JP2012025672A - METHOD FOR PRODUCING HIGH-PURITY N-tert-BUTYLACRYLAMIDE AND SUBLIMATION PURIFICATION APPARATUS - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem that even if N-tert-butylacrylamide produced as a by-product in the production of 2-acrylamide-2-methylpropane sulfonic acid is separated and washed after crystallization, the crystal after washing is discolored in blue to green or in brown during storage and N-tert-butylacrylamide is limited in a field of use.SOLUTION: The method for producing N-tert-butylacrylamide includes recovering N-tert-butylacrylamide as a crude crystal and then collecting N-tert-butylacrylamide by sublimation of the crude crystal. According to the production method, the obtained crystal of N-tert-butylacrylamide has high purity, is not discolored in brown or in light yellow or bluish green and used in fields such as high-class cosmetics and printing materials demanding a fine hue and quality stability and low toxicity to human body. Further a recrystallization solvent such as an organic solvent is not required, the production method decreases a waste liquid, reduces an environmental load and is economically advantageous.

Description

The present invention relates to a method for producing high-purity N-tert-butylacrylamide (general formula 1), and more specifically, 2-acrylamido-2-methylpropanesulfonic acid (hereinafter referred to as “acrylamido-2-methylpropanesulfonic acid”) by reacting acrylonitrile, sulfuric acid and isobutylene. The present invention relates to a production method capable of obtaining N-tert-butylacrylamide of high purity and low color from by-products produced simultaneously with the production of the product, and a sublimation purification apparatus used in the production method.
That is, N-tert-butylacrylamide is recovered as crude crystals after removing ATBS from a reaction solution in which ATBS crystals are dispersed, and the crude crystals are melted and purified by sublimation. The present invention relates to a production method of tert-butylacrylamide and a sublimation purification apparatus used in the production method.

Conventionally, N-tert-butylacrylamide has been used as a raw material for rubber chemicals, paint products and the like by copolymerizing with monomers such as acrylonitrile and acrylate esters. Further, in recent years, usefulness has been recognized as a raw material for cosmetics, medical materials, and printing materials, and its uses are expanding.
In cosmetic applications, skin irritation and inflammation due to impurities contained in raw material components have become problems, and in the field of printing materials, ink coloring and stability have been problematic.
Further, when the hue of a product changes due to coloring, the commercial value is remarkably lowered, so that a raw material without coloring has been demanded.

N-tert-butylacrylamide is generally obtained by reaction and purification of acrylonitrile and tert-butyl alcohol.
As a specific method for producing N-tert-butylacrylamide, a method is known in which acrylonitrile and tert-butyl alcohol are reacted under a strong acid such as sulfuric acid.
In this method, various impurities are contained in the obtained reaction liquid, and the purification process after the reaction is the main point. It is not easy to distill N-tert-butylacrylamide, and a method used for purification of solids such as crystallization is used as the purification method.
For example, when water or an aqueous solution of a lower alcohol is added to the reaction solution obtained by the above reaction to precipitate N-tert-butylacrylamide crystals, the water or aqueous solution adjusted to pH 0.1 to 3 is used. A method of adding to a reaction solution (Patent Document 1), or N-tert-butylacrylamide obtained by neutralizing a reaction solution similar to the above with an alkaline aqueous solution in the presence of an aminopolyphosphoric acid or aminopolycarboxylic acid as a chelating agent A method of precipitating (Patent Document 2) is known.

On the other hand, it is known that N-tert-butylacrylamide is produced as a by-product when ATBS is produced by a three-way addition reaction of acrylonitrile, sulfuric acid and isobutylene. N-tert-butylacrylamide produced as a by-product is an impurity for ATBS, and conventionally, the waste liquid containing it has been disposed of as industrial waste.
As an effective use of such waste liquid, a method (Patent Document 3) in which crude crystals of N-tert-butylacrylamide are recovered from the waste liquid and the crude crystals are purified with a solvent such as acrylonitrile has been proposed.

