JPH0789917A - Purification of n-vinylcarboxylic acid amide - Google Patents

Abstract

PURPOSE:To provide a method for easily and efficiently purifying crude N- vinylcarboxylic acid amide into highly pure N-vinylcarboxylic acid amide excellent in polymerizability. CONSTITUTION:Crude N-vinylcarboxylic acid amide containing the N- vinylcarboxylic acid amide in an amount of >=50wt.% is pressed with a pressure of 500-3000atm. at 0-100 deg.C to deposit the crystals of the N-vinylcarboxylic acid amide, and the crystals of the N-vinylcarboxylic acid amide are separated from the liquid phase under a high pressure to obtain the N-vinylcarboxylic acid amide excellent in polymerizability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying N-vinylcarboxylic acid amide, and more specifically, to N-vinylcarboxylic acid amide-containing crude N-vinylcarboxylic acid amide having high purity and excellent polymerizability. It relates to a method for obtaining a vinylcarboxylic acid amide.

[0002]

2. Description of the Related Art N-Vinylcarboxylic acid amides are prepared from N- (1
It is known that it can be produced by synthesizing -alkoxyethyl) carboxylic acid amide and thermally or catalytically decomposing it. However, the physical properties of N-vinylcarboxylic acid amide and unreacted carboxylic acid amide or N- (1-alkoxyethyl) carboxylic acid amide, especially the boiling point and solubility are very close, and their separation is not easy. A method has been proposed.

For example, Japanese Unexamined Patent Publication (Kokai) No. 61-286069 discloses extraction / separation with water and aromatic hydrocarbons, since mixing of formamide which is an unreacted raw material into N-vinylformamide is inevitable in distillation. ing.

On the other hand, as another promising method for producing N-vinylcarboxylic acid amide, ethylidene biscarboxylic acid amide was synthesized from acetaldehyde and carboxylic acid amide, and this was converted into carboxylic acid amide and N-vinylcarboxylic acid amide. It is known to be obtained by decomposing. However, when an N-vinylcarboxylic acid amide is produced in this manner, equimolar amounts of a carboxylic acid amide and N-vinylcarboxylic acid amide having similar physical properties are formed, and it becomes very difficult to separate them. JP 63-1
No. 32868 discloses a method by cooling crystallization from a mixed organic solvent, JP-A No. 2-188560 discloses a method by extraction with an aqueous solution of an inorganic salt and an aromatic hydrocarbon, and US Pat. A method by extractive distillation using alcohol is disclosed.

However, in any case, it is difficult to obtain a sufficiently pure N-vinylcarboxylic acid amide by these methods. Furthermore, the extraction method requires an expensive organic solvent and a facility for recovering and purifying these. Further, since N-vinylcarboxylic acid amide is relatively unstable to water, it may cause hydrolysis of N-vinylcarboxylic acid amide during the extraction operation, which is not an industrially satisfactory method. In addition, the method by cooling crystallization using an organic solvent requires a drying step in addition to the problem caused by using an organic solvent as in the extraction method, and there is a possibility that N-vinylcarboxylic acid amide will be thermally polymerized. There is a problem. Furthermore, since the extractive distillation method uses an organic solvent, it is necessary to increase the reflux ratio in order to obtain the necessary rectification effect, and therefore the N-vinylcarboxylic acid amide must be heated for a long time.

[0006] On the other hand, Japanese Patent Publication No. 56-41282 discloses a so-called pressure crystallization method in which a mixture is pressurized to a high pressure to precipitate a part of components, and a liquid phase and a crystal present under pressure are separated. Is disclosed. Such pressure crystallization method is disclosed in JP-A-62-209034, JP-A-1-250329, and JP-A-4-120027.
It is known that it can be used for separation of positional isomers such as xylene, naphthalene, cresol, etc., or separation of alkylated phenols from an alkylation reaction solution of phenols, etc. ing. However, it has not been disclosed to use the pressure crystallization method for purifying vinyl compounds, particularly N-vinylcarboxylic acid amide, from the viewpoint of imparting excellent polymerizability to N-vinylcarboxylic acid amide.

[0007]

It is an object of the present invention to remove impurities from a crude N-vinylcarboxylic acid amide to produce an N-vinylcarboxylic acid amide having high purity and excellent polymerizability. It is intended to provide a method for purifying an amide.

[0008]

SUMMARY OF THE INVENTION According to the present invention, a crude N-vinylcarboxylic acid amide containing N-vinylcarboxylic acid amide in an amount of 50% by weight or more is pressurized at 0 to 100 ° C. to 500 to 3000 atm to obtain N. -Precipitate crystals of vinylcarboxylic acid amide,
A method for purifying N-vinylcarboxylic acid amide is provided, which comprises separating the crystals from a liquid phase under pressure.

