TWI453185B - Purification of acetonitrile - Google Patents

Description

Method for purifying acetonitrile

This invention relates to a process for the purification of acetonitrile.

At present, commercially available acetonitrile is mainly obtained by recovering and purifying crude acetonitrile obtained as a by-product from the production of acrylonitrile or methacrylonitrile by ammoxidation of propylene or isobutylene with ammonia and oxygen.

Acetonitrile can be used as a solvent for chemical reaction, especially a solvent for synthesis or purification of a pharmaceutical intermediate, or a fluidized layer solvent for high performance liquid chromatography. Moreover, it can also be used for DNA (deoxyribonucleic acid) synthesis, purification solvent, solvent for organic EL (electroluminescence) synthesis, cleaning solvent for electronic components, etc., especially in the case of the above applications. Purification is required in high purity.

a crude acetonitrile obtained as a by-product in the production of acrylonitrile or methacrylonitrile, containing allyl alcohol or Azole, water, acetone, cyanic acid, acrylonitrile, methacrylonitrile, propionitrile, cis and trans-butenenitrile, acrylic acid, methyl acrylate, methacrylic acid, methyl methacrylate, acetic acid, acrolein , impurities such as methacrolein, acetone, ammonia, or impurities that cannot be analyzed.

Heretofore, a method for recovering and purifying crude acetonitrile obtained as a by-product from the production of acrylonitrile or methacrylonitrile by ammoxidation of propylene or isobutylene with ammonia and oxygen has been proposed.

Patent Document 1 discloses a method of dehydrating acetonitrile in which an alkali is added to an aqueous acetonitrile in an amount sufficient to extract water present therein and mixed, followed by separation. The aqueous phase is removed. Further, Patent Document 2 describes a production increase of acetonitrile, and discloses a method in which acetone or ethanol or both are allowed to coexist in a reaction system when an unsaturated nitrile and acetonitrile are produced by ammoxidation.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 55-153757

[Patent Document 2] Japanese Patent Laid-Open No. Hei 03-246269

According to the method described in Patent Document 1 or 2, high-purity acetonitrile can be produced. However, in order to obtain high purity, it is necessary to pass a plurality of processing steps, and therefore, a large number of apparatuses are required. As a result, the amount of energy consumption required for purification (for example, the amount of steam used to heat the distillation column, the cooling water used to generate the overhead stream) is increased, and the cost is greatly increased. Here, when the countermeasure for reducing the energy consumption, which is generally used for the utilization of waste heat, is simply applied to the acetonitrile purification process, there is a problem that temperature or pressure changes occur in the apparatus for performing heat exchange. The disorder causes a problem such as an increase in the concentration of impurities in the purification stream or an unstable quality, and cannot be supplied to a user who requires high-purity acetonitrile. Therefore, the current situation is to expect a method of purifying high-purity acetonitrile with a small amount of energy consumption.

In view of the above, it is an object of the present invention to provide a process for purifying high purity acetonitrile by a process with a small energy consumption.

In order to solve the above problems, the inventors of the present invention have conducted intensive studies and found that in the method of purifying crude acetonitrile recovered in the step of producing acrylonitrile or methacrylonitrile by ammoxidation using two or more distillation columns. The overhead stream of the second distillation column can be used as a heat source for the reboiler of the first distillation column. Further, it has been found that by using the heat source, a process for purifying a small amount of energy consumption for purification can be provided, thereby completing the present invention.

That is, the present invention is as follows.

[1]

A method for purifying acetonitrile, comprising the steps of: adding a base to an acetonitrile containing water formed by an ammoxidation reaction, and then supplying the reaction mixture to a first distillation column to obtain a distillate Further, the mixture is mixed with an alkali to separate the acetonitrile phase from the aqueous phase, and then the aqueous phase is removed, and the acetonitrile phase is supplied to the second distillation column; and the distillate vapor from the second distillation column is used as the first distillation. The heat source of the reboiler of the tower.

[2]

The method for purifying acetonitrile according to the above [1], wherein a part of the distillate vapor is supplied to the reboiler, and the remaining portion is supplied to a condenser connected to the second distillation column.

[3]

A method for purifying acetonitrile according to the above [1] or [2], wherein a reboiler pressure (distillation vapor side, gauge pressure) of the first distillation column and a column top pressure (gauge pressure) of the second distillation column are used The supply amount of the above-mentioned distillate vapor to the above reboiler is determined based on the standard.

[4]

The method for purifying acetonitrile according to the above [3], wherein the reboiler pressure of the first distillation column is set to be 0.90 times or less of the column top pressure of the second distillation column.

[5]

A purification device for acetonitrile, which is provided with a reaction tank, a first distillation column, a dehydration column, and a second distillation column in this order. After the reaction of the acetonitrile containing water and the alkali in the reaction tank, the reaction mixture flows into the first distillation column. The distillate of the first distillation column flows into the dehydration column, the acetonitrile phase obtained in the dehydration column flows into the second distillation column, and the distillate vapor of the second distillation column is used as the first distillation. Tower reboiler Heat source.

[6]

The acetonitrile purification apparatus according to the above [5], wherein a part of the distillate vapor is supplied to the reboiler, and the remaining part is supplied to a condenser connected to the second distillation column.

[7]

The acetonitrile purification apparatus according to the above [5] or [6], wherein the supply amount of the distillate vapor to the reboiler is a reboiler pressure (distillation vapor side, gauge pressure) of the first distillation column and The column top pressure (gauge pressure) of the second distillation column is determined based on the standard.

[8]

The acetonitrile purification apparatus according to the above [7], wherein the reboiler pressure of the first distillation column is 0.90 times or less of the column top pressure of the second distillation column.

By the purification method of the acetonitrile of the present invention, high-purity acetonitrile can be purified by a process with a small energy consumption.

1‧‧‧ acetonitrile enrichment tower

2‧‧‧Reaction tank

3‧‧‧High boiling separation tower

3a‧‧‧High boiling separation tower reboiler

3b‧‧‧High boiling separation tower additional reboiler (for product tower)

3c‧‧‧High boiling separation tower additional reboiler (for low boiling separation tower)

3d‧‧‧High boiling separation tower condenser

4‧‧‧Dehydration Tower

5‧‧‧Low boiling separation tower

5a‧‧‧Low boiling separation tower reboiler

5b‧‧‧Low boiling separation tower reflux

5d‧‧‧low boiling separation tower condenser

5v‧‧‧ branch valve in the direction of the condenser of the low boiling separation column

6‧‧‧Product Tower

6a‧‧‧Product Tower Reboiler

6b‧‧‧Product tower reflow tube

6d‧‧‧Product Tower Condenser

6v‧‧‧ branch valve in the direction of the condenser of the product tower

7~21‧‧‧ pipeline

18a‧‧‧ pipeline

21a‧‧‧ pipeline

51v‧‧‧High boiling separation tower additional reboiler bypass valve (for low boiling separation tower bottom liquid)

Fig. 1 is a view showing an example of a schematic view of an apparatus for producing acetonitrile in the present embodiment.

