Preparation Of Ru/Hβ And Its Catalytic Kinetics Of Benzene Hydroalkylation

Cyclohexylbenzene is a fine chemical with extremely high added value,which can be used as a raw material for synthesizing liquid crystal material TFT and an additive for electrolyte of lithium ion secondary battery.At the same time,cyclohexylbenzene can be used as a chemical intermediate to produce phenol and cyclohexanone through oxidation and decomposition,which has high application value.In the existing synthesis methods,the raw material cyclohexene for the alkylation of benzene and cyclohexene is expensive,the traditional catalyst is not friendly to the environment,the preparation of ionic liquids is complicated and difficult to recover,and the solid-acid catalysts system is not yet mature;The biphenyl hydrogenation technology offers several advantages,such as mild reaction conditions and high product yield,but it is not economical because of the high price of the raw material biphenyl.Although the catalytic system of benzene hydroalkylation technology is still immature at present,the source of raw materials for this technology are widely available,and it is most likely to realize large-scale industrialization.Therefore,the research on the kinetics and reaction mechanism of benzene hydroalkylation technology is of great significance for the development and industrialization of this catalytic process.In this thesis,Ru/Hβwas prepared by impregnation method using an aqueous Ru Cl₃ solution as the Ru precursor,Hβzeolite as support.The impregnated catalyst was used for hydroalkylation of benzene,the kinetic model was established and its parameters were estimated.In this thesis,the catalyst precursors D-Ru O_x/Hβand G-Ru O_x/Hβwere prepared by incipient wetness impregnation method and wet impregnation method,respectively,and then the precursors were activated by hydrogen reduction method and chemical reduction method to prepare DH-Ru/Hβ,GH-Ru/Hβ,DC-Ru/Hβand GC-Ru/Hβ.Catalytic performance of the catalysts for hydroalkylation of benzene were investigated.The results show that the catalytic performance of DC-Ru/Hβis the best.The selectivity of cyclohexylbenzene reaches 60%while the conversion of benzene reaches 40%.Through various characterization methods,it was shown that compared with GH-Ru/Hβand GC-Ru/Hβprepared by wet impregnation method,the interaction between metal particles and the support of DH-Ru/Hβand DC-Ru/Hβprepared by incipient wetness impregnation method is stronger,the size of the metal particles is smaller and the dispersion is more uniform.Compared with DC-Ru/Hβprepared by chemical reduction method,DH-Ru/Hβprepared by hydrogen reduction method has slightly higher catalytic activity but lower selectivity to cyclohexylbenzene.Chemisorption characterization shows that the acid content of DH-Ru/Hβis twice that of DC-Ru/Hβ,especially the strong acid content of the former is 2.3 times that of the latter,resulting in the deep alkylation of the main product cyclohexylbenzene to by-products such as dicyclohexylbenzene and polycyclohexylbenzene.Therefore,it is not advisable to blindly pursue the increase of acid content and acidity.Finally,DC-Ru/Hβwas selected as the catalyst for subsequent kinetic experiments.Secondly,several batches of DC-Ru/Hβwith the best catalytic performance were prepared and mixed uniformly for kinetic experiments.The results show that when the stirring speed of the reactor reaches 600 rpm and above,the influence of external diffusion on the reaction system was eliminated,and when the catalyst particle size superior to 70 mesh,the influence of internal diffusion on the reaction system could be wiped off.The experimental results of continuous hydrogenation of benzene showed that the reaction order of benzene is one.The nonlinear fitting results of the kinetic data of benzene hydroalkylation at different initial hydrogen pressures show that the reaction order of hydrogen is 1.94 at low pressure(P_H2≤3MPa),and the order of hydrogen at medium pressure is fractional.Finally,the kinetic model of benzene hydroalkylation was established,and it was tried and optimized according to the analysis of experimental data.The parameters in the selected model were calculated by genetic algorithm and the reaction mechanism was further discussed.K₁～K₈ are the adsorption constant of benzene on the acid center and the metal center,hydrogen on the metal center,cyclohexene on the acid center and the metal center,cyclohexylbenzene on the acid center,and cyclohexane on the acid center and the metal center,respectively.The pre-exponential factors of K₁～K₈ are 0.295,0.324,0.029,0.221,3.386×10^-4,0.906,8.880×10^-12,9.987×10^-4mol/l/h,respectively,and the adsorption heats of K₁～K₈ are 3.12,2.85,-6.75,6.34,0.02,8.99,4.62,10.12KJ/mol.The K₉～K₁₁ are rate constants of the hydrogenation of benzene to cyclohexene,the alkylation of benzene with cyclohexene to cyclohexylbenzene and the deep hydrogenation of cyclohexene to cyclohexane,the pre-exponential factors of K₉～K₁₁ are 4.079×10⁴,5.649×10³ and 6.548×10⁶ mol/l/h,respectively,and the activation energies of K₉～K₁₁ are 7.03,7.29,and 5.66 KJ/mol,respectively.The calculation results show that the adsorption of hydrogen on the catalyst is dissociative adsorption,the adsorption strength of cyclohexene on the acid center of the catalyst is much stronger than that on the metal center,and the adsorption strength of the product cyclohexane on the catalyst is very weak,The adsorption strength of cyclohexylbenzene is strong,indicating that the cyclohexene,the main product is prone to side reactions of deep isomerization,deep alkylation.The rate of alkylation of benzene and cyclohexene to cyclohexylbenzene is the slowest,and the macrokinetics rate-determining step in the experiment presents as R-E mechanism,which is consistent with the estimated results.