JP3503776B2 - Supported catalyst containing palladium and lead for carboxylic acid ester production - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst used for producing a carboxylic acid ester by reacting an aldehyde with 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 industrially useful production of methyl methacrylate or methyl acrylate, a production method called direct acid method for producing methacrylic acid from methacrolein and converting it to methacrylic acid methyl ester has already been industrialized. There is. However, although the yield of the step of oxidizing methacrolein to methacrylic acid has been improved to the low 80's by the catalyst improvement over many years, it is still low and there is a lot of room for improvement. Further, the heteropolyacid catalyst used has a difficulty due to thermal stability, and there is a problem that decomposition 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, a new route for reacting methacrolein or acrolein with methanol and molecular oxygen to produce methyl methacrylate or methyl acrylate all at once has been highlighted recently. It is carried out by reacting methacrolein or acrolein with molecular oxygen in methanol and the presence of a catalyst containing palladium is essential.

Conventionally, according to this production method, hydrocarbons and carbon dioxide gas are produced by simultaneously causing the decomposition reaction of aldehydes, the yield of the desired carboxylic acid ester is low, and in parallel with the carboxylic acid ester production reaction, Different aldehydes and different carboxylic acid esters (for example, methyl formate when methanol is used as alcohol and ethyl acetate when ethanol is used) are produced as by-products from the oxidization of alcohol itself, and the selectivity based on alcohol is also poor. It was Moreover, there is a drawback that the catalytic activity cannot be maintained for a long time. Particularly when α / β-unsaturated aldehydes such as methacrolein and acrolein, which are of high industrial practical value, are used as starting materials, the stability of these reaction intermediates is much lower, and therefore a large amount of carbon dioxide and olefins are generated during the reaction. Decomposition products such as (propylene in the case of methacrolein) were generated, which was far from the practical level.

The present inventors have found that Japanese Patent Publication No. 57-035856.
No. 57-35857 and 57-3535
In each publication of 859, a catalyst system containing palladium and lead is proposed, and it is shown that the selectivity to the methyl ester based on methacrolein or acrolein is significantly improved to a high value exceeding 90%. , The reaction temperature is at most 50
It was up to ° C. Continued Japanese Examined Japanese Patent Publication 62-007902
In the publication, a catalyst containing an intermetallic compound in which palladium and lead are bonded in a simple integer ratio is proposed, the decomposition reaction of methacrolein or acrolein is almost completely suppressed, and the catalytic activity is not lost for a long period of time. It was shown to be a catalyst system. As described above, the new production method using these new catalyst systems has advantages such as a shorter process than the direct acid method, which has a feeling of improvement in yield and improvement in catalyst life. Industrialization is awaited as a new manufacturing method.

However, if this reaction is carried out at a high temperature of 60 ° C. or higher, which is an economically advantageous reaction condition on the premise of industrial implementation, and at a high concentration of 20% or more of aldehyde, the selectivity of methyl methacrylate in the above catalyst system is high. (Hereinafter referred to as MMA selectivity) decreases. That is, Japanese Patent Publication No. 62-007
The 902 publication exemplifies that a high MMA selectivity of over 90% can be obtained, but these were carried out under mild conditions where the aldehyde concentration was 10% or less and the reaction temperature was 40 to 60 ° C. is there. Under these conditions, the MMA concentration produced is low, so that the amount of unreacted methanol recycled is large, and as a result, the amount of steam used increases and economic efficiency deteriorates. Moreover, the productivity is low and the reactor is large. In order to improve the economic efficiency, it is desirable to increase the aldehyde concentration and the reaction temperature as much as possible, and Japanese Patent Publication No. 069813/1993 discloses a reaction example at a methacrolein concentration of 20% and a reaction temperature of 80 ° C. . However, under such high methacrolein concentration and high reaction temperature conditions, 90%
A high MMA selectivity exceeding 10 cannot be obtained. Furthermore, under severer conditions in which the methacrolein concentration is increased to 30%, the MMA selectivity is further reduced.

In order to improve the economical efficiency, the advent of a catalyst system capable of obtaining a high MMA selectivity of more than 90% under high temperature and high aldehyde concentration has been awaited.

