Method for producing unsaturated carboxylic acid ester

Abstract

To provide a method for producing an unsaturated carboxylic ester, which reduces the risk of clogging due to polymerization while maintaining a high conversion ratio in an esterification reaction of an unsaturated carboxylic acid, and which achieves a reduction in the equipment cost and workload involved.SOLUTION: A method for producing an unsaturated carboxylic ester is provided, which uses a reactor R11 filled with a solid catalyst C11 to perform an esterification reaction, the method continuously supplying an unsaturated carboxylic acid and alcohol to the reactor from an inlet of the reactor to form a reaction liquid in the reactor, and continuously supplying a vaporized organic solvent f16 into the reactor from the inlet of the reactor or a vicinity thereof.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for producing an unsaturated carboxylic acid ester using an unsaturated carboxylic acid and an alcohol as raw materials in a gas-liquid mixed phase state using a solid catalyst. [Background technology]

[0002] A common method for producing unsaturated carboxylic acid esters is an esterification reaction using unsaturated carboxylic acid and alcohol as raw materials. In the esterification reaction, a catalyst is usually used to increase the reaction rate. The catalyst is divided into two types: one in which it is dissolved in the reaction fluid (homogeneous system) and one in which it exists as a solid in the reaction fluid (heterogeneous system). Heterogeneous systems are further classified into a fluidized bed in which the catalyst flows together with the reaction fluid, and a fixed bed in which the catalyst is stationary and does not move. Esterification reactions using fixed beds have the characteristics that the catalyst concentration per unit space can be made higher than in fluidized beds and homogeneous systems, and that the reaction fluid and the catalyst can be easily separated.

[0003] Since the unsaturated carboxylate produced in the esterification reaction reacts with water, which is a by-product of the reaction, and is hydrolyzed to an unsaturated carboxylate and an alcohol, the reaction conversion rate is in equilibrium between the esterification reaction and the hydrolysis reaction (reverse reaction), and cannot exceed this. Therefore, the reaction by-product water needs to be separated and recovered from the unsaturated carboxylate. For example, Non-Patent Document 1 discloses a method for producing an acrylic ester, in which 1.1 to 1.3 times the equivalent of acrylic acid and methanol or ethanol are supplied to a fixed bed reactor filled with a cation exchange resin catalyst, and an esterification reaction is carried out at 60°C to 80°C, and then the reaction liquid is supplied to a distillation column to separate unreacted acrylic acid as a column bottom liquid, and the acrylic ester, unreacted alcohol, and reaction by-product water are separated as a distillate, and the reaction by-product water is separated by two-liquid separation of the distillate, and the unreacted alcohol is separated from the separated crude acrylic ester solution by extraction and distillation, and the separated acrylic acid and alcohol are recycled to an esterification reactor.

[0004] By removing water, which is a by-product of the reaction, from the reaction system during the esterification reaction, it is possible to suppress the hydrolysis reaction and increase the reaction conversion rate between unsaturated carboxylic acids such as acrylic acid and alcohols. The higher the reaction conversion rate, the less unsaturated carboxylic acids such as acrylic acid and alcohols remain at the reactor outlet, so the load of separating and recovering them is reduced, enabling more efficient production. Patent Document 1 discloses a method for producing an acrylic ester in which acrylic acid, methanol or ethanol are supplied to a reactor filled with a strongly acidic ion exchange resin, and the temperature and pressure in the reactor are adjusted to bring the entire reaction system into a gas-liquid mixed phase state (bubbling state), thereby moving the water by-produced in the esterification reaction in the liquid phase to the gas phase and increasing the reaction conversion rate in the liquid phase. Similarly, Patent Document 2 discloses a method for producing an acrylic ester with a high reaction conversion rate while reducing by-products by reacting an excess amount of acrylic acid with an alcohol having 1 to 3 carbon atoms at 60°C to 130°C under a reduced pressure of 13 kPa to 67 kPa. Also, Non-Patent Document 2 discloses a method in which a reaction section having an acidic ion exchange resin is provided in the middle stage of a distillation column, acrylic acid is supplied from above the reaction section, butanol is supplied from below the reaction section, reaction by-product water is extracted from the top of the column, and butyl acrylate is obtained from the bottom of the column. All of these methods are similar to so-called trickle bed reactors (hereinafter sometimes referred to as "TBR"), which have a solid catalyst in the reactor and in which the reaction fluid exists in a mixed phase state of liquid and gas.

