JP2008284439A - Heteropolyacid catalyst for preparing methacrylic acid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heteropolyacid catalyst having a high productivity of high methacrylic acid. <P>SOLUTION: A heteropolyacid catalyst containing water-soluble heteropolyacid and hardly water-soluble heteropolyacid salt for preparing methacrylic acid is disclosed. The water-soluble heteropolyacid and the hardly water-soluble heteropolyacid salt of the finished catalyst has the degree of reduction controlled by controlling the degree of reduction controlled at the time of preparing a slurry. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a heteropolyacid catalyst used in the production of methacrylic acid by vapor phase catalytic oxidation of methacrolein with molecular oxygen.

  There is a heteropolyacid catalyst as a catalyst used for producing methacrylic acid by vapor-phase catalytic oxidation of methacrolein with molecular oxygen. Examples of such heteropolyacid catalysts include heteropolyacids whose counter cations are protons, such as molybdophosphoric acid and molybdovanadolinic acid, and heteropolyacids in which part of the protons are substituted with cesium, rubidium, thallium, potassium, etc. Salt is known. Since the heteropolyacid has high acidity, when it is used alone as a catalyst, the selectivity / productivity (single-flow yield) of methacrylic acid is lowered. Therefore, Non-Patent Document 1 describes that a catalyst whose acidity is adjusted by partially neutralizing a part of protons of a counter cation is used.

  Heteropolyacids whose protons are counter cations are water-soluble, but heteropolyacid salts in which protons are substituted with cesium (Cs), rubidium (Rb), thallium (Tl), potassium (K), etc. are ions of these cations. Due to its large radius, it is generally poorly soluble in water. In particular, Cs, Rb, Tl, and K have an ionic radius of cations of these elements of 1.1 Å or more. Therefore, heteropolyacid salts substituted with these elements are extremely hardly soluble or insoluble, for example, Patent Document 1 discloses that a compound such as a hydroxide containing these elements can be used as a precipitant for a heteropoly acid.

  Patent Document 1 relates to a method for recovering a catalyst component. After dissolving a hardly soluble heteropolyacid salt with sodium hydroxide in an alkaline manner, treatment with a strongly acidic ion exchange resin results in a proton type, that is, a water-soluble heteropolyacid salt. A method for recovery as an acid is disclosed. However, there is no description about producing a heteropolyacid catalyst for producing methacrylic acid from a water-soluble heteropolyacid and a hardly water-soluble heteropolyacid.

  In addition to the above-mentioned method for adjusting the acidity as a method for improving the selectivity and productivity when producing methacrolein by vapor-phase catalytic oxidation of molecular metholine with molecular oxygen, the reduction degree of the heteropolyacid or its salt There is a way to adjust. For example, in Patent Document 2, when isobutane is oxidized, a heteropolyacid or a salt thereof containing P or As as a central element and containing Mo is used as a catalyst in a highly reduced state, in particular, one molecule per heteropolyacid. It is disclosed that the selectivity of methacrylic acid is improved when a catalyst reduced by ˜6-electron is used.

  In Patent Document 2, the number of electrons corresponding to electron reduction per molecule of heteropolyacid is shown as an average value of the entire system. However, in the catalyst described in the patent document, the oxidation reaction from methacrolein to methacrylic acid has a sufficient productivity because the reduction is excessive and the oxidation reaction by the efficient oxygen supply from the heteropolyacid cannot be performed. Because it is not industrially suitable. Patent Document 2 describes that “a catalyst obtained by reducing a heteropolyacid or salt thereof containing P or As as a central element and containing Mo by 1 to 6 electrons per molecule of the heteropolyacid” is used. However, the degree of reduction is an average expression of the entire system as described in Patent Document 2. These heteropolyacids and heteropolyacid salts are in a state of different oxidation functions adjusted for acidity, and it is necessary to quantify and optimize the respective reduction eases and reduction states to clarify a preferable range.

Okuhara, et, al, J.catal, 83,121 (1983) JP 07-213992 A Japanese Patent Publication No. 7-33344

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a heteropolyacid-based catalyst with high productivity of methacrylic acid.

The present inventors have found that a hardly water-soluble heteropolyacid salt and a water-soluble heteropolyacid can be individually controlled in the oxidation / reduction state of the catalyst by the difference in the counter cation species of the heteropolyacid, and have completed the present invention. .
That is, the present invention is a heteropolyacid catalyst for the production of methacrylic acid containing a water-soluble heteropolyacid and a poorly water-soluble heteropolyacid salt, the degree of reduction being adjusted during slurry preparation, And a heteropolyacid catalyst for the production of methacrylic acid in which the degree of reduction of the poorly water-soluble heteropolyacid salt is controlled.

