Water vapor permeability and competitive sorption in thermally rearranged (TR) membranes

作者：Scholes Colin A^*; Freeman Benny D; Kentish Sandra E

来源：Journal of Membrane Science, 2014, 470: 132-137.

DOI：10.1016/j.memsci.2014.07.024

• Thermal rearrangement
• Gas separation
• Water
• Competitive sorption

Thermal rearrangement (TR) of alpha-hydroxyl-polyimides (PI) into polybenzoxazoles (PBO) produces membranes with improved gas separation properties. In addition, PBO membranes have high thermal and chemical resistance, which is advantageous for many applications because of the presence of condensable vapors, in particular water in the feed gas. Here, PI and TR produced PBO membranes are studied for their water sorption and permeability. The PI precursor was 3,3'-dihydroxy-4,4'-diaminobiphenyl 4,4'-hexafluoroisopropylidene diphthalic anhydride (HAB-6FDA), and its TR conversion is well characterized. It was observed that water sorption into the PI and TR PBO membranes followed a slightly convex sorption isotherm characteristic of water clustering as the water activity increased. The corresponding water permeabilities through both membranes varied with the water activity. Water permeability through the TR PBO was an order of magnitude greater than the PI membrane, ranging from 35,000 to 43,500 Barrer. It was also observed that the presence of water reduced the permeability of CO2 and CH4 for both membranes clue to competitive sorption. However, the CO2/CH4 selectivity of the TR PBO membrane was relatively constant because of similar decreases in CO2 and CH4 permeability when exposed to water vapor. Conversely, the PI membrane CO2/CH4 selectivity was reduced when exposed to water vapor, because CO2 experienced greater competitive sorption from water than CH4.

• 出版日期2014-11-15