JPS606340B2 - Method for producing methacrylic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for producing the corresponding methacrylic acid by subjecting unsaturated aldehydes, particularly methacrolein, to a gas phase catalytic oxidation reaction in the presence of a catalyst. The present invention also relates to a method for producing methacrylic acid characterized by using a catalyst with a long active life.

Until now, patents proposed regarding catalysts for the gas-phase catalytic oxidation reaction of unsaturated aldehydes have mainly focused on methods for producing acrylic acid from acrolein, while others have focused on methods for producing methacrylic acid from methacrolein. There are few that did. Even when catalysts that actually show good performance 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, CQ generation) Significant side reactions such as
Selection rate is low. On the other hand, proposed oxidation catalysts for methacrolein either have low activity or are difficult to use due to the possible reaction conditions, particularly the need to lengthen the reaction time and/or to reduce the methacrolein concentration in the combined raw material gas. 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, even though the production of acrylic acid by oxidation of acrolein is carried out industrially, methacrylic acid is not available. It is said that it is quite difficult to industrially produce methacrylic acid by oxidizing rhein. Therefore,
In searching for a catalyst effective for oxidizing methacrolein 0, it is necessary to research from a different perspective from that of the oxidation catalyst for acrolein. Based on these points, the present inventors have improved these shortcomings in methacrolein oxidation catalysts, and achieved excellent catalytic activity (i.e., yield, selectivity, and productivity of the desired product), as well as improved catalytic As a new catalyst with a long active life, we have developed a catalyst having the following components: Mo-P-V-x (X is at least one selected from K, Bb, Cs, and T1) (Japanese Patent Application No. 131325-1982) ).

The present inventors continued to conduct intensive research to develop the above-mentioned catalyst into a catalyst with even higher performance without impairing the feature of long active life of the catalyst, and found that Mo-P-V1X By adding at least one member selected from the group consisting of Sr, Zn, Cd, Nb, B, Pb and W to the Mo-P-
It was discovered that the yield and productivity (STY) of methacrylic acid were further improved compared to V-x type catalysts, and the present invention was completed.

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 MoaPhVCYe○f. It is.

In the above formula, × is at least one metal selected from the group consisting of K, Rb, Cs, and TI (excluding the case of potassium alone), and Y is Sr, Zn, Cd, Nb,
It is at least one type selected from the group consisting of B, Pb and W. 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:
0.01~6, and further 12:0.3~5:0.3~
5:0.3 to 5:0.05 to 3 is suitable, and f is M
The number of oxygen atoms is sufficient to satisfy the valences of o, P, V, x, and Y. Molybdenum, phosphorus and vanadium catalysts have been known as catalysts for oxidizing acrolein. In the case of such a catalyst, it is said that it may be prepared in the form of sodium salt, gallium salt, or ammonium salt of phosphomolybdic acid, but there are also examples prepared in the form of potassium salt. There was no example of an oxidation reaction of acrolein using the prepared catalyst, and even less was known about the behavior of the catalyst in the oxidation reaction of methacrolein (
Special Publication No. 46-122457). At this state of the art, the present inventors succeeded in developing a catalyst with a long active life and a significant improvement in catalytic activity by combining the above-mentioned X component and Y component with a molybdenum, phosphorus, and vanadium-based catalyst. This is what I did.

The difference between the catalyst of the present invention and the catalyst of the prior application is that the catalyst contains a Y component, that is, at least one element selected from the group consisting of Sr, Zn, Cd, Nb, B, Pb, and W. This difference in catalyst composition significantly improves catalyst performance.

According to the catalyst of the present invention, methacrylic acid can be obtained from methacrolein in a high yield and with good productivity through a stable reaction under practical reaction conditions, and excellent catalytic activity can be maintained even over a long period of time. Therefore, continuous reaction can be carried out for a long time. The preparation conditions for the catalyst of the present invention are simple, and a catalyst with good activity can always be 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.

The 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 0 is phosphomolybdic acid, etc. Examples include heteropolyacids containing molybdenum, or heteropolyacid salts such as ammonium salts thereof.A preferred method for preparing the catalyst is such that the components constituting the catalyst of the present invention are heteropolyacids, acidic salts thereof, or ammonium salts thereof. Preferably, the catalyst is prepared in such a way that it can form the key compound, such as the Tam salt.
After firing at a temperature of 0 in air, in a reducing atmosphere, or in a raw material composition gas for several hours to several tens of hours,
Used as a catalyst.

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 the catalyst preparation method is to add and mix an aqueous solution containing a vanadium compound to an aqueous solution containing ammonium molybdate, and then add an aqueous solution containing phosphoric acid, an aqueous solution containing a water-soluble compound of element X, and an aqueous solution of element Y. An aqueous solution containing a chemical compound is added and evaporated to dryness while 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. 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, silicone carbide,
Known materials such as alpha alumina, refractories, graphite, and titania may be used. 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 with diluents, such as water vapor, nitrogen, carbon dioxide, helium, argon,
Saturated hydrocarbons (eg, methane, ethane, propane, butane, bentane, 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 of ZO, and the ratio of methacrolein to oxygen is 1:0.
．． A suitable ratio is 1 to 25.0, preferably 1:0.1 to 20.0. The reaction temperature is 300 to 500°C, preferably 330 to 45,000°C, and the reaction contact time (
000, 1 atm standard) is 0.1 to 20 seconds, preferably Z is in the range of 0.1 to 15 seconds. 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 pressure20. can.

