JPS5827779B2 - Methacryl Sanno Seizouhouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process for the vapor phase catalytic oxidation of methacrolein using a novel catalyst to produce the corresponding methacrylic acid.

Various catalyst systems have been proposed for the production of methacrylic acid by vapor phase catalytic oxidation of methacrolein (1), but these catalysts have advantages and disadvantages.

That is, conventional catalysts have low activity or high yield/-
Even if J6 is available, many of them have shortcomings such as a short initial life and a low selectivity, which is an important industrial factor, and poor reproducibility. It has drawbacks and is not necessarily industrially satisfactory.

For example, many products whose main components are phosphorus-molybdenum have a short lifespan, and products whose main components are molybdenum-vanadium generate large amounts of carbon monoxide and carbon dioxide, making it impossible to secure the necessary selectivity. .

When an alkanometal is added to the phosphorus-molybdenum binary component, the conversion rate and selectivity increase slightly, the activity becomes stable, and the life span becomes longer.

Furthermore, adding vanadium to the phosphorus-molybdenum binary component has the effect of suppressing the machinability of carbon monoxide and carbon dioxide, and at the same time increases the selectivity.

Furthermore, all these components may be combined or a non-molybdenum alkali metal-vanadium catalyst (Japanese Patent Application Laid-open No. 508201
3. 5O-96522) is relatively excellent among the known catalysts for producing methacrylic acid, but from an industrial standpoint, the selectivity was still low, and a catalyst with even higher selectivity was desired. .

Next, the reason why a particularly high selectivity is desired as a catalyst for producing methacrylic acid will be described.

The catalyst for producing methacrylic acid is charged into a reactor before use.

The shape of the catalyst to be filled may be one made by crushing a lumpy catalyst and then classifying it with a sieve to collect the appropriate particle size, or a porous one such as alumina or silicon carbide that is commercially available in molded form.
There are those prepared by adhering a catalyst to a jjl1 body, and those prepared by compressing the catalyst components into tablets as they are or using some kind of diluent.

Catalysts that can be used commercially must have sufficient physical strength to not be destroyed during the reaction, so crushed and classified catalysts that tend to become powder or catalysts that are easily flaked off on a carrier are not recommended. Since it is less practical, a tablet-formed catalyst is preferable.

However, molded catalysts have the drawback of lower conversion rates and selectivities, especially selectivity, compared to other catalysts.

The conversion of a2 from acrolein to methacrylic acid is different from the oxidation of acrolein to acrylic acid.
Since the conversion rate in the pass is low, the final reaction material is recovered and sent to the reaction system repeatedly.

Therefore, for economical production, it is important to have a high conversion rate in one pass, but it is even more important to have a high selectivity to the target unsaturated carboxylic acid.

The present inventors have conducted intensive research to obtain a catalyst with particularly high selectivity for methacrylic acid, which is used when oxidizing tutacrolein to obtain methacrylic acid. We have discovered a new catalyst that has a low selectivity for carbon oxide, tricarbon dioxide, etc., is easy to control the reaction, and is extremely advantageous for industrial production, and has arrived at the present invention.

The present invention provides at least one type of phosphorus selected from the general formula % group, a, b,
c, d, e, f are respectively Mo, P, V, Mn, X,
Represents the atomic ratio of 0, when a-12, b-05-5
, c=0.05-3, d=0.012, e=0.1-
3 and f is the number of oxygen atoms sufficient to satisfy the valences of other elements).

The catalyst used in the method of the present invention has very good selectivity and can be used as it is or after being formed into a tablet. It can also be used by attaching it to a carrier.

However, the method of using it by adhering it to the +11 body is different from the method of using di-molybdenum※※] As a general feature of phallic-based catalysts, the adhesion between the carrier and the active component of the catalyst is not very good. This is not the preferred method as it may gradually peel off.

As a method for preparing the catalytic active component, conventional methods such as oxide mixing method, evaporation to dryness method, etc. can be adopted.

Raw materials for each element used in the preparation of the catalyst include ammonium, nitric acid, halides, peroxides, acid anhydrides, condensed acids, hydroxides, oxides, and Examples include telopolyacid and heteropolyacid salts.

Catalysts prepared by the above-mentioned methods are usually heated at 25°C under air flow.
It is used as a catalyst after being calcined at 0-500'C, particularly preferably at 300,470'C for 2-40 hours.

