JP2010241765A - Method for producing carboxylic acid ester - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for industrially efficiently producing the corresponding carboxylic acid ester from an aliphatic carboxylic acid and an aliphatic alcohol at a low cost. <P>SOLUTION: The method for producing the corresponding carboxylic acid ester by reacting an aliphatic carboxylic acid with an aliphatic alcohol in the presence of a catalyst comprises a step A of reacting the aliphatic carboxylic acid with the aliphatic alcohol in a reaction vessel; a step B of supplying the reaction solution obtained in the step A to a distillation column, distilling off the produced carboxylic acid ester and secondarily produced water from the top of the column, and recovering unreacted aliphatic carboxylic acid from the bottom of the distillation column; and a step C of recirculating the unreacted aliphatic carboxylic acid recovered in the step B to the step A. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing a corresponding carboxylic acid ester by reacting an aliphatic carboxylic acid with an aliphatic alcohol. Carboxylic acid esters are useful compounds as solvents and raw materials for organic synthetic products.

  As a method for producing a carboxylic acid ester, a method in which a carboxylic acid and an alcohol are reacted in the presence of a catalyst is known. For example, Japanese Patent Application Laid-Open No. 2001-302585 discloses an aliphatic carboxylic acid having 2 to 5 carbon atoms and an aliphatic alcohol having 2 to 5 carbon atoms under the condition that the latter is in excess of the stoichiometric reaction amount. An azeotrope composed of a three-component composition of ester / water / alcohol by continuously feeding to a reaction zone, reacting them in the presence of an esterification catalyst, and distilling the resulting reaction crude liquid with water replenishment Is continuously produced, and an ester is obtained from this azeotropic mixture through a phase separation operation.

  However, in the above method, in order to supply alcohol excessively to the reaction system, in the step of purifying the obtained ester, alcohol having a boiling point lower than that of the ester is distilled together with the target product ester in the distillation column. It is necessary to distill from the top. Moreover, not only is it necessary to further distill and separate alcohol from the resulting distillate, but water is added to the reaction crude liquid for distillation, so that the amount of energy required for distillation is extremely large.

JP 2001-302585 A

Accordingly, an object of the present invention is to provide a method for industrially efficiently producing a corresponding carboxylic acid ester from an aliphatic carboxylic acid and an aliphatic alcohol at a low cost.
Another object of the present invention is to provide a method capable of producing a carboxylic acid ester with a small amount of energy consumption.

  As a result of intensive investigations to achieve the above object, the inventors of the present invention supplied a reaction liquid of an aliphatic carboxylic acid and an aliphatic alcohol to a distillation column, and the carboxylic acid ester generated from the top of the column and a byproduct. That the unreacted aliphatic carboxylic acid is recovered from the bottom of the column, and the recovered aliphatic carboxylic acid is recycled to the reactor to efficiently produce a carboxylic acid ester industrially. The headline and the present invention were completed.

  That is, the present invention is a method for producing a corresponding carboxylic acid ester by reacting an aliphatic carboxylic acid and an aliphatic alcohol in the presence of a catalyst, wherein the aliphatic carboxylic acid and the aliphatic alcohol are reacted in a reactor. The reaction solution obtained in the step A and the reaction solution obtained in the step A is supplied to the distillation column, the carboxylic acid ester generated from the top of the column and the by-product water are distilled off, and unreacted aliphatic from the bottom of the column. Provided is a method for producing a carboxylic acid ester, comprising: a step B for recovering a carboxylic acid; and a step C for recycling the unreacted aliphatic carboxylic acid recovered in the step B to the step A.

  In this production method, in Step A, it is preferable to supply the aliphatic carboxylic acid and the aliphatic alcohol to the reactor under conditions that the former is excessive.

  This production method may further include a step D in which at least a part of the stream distilled from the top of the distillation column in the step B is treated with an alkaline aqueous solution to neutralize a trace amount of acid.

