JP3408700B2 - Method for continuous production of carboxylic acid ester - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention provides an industrially advantageous method for producing methacrylic acid methyl ester by reacting methacrolein and methanol with a catalyst containing palladium.

[0002]

2. Description of the Related Art Recently, as a method for industrially useful production of methyl methacrylate or methyl acrylate, methacrolein or acrolein is reacted with methanol and molecular oxygen to produce methyl methacrylate or methyl acrylate all at once. A new route to do is in the limelight.
This route 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 a decomposition reaction of an aldehyde, the yield of a desired carboxylic acid ester is low, and alcohol is produced in parallel with the production reaction of the carboxylic acid ester. Different aldehydes are generated by oxidation of itself, and further different carboxylic acid esters (for example, methyl formate when methanol is used as alcohol, ethyl acetate when ethanol is used) are by-produced as alcohols. The standard selectivity was also poor.

Further, in this reaction, the aldehyde and alcohol react with oxygen by the catalyst containing palladium to produce carboxylic acid ester and water. When this water reacts with aldehyde, a small amount of carboxylic acid is by-produced, and the by-produced carboxylic acid lowers the pH of the reaction solution and produces acetal, deteriorating the selectivity of aldehyde standard or converting aldehyde. It is known to cause problems such as slowing down.

Japanese Patent Publication No. 5-69813 discloses that when the reaction is carried out in a liquid phase, the reaction system contains an alkali metal or alkaline earth metal compound (eg, hydroxide, carboxylate, carbonate, bicarbonate). (Salt, oxide, etc.) to maintain the pH of the reaction system at 6 or more and 9 or less, more preferably at a neutral condition, that is, near pH 7 infinitely, so that the carboxylic acid by-produced by oxidation of the alcohol itself is produced. It is disclosed that by-products such as acid esters, for example, methyl formate are suppressed, and further, formation of the above-mentioned acetal and β-methoxy compound, which is a polymer of the starting aldehyde, is suppressed.
However, the suppression of the production of by-products by the method described in the publication is still insufficient, and the basic substance used in a large amount to adjust the pH of the reaction solution is finally treated as a waste product by detoxifying treatment. There was a process problem.

[0006]

DISCLOSURE OF THE INVENTION The present invention provides a process having a high selectivity on an aldehyde basis and an alcohol basis and a high aldehyde conversion rate, in which the production of by-products from the raw materials aldehyde and alcohol is sufficiently suppressed. It is intended to be provided.

[0007]

Means for Solving the Problems In view of the present situation, the present inventors have made earnest studies, and as a result, have found that the pH of the reaction solution, the supply amount of the substance containing lead and the oxygen partial pressure in the gas outflowing from the reactor. When controlled to a specific value for the reaction, the production of by-product carboxylic acid ester, acetal, and β-methoxy compound is suppressed,
It has been found that deterioration of selectivity of aldehyde standard and alcohol standard can be suppressed, and the present invention has been completed.

That is, according to the present invention, (1) in 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, the pH of the reaction solution is maintained at 4 to 6. In addition, the content of lead is 0.1 to 20 based on the lead metal standard.
Continuous production method of carboxylic acid ester, characterized in that oxygen partial pressure in the reactor outflow gas is reacted at 0.8 kg / cm ² or less while adding to the reactor in the range of 00 ppm (2) 100 weight of carrier Aluminum to aluminum
Silica-alumina containing 5 to 40 parts by weight as ₂ O ₃ , or 5 to 40 parts by weight of aluminum as Al ₂ O ₃ , ₃ to 30 parts by weight of magnesium as MgO, and 50 to 92 parts by weight of silicon as SiO _2. A method for continuously producing a carboxylic acid ester according to (1), characterized in that a catalyst using silica-alumina-magnesia contained in a range is used as a carrier (3) The aldehyde is methacrolein or acrolein, and the alcohol is methanol. The above (1)
It is a continuous production method of the carboxylic acid ester described.

