• Bulletin of the Korean Chemical Society
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• 제23권1호
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• pp.59-64
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• 2002

A facile and precise batch oxidation reaction system allows continuous monitoring of the oxidation rate and cumulated oxygen conversion of xylenes, and the side reactions to carbon monoxide and carbon dioxide may also be studied. The oxidation reaction can be analyzed precisely with the rate and amount of oxygen consumed. The reaction reveals that 4-carboxybenzaldehyde is an unstable intermediate of p-xylene oxidation as the reaction proceeds instantaneously from p-toluic acid to TPA (terephthalic acid). The alkali metals accelerate oxidation, even though they retard the reaction initially. The oxidation rate increases with decreasing water concentration. However, in the later part of reaction, the reactivity decreases a bit if the water concentration is very low. This retarding effect of water can be overcome partly by the addition of potassium. The oxidation of o-xylene, compared with the oxidation of p-xylene and m-xylene, proceeds quite fast initially, however, the oxidation rate of xylene isomers in the later stage of reaction is in the order of p-xylene > mxylene > o-xylene.

• Bulletin of the Korean Chemical Society
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• 제23권3호
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• pp.503-506
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• 2002

• Bulletin of the Korean Chemical Society
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• 제23권3호
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• pp.369-373
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• 2002

The liquid phase oxidation of p-xylene has been carried out with oxygen-enriched gas, and the manganese component was precipitated probably via over-oxidation to $Mn^{4+}$. The precipitation increased with rising oxygen concentration in the reaction gas and occurred mainly in the later part of the oxidation. The activity of the reaction decreased, and the blackening of the product and side reactions to carbon dioxide increased with the degree of precipitation. Precipitation can be decreased with the addition of metal ions, such as cerium, chromium and iron.

• 공업화학
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• 제7권6호
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• pp.1204-1208
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• 1996

파라자일렌(p-xylene)을 산화반응시켜 테레프탈산(terephthatic acid)을 제조하는 과정 중에 발생하는 주요 유기불순물을 효과적으로 분석하는 방법을 수립하였다. 이 제조공정 중에 발생하는 유기불순물은 매우 다양하나, 여기에서는 주로 benzoic acid, p-toluic acid, p-tolualdehyde, 4-carboxybenzaldehyde, phthalic acid, isophthalic acid, trimellitic acid와 4-hydroxymethyl benzoic acid 등의 유기불순물을 분석하는데 촛점을 맞추었다. 이 유기물들은 공정 중의 모액이나 고체상태의 테레프탈산 입자에 존재하는데, 이들을 동시에 분석하기 위해 99% bis(trimethylsilyl)trifluoroacetamide와 1% trimethylchlorosilane의 내부표준용액과 pyridine의 혼합용액내에서 trimethylsilylation으로 시료를 전처리하고 gas chromatography를 이용하여 분석한 결과 상기한 유기물이 모두 성공적으로 분리되어 50분 이내에 정량분석할 수 있었다.

• 한국환경과학회지
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• 제17권11호
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• pp.1195-1201
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• 2008

Enhancing with non-metallic elemental nitrogen(N) is one of several methods that have been proposed to modify the electronic properties of bulk titanium dioxide($TiO_2$), in order to make $TiO_2$ effective under visible-light irradiation. Accordingly, current study evaluated the feasibility of applying visible-light-induced $TiO_2$ enhanced with N element to cleanse aromatic compounds, focusing on xylene isomers at indoor air quality(IAQ) levels. The N-enhanced $TiO_2$ was prepared by applying two popular processes, and they were coated by applying two well-known methods. For three o-, m-, and p-xylene, the two coating methods exhibited different photocatalytic oxidation(PCO) efficiencies. Similarly, the two N-doping processes showed different PCO efficiencies. For all three stream flow rates(SFRs), the degradation efficiencies were similar between o-xylene and m,p-xylene. The degradation efficiencies of all target compounds increased as the SFR decreased. The degradation efficiencies determined via a PCO system with N-enhanced visible-light induced $TiO_2$ was somewhat lower than that with ultraviolet(UV)-light induced unmodified $TiO_2$, which was reported by previous studies. Nevertheless, it is noteworthy that PCO efficiencies increased up to 94% for o-xylene and 97% for the m,p-xylene under lower SFR(0.5 L $min^{-1}$). Consequently, it is suggested that with appropriate SFR conditions, the visible-light-assisted photocatalytic systems could also become important tools for improving IAQ.

• Journal of Microbiology
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• 제43권4호
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• pp.325-330
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• 2005

Rhodococcus sp. strain YU6 was isolated from soil for the ability to grow on o-xylene as the sole carbon and energy source. Unlike most other o-xylene-degrading bacteria, YU6 is able to grow on p-xylene. Numerous growth substrate range experiments, in addition to the ring-cleavage enzyme assay data, suggest that YU6 initially metabolizes 0- and p-xylene by direct aromatic ring oxidation. This leads to the formation of dimethylcatechols, which was further degraded largely through meta-cleavage path-way. The gene encoding meta-cleavage dioxygenase enzyme was PCR cloned from genomic YU6 DNA using previously known gene sequence data from the o-xylene-degrading Rhodococcus sp. strain DK17. Subsequent sequencing of the 918-bp PCR product revealed a $98\%$ identity to the gene, encoding meth-ylcatechol 2,3-dioxygenase from DK17. PFGE analysis followed by Southern hybridization with the catechol 2,3-dioxygenase gene demonstrated that the gene is located on an approximately 560-kb megaplasmid, designated pJY J1

