Chemistry of hydrocarbon compounds – Unsaturated compound synthesis – By dehydrogenation
Reexamination Certificate
2000-09-25
2002-07-02
Griffin, Walter D. (Department: 1764)
Chemistry of hydrocarbon compounds
Unsaturated compound synthesis
By dehydrogenation
C585S654000, C585S660000, C502S213000, C502S226000, C502S230000, C502S231000, C502S303000, C502S310000, C502S314000
Reexamination Certificate
active
06414209
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a calcined catalyst for converting paraffin hydrocarbons into corresponding olefins by dehydrogenation, wherein the catalyst contains an oxidic, thermally stabilized substrate material and a catalytically active component that is applied to the substrate material. The invention also relates to a method for converting paraffin hydrocarbons into corresponding olefins, in which a stream of the paraffin hydrocarbons is mixed with water vapor and put into contact with a catalyst. The paraffins addressed within the scope of the invention are in the range from C
2
to C
20
, preferably in the range from C
2
to C
5
.
BACKGROUND OF THE INVENTION
A large number of catalysts that are used to dehydrogenate paraffins are known. Such catalysts have a thermally stabilized, inorganic oxide as the substrate material, an active component (preferably a metal of the platinum group), and one or more promoters. Active Al
2
O
3
, which has an especially large specific surface area, is often used as the substrate material.
U.S. Pat. No. 4,788,371, describes a catalyst and a method for dehydrogenating paraffins in a water vapor atmosphere. The substrate of the catalyst comprises Al
2
O
3
and is coated both with a noble metal (preferably platinum) and several promoters, which are selected from Group III or IV of the Periodic table and the gallium or germanium subgroup (preferably tin) and alkaline metals (preferably potassium or cesium). The dehydrogenation method described in this reference can function in the presence of a limited amount of oxygen, which is used to heat the reaction zone by combusting hydrogen.
From U.S. Pat. No. 5,220,091, a catalyst and a method for dehydrogenating C
2
to C
8
paraffins in the presence of water vapor is known. The catalyst used here comprises platinum (approximately 0.7 weight %) as well as zinc aluminate and potassium aluminate. In the dehydrogenation of isobutane (iC
4
), a conversion rate of 50% and a selectivity of 94 mol-% was attained; the pressure was adjusted to P=3.5 bar, the temperature was adjusted to T=571° C., and the ratio of steam to isobutane (mol) was adjusted to 3.96. After a cycle time of 7 hours, the catalyst had to be subjected to a reactivation treatment by oxidative regeneration.
A further method and a catalyst for dehydrogenation of organic compounds is described in European Patent Disclosure EP 0 568 303 A2. This method uses a hydrogen atmosphere. The catalyst contains nickel and various promoters of Groups I-VIII of the Periodic table on a non-acid substrate material (base-treated Al
2
O
3
, zeolites, etc.). The special feature of the technology described in this reference is many dehydrogenation zones with intermediate zones for oxidizing hydrogen produced, on a special catalyst. The best results in the dehydrogenation of isobutane were obtained with a nickel catalyst (3.4% Ni and 3.4% Cr on a Ba-exchanged zeolite L), using a temperature of T=602° C., a molar ratio H
2
/iC
4
=6 and a space velocity of WHSV=650 h
−1
. Over an operating duration of 6 hours, the conversion rate was 30-36.6% and the selectivity was 75.1-83.4%. For an operating duration of 50-65 hours, the conversion rate was in the range from 22.2-27.9% and the selectivity was in the range from 78.8-81.1%.
Another catalyst and a method for dehydrogenation of hydrocarbons is known from International Patent Disclosure WO 94/29021. The method operates in a water vapor and hydrogen atmosphere, using a platinum catalyst, which as promoters contains elements of the tin subgroup and alkaline metals (potassium, cesium). The special feature of the catalyst is a special substrate material, which comprises a mixture of magnesium oxide and aluminum oxide. This composition requires a special pretreatment of the catalyst, which comprises a reduction with hydrogen, a calcination in an O
2
atmosphere, and another reduction (called an ROR treatment). With this ROR treatment, the catalyst has an activity three times higher than without this treatment. The dehydrogenation of propane (C
3
) with the aid of the described catalyst, at a temperature of T=600° C., a pressure of P=1 bar, a space velocity WHSV=1.3 h
−1
and a ratio of H
2
/H
2
O/C
3
=0.14/1.2/1 and an operating time of 25 hours, led to the following results: The propylene yield was 55.5 mol-%, and the selectivity was 96.1 mol-%. A comparative test described in this reference, using a catalyst known from U.S. Pat. No. 4,788,371, under otherwise identical conditions, led to a propylene yield of 25.7 to 29.7 mol-% and a selectivity of 95.0 to 95.9 mol-%. Thus WO 94/29021 represents the performance standard thus far in the field of catalytic conversion of paraffin hydrocarbons into corresponding olefins.
OBJECTS AND SUMMARY OF THE INVENTION
The object of the present invention is to disclose a catalyst for converting paraffin hydrocarbons into corresponding olefins that not only assures high effectiveness, or in other words has a good conversion rate and good selectivity, but furthermore exhibits high operating stability; that is, it can be used over comparatively long cycle times before having to be subjected to a reactivation treatment. The production of the catalyst should be as simple as possible. A method for converting paraffin hydrocarbons into corresponding olefins, which leads to good olefin yields and can be operated over cycle times that are as long as possible before catalyst reactivation has to be done is also to be disclosed.
In terms of the catalyst, this object is attained by the characteristics recited in claim 1, and in terms of the method, it is attained by the characteristics recited in claim 16. Advantageous features of the invention are defined by the dependent claims.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
In the course of the tests that led to the present invention, it was discovered that catalysts known per se on Al
2
O
3
substrates, which have platinum, a metal of the germanium or gallium group (preferably tin or indium) and an alkali metal (preferably potassium or cesium) can be improved substantially in terms of their activity by the addition of certain promoters. Along with progress in increasing the catalytic activity, it can be noted as a particular advantage of the invention that no special activation treatment, such as the ROR treatment, is necessary in the production of the catalyst. Furthermore, in the use of the catalyst, there is no need to add hydrogen to the feed material. On the contrary, the catalyst functions quite reliably in the presence of oxygen. The production of the catalyst can be done by known methods on conventional substrate materials.
The calcined catalyst of the invention comprises a thermally stabilized substrate material, onto which a catalytically active component is applied. The substrate material is preferably aluminum oxide, in particular in the form of &THgr;-Al
2
O
3
. The catalytically active component comprises the material groups a) through g), explained in further detail hereinafter, in which the quantities are given in weight % and are referred to the total weight of the
The material group a) includes the elements Pt and Ir, which represents the substance that is catalytically effective in the narrower sense, while the other material groups can be considered essentially as promoters, which promote the catalytic activity. The catalyst must have at least one of the elements of group a), specifically in a quantity of from 0.2 to 2%. The element Pt is especially preferred. It is recommended that the content of the element or elements of material group a) be limited to 0.3 to 0.6%.
As the promoter in the catalyst of the invention, at least one of each of the elements listed in material groups b) through g) described below must be represented. The material group b) comprises the elements Ge, Sn, Pb, Ga, In and Tl. The content of material group b) in the catalyst is in the range from 0.2 to 5%, and expediently in the range from 0.
Herskowitz Mordechay
Kogan Shimson
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Griffin Walter D.
Mannesman AG
Nguyen Tam M.
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