JPS5929179B2 - Method for producing methacrylic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention aims at producing methacrylic acid by producing the corresponding methacrylic acid by subjecting unsaturated aldehydes, especially methacrolein, to a gas phase catalytic oxidation reaction in the presence of a catalyst. The present invention relates to a method for producing methacrylic acid characterized by using a catalyst having excellent properties and a long active life.

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 acrolein, and patents have focused on methods for producing methacrylic acid from methacrolein. There are few that did. Even when catalysts that actually show good results in acrolein oxidation are applied to methacrolein oxidation, many of them have low activity.On the other hand, if the reaction is carried out at high temperature to increase the total reaction rate, complete oxidation reaction (co, CO2 production) ) and other side reactions occur significantly, resulting in low yield and selectivity of methacrylic acid (per single pass). On the other hand, proposed oxidation catalysts for methacrolein either have low activity or require lower possible reaction conditions, in particular longer reaction times and/or lower methacrolein concentrations in the feed gas. Therefore, the productivity (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, in searching for a catalyst effective for oxidizing methacrolein, it is necessary to conduct research from a different perspective from that for the oxidation catalyst of acrolein. The present inventors have improved the conventional drawbacks of methacrolein oxidation catalysts, and have developed a new catalyst that has excellent catalytic activity (i.e., yield, selectivity, and productivity of the desired product) and has a long active life. As a result of conducting intensive research for the purpose of searching for the following, the following catalyst was found to be extremely effective, leading to the completion of the present invention.

That is, the present invention provides a method for producing methacrylic acid, which is characterized in that a gaseous mixture containing methacrolein and molecular oxygen is oxidized in the gas phase in the presence of a catalyst represented by the formula M0aPbVcXdOe.

In the earth style, X is K. Rb. Cs,. At least one metal selected from the group consisting of Tl (excluding the case of potassium alone); b. c, d and e each indicate the number of atoms of each element, and when a=12, a:
The value of b:c:d is 12:0.1~8:0.1~8:0
．． 1 to 8 are preferred, and more preferably 12:0.3 to 5:0.3
5:0.3-5 is suitable, and e is MO. P. V. This is the number of oxygen atoms sufficient to satisfy the valence of X. According to the catalyst of the present invention, methacrylic acid can be obtained from methacrolein in high yield, high selectivity, and with good productivity through a stable reaction under practical reaction conditions. The problem of active life has been solved, and since the catalyst exhibits excellent catalytic activity over a long period of time, continuous reactions can be carried out for a long period of time.

In addition, conventional catalysts generally have delicate catalyst preparation conditions and require complicated operations, which makes it difficult to reproduce 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 evaporation to dryness 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,
Examples include oxides, heteropolyacids containing molybdenum such as phosphomolybdic acid, and heteropolyacid salts such as ammonium salts thereof. As a preferred method for preparing the catalyst, it is preferable to prepare the catalyst so 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, in a reducing atmosphere, or in a raw material composition gas for several hours to several tens of hours, and then used as a catalyst. Ru.

Note that during the reaction, the state of existence of each element, including oxygen, in the catalyst in a state in which the catalyst is exhibiting catalytic action is not clear. Here, an example of a catalyst preparation method is shown by adding and mixing an aqueous solution containing a vanadium compound to an aqueous solution containing ammonium molybdate brick*, and then adding an aqueous solution containing phosphoric acid and an aqueous solution containing a water-soluble compound of element X. is added and evaporated to dryness with stirring, then calcined, pulverized, and then molded into a suitable shape to form a catalyst. A method for preparing the catalyst can be selected as necessary by those skilled in the art. Although the catalyst can be used as is,
It can also be used by depositing it on a suitable carrier.

Examples of carriers include silicone carbide, silica,
Known materials such as alpha alumina, refractories, graphite, and titania can be mentioned. As the molecular oxygen source used in the method of the present invention, oxygen can of course be used alone, but air is industrially practical.

