Catalyst for oxidation of isobutylene

A catalyst for oxidation of isobutylene which has a composition of the general formula EQU Mo.sub.a Bi.sub.b Fe.sub.c Co.sub.d Ni.sub.e P.sub.f Pb.sub.g X.sub.h O.sub.i wherein X is at least one alkali metal element selected from K, Rb and Cs; a, b, c, d, e, f, g and h respectively represent the number of Mo, Bi, Fe, Co, Ni, P, Pb and X atoms, and when a is 12, b is 0.1-10, c is 9-20, d is 0-12, e is 0-12 with the proviso that the sum of d and e is 0.5-15, f is 0.1-5, g is 0.05-8 and h is 0.01-5; and i is the number of oxygen atoms which satisfies the atomic valences of the other elements.

This invention relates to a catalyst for oxidation of isobutylene, and a 
process for producing methacrolein by oxidizing isobutylene in the 
presence of the aforesaid catalyst. 
Some of the terms used in the present application are defined as follows: 
The "first-stage oxidation" denotes the catalytic vapor-phase reaction of 
isobutylene with molecular oxygen at high temperatures in the presence of 
a catalyst to form methacrolein. 
The "second-stage oxidation" denotes the catalytic vapor-phase reaction of 
methacrolein with molecular oxygen at high temperatures in the presence of 
a catalyst to form methacrylic acid. 
The "continuous first stage-second stage method" denotes a method for 
producing methacrylic acid from isobutylene by feeding the gaseous 
reaction mixture formed in the first-stage oxidation directly to a 
second-stage oxidation zone to perform the second-stage oxidation. 
The "catalyst for oxidation of isobutylene", or the "catalyst for the 
first-stage oxidation" denotes a catalyst which is used in the first-stage 
oxidation. 
The "catalyst for the second-stage oxidation" denotes a catalyst which is 
used in the second-stage oxidation. 
It is known to produce methacrolein by oxidizing isobutylene, and to 
produce methacrylic acid by oxidizing methacrolein. Known prior techniques 
for the production of methacrylic acid from isobutylene include a method 
which comprises separating methacrolein from the reaction mixture obtained 
by the first-stage oxidation, and after purifying it, submitting it to a 
second-stage oxidation, and a method which involves performing the 
first-stage oxidation and the second-stage oxidation successively without 
working up the first-stage reaction mixture (British Pat. No. 939,713). 
The latter is considered to be commercially advantageous because it does 
not require a treating step such as the separation and purification of 
methacrolein, and therefore is advantageous in apparatus, operation and 
economy. 
However, the continuous first stage-second stage method generally gives far 
inferior results compared to the case of independently performing the 
second-stage oxidation using the purified methacrolein as a starting 
material. For this reason, no suggestion has been made so far which would 
make possible the commercial production of methacrylic acid by the 
continuous first stage-second stage method. 
The underlying difficulties are believed to be the formation of by-product 
impurities and the remaining of unreacted isobutylene in the first-stage 
oxidation. The present inventors carefully studied these difficulties, and 
found that the reaction mixture obtained by the first-stage oxidation 
contains, as by-products, unsaturated hydrocarbons such as diisobutylene, 
benzene, toluene, xylene and ethylbenzene in addition to the unreacted 
isobutylene, and the presence of these hydrocarbons is a main cause for 
the inferior reaction results in the second-stage oxidation. 
In the production of methacrylic acid from isobutylene by the continuous 
first stage-second stage method, it is desired to develop a novel 
oxidation catalyst that simultaneously meets the following two 
requirements which seem to be inconsistent with each other. 
(1) It should afford a high conversion of isobutylene and thus reduce the 
amount of the unreacted isobutylene. 
(2) It should reduce the formation of unsaturated hydrocarbons such as 
diisobutylene, benzene, toluene, xylene and ethylbenzene. 
In addition to these requirements, such a catalyst should also meet normal 
requirements for industrial catalysts such as a high selectivity to MAL 
(which is associated with a high one-pass yield), and a long active 
lifetime. 
