Method for producing highly polymerizable N-vinyl carboxylic acid amide monomer

Abstract

Provided is a method with which it is possible to purify N-vinylcarboxamide efficiently and produce a highly polymerizable N-vinylcarboxamide monomer.　This method for producing a highly polymerizable N-vinylcarboxamide monomer is characterized in that: the method includes (A) a step for melting by heating a crude N-vinylcarboxamide monomer containing 50-88 mass% of N-vinylcarboxamide monomer, subsequently precipitating N-vinylcarboxamide monomer crystals through cooling (cooling precipitation), and subjecting the precipitated N-vinylcarboxamide monomer crystals to solid-liquid separation (step (A)), and (B) a step for furthermore dissolving the N-vinylcarboxamide monomer crystals separated in step (A) in a mixed solvent of acetonitrile and a C6-7 aliphatic hydrocarbon, conducting crystallization (solvent crystallization), and performing solid-liquid separation to recover an N-vinylcarboxamide monomer purified product (step (B)); the mass ratio of acetonitrile / N-vinylcarboxamide monomer crystals in step (B) is 0.01-0.5 (inclusive); and the mass ratio of C6-7 aliphatic hydrocarbon / N-vinylcarboxamide monomer crystals in step (B) is 0.5-3.0 (inclusive).

Description

[Technical field]

[0001] The present invention relates to a method for producing a highly polymerizable N-vinyl carboxylic acid amide monomer, and more particularly to a method for producing an N-vinyl carboxylic acid amide monomer having improved polymerizability with high productivity. [Background technology]

[0002] N-vinyl carboxylic acid amide polymers derived from N-vinyl carboxylic acid amides are water-soluble polymers that dissolve not only in water but also in polar solvents such as alcohol and dimethyl sulfoxide (DMSO). As they are non-ionic polymers, they are not affected by salts or pH, and have high weather resistance, especially high stability against heat. Taking advantage of these properties, they are used industrially as binders, dispersants, adhesives, thickeners, flocculants, etc.

[0003] Many methods have been proposed for producing N-vinyl carboxylic acid amides, such as a method in which an intermediate N-(1-alkoxyethyl) carboxylic acid amide is produced from carboxylic acid amide, acetaldehyde, and alcohol as raw materials, and then the intermediate is synthesized by thermal or catalytic decomposition. In addition to N-vinyl carboxylic acid amide, the synthesis reaction of this N-vinyl carboxylic acid amide contains intermediates such as unreacted N-(1-alkoxyethyl) carboxylic acid amide and carboxylic acid amide. These compounds have physical properties such as boiling point, vapor pressure, and solubility close to those of N-vinyl carboxylic acid amide, making it difficult to purify N-vinyl carboxylic acid amide by distillation. Therefore, a method for purifying N-vinyl carboxylic acid amide has also been proposed.

[0004] Patent No. 2619204 discloses a purification method using pressure crystallization, which allows the production of highly polymerizable N-vinyl carboxylic acid amides with relatively high purity. However, this method requires a large investment in equipment, and the product cannot be provided at low cost unless it is produced on an industrial scale. Patent No. 5126764 discloses a solvent crystallization method using alcohol and aliphatic hydrocarbons. However, this solvent combination requires a large amount of poor solvent and has low volumetric efficiency, resulting in poor productivity. Furthermore, as a polymerization inhibitor of N-vinyl carboxylic acid amide, Japanese Patent No. 4099831 specifies N-1,3-butadienyl carboxylic acid amide, and WO 17 / 145569 specifies unsaturated aldehydes. However, there were cases where good polymerizability was not obtained even after removing the above. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 2619204 [Patent Document 2] Patent No. 5126764 [Patent Document 3] Patent No. 4099831 [Patent Document 4] WO 17 / 145569 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a method for efficiently purifying N-vinyl carboxylic acid amide and producing a highly polymerizable N-vinyl carboxylic acid amide monomer, and further to produce a high molecular weight N-vinyl carboxylic acid amide polymer by using the produced N-vinyl carboxylic acid amide monomer. [Means for solving the problem]

[0007] As a result of extensive investigations into a method for producing a highly polymerizable N-vinyl carboxylic acid amide monomer, it was found that a highly polymerizable N-vinyl carboxylic acid amide monomer can be produced by combining cooling crystallization with solvent crystallization using acetonitrile and an aliphatic hydrocarbon having 6 to 7 carbon atoms, and thus the present invention was completed.

