JP2015147737A - PURIFICATION METHOD OF N-tert-BUTYLACRYLAMIDE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a purification method performed under specific conditions which, when purifying N-tert-butylacrylamide (TBAM) by a sublimation method, can provide TBAM of high purity with little impurity contained in TBAM after purification and little coloration.SOLUTION: The purification method of TBAM comprises: separating from a reaction mixture 2-acrylamido-2-propanesulfonic acid obtained by reacting acrylonitrile, sulfuric acid, and isobutylene; recovering byproduct TBAM contained in the reaction mixture after the separation as crude crystals; and thereafter subliming the crude crystals from a molten liquid of 135 to 160°C under 600 Torr or less, and cooling the sublimation gas in stages in the order of 130 to 150°C at the outlet of a melting tank, 80 to 100°C at an upper part of a sublimation and collection tower, and 40 to 60°C at a lower part of the sublimation and collection tower. A content of the impurity, 3,3'-iminopropionitrile, in TBAM is 1000 ppm or less.

Description

The present invention relates to a method for purifying N-tert-butylacrylamide (hereinafter abbreviated as TBAM) represented by the following formula (1), and more specifically, TBAM crude crystals are melted and purified by sublimation. It is related with the purification method.
The present invention also relates to a method for producing high-purity TBAM with little brown, pale yellow and / or blue-green coloration and low impurity content.

TBAM is used in a wide range of industrial fields such as cosmetic raw materials, paint / ink raw materials, adhesive raw materials, and pharmaceutical raw materials by copolymerizing with monomers such as acrylamide, acrylic ester, acrylic acid and methacrylic acid.
However, especially in cosmetic applications, skin irritation and irritation caused by impurities contained in the raw material components may be a problem, and if the hue of the product changes due to coloring, the product value may be significantly reduced. Therefore, a raw material without coloring has been demanded.

Conventionally, as a method for producing TBAM, a method in which acrylonitrile and tert-butyl alcohol are reacted under a strong acid such as sulfuric acid is generally employed. In this method, various impurities are contained in the obtained reaction liquid, and the purification process after the reaction is the main point. However, since it is not easy to distill TBAM because of the boiling point, a method used for purification of solids such as crystallization is used as the purification method.
For example, in order to precipitate TBAM crystals by adding water or an aqueous solution of lower alcohol to the reaction solution obtained by the above reaction, water or an aqueous solution adjusted to pH 0.1 to 3 is added to the reaction solution. There are known a method (Patent Document 1) or a method of depositing TBAM by neutralization with an alkaline aqueous solution in the presence of aminopolyphosphoric acid or aminocarboxylic acid as a chelating agent (Patent Document 2).

  On the other hand, when 2-acrylamido-2-methylpropanesulfonic acid is produced by addition reaction of acrylonitrile, sulfuric acid and isobutylene, TBAM is produced as a by-product. TBAM produced as a by-product is an impurity for 2-acrylamido-2-methylpropanesulfonic acid, and has been disposed of as industrial waste in the past. However, TBAM was recovered as crude crystals, and the crude crystals were recovered as acrylonitrile. A method of recrystallization purification using a solvent such as (Patent Document 3) has been proposed.

However, the methods described in Patent Document 1 and Patent Document 2 require a large excess of methanol water to purify TBAM, and the used methanol water is discarded as a waste liquid, resulting in an increase in environmental burden. It is also disadvantageous economically.
In addition, the method described in Patent Document 3 is a simple method and may be applied to a use or field that may be colored, but there remains a problem that the TBAM crystal is colored blue-green.
For this reason, the prior art is insufficient to reduce the environmental load that has recently increased and to satisfy the demand for high purity and coloring.

Furthermore, the inventors have invented a method for purifying TBAM by a sublimation method as an epoch-making purification method not based on a recrystallization method (Patent Document 4).
The method described in Patent Document 4 is an excellent method because it can obtain TBAM with little coloring without requiring a recrystallization solvent or the like. However, the effect on coloring is not sufficient, and recently, Then, the thing with few impurities in TBAM has come to be requested | required.

