ZSM-5和ZSM-11分子筛催化苯与甲醇烷基化反应研究

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3 h-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。

STUDY ON ALKYLATION OF BENZENE WITH METHANOL OVER ZSM-5 AND ZSM-11 ZEOLITES

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, 0.20MPa and the WSHV of 3h-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.