• Membrane Journal
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• v.18 no.1
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• pp.65-74
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• 2008

NOM and fine particles are the main target materials in water treatment using membranes. Particularly, humic substances extracted from soils are frequently used in many fundamental studies representing natural organic matter in raw water for drinking water treatment. In this study, ultrafiltration (UF) of artificial humic water and natural river water was conducted and the characteristics of removal efficiency and permeability were compared. In the UF of river water, the transmembrane pressure increased in the same pattern with that of 5 mg/L humic water. For the removal of organic matter and fine particles, however, two types of feed water had shown different trends. Kaolin particles and humic acids added to artificial water were better removed, while colloids and organics in natural water were relatively poorly removed. From the $UV_{254}$ and GPC analyses, it seemed that the hydrophobicity and size of humic substances contributed to the greater removal of organic matter. The UF membrane applied for humic water also showed a higher flux recovery by caustic chemical cleaning than that for river water.

• Membrane Journal
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• v.27 no.5
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• pp.389-398
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• 2017

The most important characteristic of the polymer electrolyte membranes (PEMs) for fuel cells, the proton conducting ability is mainly influenced by the distribution and morphology of the water channels inside the PEMs. Non-perfluorinated hydrocarbon PEMs are known to have weaker water channels than perfluorinated PEM, Nafion, and thus relatively low proton conducting ability. In this study, we used a mesoscale simulation technique to observe the water channel formation and phase separation behavior of hydrocarbon PEM, sulfonated polyimides, under the humidification condition. It was observed that the water molecules were distributed evenly through the entire hydrophilic region, and clear water clusters were formed only in the sulfonated polyimide having high sulfonation degree. In addition, it was observed that sulfonated polyimides have a difficulty in forming water channel under the low hydrated condition. These results clearly support the theories of the formation of water channels in non-perfluorinated hydrocarbon PEMs, and also well explain the tendency of proton conducting abilities of sulfonated polyimides. Thus, it is confirmed that mesoscale simulation techniques can be very effective in analyzing phase separation behavior and water channel formation in PEMs for fuel cells and elucidating the ion conducting abilities.

• Membrane Journal
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• v.26 no.2
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• pp.126-134
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• 2016

To produce renewable biomethane from biogas, the properties of physical absorbents such as water, methanol, 1-methyl-2-pyrrolidone (NMP), poly(ethylene glycol) dimethylether (PEGDME), and propylene carbonate (PC) were studied, and PC was applied to membrane contactor systems. Among physical absorbents, PC exhibited a high contact angle of $58.3^{\circ}$ on polypropylene surface, and a PC/water mixture (5 wt%) increased the contact angle to $90^{\circ}$. Furthermore, the PC/water mixture presented higher $CO_2$ absorption capacities (0.148-0.157 mmol/g) than that of water (0.121 mmol/g), demonstrating a good property as an absorbent for membrane contactors. Actual operations in membrane contactors using the PC/water mixture resulted in $CO_2$ removal of 98.0-97.8% with biomethane purities of 98.5-98.3%, presenting a strong potential for biogas treatment. However, the PC/water mixture yielded moderate improved in $CO_2$ removal and methane recovery, as compared with water in the membrane contactor operation. This is originated from insufficient desorption processes to reuse absorbent and low $CO_2$ flux of the PC/water absorbent. Thus, it is requiring optimizations of membrane contactor technology including development of absorbent and improvement of operation process.

• Membrane Journal
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• v.22 no.3
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• pp.224-233
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• 2012

To improve permeation performance of gas separation membrane, polysulfone hollow fiber membrane was prepared by wet-dry phase inversion method using Triton X-100 as non-ionic additive. And variation of gas permeation behavior by additive was investigated. Various spinning conditions such as air gap, concentration of polymer, dope tank temperature were controlled and these effects were studied. The morphology and gas permeation property of hollow fiber membranes were investigated using scanning electron microscope (SEM) and bubble flow meter respectively. We confirmed that the membranes added with Triton X-100 had a smooth external skin at various air gap length conditions. The macrovoids of these hollow fiber membranes were more developed with increase of air-gap from 4 to 90 cm and that induced higher permeance. The permeance of polysulfone membranes has the higher value at comparatively lower concentration polymer (30 wt% polysulfone) and lower concentration of additive (15 wt% Triton X-100). When temperature in dope tank was controlled, the membranes prepared at $100^{\circ}C$ showed low permeance because of volatilization of additive and solvent.

