JP2015140336A - Method for producing butyl acrylate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an efficient method for removing by-produced dibutyl ether in order to, in a production process of butyl acrylate, mitigate restrictions on an esterification reaction and a heat decomposition reaction, which are for suppressing by-production of dibutyl ether.SOLUTION: Provided is a method for continuously producing butyl acrylate, comprising: an esterification reaction step of obtaining a reaction mixture by an esterification reaction of acrylic acid and butanol in a reactor in the presence of an acid catalyst, and continuously separating the reaction mixture under reduced pressure into crude butyl acrylate and a volatile component; a distillation step of distilling the volatile component in a reactive distillation column, returning a discharge component to the reactor, separating a distillate component into an organic layer and an aqueous layer, and circulating the organic layer into the reactive distillation column; and a purification step of obtaining butyl acrylate by distillation purification of the crude butyl acrylate. In the distillation step, a part of the organic layer is distilled in a separation distillation column while forming two liquid layers of an aqueous layer and an organic layer by supplying water, and at least a part of a distillate component is removed out of the system.

Description

  The present invention relates to a process for continuously producing butyl acrylate from acrylic acid and butanol. Specifically, the present invention relates to a method for separating and removing dibutyl ether generated when butyl acrylate is continuously produced.

The most common method for producing commercial acrylic esters is an esterification reaction using acrylic acid and alcohol as raw materials. Most of them are liquid phase reactions, and organic acids and inorganic acids different from acrylic acid or ion exchange resins are used as homogeneous or heterogeneous catalysts.
Accompanying the esterification reaction, several side reactions also proceed. By-products by the side reaction include ethers by dehydration condensation of raw material alcohols, alkenes by intramolecular dehydration of raw material alcohols, addition of raw acrylic acid to the resulting acrylic ester, or acrylic acid dimer and raw material by dimerization of raw acrylic acid Examples include 3-acryloxypropionic acid ester obtained by esterification reaction with alcohol, and 3-alkoxypropionic acid ester obtained by adding a raw material alcohol to the produced ester.

The generation of these impurities causes a deterioration in economic efficiency due to the deterioration of the raw material basic unit, so it is desirable that the generation of impurities be less. For this reason, temperature, pressure, concentration, molar ratio, catalyst type, etc. Improvements have been made.
For example, Patent Document 1 discloses a method in which sulfuric acid is used as a catalyst for esterification reaction of acrylic acid and alcohol, alcohol is first separated from the reaction solution, and then sulfuric acid is separated.

Patent Document 2 describes the use of arylsulfonic acid as a catalyst for the esterification reaction between acrylic acid and alcohol, and the reuse of the catalyst.
On the other hand, it is known that by-products such as 3-alkoxypropionic acid ester and 3-acryloxypropionic acid ester can be recovered as raw acrylic acid, raw alcohol, and acrylic ester by thermal decomposition. Since the thermal decomposition reaction is usually performed at a higher temperature than the esterification reaction and in the presence of an acid catalyst, the formation of ethers and alkenes by the alcohol generated by the decomposition reaction is also accelerated. These side reactions of alcohol include a problem of a decrease in alcohol recovery rate due to thermal decomposition.

Patent Document 3 discloses a method for suppressing by-production of alkenes and ethers by thermally decomposing the bottoms after esterification reaction of acrylic acid and alcohol in the presence of Lewis acid and water.
Patent Document 4 discloses a method of decomposing a heavy product produced by an esterification reaction of acrylic acid and alcohol with an aqueous alkali solution.

Patent Document 5 discloses that acrylic acid is added to and reacted with 3-alkoxypropionic acid ester by-produced by esterification reaction of acrylic acid and alcohol.
On the other hand, apart from suppressing the production of by-products, a method for distilling and separating once-produced by-products is also shown.

The impurities to be separated include those contained in the raw material and those produced by the reaction of the impurities in the raw material, in addition to the by-products from acrylic acid and alcohol. For example, acetic acid ester, propionic acid ester or maleic acid ester produced by the reaction of acetic acid, propionic acid or maleic acid contained in acrylic acid with raw material alcohol, isomer of alcohol contained in raw alcohol and raw acrylic acid Examples include isomers of acrylic acid esters produced by reaction, aldehydes such as furfural and benzaldehyde contained in raw acrylic acid, and ethers contained in raw alcohol.

