Studies On The Gas Presulfidation And Passivation Of Ni-Mo/γ-Al₂O₃ Hydro-Treatment Catalysts

To meet the specification of sulfur and aromatic contents of pyrolysis gasoline hydrogenation in petrochemical and refining processes, it is necessary for refiners to develop catalysts with high activity of hydrogenation catalysts. The fresh catalysts for hydrotreating catalyst are commercially available in their oxide forms which are inactive. The oxidized catalysts should be converted into the sulfided catalysts prior to hydrogenation. The sulfurization step executed in situ before which uses a lot of production time. In recent years quite some research has carried out in ex-situ presulfided hydrotreating catalysts. Ex-situ presulfidation is preferred for hydrotreating catalyst catalysts. The sulfided catalysts have high activity, however, the sulfided catalysts can't deposit exposure to air for a long time. In order to improve the stability of sulfided catalysts, presently we have studied the use of passivation on the stability catalysts. The paper has the commercial catalysts NiO-MoO₃/γ-AL₂O₃ as pretreating medal catalysts to presulfide and passivate by gas in a fixed bed flow reactor. The results show that different presulfided methods have various effects on the catalyst activity. They were characterized by means of N₂ adsorption, TEM, TG-DTA, XRD and H₂-TPR. The Main research contents are as follows:1. Sulfided hydrogenation catalysts with high activity are prepared by a kind of new ex-situ gas presulfidation method. Its characteristics are to take H₂S as the vulcanization material, and control the composition of H₂S and H₂ in the vulcanization gas to repress the reduction of the metals oxide, and then sulfided hydrogenation catalysts with the high activity are prepared. At the same time, the inactive gas is lead in the vulcanization gas, which can cut down the reaction heat.The optimization presulfided conditions are acquired by studies on reaction influence factors, such as sulfided time and temperature. Namely, the vulcanization gas is constituted by H₂S, H₂ and N₂, the corresponding volume concentration percentages are 3%, 24% and 73%, and the sulfided time is 3 hours, and the sulfided temperature is from 400℃ to 450℃. The sulfided catalysts which the amount of sulphur is up to 8.93% can be achieved.2. Passivated catalysts with the ability of stable storage are prepared by a kind of gas passivation method. Its characteristics are that the concentration of oxygen transforms regularly with the reaction time. Under the condition of low temperature, the fine oxide protection layers which make catalysts stabilize in the air are formed on the surfaces of sulfided catalysts.The optimization passivated conditions are acquired by studies on reaction influence factors, such as passivated time and temperature. Namely, the passivation gas is constituted by O₂ and N₂, and the volume concentration percentage transforms regularly from 1.25% to 21%, and the passivation temperature is 60℃. The passivated catalysts with high stability can be achieved.3. The reaction mechanisms for the sulfided reaction and the passivation reaction were studied and put forward the reaction model. Those characterization measurements show that catalysts have stable activity after passivation. The gas-solid sulfided and passivation reactions match the volume reaction models. It is observed that for passivated Ni-Mo/γ-Al₂O₃ catalysts with compositions typical of those used industrially, the surface of catalysts have oxidized coats.The above researches provide fundamental evidence for determining the proper presulfided and passivation methods and conditions for industry, and have important practical value.