A theoretical treatment of catalyst decay

Wojciechowski, B. W.

doi:10.1002/cjce.5450460109

Cited by 112 publications

(34 citation statements)

References 2 publications

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“…In an earlier work reported by Best et al (1971) it was shown that the hyperbolic aging function (Wojciechowski, 1968) can be used to describe gas oil conversion in both diffusion limited and diffusion free systems. In this paper we will show that their treatment can be extended to describe the effects of diffusion on gas oil selectivity by observing the changes in the parameters of the selectivity model (Pachovsky et al, 1973) …”

Section: Scopementioning

confidence: 98%

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Effects of diffusion resistance on gasoline selectivity in catalytic cracking

Pachovsky

Wojciechowski

1973

AIChE Journal

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The time on stream theory of catalyst decay is applied to gas oil cracking selectivity data from a static bed reactor operating with a diffusion limited catalyst. It is found that intraparticle diffusion affects the reactions leading to the disappearance of gas oil to a much greater extent than the reaction leading to the recracking of gasoline and catalyst poisoning. Reasons for this behavior are postulated. It is also found that the overall kinetic order for the rate of disappearance of gas oil is decreased with the result that maximum selectivity occurs at a higher conversion value than for a corresponding diffusion-free catalyst. It is concluded that probably diffusion limitation is not a serious problem with respect to gasoline selectivity in commercial reactors. ROMAN SCOPEDiffusional limitations are generally to be avoided in catalytic systems. Various steps are therefore taken to ensure that reactions are not carried out under conditions involving diffusion limitations. Despite such precautions, in some cases it is impossible to avoid the use of a diffusion limited catalyst. One industrial example of this may be the moving bed reactor. Various physical factors conspire to make this reactor configuration a candidate for diffusion problems since they dictate the use of a hard bead catalyst which must be strong enough to withstand abrasion while at the same time large enough to allow proper transport and to forestall large pressure drops through the bed.The importance of diffusion within porous catalyst systems has long been recognized, and considerable work has been done both in predicting the effect of diffusion on reaction rates and on the selectivity of some simplified systems. One of the earliest such attempts was made by Wheeler (1951Wheeler ( , 1955 in which three basic types of selectivity behavior were defined and the effects of diffusion limitations under isothermal conditions on selectivity were described. Wheeler's theoretical analyses were extended and generalized by Carberry (1962) for a series reaction with various combinations of diffusion limitations in the bulk phase, in the pores, and i n the micro-macro pore structure. Unfortunately, predicting selectivity behavior under conditions involving diffusion for a complex system such as gas oil cracking is an even more complex task and is not likely to be treated successfully by the methods used by the above authors. For instance, Johnson et al. (1957) attempted to describe gas oil cracking as following Wheeler's type I11 selectivity. Subsequently, Campbell and Wojciechowski (1969) and Pachovsky and Wojciechowski (1971) showed that a more complex mechanism is required to describe gas oil cracking and postulated a more complex form of behavior.In an earlier work reported by Best et al. (1971) it was shown that the hyperbolic aging function (Wojciechowski, 1968) can be used to describe gas oil conversion in both diffusion limited and diffusion free systems. In this paper we will show that their treatment can be extended to describe the effects o...

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Section: Scopementioning

confidence: 98%

“…The catalyst decay in Equations (1) is described using the time on stream theory of Wojciechowski (1968) which yields the expression…”

Section: Theorymentioning

confidence: 99%

Effects of diffusion resistance on gasoline selectivity in catalytic cracking

Pachovsky

Wojciechowski

1973

AIChE Journal

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“…However, over a wide range of conversions the linear expansion assumption appears to be adequate. The decay function has been previously derived (Wojciechowski, 1968) and is based on the premise that the rate of loss of active sites on surface of a catalyst can be described as following an mth order decay. This suggestion was first reported by Schlaffer et al in 1957 and more recently by Szepe and Levenspiel (1968).…”

Section: C-i3 Ksmentioning

confidence: 99%

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Theoretical interpretation of gas oil selectivity data on X‐sieve catalyst

1973

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A six-parameter multiresponse model based on the catalyst aging theory of Wojciechowski (1968) is applied to experimental selectivity data in gas oil cracking. Within the range of conditions studied, the model gave an adequate fit to the data. It was found that the selectivity curves at various cat/oil ratios were contained within optimum and minimum performance envelopes but that the relationships between these envelopes and the selectivity curves were not quite as simple as had previously been reported for a theoretical example (Campbell and Wojciechowski, 1969). The optimum time-on-stream for each of the cat/oil ratios was about one minute. Maximum gasoline production was 59 weight yo at 81 weight 7 ' total cumulative conversion, resulting in a gasoline efficiency of 72.8y0.

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“…La teoría del tiempo de reacción (Time on Stream, TOS 93 ) es una generalización de todas estas formulas empíricas, y se desarrolló principalmente para modelizar las conversiones obtenidas con el MAT en el craqueo de compuestos puros y gasóleo. Se asume que la actividad del catalizador es una función del número de sitios activos, y se propone que éste disminuya con el tiempo a una velocidad proporcional a la concentración de sitios activos.…”

Section: Funciones Del Tiempounclassified

Desarrollo de un micro-reactor de lecho transportado y su aplicación al estudio craqueo catalítico.

Sauvanaud¹,

Laurent²

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GraciasA Jean-Michel Colin y Jean-Yves Carriat de Total Raffinage Distribution S.A. por haberme puesto en contacto con el Instituto de Tecnología Química e haber ayudado a iniciar esta investigación.Al Pr. Avelino Corma y al Dr. Francisco Melo por darme la oportunidad de realizar mi tesis doctoral en el ITQ, por sus consejos, su disponibilidad y su confianza durante todos estos años.A la Dra. Amparo Mifsud, gerente del ITQ, por su constante apoyo, y al personal de secretaria por facilitarme enormemente todo tipo de tramites Al personal investigador del ITQ, en particular al Pr. Vicente Fornés, y a los Dres.

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A theoretical treatment of catalyst decay

Cited by 112 publications

References 2 publications

Effects of diffusion resistance on gasoline selectivity in catalytic cracking

Effects of diffusion resistance on gasoline selectivity in catalytic cracking

Theoretical interpretation of gas oil selectivity data on X‐sieve catalyst

Desarrollo de un micro-reactor de lecho transportado y su aplicación al estudio craqueo catalítico.

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