JP3511350B2 - Catalyst for carboxylic acid ester production - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD 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 an industrially useful method for producing methyl methacrylate or methyl acrylate, for example, in the case of methyl methacrylate, methacrolein is oxidized with oxygen to produce methacrylic acid, and then methacrylic acid and methanol are used. A production method called a direct acid method for producing methyl methacrylate by reacting with is already industrialized. However, although the yield of the step of oxidizing methacrolein to methacrylic acid has been improved to the low 80% range through many years of catalyst improvement, it is still low and there is a lot of room for improvement. In addition, the heteropolyacid catalyst used has a difficulty due to thermal stability, and the decomposition thereof gradually progresses under reaction temperature conditions. Although catalyst improvements for improving heat resistance have been reported, it is said that the catalyst life is still insufficient for industrial catalysts.

On the other hand, methacrolein or acrolein (hereinafter referred to as (meth) acrolein) is reacted with methanol and molecular oxygen to give methyl methacrylate or methyl acrylate (hereinafter referred to as methyl (meth) acrylate) all at once. New ways to manufacture are in the limelight these days. This method is carried out by reacting (meth) acrolein with molecular oxygen in methanol, and the presence of a catalyst containing palladium is essential.

Conventionally, in this production method, hydrocarbons and carbon dioxide gas are produced by concurrent decomposition reaction of aldehyde, yield of the desired carboxylic acid ester is low, and alcohol itself is produced in parallel with the production reaction of carboxylic acid ester. Of different aldehydes by oxidation of carboxylic acid and different carboxylic acid ester from the aldehyde (for example, methyl formate when methanol is used as alcohol, ethyl acetate when ethanol is used)
Was produced as a byproduct, and the selectivity for alcohol standards was poor. Moreover, there is a drawback that the catalytic 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 the case of, a decomposition product such as propylene) was generated, which was far from the practical level.

The present inventors have found that the Japanese Examined Patent Publication Sho 62-007902.
In Japanese Patent Publication, a catalyst containing an intermetallic compound in which palladium and bismuth are bonded at a constant integer ratio is proposed, the decomposition reaction of (meth) acrolein is almost completely suppressed, 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 an advantage that the steps are shorter than the method via (meth) acrylic acid, which has a feeling of improvement in yield and improvement in catalyst life, as described above, and is industrially useful. Industrialization has been eagerly awaited as a new production method of polymer raw materials.

However, on the premise of industrial implementation, from the viewpoint of productivity and economic efficiency, the above Japanese Patent Publication No. 62-
The new production method using the catalyst proposed in Japanese Patent No.
The aldehyde concentration is as low as 10% or less and the reaction temperature is 6
The reaction is carried out under mild conditions of 0 ° C. or lower, and under these conditions, the MMA concentration produced is low, so the amount of unreacted methanol recycled is large, resulting in an increase in the amount of steam used and a deterioration in economic efficiency. Moreover, the productivity was low and the reactor was large. In order to improve economic efficiency, it is desirable to increase the aldehyde concentration and reaction temperature as much as possible.
In Japanese Patent Publication No. 069813, a catalyst system containing palladium and bismuth, a methacrolein concentration of 20% and a reaction temperature of 80 ° C.
An example of the reaction is shown. However, under such high methacrolein concentration and high reaction temperature conditions, 9
High MMA selectivity based on methacrolein above 0% has not been obtained. The inventors of the present invention have found that when the methacrolein concentration is further increased to 30% under more severe conditions, the decomposition reaction of methacrolein is likely to occur and the MMA selectivity based on methacrolein is further deteriorated. .

A palladium-bismuth-supported catalyst (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 MMA selectivity based on methacrolein decreased. In addition, the palladium-bismuth-supported catalyst of Example 2 (Paid / Bi atomic ratio is 3 /
It is considered that 2.55) contains an excessive amount of bismuth, and a different aldehyde due to oxidation of alcohol itself and a different carboxylic acid ester from the aldehyde (for example, when methanol is used as alcohol, methyl formate, ethanol 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
The advent of a catalyst system with a high MMA selectivity of over 10% and a low methyl formate byproduct is awaited.

