CO[sub.2] Absorption by Solvents Consisting of TMG Protic Ionic Liquids and Ethylene Glycol: The Influence of Hydrogen Bonds

Herein, the absorption of CO[sub.2] by the TMG-based (TMG: 1,1,3,3-tetramethylguanidine) ionic liquids (ILs) and the absorbents formed by TMG ILs and ethylene glycol (EG) is studied. The TMG-based ILs used are formed by TMG and 4-fluorophenol (4-F-PhOH) or carvacrol (Car), and their viscosities are low at 25 °C. The CO[sub.2] uptake capacities of [TMGH][4-F-PhO] and [TMGH][Car] are low (~0.09 mol CO[sub.2] /mol IL) at 25 °C and 1.0 atm. However, the mixtures [TMGH][4-F-PhO]-EG and [TMGH][Car]-EG show much higher capacities (~1.0 mol CO[sub.2] /mol IL) than those of parent ILs, which is unexpected because of the low CO[sub.2] capacity of EG (0.01 mol CO[sub.2] /mol EG) in the same conditions. NMR spectra and theoretical calculations are used to determine the reason for these unexpected absorption behaviors. The spectra and theoretical results show that the strong hydrogen bonds between the [TMGH][sup.+] cation and the phenolate anions make the used TMG-based ILs unreactive to CO[sub.2] , resulting in the low CO[sub.2] capacity. In the Ils-EG mixtures, the hydrogen bonds formed between EG and phenolate anions can weaken the [TMGH][sup.+] –anion hydrogen bond strength, so ILs-EG mixtures can react with CO[sub.2] and present high CO[sub.2] capacities.