JP2010259961A - Catalyst and method for producing methacrylic acid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst having an excellent effect of suppressing a hot spot, as the catalyst for producing methacrylic acid, which is used for producing methacrylic acid by subjecting methacrolein to vapor-phase catalytic oxidation using molecular oxygen. <P>SOLUTION: The catalyst for producing methacrylic acid is used for producing methacrylic acid by subjecting methacrolein to vapor-phase catalytic oxidation using molecular oxygen and contains at least molybdenum and phosphorus, wherein a fibrous material having thermal conductivity of ≥300 W/(m×K) is contained. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a catalyst used for producing methacrylic acid by vapor-phase catalytic oxidation of methacrolein with molecular oxygen (hereinafter referred to as a catalyst for producing methacrylic acid) and a method for producing methacrylic acid using the catalyst. .

  Numerous proposals have been made regarding a catalyst used in producing methacrylic acid by gas phase catalytic oxidation reaction of methacrolein (hereinafter, this gas phase catalytic oxidation reaction is simply referred to as “oxidation reaction” unless otherwise specified). ). These proposals mainly relate to the elements constituting the catalyst and their proportions.

  Since the oxidation reaction is an exothermic reaction, heat storage occurs in the catalyst layer. The local abnormally high temperature zone resulting from excessive heat storage is called a hot spot, and in this part, the yield decreases due to excessive oxidation reaction. For this reason, in the industrial implementation of the oxidation reaction, the occurrence of hot spots is a serious problem. In particular, when the concentration of methacrolein in the raw material gas is increased in order to increase productivity, hot spots tend to be easily generated. As a result, there are currently great constraints on the reaction conditions.

  Therefore, it is very important to suppress the temperature of the hot spot part in industrially producing methacrylic acid with a high yield. In particular, when a molybdenum-containing solid oxidation catalyst is used, it is important to prevent the occurrence of hot spots because the molybdenum component tends to sublime.

  As a method for suppressing the temperature of the hot spot part, several proposals have been made so far. For example, in Patent Document 1, a plurality of catalysts having different activities are packed so that the activity becomes higher from the raw material gas inlet side to the outlet side, and the raw material gas containing methacrolein and oxygen is circulated through this catalyst layer. A method is disclosed.

  In Patent Document 2, there is no place in the catalyst layer where the difference between the temperature of the heat medium bath and the temperature of the catalyst layer (ΔT = temperature of the catalyst layer−temperature of the heat medium bath) exceeds 35 ° C., and ΔT Has disclosed a method for producing methacrylic acid, characterized by providing two or more high-temperature zones at a temperature of 15 to 35 ° C.

  Patent Document 3 discloses that carbon fibers having an average diameter of 1 to 20 μm, an average length of 10 to 3000 μm, and a carbon content of 93% or more are 0.05% relative to the catalyst for the purpose of improving the strength of the catalyst molded body. A catalyst for the synthesis of unsaturated carboxylic acids by gas phase catalytic oxidation of unsaturated aldehydes, characterized in that it is present in an amount of -10% by weight, is disclosed.

JP-A-4-210937 International Publication No. 2001/042184 Pamphlet Japanese Patent Application Laid-Open No. 7-251075

  However, the catalysts obtained by these known methods are not necessarily sufficient for suppressing hot spots as industrial catalysts, and further improvements are desired.

  The present invention has been made in view of the above circumstances, and in a catalyst for producing methacrylic acid used for producing methacrylic acid by vapor-phase catalytic oxidation of methacrolein with molecular oxygen, the effect of suppressing hot spots is excellent. It is an object of the present invention to provide a catalyst.

  The present invention relates to a catalyst for producing methacrylic acid containing at least molybdenum and phosphorus, which is used for producing methacrylic acid by vapor phase catalytic oxidation of methacrolein with molecular oxygen, and has a thermal conductivity of 300 W / (m · K). ) A catalyst for producing methacrylic acid, which contains the above fibrous material.

