KR101648653B1 - Method for purifying acetonitrile - Google Patents

Abstract

The present invention relates to a process for the production of acetonitrile, which comprises reacting an acetonitrile containing water produced by an ammoxidation reaction with an alkali and reacting the reaction mixture, supplying the reaction mixture to the first distillation column, further mixing the obtained effluent with the alkali, Removing the aqueous phase and supplying the acetonitrile phase to a second distillation column, the method comprising the steps of: discharging the effluent from the second distillation column to the reboiler of the first distillation column; As a heat source of acetonitrile.

Description

METHOD FOR PURIFYING ACETONITRILE < RTI ID = 0.0 >

The present invention relates to a method for purifying acetonitrile.

At present, generally commercially available acetonitrile is used mainly as a byproduct in the production of acrylonitrile or methacrylonitrile by catalytic ammoxidation reaction of propylene or isobutene with ammonia and oxygen, Acetonitrile was recovered and purified.

Acetonitrile is used as a solvent for chemical reactions, in particular in the synthesis and purification of medicinal intermediates, as a mobile phase solvent for high-performance liquid chromatography, and the like. In recent years, it has also been used in DNA synthesis and purification solvents, solvents for synthesizing organic EL materials, cleaning solvents for electronic components, and the like.

The acetonitrile obtained as a by-product in the production of acrylonitrile or methacrylonitrile includes allyl alcohol, oxazole, water, acetone, cyanide, acrylonitrile, methacrylonitrile, propionitrile, cis- and trans - impurities such as croton nitrile, acrylic acid, methyl acrylate, methacrylic acid, methyl methacrylate, acetic acid, acrolein, methacrolein, acetone and ammonia, impurities which can not be analyzed and the like.

Up to now, there has been proposed a method for recovering and purifying crude acetonitrile, which is obtained as a by-product when acrylonitrile or methacrylonitrile is produced by catalytic ammoxidation reaction of propylene or isobutene with ammonia and oxygen .

Patent Document 1 discloses a dehydration method of acetonitrile in which a sufficient amount of an alkali is added to and mixed with a functional acetonitrile to extract the water present therein, and subsequently the separated aqueous phase is removed. Patent Document 2 discloses a method for producing acetonitrile, and discloses a method in which acetone, ethyl alcohol, or both are coexisted in a reaction system when unsaturated nitrile and acetonitrile are produced by ammoxidation.

Patent Document 1: Japanese Patent Application Laid-Open No. 55-153757 Patent Document 2: JP-A-03-246269

According to the method described in Patent Document 1 or 2, although it is possible to produce acetonitrile of high purity, a lot of facilities are required because a plurality of treatment steps must be performed in order to obtain high purity. As a result, the energy consumption necessary for the purification (for example, the steam for heating the distillation column, the energy for generating the cooling water of the column top) is increased, and the cost is greatly increased. Here, when a measure for reducing the energy consumption generally performed, such as the utilization of waste heat, is simply applied to the acetonitrile refining process, a disturbance such as temperature or pressure fluctuation occurs in the apparatus for exchanging heat, There arises a problem that the impurity concentration in the raw material is increased and the quality is not stabilized, and therefore, there is a problem that it is not possible to supply acetonitrile with high purity to a user who needs it. Therefore, it is a phenomenon that a method of purifying acetonitrile with a low purity and high purity is required.

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

DISCLOSURE OF THE INVENTION As a result of intensive studies to solve the above problems, the present inventors have found that a method of purifying crude acetonitrile recovered in a step of producing acrylonitrile or methacrylonitrile by ammoxidation using two or more distillation columns , It has been found that the tower rectification of the second distillation column can be used as the heat source of the reboiler of the first distillation column. It has been found that the use of this heat source can provide a process with a small energy consumption to be used for purification, thereby completing the present invention.

That is, the present invention is as follows.

[One]

The reaction mixture is supplied to the first distillation column, and the resultant effluent is further mixed with the alkali, which is separated from the acetonitrile phase and the water phase Removing the water phase, and supplying the acetonitrile phase to the second distillation column,

And the effluent steam from the second distillation column is used as a heat source of the reboiler of the first distillation column.

[2]

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

[3]

(1) above, wherein the supply amount of the outflow steam to the reboiler is determined based on the reboiler pressure (outflow steam side, gauge pressure) of the first distillation tower and the top pressure (gauge pressure) of the second distillation tower, Or the acetonitrile described in [2].

[4]

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

[5]

A reaction tank, a first distillation column, a dehydration column, and a second distillation column are installed in this order,

The reaction mixture is introduced into the first distillation column, the effluent of the first distillation column flows into the dehydration column, and the acetonitrile phase obtained from the dehydration column is separated from the second Is introduced into the distillation column,

And the effluent steam of the second distillation tower serves as a heat source of the reboiler of the first distillation column.

[6]

The apparatus for purifying acetonitrile according to [5], wherein a part of the effluent vapor is supplied to the reboiler and the remainder is supplied to a condenser connected to the second distillation column.

[7]

Wherein the supply amount of the outflow steam to the reboiler is determined based on the reboiler pressure (outflow steam side, gauge pressure) of the first distillation tower and the top pressure of the second distillation tower (gauge pressure) The apparatus for purifying acetonitrile according to [6].

[8]

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

By the method of purifying acetonitrile of the present invention, it is possible to purify acetonitrile of high purity with a process with a small energy consumption.

Fig. 1 shows an example of a schematic diagram of an acetonitrile production apparatus in this embodiment.
Figure 2 shows a schematic view of an apparatus for feeding at least a part of the vapor exiting from the top of the product tower as a heat source to a reboiler of a high boiling separation tower.
Fig. 3 shows a schematic diagram of an apparatus for supplying at least a part of the vapor exiting from the top of a low-boiling separation column as a heat source to a reboiler of a high boiler separation column.
4 is a schematic view of an apparatus for supplying at least a part of the bottom liquid of the low-boiling-off column as a heat source to the reboiler of the high boiling-off column.

Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as " present embodiment ") will be described in detail. The following embodiments are illustrative of the present invention and are not intended to limit the present invention to the following contents. The present invention can be appropriately modified within the scope of the gist of the invention. In the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. Further, the positional relationships of the up, down, left, and right sides are based on the positional relationships shown in the drawings unless otherwise specified. The dimension ratio of the device or member is not limited to the illustrated ratio.

