The molecular characteristics dominating the solubility of gases in ionic liquids

Abstract

This critical review provides a critical discussion of the current state of knowledge of the key factors influencing the solubility of gases in ionic liquids (ILs), including sample purity, experimental methodology, "molecular" characteristics of ILs, temperature and pressure. The review starts with a brief introduction to the current developments and the existing problems in the studies of the gas solubility in ILs. Then, the experimental, computational and theoretical developments in conformational equilibria of ions, in nanosegregated polar and nonpolar domains in ILs, and in the mechanisms for dissolution of gases in ILs are discussed and subsequently collaborated together with our freeze-fracture transmission electron microscopic and Raman measurements to propose the new microscopic mechanism for dissolving the gases in ILs. Next, a critical and quantitative analysis of the influences of the sample purity and the experimental methodology on the gas solubility is made so that the "real" relationships between structure and solubility property can be revealed. In addition, a systematic and deeper understanding of how the "molecular" features of the ILs, the temperature, and the pressure influence the gas solubility is provided at the molecular level. In the section of concluding remarks, the comments are made on the molecular criteria for the future design of the ILs to enhance the gas solubility by specifically optimizing the molecular characteristics of the ILs (265 references).

Design and screening of ionic liquids for C2H2/C2H4 separation by COSMO‐RS and experiments

“…As shown in Table 3 Table 3, the selectivity of C 2 H 2 to C 2 H 4 in [P 666 (14) ][OAc] is less than 10 at 298.1 K. This may be attributed to the excessive molecular size of the [P 666 (14) ] + cation.…”

Gaseous Hydrocarbon Separations Using Functionalized Ionic Liquids

“…Unsaturated hydrocarbons frequently present a higher solubility in ionic liquids than their saturated counterparts and so these fluids are considered promising for saturated/unsaturated hydrocarbon separation. The exact reasons for the observed trends are still poorly understood, even if they are essential for the development of new gas separation processes [3,4].…”

“…The functionalization of the side chains or the modification of the ionic liquid anion are popular approaches to tailor its properties for particular applications such in catalysis [5], energy storage [6], capture of carbon dioxide [3] and in separation technology [7]. In this work, we have studied the possibility of using ionic liquids for the separation of light saturated and unsaturated hydrocarbons and have started by compiling the literature results on the solubility of ethane and ethylene in different ionic liquids formed by the cations and anions in Table 1.…”

Multiple headspace extraction for gas detection in ionic liquids

“…A reason for such a behaviour might be the different macromolecular ionic structure and the presence of a certain conformational equilibrium in the ionic domains. The small differences of the solubility of the three TCB ILs suggest on the other hand that the solubility is rather insensitive to the cations chain length -a phenomenon also well known from carbon dioxide [33,51,9]. A proper investigation of the structures of ILs and their interactions with CO, however, is not a goal of this paper so that the effects on the solubility should be discussed elsewhere.…”

“…The main drawback of this method is that low-molecular weight gases like hydrogen or carbon monoxide usually have solubilities below the detection limit of the microbalance. Another disadvantage is a certain error rate because of buoyancy effects [33]. Latter provoke that the IL weighs generally less in a gas atmosphere than in a vacuum -independent from any gas solvation behaviour.…”