JPH0678284B2 - Method for producing N-methyl acrylamide - Google Patents

Description

TECHNICAL FIELD The present invention relates to the production of N-methylolacrylamide.

N-methylol acrylamide can be homopolymerized or copolymerized with other vinyl monomers, and can be widely applied to the application fields of water-soluble or hydrophilic polymers.

[Conventional technology]

N-methylol acrylamide can be obtained by methylating acrylamide with formaldehyde in the presence of a basic catalyst such as sodium hydroxide or organic amine.

Specifically, a method of obtaining N-methylolacrylamide as an aqueous solution using an aqueous formaldehyde solution as in the method described in US Pat. No. 2,173,005, or reacting acrylamide with paraformaldehyde in an organic solvent to produce N-methylolacrylamide
There is a method of taking out methylol acrylamide as crystals, and a solventless method in which acrylamide and paraformaldehyde are melted and reacted in the presence of an organic amine without using a solvent like the method described in US Pat. No. 2,864,861.

[Problems to be solved by the invention]

However, in any of the above methods, the content of N, N'-methylenebisacrylamide is usually 20 ppm or more based on the weight of the amide group-containing monomer, and therefore, as it is, it has a sufficiently high molecular weight and water-soluble heavy weight. It could not be used as a raw material for coalescence.

An object of the present invention is to provide a method for producing an N-methylol acrylamide monomer that does not contain a cross-linking substance and the like, rather than acrylamide and foraldehyde.

[Means for solving problems]

N-methylol acrylamide is obtained as an addition reaction product from acrylamide and formaldehyde in the presence of a basic catalyst.

On the other hand, N, N'-methylenebisacrylamide, which is a crosslinkable substance, is produced under acidic conditions.

Generally, commercially available formaldehyde aqueous solution is produced mainly by oxidation of methanol at high temperature, but when it is absorbed in water, a small amount of formic acid is always produced as a by-product, so that it is made into a product through an ion exchange resin.

However, about 300-800 ppm of formic acid remains in the product, relative to the weight of formaldehyde, and increases further during storage.

The present inventors have studied the action of formic acid in formaldehyde, and as a result, although the reaction for producing N-methylolacrylamide is carried out in the presence of a basic catalyst, N, N′-methylenebisacrylamide still remains. I decided to generate it. As a result of further studies based on such findings, the present inventors have found that formaldehyde and acrylamide substantially free of formic acid are used to obtain N-methylolacrylamide free of N, N′-methylenebisacrylamide. The inventors have found that the object of the present invention can be achieved by contacting them in the presence of a basic catalyst, and have completed the present invention.

In the present invention, formaldehyde containing substantially no formic acid is used, but the smaller the content of formic acid, the more preferable, and the content is 100 ppm or less based on the weight of formaldehyde.

Formaldehyde substantially free of formic acid can be obtained, for example, by heating paraformaldehyde to 150 ° C. and dissolving the generated formaldehyde in cold water. Alternatively, formaldehyde may be supplied to the reaction system in a gaseous form. However, this object can be easily achieved by a simple operation in which the formic acid in the aqueous formaldehyde solution is previously neutralized with a base and used as a formate salt.

As the base used in this case, any general basic compound can be used. Alkali metals, alkaline earth metals, hydroxides such as quaternary ammonium, tertiary amines, weakly basic salts consisting of strong bases and weak acids, etc., using the same base as the base catalyst used in the reaction. Is also good.

For neutralization, it is desirable to add the same amount of base as formic acid. Further, in order to avoid the formation of formic acid by the Cannizzaro reaction as much as possible, the temperature at the time of neutralization is preferably low, and it is desirable to carry out the neutralization reaction at 25 ° C. or lower and use it immediately.

The acrylamide used in the present invention is usually used as an aqueous solution within the range of 10% by weight to a saturated solution.

The concentrations of formaldehyde and acrylamide in the present invention are appropriately combined and used so that the reaction system after contact is a uniform aqueous solution. When the aqueous solution of the obtained reaction product has a high concentration, it is cooled to cool N-methylol. It is also possible to extract acrylamide as crystals.

The ratio of formaldehyde used in the reaction to acrylamide is in a wide range of 0.1 to 5 times mol.

As a catalyst for the reaction of acrylamide and formaldehyde, any of the common basic compounds can be used. Specifically, the same basic compound as the above-mentioned base used for neutralizing formic acid in formaldehyde, and an ion exchange resin that acts strongly or weakly basic are used.

The amount of the basic compound used as a catalyst for the reaction varies depending on the basicity thereof, and is adjusted depending on the pH of the reaction system. If the pH of the reaction system is low, the reaction rate will be slow, and if it is too high, water decomposition reaction such as acrylamide will occur. Therefore, usually pH 8-12,
It is preferably added and used so as to have a pH range of 9 to 10.5.

Reaction temperature of acrylamide and formaldehyde is 10 ~ 90
The temperature can be selected from a wide range of 0 ° C, but it is preferably in the range of 10 to 50 ° C from the viewpoint of suppressing side reactions.

The formation of N, N'-methylenebisacrylamide is very slow under basic conditions, but it gradually forms during long-term storage, so after the methylolation reaction is completed, the basic compound used as a catalyst is promptly added. It is desirable to neutralize.

