Performance of nitrile-containing anions in task-specific ionic liquids for improved CO2/N2 separation

This work explores the performance of a series of ionic liquids that incorporate a nitrile-containing anion paired to 1-alkyl-3-methylimidazolium cations in tailoring the selectivity and permeance of supported ionic liquid membranes for CO2/N2 separations. The permeance and selectivity of three ioni...

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Bibliographic Details
Published in:Journal of membrane science 2010, Vol.353 (1-2), p.177-183
Main Authors: Mahurin, Shannon M., Lee, Je Seung, Baker, Gary A., Luo, Huimin, Dai, Sheng
Format: Article
Language:English
Subjects:
AMINO ACIDS
ANIONS
BASIC BIOLOGICAL SCIENCES
CARBON DIOXIDE
CATIONS
GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE
LIQUIDS
MEMBRANES
NITRILES
SOLUBILITY
SOLUTIONS
VISCOSITY
VOLUME
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Summary:This work explores the performance of a series of ionic liquids that incorporate a nitrile-containing anion paired to 1-alkyl-3-methylimidazolium cations in tailoring the selectivity and permeance of supported ionic liquid membranes for CO2/N2 separations. The permeance and selectivity of three ionic liquids, each with an increasing number of nitrile groups in the anion (i.e., two, three, and four), were measured using a non-steady-state permeation method. By predictably varying the molar volume and viscosity of the ionic liquids, we show that the solubility, selectivity, and permeance can be optimized for CO2/N2 separation through controlled introduction of the nitrile functionality into the anion. Of the three nitrile-based ionic liquids studied, 1-ethyl-3-methylimidazolium tetracyanoborate, [emim][B(CN)4], showed the highest permeance with a value of 2.55 10 9 mol/(m2 Pa s), a magnitude 30% higher than that of the popular ionic liquid [emim][Tf2N]. This same nitrile-bearing ionic liquid also exhibited a high CO2/N2 selectivity of approximately 53. Additionally, the carbon dioxide solubility for each ionic liquid was measured at room temperature with [emim][B(CN)4] again exhibiting the highest CO2 solubility. Results from our study of the nitrile-based ionic liquids can be rationalized in terms of regular solution theory wherein the selectivity and permeance of a given SILM system are largely determined by the molar volume and viscosity of the corresponding ionic liquid phase.
ISSN:0376-7388
1873-3123
DOI:10.1016/j.memsci.2010.02.045