[0005] On the other hand, unsaturated carboxylic acids and unsaturated carboxylic acid esters (hereinafter collectively referred to as "unsaturated carboxylic acids") may cause unintended polymerization due to their unsaturated bonds. In particular, acrylic acid, methacrylic acid, and their esters (hereinafter collectively referred to as "unsaturated carboxylic acids") may cause unintended polymerization due to their unsaturated bonds. Acrylic acids are easily polymerizable compounds that start to polymerize naturally without the addition of a polymerization initiator. If the accumulation of solids due to unintended polymerization progresses in a production facility, the facility will be forced to stop operation due to blockages, etc., so it is necessary to avoid or at least reduce polymerization blockages. Examples of countermeasures include distillation operations under reduced pressure to reduce polymerization by lowering the operating temperature, addition of a polymerization inhibitor to capture radicals that cause polymerization, and adoption of an internal structure of the device with a short average residence time and few retention areas to alleviate blockages due to polymers. Non-Patent Document 1 shows a method of distilling acrylic acids under reduced pressure and adding hydroquinone or phenothiazine as a polymerization inhibitor to prevent polymerization. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 55-122740 [Patent Document 2] Japanese Patent Application Publication No. 10-279523 [Non-patent literature]

[0007] [Non-Patent Document 1] Ullmann's Encyclopedia of Industrial Chemistry 5th-Ed. Vol.A1 pp.161-176 “Acrylic Acid and Derivatives” [Non-Patent Document 2] Chem. Eng. Sci. 61(2006) 4417-4431 “Design and control of butyl acrylate reactive distillation column system” Summary of the Invention [Problem to be solved by the invention]

[0008] In an esterification reaction, a TBR is a very efficient device that uses a fixed-bed type catalyst layer that has a high catalyst density per space and is easily separated from the reaction fluid, and that can perform dehydration in parallel to increase the reaction conversion rate. A reactive distillation type device as shown in Non-Patent Document 2, in which the reaction fluid, that is, the reaction liquid, and the reaction gas are brought into countercurrent contact, is particularly excellent in that it can selectively separate water, which is a reaction by-product.

[0009] However, in the case of unsaturated carboxylic acids, attention should be paid to polymerization blockage as much as or more than the efficiency of the esterification reaction. Polymerization of unsaturated carboxylic acids in the liquid phase can be prevented by eliminating local high temperature areas and stagnant areas and maintaining the polymerization inhibitor concentration in the liquid phase at a certain value or higher on average. Since the concentration of unsaturated carboxylic acids is low in the gas phase, polymerization does not substantially occur. However, the vapor pressure of the polymerization inhibitor used is often lower than that of unsaturated carboxylic acids, and there is almost no polymerization inhibitor in the gas phase. Unsaturated carboxylic acids condensed from the gas phase also do not contain polymerization inhibitors and have high polymerizability, so it is necessary to prevent condensation of unsaturated carboxylic acid vapor by keeping the gas phase warm or heating it, or to quickly add a polymerization inhibitor to the condensed liquid.

[0010] For the above reasons, the inside of a distillation column where evaporation and condensation of unsaturated carboxylic acids are continuously repeated is one of the places where polymerization blockage is likely to occur. The method described in Non-Patent Document 2 is similar to this method, and requires rapid mixing of the condensate and the polymerization inhibitor, but it is extremely difficult to do so under conditions where the column is packed with a solid catalyst, and no solution has been shown, making this method unrealistic.

[0011] In the methods described in Patent Documents 1 and 2, a tubular reactor is used, and a so-called plug flow is adopted in which liquid and gas flow in the same direction inside the tube. This somewhat sacrifices selective separation of water, but minimizes the frequency of evaporation and condensation of acrylic acid and the like, and also makes the liquid and gas flows in the reactor uniform to suppress polymerization blockages in the equipment. It is also considered that this method has the function of quickly discharging polymers with relatively small molecular weights that have not yet precipitated out of the reactor. In terms of measures against polymerization blockages, This is a more realistic approach.

[0012] The high reaction conversion rate in the esterification reaction in TBR is believed to be due to the separation of water, a reaction by-product, from the liquid phase by rapid evaporation. Heat of evaporation is required for the evaporation of water, and in the case of the tubular reactor, the heat of evaporation is supplied to the reaction fluid in the tube through the inner wall surface of the reaction tube. It is similar to the case where a multi-tubular heat exchanger is used as a reboiler for a distillation column, but compared to a multi-tubular heat exchanger in which the reaction fluid, which is entirely or mostly liquid, flows through the tube at a linear velocity of 0.3 to 3 m / sec, in a tubular reactor in which a gas-liquid mixed phase flow, in which the gas is greater than the liquid in terms of volume ratio, flows through a tube filled with a solid catalyst at a linear velocity of less than 0.3 m / sec, the possibility of localized retention of the reaction fluid on the inner wall surface of the tube and the associated polymerization blockage is significantly increased. It is not practical to increase the linear velocity of the reaction fluid in the tube to the same level as that of a reboiler, because the residence time required for the reaction cannot be secured and the increase in differential pressure due to the packed catalyst becomes extremely large. By reducing the temperature difference (ΔT) between the reaction fluid flowing inside the tube and the heat transfer fluid flowing outside the tube, it is possible to alleviate local overheating and reduce polymerization blockage, but it is necessary to increase the surface area (heat transfer area) inside the reaction tube in inverse proportion to ΔT to supply the required amount of heat. Increasing the length of the reaction tube to increase the heat transfer area increases the reactor capacity, which is not preferable because it impairs the efficient esterification reaction, which is an advantage of TBR. By making the reaction tube thinner, the heat transfer area can be increased in inverse proportion to the tube diameter, but since the number of reaction tubes increases, not only does the manufacturing cost of the reactor increase, but the workload when filling the reaction tube with a catalyst also increases, and further, the thinner the reaction tube, the more difficult it becomes to perform recovery work when polymerization blockage occurs in the reaction tube.

