JPH07116071B2 - Method for producing methacrylic acid and / or methacrolein - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Prior Art Saturated hydrocarbons such as isobutane were conventionally considered to be inert gases. For example, JP-A-55-2619 describes that it is used as a diluent for a reaction gas in the oxidation of olefin or aldehyde.

As described above, since isobutane is poor in reactivity, it is common to convert it to isobutylene using a dehydrogenation catalyst or an oxidative dehydrogenation catalyst, and then oxidize this to methacrolein or methacrylic acid (for example, JP 58-
No. 189130).

On the other hand, as an attempt to oxidize isobutane and directly convert it to methacrolein or methacrylic acid, British Patent 1340
No. 891 shows that methacrolein can be obtained by a single-step oxidation of isobutane, although the mixed gas of isobutane and oxygen is vapor-contacted with an oxide of antimony and molybdenum in a gas phase. There is. However, methacrylic acid has not been obtained by this method. JP-A-55-62041 was the first to show that methacrylic acid can be produced from isobutane in a single step. The catalyst uses an oxide catalyst consisting of antimony, molybdenum and phosphorus, and this combination of oxides seems to be essential for achieving a high selectivity of methacrylic acid. In this method, the selectivity of methacrylic acid tends to decrease as the isobutane concentration increases, and attempts to increase the isobutane concentration to increase productivity per reactor have not always been successful.

In contrast to these oxide catalysts, JP-A-62-132832 proposes a method using a heteropolyacid as a catalyst. That is, conventionally, only an oxide catalyst composed of antimony, molybdenum and phosphorus was able to directly convert isobutane to methacrylic acid in a one-step reaction, whereas a heteropolyacid containing phosphorus as a central element and molybdenum was used as a catalyst, and We have made possible a highly selective conversion to methacrylic acid by creating a reaction method characterized by alternately contacting oxygen and oxygen with the catalyst. While the above-mentioned oxide catalyst uses antimony as an essential element, antimony is not required in the new method using a heteropolyacid as a catalyst. Alternately contacting isobutane and oxygen with the catalyst has been a very important discovery for improving the methacrylic acid selectivity, but a special reactor is required to alternately contact isobutane and oxygen with the catalyst. Therefore, in industrial practice, this may be economically disadvantageous in comparison with the method of contacting a mixed gas of isobutane and oxygen with the catalyst.

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

[Problems to be Solved by the Invention] Therefore, the object of the present invention is to obtain a methacrylic acid with a high selectivity and a high productivity by using a novel catalyst, and to provide a mixed gas containing isobutane and oxygen. To provide a one-step oxidation method of isobutane that does not require a special reactor as a catalyst.

[Means for Solving the Problem] The inventors of the present invention have conducted intensive studies on a catalyst that can convert isobutane and a mixed gas containing oxygen into methacrylic acid in a single step, and as a result, have high activity and selectivity. A catalyst was found and the present invention was completed.

That is, the present invention relates to a heteropolyacid containing phosphorus and / or arsenic as a central element and molybdenum and / or a salt thereof, which comprises Ag, Zn, Cd, Ti, Zr, Nb, Ta, Cr, W, Mn, Fe and C.
characterized in that a mixed gas containing isobutane and molecular oxygen is contacted in a gas phase with a catalyst containing at least one selected from the group consisting of o, Ni, Rh, Sn, Bi and Te as a catalyst constituent element. It 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) high productivity can be obtained, and (3) methacrylic acid can be obtained with a good selectivity.

There are many unclear points about the reason why such an excellent effect is obtained, and it is not clear in detail what kind of action mechanism the series of catalyst constituent elements described above contribute to the improvement of the reaction results, but These elements form stable salts with heteropolyacids, or replace some of the coordination elements of heteropolyacids, and firstly, oxygen species that cause excessive oxidation of methacrylic acid and methacrolein. Are difficult to form on the catalyst. Second, it is considered that isobutane, which is usually considered to be inactive, is relatively easily adsorbed and activated.

Hereinafter, the present invention will be described in more detail. The catalyst used in the present invention is a heteropoly acid containing phosphorus and / or arsenic as a central element and molybdenum and / or a salt thereof, and Ag, Zn, Cd, Ti, Zr, Nb, Ta, Cr, W,
It is important to include at least one selected from the group consisting of Mn, Fe, Co, Ni, Rh, Sn, Bi and Te as a catalyst constituent element. The ratio of these constituent elements is such that the central element is 0.5 to 3 gram atom to 12 gram atom of molybdenum, Ag, Z.
n, Cd, Ti, Zr, Nb, Ta, Cr, W, Mn, Fe, Co, Ni, R
It is preferred that h, Sn, Bi or Te be 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 complicated and is not exactly clear. It exists as a metal salt of heteropolyacid. Alternatively, it is highly possible that a part of the coordination element of the heteropolyacid is replaced, but it may be present in a state other than the heteropolyacid such as an oxide or an oxygen acid. Further, the catalyst used in the present invention, in addition to the above elements, T1 or alkali metal, alkaline earth metal,
Those containing rare earth metals are also effective as catalysts.

