JP5428942B2 - Method for producing N-tert-butylacrylamide with reduced coloring - Google Patents

Description

The present invention relates to a method for producing N-tert-butylacrylamide (general formula 1) with reduced coloring. More specifically, acrylonitrile, sulfuric acid and isobutylene are reacted to give 2-acrylamido-2-methylpropanesulfonic acid. The present invention relates to a production method capable of reducing coloring during storage of N-tert-butylacrylamide produced at the same time when producing (hereinafter referred to as ATBS).
That is, after removing ATBS from the reaction solution in which ATBS crystals are dispersed, N-tert-butylacrylamide is recovered as crude crystals, brought into contact with an alkaline aqueous solution, and then the crude crystals are converted to alcohol in the presence of activated carbon. The present invention relates to a method for producing N-tert-butylacrylamide, which comprises dissolving, then separating and recrystallizing activated carbon.

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. Furthermore, in recent years, its usefulness has been recognized as a raw material for cosmetics and high-grade inks, and its uses are expanding.
In the use of cosmetics and high-grade ink, if the hue of a product changes due to coloring of raw material components, the commercial value will be significantly reduced. For this reason, raw materials not colored during the storage period as well as the initial stage have 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 the 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 a chelating agent, aminopolyphosphoric acid or aminopolycarboxylic acid There is known a method of depositing (Patent Document 2) and the like.

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 of recovering crude crystals of N-tert-butylacrylamide from the waste liquid and purifying the crude crystals with a solvent such as acrylonitrile (Patent Document 3) has been proposed.

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

N-tert-butylacrylamide obtained by reacting acrylonitrile and tert-butyl alcohol tended to be colored during storage even though the coloration was reduced after production.
In addition, even when N-tert-butylacrylamide obtained from ATBS waste liquid is purified with acrylonitrile or the like, the crystals after the trial production are colored blue to green and brown during storage. Thus, there is a problem that the field of use is limited.

  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. Then, crude crystals of N-tert-butylacrylamide taken out from the reaction solution or those purified with an organic solvent such as acrylonitrile (hereinafter referred to as “crude crystals” together) were brought into contact with an aqueous alkali solution. Later, it was found that N-tert-butylacrylamide without brown, pale yellow, or blue-green coloration can be produced during storage by recrystallization in alcohol that may contain water in the presence of activated carbon. The 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 performing the following steps when purifying butylacrylamide.
(1) 2-acrylamido-2 after methylpropanesulfonic acid were separated and the reaction was neutralized with A alkali, recovering as the N-tert-butylacrylamide crude crystals.
(2) A step of bringing the crude crystals into contact with an alkaline aqueous solution.
(3) dissolved in a mixture of alcohol or alcohol and water, chemical activation or Mizu蒸 gas activated by the step of treating with activated carbon.
(4) A step of recrystallizing N-tert-butylacrylamide from the solution after separating the activated carbon.

  The second invention of the present invention is the method for producing N-tert-butylacrylamide according to the first invention, wherein the alcohol used for recrystallization is methyl alcohol or a mixture of methyl alcohol and water.

  A third invention of the present invention is the method for producing N-tert-butylacrylamide according to the first invention or the second invention, wherein the aqueous alkali solution to be brought into contact with the crude crystals is an alkali metal compound.

  According to the fourth aspect of the present invention, when N-tert-butylacrylamide is stored at 25 ° C. for 1 week, the hue when a 10% by mass methyl alcohol solution is obtained is that a * is −0.20 to +0 and b * is The method for producing N-tert-butylacrylamide according to any one of the first to third inventions, wherein 0 to +3.00 and APHA is 10 or less.

  According to the production method of the present invention, N-tert-butylacrylamide having no color and good purity can be produced from ATBS waste liquor. The crystals are not colored during storage, and can be used in the field of high-grade cosmetics and high-grade inks in which a fine hue is particularly important among cosmetics and high-grade inks.

Hereinafter, the present invention will be described in more detail.
In the addition reaction of acrylonitrile, sulfuric acid and isobutylene in the present invention, ATBS is a product obtained by reacting the above three components in equimolar amounts. Acrylonitrile in the reaction is used in a large excess relative to the other two components in order to use it as a reaction solvent. It is preferable to use approximately equimolar amounts of 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 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 ATBS produced by the reaction is insoluble in acrylonitrile as a solvent, 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. Need to be removed.

