JP2000169420A - Production of acrylic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce acrylic acid causing little lowering of selectivity while selectively suppressing the formation of propionic acid by oxidizing an acrolein- containing gas with molecular oxygen in the presence of a specific multiple oxide catalyst. SOLUTION: (A) An acrolein-containing gas is oxidized with molecular oxygen in the presence of (B) a multiple oxide catalyst containing (i) molybdenum, (ii) vanadium and/or niobium, (iii) antimony and (iv) lead. Preferably, the component B is expressed by formula (Z is the component (ii); X is silicon and/or aluminum; Y is copper and tungsten; (a) to (h) are each the atomic ratio of element; (a), (c) and (d) are each 1-100; (b), (e) and (g) are each 0.1-50; (f) is 0-200; (h) is a number defined by the oxidation degree of each component) and the source of the component (iii) is an antimony multiple oxide produced by heating nickel carbonate as a part of raw material at 600-900 deg.C and expressed by Sb-Ni-X-O.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing acrylic acid. More specifically, the present invention relates to a method for oxidizing an acrolein-containing gas in the presence of a specific composite oxide catalyst to produce acrylic acid while suppressing the production of propionic acid.

[0002]

2. Description of the Related Art As a method for producing acrylic acid, there has been known a method in which propylene is used as a raw material and gas phase oxidation is performed. As a method for producing acrylic acid by gas phase catalytic oxidation of propylene, first, a single-step oxidation method in which propylene is oxidized from propylene to acrylic acid with the same catalyst at once, and second, mainly in the first oxidation step. Acrolein is produced, separated from by-products such as acrylic acid by-produced, and the resulting acrolein is oxidized in a second-stage oxidation step in a two-step method. There is a continuous method (hereinafter referred to as "continuous method") in which acrolein is produced and oxidized together with acrylic acid and off-gas as a by-product in the second oxidation step without being separated. It is mainly used industrially.

[0003] In any method, a small amount of propionic acid is present as a by-product in the acrylic acid produced at present. Since propionic acid has a very similar molecular weight to acrylic acid, it has very similar physical properties, such as boiling point, and also has a similar chemical structure, and therefore has similar chemical properties. There is a problem that the separation is difficult depending on the method and the chemical treatment. And since propionic acid or its ester does not polymerize, depending on the application, it greatly affects the quality of acrylic acid or acrylic acid ester,
It has been desired to suppress by-produced propionic acid.

[0004] In order to reduce by-produced propionic acid, for example, as a second stage catalyst in a continuous process, JP-A-48-9101 is used.
No. 4 discloses a Mo-VTAO (where T represents tungsten or antimony and A represents an alkali metal) catalyst, and JP-A-52-29483 discloses a Mo-based catalyst. A catalyst of —Nb—Cu—Fe—X—O (where X represents one or more elements selected from sodium, potassium, rupidium, magnesium, calcium, strontium and barium) is proposed. Have been. It is disclosed that when the catalyst contains an alkali metal, it is effective in suppressing the production of propionic acid from propylene. However, even though these catalysts reduce the production of propionic acid from propylene, the amount of propionic acid by-produced was 500 ppm or more based on the generated acrylic acid, and was not satisfactory.

On the other hand, Japanese Patent Application Laid-Open No.
JP-A-2-213846 discloses a catalyst of Sb-Mo- (V and / or Nb) -Ni-XYO (X represents silicon and / or aluminum, and Y represents copper and / or tungsten). Has been proposed. This catalyst has low activity on propylene at a reaction temperature suitable for oxidation of acrolein, so that by-products from propylene to propionic acid can be suppressed, but still, although slightly, oxidized propylene is formed in propionic acid. There was a problem.

[0006]

SUMMARY OF THE INVENTION The present inventors have found that by-products of propionic acid are generated in the oxidation step by the following two routes. One is that the propylene contained in the off-gas as unreacted propylene in the first oxidation step is catalytically oxidized on the catalyst mainly composed of Mo and V in the second oxidation step to produce propionic acid. Second, propionic acid is also produced from acrolein, which is a main reactant in the second oxidation step, and acrylic acid produced by oxidation of acrolein. In addition, there is a route in which propionaldehyde is formed in the first-stage oxidation step and further oxidized to form propionic acid, but the amount generated in this route is slight and does not cause any problem.