The present invention will be described in detail below. A feature of the present invention is that the supply amount of a substance containing lead and the oxygen partial pressure in the reactor outflow gas are controlled to a specific value to cause a reaction,
It is possible to realize higher selectivity of aldehyde standard and alcohol standard and higher aldehyde conversion rate. Perhaps by controlling the feed rate of the substance containing lead and the oxygen partial pressure in the reactor effluent gas to a specific value, it is possible to effectively suppress the oxidation reaction site of alcohol without changing the main reaction activity. Was successfully controlled, the amount of water produced by the by-product of different carboxylic acid ester and its by-product due to the oxidation of alcohol itself was suppressed, and further the carboxylic acid produced by this water and the raw material aldehyde was reduced, As a result, it is speculated that the selectivity of the aldehyde standard and the alcohol standard was improved.

The supply amount of the lead-containing substance and the value of the oxygen partial pressure in the reactor effluent gas are mutually related and are determined from the operating conditions, and therefore cannot be uniquely determined. The amount may be selected in the range of 0.1 to 2000 ppm, preferably 1 to 200 ppm on the basis of lead metal, and when the amount supplied to the reactor is large, the treatment cost for detoxifying lead in the wastewater is high, The minimum necessary amount is selected for practical use.

The oxygen partial pressure in the reactor outflow gas is 0.8 kg.
/ Cm ² or less, preferably 0.4 kg / cm ² or less, more preferably 0.2 kg / cm ² following conditions.
The substance containing lead is appropriately selected from organic acid salts such as formates and acetates, inorganic acid salts represented by sulfates, nitrates, hydrochlorides, and further oxides, hydroxides, metallic lead, and the like. However, acetate, nitrate and the like are preferable. These substances containing lead may be anhydrous or may contain water of crystallization.

The method of adding lead is not particularly limited, and may be a method of supplying in a solid state and gradually dissolving it, or a method of continuously supplying in a liquid state dissolved in water or alcohol. The method of supplying is common as an industrial mode. The basic substance may be supplied separately or mixed in advance and supplied, but a method of supplying separately is preferable.

The oxygen used in 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 reaction-inert diluent gas such as nitrogen, carbon dioxide gas, combustion exhaust gas or the like. It is also possible to use air. The oxygen partial pressure in the reactor outflow gas is selected to be a specific value according to the supply amount of the substance containing lead, but practically, it contains lead within a range in which oxygen necessary for the reaction is sufficiently supplied. The material supply is chosen to be minimal. If the oxygen partial pressure in the gas discharged from the reactor exceeds 0.8 kg / cm ² , the supply amount of the substance containing lead increases, and the treatment cost for detoxifying waste water increases.

It is preferable that the oxygen partial pressure in the gas discharged from the reactor and the supply amount of the substance containing lead are always maintained at a specific value. There is no problem in operating the vehicle with out-of-value conditions and returning it to the original specific value again. As described above, by controlling the supply amount of the substance containing lead and the oxygen partial pressure in the reactor effluent gas to specific values, it is possible to suppress the generation of different carboxylic acid by-products and acetal due to the oxidation of alcohol itself. However, in the present invention, it is necessary to further carry out the reaction while maintaining the pH of the reaction solution at 4 to 6. The preferable pH is 5 to 6, and more preferably 5 to 5.5.

When the reaction was carried out by lowering the pH of the reaction solution to less than 4, a part of the raw material aldehyde was converted into acetal,
The carboxylic acid ester selectivity based on aldehyde is deteriorated. Moreover, the conversion rate of aldehyde is also greatly reduced. On the other hand, when the pH of the reaction solution exceeds 6, the conversion of the raw material aldehyde to the β-methoxy form increases, and similarly, the carboxylic acid ester selectivity based on the aldehyde deteriorates.

