• 한국환경과학회지
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• 제26권7호
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• pp.859-868
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• 2017

In this study, the reductive dechlorination of triclosan using zero-valent iron (ZVI, $Fe^0$) and modified zero-valent iron (i.e., acid-washed iron (Aw/Fe) and palladium-coated iron (Pd/Fe)) was experimentally investigated, and the reduction characteristics were evaluated by analyzing the reaction kinetics. Triclosan could be reductively decomposed using zero-valent iron. The degradation rates of triclosan were about 50% and 67% when $Fe^0$ and Aw/Fe were used as reductants, respectively, after 8 h of reaction. For the Pd/Fe system, the degradation rate was about 57% after 1 h of reaction. Thus, Pd/Fe exhibited remarkable performance in the reductive degradation of triclosan. Several dechlorinated intermediates were predicted by GC-MS spectrum, and 2-phenoxyphenol was detected as the by-product of the decomposition reaction of triclosan, indicating that reductive dechlorination occurred continuously. As the reaction proceeded, the pH of the solution increased steadily; the pH increase for the Pd/Fe system was smaller than that for the $Fe^0$ and Aw/Fe system. Further, zero-order, first-order, and second-order kinetic models were used to analyze the reaction kinetics. The first-order kinetic model was found to be the best with good correlation for the $Fe^0$ and Aw/Fe system. However, for the Pd/Fe system, the experimental data were evaluated to be well fitted to the second-order kinetic model. The reaction rate constants (k) were in the order of Pd/Fe > Aw/Fe > $Fe^0$, with the rate constant of Pd/Fe being much higher than that of the other two reductants.

• 한국수소및신에너지학회논문집
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• 제22권5호
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• pp.649-655
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• 2011

Methane direct cracking can be utilized to produce $CO_x$ and $NO_x$-free hydrogen for PEM fuel cells, oil refineries, ammonia and methanol production. We present the results of a systematic study of methane direct cracking using a mixed conducting oxide, Y-doped $BaZrO_3$ ($BaZr_{0.85}Y_{0.15}O_3$), membrane. In this paper, dense $BaZr_{0.85}Y_{0.15}O_3$ membrane with disk shape was successfully sintered at $1400^{\circ}C$ with a relative density of more 93% via addition of 1 wt% ZnO. The ($BaZr_{0.85}Y_{0.15}O_3$) membrane is covered with Pd as catalyst for methane decomposition with an DC magnetron sputtering method. Reaction temperature was $800^{\circ}C$ and high purity methane as reactant was employed to membrane side with 1.5 bar pressure. The $H_2$ produced by the reaction was transported through mixed conducting oxide membrane to the outer side. In addition, it was observed that the carbon, by-product, after methane direct cracking was deposited on the Pd/ZnO-$BaZr_{0.85}Y_{0.15}O_3$ membrane. The produced carbon has a shape of sphere and nanosheet, and a particle size of 80 to 100 nm.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제35회 추계학술대회논문집
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• pp.294-299
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• 2010

본 연구의 목적은 열안정성을 향상시키는 첨가제 (열안정제)를 이용하여 exo-tetrahydrodicyclopentadiene (exo-THDCP, $C_{10}H_{16}$)의 열안정성을 향상시키는 것이다. 실험은 반응 진행 중 미량의 시료 추출이 가능한 회분식 반응기에서 수행되었다. 추출한 시료를 gas chromatography-mass spectrometry (GC-MS)를 이용해 성분 분석하여 첨가제 성능-exo-THDCP의 열분해성-을 확인하고, 반응시간에 따른 exo-THDCP의 분해생성물의 성분 및 조성 변화를 통해 첨가제의 작용 메커니즘을 규명하였다. 열안정제로써 수소공여체를 사용하여 실험한 결과 1,2,3,4-tetrahydroquinoline (THQ), benzyl alcohol (BnOH) 등을 첨가하였을 때 exo-THDCP의 열안정성이 향상되었다. 이러한 수소공여체 물질들은 개시반응이 진행된 exo-THDCP 라디칼에 수소원자 (hydrogen radical)를 제공함으로 라디칼의 반응성을 완화시켜 1차 생성물의 활성을 감소시키어 2차생성물질인 $C_{11}$ 이상 생성물의 발생을 감소시키는 것으로 밝혀졌다.

