JP2003267922A - Method for producing unsaturated carboxylic acid ester - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an unsaturated carboxylic acid ester by performing a reaction of an unsaturated aldehyde with an alcohol in the presence of oxygen, stably maintaining a high unsaturated carboxylic acid ester production rate and a high unsaturated aldehyde conversion rate, and eliminating a risk of the damage of a reactor or the ignition of a catalyst. <P>SOLUTION: This method for producing the unsaturated carboxylic ester by performing the reaction of the unsaturated aldehyde with the alcohol in the presence of oxygen is characterized by discharging the catalyst so that the remaining catalyst in the reactor becomes ≤3 wt.% based on the weight of the inputted catalyst. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing an unsaturated carboxylic acid ester by reacting an unsaturated aldehyde with an alcohol in the presence of oxygen, which has a high unsaturated carboxylic acid ester production rate and a high unsaturated aldehyde conversion. A method for producing an unsaturated carboxylic acid ester, which maintains a stable rate and eliminates the risk of reactor damage and catalyst ignition.

[0002]

2. Description of the Related Art An industrially useful method for producing methyl methacrylate or methyl acrylate is an oxidative esterification method for directly producing methyl methacrylate or methyl acrylate by reacting methacrolein or acrolein with methanol. Proposed. In this production method, methacrolein or acrolein is reacted with molecular oxygen in methanol, and an example using a catalyst containing palladium and lead, bismuth, thallium, and mercury is disclosed in JP-B-57-35856-35861. Japanese Patent Publication No. 62-7902 discloses an example in which an intermetallic compound of palladium and these metals is used as a catalyst.

A catalyst using palladium and bismuth is disclosed in JP-A-9-216850 and others.
1-220367 exemplifies a catalyst using ruthenium and lead. The catalysts shown in these disclosures are all
A solid catalyst supported on a carrier such as calcium carbonate, silica, or alumina. The reaction is carried out by dispersing these solid catalysts in a solution of an alcohol and an unsaturated aldehyde (hereinafter, abbreviated as catalyst slurry in some cases) oxygen. In general, the present inventors have conducted an experiment of producing methyl methacrylate from methacrolein and methanol using a bubble column reactor continuously for a long period of time.

Now, in an actual industrial process, there is always an opportunity to stop the operation for a reason such as periodical inspection and repair, replacement of devices and catalysts, and an opportunity to restart the operation. The inventors of the present invention who have been operating for a long period of time also, after achieving the purpose, when the operation is stopped, withdraw the catalyst slurry, wash the inside of the reactor, inspect the inside of the reactor, damage and corrosion Checked for abnormalities on the wall surface and deterioration of connection packing.

First, the catalyst slurry was extracted from the reactor. Although some catalyst remained on the bottom surface of the reactor, the thermometer pod, and the top surface of the additive input tube, the processing of the residual catalyst was postponed due to the processing of the extracted slurry. Therefore, as a precaution, when the performance of the catalyst retained in this reactor was evaluated, it was found that the unsaturated aldehyde conversion rate and unsaturated carboxylic acid ester selectivity were higher than those of the catalyst that was constantly circulated as a catalyst slurry. Both were significantly decreased, and there was a possibility that the catalyst was chemically changed.

Further, when the inside of the reactor was inspected in detail, part of the catalyst adhered to the reactor wall. From this, the wear of the catalyst due to the friction between the fixed catalyst mass and the slurry, the wear of the reactor wall due to the detached fixed catalyst mass, the erosion-corrosion corrosion from the wear point, and the fixed catalyst mass that violently flows in the slurry. Various troubles due to the stuck catalyst mass were assumed, such as damage due to collision with the vessel wall, decrease in reactivity due to damaged catalyst mass, and so on. Any one of these is a serious trouble that can pose a very dangerous situation for an industrial plant.

[0007] Further, when an attempt was made to scrape off the adhered catalyst and analyze it, it was found that it was extremely dangerous and accompanied by an extremely high heat generation. Got In addition, in experiments using activated carbon as a carrier, the catalyst itself may ignite red heat, which may lead to a large-scale explosion or fire in the actual industrial process that handles a large amount of combustible materials. This is a very serious emergency, and above all, it is a fatal obstacle to the practical application of a chemical plant where safety is the first priority.