[0009]

DETAILED DESCRIPTION OF THE INVENTION The method for purifying N-vinylcarboxylic acid amide according to the present invention will be specifically described below.

In the method for purifying N-vinylcarboxylic acid amide according to the present invention, the produced N-vinylcarboxylic acid amide,
N-vinylcarboxylic acid amide (hereinafter referred to as crude N-vinylcarboxylic acid amide) containing unreacted substances (for example, carboxylic acid amide, N- (1-alkoxyethyl) carboxylic acid amide) and the like is pressure-crystallized. The N-vinylcarboxylic acid amide is purified by treating it by a precipitation method to separate N-vinylcarboxylic acid amide and unreacted substances.

The N-vinylcarboxylic acid amides to be purified in the present invention include N-vinylacetamide, N-vinyl-N-methylacetamide, N-vinylformamide, N-methyl-N-
Examples thereof include vinylformamide, and N-vinylacetamide is particularly preferable.

The crude N-vinylcarboxylic acid amide used in the present invention desirably contains N-vinylcarboxylic acid amide in an amount of 50% by weight or more, preferably 70% by weight or more. Other components contained in the crude N-vinylcarboxylic acid amide are not particularly limited, but alcohols having 5 or less carbon atoms, carboxylic acid amides, N- (1-alkoxyethyl) carboxylic acid amides, ethylidene biscarboxylic acid amides, etc. Is mentioned. When the amount of the N-vinylcarboxylic acid amide contained in the crude N-vinylcarboxylic acid amide is less than 50% by weight, the recovery rate of the N-vinylcarboxylic acid amide is poor, and the N-vinylcarboxylic acid amide obtained is The purity is low,
It does not show excellent polymerizability.

In the present invention, the pressure crystallization operation of the crude N-vinylcarboxylic acid amide is preferably carried out in the presence of an alcohol having 5 or less carbon atoms. When pressure crystallization operation of crude N-vinylcarboxylic acid amide is performed in the presence of such alcohol, melting point of N-vinylcarboxylic acid amide is lowered or solubility is increased, and pressure crystallization operation is performed at a lower temperature. It is possible to prevent deterioration of N-vinylcarboxylic acid amide due to heat.

Alcohols used include methanol, ethanol, n- and iso-propyl alcohol, n-
And iso-butyl alcohol, 2-butanol, n- and
Examples include iso-amyl alcohol, 2- and 3-pentanol, and methanol is particularly preferable. Also, N- (1
In the case of N-vinylcarboxylic acid amide synthesized via -alkoxyethyl) carboxylic acid amide, pressure crystallization can be simplified by performing pressure crystallization in the presence of the same type of alcohol as the by-product alcohol. It is preferable because it can be converted into

The crude N-vinylcarboxylic acid amides are, for example, disclosed in JP-A-61-106546 (a thermal decomposition method of ethylidene bisacetamide) and JP-A-50-76015 (a secondary N-vinylcarboxylic acid amide). Production method), etc., but the content of N-vinylcarboxylic acid amide in the obtained crude N-vinylcarboxylic acid amide is 5
If it is 0% by weight or more, the thermal decomposition products of these methods may be directly used as crude N-vinylcarboxylic acid amides, or N-vinylcarboxylic acid amides may be concentrated or distilled by distillation to obtain N-vinylcarboxylic acid amides. You may use what increased the content of vinylcarboxylic acid amide. Crude N- after these purification operations
It is desirable to perform pressure crystallization operation using vinylcarboxylic acid amide, because the recovery rate of N-vinylcarboxylic acid amide is naturally improved, and the purity and the polymerizability are also improved.

N-vinylcarboxylic acid amide is unstable to water and absorbs moisture in the air to gradually decompose. In particular, the presence of acid is extremely unstable and causes hydrolysis. Therefore, when refining N-vinylcarboxylic acid amide, the pressure crystallizer including the pressure separator and the raw material tank, and the auxiliary equipment such as the product container and the filtrate tank should be kept under an atmosphere such as nitrogen or dry air. It is desirable to keep. Further, in order to prevent the hydrolysis reaction of N-vinylcarboxylic acid amide, a small amount of a drying agent such as magnesium sulfate may be added to the crude N-vinylcarboxylic acid amide.

Further, N-vinylcarboxylic acid amide is extremely unstable in the presence of an acid and is easily hydrolyzed in the presence of water. In the present invention, when performing pressure crystallization, it is preferable to add a basic compound to the crude N-vinylcarboxylic acid amide.