Accordingly, it is an object of this invention to provide a novel catalyst 
for oxidation of isobutylene, which can afford methacrolein from 
isobutylene in a high selectivity and a high one-pass yield, and has a 
long active lifetime. 
Another object of this invention is to provide a novel catalyst for 
oxidation of isobutylene which meets the two requirements described above. 
Still another object of this invention is to provide a process for 
preparing methacrolein in a high selectivity and a high yield by using 
such a catalyst for oxidation of isobutylene. 
According to this invention, there is provided a catalyst which can achieve 
these objects, said catalyst having the composition 
EQU Mo.sub.a Bi.sub.b Fe.sub.c Co.sub.d Ni.sub.e P.sub.f Pb.sub.g X.sub.h 
O.sub.i 
wherein X is at least one alkali metal element selected from K, Rb and Cs; 
a, b, c, d, e, f, g and h respectively represent the number of Mo, Bi, Fe, 
Co, Ni, P, Pb and X atoms, and when a is 12, b is 0.1-10, c is 9-20, d is 
0-12, e is 0-12 with the proviso that the sum of d and e is 0.5-15, f is 
0.1-5, g is 0.05-8 and h is 0.01-5; and i is the number of oxygen atoms 
which satisfies the atomic velences of the other elements. 
A catalyst of the above general formula in which when a is 12, b is 0.5-7, 
c is 10-15, d is 0-10, e is 0-10 with the proviso that the sum of d and e 
is 0.5-12, f is 0.1-4, g is 0.1-4 and h is 0.01-4 is a preferred 
embodiment of the present invention. 
Although the exact structure of the catalyst of this invention is not 
clear, the composition of the ingredients forming the catalyst is believed 
to be basically expressed by the above general formula. 
The use of these catalysts of the invention can afford methacrolein in a 
high yield and a high selectivity even when the conversion of isobutylene 
in its oxidation is high, and can drastically reduce the amounts of 
by-product unsaturated hydrocarbons such as diisobutylene, benzene, 
toluene, xylene or ethylbenzene. Accordingly, the catalysts of this 
invention are very suitable for production of methacrolein, and when used 
as a first-stage oxidation catalyst in the continuous first stage-second 
stage method, they do not substantially hamper the second-stage oxidation 
reaction over long periods of time. 
Such an effect of this invention can be specifically obtained by the 
inclusion of Pb in the catalyst ingredients as shown in the above general 
formula. If this ingredient is not present, the activities of the 
catalysts are low, and the formation of by-product unsaturated 
hydrocarbons greatly increases. 
Known catalysts having a composition similar to that of the catalysts of 
this invention show good performance only when the number of Fe atoms is 
within a range of 0.5 to 7 with the number of Mo atoms taken as 12 (for 
example, Japanese Patent Publication No. 17253/73). In contrast, the 
catalysts of this invention exhibit a high activity when the number of Fe 
atoms is within a range of 9 to 20. 
The catalysts of this invention can be prepared by various methods known in 
the art such as an evaporation method, an oxide mixing method and a 
coprecipitation method. The starting materials for the individual elements 
in the catalyst may be not only their oxides, but any other compounds 
which will constitute the catalyst of this invention by calcination. 
Examples of these starting materials are salts containing these elements 
(such as ammonium salts, nitrate salts, carbonate salts, organic acid 
salts, and halides), free acids, acid anhydrides, condensed acids, and 
heteropolyacids containing molybdenum such as phosphomolybdic acid or 
silicomolybdic acid, and their salts such as ammonium salts or metal salts 
The use of a silicon-containing compound such as silicomolybdic acid does 
not adversely affect the activity of the resulting catalyst. 
Calcination treatment for the purpose of catalyst preparation, catalyst 
activation, etc. is performed usually at 300.degree. to 900.degree. C., 
preferably 450.degree. to 700.degree. C. for about 4 to 16 hours. If 
desired, a primary calcination treatment may be performed at a temperature 
below the above-mentioned calcination temperature before the above 
calcination treatment. 
