This overview article discusses fundamental principles of gas sorption and transport in rubbery and glassy polymers and material selection guidelines for gas separation membranes. Comparisons between the performance of membrane‐based gas separation systems and more conventional technologies in key commercial applications are provided. Companion articles in this special edition focus on state‐of‐the‐art reviews and descriptions of theoretical and experimental developments important in the technology of gas separations using polymeric membranes.
The gas permeability, diffusivity, and solubility of a series of
polysulfones bearing basic
aryl substituents were determined at 35 °C and pressures up to 20
atm. Gas permeability and diffusivity
values of the aryl-substituted polysulfones were markedly lower than
those of unmodified polysulfone.
These effects were ascribed to decreased fractional free volume
and increased restriction to sub-T
g
torsional
motion in the substituted polymers. Polysulfone bearing benzylic
amine substituents exhibited higher
CO2 solubility and CO2/CH4
solubility selectivity than polysulfone, presumably due to favorable
interactions
between acidic CO2 molecules and basic
−CH2-NH2 groups. CO2
diffusivity in polysulfone bearing benzylic
amine substituents is lower than expected based on free volume
considerations, suggesting that
interactions between CO2 and benzylic amine moieties may be
strong enough to impede CO2 mobility in
the modified polymer. These results are consistent with infrared
spectroscopy data which suggest that
the benzylic amino groups undergo reversible reaction with
CO2 to form carbamate moieties.
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