(727a) Water Vapor Permeation through Amine-Containing CO2-Selective Facilitated Transport Membranes for Hydrogen Purification

We have synthesized carbon dioxide-selective membranes by incorporating amino groups into polymer networks.  The membranes have shown high carbon dioxide permeability and selectivity vs. hydrogen, carbon monoxide and nitrogen up to 180^oC.  Hydrogen sulfide permeates through the membrane much faster than carbon dioxide due to much higher reactivity as a result of small-size proton transfer, allowing nearly complete removal of hydrogen sulfide to about 10 ppb in the treated synthesis gas before water-gas-shift (WGS) reaction.  In some applications, it is also required to selectively separate CO₂ by restricting the amount of water permeated.  The amine-containing membranes are highly hydrophilic, and they exhibit not only high CO₂ permeance but also high water vapor permeance.  This work demonstrates various water and CO₂ transport results exhibited by these thin-film composite amine membranes.  Water vapor permeance higher than 3500 GPU has been experimentally demonstrated with >3000 Barrers of CO₂ permeability and >150 CO₂/H₂ ideal selectivity.  Gas permeation experiments showed water vapor permeance to be not sensitive to the amine-containing selective layer thickness.  The water transport resistance offered by the polymeric substrate appeared to be the controlling mass transfer resistance, independent of the resistance offered by the selective amine layer.  Water vapor permeance was experimentally demonstrated to reduce on increasing the polymeric substrate resistance via increasing the number of substrate layers used to synthesize the membrane.  The hydrophilic amine-containing selective layer was expected to retain moisture and served as the governing layer for CO₂ and H₂ permeation.  Effect of the extent of water retention by the polymer matrix on the overall transport result was also investigated by use of different fixed-site amine carriers.  The use of commercial polyvinylamine (containing >60% salts) as a fixed carrier was shown to retain more moisture and aid the CO₂ permeance as compared to the laboratory synthesized pure polyvinylamine (without containing salts).  Water vapor permeance was shown to be related to the moisture retention capacity of the matrix.  Furthermore, the use of a relatively hydrophobic PDMS as an additional barrier/support layer was shown to reduce the water permeance to as low as 600 GPU.