JPS6357415B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing unsaturated carboxylic acids using a novel catalyst, and more specifically, the present invention relates to a method for producing unsaturated carboxylic acids using a novel catalyst. This invention relates to a method for producing a corresponding unsaturated carboxylic acid by phase catalytic oxidation. In recent years, a method of producing corresponding unsaturated aldehydes such as acrolein and methacrolein by catalytic gas-phase oxidation reaction of olefins such as propylene and isobutylene or tertiary butyl alcohol using molecular oxygen (hereinafter referred to as first-stage oxidation) has been developed.
The catalyst used in this reaction is called a pre-oxidation catalyst), and the unsaturated aldehyde is further subjected to gas phase catalytic oxidation reaction with molecular oxygen to produce corresponding unsaturated carboxylic acids such as acrylic acid and methacrylic acid ( There has been a lot of research into (hereinafter referred to as post-oxidation, and the catalyst used in this reaction is called post-oxidation catalyst), and a large number of pre- and post-oxidation catalysts have already been proposed. However, its catalytic activity is still not necessarily satisfactory, and there is a desire to develop a catalyst with even better performance, especially a post-oxidation catalyst. In addition, when producing unsaturated carboxylic acids, there are two methods: a method in which a purified unsaturated aldehyde is used for second-stage oxidation, and a method in which the reaction mixture obtained in the first-stage oxidation is directly oxidized in the second stage (hereinafter referred to as the front-end direct connection method). Both are known, and the latter is considered to be more advantageous in terms of equipment, operation, and economy because it does not require treatment steps such as separation and purification of unsaturated aldehydes, and is also industrially advantageous. However, when performing a front-front and front-stage direct connection method using known front-stage and rear-stage oxidation catalysts, the catalytic activity of the rear-stage oxidation catalyst (conversion rate of unsaturated aldehydes, yield and selectivity of unsaturated carboxylic acids, etc.) generally This is significantly inferior to the case where only post-oxidation is performed under the same reaction conditions using a purified unsaturated aldehyde, and this tendency is particularly noticeable when producing methacrylic acid from isobutylene. This phenomenon is known to be caused by a small amount of tar-like substances produced as by-products in the first stage oxidation, a small amount of remaining unreacted isobutylene, etc., and is particularly affected by unsaturated hydrocarbons such as unreacted isobutylene. For this reason, no proposal has yet been made to enable industrial implementation of methacrylic acid using a direct front-end oxidation method, but in order to make such a method possible, it is insufficient to improve the catalytic activity in the later stage oxidation. There is a need to develop a new post-oxidation catalyst that does not cause deterioration of the catalyst even in the presence of small amounts of by-products, unreacted isobutylene, etc. contained in the pre-oxidation reaction mixture. The present inventors have improved the above-mentioned drawbacks of conventionally known methacrolein oxidation catalysts,
As a result of intensive research aimed at developing a new post-oxidation catalyst with excellent catalytic activity and less deterioration due to olefins, etc., we discovered that the catalyst represented by the general composition formula [] below is extremely effective. They discovered that the catalyst is similarly suitable as an oxidation catalyst for other unsaturated aldehydes such as acrolein, and completed the present invention. A _a B _b C _c Mo _d P _e Zr _f O _g … [] (Here, A represents one or more elements selected from K, Rb, Cs and Tl, and B represents Ga, B, Zn, Te
and one or more elements selected from Th,
C represents one or more elements selected from V and Cr, and a, b, c, d, e, f and g are the number of atoms of A, B, C, Mo, P, Zr and O, respectively. , d=12, a, b, c, e and f each independently take a value of 0.05 to 12, and g is the number of oxygen atoms satisfying the valences of other elements. ) In the present invention, the preferred component ratio of the catalyst is d
=12, a, b, c, e and f each independently take a value of 0.1 to 8, and g is the number of oxygen atoms satisfying the valences of other elements. The catalyst of the present invention is characterized by the presence of component B, which allows unsaturated carboxylic acids to be obtained from unsaturated aldehydes in high yield and high selectivity through a stable reaction under practical reaction conditions. Even if a small amount of unsaturated hydrocarbons is present in the raw material gas containing methacrolein, the catalyst activity hardly decreases. As a result, it becomes possible to produce methacrylic acid by a method of directly connecting the front and rear stages, which was considered impossible with known catalysts. Further, while conventional catalysts often have problems in reproducibility of catalytic activity, the catalyst of the present invention always shows good activity. The catalyst used in the method of the present invention can be prepared by the so-called evaporation to dryness method, coprecipitation method, etc. known in this field. Raw materials for each element used in the preparation of the catalyst include salts such as ammonium salts, nitrates, and halides of each element, free acids, acid anhydrides, condensed acids, oxides, and heteropolymers containing molybdenum such as phosphomolybdic acid. Examples include heteropolyacid salts such as acids or their ammonium salts and alkali metal salts. especially,
It is preferable to use a raw material that can form a complex compound, such as a heteropolyacid or its acid salt, ammonium salt, or alkali metal salt. The catalytic composition thus prepared is prepared before use.
After being calcined at a temperature of 250 to 700°C, preferably 300 to 550°C in air, a reducing atmosphere, or a raw material composition gas for several hours to several tens of hours, it is used as a catalyst. The state of existence of each element, including oxygen, in a state where such a catalyst is exhibiting catalytic action is not necessarily clear, but according to an examination using an X-ray diffraction diagram, when oxides of each element are used as catalyst raw materials, However, since the X-ray diffraction patterns before and after firing are completely different, it is believed that this is not just a mixture of oxides of each element. The catalyst of the present invention can be used as it is, but it can also be attached to a carrier of an appropriate shape, or it can be used in powdered form.
It can also be used after being diluted with a carrier (diluent) in the form of a sol or gel. Any known carrier may be used, and examples thereof include titanium dioxide, silica gel, silica sol, diatomaceous earth, silicon carbide, alumina, pumice, silica-alumina, bentonite, graphite, refractories, and zeolite. The unsaturated aldehydes used in the method of the present invention are preferably acrolein and methacrolein, and in the case of a direct connection method, propylene,
A reaction mixture for the first stage oxidation using isobutylene or tertiary butyl alcohol as a raw material is preferred.
Oxygen can be used alone as a molecular oxygen source, but air is more practical industrially, and in the case of a direct connection method between the front and rear stages, unreacted oxygen contained in the reaction mixture of the first stage oxidation is used. You can also use it. Gases that do not affect the reaction may also be used as diluents, such as water vapor, nitrogen, carbon dioxide, helium, argon, saturated hydrocarbons (such as methane,
Ethane, broban, butane, pentane, etc.) may be introduced into the reaction system, and in the case of a direct connection method, unreacted raw materials (propylene, isobutylene, tert-butyl alcohol, etc.) contained in the reaction mixture of the first stage oxidation may be introduced. Even if oxygen, diluents, by-products, etc. are introduced, there is no substantial adverse effect. The concentration of unsaturated aldehyde in the raw material mixture is from 1 to
A range of 25% by volume is preferred, and the ratio of unsaturated aldehyde to oxygen is 1:0.1 to 25.0, preferably 1:
A range of 0.1 to 20.0 is appropriate. Reaction temperature is 250~
500°C, preferably 300 to 450°C, and the reaction contact time (0°C, 1 atm standard) is 0.1 to 20 seconds,
Preferably, a range of 0.5 to 15 seconds provides favorable buildup. In the present invention, the reaction pressure is not a particularly important factor, and although it is possible to operate at a high pressure, a pressure of about 1 to 10 atm is practical. A fixed bed, fluidized bed, moving bed, etc. can be employed as the reaction apparatus, and the reaction product can be separated and purified by known general methods. The present invention will be specifically explained below with reference to Examples. In the Examples, the definitions of the conversion rate of unsaturated aldehyde, the yield of unsaturated carboxylic acid, and the selectivity are as follows. All analyzes were performed using a gas chromatograph. Conversion rate (%) = Reacted unsaturated aldehyde (mol) / Supplied unsaturated aldehyde (mol) × 100 Yield (%) = Produced unsaturated carboxylic acid (mol) / Supplied unsaturated aldehyde (mol) × 100 Selectivity (%) = Yield/Conversion rate x 100 Note that the representation of oxygen in the catalyst components shown in Examples is omitted for the sake of brevity. Example 1 (i) 212 g of ammonium molybdate and 7.6 g of ammonium chromate were dissolved by heating in 300 ml of water, and an aqueous solution of 23 g of 85% phosphoric acid dissolved in 50 ml of water and 20.2 g of potassium nitrate were added to 200 ml of water. Add the heated and dissolved aqueous solution and stir. Add zirconyl nitrate or gallium nitrate to this at 500℃.
6.15 g of finely powdered zirconium oxide and gallium oxide obtained by decomposition in an air stream for 16 hours
4.69 g was added and evaporated to dryness with vigorous stirring, and the resulting product was calcined for 16 hours in a Matsufuru furnace kept at 450°C, then ground and sieved into 4 to 8 meshes to form a catalyst. The catalyst composition thus obtained was Mo ₁₂ P ₂ Cr _{0.5 Zr 0.5 Ga 0.5 K 2} [Catalyst No. ( ₁ ) in Table 1]. Similarly, 29.5 g of rubidium nitrate, 39.0 g of cesium nitrate, and 53.3 g of thallium nitrate were used in place of potassium nitrate, and catalysts No. (2) to 1 in Table 1 were used.
No. (4) was prepared. Catalysts No. (5) to No. (10) were prepared in the same manner by changing the catalyst composition ratio. (ii) In the method of (i), some components are removed and the first
Comparative catalyst No. (C-1) to No. (C-5) shown in the table
was prepared. Next, 100ml of the catalyst was filled into a stainless steel reaction tube with an inner diameter of 2.5cm and a length of 60cm, and heated to 350℃ in a metal bath.
Methacrolein: O ₂ : N ₂ : H ₂ O=1:1.5:
A feed gas having a composition of 17.5:10 (molar ratio) was passed for a contact time of 1.8 seconds (0° C., 1 atm standard) to cause a reaction.
The results obtained are shown in Table 1. The purity of methacrolein used was 99.5% by weight.

