Water permeation and sorption properties of Nafion 115 at elevated temperatures

There is the potential to use membrane technology to recover high purity water from power station flue gas streams. In this work, the permeation of water, CO2 and N2 through Nafion 115 was investigated as a function of water activity at 70-150 °C. It was found that all permeances increased with increasing water activity but reduced with increasing temperature. This data was supplemented by sorption analysis at lower temperature which conversely showed decreasing solubility as temperature increased. The changes in solubility and permeance with water activity were attributed to membrane swelling as water activity increased. A comparison with a thinner perfluoro-sulphonic acid polymer, from an alternate supplier, suggested that permeance did not scale linearly with membrane thickness, possibly reflecting inhomogeneity in membrane swelling. The results were used to simulate the capture of water from a brown coal power station flue gas and it was found that a permeate pH of 3.3-4.0 is achievable with Nafion 115 at 150 °C. This suggests that for use as boiler feed this stream will need to undergo further treatment.