JPH0924277A - Catalyst and process for preparing methacrylic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a heteropolymerization catalyst of a specified composition used for the preparation of methacrylic acid by gas phase contact oxidization by mixing a catalyst raw material into water, dissolving or suspending, heating in the state of presence of ammonium in a mixed liquid, concentrating and drying a suspension, burning the suspension in an inactive gas. SOLUTION: The heat treatment is carried out at the temperature of 80-200 deg.C for 1-24 hours in the state of the presence of ammonium in a liquid mixed with an ammonium salt and the like, and a suspension is concentrated, dried and solidified, and a dry solidified material is burnt in an inactive gas up to 400-500 deg.C to prepare a catalyst for preparing methacrylic acid. The catalyst is a partially neutralized salt of a heteropoly-acid represented by the formula. In the formula, X represents at least one kind of element selected from the group consisting of rubidium, cesium and thallium. The letters of (a), (b), (c), (d), (e), (f) and (g) represent the atomic ratio of respective elements and when b=12 is set, (a), (b), (c), (d), (e) and (f) represent the values of less than 3 not including 0 respectively, while (g) represents the value by the valences and atomic ratios of other elements.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an improvement in a heteropolyacid catalyst used for the production of methacrylic acid by vapor phase catalytic oxidation. Specifically, it relates to improvement of a heteropolyacid catalyst used for producing methacrylic acid by vapor-phase catalytic oxidation of methacrolein, isobutane and the like with molecular oxygen.

[0002]

2. Description of the Related Art Many catalysts have been proposed for producing methacrylic acid by vapor-phase catalytic oxidation of methacrolein (for example, JP-A-50-101316 and JP-A-5-101316).
7-177347, JP-A-4-63139, JP-A-5-31368, and JP-A-5-3136.
No. 8, JP-A-6-91172, etc.), a part of which is already used for industrial scale production.

A catalyst for producing methacrylic acid by oxidative dehydrogenation of isobutyric acid (for example, JP-A-57-72936) and oxidation of isobutyraldehyde (for example, JP-A-57-144238). Is also well known. Further, a catalyst for producing methacrylic acid or methacrolein by oxidizing isobutylene or tertiary butanol (for example, JP-A-55-127328),
Recently, catalysts for directly oxidizing isobutane to produce methacrylic acid and methacrolein (JP-A-2-42032, etc.) have also been proposed.

The catalyst used in these reactions is
It is known that those having a structure of a heteropoly acid containing molybdenum and phosphorus as main components and salts thereof are effective, and regarding the composition, partial substitution of molybdenum with vanadium, co-catalyst components such as copper, antimony and arsenic In addition, various improvements have been made regarding the addition and preparation method of cyclic amine.

[0005]

However, these conventional catalysts do not always sufficiently satisfy the reaction yield (activity and selectivity) even in the oxidation of methacrolein that has already been put to practical use. For example, compared with a catalyst that produces acrylic acid from acrolein, not only the selectivity of the reaction is poor, but also the reaction activity and life are poor, and therefore a large amount of catalyst is required, and the burden of equipment cost and catalyst cost is large at present. is there. One of the major reasons why the performance of the catalyst is not sufficient is that it has not been industrialized even when using isobutane, isobutyric acid or the like as a raw material. An object of the present invention is to improve the existing catalyst and provide a catalyst having higher reaction activity and selectivity.

[0006]

Means for Solving the Problems In order to achieve the above objects, the inventors of the present invention have made extensive studies on improvement of a heteropolyacid catalyst, and as a result, found that a catalyst having a specific catalyst composition and prepared by a specific method was used. The inventors have found that the above objects can be achieved and achieved the present invention.

