JP2619202B2 - Purification method of polar vinyl compound - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a method for purifying a polar vinyl compound, and more particularly to a mixture of a polymerization inhibitor and a polar vinyl compound having at least one oxygen, nitrogen or sulfur atom, that is, a polymerization reaction. A polar vinyl compound containing an inhibitor (hereinafter referred to as a crude polar vinyl compound) is pressurized to 500 to 3000 atm at 0 to 100 ° C. to precipitate crystals of the polar vinyl compound. And a method for obtaining a high-purity polar vinyl compound by separation from a polar vinyl compound.

[0002]

2. Description of the Related Art Many useful high molecular compounds can be obtained by addition polymerization such as radical polymerization, cationic polymerization or anionic polymerization of vinyl compounds. When a compound having a chain termination action or a chain transfer action is included in the composition, adverse effects such as a slow polymerization reaction and a decrease in molecular weight occur. Many of these polymerizable inhibitors act on the polymerization reaction in very small amounts,
Therefore, in order to impart excellent polymerizability to the vinyl compound, it is necessary to thoroughly remove these polymerization inhibitors.

[0003] Further, radically polymerizable vinyl compounds include:
In order to prevent polymerization during production, storage or transportation, a polymerization inhibitor is often added during or after production of the vinyl compound. Therefore, when polymerizing the vinyl compound, a polymerization initiator may be used in consideration of the amount of the added inhibitor, but in order to obtain a high quality polymer, the polymerization inhibitor was removed from the vinyl compound. It is desirable to polymerize afterwards.

It is often difficult to remove a polymerization inhibitor or the like from a vinyl compound having an oxygen atom, a nitrogen atom or a sulfur atom, that is, a vinyl compound having a polar group (a polar vinyl compound). When trying to purify a polar vinyl compound by distillation, the polar vinyl compound has a relatively high boiling point and melting point. Therefore, it is generally necessary to distill the polar vinyl compound under reduced pressure and at a temperature higher than the melting point. May be restricted. Further, there is a possibility that the polar vinyl compound is polymerized during the distillation operation, and there is a problem in industrial implementation.

[0005] Further, the purification of the polar vinyl compound by recrystallization is also performed. However, a purification step of the recrystallization solvent and a drying step of the product are required, and the drying of the polar vinyl compound is caused by local overheating. Polymer may be generated. Therefore, industrially purifying the polar vinyl compound by recrystallization is economically disadvantageous.

A method for adsorbing and removing a polymerization inhibitor by passing a solution of a vinyl compound, particularly a polar vinyl compound, through a column filled with an ion exchange resin or activated carbon does not require the vinyl compound to be separated from the treatment solution, and the polymerization is carried out as it is. And is widely used for purification of polar vinyl compounds. However, a solvent that is suitable for the adsorption operation and also for the polymerization reaction must be selected in consideration of availability, economy, etc., and it is practically impossible to find a solvent that satisfies all these conditions. Met. In addition, regeneration or replacement of the adsorbent has to be performed, which is troublesome on an industrial scale. In addition, when transporting to remote locations, storing in cold areas, or depending on the application, crystallized vinyl compounds may be required, and in these cases, the same problems as those in the above purification method may occur. was there.

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 some components, and the liquid phase and crystals existing under the pressure are separated. Is disclosed. Such a 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, naphthalenes and cresol, or separation of alkylated phenols from a phenol alkylation reaction solution, as disclosed in Japanese Patent Application Publication No. ing. However, it has not been disclosed that the pressure crystallization method is used for purifying the vinyl compound from the viewpoint of imparting excellent polymerizability to the polymerizable vinyl compound.

For example, N-vinylcarboxylic acid amide is obtained by synthesizing N- (1-alkoxyethyl) carboxylic acid amide from carboxylic acid amide, acetaldehyde and alcohol,
It is known that it can be 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 the separation is not easy, and some A method has been proposed.

Further, Japanese Patent Application Laid-Open No. 61-286069 discloses an extraction separation using water and an aromatic hydrocarbon, since it is inevitable to mix formamide, which is an unreacted raw material, into N-vinylformamide by distillation. I have.

On the other hand, as another influential 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 manner, carboxylic acid amide and N-vinyl carboxylic acid amide having similar physical properties are generated in equimolar amounts, and it is very difficult to separate them. . And JP 6
JP-A-3-132868 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 US Pat. A method by extractive distillation using a polyhydric alcohol and the like are 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.

