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

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)