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Synthesis of polymer-based composite membranes for desalination and gas separation
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posted on 15.05.2017by He, Li
Membranes are widely used in industrial separation processes, particularly for gas
separation and desalination processes. To develop membrane materials with improved
permeability, selectivity can achieve more energy-efficient membrane separations and reduce
costs. Since composite membranes offer improved performance, the aim of this research is to
develop polymer-based composite membranes with improved performance for gas separation
and water desalination applications.
First, in order to obtain a composite membranes with high chlorine tolerance, a
carbonaceous poly(furfuryl alcohol) (PFA) composite membrane was synthesized at a low
temperature carbonation by formation and post-treatment of a thin PFA layer on porous
polymer substrates. The carbonaceous PFA membrane exhibits high selectivity and excellent
chemical stability in seawater desalination. The low-temperature carbonization method
developed in this study is promising for developing a wide range of other carbonaceous
polymer composite membranes for water desalination.
Next, in order to apply PFA to other applications, understanding the effects of
polymerization conditions on the properties of the PFA composite membrane is required. The
PFA membrane was fully characterized in terms of microstructure and separation properties.
Suitable synthesis conditions for the preparation of PFA composite membranes with smooth
surfaces and uniform structure were (1) FA/ H2SO4 molar ratios: 74-300, (2) polymerization
temperatures: 80-100°C and (3) solvents: ethanol and acetone. The preparation conditions
were also optimized. The PFA composite membrane prepared with a FA/ H2SO4 molar ratio of
250, a polymerization temperature of 80°C and with ethanol as the solvent exhibited the
highest H2/N2 ideal selectivity (αH2/N2=24.9), and a H2 permeability of 206 Barrers. This
work led to a better understanding of the effect of the preparation procedures on the membrane
In order to investigate the effects of the incorporation of molecular sieve nanoparticles on
the membrane structure and membrane performance, silicalite-poly(furfuryl alcohol) (PFA)
mixed matrix composite membranes were successfully synthesized based on the best synthesis
condition obtained previously. The silicalite-PFA mixed matrix composite membrane with
20% w/w silicalite loading had a high ideal selectivity (αo2/N2= 3.5 and αco2/N2= 5.4) and a
good permeability (Po2= 821.2, Pco2= 1263.7, PN2= 233.3 Barrers) at room temperature. This
membrane can be a good candidate for oxygen enrichment applications.
Finally, in order to investigate the effects of the incorporation of silicalite nanocrystals on
the desalination property of polyamide membranes, silicalite nanocrystals were also
incorporated into polyamide matrix to synthesize silicalite-polyamide mixed matrix
membranes. With an increase in the loading of silicalite nanocrystals, the water flux of
silicalite-polyamide mixed matrix composite membranes increased whereas the salt selectivity
significantly decreased. The silicalite-polyamide mixed matrix composite membrane prepared
from TMC-hexane with 0.5% (w/v) silicalite had water flux of 2.7×10-6 m3/m2·s and NaCl
rejection of 50% at a feed pressure of 34.5 bar which 2000 ppm salt solution was used as the
feed. The silicalite-polyamide mixed matrix composite membrane is promising for developing
high water flux composite membranes for water desalination.
In this research, composite membranes with improved permeability, selectivity and
chemical resistance were successfully synthesized for desalination and gas separation. For
desalination, carbonaceous PFA composite membranes with high chlorine tolerance and
silicalite-PA mixed matrix composite membranes with high salt rejection and water flux were
successfully obtained. For gas separation, an optimized composite membranes PFA synthesis
condition was found and silicalite-PFA mixed matrix composite membranes with high O2/N2
separation were successfully synthesized.