  According to the present invention, a heteropolyacid catalyst capable of producing methacrylic acid with high selectivity can be provided.

Hereinafter, the present invention will be described in detail.
The present invention relates to a heteropolyacid catalyst for producing methacrylic acid. More specifically, the present invention relates to a heteropolyacid catalyst in which the reduction degree is adjusted during slurry preparation to control the reduction degree of the water-soluble heteropolyacid and the poorly water-soluble heteropolyacid salt of the completed catalyst.

The heteropolyacid catalyst for producing methacrylic acid according to the present invention has a degree of reduction per molecule of the heteropolyacid of the water-soluble heteropolyacid of the finished catalyst α, and a degree of reduction per molecule of the heteropolyacid of the poorly water-soluble heteropolyacid salt. When β is defined, it is preferable that the reduction degrees α and β satisfy the relationships represented by the following formulas (1) to (3).
0 <α ≦ 1 (1)
0.01 <β ≦ 2 (2)
α−β ≦ 0.2 (3)

  The degree of reduction per one molecule of the water-soluble heteropolyacid or poorly water-soluble heteropolyacid salt is in accordance with the chemical oxygen consumption (also known as COD method) defined in JIS K0102 (Factory Wastewater Test Method). It is determined by the method. In this method, the reaction of permanganic acid (not shown, but potassium salt) when the water-soluble heteropolyacid or the poorly water-soluble heteropolyacid salt is oxidized can be represented by the following formula (4). For example, when the water-soluble heteropolyacid or the poorly water-soluble heteropolyacid salt consumes 1 mol of permanganate per molecule of the heteropolyacid, 5 mol of electrons are converted into the water-soluble heteropolyacid as shown in the following formula (4). Or it is deprived of water-insoluble heteropoly acid salt and oxidized. Thus, Mn in the permanganic acid is reduced from 7-valent to 2-valent. In the present invention, the degree of reduction α or β in this case is defined as 5.

  The reduction degree α or β in the present invention was calculated using this reaction.

  In the heteropolyacid catalyst of the present invention, as shown in the formula (1), the reduction degree α per molecule of the heteropolyacid of the water-soluble heteropolyacid contained in the catalyst is greater than 0 and 1 or less. Preferably there is. Further, it is more preferably greater than 0 and 0.5 or less, and more preferably greater than 0 and 0.2 or less. It is preferable that the degree of reduction α per one molecule of the water-soluble heteropolyacid is within such a fine reduction range because the activity of the catalyst becomes high.

  On the other hand, in the heteropolyacid catalyst of the present invention, as shown in the formula (2), the degree of reduction β per molecule of heteropolyacid of the poorly water-soluble heteropolyacid salt contained in the catalyst is 0.01 Is preferably 2 or less. Further, it is more preferably greater than 0.01 and not greater than 1. By setting the degree of reduction β per molecule of heteropolyacid of the poorly water-soluble heteropolyacid salt to such a reduction degree, in addition to this mild active site possessed by the poorly water-soluble heteropolyacid salt itself, such reduction The sequential oxidation reaction can be suppressed by the effect of suppressing the oxygen supply by increasing the temperature. For example, when the degree of reduction β per molecule of heteropolyacid is 2 or less, it can be imagined that one of about 40 oxygen atoms in the heteropolyacid structure is extracted or hydrogenated to the oxygen. it can. In this state, the heteropolyacid salt hinders the inflow and removal of excess oxygen supplied to the methacrolein oxidation reaction, and its effect is to suppress oxidation, that is, methacrolein is oxidized to methacrylic acid, and the oxidation reaction continues. Thus, there is an effect of suppressing the so-called sequential oxidation reaction such as increase of carbon monoxide, carbon dioxide, acetic acid and the like that burns, which is considered to contribute to the improvement in selectivity of methacrylic acid.

  Moreover, the heteropolyacid catalyst of the present invention includes a reduction degree α per molecule of the heteropolyacid of the water-soluble heteropolyacid and a reduction degree β per molecule of the heteropolyacid of the poorly water-soluble heteropolyacid, It is preferable to satisfy the relationship shown in Formula (3). Satisfying such a relationship is preferable because it is a highly selective catalyst that suppresses sequential oxidation while being highly active, and the productivity of methacrylic acid is improved.