• 실내환경 및 냄새 학회지
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• 제17권4호
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• pp.381-388
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• 2018

In this study, various conditions and phenomena that occur in the process of removing odorous VOCs by using electrolyzed oxidant were examined. The formation of hypochlorous acid, which is an oxidant produced by electrolysis, was investigated and the properties of the oxidizing agent used to decompose toluene, xylene, and cyclohexane were investigated. As a result, it was found that the production rate and the final concentration of the oxidizing agent increased with the current density. It was found that the degree of removal varies depending on the property of each pollutant. Interestingly, in the batch experiments in which the pH of the produced oxidant was controlled, it was found that the degree of elimination varied depending on the pH of the substance. These results suggest that the difference in the concentration and distribution of hypochlorous acid (HOCl) and hypochlorite ($OCl^-$) due to the pH change leads to the difference in oxidizing power on the oxidation characteristics of each substance. Styrene and terpineol showed better degradation characteristics than toluene and xylene in odorous VOC removal experiments by spraying electrolytic oxidant using a lab-scale continuous reactor. In conclusion, the removal of odorous VOCs by the electrolytic oxidant can have various applications in that it can oxidize pollutants of various spectra.

• 한국환경과학회지
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• 제28권11호
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• pp.971-981
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• 2019

This study evaluated the photocatalytic oxidation efficiency of volatile organic compounds by $Cu_2O-TiO_2$ under visible-light irradiation. $Cu_2O-TiO_2$ was synthesized by an ultrasonic-assisted method. The XRD result indicated successful p-n type photocatalysts. However, no diffraction peaks belonging to $TiO_2$ were observed for the $Cu_2O-TiO_2$. The Uv-vis spectra result revealed that the synthesized $Cu_2O-TiO_2$ can be activated under visible-light irradiation. The FE-TEM/EDS result showed the formation of synthesized nanocomposites in the commercial P25 $TiO_2$, the undoped $TiO_2$, and $Cu_2O-TiO_2$ and componential analysis in the undoped $TiO_2$ and $Cu_2O-TiO_2$. The photocatalytic oxidation efficiencies of benzene, toluene, ethylbenzene, and o-xylene with $Cu_2O-TiO_2$ were higher than those of P25 $TiO_2$ and undoped $TiO_2$. These results indicate that the prepared $Cu_2O-TiO_2$ photocatalyst can be applied effectively to control gaseous BTEX.

• 환경위생공학
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• 제18권2호
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• pp.52-59
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• 2003

This study was progressed in photocatalysis of VOCs using $UV/TiO_2$ which was a benign process environmentally. The experiments were peformed to know photodegradation characteristics as crystalline structure of $TiO_2$ which had anatase, rutile and P-25 (anatase : rutile = 70 : 30). The main purpose of this study was to identify photocatalytic characteristics as inlet concentration of reactants, $H_2O$, and residence time. The inlet concentration of VOCs was changed 50, 100 and 200 ppmv, and amount of $H_2O$ was changed 0, 500 and $1000{\;}mg/m^3$, respectively. The deep conversion was increased as the inlet concentration decreased, and the amount of $H_2O$ increased. The deep conversion of benzene had the highest value at $1000{\;}mg/m^3${\;}H_2O$ and 50 ppmv of inlet concentration. The reactivity of reactants was decreased in order benzene > toluene > m-xylene. Also, the photocatalytic deep conversion was increased as residence time increased, because the contact time between reactants and catalyst was increased. In this study, intermediates had not found by GC/MSD analysis. Therefore, the reactants were completely converted to $H_2O{\;}and{\;}CO_2$.

• 한국지하수토양환경학회지:지하수토양환경
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• 제18권2호
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• pp.36-44
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• 2013

The objectives of this study were to identify the characteristics of shallow groundwater from the oil-contaminated site for a long period and to evaluate the applicability of biopile technology to treat the soil excavated from it. The eight monitoring wells were installed in the contaminated site and pH, Electrical Conductivity (EC), Dissolved Oxygen (DO), Oxidation Reduction Potential (ORP), Temperature and the concentrations of major ions and pollutants were measured. The VOCs in soil gas were monitored during biopile operation and TPH concentration was analyzed at the termination of the experiment. The pH was 6.62 considered subacid and EC was 886.19 ${\mu}S/cm$. DO was measured to be 2.06 mg/L showing the similar characteristic of deep groundwater. ORP was 119.02 mV indicating oxidation state. The temperature of groundwater was measured to be $16.97^{\circ}C$. The piper diagram showed that groundwater was classified as Ca-$HCO_3$ type considered deep groundwater. The ground water concentration for TPH, Benzene, Toluene, Xylene of the first round was slightly higher than that of the second round. The concentration of carbon dioxide of soil gas was increased to 1.3% and the concentration of VOCs was completely eliminated after the 40 days. The TPH concentration showed 98% remediation efficiency after the 90 days biopile operation.