| PATENT ASSIGNEE'S COUNTRY | India |
| UPDATE | 09.99 |
| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | 14.09.99 |
| PATENT TITLE |
Process for the preparation of a highly active and selective ammoxidation catalyst and its use in preparing heteroaromatic nitriles |
| PATENT ABSTRACT |
This invention relates to a process for the preparation of highly active and selective ammoxidation catalyst of formula (VO).sub.2 P.sub.2 O.sub.7, TiO.sub.2 or (VO).sub.2 P.sub.2 O.sub.7, Al.sub.2 O.sub.3, which process comprises refluxing a vanadium source in the presence of alcohols; adding a source of phosphorous to form vanadyl pyrophosphate hydrate (VO).sub.2 H.sub.4 P.sub.2 O.sub.9 or (VO).sub.2 P.sub.2 O.sub.7.2H.sub.2 O; Physical mixing of (VO).sub.2 H.sub.4 P.sub.2 O.sub.9 with oxides selected from titania or alumina, and heating the resultant mixture in the presence of air at a temperature in the range of 300-600.degree. C. for a period in the range of 1 to 10 hours; and the use of said ammoxidation catalyst in the preparation of heteroaromatic nitrites. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | 10.03.98 |
| PATENT REFERENCES CITED | This data is not available for free |
| PATENT PARENT CASE TEXT | This data is not available for free |
| PATENT CLAIMS |
We claim: 1. A process for the production of 3 & 4 cyanopyridines in high yields by vapour phase ammoxidation of the respective methyl pyridines in the presence of air and ammonia over a V--P--Ti--O catalyst wherein the ratio of the salts of the vanadium, phosphorous and titanium is in the range of 1:3:50 to 1:8:200 at a temperature in the range of 320.degree. to 450.degree. C. 2. A process as claimed in claim 1 wherein the yields of 3 & 4 cyanopyridines are greater than 92% and 97% respectively. 3. A process as claimed in claim 1 wherein the molar concentrations of 3 & 4 methyl pyridines respectively are in the range of 0.5 to 3.0%. 4. A process as claimed in claim 1 wherein the O/NH.sub.3 is in the range of 1 to 5. 5. A process as claimed in claim 1 wherein the space velocities are in the range of 1500 to 4000 hour.sup.-1. 6. A process as claimed in claim 1 wherein the dilution of catalyst with an inert medium is in the range of 0.5 to 5 (by volume) with respect to the volume of the catalyst. -------------------------------------------------------------------------------- |
| PATENT DESCRIPTION |
FIELD OF THE INVENTION The present invention relates to a process for the preparation of a highly active and selective ammoxidation catalyst and its use in preparing heteroaromatic nitriles. The catalyst prepared by the process of the present invention is useful for the production of heteroaromatic nitriles in high yields. BACKGROUND OF THE INVENTION The heteroaromatic nitriles are valuable intermediates for the preparation of corresponding amides which are used in pharmaceuticals. For example, 3-cyanopyridine is used in the preparation of the niacin or nicotinamide useful for the prevention of pellagra and 4-cyanopyridine is used in the preparation of isoniazid, an anti tuberculosis drug. The heteroaromatic nitrites are hitherto being prepared by a vapour phase reaction of a gas mixture consisting of alkyl substituted heteroaromatic compound, ammonia and oxygen (namely ammoxidation) over a mixed oxide catalyst. PRIOR ART REFERENCES Hitherto, for the catalytic ammoxidation of alkyl substituted heteroaromatic compound to get corresponding nitriles, a number of processes were reported. One of such processes, in the U.S. Pat. No. 2,510,605 discloses a catalyst comprising of vanadium, molybdenum and phosphorous with alumina as a carrier for the ammoxidation of .alpha.-, .beta.-, .tau.- picolines. Although this process reported a reasonably good yield (60%) at 450.degree. C., this high temperature of reaction is undesirable in industrial point of view. Another U.S. Pat. No. 2,839,535 discloses a variety of V.sub.2 O.sub.5 catalyst supported on Al.sub.2 O.sub.3 heated at different temperatures and the process described in this patent resulted a 80% and 74% yields of isonicotinonitrile and nicotinonitrile respectively. Another U.S. Pat. No. 2,861,999 discloses more or less same yield of isonicotinionitrile and nicontinionitrile in the presence of a large excess of air over a catalyst comprising oxides of vanadium, molybdenum, and phosphorous supported on activated alumina. Yet another U.S. Pat. No. 3,981,879 discloses a (V.sub.2 O.sub.5 +MoO.sub.3 +P.sub.2 O.sub.5 +SnO.sub.2)/pumice catalyst composition to prepare 3-cyanopyridine with 90% selectivity at 76% conversion. A Japanese Patent Publication No. 19706 discloses a catalyst comprising antimony oxide, vanadium oxide and a metal selected from the group consisting of iron, copper, titanium, cobalt, manganese and nickel, for the ammoxidation of the alkyl substituted heteroaromatic compound. Although this catalyst has high selectivity, it suffers from deactivation through reduction