JPH10263399A - Catalyst for production of carboxylic ester - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a catalyst enabling the production of carboxylic ester with high selectivity and a little by-product by specifying the atomic ratio between Pd and Bi in a catalyst and specifying X-ray diffraction angle at the highest peak in the powder X-ray diffraction pattern of the catalyst. SOLUTION: In this catalyst, the atomic ratio between Pd and Bi is 3:0.8 to 3:1.4. The powder X-ray diffraction pattern of this catalyst has the highest intensity peak at 38.55-38.85 deg. X-ray diffraction angle (2θ). The atomic ratio between Pd and Bi is measured by an induction coupling emission spectrochemical analysis method. The X-ray diffraction angle (2θ) at the highest intensity peak is measured using CuKα1 rays (1.5405981 Å) after the catalyst is freed of low molecular absorbed and occluded components.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a catalyst used for producing a carboxylic acid ester from an aldehyde, an alcohol and molecular oxygen, and a method for producing a carboxylic acid ester using the catalyst.

[0002]

2. Description of the Related Art As a method for producing industrially useful methyl methacrylate or methyl acrylate, for example, in the case of methyl methacrylate, methacrylic acid is produced by oxidizing methacrolein with oxygen, and then methacrylic acid and methanol A method called the direct acid method for producing methyl methacrylate by reacting with methacrylate has already been industrialized. However, although the yield of the process of oxidizing methacrolein to methacrylic acid has been improved to the lower 80% level due to the improvement of the catalyst over many years, it is still low and there is much room for improvement. Further, the heteropolyacid catalyst to be used originally has a difficulty in thermal stability, and decomposition gradually proceeds under the reaction temperature conditions. Although improvements in catalysts for improving heat resistance have been reported, it is said that the catalyst life is still insufficient as an industrial catalyst.

On the other hand, methacrolein or acrolein (hereinafter referred to as (meth) acrolein) is reacted with methanol and molecular oxygen to form methyl methacrylate or methyl acrylate (hereinafter referred to as methyl (meth) acrylate) at once. New methods of manufacturing have recently been in the spotlight. This method is carried out by reacting (meth) acrolein with molecular oxygen in methanol, and the presence of a catalyst containing palladium is essential.

Heretofore, in this production method, hydrocarbons and carbon dioxide gas have been produced in combination with the decomposition reaction of the aldehyde, and the yield of the desired carboxylic acid ester has been low. Of different types of aldehydes by oxidation of aldehydes and carboxylic acid esters of different types of aldehydes (eg, methyl formate when methanol is used as the alcohol, ethyl acetate when ethanol is used)
As a by-product, the alcohol-based selectivity was poor. In addition, there is a disadvantage that the catalyst activity cannot be maintained for a long time. In particular, when an α · β-unsaturated aldehyde such as (meth) acrolein is used as a starting material, which is a method for producing a carboxylic acid ester having high industrial practical value, a large amount of carbon dioxide gas or olefin (methacrolein) is used during the reaction. In this case, propylene and other decomposition products were generated, which was far from practical use.

The present inventors have disclosed Japanese Patent Publication No. 62-007902.
Publication proposes a catalyst containing an intermetallic compound in which palladium and bismuth are combined at a fixed integer ratio, and the decomposition reaction of (meth) acrolein is almost completely inhibited and the catalyst life is not lost for a long time It was shown to be a catalyst system. As described above, the production method using these catalyst systems has the advantage that the process is shorter than the method using (meth) acrylic acid, which has the effect of improving the yield and catalyst life, and is industrially useful. Industrialization is awaited as a new method for producing polymer raw materials.

[0006] However, considering industrial implementation and considering from the viewpoints of productivity and economy,
A new production method using a catalyst proposed in 007902 is
Aldehyde concentration is as low as 10% or less and reaction temperature is 6
The reaction was carried out under mild conditions of 0 ° C. or lower, and under these conditions, the amount of MMA produced was low, so that the amount of unreacted methanol recycled was large, and as a result, the amount of steam used increased and the economic efficiency deteriorated. Moreover, the productivity was low and the reactor was large. To improve the economy, it is desirable to increase the aldehyde concentration and the reaction temperature as much as possible.
JP-069813 discloses a catalyst system containing palladium and bismuth with a methacrolein concentration of 20% and a reaction temperature of 80 ° C.
Is shown. However, under such high methacrolein concentration and high reaction temperature conditions, 9
No high methacrolein-based MMA selectivity of more than 0% has been obtained. Further investigations by the present inventors have revealed that, under more severe conditions in which the concentration of methacrolein is increased to 30%, the degradation reaction of methacrolein is likely to occur, and the selectivity of MMA based on methacrolein is further deteriorated. .

The catalyst supported on palladium-bismuth (Pd / Bi) of Example 17 described in JP-B-62-007902
Atomic ratio is 3 / 1.53, X-ray diffraction angle (2θ) is 38.9
In (0), the decomposition reaction of methacrolein was likely to occur, and the selectivity of MMA based on methacrolein was lowered. Further, the palladium-bismuth supported catalyst of Example 2 described in JP-B-5-069813 (Pd / Bi atomic ratio: 3 /
2.55) is thought to contain excess bismuth, and is considered to be due to the oxidation of the alcohol itself to a different aldehyde and a different carboxylic acid ester from the aldehyde (for example, methyl formate and ethanol when methanol is used as the alcohol). In this case, ethyl acetate) was produced as a by-product, and it was revealed that the selectivity based on alcohol was reduced.
90% at high temperature and high aldehyde concentration to improve economy
It has been awaited to develop a catalyst system having a high MMA selectivity higher than the above and a catalyst having a low by-product of methyl formate.