The catalysts of this invention can be used directly as prepared, and also 
as deposited on a carrier of a suitable shape, or as diluted with a 
carrier (diluent) in the form of powder, sol, gel, etc. Known carriers can 
be used for this purpose. Examples include titanium dioxide, silica gel, 
silica sol, diatomaceous earth, silicon carbide, alumina, pumice, 
silica-alumina, bentonite, zirconia, zeolite, and refractories. 
Silicon-containing carriers are especially suitable. 
The amount of the carrier can be suitably chosen. The catalyst is made into 
a suitable shape such as powder or tablets, and can be used in any of a 
fixed bed, a moving bed, and a fluidized bed. 
Isobutylene used in the reaction need not always be of high purity, and may 
contain impurities. However, when the oxidation is performed by the 
continuous first stage-second stage method, the inclusion of large amounts 
of n-butene, butadiene and the like impurities is undesirable because it 
will possibly result in the inclusion of unsaturated hydrocarbons in the 
reaction gas obtained in the first-stage oxidation. Molecular oxygen may 
be singly used, but for commercial operations, the use of air is 
practical. Furthermore, in this reaction, the molecular oxygen may be 
diluted with an inert gas which does not adversely affect the reaction, 
such as steam, nitrogen, argon or carbon dioxide gas. It is especially 
preferred to dilute it with steam. 
In the production of methacrolein from the corresponding isobutylene using 
the catalysts of this invention, the reaction temperature is 250.degree. 
to 700.degree. C., preferably 250.degree. to 550.degree. C.; the reaction 
pressure is normal atmospheric pressure to 10 atmospheres; the space 
velocity (SV) of the entire starting gases is 200 to 10000 hr.sup.-1, 
preferably 300 to 6000 hr.sup.-1 (based on STP); isobutylene concentration 
in the fed starting gases is 0.5 to 25% by volume; and the isobutylene to 
oxygen ratio is 1:0.5-7. The preferred composition of the starting gaseous 
mixture is olefin:air:steam=1:3-30:5-90 (molar ratio). 
The reaction conditions in the first-stage oxidation in the continuous 
first stage-second stage method can be easily determined experimentally if 
a catalyst for the second-stage oxidation is set. Hence, the reaction 
conditions for the first-stage oxidation cannot be definitely fixed. 
Usually, however, the reaction temperature is 250.degree. to 700.degree. 
C., preferably 250.degree. to 550.degree. C.; the reaction pressure is 
normal atmospheric pressure to 10 atmospheres; the space velocity of the 
entire starting gases is 200 to 10000 hr.sup.-1, preferably 300 to 4000 
hr.sup.-1 ; the isobutylene concentration is 0.5 to 10% by volume, 
preferably 0.5 to 8% by volume; the isobutylene to oxygen ratio is 
1:1.5-7; and the preferred composition of the gaseous mixture is 
isobutylene:air:steam=1:7.5-30:5-90 (molar ratio). 
For the second-stage oxidation in the continuous first stage-second stage 
method, any known catalysts can be used. Examples include (1) P-Mo-R (R is 
at least one of Tl, alkali metals and alkaline earth metals) type 
oxidation catalysts; oxidation catalysts having compositions resulting 
from incorporating the above P-Mo-R type oxidation catalysts with at least 
one element selected from Si, Cr, Al, Ge, Ti, V, W, Bi, Nb, B, Ga, Pb, Sn, 
Co, Pd, As, Zr, Sb, Te, Fe, Ni, In, Cu, Ag, Mn, La, Nb, Ta and Sm; (2) 
P-Mo-As type oxidation catalysts; (3) P-Mo-As-alkali metal type oxidation 
catalysts; oxidation catalysts having compositions resulting from the 
incorporation of the P-Mo-As-alkali metal type catalysts with at least one 
element selected from V, W, Cu, Fe, Mn and Sn; (4) P-Mo-Sb type oxidatiaon 
catalysts, oxidation catalysts having compositions resulting from the 
incorporation of the P-Mo-Sb type catalysts with at least one element 
selected from W, Fe, Co, V, Al, Pb, Cr, Sn, Bi, Cu, Ni, Mg, Ca, Ba and Zn; 
(5) P-Mo-Pd type oxidation catalysts; (6) P-Pd-Sb type oxidation 
catalysts; oxidation catalysts having compositions resulting from the 
incorporation of the P-Pd-Sb type catalysts with at least one element 
selected from Bi, Pb, Cr, Fe, Ni, Co, Mn, Sn, U and Ba; and oxidation 
catalysts having compositions resulting from the incorporation of the 
aforementioned oxidation catalysts with ammonium. 
