Publication: Zif-l@pdms/pes supported ionic liquid membrane for co2/n2 and co2/ch4 separation
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Date
2024-04-01
Authors
Meor Muhammad Hafiz, Shah Buddin
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Abstract
Supported ionic liquid membrane (SILM) formed through the impregnation of
ionic liquid (IL) in polymeric membrane structure is effective for selective separation
of CO2. This study fabricated a novel SILM configuration by locating zeolitic-
imidazole framework-L (ZIF-L) on the skin of a polyethersulfone (PES) hollow fiber
membrane to form the composite ZIF-L@PDMS/PES membrane. Subsequently, ZIF-
L@PDMS/PES SILM was derived by impregnating [BMIM][BF4] IL. Through the
incorporation of ZIF-L and IL in the membrane, the gas transport properties
(diffusivity and solubility) of CO2 in the membrane are expected to be enhanced. Since
this study fabricates a unique configuration of SILM, the modification of the
Resistance-in-Series model is necessary to accurately determine SILM performance.
Considering the model's reliance on the permeability data of each composite layer, the
first objective of this study focused on investigating ZIF-L@PDMS layer
independently. The impact of filler shape, IL type, suitable IL impregnation method
and gas transport properties of the ZIF-L@PDMS layer were investigated. The usage
of 5 wt% ZIF-L and 0.2M IL enhanced the separation performance of ZIF-L@PDMS.
The membrane recorded CO2 permeability, CO2/N2 selectivity and CO2/CH4
selectivity of 5017 Barrer, 36.46 and 23.22, respectively. The time lag analysis
confirmed the performance of the IL-modified ZIF-L@PDMS was enhanced due to
improved CO2 solubility. Furthermore, the performance data of ZIF-L@PDMS layer
was found to be well-fitted by the modified Cussler model that considered aspect ratio.
The subsequent phase involved optimizing the coating conditions of ZIF-L@PDMS/PES hollow fiber membranes using a Box-Behnken design (BBD). The
optimized conditions (4.70 wt% PDMS, 5 mm/s withdrawal speed, 74 s holding time,
and a 1.5:1 ZIF-L:PDMS ratio) were then employed to fabricate ZIF-L@PDMS/PES
SILM through post-modification method. The SILM recorded 10.56 GPU of CO2
permeance for pure gas fed at 375 cmHg. Furthermore, the selectivity of CO2/N2 and
CO2/CH4 is 42.97 and 21.78, respectively. The combination of the modified Cussler
and Resistance-in-series models accurately determined ZIF-L@PDMS/PES SILM
performance, at an average absolute relative error (AARE) of less than 5%, even
during long operating hours. Minimal error was obtained via the modification of
Resistance-in-Series model that considered surface porosity and pore penetration
depth. For binary gas feed, the modified Resistance-in-series model was coupled with
the operational model to predict ZIF-L@PDMS/PES SILM performance at various
CO2 compositions and feed pressures. This approach estimated the performance of
SILM at minimal AARE (<5%) for binary gas separation. At 18 mol% CO2, the
membrane recorded CO2/N2 and CO2/CH4 selectivity of 28.56 and 19.30, respectively.