Process for production of prussic acid

A process for producing prussic acid by subjecting methanol to a gas-phase contact reaction with molecular oxygen and ammonia in the presence of a catalyst, wherein said catalyst is an oxide composition containing iron, antimony, phosphorus and vanadium with a content of vanadium content being at least 0.6 in terms of atomic ratio relative to iron content taken as 10, and a mixed raw material gas for the gas-phase contact reaction contains oxygen at an oxygen-to-methanol molar ratio of less than 1.6.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a process for producing prussic acid. More 
particularly, the present invention relates to a process for producing 
prussic acid by subjecting methanol to ammoxidation in a gas-phase contact 
reaction. 
2. Description of the Related Art 
Prussic acid is produced by decomposition of formamide, reaction of methane 
with ammonia, ammoxidation of methane, etc. A large portion of the prussic 
acid consumed is a by-product formed when propylene is subjected to 
ammoxidation to produce acrylonitrile. 
Prussic acid has been increasingly used as raw material for acetone 
cyanohydrin, adiponitrile, chelating agent such as EDTA and the like, and 
also used for gold recovery. The gap between its supply and demand has 
been becoming more obvious. 
In view of the above situation, the present invention have been completed 
in order to develop a novel process for producing prussic acid by 
ammoxidation of methanol, which has excellent industrial applicability. 
For production of prussic acid by ammoxidation of methanol, various 
catalysts are known such as molybdenum oxide, described in U.R.S.S. Patent 
No. 106226; an oxide containing molybdenum, bismuth and other elements, 
described in U.S. Pat. No. 3,911,089; an oxide containing antimony and at 
least one element selected from the group consisting of iron, cobalt, 
nickel, manganese, zinc and uranium, described in JP-A-51-10200; an oxide 
catalyst containing manganese and phosphorus, described in U.S. Pat. No. 
4,457,905; an antimony phosphate, described in U.S. Pat. No. 4,511,548; 
and so forth. 
In order to improve the iron and antimony-based oxide catalyst described in 
JP-A-51-10200, the present inventors proposed an oxide catalyst containing 
iron, copper and antimony, in U.S. Pat. No. 4,461,752; an oxide catalyst 
containing iron, copper, antimony and phosphorus, in U.S. Pat. No. 
5,158,787; and a catalyst containing iron, antimony and phosphorus as 
essential components and iron antimonate as a crystal phase, in U.S. Pat. 
No. 5,094,990. The present inventors further proposed improved processes 
for catalyst production, in U.S. Pat. No. 4,946,819, U.S. Pat. No. 
4,981,830, etc. Theses processes showed progresses in various respects, 
but still had points to be improved for industrial application. 
That is, in producing prussic acid by ammoxidation of methanol, the 
above-mentioned catalysts require a high oxygen-to-methanol ratio in a 
mixed raw material gas in order to avoid a reduction in prussic acid yield 
or a reduction in catalytic activity with time. Consequently, when prussic 
acid is produced industrially with the catalysts, the reaction must be 
conducted at a low methanol concentration, which results in a lower 
productivity. 
The present invention has been completed in order to (1) alleviate the 
above-mentioned problems of the prior art and (2) provide an economical 
process for producing prussic acid, which uses a catalyst having 
significantly improved redox stability, which enables an efficient 
reaction at a low oxygen-to-methanol ratio of mixed raw material gas, and 
which gives prussic acid as intended product at a high yield, at a high 
selectivity and stably with the lapse of reaction time. 
SUMMARY OF THE INVENTION 
In order to achieve the above object, the present inventors made an 
extensive study on the improvement of the oxide catalyst containing iron, 
copper, antimony and phosphorus, described in U.S. Pat. No. 5,158,787 and 
the catalyst containing iron, antimony and phosphorus as essential 
components and iron antimonate as a crystal phase, described in U.S. Pat. 
