• Journal of Mechanical Science and Technology
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• 제20권2호
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• pp.242-250
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• 2006

Detailed structures of the counterflow flames formed for different inlet fluid temperatures and different amount of additives are studied numerically. The detailed chemical reactions are modeled by using the CHEMKIN-II code. The discrete ordinates method and the narrow band based WSGGM with a gray gas regrouping technique (WSGGM-RG) are applied for modeling the radiative transfer through non-homogeneous and non-isothermal combustion gas mixtures generated by the counterflow flames. The results compared with those obtained by using the SNB model show that the WSGGM-RG is very successful in modeling the counterflow flames with non-gray gas mixture. The numerical results also show that the addition of $CO_2\;or\;H_2O$ to the oxidant lowers the peak temperature and the NO concentration in flame. But preheat of fuel or oxidant raises the flame temperature and the NO production rates. $O_2$ enrichment also causes to raise the temperature distribution and the NO production in flame. And it is found that the $O_2$ enrichment and the fuel preheat were the major parameters in affecting the flame width.

• 한국수소및신에너지학회논문집
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• 제21권6호
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• pp.500-506
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• 2010

The metal monolith catalyst coated with 15wt% Ni/$MgAl_2O_4$ is applied to the natural gas steam reforming for hydrogen production. To address the improvement of adherence between metal monolith and catalyst coating layer, the pre-calcination temperature as well as the coating conditions of $Al_2O_3$ sol are optimized. When the Fe-Cr alloy monolith is pre-calcined at $900^{\circ}C$ for 6 h, $Al_2O_3$ layer was formed uniformly on the entire surface of the metal substrate. It is seen that the formation of $Al_2O_3$ layer on the monolith surface is essential for the uniform coating of $Al_2O_3$ sol onto the monolith substrate. The monolith catalyst coated with 10wt% $Al_2O_3$ sol shows high $CH_4$ conversion and good thermal stability as compared with the monolith catalyst without $Al_2O_3$ sol coating under severe reaction conditions with high GHSV of 30,000 $h^{-1}$ at $700^{\circ}C$. In addition, the metal monolith catalyst shows higher catalytic activity and better thermal conductivity than 15wt% Ni/$MgAl_2O_4$ pellet catalyst.

• 한국응용과학기술학회지
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• 제33권2호
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• pp.286-292
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• 2016

화장품용 방부제로 사용하고 있는 1, 2-hexanediol (HD)에 높은 농도의 lactose (300 g/l)를 넣고, 재조합 대장균 ${\beta}$-galactosidase (${\beta}$-gal)를 이용하여 galactose 한 분자를 결합시키는 transgalactosylation 반응을 시켜서, 1, 2-hexanediol galactoside (HD-gal)을 합성하였다. 그리고, 합성된 HD-gal 분자를 확인하기 위하여, HD-gal에 대한 NMR ($^1H$- and $^{13}C$-) 스펙트럼 분석과 mass 스펙트럼 분석을 실시하였다. HD-gal의 $^1H$ NMR 스펙트럼에서 HD에 갈락토실화가 되었음을 보여주는 다양한 피크를 확인하였다. $^1H$ NMR 스펙트럼의 다운필드인 ${\delta}_H$ 4.44 ppm과 ${\delta}_H$ 3.96~3.58 ppm에서 나타나는 다양한 피크들은 HD에 갈락토실화가 되었다는 것을 잘 암시하고 있으며, 또한 $^1H$ NMR 스펙트럼의 업필드에서 나타나는 ${\delta}_H$ 1.60~1.35 ppm과 0.92 ppm의 피크는 HD의 $CH_2$와 $CH_3$ 작용기로부터 나타나는 피크로써 HD가 본 물질에 존재한다는 것을 나타내고 있다. $^{13}C$ NMR 스펙트럼에서는 HD-gal의 알파-아노머와 베타-아노머의 구조에서 기인하는 총 21의 카본피크가 나타났고, 각 아노머마다 12개의 카본이 존재하는데 이중 ${\delta}_C$ 68.6, 60.9 and 13.2 ppm에 보이는 3개의 카본은 겹쳐서 나타나 총 24개의 피크 중 21개가 나타났다. 또한, 질량스펙트럼 분석에서는 protonated HD-gal인 281.1601 (m/z)의 peak를 확인할 수 있었다. 이를 종합하면, NMR ($^1H$- and $^{13}C$-) 스펙트럼 분석 결과와 질량분석 결과들은 우리가 기대했던 HD-gal의 구조와 매우 잘 일치하고 있다는 것을 알 수 있었다. 앞으로 추가적으로, 세균에 대한 minimum inhibitory concentrations (MICs) 조사와 human skin cell에 대한 독성연구를 추가적으로 진행할 예정이며, 이러한 결과를 근거로 항균력을 유지하면서 피부세포에 대한 독성이 감소된 화장품용 방부제의 연구/개발이 계속되기를 기대하고 있다.

