• 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.

• Korean Chemical Engineering Research
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• v.48 no.5
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• pp.660-667
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• 2010

In this research polyimide, Matrimid 5218, hollow fiber membrane was used to recover sulfur hexafluoride($SF_6$) which is one of the six greenhouse gases from $N_2/SF_6$ mixture gas. Fibers were spun from using dry-wet phase inversion method. The module was manufactured by fabricating fibers after surface coating with silicone elastomer. The scanning electron microscopy(SEM) studies showed that the produced fibers typically had an asymmetric structure; a dense top layer supported by a sponge-like substructure. The developed module had a permeance of 0.78-1.36 GPU for $N_2$ with $N_2/SF_6$ selectivity of 2.44-5.08 at various pressure and temperature. For recovery of $SF_6$, a membrane module and 10 vol.% $SF_6$ from $N_2/SF_6$ mixture gas was used. The effects of various operating condition such as pressure, temperature, and retentate side flow rate were tested. When pressure and temperature were increased and retentate flow rate was decreased, the $SF_6$ purity in recovered gas was increased up to 37.5 vol.% with decreasing recovery ratio. When retentate flow rate was increased pressure and temperature was decreased, the $SF_6$ recovery ratio in retentate side was increased up to 89% with decreasing the $SF_6$ purity in retentate side.

• Membrane Journal
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• v.14 no.2
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• pp.166-172
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• 2004

As a preliminary study for esterification membrane reactor used to produce 2,2,2-trifluoroethylmetacrylate (TFEMA), Pervaporation behaviors with crosslinked Poly(vinyl alcohol) composite membranes were investigated for aqueous TFEA (2,2,2-trifluoroethanol) feed solutions. In this study, crosslinked PVA composite membranes were prepared by reacting PVA with glutaraldehyde (CA)/acid catalyst onto porous polyethersulfone (PES) supports. SEH images (scanning electron microscopy) showed the thicknesses of selective coating layer was about 2-3 ${\mu}{\textrm}{m}$. The swelling tests showed the dogree of crosslinking decreased as content of the crosslinking agent, GA, increased. Total permeation flux decreased while separation factor increased as the CA content increased. As operating temperature increased, total permeation flux remarkably increased in the range of 85-95 wt% TFEA aqueous solutions. Interestingly, however, separation factor decreased in 85-90 wt% with operating temperature, while that increased in 95 wt%. In case of 90 wt% TFEA concentration and operating temperature 8$0^{\circ}C$, the PVA composite membrane crosslinked with 0.1 mol GA per PVA repeating unit showed high permeation flux of 1.5 kg/$m^2$hr and separation factor of 320. These results confirmed the applicability of the PVA composite membranes for the esterification membrane reactor of TFEMA.

• Membrane Journal
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• v.15 no.3
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• pp.206-212
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• 2005

Acid-resistant poly(vinyl alcohol) (PVA) membranes connected with ethylene and ether groups were prepared via a thermal crosslinking reaction by varying the ratio of PVA to ethylene glycol diglycidyl ether (EGDE). The crosslinked membranes were characterized using FT-IR and swelling tests, respectively. Pervaporation behaviors with the PVA membranes were investigated for aqueous TFEA (2,2,2-trifluoroethanol) as a function of EGDE content and operating temperature. The pervaporation properties far MA (methacrylic acid)/water mixture were also carried out with the optimized PVA membrane. The PVA membranes prepared with EGDE showed more excellent acid-resistance than those crosslinked with gluaraldehyde. The membranes showed high permeation fluxes of 0.1 and $0.3\;km^2h$ and high separation factors of 100 and 900 in the $96\;wt\%$ TFEA and MA aqueous fred mixtures at high temperature above $80^{\circ}C$, respectively. These confirmed theses membranes could be used in esterification membrane reactor process for the production of 2,2,2-trifluoroethylmetacrylate (TFEMA).

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.9
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• pp.31-36
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• 1999

A capacitance-type sensor using porous silicon layer is developed to measure aqueous alcohol concentration. Since alcohol, so called ethanol, is very permeable into the silicon wafer, it is often used to help chemical reaction when the silicon wafer is processed under some aqueous solution. In this work, the sensing property was measured for the alcohol concentration from zero to near 100 percent with two types of samples with porous silicon layer formed in 25 and 35% HF solution, respectively. Good reliability as well as fast response time and good linearity were shown over 10kHz and the measured capacitance was observed to be inverse to alcohol concentration due to the decrease of the whole dielectric constant in porous silicon layer.

• Korean Journal of Environmental Agriculture
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• v.7 no.2
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• pp.130-135
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• 1988

The study was performed to evaluate the usefulness of windbreaks to reduce the effect of sulfur dioxide and hydrogen fluoride on the growth of rice plants. It was observed that various pollution indicators such as the ambient concentrations of sulfur oxide and fluoride, sulfur and fluorine contents found in leaves appear to be significantly reduced within 3 meters behind the break. In that region yield components seemed normal. It is, however, observed that the pollutional indicators appear to increase gradually back to the same level as they were on the upwind side of the break. As for the relationships between pollution indicators and yields and also yield components it was believed that pollutants found in leaves might serve as the most important indicators of pollutional damage to rice plant Cultivation in fields. There was high correlation between ambient concentrations and yield, and also yield components. More significantly, a better correlation seemed to exist between sulfur and fluorine contents observed in leaves and yield ; And between those contents and yield components.

