Nickel-Tungsten Hydrodesulfurization Catalyst Supported on Multistage Porous Zeolite

Desulfurization process is a necessary process in petroleum refining, which mainly provides protection for subsequent catalysts, because sulfur element is very easy to cause subsequent cracking, catalytic reforming and other acidic catalysts poisoning and rapid deactivation. In addition, reducing the sulfur content in fuel is also conducive to reducing engine corrosion and wear, and improving the quality of petroleum products.

At present, there are three main desulfurization methods: hydrodesulfurization (HDS), adsorptive desulfurization (ADS) and oxidative desulfurization (ODS). Among them, hydrodesulfurization (hydrodesulfurization) is the mainstream method used in industry. Using highly acidic carriers, such as zeolites, through additional reactions such as isomerization, hydrogenation and cracking, the regional blocking effect of 4,6-methyl can be removed, thus reducing the difficulty of the reaction. However, the carrier will also be rapidly inactivated and the load is uneven. Therefore, it is necessary to find more efficient and cheaper desulfurization catalysts. A multi-stage porous zeolite supported nickel-tungsten hydrodesulfurization catalyst has been proposed by some scholars. The manufacturing process of the catalyst involves these steps:

Firstly, microporous hydrogen zeolite was obtained by calcining zeolite at 500-600 C for 4.5-5.5 hours.

Secondly, the microporous hydrogen zeolite obtained in step one is added to acid solution with concentration of 0.1-4 mol/L, heated and refluxed for 0.5-4 h, then washed with deionized water until the filtrate is neutral. After drying, the zeolite is calcined for 4.5-5.5 h at 500-600 ℃ to obtain the de-aluminized zeolite.

Third, the dealuminized zeolite obtained in step 2 was added to the alkali solution with the concentration of 0.1-2 mol/L, stirred for 0.2-3 h at 60-70 ℃, then washed with deionized water until the filtrate was neutral. After drying, the ammonium nitrate solution was used for ion exchange, and then calcined at 500-600 ℃ for 4-6 h to obtain the hydrogen-type desilicated multistage porous zeolite molecular sieves.

Fourth, hydrogen-type desiliconized multistage porous zeolite molecular sieves obtained in step 3 are added to acid solution with concentration of 0.05-2 mol/L, stirred for 0.5-7 h at 60-70 ~℃, washed with deionized water until the filtrate is neutral, and calcined for 3-7 h at 500-600 ~C after drying to obtain highly acidic multistage porous zeolite.

Fifth, nickel nitrate and ammonium metatungstate ((NH₄)₆H₂W₁₂O₄₀) were collocated into nickel-tungsten aqueous solution according to the atomic ratio of tungsten to nickel 2-3. The nickel-tungsten aqueous solution was used to adsorb nickel-tungsten on the strong acidic multi-stage porous zeolite obtained in step 4 by dry impregnation. Finally, the multi-stage porous zeolite supported nickel-tungsten deep hydrodesulfurization catalyst was obtained by calcination for 4.5-5 h at 500-600 ℃.

Compared with traditional catalysts supported on alumina, nickel-tungsten hydrodesulfurization catalysts supported on multistage porous zeolites have better catalytic effect on 4,6-DMDBT. In contrast, mesoporous mordenite supports have better catalytic performance, which is due to the existence of mesoporous structure, which improves the distribution of active sites. At the same time, the selectivity of the reaction will not be changed by using mesoporous mordenite carrier. Nickel-tungsten hydrodesulfurization catalyst has better catalytic effect on 4,6-DMDBT. In contrast, mesoporous mordenite supports have better catalytic performance, which is due to the existence of mesoporous structure, which improves the distribution of active sites. At the same time, the selectivity of the reaction will not be changed by using mesoporous mordenite carrier.

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