[0008] The present invention is configured as follows. [1] (A) a step (A) of melting a crude N-vinyl carboxylic acid amide monomer containing 50 to 88% by mass of the N-vinyl carboxylic acid amide monomer by heating, followed by precipitating the N-vinyl carboxylic acid amide monomer by cooling (cooling crystallization), and subjecting the precipitated N-vinyl carboxylic acid amide monomer crystals to solid-liquid separation; and (B) further dissolving the N-vinyl carboxylic acid amide monomer crystals separated in the step (A) in a mixed solvent of acetonitrile and an aliphatic hydrocarbon having 6 to 7 carbon atoms, followed by crystallization (solvent crystallization), and then performing solid-liquid separation to recover a purified N-vinyl carboxylic acid amide monomer (step (B)); the mass ratio of acetonitrile / N-vinyl carboxylic acid amide monomer crystals in step (B) is 0.01 or more and 0.5 or less; A method for producing a highly polymerizable N-vinylcarboxylic acid amide monomer, characterized in that in step (B), the mass ratio of an aliphatic hydrocarbon having 6 to 7 carbon atoms / N-vinylcarboxylic acid amide monomer crystals is 0.5 or more and 3.0 or less. [2] The method for producing a highly polymerizable N-vinyl carboxylic acid amide monomer according to [1], wherein the mass of the acetonitrile is 0.003 to 1.0 relative to the mass of the aliphatic hydrocarbon having 6 to 7 carbon atoms. [3] The method for producing a highly polymerizable N-vinyl carboxylic acid amide monomer according to [1] or [2], wherein the crystallization in the step (A) is carried out by melting a crude N-vinyl carboxylic acid amide monomer at 30°C to 80°C and then cooling it to -20°C to 20°C. [4] A method for producing a highly polymerizable N-vinylcarboxylic acid amide monomer according to any one of [1] to [3], wherein the crystallization in the step (B) is carried out by dissolving N-vinylcarboxylic acid amide monomer crystals in a mixed solvent of acetonitrile and an aliphatic hydrocarbon having 6 to 7 carbon atoms at 30°C to 80°C, and then cooling to -20°C to 20°C. [5] The method for producing a highly polymerizable N-vinyl carboxylic acid amide monomer according to any one of [1] to [4], wherein the aliphatic hydrocarbon having 6 to 7 carbon atoms used in the step (B) is at least one selected from normal hexane, cyclohexane, normal heptane, cycloheptane, and methylcyclohexane. [6] The method for producing a highly polymerizable N-vinyl carboxylic acid amide monomer according to any one of [1] to [5], wherein the method for solid-liquid separation in the step (A) and the step (B) is filtration separation. [7] The method for producing a highly polymerizable N-vinylcarboxylic acid amide monomer according to any one of [1] to [6], wherein the N-vinylcarboxylic acid amide monomer is an N-vinylacetamide monomer. Effect of the Invention

[0009] According to the present invention, it is possible to produce a highly polymerizable N-vinylcarboxylic acid amide monomer with higher productivity than conventional methods. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] A method for carrying out the present invention comprises the following steps. (A) a step (A) of melting a crude N-vinyl carboxylic acid amide monomer containing 50 to 88% by mass of the N-vinyl carboxylic acid amide monomer by heating, followed by precipitation by cooling (cooling crystallization), and subjecting the precipitated N-vinyl carboxylic acid amide monomer crystals to solid-liquid separation; and (B) A step (B) of further dissolving the N-vinylcarboxylic acid amide monomer crystals separated in the step (A) in a mixed solvent of acetonitrile and an aliphatic hydrocarbon having 6 to 7 carbon atoms, followed by crystallization (solvent crystallization) and solid-liquid separation to recover a purified N-vinylcarboxylic acid amide monomer (step (B)).

[0011] In this specification, the term "crude N-vinylcarboxylic acid amide monomer" means that the crude N-vinylcarboxylic acid amide monomer contains impurities as well as a component consisting of the N-vinylcarboxylic acid amide monomer, that is, the crude N-vinylcarboxylic acid amide monomer is an "unpurified" N-vinylcarboxylic acid amide monomer.

[0012] Engineering(A) Examples of the N-vinyl carboxylic acid amide monomer include N-vinyl formamide, N-vinyl acetamide, N-methyl-N-vinyl acetamide, N-vinyl benzamide, N-vinyl-N-methyl formamide, N-vinyl-N-ethyl formamide, N-vinyl-N-ethyl acetamide, and N-vinyl pyrrolidone. N-vinyl acetamide is preferred.

