JPS6041665B2 - Method for producing methacrylonitrile - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a process for producing methacrylic acid by contacting tertiary-butanol, ammonia, and oxygen in the gas phase at high temperature in the presence of a multi-promoted oxygenate catalyst containing molybdenum, bismuth, and iron supported on silica. The present invention relates to a method for producing nitriles.

Conventionally, as a method for producing methacrylonitrile, there is a method of catalytic ammoxidation of isobutylene in a high temperature gas phase.
Many catalysts have been proposed.

On the other hand, various proposals have been made to separate and recover isobutylene from the Co fraction obtained by catalytic cracking of naphtha, but in recent years, a method of hydrating isobutylene and separating and recovering it as tertiary butanol has been proposed, which is easy to separate. difference,
It is attracting industrial attention due to its economic efficiency. A method for producing methacrylonitrile using tertiary butanol as a raw material and simultaneously carrying out a dehydration reaction and an ammoxidation reaction in a high-temperature gas phase is already known and described in JP-A-53-18508.

However, the method disclosed in the publication uses a catalyst made of many types of metals, and the method for preparing the catalyst is complicated. The present inventors have developed an industrial catalyst for the production of methacrylonitrile by ammoxidation of tertiary butanol, particularly suitable for use in a fluidized bed reactor, having high activity, high selectivity, and a long lifetime. As a result of intensive research into the structure and function of the above-mentioned catalyst system, we were able to limit the component composition of molybdenum, bismuth, and iron to an extremely narrow range, and add one or more types selected from potassium, rubidium, and cesium as trace amounts of essential components. The activity, especially the selectivity, is greatly improved by using the elements;
By keeping the relative amount of molybdenum in the catalyst relatively small and using sodium, sublimation escape of molybdenum from the catalyst is suppressed, and by selecting silica as a carrier component and using a small amount of phosphorus. In particular, the inventors found that strong wear resistance was imparted to the catalyst, and based on these findings, the present invention was completed.

That is, the present invention provides a general compositional formula [wherein A is potassium, rubidium, One or more elements selected from A. ．． b. ．． fln. ．． p and q respectively represent the atomic ratios of the elemental components A1 bismuth, iron, sodium, phosphorus and oxygen to one atom of molybdenum, a is a number in the range of 0.002 to 0.06, B, .
f and n are numbers determined by the formula and n=112Z, respectively, where X. ．． Y is (0.45, 0.35
), (0.45, 0.65), (4). 85,0.50
), (4). 85, 0.65) are connected. Z is a number in the range of 0 to 0.6, p is a number in the range of 0 to 0.2, and q is the number of oxygen atoms that satisfies the valence of the element in the catalyst. be.

This invention provides a method for producing methacrylonitrile, which is characterized by using a catalyst in which 30 to 70% by weight of the composition shown in the following is supported on silica. When the catalyst of the present invention contains sodium and/or phosphorus as an optional component, measurements such as X-ray diffraction show that some of the sodium or phosphorus may of course exist in other forms, but mainly in the compound BiO. 5NaO. 5MOO4 or BiPO
It was found that there are 4.

General compositional formula of the catalyst of the present invention in this case AaMOB
ibF′E, NanPpOq is BIO. 5NaO. 5
It can be expressed as the following formula using MOO4 and BiPO4 as structural units: In this formula, Z is BiC5NaO. It represents the fraction occupied by molybdenum in 5MOO4.

In addition, X and Y represent BIO among the active components of the catalyst. 5N
aO. 5MOO4, other components except A and BiPO4MO(1-z)BiOlゝ0ma0014Feゝ16
In ♀σ14, the number of atoms of molybdenum, bismuth and iron is set to NMO. ．． It represents the fraction defined when NB and NFe.

In order to obtain effective action and characteristics, the catalyst of the present invention has a very limited composition ratio of components as seen in the above structure, and it is particularly important that it contains an essential trace component A. It is a feature.

Not only is the selectivity for methacrylonitrile relatively low in catalysts that do not contain component A, but as the conversion of tert-butanol is increased by increasing the catalyst time, the amount of methacrylonitrile produced increases. A portion undergoes secondary decomposition, greatly reducing selectivity. The meaning of the conversion rate of tertiary butanol in the present invention is as follows.

According to experiments conducted by the present inventors, the supplied tertiary-butanol was converted into methacrylonitrile, methacrolein, carbon dioxide, carbon monoxide, acetonitrile, hydrogen cyanide, and isobutylene, and the raw material tertiary-butanol was It was not detected at all in any reaction.