No. 5,094,990. As a result, the present inventors found out that an oxide 
catalyst obtained from a combination of iron, antimony, phosphorus and 
vanadium can well utilize oxygen in a catalytic reaction of methanol, 
oxygen and ammonia for production of prussic acid and can prevent a 
reduction in prussic acid yield even at a low oxygen-to-methanol molar 
ratio and that the catalyst, when the content of vanadium component 
therein is at a certain level or higher, can have a significantly improved 
redox stability and has very high resistance to deterioration. The present 
invention has been completed based on the above finding. 
The present invention relates to a process for producing prussic acid by 
subjecting methanol to a gas-phase contact reaction with molecular oxygen 
and ammonia in the presence of a catalyst, wherein the catalyst used is an 
oxide composition containing iron, antimony, phosphorus and vanadium with 
the content of vanadium being 0.6 in terms of atomic ratio relative to the 
iron content taken as 10, and the mixed raw material gas fed into the 
reaction system contains oxygen at an oxygen-to-methanol molar ratio of 
less than 1.6. 
PREFERRED EMBODIMENTS OF THE INVENTION 
Catalyst 
The catalyst used in the present process contains, as essential components, 
not only iron, antimony and phosphorus but also a particular amount of 
vanadium, and thereby has improved activity and other properties and can 
give a high prussic acid productivity. The content of vanadium in the 
catalyst is at least 0.6, preferably 0.6-3 in terms of atomic ratio to the 
iron content taken as 10. 
The present catalyst, when specifically shown, is an oxide composition 
represented by the following empirical formula: 
EQU Fe.sub.a Sb.sub.b P.sub.c V.sub.d Mo.sub.e Cu.sub.f W.sub.g X.sub.h Y.sub.i 
Z.sub.j O.sub.k (SiO.sub.2)l 
wherein X is at least one element selected from the group consisting of Mg, 
Zn, La, Ce, Al, Cr, Mn, Co, Ni, Bi, U and Sn (preferably at least one 
element selected from the group consisting of Zn, Al, Mn, Co and Ni); Y is 
at least one element selected from the group consisting of B and Te; Z is 
at least one element selected from the group consisting of Li, Na, K, Rb, 
Cs, Ca and Ba; and a, b, c, d, e, f, g, h, i j, k and l are atomic ratios, 
and when a is 10, b=12-30 (preferably 15-27), c=1-30 (preferably 3-20, 
more preferably 5-15, and b/c&gt;1.5), d=0.6-3 (preferably 0.8-2.8, more 
preferably 1-2.5), e=0-0.3, f=0-5, preferably 0.5-4, g=0-3, h=0-6, i=0-5, 
j=0-3, k=a number corresponding to the oxides formed by the elements Fe, 
Sb, P, V, Mo, Cu, W, X, Y and Z, and l=0-200. 
In the present catalyst containing iron, antimony, phosphorus and vanadium 
as essential components, it is not clear what compound these components 
form in the catalyst to exhibit improved activity and other properties. It 
is presumed, however, that the components are closely related to each 
other to exhibit improved activity and other properties, in view of the 
fact that, when the composition of the catalyst deviates from the range of 
the above empirical formula, the selectivity of prussic acid formation 
decreases or the properties of the catalyst are deteriorated, making it 
difficult to achieve the intended object of the present invention. It is 
preferred that iron antimonate is contained as a crystal phase in the 
catalyst. The vanadium component is presumed to form a solid solution with 
iron antimonate. The presence of iron antimonate is effective for the 
improvement of prussic acid yield, the prevention of reduction in yield 
during long-term operation, and the optimization of catalyst properties. 
It is already known in the ammoxidation of propylene that the addition of a 
vanadium, molybdenum or tungsten component to an iron and 
antimony-containing catalyst is effective for increased reaction rate and 
increased resistance to reductive deterioration. In an iron, antimony and 
phosphorus-containing catalyst, addition of, in particular, a vanadium 
component has shown an excellent effect and addition of a particular 
amount of the vanadium component has shown remarkable effects that prussic 
acid can be stably obtained at a high yield and a high selectivity with 
the long lapse of reaction time even when the oxygen-to-methanol ratio in 
the mixed raw material gas fed into the reaction system is low, that is, 
the concentration of methanol is high. Neither molybdenum component nor 
tungsten component shows such effects. The above fact is unpredictable 
from the past knowledge. 
