Regeneration and stabilization of dehydrogenation catalyst

Details Regeneration and stabilization of dehydrogenation catalyst Regeneration and stabilization of dehydrogenation catalyst

1995-12-05

1997-12-09

Kim, Christopher

Chemical apparatus and process disinfecting, deodorizing, preser

Chemical reactor

Including solid, extended surface, fluid contact reaction...

422110, 422188, B01J 802

Patent

active

056957246

DESCRIPTION:

BRIEF SUMMARY
CROSS-REFERENCE TO RELATED PATENT

This application, filed under 35 U.S.C. .sctn.371, is based on international application PCT/US94/07474, which claimed priority based on U.S. Ser. No. 08/088,306, filed Jul. 7, 1993, now U.S. Pat. No. 5,461,179, issued Oct. 24, 1995.
The present invention relates generally to a method and associated apparatus for greatly extending the useful life of a catalyst bed used in the catalytic dehydrogenation of alkylaromatic hydrocarbons while maintaining a very high level of conversion and a very high level of selectivity and without the need to interrupt the conversion process.


BACKGROUND OF THE INVENTION

It is known in the art that an alkylaromatic hydrocarbon can be catalytically dehydrogenated to form an alkenylaromatic hydrocarbon, such as in the conversion of ethylbenzene to styrene. The prior art teaches a variety of different dehydrogenation catalysts and process parameters, each having different advantages and disadvantages. In general, the prior art teaches that certain tradeoffs ordinarily must be made between level of conversion and level of selectivity, between level of conversion and catalyst life, and so forth. For example, the disadvantage of obtaining a higher degree of dehydrogenation of the alkylaromatic in some processes may be a lower level of selectivity, i.e., a higher percentage of undesired dehydrogenation byproducts. Obviously, it is most advantageous and cost-effective to obtain both high levels of conversion and high levels of selectivity, if possible.
Catalyst life, and the related cost factors, is another important process parameter in these dehydrogenation reactions. First are the costs related to the catalyst itself. Although the unit cost of the catalyst may not be great, because of the large amounts of catalyst required as well as the cost of disposing of used, contaminated catalyst in an environmentally acceptable way, the life of the catalyst and the ability to regenerate used catalyst are critical elements in a commercial dehydrogenation process. Second are the costs related to shutting down a large, perhaps multistage, dehydrogenation reactor, operating at temperatures on the order of 600.degree. C., in order to either replace or regenerate the catalyst bed. In addition to the obvious labor costs, there are also the capital costs of having expensive equipment off-line for any length of time. Heat losses add still further costs to this catalyst replacement or regeneration step. Of even greater significance is the cost of lost production during the shutdown period.
Thus, on the one hand, it is preferred to maximize catalyst life. But, on the other hand, normal catalyst degeneration during use tends to reduce the level of conversion, the level of selectivity, or both, resulting in an undesirable loss of process efficiency. Various possible explanations for the typical degeneration of dehydrogenation catalysts during use are found in the literature. These include carbonization of catalyst surfaces, physical breakdown of the interstitial structures of the catalysts, loss of catalization promoters, and others. Depending on the catalyst and the various process parameters, one or more of these mechanisms, or other mechanisms not yet identified, may be at work.
Although the prior art teaches various methods for regenerating used catalyst in order to restore temporarily and only partially the catalyst's effectiveness, these methods generally involve stopping the dehydrogenation, shutting down the dehydrogenation reactor or, in some cases, removing the catalyst for external regeneration. Furthermore, the process impact of such periodic catalyst regeneration is an undesirable saw-tooth pattern of output: levels of conversion and selectivity start out relatively high but slowly and continuously deteriorate until the point where the catalyst is regenerated to restore a relatively high level of conversion and selectivity. But, immediately thereafter, catalyst effectiveness begins again to deteriorate. As a result, it is not possible utilizing conventio

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