Further, when the carboxylate production reaction is continued at a high methacrolein concentration and a high reaction temperature, which are severe reaction conditions, a problem has emerged that the change was not recognized as small under conventional mild conditions. That is, it has been found from the studies of the present inventors that the catalytic activity and the selectivity of the carboxylic acid ester are gradually reduced. To ensure a certain level of reactivity,
It has to be taken into account that the catalyst is extracted out of the system in a relatively short cycle and a new catalyst is charged, or a regeneration treatment or the like is performed, and then the catalyst is charged again, which is a problem in terms of operability and economy.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a method for producing a carboxylic acid ester by reacting an aldehyde with an alcohol and molecular oxygen in the presence of a catalyst containing palladium and bismuth. Even under the reaction conditions, the selectivity of the carboxylic acid ester is high, and a catalyst that enables a method for producing a carboxylic acid ester with a small amount of by-products derived from alcohol, and a method for producing a carboxylic acid ester using the catalyst, Provides an economical manufacturing method that enables continuous operation while maintaining stable catalyst performance, stably developing excellent reactivity over a long period of time without removing the catalyst from the reactor and adding regeneration treatment etc. Is to do.

[0010]

The present inventors have found that even under reaction conditions in which the reaction temperature is high and the aldehyde concentration in the reaction system is high, the selectivity of the target carboxylic acid ester is high, and furthermore, for example, formic acid In order to develop a catalyst having a small amount of by-products derived from alcohols such as methyl, the present inventors have made intensive studies on a catalyst system containing palladium and bismuth and completed the present invention.

That is, the present invention provides: Palladium and bismuth supported on a carrier,
A catalyst for producing a carboxylic acid ester from an aldehyde, an alcohol and molecular oxygen, comprising (P
d / Bi) The atomic ratio (S) is 3 / 0.8 ≦ (S) ≦ 3 /
1.4, and the X-ray diffraction angle (2θ) of the maximum intensity peak in the powder X-ray diffraction pattern of the catalyst is 3
1. a catalyst for producing a carboxylic acid ester, which is in the range of 8.55 to 38.85 degrees; 2. A method for producing a carboxylic acid ester, which comprises using the catalyst described in 1 above when producing a carboxylic acid ester from an aldehyde, an alcohol, and molecular oxygen. A carboxylic acid characterized in that, when continuously producing a carboxylic acid ester from an aldehyde, an alcohol and molecular oxygen, the reaction is carried out while using the above-mentioned catalyst and adding a substance containing bismuth to a reactor. 3. a method for producing an ester; The partial pressure of oxygen at the outlet of the reactor was maintained at 0.8 kg / cm ² or less, and the bismuth concentration in the reactor was set at 0.
4. the method for producing a carboxylic acid ester according to the above item 3, wherein the content is in the range of 01 to 100 ppm; 5. The catalyst for producing a carboxylic acid ester according to 1 above, wherein the aldehyde is methacrolein, acrolein or a mixture thereof, and the alcohol is methanol. Wherein the aldehyde is methacrolein, acrolein or a mixture thereof, and wherein the alcohol is methanol, the method for producing a carboxylic acid ester of the above 2, 3 or 4;
Is provided.

The inventors of the present invention have previously described Japanese Patent Publication No. 62-0790.
Palladium and bismuth, which were proposed in Japanese Patent Publication No.
Of the intermetallic compound species bonded in a number ratio, an atomic ratio of 3/1
Pd _ThreeBi₁Species and X-ray diffraction angle for highly active catalysts
Pd in the measurement of (2θ)_FiveBi _TwoThe peak corresponding to the species
From what was seen, Pd with an atomic ratio of 5/2_FiveBi_TwoNote to seed
And the composition and catalyst properties etc.
Detailed research was advanced.

As a result, in the method for producing a carboxylic acid ester from an aldehyde, an alcohol and molecular oxygen, palladium and bismuth have an atomic ratio (Pd / Bi) of 3
/0.8 to 3 / 1.4 so as to have the maximum peak in the X-ray diffraction angle (2θ) of 38.55 to 38.85 degrees in the powder X-ray diffraction pattern of the catalyst. When a novel catalyst is used, even when the reaction is carried out under a reaction condition in which the aldehyde concentration and the reaction temperature are high, the selectivity of the carboxylic acid ester is high, and the by-product derived from alcohol such as methyl formate is small. I found it.

Further, under these reaction conditions, the catalytic activity and the selectivity of the carboxylic acid ester decrease over time, and the cause was also examined. As a result, the amount of bismuth carried by the deteriorated catalyst decreased. It was found that about 0.01 to several ppm of bismuth was eluted in the reaction solution. Therefore, as a result of a detailed study of the mechanism of dissolution and degradation of bismuth from the catalyst, when the reaction was performed while supplying a small amount of bismuth-containing substance to the reactor, bismuth was taken into the catalyst to suppress catalyst deterioration and ensure stable continuous operation. I found that I can do it. The present invention has been completed based on these findings.

Hereinafter, the present invention will be described in detail. In the catalyst of the present invention, palladium and bismuth are added to the support at a (palladium / bismuth) atomic ratio of 3 / 0.8 to 3 /
It is necessary to be carried in the range of 1.4. If the amount of bismuth exceeds 1.4 in the above atomic ratio, in the production of carboxylic acid ester by reaction of aldehyde with alcohol and molecular oxygen using this catalyst, formation of by-products such as methyl formate is remarkable. Becomes If it is less than 0.8, the selectivity of the target carboxylic acid ester such as methyl methacrylate (hereinafter referred to as MMA) is greatly reduced due to the decomposition of the aldehyde.

In the catalyst of the present invention, the powder X-ray diffraction pattern has a maximum intensity peak at an X-ray diffraction angle (2θ) 3.
It is necessary to show in the range of 8.55 to 38.85 degrees. Below 38.55 degrees, by-products such as methyl formate are significantly generated. When the temperature exceeds 38.85 degrees, the decomposition of the aldehyde as a starting material becomes remarkable, and the selectivity of the target carboxylic acid ester such as MMA decreases.

The catalyst of the present invention which satisfies these two requirements has a carboxylic acid ester such as MMA of 90%.
High selectivity exceeding. This effect is particularly important when producing a carboxylic acid ester under industrially advantageous reaction conditions of high temperature and high aldehyde concentration. The method for producing the catalyst of the present invention will be described. Reducible palladium compounds,
Or a catalyst precursor supporting a reducible palladium compound and a reducible bismuth compound, containing a bismuth ion or a bismuth complex, and further containing at least one selected from C1 to C5 fatty acids, alkali metal salts and alkaline earth metal salts. The catalyst of the present invention can be produced by reduction in a solution of water, alcohol or a mixture thereof containing the compound.

