JPH09299802A - Manufacture of oxidation catalyst and preparation of methacrylic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a heteropoly acid based catalyst having high reaction reactivity and selectivity and long catalytic life by calcining solid substances obtained by drying a solution produced by suspending catalyst raw materials in water at a specified temperature and then kneading the calcined solid substances with ammonia water and adding oxides of specified elements. SOLUTION: This oxidation catalyst is a heteropoly acid based catalyst used for methacrylic acid production by gas-phase oxidation of methacrolein, t-butanol, etc., by bringing them into contact with molecular oxygen and at the time of producing the oxidation catalyst containing phosphorus, molybdenum, etc., the catalyst raw materials are at first dissolved or suspended in water and drying the resultant solution or suspension. Then the obtained solid substances are calcined at 150-350 deg.C and then kneaded with ammonia water to make the solid substances to be neutral or alkaline. After that one or more oxides of elements selected from Zn, Ce, Sn, etc., are added. Methacrylic acid is produced by gas-phase oxidation of methacrole in the presence of an oxidation catalyst produced in this way.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing an oxidation catalyst and a method for producing methacrylic acid using the catalyst.
More specifically, the present invention relates to a method for producing a heteropolyacid catalyst used to produce methacrylic acid by vapor-phase catalytic oxidation of methacrolein, t-butanol, isobutane, isobutene, etc., and methacrylic acid using the catalyst. It relates to a method for producing an acid.

[0002]

2. Description of the Related Art It has been conventionally known that a heteropolyacid compound having a Keggin structure such as phosphomolybdic acid is effective as a catalyst for producing methacrylic acid by vapor-phase catalytic oxidation of methacrolein. However, Mo-
Vapor-phase catalytic oxidation of acrolein to acrylic acid with V-based catalysts has an industrial conversion rate of 99% or higher and 97%.
Compared with achieving stable operation results for more than three years with the above selectivity, the production of methacrylic acid is still at a significantly low level. Therefore, the reaction composition, the selectivity of methacrylic acid, the improvement of the catalyst life or the stability of the catalyst production are required, and the catalyst composition, the preparation method, the drying method,
Energetic research and development has been conducted on the calcination method, catalyst shape, etc., and various proposals have been made so far.

For example, regarding the composition of the catalyst, JP-A-55-
In many patent publications such as Japanese Patent No. 39236, V is essentially essential as a catalyst constituent element, and many elements such as alkali metal, alkaline earth metal, transition metal, and rare earth metal are effective for improving catalyst performance. Is described. JP-A-61-5043 and JP-A-61-72
33 and JP-A-3-21346 show that a specific Ce compound is effective, and JP-A-3-21346.
No. 238051 discloses that specific Bi raw materials are effective.

Japanese Unexamined Patent Publication (Kokai) No. 6-91172 describes that high catalytic performance can be obtained by pre-calcining Sb and Mo, Cu or V among the catalyst components to use as a complex oxide. . Also, a method for preparing the catalyst, for example,
A step of dissolving and mixing and heating the catalyst raw material, specifying the catalyst raw material, controlling the amount of ammonium and nitric acid, etc. (JP-A-61-283352)
JP, JP-A-3-238050, JP, 6-8
Many proposals have been made also in Japanese Patent No. 6932 and Japanese Patent Laid-Open No. 6-86933.

Japanese Unexamined Patent Publication No. 4-7037 and Japanese Unexamined Patent Publication No. 4-1
No. 6242 discloses p of a solution prepared by dissolving and mixing catalyst raw materials.
A Keggin-type heteropolyacid is prepared by keeping H acidic and heating the solution to 85 ° C. or higher.
After cooling to 0 ° C or lower, alkali ions and ammonium ions or a base such as pyridine is added to give an oxygen concentration of 5
A method of firing with a gas of not less than 100% has been proposed.