Among these, the catalysts of type (1) are desirable as second-stage 
oxidation catalysts because they exhibit very high activity. However, when 
methacrylic acid is to be produced by the continuous first stage-second 
stage method, they tend to decrease in activity owing to the presence of 
unsaturated hydrocarbons in the reaction mixture obtained by the oxidation 
of isobutylene, and this tendency is more outstanding than the other 
second-stage catalysts. However, when the catalyst in accordance with this 
invention is used in the first-stage oxidation, the production of 
by-product unsaturated hydrocarbons in the first-stage oxidation step is 
markedly inhibited, and therefore, the decrease in activity of the 
catalysts (1) can be prevented. As a result, the inherent activity of 
these catalysts can be maintained for long periods of time. Catalysts of 
this type are disclosed in detail, for example, in Japanese Patent 
Publications Nos. 19774/72, 24288/75, 10845/75, 10846/75, 15011/76, and 
31327/77, and Japanese Laid-Open Patent Publications Nos. 82013/75, 
123619/75, 83321/75, 83322/75, 84517/75, 84518/75, 84519/75, 84520/75, and 
123616/75. 
The second-stage oxidation is performed under substantially the same 
reaction conditions as in the first-stage oxidation, but as described 
above, specific conditions are selected according to the catalyst used. 
Preferably, the first-stage reaction mixture obtained under the aforesaid 
reaction conditions is directly offered as a starting material in the 
second-stage oxidation, and reacted under conditions suitable for the 
catalyst used. 
The following examples specifically illustrate the present invention. In 
these examples, the conversion, selectivity and one-pass yield are 
calculated in accordance with the following equations. All analyses were 
made by gas chromatography. For simplicity, the indication of oxygen in 
the catalyst composition is omitted. 
In the following description, i-B stands for isobutylene, MAL for 
methacrolein; and MAA for methacrylic acid. 
##EQU1##

EXAMPLES 1 to 10 
Bismuth nitrate (48.5 g), 116.5 g of cobalt nitrate, 29.1 g of nickel 
nitrate, 484.8 g of ferric nitrate, 33.1 g of lead nitrate and 10.1 g of 
potassium nitrate were added to 150 ml of water and dissolved by heating 
to form a solution (solution A). Separately, 212 g of ammonium molybdate 
was dissolved in 400 ml of water by heating, and 5.76 g of 85% phosphoric 
acid was added to form a solution (solution B). 
Solution B was mixed with solution A which was stirred at an elevated 
temperature. With thorough stirring, the mixture was evaporated to 
dryness, and then dried at 120.degree. C. for 8 hours. The dried product 
was calcined at 600.degree. C. for 16 hours in a muffle furnace. The solid 
obtained was pulverized to form particles having a size of 4 to 8 mesh. 
The composition of the catalyst of the invention so prepared was Mo.sub.12 
Bi.sub.1 Fe.sub.12 Co.sub.4 Ni.sub.1 Pb.sub.1 P.sub.0.5 K.sub.1. 
By the same procedure as above, various catalysts having different 
compositions as shown in Table 1 were prepared. 
Using these catalysts as first-stage oxidation catalysts, a continuous 
first stage-second stage reaction was performed by the following 
procedure. 
(1) First-stage oxidation reaction 
100 ml of the catalyst obtained was filled into a stainless steel reaction 
tube having an inside diameter of 2.5 cm and a length of 60 cm, and heated 
over a metal bath. A starting gaseous mixture of isobutylene, air and 
steam in a mole ratio of 4:55:41 was passed through the catalyst layer at 
a space velocity of 2000 hr.sup.-1. 