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, phenothiazine, diphenylpicrine hydrazyl, nitrobenzene, dithiobenzoyl sulfide and the like may be used.
If necessary, two or more types may be used in combination.

Although it does not specifically limit as a method of obtaining the crude crystal | crystallization of N-tert- butylacrylamide from the said concentrate, There exist the following three methods. The first method is a method of gradually cooling the concentrated solution to 10 ° C. or less, and the second method is pouring into a large amount of solvent having low solubility of N-tert-butylacrylamide, such as water. In the third method, a crude crystal is obtained by precipitating crystals of N-tert-butylacrylamide, and the third method is to pour the concentrated solution into an alkaline aqueous solution instead of a large amount of water, and add N-tert-butylacrylamide. This is a method for precipitating crude crystals.
Further, the crude crystals are added to acrylonitrile and dissolved again by heating, and the resulting solution is cooled again to 10 ° C. or lower or poured into a large amount of water to precipitate crystals, which are purified by filtration and purified by N-tert- There is also a method for obtaining crystals of butylacrylamide.

The N-tert-butylacrylamide crude crystals obtained by the above operation are washed with an alkaline aqueous solution, dissolved in a solvent, and subjected to activated carbon treatment.
There are no particular limitations on the alkali compound used in the aqueous alkali solution, but for the operation of washing with the aqueous solution, sodium hydroxide, potassium hydroxide, sodium carbonate, ammonium hydroxide, etc. having high water solubility are preferable, and are easily available. Sodium hydroxide or potassium hydroxide is preferably used.
The concentration of the aqueous alkaline solution is not particularly limited, but it is 0.2% by mass or more as the concentration that can obtain the effect of preventing coloring during storage. If it becomes too economical and too dark, it becomes difficult to remove the brown color in recrystallization. 5 mass% or less is preferable.
The amount of the alkaline aqueous solution used is not particularly limited, but it is preferably 1 to 5 times by mass with respect to the crude crystal cake to be washed in consideration of the amount sufficient for washing and economy.

The solvent that dissolves the crude crystals after contact with the alkaline aqueous solution is an alcohol such as methyl alcohol, ethyl alcohol, or isopropyl alcohol having high solubility of N-tert-butylacrylamide, or a mixture of the alcohol and water.
The solvent may be a single solvent of alcohol, but it is preferable that water is contained in the solvent, because water-soluble impurities migrate to the water layer during recrystallization in the next step, and impurities in the crystals can be reduced.
On the other hand, if the water content of the solvent increases too much, the solubility of N-tert-butylacrylamide decreases, which requires a large amount of solvent and is economically disadvantageous.
The ratio of alcohol to water is preferably 95: 5 to 30:70 (mass ratio), more preferably 80:20 to 40:60 (mass ratio), and most preferably 70:30 to 50:50 (mass ratio). .
In addition, in order to prevent the coloring derived from a metal, the water to use the thing with little content of a trace metal is preferable. Specifically, pure water, ion exchange water, distilled water and the like.

The solvent may be used as a mixture with an organic solvent such as acrylonitrile, acetone, or ethyl acetate, as long as it contains 50% by mass or more of the alcohol.
A preferred alcohol is methyl alcohol, which has a particularly high solubility in N-tert-butylacrylamide and a high miscibility with water.
The amount of alcohol used is not limited as long as N-tert-butylacrylamide can be completely dissolved in a state heated at 40 to 80 ° C. (but below the boiling point) and recrystallization is precipitated at 20 ° C. Usually, it is in the range of 3/1 to 1/3 (mass ratio) with respect to the crude crystals of N-tert-butylacrylamide.

