TWI488834B - 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 a contact ammoxidation reaction of propylene or isobutylene, ammonia and oxygen.

Acetonitrile is used in a solvent for chemical reaction, particularly a solvent used in the synthesis or purification of a pharmaceutical intermediate, or a mobile layer solvent of high performance liquid chromatography. In addition, acetonitrile has been gradually used in the preparation of a solvent (deoxyribonucleic acid), a solvent for synthesis of an organic EL (electron luminescence) material, a cleaning solvent for an electronic component, and the like. In the case of the use as described above, in particular, purification to high purity acetonitrile is required.

The crude acetonitrile obtained by the ammoxidation reaction contains various impurities. Heretofore, as a method for purifying crude acetonitrile, a method of mixing crude acetonitrile with a base has been proposed.

Patent Document 1 discloses that when crude acetonitrile containing impurities is purified, the pH is adjusted to a range of 10 to 13.5 by adding a base, and then heat treatment is performed, and then treated with a formaldehyde adjusting solution to decompose acrylonitrile. And the method of cyanic acid. Examples of the base added to the crude acetonitrile include sodium hydroxide, potassium hydroxide, and ammonia.

Patent Document 2 discloses a method for dehydrating and purifying acetonitrile by adding a base to aqueous acetonitrile and stirring at 10 to 50 ° C to separate and remove the aqueous phase. The separated aqueous phase contains hydrogen cyanide and acrylonitrile in addition to alkali and water, and the water is revealed. The phase can be used as an alkali source in the purification step of acetonitrile disclosed in Patent Document 1.

Patent Document 3 discloses a method of dehydrating acetonitrile by subjecting acetonitrile produced by an ammoxidation reaction to alkali treatment at 60 ° C to decompose hydrogen cyanide and acrylonitrile, and further adding a base in a dehydration column. . The aqueous alkali solution used in the treatment of acetonitrile is concentrated by heating and recovered, and used as an alkali source supplied to the dehydration column.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 48-81816

[Patent Document 2] Japanese Patent Laid-Open No. 55-153757

[Patent Document 3] Japanese Patent Laid-Open Publication No. 2000-128847

In the purification step of acetonitrile disclosed in the above patent documents, metal hydroxides such as sodium hydroxide and potassium hydroxide and/or ammonia are used as the alkali source. However, the present inventors have discussed it, and as a result, it has been clarified that the acetonitrile is simultaneously hydrolyzed by the use of a base to decompose impurities. When acetonitrile is decomposed, the acetonitrile becomes an organic acid such as acetic acid, and thus it is a factor for lowering the production amount of high-purity acetonitrile. Further, the production of an organic acid as described above lowers the pH, and the decomposition of impurities requires a larger amount of alkali, which also becomes a problem. The base promotes the hydrolysis of acetonitrile, so it is not considered to be a preferred method to increase the amount of base added.

In view of the problems of the prior art mentioned above, it is an object of the present invention to provide a method for purifying acetonitrile which inhibits hydrolysis of acetonitrile when decomposing impurities and which can increase the production amount of high-purity acetonitrile.

In order to solve the above problems, the inventors of the present invention have conducted intensive studies and found that acetonitrile is inhibited by supplying acetamide and/or acetic acid to a reaction tank in which impurities such as acrylonitrile and cyanic acid contained in crude acetonitrile are decomposed. Hydrolysis, thereby completing the present invention. and then, Focusing on the acetamide and acetic acid produced in the purification process, the method of using the same was investigated, and it was found that the hydrolysis of acetonitrile can also be inhibited when a base containing the above acetamide and/or acetic acid is used.

That is, the present invention is as follows.

[1] A method for purifying acetonitrile, comprising the steps of: supplying a crude acetonitrile obtained by an ammoxidation reaction and a base to a reaction tank to obtain a reaction liquid; and distilling the reaction liquid to obtain a distillate; Ethylamine and/or acetic acid is supplied to the reaction tank.

[2] The method for purifying acetonitrile according to the above [1], wherein the step of distilling the reaction liquid to obtain a distillate comprises introducing the reaction liquid into a distillation column to remove high boilers, and obtaining the obtained The distillate is supplied to the dehydration column, and an aqueous alkali solution is added to the dehydration column to separate the aqueous phase.

[3] The method for purifying acetonitrile according to [2] above, wherein the alkali supplied to the reaction tank contains a part of the aqueous phase.

[4] The method for purifying acetonitrile according to [2] or [3] above, which comprises adding the aqueous alkali solution to the dehydration column at 40 ° C or higher and 90 ° C or lower.

[5] A process for producing high-purity acetonitrile, which comprises purifying acetonitrile by a purification method of acetonitrile according to any one of [1] to [4] above.

According to the method for purifying acetonitrile of the present invention, hydrolysis of acetonitrile in a reaction vessel in which impurities are decomposed is suppressed, and the production amount of high-purity acetonitrile can be improved.

1‧‧‧ acetonitrile enrichment tower

2‧‧‧Reaction tank

3‧‧‧High boiling separation tower

4‧‧‧Dehydration Tower

5‧‧‧Low boiling separation tower

6‧‧‧Product Tower

7~21‧‧‧ pipeline

Fig. 1 is a schematic view showing an outline of an apparatus for producing acetonitrile according to an embodiment of the present invention.

Fig. 2 is another example of a schematic view of an apparatus for producing acetonitrile according to an embodiment of the present invention.