[0013] The crude N-vinyl carboxylic acid amide monomer may be obtained by any production method. For example, it may be obtained by synthesizing N-(1-alkoxyethyl) carboxylic acid amide from carboxylic acid amide, acetaldehyde and alcohol, and subjecting it to thermal or catalytic decomposition (see JP-A-50-76015). It may also be obtained by synthesizing ethylidene biscarboxylic acid amide from carboxylic acid amide and acetaldehyde, and subjecting it to thermal decomposition (see JP-A-61-106546). The crude N-vinyl carboxylic acid amide monomer mainly contains, other than the N-vinyl carboxylic acid amide monomer, N-(1-alkoxyethyl) carboxylic acid amide, carboxylic acid amide, alcohols having 1 to 5 carbon atoms, etc., which are impurities derived from the production method of the N-vinyl carboxylic acid amide monomer, etc.

[0014] The crude N-vinyl carboxylic acid amide monomer contains the N-vinyl carboxylic acid amide monomer in an amount of 50 to 88% by mass, preferably 55 to 85% by mass, and more preferably 60 to 85% by mass. When the N-vinyl carboxylic acid amide monomer is contained in this range, the recovery rate of the N-vinyl carboxylic acid amide monomer can be increased, and the obtained N-vinyl carboxylic acid amide monomer has high purity and excellent polymerizability, which is desirable. When the amount of the N-vinyl carboxylic acid amide monomer contained in the crude N-vinyl carboxylic acid amide monomer is in the range of 50 to 88% by mass, it may be used as it is in the production method of the present invention, but the content of the N-vinyl carboxylic acid amide monomer may be adjusted by appropriate operations such as distillation and extraction. In addition, insoluble components in the crude N-vinyl carboxylic acid amide monomer can be removed in advance by such operations.

[0015] Usually, the upper limit of the content of the N-vinylcarboxylic acid amide monomer in the crude N-vinylcarboxylic acid amide monomer obtained by a known production method is within the above-mentioned range. However, even if a crude N-vinylcarboxylic acid amide monomer having a content higher than this upper limit is treated by the production method of the present invention, it is possible to obtain a purified N-vinylcarboxylic acid amide monomer. In step (A), the N-vinyl carboxylic acid amide monomer is cooled and crystallized from the crude N-vinyl carboxylic acid amide monomer. In the cooling crystallization, the crude N-vinyl carboxylic acid amide monomer is first melted. The melting temperature is preferably 30 to 80° C., more preferably 30 to 60° C., and further preferably 35 to 45° C. If the melting temperature is within the above range, the N-vinyl carboxylic acid amide monomer is easily dissolved and is not thermally denatured, which is desirable.

[0016] Next, the solution in which the N-vinyl carboxylic acid amide monomer is dissolved is cooled to precipitate N-vinyl carboxylic acid amide monomer crystals. The cooling temperature is preferably -20°C to 20°C, more preferably -15 to 15°C, and even more preferably -10°C to 10°C. If the cooling temperature is within the above range, the cost of equipment such as a refrigerator is low, and the crystallization yield of the N-vinyl carboxylic acid amide monomer is high, which is desirable. The temperature difference between the melting temperature and the cooling temperature is not particularly limited, but is preferably 10°C to 100°C, more preferably 20 to 60°C, and is appropriately selected depending on the processing efficiency and the filterability of the precipitate.

[0017] As a method for efficiently separating the N-vinyl carboxylic acid amide monomer crystals precipitated in step (A) from solid-liquid, separation by filtration is preferred. Although there is no limitation on the method for separation by filtration, centrifugal filtration, pressure filtration, etc. are preferred from the viewpoint of separation from the crystallization mother liquor and productivity. In addition, rinsing after filtration is also preferred in terms of improving the separability from the mother liquor. As the solvent used for rinsing, acetonitrile and an aliphatic hydrocarbon having 6 to 7 carbon atoms, similar to the crystallization solvent used in step (B), are preferred. The mass of acetonitrile used for rinsing is preferably used in a ratio of 0.01 to 0.3, more preferably 0.01 to 0.2, and even more preferably 0.02 to 0.1, relative to the mass of the crystallization raw material, i.e., the crude N-vinyl carboxylic acid amide monomer to be treated. In addition, the mass of the aliphatic hydrocarbon having 6 to 7 carbon atoms used for rinsing is preferably used in a ratio of 0.1 to 3.0, more preferably 0.1 to 2.0, and even more preferably 0.1 to 1.0, relative to the mass of the crude N-vinyl carboxylic acid amide monomer to be used. The mass of acetonitrile used is preferably 0.001 to 3.0, more preferably 0.005 to 2.0, and still more preferably 0.01 to 0.5, relative to the mass of the aliphatic hydrocarbon having 6 to 7 carbon atoms used.