Examples of such basic compounds include sodium carbonate, sodium hydrogen carbonate, sodium hydroxide, sodium (hydrogen) phosphate, sodium salts such as sodium acetate, potassium carbonate, potassium hydrogencarbonate, potassium hydroxide, phosphoric acid (hydrogen). ) Potassium, potassium salts such as potassium acetate, N-phenyl-α-naphthylamine, 4,4′-bis (α,
α-Dimethylbenzyl) diphenylamine, N-phenyl-
N '-(1,3-dimethylbutyl) -p-phenylenediamine, N-phenyl-N'-isopropyl-p-phenylenediamine, N-phenyl-N'-(1-methylheptyl) -p-phenylenediamine, N-phenyl-N'-cyclohexyl-p-phenylenediamine, N, N'-diphenyl-p-phenylenediamine, N, N'-
Di-β-naphthyl-p-phenylenediamine, N, N'-bis (1,4
-Dimethylpentyl) -p-phenylenediamine, N, N'-bis
(1-ethyl-3-methylpentyl) -p-phenylenediamine,
N, N'-bis (1-methylheptyl) -p-phenylenediamine,
Examples thereof include aromatic amines such as N-phenyl-N ′-(p-toluenesulfonyl) -p-phenylenediamine. Of these, sodium salts are preferable, and sodium hydrogen carbonate is particularly preferable.

It is desirable that such a basic compound is usually used in an amount of 10,000 to 1 ppm, preferably 1000 to 10 ppm, in the crude N-vinylcarboxylic acid amide. Even if it is used in an amount of 10,000 ppm or more, it is not sufficiently dissolved in the case of inorganic salts, and the effect corresponding to the addition cannot be expected in practice. Further, when this amount is 10000 ppm or more using aromatic amines as the basic compound, it becomes difficult to completely remove the aromatic amine in the refining process, and the N-vinylcarboxylic acid amide becomes less polymerizable. Instead, it drops. Further, even if these basic compounds are used in an amount of 1 ppm or less, almost no effect as a stabilizer is observed.

The crystallization pressure in the present invention is 500 to 300.
It is 0 atm, and particularly preferably 1000 to 2000 atm. If the crystallization pressure is lower than 500 atm, the degree of polymerization of the N-vinylcarboxylic acid amide obtained will not improve significantly, and the amount of crystals obtained by one crystallization operation will be small, resulting in low productivity. Will be disadvantageous. On the other hand, even if the crystallization operation is performed at a pressure higher than 3000 atm, a large increase in the amount of crystallization is not obtained, and the purity of the obtained N-vinylcarboxylic acid amide is lowered and the improvement of the polymerizability is also reduced. Further, a device that can withstand such a high pressure is large and expensive.

Generally, in order to efficiently carry out the pressure crystallization operation of the crude N-vinylcarboxylic acid amide, it is possible to carry out the crude N-vinylcarboxylic acid amide at a low temperature at a low pressure, but to raise the temperature at a high temperature. Is required.

In the present invention, the crude N-vinylcarboxylic acid amide is preliminarily adjusted to 0 to 100 ° C., preferably 10 to 70 ° C., and then the crude N-vinylcarboxylic acid amide is placed in a pressure crystallizer (pressurizing cylinder). Introduce. The temperature of the pressurizing cylinder of the pressure crystallizer slightly increases due to adiabatic compression and heat of crystallization when the crude N-vinylcarboxylic acid amide is pressurized. It is advisable to set the crystallization temperature of. When the crystallization temperature is lower than 0 ° C, the concentration of the crude N-vinylcarboxylic acid amide becomes too high and the fluidity is lowered, and it becomes difficult to introduce the crude N-vinylcarboxylic acid amide into the pressure cylinder. Meanwhile, crude N-vinylcarboxylic acid amide was added to 10
When heated above 0 ° C., thermal polymerization and alteration of N-vinylcarboxylic acid amide begin to occur, resulting in deterioration of quality and yield.

The crude N-vinylcarboxylic acid amide introduced into the pressurizing cylinder in the present invention may be a liquid or a slurry containing seed crystals, but for the following reasons, a slurry containing seed crystals is used. Is preferred. That is, when pressure is applied to the pressure cylinder of the pressure crystallizer, the crude N-vinylcarboxylic acid amide is rapidly increased in pressure, and the pressure energy is evenly transmitted in the liquid phase at the sonic velocity. Therefore, if seed crystals are not contained in the crude N-vinylcarboxylic acid amide supplied to the pressurizing cylinder, the N-vinylcarboxylic acid amide will be in a supersaturated state even when pressurized, and crystals will not be sufficiently formed. There is. Therefore, prior to pressure crystallization, the crude N-vinylcarboxylic acid amide is kept at a temperature and for a time sufficient to generate seed crystals to generate N-vinylcarboxylic acid amide crystals in advance, or
A part of the N-vinylcarboxylic acid amide is diverted, and this is cooled to give crystals, and the crude N-vinylcarboxylic acid amide containing the crystals is mixed with the crude N-vinylcarboxylic acid amide, or Alternatively, it is desirable to add a seed crystal to the crude N-vinylcarboxylic acid amide from the outside.

