Molecular Design of High Capacity, Low Viscosity, Chemically Tunable Ionic Liquids for CO₂ Capture

Abstract

The discovery of materials that combine selectively, controllably, and reversibly with CO2 is a key challenge for realizing practical carbon capture from flue gas and other point sources. We report the design of ionic liquids (ILs) with properties tailored to this CO2 separation problem. Atomistic simulations predict that suitably substituted aprotic heterocyclic anions, or “AHAs,” bind CO2 with energies that can be controlled over a wide range suitable to gas separations. Further, unlike all previously known CO2-binding ILs, the AHA IL viscosity is predicted to be insensitive to CO2. Spectroscopic, temperature-dependent absorption, rheological, and calorimetric measurements on trihexyl(tetradecyl)-phosphonium 2-cyanopyrrolide ([P66614][2-CNpyr]) show CO2 uptakes close to prediction as well as insignificant changes in viscosity in the presence of CO2. A pyrazolide-based AHA IL behaves qualitatively similarly but with weaker binding energy. The results demonstrate the intrinsic design advantages of ILs as a platform for CO2 separations.

Computer‐Aided Design of Ionic Liquids as CO2 Absorbents

“…A predictive estimate with ac lear distinction between physical and chemical absorption can be simply obtained according to geometries optimized in the presence of as olvation model instead of optimizing it only in gas phase as has been done to date.The resulting Gibbsfree energies compare very well with experimental values and the energies were correlated with experimental capacities.P romising anions,f or ionic liquids with reversible CO 2 absorption properties can be defined by areaction Gibbs free energy of absorption in the range of À30 to 16 kJ mol À1 .Ionic liquids (ILs) are promising solvents for CO 2 absorption from various waste gases,a nd this property has been attracting significant scientific and technological attention in the last decade.T oachieve maximum efficiencyregarding the energy needs of both the transport and the regeneration of the absorbent, the absorption enthalpy must be in ar elatively narrow range, [1][2][3] but it can, of course,d eviate from this desired value depending on the aims and the circumstances. Owing to the great variety of ILs (the estimated number of potential IL candidates is ca.…”

Ionic Liquid Co-catalyzed Artificial Photosynthesis of CO

“…Recently, Dai's group developed basic and superbase-derived ILs that showed promise in rapid and switchable CO 2 capture with an equimolar absorption capability 24 . The combination of ILs with alkanolamines has also been developed as a viable approach to achieve high levels of reversible CO 2 capture in IL solvents 25 . Interestingly, in the above-mentioned carbon …”

“…Although the uses of ILs to promote CO 2 capture and conversion are already evident and has been proposed for future carbon photofixation in high pressure biphasic ILs-CO 2 (liquid) systems 13,[23][24][25]27,28 , the merging of IL chemistry with photoredox organocatalysis to achieve gas CO 2 fixation with visible light under ambient conditions is rarely covered. Herein, we delineate the application of ILs to facilitate CO 2 capture under ambient conditions, and then integrating to a classic photoredox catalytic cycle for efficient CO 2 conversion to CO 29 .…”

Intramolecular Hydrogen Bonds Enhance Disparity in Reactivity between Isomers of Photoswitchable Sorbents and CO2: A Computational Study

“…[53] The hybrid functional B3LYP [54] of DFT and the 6-311 ++(d,p) [55] basis set were used for ground-state geometry optimization without symmetry constraint. [5,6,[24][25][26] Frequency calculations at the same level of theory were carried out to confirm the stationary points as minima. Solvent effects were accounted implicitly by using the conductor-like polarizable continuum model (CPCM).…”