Claims
- 1. A process for the ammoxidation of a paraffin selected from propane and isobutane to make acrylonitrile and methacrylonitrile, respectively, by the catalytic vapor phase reaction of such a paraffin in admixture with oxygen and ammonia by contact with a complex metal oxide catalyst which is essentially free of bismuth, and has the elements and the proportions which are represented by the following empirical formula:
- VSb.sub.m A.sub.a D.sub.b C.sub.c O.sub.x,
- where
- A is one or more of W, Sn, B Mo and Ge;
- D is one or more of Fe, Co, Ni, Cr, Mn, Cu, Pb, Zn, Se, Te and As;
- C is one or more of an alkali metal, Ca, Sr, Ba, Tl and where m is greater than 1 and up to 20; a is 0.2-10; b is 0-5; c is 0-1; a is equal to or less than m; b is equal to or less than m; wherein x is determined by oxidation state of the other elements present, and wherein the antimony has an average valency higher than +3 and the vanadium has an average valency lower than +5, wherein A includes at least 0.2 atoms of W, crystalline Sb.sub.2 O.sub.4 is present in said catalyst, and wherein the foregoing catalyst is on an inorganic oxide support material selected from silica, alumina, titania, zirconia, silica-niobia, silica-zirconia, silica-titania, silica-alumina, Nb.sub.2 O.sub.5 and magnesia.
- 2. A process of claim 1 wherein m is 2-10.
- 3. A process of claim 1 wherein m is 3-7.
- 4. A process of claim 1 wherein said support contains 20 to 100 weight percent alumina and is selected from silica-alumina and alumina.
- 5. A process of claim 1 wherein said support contains 50 to 100 weight percent alumina and is selected from alumina and silica-alumina.
- 6. A process of claim 4 wherein A includes at least 0.4 atoms of W per atom of V.
- 7. A process of claim 1 wherein said support is selected from silica-alumina and alumina having 20 to 100 weight percent alumina; silica-titania and titania having 20-100 weight percent titania; silica-zirconia and zirconia having 80-100 weight percent zirconia; and silica-niobia and niobia having 30-100 weight percent niobia (Nb.sub.2 O.sub.5).
- 8. A process of claim 1 wherein b is at least 0.2.
- 9. A process of claim 6 wherein b is at least 0.2.
- 10. A process of claim 5 wherein A includes at least 1 atom of W per atom of V.
- 11. A process of claim 1 wherein said support contains 60 to 100 weight percent alumina and is selected from alumina and silica-alumina.
- 12. A process of claim 1 wherein A includes at least 0.4 atoms of W per atom of V.
- 13. A process of claim 2 wherein A includes at least 0.4 atoms of W per atom of V.
- 14. A process of claim 7 wherein A includes at least 0.4 atoms of W per atom of V.
- 15. A process of claim 11 wherein A includes at least 0.4 atoms of W per atoms of V.
- 16. A process according to any one of the preceding claims wherein said catalyst, in addition to the elements and proportions represented by said empirical formula, contains P as a part of said complex catalyst in an amount up to 10 atoms of P per atom of V.
- 17. A process of any one of claims 1 to 15 wherein said paraffin is propane.
- 18. A process for the amoxidation of a paraffin selected from propane and isobutane to make acrylonitrile and methacrylonitrile, respectively, by the catalytic vapor phase reaction of such a paraffin in admixture with oxygen and ammonia by contact with a complex metal oxide catalyst, which is essentially free of bismuth, having the elements and proportions which are represented by the following empirical formula:
- VSb.sub.m A.sub.a D.sub.b C.sub.c O.sub.x,
- where
- A is one or more of W, Sn, B, Mo and Ge and includes at least 0.2 atoms of W per atom of V;
- D is one or more of Fe, Co, Ni, Cr, Mn, Cu, Pb, Zn, Se, Te and As;
- C is one or more of an alkali metal, Ca, Sr, Ba, Tl and where m is greater than 1 and up to 20; a is 0.4-10; b is 0-5; c is 0-1; a is equal to or less than m; b is equal to or less than m; wherein x is determined by the oxidation state of the other elements present, and wherein the antimony has an average valency higher than +3 and the vanadium has an average valency lower than +5, wherein crystalline Sb.sub.2 O.sub.4 is present in said catalyst, and wherein the foregoing catalyst is on an inorganic oxide support material selected from alumina and silica-alumina which is 50 to 100 weight percent alumina.
