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This paper describes the identification of nitrogen-containing compounds in a typical feed for diesel oil hydrotreating and how their individual concentrations change upon hydrotreating over a conventional sulfided CoMo/Al2O3 catalyst at commercial conditions. A preconcentration procedure followed by gas chromatographic (GC) analysis utilizing a highly sensitive nitrogen-specific detector (atomic emission detector) allowed the quantitative analysis of individual nitrogen-containing compounds (N compounds) at levels as low as 0.05 μg N/mL. The nitrogen compounds in the feed and products were identified by comparison with reference compounds as well as by high-resolution GC/mass spectrometric characterization. The relative reactivities of individual compounds in the diesel fuel feed were determined and the most refractory compounds identified. Alkyl-substituted carbazoles were found to be the major compound class in the feed and to be among the least reactive N compounds in the feed. Just as in the case of alkyldibenzothiophene hydrodesulfurization, carbazoles having alkyl substituents at positions adjacent to the nitrogen atom were found to be the least reactive N compounds in the diesel fuel feed for hydrodenitrogenation.

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In this paper, we describe the investigation of chemical vapor deposition (CVD) of carbon from benzene and cyclohexane on a particular pitch-based active carbon fiber (ACF) at different deposition temperatures as a means of controlling the pore size of ACF in order to induce true molecular sieving capability and to discuss the mechanism of carbon deposition. This study showed that the specific temperature range 700−800 °C was very effective. In this range, deposition of amorphous carbon was restricted to the pore wall and became saturated at the level of 11% weight increase, as further deposition stopped. This treatment greatly enhanced the molecular sieve separation of CH4 from CO2. Reduction of pore size appeared to be limited by the thickness of the benzene plane, since no further carbon deposit took place when the pore could no longer accept benzene. Higher temperatures allowed deposition to occur on the outer surface of ACF, which plugged the pore completely on extended reaction time. Cyclohexane was found to be inferior to benzene as a carbon precursor, as it decomposed too rapidly in the gas phase at the temperature range used and precipitated the carbon plugging the pores. Thus, high molecular sieving selectivity was not obtained.

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Hydrodesulfurization of 4,6-dimethyldibenzothiophene (4,6-DMDBT) in decane has been investigated over a Co−Mo/C catalyst, using a magnetically stirred autoclave reactor. The hydrodesulfurization reaction was found to be pseudo-first order with respect to 4,6- DMDBT. Direct desulfurization was detected to be Arrhenius-dependent with an activation energy of 35.7 kcal/mol, while hydrogenation pathway showed a maxima at 340 °C. The activation energy of hydrogenation in the Arrhenius-dependent region was calculated to be 17.9 kcal/mol, as hydrogenation is thermodynamically limited at high temperature. The reaction of hydrodesulfurization appears to proceed via two different partially dependent routes, hydrogenation and desulfurization, over the present catalyst. Hydrogenation of 3,3‘-dimethylbiphenyl at different temperatures was also measured to identify the rates of the step involved in the hydrodesulfurization network of 4,6-DMDBT. Attention was particularly paid to the effects of naphthalene and H2S on the two different reaction pathways to propose the mechanism of their inhibition. Two different catalytic active sites, one for hydrogenation and the other for both hydrogenation and direct desulfurization, are discussed to be present.