Carbon dioxide (CO2) absorption by the amine-functionalized ionic liquid (IL) dihydroxyethyldimethylammonium taurinate at 310 K was studied using surface- and bulk-sensitive experimental techniques. From near-ambient pressure X-ray photoelectron spectroscopy at 0.9 mbar CO2, the amount of captured CO2 per mole of IL in the near-surface region is quantified to ~0.58 mol, with ~0.15 mol in form of carbamate dianions and ~0.43 mol in form of carbamic acid. From isothermal uptake experiments combined with infrared spectroscopy, CO2 is found to be bound in the bulk as carbamate (with nominally 0.5 mol of CO2 bound per 1 mol of IL) up to ~2.5 bar CO2, and as carbamic acid (with nominally 1 mol CO2 bound per 1 mol IL) at higher pressures. We attribute the fact that at low pressures carbamic acid is the dominating species in the near-surface region, while only carbamate is formed in the bulk, to differences in solvation in the outermost IL layers as compared to the bulk situation.

Ionic liquids (ILs) are promising solvents for gas separation processes such as carbon dioxide (CO2) capture from flue gases. For the design of corresponding processes and apparatus, thermophysical properties of ILs containing dissolved gases are required. In the present study, it is demonstrated that with a single optical setup, mutual and thermal diffusivities as well as refractive indices can be measured quasi-simultaneously for such mixtures. Dynamic light scattering (DLS) from bulk fluids was applied to determine mutual and thermal diffusivities for mixtures of 1-butyl-3-methylimidazolium tricyanomethanide ([BMIM][C(CN)3]) or 1-butyl-3-methylimidazolium tetracyanoborate ([BMIM][B(CN)4]) with dissolved CO2 at temperatures from 303.15 to 333.15 K and pressures between 2 and 26 bar in macroscopic thermodynamic equilibrium. Good agreement with literature data and only slight differences between the diffusivities measured for the two systems at the same temperature and comparable mole fractions of CO2 were found. Increasing mutual diffusivities with increasing mole fractions of CO2 are consistent with decreasing viscosities reported for other IL-CO2 mixtures in the literature and can be attributed to weakening of molecular interactions by the dissolved gas. For the conditions studied, no dependence of the thermal diffusivity on the temperature or the mole fraction of CO2 could be found.

We report novel supported ionic liquid (IL) phase systems, described as “inverse” SILPs, consisting of micron size IL droplets within an envelope of silica nanoparticles. These novel IL-in-air powders, produced by an easily scalable phase inversion process, are stable up to 60 °C and 30 bar and are proposed as a means to confront the major drawbacks of conventional SILPs for gas separation. SILPs are usually formed by filling the channels of nanoporous materials with the IL phase. In case the core space of the pores remains open, such conventional SILPs exhibit lack of gas absorption specificity, while complete pore filling leads to diffusivity that is very low compared to that for corresponding bulk ILs; the latter drop is largely due to the high tortuosity of the pore network of the support. The inverse SILPs prepared in this work exhibited promising CO2/N2 separation performance that had reached the value of 20 at absorption equilibrium and enhanced CO2 absorption capacity of 1.5–3 mmol g–1 at 1 bar and 40 °C. Moreover, the CO2 absorption kinetics were very fast compared to conventional SILP systems and to simultaneous N2 absorption; the CO2/N2 selectivity at the short times of the transient stage of absorption had reached values in excess of 200.

Here we present novel CO2 sorbents based on chitosan ionogels. The powder sorbents called inverse supported ionic liquid phase (SILP) materials were prepared by dissolving chitosan in various ionic liquids (ILs) followed by encapsulation of the ionogel droplets with nanoporous fumed silica. CO2 absorption was determined at 40 °C in the range of 200 to 5500 mbar. At 1 bar, absorption capacities of these materials were 0.1–0.8 mol kg–1; at 5 bar, values of 0.2–1.5 mol kg–1 were reached. A comparison of inverse SILP materials with and without chitosan dissolved in the applied IL indicated that the presence of chitosan increased the CO2 absorption efficiency of the materials. The aim of the study was also to compare the CO2 absorption in pure chitosan and chitosan dissolved in ILs. It was found that dissolution increases the absorption capacity of chitosan about 10 times.

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