Japanese Patent Laid-Open No. 10-87587 JP-A-9-124568 JP 2005-29476 A JP 2012-25672 A

  In purifying TBAM by a sublimation method, it is an object of the present invention to provide a purification method under specific conditions in which high-purity TBAM with little impurities and less coloration is obtained in the purified TBAM.

  As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention sublimed crude crystals of TBAM separated from a reaction solution obtained by reacting acrylonitrile, sulfuric acid and isobutylene under specific conditions to obtain methanol. Without using water, the content of 3,3′-iminodipropionitrile represented by the following formula (2), which is a main impurity and has little coloring of brown, light yellow and / or blue-green, is 1000 ppm. It was found that the following high purity TBAM was obtained.

  That is, in the first invention of the present invention, 2-acrylamido-2-methylpropanesulfonic acid obtained by reacting acrylonitrile, sulfuric acid and isobutylene is separated from the reaction solution, and N-tert- contained in the reaction solution thereafter. When purifying butylacrylamide, after collecting N-tert-butylacrylamide as crude crystals, sublimation gas obtained by sublimating the crude crystals is 130-150 ° C. at the outlet of the melting tank, followed by 80 at the top of the sublimation collection tower. It is a purification method of N-tert-butylacrylamide characterized by cooling in steps of 40 to 60 ° C. in the order of 100 ° C. to 100 ° C. and further at the lower part of the sublimation collection tower.

  The second invention of the present invention is the N-tert-butyl according to the first invention, characterized in that the temperature of the melt when sublimating the crude crystals of N-tert-butylacrylamide is 135 ° C to 160 ° C. This is a method for purifying acrylamide.

  The third invention of the present invention is the N-tert-butylacrylamide according to the first or second invention, wherein the degree of vacuum when sublimating the crude crystals of N-tert-butylacrylamide is 600 Torr or less. This is a purification method.

  According to the fourth aspect of the present invention, the coloring of a 5% by mass methyl alcohol solution of N-tert-butylacrylamide after purification by sublimation is APHA 20 or less, a * is 0 to +0.20, and b * is 0 to 0. It is +1.50, It is a purification method of N-tert- butyl acrylamide in any one of 1st invention-3rd invention characterized by the above-mentioned.

  In the fifth invention of the present invention, the content of 3,3′-iminodipropionitrile contained in N-tert-butylacrylamide obtained by the purification method of any of the first to fourth inventions is 1000 ppm or less. This is a method for producing high purity N-tert-butylacrylamide.

  According to the purification method of the present invention, since the TBAM crystals obtained are not colored brown, light yellow and / or blue-green, the field of use is not limited. Further, since a recrystallization solvent such as an organic solvent is not required, waste liquid such as an organic solvent generated can be reduced by the conventional purification method by recrystallization, which is a method that is environmentally advantageous and economical.

The schematic of the sublimation purification apparatus of the crude crystal | crystallization of N-tert- butyl acrylamide is shown.

Hereinafter, the present invention will be described in more detail.
The crude crystal of TBAM in the present invention is a compound obtained as a by-product during the production of 2-acrylamido-2-methylpropanesulfonic acid obtained by addition reaction of acrylonitrile, sulfuric acid and isobutylene.
Production of 2-acrylamido-2-methylpropanesulfonic acid can be carried out by a known method, and production examples are as follows.
The amount of acrylonitrile used relative to sulfuric acid and isobutylene is preferably 10 to 20 moles. In the reaction of the three components, sulfuric acid is mixed in acrylonitrile cooled to −20 ° C. to −10 ° C., and then isobutylene gas is blown into the resultant mixed liquid with stirring. The reaction is started by blowing isobutylene gas. The reaction is preferably performed at a temperature of 30 to 70 ° C. for 30 minutes or more under normal pressure.
Since 2-acrylamido-2-methylpropanesulfonic acid produced by the reaction is insoluble in acrylonitrile as a solvent, the reaction solution is obtained as a slurry in which crystals of 2-acrylamido-2-methylpropanesulfonic acid are precipitated in acrylonitrile. It is done. The solid content concentration in the slurry is usually 10 to 25% by mass.

