JPH0680611A - Production of carboxylic acid ester - Google Patents

Abstract

PURPOSE:To suppress the side reaction due to reducing reaction, simultaneously achieve the miniaturization of a reactor and a purifier and stably and continuously carry out the reaction and the separation of a reactional product solution from a catalyst for a long period by shortening the separation residence time of the reactional product solution from the catalyst as much as possible. CONSTITUTION:The objective method for producing a carboxylic acid ester is to carry out the reaction in a suspension state and perform the separation by cross-flow type filtration in reacting an unsaturated aldehyde or an aromatic aldehyde with an alcohol in the presence of a solid catalyst and oxygen and producing a carboxylic acid ester so as to continuously and smoothly separate the reactional product solution from a concentrated catalyst slurry for a long period.

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 specifically, to a liquid phase after contacting an unsaturated aldehyde or aromatic aldehyde and alcohol with a specific catalyst in the presence of oxygen. The present invention relates to a method for producing a carboxylic acid ester. Carboxylic acid esters are highly valuable 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,
A carboxylic acid that suspends a catalyst in which palladium or the like is supported on a carrier such as activated carbon or zeolite in a mixture of an aldehyde and an alcohol, and blows a molecular oxygen-containing gas into the catalyst to liquid-phase-oxidize the aldehyde and simultaneously perform esterification. A method for producing an ester is known. (See, for example, Japanese Patent Publications 45-34368, 57-35858, 57-35859, 61-60820, and 62-7902).

[0003]

However, these methods have the following drawbacks 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 double bond reduction reaction is likely to occur. These by-products have a boiling point close to that of the desired carboxylic acid ester, and thus are difficult to separate.

For example, when methacrolein is used as the aldehyde and methanol is used as the alcohol, methyl methacrylate is produced by the oxidative esterification of methacrolein as the main reaction, but in a system having a low oxygen concentration in the presence of a catalyst. As a side reaction, isobutyraldehyde and isobutyric acid methyl ester are produced by the reduction of methacrolein. These by-products are substances that inhibit the polymerization reaction when the main reaction product is polymerized to produce a polymer, and therefore must be sufficiently purified and separated. That is, the high selectivity of these by-products increases the size of the refining equipment and the refining energy. In addition, a loss of raw materials due to a decrease in the selectivity of the main reaction components and a large esterification reactor are required. Therefore, the selectivity of isobutyraldehyde and isobutyric acid methyl ester must be suppressed as much as possible.

In a suspended fluidized bed in which air or oxygen is blown into the catalyst slurry liquid, the oxygen concentration in the liquid is kept relatively high and the production of by-products is suppressed. However, when a normal settling separator (4) as shown in FIG. 4 is adopted when separating the catalyst when the liquid reaction product is taken out, it becomes a reducing atmosphere in the settling separation device and side reactions easily proceed. I found it. In order to avoid the reduction reaction, that is, in order to sufficiently increase the oxygen concentration in the sedimentation separator, when the reaction gas is mixed with the catalyst suspension to create a suspended state of bubbles, the catalyst is entrained in the liquid reaction product together with the bubbles. However, there are problems such as loss of catalyst and clogging of pipes in the process after separation. That is, it is necessary for the liquid supplied to the sedimentation separator to sufficiently separate air bubbles. Further, a method of reducing the catalyst separation time as much as possible can be considered because the decrease in oxygen concentration due to reaction consumption is suppressed and the catalyst suspension is not kept in the reducing atmosphere for a long time. Specifically, it is possible to use a liquid cyclone or a centrifuge, but in the case of separation with a short residence time, the separation speed of the catalyst is involved, and naturally there is a lower limit on the particle size, and the particles during the operation flow Is not practical because there are problems such as abrasion and damage resulting in fine particles and insufficient separation, loss of catalyst through the separator as in the case of the sedimentation separator, and clogging of pipes in the process after separation. Furthermore, as a result of examining filtration, etc., in simple pressure or vacuum filtration, the finely divided catalyst causes clogging of the pores of the filter medium,
Even if it was back-washed with the filtered reaction solution, it could not be sufficiently regenerated, the filtration resistance of the filter medium was increased, and the amount of the filtrate was finally reduced to a very small amount, which was not industrially practical.