  According to the production method of the present invention, a reaction liquid obtained by reacting an aliphatic carboxylic acid and an aliphatic alcohol in the presence of a catalyst is supplied to a distillation column, and by-produced with a carboxylic acid ester generated from the top of the column. Since water is distilled off, unreacted aliphatic carboxylic acid is recovered from the bottom of the column and recycled to the reaction step, the utilization rate of aliphatic carboxylic acid can be increased. Further, since a strong acid catalyst is usually used as the catalyst, the strong acid catalyst can be recovered from the tower bottom together with the unreacted aliphatic carboxylic acid and recycled to the reaction step, so that the catalyst can be effectively used. In addition, since it is possible to remove the strong acid catalyst at an early stage of the process, it is possible to prevent the decomposition of the target compound based on the shift of the equilibrium state by the strong acid catalyst and the progress of the side reaction using the strong acid as a catalyst in the later process. This eliminates the need for equipment using high-grade materials having high durability in the subsequent process, and thus reduces initial investment or avoids additional investment associated with equipment replacement. Furthermore, by using an excess amount of the aliphatic carboxylic acid relative to the aliphatic alcohol, it is not necessary to distill a large amount of alcohol together with the carboxylic acid ester in the purification step of the produced carboxylic acid ester, and water is added. However, it is not necessary to distill, and furthermore, by separating the distillate, the carboxylic acid ester and water can be easily separated, so that the amount of energy used can be greatly reduced. Since the excessively used aliphatic carboxylic acid is recovered from the bottom of the distillation column and recycled to the reaction process, the energy required for recovery is very small. Therefore, according to the present invention, the carboxylic acid ester can be industrially efficiently produced at a low cost.

It is a schematic flowchart which shows an example of the manufacturing method of carboxylic acid ester of this invention.

  In the present invention, an aliphatic carboxylic acid and an aliphatic alcohol are reacted in the presence of a catalyst to produce a corresponding carboxylic acid ester.

  Examples of the aliphatic carboxylic acid used as a raw material include saturated aliphatic carboxylic acids having 2 to 5 carbon atoms such as acetic acid, propionic acid and butanoic acid; unsaturated fatty acids having 2 to 5 carbon atoms such as acrylic acid and methacrylic acid. Group carboxylic acid. Aliphatic carboxylic acids can be used alone or in combination of two or more. On the other hand, examples of the aliphatic alcohol used as a raw material include C2-C5 aliphatic alcohols such as ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, and amyl alcohol. The aliphatic alcohols can be used alone or in combination of two or more. A preferred combination of the aliphatic carboxylic acid and the aliphatic alcohol is a combination in which the carboxylic acid ester to be produced has a lower boiling point than that of the starting aliphatic carboxylic acid. More specifically, for example, a combination of acetic acid and ethanol, n-propyl alcohol or isopropyl alcohol is preferable, and a combination of acetic acid and ethanol is particularly preferable. In addition, the present invention has a great effect when the boiling point of the aliphatic alcohol is lower than the boiling point of the aliphatic carboxylic acid.

  When impurities (especially low-boiling components) are contained in the aliphatic carboxylic acid and aliphatic alcohol used as raw materials, the impurities or by-products resulting from the impurities are separated and removed in the carboxylic acid ester purification process. In doing so, a considerable amount of the carboxylic acid ester is lost. Therefore, in order to reduce the loss of the target product, if the aliphatic carboxylic acid or aliphatic alcohol used as a raw material contains a large amount of impurities, it must be distilled or other purification means in advance before being subjected to the reaction. It is preferable to purify by. In addition, as the aliphatic carboxylic acid and the aliphatic alcohol used as raw materials, the aliphatic carboxylic acid and the aliphatic alcohol recovered from the subsequent purification step can be respectively recycled.