That is, the present invention has the general formula PaMobV
cSbdCueXfOg (in the formula, P, Mo, V, Sb,
Cu and O respectively represent phosphorus, molybdenum, vanadium, antimony, copper and oxygen, X represents at least one element selected from the group consisting of rubidium, cesium and thallium, and subscripts a, b, c and d. , E, f and g represent the atomic ratio of each element, and when b = 12,
a, c, d, e, f do not include 0 (zero) respectively 3
The following values are taken, and g represents a value determined by the valence and atomic ratio of other elements. ) Is a partially neutralized salt of a heteropoly acid, wherein the catalyst raw material is mixed and dissolved or suspended in water, and ammonium root is present in the mixed solution at a temperature of 80 to 200 ° C. A catalyst for producing methacrylic acid prepared by heating for 24 hours.

The basic structure of the catalyst of the present invention is a conventionally well-known partially neutralized salt of phosphomolybdic acid with rubidium, cesium and thallium, but further contains vanadium, antimony and copper as essential components. I'm out. Although it is already known that these elements are effective, the combination of their composition and preparation method changes the catalytic performance.

The catalyst containing antimony but not vanadium has a high reaction selectivity, but has a drawback that the reaction rate tends to decrease with use for a long time and is not durable for industrial use. On the other hand, a catalyst containing vanadium but not antimony can provide some degree of reaction selectivity and life with conventional preparation methods, but it is not sufficient. Further, even in the case of a catalyst containing both vanadium and antimony, only a catalyst having a poor reaction activity and a short life can be obtained by the conventional preparation method.
In order to combine reaction selectivity, activity, and lifetime, it is necessary to include both vanadium and antimony and use the special preparation method of the present invention. Also, copper is essential in terms of improving reaction activity. In addition, arsenic, silver, iron, cobalt, lanthanum, cerium, etc. may be contained as optional components.

As a raw material used for preparing the catalyst, a combination of oxides, nitrates, carbonates, ammonium salts, hydroxides, halides and the like of each element can be used.
For example, molybdenum raw materials include ammonium paramolybdate, molybdenum trioxide, molybdenum chloride, etc., vanadium raw materials include ammonium metavanadate, vanadium pentoxide, vanadium chloride, etc., and antimony raw materials include antimony trioxide, antimony pentoxide, etc. Can be used. Further, it is necessary that ammonium root is contained in the stage of heat treatment of the suspension described later. Therefore,
When ammonium salt is not contained, it is necessary to add ammonia or the like.

The above raw materials are mixed in water to dissolve or suspend them, and ammonium root is present in the mixed solution.
The mixed solution is about 80 to 200 ° C., preferably about 100 to 18
By heat-treating at 0 ° C. for about 1 to 24 hours, preferably about 10 to 20 hours, a catalyst having a high methacrylic acid selectivity can be obtained. If the temperature of the heat treatment is lower than about 80 ° C. or the time is shorter than 1 hour, the reaction does not proceed sufficiently and the catalyst has a low methacrylic acid selectivity. The temperature may be higher than about 200 ° C. or the time may be longer than 24 hours, but the corresponding effect is not obtained. The water-soluble raw material may be used by dissolving it in water separately in advance, but there is no problem if it is charged as a powder.

When the suspension obtained by heat treatment was evaporated to dryness, the solid obtained was found to be P: Mo from X-ray diffraction and infrared absorption.
It can be seen that a salt of so-called Dawson type heteropolyacid having a ratio of 1: 9 is formed. When this is heated to about 180 to 350 ° C. in an oxidizing gas such as air or an inert gas such as nitrogen, it changes into a so-called Keggin-type heteropolyacid salt having a P: Mo ratio of 1:12. Since it is prepared by containing the ammonium root, the solid at this stage is a mixed salt of the X component of the heteropolyacid (rubidium, cesium, etc.) and ammonium. As it is, it does not have the property of a solid acid and its activity is low, so it is necessary to activate it by firing. Baking at a temperature of about 400 to 500 ° C., preferably about 420 to 450 ° C. in an inert gas such as nitrogen. As a result, almost all of the ammonium components are eliminated to form a protonic acid, which exhibits high activity. When fired in air, the heteropolyacid decomposes and sinters at 400 ° C. or higher, resulting in low activity. On the other hand, at 400 ° C. or lower, many ammonium roots remain and the activity is low. After firing in an inert gas,
There is no problem in firing in air at a temperature of 400 ° C. or lower.

