Method for the preparation of methacrylic acid

Methacrylic acid can be produced from methacrolein with a high reaction percentage of methacrolein and a high selectivity percentage of methacrylic acid, by bringing a reaction feed containing methacrolein and molecular oxygen into contact with an oxidation catalyst at a temperature of 200 to 450.degree. C, the oxidation catalyst comprising oxides of molybdenum, phosphorus, calcium, at least one element selected from the group consisting of arsenic, bismuth, tin, titanium, tantalum and boron and, optionally, at least one element selected from the group consisting of antimony, niobium and magnesium.

The present invention relates to a method for the preparation of 
methacrylic acid. More particularly, the present invention relates to a 
method for the preparation of methacrylic acid by catalytically oxidizing 
methacrolein in vapor phase with molecular oxygen at an elevated 
temperature. 
Various methods are known for the preparation of unsaturated aliphatic 
carboxylic acids, for example, acrylic acid and methacrylic acid, by 
catalytically oxidizing unsaturated aliphatic aldehydes, for example, 
acrolein and methacrolein, in vapor phase with molecular oxygen in the 
presence of an oxidation catalyst at an elevated temperature. In these 
conventional methods, the major methods relate to the production of 
acrylic acid and the minor methods concern the preparation of methacrylic 
acid. Broadly, it is known that when the conventional oxidation catalyst 
is applied to the oxidation of methacrolein into methacrylic acid, the 
percentage of selective conversion of the oxidized methacrolein into the 
methacrylic acid is smaller than that of the acrolein into acrylic acid 
when the same catalyst as mentioned above is applied to the oxidation of 
acrolein. It is also known that when the conventional oxidation catalyst 
which is useful for the conversion of acrolein into acrylic acid is 
utilized to oxidize the methacrolein into methacrylic acid, the percentage 
of selective conversion of the oxidized methacrolein into methacrylic acid 
is relatively low. The difference in the catalytic effect of the 
conventional oxidation catalyst between the oxidation of acrolein and the 
oxidation of methacrolein seems to be derived from the difference in 
molecular structures between acrolein and methacrolein. Methacrolein has a 
branched atomic group from a backbone atomic group thereof, while acrolein 
has no branched atomic group. Due to the branched atomic group, the 
oxidation of methacrolein is more difficult than that of acrolein. One 
attempt to oxidize methacrolein is contained in Japanese Patent 
Application Publication No. 10308/1960 which discloses a new oxidation 
catalyst consisting of oxides of molybdenum and phosphorus, that is, 
Mo-P-O type. This type of catalyst is effective to oxidize both acrolein 
and methacrolein. However, when this type of catalyst is utilized for 
oxidizing methacrolein to prepare methacrylic acid, the percentage of 
selective conversion of the oxidized methacrolein into methacrylic acid is 
relatively low, that is about 44%, as indicated in Example 5 in the above 
Publication. 
Under these circumstances, a new catalyst capable of oxidizing methacrolein 
into methacrylic acid with a high percentage of selective conversion of 
the oxidized methacrolein into methacrylic acid, is desired. 
As a result of various studies, the inventors have discovered that in the 
Mo-P-O type catalyst, the addition of catalytic calcium ingredient thereto 
is effective to improve the percentage of selective conversion of the 
oxidized methacrolein into methacrylic acid. Further, it was discovered by 
the inventors that the addition of at least one catalytic ingredient 
selected from the group consisting of arsenic, bismuth, tin, titanium, 
tantalum and boron, to the Mo-P-Ca-O type catalyst, is highly effective to 
improve both the percentage of reaction of methacrolein and the percentage 
of selective conversion of the oxidized methacrolein into methacrylic 
acid. The present invention has been developed on the basis of the 
above-mentioned discoveries. 
An object of the present invention is to provide a method for the 
preparation of methacrylic acid by oxidation of methacrolein with a high 
percentage of selective conversion of the oxidized methacrolein into 
methacrylic acid. 