  ADVANTAGE OF THE INVENTION According to this invention, the catalyst excellent in the suppression effect of a hot spot can be provided in the catalyst for methacrylic acid manufacture used when vapor-phase catalytic oxidation of methacrolein with molecular oxygen is manufactured.

  The catalyst of the present invention is a catalyst for producing methacrylic acid containing at least molybdenum and phosphorus, which is used for producing methacrylic acid by vapor-phase catalytic oxidation of methacrolein with molecular oxygen, and has a thermal conductivity of 300 W / (m K) A catalyst for producing methacrylic acid by gas-phase catalytic oxidation of methacrolein, which contains the above fibrous material.

  In the present invention, the fibrous material having a thermal conductivity of 300 W / (m · K) or more is contained in the catalyst and, when present, functions to suppress the temperature of the hot spot portion.

  In the present invention, the fibrous material having a thermal conductivity of 300 W / (m · K) or more is not particularly limited, and examples thereof include carbon fibers and metal fibers such as copper and silver.

  In order to effectively suppress the temperature of the hot spot portion, the content of the fibrous material having a thermal conductivity of 300 W / (m · K) or more is preferably 0.5 to 30% by mass, more preferably 1 to 20% by mass. The more the amount of the fibrous material having a thermal conductivity of 300 W / (m · K) or more, the more the effect of suppressing the temperature of the hot spot portion tends to be improved, and the smaller the amount, the more the catalyst component that can be charged in the reactor is increased. Can do.

  In the present invention, the fibrous material having a thermal conductivity of 300 W / (m · K) or more preferably has an average diameter of 1 to 20 μm and an average length of 10 to 3000 μm, an average diameter of 3 to 15 μm, and an average length of 100 to 1000 μm. Is more preferable.

  The composition of the catalyst component constituting the catalyst of the present invention can be appropriately selected according to the target catalyst for producing methacrylic acid. The catalyst for producing methacrylic acid, which is an object of the present invention, is not particularly limited as long as it contains molybdenum and phosphorus as catalyst components, but preferably has a composition represented by the following formula (1). .

_{P a Mo b V c Cu d} X e Y f Z g O h (1)
(In the formula (1), P, Mo, V, Cu and O represent phosphorus, molybdenum, vanadium, copper and oxygen, respectively, and X is at least one selected from the group consisting of arsenic, antimony and tellurium. Y represents an element, Y is selected from the group consisting of bismuth, germanium, zirconium, silver, selenium, silicon, tungsten, boron, iron, zinc, chromium, magnesium, tantalum, cobalt, manganese, barium, gallium, cerium and lanthanum Z represents at least one element selected from the group consisting of potassium, rubidium and cesium, a, b, c, d, e, f, g and h are each element. And when b = 12, a = 0.1-3, c = 0.01-3, d = 0.01-2, e = 0-3, f = To 3, a g = 0.01 to 3, h is an atomic ratio of oxygen required to satisfy the valence of each element.)
The catalyst raw material used for the preparation of the catalyst is not particularly limited, and nitrates, carbonates, acetates, ammonium salts, oxides, halides, oxoacids, oxoacid salts, etc. of the respective constituent elements of the catalyst may be used in combination. it can. Examples of the molybdenum raw material include molybdenum oxides such as molybdenum trioxide; and ammonium molybdates such as ammonium paramolybdate and ammonium dimolybdate. Examples of the phosphorus source compound include phosphoric acid, phosphorus pentoxide, and ammonium phosphate. Examples of the vanadium raw material compound include ammonium metavanadate, vanadium pentoxide, and vanadyl oxalate. The raw material compound of the catalyst component may be used alone or in combination of two or more for each element constituting the catalyst component.