The catalyst of the present invention is used for the production of methacrylic acid by the oxidation of various raw materials including the oxidation of methacrolein. In use, the catalyst is used alone or supported or diluted on a carrier such as alumina, silica or silicon carbide. It is used in a mixed form, and in the case of a fixed bed, it is used after being formed into a columnar shape, a spherical shape, a ring shape or the like. A reaction type such as a fluidized bed or a moving bed can also be used. The firing in the above-mentioned inert gas may be performed after molding.

When methacrolein is catalytically oxidized in the gas phase to produce methacrylic acid using the catalyst of the present invention, the raw material used does not necessarily have to be pure methacrolein, but isobutylene or tertiary butanol. A methacrolein-containing gas obtained by vapor-phase catalytic oxidation of methacrolein or a vaporized methacrolein obtained by a liquid phase method may be used. The oxygen source may be pure oxygen, but industrially air is used. As other diluent gas, nitrogen, carbon dioxide, carbon monoxide, steam or the like can be used. The concentration of methacrolein in the reaction raw material gas is about 1
-10%, and a ratio of oxygen to methacrolein of about 1 to 5 is used. Space velocity of raw material gas is about 500-50
The range of 00h ^-1 and the reaction temperature are preferably about 250 to 350 ° C. The reaction pressure is usually around normal pressure or under slight pressure.

When isobutane is directly oxidized using the catalyst of the present invention to produce methacrylic acid or methacrolein, the isobutane concentration in the raw material gas is about 1 to 85%,
Pure oxygen, oxygen-enriched air, air, or the like is used as the oxygen source. The ratio of oxygen to isobutane is about 0.05-
4 is appropriate. About 3 to 30% water vapor in the reaction gas
It is desirable to contain it within the range. The raw material gas may contain nitrogen, carbon dioxide, carbon monoxide or the like as a diluent gas. Unreacted isobutane and optionally oxygen are recovered and recycled, as the activity cannot be very active in this reaction. By-product methacrolein is recycled or introduced into another reactor to oxidize methacrylic acid. The space velocity is about 400 to 5000 h ^-1 , and the reaction temperature is about 270 to 40.
0 ° C. is preferred. The reaction pressure may be atmospheric pressure or increased pressure.

The catalyst of the present invention is oxidative dehydrogenation of isobutyric acid,
It can also be used for the production of methacrylic acid by the oxidation of isobutyraldehyde. It can also be used when producing methacrylic acid from isobutylene in a single step. In these reactions, the reaction conditions similar to the oxidation of methacrolein can be adopted.

[0017]

The catalyst of the present invention has higher reaction activity and selectivity than conventional catalysts in the production of methacrylic acid.

[0018]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. The definitions of conversion rate and selectivity are as follows. Conversion rate of methacrolein (%) = (moles of reacted methacrolein)
÷ (Number of moles of methacrolein supplied) × 100 Methacrylic acid selectivity (%) = (Number of moles of methacrylic acid formed)
÷ (number of moles of reacted methacrolein) × 100

