Study On Grading Method Of Catalyst Based On Multi-Dimensional Synergistic Mechanism For Hydrogenation Of Diesel

With the strict restrictions on the quality of oil products and the deterioration of oil products,it is difficult to obtain clean diesel by using the traditional hydrogenation process.At present,the main methods to solve this difficulty are to develop more active hydrodesulfurization catalysts or to develop new desulfurization processes.However,these methods are faced with problems such as long required cycle,high cost and complex process.Therefore,how to produce clean diesel economically and reasonably is the key to solve the problem.In this paper,combined with the traditional hydrodesulfurization process and hydrodesulfurization catalyst,considering the mutual influence between hydrodesulfurization and hydrodenitrogenation reactions in the process of diesel hydrogenation process,as well as the temperature gradient distribution of the industrial hydrogenation reactor and the spatial distribution of sulfides and nitrides in diesel,under the multi-dimensional influencing factors,the influence of the grading and filling methods of different catalysts on the hydrogenation performance of diesel was explored to provide guidance for the design of deep hydrogenation process of diesel.Firstly,dibenzothiophene（DBT）and quinoline were used as model compounds,FDS-1A（NiMo P/γ-Al₂O₃）and FDS-1C（CoMo P/γ-Al₂O₃）catalysts were used to investigate the effects of different catalyst loading methods on hydrodesulfurization and hydrodenitrogenation,and the competitive reaction between sulfide and nitride in simulated diesel.The results show that quinoline has a strong inhibitory effect on the hydrodesulfurization reaction of DBT,while DBT promotes the hydrodenitrogenation reaction of quinoline.During the reaction process,CoMo catalyst shows high hydrogenolysis activity,while NiMo catalyst shows high hydrogenation activity.The CoMo//NiMo and NiMo//CoMo gradation filling methods are respectively combined with the reaction advantages of CoMo and NiMo catalysts.The evaluation results show that the hydrogenation activity of the catalyst system can be improved to varying degrees through the hierarchical loading of the catalyst,which is higher than that of the single catalyst.Among them,in the case of coexistence of DBT and quinoline,the hydrogenation activity of NiMo//CoMo grading loading method was higher than that of CoMo//NiMo grading loading method,which proved that there was a synergistic effect between catalysts in the reaction process,but it also reflected that the loading sequence of catalysts limited the synergistic effect.By filling the CoMo and NiMo catalysts with uniform mixed gradation,it is found that the desulfurization and denitrification effects are far better than the hierarchical loading method.It shows that the uniform mixed loading of catalysts can avoid the limitation of catalyst loading sequence,shorten the contact distance between catalysts,maximize the synergy between catalysts,and achieve the best reaction effect.The mixed oil of straight-run diesel（70 wt%）and catalytic cracking diesel（30 wt%）from Qingdao refinery was used as raw material to simulate the temperature rise trend of the upper and lower bed of the industrial hydrogenation reactor.The effect of different catalyst gradation loading methods on the hydrofining reaction of real oil was further explored.The results show that the hydrodesulfurization effect of CoMo and NiMo catalysts with uniform mixing gradation is significantly better than that of catalysts with hierarchical loading and single catalyst loading.Among them,the sulfur content of hydrogenation products of NiMo//CoMo catalyst grading filling method decreased to 38.2μg·g^-1,while the hydrodesulfurization activity of CoMo and NiMo uniform mixed grading filling method was more advantageous,and the sulfur content of hydrogenation products could reach 21.8μg·g^-1,which confirmed that the uniform mixed grading filling method of catalyst fully played the synergistic effect between catalysts,making the hydrodesulfurization activity of catalyst more advantageous and the desulfurization effect of oil products more significant.Finally,the effect of catalyst micro-area coupling gradation loading ratio on diesel hydrofining reaction was explored.The experimental results show that the hydrodesulfurization effect of CoMo and NiMo catalyst mixed ratio of 7:3（CoMo:NiMo）is slightly better than that of mixed ratio of 10:0,because CoMo catalyst accounts for the majority of the mixed ratio of7:3,the desulfurization effect mainly depends on the hydrodesulfurization activity of CoMo catalyst,and the mixed part of NiMo catalyst makes the catalyst system have synergistic effect,the hydrodesulfurization effect is better than that of the mixed ratio of 10:0,and the sulfur content of the hydrogenation product can be reduced to 38.1μg·g^-1.However,the desulfuriza-tion effect was the best when the mixing ratio was 5:5,and the sulfur content of the hydrogenation product was 21.8μg·g^-1.Therefore,the mixing ratio of CoMo and NiMo catalysts was 5:5,which was the best catalyst mixing ratio.