DK155932B - METHOD OF PREPARING ACRYLIC ACID OR METHACRYLIC ACID - Google Patents

Description

DK 155932 B

The invention relates to a process for preparing acrylic acid or methacrylic acid by catalytic: oxidation of acrolein or methacrolein in the gas phase at a temperature of 240-390 ° C with molecular oxygen.

Various catalysts are known for use in catalytic gas phase oxidation of unsaturated aldehydes. Eg. catalysts disclosed in U.S. Patent Nos. 3,475,488, 3,567,773, 3,646,127, 3,649,684 and 3,686,294 and DE Patent Nos. 2,251,364. Among these catalysts, a catalyst of molybdenum vanadium type has an excellent effect on the oxidation of acrolein, but this catalyst is not so suitable for the oxidation of methacrolein. A phosphorus-molybdenum-arsenic-type catalyst gives good results in methacrolein oxidation when it has a specific composition, but it is still insufficient and presents problems that need to be addressed. Eg. it has a very short catalyst life. Second type catalysts do not produce good results in the oxidation of methacrolein.

In attempts to ameliorate such disadvantages of this phosphorus-molybdenum-arsenic type catalyst, it has been found that when an ammonium group is incorporated into a catalyst of this type and at least one specific metal is present in the catalyst system, For example, the catalyst life can be greatly extended while maintaining activity and selectivity at a high level. The invention is based on this realization.

Thus, the object of the invention is to provide a process for producing high yield acrylic acid or methacrylic acid from acrolein or methacrolein using a long-life catalyst which provides high yield unsaturated carboxylic acids when used for catalytic oxidation of unsaturated aldehydes.

The process according to the invention is characterized by the characterizing part of claim 1.

DK 155932B

2

The atomic ratio of each component of the catalyst in question is critical and if the atomic ratio is outside the specified range, a catalyst with sufficient properties cannot be obtained. The amount of the metal element represented by X in the formula set forth in claim 1 may be selected within a range expressed. at atomic to molybdenum ratio of 0.003-1 · When vanadium, tungsten, copper, iron or manganese is used as the metal X, it is preferred that the atomic ratio of the metal X to molybdenum be in the range of 0.003-0.25, especially 0.006-0.2. When two or more such metals are present, it is preferred that the sum of the atomic ratios of the metals relative to molybdenum is within the above range. If the atomic ratio is below the above range, a sufficient effect cannot be obtained and if the atomic ratio is above the above range, the catalyst life is further extended but the selectivity is diminished. When tin is used as the metal X, it is preferred that the atomic ratio to molybdenum is within a range of 0.003-1, especially 0.006-0.5. In the case of using a combination of tin and a metal selected from vanadium, tungsten, copper, iron and manganese as the metal component X, it is preferred that the sum of the atomic ratios of tin and the other metal be within a range of 0.003-1. , in particular 0.01-0.5, and that the atomic ratio of the second metal to molybdenum is less than 0.25, especially less than 0.2.

In the case of tin being used as the metal X, the reduction in selectivity is not so significant, even if present in a relatively large amount compared to another metal, and therefore a strong improvement in catalyst life can be expected. Of the metal elements represented by X, copper is the most preferred.

The amount of an alkali metal represented by Y in the formula of claim 1 is selected within a range, expressed by the atomic to molybdenum ratio, of 0-0.17, especially 0.001-0.12. If the amount of the alkali metal Y is in addition to the above range, a reduction in the selectivity is observed.

In the catalyst in question, it is believed that the ammonium group is present in the form of a salt. The ammonium group is incorporated into the cat 3

DK 155932 B

the lysator in an amount of 0.01-0.3 molecules per atomic molybdenum, preferably 0.01-0.2 molecules.

The chemical state of each component element of the catalyst is very complicated and it has not been fully disclosed in what chemical state each element is present in the catalyst. However, it is believed that each component is not present in the form of a bare and bare oxide, but that the catalyst is in the form of a heteropoly acid compound and that the ammonium group is in the form of a salt of this heteropoly acid. According to the invention, it is not preferred that all the heteropoly acid in the catalyst is combined with the ammonium group to form a salt, because the desired reaction does not proceed in this case.

