JP2619203B2 - Method for purifying N-vinylcarboxylic acid amide - Google Patents

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-vinyl carboxylic acid amide, and more particularly, to a method for purifying N-vinyl carboxylic acid amide containing N-vinyl carboxylic acid amide which has high purity and excellent polymerizability. The present invention relates to a method for obtaining a vinylcarboxylic acid amide.

[0002]

2. Description of the Related Art N-vinyl carboxylic acid amides are obtained from carboxylic acid amides, acetaldehydes and alcohols.
It is known that (alkoxyethyl) carboxylic acid amide can be synthesized and produced by pyrolysis or catalytic decomposition. 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 extremely close, and their separation has not been easy. A method has been proposed.

For example, according to JP-A-61-286069, extraction by water and aromatic hydrocarbons is disclosed because distillation involves inevitably mixing formamide, an unreacted raw material, into N-vinylformamide. Have been.

On the other hand, as another promising method for producing N-vinylcarboxylic acid amide, ethylidene biscarboxylic acid amide is synthesized from acetaldehyde and carboxylic acid amide, and this is converted into carboxylic acid amide and N-vinylcarboxylic acid amide. It is known that it can be obtained by decomposition. However, when trying to produce N-vinyl carboxylic acid amide in this way, carboxylic acid amide and N-vinyl carboxylic acid amide having similar physical properties are produced in an equimolar manner, and it becomes very difficult to separate them. JP-A-63-1
JP-A-32868 discloses a method by cooling crystallization from a mixed organic solvent, JP-A-2-188560 discloses a method by extraction using an aqueous solution of an inorganic salt and an aromatic hydrocarbon, and U.S. Pat. A method based on extractive distillation using alcohol is disclosed.

However, in any case, it is difficult to obtain N-vinylcarboxylic amide of sufficient purity by these methods. Furthermore, the extraction method requires an expensive organic solvent, and equipment for recovering and refining these is required. In addition, N-vinylcarboxylic acid amide is relatively unstable to water, and 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 of using an organic solvent as in the case of the extraction method, and there is a possibility that N-vinylcarboxylic acid amide is thermally polymerized. There is a problem. Further, in the extractive distillation method, since an organic solvent is used, it is necessary to increase the reflux ratio in order to obtain a 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 in which a mixture is pressurized to a high pressure to precipitate some components, and a liquid phase and crystals existing under pressure are separated. A law is disclosed. Such a pressure crystallization method is disclosed in JP-A-62-209034,
JP-A-1-250329, JP-A-4-12002
As disclosed in, for example, Japanese Patent Application Laid-Open No. 7-107, it is known that it can be used for separation of positional isomers such as xylene, naphthalenes and cresol, or separation of alkylated phenols from an alkylation reaction solution of phenols. ing. However, it has not been disclosed that the pressure crystallization method is used for purification of vinyl compounds, particularly N-vinylcarboxylic acid amide, from the viewpoint of imparting excellent polymerizability to N-vinylcarboxylic acid amide.

[0007]

An object of the present invention is to provide an N-vinyl carboxylic acid amide having a high purity and excellent polymerizability by removing impurities from the crude N-vinyl carboxylic acid amide. An object of the present invention is to provide a method for purifying a carboxylic acid amide.

[0008]

According to the present invention, when separating and purifying high-purity N-vinylcarboxylic acid amide from crude N-vinylcarboxylic acid amide, (a) pressure crystallization from crude N-vinylcarboxylic acid amide After precipitating the crystals of N-vinylcarboxylic acid amide in the first step of separating the N-vinylcarboxylic acid amide crystals and the liquid phase to obtain high-purity N-vinylcarboxylic acid amide, (b) ) A second crystal of N-vinyl carboxylic acid amide is obtained from the liquid phase separated in the first step at a lower temperature than the first step by pressure crystallization or N-vinyl carboxylic acid by cooling crystallization. A second step of obtaining a second crystal of the amide, and (c) a third step of adding the second crystal obtained in the second step to the crude N-vinylcarboxylic acid amide in the first step and reusing it. A method for purifying N-vinylcarboxylic acid amide is provided.

[0009]

DETAILED DESCRIPTION OF THE INVENTION The method for purifying N-vinylcarboxylic acid amide according to the present invention will be specifically described below. First Step In the method for purifying N-vinyl carboxylic acid amide according to the present invention, first, in the first step, the produced N-vinyl carboxylic acid amide and unreacted substances (for example, carboxylic acid amide, N- (1- N-vinylcarboxylic acid amide (hereinafter, referred to as crude N-vinylcarboxylic acid amide) containing (alkoxyethyl) carboxylic acid amide) and the like are treated by a pressure crystallization method,
High purity N-vinylcarboxylic acid amide is obtained by separating the N-vinylcarboxylic acid amide crystal and the liquid phase.

The crude N-vinylcarboxylic acid amide compound used in the present invention includes N-vinylacetamide, N-vinyl-N-methylacetamide, N-vinylformamide, N-vinylformamide,
Methyl-N-vinylformamide and the like, especially N-
Vinyl acetamide is preferred.