[0008]

DISCLOSURE OF THE INVENTION In the present invention, when a carboxylic acid ester is produced by reacting an aldehyde with an alcohol and molecular oxygen in the presence of a catalyst containing palladium and lead, the concentration of the aldehyde and the reaction temperature are increased to achieve economic efficiency. There is provided a catalyst that enables a method for producing a carboxylic acid ester having a high carboxylic acid ester selectivity even under reaction conditions with improved properties, and a method for producing a carboxylic acid ester using the catalyst.

[0009]

In view of such a situation, the inventors of the present invention have made earnest studies on a catalyst system containing palladium and lead in order to develop a catalyst having an improved MMA selectivity. Among the intermetallic compound species proposed in Japanese Patent Publication No. 62-007902, in which palladium and lead are bonded at a simple integer ratio, attention is focused on Pd ₃ Pb ₁ species with an atomic ratio of 3/1, and a more detailed study is advanced. , Pd ₃ Pb ₁ intermetallic compound with high purity and high quality Pd ₃ Pb ₁ with few defects in the crystal lattice can be used even under severe reaction conditions such as high aldehyde concentration and high reaction temperature. The present invention has been completed by finding that the MMA selectivity does not deteriorate.

That is, the present invention is as follows. 1. A supported catalyst for producing a carboxylic acid ester from an aldehyde, an alcohol and molecular oxygen, which contains palladium and lead and satisfies the following (1) and (2). (1) The supported composition ratio of palladium / lead is 3/0.
7 to 3 / 1.3, the (111) plane X-ray diffraction angle (2θ) of the (2) palladium / lead intermetallic compound is 38.55 to 3
8.70, 2. A method for producing a carboxylic acid ester by reacting an aldehyde with an alcohol and molecular oxygen, wherein the aldehyde is reacted with the alcohol and the molecular oxygen in the presence of the catalyst of the above 1. . 3. The method for producing a carboxylic acid ester according to 2 above, wherein the aldehyde is methacrolein, acrolein or a mixture thereof, and the alcohol is methanol.

The catalyst of the present invention will be described in more detail below.
It The present inventors opened it in Japanese Patent Publication No. 62-007902.
The catalyst shown is M under severe reaction conditions for whatever reason.
As a result of diligent research into whether the MA selectivity deteriorates,
Each of the catalysts contains a large amount of lead-derived impurities,₃
Pb₁Was found to be due to the extremely low purity of
It was For example, the Pd / Pb supporting composition ratio (atomic ratio) is 3/1.
5 of the above Japanese Patent Publication No. 62-007902.
The catalyst of Example 1 contained 0.5 atom of lead in Pd.₃Pb₁
Not as a free or metallic lead component.
It is assumed that these are impurities derived from the lead component.
Nari Pd ₃Pb₁Greatly reduces the purity of. Also, P
d / Pb supported composition ratio (atomic ratio) was 3/3
The catalyst of Example 4 of the publication uses lead equivalent to 2 atoms as an impurity.
Including Pd₃Pb₁Is even less pure. That is, the same publication
Catalyst is Pd₃Pb₁Lead component that is not used to form
d₃Pb₁50 to 200% of lead forming
It was a very low purity catalyst. These lead impurities
Is the main cause of worsening MMA selectivity, and
Under harsh reaction conditions such as aldehyde concentration and high reaction temperature
We have found that it causes reduced MMA selectivity
I did.

The inventors of the present invention further advanced the research and attempted to prepare a catalyst by reducing the amount of supported lead to a Pd / Pb supported composition ratio (atomic ratio) of 3/1 as much as possible. However, with the conventional manufacturing method, only Pd / P
Even when prepared so that the b-supporting composition ratio (atomic ratio) is 3/1, only a low-grade Pd ₃ Pb ₁ -supporting catalyst having many lattice defects can be obtained, which is described in JP-B-62-007902. On the contrary, it was revealed that the MMA selectivity was further reduced as compared with the catalyst. That is, Pd ₃ P with few lattice defects
An ideal supported catalyst has not been realized for the present invention containing b ₁ as a catalyst species and containing few lead impurities.

An ideal supported catalyst for the present invention, which contains Pd ₃ Pb ₁ having a small number of lattice defects as a catalyst species and a small amount of lead impurities, can be obtained by going through a catalyst structure completion step described later. The inventors have found.
Through this catalyst structure completion step, the lattice defects of Pd ₃ Pb ₁ can be easily reduced without increasing the impurities derived from lead, and high-quality Pd ₃ Pb ₁ can be obtained. That is, a supported catalyst containing high-quality Pd ₃ Pb ₁ in high purity can be obtained. This catalyst system also has a high MMA under severe reaction conditions.
It also became clear that it showed selectivity.

