JPH10218831A - Reduction in propinic acid in mixed gas of acrylic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce propionic acid by heat-treating an acrylic acid mixed gas obtained by vapor-phase oxidation of propylene and/or propane in the presence of a specific compound oxide. SOLUTION: An acrylic acid-containing preferably obtained by two-step or one-step oxidation of propylene is heat-treated in the presence of a molybdenum- or bismuth-containing compound oxide [especially preferably a Mo-Bi- based compound oxide of the formula Moa Bib Fec Ald A2e A3f A4g A5h Ox (Al is cobalt, etc.; A2 is tellurium, etc.; A3 is boron, etc.; A4 is an alkali metal, etc.; A5 is silicon, etc.; (a)-(h) are each the atomic ratio of each element, when (a) is 12, (b) is 0.5-7, (c) is 0-3, (d) is 0-10, (e) is 0-20, (f) is 0-3, (g) is 0-1 and (h) is 0-75; (x) is the number of necessary oxygen atoms)] at 300-500 deg.C at 5,000-80,000hr<-1> gas space velocity SV to reduce propionic acid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for reducing propionic acid in an acrylic acid mixed gas. Specifically, the present invention relates to a method for selectively reducing propionic acid contained in a mixed gas obtained by treating an acrylic acid mixed gas obtained by gas-phase oxidation of propylene and / or propane under specific conditions.

[0002]

2. Description of the Related Art As a method for producing acrylic acid, there is known a method in which propylene and / or propane are used as raw materials and gas phase oxidation is performed. The method for producing acrylic acid using propylene as a raw material includes: A single-stage oxidation method that oxidizes propylene to acrylic acid with the same catalyst at once. 2. Acrolein is mainly produced in the first oxidation step, and is separated from by-products such as acrylic acid as a by-product,
A two-stage method in which the obtained acrolein is oxidized in a second-stage oxidation step. 3. Acrolein is mainly produced in the first oxidation step,
A method of oxidizing this in a second oxidation step without separating it from acrylic acid and off-gas by-produced (hereinafter abbreviated as a continuous method). At present, the three methods are mainly implemented industrially. Further, a method for producing acrylic acid by directly oxidizing propane as a raw material has not been commercialized until now, but a single-step oxidation method for oxidizing propane to acrylic acid with the same catalyst at once is disclosed in JP-A-6-279351. And Japanese Patent Application Laid-Open No. 7-10801.

In any of the methods, the obtained mixed gas of acrylic acid contains a small amount of by-produced propionic acid. Particularly, in the case of acrylic acid production by a single-stage oxidation method of propylene or propane, such a small amount of propionic acid is contained. High production. However, since propionic acid has a boiling point close to that of acrylic acid and has similar chemical properties, it is difficult to separate it by distillation or other physical means or chemical treatment.

[0004] Since propionic acid or its ester does not polymerize, a method for reducing the amount of by-produced propionic acid has been described in spite of having a large effect on the quality of acrylic acid or acrylic ester depending on the use. Almost no proposal has been made in Japanese Patent Application Laid-Open No. 48-9101.
JP-A No. 4 or JP-A-52-29483 only discloses a catalyst which produces less propionic acid as the second stage catalyst in the continuous process.

[0005]

However, even in the catalyst of the above-mentioned method, the amount of by-produced propionic acid is several hundred ppm or more based on the produced acrylic acid, which is not satisfactory. An object of the present invention is to provide a method for selectively reducing propionic acid in an acrylic acid mixed gas obtained by vapor-phase oxidation of propylene and / or propane.