• Journal of Preventive Medicine and Public Health
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• 제23권1호
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• pp.1-10
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• 1990

셀레늄이 수은, 카드뮴 및 크롬의 세포독성에 미치는 영향을 파악하고자 이들 중금속을 $0.3{mu}M$에서 $10{mu}M$까지 6개 농도로 각각 희석하여 $1.2{mu}M$의 셀레늄과 함께 혈액 배양에 첨가하고, 48시간 경과후 fluorescence-plus-Giemsa 염색에 의해 2차분열 중기의 염색체에서 자매염색분체교환(SCE)현상을 관찰하여, 셀레늄을 첨가하지 않았을 때의 결과와 비교하였다. 셀레늄을 다른 중금속들의 경우와 동일한 농도로 단독 첨가한 경우 SCE빈도는 $5.9{\pm}2.64$회에서 $12.3{\pm}3.99$회의 범위로 변하였고, 수은은 $6.5{\pm}2.70$회에서 $15.7{\pm}2.75$회, 카드뮴은 $6.7{\pm}2.65$회에서 $11.2{\pm}4.13$회, 크롬은 $7.0{\pm}2.58$회에서 $14.9{\pm}6.43$회의 범위로 농도증가에 비례하여 SCE빈도가 상승하였으며, 이때 세포분열지수는 공히 농도증가에 반비례하여 고농도군에서는 현저히 낮았다. 중금속들과 $1.2{mu}M$의 셀레늄을 동시에 첨가시킨 조건에서는 수은의 경우, 셀레늄과 수은의 몰(mol)농도비가 1:1, 1:2, 1:4의 조건에서, 카드뮴의 경우 1:2 및 1:4의 조건에서 SCE빈도의 현저한 감소를 나타냈으나 크롬의 경우는 셀레늄의 첨가와 무관하였으며, 세포분열지수는 전반적으로 셀레늄의 첨가에 별다른 영향을 받지 않았다.

• 한국펄프종이공학회:학술대회논문집
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• 한국펄프종이공학회 1999년도 춘계학술발표논문집
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• pp.84-88
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• 1999

In chlorine dioxide delignigication or bleaching, chlorate is mainly formed by the reaction between chlorite and hypochlorous acid, thus scavengers of chlorine or hypochlorous acid can be used to reduce the formation of chlorate which is unfavorable to environment. In this study, additives such as sulfamic acid, DMSO, hydrogen peroxide, or sodium chlorite was added to chlorine solution or pure $ClO_2$ solution to check their reactivity with $Cl_2$ and $ClO_2$. These additives were also added directly into general $ClO_2$ solution which contained certain amount of chlorine, then the additive-treated $ClO_2$ solution were used in bleaching stages. The aim of this procedure was to remove the original amount of chlorine that was thought to be possibly the main reason for the formation of chlorate and AOX. The additives were found to be able to eliminate chlorine very fast and selectively, but $H_2$ $O_2$ should be used under pH4, otherwise it also reacts with $ClO_2$. After the additives reacted With $Cl_2$, DMSO turned into an inactive product $(CH_3)_2SO_2$, While Sulfamic acid turned into $HClSO_3H$ that still remained active in oxidation, and $NaClO_2$ produced $ClO_2$. The addition of $HNaClO_2$ showed significant improvement in delignification but the deeper delignification led to higher formation of chlorate. When the additive-treated chlorine dioxide solutions were used in bleaching, both sulfamic acid, DMSO, and hydrogen peroxide showed no significant changes of DE brightness and Kappa number. The formation of chlorate was reduced by addition of sulfamic acid, DMSO and hydrogen peroxide.

• Bulletin of the Korean Chemical Society
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• 제28권7호
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• pp.1119-1126
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• 2007

Hydrogen gas and carbon nanotubes along with nanocarbon were produced from commercial natural gas using fixed bed catalyst reactor system. The maximum amount of carbon (491 g/g of catalyst) formation was achieved on 25% Ni, 3% Cu supported catalyst without formation of CO/CO2. Pure carbon nanotubes with length of 308 nm having balloon and horn type shapes were also formed at 673 K. Three sets of catalysts were prepared by varying the concentration of Ni in the first set, Cu concentration in the second set and doping with K in the third set to investigate the effect on stabilization of the catalyst and production of carbon nanotubes and hydrogen by copper and potassium doping. Particle size analysis revealed that most of the catalyst particles are in the range of 20-35 nm. All the catalysts were characterized using powder XRD, SEM/EDX, TPR, CHN, BET and CO-chemisorption. These studies indicate that surface geometry is modified electronically with the formation of different Ni, Cu and K phases, consequently, increasing the surface reactivity of the catalyst and in turn the Carbon nanotubes/H2 production. The addition of Cu and K enhances the catalyst dispersion with the increase in Ni loadings and maximum dispersion is achieved on 25% Ni: 3% Cu/Al catalyst. Clearly, the effect of particle size coupled with specific surface geometry on the production of hydrogen gas and carbon nanotubes prevails. Addition of K increases the catalyst stability with decrease in carbon formation, due to its interaction with Cu and Ni, masking Ni and Ni:Cu active sites.

