Kinya Sakanishi

Deep hydrodesulfurization of diesel fuel: Design of reaction process and catalysts

Abstract Deep hydrodesulfurization (HDS) of diesel fuel oil was designed based on the recognition that alkyl dibenzothiophenes such as 4-methyl-and 4,6-dimethyldibenzothiophenes were the main target for deep HDS. Multi-stage and fractional HDS were very effective to achieve satisfactory HDS in terms of both sulfur level and fluorescent color of desulfurized oil. Catalysts with the selective hydrogenation of refractory sulfur species in major aromatic partners and isomerization-disproportionation of their alkyl groups prior to HDS were also designed to promote the desulfurization of such sulfur species.

Catalytic hydrodesulfurization of gas oil and model sulfur compounds over commercial and laboratory-made CoMo and NiMo catalysts: Activity and reaction scheme

Abstract Hydrodesulfurization (HDS) of gas oil (GO), light cycle oil (LCO) and a model sulfur compound 4,6-dimethyldiben-zothiophene (4,6-DMDBT) was compared over a series of six commercial and laboratory-made catalysts. The difference between the HDS activities of the catalysts for the model compound and the real feed stocks indicates their sensitivity to the intrinsic inhibitors (aromatics and H2S) present under industrial conditions. A severe inhibition of H2S on NiMo catalysts should be noted. Detailed analysis of the HDS products from the model feed provided information on the reaction pathways involved over the present catalysts and how they are modified in presence of inhibitors. Complementary standard tests with other model compounds were examined to determine the Bronsted acidity and hydrogenation activity of each catalyst. Such activities and their relationship explain the differences in performance of the catalysts and the relative importance of the respective reaction pathways in the HDS. Isomerization and dealkylation of 4,6-DMDBT took place prior to the desulfurization over the CoMo on the acidic support enhancing the desulfurization. Moreover, such a pathway was inhibited strongly by the aromatic partners and lost stationary activity by coke formation.

Determination of sulfur compounds in non-polar fraction of vacuum gas oil

Abstract Sulfur compounds in the non-polar fraction, which represents 73 wt% of total sulfur in a vacuum gas oil (VGO), were analysed by sulfur-selective ligand exchange chromatography combined with high-performance liquid chromatographic (h.p.l.c.) separation on the basis of aromatic ring number, with subsequent capillary g.c.-mass spectrometry for identification. Quantification was achieved by independent h.p.l.c. separation based on aromatic ring number followed by capillary gas chromatography with a sulfur-selective flame photometric detector. These methods were very effective in isolating the sulfur compounds from complex mixtures of high-boiling hydrocarbon compounds and for separating the sulfur compounds according to aromatic ring number. The structures and concentrations of > 100 sulfur compounds in the non-polar fraction of the VGO were determined Alkyl benzo[b]thiophenes, dibenzo[b,d]thiophenes, benzonaphthothiophenes and phenanthro[4,5-b,c,d]thiophenes were found to be major sulfur species existing in the non-polar fraction of the VGO.

Hydrodesulfurization activity of CoMo and NiMo supported on Al2O3–TiO2 for some model compounds and gas oils

Catalytic activities of Al2O3–TiO2 supporting CoMo and NiMo sulfides (CoMoS and NiMoS) catalysts were examined in the transalkylation of isopropylbenzene and hydrogenation of naphthalene as well as the hydrodesulfurization (HDS) of model sulfur compounds, conventional gas oil (GO), and light cycle oil (LCO). Al2O3–TiO2 supporting catalysts exhibited higher activities for these reactions except for the HDS of the gas oil than a reference Al2O3 supporting catalyst, indicating the correlation of these activities. Generally, more content of TiO2 promoted the activities. Inferior activity of the catalyst for HDS of the gas oil is ascribed to its inferior activity for HDS of dibenzothiophene (DBT) in gas oil as well as in model solvent decane, while the refractory 4,6-dimethyldibenzothiophene (4,6-DMDBT) in gas oil as well as in decane was more desulfurized on the catalyst. Characteristic features of Al2O3–TiO2 catalyst are discussed based on the paper results.

Single-step microwave digestion with HNO3 alone for determination of trace elements in coal by ICP spectrometry

A microwave digestion method with HNO(3) alone was conducted at a temperature as high as 250 degrees C for determination of 19 trace elements (Li, Be, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, As, Se, Rb, Sr, Cd, Cs, Ba, Hg, and Pb) in coal jointly by inductively coupled plasma optical emission spectrometry (ICP-OES), inductively coupled plasma mass spectrometry (ICP-MS), and flow injection ICP-MS (FI-ICP-MS). The validity of determination was assessed by using three standard coals, SRM 1632c, BCR 180, and SARM 19. It was found that the high-temperature digestion led to an extensive decomposition of the organic matrix and clay in coal, and no dissolved and solid carbon remained in the final solution after evaporation. Good recoveries were observed for all trace elements in three coals, with the exception of V, Rb, and Cs in high-ash SARM 19. Additionally, FI-ICP-MS combined with the present digestion without evaporation pretreatment was proved to be a rapid and efficient approach for determination of ultra-trace elements such as Se, Cd, and Hg in coal.