[0006]

Means for Solving the Problems As a result of intensive studies in view of the above circumstances, the present inventors have found that most of acrylic acid is obtained by heat-treating an acrylic acid mixed gas in the presence of a specific composite oxide. The inventors have found that propionic acid can be selectively decomposed without decomposition, and have completed the present invention. That is, the gist of the present invention is that an acrylic acid mixed gas obtained by gas-phase oxidation of propylene and / or propane is heat-treated in the presence of a composite oxide containing molybdenum and bismuth. In the method for reducing propionic acid. Hereinafter, the present invention will be described in detail.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The acrylic acid mixed gas obtained by the gas phase oxidation of propion and / or propane, which is the subject of the present invention, refers to the conventionally known gas phase oxidation of propylene and / or propane Acrylic acid-containing gas containing Among them, the following are particularly preferable in terms of the effect of the present invention. (1) Acrylic acid mixed gas obtained by two-stage oxidation of propylene (2) Acrylic acid mixed gas obtained by one-stage oxidation of propylene (3) Acrylic acid mixed gas obtained by one-stage oxidation of propane

The acrylic acid mixed gas may contain other unreacted raw materials, by-products, etc. as long as it contains acrylic acid and propionic acid. Common gas components include acrylic acid, propionic acid, CO,
CO ₂ , acetic acid, acetaldehyde, acrolein, oxygen, nitrogen, steam, unreacted propylene or propane and the like are included. The contents of acrylic acid and propionic acid in the gas are 1 to 10 mol% and 0.0
01 to 0.1 mol%.

The composite oxide containing molybdenum and bismuth used in the present invention is not particularly limited as long as it is a composite oxide containing molybdenum and bismuth. A composite oxide used in a gas phase catalytic reaction for producing rain, acrylonitrile from propylene, a gas phase catalytic ammoxidation reaction for producing methacronitrile from isobutene, and a gas phase catalytic oxidative dehydrogenation reaction for producing butadiene from butene. Can be used as is. Among them, Mo-Bi-based composite oxide represented by the following general formula is particularly preferable.

[0010]

## STR2 ## _{Mo a Bi b Fe c Al d} A2 e A3 f A4 g
A5 _h O _x

(Wherein, Mo, Bi, Fe and O are molybdenum, bismuth, iron and oxygen, Al is at least one element selected from the group consisting of cobalt, nickel, manganese and chromium, A2 is tellurium, A3 represents at least one element selected from the group consisting of antimony, tungsten and lead, A3 represents at least one element selected from the group consisting of boron, phosphorus and arsenic,
A4 represents at least one element selected from the group consisting of alkali metals, alkaline earth metals and thallium;
A5 represents at least one element selected from the group consisting of silicon, aluminum and titanium, a to h represent the atomic ratio of each element, and when a = 12, b = 0.5
-7, c = 0-3, d = 0-10, e = 0-20, f =
0 to 3, g = 0 to 1, h = 0 to 75, and x represents the number of oxygen atoms necessary to satisfy the valence of each component.)

The method for producing the above-mentioned composite oxide does not need to be a special method, and a conventionally well-known preparation method can be employed. For example, a compound containing each component element is dissolved and mixed in the presence of water, and the resulting mixture solution or slurry is evaporated to dryness, dried, molded and calcined to obtain a catalyst. As a raw material compound used for preparing the composite oxide, a nitrate, an ammonium salt, a halide, a carbonate, a sulfate, an oxide, or the like of each element can be used in combination. For example, ammonium paramolybdate, molybdenum trioxide can be used as a molybdenum raw material, and bismuth nitrate, bismuth subcarbonate, bismuth oxide, etc. can be used as a bismuth raw material.

There is no particular limitation on the order of mixing the component compounds when producing the composite oxide. Mixing temperature is 2
The mixing time is preferably 0 to 100 ° C., and the mixing time is not particularly limited as long as the mixing can be performed uniformly. The catalyst precursor slurry thus obtained is concentrated to dryness and then subjected to a calcination step to form a composite oxide. The calcination condition is suitably calcined at a temperature of 400 to 650 ° C. The shape of the composite oxide used in the present invention is not particularly limited, and may be a columnar shape, a ring shape,
The catalyst powder may be formed into a single spherical shape of the catalyst powder, may be mixed with an inert carrier and molded, or may be supported on an inert carrier. Examples of the carrier used include alumina, silica, silicon carbide, pumice and the like.

