Time filter

Source Type

Lee H.-S.,Korea Institute of Science and Technology | Jeong J.H.,Seoul National University | Hong G.,Seoul National University | Cho H.-K.,Sogang University | And 6 more authors.
Industrial and Engineering Chemistry Research | Year: 2013

The effect of various solvents on the de-cross-linking reaction of cross-linked polyethylene under subcritical and supercritical conditions was studied. The gel content of the de-cross-linked polyethylene decreased from 60 to 0.8-2.5% at 380 °C within 5 min in all of the solvents tested in this study. When water, ethanol, and 2-propanol were used, the Mw of the de-cross-linked polyethylenes decreased from 349,000 to 200,000-227,000 g/mol, and much lower Mw values of 70,000-90,000 g/mol were observed when acetone and diisopropyl ether were used. The de-cross-linked polyethylenes treated in the different solvents had a very similar chemical structure to raw polyethylene. According to a kinetic study using a first-order reaction model, the de-cross-linking rate in each solvent increased in the order 2-propanol < ethanol < n-hexane < water < methanol ≪ diisopropyl ether ≪ acetone at 350 °C. © 2013 American Chemical Society.


Yoon D.,Sungkyunkwan University | Chung K.Y.,Korea Institute of Science and Technology | Chang W.,Korea Institute of Science and Technology | Kim S.M.,Korea Institute of Science and Technology | And 4 more authors.
Chemistry of Materials | Year: 2015

Hydrogen-enriched reduced graphene oxide (RGO) was achieved using double-oxidized graphene oxide (GO2) as an anode in high-performance lithium batteries is reported. GO2 exhibited a much lower carbon-to-oxygen ratio, lower crystallinity, higher Brunauer-Emmett-Teller surface area, higher pore volume, and higher porosity as compared to graphene oxides produced using the typical modified Hummers method (GO1). The two forms of GO were reduced using two different reduction methods: supercritical isopropanol (scIPA) and heat treatment. The four types of RGOs synthesized using GO1/GO2 and scIPA/heat treatment exhibited significantly different chemical, morphological, and textural properties. The galvanostatic charge-discharge properties were highly dependent on the physicochemical properties of the RGOs. The scIPA-reduced GO2 exhibited superior electrochemical performance as compared to the thermally reduced GO1/GO2 and scIPA-reduced GO1. Highly reversible capacity (1331 mAh g-1 at 50 mA g-1 after 100 cycles), excellent rate-performance (328 mAh g-1 at 5 A g-1), and good cycling stability up to 1000 cycles even at a current density of 10 A g-1 were observed with the scIPA-reduced GO2 electrode. The characterization results suggested that a large amount of hydrogen-terminated groups, numerous defect sites, and large interlayer spacing have beneficial effects on the electrochemical performance of scIPA-reduced GO2. © 2014 American Chemical Society.


Brand S.,Korea Institute of Science and Technology | Brand S.,Korean University of Science and Technology | Susanti R.F.,Korea Institute of Science and Technology | Susanti R.F.,Korean University of Science and Technology | And 6 more authors.
Energy | Year: 2013

In this study, the influence of various physical process parameters on the liquefaction of lignocellulosic biomass (pine wood) in supercritical ethanol was investigated. The parameters include reaction temperature (280-400°C), initial nitrogen pressure (0.4-7.5MPa), reaction time (0-240min), and biomass-to-solvent ratio (0.06-0.25g/g). The reaction temperature and residence time were found to have a more significant effect on biomass conversion and product yield than pressure and biomass-to-solvent ratio had; conversion in the range 34.0-98.1% and biocrude yield in the range 15.8-59.9wt% were observed depending on the process parameters. Despite the absence of catalysts and external hydrogen source, solid biomass to liquid and gaseous products conversion of 98.1%, and a high biocrude yield of approximately 65.8wt% were achieved at 400°C, 120min, and a biomass-to-solvent ratio of 0.06g/g. Moreover, the biocrude contained considerably lower amounts of oxygen and higher amounts of carbon and hydrogen, resulting in a substantially higher heating value (>30MJ/kg) as compared to raw feedstock (20.4MJ/kg). A comparison with sub- or supercritical water-based liquefaction revealed that supercritical ethanol produced biocrude with a lower molecular weight and much better yield. Finally, a new biomass liquefaction reaction mechanism associated with supercritical ethanol is proposed. © 2013.