The molecular oxygen goldstone scum used in the method of the present invention includes scum inert to air or oxygen, such as water vapor, nitrogen,
A mixture of tricarbon dioxide, helium, argon, lower saturated hydrocarbons, etc. can be used.

The reaction conditions for carrying out the process of the present invention can be suitably varied over a wide range depending on the composition of the catalyst used, but are as follows.

(1) Reaction temperature: 250-i, 00°C (2) Reaction pressure: 250-3000 hr-1 (0
(4) Molar ratio of methacrolein to oxygen ]: 1-3 (5) Molar ratio of methacrolein to water vapor ]: 0-50 The reaction product can be prepared by a commonly used method, such as condensation. It can be separated and recovered by a method such as a method, an extraction method, a distillation method, or other suitable method.

Analysis in the following examples was by gas chromatography.

Further, the conversion rate, selectivity, and yield were calculated according to the following formula.

In addition, in the following examples, these mol% are simply abbreviated as %.

Example 1 In a 11 beaker, add 570y of phosphorous-molybdic acid (15,
6 mmol) and make an aqueous solution.

On the other hand, 0.81' (3.90 mmol) of manganese dihydrogen phosphate and 0.90 P (7.81 mmol) of 85% orthophosphoric acid were prepared into an aqueous solution, added to the phosphomolybdic acid aqueous solution, and stirred well.

There, ammonium metavanadate 0.91P (7,
An aqueous solution of 81 mmol) was added to the mixture and stirred well.

Next, potassium hydroxide 2.97 @ (53.0 mmol) and cesium nitrate 1.52? An aqueous solution of (7.81 mmol) was added and stirred well.

This was evaporated to dryness in hot water bath L, transferred to an evaporating dish, and calcined in an air atmosphere at 400°C for 1 hour, then at 450°C for 2 hours using a Matsufuru furnace.

Grind the fired product in a mortar and add 5w of graphite powder.
t% was added, stirred well, and made into a tablet using a tablet molding machine.
It was molded into pellets of mmφ×3rn, rn) and used as a catalyst.

The atomic ratio in the obtained catalyst components was Mo:P:V:Cs:Mn = 12:1.5:0.25
:], 7:0.25:0.125.

25 cc of the above catalyst was packed into a Pyrex glass reaction tube with an inner diameter of 20 mTLφ, and the raw material residue with a molar ratio of methacrolein:air:hydrogen gas-4,6:35.0:60.4 was heated in a space of 5V-1000hr-1. speed, 340
The sample was passed at a reaction temperature of 'C, and data were taken 34 hours after the start of the reaction.

The results are shown in Table 1. Comparative Example 1 A catalyst was prepared in the same manner as in Example 1 except that no manganese compound was added.

All reaction experiments were conducted in the same manner as in Example 1.

The results are shown in Table 1.

From the results in Table 1, Example 10 Using the catalyst of the present invention increases the selectivity to methacrylic acid by -L, while carbon monoxide, ]-
It can be seen that the selectivity to carbon dioxide is decreasing.

Selectivity to carbon monoxide and carbon dioxide is 10.5% to 7
This difference of 3% indicates that the heat generation inside the reaction tube is significantly reduced, and the reactor control operation becomes significantly easier.

Examples 2 to 7 and Comparative Examples 2 to 5 Using the same catalyst preparation method as in Example 1, catalysts with different composition ratios of mankan and catalysts with different types of X were prepared, and the same reactions as in Example 1 were carried out. The oxidation reaction of methacrolein was carried out under the following conditions.

In Example 3, manganese dihydrogen phosphate and manganese nitrate were used together.

Here, potassium hydroxide, cesium nitrate, rubidium oxide, and thallium nitrate were used as raw materials for X.

Claims (1)

[Claims] 1. In producing methacrylic acid by gas-phase catalytic oxidation of methacrolein with molecular oxygen-containing scum, the general formula: (where X is at least one selected from the group of Rb, Cs and Tl) It is a kind of element, a, b, c, d, e,
f represents the atomic ratio of Mo, P, V, Mn, X, and O, respectively; when a-12, bO,5-5, c=0.05
-3, d = 0.01---2, eOl-3, and f is the number of oxygen sufficient to satisfy the valence of other elements). Method.