JP3268022B2 - Method for producing carboxylic acid ester - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a carboxylic acid ester, and more particularly, to a method in which an unsaturated aldehyde or an aromatic aldehyde and an alcohol are brought into contact with a specific catalyst in the presence of oxygen to form a liquid phase. The present invention relates to a method for producing a carboxylic acid ester. Carboxylic acid esters have high value as monomers for resin products, and are particularly important as acrylic resin monomers.

[0002]

2. Description of the Related Art Conventionally, silica, alumina, diatomaceous earth,
Carboxylic acid in which a catalyst in which palladium or the like is supported on a carrier such as activated carbon or zeolite is suspended in a mixture of aldehyde and alcohol, and a molecular oxygen-containing gas is blown into the aldehyde to perform liquid phase oxidation of the aldehyde and simultaneously esterification. Methods for producing esters are known. (See, for example, JP-B-45-34368, JP-B-57-35858, JP-B-57-35859, JP-B-61-60820, and JP-B-62-7902).

[0003]

However, these methods have the following disadvantages when the aldehyde as a reaction raw material has a double bond. That is, when the solid catalyst and the reaction product-containing liquid are separated, a reduction reaction of the double bond is likely to occur. These by-products are difficult to separate because the boiling point is close to that of the desired carboxylic acid ester.

For example, when methacrolein is used as an aldehyde and methanol is used as an alcohol, methyl methacrylate is formed by oxidative esterification of methacrolein as a main reaction, but in a system having a low oxygen concentration in the presence of a catalyst. As a side reaction, isobutyraldehyde, methyl isobutyrate, etc. are generated by reduction of methacrolein. Since these by-products are substances that inhibit the polymerization reaction when polymerizing the main reaction product to produce a polymer, they must be sufficiently purified and separated. That is, an increase in the selectivity of these by-products results in an increase in the size of the purification equipment and an increase in the purification energy. In addition, loss of raw materials due to a decrease in selectivity of the main reaction component, and a large-sized esterification reactor are required. For this reason, the selectivity of isobutyraldehyde and isobutyric acid methyl ester must be minimized.

[0005] In a suspended fluidized bed in which air or oxygen is blown into a catalyst slurry liquid, the oxygen concentration in the liquid is kept relatively high, and the generation of by-products is suppressed. However, when a conventional sedimentation separator (4) as shown in FIG. 4 is used to separate the catalyst when the liquid reaction product is taken out, a reducing atmosphere is formed in the sedimentation separation device, and the side reaction tends to proceed. I found it. If the reaction gas is mixed with the catalyst suspension to create a suspended state of the bubbles in order to avoid the reduction reaction, that is, to sufficiently increase the oxygen concentration in the sedimentation separator, the catalyst accompanies the liquid reaction product together with the bubbles. And causes problems such as loss of catalyst and clogging of pipes in a process after separation. That is, the liquid supplied to the sedimentation separator needs sufficient bubble separation. In addition, a method of minimizing the catalyst separation time can be considered in order to suppress a decrease in the oxygen concentration due to reaction consumption and not to keep the catalyst suspension in a reducing atmosphere for a long time. Specifically, it is conceivable to use a hydrocyclone or a centrifugal separator.However, in the case of separation with a short residence time, the separation speed of the catalyst is involved, and the particle size naturally has a lower limit. However, it was not practical because there were problems such as loss of catalyst through the separator as in the case of the sedimentation separator and clogging of the piping in the process after the separation, because the particles became fine due to abrasion and breakage. Furthermore, as a result of examining filtration and the like, with simple pressurized or reduced pressure filtration, the atomized catalyst causes clogging of the pores of the filter medium,
Even if the backwashing was performed with the filtered reaction solution, sufficient regeneration could not be performed, the filtration resistance of the filter medium increased, and the amount of the filtrate eventually became small, which was not industrially practical.

As described above, a method for separating a solid catalyst from a reaction product liquid which is extremely short in residence time while suppressing the generation of undesired side reactions in a catalyst dispersion apparatus and which is stable for a long time has been long-awaited. Discovery seemed impossible.

[0007]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that by using a specific reaction method, the activity is higher than that of the conventional method, The present inventors have found a method for suppressing the reaction, and have accomplished the present invention. That is, when a liquid reaction product containing a carboxylic acid ester is obtained by a reaction between an unsaturated aldehyde or an aromatic aldehyde and an alcohol in the presence of a solid catalyst containing palladium and oxygen, the following (1) to (3) A method for producing a carboxylic acid ester, which is performed in the order of steps.

