JPH0242034A - Production of methacrylic acid and/or methacrolein - Google Patents

Abstract

PURPOSE:To advantageously obtain methacrylic acid in high selectivity even at low temperatures by using a catalyst containing heteropoly-acids, having phosphorus, etc., as the central element and containing silver, etc., as a constituent element in catalytically oxidizing isobutane in the vapor phase and producing the subject compound. CONSTITUTION:A mixed gas containing isobutane and molecular oxygen in the vapor phase is brought into contact with a catalyst to produce methacrylic acid and/or methacrolein. In the process, a catalyst containing a heteropoly-acid and/or salt thereof, having P and/or As as the central atom and containing Mo and at least one selected from Ag, Zn, Cd, Ti, Zr, Nb, Ta, Cr, W, Mn, Fe, Co, Ni, Rh, Sn, Bi and Te as a catalyst constituent element is used as the above-mentioned catalyst to afford the methacrylic acid in good selectivity even at low reaction temperatures in one stage without requiring a special apparatus. Furthermore, since the low reaction temperatures suppress decomposition of the catalyst, the afore-mentioned method is economically advantageous to industrial practice.

Description

DETAILED DESCRIPTION OF THE INVENTION [Prior Art] In the past, saturated hydrocarbons such as isobutane were considered to be inert gases. For example, JP-A-55-2619 describes that it is used as a diluent for reaction gas in the oxidation of olefins and aldehydes.

Because isobutane has poor reactivity, the common method is to convert it to inbutylene using a dehydrogenation catalyst or oxidative dehydrogenation catalyst, and then oxidize it to methacrolein or methacrylic acid (for example, 1978
On the other hand, as an attempt to oxidize isobutane and directly convert it into methacrolein or methacrylic acid, British Patent No. 13
No. 40891 discloses that methacrolein can be obtained by one-step oxidation of isobutane by contacting antimony and molybdenum oxides with a mixed gas of isobutane and oxygen in the gas phase, although the yield is extremely low. There is. However, methacrylic acid has not been obtained by this method. JP-A-55-62041 first showed that methacrylic acid could be prepared in one step from isobutane. The catalyst used is an oxide catalyst consisting of antimony, molybdenum, and phosphorus, and this combination of oxides appears to be essential for achieving high selectivity for methacrylic acid. In this method, increasing the isobutane concentration tends to lower the selectivity of methacrylic acid, and attempts to increase the productivity per reactor by increasing the isobutane concentration have not always been successful.

For these oxide catalysts, JP-A-62-1328;32
In the publication, a method using a heteropolyacid as a catalyst was proposed. That is, conventionally, only an oxide catalyst consisting of antimony, molybdenum, and phosphorus was able to convert isobutane directly into methacrylic acid in a one-step reaction, whereas a heteropolyacid containing phosphorus as a central element and molybdenum was used as a catalyst.
By creating a very unique reaction method in which isobutane and oxygen are brought into contact with a catalyst alternately, highly selective conversion to methacrylic acid was made possible. While the oxide catalyst mentioned above also requires antimony as an essential element, the new method using a heteropolyacid as a catalyst does not require antimony. Alternating contact of isobutane and oxygen with the catalyst has been an extremely important discovery in improving methacrylic acid selectivity, but in order to bring isobutane and oxygen into contact with the catalyst alternately, a special reaction device is required. Therefore, in industrial implementation, this may be economically disadvantageous compared to a method in which a mixed gas of isobutane and oxygen is brought into contact with a catalyst.

Although each of the above-mentioned methods has its own characteristics, it has not yet reached a satisfactory level as an industrial production method.

[Problems to be Solved by the Invention] Therefore, the purpose of the present invention is to solve the problems by using a new catalyst.
Methacrylic acid is obtained with high selectivity and high productivity,
Moreover, it is an object of the present invention to provide a one-step oxidation method for isobutane that does not require a special reaction device by bringing a mixed gas containing isobutane and oxygen into contact with a catalyst.

[Means for Solving the Problem] The present inventors have developed a catalyst that can convert a mixed gas containing isobutane and oxygen into methacrylic acid in one step by bringing them into contact with fA.
As a result of repeated research, the present invention was completed by discovering a catalyst with high practicality in both activity and selectivity.

