Catalyst for the oxidation of acrolein and methacrolein to acrylic acid and methacrylic acid, respectively

Catalysts which consist of a molded carrier, the surface of which is coated with an active catalyst composition of the general formula Mo.sub.12 A.sub.a B.sub.b C.sub.c D.sub.d O.sub.x, where A is V and/or W, B is Cu and/or Fe and/or Mn and/or Ni and/or Cr, C is Nb and/or Ta and/or Bi and/or Sb and/or Sn and/or Th and/or Ce and/or U, D is Li and/or Na and/or K and/or Rb and/or Cs and/or Tl and a is from 0.1 to 18, b is from 0 to 8, c is from 0 to 10, d is from 0 to 2 and x is from 36 to 135, which are particularly active and selective for the oxidation of acrolein and methacrolein with oxygen-containing gases to give acrylic acid and methacrylic acid, respectively, are obtained by first manufacturing the catalyst composition, before applying it to the carrier, from thermally easily decomposed salts of the components by mixing aqueous solutions, slurries or moist solid masses of the salts of the components, drying the mixture and calcining the dried composition at from 140.degree. to 600.degree. C., then milling it to a particle size of less than 150 .mu.m and thereafter applying it, as a mixture with water, as a layer from 10 to 1,500 .mu.m thick, to the premolded carrier, which has a rough surface.

The present invention relates to a new catalyst for the gas phase oxidation 
of acrolein and methacrolein to give acrylic acid and methacrylic acid, 
respectively, in which an active catalyst layer is applied to an inert 
carrier core. 
A large number of catalysts containing molybdenum oxide have been disclosed 
for the gas phase oxidation of acrolein and methacrolein to acrylic acid 
and methacrylic acid, respectively. As additional activating components, 
these catalysts in most cases contain vanadium and/or tungsten and may or 
may not contain iron and/or copper and/or manganese and/or nickel and/or 
phosphorus as well as niobium and/or tantalum and/or bismuth and/or 
antimony and/or tin and/or thorium and/or cerium, alkali metals, 
especially sodium, potassium and cesium, and thallium. Such catalysts are 
disclosed, for example, in U.S. Pat. No. 3,567,772, Canadian Pat. No. 
941,384, British Pat. No. 1,353,864, U.S. Pat. No. 3,773,692, British Pat. 
No. 1,337,865, British Pat. No. 1,387,776 and German Laid-Open Application 
DOS No. 2,517,148. They may be represented by the general formula 
Mo.sub.12 A.sub.a B.sub.b C.sub.c D.sub.d P.sub.e O.sub.x where A is V 
and/or W, B is Cu and/or Fe and/or Mn and/or Ni and/or Cr, C is Nb and/or 
Ta and/or Bi and/or Sb and/or Sn and/or U and/or Th and/or Ce, D is Li 
and/or Na and/or K and/or Rb and/or Cs and/or Tl, and a is from 0.1 to 18, 
b is from 0 to 8, c is from 0 to 10, d is from 0 to 2, e is from 0 to 5 
and x is from 36 to 136. Oxidic catalysts of this nature may be employed 
for the gas phase oxidation of acrolein and methacrolein, either 
unsupported or supported, and in the latter case the inert carriers used 
are mostly aluminum oxides, silicon dioxide and their mixtures, silicon 
carbide, titanium dioxide and also zirconium dioxide. To manufacture 
catalysts of this nature, the common procedure is to mix mixtures of 
aqueous solutions of salts of the components, eg. of ammonium molybdate, 
ammonium vanadate, ammonium tungstate and nitrates of iron, copper or 
manganese, and impregnate the carrier with the mixture, from which the 
water may or may not have been evaporated completely or partially, or to 
coat the carrier with the composition. If the composition contains water, 
the material is dried and calcined, after the water has been evaporated 
off, the calcination being carried out in most cases at above 150.degree. 
C., especially at from 180.degree. to 600.degree. C. This gives oxide 
catalysts which carry the active catalyst composition on the inner and/or 
outer surface of the carrier. A disadvantage of the supported oxide 
catalysts thus obtained is that they are sensitive to mechanical stresses 
resulting from friction, as occurs, eg. in the calcination stages of the 
process of manufacture or when filling reactor tubes. In addition, their 
activity and selectivity is in many cases not fully satisfactory. Finally, 
the active composition is frequently not distributed uniformly over the 
surface of the carrier. The manufacture of supported catalysts by applying 
a mixture of the active metal oxides to carriers was proposed in British 
Pat. No. 1,296,922. 