[Table] Example 2 (i) 212 g of ammonium molybdate was dissolved in 300 ml of water, which contained 17.6 g of oxalic acid.
Add a solution of 11.5 g of ammonium metavanadate dissolved in 200 ml of warm water and stir. To this are added an aqueous solution of 23 g of 85% phosphoric acid dissolved in 50 ml of water and an aqueous solution of 20.2 g of potassium nitrate dissolved in 200 ml of water under heating, and stirred. 6.15 g of finely powdered zirconium oxide and 4.69 g of potassium oxide were added to this, and the mixture was evaporated to dryness with vigorous stirring. The resulting product was fired for 16 hours in a Matsufuru furnace kept at 450°C, and then pulverized. , sieved into 4 to 8 meshes and used as a catalyst. The catalyst composition thus obtained was Mo ₁₂ P ₂ V _0.5 Zr _{0.5 Ga 0.5} K ₂ (Catalyst No. ( ₁₁ ) in Table 2) _. Similarly, 29.5 g of rubidium nitrate, 39.0 g of cesium nitrate, and 53.3 g of thallium nitrate were used in place of potassium nitrate, and catalysts No. (12) to No. (14) were used.
was prepared. (ii) Comparative catalysts No. (C-6) to No. (C-10) were prepared by omitting some components in the method of (i). Next, an oxidation reaction of methacrolein was carried out in the same manner as in Example 1, and the results shown in Table 2 were obtained.