Crystals of 2-acrylamido-2-methylpropanesulfonic acid are obtained by solid-liquid separation of the slurry by an operation such as filtration or centrifugation.
On the other hand, the filtrate obtained by the above solid-liquid separation, that is, the acrylonitrile solution usually contains TBAM at a concentration of 1% by mass or more. Therefore, acrylonitrile is evaporated and concentrated for the purpose of separating TBAM from the filtrate. However, since some of the sulfuric acid used in the above reaction remains unreacted in the filtrate, it is preferable to remove the sulfuric acid by alkali washing before concentration of the filtrate.

  Here, when ammonia is used in the alkaline washing for the purpose of removing sulfuric acid before concentration of the filtrate, acrylonitrile remaining in the filtrate reacts with ammonia, and 3,3′− which is an impurity in the purified TBAM of the present invention. Iminodipropionitrile is formed. 3,3'-iminodipropionitrile is a compound represented by the above formula (2) and having a melting point of -6 ° C and a boiling point of 205 ° C / 25 mmHg.

Furthermore, the filtrate from which the acidic substance has been removed is heated to evaporate acrylonitrile to obtain an acrylonitrile solution having a solid content of 50 to 70% by mass. This operation is performed by ordinary simple distillation or the like, and acrylonitrile distilled thereby is further purified as necessary, and then used again as a raw material for producing 2-acrylamido-2-methylpropanesulfonic acid. The target product, TBAM, is concentrated in the can after distillation (generally referred to as the kettle residue).
During distillation, in order to prevent polymerization of acrylonitrile and TBAM having radical polymerizability, a mixed gas of oxygen gas and inert gas is blown into the distillation can, or hydroquinone monomethyl ether ( Hereinafter, it is preferable to spray a polymerization inhibitor such as MQ).

  A method for obtaining TBAM crude crystals from the concentrated liquid is not particularly limited, and there are the following two methods. One is to use the crude crystals precipitated from the concentrated solution, and the other is to pour TBAM crystals into a large amount of solvent such as water, which has low solubility of TBAM. Get.

  The present invention is to melt a crude crystal of TBAM obtained by the above operation and purify it by a sublimation method. The sublimation method may be either a batch type or a continuous type. For melting a TBAM crude crystal and generating a sublimation gas, a sublimation gas is cooled, and the generated sublimation gas is cooled to collect the TBAM crystal. It is necessary to carry out with an apparatus in which a sublimation collection tower is installed. Although the example of a typical apparatus is shown in FIG. 1, it is not limited to this.

The purification method of the present invention will be described with reference to FIG.
1) Melting tank The melting tank is exemplified by a box-shaped, spherical, or cylindrical container with a heating device, and a cylindrical shape is preferable from the viewpoint of heating efficiency. For heating, there is a method of directly warming the melting tank by electric heating such as a mantle heater or a band heater, but a method of heating with a jacket or a warm bath using a heat medium such as water, steam or oil is preferred.
The supply of the crude crystals of TBAM to the melting tank may be in the form of a solid, a melt, or a slurry. In the melting tank, it is desirable to stir with a stirrer in order to promote the generation of TBAM sublimation gas.
Furthermore, in order to increase the generation efficiency of TBAM sublimation gas, an apparatus that increases the surface area of the TBAM melt is desirable. Specific examples include a rotary evaporator, a wall wetter manufactured by Kansai Chemical Machinery Co., Ltd., and a thin film evaporator represented by a wiper manufactured by Shinko Environmental Solution Co., Ltd.
Examples of the material of the melting tank include metals such as stainless steel and titanium, heat resistant glass such as borosilicate glass, and glass lining.
An inert gas such as nitrogen or argon is preferably flowed into the melting tank for the purpose of preventing the explosion of TBAM sublimation gas and preventing oxidation.