In the present invention, the catalyst precursor is a palladium compound that can be reduced (hereinafter referred to as a palladium compound), or a palladium compound and a bismuth compound that can be reduced (hereinafter referred to as a bismuth compound) supported on a carrier. And is used as a starting material in one embodiment of the method for producing a catalyst of the present invention.

In the catalyst of the present invention, the supported palladium / bismuth atomic ratio is important. Therefore,
The loading ratio of the palladium compound / bismuth compound of the catalyst precursor used in the production of the catalyst of the present invention must be selected from the range of 3/0 to 3 / 1.4 by the atomic ratio of Pd / Bi. Preferably it is selected from the range of 3/0 to 3 / 0.8.

In the present invention, the loading ratio of palladium compound / bismuth compound is 3/0 to 3/0 in atomic ratio of Pd / Bi.
The catalyst precursor in the range of 3 / 1.4 can be prepared by a known method. To explain a typical preparation method, a carrier is added to an aqueous solution containing a palladium compound or a palladium compound and a bismuth compound. , 20-10
It is obtained by holding the carrier at 0 ° C. for 1 to 24 hours, impregnating the carrier with an aqueous solution of a palladium compound or an aqueous solution containing a palladium compound and a bismuth compound, and supporting the carrier with the palladium compound or the palladium compound and the bismuth compound.

Examples of the palladium compound or bismuth compound used for preparing the catalyst precursor include organic acid salts such as formate and acetate; inorganic acid salts such as sulfate, hydrochloride and nitrate; ammine complexes and benzonitrile An organic metal complex such as a complex is appropriately selected from oxides, hydroxides, and the like. As the palladium compound, palladium chloride, palladium acetate, and the like, and as the bismuth compound, an organic bismuth compound such as triphenylbismuth is preferably used. You.

The carrier used in the present invention can be widely selected from silica, alumina, silica-alumina, crystalline metallosilicate, magnesia, silica-alumina-magnesia, magnesium hydroxide, titania, calcium carbonate, activated carbon and the like. From the viewpoint of mechanical strength, it is preferable to select from silica-alumina, silica-alumina-magnesia, and crystalline metallosilicate.

The amount of palladium carried on the carrier is not particularly limited, but is usually 0.1 to 20% by weight, preferably 1 to 10% by weight based on the weight of the carrier. The amount of bismuth supported is not particularly limited either, and is usually 0.1 to 20% by weight, preferably 1 to 10% by weight, based on the weight of the carrier. The atomic ratio is important.

The catalyst metal species contained in the catalyst precursor includes, in addition to palladium and bismuth,
For example, lead, mercury, thallium, tellurium, nickel, chromium, cobalt, indium, tantalum, copper, zinc, zirconium, hafnium, tungsten, manganese, silver,
Rhenium, antimony, tin, rhodium, ruthenium,
Iridium, platinum, gold, titanium, aluminum, boron,
It may contain silicon or the like. The content of these different elements is usually not more than 5% by weight, preferably not exceeding 1% by weight, based on the amount of all the catalyst species after reduction. Further, those containing at least one selected from alkali metals and alkaline earth metals have the advantage of increasing the reaction activity. The amount of alkali metal and alkaline earth metal added
It is usually selected from the range of 0.01 to 30% by weight, preferably 0.01 to 5% by weight, based on the amount of all the catalyst species after reduction. These dissimilar elements or alkali metals and alkaline earth metals may penetrate a small amount between crystal lattices, or may be substituted with some of the crystal lattice metals. Also,
These different element compounds, alkali metal compounds and alkaline earth metal compounds may be added to a solution containing a palladium compound or a bismuth compound at the time of preparing the catalyst precursor, and may be adsorbed or adhered to the carrier, or may be a carrier previously loaded with these. Can be used to prepare a catalyst precursor. It is also possible to add a different element to the catalyst by adding it to the reaction system when performing the reduction reaction for preparing the catalyst.

The catalyst of the present invention is obtained by dispersing the above-mentioned catalyst precursor supporting the palladium compound or the palladium compound and the bismuth compound in a solvent comprising water, an alcohol such as 1-propanol or a mixture thereof, 2
It is necessary to obtain the supported palladium / bismuth catalyst of the present invention having a supported composition ratio of 3 / 0.8 to 3 / 1.4 at a palladium / bismuth atomic ratio at 0 to 200 ° C, preferably 40 to 160 ° C. Amount of bismuth is present and furthermore C1-C5
In a solution containing at least one compound selected from fatty acids, alkali metal salts and alkaline earth metal salts,
It can be obtained by reduction with a reducing agent such as formalin, formic acid, hydrazine or molecular hydrogen.

When the reducing agent is formalin, hydrazine or formic acid, it is only necessary to add a water and / or 1-propanol solution of formalin, hydrazine and formic acid to the catalyst precursor dispersion. The amount of formalin, formic acid, hydrazine, methanol, or molecular hydrogen used is generally 0.1 to 100 with respect to the amount of the palladium compound carried on the catalyst precursor.
The mole is used, and practically 0.5 to 10 moles is used.
There is no particular problem if the amount exceeds this amount. If an alkali such as caustic soda is added at the same time as the reducing agent, the reduction proceeds more easily. Usually, the amount of alkali is about 1/100 to equimolar to the reducing agent.

At the time of reduction, a bismuth ion or a bismuth complex is allowed to coexist. For that purpose, it is common to add the bismuth-containing substance to water in which the catalyst precursor is dispersed, 1-propanol or a mixed solution thereof.
When adding the bismuth-containing substance, there is no particular limitation as long as the substance can be dissolved as a bismuth ion or a bismuth complex. The amount of the bismuth compound to be added varies depending on the target catalyst precursor, but is 3 / 0.8 to Pd / Bi atomic ratio.
The amount of bismuth compound necessary to obtain the catalyst of the present invention having a supported composition ratio of 3 / 1.4 is calculated by adding (Pd in a palladium compound supported on a catalyst precursor) / (added Bi)
Select the required amount from the range of 3/0 to 3 / 1.4 in atomic ratio,
The catalyst is dispersed in a solution of a bismuth compound corresponding to this amount, such as 1-propanol, to effect reduction. The bismuth compound may be added before starting the reduction operation, or may be added continuously or intermittently during the reduction operation.

