Novel Tetramethylammonium Cation-Based Ionic Liquid Solutions for Highly Efficient CO₂ Absorption

Abstract

In this work, a series of novel CO 2 absorption solvents were prepared using solid tetramethylammonium cation-based ionic liquids and water. Herein, for the first time, tetramethylammonium cations-based ionic liquids ([N 1111 ][AHA], namely [N 1111 ][Py], [N 1111 ][Im], and [N 1111 ]-[1,2,4-Tz]) with aprotic heterocyclic anion were synthesized. The viscosity of these absorbents ([N 1111 ][AHA]/H 2 O), composed of different contents of [N 1111 ][AHA] and H 2 O, was measured, indicating that their viscosity was below 50 mPa•s at 313.15 K. Moreover, the anion structure significantly affected the CO 2 absorption performance. The CO 2 absorption capacity increased in the order of [N 1111presenting excellent reversibility (5 cycles). The optimal solvent composition was 80 wt % [N 1111 ][1,2,4-Tz] and 20 wt % H 2 O, yielding a CO 2 absorption capacity of 0.268 g CO 2 /g absorbent and the ideal selectivity for CO 2 /N 2 and CO 2 /O 2 was 1217.8 and 911.1, respectively, at 313.15 K and 100 kPa CO 2 . The study of the CO 2 absorption mechanism was investigated using 13 C NMR, in situ FTIR, and DFT calculations, showing that water can cooperate with ILs to absorb CO 2 . Carbamate and carbonate were formed during CO 2 absorption, which is beneficial for CO 2 capture. These novel [N 1111 ][AHA] solutions are potential absorbents for CO 2 separation in flue gas.