  Furthermore, in the heteropolyacid catalyst of the present invention, the content of the water-soluble heteropolyacid is preferably 10 to 60% by mass, more preferably 20 to 60% by mass, based on the total mass of the heteropolyacid catalyst. preferable. The content of the poorly water-soluble heteropolyacid salt is preferably 90 to 40% by mass, and more preferably 80 to 40% by mass. The heteropolyacid catalyst of the present invention contains 0 to 5% by mass of components other than water-soluble heteropolyacid or poorly water-soluble heteropolyacid salt, such as impurities that could not become heteropolyacid, with respect to the total mass of the catalyst. It may be a thing. When the content of the water-soluble heteropolyacid and the poorly water-soluble heteropolyacid salt is within the above range, the acidity and reduction degree of the heteropolyacid catalyst of the present invention are optimized, and improvement in selectivity and productivity can be achieved. .

  In order to produce a heteropolyacid-based catalyst having such a configuration, for example, a slurry containing a water-soluble heteropolyacid and a slurry containing a poorly water-soluble heteropolyacid salt are prepared separately, and these are prepared as a water-soluble solution of the finished catalyst. It is preferable that the heteropolyacid and the poorly water-soluble heteropolyacid salt are mixed at a ratio such that the content is the above-mentioned content.

  The water-soluble heteropolyacid refers to one in which the countercation of the heteropolyacid is hydrogen (proton) in three substitutions. The presence of protons is an important chemical structure for making methacrolein into methacrylic acid upon receiving the molecular attracting effect of methacrolein and the supply of oxygen of the heteropolyacid.

  The poorly water-soluble heteropoly acid salt is a compound in which at least one proton, which is a counter cation of a heteropoly acid, is substituted with an alkali element such as potassium, rubidium or cesium, or an element such as thallium or ammonium. Since the molecular attracting effect of methacrolein is mild due to the decrease in protons in the poorly water-soluble heteropolyacid salt, the combination of the water-soluble heteropolyacid and the hardly water-soluble heteropolyacid salt is important.

  The outline of the method for quantifying the water-soluble heteropolyacid and the poorly water-soluble heteropolyacid salt contained in the heteropolyacid catalyst of the present invention is as follows. That is, the heteropolyacid catalyst of the present invention is dissolved or dispersed in pure water, subjected to ultrasonic elution treatment, and the water elution part and the water insoluble part are separated by a centrifuge. The water-insoluble portion is dried and weighed to calculate the mass% of the poorly water-soluble heteropolyacid salt. Then, what is necessary is just to calculate content of water-soluble heteropolyacid by reducing the mass% of the said poorly water-soluble heteropoly acid salt from 100 mass%. In order to improve the quantitativeness of the water-soluble heteropolyacid, an aqueous solution of cesium, rubidium, thallium, potassium, etc. is added to the water elution part to precipitate a poorly water-soluble heteropolyacid salt, and this amount is measured, The content of the water-soluble heteropolyacid may be determined.

Moreover, it is preferable that the heteropolyacid catalyst for methacrylic acid production of the present invention has a composition represented by the following formula.
A _a Mo _b V _c Cu _{d De} Y _f Z _g O _h (5)
(In the formula, Mo, V, Cu and O represent molybdenum, vanadium, copper and oxygen, respectively, A represents at least one element selected from the group consisting of phosphorus, arsenic, silicon and boron; D Represents at least one element selected from the group consisting of antimony, bismuth, germanium, zirconium, tellurium, silver, selenium, silicon, tungsten and boron, and Y represents iron, zinc, chromium, magnesium, tantalum, manganese And at least one element selected from the group consisting of cobalt, barium, gallium, cerium and lanthanum, and Z represents at least one element selected from the group consisting of sodium, potassium, rubidium, cesium and thallium Moreover, a, b, c, d, e, f, g, and h represent the atomic ratio of each element, = 12 represents a real number of a = 0.5-3, c = 0.01-3, d = 0-2, e = 0-3, f = 0-3, g = 0.01-3, h is an atomic ratio of oxygen necessary to satisfy the valence of each component.)

  Next, the method for preparing the heteropolyacid catalyst of the present invention will be described in detail.

(Scale of preparation)
The heteropolyacid catalyst of the present invention can be produced regardless of the scale of preparation. The amount of the molybdenum raw material used at one time is preferably 100 g or more and 10 t or less, and more preferably 1 kg or more and 1 t or less.

(Raw material of catalyst)
As raw materials for the heteropolyacid catalyst of the present invention, oxides, nitrates, carbonates, ammonium salts and the like of each element can be appropriately selected and used. For example, as a raw material of molybdenum, molybdic acid or molybdenum trioxide is preferable, but ammonium paramolybdate or the like can also be used. Moreover, as a raw material of phosphorus, orthophosphoric acid, phosphorus pentoxide, ammonium phosphate, etc. can be used. Moreover, as a raw material of vanadium, ammonium metavanadate, divanadium pentoxide, etc. can be used. Moreover, copper nitrate, copper sulfate, copper carbonate, etc. can be used as a raw material of copper.

