KR20010078860A - Process for producing N-Methylol acrylamide solution in high yield - Google Patents

Abstract

PURPOSE: An N-methylol acrylamide solution with a high purity is provided to improve yield thereof at a low cost by recycling and not generating any waste from the process, and to simplify manufacturing process. CONSTITUTION: An N-methylol acrylamide solution is prepared by the reaction of water-soluble weak acidic formaldehyde solution whose pH is adjusted by an alkali catalyst, with acrylamide at the presence of alkali at the reaction temperature of 20 to 60 deg.C. The pH of the weak acidic formaldehyde solution ranges from 8 to 11. Typically used alkali catalyst includes alkali metals, hydroxide of alkali earth metals, alkali earth metal salts. The reactant, formaldehyde (or para-formaldehyde) is used in an amount of 0.8 to 1.4 mol on the basis of acrylamide.

Description

Process for producing N-Methylol acrylamide solution in high yield

N-methylol acrylamide is a crosslinkable monomer, and is widely used in industrial applications such as fiber leather modification, synthetic resin coating, paper processing enhancer, photosensitive resin and adhesive.

N-methylol acrylamide has been devised in various production methods by hydroxymethylation of acrylamide with formaldehyde or paraformaldehyde.

For example, a method of preparing a tertiary amine (e.g., triethylamine, triethanolamine) without a solvent as a catalyst (US Pat. No. 2,864,861), using a water as a solvent, tertiary-containing 60 to 97% acrylamide solution and paraformaldehyde Process for preparing amine or alkali metal hydroxide as catalyst (US Pat. No. 3,064,050), Process for preparing quaternary ammonium hydroxide compound in aqueous solution as catalyst (Japanese Patent Application Laid-Open No. 43-21658), Acrylic in aqueous solution Method for producing amide and formaldehyde by using at least one selected from the group consisting of salts of Pd-oxy acid and salts of W-oxy acid and a basic compound (Japanese Patent Application Laid-Open No. 43-16547), water-soluble At least one basic compound selected from the group consisting of salts of Mo-containing acids and salts of W-containing acids in acrylamide and formaldehyde; Rice method (4), which is prepared using a quaternary ammonium hydroxide compound as a catalyst (Japanese Patent Application Laid-Open No. 50-39251, US Patent No. 5,220,065, European Patent No. 508,455, German Patent No. 69,206,307, Republic of Korea Publication No. 1992-0019724), Process for preparing tertiary amine or alkali metal salt without solvent as catalyst (US Pat. No. 5,763,665), Process for preparing basic anion exchange resin in water or organic solvent without solvent (US Pat. No. 4,567,297, Japanese Patent Application Publication Nos. 49-14418, 49-36615, 49-127912) and the like have been proposed.

However, there is an industrially inefficient problem in the method for producing N-methylol acrylamide. That is, tertiary amine, salt of Pd-oxy acid, salt of W-oxy acid, salt of Mo-containing acid, salt of W-containing acid, quaternary ammonium hydroxide compound, etc. used as a catalyst are expensive, and basic anion exchange resin The investment is expensive. In addition, due to side reactions, the yield is low, and the method for preparing the catalyst solution and its usage are very complicated.

The present invention, on a simple principle, solves this problem and provides a method for producing N-methylol acrylamide solution in high yield efficiently and economically. When formaldehyde or paraformaldehyde reacts with acrylamide, different types of substances are produced under acidic or alkaline catalysts.

For example, N-methylol acrylamide is produced upon reaction under an alkali catalyst, but methylenebisacrylamide is produced upon reaction under an acidic catalyst.

In order to suppress the methylenebisacrylamide produced by the side reaction, the formaldehyde solution reacted with acrylamide is alkalinized to selectively prepare the N-methylol acrylamide solution in a high yield in the absence of acidic conditions.

Until now, the proposed patent for the method for preparing N-methylol acrylamide has been prepared by reacting an acrylamide in water or an aqueous solvent without adding a solvent and adding a weakly acidic formaldehyde or paraformaldehyde to make N-methylol acrylamide. Or an acrylamide, an alkali catalyst, formaldehyde or paraformaldehyde at the same time and react to produce N-methylol acrylamide. This hydroxymethylation reaction is very fast. When weakly acidic formaldehyde or paraformaldehyde is added to the alkaline acrylamide, the reaction system partially creates acidic conditions, thereby selectively producing N-methylol acrylamide and competitively producing N-methylol acrylamide and methylenebisacrylamide. Is generated.