In the method for purifying acetonitrile in this embodiment,

The reaction mixture is supplied to the first distillation column, and the resultant effluent is further mixed with the alkali, which is separated from the acetonitrile phase and the water phase Removing the water phase, and supplying the acetonitrile phase to the second distillation column,

And the effluent steam from the second distillation column serves as a heat source for the reboiler of the first distillation column.

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

A reaction tank, a first distillation column, a dehydration column, and a second distillation column are installed in this order,

The reaction mixture is introduced into the first distillation column, the effluent of the first distillation column flows into the dehydration column, and the acetonitrile phase obtained from the dehydration column is separated from the second Is introduced into the distillation column,

Wherein the effluent vapor of the second distillation tower serves as a heat source of the reboiler of the first distillation column.

Fig. 1 shows an example of a schematic diagram of an apparatus for purifying acetonitrile in this embodiment. The apparatus shown in Figure 1 has a concentrating tower 1 into which the zeatonitonitrile is introduced and is connected to a concentrating tower 1 through a reactor 2 through a gaseous separation tower 3, a dehydration tower 4, (5) and product tower (6) are connected in this order.

Joacetonitrile is obtained as a by-product when acrylonitrile or methacrylonitrile is produced from propylene, propane, isobutene and isobutane by catalytic ammoxidation reaction. In general, the product of the ammoxidation reaction is subjected to extraction and distillation, and the crude acetonitrile is recovered as an oil separate from the distillate containing acrylonitrile or methacrylonitrile as a main component. Here, the term " crude acetonitrile " means that the content of acetonitrile is the highest in the oil fraction obtained by extractive distillation of the product of the ammoxidation reaction. Joacetonitrile is generally separated from a distillation column which collects most of acrylonitrile and is generally used in an amount of from 5 to 40 mass% of acetonitrile, from 50 to 95 mass% of water, in addition to hydrogen cyanide, allyl alcohol, Propionitrile, ammonia, and the like.

The zeacatonitrile is sent from line 7 to the halt of the acetonitrile concentration tower 1. The acetonitrile concentrating tower 1 has a reboiler (not shown) on the column bottom and a condenser (not shown) on the column top as an upright distillation column. (Hereinafter also referred to as " concentrated acetonitrile ") from the tower core (line 8) while removing water from the column bottom (line 9) Out. The line 10 is provided with a side cut condenser (not shown), and the gaseous concentrated acetonitrile is condensed by the side cut condenser. Concentrated acetonitrile in the liquid phase flowing out of the side cut condenser flows into the reaction tank 2. The concentration of acetonitrile in the concentrated acetonitrile supplied from the concentrating tower 1 to the reaction tank 2 is usually 50 to 70 mass%, and further contains 25 to 70 mass% of water, other impurities such as hydrogen cyanide and allyl alcohol .

An alkaline aqueous solution such as an aqueous solution of sodium hydroxide or an aqueous solution of potassium hydroxide is added to the reaction tank 2 through the line 11 to convert acrylonitrile and hydrogen cyanide contained in the concentrated acetonitrile as impurities into succinonitrile and dimer Change into a polymer. The temperature of the reaction tank 2 is preferably 20 占 폚 to 80 占 폚, more preferably 60 占 폚 to 75 占 폚 for 1 to 15 hours, further preferably 60 占 폚 to 75 占 폚 For 3 to 10 hours.

The liquid flowing out from the reaction tank 2 is sent to the goby separation column 3 through the line 12. From the viewpoint of separation of high boiling point water, the gaseous separation column 3 is preferably a reduced pressure distillation column. Acetonitrile is recovered from the top of the giant fractionation column 3 as an azeotropic mixture with water or a composition mixture close thereto, and is liquefied by a condenser (not shown). A portion of the condensate is refluxed to the gaseous separation column 3 by a line not shown and the remainder is sent to the dehydration tower 4 through the line 14. Alkali, allyl alcohol, propionitrile, water, and a small amount of acetonitrile produced in the reaction tank 2, such as succinonitrile or dimer, are separated from the bottom line 13 and sent to a wastewater treatment facility. A reboiler (not shown) for supplying heat required for distillation is provided in the bottom of the column, and supplies heat required for distillation. In the goby separation column 3, it is important to constantly and stably supply the amount of heat required for distillation in order to stably separate and remove allyl alcohol and propionitrile. The allyl alcohol and propionitrile are particularly difficult to separate, and it is preferable to separate them as far as possible from the goby separation column (3).

The pressure of the goby separation column 3 is preferably in the range of 80 to 300 at an absolute pressure in view of separation of high boiling substances such as allyl alcohol and propionitrile and decomposition of succinonitrile and dimer produced in the reaction tank 2 mmHg, and more preferably 100 to 250 mmHg. When the pressure is set within the above range, the temperature of the bottom of the tower is preferably 45 to 65 ° C, more preferably 50 to 60 ° C, and the temperature of the tower top is preferably 35 to 60 ° C, And more preferably 40 ° C to 50 ° C.

In addition to the tower rectification of the goby separation column 3, the dehydration tower 4 is further provided with an alkali in an amount sufficient for extracting the water present therein, through the line 15 and mixing, (16) to obtain an acetonitrile phase from line (17). As the alkali, it is preferable to use an aqueous solution or solid of sodium hydroxide and / or potassium hydroxide, more preferably an aqueous solution thereof.

The extraction temperature in the dehydration tower 4 is preferably 5 to 60 캜, more preferably 10 to 35 캜. Here, the extraction temperature refers to the temperature in the dehydration tower 4, and more specifically, the temperature of the internal solution at the alkali feed position from the top feed side feed position of the high boiling separation column 3 in the dehydration tower 4 .

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

After the dehydration, two or more distillation columns are preferably used in order to separate and remove the compound having a low boiling point and the compound having a high boiling point compared to acetonitrile. Concretely, the low-boiling point compound 5 is separated and removed from the column top through the line 18 in the low-boiling separation column 5, and the bottom column of the low-boiling separation column 5 is fed via line 19 to the product column 6 It is preferable to separate the high boiling point compound from the column through the line 20 in the product column 6 to obtain purified acetonitrile from the line 21 of the column.