Among these impurities, except for those which are very difficult to separate by distillation, such as isomers of acrylic acid esters and propionate esters, they are subject to distillation separation in the same manner as by-products.
In Patent Document 6, dibutyl ether contained in the low boiling point compound is obtained by distilling butyl acrylate produced by esterification reaction of acrylic acid and butanol, and then distilling and separating the low boiling point compound contained in the distillate. A method of distilling and separating equiimpurities in a further distillation column is shown.

  Patent Document 7 discloses a method of discarding a part of an organic layer distilled together with reaction product water by esterification reactive distillation.

JP-T-2001-504506 JP-A-6-287162 Japanese Laid-Open Patent Publication No. 5-25086 JP-A-57-62229 Japanese Patent Laid-Open No. 9-183753 Special Table 2002-507194 US Pat. No. 6,353,130

  However, in these conventional techniques, for example, the invention described in Patent Document 1 or 2 neither describes nor suggests removal of impurities by-produced during the production of the produced butyl acrylate. Although it is disclosed that the invention of Patent Document 3 suppresses by-products in the production of acrylate esters, it does not describe a method for removing once-produced by-products. Patent Document 4 is an invention for decomposing heavy substances, and there is no description about removal of light boiling components such as dibutyl ether. Patent Document 5 is an invention in which a once-produced by-product is reacted with another compound, and does not describe a method for removing the by-product from the system. Patent Documents 6 and 7 describe that dibutyl ether produced as a by-product in the production of acrylic ester is removed from the system, but does not disclose that valuables are efficiently returned to the reaction system. At the same time, valuables are removed from the system.

  As described above, in the prior art, by-products such as dibutyl ether generated in the continuous production method of butyl acrylate can be removed from the system by distillation together with the esterification reaction. By-products such as dibutyl ether Since the boiling point of this product is close to butanol and acrylic acid as raw materials, valuable materials are also removed from the system together with by-products such as dibutyl ether, and the production method is very low in productivity.

  The present invention has been made to solve the above conventional problems. That is, in a continuous production method of butyl acrylate, acrylic acid that can efficiently remove by-products such as dibutyl ether out of the system without losing valuable materials such as butyl acrylate and butanol as much as possible. It is an object to provide a method for continuously producing butyl.

  As a result of intensive studies to solve the above problems, the present inventor is a by-product in a method of continuously producing butyl acrylate using acrylic acid and butanol as raw materials while distilling volatile components in a reactive still. Impurities such as dibutyl ether are concentrated in an organic reflux liquid distilled in a reactive distillation column, the organic reflux liquid is further distilled under suitable conditions, and components containing a large amount of the above valuables and impurities such as dibutyl ether are removed. It was found that dibutyl ether can be efficiently removed out of the system without a large amount of valuables by separating it into components containing a large amount and removing components containing a large amount of impurities such as dibutyl ether out of the system.

The present invention has been achieved based on such findings, and the gist thereof is as follows.
[1] An esterification reaction step in which, in the presence of an acid catalyst, acrylic acid and butanol are converted into a reaction solution by an esterification reaction in the reactor, and the reaction solution is continuously separated into crude butyl acrylate and a volatile component under reduced pressure;
A distillation step of distilling the volatile component in a reactive distillation column, returning the bottom component to the reactor, separating the distillate component into an organic layer and an aqueous layer, and circulating the organic layer to the reactive distillation column; A purification step of obtaining butyl acrylate by distillation purification from the crude butyl acrylate,
A part of the organic layer in the distillation step is distilled in a separation distillation column while forming a two-liquid layer of an aqueous layer and an organic layer by supplying water, and at least a part of the distillate component of the separation distillation column is obtained. Continuous production method of butyl acrylate to be removed out of the system.
[2] The continuous production method of butyl acrylate according to [1], wherein the water is supplied by water vapor.
[3] The method for continuously producing butyl acrylate according to [1], wherein the liquid in the separation distillation column sampled from the bottom of the separation distillation column is a two-liquid layer.
[4] The continuous production method of butyl acrylate according to [1], wherein the pressure in the separation distillation column is 10 kPa to 95 kPa.

  According to the present invention, in a continuous production method of butyl acrylate, dibutyl ether produced as a by-product is removed out of the system as much as possible without losing valuable materials such as butyl acrylate and butanol. And high-purity butyl acrylate can be produced. As described above, high-efficiency butyl acrylate can be obtained without suppressing excessive reaction conversion rate and complicated by-product thermal decomposition method in the esterification reaction process, which has been conventionally performed to reduce the amount of dibutyl ether byproduct. Can be provided.

