Kiyoshi Fuda

The cation exchange properties of the heat-treated Australian brown coal in the water-organic compounds mixed solutions

Abstract The distribution of acid strength of carboxyl groups in raw and heat-treated Australian Loy Yang brown coals was estimated by the sodium titration method. The acidity of raw coal varies widely. The total amount of carboxyl groups for heat-treated coals is reduced by thermal decomposition, but the distribution of the acidity barely changes. Also, the interaction between surface functional groups of brown coal and metal cations was examined by cation exchange experiments. For all cations, the extent of cation exchange (ECE) of the raw coal increased with pH, which suggests that the ECE for raw coal is controlled mainly by the acid dissociation equilibrium of carboxyl groups. For magnesium and cobalt ions, the ECEs of heat treated coals were smaller than those estimated from thermal decomposition of the carboxyl groups. In contast, the ECEs in water-organic mixed solution were larger than those in aqueous solution. ECEs increased linearly with swelling of coal caused by addition of organic compounds. The gradient of this increase was larger for cobalt than for magnesium and also the slope for samples treated at higher temperatures or measured at higher pH levels. These results are discussed in terms of the change of the pore size distribution by the heat treatment of the coal as well as swelling of coal by addition of organic compounds which causes a change in the cation accessibility to the carboxyl groups. From these results, the variation of the macromolecular network structure is considered to be an important factor for the cation exchange properties of brown coal in addition to chemical factors, such as acid dissociation equilibrium.

Chemical changes occurring during sulphidation and regeneration of iron-containing sorbents

Abstract Four solid byproducts from the steel industry were sulphided using a gas resembling gasifier products. Chemical changes occurring during sulphidation were interpreted in terms of the FeSO phase diagram. COS was formed during the entire sulphidation mainly by reaction of H 2 S with CO 2 and CO. The presence of diffusion phenomena in the pellet during sulphidation was confirmed. The sorbent regeneration was influenced by sulphidation conditions. The structure of regenerated pellets depended on regeneration temperature, whereas the O 2 concentration in the oxidizing gas had a lesser effect.

Acidity distribution of carboxyl groups in Loy Yang brown coal: its analysis and the change by heat treatment.

Brown coals have a considerable number of acidic functional groups of which the main component is carboxyl groups, and the acidity has a wide distribution. In this paper, changes of the acidity distribution were examined by aqueous titration when brown coal was heat-treated to control its acidity distribution. For Loy Yang brown coal from Australia dried at 50 degrees C under vacuum (LY50), the acid dissociation constant, Ka, was distributed over a wide pKa range between 2 and 9. Then, using Gaussian functions, the acidity distribution was divided into four groups, which were characterized by average pKa values: average pKa value of 3.8 (hereafter referred to as Group A), 5.2 (Group B), 6.8 (Group C), and 8.3 (Group D). Among them, Groups A, B, and C were assigned to carboxyl groups. From the changes of the number of carboxyl groups when brown coal was heat-treated up to 400 degrees C, it was found that the way of decrease was different among these acidic groups. The decrease of the amount of carboxyl groups in Group C was significant, and at 325 degrees C most of them disappeared. On the other hand, the carboxyl groups in Group A remained even at a high temperature of 400 degrees C. We estimated approximately the structures around carboxyl groups for LY50 and their structural changes by heat treatment using the known pKa values for simple carboxylic acids and the pKa values calculated by the MOPAC program for complicated carboxylic acids.

Cation exchange properties of heat-treated Australian brown coal: influences of pre-exchanged calcium ions

Abstract Loy Yang brown coals, Australia, with pre-exchanged calcium ions (Ca-LY) or without pre-exchanged calcium ions (LY) were heat-treated at a desired temperature between 50 and 400°C and their exchanged amounts of Co 2+ or Mg 2+ were measured as a function of pH of the aqueous solution. The exchanged amount of divalent cations for Ca-LY heat-treated at 50°C was larger than that for LY heat-treated at the same temperature over the whole pH range. In the low pH region between 2 and 4.5, the exchanged amount of divalent cations for LY heat-treated above 250°C was almost zero, while that for Ca-LY heat-treated at the higher temperature such as 300°C was 0.1–0.3 mmol g −1 . These results were discussed based on the amounts and the types of the carboxyl groups present on the heat-treated brown coal surfaces.

