CS196317B2 - Method of producing acrylic or methacrylic acid - Google Patents

Abstract

1526365 Unsaturated carboxylic acids STANDARD OIL CO 18 Aug 1976 [18 Aug 1975] 34384/76 Heading C2C (Meth)acrylic acids are prepared by the oxidation of (meth)acrolein with molecular oxygen in the vapour phase at 200‹ to 500‹ C. in the presence of a catalyst of empirical formula where A is at least one of rubidium, thallium, cesium, arsenic, titanium, and potassium, a is a positive number less than 3, b is 0 to 3, c is a positive number less than 2, and X is the number of oxygens required by the valency state of the other elements present, and wherein at least part of the molybdenum used in the preparation of the catalyst is in the form of molybdenum trioxide. Preferred catalysts use rubidium, thallium, titanium, cesium, potassium and arsenic and examples are described with A 0À5 Mo 3 P 0À33 O x as the catalyst.

Description

The present invention relates to a process for the production of acrylic or methacrylic acid by oxidation of acrolein or methacrolein.

U.S. Patent No. 3,882,047 and Japanese Patent No. 4,733,082 protect catalysts that are suitable for oxidizing unsaturated aldehydes to unsaturated acids, wherein the catalysts are prepared in aqueous phosphomolybdic acid solution. The US patent protects catalysts based on molybdenum, phosphorus and at least one element selected from the group consisting of thallium, rubidium, cesium and potassium and at least one element selected from the group comprising chromium, silicon, aluminum, iron and titanium. Japanese Patent No. 4,733,082 protects molybdenum, phosphorus and at least one element selected from the group consisting of arsenic, boron, silicon, cadmium, lead, tungsten, thallium, indium, germanium and tin. The present invention is. the result of seeking more efficient catalysts useful in the oxidation of acrolein or methacrolein to acrylic or methacrylic acid. .

According to the invention, a process for the preparation of acrylic or methacrylic acid by oxidation of acrolein or methacrolein with molecular oxygen in the vapor phase at a reaction temperature of 200 to 500 ° C in the presence of an oxide catalyst and optionally in the presence of steam has been discovered.

A _and Cr _{b of} MosPcOx (I) where represents

And at least one element selected from the group consisting of rubidium, thalium, cesium, arsenic, titanium and potassium, and a positive number less than 3b 0 to 3, c a positive number less than 2, x the number of oxygen atoms corresponding to the valence of the other elements present The molybdenum used for preparing the catalyst is in the form of molybdenum oxide.

An unexpected improvement is achieved in the yield of acrylic or methacrylic acid using the catalysts of the present invention when molybdenum trioxide is introduced into the catalyst as compared to using catalysts prepared from phosphomolybdic acid.

In the present invention, the most important process is the preparation of the catalyst used. In the present invention, the most important is the introduction of molybdenum trioxide into the catalysts. The main advantage is that the stability, activity and selectivity of the catalyst is greatly enhanced if:. at least a portion of the molybdenum used in the preparation of the catalyst is supplied in the form of molybdenum oxide.

In a preferred process of the invention, at least 25% of the molybdenum used to prepare the catalyst is introduced in the form of molybdenum oxide. However, it is even more preferred to introduce at least 50% of the molybdenum used in the preparation of the catalyst in the form of molybdenum oxide.

However, the catalysts of the present invention are of utmost importance in the preparation of which all the molybdenum used is introduced in the form of molybdenum oxide; optimum results are achieved with them.

In the preparation of the catalysts according to the invention, molybdenum oxide can be introduced in a variety of ways. All of these techniques are known to those skilled in the art. When preparing the catalyst, molybdenum oxide may be introduced before or after the addition of the other components.

The most preferred process of the present invention is to reflux an aqueous molybdenum oxide suspension.

As already mentioned, catalysts derived from the process of the invention are used. from said empirical formula. Catalysts. can. prepared by a variety of methods known to those skilled in the art, such as co-precipitation of soluble salts, evaporative drying or mixing of oxides followed by calcination of the resulting catalyst. In the present invention, the manner in which the catalyst is prepared is not critical.

A preferred method of preparing the catalyst of the invention comprises refluxing an aqueous suspension of molybdenum trioxide for one and a half to three hours, followed by the addition of phosphorus-containing compounds and the remaining catalyst components; welding the aqueous mixture to a thick paste; air drying at 110-120 ° C; crushing and sorting the resulting product for testing purposes. Apart from molybdenum, it is preferred to use soluble salts of the catalyst components, but insoluble salts or oxides may also be used. Suitable phosphorus compounds which may be used in the preparation of the catalyst include orthophosphoric acid, triphosphoric acid, phosphorus tribromide, phosphorus pentachloride and the like. The remaining catalyst components may be added in the form of oxides, acetates, formates, sulfates, nitrates, carbonates and the like.