Fig. 2 is a schematic view showing an apparatus for supplying at least a part of the vapor distilled from the top of the product column as a heat source to the reboiler of the high boiling separation column.

Fig. 3 is a schematic view showing an apparatus for supplying at least a part of the vapor distilled from the top of the low boiling separation column as a heat source to the reboiler of the high boiling separation column.

Fig. 4 is a schematic view showing an apparatus for supplying at least a part of a bottom liquid of a low boiling separation column as a heat source to a reboiler of a high boiling separation column.

Hereinafter, the form for carrying out the present invention (hereinafter, simply referred to as "this embodiment") will be described in detail. The following embodiments are used to illustrate the examples of the present invention, and The present invention is not limited to the following contents. The present invention can be carried out with appropriate changes within the scope of the gist of the invention. In the drawings, the same components are denoted by the same reference numerals, and the description thereof will not be repeated. Further, unless otherwise specified, the positional relationship such as up, down, left, and right is based on the positional relationship shown in the drawing. The size ratio of the device or member is not limited to the ratio shown.

The method for purifying acetonitrile in the present embodiment includes the steps of: adding a base to an acetonitrile containing water produced by an ammoxidation reaction, and then supplying the reaction mixture to the first distillation column to obtain a distillation product. The liquid is further separated from the alkali to be separated into an acetonitrile phase and an aqueous phase, and then the aqueous phase is removed, and the acetonitrile phase is supplied to the second distillation column; and the distillate vapor from the second distillation column is used as the above A heat source for a reboiler of a distillation column.

The method for purifying acetonitrile in the present embodiment can be carried out, for example, by using the following acetonitrile purification apparatus.

A purification device for acetonitrile, which is provided with a reaction tank, a first distillation column, a dehydration column, and a second distillation column in this order. After the reaction of the acetonitrile containing water and the alkali in the reaction tank, the reaction mixture flows into the first distillation column. The distillate of the first distillation column flows into the dehydration column, the acetonitrile phase obtained in the dehydration column flows into the second distillation column, and the distillate vapor of the second distillation column is used as the first distillation. The heat source of the reboiler of the tower.

Fig. 1 is a view showing an example of a schematic view of an apparatus for purifying acetonitrile in the present embodiment. The apparatus shown in Fig. 1 has a concentration column 1 into which crude acetonitrile is introduced, and the high boiling separation column 3, the dehydration column 4, the low boiling separation column 5, and the product column 6 are sequentially connected to the concentration column 1 via the reaction tank 2.

The crude acetonitrile is obtained as a by-product from the production of acrylonitrile or methacrylonitrile from propylene, propane, isobutylene or isobutane by contact ammoxidation. In general, the product of the ammoxidation reaction is subjected to extractive distillation to recover crude acetonitrile in a fraction different from the fraction containing acrylonitrile or methacrylonitrile as a main component. Here, the crude acetonitrile system means that the fraction obtained by extractive distillation of the product of the ammoxidation reaction has the highest content of acetonitrile. The crude acetonitrile is usually separated from most of the distillation columns for recovering acrylonitrile, and usually contains 5 to 40% by mass of acetonitrile, 50 to 95% by mass of water, and further hydrogen cyanide, allyl alcohol, More kinds of impurities such as azole, propionitrile and ammonia.

The crude acetonitrile is sent from line 7 to the middle of the acetonitrile concentration column 1. The acetonitrile concentration column 1 is an upright distillation column having a reboiler (not shown) at the bottom of the column and a condenser (not shown) at the top of the column. The hydrogen cyanide is removed from the top of the column (line 8), water is removed from the bottom of the column (line 9), and the concentrated gaseous acetonitrile (hereinafter also referred to as "concentrated acetonitrile") is extracted from the middle of the column (line 10). . The line 10 is provided with a side cut condenser (not shown), and the gaseous concentrated acetonitrile is condensed by the side cut condenser. The liquid concentrated acetonitrile flowing out of the side cut condenser flows into the reaction tank 2. The concentration of acetonitrile in the concentrated acetonitrile supplied from the concentration column 1 to the reaction tank 2 is usually 50 to 70% by mass, and further contains 25 to 70% by mass of water, hydrogen cyanide, allyl alcohol and the like.

In the reaction tank 2, an aqueous alkali solution such as an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution is added from the line 11, and the acrylonitrile or hydrogen cyanide contained as an impurity in the concentrated acetonitrile is changed to succinonitrile or a dimer. polymer. The temperature of the reaction tank 2 is preferably from 20 to 80 ° C, more preferably from 1 to 15 hours at 60 to 75 ° C, and more preferably from 60 to 75 ° C from the viewpoint of allowing the polymerization to proceed sufficiently. Perform a 3 to 10 hour reaction.

The liquid flowing out of the reaction tank 2 is sent to the high boiling separation column 3 through the line 12. From the viewpoint of separation of high boilers, the high boiling separation column 3 is preferably a vacuum distillation column. The acetonitrile is recovered from the top of the high boiling separation column 3 by azeotrope composition mixture of acetonitrile and water, or a mixture thereof, and liquefied in a condenser (not shown). One part of the condensate is refluxed to the high boiling separation column 3 by a line (not shown), and the remainder is sent from the line 14 to the dehydration column 4. A polymer such as succinonitrile or a dimer formed in the reaction tank 2, a base, allyl alcohol, propionitrile, water, and a small amount of acetonitrile are separated from the bottom line 13 and sent to a wastewater treatment facility or the like. The reboiler (not shown) that supplies the heat necessary for the distillation is provided at the bottom of the column to supply the heat necessary for the distillation. In the high boiling separation column 3, in order to stably separate and remove allyl alcohol and propionitrile, it is important to supply the heat necessary for distillation in a fixed and stable manner. Allyl alcohol and propionitrile are particularly difficult to separate, and it is preferred to preliminarily separate and remove allyl alcohol and propionitrile in the high boiling separation column 3.

From the viewpoints of separating high-boiling substances such as allyl alcohol and propionitrile and suppressing decomposition of succinonitrile or dimer formed in the reaction tank 2, the pressure of the high boiling separation column 3 is measured by absolute pressure. Preferably, it is 80~300mmHg, more preferably 100~250mmHg. When the pressure is set within the above range, the temperature at the bottom of the column is preferably 45 to 65 ° C, more preferably 50 to 60 ° C, and the temperature at the top of the column is preferably 35 to 60 ° C, more preferably 40 to 50 ° C.