(Preparation of slurry)
In the method for producing a heteropolyacid catalyst in the present invention, in principle, various raw materials are charged into water, heated and stirred to prepare a slurry, and the degree of reduction is adjusted at the time of slurry preparation. Examples of methods for adjusting the degree of reduction during slurry preparation include electroreduction and reduction with a reducing substance (inorganic {eg, divalent iron or hydrazine, hydrogen}, organic {eg, ascorbic acid, formalin}). A method can be mentioned.

  When adjusting the degree of reduction by separately preparing a slurry containing a water-soluble heteropolyacid and a slurry containing a poorly water-soluble heteropolyacid and mixing them, the slurry can be prepared as follows, for example. it can.

(Preparation of solution A)
First, at least molybdenum, phosphorus, and vanadium, and in the case where D element is included, each raw material of D element is dissolved or suspended in water, so that solution A or slurry containing at least molybdenum, phosphorus, and vanadium is obtained. To prepare. The amount of water used is preferably 200 parts by mass or more and more preferably 300 parts by mass or more with respect to 100 parts by mass of the molybdenum raw material. Moreover, 2000 mass parts or less are preferable, and 1000 mass parts or less are more preferable. Although the temperature at the time of preparing the liquid A is not limited, the higher the temperature, the higher the production rate of the heteropolyacid, so 80 ° C. to 100 ° C. is preferable. The A liquid may contain any raw material other than the Z element raw material, and may contain, for example, a copper element raw material or a Y element raw material. When pH of A liquid is high, it is preferable to select a raw material so that many phosphate groups and nitrate groups may be included, and to set pH to 4 or less, more preferably 2 or less. Stirring at the time of preparing the liquid A is sufficient as long as the raw material does not settle, and there is almost no influence on the reaction.

(Preparation of liquid B)
Further, a Z-element raw material is dissolved or suspended in water to prepare a solution B that becomes a solution or slurry containing at least the Z element. The amount of water used is preferably 100 parts by mass or more and more preferably 200 parts by mass or more with respect to 100 parts by mass of the Z element raw material. Moreover, 500 mass parts or less are preferable, and 400 mass parts or less are more preferable. The temperature at the time of preparing the B liquid is preferably 30 ° C. to 80 ° C., but stirring is not necessarily required. The liquid B may contain other arbitrary raw materials. For example, it may contain a copper element raw material or a Y element raw material, but preferably does not contain a D element raw material.

(Mixing of liquid A and liquid B)
Next, said A liquid and B liquid are mixed and AB mixed liquid used as the slurry liquid containing a water poorly soluble heteropolyacid salt is prepared. The temperatures of the A liquid and the B liquid may be different, but it is preferable that the temperature after mixing be 0 ° C. to 40 ° C. During this mixing, a precipitate is formed, but since the reaction occurs instantaneously and there is little reaction heat, the temperature after mixing can be easily predicted from the temperatures of the liquid A and the liquid B. Just choose. It is more preferable that the temperature of the liquid A and the liquid B is in the range of 10 ° C. to 30 ° C. and the same temperature. The method for mixing the A solution and the B solution is not particularly limited, but mixing in a shorter time is preferable in terms of production efficiency. Usually, the liquid A is more than the liquid B, so it is practical to inject the liquid B into the liquid A.

(Preparation of liquid C)
First, a solution containing at least molybdenum, phosphorus and vanadium, and a water-soluble heteropolyacid containing at least molybdenum, phosphorus and vanadium by dissolving or suspending each raw material of water in the case of containing element D. Alternatively, a C liquid which is a slurry liquid is prepared. The amount of water used is preferably 200 parts by mass or more and more preferably 400 parts by mass or more with respect to 100 parts by mass of the molybdenum raw material. Moreover, 2000 mass parts or less are preferable, and 1000 mass parts or less are more preferable. Although the temperature at the time of preparation of C liquid is not ask | required, since heteropoly acid production | generation rate increases so that it is high temperature, it is preferable to set it as 0 to 150 degreeC. The liquid C may contain any raw material other than the Z element raw material, for example, a copper element raw material or a Y element raw material. When pH of C liquid is high, it is preferable to select a raw material so that many phosphate radicals and nitrate radicals may be included, and to make pH into 4 or less, More preferably, 2 or less. About stirring at the time of C liquid preparation, it should just be a grade which a raw material does not precipitate, and there is almost no influence on reaction.