(1) Step of obtaining a liquid reaction product in a suspension fluidized bed (2) Cross-flow of a catalyst suspension mainly consisting of a liquid reaction product with a cross-flow linear velocity of 0.05 m / sec or more (3) circulating the concentrated catalyst suspension to a suspension fluidized bed by a cross-flow filtration. Applies a pressure difference between the slurry (suspension) side and the filtrate side across a filter medium (filter) (the pressure difference at this time is referred to as a filtration differential pressure: the same applies hereinafter), and filtration is performed using this as a driving force. Is to continuously filter while flowing in parallel to the filtration surface (the average flow velocity of the slurry per flow path cross-sectional area at this time is referred to as a cross-flow linear velocity). For example, when a tubular filter is used, a method is used in which the slurry extracted from the reactor is supplied from one of the filter tubes, the concentrated slurry is discharged from the other of the filter tubes, and the filtrate is separated through the filter tube filtration surface. However, this filter tube has a filtering surface on the whole or a part of the tube wall surface, and the cross-sectional shape of the tube is not limited to a circular shape. Further, the slurry may be inside the filter tube and the filtrate may be inside the filter tube.

A feature of the present invention is that the retention time in a system having a low oxygen concentration for filtering and separating a circulating liquid can be shortened by using a cross flow type filtration. In addition, when the sedimentation separation method is used, the catalyst suspension supplied to the separator requires sufficient air separation, but according to the method of the present invention, air bubbles are mixed in the liquid supplied to the filter. However, precise filtration becomes possible, and separation in a system having a high oxygen concentration becomes possible. This is because in cross-flow filtration, even if gas is mixed into the slurry, if the liquid phase is a continuous phase, the bubbles in the flowing slurry flow through the center of the filter tube where the flow velocity of the slurry is high, and the slurry This is because it hardly exists near the filter wall surface where the flow velocity is slow. As a result, in a system with a low oxygen concentration, the residence time is short, and separation is possible even if bubbles are mixed in, so that the generation of by-products due to the double bond reduction reaction can be suppressed.

The most significant feature of the method of the present invention is that it has an extremely large effect in suppressing the progress of side reactions, as described above. Has a meaningful effect. That is, in the sedimentation separation method, it was difficult to efficiently separate the fine particle catalyst having a particle diameter of several tens of microns or less from the reaction solution, but the method of the present invention does not have this. This suppresses the growth of the solid cake of the slurry on the filtration surface due to the shearing force of the slurry flowing parallel to the filtration surface, and suppresses the reduction in the filtration rate over time. As a result, a fine particle catalyst can be used, high reaction activity can be realized, and the size of the reactor can be reduced. Furthermore, it eliminates the need for intermittent backwashing and enables stable continuous operation.

Here, the reason why the atomized catalyst has high activity is considered as follows. The catalyst used in the present invention is preferably one in which palladium is preferably supported on a carrier.Aldehyde used as a raw material of the present invention has a relatively large molecular diameter, and is relatively low in temperature and in a liquid phase. Therefore, the degree of freedom of the molecules in the pores is restricted, and it is difficult to approach the active site inside the catalyst. As a result, it seems that the reaction proceeds only at the outer surface active site. This indicates that the activity of methacrolein and methanol in an oxidative esterification reaction carried out by a known method was compared with the activity of a catalyst in which the same weight of a metal species was supported on the same weight of a carrier having a different particle size. This is presumed from the fact that the use of a carrier having a smaller diameter shows higher activity.

As described above, it is considered that the smaller the catalyst particle diameter, the higher the specific surface area and the higher the activity. Usually, those having an average particle size of 500 microns or less are used. Preferably, those having a size of 300 microns or less are used. The effect of the present invention becomes clear as the particle size becomes finer. The particle size of these primary particles can be measured by an electron microscope, which is a usual method. There are various shapes of these primary particles, and the particle size referred to here indicates the arithmetic average diameter at the narrowest part. Further, the numerical values shown here mean those having a particle size of less than 50% by weight or more. In addition, such fine particles may form secondary particles as an aggregate thereof in some cases. The formation of such secondary particles is effective irrespective of the effects of the present invention.

