JP2013075844A - Method for obtaining aqueous acetonitrile with reduced water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for obtaining an aqueous acetonitrile with reduced amount of water from an aqueous acetonitrile.SOLUTION: In the method, an aqueous acetonitrile with reduced water is obtained from an aqueous acetonitrile containing water and acetonitrile. The method includes: a step (1) of mixing the aqueous acetonitrile with a 3-8C alkene; a step (2) of separating the mixture obtained in the step (1) into liquids in an upper layer and a lower layer; and a step (3) of collecting the liquid in the upper layer separated in the step (2).

Description

  The present invention relates to a method for obtaining water-containing acetonitrile with reduced water content, and more particularly, to a method for obtaining water-containing acetonitrile with reduced water content by removing a part of water from the water-containing acetonitrile.

  A method of using a mixed solvent of acetonitrile / water as a solvent when producing propylene oxide from propylene using hydrogen peroxide in the presence of a catalyst is known. For example, Patent Document 1 below discloses a method for obtaining propylene oxide by reacting propylene and hydrogen peroxide in a mixed solvent containing acetonitrile and water in a ratio of 50:50 by weight.

  In this method, since water is generated as a by-product from hydrogen peroxide, the amount of water in the mixed solvent increases. That is, when acetonitrile / water is used as a mixed solvent, the proportion of water in the mixed solvent increases due to the production of propylene oxide.

  Further, in Patent Document 2 below, in the method of obtaining propylene oxide by reacting propylene and hydrogen peroxide, the concentration of water in acetonitrile / water as a mixed solvent affects the production of propylene oxide, And when it contains excessively much water, it is disclosed that the production | generation rate of a propylene oxide becomes small. Therefore, if the excessively increased water is not removed, the proportion of water in the mixed solvent becomes too large to deviate from the desired range, which may adversely affect the reaction. It is necessary to remove some of the water from the water.

  As used herein, the term “hydrated acetonitrile” means a liquid mixture containing acetonitrile and water. When producing an alkene oxide from an alkene and hydrogen peroxide in a mixed solvent of acetonitrile / water, the mixed solvent is at least selected from the group consisting of alkene oxide and a polyhydric alcohol derived therefrom in addition to water and acetonitrile. A kind of organic compound may be contained, and in the present specification, hydrous acetonitrile may further contain such an organic compound. The water-containing acetonitrile may further contain remaining unreacted reaction raw materials.

JP 2003-327581 A JP 2009-256301 A

  As a method for obtaining water-containing acetonitrile with reduced water content from water-containing acetonitrile, there is a method in which water-containing acetonitrile is subjected to a distillation treatment to obtain water-containing acetonitrile with reduced water content. However, since this method uses a distillation process in which the water to be removed is taken out from the bottom of the column and the remainder is distilled, it consumes a large amount of energy and is not necessarily a satisfactory method. Therefore, it is desired to propose a new method for obtaining hydrous acetonitrile with reduced water content from hydrous acetonitrile.

  As a result of studying the above problems, the present inventors have reached the present invention.

The present invention provides a method for obtaining water-containing acetonitrile with reduced water content from water-containing acetonitrile containing water and acetonitrile.
Step (1) for mixing the water-containing acetonitrile containing water and acetonitrile and an alkene having 3 to 8 carbon atoms (hereinafter also referred to as “specific alkene”) (hereinafter also referred to as “mixing step (1)”) ),
Step (2) for separating the mixture obtained in step (1) into an upper layer and a lower layer (hereinafter also referred to as “liquid separation step (2)”), and collecting the upper layer separated in step (2) Step (3) (hereinafter also referred to as “upper layer recovery step (3)”)
including. In other words, the method of the present invention can also be called a method of removing a part of water contained in water-containing acetonitrile from water-containing acetonitrile.