(2) Second-stage oxidation reaction 
As a catalyst for the second-stage oxidation, 100 ml of the Mo-P-Cs-Cr 
catalyst disclosed in Example 1 of the specification of Japanese Patent 
Publication No. 10846/75 [Mo:P:Cs:Cr=1:0.16:0.16:0.16 (atomic ratio); 
calcined at 450.degree. C.; catalyst particle diameter 4-8 mesh] was 
filled into a stainless steel reaction tube having an inside diameter of 
2.5 cm and a length of 60 cm, and heated over a metal bath. The reacted 
gas obtained by the first-stage oxidatiaon was directly passed through the 
catalyst layer. 
The results obtained in the first-stage oxidation and the second-stage 
oxidation are shown in Table 1. In Table 1, the reaction temperatures 
refer to those of the metal bath which were maintained constant (the same 
will apply hereinbelow). 
For comparison, a catalyst not containing Pb (Example 8) and the catalyst 
(Example 9) described in Example 1 of Japanese Patent Publication No. 
17253/73 were prepared (catalyst particle diameter 4-8 mesh), and their 
performances were rated in the same manner. 
As a control, a gaseous mixture of methacrolein (purity 99.5% by 
weight):O.sub.2 :N.sub.2 :H.sub.2 O=1:1.5:13.0:17.5 (mole ratio) was fed 
at a space velocity of 2000 hr.sup.-1 through the second-stage oxidation 
catalyst, and the results are also shown in Table 1 (Example 10). 
TABLE 1 
__________________________________________________________________________ 
Results of the first-stage oxidation 
Proportion of 
MAL 
Reaction 
i-B unsaturated 
One- 
Catalyst composition tempera- 
con- 
hydrocarbons 
pass 
Selec- 
(atomic ratio) ture version 
formed yield 
tivity 
Example 
Mo Bi 
Fe 
Co 
Ni 
Pb 
P K Rb 
Cs 
(.degree.C.) 
(%) (%) (%) 
(%) 
__________________________________________________________________________ 
Invention 
1 12 1 12 
4 1 1 0.5 
1 -- 
-- 
340 98.4 
2.7 76.4 
77.6 
2 12 3 15 
4 1 0.5 
0.5 
1 -- 
-- 
345 98.1 
2.9 76.2 
77.7 
3 12 1 10 
4 1 3 1 1.5 
-- 
-- 
350 97.5 
3.4 75.8 
77.7 
4 12 1 12 
4 1 0.1 
0.5 
0.75 
-- 
-- 
330 98.0 
2.7 77.0 
78.6 
5 12 1 12 
6 1 1 3 2 -- 
-- 
355 97.4 
3.2 76.5 
78.5 
6 12 1 12 
4 1 1 0.5 
-- 0.5 
-- 
340 98.2 
2.8 77.0 
78.4 
7 12 1 12 
4 1 1 0.5 
-- -- 
0.2 
345 97.9 
2.9 75.1 
76.7 
Comparison 
8 12 1 12 
4 1 -- 
0.5 
1 -- 
-- 
340 95.5 
7.3 69.4 
72.7 
9 12 1 3 
4.5 
2.5 
-- 
0.5 
0.07 
-- 
-- 
340 90.0 
13.0 57.7 
64.1 
Control 
10 -- -- 
-- 
-- 
-- 
-- 
-- 
-- -- 
-- 
-- -- -- -- -- 
__________________________________________________________________________ 
Results of the second-stage oxidation 
Reaction MAA (based on MAL) 
Conversion of 
One-pass yield 
tempera- 
MAL con- 
One-pass unsaturated 
of MAA 
ture version 
yield 
Selectivity 
hydrocarbons 
(based on i-B) 
Example 
(.degree.C.) 
