Preparation of iron-, potassium- and cerium-containing catalysts

Details Preparation of iron-, potassium- and cerium-containing catalysts Preparation of iron-, potassium- and cerium-containing catalysts

1995-02-13

1996-09-24

McFarlane, Anthony

Catalyst, solid sorbent, or support therefor: product or process

Regenerating or rehabilitating catalyst or sorbent

585661, B01J 3800

Patent

active

055590667

DESCRIPTION:

BRIEF SUMMARY
The regeneration of datalysts is a very old aim in catalyst research, since spent catalysts are generally a valuable source of the elements present in them, or compounds thereof. For environmental protection reasons, disposable to landfill, i.e. avoidance of regeneration, is no longer acceptable, even in cases where they comprise inexpensive constituents such as iron oxide or aluminum oxide.
There have therefore already been many proposals, some very old, for recovery or reprocessing of the catalyst material.
In principle, a distinction is made between shape-retaining and re-shaping regeneration. While in the first case only impurities (for example carbon black and the like) are removed (cf. U.S. Pat. No. 2,831,041 (1954)) and any missing constituents are replaced, for example by impregnation with an appropriate solution of the constituent, reshaping is frequently preferred, in particular in the case of unsupported catalysts, which have a long life per se.
This was originally (cf. U.S. Pat. No. 2,666,086 (1949)) carried out, in the case of dehydrogenation catalysts, which traditionally essentially comprise iron oxide, by dissolving the entire catalyst in an acid, re-establishing the composition, and then precipitating or evaporating the solution in the conventional manner and reshaping the desired catalyst from the resultant solid.
However, it is desirable to avoid the chemical recreation of the active constituents (is. dissolution and reprecipitation).
It is an object of the present invention to provide a process for the preparation of iron-, potassium- and cerium-containing catalysts (cf. EP 195 252, German Patent 28 15 874) for the dehydrogenation of hydrocarbons from the same spent catalysts (regeneration) by comminuting, for example by grinding, and, if necessary, purifying the spent material, restoring the original activity by adjusting the composition, and restoring the external shape, using a novel catalyst without the need for a chemical reaction. It has been found that the restoration of the original composition in the specific case of cerium-containing catalysts is not sufficient to restore the original activity.
We have found that this object is achieved by a process of the above type which essentially comprises adding to the comminuted, e.g. ground, material an effective amount of potassium and such an amount of cerium that the total amount of cerium is greater than the amount originally present.
It is naturally also possible for other constituents conventionally used in Fe/K/Ce catalysts to be restored to their original content or to another desirable content. Catalysts of this type are described in the aforementioned publications (EP and German patent), to which reference is made herein.
The invention is based on the surprising finding (which is not intended to restrict the invention) that specifically cerium is in no way completely extracted, i.e. disappears, from the catalysts according to the invention, but instead is converted into a form which cannot be regenerated by comminuting, e.g. grinding, alone.
The analytical composition must therefore be corrected with respect to the cerium content; whereas fresh catalysts contain from about 5 to 40 (in particular 5 to 20) % by weight of potassium, from 0.1 to 20 (in particular 1 to 20) % by weight of cerium and possibly further constituents in addition to a predominant amount (for example from 40 to 90% by weight, in particular from 70 to 90% by weight) of iron oxide (Fe.sub.2 O.sub.3), the total amount of the catalyst constituents being 100% by weight, a regenerated catalyst should now contain from 2 to 40% by weight of cerium in addition to the other constituents, which are present in correspondingly smaller amounts. Further regeneration, i.e. repetition of the regeneration of a catalyst which has already been regenerated one or more times, is possible, the cerium content increasing further in purely analytical terms. This is unimportant for the activity since it is known that even catalysts which comprise predominantly cerium oxide, i.e. fr

REFERENCES:
patent: 2666086 (1954-01-01), Pitzer
patent: 2831041 (1958-04-01), Steg et al.
patent: 4888316 (1989-12-01), Gardner et al.
patent: 4975399 (1990-12-01), Gardner
patent: 5324695 (1994-06-01), Karrer et al.

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