The Pd / Bi ratio of the catalyst precursor is already 3/0.
Even if it is in the range of 8 to 3 / 1.4, the required amount of bismuth compound is added as long as the atomic ratio of Pd / Bi does not finally exceed 3 / 1.4, and the reduction is performed as described above. Can be. When the Pd / Bi ratio of the catalyst precursor is already 3 / 1.4, the reduction reaction is performed without adding a bismuth compound.

Further, at the time of the reduction, a lower (C 1 -C 5) fatty acid and at least one compound of an alkali metal salt and an alkaline earth metal salt are allowed to coexist. The alkali metal compound and the alkaline earth metal compound are selected from organic acid salts, inorganic acid salts, hydroxides and the like. The amount of addition is about 0.1 to 30 times mol based on the supported palladium compound.
More preferably, it is selected from the range of 1 to 15 times mol.

The lower (C 1 -C 1) used in the present invention
5) Examples of the fatty acid include propionic acid, acetic acid, butyric acid, and maleic acid. The amount of the lower fatty acid to be added is about 0.1 to 30 times the molar amount of the supported palladium compound. More preferably, it is selected from the range of 1 to 15 times mol. Practically, it is preferable to select acetic acid which is easily available. These lower fatty acids may be added simultaneously with the reducing agent, but it is more effective to add them before adding the reducing agent. The addition of these lower fatty acids is particularly effective when applied to a catalyst precursor in which both a palladium compound and a bismuth compound are supported.

According to the above-mentioned production method, the present inventors
Pd ₃ Bi which is a good Pd—Bi intermetallic compound having an X-ray diffraction angle (2θ) in the range of 38.85 to 38.85 degrees
It has been found that a catalyst in which ₁ and Pd ₅ Bi ₂ are supported can be obtained. It can be produced using any of a catalyst precursor in which only a palladium compound is supported and a catalyst precursor in which both a palladium compound and a bismuth compound are supported. According to the above manufacturing method, the X-ray diffraction angle (2
(θ) is in the range of 38.85 to 38.85 degrees. The reason why a catalyst in which Pd ₃ Bi ₁ and Pd ₅ Bi ₂ having high catalyst perfection are supported can be obtained is that hydrogen ions, alkali metal cations or alkaline earths are obtained. It is presumed that bismuth ions selectively interact with lattice defect portions of the Pd / Bi compound by the action of the metal-like cations, thereby helping Bi to be easily introduced into the crystal lattice.

Further, in the above method for producing a catalyst of the present invention, instead of adding a lower (C 1 -C 5) fatty acid and at least one compound of an alkali metal salt and an alkaline earth metal salt, a lower (C 1 -C 5) It is more preferable to add an alkali metal salt or an alkaline earth metal salt of a fatty acid. The alkali metal salt or alkaline earth metal salt of a lower fatty acid to be added is added in an amount of about 0.1 to 30 moles based on the supported palladium compound (as palladium) of the catalyst precursor. More preferably, it is selected from the range of 1 to 15 times mol. As the alkali metal salt or alkaline earth metal salt of a lower fatty acid, sodium acetate, magnesium acetate and the like are preferable.

The present inventors have found that by adding these metal salts, the lattice defects of the resulting Pd ₃ Bi ₁ and Pd ₅ Bi ₂ intermetallic compounds can be reduced, resulting in good Pd-B
It has been found that a catalyst in which the i intermetallic compound is supported can be obtained. This effect is effective for both a catalyst precursor in which only a palladium compound is supported and a catalyst precursor in which both a palladium compound and a bismuth compound are supported.

The above-mentioned reduction operation can be performed at a temperature of from room temperature to 200 ° C. This is performed by applying a pressure necessary for maintaining the liquid phase. Preferably, it is carried out at 40 to 160 ° C. and normal pressure to several atmospheres. The reduction treatment time varies depending on the type of catalyst and treatment conditions, but is generally several minutes to 100 hours. It is convenient to set conditions so that the process is completed within a few hours. Completion of the reduction treatment can be easily determined by measuring the X-ray diffraction angle of the maximum intensity peak at the powder X-ray diffraction angle of the obtained catalyst. If the X-ray diffraction angle does not change, the process may be completed. The reactor used for the reduction is not particularly limited, and can be a usual stirred tank reactor.

The catalyst of the present invention can be suitably used in a reaction for producing a carboxylic acid ester by reacting an aldehyde with an alcohol and molecular oxygen. The amount of catalyst used depends on the type of reaction raw materials, catalyst composition and preparation method, reaction conditions,
Although it can be largely changed depending on the reaction mode and the like, there is no particular limitation, but when the catalyst is reacted in a slurry state, it is preferable to use 0.04 to 0.5 kg per liter of the reaction system.

The aldehyde used in the production of the carboxylic acid ester of the present invention includes, for example, formaldehyde; C1-C10 aliphatic saturated aldehydes such as acetaldehyde, propionaldehyde, isobutyraldehyde and glyoxal; acrolein, methacrolein;
C3-C10 aliphatic α / β-unsaturated aldehydes such as crotonaldehyde; C6 such as benzaldehyde, tolylaldehyde, benzylaldehyde and phthalaldehyde
-C20 aromatic aldehydes; and derivatives of these aldehydes. These aldehydes can be used alone or as a mixture of two or more kinds.

The alcohol used in the production of the carboxylic acid ester includes, for example, C 1 -C 10 such as methanol, ethanol, isopropanol and octanol.
Aliphatic saturated alcohols; C2-C10 diols such as ethylene glycol and butanediol; allyl alcohol;
C3-C10 aliphatic unsaturated alcohols such as methallyl alcohol; C6-C20 aromatic alcohols such as benzyl alcohol; These alcohols can be used alone or as a mixture of two or more kinds.