Hereinafter, the form for carrying out the present invention (hereinafter, simply referred to as "this embodiment") will be described in detail. The following examples are intended to illustrate the invention, but are not intended to limit the invention. The present invention can be carried out by appropriately deforming within the scope of the gist of the invention. In the drawings, the same elements are denoted by the same reference numerals, and the repeated description is omitted. Further, the positional relationship such as up, down, left, and right is based on the positional relationship shown in the drawing unless otherwise specified. 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: supplying a crude acetonitrile obtained by an ammoxidation reaction and a base to a reaction tank to obtain a reaction liquid; and distilling the reaction liquid to obtain a distillate; and Ethylamine and/or acetic acid is supplied to the reaction tank.

As an example of the purification apparatus of the acetonitrile in the present embodiment, as shown in Fig. 1, a concentration column 1 having crude acetonitrile introduced therein is provided, and a high boiling separation column is sequentially connected to the concentration column 1 via the reaction tank 2. 3. Dehydration column 4, low boiling separation column 5 and product column 6.

The crude acetonitrile is obtained as a by-product when acrylonitrile, propane, isobutylene or isobutane is produced by contact ammoxidation to produce acrylonitrile or methacrylonitrile. Usually, the product of the ammoxidation reaction is subjected to extractive distillation, and the crude acetonitrile is recovered as a fraction different from the fraction containing acrylonitrile or methacrylonitrile as a main component. Here, the "crude acetonitrile" means the fraction obtained by extractive distillation of the product of the ammoxidation reaction, and the acetonitrile content is the highest. The crude acetonitrile is usually separated from a distillation column in which most of acrylonitrile or methacrylonitrile is recovered, and usually contains 5 to 40% by mass of acetonitrile and 50 to 95% by mass of water, and contains hydrogen cyanide and allyl alcohol. , Azole, acrylonitrile, propionitrile, acetone, cyanic acid, methacrylonitrile, crotononitrile and anti-crotononitrile, acrylic acid, methyl acrylate, methacrylic acid, methyl methacrylate, acrolein, methacrolein, Many kinds of impurities such as ammonia.

The crude acetonitrile is transferred from line 7 to the middle of the acetonitrile concentration column 1. The acetonitrile concentration column 1 is a vertical distillation column, and has a reboiler (not shown) at the bottom of the column, and has a cold (not shown) at the top of the column. Condenser. Hydrogen cyanide is removed from the top of the column (line 8) and water is removed from the bottom of the column (line 9) while the concentrated crude acetonitrile is withdrawn from the middle of the column (line 10). Hereinafter, the crude acetonitrile extracted as described above is also referred to as "concentrated crude acetonitrile". The line 10 is provided with a side cut condenser (not shown), and the concentrated side acetonitrile can be condensed by the side cut condenser. The liquid concentrated crude acetonitrile flowing out from the side cut condenser flows into the reaction tank 2. The concentration of acetonitrile in the concentrated crude acetonitrile supplied from the concentration column 1 to the reaction tank 2 is usually 50 to 70% by mass, and other impurities containing 25 to 70% by mass of water, hydrogen cyanide, acrylonitrile, allyl alcohol and the like are contained. .

In the reaction tank 2, the concentrated crude acetonitrile is treated with a base to convert acrylonitrile or hydrogen cyanide contained as an impurity into a polymer such as succinonitrile or a dimer. The temperature of the reaction tank 2 is preferably 50° C. or higher and 80° C. or lower, and more preferably 60° C. or higher and 75° C. or lower for 3.0 hours or longer and 15 hours or shorter, and more preferably 60 or less. The reaction is carried out at a temperature of from °C to 75 ° C for from 4.0 hours to 10 hours.

In the purification method of the present embodiment, acetamide and/or acetic acid may be added to the reaction tank 2 from the line 11 or the like. Acetonitrile causes hydrolysis at high temperatures, especially at temperatures above 50 °C. Therefore, in general, under the reaction conditions of the reaction tank 2, acetonitrile is easily decomposed into acetic acid and ammonia by hydrolysis of acetamide to reduce the amount of acetonitrile recovered. However, it is understood that when acetamide and/or acetic acid are supplied into the reaction tank 2, hydrolysis of acetonitrile in the reaction tank 2 is suppressed, and the amount of recovery of acetonitrile is improved. The concentration of the acetamide and/or acetic acid to be supplied to the reaction tank 2 is not particularly limited, but the concentration of the acetamide and/or acetic acid in the supply liquid such as the line 11 is preferably 0.50% by mass or more and 25% by mass or less. It is more preferably 1.0% by mass or more and 20% by mass or less, further preferably 3.0% by mass or more and 15% by mass or less. The concentration of the acetamide and/or acetic acid in the reaction tank 2 is preferably 0.050% by mass or more and 2.5% by mass or less, more preferably in consideration of the amount of the inflow from the concentration column 1 to the reaction tank 2 and the amount of the supplied liquid of the line 11 or the like. It is 0.25 mass% or more and 1.5 mass% or less, and more preferably 0.5 mass% or more and 1.5 mass% or less. In other words, when the concentration of acetamide and/or acetic acid contained in the supply liquid of the line 11 or the like is 0.5% by mass or more, the hydrolysis inhibiting effect of acetonitrile tends to occur remarkably. Also, set to 25 In the case of a mass % or less, not only the above effects can be sufficiently ensured, but also the viscosity of the above-mentioned supply liquid can be reduced, so that sufficient operability can be ensured.

Further, the concentration of acetaminophen and/or acetic acid in the alkali supplied from the line 11 can be adjusted by adjusting the temperature and residence time of the aqueous alkali solution supplied to the dehydration column 4.