In order to suppress the formation of by-product methylenebisacrylamide and to selectively prepare an N-methylol acrylamide solution in high yield, the reaction system is reacted with acrylamide under alkaline conditions by alkalizing a weak acid formaldehyde solution. It is characteristic.

Formaldehyde used as the starting material in the present invention is preferably to use a commercially available 37% formalin solution and may be used as the crystal paraformaldehyde. In terms of price, using a commercially available 37% formalin solution is cheaper and more economical than using paraformaldehyde in crystals on a 100% formaldehyde basis.

In addition, although acrylamide may be in any form of aqueous solution or crystal, it is economical to use a mixture of 50% acrylamide aqueous solution and crystal acrylamide. It is economically advantageous to use crystalline acrylamide to produce crystalline N-methylol acrylamide. In order to prepare N-methylol acrylamide as a starting material with acrylamide in an aqueous solution, a lot of energy is required for concentration, and it is uneconomical because it has a lower production capacity than using crystalline acrylamide as a starting material in the same reactor.

Water is used as the reaction solvent, and formaldehyde or paraformaldehyde used in the reaction is 0.8 to 1.4 mol, preferably 0.9 to 1.2 mol, based on acrylamide.

The alkali acid formaldehyde solution is adjusted to PH 8-11, preferably PH 8.5-10.5 with an alkali catalyst. The catalyst used to adjust the weakly acidic formaldehyde solution to alkali uses hydroxides of alkali metals and alkali earth metals or salts of alkali metals and alkali earth metals. Preferably alkali metal hydroxides (eg sodium hydroxide, lithium hydroxide, potassium hydroxide) are used.

The reaction temperature is advantageously carried out at a temperature of 20 ~ 60 ℃, preferably 30 ~ 50 ℃. The reaction time is 1 to 4 hours, preferably 1.5 to 3 hours.

After completion of the reaction, the alkaline solution is adjusted to pH 6.0-8.0, preferably 6.0-7.0 with a strong acid (eg hydrochloric acid, sulfuric acid, nitric acid). When the solution is below pH 6, methylenebisacrylamide is formed, and when the pH is above 8, decomposition and polymerization of the product occur during storage. In addition, when the polymerization inhibitor is added, oxidation occurs in an alkaline state, and the color of the N-methylol acrylamide solution turns pale pink or light brown so that the pH is adjusted to 6.0-7.0 after completion of the reaction.

The amount of the polymerization inhibitor is suitably 20 to 100 ppm, preferably 30 to 70 ppm, based on the weight of the N-methyrol acrylamide solution. The N-methylol acrylamide solution is unstable, and polymerization may occur when the temperature is 70 ° C. or higher during the concentration process or storage. Thus, the polymerization reaction may be suppressed by adding a polymerization inhibitor after completion of the reaction. Polymerization inhibitors that can be used include hydroquinone, hydroquinone dimethyl ether, hydroquinone monomethyl ether, phenothiazine, sodium nitrite, 2,6-di-t-butylcatechol, couperone and the like.

To obtain the product of crystals, N-methylol acrylamide aqueous solution is concentrated under reduced pressure to 60-80%, preferably 70-75%, and cooled and crystallized to obtain a high concentration of N-methylol acrylamide. The vacuum degree at the time of concentration under reduced pressure is 5 to 50 mmHg, the concentration temperature is 40 to 75 ° C, preferably 55 to 65 ° C, the pH is 6.0 to 8.0, preferably 6.0 to 7.0, the polymerization inhibitor is 20 to 100 ppm, preferably 30 to Concentrate using 70 ppm, and concentrate the concentration of N-methylol acrylamide solution to 60 to 80%, preferably 70 to 75%. If the concentration temperature is too low, it takes a lot of time, if the temperature is 70 ℃ or more suddenly a polymerization reaction occurs. When the concentration is above 90%, polymerization occurs easily. The concentrated solution is cooled and crystallized in the range of -5 to 20 ° C, preferably 0 to 10 ° C, and vacuum filtered to obtain crystalline N-methylol acrylamide of high purity. After filtration, the mother liquor is reused as a solvent in the next reaction.