It is a figure which shows an example of the esterification reaction process and distillation process in this invention. It is a figure which shows an example of the process of carrying out the thermal decomposition of the refinement | purification process and by-product in this invention. It is a figure which shows an example of the processing method by the distillation tower of the organic layer in this invention. It is a figure which shows an example of the processing method by the distillation tower of the organic layer in this invention. It is a figure which shows the form of the Example in this invention.

Hereinafter, the method of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a flow sheet showing an example of an esterification reaction step and a distillation step in the continuous production method of butyl acrylate of the present invention.
Reactor (R1) at the most upstream side of reactors (R1 to R5) arranged in series with acrylic acid as raw material by line (1), butanol by line (2), and acid catalyst by line (3) ).

Examples of the acid catalyst include inorganic acids such as sulfuric acid, organic acids such as p-toluenesulfonic acid and methanesulfonic acid, and solid acids such as cationic ion exchange resins.
As the number of reactors increases, an efficient esterification reaction becomes possible. However, in consideration of problems such as complicated operation control due to an increase in equipment, the number of reactors is preferably 2-8. The reactor may be an individual container or may be divided into a plurality of reaction chambers by a partition plate. When divided into a plurality of reaction chambers, the reaction chamber 1 is converted into one reactor. In addition, you may employ | adopt the form with which butanol of a raw material is supplied to the reaction distillation column mentioned later, and is sent to a reactor through a line.

  Water produced by the esterification reaction is azeotroped with butanol and butyl acrylate by heating and sent to the reactive distillation column (C1) as a volatile component. Furthermore, by-products such as dibutyl ether produced by the side reaction accompanying the esterification reaction are also sent to the reactive distillation column (C1) as a volatile component. There may be one reactive distillation column for each reactor, or there may be one reactive distillation column for a plurality of reactors. The number of reactive distillation columns is preferably 1 to 4 and more preferably 2 to 4 in consideration of problems such as complicated operation control due to an increase in equipment as in the case of the reactor.

  Distilled components from the reactive distillation column are extracted by a recovery line (15), condensed by a condenser (E1), recovered by a decanter (D1), and separated into an organic layer and an aqueous layer. The organic layer is circulated to the reactive distillation column (C1) as a reflux liquid through a reflux line (16). By circulating the reflux liquid to the reactive distillation column (C1), by-products such as dibutyl ether having a boiling point close to those of valuable materials such as acrylic acid, butanol and butyl acrylate are concentrated in the reflux liquid.

The aqueous layer is recovered as a recovery liquid by the recovery line (17). Since the recovered liquid contains a small amount of butanol, it may be sent to a butanol separation column (not shown) for the purpose of separating and reusing butanol, and recovered after separating butanol. In addition, the bottom component from the reactive distillation column (C1) is returned to the reactor through the line (14).
The conditions for distillation in the second and subsequent reactive distillation columns (C2) and the like are the same as those in the reactive distillation column (C1).

  Although the reaction conversion rate of acrylic acid to butyl acrylate is higher in the downstream reactor, in the production of butyl acrylate, it is most difficult to separate and recover unreacted acrylic acid from the reaction system. In the downstream reactor, the reaction conditions are selected so that the reaction conversion rate reaches 95% or more. The reaction conversion rate is preferably as high as possible from the viewpoint of improving the acrylic acid raw material basic unit. However, if the reaction conversion rate is excessively increased, the increase of by-products increases rapidly, so the reaction conversion rate is 99.5. % Or less is preferable. Since butanol supplied to the reactor is excessive with respect to acrylic acid, the composition in the most downstream reactor is 5% to 15% by weight of butanol and 100% by weight of butyl acrylate and butanol. Also contain small amounts of acrylic acid, acid catalyst, and trace amounts of by-products.

  The higher the temperature, the higher the esterification reaction rate, which is more efficient. However, the polymerization of acrylic acid and butyl acrylate is more likely to occur, and the reaction rate of side reactions is relatively faster. Therefore, the temperature of the reactor is usually preferably in the range of 80 ° C to 110 ° C, and more preferably in the range of 85 ° C to 105 ° C. In order to perform distillation at the temperature of the reactor, it is necessary to reduce the pressure, and the pressure at the top of the reactive distillation column is preferably 10 kPa to 40 kPa.