【table】

[Table] Example 3 Same as Example 1 or Example 2 except that fine powdered zinc oxide, thorium oxide, boron oxide, and tellurium dioxide were used instead of the gallium oxide used in Examples 1 and 2. Catalysts of various compositions were prepared by the method described above, and reactions were carried out in the same manner as in Example 1. The results shown in Table 3 were obtained.

[Table] Example 4 Catalysts of the present invention and comparative catalysts used in Examples 1 to 3 [Catalyst Nos. (1), (2), (3), (4), (13), (14), (1
Five),
(16), (17), (18), (C-1), (C-2), (
C-
3) and (C-8)], each catalyst 100
ml was filled into a stainless steel reaction tube with an inner diameter of 2.5 cm and a length of 60 cm, heated to 350°C in a metal bath, and methacrolein: O ₂ : N ₂ : H ₂ O: Isobutylene = 1: 1.5:
A supply gas having a composition of 17.5:9.9:0.1 (molar ratio) was passed for a contact time of 1.8 seconds (0° C., 1 atm standard) to cause a reaction. The results obtained are shown in Table 4. The purity of methacrolein used was 99.5% by weight. From the results in Table 4, it can be seen that even when the supplied gas contains isobutylene, according to the catalyst of the present invention,
The comparative catalyst showed the same catalytic activity as the case without isobutylene (see Tables 1 to 3), whereas the It can be seen that the catalytic activity is significantly inferior.