Hong S.-A.,Korea Institute of Science and Technology | Kim S.J.,Korea Institute of Science and Technology | Chung K.Y.,Korea Institute of Science and Technology | Lee Y.-W.,Seoul National University | And 3 more authors.
Chemical Engineering Journal | Year: 2013

This study investigates the effect of various process parameters during continuous synthesis in supercritical water on the physicochemical and electrochemical properties of lithium iron phosphate (LiFePO4) for use in large-scale lithium 2nd battery applications. The process parameters include reaction temperature (300-400°C), precursor solution concentration (0.01-0.18M), precursor solution flow rate (1.5-3.0g/min), water flow rate (9.0-36.0g/min), and residence time (9-72s). Under subcritical water conditions, mixed Fe3(PO4)2{dot operator}8H2O, Fe2O3, and Fe3O4 particles formed; in contrast, under supercritical fluid conditions, well-crystallized LiFePO4 particles with some Fe3+ impurities (i.e., Fe2O3 and Fe3O4) were obtained. In supercritical water, an increase in the precursor concentration leads to an increase in the Fe3+ impurity content. At a high water flow rate, a significant decrease in crystallinity and the formation of Fe3(PO4)2{dot operator}8H2O and Li6P6O18{dot operator}9H2O phases rather than LiFePO4 were observed. Highly crystalline LiFePO4 with good discharge capacity was obtained with high temperature, low precursor concentration, and low flow rate conditions. Depending on the synthetic conditions, bare LiFePO4 particles exhibit discharge capacities of 55-85mAh/g at 0.1 C-rate after 30 cycles. After carbon coating, a marginal capacity decay from 141 to 135mAh/g was observed during the 30 charge-discharge cycles. © 2013.


Brand S.,Korea Institute of Science and Technology | Kim J.,Sungkyunkwan University | Kim J.,Sungkyun Advanced Institute of Nano Technology SAINT
Energy | Year: 2015

Herein, α-cellulose, d-xylose, and lignin, which are major lignocellulosic biomass constituents, are subject to being liquefied in scEtOH (supercritical ethanol). Biomass conversion, biocrude yield, gas composition and energy content resulting from the liquefaction are analyzed. When cellulose is used, the biocrude yield increased significantly from 1.6 to 48.4wt% with an increase in temperature from 265 to 350°C, while the yields of biocrudes obtained from lignin (25.2-28.8wt%) and xylose (32.1-42.0wt%) do not change significantly with varying temperature. The chemical composition of the biocrudes obtained from the cellulose and xylose liquefaction in scEtOH significantly differ when compared to those of the biocrudes obtained from fast pyrolysis and hydrothermal liquefaction. The unique chemical species in the scEtOH-liquefied biocrude include long-chain esters/ethers (C5-C10), long-chain acids (C4-C9), and tetrahydrofurans, which could be due to the enhanced esterification and hydrogenation reactions in the scEtOH medium. Plausible reaction pathways of xylose liquefaction in scEtOH are proposed. © 2014.


Kim J.,Sungkyunkwan University | Kim J.,Sungkyun Advanced Institute of Nano Technology SAINT | Hong S.-A.,Korea Institute of Science and Technology | Yoo J.,Sungkyun Advanced Institute of Nano Technology SAINT | Yoo J.,Sungkyunkwan University
Chemical Engineering Journal | Year: 2015

Carbon-coated, hierarchical porous ZnO microspheres are synthesised continuously in supercritical methanol using oleic acid as the surface modifier and subsequent carbon coating, using sucrose as the carbon source. The physicochemical properties and the electrochemical performance of the ZnO microspheres are compared with those of commercially available ZnO and rod-type ZnO synthesised in supercritical water. The addition of oleic acid effectively inhibits the particle growth, resulting in nanosized primary ZnO particles with sizes of 10-50nm that are loosely agglomerated and form secondary microspheres with sizes of 100-800nm with a high porosity of 42.2%. After the carbon coating, the porous hierarchical ZnO microspheres with 6.8wt% carbon exhibit a much higher reversible capacity of 546.5mAhg-1 compared to the rod-type ZnO (361.2mAhg-1) and commercial ZnO (151.1mAhg-1) at a current density of 97.8mAg-1 (0.1C) after 30 cycles. In particular, at a high rate of 1.0C, a reversible capacity of 428.5mAhg-1 can be obtained after 100 cycles. The enhanced discharge capacity of the carbon-coated ZnO may be attributed to the combined beneficial effects of nanosized primary particles, hierarchical porous morphology and carbon-coating on Li+ storage. © 2014 .