[0018] Engineering(B) In step (B), the recovered N-vinyl carboxylic acid amide monomer crystals are dissolved in acetonitrile, which is a crystallization solvent, in the presence of an aliphatic hydrocarbon having 6 to 7 carbon atoms, which is a poor solvent, and then crystallized. This type of crystallization method is called solvent crystallization. The recovered N-vinyl carboxylic acid amide monomer crystals contain 88% by mass or more of the N-vinyl carboxylic acid amide monomer, preferably 90% by mass or more, and more preferably 92% by mass or more. The N-vinyl carboxylic acid amide monomer crystals may contain the crystallization mother liquor and the mother liquor used for rinsing, in addition to the N-vinyl carboxylic acid amide monomer.

[0019] The ratio of the mass of acetonitrile used to the mass of the N-vinylcarboxylic acid amide monomer crystals used is 0.01 or more and 0.5 or less, preferably 0.02 to 0.4, and more preferably 0.03 to 0.3.

[0020] In addition, the aliphatic hydrocarbon having 6 to 7 carbon atoms used is preferably normal hexane, cyclohexane, methylcyclohexane, normal heptane, or cycloheptane, and more preferably cyclohexane or methylcyclohexane. Aliphatic hydrocarbons having 5 or less carbon atoms have a low boiling point and are difficult to handle, while aliphatic hydrocarbons having 8 or more carbon atoms have a high boiling point and may not be completely removed from the crystals. In addition, the mass of the aliphatic hydrocarbon having 6 to 7 carbon atoms is a ratio of 0.5 to 3.0, preferably 0.5 to 2.0, to the mass of the N-vinyl carboxylic acid amide monomer crystals used. This ratio range is desirable because the recrystallization of the N-vinyl carboxylic acid amide monomer is sufficiently precipitated, the amount of solvent used is not large, and the volume efficiency of the crystallizer can be increased. The mass of acetonitrile used is preferably 0.003 to 1.0, more preferably 0.005 to 0.8, and even more preferably 0.01 to 0.5, relative to the mass of the aliphatic hydrocarbon having 6 to 7 carbon atoms used.

[0021] The temperature for dissolving the N-vinylcarboxylic acid amide monomer crystals is preferably 30 to 80° C., more preferably 30 to 60° C., and further preferably 35 to 45° C. This temperature range is desirable because the N-vinylcarboxylic acid amide is sufficiently dissolved without being denatured.

[0022] Next, the dissolved N-vinyl carboxylic acid amide monomer is cooled to precipitate recrystallization. The cooling temperature is preferably from -20°C to 20°C, more preferably from -15°C to 15°C, and further preferably from -10°C to 10°C. This temperature range is desirable because it reduces equipment costs and provides a sufficient crystallization yield. The recrystallized N-vinyl carboxylic acid amide monomer is recovered to produce a purified N-vinyl carboxylic acid amide monomer.

[0023] As a method for efficiently separating the recrystallized N-vinyl carboxylic acid amide monomer precipitated in step (B), separation by filtration is preferred. Although there is no limitation on the filtration method, centrifugal filtration, pressure filtration, etc. are preferred from the viewpoint of separation from the crystallization mother liquor and productivity. In addition, rinsing after filtration is also preferred in terms of improving the separability from the mother liquor. As the solvent used for rinsing, acetonitrile and an aliphatic hydrocarbon having 6 to 7 carbon atoms, similar to the crystallization solvent, are preferred. The mass of acetonitrile used for rinsing is preferably used in a ratio of 0.01 to 0.3, more preferably 0.01 to 0.2, and even more preferably 0.02 to 0.1, relative to the mass of the N-vinyl carboxylic acid amide monomer crystals recovered from step (A). In addition, the mass of the aliphatic hydrocarbon having 6 to 7 carbon atoms used for rinsing is preferably used in a ratio of 0.1 to 3.0, more preferably 0.1 to 2.0, and even more preferably 0.1 to 1.5, relative to the mass of the N-vinyl carboxylic acid amide monomer crystals recovered from step (A).

[0024] In order to obtain a purified N-vinyl carboxylic acid amide monomer product with a higher purity, steps (A) and (B) may be repeated. The highly polymerizable N-vinylcarboxylic acid amide monomer thus produced has high purity and high polymerizability.

