Takami Kai

Kinetic model for simultaneous leaching of zinc sulfide and manganese dioxide in the presence of iron-oxidizing bacteria

The effect of iron-oxidizing bacteria on the simultaneous leaching of zinc sulfide and manganese dioxide was studied. Some researchers have reported the enhancement of the leaching rate during the simultaneous leaching of metal oxides and metal sulfides. In the present study, we examined the effect of the presence of Thiobacillus ferrooxidans in the simultaneous leaching. We also examined the reaction rates during the simultaneous leaching in the presence of the bacteria in order to study the reaction kinetics. The rate equation was obtained for each reaction: the oxidation of zinc sulfide by ferric iron, the oxidation of zinc sulfide by ferric iron and by the bacteria, the reductive dissolution of manganese dioxide by ferrous iron, and the simultaneous dissolution of zinc sulfide and manganese dioxide. A kinetic model based on these equations was proposed and the extent of leaching during the simultaneous dissolution with T. ferrooxidans was determined.

Effect of metal composition on hydrogen selectivity in steam reforming of methanol over catalysts prepared from amorphous alloys

Methanol steam reforming was carried out over catalysts prepared from amorphous Cu50Zr50, (Cu50Zr50)100−xAux and (Cu50Zr50)100−xPdx alloys in a fixed bed reactor operated at atmospheric pressure. The selectivity for carbon dioxide, which is a measure of steam reforming, was dependent on the composition of the amorphous alloy. When the reaction was performed over Cu50Zr50 amorphous alloy, the selectivity for carbon dioxide was essentially unity, whereas methanol conversion was very low. On the other hand, methanol conversion increased with the palladium content over the Cu–Zr–Pd amorphous alloy, but the selectivity for carbon dioxide was lower than that over Cu–Zr alloy. When the reaction was carried out over catalysts prepared from amorphous Cu–Zr–Au alloy, the methanol conversion increased with the gold content, whereas the carbon dioxide selectivity was almost unity over the range of gold content. The surface area measurement revealed that the dispersion of copper, which was effective for the steam reforming reaction, increased with the content of gold in the amorphous alloy. On the other hand, the dispersion of palladium, which was effective for dehydrogenation of methanol, increased with the palladium content. These results indicate that gold in the Cu–Zr alloy plays an important role in increasing the dispersion of copper.

Effects of acid strength and micro pore size on ε-caprolactam selectivity and catalyst deactivation in vapor phase Beckmann rearrangement over acid solid catalysts

The vapor phase Beckmann rearrangement of cyclohexanone oxime (CHO) over solid acid catalysts including zeolites was carried out to elucidate the effects of the acid strength and the micropore size of the catalysts on the selectivity of e-caprolactam (CL) and the catalyst deactivation rate. It was found that the catalyst deactivation rate was strongly dependent on the acid strength of the acid catalysts. The improvement of catalyst life was achieved by using MFI-type metallosilicates having weak acid sites. The CL selectivity decreased over the acid catalysts with micropores larger than those of the MFI zeolites. Furthermore, using methanol and carbon dioxide as the diluent solvent and diluent gas improved CL selectivity and catalyst life, respectively.

Hydrodynamic influences on mass transfer between bubble and emulsion phases in a fine particle fluidized bed

The overall mass transfer coefficient between the bubble phase and the emulsion phase was measured at ambient temperature in a fine particle fluidized bed. The measurements were carried out using the absorption of carbon dioxide in air by porous alumina particles impregnated with an aqueous solution of NaOH. The pressure fluctuations and the ascending velocity of bubbles were also measured. The overall reaction rate was influenced by the mass transfer between the two phases and the fraction of particles in the freeboard at high gas velocity. The flow pattern of bubbles was discussed in relation to the surface area of bubbles calculated from the mass transfer coefficient and the bubble signals detected by optical probes.

Production of biodiesel fuel from canola oil with dimethyl carbonate using an active sodium methoxide catalyst prepared by crystallization.

