• 한국토양비료학회지
• /
• 제33권1호
• /
• pp.32-39
• /
• 2000

하수 오니에 의한 Cd 의 흡착반응을 조사하기 위하여, Cd의 처리농도 (5, 10, 15, 20, 25 및 $50{\mu}g\;Cd\;ml^{-1}$를 달리하여 흡착실험을 수행하였으며, 반응시간 (흡착 반응 후 0.5, 1.0, 1.5, 2.5, 4.5, 6.6, 8.5, 12.5, 24.5 및 48.5 h) 별로 Cd 의 농도를 구하여 흡착반응의 속도상수를 계산하였다. 모든 처리 농도에서 처음 반응시간 30분 이내에 처리 한 Cd의 약 95% 가 흡착되었다. 초기의 빠른 1단계 Cd 흡착반응 후에는 1차 가역 반응식으로 기술할 수 있는 1단계 반응보다는 느린 2단계의 Cd 흡착 반응이 일어났다. 1차 가역 반응식으로 기술할 수 있는 2단계의 Cd 흡착 반응의 속도상수는 $-0.137{\sim}-0.521h^{-1}$의 범위로서 Cd처리 농도가 증가할수록 속도상수는 감소하였다. 흡착 반응에서 평형에 도달하는 시간 (약 6-24 h) 이나, 평형에서의 Cd 의 흡착량 (약 $276-2720{\mu}g\;g^{-1}$) 또는 흡착되지 않고 용액에 남아있는 Cd의 농도 (약 $60-400{\mu}g\;L^{-1}$) 도 Cd 의 처리 농도에 의하여 결정되었다. 즉 Cd 의 처리 농도가 증가할수록 평형에 도달하는 시간, 흡착량 및 평형 농도는 증가하였다. 하수 오니에 의하여 흡착된 Cd 의 일부는 시간이 경과함에 따라 하수 오니로 부터 방출되었으나 그 양은 전체 Cd 흡착량에 비하면 매우 적었다.

• 자원리싸이클링
• /
• 제28권3호
• /
• pp.15-20
• /
• 2019

폐수내 질소와 인을 이용한 struvite 회수는 수계 부영양화 방지 및 비료자원화에 효과적인 기술이나, 해결해야 할 이론 및 기술적 문제점이 있다. 본 연구에서는, 기존 문헌의 상세한 검토를 통하여, 이론적 측면에서 적절한 반응식 선정 및 이론적 고찰을 이용한 struvite 생성 반응예측 가능성을 논의하고, 기술적 측면에서는 struvite 생성의 대표적인 저해물질인 Ca의 배제를 통해 struvite 결정의 순도를 높일 수 있는 효과적인 방법을 소개하려 한다. 반응예측 측면에서는 중성~염기성 pH 영역에서 효과적인 struvite 반응식 및 반응계수를 이용, 정량적 모델을 구축할 수 있다. 이러한 모델은 실제 회분식 실험결과와 잘 일치하며 특히 이온들의 charge balance도 함께 고려하여 struvite 생성시 희석된 수용액에서 흔히 동반되는 pH 저하를 합리적으로 예측할 수 있다. 한편, Ca의 배제를 통한 struvite 순도 향상은 ${HPO_4}^{2-}-P$ 대비 고농도의 ${NH_4}^+-N$을 조성하여 해결할 수 있는데, 이는 고농도 암모늄 이온의 존재가 struvite 생성 관련 열역학적 구동력을 강화시켜 인산염이 Ca 대신 고농도 암모니아와 용이하게 반응하여 struvite 생성에 유리한 이온환경을 조성하기 때문이다. 즉 인산염이 $Ca^{2+}$과 빠르게 반응하여 이미 침전물이 형성하였을지라도, 고동도 암모늄으로 인한 열역학적 구동력으로 인산-칼슘 침전물이 재용해 되어 struvite를 생성시킬 수 있다.

• Biotechnology and Bioprocess Engineering:BBE
• /
• 제11권4호
• /
• pp.299-305
• /
• 2006

Aromatic L-amino acid transaminase is an enzyme that is able to transfer the amino group from L-glutamate to unnatural aromatic ${\alpha}-keto$ acids to generate ${\alpha}-ketoglutarate$ and unnatural aromatic L-amino acids, respectively. Enrichment culture was used to isolate thermophilic Bacillus sp. T30 expressing this enzyme for use in the synthesis of unnatural L-amino acids. The asymmetric syntheses of L-homophenylalanine and L-phenylglycine resulted in conversion yields of >95% and >93% from 150 mM 2-oxo-4-phenylbutyrate and phenylglyoxylate, respectively, using L-glutamate as an amino donor at $60^{\circ}C$. Synthesized L-homophenylalanine and L-phenylglycine were optically pure (>99% enantiomeric excess) and continuously pre-cipitated in the reaction solution due to their low solubility at the given reaction pH. While the solubility of the ${\alpha}-keto$ acid substrates is dependent on temperature, the solubility of the unnatural L-amino acid products is dependent on the reaction pH. As the solubility difference between substrate and product at the given reaction pH is therefore larger at higher temperature, the thermophilic transaminase was successfully used to shift the reaction equilibrium toward rapid product formation.