As described above, a method for separating a solid catalyst and a reaction product solution which is stable for a long period of time while suppressing the generation of inconvenient side reactions in the catalyst dispersing device and which is stable for a long time has long been desired. It was thought impossible to find.

[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 in the conventional method, The inventors have found a method of suppressing the reaction and completed the present invention. That is, in obtaining 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 (3) are It is a method for producing a carboxylic acid ester, which is carried out 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 composed of the liquid reaction product with a cross flow linear velocity of 0.05 m / sec or more Separation into a liquid reaction product and a concentrated catalyst suspension by a system-type filtration (3) A step of circulating the concentrated catalyst suspension in a suspension fluidized bed Creates a pressure difference between the slurry (suspension) side and the filtrate side across the filter material (filter) (the pressure difference at this time is referred to as filtration differential pressure: the same applies below), and this is used as a driving force for filtration. Is to continuously perform filtration while flowing in parallel to the filtration surface (the average flow velocity per flow passage cross-sectional area of the slurry at this time is referred to as a cross flow linear velocity: hereinafter the same). For example, when a tubular filter is used, 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 at the same time, 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 wall surface of the tube, and the cross-sectional shape of the tube is not limited to a circular shape. Further, the slurry may be outside the filter tube and the filtrate may be inside the filter tube.

A feature of the present invention is that by using the cross-flow type filtration, the residence time in a system having a low oxygen concentration can be shortened because the circulating liquid is filtered and separated. Further, when the sedimentation separation method was used, the catalyst suspension supplied to the separator required sufficient air bubble separation, but according to the method of the present invention, air bubbles are mixed in the liquid supplied to the filter. However, precise filtration is possible and separation in a system with high oxygen concentration is also possible. This is because in cross-flow filtration, even if gas is mixed into the slurry, the bubbles in the flowing slurry will flow through the center of the filter tube where the flow velocity of the slurry is high if the liquid phase is a continuous phase. This is because there is almost no near the wall surface of the filter with a slow flow velocity. As a result, in a system with a low oxygen concentration, the residence time is short, and even if air bubbles are mixed in, separation is possible, so that the production 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 a very large effect in suppressing the progress of side reactions as described above. However, as will be described below, it is extremely effective in industrial practice. It has a meaningful effect. That is, it was difficult to efficiently separate a fine particle catalyst having a particle diameter of several tens of microns or less from the reaction solution by the sedimentation separation method, but the method of the present invention does not have that. This suppresses the growth of the solid cake of the slurry on the filtration surface due to the shearing force of the slurry that flows parallel to the filtration surface, and suppresses the decrease in the filtration rate with time. As a result, a fine particle catalyst can be used, high reaction activity can be realized, and the reactor can be downsized. Furthermore, intermittent backwashing is not required, and stable continuous operation is possible.

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, but the aldehyde used as the raw material of the present invention has a relatively large molecular diameter, and at a relatively low temperature and in a liquid phase. Since the reaction is the above, the degree of freedom of the molecule in the pores is restricted, it is difficult to approach the active site inside the catalyst, and as a result, the reaction seems to proceed only at the outer surface active site. This means that in the oxidative esterification reaction of methacrolein and methanol carried out by a known method, when the activity was compared with the catalyst in which the same weight of metal species was supported on the same weight of different particle size carriers, It is presumed that the use of a carrier having a small diameter shows higher activity.

As described above, it is considered that the smaller the catalyst particle size, 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. It is preferably 300 microns or less. The finer the particle size, the clearer the effect of the present invention. The particle size of these primary particles can be measured by an ordinary electron microscope. There are various shapes of these primary particles, but the particle size referred to here indicates the arithmetic mean diameter of the narrowest part. Further, the numerical values shown here are those having a particle size of less than 50% by weight or more. In addition, such fine particles may sometimes form secondary particles as an aggregate thereof. The formation of such secondary particles is effective regardless of the effect of the present invention.