In the production of the carboxylic acid ester according to the present invention, the amount ratio of the aldehyde to the alcohol is not particularly limited.
Although it can be carried out in a wide range such as 1 to 1000, it is generally carried out in a range of 1/2 to 1/50 in molar ratio.
Further, the method for producing a carboxylic acid ester of the present invention can be carried out by any conventionally known method such as a gas phase reaction, a liquid phase reaction, and a perfusion solution. For example, when the reaction is carried out in the liquid phase, any reactor type such as a bubble column reactor, a draft tube reactor, a stirred tank reactor, etc. can be used.

The oxygen used in the method for producing a carboxylic acid ester of the present invention is molecular oxygen, that is, oxygen gas itself or a mixed gas obtained by diluting oxygen gas with a diluent inert to the reaction, such as nitrogen or carbon dioxide gas. And air can also be used. The reaction pressure can be carried out in any wide pressure range from reduced pressure to increased pressure.
It is performed at a pressure of ２０20 kg / cm ² . The total pressure should be set so that the oxygen concentration of the gas discharged from the reactor does not exceed the explosion limit (8%).

When the carboxylic acid ester is continuously produced, it is preferable to carry out the reaction by adding bismuth to the reaction system. The amount of bismuth added to the reactor varies depending on the reaction conditions, reaction type, and type of catalyst used, and it is difficult to determine a specific value.However, when there is a large amount of bismuth to be added, treatment to recover and detoxify wastewater It is not preferable because the cost increases. The present inventors have found that the required amount of bismuth in the reaction system depends on the oxygen partial pressure. Therefore, by setting the oxygen partial pressure at the reactor outlet to 0.8 kg / cm ² or less, 0.01 to It has been found that it can be reduced to 100 ppm. Therefore, the amount of bismuth can be reduced as much as possible by lowering the oxygen partial pressure at the reactor outlet, and 0.01 to 100 ppm (weight basis; hereinafter,
Omitted. It is preferable to set the necessary minimum amount of bismuth from the range of)). Oxygen partial pressure at reactor outlet 0.8
Even if it is higher than kg / cm ² , the amount of bismuth
If more than pm, but not any problem in going to maintain the catalyst performance, since undesirable in view of cost and the like economical as described above, by setting a 0.8 kg / cm ² or less, adding The amount of bismuth is reduced to 0.01 to 100 ppm.

Oxygen partial pressure at the outlet of the reactor is 0.02 kg
/ Cm ² or more is sufficient if 0.8 kg / cm ² or less, and more preferably the oxygen partial pressure at the reactor outlet side 0.
When the content is 4 kg / cm ² or less, the amount of bismuth can be reduced, which is preferable. The bismuth-containing substance added to the reactor can be used in principle as long as it dissolves as bismuth ions in the reactor, but an organic bismuth compound such as triphenylbismuth is preferably used.

In the method for producing a carboxylic acid ester according to the present invention, a compound of an alkali metal or an alkaline earth metal (for example, oxide, hydroxide, carbonate,
It is preferable to maintain the pH of the reaction system at 6 to 9 by adding a carboxylate. These alkali metal or alkaline earth metal compounds can be used alone or in combination of two or more.

The method for producing a carboxylic acid ester using the catalyst of the present invention can be carried out at a high temperature of 100 ° C. or more when the aldehyde concentration of the reaction system is increased to 30% by weight or more, but preferably 30 to 100 ° C. ° C, more preferably 60-90 ° C. The reaction time is not particularly limited, and cannot be unambiguously determined because it varies depending on the set conditions, but is usually 1 to 20 hours.

[0044]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described more specifically with reference to the following Examples and Comparative Examples. In the following Examples and Comparative Examples, the Pd / Bi atomic ratio of the catalyst and the X-ray diffraction angle of the maximum intensity peak in the powder X-ray diffraction pattern were measured by the following methods. [Determination of Pd / Bi Atomic Ratio] The Pd / Bi atomic ratio was measured by inductively coupled plasma (ICP) emission spectrometry using JY-38P2 manufactured by Seiko Instruments Inc. as an ICP emission spectrometer. [Measurement of X-ray diffraction angle (2θ) of maximum intensity peak in powder X-ray diffraction pattern] The X-ray diffraction angle (2θ) of the maximum intensity peak in the powder X-ray diffraction pattern was 3 ° C. at 160 ° C. under vacuum exhaust. After removing the low-molecular adsorbing / occluding components (mainly hydrogen) by performing a time treatment, use an X-ray diffractometer RAD-RA manufactured by Rigaku Denki Co., Ltd. according to the usual measurement procedure of powder X-ray diffraction. , CuKα1 wire (1.54
05981 °), the diffraction angle 2θ of the maximum intensity peak of the catalyst was measured. The measurement must be performed with particularly high precision. For example, United States, National Institute of Standards
The X-ray diffraction angle (2θ) of the maximum intensity peak attributed to the diffraction of each of the (111) plane and the (200) plane of the LaB ₆ compound as determined by & Technology as the standard reference substance 660 is 37.441 °, 43 .506 °. As a result, a result with high measurement accuracy and good reproducibility can be obtained.