The heat treatment conditions for reducing propionic acid in the present invention are as follows: (1) The pressure is generally good from normal pressure to several atmospheres, and most preferably normal pressure to 3 atmospheres.
(2) The temperature is preferably in the range of 300 to 500 ° C.
The range of 50 to 450 ° C. is effective, and more preferably the range of 400 to 450 ° C. is optimal. At low temperatures outside the above range, the decomposition of propionic acid is slow, and at high temperatures, decomposition of acrylic acid may also proceed.
(3) Gas space velocity (SV): SV = 5,000-8
It is preferably in the range of 10,000 hr ^-1 and SV = 10000
Optimally within the range of ⁰ to 50,000 hr ^-1 . In large SVs other than the above range, the decomposition of propionic acid is small,
Conversely, with a small SV, the decomposition of acrylic acid may also proceed.

[0015]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to examples and comparative examples, but the present invention is not limited to these examples unless it exceeds the gist. In Examples and Comparative Examples, the residual ratio of acrylic acid and the residual ratio of propionic acid are defined as follows.

[0016]

(Equation 1)

[0017]

(Equation 2)

Example 1 (a) Production of composite oxide 94.1 g of ammonium paramolybdate was added to 500 ml of pure water.
Heat to dissolve. Next, 7.18 g of ferric nitrate,
25.8 g of cobalt nitrate and 38.7 g of nickel nitrate
Is dissolved in 60 ml of pure water by heating. The two liquids are gradually mixed with sufficient stirring. 0.85 g of borax and 0.36 g of potassium nitrate were added to this mixed solution in 40 m of pure water.
Add the solution dissolved by heating to 1 and stir well. Next, 57.9 g of bismuth subcarbonate and 64.1 g of silica are added and mixed with stirring. Next, after heating and drying this slurry, it is subjected to a heat treatment at 300 ° C. for 1 hour in an air atmosphere. The obtained granular solid is pulverized into particles having a particle size of 12 to 16 mesh. Next, baking was performed at 500 ° C. for 4 hours in a muffle furnace to obtain a composite oxide. The composition ratio of the metal component of the catalyst calculated from the charged raw materials is a composite oxide having the following atomic ratio. Mo: Bi: Fe: Co: Ni: Na: B: K: Si =
12: 5: 0.4: 2: 3: 0.1: 0.2: 0.0
8:24

(B) Production of raw material gas As a propylene oxidation catalyst, a catalyst 40 having the following composition prepared by the method disclosed in JP-A-63-54942.
ml Mo: Bi: Co: Fe: Na: B: K: Si = 12:
1: 0.6: 7: 0.1: 0.2: 0.1: 18 was charged into a stainless steel night game jacketed reactor having an inner diameter of 20 mm, propylene concentration 10%, steam concentration 17%, and air concentration. A reactor equipped with a stainless steel night game jacket with a 20 mm inner diameter and connected continuously by providing a nozzle at the connecting portion and continuously connecting 73% of the raw material gas at normal pressure at a gas space velocity of 750 hr ^-1 and a reaction bath temperature of 310 ° C. JP-A-62-2 as a catalyst for acrolein oxidation
Sb: Ni: Mo: V: Nb: Cu: Si = 100: 4 Catalyst 50 ml of the following composition prepared by the method disclosed in JP-A-01646.
3: 35: 7: 3: 3: 80, intermediate air was introduced from a nozzle, and the mixture was passed at a gas space velocity of 1350 hr ^-1 and a reaction bath temperature of 270 ° C. As a result, 8.9% of acrylic acid and 0.003 of propionic acid
%, Acetic acid 0.3%, propylene 0.3%, acrolein 0.03%, oxygen 3.5%, steam 23%, CO + C
An acrylic acid mixed gas containing an O ₂ + nitrogen balance was obtained.