  The method for preparing the catalyst of the present invention is not particularly limited, and various methods such as a coprecipitation method, an evaporation to dryness method, and an oxide mixing method, which are well known in the art, are used as long as there is no significant uneven distribution of components. Can be used. For example, a nitrate solution, carbonate, acetate, ammonium salt, oxide, halide or the like of each element is dissolved or dispersed in water to prepare a raw material solution or slurry.

  Next, the mixed solution or slurry obtained above is dried. The method of drying is not particularly limited, and for example, a method of drying using a spray dryer, a method of drying using a slurry dryer, a method of drying using a drum dryer, a method of evaporating to dryness, etc. can be applied. In these, since a particle | grain is obtained simultaneously with drying and the shape of the particle | grains obtained is in order, it is preferable to use a spray dryer.

  Next, the obtained dried product is molded. The molding method is not particularly limited, and examples thereof include known methods such as extrusion molding, tableting molding, support molding, and rolling granulation. The shape of the molded body is not particularly limited, and can be formed into an arbitrary shape such as a ring shape, a columnar shape, a star shape, a spherical shape, and the like.

  In the case of molding by extrusion molding, water and / or alcohol is added to the dried product and kneaded, followed by extrusion molding. In kneading, in addition to water and / or alcohol, an organic binder such as gelatin, cellulose, methyl cellulose, ethyl cellulose, hydroxypropyl cellulose or the like can be added.

  Next, the molded body is dried as necessary, and then heat-treated. There are no particular limitations on the drying conditions and heat treatment conditions at this time, and known processing conditions can be applied. Usually, drying is performed at a temperature of 60 to 150 ° C. for 1 to 24 hours, and heat treatment can be performed at a temperature of 200 to 500 ° C., preferably 300 to 450 ° C. for 1 to 24 hours. Note that heat treatment may be performed without drying.

  In order to obtain the catalyst of the present invention, a step in the process of incorporating a fibrous material having a thermal conductivity of 300 W / (m · K) or more into the catalyst may be any time before the catalyst molding, and is particularly limited. It is not a thing. For example, after adding and mixing a fibrous material having a thermal conductivity of 300 W / (m · K) or more into a mixed solution containing a catalyst component, a method of forming the resulting dry particles, and drying the mixed solution containing the catalyst component After that, a method of molding using a product obtained by adding and mixing a fibrous material having a thermal conductivity of 300 W / (m · K) or more to the obtained dried product can be mentioned.

  Next, the manufacturing method of methacrylic acid of this invention is demonstrated. The method for producing methacrylic acid of the present invention is a method for producing methacrylic acid by vapor-phase catalytic oxidation of methacrolein with molecular oxygen in the presence of the methacrylic acid production catalyst obtained as described above.

  The gas phase catalytic oxidation reaction is usually performed in a fixed bed. The catalyst layer is not particularly limited, and may be an undiluted layer containing only a catalyst, a diluted layer containing an inert carrier, or a single layer or a mixed layer composed of a plurality of layers.

  In the reaction, it is preferable to use a source gas containing methacrolein and molecular oxygen.

  The concentration of methacrolein in the raw material gas can be varied within a wide range, but is preferably 1% by volume or more, and more preferably 3% by volume or more. Moreover, 20 volume% or less is preferable and 10 volume% or less is more preferable.

  The molecular oxygen concentration in the raw material gas is preferably 0.4 mol or more, more preferably 0.5 mol or more with respect to 1 mol of methacrolein. Moreover, 4 mol or less is preferable with respect to 1 mol of methacrolein, and 3 mol or less is more preferable. Although it is economical to use air as the molecular oxygen source, air or the like enriched with pure oxygen can also be used if necessary.

  The source gas preferably contains water (water vapor) in addition to methacrolein and molecular oxygen. By performing the reaction in the presence of water, methacrylic acid can be obtained in a higher yield. The concentration of water vapor in the raw material gas is preferably 0.1% by volume or more, and more preferably 1% by volume or more. Moreover, 50 volume% or less is preferable and 40 volume% or less is more preferable. The source gas may contain a small amount of impurities such as a lower saturated aldehyde, but the amount is preferably as small as possible. Moreover, inert gas, such as nitrogen and a carbon dioxide gas, may be included.