Furthermore, when the carboxylic acid ester production reaction is continued at a high methacrolein concentration and a high reaction temperature, which are severe reaction conditions, a problem has emerged, in which a small change was not recognized under the conventional mild conditions. That is, it has been found from the study by 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 consideration that the catalyst is taken out of the system in a relatively short cycle, a new catalyst is charged, or a catalyst is subjected to a regeneration treatment and then charged again, which is a problem in terms of operability and economy.

[0009]

DISCLOSURE OF THE INVENTION The present invention involves reacting an aldehyde with an alcohol and molecular oxygen in the presence of a catalyst containing palladium and bismuth to produce a carboxylic acid ester, which has a high aldehyde concentration and a high reaction temperature. 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 less by-products derived from alcohol, and a method for producing a carboxylic acid ester using the catalyst, and Provides an economical manufacturing method that maintains constant catalyst performance and enables continuous operation while stably exhibiting excellent reactivity for a long period of time without extracting the catalyst from the reactor and adding regeneration treatment. To do.

[0010]

The present inventors have found that even under the reaction conditions of high reaction temperature and high aldehyde concentration in the reaction system, the selectivity of the desired carboxylic acid ester is high, and for example, formic acid is used. The present invention has been completed by intensively researching a catalyst system containing palladium and bismuth in order to develop a catalyst with less by-products derived from alcohols such as methyl.

That is, the present invention is: A catalyst for producing a carboxylic acid ester from an aldehyde, an alcohol and molecular oxygen, which comprises palladium and bismuth supported on a carrier, wherein the catalyst (Pd
/ Bi) 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 38.
1. A catalyst for producing a carboxylic acid ester, which is in the range of 55 to 38.85 degrees. 2. A method for producing a carboxylic acid ester, which comprises using the catalyst of the above 1 in producing a carboxylic acid ester from an aldehyde, an alcohol and molecular oxygen. When the carboxylic acid ester is continuously produced from aldehyde, alcohol and molecular oxygen, the reaction is carried out while using the catalyst of the above 1 and adding a substance containing triphenylbismuth to the reactor. 3. A method for producing a carboxylic acid ester, The oxygen partial pressure at the reactor outlet is maintained at 0.8 kg / cm ² or less, and the bismuth concentration in the reactor is 0.0 based on the weight.
The above 3 characterized in that the range is 1 to 100 ppm
4. The method for producing a carboxylic acid ester according to 5. 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. The method for producing the carboxylic acid ester according to the above 2, 3 or 4 wherein the aldehyde is methacrolein, acrolein or a mixture thereof and the alcohol is methanol.

The inventors of the present invention have previously proposed Japanese Patent Publication No. 62-00790.
Proposed in No. 2 gazette, palladium and bismuth have a uniform
Of the intermetallic compound species bonded at a numerical ratio, the atomic ratio of 3/1
Pd ₃Bi₁Seeds and X-ray diffraction angles for highly active catalysts
Pd in the measurement of (2θ)_FiveBi ₂The peak corresponding to the seed
From what was seen, Pd with an atomic ratio of 5/2_FiveBi₂Note to seeds
Furthermore, regarding its composition and catalyst physical properties, etc.
Detailed research was advanced.

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

Further, under such reaction conditions, the catalytic activity and the selectivity of the carboxylic acid ester are decreased with time. Therefore, as a result of investigating the cause, the amount of bismuth supported is decreased in the deteriorated catalyst. Correspondingly, 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 elution and deterioration mechanism of bismuth from the catalyst, when the reaction is carried out while supplying a small amount of the bismuth-containing substance to the reactor, bismuth is taken into the catalyst and the deterioration of the catalyst is suppressed to ensure stable continuous operation. I found that I can do it. The present invention has been completed based on these findings.

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

Further, the powder X-ray diffraction pattern of the catalyst of the present invention shows the maximum intensity peak at the X-ray diffraction angle (2θ) 3
It is necessary to show in the range of 8.55-38.85 degrees. If it is less than 38.55 degrees, the formation of by-products such as methyl formate is remarkable. If the temperature exceeds 38.85 degrees, the decomposition of the aldehyde as the starting material becomes remarkable, and the selectivity of the desired carboxylic acid ester such as MMA decreases.

The catalyst of the present invention satisfying these two requirements is 90% to carboxylic acid ester such as MMA.
Shows a high selectivity of over. 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,
Alternatively, a catalyst precursor carrying a reducible palladium compound and a reducible bismuth compound is contained in a bismuth ion or a bismuth complex, and 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 reducing in a solution of water, alcohol or a mixture thereof containing a compound.