(%) (%) (%) (%) (%) 
__________________________________________________________________________ 
Invention 1 
335 78.9 60.8 77.1 100 46.5 
2 335 78.6 60.0 76.3 100 45.7 
3 335 77.1 59.7 77.4 100 45.3 
4 335 79.1 61.3 77.5 100 47.2 
5 335 77.8 60.3 77.5 100 46.1 
6 335 78.4 60.5 77.2 100 46.6 
7 335 78.5 61.1 77.8 100 45.9 
Comparison 8 
335 65.4 44.5 68.0 100 30.9 
9 335 50.4 30.2 59.9 100 17.6 
Control 10 
335 81.1 62.8 77.4 -- -- 
__________________________________________________________________________ 
It is seen from the results shown in Table 1 that the use of the catalysts 
of this invention gives good reaction results in the first-stage 
oxidation, and also as good results in the second-stage oxidation reaction 
as are comparable to the case of using purified methacrolein. On the other 
hand, the catalyst not containing Pb gives poor results both in the 
first-stage oxidation reaction and in the second-stage oxidation reaction. 
It is also clear from the table that the catalysts of this invention 
exhibit far superior performances to a known similar catalyst. 
EXAMPLE 11 
As second-stage oxidation catalysts, the following catalysts A to F 
containing at least (1) phosphorus, (2) molybdenum and (3) R (R represents 
at least one element selected from thallium, alkali metals and alkaline 
earth metals) were prepared in accordance with the disclosures of Japanese 
Patent Publications or Laid-Open Patent Publications indicated (the 
catalyst particle size 4 to 8 mesh). 
A: Mo.sub.12 P.sub.2 V.sub.1 Sr.sub.1 catalyst described in Example 1 of 
Japanese Patent Publication No. 31327/77 
B: Mo.sub.12 P.sub.2 V.sub.1 Cs.sub.2 catalyst described in Example 1 of 
Japanese Laid-Open Patent Publication No. 82013/75 
C: Mo.sub.12 P.sub.2 Cr.sub.1.5 Rb.sub.2 V.sub.0.1 catalyst described in 
Example 1 of Japanese Laid-Open Patent Publication 123616/75 
D: Mo.sub.1 P.sub.0.08 Tl.sub.0.16 Si.sub.0.08 catalyst (calcined at 
450.degree. C.) described in Example 3 of Japanese Patent Publication No. 
24288/75 
E: Mo.sub.1 P.sub.0.08 K.sub.0.16 Ge.sub.0.08 catalyst described in Example 
4 of Japanese Patent Publication No. 15011/76 
F: Mo.sub.12 P.sub.2 Ba.sub.1 Zn.sub.0.5 B.sub.0.5 catalyst described in 
Example 2 of Japanese Laid-Open Patent Publication No. 84519/75. 
Using the catalyst used in Example 1 as a firststage oxidation catalyst, 
and each of the catalysts A to F as a second-stage oxidataon catalyst, the 
continuous first stagesecond stage method was performed in the same way as 
in Example 1. The results are shown in Table 2. 
For comparison, the same continuous first stagesecond stage reaction was 
performed using the comparative catalyst used in Example 8. The results 
are shown in Table 2. 
As a control, instead of the first-stage oxidatiaon reaction gas, a gaseous 
mixture of methacrolein (purity 99.5% by weight):O.sub.2 :N.sub.2 :H.sub.2 
O=1:1.5:13.0:17.5 (mole ratio) was fed at a space velocity of 2000 
hr.sup.-1 through each of the second-stage oxidation catalysts A to F. The 
results are also shown in Table 2. 
Since the results of the first-stage oxidation reaction were the same as in 
Example 1 and 8, they are omitted in Table 2. Table 2 therefore gives the 
results of the secondstage oxidataion reaction alone. The reaction 
temperatures tabulated are the maximum temperatures of the catalyst layer. 
TABLE 2 
__________________________________________________________________________ 
Invention Comparison Control 
MAA MAA MAA 
Second- 
Reac- (based on MAL) 
Reac- (based on MAL) 
Reac- (based on MAL) 
stage 
tion Con- One- tion Con- One- tion Con- One- 
oxi- temp- 
version 
pass Selec- 
temp- 
version 
pass 
Selec- 
temp- 
version 
pass 
Selec- 
dation 
erature 
of MAL 
yield 
tivity 
erature 
of MAL 
yield 
tivity 
erature 
of MAL 
yield 
tivity 
catalyst 
(.degree.C.) 
(%) (%) (%) (.degree.C.) 