The acetonitrile is converted to acetamide under alkaline conditions, and then ammonia is released and gradually hydrolyzed to acetic acid. According to the discussion of the inventors et al., it is known that the conversion of acetonitrile to acetamide is slower than the rate at which acetamide is converted to acetic acid. That is, the reaction of hydrolysis of acetonitrile to acetic acid limits the rate at which acetonitrile is converted to acetamide.

Acetamide and/or acetic acid have the effect of reducing the rate of decomposition of the acetonitrile, and it is considered to inhibit the decomposition of acetonitrile. In most cases, the industrial production of acetonitrile is carried out by a continuous process, and the supply of the raw material to the reaction tank and the extraction of the reaction mixture are always balanced. The case where only a specific component is retained is hardly generated, and in order to reduce the rate of decomposition reaction of acetonitrile, it is necessary to supply acetamide and/or acetic acid. Moreover, in the case of producing acetonitrile by a discontinuous process, acetonitrile is decomposed into acetamide and acetic acid, so that it is considered that the rate of decomposition of acetonitrile is naturally reduced at the time of generating a certain amount of acetamide and/or acetic acid. The phenomenon. However, when acetonitrile is decomposed in the reaction tank, acetic acid is generated to lower the pH, so that the decomposition of impurities such as acrylonitrile or hydrogen cyanide is slow. In order to prevent this, it is necessary to re-feed the alkali into the reaction tank, but the alkali promotes the decomposition reaction of acetonitrile, so that the acetonitrile decomposition reaction proceeds further. In this case, by increasing the relative amounts of acetamide and/or acetic acid, the decomposition inhibition effect of acetonitrile can be improved, so that it is effective to supply acetamide and/or acetic acid from outside the system.

Thereby, in either of the continuous process and the discontinuous process, the decomposition of acetonitrile can be suppressed and the impurities can be decomposed by supplying acetamide and/or acetic acid into the reaction vessel.

The acetic acid supplied to the reaction tank does not have to be purely in the form of acetic acid. Even if acetic acid is in the form of either an acetate ion or an acetate (sodium acetate or potassium acetate), there is no problem, and decomposition of acetonitrile can be suppressed.

The reaction liquid 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. From the top of the high boiling separation column 3, acetonitrile is recovered as a mixture of azeotrope with water or a mixture of the same composition, and liquefied by a condenser (not shown). One portion of the condensate is returned to the high boiling separation column 3 by a line (not shown), and the remainder is transferred from the line 14 to the dehydration column 4. A polymer such as a succinonitrile or a dimer formed in the reaction tank 2, a base, an acetate, an allyl alcohol, a propionitrile, a water, and a small amount of acetonitrile are separated from the line 13 at the bottom of the high boiling separation column 3. Transfer to wastewater treatment equipment, etc. A reboiler (not shown) for imparting heat required for distillation is provided at the bottom of the column to supply heat required for distillation.

The pressure of the high boiling separation column 3 is preferably 80 mmHg or more and 760 mmHg or less in terms of absolute pressure, from the viewpoint of separation of high boilers and decomposition of succinonitrile or dimer formed in the reaction tank 2. Preferably, it is 100 mmHg or more and 300 mmHg or less. When the pressure is set within the above range, the temperature at the bottom of the column is preferably 30 ° C or more and 80 ° C or less, more preferably 40 ° C or more and 60 ° C or less, and the temperature at the top of the column is preferably 20 ° C or more and 70 ° C or less, more preferably It is 30 ° C or more and 50 ° C or less.

In the dehydration column 4, in addition to the distillate obtained from the top of the high boiling separation column 3, a sufficient amount of the base for extracting the water present in the distillate is in the form of an aqueous solution at 40 ° C or higher and 75 ° C or lower. Add from line 15 and mix. Then, the aqueous phase obtained by extractive separation is carried out from the bottom of the dehydration column 4 at 10 ° C or more and 50 ° C or less for 0.10 hours or more and 3.0 hours or less, whereby the acetonitrile phase can be obtained from the line 17. The aqueous alkali solution is not particularly limited, but an aqueous solution of sodium hydroxide and/or potassium hydroxide is preferably used.

As shown in Fig. 2, another example of the schematic diagram of the purification apparatus for acetonitrile in the present embodiment is the same as Fig. 1 except that one of the aqueous phases separated from the dehydration column 4 is circulated in the reaction vessel 2. Device. That is, a part of the aqueous phase separated from the dehydration tower 4 is supplied from the line 11 into the reaction tank 2.

In the purification method of the present embodiment, a part of the aqueous phase separated from the dehydration column 4 The circulation is carried out so that it can be used as an alkali source supplied into the reaction tank 2. By using the aqueous phase separated in the dehydration column 4, it is not necessary to re-feed the alkali from outside the system, or the supply amount of the alkali outside the system can be reduced, thereby contributing to the reduction of the supply amount of the alkali throughout the purification step.

In the dehydration column 4, acetonitrile is also slightly decomposed to form acetamide and/or acetic acid. At this time, from the viewpoint of controlling the formation of acetamide and/or acetic acid in the dehydration column 4, it is preferred to heat the aqueous alkali solution supplied into the dehydration tower 4 in advance. The temperature of the aqueous alkali solution supplied to the dehydration tower 4 is preferably 40 ° C or more and 90 ° C or less, more preferably 45 ° C or more and 75 ° C or less, and further preferably 45 ° C or more and 65 ° C or less. The residence time in the dehydration column 4 is 0.10 hours or more and 3.0 hours or less, more preferably 0.20 hours or more and 2.8 hours or less. Since the aqueous phase extracted and separated from the dehydration column 4 contains an alkali, acetamide, and/or acetic acid, when the aqueous phase is introduced into the reaction tank 2, the effect of suppressing hydrolysis of acetonitrile is exhibited. On the other hand, the residence time of the reaction tank 2 is 3.0 hours or more and 15 hours or less, more preferably 4.0 hours or more and 10 hours or less, and is longer than the residence time of the dehydration tower 4. Therefore, the hydrolysis of acetonitrile in the reaction tank 2 tends to proceed more easily. Even if the amount of acetonitrile hydrolyzed in the dehydration column 4 is increased, the acetonitrile decomposition inhibition effect in the reaction tank 2 can be greatly assisted by the supply of acetamide and/or acetic acid, so that the yield of high-purity acetonitrile is increased. tendency. Therefore, from the viewpoint of achieving both the reduction of the alkali supply amount in the entire purification step and the inhibition of the decomposition of acetonitrile in the reaction tank 2, it is preferred to circulate one of the water phases separated from the dehydration column 4 to be set. The alkali source supplied to the reaction tank 2.