Japanese Patent Laid-Open No. 165040/1982 discloses that
The raw material solution containing ammonium ions is concentrated, dried, and baked.
It is described that the composition is formed at 400 to 550 ° C. Special
NHK in Kaihei 6-86932_Four/ Mo = (6-1
8) / 12 and NO _Three/Mo=(0.1-5)/1
The amount of ammonia and nitrates in the solution so that
Special conditions of 110-200 ℃ in autoclave
To produce Dawson-type heteropoly acid in solution and inactivate
It is described that firing is carried out in a gas atmosphere. JP
In 6-86933, coexistence of sulfate is Dawson type.
Effective in the production of heteropolyacids, in this case an autoclave
It is stated that heating is not always necessary.

Japanese Patent Laid-Open No. 63-130143 describes that the catalyst performance is improved by redispersing a dry solid matter in water in an amount of 1 to 10 times the solid matter. The calcination of the catalyst also has a great influence on the catalyst performance, and the control of the oxygen concentration and the calcination temperature (JP-A-56-161841, JP-A-3-238050) and the control of ammonia / steam (JP-A-58-58). 67643), firing in an inert gas (JP-A-57-165040), and the like.

On the other hand, for the purpose of controlling the surface area and pores, for example, the addition of pyridine / quinoline (JP-A-57-1714).
44, JP-A-60-209258), addition of activated carbon (JP-A-6-374), addition of alcohol / aldehyde / organic acid (JP-A-6-15178), and the like. There is.

[0009]

However, none of the catalysts proposed hitherto has sufficient reaction results, low productivity, large deterioration with time of the catalyst, high reaction temperature, or catalyst preparation methods. It has problems such as lack of reproducibility and cannot be said to have sufficient performance as an industrial catalyst, and further improvement is desired. An object of the present invention is to provide a method for producing a heteropolyacid catalyst having a higher reaction activity and selectivity and a longer catalyst life, which is used for producing methacrylic acid by gas phase oxidation of methacrolein, and a method for producing methacrylic acid by the catalyst. To provide.

[0010]

Means for Solving the Problems The inventors of the present invention have extensively studied a method for producing an oxidation catalyst containing phosphorus, molybdenum and an alkali metal or thallium in order to solve the above-mentioned problems, and as a result, the catalyst raw material was dissolved in water or After the suspended solution is dried and pre-calcined in advance, the obtained solid matter is kneaded with aqueous ammonia and a specific oxide is added to obtain high reaction activity and selectivity and long catalyst life. It was found that a catalyst having the above can be obtained, and the present invention has been completed.

That is, the present invention provides: When producing an oxidation catalyst containing phosphorus, molybdenum and an alkali metal or thallium, a solution prepared by dissolving or suspending a catalyst raw material in water is dried, and then the obtained solid matter is pre-baked at 150 to 350 ° C., The preliminarily baked solid is kneaded with ammonia water so as to be neutral or alkaline, and Zn, Ce, Sn and M are mixed.
O, Nb, Fe, Co, Ni and at least one oxide selected from Ti is added, and a method for producing an oxidation catalyst, and methacrolein in the presence of the oxidation catalyst according to 2.1. The method for producing methacrylic acid is characterized in that the methacrylic acid is vapor-phase oxidized. Hereinafter, the present invention will be described in detail.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION

(1) Method for producing oxidation catalyst The oxidation catalyst containing phosphorus, molybdenum and alkali metal or thallium of the present invention is not particularly limited, but is preferably a compound represented by the general formula (I)

[0013]

## STR2 ## _{P a Mo b V c Ba d} Sb e Cu f X g Y h O i -Z j O k (I)

(Wherein X represents one or more elements selected from the group consisting of K, Rb, Cs and Tl, and Y represents
Represents one or more elements selected from the group consisting of Bi, Mn, Cr, Zr, Co, Ce, Zn, Fe and Ni,
Z is Zn, Ce, Sn, Mo, Nb, Fe, Co, N
represents one or more elements selected from i and Ti, Z _j
O _k is added in the kneading treatment step of the pre-baked solid matter and aqueous ammonia. Subscripts a, c, d, e, f, g,
h, i, and j represent atomic ratios of the respective elements when b = 12, a = 0.1-5, c = 0-5, d = 0-5,
e = 0 to 5, f = 0 to 2, g = 0.1 to 3, h = 0 to
2, j = 0.1 to 2, and i and k are values determined by the valence and atomic ratio of other elements).

