Inhibition, hydrodesulfurization

Because of their high molecular weight and complexity, the asphaltenes remain an unknown entity in the hydrodesulfurization process. There are indications that, with respect to some residua and heavy oils, removal of the asphaltenes prior to the hydrodesulfurization step brings out a several fold increase in the rate of hydrodesulfurization and that, with these particular residua (or heavy oils), the asphaltenes must actually inhibit hydrodesulfurization. As a result of the behavior of the asphaltenes, there have been several attempts to focus attention on the asphaltenes during hydrodesulfurization studies. The other fractions of a... 

In spite of all of the work, the kinetics and mechanism of alkyl-substituted dibenzothiophene, where the sulfur atom may be sterically hindered, are not well understood and these compounds are in general very refractory to hydrodesulfurization. Other factors that influence the desulfurization process such as catalyst inhibition or deactivation by hydrogen sulfide, the effect of nitrogen compounds, and the effect of various solvents need to be studied in order to obtain a comprehensive model that is independent of the type of model compound or feedstock used. 

Koltai T., Macaud M., Guevara A., Schulz E., Lemaire M., Bacaud R. and Vrinat M., Comparative inhibiting effect of polycondensed aromatics and nitrogen compounds on the hydrodesulfurization of alkyldibenzothiophenes, Appl. Catal. A Gen. 231 (2002) pp. 253-261. 

An example of a product-inhibited conversion is the hydrodesulfurization of medium-to-heavy petroleum fractions. The removal of sulfur from such oils can generally be described as a second-order reaction in total sulfur [1]. This high apparent order is a reflection of the presence of a variety of sulfur-containing compounds that have widely differing reactivities for hydrodesulfurization and implies that a relatively large proponion of sulfur is removed from the oil by conversion of the bulk of more reactive compounds in an early stage of the reaction. The conversion of the more refractive sulfur compounds occurs far more slowly in a later stage. 

Hatanaka, S., Yamada, M., and Sadakane, O. Hydrodesulfurization of catalytic cracked gasoline. 1. Inhibiting effects of olefins on HDS of alkyl(benzo)thiophenes contained in catalytic cracked gasoline. Industrial Engineering Chemistry Research, 1997, 36, 1519. 

Farag, H., Sakanishi, K. Mochida, I., and Whitehurst, D.D. Kinetic analyses and inhibition by naphthalene and H2S in hydrodesulfurization of 4,6-dimethyldibenzothiophene (4,6-DMDBT) over CoMo-based carbon catalyst. Energy Fuels, 1999, 13, 449. 

The simulation results teU us that Ti02 surface has a severe inhibition effect on the transport behavior of polar molecules. In mesopores, polar molecules closed to the pore waU of Ti02 display obviously low transport rate. H2S, hydrodesulfurization reaction resultant, is a kind of typical polar molecule. Provided that the transport rate of H2S molecules in the pore of mesoporous Ti02 was influenced, the whole hydrodesulfiirization reaction could be inhibited. 

Deep HDS of diesel fuel is currently a very important topic in refining. Basically, deep hydrodesulfurization of diesel involves the extensive elimination of refractory sulfur species such as 4-MDBT, 4,6-DMDBT, and 4,6,X-TMDBTs. Such deep hydrodesulfurization is difficult because of the lower reactivities of these compounds and strong inhibition by coexisting species such as H2S, NH3, nitrogen species and even aromatic species, especially when the sulfur level must be lowered to <300 ppm. H2S and NH3 are produced from the reactive sulfur and nitrogen species contained in the same feed. 

Isoda, T. Ma, X. and Mochida, . Reactivity of Refractory Sulfur Compounds in Diesel Fuel (Part 2) Inhibition of Hydrodesulfurization Reaction of 4,6-Dimethyldibenzothiophene by Aromatic Compound. J. Japan Petrol. Inst. 1994, 37, 506. Farag, H. Sakanishi, K. Mochida, L Whitehurst, D. D. Kinetic Analyses and Inhibition by Naphthalene and H2S in Hydrodesulfurization of 4,6-Dimethyldibenzothiophene (4,6-DMDBT) over CoMo-Based Carbon Catalyst. Energy Fuels 1999, 13,449. 

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