The Reaction Mechanism Of Hydrocracking Of Light Cyclic Oil And Synthesis Of Hydrocracking Catalyst

It is required to convert oversupplied light cycle oil(LCO)into high valuable monocyclic aromatics(such as benzene,toluene,xylene(BTX))in recent years.In this study,we used 1-methylnaphthalene(1-MN)as model reactant of LCO and identified the product species of 1-MN hydrocracking.By studying distribution of product species and reaction properties,we proposed the possible reaction network of 1-MN hydrocracking.Based on requirements of catalysts evaluation,we divided the reactant and products into 6 lumps.A mathematic model was established based on the reaction network and mole balance.Six sets experimental data were used to regress six kinetic parameters in the mathematic model.The calculated data agreed well with the experimental data,indicating that the obtained kinetic parameters were reliable,and the kinetic model can reflect the 1-MN hydrocracking process.Based on the thermodynamic calculation and reaction results,we found that the reaction of completely saturated hydrogenation of aromatic rings of 1-MN,methylteteralin,methylindan and C9-C11 alkyl-benzene is almost impossible to take place at high temperature(T > 400 ℃).And thus,the 1-MN hydrocracking reaction network consisted of four reactions: partial hydrogenation of one aromatic ring of 1-MN,ring opening of methyltetralin,secondary hydrogenation of BTX and ring opening of alkyl-cyclohexane.The selective hydrogenation activity of catalyst determined the yield of BTX.According to the obtained kinetic parameters of different catalysts,tungsten-based catalyst has higher selective hydrogenation activity than molybdenum-based catalyst.Tungsten-based catalyst has high catalytic activity to catalyze the partial hydrogenation of polynuclear aromatic hydrocarbons,and relatively low catalytic activity to catalyze the hydrogenation of mono-cyclic aromatic hydrocarbons.The loadings of tungsten oxides also affected the selective hydrogenation activity of catalyst,and optimum metal loading is 25 w.t.%.For 1-MN hydrocracking,the balance between metal active sites and acidic active sites and high selective hydrogenation activity of catalyst are required to obtain high BTX yield at high space velocity.The catalyst for 1-MN hydrocracking was prepared by using tungsten-complex as metal precursor and teteraethoxysilane was token to modify the external acidity of zeolite through chemical liquid deposition.The characterization of catalyst and kinetic study showed that this catalyst has high hydrogenation and cracking activity simultaneously.Due to bicyclic aromatics and monocyclic aromatics have different molecular sizes,properly improving the dispersion of metal of catalyst is an efficient way to improve the selective hydrogenation activity of catalyst.Comparing the performance of catalysts with different metal loadings and acidity,we found that the balance of metal active sites and acidic active sites and the selective hydrogenation activity were affected by the ratio of metal and acid sites and their interaction.Based on the references and thermodynamic calculation of aromatics hydrogenation reactions,we hypothesized the reaction route of each composite in LCO under reaction condition and proposed a possible reaction network of LCO hydrocracking.A 7-lump kinetic model and a mathematic model were established based on the reaction network and mass balance.To verify the established kinetic model,LCO-1 and LCO-2,respectively coming from Petro China Dagang oil Petrochemical Company and Sinopec Shanghai Petrochemical Company,were used as feedstocks.Six sets experimental data were used to regress 6 kinetic parameters for each catalyst.The calculated data agreed very well with the experimental data,indicating that the established kinetic model is reliable and can be used to predict reaction results of feedstocks with different compositions.Based on the reaction results and kinetic results,we can find tungstenbased catalyst achieved high BTX yield due to its high selective hydrogenation activity.And a bifunctional catalyst using tungsten complex as metal precursor achieved the highest BTX due to its highest selective hydrogenation activity and balance between metal and acid sites.A polymerized carbohydrate was used as mesoporous templating agent to synthesize a mesoporous Beta zeolite.It was found that with increasing of the carbohydrate,the mesoporous surface and volume of zeolite increased,but the acidity decreased.And when the content of the carbohydrate exceeded 10 w.t.%,the crystallinity of Beta zeolite decreased significantly.The increment of mesoporous surface area and volume improved the accessibility of some polycyclic aromatic hydrocarbon molecules which cannot enter the micropores of Beta zeolite.And ratio of rate of polycyclic aromatic hydrogenation and rate of BTX hydrogenation increased.Therefore,the selective hydrogenation activity of catalyst improved.