Process for the manufacture of acrylonitrile and methacrylonitrile

High yields of unsaturated nitriles are obtained by the oxidation of olefin-ammonia mixtures in the presence of a catalyst comprising the oxides of bismuth, molybdenum, iron and at least one element of the Group II metals as essential components, and optionally the oxides of cobalt, nickel, phosphorus, arsenic and an alkali metal.

This invention relates to an improved process and catalyst for the 
oxidation of olefin-ammonia mixtures to unsaturated nitriles, and more 
particularly to an improved process and catalyst for the oxidation of 
propylene-ammonia and isobutylene-ammonia to acrylonitrile and 
methacrylonitrile, respectively. The oxidation is conducted in the 
presence of a catalyst consisting essentially of the oxides of bismuth, 
molybdenum and iron in combination with at least one element of the Group 
II metals as essential ingredients, and optionally the oxides of the 
elements of cobalt, nickel, phosphorus, arsenic and an alkali metal. 
The catalyst employed in the process of this invention has a high activity 
for the production of unsaturated nitriles at a lower reaction temperature 
than is normally employed for this type of process. In addition to high 
activity for nitrile production, the catalyst has a number of other 
important advantages that contribute greatly to the efficient and economic 
operation of the process. The catalyst has excellent redox stability under 
the reaction conditions of the process. This permits the use of low 
process air to olefin ratios and high weight hourly space velocities. The 
catalyst exhibits efficient ammonia utilization thus greatly reducing the 
amount of unreacted ammonia appearing in the reactor effluent and thus 
lowering the amount of sulfuric acid required to neutralize the ammonia in 
the effluent. This results in improvements in the operation of the 
recovery section of the process and in improved pollution control 
resulting from the lowering of polymer waste products that are formed. The 
catalyst performs optimally at a lower reactor temperature than is 
normally employed for this type of reaction, and the use of lower 
operating temperatures favors longer catalyst life and minimizes effluent 
problems such as afterburning. Despite the lower reaction temperatures per 
pass conversions to the nitrile product as high as 80 percent and above 
are obtained. A further important advantage associated with the catalyst 
of this invention is the low cost of the essential catalytic components 
and the ease of catalyst preparation. 
The high activity of this catalyst at a low reaction temperature and at a 
low bismuth content is surprising in view of the disclosure in U.S. Pat. 
No. 2,904,580 issued Sept. 15, 1959, which describes a process for the 
production of acrylonitrile from propylene and ammonia in the presence of 
a catalyst selected from the group consisting of bismuth, tin and antimony 
salts of molybdic and phosphomolybdic acids and bismuth phosphotungstate, 
and U.S. Pat. No. 3,226,422 issued Dec. 28, 1965, which discloses a 
catalyst containing the oxides of iron, bismuth, molybdenum, and 
phosphorous for the production of unsaturated nitriles from olefin-ammonia 
mixtures. 
The reactants employed in producing the unsaturated nitriles of this 
invention are oxygen, ammonia, and an olefin having three carbon atoms in 
a straight chain such as propylene or isobutylene, and mixtures thereof. 
The olefins may be in admixture with paraffinic hydrocarbons, such as 
ethane, propane, butane and pentane; for example, a propylene-propane 
mixture may constitute the feed. This makes it possible to use ordinary 
refinery streams without special separation. Likewise, diluents such as 
nitrogen and the oxides of carbon may be present in the reaction mixture 
without deleterious effect. 
In its preferred aspect, the process comprises contacting a mixture 
comprising propylene or isobutylene, ammonia and oxygen with the catalyst 
at an elevated temperature and at atmospheric or near atmospheric 
pressure. 
Any source of oxygen may be employed in this process. For economic reasons, 
however, it is preferred that air be employed as the source of oxygen. 
From a purely technical viewpoint, relatively pure molecular oxygen will 
give equivalent results. The molar ratio of oxygen to the olefin in the 
feed to the reaction vessel should be in the range of 0.5:1 to 4:1 and a 
ratio of about 1:1 to 3:1 is preferred. 
