JP2012245433A - Method for producing catalyst for producing methacrylic acid method for producing methacrylic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst for producing methacrylic acid having high mechanical strength, excellent catalyst activity, and catalyst life.SOLUTION: The catalyst for producing methacrylic acid comprising a heteropolyacid compound including P and Mo has water content of 0.7 to 2.5 wt.%. The catalyst for producing methacrylic acid can be obtained by drying aqueous mixture containing the raw material of the catalyst shaping and firing the same and thereafter adjusting the water content of the fired substance to 0.7 to 2.5 wt.%.

Description

  The present invention relates to a catalyst for producing methacrylic acid and a method for producing the same, and further relates to a method for producing methacrylic acid using the catalyst.

  Conventionally, as a catalyst used when producing methacrylic acid by a gas phase catalytic oxidation reaction such as methacrolein, it is known that a heteropoly acid containing phosphorus and molybdenum or a salt thereof is effective (patent document) 1-6). For example, in Patent Document 1, a catalyst obtained by calcination is stored in a container having a predetermined moisture permeability, and the water content is 0% by weight, 0.08% by weight, 0.27% by weight, 0.52% by weight, It is disclosed that 3.24 wt% and 3.06 wt% catalysts for the production of methacrylic acid were obtained.

JP 2003-10695 A JP 2004-188231 A JP 2005-21727 A JP 2007-90193 A JP 2008-284508 A JP 2009-248035 A

  However, the conventional catalyst for producing methacrylic acid is not always satisfactory in terms of mechanical strength, catalyst activity and catalyst life.

  An object of the present invention is to provide a catalyst for producing methacrylic acid having high mechanical strength and excellent catalytic activity and catalyst life. Furthermore, another object of the present invention is to provide a method for producing this catalyst and a method for producing methacrylic acid stably over a long period of time by converting a raw material at a good conversion rate using this catalyst.

As a result of intensive studies to solve the above problems, the present inventor has found a solution means having the following configuration, and has completed the present invention.
(1) A catalyst for producing methacrylic acid, comprising a heteropolyacid compound containing phosphorus and molybdenum, wherein the water content is 0.7 to 2.5% by weight.
(2) The heteropolyacid compound further comprises:
Vanadium,
At least one selected from the group consisting of potassium, rubidium, cesium and thallium;
At least one selected from the group consisting of copper, arsenic, antimony, boron, silver, bismuth, iron, cobalt, lanthanum and cerium;
The catalyst for producing methacrylic acid according to (1), characterized by comprising:
(3) A method for producing a catalyst for producing methacrylic acid comprising a heteropolyacid compound containing phosphorus and molybdenum,
For drying methacrylic acid, characterized in that an aqueous mixture containing the catalyst raw material is dried, molded and fired, and then the moisture content of the fired product is adjusted to 0.7 to 2.5% by weight. A method for producing a catalyst.
(4) The heteropolyacid compound is further
Vanadium,
At least one selected from the group consisting of potassium, rubidium, cesium and thallium;
At least one selected from the group consisting of copper, arsenic, antimony, boron, silver, bismuth, iron, cobalt, lanthanum and cerium;
The method as described in (3) characterized by including.
(5) Gas phase contact with at least one compound selected from the group consisting of methacrolein, isobutyraldehyde, isobutane and isobutyric acid in the presence of the catalyst for producing methacrylic acid according to (1) or (2) A method for producing methacrylic acid, characterized by being subjected to an oxidation reaction.
(6) At least one selected from the group consisting of methacrolein, isobutyraldehyde, isobutane and isobutyric acid in the presence of the catalyst for producing methacrylic acid obtained by the production method according to (3) or (4) A method for producing methacrylic acid, comprising subjecting a compound to a gas phase catalytic oxidation reaction.

  According to the present invention, there is an effect that a catalyst for producing methacrylic acid having high mechanical strength and excellent catalyst activity and catalyst life can be obtained. Furthermore, when this catalyst is used, the raw material can be converted at a good conversion rate, and methacrylic acid can be produced stably over a long period of time.

(Catalyst for methacrylic acid production)
The catalyst for producing methacrylic acid of the present invention comprises a heteropolyacid compound containing phosphorus and molybdenum. Such a heteropolyacid compound may be composed of a free heteropolyacid or a salt of a heteropolyacid. Among these, what consists of acidic salt (partially neutralized salt) of heteropolyacid is preferable, and what consists of acidic salt of Keggin type heteropolyacid is more preferable.

