JPH0686933A - Production of catalyst for producing methacrylic acid - Google Patents

Abstract

(57) [Summary] (Modified) [Objective] To provide a catalyst for producing methacrylic acid having high reaction activity, selectivity and long catalyst life. [Structure] General formula PaMobVcAsdXeYfOg (wherein P, Mo, V, As, and O represent phosphorus, molybdenum, vanadium, arsenic, and oxygen, respectively, and X is at least selected from the group consisting of potassium, rubidium, cesium, and thallium. Represents one element, and Y represents at least one element selected from the group consisting of copper, silver, bismuth, iron, cobalt, antimony, lanthanum and cerium), and substantially represents an ammonium group and a sulfate group. When producing a catalyst for producing methacrylic acid consisting of a partially neutralized salt of heteropolyacid, which is not contained, ammonium root is adjusted so that the pH of the solution obtained by dissolving or suspending all the catalyst raw materials in water is in the range of 3 to 9. And sulfate, and the solid obtained by concentrating and drying the solution is added to 400-
Bake at 500 ° C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a heteropolyacid catalyst used for producing methacrylic acid by vapor phase catalytic oxidation. More particularly, it relates to a method for producing a heteropolyacid catalyst used for producing methacrylic acid by vapor-phase catalytic oxidation of methacrolein, isobutane, etc. with molecular oxygen.

[0002]

2. Description of the Related Art Various catalysts have been proposed for producing methacrylic acid by vapor-phase catalytic oxidation of methacrolein (JP-A-50-101316, JP-A-50-1425).
No. 10, JP-A-59-4445, etc.), a part of which is already used for industrial scale production. Further, catalysts for producing methacrylic acid by oxidative dehydrogenation of isobutyric acid (JP-A-57-72936, etc.) and oxidation of isobutyraldehyde (JP-A-57-144238, etc.) are also well known.

Further, a catalyst for oxidizing methacrylic acid and methacrolein by oxidizing isobutylene or tertiary butanol (JP-A-55-127328), and recently, direct oxidation of isobutane to obtain methacrylic acid and methacrolein. Catalysts (JP-A-2-42032, JP-A-3-6)
No. 3139) is also proposed.

The catalyst used in these reactions is
It is known that it has a structure of a heteropolyacid containing molybdenum and phosphorus as main components and / or a salt thereof, and that partial replacement of molybdenum with vanadium and addition of cocatalyst components such as copper, antimony and arsenic are effective. There is.

Regarding the preparation method, addition of carboxylic acid and the like (JP-A-51-136615), addition of pyridines (JP-A-57-177347) and addition of quinolines (JP-A-60-209258). , A method of using various additives such as the addition of ammonium nitrate (JP-A-57-165040), and aging the slurry at a temperature of 80 ° C. or higher using a raw material containing no nitrate radical (JP-A-59-12758).
No.) and firing in an inert gas atmosphere (JP-A-57-165).
040), ammonia and steam atmosphere firing (Japanese Patent Laid-Open No. 58-61833), and various other improvements have been made.

[0006]

However, the problems of these known catalyst systems are that both the reaction yield (activity and selectivity) and the catalyst life are long in the oxidation of methacrolein which has already been put to practical use. It is not always sufficient to satisfy For example, in comparison with a Mo-V type composite oxide catalyst for producing acrylic acid from acrolein, not only the selectivity of the reaction is poor but also the reaction activity and the life are poor,
Therefore, a large amount of catalyst is required and the burden of equipment cost and catalyst cost is large at present. 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 to provide a catalyst having higher reaction activity, selectivity and long catalyst life.

[0007]

In order to achieve the above-mentioned objects, the inventors of the present invention have made earnest studies on improvement of a heteropolyacid catalyst, and as a result, a catalyst prepared by a specific method achieves the above objects. The present invention has been discovered and has reached the present invention.