As described above, none of the above-mentioned methods discloses a method for efficiently and stably separating a polar vinyl compound such as N-vinylcarboxylic acid amide having high purity and excellent polymerizability on an industrial scale. .

[0013]

An object of the present invention is to provide a method for purifying a polar vinyl compound capable of producing a vinyl compound having excellent polymerizability by removing impurities such as a polymerization inhibitor from the vinyl compound having a polar group. It is intended to be.

[0014]

SUMMARY OF THE INVENTION According to the present invention, a crude polar vinyl compound containing a polymerization inhibitor and having at least one oxygen, nitrogen or sulfur atom is prepared at a temperature of from 0 to 100.degree.
A method for purifying a polar vinyl compound is provided, which comprises precipitating crystals of a polar vinyl compound by pressurizing to about 3000 atm and separating the crystals from a liquid phase under pressure.

[0015]

DETAILED DESCRIPTION OF THE INVENTION The method for purifying a polar vinyl compound according to the present invention will be specifically described below. In the present invention,
A vinyl compound containing a polymerization inhibitor such as a polymerization inhibitor and having at least one oxygen atom, nitrogen atom or sulfur atom (coarse-polar vinyl compound) is treated by pressure crystallization to obtain a polar vinyl compound and a polymerization inhibitor. To purify the polar vinyl compound.

The crystallization pressure in the present invention is 500 to 300.
It is 0 atm, and particularly preferably 1000 to 2000 atm. When the crystallization pressure is lower than 500 atm, the degree of polymerization of the obtained polar vinyl compound is not significantly improved, and the amount of crystals obtained by one crystallization operation is small, and the productivity is low, which is economically disadvantageous. Becomes 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 polar vinyl compound 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 the crude polar vinyl compound, the crude polar vinyl compound can be carried out at a low pressure when the temperature is lowered, but when the temperature is raised, a high pressure is required.

In the present invention, the crude polar vinyl compound is preliminarily adjusted to 0 to 100 ° C., preferably 10 to 70 ° C., and then introduced into the pressure crystallization apparatus (pressure cylinder). The temperature of the pressure cylinder of the pressure crystallizer rises slightly due to adiabatic compression and heat of crystallization when the crude polar compound is pressurized. Considering this temperature rise, the crystallization temperature of the polar vinyl compound is set. Good to do. When the crystallization temperature is lower than 0 ° C., the concentration of the coarse polar vinyl compound becomes too high, and the fluidity is reduced, and it becomes difficult to introduce the coarse polar vinyl compound into the pressure cylinder. On the other hand, when the crude polar vinyl compound is heated above 100 ° C., thermal polymerization or deterioration of the vinyl compound starts to occur, which causes deterioration in quality and yield.

In the present invention, the crude polar vinyl compound introduced into the pressurizing cylinder may be a liquid or a slurry containing a seed crystal, but a slurry containing a seed crystal 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 polar vinyl compound 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 polar vinyl compound supplied to the pressurizing cylinder, the polar vinyl compound will be in a supersaturated state even when pressurized, and crystals may not be generated sufficiently. For this reason, prior to pressure crystallization, the crude polar vinyl compound is kept at a temperature and time sufficient for generating seed crystals to generate crystals of the polar vinyl compound in advance, or a part of the crude polar vinyl compound is diverted, It is desirable to cool this to produce crystals, and to mix the crude polar vinyl compound containing the crystals with the crude polar vinyl compound, or to add a seed crystal to the crude polar vinyl compound from outside.

In general, in pressure crystallization, the crystallization rate is higher than in cooling crystallization, and the time required to reach a state close to equilibrium is short. However, since the amount of crystallization per pressurization is maximized, it is completely eliminated. It is preferable to maintain the pressurized state until the equilibrium state is reached. Since the polar vinyl compound has relatively high crystallinity, the holding time in the pressurized state is within 5 minutes, preferably within 3 minutes.

In the present invention, by separating a polar vinyl compound precipitated as a solid phase (crystal) under pressure from a liquid phase enriched with a polymerization inhibitor (impurity), a polymer having excellent polymerizability is obtained. Although a pure polar vinyl compound is obtained, the pressure at which the solid and liquid phases are decomposed is 10
The pressure is preferably from 00 to 2000 atm, and the separation is performed at a pressure slightly lower than the crystallization pressure. In this process, a part of the crystals is dissolved and sweated in a liquid phase (mother liquor) in which the remaining, and the impurities contained in the crystals of the polar vinyl compound are discharged into the mother liquor. It becomes excellent in polymerizability.