The extraction temperature in the dehydration column 4 is preferably 5 ° C or more and 40 ° C or less, more preferably 10 ° C or more, from the viewpoint of reducing the water content in the acetonitrile flowing out from the line 17 and suppressing the hydrolysis of the acetonitrile necessary or more. Below °C. In order to maintain the above extraction temperature, the liquid from the line 14 may be cooled in advance and supplied to the dehydration tower 4, or the main body of the dehydration tower 4 may be cooled. Here, the extraction temperature means the temperature in the dehydration column 4, 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 used in the dehydration column 4 varies depending on the water content contained in the acetonitrile, but is usually 10% by mass or more and 90% by mass or less, preferably 30% by mass or more and 60% by mass or less based on the water contained in the acetonitrile. The scope. 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.

When at least a portion of the bottom liquid (aqueous phase) of the dehydration column 4 is transferred to the reaction tank 2 through the line 11, the remaining portion of the bottom liquid of the dehydration column 4 is passed through the line 16 to the wastewater treatment facility. Process it. The bottom liquid of the dehydration tower 4 mainly contains sodium hydroxide and/or potassium hydroxide or water as an alkali, and further contains acetamide, acetic acid (also containing an alkali salt), and a small amount of acetonitrile.

From the viewpoint of removing acrylonitrile and hydrogen cyanide from acetonitrile and suppressing hydrolysis of acetonitrile, the liquid supply amount of the bottom liquid of the dehydration column 4 to the reaction tank 2 is preferably such that the liquid cyanide in the reaction tank 2 The hydrogenation is adjusted in such a manner that the hydrogen is 1.0 mol or more and 3.5 mol or less of sodium hydroxide and/or potassium hydroxide per 1 mol. In this case, the pH of the mixed solution in the reaction tank 2 was 12.0 ± 1.5. By recycling the bottom liquid of the dehydration column 4 to the reaction tank 2, the amount of alkali added to the reaction tank 2 is not required or reduced, and the amount of wastewater treatment of the bottom liquid of the dehydration tower 4 is reduced. Further, it has an advantage that the acetonitrile contained in a small amount in the bottom liquid of the dehydration column 4 can be recovered.

The amount of decomposition of acetonitrile in the reaction tank 2 is reduced, whereby the mass of acetonitrile recovered from the overhead line 21 of the product column 6 as the final distillation column is increased. When the quality of the high-purity acetonitrile produced is the same, the quality of the crude acetonitrile supplied to the acetonitrile purification unit can be reduced, so that the acetonitrile purification apparatus can be miniaturized. Further, since the amount of acetonitrile to be decomposed is reduced, the amount of waste water that must be treated can be reduced, so that the miniaturization and environmental load of the wastewater treatment equipment can be reduced.

After dehydration in the dehydration column 4, in order to separate and remove a compound having a low boiling point and a compound having a high boiling point from acetonitrile, it is preferred to use two or more distillation columns. Specifically, first, the low boiling point separation compound 5 is separated from the top of the column through the line 18 to remove low boiling point compounds, and will be low boiling. The bottoms of the separation column 5 are passed through line 19 to the product column 6. Thereafter, it is preferred to separate the high boilers from the bottom of the column 6 through the line 20 in the product column 6, and to obtain purified acetonitrile from the overhead line 21 of the column.

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 until the desired degree of purification is achieved. Depending on the target degree of purification, the reflux of the low boiling separation column 5 and the product column 6 is preferably 1 or more and 50 or less, more preferably 2 or more and 30 or less. 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 separating and removing impurities by distillation, in purifying high-purity acetonitrile, it is preferred to stably maintain a reflux ratio at a predetermined value during the operation. The lower limit of the pressure of the low boiling separation column 5 and the product column 6 is set such that the components to be separated in the distillation column respectively indicate an appropriate boiling point, and the absolute pressure is preferably 0.05 MPa or more, more preferably 0.08 MPa or more, and further Good is 0.09MPa or more. The upper limit of the pressure is preferably 0.27 MPa or less, more preferably 0.20 MPa or less, and still more preferably 0.15 MPa or less in terms of absolute pressure. When the pressure is set to the above preferred pressure, the bottom temperature of the low boiling separation column 5 and the product column 6 is preferably 80 ° C or more and 95 ° C or less, more preferably 80 ° C or more and 88 ° C or less, and the temperature at the top of the column is preferably 70 ° C or more and 90 ° C or less, more preferably 75 ° C or more and 85 ° C or less.