[0025] The mother liquors recovered in steps (A) and (B) contain raw materials for synthesizing N-vinyl carboxylic acid amide monomers, such as alcohols, carboxylic acid amides, N-(1-alkoxyethyl) carboxylic acid amides, etc. These may be recycled by being sent to a process for producing a crude N-vinyl carboxylic acid amide monomer, for example, a process for synthesizing N-(1-alkoxyethyl) carboxylic acid amides.

[0026] The thus-produced highly polymerizable N-vinyl carboxylic acid amide monomer can be used by being appropriately polymerized. For example, it can be used as a homopolymer obtained by polymerizing a monomer containing the high-purity N-vinyl carboxylic acid amide monomer obtained by the above-mentioned production method, or as a copolymer obtained by polymerizing the N-vinyl carboxylic acid amide monomer with another monomer. These (co)polymers are water-soluble and can be used for various purposes.

[0027] Examples of the other monomers include (meth)acrylic acid or a salt thereof, methyl (meth)acrylate, ethyl (meth)acrylate, (iso)propyl (meth)acrylate, butyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, methoxyethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and polyoxyalkylene glycol mono(meth)acrylate (meth)acrylic acid-based monomers; (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-methylol(meth)acrylamide, 2-(meth)acrylamide-2-methylpropanesulfonic acid or vinyl ester monomers such as vinyl acetate, vinyl butyrate, vinyl valerate, etc.; styrene monomers such as styrene, α-methylstyrene, p-methylstyrene, p-methoxystyrene, m-chlorostyrene, etc.; vinyl ether monomers such as methyl vinyl ether, butyl vinyl ether, vinyl benzyl ether, etc.; dicarboxylic acid monomers such as maleic anhydride, maleic acid or a salt thereof, fumaric acid or a salt thereof, dimethyl maleate, diethyl fumarate, etc.; allyl monomers such as allyl alcohol, allyl phenyl ether, allyl acetate, etc.; and monomers such as (meth)acrylonitrile, vinyl chloride, ethylene, propylene, etc.

[0028] The other monomers may be used alone or in combination of two or more. The amount of the other monomers may be appropriately determined depending on the application of the copolymer, but it is desirable to use the other monomers in an amount of usually 60% by mass or less, preferably 40% by mass or less, based on the total monomers.

[0029] A polymerization initiator may be used when polymerizing the highly polymerizable N-vinyl carboxylic acid amide monomer of the present invention. As the polymerization initiator, any initiator generally used for the radical polymerization of vinyl compounds can be used without limitation. For example, a redox-based polymerization initiator, an azo compound-based polymerization initiator, and a peroxide-based polymerization initiator can be mentioned.

[0030] These may be used alone or in combination of two or more. The above (co)polymers are suitably used in a wide range of fields by utilizing their functions such as thickening effect, dispersing effect, etc. Specific examples are given below, but are not limited to these.

[0031] (1) Industrial dispersants For example, it is used as a dispersant for various inorganic and organic powders. More specifically, it is used as a dispersant for various polar solvents such as water for inorganic powders such as silica, alumina, titania, calcium carbonate, etc., mineral powders such as talc, kaolin, etc., various pigment powders such as carbon black, resin powders such as polyurethane, polyacrylic ester, polyethylene, etc., and organic powders such as stearates. (2) Thickeners and dispersants used in paints, inks, etc. For example, in paints, inks, etc., they are used as additive dispersants, viscosity and leveling regulators, and wettability improvers. (3) Treatment and collection agents for water and oil (4) Cosmetics For example, they are used in cosmetics such as shampoos, rinses, and lotions as emulsion stabilizers, lubricants, emulsion-type cosmetics (used as emulsifiers), film-type packs, and setting agents. (5) Toiletries For example, it is used as a thickening agent in liquid detergents (for laundry, kitchen, toilets and tiles), toothpaste, cleansers, fabric softeners, industrial cleaners, etc. (6) Adhesives and their auxiliaries (7) Medical field For example, they are used for the retention and sustained release of drugs in tablets (sustained-release drugs), enteric-coated drugs, base materials for patches such as poultices and plasters, external ointments, drug release controlled preparations, intragastric floating sustained-release preparations, mucosal administration preparations, compositions for epidermis (medical films), wound covering protective materials, dental materials, oral absorbents, interdental cleaning tools, etc., as well as lubricants for medical instruments such as urethral catheters and enema apparatuses that are heated in a disinfecting autoclave for repeated use, and as viscosity adjusters for diagnostic drugs. (8) Water absorbents, water retention agents, sealing agents, cooling agents (9)Other For example, they are used as papermaking treatment agents, deodorizers, drying agents, fermentation aids, packing materials, and stripping agents for old walls, as well as thickening agents in toys, sweat-absorbing accessories, contact media for ultrasonic flaw detection, ultrasonic probes, and electrolyte supports for batteries and sensors. EXAMPLES

[0032] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples. The analytical method for the highly polymerizable N-vinylacetamide monomer obtained by the production method of the present invention is described below. However, the analytical method is not limited to the following, and any known method can be used.