That is, the present invention provides the general formula PaMobVcAsdXeYfOg (wherein P, Mo, V, As and O represent phosphorus, molybdenum, vanadium, arsenic and oxygen, respectively, and X represents a group consisting of potassium, rubidium, cesium and thallium. Represents at least one element selected from Y, Y represents at least one element selected from the group consisting of copper, silver, bismuth, iron, cobalt, antimony, lanthanum and cerium, and subscripts a, b, c, d, e, f and g represent the atomic ratio of each element, and when b = 12, a, c and e are 0
A value of 3 or less that does not include (zero), d and f are 0 (zero)
Methacrylic acid consisting of a partially neutralized salt of a heteropolyacid that does not substantially contain ammonium radicals and sulfate radicals, and g is a value of 3 or less, including g, and g is a value determined by the valence and atomic ratio of other elements. When producing a production catalyst, the pH of a solution obtained by dissolving or suspending all catalyst raw materials in water is 3 to
A catalyst for producing methacrylic acid, characterized in that an ammonium group and a sulfate group are present in the range of 9 and the solid obtained by concentrating and drying the solution is calcined at 400 to 500 ° C. in an inert gas atmosphere. Is a manufacturing method.

The basic structure of the catalyst of the present invention is a partially neutralized salt of phosphomolybdate, which is well known in the art, with potassium, rubidium, cesium and thallium.
Furthermore, vanadium is contained as an essential component. Arsenic is effective in improving methacrylic acid selectivity, and it is recommended to add it for this purpose. Further, it is desirable that the Y element is contained because it is effective in improving the reaction activity and the selectivity.
Above all, the effect is large when copper is selected.

Although the combination of these elements has already been known, the performance of the catalyst depends largely on the composition thereof as well as the preparation method such as raw materials, additives and calcination method, and the specific preparation conditions of the present invention should be adopted. Makes the catalyst even higher in performance.

One of the requirements of the present invention is to include ammonium radicals and sulfate radicals at the stage of the aqueous solution and suspension for preparing the catalyst precursor. This can be easily achieved by using a raw material containing ammonium and sulfate.

It is preferable to use ammonium molybdate as a raw material for molybdenum and ammonium. When using molybdenum oxide, phosphomolybdic acid, or the like, it is necessary to add ammonia or the like so that the ammonium root falls within a predetermined range. As the vanadium raw material, ammonium metavanadate, vanadium pentoxide and the like can be used. Phosphoric acid and arsenic are generally used as phosphorus and arsenic, but they may be used in the form of salts with other essential components such as ammonium phosphate, ammonium arsenate or copper phosphate. Sulfate is conveniently introduced in the form of a sulfate salt of an X component such as potassium and / or a Y component such as copper. Of course sulfuric acid,
Ammonium sulfate or the like can also be added. If sulfate radicals are present in any of the raw materials, nitrates, chlorides, carbonates, hydroxides, phosphates and the like can be used as the other X component and Y component.

A liquid obtained by dissolving or suspending these raw materials in water and mixing them is usually a suspension. This solution needs to have a pH in the range of about 3 to 9, and the solid obtained by evaporating this solution to dryness is a so-called Dawson type heteropoly acid having a P: Mo ratio of 1: 9. The main component is salt. If ammonium salt is not used or the pH of the solution becomes less than 3 due to too much sulfate, the salt has a so-called Keggin structure with a P: Mo ratio of 1:12 from the stage of evaporation to dryness. It is not possible to obtain a highly active catalyst as in the present invention. When the pH is higher than 9, such as when the amount of ammonium roots is relatively too large, it is difficult to form the precursor polyacid, and the activity is also lowered. Ammonium roots and sulfate roots are 6 for each 12 mol of molybdenum.
-18 mol, 0.1-3 mol is preferably present.

Although the reason why a high-performance catalyst can be obtained by using a sulfate as compared with a commonly used nitrate or the like is not clear, it is observed that the crystal grain size in the suspension becomes smaller. ing.

Further, it is considered to be advantageous for pore formation when components such as ammonium sulfate are volatilized in the firing step described below. Further, when adding an organic molding aid such as methoxycellulose or polyvinyl alcohol during molding, when ammonium nitrate coexists, a large amount of heat may be generated during firing, but in the case of ammonium sulfate coexistence, there is no such problem. It is advantageous.