It is preferable to carry out the reaction by adding a basic substance to the extent that it does not deviate from the above pH range, in order to keep the reaction rate, but if the amount is too large, the formation of β-methoxy compound is promoted. Therefore, the preferable addition amount of the basic substance is 1 to 50 mol%, more preferably 5 to 20 mol% with respect to the carboxylic acid by-produced. The basic substance is selected from hydroxides, carboxylates, carbonates, bicarbonates and oxides of alkali or alkaline earth metals, either alone or in combination of two or more. Hydroxides and carboxylates are industrially easily available,
It is important for implementing the present invention because it can be handled easily.

The alkali metal is selected from lithium, sodium, potassium and the like, and the alkaline earth metal is selected from magnesium, calcium, strontium, barium and the like. As the corresponding carboxylic acid, saturated fatty acids such as formic acid, acetic acid and propionic acid or aromatic carboxylic acids such as benzoic acid can be used, but lower fatty acids are generally preferred. These basic substances may be anhydrous or may contain water of crystallization.

The basic substance may be supplied as a solid as it is or may be supplied in a liquid state, but it is general to supply it as a small amount of an aqueous solution or an alcohol solution. The amount of basic substance added should always be 5 relative to the by-produced carboxylic acid.
There is no particular need to maintain the content below 0 mol%, economic efficiency,
Due to operating conditions and the like, there is no problem in raising the amount of the basic substance to 50 mol% or less with respect to the by-produced carboxylic acid and then again reducing it to 50 mol% or less.

The amount ratio of the by-produced carboxylic acid to the basic substance to be added is adjusted by analyzing the reaction product as needed for several times the reaction time. The catalyst used in the present invention is a supported catalyst containing palladium, and it is essential to contain palladium. The form of palladium is reduced metal-like palladium such as zero valence, and is not in a cation state. If it is a catalyst containing at least one of a lead metal or a compound, it may have a favorable effect on the activity and selectivity of the reaction,
It may be even more preferable if palladium and these lead metals or compounds form a compound represented by a simple integer ratio.

That is, by using such a catalyst containing a metal of palladium and lead or a compound thereof, generation of carbon dioxide gas or hydrocarbon due to the decomposition reaction of the raw material aldehyde is suppressed and the selectivity of the aldehyde standard is improved. In addition, it also suppresses the formation of carboxylic acid ester (methyl formate when methanol is used as alcohol) due to the oxidation of alcohol itself, improves the selectivity of alcohol standard, and makes it highly selective and daily. It becomes possible to produce a carboxylic acid ester.

The palladium compound used for preparing the catalyst includes organic acid salts such as formate salts and acetate salts, inorganic acid salts represented by sulfates, nitrates, hydrochlorides, ammine complexes, benzonitrile complexes and the like. Organometallic complex, further selected from oxides, hydroxides and the like, as the palladium compound, palladium chloride, palladium acetate,
Ammine complexes and the like are suitable.

For the preparation of the catalyst, known methods for preparing a supported catalyst such as an impregnation method and an ion exchange method can be applied. Explaining a typical catalyst preparation method, a solution containing a soluble palladium compound is impregnated with a carrier and then reduced with a reducing agent such as formalin, formic acid, hydrazine or a reducing agent such as hydrogen gas, Obtain the catalyst. 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.

As described above, the catalyst used in the present invention is a catalyst comprising palladium alone, a metal of palladium and lead, or at least one compound of palladium and lead. As the lead compound, any compound containing lead can be used, and examples thereof include lead carboxylates such as lead acetate and lead formate, lead oxide, and lead hydroxide.

