Study On The Preparation Of NiMoAl Catalyst And Its Hydrodenitrification Performance

Recent years,the regulations for NO_x emissions have become more and more strict.During the hydrorefining process of petroleum,the presence of trace amounts of nitrogen compounds will obviously inhibit the catalytic hydrodesulfurization reaction of oil products.To achieve deep desulfurization,the nitrogen compounds in the petroleum must be removed firstly.Therefore,hydrodenitrification(HDN)has become an important process in the modern petroleum refining industry,which is of great significance to develop efficient hydrodenitrification catalysts.In this work,NiMoAl catalysts were prepared by a complete liquid phase method independently developed by the research group,and the effects of the heat treatment method of the catalyst precursor,the addition ways of the active components,and the modification of boron and silicon additives on the physical and chemical properties of the NiMoAl catalyst were studied;The HDN structure-activity relationship of the catalyst was evaluated by the quinoline hydrodenitrification(HDN)reaction as a probe,and the catalytic cracking(FCC)oil slurry was used as the raw material to investigate the heavy oil hydrogenation activity of the catalyst.The main conclusions are as follows:(1)Seven catalysts were obtained by changing the heat treatment method,temperature and atmosphere.The structures of catalysts were characterized,and it is concluded that different types of Aluminum species in catalyst were obtained at different heat treatment temperatures.Al OOH was gotten when the heat treatment temperature was 300?,and?-Al₂O₃ and partially unconverted Al OOH were obtained when the heat treatment temperature was 400?.Compared with traditional calcination,the catalyst prepared by the complete liquid phase method has higher crystallinity,more medium strong acid content,and more octahedral coordination Mo species.When the heat treatment temperature was increased from 300 to 400?,the quinoline hydrodenitrification products of the catalyst decreased obviously.(2)Four kinds of catalysts were obtained by adding active components before and after hydrolysis,when the temperature was raised to 95?and when it was opened.The effect of the addition ways of the active component on the physicochemical properties of the catalyst was investigated.It was concluded that with the delay of the position of adding the active component,the characteristic diffraction peak intensity of the obtained aluminum species of the catalyst gradually increased.Adding the active component before hydrolysis,the HDN performance of the catalyst was poor.(3)By adding Boron to the preferred NiMoAl catalyst for modification,four kinds of B-NiMoAl catalysts with different addition amounts and addition ways were obtained.Aluminum exists in the form of Al OOH species,Ni species and Mo species are well dispersed on the surface of Al OOH,and after heating up to 95?,boric acid is added to obtain better crystal phase structure of Al OOH more easily.The specific surface area of the catalyst increased after boron modification.The acidity of the catalyst can be regulated by changing the addition ways and amount of boron in the precursor synthesis:After the introduction of boron,the amount of medium-strong acid and the amount of strong acid in the catalyst were significantly increased;By changing the introduction ways of boric acid,the amount of medium-strong acid of the catalyst was significantly different,and more medium-strong acid were produced by adding boric acid when heated to 95?than adding boric acid in the hydrolysis stage.The addition of boron component can obviously improve the Br?nsted acid contant and the performance of denitrification and desulfurization of NiMoAl catalyst.After catalytic hydrogenation of FCC slurry,the denitrification rate of B-NiMoAl reached 20.8%and desulfurization rate reached are 67.1%;The content of>350?fraction decreased significantly,the aromatic fraction increased,the colloid content decreased significantly,and the lightweight effect was obvious.(4)By adding Silicon to the optimized NiMoAl catalyst for modification,Si-NiMoAl catalysts with four different silica sol additives were obtained.The amount of Br?nsted acid in the silicon modified catalyst increased obviously;With the increase of the amount of silicon introduced into the catalyst,the low temperature reduction temperature peak of the catalyst decreased gradually.The amount of strong acid and the amount of Br?nsted acid both decreased first and then increased.The denitrification effect of the Si-NiMoAl catalyst also showed a trend of decreased first and then increased.After catalytic hydrogenation of FCC slurry by Si-NiMoAl,the denitrification rate and desulfurization rate reached 14.7%and 68.1%respectively;The content of>350?fraction decreased significantly,and the effect of light-weight was obvious.