The constitution of the catalyst of the present invention will be described below. The supported catalyst of the present invention contains palladium and lead. First, the supported composition ratio of palladium / lead is 3 / 0.7 to 3 / in atomic ratio.
Must meet 1.3. Preferably 3 / 0.9-
It is 3 / 1.1. It is more preferable to approach 3/1 as much as possible. Secondly, the palladium / lead intermetallic compound (11
The X-ray diffraction angle (2θ) of the 1) plane is 38.55 to 38.70.
Is the range. The supported catalyst satisfying the first and second requirements surprisingly exhibits a high MMA selectivity of more than 90%. In particular, these characteristics become clear under industrial reaction conditions at high temperature and high aldehyde concentration.

In addition to palladium and lead as a catalyst component, other elements such as mercury, thallium, bismuth, tellurium, nickel, chromium, cobalt, indium, tantalum, copper, zinc, zirconium, hafnium, tungsten, manganese, silver and rhenium. , Antimony, tin, rhodium, ruthenium, iridium, platinum, gold, titanium, aluminum, boron, silicon and the like may be contained. These different elements can be contained in the range of usually 5% by weight, preferably 1% by weight. Further, compounds containing at least one member selected from alkali metal compounds and alkaline earth metal compounds are advantageous in that the reaction activity becomes high. Alkali metal and alkaline earth metal are usually 0.01
To 30% by weight, preferably 0.01 to 5% by weight. These different elements, alkali metals, alkaline earth metals, etc. may penetrate in a small amount between the crystal lattices or may be substituted with a part of the crystal lattice metal. Further, the alkali metal and / or alkaline earth metal compound may be added to a solution containing a palladium compound or a lead compound at the time of catalyst preparation and may be adsorbed or attached to a carrier, or a carrier supporting these in advance may be used as a catalyst. Can also be prepared. It is also possible to add it to the reaction system under the reaction conditions.

Palladium compounds and lead compounds used for catalyst preparation are organic acid salts such as formate salts and acetate salts, inorganic acid salts such as sulfate salts, hydrochloride salts and nitrate salts, organic salts such as ammine complexes and benzonitrile complexes. It is appropriately selected from metal complexes, oxides, hydroxides and the like, but as the palladium compound, palladium chloride, palladium acetate and the like are preferable, and as the lead compound, lead nitrate, lead acetate and the like are preferable. The alkali metal compound and alkaline earth metal compound are also selected from organic acid salts, inorganic acid salts, hydroxides and the like.

The carrier can be widely selected from activated carbon, silica, alumina, silica-alumina, zeolite, magnesia, magnesium hydroxide, titania, calcium carbonate, activated carbon and the like. 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 amount of lead supported is not particularly limited, but is usually selected from the range of 0.05 to 17% by weight, preferably 0.45 to 8.5, with respect to the weight of the carrier.
However, as described above, the supported composition ratio of palladium / lead must be in the range of 3 / 0.7 to 3 / 1.3 in terms of atomic ratio.
It is preferably 3 / 0.9 to 3 / 1.1.

In order to obtain the catalyst of the present invention, first, a palladium / lead-containing supported catalyst is prepared according to a usual preparation method. At this time, the supported composition ratio (atomic ratio) of palladium / lead is usually selected from the range of 3 / 0.1 to 3/10. Practically 3 / 0.1 to 3/3, more preferably 3 / 0.7 to 3
It is preferably set to /1.3. However, beyond this range, eg less than 3 / 0.1 or 3/10
Even if it exceeds, it is possible to additionally support lead or remove excess lead in the catalyst structure completion step to be described below, and it is not always limited to the above palladium / lead composition ratio (atomic ratio). Not a thing.