Generally, pressure crystallization has a higher crystallization rate than cooling crystallization, and the time required to reach a state close to equilibrium is short, so that the amount of crystallization per pressurization is maximized to achieve complete equilibration. It is preferable to maintain the pressurized state until reaching the state. Since N-vinylcarboxylic acid amide has relatively high crystallinity, the holding time under pressure is 0 to 10 minutes, preferably 0.
~ Within 5 minutes.

In the present invention, N-vinylcarboxylic acid amide precipitated as a solid phase (crystal) under pressure,
By separating from the liquid phase in which the polymerization inhibitor (impurity) is concentrated, N-vinylcarboxylic acid amide having excellent polymerizability can be obtained, but when separating and removing the liquid phase from the solid phase, separation is performed. It is preferable to perform the separation while gradually reducing the pressure from the starting pressure. In this process, some of the crystals dissolve in the remaining mother liquor and sweat, and the impurities contained in the crystals of N-vinylcarboxylic acid amide are discharged into the mother liquor.
The vinyl carboxylic acid amide has high purity and further excellent polymerizability.

On the other hand, the liquid phase (mother liquor) contains carboxylic acid amide, N- (1-alkoxyethyl) carboxylic acid amide, alcohol or ethylidene biscarboxylic acid amide, which are raw materials for synthesizing N-vinylcarboxylic acid amide. ing.
Therefore, this liquid phase is used in a reaction step of a raw material for synthesizing N-vinylcarboxylic acid amide, for example, a synthetic step of N- (1-alkoxyethyl) carboxylic acid amide, synthesis of ethylidenebiscarboxylic acid amide or N-vinylcarboxylic acid amide. It may be sent to a process or the like for reuse. Further, N-vinylcarboxylic acid amide may be recovered from the liquid phase by a treatment such as pressure crystallization, cooling crystallization or distillation.

The reason why the N-vinylcarboxylic acid amide obtained by the method for purifying N-vinylcarboxylic acid amide according to the present invention is high in purity and excellent in polymerizability is not clear. In addition, the eutectic point under pressure is more advantageous for crystallization of N-vinylcarboxylic acid amide than the eutectic point during cooling crystallization, or pressure crystallization causes cooling crystallization due to pressure treatment. In comparison, the mechanical shock due to stirring, etc. is small, the state of the system is uniform, and the processing time is short, so that the impurities concentrated in the mother liquor are hard to precipitate, and because the separation process is performed at a relatively low temperature for a short time, the N -It is considered that the vinylcarboxylic acid amide does not deteriorate, and that the obtained crystals are solidified into a cylindrical shape and have a small surface area, so that they are not easily deteriorated due to moisture absorption.

The N-vinylcarboxylic acid amide thus obtained is polymerized or copolymerized with another monomer to obtain a polyN-vinylcarboxylic acid amide or copolymer which is a water-soluble polymer. it can.

Next, the method for purifying N-vinylcarboxylic acid amide according to the present invention will be described more specifically with reference to FIG. In FIG. 1, it is obtained by synthesizing dimethylcetal from acetaldehyde and methanol, then purifying it, and reacting this dimethylcetal with acetamide.
The case of separating N-vinylacetamide, which is a raw material of a hydrophilic polymer, is shown.

In FIG. 1, A is a reactive distillation column, B is a distillation column, C is a countercurrent extraction column, D is an ether amidation reactor, and E is E.
Is an acetal recovery distillation column, F is a methanol recovery distillation column,
G is an ether amide decomposition reactor, H is an N-vinylacetamide vacuum distillation column, I is a pressure crystallizer, and the solid line and 1 to 19 represent material flows.

Acetal synthesis step: A necessary amount of the raw material acetaldehyde 1 is introduced into the lower part of the reactive distillation column A, and a small amount of recovered from the countercurrent extraction column C is introduced into the column A from the upper part of the reactive distillation column A. Of acetal and water containing methanol 2
What is added with methanol 3 recovered from the N-vinylacetamide vacuum distillation column H is continuously introduced into the above. A required amount of the acid catalyst is dissolved and mixed in this methanol. Water previously contained in the raw material acetaldehyde and water 5 produced in the reaction process are discharged from the bottom of the tower. Since a catalytic amount of acid is dissolved in this water, appropriate neutralization, if necessary,
Waste water is treated and then discarded.

