Frontiers of Chemical Science and Engineering
>> 2015,
Volume 9,
Issue 4
doi:
10.1007/s11705-015-1542-2
RESEARCH ARTICLE
Alkaline modification of ZSM-5 catalysts for methanol aromatization: The effect of the alkaline concentration
1. State Key Laboratory of Chemical Engineering, School of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China.2. Research Institute of Urumchi Petrochemical Company, PetroChina Company Limited, Urumchi 830019, China
Accepted: 2015-11-16
Available online: 2015-11-26
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Abstract
The effects of alkaline treatment on the physical properties of ZSM-5 catalysts and on their activities for methanol to aromatics conversion have been investigated. A mild alkaline treatment (0.2 and 0.3 mol/L NaOH) created mesopores in the parent zeolite with no obvious effect on acidity. The presence of mesopores gives the catalyst a longer lifetime and higher selectivity for aromatics. Treatment with 0.4 mol/L NaOH decreased the number of Brønsted acid sites due to dealumination and desilication, which resulted in a lower deactivation rate. In addition, more mesopores were produced than with the mild alkaline treatment. As a result, the lifetime of the sample treated with 0.4 mol/L NaOH was almost five times that of the parent ZSM-5. Treatment with a higher alkaline concentration (0.5 mol/L) greatly reduced the number of Brønsted acid sites and the number of micropores resulting in incomplete methanol conversion. When the alkaline-treated catalysts were washed with acid, some of the porosity was restored and a slight increase in selectivity for aromatics was obtained.
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