JP4783249B2 - Composite metal oxide catalyst and method for producing composite metal oxide catalyst - Google Patents

Description

The present invention is a composite metal oxide catalyst, further from details gas phase catalytic oxidation reaction with an unsaturated aldehyde, a manufacturing method and a composite metal oxide catalyst of the composite metal oxide catalyst suitable for producing unsaturated acids.

  The production of unsaturated acids such as acrylic acid and methacrylic acid is generally carried out by a two-stage oxidation reaction. That is, taking the production method of acrylic acid or methacrylic acid as an example, first, in the first stage reaction, acrolein or methacrolein is produced from propylene or isobutylene using a Bi-Mo composite oxide catalyst, and then the second stage reaction. Then, acrylic acid or methacrylic acid is produced using a Mo-V composite oxide catalyst, respectively.

  As a composite metal oxide catalyst used in these reactions, for example, as a catalyst for producing acrylic acid by vapor-phase catalytic oxidation of acrolein, Patent Document 1 discloses that the weight ratio of molybdenum oxide to vanadium oxide is 2: 1. A catalyst having a composition of ˜8: 1 and having a silica as a carrier is described. By using the catalyst, acrolein conversion rate of 92% and acrylic acid yield of 82% (reaction temperature of 300 ° C.) were obtained. Yes.

  Patent Document 2 describes a catalyst containing antimony, molybdenum, vanadium, and tungsten as essential components, and copper or the like as a minor component. By using the catalyst, acrolein conversion is 99%, acrylic acid yield is 91% (reaction temperature) 272 ° C).

  Patent Document 3 describes a catalyst having molybdenum, vanadium, copper, and antimony as essential components and having a maximum peak intensity of 22.2 ± 0.3 ° in the 2θ value of X-ray diffraction (using Cu—Kα ray). By using this catalyst, results of acrolein conversion of 99.1% and acrylic acid yield of 98.6% (reaction temperature: 250 ° C.) were obtained.

  Recently, a catalyst with relatively high crystallinity that can be directly oxidized from propane to acrylic acid or acrylonitrile without passing through an unsaturated aldehyde is known, and an example of using this catalyst in an acrolein oxidation reaction is shown. Yes. For example, Patent Document 4 includes molybdenum, vanadium, antimony, and niobium or tantalum as essential components, and four specific peaks (2θ = 22.1 °, 2θ value of 2θ value of X-ray diffraction (using Cu—Kα ray)). By using a highly crystalline catalyst having 22.3 °, 28.2 °, 36.2 °), an acrolein conversion rate of 99.2% and an acrylic acid yield of 89.4% (reaction temperature of 220 ° C.) Response results are obtained.

Further, Patent Document 5 uses a catalyst having molybdenum, vanadium, tellurium, niobium or tantalum as essential components and having at least two crystal phases, whereby acrolein conversion is 99.1% and acrylic acid yield is 89.000. A reaction result of 4% (reaction temperature 220 ° C.) is obtained.

  Further, in Patent Document 6, a compound containing molybdenum and a compound containing vanadium are mixed with water, and the obtained slurry is heat-treated (hydrothermal synthesis) under pressure, and the solid content obtained by firing is acrolein. A catalyst having a conversion rate of 98.7% and an acrylic acid yield of 89.4% (reaction temperature 240 ° C.) has been obtained.

Japanese Patent Publication No.41-001775 JP 47-008360 A JP-A-8-299797 Japanese Patent Laid-Open No. 11-343262 JP 2001-137709 A JP 2004-275868 A

  Patent Document 1 has few catalyst constituent elements and is easy to prepare, but the reaction results are not satisfactory. The catalysts described in Patent Documents 2 and 3 have a high yield, but have many catalyst constituent elements and a complicated preparation process, resulting in poor workability. Moreover, although the favorable reaction results are obtained using the catalyst which has a specific structure in 4, 5, since it uses comparatively expensive raw materials, such as Nb, as an essential element, it is inferior to economical efficiency. In Patent Document 6, there are few catalyst constituent elements and good reaction results are obtained, but further improvement in catalyst performance has been desired.

  As a result of various studies on catalysts that can be used to produce unsaturated acids from unsaturated aldehydes, the present inventors have produced a composite metal oxide consisting of only three elements of molybdenum, vanadium and oxygen by a specific production method. Thus, the activity of the obtained catalyst was found to be high, and the present invention was completed.

