ZSM-5和ZSM-11分子筛催化苯与甲醇烷基化反应研究

摘要

采用水蒸气辅助晶化法合成ZSM-5、ZSM-11和多级孔ZSM-11分子筛,运用XRD、SEM、NH3-TPD、N2吸附-脱附和TG方法对合成的分子筛进行表征.结果表明:所合成的ZSM-5和ZSM-11分子筛的比表面积、微孔体积、晶粒大小和酸性等物化性质相似;多级孔ZSM-11分子筛引入了大量介孔,微孔体积得以保留.合成的分子筛催化苯与甲醇烷基化反应结果表明,ZSM-11相对于ZSM-5表现出更高的反应活性和稳定性,这是因为C7、C8等芳烃分子在ZSM-11孔道内扩散更快;多级孔ZSM-11相对于微孔ZSM-11反应活性进一步提升,在反应温度460℃、压力0.2 MPa、质量空速3h-1的条件下,苯转化率达到54.3％,甲苯和二甲苯总选择性达到91.9％,其中二甲苯选择性为37.9％,该催化剂在反应240 h内保持良好的稳定性,相对于微孔 ZSM-11,寿命显著提升.%Zeolites of ZSM-5,ZSM-11 and hierarchical pore structure ZSM-11 were synthesized via steam-crystallization and characterized by XRD,SEM,NH3-TPD,BET and TG techniques.The results show that synthesized ZSM-5 and ZSM-11 possesses similar BET surface area,micropore volume,crystal size,and acidity.Mesopores were introduced in hierarchical ZSM-11,and the micropores of the ZSM-11 sieve were retained.In the alkylation of benzene with methanol,ZSM-11 showed better activity and stability compared with ZSM-5,owing to the higher diffusion rates of the C7,C8 and other aromatics in ZSM-11 sieve.Hierarchical ZSM-11 performed further improvement in activity in contrast with conventional ZSM-11.At 460 C,0.20 MPa and the WSHV of 3 h 1,the benzene conversion reaches 54.3％,and the total selectivity for toluene and xylene is 91.9％ with xylene selectivity of 37.9％.Meanwhile,the activity of hierarchical ZSM-11 is stable after 240 h on stream,showing better stability than micropore ZSM-5 sieve.