This solution is stirred at a temperature of about 80.degree.
Over time, more preferably about 11 using a closed pressure vessel
It is preferable to perform the heat treatment at a temperature of 0 ° C to 200 ° C.
When the heat treatment is not performed or the heating temperature is about 80 ° C. or lower, the catalyst has a low conversion rate to methacrylic acid. Again 2
Even if the temperature is higher than 50 ° C., the corresponding effect cannot be obtained.
The treatment time is not particularly limited, but is usually 1 to 24 hours. At this stage, some solid-liquid reaction proceeds, and the activity of the finally obtained catalyst becomes higher.

The suspension may be filtered to separate solids, but it is usually concentrated and dried at a temperature of about 100 to 150 ° C.
The obtained solid contains ammonium radicals and sulfate radicals, but a part of ammonium forms a salt of Dawson type heteropolyacid. Although the presence of sulfate is unknown, it is presumed that at least part of it forms ammonium sulfate. Since the solid after drying is almost inactive as it is, it needs to be activated by firing. During the calcination stage, a crystal transition from a Dawson type to a Keggin type occurs between about 200 and 300 ° C., and free ammonium sulfate and other components are removed by 370 ° C., but this alone is still low in activity. In order to avoid adverse effects on catalyst activity and strength due to rapid calcination, it is preferable to gradually calcine at a temperature of up to about 350 to 370 ° C. before calcination and activation in an inert gas atmosphere.

The activation is about 400-in an inert gas atmosphere.
About 1 at a temperature of 500 ° C, preferably about 420-450 ° C.
It is performed by firing for 10 hours. When fired in air as is usually done, the decomposition and sintering of the heteropolyacid occur at temperatures above 400 ° C, resulting in low activity, and at temperatures below 400 ° C, many ammonium and sulfate radicals remain. After all activity is low. By baking in an inert gas at a temperature of 400 ° C. or higher, substantially all ammonium radicals and sulfate radicals can be removed without destroying the structure of the heteropolyacid. After firing in an inert gas atmosphere, firing may be performed at about 400 ° C. or lower in air.

Japanese Unexamined Patent Publication Nos. 54-14311 and 54-5
No. 7-11895 discloses that a sulfate is used as a raw material for preparing a catalyst and a sulfate group or a sulfur component is contained as a catalyst component. However, the present invention is characterized in that the catalyst after calcination contains a sulfur component. Is clearly different.

Since the product calcined in an inert gas is in a slightly reduced state, it may be further calcined in air at a temperature of about 400 ° C. or lower and reoxidized for use in the reaction.

The catalyst of the present invention is used for various reactions such as oxidation of methacrolein. In use, the catalyst is used alone or in the form of being supported or diluted and mixed on a carrier such as alumina, silica, silicon carbide, and fixed. In the case of a floor, it is formed into a columnar shape, a spherical shape, a ring shape or the like before use.
It can also be used in a reaction format such as a fluidized bed or a moving bed.

When methacrolein is catalytically oxidized in the gas phase to produce methacrylic acid using the catalyst obtained in the present invention, the raw material used does not necessarily have to be pure methacrolein, but isobutylene or tert. A methacrolein-containing gas obtained by vapor-phase catalytic oxidation of libutanol or a vaporized methacrolein obtained by a liquid phase method may be used. The oxygen source may be pure oxygen,
Air is used industrially.

As the other diluent gas, nitrogen, carbon dioxide, carbon monoxide, steam or the like can be used. The concentration of methacrolein in the reaction material gas is about 1 to 10%, and the ratio of oxygen to methacrolein is about 1 to 5. The space velocity of the raw material gas is preferably in the range of about 500 to 5000 h ⁻¹ , and the reaction temperature is preferably about 260 to 340 ° C.
The reaction pressure is usually around normal pressure or under slight pressure.

When isobutane is directly oxidized using the catalyst obtained in the present invention to produce methacrylic acid or methacrolein, the concentration of isobutane in the raw material gas is about 15.
It is better to have a high concentration of at least% As an oxygen source, pure oxygen,
Oxygen-enriched air, air, etc. are used. A suitable ratio of oxygen to isobutane is about 0.2 to 2.