The molar ratio of ammonia to olefin in the feed to the reaction may vary 
between about 0.5:1 to 5:1. There is no real upper limit for the 
ammonia-olefin ratio, but there is generally no reason to exceed a ratio 
of 5:1. At ammonia-olefin ratios appreciably less than the stochiometric 
ratio of 1:1, various amounts of oxygenated derivates of the olefin will 
be formed. Outside the upper limit of this range only insignificant 
amounts of aldehydes and acids will be produced, and only very small 
amounts of nitriles will be produced at ammonia-olefin ratios below the 
lower limit of this range. It is surprising that within the ammonia-olefin 
range stated, maximum utilization of ammonia is obtained, and this is 
highly desirable. It is generally possible to recycle any unreacted olefin 
and unconverted ammonia. 
We have found that in some cases water in the mixture fed to the reaction 
vessel improves the selectivity of the reaction and yield of nitrile. 
However, addition of water to the feed is not essential in this invention, 
inasmuch as water is formed in the course of the reaction. 
In general, the molar ratio of added water to olefin, when water is added, 
is above about 0.25:1. Ratios on the order of 1:1 to 4:1 are particularly 
desirable, but higher ratios may be employed, i.e., up to about 10:1. 
The reaction is carried out at a temperature within the range of from about 
500.degree. to about 1100.degree. F. The preferred temperature range is 
from about 600.degree. to 900.degree. F. 
The pressure at which reaction is conducted is another variable, and the 
reaction is carried out at about atmospheric or above atmospheric (2 to 5 
atmospheres) pressure. 
The apparent contact time is not critical, and contact times in the range 
of from 0.1 to about 50 seconds may be employed. The optimum contact time 
will, of course, vary depending upon the olefin being reacted, but in 
general, a contact time of from 1 to 15 seconds is preferred. 
Generally any apparatus of the type suitable for carrying out oxidation 
reactions in the vapor phase may be employed in the execution of this 
process. The process may be conducted either continuously or 
intermittently. The catalyst bed may be a fixed-bed employing a large 
particulate or pelleted catalyst or, alternately a so-called "fluidized" 
bed of catalyst may be employed. The fluid reactor may comprise an open 
column or the reactor may contain a plurality of perforated trays stacked 
horizontally throughout the length of the column, as described in U.S. 
Pat. No. 3,230,246 issued Jan. 18, 1966. 
The reactor may be brought to the reaction temperature before or after the 
introduction of the reaction feed mixture. However, in a large scale 
operation it is preferred to carry out the process in a continuous manner, 
and in such a system the circulation of the unreacted olefin is 
contemplated. Periodic regeneration or reactivation of the catalyst is 
also contemplated, and this may be accomplished, for example, by 
contacting the catalyst with air at an elevated temperature. 
The products of the reaction may be recovered by any of the methods known 
to those skilled in the art. One such method involves scrubbing the 
effluent gases from the reactor with cold water or an appropriate solvent 
to remove the products of the reaction. If desired, acidified water can be 
used to absorb the products of reaction and neutralize unconverted 
ammonia. The ultimate recovery of the products may be accomplished by 
conventional means. The efficiency of the scrubbing operation may be 
improved when water is employed as the scrubbing agent by adding a 
suitable wetting agent in the water. Where molecular oxygen is employed as 
the oxidizing agent in this process, the resulting product mixture 
remaining after the removal of the nitriles may be treated to remove 
carbon dioxide with the remainder of the mixture containing the unreacted 
olefin and oxygen being recycled through the reactor. In the case where 
air is employed as the oxidizing agent in lieu of molecular oxygen, the 
residual product after separation of the nitriles and other carbonyl 
products may be scrubbed with a non-polar solvent, e.g., a hydrocarbon 
fraction in order to recover unreacted olefin, and in this case the 
remaining gases may be discarded. The addition of a suitable inhibitor to 
prevent polymerization of the unsaturated products during the recovery 
steps is also contemplated. 
