Dionysios VROULIAS1, ?theophilos IOANNIDES?1, Vassileios DRACOPOULOS1
1Foundation for Research and Technology-Hellas, Institute of Chemical Engineering Sciences (FORTH/ICE-HT), Patras, Greece
Membrane-based technology for gas dehumidification in comparison to liquid absorption, solid adsorption and refrigeration is at the forefront because of its beneficial technical, energy-efficiency and ecofriendly characteristics [1]. Typically, hydrophilic polymers have been investigated as membranes in different applications such as natural gas and flue gas dehydration, dehumidifiers, and air conditioning systems [1]. However, they face performance limitations, and the combination of ionic liquids with membranes could be an alternative strategy to tackle such issues.
In this work, the effect of the anion in the ionic liquid (IL) structure has been studied considering water vapor/gas separation performance. After preparation of ILs, their chemical structure was confirmed by attenuated total reflectance (ATR) Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy. Physicochemical characterization was followed. In specific, viscosity of ILs was measured while the density of ILs was theoretically calculated with the Valderrama-Robles group contribution method. Thermal properties (short-term thermal stability, glass transition temperature) of ILs were also determined using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). ILs were, then, immobilized on porous PVDF substrates, thus forming supported ionic liquid membranes (SILMs). Gas and water vapor permeability measurements conducted using the Wicke-Kallenbach method. Apart from single gas measurements, mixed gas experiments were also carried out under dry and wet conditions.
It has been demonstrated that the permeability of water vapor through SILMs can be tuned by selection of a counter anion with high hydrophilicity. Thus, the membrane containing the IL with the more hydrophilic anion presented the highest water vapor permeability and H2O/gas selectivities, which are among the highest reported in the literature. Finally, H2O/gas separation factors were lower by one order of magnitude than ideal selectivities obtained under dry conditions. This is due to membrane swelling under humid conditions.
ACKNOWLEDGEMENTS
This research has been co?financed by the European Union and Greek national funds through the Operational Program Competitiveness, Entrepreneurship and Innovation, under the call RESEARCH–CREATE–INNOVATE(project code:T1EDK-00279).
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REFERENCES
[1] P. Scovazzo. 2010. J. Membr. Sci. , 355: 7 – 17.