Anion Effects on Gas Solubility in Ionic Liquids

Department of Chemical and Biomolecular Engineering, University of Notre Dame, South Bend, Indiana, United States
The Journal of Physical Chemistry B (Impact Factor: 3.3). 05/2005; 109(13):6366-74. DOI: 10.1021/jp046404l
Source: PubMed


This work presents the results of solubility measurements for a series of gases in 1-n-butyl-3-methyl imidazolium tetrafluoroborate and 1-n-butyl-3-methyl imidazolium bis(trifluoromethylsulfonyl) imide. The gases considered include benzene, carbon dioxide, nitrous oxide, ethylene, ethane, oxygen, and carbon monoxide. Carbon dioxide and oxygen solubilities are also reported in methyl-tributylammonium bis(trifluoromethylsulfonyl) imide, butyl-methyl pyrrolidinium bis(trifluoromethylsulfonyl) imide, and tri-isobutyl-methyl phosphonium p-toluenesulfonate. We report the associated Henry's constants and enthalpies and entropies of absorption. In general, benzene, followed by carbon dioxide and nitrous oxide, have the highest solubilities and strongest interactions with the ionic liquids, followed by ethylene and ethane. Oxygen had very low solubilities and weak interactions. Carbon monoxide had a solubility below the detection limit of our apparatus. Ionic liquids with the bis(trifluoromethylsulfonyl) imide anion had the largest affinity for CO(2), regardless of whether the cation was imidazolium, pyrrolidinium, or tetraalkylammonium. These results suggest that the nature of the anion has the most significant influence on the gas solubilities.

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    • "As gas solubility studies in ILs continue to highlight the importance of developing " task-specific " materials for CO 2 capture [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35], different engineered approaches have been investigated to take advantage of the desirable properties of ILs for gas separation applications, namely the use of supported ionic liquid membranes (SILMs), in which the IL is immobilized into the pores of a solid inert polymeric membrane [14]. Given that membrane technology has competitive advantages compared to bulky-fluid absorption, including lower capital costs and energy consumption, small scale equipment and environmentally benign operation [36], a wide range of different IL phases has been used to develop SILM configurations for CO 2 separation from gas streams [37] [38] [39] [40] [41] [42] [43] [44] [45] [46]. "
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    ABSTRACT: Polymeric ionic liquids (PILs) are blossoming as a new generation of materials at the interface of many areas leading to a renaissance of the field of ionic polymers. Although PILs are interesting membranes materials for CO 2 separation, additional research is still required to realize their full potential. In this work, pyrrolidinium-based polymers containing different cyano-functionalized counter-anions were synthesized by straightforward anion exchange reactions and characterized. Their film forming ability blended with different amounts of free ionic liquid (IL) was evaluated and the CO 2 and N 2 permeation properties through the prepared composites were determined. The results show that increasing the IL content in the composites not only increased CO 2 permeability but also boosted the CO 2 /N 2 permselec-tivity, leading to improved separation performances. The best performance was achieved for the C(CN) 3-based membrane containing 60 wt% of IL, which overcomes the Robeson 2008 upper bound, with CO 2 permeability of 439.3 Barrer and CO 2 /N 2 permselectivity of 64.4. Therefore, the pyrrolidinium-based PIL combined with the [C(CN) 3 ] À as counter-anion has potential for efficient post-combustion CO 2 separation, suggesting the preparation of high performance membranes for industrial applications. &
    Full-text · Article · Jun 2015 · Journal of Membrane Science
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    • "Note that the last equality assumes that the effect of diffusivity on the selectivity is relatively small compared to that of the solubility. This is supported by some experiments suggesting that the ratio of gas diffusivity is nearly unity in certain ILs (Camper et al., 2006b) Furthermore, Henry's law constant is directly related to the Gibbs energy of solvation ΔG sol 1 , i.e., the free energy of transfer of a gas molecule from the pure perfect gas state at some standard pressure p 0 (1 bar) to the solution (Anthony et al., 2005), "
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    ABSTRACT: In this work, we develop a simple method that can be used to screen for the ionic liquid (IL) candidates for use in various CO2 capture processes. In particular, Henry׳s law constant, an important physical quantify determining the capacity and selectivity of CO2 absorption, is determined from the product of infinite dilution activity coefficient (IDAC) of a gas molecule in an IL and the fugacity of the gas in a hypothetical liquid state. The IDAC is calculated using the predictive COSMO-SAC activity coefficient model, where the interaction between the gas and the IL are determined through the screening charges on the molecular surfaces obtained from quantum mechanical solvation calculations. We have developed a simple model for the fugacity of 4 gas molecules, including CO2, CH4, N2 and H2, and examined the solubility, selectivity, and the temperature dependency of solubility. The predicted results for Henry׳s law constant of CO2 in ILs are in good agreement with experimental data (53 data points) over a wide range of temperatures (from 283 K to 303 K), with an average absolute relative deviation (ARD) of 17%. This method is used to screen for the best IL candidates for CO2 capture from a set of 2080 ILs combined from 65 cations and 32 anions. The computational time used for screening for this set of IL is less than 3 min on a personal computer. Our results show that the COSMO-SAC model can be a powerful method for the design and screening of new ILs as a medium for CO2 capture.
    Full-text · Article · Jan 2015 · Chemical Engineering Science
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    • "The TOFs for the 2 wt% RuCl 3 ·xH 2 O + 10 wt% [C 4 mim][NTf 2 ] + PI membrane are lower than those for the 2 wt% RuCl 3 ·xH 2 O + PI membrane. Since [C 4 mim][NTf 2 ] has a low H 2 O solubility [29], the concentration of H 2 O within the membrane will be relatively low. Since H 2 O is a reactant, a low concentration leads to the reduced TOF. "
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    ABSTRACT: Novel composite ionic liquid and polyimide membranes with dissolved RuCl3 catalyst for H2/CO reactive separation were fabricated to combine gas diffusive separation and water-gas shift reaction. The CO concentration in the membranes is reduced via its reaction with H2O to form CO2 and H2, catalysed by the Ru carbonyl complex which forms in the reaction between dissolved RuCl3 and CO. In order to optimize the membrane configurations and operating conditions, water-gas shift reaction turnover frequencies (TOFs) of the membranes with various concentrations of ionic liquid and RuCl3 were determined at different pressures, temperatures and times-on-stream on a purpose-built test rig. The results show that the ionic liquid, [C4mim][OTf], improves TOFs by increasing the solubilities of H2O and the gases solubilities within the membrane. TOFs were found to increase initially, but reduce as time-on-stream increased, due to the formation and subsequent evaporation of a Ru carbonyl complex. Lower temperature and lower concentration of [C4mim][OTf] were found to minimize the loss of the catalyst. It is suggested that the 2 wt% RuCl3·xH2O+20 wt% [C4mim][OTf]+PI membrane operated at 140 °C and 2 bar has the best combination of reactivity and durability.
    Full-text · Article · Dec 2014 · Journal of Membrane Science
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