Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Halogen or compound containing same
Reexamination Certificate
1999-06-01
2001-04-10
Wood, Elizabeth D. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Halogen or compound containing same
C502S224000, C502S226000, C502S229000, C502S231000, C502S355000
Reexamination Certificate
active
06214764
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an improved catalyst and its use for the conversion of hydrocarbons, particularly for the isomerization of alkanes.
2. General Background
The isomerization of light naphtha is an increasingly important process for the upgrading of petroleum refiners' gasoline pool. The widespread removal of lead antiknock additive from gasoline and the rising demands of high-performance internal-combustion engines are increasing the need for “octane,” or knock resistance, in the gasoline pool. In the early years of lead removal, refiners relied principally upon increasing the octane of products from catalytic reforming and fluid catalytic cracking operations. Refiners have largely capitalized on these relatively low-cost upgrading options, however, and attention has turned in recent years to upgrading the relatively low-octane high-naphtha component.
There is a long history of catalyst and process technology for the isomerization of light alkanes. The recent expansion of interest, however, has led to significant improvements in this technology. Catalyst and process developments have led to lower operating temperatures, wherein product octane is favored by isomer equilibrium. Substantial reduction in the hydrogen requirement for a stable operation has resulted in a significant cost reduction, principally through elimination of the need for a hydrogen-recycle system. Both of the aforementioned developments have led toward a predominance of liquid in the isomerization reactor feed, in contrast to the vapor-phase operation of the prior art.
Catalysts exhibiting dual hydrogenation-dehydrogenation and cracking functions are applied widely in the petroleum refining and petrochemical industries to the reforming and isomerization of hydrocarbons. Such catalysts generally have the cracking function imparted by an inorganic oxide, zeolite, or halogen, with a platinum-group component usually imparting the hydrogenation-dehydrogenation function. A catalyst useful in isomerization should be formulated to balance its hydrogenation-dehydrogenation and cracking functions to achieve the desired conversion over a prolonged period of time, while effectively utilizing the expensive platinum group metal component.
The performance of a catalyst in isomerization service typically is measured by its activity, selectivity, and stability. Activity refers to the ability of a catalyst to isomerize the reactants into the desired product isomers at a specified set of reaction conditions. Selectivity refers to the proportion of converted feed reacted into the desired product. Stability refers to the rate of change of activity and selectivity during the life of the catalyst. The principal cause of low catalyst stability is the formation of coke, a high-molecular-weight, hydrogen-deficient, carbonaceous material on the catalytic surface. Workers in the isomerization art thus must address the problem of developing catalysts having high activity and stability, and which also either suppress the formation of coke or are not severely affected by the presence of coke.
Catalysts for paraffin isomerization containing a platinum-group metal component and a halide on an alumina support are known in the art. For example, U.S. Pat. No. 3,963,643 (Germanas et al.) teaches a method of manufacturing a catalyst useful in the isomerization of paraffins by compositing a platinum-group metal with gamma or eta alumina and reacting the composite with a Friedel-Crafts metal halide and a polyhalo compound. U.S. Pat. No. 5,607,891 (Travers et al.) teaches a catalyst consisting of chlorine, Group VIII metal, and a support consisting essentially of 85-95% eta alumina and the remainder gamma alumina and its use for benzene reduction and isomerization. However, the art does not suggest a catalyst having the particular characteristics of the present catalyst or the surprising benefits of using this catalyst in the context of modern, primarily liquid-phase, isomerization operations.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a novel catalyst useful particularly for the isomerization of isomerizable hydrocarbons. A corollary object of the invention is to provide a process for isomerizing isomerizable hydrocarbons, particularly alkanes having from four to seven carbon atoms per molecule.
This invention is based on the discovery that a catalyst comprising a Friedel-Crafts metal halide and a platinum-group metal on a primarily eta-alumina support having defined critical characteristics demonstrates surprising results in increasing the octane number of C
5
/C
6
naphtha streams.
A broad embodiment of the present invention is an isomerization catalyst comprising a Friedel-Crafts metal halide and a platinum-group metal component on a principally eta-alumina support which has critical diffusion-path, pore-size and acidity characteristics. Platinum is the preferred platinum-group component and aluminum chloride is the preferred Friedel-Crafts metal halide. The catalyst support preferably comprises eta and gamma alumina in an eta:gamma ratio on a mass basis of from about 9:1 to about 99:1, with the ratio more preferably being at least about 15:1 and most preferably at least about 24:1; optimally, the support consists essentially of eta and gamma alumina. A triclover extrudate is a preferred shape of the catalyst of the invention.
A preferred catalyst has an average pore diameter of between about 35 and about 60 angstroms and a extruded trilobal cross-section.
In another aspect, the invention is a preferred method of preparing the present catalyst by a procedure comprising peptizing an alumina source, forming extrudates from the resulting base material, calcining the extrudates at defined critical conditions, impregnating a platinum-group metal component on the calcined extrudates, oxidizing and reducing the impregnated extrudates and subliming the Friedel-Crafts metal component onto the catalyst.
In yet another aspect, the invention comprises a process for the use of the present catalyst to isomerize isomerizable hydrocarbons. The preferred feedstock comprises C
4
to C
7
alkanes which are upgraded with respect to their degree of branching and octane number.
These as well as other objects and embodiments will become apparent from the detailed description of the invention.
REFERENCES:
patent: 3963643 (1976-06-01), Germanas et al.
patent: 5017541 (1991-05-01), Schmidt et al.
patent: 5607891 (1997-03-01), Travers et al.
patent: 5922639 (1999-07-01), Alario et al.
Spears, Jr. John F.
Tolomei John G.
UOP LLC
Wood Elizabeth D.
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