JPS5817178B2 - Method for producing methacrylic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing methacrylic acid by gas phase catalytic oxidation of methacrolein.

More specifically, it relates to a method for producing methacrylic acid, which comprises using a catalyst containing an alkali metal salt of lean molybdic acid and containing no ammonium group when producing methacrylic acid by oxidizing methacrolein with molecular oxygen. It is.

Conventionally, many methods have been proposed for producing the corresponding unsaturated carboxylic acid by vapor phase catalytic oxidation of unsaturated aldehydes, but there are only a few methods for producing methacrylic acid from methacrolein, and there is a patent for producing acrylic acid from acrolein. There are many things that are also listed inside.

Moreover, in many cases it is not possible to reproduce the embodiments described in the patent.

Although high-yield catalysts have recently begun to appear, there are still many problems and it is difficult to say that they are industrially sufficient catalysts.

Methacrolein is highly reactive and causes various side reactions, making it extremely difficult to obtain methacrylic acid in good yield.

In order to obtain the target product in good yield, it is necessary to develop a catalyst with good selectivity even at a high conversion rate.

Catalytic active sites effective for oxidizing methacrolein to obtain methacrylic acid exist on a catalyst containing molybdenum, phosphorus, ammonium, and oxygen, and are (NH4) 3
It has already been found that ammonium phosphomolybdate represented by (PO4Mo -r2 o36 ) is the active center, and an application is currently pending (Japanese Patent Laid-Open No. 49-69612).

This catalyst containing ammonium phosphomolybdate is
Excellent activity and selectivity. Methacrylic acid yield 60.3 using a catalyst with molybdenyline:ammonium=12:2:2.5.
%, and the selectivity to methacrylic acid was 62.5%.

However, ammonium phosphomolybutate decomposes at relatively low temperatures, as stated in Kagaku Daijiten, Vol. 9, page 830 (Kyoritsu Shuppan), ``At 410 to 540°C, it loses ammonia water and decomposes.''

This fact remains a problem in terms of catalyst life.

We searched for a catalyst with better thermal stability and higher yield than ammonium phosphomolybdate, and found that a catalyst containing an alkali metal salt of phosphomolybdate and no ammonium group was effective in gas phase catalytic oxidation of methacrolein to methacrylic acid. was found to be effective as a catalyst.

These alkali metal salts of phosphomolybdic acid are bi3(PO4MO12036)tNa5(PO
4MO12036)tK3 (PO4MO12036)
, Rb3 (P'04 Mo '12036)tC
53 (PO4Mo□2036), but some parts are M crosspiece (PO4MO□2036).
), which is also included in the alkali metal salt of phosphomolybdic acid as used in the present invention.

Here, M represents an alkali metal, and n is a value smaller than 3 and does not include O.

In any case, a catalyst having a (PO4Mo□203ρ) skeleton is effective.

In the present invention, (Mo)a(
When using a catalyst that does not contain an ammonium group and has a composition represented by P)b(T)c(0)d, and some of these constituent elements form an alkali metal salt of phosphomolybdic acid. It is.

In the formula, T represents at least one element selected from alkali metals, or in some cases, an alkali metal and hydrogen.

a, b, c, and d represent the numbers of atoms of Mo, P, T, and O.

Here a:b:c is 12:0.2-5:0.2-5, especially a:b:c=12:0.5-3
: The range of 0.5 to 3 is preferable, and d is the number of atoms inevitably determined by the bonding state of MO, P, and alkali metal.

Note that this catalyst may also contain compounds such as molybdenum trioxide in addition to the alkali metal salt of phosphomolybdic acid.

The catalyst in the present invention is prepared, for example, as follows.

Molybdic acid and potassium dihydrogen phosphate are mixed with a small amount of water using a crusher.

After kneading, evaporate to dryness and pre-baking at 150°C.
Firing is performed at 0°C, preferably 300 to 450°C while flowing air.

Alternatively, when molybdenum trioxide is dispersed in an aqueous solution of dipotassium hydrogen phosphate and heated, potassium phosphomolybdate is produced.

After this is evaporated to dryness, a catalyst can be prepared in the same manner as above.

The starting materials for molybdenum, phosphorus, and alkali metals are not limited to special ones.Any materials containing commonly used constituent elements can be used, and after firing, the alkali metal salt of phosphomolybdic acid is finally formed. Just generate it.

Preferably, the reaction is carried out at 200-450°C.

The reaction can be carried out under normal pressure, reduced pressure, or increased pressure.

The molecular oxygen used here may coexist with an inert gas such as nitrogen or water vapor, or the reaction product 1 gas obtained when inbunalene is catalytically oxidized in the gas phase may be used as it is.

The ratio of methacrolein and oxygen is methacrolein:oxygen=
A molar ratio of 1:0.5 to 15, particularly 1:1 to 7 is preferred.

A carrier may or may not be used.

As carriers, common inert materials such as silica, silicon carbide, and celite can be used.