In contrast, if each component is present in the form of a heteropoly acid without the formation of a salt with the ammonium group, the anionic structure of the heteropoly acid is rapidly decomposed to oxides, while the oxidation proceeds at a temperature above 300 ° C and the activity decreases. In this case, the activity of removing hydrogen from the unsaturated aldehyde is reduced and a high activity catalyst cannot be obtained. However, if the heteropoly acid with a proton-releasing activity and an ammonium salt thereof is present together in the catalyst, the anion structure can be maintained more stable in the heteropoly acid than in the case where only the heteropoly acid is present in the catalyst, with the result that the selectivity is improved and the catalyst lifetime can simultaneously extended.

When incorporating a metal element represented by X in the catalyst consisting of molybdenum, phosphorus, arsenic, an ammonium group and oxygen, the lifetime of the catalyst can be greatly improved. The reason for this is not fully elucidated, but given the known fact that the activity and selectivity of a molybdenum-containing catalyst are reduced as the concentration of adsorbed oxygen is reduced, it is interpreted as increasing the concentration of adsorbed oxygen by the presence of element X, and that the activity is therefore increased and the catalyst life is extended.

4

DK 155932 B

The present catalyst is heat treated at a temperature of 300-440 ° C before being used for the reaction. A preferred heat treatment temperature is in the range of 360-430 ° C. If the heat treatment temperature exceeds 440 ° C, both the activity and selectivity of the catalyst are diminished, and if the heat treatment temperature exceeds 460 ° C, the said reduction becomes very apparent. Thus, in the catalyst to be used in the process of the invention, there is a definite upper limit to the heat treatment temperature. On the other hand, the lower limit of the heat treatment temperature is not so critical, but at a heat treatment temperature below 300 ° C it is difficult to obtain a catalyst with stable properties. The heat treatment time varies depending on. heat treatment temperature, but generally it is preferred that the heat treatment be carried out for from 30 minutes to several days. It is desirable that the heat treatment be carried out in air or air diluted with an inert gas. If necessary, it is possible, as a treatment atmosphere, to use air in which a reducing agent is incorporated in a low concentration.

The preparation of the present catalyst can be carried out by known methods in the art. It is desirable that the starting materials be intimately mixed, but the mixing method is not very critical. By simply irregular distribution of the components being avoided, any of the conventional methods such as evaporation to dryness, precipitation, oxide mixture and the like can be used to prepare the catalyst.

As starting materials for the catalyst, ammonium compounds such as ammonium molybdate, ammonium phosphate, ammonium phosphomolybdate, ammonium arsenomolybdate, etc., elements represented by X are used in the form of oxides, nitrates, ammonium salts and the like, and the hydroxides and the like.

When the catalyst components are used in the form of ammonium salts, such as those mentioned above, the introduction of the ammonium group into the catalyst is achieved through such ammonium salts. In case no such ammonium salts are used as starting material,

s DK 155932 B

stepwise aqueous ammonia. Eg. For example, a homogeneous mixture for use in the preparation of the catalyst can be obtained by dissolving a previously used phosphorus-molybdenum-arsenic type catalyst in aqueous ammonia and adding the other metal components to the resulting solution.

A homogeneous mixture of the starting materials is dried and heat-treated at a temperature of 300-440 ° C for from 30 minutes to several days, thereby obtaining a catalyst in which the ammonium group is incorporated. The incorporated amount of the ammonium group in the catalyst is 0.01-0.3 molecules per minute. atom molybdenum.

As another method for introducing the ammonium group into the catalyst, there may be mentioned a method which consists in treating a deactivated catalyst with ammonia or aqueous ammonia. For example, If a catalyst which is deactivated by use at high temperature or for a long time is treated in a reaction vessel with liquid or gaseous aqueous ammonia, a prescribed amount of the ammonium group may be introduced.

The catalyst used in the process of the invention can be introduced into the reaction in supported form on an inert carrier such as alumina, silicon carbide and perlite, or in dilute form with such an inert substance. If the content of such a carrier is too high in the total catalyst mixture, the apparent activity of the catalyst is diminished; therefore, it is desirable that the content of the carrier in the total catalyst mixture be less than 70% by weight.

The type of reaction vessel in which the above catalyst is packed is not very critical and either a fixed bed reaction vessel or a fluid bed reaction vessel can be used in the process of the invention.