The crude polar vinyl compound used in the present invention contains a polar vinyl compound having at least one oxygen atom, nitrogen atom or sulfur atom, and a polymerization inhibitor of the vinyl compound.

The polar vinyl compounds as described above include:
For example, a compound represented by the following general formula (1), (2) or (3) can be mentioned. _{^{CH 2 = CHNR 1 COR 2 (}} 1) ( in the formula, indicating each R ¹ and R ² are independently a hydrogen atom or a methyl ^{_{group.) CH 2 = CR 1 COOR}} 2 (2) ( wherein, R ¹ is hydrogen R ² represents a hydrogen atom, an alkali metal, an alkyl group having 1 to 5 carbon atoms or a lower alkyl group substituted with a hydroxyl group, a dialkylamino group or a quaternary ammonium group. CH ₂ ＣＲCR ¹ CONR ² R ³ (3) (wherein, R ¹ represents a hydrogen atom or a methyl group, and R ² and R ³ each independently represent a hydrogen atom, an alkyl group having 1 to 5 carbon atoms or a hydroxyl group) , A lower alkyl group substituted with a dialkylamino group, a sulfonic acid group or a quaternary ammonium group.) Further, an aromatic vinyl compound substituted with a hydroxyl group, an amino group, or the like may be used in the present invention. It can be.

Examples of such a polar vinyl compound include N-vinylacetamide, N-vinyl-N-methylacetamide, N-vinylformamide and N-methyl-N-vinylformamide. Acid amide, N-
Methylacrylamide, N-ethylacrylamide, N-isopropylacrylamide, monomethylolacrylamide, diacetoneacrylamide, N, N-dimethylacrylamide, N, N-diethylacrylamide, N, N'-methylenebisacrylamide, 2-acrylamide-2- Methylpropane sulfonic acid or its sodium salt, acrylamide such as N-methylolacrylamide, and methacrylamide derivatives, acrylic acid and methacrylic acid ester such as acrylic acid, methacrylic acid, itaconic acid, pentaerythritol monoacrylate, maleic anhydride, α -Ethyl cyanoacrylate, o-, m-, p-hydroxystyrene, o-, m-, p-aminostyrene, n-vinylcarbazole and the like.

The polymerization inhibitor contained in the crude polar vinyl compound used in the present invention is a substance which adversely affects the polymerization of the polar vinyl compound (monomer) or inhibits the polymerizability. Examples of such a polymerization inhibitor include a polymerization inhibitor (substance) that does not cause polymerization of a polar vinyl compound at all for a certain period of time, a polymerization inhibitor (substance) that slows down the polymerization rate, and a chain transfer agent (substance) that causes a decrease in molecular weight. And
There is no particular limitation. The following are mentioned as an example of a polymerization inhibitor. (1) A metal salt or the like that easily carries out an electron transfer reaction with a growing radical.

Iron (III) salt, copper (II) salt and the like. (2) A compound that easily undergoes a chain transfer reaction with a primary radical or a growing radical to generate a stable radical.

Compounds having a phenolic hydroxyl group such as hydroquinone, aromatic amines, allyl compounds, benzyl compounds and the like. (3) A compound that easily generates an addition reaction with a primary radical or a growing radical to generate a stable radical.

Oxygen, benzoquinone, nitroso compounds, etc. In the crude polar vinyl compound used in the present invention, the content of the polar vinyl compound in the crude polar vinyl compound is preferably as large as possible, preferably contained in an amount of 40% by weight or more, particularly preferably 70% by weight or more. Is preferred. Components other than the polymerization inhibitor contained in the crude polar vinyl compound are not particularly limited. If the content of the polar vinyl compound in the crude polar vinyl compound is less than 40% by weight, the recovery rate of the polar vinyl compound is poor, and the obtained polar vinyl compound often does not reach a satisfactory level of polymerizability. .

