Effect of Water on CO₂ Capture by Aprotic Heterocyclic Anion (AHA) Ionic Liquids

Abstract

The reaction between three aprotic heterocyclic anion (AHA) ionic liquids (ILs) (triethyl(octyl)phosphonium 2-cyanopyrrolide [P 2228 ]-[2CNPyr], triethylphosphonium benzimidazolide [P 2222 ][BnIm], and triethyl-(octyl)phosphonium indazolide [P 2228 ][Inda]) and CO 2 , in the presence of water, is investigated in this study. We propose a reaction mechanism where, in addition to the reaction of the anion with CO 2 to form carbamate, the anion reacts with water (i.e., hydronium ions in water from either the natural dissociation of water or the formation of carbonic acid) and is reprotonated, leaving CO 2 to react with hydroxide to form bicarbonate. This mechanism is confirmed for [P 2228 ][2CNPyr] and [P 2222 ][BnIm] by 1 H NMR, 13 C NMR, heteronuclear single quantum correlation NMR, and heteronuclear multiple bond correlation NMR, which were used to identify and quantify the reaction products. However, unlike the other two ILs, [P 2228 ][Inda] exhibits reprotonation of the anion when in contact with water only; i.e., CO 2 is not needed to form carbonic acid to increase the proton concentration in water. The reversibility of the reprotonation reaction was tested by measuring the CO 2 solubility in [P 2228 ][2CNPyr] and [P 2222 ][BnIm] in the presence of water for several cycles using a volumetric method. Previously, we have shown that the reaction of AHA ILs with CO 2 to form carbamate (in the absence of water) is reversible. Additionally, encapsulated [P 2228 ][2CNPyr] and [P 2222 ][BnIm]were subjected to a CO 2 solubility recyclability test in the presence of water. Both reactions between AHA ILs and CO 2 in the presence of water appear to be fully reversible. The encapsulated ILs showed good CO 2 capture capacity in the presence of water and good recyclability results, as well.

Insight into the Interactions between Azole-Anion-Based Ionic Liquids and Propargylic Alcohol: Influence on the Carboxylative Cyclization of Propargylic Alcohol with Carbon Dioxide

“…At present, to improve the performance of AILs-catalyzed carboxylative cyclization of PA with CO 2 , the most popular strategy is to tune the basicity of AILs to enhance the interaction between AILs and PA or CO 2 . Generally speaking, as the basicity of AILs increases, the interaction between AILs and CO 2 increases, resulting in an increase in CO 2 absorption and higher absorption enthalpy. − Surprisingly, as the basicity of AILs increased, the conversion of PA increased accordingly as expected, and the yield of α-alkylidene cyclic carbonate products increased first and then decreased. Wang and co-workers investigated with DFT calculations how the basicity of AILs (quantified by the p K a of the azole-based anions in t BuOH) affects the conversion of PA and the yield of alkylidene carbonates (Figure ).…”

Economic Optimization of Carbon Capture Processes Using Ionic Liquids: Toward Flexibility in Capture Rate and Feed Composition

“…We also assume that water is removed prior to the CO 2 capture process by a flue gas dehydration treatment. However, the effect of water is interesting since recent studies have shown that water has a favorable effect on CO 2 absorption by AHA ILs. , Thus, developing a reliable thermodynamic model for this phenomenon is a topic of interest. A further discussion of the impact of water absorption on the process performance has been presented by Hong et al .…”

Quantification of Ylide Formation in Phosphonium-Based Ionic Liquids Reacted with CO2

“…We have developed a class of ILs for CO 2 capture that contain aprotic heterocyclic anions (AHA). They react stoichiometrically and reversibly with CO 2 with almost no increase in viscosity. − We have shown that they can be encapsulated to increase mass transfer area, while maintaining reversibility, and have investigated the reaction chemistry that takes place when water is present . In that case bicarbonate is formed along with the carbamate.…”