The catalyst useful in the process of the present invention is a mixture, 
compound or possibly complex of the oxides of iron, bismuth, molybdenum, 
and at least one element selected from Group II of the Periodic 
Classification, and optionally the oxides of nickel or cobalt or both, 
phosphorus and/or arsenic, and an alkali metal. The composition is 
conveniently expressed in the following empirical formula: 
EQU A.sub.a B.sub.b C.sub.c D.sub.d Fe.sub.e Bi.sub.f Mo.sub.g O.sub.x 
wherein A is an alkali metal, B is one or more of the elements selected 
from the group consisting of nickel and cobalt, C is phosphorus or arsenic 
or both, and D is at least one element selected from Group II A and Group 
II B of the Periodic Classification of elements, and wherein (a) is a 
number from 0 to less than 0.1, (b) is a number from 0 to 12, (c) is a 
number from 0 to 3, (d) is a number from 0.1 to 10, (e) and (f) are each a 
number from 0.1 to 6, (g) is a number from 8 to 16, and (x) is a number 
determined by the valence requirements of the other elements present. A 
preferred catalyst composition is one in which A is potassium, D is 
magnesium, and the atom ratios of the elements in the foregoing empirical 
formula are within the range wherein (a) is a number from 0 to 0.09, (b) 
is from 1 to 6, (c) is from 0 to 1, (d) is a number from 0.1 to 7, (e) and 
(f) are each a number of from 1 to 4, and (g) is 12. 
The catalyst of this invention may be prepared by any of the numerous 
methods of catalyst preparation which are known to those skilled in the 
art. For example, the catalyst may be manufactured by co-precipitating the 
various ingredients. The co-precipitated mass may then be dried and ground 
to an appropriate size. Alternately, the co-precipitated material may be 
slurried and spray-dried in accordance with conventional techniques. The 
catalyst may be extruded as pellets or formed into spheres in oil as is 
well-known in the art. Alternatively, the catalyst components may be mixed 
with the support in the form of the slurry followed by drying, or they may 
be impregnated on silica or other supports. 
A particularly attrition-resistant form of the catalyst may be prepared by 
adding the support material to the catalyst in two stages, first by 
preparing and heat-treating a mixture of active catalyst components and 
from 0 to 60% by weight of the total support material, followed by adding 
the remainder of the support material to the powdered form of the 
heat-treated catalyst. A more detailed description of the preparation of 
an attrition-resistant catalyst may be obtained from the examples. 
The alkali metal may be introduced into the catalyst as an oxide or as any 
salt which upon calcination will yield the oxide. Preferred salts are the 
nitrates which are readily available and easily soluble. 
Bismuth may be introduced into the catalyst as an oxide or as any salt 
which upon calcination will yield the oxide. Most preferred are the 
water-soluble salts which are easily dispersible within the catalyst and 
which form stable oxides upon heat-treating. The most preferred salt for 
introducing bismuth is bismuth nitrate. 
To introduce the iron component into the catalyst one may use any compound 
or iron which, upon calcination, will result in the oxides. As with the 
other elements, water-soluble salts are preferred for the ease with which 
they may be uniformly dispersed within the catalyst. Most preferred is 
ferric nitrate. Cobalt, nickel and the Group II metals may be similarly 
introduced. However, the Group II metals may also be introduced into the 
catalyst as the insoluble carbonates or hydroxides which upon 
heat-treating result in the oxides. 
To introduce the molybdenum component, any molybdenum oxide such as the 
dioxide, trioxide, pentoxide, or sesquioxide may be used; more preferred 
is a hydrolyzable or decomposable molybdenum salt such as a molybdenum 
halide. A preferred starting material is ammonium heptamolybdate. 
Arsenic may be introduced as orthoarsenic acid. Phosphorus may be 
introduced as an alkali metal, an alkaline earth metal or the ammonium 
salt, but is preferably introduced as phosphoric acid. 
Other elements may be introduced, starting with the metal, oxidizing the 
metal with an oxidizing acid such as nitric acid, and then incorporating 
the nitrate into the catalyst. Generally, however, the nitrates are 
readily available and form a very convenient starting material. 
Other variations in starting materials will suggest themselves to one 
skilled in the art, particularly when the preferred starting materials 
mentioned hereinabove are unsuited to the economics of large-scale 
manufacture. In general, any compounds containing the desired catalyst 
components may be used provided that they result in the oxides of the 
instant catalyst upon heating to a temperature within the range disclosed 
hereinafter. 
