• 한국연소학회:학술대회논문집
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• 한국연소학회 2014년도 제49회 KOSCO SYMPOSIUM 초록집
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• pp.59-62
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• 2014

Predicting coal combustion by computational fluid dynamics (CFD) requires a combination of complicated flow and reaction models for turbulence, radiation, particle flows, heterogeneous combustion, and gaseous reactions. There are various levels of models available for each of the phenomena, but the use of advanced models are significantly restricted in a large-scale boiler due to the computational costs and the balance of accuracy between adopted models. In this study, the influence of coal devolatilization model and turbulent mixing rate was assessed in CFD for a commercial boiler at 500 MWe capacity. For coal devolatilization, two models were compared: i) a simple model assuming single volatile compound based on proximate analysis and ii) advanced model of FLASHCHAIN with multiple volatile species. It was found out that the influence of the model was observed near the flames but the overall gas temperature and heat transfer rate to the boiler were very similar. The devolatilization rate was found not significant since the difference in near-flame temperature became noticeable when it was multiplied by 10 or 0.1. In contrast, the influence of turbulent mixing rate (constant A in the Magnussen model) was found very large. Considering the heat transfer rate and flame temperature, a value of 1.0 was recommended for the rate constant.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.73-78
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• 2003

The InP thin films grown by metalorganic chemical vapor deposition (MOCVD) are widely used to optoelectronic devices such as laser diodes, wave-guides and optical modulators. Effects of various parameters controlling film growth rate such as gas-phase reaction rate constant, surface reaction rate constant and mass diffusivity are numerically investigated. Results show that at the upstream region where film growth rate increases with the flow direction, diffusion including thermal diffusion plays an important role. At the downstream region where the growth rate decreases with flow direction, film deposition mechanism is revealed as a mass-transport limited. Mass transport characteristics are also studied using systematic analyses.

• 한국환경과학회지
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• 제21권5호
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• pp.585-596
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• 2012

This study is mainly focused on micellar effect of cetyltrimethyl ammonium bromide(CTABr) solution including alkylbenzimidazole(R-BI) on dephosphorylation of isopropyl-4-nitrophenylphosphinate(IPNPIN) in carbonate buffer(pH 10.7). The reactions of IPNPIN with R-$BI^{\ominus}$ are strongly catalyzed by the micelles of CTABr. Dephosphorylation of IPNPIN is accelerated by $BI^{\ominus}$ ion in $10^{-2}$ M carbonate buffer(pH 10.7) of $4{\times}10^{-3}$ M CTABr solution up to 89 times as compared with the reaction in carbonate buffer by no benzimidazole(BI) solution of $4{\times}10^{-3}$ M CTABr. The value of pseudo first order rate constant($k_{\Psi}$) of the reaction in CTABr solution reached a maximum rate constant increasing micelle concentration. Such rate maxima are typical of micellar catalyzed bimolecular reactions. The reaction mediated by R-$BI^{\ominus}$ in micellar solutions are obviously slower than those by $BI^{\ominus}$, and the reaction rate were decreased with increase of lengths of alkyl groups. It seems due to steric effect of alkyl groups of R-$BI^{\ominus}$ in Stern layer of micellar solution. The surfactant reagent, CTABr, strongly catalyzes the reaction of IPNPIN with R-BI and its anion(R-$BI^{\ominus}$) in carbonate buffer(pH 10.7). For example, $4{\times}10^{-3}$ M CTABr in $1{\times}10^{-4}$ M BI solution increase the rate constant($k_{\Psi}=98.5{\times}10^{-3}\;sec^{-1}$) of the dephosphorylation by a factor ca.25, when compared with reaction($k_{\Psi}=3.9{\times}10^{-4}\;sec^{-1}$) in $1{\times}10^{-4}$ M BI solution(without CTABr). And no CTABr solution, in $1{\times}10^{-4}$ M BI solution increase the rate constant($k_{\Psi}=3.9{\times}10^{-4}\;sec^{-1}$) of the dephosphorylation by a factor ca.39, when compared with reaction ($k_{\Psi}=1.0{\times}10^{-5}\;sec^{-1}$) in water solution(without BI). This predicts that the reactivities of R-$BI^{\ominus}$ in the micellar pseudophase are much smaller than that of $BI^{\ominus}$. Due to the hydrophobicity and steric effect of alkyl group substituents, these groups would penetrate into the core of the micelle for stabilization by van der Waals interaction with long alkyl groups of CTABr.

