Catalyst useful for oxidation of alkanes

Details Catalyst useful for oxidation of alkanes Catalyst useful for oxidation of alkanes

2002-12-09

2004-10-26

Zucker, Paul A. (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Carboxylic acids and salts thereof

C568S469900, C502S312000

Reexamination Certificate

active

06809219

ABSTRACT:

This invention relates to catalysts useful in the preparation of unsaturated aldehydes and acids. In particular, the invention relates to a catalyst which is efficient in converting alkanes to unsaturated aldehydes and carboxylic acids and a process for preparing unsaturated aldehydes and carboxylic acids using the catalyst.
Unsaturated aldehydes and carboxylic acids are important commercial chemicals. Of particular importance is (meth)acrylic acid. The highly reactive double bond and acid function of (meth)acrylic acid makes it especially suitable as a monomer which may be polymerized alone or with other monomers to produce commercially important polymers. These unsaturated acids are also useful as a starting material for esterification to produce commercially important (meth)acrylate esters. Materials derived from (meth)acrylic acid or esters of (meth)acrylic acids are useful as plastic sheets and parts, paints and other coatings, adhesives, caulks, sealants, and detergents as well as other applications.
The production of unsaturated carboxylic acids by oxidation of an olefin is well known in the art. Acrylic acid, for instance, may be commercially manufactured by the gas phase oxidation of propylene. It is also known that unsaturated carboxylic acids may also be prepared by oxidation of alkanes. For instance, acrylic acid may be prepared by the oxidation of propane. Such a process is especially desirable because alkanes generally have a lower cost than olefins. A suitable catalyst and process for the oxidation of alkanes to unsaturated aldehydes or carboxylic acids, which are commercially viable, is a continuous goal of (meth)acrylic acid manufactures and has yet to be achieved.
One impediment for the production of a commercially viable process for the catalytic oxidation of an alkane to an unsaturated carboxylic acid or aldehyde is the identification of a catalyst having adequate conversion and suitable selectivity, thereby providing sufficient yield of the unsaturated carboxylic acid or aldehyde end-product. U.S. Pat. No. 5,380,933 discloses a method for preparing a catalyst useful in the gas phase oxidation of an alkane to an unsaturated carboxylic acid. In the disclosed method, a catalyst was prepared by combining ammonium metavanadate, telluric acid and ammonium paramolybdate to obtain a uniform aqueous solution. To this solution was added ammonium niobium oxalate to obtain a slurry. The water was removed from the slurry and a solid catalyst precursor resulted. The solid catalyst precursor was molded into a tablet, sieved to a desired particle size and then calcined at 600° C. under a nitrogen stream to obtain the desired catalyst. The resulting catalyst was asserted to be effective to convert propane to acrylic acid.
Co-pending U.S. patent application Ser. No. 09/316,007 discloses an improved process for preparing a catalyst useful in the conversion of propane to acrylic acid. The process was characterized by the use of a mixed mixed oxide solution which was stripped by various processes and calcined under an inert atmosphere.
The present inventors have now discovered a novel catalyst useful for catalyzing the oxidation of an alkane into an unsaturated aldehyde or carboxylic acid.
In one aspect of the present invention, there is provided a catalyst including: a mixed metal oxide of the formula A
a
M
m
N
n
X
x
O
o
; and an acid selected from at least one of: (i) heteropolyacids, (ii) aluminas, (iii) zirconias, (iv) titanias, (v) zeolites, and (vi) acid combinations thereof; wherein 0.25<a<0.98, 0.003<m<0.5, 0.003<n<0.5, 0.003<x<0.5; the acid is present at from 0.05 to 5 weight percent based on the total weight of the catalyst; o is dependent on the oxidation state of the other elements; and A is selected from Mo, W, Fe, Nb, Ta, Zr, Ru, and mixtures thereof, M is selected from V, Ce, Cr, and mixtures thereof; N is selected from Te, Bi, Sb, Se, and mixtures thereof, and X is selected from Nb, Ta, W, Ti, Al, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pd, Pt, Sb, Bi, B, In, Ce, and mixtures thereof.