The catalyst used in the present invention contains at least one of metallic palladium and palladium compounds, preferably lead, mercury, thallium, or bismuth. These catalyst components may be present separately in the system, but it is preferable that they are present in the reaction system in a form capable of mutually interacting with palladium, more preferably an intermetallic compound. It is better to form. These catalyst components are activated carbon,
It can be used by supporting it on a carrier such as silica, alumina, titania and zeolite, or can be used directly without using such a carrier.

The amount of the catalyst used depends on the kind and amount of the reaction raw material,
It can be arbitrarily changed depending on the method of adjusting the catalyst, operating conditions, etc., but is not particularly limited, but generally, for example, 0.01 to 20 mol% of palladium, lead, mercury, thallium, bismuth, or a molar ratio to the raw material aldehyde is used. The metal compound content is preferably in the range of 0.001 to 10 mol%. However, as mentioned above, there is no problem even if it is used outside these ranges. It goes without saying that this is not the case particularly in the case of a reaction in the distribution system. In addition to the lead compound, it may be preferable to add a salt such as sodium acetate.

The catalyst can be adjusted by 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 the soluble palladium salt is appropriately adjusted. The supported palladium catalyst can be prepared by impregnating the carrier and reducing with a reducing agent. When preparing a catalyst in which a palladium and a lead compound is supported on a suitable carrier, an appropriate carrier is impregnated with an aqueous solution of a soluble palladium salt and then reduced with a suitable reducing agent, which is then converted into, for example, lead acetate. Can be dipped in an aqueous solution, evaporated to dryness, dried and then used. For example, as the lead compound, any compound containing lead can be used, but preferred examples are lead fatty acid salts such as lead acetate, lead stearate, and naphthene lead, and lead oxide, lead hydroxide, lead nitrate. The lead compounds may be anhydrous or may have water of crystallization. The same applies to mercury, thallium, and bismuth other than lead.

The slurry concentration may be within a range that can be handled, for example, within a range that does not cause clogging of solid pipes or sedimentation. At low concentration, the filtration is stable even with the conventional differential pressure type filter, and the backwashing cycle can be lengthened. However, when the concentration is higher than 3% by weight, this reaction method provides stable filtration speed and backwashing cycle. Very effective in prolonging the. Also, in order to increase the productivity per unit volume,
The higher the catalyst concentration, the better.

The viscosity of the slurry may be in a fluid range. 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 on the filter wall surface) and the filtration differential pressure become large. In some cases, solids may be clogged in the piping, and the rate of withdrawing the filtrate from the filter may be extremely slow due to a decrease in the fluidity of the liquid. Here, the upper limit of the slurry viscosity cannot be uniquely limited because it depends on the characteristics and purpose of the system.

The pore size of the filter material of the filter is 0.05 to 50 microns, preferably 0.1 to 20.
Micron. With a filter medium having a pore size smaller than 0.05 micron, there is a problem in manufacturing the filter and a problem that the filtration area is increased because the filtration pressure is increased and the filtration speed is restricted by the limit of the strength of the filter medium. There is. Further, the molecular diameter of the monomer of the substance handled in this reaction system is at most about several tens of angstroms, and if the pore diameter is 0.05 micron or more, there is no problem in filtration performance. Basically,
This means that the filter medium should have a pore size smaller than the minimum catalyst size. 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, there are cases where bridging or formation of a cake causes few particles to pass through the cake (cake filtration). Further, the inventors have found that the suspended catalyst is mechanically pulverized by collision of the solid catalyst with a stirring blade, a circulation pump, piping, etc., and thus fine particles much smaller than the initial average particle diameter are generated, and the fine particles are clogged in the filter. It was confirmed that the filtration rate was lowered. Therefore, as a result of further research using various suspension catalysts, this atomization is almost stable at a certain value (this is because the dispersion and aggregation of particles are balanced and the energy required for atomization is It is believed that this is because the smaller the particle size, the larger the particle size). That is, from the smallest particle size in the cumulative particle size distribution, about 2 to
The particles of 5% by weight showed almost no change with time such as further atomization or increase. Further, the stable particle size is about 0.5 to 20 μm, and it was found that the catalyst separation can be carried out smoothly without the problem of clogging by using the filter medium having the same pore size.