As raw materials of metal components, for molybdenum, ammonium paramolybdate, molybdic acid, molybdenum oxide, etc., and for vanadium, ammonium metavanadate, vanadium oxide, vanadyl oxalate, etc.
For phosphorus, orthophosphoric acid, metaphosphoric acid, phosphorus pentoxide, pyrophosphate, ammonium phosphate, etc., for copper, copper nitrate, copper sulfate, cuprous chloride, cupric chloride, etc .; for antimony, antimony oxide, antimony chloride. Compounds such as can be used. Regarding other metals, oxides, hydroxides, nitrates, acetates, which can be converted into oxides by firing,
Compounds such as oxalates, carbonates and chlorides can be used, and among them, nitrates are preferable. Further, a heteropolyacid such as phosphomolybdic acid or ammonium phosphomolybdate can be used as a raw material for molybdenum and phosphorus.

A solution prepared by dissolving or suspending the catalyst raw material in water is added with stirring at 40 to 100 ° C. for 0.5 to 24 hours, more preferably 50 to 90 ° C. for 1 to 6 hours. Warm. High selectivity may not be obtained at lower temperatures and shorter times, and activity may decrease at higher temperatures and longer times. A carrier component such as silica, diatomaceous earth, or celite may be added to this mixed solution.

The mixed solution containing the catalyst component which has been subjected to the heating treatment is dried by a usual method. Generally 100-25
Evaporate to dryness in a hot air drier kept at 0 ° C. The spray drying method is also a more industrially advantageous method because it is possible to obtain uniform dried particles without uneven distribution of catalyst components, and is particularly suitable as a fluidized bed reaction catalyst.

The dried catalyst component is pre-calcined under a temperature condition of 150 to 350 ° C., preferably 200 to 300 ° C. by circulating air. Here, 0.0 to the pre-baked solid so that the pre-baked solid becomes neutral or alkaline.
15 to 0.15 times by weight, preferably 0.018 to 0.05
0.2 to 0.8 weight times ammonia water containing weight times ammonium hydroxide is added and kneaded, and the solid matter is selected from Zn, Ce, Sn, Mo, Nb, Fe, Co, Ni and Ti. Add oxides of one or more elements.

When the amount of the ammonia water is less than 0.2 times by weight, the kneading cannot be sufficiently performed, and when it exceeds 0.8 times by weight, the catalyst performance is deteriorated due to unnecessary dissolution of the catalyst component. If the amount of ammonium hydroxide added is less than 0.015 weight times that of the pre-calcined catalyst, the effect of ammonia addition is not clear, and if it exceeds 0.15 weight times, the initial activity decreases and the stability of the catalyst is impaired. Be done. An oxide is used as the compound added in this step. Addition with hydroxide, nitrate, etc. will impair the catalytic activity. A suitable addition amount of the oxide is 0.2 to 2 moles, preferably 0.3 to 2 moles, when the number of moles of Mo contained in the pre-calcination catalyst is 12.
The amount is 1.5 mol, and if the amount is small, the effect is not clear, and if the amount is too large, the activity and selectivity may decrease. It is important that these oxides are used together with aqueous ammonia in the kneading step, and if added during mixing and dissolution of other catalyst components, expected improvement in catalyst performance is not observed,
Rather, it causes a marked decrease in activity. The catalyst component which has been kneaded is dried by a usual method.

When used as a supported catalyst, water is added to the obtained kneaded product to adjust the viscosity, if necessary, and the resulting mixture is supported on a carrier such as alumina or silicon carbide by an appropriate method. The dried catalyst component is crushed and tableted. In addition to this, a general molding method such as extrusion molding in a paste form and drying can be arbitrarily selected. There is no particular limitation on the shape of the catalyst, and the shape of sphere, cylinder, pellet, ring, etc. can be selected in consideration of the reactor type, conditions, etc. The shape of the ring gives favorable results when used in vessels.