The lead compounds mentioned above may be anhydrous or may have water of crystallization. As a different element in addition to palladium as a catalyst component, for example, tellurium, nickel, chromium, cobalt, indium, tantalum, copper, zinc, zirconium, hafnium, tungsten, manganese, silver, rhenium, antimony, tin, rhodium, ruthenium, iridium, It may contain platinum, gold, titanium, aluminum, boron, silicon and the like. These different elements can be contained usually in a range not exceeding 5% by weight, preferably not exceeding 1% by weight. Further, a compound containing at least one selected from alkali metal compounds and alkaline earth metal compounds has an advantage that the reaction activity becomes high. The alkali metal and alkaline earth metal are usually selected in the range of 0.01 to 30% by weight, preferably 0.01 to 5% by weight. These different elements or alkali metal and alkaline earth metal compounds, when palladium alone or when forming a compound in which palladium and lead are represented by a simple integer ratio,
A small amount may enter between crystal lattices or may be substituted with a part of 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 adsorbed or adhered to a carrier, or a catalyst supporting them in advance may be used as a catalyst. May be prepared. It is also effective to prepare and use a compound in which an alkali metal or an alkaline earth metal penetrates or substitutes in the crystal lattice.

The amount of the catalyst used can be largely changed depending on the kind of the 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 Is 0.
It is preferable to use 04 to 0.5 kg. In the present invention, since the catalyst is used in a liquid phase suspension state, it may be in the form of powder finer than 30 mesh, and a particle size of 200 to 350 mesh is preferable.

The carrier used for preparing the catalyst is not particularly limited, but above all, 5 to 40 parts by weight, preferably 5 to 1 part, of aluminum as Al ₂ O ₃ with respect to 100 parts by weight of the carrier.
Silica-alumina contained in the range of 0 parts by weight, or aluminum as Al ₂ O ₃ is 5 to 40 parts by weight, preferably 5 to 10 parts by weight, and magnesium is MgO as 3 to 3 parts by weight.
30 parts by weight, preferably 3 to 10 parts by weight, silicon as SiO
₂ is preferably silica-alumina-magnesia, which is contained in the range of 50 to 92 parts by weight. When a catalyst using these as a carrier is used, the reaction can be carried out with almost no reduction in the aldehyde conversion rate.

It is not yet fully clarified why the use of silica-alumina or silica-alumina-magnesia as a carrier can prevent the reduction of the conversion rate of aldehyde, but it is not clear yet. It is presumed that the hydrophobic nature of the magnesia carrier had a favorable effect on the durability of the activity and did not cause a decrease in the aldehyde conversion rate.

Various methods are known for obtaining silica-alumina or silica-alumina-magnesia, and a typical production method will be introduced. (1) Those obtained by forming silica-alumina gel or silica-alumina-magnesia gel in advance. (2) A product obtained by reacting a solution such as silica sol with an aluminum solution and / or a magnesium solution. (3) A product obtained by reacting a silica sol with a water-insoluble aluminum compound and / or a water-insoluble magnesium compound. (4) A product obtained by reacting silica gel with an aqueous solution of a water-soluble aluminum compound and / or an aqueous solution of a water-soluble magnesium compound. (5) Those obtained by solid-phase reaction of silica gel with an aluminum compound and / or a magnesium compound are generally used.

The obtained magnesium-, aluminum-, and silica-containing composition can be used as silica-alumina or silica-alumina-magnesia by baking at a suitable baking temperature and time. Furthermore, the silica-alumina or silica-alumina-magnesia used in the present invention is preferably used after being calcined at a suitable temperature before or during the catalyst preparation. The firing temperature is generally selected from the range of 200 to 800 ° C.
Firing at a temperature exceeding 800 ° C. is not preferable because the specific surface area is significantly reduced. The firing atmosphere is not particularly limited, but firing is generally performed in air or nitrogen. The firing time can be determined according to the specific surface area after firing, but is generally selected from the range of 1 to 48 hours.

As the silica raw material, silica sol, water glass, or silica gel can be used. The aluminum compound is preferably sodium aluminate, aluminum chloride hydrate, aluminum perchlorate hydrate, aluminum sulfate, aluminum nitrate nonahydrate, water-soluble compound such as aluminum diacetate, but aluminum hydroxide In principle, it is possible to use any water-insoluble compound such as aluminum oxide as long as it is a compound that reacts with them in silica sol or silica gel.