FIG. 2 is a flow sheet showing an example of a purification step and a step of thermally decomposing by-products in the continuous production method of butyl acrylate of the present invention.
Crude butyl acrylate obtained from the most downstream reactor is supplied from the line (30) to the bottom of the acid catalyst recovery tower (C3), and water for acid catalyst recovery is from the line (31) near the top of the tower. Supplied. As the acid catalyst recovery tower (C3), an extraction tower having two or more theoretical plates is generally used, but a plurality of decanters in series or a combination of a decanter and an extraction tower may be used. At least a part of the acid catalyst recovered water obtained from the bottom of the acid catalyst recovery tower may be circulated to the esterification reaction step to reuse the contained acid catalyst.

As the water for acid catalyst recovery, it is preferable to use recovered water separated and recovered by the decanter (D1) or the like in the distillation step and other process waste water from the viewpoint of reducing the amount of waste water. In addition, it is preferable that the water for acid catalyst collection | recovery does not contain an alkali from a viewpoint of maintaining the activity of the acid catalyst used for a reuse.
The amount of acid catalyst recovery water is preferably as small as possible in order to reduce the thermal load of the reactors (R1 to R5) when reusing the acid catalyst, but if it is too small, the amount of acid catalyst to be reused is reduced. there's a possibility that. Therefore, the amount of water for acid catalyst recovery is preferably 1/5 to 1/30 by weight with respect to the amount of crude butyl acrylate.

The crude butyl acrylate from which the acid catalyst has been removed is supplied to the neutralization washing tower by the line (40), and the remaining acid catalyst and acrylic acid are washed by the washing water (42) supplied from the line (42). Is called. Alkaline water can be supplied from the line (41) in order to increase the cleaning efficiency.
As the neutralization washing tower (C4), an extraction tower having two or more theoretical plates is the most efficient. However, a plurality of series decanters or a combination of decanters and extraction towers are used. And washing water may be supplied to the downstream apparatus.

The remaining acid catalyst and the crude butyl acrylate from which acrylic acid has been removed are fed to the alcohol separation column (C5) via line (50). The distillate distilled from the top of the alcohol separation column (C5) is withdrawn through the line (52), condensed in the condenser (E3), and recovered in the reflux tank (D3). The recovered liquid contains separated butanol, and at least a part of the recovered liquid is circulated as a recovered butanol liquid to the esterification reaction step by the circulation line (54), and the other is the reflux line (53). Is circulated as a reflux liquid.
Crude butyl acrylate from which alcohol has been removed is discharged from the bottom of the alcohol separation column (C5) through the line (51), and a part of the butyl acrylate is heated and volatilized by the reboiler (B1), and the alcohol separation column (C5 ). The crude butyl acrylate from which the remaining alcohol has been removed is fed to the purification tower (C6) via the line (60). The purified butyl acrylate vapor distilled from the top of the purification column (C6) is condensed in the condenser (E4) and recovered in the reflux tank (D4). At least a part of the recovered liquid is circulated by the reflux line (63), and the others can be purified butyl acrylate by the recovery line (64).
A part of the bottoms (51) containing impurities having a boiling point higher than that of butyl acrylate is heated and volatilized by the reboiler (B2) and circulated to the purification tower (C6). 70) to the thermal decomposition apparatus (R7).

  An acid catalyst for promoting decomposition is supplied to the thermal decomposition apparatus (R7), and the bottoms supplied from the purification tower (C6) is thermally decomposed. The heat decomposition temperature is preferably in the range of 140 ° C to 220 ° C, and more preferably in the range of 150 ° C to 210 ° C. In the thermal decomposition apparatus (R7), water, acrylic acid, or the like may be supplied to the thermal decomposition apparatus (R7) in order to further suppress the generation of by-products such as dibutyl ether.

A decomposition recovery product containing butyl acrylate and butanol is obtained from the top of the thermal decomposition apparatus (R7), and at least a part thereof is circulated in the esterification reaction step. The bottoms from the bottom of the thermal decomposition apparatus (R7) is discharged out of the system.
FIG. 3 is a flow sheet showing an example of a method for treating an organic layer with a distillation tower in the method for continuously producing butyl acrylate according to the present invention.

Usually, the distillate from the reactive distillation column (C1) is extracted by the recovery line (15), condensed by the condenser (E1), and then separated into an organic layer and an aqueous layer by the decanter (D1), and the organic layer is refluxed. Although it circulates to the reactive distillation column (C1) as a reflux liquid by a line (16), in the present invention, a part is supplied to a separation distillation column (C8) by a line (80).
When there are a plurality of reactive distillation columns, the reflux liquid in the upstream reactive distillation column may have a higher dibutyl ether concentration, so it is preferable to supply the reflux liquid in the most upstream reactive distillation column to the separation distillation column. Further, the reflux liquid in each reactive distillation column, for example, a part of the reflux liquid in the reflux line (16) and the reflux line (28) in FIG. 1 may be mixed and supplied to the separation distillation column (C8). .

