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Kinetic Analysis for Decomposition of 2,4-Dichlorophenol by Supercritical Water Oxidation
이창하,황경엽,이현철,Jung-Hyun In,Jong-Hwa Kim 한국화학공학회 2005 Korean Journal of Chemical Engineering Vol.22 No.6
2,4-Dichlorophenol (2,4-DCP), as a halogenated model pollutant, was decomposed by using supercritical water oxidation (SCWO) in a batch reactor made of Hastelloy C-276. SCWO experiments for 2,4-DCP decomposition were performed in the range of 380-420 oC, 230-280 bar and 0.074- 0.221 mol/L H2O2. The effect of oxidant concentration on decomposition rate and efficiency was significant near the critical temperature of 380 oC. However, the role of the oxidant concentration in the SCWO process decreased with an increase in temperature; also, excess oxidant played a key role in quite significantly decreasing the activation energy of 2,4-DCP oxidation. Variation of the reaction rate by the change of pressure was negligible even at a near critical temperature. The kinetic rate for the decomposition of 2,4-DCP in the SCWO process was well described by a simple first-order kinetic and global reaction rate model. From the SCWO experiments, the various intermediates identified with a GC/MS implied that the first reaction pathway for 2,4-DCP decomposition led to dimers such as dichlorophenoxyphenols, and the second led to single-ring and ringopening products.
( Muruganantham Rethinasabapathy ),강성민,곽철환,허윤석 한국공업화학회 2018 한국공업화학회 연구논문 초록집 Vol.2018 No.0
Prussian blue (PB)/Chitosan (CS)/Graphene oxide (GO) has been syn-thesized and utilized as a potential adsorbent for the removal of cesium ions (Cs<sup>+</sup>) from aqueous solution. The effects of adsorbate concen-tration, reaction pH, and time on the removal efficiency of Cs<sup>+</sup> were investigated. The optimal pH and reaction time for the removal of Cs<sup>+</sup> were pH 7 and 24 h, respectively, with an adsorbent dosage of 20 mg. The adsorption isotherm is better fitted to the Freundlich model than the Langmuir model with a maximum Cs<sup>+</sup> adsorption capacity of 33 mg g-1. In addition, the kinetic study showed that the adsorption behavior followed a pseudo-second-order kinetics. The adsorbent showed good selectivity towards Cs<sup>+</sup> even in the presence of competitive cations. Therefore, it is expected that this composite can be used for the removal of radioactive cesium.
Bae, Sanghyun,Kim, Hyunwoo,Jeon, Dasom,Ryu, Jungki American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.8
<P>We studied the kinetics of photoelectrochemical (PEC) water oxidation using a model photoanode BiVO<SUB>4</SUB> modified with various water oxidation catalysts (WOCs) by electrochemical impedance spectroscopy. In particular, we prepared BiVO<SUB>4</SUB> photoanodes with catalytic multilayers (CMs), where cationic polyelectrolytes and anionic polyoxometalate (POM) WOCs were assembled in a desired amount at a nanoscale precision, and compared their performance with those with well-known WOCs such as cobalt phosphate (CoPi) and NiOOH. Our comparative kinetics analysis suggested that the deposition of the CMs improved the kinetics of both the photogenerated charge carrier separation/transport in bulk BiVO<SUB>4</SUB> due to passivation of surface recombination centers and water oxidation at the electrode/electrolyte interface due to deposition of efficient molecular WOCs. On the contrary, the conventional WOCs were mostly effective in the former and less effective in the latter, which is consistent with previous reports. These findings explain why the CMs exhibit an outstanding performance. We also found that separated charge carriers can be efficiently transported to POM WOCs via a hopping mechanism due to the delicate architecture of the CMs, which is reminiscent of natural photosynthetic systems. We believe that this study can not only broaden our understanding on the underlying mechanism of PEC water oxidation but also provide insights for the design and fabrication of novel electrochemical and PEC devices, including efficient water oxidation photoanodes.</P> [FIG OMISSION]</BR>
Reaction kinetics of reduction and oxidation of metal oxides for hydrogen production
Go, Kang Seok,Son, Sung Real,Kim, Sang Done Elsevier 2008 International journal of hydrogen energy Vol.33 No.21
