Mixed matrix membranes (MMMs) have gained importance because they combine the desirable
properties of the polymers and the organic/inorganic filler materials and they may have a very big
potential. In this study polyethersulfone (PES) was used as polymeric material, and Zeolitic
Imidazolate Framework-8 (ZIF-8) was used as porous filler material, and 2-hydroxy 5-methyl
aniline(HMA), was used as a third component in membrane formulation.
In this study, ZIF-8 crystals were synthesized with varying particle sizes, and a novel recycling
methodology was developed to improve the efficiency of ZIF-8 production. ZIF-8 nano-crystals were
synthesized by a 1-hour stirring method at room temperature and characterized by X-ray
diffractometer, scanning electron microscopy (SEM), transmission electron microscopy (TEM),
dynamic light scattering (DLS) and thermal gravimetric analysis (TGA). In order to investigate the
effect of ZIF-8 loading on the membrane performance, different types of membranes were prepared
with varying amounts of ZIF-8 between 10-60% (w/w). Moreover, ternary mixed matrix membranes
were synthesized consisting of different amounts of ZIF-8 between 10-30% (w/w) and HMA 1-10%
(w/w). Gas transport properties of the membranes were investigated by single gas permeation
experiments of H2, CO2 and CH4 at 3 bar feed pressure. In order to investigate the effect of feed
pressure on the gas transport properties of the membranes, single gas experiments were conducted on
3, 6, 8, 10 and 12 bar feed pressures. Moreover, binary gas permeation experiments of CO2/CH4 pair
were conducted through selected membranes at 3 bar and 12 bar feed pressures. In addition to gas permeation experiments, the morphology and thermal characteristics of the membranes were
characterized by SEM, TGA and differential scanning calorimetry (DSC) analysis.
The incorporation of ZIF-8 crystals into continuous PES matrix resulted in high performance gas
separation membranes. The permeabilities of all studied gases increased with ZIF-8 loading while the
ideal selectivities showed a slight decrease compared to neat PES membrane. Highly reproducible and
repeatable results were obtained up to 30 % w/w ZIF-8 loading, while membrane formulation
reproducibility was decreased for higher ZIF-8 contents (> / 30 w/w %). Addition of HMA improved
the gas separation performances of the binary membranes significantly by decreasing permeabilities
and increasing ideal selectivities. PES/ZIF-8(%20)/HMA(%7) membrane has the best separation
performance for all gases among the ternary membranes. When 7 w/w % HMA was added to
PES/ZIF-8(%20) membrane, H2 permeability decreased from 26.3 to 13.7 barrer, while H2/CH4 ideal
selectivity increased from 61.8 to 103.7.
Increasing feed pressures appreciably increased the separation performances of all membranes. While
the H2 permeability is pressure independent, the CO2 and CH4 permeabilities were reduced with
increasing feed pressures and the highest selectivity improvement was observed in H2/CH4 pair for all
membrane compositions. For instance, when the feed pressure was increased from 3 bar to 12 bar, the
percentage improvements in ideal selectivities through PES/ZIF-8(%10)/HMA(%4) membrane were
calculated as 26, 69, 113 % for the H2/CO2, CO2/CH4 and H2/CH4 gas pairs / respectively. This results
show that working at higher feed pressures will be more advantageous for separation of the studied
gas pairs. The ideal selectivities and the separation factors were equal to each other for all membrane
compositions both for 3 and 12 bar operating pressures.
| Identifer | oai:union.ndltd.org:METU/oai:etd.lib.metu.edu.tr:http://etd.lib.metu.edu.tr/upload/12614571/index.pdf |
| Date | 01 August 2012 |
| Creators | Keser, Nilay |
| Contributors | Yilmaz, Levent |
| Publisher | METU |
| Source Sets | Middle East Technical Univ. |
| Language | English |
| Detected Language | English |
| Type | M.S. Thesis |
| Format | text/pdf |
| Rights | To liberate the content for public access |
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