Shinyoung Oh

Fast pyrolysis of potassium impregnated poplar wood and characterization of its influence on the formation as well as properties of pyrolytic products

TGA results indicated that the maximum decomposition temperature of the biomass decreased from 373.9 to 359.0°C with increasing potassium concentration. For fast pyrolysis, char yield of potassium impregnated biomass doubled regardless of pyrolysis temperature compared to demineralized one. The presence of potassium also affected bio-oil properties. Water content increased from 14.4 to 19.7 wt% and viscosity decreased from 34 to 16.2 cSt, but the pH value of the bio-oil remained stable. Gas chromatography/mass spectroscopy (GC/MS) analysis revealed that potassium promoted thermochemical reactions, thus causing a decrease of levoglucosan and an increase of small molecules and lignin-derived phenols in bio-oil. Additionally, various forms of aromatic hydrocarbons, probably derived from lignins, were detected in non-condensed pyrolytic gas fractions.

Effects of various reaction parameters on solvolytical depolymerization of lignin in sub- and supercritical ethanol.

Organosolv lignin was treated with ethanol at sub/supercritical temperatures (200, 275, and 350 °C) for conversion to low molecular phenols under different reaction times (20, 40, and 60 min), solvent-to-lignin ratios (50, 100, and 150 mL g(-1)), and initial hydrogen gas pressures (2 and 3 MPa). Essential lignin-degraded products, oil (liquid), char (solid), and gas were obtained, and their yields were directly influenced by reaction conditions. In particular, concurrent reactions involving depolymerization and recondensation as well as further (secondary) decomposition were significantly accelerated with increasing temperature, leading to both lignin-derived phenols in the oil fraction and undesirable products (char and gas). As the main components in the oil fraction, oxygenated phenols, guaiacol, and syringol as well as their alkylated forms were detected. The yield of alkylated phenols showed a drastic increase at 350 °C in the presence of initial hydrogen gas due to prevailing hydrodeoxygenation and hydrogenation reactions of the vinyl/allyl/oxygenated phenols. These reactions were also demonstrated indirectly from the results of atomic H/C and O/C of the oils. The highest amount of monomeric phenols released from lignin (1.0 g) was measured as ca. 96.7 mg at 350 °C, 40 min, 100 mL g(-1), and 3 MPa of H2. In addition, GPC analysis suggested a possibility of condensation between lignin-degraded fragments during the solvolysis reaction.

Investigation of structural modification and thermal characteristics of lignin after heat treatment

Milled wood lignin was subjected to heat treatment between 150 and 300°C to understand the pattern of its structural modification and thermal properties. When the temperature was elevated with interval of 50°C, the color of the lignin became dark brown and the lignin released various forms of phenols from terminal phenolic groups in the lignin, leading to two physical phenomena: (1) gradual weight loss of the lignin, up to 19% based on dry weight and (2) increase in the carbon content and decrease in the oxygen content. Nitrobenzene oxidation and (13)C NMR analyses confirmed a cleavage of β-O-4 linkage (depolymerization) and reduction of methoxyl as well as phenolic hydroxyl group were also characteristic in the lignin structure during heat treatment. Simultaneously with lignin depolymerization, GPC analysis provided a possibility that condensation between lignin fragments could also occur during heat treatment. TGA/DTG/DSC data revealed that thermal stability of lignin obviously increased after heat treatment, implicating the structural rearrangement of lignin to reduction of β-O-4 linkage as well as accumulation of CC bonds.

Core-Level X-Ray Photoemission Satellites in Ruthenates: A New Mechanism Revealing The Mott Transition

Core-level x-ray photoemission spectra for the Mott-Hubbard systems are calculated by the dynamical mean-field theory based on the exact diagonalization method. The spectra show a two-peak structure, screened and unscreened peaks. The screened peak is absent in a Mott insulator, but develops into the main peak when the correlation strength becomes weak and the system turns metallic. The calculated spectral behavior is consistent with the experimental Ru 3d core-level spectra of various ruthenates. This new mechanism of the core-level photoemission satellite can be utilized to reveal the Mott transition phenomenon in various strongly correlated electron systems, especially in nanoscale devices and phase-separated materials.

