CS196364B2 - Process for preparing acrylic acid - Google Patents

Abstract

This invention relates to a process for the preparation of acrylic acid from acrolein by catalytic oxidation in the gas phase with molecular oxygen or an oxygen-containing gas.

Description

The present invention relates to a process for preparing acrylic acid from acrolein by gas-phase catalytic oxidation with molecular oxygen or oxygen-containing gas.

Thus, the present invention provides a process for preparing acrylic acid by reacting acrolein gas with molecular oxygen or oxygen-containing gases at a temperature of 200 to 370 ° C and a contact time of 0.5 to 5 seconds in the presence of a solid catalyst consisting of molybdenum, vanadium, cobalt and optionally tungsten, wherein said elements are chemically bonded to oxygen and the atomic proportions of the elements ^x are expressed by the empirical formula 'Mo ₁₂ V' _and W _b CO _c O _d '.

where a denotes a number 1.5 to 3.0, b number 0 to 0.5, c number 3.5 to 5.5, d number Corresponding valency of the other elements, which is carried out by using a catalyst prepared from an aqueous a solution of soluble salts of said elements by co-precipitation at a pH of 2 to 5 and at a temperature of 20 to 90 ° C by adding a solution containing molybdenum, vanadium or tungsten in the form of ammonium salts to the solution containing cobalt nitrate.

This empirical catalyst formula captures the atomic proportions of the individual elements in the catalyst and does not reflect the actual chemical bond between the elements.

The oxidation of unsaturated aldehydes to the corresponding acids on molybdenum, vanadium, tungsten, cobalt and oxygen containing catalysts is already known in the art. In particular, U.S. Pat. No. 3,736,354 discloses a catalytic system consisting essentially of molybdenum, vanadium and oxygen with one or more of tungsten and cobalt. All these catalysts are prepared by drying solutions containing salts of catalytically active elements together with silica salt or impregnating the preformed carrier with a suitable solution. .

Surprisingly, however, it has now been found that a catalyst comprising molybdenum, vanadium, cobalt and optionally tungsten, prepared by coprecipitation, has unexpectedly improved properties in the preparation of acrylic acid from acrolein; the improvement of the catalytic properties is apparent from a comparison of the results obtained by the method of Examples 1 and 5 and Comparative Examples 1a and 5a.

In addition, it has been found that the catalyst prepared by coprecipitation is generally characterized by a solid stoichiometry expressed by sho196364 and by the above formula with atomic indices determining the preferred range.

The precipitation conditions and especially the concentration of the salts containing the active elements and their ratio in the starting solutions influence the slightly stoichiometric composition of the precipitate. Examples 2, 3; 5, 6 and 7 show that even when the starting salts are precipitated in ratios very different from the preferred ratio, the composition of the precipitate slightly differs from the preferred composition without affecting the catalytic activity. This shows that co-precipitation of small amounts of free oxides derived only from a portion of the excess salts introduced.

The process for preparing the catalyst is important for achieving optimal catalytic activity and the catalyst is prepared by coprecipitation.

The catalyst may be used without a carrier or with a suitable carrier, such as silica, alumina, silica-alumina systems, silicon carbide, pumice, etc., using the most appropriate techniques generally known to those skilled in the art of catalyst preparation.

The catalyst of the invention is prepared from two liquid aqueous solutions of some of the soluble salts of the elements that form the catalyst.

The first solution containing cobalt, preferably in the form of nitrate, is subjected to vigorous stirring and a second solution containing molybdenum, vanadium and optionally also tungsten, preferably in the form of ammonium salts, is added thereto.

Since the catalytic activity of the precipitate mass does not depend on the concentration of the salts containing the catalyst constituents and does not depend on their ratio in the starting solutions, it is not necessary to prepare these solutions in stoichiometric ratios. the yields can then be 90% higher.

The pH at shunting is 2 to 5 and the temperature may be 20 to 90 ° C; a temperature of 50 to 70 ° C is preferred.

The precipitation time is not critical to obtaining a good catalyst; it can vary over a very wide range depending on the amount of salt to be treated: generally this time is 1-5 minutes to three hours.

After the precipitation is complete, the mass is separated from the solution, washed and subjected to numerous air processing operations, including drying at 90 to 130 ° C for 10 to 20 hours, followed by calcination at 200 to 300 ° C. for six and%. 24 hours and activation at 350 to 450 ° C for no less than two hours.