[0013] The present invention has an object to solve the above-mentioned conventional problems and to provide a method for producing an unsaturated carboxylic acid ester, which maintains a high conversion rate in an esterification reaction of an unsaturated carboxylic acid, reduces the risk of polymerization blockage, and keeps the required equipment costs and workload low. [Means for solving the problem]

[0014] As a result of extensive investigations aimed at solving the above problems, the present inventors have discovered that, in an esterification reaction of an unsaturated carboxylic acid, a reactor packed with a solid catalyst is used, and raw material unsaturated carboxylic acid and alcohol are supplied to the reactor, and a vaporized organic solvent is supplied to the reactor. average It has been found that by supplying the gas in a stream, a high reaction conversion can be obtained without substantially supplying heat to the reactor. The present invention has been achieved based on these findings, and has the following gist.

[0015] [1] A method for producing an unsaturated carboxylic acid ester by an esterification reaction between an unsaturated carboxylic acid and an alcohol using a reactor packed with a solid catalyst, comprising the steps of: A method for producing an unsaturated carboxylic acid ester, comprising: a step of continuously supplying an unsaturated carboxylic acid and an alcohol to a reactor through an inlet of the reactor to form a reaction liquid fluid in the reactor; and a step of continuously supplying a vaporized organic solvent into the reactor through the inlet of the reactor or in the vicinity thereof. [2] The method for producing an unsaturated carboxylic acid ester according to [1], wherein the organic solvent is an aliphatic hydrocarbon or an aromatic hydrocarbon. [3] The method for producing an unsaturated carboxylic acid ester according to [1] or [2], wherein the boiling point of the organic solvent under atmospheric pressure is lower than the boiling point of the unsaturated carboxylic acid under atmospheric pressure. [4] The method for producing an unsaturated carboxylic acid ester according to any one of [1] to [3], wherein the organic solvent is toluene. [5] The method for producing an unsaturated carboxylic acid ester according to any one of [1] to [4], wherein the reactor is a vertical reactor and the reaction liquid fluid is a downflow. [6] separating the esterification reactant discharged from the reactor into a liquid phase and a gas phase; A step of continuously supplying the liquid phase to a reactor (A) from an inlet of the reactor (A) separately installed downstream of the reactor, and forming a reaction liquid fluid in the reactor (A); A gaseous organic solvent is recovered from the gas phase, and the recovered gaseous organic solvent is added to the reactor (A). continuously supplying the reaction mixture to the reactor (A) from an inlet or a vicinity thereof. [7] separating the esterification reactant discharged from the reactor into a liquid phase and a gas phase; purifying the separated liquid phase to obtain an unsaturated carboxylic acid ester; and and recovering a gaseous organic solvent from the separated gas phase, and continuously supplying the recovered gaseous organic solvent to the reactor from an inlet of the reactor or near an inlet of the reactor.

[0016] [8] A method for producing an unsaturated carboxylic acid ester by an esterification reaction between an unsaturated carboxylic acid and an alcohol using a reactor filled with a solid catalyst, comprising the steps of: continuously feeding a vaporized organic solvent into the reactor at or near an inlet of the reactor; and and after the internal pressure of the reactor has remained within ±5% of a predetermined pressure for at least 30 minutes, continuously supplying an unsaturated carboxylic acid and an alcohol to the reactor through an inlet of the reactor. [9] The method for producing an unsaturated carboxylic acid ester according to [8], further comprising the step of: continuously supplying the unsaturated carboxylic acid and the alcohol to the reactor through an inlet of the reactor after the internal temperature of the reactor has been maintained for at least 30 minutes with a fluctuation range of 0.5°C or less. Effect of the Invention

[0017] According to the present invention, in an esterification reaction, it is possible to reduce the risk of polymerization in a reactor, keep the work load low, and produce an unsaturated carboxylic acid ester with a high conversion. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic diagram showing an example of a conventional reactor for producing an unsaturated carboxylic acid ester. [Diagram 2]FIG. 1 is a conceptual diagram of temperature distribution in a conventional reactor for producing an unsaturated carboxylic acid ester. [Diagram 3] FIG. 1 is a schematic diagram showing an example of a reactor for producing an unsaturated carboxylic acid ester of the present invention. [Figure 4] FIG. 2 is a schematic diagram showing another example of a reactor for producing an unsaturated carboxylic acid ester of the present invention. [Diagram 5] FIG. 1 is a schematic diagram showing an example of a process including a reactor for producing an unsaturated carboxylic acid ester of the present invention. [Figure 6] FIG. 1 is a schematic diagram of an experimental apparatus for producing an unsaturated carboxylic acid ester of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The method of the present invention will be described in detail below with reference to the drawings. However, the present invention is not limited to the following description in any way, and various modifications can be made within the scope of the gist of the present invention.