(Mixing of AB liquid mixture and C liquid)
And said C liquid is mixed with said AB mixed solution, and it is set as ABC mixed liquid. At this time, it is preferable to adjust the pH of the ABC mixed solution to 8 or less. Usually, it is preferable to inject a smaller amount of C liquid into the AB mixed liquid, and it is more preferable to inject C liquid in a period of 1 minute to 20 minutes. In this case, the temperature of the AB mixed solution and the solution C is preferably 25 ° C. to 100 ° C., more preferably 25 ° C. to 80 ° C. for both solutions.

(Retention of ABC liquid mixture)
Thereafter, the ABC mixed solution needs to be kept at 40 ° C. to 100 ° C., more preferably 40 ° C. to 80 ° C., for 1 to 15 minutes with stirring. The retention time of the ABC mixed solution is required to be at least 1 minute in order to produce a good slurry, and is 15 minutes or less, preferably 12 minutes or less in consideration of productivity. In preparing the heteropolyacid catalyst of the present invention, the final slurry pH is important. The final slurry preferably has a pH of 8 or less. When the final slurry has a pH of 8 or less, catalyst particles are easily formed, and the catalyst performance is improved. Further, the final slurry pH is more preferably 3 or less in order to prepare the catalyst of the present invention.

(Drying process)
As a method for drying the ABC mixed solution, various methods can be used. For example, an evaporating and drying method, a spray drying method, a drum drying method, an air current drying method and the like can be mentioned. There are no particular limitations on the model of the dryer used for drying, the temperature, atmosphere, etc. during drying, and a dried catalyst precursor according to the purpose can be obtained by appropriately changing the drying conditions.

(Molding process)
The dried catalyst precursor obtained by drying the ABC mixed solution may be calcined as it is, or may be calcined after performing some preforming. The preforming method is not particularly limited, and various dry and wet molding methods known in the art can be applied, but a method of molding only with a catalyst component without including a carrier or the like is preferable. Specific examples of the molding method include tableting molding, press molding, extrusion molding, granulation molding, and the like. The shape of the molded product is not particularly limited, and for example, it can be molded into a columnar shape, a ring shape, a spherical shape, or the like.

(Baking process)
There are no particular limitations on the method and firing conditions for firing the dried catalyst precursor or the molded product thereof, and known processing methods and conditions can be applied. Optimum conditions for calcination vary depending on the catalyst raw material, catalyst composition, and preparation method to be used, but are usually 200 to 500 ° C., preferably 300 to 400 ° C. under an oxygen-containing gas stream such as air or an inert gas stream. .5 hours or more, preferably 1 to 40 hours. Here, the inert gas refers to a gas that does not decrease the catalytic activity, and examples thereof include nitrogen, carbon dioxide, helium, and argon.

(Usage as a catalyst)
When producing methacrylic acid using the heteropolyacid catalyst of the present invention, a raw material gas containing methacrolein and molecular oxygen is brought into contact. Although the concentration of methacrolein in the raw material gas can be varied within a wide range, it is usually suitably 1 to 20% by volume, particularly preferably 3 to 10% by volume. The molecular oxygen concentration in the raw material gas is preferably 0.5 to 4 mol, particularly 1 to 3 mol, per 1 mol of methacrolein. The source gas may be diluted by adding an inert gas such as nitrogen or carbon dioxide, or water vapor may be added to the source gas.

  The reaction pressure is preferably from normal pressure to several atmospheres. The reaction temperature can be selected in the range of 230 to 450 ° C, but 250 to 400 ° C is particularly preferable.

  Hereinafter, the present invention will be described in more detail with reference to examples. In this example, “part” means “part by mass” unless otherwise specified.

  In this example, the degree of reduction α and β per molecule of the heteropolyacid of the water-soluble heteropolyacid and the poorly water-soluble heteropolyacid salt contained in the obtained catalyst and the content (%) of these catalysts relative to the total mass are the following methods: Was analyzed.

[Analysis of content of water-soluble heteropolyacid and poorly water-soluble heteropolyacid salt in catalyst]
0.2 g of catalyst is added to 100 ml of pure water and sonicated at about 25 ° C. for 30 minutes. Subsequently, the ultrasonically treated catalyst dispersion is quickly transferred to a stainless steel centrifuge tube, and centrifuged at 16,000 rpm for 5 minutes at room temperature using a centrifuge. Separate the insoluble part. The supernatant liquid separated by the centrifugation operation is transferred to another container. On the other hand, the water-insoluble portion remaining at the bottom of the centrifuge tube is vacuum-dried overnight at 40 ° C. and weighed. The percentage of the mass of the water-insoluble portion relative to the mass of the catalyst charged in pure water is defined as the content (mass%) of the poorly water-soluble heteropolyacid salt. Subsequently, the mass% of the poorly water-soluble heteropolyacid salt is subtracted from 100 mass% to obtain the content of the water-soluble heteropolyacid.