That is, the present invention is a heteropolyacid and/or a salt thereof having phosphorus and/or arsenic as a central element and containing molybdenum, including 8g, Zn, Cd, Ti, Zr, Nb, Ta, Cr,
A mixed gas containing isobutane and molecular oxygen is brought into contact with a catalyst containing at least one selected from the group consisting of W, Mn, Fe, Co, Ni, Rh, Sn, Bi, and Te as a catalyst constituent element in a gas phase. This is a method for producing methacrylic acid and/or methacrolein.

According to the method of the present invention, (1) a mixed gas containing isobutane and oxygen is brought into contact with a catalyst, and (2) methacrylic acid can be obtained with high productivity and (3) with good selectivity.

There are many unknowns as to why such excellent effects are obtained, and it is not clear in detail what mechanism of action the series of catalyst constituent elements mentioned above contribute to improving reaction performance. However, these elements primarily cause overoxidation of methacrylic acid and methacrolein by forming stable salts with heteropolyacids or substituting some of the coordination elements of heteropolyacids. This causes oxygen species to form on the catalyst. Second, it is thought that this is because isobutane, which is usually considered inert, is relatively easy to adsorb and activate.

The present invention will be explained in more detail below.

The catalyst used in the present invention is a heteropolyacid containing phosphorus and/or arsenic as a central element and containing molybdenum, and/or
or its salt, and also Ag, Zn, Cd, Ti, Zr
, Nb, Ta, Cr, W, Mn, Fe, Co, Ni, R
It is important that the catalyst contains at least one selected from the group consisting of h, Sn, Bi, and Te as a catalyst constituent element. The ratio of these constituent elements is 0.5 to 3 gram atoms of the central element to 12 gram atoms of molybdenum, Ag, Zn
, Cd.

Ti, Zr, Nb, Ta, Cr, W, Mn, Fe, CO
5Ni, Rh, Sn, Bi or Te is preferably in the range of 0.01 to 3 gram atoms.

More preferably, it is 0.05 to 1 gram atom.

The chemical state of existence of these elements is extremely complex and is not strictly clear. It is highly likely that it exists as a metal salt of a heteropolyacid or partially replaces the coordination element of a heteropolyacid, but it may exist in a state other than a heteropolyacid, such as an oxide or an oxyacid. You can leave it there. In addition, catalysts used in the present invention that contain TI, alkali metals, alkaline earth metals, and rare earth metals in addition to the above-mentioned elements are also effective as catalysts.

The basic structure of these heteropolyacids or their salts is phosphomolybdic acid, arsenic molybdic acid, or a mixture thereof. It is known that these have various structures (Kagaku no Todai, Vol. 29, No. 12, p. 853, Sasaki, Matsumoto), and the ratio of the central element to the coordination element is 1/12.1/
It may take various structures such as 11.1/10.1/9.2/I7.2/18. Among these, one having a 1/12 Vt structure called a Keggin structure is particularly suitable. Furthermore, an excess amount of the central element phosphorus or arsenic may be present in the catalyst as an oxide or oxygen acid.

These heteropolyacids are known to assume a wide range of reduced states. Although it is unclear to what extent the catalyst used in the present invention is working in a reduced state under the reaction conditions, those used for oxidation reactions often have a color close to yellow-green, and are heteropolyblue. Since it does not exhibit the black-blue color known as black-blue, the degree of reduction is thought to be quite shallow, and it is inferred that it is in a shallow reduction state below -electron. However, since the reduction state varies greatly depending on the catalyst composition, reaction gas composition, reaction temperature, etc., the degree of reduction is not limited to this range.

In order to prepare the catalyst of the present invention, it is easy to mix a compound containing these additive elements into a heteropolyacid or its salt in a solution or slurry state, and then dry and calcinate the mixture. It may be added by impregnation or kneading after drying or baking.

These elements can be added in the form of metal oxides, hydroxides, carbonates, nitrates, chlorides, oxyacids, phosphates, oxalates, acetates or organic complexes. Also, metal can be used.