Example 1

Put 130g of 37% formalin solution into 500ml four-necked flask equipped with stirrer, thermometer, and pH meter and adjust the pH to 9.27 with 50% sodium hydroxide solution. The reactor internal temperature is maintained at 35 ° C. in a water bath and 41.4 g of crystalline acrylamide and 138.6 g of 50% acrylamide aqueous solution are added. The reaction is carried out for 2 hours while maintaining the temperature inside the reactor at 34-37 ° C. After the reaction was completed, the pH was adjusted to 6.63 by adding dropwise 35% hydrochloric acid with the dropper. As a polymerization inhibitor, 0.0158 g of hydroquinone is weighed and added to the reaction. The agitation is stopped when the hydroquinone is completely dissolved. The reaction solution was cooled to 25 ° C and analyzed by HPLC (high performance liquid chromatography) to obtain 309.6 g of N-methylol acrylamide solution (purity 49.1%, yield 96.5%) in which methylene bisacrylamide was not produced.

Comparative Example 1

Into a 500 ml four-necked flask equipped with a stirrer, a thermometer and a pH meter, 138.6 g of 50% acrylamide aqueous solution and 41.4 g of crystalline acrylamide were added thereto, and the reactor was maintained at 35 ° C. while stirring. After adjusting the pH to 9.35 with 50% sodium hydroxide solution, 130 g of 37% formalin solution was added thereto. The reaction is carried out for 2 hours while maintaining the temperature inside the reactor at 33-37 ° C. After the reaction, 35% hydrochloric acid was added dropwise with the dropper to adjust the pH to 6.57. 0.0155 g of hydroquinone is weighed into the polymerization inhibitor and added to the reaction. The agitation is stopped when the hydroquinone is completely dissolved. The reaction solution was cooled to 25 ° C, and analyzed by HPLC (high performance liquid chromatography) to obtain 308.8 g of N-methylol acrylamide solution (purity 46.8%, 91.8% yield) containing 1.9% of methylenebisacrylamide.

Example 2

Put 130g of 37% formalin solution and 73g of water in a 500ml four-necked flask equipped with a stirrer, a thermometer and a pH meter and adjust the pH to 9.47 with 50% sodium hydroxide solution while stirring. Maintain the reactor internal temperature at 32 ° C. in a water bath and add 112 g of crystalline acrylamide. The reaction is carried out for 2 hours and 30 minutes while maintaining the reactor internal temperature at 30 ~ 35 ℃. After the reaction was completed, the pH was adjusted to 6.58 by adding dropwise 35% hydrochloric acid with the dropper. 0.0155 g of hydroquinone monomethyl ether is weighed as a polymerization inhibitor and added to the reaction. The agitation is stopped when the hydroquinone monomethyl ether is completely dissolved. Analysis by HPLC (high performance liquid chromatography) yielded 314.2 g (quantity purity 48.8%, yield 96.2%) of N-methylol acrylamide solution without methylenebisacrylamide.

Example 3

In a 500 ml four-necked flask equipped with a stirrer, a thermometer, and a pH meter, 55 g of 89% crystalline paraformaldehyde and 150 g of water are completely dissolved while stirring, and the pH is adjusted to 9.54 with 50% sodium hydroxide solution. Maintain the reactor internal temperature at 42 ° C. in a water bath and add 113 g of crystalline acrylamide. The reaction is carried out for 2 hours while maintaining the reactor internal temperature at 40 ~ 44 ℃. After the reaction, 35% hydrochloric acid was added dropwise with the dropper to adjust the pH to 6.52. As a polymerization inhibitor, 0.0129 g of 2,6-di-t-butylcatechol is weighed and added to the reaction. The stirring is stopped when 2,6-di-t-butylcatechol is completely dissolved. The reaction solution was cooled to 25 ° C and analyzed by HPLC (high performance liquid chromatography) to obtain 317.1 g of N-methylol acrylamide solution (purity 48.7%, yield 96.1%) in which methylene bisacrylamide was not produced.