The catalyst used in the present invention contains at least one of metallic palladium and a palladium compound, and preferably further contains lead, mercury, thallium or bismuth. These catalyst components may be present separately in the system, but are preferably present in the reaction system in such a manner that they can have some action with palladium, and more preferably the intermetallic compound is used. It is good to form. These catalyst components are activated carbon,
It can be used by being supported on a carrier such as silica, alumina, titania and zeolite, and can also be used directly without using such a carrier.

The amount of the catalyst used depends on the type and amount of the reaction raw materials,
It can be arbitrarily changed depending on the method of adjusting the catalyst, operating conditions, etc., and is not particularly limited. For example, in general, 0.01 to 20 mol% of palladium, lead, mercury, thallium, bismuth or The metal compound is desirably in the range of 0.001 to 10 mol%. However, as described above, there is no problem even if used outside these ranges. Needless to say, this is not particularly the case in a flow-through reaction. In some cases, it is preferable to add a salt such as sodium acetate in addition to the lead compound.

The preparation of the catalyst can be carried out according to a conventional method as described in JP-B-61-60820 and JP-B-62-7902. For example, a soluble salt such as palladium chloride is reduced in an aqueous solution with a reducing agent such as formalin to precipitate a metal palladium catalyst, and the metal palladium catalyst is adjusted by filtration, or an acidic aqueous solution of a soluble palladium salt is appropriately treated. The supported palladium catalyst can be prepared by impregnating the carrier and reducing with a reducing agent. When preparing a catalyst in which palladium and a lead compound are supported on a suitable carrier, a suitable carrier is impregnated with an aqueous solution of a soluble palladium salt, and then reduced with a suitable reducing agent. In water, evaporate to dryness, and dry for use. For example, as the lead compound, any compound containing lead can be used. Preferred examples include lead fatty acid salts such as lead acetate, lead stearate, and naphthene lead, lead oxide, lead hydroxide, and lead nitrate. These lead compounds may be anhydrous or those having water of crystallization. The same applies to mercury other than lead, thallium, and bismuth.

The slurry concentration may be in a range that allows handling, for example, a range in which there is no clogging or settling of solids in the piping. At low concentrations, conventional differential pressure filters are sufficiently stable for filtration, and the backwashing cycle can be lengthened. However, when the concentration is higher than 3% by weight, the present reaction system has a stable filtration rate and a backwashing cycle. Very effective in prolonging Also, to increase productivity per unit volume,
The higher the catalyst concentration, the better.

[0017] The viscosity of the slurry may be in the range in which it can flow. There is no particular problem in the low viscosity region up to about 100 cP (centipoise), but in the fluid in the high viscosity region, the pressure difference between the inlet and the outlet of the slurry filter (pressure loss at the filter wall) and the filtration pressure difference increase. In some cases, clogging of the solids in the piping may occur, or the rate of withdrawing the filtrate from the filter may become extremely slow due to a decrease in the fluidity of the liquid. Here, the upper limit of the slurry viscosity differs depending on the characteristics and purpose of the system and cannot be uniquely limited.

The pore size of the filter medium of the filter is 0.05 to 50 μm, preferably 0.1 to 20 μm.
Micron. With a filter medium having a pore diameter of less than 0.05 micron, there are problems in the manufacture of the filter, and problems such as an increase in filtration area due to an increase in filtration pressure and a limitation on the strength of the filter medium, which limits the filtration speed. There is. Further, the molecular diameter of the monomer of the substance handled in the present reaction system is at most about several tens angstroms, and there is no problem in the filtration performance when the pore diameter is 0.05 μm or more. Basically,
This means that the pore size of the filter medium should be smaller than the minimum catalyst diameter. However, it is difficult to define the minimum diameter of the catalyst, including problems such as measurement accuracy. Even when the pore size of the filter medium is larger than the minimum catalyst particle size, bridging or cake formation may cause few particles to pass through the cake (cake filtration). In addition, the inventors found that the suspended catalyst was mechanically pulverized by collision of the solid catalyst with stirring blades, circulation pumps, pipes, etc., to generate fine particles much smaller than the initial average particle diameter, and the fine particles clogged the filter. It was confirmed that the filtration rate was reduced. Therefore, as a result of further research using various types of suspension catalysts, this atomization is almost stable at a constant value (this is because the dispersion and agglomeration of particles are balanced and the energy required for atomization is reduced). It is considered that the smaller the particle size, the larger the size.) That is, in the integrated particle size distribution, from the smallest particle size to about 2 to
5% by weight of the particles hardly changed over time such as further atomization or increase. Furthermore, it has been found that the stable particle size is about 0.5 to 20 microns, and the use of a filter medium having the same pore size enables smooth catalyst separation without clogging problems.