  Depending on the catalyst, in order to improve the accuracy of quantitative determination of the amount of water-soluble heteropolyacid, an aqueous solution of a salt such as cesium, rubidium, thallium, potassium, etc. was added to the supernatant separated by centrifugation, and it was allowed to stand overnight. A new precipitate portion is separated and weighed by the above-mentioned method and converted into the mass of the water-soluble heteropolyacid, and then the percentage with respect to the mass of the catalyst is obtained, and this may be the content of the water-soluble heteropolyacid.

[Analysis of reduction degree α and β of water-soluble heteropolyacid and poorly water-soluble heteropolyacid salt]
Analysis of the degree of reduction α and β per molecule of the water-soluble heteropolyacid and poorly water-soluble heteropolyacid salt contained in the catalyst was obtained in the analysis of the content of the water-soluble and poorly water-soluble heteropolyacid salt. Perform using water elution part and water insoluble part.

  Analysis of the water-soluble heteropolyacid contained in the water-eluting portion and the poorly water-soluble heteropolyacid salt contained in the water-insoluble portion is performed by oxidation / reduction measurement according to JIS K0102 (drainage test method).

A specific analysis method will be described below.
In the case of the water elution part, an appropriate amount (for example, 0.1 to 1 g) of the water elution part is accurately weighed and added to 100 ml of pure water to prepare an aqueous solution thereof. Next, 10 ml of sulfuric acid (1 volume of sulfuric acid + 2 volumes of water) is added. Further, 10 ml of a 5 mmol / L potassium permanganate solution is added thereto and heated in a boiling water bath for 30 minutes. Then 10 ml of a 12.5 mmol / L oxalic acid solution is added. Next, excess oxalic acid is titrated with a 5 mmol / L potassium permanganate solution (so-called back titration). The amount of the 5 mmol / L potassium permanganate solution required for the titration is Aml.

  On the other hand, in the case of a water-insoluble portion, an appropriate amount (for example, 0.1 to 1 g) of the water-insoluble portion is precisely weighed and dispersed in 100 ml of pure water to prepare a dispersion. Next, 10 ml of sulfuric acid (1 volume of sulfuric acid + 2 volumes of water) is added. Further, 10 ml of a 5 mmol / L potassium permanganate solution is added thereto and heated in a boiling water bath for 30 minutes. Next, after adding 10 ml of a 12.5 mmol / L oxalic acid solution, the solution was filtered with a 0.45 μm filter, washed with a small amount of pure water, combined with this washing solution, and then the filtrate was again added in a boiling water bath. Heat for minutes. Next, excess oxalic acid is titrated with a 5 mmol / L potassium permanganate solution (so-called back titration). The amount of the 5 mmol / L potassium permanganate solution required for the titration is Aml.

  Separately, 100 ml of pure water used in the above analysis is used as a test sample, and titration is performed in the same manner as in the case of the water elution part. The amount of 5 mmol / L potassium permanganate solution required for titration is defined as B (ml).

Then, the reduction degree α or β per molecule of the heteropolyacid of the water-soluble heteropolyacid or poorly water-soluble heteropolyacid salt in the present invention can be obtained by the following formula.
α (or β) = 5 × 10 ⁻⁶ (mol / ml) × (AB) × 5 × (Mw _H / Cw) (5)
(Wherein, Mw _H represents the molecular weight of the water-soluble heteropolyacid contained in the water-eluting part or the poorly water-soluble heteropolyacid salt contained in the water-insoluble part, and Cw represents the water-soluble heteropolyacid contained in the water-eluting part or (The mass (g) of the poorly water-soluble heteropolyacid salt contained in the water-insoluble part is shown.)

[Molecular weight of water-soluble heteropolyacid and poorly water-soluble heteropolyacid salt]
The molecular weight of the water-soluble heteropolyacid and the poorly water-soluble heteropolyacid salt was calculated from the structural formula.

[Catalyst composition analysis]
Quantitative analysis of the elements contained in the catalyst prepared in this example was performed by ICP emission spectrometry and atomic absorption spectrometry.

[Analysis of reaction products]
The quantitative analysis of the raw material gas methacrolein and products in the production of methacrylic acid by gas phase catalytic oxidation using the heteropolyacid catalyst prepared in this example was performed using gas chromatography. In addition, the reaction rate of methacrolein, the selectivity of the methacrylic acid to produce | generate, and a single flow yield are defined as follows.
Reaction rate of methacrolein (mol%) = (B / A) × 100
Methacrylic acid selectivity (mol%) = (C / B) × 100
Single flow yield of methacrylic acid (mol%) = (C / A) × 100
Here, A is the number of moles of methacrolein supplied, B is the number of moles of reacted methacrolein, and C is the number of moles of methacrylic acid produced.