That is, the present invention is (1) mixing a compound having molybdenum and a compound having vanadium with water, and adding a strong acid so that the pH of the resulting slurry is in the range of 1.0 to 6.0, Next, a heat treatment (hydrothermal synthesis) under pressure to obtain a solid content, and firing the solid content, a method for producing a composite metal oxide catalyst,
(2) The method for producing a composite metal oxide catalyst according to (1), wherein the temperature in hydrothermal synthesis is 110 to 400 ° C., and the pressure is the saturated vapor pressure at the temperature,
(3) The method for producing a composite metal oxide catalyst according to (1) or (2), wherein the vanadium / molybdenum ratio (atomic ratio) is 0.1 to 0.5.
(4) The method for producing a composite metal oxide catalyst according to any one of (1) to (3), wherein the strong acid is an inorganic acid,
(5) The method for producing a composite metal oxide catalyst according to any one of claims (1) to (4), wherein the strong acid is sulfuric acid or nitric acid.
(6) A composite metal oxide catalyst comprising a composite metal oxide containing molybdenum and vanadium as essential constituent elements, the crystal form of which is a trigonal crystal, for obtaining an unsaturated acid by gas phase oxidation of an unsaturated aldehyde ,
About.

  Since the catalyst according to the production method of the present invention is composed only of molybdenum, vanadium, and oxygen, it is not necessary to use an expensive raw material like a conventional catalyst. In addition, the production method of the present invention can provide a composite metal oxide catalyst with high yield and high selectivity by a simple operation.

In the production method of the present invention, each compound having molybdenum and vanadium is mixed with water to form a slurry liquid, and then the pH is adjusted with a strong acid, followed by hydrothermal synthesis, and the obtained solid content is fired. Is.
The starting material compound in the production method of the present invention is not particularly limited. For example, as the compound having molybdenum, ammonium molybdate, molybdenum trioxide, molybdic acid, sodium molybdate and the like, and as the compound having vanadium, vanadium oxide. , Ammonium vanadate, vanadyl oxosulfate and the like. The composition ratio (preparation ratio) of the compound having molybdenum and the compound having vanadium is not particularly limited as long as the resulting crystal has an active structure (trigonal crystal), but vanadium / molybdenum atoms = 0.1 to 0.5 ( It is preferably used in a ratio that falls within the range of (molar ratio). The amount of water used for obtaining the slurry liquid is not particularly limited as long as these raw materials can be dissolved or can be dissolved even if they cannot be dissolved.

Next, a strong acid is added to the slurry and stirred. The strong acid is added until the slurry solution is acidic, and preferably the pH is about 1.0 to 6.0. The strong acid is a water-soluble acid, its pKa is not limited, and a salt of a strong acid and a weak base may be used as long as the pH of the slurry is within this range.
Strong acids that can be used include organic acids such as formic acid, acetic acid, benzoic acid, benzenesulfonic acid, propionic acid and lactic acid or weak base salts thereof, inorganic acids such as sulfuric acid, nitric acid, hydrochloric acid and hydrobromic acid or weak base salts thereof. In view of cost reduction, commercially available products can be used as they are, inorganic acids are preferred, and sulfuric acid or nitric acid is particularly preferred. The strong acid is usually added as an aqueous solution having an arbitrary concentration.

Hydrothermal synthesis is performed, for example, by charging the slurry liquid after pH adjustment into an autoclave.
Although the reaction can be carried out in air, it is preferred to carry out a part or the whole of the inside of the autoclave with an inert gas such as nitrogen or helium instead of air before starting the reaction. The reaction temperature of hydrothermal synthesis is usually 110 to 400 ° C., and the reaction time is usually 1 to 100 hours. The pressure in the autoclave is a saturated vapor pressure, and stirring may be performed during hydrothermal synthesis. After cooling the reaction solution after completion of hydrothermal synthesis, the solid content is filtered, washed with water, and dried.

