Mechanism of Acid-catalyzed Isomerization of the Hexanes

McCaulay, D. A.

doi:10.1021/ja01533a026

Cited by 38 publications

(16 citation statements)

References 8 publications

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“…Isomerization of normal to intermediate isomers was effectively isolated by using an n-hexane feed; the subsequent isomerization to neohexane is much slower and very little neohexane is formed. This value agrees with the value of 0.135 calculated from recent data with an HF-BFI catalyst (8). I n a batch reactor?…”

Section: S O M E R I Z a T I O N S E V E R I T Y F-f Cfsupporting

confidence: 91%

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Process-Model Approach to Process Development. Isomerization of Pentanes and Hexanes

R¹,

Malloy²

1963

Ind. Eng. Chem. Proc. Des. Dev.

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A process model based on two isomerization reactions and a cracking reaction greatly aided in optimizing process conditions, testing reactor design, and interpreting experimental data. This approach proved highly efficient in developing a process for isomerizing pentanes and hexanes. It permitted reaching the optimum operating region quickly, so that pilot-plant work could b e concentrated in the region of maximum interest. This approach should b e generally useful because, even in complex processes, only a few critical reactions usually conlrol profitability.( 8 ) P + R + e Pf R and then isomerizes: Y 1 9 6 3 2 3 9

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Section: S O M E R I Z a T I O N S E V E R I T Y F-f Cfsupporting

confidence: 91%

“…These reactions proceed by a carbonium ion mechanism (8). Carbonium ions are present in the catalyst in equilibrium with trace amounts of olefins :…”

Section: Developing the Modelmentioning

confidence: 99%

Process-Model Approach to Process Development. Isomerization of Pentanes and Hexanes

R¹,

Malloy²

1963

Ind. Eng. Chem. Proc. Des. Dev.

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“…3. Traditional n-C 6 hydroconversion mechanism [59][60][61][62][63]72,76,77]: n-C 6 feed (top) dehydrogenates into alkene intermediates ( Pt catalyzed). At acid sites, hexene isomers undergo isomerizations toward thermodynamic equilibrium ( , acid catalyzed).…”

Section: Hydroconversion Mechanismmentioning

confidence: 99%

The selectivity of -hexane hydroconversion on MOR-, MAZ-, and FAU-type zeolites

Calero

Schenk

Dubbeldam

et al. 2004

Journal of Catalysis

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Analyses of a series of published n-hexane hydroisomerization product slates suggest that MAZ-type zeolites yield more dimethylbutane and less methylpentane than either FAU-or MOR-type zeolites. Molecular simulations do not corroborate the traditional view that these selectivity differences are specifically related to the MAZ-, FAU-, or MOR-type zeolite topology. A scrutiny of the literature indicates that reported variation in selectivity relates to a variation in the efficiency of the (de)hydrogenation function relative to the acid function. The FAU-type zeolite catalyst had the most efficient hydrogenation function. The efficiency of the hydrogenation function on the MAZ-type zeolite was low enough to significantly enhance the 2,3-dimethylbutane yield relative to the methylpentane yield, but not low enough to decrease the 2,2-dimethylbutane yield. The efficiency of the hydrogenation function on the MOR-type zeolite was low enough to do both. Only at a sufficiently high n-hexane hydroconversion does the catalyst with the most efficient hydrogenation function exhibit the highest dimethylbutane yield. This new perspective on the reported hexane hydroconversion selectivities suggests that a FAU-type zeolite catalyst with a highly efficient hydrogenation function is best suited for n-hexane hydroisomerization. The FAU topology has the highest porosity which should afford the highest activity without impairing selectivity.  2004 Elsevier Inc. All rights reserved.

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“…It was then assumed that the increase in acidity changes all rates by the same factor. 10 Because the reaction of eqn. (2) exhibited rates roughly proportional to the amount of HF used, it was concluded that the reaction occurred in the acid layer.…”

Section: Introductionmentioning

confidence: 99%

The kinetics of isomerization of 3-methylpentane catalyzed by trifluoromethanesulfonic acid 1

Fǎrcaşiu¹,

Lukinskas²

1999

J. Chem. Soc., Perkin Trans. 2

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Reaction of 3-methylpentane (3MP) was conducted in a two-phase liquid phase system, with the weak superacid trifluoromethanesulfonic acid (TFMSA) as catalyst, below 40 ЊC. The reaction pattern depended upon the way in which the process was conducted. If the acid layer was homogenized periodically, isomerization to 2-methylpentane occurred, with very little cracking. If the acid layer was left undisturbed, a yellow zone (indicating unsaturated organic species) at the interface with the hydrocarbon layer was formed, the reaction showed an induction period after which the overall conversion was greater than for the other reaction mode, and the extent of cracking (direct or following alkylation) increased significantly. For the same quantities of TFMSA and 3MP, increasing the diameter of the reaction tube increased the reaction rate, indicating that the reaction takes place at the interface. The reaction kinetics for the clean isomerization mode (dispersion of the unsaturated organic species formed in the acid layer from the interface) were analyzed by the rate equations reported previously, allowing for catalyst deactivation. Rate measurements at five temperatures between 14 and 32 ЊC gave the activation parameters ∆H ‡ = 19 kcal mol Ϫ1 and ∆S ‡ ≈ Ϫ16 cal mol Ϫ1 deg Ϫ1 , which did not change when the ratio of catalyst to substrate was varied by a factor of two. These values are not compatible with a mass-transfer controlled reaction as found for the HF-SbF 5 catalyst. Instead, the ionization of an alkyl trifluoromethanesulfonate intermediate or a methyl group shift in the cation could be ratedetermining. No intermediate could be evidenced by NMR in either layer, but the 13 C NMR spectrum of the acid layer at the end of the reaction showed the presence of several alkenyl cations (polyalkylcyclopentenyl and possibly even some polyalkylcyclohexenyl cations).

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Mechanism of Acid-catalyzed Isomerization of the Hexanes

Cited by 38 publications

References 8 publications

Process-Model Approach to Process Development. Isomerization of Pentanes and Hexanes

Process-Model Approach to Process Development. Isomerization of Pentanes and Hexanes

The selectivity of -hexane hydroconversion on MOR-, MAZ-, and FAU-type zeolites

The kinetics of isomerization of 3-methylpentane catalyzed by trifluoromethanesulfonic acid 1

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