Such crude polar vinyl compounds are disclosed, for example, in JP-A-61-106546 (thermal decomposition method of ethylidene bisacetamide) and JP-A-50-76015 (secondary N-vinylcarboxylic acid amide). If the content of N-vinylcarboxylic acid amide is 50% by weight or more, the pyrolysis products of these methods may be used as they are, or N-vinylcarboxylic acid amide may be obtained by distillation. -Concentration or distillation of vinyl carboxylic acid amide to increase the content of N-vinyl carboxylic acid amide may be used.
It is desirable to use a crude polar vinyl compound that has been subjected to these purification operations, since naturally the recovery rate of the polar vinyl compound is improved, and the purity and the polymerizability are also improved.

N-vinylcarboxylic acid amide as a polar vinyl compound is unstable to water, and gradually decomposes by absorbing moisture in the air. In particular, the presence of an acid is extremely unstable and causes hydrolysis. Therefore, when N-vinylcarboxylic acid amide is used as the polar vinyl compound, the pressure crystallization equipment including the pressure separation device and the raw material tank, as well as the auxiliary equipment such as the product container and the filtrate tank, require nitrogen and dry air. It is desirable to keep the atmosphere. Also N-
In order to prevent the hydrolysis reaction of vinyl carboxylic acid amide,
A small amount of a drying agent such as magnesium sulfate or a basic substance such as baking soda may be added to the crude polar vinyl compound.

The liquid phase obtained by pressure crystallization of the crude polar vinyl compound as described above contains, in addition to the polymerizable inhibitor, a raw material for synthesizing the vinyl compound and a solvent. The compound itself may be considerably contained. Therefore, this liquid phase may be discarded as it is, or may be sent to a previous step such as a vinyl compound reaction step and used again. Further, the vinyl compound may be recovered from the liquid phase by a treatment such as pressure crystallization, cooling crystallization or distillation. When these secondary recovered products do not show sufficient polymerizability, they may be mixed with a crude polar vinyl compound and returned to the pressure crystallization step.

The reason why the polar vinyl compound obtained by the method for purifying a polar vinyl compound according to the present invention has excellent high polymerizability is not clear, but in addition to the sweating action by pressure crystallization, the eutectic point under pressure can be cooled. Compared to the eutectic point at the time of crystallization, it is advantageous for crystallization of vinyl compounds.Because the separation process is performed at a relatively low temperature for a short time, deterioration of the vinyl compounds due to heat does not occur. It is conceivable that the resin is hardened into a cylindrical shape and has a small surface area, so that it is hardly deteriorated by moisture absorption or oxidation.

[0033]

According to the present invention, a polar vinyl compound having high purity and excellent polymerizability can be easily and efficiently produced from a crude polar vinyl compound containing a polymerization inhibitor.

[0034]

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.

[0035]

Example 1 An acrylamide-containing reaction solution was obtained by catalytic hydration of acrylonitrile using a copper-containing catalyst. Acronitrile was distilled off from the reaction solution according to a conventional method to obtain an aqueous solution of acrylamide having a concentration of 50% by weight.

After cooling the aqueous acrylamide solution (I) to 10 ° C., it was placed in a pressure crystallization vessel at 1800 kg / cm ² and 10 ° C.
And the crystals of acrylamide were precipitated, from which the crystals were separated from the liquid phase (mother liquor). In this way, purity 9
9.9% of acrylamide was obtained.

To evaluate the polymerizability of the obtained acrylamide, water was added to make up to 20% by weight, and V-50 (N, N'-) was added.
600 ppm of azobis- (2-amidinopropane) dihydrochloride
In addition, it 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 number of revolutions was 30 ° C. and 30 ° C.
It was 120 cps when the viscosity was measured by RPM.

[0038]

Comparative Example 1 The 50% aqueous acrylamide solution (I) obtained in Example 1 was cooled to 5 ° C., and the crystallized acrylamide was separated by filtration and dried in vacuum at 40 ° C. for 6 hours. The obtained acrylamide contained 10 PPM of copper ions and 0.5% of a polymer, and the result of the polymerization evaluation performed in the same manner as in Example 1 was that the viscosity was 5 cps.

[0039]

Comparative Example 2 The 50% aqueous acrylamide solution obtained in Example 1 was decopperized with a strongly acidic cation exchange resin, and then neutralized with caustic soda to obtain a 50% aqueous acrylamide solution. The result of polymerization evaluation performed in the same manner as in Example 1 was that the viscosity was 85 cps.