- 19. A process of claim 18 wherein A includes at least 0.4 atoms of W per atom of V.
- 20. A process according to claim 18 wherein said catalyst, in addition to the elements and proportions represented by said empirical formula, contains P as a part of said complex catalyst in an amount up to 10 atoms of P per atom of V.
- 21. A process according to claim 18 wherein said catalyst, in addition to the elements and proportions represented by said empirical formula, contains P as a part of said complex catalyst in an amount of 0.1 to 5 atoms of P per atom of V.
- 22. A process according to claim 19 wherein said catalyst, in addition to the elements and proportions represented by said empirical formula, contains P as a part of said complex catalyst in an amount up to 10 atoms of P per atom of V.
- 23. A process according to claim 19 wherein said catalyst, in addition to the elements and proportions represented by said empirical formula, contains P as a part of said complex catalyst in amount of 0.1 to 5 atoms of P per atom of V.
Parent Case Info
This application is a continuation-in-part of application Ser. No. 826,695, filed Feb. 6, 1986, now abandoned which in turn is a division of Ser. No. 724,226, filed Apr. 17, 1985, now U.S. Pat. No. 4,746,641, issued 5-24-88, which is a continuation-in-part of parent application Ser. No. 643,208 filed Aug. 22, 1984, now abandoned. This application is also a continuation-in-part of application Ser. No. 919,105, filed Oct. 15, 1986 now abandoned.
This invention relates to the catalytic ammoxidation of paraffins containing from 3 to 5 carbon atoms to .alpha.,.beta. unsaturated nitriles, especially paraffins containing 3 to 4 carbon atoms. Most important is the ammoxidation of propane to acrylonitrile and the ammoxidation of isobutane to methacrylonitrile.
Because of the price differential between propylene and propane an economic incentive exists for the development of a viable catalytic process for conversion of propane to acrylonitrile.
Earlier attempts to develop an efficient process for the ammoxidation of propane to acrylonitrile produced either insufficient yields or processes that necessitated adding halogen promoters to the feed. The latter procedure would require not only reactors made of special corrosion resistant materials, but also the quantitative recovery of the promoter. The added costs thus eliminated the advantage of the propane/propylene price differential.
It is thus an object of the present invention to provide an improved process for the ammoxidation of paraffins to unsaturated nitriles.
It is a further object of the invention to provide new catalysts for such reaction.
It is still another object of the present invention to provide improved methods of preparing such catalysts, and precursors for such catalysts.
Still another object is to provide an improved catalytic ammoxidation process for making unsaturated nitriles from lower paraffins without the use of halogen promoters.
Other objects, as well as aspects, features and advantages, of the present invention will become apparent from a study of the accompanying disclosure and the claims.
These and other objects are achieved by the present invention according to one aspect of which there is provided a process for the ammoxidation of paraffins containing 2 to 5 carbon atoms by the catalytic reaction of such paraffins with oxygen and ammonia by catalytic contact with an essentially bismuth free complex metal oxide catalyst having the ingredients and the proportions which are represented by the following empirical formula:
A is one or more of W, Sn, Mo, B and Ge;
D is one or more of Fe, Co, Ni, Cr, Mn, Cu, Zn, Se, Te, Pb and As;
C is one or more of an alkali metal, Ca, Sr, Ba, and Tl and where m is greater than 1 and up to 20 (usually 2-10, most usually 3-7); a is 0-10; b is 0-5; c is 0-1; a is equal to or less than m; b is equal to or less than m; wherein x is determined by the oxidation state of the other elements, and wherein the antimony has an average valency higher than +3 and the vanadium has an average valency lower than +5, wherein crystalline Sb.sub.2 O.sub.4 is present in said catalyst, and wherein the foregoing catalyst is on a inorganic oxide support material. All of the subscripts in formula (1) are of course atoms. A now preferred support material is alumina or silica-alumina, as further discussed herein.
