Kinetics and reaction engineering of selective hydrogenation of benzene towards cyclohexene

Döbert, Frank; Gaube, Johann

doi:10.1016/0009-2509(96)00167-4

Cited by 15 publications

(3 citation statements)

References 4 publications

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“…On the basis of radiotracer studies, Paal and Tetenyi suggest that hydrogenation proceeds in a random fashion 4 or via a reaction path that does not pass via cyclohexene . Experimentally, little cyclohexene formation is observed during benzene hydrogenation over transition metal catalysts, except for Ru-based processes, consistent with the reaction path proposed by Tetenyi and Paal . Actually, for the six sequential hydrogenation steps in benzene hydrogenation, 14 possible reaction paths can be proposed (Figure ).…”

Section: Introductionsupporting

confidence: 66%

Ab Initio Reaction Path Analysis of Benzene Hydrogenation to Cyclohexane on Pt(111)

et al. 2004

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First-principles density functional theory calculations were performed to obtain detailed insight into the mechanism of benzene hydrogenation over Pt(111). The results indicate that benzene hydrogenation follows a Horiuti-Polanyi scheme which involves the consecutive addition of hydrogen adatoms. A first-principles-based reaction path analysis indicates the presence of a dominant reaction path. Hydrogenation occurs preferentially in the meta position of a methylene group. Cyclohexadiene and cyclohexene are expected to be at best minor products, since they are not formed along the dominant reaction path. The only product that can desorb is cyclohexane. Along the dominant reaction path, two categories of activation energies are found: lower barriers at approximately 75 kJ/mol for the first three hydrogenation steps, and higher barriers of approximately 88 kJ/mol for steps four and six, where hydrogen can only add in the ortho position of two methylene groups. The highest barrier at 104 kJ/mol is calculated for the fifth hydrogenation step, which may potentially be the rate-determining step. The high barrier for this step is likely the result of a rather strong C-H...Pt interaction in the adsorbed reactant state (1,2,3,5-tetrahydrobenzene) which increases the barrier by approximately 15 kJ/mol. Benzene and hydrogen are thought to be the most-abundant reaction intermediates.

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Section: Introductionsupporting

confidence: 66%

Ab Initio Reaction Path Analysis of Benzene Hydrogenation to Cyclohexane on Pt(111)

et al. 2004

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“…Liquid-phase selective hydrogenation of benzene to cyclohexene has attracted much attention during the past several decades owing to its environmentally benign process and great industrial interest compared to the total hydrogenation of benzene. , However, the process is very difficult to realize industrially because benzene is thermodynamically favored to be hydrogenated to cyclohexane (free-energy change for cyclohexene formation is −23 kJ mol −1 , while it is −98 kJ mol −1 for cyclohexane formation). Because cyclohexene as a reaction intermediate was first detected in the hydrogenation of benzene on a nickel film by Anderson in 1957, numerous papers – have reported the selective hydrogenation of benzene to cyclohexene in a stirred batch reactor.…”

Section: Introductionmentioning

confidence: 99%

Selective Hydrogenation of Benzene to Cyclohexene on a Ru/Al₂O₃/Cordierite Monolithic Catalyst: Effect of Mass Transfer on the Catalytic Performance

Zhao

Zhou

Zhang

et al. 2008

Ind. Eng. Chem. Res.

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A Ru/Al2O3/cordierite monolithic catalyst was prepared, characterized, and examined in selective hydrogenation of benzene to cyclohexene in a monolithic fixed-bed reactor with an aqueous solution of ZnSO4. The Carberry number and Wheeler−Weisz group were calculated to analyze the effects of external and internal diffusions of H2, benzene, and cyclohexene. According to the results of calculations, the water film, solubility, and diffusion coefficients of the three reactants (H2, benzene, and cyclohexene) play important roles in the mass-transfer rate. Under proper reaction conditions, the effects of the external mass transfer of H2 and benzene on the reaction rate are negligible. For the hydrogenation of cyclohexene, the diffusion of cyclohexene from the organic phase to the catalyst is the limiting step in the presence of water, which is the most important factor for obtaining high cyclohexene selectivity. The absence of pore diffusion of the three reactants, which is attributed to the thin eggshell distribution of in the catalyst, is another important factor for the higher cyclohexene selectivity. In addition, the optimum reaction conditions were found to be 413−423 K and 5 MPa.

