Masazumi Godo

Elucidation of molybdenum-based catalysts using a radioisotope tracer method Part 2 Promotion effect of cobalt on molybdena/alumina catalyst

Hydrodesulfurization (HDS) reactions of radioactive 35S-labelled dibenzothiophene were carried out over a series of cobalt-promoted molybdena/alumina catalysts at temperatures between 240 and 320°C and under 50 kg cm-2 pressure. HDS and hydrogenation (HYD) activities of Mo/Al2O3 catalysts were remarkably enhanced with the addition of cobalt, the maximum promotional effect occurring with a Co/Mo molar ratio of ca. 0.5. The amount of labile sulfur and the rate constant of sulfur exchange increased significantly with the addition of cobalt, indicating that cobalt makes the sulfur more mobile and that the active phases in the promoted catalysts are different from that in the unpromoted catalyst. The promoting effect of cobalt was thus attributed to the formation of more active sites. On the other hand, the amount of labile sulfur increased linearly with the Co/Mo ratio up to ca. 0.5 whereas the rate constant of sulfur exchange remained almost constant. Moreover, the enhancement in catalytic activity did not change significantly with the cobalt content. The increase in the catalytic activity with the cobalt content was thus ascribed to an increase in the number of the same active sites.

Elucidation of coal liquefaction mechanisms using a tritium tracer method: hydrogen exchange reaction of solvents with tritiated molecular hydrogen in the presence and absence of H2S

Abstract To estimate the hydrogen mobility of solvents quantitatively, reactions of tetralin, decalin and naphthalene with tritiated gaseous hydrogen in the presence and absence of H2S were performed under the conditions generally used for coal liquefaction (400°C, initial hydrogen pressure 60 kg/cm2). The conversions of tetralin and decalin to other organic structures in the presence and absence of H2S were very close to each other. However, the conversion of naphthalene in the presence of H2S was promoted about four times of that in the absence of H2S. In the absence of H2S, the hydrogen exchange ratio (HER: the ratio of hydrogen exchanged in a solvent to total hydrogen in the solvent) of naphthalene was highest among the solvents. However, in the presence of H2S, the HERs of tetralin and decalin were promoted about 10 times. In the presence of H2S, the HER of tretalin was highest in comparison with those of decalin and naphthalene. It was suggested that H2S promoted the hydrogen exchange through tetralyl radical.

Estimation of the behaviour of hydrogen in naphthalene in pyrolysis of coal tar using tritium tracer methods

Abstract The behaviour of hydrogen in naphthalene in the pyrolysis of coal tar was investigated using a tritium tracer technique to elucidate the pyrolysis mechanism of coal tar. The pyrolysis of coal tar containing tritiated naphthalene was carried out using a batch reactor at 800–950°C for 50 sec. The ratios of amounts of naphthalene in the tars pyrolysed at 800, 900, and 950°C to that in the feed tar were 80.1, 73.4, and 42.5 wt%, respectively. However, the ratios of the radioactivity of naphthalene in tars after pyrolysis to that in the feed tar also decreased significantly with increasing temperature and it was only 12.9% for the reaction at 950°C. The ratio of the recovered radioactivity of naphthalene to the initial radioactivity of naphthalene in the feed tar was about one-third of that of the recovered amount of naphthalene to the initial amount of naphthalene in the feed tar at 950°C. The results indicated that the hydrogen in naphthalene transferred to other compounds in the pyrolysis of coal tar. It is suggested that naphthalene could play an important part in the radical reaction mechanism in the pyrolysis of coal tar.

Elucidation of Hydrogen Mobility of Coal Tar Using a Tritium Tracer Method

The hydrogen exchange of coal tar and model compounds of coal tar with water was investigated using a tritium tracer method to elucidate the mobility of hydrogen in coal tar. The reactions at several temperatures in the range from 50 to 300°C were carried out using a batch reactor for 1-12h. The hydrogen exchange ratio (HER) of coal tar with water approached a constant value at 100°C after 6h; however, the HER of coal tar increased remarkably at 200°C and at 300°C with time. From the results obtained from the hydrogen exchange of naphthol and indole as model compounds of coal tar, it was proposed that only hydrogen in functional groups with hetero-atom was exchangeable at 100°C while the hydrogen in the aromatic ring substituted by functional groups with hetero-atom also became exchangeable at 300°C. In contrast to this, the hydrogen in naphthalene hardly exchanged with water even at 300°C. Therefore, it was suggested that the constant value of HER of coal tar at 100°C represented the amount of hydrogen in the coal-tar functional groups with hetero-atom such as hydroxyl group and imino group. It was found that the tritium tracer method was an efficient approach to elucidate the behavior of hydrogen in coal tar and to determine the content of hydrogen related to the functional groups with hetero-atom in coal tar.

Novel aspects on coal liquefaction mechanism by the use of tritium and 35S tracer methods

Publisher Summary This chapter discusses the effects of the addition of the catalyst––pyrrhotite––and sulfur on liquefaction of Taiheiyo coal using tritium and 35 S. The hydrogen-exchange reaction between gas phase and solvent is promoted by added catalyst and sulfur. Using the pyrrhotite catalyst and by adding sulfur, the hydrogen addition to coal and liquefaction products increased. Added sulfur reacted mainly with the hydrogen of solvent to produce hydrogen sulfide. A part of added sulfur participated in the sulfur-exchange reaction with the pyrrhotite catalyst. Tritium tracer techniques are effective to trace the behavior of hydrogen atoms in coal liquefaction and gave quantitative information related to hydrogen exchange.