Addition of a copper component and an X component is effective for (1) 
prevention of the formation of protruding substance, crystalline antimony 
oxide on catalyst surface which is liable to occur when the antimony 
content in catalyst is high, (2) increased catalyst strength and (3) 
control of reaction rate and catalyst physical properties. Addition of a Y 
component contributes to improved selectivity. Addition of a Z component 
contributes to control of reaction rate and by-product formation. 
The present catalyst can be used per se without using any carrier, but is 
preferably used by supporting it on a carrier. The amount of the carrier 
can be varied as desired within a range of 10-90% by weight of the total 
catalyst weight. The preferred carrier is silica, although there can be 
used alumina, silica-alumina, titania, zirconia and the like. 
Production of Catalyst 
The present catalyst can be produced by any known method. There can be used 
any of the methods described in, for example, U.S. Pat. No. 4,946,819, 
U.S. Pat. No. 4,981,830 and U.S. Pat. No. 5,094,990. (Raw materials for 
catalyst) 
The starting material for each component constituting the present catalyst 
can be selected from the metal, oxide, hydroxide, chloride, nitrate, etc. 
of each component. The starting material also includes such materials as 
each can become an oxide of each component when subjected to a chemical 
treatment, a calcining treatment or the like. 
As the raw material for the iron component, there can be used iron oxides 
such as ferrous oxide, ferric oxide, tri-iron tetroxide and the like; 
mineral acid salts of iron such as ferrous chloride, ferric chloride, 
ferric nitrate, iron carbonate and the like; product of iron oxidation 
with nitric acid; organic acid salts of iron such as iron oxalate, iron 
citrate and the like; and so forth. 
As the raw material for the antimony component, there can be used antimony 
trioxide, antimony tetroxide, antimony pentoxide, antimonic acid, 
polyantimonic acid(s), sodium antimonate, potassium antimonate, antimony 
trichloride, antimony pentachloride, etc. A product of metal antimony 
oxidation with nitric acid can also be used. 
As the raw material for the phosphorus component, there can be used 
phosphorus pentoxide, orthophosphoric acid, ammonium dihydrogenphosphate, 
ammonium hydrogenphosphate, ammonium phosphate, etc. 
As the raw material for the vanadium component, there can be used vanadium 
pentoxide, ammonium metavanadate, vanadyl oxalate, vanadyl sulfate, etc. 
As the raw material for the copper component, there can be used cuprous 
oxide, cupric oxide, copper nitrate, etc. 
As the raw material for the molybdenum component, there can be used 
molybdenum trioxide, molybdic acid, ammonium paramolybdate, ammonium 
metamolybdate, molybdenum halides, etc. As the raw material for the 
tungsten component, there can be used tungsten trioxide, ammonium 
paratungstate, ammonium metatungstate, tungstic acid, etc. 
As the raw materials for the X, Y and Z components, there can be used 
oxides, hydroxides, nitrates, carbonates, organic acid salts, etc. of 
respective components. 
As the raw material for the silica carrier, silica sol can be used 
preferably. Part or the whole thereof may be silica hydrogel, fumed silica 
or the like. 
(Preparation of catalyst) 
In the present invention, the catalyst can be used in a fixed bed or in a 
fluidized bed. 
When a fixed-bed catalyst is produced, raw material powders are subjected 
to pressure molding or a slurry of raw materials is dried, and the 
resulting material is subjected to molding and calcining. When a 
fluidized-bed catalyst is produced, a slurry of raw materials is, if 
necessary, subjected to pH adjustment (to about 7 or less, preferably 
about 1-4) and heat treatment at about 40-150.degree. C.; the resulting 
slurry is subjected to spray drying; and the resulting fine spherical 
particles are calcined. 
