(253d) Benzene Methylation Catalysed By Hierarchically Porous Zeolite: An Effective Way to Promote Xylene Selectivity and Catalyst Lifetime for Large Scale Commercial Use

Authors: 
He, X., East China University of Science and Technology
Zhu, X., East China University of Science and Technology
Zhu, K., East China University of Science and Technology

Benzene Methylation
Catalysed by Hierarchically Porous Zeolite: An Effective Way to Promote Xylene
Selectivity and Catalyst Lifetime for Large Scale Commercial Use

 

Methylation of benzene is
an alternative low-cost route to produce xylenes, but selectivity to xylene
remains low over conventional zeolitic catalysts. In this work, a combined
dry-gel-conversion and steam-assisted-crystallization method is used to
synthesize hierarchically porous zeolite ZSM-5 with varied Si/Al ratios. N2
physisorption, NH3- TPD, SEM and FT-IR are employed to characterize
the texture and acidity of both hierarchically porous zeolites and their
conventional counterparts. The method is found to be applicable to ZSM-5 with
Si/Al ratios from 20 to 180. Catalytic properties are test on benzene
methylation at 460 oC to investigate the effect of additional
porosity and Si/Al ratios. At low Si/Al ratios, the benzene conversions over
conventional and hierarchical ZSM-5 are close, and selectivity to toluene is
high over hierarchical ZSM-5. It is found that hierarchical porosity markedly
enhances the utility of zeolite and selectivity towards xylenes via improved
mass transport at higher Si/Al ratios. Under optimized hierarchical ZSM-5
catalyst, xylene selectivity reaches 34.9 % at Si/Al
ratio of 180, and a remarkable lifetime of 3000 h is accomplished in industrial
sideline evaluation.

Fig.1 Crystallization mechanism on hierarchical porous ZSM-5 in
this work

Fig.2 MFI topology and para-xylene

Fig.3 Mechanism on benzene alkylation with methanol

 

Fig.4 SEM image of conventional ZSM-5 (a, c, d) and
hierarchically porous (b, e, f) ZSM-5-HTS with Si/Al ratios of 20 (a, b) and
180 (c-f)