In the present invention, the catalyst precursor is a reducible palladium compound (hereinafter referred to as a palladium compound) or a palladium compound and a reducible bismuth compound (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 in the catalyst precursor used for producing the catalyst of the present invention needs to be selected from the range of 3/0 to 3 / 1.4 in terms of Pd / Bi atomic ratio. It is preferably selected from the range of 3/0 to 3 / 0.8.

In the present invention, the loading ratio of the palladium compound / bismuth compound is 3/0 in terms of the 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 a palladium compound or an aqueous solution containing a palladium compound and a bismuth compound. , 20-10
It is maintained at 0 ° C. for 1 to 24 hours, and the carrier is impregnated with an aqueous palladium compound solution or an aqueous solution containing a palladium compound and a bismuth compound, and the palladium compound or the palladium compound and the bismuth compound is supported on the carrier.

Examples of the palladium compound or bismuth compound used for preparing the catalyst precursor include organic acid salts such as formates and acetates; inorganic acid salts such as sulfates, hydrochlorides and nitrates; ammine complexes and benzonitriles. An organic metal complex such as a complex is appropriately selected from oxides, hydroxides and the like. Palladium compounds such as palladium chloride and palladium acetate are preferably used, and bismuth compounds such as triphenylbismuth are preferably used. It

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 supported 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 supported amount of bismuth is also not particularly limited and is usually 0.1 to 20% by weight, preferably 1 to 10% by weight, based on the weight of the carrier. However, the supported amount of palladium / bismuth is rather than that of palladium / bismuth. Atomic ratio is important.

As the catalytic metal species contained in the catalyst precursor, in addition to palladium and bismuth, as a different element,
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 5% by weight or less, preferably 1% by weight or less, based on the total amount of the catalyst species after reduction. Further, those containing at least one selected from alkali metals and alkaline earth metals have advantages such as high reaction activity. The amount of alkali metal or alkaline earth metal added is
It is usually selected from the range of 0.01 to 30% by weight, preferably 0.01 to 5% by weight, based on the total amount of the catalyst species after reduction. A small amount of these different elements or alkali metals and alkaline earth metals may penetrate into the crystal lattice or may be substituted with a part of the crystal lattice metal. 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 a catalyst precursor and adsorbed or attached to a carrier, or a carrier carrying them in advance. Can also 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 carrying out the reduction reaction for preparing the catalyst.

In the catalyst of the present invention, the above-mentioned catalyst precursor carrying the palladium compound or the palladium compound and the bismuth compound is dispersed in a solvent consisting of water, an alcohol such as 1-propanol or a mixture thereof. Two
It is necessary to obtain a palladium / bismuth supported catalyst of the present invention having a supported composition ratio of 3 / 0.8 to 3 / 1.4 in a palladium / bismuth atomic ratio at 0 to 200 ° C, preferably 40 to 160 ° C. Amount of bismuth is present, and further 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, a solution of formalin, hydrazine or formic acid in water and / or 1-propanol may be added to the catalyst precursor dispersion solution. The amount of formalin, formic acid, hydrazine, methanol, or molecular hydrogen used is generally 0.1 to 100 relative to the amount of palladium compound supported on the catalyst precursor.
Double mole, and practically 0.5 to 10 mole is used.
Further, there is no particular problem even if this amount is exceeded. Further, if an alkali such as caustic soda is added together with the reducing agent, the reduction will proceed more easily. Usually, the amount of alkali is about 1/100 to equimolar to the reducing agent.

At the time of reduction, bismuth ions or bismuth complexes are made to coexist. For that purpose, it is general to add the bismuth-containing substance to water, 1-propanol or a mixed solution thereof in which the catalyst precursor is dispersed.
When adding the bismuth-containing substance, there is no particular limitation as long as it dissolves 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 the Pd / Bi atomic ratio is 3 / 0.8 to
The amount of bismuth compound necessary to obtain the catalyst of the present invention having a supported composition ratio of 3 / 1.4 was calculated by (Pd in palladium compound supported on 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 1-propanol or the like in which a bismuth compound corresponding to this amount is dissolved to carry out 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 necessary amount of bismuth compound is added within the range where the Pd / Bi atomic ratio does not finally exceed 3 / 1.4 and reduction is performed as described above. You can When the Pd / Bi ratio of the catalyst precursor is already 3 / 1.4, the reduction reaction is performed without adding the bismuth compound.