[0040]

EXAMPLE 2 640 g of a 50% by weight aqueous acrylamide solution (4.5 g) was placed in a four-necked flask equipped with a stirrer, a condenser and a thermometer.
Mol) and 11.7 ml of a 0.1 N aqueous sodium hydroxide solution, and the mixture was adjusted to 30 ° C. To this flask was added 37% by weight formaldehyde (3.8 mol) neutralized with formic acid with sodium hydroxide with stirring. After 4 hours, the yield of N-methylolacrylamide was 75%. The reaction was neutralized with 0.1N sodium dihydrogen phosphate.

The neutralized reaction solution (II) was cooled to 20 ° C., and kept at 1800 kg / cm ² and 20 ° C. in a pressure crystallization vessel to precipitate crystals of N-methylolacrylamide. Mother liquor). Purity 99.
9% of N-methylolacrylamide was obtained.

To evaluate the polymerizability of this N-methylolacrylamide, water was added to make up to 20% by weight.
(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.

[0043]

Comparative Example 3 In order to evaluate the polymerizability of the neutralized reaction solution (II) obtained in Example 2, water was added to 20% by weight, and the viscosity was measured in the same manner as in Example 2. there were.

[0044]

Example 3 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
The mixture was stirred and dissolved at 5-48 ° C until it became uniform. A solution prepared by dissolving 0.43 g (0.1% by weight based on the charged amount) of concentrated sulfuric acid in 2 g (33 mmol) of isopropyl alcohol (the same applies to the following examples) was added, followed by stirring, followed by stirring of 1.76 g (0.4%) of acetaldehyde. Mol) was added via a 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%. Of ethylidene bisacetamide was 5.3%. The increase or decrease in the amount of acetal produced is limited to 1 in the range of 30 minutes to 3 hours.
The mmoles were reduced and the ethylidene bisacetamide was equilibrated. 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 pyrolysis solution (III) thus obtained was cooled to 20 ° C., and was cooled to 1800 kg / cm using a pressure crystallization vessel.
^{2. While} maintaining the temperature at 20 ° C., crystals of N-vinylacetamide were precipitated, and the crystals were separated from the liquid phase (mother liquor). Purity 9
9.9% of N-vinylacetamide was obtained. To evaluate the polymerizability of this N-vinylacetamide, water was added to make up to 20% by weight, and V-50 (N, N'-azobis- (2-amidinopropane) dihydrochloride (600 ppm) was added. 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 to find that the viscosity was 130 cps.

[0046]

Comparative Example 4 The pyrolysis solution (III) obtained in Example 3 was
Reflux ratio of 2, 3 using an Oldershaw type rectification device
After distillation under reduced pressure at torr, N-vinylacetamide having a purity of 97.5% was obtained. When a polymerization evaluation test of N-vinylacetamide was performed in the same manner as in Example 3, the viscosity was 40 cp.
s.

[0047]

Example 4 87% by weight of N-vinylacetamide, N- (α-
A mixture (IV) consisting of 9% by weight of (methoxyethyl) acetamide and 4% by weight of acetamide was cooled to 20 ° C., and kept at 1800 kg / cm ² and 50 ° C. in a pressure crystallization vessel to precipitate N-vinylacetamide crystals. The crystals were separated from the liquid phase (mother liquor). Thus, N- (α-methoxyethyl) acetamide was 600 ppm and acetamide was 300 pp.
N-vinylacetamide with a purity of 99.9% containing m
Obtained at 0%.

To evaluate the polymerizability of this N-vinylacetamide, water was added to make up to 20% by weight, and V-50 (N, N ') was added.
600 ppm of -azobis- (2-amidinopropane) dihydrochloride
In addition, it 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 number of revolutions was 30 ° C. and 30 ° C.
It was 150 cps when the viscosity was measured by RPM.

[0049]

[Comparative Example 5] A rectification column filled with a 5 mm sludge type filler having 20 theoretical plates was placed at the 10th stage from the top to prepare a rectifier according to Example 4.
The mixture (IV) containing N-vinylacetamide as a main component used in (1) was charged into a heating kettle connected to the bottom of the tower, and the pressure was reduced to 2 mmH.
g, rectification was performed at a reflux ratio of 3. N-vinylacetamide having a purity of 89% and containing 7% by weight of N- (α-methoxyethyl) acetamide and 4% by weight of acetamide was obtained from the top of the column.

When a polymerization evaluation test was carried out on the obtained fraction in the same manner as in Example 4, the viscosity was 50 cps.

