JPS584696B2 - Method for producing unsaturated carboxylic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for producing a corresponding unsaturated carboxylic acid by subjecting an unsaturated aldehyde to a gas phase catalytic oxidation reaction in the presence of a catalyst. The present invention relates to a method for producing an unsaturated carboxylic acid, which is characterized by having a long life and using a catalyst.

Until now, patents proposed regarding catalysts for gas-phase catalytic oxidation reactions of unsaturated aldehydes have mainly focused on methods for producing acrylic acid from acrylic acid; There are few things to focus on.

In fact, many of the catalysts that show good performance in the oxidation of methacrolein have low activity even when applied to the oxidation of methacrolein.On the other hand, when the reaction is carried out at high temperature to increase the total reaction rate, the complete oxidation reaction (CO, CO2 Side reactions such as methacrylic acid (formation) occur significantly, and the yield and selectivity of methacrylic acid (per single pass) are low.

On the other hand, proposed oxidation catalysts for methacrolein either have low activity or have low productivity due to the possible reaction conditions, especially the need to lengthen the reaction time or reduce the methacrolein concentration in the feed gas. (Space-time yield: STY) is too low, or the active life of the catalyst is short, making it industrially unsuitable and not necessarily satisfactory.

Due to these circumstances, although the production of acrylic acid by the oxidation of acrolein is carried out industrially, it is quite difficult to produce methacrylic acid by the oxidation of methacrolein. has been done.

Therefore, when searching for a catalyst that is effective for oxidizing methacrolein, it is necessary to conduct research from a different perspective from that for the oxidation catalyst for acrolein.

The present inventors have improved the conventional drawbacks of methacrolein oxidation catalysts, and have improved the catalytic activity (i.e., the yield of the desired product).
As a result of intensive research aimed at searching for a new catalyst with excellent selectivity and productivity) and a long active life, the following catalyst was found to be extremely effective. The present inventors have discovered that it is similarly effective as an oxidation catalyst for other unsaturated aldehydes, and have completed the present invention.

That is, the present invention provides a method for producing an unsaturated carboxylic acid, which is characterized in that a mixed gas containing an unsaturated aldehyde and molecular oxygen is oxidized in the gas phase in the presence of a catalyst represented by the formula MOaPbBicXdYeOf. be.

In the above formula, X is at least one alkali metal selected from the group consisting of K, Rb and Cs, and Y is Ba,
At least one metal selected from the group consisting of Cd, W and Nb, a, b, c, d, e and f each indicate the number of atoms of each element, and when a = 12, a: b: c:d
:The value of e is 12:0.1~8:0.1~8:0.1~8
:0.1-8 is preferable, and 12:0.3-5:0.
3-5:0.3-5:0.3-5 is particularly suitable, f
is the number of oxygen atoms sufficient to satisfy the valences of MO, P, Bi, X, and Y.

The catalyst of the present invention is characterized by adding bismuth to a conventionally known phosphorus, molybdenum, and alkali metal catalyst, and further adding the above-mentioned Y component. According to this catalyst, it is stable under practical reaction conditions. Through this reaction, unsaturated carboxylic acids can be obtained from unsaturated aldehydes in high yield, high selectivity, and with good productivity.Furthermore, the problem of active life, which was unresolved with conventional catalysts, has been solved, and the catalyst has excellent properties over a long period of time. Since it exhibits high catalytic activity, continuous reactions can be carried out over a long period of time.

In addition, conventional catalysts generally require delicate preparation conditions and complicated operations, and therefore there is a melting point in the reproducibility of the catalyst, but the catalyst of the present invention has simple preparation conditions and always has good activity. of catalyst is obtained.

The catalyst used in the method of the present invention can be prepared by the so-called steam drying method, coprecipitation method, etc. known in this field.

Raw materials for each element used in the preparation of the catalyst include salts such as ammonium salts, nitrates, and halides of each element, free acids, acid anhydrides, condensed acids, oxides, and molybdenum such as phosphomolybdic acid. Examples include heteropolyacids and heteropolyacid salts such as ammonium salts thereof.

As a preferred method for preparing the catalyst, it is preferable to prepare the catalyst in such a manner that the components constituting the catalyst of the present invention can form a complex compound such as a heteropolyacid or its acid salt or ammonium salt.

Before use, the catalyst composition is calcined at a temperature of 250 to 700°C, preferably 350 to 600°C, in air, a reducing atmosphere, or a raw material composition gas for several hours to several tens of hours, and then used as a catalyst.

Further, during the reaction, the state of existence of each element, including oxygen, in the catalyst in a state where the catalyst is exhibiting catalytic action is not clear.

Here, an example of a catalyst preparation method is to add and mix an aqueous solution containing bismuth and a water-soluble compound of element Y to an aqueous solution containing ammonium molybdate, and then add an aqueous solution containing phosphoric acid and a water-soluble compound of element X to an aqueous solution containing ammonium molybdate. The catalyst is prepared by adding an aqueous solution containing it, steaming it to dryness with stirring, calcining it, pulverizing it, and then molding it into a suitable shape.

A method for preparing the catalyst can be selected as necessary by those skilled in the art.

The catalyst can be used as it is, but it can also be used after being deposited on a suitable carrier.

Examples of carriers include silicone carbide, silica,
Known materials such as alpha alumina, refractories, graphite, and titania may be used.