Further, at the time of reduction, a lower (C1 -C5) fatty acid and at least one compound selected from alkali metal salts and alkaline earth metal salts are made to coexist. The alkali metal compound and alkaline earth metal compound are selected from organic acid salts, inorganic acid salts, hydroxides and the like. The addition amount 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 grade (C1-C used in the present invention
5) Examples of fatty acids include propionic acid, acetic acid, butyric acid, and maleic acid. The amount of lower fatty acid to be added 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. Practically, it is preferable to select acetic acid that is easily available. These lower fatty acids may be added at the same time as 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 which carries both a palladium compound and a bismuth compound.

According to the above manufacturing method, the present inventors
Pd ₃ Bi which is a good Pd-Bi intermetallic compound having an X-ray diffraction angle (2θ) of 38.55 to 38.85 degrees.
It was found that a catalyst comprising ₁ and Pd ₅ Bi ₂ supported was 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
The reason why a catalyst comprising Pd ₃ Bi ₁ and Pd ₅ Bi ₂ with a high degree of catalyst perfection, in which θ) falls within the range of 38.55 to 38.85 degrees, is obtained is hydrogen ion, alkali metal cation or alkaline earth. It is presumed that the bismuth ion selectively interacts with the lattice defect portion of the Pd / Bi compound by the action of the metal cation, thereby helping Bi to be easily introduced into the crystal lattice.

Further, instead of adding at least one compound selected from the group consisting of lower (C1 -C5) fatty acids and alkali metal salts and alkaline earth metal salts in the above method for producing a catalyst of the present invention, a lower (C1 -C5) fatty acid is added. 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 the lower fatty acid to be added is added in an amount of about 0.1 to 30 times mol 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 and the alkaline earth metal salt of the lower fatty acid, sodium acetate, magnesium acetate and the like are preferable.

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

The above-mentioned reduction treatment operation can be carried out at a temperature of room temperature to 200 ° C. Perform by applying the pressure necessary to maintain the liquid phase. It is preferably carried out under the conditions of 40 to 160 ° C. and atmospheric pressure to several atmospheres. The reduction treatment time varies depending on the catalyst species and treatment conditions, but is generally several minutes to 100 hours. It is convenient to set the conditions so that the treatment is completed within a few hours. The completion of the reduction treatment can be easily determined by measuring the X-ray diffraction angle of the maximum intensity peak in the powder X-ray diffraction angle of the obtained catalyst. When the X-ray diffraction angle does not change, the process may be completed. Further, the reactor used for the reduction is not particularly limited, and a usual stirred tank reactor can be used.

The catalyst of the present invention can be suitably used in a reaction of reacting an aldehyde with an alcohol and molecular oxygen to produce a carboxylic acid ester. The amount of the catalyst used depends on the types of reaction raw materials, the composition and preparation method of the catalyst, the reaction conditions,
Although it can be varied widely depending on the reaction mode and the like, it is not particularly limited, but when the catalyst is reacted in a slurry state, it is preferable to use 0.04 to 0.5 kg in 1 liter of the reaction system.

Examples of the aldehyde used in the production of the carboxylic acid ester of the present invention include formaldehyde; C1-C10 saturated aliphatic aldehydes such as acetaldehyde, propionaldehyde, isobutyraldehyde, glyoxal; acrolein, methacrolein,
C3-C10 Aliphatic α / β-unsaturated aldehydes such as crotonaldehyde; C6 such as benzaldehyde, tolylaldehyde, benzylaldehyde and phthalaldehyde
-C20 aromatic aldehyde; 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 is, for example, C1 to C10 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 aldehyde and alcohol is not particularly limited, and for example, the molar ratio of aldehyde / alcohol is 10
Although it can be carried out in a wide range such as ˜1 / 1000, it is generally carried out in a range of ½ to 1/50 in terms of molar ratio.
Further, the method for producing the 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 reaction. For example, when it is carried out in the liquid phase, it may be carried out in any reactor type such as a bubble column reactor, a draft tube type reactor and a stirred tank reactor.

