Desactivacion de catalizadores

Applied Catalysis A: General 212 (2001) 3–16

Catalyst deactivation: is it predictable? What to do?
J.A. Moulijn, A.E. van Diepen∗ , F. Kapteijn
Department of Chemical Process Technology, Section of Industrial Catalysis, Faculty of Applied Sciences, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands

Abstract Catalyst deactivation is usually inevitable, althoughthe rate at which it occurs varies greatly. This article discusses the causes of deactivation and the influence on reaction rate. Methods for minimising catalyst deactivation, by tailoring catalyst properties and/or process operations, are presented, as well as reactor configurations suitable for the regeneration of deactivated catalysts. Alkane dehydrogenation is used as an example to demonstratethe variety of engineering solutions possible. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Catalyst deactivation; Regeneration; Reactor; Alkane dehydrogenation; Engineering

1. Introduction What makes a catalyst a good catalyst? Obviously, a good catalyst shows high activity. A high activity allows the use of relatively small reactors and operation at mild conditions. However,activity is not the only crucial property of a catalyst. A high selectivity for the desired products is often of even greater importance. Furthermore, it is important that a catalyst retains its activity and selectivity for some time. Ideally, a catalyst does not change and should have eternal life. In practice, this is not the case. Depending on the process used the catalyst cycle life may varyfrom a few seconds, as in fluid catalytic cracking (FCC), to several years, as in for instance ammonia synthesis. Catalyst deactivation is highly relevant for the application of catalysis and scientifically it has many challenges. An

∗ Corresponding author. Tel.: +31-15-278-6725; fax: +31-15-278-5006. E-mail address: a.e.vandiepen@tnw.tudelft.nl (A.E. van Diepen).

excellent introduction is givenin the recent book by Bartholomew and Farrauto [1]. The time scale of deactivation has profound consequences for process design. Fig. 1 shows the deactivation time for several processes in the refining and petrochemical industry. The two most important applications in environmental catalysis are also included. This deactivation time refers to the time after which a catalyst has lost so much of itsinitial activity that it must be regenerated or replaced. Often regeneration is possible, but there is a limit. At the end of the cycle life the catalyst is recycled or, when this is more economical, disposed. It is obvious that disposal should be postponed as long as possible and that recycling is becoming more and more important. Regeneration technology develops with time. Several proceduresare in use and besides regeneration milder treatments are used, referred to as rejuvenation. As can be seen from Fig. 1, the deactivation time varies greatly for the different processes. At the lower end, we find the FCC process with a deactivation time of seconds. Deactivation of a hydrodesulfuri-

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J.A. Moulijn et al. / Applied Catalysis A: General 212 (2001) 3–16

Fig. 1. Time scale of deactivation of various catalytic processes.

sation (HDS) catalyst is much slower, depending on the feed, in the order of months or a year. The importance of catalyst stability is often underestimated, not only in academia but also in certain sectors of industry,notably in the fine chemicals industry. In bulk chemicals production, its importance generally has been acknowledged. In fine chemicals production, chemists sometimes look upon the catalyst as a reactant: when it does not function anymore, it is disposed and new catalyst is added. So, it is understandable that catalyst stability is not always a point of strong concern. With increasing environmental...