Thermoelectric Properties of Nb-Doped SrTiO3 / TiO2 Multiphase Composite

In this study, we fabricated and examined a series of multiphase type composites constructed of Nb-doped SrTiO3 / TiO2 fine particles. The composition of the composites and the sintering temperatures were selected in a two-phase region where a perovskite SrTiO3 and a rutile TiO2 phases coexist. The composites obtained here were found to commonly have a mosaic type texture constructed of TiO2 and SrTiO3 fine particles with a typical size of about 500 nm. In some samples we also found additive phases such as Sr6Ti7Nb9O42. The thermal conductivity values measured for the most samples with different contents are ranged between 2 and 5 Wm K. The values are apparently lower than the value for single crystal SrTiO3 samples presented in literature. A sample with rather low relative density of about 80% showed a quite low thermal conductivity, about 1 WmK. Taking account the other TE data, e.g. Seebeck coefficient and electrical conductivity, we calculated dimensionless figure of merit, ZT, to be at maximum 0.24 at 600°C.

Geometrical Study on Change of Pore Volume of MCM-41 Functionalized with Aminopropyl Groups

Mesoporous silicas functionalized with aminopropyl groups were synthesized by co-condensation of tetraethoxysilane (TEOS) and 3-aminopropyl triethoxysilane (APTES) and characterized by nitrogen adsorption-desorption measurements. The pore volume drastically decreased from about 900 mm 3 /g for the unfunctionalized mesoporous silica to about 300 mm 3 /g for the aminopropyl-functionalized mesoporous silica (1.65 mmol-NH 2 /g). This result was explained in terms of the surface density of the aminopropyl groups in the pore.

Effect of Rare-Earth Cation Doping on Enhancement of The Thermoelectric Power of Zinc Oxide

We investigated the effects of doping of rare-earth ions (Ce, Pr, Nd, Sm, and Eu) on the thermoelectric properties of ZnO, especially Seebeck coefficient in the temperature range from 100 to 800 °C. The data were scattered more or less depending on the doping species, but it was commonly found that the rare-earth doped samples showed higher Seebeck coefficients with compared to those for Al-doped samples. The highest values were observed for Nd-doped one ranging from -360 to -400μVK −1 in the temperature range observed, the lowest ones for Pr-doped one ranging from -250 to -310 μVK −1 , whereas those for Al-doped one ranging from -80 to -140 μVK −1 . It should also be pointed out that the power factor at 100 °C for Pr-doped ZnO was twice or more as much as that for Al-doped one. From the results it seemed that rare earth doping is effective for enhancement of thermoelectric power of ZnO.

Thermoelectric Properties of Phase Separated Composite of Ln-Doped SrTiO3 and TiO2 Micro Crystals

It seems that no satisfactory TE property has been found in n-type oxide bulk materials even though Al-doped ZnO and La-doped SrTiO 3 have high thermoelectric (TE) responses. Difficulty in developing high-performance TE materials seems to lie in finding low thermal conductivity in such oxides. The purpose of this study is to find a possibility to make an n-type TE oxide bulk material having low thermal conductivity and excellent TE properties as well. For this purpose, we fabricated and examined a series of composites constructed of TiO2 and Ln-doped SrTiO 3 fine crystals. The composites were prepared via two processing steps: (1) precursor oxide preparation by wet processes; (2) sintering by using spark plasma sintering (SPS) apparatus. The microscopic structure was examined by using scanning electron microscope (SEM; HITACHI S-4500 model) attached with an energy dispersive x-ray spectroscopy. The electrical conductivities and the Seebeck coefficients were measured simultaneously using an ULVAC ZEM-1 instrument in helium atmosphere. The thermal diffusivities were measured by a laser flash method in vacuum. The composites obtained here were found to commonly have a mosaic type texture constructed of TiO 2 and SrTiO 3 fine particles with a typical size of 500 nm. The thermal conductivity values measured for three samples with different contents are ranged between 3 and 4 Wm-1K-1 in the temperature range from room temperature to 800 C. The values are apparently lower than the value for single crystal SrTiO3 samples presented in literature. Taking account the other TE data, e.g. Seebeck coefficient and electrical conductivity, we calculated dimensionless figure of merit, ZT, to be at maximum 0.15 at 800°C.

Sorption and Methanation of CO32- Ions in Anion-Exchange Layered Double Hydroxides.

Layered double hydroxides (LDHs), M (II) 1-x M (III) x (OH) 2 (CO3) x/2·nH2O (M (II) =Mg, Mn, Co, Ni, Cu, Zn, M (III) =Al, Fe) were prepared by the conventional coprecipitation method. The structures of the samples were analyzed by XRD and FT-IR measurements. Methanation of the sorbed CO2-3 ions was carried out using a thermo-balance system in H2 Gas flow of the atmospheric pressure. Apparent CH4 evolution was observed in the cases of Ni/Al-, Ni/ Fe-, Co/Al- and Co/Fe-systems. Following features ware found concerning to catalytic effects: (1) Nickel-containing LDHs have high activity for methanation, (2) Cobalt-containing LDHs have relatively low methanation activity, (3) The existence of Fe (III) is effective both on lowering the methanation temperature and on increasing conversion to CH4. Methane generation from these compounds was interpreted in terms of thermodynamic property of metals composing the brucite layers.