• 한국환경과학회지
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• 제19권5호
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• pp.565-575
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• 2010

This study is mainly focused on micellar effect of cetylpyridinium chloride(CPyCl) solution including alkylbenzimidazole(R-BI) on dephosphorylation of diphenyl-4-nitrophenylphosphinate(DPNPIN) in carbonate buffer(pH 10.7). The reactions of DPNPIN with R-BI$^{\ominus}$ are strongly catalyzed by the micelles of CPyCl. Dephosphorylation of DPNPIN is accelerated by BI$^{\ominus}$ ion in $10^{-2}M$ carbonate buffer(pH 10.7) of $4{\times}10^{-3}M$ CPyCl solution up to 100 times as compared with the reaction in carbonate buffer by no BI solution of $4{\times}10^{-3}M$ CPyCl. The value of pseudo first order rate constant($k^m_{BI}$) of the reaction in CPyCl solution reached a maximum rate constant increasing micelle concentration. Such rate maxima are typical of micellar catalyzed bimolecular reactions. The reaction mediated by R-BI$^{\ominus}$ in micellar solutions are obviously slower than those by BI$^{\ominus}$, and the reaction rate were decreased with increase of lengths of alkyl groups. It seems due to steric effect of alkyl groups of R-BI$^{\ominus}$ in Stern layer of micellar solution. The surfactant reagent, cetylpyridinium chloride(CPyCl), strongly catalyzes the reaction of diphenyl-4-nitrophenylphosphinate(DPNPIN) with alkylbenzimidazole (R-BI) and its anion(R-BI$^{\ominus}$) in carbonate buffer(pH 10.7). For example, $4{\times}10^{-3}M$ CPyCl in $1{\times}10^{-4}M$ BI solution increase the rate constant ($k_{\Psi}=1.0{\times}10^{-2}sec^{-1}$) of the dephosphorylation by a factor ca.14, when compared with reaction ($k_{\Psi}=7.3{\times}10^{-4}sec^{-1}$) in $1{\times}10^{-4}M$ BI solution(without CPyCl). And no CPyCl solution, in $1{\times}10^{-4}M$ BI solution increase the rate constant ($k_{\Psi}=7.3{\times}10^{-4}sec^{-1}$) of the dephosphorylation by a factor ca.36, when compared with reaction ($k_{\Psi}=2.0{\times}10^{-5}sec^{-1}$) in water solution(without BI). This predicts that the reactivities of R-BI$^{\ominus}$ in the micellar pseudophase are much smaller than that of BI$^{\ominus}$. Due to the hydrophobicity and steric effect of alkyl group substituents, these groups would penetrate into the core of the micelle for stabilization by van der Waals interaction with long alkyl groups of CPyCl.

• BMB Reports
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• 제28권1호
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• pp.40-45
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• 1995

Acetolactate synthase purified from Serratia marcescens ATCC 25419 was rapidly inactivated by the thiol specific reagent p-chloromercuribenzoate (PCMB), the tryptophan specific reagent N-bromosuccinimide (NBS), and the arginine modifying reagent phenylglyoxal (PGO). Inactivation by PCMB was prevented by both ${\alpha}$-ketobutyrate and pyruvate, and the second order rate constant for the inactivation was $2480\;M^{-1}{\cdot}min^{-1}$. The reaction order with respect to PCMB was 0.94. The inactivation of the enzyme by NBS was also substantially reduced by both ${\alpha}$-ketobutyrate and pyruvate. The second order rate constant for inactivation by NBS was $15,000\;M^{-1}{\cdot}min^{-1}$, and the reaction order was 2.0. On the other hand, inactivation by PGO was partially prevented by ${\alpha}$-ketobutyrate, but not by pyruvate. The second order rate constant for the inactivation was $1480\;M^{-1}{\cdot}min^{-1}$ and the order of reaction with respect to PGO was 0.75. These results suggest that essential cysteine, tryptophan and arginine are located at or near the substrate binding site.