Optimum conditions vary depending on the catalyst raw material used, catalyst composition, and preparation method, but generally 300 to 500 ° C. for 1 to 24 hours, preferably 350 to 450 ° C. for 2 to 12
The catalyst is activated by firing for a time. Firing
It is carried out in an atmosphere of an inert gas in which the oxygen concentration is controlled to 0.1 to 5% by volume, preferably 0.2 to 2% by volume, preferably under the flow of the inert gas. When the oxygen concentration is less than 0.1% by volume, in order to sufficiently desorb ammonia, a high temperature at which the catalyst itself becomes unstable, or when treated at an appropriate temperature, is remarkably increased. There are problems such as requiring a long time.

On the contrary, if it exceeds 5% by volume, it may be difficult to control the firing, probably because some ammonia burns on the catalyst.
In an extreme case, a large amount of molybdenum trioxide may be generated due to the decomposition of the catalyst component, and the catalytic performance may be significantly reduced.

In the preparation of conventional heteropolyacid catalysts,
Generally, the pH of the solution in which the catalyst component is dissolved is kept strongly acidic so that the Keggin structure can exist stably, and the solution is refluxed for a long time (JP-A-4-7037 and JP-A-4-1624).
No. 2). Recently, it has also been reported that a Dawson type heteropolyacid produced by adjusting a solution to be weakly acidic is a precursor of a highly active Keggin type heteropolyacid by subsequent firing (Japanese Patent Laid-Open No. 6-86932, JP-A-6-869
No. 33).

However, the present inventors have surprisingly found that
Higher catalytic performance can be obtained by kneading the pre-calcined catalyst precursor with aqueous ammonia, and at this time, Zn, Ce, Sn, Mo, Nb, Fe, Co, Ni
It was found that higher catalytic activity can be achieved by adding and kneading one or more oxides of one or more elements selected from Ti and Ti.

Although the reason for the performance improvement is not always clear, it has been found that the addition of ammonia causes a change in the crystal structure in the catalyst production process. The catalyst component oxide that has been pre-calcined gives only the peak of the Keggin structure in X-ray diffraction, but the diffraction peak of the Keggin structure is lowered by the kneading treatment with aqueous ammonia, and the heteropoly acid of P ₂ Mo ₅ O ₂₃ The peak will be confirmed. The metal oxide powder added in this state is accompanied by dissolution of a part of the surface,
It appears to be highly dispersed by the interaction of the catalytically active components. The fact that hydroxides or nitrates other than oxides show rather negative effects is presumed to be the result of the interaction between the oxides and the catalytically active components in the solution changing depending on the liquid state such as pH. When a complex of the metal oxide thus added and a catalytically active component in which at least a part of the Keggin structure is structurally changed is calcined in an atmosphere of an inert gas containing 0.1 to 5% by volume of oxygen, again The Keggin structure is regenerated. The active species of the high activity catalyst of the present invention is P ₂
It is considered to be generated by solid-state reaction in the heat treatment step of the composite of the amorphous precursor containing Mo ₅ and the added oxide.
Therefore, in order to develop good catalytic performance, it is important to control the solid-phase reaction for generating active species from the precursor, and it is considered that it is necessary to perform the calcination under the condition of controlling the oxygen concentration. At this time, the catalyst having improved catalytic performance has a value of 0.
It was found that the pores in the meso / macropore portion of 1 to 1 μm were increased.

The catalyst according to the production method of the present invention is characterized in that it has higher activity than conventional catalysts, and that the specific gravity of the molded catalyst is small and that the strength upon firing is large. It is considered that the oxide added in the kneading with the addition of aqueous ammonia partly acts as a binder, and the merit as a practical catalyst is remarkably large.

