Operating temperature effects on the plasticization of polyimide gas separation membranes

Abstract

Membrane plasticization is the process whereby penetrant dissolution causes membrane swelling or dilation, which in turn, can increase membrane diffusivity and solubility and lead to long time frame polymer relaxation processes. In this work, the effect of temperature upon the plasticization of a rigid polyimide, poly(4,4'-hexafluoroisopropylidene diphthalic anhydride-2,3,5,6-tetramethyl-1,4-phenylenediamine) (6FDA-TMPDA), by carbon dioxide is investigated. It is found that across the full range of temperatures studied, plasticization has little effect on carbon dioxide solubility as all results can be characterized by a standard dual mode sorption model. However, the effect upon diffusivity is significant and this can be described by both an exponential relationship with penetrant concentration and an Arrhenius relationship with temperature. The polymer relaxation processes induced by plasticization are also temperature dependent. However, the total proportion of penetrant sorption associated with such relaxation processes is relatively unaffected by temperature. This paper shows that plasticization effects are dominated by Henry's law dissolution. Conversely, while Henry's Law species contribute most to diffusion at high temperatures, at lower temperatures the movement of Langmuir component species also contributes to the total diffusion coefficient.

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 6FDA-TMPDA membrane permeabilities are comparable to literature [22,25], given the differences in annealing temperature, and clearly demonstrate the high water permeance and corresponding large water selectivity relative to CO 2 . PIM-1 permeabilities are higher than the majority of the literature [21,26,27].…”

“…Furthermore, the thickness of the Teflon AF1600 layer was dictated by the needed to form a uniformed film on the membrane, as lower amount of perfluorinated polymer do not form a consistent membrane. Single gas permeabilities were undertaken on a variable pressure constant volume apparatus that has previously been reported [22]. Single gas measurements were undertaken with a feed pressure of 0.987 atm at 35 • C. Mixed gas permeability measurements were undertaken on a constant pressure variable volume instrument, which has also been previously reported and the protocol for exposure to water vapor has also been previously reported [6].…”

Hyper-crosslinked, hybrid membranes via interfacial polymerization

“…The high CO 2 uptake, also observed for 6FDA based polymers, is attributed to the presence of CF 3 groups in the structure. 10,64,65 The data from Wind et al for an ester modified 6FDA-DAM:DABA-based polyimide has a similar order of magnitude CO 2 concentration. The magnitude of CO 2 uptake increases with a decreasing concentration of the POSS solution used for the synthesis.…”

“…Particularly in membrane science and composite materials science, the combination of inorganic particles in a polymer matrix is regularly denoted as "hybrid". [62][63][64][65][66] Although such materials do combine two constituents in one material, the physical properties will in general be in between those of the two individual constituents. Examples of this class include polymer modification by dispersing polyhedral oligomeric silsesquioxanes (POSS), 67,68 zeolite, 69 or silica [70][71][72] particles in the polymeric phase during processing.…”