Thus, when the catalyst is withdrawn for some reason or when operation is stopped, the catalyst remains in the reactor.
It was found that not only irreversible deterioration of the catalyst but also seriously impairing safety against explosion and fire, which is a lifeline for a chemical plant, resulting in extremely dangerous trouble. Further, as a cause of the catalyst remaining, not only is it retained on the bottom surface of the reactor, the sheath of the thermometer or the upper flat surface of the additive feeding pipe, but also the adhesion of the catalyst on the uneven portion of the reactor is serious. The adhered catalyst not only poses a direct ignition source such as an explosion fire, but it can also cause corrosion and wear of the reactor, and damage gradually progresses without noticing. At one point, it turned out that there was a fatal risk of sudden reactor damage, and it was also found that without the solution of those safety aspects, industrialization of the process would never be possible.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and secures process safety, prevents catalyst deterioration, is stable over a long period of time, and is continuous. It is an object of the present invention to provide a method capable of producing an unsaturated carboxylic acid ester.

[0010]

[Means for Solving the Problem] The present inventors have solved this problem with the highest priority. First, it is important not to allow the catalyst to remain in the reactor, and it has been found that the catalyst can be prevented from deteriorating and safety can be ensured by extracting the entire amount as much as possible, and always extracting at least a certain ratio or more. It was a start. In addition, when removing the catalyst, wash it to keep the amount of residual catalyst as small as possible, and use the reaction solution and raw materials such as unsaturated aldehydes and alcohols for washing. Even so, it was confirmed that stable reaction results could be obtained, and the present invention was further developed.

[0011] Then, by carrying out a treatment to prevent the catalyst from sticking in the reactor, it is possible to prevent the catalyst from sticking, which threatens the safety of the plant, and the present invention was completed based on these findings. That is, the present invention is: In the method for producing an unsaturated carboxylic acid ester by reacting an unsaturated aldehyde and an alcohol with a catalyst in the presence of oxygen, the amount of the catalyst remaining in the reactor is 3% by weight or less based on the weight of the catalyst added to the reaction. The present invention relates to a method for producing an unsaturated carboxylic acid ester, which is characterized in that it is discharged as follows.

2. The reaction relates to the method for producing an unsaturated carboxylic acid ester according to the above 1, wherein the reaction is restarted after the operation of the reactor is stopped. 3. The reaction relates to the method for producing an unsaturated carboxylic acid ester according to the above 1 or 2, wherein the catalyst is discharged by washing the inside of the reactor. 4. The reaction relates to the method for producing an unsaturated carboxylic acid ester according to the above 3, wherein the reactor is washed with at least one of a reaction solution, a catalyst slurry, alcohol and water. 5. The reaction relates to the method for producing an unsaturated carboxylic acid ester described in 1 to 4 above, which prevents the catalyst from adhering to the liquid contact part of the reactor.

6. In the reaction, the amount of catalyst adhering to the liquid contact part of the reactor immediately after the operation of the reactor is stopped is 3% by weight or less based on the weight of the catalyst charged into the reactor.
The method for producing an unsaturated carboxylic acid ester according to 1. 7. The catalyst is palladium and / or ruthenium and X
The method for producing an unsaturated carboxylic acid ester according to any one of 1 to 6 above, which is a catalyst containing (X represents at least one metal selected from lead, bismuth, mercury, and thallium). 8. The method for producing an unsaturated carboxylic acid ester according to the above 1 to 7, wherein the unsaturated aldehyde is acrolein or methacrolein and the alcohol is methanol.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below.
Examples of the unsaturated aldehyde used in the present invention include aliphatic unsaturated aldehydes such as acrolein, methacrolein, and crotonaldehyde, and derivatives of these aldehydes, and acrolein and methacrolein are preferably used. These unsaturated aldehydes can be used alone or as a mixture of two or more kinds.