The oxygen used in the method for producing a carboxylic acid ester of the present invention is molecular oxygen, that is, in the form of 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. It is also possible to use air. The reaction pressure can be carried out in any wide pressure range from reduced pressure to increased pressure, but is usually 0.5.
It is carried out at a pressure of -20 kg / cm ² . It is advisable to set the total pressure so that the oxygen concentration in the gas discharged from the reactor does not exceed the explosion limit (8%).

When the carboxylic acid ester is continuously produced, bismuth is preferably added to the reaction system to carry out the reaction. The amount of bismuth added to the reactor varies depending on the reaction conditions, reaction type, and catalyst species used, and it is difficult to determine a specific value.However, if there is a large amount of bismuth to be added, a treatment for recovering from the wastewater and detoxifying it The cost is high, which is not preferable. Since the necessary amount of bismuth in the reaction system depends on the oxygen partial pressure, the present inventors set the oxygen partial pressure at the outlet of the reactor to 0.8 kg / cm ² or less, so that the weight of 0.01 to It has been found that it can be reduced to 100 ppm. Therefore, it is possible to reduce the amount of bismuth as much as possible by lowering the oxygen partial pressure at the reactor outlet, and 0.01 to 100 ppm (weight basis;
Omit it. It is preferable to set the necessary minimum amount of bismuth from the range of)). Oxygen partial pressure at reactor outlet is 0.8
The amount of bismuth added is 100p even if it is higher than kg / cm ^2.
If it is more than pm, there will be no problem in maintaining the catalyst performance, but it is not preferable in terms of cost and other economical efficiency as described above. Therefore, the amount of addition should be 0.8 kg / cm ² or less. The amount of bismuth is reduced to 0.01-100 ppm.

Oxygen partial pressure on the outlet side of the reactor is 0.02 kg
/ Cm ² or more and 0.8 kg / cm ² or less is sufficient, but more preferably the oxygen partial pressure on the outlet side of the reactor is 0.
When it 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, the reaction system contains an alkali metal or alkaline earth metal compound (eg, oxide, hydroxide, carbonate,
It is preferable to maintain the pH of the reaction system at 6 to 9 by adding a carboxylic acid salt or the like). 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 even at a high temperature of 100 ° C. or higher when the aldehyde concentration in the reaction system is increased to 30% by weight or more, but preferably 30 to 100. C., more preferably 60 to 90.degree. The reaction time is not particularly limited and cannot be uniquely determined because it varies depending on the set conditions, but it is usually 1 to 20 hours.

[0044]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described more specifically with reference to 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 an inductively coupled plasma (ICP) emission spectrometry, using JY-38P2 manufactured by Seiko Instruments Inc. as an ICP emission spectrometer. [Measurement of the X-ray diffraction angle (2θ) of the maximum intensity peak in the 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 at 160 ° C. under vacuum evacuation of the catalyst. After removing low-molecular adsorption / storage components (mainly hydrogen) by treating for a period of time, using an RAD-RA X-ray diffractometer manufactured by Rigaku Denki Co., Ltd., according to a usual measurement procedure for powder X-ray diffraction. , CuKα1 ray (1.54
05981Å) was used to measure the diffraction angle 2θ of the maximum intensity peak of the catalyst. The measurement must be performed with high precision. For example, National Institute of Standards, USA
& Technology defines the standard reference material 660, the X-ray diffraction angle (2θ) of the maximum intensity peak attributed to each diffraction of the (111) plane and the (200) plane of the LaB ₆ compound is 37.441 °, 43. Normalize to be 0.506 °. As a result, highly accurate measurement results with high reproducibility can be obtained.

[0045]

