Modulation Of Active Components Of Catalyst For Hydrocracking Of 1-Methylnaphthalene To BTX In High Temperature System

Diesel coming from fluid catalytic cracking unit contains a large number of bicyclic aromatics and monocyclic aromatics,and has a series of shortcomings such as low cetane number and high density.With the improvement of environmental protection standards in China,the issue of how to reprocess and reuse catalytic diesel has gradually attracted the attention of the petrochemical industry.Hydrocracking of catalytic diesel to BTX can not only solve the problems of substandard quality of diesel and overcapacity of diesel,but also alleviate the current shortage of BTX in our country.It has very important industrial and economic value,and the core of this technology is how to improve the selectivity and yield of BTX.Aiming at this critical issue,this paper studied the influence selectivity to hydrocracking rection from the perspective of reaction temperature,catalyst hydrogenation metal center and catalyst cracking acid center by using 1-methylnaphthalene as a model feedstock for catalytic diesel.Firstly,the hydrocracking catalyst was prepared by impregnating 10 wt%WO₃ and5 wt%Ni O to the Beta zeolite.In the conditions（pressure:6 MPa and hydrogen-to-oil ratio 1300）,the effect of reaction temperature on the hydrocracking performance of1-methylnaphthalene was studied by testing the catalyst at three different temperatures（420℃,460℃,and 500℃）.The results showed that the yield of BTX increased from61.03 mol%at 420℃to 79.08 mol%at 500℃.Secondly,the effect of the hydrogenation metal center of the catalyst on its high-temperature hydrocracking performance was studied.A series of Ni W/Beta catalysts with different metal ratios and total loadings（10W5Ni/Beta,15W/Beta,20W5Ni/Beta,25W/Beta,and 35W/Beta）were prepared,and their physical-chemical characteristics were tested.And the catalytic performance was evaluated at temperature of 500℃,pressure of 6 MPa and hydrogen-to-oil ratio of 1300.And the experimental results showed that the hydrogenation activity of the catalyst Ni W/Beta is higher than the catalyst W/Beta.And with the increase of metal oxide loading,the balance index（BI）of acid center and metal center gradually increased.The 25W/Beta catalyst had better matching relationship between acid center and metal center balance,and the BTX selectivity and yield were the highest,the yield of BTX is as high as 84.62 mol%.Finally,the effect of the cracking acid center of the catalyst on the high temperature hydrocracking performance was studied.A series of Beta zeolites with different silica-to-aluminum ratio（Si O₂/Al₂O₃=23,46,60,180,and 351 mol/mol）were prepared.After loading 25 wt%of WO₃,the catalytic performance was evaluated in the reaction conditions of 500℃,6 MPa and hydrogen-to-oil ratio of 1300.The results showed that with the increase of the silica-alumina ratio of Beta zeolites,the yield of BTX increased first and then decreased.The catalyst prepared by the zeolite with a silicon-aluminum ratio of 183 had the largest BTX yield.Afterwards,Beta zeolite was modified by boric acid using ion exchange method and in-situ synthesis method,and their physical-chemical characterization were tested.The evaluation of catalytic performance in the same reaction conditions showed that ion exchange of Beta zeolites under different boric acid concentrations did not allow boron atoms to enter the zeolite framework,and the acid properties of molecular sieves did not change much,so the catalytic performance of the corresponding catalysts did not change significantly.However,the in-situ synthesis method was used to modify the Beta zeolites,so that boron atoms can enter the zeolites framework.And with the increase of boron content,the acid gradually decreased,and the yield of BTX increased first and then decreased.When Al₂O₃:B₂O₃=3:7,the BTX yield of the corresponding catalyst was the highest.