Catalytic dehydrogenation processes and chromium catalysts...

Details Catalytic dehydrogenation processes and chromium catalysts... Catalytic dehydrogenation processes and chromium catalysts...

2001-03-15

2002-11-05

Hendrickson, Stuart L. (Department: 1754)

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

Catalyst or precursor therefor

Metal, metal oxide or metal hydroxide

C502S305000, C502S306000, C502S307000, C502S308000, C502S310000, C502S317000, C502S320000, C501S126000, C501S127000, C501S128000, C501S132000, C501S117000, C423S595000, C423S596000, C423S607000

Reexamination Certificate

active

06475950

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a novel catalyst comprising chromium and its use in dehydrogenation or dehydrocyclization of C
2
-
10
hydrocarbon processes.
BACKGROUND OF THE INVENTION
The dehydrogenation of paraffins to olefins is commercially significant because of the need for olefins for the manufacture of high octane gasolines, elastomers, detergents, plastics, ion-exchange resins and pharmaceuticals. Important hydrocarbon dehydrocyclization reactions are the conversion of diisobutylene and isooctane to p-xylene.
Processes for the conversion of paraffin hydrocarbons to less saturated hydrocarbons are known. For example see U.S. Pat. No. 4,513,162, U.S. Pat. No. 5,378,350 and European Patent Application No. EP 947,247. Nonetheless, there is a continuing need to develop new catalysts which are more effective or otherwise improved for use in dehydrogenation processes.
SUMMARY OF THE INVENTION
Disclosed herein is a composition having the formula Cr
a
A
b
B
c
(O
1−z
(OH)
2z
)
y
, wherein a+b+c=1; wherein A is an element selected from the group consisting of Zn, Sn, Rh, Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ce, and Ba; B is at least one element selected from the group consisting of Al, Si, and Mg; a is greater than 0.01 but less than 0.5; b is greater than 0.01 but less than or equal to 0.5; c is greater than 0.2 but less than or equal to 0.999; y is determined by the sum of the oxidation states of Cr, A and B individually multiplied by the corresponding stoichiometric coefficent a, b, c, said sum then divided by 2; and z is greater than or equal to 0 but less than or equal to 2.
This invention provides a process for converting at least one C
2
to C
10
hydrocarbon to less saturated hydrocarbons comprising the step of contacting at least one C
2
to C
10
hydrocarbon with at least one catalyst selected from the group consisting of Cr
a
A
b
B
c
(O
1−z
(OH)
2z
)
y
, wherein A is an element selected from the group consisting of Zn, Sn, Rh, Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ce, and Ba; B is at least one element selected from the group consisting of Al, Si, and Mg; a+b+c=1; a is greater than 0.01 but less than 0.5; b is greater than 0.01 but less than or equal to 0.5; c is greater than 0.2 but less than or equal to 0.999; y is determined by the sum of the oxidation states of Cr, A and B individually multiplied by the corresponding stoichiometric coefficient (a, b, or c), and said sum then divided by 2; and z is greater than or equal to 0 but less than or equal to 2; with a catalyst composition comprising rhodium and rare earth oxides; at a temperature of about 300° C. to about 650° C.
DETAILED DESCRIPTION OF THE INVENTION
The catalyst compositions of the present invention are of the formula Cr
a
A
b
B
c
(O
1−z
(OH)
2z
)
y
, wherein a+b+c=1; wherein A is an element selected from the group consisting of Zn, Sn, Rh, Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ce and Ba; B is at least one element selected from the group consisting of Al, Si, and Mg; a is greater than or equal to 0.01 but less than or equal to 0.5; b is greater than or equal to 0.01 but less than or equal to 0.5; c is greater than or equal to 0.2 but less than or equal to 0.999; y is determined by the sum of the oxidation states or Cr, A and B individually multiplied by the corresponding stoichiometric coefficent a, b, or c, said sum then divided by 2; and z is greater than or equal to 0 less than or equal to 2 can be prepared by a variety of known art methods such as impregnation, gel formation (including xerogel or aerogel formation), freeze-drying, spray drying, and spray roasting.
Impregnation