The low boiling separation column 5 and the product column 6 are preferably a layered column or packed column having a condenser at the top of the column and 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 counter current contact type having no downflow tube. Further, as the opening of the tray, a blister type, a perforated plate type, a valve type or the like can be used. The number of the plates of the distillation column is not particularly limited as long as it is 10 or more, but is preferably 30 or more and 80 or less. 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, a Raschig ring, a Lessing ring, a Pall ring, a Berl saddle, an interlock saddle, a Taylor filler can be used. (Terra let packing), Dixon ring or McMahon packing, etc. As a regular filler, 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 provide a liquid redistribution plate at an appropriate height to improve the gas-liquid contact efficiency.

The vapor pressure supplied to the reboiler of the low boiling separation column 5 and the product column 6 is preferably 1.0 MPaG or less, more preferably 0.6, from the viewpoint of appropriately setting the temperature difference with the liquid to be heated. Below MPaG.

As described above, in the present embodiment, the purification method of acetonitrile preferably includes the first step of supplying crude acetonitrile, a base, and acetamide and/or acetic acid obtained by the ammoxidation reaction into the reaction tank. The reaction liquid is obtained; and in the second step, a mixture of the above reaction liquid and the above acetamide and/or acetic acid is distilled to obtain a distillate.

The method for producing high-purity acetonitrile in the present embodiment includes a production method for purifying acetonitrile by the above purification method. Here, in the case of producing high-purity acetonitrile, the purification method in the present embodiment can be used, and a conventionally known method can be used. Here, the "high purity" of the high-purity acetonitrile means a purity of 99.9% by mass or more.

[Examples]

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

For the determination of acetonitrile, acrylonitrile, allyl alcohol, When the concentrations of azole, propionitrile and acetonitrile are used, gas chromatography is used, and the conditions at this time are as follows.

Gas chromatography was performed using HP-6890 manufactured by Hewlett-Packard Co., Ltd., and the column was DB-624 manufactured by Agilent Technologies. That is, as the above-mentioned column, the length was 60 m × the inner diameter was 0.32 mm, and the film thickness was 5.0 μm. As the detector, a FID (flame ionization detector) is used, and a carrier gas system uses helium.

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

Last time: 10 minutes

Final temperature: 250 ° C

The hydrogen cyanide concentration measurement was carried out by a silver nitrate titration method, the ammonia concentration measurement was carried out by ion chromatography, and the water concentration measurement was carried out by the Karlsfeld method.

It is considered that when the acetic acid concentration is measured, a part thereof becomes an alkali salt. Therefore, the pH is adjusted to 6 by sulfuric acid, thereby dissociating into acetic acid, and the analysis is carried out by the above gas chromatography.

The sodium hydroxide concentration measurement is performed by calculating the hydroxide ion concentration by using an acetic acid neutralization titration method. Further, the concentration of sodium ions was determined by ion chromatography and confirmed by conversion.

Considering that the concentration of acetamide and the concentration of acetic acid are affected by the liquid temperature and the time required for the analysis, after sampling, the liquid is cooled while the analysis is performed quickly. Depending on the case, it is expressed as the total concentration of acetamide and acetic acid.

Substances other than the above are not identified and quantified, and are balanced as other substances. In particular, in the reaction tank 2, acrylonitrile and hydrogen cyanide are separately and compositely reacted and polymerized to disappear, and these products are additionally counted.

The sample for analysis was collected from the nozzle of the designated line set in Fig. 1 or 2 by the analysis of the representative sample of the portion, and analyzed by the above method.

[Experimental Example 1]

To the mixer, 500 g of concentrated crude acetonitrile containing 65 mass% of acetonitrile (MeCN) and 35 mass% of water, and 53.4 g of an alkali liquid containing water, sodium hydroxide and acetamide were placed to prepare a mixed liquid. The mixture was stirred while being kept at 70 ° C for 5 hours. The sodium hydroxide concentration in the above alkali solution was 25% by mass, and the acetaminophen concentration was 1% by mass.

The composition of each liquid and the decomposition rate of acetonitrile (MeCN) are shown in Table 1. Further, the acetonitrile decomposition rate is a value defined by the following formula.

Acetonitrile decomposition rate (%) = (1 - acetonitrile mass in the reaction liquid / mass of acetonitrile in the concentrated crude acetonitrile) × 100

[Experimental Example 2]

The stirring was carried out at 70 ° C for 5 hours in the same manner as in Experimental Example 1, except that the concentration of acetic acid in the lye was 3% by mass. The composition of each liquid and the acetonitrile decomposition rate are shown in Table 2.

[Experimental Example 3]

The concentrations of acetaminophen and acetic acid in the lye were set to 5.0% by mass and 4.0% by mass, respectively. Otherwise, stirring was carried out at 70 ° C for 5 hours in the same manner as in Experimental Example 1. The composition of each liquid and the acetonitrile decomposition rate are shown in Table 3.

[Experimental Example 4]

The mixture was stirred at 70 ° C for 5 hours in the same manner as in Experimental Example 1 except that the concentrations of the acetamide and the acetic acid in the lye were 7.0% by mass and 8.0% by mass, respectively. The composition of each liquid and the acetonitrile decomposition rate are shown in Table 4.

[Example 1]

Purification of acetonitrile was carried out using the purification apparatus shown in Fig. 2. 15% by mass of crude acetonitrile containing acetonitrile as a by-product of the ammoxidation reaction of propylene 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 taken out from the line 10, and condensed by a condenser (not shown) provided in the line 10 to obtain a concentrated crude acetonitrile containing 65% by mass of acetonitrile. As another composition of the concentrated crude acetonitrile, water is 32% by mass, hydrogen cyanide is 1.1% by mass, acrylonitrile is 360 ppm by mass, and ammonia is 100 ppm by mass, and otherwise, allyl alcohol is contained. Oxazole and propionitrile.