As long as the heteropolyacid compound contains phosphorus and molybdenum as essential elements, it may contain other elements as long as the catalytic activity is not inhibited. Examples of other elements include vanadium, potassium, rubidium, cesium, thallium, copper, arsenic, antimony, boron, silver, bismuth, iron, cobalt, lanthanum, and cerium. For example, the heteropolyacid compound preferably contains the following elements.
Rin;
molybdenum;
vanadium;
At least one element selected from the group consisting of potassium, rubidium, cesium and thallium (hereinafter sometimes referred to as “element X”); and copper, arsenic, antimony, boron, silver, bismuth, iron, cobalt , At least one element selected from the group consisting of lanthanum and cerium (hereinafter sometimes referred to as “Y element”).

  In particular, the heteropolyacid compound preferably contains phosphorus, vanadium, an X element and a Y element at a ratio of 3 atoms or less to 12 atoms of molybdenum.

  The catalyst for producing methacrylic acid of the present invention has a water content of 0.7 to 2.5% by weight. When the moisture content satisfies such a range, the catalyst for producing methacrylic acid according to the present invention has high mechanical strength, excellent catalytic activity and catalyst life, and is obtained by converting the raw material at a good conversion rate. Methacrylic acid can be produced stably over a period of time. If the water content is less than 0.7% by weight, the mechanical strength of the catalyst is low, and it may not be usable under severe conditions. On the other hand, when the water content exceeds 2.5% by weight, the catalyst life is short, and the conversion rate may decrease in a short period. The water content is preferably 1.5 to 2.2% by weight.

(Method for producing catalyst for producing methacrylic acid)
As described above, the method for producing a catalyst for producing methacrylic acid according to the present invention (hereinafter sometimes referred to as “the production method of the present invention”) is for producing methacrylic acid comprising a heteropolyacid compound containing phosphorus and molybdenum. In the method for producing a catalyst, an aqueous mixture containing a catalyst raw material is dried, molded and calcined, and then the moisture content of the obtained calcined product is adjusted to 0.7 to 2.5% by weight.

  Examples of the compound used as a raw material for the catalyst include oxo acids, oxo acid salts, oxides, nitrates, carbonates, bicarbonates, hydroxides, halides and the like of each element. For example, phosphoric acid, a phosphate, etc. are mentioned as a compound containing phosphorus. Examples of the compound containing molybdenum include molybdic acid, molybdate, molybdenum oxide, and molybdenum chloride. Examples of the compound containing vanadium include vanadic acid, vanadate, vanadium oxide, and vanadium chloride. Examples of the compound containing X element include oxides, nitrates, carbonates, bicarbonates, hydroxides, halides, and the like. Examples of the compound containing the Y element include oxo acids, oxo acid salts, nitrates, carbonates, hydroxides, halides, and the like.

These compounds are mixed with water in a desired ratio (preferably, phosphorus, vanadium, X element and Y element are each in a ratio of 3 atoms or less with respect to 12 atoms of the above molybdenum) Or an aqueous mixture such as a suspension. That is, the heteropolyacid compound preferably contains the following elements.
Rin;
molybdenum;
vanadium;
At least one element selected from the group consisting of potassium, rubidium, cesium and thallium (element X); and selected from the group consisting of copper, arsenic, antimony, boron, silver, bismuth, iron, cobalt, lanthanum and cerium At least one element (Y element).

  This aqueous mixture is dried by spray drying using a spray dryer or the like. After drying, the dried product is usually formed into a desired shape (for example, a columnar shape, a spherical shape, a ring shape, etc.), and a molding aid may be used as necessary at the time of molding. The obtained molded body is preferably subjected to heat treatment (pre-baking) at a temperature of about 180 to 300 ° C. in an oxidizing gas or non-oxidizing gas atmosphere. In addition, you may shape | mold after heat-processing (pre-baking) to a dried material.

  In preparing the aqueous mixture, it is preferable to further add ammonia or an ammonium salt to obtain an aqueous mixture containing an ammonium root. Instead of adding ammonia or an ammonium salt, an ammonium compound may be used for at least one of the above compounds containing phosphorus, molybdenum, vanadium, X element or Y element. In the case of such a prescription, a dry product composed of a non-Keggin type heteropolyacid salt is obtained, and by performing a heat treatment (pre-baking), a transition reaction from the non-Keggin type to the Keggin type occurs. Can be obtained.