As the magnesium raw material, magnesium oxide, magnesium hydroxide, magnesium acetate tetrahydrate, magnesium nitrate hexahydrate, magnesium chloride, magnesium sulfate heptahydrate and the like can be used. In principle, any water-insoluble magnesium compound can be used as long as it is a compound that reacts with them in silica sol or silica gel.

An example of the industrial production method of silica-alumina-magnesia will be described below, but the production method of the carrier is not limited to this. An aqueous solution of silica sol is used as a silica raw material, and an aqueous solution of a water-soluble aluminum compound such as aluminum nitrate and an aqueous solution of a water-soluble magnesium compound such as magnesium nitrate are mixed to obtain a predetermined composition, and the mixed slurry is then mixed. For example, it is possible to obtain a magnesium-, aluminum-, and silica-containing composition having a desired particle diameter by granulating and finely pulverizing by a usual spray drying method.

The obtained magnesium-, aluminum-, and silica-containing composition can be generally calcined at about 300 ° C to 600 ° C to obtain a silica-alumina-magnesia carrier. Examples of the aldehyde used in this reaction include aliphatic saturated aldehydes such as formaldehyde, acetaldehyde, propionaldehyde, isobutyraldehyde and glyoxal, and aliphatic α / β such as acrolein, methacrolein and crotonaldehyde.
-Aromatic aldehydes such as unsaturated aldehydes, benzaldehydes, tolyl aldehydes, benzyl aldehydes and phthal aldehydes, and derivatives of these aldehydes. These aldehydes can be used alone or as a mixture of two or more kinds.

When the aldehyde is acrolein or methacrolein, it is industrially particularly important. Examples of the alcohol used in the present invention include aliphatic saturated alcohols such as methanol, ethanol, isopropanol and octanol, diols such as ethylene glycol and butanediol, aliphatic unsaturated alcohols such as allyl alcohol and methallyl alcohol, and benzyl alcohol. Aromatic alcohols and the like. These alcohols can be used alone or as a mixture of two or more kinds.

When the alcohol is methanol,
It is of particular industrial importance. The ratio of aldehyde to alcohol used in the present invention 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, but generally 1/2 to 1 /
It is carried out in the range of 50. The methacrolein or acrolein used in the present invention is industrially generally produced by oxidation of isobutylene and / or t-butanol or propylene, but may be obtained by any other method. As the methanol, it is preferable to use substantially anhydrous methanol, particularly pure methanol. As the raw materials to be supplied to the reactor, methacrolein or acrolein and methanol may be supplied separately or by mixing in advance.

The embodiment of the reaction may be a batch type or a flow type, and the reactor type may be any type of reactor such as a bubble column reactor, a draft tube type reactor and a stirred tank type reactor. Can be adopted. The reaction can be carried out without a solvent, but can be carried out using a solvent inert to the reaction components, such as hexane, decane, benzene, dioxane and the like.

The reaction pressure can be carried out in a wide pressure range from reduced pressure to increased pressure, but usually 0.5 to 20.
It is carried out at a pressure of kg / cm ² . The total pressure may be set so that the oxygen concentration in the gas phase of the reactor does not exceed the explosive range of the combustible components in the gas phase of the reactor. The reaction time (residence time, that is, the amount of liquid retained in the reactor / the amount of liquid supplied) is not particularly limited and varies depending on the set conditions, so it is not uniquely determined, but usually 1 to 20 as the total reaction time. It's time.

This reaction can be carried out at 0 to 200 ° C. as described in JP-B-57-45423, but it is preferably carried out at a relatively low temperature of room temperature to 150 ° C., and further 40 to 100. It is more preferable to set the reaction temperature to ° C.