In the low-boiling separation column 5 and the product column 6, the reflux ratio, the amount of the low boiling point compound and the high boiling point compound can be suitably determined so as to be a refining degree suitable for the purpose. The reflux ratio of the low-boiling separation column 5 and the product column 6 is preferably 1 to 50, and more preferably 2 to 30, depending on the target refining scheme. The reflux ratio is defined as the mass of reflux to the distillation column divided by the mass exiting the distillation column. The reflux ratio is suitable for purifying acetonitrile of high purity to maintain a predetermined value stably during operation from the viewpoint of efficient separation and removal of impurities by distillation. The overhead pressure of the low-boiling-off column 5 and the product column 6 is set in the vicinity of the normal pressure in view of energy efficiency and impurity separation. The lower limit of the overhead pressure is preferably 0.090 MPa or higher, more preferably 0.095 MPa or higher, even more preferably 0.100 MPa or higher, and the upper limit is preferably 0.180 MPa or lower, more preferably 0.150 MPa or lower, Or less, more preferably 0.130 MPa or less. When the column top pressure is set in the above preferable range, the column bottom temperatures of the low-boiling separation column 5 and the product column 6 are preferably 80 ° C to 95 ° C, more preferably 80 ° C to 88 ° C, Is preferably 70 ° C to 90 ° C, and more preferably 70 ° C to 85 ° C.

In the purification method of the present embodiment, at least a part of the steam flowing out from the top of the product column 6 and / or the low-boiling-off column 5 is supplied as a heat source to the reboiler of the boiler-

Fig. 2 shows a schematic view of an apparatus for supplying at least a part of the steam flowing out of the top of the product column 6 as a heat source to the reboiler 3b of the boiler separation column 3. In the example shown in Fig. 2, the reboiler 3b is a shell tube type in which the outflow steam from the top of the product column 6 is supplied to the shell side, and the bottom column of the goby separation column 3, Heat it. A plurality of reboilers 3a and 3b are installed in the goby separation column 3 and the outflow steam of the product column 6 is introduced into the reboiler 3b of the boiler- , And the other reboiler 3a is supplied with a separate heat source. The steam drain discharged from the reboiler of the goby separation column 3 passes through a heat exchanger such as a condenser or the like and is cooled by water or the like and then discharged from the product tower 6). ≪ / RTI >

3 shows a schematic view of an apparatus for supplying at least a part of the steam flowing out of the column top of the low-boiling-off column 5 as a heat source to the reboiler 3c of the high boiling column 3. The apparatus shown in Fig. 3 is the same as the example shown in Fig. 2 except that the steam flowing out from the low-boiling-off column 5 is supplied to the reboiler 3c of the goby separation column 3, The following description is given below. Although the top temperature of the low-boiling separation column 5 may be lower than the column top temperature of the product column 6, depending on the design and operating conditions such as the pressure in the column, If it is higher than the column bottom temperature, it can be used as a heat source. Since the overhead vapor of the low boiling separation column 5 contains a low boiling point component at a high concentration, it may be difficult to condense in the reboiler 3c as compared with that of the product column 6, Setting the reboiler temperature is a preferred mode.

Desired pressures and overhead temperatures of the low-boiling separation column 5 and product column 6 have been described above, but since they also affect the utilization of the effluent vapors, there are also desirable pressures and overhead temperatures in that respect. Concretely, in order to utilize the outflow steam as a heat source, the temperature of the outflow steam must be higher than the temperature of the bottom liquid of the distillation tower which is fed to the reboiler to be supplied. It is then desirable to set the pressure of the distillation column. Of course, it is also effective to adjust the pressure of the distillation column to which the reboiler is connected, because the effluent vapor can be used even by lowering the temperature of the bottom side of the column of the distillation column. The operation of the low boiling separation column 5 and / or the product column 6 at atmospheric pressure or a pressure near that and the decomposition distillation of the gaseous separation column 3 is carried out in such a manner that the outlet vapor temperature is lowered to the lower boiling point Temperature is higher than the temperature.

The reboilers 3b and 3c through which the outflow vapors pass may be dedicated to idle facilities or may be newly designed. In the case of a new design, it is designed in the following manner.

First, the heat quantity q that can be supplied to the gaseous separation column 3 through the reboiler is calculated from the flow rate of the outflow steam and the enthalpy when all of the steam is condensed. Subsequently, the heat transfer area is calculated to determine the size of the reboiler. The heat quantity q is the product of the total heat transfer coefficient U, the heat transfer area A and the temperature difference T, that is q = U · A · ΔT. U can be obtained by using the actual value of the reboiler generally used as a chemical plant, or by a chemical engineering method. In the present embodiment,? T is a temperature difference between the temperature of the effluent vapor and the bottom liquid of the high boiling separation column (3). ΔT arises from the difference in the operating conditions of the first distillation column and the second distillation column. Since the present embodiment is for purifying acetonitrile containing water produced by the ammoxidation reaction, the composition ratios of the first distillation column and the second distillation column do not greatly vary. Thus, the conditions of each distillation column are controlled to be substantially constant.

In the purification of the acetonitrile of the present embodiment, the temperature of the first distillation column and the temperature of the second distillation column are preferably in the range of 45 ° C. to 65 ° C. Deg.] C, more preferably 50 [deg.] C to 60 [deg.] C, and the top temperature of the second distillation column is preferably 70 [deg.] C to 90 [deg.] C, Therefore,? T is preferably 10 to 35 占 폚, and more preferably 15 to 25 占 폚. From this, the heat transfer area A is inevitably set in a specific range. By using a reboiler having a heat transfer area (A) capable of procuring the heat quantity (q) necessary for distillation in a range of 10 ° C to 35 ° C, the outlet steam from the second distillation tower is supplied to the reboiler of the first distillation tower Stable operation using as a heat source becomes possible.

On the other hand, in the case where the idle facility is dedicated, the heat transfer area (A) becomes the prescribed value, but the heat transfer area (A) in which the heat quantity (q) necessary for the distillation can be procured within the range of 10 [ It is possible to use the effluent steam from the second distillation column as a heat source of the reboiler of the first distillation column to perform stable operation.