Particularly, acrolein and methacrolein produced by partial oxidation with oxygen from isobutylene and propylene in the presence of a catalyst are more preferably used. 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; benzyl alcohol. Such as aromatic alcohol. Particularly, lower alcohols such as methyl alcohol and ethyl alcohol are preferred because of quick reaction. These alcohols can be used alone or as a mixture of two or more kinds.

The amount ratio of unsaturated aldehyde to alcohol used in the reaction of the present invention is not particularly limited, and for example, unsaturated aldehyde / alcohol molar ratio is from 10 to 1/1000.
However, it is generally preferable that the amount of unsaturated aldehyde is small, and it is preferable that the amount is in the range of 1/2 to 1/50. 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 reaction-inert diluent such as nitrogen or carbon dioxide, and air is used. You can also The amount of oxygen present in the reaction system is sufficient if it is at least the stoichiometric amount necessary for the reaction, preferably at least 1.2 times the stoichiometric amount.

The total pressure of the reaction can be carried out in any wide pressure range from reduced pressure to increased pressure, but usually 1 to 20 k.
It is carried out at a pressure of g / cm ² . The partial pressure of oxygen supplied to the reaction system is such that the oxygen partial pressure on the outlet side of the reactor is 0.8 kg / cm.
^It is preferable to control it to be ² or less, and more preferably 0.4 kg / cm ² or less. On the other hand, it is advisable to set the total pressure so that the oxygen concentration of the reactor outflow gas does not exceed the explosion range (8%). 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. The reactor type may be any conventionally known type such as a fixed bed type, a fluidized bed type, and a stirring tank type. 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 reaction can be carried out without a solvent, but a solvent inert to the reaction components, such as hexane, decane,
It can be carried out using benzene, dioxane or the like. The catalyst can be extracted by dropping it from the bottom of the reactor, recovering the catalyst separated by a catalyst separator such as a filter separator, centrifuge, or sedimentation separator without returning it to the reactor, or vapor of gas or compound. Any known method such as a method of scattering and collecting with a cyclone or the like can be adopted.For example, when the reaction is carried out in the bubble column reactor in the liquid phase, the catalyst slurry is made to flow while blowing gas. It is preferable to remove the catalyst slurry as it is from the bottom of the reactor by gravity drop, or remove it from the sedimentation separator or the filter separator.

When the catalyst is withdrawn, the amount allowed to stay in the reactor is 3% by weight, preferably 1% by weight, more preferably 0.3% by weight or less based on the weight of the reaction. . If the catalyst remains in the reactor in an amount of 3% by weight or more, the catalyst deteriorates and it is difficult to obtain a predetermined reaction result even after restarting. Further, if a large amount of catalyst of 3% by weight or more stays or adheres, once the heat is generated for some reason, heat is accumulated in the adhered catalyst mass and induces further reaction, resulting in red heat as described in the prior art. There is a high risk of being linked to a phenomenon, and such a situation must be absolutely avoided for plant safety.

Regarding the method of storing the extracted catalyst, since combustible substances such as alcohol, unsaturated aldehyde, unsaturated carboxylic acid ester and unsaturated carboxylic acid are contained, in order to ensure the safety of the plant, It is essential for safety to avoid the combustibles, oxygen, and ignition sources, which are the three elements, and store them. Therefore, a preferable method for storage is a method of storing under conditions that are not substantially exposed to oxygen (for example, in nitrogen or carbon dioxide) or in a state where there is substantially no ignition source (for example, in a reaction solution, alcohol, or water). It Although avoiding flammable substances is not as simple as comparing with the other two methods, it is also possible to wash catalyst slurry thoroughly with water-soluble alcohol, etc., and then wash it thoroughly with water. is there.