U.S. Pat. No. 3,956,377 discloses a special process for the manufacture of 
oxide catalysts, in the form of layers, for the gas phase oxidation of 
acrolein and methacrolein to acrylic acid and methacrylic acid 
respectively, in which, for example, molybdenum oxide, vanadium oxide and 
tungsten metal powder are suspended in water by heating under reflux, the 
resulting slurry is evaporated and the residue is dried for several days 
at 115.degree. C. The active catalyst composition thus obtained is then 
applied to the carrier, which has been pre-moistened with water, the 
application being effected by tumbling the moist carrier with a powder of 
the active catalyst. Catalysts manufactured in this way are frequently 
non-selective. 
We have found that catalysts for the oxidation of acrolein and methacrolein 
with oxygen-containing gases to give acrylic acid and methacrylic acid, 
respectively, which catalysts consist of a conventional molded carrier, 
the surface of which is coated with an active catalyst composition of the 
general formula Mo.sub.12 A.sub.a B.sub.b C.sub.c D.sub.d O.sub.x, where A 
is V and/or W, B is Cu and/or Fe and/or Mn and/or Ni and/or Cr, C is Nb 
and/or Ta and/or Bi and/or Sb and/or Sn and/or Th and/or Ce and/or U, D is 
Li and/or Na and/or K and/or Rb and/or Cs and/or Tl and a is from 0.1 to 
18, b is from 0 to 8, c is from 0 to 10, d is from 0 to 2 and x is from 
36.25 to 135 are particularly advantageous if the catalyst composition, 
before applying to the carrier, is manufactured from thermally easily 
decomposed salts of the components by mixing aqueous solutions, slurries 
or moist solid masses of the salts of the components, drying the mixture 
and calcining the dried composition at from 140.degree. to 600.degree. C., 
and is comminuted, for example by milling to a particle size of less than 
150 .mu.m, and applied, as a mixture with water, as a layer from 10 to 
1,500 .mu.m thick, to the premolded carrier, which has a rough surface. 
Suitable carriers for the manufacture of the new oxide catalysts are the 
conventional inert carriers, for example highly calcined aluminum oxides 
(preferably in the .alpha.-phase), natural and synthetic silicates and 
aluminosilicates, eg. mullite and steatite, silicon carbide and zirconium 
oxides and/or titanium oxides. The inner surface area of the carriers may 
be varied within wide limits and is in general from less than 1 to 20 
m.sup.2 /g, eg. frequently from 1 to 20 m.sup.2 /g, especially from 1 to 
10 m.sup.2 /g. The porosity is generally not critical and is mostly from 1 
to 65%, and from 50 to 85% of the pores have a diameter of from 20 to 
1,500 .mu.m. The carriers are pre-molded in the conventional manner and 
are preferably spherical, but it is also possible to employ, for example, 
pre-molded carriers in the shape of rings or cylinders. The mean diameter 
of the pre-molded carrier is in most cases from 2 to 10 mm, preferably 
from 2 to 7 mm and especially from 3 to 6 mm. The materials have a rough 
surface, the recesses being mostly from 10 to 1,500 .mu.m, especially from 
20 to 750 .mu.m. 
Preferred active catalyst compositions for oxidizing acrolein to acrylic 
acid are those of the formula Mo.sub.12 A.sub.a B.sub.b C.sub.c D.sub.d 
O.sub.x, where A is vanadium and/or tungsten, especially vanadium and 
tungsten, B is copper, iron, chromium and/or manganese, especially copper, 
or copper in combination with one or more of the other components B, C is 
antimony, niobium, tantalum and/or tin, D is lithium, sodium, potassium, 
rubidium, cesium and/or thallium and a is from 2 to 18, preferably from 
0.5 to 12 for vanadium, from 0.2 to 6 for tungsten and from 2.5 to 18 for 
vanadium+tungsten, b is from 0.5 to 8, and for copper is preferably from 
0.5 to 6, especially from 1 to 5, c is from 0 to 10 and d is from 0 to 
0.5, preferably from 0 to less than 0.1, and x is from 41 to 127.75. 