In the study of the present inventors, JP-A-48-91 discloses
No. 014, etc., the catalyst containing an alkali metal is effective in suppressing the production of propionic acid from propylene, but not effective in suppressing the production of propionic acid by-produced from acrolein or acrylic acid. I know. Therefore, the method for producing acrylic acid of the present invention, when producing acrylic acid from propylene by a continuous method, suppresses the amount of propionic acid produced under the condition that the propylene conversion rate is as high as 97% or more. ,
By suppressing the production of propionic acid from acrolein or acrylic acid, when oxidizing the acrolein-containing gas to produce acrylic acid, the production of propionic acid can be selectively reduced with almost no decrease in the selectivity of acrylic acid. An object of the present invention is to provide a method for producing acrylic acid while suppressing the production of acrylic acid.

[0008]

The gist of the present invention is to provide an acrylic acid which oxidizes an acrolein-containing gas with molecular oxygen in the presence of a composite oxide catalyst containing the following elements (1) to (4): And a method for producing the same. (1) molybdenum, (2) vanadium and / or niobium, (3) antimony, (4) lead

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The composite oxide catalyst used in the method for producing acrylic acid of the present invention includes (1) molybdenum,
The complex oxide catalyst is not particularly limited as long as it is a complex oxide catalyst containing each element of (2) vanadium and / or niobium, (3) antimony and (4) lead, and the complex oxide catalyst represented by the following general formula (I) is used. Particularly preferred.

[0010]

## STR2 ## _{Mo a Z b Ni c Sb d} Pb e X f Y g O h (I)

(Wherein, Z represents vanadium and / or niobium, X represents silicon and / or aluminum, Y represents copper and / or tungsten, and a to h
Represents the atomic ratio of each element, a = 1 to 100, b = 0.
1-50, c = 1-100, d = 1-100, e = 0.
1 to 50, f = 0 to 200, g = 0.1 to 50, and h are numbers determined by the degree of oxidation of each component.) Further, the antimony source in the composite oxide is obtained by using carbon nickel as a part of the raw material. And an antimony composite oxide represented by Sb-Ni-X-O (where X represents silicon and / or aluminum) obtained by heat treatment at 600 to 900 ° C. Further, as a lead source of the composite oxide catalyst, lead oxide, lead nitrate and the like are preferable.

Further, various compounds can be used as raw materials for other components used in producing the catalyst. As a specific compound, for example, as a compound of Mo source,
Ammonium molybdate, molybdenum trioxide, molybdic acid and the like, and examples of the compound of V source include ammonium metavanadate, vanadium pentoxide and the like. Further, as the compound of the Nb source, niobium hydroxide, niobium pentoxide and the like, and as the compound of the Cu source, copper sulfate, copper nitrate,
Examples of the compound used as a W source such as copper chloride include ammonium paratungstate, tungsten trioxide, and tungstic acid.

Next, a method for producing the composite oxide catalyst will be specifically described. First, Sb-Ni-X-O
Are metal antimony or antimony oxide as a Sb supply source, nickel carbonate or the like as a Ni supply source, colloidal silica or granular silica as a Si source as X element, and alumina or the like as an Al supply source. Manufactured. As a specific operation, for example, antimony pentoxide or antimony trioxide powder and silica or alumina are added to an aqueous slurry of nickel carbonate and evaporated to dryness with stirring, and the resulting solid is heated to 600 to 900 ° C., preferably. Is calcined at 650 to 850 ° C. in the presence of air.

The atomic ratio of each element in Sb—Ni—X—O is Sb: 1 to 40, preferably 1 to 40.
20, Ni: 1 to 20, preferably 1 to 10, X: 0
10, preferably 0 to 5, and O is a value determined by the degree of oxidation of each component. Then, the Sb—Ni— (X) —O composite oxide powder obtained as described above is mixed with the Mo, V and / or Nb compounds, a copper compound and / or a tungsten compound as the Y element, and The lead compound is mixed by a wet method, concentrated, dried, and pulverized.

The compound thus obtained is formed as it is or together with a suitable carrier and excipient, for example, silica, graphite, apicel, etc., into a suitable shape, for example, a small particle, a small column, a ring, etc. Tablets, extrusions,
Or by other methods) and then 300-500
The composite oxide can be manufactured by heating at a temperature of about 1 ° C. for about 1 to 10 hours. The heating atmosphere in this case is preferably non-reducing, preferably in the presence of molecular oxygen.

The acrolein-containing gas used in the production method of the present invention refers to pure acrolein as well as acrolein mixed gas containing acrolein and other components. Specific examples of the acrolein mixed gas include an acrolein-containing gas obtained by oxidizing propylene and an acrolein-containing gas obtained by oxidizing propane. Among them, an acrolein-containing gas obtained by oxidizing propylene is preferably used.