[0051]

Example 5 Crude acrylic acid obtained by adding an absorption step with water, an extraction step with butyl acetate of an aqueous solution, an azeotropic distillation step, and a rectification step to acrylic acid synthesized by a gas-phase oxidation reaction of propylene ( V) contained 500 ppb of acrolein, 2000 ppm of acetic acid, 1500 ppb of benzaldehyde, 700 ppb of furfurylaldehyde, 400 ppm of propionic acid, and 2000 ppm of acrylic acid dimer.

The crude acrylic acid was cooled to 15 ° C., kept at 1800 kg / cm ² and 18 ° C. in a pressure crystallization vessel to precipitate crystals of acrylic acid, and the crystals were separated from the liquid phase (mother liquor). , 99.9% purity acrylic acid recovery rate 7
Obtained at 5%. This acrylic acid contains acrolein 1
It contained 0 ppb, 25 ppm of acetic acid, 110 ppb of benzaldehyde, 5 ppb of furfurylaldehyde, 30 ppm of propionic acid, and 15 ppm of acrylic acid dimer.

In order to evaluate the polymerizability of this acrylic acid,
Water was added to make up to 20% by weight in a test tube, and V-50 (N, N ') was added.
2% by weight of -azobis- (2-amidinopropane) dihydrochloride
In addition, it was immersed in a 45 ° C. constant temperature water bath. After 10 minutes, the temperature of the aqueous acrylic acid solution rose to 46.5 ° C.

[0054]

Comparative Example 6 4 m of the crude acrylic acid (V) obtained in Example 5 was used.
Vacuum distillation was performed at mHg and 60 ° C. Acrylein 300 ppb, acetic acid 600 ppm, benzaldehyde 400 ppb, furfuryl aldehyde 500 ppb,
300 ppm propionic acid, 150 ppm acrylic acid dimer
Was included. The acrylic acid thus purified by distillation was evaluated for polymerizability in the same manner as in Example 5. After immersion in a 45 ° C.
Even after a lapse of minutes, the temperature of the acrylic acid aqueous solution did not rise to 46 ° C.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical indication location C07C 233/27 C07C 233/27 233/38 233/38 255/23 255/23 309/69 309 / 69 (72) Inventor Hitoshi Nakamura 2 Onaka-shi, Oita City, Oita Prefecture Showa Denko KK Oita Research Laboratories (72) Inventor Katsufumi Tobe 1-3-18 Wakihama-cho, Chuo-ku, Kobe City, Hyogo Prefecture Kobe Steel, Ltd.Kobe headquarters (72) Inventor Shingo Yoshida 1-3-18 Wakihama-cho, Chuo-ku, Kobe-shi, Hyogo Kobe Steel Ltd.Kobe headquarters

Claims (4)

(57) [Claims] A crystal of a polar vinyl compound comprising a polymerization inhibitor and a crude polar vinyl compound having at least one oxygen atom, nitrogen atom or sulfur atom, which is pressurized to 500 to 3000 atm at 0 to 100 ° C. A method for purifying a polar vinyl compound, comprising separating crystals of the polar vinyl compound from a liquid phase under pressure to obtain a high-purity polar vinyl compound. 2. The method according to claim 1, wherein the polar vinyl compound is a compound represented by the general formula (1). CH ₂ ＣＨCHNR ¹ COR ² (1) (wherein, R ¹ and R ² each independently represent a hydrogen atom or a methyl group.) 3. The method according to claim 1, wherein the polar vinyl compound is a compound represented by the general formula (2). CH ₂ ＣＲCR ¹ COOR ² (2) (wherein, R ¹ represents a hydrogen atom, a methyl group, or a cyano group; R ² represents a hydrogen atom, an alkali metal, an alkyl group or hydroxyl group having 1 to 5 carbon atoms, a dialkyl It represents a lower alkyl group substituted with an amino group or a quaternary ammonium group.) 4. The method according to claim 1, wherein the polar vinyl compound is a compound represented by the general formula (3). CH ₂ ＣＲCR ¹ CONR ² R ³ (3) (wherein, R ¹ represents a hydrogen atom or a methyl group, R ² and R ³ each independently represent a hydrogen atom, an alkyl group having 1 to 5 carbon atoms or a hydroxyl group, It represents a lower alkyl group substituted with a dialkylamino group, a sulfonic acid group or a quaternary ammonium group.)