with ammonia and hence lacks consideration for continuous industrial production An Indian Patent publication No. discloses a process relating to the production of 3-cyanopyridine with 83% yield over a vanadium pentoxide-molybdenum trioxide-phosphorous pentoxide catalyst. Nevertheless, the catalyst mentioned above involve many problems left unsolved for industrial production point of view such as necessity of using large excess of ammonia or air, catalyst deactivation, low yields of nitriles, high reaction temperature. OBJECTS OF THE INVENTION The main object of the present invention is to provide a process for inventing a versatile ammoxidation catalyst by physical mixing of an active phase (vanadium-phosphorousoxide) with other oxides, titanium oxide, aluminium oxide either with or without promoter in a solid state, a technique called solid-solid wetting. The other object of the present invention is to provide a process for preparing a highly active (conversion 90-100%) and selective (90-99%) catalyst comprising vanadium oxide-phosphorous oxide and titanium oxide for producing heteroaromatic nitrites. Another object of the present invention is to provide a process for preparing heteroaromatic nitriles such as nicotinonitrile, isonicotinonitrile, 3-cyanopyridine and 4-cyanopyridine in greater yields (90-99%). Yet another object of the invention is to provide a process for preparing a versatile ammoxidation catalyst by physical mixing of an active phase (vanadium-phosphorous-oxide) with other oxides such as titanium oxide or aluminium oxide either with or without promoter such as bismuth oxide or bismuth nitrate, in solid state, a technique called solid-solid wetting. SUMMARY OF THE INVENTION The above objects are achieved by providing a process for the preparation of highly active and selective ammoxidation catalyst of formula (VO).sub.2 P.sub.2 O.sub.7,TiO.sub.2 or (VO).sub.2 P.sub.2 O.sub.7,Al.sub.2 O.sub.3, which comprises, i. refluxing a vanadium source in the presence of alcohols as described in the following text; ii. adding a source of phosphorous to form vanadyl pyrophosphate hydrate (VO).sub.2 H.sub.4 P.sub.2 O.sub.9 or (VO).sub.2 P.sub.2 O.sub.7.2H.sub.2 O; iii Physical mixing of (VO).sub.2 H.sub.4 P.sub.2 O.sub.9 with oxides like titania, alumina and iv. heating the resultant mixture at a temperature in the range of 300.degree. C. to 600.degree. C. for a period in the range of 1 to 10 hours. DETAILED DESCRIPTION OF THE INVENTION The process for the preparation of a catalyst according to the present invention involves the preparation of vanadyl pyrophosphate hydrate and the addition of TiO.sub.2 support. The preparation of the vanadyl pyrophosphate hydrate involves refluxing of vanadium rich compounds, preferably vanadium salts, ammonium meta vanadate, vanadyl sulphate, oxides of vanadium like vanadium pentoxide in a mixture of aliphatic and aromatic alcohols like ethanol, propanol, butanol, benzyl alcohol followed by addition of phosphorous containing molecules like ortho phosphoric acid. The phosphorous to vanadium ratio is kept not greater than 10, particularly not more than 5, more particularly not more than 2. According to another feature of the present invention, there is provided a process wherein the vanadyl pyrophosphate hydrate is thoroughly mixed with titanium dioxide in the range of ratio of 1:1 to 1:15, preferably in the range of 1:5 to 1:15 and heating the resultant mixture in air for a period in the range of 1 to 10 hours, preferably not more than 8 hours, more preferably not more than 5 hours. The present invention also describes a process wherein the titanium used is either anatase or rutile forms or a mixture of both with a surface area preferably of not more than 120 m.sup.2 g.sup.-1, particularly not more than 100 m.sup.2 g.sup.-1 more particularly not more than 60 m.sup.2 g.sup.-1. In the present invention, the source of phosphorous is selected from ortho phosphoric acid, pyro phosphoric acid, meta phosphoric acid and the like, and said oxide of titania is titanium dioxide. Further, the ratio of the salts of vanadium, phosphorous and titanium is in the range of 1:3:50 to 1:8:200. The invention also provides a process for the production of 3 & 4 cyanopyridines in high yields by vapour phase ammoxidation of respective methyl pyridines in presence of air and ammonia over V--P--Ti--O catalyst at moderate temperature in the range of 320.degree. to 450.degree. C. Preferably, the yields of 3 & 4 cyanopyridines are greater than 92% and 97% respectively, the molar concentrations of 3 & 4 methyl pyridines respectively are in the range of 0.5 to 3.0%, the O/NH.sub.3 is in the range of 1 to 5. In addition, the space velocities are in the range of 1500 to 4000 hour.sup.-1 and the dilution of catalyst with an inert medium is in the range of 0.5 to 5 (by volume) with respect to the volume of catalyst. |
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