Although there is no particular limitation on the water content of the crude TBAM crystal used, it is preferable to generate steam from the TBAM melt and entrain the sublimation gas in the steam for the purpose of increasing the amount of TBAM sublimation gas generated. . Therefore, the water content of the crude TBAM crystal is preferably 10 to 50% by mass, and more preferably 20 to 40% by mass.
Moreover, the coarse crystal | crystallization of TBAM dried to moisture content less than 10% can also be used, and water can also be dripped at a melting tank.

The internal temperature of the TBAM crude crystal melt in the melting tank is preferably 135 ° C to 160 ° C, and more preferably 135 ° C to 155 ° C.
If the internal temperature of the melting tank is less than 135 ° C., high-purity TBAM cannot be obtained. The melting point of TBAM is 128 ° C. to 130 ° C., but in the state of crude TBAM, it does not melt completely at less than 135 ° C. Therefore, a part remains in the melting tank as a solid. When solid crude TBAM is present in the melting tank, the powder of crude TBAM is entrained in the gas flow of the sublimation gas and flows into the product tank, so that high-purity TBAM cannot be obtained.
On the other hand, when the internal temperature of the raw material of TBAM in the melting tank exceeds 160 ° C., TBAM may be decomposed, and the yield of TBAM is lowered.

2) Connection pipe between melting tank and sublimation collection tower In order to prevent the formation of TBAM crystals in the pipe connecting the melting tank and sublimation collection tower, the pipe connecting the melting tank and sublimation collection tower should be 140 ° C or higher. It is desirable to keep warm. Examples of the heat retaining method include a method using a heat insulating material, a method using a jacket, and an explosion-proof heater.

3) Sublimation collection tower The sublimation collection tower is preferably cylindrical. The installation direction may be horizontal or vertical, and may be inclined. In order to make it easy to drop the sublimated TBAM into the product tank, the vertical direction is desirable.
Examples of the material of the sublimation collection tower and the pipe include metals such as stainless steel and titanium, and heat-resistant glass such as borosilicate glass.
The pressure in the sublimation collection tower is not limited, and any of atmospheric pressure, reduced pressure, and increased pressure may be used. In order to increase the sublimation rate, reduced pressure is preferable, and the degree of vacuum is 600 Torr or less. It is preferable.

In the sublimation collection tower, in order to produce high purity TBAM crystals, it is preferable to cool the sublimation gas through a slow stage. To cool the sublimation gas slowly, the internal temperature of the melting tank is heated at 135 to 160 ° C., and the generated sublimation gas is heated at 130 to 150 ° C. at the outlet of the melting tank and the outside of the pipe at 130 to 150 ° C. The sublimation gas is cooled in steps of 80 ° C. to 100 ° C. at the upper part of the sublimation collection tower and further from 40 ° C. to 60 ° C. at the lower part of the sublimation collection tower. Of TBAM crystals are collected.
On the other hand, when a sublimation gas at 130 ° C. to 150 ° C. is suddenly cooled to 40 ° C. or less, a high-purity TBAM crystal cannot be obtained. In the melting tank, the vapor of 3,3′-iminodipropionitrile, which is an impurity generated simultaneously with the sublimation gas of TBAM, is taken in at the same time as the sublimation gas of TBAM is quenched and crystallized, so that high purity TBAM is produced. It is estimated that it cannot be obtained.

  In the sublimation collection tower, a stirrer that mechanically scrapes TBAM crystals generated in a cotton candy shape can be installed in order to ensure the circulation of the sublimation gas of TBAM. It is also possible to generate a pulse of nitrogen gas in the sublimation collection tower and drop the TBAM crystal into the product tank by mechanical impact or ultrasonic waves.

Instead of the sublimation collection tower, a TBAM crystal can be obtained by using a conductive heat transfer type grooved stirring and cooling machine. Examples of the conductive heat transfer type grooved agitator cooler include a Bono cooler manufactured by Nara Machinery Co., Ltd.
In addition, a polymerization inhibitor such as MQ can be added to the coarse crystal of TBAM in order to prevent the polymerization of TBAM.