The other object of the present invention is to provide a method for the 
preparation of methacrylic acid by using an oxidation catalyst which is 
capable of converting methacrolein into methacrylic acid with a high 
percentage of selective conversion of the oxidized methacrolein into 
methacrylic acid and with a high reaction percentage of methacrolein. The 
percentage of selective conversion of the oxidized methacrolein into 
methacrylic acid used above is expressed by the term "selectivity 
percentage of methacrylic acid" hereinafter. 
The objects mentioned above can be accomplished by the method of the 
present invention, which comprises bringing a reaction feed containing 
methacrolein in vapor phase and molecular oxygen into contact with an 
oxidation catalyst comprising oxides of molybdenum, phosphorus, calcium 
and at least one element selected from the group consisting of arsenic, 
bismuth, tin, titanium, tantalum and boron, at a temperature of 
200.degree. to 450.degree. C. 
In the method of the present invention, the oxidation catalyst may consists 
of an oxide composition of the formula (I): 
EQU mo.sub.a P.sub.b Ca.sub.c X.sub.d O.sub.e (I) 
wherein X represents at least one member selected from the group consisting 
of arsenic, bismuth, tin, titanium, tantalum and boron atoms, the 
subscripts a, b, c and d respectively denote the numbers of the respective 
element atoms, said numbers being within the ranges, a=5 to 15, b=1 to 3, 
c=0.1 to 3 and d=0.1 to 3, and the subscript e represents the number of 
oxygen atoms which corresponds to the oxides formed from the 
above-mentioned elements and satisfies the average valency of the 
elements, said number e being within the range of 16 to 60. 
As is mentioned above, the catalyst usable for the method of the present 
invention may be an oxide composition in which the catalytic ingredient 
element atoms are combined with oxygen atoms so as to form simple oxides 
or complex oxides wherein two or more catalytic ingredient element atoms 
are combined with each other and with oxygen atoms. Further, in the 
catalyst, one or more catalytic ingredient elements other than molybdenum 
may be combined with molybdenum and oxygen so as to form a molybdate salt. 
The oxidation catalyst mentioned above can be prepared by any of known type 
of methods for the conventional oxidation catalyst, for example, by 
providing an aqueous liquid containing therein a molybdenum-containing 
compound, a phosphorus-containing compound, a calcium-containing compound 
and at least one compound selected from the group consisting of arsenic-, 
bismuth-, tin-, titanium-, tantalum- and boron-containing compounds; 
evaporating the aqueous liquid to form a solid material, and; calcining 
the dried solid material at a temperature of 300.degree. to 500.degree. C. 
The compounds containing the catalytic ingredient elements may be salts 
such as nitrate, hydroxides, oxides and acids containing the catalytic 
ingredient elements. For example, the sources of molybdenum, phosphorus, 
calcium, arsenic, bismuth, tin, titanium, tantalum and boron may 
respectively be ammonium molybdate, phosphoric acid or ammonium phosphate, 
calcium nitrate, arsenic pentoxide, bismuth nitrate, stannic oxide, 
titanium dioxide, tantalum pentoxide and boric acid. 
In a preferable preparation of the catalyst, a predetermined amount of a 
molybdate, for example, ammonium molybdate, is dissolved in water at an 
elevated temperature, for example, 60.degree. C.; predetermined amounts of 
phosphoric acid or ammonium phosphate and a water-soluble calcium salt, 
for example, calcium nitrate, are dissolved into the solution and, 
thereafter, predetermined amounts of the salts, hydroxide, oxide or acids 
of the desired catalytic ingredients are dissolved or suspended into the 
solution. The resultant solution or suspension is subjected to an 
evaporation to concentrate it. The concentrated solution or suspension is 
completely dried to obtain a solid material. The solid material is 
calcined at a temperature of 300.degree. to 500.degree. C. for a period of 
time sufficient for converting the solid material into an activated 
catalyst. 