Then, the above palladium / lead-containing supported catalyst was subjected to the following method to obtain a palladium / lead supported composition ratio (atomic ratio) of 3 / 0.7 to 3 / 1.3 and a palladium / lead intermetallic compound (111). ) Plane X-ray diffraction angle (2θ) is 38.55
It is necessary to complete the catalyst structure so as to satisfy ˜38.70. For example, the catalyst obtained by the above-mentioned usual preparation method is formalized with formalin, formic acid, hydrazine, methanol or molecular hydrogen in the presence of a lead compound. In addition, as another method, as shown in Example 7, the loading composition ratio of palladium / lead is 3 / atomic ratio by a usual method.
A supported catalyst of 0.98 was prepared, and then the supported catalyst was dispersed in methanol in which lead acetate was dissolved so that the supported composition ratio of palladium / lead became, for example, 3 / 1.3 in atomic ratio, and the reaction was carried out. Temperature = 90 ° C., reaction pressure = 5 kg / cm
² (hereinafter, the pressure is expressed in absolute pressure and expressed in kg / cm ² unit), air may be supplied to the reactor so that the outlet oxygen concentration is 2.0%, and the structure completion treatment step may be performed. It is possible to obtain the catalyst of the present invention.

The method for obtaining the supported catalyst of the present invention is not necessarily limited to the above method. For example, it is also possible to obtain a catalyst whose structure is completed by carrying out at least one series of redox operations consisting of oxidation of the catalyst for completion of the catalyst structure with molecular oxygen and subsequent reduction with methanol. However, the structure-completed catalyst can also be obtained by simultaneously performing oxidation with molecular oxygen and reduction with methanol.

Although the details of the mechanism for completing the catalyst structure are unknown, it is assumed by the present inventors that the active hydrogen present on the catalyst plays an important role under the conditions, and It is presumed that it is necessary to reduce the oxygen partial pressure in order to enhance the work. The supported catalyst, which is a target for completion of the catalyst structure, can be prepared by a known preparation method as described above. Explaining a typical catalyst preparation method, a carrier is added to an aqueous solution containing a soluble lead compound and a soluble palladium salt such as palladium chloride to impregnate the palladium and lead components. Then formalin, formic acid,
Reduce with hydrazine or hydrogen gas. Although the resulting catalyst contains the Pd ₃ Pb ₁ intermetallic compound disclosed by the present inventors in Japanese Patent Publication No. 62-007902, it has a low purity like the catalyst described in that publication. Therefore, the catalyst obtained by such a conventional production method is composed of palladium / lead-supported composition ratio (atomic ratio) and palladium / lead intermetallic compound (11
The X-ray diffraction angle of the 1) plane cannot be a catalyst that simultaneously satisfies the requirements of the present invention. A supported catalyst satisfying the requirements of the present invention can be obtained only by completing the structure of the catalyst under the above specific conditions.

The supported 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 supported catalyst used can be largely changed depending on the type of reaction raw material, the composition and preparation method of the catalyst, the reaction conditions, the reaction format, etc., but is not particularly limited, but when the catalyst is reacted in a slurry state, 0.04-0.5kg in 1 liter of reaction solution
Preference is given to using.

Examples of the aldehyde used in the reaction for producing the carboxylic acid ester of the present invention include aliphatic saturated aldehydes such as formaldehyde, acetaldehyde, propionaldehyde, isobutyraldehyde and glyoxal, and fats such as acrolein, methacrolein and crotonaldehyde. Aromatic aldehydes such as group α / β-unsaturated aldehydes, benzaldehydes, tolylaldehydes, benzylaldehydes, and phthalaldehydes, and derivatives of these aldehydes. These aldehydes can be used alone or as a mixture of two or more kinds.

Examples of the alcohol used in the reaction for producing the carboxylic acid ester of the present invention include aliphatic saturated alcohols such as methanol, ethanol, isopropanol and octanol, diols such as ethylene glycol and butanediol, allyl alcohol and methallyl. Aliphatic unsaturated alcohols such as alcohol, aromatic alcohols such as benzyl alcohol and the like can be mentioned. These alcohols can be used alone or as a mixture of two or more kinds.

In the reaction for producing the carboxylic acid ester of the present invention, the ratio of the amount of aldehyde used to the amount of alcohol used is not particularly limited, and it can be carried out in a wide range such as an aldehyde / alcohol molar ratio of 10 to 1/1000. ,
Generally, it is carried out in the range of 1/2 to 1/50. The reaction 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 present invention may be in the form of 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, but it is usually carried out at a pressure of 0.5 to ²⁰ kg / cm ² . The total pressure should be set so that the oxygen concentration in the gas discharged from the reactor does not exceed the explosion range (8%).