• 한국추진공학회지
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• 제20권2호
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• pp.46-55
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• 2016

Differential Scanning Calorimetry(DSC) 실험 데이터를 이용하여 고에너지 물질의 반응속도식을 추출해내는 이론적 방법을 제안하고 알루미늄 고함유 화약(RDX/HTPB/Al)에 대한 반응속도식 추출을 수행하였다. DSC 실험 결과는 Friedman 등전환법으로 분석되었다. 질량분율에 따른 활성화에너지와 빈도인자를 추출해 내어 반응속도식을 완성하였다. 추출된 반응속도식은 고에너지 물질의 화학반응과정을 몇 단계의 주요단계로 가정하는 형태가 아닌 전체 화학반응 과정을 나타내는 형태를 갖는다. 이는 기존의 ODTX 실험을 통해 추출되는 화학반응속도식 형태에 비해 이론적 측면과 정확성 측면에서 상당한 장점을 갖는다. 추출된 반응속도식의 검증을 위해 화학반응률 그리고 생성물 질량분율에 대해 DSC 실험과 동일한 조건하에서 전산모사를 수행하였으며 실험값과 잘 일치함을 확인하였다. 또한 완속가열 전산모사를 수행하였으며 실험결과와 비교하여 DSC 반응속도식의 전산모사에의 적용가능성을 확인하였다.

• 청정기술
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• 제22권4호
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• pp.250-257
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• 2016

As an attempt to replacing petroleum-based chemicals with bio-based ones, synthesis of furfural from biomass-derived xylose attracts much attention in recent days. Conventionally, furfural from xylose has been produced via the utilization of highly corrosive, toxic, and environmentally unfriendly mineral acids such as sulfuric acid or hydrochloric acid. In this study, microwave-assisted biphasic reaction process in the presence of novel bio-based heterogeneous acid catalysts was developed for the eco-benign and effective synthesis of furfural from xylose. The microwave was irradiated for reaction acceleration and a biphasic system consisting of $H_2O$ : MIBK (1 : 2) was designed for continuous extraction of furfural into the organic phase in order to reduce the undesired side products formed by decomposition/condensation/oligomerization in the acidic aqueous phase. Moreover, sulfonated amorphous carbonaceous materials were prepared from wood powder, the most abundant lignocellulosic biomass. The prepared catalysts were characterized by FT-IR, XPS, BET, elemental analysis and they were used as bio-based heterogeneous acid catalysts for the dehydration of xylose into furfural more effectively. For further optimization, the effect of temperature, reaction time, water/organic solvent ratio, and substrate/catalyst ratio on the xylose conversion and furfural yield were investigated and 100% conversion of xylose and 74% yield of furfural was achieved within 5 h at $180^{\circ}C$. The bio-based heterogeneous acid catalysts could be used three times without any significant loss of activity. This greener protocol provides highly selective conversion of xylose to furfural as well as facile isolation of product and bio-based heterogeneous acid catalysts can alternate the environmentally-burdened mineral acids.

• 자원리싸이클링
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• 제25권5호
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• pp.57-63
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• 2016

본 연구는 호주산 저품위 동광의 선광실험결과로 얻은 고품위 광물의 황산화 배소 및 선택적 침출반응 조건 확립을 통해 유가 광물 중에 함유된 성분을 선별적으로 용해해냄으로써 철 성분을 비롯한 불순물을 줄이거나, 동 및 니켈 성분을 용해 혹은 잔사에 잔류시킴으로써 유가금속회수를 효과적으로 회수하고자 하는데 목적이 있다. 본 연구실험결과 얻은 최적조건은 황산화 배소시 $450^{\circ}C$, $Na_2SO_4$ 2 mole ratio 및 1.5 h이었고, 배소산물의 침출온도는 상온 및 침출제는 $H_2O$ 혹은 1M $H_2SO_4$이었다. 최적조건 하에서 Cu 성분은 90 wt.% 침출율을 Fe성분은 20 wt.%내외, Ni성분은 15 wt.% 정도를 나타내는 것으로 보아 선택적 분해침출이 가능하다.

• Nuclear Engineering and Technology
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• 제52권5호
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• pp.1013-1021
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• 2020

A combination of simultaneous thermal analysis, evolved gas analysis and non-ambient XRD techniques was used to characterise and investigate the conversion reactions of ammonium uranates into uranium oxides. Two solid phases of the ternary system NH₃ - UO₃ - H₂O were synthesised under specified conditions. Microspheres prepared by the sol-gel method via internal gelation were identified as 3UO₃·2NH₃·4H₂O, whereas the product of a typical ammonium diuranate precipitation reaction was associated to the composition 3UO₃·NH₃·5H₂O. The thermal decomposition profile of both compounds in air feature distinct reaction steps towards the conversion to U₃O₈, owing to the successive release of water and ammonia molecules. Both compounds are converted into α-U₃O₈ above 550 ℃, but the crystallographic transition occurs differently. In compound 3UO₃·NH₃·5H₂O (ADU) the transformation occurs via the crystalline β-UO₃ phase, whereas in compound 3UO₃·2NH₃·4H₂O (microspheres) an amorphous UO₃ intermediate was observed. The new insights obtained on these uranate systems improve the information base for designing and synthesising minor actinide-containing target materials in future applications.