(C) Heat treatment for reducing propionic acid 1 ml of the obtained composite oxide is filled in a glass reactor having an inner diameter of 4 mm, and an acrylic acid mixed gas is supplied at normal pressure and a gas space velocity of 18,000 hr ^-1. The reaction was carried out at a reaction temperature of 400 ° C. The product was collected and analyzed by gas chromatography to find that the residual ratio of acrylic acid was 98.9% and the residual ratio of propionic acid was 68%. Example 2 Example 2 was carried out in the same manner as in Example 1 except that the composite oxide of Example 1 was used and the heat treatment temperature for reducing propionic acid was changed to 450 ° C. The product was collected and analyzed by gas chromatography. As a result, the residual ratio of acrylic acid was 95.6%, and the residual ratio of propionic acid was 24%.

Example 3 (a) Production of composite oxide 89.6 g of ammonium paramolybdate was added to 450 ml of pure water.
Heat to dissolve. Next, 8.5 g of ferric nitrate and 73.9 g of cobalt nitrate are dissolved in 60 ml of pure water by heating. The two liquids are gradually mixed with sufficient stirring.
To this mixed solution, a solution prepared by heating and dissolving 0.81 g of borax and 0.43 g of potassium nitrate in 40 ml of pure water is added, and the mixture is sufficiently stirred. Next, 11.0 g of bismuth subcarbonate and 45.8 g of silica are added and mixed with stirring. Next, after heating and drying the slurry, the slurry was heated at 300 ° C. /
Subject to heat treatment for 1 hour. The obtained granular solid is pulverized into particles having a particle size of 12 to 16 mesh. Next, calcination was performed at 530 ° C./2 hours in a muffle furnace to obtain a composite oxide. The composition ratio of the metal component of the catalyst calculated from the charged raw materials is a composite oxide having the following atomic ratio. Mo: Bi: Fe: Co: Na: B: K: Si = 12:
1: 0.5: 6: 0.1: 0.2: 0.1: 18

(B) Production of raw material gas The same procedure as in Example 1 was carried out except that 8.9% of acrylic acid, 0.003% of propionic acid, 0.3% of acetic acid and 0.3% of propylene were used.
%, Acrolein 0.03%, oxygen 3.5%, steam 23%, and a mixed gas of acrylic acid containing a balance of CO + CO ₂ + nitrogen. (C) Heat treatment for reducing propionic acid The same operation as in Example 1 was performed except that the SV was set at 15,000 hr ^-1 . The product was collected and analyzed by gas chromatography to find that the residual ratio of acrylic acid was 99.8% and the residual ratio of propionic acid was 60%.

Example 4 Using the composite oxide of Example 3, a raw material gas was produced in the same manner as in Example 3, and the heat treatment temperature for reducing propionic acid was changed to 450 ° C. in the same manner as in Example 3. went. The product was collected and analyzed by gas chromatography to find that the residual ratio of acrylic acid was 97.4% and the residual ratio of propionic acid was 24%. Example 5 (a) Production of composite oxide 75.4 g of ammonium paramolybdate was added to 400 ml of pure water.
Heat to dissolve. Next, 8.6 g of ferric nitrate and 72.5 g of cobalt nitrate are dissolved by heating in 60 ml of pure water. The two liquids are gradually mixed with sufficient stirring.
To this mixture, a solution prepared by heating and dissolving 0.68 g of borax and 0.36 g of potassium nitrate in 40 ml of pure water is added, followed by sufficient stirring. Next, 27.8 g of bismuth subcarbonate and 42.8 g of silica are added and mixed with stirring. Next, after heating and drying the slurry, the slurry was heated at 300 ° C. /
Subject to heat treatment for 1 hour. The obtained granular solid is pulverized into particles having a particle size of 12 to 16 mesh. Next, baking was performed at 500 ° C. for 4 hours in a muffle furnace to obtain a composite oxide. The composition ratio of the metal component of the catalyst calculated from the charged raw materials is a composite oxide having the following atomic ratio. Mo: Bi: Fe: Co: Na: B: K: Si = 12:
3: 0.6: 7: 0.1: 0.2: 0.1: 20