The catalysts of formula (1) can, in general, contain oxides of other elements not set forth in formula (1), as long as they do not materially detrimentally affect the catalytic ammoxidation of the paraffin to the desired nitriles. When bismuth is optionally present in oxidized form as part of the catalyst of formula (1), it is usually present in amounts of no more than 0.2 atoms of Bi per atoms of V.
In the catayst of the invention having the ingredients and proportions which are represented by formula (1), in an especially advantageous embodiment, P is also present in the catalyst inan amount up to 10 atoms P per atom of V (usually 0.1-5 atoms, most usually 0.1-1 atoms per atom of V). Thus, the formula (1) in such event could be written as
Such P-containing catalysts are particularly useful when the catalysts contain tungsten and have an alumina-containing support/diluent as disclosed herein.
It should be noted that the present ammoxidation reaction is effected in the substantial absence of halogen or sulfur or compounds thereof. Preferably also, a halide or halogen is not employed in the preparation of the catalyst precursor of the invention.
The present process is especially useful in the ammoxidation of propane and isobutane.
Especially useful catalyst compositions of the foregoing description are those in which a is at least 1 and includes at least 1 atom of W.
According to the present invention, the foregoing catalysts are prepared under conditions such that in the final composition the average oxidation state of vanadium is less than +5, and often approaches +3. One method of the present invention for preparing the catalysts is by a redox reaction between a compound of trivalent antimony such as Sb.sub.2 O.sub.3 and a compound of pentavalent vanadium, such as V.sub.2 O.sub.5, during which at least part of the antimony is oxidized and at least part of the the vanadium reduced, presumably according to the equation
The foregoing redox reaction was described by Birchall and Sleight (Inorganic Chem. 15, 868-70 [1976]) and by Berry et al. (J. Chem. Soc. Dalton Trans., 1983, 9-12), who effected the reaction by heating a dry mixture of the above reactants at temperatures above 600.degree. C.
We have now found that a redox reaction can successfully and more conveniently be carried out in an aqueous medium by heating at a temperature of at least 80.degree. C. and up to 200.degree. C., for instance, by heating an aqueous dispersion of a V.sup.5+ compound, such as NH.sub.4 VO.sub.3 or V.sub.2 O.sub.5, with an Sb.sup.3+ compound in excess over that called for by Equation (1), such as by reacting Sb.sub.2 O.sub.3 and NH.sub.4 VO.sub.3 (or V.sub.2 O.sub.5). This step is followed by evaporation, drying and then calcining the product in an oxygen-containing atmosphere, such as air, at from 350.degree. to 700.degree. or 750.degree. C., usually 400.degree. to 600.degree. C. The length of the calcination period may range from 30 minutes to 12 hours, but satisfactory catalysts are usually obtained by calcination at such temperatures for a period of from 1 to 5 hours.
At least part of the excess of trivalent antimony compound, such as Sb.sub.2 O.sub.3, is oxidized to Sb.sub.2 O.sub.4 during the calcination in molecular oxygen containing atmosphere, such as air. The presence in the finished catalyst of the excess antimony oxide as Sb.sub.2 O.sub.4 results in superior catalytic performance.