  The separation distillation column (C8) is preferably separated into a concentration section and a recovery section, and the number of theoretical plates in the concentration section is preferably 5 or more, more preferably 10 or more, and even more preferably 20 or more. The number of theoretical plates of the recovery unit is preferably 5 or more, more preferably 10 or more, and still more preferably 20 or more. If the number of theoretical plates in the concentrating section is small, the concentration of dibutyl ether in the distillate components of the separation distillation column will be insufficient, and the amount of butanol and butyl acrylate will increase, so the amount of dibutyl ether removed outside the system will decrease. In contrast, the amount of valuables such as butanol and butyl acrylate may increase.

There are no particular restrictions on the interpolated column of the separation distillation column (C8), and various types of plates, irregular packings, and regular packings can be used. However, packings having a large surface area per volume (specific surface area) or Irregular packing is preferred. The specific surface area is preferably 100 m ² / m ³ or more, more preferably 250 m ² / m ³ or more, and still more preferably 400 m ² / m ³ or more.
Examples of the regular packing include gauze type regular packing such as sulzer packing (manufactured by Sulzer Chemtech Co., Ltd.), techno pack (manufactured by Sansho Techno Co., Ltd.), mela pack (manufactured by Sulzer Chemtech Co., Ltd), Sheet type regular packing such as MC pack (manufactured by Mitsubishi Chemical Engineering Co., Ltd.), good roll packing (manufactured by Touto Quench Co., Ltd.) knitted by bundling metal wires, and the like. Examples of the irregular packing include cascade mini-rings, IMTP, interlocks (manufactured by Coke Glitch), and the like.

  The supply liquid supplied by the line (80) to the separation distillation column (C8) contains butyl acrylate, which is an easily polymerizable compound, so as to avoid clogging of the polymerization in the separation distillation column (C8). The bottom temperature of the separation distillation column is preferably less than 100 ° C, more preferably less than 80 ° C, and still more preferably less than 60 ° C. Reducing the column bottom temperature is achieved by reducing the pressure. The lower the pressure, the lower the bottom temperature, but the condensing temperature of the distillate obtained from the top of the tower is also low, making it difficult to condense. Therefore, the bottom pressure of the separation distillation column is in the range of 10 kPa to 95 kPa. The range of 10 kPa to 50 kPa is more preferable.

  When the bottom temperature of the separation distillation column is high, or when there is a concern about a temporary increase in the temperature in the column or the concentration of butyl acrylate in the column due to operational fluctuations, the risk of butyl acrylate polymerization increases. As a measure against this, it is preferable to supply a polymerization inhibitor to the separation distillation column (C8). Examples of the polymerization inhibitor to be supplied include phenolic compounds such as hydroquinone and methoquinone, copper or manganese complexes of dialkyldithiocarbamic acid such as 2,2-dibutyldithiocarbamic acid, 4-hydroxy-2,2,6,6-tetramethylpyridyl Examples thereof include nitroxyl radical compounds such as oxide, phenothiazine, and the like.

In order to use dibutyl ether having a boiling point close to that of butyl acrylate as a distillation component of the separation distillation column (C8), it is preferable to promote azeotropy of dibutyl ether and water. Specifically, water is supplied to the separation distillation column (C8), and the liquid layer in the separation distillation column is a water layer mainly composed of water, or a two-liquid layer of an organic layer and an aqueous layer is formed. In this state, distillation is performed while forming a two-component layer of an organic layer and an aqueous layer.

This state is maintained by continuously supplying a sufficient amount of water to the separation distillation column (C8). When water is not supplied or insufficient, the liquid layer is only an oil layer mainly composed of organic matter, and it may be difficult to separate dibutyl ether.
Although the supply location of water in the separation distillation column is not particularly limited, for example, the vicinity of the top of the column and the line (86) near the line (80) to which the organic layer is supplied can be mentioned. There may be one supply location or a plurality of supply locations. In addition, formation of the two liquid layer of the said organic layer and an aqueous layer can be confirmed from the liquid in the separation distillation tower sampled from the vicinity of the water supply location being a two liquid layer.
Furthermore, it is preferable that the liquid in the separation distillation column sampled from the bottom of the separation distillation column is a two-liquid layer in order to remove dibutyl ether stably and efficiently.

