Simulation of liquid and vapour phase xylene isomerization over deactivating H-Y-Zeolite

Gendy, Tahani S.

doi:10.1002/(sici)1097-4660(1998100)73:2<109::aid-jctb876>3.0.co;2-i

Cited by 9 publications

(12 citation statements)

References 1 publication

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“…To ensure thermodynamic consistency at equilibrium, the rate constants for the m - to p -xylene and m - to o -xylene reactions in the above equations are expressed as follows, where K pm = ( C p / C m ) eq and K om = (C o / C m ) eq are temperature-dependent equilibrium constants for both reactions, respectively. However, an average value can be computed for both constants, since the thermodynamic equilibrium concentrations of the xylenes remain fairly constant within the temperature range of this work.…”

Section: Kinetic Model Developmentmentioning

confidence: 99%

“…Regarding the kinetics of xylene transformations over zeolitic catalysts, several modeling techniques have been applied to obtain the numerous kinetic parameters of this complex reaction system. Among the techniques employed in the literature include analytical methods such as Wei−Prater method, ,, Laplace transform, and finite integral transform. , Curve fitting methods, such as the Himmelblau method 5 and the least-squares method, , have also been applied. Recently, Iliyas and Al-Khattaf, in their investigation of xylene isomerization over Y-zeolite, obtained the various kinetic parameters of the overall xylene transformation reactions from simplified effective kinetic models applied to each xylene isomer.…”

Section: Introductionmentioning

confidence: 99%

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Modeling Xylene Reactions over ZSM-5 Zeolite in a Riser Simulator: 1,3- versus 1,2-Methyl Shift

Al-Khattaf

Tukur

Al-Amer

2005

Ind. Eng. Chem. Res.

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Xylene transformation reactions have been investigated over ZSM-5 zeolite in a riser simulator that mimics closely the operation of commercial fluidized-bed reactors. Two reaction schemes have been used to model the transformation reactions. The first is based on a triangular reaction path which assumes a direct interconversion between o- and p-xylene isomers (1,3-methyl shift), and a second scheme assumes the reactions proceed via 1,2-methyl shift only (o-xylene ⇄ m-xylene ⇄ p-xylene). The rate constants and activation energies are obtained from simplified kinetic models based on the isomerization of the pure xylene isomers using the “time on stream” decay model. The results provide ample evidence to suggest that direct interconversion between o- and p-xylene isomers (a 1,3-methyl shift) occurs with the same rate as the conversion of m- to o-xylene (a 1,2-methyl shift) over ZSM-5 zeolite catalyst, and the 1,3-methyl shift reaction path is a better representation of the xylene isomerization mechanism in ZSM-5 zeolite than that of the 1,2-methyl shifts only. In addition, the riser simulator and the modeling procedures employed have shown to be very effective in investigating xylene isomerization kinetics.

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Section: Kinetic Model Developmentmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Modeling Xylene Reactions over ZSM-5 Zeolite in a Riser Simulator: 1,3- versus 1,2-Methyl Shift

Al-Khattaf

Tukur

Al-Amer

2005

Ind. Eng. Chem. Res.

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“…In order to ensure thermodynamic consistency at equilibrium, the rate constants for m-to pxylene, and m-to o-xylene reactions in the above equations are expressed as follows [40,41]:…”

Section: P O T + T M B Smentioning

confidence: 99%

“…However, an average value can be computed for both constants, because the thermodynamic equilibrium concentrations of the xylenes remain fairly constant within the temperature range of this work. The xylene equilibrium concentrations are obtained from published works [37,40,41].…”

Section: P O T + T M B Smentioning

confidence: 99%

Enhancing p -xylene selectivity during m -xylene transformation using mildly pre-coked ZSM-5 catalyst