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 methacrylic acid, a method of condensing and collecting it in a condenser 2, a method of collecting it with a solvent, etc. are used.
The present invention will be specifically described below with reference to Examples. In the Examples, the conversion rate of methacrolein, the yield of methacrylic acid, and the selectivity are defined as 3 as follows.

All analyzes were conducted using a gas chromatograph. You are also behind〉-Kamitsuseta)X,.

〇3 cavalry carp = Methacrolein supplied (mol) Methacrylic acid produced (mol) Yield (%) = Metac fed.

Rain (mol) XIOO selection rate <%) = Poison cover ink
4 Example 1 '1' Ammonium metavanadate 212 ml was dissolved in 300 ml of water by heating, and 1 ml of ammonium metavanadate was added to the solution.
1.72 and 35.1 oxalic acid dissolved in advance 200
Dissolve it in a warm water solution of M and add it.

In addition, an aqueous solution of 85% phosphoric acid 23% dissolved in 50ml of water, an aqueous solution of cesium nitrate 39.0ml dissolved in 200ml of water by heating, and strontium nitrate 105%.
Add a 200ml aqueous solution of 50ml of water and evaporate to dryness while stirring. The obtained composition was fired in a muffle furnace kept at 430°C for 16 hours, and then pulverized.
Separate it into mesh and use it as a catalyst. The atomic ratio of Mo:P:V:Cs:Sr in the catalyst composition thus obtained was 12:
The ratio is 2:1:2:0.5 (catalyst No. 01).

Similarly, instead of strontium nitrate, Zn(N03
)2・Mother L07.43 evening, Cd(N03)2・4 ratio 07
．． 7 evening, Nb (HC204) 513.45 evening, sun 3B0
33.1 evening, Pb(N03) 216.55 evening and 5(N
H4) Catalytic NO
．． (1) to (13) were prepared.

Comparative Catalyst No. 1 was prepared by further removing some components or using KN0320.2 in place of cesium nitrate. (c-1)~No. (c-10) was prepared.
However, among the comparative catalysts, the firing temperature of the catalyst containing no V component was set to 45,000. Next, the inner diameter of the catalyst 100 is 2.5
Fill a stainless steel reaction tube with a length of 60 mm, heat it with a metal sieve, and mix methacrolein:02:N2:&○=1:1.
．． A raw material gas having a composition of 5:17.5:10 (molar ratio) was heated for a contact time of 1. The reaction was carried out using parent sand (000, 1 atm standard).

The obtained results are shown in Table 1-1 for the invention examples and Table 1-2 for the comparative examples.

The reaction temperature is the highest temperature of the catalyst layer when good results were obtained (the same applies hereinafter). From the results in Tables 1-1 and 1-2, (1-molybdenum, (2) phosphorus, glue vanadium, (
4) Rubidium, cesium or thallium based catalysts, strontium, zinc, cadmium, niobium, boron,
It can be seen that the catalyst activity is further improved by adding lead or tungsten. Further, the catalyst system of the present invention is
'1}Molybdenum, (2'Litho, [31/Nazium,
[4} Potassium-based catalyst [Catalyst No. (c-3)] shows far superior catalytic activity. 1-1
Table Example 2 Catalysts of the present invention (Nos. (14) to (24)) having compositions shown in Table 2 were prepared in the same manner as in Example 1, and reacted under the same conditions as in Example 1. I did it.

For comparison, a comparative catalyst N was added in the same manner as in Example 1.
o. (c-11) to (c-16) were prepared and reacted under the same conditions as in Example 1. The results obtained are shown in Table 2. From the results in Table 2, it can be seen that good catalytic activity is exhibited even when the composition ratio of each element is changed.

Further, when rubidium, cesium or thallium is used in combination, or potassium is used in combination with these, similarly excellent catalytic activity is exhibited. Table 2 Example 3 Table 3 shows an example in which the catalyst described in Example 1 was used to conduct a long-term continuous reaction.

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.

Table 3 x indicates the initial stage of the reaction

Claims (1)

[Claims] 1. A mixed gas containing methacrolein and molecular oxygen,
Formula Mo_aP_bV_CX_dY_eO_f (where X
is at least one metal selected from the group consisting of K, Rb, Cs, and Tl (excluding the case of potassium alone), and Y is a group consisting of Sr, Zn, Cd, Nb, B, Pb, and W. At least one type selected from a, b, c
, d, e and f each indicate the number of atoms of each element, and a=
When set to 12, the value of a:b:c:d:e is 12:0.
1 to 8: 0.1 to 8: 0.1 to 8: 0.01 to 6, and f is the number of oxygen atoms sufficient to satisfy the valences of Mo, P, V, X, and Y. . ) A method for producing methacrylic acid, characterized by carrying out gas phase oxidation in the presence of a catalyst shown in (a).