(%) (%) (%) (.degree.C.) 
(%) (%) (%) 
__________________________________________________________________________ 
A 408 56.7 37.7 66.5 408 46.1 27.7 
60.1 408 57.3 38.2 
66.7 
B 400 79.1 61.4 77.6 400 65.6 44.2 
67.4 400 80.0 63.8 
79.8 
C 410 76.1 54.9 72.1 410 63.0 39.3 
62.4 410 77.7 56.1 
72.2 
D 379 70.9 49.1 69.3 379 59.0 36.1 
61.2 379 72.8 51.1 
70.2 
E 385 69.3 47.3 68.3 385 56.1 33.8 
60.2 385 70.4 49.0 
69.0 
F 418 57.0 37.8 66.3 418 45.5 26.0 
57.1 418 57.5 38.3 
66.6 
__________________________________________________________________________ 
The results of Table 2 demonstrate that when the catalyst of the invention 
is used as a first-stage oxidation catalyst in the continuous first 
stage-second stage reaction, the results are much the same as in the 
control in which purified methacrolein is used. On the other hand, the use 
of the comparative catalyst not containing Pb as a first-stage oxidation 
catalyst gives far inferior results compared to those in the control. 
EXAMPLES 12 to 14 
The continuous first stage-second stage methods shown in Examples 1 to 8 
were continued respectively for 1000 hours while maintaining the reaction 
conditions constant. Changes in the results of the reaction were examined 
(Examples 12 and 13). The results are shown in Table 3. 
As a control, the second-stage oxidation reaction shown in Example 10 was 
continued for 1000 hours while maintaining the reaction conditions 
constant. Changes in the results of the reaction were examined (Example 
14). The results are also shown in Table 3. The reaction temperatures in 
Table 3 show the temperatures of the metal baths. 
TABLE 3 
__________________________________________________________________________ 
Example 12 13 14 
__________________________________________________________________________ 
Composition (atomic ratio) of catalyst 
Mo.sub.12 Bi.sub.1 Fe.sub.12 Co.sub.4 Ni.sub.1 
Pb.sub.1 P.sub.0.5 K.sub.1 
Mo.sub.12 Bi.sub.1 Fe.sub.12 
Co.sub.4 Ni.sub.1 P.sub.0.5 
K.sub.1 -- 
Reaction time which elapsed (hrs) 
0* 1000 0* 1000 0* 1000 
Reaction temperature (.degree.C.) 
340 340 340 340 -- -- 
Results 
i-B conversion 98.4 98.5 95.5 94.0 -- -- 
of the 
first-stage 
Proportion of unsaturated 
oxidation 
hydrocarbons formed (%) 
2.7 2.6 7.3 8.5 -- -- 
One-pass yield (%) 
76.4 76.5 69.4 68.1 -- -- 
MAL Selectivity (%) 
77.6 77.7 72.7 72.4 -- -- 
Reaction temperature (.degree.C.) 
335 335 335 335 335 
335 
MAL conversion (%) 78.9 79.0 65.4 54.8 81.1 
80.9 
Results One-pass 
of the MAA yield (%) 60.8 60.8 44.5 33.5 62.8 
62.8 
second-stage 
(based on MAL) 
Selec- 
oxidation tivity (%) 
77.1 77.0 68.0 61.1 77.4 
77.6 
Conversion of unsaturated 
hydrocarbons (%) 100 100 100 100 -- -- 
One-pass yield (%) of 
MAA (based on i-B) 46.5 46.5 30.9 22.8 -- -- 
__________________________________________________________________________ 
*The symbol (*) denotes the early stage of reaction. 
It is seen from the results of Table 3 that the catalyst of this invention 
gives high conversions and selectivities in the first-stage oxidation, and 
is suitable as a catalyst for a continuous first stage-second stage 
oxidation method. The comparative catalyst has poor performance in the 
first-stage oxidation and induces the production of large amounts of 
by-product unsaturated hydrocarbons, and for this reason, in the 
continuous first stage-second stage method using such a catalyst in the 
first stage, the lifetime of the second-stage oxidation catalyst decreases 
.