The catalyst can be employed without a support and will display excellent 
activity. The catalyst can also be combined with a support, and preferably 
it is combined with at least 10 percent up to about 90 percent of the 
supporting compound by weight of the entire composition. Any known support 
materials can be used, such as, for example, silica, alumina, zirconia, 
titania, alundum, silicon carbide, alumina-silica, the inorganic 
phosphates such as aluminum phosphate, silicates, aluminates, borates, 
carbonates, and materials such as pumice, montmorillonite, and the like 
that are stable under the reaction conditions to be encountered in the use 
of the catalyst. 
The catalytic activity of the system is enhanced by heating at an elevated 
temperature. Generally, the catalyst mixture is dried and heated at a 
temperature of from about 500.degree. to about 1850.degree. F., preferably 
at about 900.degree. to 1300.degree. F., for from about 1 to 24 hours or 
more. If activity then is not sufficient, the catalyst can be further 
heated at a temperature above about 1000.degree. F. but below a 
temperature deleterious to the catalyst. 
In general, activation of the catalyst is achieved in less time at higher 
temperatures. The sufficiency of activation at any given set of conditions 
is ascertained by a spot test of a sample of the material for catalytic 
activity. Activation is best carried out in an open chamber, permitting 
circulation of air or oxygen, so that any oxygen consumed can be replaced. 
Further, pre-treatment or activation of the catalyst before use with a 
reducing agent such as ammonia in the presence of a limited amount of air 
at a temperature in the range of 500.degree. to 1000.degree. F. is also 
beneficial. 
A preferred method of preparing the catalyst of this invention and a more 
complete description of the process of the invention can be obtained from 
the following examples. In addition to the production of unsaturated 
nitriles, the catalyst of this invention is also useful for the conversion 
of olefins, such as propylene and isobutylene, to the corresponding 
unsaturated aldehydes and unsaturated carboxylic acids.

EXAMPLES 1 to 18, and 20 to 22 
The catalysts employed in the examples of this invention were prepared by 
essentially the same procedure as described herein below, using the 
appropriate starting materials. 
A catalyst having the composition 80 wt.%--Mg.sub.4.5 Fe.sub.4 Bi.sub.2 
P.sub.0.5 Mo.sub.12 O.sub.51 --20 wt.%--SiO.sub.2 was prepared by 
dissolving 70.6 grams of (NH.sub.4).sub.6 Mo.sub.7 O.sub.24.4H.sub.2 O in 
water with a minimum amount of heating. To this were added in succession 
with stirring 1.9 grams of H.sub.3 PO.sub.4 (85 wt.%) and 76.7 grams of Du 
Pont Ludox AS (30 wt.%) colloidal silica sol. The solution was stirred for 
15 minutes at room temperature. 53.7 Grams of Fe(NO.sub.3).sub.3.9H.sub.2 
O dissolved in water were added to this solution followed by the 
successive addition of 38.5 grams of Mg(NO.sub.3).sub.2.6H.sub.2 O, and 
32.4 grams of Bi(NO.sub.3).sub.3.5H.sub.2 O dissolved in water containing 
8 cc of concentrated HNO.sub.3 (68 wt.%). The slurry was heated with 
constant stirring until gel formation occurred. The gel was then dried at 
approximately 270.degree. F. The resulting catalyst was heat-treated at 
600.degree. F. for 5 hours and then at 1020.degree. F. for 20 hours, and 
was then sized to 20-35 Tyler screen mesh. 
