Using a Gravimetric Method to Measure the Solubility and Diffusivity of H2 and CO2 in the Ionic Liquid [bmim][PF6]
Seyed Hamed Barghi, Theodore T. Tsotsis, and Muhammad Sahimi[1]
Mork Family Department of Chemical Engineering & Materials Science, University of Southern California, Los Angeles, California 90089-1211 <> <>Abstract
In this talk, we will report on the measurement of the solubility and diffusivity of H2 and CO2 in the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) over the temperature range 25 oC - 55 oC and for pressures of up to 10 MPa. The data were obtained using a magnetic suspension balance, a gravimetric instrument that is capable of simultaneously and accurately measuring the gas solubility and diffusivity in such liquids. To our knowledge, this is the first time that the H2 diffusivity has been measured in an ionic liquid. While solubility data for H2 have been previously reported, they vary widely. The cause for such variations will be discussed as well. The diffusivity data for both H2 and CO2 follow an Arrhenius-like dependence on temperature:
where
(cm2/s) is
the diffusivity, T (K), 
the pre-exponential factor (cm2/s), 
(kJ/mol) the activation energy, and 
the gas constant (0.008314 kJ/mol. K). For H2,
=146 and 
=42.43. For CO2, 
=0.64 and 
=32.
The diffusivity data for both gases indicate very little, if any, dependence on the pressure, indicative of Fickian-like diffusion and the lack of swelling effects. The solubility data for both H2 and CO2 in the same ionic liquid indicate a Henry-like dependence for the entire ranges of pressures and temperatures studied. Both Henry's constants increase with increasing temperature, as one may have expected. The success of the technique of measuring the transport of thermodynamic properties of this important gas pair will, hopefully, motivate its use for measuring the transport and thermodynamic properties of other important gas mixtures in this and other ionic liquids.
Keywords: Hydrogen, Carbon dioxide, solubility, diffusivity, ionic liquids
See more of this Group/Topical: Engineering Sciences and Fundamentals