Li W.,Sungkyunkwan University | Hwang J.,Sungkyunkwan University | Chang W.,Korea Institute of Science and Technology | Setiadi H.,Sungkyun Advanced Institute of Nano Technology SAINT | And 3 more authors.
Journal of Supercritical Fluids | Year: 2016

Uniform and complete coverage of ultrathin carbon layer coatings on the surface of nano-sized LiFePO4 (LFP) particles prepared using a supercritical alcohol route was investigated. In the presence of oleylamine, nanosized oleylamine-modified LFP particles were synthesized in supercritical ethanol because particle growth was inhibited. When the oleylamine-modified LFP was calcined, uniform coverage of carbon layers with thicknesses of 1.5–2.0 nm on individual LFP particles was achieved. The carbon-coated LFP (C-LFP) exhibited hierarchical porous nano/micro sphere morphology with a porosity of 45.6%. In comparison with bare LFP synthesized in the absence of oleylamine, C-LFP exhibited excellent Li ion uptake performance; C-LFP delivered a reversible discharge capacity of 158.4 mAh g−1 after 100 cycles at 0.1 C and a rate performance of 84.0 mAh g−1 at 20 C. In addition, after 700 continuous cycles at 10 C, the C-LiFePO4 electrode exhibited a reversible discharge capacity of 84.0 mAh g−1 with small capacity loss. Electrochemical impedance tests revealed that the uniform and ultrathin carbon coating improved charge transfer kinetics and lithium diffusion into the active material. © 2016


Seo M.,Korea Institute of Science and Technology | Yoon D.,Sungkyunkwan University | Hwang K.S.,Korea Institute of Science and Technology | Kang J.W.,Korea University | And 2 more authors.
Carbon | Year: 2013

We report on a facile, simple, and green graphene oxide (GO) reduction method based on a supercritical alcohol approach. The influence over the chemical, thermal, morphological, and textural properties of reduced graphene oxides (RGOs) of five different alcohols in their supercritical conditions - methanol, ethanol, 1-propanol, 2-propanol, and 1-butanol - was investigated in detail. Although the thermal stabilities and Fourier-transform infrared spectra of RGOs produced using the different alcohols are very similar, a substantial difference in the carbon-to-oxygen ratios measured by X-ray photoelectron spectroscopy and Brunauer-Emmett-Teller surface areas are observed. The RGO produced using supercritical ethanol exhibited a much higher carbon-to-oxygen ratio of 14.4 and a much larger surface area of 203 m2/g compared with that produced using the other supercritical alcohols. Raman spectra showed that the RGOs produced using supercritical ethanol and supercritical 2-propanol retained more of the graphitic structure. X-ray diffraction analysis revealed that RGOs produced using supercritical 1-propanol and supercritical 1-butanol retained at least two different interlayer spacings. The deoxygenation mechanism of GO in supercritical ethanol is proposed based on gas and liquid product analysis. © 2013 Elsevier Ltd. All rights reserved.


Brand S.,Korea Institute of Science and Technology | Brand S.,Korean University of Science and Technology | Hardi F.,Korea Institute of Science and Technology | Hardi F.,Korean University of Science and Technology | And 5 more authors.
Energy | Year: 2014

This study investigates the influence of heating and cooling rate on liquefaction of lignocellulosic biomass in subH2O (subcritical water) or in scEtOH (supercritical ethanol), in dependency of final reaction temperatures (250-350°C) and residence times (1-40min). The heating rate has been identified as a crucial parameter in the subH2O-based liquefaction, whereas it has marginal influence in the scEtOH-based liquefaction. Detailed characterization of gas, liquid and solid products enables to identify the individual reaction steps, which results in a new insight into the reaction mechanisms, depending on the liquefaction solvents and conditions. Similar to fast pyrolysis, hydrothermal liquefaction consists of beneficial primary reactions (pyrolytic & hydrolytic degradation) and non-beneficial secondary reactions i.e. recombination and secondary cracking. In scEtOH, biomass was decomposed by pyrolysis and alcoholysis at relatively high reaction temperatures while the recombination of reaction intermediates are retarded by the unique reactions of scEtOH such as hydrogen donation and hydroxylalkylation. © 2014.


Lee H.-S.,Korea Institute of Science and Technology | Lee H.,Korea Institute of Science and Technology | Lee H.,Korean University of Science and Technology | Ha J.-M.,Korea Institute of Science and Technology | And 5 more authors.
Industrial Crops and Products | Year: 2015

The production of bio-crude oil (BCO) from oil palm empty fruit bunches (EFB) by hydro- and solvothermolysis methods was investigated. The effects of the reaction temperature, reaction time, the solvent and inorganic matter were studied using a batch reactor. The yield of BCO, the molecular weight of BCO, and the yield of aromatic compounds contained in the BCO were measured. The molecular weight of BCO decreased as the reaction temperature increased; however, the yield of BCO and aromatic compounds decreased at a high temperature and with a long reaction time. The maximum yield of the total BCO was obtained when the ratio of water and ethanol was 50:50, while the yield of most monomeric compounds was highest when the ratio of water and ethanol was 25:75. The inorganic matter in the raw EFB increased the yield of BCO and monomeric compounds compared to that with washed EFB. © 2015 Elsevier B.V.

Loading Sungkyun Advanced Institute of Nano Technology SAINT collaborators
Loading Sungkyun Advanced Institute of Nano Technology SAINT collaborators