As a specific method, as a catalyst for producing acrolein by oxidizing propylene, a Mo-Bi type composite oxide catalyst is known and widely used industrially. For example, Mo-Bi-Ni-Co-Fe-Mn-BK disclosed in JP-A-55-102536.
Using a -Si-O-based catalyst, a propylene concentration of 4 to 12%,
When a catalytic oxidation reaction is performed at a temperature of 280 to 350 ° C. and a contact time of 1 to 8 seconds, acrolein 2 to 8 mol%, acrylic acid 0.1 to 4 mol%, unreacted propylene 0.01 to 0.3
An acrolein-containing gas containing mol% and the remainder nitrogen, carbon dioxide, carbon monoxide and the like can be obtained.

In the production method of the present invention, as the conditions for producing acrylic acid by catalytic oxidation using a composite oxide catalyst, conditions generally carried out by a general continuous method can be employed. At a reaction temperature of about 180 to 400 ° C. and a pressure of about 0.5 to 10 atm. The reaction raw material is an acrolein-containing gas obtained by oxidation of acrolein or propylene, and is preferably performed in the presence of water vapor in addition to molecular oxygen or a mixed gas containing molecular oxygen (for example, air) as an oxidizing agent. . Then, the mixed gas used for these reactions is passed through a catalyst to produce acrylic acid. The contact time with the catalyst is usually preferably about 0.5 to 10 seconds. As a composition of the reaction mixture gas, for example, 1 to 20 mol of molecular oxygen is used per 1 mol of acrolein. As the reaction mixed gas, a product gas obtained by catalytically oxidizing propylene for the purpose of producing acrolein may be introduced as it is, or oxygen and the like may be added thereto to form a reaction gas. Air is generally used as the oxygen source, but pure oxygen (molecular oxygen) or a mixed gas obtained by diluting oxygen with an inert gas such as carbon dioxide or nitrogen can also be used. In addition to this, the catalytic oxidation reaction can refer to the knowledge on ordinary gas-phase catalytic oxidation of acrolein as long as it does not exceed the gist of the present invention.

[0019]

EXAMPLES Hereinafter, the content of the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to the Examples unless it exceeds the gist thereof. Example 1 (a) Preparation of catalyst Basic nickel carbonate (NiCO ₃ .2Ni (OH) _2.
228 g of 4H ₂ O) (however, a basic nickel carbonate having a water content of 76% is used in the reduced amount (the same applies hereinafter)) to pure water 300
Then, 50 g of silica ("Carflex # 67" manufactured by Shionogi Pharmaceutical Co., Ltd.) and 150 g of antimony trioxide were added thereto, and the mixture was sufficiently stirred. The slurry was concentrated by heating and dried. Next, the obtained solid was calcined in a muffle furnace at 800 ° C. for 3 hours, crushed,
0 mesh or less (Sb-Ni-Si-O powder).

540 ml of pure water is heated to about 80 ° C., and 63.9 g of ammonium paramolybdate, 8.4 g of ammonium metavanadate, 4.6 g of niobium hydroxide, 10.2 g of lead nitrate and 21.2 g of copper sulfate are stirred. The Sb-Ni-Si-O powder was added to the solution, and the mixture was sufficiently stirred and mixed. This slurry was heated and dried at 80 to 100 ° C., and the dried product was pulverized to 24 mesh or less, and 1.5% by weight of graphite was added and mixed. Next, use a small tableting machine to make 5φ × 4
mm. This was calcined in a muffle furnace at 400 ° C. for 5 hours to obtain a catalyst. The composition of the catalyst obtained here was as follows in atomic ratio. Mo: V: Nb: Sb: Pb: Ni: Cu: Si = 3
5: 7: 3: 100: 3: 43: 9: 80

(B) Reaction A catalyst for propylene oxidation in the first stage oxidation step
40 ml of a catalyst having the following composition, prepared by the method disclosed in US Pat. No. 13097, 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 73% raw material gas was passed at a normal pressure and a gas space velocity of 750 hr ^{-1 at} a reaction bath temperature of 310 ° C.

9 of propylene supplied in the first oxidation step
7.5% had reacted and the remaining 2.5% was present as unreacted propylene in the output of the first oxidation step. 86% of the reacted propylene was converted to acrolein, and 9% was acrylic acid by-product. The rest consisted mainly of carbon dioxide and carbon monoxide, and contained a small amount of acetic acid. The outgas from the first oxidation step, consisting of these gases, the remaining oxygen of the reaction, nitrogen not involved in the reaction, and water vapor, was sent directly to the second oxidation step.