[0020] FIG. 1 is a schematic diagram showing an example of a conventional reactor for producing an unsaturated carboxylic acid ester. The following description will focus on the use of acrylic acid as the unsaturated carboxylic acid. This is because, among unsaturated carboxylic acids, acrylic acid has high polymerizability and benefits greatly from the reduced polymerization risk of the reactor, which is one of the features of the present invention. However, the same effect can be obtained with other unsaturated carboxylic acids such as methacrylic acid.

[0021] The feed liquid (f1) containing raw material acrylic acid, alcohol, polymerization inhibitor, acrylic ester recycled from the downstream process, and further solvent, etc., as required, is heated to near the reaction temperature by a heater (E1) and then continuously fed to a multi-tubular reactor (R1) packed with a solid catalyst (C1). A heat transfer medium (f4) is supplied to the multi-tubular reactor (R1) and circulates around the outer periphery of each reaction tube. The heat transfer medium (f4) is discharged from the reactor (R1), thereby controlling the temperature inside the reactor. The pressure inside the reactor is adjusted so that a gas-liquid mixed phase state is created, and the reaction fluid at the reactor outlet is separated into a liquid flow (f2) and a gas flow (f3).

[0022] FIG. 2 is a conceptual diagram of the temperature distribution in the multi-tubular reactor (R1) in FIG. 1. The raw material concentration is higher toward the inlet side of the multi-tubular reactor, so the amount of water by-produced in the esterification reaction is also larger. When the by-product water evaporates, it takes the heat of evaporation from the reaction fluid, so its temperature drops. For example, when producing 2-ethylhexyl acrylate from acrylic acid and 2-ethylhexanol, the temperature of the reaction fluid drops by about 1°C to evaporate the water produced at a reaction conversion rate of 1%. Heat is supplied to the reaction fluid from the heat medium circulating outside the reaction tube, but the amount of heat transfer is proportional to the temperature difference between the heat medium and the reaction fluid, so the reaction fluid temperature drops once and then starts to rise, reaching the vicinity of the heat medium temperature at the outlet of the multi-tubular reactor. In order to evaporate the reaction by-product water while maintaining the reaction temperature required for the esterification reaction, a multi-tubular reactor having a large heat transfer area for the reaction fluid is essential for commercial production.

[0023] It is possible to omit the heater (E1) and supply all the required heat by the multi-tubular reactor (R1), but the economic efficiency is reduced because the multi-tubular reactor (R1) becomes larger with an increase in the amount of heat supplied to the multi-tubular reactor (R1). The amount of liquid supplied to the multi-tubular reactor is increased by adding a solvent not involved in the esterification reaction or increasing the proportion of the liquid circulated from the downstream process to the multi-tubular reactor, and the temperature drop in the reaction fluid is reduced in inverse proportion to the amount of the liquid supplied, but this is not an essential solution to the temperature drop.

[0024] FIG. 3 is a schematic diagram showing an example of a reactor for producing an unsaturated carboxylic acid ester of the present invention. This reactor includes, from the top in the figure, an inlet section, a reaction section containing a solid catalyst, and an outlet section. A feed liquid (f11) containing raw material acrylic acid, alcohol, polymerization inhibitor, and an acrylic acid ester recycled from a downstream process, etc. is continuously fed to the inlet section of the reactor (R11). A shower nozzle or an atomizing nozzle is used to feed the feed liquid (f11) so that the feed liquid (f11) is uniformly distributed over the cross section of the reactor (R11), but is not limited thereto. The feed liquid (f11) fed to the reactor (R11) exists as a reaction liquid fluid in the reactor, and can be esterified by contacting with a vaporized organic solvent (f16) described later.

[0025] Separately from this, an organic solvent (f16) is vaporized by an evaporator (E11) and then continuously supplied to the inlet of a reactor (R11). The organic solvent (f16) does not necessarily need to be supplied to the inlet of the reactor, and may be continuously supplied to the vicinity thereof, i.e., the inlet side of the reaction section. Specifically, the vicinity may be closer to the inlet than 1 / 2, closer to the inlet than 1 / 3, closer to the inlet than 1 / 4, or closer to the inlet than 1 / 5 in the vertical direction of the solid catalyst (C11) in the figure. The reactor (R11) is a jacketed reactor having a tank filled with a solid catalyst (C11) and a path through which a heat transfer medium (f14) flows on the outer periphery, and is a downflow reactor in which fluid moves vertically.

[0026] A packed bed having no catalytic activity may be provided on the packed solid catalyst (C11) for the purpose of more uniform diffusion of the feed liquid (f11), preheating with a vaporized organic solvent, etc. The type of packed bed is not particularly limited, and may be, for example, irregular packing made of metal because of its large porosity, small pressure loss, and high thermal conductivity, or irregular packing made of a fluororesin such as polytetrafluoroethylene because polymers of acrylic acids are unlikely to accumulate. The irregular packing or wire mesh surface-treated with the fluororesin is preferred, and wire mesh is more preferred because of its ease of handling when attaching and detaching. Unlike the multi-tubular reactor (R1), which actively supplies heat from the heat transfer medium to the reaction fluid, The heat transfer medium in (R11) is intended to prevent heat loss from the reaction fluid to the outside air, and does not require a large amount of heat. Therefore, instead of introducing a heat transfer medium into the reactor (R11), heating means such as an electric heater or steam tracing can be used. In addition, in order to prevent the solid catalyst and reaction fluid in the reactor (R11) from being locally overheated, it is preferable to place insulation between the electric heater and steam tracing piping so that they do not directly contact the outer wall surface of the vessel. The reaction fluid is a mixed fluid in a reactor that contains, in addition to the common liquid (f11) and the organic solvent (f16), an unsaturated carboxylate ester such as an acrylate ester, which is a reaction product, and water, which is a reaction by-product, and may be a mixture of liquids and gases.