(2) Method for producing methacrylic acid The catalyst according to the method for producing methacrylic acid of the present invention can be applied to a method for producing methacrylic acid by a usual catalytic oxidation reaction,
It is preferable to carry out the reaction in the presence of water vapor at a reaction temperature of about 400 ° C. and a reaction pressure of about 0.5 to 10 atm. As the methacrolein of the reaction raw material, for example, a product gas obtained by catalytically oxidizing isobutene or t-butanol for the purpose of producing methacrolein may be used as it is, or the product gas may be purified to produce methacrolein. It may be used after being separated from other gases.

Air is generally used as the oxygen source for the oxidation, but a mixed gas obtained by diluting oxygen (molecular oxygen) with an inert gas such as carbon dioxide or nitrogen may be used. Mixed gas of water vapor, reaction raw material, oxygen, etc. (hereinafter,
The reaction mixture gas) is passed through the catalyst, and the contact time is usually about 1 to 20 seconds. As the composition of the reaction mixed gas, for example, 0.2 to 4 mol of molecular oxygen and 1 to 20 mol of water vapor are used with respect to 1 mol of methacrolein.

In addition, this catalytic oxidation reaction can be carried out with reference to the usual knowledge about methacrolein oxidation unless it goes against the gist of the present invention. The catalyst obtained according to the present invention can also be used for the production of methacrylic acid by oxidative dehydrogenation of isobutyric acid and 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.

[0030]

EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the examples as long as the gist thereof is not exceeded. The conversion rate, selectivity and yield were determined by the following formulas and displayed on a molar basis.

[0031]

## EQU1 ## Conversion (%) = [(moles of reacted methacrolein) / (moles of supplied methacrolein)] × 1
00

[0032]

## EQU2 ## Selectivity (%) = [(moles of methacrylic acid formed) / (moles of reacted methacrolein)] × 10
0

[0033]

## EQU3 ## Yield (%) = [(moles of methacrylic acid produced) / (moles of methacrolein fed)] × 100

Example 1 (Catalyst preparation) 212 g of ammonium paramolybdate and 11.7 ammonium ammonium metavanadate were added to 580 ml of pure water.
g was added and the mixture was heated to 70 ° C. Phosphoric acid 23 with stirring
g, 9.75 g of cesium nitrate, and 4.83 g of copper nitrate were added, then 14.5 g of antimony trioxide was added, the temperature was raised to 80 ° C., and then the temperature was kept at 80 ° C. for 2 hours.
The obtained slurry solution was dried and prebaked in an oven maintained at 250 ° C. for 10 hours. To 100 g of the obtained solid, 50 ml of 5% aqueous ammonia and 3.8 g of ZnO powder were added, and the mixture was kneaded for 20 minutes and then dried in an oven kept at 130 ° C. The obtained solid was tablet-molded into a cylindrical shape having an outer diameter of 5 mm, and calcined at 400 ° C. for 6 hours under a nitrogen flow containing 0.6% of oxygen to obtain a catalyst. The composition of the obtained catalyst was Mo ₁₂ P ₂ V ₁ Sb ₁ C in terms of atomic ratio of each component.
u _0.2 Cs _0.5 Zn ₁ . (However, O, H, N atoms are excluded)

(Catalytic Oxidation Reaction) 30 ml of this catalyst was filled in a stainless steel reaction tube (inner diameter: 18 mm) and heated through a niter bath to carry out catalytic oxidation of methacrolein.
Source gas is methacrolein 5 mol%, oxygen 12 mol%,
A mixed gas of 30 mol% steam and 53 mol% nitrogen,
Under normal pressure, the reaction temperature was 290 ° C. and the space velocity was 1400 /
Reacted at time. As a result, methacrolein (MACR)
Conversion 95.0%, methacrylic acid (MAA) selectivity 8
The yield was 0.2% and the yield of methacrylic acid (MAA) was 76.2%.

Comparative Example 1 A catalyst was prepared and reaction was evaluated in the same manner as in Example 1 except that ZnO powder was not added. As a result, the methacrolein conversion rate was 89.1% and the methacrylic acid selectivity was 83.1.
%, And the yield of methacrylic acid was 74.7%.