  In step A of the present invention, the aliphatic carboxylic acid and the aliphatic alcohol are supplied to the reactor and reacted. The reactor is not particularly limited, and may be any of a stirred tank reactor, a tower reactor, a packed tower reactor (for example, a reactor filled with an ion exchange resin, etc.) and the like. The supply ratio of the aliphatic carboxylic acid to the aliphatic alcohol is not particularly limited, but it is preferable to supply the aliphatic carboxylic acid to the reactor under the condition that the aliphatic carboxylic acid is excessive with respect to the aliphatic alcohol. By using the aliphatic carboxylic acid excessively with respect to the aliphatic alcohol in this way, it is not necessary to distill a large amount of unreacted alcohol in the subsequent carboxylic acid ester distillation step, and the amount of energy used can be reduced. Moreover, since excess aliphatic carboxylic acid is collect | recovered from the tower bottom in the next distillation process, and is further recycled to a reactor, it is not necessary to use much energy. In step A, the supply ratio (molar ratio) of the aliphatic carboxylic acid and the aliphatic alcohol to the reactor is preferably excessive in the former (for example, the former is 1.2 times or more moles, preferably 1.8 times the latter). More preferably, the former: the latter (molar ratio) = 1.8 to 4.0: 1, and more preferably the former: the latter (molar ratio) = 2.0 to 3.5: 1. It is a range.

  A known esterification catalyst can be used as the catalyst. Examples of esterification catalysts include mineral acids such as sulfuric acid; benzenesulfonic acid, p-toluenesulfonic acid (PTS), p-octylbenzenesulfonic acid (OBSA), dodecylbenzenesulfonic acid (DBSA), naphthalenesulfonic acid, methanesulfone. Sulfonic acids such as acids (MSA), ethanesulfonic acid, trifluoromethanesulfonic acid; salts of these acids with organic bases (for example, pyridinium p-toluenesulfonic acid (PPTS)); strongly acidic ion exchange resins; magnesium chloride , Aluminum chloride, titanium tetrachloride; solid acid catalyst and the like. Among these, p-toluenesulfonic acid (PTS), sulfuric acid, and strong acidic ion exchange resin are preferable, and p-toluenesulfonic acid (PTS) and strong acidic ion exchange resin are particularly preferable.

  The amount of catalyst used varies depending on the type, but is 0.01 to 5% by weight, preferably 0.05 to 2% by weight, for example, based on the total amount of aliphatic carboxylic acid and aliphatic alcohol fed to the reactor. Degree.

  As the reaction conditions other than the supply ratio in step A, generally usual conditions in the esterification reaction can be adopted. For example, although reaction temperature changes with raw materials, it is 60-140 degreeC generally, Preferably it is 70-100 degreeC, More preferably, it is 65-95 degreeC. The reaction may be performed under reduced pressure, normal pressure, or increased pressure, but normal pressure is preferred from the viewpoint of operability and the like. The reaction time (residence time in the reactor) is usually about 3 to 120 minutes (for example, 3 to 30 minutes).

  In the present invention, most of the reaction is performed in step A, and the remaining reaction is performed in step B. In step A, the reaction may be completed completely. The conversion rate of the aliphatic alcohol in the step A is usually 70 to 100%, preferably about 80 to 100% (for example, 80 to 90%).

  In the step B of the present invention, the reaction liquid obtained in the step A is supplied to a distillation column, and a carboxylic acid ester generated from the top of the column and water produced as a by-product are distilled off, and an unreacted aliphatic carboxylic acid is discharged from the column bottom. The acid is recovered. When the catalyst is dissolved or dispersed in the reaction solution, the catalyst is also supplied to the distillation column, so that the reaction further proceeds in the distillation column. When the catalyst is an ion exchange resin or a solid acid catalyst and is used in a form packed in a reactor, the catalyst is not supplied to the distillation column, but the acid partially liberated from the catalyst is transferred to the distillation column. Sometimes supplied. Thus, when the reaction is also performed in the distillation column, the reaction is performed while distilling off the water produced as a by-product in the reaction, so that the equilibrium of the reaction is inclined toward the product side, the reaction proceeds efficiently, and the acid proceeds. A crude carboxylic acid ester having a low value is obtained. In addition, when an excessive amount of aliphatic carboxylic acid is used, the amount of unreacted aliphatic alcohol is small, so that the energy consumed for distilling off the alcohol can be greatly reduced, and water can be used as in the prior art. Since it is not necessary to add, the energy can be reduced accordingly.