The unsaturated aldehyde to be oxidized by the process of the invention comprises acrolein and methacrolein, and if desired, a mixture of acrolein and methacrolein can be used as starting material. The process of the invention is particularly effective for the oxidation of methacrolein. Methacrolein obtained at 6

DK 155932 B

catalytic oxidation of isobutylene or tertiary butanol can be used as is or after it is purified.

The concentration of the unsaturated aldehyde in the feed gas can be varied within a wide range, but it is generally preferred that the concentration of the unsaturated aldehyde is in a range of 1-20% by volume, especially 3-15% by volume. Molecular oxygen is used as the oxidizing agent in the process of the invention, and from an economic point of view it is preferable to use air. If necessary, air enriched with pure oxygen may be used. "It is preferred that the concentration of oxygen in the feed class, expressed by the molar ratio to the unsaturated aldehyde, is within a range of 0.3-4, especially 0.4-2, 5th

The gaseous starting mixture can be diluted with such inert gases as nitrogen, steam, carbon dioxide and the like.

The oxidation reaction is carried out under pressure from atmospheric pressure to several atmospheres. The space velocity of the feed gas varies depending on the reaction temperature and pressure, but it is generally preferred that the gaseous starting mixture be supplied at a space velocity of 300-10,000 h ”1. The reaction temperature is selected within a range of 240-390 ° C, but it is generally preferred to carry out the reaction at 270-340 ° C. One of the prominent features of the invention is that the oxidation reaction can be carried out at such a low temperature.

The process according to the invention is illustrated in more detail by the following examples. In these examples, all "portions" are by weight and the selectivity to the unsaturated carboxylic acid is expressed by the percent ratio of the amount (mole) of the unsaturated carboxylic acid formed to the amount (mole) of the unsaturated aldehyde reacted. The reaction time was measured from the time when the reaction conditions described in the examples were actually established.

7

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EXAMPLE 1 177 parts of ammonium paramolybdate were disclosed in 500 parts of pure water held at ca. 60 ° C and 9.6 parts of 85% phosphoric acid and 10.5 parts of a 50% aqueous solution of arsenic acid were added to the above solution. Then a solution of 4.88 parts of ammonium metavanadate in 150 parts of water was added to the above mixture. The resulting mixed solution was subjected to evaporation to dryness by heating with stirring, and the resulting solid was dried at 150 ° C for 16 hours. The dried solid was pulverized in a ball mill, die-cast, placed in an electric oven and heat treated. The heat treatment was carried out by raising the temperature from 100 ° C to 400 ° C at a rate of 20 ° C per minute. hour and maintaining the solid at 400 ° C for 16 hours. The catalyst thus obtained contained the phosphorus and metal components in the following atomic ratio:

MolP0.083As0.037V0.042 0.078

This catalyst was packed in a solid-bed type reaction vessel and maintained at 295 ° C, and a gaseous mixture consisting of 5 volume% methacrolein, 5 volume% oxygen, 20 volume% vapor and 70 volume% nitrogen was introduced into the reaction vessel. space velocity of 2,000 h. Under the above conditions, the reaction was carried out for a long time. At prescribed intervals, samples of the reaction gas discharged from the reaction vessel were collected, which were analyzed by gas chromatography or the like to examine the activity of the catalyst. The results are listed in Table 1.

8

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Table 1

Reaction Time Reaction of Selectivity to Methacrolein Methacrylic Acid (Hours) _ (#) (#) _ 4 57.1 84.9 240 58.0 85.2 480 57.7 85.5 960 57.5 85.8 1440 55.9 EXAMPLE 2

An oxidation of acrolein was carried out using the catalyst prepared in Example 1. The gaseous starting mixture consisted of 5 volume # acrolein, 5 volume # oxygen, 20 volume # steam and 70 volume # nitrogen. The reaction temperature was set to 300 ° C. The other working procedures and conditions were the same as in Example 1. The results of the experiment are summarized in Table 2.

Table 2

Reaction Time Reaction of Selectivity to Acrolein Acrylic Acid (Hours) (#) _ (#) _ 4 55.3 86.9 240 56.1 87.2 480 55.9 87.5 960 56.0 87.0 1440 55.1 86.7 EXAMPLE 5

A catalyst was prepared in the same manner as in Example 1, except that the aqueous arsenic acid solution was changed to 4.95 parts of arsenic acid anhydride, the aqueous solution of ammonium metavanadate was changed to a solution of 3.37 parts of ferric nitrate in 50 parts of water. and that the heat treatment conditions were changed 9

DK 155932B

so that the maximum temperature was 380 ° C and the time during which this maximum temperature was maintained was 24 hours. The atomic ratio of the phosphorus to the metal components of the resulting catalyst was as follows:

MolP0.083As0.05Fe0.0083 ^ 4 ^ 0.125

Using the catalyst thus obtained, an oxidation of methacrolein was carried out under the same conditions as in Example 1, except that the reaction temperature was changed to 305 ° C to obtain the results given in Table 3.