  Next, the obtained molded body is fired. Firing is not particularly limited, and oxidizing gas (air, oxygen, etc.), non-oxidizing gas (inert gas (nitrogen, argon, helium, neon, etc.), reducing gas (carbon dioxide, hydrogen, ammonia, etc.), etc. ) And so on. Among these, it is preferably performed in an atmosphere of nitrogen, air, argon, helium or carbon dioxide, and more preferably in an atmosphere of nitrogen or air. These gases may be used alone or in combination of two or more.

  Firing is preferably performed at 360 to 500 ° C., more preferably 380 to 450 ° C., preferably 1 to 20 hours, more preferably 1 to 10 hours. Further, the firing may be performed in multiple stages at different temperatures. As a multi-stage firing method, for example, after firing (first firing) in a non-oxidizing gas atmosphere at 420 to 500 ° C. for 1 to 10 hours, 1 in an oxidizing gas atmosphere at 360 to 410 ° C. After firing for 10 to 10 hours (second firing) or after firing for 1 to 10 hours in a non-oxidizing gas or oxidizing gas atmosphere at 360 to 410 ° C. (first firing), 420 to 500 ° C. And a method of firing (second firing) in a non-oxidizing gas atmosphere for 1 to 10 hours.

A catalyst for methacrylic acid production is obtained by adjusting the water content of the fired product thus obtained to 0.7 to 2.5% by weight, preferably 1.5 to 2.2% by weight. The method for adjusting the moisture content is not particularly limited, and examples thereof include the following methods.
(I) It exposes to the atmosphere containing a water | moisture content and makes it moisture-absorb so that a moisture content may be 0.7 to 2.5 weight%.
(II) When the moisture content of the fired product exceeds 2.5% by weight, the fired product is dried.

  In the case of the above (I), the temperature and humidity are not particularly limited as long as the moisture content can be adjusted. Just do it. Moreover, in the case of said (II), what is necessary is just to dry so that a moisture content may be set to 0.7 to 2.5 weight% by arbitrary drying methods, such as air drying, hot air drying, and vacuum drying.

(Method for producing methacrylic acid)
The catalyst for producing methacrylic acid of the present invention has high mechanical strength and has excellent catalytic activity and catalyst life. Using this methacrylic acid production catalyst, for example, by subjecting raw material compounds such as methacrolein, isobutyraldehyde, isobutane, and isobutyric acid to a gas phase catalytic oxidation reaction, the raw material compounds are converted at a good conversion rate, Methacrylic acid can be produced stably over a long period of time.

  The production of methacrylic acid is usually carried out by filling a fixed bed multitubular reactor with a catalyst and supplying a raw material compound and a gas containing oxygen to the reactor. Moreover, the form of a fluidized bed or a moving bed can be adopted instead of the fixed bed. As the gas containing oxygen, air or pure oxygen is generally used. In addition to the gas containing oxygen and the raw material compound, nitrogen, carbon dioxide, carbon monoxide, water vapor, or the like may be supplied to the reactor. Since the catalyst for producing methacrylic acid of the present invention has high mechanical strength, it is possible to suppress the generation of dust due to pulverization or destruction of the catalyst at the time of filling into a fixed bed multi-tubular reactor, and to reduce the number of fixed beds. It is possible to stably produce methacrylic acid by suppressing variations in pressure loss of each reaction tube in the tubular reactor.

When using methacrolein as a raw material compound, the reaction is preferably carried out under the following conditions. The space velocity is obtained by dividing the supply amount (L / h) of raw materials (raw material compounds and other gases) per hour passing through the reactor by the catalyst capacity (L) in the reactor.
Concentration of methacrolein in the raw material: 1 to 10% by volume
Concentration of water vapor in raw material: 1-30% by volume
Molar ratio of methacrolein to oxygen: 1/1 to 1/5 (methacrolein / oxygen)
Space velocity: 500-5000h ^-1 (standard condition standard)
Reaction temperature: 250-350 ° C
Reaction pressure: 0.1-0.3 MPa