The basic structure of these heteropoly acids or salts thereof is phosphomolybdic acid, arsenic molybdic acid, or a mixture thereof. These are known to have various structures (Chemistry, Vol. 29, No. 12, page 853, Sasaki, Matsumoto), and the ratio of the central element to the coordination element is 1/12, 1/11, 1 / 10, 1 /
It may have various structures such as 9, 2/17 and 2/18.
Among them, those having a 1/12 structure called Keggin structure are particularly preferable. Further, phosphorus or arsenic, which is the central element, may be present in the catalyst in an excessive amount as an oxide or an oxygen acid.

It is known that these heteropolyacids have a wide range of reduction states. The catalyst used in the present invention, under the reaction conditions, it is unclear how much reduction state works, but the one used for the oxidation reaction often exhibits a color close to yellow green, and heteropoly blue. It is considered that the degree of reduction is rather shallow, and it is inferred to be in a shallow reduced state of one electron or less. However, the reduction state greatly changes depending on the catalyst composition, the reaction gas composition, the reaction temperature, and the like, and thus the reduction degree is not limited to this range.

To prepare the catalyst of the present invention, it is easy to mix a compound containing these additional elements with the heteropoly acid or its salt in a solution state or a slurry state, and to dry and calcine. It may be added by a method such as impregnation or kneading after drying or firing. These elements are metal oxides,
It can be added in the form of hydroxides, carbonates, nitrates, chlorides, oxyacids, phosphates, oxalates, acetates or organic complex compounds. Also, metal can be used.

As the catalyst, salts of various nitrogen-containing compounds of these heteropoly acids can be used. Effective salts include ammonium salts or salts with organic amines such as pyridine, quinoline, piperazine. This may be one which partially forms a salt with a nitrogen-containing compound or the like, or one in which the nitrogen-containing compound is partially or wholly removed by firing. An ammonium salt or an organic amine salt can be synthesized from a heteropoly acid. In the case of ammonium salt, aqueous ammonium salt, water-soluble ammonium salt such as ammonium chloride, ammonium nitrate and the like can be used as the ammonium ion source. These ammonium salts or amine salts are used after calcining at 300 to 600 ° C. Baking in an inert gas is more preferable. After firing in an inert gas, firing with an oxygen-containing gas is also possible.

These catalysts can be used in the form of being carried on a carrier or diluted and mixed. Examples of the carrier include silica, α-alumina, silicon carbide, titania, zirconia, diatomaceous earth and the like. A high porosity inert carrier with many macropores is preferred. On these carriers, in the presence or absence of water, an amount of up to about 50% by weight is usually deposited. Alternatively, by mixing with a finely divided carrier,
For example, it can be formed into a cylindrical shape. Such a catalyst shape can be molded with or without a tableting machine, an extrusion molding machine, a Marumerizer (trade name of Fuji Paudal Co., Ltd.), a rolling granulator, or the like.

As a raw material gas supplied to the reaction, a mixed gas of isobutane and oxygen is used.

A suitable concentration of isobutane is 1 to 80 mol%, more preferably 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, and the economical efficiency that can be industrially implemented cannot be obtained. Other hydrocarbons may be mixed in as long as they do not affect the reaction.

The oxygen molar ratio in the feed gas is 0.05 with respect to isobutane.
The molar ratio is from 1 to 2, preferably between 0.1 and 1. If the oxygen molar ratio is high, complete oxidation will proceed too much and carbon dioxide will be generated in large amounts. On the contrary, when the oxygen molar ratio is small, a sufficient amount of oxygen is not supplied for isobutane oxidation, so that the productivity of methacrylic acid decreases. Furthermore, if the oxygen molar ratio is small,
As the reaction proceeds, the catalyst is excessively reduced, which is not preferable. On the other hand, when selecting the oxygen concentration and the isobutane concentration, it is preferable to consider so that the mixed gas composition does not fall within the explosion range. As the oxygen source, pure oxygen gas may be used or air may be used.

Further, in order to prevent the reaction product methacrylic acid from being further oxidized on the catalyst to become carbon dioxide, it is effective to add water vapor in the range of 5/1 to 1/5 with respect to isobutane. , The selectivity of methacrylic acid becomes high. It is preferably in the range of 3/1 to 1/3.