Example 1 Aqueous silica sol (Snowtex N-30
(SiO ₂ min: 30% by weight) Nissan Chemical Co., Ltd.
Aluminum nitrate and magnesium nitrate are Al /
After adding and dissolving so that the ratio of Si is 10 mol% and the ratio of Mg / Si is 10 mol%, spray drying is performed by 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.
Add 1 kg of carrier to 5 liters of water and add 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 stirred at 90 ° C. for 30 minutes to completely adsorb palladium chloride on the carrier to prepare a catalyst precursor.
Then, the aqueous solution is made up of 50% 1-propanol aqueous solution 375
Replaced with 0 g and heated to 90 ° C., then sodium acetate 320
g in 800 cc of water was added, then
96.7 g of triphenylbismuth was added to 1-propanol 8
A solution dissolved in 70 g was added, and 1-propanol solution containing 235 g of hydrazine was added dropwise with stirring to carry out reduction and adsorption treatment for 6 hours. The catalyst [Pd ⁵ Bi ^4.58 / SiO 2
_2- Al ₂ O ₃ -Mg ⁴ O (Pd and Bi on the right shoulder represent parts by weight per 100 parts by weight of the carrier, and Mg on the right shoulder represent the parts by weight per 100 parts by weight of SiO ₂ ) ]
Got When the obtained catalyst was analyzed by the above method, the Pd / Bi supported composition ratio 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. It was degree. This catalyst 240
g was equipped with a catalyst separator, and the liquid phase part was charged into an external circulation type bubble column reactor made of stainless steel, and the reaction was carried out. 0.54 liter / hr of 36.7 wt% methacrolein / methanol solution, 2-4 wt% NaOH /
A methanol solution was continuously fed to the reactor at 0.06 liter / hr (the methacrolein concentration of the reaction system consisting of the above two solutions was about 33% by weight), the reaction temperature was 80 ° C., and the reaction pressure was 5 kg / cm ^2. Then, 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 concentration of NaOH 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 extracted after 10 hours was analyzed, the conversion of methacrolein was 63.4.
%, MMA selectivity was 90.8%, propylene was produced as a by-product with a selectivity of 1.12%, and methyl formate was produced at 0.064 mol / mol MMA.

[0046]

[Example 2] Supported catalyst without adding Mg to the carrier in Example 1
[Pd^FiveBi^4.58/ SiO₂-Al ₂O₃]
It was The obtained supported catalyst was analyzed by the method described above.
B, Pd / Bi supported composition ratio is 3 / 1.37 in atomic ratio, powder
X-ray diffraction of maximum intensity peak in terminal X-ray diffraction pattern
The angle (2θ) was 38.780 degrees. With this catalyst
And the reaction was carried out under the same conditions as in Example 1. 10 after starting the reaction
When the reaction product was analyzed after a lapse of time,
Tacrolein conversion 58.5%, MMA selectivity
90.4%, propylene has a selectivity of 1.5 as a by-product
2% and methyl formate is 0.063 mol / molar.
Le MMA was being 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 6 mol%.
_{^{Bi 4.58 / SiO 2 -Al 2 O}} 3 -Mg 2.4 O ] were prepared. When the obtained supported catalyst was analyzed by the above-mentioned method, the Pd / Bi supported composition ratio was 3 / 1.40 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, the reaction was carried out under the same conditions as in Example 1. 10 after starting the reaction
When the reaction product was analyzed after a lapse of time, the conversion of methacrolein was 60.8%, the selectivity for MMA was 91.3%, and the selectivity for propylene as a by-product was 0.4.
It was produced at 1%, and methyl formate was produced at 0.073 mol / mol MMA.

[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 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 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 producing reaction was carried out 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 5
9.2%, MMA had a selectivity of 90.1%, and propylene was produced as a by-product with a selectivity of 1.90%.
Methyl formate was produced in an amount of 0.038 mol / mol MMA.

[0049]

Comparative Example 1 A supported catalyst [Pd ⁵ Bi ^1.64 / was ^{prepared in the same} manner as in Example 1 except that the supported amount of bismuth was 1.64 parts by weight.
SiO ₂ —Al ₂ O ₃ —Mg ⁴ O, Pd / Bi supported composition ratio was 3 / 0.51 in atomic ratio, and X-ray diffraction angle (2θ) of maximum intensity peak in powder X-ray diffraction pattern was 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 with a selectivity of 79.7%, propylene was produced with a selectivity of 12.35%, and methyl formate was produced with 0.024 mol / mol MMA.

[0050]

Comparative Example 2 A supported catalyst [Pd ⁵ Bi ^6.5 / S was used in the same manner as in Example 3 except that the amount of bismuth supported was 6.5 parts by weight.
iO ₂ -Al ₂ O ₃ -Mg ^2.4 O, Pd / Bi supported composition ratio was 3 / 1.98 in atomic ratio, and X-ray diffraction angle (2θ) of maximum intensity peak in powder X-ray diffraction pattern was 38.51.
(8 degrees) 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 53.1%,
MMA was produced with a selectivity of 86.5% and propylene was produced as a by-product with a selectivity of 0.11%.
195 mol / mol MMA had been produced.