  The reaction in the distillation tower in the step B (when the catalyst is supplied to the distillation tower) is performed in a region (reaction zone) where the catalyst below the reaction liquid supply position obtained in the step A exists. The raw material aliphatic carboxylic acid (which may be recycled aliphatic carboxylic acid) and aliphatic alcohol (which may be recycled aliphatic alcohol) may also be supplied to this reaction zone, respectively. it can. In particular, when the aliphatic alcohol is supplied to the reaction zone of the distillation column, the reaction efficiency is improved. In this case, the supply amount of the aliphatic alcohol to the reaction zone of the distillation column is about 10 to 30 parts by weight with respect to 100 parts by weight of the reaction solution supply amount to the distillation column. In addition, an evaporator may be provided in the distillation tower, the reaction liquid obtained in the step A may be supplied to the evaporator, and the obtained vapor may be charged into the distillation tower. In this case, the evaporator functions as the bottom of the distillation column and becomes a reaction zone (when the catalyst is supplied to the distillation column). The liquid at the bottom of the distillation column is returned to the evaporator, and unreacted aliphatic carboxylic acid (usually including the catalyst when the catalyst is supplied to the distillation column) is recovered from the evaporator.

  The conversion rate of the aliphatic alcohol through the process A and the process B is usually 75 to 100%, preferably 80 to 100%. Unreacted aliphatic carboxylic acid is withdrawn from the bottom of the distillation column. In the present invention, the recovered aliphatic carboxylic acid is recycled to the reactor, and a step is provided in which a part of the recovered aliphatic carboxylic acid is recycled as it is or as appropriate to the reaction zone of the distillation column in Step B. May be.

  The type of distillation column in step B is not particularly limited, and may be any of a packed column, a plate column, a bubble bell column, and the like. The number of stages of the distillation column is, for example, 10 to 100 theoretical plates, preferably 20 to 60 theoretical plates, and the pressure during distillation is usually normal pressure, but may be distilled under reduced pressure or increased pressure. The reflux ratio can be appropriately selected in consideration of the separation efficiency (mainly the separation efficiency between the carboxylic acid ester and the unreacted aliphatic carboxylic acid), the liquid separation property of the distillate, the energy cost, and the like.

  In Step C of the present invention, the unreacted aliphatic carboxylic acid recovered in Step B is recycled to Step A. The recovered unreacted aliphatic carboxylic acid usually contains a catalyst (note that the catalyst is an ion exchange resin or a solid acid catalyst and is used in a form packed in a reactor. In some cases, the catalyst is usually not included). The recovered unreacted aliphatic carboxylic acid may be recycled to the process A together with the catalyst, or may be appropriately purified and recycled to the process A.

  The stream (distillate) distilled from the top of the distillation column in step B may be a single layer depending on the conditions, but is often separated into two layers. In particular, when an excessive amount of aliphatic carboxylic acid is used in the reaction, since the amount of unreacted aliphatic alcohol that is easily dissolved in water during distillation is extremely small, a distillate in a distillation column is usually generated. It is easily separated into an organic layer mainly composed of the carboxylic acid ester and an aqueous layer mainly composed of by-produced water. Therefore, it is possible to efficiently recover the carboxylic acid ester from this organic layer.

  The flow (distillate) distilled from the top of the distillation column in the step B may contain a small amount of acid. For this reason, at least a part of the stream distilled from the top of the distillation column, preferably an organic layer (carboxylic acid ester layer) obtained by separating the distilled stream is treated with an alkaline aqueous solution to produce the trace amount of acid. You may provide the process D which neutralizes a part. By providing this step D, it is possible to more reliably prevent the decomposition of the target compound based on the shift of the equilibrium state by the strong acid catalyst and the progress of the side reaction using the strong acid as a catalyst in the later process, and it is high in the later process. Equipment that uses high-quality materials with durability is completely unnecessary, and equipment costs can be greatly reduced.

