Oxidation catalyst

An oxidation catalyst comprising boron phosphate impregnated with from 5 to 20 weight percent silver and its use to oxidize propylene, butene-1, butadiene-1,3 and methanol is disclosed. The oxidation takes place at from 200.degree. to 700.degree. C. Preferably water vapor is present.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a process for oxidizing olefins to 
unsaturated aldehydes and diolefins to cyclic ethers and alcohols to 
aldehydes and ethers using a silver/boron phosphate catalyst. 
2. Prior Art 
U.S. Pat. No. 4,320,031 discloses a process of catalytic oxidation 
dehydrogenation of alkenes or alkadienes to furan compounds using a silver 
molybdate catalyst promoted with phosphorus, arsenic, antimony or bismuth. 
Br. No. 967,241 discloses a process for the production of 
.alpha.,.beta.-unsaturated aliphatic carboxylic acids from olefins using a 
solid phosphoric acid catalyst which has been activated with one or more 
of copper, silver, iron, cobalt, nickel, antimony, bismuth, molybdenum, 
tungsten and uranium. 
German Auslegeschrift No. 1,160,858 discloses using a catalyst comprising a 
heavy metal oxide selected from copper oxide, silver oxide, chromium 
oxide, bismuth oxide, tungsten oxide and molybdenum oxide with boric acid 
and phosphoric acid to oxidize propylene. Acetic acid is the major product 
in the Examples. 
SUMMARY OF THE INVENTION 
The present invention relates to novel silver on boron phosphate catalysts 
and their use in the oxidation of methanol, propylene, butenes and 
butadiene under oxygen limiting conditions. 
DETAILED DESCRIPTION 
The catalysts of the present invention are silver impregnated on boron 
phosphate (BPO.sub.4). They are prepared by treating boron phosphate with 
a solution of a silver salt in a solvent. Silver nitrate is the preferred 
salt because the nitrate ion is readily removed by heating the impregnated 
boron phosphate. The resulting slurry of boron phosphate and silver salt 
solution is stirred for a suitable period such as from 10 mins. to 2 
hours. Following stirring, the solvent is removed by evaporation. The 
evaporation can be done under reduced pressure if desired. Following 
removal of the solvent, the catalyst is calcined in air using a gradual 
heat-up. If needed, the calcined catalyst can be reduced using hydrogen 
diluted with an inert gas such as nitrogen. Generally, the catalyst will 
contain from 5 to 20 percent by weight, based on boron phosphate, of 
silver. The resulting catalyst is in the form of a powder and it can be 
used either as the powder or it can be pelletized or granulated and the 
pellets or granules used. 
The catalyst is most useful for oxidizing propylene, butenes, butadiene-1,3 
and methanol. When oxidizing propylene, the predominant product is 
acrolein. When oxidizing butene-1, the predominant product is a mixture of 
methyl vinyl ketone and methyl ethyl ketone. When oxidizing butadiene-1,3, 
the predominant product is furan and hydrogenated furans such as 
dihydrofuran and tetrahydrofuran. When oxidizing methanol, the predominant 
products are formaldehyde and dimethyl ether. Depending on the starting 
material, the amount of oxygen in the feed stream should be from 0.05 to 
0.5 atom of oxygen per atom of starting material. Generally, the oxidation 
reaction is carried out at from 200.degree. to 700.degree. C., with from 
300.degree. to 500.degree. C. being the preferred range for oxidizing the 
olefins and from 500.degree. to 600.degree. C. being the preferred range 
when methanol is the starting material. 
Generally, the residence time when the material being oxidized is in 
contact with the catalyst is from 0.01 to 2 seconds with from 0.1 to 0.4 
seconds being the preferred range. 
The oxygen used generally will be diluted with an inert gas such as 
nitrogen or helium. Generally, air is a satisfactory source of oxygen. In 
some instances, it may be desired to further dilute the air with nitrogen 
or helium. 
In an especially preferred aspect of the invention, water vapor is 
incorporated in the feed stream. The water vapor serves to moderate the 
catalyst and thus improve both the conversion of the feedstock as well as 
the selectivity of the catalyst.

EXAMPLE 1 
Catalyst Preparation I 
In a 250 ml round bottom flask is placed 20 g of powdered boron phosphate. 
To this is added a solution of 3.4 g silver nitrate dissolved in 100 ml of 
acetonitrile solvent. The slurry is stirred at room temperature for 1/2 
hour. The solvent is then removed under reduced pressure. 
The resulting whitish powder is then charged into a quartz tube and heated 
to 200.degree. C. and maintained at that temperature for 2 hours with a 
current of air going through. Th temperature is raised over a period of 
about 1/2 hour to 500.degree. C. and kept at that temperature for 1 hour, 
after which the temperature is raised to 600.degree. C. and kept at this 
temperature for 2 hours. The resulting Ag/BPO.sub.4 catalyst is allowed to 
cool resulting in a slightly greyish, coarse powder. The catalyst can be 
used as such or in granular or pellet form in actual experimental 
evaluations. 