  The upper layer in the liquid separation step (2) comprises acetonitrile, water and a specific alkene, and has a lower concentration in the water-containing acetonitrile (also referred to as “original water-containing acetonitrile”) to be dewatered in the mixing step (1). Contains water. On the other hand, the lower layer in the liquid separation step (2) similarly includes acetonitrile, water, and a specific alkene, and includes water at a higher concentration than the water-containing acetonitrile in the mixing step (1). In the present specification, the term “lower concentration” is used when the ratio of the amount of water to the total amount of water and acetonitrile in the water-containing acetonitrile is small, while the ratio of the amount of such water is large. In some cases, the term “higher concentration” is used.

  Therefore, the concentration of water contained in the upper layer recovered in the upper layer recovery step (3) is lower than the concentration of water contained in the original water-containing acetonitrile in the mixing step (1). Water-containing acetonitrile from which parts have been removed is obtained.

  In the process of the present invention, specific alkenes specifically include propylene, butene, pentene and hexene. The process of the present invention is preferably carried out under conditions where the particular alkene is in the liquid state. Therefore, the conditions for carrying out the method are selected so that the specific alkene is in a pressurized state as necessary so that the specific alkene exists in the liquid state. For example, when propylene or butene is used as a specific alkene, it is preferable to employ pressure conditions. When using pentene or hexene as a specific alkene, normal pressure conditions can usually be employed. A preferred specific alkene is propylene, and in the production of propylene oxide, since propylene is used as a reaction raw material, even if propylene is contained in water-containing acetonitrile with reduced water content, it is not necessary to remove it. This is advantageous in that it can be used in the production of propylene oxide as a mixed solvent without removing propylene from water-containing acetonitrile with reduced water content.

  The amount of the specific alkene mixed with the original water-containing acetonitrile in the step (1) is not particularly limited as long as an upper layer containing water at a lower concentration than the original water-containing acetonitrile can be obtained. Preferably it is 5-40 weight part with respect to 100 weight part of acetonitrile contained in acetonitrile, More preferably, it is 10-40 weight part.

  Depending on the conditions in the method of the present invention, the progress of liquid separation may be slow, and as a result, it may take time for the interface between the upper layer and the lower layer to appear, or, under normal operating conditions, between the upper layer and the lower layer. In some cases, a clear interface does not substantially appear. In such a case, in a preferred embodiment of the present invention, in the mixing step (1), an alkali metal ion is allowed to coexist, specifically, in addition to a specific alkene, such an alkali metal hydroxide is further added. It is preferable to do this. Thus, by coexisting the alkali metal hydroxide, the liquid separation in the liquid separation step (2) is promoted, and the interface between the upper layer and the lower layer appears more rapidly and / or the interface becomes clearer. . Preferred alkali metal hydroxides are, for example, sodium hydroxide, potassium hydroxide and the like, and these are advantageous in that acetonitrile water can be separated with a small addition amount. Usually, the alkali metal hydroxide may be added as it is to the mixture obtained in the step (1), but it is preferably added in the form of an aqueous solution and used in the mixing step (1).

  In the method of the present invention, when an alkene oxide (for example, propylene oxide) is produced by reacting an alkene (for example, propylene) with hydrogen peroxide in a mixed solvent containing acetonitrile and water, the alkene as a reaction product is produced. It can be suitably used to obtain water-containing acetonitrile with reduced water content from water-containing acetonitrile containing acetonitrile and water obtained through the step of removing the oxide from the reaction mixture.

  In the method of the present invention, water-containing acetonitrile and a specific alkene are mixed, then separated into an upper layer and a lower layer, and the upper layer is collected, whereby water-containing acetonitrile with reduced water content can be obtained from the original water-containing acetonitrile. Therefore, it is advantageous in that a part of water can be removed from water-containing acetonitrile by a very simple operation.

FIG. 1 is a flow sheet schematically showing a process for obtaining water-containing acetonitrile with reduced water content from water-containing acetonitrile produced in the propylene oxide production process using the method of the present invention.

  In the method of the present invention, the mixing step (1) and the liquid separation step (2) may be performed by any appropriate method. The operation of mixing the original water-containing acetonitrile and a specific alkene and then separating the liquid to form the upper layer and the lower layer is essentially a liquid that uses the properties of, for example, a ternary system with limited mutual solubility. This is the same as the liquid extraction operation. Thus, the method of the present invention can be performed using an apparatus that performs the extraction operation, and any suitable extraction apparatus can be used.