The process according to the invention can be carried out in any type of reactor suitable for carrying out gas phase oxidation; bucB solid or fluidized bed reactors may be used.

acroleimv conversion% = ·

The reaction temperature is 200 to 370 ° C, the reaction can be carried out at atmospheric pressure or, for example, at a pressure of up to 10 bar.

The contact time, defined as the ratio between the apparent volume of catalyst and the volume of gas introduced under the reaction conditions, in the time unit corresponds to 0.5 to 5 seconds.

The acrolein concentration is preferably 2.5 to 8.5% by volume with respect to the feed mixture. The molar ratio between oxygen and aldehyde is preferably 0.5 to 6. The oxygen required for the oxidation process can be introduced in pure form. However, if there are no particular reasons for this, air is the preferred oxidizing agent.

The oxidation of acrolein is preferably carried out in the presence of one or more diluents such as nitrogen, carbon dioxide, water vapor, etc. Of the possible diluents, water vapor is a particularly preferred diluent. The water vapor concentration is preferably. 20 to 50% with respect to the feed mixture.

The following examples illustrate the process according to the invention, but do not limit it in any way. The terms "conversion" and "selectivity" have the following meanings:

moles of acrolein introduced - moles of unreacted acrolein moles of acrolein introduced moles of carbon in the product grams of carbon in the reacted acrolein in the examples are percentages and parts by weight. unless otherwise stated.

Example 1

Catalyst of composition

MoijVgGo ^ i.

are prepared as follows:

164.9 g of cobalt nitrate hexahydrate and deionized water up to a volume of 240 ml are introduced into a 2-liter flask. Dissolution occurs at room temperature with continued stirring; the final pH of the solution is 2.2.

Separately, a solution 2: 82.4 g sloučeniny'molybdenu formula (NHajzMozQz and 34.0 g of vanadium compounds of formula NH4VO5 in an amount of deionized water to a final solution volume was 760 ml, the solution is prepared at 70 ^ia D.

In both solutions catalyst element elements are present in atomic proportions represented by the theoretical formula selectivity with respect to product =.

198364

MOizVž.iCcbj.

Into the first solution heated to 50 ° C. 60 ° C while stirring, an expensive solution was added over 60 minutes. It is then agitated for a further 15 minutes. The resulting precipitate was filtered, washed with two liters of deionized Christians water, dried for 12 hours at 110 ° C then calcined ^for: for 12 hours at 250 DEG C. and then activated for 5 hours at 400 ° C per. reaching the activation temperature by heating at 2 ° C / min.

The precipitate yield, calculated with respect to the total amount of oxides of the elements introduced as salts into the starting solutions, is 90%. The solid obtained is crushed and a 60 to 00 mesh fraction is collected.

ml of catalyst in the form of a solid layer are introduced into a 10 mm diameter steel reactor whose temperature is controlled in a bath of molten salts. The gaseous mixture consisting of -5.5% acrolein, 59.5% air and 35% steam is carried out by the catalyst at a volumetric rate corresponding to a contact time of 1 second at 280 ° C.

The following results were obtained:

acrolein conversion 97.8% selectivity with respect to acrylic acid 93.3%

Example la

Catalyst of composition

M012V24C04J is prepared as follows:

An aqueous solution of ammonium dimebidate and ammonium metavanadate, prepared from the amounts shown in Example 1, is added together with 13 ml of ammonium hydroxide (32%) to a porcelain vessel to which an aqueous solution of cobalt nitrate or according to Example 1 is added.

Evaporate to dryness on a water-bath with stirring; the solid obtained is dried at 110 ° C for 12 hours, calcined at 285 ° C for. 12 hours and finally activated for 5 hours at 400 degrees Celsius. The reaction test carried out as described in Example 1 but at 340 ° C (this temperature corresponds to the highest yield of acid) gives the following results:

acrolein conversion 95.2% selectivity with respect to acrylic acid ^x 59.4%

Example 1 a d 2

Catalyst of composition

MoijV + jCoí)!

is prepared and activated as described in. of Example I but using: 48.0 g of ammonium metavanadate of formula NH4VO3;

After coupling, the elements are contained in the atomic proportions corresponding to the theoretical formula * MOnVs.oCo, ^! ·

In the reaction test described in Example 1, the following results are obtained:

acrolein conversion .100% selectivity with respect to acrylic acid 92.5%

Example 3

Catalyst er composition

MG ₁₂ V _{1> 6} Co ₄ , ₆ is prepared and activated as described in Example 1, but using 16.0 g of ammonium meth-methanaidate.