One embodiment of the method of the present invention comprises bringing a 
reaction feed containing methacrolein in vapor phase and molecular oxygen 
into contact with an oxidation catalyst comprising oxides of molybdenum, 
phosphorus, calcium, at least one element selected from the group 
consisting of arsenic, bismuth, tin, titanium, tantalum and boron, and at 
least one element selected from the group consisting of antimony, niobium 
and magnesium, at a temperature of 200.degree. to 450.degree. C. 
In the above mentioned special embodiment, the oxidation catalyst may 
consist of an oxide composition of the formula (II): 
EQU mo.sub.a P.sub.b Ca.sub.c X.sub.f Y.sub.g O.sub.e (II) 
wherein X represents at least one member selected from the group consisting 
of arsenic, bismuth, tin, titanium, tantalum and boron atoms, Y represents 
at least one member selected from the group consisting of antimony, 
niobium and magnesium, the subscripts a, b, c, f and g respectively denote 
the numbers of the respective element atoms, said numbers being within the 
ranges, a=5 to 15, b=1 to 3, c=0.1 to 3, f=0.1 to 3 and g=0.1 to 3, and 
the subscript e represents the number of oxygen atoms which corresponds to 
the oxides formed from the above-mentioned elements and satisfies the 
average valency of the elements, said number e being within the range of 
16 to 68. 
The oxidation catalyst mentioned above can be prepared by providing an 
aqueous liquid containing therein a molybdenum-containing compound, a 
phosphorus-containing compound, a calcium containing compound, at least 
one compound selected from the group consisting of arsenic-, bismuth-, 
tin-, titanium-, tantalum- and boron-containing compounds and at least one 
compound selected from the group consisting of antimony-, niobium- and 
magnesium-containing compounds; evaporating the aqueous liquid to form a 
solid material, and; calcining the dried solid material at a temperature 
of 300.degree. to 500.degree. C. 
The compound containing antimony, niobium or magnesium may be salt, 
hydroxide or oxide thereof. The sources of antimony, niobium and magnesium 
are preferably, antimony trioxide, niobium pentoxide and magnesium 
nitrate. 
In a preferable embodiment, the method of the present invention may 
comprise bringing a reaction feed containing methacrolein in vapor phase 
and molecular oxygen into contact with an oxidation catalyst comprising 
oxides of molybdenum, phosphorus, calcium, arsenic and at least one 
element selected from the group consisting of bismuth, tin, titanium, 
tantalum, boron, antimony, niobium and magnesium, at a temperature of 
200.degree. to 450.degree. C. 
In the above embodiment, the oxidation catalyst usable for the present 
invention may consist of an oxide composition of the formula (III): 
EQU mo.sub.a P.sub.b Ca.sub.c As.sub.h Z.sub.i O.sub.e (III) 
wherein Z represents at least one member selected from the group consisting 
of bismuth, tin, titanium, tantalum, boron, antimony, niobium, and 
magnesium atoms, the subscripts a, b, c, h and i respectively represent 
the numbers of the respective element atoms, the numbers being within the 
following ranges, a=5 to 15, b=1 to 3, c=0.1 to 3, h=0.1 to 3, and i=0.1 
to 3, and the subscript e represents the number of oxygen atoms which 
corresponds to the oxides formed from the above-mentioned elements and 
satisfies the average valency of the elements, said number e being in a 
range of 16 to 68. 
The oxidation catalyst mentioned above can be prepared by providing an 
aqueous liquid containing therein a molybdenum-containing compound, a 
phosphorus-containing compound, a calcium-containing compound, an 
arsenic-containing compound and at least one compound selected from the 
group consisting of bismuth-, tin-, titanium-, tantalum-, boron-, 
antimony-, niobium- and magnesium-containing compounds; evaporating said 
aqueous solution to form a solid material, and; calcining the dried solid 
material at a temperature of 300.degree. to 500.degree. C. 