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

However, the methods described in Patent Documents 1 and 2 require a large excess of methanol water when purifying N-tert-butylacrylamide, and the used methanol water is disposed of as a waste liquid. It was also disadvantageous from an economic point of view.
On the other hand, although the method described in Patent Document 3 can be applied to uses and fields that may be colored, there is a problem that N-tert-butylacrylamide is colored brown, light yellow, or blue-green. .
For this reason, in the prior art, there has been a problem that in recent years, the burden on the environment that has been increased has been reduced, and at the same time, it is insufficient to satisfy the demand for high purity and color prevention, and the field of use has to be restricted.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a reaction liquid obtained by addition reaction of acrylonitrile, sulfuric acid and isobutylene (a dispersion liquid in which ATBS crystals are dispersed in acrylonitrile as will be described later) is converted into ATBS. The N-tert-butylacrylamide crude crystals taken out from the reaction solution are sublimated, and without using an organic solvent such as methanol, there is no brown, light yellow or blue-green coloration. It has been found that -tert-butylacrylamide can be produced, and the present invention has been completed.

  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. A method for producing N-tert-butylacrylamide, which comprises collecting N-tert-butylacrylamide as crude crystals and then collecting the crude crystals by sublimation when purifying butylacrylamide.

  According to the second invention of the present invention, a crude crystal of N-tert-butylacrylamide is melted, and water vapor is generated by adding water and / or by adding water, and the water vapor is converted into N-tert- The method for producing N-tert-butylacrylamide according to the first invention, wherein the method is accompanied with a sublimation gas of butylacrylamide.

  The third invention of the present invention is the N-tert-butyl according to the first or second invention, wherein the temperature of the melt of the crude crystal of N-tert-butylacrylamide is 100 ° C to 140 ° C. This is a method for producing acrylamide.

  According to a fourth aspect of the present invention, the water content of the N-tert-butylacrylamide crude crystal is 10 to 50% by mass, and the water content is 0.01 to 1.0 part by mass with respect to 100 parts by mass of the water-containing crude crystal. It is a method for producing N-tert-butylacrylamide according to the second or third invention, wherein the N-tert-butylacrylamide is added continuously at a rate of / min.

  The fifth invention of the present invention is characterized in that a sublimation gas of N-tert-butylacrylamide entrained with water vapor is cooled by contact with water and the crystals of N-tert-butylacrylamide are sublimated and collected. The method for producing N-tert-butylacrylamide according to any one of the second to fourth inventions.

  The sixth invention of the present invention is the method for producing N-tert-butylacrylamide according to the fifth invention, characterized in that water to be contacted with the sublimation gas is sprayed from the top of the container for sublimation collection.

  According to the seventh aspect of the present invention, the purity of N-tert-butylacrylamide by liquid chromatography is 99.5% or more, and the hue when the N-tert-butylacrylamide is made into a 10% by mass methyl alcohol solution, The N-tert-butylacrylamide according to any one of the first to sixth inventions, wherein a * is 0 to +0.20, b * is 0 to +1.50, and APHA is 15 or less. It is a manufacturing method.

  The eighth invention of the present invention is a sublimation purification apparatus for N-tert-butylacrylamide comprising at least a melting tank and a sublimation collection tower used in any of the first to seventh inventions.

According to the production method of the present invention, it is possible to produce N-tert-butylacrylamide having no coloration and high purity from ATBS waste liquid.
That is, the obtained crystals have a high purity of at least 98.5% or more, further 99.5% or more, and are not colored brown, light yellow or blue-green. It can be suitably used in fields where quality stability is required and toxicity to the human body is low.
Furthermore, since a recrystallization solvent such as an organic solvent is not required, the waste liquid can be reduced, which is advantageous in terms of environmental load reduction and economy.
In addition, according to the production method of the present invention, high-purity N-tert-butylacrylamide can be produced with high yield and high productivity, which is effective in reducing costs.

Hereinafter, the present invention will be described in more detail.
In the present invention, first, ATBS is produced by addition reaction of three components of acrylonitrile, sulfuric acid and isobutylene.
The specific amount of acrylonitrile used with respect 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 starts when the isobutylene gas is blown. The reaction is preferably performed at a temperature of 30 to 70 ° C. for 30 minutes or more under normal pressure.
Since ATBS produced by the reaction is insoluble in acrylonitrile, the reaction solution is obtained as a slurry in which ATBS crystals are precipitated in acrylonitrile.
The solid content concentration in the slurry is usually 10 to 25% by mass.