The ingredients of the catalysts other than vanadium and antimony (and of course part of the oxygen) can be incorporated after completion of the foregoing redox reaction. Thus, the additives P, A, D and C can be added in the slurry after the redox reaction, or the solid particles containing the vanadium and antimony values after separation from the aqueous medium can be coated or impregnated in a known manner with such additives at any suitable stage prior to final calcination of the catalyst, by methods generally known in the art, using oxides, hydroxides, acids, salts (particularly organic salts such as acetates), and other compounds of such elements.
According to one aspect of the present process there is provided a catalyst precursor which comprises an aqueous slurry of the redox reaction product of a V.sup.5+ compound and an Sb.sup.3+ compound where the Sb.sup.3 + compound is in excess, said redox reaction product having the empirical formula
Usually, in the above precursor slurries m is 2-10, more usually 3-7.
The catalyst precursor slurry can be dried and calcined in a molecular oxygen containing gas at temperatures of 350.degree. to 850.degree. C., more often, 350.degree. to 700.degree. C., usually 400.degree. to 600.degree. C. or 650.degree. C., to produce a catalyst useful in the process of the invention for ammoxidizing C.sub.3 to C.sub.5 paraffins. The additives A, D and/or C, if any, can be added in the slurry after the redox reaction, or the solid particles containing the vanadium and antimony values after separation from the aqueous medium can be coated or impregnated in a known manner with such additives at any suitable stage prior to final calcination of the catalyst.
It should be noted that when the oxidation of the unreacted excess Sb.sub.2 O.sub.3 during calcination is prevented by an exclusion of oxygen, such as by calcination in a nitrogen atmosphere, a very inferior catalyst results.
If vanadium-antimony catalysts are prepared by using pentavalent vanadium and pentavalent antimony compounds, thus eliminating the redox reaction, both the vanadium and antimony remain in the high oxidation state and the resulting catalyst is very inferior, with or without additives. It has also been found that inferior catalysts are made when the vanadium-antimony compound is made by reacting Sb.sub.2 O.sub.3 and V.sub.2 O.sub.5 (or other V.sup.5+ compound) in the presence of compounds that may act as oxidizing or reducing agents, such as nitric acid, nitrates, or multivalent ions, since these tend to interfere with the desired redox reaction between antimony and vanadium.
Thus, according to the present invention the superior catalytic performance in paraffin ammoxidation is obtained with the catalysts of the invention which contain a complex vanadium-antimony oxide composition with vanadium in a low oxidation state and antimony in a high oxidation state greater than +3, plus some excess antimony oxide as crystalline Sb.sub.2 O.sub.4, plus an inorganic oxide support, as will be shown by comparative examples hereafter.
Whether or not tungsten is present in the catalysts shown in formula (1) of the catalysts of the invention, the promoting element Sn from the A Group and the promoting elements Te and Fe from the D Group give especially good results in the catalyst of the invention, either when one or any two or three of these elements are present.
Thus, an especially useful group of complex metal oxide catalysts of the invention for use in the paraffin ammoxidation process of the invention are the essentially bismuth free catalysts having the elements and the proportions which are represented by the formula
A is one or more of W and Sn;
D is one or more of Fe and Te; and where m is greater than 1 and up to 20 (usually 2-10, most usually 3-7); a is 0-10; b is 0-5; a is equal to to less than m; b is equal to or less than m and usually is at least 0.2; wherein x is determined by the oxidation state of the other elements; and wherein the antimony has an average valency higher than +3 and the vanadium has an average valency lower than +5, wherein crystalline Sb.sub.2 O.sub.4 is present in said catalyst, and wherein the foregoing catalyst is on a inorganic oxide support material. Now preferred support materials are silica-alumina and alumina as previously discussed herein.
In formulas (1) and (3) subscript a usually is at least 0.2, more usually at least 0.4 to 0.5. In formula (1) at least 0.2 atoms of W are preferably present (more often at least 0.4 atoms) per atom of V, and the total of W plus Sn atoms (if any Sn is present) is usually at least 0.4 atoms. The same is true of formula (3).