Acetal separation step: The reaction solution 4 consisting of methanol and dimethyl acetal and the methanol-dimethyl acetal azeotrope 15 recovered from the demethanol distillation column (methanol recovery distillation column) F are normal hexane containing a trace amount of dimethyl acetal. Is introduced into the distillation column B together with the light liquid 6 of the countercurrent extraction column C, and is separated by distillation under normal pressure to obtain a high-purity acetal 8 from the bottom of the column. Methanol is distilled from the top of the column as a ternary azeotrope 7 of normal hexane-methanol-dimethyl acetal. Normal hexane is supplied in an amount necessary to form a ternary azeotrope of normal hexane-methanol-dimethyl acetal.

Hexane recovery step: The normal-hexane-methanol-dimethylacetal ternary azeotrope 7 extracted from the top of the distillation column B is fed to the countercurrent extraction column C in a small amount of water 9
Contact countercurrent with. The heavy liquid 2 obtained by extracting almost all the amount of methanol and most of dimethyl acetal from the light liquid is withdrawn from the bottom of the column and recovered as a part of the raw material for the reactive distillation in the acetal synthesis step. In practice, the light liquid 6 consisting of normal hexane is recovered from the top of the column and reused as an entrainer in the acetal separation step.

Α-methoxyethylacetamide synthesis step; α-methoxyethylacetamide (hereinafter referred to as MEA) is carried out by the following known method (for example, US Pat. No. 4554).
No. 377). That is, the following chemical formula 1
MEA is synthesized by the exchange reaction of dimethyl acetal and acetamide as shown in (3).

[0035]

[Chemical 1]

At this time, methanol that is equimolar to MEA is by-produced. Since the vapor pressures of acetamide and MEA are very close and their solubilities in various solvents are similar, separation by distillation or recrystallization is difficult. Therefore, it is preferable to keep the conversion of acetamide as high as possible, for example, 95% or more is desirable. In order to keep the conversion of acetamide high as described above, it is desirable that dimethyl acetal is used in an amount of about 20 times the molar ratio of acetamide. If dimethyl acetal is used in an amount less than about 20 times, the conversion of acetamide may not be sufficiently increased. When dimethyl acetal is used in an amount that greatly exceeds 20 times, the productivity is reduced, but a large improvement in the acetamide conversion rate may not be obtained. Furthermore, it is preferable to add a small amount of methanol to this reaction system. Since this reaction is an equilibrium reaction, the addition of methanol is not preferable in terms of equilibrium. However,
When MEA further reacts with acetamide, ethylidene bisacetamide (EBA) having extremely low solubility in dimethyl acetal is produced. Here again, in the absence of methanol, this EBA precipitates from the system and is no longer involved in this equilibrium reaction, and this equilibrium reaction leans to the right, reducing the MEA yield. Therefore, in order to dissolve a small amount of by-produced EBA in Chemical Formula 2 below and participate in the equilibrium reaction, it is preferable to add methanol in a molar ratio of about 3 times with respect to acetamide.

[0037]

[Chemical 2]

That is, it is preferable to prepare a reaction raw material liquid by setting the molar ratio of acetamide / dimethyl acetal / methanol to 1/20/3. The ether amidation reactor D filled with a strongly acidic ion exchange resin such as Amberlyst contains the high-purity acetal 8 obtained from the bottom of the distillation column B and a small amount of methanol obtained from the bottom of the demethanol distillation column F. The dimethyl acetal 14 and the acetamide 10 are supplied and MEA synthetic reaction is performed. From the outlet of the ether amidation reactor D, a reaction liquid 11 consisting of MEA, unreacted dimethyl acetal, methanol produced by the reaction and a trace amount of unreacted acetamide is obtained.

Acetal recovery step: The reaction liquid 11 obtained from the outlet of the ether amidation reactor D is introduced into an acetal recovery distillation column E and subjected to simple distillation as a light-boiling fraction from the top of the column to distill a dimethyl acetal containing a small amount of methanol. Minute 1
2 and a MEA fraction 13 obtained from the bottom of the column as a heavy boiling fraction.

Methanol recovery step: The dimethyl acetal fraction 12 containing a small amount of methanol obtained from the top of the acetanol recovery distillation column E is supplied to the methanol recovery distillation column F, and the methanol-dimethyl acetal azeotropic distillation is performed from the top of the column. Min. 15 is obtained and sent to the acetal refining step to be refined into high-purity dimethyl acetal. The dimethyl acetal fraction 14 containing a smaller amount of methanol obtained from the bottom of the methanol recovery distillation column F is an ether amidation reactor D.
And reused as a raw material for the ether amidation reaction.