  For example, water-containing acetonitrile and a specific alkene are supplied to a tank having a stirring device, and the mixing step (1) is performed by mixing them with the stirring device, and then the stirring device is stopped and left to stand. The liquid separation step (2) is performed by separating the liquid into an upper layer and a lower layer, and the method of the present invention can be performed by performing the upper layer recovery step (3) by collecting the separated upper layer. In this case, the method of the present invention is carried out batchwise.

  In another embodiment, the method of the present invention is performed using an apparatus capable of performing a continuous extraction operation. For example, using a mixer-settler apparatus, water-containing acetonitrile and a specific alkene are continuously fed to the mixer, where they are mixed, and these mixtures are continuously removed from the mixer and continuously fed to the settler. Liquid separation is performed, and the upper layer and the lower layer are continuously collected from the settler.

  In still another embodiment, a tower-type continuous extraction apparatus is used to supply water-containing acetonitrile to be removed of water to the upper part of the tower, supply a specific alkene to the lower part of the tower, and contact them in countercurrent. Recover the separated upper layer as the acetonitrile-rich phase from the top of the apparatus, i.e. the upper layer containing water at a lower concentration, and separate the lower layer as the water-rich phase from the bottom of the apparatus, i.e. higher Remove the upper layer containing water at a concentration.

  In the method of the present invention, an acetonitrile-rich phase having a reduced water concentration is obtained as an upper layer, and an aqueous phase having a higher water concentration is obtained as a lower layer, compared to the original water-containing acetonitrile. Certain alkenes have very little solubility in water and are therefore hardly distributed in the lower layer. Most of the acetonitrile contained in the original water-containing acetonitrile is usually distributed to the upper layer (for example, about 70 to 80%), and the rest is distributed to the lower layer. The water contained in the original hydrous acetonitrile is distributed to both the upper and lower layers.

  The method of the present invention may be carried out under any suitable operating conditions. The method of the present invention is carried out under conditions such that the original hydrated acetonitrile and the specific alkene are present in liquid, with appropriate selection of operating temperature and operating pressure. Usually, in terms of the liquid separation speed, higher temperature is advantageous, but on the other hand, the mutual solubility increases, so that the efficiency of liquid separation decreases. For example, it is advantageous to carry out at 20 ° C to 60 ° C.

  In the method of the present invention, for example, when an alkene oxide (for example, propylene oxide) is produced by reacting an alkene (for example, propylene) and hydrogen peroxide in a mixed solvent containing acetonitrile and water as described above, It can be used to remove a portion of water from hydrous acetonitrile containing acetonitrile and water obtained through the step of removing the product alkene oxide from the reaction mixture. Specifically, in the propylene oxide production process, after taking out propylene oxide from the reaction mixture containing propylene oxide, the resulting mixture is taken out as the original water-containing acetonitrile. The water concentration in the mixture is maintained in a predetermined concentration region generally in the range of 20 to 60% by weight, for example about 30% by weight, depending on other production conditions of propylene oxide, and the production process is continued. The Since the water concentration in the mixed solvent increases as propylene oxide is formed, a portion of the water is removed from the original hydrous acetonitrile using the method of the present invention.

  More specifically, the original water-containing acetonitrile and a specific alkene are mixed and separated into an upper layer and a lower layer. The upper layer is an acetonitrile-rich phase with reduced water concentration and further contains a specific alkene. If necessary, this alkene is removed by any suitable method to obtain hydrous acetonitrile with reduced water concentration, which is returned to the alkene oxide production process and used as a mixed solvent. The lower layer is a water-rich phase containing acetonitrile, and the acetonitrile contained therein can also be recovered and returned to the alkene oxide production process. Any suitable method may be used to recover acetonitrile from the lower layer. For example, the lower layer is subjected to an azeotropic distillation operation to obtain an azeotropic composition of acetonitrile / water from the top of the column and from the bottom of the column. You can get water. Since the azeotropic composition contains acetonitrile in an amount of about 80% by weight or more, it can be returned to the alkene oxide production process and used as a mixed solvent.