Preferred catalysts of the invention are those prepared by adding compounds containing phosphorus, chromium and at least one A-labeled component to a refluxing aqueous molybdenum oxide suspension. Even more preferred are catalysts in the preparation of which phosphorus-containing compounds and at least one A-labeled compound are added to a refluxing aqueous suspension of molybdenum trioxide. However, the most preferred catalysts are phosphorus and at least one catalyst. an element selected from the group consisting of thibidium, cesium and thallium.

The reactants in the process of the invention are acrolein. or methacrolein and molecular oxygen. Molecular oxygen is normally supplied to the reaction mixture in the form of air, but gaseous oxygen may also be used. Normally, 0.5 to 0.5 is added. . 10.. mole of oxygen per mole of acrolein or methacrolein.

Optionally, steam or an inert diluent is added to the reaction mixture. Preferably, the reaction is carried out with a substantial amount of steam in the range of 2 to 20 moles of steam per mole of acrolein or methacrolein.

The reaction temperature may vary depending on the catalyst used. Temperatures of 200-500 ° C are normally used, temperatures of 250-400 ° C being preferred.

The reaction may conveniently be carried out in a solid-bed reactor or in a fluidized-bed reactor. The contact time may be a fraction of a second or up to 20 seconds or more, but a contact time of 4 to 5 seconds is preferred. The reaction may be carried out at atmospheric pressure, or a pressure that is higher or lower, preferably an absolute pressure of 50 to 400 kPa is preferred.

When used in a reactor, the catalyst may be supported or a catalyst without support. Suitable carriers include silica, alumina, boron, phosphate, zirconia, titanium dioxide, and the like, but zirconia is preferred.

The examples which follow describe the preparation of catalysts which are suitable for the process according to the invention, but do not limit the scope of the invention. A preferred reaction of the invention is the oxidation of methacrolein to methacrylic acid. However, the process of the invention can also convert acrolein to acrylic acid.

Example 1, Comparative Examples A, B and C describe a process for preparing methacrylic acid using catalysts using molybdenum in the form of molybdenum oxide as compared to catalysts using different sources of molybdenum.

The catalyst is prepared in the following ways:

Example 1

Preparation of catalyst from molybdenum trioxide

An aqueous suspension is prepared by adding 35.3 grams of molybdenum trioxide to 1 liter of boiling distilled water with stirring; the suspension is boiled for 2 hours. To this aqueous suspension was added 4.9 g of 85% phosphoric acid; the color of the suspension changes to yellow 196317 tou. About 200 mL of distilled water is added to maintain a volume of about 800 mL of solution. After about 1 hour or 1.5 hours after the addition of 85% phosphoric acid, the color of the suspension changes to a bright yellow-green color; 100 ml of distilled water is then added again to maintain the desired volume of the solution. To this aqueous mixture was added 7.5 g rubidium carbonate; the suspension becomes brilliant yellow. After 30 minutes, 25 mL of distilled water was added. The catalyst is heated with stirring, evaporated to dryness and air-dried at a temperature of about 110 ° C.

Comparative example

Preparation from phosphomolybdic acid

An aqueous solution is prepared by dissolving 118.3 grams of phosphomolybdic acid in about 1400 milliliters of distilled water. To this solution was added 1.92 g of 85% phosphoric acid. The light yellow solution was boiled for 8 hours and stirred without heating for 12 hours. Resume heating, add 11.6 g of rubidium carbonate and quickly turn a bright yellow color. The aqueous mixture was evaporated to dryness and air-dried at 110 ° C overnight.

Comparative example В

Preparation from ammonium heptamolybdate

Suspension consisting of 105,9 g of ammonium heptamolybdate of formula (ΝΗ4) 6Μθ7θ24.4 H2O

7.7 g of 85% phosphoric acid and 1400 ml of distilled water are boiled with stirring. The color of the suspension changes slowly from pale yellow to white. After boiling, the suspension was stirred for 12 hours without heating. Resume heating and add 11.6 g of rubidium carbonate; the color of the aqueous mixture remains white. The aqueous mixture was evaporated to dryness and air dried at 110 ° C overnight.

Comparative Example

Preparation from molybdic acid

This catalyst was prepared in the same manner as described in Comparative Example V except that it was used

7.7 g of 85% phosphoric acid and ammonium heptamolybdate are replaced by 101.6 g of molybdic acid.

Catalysts prepared as described in Example 1 and Comparative Examples A, V and C are crushed and screened to separate 20 to 30 mesh particles. A portion of these catalyst particles is introduced into a 20 cm reactor with a solid layer consisting of

1.3 cm stainless steel tubes equipped with a 0.3 cm axial heat source. The reactor is heated to a reaction temperature of 343 ° C with air flow and a 1: 6.2: 5.2 mixture of methacrolein, air and steam is introduced into the reactor and passed over the catalyst for 4.6 seconds.