[0039]

DETAILED DESCRIPTION OF THE INVENTION

[0040]

[Example 1] As a silica sol aqueous solution, Snowtex N-30 (SiO ₂ content: 30% by weight) manufactured by Nissan Chemical Co., Ltd. was added with aluminum nitrate and magnesium nitrate respectively 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 130 ° C. to obtain a spherical carrier having an average particle diameter of 60 μ, and 300 ° C. Then, after firing at 600 ° C., it was used as a carrier. The composition of the carrier is Al ₂ O ₃ , SiO ₂ , MgO.
As 7.4% by weight, 86.8% by weight and 5.8%, respectively.
% By weight. Specific surface area is 148 m2 by BET measurement method
/ G, the average particle diameter of 60μ was a spherical carrier.

Using this as a carrier, a catalyst was obtained in which palladium chloride was carried in an amount of 5 parts by weight of palladium and 4.2 parts by weight of lead per 100 parts by weight of the carrier.
240 g of the obtained catalyst was charged into an external circulation type stainless steel reactor having a catalyst separation device and a condenser and a liquid phase portion of 1.2 L to carry out a reaction. The reactor was charged with 36.7 wt% methacrolein / methanol solution at 0.54 L / h, Na.
OH / methanol solution was supplied to the 0.06 L / h continuously at a reaction temperature 80 ° C., the outlet oxygen concentration of 4.0% at a reaction pressure of 5 kg / cm ² (corresponding to an oxygen partial pressure of 0.20 kg / cm ²⁾ The reaction is carried out for 100 hours while adjusting the amount of air so that the amount of NaOH supplied is 1 byproduct methacrylic acid.
It was 0 mol%. The pH of the reaction solution was 5.0-5.5.

Lead acetate was added to a 36.7 wt% methacrolein / methanol solution fed to the reactor so that the lead concentration in the feedstock solution was 20 ppm. Analysis of the reaction product revealed that the conversion of methacrolein was 55.1%,
The selectivity of methyl methacrylate is 93.7%, and methacrylic acid is 4.1% and propylene is 1.2% as by-products.
%, Methoxy compound was 0.2%, and methyl formate was 0.037 mol / mol MMA.

[0043]

Example 2 The reaction was carried out for 100 hours in the same manner as in Example 1 except that the basic substance supplied was changed to sodium methacrylate and 40 mol% of the by-product methacrylic acid was used. The pH of the reaction solution was 5.5 to 6.0. When the reaction product was analyzed, the conversion of methacrolein was 58.1%, the selectivity of methyl methacrylate was 92.7%, methacrylic acid was 4.4%, propylene was 1.0%, and methoxy was a by-product. The body was 0.3% and methyl formate was 0.041 mol / mol MMA.

[0044]

Example 3 The reaction was carried out for 100 hours in the same manner as in Example 1 except that NaOH was not supplied. The pH of the reaction solution was 4.0 to 4.5. When the reaction product was analyzed, the conversion of methacrolein was 48.9%, the selectivity of methyl methacrylate was 91.4%, methacrylic acid was 4.7%, propylene was 0.9%, and methoxy was a by-product. Body is below detection limit, methyl formate 0.012 mol / mol M
MA was generated.

[0045]

Example 4 The partial pressure of oxygen in the gas discharged from the reactor was adjusted to 0.05 k.
The reaction was carried out in the same manner as in Example 1 except that the reaction rate was 10 g / cm ^2.
I went for 0 hours. When the reaction product was analyzed, the conversion of methacrolein was 51.0%, the selectivity of methyl methacrylate was 88.5%, methacrylic acid was 6.9%, propylene was 0.7%, and methoxy was a by-product. Body is 0.2
%, Methyl formate was produced at 0.040 mol / mol MMA.

[0046]

[Comparative Example 1] Reaction 1 was carried out in the same manner as in Example 1 except that the amount of NaOH supplied was 60 mol% of the by-product methacrylic acid.
I went for 00 hours. The pH of the reaction solution was 7.0 to 7.5. Analysis of the reaction product revealed that the conversion of methacrolein was 61.2% and the selectivity of methyl methacrylate was 87.3.
%, Methacrylic acid was 8.0%, propylene was 1.3%, methoxy was 1.0%, and methyl formate was 0.063 mol / mol MMA.