The above-mentioned oxidation catalyst of the present invention may be 
composed of the catalytic ingredient alone. However, in order to improve 
the mechanical rigidity of the catalyst, it is preferable that the 
catalytic ingredient is supported on a carrier. The carrier may consists 
of any type of conventional carrier material. However, it is preferable 
that the carrier consists of at least one material selected from the group 
consisting of diatomaceous earth, silica, alumina, silicon carbide, 
silica-alumina and water-soluble silica sol. There is no limitation to 
size and form of the catalyst. That is, the oxidation catalyst of the 
present invention can be screened into a desired size and can be formed 
into a desired form, for example, powder, grains, granules, pellets or 
tablets having a desired rigidity, depending upon the purpose and 
conditions under which the catalyst is used. Further, it should be noted 
that the formation of the catalyst results is no change in the catalytic 
activity of the catalyst. 
In the method of the present invention, the reaction feed comprises 
methacrolein and molecular oxygen. This reaction feed can be prepared by 
mixing a methacrolein source in vapor phase with a molecular 
oxygen-containing gas. The molecular oxygen-containing gas may be 
industrially pure oxygen gas. However, it is not required that the 
molecular oxygen-containing gas have a particularly high concentration of 
oxygen. Accordingly, the molecular oxygen-containing gas may be air, which 
is economically advantageous. The molecular oxygen-containing gas can 
contain an inert gas which does not affect the conversion of methacrolein 
into methacrylic acid, for example, nitrogen, carbon dioxide and steam. 
Especially, steam is effective for increasing not only the selectivity 
percentage of methacrylic acid but the durability in catalytic activity of 
the catalyst. 
The methacrolein source to be used in the method of the present invention 
is not required to have a high concentration of methacrolein. Accordingly, 
the source of methacrolein may be an oxidation product of isobutylene or 
an oxidation product of a spent BB which is a residue obtained by 
separating 1,3-butadiene from C.sub.4 fraction which is a by-product from 
thermally-cracking naphtha. The spent BB contains n-butene and 
isobutylene. However, it is not preferable that the source of methacrolein 
contain a large amount of unsaturated aldehydes other than methacrolein 
therein, because the other aldehydes cause not only a lowering of the 
reaction velocity but produce a large amount of by-products, and 
polymerized materials. Accordingly, it is desired that the methacrolein 
source contain no impurity which will result in an undesirable influence 
on the conversion of methacrolein into methacrylic acid. 
The oxidation catalyst of the present invention may be used in a fluidized 
bed, moving bed or fixed bed. However, it is most advantageous that the 
oxidation catalyst is employed in the fixed bed, because in the fixed bed 
the oxidation catalyst not only can convert methacrolein into methacrylic 
acid with a high reaction percentage of methacrolein and a high 
selectivity percentage of methacrylic acid while preventing undesirable 
side-reactions, but can maintain the catalytic activity thereof at a high 
level. 
The contact of the reaction feed with the oxidation catalyst may be 
effected under an ambient pressure, increased pressure or reduced 
pressure. However, it is convenient that the contact be effected under an 
ambient pressure. The oxidation temperature in the method of the present 
invention is in a range from 200.degree. to 450.degree. C., preferably, 
from 250.degree. to 400.degree. C. There is no limitation with regard to 
the contact time, of the reaction feed with the oxidation catalyst as far 
as the desired oxidation is completed within the time. However, it is 
preferable that the reaction feed is kept in contact with the oxidation 
catalyst for 0.1 to 12 seconds, more preferably, 0.5 to 10 seconds, under 
an ambient pressure. 
In a preferable embodiment of the method of the present invention, the 
reaction feed contains methacrolein in vapor phase, air and steam. In this 
reaction feed, it is preferable that the ratio by mole of methacrolein to 
molecular oxygen is 1:0.5 to 10, more preferably 1:1 to 8, and the ratio 
by mole of methacrolein to steam is 1:1 to 30, more preferably, 1:2 to 25. 
The resultant methacrylic acid from the method of the present invention may 
be isolated from the oxidation mixture by any conventional isolating 
method. That is, the resultant methacrylic acid may be isolated by 
distillation at a temperature of 161.degree. C. under a pressure of 760 
Torr, or by extraction using, for example n-hexane as an extraction 
solvent.