(B) Production of raw material gas The same procedure as in Example 1 was carried out except that 8.9% of acrylic acid, 0.003% of propionic acid, 0.3% of acetic acid and 0.3% of propylene were used.
%, Acrolein 0.03%, oxygen 3.5%, steam 23%, and a mixed gas of acrylic acid containing a balance of CO + CO ₂ + nitrogen. (C) Heat treatment for reducing propionic acid This was performed simultaneously with Example 1 except that the SV was set to 20,000 hr ^-1 . The product was collected and analyzed by gas chromatography. As a result, the residual ratio of acrylic acid was 99.1%, and the residual ratio of propionic acid was 60%.

Example 6 Using the composite oxide of Example 5, a raw material gas was produced in the same manner as in Example 5, and the heat treatment temperature for reducing propionic acid was changed to 450 ° C. in the same manner as in Example 5. went. The product was collected and analyzed by gas chromatography. As a result, the residual ratio of acrylic acid was 96.6%, and the residual ratio of propionic acid was 30%. Example 7 (a) Production of composite oxide 63.5 g of ammonium paramolybdate was added to 400 ml of pure water.
And 20% silica sol.
Add 7 g and disperse thoroughly (solution-1). next,
14.5 g of bismuth nitrate was added to 3.5 ml of concentrated nitric acid and 70 parts of pure water.
Dissolve in the mixture with ml. Subsequently, ferric nitrate 36.
4g, cobalt nitrate 39.4g and nickel nitrate 2
Dissolve 1.7 g (solution-2). 1.7 g of 85% phosphoric acid solution and 0.35 g of potassium nitrate were added to 20 ml of pure water.
(Solution-3).

While sufficiently stirring the solution-1, the solution-2 and then the solution-3 are gradually added, and the resulting precipitate is evaporated to dryness while stirring. The solid obtained by evaporation to dryness is subjected to a heat treatment at 300 ° C./1 hour in an air atmosphere. The obtained granular solid is pulverized into particles having a particle size of 12 to 16 mesh. Next, baking was performed at 500 ° C. for 4 hours in a muffle furnace to obtain a composite oxide. The composition ratio of the metal component of the catalyst calculated from the charged raw materials is a composite oxide having the following atomic ratio. Mo: Bi: Fe: Co: Ni: P: K: Si = 12:
1: 3: 4.5: 2.5: 0.5: 0.1: 11.6

(B) Production of raw material gas The same procedure as in Example 1 was carried out except that 8.9% of acrylic acid, 0.003% of propionic acid, 0.3% of acetic acid and 0.3% of propylene were used.
%, Acrolein 0.03%, oxygen 3.5%, steam 23%, and a mixed gas of acrylic acid containing a balance of CO + CO ₂ + nitrogen. (C) Heat treatment for reducing propionic acid 1 ml of the obtained composite oxide was charged into a glass reactor having an inner diameter of 4 mm, and an acrylic acid mixed gas was supplied at normal pressure and a gas space velocity of 32000 hr ^-1 , and the reaction temperature was 450 ° C. The reaction was carried out. The product was collected and analyzed by gas chromatography. As a result, the residual ratio of acrylic acid was 94.4%, and the residual ratio of propionic acid was 13.6%.