After coupling, the elements are contained in the atomic ratios corresponding to the theoretical formula in both solutions

The reaction test is carried out as described in Example 1, but at a temperature of 300 ° C and the following results are obtained:

kotícerse acrolein 90.3% Selectivity to acrylic acid _in ¹ · 92.7%

He attaches

The catalyst of the composition was prepared and activated as described in Example 1, but with the addition of a solution of ammonium salts 7.1 g of ammonium tungstate with 90.6% tungsten oxide of the formula (NH4) 6-112W12O40. n H 2 O and using these amounts of other salts

168.9 · g CofNOojz. 6 H2O '

282.4 g (NH + zMozO?

38.9 g NH4VO3. .

After coupling, the elements are contained in the atomic ratios corresponding to the theoretical formula in both solutions

MOi2V2.4Wo, 2C04.2 ·

The catalytic activity was tested by the method described in Example 1 but at 300 ° C and the following results were obtained:

acrolein conversion 100% (selectivity with respect to acrylic acid 95.5%

Example 5 Composition catalyst

MO12V2.3W0.1CO4.2 was prepared and activated as described in Example 4, but using salts in the following amounts:

29.5 g Co (NH3) 2.6H2O

94.1 g (ΝΗ4) 2Μθ2θ7

10.8 g NH4VO3

47.2 g of ammonium tungstate containing

90.6% of tungsten oxide.

The volume of the solution containing cobalt nitrate is 450 ml, the volume of the second solution is 1000 ml.

After coupling, the elements are contained in the atomic ratios corresponding to the theoretical formula in both solutions

2'Οι 2 V2, o W4, οθ 02.2.

Catalytic activity was tested as described in Example 1 to give the following results:

acrolein conversion 99.4% selectivity with respect to acrylic acid 94.0%

Example 5a Catalyst of composition

M122V2.41 ^ 0.2 (104.2 was prepared by evaporating aqueous solutions

56.3 g Co (NO3) 2.6 H2O

94.12 g (ΝΗ4) 2Μθ2θ7

12.96 g NH4VO3

2.36 g of ammonium tungstate containing

90.6% of tungsten oxide.

The resulting solid is milled for 12 hours at 110 ° C, calcined for 12 hours at 300 ° C, and finally activated after 1 hour. for five hours at 400 degrees Celsius, ground and tested for catalytic activity as described in Example 1, but at 300 ° C. The following results were obtained:

acrolein conversion of 93.3% selectivity with respect to acrylic acid 84.9% at 28 ° C, on the other hand, obtained the following results:

acrolein conversion of 83.9% selectivity with respect to acrylic acid 87.2%

Example

Catalyst of composition

MO12V2.4 Wo, 2θθ5.1 was prepared and activated as described in Example 1, but using 253.5 g of cobalt nitrate as hexahydrate.

After connection, the elements are contained in both solutions. in atomic ratios corresponding to the theoretical formula

MO ^ V ^ Wo ^ CO ^.

The catalytic activity was tested as described in Example 1, but at 270 ° C. The following results were obtained:

acrolein conversion · 100% selectivity with respect to acrylic acid ¹ 93.8%

Example 7

Catalyst of composition

MO12V2.5W0.2C05.5 was prepared and activated as described in Example 1, but using 337.8 g of cobalt nitrate as hexahydrate.

After coupling, the elements are contained in the atomic ratios corresponding to the theoretical formula in both solutions

MOi2V2.5Wo, 2C08.4.

The catalytic activity was tested as described in Example 1, but at 300 ° C. The following results are obtained:

acrolein conversion of 99.0% selectivity with respect to acrylic acid 93.0%

196384

Claims (1)

* SUBJECT A process for the preparation of acrylic acid by reaction in the gas phase of acrolein with molecular oxygen or oxygen-containing gases at a temperature of 200 to 370 ° C and a contact time of 0.5 to 5 seconds in the presence of a solid catalyst consisting of molybdenum, vanadium, cobalt and optionally tungsten; said elements are chemically bonded to oxygen and the atomic proportions of the elements are expressed by an empirical formula Mo ₁₂ VW _b Có _c O ,, where denotes A number 1,5 to 3,0, b number 0 to 0,5, c number 3,5 to 5,5, d a number corresponding to the valence of the other elements, characterized in that a catalyst prepared from an aqueous solution is used soluble salts of said elements by precipitation at a pH of 2 to 5 and at a temperature of 20 to 90 ° C by the addition of a solution containing molybdenum, vanadium and optionally tungsten in the form of ammonium salts. into a solution containing cobalt disulphate.