Preparation Of Supports For Hydrotreating Catalysts For Low-quality Gas Oil

As the crude oil becomes sticker and more inferior and the coking capacity increases rapidly,the processing and utilization of coker gas oil has become an important issue in the field of oil refining.The common use of coker gas oil is to be a part of cracking raw material.However,since the nitrides within it are extremely poisonous to the cracking catalysts,coker gas oil must be hydrotreated in order to increase its utilization rate.The nitrides are generally aromatic and the C-N is stable,thus the hydrotreating catalysts must possess both excellent hydrogenation and hydrogenolysis functions.What’s more,since the gas oil is usually heavy,the catalysts should also have large pore volume,pore size and specific surface area.This paper aims to prepare a kind of high-quality support material to meet the requirements of high performance hydrotreating catalysts.The paper firstly compares the advantages and disadvantages of co-current precipitation method and pH swing method in preparing alumina.Then,the effects of the nature of raw materials and preparation conditions on the properties of alumina are investigated for the better pH swing method.It is found that in the investigated range,when using aluminum nitrate and ammonia as raw materials and choosing 80°C as precipitation temperature,3 times as swing times,30 min as aging time and 4 g/0.143molAl as the amount of expanding agent,the alumina can get the best properties,with the specific surface area of 235.4 m²·g^-1,the pore diameter of 11.79 nm and the pore volume of 0.80 cm³·g^-1.Based on above results,titanium is introduced into alumina by three approaches,namely swinging together,swinging in sequence and swinging and flowing in parallel.Titanium-aluminum composite oxides with different amount of TiO₂ and hydrotreating catalysts based on them are thus obtained.The physicochemical properties of the supports and catalysts are characterized by XRD,BET,SEM,FT-IR,NH₃-TPD and UV-Vis DRS.The results show that the introduction of TiO₂ into the alumina supports can increase the density and strength of the L acid sites on the catalyst surface.Besides,it can also weaken the strong interaction between the metal and the support and thus promote the reduction and sulfuration of the active component.The adsorption properties of Al₂O₃ and TiO₂-Al₂O₃ were evaluated with indole and quinoline in cyclohexane.It is found that the introduction of TiO₂ can promote the adsorption of nitrides on the supports.Taking Liaohe coker gas oil as raw material and HDN rate as evaluation index,NiW/TiO₂-Al₂O₃ catalysts were evaluated under the reaction conditions of 360°C,8 MPa,1.0 h^-1 and 1000（H₂/Oil）.The result shows that the introduction of TiO₂ into the supports can improve the hydrodenitrogenation performance of the catalysts.With the increase of TiO₂ content,the hydrodenitrogenation performances of the catalysts all increase at first and then decrease.When the content of TiO₂ is 20%,the catalysts show the best hydrodenitrogenation performance,and the HDN rate can reach 84.1%under the given conditions.