The component of group C as a rule does not improve the catalyst properties 
as far as the oxidation of acrolein to acrylic acid is concerned. This is 
also true of the component of group D, and higher concentrations of alkali 
metal oxides (d&gt;0.5) in general reduce the activity, so that as a rule 
alkali metals are only present in the active catalyst composition in such 
concentration in such concentrations as result from using raw materials of 
commercial purity; for example, commercial grades of ammonium molybdate or 
molybdic acid of technical catalyst quality frequently contain up to 200, 
sometimes up to 500, ppm of potassium, whilst technical-grade carriers may 
contain up to 0.5% by weight of sodium and/or potassium. 
The starting materials for the manufacture of the active catalyst 
composition are, in general, thermally easily decomposed salts of the 
components, of which an intimate mixture is prepared by, for example, 
mixing their aqueous solutions and then dehydrating the solution and 
drying the residue. Thereafter, the mixture is converted to the oxides by 
one or more calcinations at above the decomposition point of the salts and 
below or at the optimum final calcination temperature, this process being 
carried out in the absence of the molded carrier. Preferred easily 
decomposed salts are the ammonium salts of the oxy-acids of molybdenum, 
vanadium and tungsten, vanadyl oxalate, and the nitrates, oxalates, 
hydroxides, carbonates, sulfates, acetates and/or formates of the cationic 
components, of which aqueous solutions are preferably prepared at an 
elevated temperature, eg. at from 50.degree. to 100.degree. C., and 
preferably at a pH of from 2 to 6. On mixing, suspensions are in most 
cases obtained, which can be dried and can then, if necessary after 
addition of water, be homogenized, eg. by kneading, and densified. The 
calcination is carried out at from 140.degree. to 600.degree. C., 
preferably from 180.degree. to 450.degree. C. and especially from 
230.degree. to 420.degree. C. In a preferred embodiment of the manufacture 
of the catalysts, the dehydrated mixtures of the easily decomposed salts 
are first calcined at from 180.degree. to 350.degree. C., especially at 
from 230.degree. to 300.degree. C., and then at from 350.degree. to 
600.degree. C., preferably at from 370.degree. to 450.degree. C., and 
especially at from 380.degree. to 420.degree. C., in air. For the 
manufacture of certain active catalyst compositions, eg. those containing 
iron, it is sometimes of advantage to carry out the calcination in an 
inert atmosphere (eg. nitrogen) or a slightly reducing atmosphere (eg. a 
gas mixture containing propylene and/or acrolein). 
After calcining the oxide mixture and comminuting it to a particle size of 
less than 150 .mu.m, the active catalyst composition, preferably mixed 
with a wetting liquid which evaporates easily, is applied to the 
pre-molded carrier, the particle size of the pulverulent active catalyst 
composition being less than 150 .mu.m, preferably less than 80 .mu.m and 
especially less than 50 .mu.m. The composition may be applied, for 
example, by granule coating or spraying the pre-molded, eg. spherical, 
carrier with a suspension of the active catalyst composition in water, the 
carrier being at from room temperature, ie. about 20.degree. C., to 
300.degree. C. The thickness of the layer of active catalyst composition 
on the carrier surface should be from 10 to 1,500 .mu.m, preferably from 
20 to 750 .mu.m and especially from 50 to 400 .mu.m, corresponding to the 
finished catalyst containing from about 0.05 to 0.60 kg of active catalyst 
composition per liter (Bulk volume) of finished catalyst. 
When applying the active catalyst composition to the premolded carrier it 
can be of advantage to add small amounts, in general from 0.5 to 20, 
preferably from 1 to 10, percent by weight of materials which improve the 
adhesion of the active composition to the carriers. Suitable materials of 
this nature are inorganic hydroxo salts and compounds which in aqueous 
solution hydrolyze to give hydroxides by hydroxo complexes and which are 
catalytically inert or are in any case a constituent of the active 
catalyst composition. Examples are aluminum chloride, molybdenum sulfide 
and/or basic aluminum salts, eg. basic aluminum nitrate. However, in the 
case of the active catalysts having the compositions stated above to be 
preferred, the addition of such materials is in general not necessary. 
The carriers coated with the active composition are then dried, if 
necessary, at below 180.degree. C., preferably below 150.degree. C. In the 
case of granule coating, the pulverulent active catalyst composition is 
fed, at constant speed, onto the vigorously agitated, continuously 
moistened carrier in a rotary mixer or on a granulating disc. 
