(706e) High Performance Gas Separation Membrane From a Polymer of Intrinsic Microporosity by Photochemical Surface Modification

The
concept of design in next-generation chemical separation membrane is to develop
porous materials by tuning the pore size approximate to the kinetic diameter of
molecules (sub-nanometer scale) to achieve highly
selective separation with high rates of permeation. Among many microporous organic polymers (MOPs) materials, solution-processable polymers of intrinsic microporosity
(PIMs) have attracted significant interest in recent
years, showing high gas permeability and reasonable selectivity as gas separation
membrane.

In this
study, we demonstrate a method of surface modification of a microporous
polymer (PIM-1) membrane by combination of ultraviolet light irradiation and
ozone (UVO) treatment to enhance the gas separation performance. The
ultraviolet irradiation in the presence of atmospheric oxygen produced ozone
and atomic oxygen which transformed the polymer chains and generated a nanoporous asymmetric thin layer over the pristine
membrane. The chemical changes, structure and morphologies of the membranes exposure to UVO treatment were examined by various
techniques. We found significant sensitivity of gas permeation properties with
respect to the operation conditions, such as the atmosphere of UV irradiation
and exposure time.

The
pure PIM-1 membrane presents a CO₂ permeability of ~5600 Barrer and CO₂/N₂ selectivity of 20,
and CO₂/CH₄ selectivity at ~13, which are in agreement
with the literature data of PIM-1 membrane. Control experiments of UV
irradiation in pure N₂ showed that the permeability and selectivity
were approximate to that of neat polymer. Upon exposure to UV irradiation in
air or controlled O₂/N₂ atmosphere, the permeability of
CO₂ showed slight increase (up to 7000 Barrer)
after short exposure for 5-10 min, but then decreased with extended exposure
for 20-60 min, while the selectivity evidently increased. Particularly, the
selectivity of H₂ over N₂ and CH₄ increased
evidently (up to ~60) with moderate permeability of H₂ (~2000 Barrer). The CO₂ permeability reached ~2000 Barrer and both selectivity of CO₂/N₂
and CO₂/CH₄ increased to approximately 30 after exposure
to UV/ozone for 30 min. Most of these data surpassed the Robeson's 2008 upper
bound.

The
mixed gases permeation properties of PIM-1 membranes with UV/ozone treatment
were also investigated using certified gas mixtures of CO₂/N₂
and CO₂/CH₄ with feed pressure up to 30 bar. The surface modification by UV/ozone treatment could
enhance the selectivities of mixed gases, which are
higher and more stable than that of unmodified membrane, particularly for CO₂/CH₄
separation, at slight expense of CO₂ permeability.

In sum,
the photochemical surface modification via
the UVO treatment could enhance the selectivity of the composite-layered
membrane while the permeability was still maintained at reasonable high level,
showing high potential for CO₂ capture, natural gas separation and
hydrogen purification. The concept of this process could offer a direction on
improving the separation performance of various microporous
polymer membrane materials.

Acknowledgements

We acknowledge the NPRP grant
from the Qatar National Research Fund (QNRF), the Engineering and Physical
Sciences Research Council (EPSRC, UK), and the China Scholarship Council.

Notes

Corresponding author: es10009@cam.ac.uk (Dr. Easan
Sivaniah)

References

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