Kinetics of toluene disproportionation over unmodified and modified ZSM-5 zeolites

The kinetics of toluene disproportionation has been studied over both unmodified and Si-Mg modified ZSM-5 catalysts using an integral reactor and taking into account the reversibility of the reaction. It has been found that xylene dealkylation is the major secondary reaction, whereas toluene dealkyl...

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Bibliographic Details
Published in:Industrial & engineering chemistry research 1993-01, Vol.32 (1), p.49-55
Main Authors: Uguina, Maria A, Sotelo, Jose L, Serrano, David P
Format: Article
Language:English
Subjects:
02 PETROLEUM
020400 - Petroleum- Processing
ADSORPTION
ALKALINE EARTH METALS
ALKYLATED AROMATICS
AROMATICS
Catalysis
CATALYTIC EFFECTS
Catalytic reactions
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
Chemistry
DEALKYLATION
DISSOCIATION
ELEMENTS
EQUATIONS
Exact sciences and technology
General and physical chemistry
HYDROCARBONS
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
KINETIC EQUATIONS
KINETICS
MAGNESIUM
MATERIALS
MATHEMATICAL MODELS
METALS
MINERALS
ORGANIC COMPOUNDS
PH VALUE
REACTION KINETICS
SEMIMETALS
SILICATE MINERALS
SILICON
SORPTION
SURFACE PROPERTIES
SYNTHESIS
Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
TOLUENE
XYLENE-PARA
XYLENES
ZEOLITES
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Description
Summary:The kinetics of toluene disproportionation has been studied over both unmodified and Si-Mg modified ZSM-5 catalysts using an integral reactor and taking into account the reversibility of the reaction. It has been found that xylene dealkylation is the major secondary reaction, whereas toluene dealkylation can be considered negligible. For the unmodified ZSM-5, heterogeneous models based in the alkyl-transfer mechanism allowed the experimental results to be fit better than first and second pseudohomogeneous models, the best concordance being obtained when toluene adsorption is assumed as the rate-limiting step. The corresponding kinetic equation has been further applied to the modified zeolite (SiMg/ZSM-5), leading to the development of a kinetic model which includes the effect of the toluene and p-xylene intracrystalline diffusion rate and the presence of nonselective acid sites on the external zeolite surface. This model describes adequately the selective formation of p-xylene over modified ZSM-5, reproducing the experimental product distribution with an average relative error of 2.8%.
ISSN:0888-5885
1520-5045
DOI:10.1021/ie00013a008