Therefore, the present inventors temporarily regarded isobutylene as an unreacted substance and defined the total conversion rate of tertiary-butanol as follows. When using the catalyst of the present invention containing component A, a large selectivity is maintained even at a tertiary-butanol conversion rate close to 100%.

The A component of the present invention is calculated using the above defined index.
= selected from the range of 0.002 to 0.06. Component A
can be used as one selected from potassium, rubidium and cesium, or a combination thereof. When rubidium or cesium is used alone, it has the effect of improving the same methacrylonitrile selectivity with a smaller amount than potassium. If the amount of component A used exceeds the range of the present invention, the conversion rate of tertiary-butanol will decrease, the utilization of ammonia will be impaired, and the by-product of methacrolein will increase, which is undesirable. Among the photogenic components of the catalyst of the present invention, BjO. 5NaO. 5MOO4, components A and B
Regarding other constituent elements other than jPO4, molybdenum, bismuth and iron, the index X representing the fraction of iron to bismuth and the index Y representing the relative ratio of molybdenum are X.
Four coordinate points (a) in the Y coordinate. 45,0.35)
,(stomach). 45, 0.65), (a). 85,.

0.50) and (a). 85, 0.65) from within the rectangle connecting them.

X. ．． If the combination of Y is outside this range, then A
Even with the addition of components, it is not possible to obtain a high selectivity for methacrylonitrile. If the value of Y is larger than this range, not only will the yield of methacrylonitrile be low, but also the escape of molybdenum will be significant, causing troubles such as clogging of the reaction system. The amount of sodium used, which is one of the optional components of the catalyst in the present invention, is determined by BjO. 5NaO.
Z = 0 to 0 using an index representing the relative proportion of 5MOO4
．． Selected from a range of 6.

Particularly preferably, Z=0 to 0.45. X. ．．
If the value of Y is within the limited range of the present invention and a trace amount of component A within the range of the present invention is included, the catalyst has excellent activity and selectivity even in the absence of sodium, that is, when Z=0. is obtained. However, when the value of Y is within the range of the present invention and is relatively large, such as 0.55 to 0.65, the degree of escape of molybdenum becomes relatively large, but the addition of sodium to such a catalyst system is , effectively suppressing the escape of molybdenum. When the value of Y is relatively small, the degree of molybdenum escape is sufficiently suppressed even without the addition of sodium, and it can be used for industrial implementation. In order to use the catalyst stably for a long period of time, it is necessary to suppress the escape of molybdenum, and for this purpose, the value of Z is sufficient within the range of the present invention. If it is used beyond this range, not only will expensive bismuth and molybdenum be consumed, but also the yield of methacrylonitrile will decrease. In the catalyst used in the present invention, silica is used as a carrier.

Silica itself is inert compared to other carriers, exhibits the effect as a binder without substantially impairing the selectivity of the catalyst itself, and imparts high wear resistance to the catalyst. When other carriers, such as titania or zirconia, are applied to the catalyst used in the present invention, their effect as a binder is extremely small, and when alumina is used, even though they have a binder effect, the selectivity of the catalyst is greatly reduced. .
Furthermore, even if the catalyst used in the present invention contains 1% by weight of aluminum, the selectivity will decrease. The amount of silica used is selected from a range of 30 to .7% by volume. Particularly preferably, the amount is 40 to 6%. The amount of silica used is 3
Strong abrasion resistance can be obtained when the slag weight is % or more. However, 7
If it is used in an amount exceeding 0% by weight, the catalytic active component will be diluted, and not only will sufficient activity not be obtained, but the selectivity will also be greatly reduced. The amount of phosphorus used, which is another optional ingredient, is
Using an index representing the relative proportion of BiPO4, p = 0 to 0
．． Selected from a range of 2.

By adding a small amount of phosphorus within this range to the catalyst of the present method, the wear resistance strength of the catalyst can be further improved. The addition of phosphorus refines the viscosity of the suspended matter in the slurry and improves its dispersibility in the preparation of the raw material slurry in the catalyst manufacturing process described below. It is thought that this allows the silica sol, which is suitably used as the carrier silica liquid, and the active ingredient to be in a homogeneous mixed state in the slurry, resulting in excellent wear resistance strength being obtained in the final form of the catalyst. Phosphorus can be used beyond the scope of the present invention, but will not increase the wear strength any further. Since phosphorus is present primarily as BlPO4 in the final catalyst form, using large amounts of phosphorus is not advantageous as it consumes expensive bismuth. When a catalyst is used industrially, its action must last for a long time under the reaction conditions.