The tube diameter of the cross section on the slurry side of the filter medium of the filter, or the minimum gap size in the case of a flat plate, is preferably 1 mm or more and 100 mm or less. This is because if the size is smaller than 1 millimeter, clogging of the slurry will occur, stable operation will be difficult, and regeneration of the filtration capacity will be impossible. Further, if the dimension is larger than 100 mm, it is difficult to take a large filtration area, that is, even if the filtration area is the same, the larger the dimension, the larger the filtration device becomes.

In the cross-flow filter, the slurry linear velocity in order to give the shearing force of the flowing slurry on the filtering surface depends on the slurry concentration of the system, viscosity, catalyst particle size, filter diameter of the filter, etc. It is 0.05 m / sec or more, preferably 0.1 to 20 m / sec. When the linear velocity of the slurry is increased, the shearing force is increased and the thickness of the cake is decreased, so that the filtration speed is increased, but the pressure difference between the inlet and the outlet of the slurry passing through the filter is increased, and the power required for slurry circulation is increased. turn into. On the contrary, when the slurry linear velocity is less than 0.05 m / sec, the shearing force becomes small, the cake thickness becomes large, and the filtration speed becomes small.

The filtration differential pressure 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 substantially proportional to the filtration rate if the cake thickness is constant. However, if the filtration pressure difference is increased excessively in order to increase the filtration rate, the adhesion of the cake to the filtration surface becomes stronger, and at the same slurry linear velocity, the cake thickness increases due to the balance between the adhesion to the cake and the shearing force. Therefore, the filtration rate is reduced. From this, the filtration differential pressure is 2
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, the pressure drop
Not only is there a power loss for pressurization, but the reaction substances adsorbed on the surface of the catalyst are repeatedly adsorbed and desorbed, so that the catalytic activity is greatly reduced and by-products are easily generated. Therefore, it is desirable that the reactor pressure and the pressure on the slurry side of the filter are set to a pressure substantially equal to the differential pressure of the flow pressure loss. Further, the reaction pressure is set to 0.1 in order to secure the filtration differential pressure.
It is desirable that the pressure reaction is not less than Kg / cm ² gauge pressure.

The slurry temperature in the filter may be such that the slurry is in a liquid phase and kept in a fluidized state. That is, it may be maintained so as not to boil or solidify in the filter. Normally, the filter is circulated at the product temperature in the reactor, but if there is a problem with the material of the sealing material, it is possible to prevent corrosion by lowering the temperature on the filter side below the reaction temperature. Therefore, the reaction temperature and the filtration temperature do not necessarily have to match.

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.

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. An aromatic alcohol such as benzyl alcohol or a phenol. Especially methyl alcohol,
Lower alcohols such as ethyl alcohol are preferred because of rapid reaction. These alcohols can be used alone or as a mixture of two or more kinds.

The aldehyde / alcohol usage ratio in the present invention is 10 in terms of aldehyde / alcohol molar ratio.
The range of 1 to 50 is preferable, and the range of 3 to 1/20 is more preferable. If the molar ratio exceeds 10, it is not preferable because decomposition of aldehyde and other side reactions become remarkable and the selectivity of the reaction decreases, and conversely, if it is less than 1/50, recovery energy of alcohol increases, 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, such as nitrogen and carbon dioxide gas, and air. Can also be used. 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.

By using the finely divided catalyst of the present invention,
Compared with the conventional catalyst, it is possible to obtain a high conversion rate at the same reaction time even at a low temperature. Here, the reaction temperature is 0 to 120 ° C, preferably 20 to 100 ° C. The reaction of the present invention can be carried out under reduced pressure, atmospheric pressure, or increased pressure.However, the desired carboxylic acid ester can be easily obtained with a high yield by a simple method of blowing oxygen at a slight pressure around normal pressure. It has the characteristic that it can be obtained at a rate. The reaction can be carried out in either a batch system or a continuous system, and in the case of a continuous system, the closer the flow is to the extrusion flow, that is, the number of reactors is two or more than in a complete mixing tank. It goes without saying that the reaction amount or the one-pass tubular reactor has a larger reaction amount per reactor volume.