[Table] Example 5 Methacrylic acid is produced from isobutylene by a front-end direct coupling method according to the method shown below, and unreacted isobutylene and other by-products contained in the first-stage oxidation reaction mixture affect the activity of the second-stage oxidation catalyst. We investigated the impact. Preparation of first-stage oxidation catalyst: 48.5 g of bismuth nitrate, 116.5 g of cobalt nitrate,
Add 29.1g of nickel nitrate, 484.8g of ferric nitrate, and 10.1g of potassium nitrate to 150ml of water and dissolve by heating.
This was called liquid A. On the other hand, 212 g of ammonium molybdate was dissolved in 400 ml of water by heating, and 57.6 g of 85% phosphoric acid was further added thereto to obtain Solution B. Add solution B while heating and stirring solution A, evaporate to dryness while stirring thoroughly, and dry this at 120°C for 8 hours.
It was fired in a Matsufuru furnace at 600°C for 16 hours, and the resulting solid was pulverized and sieved into 4 to 8 meshes. The composition of the pre-oxidation catalyst thus prepared is shown as Mo ₁₂ Bi ₁ Fe ₁₂ Co ₄ Ni ₁ P _0.5 K ₁ . Preparation of post-oxidation catalyst The catalyst of the present invention used in Examples 1 to 3 [Catalyst No.
(3), (13), (15), (16), (17) and (18)] and comparative catalysts [Catalyst No. (C-2), (C-3) and (C-
8)] was used. 100 ml of the catalyst prepared by the first stage oxidation reaction method was placed into a tube with an inner diameter of 2.5 cm and a length of 60 cm.
Fill a stainless steel reaction tube and heat at 340℃ in a metal bath.
A feed gas having a molar ratio of isobutylene:air:steam of 4:55:41 is added to this at a space velocity of
Passed at 2000hr ^-1 . As a result, the conversion rate of isobutylene was 95.5%, and the single flow yield of methacrolein was
The selectivity for methacrolein was 72.7%, and the production rate of unreacted isobutylene and by-product unsaturated hydrocarbons contained in the reaction gas was 7.3% based on the isobutylene supplied. All of these reaction products were calculated on a carbon basis. In addition, small amounts of tar-like substances that solidify at temperatures below 200°C, methacrylic acid, acetic acid, acetone, furan, diacetyl, etc. were also produced, as well as carbon dioxide gas and carbon monoxide. After-stage oxidation reaction method 100ml of the catalyst prepared in the inner diameter 2.5cm and length 60cm
Fill a stainless steel reaction tube and heat at 350℃ in a metal bath.
The reaction mixture obtained by the preliminary oxidation reaction was immediately introduced into the reactor and allowed to pass through. The results obtained are shown in Table 5. From the results in Table 5, it is clear that when methacrylic acid is produced from isobutylene by the front-end direct coupling method, unreacted isobutylene and byproducts are present in the first-stage oxidation reaction mixture when the catalyst of the present invention is used as a second-stage oxidation catalyst. Even if they are mixed, if these etc. are not mixed (Example 1)
It can be seen that it exhibits virtually the same catalytic activity as (see 3). On the other hand, when the comparative catalyst is used as a second-stage oxidation catalyst, the catalytic activity is greatly reduced by unreacted isobutylene and by-products contained in the first-stage oxidation reaction mixture, making it completely unsuitable for the front-to-front direct connection method. I understand.

[Table] Example 6 Catalyst No. (3) and No. used in Example 1 and Example 3.
Using (16), convert methacrolein to acrolein and change the feed gas composition to acrolein:
The oxidation reaction of acrolein was carried out under the same conditions as in Example 1 except that O ₂ :N ₂ :H ₂ O=1:2:8:9 (molar ratio). As a result, when catalyst No. (3) was used, the reaction product was a conversion of acrolein of 96.1% and a yield of acrylic acid of 86.9% (selectivity of 90.4%). In addition, when catalyst No. (16) was used, the acrolein conversion rate was 95.5% and the acrylic acid yield was 87.2% (selectivity was 91.3%).
%). Further, propylene is added to the above supply gas to obtain acrolein:O ₂ :N ₂ :H ₂ O:propylene=1:2:
When a similar reaction was performed with 8:8.9:0.1,
Despite the presence of propylene in the feed gas, no substantial reduction in catalytic activity was observed for either catalyst.

Claims (1)

[Claims] 1. An unsaturated aldehyde and molecular oxygen are defined by the general composition formula A _a B _b C _c MO _d P _e Zr _f O _g (where A is selected from K, Rb, Cs and Tl). Represents one or more elements, B is Ga, B, Zn,
Represents one or more elements selected from Te and Th, C represents one or more elements selected from V and Cr, a, b, c, d, e, f and g are A, B, respectively. , C, Mo, P, Zr and O atoms, and when d=12, a, b, c, e and f
each takes a value of 0.05 to 12 independently, and g is the number of oxygen atoms satisfying the valences of other elements. ) A method for producing an unsaturated carboxylic acid, which comprises carrying out gas phase catalytic oxidation in the presence of a catalyst represented by: 2 When d=12, a, b, c, e, and f each independently take a value of 0.1 to 8, and g is the number of oxygen atoms that satisfies the valence of other elements. The method described in paragraph 1. 3. The method according to claim 1, wherein the unsaturated aldehyde is methacrolein or acrolein.