In the dehydration column 4, in addition to the overhead stream of the high boiling separation column 3, a sufficient amount of alkali is extracted from the line 15 for extracting the water present therein, and then the separated aqueous phase is removed from the line 16 Thereby the acetonitrile phase is obtained from line 17. As the base, an aqueous solution or a solid matter of sodium hydroxide and/or potassium hydroxide is preferably used, and more preferably these aqueous solutions.

The extraction temperature in the dehydration column 4 is preferably from 5 ° C to 60 ° C, more preferably from 10 ° C to 35 ° C. Here, the extraction temperature means the temperature in the dehydration column 4, and more specifically, the temperature of the internal liquid in the dehydration column 4 from the top liquid feed position of the high boiling separation column 3 to the alkali feed position.

The amount of the base to be used varies depending on the water content in the acetonitrile, and is usually in the range of 10 to 90% by mass, preferably 30 to 60% by mass based on the water contained in the acetonitrile. The amount of water in the acetonitrile is preferably 10% by mass or less, and more preferably 3% by mass or less, by a method of extracting water by an alkali.

After dehydration, in order to separate and remove a compound having a lower boiling point than acetonitrile and a compound having a higher boiling point than acetonitrile, it is preferred to use two or more distillation columns. Specifically, it is preferred to first separate and remove the low boiling point compound from the top of the column through the line 18 in the low boiling separation column 5, and send the bottom liquid of the low boiling separation column 5 to the product column 6 through the line 19. In the product tower 6 The high boilers are separated from the bottom of the column via line 20 and purified acetonitrile is obtained from overhead line 21 .

In the low boiling separation column 5 and the product column 6, the reflux ratio or the extraction amount of the low boiling point compound and the high boiling point compound can be appropriately determined in such a manner as to satisfy the target degree of purification. The reflux ratio of the low boiling separation column 5 and the product column 6 depends on the degree of purification of the target, but is preferably from 1 to 50, more preferably from 2 to 30. The reflux ratio is defined as the value obtained by dividing the mass returned to the distillation column by the mass discharged to the outside of the distillation column. From the viewpoint of efficiently performing separation and removal of impurities by distillation, it is preferable that the reflux ratio is stably maintained at a predetermined value in the operation to purify high-purity acetonitrile. From the viewpoint of energy efficiency and separation of impurities, the column top pressure of the low boiling separation column 5 and the product column 6 is set near the normal pressure. The lower limit of the column top pressure is preferably 0.090 MPa or more, more preferably 0.095 MPa or more, further preferably 0.100 MPa or more, and the upper limit is an absolute pressure, preferably 0.180 MPa or less, more preferably 0.150 MPa. Hereinafter, it is more preferably 0.130 MPa or less. When the top pressure is set within the above preferred range, the bottom temperature of the low boiling separation column 5 and the product column 6 is preferably 80 to 95 ° C, more preferably 80 to 88 ° C, and the temperature at the top of the column is preferably It is 70 to 90 ° C, more preferably 70 to 85 ° C.

In the purification method in the present embodiment, at least a part of the vapor distilled from the top of the product column 6 and/or the low boiling separation column 5 is supplied as a heat source to the reboiler of the high boiling separation column 3.

Fig. 2 is a schematic view showing an apparatus for supplying at least a part of the vapor distilled from the top of the product column 6 as a heat source to the reboiler 3b of the high boiling separation column 3. In the example shown in Fig. 2, the reboiler 3b is of a shell tube type, and the vapor distilled from the top of the product column 6 is supplied to the shell side, and the bottom liquid of the high boiling separation column 3 which is heated on the tube side is heated. . A plurality of reboilers (3a and 3b) are disposed in the high boiling separation column 3, and preferably, the distillate vapor of the product column 6 is introduced into the reboiler 3b of the high boiling separation column 3 for the steam, The other reboiler 3a supplies other heat sources. Heat exchange with the bottom liquid of the high boiling separation column 3 from the reboiler row of the high boiling separation column 3 The steam drain is cooled by water or the like as needed, and then returned to the product tower 6 and/or extracted by cooling with water or the like.

Fig. 3 is a schematic view showing an apparatus for supplying at least a part of the vapor distilled from the top of the low boiling separation column 5 as a heat source to the reboiler 3c of the high boiling separation column 3. The apparatus shown in Fig. 3 is the same as the example shown in Fig. 2 except that the vapor distilled from the low boiling separation column 5 is supplied to the reboiler 3c of the high boiling separation column 3, and therefore, only differences will be described below. The setting of the pressure in the column and the like also depends on the design or operating conditions, but the temperature at the top of the low boiling separation column 5 is lower than the temperature at the top of the product column 6, in which case, as long as it is higher than the high boiling separation column 3 The bottom temperature can also be used as a heat source. The overhead vapor of the low boiling separation column 5 contains a low boiling component at a high concentration, so that it is difficult to condense in the reboiler 3c as compared with the vapor of the product column 6. Therefore, it is preferable to consider the overhead flow. Set the reboiler temperature.

The preferred pressures and column top temperatures for the low boiling separation column 5 and the product column 6 are described above. Since these also affect the utilization of the distillate vapor, there is also a preferred pressure and top for this point of view. temperature. Specifically, in order to use the distillate vapor as a heat source, the temperature of the distillate vapor must be higher than the temperature of the bottom liquid of the distillation column to be supplied to the reboiler, and therefore it is preferable to consider this viewpoint. The pressure of the distillation column is set based on the desired temperature at the top of the column. Of course, it is also possible to use the distillate vapor by lowering the temperature of the bottom liquid side of the distillation column, so that it is also effective to adjust the pressure of the distillation column to which the reboiler is connected. From the viewpoint of making the temperature of the distillate vapor higher than the temperature of the bottom liquid of the high boiling separation column 3, it is preferred that the low boiling separation column 5 and/or the product column 6 are under normal pressure or near normal pressure. In operation, the high boiling separation column 3 was set to vacuum distillation.

The reboiler (3b, 3c) that is passed through the distillate vapor can be used to steal the idle equipment or can be redesigned. In the case of redesign, the design is based on the following points.

First, the amount of heat q that can be supplied to the high boiling separation column 3 by the reboiler is calculated based on the flow rate of the distillate vapor and the case where the vapor is completely condensed. Then, in order to determine the size of the reboiler, the calculation of the heat transfer area is performed. Heat q is the total heat transfer coefficient U, heat transfer surface The product of product A and temperature difference ΔT, ie q=U. A. △T. U can use the actual value of the reboiler used in normal chemical equipment, and can also be estimated by chemical engineering methods. In the present embodiment, the temperature of the ΔT-based distillate vapor is different from the temperature of the bottom liquid of the high-boiling separation column 3. The ΔT system is produced by the difference in operating conditions between the first distillation column and the second distillation column. In the present embodiment, since the acetonitrile containing water produced by the ammoxidation reaction is purified, the composition ratio in the first distillation column and the second distillation column does not largely vary. Therefore, the conditions of each distillation column are controlled to be substantially constant.