Although the water used for supply is not specifically limited, For example, it is preferable that the recovered water recovered by the decanter (D1) in the distillation step is included. Although other process wastewater can be used, it is preferably neutral to prevent hydrolysis reaction of butyl acrylate.
The distillate component distilled from the top of the separation distillation column (C8) is condensed by the condenser (E8) by the line (81), recovered by the decanter (D8), and separated into the organic layer and the aqueous layer. In order to increase the concentration of dibutyl ether, a part of the organic layer is circulated as a reflux liquid to the separation distillation column (C8) by the reflux line (82), and the other is removed out of the system as a discharge liquid by the discharge line (83). . The reflux ratio of the organic layer depends on the number of theoretical plates of the separation distillation column (C8), but is preferably at least 3 or more and more preferably 5 or more.

You may circulate at least one part of the water layer isolate | separated by the decanter (D8) to the separation distillation column (C8). Thereby, it becomes possible to reduce the water supplied to the separation distillation column (C8). The remainder of the water layer is removed out of the system by the discharge line (85) as discharged water, but a part of the discharged water may be circulated to the decanter (D1) of the distillation step.
The bottom component of the separation distillation column (C8) is discharged from the bottom, and a part thereof is heated and volatilized by the reboiler (B8) and circulated to the separation distillation column. The remaining canned components are combined with the low boiling components of the distillation process through a line (87) as a circulating liquid. As a result, valuable materials such as butyl acrylate and butanol contained in the circulating liquid can be recovered. The circulating destination of the circulating liquid is not limited to the merging with the low boiling component, and may be a reactive distillation column (C1).
By the above operation, the discharged liquid discharged out of the system in the discharge line is about dibutyl ether: butanol = 1: 3 to 3: 1 (weight ratio) and dibutyl ether / butyl acrylate> 5 (weight ratio). It becomes possible.

In addition, since this preferentially distills in the presence of butyl acetate, it is necessary to additionally extract about 0.2 to 0.5 weight times butanol with respect to butyl acetate.
FIG. 4 is a flow sheet showing an example of a method for treating an organic layer with a distillation tower in the method for continuously producing butyl acrylate according to the present invention.
Unlike the specification of FIG. 3, by supplying steam directly from the bottom of the separation distillation column (C9) through the steam line (94), it also serves as a heat source necessary for distillation and water necessary for promoting azeotropic distillation. ing. This specification reduces reboiler and water supply lines.

The component gas at the top of the separation distillation column is condensed in the condenser (E9) by the line (91), then passes through the reflux tank (D9), and partly circulates to the distillation column as a reflux liquid by the reflux line (92). The discharged liquid is removed out of the system through the discharge line (93). In FIG. 4, compared with FIG. 3, the two liquids are changed to be handled without being separated. This change can simplify the flow. In addition, in order to prevent a change in liquid feeding due to two-liquid separation in the reflux line (92) due to the change, mixing by stirring the liquid in the reflux tank (D9), a part of the reflux liquid is circulated to the reflux tank (D9) (illustrated). No mixing), mixing by installing a static mixer in the reflux line (92), and the like.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in more detail, the scope of the present invention is not limited to these.

[Thermal decomposition equipment]
The bottom of butyl acrylate purification tower, butyl acrylate 32%, 3-butoxypropionate butyl 62%, dibutyl ether less than 1 ppm, 1/10 times the amount of 13% p-toluenesulfonic acid aqueous solution was added. Under normal pressure, the reaction temperature was 180 ° C., and the valuable materials were decomposed by heating. The recovery rate with respect to the supply liquid was 71% in terms of acrylic acid and butanol. Among the components in the distillate, acrylic acid, butanol and butyl acrylate were used for conversion of the recovery rate. In the esterification reaction step at the circulation destination such as butyl 3-butoxypropionate, butyl acrylate was used. Those not involved in the generation of are not included. Dibutyl ether produced as a by-product at this time was 1.7% in terms of a molar ratio with respect to acrylic acid and butanol converted values of the recovered valuables.

When the thermal decomposition was similarly carried out by raising the temperature of the thermal decomposition by 3 ° C. and increasing the residence time by about 10%, the recovery rate with respect to the feed liquid increased to 79% in terms of acrylic acid and butanol. Dibutyl ether produced as a by-product at this time was 3.5% in terms of molar ratio with respect to the recovered valuables in terms of acrylic acid and butanol.
If converted only for the increased recovery, the by-produced dibutyl ether is 19% in terms of a molar ratio with respect to the recovered valuables in terms of acrylic acid and butanol. In order to maintain the quality of purified butyl acrylate, it is necessary to discharge the increased amount of by-product dibutyl ether out of the system, but in order to improve the raw material basic unit, The ratio needs to be smaller than this, that is, less than 5 times that of dibutyl ether, and in view of economy, it is preferably less than 3 times at most.