The following processes can be considered as a concrete reaction system. However, the present invention is not limited to these processes, and may be a combination of these processes in multiple stages. FIG. 1 is 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 crossflow filter (2), and a circulation pump (3). The circulation discharge slurry of the crossflow filter is provided in the gas phase portion in the upper part of the reactor. By spraying the liquid, the contact and absorption of gas and liquid are satisfactorily performed and the reaction is performed. In this case, since the solid / liquid mixture and the gas absorption in the reactor are carried out by the circulating slurry by the circulating pump, the agitator of the reactor is unnecessary as compared with the case of FIG. This eliminates problems such as a shaft seal of a stirrer, especially in high-pressure reactions.

FIG. 3 shows a gas lift type reactor (1),
It is a combination of a cross flow filter (2).
In this case, the liquid circulation method using the principle of the bubble pump,
The circulation pump is not needed as compared with the case of FIG. As a result, since the reaction system is close to the extrusion flow, the reactor becomes smaller than the complete mixing tank. Further, in the cross-flow filter, even if gas is mixed into the slurry due to insufficient gas separation, there is no problem in filtering performance.

1 to 3, the filter may be installed horizontally or vertically. Further, there is no particular restriction on the slurry inflow / outflow direction 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 the same thickness and high strength is preferable. In addition, the slurry is in the pipe,
It may be flowed outside the pipe, but it is preferable to flow the slurry inside the pipe 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 was used as the raw material aldehyde,
Using methanol as alcohol, methyl methacrylate was produced by a continuous oxidative esterification reaction in the presence of oxygen in the process shown in FIG. 1 under the reaction conditions shown below. 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 steel stirring type reactors 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 is agitated by an electromagnetic rotary stirrer. The heating is done by the jacket.

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

Γ-alumina (Mizusawa Chemical Neobi
2.5% palladium, 5.0% lead, magnesi
Charge 0.3 kg of catalyst supporting 2.0% of
22.3% methacrolein / methanol 0.
86 liters / Hr, NaOH / MeOH 0.05
Supply at liter / hr, temperature 80 ℃, 3Kg / cm ²
Air at a rate of 2.5 Nl / Hr under gauge pressure
The reaction was carried out while ventilating through the stainless sintered plate.
The reaction solution from the reactor is passed through a slurry circulation pump to a valve.
The specified circulation amount, that is, the cross flow linear velocity
The operation was performed at a rate of about 1 to 3 m / sec. This reaction liquid
And a NaOH / MeOH solution of 0.
Introduced together with 05 liter / Hr, temperature 80 ℃, approx.
2.0-2.8Kg / cm²1st step under gauge pressure
Vent the gas discharged from the reactor to the second-stage reactor, and
The reaction was performed by adding 1.5 Nl / Hr. Reaction liquid
PH of the first stage and the second stage reactor are 7.0-7.5
The amount of NaOH was controlled so as to keep it.

Analysis of the second-stage reaction liquid revealed that the conversion of methacrolein was 84.7% and the yield of methyl methacrylate was 7
5.2% (selectivity 88.8%), and a small amount of isobutyraldehyde and isobutyric acid methyl ester (selectivity 0.0
5%) produced. Here, the filtration rate decreased rapidly after the start of the reaction, but was stabilized in about 100 hours, and the filtration rate after stabilization was 200 to 300 liters / m ² / hr (the amount of the filtrate per unit area per unit time of the filter unit). : Same below). Also, in order to see the effect of backwashing, when backwashing was performed and restarted, the filtration rate was recovered to almost the initial filtration rate and was substantially stabilized after about 100 hours. The filtration rate at this time was equivalent to the stable value before back washing. Moreover, the catalyst did not flow out.

[0038]

[Example 2] In Example 1, air was blown in the middle of the pipe for supplying from the slurry circulation pump to the cross-flow filter (this was carried out at a temperature and pressure of the filter of about 7% by volume). As a result, the circulating flow rate of the liquid was reduced and the residence time in the filter was lengthened, but isobutyraldehyde and isobutyric acid methyl ester were scarcely produced. In addition, there was almost no effect on the filtration performance due to the inclusion of air bubbles in the slurry, that is, no effect on the filtration rate and no effect on the filtration rate.

