Synthesis Of 4, 4'-dimethylbiphenyl Over High-silica ZSM-5 Zeolite Catalysts

4,4'-dimethylbiphenyl(4,4'-DMBP),a product of high added-value,is the raw material of the monomer of function materials.The synthesis of 4,4'-Dimethylbiphenyl attracts more and more attention of researchers all over the world.With traditional alkylation agents such as AlCl₃,SiO₂-Al₂O₃ as catalysts,the selectivity to 4,4'-dimethylbiphenyl is low.As environment -friendly catalysts,zeolites have the advantages of high - selectivity,good-stability,lowcausticity. In this paper,the process for preparing 4,4'-dimethylbiphenyl by methylation of 4-methylbiphenyl over HZSM-5 is employed.The effects of reaction conditions,technologcial conditions and modifications are studied.The results are shown as follows:(1) The n(SiO₂)/n(Al₂O₃) of HZSM-5 as well as reaction conditions have effect on the methylation of 4-MBP.With an increase in the ratio of n(SiO₂)/n(Al₂O₃) and space velocity increase,the selectivity to 4,4'-DMBP increases,while the conversion of 4-MBP decreases. The results show that the suitable catalyst for this reaction is HZSM-5(n(SiO₂)/n(Al₂O₃) =360),and the space celocity 2 h^-1,reaction temperature 380℃are the optimal conditions.(2) A complex modification of hydrothermal treatment and lanthanum load is conducted to high-silica ZSM-5.The results show that the stability of the modified catalyst improved; the order of hydrothermal treatment and Lanthanum load,the order of HCl leaching and calcinations,and the amount of loading has effect on the catalytic properties,repectively.(3) NH₄F/Pt is used for modifying high-silica ZSM-5 zeolite.As a result,the stability of modified ZSM-5,the selectivity to 4,4'-DMBP and the yield of DMBPs are all improved; Increasing the amount of Pt is benifical for upgrading the activity of the catalyst;HCl leaching can improve the stability of modified catalyst,which can remove the residual aluminum in the zelite;It can further improve the catalyst's stability and selectivity of 4,4,'-DMBP by adding water.(4) It can improve the NH₄F modified catalyst's stability and selectivity of 4,4'-DMBP significantly by adding water;However,more amount of NH₄F is not necessary for improve the catalytic properties;It is showed that 10%amount of NH₄F is optimal.