First, in the first step, N-vinylcarboxylic acid amide is separated from crude N-vinylcarboxylic acid amide by a pressure crystallization method. It is desirable that the crude N-vinylcarboxylic acid amide used in the first step 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 include alcohols having 5 or less carbon atoms, carboxylic acid amides, N- (1-alkoxyethyl) carboxylic acid amides, and ethylidene biscarboxylic acid amides. Is mentioned. If the amount of the N-vinylcarboxylic acid amide contained in the crude N-vinylcarboxylic acid amide is less than 50% by weight, the recovery of the N-vinylcarboxylic acid amide is poor, and the N-vinylcarboxylic acid amide It has low purity and does not show excellent polymerizability.

The crude N-vinyl carboxylic acid amide can be produced, for example, by the method described in JP-A-61-106546 (a method for thermally decomposing ethylidene bisacetamide) and JP-A-50-76015 (for the secondary N-vinyl carboxylic acid amide). Production method), 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 product of these methods may be used as it is as crude N-vinylcarboxylic acid amide, or N-vinylcarboxylic acid amide may be concentrated or distilled off by distillation to obtain N-vinylcarboxylic acid amide. You may use what raised the content of carboxylic acid amide. When pressure crystallization is performed using the crude N-vinyl carboxylic acid amide that has been subjected to these purification operations,
Naturally, the recovery rate of N-vinyl carboxylic acid amide improves,
It is desirable because the purity and the polymerizability are also improved.

N-vinylcarboxylic acid amide is unstable to water, and gradually decomposes by absorbing moisture in the air. Therefore, when purifying N-vinyl carboxylic acid amide, pressure crystallization equipment including pressure separation equipment and raw material tanks, as well as auxiliary equipment such as product containers and filtrate tanks, should be kept under an atmosphere such as nitrogen or dry air. It is desirable to keep. 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 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 first step, when performing pressure crystallization, it is preferable to add a basic compound to the crude N-vinylcarboxylic acid amide.

Examples of such a basic compound include sodium salts such as sodium carbonate, sodium hydrogen carbonate, sodium hydroxide, sodium (hydrogen) phosphate, sodium acetate, potassium carbonate, potassium hydrogen carbonate, potassium hydroxide, and 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,
Aromatic amines such as N-phenyl-N ′-(p-toluenesulfonyl) -p-phenylenediamine are exemplified. Of these, sodium salts are preferable, and sodium hydrogencarbonate is particularly preferable.

Such a basic compound is desirably used in the crude N-vinylcarboxylic acid amide in an amount of usually 10,000 to 1 ppm, preferably 1,000 to 10 ppm. Even when used in an amount of 10,000 ppm or more, the inorganic salts are not sufficiently dissolved in the case of inorganic salts, and the effect corresponding to the addition cannot be expected in practice. If the amount is at least 10,000 ppm using aromatic amines as the basic compound, it will be difficult to completely remove the aromatic amines in the purification step, and the polymerizability of N-vinylcarboxylic acid amide will increase. Instead, it drops. In addition, 1 ppm of these basic compounds
Even when used in the following amounts, almost no effect as a stabilizer is observed.

The crystallization pressure in the first step is from 500 to 30.
The pressure is 00 atm, 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 be significantly improved, and the amount of crystals obtained by one crystallization operation will be small, and the productivity will be low. 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 cannot be obtained, and the purity of the obtained N-vinylcarboxylic acid amide decreases, and the improvement in the polymerizability also decreases. Further, a device capable of withstanding such a high pressure is large and expensive.

Generally, in order to efficiently perform the pressure crystallization operation of crude N-vinylcarboxylic acid amide, it is possible to perform the operation at a low pressure when the crude N-vinylcarboxylic acid amide is at a low temperature. Is required.

In the first step, the crude N-vinylcarboxylic acid amide is previously adjusted to 0 to 100 ° C., preferably 10 to 70 ° C., and then the crude N-vinylcarboxylic acid amide is subjected to pressure crystallization (pressure cylinder). To be introduced. The temperature of the pressure cylinder of the pressure crystallization apparatus rises slightly due to adiabatic compression and heat of crystallization when the crude N-vinylcarboxylic acid amide is pressurized. The crystallization temperature is preferably set. If the crystallization temperature is lower than 0 ° C., the concentration of the crude N-vinylcarboxylic acid amide becomes too high and the fluidity is reduced, and it becomes difficult to introduce the crude N-vinylcarboxylic acid amide into the pressure cylinder. On the other hand, crude N-vinylcarboxylic acid amide
When heated above 0 ° C., thermal polymerization and alteration of the N-vinylcarboxylic acid amide begin to occur, causing a decrease in quality and yield.