The use of at least a part of the vapor flowing out from the low-boiling separation column 5 and / or the product column 6 as a heat source necessary for distillation of the gaseous fractionation column 3 adversely affects the accuracy of distillation in the column Do not let it go crazy. The low-boiling separation column 5 and the product column 6 are apparatuses for precisely distilling a liquid having an acetonitrile concentration of 95 mass% or more and 99 mass% or more, respectively. If the disturbance accuracy is adversely affected, it is considered that the disturbance of the low-boiling-separation column 5 and / or the product column 6 providing the effluent vapor is disturbed by the disturbance of the goby- There is a case where the following occurs. On the other hand, on the other hand, disturbance of the goby separation column 3 may lead to disturbance of the low-boiling separation column 5 and / or product column 6. For example, when the temperature and / or pressure of the low-boiling-separation column 5 and / or the product column 6 deviate from the target value during normal operation (see, for example, Disturbed), the amount of vapor flowing out of the distillation column fluctuates. As a result, the amount of steam supplied as a heat source to the reboiler of the goby separation column 3 fluctuates, so that the amount of heat supplied to the goby separation column 3 fluctuates continuously. Further, the distillation operation becomes unstable due to fluctuation of the reflux ratio in the gaseous separation column (3), and the accuracy of the distillation is adversely affected. When the distillation in the goby separation column (3) becomes unstable, separation and removal of allyl alcohol and propionitrile can not be sufficiently carried out, resulting in a serious impact on the quality of high purity acetonitrile. On the contrary, when the temperature and / or the pressure of the goby separation column 3 are disturbed, the amount of the outflow steam condensed on the shell side of the reboiler of the goby separation column 3 varies. The effluent steam is condensed in the reboiler and then introduced into the condenser of the low boiling separation column 5 and / or the product column 6 to be refluxed. Therefore, if the condensation amount fluctuates, the low boiling separation column 5 and / The change in the reflux amount of the column 6 and the thermal load naturally fluctuate. Therefore, the disturbance of the goby separation column 3 is transferred to the low-boiling separation column 5 and / or the product column 6, adversely affecting the stability of the column pressure. The low-boiling separation column 5 and the product column 6 are distillation columns for precisely distilling acetonitrile, and impurities in high purity acetonitrile such as oxazole, hydrogen cyanide, water, ammonia, and other trace impurities There is an adverse effect on the separation of

If there is disturbance in the distillation of each tower, the purity of the obtained acetonitrile is lowered, and in some cases, the value as a product is lost. Since high purity acetonitrile is required to be used in DNA synthesis and purification solvents, solvents for synthesizing organic EL materials, cleaning solvents for electronic components, etc. in addition to HPLC solvents, the products are required to have a high purity and a concentration of impurities It is desired to be constant without elevation. In view of the above, the inventors of the present invention have made extensive studies on a method for stabilizing the system to exchange heat in the utilization of the effluent vapor of the distillation column.

In the case where the effluent vapor of the product tower 6 is supplied to the shell side of the reboiler 3b of the goby separation column 3 and used as a heat source in view of the stability of the product column 6, It is preferable to stabilize the amount of heat supplied by passing a certain amount of steam from a utility supply facility which is a facility for generating and supplying steam exclusively without using outflow steam such as other distillation towers. The pressure of the steam supplied from the utility supply equipment is preferably 1.0 MPaG or less, more preferably 0.6 MPaG or less, from the viewpoint that the temperature difference with the liquid to be heated is proper.

Further, the inventors of the present invention have found that the precision of the distillation purification can be well maintained by adjusting the relationship between the column top pressure of the distillation column supplying the effluent vapor and the pressure of the goble separation column reboiler passing the effluent vapor to a specific range .

The amount of steam supplied from the second distillation tower (low-boiling-down column 5 and product column 6) to the reboiler 3b of the first distillation column (high boiling column 3) It is preferable to determine the pressure on the basis of the pressure (outlet vapor side, gauge pressure) and the top pressure (gauge pressure) of the second distillation column. Generally, the gauge pressure of the reboiler shell is zero when the effluent vapor is fully condensed in the reboiler shell, since the gauge pressure represents the relative value of the pressure at zero atmospheric pressure. Depending on the fluid temperature on the side of the reboiler tube (the temperature of the bottom of the distillation tower). The pressure (gauge pressure) measured by the pressure gauge attached to the shell side of the reboiler of the first distillation tower is preferably not more than 0.90 times the top pressure (gauge pressure) of the second distillation tower, More preferably 0.50 times or less, and further preferably 0.20 times or less. Although the lower limit value is not particularly limited, assuming that all the outflow vapors are condensed, a value of -0.1 times or more or 0 times or more is a realistic value. In the following embodiment, the top static pressure (gauge pressure) of the product column 6 is denoted by A, the shell pressure (gauge pressure) of the reboiler 3b is denoted by B, .

The fact that the magnification is reduced means that the pressure difference is enlarged. When the pressure difference is enlarged, the flow of the vapor from the top of the second distillation column to the reboiler of the first distillation column tends to be stabilized. When the steam flow is stabilized, the supply of heat is stabilized, and the evaporation amount in the reboiler of the first distillation column is stabilized. As a result, the amount of vapor rising in the first distillation column is stabilized. Liquid contact with the tray in the tower is repeated, and the vapor from the tower is condensed by the condenser, and part of the vapor is refluxed to the tower. The stability of the gas-liquid contact of the distillation column is shown by the pressure and temperature in the column, but can be found by observing the fluctuation of the pressure in particular. When the supply of heat is stable, the variation of the pressure value of the first distillation column is within ± 7% of the median value. In addition, from the viewpoint of reducing impurities in acetonitrile, it is preferably controlled within 5%, more preferably within 3%. When the pressure fluctuation is controlled within ± 5%, heat exchange between the vapor rising in the tray in the first distillation tower and the liquid descending in the tray is appropriately performed. As a result, the impurities such as allyl alcohol and propionitrile to be separated from the first distillation column are concentrated in the bottom of the column by gas-liquid contact, and the amount of the outflow from the column is remarkably reduced.