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“…In some cases, the difference in the solubility of the desired product in two liquid phases can lead to increased selectivity of the desired product. For instance, in the case of benzene to cyclohexene hydrogenation, the desired partial hydrogenated product is separated from the reactive liquid phase by virtue of its solubility difference in the two liquid phases, and further hydrogenation is inhibited, also reducing the mass transfer of reactants to catalyst surface after addition of the fourth phase, playing a major role in promotion. − For hydrogenation of carbobenzoxy phenylalanine, the product phenylalanine is strongly adsorbed on the catalyst surface which reduces the catalytic activity, it can be separated effectively in GLLS by adding an aqueous phase . A similar mechanism can be beneficial in the case of hydrogenation of aniline to cyclohexylamine in GLLS, while in situ rearrangements of the intermediate hydrogenation product, because of the presence of aqueous acid (as the fourth phase), leads to the formation of p -aminophenol as the major product for hydrogenation of nitrobenzene. − In the case of hydrogenation of unsaturated aldehydes to alcohols, for instance, cinnamaldehyde to cinnamyl alcohol, the selectivity of cinnamyl alcohol is increased by the presence of alkaline aqueous phase .…”

Section: Introductionmentioning

confidence: 99%

Continuous Hydrogenation of Cinnamaldehyde: Gas–Liquid–Liquid–Solid Helical Coil Reactor

Khan

Joshi

Ranade

2023

Ind. Eng. Chem. Res.

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The advantages and challenges of using the gas−liquid− liquid−solid (GLLS) hydrogenation system are discussed in this work using the case of selective hydrogenation of cinnamaldehyde to cinnamyl alcohol (an important ingredient in the perfume and flavoring industry). The four phases in this system include gas (hydrogen)-liquid (organic, reactant + solvent)-liquid (aqueous KOH)-solid (5% Pt/C catalyst). The addition of second liquid phase, i.e., aqueous KOH significantly increases selectivity toward cinnamyl alcohol compared to the conventional three-phase hydrogenation. The four-phase GLLS reactions were carried out and optimized in a continuous helical coil reactor. The role of key aspects such as gas solubility, kinetics, flow hydrodynamics, axial dispersion, and mass transfer on the performance of a continuous GLLS reactor is presented and discussed in this work. The presented results and discussion will be useful for addressing conflicting demands like long residence time, low axial dispersion, and high mass transfer. The experimental studies and results of the developed mathematical model indicate that the continuous GLLS helical coil reactor outperforms the batch operation. The production rates (kg day −1 ) of cinnamyl alcohol achieved in continuous operation were at least double in comparison to batch operation, with 32% less consumption of precious catalyst (per kg of product). The presented results will open up new opportunities for enhancing selectivity and overall performance of hydrogenations via introducing a second immiscible liquid phase and designing continuous tubular reactors for the same.

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Kinetics and reaction engineering of selective hydrogenation of benzene towards cyclohexene

Cited by 15 publications

References 4 publications

Ab Initio Reaction Path Analysis of Benzene Hydrogenation to Cyclohexane on Pt(111)

Ab Initio Reaction Path Analysis of Benzene Hydrogenation to Cyclohexane on Pt(111)

Selective Hydrogenation of Benzene to Cyclohexene on a Ru/Al₂O₃/Cordierite Monolithic Catalyst: Effect of Mass Transfer on the Catalytic Performance

Continuous Hydrogenation of Cinnamaldehyde: Gas–Liquid–Liquid–Solid Helical Coil Reactor

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Kinetics and reaction engineering of selective hydrogenation of benzene towards cyclohexene

Cited by 15 publications

References 4 publications

Ab Initio Reaction Path Analysis of Benzene Hydrogenation to Cyclohexane on Pt(111)

Ab Initio Reaction Path Analysis of Benzene Hydrogenation to Cyclohexane on Pt(111)

Selective Hydrogenation of Benzene to Cyclohexene on a Ru/Al2O3/Cordierite Monolithic Catalyst: Effect of Mass Transfer on the Catalytic Performance

Continuous Hydrogenation of Cinnamaldehyde: Gas–Liquid–Liquid–Solid Helical Coil Reactor

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Selective Hydrogenation of Benzene to Cyclohexene on a Ru/Al₂O₃/Cordierite Monolithic Catalyst: Effect of Mass Transfer on the Catalytic Performance