Xylene isomerization and disproportionation over lanthanum Y catalyst

Collins, Dermot J.; Mulrooney, Kevin J.; Medina, Roger J.; Davis, Burtron H.

doi:10.1016/0021-9517(82)90212-3

Cited by 34 publications

(18 citation statements)

References 7 publications

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“…In the intermolecular mechanism, two reactant molecules disproportionate to yield toluene and trimethylbenzene. The experiments strongly favor 1,2,4-trimethylbenzene over formation of 1,2,3-trimethylbenzene, as consistent with previous studies. , Given the low conversion, the essentially zero yield of 1,3,5-trimethylbenzene is also expected. The disproportionation reaction is favored in materials with two adjacent active sites to accommodate migration of the proton from one ring to another.…”

Section: Resultsmentioning

confidence: 99%

Pushing the Limits on Metal–Organic Frameworks as a Catalyst Support: NU-1000 Supported Tungsten Catalysts for o-Xylene Isomerization and Disproportionation

et al. 2018

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Acid-catalyzed skeletal C-C bond isomerizations are important benchmark reactions for the petrochemical industries. Among those, o-xylene isomerization/disproportionation is a probe reaction for strong Brønsted acid catalysis, and it is also sensitive to the local acid site density and pore topology. Here, we report on the use of phosphotungstic acid (PTA) encapsulated within NU-1000, a Zr-based metal-organic framework (MOF), as a catalyst for o-xylene isomerization at 523 K. Extended X-ray absorption fine structure (EXAFS), P NMR, N physisorption, and X-ray diffraction (XRD) show that the catalyst is structurally stable with time-on-stream and that WO clusters are necessary for detectable rates, consistent with conventional catalysts for the reaction. PTA and framework stability under these aggressive conditions requires maximal loading of PTA within the NU-1000 framework; materials with lower PTA loading lost structural integrity under the reaction conditions. Initial reaction rates over the NU-1000-supported catalyst were comparable to a control WO-ZrO, but the NU-1000 composite material was unusually active toward the transmethylation pathway that requires two adjacent active sites in a confined pore, as created when PTA is confined in NU-1000. This work shows the promise of metal-organic framework topologies in giving access to unique reactivity, even for aggressive reactions such as hydrocarbon isomerization.

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Section: Resultsmentioning

confidence: 99%

Pushing the Limits on Metal–Organic Frameworks as a Catalyst Support: NU-1000 Supported Tungsten Catalysts for o-Xylene Isomerization and Disproportionation

et al. 2018

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“…Techniques that have been used include analytical methods such as the Wei-Prater method [30,31,27], Laplace transform [35] and finite integral transform [24,36], Curve fitting method [23] and least squares method [36,37]. Numerous kinetic parameters have been reported by these authors, adopting 1,3-methyl shift pathway or 1,2-methyl shift pathway for xylene transformation over zeolitic catalysts.…”

Section: Reaction Modelmentioning

confidence: 98%

“…This phenomenon is explained by the fast movement of the para isomer inside the porous catalyst which might cause an apparent 1,3 shift of the methyl group in the benzene ring [28]. The second scheme on the other hand, assumes that the reaction proceeds via 1,2-methyl shift only (o-Xylene to m-Xylene to p-Xylene) where one of the methyl groups in m-Xylene might shift to the adjacent positions through a series of consecutive, reversible 1,2-methyl shift mechanism and become o-Xylene or p-Xylene [29][30][31][32][33][34][35].…”

Section: Reaction Modelmentioning

confidence: 99%

Modelling and sensitivity analysis of a nanocomposite MFI-alumina based extractor-type zeolite catalytic membrane reactor for m-Xylene isomerization over Pt-HZSM-5 catalyst

Daramola

Burger

Giroir‐Fendler

2011

Chemical Engineering Journal

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“…Xylene isomerization can be carried out either over amorphous silica alumina (Cortes andCorma, 1978, Chutoransky andDwyer, 1973;Silvestri and Prater, 1964) or over various types of zeolite (Robschlager and Christoffel, 1980;Collins et al, 1982). Usually, an equilibrium of 24% of p-xylene is observed for most untreated zeolites.…”

Section: Introductionmentioning

confidence: 99%

“…Usually, an equilibrium of 24% of p-xylene is observed for most untreated zeolites. A comparison between acid zeolite catalyst and amorphous silica-alumina catalyst was made by Collins et al (1982), and they found that over Lay zeolite o-xylene isomerizes rapidly, while mand p-xylenes isomerize at about the same rate, and the amorphous silica alumina catalyst has a lower activity than the zeolite catalyst. The relative rate constants were calculated using Wei's method (1962a).…”

Section: Introductionmentioning

confidence: 99%

Enhanced paraxylene selectivity in a fixed‐bed reactor

1985

AIChE Journal

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Simulations of enhanced paraxylene selectivity in a fixed-bed reactor are presented in this paper. The primary reaction of alkylation of toluene with methanol and the secondary isomerization of the xylene products occurring inside zeolite catalysts ZSM-5 are considered. The selectivity of paraxylene is enhanced due to the great difference between the effective diffusivities of xylene isomers. Such enhancement is found to decrease with toluene conversion along the reactor. Behaviors of intrrcrystal concentration profiles of three xylene isomers and toluene are also investigated. SCOPEParaxylene is a valuable product in chemical industries because of large demand for oxidation to terephthalic acid, a major component in polyester fibers, and demand in the synthesis to vitamins and pharmaceuticals. One of the main sources of paraxylene production is the alkylation of toluene with alcohol. This reaction of alkylation produces a primary distribution of xylene isomers at the catalytic site (microscopic level). A typical primary distribution of xylene isomers from a Friedelcrafts reaction of ( 0 : 60%, m: 14%, p: 26%) has been reported by Allen and Yats (1961). This primary distribution is subsequently changed by the coupling of the physical transport process (pore diffusion) and the isomerization of xylene isomers.This results in the secondary distribution of these isomers at the surface of the catalyst pellet or in the bulk solution. The aim of this paper is to determine how these xylene isomers are distributed in the bulk solution (i.e., secondary distribution) as a function of crystal size, speed of chemical reaction, ratio of reaction rate constants of alkylation to isomerization, ratio of diffusivities, and the degree of conversion of the primary reaction of alkylation of toluene with methanol. CONCLUSIONS AND SIGNIFICANCEEnhanced paraxylene selectivity in a fixed-bed reactor was theoretically studied using a method of finite integral transform. The primary distribution of xylene isomers from the reaction of alkylation of toluene with methanol has been shown to influence substantially the secondary distribution of these isomers in bulk solution, especially when the chemical reaction is slow. However, when the chemical reaction i s fast (Thiele modulus, 4, is greater than about 100) this primary distribution of xylene isomers at the catalytic site has very little influence on the sec-

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Xylene isomerization and disproportionation over lanthanum Y catalyst

Cited by 34 publications

References 7 publications

Pushing the Limits on Metal–Organic Frameworks as a Catalyst Support: NU-1000 Supported Tungsten Catalysts for o-Xylene Isomerization and Disproportionation

Pushing the Limits on Metal–Organic Frameworks as a Catalyst Support: NU-1000 Supported Tungsten Catalysts for o-Xylene Isomerization and Disproportionation

Modelling and sensitivity analysis of a nanocomposite MFI-alumina based extractor-type zeolite catalytic membrane reactor for m-Xylene isomerization over Pt-HZSM-5 catalyst

Enhanced paraxylene selectivity in a fixed‐bed reactor

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