Toshiaki Kabe

Deep desulfurization of light oil. Part 2: hydrodesulfurization of dibenzothiophene, 4-methyldibenzothiophene and 4,6-dimethyldibenzothiophene

Abstract The hydrodesulfurization of dibenzothiophene (DBT), 4-methyldibenzothiophene (4-MDBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) was investigated under deep desulfurization conditions (sulfur concentration 2 O 3 . The conversion of DBTs into cyclohexylbenzenes (CHBs) was nearly the same while that of DBTs into biphenyls (BPs) decreased in order DBT > 62;4-MDBT > 62;4,6-DMDBT. This result indicates that, when an aromatic ring in DBTs is hydrogenated, the extent of steric hinderance of the methyl group decreases and differences between the HDS rates of DBTs disappear. Data for DBTs could be arranged by the Langmuir-Hinshelwood rate equation. Activation energies of DBT, 4-MDBT and 4,6-DMDBT were 24,31 and 40 kcal/mol, respectively. Heats of adsorption for DBT, 4-MDBT and 4,6-DMDBT were 12,20 and 21 kcal/mol, respectively. These results show that 4-MDBT or 4,6-DMDBT can be adsorbed on the catalyst through a π-electron in the aromatic rings more strongly than DBT, and that the C-S bond cleavage of adsorbed DBTs is disturbed by steric hinderance of the methyl group.

Selectivity of molybdenum catalyst in hydrodesulfurization, hydrodenitrogenation, and hydrodeoxygenation: Effect of additives on dibenzothiophene hydrodesulfurization

Abstract Kinetic studies of the hydrodesulfurization of dibenzothiophene on a presulflded molybdenaalumina catalyst were carried out in a high-pressure-flow microreactor. The mechanism discussed is based on selective poisoning studies, using various nitrogen, polyaromatic, sulfur, and oxygen compounds. The nitrogen compounds inhibited the hydrogenation of dibenzothiophene because they adsorbed more strongly than did dibenzothiophene at lower temperatures. At higher temperatures, the nitrogen compounds also hinder the desulfurization together with the hydrogenation of dibenzothiophene. The sulfur and the oxygen compounds retarded all reactions of the desulfurization of dibenzothiophene. The reactions of the desulfurization, the denitrogenation, and the deoxygenation proceed on one type of site and the hydrogenation reactions on another site.

Effects of H2S on hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene on alumina-supported NiMo and NiW catalysts

Abstract Effects of the H2S partial pressure on the catalytic activity and product selectivity of the hydrodesulfurization (HDS) reactions of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) were investigated over the sulfided NiMo/Al2O3 and NiW/Al2O3 catalysts under the deep desulfurization conditions (sulfur concentrations

Elucidation of promotion effect of cobalt and nickel on Mo/TiO2 catalyst using a 35S tracer method

Abstract A series of CoMo and NiMo catalysts supported on TiO 2 with various Co/Mo and Ni/Mo molar ratios were prepared to investigate the relationship between the nature of the support and the promotion effect of Co and Ni. The catalytic activities of these catalysts for the hydrodesulfurization (HDS) of dibenzothiophene (DBT) were measured. The HDS activity of CoMo/TiO 2 catalysts increased linearly with the addition of cobalt up to Co/Mo ratio of 0.6 and then decreased slightly above this value. Similarly, the HDS activity of NiMo/TiO 2 catalysts increased linearly with the addition of nickel up to Ni/Mo ratio of 0.6 and remained almost constant above this value. The sulfur mobility on the CoMo/TiO 2 and NiMo/TiO 2 catalysts under the reaction conditions was elucidated by a 35 S radioisotope tracer method using 35 S -labeled DBT. The amount of labile sulfur ( S 0 ) increased linearly with the addition of cobalt or nickel up to molar ratio of 0.6. In contrast, no significant difference in the rate constants of H 2 S release ( k RE ) was observed between Co- or Ni-promoted catalysts and non-promoted Mo catalysts at a given temperature. Therefore, the increase in catalytic activity with the addition of cobalt or nickel can be attributed to an increase in the number of active sites.

Elucidation of molybdenum-based catalysts using aradioisotope tracer method Part 1.—Hydrodesulfurization activityand structure of sulfided molybdena–aluminacatalysts

Hydrodesulfurization of radioactive 35 S-labelled dibenzothiophene was carried out over a series of sulfided molybdena–alumina catalysts containing 6–20 wt.% molybdena at temperatures in the range 280–380°C and at a pressure of 50 kg cm -2 . The sulfur exchange data and hydrodesulfurization activity were simultaneously obtained and the effect of molybdenum content on the structure of sulfided catalysts was estimated. The sulfur exchange rates were approximately the same for all samples at the same temperature and apparent activation energies of hydrodesulfurization reactions were 20±2 kcal mol -1 for all catalysts. These results suggest that the mechanism of hydrodesulfurization and the nature of active sites did not vary with molybdenum content. On the other hand, the amount of labile sulfur increased linearly with the molybdenum content up to 2.89 atom nm -2 but then levelled off with further loading of molybdenum. Thus, it was suggested that a monolayer dispersion of molybdenum sulfide on alumina was maintained up to 2.89 atom nm -2 but some crystallites of molybdenum sulfide would be formed when molybdenum was added beyond 2.89 atom nm -2 . Moreover, the sulfur exchange rate hardly varied with the molybdenum content and the hydrodesulfurization rates of dibenzothiophene on the catalysts paralleled the amount of labile sulfur.