  Examples of the alkali aqueous solution used for the neutralization include an aqueous solution of an alkali metal hydroxide such as an aqueous sodium hydroxide solution and an aqueous potassium hydroxide solution; an aqueous solution of an alkali metal carbonate such as an aqueous sodium carbonate solution; an alkali such as an aqueous sodium hydrogen carbonate solution. An aqueous solution of a metal hydrogen carbonate; an aqueous solution of an alkaline earth metal hydroxide such as an aqueous magnesium hydroxide solution. Among these, an aqueous solution of an alkali metal hydroxide such as an aqueous sodium hydroxide solution is preferable.

  The alkali concentration in the aqueous alkali solution is, for example, about 1 to 40% by weight, preferably 2 to 30% by weight, and more preferably about 5 to 20% by weight.

  You may perform the process by aqueous alkali solution in multiple times. It is preferable to repeat the treatment until the pH of the aqueous layer becomes 7 or more. Further, the treatment with the aqueous alkali solution is carried out until the acid content (in terms of acetic acid) in the treated organic layer (carboxylic acid ester layer) is, for example, 0.01% by weight or less, particularly 0.001% by weight or less. desirable.

  After the treatment with the alkaline aqueous solution, it may be washed with water as necessary.

  The crude carboxylic acid ester thus obtained is further subjected to conventional purification means to produce a product. Examples of the purification means include purification using a distillation column (rectification column). The distillation tower is not particularly limited, and may be any of a packed tower, a plate tower, a bubble bell tower, and the like. The number of stages of the distillation column is, for example, 5 to 100 theoretical plates, preferably 10 to 80 theoretical plates, and the pressure during the distillation is usually normal pressure, but may be distilled under reduced pressure or increased pressure. This purification step may be composed of a low boiling point step for separating and removing low boiling point components and a high boiling point step for separating and removing high boiling point components, and a low boiling point component and a high boiling point component in one distillation column. And may be configured in one step of separating them simultaneously.

  FIG. 1 is a schematic flow diagram showing an example of a method for producing a carboxylic acid ester of the present invention. In this example, ethyl acetate is produced from acetic acid and ethanol. Carboxylic acid esters other than ethyl acetate can be basically produced according to this example, but may be appropriately changed depending on the physical properties (boiling point, solubility in water, etc.) of the raw materials and products. Hereinafter, the flow of FIG. 1 will be described.

  A raw material acetic acid is continuously supplied to the reactor 4 from the line 2, a raw material ethanol is supplied from the line 1, and a catalyst solution (for replenishment; if necessary) is continuously supplied from the line 3 to react. The catalyst solution (for replenishment) may be supplied to the distillation column bottoms line 8. The reaction solution was continuously supplied to the distillation column 6 through the line 5, and when the catalyst was supplied to the distillation column, the reaction was further progressed in the distillation column 6, and the reaction was generated from the top of the column through the line 7. Distill off ethyl acetate and water by-produced in the reaction. The distillate is separated by a decanter 9, and a part of the upper layer (organic layer; ethyl acetate is the main component) is refluxed to the distillation column 6, and the rest is supplied to the neutralization tank 14 through the line 11. An aqueous alkali solution is supplied to the neutralization tank 14 through a line 13 and stirred and mixed with the upper layer (organic layer) of the decanter 9 to transfer a trace amount of acid contained in the upper layer to the aqueous layer. The mixed solution is supplied to the decanter 16 through the line 15 and is allowed to stand to separate into an upper layer (ethyl acetate is the main component) and a lower layer (water is the main component and contains a small amount of ethanol). The upper layer (organic layer) of the decanter 16 is supplied to a reaction crude liquid tank 19 through a line 18 and further subjected to a purification process to obtain a product of ethyl acetate.

