• Proceedings of the Membrane Society of Korea Conference
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• 1999.07a
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• pp.39-42
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• 1999

Perfluoropolymers represent the ultimate resistance to hostile chemical environments and high service temperature, attributed to the presence of fluorine in the polymer backbone, i.e. to the high bond energy of C-F and C-C bonds of fluorocarbons. Copolymers of Tetrafluoroethylene (TEE) and 2, 2, 4Trifluoro-5Trifluorometoxy- 1, 3Dioxole (TTD), commercially known as HYFLON AD, are amorphous perfluoropolymers with glass transition temperature (Tg)higher than room temperature, showing a thermal decomposition temperature exceeding 40$0^{\circ}C$. These polymer systems are highly soluble in fluorinated solvents, with low solution viscosities. This property allows the preparation of self-supported and composite membranes with desired membrane thickness. Symmetric and asymmetric perfluoropolymer membranes, made with HYFLON AD, have been prepared and evaluated. Porous and not porous symmetric membranes have been obtained by solvent evaporation with various processing conditions. Asymmetric membranes have been prepared by th wet phase inversion method. Measure of contact angle to distilled water have been carried out. Figure 1 compares experimental results with those of other commercial membranes. Contact angles of about 120$^{\circ}$for our amorphous perfluoropolymer membranes demonstrate that they posses a high hydrophobic character. Measure of contact angles to hexandecane have been also carried out to evaluate the organophobic character. Rsults are reported in Figure 2. The observed strong organophobicity leads to excellent fouling resistance and inertness. Porous membranes with pore size between 30 and 80 nanometers have shown no permeation to water at pressures as high as 10 bars. However high permeation to gases, such as O2, N2 and CO2, and no selectivities were observed. Considering the porous structure of the membrane, this behavior was expected. In consideration of the above properties, possible useful uses in th field of gas- liquid separations are envisaged for these membranes. A particularly promising application is in the field of membrane contactors, equipments in which membranes are used to improve mass transfer coefficients in respect to traditional extraction and absorption processes. Gas permeation properties have been evaluated for asymmetric membranes and composite symmetric ones. Experimental permselectivity values, obtained at different pressure differences, to various single gases are reported in Tab. 1, 2 and 3. Experimental data have been compared with literature data obtained with membranes made with different amorphous perfluoropolymer systems, such as copolymers of Perfluoro2, 2dimethyl dioxole (PDD) and Tetrafluorethylene, commercialized by the Du Pont Company with the trade name of Teflon AF. An interesting linear relationship between permeability and the glass transition temperature of the polymer constituting the membrane has been observed. Results are descussed in terms of polymer chain structure, which affects the presence of voids at molecular scale and their size distribution. Molecular Dyanmics studies are in progress in order to support the understanding of these results. A modified Theodoru- Suter method provided by the Amorphous Cell module of InsightII/Discover was used to determine the chain packing. A completely amorphous polymer box of about 3.5 nm was considered. Last but not least the use of amorphous perfluoropolymer membranes appears to be ideal when separation processes have to be performed in hostile environments, i.e. high temperatures and aggressive non-aqueous media, such as chemicals and solvents. In these cases Hyflon AD membranes can exploit the outstanding resistance of perfluoropolymers.

• Membrane Journal
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• v.22 no.6
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• pp.404-414
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• 2012

In order to investigate $SO_2$ removal, PEI hollow fiber membranes were produced by a dry-wet phase inversion method. The membrane support layer on surface was coated with PEBAX1657$^{(R)}$ and PEG blending materials. Modules were prepared for the single gas permeation characteristics of composite membrane according to temperature and pressure. As a result, $SO_2$ permeance and $SO_2/N_2$ selectivity were 220~1220 GPU and 100~506 through operating condition, respectively. Moreover, $SO_2/CO_2/N_2$ mixture gas was used to compare the performance of separation properties according to temperature, pressure and retentate flow rate difference. $SO_2$ removal efficiency was increased with pressure and temperature.

• Membrane Journal
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• v.20 no.3
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• pp.210-216
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• 2010

The hydrogen permselective membrane were prepared by chemical vapor deposition (CVD) aiming at the applications to hydrogen iodide decomposition in the thermochemical IS process, and it was evaluated for the possibility as a separation membrane. An electron probe X-ray microanalyzer (EPMA) and SEM picture were used to analyze the morphology and structure of the prepared membranes. It was confirmed that Zr-Si-O layer exist in the surface of the prepared membrane using zirconia coated support. Single-component permeance to $H_2$ and $N_2$ were measured at $300{\sim}600^{\circ}C$. Hydrogen permeance through the Z-1 membrane at a permeation temperature of $600^{\circ}C$ was about $1{\times}10^{-7}\;mol{\cdot}Pa^{-1}{\cdot}m^{-2}{\cdot}s^{-1}$. The selectivities of $H_2/N_2$ at $600^{\circ}C$ were 5.0 and 5.75 for Z-1 and Z-2 membrane, respectively.