In the first step, crude N-
The vinyl carboxylic acid amide may be a liquid or a slurry containing seed crystals, but a slurry containing seed crystals is preferred for the following reasons. That is, when pressure is applied to the pressure cylinder of the pressure crystallization apparatus, the pressure of the crude N-vinylcarboxylic acid amide is rapidly increased, and the pressure energy is transmitted uniformly through the liquid phase at the speed of sound. Therefore, if no seed crystal is 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 sufficient crystals will not be generated. There is. Therefore, prior to pressure crystallization, the crude N-vinylcarboxylic acid amide should be 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 acid amide is separated and cooled to form a crystal, and the crude N-vinylcarboxylic amide containing the crystal and the crude N-vinylcarboxylic amide are mixed, or the crude It is desirable to add seed crystals to the N-vinylcarboxylic acid amide.

In general, 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 completely equilibrate. It is preferable to maintain the pressurized state until the state is reached. Since N-vinylcarboxylic acid amide has relatively high crystallinity, the holding time in a pressurized state is 0 to 5 minutes, preferably 0 to 5 minutes.
Less than 3 minutes.

In the first step, N-vinylcarboxylic amide precipitated as a solid phase (crystal) under pressure;
By separating the polymerization inhibitory substance (impurity) from the concentrated liquid phase, N-vinylcarboxylic acid amide having excellent polymerizability can be obtained, but the pressure at which the solid phase and the liquid phase are decomposed is 500. ~ 1500 atmospheres, preferably 1
Separated at a pressure of 000 atmospheres lower. In this process, part of the crystals dissolves in the remaining mother liquor, sweats, and the impurities contained in the crystals of N-vinyl carboxylic acid amide are discharged into the mother liquor. , High purity.

The liquid phase (mother liquor) obtained in the first step contains N-
It contains carboxylic acid amide, N- (1-alkoxyethyl) carboxylic acid amide, ethylidenebiscarboxylic acid amide, and the like, which are raw materials for synthesizing vinylcarboxylic acid amide.
Therefore, in the next second step, N-vinylcarboxylic amide is further recovered from this liquid phase (mother liquor) by pressure crystallization. Second step In the second step, (b) the liquid phase (pressure crystallization waste liquid I) separated in the first step is subjected to pressure crystallization at a lower temperature than in the first step by pressure crystallization.
Crystals of vinylcarboxylic acid amide (second crystal) are obtained, or (b) N-vinylcarboxylic acid amide is obtained by cooling crystallization from the liquid phase (pressure crystallization waste liquid I) separated in the first step. (Second crystal) is obtained.

(A) From the liquid phase (pressure crystallization waste liquid I) separated in the first step, N-vinylcarboxylic amide crystals (second crystal) are subjected to pressure crystallization at a lower temperature than the first step. To explain the method of obtaining, in this second step, the pressure crystallization operation
Except for the crystallization temperature, the reaction is carried out under substantially the same operating conditions as in the first step. That is, since the concentration of N-vinylcarboxylic acid amide in the pressure crystallization waste liquid I used in the second step is lower than that of the crude N-vinylcarboxylic acid amide used in the first step, Perform pressure crystallization at low temperature. That is, in the second step, the pressure crystallization waste liquid I is
After the temperature is adjusted to 10 to 80 ° C., preferably 0 to 50 ° C., it is desirable to introduce the pressure crystallization waste liquid I into a pressure crystallization apparatus (pressure cylinder).

In the second step, pressure crystallization of the pressure crystallization waste liquid I is performed, and a small amount of N is added to the waste liquid (pressure crystallization waste liquid II) separated from the N-vinylcarboxylic acid amide crystals (second crystal). -Waste liquid (liquid phase) containing vinyl carboxylic acid amide
, The N-vinylcarboxylic acid amide may be further recovered from the solution, but since its content is small, pressure crystallization must be performed at a lower temperature, and the separation efficiency is further reduced. Therefore, the liquid phase after pressure crystallization in the second step (pressure crystallization waste liquid II) may be discarded.

The crystallization apparatus used in the second step may be of a continuous type or a batch type. The crystallization method may be a method of exchanging heat with a refrigerant. And there is no strict condition for the structure.

There are no particular restrictions on the crystal filtering device, such as a device using vacuum pressure or pressurization, a device using gravity or centrifugal force. For example, when filtering a high-concentration slurry, a filter such as a Rosenmund filter is used. An automatic Nutsche filter is preferably used.

(B) Next, the cooling crystallization method will be described. From the liquid phase (pressure crystallization waste liquid I) separated in the first step, N-vinylcarboxylic acid amide crystals (cooling crystallization method) are obtained by the cooling crystallization method. In the case of obtaining the second crystal), since the concentration of N-vinylcarboxylic acid amide in the pressure crystallization waste liquid I is low, the temperature is relatively low, that is, -10 to 80 ° C, preferably 0 to 50 ° C.
It is preferable to cool the pressure crystallization waste liquid I until the crystallization of N-vinylcarboxylic acid amide.