[Example 1]
68 parts of molybdic oxide, 1 part of metavanadate and 7 parts of 85% phosphoric acid were dispersed in 200 parts of water, heated to reflux for 1 hour to prepare a slurry (liquid A). Separately, 14 parts of cesium nitrate was dissolved in 25 parts of water to prepare liquid B, which was added to the slurry (liquid A) to prepare liquid AB.

  Separately, 50 parts of molybdenum oxide and 1 part of metavanadate were dispersed in 200 parts of water, heated to reflux for 1 hour. After cooling this to room temperature, C part was prepared by adding 13 parts of 60% arsenic acid, 40 parts of 28% aqueous ammonia, 0.2 part of zirconium nitrate, 1 part of copper nitrate and 2 parts of iron nitrate. After the addition of arsenic acid, electroreduction treatment was performed for 1 hour under the condition of a direct current of 3 V in which two dry batteries were connected. An electrode in which a 0.1 mm platinum wire was knitted into a 1 cm square mesh with an opening of 0.1 mm and an electrode in which a 5 cm platinum wire with a diameter of 2 mm was coiled were used.

Thereafter, the C solution was added to the AB solution to prepare an ABC solution, which was then evaporated to dryness while stirring with heating to obtain a solid. The resulting solid was dried at 130 ° C. for 16 hours. This was press-molded at a temperature of 20 to 30 ° C. and a pressure of 20 MPa, and the obtained molded body was crushed at a temperature of 20 to 30 ° C. and about 1 MPa. The obtained crushed material was classified using a sieve, and a powder having a particle size of 0.85 to 1.70 mm was collected to obtain a catalyst precursor. This was calcined at 380 ° C. for 5 hours under air flow to obtain a catalyst. The metal component composition (composition excluding oxygen) of this catalyst was P ₁ As ₁ Mo ₁₂ V _0.3 Cu _0.1 Zr _0.02 Fe _0.1 Cs _1.3 .

  With respect to the obtained catalyst, the reduction degree α of the water-soluble heteropolyacid and the reduction degree β of the poorly water-soluble heteropolyacid salt and the contents of the water-soluble and poorly water-soluble heteropolyacid per molecule of the heteropolyacid were measured by the above method. The degree of reduction α per molecule of the water-soluble heteropolyacid of this catalyst was 0.383, and the degree of reduction β per molecule of the heteropolyacid of the poorly water-soluble heteropolyacid salt was 0.216. The contents of the water-soluble heteropolyacid and the poorly water-soluble heteropolyacid salt in this catalyst were 47% and 53%, respectively, with respect to the total mass of the catalyst.

  This catalyst is filled in a reaction tube, charged with a mixed gas of 5% by volume of methacrolein, 10% by volume of oxygen, 30% by volume of steam and 55% by volume of nitrogen, a reaction temperature of 270 ° C., a reaction pressure of 101 kPa, and a contact time of 3. The reaction was evaluated under the condition of 6 seconds to evaluate the performance of the catalyst. The methacrolein conversion was 68.0 mol%, the methacrylic acid selectivity was 88.9%, and the single flow yield of methacrylic acid was 60.3 mol%.

[Comparative Example 1]
118 parts of molybdenum oxide, 2 parts of metavanadate, and 7 parts of 85% phosphoric acid are dispersed in 200 parts of water, and while raising the temperature, 13 parts of 60% arsenic acid, 14 parts of cesium nitrate, 40 parts of 28% by weight ammonia water, nitric acid A catalyst was obtained in the same manner as in Example 1 except that 0.2 part of zirconium, 1 part of copper nitrate and 2 parts of iron nitrate were added, and heated and stirred to evaporate to dryness to obtain a solid. The catalyst was analyzed and the performance of the catalyst was evaluated. The metal component composition of this catalyst was P ₁ As ₁ Mo ₁₂ V _0.3 Cu _0.1 Zr _0.02 Fe _0.1 Cs _1.3 .

  The degree of reduction α per molecule of the heteropolyacid of the water-soluble heteropolyacid of this catalyst was 0.402, and the degree of reduction β per molecule of the heteropolyacid of the poorly water-soluble heteropolyacid salt was 0.182. Further, the contents of the water-soluble heteropolyacid and the poorly water-soluble heteropolyacid salt in this catalyst were 40% and 60%, respectively, with respect to the total mass of the catalyst.

  Moreover, the methacrolein conversion rate of this catalyst was 62.1 mol%, the methacrylic acid selectivity was 90.1 mol%, and the single stream yield of methacrylic acid was 56.0 mol%.