The above calcination is important to allow the obtained catalyst to have 
desired activity and selectivity. The preferable conditions for the 
calcination are 200-800.degree. C., preferably 400-750.degree. C. and 
0.5-10 hours. The atmosphere used in the calcination is not particularly 
restricted and may be any of an non-reductive gas. The atmosphere is 
ordinarily air from an economical reason. In the calcination can be used a 
tunnel kiln, a rotary kiln, a fluidized-bed calciner, or the like. 
The shape and size of the catalyst can be determined depending upon the 
application purpose. When used in a fixed bed, the catalyst ordinarily has 
a cylindrical or spherical shape of several millimeters; when used in a 
fluidized bed, the catalyst ordinarily takes a particulate shape of 10-200 
.mu.m. 
Reaction 
The present catalyst can be favorably used in production of prussic acid by 
ammoxidation of methanol. This reaction can be carried out by any of a 
fixed-bed reaction and a fluidized-bed reaction, but is preferably 
conducted by the latter reaction. 
The reaction is conducted by contacting a mixed gas containing methanol, 
molecular oxygen and ammonia, with the present catalyst. The reaction can 
be conducted stably at a low oxygen-to-methanol ratio and at a low 
ammonia-to-methanol ratio, because the catalyst shows a high selectivity 
of prussic acid formation, gives a sufficiently high reaction rate and has 
high redox stability. The methanol concentration in the feed gas can be 
varied in a range of 3-20%. The molar ratio of oxygen to methanol in the 
feed gas is less than 1.6, preferably 0.8-1.5; and the molar ratio of 
ammonia to methanol in the feed gas is 1.2 or less, preferably 0.7-1.1. 
The reaction temperature is 350-500.degree. C., preferably 380-470.degree. 
C. 
The reaction pressure may be any of ordinary pressure, an applied pressure 
and a reduced pressure, but is appropriately in the range of about 
ordinary pressure to 2 kg/cm.sup.2 G. 
The contact time is 0.01-20 seconds, preferably 0.05-10 seconds, 
particularly preferably 0.1-6 seconds, based on the gas volume at the 
reaction temperature and the reaction pressure. 
In the ammoxidation of methanol according to the present process, 
propylene, isobutene, tertiary butanol or the like may be fed into the 
reaction system together with the feed gas, whereby acrylonitrile (in the 
case of propylene) or methacrylonitrile (in the case of isobutene or 
tertiary butanol) can be produced together with prussic acid. 
The embodiments and effects of the present invention are specifically 
described below by way of Examples. However, the present invention is not 
restricted to these Examples alone. 
Test Method for Catalytic Activity 
Each catalyst was filled in a fluidized-bed reactor having an inner 
diameter (of catalyst-fluidizing portion) of 25 mm and a height of 400 mm. 
Into the reactor was fed a mixed gas consisting of methanol, ammonia and 
air. The composition of the mixed gas fed is shown in Examples. The 
reaction pressure employed was atmospheric pressure. 
Incidentally, "contact time" had the following definition. 
EQU Apparent contact time (sec)=[catalyst volume (l) based on apparent bulk 
density]/[volume of fed gas (l/sec) expressed as that under reaction 
conditions] 
Prussic acid yield and methanol conversion had the following definitions. 
______________________________________ 
= [carbon weight of prussic acid formed] .div. 
[carbon weight of methanol fed] .times. 100 
Methanol conversion (%) 
= [carbon weight of methanol reacted] .div. [carbon 
weight of methanol fed] .times. 100 
______________________________________ 
Catalysts Used for Reaction and Preparation Thereof 
[Catalyst 1] 
A catalyst having the following empirical formula: 
EQU Fe.sub.10 Sb.sub.19 P.sub.6 V.sub.0.8 Cu.sub.2.5 O.sub.72.5 
(SiO.sub.2).sub.60 
was prepared as follows. 
247.3 g of an antimony trioxide powder (a) was taken. 
