Catalyst – solid sorbent – or support therefor: product or process – Regenerating or rehabilitating catalyst or sorbent – Gas or vapor treating
Reexamination Certificate
2000-06-23
2003-10-14
Silverman, Stanley S. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Regenerating or rehabilitating catalyst or sorbent
Gas or vapor treating
C585S646000
Reexamination Certificate
active
06632765
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the regeneration of coked catalysts, in particular coked molecular redistribution catalysts.
BACKGROUND OF THE INVENTION
Catalytic processes for converting various feedstocks, such as crude oil and natural gas, to commercial products, such as distillate fuels, lubricants and waxes, are important commercial processes. Examples of such processes include catalytic reforming, alkane dehydrogenation, olefin metathesis, isodewaxing, hydrocracking, gas-to liquid conversions, and methanol-to-olefin conversions. Reforming is a complex process that can involve dehydrogenation of naphthenes to aromatics, dehydrocyclization of paraffins, isomerization of paraffins and naphthenes, dealkylation of alkylaromatics, hydrocracking of paraffins to light hydrocarbons, and formation of coke which is deposited on the catalyst.
In most catalytic processes for converting hydrocarbons, the catalysts invariably become deactivated for one or more reasons. When the catalysts are deactivated due to the accumulation of coke deposits, the catalysts must be regenerated to remove the coke deposits and restore the catalyst activity, resulting in downtime.
Coke is normally removed from catalysts by contacting the coke-containing catalysts at high temperature with an oxygen-containing gas to combust and remove the coke. Catalytic activity is then restored by reducing the catalysts at high temperature in a hydrogen atmosphere. The regeneration is either performed in situ or by removing the coked catalyst from the reactor and transporting the coked catalyst to a separate regeneration zone for coke removal.
Coke combustion is typically controlled by recycling the oxygen-containing gas, by adding a small stream of make-up air to replace oxygen consumed in the combustion of coke, and by venting off a small amount of flue gas containing the by-products of coke combustion to allow for the addition of the make-up air. While coke burning progresses from one reactor to the next reactor, the steady addition of make-up gas and the venting of flue gas establishes a steady state condition that produces a nearly constant concentration of water in the circulating regeneration gases.
One problem associated with coke combustion is catalyst deactivation. The combination of temperature, water vapor, and exposure time determines the useful life of the catalyst. Exposing a high surface area catalyst to high temperatures for prolonged periods of time can create amorphous materials with reduced surface areas, which lower the cataltyst activity of the catalyst. In contrast to catalyst deactivation by coke deposition, deactivation of this type is permanent, rendering the catalyst unusable. When moisture is present (water is a by-product of coke combustion) the deactivating effects of high temperature exposure are compounded.
Various methods have been proposed in the prior art for reducing the water present during regeneration of catalysts, but these methods require the use of expensive additional drying equipment, such as large beds of desiccant. These beds of desiccant are expensive both to construct and to operate, in part because of the water produced as a by-product of coke combustion.
It would be advantageous to provide methods for reducing the water content during catalyst regeneration in a hydrocarbon conversion unit, and for minimizing the amount of time the catalysts are exposed to temperatures high enough to reduce their surface areas.
SUMMARY OF THE INVENTION
The present invention is directed to a method for regenerating catalysts used in catalytic hydrocarbon conversion processes, which catalysts are deactivated by coke deposits. The coked catalysts are regenerated by reducing the coke present on the catalysts with hydrogen, without first exposing the coke to an oxygen-containing gas at high temperatures. The regeneration methods do not produce water, and minimize the amount of time the catalysts are exposed to relatively high temperatures. Accordingly, the methods reduce the risk of permanent deterioration of surface area of the catalysts. A further advantage is that no additional drying equipment is necessary to remove water, because no additional water is formed during the regeneration process. The methods also maximize the use of existing equipment and minimize the need for additional equipment used solely for catalyst regeneration.
The source of hydrogen for removing the coke deposit can be hydrogen gas, syngas (a mixture of hydrogen and carbon monoxide), or hydrogen produced by the catalytic dehydrogenation of a C
2-5
alkane stream. It can be advantageous to use syngas when a syngas generator is present on-site. It can be advantageous to use a C
2-5
alkane stream when such a stream is present on site and a dehydrogenation catalyst is being regenerated, or is present on site and can direct a product stream containing hydrogen and C
2-5
alkenes to the catalyst being regenerated. In this embodiment, ethane is a preferred alkane for the dehydrogenation, as it is least likely to form coke when exposed to the catalysts at relatively high temperatures.
A preferred embodiment of the catalyst regeneration involves regeneration of dehydrogenation/hydrogenation and/or olefin metathesis catalysts. Such catalysts are present in a number of commercial processes, including catalytic reforming processes and molecular redistribution processes which involve the dehydrogenation of alkanes to form alkenes, metathesis of the resulting alkenes, and rehydrogenation of the metathesized alkenes.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to methods for regenerating catalysts used in catalytic hydrocarbon conversion processes, which catalysts are deactivated by coke deposits. The coked catalysts are regenerated by reducing the coke present on the catalysts with hydrogen, without first exposing the coke to an oxygen-containing gas at high temperatures. The regeneration methods do not produce water, and minimize the amount of time the catalysts are exposed to relatively high temperatures. Accordingly, the methods reduce the risk of permanent deterioration of surface area of the catalysts. A further advantage is that no additional drying equipment is necessary to remove water, because no additional water is formed during the regeneration process. The methods also maximize the use of existing equipment and minimize the need for additional equipment used solely for catalyst regeneration.
Coke
Coke is comprised primarily of carbon, but also includes a relatively small quantity of hydrogen. On an overall basis, hydrogen generally comprises between about 0.5-10 percent of the overall weight of coke. The methods described herein do not involve oxidizing the coke with oxygen-containing gases (although the presence of minor amounts of oxygen may be unavoidable). By minimizing contact with oxygen during catalyst regeneration, water formation is minimized. Although the amount of water generated as a by-product of coke combustion (using oxygen) may be relatively minor, catalyst life can be significantly increased using the methods described herein by minimizing the formation of moisture during catalyst regeneration.
Of course, the amount of water present during regeneration of a hydrocarbon conversion catalyst depends in part on whether the circulating regeneration gases are contacted with an aqueous solution. It is often necessary or desirable to contact the regeneration gases with a basic aqueous solution, for example if the regeneration gases contain an acidic halogen-containing compound. In such a case, the advantage gained by avoiding the formation of water by not using oxygen-containing gases is minimized, since the amount of water from the aqueous solution is generally significantly greater than the amount of water due solely to the combustion of coke.
Hydrocarbon Feeds
Hydrocarbon feeds which can be converted using hydrocarbon conversion catalysts can include paraffins, naphthenes, olefins and mono- and polycyclic aromatics. Preferred feedstocks do not include imp
Chervon U.S.A. Inc.
Fallon Martin C.
Silverman Stanley S.
Strickland Jonas N.
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