The catalysts of the invention are outstandingly suitable for oxidizing 
acrolein and methacrolein with oxygen-containing gases, under otherwise 
conventional conditions, to give acrylic acid and methacrylic acid, 
respectively. The catalysts of the invention are distinguished by a 
particularly high selectivity and activity when used for the industrial 
manufacture of acrylic acid by oxidizing acrolein; surprisingly, the 
selectivity and activity achieved in tubes with diameters useful for 
production purposes, ie. 15 mm and above, are greater, under comparable 
conditions, than those achieved with catalysts disclosed in, for example, 
U.S. Pat. No. 3,956,377. Furthermore, the new catalysts show lower 
abrasion losses of catalytic composition, for example whilst being packed 
into a reactor, and have a particularly uniform composition and uniform 
thickness of the active layer. They are especially suitable for use with 
high space velocities of greater than 2,000 h.sup.-1 and low water vapor 
concentrations of less than 20% by volume, and with linear gas velocities 
of greater than 100 cm/sec. especially in tubes having a diameter of from 
15 to 40 mm at from 200.degree. to 350.degree. C. In the case of tubes 
having diameters greater than 20 mm it can be of advantage to dilute the 
catalyst with from 10 to 60% by volume of moldings of an inert material or 
of a catalyst of lower activity, so that in the direction of flow the 
activity increases from a value of from 40 to 80% of the maximum to 100% 
of the latter.

In the Examples which follow, parts are by weight, bearing the same 
relation to parts by volume as one kilogram to the liter. To test the 
catalytic properties of the catalysts from Examples 1 to 14, 40 ml of one 
of the catalysts are packed into a tube of 15 mm internal diameter and the 
tube is then heated to the test temperature in a salt bath. Per hour, 3.4 
liters (S.T.P.) of acrolein, 28 liters (S.T.P.) of air, 30 liters (S.T.P.) 
of nitrogen and 25 liters (S.T.P.) of steam are passed through the tube. 
The analysis of the off-gas gives the conversions of acrolein and yields 
of acrylic acid, acetic acid and carbon oxides (CO.sub.x) shown in the 
Tables. 
EXAMPLES 1 to 9 
(Active composition Mo.sub.12 V.sub.4.6 W.sub.2.4 Cu.sub.2.2 O.sub.56.9 ; 
various carriers) 
Manufacture of the catalysts: 
65 parts of ammonium paratungstate, 54 parts of ammonium metavanadate and 
212 parts of ammonium heptamolybdate are dissolved, in this sequence, in 
2,500 parts of water at 95.degree. C. A solution of 54 parts of copper 
nitrate in 125 parts of water is then added, the mixture is evaporated and 
the residue is dried at 110.degree. C. It is then kneaded, with addition 
of 50 parts of water, for 31/2 hours, dried for 4 hours at 250.degree. C. 
in a rotary oven, and calcined for 3 hours at 395.degree. C. The calcined 
composition is milled to a particle size less than 150 .mu.m. 
30 parts of the active pulverized catalyst composition mixed with from 10 
to 30 parts of water are applied to 100 parts by volume (bulk volume) of 
magnesium silicate spheres of diameter 3 mm, and then dried at 100.degree. 
C. (Example 1). To manufacture the catalysts of Examples 2 to 9, 100 parts 
by volume of the carriers stated for these Examples are used, and in other 
respects the procedure described above is followed. The catalysts are 
tested as described above; the results, together with the abrasion loss, 
are shown in Table 1. The abrasion loss is the proportion of active 
catalyst composition, in percent by weight of the composition present on 
the carrier, which is abraded under the following conditions: 50 parts by 
volume of catalyst are tumbled for 5 minutes at constant speed on a 
covered disc and the proportion abraded is then sieved off and weighed. 
TABLE 1 
__________________________________________________________________________ 
Catalyst: 
parts 
Carrier of active 
Active Proportion 
Inner 
composition 
mean 
composition Open (in %) of 
surface 
per part by 
thickness 
particle size 
porosity, 
macropores of 
area 
volume of 
of layer 
Example 
in .mu.m 
Nature 
% 20-1,500 .mu.m 
m.sup.2 /g 
carrier 
.mu.m 
__________________________________________________________________________ 
1 &lt;80 Mg silicate 
0 0 &lt;&lt;1 0.300 130 
spheres 
3-3.5 mm 
2 &lt;80 SiO.sub.2 
&gt;50 8 622 0.300 175 
spheres 
3.5 mm 
3 &lt;50 .alpha.-Al.sub.2 O.sub.3 
3 about 50 
0.04 
0.15 70 
3-5 mm 
Al.sub.2 O.sub.3ha. 
