Catalytic dealkylation of alkylaromatic compounds. XIV. The effect of structure of monoalkylbenzenes on their reactivity in hydrodealkylation on a nickel catalyst

Beránek, L.; Kraus, M.

doi:10.1135/cccc19660566

Cited by 16 publications

(6 citation statements)

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“…Favorable dealkylation with iso -PPs may be ascribed to the formation of a more stable secondary carbenium ion, whereas a less stable primary carbenium intermediate is formed during n -PPs dealkylation. This phenomenon is consistent with the results of n - and iso -propylbenzene cracking over zeolites. ,, …”

Section: Resultssupporting

confidence: 92%

“…This phenomenon is consistent with the results of n-and iso-propylbenzene cracking over zeolites. 45,83,84 C−C cracking to form cresols appearing at high reaction temperature is more pronounced with the ortho isomers. For instance, conversion of 2-iso-PP and 2-n-PP at the highest temperature yields close to 20% cresols, whereas this value is below 5% in the case of 4-substituted PPs.…”

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confidence: 99%

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Propylphenol to Phenol and Propylene over Acidic Zeolites: Role of Shape Selectivity and Presence of Steam

et al. 2018

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This contribution studies the steam-assisted dealkylation of 4-npropylphenol (4-n-PP), one of the major products derived from lignin, into phenol and propylene over several micro-and mesoporous acidic aluminosilicates in gas phase. A series of acidic zeolites with different topology (e.g., FER, TON, MFI, BEA, and FAU) are studied, of which ZSM-5 outperforms the others. The catalytic results, including zeolite topology and water stability effects, are rationalized in terms of thermodynamics and kinetics. A reaction mechanism is proposed by (i) analyzing products distribution under varying temperature and contact time conditions, (ii) investigating the dealkylation of different regio-and geometric isomers of propylphenol, and (iii) studying the reverse alkylation of phenol and propylene. The mechanism accords to the classic carbenium chemistry including isomerization, disproportionation, transalkylation, and dealkylation, as the most important reactions. The exceptional selectivity of ZSM-5 is attributed to a pore confinement, avoiding disproportionation/transalkylation as a result of a transition state shape selectivity. The presence of water maintains a surprisingly stable catalysis, especially for ZSM-5 with low acid density. The working hypothesis of this stabilization is that water precludes diphenyl ether(s) formation in the pores by reducing the lifetime of the phenolics at the active site due to the high heat of adsorption of water on H-ZSM-5, besides counteracting the equilibrium of the phenolics condensation reaction. The water effect is unique for the combination of (alkyl)phenols and ZSM-5.

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Section: Resultssupporting

confidence: 92%

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confidence: 99%

Propylphenol to Phenol and Propylene over Acidic Zeolites: Role of Shape Selectivity and Presence of Steam

et al. 2018

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“…This is not similar to the more classical behaviour of hydrodealkylation of alkylbenzene or thermal cracking of EP. [67] In that case, the alkyl group undergoes a successive cleavage of the terminal CeC bond, yielding (the less valuable) methane as the main product of alkyl group. [67] The catalytic results of ZSM-5 indicate that isomerisation reaches equilibrium rapidly; the ratio of isomers is independent of the temperature after a certain conversion (ca.…”

Section: Reaction Pathwaymentioning

confidence: 99%

Shape selectivity vapor-phase conversion of lignin-derived 4-ethylphenol to phenol and ethylene over acidic aluminosilicates: Impact of acid properties and pore constraint

Liao

d’Halluin

Makshina

et al. 2018

Applied Catalysis B: Environmental

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Selective dealkylation of alkylphenols, the opposite reaction of the more commonly studied phenol alkylation, may represent an important reaction in the production of base chemicals like phenol and olefins from fossilized and raw lignocellulosic matter. This study reports the first thermodynamics and kinetics studies of the vaporphase conversion of ethylphenol (EP) over acidic γ-Al2O3, amorphous (ASA) and crystalline aluminosilicates (like ferrierite, ZSM-22, ZSM-5, beta, and USY) in the absence of hydrogen and noble metals, as a way to produce phenol and ethylene. The reaction was studied deliberately in presence of steam to get stable time on stream catalysis. The thermodynamic analysis shows an endothermal EP conversion to phenol and ethylene, favoured at high reaction temperature, while isomerisation, disproportionation and transalkylation are thermodynamically preferred at low temperature. The kinetic study examines the role of the catalytically active sites; it reveals the importance of site constraint on the activity, selectivity and stability, and shows the complex temperature dependency of the dealkylation. Both Brønsted and Lewis acid sites are active, but multifactor dependency (such as acid strength and site accessibility) complicates the establishment of simple quantitative relationships with the acid type. EP does not enter the micropores of ferrierite and ZSM-22, as suggested by adsorption experiments. Kinetics without significant diffusion limitations were obtained with ZSM-5, beta and USY. Thus, in absence of intracrystalline diffusion limitation (as verified by calculations using reported effective diffusivities, and substantiated by a comparably high apparent activation energy for all zeolites), the increased reaction turnover rate with increasing pore size from medium to large pore zeolites is largely explained by a change in reaction pathway (from monolecular to bimolecular) to convert EP to phenol and ethylene. A pathway proceeding through fast thermodynamically favourable bimolecular reactions occurs in the spatially non-constrained pores and crystal surface, whereas monomolecular reactions take place in the micropores of ZSM-5. Despite the lower rate, the selectivity over ZSM-5 strongly benefits from active site confinement, being responsible to achieve quantitative formation of phenol and ethylene from ethylphenol. The excellent performance of ZSM-5 thus accords with its shape selective property that avoids undesired side reactions such as the sterically demanding bimolecular reactions like disproportionation, transalkylation and CC cracking, and severe cokes formation.

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“…However, only little tetralin is formed in the hydrocracking of n-butylbenzene. A suitable mechanism to explain the formation of tetralin and indane type hydrocarbons is available (27).…”

Section: Hydrocracking Reactionsmentioning

confidence: 99%

“…While the ring is conserved for both the families of hydrocarbons, only alkylaromatics undergo cyclization (156). If nonacidic catalyst is used, successive removal of methyl groups from the side chains is the principal reaction and the isomerization reaction is at a minimum (27,156,219,233,264). Commercial uses of both catalytic and thermal hydrogenolysis to produce gasoline and naphthalene have been reported (17,94,169,270,321).…”

Section: Hydrocracking Reactionsmentioning

confidence: 99%

Hydrocracking: A Review

Choudhary¹,

Saraf²

1975

Product R&D

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This paper conforms to the usual concept of an embellished literature survey and as such is useful as a review of technology. In an area of such broad scope no authors can be expected to offer a meaningful assessment of differing effects from the so numerous variables. There is value in the paper as an up-dating of events since the notable publications "Advances in . Hydrocracking" (Advan. Petrol. Chem. Refining, 8, 169 (1964)) and "Hydrocracking To-day and Tomorrow" (Petro/Chem Eng., 37, 32-35 (Oct 1965)).

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Catalytic dealkylation of alkylaromatic compounds. XIV. The effect of structure of monoalkylbenzenes on their reactivity in hydrodealkylation on a nickel catalyst

Cited by 16 publications

References 0 publications

Propylphenol to Phenol and Propylene over Acidic Zeolites: Role of Shape Selectivity and Presence of Steam

Propylphenol to Phenol and Propylene over Acidic Zeolites: Role of Shape Selectivity and Presence of Steam

Shape selectivity vapor-phase conversion of lignin-derived 4-ethylphenol to phenol and ethylene over acidic aluminosilicates: Impact of acid properties and pore constraint

Hydrocracking: A Review

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