4, the viscosity of the system is 4.15\nmPa·s and the maximum CO<sub>2</sub> capacity is 2.82 mol of\nCO<sub>2</sub>/mol of [TEPAH][Lys]. After the phase change, the CO<sub>2</sub>-rich phase accounts for only 45% of the total volume, which\nsignificantly reduces the energy consumption required for regeneration.\nFurthermore, after five cycles of absorption, the absorption capacity\nremained at 91% of the initial load. The absorption and desorption\nmechanisms were investigated by TG-DSC and <sup>13</sup>C NMR spectra.\nIt was found that only 1-propanol existed in the CO<sub>2</sub>-lean\nphase after the phase change. In contrast, the CO<sub>2</sub> absorption\nproducts urethane, HCO<sub>3</sub><sup>–</sup>/CO<sub>3</sub><sup>2–</sup>, and C<sub>3</sub>H<sub>7</sub>OCOO<sup>–</sup> are concentrated in the CO<sub>2</sub>-rich phase. Furthermore,\nthe reason for the phase transition was explained theoretically in\ncombination with quantum chemical calculations.