The effects of water vapor on CO2/CH4 separation using commercially available poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and Cardo-type polyimide hollow fiber membranes were investigated. Pure methane and CO2/CH4 mixture permeation experiments were carried out in the absence and presence of water vapor (60% RH). Pure methane permeance decreased in the presence of water vapor for both membrane types. The decrease was 28% for hydrophilic Cardo-type polyimide and 6% for hydrophobic PPO membranes. The decline in the permeance was also observed for CO2/CH4 mixture separation through both membranes. However, selectivities of the two membranes were affected differently by water vapor. The Cardo-type polyimide membrane exhibited 43% decline in the permeances of both CO2 and CH4, which resulted in an unchanged selectivity in the presence and absence of water vapor. The PPO membrane, on the other hand, showed different rates of decline for the two gases. While CO2 permeance decreased by 11%, CH4 experienced an average of only 4% decrease in permeance. Therefore, the selectivity of PPO membrane significantly declined in the presence of water vapor. It was also observed that the permeance of pure CH4 was partially recovered when the experiment was conducted after a series of experiments with wet gas mixtures.

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