Example 8 (a) Production of composite oxide 13.0 g of ammonium paratungstate was added to 400 m of pure water.
33.1 g of lead nitrate was added to an aqueous solution dissolved in 100 l of pure water.
Dissolve in ml and add (solution-1). Next, 19.4 g of ammonium paramolybdate is dissolved in 100 ml of pure water by heating, and 196.8 g of a 20% silica sol is added thereto and sufficiently dispersed (solution-2). Next, 19.4 g of bismuth nitrate is dissolved in a mixed solution of 4 ml of concentrated nitric acid and 80 ml of pure water (solution-3). While sufficiently stirring the solution-1, the solution-2 and then the solution-3 are gradually added, and the resulting precipitate is evaporated to dryness while stirring. The solid obtained by evaporation to dryness is subjected to a heat treatment at 300 ° C./1 hour in an air atmosphere. The obtained granular solid is pulverized into particles having a particle size of 12 to 16 mesh. Next, baking was performed at 500 ° C. for 4 hours in a muffle furnace to obtain a composite oxide. The composition ratio of the metal component of the catalyst calculated from the charged raw materials is a composite oxide having the following atomic ratio. Mo: Bi: W: Pb: Si = 12: 4.4: 5.5:
10.9: 71.5

(B) Production of raw material gas This was carried out in the same manner as in Example 1, except that 8.9% of acrylic acid, 0.003% of propionic acid, 0.3% of acetic acid and 0.3 of propylene were used.
%, Acrolein 0.03%, oxygen 3.5%, steam 23%, and a mixed gas of acrylic acid containing a balance of CO + CO ₂ + nitrogen. (C) Heat treatment for reducing propionic acid 1 ml of the obtained composite oxide was charged into a glass reactor having an inner diameter of 4 mm, and an acrylic acid mixed gas was supplied at normal pressure and a gas space velocity of 20,000 hr ^-1 , and a reaction temperature of 450 ° C. The reaction was carried out. The product was collected and analyzed by gas chromatography. As a result, the residual ratio of acrylic acid was 94.6%, and the residual ratio of propionic acid was 36.8%.

Example 9 (a) Production of Composite Oxide The same composite oxide was produced according to Example 1. (B) Production of raw material gas JP-A-7-53448 as a catalyst for propylene one-stage oxidation
A catalyst having the following composition prepared according to Example 1 of
5 ml Mo: V: Te: Nb = 1: 0.3: 0.23: 0.1
2 was filled in a glass reaction tube having an inner diameter of 6 mm, and a raw material gas having a propylene concentration of 3%, an oxygen concentration of 10%, a nitrogen concentration of 57%, and a steam concentration of 30% was subjected to a gas space velocity of 7,200 h at normal pressure
The reaction was passed at r ^{-1 at} a reaction temperature of 320 ° C. As a result, 1.0% of acrylic acid, 0.045% of propionic acid, 0.16% of acetic acid, 1.44% of propylene, 0.23% of acetone
%, Oxygen 5.5%, CO + CO ₂ + nitrogen + steam balance containing acrylic acid mixed gas was obtained. (C) Heat treatment for reducing propionic acid 1 ml of the obtained composite oxide was charged into a glass reactor having an inner diameter of 4 mm and reacted at a normal pressure and a gas space velocity of 18,000 hr ^-1 at a reaction temperature of 450 ° C. . The product was collected and analyzed by gas chromatography. As a result, the residual ratio of acrylic acid was 96.8%, and the residual ratio of propionic acid was 20%.

Example 10 (a) Production of composite oxide The same composite oxide was produced according to Example 1. (B) Production of raw material gas JP-A-6-279351 as a catalyst for propane one-stage oxidation
A catalyst having the following composition prepared according to Example 1 of
1 ml Mo: V: Te: Nb = 1: 0.3: 0.23: 0.1
2 was filled in a glass reaction tube having an inner diameter of 6 mm, and a raw material gas having a propane concentration of 6%, an oxygen concentration of 20%, a nitrogen concentration of 64%, and a steam concentration of 10% was subjected to a gas space velocity of 6000 hr at normal pressure.
^-1 and passed at a reaction temperature of 400 ° C. As a result, acrylic acid 0.4%, propionic acid 0.0014%, acetic acid 0.023%, propylene 0.16%, propane 5.2
%, Oxygen 18%, CO + CO ₂ + nitrogen + steam balance was obtained. (C) Heat treatment for reducing propionic acid 1 ml of the obtained composite oxide was charged into a glass reactor having an inner diameter of 4 mm and reacted at a normal pressure and a gas space velocity of 18,000 hr ^-1 at a reaction temperature of 450 ° C. . The product was collected and analyzed by gas chromatography to find that the residual ratio of acrylic acid was 96.6% and the residual ratio of propionic acid was 21%.