The shell pressure of the reboiler 3b of the goby separation column 3 depends on the condensable ability of the steam in the shell and the shell pressure tends to decrease as the heat transfer area of the reboiler 3b is larger. It is preferable that the heat transfer area of the reboiler 3b of the goby separation column 3 is calculated based on the above-mentioned calculation and the new facility is installed, but the idle facility may be dedicated. The supply amount of the outflow steam is adjusted on the basis of the shell pressure of the reboiler 3b of the goby separation column 3 and the column top pressure of the product column 6 It is possible to suppress the fluctuation of the supply flow rate, consequently to stabilize the heat supply amount in the reboiler 3b, and to stabilize the distillation purification of the goby separation column 3. That is, when the outflow steam is not condensed or does not occur in the reboiler 3b, pressure fluctuation occurs in the reboiler shell, and this influence is spread to the product column 6 as the supply source of the outflow steam. Since it is possible to stably condense the effluent vapor in the reboiler 3b and return it to the condenser of the product tower 6 at a constant vapor / liquid ratio to contribute to the stabilization of the entire system, the effluent vapor can be stably It is preferable to employ the pressure of the reboiler 3b as an operation indicator for condensing. From the viewpoint of the flow of the fluid, the reboiler pressure is lower than the column top pressure of the product column 6 supplying the effluent steam, and since it is necessary that the pressure value is stable from the viewpoint of stable operation, Do.

When the effluent vapors of the product column (6) are passed through a goby separation column reboiler, the pressure relationship of both columns affects the concentration of allyl alcohol and propionitrile in the purified acetonitrile. For this reason, if the amount of heat supplied to the goby separation column 3 is unstable, the separation performance of allyl alcohol and propionitrile in the gypsum separation column 3 is deteriorated and the column pressure fluctuation of the product column 6 It is presumed that the deterioration of the separation performance of propionitrile in the product column 6 is also caused by the fluctuation of the reflux amount. Therefore, by setting the relationship between the tower top pressure of the product tower 6 and the reboiler pressure of the high boiling tower 3 within the above preferable range, it is easy to keep the concentration of allyl alcohol and propionitrile low.

Similarly, when the effluent vapor of the low-boiling-off column 5 is passed through the boiling-point column reboiler, the pressure relationship between the two columns also influences the concentration of allyl alcohol, propionitrile, oxazole and ammonia in the purified acetonitrile give. For this reason, the present inventors have found that if the amount of heat supplied to the gaseous separation column 3 is unstable for the same reason as the case of the product column 6, separation of allyl alcohol and propionitrile in the grate column 3 It is presumed that the separation performance of oxazole and ammonia in the low-boiling separation column 5 is deteriorated due to variations in the top pressure and the reflux amount of the low-boiling separation column 5 . The pressure (gauge pressure) measured by the pressure gauge attached to the shell side of the reboiler 3c of the goby separation column 3 is lower than the top pressure of the low boiling separation column 5 ), Preferably not more than 0.90 times, more preferably not more than 0.50 times, and more preferably not more than 0.20 times. By regulating the relationship between the top static pressure of the low-boiling separation column 5 and the reboiler pressure of the high boiling separation column 3 to the preferable range, the pressure in the high boiling separation column is stabilized, and the fluctuation of the pressure value of the first distillation column, Respectively, within ± 7%, ± 5%, ± 3% of the median value. Thereby, accurate distillation in the first distillation column becomes possible, and the concentration of allyl alcohol, propionitrile, oxazole and ammonia in the purified acetonitrile can be easily kept low.

The steam drain generated in the reboiler 3b is accumulated in a steam drain drum (not shown) installed if necessary, and is sent to a condenser of the product tower 6 by a pump (not shown). It is preferable that a vent line is provided in the vapor phase portion of the steam drain drum as required and the uncombusted gas is returned to the condenser of the product column 6. [ The condenser of the product tower 6 flows out of the vapor drain, uncondensed gas, and outflow steam flowing from the product column 6 via the branch valve 6v. As the refrigerant of the condenser of the product tower 6, water of 35 DEG C or less is used, and the fluid is condensed and cooled. The condensate flows down to the reflux drum, part of which is returned to the product tower 6 as reflux, and the other is withdrawn as product through the line 21. In the reflux drum, a vent line 21a is provided to extract the gas of non-condensation. It is preferable that the un-condensed gas is introduced into a scrubber, absorbed by water or the like, and then discharged to the atmosphere.

Similarly, the steam drain generated in the reboiler 3c is accumulated in a steam drain drum (not shown) to be installed as required, and is sent to a condenser of the low boiling separation column 5 by a pump (not shown) . It is preferable that a vent line is provided in the vapor phase portion of the vapor drain drum as required and the unconcentrated gas is returned to the condenser of the low boiling separation column 5. [ The condenser of the low boiling point separation column 5 flows out of the vapor drain, uncombusted gas, and outflow steam flowing from the low boiling point separation column 5 via the branch valve 5v. As the refrigerant of the condenser of the low-boiling separation column 5, water of 35 DEG C or less is used, and the fluid is condensed and cooled. The condensate flows down to the reflux drum, part of which is returned to the low boiling separation column 5 as reflux, and the other is withdrawn as the low boiling point compound via the line 18. [ In the reflux drum, a vent line 18a is provided to extract the gas of non-condensation. It is preferable that the un-condensed gas is introduced into a scrubber, absorbed by water or the like, and then discharged to the atmosphere.

By using the steam flowing out from the low-boiling separation column 5 and / or the product column 6 as a heat source for the distillation of the gaseous separation column 3, it is possible to reduce the amount of reboiler steam used in the high boiling separation column 3, It is possible to achieve energy efficiency by reducing the amount of condenser cooling water used in the tower 5 and / or the product tower 6 and to achieve the miniaturization of the condenser of the low-boiling-separation column 5 and / . The steam flowing out from the low-boiling-off column 5 and / or the product column 6 is passed through a dedicated reboiler, and then returned and discharged. By providing a dedicated reboiler, it is possible to independently and stably supply heat to the goby separation column 3 and to reflux the product to the low-boiling separation column 5 and / or the product column 6 without contamination have. In addition, the reflux amount can be stabilized and does not easily lead to disturbance of the entire acetonitrile purification process.