385 ml of nitric acid (specific gravity: 1.38) was mixed with 480 ml of 
water and the mixture was heated. Thereto was added 49.9 g of an 
electrolytic iron powder in small portions to obtain a solution. In this 
solution was dissolved 54.0 g of copper nitrate to obtain a solution (b). 
8.4 g of ammonium metavanadate was dissolved in 300 ml of water to obtain a 
solution (c). 
1,612 g of silica sol (SiO.sub.2 : 20% by weight) (d) was taken. 
To (b) were added (d), (a) and (c) in this order, with sufficient stirring. 
The resulting slurry was adjusted to pH 2 with 15% ammonia water and then 
subjected to a heat treatment at 98.degree. C. for 3 hours, with stirring. 
Then, 61.8 g of phosphoric acid (85%) was added to the heat-treated 
slurry, followed by sufficient stirring. Then, the slurry was subjected to 
spray drying by the use of a rotary disc type spray dryer. The resulting 
fine spherical particles were calcined at 200.degree. C. for 2 hours, 
further at 500.degree. C. for 3 hours, furthermore at 800.degree. C. for 3 
hours. 
[Catalyst 2] 
A catalyst represented by the following empirical formula: 
EQU Fe.sub.10 Sb.sub.22 P.sub.10 V.sub.1.1 Cu.sub.3 Mg.sub.1 O.sub.90.8 
(SiO.sub.2).sub.80 
was produced in the same manner as in the case of catalyst 1 except that 
magnesium nitrate was used as a raw material for the Mg component and an 
aqueous solution thereof was added after the antimony trioxide powder (a). 
[Catalyst 3] 
A catalyst represented by the following empirical formula: 
EQU Fe.sub.10 Sb.sub.20 P.sub.10 V.sub.1.2 B.sub.0.2 O.sub.83.3 
(SiO.sub.2).sub.60 
was produced in the same manner as in the case of catalyst 1 except that 
boric acid anhydride was used as a raw material for the B component and an 
aqueous solution thereof was added after the antimony trioxide powder (a). 
[Catalyst 4] 
A catalyst represented by the following empirical formula: 
EQU Fe.sub.10 Sb.sub.15 P.sub.5 V.sub.0.8 Cu.sub.2 K.sub.1 O.sub.62 
(SiO.sub.2).sub.120 
was produced in the same manner as in the case of catalyst 1 except that 
potassium nitrate was used as a raw material for the K component and an 
aqueous solution thereof was added after the antimony trioxide powder (a). 
[Catalyst 5] 
A catalyst represented by the following empirical formula: 
EQU Fe.sub.10 Sb.sub.20 P.sub.12 V.sub.1 Mo.sub.0.1 Cu.sub.2.5 Na.sub.0.2 
O.sub.90.4 (SiO.sub.2).sub.75 
was produced in the same manner as in the case of catalyst 1 except that 
ammonium paramolybdate was used as a raw material for the Mo component, 
sodium nitrate was used as a raw material for the Na component, and 
aqueous solutions thereof were added after the antimony trioxide powder 
(a). 
[Catalyst 6] 
A catalyst represented by the following empirical formula: 
EQU Fe.sub.10 Sb.sub.28 P.sub.10 V.sub.2 Cu.sub.3.5 W.sub.0.2 Co.sub.2 
O.sub.107.1 (SiO.sub.2).sub.100 
was produced in the same manner as in the case of catalyst 1 except that 
ammonium paratungstate was used as a raw material for the W component, 
cobalt nitrate was used as a raw material for the Co component, and 
aqueous solutions thereof were added after the antimony trioxide powder 
(a). 