[Comparative Example 2]
Except that the catalyst precursor was calcined at 380 ° C. for 5 hours under a flow of nitrogen / air = 90/10, a catalyst was obtained in the same manner as in Comparative Example 1, the catalyst was analyzed, and the performance of the catalyst was evaluated. It was. The metal component composition of this catalyst was P ₁ As ₁ Mo ₁₂ V _0.3 Cu _0.1 Zr _0.02 Fe _0.1 Cs _1.3 .

  Further, the degree of reduction α per molecule of the heteropolyacid of the water-soluble heteropolyacid of this catalyst was 0.779, and the degree of reduction β per molecule of the heteropolyacid of the poorly water-soluble heteropolyacid salt was 0.302. The contents of the water-soluble heteropolyacid and the hardly water-soluble heteropolyacid salt in this catalyst were 45% and 55%, respectively, with respect to the total mass of the catalyst.

  Further, the methacrolein conversion rate of this catalyst was 51.2 mol%, the methacrylic acid selectivity was 91.0 mol%, and the single flow yield of methacrylic acid was 46.6%.

[Comparative Example 3]
Except that the catalyst precursor was calcined at 380 ° C. for 7 hours under a flow of nitrogen / air = 90/10, a catalyst was obtained in the same manner as in Comparative Example 1, the catalyst was analyzed, and the performance of the catalyst was evaluated. . The metal component composition of this catalyst was P ₁ As ₁ Mo ₁₂ V _0.3 Cu _0.1 Zr _0.02 Fe _0.1 Cs _1.3 .

  In addition, the degree of reduction α per molecule of the heteropolyacid of the water-soluble heteropolyacid of this catalyst was 0.742, and the degree of reduction β per molecule of the heteropolyacid of the poorly water-soluble heteropolyacid salt was 0.514. The contents of the water-soluble heteropolyacid and the hardly water-soluble heteropolyacid salt in this catalyst were 42% and 58%, respectively, with respect to the total mass of the catalyst.

  Further, the methacrolein conversion rate of this catalyst was 40.1 mol%, the selectivity of methacrylic acid was 91.2 mol%, and the single flow yield of methacrylic acid was 36.6 mol%.

[Comparative Example 4]
A solid was obtained in the same manner as in Comparative Example 1 except that 60% arsenic acid was not added, a catalyst was obtained, this catalyst was analyzed, and the performance of this catalyst was evaluated. The metal component composition other than oxygen of this catalyst was P ₁ Mo ₁₂ V _0.3 Cu _0.1 Zr _0.02 Fe _0.1 Cs _1.3 .

  In addition, the degree of reduction α per molecule of the heteropolyacid of the water-soluble heteropolyacid of this catalyst was 0.415, and the degree of reduction β per molecule of the heteropolyacid of the poorly water-soluble heteropolyacid salt was 0.199. Further, the contents of the water-soluble heteropolyacid and the poorly water-soluble heteropolyacid salt in this catalyst were 45% and 55% with respect to the total mass of the catalyst.

  Further, the methacrolein conversion rate of this catalyst was 57.4 mol%, the methacrylic acid selectivity was 87.5 mol%, and the single flow yield of methacrylic acid was 50.2 mol%.

Claims (4)

  A heteropolyacid catalyst for the production of methacrylic acid including a water-soluble heteropolyacid and a poorly water-soluble heteropolyacid salt, the degree of reduction being adjusted during slurry preparation, and the water-soluble heteropolyacid and the poorly water-soluble heteropolyacid of the finished catalyst A heteropolyacid catalyst for the production of methacrylic acid with a controlled degree of salt reduction. When the reduction degree per molecule of the heteropolyacid of the water-soluble heteropolyacid is α and the reduction degree per molecule of the heteropolyacid of the poorly water-soluble heteropolyacid salt is β, the reduction degrees α and β are represented by the following formula (1): The heteropolyacid catalyst according to claim 1, which satisfies the relationship represented by (3) to (3).
0 <α ≦ 1 (1)
0.01 <β ≦ 2 (2)
α−β ≦ 0.2 (3)   The water-soluble heteropolyacid content of the heteropolyacid catalyst is 10 to 60% by mass relative to the total mass of the heteropolyacid catalyst, and the water-insoluble heteropolyacid salt content is the total mass of the heteropolyacid catalyst. The heteropolyacid catalyst according to claim 1, wherein the amount is 90 to 40% by mass.   The reduction degree at the time of the said slurry preparation is adjusted by preparing the slurry containing the said water-soluble heteropoly acid and the slurry containing the said poorly water-soluble heteropoly acid salt individually, and mixing these. The heteropolyacid catalyst as described.