In the purification of the acetonitrile of the present embodiment, regarding the temperature of the first distillation column and the temperature of the second distillation column, the bottom temperature of the first distillation column is preferably 45 to 65 in terms of impurity separation and energy efficiency. °C, more preferably 50 to 60 ° C, the temperature of the top of the second distillation column is preferably 70 to 90 ° C, more preferably 70 to 85 ° C. Therefore, ΔT is preferably from 10 to 35 ° C, more preferably from 15 to 25 ° C. Therefore, the heat transfer area A is also necessarily limited to a specific range. The distillate vapor from the second distillation column can be used as the first distillation by using a reboiler having a heat transfer area A capable of maintaining the heat q necessary for the distillation in the range of ΔT of 10 to 35 ° C. The stable operation of the heat source of the reboiler of the tower.

On the other hand, when the idle device is used, the heat transfer area A has a predetermined value, but the heat transfer area A having the heat q necessary for maintaining the distillation in the range of ΔT of 10 to 35 ° C is required. The reboiler can stably operate the distillate vapor from the second distillation column as a heat source of the reboiler of the first distillation column.

Although at least a part of the vapor distilled from the low boiling separation column 5 and/or the product column 6 is used as a heat source necessary for the distillation of the high boiling separation column 3, it does not adversely affect the accuracy of the distillation in the three columns. The way. The low boiling separation column 5 and the product column 6 are devices for precisely distilling a liquid having an acetonitrile concentration of 95% by mass or more and 99% by mass or more, respectively. The adverse effect on the accuracy of the above distillation is, for example, a case where the disorder of the low boiling separation column 5 and/or the product column 6 which supplies the distillate vapor causes the disorder of the high boiling separation column 3 which utilizes the distillate vapor. Further, conversely, the disorder of the high boiling separation column 3 may also cause disorder of the low boiling separation column 5 and/or the product column 6. The mechanism for transferring the "disorder" of a certain distillation column to other distillation columns is specifically described. For example, in a routine operation, the temperature and/or pressure of the low boiling separation column 5 and/or the product column 6 deviate from the target value (disorder In the case of ), the amount of vapor distilled from the distillation column fluctuates. As a result, the amount of vapor supplied to the reboiler of the high boiling separation column 3 as a heat source fluctuates, so that the amount of heat supplied to the high boiling separation column 3 changes in a chain. In addition, the distillation operation becomes unstable due to fluctuations in the reflux ratio in the high boiling separation column 3, and the distillation accuracy is adversely affected. If the distillation in the high boiling separation column 3 becomes unstable, the separation and removal of allyl alcohol and propionitrile are not sufficiently performed, and the quality of the high purity acetonitrile is fatally affected. On the other hand, when the temperature and/or pressure of the high boiling separation column 3 is disturbed, the amount of distillate vapor condensed on the shell side of the reboiler of the high boiling separation column 3 fluctuates. The distillate vapor is condensed in the reboiler, introduced, and refluxed to the condenser of the low boiling separation column 5 and/or the product column 6, so that if the amount of condensation changes, the low boiling separation column 5 and/or the product column 6 The change in the return flow or the heat load also changes course. Thereby, the disorder of the high boiling separation column 3 is transmitted to the low boiling separation column 5 and/or the product column 6 to adversely affect the stability of the column pressure. The low boiling separation column 5 and the product column 6 are distillation towers for precisely distilling acetonitrile, and impurities in high purity acetonitrile due to disorder of distillation, for example The separation of azole, hydrogen cyanide, water, ammonia, and other trace impurities causes adverse effects.

If the distillation of each column is disordered, the purity of the obtained acetonitrile is lowered, so that the value as a product is lost as the case may be. In addition to the solvent of HPLC (High Performance Liquid Chromatography), high-purity acetonitrile is required for applications such as DNA synthesis, purification solvents, solvents for organic EL material synthesis, and cleaning solvents for electronic components. In addition to high purity, it is also expected that the concentration of impurities contained in a trace amount does not rise and is fixed. From the above viewpoints, the inventors of the present invention have conducted an effort to study a method for stabilizing a system for exchanging heat when distilling off steam by a distillation column.

In the case where the distillate vapor of the product column 6 is supplied to the shell side of the reboiler 3b of the high boiling separation column 3 to be used as a heat source, it is preferable from the viewpoint of the stability of the product column 6 In the reboiler of the column 6, the distillation steam or the like of another distillation column or the like is not used, and the supply of heat is stabilized by supplying a fixed flow of steam from a practical supply device which is a device for generating and supplying steam. The pressure of the vapor supplied from the practical supply device is preferably 1.0 MPaG or less, and more preferably 0.6 MPaG or less from the viewpoint of making the temperature difference between the vapor and the heated liquid appropriate.

Moreover, the inventors of the present invention have found that the relationship between the column top pressure of the distillation column to which the distillate vapor is supplied and the pressure of the high boiling column deoiler to which the distillate vapor is supplied is adjusted to a specific range, which is good. Maintain the accuracy of distillation purification.

The amount of the reboiler 3b that supplies the vapor distilled from the second distillation column (the low boiling separation column 5 and the product column 6) to the first distillation column (the high boiling separation column 3) is preferably the first distillation column. The reboiler pressure (distillation vapor side, gauge pressure) and the top pressure (gauge pressure) of the second distillation column are determined based on the standard. Generally, the gauge pressure indicates the relative value of the pressure at which the atmospheric pressure is set to 0. Therefore, when the distillate vapor is completely condensed in the reboiler shell, the gauge pressure of the reboiler shell becomes zero. Depending on the fluid temperature on the reboiler tube side (distillation tower bottom liquid temperature), it may also become a negative value. From the viewpoint of stable continuous operation, the pressure (gauge pressure) measured by a pressure gauge attached to the reboiler shell side of the first distillation column is the peak pressure (gauge pressure) of the second distillation column. The branch valve 6v is preferably adjusted to 0.90 times or less, more preferably 0.50 times or less, and still more preferably 0.20 times or less. In addition, the lower limit is not particularly limited, and if it is assumed that all of the distillate vapor is condensed, -0.1 times or more or 0 times or more is an actual value. Further, in the following examples, the column top pressure (gauge pressure) of the product column 6 is denoted as A, and the shell pressure (gauge pressure) of the reboiler 3b is denoted as B, and the pressure ratio B/A Conduct an evaluation.