As a catalyst, salts of various nitrogen-containing compounds of these heteropolyacids can be used. Useful salts include ammonium salts or salts with organic amines such as pyridine, quinoline, piperazine, etc. This may partially form a salt with a nitrogen-containing compound or the like, or it may be a salt obtained by removing part or all of the nitrogen-containing compound by firing. Ammonium salts or organic amine salts can be synthesized from heteropolyacids. In the case of ammonium salts, water-soluble ammonium salts such as aqueous ammonia, ammonium chloride, and ammonium nitrate can be used as ammonium ion sources. These ammonium salts or amine salts are calcined at 300 to 600°C before use.

It is more preferable to calcinate in an inert gas. It is also possible to perform firing in an oxygen-containing gas after firing in an inert gas.

These catalysts can be supported on a carrier or used as a diluted mixture. Examples of the carrier include silica, α-alumina, silicon carbide, titania, zirconia, and diatomaceous. A high porosity inert carrier with many macropores is preferred. Usually up to about 50% by weight is deposited onto these carriers in the presence or absence of water. Or mixed with a fine particulate carrier,
For example, it can be formed into a cylindrical shape. Such a catalyst shape can be formed with or without using a tablet press, an extrusion molding machine, a Marmerizer (trade name of Fuji Paudal Co., Ltd.), a relocation type granulator, or the like.

A mixed gas of isobutane and oxygen is used as the raw material gas supplied to the reaction.

The concentration of isobutane is suitably in the range of 1 to 80 mol 2 , more preferably in the range of 10 to 70 mol %.

When the concentration of isobutane is lower than 10 mol%, the amount of methacrylic acid produced per reactor becomes extremely small.
It is not economical enough to be implemented industrially. Other hydrocarbons may be mixed in as long as they do not affect the reaction.

The molar ratio of oxygen to isobutane in the feed gas is 0.
The molar ratio is between 0.05 and 2, preferably between 0.1 and 1. When the oxygen molar ratio is high, complete oxidation progresses too much and more carbon dioxide is produced. Conversely, if the oxygen molar ratio is small, a sufficient amount of oxygen will not be supplied for isobutane oxidation, resulting in a decrease in methacrylic acid productivity. Furthermore, if the oxygen molar ratio is small, the catalyst tends to be reduced as the reaction progresses, which is not preferable.

On the other hand, when selecting the oxygen concentration and isobutane concentration, it is preferable to take into consideration so that the mixed gas composition does not fall within the explosive range. As the oxygen source, pure oxygen gas or air may be used.

Additionally, in order to prevent the reaction product methacrylic acid from being further oxidized on the catalyst and becoming carbon dioxide, it is effective to add water in a ratio of 5/1 to 115 to isobutane. , the n refractive index of methacrylic acid increases. Preferably it is in the range of 3/1 to 1/3.

Further, the source gas can also be diluted using a diluent gas. Nitrogen, helium, argon, and carbon dioxide can be used as diluent gases. Unreacted isobutane can be recovered and used again. At that time, carbon monoxide, carbon dioxide, and other reaction products may be mixed in as long as they do not affect the reaction. Furthermore, methacrolein produced at the same time can be recovered and added to the raw material gas.

The reaction temperature is selected from the range of 200 to 400°C.

Preferably it is 240 to 370°C. High reaction temperatures tend to cause decomposition of the catalyst and complete oxidation of the reaction products.

The reaction pressure can be set over a wide range from reduced pressure to increased pressure, but from normal pressure to 2 atmospheres is industrially advantageous.

The contact time between the reaction gas and the catalyst varies depending on the isobutane concentration, reaction temperature, etc., but is suitably 0.1 to 10 seconds, preferably 0.5 to 5 seconds.

In carrying out the present invention, the type of reactor used can be appropriately selected from fixed bed, fluidized bed, moving bed and other types of reactors.

The generated methacrylic acid and methacrolein are cooled.

They can be separated and purified by known appropriate methods such as absorption and silent distillation to produce the respective products. Unreacted isobutane can be recovered and used again as a raw material. Further, after recovering methacrylic acid from the reaction gas by a known method such as cooling condensation, absorption, or adsorption, part or all of the recovered gas containing methacrolein can be supplied to the reactor again as a raw material gas.

