Mechanisms of low temperature capture and regeneration of CO₂ using diamino protic ionic liquids

Abstract

Carbon dioxide (CO2) chemical absorption and regeneration was investigated in two diamino carboxylate protic ionic liquids (PILs), dimethylethylenediamine formate (DMEDAH formate) and dimethylpropylenediamine acetate (DMPDAH acetate), using novel calorimetric techniques. The PILs under study have previously been shown to possess a CO2 absorption capacity similar to the industrial standard, 30% aqueous MEA, while requiring much lower temperatures to release the captured CO2. We show that this is in part due to the fact that the PILs exhibit enthalpies of CO2 desorption as low as 40 kJ mol(-1), significantly lower than the 85 kJ mol(-1) required for 30% aqueous MEA. Computational and spectroscopic analyses were used to probe the mechanism of CO2 capture, which was found to proceed via the formation of carbamate moieties on the primary amine of both DMEDAH and DMPDAH. Evidence was also found that weakly acidic counter-ions such as formate and acetate provide, unexpectedly, an additional proton acceptor site in the traditional carbamate mechanism, revealing opportunities to increase CO2 uptake capacity in the future through careful design of the anion and cation used in the PIL capture agent.

Protic ionic liquid as excellent shuttle of MDEA for fast capture of CO2

“…Since the value of Δ H SOL at x = 1.82 mol kg −1 represents an averaged level of absorption heat, the comparison of Δ H SOL in different absorbents (Entries 2, 4, and 5) is then made under this condition. It is noted that Δ H SOL in the 70 wt % PIL aqueous solution is only −44.7 kJ·mol −1 (Entry 4), consistent with the literature data −40 kJ·mol −1 . This is almost the smallest enthalpy change of chemical reaction, because even the absorption of CO 2 into aqueous MDEA results in an enthalpy change of −58 kJ·mol −1 .…”

CO2 Absorption Mechanism by Diamino Protic Ionic Liquids (DPILs) Containing Azolide Anions

“…As shown in Figure 1A, the hydrogen peak of -NH 3 (H-4) can be clearly identified in the 1 H NMR spectra of [DMEDAH] [Im], and there was no N-H peak of imidazole in the spectra. The -NH 2 peak of DMEDA was also completely missing from the 1 In order to study the absorption mechanism, we investigated the 1 H NMR and 13 C NMR spectra of [DMEDAH] [Im] before and after CO 2 absorption. As shown in Figure 1A, there were several new peaks (H-1 , H-3 , and H-c') in the 1 H NMR spectrum after CO 2 absorption.…”

“…However, tedious procedures are needed to synthesize these aprotic ILs, resulting in high costs. Recently, protic ILs [12][13][14] have been investigated to capture CO 2 because they can be easily prepared and exhibit promising capacity.…”

An ab initio Study of the Structure and Energetics of Hydrogen Bonding in Ionic Liquids

“…The C2-H bond, which is the most acidic proton on the imidazolium cation, is often involved in these non-directional hydrogen bonds. Conversely, protic ionic liquids, which are formed via a proton transfer reaction from a Brønsted acid to Brønsted base (Greaves et al, 2008; Simons et al, 2016), are more likely to form directional hydrogen bonds. This proton can subsequently be involved in a hydrogen bonding interaction with the anion.…”