The tube diameter of the cross section of the filter medium on the slurry side of the filter, or the minimum gap if the plate is flat, is preferably 1 mm or more and 100 mm or less. This is because if the size is smaller than 1 mm, clogging of the slurry occurs, making stable operation difficult and making it impossible to regenerate the filtration capacity. When the size is larger than 100 mm, it is difficult to obtain a large filtration area. That is, even if the filtration area is the same, the larger the size is, the larger the filtering device becomes.

In a cross-flow filter, the linear velocity of the slurry in order to apply a shearing force to the slurry flowing on the filtration surface depends on the slurry concentration of the system, viscosity, catalyst particle diameter, filter diameter of the filter, and the like. 0.05 m / sec or more, preferably 0.1 to 20 m / sec. When the slurry linear velocity is increased, the shearing force increases and the cake thickness decreases, so the filtration rate increases.However, the pressure difference between the inlet and outlet of the slurry passing through the filter increases, and the power required for slurry circulation increases. turn into. Conversely, if the slurry linear velocity is less than 0.05 m / sec, the shearing force will be small, the cake thickness will be large, and the filtration speed will be small.

[0021] The differential pressure of filtration in the cross flow filter is 20K.
g / cm ² or less, preferably 0.05 to 10 kg /
cm ² . The filtration pressure difference is approximately proportional to the filtration speed if the cake thickness is constant. However, when the filtration pressure difference is excessively increased to increase the filtration speed, the adhesion of the cake to the filtration surface increases, and at the same slurry linear velocity, the thickness of the cake increases due to the balance between the adhesion to the cake and the shearing force. Therefore, the filtration speed decreases. Thus, the filtration pressure difference is 2
Making it higher than 0 kg / cm ² only lowers the filtration performance.

The reaction pressure and the slurry side pressure in the filter can be set completely separately by using a circulation pump. But,
For example, if the pressure on the filter side is lower than the reactor pressure,
Not only is there a power loss due to pressure increase, but also because the reactant adsorbed on the catalyst surface repeatedly absorbs and desorbs, the catalyst activity is greatly reduced, and a by-product is easily generated. Therefore, it is desirable that the pressure of the reactor and the pressure of the slurry on the side of the filter be substantially equal to the pressure difference of about the flow pressure loss. In addition, the reaction pressure is set at 0.1 to secure a filtration pressure difference.
It is desirable that the reaction be a pressurized reaction of at least Kg / cm ² gauge pressure.

The temperature of the slurry in the filter may be such that the slurry is kept in a fluid state in a liquid phase. That is, it is only necessary to keep the filter from boiling or solidifying in the filter. Usually, the filter is circulated at the temperature of the product in the reactor. For example, when there is a problem with the material of the sealing material, it is conceivable to prevent corrosion by lowering the filter side temperature below the reaction temperature. Therefore, it is not always necessary to make the reaction temperature equal to the filtration temperature.

The aldehyde used in the present invention is an aldehyde having an unsaturated moiety.
Aliphatic α / β-unsaturated aldehydes such as acrolein, methacrolein and crotonaldehyde; aromatic aldehydes such as benzaldehyde, tolylaldehyde, benzylaldehyde and phthalaldehyde; and derivatives of these aldehydes. These aldehydes can be used alone or as a mixture of two or more kinds.

The alcohol used in the present invention includes, for example, 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. Aromatic alcohols such as benzyl alcohol and phenols. Especially methyl alcohol,
A lower alcohol such as ethyl alcohol is preferred because the reaction is rapid. These alcohols can be used alone or as a mixture of two or more kinds.

In the present invention, the amount ratio of the aldehyde to the alcohol is 10% by mole of aldehyde / alcohol.
The range is preferably 1 to 50, and more preferably 3 to 1/20. If the molar ratio exceeds 10, the decomposition of aldehydes and other side reactions become remarkable, and the selectivity of the reaction is lowered, which is not preferable. Conversely, if the molar ratio is less than 1/50, the energy for recovering and separating the alcohol is increased, which is not preferable. .

