• Journal of Forest and Environmental Science
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• 제31권1호
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• pp.1-6
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• 2015

Microwave assisted biodiesel production from crude Pongamia pinnata oil using homogeneous base catalyst (KOH) was unsuccessful because of considerable soap formation. Therefore, a two step process of biodiesel production from high free fatty acid (FFA) oil was investigated. In first step, crude P. pinnata oil was acid catalyzed using $H_2SO_4$ and acid value of oil was reduced to less than 4 mg KOH/g. Effect of sulfuric acid concentration, alcohol-oil molar ratio and microwave irradiation time on acid value of oil was studied. Result suggested that 1.5% $H_2SO_4$ (w/w), 6:1 methanol oil molar ratio and 3 min microwave irradiation time was sufficient to reduce the acid value of oil from 12 and 22 mg KOH/g to 2.9 and 3.9 mg/KOH/g, respectively. Oil obtained after pretreatment was subsequently used for microwave assisted alkali catalyzed transesterification. A higher biodiesel yield (99.0%) was achieved by adopting two step processes. Microwave energy efficiency during alkali catalyzed transesterification was also investigated. The results suggested a significant energy saving because of reduced reaction time under microwave heating.

• 대한화학회지
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• 제66권6호
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• pp.442-450
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• 2022

생리학적 활성을 보일 것으로 기대되는 다양한 pyrrolopyrimidine 유도체를 O-arylation과 Suzuki 짝지움 반응을 통해 합성하였다. 금속 촉매 Cu를 사용하고 마이크로파 조사 조건에서O-arylation을 성공적으로 진행하여 pyrrolo[3,2-d]pyrimidine의 4번 위치에 phenol기를 도입할 수 있었다. 또한, 금속촉매 Pd를 사용하는 Suzuki짝지움 반응도 마이크로파를 사용하여 pyrrolo[3,2-d]pyrimidine의 4번 위치에 aryl 기를 도입할 수 있었다. 유도체의 다양화를 위한 반응 조건으로 마이크로파를 사용함으로써 긴 반응 시간과 열전달 효율성 문제를 가지고 있는 전통적인 열 반응의 단점을 획기적으로 극복할 수 있었다. 본 연구 결과는 신약개발 연구에 중요한 역할을 할 것으로 기대되는 pyrrolo[3,2-d]pyrimidine 유도체를 다양화하는데 사용할 수 있다.

• 분석과학
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• 제30권3호
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• pp.138-145
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• 2017

Microwave-assisted organic synthesis has gained a remarkable interest over the past years because of its advantages - (i) rapid energy transfer and superheating, (ii) higher yield and rapid reaction, (iii) cleaner reactions. Ionic liquids are well known for their unique properties such as negligible vapor pressure and high thermal stability. With these properties, ionic liquids have gained increasing attention as green, multi-use reaction media. Recently, ionic liquids have been applied as reaction media for biocatalysis. Lipase-catalyzed reactions in ionic liquids provide high activity and yield compared to conventional organic solvents or solvent free system. Since polar molecules are generally good absorbent to microwave radiation, ionic liquids were investigated as reaction media to improve activity and productivity. In this study, therefore, the effect of microwave irradiation in ionic liquids was investigated on lipase catalyzed reactions such as benzyl acetate synthesis and caffeic acid phenethyl ester synthesis. Comparing to conventional heating, microwave heating showed almost the same final conversion but increased initial reaction rate (3.03 mM/min) compared to 2.11 mM/min in conventional heating at $50^{\circ}C$.

• Korean Chemical Engineering Research
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• 제56권2호
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• pp.275-280
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• 2018

Methyl ester derived from coconut oil is very interesting to study since it contains free-fatty acid with chemical structure of medium carbon chain ($C_{12}-C_{14}$), so the methyl ester obtained from its part can be a biodiesel and another partially into biokerosene. The use of heterogeneous catalysts in the production of methyl ester requires severe conditions (high pressure and high temperature), while at low temperature and atmospheric conditions, yield of methyl ester is relatively very low. By using microwave irradiation trans-esterification reaction with heterogeneous catalysts, it is expected to be much faster and can give higher yields. Therefore, we studied the production of methyl ester from coconut oil using CaO catalyst assisted by microwave. Our aim was to find a kinetic model of methyl ester production through a transesterification process from coconut oil assisted by microwave using heterogeneous CaO catalyst. The experimental apparatus consisted of a batch reactor placed in a microwave oven equipped with a condenser, stirrer and temperature controllers. Batch process was conducted at atmospheric pressure with a variation of CaO catalyst concentration (0.5; 1.0; 1.5; 2.0, 2.5%) and microwave power (100, 264 and 400 W). In general, the production process of methyl esters by heterogeneous catalyst will obtain three layers, wherein the first layer is the product of methyl ester, the second layer is glycerol and the third layer is the catalyst. The experimental results show that the yield of methyl ester increases along with the increase of microwave power, catalyst concentration and reaction time. Kinetic model of methyl ester production can be represented by the following equation: $-r_{TG}=1.7{\cdot}10^6{_e}{\frac{-43.86}{RT}}C_{TG}$.