As mentioned above, the catalyst of the present invention not only has improved activity and selectivity at the initial stage of use, but also has the properties required from this point of view, namely, the stability of catalyst components and excellent wear resistance. High activity and selectivity are maintained over a long period of time. The production of methacrylonitrile of the present invention can be carried out in either a fluidized bed reactor or a fixed bed reactor.

Generally, when a fluidized bed reactor is used, heat can be easily removed and a uniform reaction temperature can be obtained, making it suitable for large-scale production. Generally, when a catalyst is used in a fluidized bed reactor, it is abraded due to collisions between catalyst particles or between particles and the vessel wall, but the catalyst of the present invention can sufficiently withstand this. The catalyst of the present invention can be suitably produced through three steps: first preparing a raw material slurry, then spray drying the slurry, and finally heat-treating and calcining the dried product.

Silica sol can be suitably used as the carrier silica source for the catalyst, and phosphoric acid can be suitably used as the phosphorus source. The sources of molybdenum, bismuth, iron, sodium, potassium, rubidium and cesium are preferably used in the form of ammonium salts, nitrates, hydrochlorides, sulfates or organic acid salts soluble in water or nitric acid. In particular, it is preferable to use the molybdenum source in the form of an ammonium salt, and the bismuth, iron, sodium, potassium, rubidium and cesium sources in the form of their respective nitrates.
To prepare the raw material slurry, first add phosphoric acid to the silica sol while stirring, then add an aqueous solution of ammonium molybdate, and finally add bismuth nitrate, ferric nitrate, sodium and potassium nitrate, rubidium nitrate, or cesium nitrate to dilute nitric acid. You can choose from.

This can be suitably carried out by adding a mixed solution in which one or more of the above substances are dissolved. In this step, a slurry of fine suspended solids uniformly dispersed in the silica colloid sol is obtained. The slurry is then dried using a known spray dryer to obtain spherical dry fine particles. Atomization of the raw material slurry can be carried out by any of the centrifugal, two-fluid nozzle, or high-pressure nozzle methods commonly used in industrial practice, but the centrifugal method is particularly preferred.

In the centrifugal system, the particle size can be distributed between 10 and 150 microns, which is suitable for use in a fluidized bed reactor, by adjusting the rotational speed of the disk and the feed rate of the slurry. Finally, the dried product is heat-treated and fired using a conventional tunnel or rotary kiln.

Firing temperature is 600-750℃, preferably 620-73℃
It can be carried out in the range of 0°C. The firing time may vary depending on the firing temperature, but is selected within the range of 1 to 2 hours. The raw material tertiary-butanol used in the ammoxidation reaction of tertiary-butanol does not necessarily need to be highly pure.

Air is usually used as the oxygen source. The volume ratio of tertiary butanol, ammonia and air was 1:0.
9-2.0:8-20, especially 1:1-1.5:9-15
A range of is preferred. Additionally, steam or inert gas may be introduced as necessary. The reaction temperature is 360-5
00°C, particularly preferably in the range of 380 to 450°C. The reaction pressure may be normal pressure, but the reaction may be carried out under increased pressure if necessary.
The contact time between the raw material mixed gas and the catalyst is between 0.3 and 15 seconds, preferably between 0.5 and m seconds. By using a catalyst with a specific composition as described above, the method of the present invention significantly improves the selectivity of methacrylonitrile by ammoxidation of tertiary-butanol, and also improves the long-term stability and wear resistance of the catalyst itself. The method is extremely advantageous for implementation on an industrial scale.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example (1) The manufacturing composition index of the catalyst is X=0.70, Y=0.54, Z=0, (k
) = 0.006, p = 0.1, and the empirical formula of the catalyst supported on 5% silica, i.e. its active component, is M
OBlO. 36FeO. 6OKO. .

O6PO. 1Oq of catalyst was prepared as follows. Take 5000 g of silica sol (Snowtex N manufactured by Nissan Chemical) containing 30 wt% SiO2, add 61.2 g of 85 wt% phosphoric acid to it while stirring, and then add ammonium 7-molybdate [(M
H4) 6M07024・4H20] 948g of dissolved solution was added, and finally, 921g of bismuth nitrate [B1(NO3)3・■
theory], 1293 g of ferric nitrate [Fe(NO3)3.1
・9H20], and 3.26 g of potassium nitrate [KN
A mixed solution in which O3] was dissolved was added.