34 84 &lt;1 0.300 125 
spheres 
3-3.5 mm 
5 &lt;80 .alpha.-Al.sub.2 O.sub.3 
34 84 &lt;1 0.300 125 
spheres 
3-3.5 mm 
6 &lt;80 .alpha.-Al.sub.2 O.sub.3 
34 84 &lt;1 0.224 105 
spheres 
3-3.5 mm 
7 &lt;50 .alpha.-Al.sub.2 O.sub.3 
34 84 &lt;1 0.182 90 
spheres 
3-3.5 mm 
8 &lt;80 mullite 
25 63 4.5 0.258 215 
spheres 
5-6 mm 
9 &lt;50 mullite 
25 63 4.5 0.15 130 
spheres 
5-6 mm 
__________________________________________________________________________ 
The surface recesses are &lt;10 .mu.m for the carrier of Example 1, &lt;20 .mu. 
for the carrier of Example 2, from 50 to 250 .mu.m for the carriers of 
Examples 3 to 7 and from 20 to 300 .mu.m for the carriers of Examples 8 
and 9. 
Activity test 
Bath 
temperature Conversion 
yield, mole % Abrasion loss, 
Ex. .degree.C. 
mole % acrylic acid 
acetic acid 
CO.sub.x 
% by weight 
__________________________________________________________________________ 
1 289 99.5 93 2 4.5 7 
2 275 94.5 84 1.7 8.5 5 
3 282 99.1 93 1.6 4.5 2 
4 279 97.4 92 1.4 4 3 
5 275 98.4 93 0.9 4.5 2 
277 .about.100 
6 295 98.5 92 1.5 5 2 
7 298 97.5 91.5 1.2 4.7 0.2-0.7 
8 284 99 92.9 1.1 5 1.5 
9 305 96.7 89.5 1.9 5.3 0.5 
__________________________________________________________________________ 
EXAMPLES 10 to 14 
(Catalysts obtained from various active compositions) 
Catalyst compositions of various constitutions (cf. Table 3) are 
manufactured by the method described for Examples 1 to 9, using the easily 
decomposed salts shown in Table 2. After calcining, the active composition 
is in each case milled to a particle size of less than 80 .mu.m and 
sprayed, as an aqueous suspension with a weight ratio of active catalyst 
composition to water of from 1:1 to 1:2, onto the carrier spheres at from 
25.degree. to 80.degree. C. The activity of the catalysts is tested as 
described above and the results are summarized in Table 3 below. 
TABLE 2 
______________________________________ 
Parts by weight in Example 
Easily decomposed salt 
10 11 12 13 14 
______________________________________ 
iron(III) nitrate 44.5 222. -- -- -- 
Mn-acetate-tetrahydrate 
-- -- 30 -- -- 
SnO.sub.2 -- -- -- 22.5 -- 
Ammonium dichromate 
-- -- -- -- 7.5 
Copper(II) nitrate 
28.5 54 28.5 28.5 54 
Ammonium heptamolybdate 212 
Ammonium metavanadate 
54 35 54 54 54 
Ammonium paratungstate 
65 32.3 65 65 65 
______________________________________ 
TABLE 3 
__________________________________________________________________________ 
Parts of 
active 
composi- 
tion per 
Particle part by 
Active composition 
size volume of 
Example 
formula .mu.m 
Carrier carrier 
__________________________________________________________________________ 
10 Mo.sub.12 V.sub.4.6 W.sub.2.4 Cu.sub.1.2 Fe.sub.1.1 O.sub.57.6 
&lt;50 .alpha.-Al.sub.2 O.sub.3, 3-4 mm, 
0.3 
inner surface area 
&lt;1 m.sup.2 /g 
porosity = 34% 
proportion of pores 
of 20-1,500 .mu.m = 84%, 
surface recesses from 
20 to 300 .mu.m 
11 Mo.sub.12 V.sub.3 W.sub.1.2 Cu.sub.2.2 O.sub.49.3 
&lt;50 .alpha.-Al.sub.2 O.sub.3, 3-4 mm, 
0.3 
inner surface area 
&lt;1 m.sup.2 /g, 
porosity = 34% 
proportion of pores 
of 20-1,500 .mu.m = 84%, 
surface recesses from 
20 to 300 .mu.m 
12 Mo.sub.12 V.sub.4.6 W.sub.2.4 Cu.sub.1.2 Mn.sub.1.2 O.sub.57.1 
&lt;20 .alpha.-Al.sub.2 O.sub.3, 3-4 mm, 
0.3 
inner surface area 
&lt;1 m.sup.2 /g, 
porosity = 34% 
proportion of pores 
of 20-1,500 .mu.m = 84%, 
surface recesses from 