A decrease in the above magnification means that the difference in pressure is widened. When the pressure difference is increased, the flow from the top of the second distillation column to the vapor of the reboiler of the first distillation column tends to be stabilized. When the flow of the vapor is stabilized, the supply of heat is stabilized, and the amount of evaporation in the reboiler of the first distillation column is stabilized. Thereby, the amount of vapor rising in the first distillation column is stabilized. Gas-liquid contact is repeated on the tray in the tower, and the vapor distilled from the top is condensed in the condenser, and a part of the reflux To the tower. The stability of the gas-liquid contact of the distillation column is reflected in the pressure or temperature in the column, especially by observing the change in pressure. When the supply of heat is stabilized, the fluctuation of the pressure value of the first distillation column is within ±7% of the median value. Further, from the viewpoint of reducing impurities in acetonitrile, it is preferably controlled within ±5%, and more preferably within ±3%. When the pressure fluctuation is controlled within ±5%, heat exchange between the vapor rising at the tray in the first distillation column and the liquid falling at the tray can be appropriately performed. As a result, impurities such as allyl alcohol and propionitrile to be separated in the first distillation column are concentrated at the bottom of the column by gas-liquid contact, and the amount of distillation from the top of the column is remarkably reduced.

The shell pressure of the reboiler 3b of the high boiling separation column 3 depends on the condensation performance of the vapor in the shell, and the larger the heat transfer area of the reboiler 3b, the smaller the shell pressure tends to be. Preferably, the heat transfer area of the reboiler 3b of the high boiling separation column 3 is calculated by the above calculation to calculate an appropriate value and a new device is provided, but the idle device can also be used. By adjusting the supply amount of the distillate vapor based on the shell pressure of the reboiler 3b of the high boiling separation column 3 and the column top pressure of the product column 6, the distillate vapor of the product column 6 is suppressed from flowing to the reboiler 3b. As a result of the fluctuation in the supply flow rate, the amount of heat supplied to the reboiler 3b can be fixed, and the distillation purification of the high boiling separation column 3 can be stabilized. That is, when the vaporization of the distillate vapor in the reboiler 3b does not occur, the pressure fluctuation of the reboiler shell occurs, and the influence is transmitted to the product tower 6 which is the supply source of the distillate vapor. Stabilizing the distillate vapor in the reboiler 3b and returning it to the condenser of the product column 6 at a fixed gas/liquid ratio contributes to the stability of the entire system. Therefore, it is preferred to use the reboiler 3b pressure as a The operating index of the distillate vapor condensed stably in the reboiler 3b. From the viewpoint of the flow of the fluid, the reboiler pressure must be lower than the column top pressure of the product tower 6 to which the distillate vapor is supplied, and the pressure value must be stable from the viewpoint of stable operation, and therefore it is suitable as an index.

When the distillate vapor of the product column 6 is passed to the high boiling separation column reboiler, the pressure relationship between the two columns affects the concentration of allyl alcohol and propionitrile in the purified acetonitrile. It is presumed that the reason is that if the heat supplied to the high boiling separation column 3 is unstable, the allyl alcohol and the sodium in the high boiling separation column 3 The separation performance of the nitrile is reduced, and the variation in column pressure or backflow of the product column 6 further results in a decrease in the separation performance of the propionitrile in the product column 6. Therefore, by setting the relationship between the column top pressure of the product column 6 and the reboiler pressure of the high boiling separation column 3 within the above preferred range, the concentration of allyl alcohol and propionitrile is easily maintained low.

Regarding the case where the distillate vapor of the low boiling separation column 5 is passed to the high boiling separation column reboiler, the pressure relationship between the two columns also affects the allyl alcohol and propionitrile in the purified acetonitrile. The concentration of azole and ammonia. Regarding the reason, the inventors of the present invention presumed that the reason is the same as that of the product column 6, that is, if the heat supplied to the high boiling separation column 3 is unstable, it causes the allyl alcohol and propionitrile in the high boiling separation column 3. The decrease in separation performance, in turn, is caused by fluctuations in column pressure or return flow of the low boiling separation column 5, resulting in the low boiling separation column 5. Reduction in separation performance of azole, ammonia, and the like. With respect to the pressure relationship between the two columns, the pressure (gauge pressure) measured by a pressure gauge attached to the shell side of the reboiler 3c of the high boiling separation column 3 becomes the column top pressure (gauge pressure) of the low boiling separation column 5. The branch valve 5v is preferably adjusted to 0.90 times or less, more preferably 0.50 times or less, and still more preferably 0.20 times or less. By adjusting the relationship between the column top pressure of the low boiling separation column 5 and the reboiler pressure of the high boiling separation column 3 to the above preferred range, the pressure in the high boiling separation column can be stabilized, and the first distillation can be performed. The variation of the pressure value of the tower is controlled within ±7% of the central value, within ±5%, and within ±3%. Thereby, precise distillation can be carried out in the first distillation column, and it is easy to purify allyl alcohol and propionitrile in acetonitrile. The concentration of azole and ammonia is kept low.

The steam water generated in the reboiler 3b is stored in a steam water tank (not shown) provided as needed, and sent to a condenser of the product tower 6 by a pump (not shown). Preferably, an exhaust line is provided in the gas phase portion of the steam water tank as needed to return the non-condensed gas to the condenser of the product column 6. The vapor water, the uncondensed gas, and the distillate vapor flowing out of the product column 6 via the branch valve 6v flow into the condenser of the product column 6. As the refrigerant of the condenser of the product tower 6, the fluid is condensed and cooled using water of 35 ° C or lower. The condensate flows down to the reflux drum, a portion of which is returned to the product column 6 as reflux, and the other is passed through line 21 The product is extracted. In the reflux cylinder, an exhaust line 21a is provided for extracting uncondensed gas. Preferably, the non-condensed gas is introduced into the scrubber, and is subjected to absorption treatment with water or the like, and then released into the atmosphere.

Similarly, the steam water generated in the reboiler 3c is stored in a steam water tank (not shown) provided as needed, and sent to a condenser of the low boiling separation column 5 by a pump (not shown). Preferably, an exhaust line is provided in the gas phase portion of the steam water tank as needed to return the non-condensed gas to the condenser of the low boiling separation column 5. The vapor water, the non-condensed gas, and the distillate vapor flowing out of the low-boiling point separation column 5 via the branch valve 5v flow into the condenser of the low-boiling separation column 5. As the refrigerant of the condenser of the low boiling separation column 5, condensation and cooling of the above fluid are carried out using water of 35 ° C or lower. The condensate flows down to the reflux drum, a portion of which is returned to the low boiling separation column 5 as reflux, and the other is extracted as a low boiling point compound through line 18. In the recirculation cylinder, an exhaust line 18a is provided for extracting uncondensed gas. Preferably, the non-condensed gas is introduced into the scrubber, and is subjected to absorption treatment with water or the like, and then released into the atmosphere.