[Example] Example 1 12-molybdophosphoric acid (83FMo) 204o/301
1゜0: Nippon Inorganic Chemical) 23.6 g of crystals and 1.4 g of ferric chloride were dissolved in 200 ml of water, and in this solution,
6. Add 100 g of ammonium nitrate aqueous solution of 4ffi amount X, stir well, and concentrate the obtained slurry solution.
It was then dried at 120°C for 12 hours, crushed, and
20 mesh particles were selected from the sample. This was baked at 450°C in a nitrogen stream for 3 hours and then in air at 350°C for 2 hours.

A catalyst with the composition P Mo 12F e O-5 was obtained.

A Pyrex W U-shaped tube with an inner diameter of 6 mm was filled with 5 g of this catalyst and set in a constant temperature bath. The temperature of the constant temperature bath is 370°
C, 60 mol% of isobutane, 20 mol% of oxygen,
Water 7! A mixed gas containing 20 mol % of S gas was supplied for a contact time of 1.5 seconds. When the reaction gas was analyzed by gas chromatography after 6 hours, 7.8% of the isobutane was evaporated.
The selectivity for methacrylic acid was 41.8%, and the selectivity for methacrolein was 15.3%. No isobutylene was detected.

Comparative example 1 12-molybdophosphoric acid (113PM012040.30
H20: Nippon Inorganic Chemical) 23.2g was dissolved in 200ml of water, and a catalyst was prepared in the same manner as in Example 1, except that ferric chloride was not added. A reaction was carried out using this catalyst under the same conditions as in Example 1. After 6 hours, the reaction gas was analyzed by gas chromatography, and it was found that 10.3% of isobutane had been converted, the selectivity for methacrylic acid was 15.3%, and the selectivity for methacrolein was 18.5%.

Example 2 A catalyst having a composition of P Mo 12W 1.1 was prepared as in Example 1 except that 3.0 g of ammonium 12 tungstate decahydrate was used instead of ferric chloride. Manufactured.

Using this catalyst, a reaction was carried out under the same conditions as in Example 1. Gas chromatography analysis of the reaction gas after 6 hours showed that 8.7x of isobutane had been converted, the selectivity for methacrylic acid was 35.8%, and the selectivity for methacrolein was 26.3%.

Example 3 12-Molybdophosphoric acid (H3PMot204o・30H
20: 23.6 g of crystals (Japan Inorganic Chemical), 0.28 g of rhodium chloride and 5.26 g of thallium acetate were added to 200+n
After dissolving in 1 of water, 8.0 g of pyridine and 100 ml of water were added to this solution and stirred well. The resulting slurry solution was concentrated, then dried at 120° C. for 12 hours, and then ground to separate particles of 10 to 20 meshes. This was fired at 450°C in a nitrogen stream for 3 hours and then in air at 350°C for 2 hours. P Mo 1゜Rh,
,,Tl. A catalyst with the composition was obtained.

The reaction was carried out in the same manner as in Example 1, except that the reaction temperature was 350° C. and the contact time was 3.6 seconds.

Gas chromatography analysis of the reaction gas after 6 hours showed that 5.9% of isobutane had been converted, the selectivity for methacrylic acid was 38.7%, and the selectivity for methacrolein was 2.
It was 1.6%.

Example 4 Slurry composition is P,, 5M o 1□Nbo-,
Bio-.

Add 12-molybdophosphoric acid (Nippon Inorganic Chemical), phosphoric acid (85% by weight), bismuth nitrate, and niobium oxalate to give Cs2, and further add quinoline 13 to this solution.
g and 100 ml of water were added and stirred, and the resulting slurry was concentrated. After drying at 120°C for 12 hours,
It was ground and 10 to 20 mesh particles were sorted. This was heated at 450°C in a nitrogen stream for 3 hours, then at 350°C in air.
It was baked at ℃ for 2 hours.

A reaction was carried out using this catalyst in the same manner as in Example 3. After 6 hours, the reaction gas was analyzed by gas chromatography and found that 5.3% of isobutane had been converted, the selectivity for methacrylic acid was 39.3%, and the selectivity for methacrolein was 19.3%.
It was 5%.

