Kinetic, transport, and deactivation rate interactions on steady state and transient responses in heterogeneous catalysis

“…The basic experimental information obtained is intraparticle and interphase temperature gradients in a single pellet reactor; hydrogenation of benzene on nickel/kieselguhr is the test reaction employed, and thiophene is used as a catalyst poison. Most measurements were obtained in a start-up experiment, described in detail previously (Lee et al, 1978) in which a fresh or partially deactivated catalyst pellet initially in flowing hydrogen is subjected to a step input in benzene concentration to the reactor. Catalysts were deactivated either by introduction of thiophene with the benzene feed under steady state conditions or by introduction with the feed in a start-up experiment.…”

Section: Methodsmentioning

confidence: 99%

“…Since this work had as a major concern the influence of parametric values on system response and simu!ation two pellets, composed of 9 0 % nickel/kieselguhr and 10% of either graphite or silica, were investigated in addition to the undiluted material studied by Lee (1976). The addition of diluent affects the catalyst pellet by changing the rate of reaction per unit volume of material and varying the thermal conductivity and heat capacity.…”

Section: Methodsmentioning

confidence: 99%

“…In a recent paper (Lee et al, 1978), we reported on the computer simulation of a series of experiments dealing with the steady state and transient behavior of partially deactivated catalyst particles for the hydro, nenation of benzene. The simulation was attempted on an a priori basis in that all model parameters such as kinetic coefficients and transport properties were determined either in separate, off line experiments or from steady state measurements on the catalyst particle itself.…”

Section: Conclusion and Significancementioning

confidence: 99%

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Simulation models for intraparticle deactivation: Scope and reliability

1979

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An experimental and modeling study of the dynamic behavior of an individual catalyst pellet as influenced by deactivation and dilution has been made. The reaction system employed was benzene hydrogenation over nickel/kieselguhr catalyst pellets diluted with 10% graphite, 10% silica, or undiluted; thiophene was employed as the catalyst poison.A one-dimensional effective transport model was developed, and the parameters for this model were determined principally from separate off line experiments or steady state experimental information. The adequacy of the model was determined from a direct comparison of the experimental and computed time-temperature profiles. SCOPEThe application of simulation models to the transient response of fresh and deactivated catalyst particles, differing in physical properties, is treated. Benzene hydrogenation over a nickel/kieselgehr catalyst, poisoned by thiophene is used as an experimental example of the class of exothermic catalytic reactions subject to irreversible poisoning. The catalysts investigated included formulations diluted with silica or graphite as well as the original material and exhibited a range of physical properties.Major objectives of the study are investigations of the feasibility of completely a priori simulations (all parameters determined independently) to the extreme case of transient response represented by start-up of the fresh and deactivated catalyst, the effort required to obtain a given level of detail in simulation, and the parametric sensitivity of such catalyst reaction-poison systems. CONCLUSIONS AND SIGNIFICANCESteady state and transient response behavior are strongly influenced by catalyst deactivation. A full distributed parameter model, described previously, was used to simulate the transient response of fresh and deactivated catalyst pellets possessing differing intraparticle transport properties. Attempts at full a priori simulation at the highest level of detail (spatial and temporal variation of intraparticle temperature profiles) were not successful. Investigation of the parametric response of the model revealed extreme sensitivity to the pellet intraparticle diffusivity and external heat transfer coefficient. Both the full model and simplified versions employing an active shell (undeactivated pellet) or a dead zone (deactivated pellet) at the surface could be used for successful simulation of the experimentally observed behavior, but only in the sense of parameter fit models.I t would appear that global, averaged quantities such as steady state activity and overall rates of deactivation can be simulated using a priori parameter sets; however, detailed simulations apparently require parameters to be known to an accuracy beyond current capabilities in estimation or measurement.In a recent paper (Lee et al., 1978), we reported on the computer simulation of a series of experiments dealing with the steady state and transient behavior of partially deactivated catalyst particles for the hydro, nenation of benzene. The simulation was attempted on ...

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“…Intraparticle thermal gradients are negligible; that is, the catalyst particles are internally isothermal 2. No mixing of heat or mass occurs in the axial direction, while the fluid is perfectly mixed radially; that is, plug flow is assumed inside the reactor It is worth noting that while the first assumption is quite acceptable in practice (Carberry, 1975;Pereira et al, 1979), unless the special case of nonuniformly active catalyst particles is involved (Lee et al, 1978), the second is probably less realistic. This is particularly true for radial heat transfer in nondiabatic fixed-bed reactors.…”

Section: The Heterogeneous One-dimensional Plug Flow Modelmentioning

confidence: 99%

Parametric sensitivity in fixed‐bed reactors: Inter‐ and intraparticle resistance

Morbidelli

Varma

1987

AIChE Journal

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The role of inter-and intraparticle transport resistances in the sensitivity behavior of a fixed-bed catalytic reactor is fully elucidated. The parametric sensitivity regions obtained using a heterogeneous onedimensional plug flow model are reported for various values of the involved dimensionless parameters. Comparisons with previous sensitivity criteria and with experimental data are also presented.

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Kinetic, transport, and deactivation rate interactions on steady state and transient responses in heterogeneous catalysis

Cited by 20 publications

References 18 publications

Heterogeneous catalytic reactors undergoing chemical deactivation. Part I: Deactivation kinetics and pellet effectiveness

Heterogeneous catalytic reactors undergoing chemical deactivation. Part I: Deactivation kinetics and pellet effectiveness

Simulation models for intraparticle deactivation: Scope and reliability

Parametric sensitivity in fixed‐bed reactors: Inter‐ and intraparticle resistance

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