  Next, if necessary, the solid content obtained above is treated with an aqueous solution of a water-soluble dicarboxylic acid. The treatment with the aqueous solution of the water-soluble dicarboxylic acid is carried out by bringing the solid content obtained above into contact with the aqueous solution of the water-soluble dicarboxylic acid. Specifically, the solid is mixed with an aqueous solution of a water-soluble dicarboxylic acid, and then the solid is filtered, washed with water, and dried. The concentration of the aqueous solution of the water-soluble dicarboxylic acid is preferably 0.1 to 1.0M. The aqueous solution of water-soluble dicarboxylic acid is usually used in the range of 10 to 50 ml with respect to 1 g of the solid content in the preferred concentration range. A mixing process is normally performed at 10-100 degreeC over 5 to 500 minutes. In addition, you may perform this aqueous solution process operation of water-soluble dicarboxylic acid with respect to the solid content after the baking process performed after this instead of performing with respect to the solid content after hydrothermal synthesis. When a treatment with an aqueous solution of a water-soluble dicarboxylic acid is performed, it is considered that a component considered to constitute an amorphous component in the solid content is removed, and a higher performance catalyst is obtained.

  Examples of the water-soluble dicarboxylic acid include oxalic acid, tartaric acid, glutaric acid, adipic acid, pimelic acid, maleic acid, fumaric acid, and phthalic acid, and oxalic acid is preferred. These water-soluble dicarboxylic acids are not hindered in the present invention even if their hydrates are used.

  The solid content treated with the aqueous solution of the water-soluble dicarboxylic acid (solid content not treated in some cases) can be used as it is, but in the present invention, the product is calcined. The baking treatment is performed at 300 ° C. or higher, preferably 350 to 700 ° C. in an inert gas such as air, nitrogen or helium for 0.5 to 10 hours. Since the calcination step is involved in the specific surface area value of the catalyst, the activity control of the catalyst can also be performed by appropriately determining the calcination temperature.

  The composite metal oxide thus obtained is a compound containing at least 20 to 99.99% of a component having a trigonal crystal structure (area ratio by X-ray diffraction measurement, the same applies hereinafter), and the rest is amorphous. is there. This composite metal oxide can be used as it is as the composite metal oxide catalyst of the present invention (hereinafter sometimes simply referred to as catalyst), but when the purity is low, the amorphous phase is removed again with water-soluble dicarboxylic acid. Therefore, it is preferable to use it with higher ingredients.

  The composite metal oxide catalyst thus obtained is preferably used after being pulverized. The catalyst of the present invention can be applied to any reaction mode such as a fixed bed, a fluidized bed, and a moving bed. However, in the case of a fixed bed, a powdered composite metal compound is preferably used on a spherical support such as silica, alumina, or silicon carbide. A supported molding catalyst or a catalyst obtained by molding a powdered composite metal oxide with a molding machine such as tablet molding is advantageous. For fluidized bed and moving bed reactors, it is advantageous to use a uniform catalyst of about several tens of microns prepared by adding a silica component or the like to improve wear resistance.

Preferred catalysts of the present invention are those of general formula (1)
Mo _a V _b O _c (1)
It is represented by In the formula, Mo and V represent molybdenum and vanadium, a and b represent respective element component amounts, and b = 0.1 to 0.5 with respect to a = 1.0. c is a number that varies depending on the oxidation state of other elements.

The catalyst of the present invention can be used in a reaction for producing a corresponding unsaturated acid from an alkane such as propane. However, the catalyst such as acrylic acid or methacrylic acid by gas phase catalytic oxidation from an unsaturated aldehyde such as acrolein or methacrolein can be used. It can be preferably used for the production of unsaturated acids.
The raw material gas composition ratio in the gas phase catalytic oxidation reaction for producing an unsaturated acid from an unsaturated aldehyde is not particularly limited, but unsaturated aldehyde: oxygen: water vapor: diluted gas (nitrogen, argon, etc.) = 1: 0.1 It is preferable to carry out at -10: 0 to 30: 0 to 60 (volume ratio).
The gas phase catalytic oxidation reaction may be carried out under pressure or under reduced pressure, but generally it is preferably carried out at a pressure around atmospheric pressure. The reaction temperature is usually 150 to 400 ° C, preferably 150 to 350 ° C.
The supply amount of the raw material gas is usually 100～100000Hr ^-1 in the space velocity (SV), preferably 400~30000hr ^-1.

