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Issue 20, 2013
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Reaction kinetics of CO2 absorption in to phosphonium based anion-functionalized ionic liquids

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Abstract

The reaction kinetics between CO2 and trihexyl(tetradecyl)phosphonium ([P66614]) – based ionic liquids (ILs) with prolinate ([Pro]), 2-cyanopyrrolide ([2-CNpyr]), and 3-(trifluoromethyl)pyrazolide ([3-CF3pyra]) anions are studied at temperatures from 22–60 °C. The absorption of CO2 is carried out in a stirred reactor under pseudo first order conditions. ILs are diluted to concentrations of 0.05, 0.1 and 0.15 M with tetraglyme – a nonreactive, low volatility solvent with much lower viscosity than the ILs. Physical solubility of CO2 in the mixtures is calculated using correlations developed from CO2 solubility measurements in tetraglyme and the N2O-analogy for ILs and dilute IL solutions. The diffusivity of CO2 is estimated from viscosity-dependent correlations chosen after a thorough literature review. The results indicate partial first order reaction kinetics with respect to IL with values ranging from 19 500 L mol−1 s−1 ([P66614][Pro]) to 3200 L mol−1 s−1 ([P66614][3-CF3pyra]) at 22 °C. The second order reaction rate constants follow Arrhenius behavior with the highest activation energy of 43 kJ mol−1 measured for [P66614][Pro]. ILs with aprotic heterocylic anions (AHA), on the other hand, show small activation energies of 18 and 11 kJ mol−1 for [P66614][3-CF3pyra] and [P66614][2-CNpyr], respectively. The ILs studied in this work exhibit reactivity comparable to or higher than common aqueous amines. High reaction rates and tunable capacity make ILs, and AHA ILs in particular, attractive solvents for CO2 separations.

Graphical abstract: Reaction kinetics of CO2 absorption in to phosphonium based anion-functionalized ionic liquids

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Publication details

The article was received on 27 Mar 2013, accepted on 27 Mar 2013 and first published on 03 Apr 2013


Article type: Paper
DOI: 10.1039/C3CP51289D
Citation: Phys. Chem. Chem. Phys., 2013,15, 7796-7811
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    Reaction kinetics of CO2 absorption in to phosphonium based anion-functionalized ionic liquids

    B. E. Gurkan, T. R. Gohndrone, M. J. McCready and J. F. Brennecke, Phys. Chem. Chem. Phys., 2013, 15, 7796
    DOI: 10.1039/C3CP51289D

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