Hydrodesulfurization and hydrogenation on alumina-supported tungsten and nickel-promoted tungsten catalysts

Hydrodesulfurization (HDS) of radioactive 35S-labeled dibenzothiophene was carried out over a series of alumina-supported W-based catalysts containing ca. 10–35 wt.% WO3 and 0–9 wt.% NiO at temperatures in the range 220–400°C and under a reaction pressure of 50 kg cm-2. The catalytic activities of the catalysts changed depending on the W loadings and sulfidation temperature for W–Al2O3 catalysts. Moreover, the HDS and hydrogenation (HYD) activity of W–Al2O3 catalysts were remarkably enhanced with the addition of nickel. Further, the amount of labile sulfur (S0) on the W–Al2O3 catalyst was much less than that on the corresponding Mo catalyst although the strength of the W–S bond is weaker than that of Mo–S. This is attributed to the fact that the sulfidation of the W–Al2O3 catalyst and the formation of the W–S bond are more difficult. On the other hand, S0 and the rate constant of H2S release (kRE) increased significantly on addition of nickel, as in the case of the Co–Mo catalyst. Moreover, the Ni-promoted W–Al2O3 catalyst with higher Ni/W ratio (0.6) also showed S0 and kRE comparable to those of the corresponding Co–Mo catalyst. These results suggested, therefore, that the promoting effect of nickel enhanced the relative ease of sulfidation of W catalysts and resulting in formation of more active sites simultaneously.

Elucidation of hydrogen transfer mechanisms in coal liquefaction using a tritium tracer method: Effects of solvents on hydrogen exchange reactions of coals with tritiated molecular hydrogen

Abstract To estimate the hydrogen mobility of coal and solvent quantitatively, reactions of tetralin, decalin and 1-methylnaphthalene with tritiated gaseous hydrogen in the absence and presence of Wandoan coal were performed under conditions generally used for coal liquefaction: 300–400°C, initial H 2 pressure 5.9 MPa. Tritium in the gas phase was transferred to coal and solvent mainly through hydrogen exchange and slight hydrogen addition. The amount of hydrogen exchanged between the gas phase, coal and solvents was estimated from hydrogen and tritium balances. At 400°C and 120 min, coal conversion in the presence of tetralin, decalin and 1-methylnaphthalene was 87, 45 and 54%, respectively. Under these conditions, the amount of hydrogen exchanged between the gas phase and coal decreased in the order 1-methylnaphthalene (1.38 g 30 g −1 of coal) > tetralin (0.85 g 30 g −1 of coal) > decalin (0.72 g 30 g −1 of coal). Compared with the amount of hydrogen exchanged, the amount of hydrogen added from the gas phase to the coal was smaller than 0.07 g in each solvent. Coal hydrogen exchange reactions in the presence of tetralin or decalin were similar to those in the absence of solvent. On the contrary, remarkable hydrogen exchange with coal in the presence of 1-methylnaphthalene occurred with a rise from 350 to 400°C. Further, a significant amount of 1-methylnaphthalene decomposed to naphthalene and methane in this temperature range, while hydrogen addition from 1-methylnaphthalene to coal did not occur. This suggests that hydrogen exchange reactions among the gas phase, coal and 1-methylnaphthalene proceeded by radical chain mechanisms, with the supply of radicals from coal.

Elucidation of sulfidation state and hydrodesulfurization mechanism on ruthenium–cesium sulfide catalysts using 35S radioisotope tracer methods

Abstract Alumina-supported ruthenium–cesium catalysts were presulfided using [ 35 S]H 2 S pulse tracer method to evaluate their sulfidation state. Subsequently, using these previously 35 S-labeled catalysts, HDS reactions of dibenzothiophene (DBT) were performed and the mobility of 35 S introduced during the presulfidation stage was investigated. The results showed that the amount of labile sulfur ( S 0 ) was much smaller than the total amount of sulfur accommodated on the catalyst (S total ). DBT conversion and S total increased linearly with Ru content. In a second part, labile sulfur amount was also determined under the catalyst working conditions and different results were obtained. Indeed, when the catalysts were marked with [ 35 S] and with [ 35 S]DBT under HDS reaction conditions, the obtained labile sulfur quantities (S 0A ) were significantly higher than the ones measured during the presulfidation stage ( S 0 ). These results showed that the labile sulfur is not formed on RuCs catalysts until the HDS reaction proceeds, which is quite different from that reported before for Mo, Pt, or Pd systems.

Fine-tuning of pore size of MCM-41 by adjusting the initial pH of the synthesis mixture

The pore size of MCM-41 can be finely tuned from 38.3 to 52.7 A with a narrow distribution by carefully adjusting the initial pH of the synthesis mixture from 11.5 to 10.0.

Sulfur exchange on CoMo/Al2O3 hydrodesulfurization catalyst using 35S radioisotope tracer

Abstract A commercial CoMo/Al 2 O 3 catalyst was labeled with the radioisotope 35 S in hydrodesulfurization (HDS) of 35 S-labeled dibenzothiophene ( 35 S-DBT) in a high-pressure flow reactor at 50 kg/cm 2 . Then, HDS of 4-methyldibenzothiophene (4-MDBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) or sulfur exchange of H 2 S were carried out on the labeled catalyst at 50 kg/cm 2 and 260–360°C. The amounts of labile sulfur participating in the reaction were determined from the radioactivity of 35 SH 2 S released from the 35 S-labeled catalyst. In the HDS reactions, the amount of labile sulfur participating in the reaction decreased in the order: DBT > 4-MDBT > 4,6-DMDBT. In the sulfur exchange reaction with H 2 S, the adsorption of H 2 S on the catalyst reached saturation above a H 2 S partial pressure of 0.36 kg/cm 2 . It was suggested that the release of H 2 S from the labile sulfur may be the rate determining step of the HDS reaction.