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Mass Transfer Advantage of Hierarchical Zeolites Promotes Methanol Converting into para-Methyl Group in Toluene Methylation

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journal contribution
posted on 21.07.2017 by Jian Zhou, Yangdong Wang, Wei Zou, Chuanming Wang, Liyuan Li, Zhicheng Liu, Anmin Zheng, Dejin Kong, Weimin Yang, Zaiku Xie
Investigating the mass transfer of toluene methylation with methanol will contribute to converting more methanol feedstock into the para-methyl group. The reaction system was considered as three competing reactions: toluene methylation and isomerization of para-xylene and methanol to light hydrocarbons. When the thiele modulus analysis method was employed, the degree of utilization of each reaction was calculated over varied ZSM-5 zeolite catalysts. It was found that improvement of mass transfer leads to a more significant increase in the degree of utilization of the methylation reaction. And to further reduce the degree of isomerization, modification of the micropore mouth and coverage of the external acid sites by MgO addition etc. is essential, which can lead to higher para-selectivity, with values from 34.9% to 86.2%. Constructing hierarchical pores in the ZSM-5 zeolite catalyst or reducing crystal size is of significance to converting methanol feedstock into the methyl group of xylene. To obtain a zeolite catalyst with higher methylation efficiency, mass transfer must be preimproved before surface modification.