[0027] The solid catalyst (C11) used is not particularly limited, and a general catalyst that can be used in the esterification reaction of unsaturated carboxylic acid and alcohol can be used. The smaller the particle size, the larger the catalyst surface area per unit space, and the more efficiently the esterification reaction can be carried out, but the average particle size is preferably 0.1 mm or more, more preferably 0.2 mm or more, so that the pressure loss caused by the gas flow does not become too large. As the solid catalyst, a porous ion exchange resin is preferred because it has a high catalyst concentration per unit space and a narrow particle size distribution, and activated clay obtained by thermally treating acid clay such as montmorillonite is preferred because of its physical strength and cost. When the scale of the ester production plant is large and the operation period is long, from 3 months to several years, a porous ion exchange resin is economically superior. On the other hand, when the scale of the plant is small and the operation period is short, from about 1 week to several months, and the catalyst is frequently updated due to changes in the product, activated clay is economically superior and reduces the workload.

[0028] Water produced as a by-product in the esterification reaction evaporates through heat exchange with the vapor of the organic solvent, and the organic solvent that has been heat exchanged is condensed. When the composition of an azeotropic mixture of water and an organic solvent is A (water):B (organic solvent) (molar ratio), the minimum required amount of gasified organic solvent (hereinafter sometimes referred to as "organic solvent vapor") is B / A times the molar amount of the reaction by-product water. However, since it is not possible for all of the supplied organic solvent vapor to exchange heat with the reaction by-product water, the supply amount of organic solvent vapor must be at least 1.2 times the minimum required amount, and is preferably 1.3 times or more.

[0029] The greater the amount of organic solvent vapor supplied, the more rapidly the reaction by-product water is evaporated. However, taking into consideration the increase in the amount of heat required for evaporating the organic solvent and the load required for separating and recovering the organic solvent in the downstream process, the amount of organic solvent vapor supplied is preferably 5 times or less, more preferably 3 times or less, the minimum required amount. The organic solvent used is preferably an aliphatic or aromatic hydrocarbon, which is easy to separate and recover for reuse and has high chemical stability. If the boiling point of the organic solvent is too low, heat exchange with the reaction by-product water is difficult to proceed, which is not economical. On the other hand, if the boiling point is too high, heat exchange with the unreacted acrylic acid in the process liquid is also performed, resulting in evaporation of the acrylic acid, which is likely to cause polymerization blockage due to the evaporated acrylic acid. Furthermore, since the esterification reaction does not proceed in the gas phase, the reaction conversion rate of acrylic acid may also decrease. In view of these, the boiling point of the organic solvent is preferably lower than the boiling point of acrylic acid, more preferably 70°C to 130°C, and even more preferably 80°C to 120°C.

[0030] The temperature of the reaction fluid is controlled by the pressure in the reactor. Since the composition of the reaction fluid changes continuously along the reaction axis and pressure loss occurs due to the flow of the reaction fluid, it is difficult to make the temperature equal in all reaction zones. Examples of the operation control method of the reactor include a method of measuring the temperature in the reactor at multiple points along the reaction axis and adjusting the pressure in the reactor so that the temperature at a specific position is constant, a method of keeping the pressure in the reactor constant and adjusting the amount and temperature of the organic solvent vapor generated in the evaporator (E11) to keep the temperature at a specific position in the reactor constant, and a method of keeping the pressure in the reactor and the amount and temperature of the vapor supplied constant and allowing some temperature fluctuation in the reactor. The higher the reaction temperature, the higher the reaction rate, which is preferable. However, the polymerization reaction and the associated blockages are also increased. The appropriate reaction temperature varies depending on the type of ester, but is generally in the range of 60°C to 120°C, and preferably in the range of 70°C to 110°C. The reaction pressure depends on the type of organic solvent used, but is generally 0.2 to 1.0 times the vapor pressure of water at the reaction temperature. The reaction fluid at the reactor outlet is separated into a liquid stream (f12) mainly composed of acrylic ester and a gas stream (f13) mainly composed of the organic solvent and reaction by-product water.