N-vinylacetamide synthesis step: The MEA fraction 13 obtained from the bottom of the acetal recovery distillation column E is converted into N-vinylacetamide by thermal decomposition in the etheramide decomposition reactor G or catalytic decomposition using an acid catalyst. Decomposed into methanol, N-from the etheramide decomposition reactor G outlet
A solution 16 of vinylacetamide in methanol is obtained.

N-vinylacetamide concentration step: The methanol solution 16 of N-vinylacetamide obtained from the outlet of the etheramide decomposition reactor G was a vacuum distillation column H of N-vinylacetamide, and methanol 3 and crude N-vinylacetamide were obtained by vacuum distillation. It is separated into 17. Methanol 3 obtained from the top of the column is reused in the reactive distillation column A in the acetal synthesis step.

N-vinylacetamide refining step: Crude N-vinylacetamide 17 obtained from the bottom of the vacuum distillation column H in the N-vinylacetamide concentrating step was purified by a pressure crystallizer I to obtain high-purity N-vinylacetamide. And drainage.

[0044]

INDUSTRIAL APPLICABILITY According to the present invention, N-vinylcarboxylic acid amide having high purity and excellent polymerizability can be easily and efficiently purified.

[0045]

EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0046]

Example 1 In a three-necked flask (200 ml) equipped with a thermometer and a dry ice-ethanol trap, 5.9 g (0.1 mol) of acetamide, 40 g (0.67 mol) of isopropyl alcohol, and ethylidene bisacetamide 2. 16 g (15 mmol) and 14.6 g (0.1 mol) of acetaldehyde diisopropyl acetal were added, and 4
The mixture was stirred and dissolved at 5 to 48 ° C until uniform. A solution prepared by dissolving 0.43 g of concentrated sulfuric acid (0.1% by weight based on the charged amount) in 2 g (33 mmol) of isopropyl alcohol (also in the following examples) was added and stirred, and then acetaldehyde 1 was added.
7.6 g (0.4 mol) was added with a dropping funnel over 3 minutes. After completion of the dropwise addition, the reaction was carried out at 50 ° C. for 3 hours to neutralize the catalyst, and then the gas chromatographic determination revealed that the acetamide conversion rate was 88% and the N- (α-propoxyethyl) acetamide selectivity was 94%. And the selectivity of the by-product ethylidene bisacetamide was 5.3%. The increase / decrease in the production amount of acetal decreased by 1 mmol of the addition amount in the reaction range of 30 minutes to 3 hours, and the ethylidene bisacetamide was in equilibrium.

N- (α-propoxyethyl) acetamide was obtained from the obtained reaction solution by distillation under reduced pressure, and N-vinylacetamide was thermally decomposed into isopropyl alcohol at 450 ° C. and a residence time of 1 second.

This decomposed solution [I] was cooled to 20 ° C. and kept at 1800 kg / cm ² and 20 ° C. in a high-pressure container to precipitate N-vinylacetamide crystals, and the obtained N-vinylacetamide crystals were collected. Separated from liquid phase (mother liquor). Thus, N-vinylacetamide having a purity of 99.9% was obtained.
In order to evaluate the polymerizability of the obtained N-vinylacetamide, water was added to make it 20% by weight, 600 ppm of V-50 (N, N'-azobis- (2-amidinopropane) dihydrochloride was added, and the temperature was 45 ° C. After 10 minutes, dip it to 10% by weight with water and use a BL type viscometer at 30 ° C and a rotation speed of 30RP.
When the viscosity was measured with M, it was 130 cps.

[0049]

Comparative Example 1 The pyrolysis solution [I] obtained in Example 1 was used with a 20-stage Oldershaw type rectification apparatus to give a reflux ratio of 2 to 3 to.
After vacuum distillation at rr, N-vinylacetamide having a purity of 97.5% was obtained. When the obtained N-vinylacetamide was subjected to a polymerization evaluation test in the same manner as in Example 1, the viscosity was 40 cps.

[0050]