[0047]

Comparative Example 2 The reaction was carried out for 100 hours in the same manner as in Example 1 except that the amount of NaOH supplied was 100 mol% of the by-product methacrylic acid. The pH of the reaction solution was 8.0 to 8.5. When the reaction product was analyzed, the conversion of methacrolein was 65.0% and the selectivity of methyl methacrylate was 87.
1%, methacrylic acid 8.1% as a by-product,
Propylene was 1.7%, methoxy was 1.9%, and methyl formate was 0.091 mol / mol MMA.

[0048]

[Comparative Example 3] The partial pressure of oxygen in the gas discharged from the reactor was 0.84 k.
The reaction was carried out in the same manner as in Example 1 except that the reaction rate was 10 g / cm ^2.
I went for 0 hours. When the reaction product was analyzed, the conversion of methacrolein was 57.3%, the selectivity of methyl methacrylate was 85.8%, methacrylic acid was 8.3% and propylene was 4.2% as byproducts. Methoxy is 0.2
%, Methyl formate was produced at 0.086 mol / mol MMA.

[0049]

Comparative Example 4 The reaction was carried out for 100 hours in the same manner as in Example 1 except that lead was not supplied. When the reaction product was analyzed, the conversion of methacrolein was 57.1%, the selectivity of methyl methacrylate was 85.4%, methacrylic acid was 6.6% and propylene was 4.9% as by-products. Methoxy form 0.2%, methyl formate 0.035 mol / mol M
MA was generated.

[0050]

Example 5 Silica gel (manufactured by Fuji Silysia Ltd.) was used as a carrier.
A catalyst was prepared and reacted in the same manner as in Example 1 except that the trade name Caractact 10) was used. The pH of the reaction solution is 5.
It was 0 to 5.5. When the reaction product was analyzed, the conversion of methacrolein was 36.0%, the selectivity of methyl methacrylate was 76.7%, and the methoxy form was 0.2%.

[0051]

[Comparative Example 5] Reaction 1 was conducted in the same manner as in Example 3 except that the amount of NaOH supplied was 60 mol% of the by-product methacrylic acid.
I went for 00 hours. The pH of the reaction solution was 7.0 to 7.5. Analysis of the reaction product revealed that the conversion of methacrolein was 63.1% and the selectivity of methyl methacrylate was 89.1.
%, The methoxy form was 1.0%.

[0052]

Example 6 A catalyst was prepared and reacted in the same manner as in Example 1 except that alumina (trade name: Neo-bead manufactured by Mizusawa Chemical Co., Ltd.) was used as the carrier. The pH of the reaction solution was 5.0 to 5.5. When the reaction product was analyzed, the methacrolein conversion rate was 21.0% and methyl methacrylate selectivity was 7
It was 1.3% and the methoxy form was 0.2%.

[0053]

[Comparative Example 6] Reaction 1 was repeated in the same manner as in Example 3 except that the amount of NaOH supplied was 60 mol% of the by-product methacrylic acid.
I went for 00 hours. The pH of the reaction solution was 7.0 to 7.5. Analysis of the reaction product revealed that the conversion of methacrolein was 58.2% and the selectivity of methyl methacrylate was 88.9.
%, The methoxy form was 1.0%.

[0054]

Example 7 A silica-alumina carrier was prepared in the same manner as in the carrier preparation method of Example 1 except that magnesium nitrate was not used, and the composition of the carrier was Al ₂ O ₃ and SiO ₂ , respectively, 8.0 wt. %, 92.0% by weight, specific surface area 1
A spherical carrier having a particle size of 40 m ² / g and an average particle diameter of 60 μm was obtained.

Using this carrier, a catalyst was prepared and reacted in the same manner as in Example 1. The pH of the reaction solution is 5.0 to 5.5.
Met. When the reaction product was analyzed, the methacrolein conversion rate was 51.1% and methyl methacrylate selectivity was 9
2.8% and 4.7% methacrylic acid as a by-product.
%, Propylene was 1.2%, methoxy was 0.2%, and methyl formate was 0.039 mol / mol MMA.