[0033] ·Composition analysis The purity of the N-vinylacetamide monomer obtained in the Examples and Comparative Examples is determined by GC analysis under the following conditions. Equipment: High-performance general-purpose gas chromatograph "GC-2014" (Shimadzu Corporation) Column: DB-WAX (φ0.25mm × 30m, Agilent Technologies) Carrier gas type: He Carrier gas flow rate: 1mL / min Split ratio: 40 Column temperature: Set the temperature rise program in the following order: 40°C (7 min) → Heating (25°C / min) → 130°C (15 min) → Heating (30°C / min) → 220°C (7 min) Injection temperature: 200℃ Detector: Flame ionization detector (FID) Detector temperature: 230℃

[0034] The N-vinylacetamide monomer was confirmed and identified by ultraviolet-visible absorption spectroscopy using high performance liquid column chromatography (HPLC). The measurement conditions were as follows: Column: Showa Denko K.K.: Shodex (registered trademark) SIL-5B Eluent: isopropyl alcohol (IPA) / n-hexane = 1 / 9 (mass ratio) Column temperature: 40℃ Flow rate: 1.0mL / min Detector: UV-Visible Spectroscopic Detector, 254 nm

[0035] Polymerization test The polymerizability of the resulting purified N-vinylacetamide monomer is evaluated by the following polymerizability test.

[0036] [1] Prepare a 100 ml glass container equipped with a catalyst injection tube, a nitrogen gas inlet tube, a nitrogen gas exhaust tube, and a thermometer. [2] Weigh 20 g of purified N-vinylacetamide monomer and 58 g of ion-exchanged water into the glass container in [1]. [3] Nitrogen gas, 50 cm 3 The mixture was heated to 30°C in a water bath while bubbling at 1 / min. Nitrogen gas was passed through the mixture until the end of polymerization. [4] As a polymerization initiator, 1.6 g of 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (V-044, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) is dissolved in 48.4 g of ion-exchanged water. [5] Add 4.0 g of 2,2'-azobis(2-methylpropionamidine) dihydrochloride (V-50, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator to 46.0 g of ion-exchanged water and dissolve. [6] After one hour of nitrogen gas aeration, add 1.0 g of the polymerization initiator solution [4], followed by 1.0 g of the polymerization initiator solution [5] using a syringe. [7] Remove the glass container from the water bath, remove any moisture on the surface of the glass with paper, then transfer it to an insulated container to continue polymerization. [8] The polymerization temperature was monitored, and the time to reach the standard peak temperature (the time from injection of the polymerization initiator to the time when the temperature reaches the peak) was used as an index of polymerization. The polymerization was judged to be good or bad based on the time to reach the standard peak temperature, with less than 120 minutes being considered good.

[0037] [Synthesis Example 1] 224g of acetaldehyde, 325g of methanol, and 100g of acetamide were reacted under sulfuric acid catalyst at 40°C to synthesize N-(1-methoxyethyl)acetamide with a pH of 1.2. The reaction liquid was adjusted to pH 8.3 by adding 48% by mass of sodium hydroxide aqueous solution. After that, low boiling point components were distilled off at a temperature of 60-70°C and a pressure of 33kPa (absolute pressure) using a simple distillation apparatus, and then water and methanol were distilled off at a temperature of 70°C and a pressure of 0.3kPa (absolute pressure), to obtain 151g of N-(1-methoxyethyl)acetamide with a purity of 92% by mass.

[0038] Next, N-(1-methoxyethyl)acetamide was fed at a rate of 1.5 g / min to a reactor (tube reactor with an inner diameter of 20 mm and a length of 240 mm) maintained at 400°C and 20 kPa (absolute pressure). A mixture of N-vinylacetamide and methanol produced by the thermal decomposition reaction was condensed in a cooling tube installed at the reactor outlet to obtain a crude N-vinylacetamide recovered product. The conversion rate of N-(1-methoxyethyl)acetamide was 90%.