It is desirable that the reaction gas contains water vapor in the range of about 3 to 30%. Nitrogen in the source gas,
Carbon dioxide, carbon monoxide, etc. may be contained as a diluent gas. The conversion cannot be so high in this reaction, so unreacted isobutane and optionally oxygen are recovered and recycled.

The by-product methacrolein is recycled or introduced into another reactor to oxidize methacrylic acid. Space velocity is about 30
The reaction temperature is preferably 0 to 3000 h ^-1 , and the reaction temperature is preferably about 270 to 340 ° C. The reaction pressure is usually atmospheric pressure or under pressure.

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

[0028]

INDUSTRIAL APPLICABILITY The catalyst of the present invention has high reaction activity, selectivity and long catalyst life in the production of methacrylic acid.

[0029]

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 the conversion rate and the selectivity are as follows. Conversion rate (%) = [(moles of carbon atoms in the reacted raw material) x
100] ÷ (moles of carbon atoms of the supplied raw material) Selectivity (%) = [(moles of carbon atoms of the produced product)
× 100] ÷ (number of moles of carbon atoms of reacted raw material)

Example 1 Ammonium molybdate was added to 330 ml of ion-exchanged water.
((NH_Four)₆Mo₇O _{twenty four}・ 4H₂O) 296.5g and
And ammonium metavanadate (NH_FourVO₃) 8.1
85% phosphoric acid (H₃PO_Four) 2
4.2 g, 60% arsenic acid aqueous solution (H₃AsO_Four) 13.3
g, 50% cesium sulfate aqueous solution (Cs₂SO _Four) 70.
3 g and copper sulfate (CuSO_Four・ 5H₂O) 10.5 g
Add 225 ml of deionized water, mix and mix
It was In the obtained slurry, 12 moles of Mo
Contains 10.8 moles of roots and 1 mole of sulfate, p
H was about 6.0.

The slurry was concentrated by a rotary evaporator and dried in an electric furnace at 120 ° C. The dry solid at this stage has a 2θ (CuKα) of 9.6 ° and 1 by X-ray diffraction.
1.1 °, 12.4 °, 15.5 °, 19.1 °, 2
It has peaks at 0.7 °, 22.7 °, 25.9 °, 27.6 ° and has a so-called Dawson type heteropolyacid salt structure.

This is crushed, water is added, and the diameter is 5 m with a mold.
m, length 7mm, extrusion molding, then 3 in air
It was baked at 20 ° C. for 5 hours. This is 10.
5 °, 18.4 °, 23.8 °, 26.1 °, 30.2
It had a peak at ° etc. and was a so-called Keggin-type heteropolyacid salt.

Further, this was baked in a nitrogen stream at 450 ° C. for 5 hours and then in air at 390 ° C. for 3 hours. As a result of X-ray diffraction, the catalyst had a Keggin-type heteropolyacid salt structure. In addition, the results of analyzing ammonium roots and sulfates were both below the detection limit (0.01% by weight). The composition of this catalyst is P _1.5 Mo ₁₂ V _0.5 As _0.4 Cs _1.4 Cu
_0.3 (but excluding oxygen and hydrogen).

9 ml of this catalyst was filled in a glass reaction tube having an inner diameter of 15 mm, and a raw material gas having a composition consisting of 4 mol% of methacrolein, 12 mol% of oxygen, 16 mol% of steam, and the balance of nitrogen was supplied at a space velocity (STP standard). ) Through the reaction tube at 670 h ⁻¹ , an activity test was conducted at a reaction temperature of 280 ° C. As a result, the conversion of methacrolein was 84.5% and the selectivity of methacrylic acid was 87.0%.

Comparative Example 1 Instead of an aqueous solution of cesium sulfate, cesium nitrate (CsNO
₃ ) 38.2 g and copper nitrate (CuNO) instead of copper sulfate
₃ · 3H ₂ O) except for using 10.2g A catalyst was prepared in the same composition in the same manner as in Example 1. The X-ray diffraction of this catalyst was the same as in Example 1. In the same activity test as in Example 1, the methacrolein conversion was 70.3% and the methacrylic acid selectivity was 88.2%. It can be seen that the activity is low when nitrate is used instead of sulfate.