  The bottoms of the distillation column 6 [unreacted acetic acid and catalyst (if included)] are recycled to the reactor 4 via line 8. On the other hand, the lower layer (aqueous layer) of the decanter 9 and the lower layer (aqueous layer) of the decanter 16 are supplied to the alcohol recovery system through the line 12, the line 17 and the line 20, respectively, and recover ethanol. Part or all of the recovered ethanol is recycled to the reactor 4 through the line 21.

  Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited thereto.

Example 1
Ethyl acetate was produced according to the flow shown in FIG.
Feed rate ratio (molar ratio) in the starting material was ethanol: acetic acid = 1.0: 2.2, concentration of esterification catalyst (sulfuric acid) in starting material: 0.7 to 1.7% by weight, reactor Reaction temperature at 4: 70-80 ° C., reaction pressure: normal pressure, reaction time: pre-reaction in the reactor 4 was carried out for about 5 minutes. The obtained reaction liquid is charged into a distillation column 6 (number of stages: 60 stages), the produced ethyl acetate and by-produced water are azeotroped, and the condensed distillate is separated in a decanter 9, and all the lower layer liquids are separated. It was supplied to the alcohol recovery system, and the upper layer liquid was partially refluxed to the distillation column 6 and the rest was supplied to the neutralization tank 14. The can temperature of the distillation column 6 was 120 ° C., the top pressure of the distillation column 6 was normal pressure, and the liquid residence time in the distillation column 6 was about 1 hour.
The composition (component ratio; molar ratio) of the decanter 9 was ethanol: acetic acid: water: ethyl acetate = 0.12: 0.005: 0.28: 0.6. Moreover, the composition (component ratio; molar ratio) of the bottoms of the distillation column 6 was ethanol: acetic acid: water: ethyl acetate = 0: 0.998: 0.002: 0. The composition (component ratio; molar ratio) of the lower liquid of the decanter 9 was ethanol: acetic acid: water: ethyl acetate = 0.06: 0.001: 0.92: 0.02. Moreover, the weight ratio of the upper layer liquid of the decanter 9 supplied to the neutralization tank 14, the bottom liquid of the distillation column 6, and the lower layer liquid of the decanter 9 was 3: 3: 1 in this order. About the sulfuric acid which is a catalyst, the whole amount charged remained in the bottoms of the distillation column 6. This was recycled to reactor 4 along with unreacted acetic acid. The acid content (in terms of acetic acid) of the upper layer liquid of the decanter 9 was about 0.47% by weight.
The neutralization tank 14 to which the upper layer solution of the decanter 9 is supplied was charged with a 10% by weight aqueous sodium hydroxide solution so as to have a pH of 7, and neutralized and removed from the acid content. The same operation was performed on the upper layer liquid obtained by the liquid separation operation using the decanter 16 so that the pH would be 10 to 11. Thereafter, washing with water alone and a liquid separation operation were performed. The obtained process liquid [upper layer liquid of decanter 16 (after washing with water)] was sent to reaction crude liquid tank 19.
As a result, the acid content (in terms of acetic acid) in the process liquid is 0.0001% by weight, and this is a low value that does not require special consideration for the acid content in the subsequent steps. A material was sufficient. This process liquid was then rectified in a rectification column to obtain ethyl acetate as a product. The consistent yield from the reaction process was 98%.