In the reaction of the present invention, the pH of the reaction system is adjusted to 6 to 9 by adding an alkali metal or alkaline earth metal compound (eg, oxide, hydroxide, carbonate, carboxylate) to the reaction system. It is preferable to hold at. Especially pH 6
With the above, there is an effect of preventing dissolution of the lead component in the catalyst. These alkali metal or alkaline earth metal compounds can be used alone or in combination of two or more.

In the reaction of the present invention having a high aldehyde concentration, it can be carried out at a high temperature of 100 ° C. or higher, but it is preferably 30 to 100 ° C. More preferably 60 to 90 ° C
Is. 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.

[0029]

EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples. <Reference Production Example 1> As a silica sol aqueous solution, NISSAN CHEMICAL CO., LTD. Snowtex N-30 (SiO ₂ content: 30% by weight) was added with aluminum nitrate and magnesium nitrate Al /
Si + Al = 10 mol% and Mg / Si + Mg = 10 mol% were added and dissolved, and then spray-dried with a spray dryer set at a temperature of 130 ° C. to obtain a spherical carrier having an average particle size of 60 μm. After firing at 300 ° C. and then at 600 ° C., this was used as a carrier. Palladium chloride and lead nitrate are added as 5 parts by weight of palladium and 100 parts by weight of the carrier, respectively.
1 part by weight and 6.5 parts by weight, and then reduced with hydrazine to obtain a catalyst (Pd5.0Pb6.5 / Mg, A
It is designated as 1-SiO ₂ . ) Got. The Pd / Pb supported composition ratio of the obtained supported catalyst was 3 / 1.95 in atomic ratio, and the X-ray diffraction angle (2θ) of the (111) plane of the palladium / lead intermetallic compound was 38.745 degrees. <Measurement of X-ray diffraction angle of Pd (111) plane> The measurement was performed using RAD-RA manufactured by Rigaku Co., Ltd. according to the usual measurement procedure of powder X-ray diffraction, and the palladium / lead compound was used using CuKα1 ray (1.5405981Å). Diffraction angle 2θ of (111) plane
Was measured. The measurement must be performed with high precision. Na
(1 of the LaB ₆ compound as defined by the National Institute of Standards & Technology as the standard reference substance 660).
11) plane and (200) plane were measured and the respective values were set to 37.
441, 43.506. As a result, highly accurate measurement results with high reproducibility can be obtained.

The catalyst is evacuated at 160 ° C. and treated for 3 hours to remove low-molecular adsorption / occlusion components, and then measured.

[0031]

Example 1 300 g of the catalyst of Reference Production Example 1 was charged into an external circulation type stainless steel bubble column reactor having a catalyst separator and a liquid phase portion of 1.2 liter to complete the catalyst structure. A 36.7 wt% methacrolein / methanol solution was continuously fed to the reactor at 0.54 liters / hr and a NaOH / methanol solution was 0.06 liters / hr (corresponding to an aldehyde concentration of about 33%) at a reaction temperature. Air was supplied to the reactor while adjusting the amount of air so that the outlet oxygen concentration was 3.0% (corresponding to an oxygen partial pressure of 0.15 kg / cm ² ) at 80 ° C. and a reaction pressure of 5 kg / cm ² . The concentration of NaOH supplied to the reactor was controlled so that the pH of the reaction solution was 7.1. The structure completion process is completed in 50 hours,
When the catalyst was analyzed, Pd / Pb supported composition ratio (atomic ratio)
Is 3 / 1.24, and the palladium / lead intermetallic compound (11
The X-ray diffraction angle (2θ) of the 1) plane was 38.652 degrees.

240 g of this catalyst was placed in an external circulation type bubble column reactor made of stainless steel, which was equipped with a catalyst separator and had a liquid phase portion of 1.2 liter to carry out the reaction. 0.53 liters / h of a 36.7 wt% methacrolein / methanol solution
r, NaOH / methanol solution 0.06 liter / h
r, continuously supplied to the reactor (aldehyde concentration of about 33%
At a reaction temperature of 80 ° C. and a reaction pressure of 5 kg / cm ² and an outlet oxygen concentration of 4.0% (oxygen partial pressure of 0.20 kg / cm).
^The MMA formation reaction was performed while adjusting the air amount so that it became ² ), and the reaction product was analyzed after 10 hours, the methacrolein conversion rate was 57.3%, M
The MA selectivity was 90.7%, and propylene had a selectivity of 1.7% and methyl formate as 0.085 mol / mol MMA as by-products.