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, for example, nitrogen or carbon dioxide. Can also be used. It is sufficient that the amount of oxygen to be present in the reaction system is not less than the stoichiometric amount necessary for the reaction, preferably not less than 1.2 times the stoichiometric amount.

By using the catalyst atomized in the present invention,
Compared with a conventional catalyst, a high conversion can be obtained in the same reaction time even at a low temperature. Here, the reaction temperature is 0 to 120 ° C, preferably 20 to 100 ° C. Although the reaction of the present invention can be carried out under reduced pressure, atmospheric pressure, or under pressure, the target carboxylic acid ester can be easily produced at a high yield by a simple method of blowing oxygen at a slight pressure near normal pressure. It has the characteristic that it can be obtained at a rate. The reaction can be carried out either in a batch system or in a continuous system.In the case of a continuous system, the reaction is closer to the extrusion flow, that is, the reactor is a multi-tank two or more tanks than the reaction of a complete mixing tank. It is needless to say that the reaction amount per reactor volume is larger in the above reaction or in a one-pass tubular reactor.

As a specific reaction system, the following process can be considered. However, the present invention is not limited to only these processes, and may be, for example, a combination of these processes in multiple stages. FIG. 1 shows a combination of a stirred tank reactor (1), a cross flow filter (2), and a circulation pump (3).

FIG. 2 shows a combination of a reactor (1), a cross-flow filter (2), and a circulation pump (3). By spraying the liquid, gas-liquid contact and absorption are favorably performed to cause a reaction. In this case, since the mixing of solid and liquid and the absorption of gas in the reactor are performed by the circulating slurry by the circulating pump, the stirrer of the reactor is unnecessary as compared with the case of FIG. This eliminates problems such as a shaft seal of a stirrer, particularly in a high-pressure reaction.

FIG. 3 shows a gas lift type reactor (1),
It is a combination of a cross flow filter (2).
In this case, with the liquid circulation method using the principle of the bubble pump,
The circulating pump is not required in the case of FIG. Thus, the reaction system is close to the push-out flow, so that the reactor is smaller than the complete mixing tank. Further, in the cross-flow filter, there is no problem in filtration performance even if gas is mixed into the slurry due to insufficient gas separation.

1 to 3, the installation direction of the filter may be either horizontal or vertical. Also, there are no particular restrictions on the direction of slurry inflow / outflow of the filter, such as the upper or lower part of the filter. Further, the shape of the filter medium may be a circular tube or a flat surface. However, when the filtration pressure is high, a circular tube having a high strength is desirable even with the same thickness. In addition, the slurry is
The slurry may flow outside the tube, but it is preferable to flow the slurry into the tube because the slurry flows smoothly.

[0033]

EXAMPLES Examples of the present invention will be described below, but the scope of the present invention is not limited to these examples. In addition, "%" in an example shows "weight%" unless there is particular notice.

[0034]

Example 1 Methacrolein as a raw material aldehyde
Production of methyl methacrylate by continuous oxidative esterification reaction in the presence of oxygen using methanol as an alcohol was carried out by a process as shown in FIG. 1 under the following reaction conditions. The device has an inner diameter of 40 mm and an internal volume of 1.
The reaction was carried out by connecting two 2-liter stainless stirring reactors in series. The reactor has a reflux condenser, a liquid feed port, a liquid outlet, a gas inlet, and a circulating liquid return port, and is stirred by an electromagnetic rotary stirrer. Heating is provided by a jacket.

The reaction liquid from the reactor is supplied to a cross-flow filter through a slurry circulation pump to perform solid-liquid separation, the concentrated slurry liquid is returned to the reactor, and the filtrate is discharged to the next reactor or filtrate tank. I did it. This filter was provided with a filter tube of a ceramic porous body (average pore diameter of 1 to 2 microns), and was equipped with a backwashing device so that a backwashing operation could be performed with gas or liquid.