• Membrane Journal
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• v.21 no.4
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• pp.377-388
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• 2011

Flat sheet microfiltration membranes were prepared with polysulfone (PSF), polyethersulfone (PES), and polyphenylsulfone (PPS) by an immersion precipitation phase inversion method. In this method, dimethyl formamide (DMF) and polyvinylpyrrolidone (PVP) were used as a solvent and a wetting polymer additive, respectively. 2-butoxyethanol (BE) was used as a nonsolvent additive catalyst to form pore. The morphology of membranes was investigated by scanning electron microscopy and micropermporometer. The permeability of the membranes was evaluated with the flux of pure water. When the BE was added, the pore size of membranes became larger than blank membranes. The changes in the morphology of membrane due to the BE addition depend on polymer structure. All membranes have similar mean pore size and porosity. The mean pore sizes of PSF, PES, and PPS membranes were 0.282, 0.330 $0.308{\mu}m$, respectively. The porosities of PSF, PES and PPS membranes were 68.5, 66.1, 66.4%, respectively. However, the PPS membrane showed higher pore density on surface and narrower pore size distribution than PSF or PES membrane does. As a result, the pure water flux of PPS membrane ($357L/m^2\;hr$) was higher than that of PSF ($196L/m^2\;hr$) or PES membrane ($214L/m^2\;hr$).

• Membrane Journal
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• v.19 no.4
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• pp.341-347
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• 2009

Nanohybrid based on environmentally friendly and biodegradable polymer, poly propylene carbonate (PPC) and cloisite 20B (PPC/C-20B) have been synthesized by solution blending method and their morphology, thermal and water absorption properties have been evaluated. The structure of PPC/C-20B nanohybrid was confirmed by X-ray diffraction (XRD). The thermal property of PPC and PPC/C-20B nanohybrid were investigated by thermal gravimetric analysis (TGA) and differential scanning calorimetric (DSC). The experimental results demonstrated that nanohybrid showed the highest thermal stability in TGA and DSC. TGA tests revealed that the thermal decomposition temperature ($T_{d50%}$) of the nanohybrid increased significantly, being $23^{\circ}C$ higher than that of pure PPC while DSC measurements indicated that the introduction of 5 mass% of clay increased the glass transition temperature from 21 to $30^{\circ}C$. Further the water absorption capacity of the PPC was significantly decreased by the incorporation of clay. Water absorption cause degradation of the coating by the moistures and affect the physical and mechanical performance. This result indicates that organic modifiers have effect on thermal and water absorption capacity of PPC and are of importance for the practical process and application of PPC.

• Membrane Journal
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• v.25 no.5
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• pp.398-405
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• 2015

Facilitated transport is considered to be a possible solution to simultaneously improve permeability and selectivity, which is challenging in normal polymeric membranes based on solution-diffusion transport only. We investigated the effect of adding mesoporous $TiO_2$ ($m-TiO_2$) upon the separation performance of facilitated olefin transport membranes comprising poly(vinyl pyrrolidone), Ag nanoparticles, and 7,7,8,8-tetracyanoquinodimethane as the polymer matrix, olefin carrier, and electron acceptor, respectively. In particular, $m-TiO_2$ was prepared by means of a facile, mass-producible method using poly(vinyl chloride)-g-poly(oxyethylene methacrylate) graft copolymer as the template. The crystal phase of $m-TiO_2$ consisted of an anatase/rutile mixture, of crystallite size approximately 16 nm as determined by X-ray diffraction. The introduction of $m-TiO_2$ increased the membrane diffusivity, thereby increasing the mixed-gas permeance from 1.6 to 16.0 GPU ($1GPU=10^{-6}cm^3$(STP)/($s{\times}cm^2{\times}cmHg$), and slightly decreased the propylene/propane selectivity from 45 to 37. However, both the mixed-gas permeance and selectivity of the membrane containing $m-TiO_2$ rapidly decreased over time, whereas the membrane without $m-TiO_2$ had more stable long-term performance. This difference might be attributed to specific chemical interactions between $TiO_2$ and Ag nanoparticles, causing Ag to lose activity as an olefin carrier.