20 to 300 .mu.m 
13 Mo.sub.12 V.sub.4.6 W.sub.2.4 Cu.sub.1.2 Sn.sub.1.2 O.sub.58.3 
&lt;20 .alpha.-Al.sub.2 O.sub.3, 3-4 mm, 
0.3 
inner surface area 
&lt;1 m.sup.2 /g, 
porosity = 34% 
proportion of pores 
of 20-1,500 .mu.m = 84% 
surface recesses from 
20 to 300 .mu.m 
14 Mo.sub.12 V.sub.4.6 W.sub.1.2 Cu.sub.2.2 Cr.sub.0.6 O.sub.54.2 
&lt;20 .alpha.-Al.sub.2 O.sub.3, 3-4 mm, 
0.3 
inner surface area 
&lt;1 m.sup.2 /g, 
porosity = 34% 
proportion of pores 
of 20-1,500 .mu.m = 84%, 
surface recesses from 
20 to 300 .mu.m 
__________________________________________________________________________ 
Activity test 
Thickness 
of layer, Bath Conversion, 
yield, mole % 
Ex. .mu.m temperature 
mole % acrylic acid 
acetic acid 
CO.sub.x 
__________________________________________________________________________ 
10 125 298 97 90 1.5 5.5 
302 100 91.5 2 7 
11 284 99.4 93 1.6 4.8 
12 290 99.3 92 1.1 6.2 
13 292 48.2 90.2 1.6 6.1 
14 288 98 91 1.4 5.6 
__________________________________________________________________________ 
EXAMPLE 15 
1,000 ml of a spherical catalyst (sphere diameter about 5.3 mm), 
manufactured as described in Example 8, were packed into a steel tube of 4 
m length and 25 mm diameter and the surrounding salt bath was heated at 
286.degree. C. (2nd stage). A catalyst specific for the conversion of 
propylene to acrolein was packed into an upstream reactor (first stage). 
This latter catalyst was precipitated by the method of Example 1 of German 
Laid-Open Application DOS No. 2,338,111, dried, calcined at 300.degree. 
C., mixed with 2% by weight of graphite powder, molded to give 3.times.3 
mm pellets and calcined for 11/2 hours at 580.degree. C. It has the 
composition Mo.sub.12 BiIn.sub.0.1 Fe.sub.2 Ni.sub.6.5 P.sub.0.06 
Si.sub.10 O.sub.6.03 and contained, relative to the above formula, 0.05 
atom of potassium, as a natural impurity of the ammonium molybdate used as 
the raw material. The catalyst in the upstream reactor was diluted with 
200 ml of 3 mm spheres of magnesium silicate in such a way that the 
proportion by volume of the catalyst increased linearly in the direction 
of flow from 60% to 100%. A mixture of 105 liters (S.T.P.) of fresh 
propylene, 1,000 liters (S.T.P.) of fresh air and 1,200 liters (S.T.P.) of 
purified off-gas from the second stage reactor was passed hourly over the 
catalyst of the upstream reactor. The gaseous mixture from the upstream 
reactor was then passed to the catalyst tube. According to analysis of the 
material leaving the catalyst tube (second stage), the yield of acrylic 
acid, based on fresh propylene employed, was 80.8 mole % and the yield of 
carbon oxides resulting from combustion of acrolein and propylene in the 
second stage was 3.5 mole %. Based on the acrolein (and acrylic acid) 
produced in the first stage, the yield of acrylic acid and carbon oxides 
was calculated to be, respectively, 93 and 3.9 mole %, the acrolein 
conversion being 98%. 
EXAMPLE 16 
The experiment of Example 15 is repeated, except that the second part of 
the reactor is packed with 832 ml of a catalyst manufactured as described 
in Example 5. The spherical catalyst (diameter about 3.5 mm) was diluted 
with 168 ml of 3 mm steatite spheres in such a way that the proportion by 
volume of the catalyst-coated spheres increased linearly in the direction 
of flow from 60% by volume to 100%. At a bath temperature of 283.degree. 