The ATBS crystals are obtained by solid-liquid separation of the slurry by an operation such as filtration or centrifugation.
The filtrate obtained by the above solid-liquid separation, that is, the acrylonitrile solution usually contains N-tert-butylacrylamide at a concentration of 1% by mass or more. Therefore, for the purpose of separating N-tert-butylacrylamide from the filtrate. It is necessary to evaporate acrylonitrile from the filtrate and concentrate it.
However, since some of the sulfuric acid used in the above reaction remains unreacted in the filtrate, in order to obtain a product that is not colored immediately after production and during storage, the sulfuric acid is applied by alkali washing before concentration of the filtrate. It is desirable to remove this.

As a method for removing sulfuric acid in acrylonitrile, the filtrate may be brought into contact with a solid base such as calcium oxide, but more preferably, the filtrate and an aqueous alkali solution are mixed together in a liquid-liquid mixture. -A liquid separation method is adopted.
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 usually performed by simple distillation or the like, and the acrylonitrile distilled thereby is further purified as necessary and then used again as a raw material for producing ATBS.
N-tert-butylacrylamide, which is the object of the present invention, is concentrated in the can after distillation (generally referred to as the kettle residue).

During distillation, in order to prevent polymerization of acrylonitrile and N-tert-butylacrylamide having radical polymerizability, a mixed gas of oxygen gas and inert gas is blown into the distillation can, or the top of the condenser tower is It is preferable to employ means for spraying a polymerization inhibitor.
As the polymerization inhibitor used in such a case, a phenol compound is preferable.
Examples of the phenol compound include hydroquinone, hydroquinone monomethyl ether, hydroquinone dimethyl ether, di-tert-butyl hydroquinone, tert-butyl catechol, bis-tert-butyl-toluene and the like. Of these, hydroquinone monomethyl ether having an appropriate ability to prevent polymerization is preferred.
Other polymerization inhibitors such as copper chloride (divalent), phenothiazine, diphenylpicrine hydrazyl, nitrobenzene, dithiobenzoyl sulfide and the like may be used.
If necessary, two or more types may be used in combination.

In the present invention, a method for obtaining a crude crystal of N-tert-butylacrylamide from the concentrated solution is not particularly limited, and there are the following two methods. The first method is a method in which the concentrated solution is gradually cooled to 10 ° C. or lower. The second method is a method in which N-tert-butylacrylamide crystals are precipitated by pouring into a solvent having low solubility of N-tert-butylacrylamide, such as water, and crude crystals are obtained by filtration. .
In addition to the above, a method of pouring the concentrated solution into an alkaline aqueous solution instead of water, or once adding the crude crystals to acrylonitrile, dissolving by heating, cooling to 10 ° C. or lower, or pouring into water to precipitate crystals again There is also a way to make it.

The crude crystals of N-tert-butylacrylamide obtained by the above operation are melted and sublimated.
The sublimation method may be any of a batch method, a semi-batch method, and a continuous method, and may be appropriately selected from the processing amount, cost, and processing time.
Although the example of the sublimation purification apparatus used for this invention is shown in FIG. 1, it is not limited to this.
The sublimation purification apparatus comprises: a melting tank that melts a crude crystal of N-tert-butylacrylamide to generate a sublimation gas of N-tert-butylacrylamide; a sublimation gas of N-tert-butylacrylamide is cooled; -Consists of a sublimation collection tower that produces butylacrylamide crystals.

○ Melting tank The melting tank is a box-shaped, spherical, or cylindrical container with a heating device. The tank shape is preferably cylindrical 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.
In order to promote generation of sublimation gas of N-tert-butylacrylamide, it is desirable to stir with a stirrer. Furthermore, in order to increase the generation efficiency of the sublimation gas of N-tert-butylacrylamide, an apparatus that increases the surface area of the N-tert-butylacrylamide 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, glass lining, fluororesin coating, and fluororesin lining.
In order to prevent explosion and oxidation of the sublimation gas of N-tert-butylacrylamide, it is desirable to flow nitrogen into the melting tank.