Example 1 In 224 g of ion-exchanged water heated to 40 ° C., 38.2 g of cesium nitrate [CsNO ₃ ] and copper nitrate [Cu (NO ₃ ) ₂ .multidot.
3H ₂ O] 10.2 g, phosphoric acid aqueous solution [85% -H ₃ P
O ₄ ] 24.2 g, nitric acid [70% -HNO ₃ ] 25.2 g
Was dissolved, and this was designated as solution A. To 330 ml of deionized water heated to 40 ° C, ammonium molybdate [(NH
_{4) 6 Mo 7 O 24 ·} 4H 2 O] was dissolved 297 g, was suspended ammonium metavanadate [NH ₄ VO _3] 8.19g, which was used as B solution. Solution A was added dropwise to solution B being stirred. The obtained suspension contains antimony trioxide [Sb
₂ O ₃ ] 10.2 g was added. The obtained suspension was heated and stirred at 120 ° C. for 17 hours in a sealed container. The obtained suspension was placed in a stainless steel vat and evaporated to dryness at 120 ° C. in an electric furnace. The dried product thus obtained has a Dawson-type heteropolyacid salt structure. The dry solid is pulverized to 1000 μm or less, a molding aid is added, water is added, and the mixture is kneaded.
It was extruded and molded on a cylinder of m and a height of 5 mm. The formed body is dried at 90 ° C. and then baked at 320 ° C. for 3 hours. This was calcined in a nitrogen stream at 435 ° C for 3 hours and further in an air stream at 390 ° C for 3 hours to obtain a catalyst.
The composition of this catalyst excluding oxygen is P _1.5 Mo ₁₂ V _0.5 Sb.
_{It is 0.5} Cu _0.3 Cs _1.4 .

9 g of this catalyst was filled in a glass reaction tube having an inner diameter of 15 mm, and 4 mol% of methacrolein and 12 m of oxygen were filled.
An activity test was carried out at a reaction temperature of 290 ° C. through a reaction tube with a raw material gas having a composition of ol%, water vapor 17 mol%, and the balance nitrogen at a space velocity (STP standard) of 670 h ⁻¹ . As a result, when the steady state was reached, the conversion of methacrolein was 93.6%, the selectivity of methacrylic acid was 81.1%, and the yield of methacrylic acid was 75.9%. When the conditions were varied, the methacrylic acid selectivity at a methacrolein conversion rate of 90% was calculated to be 83.1%.

Comparative Example 1 A catalyst was prepared in the same manner as in Example 1 except that antimony trioxide was not used. The composition of the catalyst excluding oxygen is P _1.5 Mo ₁₂ V _0.5 Cu _0.3 Cs _1.44 . Example 1
The result of the same activity test as that _of methacrolein conversion was 97.
7%, methacrolein selectivity 70.2%, methacrylic acid yield 68.5%, and methacrylic acid selectivity at a methacrolein conversion rate of 90% was 75.2%.

Comparative Example 2 A solution of phosphoric acid [85% -H ₃ P in 350 g of ion-exchanged water]
O ₄ ] 4.6g was added, and molybdovanadolinic acid [H
115 g of ₄ P ₁ Mo ₁₁ V ₁ O ₄₀ · 18H ₂ O] and 3.64 g of antimony trioxide [Sb ₂ O ₃ ] were added, and refluxed at 100 ° C. for 14 hours to dissolve. This solution was cooled to 13 ° C. and designated as solution A. To 250 g of ion-exchanged water cooled to 13 ° C., 13.7 g of cesium nitrate [CsNO ₃ ], 3.62 g of copper nitrate [Cu (NO ₃ ) ₂ .3H ₂ 0], and 10.4 g of ammonium nitrate [NH ₄ NO ₃ ]. It was dissolved and this was designated as solution B. Solution B was added dropwise to solution A and concentrated under reduced pressure at 65 ° C. The obtained dried solid matter was placed in a stainless steel vat and dried at 120 ° C. in an electric furnace. The molding step and firing step were the same as in Example 1. The composition of this catalyst excluding oxygen is P _1.5 M.
o ₁₂ V _1.1 Sb _0.5 Cu _0.3 Cs _1.4 . Example 1
The result of the same activity test as that of methacrolein conversion is 35.
2%, methacrolein selectivity was 85.8%, and methacrylic acid yield was 30.2%.

Example 2 A catalyst was prepared in the same manner as in Example 1 except that the addition amount of nitric acid [70% -HNO ₃ ] was changed to 12.6 g. The composition of the catalyst excluding oxygen is P _1.5 Mo ₁₂ V _0.5 Sb _0.5 Cu _0.3 C.
s _1.4 . The results of the same activity test as in Example 1 show that the conversion of methacrolein is 97.3% and the selectivity of methacrolein is 7
The methacrylic acid selectivity was 78.5% when the methacrylic acid yield was 3.5%, the methacrylic acid yield was 71.5%, and the methacrolein conversion rate was 90%.