By using the vapor distilled from the low boiling separation column 5 and/or the product column 6 as a heat source for distillation of the high boiling separation column 3, it is possible to reduce the amount of reboiler vapor used in the high boiling separation column 3. The energy reduction of the use of the condenser cooling water in the low boiling separation column 5 and/or the product column 6 can be achieved, and the miniaturization of the condenser of the low boiling separation column 5 and/or the product column 6 can be achieved. The vapor distilled from the low boiling separation column 5 and/or the product column 6 is passed through a dedicated reboiler, refluxed, and extracted. By providing a dedicated reboiler, heat can be independently and independently supplied to each of the columns of the high boiling separation column 3, and can be refluxed to the low boiling separation column 5 and/or the product column 6 without contamination. Moreover, the reflux flow can be stabilized, and the overall acetonitrile purification process is less likely to be disturbed.

Each of the distillation columns preferably has a condenser at the top of the column and a layered column or packed column having a reboiler at the bottom of the column. Examples of the layered tower include a cross flow contact type having a downflow tube or a convection contact type having no downflow tube. Further, a blister type, a perforated plate type, a valve type or the like can be used as the opening of the tray. As the number of stages of the distillation column, as long as it is 10 or more There is no particular limitation, and it is preferably 30 to 80. As an example of the packed column, a column filled with an irregular filler and/or a regular filler as a filler can be used. As the irregular filler, for example, Raschig ring, Lexin ring, Pall ring, PSA saddle, Intalus saddle, Teller Packing, Dixon ring or McMahon Packing can be used. Wait. As the regular filler, for example, a filler of a mesh structure can be used. As the material of the irregular and regular fillers, magnetic, metal, plastic or carbon can be used. Moreover, the packed tower can also be provided with a liquid redistribution plate at a suitable height to improve the gas-liquid contact efficiency.

[Examples]

Hereinafter, the present invention will be described in more detail by way of examples, but the invention is not limited to the examples.

Gas chromatography was used for the measurement of the impurity concentration in acetonitrile, and the conditions at this time were as follows.

The gas chromatography method was HP-6890 manufactured by Hewlett-Packard Co., Ltd., and the column was a DB-624 (length 60 m × inner diameter 0.32 mm, film thickness 5.0 μm) manufactured by Agilent Technologies. As the detector, FID (Flame Ionization Detector) was used, and the carrier gas system used helium gas.

The column temperature conditions are as follows.

Initial temperature: 70 ° C

Initial time: 10 minutes

Heating rate: 5.0 ° C / min

Intermediate temperature: 120 ° C

Late time: 10 minutes

Final temperature: 220 ° C

[Comparative Example 1]

Purification of acetonitrile was carried out using the purification apparatus shown in Fig. 1.

From the line 7, a liquid containing 15% by mass of acetonitrile as a by-product of the ammoxidation reaction of propylene was supplied to the acetonitrile concentration column 1. Hydrogen cyanide is separated from line 8 and a portion of the water is separated from line 9. The vapor was taken out from the line 10, and condensed in a condenser (not shown) provided in the line 10 to obtain a liquid containing 65% by mass of acetonitrile. As another composition, water is 32% by mass, hydrogen cyanide is 1.6% by mass, acrylonitrile, allyl alcohol, The total of azole and propionitrile was 1.4% by mass.

The obtained liquid is supplied to the reaction tank 2 through the line 10. A 48% by mass aqueous sodium hydroxide solution was added to the reaction tank 2 from the line 11, and the reaction was carried out at 73 ° C for 8 hours.

The liquid of the reaction tank 2 was sent to the high boiling separation column 3 through the line 12 at 2810 kg/h. The steam of 0.4 MPaG was distilled at 2.8 t/h to a reboiler provided at the bottom of the column. The column top pressure and the bottom pressure are 235 mmHg and 255 mmHg, respectively, and the top temperature and the bottom temperature are 41.5 ° C and 58.9 ° C, respectively. The pressure fluctuation of the high boiling separation column is ±1% based on the above numerical value. The wastewater was treated by extracting a liquid containing allyl alcohol, propionitrile, sodium hydroxide, water, and the like at 770 kg/h from the bottom of the column. The vapor distilled from the overhead is condensed in a condenser. The condensate was refluxed to the high boiling separation column 3 at 3940 kg/h, and supplied from the line 14 to the lower portion of the dehydration column 4 at 2040 kg/h.

The line 15 from the upper portion of the dehydration column 4 was supplied with a 48 mass% aqueous sodium hydroxide solution at 300 kg/h to make liquid-liquid contact with the aqueous crude acetonitrile supplied from the line 14. The aqueous phase is extracted from line 16. The acetonitrile phase was extracted from the line 17 at 1850 kg/h and supplied to the low boiling separation column 5.

The steam of 0.4 MPaG was distilled at 2.6 t/h into the reboiler of the low boiling separation column 5 to carry out distillation. The top pressure and the bottom pressure of the column are 0.1172 MPa and 0.1181 MPa, respectively, and the top temperature and the bottom temperature are 78.8 ° C and 86.4 ° C, respectively. The pressure fluctuation of the low boiling separation column is ±1% based on the above value. The vapor distilled from the overhead is condensed in a condenser. Water at 28 ° C was used as a refrigerant for the condenser. The condensate was refluxed to the low boiling separation column 5 at 4150 kg/h, and extracted from the line 18 at 300 kg/h to remove Oxazole and low boiling point substances. The liquid system of line 18 is treated with wastewater. The 1550 kg/h liquid extracted from line 19 is sent to product column 6.

The steam of 0.4 MPaG was distilled at 1.6 t/h into the reboiler of the product column 6 to carry out distillation. The top pressure and the bottom pressure of the column are 0.1100 MPa and 0.1112 MPa, respectively, and the top temperature and the bottom temperature are 81.2 ° C and 82.2 ° C, respectively. The pressure fluctuation of the product tower is ±1% based on the above numerical value. Wastewater treatment was carried out from line 20 at 70 kg/h to extract a liquid containing propionitrile or a high boiling point substance. The vapor distilled from the overhead is condensed in the condenser and flows down to the reflux drum. As the refrigerant of the condenser, water at 28 ° C was used. The condensate in the reflux drum was refluxed to the product column 6 at 4380 kg/h using a pump, and extracted from the line 21 at 1480 kg/h to obtain purified acetonitrile.

The impurities in the purified acetonitrile were analyzed, and the results shown in Table 1 were obtained.

The amount of reboiler vapor and condenser cooling water used is shown in Table 2.

[Example 1]

As shown in Fig. 2, one reboiler 3b is added to the high boiling separation column 3, and the distilled vapor of the product column 6 is passed to serve as a heat source. Further, a steam water cylinder (not shown) for storing the steam water generated in the reboiler 3b and a pump (not shown) for supplying the steam water in the cylinder to the condenser of the product tower 6 are provided. Except for these, acetonitrile was purified by the same apparatus as in Comparative Example 1.