After dissolving N-tert-butylacrylamide in the solvent or during dissolution, activated carbon is added to perform activated carbon treatment.
As the activated carbon, chemical activated carbon, water vapor activated activated carbon, or the like can be used. Specifically, chemical activated activated zinc chloride charcoal made by Nippon Enviro Chemicals, such as “Dazai S”, activated carbon activated by Futamura Chemical, “Dazai K” activated by steam, “Dazai P”, etc. Steam-activated “Shirasagi C”, “Shirasagi M”, “Shirasagi A”, “Shirasagi P”, etc. can be used, such as “Calboraphin”, “Strength White Shiraka”, “Refined White Shirakaba”, “Special White Shirakaba”.
The activated carbon may be any of powder, granule, crush, granulation and the like. The activated carbon may be added in either a dry product or a mixture with water. The activated carbon treatment method may be a batch method or a continuous method.
The usage-amount of activated carbon is 0.01 mass%-10 mass% with respect to a crude crystal. If it is less than 0.01% by mass, there is no effect of reducing coloring, and if it exceeds 10% by mass, it is not economical. Preferably they are 0.5 mass%-5 mass%, More preferably, they are 1 mass%-3 mass%.
The conditions for the treatment are not particularly limited because they vary depending on the treatment amount, the crude crystal concentration, and the like, but are preferably 15 minutes to 5 hours under a heating condition of 40 ° C. to 60 ° C. under normal stirring.

After performing the activated carbon treatment, the activated carbon is removed by filtration and recrystallization is performed.
As a recrystallization method, a method of crystallizing by cooling or a crystallization apparatus can be applied. In addition to cooling, it can be cooled by forced cooling by a jacket and temperature control. The recrystallization temperature is preferably 20 ° C. or less, more preferably 15 ° C. or less, and most preferably 10 ° C. or less. The lower limit is the temperature at which the solvent freezes.
Nutsche filter, single plate filter, horizontal filter plate filter, belt filter, etc. can be applied to recover crystal from liquid containing recrystallized material, either open or sealed good.
The filtration atmosphere may be atmospheric pressure, pressurization, or depressurization, but pressure filtration with a nitrogen-containing gas is preferable in handling organic solvents.

  The obtained N-tert-butylacrylamide recrystallized product may be used as it is, but washing with water or an organic solvent containing water is preferable because it can further reduce coloration. Since N-tert-butylacrylamide has a high solubility in an organic solvent, the amount obtained is reduced when the organic solvent is washed alone. It is preferably washed with water or an organic solvent containing water, and more preferably washed with water.

The N-tert-butylacrylamide crystal obtained by the above recrystallization treatment may be used as it is, but can be used for various industrial applications by drying.
As a drying method, a stationary shelf dryer, a rotary dryer, a paddle dryer or other agitation dryer, a filter dryer, a vibration dryer, a fluid dryer, or the like can be applied. Although the drying atmosphere is not limited, since N-tert-butylacrylamide has sublimation properties, it is preferable to dry under reduced pressure at 70 ° C. or lower, and it is preferable to dry under reduced pressure at a low temperature to reduce deterioration. .

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 high-grade inks, which have a great influence on the product value even if the hue changes finely, in particular in applications where the change in color is a concern (high-grade cosmetics and high-grade inks), any subtle changes in hue are not preferable.
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 at 25 ° C. for 1 week, it is 10% by mass. As for the hue when it is set as the methyl alcohol solution, it is preferable that a * is −0.20 to +0.05, b * is 0 to +4.00, and APHA is 20 or less.
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 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 10 or less because it is almost white to colorless in visual sensory evaluation.
More preferably, a * is −0.18 to 0, b * is 0 to +1.50, and APHA is 5 or less.

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, which is a combination of 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
16.1 g of a 1% by mass aqueous sodium hydroxide solution was added to 16.1 g of the coarse TBAM cake obtained in Reference Example 2, and after stirring for 10 minutes, an alkali-washed cake was obtained by vacuum filtration.
Futamura Chemical "Taiko Activated Carbon S" (0.33 g), methyl alcohol (32.5 g) and water (27.9 g) were heated to 50 ° C. and held, and the alkali-cleaned cake was added.
The TBAM solution to which the activated carbon was added was kept at 50 ° C. for 1 hour with stirring to perform activated carbon treatment. Thereafter, the solution was heated and filtered with a jacketed pressure filter while maintaining the solution at 50 ° C.
The obtained filtrate was allowed to cool to 15 ° C. to obtain a recrystallized slurry.
The recrystallization slurry was filtered off to obtain a recrystallization cake. 14.3 g of water was added to the recrystallization cake, and the crystal was washed by stirring for 5 minutes.
Then, it filtered and dried and obtained 8.9g of the refined crystalline substance of white powder. The yield was determined from the following formula (Formula (1)) and found to be 55%.
The obtained TBAM 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
The purified crystal was spread on a petri dish, stored at 25 ° C. for one week, and then dissolved so as to be 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 −0.04, b * was +0.46, and APHA was 4 when measured.
At this time, the white color was maintained visually.
Yield (%) = {Purified TBAM crystal (g) / TBAM crude cake (g)} × 100 (Formula 1)

The results are shown in Table 1.

