Thermally rearranged polymeric membranes for CO2 separation from humidified ternary mixtures

The application of thermally rearranged polymer membranes [ ] in gas separation offers great advantages owing to the presence of micropores, appropriately tuned cavities size and distribution, which provides highly permeable and selective structures. Their use in CO2 separation from flue gas type streams is an important field of application currently under development. In this work, the transport properties (permeation flux, permeance and selectivity) of a thermally rearranged hollow fibre membrane module were evaluated with both single gases (CO2, N2 and O2) and gas mixtures (CO2:N2:O2=15:80:5) at different temperatures (25, 50 and 75°C) and trans-membrane pressure differences (2-5 bars). Owing to the higher condensability of CO2 in polymer matrix, its permeance measured with dry mixture did not significantly change in comparison with the pure gas permeance. In contrast, a reduction in the mixed -gas permeances of N2 and O2 over their pure gas permeances was observed. As a consequence, a higher mixed-gas CO2/N2 selectivity of 20 than the pure gas ideal selectivity of 16 was observed at 25°C. Even though less evident, analogous trend was also obtained at higher temperatures, where a favoured diffusivity and a depleted solubility, promotes the permeation of incondensable gases (N2 and O2) than that of CO2, which the permeation is significant owing to its solubility. The presence of water vapour in the mixture showed great influences on the permeation behaviour; a drop in permeance of ca. 48% was measured for CO2 with respect to ca. 30 and ca. 40%, for N2 and O2, respectively. This was translated in a 20% reduction in CO2/N2 selectivity from 20 (dry condition) to 16 (wet condition) at 25°C. The results present in this work indicated that, even under the industry relevant harsh conditions (e.g. high relative humidity and high temperature), the membrane module showed satisfactory performance, making these thermally rearranged polymer membranes promising for the application in CO2 separation from flue gas streams.