Comparative Example 1 A raw material gas was produced in the same manner as in Example 1 except that glass wool was used instead of the composite oxide of the present invention.
In the same manner as described above, heat treatment for reducing propionic acid was performed. When the product was collected and analyzed by gas chromatography, there was no change in the amounts of acrylic acid and propionic acid. Comparative Example 2 A raw material gas was produced in the same manner as in Example 1 except that FePO ₄ (commercial product) was used in place of the composite oxide of the present invention, and a heat treatment temperature for reducing propionic acid was 450 ° C.
The same operation as in Example 1 was performed except that the SV was set to 12000 hr ^-1 . The product was collected and analyzed by gas chromatography to find that the residual ratio of acrylic acid was 94.9% and the residual ratio of propionic acid was 77.7%.

Comparative Example 3 A raw material gas was produced in the same manner as in Example 1 except that the composite oxide of the present invention was replaced with RuO ₂ (Kishida Chemical Co., Ltd.), and the heat treatment temperature for reducing propionic acid was changed to the reaction temperature. Was carried out in the same manner as in Example 1 except that the temperature was changed to 300 ° C. and the SV was set to 53,000 hr ⁻¹ . The product was collected and analyzed by gas chromatography.
%, And the residual ratio of propionic acid was 160%.

[0034]

According to the method of the present invention, propionic acid content in a product can be reduced by reducing propionic acid from an acrylic acid mixed gas obtained by gas-phase oxidation of propylene and / or propane. Alternatively, it is advantageous in polymerization of acrylic acid ester, and its industrial significance is large.

Continued on the front page (72) Inventor Shigeyasu Kanuka 8-3-1 Chuo, Ami-cho, Inashiki-gun, Ibaraki Pref.

Claims (7)

[Claims] A propion in an acrylic acid mixed gas characterized by subjecting an acrylic acid mixed gas obtained by vapor-phase oxidation of propylene and / or propane to heat treatment in the presence of a composite oxide containing molybdenum and bismuth. How to reduce acid. 2. The method according to claim 1, wherein the composite oxide containing molybdenum and bismuth is a Mo—Bi-based composite oxide represented by the following general formula. ## STR1 ## _{Mo a Bi b Fe c Al d} A2 e A3 f A4 g
During A5 _h O _x (wherein, Mo, Bi, Fe and O represent molybdenum, bismuth, iron and oxygen, Al is cobalt, nickel, at least one selected from the group consisting of manganese and chromium, A2 tellurium A3 represents at least one element selected from the group consisting of boron, phosphorus and arsenic, A4 represents an alkali metal, an alkaline earth metal A5 represents at least one element selected from the group consisting of silicon, aluminum and titanium; a to h represent the atomic ratio of each element; = 12, b = 0.5-7, c =
0-3, d = 0-10, e = 0-20, f = 0-3, g
= 0 to 1, h = 0 to 75, and x indicates the number of oxygen atoms necessary to satisfy the valence of each component.) 3. The method according to claim 1, wherein the heat treatment temperature is in a range of 300 to 500 ° C. 4. The heat treatment is performed at a gas hourly space velocity SV = 5,000.
The method according to any one of claims 1 to 3, wherein the method is performed at ⁰ to 80,000 hr ^-1 . 5. The method according to claim 1, wherein the acrylic acid mixed gas is an acrylic acid mixed gas obtained by two-stage oxidation of propylene. 6. The method according to claim 1, wherein the acrylic acid mixed gas is an acrylic acid mixed gas obtained by one-stage oxidation of propylene. 7. The method according to claim 1, wherein the acrylic acid mixed gas is an acrylic acid mixed gas obtained by one-stage oxidation of propane.