Thermally rearranged membranes permeability

As shown in Fig. 14, PIM-1 and PIM-7 have been found to exhibit substantially higher O /Nj selectivities (a(O2/N2)>3.0) than other polymers of similar permeability [41]. Other thermally rearranged [78] polyimides show excellent CO /CH separation selectivities. These materials were also shown to function as fuel cell membranes when doped with H3PO4 and proton conductivities of 0.15 S cm" were observed at 130°C [78] that is, higher than polybenzimidazole membranes. 

Choi Jl, Jung CH, Han SH, Park HB, Lee YM. Thermally rearranged (TR) poly(benzoxazole-co-pyrrolone) membranes tuned for high gas permeability and selectivity. J Membr Sci 2010 349(l-2) 358-368. 

Han et al. investigated the gas separation behavior of the PBOs (Figure 5.57) prepared from thermal rearrangement of the fluorinated o-HPAs [80]. The thermal rearrangement occurred at a comparatively low temperature (350 °C) than the precursor poly-imides. The cavity sizes and distribution of FFV elements were tuned to obtain a higher combination of permeability (Phj = 206 Barrer) and selectivity by changing the precursor HPA structure and thermal treatment. The reduction of CO2 solubility for PBO in comparison to the precursor HPAs improved the H2/CO2 selectivity (a = 6.2 at 210 °C, in which Ph2 > 200 Barrer) and moved the membrane performance to polymeric upper bound (Robeson upper bound). 

Copolymerization is a method to control the gas transport performances of copolymer membranes as well as to confirm the effect of thermal rearrangement. Poly(benzoxazole-co-imide) membranes were obtained from the thermal rearrangement of poly(hydroxyl imide-c -imide)." Size and distribution of free volume cavities created during thermal conversion could be easily controlled by varying HPI composition in the copolymer. CO2 permeability of copolymer TR... 

Poly(substituted acetylene)s such as PTMSP and PMP, amorphous fluoro-polymers like Teflon AF and Hyflon AD, polymers with intrinsic microporosity, and thermally rearranged (TR) polymers are the candidate polymers for highly permeable glassy polymer membranes. The high free volume in glassy polymers contributes to enhanced diffusion and permeation of small gas molecules. The gas permeation performances of these highly permeable polymers even surpass upper bounds for CO2/N2, CO2/CH4 and H2/CO2 separations. 

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