In addition, gases that do not affect the reaction as diluents, such as water vapor, nitrogen, carbon dioxide, helium, argon,
Saturated hydrocarbons (eg, methane, ethane, propane, butane, pentane, etc.) may be introduced into the reaction system. The concentration of methacrolein in the raw material gas is preferably in the range of 1 to 25% by volume, and the ratio of methacrolein to oxygen is 1:0.
A suitable range is 1 to 25.01, preferably 1:0.1 to 20.0. The reaction temperature is 300-500°C, preferably 330-450°C, and the contact time of the reaction (0
℃, 1 atm) τ is 0.1 to 20 seconds, preferably 0.
A range of 1 to 15 seconds gives favorable 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 a pressure slightly higher than atmospheric pressure. I can do it.

A fixed bed, fluidized bed, moving bed, etc. can be employed as the reaction apparatus. Moreover, the reaction product can be collected by known general methods. For example, in order to separate and collect the desired unsaturated carboxylic acid, a method of condensing and collecting it in a condenser, 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 methacrolein, the yield of methacrylic acid, and the selectivity in the Examples are as follows.

All analyzes were conducted using a gas chromatograph. Example 1 Ammonium molybdate 212y was dissolved in 300 ml of water under heating, and ammonium metavanadate 23.
200ml of 4y dissolved in 35.1y of oxalic acid in advance
Dissolve in a warm aqueous solution and stir.

Further, an aqueous solution in which 85% phosphoric acid 237 was dissolved in 50 ml of water and an aqueous solution in which cesium nitrate 39.07 was dissolved in 200 ml of water by heating were added, and the mixture was evaporated to dryness while stirring. The obtained composition is calcined for 16 hours in a Matsufuru furnace kept at 430°C, then pulverized and sieved into 4 to 8 meshes to form a catalyst. M in the catalyst composition thus obtained. :
The atomic ratio of P:Cs:V is 12:2:2:1. Similarly, instead of cesium nitrate, rubidium nitrate 29.5
The catalysts shown in Table 1 were prepared using 53.3y of thallium nitrate and 53.3y of thallium nitrate.

In addition, as a comparative example, catalysts shown in Table 1 were prepared in the same manner. However, among the comparative catalysts, the firing temperature of the catalyst containing no V component was 450°C. Furthermore, we prepared catalysts using ammonium chromate, ferric nitrate, nickel nitrate, cerium nitrate, or zirconium nitrate in place of phosphoric acid, and compared the performance of catalysts containing P components and catalysts not containing P components. I went.

Next, 100 m1 of the catalyst has an inner diameter of 2.501 rL and a length of 60 m.
Fill a stainless steel reaction tube with cTrL, heat in a metal bath, and mix methacrolein:02:N2:H2O-1:1.5.
:17.5:10 (molar ratio) of raw material gas was passed through the reactor for a contact time of 1.8 seconds (0° C., 1 atm standard) to react.

The results obtained are shown in Table 1. The reaction temperature is the highest temperature of the catalyst layer when good results were obtained (the same applies hereinafter). These results show that even with alkali metals, catalysts that contain sodium components instead of rubidium or cesium have significantly inferior performance, and catalysts that contain potassium components have significantly lower performance compared to the three elements of molybdenum, phosphorus, and vanadium. The results show that although the catalyst exhibits far superior performance, it is not as good as catalysts containing rubidium and cesium components.

Furthermore, catalysts containing chromium, iron, nickel, cerium, or zirconium components instead of phosphorus components have conventionally been used to
Although these catalysts are known as catalysts for producing methacrylic acid, these catalysts also have extremely poor performance and are found to be unsuitable for practical use as catalysts for producing methacrylic acid. Example 2 Example 1
The catalysts shown in Table 2 were prepared in the same manner as in Example 1.
The reaction was carried out under the same conditions.

The results obtained are shown in Table 2. Example 3 Table 3 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. In this reaction, the bath temperature was kept constant. From Table 3, 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.

Claims (1)

[Claims] 1 A mixed gas containing methacrolein and molecular oxygen,
(1) Molybdenum, (2) Phosphorus, (3) Vanadium, (
4) at least one metal selected from the group consisting of potassium, rubidium, cesium, and thallium (however, excluding the case of potassium alone); and (5) carrying out a gas phase catalytic reaction in the presence of a catalyst consisting of oxygen. Characteristic method for producing methacrylic acid.