Pyridinium based Poly(Ionic Liquids) membranes with exceptional high water vapor permeability and selectivity

Abstract

Removing water vapor from gas streams via condensation is an energy-intensive process. Membrane-based technology is an attractive alternative for water vapor separation over other conventional dehumidification technologies, reducing the energy consumption and the overall operational cost. Polymeric membranes exhibiting high water vapor permeability and selectivity are promising candidates for water removal from applications including compressed air drying and flue gas dehydration. In this work, a precursor polymeric membrane based on aromatic polyether copolymer containing main chain pyridine units (PY-APE) and its pyridinium-based polymeric ionic liquids (PILs) films containing different counter anions (MeSO4−, BF4−, TFSI−) were prepared and evaluated as dehumidification membranes. Single gas and water vapor measurements were carried out and the selectivity of different gas pairs (H2O/H2, Η2Ο/Ν2, H2O/CO2, H2O/CH4) was measured. Among all membranes, PIL-MeSO4 had the highest water vapor permeability of 1.84 × 105 Barrer combined with the highest H2O/gas selectivity (e.g.H2O/CO2 selectivity is 2.0 × 105), which is one of the highest reported in the literature. The activation energies of water vapor and single gases (H2, CO2, CH4) permeation through the PIL-MeSO4 membrane were calculated suggesting that water vapor permeation is controlled by solubility while diffusion is the main transport mechanism for the other gases. The study of the water vapor effect on gas permeation under process gas streams conditions using a mixture of 3% H2O-24.25% CO2-72.75% H2 revealed that gas permeability increased one or two orders of magnitude. As a consequence, the separation factors decreased in comparison with the ideal selectivities obtained in dry conditions. This marked improvement in permeability is related to the presence of water vapor which causes swelling of the hydrophilic matrix thus producing water like domains that mainly govern gas permeation.