Yasukatsu Tamai

Reactivities of 34 coals under steam gasification

The reactivities of 34 coal chars of varying rank with H2O have been determined to examine the effect of coal rank on the gasification rate of coal char. The reactivities of chars derived from caking coals and anthracites (carbon content > 78 wt%, daf) were very small compared with those from non-caking (lower-rank) coals. The reactivities of low-rank chars do not correlate with the carbon content of the parent coals. To clarify which factor is more important in determining the reactivity, the evolution of CO and CO2 from char, the moisture content of char and the amount of exchangeable cations were determined for these low-rank coals or their chars. These values were considered to represent the amount of active carbon sties, the porosity and the catalysis by inherent mineral matters, respectively. It was concluded that the amount of surface active sites and/or the amount of exchangeable Ca and Na control the reactivity of low-rank chars in H2O.

Hydrogenation of carbons catalyzed by transition metals

Abstract The catalytic activities of transition-metal catalysts in methane formation from carbons were investigated at temperatures up to 1050 °C under atmospheric pressure of hydrogen. The studies in a thermobalance revealed that methane was produced in several stages and the temperature of maximal rate varied from one metal catalyst to another. When the most active metal was used, the methane formation from an active carbon occurred below 200 °C and the carbon was completely gasified upon heating up to 1050 °C at the rate of 100 °C/hr. Without catalyst, carbons of only 10% were gasified under the same condition. The order of activity at the lower temperature region was Rh ≳ Ru ≳ Ir > Pt > Ni ⪢ Pd ≳ Co ≳ Fe. The reactivity depended not only on the kind of catalyst, but on the kind of carbon and the preparative method of metal-carbon mixtures. The role of metal catalysis was discussed in connection with the spill-over phenomenon.

Catalytic gasification of carbon with steam, carbon dioxide and hydrogen

Abstract Nine transition metals in Group VIII were examined as catalysts for the carbon gasification with steam, carbon dioxide and hydrogen. Metal-doped carbons were heated up to 950°C at a constant rate of 200°C/hr in a flowing reactant gas. The relative activities of metal catalysts are nearly the same for all gases regardless of their quite different chemical nature. Metals like Ru, Rh, Ir and Pt are invariably active, whereas Fe, Co and Pd have small activities. The reaction pattern differs from catalyst to catalyst. Only four metals (e.g. Ni, Ru, Rh and Os) exhibit the maximum reactivity in the low-temperature region, and this behavior is common to three gases. It is speculated from these observations that the metal-carbon interaction is more important than the metal-gas interaction in determining the reaction profile.

Carbon formation on copper-nickel alloys from benzene

Abstract Carbon formation by the decomposition of benzene on copper-nickel alloy sheets and powders was studied in a temperature range from 580 to 900 °C. Two types of carbon were observed: one (type A) formed at higher temperatures was a flat thin film and the other (type B) formed at lower temperatures was a black powder. The rate of type A formation was small and nickel-rich substrates catalyzed it only at the initial stage. The rate of type B formation was considerably large and the alloys of 80 to 40% nickel had stronger catalytic activity than pure nickel. In this carbon, large amounts of metal particles were present in the same composition as that of substrates. A possible mechanism for the deposition is discussed.

Hydrogenation of carbons catalyzed by nickel, platinum and rhodium

Abstract Catalytic hydrogenation of a carbon was investigated at a constant temperature. The reaction occurred in two stages as observed thermogravimetrically. For a nickel-catalyzed reaction at 540°C, about a half of active carbon was rapidly gasified to methane and the remaining carbon was gasified at a very slow rate. The activation energy for the latter reaction was estimated as 25 kcal/mole. When the carbon was partially oxidized to increase the concentration of surface functional groups, the methane formation in the first stage decreased. An X-ray study showed the formation of crystalline carbon during the course of the reaction. The presence of two stages is attributed to the presence of two components with different reactivities in carbon. The carbon gasified in the first stage may be an amorphous one, and a more crystalline fraction remains without reacting until the temperature is raised up to the reaction temperature for the second stage.