  The reaction pressure of the gas phase catalytic oxidation reaction is preferably from normal pressure (atmospheric pressure) to 5 atm. The reaction temperature is preferably 230 ° C. or higher, more preferably 250 ° C. or higher. Moreover, 450 degrees C or less is preferable and 400 degrees C or less is more preferable.

  The flow rate of the raw material gas is not particularly limited, and can be appropriately set so as to have an appropriate contact time. The contact time is preferably 1.5 seconds or longer, and more preferably 2 seconds or longer. Moreover, 15 seconds or less are preferable and 10 seconds or less are more preferable.

EXAMPLES Hereinafter, although this invention is demonstrated concretely using an Example and a comparative example, this invention is not limited to these Examples. The “parts” in the following examples and comparative examples are parts by mass.
Each value in this example was determined according to the following method.
(1) The analysis of the raw material gas and the product 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 (%) = (B / A) × 100
Methacrylic acid selectivity (%) = (C / B) × 100
Methacrylic acid yield (%) = (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.
(2) ΔTmax was defined and measured as follows.
The temperature in the catalyst layer was measured by a thermocouple inserted in a protective tube installed at the center of the cross section perpendicular to the tube axis direction of the reaction tube. The inside of the protective tube is isolated from the reaction system (catalyst layer side), and the measurement position can be changed by adjusting the length of the thermocouple to be inserted.
A hot spot was detected by measuring a difference ΔT (temperature of the catalyst layer−temperature of the heat medium bath) between the temperature in the catalyst layer measured at this time and the temperature of the heat medium bath.
Of the ΔT distribution detected at this time, the local abnormally high temperature zone was called a hot spot, and the highest temperature ΔT was shown as ΔTmax.
(3) The thermal conductivity of the carbon fiber was determined from the following formula (1) representing the relationship between the thermal conductivity and electrical resistivity disclosed in JP-A-11-117143.
K = 1272.4 / ER-49.4 (1)
Here, K represents the thermal conductivity W / (m · K) of the carbon fiber, and ER represents the electrical specific resistance μΩm of the carbon fiber.
(4) The average diameter and average length of the carbon fibers were determined from average values obtained by observing and measuring 100 randomly extracted samples with an electron microscope.

Example 1
In 400 parts of pure water, 100 parts of molybdenum trioxide, 3.4 parts of ammonium metavanadate, 8.0 parts of 85 mass% phosphoric acid aqueous solution and 1.1 parts of copper nitrate were dissolved, and the temperature was raised to 95 ° C. while stirring. The mixture was warmed and stirred for 3 hours while maintaining the liquid temperature at 95 ° C. After cooling to 40 ° C., a solution obtained by dissolving 13.5 parts of cesium bicarbonate in 20 parts of pure water was added and stirred for 15 minutes while stirring using a rotary blade stirrer. Next, a solution obtained by dissolving 11.6 parts of ammonium nitrate in 20 parts of pure water was added and further stirred for 20 minutes.

  The mixed slurry containing the raw material compound of the catalyst component obtained as described above was dried under the conditions of a dryer inlet temperature of 300 ° C. and a slurry spraying rotating disk at 18,000 rpm using a co-current spray dryer. . When the particle size of the obtained dry particles was measured by a laser type particle size distribution measuring device, it was in the range of 5 to 150 μm, and the average particle size was 30 μm.

  To 100 parts of the obtained dry particles, 5 parts of pitch-based carbon fiber having a thermal conductivity of 500 W / (m · K), an average diameter of 8 μm and an average length of 200 μm and 3 parts of hydroxypropylmethylcellulose were added and dry-mixed. 50 parts of ethyl alcohol was added and mixed here, mixed (kneaded) with a kneader until it became a clay, and then molded using a piston-type extrusion molding machine, and was formed into a cylindrical shape having an outer diameter of 5 mm and an average length of 5 mm. A molded body of was obtained.