Each distillation column is preferably a tray tower or a packed column having a condenser at the top and a reboiler at the bottom. Examples of the roofing tower include cross-flow contact type having a downcomer and countercurrent contact type having no downcomer. Further, as the opening of the tray, a bubble cap type, a porous plate type, a valve type, or the like can be used. The number of stages of the distillation tower is not particularly limited as long as it is 10 or more stages, but it is preferably 30 to 80 stages. As examples of the packed column, a column filled with a random packing and / or a regular packing may be used as the packing. As the irregular filling, for example, Rashihing, Lessing ring, Polling, Berl saddle, Interlock saddle, Terrarette packing, Dickson ring or McMahon packing can be used. As a regular packing, for example, a packing of a mesh structure can be used. As materials of these irregular and regular packing materials, magnetic agents, metals, plastics or carbon materials can be used. In addition, the packed column may be provided with a liquid distribution plate at a suitable height to increase the contact efficiency of the gas liquid.

Example

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

The impurity concentration in acetonitrile was measured by gas chromatography, and the conditions at that time were as follows.

HP-6890 manufactured by Hewlett-Packard Company was used for the gas chromatography. DB-624 (length 60 m x inner diameter 0.32 mm, film thickness 5.0 m) manufactured by Agilent Technologies, Inc. was used as the column. FID was used as the detector, and helium was used as the carrier gas.

Column temperature conditions were as follows.

Initial temperature: 70 ℃

Initial time: 10 minutes

Heating rate: 5.0 占 폚 / min

Medium temperature: 120 ° C

Post time: 10 minutes

Final temperature: 220 ° C

[Comparative Example 1]

Acetonitrile was purified using the purification apparatus shown in Fig.

A liquid containing 15 mass% of acetonitrile, which is a byproduct of the ammoxidation reaction of propylene, was supplied to the acetonitrile concentration tower (1) through the line (7). A portion of the water was separated off via line 8, hydrogen cyanide, line 9. Vapor was taken out through the line 10 and condensed with a condenser (not shown) provided in the line 10 to obtain a liquid containing 65 mass% of acetonitrile. Other compositions were 32% by mass of water, 1.6% by mass of hydrogen cyanide, and 1.4% by mass of the total of acrylonitrile, allyl alcohol, oxazole and propionitrile.

The obtained solution was supplied to the reaction tank 2 through the line 10. [ In the reaction tank 2, a 48 mass% aqueous sodium hydroxide solution was added via the line 11, and the reaction was carried out at 73 캜 for 8 hours.

2810 kg / h of the solution of the reaction tank 2 was sent to the goby separation tower 3 through the line 12. Distillation was carried out by flowing 2.8 t / h of steam of 0.4 MPaG into the reboiler installed at the bottom of the column. The tower top pressure and the tower bottom pressure were 235 mmHg and 255 mmHg, respectively, and the top and bottom temperatures were respectively 41.5 ° C and 58.9 ° C. The pressure fluctuation of the goby separation column was ± 1% with the above value as a median value. 770 kg / h of a solution containing allyl alcohol, propionitrile, sodium hydroxide and water was withdrawn from the bottom of the column and treated with wastewater. The steam flowing out of the tower was condensed by a condenser. The condensate 3940 kg / h was refluxed into the gaseous separation column 3, and 2040 kg / h was supplied from the line 14 to the lower portion of the dehydration column 4.

From the line 15 at the top of the dehydration tower 4, a 48 mass% sodium hydroxide aqueous solution of 300 kg / h was fed and brought into liquid-liquid contact with the hydroquinone cetonitrile fed from the line 14. [ The water phase was extracted from the line 16. From line 17, 1850 kg / h of acetonitrile phase was withdrawn and fed to low-boiling separation column 5.

Distillation was carried out by flowing 2.6 t / h of steam of 0.4 MPaG into the reboiler of the low-boiling separation column (5). The column top pressure and the column bottom pressure were 0.1172 MPa and 0.1181 MPa, respectively, and the top temperature and the column bottom temperature were 78.8 캜 and 86.4 캜, respectively, under an absolute pressure. The pressure fluctuation of the low-boiling separation column was ± 1% with the above value as a median value. The steam flowing out of the tower was condensed by a condenser. As the refrigerant of the condenser, 28 ° C water was used. The condensate 4150 kg / h was refluxed into the low boiling separation column 5 and 300 kg / h was withdrawn from line 18 to remove the oxazole and low boiling point materials. The liquid in the line 18 was subjected to wastewater treatment. 1550 kg / h of liquid discharged from the line 19 was sent to the product tower 6.

Distillation was carried out by flowing 1.6 t / h of steam of 0.4 MPaG into the reboiler of the product column (6). The column top pressure and the column bottom pressure were 0.1100 MPa and 0.1112 MPa, respectively, and the top temperature and the column bottom temperature were 81.2 ° C and 82.2 ° C, respectively. The pressure fluctuation of the product column was ± 1% with the above value as the median value. From line 20, 70 kg / h of liquid containing propionitrile or high boiling point material was withdrawn and treated for wastewater. Vapor discharged from the top was condensed by a condenser and flowed down to a reflux drum. As the refrigerant of the condenser, 28 ° C water was used. A condensate of 4380 kg / h in the reflux drum was refluxed to the product column 6 using a pump and 1480 kg / h was withdrawn from the line 21 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 steam and condenser cooling water used was as shown in Table 2.

[Example 1]

As shown in Fig. 2, one reboiler 3b was added to the goby separation column 3, and the effluent vapor of the product column 6 was passed through and used as a heat source. A steam drain drum (not shown) for storing the steam drain generated in the reboiler 3b and a pump (not shown) for feeding the steam drain in the drum to the condenser of the product column 6 are provided. Acetonitrile was purified by the same equipment as Comparative Example 1 except for these.

