Morphological Control And Catalytic Performance Of Toluene Alkylation With Methanol Of Pentasil Molecular Sieves

Pentasil molecular sieves consisted of five member ring structure are widely used in refining and petrochemical industry,due to their high thermal stability,deactivation resistance,high acid activity,cation exchange capacity,ordered pore structure and unique framework structure.In this thesis,the morphological control of pentasil molecular sieves and their catalytic performances for toluene alkylation with methanol were studied.The main results are shown as follows:The spherical aggregated ZSM-5 with the particle size of 20μm was synthesized by adding NaCl in the synthesis process.The aggregation is composed by cubic particles with the size of3μm.Because of its larger intercrystal space,it has stronger carbon storage capacity and better stability.The influence of molar ratio of Si/Al（n（Si/Al））on morphology and catalytic performance of ZSM-5 was investigated in different template hydrothermal systems.When using n-butylamine as template,the particle size of ZSM-5 aggregation changes unclearly,but that of the small particles composing the aggregation increases obviously with the increase of n（Si/Al）.The acid amount on ZSM-5 decreases with the increase of n（Si/Al）,which leads to the increase of p-xylene selectivity and the decrease of toluene conversion in the alkylation of toluene with methanol.When using tetrapropylammonium bromide as template,the particle size of the ZSM-5 aggregation and small particle composing the aggregation are both reduced with the increase of n（Si/Al）.The effects of impregnation modification and silica vapor treatment on the catalytic performance of alkylation of toluene with methanol over ZSM-11 were studied.It was found that impregnation modification has little effect on improving the p-xylene selectivity.The highest p-xylene selectivity obtained over modified ZSM-11 was 69%（modified by 12%SiO₂and 12%MgO）.S-1/HZSM-11 composited molecular sieve was obtained by using silica vapor treatment.The p-xylene selectivity and toluene conversion over S-1/HZSM-11 reached 75%and 33%,respectively,when the treatment was carried out for three times.The catalytic performance is better than that over H-type ZSM-5.