What Are Functional Ionic Liquids for the Absorption of Acidic Gases?

Abstract

As a kind of novel and efficient material, ionic liquids (ILs) are used for capture of acidic gases including SO2 and CO2 from flue gas. Due to very low content of acidic gases in flue gas, it is important to find functional ILs to absorb the acidic gases. However, up to now, there is no criterion to distinguish if the ILs are functional or not before use, which greatly influences the design of functional ILs. In this work, a series of ILs were synthesized and used to determine functional or normal ILs for the capture of acidic gases. It has been found that the pKa of organic acids forming the anion of ILs can be used to differentiate functional ILs from normal ILs for the capture of acidic gases from flue gas. If the pKa of an organic acid is larger than that of sulfurous acid (or carbonic acid), the ILs formed by the organic acid can be called functional ILs for SO2 (or CO2) capture, and it can have a high absorption capacity of SO2 (or CO2) with low SO2 (or CO2) concentrations. If not, the IL is just a normal IL. The pKa of organic acids can also be used to explain the absorption mechanism and guide the synthesis of functional ILs.

Investigations on the thermal stability and decomposition mechanism of an amine-functionalized ionic liquid by TGA, NMR, TG-MS experiments and DFT calculations

“…They are promising alternative absorbents for gas separation [8][9][10][11][12]. ILs exhibit negligible measurable vapor pressure, wide liquid temperature range, and high thermal stability at normal operating conditions, which make them attractive for gas processing [13,14].…”

Highly efficient and reversible absorption of SO2 by hydroxyl ammonium ionic liquids at low partial pressure

“…More importantly, the absorption capacity of SO 2 using [TEOA][CA] was up to 3.34, a three-fold increase over the other ILs. This value was much higher than those of the other hydroxyl ammonium ILs, guanidinium based ILs11,29,33 and azole based ILs18,32,34 at low SO 2 partial pressure. However, the absorption capacity of[TEOA][CA] at low SO 2 partial pressure was lower than those for some ILs with pure SO 2 , such as [TMG]2 [PBE] (8.74 mol/mol)14 and E 3 [Tetz] (4.43 mol/mol) 20.…”

The Application of Ionic Liquid Composite Materials in Denitrification from Flue Gas

“…It is found that imidazolium ionic liquids have a certain ability to absorb NO2 gas, but the higher viscosity of ionic liquids (for example,BMIMBF4, 25 ℃ and 110.308 cp) [5]. In order to reduce the viscosity of the ionic liquid and further improve the absorption of NO2 gas, we have studied a series of organic alkali and ionic liquid composite absorption system, after a lot of experiments, we found that the imidazole ionic liquid and N-alkyl imidazole organic alkali prepared by an ionic liquid composite material not only has high absorption capacity, but also has obvious synergistic absorption effect.…”