JPH0539251A - Production of crystalline n-methylolacrylamide - Google Patents

Abstract

(57) [Abstract] [Purpose] Highly pure crystalline N-methylol was obtained from the methylation reaction using an industrially obtained aqueous acrylamide solution directly without using a highly concentrated aqueous acrylamide solution or crystalline acrylamide as a raw material. An object of the present invention is to provide a method capable of obtaining luacrylamide in high yield. [Structure] An aqueous acrylamide solution having a concentration of 30 to 50% is reacted with formaldehyde or paraformaldehyde in the presence of a basic catalyst, the reaction solution is concentrated under reduced pressure, and then separated by crystallization.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing crystalline N-methylolacrylamide. N
-Methylol acrylamide is a cross-linking monomer widely used for fiber treatment, photosensitive resin, adhesives, paints and the like.

[0002]

2. Description of the Related Art Various methods have been conventionally known for producing crystalline N-methylolacrylamide.
For example, a method of reacting an aqueous solution of acrylamide having a concentration of 60 to 97% with formaldehyde in an aqueous solvent using an alkali catalyst and then cooling and crystallization from the reaction solution (Japanese Patent Publication No. 38-15358). A method of reacting with a tertiary amine such as triethylamine or triethanolamine as a catalyst in the absence of a solvent to solidify the reaction liquid by cooling (Japanese Patent Publication No. 35-35-
4208), or a method of reacting with a basic anion exchange resin as a catalyst in an organic solvent and cooling and crystallization from the reaction solution (JP-A-49-14418 and JP-A-49-36615). Is proposed.

As described above, in the conventional method, a high-concentration acrylamide aqueous solution or crystalline acrylamide is used for the reaction with formaldehyde, and the obtained reaction product is cooled to obtain crystalline N-methylolacrylamide. .. Therefore, as the acrylamide used in the above method, a 40-50% acrylamide aqueous solution obtained by an industrial method such as a catalytic hydration method or a microbial hydration method is concentrated or crystallized to obtain a high-concentration acrylamide aqueous solution or crystalline acrylamide. There is a need. However, since acrylamide is a monomer having a very high polymerizability, there is a great risk that the acrylamide polymerizes when concentrated or crystallized to obtain a high-concentration liquid or crystals. Further, since acrylamide is toxic, crystalline acrylamide, which is easily scattered, is difficult to handle. Furthermore, since these high-concentration or solvent-free methods do not sufficiently suppress the production of by-products in the reaction, the by-products are accumulated in the reaction solution and the crystalline N
-Methylolacrylamide is contaminated with by-products, resulting in a marked decrease in product purity. In addition, N obtained by these methods
In the methylol acrylamide crystals, the crystal grain size is not uniform and there are many fine crystals, so that the attached mother liquor increases and the crystal purity decreases. A complicated purification step is required to obtain highly pure crystalline N-methylolacrylamide. Furthermore, in the method using an organic solvent, a large amount of toxic or flammable organic solvent is used, and a facility for recovery and purification of the used organic solvent is required. There was a problem to be improved.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a methylosilane directly using an industrially obtained acrylamide aqueous solution without using a high-concentration acrylamide aqueous solution or crystalline acrylamide as a raw material of acrylamide.
The object of the present invention is to provide a method for producing crystalline N-methylolacrylamide, which enables highly pure crystalline N-methylolacrylamide to be obtained in a high yield from a sulfation reaction.

[0005]

According to the present invention, an acrylamide aqueous solution having a concentration of 30 to 60% is reacted with formaldehyde or paraformaldehyde in the presence of a basic catalyst, and then the reaction solution is heated at a temperature of 80 ° C. or lower and a pH of 6 or less. The present invention relates to a method for producing crystalline N-methylol acrylamide, which comprises concentrating under reduced pressure under the conditions in the range of 8 and then performing crystallization separation.

The present invention will be specifically described below. The acrylamide aqueous solution as a starting material used in the present invention may be one obtained by either a catalytic hydration method or a microbial hydration method, and may have an acrylamide concentration of 30 to 60%. Further, formaldehyde is preferably an aqueous solution,
Commercially available 37% formalin can be used. Paraformaldehyde may also be commercially available with a purity of 70 to 95%.