In each reactor, γ-alumina (Mizosawa Chemical Neobi) was used.
2.5% palladium, 5.0% lead, magnesium
0.3 kg of a catalyst supporting 2.0% of
Add 22.3% methacrolein / methanol to the staged reactor.
86 liter / hr, NaOH / MeOH solution 0.05
Liter / Hr, temperature 80 ° C, 3Kg / cm ^Two
2.5Nl / hr of air under gauge pressure
The reaction was carried out while passing air through a stainless sintered plate.
The reaction solution from the reactor is pumped through a slurry circulation pump
The predetermined circulation amount, that is, the cross flow linear velocity
The operation was performed so that the degree was about 1 to 3 m / sec. This reaction solution
Then, the NaOH / MeOH solution was added to the second-stage reactor at 0.
Introduced together with 05 liters / Hr, temperature 80 ° C, approx.
2.0-2.8Kg / cm^Two1st stage counter under gauge pressure
The reactor effluent gas is passed through the second stage reactor,
The reaction was performed by adding 1.5 Nl / Hr. Reaction liquid
PH of both the first and second stage reactors is 7.0 to 7.5
The amount of NaOH was controlled to keep it.

Analysis of the second-stage reaction solution revealed that the conversion of methacrolein was 84.7% and the yield of methyl methacrylate was 7%.
5.2% (selectivity 88.8%) and trace amounts of isobutyraldehyde and isobutyric acid methyl ester (selectivity 0.0
5%). Here, the filtration rate rapidly decreased after the start of the reaction, but stabilized after about 100 hours, and the filtration rate after stabilization was 200 to 300 liter / m ² / hr (filtrate volume per unit area per unit area of the filter. : The same applies hereinafter). Further, in order to see the effect of the backwashing, when the backwashing was performed and restarted, the filtration rate recovered to almost the initial filtration rate and was almost stabilized after about 100 hours. The filtration rate at this time was equivalent to the stable value before back washing. Also, there was no catalyst outflow.

[0038]

Example 2 In Example 1, air was blown in the middle of a pipe supplied from a slurry circulation pump to a cross-flow filter (performed at a temperature and pressure of the filter of about 7% by volume). As a result, although the circulating flow rate of the liquid was lowered and the residence time in the filter was lengthened, isobutyraldehyde and methyl isobutyrate were hardly produced. In addition, the mixing of bubbles into the slurry had no effect on the filtration performance, that is, there was no catalyst outflow, and there was almost no effect on the filtration rate.

[0039]

Comparative Example 1 Production of methyl methacrylate by continuous oxidative esterification was carried out in the same manner as in Example 1 using a sedimentation / separation apparatus (4) as shown in FIG. That is, except that the sedimentation separation method was used for the separation device of the catalyst and the reaction product liquid,
The raw materials, catalyst, reaction conditions, and the like are the same as in Example 1. As the sedimentation / separation device, a device having a diameter of 100 mm and a capacity of 1 liter was used in consideration of the sedimentation speed of the catalyst.

As a result, the conversion of methacrolein was almost the same as in Example 1, but considerable amounts of isobutyraldehyde and methyl isobutyrate were formed (selectivity: 0.4%). Also, the catalyst outflow was about 0.5% of the input amount for 200 hours of operation.

[0041]

[Comparative Example 2] In Comparative Example 1, air was blown in the middle of a pipe supplied from a slurry circulation pump to a cross-flow filter (performed at a temperature and pressure of the filter of about 7% by volume). As a result, almost no isobutyraldehyde and isobutyric acid methyl ester were formed, but there was considerable catalyst effluent (about 3.4% of the charge in a continuous operation for 24 hours).

[0042]

Example 3 As in Example 1, production of methyl methacrylate by continuous oxidative esterification was carried out by a process as shown in FIG. That is, it is the same as Example 1 except that a slurry circulation system by a gas lift is used and the reactor does not have a stirrer. The device has an inner diameter of 40 mm and an inner volume of 1.2.
Liter stainless steel gas lift reactor (8 in the tower)
The reaction was performed by connecting two mesh wire nets horizontally at 8 cm intervals) in series. The reactor is equipped with a reflux condenser, a liquid feed port, a liquid outlet, a gas inlet, and a circulating liquid return port, and heating is performed by a jacket.

The reaction solution from the reactor was subjected to solid-liquid separation through a cross-flow filter, the concentrated slurry was returned to the reactor, and the filtrate was discharged to the next reactor or filtrate tank. This filter was provided with a filter tube of a ceramic porous body (average pore diameter of 1 to 2 microns), and was equipped with a backwashing device so that a backwashing operation could be performed with gas or liquid.