[0039] Next, a 0.3% Pd-Al2O3 catalyst was packed into the column (the amount packed was set to 1 ml of catalyst per 20 g of the crude N-vinylacetamide recovered product), and the crude N-vinylacetamide recovered product was circulated and circulated at a reaction temperature of 40°C, a hydrogen gas pressure of 0.03 MPa (gauge pressure), and a space velocity (SV value) in the catalyst-packed column of 100 / hour, and N-1,3-butadienylacetamide produced as a by-product in the thermal decomposition reaction was reduced by hydrogenation.

[0040] The reaction was continued until the amount of N-1,3-butadienylacetamide was 30 mass ppm or less. The crude N-vinylacetamide recovered product with reduced N-1,3-butadienylacetamide was distilled using a simple distillation apparatus under conditions of a vacuum degree of 0.3 kPa (absolute pressure) or less and a bottom temperature of 60°C or less to remove methanol, thereby obtaining 120 g of crude N-vinylacetamide monomer. The N-vinylacetamide monomer purity in this crude N-vinylacetamide monomer was 75 mass %.

[0041] [Example 1] The crude N-vinylacetamide monomer obtained in Synthesis Example 1 was heated to 40°C in a crystallizer to melt, cooled from 40°C to 10°C for 6 hours to crystallize, transferred to a centrifugal separator, subjected to solid-liquid separation using the centrifugal separator, and then rinsed with 4g acetonitrile / 77g methylcyclohexane to obtain 52g of crystals of N-vinylacetamide monomer. The purity of N-vinylacetamide at this time was 95% by mass.

[0042] 2.6g of acetonitrile and 57g of methylcyclohexane were added to 52g of the N-vinylacetamide monomer crystals, and the mixture was heated to 40°C to dissolve, and then cooled to 5°C for 7 hours to perform solvent crystallization to precipitate recrystallized N-vinylacetamide monomer. The slurry containing the recrystallized product was then transferred to a centrifugal filter, and solid-liquid separation was performed using the centrifugal filter. After that, rinsing was performed with 1g of acetonitrile / 25g of methylcyclohexane, and the recrystallized product was recovered to obtain a purified product of N-vinylacetamide monomer. The purified product obtained was 45g, and the purity of the N-vinylacetamide monomer was 99.8% by mass. The resulting purified N-vinylacetamide monomer was subjected to a polymerization test, and the result was 104 minutes.

[0043] [Example 2] In the solvent crystallization, recrystallization of N-vinylacetamide monomer was precipitated in the same manner as in Example 1, except that the amounts of acetonitrile and methylcyclohexane used were 10 g and 57 g, respectively. Thereafter, the slurry containing the recrystallization was sent to a centrifugal separator for solid-liquid separation, and after rinsing, the recrystallization was recovered to obtain a purified product of N-vinylacetamide monomer. The obtained purified product weighed 33 g and had a purity of 99.8% by mass. The result of the polymerization test was 98 minutes.

[0044] [Example 3] Recrystallization of N-vinylacetamide monomer was precipitated in the same manner as in Example 1, except that normal hexane was used instead of methylcyclohexane in the solvent crystallization and rinsing. Thereafter, the slurry containing the recrystallization was sent to a centrifugal separator for solid-liquid separation, and after rinsing, the recrystallization was recovered to obtain a purified product of N-vinylacetamide monomer. The obtained purified product weighed 44 g and had a purity of 99.8% by mass. The result of the polymerization test was 110 minutes.

[0045] [Example 4] Recrystallization of N-vinylacetamide monomer was precipitated in the same manner as in Example 1, except that cyclohexane was used instead of methylcyclohexane in the solvent crystallization and rinsing. Thereafter, the slurry containing the recrystallization was sent to a centrifugal filter, and solid-liquid separation was performed using the centrifugal filter. After rinsing, the recrystallization was recovered to obtain a purified product of N-vinylacetamide monomer. The obtained purified product weighed 43 g and had a purity of 99.7% by mass. The result of the polymerization test was 98 minutes.

[0046] [Comparative Example 1] In Example 1, only cooling crystallization was carried out without carrying out solvent crystallization. The obtained crystals of N-vinylacetamide monomer were 52 g and had a purity of 95% by mass. The polymerization test was carried out on the obtained crystals of N-vinylacetamide monomer, and the polymerization time was 160 minutes, which was a poor result.

[0047] [Comparative Example 2] To 100 g of crude N-vinylacetamide monomer obtained after removing methanol in the same manner as in Synthesis Example 1, 5 g of acetonitrile and 110 g of methylcyclohexane were added without performing cooling crystallization, and the mixture was heated to 40°C to dissolve, and then cooled to 5°C over 7 hours to perform solvent crystallization. However, even after further cooling to 0°C over 1 hour, no crystal precipitation was observed, and N-vinylacetamide monomer could not be obtained.