When the second step is performed by such a cooling crystallization method, the liquid phase (pressure crystallization waste liquid I) separated from the crystals in the first step may be directly cooled to the above temperature. Alternatively, a recrystallization solvent which has no reactivity with N-vinylcarboxylic acid amide and has an appropriate solubility may be used. Such recrystallization solvents include, for example, benzene, toluene,
Examples include aromatic hydrocarbons such as xylene, hydrocarbons such as hexane and cyclohexane, halogenated hydrocarbons such as chloroform, ethers such as diethyl ether, and esters such as ethyl acetate.

The other points may be the same as in the pressure crystallization method (a) in the second step. Third Step In the third step, the second crystals obtained in the second step are added to the crude N-vinylcarboxylic acid amide in the first step and reused. Thus, when the amount of the second crystals added to the crude N-vinylcarboxylic acid amide (the liquid in the previous step) in the first step is smaller than the amount of the crude N-vinylcarboxylic acid amide and the temperature is not low, The crystals are rapidly dissolved in the crude N-vinylcarboxylic acid amide and easily become a homogeneous solution. When the temperature of the second crystal is low and the second crystal is difficult to dissolve in the crude N-vinylcarboxylic acid amide, the mixture of the crude N-vinylcarboxylic acid amide used in the first step and the second crystal is homogenized. , Or the second crystal may be sent to the first step in a slurry state and used as a seed crystal. Thus the second
When the crystal is used as a seed crystal in the first step, it is preferable that the second crystal is crushed in advance and then mixed with the crude N-vinylcarboxylic acid amide in the first step.

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, dimethyl cetal is synthesized from acetaldehyde and methanol, purified, and then obtained by reacting this dimethyl cetal with acetamide.
The case where N-vinylacetamide which is a raw material of a hydrophilic polymer is separated 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,
Is an acetal recovery distillation column, F is a methanol recovery distillation column,
G indicates an etheramide decomposition reactor, H indicates an N-vinylacetamide vacuum distillation column, I indicates a pressure crystallizer, J indicates a pressure crystallizer or a cooling crystallizer, and solid lines and 1 to 19 indicate the flow of substances. .

Acetal synthesis step: A required amount of the starting material acetaldehyde 1 is introduced into the lower part of the reactive distillation column A, and a small amount recovered from the countercurrent extraction column C is introduced into the column A from the upper part of the reactive distillation column A. Acetal and methanol containing water 2
A product obtained by adding methanol 3 recovered from the N-vinylacetamide vacuum distillation column H is continuously introduced. A required amount of an acid catalyst is dissolved and mixed in the methanol. Water previously contained in the raw material acetaldehyde and water 5 generated in the reaction process are discharged from the bottom of the column. Since a catalytic amount of acid is dissolved in this water, it is discarded after appropriate neutralization and wastewater treatment as required.

Acetal separation step: A reaction liquid 4 consisting of methanol and dimethyl acetal and a methanol-dimethyl acetal azeotrope 15 recovered from a methanol removal distillation column (methanol recovery distillation column) F are converted to 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, which is separated by distillation under normal pressure, and a high-purity acetal 8 is obtained from the bottom of the column. Methanol is distilled off 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 for producing a three-component azeotrope of normal hexane-methanol-dimethyl acetal.

Hexane recovery step: A normal hexane-methanol-dimethyl acetal ternary azeotrope 7 extracted from the top of the distillation column B is subjected to a countercurrent extraction column C to remove a small amount of water 9
And countercurrent contact. The heavy liquid 2 obtained by extracting almost all 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. Actually, 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 prepared by the following known method (for example, US Pat. No. 4,554,554).
377). That is, the following chemical formula 1
As shown in (1), MEA is synthesized by an exchange reaction between dimethyl acetal and acetamide.

[0037]

Embedded image

At this time, methanol in an amount equal to that of MEA is by-produced. Since the vapor pressures of acetamide and MEA are very close and their solubility in various solvents is similar, separation by distillation or recrystallization is difficult. Therefore, it is preferable to keep the conversion of acetamide as high as possible, for example, desirably 95% or more. In order to keep the conversion of acetamide high as described above, it is desirable that dimethyl acetal is used in a molar ratio of about 20 times that of acetamide. If the amount of dimethyl acetal is less than about 20 times, the conversion of acetamide may not be sufficiently increased. When dimethyl acetal is used in an amount much more than 20 times, productivity is reduced, but a large improvement in acetamide conversion may not be obtained. Further, it is preferable to add a small amount of methanol to the reaction system. Since this reaction is an equilibrium reaction, addition of methanol is not preferable from the equilibrium relationship. However,
When the MEA further reacts with acetamide, it produces ethylidene bisacetamide (EBA) having extremely low solubility in dimethyl acetal. Here, if methanol is not present, the EBA precipitates out of the system and does not participate in the equilibrium reaction, and the equilibrium reaction tilts to the right, and the MEA yield decreases. Therefore, in order to dissolve a small amount of EBA by-product of the following chemical formula 2 and to participate in the equilibrium reaction, it is desirable to add methanol in a molar ratio of about 3 times the amount of acetamide.