[0033]

COMPARATIVE EXAMPLE 1 The catalyst of Reference Production Example 1 was subjected to an MMA producing reaction under the same conditions as in Example 1, and the reaction product was analyzed 10 hours after the initiation of the reaction. The conversion of methacrolein was 55. 2%, MMA selectivity is 84.1%
As a by-product, propylene had a selectivity of 7.9%, and methyl formate produced 0.242 mol / mol MMA.

[0034]

[Examples 2 to 6 and Comparative Examples 2 to 5] MMA production reaction was carried out using various catalysts in which the catalyst structure completion treatment was performed and the carrier material was changed. Each catalyst (Examples 2-6, Comparative Examples 2-5)
Table 1 shows the Pd / Pb supported composition ratio (atomic ratio), the X-ray diffraction angle (2θ) of the (111) plane of the palladium / lead intermetallic compound, and the reaction results. The MMA formation reaction is described in Example 1.
The same conditions were used. Reference Examples 1 and 2 have an aldehyde concentration of 1
The reaction was performed at 0% and a reaction temperature of 50 ° C.

[0035]

[Table 1]

<Reference Production Example 2> 5.0% by weight of palladium on silica gel (Carriact 10) manufactured by Fuji Silysia,
A catalyst carrying 3.18 parts by weight of lead was obtained. The Pd / Pb supported composition ratio (atomic ratio) of the obtained catalyst was 3 / 0.98,
The X-ray diffraction angle (2θ) of the (111) plane of the palladium / lead intermetallic compound was 38.927 degrees.

[0037]

Example 7 In a stirred tank reactor having a liquid phase portion of 6 liters, 1 kg of the catalyst of Reference Production Example 2 and lead content which is insufficient to make the Pd / Pb supported composition ratio of the catalyst 3 / 1.3. were charged and dissolved corresponding lead acetate methanol, reaction temperature 90 ° C., a reaction pressure 5 kg / cm ² outlet oxygen concentration of 2.0% (the oxygen partial pressure of 0.10 kg / cm ² equivalent) and air volume so Air was supplied to the reactor while adjusting, and the catalyst structure completion treatment was performed for 20 hours. The composition ratio of Pd / Pb supported on the obtained catalyst was 3 / 1.27 in atomic ratio, and the X-ray diffraction angle (2θ) of the (111) plane of the palladium / lead intermetallic compound was 38.6.
It was 91 degrees.

A stirred tank reactor having the same capacity as in Example 1 was charged with 200 g of the catalyst which had been subjected to the catalyst structure completion step, and the reactor was charged with 0.54 of a 36.7 wt% methacrolein / methanol solution. L / hr, NaOH / methanol solution 0.06 L / hr continuously supplied,
The reaction temperature of 80 ° C., air was supplied to the reaction pressure 5 kg / outlet oxygen concentration in cm ² is 4.0% (the oxygen partial pressure of 0.20 kg / cm ² equivalent) and the reactor while adjusting the amount of air so that, The MMA generation reaction was performed. The concentration of NaOH supplied to the reactor was controlled so that the pH of the reaction solution would be 7.1. When the reaction product was analyzed after 10 hours, the conversion of methacrolein was 57.8%, MM
The A selectivity was 89.9%, and as by-products, propylene had a selectivity of 2.12% and methyl formate was produced at 0.103 mol / mol MMA.

[0039]

Comparative Example 6 The catalyst of Reference Production Example 2 was subjected to an MMA producing reaction under the same conditions as in Example 7. When the reaction product was analyzed after 10 hours, methacrolein conversion was 63.2%, MMA selectivity was 84.1%, propylene was 7.9% as a by-product, and methyl formate was 0%. ．
092 mol / mol MMA was produced.

