Analysis of zeolite catalyst deactivation during catalytic cracking reactions

Reyes, Sebastián C.; Scriven, L. E.

doi:10.1021/ie00049a011

Cited by 29 publications

(15 citation statements)

References 42 publications

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“…Since the total coke can be as high as 8 wt % in our experiments, the multilayer coke can be quite thick. Although multilayer coke does not deplete active sites, it can eventually lead to diffusion limitations and even pore blockage, a subject treated by, for example, Froment (1979, 1980) and Reyes and Scriven (1991). Implications for Coking Mechanism.…”

Section: Experimental and Modeling Resultsmentioning

confidence: 99%

Kinetics of Catalyst Coking in Heptane Reforming over Pt−Re/Al₂O₃

Liu

Fung

et al. 1997

Ind. Eng. Chem. Res.

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Previous studies have shown that five-membered ring naphthenes (C5N) are the key source of coke in n-heptane (nC 7 ) reforming on a Pt-Re/Al 2 O 3 catalyst. Using methylcyclopentane (MCP) as a model C5N compound, we develop a kinetic model that predicts its coking rate on the basis of the data obtained from a vibrational microbalance and a fixed-bed reactor. This rate, with an apparent activation energy of 39.7 kcal/mol, decays exponentially in coke-on-catalyst and is first order in MCP partial pressure. Its dependence on H 2 is a combination of negative first and second orders. The model considers that coke deposits randomly on both clean and coked sitessa feature that permits the distinction between monolayer and multilayer coke buildup. The model correctly predicts the coking rates of ethylcyclopentane and of nC 7 . Moreover, it predicts the observed coke profile generated from nC 7 reforming in the integral fixed-bed reactor under conditions quite different from those used in the microbalance. As such, the model may be used for probing the state of coking in a reformer and for guiding catalyst-accelerated aging studies.

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Section: Experimental and Modeling Resultsmentioning

confidence: 99%

Kinetics of Catalyst Coking in Heptane Reforming over Pt−Re/Al₂O₃

Liu

Fung

et al. 1997

Ind. Eng. Chem. Res.

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“…A generally accepted fitting of deactivation according to an empirical exponential formula (eq 1 in Experimental section), presented as solid lines in Figure S11, corroborates the partial loss of active sites due to different mechanisms. 93 Two deactivation phenomena may be distinguished: the first occurring exponentially in initial stages and the second proceeding linearly at longer time on stream. The fitting analysis reveals that increasing the amount of water reduces the total amount of effect active sites participating in the dealkylation (related to parameter a in eq 1), in accord with the high adsorption heat and the competitive adsorption of water for the sites of ZSM-5.…”

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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 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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“…A typical empirical decay formula was used to describe the loss of activity as a function of time on stream (see Supporting Information). , Figure S8 illustrates the time on stream behaviors of different catalysts at 658 K and 55.5 h –1 WHSV. The data were used to construct the relative activity vs time on stream plots, as presented in Figure .…”

Section: Results and Discussionmentioning

confidence: 99%

Aromatics Production from Lignocellulosic Biomass: Shape Selective Dealkylation of Lignin-Derived Phenolics over Hierarchical ZSM-5

Liao

Zhong

d’Halluin

et al. 2020

ACS Sustainable Chem. Eng.

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The selective conversion of lignin or lignin-derived products into bulk chemicals is the foremost challenge for nearfuture lignocellulosic biorefineries. This study investigates the production of phenol and propylene from lignin-derived 4-npropylphenol (4-n-PP) via gas-phase dealkylation over hierarchical ZSM-5 zeolites in the presence of steam. A series of hierarchical ZSM-5 zeolites with different degrees of mesoporosity and acid properties were prepared by alkaline treatment and mild acid washing. The catalytic evaluation reveals a predominant contribution of the strong acid sites to the dealkylation catalysis. Hierarchization of ZSM-5 zeolites via desilication in alkaline generates Lewis acid sites and reduces the amount of strong Brønsted acid sites. Despite their higher activation energy for dealkylation, reactions on the Lewis acid sites are faster at the thermodynamically required high temperature due to a larger entropic contribution to activation on these sites. In addition to the high catalytic activity, the hierarchical zeolites preserve the high phenol and propylene selectivity as bimolecular side reactions such as disproportionation, transalkylation and some C-C cleavage pathways were inhibited. This observation suggests that both the strong Lewis and Brønsted acid sites are located in confined spaces in which selectivity is determined by transition state shape selectivity. The catalytic stability is improved upon hierarchization as the results of lowering of the total amount of strong acid sites and prevention of substantial product diffusion issues (caused by shortening of diffusion paths). Therefore, dealkylation over mesoporous zeolites can be processed under lower water partial pressure. ASSOCIATED CONTENT Supporting informationThe experimental details, N2 sorption isotherms and pore size distribution, X-ray diffraction patterns, NH3-TPD profiles, TGA analysis, supporting catalytic data. This material is available free of charge via the Internet at http://pubs.acs.org.

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Analysis of zeolite catalyst deactivation during catalytic cracking reactions

Cited by 29 publications

References 42 publications

Kinetics of Catalyst Coking in Heptane Reforming over Pt−Re/Al₂O₃

Kinetics of Catalyst Coking in Heptane Reforming over Pt−Re/Al₂O₃

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

Aromatics Production from Lignocellulosic Biomass: Shape Selective Dealkylation of Lignin-Derived Phenolics over Hierarchical ZSM-5

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Analysis of zeolite catalyst deactivation during catalytic cracking reactions

Cited by 29 publications

References 42 publications

Kinetics of Catalyst Coking in Heptane Reforming over Pt−Re/Al2O3

Kinetics of Catalyst Coking in Heptane Reforming over Pt−Re/Al2O3

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

Aromatics Production from Lignocellulosic Biomass: Shape Selective Dealkylation of Lignin-Derived Phenolics over Hierarchical ZSM-5

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Kinetics of Catalyst Coking in Heptane Reforming over Pt−Re/Al₂O₃

Kinetics of Catalyst Coking in Heptane Reforming over Pt−Re/Al₂O₃