[0039]

Embedded image

That is, it is preferable that the molar ratio of acetamide / dimethyl acetal / methanol is 1/20/3 to obtain a reaction raw material liquid. An ether amidation reactor D filled with a strongly acidic ion exchange resin such as Amberlyst contains 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 to perform the MEA synthesis reaction. From the outlet of the ether amidation reactor D, a reaction solution 11 comprising MEA, unreacted dimethyl acetal, methanol generated by the reaction and a small amount of unreacted acetamide is obtained.

Acetal recovery step: The reaction solution 11 obtained from the outlet of the ether amidation reactor D is introduced into an acetal recovery distillation column E, and a dimethyl acetal fraction containing a small amount of methanol from the top as a low boiling point by simple distillation. Minute 1
2 and a MEA fraction 13 obtained from the bottom of the column as a heavy boiling component.

Methanol recovery step: A dimethyl acetal fraction 12 containing a small amount of methanol obtained from the top of an acetal recovery distillation column E is supplied to a methanol recovery distillation column F, and a methanol-dimethyl acetal azeotropic fraction is supplied from the top of the column. 15 is obtained, sent to an acetal purification step, and purified into high-purity dimethyl acetal. Methanol recovery distillation column F
The dimethyl acetal fraction 14 containing a smaller amount of methanol obtained from the bottom of the above is sent to the 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 to N-vinylacetamide by thermal decomposition or catalytic cracking using an acid catalyst in an etheramide decomposition reactor G. Decomposed into methanol and N-
A methanol solution 16 of vinylacetamide is obtained.

N-vinylacetamide concentration step: The methanol solution 16 of N-vinylacetamide obtained from the outlet of the etheramide decomposition reactor was subjected to vacuum distillation in an N-vinylacetamide vacuum distillation column H to give methanol 3 and crude N-vinylacetamide 17 Is separated into The methanol 3 obtained from the top of the column is reused in the reactive distillation column A in the acetal synthesis step.

First step (N-vinylacetamide purification step): The crude N-vinylacetamide 17 obtained from the bottom of the vacuum distillation column H in the N-vinylacetamide concentration step was purified by a pressure crystallization apparatus I, It is separated into purified N-vinylacetamide 19 having a purity and a first step waste liquid 18.

Second step (N-vinylacetamide recovery step): The first step waste liquid 18 obtained in the N-vinylacetamide purification step is converted into a crude N-vinylcarboxylic acid amide 20 and a second step waste liquid 21 by a pressure crystallization apparatus J. Is separated into

When the second step (N-vinylacetamide recovery step) is performed by the cooling crystallization method, the following may be performed. That is, the first step waste liquid 18 obtained in the N-vinyl acetamide purification step is introduced into a cooling crystallization apparatus J (corresponding to the position J in FIG. 1) to precipitate crude N-vinyl carboxylic acid amide. Then, the mixture is separated into a crude N-vinylacetamide 20 and a second step waste liquid 21 by a solid-liquid separator (not shown).

Third step (recycling step of recovered N-vinylcarboxylic acid amide);
The crude N-vinyl carboxylic acid amide 17 obtained from the bottom of the vacuum distillation tower H in the N-vinyl acetamide concentration step is combined with the crude N-vinyl carboxylic acid amide 17 and sent to the pressure crystallization apparatus I in the first step (N-vinyl acetamide purification step). It is reused as crude N-vinyl carboxylic acid amide to obtain high-purity purified N-vinyl acetamide.

The reason why 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. It is conceivable that N-vinyl carboxylic acid amide does not deteriorate due to the above, and that the obtained crystals are hardened into a cylindrical shape and have a small surface area so that they are hardly deteriorated by moisture absorption or the like.

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

[0051]

According to the present invention, highly pure and highly polymerizable N-
Vinylcarboxylic amide is easily and efficiently separated.

[0052]

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

[0053]