EXAMPLES The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to the following examples unless it exceeds the gist.
In the following examples, acrolein conversion and acrylic acid selectivity are defined as follows.
Acrolein conversion (mol%) = 100 × (number of moles of supplied acrolein−number of moles of unreacted acrolein) / (number of moles of supplied acrolein)
Acrylic acid selectivity (mol%) = 100 × (number of moles of acrylic acid produced) / (number of moles of supplied acrolein)

Example 1
In 125 ml of distilled water, 8.83 g of ammonium molybdate was dissolved at room temperature. In another container, vanadyl oxosulfate (3.29) was dissolved in 125 ml of distilled water, and the resulting aqueous solution was added to the previous aqueous molybdenum solution and stirred sufficiently to form a slurry. A sulfuric acid aqueous solution was added to this solution to adjust the pH of the slurry to 2.2. The slurry was transferred to an autoclave (internal volume 300 ml) while washing the beaker with distilled water so that there was no residue, and hydrothermal synthesis was performed at 175 ° C. for 24 hours. The obtained product was filtered and washed with water, and dried at 40 ° C. for a whole day and night. A solution prepared by dissolving 7.56 g of succinic acid in 150 ml of distilled water was heated to 60 ° C., 6 g of the obtained solid was added, stirred for 30 minutes, filtered, washed with water, and 2 ° C. at 400 ° C. under air flow. Calcination was performed over time to obtain a catalyst of the present invention (trigonal content of 99.9%) in a charge ratio of Mo1.00 V0.36 (excluding oxygen).
(Catalyst evaluation test)
The prepared catalyst is sufficiently pulverized and added to the catalyst powder so that the silicon carbide powder is 10% by weight, and then the catalyst granules having an average particle size of 0.56 to 1.40 mm are formed by pressure molding and pulverization. And used in the catalyst evaluation test. In the catalyst evaluation test, a fixed bed flow type reactor was used, 0.5 g of the above catalyst granules were filled in a 6 mm inner diameter Pyrex (registered trademark) tube, and acrolein / oxygen / water vapor / nitrogen = 5.0 / 7.9. The reaction test was conducted at a reaction temperature of 190 ° C. while flowing a raw material mixed gas of 27.8 / 70.4 (ml / min.). The reaction product was analyzed by gas chromatography. As a result of the reaction, the acrolein conversion was 99.4% and the acrylic acid selectivity was 92.2%.

Comparative Example 1
A catalyst for comparison was obtained in the same manner as in Example 1, except that synthesis was performed without adjusting the pH of the slurry liquid. The crystal structure of the obtained catalyst was orthorhombic. When this comparative catalyst was evaluated in the same manner as in Example 1 except that the reaction temperature was 240 ° C., the acrolein conversion was 98.6% and the acrylic acid selectivity was 92.5%.

  As described above, the catalyst of the present invention exhibited a high acrolein conversion rate at a lower reaction temperature than the comparative catalyst.

  The catalyst of the present invention is publicly used for the gas-phase catalytic oxidation of unsaturated aldehydes with molecular oxygen-containing gas at low temperature to produce the corresponding unsaturated carboxylic acids. The produced unsaturated carboxylic acid is used in a wide range of applications as a raw material for various chemicals, a monomer for general-purpose resins, a water-absorbing resin, a thickener and the like.

Claims (6)

A compound having molybdenum and a compound having vanadium are mixed with water, and formic acid, acetic acid, benzoic acid, benzenesulfonic acid, propionic acid so that the resulting slurry has a pH in the range of 1.0 to 6.0. An organic acid selected from lactic acid or a weak acid salt thereof; an inorganic acid selected from sulfuric acid, nitric acid, hydrochloric acid or hydrobromic acid or a weak base salt thereof is added; then, heat treatment is performed under pressure (hydrothermal synthesis) to obtain a solid content. And producing the mixed metal oxide catalyst for producing acrylic acid by vapor-phase oxidation of acrolein , wherein the solid content is calcined. The method for producing a composite metal oxide catalyst according to claim 1, wherein the temperature in hydrothermal synthesis is 110 to 400 ° C, and the pressure is a saturated vapor pressure at the same temperature. The method for producing a composite metal oxide catalyst according to claim 1 or 2, wherein the vanadium / molybdenum ratio (atomic ratio) is 0.1 to 0.5. The method for producing a composite metal oxide catalyst according to any one of claims 1 to 3, wherein an inorganic acid selected from sulfuric acid, nitric acid, hydrochloric acid, and hydrobromic acid is used. The method for producing a composite metal oxide catalyst according to claim 4, wherein the inorganic acid is sulfuric acid or nitric acid. A composite metal oxide catalyst for producing acrylic acid by vapor-phase oxidation of acrolein, which is composed of a composite metal oxide containing molybdenum and vanadium as essential constituent elements, and whose crystal type is trigonal.