Although there is no particular limitation on the water content of the crude crystals of N-tert-butylacrylamide, water vapor is removed from the melt of N-tert-butylacrylamide for the purpose of increasing the amount of sublimation gas generated by N-tert-butylacrylamide. It is preferable to generate N-tert-butylacrylamide sublimation gas with water vapor. Therefore, the water content of the crude crystal of N-tert-butylacrylamide is preferably 10 to 50% by mass, and more preferably 20 to 40% by mass.
A crude crystal of N-tert-butylacrylamide dried to a water content of less than 10% can be used, and water can be added dropwise to the melting tank.

It is preferable to continuously and quantitatively supply water so that the water content in the N-tert-butylacrylamide melt in the melting tank can be maintained constant.
Such water is preferably supplied at a rate of 0.01 to 1.0 part by mass / min of 100 parts by mass of crude crystals of N-tert-butylacrylamide per 100 parts by mass, It is more preferable to supply at 0.5 parts by mass / min.
By performing this continuous supply of water, it is possible to increase the production rate of the sublimated collection product (production amount per unit time) to 1.5 times or more of the case where the sublimation collection product is not performed.
A polymerization inhibitor such as hydroquinone monomethyl ether or phenothiazine can be added to the crude crystals of N-tert-butylacrylamide to prevent polymerization.

○ Sublimation collection tower The sublimation collection tower is an apparatus that cools the sublimation gas and sublimates and collects purified crystals, and may have any shape, but a cylindrical one is preferable because it can be efficiently crystallized. .
The installation direction of the sublimation collection tower may be either horizontal or vertical, or may be inclined. The vertical direction is desirable for facilitating dropping of the sublimated collected N-tert-butylacrylamide into the product storage tank.
In order to efficiently sublimate and collect purified crystals of N-tert-butylacrylamide from the sublimation gas of N-tert-butylacrylamide, it is preferable to cool inside and outside the sublimation collection tower.
The cooling method may be either air cooling or water cooling. Cooling may be performed by passing cold water through the jacket, or a sublimation gas can be directly cooled by installing a spray nozzle inside the sublimation collection tower and spraying cold water. .
A cooling pipe may be installed inside the sublimation collection tower. The shape of the cooling pipe may be a straight pipe, a serpentine pipe, a cylindrical shape, a plate shape, or the like.

By spraying cold water on the inner wall of the sublimation collection tower, or by flowing water, the sublimated collection crystals of N-tert-butylacrylamide adhering to the inner wall of the sublimation collection tower were washed away and installed in the lower part. Such a method is preferred because the sublimated crystals can be transferred to the product storage tank.
From the viewpoint of cooling efficiency and not using excessive water, a spraying method is preferred. The position of the spray nozzle may be any of the top, bottom, and side of the sublimation collection tower, but the top is preferred in that gravity can be used.
By using the continuous addition of water to the melting tank and the spray, the production rate of the sublimated collection product can be increased by 2 to 6 times compared to the case where neither is used.

Examples of the material for the sublimation collection tower and the cooling pipe include metals such as stainless steel and titanium, heat resistant glass such as borosilicate glass, glass lining, fluororesin coating, and fluororesin lining.
The pressure in the sublimation collection tower is not limited and may be atmospheric pressure, reduced pressure, or increased pressure, but is preferably atmospheric pressure from the viewpoint of equipment cost.

In the sublimation collection tower, a stirrer is installed to mechanically scrape N-tert-butylacrylamide crystals generated in cotton candy for the purpose of ensuring the flow of sublimation gas of N-tert-butylacrylamide at all times. You can also
It is also possible to generate a pulse of nitrogen gas in the sublimation collection tower, or to drop N-tert-butylacrylamide crystals into the product storage tank by mechanical impact or ultrasonic waves.

  Instead of the sublimation collection tower, a sublimated and collected crystal of N-tert-butylacrylamide can be obtained by using a conductive heat transfer type grooved stirring and cooling machine. An example of such a conductive heat transfer type grooved agitator cooler is a Bono cooler manufactured by Nara Machinery Co., Ltd.

  In order to prevent N-tert-butylacrylamide from being crystallized in the pipe connecting the melting tank and the sublimation collection tower, the pipe connecting the melting tank and the sublimation collection tower also has a temperature of 100 ° C. or higher. It is desirable to keep warm. As the heat insulation method, a method using a heat insulating material, a method using a jacket, a method using an explosion-proof heater, or the like can be considered.