[Example 2] [Acetal synthesis step] 180 g of methanol containing 0.5% by weight of sulfuric acid was introduced at the fifth stage from the top of the 25 stage glass Aldershaw type rectification column at 180 g / hr, and at the 15th stage from the top. Acetaldehyde was introduced at 72 g / h. A 500 ml flask containing 100 g of water was installed at the bottom of the rectification tower.
It was heated to 00 ° C. and the contents of the flask were withdrawn at 29 g / h. The flask withdrawal liquid contained virtually no organic matter. A reflux ratio of 221 g / h of a 221 g / h dimethyl acetal-methanol mixture was withdrawn from the top of the column. The distillate did not actually contain water or acetaldehyde. The acetaldehyde conversion rate was 100% and the dimethyl acetal yield was 100%. [Acetal Separation Step] Normal hexane is added to the first stage from the top of the 25-stage glass Oldershaw type rectification column at 5 hr / hr.
6 g was introduced, and dimethyl acetal containing 28% by weight of methanol was introduced at 71 g per hour at the 10th stage from the top.
Heating was carried out at a reflux ratio of 6 so that the temperature at the top of the tower was maintained at 50 ° C. At the bottom of the rectification column, 100 dimethyl acetal is used.
A 500 ml flask containing g was placed in an oil bath at 110 ° C. and heated, and the content of the flask was withdrawn at 47 g per hour. The flask extraction liquid was dimethyl acetal containing practically no normal hexane and containing 0.3% of methanol. 80 g / h dimethyl acetal from the top of the tower
The methanol-normal hexane mixture was extracted. Actually, neither distillate nor bottom product contained water and acetaldehyde. [Hexane recovery process] In a vertical motion liquid-liquid countercurrent extraction device having column inner diameter of 50 mm with 30 baffle plates attached at 25 mm intervals, the distillate of the acetal separation process as a light liquid was discharged from the lower part of the extraction column at 2370 g / hr. Countercurrent extraction was performed by supplying 13 g of water as a heavy liquid from the upper part of the extraction tower per hour. The baffle plate moved up and down for 150 cycles with a stroke of 12.5 mm. The light liquid after extraction contained almost no water or methanol, and the light liquid contained 3% dimethyl acetal.
It was normal hexane containing a weight percentage. The heavy liquid was 80% by weight of methanol, 5% by weight of dimethyl acetal, 1% by weight of normal hexane, and the others were water. [Α-Methoxyethylacetamide Synthesis Step] The high-purity dimethyl acetal obtained in the acetal separation step and the dimethyl acetal containing methanol obtained in the methanol recovery step are mixed, and the dried acetamide is dissolved in this to obtain acetamide / dimethyl. A reaction raw material liquid having an acetal / methanol molar ratio of 1/20/3 was prepared. This solution was introduced into the lower portion of the reaction tube having an inner diameter of 40 mm filled with 60 ml of strongly acidic ion exchange resin Amberlyst 15 at a rate of 5 ml per hour. Hot water at 55 ° C was flown through the jacket of the reaction tube to control the reaction temperature at 55 ° C. Quantitative analysis of the reaction solution obtained from the outlet at the top of the reactor revealed that the molar composition of the reaction solution was approximately acetamide / dimethyl acetal / methanol / ME.
It was 0/19/4 / 0.9 in A, the conversion of acetamide was 98%, and the yield of α-methoxyethylacetamide (MEA) was 90%. [Acetal recovery step] The reaction solution obtained in the α-methoxyethylacetamide synthesis step was supplied at 600 g / hr to a jacketed thin film continuous flash evaporator having a heat transfer area of 0.04 m ² depressurized to 100 mmHg. A heating medium of 90 ° C. was circulated in the jacket. An evaporation residue of virtually α-methoxyethylacetamide was obtained at 17 g / h. A liquid obtained by condensing a volatile component consisting of dimethyl acetal containing 7% by weight of methanol was obtained in an amount of 583 g per hour. [Methanol recovery step] The dimethyl acetal fraction containing 7% by weight of methanol obtained in the acetal recovery step was introduced into the 25th-stage glass Oldershaw type rectification column from the top to the 10th step at 200 g / hr. Heating was carried out at a reflux ratio of 6 so that the temperature at the top of the column was maintained at 58 ° C. A 500 ml flask was installed in the lower part of the rectification column, immersed in an oil bath at 110 ° C. for heating, and the content of the flask was withdrawn at 185 g / hr.
The flask withdrawal liquid was dimethyl acetal containing 5.6% by weight of methanol. From the top of the column, 15 g of a dimethyl acetal-methanol azeotrope (24% by weight of methanol) was withdrawn every hour. [N-Vinylacetamide synthesis step] The liquid consisting of practically α-methoxyethylacetamide obtained in the acetal recovery step was heated to 450 ° C at 20 ml / min and depressurized to 40 mmHg into a stainless steel reaction tube with an inner diameter of 20 mm and a total length of 2 m. Supplied. A mixture of N-vinylacetamide and methanol produced by the thermal decomposition reaction was condensed and collected in a cooler provided at the outlet of the reaction tube. The conversion rate of α-methoxyethylacetamide was 95%. [N-Vinylacetamide Concentration Step] The reaction liquid obtained in the N-vinylacetamide synthesis step was introduced at 200 g / hr into the 10th tray from the top of the 10th glass Oldershaw type rectification column. The degree of vacuum was 200 mmHg, the reflux ratio was 2, and heating was performed so that the temperature at the top of the column was maintained at 40 ° C. A 500 ml flask was installed in the lower part of the rectification column, immersed in an oil bath at 80 ° C. and heated, and the contents of the flask were withdrawn at 155 g / h. The liquid extracted from the flask was a crude N-vinylacetamide solution containing 94% by weight of N-vinylacetamide. 45 g of methanol was withdrawn from the top of the column every hour. [N-vinylacetamide purification step] The crude N-vinylacetamide solution obtained in the N-vinylacetamide concentration step
The temperature was adjusted to 0 ° C., and the crude N-vinylacetamide solution was pressure-crystallized at 1800 kg / cm ² and 50 ° C. in a high-pressure vessel to precipitate N-vinylacetamide crystals, and the crystals were separated from the mother liquor. Thus, N-vinylacetamide having a purity of 99.9% was obtained. In order to evaluate the polymerizability of this N-vinylacetamide, water was added to make it 20% by weight, and V
-50 (N, N'-azobis- (2-amidinopropane) dihydrochloride 600ppm was added and immersed in a constant temperature water bath at 45 ° C. After 10 minutes, diluted with water to 10% by weight and using a BL type viscometer. Three
When the viscosity was measured at 0 ° C. and a rotation speed of 30 RPM, it was 150 cps.