[Example 1] [Acetal synthesis process] Methanol containing 0.5% by weight of sulfuric acid at a rate of 180 g / h was introduced into the fifth stage from the top of a 25-stage glass Aldershaw type rectification column, and the 15th stage from the top. Acetaldehyde was introduced at 72 g / h. At the bottom of the rectification column, a 500 ml flask containing 100 g of water was provided.
The mixture was heated to 00 ° C. and the contents of the flask were withdrawn at 29 g / h. The flask withdrawal liquid contained substantially no organic matter. 221 g / h of a dimethyl acetal-methanol mixture was withdrawn at a reflux ratio of 2 from the top of the tower. The distillate was substantially free of water and acetaldehyde. The acetaldehyde conversion was 100% and the dimethyl acetal yield was 100%. [Acetal Separation Step] Normal hexane was added to the first stage from the top of a 25-stage glass Aldershaw-type rectification column at 5 hours / hour.
6 g of dimethyl acetal containing 28% by weight of methanol was introduced at the 10th stage from the top at 71 g / h.
Heating was performed so that the reflux ratio was 6, and the temperature at the top of the column was maintained at 50 ° C. At the bottom of the rectification column, a 500 ml flask containing 100 g of dimethyl acetal was provided.
Heat by immersing in an oil bath at 0 ° C.
g. The effluent of the flask was substantially free of normal hexane, and was dimethyl acetal containing 0.3% of methanol. 80 g / h of a dimethyl acetal-methanol-normal hexane mixture was withdrawn from the top of the tower. Neither the distillate nor the bottoms contained substantially water and acetaldehyde. [Hexane separation step] A distillate from the acetal separation step was passed from the lower portion of the extraction column at 2370 g / h as a light liquid to a vertically moving liquid-liquid countercurrent extraction apparatus having a column inner diameter of 50 mm and 30 baffle plates attached at intervals of 25 mm. As a heavy liquid, 13 g of water was supplied per hour from the upper part of the extraction tower, and countercurrent extraction was performed. The baffle plate reciprocated vertically for 150 cycles with a stroke of 12.5 mm. The light liquid after extraction contained almost no water and methanol and was normal hexane containing 3% by weight of dimethyl acetal. The heavy liquid is methanol 80% by weight, dimethyl acetal 5% by weight, normal hexane 1
The other was water by weight. [Α-Methoxyethylacetamide synthesis step] The high-purity dimethylacetal obtained in the acetal separation step and the dimethylacetal containing methanol obtained in the methanol recovery step are mixed, and dried acetamide is dissolved in the mixture to form acetamide / dimethylacetal. A reaction raw material liquid having a molar ratio of 1/20/3 of methanol / methanol was prepared. This solution was introduced at a rate of 5 ml / h from the lower part of a reaction tube having an inner diameter of 40 mm filled with 60 ml of a strongly acidic ion exchange resin Amberlyst 15.
Warm water at 55 ° C. was passed 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 0 in acetamide / dimethyl acetal / methanol / MEA.
/19/4/0.9, and the conversion of acetamide is 9
8%, α-methoxyethylacetamide (ME
The yield of A) was 90%. [Acetal Recovery Step] The reaction solution obtained in the α-methoxyethylacetamide synthesis step was supplied at 600 g / h to a jacketed thin-film continuous flash evaporator with a heat transfer area of 0.04 m ² , which was reduced to 100 mmHg. A heating medium at 90 ° C. was circulated through the jacket. In practice, 17 g / h of an evaporation residue consisting of α-methoxyethylacetamide were obtained. 583 g / h of a liquid obtained by condensing a volatile component composed of dimethyl acetal containing 7% by weight of methanol was obtained. [Methanol Recovery Step] The dimethyl acetal fraction containing 7% by weight of methanol obtained in the acetal recovery step was introduced at 200 g / h into the 10th stage from the top of the 25-stage glass Aldershaw rectification column. Heating was performed 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 provided at the lower part of the rectification column, immersed in an oil bath at 110 ° C. and heated, and the contents of the flask were withdrawn at 185 g / h.
The liquid extracted from the flask was dimethyl acetal containing 5.6% by weight of methanol. An hourly dimethyl acetal-methanol azeotrope (methanol 24% by weight) was withdrawn from the top of the column. [N-Vinylacetamide synthesis step] The liquid actually consisting of α-methoxyethylacetamide obtained in the acetal recovery step was heated to 450 ° C. at 20 ml / min and reduced to 40 mmHg in 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 generated by the thermal decomposition reaction was condensed and collected by a cooler provided at the outlet of the reaction tube. The conversion of α-methoxyethylacetamide was 95%. [N-vinylacetamide concentration step] The reaction solution obtained in the N-vinylacetamide synthesis step was introduced at a rate of 200 g / h into the tenth glass Aldershaw type rectification column from the top. Heating was performed at a reduced pressure of 200 mmHg and a reflux ratio of 2 so that the temperature at the top of the column was maintained at 40 ° C. A 500 ml flask was provided at 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 flask withdrawn was a crude N-vinylacetamide solution containing 94% by weight of N-vinylacetamide. 45 g / h of methanol were withdrawn from the top of the column. [First step] 21.3 g of the concentrate obtained in the N-vinylacetamide synthesis step was adjusted to 50 ° C, and placed in a high-pressure vessel for 18 minutes.
The pressure was increased to 00 kg / cm ² and the temperature was maintained for 5 minutes to precipitate crystals of N-vinylacetamide, and the crystals were separated from the liquid phase (mother liquor) at 50 ° C. 99.6% purity
8.1 g of N-vinylacetamide and 13.1 g of waste liquid
Obtained. The recovery of N-vinylacetamide was 47%, and the composition of the waste liquid was 74% for N-vinylacetamide, α-
Methoxyethylacetamide: 16%, acetamide:
10%. In order to evaluate the polymerizability of this N-vinylacetamide, water was added to make up to 20% by weight, and V-50 was added.
(N, N'-azobis- (2-amidinopropane) dihydrochloride to 6
After adding 00 ppm, the sample was immersed in a 45 ° C. constant temperature water bath. After 10 minutes, the mixture was diluted to 10% by weight with water, and the viscosity was measured at 30 ° C. and 30 rpm using a BL viscometer. The viscosity was 150 cps. [Second Step] 21.3 g of the waste liquid from the first step was adjusted to 25 ° C., pressurized to 1800 kg / cm ² in a high-pressure vessel, and held for 5 minutes to remove N-vinylacetamide crystals (second crystals). After precipitation, the crystals were separated from the mother liquor at 25 ° C. Purity 9
5.7 g of 9.4% N-vinylacetamide and 1 waste liquid
5.6 g were obtained. N-vinylacetamide recovery rate is 3
6%, waste liquid composition: N-vinylacetamide: 59%, α
-Methoxyethylacetamide: 22%, acetamide: 13%. When the polymerizability of this N-vinylacetamide was evaluated in the same manner as above, the viscosity was 63 cps. [First Step of Recycling the Second Crystal] 14.8 g of the concentrate obtained in the N-vinylacetamide synthesis step and 6.4 g of the second crystal (crystal) obtained in the second step are mixed, The crystals were dissolved in the concentrate. The resulting mixture was adjusted to 50 ° C,
The pressure was increased to 1800 kg / cm ² in a high-pressure vessel, and held for 5 minutes to precipitate N-vinylacetamide crystals, which were separated from the mother liquor at 50 ° C. Purity 99.
10.3 g of 8% N-vinylacetamide and 1 waste liquid
0.5 g was obtained. The recovery of N-vinylacetamide is 5
6%, waste liquid composition: N-vinylacetamide: 74%, α
-Methoxyethylacetamide: 15%, acetamide: 8%. When the polymerizability of this N-vinylacetamide was evaluated in the same manner as above, the viscosity was 133 cps.