The temperature for melting the crude crystals of N-tert-butylacrylamide in the melting tank is preferably 100 to 140 ° C.
In order to increase the generation amount of sublimation gas of N-tert-butylacrylamide, 120 to 135 ° C is more preferable.
When the temperature of the melting tank is less than 100 ° C., the generation of sublimation gas is too small, and when it exceeds 140 ° C., crude crystals are colored, and the quality of N-tert-butylacrylamide after sublimation collection is deteriorated.

  The temperature of the sublimation gas of N-tert-butylacrylamide at the outlet of the melting tank is preferably 120 ° C to 140 ° C, and more preferably 125 to 135 ° C.

N-tert-butylacrylamide sublimated and collected by the sublimation collection tower is separated and recovered as crystals sublimated and collected from a liquid containing a sublimation collection product and water as a product in a product storage tank.
As a method for recovering such a product, a Nutsche filter, a single plate filter, a horizontal filter plate filter, a belt filter, a centrifuge, or the like can be applied, and either an open type or a sealed type may be used.
The filtration atmosphere may be atmospheric pressure, pressurization, or reduced pressure, but pressure filtration with a nitrogen-containing gas is preferable.

The obtained product may be used as it is, but if it is washed with water or an organic solvent containing water, it becomes more pure and the coloring can be reduced.
However, such cleaning is necessary only when it is particularly necessary because waste liquid is generated, which is time consuming and expensive. In this case, since N-tert-butylacrylamide has a high solubility in an organic solvent, the amount obtained is reduced when the organic solvent is washed alone. Therefore, washing with water or an organic solvent containing water is preferred, and washing with water is more preferred.

The sublimated and collected product may be used as it is, but when dried, it becomes a fine powder and becomes easier to use.
As the drying method, a stationary shelf dryer, a rotary dryer, a stirring dryer such as a paddle dryer, a filter dryer, a vibration dryer, a fluid dryer, or the like can be applied.
The drying atmosphere is not particularly limited, but since the product is organic, it is preferable to dry under reduced pressure at a low temperature in order to reduce deterioration due to heat.

There are two types of changes in the hue of N-tert-butylacrylamide in the present invention: a cold-colored color such as bluishness and greenishness, and a change from yellow to brown.
Even in the field of cosmetics and printing materials, which have a great influence on the product value even with a minute change in hue, in particular in applications that care about changes in color (high-grade cosmetics and high-quality inks), any subtle changes in hue are undesirable.
The hue is visually evaluated as a *, b *, and APHA.
a * and b * are called chromatic index and are 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.
It is preferable that a * is in the range of −0.20 to +0.20 and b * is in the range of 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.
It is preferable that APHA is 20 or less that is almost white to colorless in visual sensory evaluation.

The N-tert-butylacrylamide of the present invention is difficult to have such a color even after storage. Specifically, after N-tert-butylacrylamide is stored immediately after production and at 25 ° C. for 1 week, As for the hue when it is set as a 10 mass% methyl alcohol solution, it is preferable that a * is -0.20 to +0.25, b * is -0.15 to +3.00, and APHA is 20 or less.
More preferable hues of N-tert-butylacrylamide are a * of 0 to +0.20, b * of 0 to +1.50, and APHA of 15 or less.

  According to the production method of the present invention, the purity of N-tert-butylacrylamide by liquid chromatography is 98.5% or more. In order to prevent skin irritation and inflammation of cosmetics, increase the color of high-grade ink, and improve product stability, the purity is preferably 99.5% or more, and more preferably 99.9% or more.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.
○ Reference Example 1 Production of ATBS Two reactors equipped with a mixing stirrer were connected, and acrylonitrile and fuming sulfuric acid were introduced into the first-stage reactor under the following reaction conditions, and acrylonitrile and sulfuric acid were introduced. The mixture in the first stage reactor was introduced into the second stage reactor, and isobutylene gas was introduced into the second stage reactor to carry out the reaction 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 (the concentration of sulfur trioxide in sulfuric acid) is 9% by mass. 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 ATBS 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. ATBS was obtained by drying the cake after washing.

