je9b00750_si_001.pdf (2.26 MB)
Solubility and Diffusivity of Oxygen in Ionic Liquids
journal contribution
posted on 2019-10-09, 21:43 authored by Tangqiumei Song, Oscar Morales-Collazo, Joan F. BrenneckeThe solubility of
O2 was measured gravimetrically in
16 ionic liquids (ILs) containing piperidinium, pyrrolidinium, ammonium,
tetrahydrothiophenium, methyltriazabicyclodecene,
or guanidinium cations paired with bis(trifluoromethanesulfonyl)imide,
bis(perfluoroethylsulfonyl)imide, or perfluoropropanoyl(trifluoromethylsulfonyl)imide
anions. The temperature dependence of the solubility was determined
for eight of the ILs. Henry’ law constants were determined
from the solubility data as well as standard enthalpies and entropies
of absorption for systems with temperature-dependent data. Knowledge
of these thermodynamic properties is essential in guiding the structural
design of ionic liquids for different applications involving O2. The O2 solubility did not follow any obvious
trend with regard to IL structure or molar volume; instead, the dipole–quadrupole
interactions are the primary driving forces for O2 dissolution
in ionic liquids, as demonstrated by negative standard enthalpies
of absorption for all of the ILs. In addition, diffusion coefficients
of O2 in the ILs as a function of temperature (293, 313,
and 333 K) and applied O2 pressure (1, 3, and 5 MPa) were
obtained by fitting the time-dependent absorption data to a widely
used mass diffusion model. The diffusion coefficients of O2 in ionic liquids at 293 K and 1 MPa roughly correlate inversely
with the pure IL viscosity, likely due to the relatively low and similar
O2 solubilities under these conditions. As expected, O2 diffusivities increase with increasing temperature. However,
they also increase with increasing pressure, likely due to decreasing
solution viscosity with increasing gas solubility.