Example 2 296.5 g of ammonium paramolybdate was dissolved in 330 ml of deionized water, and another 85% phosphoric acid 2 was added.
4.2 g, 60% arsenic acid aqueous solution 13.3 g, copper sulfate 10.
A solution prepared by dissolving 5 g of 50% cesium sulfate aqueous solution 70.3 g in ion-exchanged water 225 ml was mixed and precipitated. Vanadium pentoxide 6.38 g was further added, and this slurry was transferred to a 1 liter autoclave and heated at 120 ° C. for 5 hours. A heating and stirring process was performed for an hour. In this slurry, 1 mol of ammonium root and 1 mol of sulfate and 12 mol of molybdenum were used.
It contained moles and had a pH of about 5.8. The slurry was dried at 120 ° C. for 5 hours, and then a catalyst having the same composition as in Example 1 was prepared by the same method as in Example 1. The result of the activity test similar to that of Example 1 shows that the conversion of methacrolein is 9
It was 3.4% and the selectivity of methacrylic acid was 83.9%.

Comparative Example 2 21.0 g of 85% phosphoric acid was prepared, and phosphoric acid was used instead of copper sulfate.
Copper (Cu₃(PO_Four) ₂・ 3H₂O) 6.05 g, sulfuric acid
Cesium carbonate (Cs instead of cesium₂CO ₃) 3
Same as Example 2 except that 1.3 g was used.
A catalyst of the same composition was prepared. Activity test similar to that of Example 1
The result is that the methacrolein conversion rate is 78.3% and methacrylic acid is
The acid selectivity was 86.4%. Compared to Example 2,
It can be seen that the property is low.

Example 3 296.5 g of ammonium paramolybdate was dissolved in 330 ml of deionized water, and another 85% phosphoric acid 2 was added.
4.2 g, copper sulfate 3.5 g, 50% cesium sulfate aqueous solution 90.4 g and 98% sulfuric acid (H ₂ SO ₄ ) 7.0 g dissolved in ion-exchanged water 225 ml were mixed, and vanadium pentoxide 12. 8 g was added, and this slurry was transferred to a 1 liter autoclave, and heated and stirred at 120 ° C. for 5 hours. Molybdenum 12 in this slurry
Ammonium roots 10.3 moles and sulfate roots 1.
It contained 45 moles and had a pH of about 5.3. After this, in the same manner as in Example 2, P _1.5 Mo ₁₂ V _1.0 Cs
A catalyst having a composition of _1.8 Cu _0.1 was prepared. The result of the activity test similar to that of Example 1 shows that the methacrolein conversion rate is 86.4.
%, And the selectivity for methacrylic acid was 81.0%.

Comparative Example 3 During the preparation of the catalyst of Example 3, the molded product was calcined in air at 360 ° C. without being calcined in a nitrogen stream to obtain a catalyst. Infrared spectroscopy of this catalyst revealed that ammonium roots remained. The result of quantitative analysis of sulfur content was 0.6% by weight. As a result of the same activity test as in Example 1, the conversion of methacrolein was 76.2% and the selectivity of methacrylic acid was 79.8%. Compared to Example 3,
Without firing in an inert gas atmosphere, the
Both selectivity is low.

Comparative Example 4 Phosphomolybdic acid (H₃PMo₁₂O₄₀・ 30H₂O) 1
18.2 g and 85% phosphoric acid 8.65 g were added to ion-exchanged water 5
In addition to 00 ml, vanadium pentoxide (V₂O _Five) 4.
Add 54 g and reflux at 100 ° C for 5 hours to obtain a uniform
A solution was obtained. 1.2g of copper nitrate was added and dissolved in this, and further
17.5 g of cesium nitrate and ammonium sulfate ((NH
_Four)₂SO_Four) Dissolve 9.9 g in 150 ml of deionized water
The solution was added to make a slurry. In this slurry
Is 3 moles of ammonium root and 12 moles of Mo, sulfate
It contained 1.5 moles and had a pH of about 2.0.