EXAMPLE 2 
Oxidation of Propylene 
A 10 mm inside diameter quartz tube is charged with a 1" (0.025 m) bed 
depth of the catalyst prepared as in Example 1 (as a coarse powder). The 
catalyst bed is heated externally using a band heater to 350.degree. to 
400.degree. C. 
A mixture of helium, air and propylene (3:2:2) is passed through this bed 
and the products leaving the reactor are analyzed by gas chromatography. 
The principal product besides unconverted starting material is acrolein. 
Small amounts of CO and CO.sub.2 are also observed. 
Oxidation of Propylene Using Metallic Silver 
Using the same reaction set up, a 1" bed depth of granular silver catalyst 
which passes a 20 mesh screen and is retained on a 30 mesh (U.S. sieve 
series) screen is evaluated as a catalyst under similar operating 
conditions. Only traces of acrolein are observed. 
Using Boron Phosphate 
Plain, powdered and granular boron phosphate is also evaluated under same 
conditions as above. Again, only traces of acrolein are found. 
EXAMPLE 3 
Catalyst Preparation II 
The catalyst was prepared as in Example 1 except as follows. After heat 
treatment in air at 600.degree. C., the catalyst is allowed to cool in a 
stream of nitrogen. After all oxygen is purged, the catalyst is heated in 
a stream of nitrogen and hydrogen. (90:10) for 1 hour at 100.degree. C. It 
is then cooled in a stream of nitrogen. The catalyst so prepared is 
greenish rather than greyish. 
EXAMPLE 4 
To a 5 inch (0.127 m) long stainless steel tube having an inside diameter 
of 3/8" (0.0095 m) is charged 9.5 g of the catalyst prepared as in Example 
1. The catalyst bed is maintained at 400.degree. C. using an external 
fluidized sand bed. The flow rates (as measured at standard temperature 
and pressure) to the catalyst bed are: propylene 63.2 cc/min., air 33.3 
cc/min. and nitrogen 56.3 cc/min. The off gases are analyzed by gas 
chromatography. Propylene conversion is 46.1% based on oxygen in the feed 
and the selectivity for acrolein is 28.8%. 
EXAMPLE 5 
Example 4 is repeated except the temperature is 500.degree. C. and the 
total flow rate (as measured at standard temperature and pressure) to the 
catalyst bed is about 150 cc/min. which contains 41.3% by volume 
propylene, 10% by volume water vapor, 21.8% by volume air and 26.9% by 
volume nitrogen. The conversion of propylene based on oxygen in the feed 
is 94.7% and the selectivity for acrolein is 81.8% 
EXAMPLE 6 
Example 4 is repeated except the temperature is 500.degree. C. and the 
total flow to the catalyst bed (as measured at standard temperature and 
pressure) is 266.1 cc/min. which contained by volume 37.6% propylene, 
19.8% air, 33.5% nitrogen and 9.1% water vapor. The conversion based on 
oxygen in the feed is 94.9% and the acrolein selectivity is 73.9%. 
EXAMPLE 7 
Oxidation of Butadiene 
Example 4 is repeated except 25.0 g of catalyst is used, the temperature is 
500.degree. C. and the total flow to the catalyst bed (as measured at 
standard temperature and pressure) is 100 ml/min. which contains by volume 
27.6 parts butadiene, 25 parts air, 25.0 parts water vapor and 22.4 parts 
nitrogen. The conversion of butadiene based on oxygen in the feed is 
90.9%. The selectivity to furan is 22.4% and to acrolein is 5.1%. Gas 
chromatographic analysis shows two other peaks besides furan and acrolein. 
They have the same retention times as a mixture of dihydrofuran and 
tetrahydrofuran. Based on this analysis the selectivity to furan, 
dihydrofuran and tetrahydrofuran mixture is 59.6%. 
EXAMPLE 8 
Boron phosphate is screen pelleted to pass a 10 mesh and be retained on a 
20 mesh U.S. sieve series screen, and then heated to 800.degree. C. for 16 
hours to reduce water sensitivity. Twenty-five grams of the thus prepared 
boron phosphate is impregnated with a solution of 3.93 g silver nitrate 
dissolved in 23 cc water. Excess water is removed under reduced pressure 
and the pellets are dried at 120.degree. C. The catalyst is reduced in a 
stream of hydrogen at 300.degree. C. for 2 hours and an additional 2 hours 
at 600.degree. C. prior to use. The thus prepared catalyst is packed in a 
3/8" (0.0095 m) inside diameter titanium tube. The tube is heated to 
500.degree. C. and the feed stream is passed through the heated catalyst 
bed at the following rates measured at standard pressure and temperature: 
helium 75 cc/min., oxygen 8 cc/min., butadiene 48 cc. min., and water 
vapor 109 cc/min. The contact time is about 0.3 seconds. The butadiene 
conversion is 3.1%. As based on carbon, the selectivity to furan is 33.2%, 
to maleic acid is 12.9%, and to monobasic acids is 9.6%.