Table 3

Reaction Time Reaction of Selectivity to Methacrolein Methacrylic Acid (Hours) _ _ [2iL_ _iÉ_ 4 48.9 84.0 240 50.2 86.3 480 50.0 86.5 960 50.1 86.0 EXAMPLES 4-7

Catalysts were prepared in the same manner as in Example 1, except that the ammonium metavanadate used in Example 1 was changed to ammonium parawolframate or manganese nitrate, and in some examples the amount of arsenic acid added, the maximum heat treatment temperature, and / or the period during which the maximum temperature was maintained. , was modified as indicated in Table 4 below.

Using the catalysts thus prepared, oxidation of methagrolene or acrolein was carried out under the same conditions as in Example 1 or 2, except that the reaction temperature was changed as indicated in Table 4.

Catalysts, reaction conditions and test results are summarized in Table 4.

DK 155932 B

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DK 155932 B

EXAMPLE 8 11 204 parts of phosphoric molybdic acid (P 2 O 2 · 24 MoO 2 Then 75.0 parts of fine powder of stannic oxide was added to the solution. With stirring, 150 parts of 28% aqueous ammonia was incorporated into the resulting suspension and the resulting mixture was evaporated to dryness by heating. The following procedures were performed in the same manner as in Example 1, and in the final step. For example, the heat treatment was carried out at 400 ° C for 16 hours to obtain a catalyst. The atomic ratio of the phosphorus to the metal components of the resulting catalyst was as follows:

MolP0.083As0.049Sn0.5 ^ tube4 ^ 0.062

Using these catalysts, oxidation of methacrolein was carried out under the same conditions as in Example 1, except that the reaction temperature was changed to 320 ° C to obtain the results set out in Table 5.

Table 5

Reaction Time Reaction of Selectivity to Methacrolein Methacrylic Acid (Hours) (%) (%) 4 78.9 84.1 480 81.3 85.2 960 81.1 85.6 Example 9

Using the catalyst prepared in Example 8, an oxidation of acrolein was carried out under the same conditions as in Example 2, except that the reaction temperature was changed to 325 ° C to obtain the results set forth in Table 6.

DK 155932B

Table 6 12

Reaction time Reaction of Selectivity to acrolein acrylic acid (hours) (%) _. (%) 4 83.4 85.9 480 83.2 86.2 960 84.0 86.0 EXAMPLES 10 - 12

Catalysts were prepared in the same manner as in Example 1 except that the added amount of ammonium metavanadate was changed to 2.94 parts and that after the addition of ammonium meta-vanadate, further: 3.37 parts of ferric nitrate, 2.24 were added. parts of ammonium parawolframate or 23.1 parts of manganese nitrate in 50 parts of pure water.

Using the catalysts thus prepared, oxidation of methacrolein was carried out under the same conditions as in Example 1, except that the reaction temperature was changed as indicated in Table 7 below.

Catalysts, reaction conditions and test results are summarized in Table 7.

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Catalysts were prepared in the same manner as in Example 1, except that the ammonium metavanadate used in Example 1 was changed to ammonium parawolframate and that, after the addition of ammonium parawolframate, an aqueous solution of a copper, iron or nitrate solution was further added. manganese. The atomic ratio of arsenic and heat treatment conditions was changed somewhat as indicated in Table 8 below.

Using the catalyst thus prepared, oxidation of methacrolein or acrolein was carried out under the same conditions as in Example 1 or 2, except that the reaction temperature was changed as indicated in Table 8.

Catalysts, oxidation conditions and results are summarized in Table 8.

