JPS584704B2 - Method for producing methyl methacrylate - Google Patents

Description

[Detailed description of the invention] The present invention relates to the production of methyl methacrylate.

More specifically, the present invention relates to a method for producing methyl methacrylate in one step from methallyl alcohol and methanol in the presence of oxygen.

Industrially useful methyl methacrylate monomer has conventionally been produced by a method of making acetone cyanohydrin with acetone and hydrocyanic acid, and esterifying it while hydrolyzing it with sulfuric acid.

However, the supply of raw material hydrocyanic acid is at its limit, and new routes for obtaining methyl methacrylate are being considered worldwide.

The main route considered so far has been to use isobutylene as a starting material, pass through methacrolein and methacrylic acid, and then reach methyl methacrylate, but this process is long and has a low yield, so it has not yet been implemented industrially. do not have.

Various methods have been proposed to shorten the process, such as a method for producing methacrylic acid from isobutylene all at once, a method for producing methyl methacrylate from inbutylene and methanol, and a method for producing methyl methacrylate from methacrolein and methanol. However, most of these methods have problems in terms of yield and conditions when operating on an industrial scale.

On the other hand, a reaction in which carboxylic acid esters are produced by oxidative esterification of alcohol is known, but it is said that it is difficult to obtain carboxylic acid esters with good selectivity when the raw alcohol is unsaturated.

Therefore, the present inventors have developed a method for producing methyl methacrylate by oxidatively esterifying relatively stable methallyl alcohol as a starting material, avoiding polymerization and other highly reactive substances such as methacrolein and methacrylic acid. As a result of extensive research, it was surprisingly possible to achieve a high yield for the first time by using a combination of at least one metal compound of palladium, lead or/and thallium, and at least one alkaline earth metal compound as a catalyst. It was discovered that methyl methacrylate could be produced with high selectivity, leading to the present invention.

The usage ratio of methallyl alcohol and methanol used in the present invention is preferably in the range of 10 to 1/1000 in molar ratio of methallyl alcohol/methanol, and 2 to 1/5.
A range of 0 is particularly preferred.

The oxygen used in the present invention can also be in the form of molecular oxygen, that is, oxygen gas itself, or a mixed gas prepared by diluting oxygen gas with a diluent inert to the reaction, such as nitrogen or carbon dioxide. But it doesn't matter.

The amount of oxygen present in the reaction system is sufficient if it is at least the stoichiometric amount required for the reaction, preferably at least 1.5 times the stoichiometric amount, but is not particularly limited depending on other conditions.

As mentioned above, the catalyst used in the present invention is (1)
Palladium A is composed of a compound of (11) lead or/and thallium and a (111) alkali metal compound.

Examples of the lead compounds include lead carboxylates such as lead acetate and lead formate, lead oxide, and lead hydroxide.
Further, as the thallium compound, thallium acetate, thallium nitrate, thallium sulfate, thallous chloride, thallium oxide, etc. can be used.

Examples of the alkali metal compounds include oxides, hydroxides, carbonates, acetates, and sulfates of magnesium, calcium, strontium, and barium.

Although these catalyst components may be present in the system separately, they are preferably present in the reaction system in such a form that they can have some effect on each other.

These catalyst components can be used by being supported on a general carrier such as activated carbon, silica, or alumina, or they can be supported on each other without using such a carrier.

The composition ratio of the catalyst can be arbitrarily changed depending on the catalyst preparation method, operating conditions, etc., and is not particularly limited, but generally palladium is 0.5 to 20% by weight, preferably 1% by weight, based on the weight of the catalyst. ~10% by weight of the lead or thallium compounds, preferably 0.01 to 20% by weight of the compound, preferably 0.05 to 10% by weight of the compound and alkaline earth metal compounds from 2 to 95% by weight of the compound. is desirable.

Further, the atomic ratio of palladium to lead or thallium as a metal is preferably in the range of 0.01 to 1.0, particularly preferably in the range of 0.05 to 0.7 to 1 part palladium.

The catalyst can be prepared according to conventional methods.

