Research On Nitrided Hydrotreating Catalyst For Heavy Wax Oil

Heavy wax oil hydrotreating is an important process for producing high quality FCC raw material,the development of hydrogenation catalyst and the optimization of process conditions are the key points of this process.The nitride catalyst is highly anticipated with its special structure and good hydrogenation activity.In this paper,many Ni-Mo-W nitriding catalysts have been prepared by changing the supporter,P and citric acid,the structure and properties of the catalysts were characterized.The hydrogenation activity of the catalysts were investigated on the fixed bed hydrogenation unit.The best nitriding catalyst and process conditions are selected to treat CGO and its denitrogenated coke wax oil,so as to produce high quality FCC feedstock.The?-Al₂O₃ supporter and magnesium-aluminum composite supporter were parpared from pseudo-boehmite,silica sol and magnesia-alumina spinel.The results show that the?-Al₂O₃ supporter with different silicon contents have the same structure and properties,large specific surface area and pore volume,while the specific surface area and pore volume of the magnesium-aluminum composite supporter are smaller.These supporters have only Lewis acid centers,and the supporter containing 10%SiO₂ have more acid centers.The co-impregnation method was used to load Ni,Mo and W metals,and the nitrided catalyst was prepared by temperature programmed nitridation.The results show that all catalysts have mainly Lewis acid sites with a small amount of Bronsted acidic sites,and the active metals are well dispersed.Increasing the amount of silicon can increase the amount of strong acid sites on the catalyst surface and decrease the amount of weak acid sites.Addition of P can significantly reduce the specific surface area and pore volume of the catalyst,and the phosphide appears,the nitride content also decreases.The catalysts prepared from the Mg-Al composite supporter contain more nitrides.The hydrogenation performance of nitriding catalyst was evaluated with VGO as a raw oil,and the results show that the hydrogenation performance of catalysts with 10%SiO₂ content is relatively well,the hydrogenation performance of phosphorus-added nitriding catalysts decreases,catalysts without citric acid during the preparation process have relatively poor hydrogenation performance.The best selection of VGO hydrotreating process conditions as follows,the reaction pressure is 15 MPa,the temperature is 390?,LHSV is 0.6h^-1,and V_?H2?/V_?Oil?is 1000:1.And the sulfur content of the obtained product oil is 19.7?g.g^-1,the nitrogen content is 11.9?g.g^-1.Catalysts with 10%SiO₂ content are used to hydrotreat CGO,through the investigation of the hydroprocessing conditions of CGO,the process conditions for the hydrotreating of the nitrided catalysts were selected as follow,reaction pressure is 15 MPa,the temperature is 360?,LHSV is 0.6h^-1,and V_?H2?/V_?Oil?is 1000:1,under this process condition,the S content of Lanzhou CGO product oil decreases from 9327.3?g.g^-1 to 1125.8?g.g^-1,and the N content decreases from 2966.4?g.g^-1 to 856.6?g.g^-1.Denitrogenation of CGO using denitrification agent can effectively improve the effect of hydrotreating,under the above reaction conditions,the S content of Lanzhou DN-CGO product oil is 805.2?g.g^-1,the N content is 237.5?g.g^-1,the S content of KenLi DN-CGO product oil decreases from 8634.2?g.g^-1 to 731.6?g.g^-1,the N content decreases from 1380.2?g.g^-1 to 240.4?g.g^-1,which meet the requirement of FCC feed stock.