Initially, the condenser row valve 6v of the product column 6 was fully opened. The valve 6v was gradually closed for one week and the supply of heat to the reboiler 3b of the goby separation column 3 was increased. At the same time, the steam of the reboiler 3a of the goby separation tower 3 was reduced. Finally, the valve 6v is completely closed. The shell pressure of the reboiler 3b (gauge pressure " B ") is 0.0002 MPaG, and the pressure of the top of the product tower 6 (indicated as gauge pressure " A ") is 0.0100 MPaG. Was ± 1%. The effluent vapor of the product column (6) was 81.2 ° C, and the bottom column of the column (3) was 58.9 ° C. In addition, the median value of the pressure ratio B / A was 0.020, and the fluctuation was ± 3%. During the complete closing of the valve 6v, there was no disturbance of the process, and there was no problem with the quality of the acetonitrile obtained. After the valve 6v is completely closed, the outlet steam of the product column 6 flows all the way to the reboiler 3b of the boiler separation column 3 and thereafter the drain discharged from the reboiler 3b is discharged to the drum ). The steam drain in the drum was introduced into the product top condenser by a pump (not shown).

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

The reboiler steam and condenser cooling water usage amounts were as shown in Table 4.

[Example 2]

Acetonitrile was purified with the same equipment as in Example 1 except that the effluent vapor of the low boiling separation column 5 was further used as the heat source of the reboiler 3c of the high boiling separation column 3 in addition to the effluent vapor of the product column 6 Respectively. The flow of the outflow vapor of the low-boiling separation column 5 was as shown in Fig.

At the beginning, the condenser row valve 5v of the low-boiling-separation column 5 was fully opened. While the valve 5v was fully opened, there was no disturbance of the process, and there was no problem with the quality of the obtained acetonitrile. The valve 5v was gradually closed over a week and finally closed 10% (90% open). At this time, the top static pressure (gauge pressure " A ") of the low-boiling separation column 5 was 0.0172 MPaG, and the top temperature and the bottom temperature were 78.8 캜 and 86.4 캜, respectively. The shell pressure (referred to as gauge pressure " B ") of the reboiler 3c of the grate separating column 3 was 0.0032 MPaG, and the top temperature and the bottom temperature were 41.5 DEG C and 58.9 DEG C, respectively. The median value of the pressure ratio B / A was 0.19. In addition, the fluctuation of the pressure of the column top of the giant fractionation tower was ± 1%.

The shell pressure (gauge pressure "B '") of the reboiler 3b is 0.0002 MPaG, and A' and B (gauge pressure) 'Each variation was ± 1%.

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

The reboiler steam and condenser cooling water usage amounts were as shown in Table 6.

[Comparative Example 2]

4, except that one reboiler 3c was added to the grate separation tower 3, and the bottom liquid of the low-boiling separation column 5 was passed through as a heat source, Lt; RTI ID = 0.0 > acetonitrile. ≪ / RTI >

The bypass valve 51v of the reboiler 3c in the early stage of the goby separation tower was made to be fully opened. The bypass valve 51v is gradually closed and the supply of heat to the reboiler 3b of the goby separation tower 3 is increased. Finally, the valve 51v is completely closed. During this time, the fluctuation of the temperature and pressure in each of the goby separation column 3 and the low-fractionation column 5 was ± 1%.

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

The reboiler steam and condenser cooling water usage amounts are shown in Table 8, and the total usage amounts of the reboiler steam and the condenser cooling water were not different from those of Comparative Example 1.

[Example 3]

Acetonitrile was purified by the same equipment and method as in Example 2 except that the valve 5v was finally closed 50%. The initial static pressure (gauge pressure) of the low-boiling separation column 5 was 0.0172 MPaG, and the column top temperature and the column bottom temperature were 78.8 캜 and 86.4 캜, respectively. The shell pressure (gauge pressure) of the reboiler 3c of the goby separation column 3 was 0.0168 MPaG, and the column top temperature and the column bottom temperature were 41.5 DEG C and 58.9 DEG C, respectively.

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

The amount of reboiler steam and condenser cooling water used was as shown in Table 10.

The pressures of the low-boiling-off column 5 and the high boiling-point column 3 were maintained at ± 10% for a while after the start of the purification, but after about one day, the shell pressures of the reboiler 3c Gauge pressure) was hunted between 0.0071 MPaG and 0.0170 MPaG. Accordingly, the hysteresis of the goby separation column 3 and the low-boiling separation column 5 was also started in a range of approximately ± 20%.

The impurity of the purified acetonitrile after the start of hunting was analyzed, and 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. Table 12 shows the degree to which the valve 5v at that time (closed state) is closed and the shell pressure of the tower top pressure of the low-boiling-off column 5 and the boiling- Table 12 also shows the impurity concentration of the valve 5v.

Regarding the amounts of reboiler steam and condenser cooling water used, the results are shown in Table 13.

[Example 10]

A solution containing 12 mass% of acetonitrile as a byproduct of the ammoxidation reaction of propane was fed to the same equipment as in Example 2 to purify acetonitrile.

A liquid containing 12% by mass of acetonitrile was supplied from line 7 to the acetonitrile concentration column 1. A portion of the water was separated off via line 8, hydrogen cyanide, line 9. Vapor was taken out through the line 10 and condensed with a condenser (not shown) provided in the line 10 to obtain a liquid containing 64 mass% of acetonitrile. Other compositions were 33 mass% of water, 1.7 mass% of hydrogen cyanide, and 1.3 mass% of the total of acrylonitrile, allyl alcohol and propionitrile.

The liquid obtained above was supplied to the reaction tank (2) through the line (10). In the reaction tank 2, a 48 mass% aqueous sodium hydroxide solution was added via the line 11, and the reaction was carried out at 73 캜 for 8 hours.

2810 kg / h of the liquid of the reaction tank 2 was sent to the goby separation tower 3 through the line 12. Distillation was carried out by flowing 2.8 t / h of steam of 0.4 MPaG into the reboiler installed at the bottom of the column. The tower top pressure and the tower bottom pressure were 235 mmHg and 255 mmHg, respectively, and the top and bottom temperatures were respectively 41.5 ° C and 58.9 ° C. The pressure fluctuation of the goby separation column was ± 1% with the above value as a median value. 770 kg / h of a solution containing allyl alcohol, propionitrile, sodium hydroxide and water was withdrawn from the bottom of the column and treated with wastewater. The steam flowing out of the tower was condensed by a condenser. The condensate 3940 kg / h was refluxed into the gaseous separation column 3, and 2040 kg / h was supplied from the line 14 to the lower portion of the dehydration column 4.