Cleaning the reactor is also important in the present invention as a method for ensuring discharge, and at least one of the reaction solution, catalyst slurry, alcohol and water is sent from outside the reactor by a pump or the like. A known cleaning method such as a method of cleaning the inside of the reactor, a method of blowing off with an inert gas such as nitrogen or carbon dioxide or water vapor, wiping, scraping, hammering can be adopted. However, a method of washing with at least one of a reaction solution, a catalyst slurry, alcohol or water is preferable for reasons such as not mixing in a substance not contained in the reaction system and protecting the catalyst from destruction due to violent flow or collision. The method of extracting the catalyst slurry while being fluidized is preferably exemplified as one means for discharging the catalyst while washing with the catalyst slurry. Preventing the catalyst from adhering to the inside of the reactor is one of the important requirements of the present invention.

It is needless to say that the surface to which the catalyst does not adhere in the method of the present invention shows the reactors, the pipes for connecting the reactors, the pipes for guiding the catalyst slurry to the catalyst separation device, and the like. Also included are a flow meter, a thermometer, a pressure gauge, etc. connected to the reactor or the pipe. Further, on the surface to which the above catalyst does not adhere, the boundary portion between the liquid phase portion and the gas phase portion of the reactor wall that gets wet or dry by the flow of the catalyst slurry, the flowing slurry or the rotating There is a possibility that the slurry that has flown as droplets from the stirrer may come into contact with the reactor, such as the inner wall top and top surfaces, the stirring shaft, the stirring blade surface, and the condenser that the slurry that accompanies with the evaporated alcohol or aldehyde touches Is also included.

As a method for preventing the catalyst from adhering or staying, a structure in which the catalyst is hard to stay is formed, an unevenness that induces the catalyst to stay in the details causing the sticking is eliminated, and the catalyst is inactive. Surface treatment (for example,
Various methods such as glass coating (GL) or fluorine coating (FL) on the surface, constant flow of a cleaning liquid downward along the wall surface from the upper part of the reactor, and prevention of static electricity can be taken. Which of these methods is preferable cannot be uniquely determined because it depends on the detailed structure and function of the reactor. The structure of the reactor in which the catalyst is hard to stay is, for example, to reduce the area of the horizontal part, to make it slightly inclined toward the discharge port, to prevent liquid pooling, such as thermometer and pressure gauge. Methods such as minimizing the protrusions of the measuring instrument such as the pod and the additive input pipe can be used.

Glass coating and fluorine coating are generally envisioned as a method for surface-inactivating the catalyst, but the cost is high and there is a concern that glass may be damaged or fluororesin may be peeled off. Therefore, it is difficult to use in a portion where the catalyst slurry in the reactor is violently flowing. For example, it can be used for surface treatment of condensers that condense evaporated organic compounds and catalysts entrained with them. The method of eliminating unevenness is simple and inexpensive for processing a large area such as surface processing in a reactor. As a method for providing such smoothness, J
Mechanical polishing such as buff polishing specified in ISH0400-1961, or "Handbook of Metal Surface Technology" (revised new edition
Chemical polishing, electrolytic polishing, etc. described in "P113, 120 Metal Surface Technology Association", Nikkan Kogyo Shimbun) are preferred.

The boundary portion between the liquid phase portion and the gas phase portion of the reactor, the stirring shaft, and the like are easily contacted by the catalyst slurry and easily dried, and so-called wet-dry adhesion is likely to occur. In such a place, for example, a method of constantly flowing a washing liquid from the upper part of the reactor is effective, and it is also possible to use the fact that alcohol condensed in a low temperature portion above the inner wall of the reactor flows down. The method of removing static electricity is these G
When combined with L, FL, surface smoothing, etc., the effect of preventing sticking is further enhanced. The prevention of static electricity is also preferable for safety purposes to prevent spark ignition due to static electricity.

Although the reason why the unsaturated aldehyde conversion rate and the unsaturated carboxylic acid ester selectivity are greatly reduced in the catalyst that has stayed or is stuck is not clear, in an experiment using methacrolein as the unsaturated aldehyde, When the accumulated catalyst was analyzed, a polymer-like substance was found in the catalyst, and as a result of the analysis, infrared absorption derived from the carbonyl group was observed.Therefore, this polymer-like substance was identified as methacrolein, methacrylic acid, and methacrylic acid. It was presumed that methyl etc. were polymerized. Therefore, it is assumed that the surface of the catalyst was covered with the polymer and was deactivated.