Example 2
Ethyl acetate was produced according to the flow shown in FIG. A tower reactor was used as the reactor 4.
The supply ratio (molar ratio) in the starting material was ethanol: acetic acid = 1.0: 3.3, and the concentration of the esterification catalyst (paratoluenesulfonic acid: PTS) in the starting material: 0.7 to 1.7. Preliminary reaction in the reactor 4 was carried out under the conditions of% by weight, reaction temperature in the reactor 4: 70 to 80 ° C., reaction pressure: normal pressure, reaction time: about 10 minutes. As a result, the composition (component ratio; molar ratio) of the obtained reaction solution was ethanol: acetic acid: water: ethyl acetate = 0.33: 2.8: 2.4: 1.0.
The obtained reaction solution was charged into the evaporator of the distillation column 6 (stage number: 60 plates) equipped with an evaporator, and vapor was supplied to the distillation column 6 to azeotrope the produced ethyl acetate and by-product water. The condensed distillate is separated with a decanter 9, all the lower layer liquid is supplied to the alcohol recovery system, the upper layer liquid is partially refluxed to the distillation column 6, and the rest is reacted without treatment with an aqueous alkali solution. The solution was sent to the crude liquid tank 19. The lowermost liquid in the distillation column 6 was returned to the evaporator. The can temperature of the evaporator was 85 ° C., the top pressure of the distillation column 6 was normal pressure, and the liquid residence time in the distillation can was about 1 hour. In addition, about the PTS which is a catalyst, the whole quantity injected | thrown-in via the bottoms of the evaporator remained in the reaction liquid. The bottoms of the evaporator were recycled to the reactor 4.
As a result, the acid content (acetic acid equivalent) in the obtained process liquid [upper liquid of the decanter 9; the liquid in the reaction crude liquid tank 19] was 0.0003 wt%. Since it is a low numerical value that does not require consideration, it is sufficient to use a normal SUS material as the equipment material. This process liquid was then rectified in a rectification column to obtain ethyl acetate as a product. The consistent yield from the reaction process was 99.5%.

Example 3
Ethyl acetate was produced according to the flow shown in FIG. This example is an ethanol-excess system.
The feed ratio (molar ratio) in the starting material was ethanol: acetic acid = 2.2: 1.0, the concentration of the esterification catalyst (sulfuric acid) in the starting material: 0.7 to 1.7% by weight, reactor Reaction temperature at 4: 70 to 80 ° C., reaction pressure: normal pressure, reaction time: pre-reaction in the reactor 4 was carried out for about 10 minutes. The obtained reaction liquid was charged into a distillation column 6 (stage number: 60 stages), the produced ethyl acetate and by-produced water were azeotroped, and the condensed distillate was led to a decanter 9. Since the distillate contained a large amount of ethanol, it was not separated by the decanter 9. A part of the distillate was refluxed to the distillation column 6 and the remainder was supplied to the neutralization tank 14. The can temperature of the distillation column 6 was 120 ° C., the top pressure of the distillation column 6 was normal pressure, and the liquid residence time in the distillation column 6 was about 1 hour.
As a result, the liquid composition (component ratio; molar ratio) of the decanter 9 was ethanol: acetic acid: water: ethyl acetate = 0.56: 0.01: 0.07: 0.36. Moreover, the composition (component ratio; molar ratio) of the bottoms of the distillation column 6 was ethanol: acetic acid: water: ethyl acetate = 0: 0.97: 0.03: 0. The weight ratio of the decanter 9 liquid (distillation tower distillate) supplied to the neutralization tank 14 and the bottom liquid of the distillation tower 6 was 4: 1 in this order. The bottoms of the distillation column 6 was recycled to the reactor 4.
A neutralization tank 14 to which the decanter 9 liquid (distillation column distillate) is supplied is charged with a 10 wt% sodium hydroxide aqueous solution so that the pH becomes 7, and neutralization and removal of the acid content are performed. went. The same operation was performed on the upper layer liquid obtained by the liquid separation operation using the decanter 16 so that the pH would be 10 to 11. Thereafter, washing with water alone and a liquid separation operation were performed. The obtained process liquid [upper layer liquid of decanter 16 (after washing with water)] was sent to reaction crude liquid tank 19.
As a result, the acid content (in terms of acetic acid) in the process liquid is 0.0001% by weight, and this is a low value that does not require special consideration for the acid content in the subsequent steps. A material was sufficient. This process liquid was then rectified in a rectification column to obtain ethyl acetate as a product. The consistent yield from the reaction process was 96%.
In comparison with Example 1, in Example 3, the amount of unreacted ethanol in the reaction crude liquid containing the same amount of the target compound as Example 1 was 9 times, and this ethanol was purified and recovered. It takes a lot of energy.
From the above, it can be seen that Example 1 can prevent a decrease in the yield of the target compound without causing the acid content to act as a reverse reaction catalyst as compared with Example 3. Further, the amount of energy required for recovering unreacted raw materials can be reduced.