When the [second step] and the [first step in which the second crystal was recycled] were repeated three times, the obtained amount of crystals, the composition of the waste liquid, and the like were almost in a steady state, and were obtained in the N-vinylacetamide synthesis step at that time. The N-vinylacetamide recovery in the concentrated solution was 70% based on N-vinylacetamide.

[0055]

Comparative Example 1 The reaction solution obtained in the N-vinylacetamide synthesis step of Example 4 was introduced at a rate of 200 g / h into the tenth stage from the top of a ten-stage glass Aldershaw rectification column.
Heating was performed at a reduced pressure of 200 mmHg and a reflux ratio of 2 so that the temperature at the top of the column was maintained at 40 ° C. 500 ml at the bottom of the rectification column
The flask was provided, immersed in an oil bath at 80 ° C. and heated, and the contents of the flask were withdrawn at 155 g / h. The flask withdrawn was a methanol solution containing 94% by weight of N-vinylacetamide. 45 g / h of methanol were withdrawn from the top of the column. Further, at the 10th stage from the top of a rectification column filled with a 5 mm sludge type packing material having 20 theoretical stages, the above flask withdrawn (a methanol solution containing 94% by weight of N-vinylacetamide) was introduced at 155 g / h. .
At a reduced pressure of 2 mmHg and a reflux ratio of 3, a 500 ml flask was provided at the lower part of the rectification column, and was immersed in an oil bath at 105 ° C. for heating.
The contents of the flask were drained at 140 g per hour. The flask withdrawn was N-vinylacetamide. 15 g / h of methanol containing a small amount of acetamide was withdrawn from the top of the tower. When a polymerization evaluation test was performed on the obtained N-vinylacetamide in the same manner as in Example 1, the viscosity was 5 cps.

[0056]

Example 2 A three-necked flask (200 ml) equipped with a thermometer and a dry ice-ethanol trap was charged with 5.9 g (0.1 mol) of acetamide, 40 g (0.67 mol) of isopropyl alcohol, and ethylidene bisacetamide. 16 g (15 mmol) and 14.6 g (0.1 mol) of acetaldehyde diisopropyl acetal were added, and
The mixture was stirred and dissolved at 5-48 ° C until it became 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 (the same applies to the following examples) was added, and the mixture was stirred.
7.6 g (0.4 mol) were added via dropping funnel over 3 minutes. After the completion of the dropwise addition, the reaction was carried out at 50 ° C. for 3 hours to neutralize the catalyst. After quantification by gas chromatography, the conversion of acetamide was 88%, and the selectivity for N- (α-propoxyethyl) acetamide was 94%. And the selectivity for by-product ethylidenebisacetamide was 5.3%. The increase or decrease in the amount of acetal formed was reduced by 1 mmol in the range of 30 minutes to 3 hours of the reaction, and the ethylidene bisacetamide became 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. at a residence time of 1 second.