Investigation of chemical modifications of micro- and macromolecules in bio-oil during hydrodeoxygenation with Pd/C catalyst in supercritical ethanol

Miscanthus bio-oil was subjected to hydrodeoxygenation (HDO) with Pd/C at different temperatures (250, 300 and 350°C) and times (30, 45 and 60 min) to investigate the chemical modification of micro- and macromolecules in bio-oil. Four main products - char, gas and two immiscible oils (light and heavy oil) - were obtained from the HDO reaction. Yields of heavy oil as a targeting product of HDO varied from 60% to 13%, whereas those of gas and char were ranged from 7% to 36% and 6% to 17%, respectively. Water content was estimated to<1% and heating value was 26-31 MJ kg(-1). Reduction of unstable oxygen-containing compounds such as acids (2-hydroxy-butanoic acid), aldehydes (furfural), alcohols (butanedial) and sugars (levoglucosan) were characteristic in heavey oil. Apart from hydrogenation and deoxygenation, micromolecules in bio-oil were plausibly modified to stable ketones, esters and saturated components via demethoxylation, dealkylation, decarbonylation, dehydroxylation and ring opening. Macromolecular lignin fragments (referred to as pyrolytic lignins in bio-oil and phenol polymers in heavy oil) were extracted and subjected to several analyses. Approximately 60% of the pyrolytic lignins were decomposed into low molecular weight compounds during HDO reaction. Moreover, essential functional groups, OCH3 and phen-OH groups attached to pyrolytic lignin, were severely modified during HDO reaction.

Electronic structures of Yb intermetallic compounds studied by photoemission spectroscopy

Abstract Electronic structures of mixed-valent and Kondo-like intermetallic Yb compounds YbAl3, YbCu2Si2, YbIn2, YbCu2, Yb4As3, Yb4Sb3 and Yb4Bi3 have been studied by photoemission spectroscopy, and they are all found to be well described by the Anderson impurity Hamiltonian with the hybridization strength Δ=πpV2 ranging between 15 and 80 meV. The high-resolution study of the 4f14a4f13 spectral weights in YbAl3 and YbCu2Si2 shows remarkable temperature-dependence between 10 and 300 K, which is consistent with the theoretical prediction for the behavior of the Kondo resonance.

Evaluation of hydrodeoxygenation reactivity of pyrolysis bio-oil with various Ni-based catalysts for improvement of fuel properties

Three Ni-based catalysts were prepared for hydrodeoxygenation (HDO) of bio-oil with three different support materials (active carbon, SBA-15 and Al-SBA-15) and their catalytic effects were tested with crude bio-oil at 300 °C and under 3 MPa H2 pressure for 60 min. After the HDO reaction, gas, liquid phase (light oil and heavy oil) and char were obtained as the primary products. Heavy oil was produced at a yield of 45.8–48.1 wt%, with no significant differences among the three catalysts. Mesoporous silica-supported catalysts (Ni/SBA-15 and Ni/Al-SBA-15) produced large amounts of char (16.3–18.6%), while Ni/C yielded 8.5 wt% char. Active carbon-supported catalysts (Ni/C) yielded more gas (27.7%) than the Ni/SBA-15 and Ni/Al-SBA-15 catalysts (6.6–8.9%), due to high surface area and low char deposition on the active carbon-supported catalysts. The HDO reaction led to improvement in the fuel properties of crude bio-oil. The water content, acidity, viscosity and oxygen content decreased via de-moisturization, i.e., dehydration, as well as dehydroxylation, resulting in an increase in heating value. The heavy oil obtained from HDO with Ni/Al-SBA-15 exhibited a low water content (9.3 wt%), while that of Ni/SBA-15 revealed a high HHV (22.8 MJ kg−1), energy efficiency (62.8%), and degree of deoxygenation (54.9%). A major factor of bio/oil instability is unstable oxygen-containing compounds, such as acetic acid, furfural, vanillin and levoglucosan, which were obviously reduced in the heavy oil in this study.

U 5f spectral weight variation in UPd3-xPtx

Abstract We report a photoemission study of the 5f spectral weight variation in UPd 3− x Pt x . Relative to a previous study the results show both agreement and very significant differences. New spectral detail is resolved.

High resolution photoemission study of YbAl3 at low temperature

Abstract The valence v and the 4f 14 →4f 13 7 4 transition energy TK of YbAl3 at low temperature were determined by the h igh resolution valence band photoemission spectroscopy. The obtained values v = 2.65±0.03 and TK=30±15 meV are consistent with the zero-temperature magnetic susceptibility χm(0), supporting the Anderson Hamiltonian description for its electronic structure.

Photoemission and BIS study of Ce4Bi3 and CeBi0.7Te0.3

Abstract The electronic structures of Ce4Bi3 and CeBi0.7Te0.3 were studied by core-level X-ray photoelectron spectroscopy (XPS), valence band resonant photoemission using synchrotron radiation, and Bremsstrahlung Isochromat Spectroscopy (BIS). The 3d core-level XPS shows that the valence of Ce ions is close to three in both compounds, and the effective hybridization between Ce 4f level with valence electrons is stronger for CeBi0.7Te0.3 than Ce4Bi3. This is probably due to the stronger p-f mixing matrix element in CeBi0.7Te0.3 resulting from the shorter distance between Ce and Bi atoms. The density of states (DOS) near the Fermi level was also measured by the ultraviolet photoelectron spectroscopy and BIS, and it is found to be larger for Ce4Bi3 than CeBi0.7Te0.3. This difference comes about primarily because a larger number of extra electrons fill the Ce 5d conduction band in Ce4Bi3.