2580 kg/h of concentrated crude acetonitrile was supplied into the reaction tank 2 through the line 10. In the reaction tank 2, 230 kg/h of the bottom liquid of the following dehydration tower 4 was added from the line 11, and the reaction was carried out at 73 ° C for 8 hours.

The reaction liquid of the reaction tank 2 was transferred to the high boiling separation column 3 through the line 12 by 2810 kg/h. Distillation was carried out by flowing 2.8 t/h of steam of 0.4 MPaG to the reboiler installed at the bottom of the column. The column top pressure and the bottom pressure were 235 mmHg and 255 mmHg, respectively, and the top temperature and the bottom temperature were 41.5 ° C and 58.9 ° C, respectively. The wastewater was treated by extracting 770 kg/h of liquid containing allyl alcohol, propionitrile, sodium hydroxide and water from the bottom of the tower. The vapor distilled from the top is condensed by a condenser. The condensate 3940 kg/h was refluxed into the high boiling separation column 3, and 2040 kg/h of the distillate was cooled from the line 14 by a heat exchanger (not shown) and supplied to the lower portion of the dehydration tower 4.

The line 15 from the upper portion of the dehydration column 4 was supplied with 300 kg/h of a 48 mass% sodium hydroxide aqueous solution at a temperature of 80 ° C, and was subjected to liquid-liquid contact with a distillate having a temperature of 7.1 ° C supplied from the line 14 . The dehydration tower 4 is configured to have a casing on the outer side thereof and to be cooled. The aqueous phase was withdrawn from the bottom of the dehydration column 4, and 230 kg/h of the internal liquid was supplied from the line 11 into the reaction tank 2. The remaining portion of the bottom liquid is transferred from the line 16 to a wastewater treatment facility (not shown) for treatment. The amount withdrawn from line 16 was 260 kg/h to achieve equilibrium. From the line 17, a 25.9 ° C acetonitrile phase of 1850 kg / h was withdrawn.

The material balance of the reaction tank 2 was taken, and the results are shown in Table 5.

[Embodiment 2]

The operation was carried out under the same conditions as in Example 1 except that the temperature of the 48 mass% sodium hydroxide aqueous solution supplied from the line 15 was changed to 65 °C. The material balance of the reaction tank 2 was taken, and the results are shown in Table 6.

[Example 3]

The operation was carried out under the same conditions as in Example 1 except that the temperature of the 48% by mass aqueous sodium hydroxide solution supplied from the line 15 was changed to 45 °C. Take the material of reaction tank 2 The materials were balanced and the results are shown in Table 7.

[Example 4]

The acetonitrile phase withdrawn from the line 17 in Example 1 was supplied to the low boiling separation column 5. The steam to the reboiler of the low boiling separation column 5 was poured into steam of 0.4 MPaG at 2.6 t/h, and distillation was carried out. The top pressure and the bottom pressure of the column were 0.1172 MPa and 0.1181 MPa, respectively, and the top temperature and the bottom temperature were 78.8 ° C and 86.4 ° C, respectively. The vapor distilled from the top is condensed by a condenser. As the refrigerant of the condenser, water at 28 ° C was used. The condensate 4150 kg/h was refluxed into the low boiling separation column 5, and 300 kg/h was taken out from the line 18 to remove Oxazole and low boiling point substances. The liquid of line 18 is subjected to wastewater treatment. The 1550 kg/h of liquid withdrawn from line 19 is transferred to product column 6.

The steam was fed to a reboiler of the product column 6 to a steam of 0.4 MPaG at 1.6 t/h, and distillation was carried out. The top pressure and the bottom pressure of the column were 0.1100 MPa and 0.1112 MPa, respectively, and the top temperature and the bottom temperature were 81.2 ° C and 82.2 ° C, respectively. A liquid containing 70% of a liquid containing propionitrile or a high-boiling substance was taken out from the line 20 to carry out wastewater treatment. The vapor distilled from the top is condensed by a condenser and flows into a reflux drum. As the refrigerant of the condenser, water at 28 ° C was used. 4380kg/h of the condensate in the reflux drum is returned to the product tower 6 using a pump, and Line 21 was withdrawn at 1480 kg/h to obtain purified high purity acetonitrile.

The impurities in the high-purity acetonitrile were analyzed, and as a result, the results shown in Table 8 were obtained.

[Example 5]

The operation was carried out under the same conditions as in Example 4 except that the acetonitrile phase extracted from the line 17 in Example 2 was supplied to the low boiling separation column 5.

Purified high purity acetonitrile 1484 kg/h was withdrawn from line 21. The impurities in the high-purity acetonitrile were analyzed, and as a result, the results shown in Table 9 were obtained.

[Embodiment 6]

The operation was carried out under the same conditions as in Example 4 except that the acetonitrile phase extracted from the line 17 in Example 3 was supplied to the low boiling separation column 5.

Purified high purity acetonitrile 1485 kg/h was withdrawn from line 21. The impurities in the high-purity acetonitrile were analyzed, and as a result, the results shown in Table 10 were obtained.

[Comparative Example 1]

500 g of concentrated crude acetonitrile containing 65 mass% of acetonitrile and 35 mass% of water, and 53.4 g of alkali liquid containing water and sodium hydroxide were added to the mixer to prepare a mixed liquid. The mixture was stirred while being kept at 70 ° C for 5 hours. The composition of each liquid and the acetonitrile decomposition rate are shown in Table 11.

[Comparative Example 2]

500 g of concentrated crude acetonitrile containing 65% by mass of acetonitrile and 35% by mass of water, and 53.4 g of an alkali solution containing water, sodium hydroxide and ammonia were placed in a mixer to prepare a mixed liquid. The mixture was stirred while being kept at 70 ° C for 5 hours. The composition of each liquid and the acetonitrile decomposition rate are shown in Table 12.