In a second aspect of the present invention, there is provided a process for preparing a catalyst including: (A) admixing metal compounds, at least one of which is an oxygen containing compound, and water to form an aqueous solution; (B) removing the water from the aqueous solution to obtain a mixed metal oxide catalyst precursor; and (C) calcining the catalyst precursor at a temperature from 400° C. to 800° C. under an inert atmosphere; and (D) admixing an acid selected from at least one of: (i) heteropolyacids, (ii) aluminas, (iii) zirconias, (iv) titanias, (v) zeolites, and (vi) acid combinations thereof to form a catalyst material including a mixed metal oxide having the formula A
a
M
m
N
n
X
x
O
o
and the acid, wherein 0.35<a<0.87, 0.045<m<0.37, 0.020<n<0.27, 0.005<x<0.35, the acid is present at from 0.05 to 5 weight percent based on the total weight of the catalyst, o is dependent on the oxidation state of the other elements, and A is selected from Mo, W, and mixtures thereof, M is selected from V, Ce, Cr, and mixtures thereof; N is selected from Te, Bi, Sb, and mixtures thereof; and X is selected from Nb, Ta, Zr, and mixtures thereof.
In a third aspect, the present invention includes a process for preparing a catalyst including: (A) admixing metal compounds, at least one of which is an oxygen containing compound, an acid selected from at least one of: (i) heteropolyacids, (ii) aluminas, (iii) zirconias, (iv) titanias, (v) zeolites, and (vi) acid combinations thereof; and water to form an aqueous solution; (B) removing the water from the aqueous solution to obtain a mixed metal oxide catalyst precursor; and (C) calcining the catalyst precursor at a temperature from 400° C. to 800° C. under an inert atmosphere to form a catalyst including a mixed metal oxide having the formula: A
a
M
m
N
n
X
x
O
o
and the acid, wherein 0.35<a<0.87, 0.045<m<0.37, 0.020<n<0.27, 0.005<x<0.35; the acid is present at from 0.05 to 5 weight percent based on the total weight of the catalyst; o is dependent on the oxidation state of the other elements, and A is selected from Mo, W, and mixtures thereof; M is selected from V, Ce, Cr, and mixtures thereof; N is selected from Te, Bi, Sb, and mixtures thereof, and X is selected from Nb, Ta, Zr, and mixtures thereof.
The present invention also provides a process for preparing a compound selected from the group consisting of an unsaturated aldehyde and a carboxylic acid including: subjecting an alkane to catalytic oxidation in the presence of the catalyst described above.
As used herein, the expression “(meth)acrylic acid” is intended to include both methacrylic acid and acrylic acid within its scope. In a like manner, the expression “(meth)acrylates” is intended to include both methacrylates and acrylates within its scope and the expression “(meth)acrolein” is intended to include both methacrolein and acrolein within its scope.
As used herein the terminology “(C
3
-C
8
) alkane” means a straight chain or branched chain alkane having from 3 to 8 carbon atoms per alkane molecule.
As used herein the term “mixture” is meant to include within its scope all forms of mixtures including, but not limited to, simple mixtures as well as blends, alloys, etc.
For purposes of this application “% conversion” is equal to (moles of consumed alkane/moles of supplied alkane)×100; “% selectivity” is equal to (moles of formed desired unsaturated carboxylic acid or aldehyde/moles of consumed alkane)×100; and “% yield” is equal to (moles of formed desired unsaturated carboxylic acid or aldehyde/moles of supplied alkane)×(carbon number of formed desired unsaturated carboxylic acid or aldehyde/carbon number of the supplied alkane)×100.
For purposes of this application by “solution” is meant that greater than 95 percent of metal solid added to a solvent is dissolved. It is to be understood that the greater the amount of metal solid not initially in solution, the poorer the performance of the

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