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Structural changes and surface activities of ethylbenzene dehydrogenation catalysts during deactivation

Paper ID Volume ID Publish Year Pages File Format Full-Text
43523 45975 2007 9 PDF Available
Title
Structural changes and surface activities of ethylbenzene dehydrogenation catalysts during deactivation
Abstract

Industrial dehydrogenation of ethylbenzene to styrene is performed using potassium-promoted iron oxide catalyst. Many attempts have been made to understand the deactivation mechanism of the catalyst based on the chemical differences between the fresh and used catalysts. In the present work, in addition to the effect of chemical changes, the effect of structural changes of the internal areas on the catalyst activity was investigated. A fresh and used commercial catalyst from an industrial reactor which had been continuously used for two years under severe conditions (LHSV = 1 h−1, T = 610 °C, mass ratio of steam to ethylbenzene = 1.2, P = 1.2 atm) was studied. Nitrogen adsorption, Hg porosimetry, X-ray diffractometer (XRD), scanning electron microscopy (SEM), X-ray fluorescence (XRF), FT-IR, Leco carbon analysis, and wet chemical analysis were performed on both fresh and used catalysts. The catalyst activity tests were performed in a lab-scale continuous fixed bed reactor, maintained at fixed temperature using an electrically heated furnace. It was found that micro and mesopores (d < 50 nm), that make 5% of the total catalyst porosity (21%), were completely filled with carbon deposits in the used catalyst (holding 1.1 wt.% carbon). This caused a surface area reduction of 29%, as measured by Brunauer–Emmett–Teller (BET) method. The remaining 95% of the pores were macropores that were slightly covered with carbon (holding only 0.6 wt.% carbon). Based on a variety of activity tests, it is proposed that the surface catalytic activity for ethylbenzene dehydrogenation follows the order: KFeO2 > Fe2O3/Fe3O4 > carbon (at 562 °C). At higher temperature of 639 °C, however, this trend reverses and carbon surface becomes more active than KFeO2 surface.

Graphical abstractIndustrial dehydrogenation of ethylbenzene to styrene is performed using potassium-promoted iron oxide catalyst. Previous attempts on deactivation mechanisms are based on the chemical differences between the fresh and used catalysts. In the present work, in addition to the chemical changes, the effect of structural changes of internal areas of the catalyst on its activity before and after deactivation are considered.Figure optionsDownload full-size imageDownload as PowerPoint slide

Keywords
Ethylbenzene; Dehydrogenation; Catalyst; Styrene; Characterization
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Structural changes and surface activities of ethylbenzene dehydrogenation catalysts during deactivation
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volume 326, Issue 2, 15 July 2007, Pages 143–151
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
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