The effects of seeding in the synthesis of zeolite MCM-22 in the presence of hexamethyleneimine

Zeolite crystallization proceeds much faster for MCM-22 in the presence of “seeds,” and crystallization times can be shortened to less than 30 h under optimal conditions. MCM-22 seems to require a very narrow range of SiO2/Al2O3 and template ratios in the reagent mixture. Under the conditions investigated, crystal development seems to progress by initially forming very thin sheets, which when isolated seem to be arranged in house-of-cards-like macrostructures. As crystallization proceeds further these sheets become thicker. Eventually the sheets coalesce, the house-of-cards structures disappear, and the crystalline mass is transformed into the denser ZSM-35 structure.

Catalysts for coal conversions of the next generation

Abstract Catalysts for coal conversions are overviewed in liquefaction, gasification, upgrading of coal liquid, flue gas cleaning, and synthetic gas conversions to find bases for innovative catalytic coal conversions of the next generation. Selection of active species, catalyst supports and their optimized combinations are keys to developing such processes. Carbons or perovskite type supports are claimed to be the most potential supports for liquefaction and upgrading or gasification and gas cleaning, respectively. Active carbon fiber is also claimed to be a promising adsorbent for the removal of SO2 and NOx in flue gas from coal combustion.

Assessment of limitations and potentials for improvement in deep desulfurization through detailed kinetic analysis of mechanistic pathways

Abstract Utilizing an improved method for the assignment of the rate constants to the complicated network of reaction pathways in the hydrodesulfurization (HDS) of polyaromatic sulfur compounds (PASCs), new understanding has been obtained concerning the intrinsic limitations to achieving the new distillate fuels standards. Establishing the relative rates for hydrogenation of the parent sulfur compound and its desulfurized products, and considering thermodynamic limitations on hydrogenated intermediates are critical to these improved kinetics. With this new approach, it has been possible to more accurately assess the differences in performance of different catalysts such as Co–MoSx/Al2O3, Ni–MoSx/Al2O3 and analogous catalysts supported on carbons, the basic causes of selectivity change with temperature, and the mechanistic consequences of inhibitors on the HDS product distributions. Ni promoted catalysts were found to possess much higher hydrogenation activities than comparable Co promoted catalysts. Carbon supported catalysts appear to have potential for HDS at high temperatures. Inhibition by H2S affects both hydrogenation and direct sulfur extraction HDS routes, but, secondary hydrogenation of desulfurized aromatic products was found to be the most sensitive to inhibition. Naphthalene inhibits all hydrogenation reactions but has little effect on direct HDS.

Hydrodesulfurization kinetics and mechanism of 4,6-dimethyldibenzothiophene over NiMo catalyst supported on carbon

Abstract 4,6-Dimethyldibenzothiophene (4,6-DMDBT), one of the most refractory sulfur compounds in gas oil, was desulfurized in n-decane using NiMo sulfide supported on active carbons (NiMo/C) with a microautoclave installed with a sampling apparatus, to establish the hydrodesulfurization (HDS) kinetics and mechanism. The NiMo/C catalysts exhibited the higher activity for the HDS of 4,6-DMDBT at relatively higher temperatures of 340–380°C than a commercial NiMo/alumina catalyst regardless of the carbon supports. The main route was the direct desulfurization in this temperature range. The main reaction at 300°C was found to be the hydrogenative desulfurization route over the same catalyst, producing 3-(3′-methyl cyclohexyl)toluene. The direct desulfurization was significantly inhibited by the coexisting H2S regardless of reaction temperatures, although the hydrogenation route was found to be enhanced by H2S to some extent. The present desulfurization network was established by the computation curve fitting through measuring the equilibrium between 4,6-DMDBT and its tetrahydroderivative.

Carboxylations of alkali metal phenoxides with carbon dioxide

The reaction mechanism of the Kolbe-Schmitt reaction of phenol and 2-naphthol has been investigated. An alkali metal phenoxide-CO2 complex is not an intermediate that can be easily transformed into a carboxylic acid, such as salicylic acid (SA) and p-hydroxybenzoic acid (pHBA). A direct carboxylation of phenoxide with CO2 takes place even at room temperature, and is competitive with the formation of the CO2 complex. The resulting complex decomposes thermally (above ca. 100 degrees C) to phenoxide, which then undergoes further competitive reactions. Experiments using a carbon-13 labeled complex support a mechanism of direct carboxylation, and not the mechanism via a CO2 complex. The reactivity, C-13 NMR and MOPAC/PM3 calculations suggest a new carbonate-like structure for the CO2 complex.