4) Product tank As a method for recovering the TBAM crystal in the product tank, a rotary valve, transportation by a mono pump, transportation by air, nitrogen, etc. can be applied, and either an open type or a sealed type may be used.

  Crystals obtained by sublimation may be used as they are, but when further reducing the water content, drying allows to obtain TBAM that can be used for various industrial purposes. As a drying method, a stationary shelf dryer, a rotary dryer, a paddle dryer or other agitation dryer, a filtration dryer, a vibration dryer, a fluid dryer, or the like can be applied. Although the drying atmosphere is not limited, since TBAM is an organic substance, it is dried at a low temperature to reduce alteration due to heat.

After TBAM obtained by the purification method of the present invention is stored at 25 ° C. for 1 week, the hue in a 5% by mass methyl alcohol solution is a * of 0 to +0.20, b * of 0 to +1.50, And it is preferable that APHA is 20 or less.
a * and b * are chromatic index, which is a value obtained from the CIELAB chromaticity diagram. a * is colored in the red direction when + is large, and in the green direction when-is large. b * changes in the yellow direction when + is large, and in the blue direction when-is large.
The level at which the sensory evaluation by visual inspection has no blueness or greenness and no yellowness corresponds to a range where a * is −0.20 to +0.40 and b * is 0 to +3.00.

APHA, also called Hazen number, measures the degree of coloring by comparing a colorimetric tube (Hazen standard solution) graded from yellow to brown with a measured object. The higher the value, the more yellow, light brown, and dark brown.
APHA which is almost white to colorless in visual sensory evaluation is preferably 20 or less, more preferably 5 or less.

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. Although the method of obtaining crude TBAM is shown in Reference Examples 1 to 3, it is not particularly limited, and a known method described in JP 2012-25672 A can be used.

Reference Example 1 Production Example of 2-acrylamido-2-methylpropanesulfonic acid Two reactors equipped with a mixed stirring apparatus were connected, and acrylonitrile was connected to the first-stage reactor under the reaction conditions shown below. And introducing fuming sulfuric acid, mixing step of acrylonitrile and sulfuric acid, leading the mixture of the first stage reactor to the second stage reactor, and introducing isobutylene gas into the second stage reactor The reaction was carried out continuously. The raw material charge ratio was 11 mol of acrylonitrile and 0.9 mol of isobutylene with respect to 1 mol of fuming sulfuric acid. The concentration of fuming sulfuric acid (concentration of sulfur trioxide in sulfuric acid) is 9%. The first stage reactor is maintained at -5 to -15 ° C, the residence time of the reaction solution is 10 minutes, the second stage reactor is maintained at 40 to 60 ° C, and the reaction solution is retained. The time was 40 minutes.
The dispersion of 2-acrylamido-2-methylpropanesulfonic acid that flowed out from the second-stage reactor was filtered through a glass filter, and separated into a crystal cake and a filtrate. The cake on the glass filter was washed by flowing down 2 times its mass of acrylonitrile, and the washing filtrate was separated. 2-acrylamido-2-methylpropanesulfonic acid was obtained by drying the cake after washing.

(Reference Example 2) Production Example of Anhydrous Crude TBAM After neutralizing 110 kg of the acrylonitrile solution, which is a combination of the filtrate obtained in Reference Example 1 and the washing filtrate, with a 25% aqueous ammonium hydroxide solution, the aqueous layer was separated and removed. 115 kg of an acrylonitrile solution containing about 4% by mass of TBAM was obtained. Hydroquinone monomethyl ether was added to this solution, the concentration was adjusted to 500 ppm, and the solution was concentrated under reduced pressure while blowing nitrogen gas containing 5% oxygen into the solution to obtain 7.6 kg of a solution containing about 60% by mass of TBAM. About 100 kg of acrylonitrile was separated in this distillation. The obtained concentrated liquid was cooled and solidified to obtain 7.6 kg of anhydrous crude TBAM.