• Advances in nano research
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• 제5권3호
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• pp.203-214
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• 2017

In this study we present the reaction mechanism of $Cu_2ZnSnSe_4$ (CZTSe) nanoparticles synthesized by microwave-assisted chemical synthesis. We performed reactions every 10 minutes in order to identify different phases during quaternary CZTSe formation. The powder samples were analyzed by x-ray diffraction (XRD), Raman spectroscopy, energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The results showed that in the first minutes copper phases are predominant, then copper and tin secondary phases react to form ternary phase. The quaternary phase is formed at 50 minutes while ternary and secondary phases are consumed. At 60 minutes pure quaternary CZTSe phase is present. After 60 minutes the quaternary phase decomposes in the previous ternary and secondary phases, which indicates that 60 minutes is ideal reaction time. The EDS analysis of pure quaternary nanocrystals (CZTSe) showed stoichiometric relations similar to the reported research in the literature, which falls in the range of Cu/(Zn+Sn): 0.8-1.0, Zn/Sn: 1.0-1.20. In conclusion, the evolution pathway of CZTSe synthesized by this novel method is similar to other synthesis methods reported before. Nanoparticles synthesized in this study present desirable properties in order to use them in solar cell and photoelectrochemical cell applications.

• Journal of Biosystems Engineering
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• 제34권5호
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• pp.371-376
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• 2009

Microwave digestion is a preferred pretreatment method for agricultural samples because of its quick chemical reaction and minimum loss of analytes. In this research, a feedback temperature controller was developed to control the temperature inside a vessel for the microwave-assisted digestion system. An existing industrial microwave oven was fitted with the temperature controller for controlling inside temperature of the vessel. Four control methods, On/Off, proportional (P), proportional integral (PI), and proportional integral derivative (PID) were used and compared. Experimental results showed that PID control produced best temperature control performance. The PID controller could maintain the temperature of water sample and rice sample in the digestion system with error range of $-2.5{\sim}3.3^{\circ}C$ and $-1.9{\sim}0.5^{\circ}C$ at set temperature of $170^{\circ}C$, respectively.

• 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.

• Bulletin of the Korean Chemical Society
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• 제24권11호
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• pp.1575-1578
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• 2003

An environmentally benign approach for the synthesis of 2-substituted-4,6-diaryl pyrimidines using inorganic solid supports for its catalytic role as well as an energy transfer medium is described. The methodology eliminates the usage of solvent during the reaction. The reaction time is brought down from hours to minutes along with yield enhancement. The rate enhancement and high yield is attributed to the coupling of solvent free conditions with microwaves. Further, the role of base is studied in the reaction and it is concluded that microwave assisted basic alumina catalysed reaction is the best in terms of catalysis as well as reaction time and yield.

• 대한화학회지
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• 제55권6호
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• pp.936-939
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• 2011

Thiamine hydrochloride (VB1) has been used as an acid catalyst in organic synthesis. One pot three component Biginelli condensation of dimedone, urea/thiourea and substituted aromatic aldehydes catalyzed by 10 mol % of thiamine hydrochloride (VB1) in solvent free condition under microwave irradiation in good to excellent yields has been investigated. Utilization of microwave irradiation, simple reaction conditions, short reaction time, ease of product isolation, and purification makes this manipulation very interesting from an economic and environmental perspective.

• Bulletin of the Korean Chemical Society
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• 제31권5호
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• pp.1155-1158
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• 2010

Microwave-assisted Michael reaction between EMME and various amines such as diphenylamine, 4-methyl-N-phenylbenzenamine, N-phenylnaphthalen-1-amine, dihexylamine, diisopropylamine, and 4-nitrobenzenamine were described. Solvent-free conditions on alumina as solid support in the presence of $K_2CO_3$ catalysts gave moderate to good yields (55 - 93%) of diethylmalonate analogues having enamine moieties under focused microwave irradiation.