[0039]

COMPARATIVE EXAMPLE 1 Methyl methacrylate was produced by a continuous oxidative esterification reaction in the same manner as in Example 1 using a sedimentation separator (4) as shown in FIG. That is, except that a sedimentation separation method was used for the separation device for the catalyst and the reaction product liquid,
The raw materials, catalyst, reaction conditions, etc. are the same as in Example 1. As the sedimentation 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 about the same as in Example 1, but isobutyraldehyde and isobutyric acid methyl ester were considerably formed (selectivity 0.4%). Further, the outflow of the catalyst was about 0.5% of the input amount for the operation for 200 hours.

[0041]

[Comparative Example 2] In Comparative Example 1, air was blown in the middle of the pipe for supplying from the slurry circulation pump to the cross flow filter (this was performed at about 7% by volume at the temperature and pressure of the filter). As a result, although isobutyraldehyde and isobutyric acid methyl ester were scarcely produced, there was a considerable amount of catalyst outflow (about 3.4% of the charged amount in 24 hours continuous operation).

[0042]

Example 3 Methyl methacrylate was produced by the continuous oxidative esterification reaction in the same manner as in Example 1 by the process shown in FIG. That is, it is the same as Example 1 except that the slurry circulation system by gas lift is adopted and the reactor does not have a stirring device. The device has an inner diameter of 40 mm and an internal volume of 1.2.
Liter stainless steel gas lift reactor (8 in the tower
The reaction was carried out by connecting two metal mesh nets horizontally at 8 cm intervals). 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 liquid from the reactor was subjected to solid-liquid separation through a cross flow filter, the concentrated slurry liquid was returned to the reactor, and the filtrate was withdrawn to the next reactor or filtrate tank. This filter was provided with a filter tube of a ceramic porous body (average pore size 1 to 2 microns), and a backwashing device was attached so that the backwashing operation could be performed with gas or liquid.

In each reactor, alumina (trade name: Sumitomo Activated Alumina) 1.5% palladium, 2.5% bismuth,
0.6 kg of catalyst supporting 2.0% lithium was charged, and 22.2% methacrolein / methanol 1.8 liter / hr and NaOH / MeOH solution were supplied at 0.1 liter / hr to the first stage reactor. , Temperature 80 ℃, 3Kg /
Under a pressure of cm ² gauge, air was aerated at a rate of 5 Nl / Hr through a stainless sintered plate to circulate a catalyst and a reaction solution to carry out a reaction. The reaction liquid is filtered by a cross-flow filter, the concentrated catalyst slurry is returned to the reactor, and the reaction liquid that is the filtrate is continuously introduced into the second-stage reactor together with 0.1 liter / Hr of NaOH / MeOH liquid, The effluent gas of the first-stage reactor was ventilated to 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 amount of NaOH 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 liquid revealed that the methacrolein conversion rate was 80.3% and the methyl methacrylate yield was 7
1.4% (selectivity 88.9%), and trace amount of isobutyraldehyde and isobutyric acid methyl ester (selectivity 0.0
5%) produced. Here, the filtration rate decreased rapidly after the reaction started, but was stabilized in about 100 hours, and the filtration rate after stabilization was 200 to 300 liters / m ² / hr.
Also, in order to see the effect of backwashing, when backwashing was performed and restarted, the filtration rate was recovered to almost the initial filtration rate and was substantially stabilized after about 100 hours. The filtration rate at this time was equivalent to the stable value before back washing. Moreover, the catalyst did not flow out.

[0046]

COMPARATIVE EXAMPLE 3 Methyl methacrylate was produced by the continuous oxidative esterification reaction in the same manner as in Example 3, using the sedimentation separation apparatus used in Comparative Example 1. That is, the raw materials, the catalyst, the reaction conditions, and the like were the same as those in Example 3 except that the separator for the catalyst and the reaction product liquid was a sedimentation separation system.