For example, when preparing a catalyst in which palladium, a lead compound, and a magnesium compound are supported on a suitable carrier,
Magnesium nitrate is baked and supported on an alumina carrier or the like in advance, and then impregnated with an aqueous solution of soluble palladium salt, reduced with an appropriate reducing agent, immersed in, for example, an aqueous solution of lead acetate, and evaporated to dryness. , and can be used after drying.

The reaction of the present invention can be carried out at a temperature range of 0°C to 200°C, and a temperature of 30°C to 150°C is particularly suitable.

Although the reaction can be carried out under reduced pressure, atmospheric pressure, or increased pressure, it is said that the desired carboxylic acid ester can be easily obtained in high yield by a simple method of blowing oxygen at normal pressure. Has characteristics.

Note that the reaction can be carried out either batchwise or continuously.

The effects obtained by the present invention are as follows.

(1) The reaction system is extremely simple, consisting of methallyl alcohol, methanol, oxygen-containing gas, and a catalyst,
No complicated reaction operations are required.

(2) Since it is highly active even below the boiling point of methanol (40 to 50°C) and has excellent selectivity, methyl methallylate can be easily synthesized in one step.

(3) There are very few side reactions, and since the catalyst is solid, it is easy to separate and purify, and the catalyst is extremely stable under the reaction conditions.

(4) The reaction rate is high even at low temperatures and normal pressure, so productivity per reactor is extremely high.

As described above, according to the present invention, methyl methacrylate can be produced in a high yield from methallyl alcohol and methanol in one step, and therefore the present invention is extremely valuable industrially.

The present invention will be explained in more detail with reference to Examples below.
The present invention is not limited to these examples.

Example 1 In a fourth flask equipped with a gas inlet, a stirrer, a reflux condenser, and a thermometer on the top, 10 cc of methallyl alcohol was added.
, 2% palladium, 5% lead oxide, 2% magnesium oxide (
% by weight) was added, the reaction temperature was set to 60°C, and air was blown at 101/H from the gas inlet.
The reaction was carried out by flowing r.

Two hours after the reaction started, the conversion rate of methallyl alcohol was 91.
．． 6%, and the yield of methyl methacrylate based on the starting material methallyl alcohol was 83.2%, and some carbon dioxide gas, acetal and methyl formate were produced as by-products.

Example 2 Into the same apparatus as in Example 1, 4cc of methallyl alcohol, 100cc of methanol, and 4g of a catalyst containing 5% palladium, 3% lead acetate, and 5% magnesium acetate (each % by weight) supported on a silica carrier were added. Reaction temperature 40
The reaction was carried out at ℃ for 2 hours while air was flowing at 10 l/hr.

As a result, the conversion rate of methallyl alcohol was almost 10
At 0%, the yield of methyl methacrylate was 87.6%, and only some carbon dioxide gas and acetal were detected as by-products.

Example 3 Under the same conditions as in Example 2, a reaction was carried out using 4g of 5% palladium and thallium acetate supported on magnesium hydroxide as a catalyst.

As a result, the conversion rate of methallyl alcohol was 97%, and the yield of methyl methacrylate was 81.8%.

Example 4 In a titanium autoclave with a capacity of 200 cc equipped with a gas inlet and a stirrer, 5 cc of methallyl alcohol, 100 cc of methanol, and a commercially available Lindlar catalyst (manufactured by Engelhard, containing palladium, lead, and calcium carbonate) were added as a catalyst. Charge 5gr, set the reaction temperature to 90℃, and stir while stirring, total pressure 20kg/cr2, oxygen pressure 5kg/c.
The reaction was carried out by adding only a reduced amount of oxygen in m2.

When the reaction solution was analyzed 3 hours after the start of the reaction, the conversion rate of methallyl alcohol was almost 100%, and the yield of methyl methacrylate was 84.5%.

Claims (1)

[Claims] 1. In producing methyl methacrylate from methallyl alcohol and methanol in the presence of oxygen, (1) palladium A, (ii) at least one selected from carboxylates and oxides of lead or thallium, (3) calcium or A method for producing methyl methacrylate, comprising using a catalyst consisting of at least one selected from the group of magnesium hydroxide, oxide carboxylate, and carbonate.