[0031] When an unsaturated carboxylic acid ester is produced using the reactor of the present embodiment, the timing of supplying the raw material containing the unsaturated carboxylic acid and the alcohol and the vaporized organic solvent to the reactor is not particularly limited. In one embodiment, the vaporized organic solvent is continuously supplied to the reactor, and after the internal pressure of the reactor has become within ±5%, preferably within ±3%, more preferably within ±2% of the predetermined pressure for at least 30 minutes, preferably 45 minutes or more, more preferably 60 minutes or more, the unsaturated carboxylic acid and the alcohol may be continuously supplied to the reactor from the inlet of the reactor. In another embodiment, the vaporized organic solvent may be continuously supplied to a reactor, and after the internal temperature of the reactor fluctuates by 0.5° C. or less, preferably 0.4° C. or less, more preferably 0.3° C. or less for at least 30 minutes, preferably 45 minutes or more, more preferably 60 minutes or more, the unsaturated carboxylic acid and the alcohol may be continuously supplied to the reactor from the inlet of the reactor. The internal temperature of the reactor may be the temperature of the catalyst layer, and the internal pressure of the reactor may be, for example, the pressure at the inlet or outlet.

[0032] In this embodiment, the reaction by-product water moves from the liquid phase to the gas phase in the reaction fluid by heat exchange with the organic solvent vapor, but since the liquid flow and the gas flow are parallel, the reaction by-product water is also present at the reactor outlet in an amount equal to the moles of the generated acrylic acid ester. Most of the water molecules are present in the gas phase, but some of them are present in the liquid phase due to gas-liquid equilibrium, which is an impediment to improving the reaction conversion rate. As an improvement measure, a method of supplying the organic solvent vapor and separating the reaction by-product water in multiple stages can be mentioned.

[0033] FIG. 4 is a schematic diagram showing another example of a reactor for producing an unsaturated carboxylic acid ester, in which the reactor shown in FIG. 3 is applied to a two-stage reactor in series. A feed liquid (f21) containing raw material acrylic acid, alcohol, polymerization inhibitor, and acrylic acid ester recycled from a downstream process, and an organic solvent vapor (f26A) are fed to the upper head section (R21A) of the reactor, and an esterification reaction is carried out in the solid catalyst (C21) of the first stage reaction section (R21B). Then, a gas flow (f23A) consisting of an organic solvent and reaction by-product water is extracted from the side in the intermediate connection section (R21C) of the reactor, and a liquid flow (hereinafter also referred to as a process liquid) containing acrylic acid ester, unreacted raw material, and condensed organic solvent, etc., falls through the plate holes while forming a liquid depth on the perforated plate (J21) installed below. In the intermediate connection section (R21C), organic solvent vapor (f26B) is newly supplied from the side downstream of the perforated plate (J21). Due to the liquid depth formed on the perforated plate (J21), the additionally supplied organic solvent vapor (f26B) is supplied to the second stage reaction section (R21D) together with the process liquid without flowing into the first stage reaction section (R21B) or the gas flow withdrawal pipe (f23A). As a measure to prevent the inflow of the organic solvent vapor (f26B), it is possible to use a tube trap such as an S-trap instead of the perforated plate (J21). However, the perforated plate is more preferable in view of the fact that a portion of the trap where the acrylic acid and the like remain is generated, and a distributor is required to distribute the process liquid at the trap outlet throughout the second-stage reaction section (R21D), etc. The process fluid that has completed the reaction on the solid catalyst (C22) is separated in the lower head section (R21E) of the reactor into a gas stream (f23B) mainly composed of uncondensed organic solvent and reaction by-product water, and a liquid stream (f22) mainly composed of acrylic ester and condensed organic solvent. The organic solvent-containing gas stream (f23A) extracted at the intermediate connection (R21C) of the reactor may be condensed and then separated into an aqueous layer and a solvent layer in a liquid storage tank (not shown), and the organic solvent recovered from the solvent layer may be vaporized again and supplied to the inlet of the second-stage reactor as organic solvent vapor (f26B). In this embodiment, the intermediate connection (R21C) constitutes the outlet of the first-stage reactor and the inlet of the second-stage reactor.

[0034] 4 shows an example of a two-stage reactor in series, but the reactor can be multi-staged. Since the reaction by-product water can be successively removed, the more stages the better. However, the structure of the equipment becomes complicated, the cost of the required equipment increases, and in view of the fact that such a reactor does not meet the object of the present invention, two to five stages are preferable. It is also possible to connect multiple reactors in series, as shown in Figure 3. In this case, multiple reactors can be stacked vertically, but from the viewpoint of construction and maintenance, it is preferable to place multiple reactors at the same height and send the reaction liquid obtained from the bottom of the reactor to the top of the next reactor using a liquid delivery pump. Since a high discharge pressure can be obtained by the liquid delivery pump, it is possible to use shower nozzles or spray nozzles to uniformly disperse the supply liquid even in reactors from the second stage onwards. In a multistage reactor or a configuration in which a plurality of reactors are connected in series, the organic solvent recovered from the fluid after the reaction may be used as an organic solvent to be subjected to the reaction together with the reaction raw materials, may be circulated to an upstream reactor, or may be further supplied to a downstream reactor.