• Membrane Journal
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• v.25 no.5
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• pp.406-414
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• 2015

In this study, partially fluorinated cation exchange membranes were prepared by direct sulfonation of Poly(VDF-co-hexafluoropropylene) copolymers (PVDF-co-HFP) followed by a casting method for application in the Membrane capacitive deionization (MCDI). The structure of sulfonated PVDF-co-HFP (SPVDF) was confirmed by Fourier-transform infrared (FT-IR) and $^1H$ Nuclear magnetic resonance ($^1H$ NMR) analysis. For quantitative analysis of the chemical composition, the X-ray Photoelectron Spectroscopy (XPS) was used. The membrane properties such as water uptake, ion exchange capacity and electrical resistance were measured. It was suggested that the optimum direct sulfonation condition of PVDF-co-HFP ion exchange membranes was $60^{\circ}C$ and 7 hours for temperature and duration of sulfonation, respectively. The water uptake of the SPVDF ion exchange membrane was 21.5%. The ion exchange capacity and electrical resistance were 0.89 meq/g and $3.70{\Omega}{\cdot}cm^2$, respectively. It was investigated that if it is feasible to apply these membranes in MCDI at various cell potentials (0.9~1.5 V) and initial flow rates (10~40 mL/min). In the MCDI process, the maximum salt removal rate was 62.5% in repeated absorption-desorption cycles.

• Membrane Journal
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• v.31 no.6
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• pp.443-455
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• 2021

In this study, polyphenylene sulfide (PPS) was used as a support and a separator was manufactured using polysulfone and inorganic additives to manufacture a separator with low membrane resistance for application of an alkali water electrolysis system, and then the effect on the thickness and porosity of the support was analyzed. The PPS felt used as a support was compressed with variables of temperature (100℃, 150℃, 200℃) and pressure (1 ton, 2 tons, 3 tons, 5 tons) to adjust the thickness. A porous separator could be manufactured by preparing a slurry with polysulfone using BaTiO₃ and ZrO₂ which have high hydrophilicity and excellent alkali resistance as inorganic particles and casting the slurry on a compressed PPS felt. Changes in morphology of the separator according to compression conditions were confirmed through an electron scanning microscope (SEM). After that, the porosity was calculated, and the thickness and porosity tended to decrease as the compression conditions increased. Various characteristics were evaluated to confirm whether it could be used as a separator for water electrolysis. As a result of measuring the mechanical strength, it was confirmed that the tensile strength gradually increased as the compression conditions (temperature and pressure) increased. Finally, it was confirmed that the porous separator manufactured through the alkali resistance test has excellent alkali resistance, and through the IV test, it was confirmed that the membranes compressed at 100℃ and 150℃ had a lower voltage and improved performance than the existing uncompressed membrane.

• Membrane Journal
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• v.32 no.6
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• pp.442-455
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• 2022

High-temperature polymer electrolyte membrane fuel cell (HT-PEMFC) has been studied as an alternative to low-temperature PEMFC due to its fast activation of electrodes and high resistance to electrode poisoning by carbon monoxide. It is highly required to develop stable PEMs operating at high temperatures even doped by ion-conducting materials for the development of high-performance and durable HT-PEMFC systems. A number of studies have been conducted to develop polybenzimidazole (PBI)-based PEMs for applications in HT-PEMFC due to their high interaction with doped ion-conducting materials and outstanding thermomechanical stability under high-temperature operation. This review focused on the development of PBI-based PEMs showing high performance and durability. Firstly, the characteristic behavior of PBI-based PEMs doped with various ion-conducting materials including phosphoric acid was systematically investigated. And then, a comparison of the physicochemical properties of the PEMs according to the different membrane manufacturing processes was conducted. Secondly, the incorporation of porous polytetrafluoroethylene substrate and/or inorganic composites to PBI matrix to improve the membrane performances was studied. Finally, the construction of cross-linked structures into PBI-based PEM systems by polymer blending method was introduced to improve the PEM properties.