〔Experimental device〕
FIG. 5 is a schematic diagram of a distillation apparatus (separation distillation column) used for dibutyl ether distillation separation study.
A glass column having an inner diameter of 3 cm and a length of 120 cm was packed with a coil pack of 3 mmφ × 3 mm to obtain a distillation column. The number of theoretical plates under this experimental condition is about 20 plates. The liquid can be continuously supplied with a pump to a position 1/4 from the bottom of the packed bed.

A 1 L three-necked flask was used at the bottom of the column, and the liquid in the flask could be continuously extracted with a pump. The flask was heated in an oil bath, and a magnetic stirrer was used for stirring the liquid in the flask. In addition, a glass tube for supplying steam was inserted for steam distillation.
A condenser was provided on the distillation column, and the upper end of the condenser was connected to a vacuum pump. The condensate by the condenser can be adjusted by a branch pipe provided with a cock to circulate as a reflux liquid to the distillation column and to take out as a distillate to a receiver. In this apparatus, even when the condensate forms a two-liquid layer, the water layer and the organic layer can be distributed to the reflux liquid and the distillate without bias.

[Production of butyl acrylate]
An organic layer was obtained using the apparatus shown in FIGS. 1 and 2 under the following conditions.
Acrylic acid: butyl alcohol = 1.0: 1.05 (molar ratio), acrylic acid from line (1) and butyl alcohol from line (2) were continuously fed to the reactor (R1). A p-toluenesulfonic acid aqueous solution as an acid catalyst was supplied from the line (3). The reaction was carried out by sending the solution to the reactor (R1) and then to the reactor (R2). The internal temperature of the reactor (R1) was 86 ° C., and the internal temperature of the reactor (R2) was 88 ° C. Volatile components from the reactor (R1) and reactor (R2) are sent to the reactive distillation column (C1), the bottom component is returned to the reactor (R1), and the distillate component is a condenser ( It was condensed in E1) and recovered in a decanter (D1). The reactive distillation column (C1) was a 15-stage sieve tray, and the column top pressure was 25 kPa.

The canned component recovered by the decanter (D1) was separated into an organic layer and an aqueous layer. The organic layer was circulated to the reactive distillation column (C1). When the organic layer was analyzed, it was 20% butyl acrylate, 52% butanol, 7% water, 4% dibutyl ether and 17% butyl acetate.
On the other hand, the crude butyl acrylate discharged from the reactor (R2) was purified by distillation using a purification tower to obtain butyl acrylate.

[Comparative Example 1]
In Comparative Example 1, a part of the organic layer was distilled while being continuously fed by a pump from the bottom of the distillation column of the distillation apparatus (separation distillation column) to a position 1/4.
The pressure at the top of the separation distillation apparatus is 15 kPa, the reflux ratio is about 8, the distillation rate from the top is 18%, and distillation takes 0.5 hours until the temperature of the entire distillation apparatus is stabilized. Analysis of the distillate after continued distillation for a period of time revealed that the composition was an organic layer and was 0.3% by weight of butyl acrylate, 28.0% by weight of butanol, 4.5% by weight of water, 5.6% by weight of dibutyl ether. %, Butyl acetate 61.7% by weight, but in the aqueous layer, butanol 9.7% by weight, water 89.5% by weight, butyl acetate 0.8% by weight.
When the distillate is discarded, the raw material lost to dibutyl ether is 8.9 times in molar ratio.

[Comparative Example 2]
In Comparative Example 2, a part of the organic layer was distilled while being continuously fed by a pump from the bottom of the distillation column of the separation column to a position 1/4. Further, water was supplied from the top of the distillation column in an amount of 0.025 times the amount of the organic layer feed solution. As a result, the ratio of water in the distillate composition was in the range of 52 to 54%. Distillation was continued for 3.5 hours, but the temperature in the distillation apparatus, particularly the fluctuation of ± 1.5 ° C. or more continued in the column part. The distillate 3.5 hours after the start of distillation was analyzed. The composition of the organic layer was 0.3% by weight of butyl acrylate, 23.2% by weight of butanol, 3.7% by weight of water, 7.5% by weight of dibutyl ether, and 65.3% by weight of butyl acetate. When the reflux liquid was sampled from the vicinity of the water supply position and examined, it was not stable because it was one phase of the organic layer or two phases of the organic layer and the water layer. In addition, when the reflux liquid was sampled from the bottom of the column and examined, it was not stable because it was one phase of the organic layer or two phases of the organic layer and the aqueous layer.

