3.5. Gas permeation analysis
Regarding the high condensability of gases studied in this
research (Methane, Ethane and Propane), the dissolution of studied
gases in the polymer may have a significant impact on polymer
(Supplementary data, Table 1). The rate of gas dissolution will
increase in the polymer by intensifying the pressure of condensable
gases in the feed [1,11]. Considering the elastomeric properties
of studied polyurethanes in this research, the dissolution of
condensable gases in the polymer is higher because of the domination
of solution mechanism in gas permeation through polymers
[2,3,11,30–32]. Therefore, it seems necessary to study the plasticizing
effect of these condensable gases on polymer. In the case of
polymer softening, the ideal selectivity would vary greatly from
the real selectivity. In order to be assured about the results from
the ideal selectivity and present it as an index for the actual behavior
of membrane, the tests of gas permeability at the pressures in
which there is no plasticizing effect on polymer should be carried
out. The test of membrane plasticizing was performed by using
pure nitrogen gas, because nitrogen has no effect on the polymer
chains. The trend is such that the permeability of the nitrogen in
a certain pressure before and after leaving each hydrocarbon gas
should be evaluated. In the case of increasing nitrogen permeability,
it is reported the membrane softens at that pressure by Hydrocarbon
gas.