○ Examples 2-5
Except that the crude crystal cake was washed under the conditions shown in Table 1, the same operation as in Example 1 was performed to obtain purified N-tert-butylacrylamide. Subsequently, the hue after one week of storage was observed and measured. The results are shown in Table 1.

○ Comparative Example 1
20 g of TBAM crude cake obtained in Reference Example 2 was added to 20 g of a 1% by mass aqueous sodium hydroxide solution, stirred for 10 minutes, and then subjected to vacuum filtration to obtain an alkali-washed cake.
9 g of methyl alcohol was heated to 60 ° C. Stirring was continued under stirring until the alkali-cleaned cake was almost completely dissolved, then heating and stirring were stopped, and after cooling, the mixture was slowly cooled to 15 ° C. to obtain a recrystallized slurry.
A recrystallized cake is obtained by filtration under reduced pressure, and 8 g of methyl alcohol cooled to 10 ° C. is poured into the cake to be washed, and the residue is again filtered under reduced pressure and dried to obtain a purified powder of a slightly brownish white powder. 7.4 g was obtained.
When stored at 25 ° C. for one week, it turned pale brown with a pale green color, and the hue was measured with a 10% ethyl alcohol solution. As a result, the a * was +0.15 and the b * was +4.20. APHA became 48. The results are shown in Table 1.

○ Comparative Example 2
Except that the aqueous sodium hydroxide solution was changed to water, the same operation as in Example 1 was performed to obtain 8.5 g of a purified crystallite having a light blue-green color. The yield was 53%. APHA and hue of a 10% by weight methyl alcohol solution of the crystal after storage for one week were measured. The results are shown in Table 1.

○ Comparative Example 3
Comparative Example 2 except that the aqueous sodium hydroxide solution was changed to water, activated carbon was not used, and methanol in which 0.02 g of diethylenetriaminepentaacetic acid sodium (DTPA) as a chelating agent was added to the recrystallization solvent was used. Operation was performed to obtain 8.0 g of purified crystals. The yield was 50%. The purified crystal after drying was slightly blue-white. APHA and hue of a 10% by weight methyl alcohol solution of the crystal after storage for one week were measured. The results are 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. .
The N-tert-butylacrylamide thus obtained has no change in color not only during storage but also after storage, and is optimal for use in, for example, high-grade cosmetics and high-grade inks.

Claims (4)

When the 2-acrylamido-2-methylpropanesulfonic acid obtained by reacting acrylonitrile, sulfuric acid and isobutylene is separated from the reaction solution and the N-tert-butylacrylamide contained in the subsequent reaction solution is purified, the following steps are performed. A process for producing N-tert-butylacrylamide, characterized in that
(1) 2-acrylamido-2 after methylpropanesulfonic acid were separated and the reaction was neutralized with A alkali, recovering as the N-tert-butylacrylamide crude crystals.
(2) A step of bringing the crude crystals into contact with an alkaline aqueous solution.
(3) dissolved in a mixture of alcohol or alcohol and water, chemical activation or Mizu蒸 gas activated by the step of treating with activated carbon.
(4) A step of recrystallizing N-tert-butylacrylamide from the solution after separating the activated carbon.   The method for producing N-tert-butylacrylamide according to claim 1, wherein the alcohol used for recrystallization is methyl alcohol or a mixture of methyl alcohol and water.   The method for producing N-tert-butylacrylamide according to claim 1 or 2, wherein the alkaline aqueous solution brought into contact with the crude crystals is an alkali metal compound.   After storing N-tert-butylacrylamide at 25 ° C. for 1 week, the hue when a 10% by mass methyl alcohol solution is obtained is that a * is −0.20 to +0, b * is 0 to +3.00, and APHA The method for producing N-tert-butylacrylamide according to any one of claims 1 to 3, wherein is 10 or less.