The specific examples, shown below will serve to more fully explain the 
practice of the present invention. However, it should be understood that 
the examples are only illustrative, and in no way limit the scope of the 
present invention. 
In the examples, the percentage of reaction of methacrolein and the 
percentage of selection of methacrylic acid were calculated in accordance 
with the following equations, respectively. 
##EQU1## 
wherein X.sub.1 denotes an amount by mole of methacrolein in the reaction 
feed prior to the start of oxidation, X.sub.2 denotes an amount by mole of 
the residual methacrolein in the oxidation mixture after the completion of 
oxidation, and Y denotes an amount by mole of the resultant methacrylic 
acid in the oxidation mixture after the completion of oxidation. 
EXAMPLE 1 
An oxidation catalyst was prepared using the following procedures. A muddy 
aqueous suspension of catalytic ingredients was prepared by dissolving 
84.75 g of ammonium molybdate [(NH.sub.4).sub.6 Mo.sub.7 O.sub.24.4H.sub.2 
O] in 200 ml of water which had been heated to a temperature of 60.degree. 
C. and, then, adding 4.6 g of 85% phosphoric acid (H.sub.3 PO.sub.4), 9.45 
g of calcium nitrate (Ca(NO.sub.3).sub.2.4H.sub.2 O) and 3.20 g of 
titanium dioxide (TiO.sub.2) into the solution successively in the 
above-mentioned order. The muddy aqueous suspension was stirred while 
heating at a temperature of 80.degree. C. so that the suspension was 
concentrated. The concentrated suspension was further concentrated by a 
drum dryer and, thereafter, completely dried at a temperature of 
120.degree. C. A solid material obtained by the above drying, was formed 
into pellets having a diameter of 5 mm and a length of 5 mm. The pellets 
were calcined at a temperature of 400.degree. C. for 5 hours in a 
calcining furnace while flowing air through the calcining furnace. The 
resultant catalyst had an atomic ratio of Mo:P:Ca:Ti of 12:1:1:1. 
The oxidation catalyst was crushed into grains and the grains were screened 
by Tyler Standard screens to collect the grains having a 16 through 28 
mesh size. 
An oxidation column was prepared by charging a U-shaped glass reaction 
tube, having an inner diameter of 6 mm, with 5 ml of the oxidation 
catalyst grains. 
An oxidation of methacrolein was carried out using the following 
procedures. The oxidation column was heated to a temperature of 
350.degree. C. A reaction feed containing 2.2% by volume of methacrolein 
in vapor phase, 10.1% by volume of oxygen, 30.1% by volume of steam and 
57.0% by volume of nitrogen, was flowed through the oxidation column at a 
flow rate of 176 ml/min while maintaining the column at the 
above-mentioned temperature. The reaction mixture gas was kept in contact 
with the oxidation catalyst for 1.7 seconds. 
It was observed that the reaction percentage of the methacrolein was 68.5 
and the selectivity percentage of the resultant methacrylic acid was 76.0. 
Further, it was observed that small amounts of acetic acid, carbon dioxide 
and carbon monoxide was by-produced in addition to the methacrylic acid. 
EXAMPLES 2 THROUGH 12 
Procedures identical to those in Example 1 were repeated eleven times, 
except that the catalytic ingredient elements in the catalysts were in the 
atomic ratios indicated in Table 1 and the oxidation temperature and time 
were as indicated in Table 1. In the preparation of the oxidation 
catalysts, ammonium molybdate was used as a source of the molybdenum 
ingredient, phosphoric acid as a source of the phosphorus ingredient, 
calcium nitrate as a source of the calcium ingredient, antimony trioxide 
as a source of the antimony ingredient, bismuth nitrate as a source of the 
bismuth ingredient, tantalum pentoxide as a source of the tantalum 
ingredient, arsenic pentoxide as a source of the arsenic ingredient and 
niobium pentoxide as a source of the niobium ingredient. The results are 
indicated in Table 1. 
