(709h) The Role of Chlorine Substituent in Gas Transport Properties of Polychlorotrifluoroethene (PCTFE)

Polymeric membranes have been widely used for
industrial gas separation due to their inherent advantages such as high energy-efficiency.
There is a great interest in understanding the polymer structure/property
relationship to design high performance membranes with high gas permeability
and selectivity. Halogenated polymers have emerged as interesting membrane
materials for gas separation. For example, perfluoropolymers govern the upper
bounds for He/H₂, He/N₂, and He/CH₄ separation
in the Robeson’s plots, which is ascribed to the more favorable interactions
for He than other gases with fluoropolymers, as shown in the Figures above.
Herein, we demonstrate that chlorine groups exhibit unique separation
properties for the removal of noble gas from mixtures, as exemplified in
polychlorotrifluoroethylene (PCTFE, -CF₂-CFCl-). At 35 ^oC,
PCTFE exhibits a He permeability of 26 Barrers and pure gas selectivity of He/H₂,
He/CO₂ and He/CH₄ of 6.2, 53 and 1,100, respectively.
These selectivity values are among the highest reported, and the performance is
near or above the upper bounds for these separations. Interestingly, PCTFE also
shows a H₂/CO₂ selectivity of 8.5 at 35 ^oC,
an attractive performance for H₂ purification and CO₂
capture. The effect of Cl substituents on CO₂ solubility can be
interpreted using the regular solution theory. Similar behavior for CO₂/CH₄
solubility selectivity is also observed in halogenated organic liquids. This
presentation will also discuss potential applications of halogenated polymers for
the separation of other noble gases (such as Argon) from their mixtures.