• Nuclear Engineering and Technology
• /
• 제48권2호
• /
• pp.482-494
• /
• 2016

The Feshbache-Kermane-Koonin (FKK) multi-step direct (MSD) theory of pre-equilibrium reactions has been used to compute the single-step cross-sections for some (p,${\alpha}$) reactions using the knock-on and pick-up reaction mechanisms at two incident proton energies. For the knock-on mechanism, the reaction was assumed to have taken place by the direct ejection of a preformed alpha cluster in a shell-model state of the target. But the reaction was assumed to have taken place by the pick-up of a preformed triton cluster (also bound in a shell-model state of the target core) by the incident proton for the pick-up mechanism. The Yukawa forms of potential were used for the proton-alpha (for the knock-on process) and proton-triton (for the pick-up process) interaction and several parameter sets for the proton and alpha-particle optical potentials. The calculated cross-sections for both mechanisms gave satisfactory fits to the experimental data. Furthermore, it has been shown that some combinations of the calculated distorted wave Born approximation cross-sections for the two reaction mechanisms in the FKK MSD theory are able to give better fits to the experimental data, especially in terms of range of agreement. In addition, the theory has been observed to be valid over a wider range of energy.

• International Journal of Computer Science & Network Security
• /
• 제22권6호
• /
• pp.91-96
• /
• 2022

The photocatalytic degradation of salicylic acid takes place in several stages involving coupled phenomena, such as the transport of molecules and the chemical reaction. The systems of transport equations and the photocatalytic reaction are numerically solved using COMSOL Mutiphysics (CM) simulation software. CM will make it possible to couple the phenomena of flow, the transport of pollutants (salicylic acid) by convection and diffusion, and the chemical reaction to the catalytic area (bauxite or TiO2 doped by nanoparticles). The simulation of the conversion rate allows to correctly fit the experimental results. The temporal simulation shows that the reaction reaches equilibrium after a transitional stage lasting over one minute. The outcomes of the study highlight the importance of diffusion in the boundary layer and the usefulness of injecting micro-agitation into the microchannel flow. Under such conditions, salicylic acid degrades completely.

• Bulletin of the Korean Chemical Society
• /
• 제16권1호
• /
• pp.47-52
• /
• 1995

The mechanism of the photodecomposition of 2-methoxy-1,2-diphenyl diazoethane has been investigated in methanol and isoprene using time-resolved laser flash photolysis techniques. The reaction of triplet carbene which is generated from 2-methoxy-1,2-diphenyl diazoethane with methanol is believed to proceed via thermal excitation to the singlet state. The activation energy and enthalpy are consistent with a mechanism involving thermal equilibrium between the triplet and singlet state followed by the reaction of the singlet with methanol to give ether.

• Bulletin of the Korean Chemical Society
• /
• 제13권2호
• /
• pp.184-187
• /
• 1992

Regeneration methods of oximes, hydrazones, and N,N-dimethylhydrazones to the related carbonyl compounds were effected using various dicarbonyl compounds which are activated with electron withdrawing substituents such as trifluoromethylated $\beta-diketones$, $\beta-acylpyruvates$, and $\alpha-diketones$ via an equilibrium exchange reaction. The chemical transformations of the dicarbonyl compounds in the exchange reaction were investigated by various spectroscopic methods.

• 한국대기환경학회지
• /
• 제9권2호
• /
• pp.154-159
• /
• 1993

Theoretical prediction of the equilibrium of temperature and relative humidity dependance involving $HNO_{3(g)}-NH_{3(g)}$ and $NH_4NH_{3(s, aq)}$ was compared with atmospheric measurement of particulate nitrate$(NO_3^-)$, Ammonia-Nitric Acid partial pressure product $([$NH_{3(g)}][HNO_{3(g)}]ppb^2$) by a triple filter pack sampler from Oct 1991 to July 1992. The measured $HNO_3NH_3$ concentration product K was greater than equilibrium constant $K_p$ calculated from thermodynamic data of $NH_4NO_{3(s, aq)}-HNO_{3(g)}-NH_{3(g)}$ during fall, winter and spring. But K was lower than $K_p$ in summer. K was greater than $K_p$ as the result of supersaturation by air pollution, particularly anthropogenic $NH_3$.The reason of $K < K_p$ was due to removal of particulate nitrate$(NO_3^-)$ by rainout and washout. $NH_4NO_3$ which consists mainly of particulate nitrate is formed by reaction between $HNO_3$ and $NH_3$. As a result of the removal of particulate nitrate$(NO_3^-)$ by rainout and washout, concentrations of $HNO_3$ and $NH_3$ are decreased by equilibrium transfer(Le Chatelier's Law) in atmosphere.

• 한국농공학회논문집
• /
• 제57권1호
• /
• pp.79-87
• /
• 2015

A thermochemical equilibrium model was constructed for predicting composition of synthesis gas in biomass gasification. The model included estimation of equilibrium constants using Gibbs free energy. After constructing the model, the results were compared with the experimental values and predictions from a previous model. Gas compositions were reasonably well agreed with them and showed effects of operational and fuel condition. When the reaction temperature increased, the lower heating values decreased due to the decrease in CH4 concentrations. The methane concentrations were lower than those observed in experimental results. The model was used to predict the gas composition and heating values for the cases of mixed fuel of charcoal and un-dry woodchips. Although downdraft gasifiers require fuels less than 15% of moisture contents, the model results indicated that the mixed fuel with charcoal and woodchips which had over 25% of moisture contents could be used in the downdraft gasifiers. It might be explained by increase in energy density resulting from mixing charcoal. The results imply that the efforts and costs for drying biomass fuels could be reduced by mixing charcoal or fuels with higher calorific values.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2010년도 제35회 추계학술대회논문집
• /
• pp.447-450
• /
• 2010

$CH_4-O_2$ vitiated 공기가열기에서의 유동 오염도 분석을 위해 가열기 및 노즐 영역에 대한 평형 및 평형 유동장 계산을 수행하였다. 유동장은 일차원 비점성 유동으로 가정하였으며 계산 결과는 측정값과 비교하였다. 연구결과 연소 지연이나 중단 현상에 영향을 주는 오염원으로써 NO 성분의 존재를 파악하기 위해서는 비평형 유동장 계산이 고려되어야 함을 알 수 있었다.