Comparative Example 2 A catalyst was prepared and reaction was evaluated in the same manner as in Example 1 except that the kneading step was omitted and the pre-fired product was fired after molding. As a result, the conversion of methacrolein was 81.5%, the selectivity of methacrylic acid was 85.5%, and the yield of methacrylic acid was 69.7%.
Met.

Example 2 A catalyst was prepared and reaction was evaluated in the same manner as in Example 1 except that the amount of ZnO powder was reduced by half. As a result, the conversion of methacrolein was 95.6% and the selectivity of methacrylic acid was 7
The yield was 9.5% and the yield of methacrylic acid was 76.0%.

Comparative Example 3 A catalyst was prepared in the same manner as in Example 1 except that Zn (NO ₃ ) ₃ was used instead of ZnO, and the reaction was evaluated. As a result, the conversion of methacrolein was 77.4%, the selectivity of methacrylic acid was 83.9%, and the yield of methacrylic acid was 64.9%.

Comparative Example 4 A catalyst was prepared in the same manner as in Example 1 except that ZnO was added in the first catalyst raw material mixing step, and the reaction was evaluated. As a result, the conversion of methacrolein was 61.0%, the selectivity of methacrylic acid was 87.7%, and the yield of methacrylic acid was 53.5%.

Examples 3 to 6 and Comparative Examples 5 to 7 Catalysts were prepared in the same manner as in Example 1 except that the oxides shown in Table 1 (hydroxides in Comparative Example 5) were used, and the reaction was evaluated. It was The results are shown in Table 1.

[0042]

INDUSTRIAL APPLICABILITY The oxidation catalyst of the present invention has higher reaction activity and selectivity and longer catalyst life in the production of methacrylic acid by gas phase oxidation of methacrolein.

[0043]

[Table 1]

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Claims (5)

[Claims] 1. When producing an oxidation catalyst containing phosphorus, molybdenum and an alkali metal or thallium, a solution prepared by dissolving or suspending a catalyst raw material in water is dried, and then the obtained solid matter is heated at 150 to 350 ° C. After the preliminary calcination, the preliminary calcination solid matter is kneaded with ammonia water so as to be neutral or alkaline, and Zn, Ce,
A method for producing an oxidation catalyst, comprising adding an oxide of at least one element selected from Sn, Mo, Nb, Fe, Co, Ni and Ti. 2. The oxidation catalyst has the general formula (I): P _a Mo _b V _c B _ad Sb _e Cu _f X _g Y _h O _i —Z _j O _k (I) Represents one or more elements selected from the group consisting of K, Rb, Cs and Tl, and Y represents Bi, Mn,
Represents one or more elements selected from the group consisting of Cr, Zr, Co, Ce, Zn, Fe and Ni, and Z is Zn,
It represents one or more elements selected from Ce, Sn, Mo, Nb, Fe, Co, Ni and Ti, and Z _j O _k is added in the kneading treatment step of the pre-baked solid matter and the aqueous ammonia. Subscripts a, c, d, e, f, g, h, i and j
Represents the atomic ratio of each element when b = 12, and a
= 0.1-5, c = 0-5, d = 0-5, e = 0-5,
f = 0 to 2, g = 0.1 to 3, h = 0 to 2, j = 0.1
To 2, and i and k are values determined by the valences and atomic ratios of other elements). 3. The kneading treatment uses 0.2 to 0.8 times by weight of aqueous ammonia containing 0.015 to 0.15 times by weight of ammonium hydroxide with respect to the pre-calcined solid matter. The manufacturing method described in. 4. After the kneading treatment with ammonia water, the dried kneaded product is fired in a temperature range of 350 to 450 ° C. in an inert gas containing 0.1 to 5% by volume of oxygen. The manufacturing method according to any one of 3 above. 5. A method for producing methacrylic acid, which comprises subjecting methacrolein to gas phase oxidation in the presence of the oxidation catalyst according to claim 1.