Initially, the valve 6v in the direction of the condenser of the product tower 6 is fully opened. The valve 6v was slowly closed for one week to increase the heat supply to the reboiler 3b of the high boiling separation column 3. At the same time, the vapor of the reboiler 3a of the high boiling separation column 3 is reduced. Finally, the valve 6v is completely closed. At this time, the top pressure of the product tower 6 (indicated as gauge pressure "A") was 0.0100 MPaG, and the shell pressure of the reboiler 3b (indicated as gauge pressure "B") was 0.0002 MPaG, and the respective changes of A and B were ±1%. The distillation vapor of the product column 6 was 81.2 ° C, and the bottom liquid of the high boiling separation column 3 was 58.9 ° C. Further, the central value of the pressure ratio B/A is 0.020, and the variation is ±3%. During the period when the valve 6v is completely closed, there is no process disorder, and the quality of the obtained acetonitrile is not problematic. After the valve 6v is completely closed, all of the distillate vapor of the product column 6 flows into the reboiler 3b of the high boiling separation column 3, and then the vapor water discharged from the reboiler 3b is discharged to a cylinder (not shown). The vapor water in the cylinder flows into the product tower condenser by means of a pump (not shown).

The impurities of the purified acetonitrile were analyzed, and the results shown in Table 3 were obtained.

The amount of reboiler vapor and condenser cooling water used is shown in Table 4.

[Embodiment 2]

In addition to the distillate vapor of the product column 6, the distillate vapor of the low boiling separation column 5 is further used as the heat source of the reboiler 3c of the high boiling separation column 3, except that the same as in the first embodiment. Equipment for purification of acetonitrile. The flow direction of the distillate vapor of the low boiling separation column 5 is as shown in FIG.

Initially, the valve 5v in the condenser direction of the low boiling separation column 5 is completely opened. During the period when the valve 5v is fully opened, there is no process disorder, and the quality of the obtained acetonitrile is not problematic. It takes 5 weeks to slowly close the valve 5v and finally closes 10% (90% open state). At this time, the column top pressure (indicated as gauge pressure "A") of the low boiling separation column 5 was 0.0172 MPaG, and the column top temperature and the bottom temperature were 78.8 ° C and 86.4 ° C, respectively. The shell pressure (denoted as gauge pressure "B") of the reboiler 3c of the high boiling separation column 3 was 0.0032 MPaG, and the temperature at the top of the column and the temperature at the bottom of the column were 41.5 ° C and 58.9 ° C, respectively. Further, the central value of the pressure ratio B/A is 0.19. Further, the pressure at the top of the high boiling separation column was ±1%.

The top pressure of the product tower 6 (denoted as gauge pressure "A'") is 0.0100 MPaG, and the shell pressure of the reboiler 3b (denoted as gauge pressure "B'") is 0.0002 MPaG, and the respective changes of A' and B' It is ±1%.

The impurities of the purified acetonitrile were analyzed, and the results shown in Table 5 were obtained.

The amount of reboiler vapor and condenser cooling water used is shown in Table 6.

[Comparative Example 2]

As shown in Fig. 4, one reboiler 3c was added to the high boiling separation column 3, and the bottom liquid of the low boiling separation column 5 was passed as a heat source, and the same equipment as in Comparative Example 1 was used. pure Acetonitrile.

Initially, the bypass valve 51v of the high boiling separation tower additional reboiler 3c is fully opened. The above bypass valve 51v is gradually closed to increase the heat supply to the reboiler 3b of the high boiling separation column 3. Finally, the valve 51v is completely closed. During this period, the temperature and pressure of each of the high boiling separation column 3 and the low boiling separation column 5 were ±1%.

The impurities of the purified acetonitrile were analyzed, and the results shown in Table 7 were obtained.

The amounts of reboiler vapor and condenser cooling water used are shown in Table 8, and the total amount of use was not different from that of Comparative Example 1.

[Example 3]

The acetonitrile was purified by the same apparatus and method as in Example 2 except that the valve 5v was finally closed by 50%. Initially, the column top pressure (gauge pressure) of the low boiling separation column 5 was 0.0172 MPaG, and the column top temperature and the bottom temperature were 78.8 ° C and 86.4 ° C, respectively. The shell pressure (gauge pressure) of the reboiler 3c of the high boiling separation column 3 was 0.0168 MPaG, and the temperature at the top of the column and the temperature at the bottom of the column were 41.5 ° C and 58.9 ° C, respectively.

The impurities of the purified acetonitrile were analyzed, and the results shown in Table 9 were obtained.

The amount of reboiler vapor and condenser cooling water used is shown in Table 10.

Shortly after the start of purification, the pressures of the low boiling separation column 5 and the high boiling separation column 3 were maintained at ±10%, respectively, but after about one day, the shell pressure (gauge pressure) of the reboiler 3c of the high boiling separation column 3 was Fluctuation between 0.0071MPaG~0.0170MPaG. Along with this, the pressures of the high boiling separation column 3 and the low boiling separation column 5 also start to fluctuate within a range of about ± 20%.

The impurities of the purified acetonitrile after the start of the fluctuation were analyzed, and as a result, the results shown in Table 11 were obtained.

[Examples 4 to 9]

The valve 5v was gradually closed from the state of the second embodiment. The degree of closure of the valve 5v at this time (closed condition) and the column top pressure of the low boiling separation column 5 and the shell pressure of the high boiling separation column reboiler 3b are shown in Table 12. Further, the impurity concentration of the valve 5v is also shown in Table 12.

The amounts of use of the reboiler vapor and the condenser cooling water are shown in Table 13.

[Embodiment 10]

Purification of acetonitrile was carried out by supplying a liquid containing 12% by mass of acetonitrile as a by-product of the ammoxidation reaction of propane to the same apparatus as in Example 2.

A liquid containing 12% by mass of acetonitrile was supplied from the line 7 to the acetonitrile concentration column 1. Hydrogen cyanide is separated from line 8 and a portion of the water is separated from line 9. The vapor was extracted from the line 10 and condensed in a condenser (not shown) provided in the line 10 to obtain a liquid containing 64% by mass of acetonitrile. As another composition, water was 33% by mass, hydrogen cyanide was 1.7% by mass, and the total of acrylonitrile, allyl alcohol, and propionitrile was 1.3% by mass.

The liquid obtained in the above is supplied to the reaction tank 2 through the line 10. A 48% by mass aqueous sodium hydroxide solution was added to the reaction tank 2 from the line 11, and the reaction was carried out at 73 ° C for 8 hours.