As a result, the conversion of methacrolein was about the same as in Example 3, but isobutyraldehyde and isobutyric acid methyl ester were considerably formed (selectivity 0.5%). The 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 carried out under the same conditions as above. As a result of measuring the particle size distribution of the catalyst used here with an electron microscope, the average particle size was about 10 microns. For 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 carried out continuously for 800 hours without backwashing. The reaction results are 90% methacrolein conversion.
A small amount of isobutyraldehyde and methyl isobutyrate (selectivity 0.06%) was produced at 8%. Furthermore, the filtration rate decreased rapidly after the start of the reaction, but stabilized in about 100 hours, and the filtration rate after stabilization was 150 to 250 liters / m ² / hr. Also, in order to see the effect of backwashing, after backwashing and restarting, the filtration rate 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. Moreover, the catalyst did not flow out.

[0050]

[Comparative Example 4] The oxidative esterification reaction was carried out under the same conditions as in Example 4, except that the sedimentation separator used in Comparative Example 1 was used as the separator for the catalyst and the reaction product liquid. As a result, the conversion of methacrolein was about the same as in Example 4, but isobutyraldehyde and isobutyric acid methyl ester were considerably formed (selectivity 0.7%). In addition, a considerable catalyst outflow (24
There was about 5.7% of the input amount for the operation for an hour.

[0051]

Example 5 The reaction was carried out in the same manner as in Example 4 except that the reaction temperature was 40 ° C. As a result, the oxidative esterification reaction and the separation of the reaction solution and the catalyst were carried out smoothly. The reaction results were such that the conversion of methacrolein was 75.3%, and trace amounts of isobutyraldehyde and methyl isobutyrate (selectivity 0.02%) were produced.

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

[0053]

Example 6 The reaction was carried out in the same manner as in Example 4 except that 33.3% methacrolein / methanol was used as the raw material concentration. As a result, the oxidative esterification reaction and the separation of the reaction solution and the catalyst were carried out smoothly. The reaction results were such that the conversion of methacrolein was 76.4%, and a small amount of isobutyraldehyde and methyl isobutyrate (selectivity 0.06%) were produced.

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

[0055]

Example 7 The 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 carried out smoothly. The reaction results were that the acrolein conversion rate was 86.8%, and a small amount of propionaldehyde and methyl propionate (selectivity: 0.05%) were produced.

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

[0057]

INDUSTRIAL APPLICABILITY Since the present invention uses cross-flow type filtration in the separation of the catalyst and the reaction product-containing liquid,
By shortening the residence time in the separation device, byproduct formation is suppressed and the selectivity of the main reaction product, carboxylic acid ester, is improved, downsizing of purification equipment, reduction of purification energy, and downsizing of reactor. Can be achieved. In addition, clogging / scaling and catalyst loss in the subsequent process due to catalyst outflow are suppressed, and a decrease in filtration speed with time is suppressed, so that smooth operation can be realized continuously for a long period of time. Further, as compared with the sedimentation separator (4) as shown in FIG. 4, the catalyst separation device can be downsized compared to the system having a slow sedimentation speed, and the closed system enables safe operation.
Furthermore, even if gas is mixed into the slurry, the filtration performance is not affected, and further atomized particles are generated by mechanical crushing due to collision of the solid catalyst on the stirring blade, circulation pump, pipe, etc. There is also an effect such as achieving precise filtration for such fine particles.

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

[Brief description of drawings]

FIG. 1 is a diagram of a reactor 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 reactor showing an example of an embodiment according to the present invention. (Slurry circulation system with circulation pump, reactor with circulating liquid spray)

FIG. 3 is a diagram of a reactor 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 device.

[Explanation of symbols]

 1 Reactor 2 Cross-flow filter 3 Slurry circulation pump 4 Sedimentation separator

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location // C07B 61/00 300

Claims (1)

[Claims] 1. When a liquid reaction product containing a carboxylic acid ester is obtained 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 ( A method for producing a carboxylic acid ester, which comprises performing 3) 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 the liquid reaction product by a cross flow method with a cross flow linear velocity of 0.05 m / sec or more Separating the liquid reaction product into a concentrated catalyst suspension by means of (3) circulating the concentrated catalyst suspension into a suspension fluidized bed