Silica Nanoparticles Infused Mixed Matrix Membrane For Carbon Dioxide Removal Via Membrane Gas Absorption
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Date
2018-04-01
Authors
Rosli, Aishah
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
Carbon dioxide (CO2) is the most produced, heat-trapping greenhouse gas and
one of the main contributors to global warming. Membrane gas absorption (MGA) is
a very attractive alternative for CO2 removal as it is simple, energy efficient, less space
consuming and easy to scale up. However, major issues in MGA process are improving
the membrane selectivity without reducing the permeability and membrane wetting,
which can increase membrane mass transfer resistance significantly. Various materials
with differing properties have been researched for the synthesis of MGA membranes
to capture CO2, however, mixed matrix membranes (MMM) are proving to be a
promising alternative, as the addition of inorganic particles into polymers opens the
possibility of augmenting the membrane performance. In this work, polyvinylidene
fluoride (PVDF) was chosen as the polymer matrix and fumed silica nanoparticles
were incorporated into the polymer dope to produce MMM. A defect-free asymmetric
membrane with both finger-like layer and sponge-like layer was successfully
synthesised using 15 wt% polymer concentration with a casting thickness of 400µm
in a coagulation bath of a mixture of ethanol and water. Among the three different
silica nanoparticles investigated in this study, TS-530 silica nanoparticles that had been
treated with hexamethyldisilazane gave superior CO2 absorption performance in MGA
process in terms of selectivity and permeability of 22.5 and 1.9 x 10-4 mol/m2s
respectively at 1 wt% silica loading. This improvement of selectivity of TS-530 MMM
compared to pristine PVDF membrane, which had a selectivity of 7.18 could be due
to the homogenous dispersion of the nanoparticles in the PVDF polymer matrix,
effectively altering the structure of the membrane to increase membrane contact area,
resulting in better selectivity of CO2 over nitrogen while hardly affecting the
permeability. The performance of the MMM was further improved by adding a layer
of low-density polyethylene (LDPE) coating on the membrane to increase its
hydrophobicity and resistance to membrane wetting. The coated MMM proved to be
better than the non-coated MMM in both permselectivity and sustainability in an
extended run, with CO2 absorption flux and selectivity of 2.4 x 10-4 mol/m2
s and 22.8 respectively. A dynamic model was then proposed to simulate CO2 absorption in the
MGA process, taking not only the gas solubility into the liquid absorbent into account,
but also the gas solubility into the membrane. The model was found to be in good fit
with experimental results, with R2 values exceeding 0.92. The optimum coated MMM
with superior selectivity and better resistance to membrane wetting with liquid entry
pressure of 13.55 bar and contact angle of 120° was used with the best operating
parameters to observe the binary gas performance over an extended period.
Throughout the study of the membrane synthesis, the potential membrane CO2
separation performance was observed in regards to a multitude of parameters and its
resulting physical properties, which allowed for the monitoring of membrane
performance under various influences.