COMISON EXAMPLES 1 THROUGH 6 
Procedures identical to those in Example 1 were repeated six times using 
oxidation catalysts outside the scope of the present invention. The 
oxidation catalysts used here consisted of the catalytic ingredients in 
the atomic ratios indicated in Table 1. The oxidation temperature and time 
were as indicated in Table 1. The results are also indicated in Table 1. 
As seen from Table 1, in examples 1, 2, 3 and 6, the reaction percentages 
of methacrolein are very low, and in Examples 3, 4 and 5, the selectivity 
percentages of the resultant methacrylic acid are very low. 
Table 1 
__________________________________________________________________________ 
Item 
Oxida- Reaction 
tion Contact 
percent- 
Selectivity 
Atomic ratio of catalytic tempera- 
period 
age 
percentage 
Example ingredient element atoms ture of time 
metha- 
of metha- 
No. Mo. 
P Ca Ta Bi As Sb Nb (.degree. C) 
Second 
crolein 
crylic 
__________________________________________________________________________ 
acid 
2 12 1 1 1 -- -- -- -- 320 1.7 62.0 74.3 
3 12 1 1 -- 1 -- -- -- 330 1.7 65.9 72.8 
4 12 1 0.5 -- -- 0.5 -- -- 300 1.7 66.0 81.5 
5 12 1 1 -- 0.3 -- -- -- 300 3.4 60.5 70.3 
6 12 1 0.5 -- -- 1 1 -- 290 3.4 69.8 77.1 
Example 
7 12 1 0.5 -- 0.3 -- 0.7 -- 300 3.4 63.3 75.7 
8 13 1.5 2 -- 0.8 1 -- -- 300 3.4 65.3 73.5 
9 12 1 1 1 -- -- 1 -- 300 3.4 60.4 75.2 
10 12 1 1 -- 1 1 -- 1 330 1.7 64.3 70.5 
11 12 1 1 0.5 -- 0.5 0.5 0.5 330 1.7 68.3 71.8 
12 12 1 1 -- -- 0.1 -- -- 330 1.7 65.1 76.8 
1 12 1 1 -- -- -- -- -- 330 1.7 50.0 67.5 
2 12 1 -- 2 -- -- -- -- 310 1.7 51.9 60.7 
Comparison 
3 12 1 -- -- -- -- -- -- 330 1.7 55.2 55.0 
Example 
4 12 1 -- -- -- -- -- 1 300 1.7 60.4 59.1 
5 12 1 -- -- 1 -- -- -- 300 1.7 59.3 57.8 
6 12 1 -- -- -- 1 -- -- 330 1.7 40.6 70.2 
__________________________________________________________________________ 
EXAMPLE 13 
Procedures identical to those in Example 1 were carried out, except that 
6.03 g of stannic oxide were used in place of the titanium dioxide, and 
the atomic ratio of Mo:P:Ca:Sn was 12:1:1:1. 
As a result of the oxidation procedures, the reaction percentage of 
methacrolein was 67.3 and the selectivity percentage of the resultant 
methacrylic acid was 75.1. 
EXAMPLES 14 THROUGH 16 
The same procedures as those in Example 1 were carried out three times, 
except that the atomic ratio of Mo:P:Ca:Ti and the oxidation temperature 
were as indicated in Table 2. The results are also indicated in Table 2. 
Table 2 
______________________________________ 
Reaction 
Selectivity 
Item Oxidation percentage 
percentage of 
Ex. Atomic ratio temp. of metha- 
methacrylic 
No. Mo P Ca Ti (.degree. C) 
crolein acid 
______________________________________ 
14 12 1 1 2 350 65.2 74.8 
15 12 0.5 0.5 1 350 64.3 75.3 
16 11 1 0.5 0.5 330 70.3 72.9 
______________________________________ 
EXAMPLES 17 THROUGH 19 
The same procedures as in Example 1 were repeated three times, except that 
tin dioxide was used in place of the titanium dioxide and the atomic ratio 
of Mo:P:Ca:Sn and the oxidation temperature were as indicated in Table 3. 
The results are also indicated in Table 3. 
