Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
2001-01-04
2004-02-17
Nguyen, Cam N. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C502S309000, C502S311000, C502S312000, C502S313000, C502S314000, C502S315000, C502S316000, C502S321000, C502S322000, C502S353000
Reexamination Certificate
active
06693059
ABSTRACT:
This invention relates to a process for preparing a catalyst and catalytic oxidation therewith. In particular, the invention relates to a process for preparing a catalyst for converting alkanes to unsaturated aldehydes and carboxylic acids, by catalytic oxidation.
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 process for the oxidation of alkanes to unsaturated aldehydes or carboxylic acids which is commercially viable has yet to be achieved.
One impediment to the attainment of a commercially viable process for the catalytic oxidation of an alkane to an unsaturated carboxylic acid is the identification of a catalyst having adequate conversion and suitable selectivity, thereby providing sufficient yield of the unsaturated carboxylic acid 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 to obtain a solid catalyst precursor. 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.
The present inventor was unable to reproduce the asserted results using the preparation method of the '933 patent. While not wishing to be bound by any theory, it is believed that the poor performance of the prior art method of the '933 patent results from the compositional or phase segregation of the component elements of the catalyst, e.g., in the slurry, between solid and liquid phases, and, during calcination, between the gas and the various solid phases.
Japanese Laid-Open Patent Application Publication No. 6-228073 discloses a method for preparing a catalyst useful in the gas phase reaction of an alkane, ammonia and oxygen to form a nitrile. In the disclosed method, a catalyst was prepared by combining ammonium metatungstenate, ammonium metavanadate and telluric acid to obtain a uniform aqueous solution. To this solution was added ammonium niobium oxalate to obtain a slurry. 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.
There is no disclosure, whatsoever, in the Japanese publication as to the use of such a catalyst in the catalytic oxidation of an alkane to form an unsaturated aldehyde and/or an unsaturated carboxylic acid.
The present inventor has now discovered a process for preparing a catalyst for catalyzing the gas phase oxidation of an alkane into an unsaturated aldehyde or carboxylic acid wherein phase segregation is minimized and improvements in selectivity, conversion and yield are achieved.
In one aspect of the present invention, there is provided a process for preparing a catalyst comprising: (A) admixing metal compounds, at least one of which is an oxygen-containing compound, and at least one solvent to form a solution; (B) removing the at least one solvent from the solution to obtain a catalyst precursor; and (C) calcining the catalyst precursor at a temperature of from 350° C. to 850° C. under an inert atmosphere to form a catalyst having the formula
W
a
V
b
X
x
Y
y
O
n
wherein a, b, x and y are molar fractions of W, V, X and Y, respectively, based on the total amount of W, V, X and Y, and n is the molar proportion of oxygen as determined by the oxidation state of W, V, X and Y,
wherein a, b, x and y satisfy the following relationships
0.25<a<0.98
0.003<b<0.5
0.003<x<0.5
0.003<y<0.5
wherein X is at least one element selected from the group consisting of Te, Bi, Sb and Se, and
wherein Y is at least one element selected from the group consisting of Nb, Ta, Ti, Al, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pd, Pt, B, In, and Ce.
In another aspect of the present invention, there is provided a process for preparing a catalyst comprising: (A) admixing metal compounds, at least one of which is an oxygen-containing compound, and at least one solvent to form a solution; (B) removing the at least one solvent from the solution to obtain a catalyst precursor; and (C) calcining said catalyst precursor at a temperature of from 350° C. to 850° C. under an inert atmosphere to form a catalyst having the formula
W
a
V
b
X
x
Y
y
O
n
wherein a, b, x and y are molar fractions of W, V, X and Y, respectively, based on the total amount of W, V, X and Y, and n is the molar proportion of oxygen as determined by the oxidation state of W, V, X and Y,
wherein a, b, x and y satisfy the following relationships
0.25<a<0.98
0.003<b<0.5
0.003<x<0.5
0.003<y<0.5
wherein X is at least one element selected from the group consisting of Te, Bi, Sb and Se, and
wherein Y is at least one element selected from the group consisting of Mo, Nb, Ta, Ti, Al, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pd, Pt, B, In, and Ce,
with the proviso that Mo cannot be present in a molar fraction greater than 0.20.
In additional aspects of the present invention, there are provided processes for preparing unsaturated aldehydes or carboxylic acids comprising subjecting an alkane to catalytic oxidation in the presence of a catalyst prepared according to the present invention.
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.
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, e.g., simples blends, alloys, etc.
As used herein, the term “glassy precursor” is meant to include materials of a glass-like morphology, as opposed to materials having a powder morphology.
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)×100.
For purposes of this application, “solution” means that greater than 95 percent of a solid metal compound added to a solvent is dissolved. In this regard, it should be understood that the greater the amount of solid metal compound not initially in solution, the poorer the performance of the catalyst derived therefrom.
In a first step of the processes for prepari
Nguyen Cam N.
Rohm and Haas Company
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