(Reference Example 3) Production of hydrous crude TBAM The concentrated liquid 7.6 kg obtained in Reference Example 2 was slowly poured into pure water to obtain a crude TBAM slurry. The slurry was subjected to solid-liquid separation with a filter to obtain 5.5 kg of hydrous crude TBAM.

The anhydrous crude TBAM and hydrous crude TBAM obtained in Reference Example 2 and Reference Example 3 were analyzed by gas chromatography, and the following composition was obtained. Further, as a 5% by mass methyl alcohol solution, the hue was measured with a color difference meter: OME2000 manufactured by Nippon Denshoku Industries Co., Ltd.
The dry residue was measured by drying in a dryer at a temperature of 110 ° C. for 30 minutes.
Anhydrous crude TBAM
TBAM 86.6%
3,3′-iminodipropionitrile 3.2%
Acrylamide 1.0%
APHA 178 a +0.25 b +14.4
Dry residue 99.9%
Hydrous TBAM
TBAM 81.0%
3,3'-iminodipropionitrile 9116ppm
Acrylamide 1678ppm
APHA 63 a +0.23 b +5.65
Dry residue 83.0%

The measurement conditions for gas chromatography are as follows.
In addition, the composition analysis of the sublimated TBAM in the examples was also measured under the same conditions. The detection limit of 3,3′-iminodipropionitrile is 300 ppm.
Gas chromatography GC-1700 manufactured by Shimadzu Corporation
Detector FID
Column J & B DB-1 ID 0.32mm x 30m, film thickness 0.5μm
Detector control gas Air / hydrogen / helium Analysis method Internal standard method Injection volume 1.0μL

The yield of the sublimate obtained by sublimation was determined by the following formula.
Yield (%) = mass of sublimate / (mass of crude TBAM × dry residue of crude TBAM (%) / 100)

Example 1 Anhydrous crude TBAM used Heating at 80 ° C., 200 Torr
Experiments were performed using the sublimation apparatus shown in FIG. A 300 mL glass flask (melting tank) was placed in the oil bath. 80.0 g of anhydrous crude TBAM obtained in Reference Example 2 was charged into the melting tank. It was connected to a vacuum pump via a glass cold trap immersed in ice water. The oil temperature was warmed at 140-148 ° C. The oil bath temperature was adjusted so that the temperature of the TBAM melt in the melting tank was 140 to 145 ° C. A ribbon heater was wound around the outside of the glass pipe connecting the melting tank and the sublimation collection tower and heated at 140 ° C. A ribbon heater was wrapped around a 150 mm portion of the upper half of a 300 mm high sublimation collection tower and heated at 80 ° C. The lower half of the sublimation collection tower was cooled with sublimation gas at room temperature without winding a ribbon heater. The product tank was kept at room temperature without heating or cooling. The outlet gas temperature of the melting tank was maintained at 140 ° C.
After confirming that the internal temperature of the melting tank reached 140 ° C. and anhydrous crude TBAM was completely melted, the degree of vacuum of the melting tank was maintained at 200 Torr. It continued continuously for 120 minutes, flowing nitrogen into the melting tank at 2.0 L / min.
The sublimated crystal TBAM obtained in 120 minutes from the start was 47.9 g, and the yield was 59.5%. Obtained purified sublimation TBAM was white, and the residue was 26.0 g.
As a result of analyzing the obtained purified crystalline substance TBAM under the above-mentioned GC conditions, the content of 3,3′-iminodipropionitrile was below the detection limit.
When dissolved in a 5% by mass methyl alcohol solution and the hue was measured with a color difference meter: OME2000 manufactured by Nippon Denshoku Industries Co., Ltd., a * was +0.05, b * was +0.37, and APHA was measured. However, it was 4. The results are shown in Tables 1 and 3.