• 대한화학회지
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• 제6권1호
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• pp.47-53
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• 1962

The "reactivity" of coal is one of the important characteristics of a coal used as a process raw material as well as a fuel. In this study, the reactivity was measured in terms of the magnitude of the reaction rate constant in the reduction of carbon dioxide with coal. A reactivity-testing apparatus was designed and constructed, and its performance characteristics were investigated by using Korean anthracite and hard-wood charcoal. Experiments were carried out at temperatures ranging from 750 to 1100$^{\circ}C$ with pulverized Korean anthracite whose sizes range from 1 to 10mm in diameter. Results showed that the reaction rate constant was not appreciably affected by the particle size investigated, and the reactivities of the anthracite and the charcoal were found to be a function of reaction temperature alone. It was also found that a straight line was produced when the logarithm of the rate constant is plotted against the reciprocal of the absolute temperature. The reactivities of the charcoal were found to be 2 to 10 times higher than those of the anthracite at a temperature ranging from 750 to 1100$^{\circ}C$, and 90% of carbon dioxide was reduced to carbon monoxide by the anthracite at a temperature above 1050$^{\circ}C$.

• 공업화학
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• 제25권6호
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• pp.648-653
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• 2014

크롬(VI)-헤테로고리 착물(2,4'-비피리디늄 클로로크로메이트)을 합성하여, 적외선 분광광도법(IR), 유도결합 플라즈마(ICP) 등으로 구조를 확인하였고, 여러 가지 용매 하에서, 2,4'-비피리디늄 클로로크로메이트를 이용하여 벤질알코올의 산화반응을 측정한 결과, 유전상수값의 증가에 따라 반응도 증가했다는 것을 보였다. 그 순서는 : N,N-디메 틸포름아미드(DMF) > 아세톤 > 클로로포름 > 시클로헥센산 촉매(HCl)를 이용한 DMF 용매 하에서, 2,4'-비피리디늄 클로로 크로메이트은 벤질 알코올(H)과 그의 유도체들(p-$CH_3$, m-Br, m-$NO_2$)을 효과적으로 산화시켰다. 전자받개 그룹들은 반응 속도가 감소한 반면에 전자주개 치환체들은 반응속도를 증가시켰고, Hammett 반응상수(${\rho}$) 값은 -0.67 (303 K)이었다. 속도결정단계에서 크로메이트 에스테르의 형성과정을 거친 후, 양성자 전이가 일어났다.

• 대한화학회지
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• 제58권1호
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• pp.17-24
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• 2014

The oxidative decarboxylation of phenylsulfinylacetic acid (PSAA) by Cr(VI) in 20% acetonitrile -80% water (v/v) medium follows overall second order kinetics, first order each with respect to [PSAA] and [Cr(VI)] at constant [$H^+$] and ionic strength. The reaction is acid catalysed, the order with respect to [$H^+$] is unity and the active oxidizing species is found to be $HCrO_3^+$. The reaction mechanism involves the rate determining nucleophilic attack of sulfur atom of PSAA on chromium of $HCrO_3^+$ forming a sulfonium ion intermediate. The intermediate then undergoes ${\alpha}$,${\beta}$-cleavage leading to the liberation of $CO_2$. The product of the reaction is found to be methyl phenyl sulfone. The operation of substituent effect shows that PSAA containing electron-releasing groups in the meta- and para-positions accelerate the reaction rate while electron withdrawing groups retard the rate. An excellent correlation is found to exist between log $k_2$ and Hammett ${\sigma}$ constants with a negative value of reaction constant. The ${\rho}$ value decreases with increase in temperature evidencing the high reactivity and low selectivity in the case of substituted PSAAs.

• 대한화학회지
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• 제21권4호
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• pp.227-234
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• 1977

황산산성에서 페닐히드라진과 브롬의 반응을 속도론적으로 검토하였다. 겉보기 2차 반응속도상수는 1M 이하의 황산농도에서는 수소이온 농도에 대략 역비례한다. KBr 첨가의 영향을 검토하여 $Br_2\;및\;Br_3^-$가 반응화학종이고, 이들의 속도상수는 $20^{\circ}C$의 0.01M $H_2SO_4$용액에서 각각 $5{\times}10^5M^{-1},sec^{-1}\;및\;0. 7{\times}10^5M^{-1},sec^{-1}$임을 밝혔다. 2,4-디니트로 페닐히드라진의 브롬과의 반응속도상수는 수소이온 농도에 거의 무관계하며 $Br_2\;및\;Br_3^-$에 대하여 각각 $1.2{\times}10^5M^{-1},sec^{-1}\;및\;2.0{\times}10^4M^{-1},sec^{-1}$이다.

• 대한화학회지
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• 제49권6호
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• pp.554-559
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• 2005