The use ratio of acrylamide and formaldehyde or paraformaldehyde in the present invention is 0.5 to 2 mol, preferably 0.8 to 1.5 mol of formaldehyde or paraformaldehyde (in terms of formaldehyde) per mol of acrylamide. The range is good.

The basic catalyst which can be used in the present invention includes alkali or alkaline earth metal hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, calcium hydroxide and barium hydroxide. , Sodium carbonate, potassium carbonate, trisodium phosphate, disodium phosphate, sodium pyrophosphate,
Alkali or alkaline earth metal salts such as tripotassium phosphate, dipotassium phosphate, sodium borate, sodium aluminate and sodium silicate, triethylamine, triethanolamine, N-ethylmorpholine and N, N-diethylhydroxylamine. Amines, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, trimethylbenzylammonium hydroxide, cetylethyldimethylammonium hydroxide, cetyldimethylbenzylammonium hydroxide, hexahydrate Quaternary ammonium hydroxide compounds such as decyltrimethylammonium, trioctylmethylammonium hydroxide and cetylpyridinium hydroxide, sodium alcohol Metal alkoxides such as Sid and potassium ethoxide, Amberlite IRA 400,
Examples thereof include strong basic anion exchange resins such as Amberlyst A26. Two or more kinds of these basic catalysts can be mixed and used.

The amount of basic catalyst used in the present invention is
It is selected from the range of 0.001 to 10 mol%, preferably 0.01 to 8 mol% relative to 1 mol of acrylamide.

By adding molybdenum oxyacid salt or tungsten oxyacid salt to the basic catalyst used in the present invention, the selectivity of the catalyst can be further improved.

Examples of molybdenum oxyacid salts include lithium molybdate, sodium molybdate, potassium molybdate, lithium phosphomolybdate, sodium phosphomolybdate, lithium silicate molybdate and sodium silicate molybdate.

As the tungsten oxyacid salts,
Lithium tungstate, sodium tungstate,
Mention may be made of potassium tungstate, lithium phosphotungstate, sodium phosphotungstate, lithium silicotungstate and sodium silicotungstate. These molybdenum oxyacid salts or tungsten oxyacid salts may be used as a mixture of two or more kinds.

In the present invention, the molybdenum oxyacid salt or tungsten oxyacid salt added to the basic catalyst is selected from the range of 0.01 to 20 mol, preferably 0.05 to 10 mol, based on 1 mol of the basic catalyst. To be elected.

This reaction is preferably carried out at a reaction temperature of 20 to 80 ° C., preferably 30 to 60 ° C., and a pH of the reaction solution of 7 or more, preferably 8 to 12. After completion of the reaction, the reaction solution is neutralized with a mineral acid such as sulfuric acid or hydrochloric acid so that the pH of the reaction solution is in the range of 6 to 8. When the pH of the reaction solution is 6 or less, bis compounds such as methylenebisacrylamide and diacrylamide dimethyl ether are by-produced, and the product purity is significantly reduced. When the production amount of the bis form is large, when the product is polymerized, the solubility of the polymer is significantly reduced. When the pH is 8 or more, decomposition of the product and polymerization under basic conditions occur simultaneously, resulting in a marked decrease in product purity.

Concentration of the reaction solution in the present invention is performed at a reduced pressure of 10 to 300 mmHg, preferably 50 to 200 m.
It may be carried out in the range of mHg and the concentration temperature of 30 to 80 ° C, preferably 40 to 70 ° C. When the concentration temperature is 80 ° C. or higher, rapid polymerization occurs and the entire concentrate is solidified. Further, if the temperature is 30 ° C or lower, it takes a long time to concentrate. Concentration is performed with N-methylol acrylamide concentration of 70 to 90
Repeat until it reaches%. When the concentration is 70% or less, the amount of N-methylolacrylamide deposited is small, and the crystallization efficiency is remarkably deteriorated. When the concentration is 90% or more, polymerization is remarkably easy, and the entire concentrated solution is rapidly polymerized and solidified. At the time of concentration, oxygen or air is introduced into the reaction solution, and further a polymerization inhibitor is added if necessary, so that concurrent polymerization is suppressed. As the polymerization inhibitor, hydroquinone, p-methoxyphenol, 2,6-ditertiarybutylcatechol, phenothiazine, cuperone, hydroxylamine sulfate, sodium nitrite, copper chloride, copper nitrate, oxalic acid and the like are used.

