Experment Study And Quantum Chemistry Simulation On The Absorption Of CO₂in Ionic Liquid

CO2, identified as a chief greenhouse gas, is a major contributor to global warming and climate change. The continuous rising of the atmospheric concentration of CO2has raised public concern worldwide. Solvent absorption method is relatively mature separation technology for CO2capture. The traditional solvent absorption process currently used is extremely expensive and suffers many drawbacks because their toxicity, degradation sensitivity, volatility, and the intensive energy consumption to enable solvent regeneration. Ionic liquids (ILs) known as the "green design solvent" with its unique properties such as nonvolatility, thermal stability and tunable chemistry offer a new opportunity for capture CO2. Just like RTILs, deep eutectic solvents (DESs) possess many unusual advantages such as negligible vapor pressure, high chemical and thermal stabilities, and high solvation capacity. However, unlike RTILs, DESs are easy to prepare from cheap raw materials with high purity. In this work, absorption of CO2by the different ILs was studied by experiment and quantum chemical simulations.In this work, the density functional theory study on the absorption of CO2by the different ILs was carried on. The ion-pairs are stable due to the existence of the hydrogen bonding which between the anion and cation. The [Bmim][Ac] ion-pair adsorb on CO2with the strong chemical bonds between the [Ac]-and CO2. The ion pairs of [P1112][Tetz] and [P1114][Tetz]can absorb the acid gas moleculars by the N atoms which have enough nagtive charge. The DES ion-pair can absorb CO2by the hydroxyls which have the electronegative O atoms.On the basis of quantum chemistry simulation, the solubilities of CO2in ionic liquid (including1-methyl-3-butyl-methylimidazolium valerate and1-methyl-3-butyl-methylimidazolium glycollate) and eutectic mixtures containing choline chloride and dihydric alcohols (including1,4-butanediol,2,3-butanediol, and1,2-propanediol) with a molar ratio of choline chloride to dihydric alcohol of1:3and1:4were measured at293.15K,303.15K,313.15K, and323.15K under pressures up to600kPa using an isochoric saturation method. Henry’s constant and the dissolution Gibbs free energy, enthalpy, and entropy changes of CO2were obtained by correlating the experimental data. The solubility of CO2in the mixtures increased linearly with the increasing pressure or decreasing temperature. The enthalpies of solution were negative at all conditions. Eutectic mixtures developed an excellently reversible carbon capture process, and thus have great potential in acid gas separations.This work provided some excellent strategies on how to improve CO2 capture performance by designing ionic liquid and Eutectic ionic liquids.