From the line 15 at the top of the dehydration tower 4, a 48 mass% sodium hydroxide aqueous solution of 300 kg / h was fed and brought into liquid-liquid contact with the hydroquinone cetonitrile fed from the line 14. [ The water phase was extracted from the line 16. From line 17, 1850 kg / h of acetonitrile phase was withdrawn and fed to low-boiling separation column 5.

Distillation was carried out by flowing 2.6 t / h of steam of 0.4 MPaG into the reboiler of the low-boiling separation column (5). The column top pressure and the column bottom pressure were 0.1172 MPa and 0.1181 MPa, respectively, and the top temperature and the column bottom temperature were 78.8 캜 and 86.4 캜, respectively, under an absolute pressure. The pressure fluctuation of the low-boiling separation column was ± 1% with the above value as a median value. The steam flowing out of the tower was condensed by a condenser. As the refrigerant of the condenser, 28 ° C water was used. The condensate 4150 kg / h was refluxed into the low boiling separation column 5 and 300 kg / h was withdrawn from the line 18 to remove the low boiling point material. The liquid in the line 18 was subjected to wastewater treatment. 1550 kg / h of liquid discharged from the line 19 was sent to the product tower 6.

Distillation was carried out by flowing 1.6 t / h of steam of 0.4 MPaG into the reboiler of the product column (6). The column top pressure and the column bottom pressure were 0.1100 MPa and 0.1112 MPa, respectively, and the top temperature and the column bottom temperature were 81.2 ° C and 82.2 ° C, respectively. The pressure fluctuation of the product column was ± 1% with the above value as the median value. From line 20, 70 kg / h of liquid containing propionitrile or high boiling point material was withdrawn and treated for wastewater. Vapor discharged from the top was condensed by a condenser and flowed down to a reflux drum. As the refrigerant of the condenser, 28 ° C water was used. A condensate of 4380 kg / h in the reflux drum was refluxed to the product column 6 using a pump and 1480 kg / h was withdrawn from the line 21 to obtain purified acetonitrile. The analytical results of the impurities in the purified acetonitrile are shown in Table 14. The amount of reboiler steam and condenser cooling water used was the same as in Comparative Example 1. [

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

The valve 6v was gradually closed and the supply of heat to the reboiler 3b of the goby separation column 3 was increased. Finally, the valve 6v is completely closed. At this time, 0.0100 MPaG for the top static pressure (referred to as gauge pressure " A ") of the product column 6, 0.0020 MPaG for the shell pressure of the reboiler 3b 0.020. Also, the fluctuation of the pressure of the column top overhead was ± 0%.

Subsequently, the valve 5v was gradually closed and finally closed 35%. At this time, the top static pressure (referred to as gauge pressure "A '") of the low-boiling separation column 5 is 0.0172 MPaG and the shell pressure of the reboiler 3c of the high boiling separation column 3 ) Was 0.0108 MPaG, and the median value of the pressure ratio B '/ A' was 0.63. In addition, the fluctuation of the pressure of the column top of the giant fractionation tower was ± 1%.

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

The amount of reboiler steam and condenser cooling water used was as shown in Table 16.

From the results of the above Examples and Comparative Examples, it was confirmed that the effluent vapors from the product column 6 and / or the low-boiling separation column 5 were removed from the reboiler of the high boiling point separation column 3 in the process of purifying high purity acetonitrile, The amount of energy consumption during the process can be remarkably reduced.

This application is based on Japanese Patent Application (Japanese Patent Application No. 2012-070086) filed with the Japanese Patent Office on Mar. 26, 2012, the content of which is incorporated herein by reference.

INDUSTRIAL APPLICABILITY The present invention is a process in which the amount of energy consumed for purification is small and the purification facility is simple and the process is simple. Therefore, it is possible to efficiently purify acetonitrile with high purity, which can be used for synthesis and purification of pharmaceutical intermediates, DNA synthesis and purification solvents, solvents for synthesis of organic EL materials, . ≪ / RTI >

1: acetonitrile concentrated tower
2: Reactor
3: Gobi separation tower
4: Dehydration tower
5: Low separation tower
6: Product Tower
7 to 21: line
18a: line
21a: line
3a: Gobi separation top reboiler
3b: Gobi Separation Tower Reboiler (product tower)
3c: Gobi Separation Tower Reboiler (for low-boiling tower)
5v: low-boiling separation top condenser row branch valve
6v: Product top condenser row branch valve
51v: Gobi Separation Tower Reboiler Bypass Valve (low-boiling separation tower)

Claims (8)

The reaction mixture is supplied to the first distillation column, and the resultant effluent is further mixed with the alkali, which is separated from the acetonitrile phase and the water phase Removing the water phase, and supplying the acetonitrile phase to the second distillation column,
The outflow steam from the second distillation column is used as a heat source of the reboiler of the first distillation column,
Wherein the supply amount of the outflow steam to the reboiler is determined based on the reboiler pressure (outflow steam side, gauge pressure) of the first distillation tower and the top pressure (gauge pressure) of the second distillation tower, ≪ / RTI > The method for purifying acetonitrile according to claim 1, wherein a portion of the effluent vapor is supplied to the reboiler and the remainder is supplied to a condenser connected to the second distillation column. delete The method for purifying acetonitrile according to claim 1 or 2, wherein the reboiler pressure of the first distillation column is 0.90 times or less the pressure of the top of the second distillation column. A reaction tank, a first distillation column, a dehydration column, and a second distillation column are installed in this order,
The reaction mixture is introduced into the first distillation column, the effluent of the first distillation column flows into the dehydration column, and the acetonitrile phase obtained from the dehydration column is separated from the second Is introduced into the distillation column,
The outflow steam of the second distillation tower serves as a heat source of the reboiler of the first distillation tower,
Wherein the supply amount of the outflow steam to the reboiler is determined based on the reboiler pressure (outflow steam side, gauge pressure) of the first distillation tower and the top pressure (gauge pressure) of the second distillation tower refinery. 6. The apparatus of claim 5, wherein a portion of the effluent vapor is fed to the reboiler and the remainder is fed to a condenser connected to the second distillation column. delete The apparatus for purifying acetonitrile according to claim 5 or 6, wherein the reboiler pressure of the first distillation column is 0.90 times or less the pressure of the top of the second distillation column.

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