• 한국재료학회지
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• 제28권12호
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• pp.725-731
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• 2018

We investigate the reduction of $SnO_2$ and the generation of syngas($H_2$, CO) using methane($CH_4$) and hydrogen($H_2$) or a mixed gas of methane and hydrogen as a reducing gas. When methane is used as a reducing gas, carbon is formed by the decomposition of methane on the reduced Sn surface, and the amount of generated carbon increases as the amount and time of the supply of methane increases. However, when hydrogen is used as a reducing gas, carbon is not generated. High purity Sn of 99.8 % and a high recovery rate of Sn of 93 % are obtained under all conditions. The effects of reducing gas species and the gas mixing ratio on the purity and recovery of Sn are not significantly different, but hydrogen is somewhat more effective in increasing the purity and recovery rate of Sn than methane. When 1 mole of methane and 1 mole of hydrogen are mixed, a product gas with an $H_2/CO$ value of 2, which is known to be most useful as syngas, is obtained.

• 한국추진공학회지
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• 제23권1호
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• pp.79-92
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• 2019

Titanium hydride potassium perchlorate (THPP)는 항공우주분야에서 일반적으로 널리 사용되는 불꽃점화장치중 하나이다. 현 연구에서는 THPP에 수분 열 노화를 가했을 때, 연소과정에 끼치는 영향과 변화된 결과들을 실험적으로 밝혀내었다. 우선, Differential Scanning Calorimetry (DSC)와 isoconversional method를 적용하여 노화된 THPP 시료의 반응개시지연 및 최대반응속도의 저하를 확인하였다. 반응속도 파라미터는 첫 번째 반응에서 Viton에 의해 낮아지며 후에 잔류한 $KClO_4$의 영향으로 상승하는 경향을 보였다. 그리고 X-ray photoelectron spectroscopy (XPS)를 통해 노화된 THPP 시료에서 산화제 성분은 감소하고 연료산화효과가 두드러짐을 확인하였다. 또한 NASA Chemical Equilibrium with Applications (CEA)을 사용하여 얻은 이론발열량이 DSC로부터 구한 실험적 발열량과 비슷한 경향을 따르므로 실험적으로 구한 발열량 트렌드가 타당함을 검증할 수 있었다.

• Nuclear Engineering and Technology
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• 제54권5호
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• pp.1825-1834
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• 2022

Performing high-fidelity computational fluid dynamics (HF-CFD) to predict the flow and heat transfer state of the coolant in the reactor core is expensive, especially in scenarios that require extensive parameter search, such as uncertainty analysis and design optimization. This work investigated the performance of utilizing a multi-fidelity reduced-order model (MF-ROM) in PWR rod bundles simulation. Firstly, basis vectors and basis vector coefficients of high-fidelity and low-fidelity CFD results are extracted separately by the proper orthogonal decomposition (POD) approach. Secondly, a surrogate model is trained to map the relationship between the extracted coefficients from different fidelity results. In the prediction stage, the coefficients of the low-fidelity data under the new operating conditions are extracted by using the obtained POD basis vectors. Then, the trained surrogate model uses the low-fidelity coefficients to regress the high-fidelity coefficients. The predicted high-fidelity data is reconstructed from the product of extracted basis vectors and the regression coefficients. The effectiveness of the MF-ROM is evaluated on a flow and heat transfer problem in PWR fuel rod bundles. Two data-driven algorithms, the Kriging and artificial neural network (ANN), are trained as surrogate models for the MF-ROM to reconstruct the complex flow and heat transfer field downstream of the mixing vanes. The results show good agreements between the data reconstructed with the trained MF-ROM and the high-fidelity CFD simulation result, while the former only requires to taken the computational burden of low-fidelity simulation. The results also show that the performance of the ANN model is slightly better than the Kriging model when using a high number of POD basis vectors for regression. Moreover, the result presented in this paper demonstrates the suitability of the proposed MF-ROM for high-fidelity fixed value initialization to accelerate complex simulation.