In each reactor, 1.5% of palladium, 2.5% of bismuth,
0.6 kg of a catalyst supporting 2.0% of lithium was charged, and 22.2% methacrolein / methanol 1.8 liter / Hr and a NaOH / MeOH solution were supplied at 0.1 liter / Hr to the first stage reactor. , Temperature 80 ° C, 3Kg /
The reaction was performed by circulating the catalyst and the reaction solution by passing air through the stainless sintered plate at a rate of 5 Nl / Hr under a pressure of cm ² gauge. The reaction solution was filtered with a cross-flow filter, the concentrated catalyst slurry was returned to the reactor, and the reaction solution, which was the filtrate, was subsequently introduced into the second-stage reactor together with 0.1 liter / Hr of a NaOH / MeOH solution. The effluent gas of the first-stage reactor was passed through the second-stage reactor at 80 ° C. under a pressure of 2.0 to 2.8 kg / cm ² gauge, and the reaction was carried out by further adding 3 Nl / Hr of air. . The NaOH amount was controlled so that the pH of the reaction solution was maintained at 7.0 to 7.5 in both the first and second stage reactors.

Analysis of the second-stage reaction solution revealed that the conversion of methacrolein was 80.3% and the yield of methyl methacrylate was 7%.
1.4% (selectivity 88.9%), and trace amounts of isobutyraldehyde and methyl isobutyrate (selectivity 0.0
5%). Here, although the filtration rate rapidly decreased after the start of the reaction, it was stabilized in about 100 hours, and the filtration rate after stabilization was 200 to 300 liter / m ² / hr.
Further, in order to see the effect of the backwashing, when the backwashing was performed and restarted, the filtration rate recovered to almost the initial filtration rate and was almost stabilized after about 100 hours. The filtration rate at this time was equivalent to the stable value before back washing. Also, there was no catalyst outflow.

[0046]

Comparative Example 3 Production of methyl methacrylate by continuous oxidative esterification was carried out in the same manner as in Example 3 using the sedimentation apparatus used in Comparative Example 1. That is, the raw material, the catalyst, the reaction conditions, and the like are the same as in Example 3 except that the sedimentation separation method is used for the separation device for the catalyst and the reaction product liquid.

As a result, the conversion of methacrolein was almost the same as that of Example 3, but considerable amounts of isobutyraldehyde and methyl isobutyrate were formed (selectivity: 0.5%). Also, catalyst outflow was about 0.2% of the input amount for 200 hours of operation.

[0048]

Example 4 Example 3 except that a finely divided catalyst was used as the catalyst.
The oxidative esterification reaction was performed under the same conditions as described above. As a result of measuring the particle size distribution of the catalyst used here by an electron microscope, the average particle size was about 10 microns. As a comparison, the average particle size of the catalyst in Examples 1-3 was about 120 microns.

As a result, the oxidative esterification reaction and the separation of the reaction solution and the catalyst were smoothly performed continuously for 800 hours without back washing. The reaction result was methacrolein conversion 90.
At 8%, trace amounts of isobutyraldehyde and isobutyric acid methyl ester were formed (selectivity: 0.06%). Furthermore, although the filtration rate rapidly decreased after the start of the reaction, it was stabilized in about 100 hours, and the filtration rate after stabilization was 150 to 250 liter / m ² / hr. Also, to see the effect of backwashing, when backwashing was performed and restarted, the filtration speed was
It recovered to almost the initial filtration rate and was almost stabilized after about 100 hours. The filtration rate at this time was equivalent to the stable value before back washing. Also, there was no catalyst outflow.

[0050]

Comparative Example 4 An oxidative esterification reaction was carried out under the same conditions as in Example 4 except that the sedimentation / separation apparatus used in Comparative Example 1 was used as the apparatus for separating the reaction solution from the catalyst. As a result, the conversion of methacrolein was almost the same as that of Example 4, but considerable amounts of isobutyraldehyde and isobutyric acid methyl ester were formed (selectivity: 0.7%). Also, considerable catalyst spill (24
(About 5.7% of the input for the hourly operation).