Example 4

In a 500 ml four-necked flask equipped with a stirrer, a thermometer and a pH meter, 55 g of 89% crystalline paraformaldehyde and 80 g of water were completely dissolved while stirring, and the pH was adjusted to 9.78 with 50% sodium hydroxide solution. Maintain the reactor internal temperature at 45 ° C. in a water bath and add 113 g of crystalline acrylamide. The reaction is carried out for 2 hours while maintaining the reactor internal temperature at 44 ~ 47 ℃. After the reaction, 35% hydrochloric acid was added dropwise with the dropper to adjust the pH to 6.74. As a polymerization inhibitor, 0.0146 g of hydroquinone was weighed and added to the reaction. The agitation is stopped when the hydroquinone is completely dissolved. The reaction is transferred to a vacuum distillation apparatus and the flask inside is kept at 55 ° C. in a water bath. Concentration was carried out at a vacuum degree of 15 mmHg, and when the distillate was about 50 mL, the concentration was stopped. The concentrate was cooled to 2 ° C and filtered to obtain 79.2 g (yield 49.1%) of crystalline N-methylol acrylamide. Analysis by HPLC (high performance liquid chromatography) gave a purity of 99.9%. The distillate and filtrate are collected and reused as the next reaction solvent.

Example 5

128.6 g (79.8% yield) of crystalline N-methylol acrylamide was obtained in the same manner as in Example 4 except that the distillate and filtrate collected in Example 4 were used instead of water. Analysis by HPLC (high performance liquid chromatography) gave a purity of 99.8%.

The present invention can produce a high yield of N-methylol acrylamide without any methylenebisacrylamide produced under acidic conditions when reacted with acrylamide by alkalizing a weakly acidic formaldehyde solution. In addition, since no side reactions are generated, wastewater is not generated by reusing the filtered mother liquor when preparing N-methylol acrylamide of crystals, which is economically advantageous.

The amount of catalyst used is considerably economically advantageous with the use of hydroxides of alkali metals and alkali earth metals or salts of alkali metals and alkali earth metals which are inexpensive and inexpensive. The production process was simplified by alkalizing the slightly acidic formaldehyde solution to react with acrylamide to produce high yield, high purity N-methylol acrylamide.

N-methylol acrylamide derivatives can be synthesized by reacting with alcohols by preparing a high purity N-methylol acrylamide solution.

Claims (12)

Method for preparing N-methylol acrylamide solution comprising reacting a weakly acidic formaldehyde solution in an aqueous solvent with an alkali catalyst and then reacting it with acrylamide in an alkaline state The method according to claim 1, wherein the pH of the weakly acidic formaldehyde solution is selected to be adjusted to 8-11, preferably 8.5-10.5. Method according to claim 1 wherein the hydroxide of alkali metal and alkaline earth metal or the salt of alkali metal and alkaline earth metal as an alkali catalyst Formaldehyde or paraformaldehyde as a starting material in claim 1 is selected from 0.8 to 1.4 moles, preferably 0.9 to 1.2 moles based on acrylamide Method of selecting a reaction temperature of 20 to 60 ℃, preferably 30 to 50 ℃ in claim 1 When the polymerization inhibitor is added in the alkaline solution state, oxidation occurs and the color of the N-methylol acrylamide solution is changed so that the pH is adjusted to 6.0-8.0, preferably 6.0-7.0 after completion of the reaction to prevent this. -Methylol Acrylamide Method according to claim 6 selected from hydroquinone, hydroquinone dimethyl ether, hydroquinone monomethyl ether, phenothiazine, sodium nitrite, 2,6-di-t- butylcatechol, couferon and the like as a polymerization inhibitor Method according to claim 6 in which the amount of the polymerization inhibitor is selected from 20 to 100 ppm, preferably 30 to 70 ppm, based on the weight of N-methyrol acrylamide. Method for producing N-methylol acrylamide of crystals comprising vacuum concentration of N-methylol acrylamide solution and cooling and separating Method according to claim 9 wherein the concentration of N-methylol acrylamide solution is selected from 60 to 80%, preferably 70 to 75% Method of selecting a range of vacuum degree 5 ~ 50mmHg at concentration under reduced pressure in claim 9 Method of selecting a concentration temperature of 40 ~ 75 ℃, preferably in the range of 55 ~ 65 ℃ in claim 9