[0051]

Comparative Example 2 The reaction liquid obtained in the N-vinylacetamide synthesis process of Example 2 was introduced at 200 g / hr into the 10th plate from the top of the 10-stage glass Oldershaw type rectification column.
The degree of vacuum was 200 mmHg, the reflux ratio was 2, and heating was performed so that the temperature at the top of the column was maintained at 40 ° C. 500 ml at the bottom of the rectification column
A flask was provided and immersed in an oil bath at 80 ° C. for heating, and the contents of the flask were withdrawn at 155 g / hour. The liquid extracted from the flask was a methanol solution containing 94% by weight of N-vinylacetamide. 45 g of methanol was withdrawn from the top of the column every hour.

Further, 155 g per hour of the above flask extraction liquid (methanol solution containing 94% by weight of N-vinylacetamide) was placed on the 10th plate from the top of the rectification column packed with a 5 mm sulzer type packing material having 20 theoretical plates. Introduced in.
The degree of reduced pressure was 2 mmHg, the reflux ratio was 3, and a 500 ml flask was installed in the lower part of the rectification column and immersed in an oil bath at 105 ° C. for heating.
The flask contents were withdrawn at 140 g / h. The flask withdrawal liquid was N-vinylacetamide. From the top of the column, 15 g of methanol containing a small amount of acetamide was withdrawn every hour. When the obtained N-vinylacetamide was subjected to a polymerization evaluation test in the same manner as in Example 4, the viscosity was 50 cps.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a production process and a purification process of N-vinylacetamide.

[Explanation of symbols]

In FIG. 1, A is a reactive distillation column, B is a distillation column, C is a countercurrent extraction column, D is an ether amidation reactor, E is an acetal recovery distillation column, F is a methanol recovery distillation column, and G is an etheramide decomposition reactor. , H represents an N-vinylacetamide vacuum distillation column, I represents a pressure crystallizer, and the solid line and 1 to 19 represent material flows.

Front page continuation (72) Inventor Hitoshi Nakamura To Oita, Oita City 2 Nakanosu, Oita Laboratory, Showa Denko Co., Ltd. (72) Inventor, Tamin Sakai, 1-3 Wakihama-cho, Chuo-ku, Kobe-shi, Hyogo No.18 Kobe Steel, Ltd. Kobe Head Office (72) Inventor Shingo Yoshida 1-3-18 Wakihama-cho, Chuo-ku, Kobe City, Hyogo Prefecture Kobe Steel Co., Ltd. Kobe Head Office

Claims (3)

[Claims] 1. N-vinylcarboxylic acid amide is 50% by weight.
The crude N-vinylcarboxylic acid amide contained in the above amount is 0 to
Pressurize at 100 ° C to 500-3000 atm to precipitate N-vinylcarboxylic acid amide crystals and pressurize to N- under pressure.
A high-purity N-vinylcarboxylic acid amide is obtained by separating the crystal of the vinylcarboxylic acid amide and the liquid phase.
Method for purifying N-vinylcarboxylic acid amide. 2. The crystal precipitation of crude N-vinylcarboxylic acid amide is carried out in the presence of alcohol.
Purification method. 3. The purification method according to claim 1, wherein the crystal precipitation of the crude N-vinylcarboxylic acid amide is carried out in the presence of a basic compound.