EXAMPLE 19 
An attrition-resistant catalyst having the composition 60 wt.%--Mg.sub.4.5 
Ni.sub.2.5 Fe.sub.3 BiP.sub.0.5 Mo.sub.12 O.sub.51 --40 wt.%--SiO.sub.2 
was prepared by dissolving 706 grams of (NH.sub.4).sub.6 Mo.sub.7 
O.sub.24.4H.sub.2 O in 570 cc of water, using minimum heating, and then 
blending with 19 grams of 85% H.sub.3 PO.sub.4. To this solution were 
added 743 grams of 30 percent silica sol (Du Pont AS Ludox), followed by 
the successive addition of 242 grams of Ni(NO.sub.3).sub.2.6H.sub.2 O 
dissolved in water, and while maintaining vigorous agitation, an aqueous 
solution containing 404 grams of Fe(NO.sub.3).sub.3.9H.sub.2 O in 190 cc 
water, and an aqueous solution containing 385 grams of 
Mg(NO.sub.3).sub.2.6H.sub.2 O in 190 cc water. To this was added a 
solution composed of 162 grams of Bi(NO.sub.3).sub.3.5H.sub.2 O, 20 cc of 
68 % HNO.sub.3 and 190 cc of water. The slurry was heated with stirring 
until a non-fluid cake was obtained. The solid was then treated at a 
temperature of 600.degree. F. for a period of 5 hours. After pulverizing 
the dry solid mechanically, 1000 grams of powder were blended with 1115 
grams of 30% silica sol (Du Pont AS Ludox) and sufficient water to result 
in a 45 wt.% solids slurry. The blend was ball-milled in a porcelain 
ball-mill for 20 hours. The resulting slurry was then spray-dried in a 
41/2 foot diameter Bowen spray-drier with an inlet temperature of 
550.degree. F. and an outlet temperature of 350.degree. F. The 
microspheroidal product from the spray-drier was put into a furnace at 
280.degree. F. The temperature was raised to 600.degree. F. over a period 
of 1 hour and maintained at that temperature for 3 hours. A final 
calcination of 17 hours duration at 1150.degree. F. was imposed upon the 
catalyst prior to charging the material to the reactor for testing. 
The reactor employed in carrying out the ammoxidation reactions in Examples 
1 through 22 was a standard reactor with a fixed catalyst bed. The 
catalyst volume was about 5 cc and the catalyst mesh size was 20 to 35 
Tyler screen mesh. The gases were metered to the reactor with rotameters. 
The products of the reaction were recovered by scrubbing the effluent 
gases from the reactor with water and hydrochloric acid and were then 
analyzed by means of a gas chromatograph. 
In the examples given, percent conversion to the unsaturated nitrile is 
defined as follows: 
Mole percent per pass conversion to unsaturated nitrile 
##EQU1## 
Ammoxidation reactions carried out with the catalyst compositions of this 
invention employing propylene and isobutylene as the hydrocarbon feeds are 
summarized in Tables I and II, respectively. These data are compared with 
conversions obtained with catalyst compositions of the prior art disclosed 
in U.S. Pat. No. 2,904,580 and U.S. Pat. No. 3,226,422, and shown in 
Examples 1 and 2 of Table I and in Example 20 of Table II. The data in 
these tables show that per pass conversions to acrylonitrile and 
methacrylonitrile obtained with catalysts of the present invention are 
substantially higher than those obtained with catalysts of the prior art. 