• Membrane Journal
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• v.14 no.3
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• pp.201-206
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• 2004

The stability of the prepared silica membrane by chemical vapor deposition (CVD) method in the HI-$H_2O$ gaseous mixture was evaluated aiming at the application for hydrogen iodide decomposition in the thermochemical IS process. Porous $\alpha$-alumina having pore size of 100 nm was modified by the different CVD temperature using tetraethoxysilane as the Si source. The CVD temperature was $700^{\circ}C$, $650^{\circ}C$, and $600^{\circ}C$. The $H_2$/H$_2$ selectivities of the modified membranes which were measured by single-component permeation experiment showed 43.2, 12.6, and 8.7 at $600^{\circ}C$ for the M1 (CVD temperature was $700^{\circ}C$), M2 (CVD temperature was $650^{\circ}C$) and M3 membranes (CVD temperature was $600^{\circ}C$), respectively. Stability experiment in the HI-$H_2O$ gaseous mixture was carried out at $450^{\circ}C$. The prepared silica membrane at $600^{\circ}C$ of CVD temperature was more stable than that at the other CVD temperature.

• Journal of the Korean Electrochemical Society
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• v.6 no.1
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• pp.59-64
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• 2003

We fabricated mixed ionic-electronic conducting membranes, $CH_4\;Using\;{0.7}Sr_{0.3}Ga_{0.6}Fe_{0.4}O_{3-\delta}$, by solid state reaction method for solid oxide fuel cell. The membranes consisted of single perovskite phase and exhibited high relative density, $>95\%$. We coated $La_{0.6}Sr_{0.4}CoO_{3-\delta}$ layer using screen printing method in order to improve surface reactivity of the $La_{0.7}Sr_{0.3}Ga_{0.6}Fe_{0.4}O_{3-\delta}$. As a result, the oxygen permeation flux of the coated $La_{0.7}Sr_{0.3}Ga_{0.6}Fe_{0.4}O_{3-\delta}$ showed higher value, $0.5ml/min{\cdot}cm^2\;at\;950^{\circ}C$ than the uncoated one. Higher oxygen permeation was observed in the porously coated Lao $La_{0.7}Sr_{0.3}Ga_{0.6}Fe_{0.4}O_{3-\delta}$membranes with larger grain sizes. Syngas, $CO+H_2$, was successfully obtained from methane gas, $CH_4$, using the $La_{0.6}Sr_{0.4}CoO_{3-\delta}$ coated $La_{0.7}Sr_{0.3}Ga_{0.6}Fe_{0.4}O_{3-\delta}$, with over $40\%\;of\;CH_4$ conversion and syngas yield. $La_{0.7}Sr_{0.3}Ga_{0.6}Fe_{0.4}O_{3-\delta}$ membrane was stable even when it was exposed to the reducing environment, methane, for 600 hrs at $950^{\circ}C$.

• Membrane Journal
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• v.28 no.6
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• pp.432-443
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• 2018

In this study, propylene/propane separation behavior of Na-type faujasite zeolite membranes is predicted by observing gravimetric adsorptions of propylene and propane on zeolite 13X. The gravimetric adsorptions were measured by using a magnetic suspension balance (MSB) at temperatures of 323, 343, 363 K and a pressure range of 0.02-1 bar. The pressure was increased at 0.1 bar intervals. As adsorption temperature increased, adsorptions of propylene and propane decreased and propylene/propane adsorption selectivity increased. Also, the diffusion coefficients of propylene and propane were increased as the adsorption temperature increased, following the Arrhenius equation. The maximum propylene/propane diffusion selectivity was 0.9753 at 323 K. The perm-selectivity was calculated from the adsorption data of zeolite 13X and compared with the perm-selectivity measured in the single gas permeation experiment for the Na-type faujasite zeolite membrane. The maximum values for the calculated and measured perm-selectivities were observed at a temperature of 323 K. It could be concluded that the prediction of propylene/propane separation of surface diffusion-based membrane by using gravimetric adsorption data is reasonable. Therefore, it is expected that this prediction method can be applied to the screening of adsorption-based microporous membrane for propylene/propane separation.