The raw material slurry obtained in this step) was sent to a co-current spray dryer and dried. The raw material slurry was atomized using a centrifugal atomizer equipped with a dish-shaped rotor, which was installed in the center of the upper part of the dryer. The obtained dry powder was fired in a tunnel kiln to obtain a catalyst. This will be referred to as catalyst 1.
Other catalysts of various compositions were produced in a similar manner.

These catalysts were subjected to the following tertiary-butanol ammoxidation test, molybdenum escape test, and abrasion resistance test.

). ) Ammoxidation reaction test of tertiary butanol (
Fill a glass reaction tube with an inner diameter of 8 mm with 1 g of the various catalysts prepared in 1), maintain it at 420-430°C, and add tertiary-butanol, ammonia, and oxygen in a molar ratio of 1:21. A gas mixture in a ratio of .5:2.5 was diluted with helium until the tertiary butanol concentration was 6% by volume, and passed through at a rate that gave a contact time of 0.5 to 1.58.

The reaction pressure at this time was atmospheric pressure. The test results of this ammoxidation reaction are shown in Table 1 along with the composition of the catalyst used. Note that rubidium nitrate and cesium nitrate were used as rubidium and cesium sources in the examples.

In addition, sodium nitrate was used as the sodium source in all cases. Further, the total conversion of tertiary-butanol and the yield of methacrylonitrile in Table 1 were determined according to the following definitions.

In addition, unreacted tertiary butanol was not detected in any of the Examples.

(3) Molybdenum fugitive test The molybdenum fugitive was determined by accurately weighing about 10 g of the catalyst in a magnetic dish and calculating the weight loss rate of the catalyst after leaving it in the presence of air at 750'C for 10 hours.

It was confirmed by elemental analysis after the test that the decrease in catalyst weight was due to the sublimation and escape of MOO3. Table 2 shows the measurement results of molybdenum fugitiveness.

As is clear from Table 2, catalysts 33 and 29, in which the value of Y exceeds the range of the present invention, have a large escape degree.

Comparative Catalyst 29 has a lower escape degree than Comparative Catalyst 33 due to the introduction of Z, but as shown in Table 1, the yield of methacrylonitrile is low. In the catalyst of the present invention, the value of Y is within a limited range, and the degree of escape is effectively suppressed by the introduction of Z. (4) Abrasion Test The abrasion of the catalyst is measured using a 1.5-inch inner diameter vertical Approximately 50 g of the catalyst was accurately weighed into the tube, and air was flowed through the perforated disk at a rate of 15 CF/hour to force the catalyst to flow.

The degree of catalyst wear was refined over a period of 5 to 50 minutes and was determined as the ratio of the weight of the catalyst lost from the top of the vertical tube to the initial charge. Table 3 shows the measurement results of the degree of catalyst wear.

As is clear from Table 3, comparative catalysts 34 and 35 with a low silica content are very susceptible to wear, whereas the catalyst of the present invention with an appropriate silica content has a low wear rate, and even with the addition of phosphorus, This shows that it is effectively suppressed.

Claims (1)

[Claims] 1. In producing methacrylonitrile by contacting tertiary butanol with ammonia and oxygen in the presence of a catalyst in the gas phase at high temperature, the general composition formula AaMoBibFef
NanPpOq [wherein A is one or more elements selected from potassium, rubidium, cesium, a, b, f,
n, p and q each represent the atomic ratio of elemental component A, bismuth, iron, sodium, phosphorus and oxygen to one atom of molybdenum, a is a number in the range of 0.002 to 0.06, b, f and n are The formula b=(1-X)(1
-Y)(1-Z)/Y+1/2Z+p, f=X(1-Y)(1-Z)/Y and n=1/2Z, where X
, Y is (0.45, 0.35), (0.45, 0.65
), (0.85, 0.50), (0.85, 0.65)
The number inside the rectangle formed by connecting the four coordinate points, Z
is a number in the range of 0 to 0.6, p is a number in the range of 0 to 0.2, and q is the number of oxygen atoms satisfying the valence of the element in the catalyst. A method for producing methacrylonitrile, which comprises using a catalyst in which 30 to 70% by weight of the composition shown in the following is supported on silica.