Comparable results to those shown in Tables I & II were also obtained with 
these catalysts in a fluid bed reactor. 
TABLE I 
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CONVERSION OF PROPYLENE TO ACRYLONITRILE 
Fixed-Bed Reactor 
Reaction Temperature: 750.degree. F Pre-Run Time: 15 minutes 
Contact Time: 2.9 seconds Run Time: 30 minutes 
Feed Ratio (Molar): C.sub.3.sup.= /NH.sub.3 /Air = 1/1.5/11 
(Mole Basis) 
% Per Pass Conversion 
Example 
Catalyst Composition to Acrylonitrile 
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1 50%-Bi.sub.9 PMO.sub.12 O.sub.52 -50% SiO.sub.2 
39.9 
2 50%-Fe.sub.4.5 Bi.sub.4.5 PMo.sub.12 O.sub.52 -50% 
41.9sub.2 
3 80%-Mg.sub.6.5 Fe.sub.3 Bi.sub.1 P.sub.0.5 Mo.sub.12 O.sub.50 -20% 
SiO.sub.2 (b) 59.1 
4 80%-Mg.sub.4.5 Fe.sub.4 Bi.sub.2 P.sub.0.5 Mo.sub.12 O.sub.51 -20% 
SiO.sub.2 (a) 65.3 
5 100%-Mg.sub.4.5 Fe.sub.4 Bi.sub.2 P.sub.0.5 Mo.sub.12 O.sub.51 
67.9 
6 80%-K.sub.0.07 Mg.sub.4.5 Fe.sub.4 Bi.sub.2 P.sub.0.5 Mo.sub.12 
O.sub.51 -20% SiO.sub.2 63.9 
7 80%-Mg.sub.4.5 Fe.sub.4 Bi.sub.2 As.sub.0.5 Mo.sub.12 O.sub.51 -20% 
SiO.sub.2 (b) 65.9 
8 80%-Mg.sub.4.5 Fe.sub.4 Bi.sub.2 Mo.sub.12 O.sub. 49 -20% 
58.0sub.2 
9 80%-Mg.sub.4.5 Ni.sub.2.5 Fe.sub.3 Bi.sub.1 P.sub.0.5 Mo.sub.12 
O.sub.51 -20% SiO.sub.2 (b) 
67.7 
10 " 72.9 
11 80%-Mg.sub.4.5 Ni.sub.2.5 Fe.sub.3 Bi.sub.1 As.sub.0.5 Mo.sub.12 
O.sub.51 -20% SiO.sub.2 (b) 
71.5 
12 " 78.3 
13 80%-Mg.sub.4.5 Co.sub.2.5 Fe.sub.3 Bi.sub.1 P.sub.0.5 Mo.sub.12 
O.sub.51 -20% SiO.sub.2 64.0 
14 80%-Mg.sub.2 N i.sub.2.5 Co.sub.4.5 Fe.sub.1 Bi.sub.1 P.sub.0.5 
Mo.sub.12 O .sub.53 -20% SiO.sub.2 
63.6 
15 80%-Mg.sub.0.1 Ni.sub.10 Co.sub.0.3 Fe.sub.1 Bi.sub.1 P.sub.1 
Mo.sub.12 O.sub.57 -20% SiO.sub.2 
60.2 
16 80%-Ca.sub.2 Ni.sub.2.5 Co.sub.2.5 Fe.sub.3 Bi.sub.1 P.sub.0.5 
Mo.sub.12 O.sub.53 -20% SiO.sub.2 (b) 
70.4 
17 80%-Zn.sub.4.5 Ni.sub.2.5 Fe.sub.3 Bi.sub.1 P.sub.0.5 Mo.sub.12 
O.sub.51 -20% SiO.sub.2 (b) 
64.9 
18 80%-Cd.sub.4.5 Ni.sub.2.5 Fe.sub.3 Bi.sub.1 P.sub.0.5 Mo.sub.12 
O.sub.51 -20% SiO.sub.2 (b) 
58.9 
19 60%-Mg.sub.4.5 Ni.sub.2.5 Fe.sub.3 Bi.sub.1 P.sub.0.5 Mo.sub.12 
O.sub.51 -40% SiO.sub.2 (b) (c) 
73.1 
(Extruded) 
__________________________________________________________________________ 
(a) 4 moles of H.sub.2 O per mole of propylene were added to the feed 
(b) contact time was 6 seconds 
(c) attrition-resistant catalyst - 2-stage addition of SiO.sub.2 support 
TABLE II 
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Conversion of Isobutylene to Methacrylonitrile 
Fixed-Bed Reactor 
Reaction Temperature: 715.degree. F Contact Time: 2.9 seconds 
Feed Ratio (Molar): IC.sub.4.sup.= /NH.sub.3 /Air = 1/1.5/11 
(Mole 
Basis) % 
Per Pass 
Conversion 
to Metha- 
cryloni- 
Ex. Catalyst Composition trile 
______________________________________ 
20 50%-Fe.sub.4.5 Bi.sub.4.5 PMo.sub.12 O.sub.52 -50% 
34.1sub.2 
21 80%-K.sub.0.07 Mg.sub.4.5 Fe.sub.4 Bi.sub.2 P.sub.0.5 Mo.sub.12 
O.sub.51 -20% SiO.sub.2 57.7 
22 80%-Mg.sub.4.5 Ni.sub.2.5 Fe.sub.3 Bi.sub.1 P.sub.0.5 Mo.sub.12 
O.sub.51 -20% SiO.sub.2 50.9 
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