C., yields of acrylic acid and CO of, respectively, 82.3 and 2.5 mole % 
based on fresh propylene employed, or of 95% and 2.9%, based on acrolein 
and acrylic acid formed in the first stage, were obtained. The acrolein 
conversion was 98 mole %. 
COMATIVE EXPERIMENTS 
(A) 65 parts of ammonium paratungstate, 54 parts of ammonium metavanadate 
and 212 parts of ammonium heptamolybdate are dissolved, in the stated 
sequence, in 2,500 parts of water at 95.degree. and a solution of 54 parts 
of copper nitrate in 125 parts of water is added to the solution, followed 
by 605 parts of .alpha.-aluminum oxide having a particle size of from 40 
to 150 .mu.m. The mixture is evaporated whilst being stirred, and is dried 
and calcined at from 230.degree. to 250.degree. C. Spheres of from 3 to 
3.5 mm diameter are molded from the resulting calcined active composition, 
and are further calcined for 3 hours at 400.degree. C. in air in a rotary 
oven. The activity of the catalyst (A) is tested as described immediately 
before Example 1. The results are shown in Table 4 below. 
(B) 65 parts of ammonium paratungstate, 54 parts of ammonium metavanadate 
and 212 parts of ammonium heptamolybdate are dissolved, in the stated 
sequence, in 2,500 parts of water at 95.degree. C., a solution of 54 parts 
of copper nitrate in 125 parts of water is added and 625 parts of 
.alpha.-aluminum oxide spheres of diameter from 3 to 3.5 mm, of the type 
described in Example 5, are impregnated with the mixture. They are then 
dried at 110.degree. C. and calcined for 5 hours at 400.degree. C. in a 
rotary oven. The catalyst (B) is tested as described immediately before 
Example 1; the results are shown in Table 4 below. 
(C) 65 parts of ammonium paratungstate, 54 parts of ammonium metavanadate 
and 212 parts of ammonium heptamolybdate are dissolved, in the stated 
sequence, in 2,500 parts by weight of water at 95.degree. C. and a 
solution of 54 parts of copper nitrate in 125 parts of water is added. 625 
parts of .alpha.-aluminum oxide spheres of diameter from 3 to 3.5 mm, of 
the type described in Example 5, are sprayed with the mixture at 
100.degree.-110.degree. C., whereupon the water evaporates. The 
impregnated spheres are then calcined for 4 hours at from 230.degree. to 
250.degree. C. followed by 3 hours at 400.degree. C. in a rotary oven. The 
catalyst obtained is tested as described immediately before Example 1; the 
results are shown in Table 4 below. 
(D) Example 5 is repeated except that the particle size of the active 
composition is from 310 to 600 .mu.m. The catalyst obtained is tested as 
described immediately before Example 1; the results obtained are shown in 
Table 4 below. 
(E) Example 6 of German Laid-Open Application DOS No. 2,526,238 was 
repeated. To do this, 216 parts of MoO.sub.3, 34.1 parts of V.sub.2 
O.sub.5, 27.59 parts of tungsten powder, 60.43 parts of Cu 
(NO.sub.3).sub.2.3 H.sub.2 O and 8.42 parts of SnO were suspended in 1,000 
parts of water and the mixture was boiled under reflux for 20 hours. The 
suspension was then evaporated and the residue dried for 3 days at 
115.degree. C. A coherent dry mass was obtained, which was milled to give 
a powder. 45 parts of powder were applied to 100 parts of Al.sub.2 O.sub.3 
(SA 5.252 Alundum) of mean particle size 1/8 inch. The catalyst was tested 
as described immediately before Example 1. The results are shown in Table 
4. 
TABLE 4 
______________________________________ 
Com- Activity test 
para- Abrasion 
Bath 
tive loss tempera- Con- Yield, mole % 
Ex- % by ture version 
acrylic 
acetic 
ample weight .degree.C. 
mole % acid acid CO.sub.x 
______________________________________ 
A 3 275 99 87 3 9 
B .sup.(1) 268 97 88 2.3 6.6 
C 12-15 330 99 87 3 8 
D &gt;20.sup.(2) 
305 97 90.5 1.5 5 
E 1-3 290 20.5 9 0.8 10.7 
320 55.6 42 1.6 12 
______________________________________ 
.sup.(1) A high proportion of the spheres was stuck together by the 
deposit of active composition, to form larger agglomerates and the 
catalyst was therefore industrially unusable in this form. 
.sup.(2) (low adhesion of the active shell)