[0056]

[Example 8] After conducting the experiment of Comparative Example 2, supplied Na
The amount of OH was set to 10 mol% of the by-product methacrylic acid, and the reaction was further continued for 100 hours. The pH of the reaction solution is 5.0-
It was 5.5. Analysis of the reaction product revealed that the conversion of methacrolein was 54.9%, the selectivity of methyl methacrylate was 93.8%, methacrylic acid was 4.0%, and propylene was 1.2% as by-products. Methoxy is 0.2
%, Methyl formate was produced at 0.039 mol / mol MMA.

[0057]

Example 9 After conducting the experiment of Comparative Example 3, the oxygen partial pressure in the gas discharged from the reactor was returned to 0.20 kg / cm ² , and the reaction was further continued for 100 hours. When the reaction product was analyzed, the conversion of methacrolein was 55.2%, the selectivity of methyl methacrylate was 93.6%, and methacrylic acid was 4.2% and propylene was 0.9% as by-products. Methoxy form 0.2%, methyl formate 0.036 mol / mol M
MA was generated.

[0058]

Example 10 After conducting the experiment of Comparative Example 4, lead acetate was added to a 36.7 wt% methacrolein / methanol solution fed to the reactor so that the lead concentration in the feedstock solution would be 20 ppm. The reaction was further continued for 100 hours. When the reaction product was analyzed, the conversion of methacrolein was 5
6.0%, methyl methacrylate selectivity 93.5%, by-products 4.1% methacrylic acid, 1.0% propylene, 0.2% methoxy, 0.2% methyl formate as by-products. 035 mol / mol MMA was produced.

[0059]

Example 11 The same reaction was carried out using the same catalyst as in Example 1 except that acrolein was used instead of methacrolein. The pH value of the reaction solution was 5.0 to 5.5. Analysis of the reaction product revealed that the acrolein conversion was 63.9% and methyl acrylate selectivity was 92.5%.
As a by-product, 4.8% of acrylic acid, 0.9% of ethylene, 0.2% of methoxy compound, and 0.036 mol / mol MMA of methyl formate were produced.

Table 1 summarizes the reaction results of the examples and comparative examples.

[0061]

[Table 1]

[0062]

According to the method of the present invention, the production of by-products from the raw material aldehyde and alcohol is sufficiently suppressed,
High aldehyde-based and alcohol-based selectivities and high aldehyde conversion rates can be maintained.

Continuation of front page (51) Int.Cl. ⁷ identification code FI // C07B 61/00 300 C07B 61/00 300 (56) References JP-A-8-337554 (JP, A) JP-A-5-148184 ( JP, A) JP 59-162947 (JP, A) JP 55-151533 (JP, A) JP 54-73723 (JP, A) JP 58-166936 (JP, A) JP JP-A-58-185540 (JP, A) JP-A-57-50942 (JP, A) JP-A-9-221452 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C07C 67 / 39 C07C 69/54

Claims (3)

(57) [Claims] 1. 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, wherein the pH of the reaction solution is 4
To 6 and hold a substance containing lead at 0.
A continuous process for producing a carboxylic acid ester, characterized in that the reaction is carried out at an oxygen partial pressure in the reactor outflow gas of 0.8 kg / cm ² or less while being added to the reactor in the range of 1 to 2000 ppm. Respect 2. A carrier 100 parts by weight, 5 to silica-alumina aluminum containing 5-40 parts by weight Al ₂ O _3, or aluminum as Al ₂ O ₃
A catalyst using as a carrier silica-alumina-magnesia containing 40 parts by weight, 3 to 30 parts by weight of magnesium as MgO and 50 to 92 parts by weight of silicon as SiO _2. A continuous method for producing the carboxylic acid ester described. 3. The continuous process for producing a carboxylic acid ester according to claim 1, wherein the aldehyde is methacrolein or acrolein and the alcohol is methanol.