<P><B>Abstract</B></P><P>Partial oxidation of methane and water splitting for hydrogen production were carried out. The reaction kinetics of reduction and oxidation (redox) of Mn and Zn iron oxides were determined using a thermogravimetric analyzer. The reduction conversion of the metal oxides increases with temperature above 1073K and all the experimental data are well represented by the diffusion-limited mechanism except ZnFe<SUB>2</SUB>O<SUB>4</SUB> due to the solid state diffusion of iron and the reaction with solid carbon. The oxidation reaction was also controlled by the product-layer diffusion mechanism. Substitution of Mn and Zn cations with iron oxides can lower the reaction temperature and increase the reaction rate. The reaction rate and the activation energy (57–110kJ/mol) for decomposition of water by oxidation of the metal oxides were also determined.</P>
초임계수 산화에서 Ethylene Glycol의 분해반응 특성
김봉진 ( Bong Jin Kim ),원양수 ( Yang Soo Won ),이주헌 ( Joo Heon Lee ) 한국공업화학회 2003 공업화학 Vol.14 No.2
등온관형반응기를 이용하여 38O~425 ℃ 영역에서 초임계순 산화법을 이용하여 ethylene glyrol (EG)외 분해반응연구를 수행하었다. Ethylene glycol의 농도범위는 1000~5000 ppm이며, 주입 산소량은 EG를 산화시키 위한 필요 공기량의100~400%로 하였으며 운전압력은 250 bar로 고정시켜 실험을 진행하였다. 400℃ 이상에서 EG와 total organic carbon (TOC)는 분해반응이 급격히 종가하기 시작하였으며 초기농도가 높을수록 분해율은 높았으며 산소농도에는 분해율이 영향을 미치지 못했다. 반응속도인자 분석결과 EG 분해반응차수는 EG에 대하여 1.38차, 산소에 대해서는 0차이며, 활성화 에너지는 30.2 kcaㅣ/mol이었다. EG 분해시 생성되는 주요 중간생성물질로는 acetaldehyde, acetic acid, formaldedyde이었으며, 미량 생성물로는 glyoxylic acid, oxalic acid, formic acid, malonic acid 등이 검출되었다. Ethylene glycol (EG) in supercritical water was oxidized in an isothermal tubular flow reactor in the temperature range of 380~425℃. The ethylene glycol concentration ranged from 1000 to 5000 ppm. The initial amount of air spanned from 100 to 400% of stoichiometrically required amount of air for complete oxidation, while the operating pressure was maintained at 250 bar for all the runs. At temperature higher than 400℃, the decomposition of ethylene glycol and total organic carbon increased rapidly. High initial EG concentration resulted in fast decomposition of EG, but oxygen was found to have no effect on the decay of EG. Analysis of the kinetic data showed that the overall oxidation rate law was 1.38 th order for EG and 0th order for oxygen. The overall reaction rate constant was a pre-exponential factor 10^10 liter^-0.38 , mol^-0.38·sec^-1, and the activation energy was 30.2 kcal/mol. The loss of EG based on these estimated kinetic parameters agreed well with the experimental observations. The major products observed were acetaldehyde, acetic acid and formaldedyde. Glyoxylic acid, oxalic acid formic acid and malonic acid were found to be minor products. A reaction mechanism based on the kinetic parameters and intermediate product distribution was proposed.
Removal of chromium(VI) from aqueous solution using manganese oxide nanofibers
Abdullah H. Qusti 한국공업화학회 2014 Journal of Industrial and Engineering Chemistry Vol.20 No.5
Manganese oxide nanofibers (MONFs) were synthesized, characterized, and successfully used for the removal of the toxic Cr(VI) ions from a model and the real solution. The results showed that the MONFs were fibers, whose shape consisted of an average diameter of 10 nm to 16 nm and a specific surface area equal to 94.1 m2 g-1, that was mainly composed of crystalline a-MnO2 (i.e., as was confirmed with the XRD measurement). The effect of different parameters that affected the adsorption process was studied and optimized. The results showed an efficient removal at pH 2.0, within 60 min, and by using 150 mg MONFs at the ambient temperature. The adsorption of Cr(VI) ions from an aqueous solution was studied kinetically at different temperatures. The results showed that the removal process followed the pseudosecond-order model, with an adsorption capacity of 14.6 mg g-1 at ambient temperature. The thermodynamic parameters were calculated and the results showed that the adsorption of Cr(VI) ions from aqueous solution by MONFs is physical, spontaneous, and exothermic (△H = 39.3 kJ mol-1) in nature, with negative entropy. Finally, MONFs were used for the removal of Cr(VI) ions from a real sample, and the result indicated that the MONFs are highly efficient at removing the toxic Cr(VI) ions.