When neutralizing the basic compound of the catalyst, any common acidic compound can be used. For example, it is a mineral acid, an organic acid, a weak acid salt consisting of a strong acid and a weak base, and the like, but it is desirable to use a buffer solution using a weak acid or a weak acid salt.

The reaction method of acrylamide and formaldehyde can be carried out by using any reaction apparatus according to various conventionally known formats, but a preferable reaction method is to charge the acrylamide aqueous solution and the catalyst in a stirring tank, and substantially stir under stirring. This is a method of dropping an aqueous formaldehyde solution containing no formic acid.

〔Example〕

Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof.

Example 639.7 g (4.5 mol) of 50 wt% acrylamide aqueous solution and 11.7 ml of 0.1 N sodium hydroxide aqueous solution were placed in a 4-necked flask equipped with a stirrer, a cooling tube and a thermometer.
It was immersed in a constant temperature water bath at 0 ° C. The pH in the container was 11.6.

Into a 500 ml beaker, 310.4 g (3.83 mol) of 37% by weight aqueous formaldehyde solution was added, and the pH was adjusted to 7 by neutralizing formic acid with 0.1 N aqueous sodium hydroxide solution with stirring. The sodium hydroxide aqueous solution required for neutralization was 10.8 ml, and contained 416 ppm of formic acid based on the weight of formaldehyde.

While stirring the inside of the flask at a speed of 125 rpm, use the dropping funnel to add the formaldehyde solution that has been subjected to the above neutralization treatment.
It was dripped in 10 minutes. The pH in the reaction system was 9.7. An exotherm of about 2 ° C was observed with the dropping.

After reacting at 30 ° C for 4 hours, the production rate of N-methylolacrylamide measured by liquid chromatography was 75.6mo.
The content of N, N'-methylenebisacrylamide was 0.1 ppm or less based on the weight of the monomer.

When residual formaldehyde was measured, it was 4.7 mol% with respect to the charged acrylamide monomer, and the selectivity of formaldehyde to N-methylolacrylamide was 94.6%.
It was.

Neutralize this reaction mixture with M / 10 sodium dihydrogen phosphate to 1
7.8 g was placed in a 50 ml sealed tube, and 11.75 g of demineralized water and 0.45 g of an aqueous solution of 1% by weight N, N'-azobis- (2-amidinopropane) dihydrochloride as a polymerization catalyst were added to make a total amount of 30 g.

The inside of the sealed tube was sufficiently replaced with nitrogen gas, and the tube was sealed and then polymerized in a constant temperature water bath at 50 ° C. for 4 hours to obtain 25% by weight of a water-soluble gel. The polymerization rate was 99.1%, and the reduced viscosity measured with an Ostwald viscometer at 25 ° C. after dissolution in 1N saline at a concentration of 0.1 g / dl was ηsp / C = 14.8.

Comparative Example 639.7 g (4.5 mol) of 50 wt% acrylamide aqueous solution in a 4-necked flask equipped with a thermometer under stirring and a thermometer.
And add 22.5 ml of 0.1N sodium hydroxide solution,
It was immersed in a constant temperature water bath at ℃. The pH in the container was 12.2.
While stirring at a rate of 125 rpm, 310.4 g (3.83 mol) of an unneutralized 37% by weight formaldehyde aqueous solution was added dropwise using a dropping funnel in about 10 minutes. The pH in the reaction system was 9.7. An exotherm of about 2 ° C was observed with the dropping.

After reacting at 30 ° C for 4 hours, the production rate of N-methylolacrylamide measured by liquid chromatography was 75.7mo.
%, and the content weight of N, N′-methylenebisacrylamide was 41 ppm with respect to the weight of the amide group-containing monomer.

The residual formaldehyde was 4.7 mol% based on the charged acrylamide monomer, and the selectivity of formaldehyde to N-methylolacrylamide was 94.6%.

After neutralizing the reaction solution with M / 10NaH ₂ PO ₄ , 17.8 g was placed in a 50 ml sealed tube, 11.75 g of demineralized water, and 1% by weight of N, N′-azobis- (2-amidinopropane) as a polymerization catalyst.
0.45 g of an aqueous solution of dihydrochloride was added to make the total amount 30 g. The inside of the sealed tube was sufficiently replaced with nitrogen gas, sealed, and then polymerized in a constant temperature water bath at 50 ° C. for 4 hours to obtain a water-insoluble gel.

〔The invention's effect〕

According to the method for producing N-methylol acrylamide of the present invention, highly pure N-methylol acrylamide containing no cross-linking substance such as N, N'-methylene bis acrylamide can be obtained. It is possible to obtain a water-soluble polymer having an extremely high molecular weight, which largely contributes to the application field of the water-soluble polymer such as a flocculant and a paper-making agent.

Claims (2)

[Claims] 1. A method for producing N-methylolacrylamide, which comprises contacting formaldehyde having a formic acid concentration of 100 ppm or less with acrylamide in the presence of a basic catalyst. 2. The production method according to claim 1, wherein the formic acid in formaldehyde is neutralized in advance to be converted into a formate salt, and then the reaction is carried out.