Example 3 A catalyst was prepared in the same manner as in Example 1 except that the amount of nitric acid [70% -HNO ₃ ] added was 37.8 g. The composition of the catalyst excluding oxygen is P _1.5 Mo ₁₂ V _0.5 Sb _0.5 Cu _0.3.
It is Cs _1.4 . The results of the same activity test as in Example 1 were: methacrolein conversion 92.8%, methacrolein selectivity 83.7%, methacrylic acid yield 77.7%, methacrylic acid selectivity at methacrolein conversion 90%. Is 85.2%
Met.

Example 4 A catalyst was prepared in the same manner as in Example 1 except that the obtained suspension was heated and stirred at 135 ° C. for 49 hours in a sealed container. The composition of the catalyst excluding oxygen is P _1.5 Mo ₁₂ V _0.5 S
b _0.5 Cu _0.3 Cs _1.4 . The results of the same activity test as in Example 1 were: methacrolein conversion 90.3%, methacrolein selectivity 84.1%, methacrylic acid yield 76.0.
%, The methacrylic acid selectivity at a methacrolein conversion rate of 90% was 84.2%.

Example 5 A catalyst was prepared in the same manner as in Example 1 except that the obtained suspension was heated and stirred in a sealed container at 160 ° C. for 17 hours. The composition of the catalyst excluding oxygen is P _1.5 Mo ₁₂ V _0.5 S
b _0.5 Cu _0.3 Cs _1.4 . The results of the same activity test as in Example 1 showed that the conversion of methacrolein was 95.7%, the selectivity of methacrolein was 81.5%, and the yield of methacrylic acid was 78.0.
%, The methacrylic acid selectivity at a methacrolein conversion rate of 90% was 83.4%.

Example 6 A catalyst was prepared in the same manner as in Example 1 except that the obtained suspension was heated and stirred at 120 ° C. for 70 hours in a sealed container. The composition of the catalyst excluding oxygen is P _1.5 Mo ₁₂ V _0.5 S
b _0.5 Cu _0.3 Cs _1.4 . The results of the same activity test as in Example 1 show that the conversion of methacrolein is 94.2%, the selectivity of methacrolein is 80.8%, and the yield of methacrylic acid is 76.1.
%, The methacrylic acid selectivity at a methacrolein conversion rate of 90% was 80.0%.

Claims (3)

[Claims] 1. The general formula PaMobVcSbdCueX
fOg (wherein P, Mo, V, Sb, Cu and O represent phosphorus, molybdenum, vanadium, antimony, copper and oxygen, respectively, and X represents at least one element selected from the group consisting of rubidium, cesium and thallium. Represents
The subscripts a, b, c, d, e, f and g represent the atomic ratio of each element. When b = 12, a, c, d, e and f do not include 0 (zero). The following values are taken, and g represents a value determined by the valence and atomic ratio of other elements. ) Is a partially neutralized salt of a heteropoly acid,
The catalyst raw material is mixed in water to be dissolved or suspended, and in the state where ammonium root is present in the mixed solution, 80 to 200 ° C.
The catalyst for methacrylic acid production prepared by heat-treating at a temperature of 1 to 24 hours, concentrating the suspension to dryness, and calcining the dried solid at a temperature of 400 to 500 ° C. in an inert gas. 2. A method for producing methacrylic acid, which comprises subjecting methacrolein to gas phase catalytic oxidation with molecular oxygen in the presence of the catalyst according to claim 1. 3. The methacrolein concentration in the reaction raw material gas is 1 to 10%, and the ratio of oxygen to methacrolein is 1 to 1.
5, the space velocity of the reaction raw material gas is 500 to 5000 h ^-1 ,
The method for producing methacrylic acid according to claim 2, wherein the reaction temperature is 250 to 350 ° C.