A Rational Approach to CO2 Capture by Imidazolium Ionic Liquids: Tuning CO2 Solubility by Cation Alkyl Branching

• Published in: ChemSusChem Vol. 8; no. 11; pp. 1935 - 1946
• Main Authors: Corvo, Marta C., Sardinha, João, Casimiro, Teresa, Marin, Graciane, Seferin, Marcus, Einloft, Sandra, Menezes, Sonia C., Dupont, Jairton, Cabrita, Eurico J.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 08.06.2015; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Subjects: Alkanes - chemistry; Carbon dioxide; Carbon Dioxide - chemistry; Carbon Dioxide - isolation & purification; carbon dioxide fixation; Carbon sequestration; Cations; Chain branching; Chains; Diffusion; Imidazoles - chemistry; Ionic liquids; Ionic Liquids - chemistry; Molecular Conformation; Molecular dynamics; Molecular Dynamics Simulation; Molecular interactions; NMR spectroscopy; Perturbation; Solubility; Solubilization; Solvents - chemistry; substituent effects; ionic liquids; NMR spectroscopy; molecular dynamics; substituent effects; carbon dioxide fixation
• ISSN: 1864-5631; 1864-564X
• DOI: 10.1002/cssc.201500104

Branching at the alkyl side chain of the imidazolium cation in ionic liquids (ILs) was evaluated towards its effect on carbon dioxide (CO2) solubilization at 10 and 80 bar (1 bar=1×105 Pa). By combining high‐pressure NMR spectroscopy measurements with molecular dynamics simulations, a full description of the molecular interactions that take place in the IL–CO2 mixtures can be obtained. The introduction of a methyl group has a significant effect on CO2 solubility in comparison with linear or fluorinated analogues. The differences in CO2 solubility arise from differences in liquid organization caused by structural changes in the cation. ILs with branched cations have similar short‐range cation–anion orientations as those in ILs with linear side chains, but present differences in the long‐range order. The introduction of CO2 does not cause perturbations in the former and benefits from the differences in the latter. Branching at the cation results in sponge‐like ILs with enhanced capabilities for CO2 capture. Catch and retain: Introduction of a methyl group at the side chain of the imidazolium cation of an ionic liquid (IL) enhances CO2 solubility. High‐pressure NMR (HP NMR) spectroscopy and molecular dynamics data show that CO2 uptake is a direct consequence of the liquid structure of the IL, which provides a matrix with a sponge‐like nature to solubilize CO2 without perturbing the supramolecular arrangement.