Example 4
Ethyl acetate was produced according to the flow shown in FIG. As the reactor 4, a packed tower (resin tower) type reactor filled with a strongly acidic ion exchange resin was used.
The feed ratio (molar ratio) in the starting material was ethanol: acetic acid: water: ethyl acetate = 1.0: 3.6: 1.8: 0.32, esterification catalyst (strongly acidic ion exchange resin: IER). The reaction in the reactor 4 was carried out under the conditions of the residence time of the process in the resin tower packed with: about 10 minutes, the reaction temperature: 60 ° C., and the reaction pressure: normal pressure. As a result, the composition (component ratio; molar ratio) of the obtained reaction solution was ethanol: acetic acid: water: ethyl acetate = 0.047: 0.44: 0.36: 0.15.
The obtained reaction liquid is charged into the distillation column 6 (stage number: 60 stages), the produced ethyl acetate and by-produced water are azeotroped, the condensate is separated in the decanter 9, and all the lower layer liquid is an alcohol recovery system. The upper liquid was partly refluxed to the distillation column 6 and the rest was sent to the reaction crude liquid tank 19 without being treated with an aqueous alkali solution. The bottoms of the distillation column 6 was cooled and returned to the reactor 4.
As a result, the acid content (acetic acid equivalent) in the obtained process liquid [upper liquid of the decanter 9; the liquid in the reaction crude liquid tank 19] was 0.0003 wt%. Since it is a low numerical value that does not require consideration, it is sufficient to use a normal SUS material as the equipment material. This process liquid was then rectified in a rectification column to obtain ethyl acetate as a product. The consistent yield from the reaction process was 99%.

DESCRIPTION OF SYMBOLS 1 Raw material alcohol supply line 2 Raw material carboxylic acid supply line 3 Catalyst solution supply (replenishment) line 4 Reactor 5 Reaction liquid line 6 Distillation tower 7 Distillation tower distilling line 8 Distillation tower can bottom liquid line 9 Decanter
10 Decanter upper liquid return line
11 Decanter upper liquid line
12 Decanter lower liquid line
13 Alkaline aqueous solution supply line
14 Neutralization tank
15 Mixed liquid line
16 Decanter
17 Decanter lower liquid line
18 Decanter upper liquid line
19 Reaction crude liquid tank
20 Recovery system supply line
21 Recovered alcohol line

Claims (3)

  A process for producing a corresponding carboxylic acid ester by reacting an aliphatic carboxylic acid and an aliphatic alcohol in the presence of a catalyst, wherein the aliphatic carboxylic acid and the aliphatic alcohol are reacted in a reactor. The step of supplying the reaction liquid obtained in the step A to the distillation column, distilling the carboxylic acid ester generated from the top of the column and the by-product water, and recovering the unreacted aliphatic carboxylic acid from the bottom of the column B and the process C which recycles the unreacted aliphatic carboxylic acid collect | recovered at the said process B to the said process A, The manufacturing method of the carboxylic acid ester characterized by the above-mentioned.   The process for producing a carboxylic acid ester according to claim 1, wherein in step A, the aliphatic carboxylic acid and the aliphatic alcohol are supplied to the reactor under the condition that the former is excessive.   Furthermore, the manufacturing method of the carboxylic acid ester of Claim 1 or 2 including the process D which processes the at least one part of the stream distilled from the distillation tower top in process B with alkaline aqueous solution, and neutralizes a trace amount acid content. .

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