Al-Khattaf

2007

Chemical Engineering and Processing - Process Intensification

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In the present work, the transformation of m-xylene was studied over fresh and pre-coked H-ZSM-5 catalyst in a riser simulator over the temperature range of 350-500 o C.Significant differences were observed in both the activity and product selectivity pattern for the two forms of the catalyst.While, the fresh catalyst generally gave higher m-xylene conversion, the pre-coked catalyst produced higher Isomerization/Disproportionation (I/D) and Para/ Ortho xylene (P/O) ratios .For both forms of the catalyst, m-xylene conversion was found to increase with both reaction temperature and reaction time (0-15 s). A maximum conversion of 30.8% was achieved at 500 o C for a reaction time of 15 s using the fresh catalyst. The corresponding value for the pre-coked catalyst was 24.6%. P/O and I/D ratios as high as 2.5 and 10 respectively were observed with the pre-coked catalyst. It was also observed that the P/O and I/D ratios decreased with increasing temperature for both catalyst and that the difference between these ratios for the two catalysts is more pronounced between 400 and 450 o C than at higher temperatures. Kinetic modeling of the m-xylene transformation over the pre-coked catalyst yielded a lower activation energy for p-xylene formation compared to the fresh catalyst. And an activation energy of 17.5 kcal/mol for the of m-xylene dispropotionation was obtained for the precoked catalyst compared to 7.82 kcal/mol for the fresh catalyst. These values are indicative of the restriction posed on disproportionation by the pre-coked catalyst as reflected by higher I/D ratios.

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“…One of the main benefits of this process is its high yield to xylenes as well as its extremely high stereoselectivity (99%) to the para isomer of xylenes; this particular attribute nearly eliminates the need for expensive xylene separation . It is well-known that o -, m -, and p -xylenes readily isomerize in the presence of solid acid catalysts, such as H-Y and H-BEA zeolite, at reaction temperatures of 240–300 °C. − However, isomerization and transalkylation have not been observed during the production of p- xylene from DMF using H-Y or other solid acid catalysts; once formed, p- xylene remains intact. , …”

Section: Introductionmentioning

confidence: 99%

Inhibition of Xylene Isomerization in the Production of Renewable Aromatic Chemicals from Biomass-Derived Furans

et al. 2016

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Inhibition of p-xylene isomerization in the presence of H-Y (Si/Al 2.6) and H-BEA (Si/Al 12.5) zeolites was studied under conditions relevant to p-xylene production from 2,5-dimethylfuran (DMF) and ethylene. Through examination of the reaction components, it was shown that both DMF and 2,5-hexanedione inhibit transalkylation and methyl shift reactions of p-xylene, while other reaction components, water and ethylene, do not. Retention of Brønsted acid sites after the reaction was shown through the use of 27Al NMR for both H-Y and H-BEA zeolites, but with a reduction in the ratio of tetrahedrally coordinated aluminum (strong acid sites) to octahedrally coordinated aluminum (Lewis acid sites) coinciding with the disappearance of the framework aluminum. Diffuse reflectance spectroscopy has shown preferential adsorption of DMF and 2,5-hexanedione (DMF + H2O) relative to p-xylene to the Brønsted acid sites located in the super and sodalite cages of the H-Y. Desorption characteristics for DMF and p-xylene in H-Y and H-BEA were determined by thermogravimetric analysis, consistent with adsorption energetics of individual chemical species and dimeric complexes evaluated by an ONIOM method. Evaluation of three mechanisms, allowing for production of p-xylene from DMF and ethylene while also inhibiting p-xylene isomerization, supports high surface coverage of the active site with 2,5-hexanedione, supported by electronic structure calculations.

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Simulation of liquid and vapour phase xylene isomerization over deactivating H-Y-Zeolite

Cited by 9 publications

References 1 publication

Modeling Xylene Reactions over ZSM-5 Zeolite in a Riser Simulator: 1,3- versus 1,2-Methyl Shift

Modeling Xylene Reactions over ZSM-5 Zeolite in a Riser Simulator: 1,3- versus 1,2-Methyl Shift

Enhancing p -xylene selectivity during m -xylene transformation using mildly pre-coked ZSM-5 catalyst

Inhibition of Xylene Isomerization in the Production of Renewable Aromatic Chemicals from Biomass-Derived Furans

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