[0045]

Example 1 Aqueous silica sol (Snowtex N-30)
(SiO ₂ content: 30% by weight) Nissan Chemical Co., Ltd.)
Aluminum nitrate and magnesium nitrate were Al /
After adding and dissolving so that the ratio of Si becomes 10 mol% and the ratio of Mg / Si becomes 10 mol%, the carrier is spray-dried with a spray dryer set at a temperature of 130 ° C. to obtain a spherical carrier having an average particle diameter of 60 μm. Obtained. 2 hours at 300 ° C in air, then 6
After firing at 00 ° C. for 3 hours, this was used as a carrier. About 2.
1 kg of carrier is added to 5 liters of water, and palladium chloride 8
A solution prepared by dissolving 3.5 g and 55 g of sodium chloride in 500 cc of water was added, and the mixture was stirred at 90 ° C. for 30 minutes to completely adsorb palladium chloride on the carrier to prepare a catalyst precursor.
Then, the aqueous solution was 375 of a 50% 1-propanol aqueous solution.
After replacing with 0 g and heating to 90 ° C., sodium acetate 320
g in 800 cc of water, and then add
96.7 g of triphenylbismuth was added to 1-propanol 8
A solution dissolved in 70 g was added, and a 1-propanol solution containing 235 g of hydrazine was added dropwise with stirring to perform reduction adsorption treatment for 6 hours, and the catalyst [Pd ⁵ Bi ^4.58 / SiO 2
^{_{2 -Al 2 O 3 -Mg 4 O}} (Pd, the right shoulder of the numbers Bi, parts by weight per 100 parts by weight of the carrier, the right shoulder of numeric Mg, refer to parts per SiO ₂ 100 parts by weight) ]
I got When the obtained catalyst was analyzed by the above method, the composition ratio of Pd / Bi supported was 3 / 1.38 in atomic ratio, and the X-ray diffraction angle (2θ) of the maximum intensity peak in the powder X-ray diffraction pattern was 38.705. Degree. This catalyst 240
g was equipped with a catalyst separator, and the liquid phase was charged to an external circulation type stainless steel bubble column reactor having a volume of 1.2 liters to carry out a reaction. 0.57 L / hr of 36.7% by weight methacrolein / methanol solution, 2-4% by weight of NaOH /
A methanol solution was continuously supplied to the reactor at a rate of 0.06 liter / hr (the methacrolein concentration of the reaction system comprising the above two solutions was about 33% by weight), the reaction temperature was 80 ° C., and the reaction pressure was 5 kg / cm ^2. , A methyl methacrylate (MMA) generation reaction was performed while adjusting the amount of air so that the outlet oxygen concentration was 4.0% by volume (corresponding to an oxygen partial pressure of 0.2 kg / cm ² ). The NaOH concentration supplied to the reactor was controlled so that the pH of the reaction system was 7.1. The reaction product was continuously withdrawn from the reactor outlet by overflow. When the reaction product withdrawn after 10 hours was analyzed, the conversion of methacrolein was 63.4.
%, The selectivity of MMA was 90.8%, propylene was produced as a by-product at a selectivity of 1.12%, and methyl formate was produced at 0.064 mol / mol MMA.

[0046]

Example 2 Supported catalyst in Example 1 without adding Mg to the carrier
[Pd^FiveBi^4.58/ SiO_Two-Al _TwoO_Three]
Was. The obtained supported catalyst was analyzed by the method described above.
The Pd / Bi supported composition ratio was 3 / 1.37 in atomic ratio,
-Ray diffraction of maximum intensity peak in powder X-ray diffraction pattern
The angle (2θ) was 38.780 degrees. Using this catalyst
The reaction was carried out under the same conditions as in Example 1. 10 after the start of the reaction
When the reaction product was analyzed after a lapse of time,
Tacrolein conversion is 58.5%, MMA is selectivity
90.4%, selectivity of propylene as by-product 1.5
2%, and methyl formate contained 0.063 mol / mol
MMA was generated.

[0047]

Example 3 A catalyst [Pd ^{5] was} prepared in the same manner as in Example 1 except that the Mg / Si ratio of the carrier was changed to 6 mol%.
Bi ^4.58 / SiO ₂ —Al ₂ O ₃ —Mg ^2.4 O] was prepared. When the obtained supported catalyst was analyzed by the above method, the Pd / Bi supported composition ratio was 3 / 1.40 in atomic ratio, and the X-ray diffraction angle (2θ) of the maximum intensity peak in the powder X-ray diffraction pattern was 38. It was 551 degrees. Using this catalyst, a reaction was carried out under the same conditions as in Example 1. 10 after the start of the reaction
When the reaction product was analyzed after a lapse of time, the conversion of methacrolein was 60.8%, the selectivity of MMA was 91.3%, and the selectivity of propylene as a by-product was 0.4.
1%, and 0.073 mol / mol MMA of methyl formate was produced.

[0048]

Example 4 A catalyst [Pd ⁵ Bi ^2.62 / SiO ₂ —Al ₂ O ₃ −] was prepared in the same manner as in Example 3 except that the amount of Bi supported was changed to 2.62 parts by weight (based on 100 parts by weight of the carrier). Mg
^2.4 O] was prepared. When the obtained supported catalyst was analyzed by the above-described method, the Pd / Bi supported composition ratio was 3 in atomic ratio.
/0.80, the X-ray diffraction angle (2θ) of the maximum intensity peak in the powder X-ray diffraction pattern was 38.849 degrees.
Using this catalyst, an MMA formation reaction was performed under exactly the same conditions as in Example 1, and the reaction product was analyzed 10 hours after the start of the reaction.
9.2%, MMA was formed at a selectivity of 90.1%, and propylene was formed as a by-product at a selectivity of 1.90%.
Methyl formate was formed at 0.038 mol / mol MMA.

[0049]

COMPARATIVE EXAMPLE 1 A supported catalyst [Pd ⁵ Bi ^1.64 / Pd ⁵ Bi ^1.64 /
SiO ₂ —Al ₂ O ₃ —Mg ⁴ O, Pd / Bi supported composition ratio is 3 / 0.51 in atomic ratio, and the X-ray diffraction angle (2θ) of the maximum intensity peak in the powder X-ray diffraction pattern is 39.08.
3 times], and the reaction was carried out under the same conditions as in Example 1.
When the reaction product was analyzed 10 hours after the start of the reaction, the conversion of methacrolein was 52.8%.
MMA was produced at a selectivity of 79.7%, propylene as a by-product was produced at a selectivity of 12.35%, and methyl formate was produced at 0.024 mol / mol MMA.