The catalyst used in the present invention is palladium and / or
Alternatively, it is essential to contain ruthenium and X (X is at least one metal selected from lead, bismuth, mercury, and thallium). Palladium and / or ruthenium and X may form an alloy or an intermetallic compound. Moreover, Fe, Te, Ni, Cr, Co, and C are used as different elements.
d, In, Ta, Cu, Zn, Zr, Hf, W, M
n, Ag, Re, Sb, Sn, Rh, Ru, Ir, P
It may contain t, Au, Ti, Al, B, Si, Ge, Se, Ta or the like. These different elements are usually 5% by weight,
It can be contained preferably in a range not exceeding 1% by weight.

Further, those containing at least one member selected from alkali metal compounds and alkaline earth metal compounds are advantageous in 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. A small amount of these different elements, alkali metals, alkaline earth metal compounds, etc. may penetrate into the crystal lattice or may be substituted with a part of the crystal lattice metal. Also, alkali metal and /
Alternatively, the alkaline earth metal compound may be added to a solution containing a palladium compound, a ruthenium compound, or a compound of X at the time of catalyst preparation and adsorbed or adhered 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.

These catalyst constituents may be supported alone or on a carrier such as silica, alumina, silica-alumina, titanium, carbonate, hydroxide, activated carbon or zirconia. The amount of the palladium- and / or ruthenium-supported catalyst supported in the present invention is not particularly limited, but is usually 0.1 to 20% by weight, preferably 1 to 10% by weight, and the amount of alkali metal compound or alkaline earth metal compound When used, the supported amount is usually 0.01 to 30% by weight, preferably 0.01 to 15% by weight.

The catalyst of the present invention can be prepared by a known preparation method. A typical catalyst preparation method will be described. For example, a carrier is added to an aqueous solution containing a soluble lead compound and a soluble palladium salt such as palladium chloride, and the mixture is warmed and impregnated with palladium and lead. Then, it is reduced with formalin, formic acid, hydrazine or hydrogen gas. In this example, lead may be loaded before loading palladium, or palladium and lead may be loaded simultaneously.

The palladium compound and ruthenium compound used for preparing the catalyst include organic acid salts such as formate salts and acetate salts, inorganic acid salts such as sulfates, hydrochlorides and nitrates, ammine complexes, benzonitrile complexes and acetyl compounds. It is appropriately selected from organic metal complexes such as an acetonate complex and a carbonyl complex, oxides, hydroxides and the like. Palladium compounds such as palladium chloride and palladium acetate are preferred, and ruthenium compounds such as ruthenium chloride are preferred.

As the compound of X, inorganic salts such as nitrates and acetates and organic metal complexes such as phosphine complexes can be used, and nitrates and acetates 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 amount of the catalyst used can be widely changed depending on the type of reaction raw material, the composition and preparation method of the catalyst, the reaction conditions, the reaction format, etc.
Although not particularly limited, when the catalyst is reacted in the slurry state, it is preferable to use 0.04 to 0.5 kg in 1 liter of the reaction liquid.

In the reaction of the present invention, the pH of the reaction system is adjusted to 6 to 6 by adding an alkali metal or alkaline earth metal compound (eg, oxide, hydroxide, carbonate, carboxylate, etc.) to the reaction system. It is preferable to hold at 9. Particularly, setting the pH to 6 or higher has the effect of preventing the dissolution of the X component in the catalyst. These alkali metal or alkaline earth metal compounds can be used alone or in combination of two or more. The reaction of the present invention can be carried out at a high temperature of 100 ° C or higher, but is preferably 30 to 100 ° C, more preferably 60 to 90 ° C. The reaction time is not particularly limited and cannot be uniquely determined because it depends on the set conditions, but it is usually 1 to 20 hours.

The embodiments of the present invention will be specifically described below with reference to examples. Silica gel manufactured by Fuji Silysia Ltd. as a carrier (Carrieract 10 trade name average particle size 5
0 μm), 3750 g of a catalyst carrying 5% by weight of palladium, 5% by weight of lead and 4% by weight of magnesium in a liquid phase part
A 0 liter stainless steel external circulation bubble column reactor was charged with 34 wt% of methacrolein / methanol.
3.5 liter / h, NaOH / methanol at 1.5 liter / h, temperature 80 ° C, pressure 5.0 kg / c
The reaction was carried out while supplying air at m ² .