• Bulletin of the Korean Chemical Society
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• 제35권3호
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• pp.839-844
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• 2014

The gas-phase radical-radical reaction $O(^3P)$ + $C_2H_5$ (ethyl) ${\rightarrow}$ $H(^2S)$ + $CH_3CHO$(acetaldehyde) was investigated by applying a combination of vacuum-ultraviolet laser-induced fluorescence spectroscopy in a crossed beam configuration and ab initio calculations. The two radical reactants $O(^3P)$ and $C_2H_5$ were respectively produced by photolysis of $NO_2$ and supersonic flash pyrolysis of the synthesized precursor azoethane. Doppler profile analysis of the nascent H-atom products in the Lyman-${\alpha}$ region revealed that the average translational energy of the products and the average fraction of the total available energy released as translational energy were $5.01{\pm}0.72kcalmol^{-1}$ and 6.1%, respectively. The empirical data combined with CBS-QB3 level ab initio theory and statistical calculations demonstrated that the title exchange reaction is a major channel and proceeds via an addition-elimination mechanism through the formation of a short-lived, dynamical addition complex on the doublet potential energy surface. On the basis of systematic comparison with several exchange reactions of hydrocarbon radicals, the observed small kinetic energy release can be explained in terms of the loose transition state with a product-like geometry and a small reverse activation barrier along the reaction coordinate.

• 한국수소및신에너지학회논문집
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• 제23권6호
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• pp.660-669
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• 2012

Gas resources captured in the form of gas hydrates are an order of magnitude larger than the resources available from conventional resources. Focus of this research is to investigate the effect of DME on phase equilibria of methane hydrate, as well as the possibility of the use of the PRO/II computer simulation to estimate the phase equilibria. In systems containing water and a gaseous component like, for instance, methane, ethane, and propane, gas hydrates may occur, if conditions in terms of pressure and temperature are satisfied. Mixtures of gases, e.g. LPG or natural gas, are also able to form gas hydrates in the presence of water. The experiments presented here were performed at temperatures varying between 268.15K and 288.15K and at pressures varying between 1.88 MPa and 10.56 MPa. It was found that the phase equilibria of methane hydrate is influenced by the addition of DME to the system. The pressure for the equilibrium hydrate-liquid water-vapor (H - $L_w$ - V) in the system water + methane is reduced upon addition of DME. The phase equilibria of methane hydrate can be estimated by the PRO/II computer simulation, whereas those of methane hydrate containing DME or LPG can't be estimated properly.

• 센서학회지
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• 제29권6호
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• pp.388-393
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• 2020

In this study, a PbS quantum dots (QDs)-based H₂ gas sensor with a Pd electrode was proposed. QDs have a size of several nanometers, and they can exhibit a high surface area when forming a thin film. In particular, the NH₂ present in the ligand of PbS QDs and H₂ gas are combined to form NH₃⁺, subsequently the electrical characteristics of the QDs change. In addition to the resistance change owing to the reaction between Pd and H₂ gas, the resistance change owing to the reaction between the NH₂ of PbS QDs and H₂ gas increases the current signal at the sensor output, which can produce a high output signal for the same concentration of H₂ gas. Using the XRD and absorbance properties, the synthesis and particle size of the synthesized PbS QDs were analyzed. Using PbS QDs, the sensitivity was significantly improved by 44%. In addition, the proposed H₂ gas sensor has high selectivity because it has low reactivity with heterogeneous gases such as C₂H₂, CO₂, and CH₄.

• 한국재료학회지
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• 제13권12호
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• pp.775-778
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• 2003

We studied InP etching in high density planar inductively coupled $BCl_3$and $BCl_3$/Ar plasmas(PICP). The investigated process parameters were PICP source power, RIE chuck power, chamber pressure and $BCl_3$/Ar gas composition. It was found that increase of PICP source power and RIE chuck power increased etch rate of InP, while that of chamber pressure decreased etch rate. Etched InP surface was clean and smooth (RMS roughness <2 nm) with a moderate etch rate (300-500 $\AA$/min) after the planar $BCl_3$/Ar ICP etching. It may make it possible to open a new regime of InP etching with $CH_4$$H_2$-free plasma chemistry. Some amount of Ar addition (<50%) also improved etch rates of InP, while too much Ar addition reduced etch rates of InP.