Further, the raw material gas can be diluted using a diluent gas. Nitrogen, helium, argon, carbon dioxide can be used as the diluent gas. Unreacted isobutane can be recovered and reused. At that time, carbon monoxide, carbon dioxide, and other reaction products may be mixed as long as they do not affect the reaction. Further, the 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. It is preferably 240 to 370 ° C. When the reaction temperature is high, decomposition of the catalyst and complete oxidation of the reaction product are likely to occur.

The reaction pressure can be widely set from reduced pressure to increased pressure, but atmospheric pressure to 2 atm is industrially advantageous.

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

In carrying out the present invention, the type of reactor used may be a fixed bed, a fluidized bed, a moving bed or any other type of reactor.

The generated methacrylic acid and methacrolein are cooled, absorbed,
Each product can be obtained by separating and purifying by a known appropriate method such as distillation. Unreacted isobutane can be recovered and used again as a raw material. Moreover, after recovering methacrylic acid from the reaction gas by a known method such as cooling condensation, absorption, and adsorption, part or all of the recovered gas containing methacrolein can be supplied to the reactor as a raw material gas again.

[Examples] Example 1 23.6 g of crystals of 12-molybdophosphoric acid (H ₃ PMo ₁₂ O ₄₀ · 30H ₂ O: Nippon Inorganic Chemistry) and 1.4 g of ferric chloride were dissolved in 200 ml of water, and to this solution, Add 100 g of 6.4 wt% ammonium nitrate aqueous solution, stir well, concentrate the resulting slurry solution, then dry at 120 ° C for 12 hours, then crush and
Particles from 0 to 20 mesh were selected. This in a nitrogen stream 4
It was calcined at 50 ° C. for 3 hours and further in air at 350 ° C. for 2 hours.

A catalyst having a composition of PMo ₁₂ Fe _0.5 was obtained.

This catalyst (5 g) was filled in a Pyrex U-shaped tube having an inner diameter of 6 mm and set in a constant temperature bath. The temperature of the constant temperature bath was set at 370 ° C., and a mixed gas of 60 mol% isobutane, 20 mol% oxygen and 20 mol% steam was supplied at a contact time of 1.5 seconds. When the reaction gas was analyzed by gas chromatography after 6 hours,
7.8% of isobutane is converted and the selectivity of methacrylic acid is 4
The selectivity was 1.8% and methacrolein was 15.3%. No isobutylene was detected.

Comparative Example 1 23.2 g of 12-molybdophosphoric acid (H ₃ PMo ₁₂ O ₄₀ · 30H ₂ O: Nippon Inorganic Chemistry) was dissolved in 200 ml of water, and the same procedure as in Example 1 was performed except that ferric chloride was not added. A catalyst was prepared. This catalyst was reacted under the same conditions as in Example 1. When the reaction gas was analyzed by gas chromatography after 6 hours, 10.3% of isobutane was converted, the selectivity of methacrylic acid was 15.3%, and the selectivity of methacrolein was 18.5%.

Example 2 Ammonium tungstate 12 in place of ferric chloride
A catalyst having a composition of PMo ₁₂ W _1-1 was prepared in the same manner as in Example 1 except that 3.0 g of decahydrate was used.

Using this catalyst, the reaction was carried out under the same conditions as in Example 1. After 6 hours, the reaction gas was analyzed by gas chromatography. As a result, 8.7% of isobutane was converted, the selectivity of methacrylic acid was 35.8%, and the selectivity of methacrolein was 26.3.
%Met.

Example 3 23.6 g of crystals of 12-molybdophosphoric acid (H ₃ PMo ₁₂ O ₄₀ · 30H ₂ O: Nippon Inorganic Chemicals), 0.28 g of rhodium chloride and 5.26 g of thallium acetate were dissolved in 200 ml of water, and then dissolved in this solution. 8.0 g of pyridine and 100 ml of water were added, and the mixture was stirred well. The resulting slurry solution was concentrated, then dried at 120 ° C. for 12 hours and then pulverized to select particles of 10 to 20 mesh.
This was calcined in a nitrogen stream at 450 ° C. for 3 hours and further in air at 350 ° C. for 2 hours. A catalyst with a composition of PMo ₁₂ Rh _0.1 Tl ₂ 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. When the reaction gas was analyzed by gas chromatography after 6 hours, 5.9% of isobutane was converted and the selectivity of methacrylic acid was 38.7.
%, The selectivity of methacrolein was 21.6%.