[0050]

Comparative Example 2 A supported catalyst [Pd ⁵ Bi ^6.5 / S] was prepared in the same manner as in Example 3 except that the amount of bismuth supported was changed to 6.5 parts by weight.
iO ₂ —Al ₂ O ₃ —Mg ^2.4 O, the composition ratio of Pd / Bi supported is 3 / 1.98 in atomic ratio, and the X-ray diffraction angle (2θ) of the maximum intensity peak in the powder X-ray diffraction pattern is 38.51.
8 °), and the reaction was carried out under the same conditions as in Example 1.
When the reaction product was analyzed 10 hours after the start of the reaction, the conversion of methacrolein was 53.1%,
MMA is produced at a selectivity of 86.5%, propylene as a by-product is produced at a selectivity of 0.11%, and methyl formate is produced at a concentration of 0.1%.
195 mol / mol MMA was produced.

[0051]

Comparative Example 3 A supported catalyst [Pd ⁵ Bi ^6.5 / S] was prepared in the same manner as in Example 1 except that the amount of bismuth supported was changed to 6.5 parts by weight.
iO ₂ —Al ₂ O ₃ —Mg ⁴ O, Pd / Bi supported composition ratio is 3 / 1.99 in atomic ratio, and the X-ray diffraction angle (2θ) of the maximum intensity peak in the powder X-ray diffraction pattern is 38.592.
) Was prepared, and the reaction was carried out under the same conditions as in Example 1. When the reaction product was analyzed 10 hours after the start of the reaction, the conversion of methacrolein was 56.3%.
MA is produced at a selectivity of 87.9%, propylene as a by-product is produced at a selectivity of 0.33%, and methyl formate is produced at a selectivity of 0.13%.
81 mol / mol MMA was produced.

[0052]

Comparative Example 4 Using the supported catalyst of Comparative Example 1 as it was, an MMA formation reaction was carried out in the same manner as in Example 1 except that the methacrolein concentration was 10% by weight and the reaction temperature was 50 ° C. When the reaction product was analyzed 10 hours after the start of the reaction, the conversion of methacrolein was 67.
The selectivity was 9%, MMA was 90.8%, propylene as a by-product was formed at a selectivity of 1.0%, and methyl formate was formed at 0.025 mol / mol MMA.

[0053]

Example 5 In Example 1, the carrier was silica gel (Carrierct 10) manufactured by Fuji Silysia Ltd., and Mg was changed to K.
A catalyst [Pd ⁵ Bi ^3.93 K ^3.20 / SiO ₂ ] was prepared in the same manner except that the Si content was 5 mol% and the amount of Bi supported was 3.93 parts by weight (based on 100 parts by weight of the carrier).
When the obtained supported catalyst was analyzed by the method described above, P
The composition ratio of d / Bi supported was 3 / 1.19 in atomic ratio, and the X-ray diffraction angle of the maximum intensity peak in the powder X-ray diffraction pattern (2
θ) was 38.627 degrees. Using this catalyst, an MMA formation reaction was performed under exactly the same conditions as in Example 1, and the reaction product was analyzed 10 hours after the start of the reaction. The conversion of methacrolein was 65.3%.
A has a selectivity of 91.2%, propylene as a by-product has a selectivity of 0.91%, and methyl formate has a selectivity of 0.05%.
6 mol / mol MMA was produced.

[0054]

EXAMPLE 6 A carrier was used in which lithium was supported on alumina (trade name: Sumitomo Activated Alumina) at a Li / Al concentration of 1.0% by weight, and the amount of Bi supported was 3.27 parts by weight (carrier). (Based on 100 parts by weight) except that the supported catalyst [Pd ⁵ Bi ^3.27 Li ^1.0 /
Al ₂ O ₃ ] was prepared. When the obtained supported catalyst was analyzed by the above-mentioned method, the Pd / Bi supported composition ratio was 3 / 0.99 in atomic ratio, and the X-ray diffraction angle (2θ) of the maximum intensity peak in the powder X-ray diffraction pattern was 38. 832 degrees. Using this catalyst, a reaction was carried out under the same conditions as in Example 1. When the reaction product was analyzed 10 hours after the start of the reaction, the conversion of methacrolein was 60.2%, the selectivity of MMA was 90.3%, and the selectivity of propylene was 1.76% as a by-product. And 0.040 mol / mol MMA of methyl formate was produced.

[0055]

EXAMPLE 7 0.32% by weight of thallium as a dissimilar metal
2. with bismuth (based on 100 parts by weight of carrier)
A supported catalyst [Pd ⁵ Bi ^3.93 Tl ^0.32 / SiO ₂ —Al ₂ O _{3 was} prepared in the same manner as in Example 1 except that 93% by weight was supported.
-Mg ⁴ O] were prepared. When the obtained supported catalyst was analyzed by the above-mentioned method, the Pd / Bi supported composition ratio was 3 / 1.21 in atomic ratio, and the X-ray diffraction angle (2θ) of the maximum intensity peak in the powder X-ray diffraction pattern was 38. 731 degrees. Using this catalyst, a reaction was carried out under the same conditions as in Example 1. When the reaction product was analyzed 10 hours after the start of the reaction, the conversion of methacrolein was 62.7%, the selectivity of MMA was 90.7%, and the selectivity of propylene was 1.20% as a by-product. In addition, 0.065 mol / mol MMA of methyl formate was produced.

[0056]

Example 8 A reaction was carried out under the same conditions as in Example 1 except that methacrolein was changed to acrolein. When the reaction product was analyzed 10 hours after the start of the reaction, the conversion of acrolein was 62.0%, the selectivity of MA was 90.5%, and the selectivity of ethylene was 1.46% as a by-product. Further, 0.066 mol / mol MMA of methyl formate was produced.