As the unsaturated aldehyde used in the method of the present invention, acrolein and methacrolein are preferred, and oxygen can of course be used alone as the molecular oxygen source, but air is industrially practical.

Additionally, gases that do not affect the reaction as diluents, such as water vapor, nitrogen, carbon dioxide, helium, argon, and saturated hydrocarbons (such as methane, ethane, fluoropane, phthane, and pentane), may be introduced into the reaction system. good.

The concentration of unsaturated aldehyde in the raw material gas is 1 to 25% by volume.
The ratio of unsaturated aldehyde to oxygen is preferably 1:0.1 to 25.0, preferably 1:0.1 to 20.0.
A range of is appropriate.

The reaction temperature is 300-500°C, preferably 330-45°C.
0℃, and reaction contact time (0℃, 1 atm standard)
A range of 0.1 to 20 seconds, preferably 0.1 to 15 seconds gives preferable results.

In the method of the present invention, the reaction pressure is not a particularly important factor, and the reaction can be operated at high pressures, but sufficiently good results can be obtained by operating at atmospheric pressure or slightly higher pressure. .

A fixed bed, a fluidized bed, a moving bed, etc. can be adopted as the reactor.

Moreover, the reaction product can be collected by known general methods.

For example, in order to separate and collect a desired unsaturated carboxylic acid, a method of condensing and liquefying it in a condenser and collecting it, a method of collecting it with a solvent, etc. are used.

The present invention will be specifically explained below with reference to Examples, and the definitions of the conversion rate of unsaturated aldehyde, yield and selectivity of unsaturated carboxylic acid in Examples are as follows.

All analyzes were performed using a gas chromatograph.

Example 1 (1) 212 g of ammonium molybdate in 300 ml
To this, an aqueous solution of 24.3 g of bismuth nitrate and 26.9 g of niobium oxalate dissolved in 200 ml of warm water was added and stirred.

Further, an aqueous solution in which 23 g of 85% phosphoric acid was dissolved in 50 ml of water and an aqueous solution in which 39.0 g of cesium nitrate was dissolved in 200 ml of water by heating were added, and the mixture was evaporated to dryness while stirring.

The obtained composition was heated in a Matsufuru furnace maintained at 450°C for 16
After being calcined for a period of time, it is pulverized and sieved to 4 to 6 mesh to obtain a catalyst.

MO:P:Bi:Cs in the catalyst composition thus obtained
:Nb:O atomic ratio is 12:2:0.5:2:0.5
:31 to 46 (Catalyst No. (1)) (The composition is omitted).

Similarly, using 13.1 g of ammonium paratungstate, 13.1 g of barium nitrate, or 15.4 g of cadmium nitrate in place of niobium oxalate, catalyst No. (2)～
No. (4) was prepared.

(ii) Same as (i), but instead of cesium nitrate, 29.5 g of rubidium nitrate or 20.2 g of potassium nitrate
Using catalyst No. (5)~No. (6) was prepared.

(iii) In the method of (i), some components were deleted and Comparative Catalyst No. (C-1)~No. (C-2) was prepared.

Next, 100ml of the catalyst was prepared with an inner diameter of 2.5cm and a length of 60cm.
Filled into a stainless steel reaction tube, heated in a metal bath, methacrolein:O2:N2:H2O=1:1.5:17.
A raw material gas having a composition of 5:10 (molar ratio) was heated for a contact time of 1.
The reaction was carried out for 8 seconds (0°C, 1 atm standard).

The results obtained are shown in Table 1. The reaction temperature is the maximum temperature of the catalyst layer when good results were obtained (the same applies hereinafter).

Example 2 Table 2 shows an example in which a long-term continuous reaction was carried out using the catalyst described in Example 1.

The reaction conditions are the same as in Example 1.

From Table 1 and Table 2, it can be seen that the catalytic activity of the catalyst of the present invention hardly decreases even after a long period of time, and therefore it is a catalyst with a long catalyst life.

In this reaction, the bath temperature was kept constant and the reaction was carried out continuously.

Example 3 Catalyst No. of Example 1 (1) and No. Using (2),
The oxidation reaction of acrolein was carried out under the same conditions as in Example 1, except that methacrolein was used as acrolein and the raw material gas composition was acrolein:O2:N2:H2O = 1:2:8:9 (molar ratio). .

As a result, catalyst No. In the case of (1), the reaction temperature is 410
℃ acrolein conversion rate 93.6%, acrylic acid yield 7
A result of 8.9% (same selection rate 84.3%) was obtained.

Also, catalyst No. In the case of (2), the reaction temperature was 415°C, the acrolein conversion rate was 92.7%, and the acrylic acid yield was 80.
A result of 1% (selection rate 86.4%) was obtained.

Claims (1)

[Claims] 1 A mixed gas containing an unsaturated aldehyde and molecular oxygen is mixed with (1) molybdenum, (2) phosphorus, (3) bismuth, (
4) at least one alkali metal selected from the group consisting of potassium, rubidium and cesium; (5) at least one metal selected from the group consisting of barium, cadmium, tungsten and niobium; and (6) a catalyst consisting of oxygen. A method for producing an unsaturated carboxylic acid, which comprises carrying out a gas phase catalytic reaction in the presence of an unsaturated carboxylic acid.