The slurry was concentrated using a rotary evaporator and dried at 120 ° C. This is X
It was a salt of Keggin-type heteropolyacid by line diffraction and infrared spectroscopy. This was baked in a nitrogen stream at 435 ° C. for 5 hours, and graphite was added to the mixture to form tablets. 3 in the air
It was calcined at 80 ° C. for 3 hours to obtain a catalyst. The catalyst composition is in Example 3
Is the same as. The result of the activity test similar to that of Example 1 shows that the conversion of methacrolein is 73.8% and the selectivity of methacrylic acid is 7
It was 6.8%. When the pH of the slurry is low, both activity and selectivity are low.

Example 4 A life test was conducted using the catalyst of Example 2. The reaction conditions are the same as in Example 1, but the reaction temperature during long-term operation is 300 ° C.
The test was carried out at 280 ° C. only during the activity test. as a result,
The reaction results 200 days after the start of the test were a methacrolein conversion rate of 92.3% and a methacrylic acid selectivity rate of 84.2%.

Comparative Example 5 Using the catalyst of Comparative Example 3, the same life test as in Example 4 was conducted. The reaction result after 200 days was 7 for the conversion of methacrolein.
The activity was 0.6% and the selectivity of methacrylic acid was 79.2%, and the activity was much lower than in Example 4.

Example 5 Using the catalyst of Example 2, an oxidation reaction of isobutane was carried out. 9 g of the catalyst was filled in a glass reaction tube having an inner diameter of 15 mm,
A source gas consisting of 42 mol% of isobutane, 33 mol% of oxygen, 12 mol% of steam, and the balance of nitrogen is a space velocity (STP).
(Reference) supplied at 600 h ^-1 . The reaction pressure was 1.5 atm. When the reaction temperature was set to 300 ° C. and analysis was carried out 15 hours after the start of the reaction, the isobutane conversion was 10.1%, methacrylic acid selectivity was 50.6%, and methacrolein selectivity was 13.2%.

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Toshiaki Ui 5-1 Sokai-cho, Niihama-shi, Ehime Sumitomo Chemical Co., Ltd. (72) Inventor Tetsuya Yamamoto 5-1 Sokai-cho, Niihama-shi, Ehime Sumitomo Chemical Co., Ltd. Within the corporation

Claims (3)

[Claims] 1. A general formula PaMobVcAsdXeYfOg (wherein P, Mo, V, As and O represent phosphorus, molybdenum, vanadium, arsenic and oxygen, respectively, and X is selected from the group consisting of potassium, rubidium, cesium and thallium. Represents at least one element, Y represents at least one element selected from the group consisting of copper, silver, bismuth, iron, cobalt, antimony, lanthanum and cerium, and subscripts a, b, c, d, e , F and g represent the atomic ratio of each element, and when b = 12, a, c and e are 0.
A value of 3 or less that does not include (zero), d and f are 0 (zero)
Methacrylic acid consisting of a partially neutralized salt of a heteropolyacid that does not substantially contain ammonium radicals and sulfate radicals, and g is a value of 3 or less, including g, and g is a value determined by the valence and atomic ratio of other elements. When producing a production catalyst, the pH of a solution obtained by dissolving or suspending all catalyst raw materials in water is 3 to
A catalyst for producing methacrylic acid, characterized in that an ammonium group and a sulfate group are present in the range of 9 and the solid obtained by concentrating and drying the solution is calcined at 400 to 500 ° C. in an inert gas atmosphere. Manufacturing method. 2. A solution prepared by dissolving or suspending all catalyst raw materials in water at 1 to 24 in the presence of saturated steam at 80 to 250 ° C.
The method for producing a catalyst for producing methacrylic acid according to claim 1, characterized in that heat treatment is carried out for a period of time. 3. The amount of ammonium radical and sulfate radical in the solution prepared by dissolving or suspending the catalyst raw material in water is 6 to 18 mol and 0.1 to 3 mol per 12 mol of molybdenum, respectively. 1. The method for producing the catalyst for producing methacrylic acid according to 1.