• Journal of Microbiology and Biotechnology
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• 제19권12호
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• pp.1596-1602
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• 2009

A lipase-catalyzed esterification reaction of (S)-naproxen ethyl ester by CALB (Candida antarctica lipase B) enzyme was performed in supercritical carbon dioxide. Experiments were performed in a high-pressure cell for 10 h at a stirring rate of 150 rpm over a temperature range of 313.15 to 333.15 K and a pressure range of 50 to 175 bar. The productivity of (S)-naproxen ethyl ester was compared with the result in ambient condition. The total reaction time and conversion yields of the catalyzed reaction in supercritical carbon dioxide were compared with those at ambient temperature and pressure. The experimental results show that the conversion and reaction rate were significantly improved at critical condition. The maximum conversion yield was 9.9% (216 h) at ambient condition and 68.9% (3 h) in supercritical state. The effects of varying amounts of enzyme and water were also examined and the optimum condition was found (7 g of enzyme and 2% water content).

• Korean Chemical Engineering Research
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• 제47권3호
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• pp.281-286
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• 2009

아임계 및 초임계 조건의 물을 이용하여 캐나다산 Athabasca 오일샌드로부터 역청 추출 및 황 제거 실험을 수행하였다. 0~120 min의 반응시간, 360, $380^{\circ}C$의 온도, 15~30 MPa의 압력 및 $0.074{\sim}0.61g/cm^3$의 물 밀도를 변화시키면서 micro reactor에서 역청 수율을 조사하였다. 역청 수율은 온도에 상관없이 압력이 증가할수록 증가하였으며, 특히 초임계 영역에서 수증기 개질반응에 의해 생성된 수소에 의해 역청의 수율이 급격히 증가하였다. 전체 기상 생성량은 압력 증가에 따라 감소하였으나 $380^{\circ}C$에서 황과 수소의 생성분율은 25 및 30 MPa로 압력 증가에 따라 소량 증가하였다. 이상의 결과는 초임계 조건이 수소의 생성과 황의 제거에 유리하다는 것을 보여준다. 초임계 조건$380^{\circ}C$, 25와 30 MPa)에서 역청 수율은 최대 약 22%였으며, 오일샌드에 함유된 황 제거율도 최대값 40%에 도달하였다.

• Nuclear Engineering and Technology
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• 제49권1호
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• pp.103-112
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• 2017

Application of the supercritical condition in reactor core cooling needs to be properly justified based on the extreme level of parameters involved. Therefore, a numerical study is presented to compare the thermalhydraulic performance of supercritical and single-phase natural circulation loops under low-to-intermediate power levels. Carbon dioxide and water are selected as respective working fluids, operating under an identical set of conditions. Accordingly, a three-dimensional computational model was developed, and solved with an appropriate turbulence model and equations of state. Large asymmetry in velocity and temperature profiles was observed in a single cross section due to local buoyancy effect, which is more prominent for supercritical fluids. Mass flow rate in a supercritical loop increases with power until a maximum is reached, which subsequently corresponds to a rapid deterioration in heat transfer coefficient. That can be identified as the limit of operation for such loops to avoid a high temperature, and therefore, the use of a supercritical loop is suggested only until the appearance of such maxima. Flow-induced heat transfer deterioration can be delayed by increasing system pressure or lowering sink temperature. Bulk temperature level throughout the loop with water as working fluid is higher than supercritical carbon dioxide. This is until the heat transfer deterioration, and hence the use of a single-phase loop is prescribed beyond that limit.

• 한국환경과학회지
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• 제14권5호
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• pp.513-520
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• 2005

For the destruction of toxic chlorinated organic compounds, this study proposes improved supercritical water oxidation method (multistep oxidation) using sodium nitrate as an oxidizer. This method solves the problems involved in the existing supercritical water oxidation method. Multistep oxidation means that $NaNO_3$ is oxidized to $N_2\;via\;NaNO_2$ and NO. Toxic and hard to destroy organic substances like para-dichlorobenzen(4-DCBz), polychlorinate biphenyl(PCB) ware oxidized to non toxic substances in a condition, in which rapid pressure and temperature rise is restrained as much as possible. 4-dichlorobenzene(4-DCBz) and Polychlorinate biphenyl(PCB) in condition$(450^{\circ}C,\;p_w=0.25g/cm^3,\;30min)$ Was discomposed perfectly.

• Elastomers and Composites
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• 제34권3호
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• pp.239-246
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• 1999

폐타이어에서 보강실과 고무로 배합된 부분(side wall)을 아임계와 초임계 상태의 세가지 용매, 물, 28% 암모니아수, 암모니아를 사용하여 용매의 분해와 추출능을 비교하였다. 6mm 입방체로 만든 폐타이어의 초임계물에 의한 분해와 추출속도는 140 kJ/mol의 활성화에너지를 갖는 1차 속도식을 잘 만족하였다. 초임계상태에서 28% 암모니아용액은 압력이 감소할수록 초기추출에서 초임계물보다 추출능이 높게 나타났다. 이 현상은 초임계물에 용해되어 있는 암모니아의 영향 때문이라고 추측된다.