• Journal of Korean Society of Environmental Engineers
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• v.33 no.1
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• pp.47-53
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• 2011

$SF_6$ (Sulfur hexafluoride) possesses high GWP (Global Warming Potential) as sepcified by the IPCC (Intergonvernmental Panel of Climate Change). Recently, the recovery-separtion of $SF_6$ research area, including permeation properties studies using various membrane's materials and the practical operation of recovery-separtion using membrane of waste $SF_6$ gas is in the initial state. The separation efficiency of a single $SF_6$ and waste $SF_6$ mixture was evaluated using a PSF (polysulfone), PC (tetra-bromo polycarbonate) and PI (polyimide) hollow fiber membranes. According to the results of single gases permeation properties, PI membrane has the highest permselectivity of $N_2$ gas in $N_2/SF_6$ gas. Under the condition of P=0.5 MPa, the highest concentration of recovered $SF_6$ is 95.6 vol % in the separation experiment of $SF_6/N_2$ mixture gas by PC membrane. Under the operation pressure of P=0.3 MPa at a fixed retentate flow rate fixed of 150 cc/min, the maximum recovery efficiency of $SF_6$ is up to 97.8% by PSF membrane. From the results above, it is thought that the separation and recovery technique of $SF_6$ gas using membrane will be used as the representative eco-technology in the $SF_6$ gas treatment in the future.

• 한국신재생에너지학회:학술대회논문집
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• 2008.05a
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• pp.602-605
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• 2008

$CO_2$ 분리는 크게 연소전 탈탄소화(pre-combustion capture)와 연소후 포획(post-combustion capture)으로 나누어지는데, post-combustion capture는 연료가 연소하면 $N_2$와 $CO_2$가 남게 되고 흡수나, 흡착, 막분리 등을 이용해서 $CO_2$를 분리하는 것이고, Pre-combustion capture(연소전 회수)는 연소 전에 이산화탄소가 발생되지 않도록 하는 기술로써, 부분 산화나 개질 및 수성가스 변위반응 등이 포함되며 생성된 수소와 이산화탄소를 분리하여 수소를 생산하는 기술($CO_2/H_2$ 분리가 핵심)이다. 우리나라는 대부분 연소 후 포획 위주로 많은 연구가 진행되어 왔지만, 최근 고유가 시장이 형성되면서 석탄화력발전 및 복합가스발전(IGCC)에 필요한 연소전 탈탄소화($H_2/CO_2$ 가스로부터 $CO_2$ 회수) 연구에 산업적 관심이 급상승 되고 있다. 특히, Pre-combustion 과정에서는 높은 자체압력(약 2.5 - 5.0MPa)과 비교적 높은 농도의 $CO_2$(약 40%의)가 발생되기 때문에, 연소전 탈탄소화는 가스하이드레이트 형성/분해 원리가 가장 잘 적용될 수 있는 기술이라 할 수 있다. 본 연구에서는 비교적 저압 조건에서도 하이드레이트를 보다 쉽게 형성시키는 촉진제를 이용하여 $CO_2/H_2$ 혼합 가스 중 $CO_2$를 분리하는 실험을 수행하였다.

• Journal of the Korean Vacuum Society
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• v.22 no.6
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• pp.277-284
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• 2013

Carbon coils could be synthesized using $C_2H_2/H_2$ as source gases and $SF_6$ as an incorporated additive gas under thermal chemical vapor deposition system. The Ni layer on the $SiO_2$ substrate was used as a catalyst for the formation of the carbon coils. The characteristics (formation densities, morphologies, and geometries) of the as-grown carbon coils on the substrate with or without the $H_2$ plasma pretreatment process were investigated. By the relatively short time (1 minute) $H_2$ plasma pretreatment on the Ni catalyst layered-substrate prior to the carbon coils synthesis reaction, the dominant formation of the carbon microcoils on the substrate could be achieved. After the relatively long time (30 minutes) $H_2$ plasma pretreatment process, on the other hand, we could obtain the noble-shaped geometrical nanostructures, namely the formation of the numerous carbon nanocoils along the growth of the carbon microcoils. This noble-shaped geometrical nanostructure seemed to play a promising role as the good catalyst support for holding the very tiny Ni catalyst grains.

• Membrane Journal
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• v.26 no.2
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• pp.159-165
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• 2016

Polyimide hollow fiber membrane modules were prepared in order to investigate the process of multi stage gas separation. The modules performance was carried out using 50/50 of $N_2/SF_6$ mixed gas. The membrane modules has been tested for measuring gas flow rate and concentration under various stage cut at 0.5 MPa. The membrane modules showed a high recovery ratio at the same stage cut as $N_2/SF_6$ selectivity increased. Two stage process was fulfilled for improving $SF_6$ recovery ratio and $SF_6$ concentration. Eventually, two stage process showed higher performance of $SF_6$ recovery ratio and concentration ($SF_6$ recovery ratio = 95%, $SF_6$ conc. = 98%).