[Catalyst 7] 
A catalyst represented by the following empirical formula: 
EQU Fe.sub.10 Sb.sub.20 P.sub.7 V.sub.1.5 Zn.sub.1.5 Bi.sub.1 O.sub.79.25 
(SiO.sub.2).sub.80 
was produced in the same manner as in the case of catalyst 1 except that 
bismuth nitrate was used as a raw material for the Bi component and an 
aqueous suspension thereof was added after the antimony trioxide powder 
[Catalyst 8] 
A catalyst represented by the following empirical formula: 
EQU Fe.sub.10 Sb.sub.25 P.sub.14 V.sub.2.5 Mn.sub.2.5 Al.sub.1.5 Te.sub.0.2 
O.sub.113.9 (SiO.sub.2).sub.100 
was produced in the same manner as in the case of catalyst 1 except that 
telluric acid was used as a raw material for the Te component and an 
aqueous solution thereof was added after the antimony trioxide powder (a). 
[Catalyst 9] 
A catalyst represented by the following empirical formula: 
EQU Fe.sub.10 Sb.sub.22 P.sub.10 V.sub.1 Cu.sub.2.5 Ni.sub.0.3 B.sub.0.5 
O.sub.90.05 (SiO.sub.2).sub.30 
was produced in the same manner as in the case of catalyst 1 except that 
nickel nitrate was used as a raw material for the Ni component, boric acid 
anhydride was used as a raw material for the B component, and aqueous 
solutions thereof were added after the antimony trioxide powder (a). 
[Catalyst 10] 
A catalyst represented by the following empirical formula: 
EQU Fe.sub.10 Sb.sub.17 P.sub.8 V.sub.1.2 Mo.sub.0.1 Cu.sub.0.5 Zn.sub.0.5 
Ba.sub.0.3 O.sub.73.6 (SiO.sub.2).sub.60 
was produced in the same manner as in the case of catalyst 1 except that 
ammonium paramolybdate was used as a raw material for the Mo component, 
zinc nitrate was used as a raw material for the Zn component, barium 
nitrate was used as a raw material for the Ba component, and aqueous 
solutions thereof were added after the antimony trioxide powder (a). 
[Catalyst 11] 
A catalyst represented by the following empirical formula: 
EQU Fe.sub.10 Sb.sub.26 P.sub.20 V.sub.1.7 Cu.sub.3 O.sub.124.25 
(SiO.sub.2).sub.80 
was produced in the same manner as in the case of catalyst 1. 
[Comparative catalyst 1] 
A catalyst represented by the following empirical formula: 
EQU Fe.sub.10 Sb.sub.19 P.sub.6 Mo.sub.0.8 Cu.sub.2.5 O.sub.72.9 
(SiO.sub.2).sub.60 
was produced in the same manner as in the case of catalyst 1 except that 
ammonium paramolybdate was used in place of ammonium metavanadate. 
[Comparative catalyst 2] 
A catalyst represented by the following empirical formula: 
EQU Fe.sub.10 Sb.sub.22 P.sub.10 V.sub.0.4 Cu.sub.3 Mg.sub.1 O.sub.89.0 
(SiO.sub.2).sub.80 
was produced in the same manner as in the case of catalyst 2. 
[Comparative Catalyst 3] 
A catalyst represented by the following empirical formula: 
EQU Fe.sub.10 Sb.sub.20 P.sub.12 V.sub.5 Mo.sub.0.1 Cu.sub.2.5 Na.sub.0.2 
O.sub.100.4 (SiO.sub.2).sub.75 
was produced in the same manner as in the case of catalyst 5. 
[Comparative Catalyst 4] 
A catalyst represented by the following empirical formula: 
EQU Fe.sub.10 Sb.sub.20 V.sub.1.7 Mo.sub.0.1 Cu.sub.2.5 Na.sub.0.2 O.sub.60.4 
(SiO.sub.2).sub.75 
was produced in the same manner as in the case of catalyst 5 except that no 
phosphoric acid was added. 
[Comparative Catalyst 5] 
A catalyst represented by the following empirical formula: 
EQU Fe.sub.10 Sb.sub.20 P.sub.12 V.sub.1 Mo.sub.0.5 Cu.sub.2.5 Na.sub.0.2 
O.sub.91.6 (SiO.sub.2).sub.75 
was produced in the same manner as in the case of catalyst 5.