[0057]

Example 9 240 g of the catalyst of Example 1 was charged into an externally circulating stainless steel bubble column reactor having a catalyst separation section and a liquid phase section of 1.2 liters, and 36.7% by weight of methacrolein / methanol was added. 0.54 l / hr, 2-4 wt% NaOH / methanol is supplied at 0.06 l / hr, the reaction temperature is 80 ° C., the reaction pressure is 5 kg / cm ² , and the outlet oxygen concentration is 4.0% by volume (oxygen Partial pressure 0.20kg / c
(corresponding to m ² ) while maintaining the reaction while adjusting the amount of air. The NaOH concentration was adjusted so that the pH of the reaction system was 7.1, and the bismuth concentration in the feed solution was 10 pp.
m, triphenylbismuth was dissolved in methacrolein / methanol and supplied continuously. When the reaction product extracted after 200 hours was analyzed, the conversion of methacrolein was 62.7% and the selectivity of MMA was 9%.
0.4%, selectivity of propylene as by-product 1.15
% And methyl formate was produced at 0.066 mol / mol MMA. At 2000 hours, the conversion of methacrolein was 62.4% and the selectivity of MMA was 90.1%.
%, Propylene as a by-product with a selectivity of 1.20%, and methyl formate containing 0.063 mol / mol MMA.
Had been generated.

[0058]

Example 10 A reaction was carried out for 2,000 hours in the same manner as in Example 9 except that bismuth was not added. Reaction time 20
At 0 hours, the conversion of methacrolein is 60.6%,
MMA is produced at a selectivity of 88.6%, propylene as a by-product is produced at a selectivity of 1.78%, and methyl formate is produced at a selectivity of 0.88%.
060 mol / mol MMA was produced. At 2000 hours, the conversion of methacrolein was 53.4%, MMA was formed at a selectivity of 81.1%, propylene was formed as a by-product at a selectivity of 7.3%, and methyl formate was formed at a rate of 0.035 mol /%. Molar MMA was formed.

[0059]

Example 11 A reaction pressure of 11 kg / cm ² and an outlet oxygen concentration of 7.2% by volume (oxygen partial pressure 0.792 kg / cm ²⁾
The reaction was continued for 2,000 hours by the same operation as in Example 9 except that the bismuth concentration in the feed solution was adjusted to 100 ppm. Analysis of the reaction product withdrawn after 200 hours showed a conversion of methacrolein of 64.3.
%, MMA was produced at a selectivity of 89.9%, propylene was produced as a by-product at a selectivity of 1.51%, and methyl formate was produced at 0.077 mol / mol MMA. 20
At 00 hours, methacrolein conversion was 63.8%, MMA was formed at a selectivity of 89.8%, propylene as a by-product was formed at a selectivity of 1.60%, and methyl formate was formed at a rate of 0.079 mol /%. Molar MMA was formed.

[0060]

Example 12 Except that the reaction pressure was 12 kg / cm ² , the outlet oxygen concentration was 7.5% by volume (corresponding to an oxygen partial pressure of 0.90 kg / cm ² ), and the bismuth concentration in the feed solution was 200 ppm. The reaction was continued for 2000 hours in the same manner as in Example 9. Analysis of the reaction product withdrawn after 200 hours showed that the conversion of methacrolein was 62.9%.
MMA was produced at a selectivity of 89.2%, propylene as a by-product was produced at a selectivity of 1.53%, and methyl formate was produced at a rate of 0.095 mol / mol MMA. 200
At 0 hours, the conversion of methacrolein is 62.5%,
MMA is produced at a selectivity of 88.9%, propylene as a by-product is produced at a selectivity of 1.82%, and methyl formate is produced at a concentration of 0.8%.
092 mol / mol MMA was produced.

[0061]

Example 13 Except that the reaction pressure was 12 kg / cm ² , the outlet oxygen concentration was 7.5% by volume (corresponding to an oxygen partial pressure of 0.90 kg / cm ² ), and the bismuth concentration in the feed solution was 100 ppm. The reaction was continued for 2000 hours in the same manner as in Example 9. When the reaction product extracted after 200 hours was analyzed, the conversion of methacrolein was 61.4%.
MMA was produced at a selectivity of 88.3%, propylene as a by-product was produced at a selectivity of 2.21%, and methyl formate was produced at 0.071 mol / mol MMA. 200
At 0 hours, the conversion of methacrolein is 55.9%,
MMA is produced at a selectivity of 84.9%, propylene as a by-product is produced at a selectivity of 5.56%, and methyl formate is produced at a yield of 0.5%.
059 mol / mol MMA was produced.

[0062]

According to the present invention, in producing a carboxylic acid ester by reacting an aldehyde and an alcohol with molecular oxygen, the yield based on the aldehyde and the alcohol can be obtained even under the reaction conditions in which the aldehyde concentration and the reaction temperature are increased to improve the economic efficiency. Can be improved at the same time. In addition, excellent catalyst performance can be maintained stably for a long period of time, the catalyst life is greatly improved, the frequency of catalyst replacement is low, and operability and economic efficiency are excellent.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hiroshige Okamoto 3-13-1, Shiodori, Kurashiki-shi, Okayama Prefecture Asahi Kasei Corporation

Claims (6)

[Claims] 1. A catalyst for producing a carboxylic acid ester from an aldehyde, an alcohol and molecular oxygen, comprising palladium and bismuth supported on a carrier, wherein the catalyst has a (Pd / Bi) atomic ratio (S) Is 3 / 0.8 ≦ (S)
≦ 3 / 1.4 and the X-ray diffraction angle of the maximum intensity peak in the powder X-ray diffraction pattern of the catalyst (2
(theta) is in the range of 38.55 to 38.85 degrees. 2. A method for producing a carboxylic acid ester, comprising using the catalyst according to claim 1 when producing a carboxylic acid ester from an aldehyde, an alcohol and molecular oxygen. 3. A method for producing a carboxylic acid ester continuously from an aldehyde, an alcohol and molecular oxygen by using the catalyst according to claim 1 and adding a bismuth-containing substance to a reactor. A method for producing a carboxylic acid ester. 4. The oxygen partial pressure at the reactor outlet is 0.8 kg / c.
m ² was kept below, and claim 3 method for producing carboxylic acid esters, wherein the in the range of 0.01~100ppm bismuth concentration by weight in the reaction system. 5. The catalyst for producing a carboxylic acid ester according to claim 1, wherein the aldehyde is methacrolein, acrolein or a mixture thereof, and the alcohol is methanol. 6. The method for producing a carboxylic acid ester according to claim 2, wherein the aldehyde is methacrolein, acrolein or a mixture thereof, and the alcohol is methanol.