  This molded body was dried at 60 ° C. for 16 hours, and then heat-treated at 380 ° C. for 15 hours under air flow to obtain a catalyst. The elemental composition other than oxygen (hereinafter the same) of the obtained catalyst was as follows.

Mo ₁₂ V _0.5 P _1.3 Cu _0.08 Cs _1.2
When the inside of the catalyst after the heat treatment was observed with a scanning microscope, the presence of the added carbon fiber was confirmed. The carbon fiber content in the catalyst was 5% by mass.

This catalyst is filled in a reaction tube, and methacrolein 5% by volume, oxygen 10% by volume, water vapor 10% by volume, nitrogen 75% by volume is passed through a reaction temperature of 290 ° C. and a contact time of 3.5 seconds. Rain-phase catalytic oxidation reaction was performed. The product was collected and analyzed by gas chromatography to determine methacrolein reaction rate, methacrylic acid selectivity, and methacrylic acid yield. In addition, ΔTmax of the hot spot during the reaction was measured. The results are shown in Table 1.
(Example 2)
In Example 1, a catalyst was produced in the same manner as in Example 1 except that the amount of pitch-based carbon fiber mixed with the dry particles was changed to 0.5 part with respect to 100 parts of dry particles. A phase catalytic oxidation reaction was performed. The results are shown in Table 1.
(Example 3)
In Example 1, except that the amount of pitch-based carbon fiber mixed with dry particles was changed to 20 parts with respect to 100 parts of dry particles, a catalyst was produced in the same manner as in Example 1, and vapor phase contact of methacrolein An oxidation reaction was performed. The results are shown in Table 1.
Example 4
In Example 1, the catalyst was produced in the same manner as in Example 1 except that the timing of mixing the pitch-based carbon fibers was changed from mixing to the catalyst dry particles before kneading to mixing to the slurry before spray drying. The gas phase catalytic oxidation reaction of methacrolein was performed. The results are shown in Table 1.

(Comparative Example 1)
In Example 1, a catalyst was produced in the same manner as in Example 1 except that the pitch-based carbon fibers were not mixed with the dry particles, and a gas phase catalytic oxidation reaction of methacrolein was performed. The results are shown in Table 1.

(Comparative Example 2)
In Example 1, the pitch-based carbon fiber mixed with the dry particles was changed to pitch-based carbon fiber having a thermal conductivity of 100 W / (m · K), an average diameter of 8 μm, and an average length of 200 μm. Thus, a catalyst was produced, and a gas phase catalytic oxidation reaction of methacrolein was performed. The results are shown in Table 1.

(Comparative Example 3)
In Example 1, the pitch-based carbon fiber mixed with the dry particles was changed to PAN-based carbon fiber having a thermal conductivity of 10 W / (m · K), an average diameter of 8 μm, and an average length of 200 μm. Thus, a catalyst was produced, and a gas phase catalytic oxidation reaction of methacrolein was performed. The results are shown in Table 1.

Claims (3)

In a catalyst for producing methacrylic acid containing at least molybdenum and phosphorus, used when producing methacrylic acid by vapor phase catalytic oxidation of methacrolein with molecular oxygen,
A catalyst for producing methacrylic acid, comprising a fibrous material having a thermal conductivity of 300 W / (m · K) or more.   2. The catalyst for producing methacrylic acid according to claim 1, wherein the fibrous material having a thermal conductivity of 300 W / (m · K) or more has an average diameter of 1 to 20 μm and an average length of 10 to 3000 μm.   A method for producing methacrylic acid, comprising subjecting methacrolein to gas phase catalytic oxidation with molecular oxygen in the presence of the catalyst for producing methacrylic acid according to claim 1 or 2.