Reference Example 2 Production of N-tert-butylacrylamide Crude Crystals After neutralizing 110 kg of the acrylonitrile solution obtained by combining the filtrate obtained in Reference Example 1 and the washing filtrate with a 25% by mass ammonium hydroxide aqueous solution, By separating and removing, 115 kg of an acrylonitrile solution containing about 4% by mass of N-tert-butylacrylamide (hereinafter referred to as TBAM) was obtained. 6. Hydroquinone monomethyl ether (hereinafter referred to as MQ) is added to this solution to 500 ppm by mass, and the solution is concentrated under reduced pressure while blowing nitrogen gas containing 5% oxygen into the solution, and a solution containing about 60% by mass of TBAM. 6 kg was obtained. About 100 kg of acrylonitrile was separated in this distillation. The obtained concentrated solution (7.6 kg) was gradually cooled in an ice bath to precipitate crystals. The resulting dispersion was filtered to obtain 2.5 kg of TBAM crude crystal cake.

○ Example 1
A cylindrical 3 L glass flask (melting tank) having a body diameter of 15 cm and equipped with a stirrer equipped with a fluororesin plate-like stirring blade was placed in an oil bath. 1300 g of the coarse TBAM cake (water content 26.2%) obtained in Reference Example 2 was charged into the melting tank. The oil was heated to 160 ° C. while nitrogen was passed through the melting tank at 2.0 L / min.
The temperature of the melt of TBAM in the melting tank was 120 to 135 ° C., and pure water was continuously added to the melting tank at 1.2 g / min to 2.8 g / min.
The test was started when the outlet gas temperature of the dissolution tank reached 128 ° C., and while maintaining the temperature at 128 to 132 ° C., sublimation gas and water vapor were continuously taken out and introduced into the sublimation collection tower.
At this time, the surface area of the melt in the melting tank was 176.6 cm ² .
Pure water was sprayed at 128 g / min from a spray nozzle installed at the top of the sublimation collection tower. The test was continued for 2 hours after the melter outlet gas temperature reached 128 ° C.
Subsequently, the sublimated TBAM collected in the product storage tank (hereinafter referred to as a collected product) was collected, washed with 100 g of pure water, and filtered through a Buchner funnel. The collected material was white.
The collected matter after air drying was 47.3 g. The amount of water measured by Karl Fischer when the collected product was measured with a 10% methanol solution was 0.5% by mass.
The obtained collected product was analyzed under the following HPLC conditions. The TBAM retention time was confirmed by comparison with the peak position using a reagent manufactured by Tokyo Chemical Industry Co., Ltd. As a result, the purity was 99.9%.
HPLC (manufactured by Shimadzu Corporation)
Column: ODS column Eluent: Acetonitrile: Water = 30: 70
Detection: 213 nm
When the collected material was dissolved in a 10% 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 +0.12, and b * was +1. It was 15 when APHA was measured, and it was 14 when visually observed. After that, it was spread on a petri dish, stored at 25 ° C. for one week, and the hue was measured again.
The results are shown in Table 1.

Example 2
In Example 1, the same operation as in Example 1 was performed except that a stainless steel Kansai Chemical Machinery manufactured wall wetter was installed instead of the fluororesin plate-like stirring blade.
By stirring the wall wetter, which is a stirring blade, the melt in the melting tank is scraped, and the inner wall of the cylindrical 3L glass flask (melting tank) is continuously melted up to a height of 12 cm from the surface of the melt. It was confirmed that a so-called wet wall was formed.
In this case, the surface area of the melt in the melting tank, the horizontal surface area 176.6Cm ^2, the sum of the surface area 565.2Cm ² of the melt in the vertical direction of the so-called wetted wall was 741.8cm ^2.
After air drying, 110.3 g of a white collection was obtained.
The water content at Karl Fischer measured with a 10% methanol solution of the collected material after air drying was 0.5%.
A 10% by mass methyl alcohol solution of the collected material after air drying had a * of +0.11, b * of +0.94, and APHA of 10.
APHA and color after one week were measured and shown in Table 1.

