D. Duayne Whitehurst

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.

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.

Depolymerization and demetallation treatments of asphaltene in vacuum residue

Abstract The asphaltene fraction [hexane insoluble (HI)] of a vacuum residue (VR) was treated under ultrasonic irradiation at 40°C in THF or 150°C in 1-methyl naphthalene (1-MN) in the presence of an adsorbent composed of modified macro-reticular polystyrene resin. Such a treatment was found effective to convert the asphaltene into the hexane soluble (HS: maltene) without any hydrogen consumption. 61 and 72% of the HI was converted by the adsorption treatment at 40°C in THF and 150°C in 1-MN, respectively, to HS materials having lower molecular weights. About 65% of the metal contaminants in the original asphaltene remained with the newly formed maltenes after this treatment. Structural analyses of the asphaltene and maltene fractions before and after the treatment suggests decoagulation and/or depolymerization of the asphaltene into maltene, while the porphyrin moiety becomes soluble, being transformed to the maltene fraction. The roles of polar solvent, ultrasonic irradiation, and adsorbent are discussed based on the above results.

Carbonization of the toluene soluble fraction of fullerene soot into a disk

Carbonization of toluene soluble fraction in the fullerene soot was examined in the disk at the bottom of the test tube. Such a carbonization was found to increase the carbon yield to 94% at 900 °C and 92% at 2400 °C. The carbon yield was also found to be influenced by the thickness of the disk and the heating rate. All these results indicate that carbonization competes with sublimation. The carbon disk thus prepared gave an appearance of glass-like carbon and had an apparent density of 1.36 g cm−3 at 900 °C and 1.29 g cm−3 at 2400 °C. The reduction of the density by graphitization reflects the hollow spheres surrounded by their graphite layers in the graphitized disk.