  In the method of the present invention, in order to promote liquid separation, in the mixing step (1), it is preferable to mix the original hydrated acetonitrile and the alkali metal hydroxide in addition to the specific alkene. Examples of the alkali metal hydroxide include sodium hydroxide and potassium hydroxide, and sodium hydroxide is preferably used. The alkali metal hydroxide is preferably used in the form of an aqueous solution thereof, and the alkali metal hydroxide is easily distributed uniformly.

  The amount of the alkali metal hydroxide to be used may be any suitable amount as long as the separation is promoted, but is usually preferably based on 1 part by weight of water contained in the original hydrous acetonitrile. It is used in an amount of 0.001 part by weight or more and 0.1 part by weight or less, preferably 0.0047 part by weight or more and 0.014 part by weight or less.

  Next, the method of the present invention will be described more specifically with reference to FIG. FIG. 1 shows a schematic flow sheet of a process for obtaining water-containing acetonitrile having a reduced water content by removing a part of water from water-containing acetonitrile obtained after taking out propylene oxide in a propylene oxide production process.

In the propylene oxide production process, water-containing acetonitrile (ATN / H ₂ O) 2 obtained after taking out propylene oxide and a specific alkene 4 are mixed, and then these are supplied to the water removing device 6. As this apparatus, what is used as a liquid-liquid extraction apparatus as described above, for example, an extraction tower such as a packed tower or a plate tower can be used. In addition, the water-containing acetonitrile 2 and the alkene 4 may be mixed by using a mixing device such as a stirring tank at a location before the water removing device 6 (a location indicated by 8). In the water removal device 6, liquid separation occurs, the phase corresponding to the upper layer rises, while the layer corresponding to the lower layer falls, one of the phases forms a continuous phase, and the other phase forms a dispersed phase. Form.

  When a differential contact type extraction device such as a packed column or a plate column is used, as shown in the figure, the water-containing acetonitrile is not mixed with the water-containing acetonitrile 2 and the specific alkene 4 in advance. A specific alkene may be supplied to the extraction apparatus from the lower part of the apparatus and from a separate location, and a mixing process and a subsequent liquid separation process may be performed in the apparatus.

  In the illustrated embodiment, a sodium hydroxide aqueous solution (for example, 40% aqueous solution) 14 is supplied as an alkali metal hydroxide from above the water removing device 6, and this promotes liquid separation while descending the device 16. Sodium hydroxide may be supplied not in an aqueous solution but in water-containing acetonitrile.

  The phase forming the upper layer in the water removal apparatus 6 contains acetonitrile as a main component, and in addition, contains water and a specific alkene, and is recovered as an upper stream 10 from above the water removal apparatus 6. As described above, the concentration (for example, 33% by weight) of water contained in the original water-containing acetonitrile 2 decreases (for example, 21% by weight) in the upper layer 10 according to the operating conditions. It can be used as a mixed solvent in the production process.

  Since the upper layer contains a specific alkene, if it becomes a problem in the alkene oxide production process, it is removed by an appropriate method, for example, a distillation operation. If the specific alkene used in the method of the present invention is the same as the alkene used in the alkene oxide production process, it is advantageous to include the specific alkene. For example, when removing water from hydrous acetonitrile used in the process for producing propylene oxide, it is advantageous to use propylene as a specific alkene.

  The phase forming the lower layer in the water removing device 6 contains water removed from the original water-containing acetonitrile, and also contains acetonitrile accompanying it. In addition, some specific alkenes are also included. Such a phase is discharged as a lower stream 12 from below the water removal device 6. Since this lower layer 12 contains a considerable amount of acetonitrile, it is supplied to the azeotropic distillation apparatus 16 in order to recover the acetonitrile.

