The Sio < Sub > 2 < / Sub > And Modified Ni P - Mo/gamma - Al < Sub > 2 < / Sub > O < Sub > 3 < / Sub > Diesel Hydrodesulfurization Catalyst Preparation, Characterization And Activity Evaluation

With people being more and more environmental conscious, guidelines on sulphurcontents in petroleum products have become more and more stringent. Considering thecomplicacy of the sulphidic components and the resulting relatively strict requirements onoperational conditions of hydrodesulfurization, it is critical to improve the catalytic preparationmethods and promote the catalytic activities, which may play a significant role on solvingincreasingly serious energy and environment problems.Amorphous hydrated silica with relatively high specific surface area, aerogel silica withhigh pore volume and pure silica powder with low specific surface area were used to modify theNi-Mo catalyst using γ-Al₂O₃as the carrier. The results show that the adding of amorphoushydrated silica can modify the interaction between the carrier and the active component,appropriate surface acidity and the active center with more type II active center. The catalystactivites were evaluated by dibenzothiophene （DBT）/octane and atmospheric straight-run dieselfuel. When using DBT/octane as the experimental system with the reaction conditions of initialDBT concentration of4000ppmS, reaction temperature of300°C, liquid hourly space velocity（LHSV）3.0h-1, hydrogen pressure2.5MPa and hydrogen-to-oil ratio200, the activity order of3kinds of SiO₂modified catalysts is: aerogel silica modified catalysts> ordinary silica modifiedcatalysts> hydrated silica modified catalysts.Molybdenum oxides were directly added in to each kind of catalysts with different silicasource when kneading, and3kinds of unsupported Ni-Mo/γ-Al₂O₃catalysts were achieved.Dependence of catalytic properties on the contents of hydrated silica and the species of silicasources was investigated. As the results indicated, kneaded molybdenum sources couldefficiently promote the contents of active components in catalysts, ideal quantity of hydratedsilica was15%, and the morphology of silica sources might affect the catalytic activities. In theDBT/octane system with the initial DBT concentration of4000ppmS, temperature of300°C,LHSV of3.0h-1, hydrogen pressure of2.5MPa and hydrogen-to-oil ratio of200, adding15%hydrated silica resulted a desulfurization degree of99.25%; in the straight-run diesel oil systemwith the initial concentration of1050ppmS, temperature of350°C, LHSV of1.8h-1, hydrogenpressure of2.6MPa and hydrogen-to-oil ratio of200, the resulting sulphur concentration inoutlet was29.8ppm after hydrogenation.Phosphorus modified Ni-Mo/15%hydrated silica-γ-Al₂O₃catalyst were prepared bydipping method with phosphorus. The results suggest that the adding of phosphorus improvesthe load for reactive metal, adjusts the disparities of Ni and Mo components, and modifies thepore structures and acidities of catalysts. In addition, the interactions between phosphorus and reactive components or carriers enhance the cooperation between each component, whichmultiplies the Type II active centers of catalyst. In the DBT/octane experimental system withthe initial concentration of4000ppmS, temperature of300°C, LHSV of3.0h-1, hydrogenpressure of2.5MPa and hydrogen-to-oil ratio of200, the sulphur concentrations in outlet were50ppm and15ppm, which is lower than using phosphorus free and containing catalysts. Undermoderate operational conditions, the target of sulfur-free diesel oil could basically be met in thecase of diesel oil system with less sulfur.