Influence of the framework composition of commerical HFAU zeolites on their activity and selectivity in m-xylene transformation

Morin, S.; Ayrault, Philippe; Gnep, N.S.; Guisnet, M.

doi:10.1016/s0926-860x(97)00263-9

Cited by 94 publications

(56 citation statements)

References 33 publications

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“…Moreover, it can be noticed that conversion passes through a maximum for all the reaction times studied, with an initial increase below 0.11 mmol/g, however it decreases subsequently. The initial increase in conversion with acidity can be explained easily, since transformation of m-xylene over Y-zeolite is enhanced with total acidity [1][2][3].…”

Section: Products Distributionmentioning

confidence: 99%

“…A convenient way to upgrade the low-valued m-xylene consists of its transformation to o-and p-xylene. In this context, the transformation of m-xylene has been studied over different types of zeolite catalysts [1][2][3][4][5][6][7][8].…”

Section: Introductionmentioning

confidence: 99%

“…Both the isomerization and disproportionation reactions have been reported to be catalyzed by BrÖnsted acid sites [1][2][3][4][5][6]. Disproportionation being a bimolecular reaction has been established to require higher concentration of acid sites [1,3,7].…”

Section: Introductionmentioning

confidence: 99%

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The effect of Y-zeolite acidity on m-xylene transformation reactions

Al-Khattaf¹,

Iliyas²,

Al-Amer³

et al. 2005

Journal of Molecular Catalysis A: Chemical

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m-Xylene transformation has been studied on as-prepared H-Y and a series of dealuminated Y zeolite catalysts. The conversion of m-xylene was found to increase initially with acidity, however, decreases subsequently. It has been proposed that the high concentration of acid sites in the H-Y catalyst increases paring reaction, in addition to the well-known isomerization and disproportionation pathways. A significant decrease was observed with respect to disproportionation/paring (D/Pa) ratio versus reaction temperature. This indicates that higher activation energy is required for paring as compared to disproportionation reaction. The p-xylene/o-xylene (P/O) was established to be independent of zeolite acidity. A higher coke deposition was found for the transformation of m-xylene over the parent H-Y as compared to the highly dealuminated USY zeolite. The formation of benzene and C 2 -C 4 gases were found to be proportional to zeolite acid concentration.Keywords: m-Xylene transformation, Y zeolite, isomerization, disproportionation, paring reaction. * Corresponding author. Tel.: +966-3-860-1429; Fax: +966-3-860-4234 E-mail address: skhattaf@kfupm.edu.sa 2 IntroductionXylenes are important starting materials for some industrial processes like the production of synthetic fibers, plasticizers and resins. The major sources of these aromatic hydrocarbons are the reforming and pyrolysis gasoline, which have a higher ratio of low-valued m-xylene. A convenient way to upgrade the low-valued m-xylene consists of its transformation to o-and p-xylene. In this context, the transformation of m-xylene has been studied over different types of zeolite catalysts [1][2][3][4][5][6][7][8].There is interest in ultrastable Y-type zeolites for m-xylene transformation, partly because of their increased chemical and thermal stability, with respect to other zeolites. Y-zeolite is made ultrastable by the removal of aluminum from the framework. The dealumination can be accomplished through the use of steam [9], acid leaching [10], or by chemical treatment with hexaflourosilicate or silicon tetrachloride [11][12][13]. However, the most common procedure is hydrothermal treatment at elevated temperatures under controlled atmosphere (steaming). The resulting material, USY (ultrastable Y) zeolites, being modified in the framework Si/Al ratio, structure and acidity, usually exhibits improved reactivity, selectivity and coking behavior for a catalytic reaction, which is of great interest to the petroleum industry. Several studies have been conducted on the effect of Y-zeolite acid properties on isomerization and disproportionation of m-xylene reactions [1,5,7]. However, studies correlating the intrinsic properties of Y-zeolite to other reaction pathways, apart from isomerization and disproportionation are somewhat limited. With this in mind, the present work reports the effect of acid properties of Y-zeolite on products selectivity and various reaction pathways during m-xylene transformation in a fluidizedbed reactor. As prepared H-Y zeolite ...

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Section: Products Distributionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The effect of Y-zeolite acidity on m-xylene transformation reactions

Al-Khattaf¹,

Iliyas²,

Al-Amer³

et al. 2005

Journal of Molecular Catalysis A: Chemical

View full text Add to dashboard Cite

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“…As a result, it can be concluded that p-xylene selectivity is favored at lower than at higher temperatures. Another reason can be due to the bimolecular transmethylation mechanism which requires the reaction between 1,2,4 TMB and o-xylene molecules to form p-xylene and 1,2,4 TMB [14,37,38]. The present result suggested that the rate of this bimolecular reaction decreases with temperature leading to an increase in P/O ratio as reaction temperature decreases.…”

Section: P-xylene To O-xylene (P/o) Ratiomentioning

confidence: 58%

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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“…In top-down approaches, mesopores are introduced after the zeolite has been synthesized, and it is usually achieved by extracting either Al or Si atoms from the zeolite framework. Common methods for demetallation include steaming [33][34][35][36][37][38][39][40], acid-leaching [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] and base treatment [47,48]. In bottom-up approaches, the mesopores are introduced in the framework during the synthesis.…”

Section: Introductionmentioning

confidence: 99%

One-pot synthesis of nano-crystalline MCM-22

Tempelman

Portilla

Martínez-Armero

et al. 2016

Microporous and Mesoporous Materials

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Nano-crystalline MCM-22 zeolite was synthesized in a one-pot procedure by the use of an organosilane (dimethyl-octadecyl-(3-trimethoxysilylpropyl)-ammonium chloride, TPOAC) in the zeolite synthesis gel. This crystal growth inhibition procedure introduced mesopores in the MCM-22 crystallites. The lower mechanical stability of the nano-crystalline MCM-22 zeolite compared with bulk MCM-22 can be countered to some extent by pillaring. The increased external surface of the microporous zeolite domains resulted in increased accessibility of the Brønsted acid sites, as followed from the better performance in liquidphase benzene alkylation with propylene as compared with bulk MCM-22. The increased accessibility of the internal acid sites in Mo-loaded hierarchical MCM-22 was also evident from the improved benzene selectivity during methane aromatization. Silylation of hierarchical Mo/MCM-22 was detrimental for the catalytic performance in MDA. The nano-crystalline MCM-22 has physico-chemical and catalytic properties intermediate between those of MCM-22 and ITQ-2 with the benefit over ITQ-2 that it can be synthesized in a single step.

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Influence of the framework composition of commerical HFAU zeolites on their activity and selectivity in m-xylene transformation

Cited by 94 publications

References 33 publications

The effect of Y-zeolite acidity on m-xylene transformation reactions

The effect of Y-zeolite acidity on m-xylene transformation reactions

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

One-pot synthesis of nano-crystalline MCM-22

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