[0051]

Example 5 A reaction was carried out in the same manner as in Example 4 except that the reaction temperature was changed to 40 ° C. As a result, the oxidative esterification reaction and the separation of the reaction solution and the catalyst were performed smoothly. The reaction result was methacrolein conversion of 75.3%, and trace amounts of isobutyraldehyde and isobutyric acid methyl ester were formed (selectivity: 0.02%).

Further, the filtration rate was the same as in Example 4, and there was no catalyst outflow.

[0053]

Example 6 A reaction was carried out in the same manner as in Example 4 except that 33.3% methacrolein / methanol was used as a raw material concentration. As a result, the oxidative esterification reaction and the separation of the reaction solution and the catalyst were performed smoothly. The conversion of methacrolein was 76.4%, and trace amounts of isobutyraldehyde and isobutyric acid methyl ester were formed (selectivity: 0.06%).

Further, the filtration rate was the same as in Example 4, and there was no catalyst outflow.

[0055]

Example 7 A reaction was carried out in the same manner as in Example 4 except that 17.8% acrolein / methanol was used as a raw material. As a result, the oxidative esterification reaction and the separation of the reaction solution and the catalyst were performed smoothly. The conversion of acrolein was 86.8%, and propionaldehyde and methyl propionate were produced in trace amounts (selectivity: 0.05%).

Further, the filtration rate was the same as in Example 4, and there was no catalyst outflow.

[0057]

According to the present invention, a cross-flow type filtration is used for separating a catalyst and a reaction product-containing liquid.
By reducing the residence time in the separation device, the generation of by-products is suppressed, the selectivity of the main reaction product, carboxylate, is improved, the purification equipment is reduced, the purification energy is reduced, and the reactor is downsized. Can be achieved. Further, clogging / scaling in a subsequent process due to catalyst outflow and catalyst loss are suppressed, and smooth operation is continuously performed over a long period of time by suppressing a reduction in filtration speed over time. Then, for a system having a slow sedimentation speed, the size of the catalyst separation device can be reduced as compared with a sedimentation separator (4) as shown in FIG. 4, and a closed system enables safe operation.
Furthermore, even if gas is mixed into the slurry, there is no effect on the filtration performance, and further pulverized particles are generated by mechanical pulverization due to collision of the solid catalyst with a stirring blade, a circulation pump, piping, etc. There is also an effect of achieving precise filtration for such fine particles.

Further, by using the method of the present invention, it is possible to use a finely divided solid catalyst, so that the reaction amount per unit volume of the catalyst and the unit time per unit time are remarkably improved, and downsizing of the reactor is achieved. Further, there is an effect that the energy for dispersing and mixing the catalyst in the reactor is reduced.

[Brief description of the drawings]

FIG. 1 is a diagram of a reaction apparatus showing an example of an embodiment according to the present invention. (Slurry circulation system with circulation pump, stirring type reactor)

FIG. 2 is a diagram of a reaction apparatus showing an example of an embodiment according to the present invention. (Slurry circulation system with circulation pump, reactor with circulation liquid spray)

FIG. 3 is a diagram of a reaction apparatus showing an example of an embodiment according to the present invention. (Slurry circulation method by gas lift)

FIG. 4 is a diagram showing an example of a known reaction apparatus.

[Explanation of symbols]

 Reference Signs List 1 reactor 2 cross flow filter 3 slurry circulation pump 4 sedimentation separator

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI // C07B 61/00 300 C07B 61/00 300 (56) References JP-A-58-198442 (JP, A) JP-A-58 JP-A-185540 (JP, A) JP-A-58-166936 (JP, A) JP-A-58-154534 (JP, A) JP-A-48-19513 (JP, A) JP-B-48-29204 (JP, B1) (JP) B-34 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) C07C 67/56 C07C 67 / 39,67 / 44 C07C 69 / 54,69 / 78,69 / 80

Claims (1)

(57) [Claims] In producing a liquid reaction product containing a carboxylic acid ester by reacting an unsaturated aldehyde or an aromatic aldehyde with an alcohol in the presence of a solid catalyst containing palladium and oxygen, the following (1) to (1) 3. A method for producing a carboxylic acid ester, wherein 3) is performed in the order of steps. (1) Step of obtaining a liquid reaction product in a suspension fluidized bed (2) Filtration of a catalyst suspension mainly composed of a liquid reaction product by a cross-flow method having a cross-flow linear velocity of 0.05 m / sec or more (3) circulating the concentrated catalyst suspension to a suspension fluidized bed