A reactor equipped with a stainless steel night game jacket having an inner diameter of 20 mm and connected continuously by providing a nozzle at the connection portion was charged with 50 ml of the catalyst prepared as described above, intermediate air was introduced from the nozzle, and the gas space velocity was 1350 hr.
^-1 , and passed at a reaction bath temperature of 260 ° C. The molar ratio of the obtained acrylic acid to the supplied propylene was 89.
0%, unreacted propylene 2.4%, by-product acrolein 0.7%, propionic acid 0.022%, and the others were mainly carbon dioxide and carbon monoxide. The propionic acid content based on the obtained acrylic acid was 198 ppm.

COMPARATIVE EXAMPLE 1 The first-stage oxidation step was performed in the same manner as in Example 1, except for the equipment, catalyst, reaction conditions, etc., and all the outgas was sent to the second-stage oxidation step. In the second oxidation step, a catalyst prepared in the same manner except that Pb was removed from the catalyst used in the second oxidation step in Example 1 (Mo: V: Nb: Sb: Ni: Cu: Si =
35: 7: 3: 100: 43: 9: 80) was used in the same manner as in Example 1. The yield of the obtained acrylic acid with respect to the supplied propylene was 89.0% in molar ratio, 2.4% of unreacted propylene, 0.7% of by-product acrolein,
Propionic acid was 0.039%, and the others were mainly carbon dioxide and carbon monoxide. The propionic acid content based on the obtained acrylic acid was 350 ppm.

Example 2 The first-stage oxidation step was carried out in the same manner as in Example 1, except for the equipment, catalyst, reaction conditions, etc., and all the gas emitted was sent to the second-stage oxidation step. In the second-stage oxidation step, a catalyst prepared in the same manner as in Example 1 except that 80.7 g of lead oxide was used instead of lead nitrate as a Pb raw material of the catalyst used in the second-stage oxidation step in Example 1. (Mo: V: Nb: Sb: Pb: Ni: Cu:
Si = 35: 7: 3: 100: 35: 43: 9: 80)
The procedure was performed in the same manner as in Example 1, except that was used. The yield of the obtained acrylic acid with respect to the supplied propylene was 8 by mole.
8.9%, unreacted propylene 2.4%, by-product acrolein 0.6%, propionic acid 0.022%, and the others were mainly carbon dioxide and carbon monoxide. The propionic acid content based on the obtained acrylic acid was 196 ppm.
Met. The following can be seen from the examples and comparative examples.
When the reaction is performed in the presence of the specific composite oxide catalyst of the present invention, the content of propionic acid relative to acrylic acid is
200 ppm (mole) or less, whereas in the case of a known composite oxide catalyst containing no Pb, 350 ppm
It is understood that the content of propionic acid is high. According to the method of the present invention, propionic acid can be greatly reduced while maintaining the yield of acrylic acid relative to propylene.

[0026]

According to the method of the present invention, when oxidizing acrolein mixed gas obtained by gas-phase oxidation of propylene to produce acrylic acid, the propionic acid content is reduced by reducing propionic acid. Is advantageous in the polymerization of acrylic acid or acrylic acid ester, and its industrial significance is large.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Shigeyasu Kashika 1 Tohocho, Yokkaichi-shi, Mie Pref. BE30 BS10 4H039 CA65 CC30

Claims (4)

[Claims] 1. An acrolein-containing gas is prepared according to the following (1) to
(4) A method for producing acrylic acid, comprising oxidizing with molecular oxygen in the presence of a composite oxide catalyst containing each element. (1) molybdenum, (2) vanadium and / or niobium, (3) antimony, (4) lead 2. The method for producing acrylic acid according to claim 1, wherein the composite oxide is a composite oxide represented by the following general formula (I). ## STR1 ## _{Mo a Z b Ni c Sb d} Pb e X f Y g O h (I) ( wherein, Z is shown the vanadium and / or niobium, X
Represents silicon and / or aluminum, Y represents copper and / or tungsten, a to h represent the atomic ratio of each element, a = 1 to 100, b = 0.1 to 50, c = 1
-100, d = 1-100, e = 0.1-50, f = 0
-200, g = 0.1-50, h is a number determined by the degree of oxidation of each component) 3. An antimony source in the composite oxide catalyst, wherein nickel carbonate is used as a part of the raw material, and 600 to 900 ° C.
Sb-Ni-X-O obtained by heat treatment (provided that
3. The method for producing acrylic acid according to claim 1, wherein X is an antimony composite oxide represented by the following formula: 4. The process for producing acrylic acid according to claim 1, wherein the acrolein-containing gas is obtained by gas-phase catalytic oxidation of propylene.