In Comparative Examples V and C, the catalysts were calcined at 430 ° C for 1 hour and then the temperature was lowered to 343 ° C. The reactor is then operated under reaction conditions for 1.6 hours and then the product is washed from the reactor into two series of water washers. The contents of the washers were then pooled and diluted to 100 ml for analysis and titration. The washed, fixed gases are dried and analyzed on a conventional column system (Houdry). The test results are shown in Table 1.

The following relations are used to assess the results:

percent yield per pass the methacrylic acid obtained Established methacrolein -x100 % conversion reacted methacrolein introduced methacrolein -x100 % selectivity the methacrylic acid obtained Reacted methacrolein -x100

Examples 2 to 5

Effect of catalytic activity using a catalyst of formula

КЬо ^ МОзРодзОх for operating hours

The catalyst was prepared as described in Example 1 and the conversion of methacrolein to methacrylic acid was determined using the methacrolein reaction. The results are shown in Table 2.

198317

Table 1

Preparation of methacrylic acid using an Rbo.5M03Po.33Ox catalyst prepared by the process of the present invention from an acidic example. Molybdenum to Molybdenum Source Compared to Catalysts Prepared Using Various Molybdenum Sources

Results in% total yield selectivity of thacrylic acid conversion per pass

1 molybdenum oxide 97.9 62.2 63.5 comparative fosfomolebdic acid 96.0 59.6 62.0 comparative В ammoniumheptamolybdate 84.9 47.1 54.8 comparative C * molybdic acid 80.5 43.1 53.5

* in operation for 4.2 hours

Table 2

Influence of operating time on catalytic activity

Example Operating hours total 2 4.3 98.1 3 16.5 96.0 4 64.4 96.4 5 94.0 95.5

Examples 6 to 10

Preparation and use of various catalysts according to the invention

Various catalysts of the invention are prepared; these catalysts have the formula

Аи.дМОзРо.ззОх

Results in% conversion yield of methacrylic acid tivita in one pass

62.563,7

69.572,4

71.676,5

70,072,2

The catalysts were prepared as described in Example 1, except that 86.2 g of molybdenum trioxide was used and

7.7 g of 85% phosphoric acid. The element, indicated by A, is added after the addition of phosphoric acid. The following compounds were used in the amounts indicated for the preparation of the catalysts:

Element Compound Quantity

thalium thallium acetate 26.3 titanium titanium dioxide 7.19 cesium cesium acetate 19.2 potassium potassium acetate 9.81 arsen arsenic oxide 9.9

After the addition of the element referred to as A, the catalyst is evaporated to dryness under boiling and dried as described in Example 1. The catalysts are then crushed and screened and tested as described above. The results of using methacrolein oxidation catalysts are shown in Table 3.

Table 3

Preparation of methacrylic acid from methacrolein

Example Catalyst Reaction temperature ° C total conversion Results in% yield selectivity methacrylic acids in one pass 6 Т1о, 5МозРо, ззО _х 343 91.9 51.0 54.4 7 Tiq ^ MOjPqjjOx 329 76.8 40.2 51.7 8 CSo _f 5Mo ₃ Po330 _x 343 98.8 58.2 58.9 9 Ко /) Мо ₃ Ро, ззОх 371 69.5 39.4 59.1 10 А8о, 5МОзР ₀ , ззО _х 355 78.0 56.0 76.0

SUBJECT OF THE INVENTION

Claims (9)

Process for the production of acrylic or methacrylic acid by oxidation of acrolein or methacrolein with molecular oxygen in the vapor phase at a temperature of 200 to 500 ° C and optionally in the presence of steam, characterized in that a catalyst of empirical formula I is used _А а СгьМозР с О х [I) wherein represents And at least one element selected from the group consisting of rubidium, thalium, cesium, arsenic, titanium and potassium, and a positive number less than 3, b 0 to 3, c a positive number less than 2, x the number of oxygen atoms corresponding to the valence of the other elements present part of the molybdenum used to prepare the catalyst is supplied in the form of molybdenum oxide. 2. Process according to claim 1, characterized in that at least 50% of the molybdenum used for the preparation of the catalyst is supplied in the form of molybdenum oxide. 3. The process of claim 1 wherein all of the molybdenum used to prepare the catalyst is supplied in the form of molybdenum oxide. 4. A process according to claim 1, wherein the catalyst is prepared from an aqueous suspension of molybdenum trioxide. 5. A process according to claim 1, wherein a catalyst of empirical formula I is used, wherein A is arsenic and b is zero. 6. The process of claim 1, wherein a catalyst of empirical formula I is used wherein A is at least one element selected from the group consisting of rubidium, cesium and thallium and b is zero. 7. The process of claim 1, wherein the catalyst is prepared by adding phosphorus, chromium, and at least one compound containing the element of symbol A to a refluxing aqueous molybdenum oxide suspension. 8. The process of claim 1, wherein the catalyst is prepared by adding a phosphorus-containing compound and at least one compound containing an element of symbol A to a refluxing aqueous molybdenum oxide suspension. 9. A process according to claim 1, wherein a catalyst of the formula is used