[0035] FIG. 5 is a schematic diagram showing an example of a process for producing an unsaturated carboxylic acid ester. Acrylic acid and alcohol are supplied from raw material tanks (T31, T32) to a three-stage reactor (R31), and the organic solvent is sent from the tank (T33) to an evaporator (E31) to be converted into organic solvent vapor, which is then divided into three and supplied to the three-stage reactor (R31). The organic solvent and reaction by-product water vapor separated from each stage are condensed in condensers (E32-E34) and then separated into an aqueous layer and a solvent layer in a liquid storage tank (V31). The aqueous layer is discharged outside the system as wastewater, and the solvent layer is circulated to the tank (T33). The reaction fluid obtained from the bottom of the three-stage reactor (R31) is once collected in a storage tank (V32) and then sent to the light-boiling separation distillation column (D31). A stream mainly composed of organic solvent, raw alcohol, raw acrylic acid, etc. is obtained from the top of the light-boiling separation distillation column (D31) and circulated to the three-stage reactor (R31). Alternatively, a side cut is taken from a concentration section other than the top of the light-boiling separation distillation column (D31) to obtain an overhead distillation stream mainly composed of organic solvent and a side cut stream mainly composed of raw alcohol, etc., and the overhead distillation stream can be circulated to a tank (T33) and the side cut stream can be circulated to the three-stage reactor (R31) (not shown). A stream mainly composed of acrylic ester obtained from the bottom of the light-boiling separation distillation column (D31) is sent to the purification distillation column (D32), and a purified acrylic ester is obtained from the top. In addition, a distillation column or an extraction device can be added arbitrarily for purification and valuable material recovery.

[0036] Figure 6 is a schematic diagram of an experimental apparatus for producing an unsaturated carboxylic acid ester. It consists of a solvent container (G41), a solvent delivery pump (P41), a heater for solvent evaporation (E41), a container for a mixed liquid of acrylic acid, alcohol, and a polymerization inhibitor (G42), a mixed liquid delivery pump (P42), a glass device at the inlet of the reactor (G43), a glass device at the reaction section (G44) filled with a solid catalyst, a glass device at the outlet (G45) for gas-liquid separation of the reaction fluid and condensation of the separated gas, and a thermocouple (TI41) bundled together to measure the temperature inside the reactor. The glass device at the reaction section (G44) is a jacketed double tube, and a high-temperature heat transfer medium (f51) is passed through the jacket section. Cold water (f53) is passed through the cooling section of the glass device at the outlet (G45). The process liquid (f45) consisting of the produced ester and condensed solvent is collected in a receiver (not shown), and the gas condensate (f46) consisting of uncondensed solvent and reaction by-product water is also collected in a different receiver (not shown). The nozzles (PI41, PI42) installed in the inlet glass device (G43) and the outlet glass device (G45) are connected to pressure gauges, and the ... It is controlled by a pressure valve (not shown). A small amount of nitrogen is supplied from (f43) to replace the nitrogen in the system at the start of operation and to avoid explosive composition in the vacuum system while operation continues.

[0037] [Example 1] (Dehydration of solid catalysts) As a solid catalyst, a porous strongly acidic ion exchange resin, PK216 (H type, Mitsubishi Chemical), was used. The resin was soaked in tetrahydrofuran, packed into a glass column, and toluene was passed through the column to remove the water contained therein.

[0038] An esterification reaction was carried out using the apparatus shown in FIG. 6. The reaction section glass apparatus (G44) (inner diameter 2 cm) was filled with 60 cm of the above-mentioned dehydrated porous strong acid ion exchange resin. 3The pressure in the inlet glass device (G43) was adjusted to 50 kPa, and the toluene in the solvent container (G41) was evaporated at a rate of 34.8 g / hour by the solvent evaporation heater (E41) and supplied to the inlet glass device (G43). The heat medium for the external circulation was set to 99°C. Cold water at 5°C was circulated in the gas cooling section. The operation was continued for 2 hours until the temperature in the catalyst layer became constant and the condensate no longer contained moisture. When the internal pressure in the device (G44) was within ±1% of the specified pressure for at least 60 minutes, the internal temperature fluctuation was 0.3°C or less.

[0039] While maintaining the reaction pressure and the flow rate of toluene, a mixed solution containing acrylic acid, an equimolar amount of 2-ethylhexanol, and 300 ppm by weight of hydroquinone as a polymerization inhibitor was then placed in the mixed solution container (G42) and the supply was started. The temperature in the catalyst layer quickly stabilized at 93°C to 94°C at both the inlet and outlet, and the composition at the reactor outlet reached a steady state about 2 hours after the start of the supply of raw materials. The experiment was continued for up to 6 hours, but no difference was observed in the reaction conversion rate. The results are shown in the table below.

[0040] [Table 1]

[0041] The conversion rate of acrylic acid was 80.0%. While repeating the same experiment, the position of the thermocouple was changed to check the temperature inside the catalyst layer, but the temperature inside the layer was found to be almost constant.

[0042] [Example 2] An esterification reaction was carried out in the same manner as in Example 1, except that the pressure in the inlet glass unit (G43) was adjusted to 40 kPa. The temperature in the catalyst layer was constant at about 85°C, and the reaction conversion rate of acrylic acid was 74.8%.