The decomposed liquid [I] was cooled to 20 ° C., and kept at 1800 kg / cm ² and 20 ° C. in a high-pressure vessel to precipitate crystals of N-vinylacetamide. Separated from the liquid phase (mother liquor). Thus, N-vinylacetamide having a purity of 99.9% was obtained.
30% of the obtained waste liquid was mixed with the pyrolysis liquid, and pressure crystallization was performed under the same conditions as the first time. To evaluate the polymerizability of the obtained N-vinylacetamide, water was added to make up to 20% by weight, and V-50 (N, N'-azobis- (2-amidinopropane)
600 ppm of dihydrochloride was added and immersed in a 45 ° C. water bath.
After 10 minutes, the mixture was diluted to 10% by weight with water, and the viscosity was measured at 30 ° C. and 30 rpm using a BL viscometer.
It was 0 cps.

[0059]

Comparative Example 2 The pyrolysis solution [I] obtained in Example 2 was refluxed at a reflux ratio of 2, 3 to using a 20-stage Oldershaw type rectifier.
Distillation under reduced pressure at rr gave N-vinylacetamide having a purity of 97.5%. When a polymerization evaluation test was performed on the obtained N-vinylacetamide in the same manner as in Example 2, the viscosity was 40 cps.

[0060]

Example 3 The procedure of Example 1 was repeated except that the second step was performed as follows. [Second step] 21.0 g of the waste liquid from the first step of Example 1 was added to 1
The mixture was cooled to 0 ° C. and filtered through a 200-mesh stainless steel wire mesh. The cake was pressurized to 100 kg / cm ² and held for 5 minutes to squeeze the mother liquor. 4.8 g of N-vinylacetamide having a purity of 99.4% was obtained, and 16.2 g of a waste liquid was obtained. The recovery of N-vinylacetamide was 31%, and the composition of the waste liquid was N-vinylacetamide: 66%, α-methoxyethylacetamide: 21%, and acetamide: 13%. When the polymerizability of this N-vinylacetamide was evaluated in the same manner as above, the viscosity was 43 cps. [First Step of Recycling the Second Crystal] 14.8 g of the concentrate obtained in the N-vinylacetamide synthesis step and 6.4 g of the crystal of the second step were mixed, and the crystals were dissolved in the concentrate. This mixture was adjusted to 50 ° C., and 1800 kg / cm
^The mixture was pressurized to ² and held for 5 minutes to precipitate N-vinylacetamide crystals, which were separated from the mother liquor at 50 ° C. In this way, 10.2 g of N-vinylacetamide having a purity of 99.7% was obtained, and 10.5 g of a waste liquid was obtained. N-
The recovery of vinylacetamide was 55%, and the composition of the waste liquid was N-vinylacetamide: 70%, α-methoxyethylacetamide: 15%, and acetamide: 8%. When the polymerizability of this N-vinylacetamide was evaluated in the same manner as above, the viscosity was 121 cps.

When the [second step] and the [first step in which the second crystal was recycled] were repeated three times, the obtained amount of crystals, the composition of the waste liquid, and the like were almost in a steady state, and were obtained in the N-vinylacetamide synthesis step at that time. The N-vinylacetamide recovery in the concentrated solution was 68% based on N-vinylacetamide.

[Brief description of the drawings]

FIG. 1 shows 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 ether amide decomposition reactor. , H indicates a vacuum distillation column of N-vinylacetamide, I indicates a pressure crystallizer, J indicates a pressure crystallizer or a cooling crystallizer, and solid lines and 1 to 21 indicate material flows.

Continuation of the front page (72) Inventor Hitoshi Nakamura 2 Onaka-shi, Oita City, Oita Prefecture Showa Denko KK Oita Research Laboratories (72) Inventor Yu Matsuda City 1-3-3 Wakihama-cho, Chuo-ku, Kobe City, Hyogo Prefecture 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 (2)

(57) [Claims] 1. A method for separating and purifying high-purity N-vinylcarboxylic acid amide from crude N-vinylcarboxylic acid amide,
(a) N-vinyl carboxamide from crude N-
After precipitation of vinyl carboxylic acid amide crystals, N-
A first step of separating the crystal and liquid phase of vinylcarboxylic acid amide to obtain N-vinylcarboxylic acid amide of high purity, (b)
A second step of obtaining a second crystal of N-vinylcarboxylic acid amide from the liquid phase separated in the first step by a pressure crystallization method at a lower temperature than the first step, and (c) a second step obtained in the second step. A third step of adding the crystals to the crude N-vinylcarboxylic acid amide in the first step and recycling the crude N-vinylcarboxylic acid amide in the first step. 2. In separating and purifying high-purity N-vinylcarboxylic acid amide from crude N-vinylcarboxylic acid amide,
(a) N-vinyl carboxamide from crude N-
After precipitation of vinyl carboxylic acid amide crystals, N-
A first step of separating the crystal and liquid phase of vinylcarboxylic acid amide to obtain N-vinylcarboxylic acid amide of high purity, (b)
A second step of obtaining a second crystal of N-vinylcarboxylic acid amide from the liquid phase separated in the first step by a cooling crystallization method, and (c) a second step of obtaining the second crystal obtained in the second step. 3. A method for purifying N-vinyl carboxylic acid amide, the method comprising the step of: