Hydrodesulfurization of Diesel

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. 

Introduction of more active sites by impregnating more active metals on the catalyst. 

Removal or reduction of inhibitors in the process during or before HDS. 

Novel catalyst designs to introduce new mechanistic pathways that are less subjective to inhibition. 

A series of catalysts in two successive layers to remove reactive sulfur species and in the first layer, and to remove remaining refractory sulfur species to less than 10 ppm under the presence of H2S, NH3 and other remaining inhibitors, such as nitrogen species and aromatic compounds, in the other layer. 

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A Catalyst Deactivation Model for Residual Oil Hydrodesulfiirization and Application to Deep Hydrodesulfurization of Diesel Fuel... 

The concept of this model for catalyst deactivation is also applicable to hydrotreating of other petroleum fractions. An example of such applications for the case of deep hydrodesulfurization of diesel fuel is also presented. 

Song, C.S., Reddy, K.M., Leta, H., Yamada, M., and Koizumi, N. Mesoporous aluminosilicate molecular sieve MCM-41 as support of Co-Mo catalysts for deep hydrodesulfurization of diesel fuels. In Chemistry of Diesel Fuels (eds. C. Song, S. Hsu, I. Mochida). New York Taylor Francis, p. 139, 2000. 

Mochida, I., Sakanishi, K., Ma, X.L., Nagao, S., and Isoda, T. Deep hydrodesulfurization of diesel fuel Design of reaction process and catalysts. Catalysis Today, 1996, 29, 185. 

Granados-Aguilar AS, Viveros-Garcla T, Perez-Cisneros ES (2008) Thermodynamic analysis of a reactive distillation process for deep hydrodesulfurization of diesel effect of the solvent and operating conditions. Chem Eng J 143 210-219... 

Deng Z, Wang T, Wang Z (2010) Hydrodesulfurization of diesel in a slurry reactor. ChemEng Sci 65 480-486... 

Turaga, U.T. Song, C. Deep Hydrodesulfurization of Diesel and Jet Fuels Using mesoporous Molecular Sieve-Supported Co-Mo/MCM-41 Catalysts. Am. Chem. Soc. Div. Petrol Chem. Preprints, 2001,46 (3), 275—279. 

Song, C., Reddy, K. M., and Beta. H. Mesoporous Aluminosilicate Molecular Sieve MCM-41 as Support of Co-Mo Catalysts for Hydrodesulfurization of Diesel Fuels. Am. Chem. Soc. Div. Petrol. Chem. Prepr., 1998,43 (4), 534-538. 

Ma, X.L., Sakanishi, K., and Mochida, I. 3-Stage deep hydrodesulfurization and decolorization of diesel fuel with CoMo and NiMo catalysts at relatively low-pressure. Fuel, 1994, 73, 1667. 

Trickle-bed reactors are widely used in hydrotreating processes, i.e., hydrodesulfurization of gasoline and diesel fuel, in petroleum refining, chemical, petrochemical, and biochemical processes. The knowledge of hydrodynamic parameters is vital in the design of a TBR because the conversion of reactants, reaction yield, and selectivity depend not only on reaction kinetics, operating pressure, and temperature, but also on the hydrodynamics of the reactor. Special care is also required to prevent flow maldistribution, which can cause incomplete catalyst wetting in some parts... 

It is a challenge to achieve low levels of sulfur imposed by the recent environmental regulations as the compoimds that remain in diesel fuel after hydrodesulfurization are highly refractory. The need to develop catalysts that can cany out deep hydrodesulfurization has become essential. This year the limit set for the sulfur content of diesel in Europe is less than 50 ppm and it will probably decrease to 10 ppm in 2008. 

The EPA s revised pollution guidelines for on-highway diesel fuels took effect on October 1, 1993, and additional Clean Air Act amendments are pending. As a result, the sulfur content of diesel fuel will have to be reduced from 1 to 2% down to 0.05% as compared with 0.3% conventionally attainable with high-pressure hydrodesulfurization. 

Hydrodesulfuration of gasoline and diesel fuels Pt, Pd, and Pt-Pd mesoporous ZSM-5 zeolite (total metal content of 0.5 wt%) Higher sulfur removal efficiency than metal/microporous zeolite or metal/y-Al203 1175]... 

Hydrodesulfuration of gasoline and diesel fuels Pd/mesoporous Beta Better catalytic performance than Pd/Al-MCM-41 (51% vs 35%) because of the higher acidity of the zeolite and than Pd/conventional Beta because of its larger mesopore volume (176,177]... 

An opposite situation happens when the liquid phase is very dilute with B, while gas-phase reactant A is highly soluble (or at high pressures). A common example of such a situation is when slurry systems are employed for hydrodesulfurization of oil fi-actions, in which ppm levels of refractory sulfur compounds (such as dibenzothiophenes and alkyl diben-zothiophenes) may be present in fuel oils like diesel. In comparison, the gas phase is pure hydrogen, which at high pressures behaves like a fairly soluble gas in the hydrocarbon liquid. In such a case, the liquid-phase concentration of the gas-phase reactant is fairly constant throughout (and much higher than the concentration of the liquid-phase reactant B), including inside the catalyst pellets. The effective depletion rate of B (Eq. 6.4) reduces to... 

The color of finished diesel oil is a stringent requirement in some countries. Presently, hydrodesulfurization of faintly yellow diesel oil feedstocks produces colorless and transparent products at 500 ppm S. However, when severe conditions are used for deep HDS, the diesel oil becomes, a fluorescent yellowish green product. High hydrogen pressures suppress color formation, while a high reaction temperature conversely retards hydrogenation and enhances color formation. ... 

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. 

Deep desulfurization of diesel fuels is particularly challenging due to the difficulty of reduce aromatic sulfur compounds, particularly 4,6-dialkyldibenzothiophenes, using conventional hydrodesulfurization processes (HDS). The HDS process is normally only effective for removing organosulfur compounds of aliphatic and alicyclic types. The aromatic sulfur molecules including thiophenes, dibenzothiophenes (DBT), and their alkylated derivatives are very difficult to convert to H2S through HDS. 

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