The impregnation technique typically comprises contacting a catalyst support with an aqueous solution of a compound of chromium and a solution of compounds containing elements A and/or B. For example, a water soluble chromium compound such as Cr(NO
3
)
3
•9H
2
O can be impregnated into preformed oxides or oxyhydroxides of elements A and B (e.g., MgSiO
3
). The contacting is followed by drying and calcining the supported materials. In some cases calcination can be accomplished in situ under reaction conditions.
Gel Formation
Pre-formed Colloidal Sol Destabilization: One or more inorganic metal colloids may be used as starting material for preparing the catalyst gels of the present invention. These colloids include colloidal alumina sols, colloidal silica sols or their mixtures. There are also several methods of preparing colloids, as described in “Inorganic Colloid Chemistry”, Volumes 1, 2 and 3, J. Wiley and Sons, Inc., 1935. The pre-formed colloidal sols are sold commercially and readily available from Nyacol Products.
It is preferred that pre-formed colloidal sols in water, or aquasols, are used in the catalyst preparation for the dehydrogenation process invention disclosed herein. The aquasols are comprised of colloidal particles ranging in size from 2 nanometers to 50 nanometers. In general, the smaller primary particle sizes (2 nm to 5 nm) are preferred. The pre-formed colloidal sols contain from 10 to 35 weight % of colloidal oxides or other materials, depending on the method of stabilization.
In this invention, the colloids, which are originally stable heterogeneous dispersions of oxides and other species in solvents, are destabilized to produce colloidal gels. Destabilization is induced, in some cases, by the addition of soluble salts, (e.g., chlorides or nitrates), which change the pH and the ionic strength of the colloidal suspensions, by the addition of acids or bases, or by solvent removal. pH changes generally accompany the addition of soluble salts; in general, this is preferred over solvent removal. Generally, a pH range of from about 0 to about 12 can be used to destabilize the colloids. It is noted that very large extremes in pH (such as pH 12) can cause flocculation and precipitation. A pH range of from about 2 to 8 is generally preferred.
The medium used is typically aqueous, although non-aqueous colloids can also be used. The additional metal or inorganic reagents (i.e., salts of Cr or the A and B components) used should be soluble in the appropriate aqueous and non-aqueous media.
Sol-Gel Synthesis Using Alkoxides: The catalysts of the present invention can also be prepared by a sol gel process. One or more metal alkoxides (e.g., tetraethylorthosilicate) may be used as starting material for preparing the gels. The inorganic metal alkoxides used to prepare the catalyst may include any alkoxide which contains from 1 to 20 carbon atoms, preferably 1 to 5 carbon atoms, in the alkoxide group. It is preferred that these alkoxides are soluble in the liquid reaction medium. C
1
-C
4
alkoxides are most preferred. An example of a most preferred C
1
-C
4
alkoxide is aluminum isopropoxide.
Commercially available alkoxides can be used. However, inorganic alkoxides can be prepared by other routes. Some examples include direct reaction of zero valent metals with alcohols in the presence of a catalyst. Many alkoxides can be formed by reaction of metal halides with alcohols. Alkoxy derivatives can be synthesized by the reaction of the alkoxide with alcohol in a ligand interchange reaction. Direct reactions of metal dialkylamides with alcohol also form alkoxide derivatives. Additional examples are disclosed in “Metal Alkoxides” by D.C. Bradley et al., Academic Press, (1978).
A solution of a soluble salt comprising at least one metal selected from the group consisting of Cr, Al, Zn, Sn, Rh, Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ce and Ba (e.g., Cr(NO
3
)
3
, chromium acetate, chromium hydroxide acetate, Al(NO
3
)
3
, Zn(NO
3
)
2
, Sn(NO
3
)
2
, RhCl
3
, LiNO
3
, NaNO
3
, KNO3, RbNO
3
, CsNO
3
, Be(NO
3
)
2
, Mg(NO
3
)
2
, Ca(NO
3
)
2
, Sr(NO
3
)
2
, and Ba(NO
3
)
2
) is prepared. Other soluble salts (for example, acetates, chlorides, nitrates, nitrites) can also be used. An aqueous solution containing at least one dissolved metal salt is added to a non-aqueous solution of at least one alkoxide selected from the group consisting of magnesiu

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