Example 2 Water-containing crude TBAM used, heated at 80 ° C., 200 Torr
In Example 1, 80.0 g of the hydrous crude TBAM obtained in Reference Example 3 was used in place of the anhydrous TBAM obtained in Reference Example 2 as a raw material for sublimation, and the experiment time was changed to 150 minutes. The same operation as in Example 1 was performed.
Sublimation crystal TBAM obtained in 150 minutes from the start of the experiment was 50.3 g, and the yield was 75.8%. The obtained purified sublimation TBAM was white and the residue in the kettle was 11.0 g.
The obtained purified crystal TBAM and the residue were analyzed under the GC conditions described above, and the content of 3,3′-iminodipropionitrile was below the detection limit.
When dissolved in a 5% by mass methyl alcohol solution and measured for hue with a color difference meter: OME2000 manufactured by Nippon Denshoku Industries Co., Ltd., a * is +0.03, b * is +0.49, APHA Was measured to be 5. The results are shown in Tables 1 and 3.

Example 3 Use of hydrous crude TBAM, heating at 100 ° C., 200 Torr
Example 2 is the same as Example 2 except that the temperature at which the ribbon heater is wrapped around the upper half of the 300 mm high sublimation collection tower is changed to 100 ° C. and the experiment time is changed to 180 minutes. The same operation was performed.
Sublimation crystal TBAM obtained in 180 minutes from the start of the experiment was 52.8 g, and the yield was 79.5%. The obtained sublimated purified product TBAM was white, and the residue in the kettle was 6.2 g.
The obtained purified crystal TBAM and the residue were analyzed under the GC conditions described above, and the content of 3,3′-iminodipropionitrile was below the detection limit.
When dissolved in a 5% by mass methyl alcohol solution and measured for hue with a color difference meter: OME2000 manufactured by Nippon Denshoku Industries Co., Ltd., a * is +0.05, b * is +0.43, APHA Was measured to be 5. The results are shown in Tables 1 and 3.

Example 4 Water-containing crude TBAM used, heated at 100 ° C., 500 Torr
In Example 3, the same operation as in Example 3 was performed except that the degree of vacuum of the melting tank was changed to 500 Torr.
Sublimation crystal TBAM obtained in 180 minutes from the start of the experiment was 50.0 g, and the yield was 75.3%. The obtained purified sublimation TBAM was white and the residue in the kettle was 6.6 g.
The obtained purified crystal TBAM and the residue were analyzed under the GC conditions described above, and the content of 3,3′-iminodipropionitrile was below the detection limit.
When dissolved in a 5% by mass methyl alcohol solution and measured for hue with a color difference meter: OME2000 manufactured by Nippon Denshoku Industries Co., Ltd., a * is +0.04, b * is +0.33, APHA Was measured to be 4. The results are shown in Tables 1 and 3.

Comparative Example 1 Using hydrous crude TBAM, no heater, 200 Torr
In Example 2, the same operation as in Example 2 was performed except that the ribbon heater was not wound around the 150 mm portion of the upper half of the 300 mm-high sublimation collection tower.
Sublimation crystal TBAM obtained in 150 minutes from the start of the experiment was 53.1 g, and the yield was 80.0%. The obtained purified sublimation TBAM was white and the residue in the kettle was 9.8 g.
The obtained purified crystal TBAM and the residue were analyzed under the GC conditions described above, and the content of 3,3′-iminodipropionitrile was 1532 ppm.
When dissolved in a 5% by mass methyl alcohol solution and measured for hue with a color difference meter: OME2000 manufactured by Nippon Denshoku Industries Co., Ltd., a * is +0.05, b * is +0.71, APHA Of 8 was measured. The results are shown in Tables 2 and 3.

Comparative Example 2 Water-containing crude TBAM used No heater, 500 ppm
In Comparative Example 1, the same operation as in Comparative Example 2 was performed except that the degree of vacuum of the melting tank was changed to 500 Torr.
Sublimation crystal TBAM obtained in 150 minutes from the start of the experiment was 51.2 g, and the yield was 77.1%. The obtained sublimated purified product TBAM was white, and the residue in the kettle was 10.3 g.
The obtained purified crystal TBAM and the residue were analyzed under the GC conditions described above, and the content of 3,3′-iminodipropionitrile was 1232 ppm.
When dissolved in a 5% by mass methyl alcohol solution and measured for hue with a color difference meter: OME2000 manufactured by Nippon Denshoku Industries Co., Ltd., a * is +0.05, b * is +0.02, APHA Of 7 was measured. The results are shown in Tables 2 and 3.