Table 3 
______________________________________ 
Reaction 
Selectivity 
Item Oxidation percentage 
percentage of 
Ex. Atomic ratio temp. of metha- 
methacrylic 
No. Mo P Ca Sn (.degree. C) 
crolein acid 
______________________________________ 
17 12 1 1 2 350 75.2 72.1 
18 12 0.5 0.5 1 350 62.4 74.0 
19 11 1 0.5 0.5 330 71.3 71.9 
______________________________________ 
COMISON EXAMPLES 7 and 8 
The same procedures as those in Example 1 were carried out three times, 
except that the calcium ingredient was not employed, oxidation catalysts 
having the atomic ratio of the catalytic ingredient elements as indicated 
in Table 4 were used. The oxidation catalyst used were outside the scope 
of the present invention. The results are also indicated in Table 4. 
Table 4 
______________________________________ 
Item Reaction 
Selectivity 
Comp. Oxidation 
% % of 
Ex. Atomic ratio temp. of metha- 
methacrylic 
No. Mo P Ca Sn Ti (.degree. C) 
crolein 
acid 
______________________________________ 
7 12 1 -- 1 -- 350 100 15.8 
8 12 1 -- -- 1 350 42.3 54.0 
______________________________________ 
EXAMPLE 20 
Procedures identical to those in Example 1 were repeated, except that 0.28 
g of boric acid (H.sub.3 BO.sub.3) and 0.54 g of antimony trioxide were 
employed instead of the titanium dioxide, the atomic ratio of Mo:P:Ca:B:Sb 
was 12:1:1:0.1:0.1, and the oxidation temperature was 330.degree. C. As a 
result of the oxidation procedure, the reaction percentage of methacrolein 
was 71.8 and the selectivity percentage of the resultant methacrylic acid 
was 81.1. Small amounts of acetic acid, carbon dioxide and carbon monoxide 
were by-produced in addition to the methacrylic acid. 
EXAMPLE 21 THROUGH 28 
Procedures identical to those in Example 1 were carried out, except that 
the oxidation catalysts had the atomic ratios of the ingredient elements 
indicated in Table 5, and the oxidation was carried out at the 
temperatures indicated in Table 5. In the preparation of the oxidation 
catalyst, the sources of the molybdenum, phosphorus, boron, calcium, 
antimony, magnesium, tantalum and arsenic ingredients employed were 
respectively ammonium molybdate, phosphoric acid, boric acid, calcium 
nitrate, antimony trioxide, magnesium nitrate, tantalum pentoxide and 
arsenic pentoxide. The results are indicated in Table 5. 
Table 5 
__________________________________________________________________________ 
Oxida- Reaction 
tion Contact 
percent- 
Selectivity 
Item tempera- 
period 
age of 
percentage 
Example 
Atomic ratio ture of time 
metha- 
of metha- 
No. Mo 
P B Ca Mg As Sb Ta (.degree. C) 
(second) 
crolein 
crylic acid 
__________________________________________________________________________ 
21 12 1 0.5 
1 -- -- 0.5 
-- 330 3.4 78.1 76.5 
22 12 1 0.1 
1 -- 0.1 
-- -- 330 1.7 80.8 79.0 
23 12 1 0.5 
0.5 
-- 0.5 
-- -- 350 1.7 85.2 72.3 
24 12 1 0.5 
1 -- -- -- 0.5 
330 1.7 75.6 74.9 
25 12 1 0.1 
0.5 
-- 0.1 
0.05 
-- 330 3.4 71.9 80.7 
26 13 1 0.2 
1 -- 0.5 
-- 0.5 
350 1.7 86.4 74.3 
27 12 1 2 1 -- 1 -- -- 350 1.7 81.5 79.8 
28 12 1 0.5 
0.5 
0.5 
0.5 
-- -- 350 1.7 76.3 81.3 
__________________________________________________________________________ 
COMISON EXAMPLE 9 
The same procedures as those in Example 20 were carried out, except that 
the oxidation catalyst consisted of oxides of molybdenum, phosphorus and 
boron in an atomic ratio of Mo:P:B of 12:1:1 and the oxidation operation 
was carried out at a temperature of 320.degree. C. The oxidation catalyst 
used was outside the scope of the present invention. The results of the 
oxidation had a high reaction percentage of methacrolein of 91.4 and a low 
selectivity percentage of the resultant methacrylic acid of 52.8. 