DK 155932 B

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16 DK 155932B

EXAMPLES 18 - 21 204 parts of phosphoric molybdic acid were dissolved in 500 parts of pure water and 28.2 parts of a 30% aqueous solution of arsenic acid were added. Then, a solution of 10.1 parts of ferric nitrate in 50 parts of pure water was added to the above solution and an additional 25.0 parts of fine powder of stannic oxide was added. With stirring, 150 parts of 28% aqueous ammonia was incorporated into the resulting suspension and the mixture was evaporated to dryness by heating. The subsequent procedures were carried out in the same manner as described in Example 1, and in the final step the heat treatment was carried out, at 400 ° C for 5 hours, to obtain a catalyst containing iron and tin.

Catalysts containing tin and tungsten, vanadium or manganese were prepared in the same way as above except that ferrin nitrate was replaced with ammonium parawolframate, ammonium meta-vanadate or manganese nitrate.

Using the catalysts thus prepared, oxidation of methacrolein or acrolein was carried out under the same conditions as in Example 1 or 2, except that the reaction temperature was changed as given in Table 9 below.

Catalysts, oxidation conditions and test results are summarized in Table 9 ·

17 DK 155932 B

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DK 155932 B

Catalysts were prepared in the same manner as in Example 1, except that the ammonium metavanadate used in Example 1 was replaced by copper nitrate, and after addition of an aqueous solution of copper nitrate, an aqueous solution of lithium nitrate, sodium nitrate, potassium nitrate, rubidium nitrate was further added. or cesium nitrate In some examples, the amount of arsenic acid added, the maximum heat treatment temperature and / or the period during which the maximum temperature was maintained was changed as indicated in Table 10 below.

Using the catalysts thus prepared, oxidation of methacrolein or acrolein was carried out under the same conditions as in Example 1 or 2, except that the reaction temperature was changed as indicated in Table 10.

Catalysts, oxidation conditions and test results are summarized in Table 10.

19; DK 155932B

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DK 155932B

Comparative Examples 1 and 2

A catalyst was prepared in the same manner as in Example 1, except that no ammonium metavanadate was added at all.

Using the catalyst thus obtained, oxidation of methacrolein or acrolein was carried out under the same conditions as in Example 1 or 2, except that the reaction temperature was changed to 300 ° C.

The results are summarized in Table 11.

Table 11

Comparative Initial Reaction Reaction Selectivity Ecaldehyde Time (%) (%) Sample No.__ (Hours) _ 1 Methacrolein 4 55.0 85.5 120 54.6 84.2 240 55.2 85.3 480 52.1 83.7 2 Acrolein 4 49.3 87.2 120 48.4 87.0 240 48.7 86.5 480 46.2 86.9

As can be seen from the results set forth in Table 11, with this comparison catalyst, the reaction or both the reaction and the selectivity tended to decrease to some extent by the time 480 hours had elapsed from the beginning of the reaction. In contrast, in the case of catalysts in which at least one metal was selected from vanadium, tungsten, copper, iron, manganese and tin, optionally together with an alkali metal element, as shown by the results in Tables 1-10, , hardly observed such a trend, even if the reaction was carried out for a much longer time.

4

Claims (7)

A process for preparing acrylic acid or methacrylic acid. by catalytic oxidation of acrolein or methacrolein in the gas phase at a temperature of 240-390 ° C with molecular oxygen, characterized in that the catalytic oxidation is carried out in the presence of a catalyst having a composition represented by the following general formula: P MOvAs (NH ), X Yf0 abc '4 d efg wherein a, b, c, e, f and g represent an atomic ratio for each component with a being within a range of 0.03 - 0.2, b being 1, c being within a range of 0.015 - 0.15, e is within a range of 0.003 - 1, f is within a range of 0 - 0.17, and g has a value determined by the valence of the elements present in the catalyst, while d means the number of ammonium groups within a range of 0.01 - 0.3, X means at least one metal selected from vanadium, tungsten, copper, iron, manganese and tin, and Y means at least one alkali metal element selected from lithium, sodium , potassium, rubidium and cesium. Process according to claim 1, characterized in that the catalyst is used in a supported state on a support. Process according to claim 1, characterized in that the catalyst is heat treated at a temperature of 300-440 ° C. Process according to claim 1, characterized in that the unsaturated aldehyde is methacrolein. Process according to claim 1, characterized in that the metal X is copper. Process according to claim 1, characterized in that the catalyst is composed of a heteropoly acid of each metal component and an ammonium salt thereof. 22 DK 155932B Method according to any one of the preceding claims, characterized in that f is within a range of 0.001 - 0.12 and d is within a range of 0.01 - 0.2.