Example 5 Sodium molybdate (Na2MoO4.2H20)
Dissolve 121g in 200ml of water and add 30%
20g of arsenic acid aqueous solution was added. Add concentrated sulfur fi80m to this solution.
After adding 300 ml of ethyl ether, the mixture was separated into three phases.

The bottom phase was taken out and air-dried to obtain arsenic molybdic acid.

23.7g of this arsenic molybdic acid, 2.7g of ferric chloride
g and 0.28 g of rhodium chloride to obtain a catalyst having the following composition: A s M O+2F e ], aRho, 1.

A reaction with this catalyst was carried out in the same manner as in Example 1, except that the reaction temperature was 320° C., the contact time was 4 seconds, and the oxygen concentration was 10 mol%. As a result, 2.8% of isobutane was converted, the selectivity of methacrylic acid was 51.2%, and the selectivity of methacrolein was 21.5%.

Example 6 Instead of adding niobium oxalate and bismuth nitrate in Example 4, arsenic acid and chromium nitrate were added to obtain P 1.5M.
A catalyst having a composition of 02A S 0-6Cr (H, 6) was prepared.

A reaction was carried out using this catalyst in the same manner as in Example 1, except that the reaction temperature was 320° C. and the contact time was 3.6 seconds, and the isobutane concentration was 20 mol%. As a result, 3.8 of isobutane
% conversion, the selectivity for methacrylic acid was 49.6%, and the selectivity for methacrolein was 19.4%.

Example 7 Aqueous solution composition is P 1-3M O+2Rho, tF
12-Molybdophosphoric acid (Nippon Inorganic Chemical), phosphoric acid (85% by weight), rhodium chloride, and ferric chloride were added so as to give e o-3, and the mixture was stirred well. to this aqueous solution.

100 to 200 meshes of spherical silica (2 microbead silica gel 100OA manufactured by Fuji Davison) calcined at 700° C. for 3 hours were immersed, impregnated with the catalyst component, and dried.

By repeating impregnation and drying, about 45 weight of the catalyst component was supported. This was made to absorb pyridine and dried at 120°C. This product was further soaked in an ethanol solution of IN-potassium hydroxide to impregnate potassium.

Next, it was dried at 120°C, and then dried at 450°C in a nitrogen stream.
It was baked at 350° C. for 3 hours and then in air at 350° C. for 2 hours. The composition of the obtained catalyst was Pl, IMo 12Rh□, 1F eO-25 and 2/S
The first table was published in j02.

140 g of this catalyst was heated at 320°C using a fluidized bed reactor with an internal volume of 400 m1, and a mixed gas of 60 mol% isobutane, 20 mol% oxygen, and 20 mol% water vapor was heated at a gas linear velocity of 20 cm.
/second, contact time 4.0 seconds. When the reaction gas was analyzed by gas chromatography after 20 hours, 4.3% of isobutane was converted, and the selectivity of methacrylic acid was 4.
0.2%, and the selectivity for methacrolein was 20.3%. After the reaction, the catalyst had a yellow-green color.

Examples 8 to 15 Catalysts having the compositions shown in Table 1 were prepared by AT and reacted in exactly the same manner as in Example 1. After 20 hours, the reaction gas was analyzed by gas chromatography and the reaction results are summarized in Table 1.

The following examples 18 to 30 of excitation were carried out using catalysts having the compositions shown in Table 2 at a reaction temperature of 340'C.
30 mol% of isobutane, 50% of air at 1 contact time of 3.6 seconds
A reaction was carried out in the same manner as in Example 1 with a mixed gas containing 20 mol % of water vapor. The reaction results are summarized in Table 2.

+ 2 It is possible to carry out this method, and it is economically advantageous when it is implemented industrially.

Claims (1)

[Claims] A heteropolyacid and/or its salt containing phosphorus and/or arsenic as the central element and molybdenum, including Ag, Zn,
Cd, Ti, Zr, Nb, Ta, Cr, W, Mn, Fe
, Co, Ni, Rh, Sn, Bi and Te, as a catalyst constituent element, is brought into contact with a mixed gas containing isobutane and molecular oxygen in a gas phase. Method for producing methacrylic acid and/or methacrolein