[Comparative Example 1]

Purification of acetonitrile was carried out using the purification apparatus shown in FIG. The bottom liquid of the dehydration tower 4 is all taken out from the line 16 and sent to the wastewater treatment facility, and to the reaction tank 2, an aqueous sodium hydroxide solution is added from the line 11. Except for these, acetonitrile was purified by the same apparatus as in Example 1.

A liquid containing 15% by mass of crude acetonitrile as a by-product of the ammoxidation reaction of propylene 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 taken out from the line 10, and condensed by a condenser (not shown) provided in the line 10 to obtain a concentrated crude acetonitrile containing 65% by mass of acetonitrile. As another composition of the concentrated crude acetonitrile, water is 32% by mass, hydrogen cyanide is 1.1% by mass, acrylonitrile is 360 ppm by mass, and ammonia is 100 ppm by mass, and otherwise, allyl alcohol is contained. Oxazole and propionitrile.

2580 kg/h of concentrated crude acetonitrile was supplied into the reaction tank 2 through the line 10. In the reaction tank 2, 180 kg/h of a 48% by mass aqueous sodium hydroxide solution was added from the line 11, and the reaction was carried out at 73 ° C for 8 hours.

The reaction liquid of the reaction tank 2 was transferred to the high boiling separation column 3 through the line 12 at 2760 kg/h. Distillation was carried out by flowing 2.8 t/h of steam of 0.4 MPaG to the reboiler installed at the bottom of the column. The top pressure of the tower and the bottom pressure of the tower are 235mmHg and 255mmHg, respectively, based on the absolute pressure. The bottom temperature was 41.5 ° C and 58.9 ° C, respectively. The wastewater was treated by extracting 790 kg/h of liquid containing allyl alcohol, propionitrile, sodium hydroxide and water from the bottom of the tower. The vapor distilled from the top was condensed by a condenser, and the condensed liquid was refluxed to the high boiling separation column 3 at 3,940 kg/h, and the 1970 kg/h of the distillate was cooled from the line 14 by a heat exchanger (not shown). It is supplied to the lower portion of the dehydration tower 4.

The line 15 from the upper portion of the dehydration column 4 was supplied with 300 kg/h of a 48% by mass aqueous sodium hydroxide solution at a temperature of 50 ° C, and was subjected to liquid-liquid contact with a distillate having a temperature of 7.3 ° C supplied from the line 14 . The dehydration tower 4 is configured to have a casing on the outer side thereof and to be cooled. The aqueous phase was withdrawn from the bottom of the dehydration column 4 at 475 kg/h, and was transferred from the line 16 to a wastewater treatment facility (not shown) for treatment. The temperature of the above aqueous phase was 15.5 °C.

The acetonitrile phase was withdrawn from line 17 at 1,795 kg/h and supplied to the low boiling separation column 5. The temperature of the above acetonitrile phase was 25.7 °C.

The material balance of the reaction tank 2 was taken, and the results are shown in Table 13.

[Comparative Example 2]

The acetonitrile phase extracted from the line 17 in Comparative Example 1 was supplied to the low boiling separation column 5. The steam to the reboiler of the low boiling separation column 5 was poured into a steam of 0.4 MPaG at 2.5 t/h, and distillation was carried out. The top pressure and the bottom pressure of the column were 0.1172 MPa and 0.1181 MPa, respectively, and the top temperature and the bottom temperature were 78.8 ° C and 86.4 ° C, respectively. The vapor distilled from the top is condensed by a condenser. As the refrigerant of the condenser, water at 28 ° C was used. The condensate 4150 kg/h was refluxed into the low boiling separation column 5, and 300 kg/h was taken out from the line 18 to remove Oxazole and low boiling point substances. The liquid of line 18 is subjected to wastewater treatment. 1495 kg/h of liquid withdrawn from line 19 was transferred to product column 6.

The steam was fed to a reboiler of the product column 6 to a steam of 0.4 MPaG at 1.6 t/h, and distillation was carried out. The top pressure and the bottom pressure of the column were 0.1100 MPa and 0.1112 MPa, respectively, and the top temperature and the bottom temperature were 81.2 ° C and 82.2 ° C, respectively. A liquid containing 70% of a liquid containing propionitrile or a high-boiling substance was taken out from the line 20 to carry out wastewater treatment. The vapor distilled from the top is condensed by a condenser and flows into a reflux drum. As the refrigerant of the condenser, water at 28 ° C was used. 4,380 kg/h of the condensate in the reflux drum was refluxed into the product column 6 using a pump, and 1425 kg/h was withdrawn from the line 21 to obtain purified high-purity acetonitrile.

The impurities in the high-purity acetonitrile were analyzed, and the results shown in Table 14 were obtained.

[Embodiment 7]

The crude acetonitrile containing 12% by mass of acetonitrile as a by-product of the ammoxidation reaction of propane was supplied to the same apparatus as in Example 1 to carry out purification of acetonitrile.

The crude acetonitrile is 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. Extracting steam from line 10 and using it The condenser (not shown) placed in the line 10 was condensed to obtain a concentrated crude acetonitrile containing 65% by mass of acetonitrile. The other composition of the concentrated crude acetonitrile is 32% by mass of water, 1.3% by mass of hydrogen cyanide, 350 ppm by mass of acrylonitrile, and 100 ppm by mass of ammonia, and includes allyl alcohol and propionitrile.