Especially useful catalyst compositions of the foregoing description are those in which a is at least 1 and includes at least 1 atom of W.
The catalysts of the present invention are essentially free of uranium. Moreover, in the process of the invention, essentially no sulfur or sulfur compounds, or halogen or halogen compounds, are present in the reaction mixture.
Phosphorus, tungsten and the optional elements shown in formulas (1) and (3) can be incorporated in the base vanadium/antimony/support precursor slurry or are added to the solids recovered from the slurry by methods generally known in the art, using oxides, hydroxides, acids, salts (particularly organic salts such as acetates), and other compounds of such elements. Examples of such incorporation are shown in the specific examples hereinafter.
Tungsten is advantageously incorporated as ammonium meta- or orthotungstate, tungstic acid, or tungsten trioxide. P can be introduced, for instance, as ammonium phosphate or (NH.sub.4).sub.2 HPO.sub.4 or phosphoric acid.
The catalyst support not only improves mechanical stability of the catalysts, but the catalytic activity is significantly improved, especially in the case of alumina and silica-alumina. This is amply shown in the examples. Besides alumina and silica-alumina other supports that can be used are silica, titania, silica-titania, Nb.sub.2 O.sub.5, silica-niobia, silica-zirconia, zirconia, and magnesia, etc.
In the usual practice of the invention the catalyst support/diluent of the empirical formula of the catalyst of the invention is not an oxide of an element named in such empirical formula.
Now preferred support materials for not only improving mechanical stability but also for improving the yield of the desired nitriles are selected from silica-alumina and alumina having 20-100, usually 50-100, preferably 60-100 weight percent alumina; silica-titania and titania having 20-100 wieght percent titania; silica-zirconia and zirconia having 80-100 weight percent zirconia; and silica-niobia and niobia having 30-100 weight percent niobia (Nb.sub.2 O.sub.5).
The weight ratio of the catalyst having the ingredients of empirical formulas (1) or (3) to the support material can vary from 9:1 to 1:9.
In the ammoxidation of the present invention, the reaction is preferably carried out in the gas phase by contacting a mixture of the paraffin, ammonia and a molecular oxygen containing gas, such as air, with a catalyst of the invention contained in a fixed bed, a gravity flowing bed, a fluidized bed or a fast transport reactor mode. It also possible to include additional diluents such as steam, nitrogen, carbon dioxide or helium.
The mole ratio of oxygen to the paraffin, such as propane, can vary from 0.1:1 to 10:1, more often 0.5:1 to 4:1, and a ratio in the range from 1:1 to 3:1 is usual. The ammonia to paraffin (such as propane) ratio can vary from 0.06:1 to 5:1, more often 0.5:1 to 5:1, but is usually from 1:1 to 5:1. When ammonia to paraffin ratios are much less than 1, various undesirable oxygenated derivatives of the paraffin can be formed.
The reaction temperature can vary from 400.degree. to 650.degree. C., but is usually 460.degree. to 520.degree. C. The latter temperature ranges are especially useful in the case of propane ammoxidation to acrylonitrile.
The average contact time can be from 0.02, usually 1, up to 20 seconds, but is usually from 0.2 to 10 seconds, more often 2 to 8 seconds. However, higher or lower contact times are within the scope of the process of the invention.
The catalysts of the present invention are believed to be unique. U.S. Pat. No. 3,860,534; 1975, describes catalysts that contain only vanadium and antimony but these require water washing after preparation and then redrying by a laborious and time consuming procedure.
US Referenced Citations (16)
Foreign Referenced Citations (1)
| Number |
Date |
Country |
| 1336136 |
Nov 1973 |
GBX |
Divisions (1)
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Number |
Date |
Country |
| Parent |
724226 |
Apr 1985 |
|
Continuation in Parts (2)
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Number |
Date |
Country |
| Parent |
826695 |
Feb 1986 |
|
| Parent |
643208 |
Aug 1984 |
|
Patent Grant
4788317