[0051]

Comparative Example 3 A supported catalyst [Pd ⁵ Bi ^6.5 / S was used in the same manner as in Example 1 except that the amount of bismuth supported was 6.5 parts by weight.
iO ₂ —Al ₂ O ₃ —Mg ⁴ O, the Pd / Bi supported composition ratio was 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 was 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% and M
MA was produced with a selectivity of 87.9%, propylene was produced as a by-product with a selectivity of 0.33%, and methyl formate was produced with a selectivity of 0.1.
81 mol / mol MMA had been produced.

[0052]

COMPARATIVE EXAMPLE 4 Using the supported catalyst of Comparative Example 1 as it was, an MMA producing 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.
9%, MMA selectivity was 90.8%, propylene was produced as a by-product with a selectivity of 1.0%, and methyl formate was produced at 0.025 mol / mol MMA.

[0053]

[Example 5] In Example 1, the carrier was silica gel manufactured by Fuji Silysia Chemical Ltd. (Carrieract 10), Mg was replaced with K, and 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 Bi loading amount was 3.93 parts by weight (based on 100 parts by weight of the carrier).
When the obtained supported catalyst was analyzed by the above method, P
The composition ratio of d / Bi supported was 3 / 1.19 in atomic ratio, and the X-ray diffraction angle (2
θ) was 38.627 degrees. Using this catalyst, an MMA producing reaction was carried out under exactly the same conditions as in Example 1, and the reaction product was analyzed 10 hours after the start of the reaction. The methacrolein conversion rate was 65.3%.
A had a selectivity of 91.2%, propylene as a by-product with a selectivity of 0.91%, and methyl formate had a selectivity of 0.05.
6 mol / mol MMA was produced.

[0054]

Example 6 As a carrier, alumina (trade name: Sumitomo Activated Alumina) on which lithium was carried so that Li / Al was 1.0% by weight was used, and the amount of Bi carried 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 ]. 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. It was 832 degrees. Using this catalyst, 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 60.2%, MMA had a selectivity of 90.3%, and propylene had a selectivity of 1.76%. In addition, methyl formate was produced in an amount of 0.040 mol / mol MMA.

[0055]

[Example 7] 0.32% by weight of thallium as a dissimilar metal
2. Supported (based on 100 parts by weight of carrier) and bismuth 3.
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 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. It was 731 degrees. Using this catalyst, 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 methacrolein conversion rate was 62.7%, MMA selectivity was 90.7%, and propylene was produced as a by-product with a selectivity of 1.20%. In addition, methyl formate was produced at 0.065 mol / mol MMA.

[0056]

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

[0057]

Example 9 240 g of the catalyst of Example 1 was charged in an external circulation type stainless steel bubble column reactor having a catalyst separation part and a liquid phase part of 1.2 liter, and 36.7 wt% of methacrolein / methanol was added. 0.54 liters / hr, 2 to 4% by weight of NaOH / methanol was supplied at 0.06 liters / hr, the reaction temperature was 80 ° C., the reaction pressure was 5 kg / cm ² , and the outlet oxygen concentration was 4.0% by volume (oxygen). Partial pressure 0.20 kg / c
The reaction was maintained while the amount of air was adjusted so as to be m ² ). 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.
Triphenylbismuth was dissolved in methacrolein / methanol so as to obtain m and then continuously supplied. When the reaction product extracted after 200 hours was analyzed, the conversion of methacrolein was 62.7%, and MMA had a selectivity of 9%.
0.4%, propylene selectivity 1.15 as by-product
%, And methyl formate was formed at 0.066 mol / mol MMA. After 2000 hours, the conversion of methacrolein was 62.4%, and MMA had a selectivity of 90.1.
%, Propylene was produced as a by-product at a selectivity of 1.20%, and methyl formate was 0.063 mol / mol MMA.
Was being generated.