Example 3
In Example 1, the same operation as in Example 1 was performed except that no spray nozzle was installed at the top of the sublimation collection tower and pure water was not sprayed.
Since the heat removal in the sublimation collection tower was poor and the collected matter adhered to the wall surface of the sublimation collection tower, the yield of TBAM collected by sublimation after air drying decreased to 31.5 g.
The collected matter was white, and the water content at Karl Fischer measured with a 10% methanol solution was 0.5%.
The 10% by mass methyl alcohol solution of the collected material after air drying had a * of +0.07, b * of +0.60, and APHA of 7.
APHA and color after one week were measured and shown in Table 1.

Example 4
In Example 2, the same operation as in Example 2 was performed except that pure water was not added to the TBAM melt in the melting tank and pure water was not supplied to the sublimation collection tower.
As a result, the yield of the collected material after air drying decreased to 20.1 g.
The obtained TBAM was white with a water content of 0.5% at Karl Fischer as measured with a 10% methanol solution.
The 10% by mass methyl alcohol solution of the collected product after air drying had a * of +0.12, b * of +1.05, and APHA of 12.
APHA and color after one week were measured and shown in Table 1.

Comparative Example The crude cake obtained in Reference Example 2 was air-dried as it was. The obtained crystal was a powder colored blue-green. The purity of TBAM was measured and found to be 98.3%. The APHA of a 10% by mass methyl alcohol solution immediately after production of the powder was 26, a * was −2.18, and b * was +4.82.
APHA and color after one week were measured and shown in Table 1.

According to the production method of the present invention, N-tert-butylacrylamide is recovered from the waste liquid during the production of ATBS and purified by an industrially easy method to obtain white high-purity crystals without coloring. .
In addition, N-tert-butylacrylamide can be obtained at a low cost without generating a waste liquid of an organic solvent such as methanol water, which can contribute to energy efficiency and preservation of the global environment.
The N-tert-butylacrylamide thus obtained has no change in color not only during storage but also after storage, and is optimal for, for example, high-grade cosmetics, printing materials, and medical uses.

It is the schematic of the apparatus (it is called a sublimation refinement | purification apparatus) which carries out sublimation and sublimation collection of the crude crystal | crystallization of N-tert- butylacrylamide.

DESCRIPTION OF SYMBOLS 1 Melting tank 2 Oil bath 3 Nitrogen gas introduction pipe 4 Addition water introduction pipe 5 Sublimation gas flow path (pipe)
6 Cooling water introduction pipe 7 Cooling water spray nozzle 8 Sublimation collection tower 9 Product storage tank 10 Drain

Claims (8)

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. -A method for producing N-tert-butylacrylamide, which comprises collecting butylacrylamide as crude crystals and then collecting the crude crystals by sublimation. The crude crystals of N-tert-butylacrylamide are melted, water vapor is generated by adding water and / or by adding water, and the water vapor is accompanied with the sublimation gas of N-tert-butylacrylamide. The method for producing N-tert-butylacrylamide according to claim 1. The method for producing N-tert-butylacrylamide according to claim 1 or 2, wherein the temperature of the melt of the crude crystal of N-tert-butylacrylamide is 100 ° C to 140 ° C. The water content of the N-tert-butylacrylamide crude crystals is 10 to 50% by mass, and water is continuously added at a rate of 0.01 to 1.0 parts by mass / min with respect to 100 parts by mass of the hydrous crude crystals. It adds, The manufacturing method of N-tert- butyl acrylamide of Claim 2 or 3 characterized by the above-mentioned. The sublimation gas of N-tert-butyl acrylamide entrained with water vapor is cooled by being brought into contact with water, and the crystals of N-tert-butyl acrylamide are sublimated and collected. A method for producing N-tert-butylacrylamide according to claim 1. The method for producing N-tert-butylacrylamide according to claim 5, wherein water to be brought into contact with the sublimation gas is sprayed from the top of the container for sublimation collection. The purity of N-tert-butylacrylamide by liquid chromatography is 99.5% or more, and the hue when the N-tert-butylacrylamide is made into a 10% by mass methyl alcohol solution has an a * of 0 to +0.20. , B * is 0 to +1.50, and APHA is 15 or less, The method for producing N-tert-butylacrylamide according to any one of claims 1 to 6. A sublimation purification apparatus for N-tert-butylacrylamide, comprising at least a melting tank and a sublimation collection tower used in any one of claims 1 to 7.

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