2580 kg/h of concentrated crude acetonitrile was supplied into the reaction tank 2 through the line 10. In the reaction tank 2, 230 kg/h of the bottom liquid of the following dehydration tower 4 was added from the line 11, and the reaction was carried out at 73 ° C for 8 hours.

The reaction liquid of the reaction tank 2 was transferred to the high boiling separation column 3 through the line 12 by 2810 kg/h. Distillation was carried out by flowing 2.8 t/h of steam of 0.4 MPaG to the reboiler installed at the bottom of the column. The column top pressure and the bottom pressure were 235 mmHg and 255 mmHg, respectively, and the top temperature and the bottom temperature were 41.5 ° C and 58.9 ° C, respectively. The wastewater was treated by extracting 770 kg/h of liquid containing allyl alcohol, propionitrile, sodium hydroxide and water from the bottom of the tower. The vapor distilled from the top was condensed by a condenser, and the condensed liquid was refluxed to the high boiling separation column 3 at 3,940 kg/h, and the distillate 2040 kg/h was cooled from the line 14 by a heat exchanger (not shown). It is supplied to the lower portion of the dehydration tower 4.

The line 15 from the upper portion of the dehydration column 4 was supplied with 300 kg/h of a 48% by mass aqueous sodium hydroxide solution at a temperature of 50 ° C, and was subjected to liquid-liquid contact with a distillate having a temperature of 7.1 ° C supplied from the line 14 . The dehydration tower 4 is configured to have a casing on the outer side thereof and to be cooled. The aqueous phase was withdrawn from the bottom of the dehydration column 4, and 230 kg/h of the internal liquid was supplied from the line 11 into the reaction tank 2. The remaining portion of the bottom liquid is transferred from the line 16 to a wastewater treatment facility (not shown) for treatment. The amount withdrawn from line 16 was 260 kg/h to achieve equilibrium.

From the line 17, a 25.9 ° C acetonitrile phase of 1850 kg / h was withdrawn. The material balance of the reaction tank 2 was taken, and the results are shown in Table 15.

[Embodiment 8]

The acetonitrile phase withdrawn from line 17 in Example 7 was supplied to the low boiling separation column 5. The steam to the reboiler of the low boiling separation column 5 was poured into steam of 0.4 MPaG at 2.6 t/h, and distillation was carried out. The top pressure and the bottom pressure of the column were 0.1172 MPa and 0.1181 MPa, respectively, and the top temperature and the bottom temperature were 78.8 ° C and 86.4 ° C, respectively. The vapor distilled from the top is condensed by a condenser. As the refrigerant of the condenser, water at 28 ° C 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 low-boiling substances. The liquid of line 18 is subjected to wastewater treatment. The 1550 kg/h of liquid withdrawn from line 19 is transferred to product column 6.

The steam was fed to a reboiler of the product column 6 to a steam of 0.4 MPaG at 1.6 t/h, and distillation was carried out. The top pressure and the bottom pressure of the column were 0.1100 MPa and 0.1112 MPa, respectively, and the top temperature and the bottom temperature were 81.2 ° C and 82.2 ° C, respectively. A liquid containing 70% of a liquid containing propionitrile or a high-boiling substance was taken out from the line 20 to carry out wastewater treatment. The vapor distilled from the top is condensed by a condenser and flows into a reflux drum. As the refrigerant of the condenser, water at 28 ° C was used. 4,380 kg/h of the condensate in the reflux drum was refluxed into the product column 6 using a pump, and 1486 kg/h was withdrawn from the line 21 to obtain purified high-purity acetonitrile.

The impurities in the high-purity acetonitrile were analyzed, and as a result, the results shown in Table 16 were obtained.

According to the results of the above examples and comparative examples, it can be seen that in the process of purifying high-purity acetonitrile, acetamide and/or acetic acid is supplied to the reaction tank 2, whereby the quality of the high-purity acetonitrile is not changed, and the acetonitrile recovery can be improved. rate. Further, it is understood that the amount of alkali used can be reduced by using the bottom liquid of the dehydration column 4 as the alkali source of the reaction tank 2.

The present application is based on Japanese Patent Application No. 2012-192215, filed on Jan. 31, 2011, the content of which is hereby incorporated by reference.

[Industrial availability]

The purification method of the acetonitrile of the present invention is that the amount of wastewater treatment and the amount of chemical used in the purification are small, and the purification equipment and the steps are simple processes. Further, according to the method of the present invention, high-purity acetonitrile which can be used for the purpose of synthesis, purification, solvent, DNA synthesis, purification solvent, organic EL material synthesis solvent, and electronic component cleaning solvent for pharmaceutical intermediates can be efficiently purified. .

Claims (5)

A method for purifying acetonitrile, comprising the steps of: supplying a crude acetonitrile obtained by an ammoxidation reaction and a base to a reaction tank to obtain a reaction liquid; distilling the reaction liquid to obtain a distillate; and Ethylamine and/or acetic acid is supplied internally. The method for purifying acetonitrile according to claim 1, wherein the step of distilling the reaction liquid to obtain a distillate comprises introducing the reaction liquid into a distillation column to remove high boilers, and then supplying the obtained liquid liquid. The step of separating the aqueous phase into the dehydration column and adding an aqueous alkali solution to the above-mentioned dehydration column. The method for purifying acetonitrile according to claim 2, wherein the base supplied to the reaction tank contains a part of the aqueous phase. A method for purifying acetonitrile according to claim 2 or 3, which comprises adding the above aqueous alkali solution to the dehydration column at 40 ° C or higher and 90 ° C or lower. A process for producing high-purity acetonitrile, which comprises: purifying acetonitrile by a purification method of acetonitrile according to any one of claims 1 to 4.