Water permeability and competitive permeation with CO 2 and CH 4 in perfluorinated polymeric membranes

Abstract

The permeability of water through polymeric membranes is of particular interest in gas separation, because of the high water vapor content found in many industrial applications. Polymeric membranes that are resistant to competitive sorption and plasticization by water are especially attractive, since they can reduce the need for gas pretreatment in many membrane applications. The perfluorinated polymers Teflon AF1600 and Hyflon AD60 are studied here for this purpose because of their strong hydrophobicity and unusual solvent properties. It was observed that water permeability through both perfluorinated polymers was of the same magnitude as CO 2 . Indeed, under the conditions studied, Teflon AF1600 was selective for CO 2 over water. Such reverse selectivity for the CO 2 -H 2 O gas pair has not been reported before for glassy polymeric membranes and reflects the very low solubility of water in the polymer. The water permeability through Hyflon AD60 was greater than that for CO 2 with a minimum at 55 o C. The change in both CO 2 and CH 4 permeability through Teflon AF1600 and Hyflon AD60 was investigated as a function of water activity in the feed gas to investigate the effects of competitive permeation. It was observed that CO 2 and CH 4 permeability in both membranes reduced with water activity. For both Teflon AF1600 and Hyflon AD60, the decrease in permeability of both gases with water activity was interpreted as water clusters blocking the diffusion of both CO 2 and CH 4 through the membrane.

Water Resistant Composite Membranes for Carbon Dioxide Separation from Methane

“…Hence, the determined Langmuir affinity constants are provided in Table 9. The affinity constant for Teflon AF1600 and 6FDA-TMPDA closely align with those previously reported in the literature [15,22], while to the best of the author's knowledge no CH 4 affinity constant has previously been reported for PIM-1. The CH 4 affinity constants for 6FDA-TMPDA and PIM-1 are considerably less than that of CO 2 , which is associated with the strong affinity CO 2 has for those two polymers; while for Teflon AF1600 the affinity constants for CO 2 and CH 4 are comparable, which is associated with the poor affinity Teflon AF1600 has for many gases and vapors.…”

“…The other fundamental parameters of the three pure membranes have already been reported in the literature and are provided in Table 4. The calculated mobility factor for Teflon AF1600 is comparable to literature, but that of 6FDA-TMPDA and PIM-1 are lower than that reported in the literature [7,15,25]. This implies that the 6FDA-TMPDA and PIM-1 membranes studied here have reduced interconnectivity between the micro-voids, which is attributed to the annealing temperature of the membranes.…”

“…The water permeability through PIM-1 is comparable to the author's previous study [7], and demonstrates that PIM-1 has selectivity for water over CO 2 . The Teflon AF1600 permeabilities are comparable with literature [15] and demonstrate the unique selectivity for CO 2 over H 2 O. The low permeability of water in Teflon AF1600 is associated with the super-hydrophobicity of the polymer and the observation of very low water sorption into the Teflon AF1600 membrane structure.…”

“…The majority of the research has focused on water removal from the feed stream, in dehydration applications [8][9][10][11][12][13][14]. In contrast, perfluorinated polymers Teflon AF1600 and Hyflon AD60 membranes demonstrate significant resistance to separation performance loss in the presence of water vapor [15]. Interestingly, under certain conditions Teflon AF1600 has selectivity for CO 2 over H 2 O, which has not been observed in any other polymeric membranes [4].…”

Review: membrane materials for the removal of water from industrial solvents by pervaporation and vapor permeation

“…The nature of the free volume elements in APFPs favors the transport of water molecules compared to the larger solvent molecules. In addition, for gas separation, the clustering of water molecules in the free volume elements has been proposed as a hindrance to transport of permanent gas molecules . Huang et al .…”