In this study, a novel method for the production of biodiesel under mild conditions using fine particles of sodium methoxide formed in dimethyl carbonate (DMC) is proposed. Biodiesel is generally produced from vegetable oils by the transesterification of triglycerides with methanol. However, this reaction produces glycerol as a byproduct, and raw materials are not effectively utilized. Transesterification with DMC has recently been studied because glycerol is not formed in the process. Although solid-state sodium methoxide has been reported to be inactive for this reaction, the catalytic activity dramatically increased with the preparation of fine catalyst powders by crystallization. The transesterification of canola oil with DMC was studied using this catalyst for the preparation of biodiesel. A conversion greater than 96% was obtained at 65°C for 2h with a 3:1M ratio of DMC and oil and 2.0 wt% catalyst.

Catalyst deactivation of high-silica HZSM-5 in the Beckmann rearrangement reaction of cyclohexanone oxime

Abstract The Beckmann rearrangement of cyclohexanone oxime was carried out over high-silica HZSM-5 zeolites and boron-modified HZSM-5 to elucidate the effects of silica alumina ratio and boron modification on the catalyst deactivation rate. The relationship between cyclohexanone oxime conversion and time on stream could be represented by the equation x ( t ) = x (0)·exp(− b · t ) where x ( t ) and x (0) are conversions at a time on stream t and at the initial stage t = 0, respectively, and b is the deactivation coefficient. The deactivation coefficient increased with increasing concentration of strong acid sites. When the deactivated zeolites were evacuated under a pressure of 1 Torr at 573 K for 5 h, the catalytic activity was recovered up to 50% of the initial activity. The deactivation of the ZSM-5-type zeolite was mainly due to the adsorption of volatile material on the acid sites.

The Effect of Start-Up Conditions on Deactivation of Hydrotreating Catalyst for Heavy Residue with High Asphaltene Content

This article describes a pilot plant test, which was carried out to examine the effect of start-up operation conditions on catalytic performance in the commercial hydrotreating equipment. From the simulated several pilot tests, it was found that the operation conditions of this commercial equipment were very severe and the hydrogen supply to the catalyst active site was critical. When the heavy residue containing large amount of asphaltene was supplied at the start of run (SOR) in the commercial equipment, the permanent adsorption of carbonaceous deposit on the active site should cause leading the catalyst deactivation.

Adaptation of Thiobacillus ferrooxidans to nickel ion and bacterial oxidation of nickel sulfide

SummaryThe Ni2+ resistance of Thiobacillus ferrooxidans was enhanced by repeated culturing in medium containing Ni2+ and gradually increasing the Ni2+ concentration. The extraction of nickel sulfide was enhanced by the adapted strain following the direct leaching mechanism of the microorganism.

The effect of support structure on CO2 hydrogenation over a rhodium catalyst supported on niobium oxide

The hydrogenation of CO2 was investigated over a rhodium catalyst supported on niobium oxide at atmospheric pressure. Niobium oxide was prepared by the hydrolysis of niobium chloride and its crystallitic structure was controlled by calcination temperature. It was found that the activity was lower but the selectivity of C2+ hydrocarbons was higher for the γ and γ′ forms than for the β and α forms of the niobium oxide.

Vapor phase Beckmann rearrangement of cyclopentanone oxime over high silica HZSM-5 zeolites

Abstract The rearrangement of cyclopentanone oxime was carried out over HZSM-5 and boron-modified HZSM-5 zeolites to elucidate the effect of acid strength distribution on the δ-valerolactam selectivity and catalyst deactivation rate. The results were compared with those of the reaction of cyclohexanone oxime. Although the rearrangement of cyclopentanone oxime was faster than that of cyclohexanone oxime, the catalyst deactivation rate for cyclopentanone oxime was slower than that for cyclohexanone oxime. These results indicated that since the molecular size of cyclopentanone oxime was smaller than that of cyclohexanone oxime, cyclopenatanone oxime could diffuse into the micropores of HZSM-5. The difference in the amount of effective acid sites between the reactions of cyclopentanone oxime and those of cyclohexanone oxime affected the rates of reaction and catalyst deactivation.