[0043] [Comparative Example 1] The same procedure as in Example 1 was followed, except that after dehydration of the ion exchange resin by passing toluene vapor through it, the pressure in the inlet glass device (G43) was increased to about 65 kPa, and the solvent toluene was supplied as droplets at 90°C to 95°C. The esterification reaction was carried out, and gas-liquid mixture was observed in the catalyst layer. Although it was possible to visually confirm that the flow was laminar, the reaction conversion rate was less than 50%. The temperature at the inlet and outlet of the catalyst layer was about 93°C, but when a thermocouple was moved to check, it was confirmed that the temperature was below 60°C at the inlet side.

[0044] [Comparative Example 2] In the same manner as in Example 1, the ion exchange resin was dehydrated by passing toluene vapor through it, and then 2-ethylhexanol and hydroquinone were fed in an amount equimolar to the raw material acrylic acid, and the raw material feed was continued for 2 hours to carry out an esterification reaction. The reaction conversion rate of acrylic acid at this time was 80.4%. Next, the esterification reaction was continued while maintaining the pressure in the inlet glass device (G43) at 50 kPa, and the toluene flow rate of the solvent liquid pump (P41) was gradually reduced and reached zero over one hour. An increase in the liquid ratio in the catalyst layer was confirmed by visual inspection. Because the amount of liquid held in the catalyst layer changed, the outlet flow rate of the reactor was not stable until it approached a steady state, and the reaction conversion rate could not be calculated. Four hours after the supply of toluene reached zero, the amount of toluene discharged from the reactor outlet was less than 0.3 g / hour, and the reaction conversion rate of acrylic acid had dropped to about 35%. [Explanation of symbols]

[0045] C1, C11, C21, C22, C41 solid catalyst D31 Light boiling separation distillation column D32 Purification distillation column E1 Heater E11, E31 evaporator E32~35, E37 Condenser E36, E38 reboiler E41 Solvent evaporation heater G41 Solvent Container G42 Mixed liquid container G43 Entrance glass device G44 Reaction glass apparatus G45 Exit glass device J21 Perforated plate P31~P39 Liquid delivery pump P41 Solvent Delivery Pump P42 Mixed liquid delivery pump PI41, PI42 nozzles R1 Multi-tube reactor R11 Reactor R21A Upper mirror section R21B 1st stage reaction section R21C Intermediate connection R21D 2nd stage reaction section R21E Lower Mirror Section R31 Three-stage reactor T31, T32, T33 Tanks TI41 Thermocouple V31~V34 Liquid storage tank f1, f11, f21 supply liquid f2, f12, f22 liquid flow f3, f13, f23B gas flow f4, f14, f51 heating medium f16 Organic solvents f26A, f26B Organic solvent vapor f23A Gas stream consisting of organic solvent and reaction by-product water f43 Nitrogen f45 process fluid f46 condensate f47 vacuum line f53 cold water

Claims

1. 1. A method for producing an unsaturated carboxylic acid ester by an esterification reaction between an unsaturated carboxylic acid and an alcohol using a reactor packed with a solid catalyst, comprising the steps of: The method includes the steps of continuously supplying an unsaturated carboxylic acid and an alcohol to the reactor through an inlet of the reactor to form a reaction liquid fluid in the reactor, and continuously supplying a vaporized organic solvent into the reactor through an inlet of the reactor in parallel flow, the unsaturated carboxylic acid is selected from acrylic acid and methacrylic acid; The method for producing an unsaturated carboxylic acid ester, wherein the organic solvent is an aliphatic hydrocarbon or an aromatic hydrocarbon.

2. The method for producing an unsaturated carboxylic acid ester according to claim 1 , wherein the boiling point of the organic solvent at atmospheric pressure is lower than the boiling point of the unsaturated carboxylic acid at atmospheric pressure.

3. The method for producing an unsaturated carboxylic acid ester according to claim 1 or 2, wherein the organic solvent is toluene.

4. The method for producing an unsaturated carboxylic acid ester according to any one of claims 1 to 3, wherein the reactor is a vertical reactor and the reaction liquid fluid is a downflow.

5. 1. A method for producing an unsaturated carboxylic acid ester by an esterification reaction between an unsaturated carboxylic acid and an alcohol using a reactor packed with a solid catalyst, comprising the steps of: continuously supplying vaporized organic solvent to the reactor in parallel flow through an inlet of the reactor; and After the internal pressure of the reactor has been maintained at within ±5% of the predetermined pressure for at least 30 minutes, continuously supplying the unsaturated carboxylic acid and the alcohol to the reactor through an inlet of the reactor, the unsaturated carboxylic acid is selected from acrylic acid and methacrylic acid; The method for producing an unsaturated carboxylic acid ester, wherein the organic solvent is an aliphatic hydrocarbon or an aromatic hydrocarbon.

6. 6. The method for producing an unsaturated carboxylic acid ester according to claim 5, further comprising the step of: continuously supplying the unsaturated carboxylic acid and the alcohol to the reactor through an inlet of the reactor after the internal temperature of the reactor has continued to fluctuate for at least 30 minutes with a fluctuation range of 0.5°C or less.

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