The contact time is preferably 0.5 to 30 seconds.

This catalyst is usually used in a fixed bed, but it can also be used in a fluidized or moving bed.

- Next, the present invention will be explained in more detail with reference to Examples.

The conversion rate, selectivity, and single flow yield in the examples shall be in accordance with the following formula.

Reaction rate Number of moles of reacted methacrolein =
xio.

(b) Number of moles of methacrolein supplied Selectivity of methacrylic acid (%) Number of moles of methacrylic acid produced = □ × 100 Number of moles of reacted methacrolein Single stream yield of methacrylic acid ('%) Produced Number of moles of methacrylic acid = X
100 Number of moles of methacrolein fed The experimental results of the following examples are summarized in the last table.

In Example O, the catalyst naturally contains oxygen atoms, but the number of oxygen atoms is a value that is inevitably determined by the bonding state of other metals, so the description is omitted.

Example 1 Molybdic acid (H2MoO4-H2O) 60.9 g Potassium dihydrogen phosphate (KH2PO4') 7.56 g
is kneaded in the presence of a small amount in a stirrer for an hour.

This was evaporated to dryness, pre-baked at 1.50℃ for 4 hours, and then
Bake at 00°C for 4 hours while blowing air.

The atomic ratio of molybdenum, sodium, and potassium in the catalyst prepared in this way is Mo: P: K = 12:
It is 22.

It was confirmed from the results of X-ray diffraction and infrared absorption spectrum that potassium phosphomolybdate was produced in this product.

The particle size of this catalyst is adjusted to 20 to 48 mesh, and this 10
ml was filled into a glass reaction tube with an inner diameter of 18 mm, and an activity test was conducted.

The reaction conditions are raw material composition ratio methacrolein:02:N2:H
202 1:2:16:12 molar ratio, space velocity 5V = 19
00HR”.

Example 2 50g of molybdic acid and 3.15g of potassium dihydrogen phosphate
A catalyst was prepared and an activity test was conducted in the same manner as in Example 1, except that .

The catalyst composition was Mo: P: 12:1:1.

It was confirmed from X-ray diffraction and infrared absorption spectrum that this catalyst also produced potassium phosphomolybdate.

Example 3 50g of molybdic acid and 8.45g of rubidium dihydrogen phosphate
A catalyst was prepared in the same manner as in Example 1, except that g was used, and an activity test was conducted.

The catalyst composition was Mo:P:Rb=12:2:2.

It was confirmed from X-ray diffraction and infrared absorption spectrum that rubidium phosphomolybdate was produced in this catalyst.

Example 4 50g of molybdic acid and 10.65g of cesium dihydrogen phosphate
A catalyst was prepared in the same manner as in Example 1 except that g was used, and an activity test was conducted.

The catalyst composition was Mo:P:Cs = 12:2:2.

It was confirmed from X-ray diffraction and infrared absorption spectrum that this catalyst produced cesium phosphomolybdate.

Example 5 50 g of molybdenum trioxide and 5.0 g of dipotassium hydrogen phosphate
Disperse 4 g in an aqueous solution of dipotassium hydrogen phosphate dissolved in 200 liters of water, heat while stirring, and evaporate to dryness.

This evaporated product is prebaked at 150° C. for 4 hours and then fired at 400° C. for 4 hours while blowing air.

The molybdenum, phosphorus and potassium ratio of the catalyst thus prepared was Mo:P:K=12:1:
It is 2.

It was confirmed from the results of X-ray diffraction that potassium phosphomolybdate was produced in this product.

After adjusting the particle size of this catalyst to 20 to 48 mesh, it was packed into a reaction tube ζ and mixed with Mekcrolein 20□2N2:H2021
:3.8:14.2:12.5V=640HR'.

Example 6 1.61 g of potassium hydroxide and 3.34 g of 85% phosphoric acid are dissolved in 200,111 g of water.

Molybdenum trioxide (50.9 g) in this aqueous solution is dispersed and heated with stirring.

After evaporation to dryness, pre-baking at 150℃ for 4 hours, then further heating at 1400℃
It was baked for 4 hours.

The composition of this catalyst is Mo:P:Ni=12:0
．． The ratio is 5:1.

This catalyst also produced potassium phosphomolybdate.

An activity test was conducted in the same manner as in Example 5. Example 7 Molybdenum trioxide 5 (L9 was replaced with dipotassium hydrogen phosphate 7.
A catalyst was prepared in the same manner as in Example 5, except that 56 g of the catalyst was dispersed in an aqueous solution of dipotassium hydrogen phosphate dissolved in 200 ml of water, and an activity test was conducted.

i The catalyst composition is Mo:P:=12:1.5:3.

This catalyst produced potassium phosphomolybdate.

Claims (1)

[Claims] 1. A method for producing methacrylic acid, which comprises using a catalyst containing an alkali metal salt of phosphomolybdic acid and containing no ammonium group when producing methacrylic acid by oxidizing methacrolein with molecular oxygen.