  In the azeotropic distillation apparatus 16, an azeotropic composition of acetonitrile / water is distilled from the top of the column as a stream 18, condensed, and a part thereof is returned to the apparatus 16 as reflux, and the rest is taken out as a stream 22 from the system. This azeotropic composition contains 84% by weight of acetonitrile when the distillation operation is carried out at normal pressure, with the balance being water. In addition, when a lower layer contains a trace amount of specific alkene, this also distills together from the tower top.

Further, water is discharged from the azeotropic distillation apparatus 16 as a canned stream 20. In addition, when mixing the original water-containing acetonitrile and sodium hydroxide, the bottoms contain sodium hydroxide. In this case, sulfuric acid (H ₂ SO ₄ ) 26 is added to the bottoms 20 to neutralize sodium hydroxide, and then it can be discharged out of the system as a stream 28.

  The stream 22 can also be used as a mixed solvent in the alkene oxide production process. Therefore, in the illustrated embodiment, the stream 22 is merged with the stream 24.

  The liquid-liquid equilibrium relationship of water, acetonitrile (ATN) and 1-hexene was measured at various temperatures. Specifically, each component is weighed in the amounts shown in Tables 1 to 4 and placed in a separatory funnel. After thoroughly shaking and mixing, the mixture is allowed to stand to separate into an upper layer and a lower layer, and the upper layer is recovered. did. The amounts of the upper layer and the lower layer were measured, and their compositions were also analyzed, and the results are also shown in the table.

測定温度：50℃、40％ＮａＯＨ水溶液使用
^１）特定のアルケンとしての１−ヘキセン
^２）仕込量については４０％水酸化ナトリウム水溶液の量、上層および下層については分析により得られたＮａ量に基づく換算ＮａＯＨ量
下記の表２および表３においても同じ。

Measurement temperature: 50 ° C, 40% NaOH aqueous solution used
¹⁾ 1-hexene as a specific alkene
^{2) The} amount of 40% sodium hydroxide aqueous solution for the amount charged, and the upper layer and the lower layer for the converted NaOH amount based on the Na amount obtained by analysis, the same applies to Tables 2 and 3 below.

測定温度：50℃、40％ＮａＯＨ水溶液使用

Measurement temperature: 50 ° C, 40% NaOH aqueous solution used

測定温度：50℃、40％ＮａＯＨ水溶液使用

Measurement temperature: 50 ° C, 40% NaOH aqueous solution used

測定温度：50℃、40％ＮａＯＨ水溶液使用

Measurement temperature: 50 ° C, 40% NaOH aqueous solution used

2 ... water-containing acetonitrile, 4 ... specific alkene, 6 ... water removal device,
10 ... upper stream, 12 ... lower stream, 14 ... sodium hydroxide,
16 ... Azeotropic distillation apparatus, 18 ... Distilled stream, 20 ... Canned stream, 22 ... Distillate,
26 ... sulfuric acid.

Claims (5)

It is a method for obtaining water-containing acetonitrile with reduced water content from water-containing acetonitrile containing water and acetonitrile,
(1) a step of mixing the water-containing acetonitrile containing water and acetonitrile with an alkene having 3 to 8 carbon atoms to obtain a mixture thereof;
Step (2) for separating the mixture obtained in step (1) into an upper layer and a lower layer, and step (3) for recovering the upper layer separated in step (2)
A method comprising the steps of:   The method according to claim 1, wherein the amount of alkene in the step (1) is 5 to 40 parts by weight with respect to 100 parts by weight of acetonitrile contained in the water-containing acetonitrile containing water and acetonitrile.   The method according to claim 1 or 2, further comprising mixing the water-containing acetonitrile containing water and acetonitrile with an alkali metal hydroxide in the step (1).   4. The method of claim 3, wherein the alkali metal hydroxide is sodium hydroxide.   The water-containing acetonitrile containing water and acetonitrile is a water-containing product obtained through a step of taking alkene oxide from a reaction mixture obtained by reacting an alkene and hydrogen peroxide in a mixed solvent containing acetonitrile and water. The method according to any one of claims 1 to 4, wherein the method is acetonitrile.

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