Example 4 1 so that the slurry composition was P _1.5 Mo ₁₂ Nb _0.5 Bi _0.5 Cs _2.
2-molybdophosphoric acid (Nippon Inorganic Chemistry), phosphoric acid (85 wt%), bismuth nitrate, and niobium oxalate were added, and further 13 g of quinoline and 100 ml of water were added to this solution and stirred, and the resulting slurry was concentrated. . Then, it was dried at 120 ° C. for 12 hours and then pulverized to select particles of 10 to 20 mesh. This was calcined in a nitrogen stream at 450 ° C. for 3 hours and further in air at 350 ° C. for 2 hours.

This catalyst was reacted in the same manner as in Example 3. When the reaction gas was analyzed by gas chromatography after 6 hours, 5.3% of isobutane was converted, the selectivity of methacrylic acid was 39.3%, and the selectivity of methacrolein was 19.5%.

Example 5 200 ml of 121 g of sodium molybdate (Na ₂ MoO ₄ .2H ₂ O)
Was dissolved in water and 20 g of a 30% aqueous arsenic acid solution was added.
After adding 80 ml of concentrated sulfuric acid to this solution, 300m of ethyl ether
Addition of l separated into three phases. The bottom phase was taken out and air-dried to obtain arsenic molybdic acid. This arsenic molybdic acid
A catalyst having an AsMo ₁₂ Fe _1.0 Rh _0.1 composition was obtained by dissolving and mixing with 23.7 g, ferric chloride 2.7 g and rhodium chloride 0.28 g.

This catalyst was reacted 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 P _1.5 Mo ₁₂ As.
_A catalyst having a composition of _0.5 Cr _0.5 was prepared.

This catalyst was reacted in the same manner as in Example 1 except that the reaction temperature was 320 ° C., the contact time was 3.6 seconds, and the isobutane concentration was 20 mol%. As a result, 3.8% of isobutane was converted, the selectivity of methacrylic acid was 49.6%, and the selectivity of methacrolein was 19.4%.

Example 7 12-molybdophosphoric acid (Nippon Inorganic Chemical), phosphoric acid (85% by weight), so that the aqueous solution composition was P _1.3 Mo ₁₂ Rh _0.1 Fe _0.3 ,
Rhodium chloride and ferric chloride were added and stirred well. 100 to 200 calcined in this aqueous solution at 700 ℃ for 3 hours
Spherical silica with a mesh (manufactured by Fuji Devison: Microbeads silica gel 1000A) was dipped, impregnated with the catalyst component, and dried. The impregnation and drying were repeated to carry about 45% by weight of the catalyst component. It was allowed to absorb pyridine and dried at 120 ° C. This was further immersed in an ethanol solution of 1N-potassium hydroxide to impregnate potassium. Then, it was dried at 120 ° C. and then calcined in a nitrogen stream at 450 ° C. for 3 hours and further in air at 350 ° C. for 2 hours. The composition of the obtained catalyst is P
_{It was 1.1} Mo ₁₂ Rh _0.1 Fe _0.25 K ₂ / SiO ₂ .

Using a fluidized bed reactor with an internal volume of 400 ml,
A mixed gas of 60 mol% of isobutane, 20 mol% of oxygen and 20 mol% of water vapor was supplied at a gas linear velocity of 20 cm / sec and a contact time of 4.0 sec. When the reaction gas was analyzed by gas chromatography after 20 hours, 4.3% of isobutane was converted, the selectivity of methacrylic acid was 40.2%, and the selectivity of methacrolein was
It was 20.3%. After the reaction, the catalyst had a yellowish green color.

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

Examples 18 to 30 A catalyst having the composition shown in Table 2 was used as in Example 1 with a mixed gas of 30 mol% isobutane, 50 mol% air and 20 mol% steam at a reaction temperature of 340 ° C. and a contact time of 3.6 seconds. And reacted. The reaction results are summarized in Table 2.

[Effect] According to the method of the present invention, (1) a mixed gas containing isobutane and oxygen is brought into contact with a catalyst, (2) high productivity, and (3) methacrylic acid can be obtained with a good selectivity. ,
When it is carried out industrially, it is economically advantageous.

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location C07C 57/05 // C07B 61/00 300

Claims (1)

[Claims] 1. A heteropolyacid containing phosphorus and / or arsenic as a central element and molybdenum and / or a salt thereof,
Ag, Zn, Cd, Ti, Zr, Nb, Ta, Cr, W, Mn, Fe, Co, N
Methacrylic acid characterized by bringing a mixed gas containing isobutane and molecular oxygen into contact with a catalyst containing at least one selected from the group consisting of i, Rh, Sn, Bi and Te as a catalyst constituent element in a gas phase. And / or a method for producing methacrolein