(545n) 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

Transformations of aromatic hydrocarbons represent one of the
most important groups of reactions in petrochemical process. In this respect,
methylation of benzene is a promising alternative to produce xylenes, by
converting the carcinogenic benzene which is almost restricted for its use in
gasoline. Also, for the purpose of our study, benzene makes monitoring of this
alkylation reaction over zeolitic catalysts easier compared to other aromatics.
In this work, a combined dry-gel-conversion and steam-assisted-crystallization
method is used to synthesize TNU-9 zeolites with varied crystal size, which in
turn show different accessibility of active sites and confinement effect. 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. Catalytic properties are test on benzene methylation
at 460 ^oC to investigate the effect of additional porosity. It is
found that hierarchical porosity markedly enhances the utility of zeolite and
selectivity towards xylenes via improved mass transport. Under optimized
hierarchical TNU-9 catalyst, xylene selectivity reaches 36.9 %, a comparable
result than that of ZSM-5, the best catalyst tested for this reaction to date.

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

Fig.2 TUN topology and para-xylene

Fig.3 Mechanism on benzene alkylation with methanol

Fig.4 Diffusion of reactants and products inside zeolite crystal

Fig.5 SEM image of TNU-9 samples applied in this work