[0058]

Example 10 The reaction was carried out for 2000 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 was 60.6%,
MMA was produced with a selectivity of 88.6%, propylene was produced as a byproduct with a selectivity of 1.78%, and methyl formate was produced at a rate of 0.78.
060 mol / mol MMA had been produced. After 2000 hours, the conversion of methacrolein was 53.4%, the selectivity of MMA was 81.1%, propylene was produced as a by-product with a selectivity of 7.3%, and methyl formate was 0.035 mol / mol. Molar MMA was produced.

[0059]

Example 11 A reaction pressure of 11 kg / cm ² and an outlet oxygen concentration of 7.2% by volume (oxygen partial pressure of 0.792 kg / cm ²
The reaction was continued for 2000 hours in the same manner as in Example 9 except that the bismuth concentration in the supply liquid was set to 100 ppm. When the reaction product extracted after 200 hours passed was analyzed, the conversion of methacrolein was 64.3.
%, MMA was produced with a selectivity of 89.9%, propylene was produced with a selectivity of 1.51%, and methyl formate was produced with 0.077 mol / mol MMA. 20
At 00 hours, the conversion of methacrolein was 63.8%, MMA had a selectivity of 89.8%, propylene was produced as a by-product with a selectivity of 1.60%, and methyl formate contained 0.079 mol / mol. Molar MMA was produced.

[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 liquid was 200 ppm. The reaction was continued for 2000 hours in the same manner as in Example 9. The reaction product extracted after 200 hours was analyzed, and the conversion of methacrolein was 62.9%.
MMA was produced with a selectivity of 89.2%, propylene was produced as a by-product with a selectivity of 1.53%, and methyl formate was produced at 0.095 mol / mol MMA. 200
At 0 hours, the conversion of methacrolein was 62.5%,
MMA was produced with a selectivity of 88.9%, propylene was produced as a by-product with a selectivity of 1.82%, and methyl formate was 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 (oxygen partial pressure was 0.90 kg / cm ² equivalent), and the bismuth concentration in the feed liquid 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 with a selectivity of 88.3%, propylene was produced as a by-product with a selectivity of 2.21%, and methyl formate was produced at 0.071 mol / mol MMA. 200
At 0 hours, the conversion of methacrolein was 55.9%,
MMA was produced with a selectivity of 84.9%, propylene was produced as a by-product with a selectivity of 5.56%, and methyl formate was 0.5.
059 mol / mol MMA was produced.

[0062]

EFFECTS OF THE INVENTION When a carboxylic acid ester is produced by reacting an aldehyde and an alcohol with molecular oxygen, the yield based on the aldehyde and the alcohol is obtained even under the reaction conditions where the concentration of the aldehyde and the reaction temperature are increased to improve the economic efficiency. Can be improved at the same time. Further, excellent catalyst performance can be continuously maintained for a long period of time, the catalyst life is greatly improved, the frequency of catalyst replacement is low, and the operability and economy are excellent.

Continuation of the front page (56) Reference JP-A-55-151533 (JP, A) JP-A-8-337554 (JP, A) JP-A-9-57114 (JP, A) JP-A-10-265435 (JP , A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) B01J 21/00-38/74

Claims (6)

(57) [Claims] 1. A catalyst for producing a carboxylic acid ester from an aldehyde, an alcohol and molecular oxygen, which comprises palladium and bismuth supported on a carrier, the (Pd / Bi) atomic ratio (S) of the catalyst. Is 3 / 0.8 ≦ (S)
Within the range of ≤3 / 1.4, and the X-ray diffraction angle (2
θ) is in the range of 38.55 to 38.85 degrees, a catalyst for producing a carboxylic acid ester. 2. A method for producing a carboxylic acid ester, which comprises using the catalyst according to claim 1 when producing a carboxylic acid ester from an aldehyde, an alcohol and molecular oxygen. 3. The catalyst according to claim 1 is used in the continuous production of a carboxylic acid ester from aldehyde, alcohol and molecular oxygen, and a substance containing triphenylbismuth is used. A method for producing a carboxylic acid ester, characterized in that the reaction is carried out while being added to a reactor. 4. The oxygen partial pressure at the reactor outlet is 0.8 kg / c.
The method for producing a carboxylic acid ester according to claim 3, wherein the bismuth concentration in the reaction system is maintained at 0.01 to 100 ppm on a weight basis while maintaining the m ² or less. 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, 3 or 4, wherein the aldehyde is methacrolein, acrolein or a mixture thereof and the alcohol is methanol.