Comparative Example 3
In Comparative Example 1, the oil temperature was heated at 130 to 138 ° C. The same operation as in Comparative Example 1 was performed except that the oil bath temperature was adjusted so that the temperature inside the melting tank was 130 to 133 ° C.
As a result, the water-containing crude TBAM partially melted until the completion of the experiment, but most of the water-containing crude TBAM did not melt as a solid.
Sublimation crystal TBAM obtained in 270 minutes from the start of the experiment was 57.8 g, and the yield was 87.3%. The obtained sublimated purified product TBAM was white, and the residue in the kettle was 8.0 g.
The obtained purified crystal TBAM and the residue were analyzed under the GC conditions described above, and the content of 3,3′-iminodipropionitrile was 9746 ppm.
When dissolved in a 5% by mass methyl alcohol solution and measured for hue with a color difference meter: OME2000 manufactured by Nippon Denshoku Industries Co., Ltd., a * is +0.05, b * is +0.75, APHA Of 8 was measured. The results are shown in Tables 2 and 3.

In Examples 1 to 4, 3,3′-iminodipropionitrile contained in sublimated and purified TBAM has a detection limit of 300 ppm or less, APHA is 5 or less, and a * is 0 to +0.20. , B * is in the range of 0 to +1.5, and the purified TBAM is less colored and has fewer impurities.
On the other hand, in Comparative Examples 1 to 3, the content of 3,3′-iminodipropionitrile exceeds 1000 ppm, and APHA exceeds 5.

  According to the method for purifying TBAM of the present invention, there is little coloration of brown, light yellow and / or blue-green, and no impurities in an industrially easy method without generating waste liquid of organic solvent such as methanol water. Can be obtained. The purified TBAM obtained by the purification method has less crystal coloring and impurities, so that the field of use is not restricted industrially and can be used for any application, and is extremely useful industrially. .

1. Melting tank 2. Oil bath 3. 3. Nitrogen gas introduction pipe Sublimation gas flow path (pipe)
5. 5. Heating heater at the top of the sublimation collection tower 6. Sublimation collection tower Product tank 8. Vacuum pump

Claims (5)

  When 2-acrylamido-2-methylpropanesulfonic acid obtained by reacting acrylonitrile, sulfuric acid and isobutylene is separated from the reaction solution, and N-tert-butylacrylamide contained in the subsequent reaction solution is purified, N-tert-butylacrylamide is purified. -After recovering butylacrylamide as crude crystals, the sublimation gas obtained by sublimating the crude crystals is 130 to 150 ° C at the outlet of the melting tank, then 80 to 100 ° C at the top of the sublimation collection tower, and further the sublimation collection tower A method for purifying N-tert-butylacrylamide, wherein cooling is performed in stages in the order of 40 to 60 ° C. at the bottom.   The method for purifying N-tert-butylacrylamide according to claim 1, wherein the temperature of the melt when sublimating the crude crystals of N-tert-butylacrylamide is 135 ° C to 160 ° C.   The method for purifying N-tert-butylacrylamide according to claim 1 or 2, wherein the degree of vacuum when sublimating the crude crystals of N-tert-butylacrylamide is 600 Torr or less.   Coloring of 5% by mass methyl alcohol solution of N-tert-butylacrylamide after purification by sublimation is APHA20 or less, a * is 0 to +0.20, and b * is 0 to +1.50. The method for purifying N-tert-butylacrylamide according to any one of claims 1 to 3.   A high-purity N-tert- having a content of 3,3'-iminodipropionitrile contained in the N-tert-butylacrylamide obtained by the purification method according to any one of claims 1 to 4 of 1000 ppm or less. A method for producing butylacrylamide.

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