The liquid of the reaction tank 2 was sent to the high boiling separation column 3 through the line 12 at 2810 kg/h. The steam of 0.4 MPaG was distilled at 2.8 t/h to a reboiler provided at the bottom of the column. The column top pressure and the bottom pressure are 235 mmHg and 255 mmHg, respectively, and the top temperature and the bottom temperature are 41.5 ° C and 58.9 ° C, respectively. The pressure fluctuation of the high boiling separation column is ±1% based on the above numerical value. The wastewater was treated by extracting a liquid containing allyl alcohol, propionitrile, sodium hydroxide, water, and the like at 770 kg/h from the bottom of the column. The vapor distilled from the overhead is condensed in a condenser. The condensate was refluxed to the high boiling separation column 3 at 3940 kg/h, and supplied from the line 14 to the lower portion of the dehydration column 4 at 2040 kg/h.

The line 15 from the upper portion of the dehydration column 4 was supplied with a 48 mass% aqueous sodium hydroxide solution at 300 kg/h to make liquid-liquid contact with the aqueous crude acetonitrile supplied from the line 14. The aqueous phase is extracted from line 16. The acetonitrile phase was extracted from the line 17 at 1850 kg/h and supplied to the low boiling separation column 5.

The steam of 0.4 MPaG was distilled at 2.6 t/h into the reboiler of the low boiling separation column 5 to carry out distillation. The top pressure and the bottom pressure of the column are 0.1172 MPa and 0.1181 MPa, respectively, and the top temperature and the bottom temperature are 78.8 ° C and 86.4 ° C, respectively. The pressure fluctuation of the low boiling separation column is ±1% based on the above value. The vapor distilled from the overhead is condensed in a condenser. As the refrigerant of the condenser, water at 28 ° C was used. The condensate was refluxed to the low boiling separation column 5 at 4,150 kg/h, and extracted from the line 18 at 300 kg/h to remove low-boiling substances. The liquid system of line 18 is treated with wastewater. The 1550 kg/h liquid extracted from line 19 is sent to product column 6.

The steam of 0.4 MPaG was distilled at 1.6 t/h into the reboiler of the product column 6 to carry out distillation. The top pressure and the bottom pressure of the column are 0.1100 MPa and 0.1112 MPa, respectively, and the top temperature and the bottom temperature are 81.2 ° C and 82.2 ° C, respectively. The pressure fluctuation of the product tower is ±1% based on the above numerical value. Waste water treatment was carried out by extracting 70 kg/h of a liquid containing propionitrile or a high-boiling substance from the line 20. The vapor distilled from the overhead is condensed in the condenser and flows down to the reflux drum. As the refrigerant of the condenser, water at 28 ° C was used. The condensate in the reflux drum was refluxed to the product column 6 at 4,380 kg/h by means of a pump, and extracted from the line 21 at 1480 kg/h to obtain purified acetonitrile. The analysis results of the impurities in the purified acetonitrile are shown in Table 14. again The amount of use of the boiler vapor and the condenser cooling water was the same as in Comparative Example 1.

In the above-described process, reboilers 3b and 3c as shown in Figs. 2 and 3 are added to the high boiling separation column 3.

The valve 6v is gradually closed to increase the heat supply to the reboiler 3b of the high boiling separation column 3. The valve 6v is finally completely closed. At this time, the top pressure of the product tower 6 (indicated as gauge pressure "A") was 0.0100 MPaG, the shell pressure of the reboiler 3b (denoted as gauge pressure "B") was 0.0020 MPaG, and the pressure ratio B/A was 0.020. . Further, the pressure at the top of the high boiling separation column was ±0%.

Then, the valve 5v is slowly closed, and finally 35% is closed. At this time, the column top pressure of the low boiling separation column 5 (indicated as gauge pressure "A'") is 0.0172 MPaG, and the shell pressure (denoted as gauge pressure "B'") of the reboiler 3c of the high boiling separation column 3 is 0.0108 MPaG, the central value of the pressure ratio B'/A' is 0.63. Further, the pressure at the top of the high boiling separation column was ±1%.

The impurities of the purified acetonitrile were analyzed, and the results shown in Table 15 were obtained.

The amount of reboiler vapor and condenser cooling water used is shown in Table 16.

As is apparent from the results of the above examples and comparative examples, in the process of purifying high-purity acetonitrile, the vapor distilled from the product column 6 and/or the low-boiling separation column 5 is used as the reboiling of the high-boiling separation column 3. The heat source of the device can significantly reduce the energy consumption in the process.

The present application is based on Japanese Patent Application No. 2012-070086, filed on Jan.

[Industrial availability]

The invention is a process for purifying the energy consumption, and the purification equipment and the steps are simple. Therefore, the increase in cost can be minimized, and the solvent which can be used for synthesis and purification of a pharmaceutical intermediate, DNA synthesis, a purification solvent, a solvent for synthesizing an organic EL material, a cleaning solvent for an electronic component, and the like can be efficiently purified. High purity acetonitrile for use.

Claims (8)

A method for purifying acetonitrile, comprising the steps of: adding a base to an acetonitrile containing water formed by an ammoxidation reaction, and then supplying the reaction mixture to a first distillation column to obtain a distillate Further, after the mixture with the alkali is separated into an acetonitrile phase and an aqueous phase, the aqueous phase is removed, and the acetonitrile phase is supplied to the second distillation column; and the distillate vapor from the second distillation column is used as the first The heat source of the reboiler of the distillation column. A method for purifying acetonitrile according to claim 1, wherein a part of the above-mentioned distillate vapor is supplied to the reboiler, and the remaining portion is supplied to a condenser connected to the second distillation column. The method for purifying acetonitrile according to claim 1 or 2, wherein the above-mentioned distillate is determined on the basis of a gauge pressure on a distilling vapor side of a reboiler of the first distillation column and a gauge pressure of a top of the second distillation column. The amount of steam supplied to the reboiler described above. The method for purifying acetonitrile according to claim 3, wherein the surface pressure of the distillate vapor side of the reboiler of the first distillation column is 0.90 times or less of the gauge pressure of the top of the second distillation column. A purification device for acetonitrile, which is provided with a reaction tank, a first distillation column, a dehydration column, and a second distillation column in this order. After the reaction of the acetonitrile containing water and the alkali in the reaction tank, the reaction mixture flows into the first distillation column. The distillate of the first distillation column flows into the dehydration column, the acetonitrile phase obtained in the dehydration column flows into the second distillation column, and the distillate vapor of the second distillation column is used as the first distillation. The heat source of the reboiler of the tower. A purification apparatus for acetonitrile according to claim 5, wherein one part of the above-mentioned distillate vapor is supplied To the above reboiler, the remainder is supplied to a condenser connected to the second distillation column. The purification apparatus of acetonitrile according to claim 5 or 6, wherein the supply amount of the distillate vapor to the reboiler is a gauge pressure of a distillate vapor side of a reboiler of the first distillation column, and the second distillation column The pressure at the top of the tower is determined based on the benchmark. The apparatus for purifying acetonitrile according to claim 7, wherein the gauge pressure on the vapor-off side of the reboiler of the first distillation column is 0.90 times or less the gauge pressure of the top of the second distillation column.