Equimolar CO₂ Absorption by Anion-Functionalized Ionic Liquids

Abstract

Amino acid ionic liquid trihexyl(tetradecyl)phosphonium methioninate [P(66614)][Met] and prolinate [P(66614)][Pro] absorb CO(2) in nearly 1:1 stoichiometry, surpassing by up to a factor of 2 the CO(2) capture efficiency of previously reported ionic liquid and aqueous amine absorbants for CO(2). Room temperature isotherms are obtained by barometric measurements in an accurately calibrated stirred cell, and the product identity is confirmed using in situ IR. Density functional theory (DFT) calculations support the 1:1 reaction stoichiometry and predict reaction enthalpies in good agreement with calorimetric measurements and isotherms.

Computational Comparison of the Reactions of Substituted Amines with CO2

“…Regardless of specific environment, the results here will be useful for guiding the selection of materials, as we are currently doing to tailor ionic liquid absorbants. [27] We have recently applied the same computational methods employed here to study the 1:1 reaction of amino acid anions with CO 2 . [27] Calculated reaction enthalpies for the methoninate and prolinate anions are À14 and À18 kcal mol À1 , in excellent relative agreement with the calorimetrically measured reaction energies of À16 and À20 kcal mol À1 .…”

“…[27] We have recently applied the same computational methods employed here to study the 1:1 reaction of amino acid anions with CO 2 . [27] Calculated reaction enthalpies for the methoninate and prolinate anions are À14 and À18 kcal mol À1 , in excellent relative agreement with the calorimetrically measured reaction energies of À16 and À20 kcal mol À1 . As a calibration, this 4 kcal mol À1 difference in reaction enthalpy corresponds to a 15 % difference in the mole ratio of dissolved CO 2 at 228C and 0.1 bar.…”

“…As a calibration, this 4 kcal mol À1 difference in reaction enthalpy corresponds to a 15 % difference in the mole ratio of dissolved CO 2 at 228C and 0.1 bar. [27] The ability to tune reaction enthalpies clearly is important to optimizing CO 2 separations.…”

“…[26,27] In these nonaqueous environments, the exact nature of the amine-CO 2 reaction is not as well understood, and optimization of these materials is largely empirical.…”

Study on Gas Permeation and CO2 Separation through Ionic Liquid-Based Membranes with Siloxane-Functionalized Cations

“…Taking into account the attractive properties of ILs for CO 2 separation, different engineered membrane approaches have been considered, [6][7][8] while gas solubility studies support the importance of the design of task-specific IL-based materials. [9][10][11][12][13] Within the several membrane configurations explored so far, 6 the simplest approach is the use of supported ionic liquid membranes composite membranes have also been intensively studied as a way to prepare membranes that can combine the adequate gas permeability and selectivity of SILMs with the robustness of polymers. [6][7][8] Actually, PILs are functional materials that merge the macromolecular architecture of polymers with the chemistry of ILs, [14][15][16] maintaining in the polymer several of the unique IL features, especially the tunability of their properties.…”