Crystallization of N-methylol acrylamide in the present invention is carried out by separating the crystals precipitated during the concentration, or by cooling the concentrated solution slowly in the range of 0 to 50 ° C.
This is done by separating the precipitated crystals. The mother liquor for crystal separation is concentrated or cooled again to further crystallize N-methylolacrylamide, or is recycled for the next reaction step.

The method of the present invention becomes more industrially advantageous by making it continuous.

According to the method of the present invention, N-methylol acrylamide having a high purity and a large crystal grain size can be produced in a high yield from an acrylamide aqueous solution which is easy to handle.

By the way, it is known that N-methylolacrylamide aqueous solution is unstable, that is, impurities, especially N, N'-methylenebisacrylamide, which is a crosslinkable substance, is formed and its quality deteriorates with time. (Japanese Patent Laid-Open No. 62-175449). However, in the method of the present invention, when the reaction solution containing N-methylolacrylamide is concentrated, highly pure crystalline N-methylolacrylamide can be obtained without causing side reactions such as condensation or polymerization. Is unexpected.

[0020]

EXAMPLES The constitution and effects of the present invention will be described more specifically below with reference to examples, but the present invention is not limited to these examples. Example 1 In a 200 cc reactor equipped with a stirrer, thermometer, pH meter,
120 g of 50% acrylamide aqueous solution is added to bring the internal temperature to 50 ° C. A 10% aqueous sodium hydroxide solution is added as a catalyst to adjust the pH of the solution to 10. Then, 9
27.2 g of 5% paraformaldehyde is added, and the reaction is carried out using the catalyst solution while keeping the pH of the reaction solution at 10. The total catalyst required for the reaction was 0.03 mol% (vs acrylamide). One hour after the start of the reaction, the reaction solution was analyzed by high performance liquid chromatography to find that the production rate of N-methylolacrylamide in the reaction solution was 88.7.
% And the by-product was 0.6%. The reaction solution was neutralized to pH 7 with 1N-sulfuric acid aqueous solution, and then 100 to 15
The mixture was concentrated under reduced pressure of 0 mmHg at 50 ° C. while introducing a small amount of air into the reaction solution until the N-methylolacrylamide concentration became 80%. The resulting concentrate was slowly cooled to 10 ° C and separated by filtration.
2.5 g of crystalline N-methylolacrylamide was obtained. When analyzed by high performance liquid chromatography, the purity of N-methylolacrylamide was 96.7%.

Examples 2 to 11 Using the acrylamide concentration, catalyst, reaction conditions and crystallization conditions shown in Table 1, acrylamide was reacted with formaldehyde or paraformaldehyde in the same manner as in Example 1, and the reaction was completed. After that, the reaction solution was concentrated under reduced pressure to crystallize and separate N-methylolacrylamide.

Table 1 shows the reaction results in the above examples.

[0023]

[Table 1]

[0024]

Industrial Applicability According to the method of the present invention, highly pure crystalline N-methylolacrylamide can be easily obtained by directly using an industrially easily available acrylamide aqueous solution having a concentration of 30 to 60%. The present invention also has the following advantages. (1) Since an acrylamide aqueous solution is used, powder is not scattered, handling is easy, and safety is high. (2) There are few by-products and the purification is easy. (3) Since the amount of by-products is small, it is easy to recycle the separated mother liquor after obtaining crystalline N-methylolacrylamide. (4) Large crystals with a uniform grain size can be obtained.

Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location // C07B 61/00 300

Claims (2)

[Claims] 1. An acrylamide aqueous solution having a concentration of 30 to 60% is reacted with formaldehyde or paraformaldehyde in the presence of a basic catalyst, and then the reaction solution is added to 8
A process for producing crystalline N-methylolacrylamide, which comprises concentrating under reduced pressure at a temperature of 0 ° C. or lower and under a pH range of 6 to 8, followed by crystallization separation. 2. The process according to claim 1, wherein the basic catalyst is a catalyst containing at least one of a quaternary ammonium compound, molybdenum oxyacid salt and tungsten oxyacid salt.