[0048] [Comparative Example 3] In the solvent crystallization, 20 g of acetonitrile was used, and methylcyclohexane was not used, but the same procedure as in Example 1 was used to precipitate recrystallized N-vinylacetamide monomer. Although the amount of solvent was small and the fluidity of the slurry was considerably deteriorated, the recrystallized N-vinylacetamide monomer was transferred to a centrifugal filter, and solid-liquid separation was performed using the centrifugal filter, and then rinsing was performed with 1 g of acetonitrile / 25 g of methylcyclohexane to recover the recrystallized product. The obtained purified product weighed 21 g and had a purity of 99.7% by mass. The result of the polymerization test was 112 minutes.

[0049] [Comparative Example 4] In the solvent crystallization, 31 g of acetonitrile and 208 g of methylcyclohexane were used, so that the crystallization apparatus had to be enlarged, and the volume efficiency was greatly reduced to one-fourth. Other than that, the recrystallization of N-vinylacetamide monomer was precipitated in the same manner as in Example 1. Since the amount of solvent used was large, the precipitate containing the recrystallized N-vinylacetamide monomer was divided and charged into a centrifugal filter, and solid-liquid separation was performed using the centrifugal filter, and then rinsing was performed with 1 g of acetonitrile / 25 g of methylcyclohexane to recover the recrystallization. The obtained purified product weighed 7 g and had a purity of 99.8% by mass. The recovered amount was small, and the polymerizability test could not be measured. The crystallization conditions and evaluation results are shown in Table 1.

[0050] [Table 1] [Industrial Applicability]

[0051] The N-vinyl carboxylic acid amide monomer obtained by the present invention can be used to produce N-vinyl carboxylic acid amide polymers that are used as flocculants, thickeners, dispersants, adhesives, etc.

Claims

1. (A) a step of melting a crude N-vinyl carboxylic acid amide monomer containing 50 to 88% by mass of the N-vinyl carboxylic acid amide monomer by heating, followed by precipitation by cooling (cooling crystallization), and subjecting the precipitated N-vinyl carboxylic acid amide monomer crystals to solid-liquid separation (step (A)); and (B) further dissolving the N-vinyl carboxylic acid amide monomer crystals separated in the step (A) in a mixed solvent of acetonitrile and an aliphatic hydrocarbon having 6 to 7 carbon atoms, followed by crystallization (solvent crystallization) and solid-liquid separation to recover a purified N-vinyl carboxylic acid amide monomer (step (B)); The mass ratio of acetonitrile / N-vinyl carboxylic acid amide monomer crystals in the step (B) is 0.01 or more and 0.5 or less; the mass ratio of the aliphatic hydrocarbon having 6 to 7 carbon atoms to the N-vinyl carboxylic acid amide monomer crystals in the step (B) is 0.5 or more and 3.0 or less; The method for producing a highly polymerizable N-vinyl carboxylic acid amide monomer is characterized in that the N-vinyl carboxylic acid amide monomer is an N-vinyl acetamide monomer.

2. The method for producing a highly polymerizable N-vinyl carboxylic acid amide monomer according to claim 1, wherein the mass of the acetonitrile is 0.003 to 1.0 relative to the mass of the aliphatic hydrocarbon having 6 to 7 carbon atoms.

3. The method for producing a highly polymerizable N-vinyl carboxylic acid amide monomer according to claim 1 or 2, wherein the crystallization in the step (A) is carried out by melting the crude N-vinyl carboxylic acid amide monomer at 30° C. to 80° C. and then cooling it to −20° C. to 20° C.

4. The method for producing a highly polymerizable N-vinyl carboxylic acid amide monomer according to any one of claims 1 to 3, wherein the crystallization in the step (B) is carried out by dissolving the N-vinyl carboxylic acid amide monomer crystals in a mixed solvent of acetonitrile and an aliphatic hydrocarbon having 6 to 7 carbon atoms at 30°C to 80°C, and then cooling to -20°C to 20°C.

5. The method for producing a highly polymerizable N-vinyl carboxylic acid amide monomer according to any one of claims 1 to 4, characterized in that the aliphatic hydrocarbon having 6 to 7 carbon atoms used in the step (B) is at least one selected from normal hexane, cyclohexane, normal heptane, cycloheptane and methylcyclohexane.

6. The method for producing a highly polymerizable N-vinyl carboxylic acid amide monomer according to any one of claims 1 to 5, characterized in that the method for solid-liquid separation in the steps (A) and (B) is filtration separation.

Images