Publication: Carbon dioxide capture using hydrophobic-modified surfacetemplated polyvinylidene fluoride membrane via membrane contactor
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Date
2024-08-01
Authors
Chang, Pei Thing
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Abstract
Membrane gas absorption (MGA) emerges as a potential technology for
separating CO2 from flue gas, offering significant advantages over conventional CO2
removal methods. In MGA, the porous membrane physically separates the gas and
liquid phases. The gas separation role is fulfilled by the absorbent which attracts the
CO2. However, MGA efficiency is often constraint by membrane wetting issues and
low CO2 permeability. To address these challenges, it is hypothesized that synthesizing
PVDF membrane with opposing surface wettability can enhance wetting resistance,
especially for long-term process and simultaneously improving CO2 capture efficiency
in MGA. In this work, two PVDF membranes were synthesized from polymers with
different molecular weight (350 kDa and 300-320 kDa). PVDF membrane fabricated
with high molecular weight PVDF powder (HMW/g-PVDF) exhibited critical wetting
issues due to the presence of a more polar -polymorph on the membrane surface,
which has a higher affinity for water. It led to a low water contact angle (WCA) of 92°.
To overcome this, high molecular weight PVDF powder was used to fabricate
superhydrophobic membrane via a non-solvent induced phase inversion method with
non-woven substrate. Membranes produced with water (tPVDF-DI) and ethanol
(tPVDF-E) coagulation bath displayed micro- and nano-level hierarchical structures
on the membrane surface. The change in the surface structure exhibited high WCA of
153.6° and 155.1° and low contact angle hysteresis (CAH) of 15° and 11.8°,
respectively. The patterned membrane showed a higher CO2 absorption flux at 7.00 x 10-2 mol/m2
s, which was nearly 10 times higher than the non-printed membrane. The
flux remained unchanged even after 20 days of contact with amine absorbent, as the
trapped air within printed structures on the membrane surface inhibited amine
penetration into the membrane pores. To further enhance CO2 capture efficiency, the
opposite side of the patterned surface was modified with ethylenediamine (EDA) and
graphene oxide (GO) to construct a CO2-philic surface. Compared to membrane
without a CO2-philic surface (tPVDF-DI) in mixed gas MGA process, the
tPVDF/EDA5/GO membrane showed better MGA performance, with a CO2
absorption flux of 4.010-3 mol/m2
s and a gas selectivity of 6.0. The presence of amine
and rich oxygen-containing functional groups on the membrane surface attracted more
CO2 molecules to flow across the membrane to be absorbed by the amine absorbent.
Overall, the combination of a printed hierarchical structure membrane surface with a
CO2-philic surface represents a significant innovation that effectively prevents
membrane wetting and enhances CO2 passage through the membrane in the MGA
process.