• 한국환경과학회지
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• 제14권10호
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• pp.919-928
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• 2005

This study introduces the development of new supercritical water oxidation(SCW)(multiple step oxidation) to destruct recalcitrant organic substances totally and safely by using sodium nitrate as an oxidant. This method has solved the problems of conventional SCW, such as precipitation of salt due to lowered permittivity, pressure increase following rapid rise of reaction temperature, and corrosion of reactor due to the generation of strong acid. Destruction condition and rate in the supercritical water were examined using Polyvinyl Chloride(PVC) and ion exchange resins as organic substances. The experiment was carried out at $450^{\circ}C$ for 30min, which is relatively lower than the temperature for supercritical water oxidation $(600-650^{\circ}C)$. The decomposition rates of various incombustible organic substances were very high [PVC$(87.5\%)$, Anion exchange resin$(98.6\%)$, Cationexchange resin$(98.0\%)$]. It was observed that hetero atoms existed in organic compounds and chlorine was neutralized by sodium (salt formation). However, relatively large amount of sodium nitrate (4 equivalent) was required to raise the decomposition ratio. For complete oxidation of PCB was intended, the amount of oxidizer was an important parameter.

• Nuclear Engineering and Technology
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• 제39권4호
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• pp.273-286
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• 2007

This paper presents the research activities performed to date for the development of a supercritical pressure water-cooled reactor (SCWR) in Korea. The research areas include a conceptual design of an SCWR with an internal flow recirculation, a reactor core conceptual design, a heat transfer test with supercritical $CO_2$, an adaptation of an existing safety analysis code to the supercritical pressure condition, and an evaluation of candidate materials through a corrosion study. Methods to reduce the cladding temperature are introduced from two different perspectives, namely, thermal-hydraulics and core neutronics. Briefly described are the results of an experiment on the heat transfer at a supercritical pressure, an experiment that is essential for the analysis of the subchannels of fuel assemblies and the analysis of a system safety. An existing system code has been adapted to SCWR conditions, and the process of a first-hand validation is presented. Finally, the corrosion test results of the candidate materials for an SCWR are introduced.

• 한국환경보건학회지
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• 제30권2호
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• pp.133-139
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• 2004

The objective of this study was to investigate the destruction efficiency and to determine the fundamental parameters of oxidation kinetics under the supercritical water(SCW) condition. Target material was cephradine, toxic and antibiotic material, in the pharmaceutical wastewater. For this purpose, the effect of reaction temperature and oxidant were investigated on the destruction efficiency of cephradine. And the oxidation kinetics of cephradine was derived by using a empirical power-law model. The experiment was carried out in a cylindrical batch reactor made of Hastelloy C-276 which was endurable high temperature and pressure. The destruction efficiency of cephradine increased with increment of the temperature and reaction time. Also the type of oxidants was effected and oxidants(Air and $H_2O$$_2$) were enhanced the destruction efficiency. The global oxidation kinetics for cephradine has led to two rate expressions according to type of oxidant. - In the presence of air oxidant: Rate=k. $e^{-Ea}$RT/(Ceph.)$^{1.0}$ ( $O_2$)$^{0.51}$$\pm$0.05(k=3.27${\times}$$10^{5}$ sec. Ea=63.25 kJ/mole) - In the presence of $H_2O$$_2$ oxidant : Rate=kㆍ $e^{-Ea}$RT/(Ceph.)$^{1.0}$ ($H_2O$$_2$)$^{0.62}$$\pm$0.02(k=2.76${\times}$$10^4$/sec. Ea=47.65 kJ/mole)ole))

• 한국세라믹학회지
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• 제37권7호
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• pp.625-631
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• 2000

In this study, the characteristics and sinterablities of TiO2 powders which were fabricated on sol-gel process and supercritical fluid process were examined. The powders fabricated on sol-gel process were amorphous. The particle size and shape were changed with the amount of water used for hydrolysis of titanium ethoxide. The powders were changed from amorphous to crystalline by heating at 400℃. The crystalline anatase TiO2 powders were directly prepared in ethanol supercritical fluid condition that temperature was 270±3℃ and pressure was 7.3 MPa. It's primary crystalline size was 20 nm and agglomerated as spherical shape whose size was 0.7∼1㎛. The powders prepared on sol-gel process were not sintered densely at 900℃ because of abnormal grain growth. However, the powders which prepared on supercritical fluid process were sintered densely at the comparatively low temperature of 800℃ by ideal growth of grain, which are fired at 900℃.

• KSBB Journal
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• 제19권4호
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• pp.284-287
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• 2004

초임계 이산화탄소를 이용하여 가시오갈피로부터 유용성분인 acanthoside-D를 추출하여 다음과 같은 결론을 유추하였다. 에탄올과 물, 그리고 50% 메탄올을 공용매로 사용하여 일정압력과 온도에서 추출한 결과물에서의 수율이 가장 높게 측정되었으며, 압력의 변화에 따른 acanthoside-D의 추출효율을 비교한 결과 300 bar에서 가장 높은 추출효율을 나타내었다. 또한 50% 메탄올을 공용매로 하여 유량을 변화시킨 결과, 높은 유량에서 높은 수율을 나타내었으나 1.5ml/g 이상의 유량에서는 수율의 변화가 없었다.