When the distillate from the top of the column is discarded, the raw material lost to dibutyl ether is 5.6 times in molar ratio.
As a result, it was found that the amount of water supplied was sufficient to form an azeotropic composition with respect to the top distillate component, but the separation promotion of dibutyl ether was limited. This is a different result from distillation calculation based on physical properties such as vapor-liquid equilibrium and azeotropic composition.

[Example 1]
Distillation was carried out in the same manner as in Comparative Example 2 except that the amount of water supplied to the separation distillation column was increased to 0.1 times the amount of the liquid supplied to the organic layer. The temperature of the entire distillation apparatus was stabilized within 0.5 hour, and when the distillate was further distilled for one hour, the composition of the organic layer was butyl acrylate 0.4% by weight, butanol 15.2. % By weight, 2.4% by weight of water, 12.5% by weight of dibutyl ether, 69.5% by weight of butyl acetate, 6.5% by weight of butanol, 92.8% by weight of water, 0.7% of butyl acetate % By weight.

When the reflux liquid was sampled from the vicinity of the water supply position and examined, it was always in two phases, an organic layer and an aqueous layer.
When the organic layer of the distillate is discarded, the raw material lost with respect to dibutyl ether is 2.2 times in molar ratio.
From this, it became clear that the addition of a sufficient amount of water during the distillation separation significantly accelerates the separation of dibutyl ether.

[Example 2]
In the same manner as in Comparative Example 1, however, steam distillation was performed by supplying saturated steam at 100 ° C. to the flask. The supply amount of water vapor was kept constant, and the reflux ratio was adjusted to be in the range of 7.5 to 8.5. Distillation took 0.5 hour until the temperature of the entire distillation apparatus was stabilized, and when the distillate after continuing distillation for another hour was analyzed, the composition of the organic layer was 0.4% by weight of butyl acrylate, Butanol 17.0 wt%, water 2.5 wt%, dibutyl ether 11.1 wt%, butyl acetate 69.0 wt%.

Sampling at each location from the nozzles on the side and bottom of the distillation column confirmed the formation of two liquid layers at all locations.
When the organic layer of the distillate is discarded, the raw material lost with respect to dibutyl ether is 2.8 times in molar ratio.
As a result, it has been clarified that steam distillation, which also serves as a heat source, is also very effective for the separation of dibutyl ether as a water supply method during the distillation operation.

  According to the method for producing butyl acrylate of the present invention, by-product dibutyl ether can be removed out of the system with as little loss of valuables as butyl acrylate and butanol as much as possible. Since high-purity butyl acrylate can be produced continuously, the application field can be expanded.

R1, R2, R3, R4, R5 Reactor R7 Thermal decomposition apparatus B1, B2, B8 Reboiler C1, C2 Reactive distillation tower C3 Acid catalyst recovery tower C4 Neutralization washing tower C5 Alcohol separation tower C6 Purification tower C8, C9 Separation distillation tower D1, D2, D8 Decanter D3, D4, D9 Reflux tank E1, E2, E3, E4, E8, E9 Condenser

Claims (4)

In the reactor, an esterification reaction step in which acrylic acid and butanol are converted into a reaction solution by esterification reaction in the presence of an acid catalyst, and the reaction solution is continuously separated into crude butyl acrylate and volatile components under reduced pressure;
A distillation step of distilling the volatile component in a reactive distillation column, returning the bottom component to the reactor, separating the distillate component into an organic layer and an aqueous layer, and circulating the organic layer to the reactive distillation column; A purification step of obtaining butyl acrylate by distillation purification from the crude butyl acrylate,
A part of the organic layer in the distillation step is distilled in a separation distillation column while forming a two-liquid layer of an aqueous layer and an organic layer by supplying water, and at least a part of the distillate component of the separation distillation column is obtained. Continuous production method of butyl acrylate to be removed out of the system.   The method for continuously producing butyl acrylate according to claim 1, wherein the water supply includes water vapor.   The method for continuously producing butyl acrylate according to claim 1, wherein the liquid in the separation distillation column sampled from the bottom of the separation distillation column is a two-liquid layer.   The method for continuously producing butyl acrylate according to claim 1, wherein the pressure in the separation distillation column is 10 kPa to 95 kPa.

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