Low temperature gasification of brown coals catalysed by nickel

Abstract Nickel catalyst exhibited an extremely high activity in the gasification of some low rank coals at a temperature as low as 750 K. Approximately 85% of Yallourn coal was converted within 30 min in steam at 773 K. A high nickel loading, > 4 wt% was necessary. It seems essential for coal high in oxygen and low in sulphur to be gasified in this manner. Oxygen-containing functional groups on the coal surface seemed to play an important role in keeping the nickel catalyst in a finely dispersed state. Hydrogen sulphide was strongly adsorbed on the nickel catalyst and retarded this reaction. Hydrogen and carbon dioxide were the main products of low-temperature steam gasification. Similar low-temperature gasification reactions were also observed in hydrogen and in carbon dioxide.

Chemisorption of Organic Compounds on a Clean Aluminum Surface Prepared by Cutting Under High Vacuum

The chemisorption of organic compounds as model compounds of lubrication additives has been studied at room temperature on a clean aluminum surface which was prepared by cutting under high-vacuum conditions. Hydrocarbons such as n-hexane, butene, and cyclohexene did not adsorb, but alkyl halides, organic acid, and alcohols adsorbed on the clean aluminum surface. The adsorption activity was monitored with a quadrupole mass spectrometer and was affected by cutting conditions. The rate of adsorption was proportional to the cutting speed. The chemisorption took place not only during but also after the cutting. From the kinetic considerations, it has been found that the activity was mainly due to the newly formed aluminum surface. The reactivity sequence of the organic compounds was as follows; alkyl halides > alcohols > organic acid >> alkane, alkene.

Gasification of coal impregnated with catalyst during pulverization: effect of catalyst type and reactant gas on the gasification of Shin-Yubari coal

Abstract Shin-Yubari coal was impregnated with several catalysts of different chemical types during pulverization. The resultant system was more homogeneous and reactive than systems prepared by impregnation of coarse coal. The relative activities of the catalysts were determined as a function of gasification temperature, catalyst loading and gasifying agent. The activity sequence in steam was K ⪢ Ba ⪢ Ni ⪢ Fe ⪢ coal ash. Each catalyst had a unique reaction profile. For example, using steam the specific rate or the rate per remaining fixed-carbon weight decreased with time for the iron-catalysed reaction, whereas it increased for the potassium-catalysed reaction. A similar order of activity was observed in carbon dioxide, but a different sequence was noted for the hydrogenation reaction. Transition metal catalysts were the most active. The hydrogenation reaction profiles were different from the oxidation profiles.

Chemical form of iron catalysts during the CO2-gasification of carbon☆

Abstract The chemical form of iron catalysts during the gasification of carbon with a CO 2 CO mixture was examined in situ by a controlled atmosphere high temperature X-ray diffraction method. Several iron compounds, Fe3O4, Fe1 − xO, Fe3C, α-Fe and γ-Fe, were identified between 700–1000 °C. Both the gasification temperature and the ratio of CO 2 CO affect the chemical form. The gasification reactivity was determined by thermogravimetry under the same experimental conditions as the X-ray study, and considered in relation to the chemical form of the catalyst.

Effectiveness of K2CO3 and Ni as catalysts in steam gasification

The catalytic steam gasification of 34 coals ranging from anthracite to peat was conducted in a thermobalance at 1023 K. When the difference in the reactivities of coals with and without catalyst is taken as a measure of the catalyst efficacy, that of K2CO3 was found to be extremely large and almost independent of coal rank. The effectiveness of Ni depends on the coal type to a great extent and it was very large for several low rank coals. SEM observation and EDAX analysis showed that the K2CO3 catalyst was finely dispersed over the char and such a good dispersion was common for all the coals examined. The dispersion state of Ni catalysts depends on the coal type, Ni catalysts were well dispersed over low rank coal chars which showed high reactivity in the Ni-catalysed gasification.