EXAMPLE 29 
A muddy aqueous suspension was prepared by dissolving 84.75 g of ammonium 
molybdate into 200 ml of water which had been heated to a temperature of 
60.degree. C. and, then, adding 5.52 g of phosphoric acid, 9.45 g of 
calcium nitrate and 0.84 g. of arsenic trioxide into the solution in the 
above-mentioned order. The muddy aqueous suspension was concentrated at a 
temperature of 80 while stirring. The concentrated suspension was further 
concentrated by a drum dryer and, thereafter, completely dried at a 
temperature of 120.degree. C. The resultant solid material was formed into 
pellets having a diameter of 5 mm and a length of 5 mm. The pellets were 
calcined at a temperature of 380.degree. C. for 5 hours in atmospheric 
air. The resultant oxidation catalyst had an atomic ratio Mo:P:Ca:As of 
12:1.2:1:0.2. 
In order to prepare an oxidation column, a U-shaped glass reaction tube 
having an inner diameter of 11 mm was filled with 25 ml of the oxidation 
catalyst. 
A reaction feed consisting of 1.5% by volume of methacrolein in vapor 
phase. 10.0% by volume of oxygen, 31.0% by volume of steam and 57.5% by 
volume of nitrogen was flowed through the oxidation column at a flow rate 
of 176 ml/min at a temperature of 280.degree. C., so that the reaction 
feed was kept in contact with the oxidation catalyst for 8.5 seconds. 
The reaction percentage of the methacrolein was 86.9 and the selectivity 
percentage of the methacrylic acid was 81.3. Small amounts of acetic acid, 
carbon dioxide and carbon monoxide were by-produced in addition to 
methacrylic acid. 
EXAMPLE 30 
Procedures identical to those in Example 29 were carried out, except that 
the contact time of the reaction feed with the oxidation catalyst was 5.1 
seconds and the oxidation temperature was 300.degree. C. The reaction 
percentage of methacrolein and the selectivity percentage of methacrylic 
acid were 82.6 and 80.0, respectively. 
EXAMPLES 31 THROUGH 35 
Procedures identical to those in Example 29 were repeated five times, 
except that the respective oxidation catalyst had the atomic ratio of the 
catalytic ingredient elements indicated in Table 6, and the respective 
oxidation temperature and the respective contact time of the reaction feed 
with the oxidation catalyst were as indicated in Table 6. In the 
preparation of the oxidation cataylsts, the sources of molybdenum, 
phosphorus, calcium, antimony, arsenic and boron ingredients employed were 
respectively ammonium molybdate, phosphoric acid, calcium nitrate, 
antimony trioxide, arsenic trioxide and boric acid. 
The oxidation catalyst pellets were crushed into grains and screened to 
collect the grains having a 16 through 28 mesh size (Tyler standard). The 
grains in an amount of 5 ml were charged into a U-shaped glass reaction 
tube having an inner diameter of 6 mm. 
The results are indicated in Table 6. 
Table 6 
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Reaction 
Oxida- 
Contact 
percent- 
Selectivity 
Item tion period 
age of 
percentage 
Ex. 
Atomic ratio temp. 
of time 
metha- 
of metha- 
No. 
Mo P Ca As Sb B .degree. C. 
(second) 
crolein 
crylic acid 
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31 12 1.2 0.1 0.2 -- -- 355 1.7 96.2 76.3 
32 12 2 0.2 0.1 -- -- 350 1.7 93.6 69.1 
33 12 1 0.01 
0.05 
0.05 
-- 350 1.7 96.9 68.9 
34 12 1 1 0.1 -- 0.1 330 3.4 90.3 78.0 
35 12 1.2 1 0.2 -- -- 340 3.4 95.6 83.1 
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