When isobutane is used as a starting compound, the reaction is preferably carried out under the following conditions.
Concentration of isobutane in the raw material: 1 to 85% by volume
Concentration of water vapor in raw material: 3 to 30% by volume
Molar ratio of isobutane to oxygen: 1 / 0.05 to 1/4 (isobutane / oxygen)
Space velocity: 400-5000h ^-1 (standard condition standard)
Reaction temperature: 250-400 ° C
Reaction pressure: 0.1-1 MPa

  When isobutyraldehyde and isobutyric acid are used as raw material compounds, the reaction is carried out under substantially the same conditions as when methacrolein is used as the raw material compound. Moreover, these raw material compounds do not need to be purified high-purity products. For example, in the case of methacrolein, methacrolein obtained by a gas phase catalytic oxidation reaction of isobutylene or t-butyl alcohol may be used without purification.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated concretely, this invention is not limited to these Examples. The air used contains 2% by volume of moisture (corresponding to the atmosphere), and nitrogen does not substantially contain moisture.

(Preparation Example 1: Preparation of catalyst precursor)
First, the following raw materials were mixed to prepare liquid A and liquid B.
<Liquid A (solution)>
Ion-exchanged water (40 ° C): 224kg
Cesium nitrate (CsNO ₃ ): 38.2 kg
Orthophosphoric acid (75% by weight product): 27.4 kg
Nitric acid (70% by weight product): 25.2kg
<Liquid B (suspension)>
Ion exchange water (40 ° C): 330 kg
Ammonium molybdate tetrahydrate ((NH ₄ ) ₆ Mo ₇ O ₂₄ · 4H ₂ O): 297 kg
Ammonium metavanadate (NH ₄ VO ₃ ): 8.19 kg

Subsequently, A liquid was dripped at B liquid, stirring. After dropping, the mixture was stirred in a sealed container at 120 ° C. for 5.8 hours. Then, 10.2 kg of antimony trioxide (Sb ₂ O ₃ ) and 10.2 kg of copper nitrate trihydrate (Cu (NO ₃ ) ₂ .3H ₂ O) were suspended in 23 kg of ion-exchanged water and It added in the airtight container and stirred at 120 degreeC for further 5 hours.

The obtained slurry was spray-dried with a spray dryer, and 4 parts by weight of ceramic fiber (SiO ₂ —Al ₂ O ₃ fiber, diameter _{2 to} 4 μm, fiber average length 400 μm with respect to 100 parts by weight of the obtained dried product. ), 13 parts by weight of ammonium nitrate, and 9.7 parts by weight of ion-exchanged water were added and kneaded and extruded into a cylindrical shape (diameter 5 mm, height 6 mm). Next, the obtained molded body was dried for 3 hours in an atmosphere of a temperature of 90 ° C. and a humidity of 30% RH. The obtained dried product was heat-treated (pre-calcined) for 22 hours in an air stream at 220 ° C. and then for 1 hour at 250 ° C. to obtain a pre-calcined catalyst precursor comprising a Keggin heteropolyacid salt.

(Comparative Example 1)
The catalyst precursor obtained in Preparation Example 1 was held at 435 ° C. for 3 hours in a nitrogen stream. Subsequently, after cooling to 300 degreeC in nitrogen stream, nitrogen was switched to air and it hold | maintained at 390 degreeC in the air stream for 3 hours. Next, the fired product was cooled to 70 ° C. in an air stream and taken out into the atmosphere. The obtained calcined product (catalyst) contains phosphorus (1.5), molybdenum (12), vanadium (0.5), antimony (0.5), copper (0.3) and cesium (1.4). It was an acid salt of the containing Keggin type heteropolyacid. The numbers in parentheses are atomic ratios.

(Examples 1-3 and Comparative Examples 2-6)
The fired product obtained in Comparative Example 1 was placed in a room (temperature 20 ° C., humidity 40% RH) to absorb moisture, and catalysts with different moisture contents were prepared by changing the moisture absorption time.

  With respect to the catalysts having different moisture contents obtained in the respective Examples and Comparative Examples, the moisture content, the drop strength, and the methacrolein conversion rate after forced deterioration were measured. The results are shown in Table 1.