[0040]

[Embodiment 8] 1 kg of the catalyst of Reference Production Example 2 was added to a stirring tank having a liquid phase portion of 6 liters, and the lead content was insufficient to make the Pd / Pb supported composition ratio of the catalyst 3 / 1.3 in atomic ratio. Was charged with water in which lead acetate was dissolved, heated to 90 ° C., added with 37% formalin aqueous solution so that formalin / supported palladium was 10 mol, and further heated with stirring for 1 hour to complete the catalyst structure. . Pd / P of the obtained catalyst
The composition ratio of supported b was 3 / 1.27 in atomic ratio, and the X-ray diffraction angle (2θ) of the (111) plane of the palladium / lead intermetallic compound was 3
It was 8.642 degrees. A catalyst having the catalyst separator used in Example 1, two external circulation type stainless steel bubble column reactors having a liquid phase portion of 1.2 liters connected in series, and each catalyst having completed the structure completion treatment. Each 240g is prepared,
The MMA formation reaction was carried out. In the first stage reactor, 36.
0.54 of 7 wt% methacrolein / methanol solution
Liter / hr, NaOH / methanol solution 0.06
L / hr is continuously supplied, and the amount of air is adjusted so that the outlet oxygen concentration becomes 4.0% (oxygen partial pressure 0.20 kg / cm ² equivalent) at a reaction temperature of 80 ° C. and a reaction pressure of 5 kg / cm ^2. While supplying air to the reactor, the reaction was carried out. The catalyst suspension is liquid-solid separated, and the catalyst is returned to the reactor and only the reaction liquid is sent to the second reactor together with NaOH / methanol solution 0.06 L / hr, and the gas discharged from the first stage reactor is the second stage. While ventilating the reactor, add an insufficient amount of air to the second-stage reactor so that the outlet oxygen concentration of the second-stage reactor will be 2.2% (oxygen partial pressure equivalent to 0.11 kg / cm ² ). The reaction was carried out at a reaction temperature of 80 ° C. and a reaction pressure of 4.6 kg / cm ² .
In addition, the pH of the reaction solution in both the first-stage reactor and the second-stage reactor
The concentration of NaOH supplied to the reactor was controlled so that the ratio was 7.1. When the reaction product was analyzed 10 hours after the reaction started, the conversion of methacrolein was 80.2.
%, MMA selectivity was 91.1%, propylene selectivity was 1.2% and methyl formate was 0.114 mol / mol MMA as by-products.

[0041]

Example 9 Using the catalyst of Example 3, an MMA producing reaction was carried out under the same operation and reaction conditions as in Example 7, except that acrolein was reacted instead of methacrolein, and the reaction product was obtained after 10 hours. Upon analysis, the acrolein conversion was 58.2%, methyl acrylate selectivity was 91.3%, propylene was 1.2% as a byproduct, and methyl formate was 0.055 mol / mol MA. .

[0042]

[Example 10] Example 4 An MMA producing reaction was carried out under the same operation and reaction conditions as in Example 7 except that benzaldehyde was changed to methanol instead of methacrolein and ethanol was reacted using the catalyst for 10 hours. Later analysis of the reaction product showed a benzaldehyde conversion of 76.2%.
The selectivity for methyl benzoate was 93.2%.

[0043]

Industrial Applicability It has become possible to provide a supported catalyst containing a high-quality Pd ₃ Pb ₁ intermetallic compound with high purity.
Therefore, in producing a carboxylic acid ester by reacting an aldehyde with an alcohol and molecular oxygen, a high carboxylic acid ester selectivity can be obtained even under the reaction conditions in which the aldehyde concentration and the reaction temperature are increased to improve the economic efficiency. In addition, since it is possible to provide a method for producing methacrylic acid ethyl ester having a high industrial practical value and having excellent economical efficiency, it is industrially very useful.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-55-151533 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B01J 21/00-38/74 C07C 67 / 00-67/62

Claims (3)

(57) [Claims] 1. A catalyst for producing a carboxylic acid ester from an aldehyde, an alcohol and molecular oxygen, which is a supported catalyst containing palladium and lead and satisfying the following (1) and (2). (1) The supported composition ratio of palladium / lead is 3/0.
7 to 3 / 1.3, the (111) plane X-ray diffraction angle (2θ) of the (2) palladium / lead intermetallic compound is 38.55 to 3
8.70, 2. A method for producing a carboxylic acid ester by reacting an aldehyde with an alcohol and molecular oxygen, wherein the aldehyde is reacted with the alcohol and molecular oxygen in the presence of the catalyst according to claim 1. A method for producing a carboxylic acid ester. 3. 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.