Fundamental Investigation of the Factors Controlling the CO₂ Permeability of Facilitated Transport Membranes Containing Amine-Functionalized Task-Specific Ionic Liquids

Abstract

Task-specific ionic liquid (IL)-based facilitated transport membranes were prepared with tetrabutylphosphonium amine-functionalized glycinate or 2-cyanopyrrolide ILs. CO 2 permeabilities and viscosity and CO 2 absorbance of ILs were evaluated. Viscosities of glycinate-or methylglycinate-containing ILs drastically increased with CO 2 absorption, probably from hydrogen bonding between their CO 2 complexes. The temperature dependence of the CO 2 permeability of the IL-based membranes was opposite to that of the viscosity of the corresponding ILs. The CO 2 permeability at low temperature under dry conditions was improved by using tetrabutylphosphonium 2-cyanopyrrolide, which barely forms hydrogen bonds among its CO 2 complexes. However, above 363 K, the tetrabutylphosphonium 2-cyanopyrrolide-based membrane had a lower CO 2 permeability than the tetrabutylphosphonium glycinate-based membrane because tetrabutylphosphonium 2-cyanopyrrolide absorbed less CO 2 . The major factors controlling CO 2 permeability of task-specific IL-based facilitated transport membranes appear to be the viscosity of the CO 2 complex (which is the most important factor) and the amount of CO 2 absorbed.

Effect of the amino-group densities of functionalized ionic liquids on the facilitated transport properties for CO2 separation

“…The volumes of both the reference and sample cells were determined before the 5 absorption experiments. [14] In this study, CO 2 and N 2 absorption tests were carried out under different conditions. Each test was conducted according to the following procedures.…”

“…The gas permeabilities of the AAIL-based membranes were measured according to a previously reported procedure. [11][12][13][14] In this study, the CO 2 partial pressure and relative humidity dependencies on the gas permeability was examined using the apparatus shown in Fig. 4.…”

“…In previous studies, it was revealed that the viscosities of AAILs after CO 2 absorption were dramatically higher than those of neat AAILs under dry conditions around room temperature. [14] The dramatic increase of the viscosity along with CO 2 absorption would be due to the formation of an intermolecular hydrogen bond network among the AAIL-CO 2 complexes. [14,36,37] Therefore, the viscosity of the AAIL in contact with CO 2 was the dominant factor in determining the CO 2 permeation properties of AAIL-FTMs when used under dry conditions around room temperature.…”

In Situ ATR and DRIFTS Studies of the Nature of Adsorbed CO2 on Tetraethylenepentamine Films

“…Amine functional groups in the form of (i) aqueous amines: monoethanolamine (MEA) 2−7 and 2-amino-2-methyl-1-propanol (AMP); 8 14 and (iii) immobilized amines for sorbents and membranes: tetraethylenepentamine (TEPA) 15−19 and polyethylenimine (PEI) 20−25 have been widely studied for capturing the emitted carbon dioxide. Aqueous amines and IL's used for CO 2 absorption have also been incorporated into the sorbents and membranes for CO 2 adsorption.…”

Fixed-site-carrier facilitated transport of carbon dioxide through ionic-liquid-based epoxy-amine ion gel membranes

“…These amine functional groups should also allow for fixed-site facilitated transport of CO 2 to occur [26][27][28][29][30]34]. Compared to conventional materials used for fixedsite-carrier facilitated transport, epoxy-amine ion gel membranes have higher ideal CO 2 permeability [15,16,27,[34][35][36].…”