Permeability of Dry Gases and Those Dissolved in Water through Hydrophobic High Free-Volume Silicon- or Fluorine-Containing Nonporous Glassy Polymer Membranes

Abstract

This study systematically investigates the oxygen and carbon dioxide permeability of dry gases and those dissolved in water through hydrophobic high free-volume silicon- or fluorine-containing nonporous glassy polymers including poly(trimethylsilylmethylmethacrylate) (PTMSMMA), poly(1-trimethylsilyl-1-propyne), 4,4′-(hexafluoroisopropylidene) diphthalic anhydride-4,4′-(9-fluorenylidene) dianiline, and 4,4′-(hexafluoroisopropylidene) diphthalic anhydride-2,3,5,6-tetramethyl-1,4-phenylene-diamine. The dry state gas permeability coefficient was almost higher than that of the wet state because the effect of the boundary layer, which is the water resistant layer, on the membrane surface depends on the gas permeability in the wet state. In addition, the gas permeability difference between the dry and wet states depends on the combination of competitive sorption between water and gas species and plasticization by water. Carbon dioxide/oxygen permselectivity increased with the decrease in gas permeability, except for PTMSMMA. The gas permeability in the wet state of PTMSMMA with low glass transition temperature was approximately equal to that in the dry state because plasticization by water increased in the wet state. Therefore, the mobility of the polymer segment depends on the plasticization by water.

Selective, Room-Temperature Transformation of Methane to C1 Oxygenates by Deep UV Photolysis over Zeolites

“…O 2 permeability decreases from 10,083˘936 Barrer at 298 K to 7024˘1050 Barrer at 333 K, while O 2 diffusivity diminishes from 5.47ˆ10´8˘1.36ˆ10´8 cm 2¨s´1 at 298 K to 3.46ˆ10´8˘7.72ˆ10´9 cm 2¨s´1 at 333 K. These values are in good agreement with those reported in the literature [17,[22][23][24][25]32,33]. However, in spite of the high oxygen permeability, the ideal O 2 /N 2 selectivity of pure PTMSP is very low, ranging from 1.32˘0.12 at 298 K to 0.94˘0.41 at 333 K. This is a characteristic behavior of PTMSP due to its high free volume and the fact that the weakly and rigid molecular sieving framework is more prone to changes in solubility than diffusivity [24,32].…”

“…Therefore, the effect of temperature on the gas permeability and diffusivity is well described in terms of Arrhenius and Van't Hoff relationships by Equations (3)-(5). The activation energies for permeation are −8.19 ± 1.72 kJ·mol −1 and −12.60 ± 4.10 kJ·mol −1 for O2 and N2, respectively, through pure PTMSP membranes, in agreement with the literature [23,24]. In this work, the activation energies for diffusion are −11.02 ± 1.71 kJ·mol −1 and −17.29 ± 8.34 kJ·mol −1 for O2 and N2, respectively, whereas the activation energies for sorption are −2.34 ± 1.89 kJ·mol −1 and 5.36 ± 2.32 kJ·mol −1 for O2 and N2, respectively.…”

Permselectivity improvement in membranes for CO2/N2 separation

“…The gas permeability through the pure PTMSP membranes prepared in our laboratory decreases with increasing temperature, from 17454 ± 5102 Barrer at 298 K to 12056 ± 2375 Barrer at 333 K, whereas the ideal CO2/N2 selectivity is not improved. This is a typical behavior for PTMSP, due to the high free volume, and the fact that the rigid and weakly molecular sieving structure is more prone to changes in solubility than diffusivity [12,13].…”

“…The CO2 permeability of PTMSP reported in literature covers a range between 16000 -38000 Barrer at 298 K [12,13], probably because the different stages of aging affecting PTMSP performance [14]. The high permeability of PTMSP is based on high solubility and high diffusivity and is probably related to its very low density (0.75 g cm -3 ) and its extremely high free volume (0.29) [15,16], accounting for the presence of microvoids [12], compared with the rest of dense glassy polyimides [17].…”

Mixed Matrix Membranes for O2/N2 Separation: The Influence of Temperature

“…The MMMs that showed the best separation ability were the 5 wt % CHA-PTMSP, the 5 wt % LTA5-PTMSP, the 5 wt % Rho-PTMSP, and the 20 wt % LTA1-PTMSP, with a slight decrease in permeability but a considerable enhancement in selectivity, surpassing the Robeson’s upper bound, even increasing the temperature up to 333 K. The O 2 permeability of PTMSP reported in the literature covers a range between 6000 and 10,000 Barrer at 308 K, decreasing with temperature. However, its high permeability is accompanied with a very low O 2 /N 2 selectivity, with values between 1.30 and 1.70 at 308 K [22,23,24,25]. Consequently, the incorporation of suitable chosen inorganic fillers is likely to improve the selectivity of a defect-free membrane [17,26,27,28,29].…”