NaO is added so that the pH of the reaction solution becomes 7.1.
The H concentration was adjusted, and the lead concentration in the feedstock liquid was 20 pp.
Lead acetate was dissolved in methacrolein / methanol so as to be m and continuously supplied. On the other hand, air was supplied to the reactor while adjusting the amount of air so that the oxygen concentration at the outlet of the reactor was 4 mol% (oxygen partial pressure 0.20 kg / cm ² ).
A schematic diagram of the reactor is shown in FIG. The reactor was grounded.

The reaction results of the catalyst that had stagnated or adhered and the catalyst appropriately discharged according to the present invention were evaluated as follows. To a 60 ml stainless steel autoclave equipped with an electromagnetic induction stirrer, 4.0 g of a catalyst and 30 ml of methanol having a methacrolein concentration of 20% by weight as a raw material were added, and a methacrolein concentration of 20% was added so that a residence time was 3 hours.
By continuously supplying wt% of methanol, a temperature of 80 ° C., a pressure of 4 kg / cm ² , a rotation speed of 1000 rpm (stirring tip speed: 1.2 m / s), and NaOH / so that the pH was 7 were obtained.
Air and nitrogen were supplied to the methanol solution so that the outlet oxygen concentration was 8%, and the continuous reaction was carried out for about 200 hours.

The conversion of unsaturated aldehyde (mol%) and the selectivity of unsaturated carboxylic acid ester (mol%) were evaluated as follows. The reaction solution and the gas at the outlet of the reactor are analyzed by an ordinary gas chromatogram method using a GC-8 manufactured by Shimadzu Corporation.
The A-100 machine was equipped with a G-100 column manufactured by the Chemicals Inspection Association (eluting in almost the order of boiling points), the temperature of the thermostat was programmed, and the hydrogen flame detector (FID) was used.

[0038]

Example 1 The reaction was continuously carried out for 240 hours using a reactor whose inner surface was polished so that the surface roughness value measured according to JIS B0601 was 100 μm or less. Then, the blowing gas was switched to nitrogen, the flow of the catalyst slurry was maintained, the reaction temperature was lowered to room temperature, and the reaction pressure was lowered to atmospheric pressure. The catalyst slurry was allowed to fall from the bottom of the reactor while keeping it flowing. The catalyst remaining in the reactor was washed with methanol and recovered immediately after the discharging work. After the evaluation of the reaction results, the weight was measured by substituting with water and found to be 9.5 g. No catalyst adhered to the wall of the reactor. The discharged catalyst was stored in methanol and returned to the reactor at the time of restart together with the remaining 9.5 g of the catalyst. 50 hours after restart (29 in total)
The reaction results for 0 hour) are summarized in Table 1 together with the reaction results for 41 hours and 235 hours. Table 2 shows the reaction results of the catalyst extracted as the catalyst slurry and the retained catalyst (retained catalyst 1).

[0039]

[Table 1]

[0040]

[Table 2]

[0041]

Comparative Example 1 When discharging the catalyst slurry, the same reaction was performed in the same reactor as in Example 1 except that the supply of nitrogen was stopped and the flow was stopped. After stopping the reaction at a reaction time of 228 hours, when the inside of the reactor was inspected, a large amount of the catalyst remained in the horizontal portion of the bottom surface of the reactor, and almost the entire amount was scooped with a small scoop several times. Room temperature 15 ℃ in the laboratory
Although it was not at a temperature of -20 ° C at which methanol and methacrolein volatilize, the catalyst dried quickly while it was on the scoop, and the bottom of the scoop was so hot that it could not be touched. After cooling to room temperature for safety, the reaction results were compared on a small scale as in Example 1, and then the weight was measured to be 235.8 g, which was 6.
It was 3%. The whole amount of the recovered catalyst was returned to the reactor and the reaction was restarted again in the large reactor. The reaction results 67 hours after the restart (295 hours in total) are summarized in Table 3 together with the reaction results of 38 hours and 220 hours. Table 4 shows the reaction results of the catalyst extracted as the catalyst slurry and the catalyst that remained (retained catalyst 2).