(Moisture content measurement)
About 10 g of the catalyst was precisely weighed, and the accurately weighed catalyst was placed in an oven and held at 300 ° C. for 1 hour. Subsequently, after cooling to 100 degreeC, it moved in the dry box, cooled to room temperature, and weighed the catalyst precisely. The moisture content of the catalyst was determined from the mass before heating and the mass after heating.
Moisture content (%) = 100 − {(mass after heating / mass before heating) × 100}

(Drop strength measurement)
About 30 g of the catalyst was precisely weighed, and the catalyst was put into the pipe from the upper part of a SUS straight pipe (inner diameter 30 mmφ, pipe length 5.0 m) installed vertically. The catalyst was received by a JIS standard mesh screen (aperture 2.36 mm) provided at the bottom (exit) of the tube, and the catalyst remaining on the screen was precisely weighed. The ratio of the amount of catalyst remaining on the sieve to the amount of catalyst charged in the pipe ((mass on sieve / input mass) × 100) was measured, and the average value measured three times was taken as the drop strength. It can be seen that the higher the ratio, the more the catalyst remains on the screen without being crushed, and the strength of the catalyst is higher.

(Conversion rate of methacrolein after forced deterioration)
9 g of the obtained catalyst was weighed and filled into a glass microreactor having an inner diameter of 16 mm, and the furnace temperature (furnace temperature for heating the microreactor) was raised to 355 ° C. Subsequently, a raw material gas (4% by volume of methacrolein, 12% by volume of molecular oxygen, 17% by volume of water vapor, 67% by volume of nitrogen) prepared by mixing methacrolein, air, water vapor, and nitrogen was converted into a space velocity of 670 h ⁻¹ . The mixture was fed into the microreactor and reacted for 1 hour to forcibly deteriorate the catalyst. Next, the furnace temperature was set to 280 ° C., and the raw material gas was supplied to the deteriorated catalyst at the space velocity (670 h ⁻¹ ) to start the reaction. One hour after the start of the reaction, the outflow gas (gas after reaction) from the microreactor outlet was sampled and analyzed by gas chromatography, and methacrolein conversion was determined based on the following formula.
Conversion rate of methacrolein (%) = (A / B) × 100
here,
A is the number of moles of reacted methacrolein.
B is the number of moles of methacrolein supplied.

  As shown in Table 1, it can be seen that the catalysts obtained in Examples 1 to 3 have a high drop strength and a high methacrolein conversion rate after forced deterioration. On the other hand, it can be seen that the catalysts obtained in Comparative Examples 1 to 5 have a low drop strength, although the methacrolein conversion after forced deterioration is high. Moreover, although the catalyst obtained in Comparative Example 6 has a high drop strength, it can be seen that the methacrolein conversion after forced deterioration is low.

Claims (6)

  A catalyst for producing methacrylic acid comprising a heteropolyacid compound containing phosphorus and molybdenum, wherein the water content is 0.7 to 2.5% by weight. The heteropolyacid compound is further
Vanadium,
At least one selected from the group consisting of potassium, rubidium, cesium and thallium;
At least one selected from the group consisting of copper, arsenic, antimony, boron, silver, bismuth, iron, cobalt, lanthanum and cerium;
The catalyst for producing methacrylic acid according to claim 1, wherein A method for producing a methacrylic acid production catalyst comprising a heteropolyacid compound containing phosphorus and molybdenum,
For drying methacrylic acid, characterized in that an aqueous mixture containing the catalyst raw material is dried, molded and fired, and then the moisture content of the fired product is adjusted to 0.7 to 2.5% by weight. A method for producing a catalyst. The heteropolyacid compound is further
Vanadium,
At least one selected from the group consisting of potassium, rubidium, cesium and thallium;
At least one selected from the group consisting of copper, arsenic, antimony, boron, silver, bismuth, iron, cobalt, lanthanum and cerium;
The method of claim 3, comprising:   Subjecting at least one compound selected from the group consisting of methacrolein, isobutyraldehyde, isobutane and isobutyric acid to a gas phase catalytic oxidation reaction in the presence of the catalyst for producing methacrylic acid according to claim 1 or 2; A process for producing methacrylic acid, characterized in that   In the presence of the catalyst for producing methacrylic acid obtained by the production method according to claim 3 or 4, at least one compound selected from the group consisting of methacrolein, isobutyraldehyde, isobutane and isobutyric acid is used in the gas phase. A method for producing methacrylic acid, which is subjected to a catalytic oxidation reaction.