[0042]

[Table 3]

[0043]

[Table 4]

[0044]

Comparative Example 2 A reaction was carried out in the same manner as in Example 1 except that the welded portion of the bubble column main body above the reactor and the condenser-connecting portion was not polished. After reacting for 213 hours, the catalyst slurry was discharged in the same manner as in Example 1, and the retained catalyst was washed with methanol and collected. When the inside of the reactor was inspected, the catalyst adhered in a bead-like shape along the welded part of the connection part, and there was a risk of ignition.Therefore, blow nitrogen with a thin tube to the adhered part and remove it. And collected. Since the fixed catalyst was agglomerated with a white solid substance, the weight is the value including the white solid.
It was 8.5 g.

The reaction results of the fixed catalysts were compared on a small scale as in Example 1, and then a white solid was partially scraped and analyzed. As a result, sodium was detected and carbonyl-derived infrared absorption was also observed. Therefore, sodium salts such as sodium methacrylate and sodium carbonate, and polymers such as methacrolein, methyl methacrylate, and methacrylic acid were assumed. The total amount of the recovered catalyst, including the white solid, was returned to the reactor and the reaction was restarted again in the large reactor. The reaction results 71 hours after the restart (284 hours in total) are summarized in Table 5 together with the reaction results of 52 hours and 284 hours. Table 6 shows the reaction results of the catalyst extracted as the catalyst slurry and the catalyst that remained (retained catalyst 3).

[0046]

[Table 5]

[0047]

[Table 6]

[0048]

EFFECTS OF THE INVENTION According to the production method of the present invention, not only a high unsaturated carboxylic acid ester production rate and a high unsaturated aldehyde conversion rate can be stably maintained for a long period of time, but also reactor damage and catalyst ignition occur. It is possible to eliminate the danger of, and to secure the safe operation of the plant, and it has high industrial utility.

[Brief description of drawings]

FIG. 1 is a reactor used in the present invention.

[Explanation of symbols]

1 condenser 2 bubble reactor, 3 flanges, 4 slurry circulation downcomer, Gas containing oxygen

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Claims (8)

[Claims] 1. A method for producing an unsaturated carboxylic acid ester by reacting an unsaturated aldehyde and an alcohol with a catalyst in the presence of oxygen, wherein the catalyst remaining in the reactor is relative to the weight of the catalyst added to the reaction. A method for producing an unsaturated carboxylic acid ester, which comprises discharging so as to be 3% by weight or less. 2. The reaction, after shutting down the reactor,
The method for producing an unsaturated carboxylic acid ester according to claim 1, wherein the reaction is started again. 3. The process for producing an unsaturated carboxylic acid ester according to claim 1, wherein the reaction discharges the catalyst by washing the inside of the reactor. 4. The method for producing an unsaturated carboxylic acid ester according to claim 3, wherein in the reaction, the reactor is washed with at least one of a reaction solution, a catalyst slurry, alcohol and water. 5. The method for producing an unsaturated carboxylic acid ester according to claim 1, wherein the reaction prevents the catalyst from adhering to the liquid contact part of the reactor. 6. The reaction, wherein the amount of catalyst adhering to the liquid contact portion of the reactor immediately after the reactor is stopped is 3% by weight or less based on the weight of the catalyst charged into the reactor.
The method for producing an unsaturated carboxylic acid ester according to 1. 7. The catalyst comprising palladium and / or ruthenium and X (X represents at least one metal selected from lead, bismuth, mercury, and thallium), and the catalyst is characterized in that: 7. A method for producing an unsaturated carboxylic acid ester according to any one of 6 to 6. 8. The method for producing an unsaturated carboxylic acid ester according to claim 1, wherein the unsaturated aldehyde is acrolein or methacrolein and the alcohol is methanol.