JP4285035B2 - Purification method of acrylamide alkanesulfonic acid - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method for purifying acrylamide alkanesulfonic acid. More specifically, an acrylamide that does not contain impurities that inhibit polymerization can be produced by copolymerizing such or a salt thereof with acrylamide or the like so that a high molecular weight copolymer can be used as a polymer flocculant or the like. The present invention relates to a purification method for obtaining alkanesulfonic acid.
In the present specification, among acrylamide alkanesulfonic acids, the production amount is the largest, and 2-acrylamido-2-methylpropanesulfonic acid, which is a representative example thereof, is referred to as ATBS.
[0002]
Conventionally, in order to purify ATBS, as described in columns 1-2 of JP-B-56-53306 (hereinafter referred to as Patent Document 1), the moisture content of ATBS is 3 to 80% by mass. A method of recrystallization after dissolving in a hydrous acetic acid solution under heating is used. Moreover, the method of recrystallizing using water as a solvent is described in the claim of Unexamined-Japanese-Patent No. 3-125037 (henceforth patent document 2). Further, in the claims of JP-A-5-163235 (hereinafter referred to as Patent Document 3), a method of washing crude ATBS crystals with acrylonitrile containing a certain amount of moisture is described.
[0003]
However, in the method described in Patent Document 1, acetic acid is required as a solvent for dissolving ATBS, and naturally, a step of removing 100% of this acetic acid is necessary (the acetic acid that is not removed is an impurity). Further, there was a problem that the yield (yield) of purified ATBS was small. Similarly, in the method described in Patent Document 2, there is a problem of yield (yield), and there is also a problem of consuming a large amount of energy to execute a process for evaporating water. . On the other hand, the method described in Patent Document 3 has a problem that a large amount of acrylonitrile is required for cleaning.
[0004]
[Problems to be solved by the present invention]
A general method for producing acrylamide alkanesulfonic acid is a method in which acrylonitrile is subjected to an addition reaction between sulfuric acid and an olefin. According to this method, acrylamide alkanesulfonic acid in a powder state is obtained, and it is predicted that a small amount of by-products such as sulfuric acid, olefin, or organic sulfone compound is contained in the powder. .
As a raw material for producing a copolymer having a high molecular weight to such an extent that it can be used as, for example, a polymer flocculant, the present inventors do not necessarily use the acrylamide alkanesulfonic acid and the salt thereof thus produced. It has been found that there is a drawback that it may not be acceptable.
As a result, it has been recognized that there is an urgent need to improve the method for purifying acrylamide alkanesulfonic acid produced by the method according to the prior art.
[0005]
Therefore, the problem to be solved by the present invention is not accompanied by various problems such as the ATBS purification method described in Patent Documents 1 to 3, etc., and with simple equipment, processes, and operations. It is another object of the present invention to provide a method capable of purifying acrylamide alkanesulfonic acid at higher speed and higher efficiency.
[0006]
The basic technical idea of the present invention, the aqueous solution of crude acrylamide alkanesulfonic acid, in addition to acrylonitrile which is an organic solvent having a property of an azeotrope with water, in under a constant pressure, by azeotropic distillation of water and acrylonitrile Then, by gradually removing the water in the distillate and replacing the reaction medium from water to acrylonitrile , the impurities contained in the crude acrylamide alkane sulfonic acid are dissolved in acrylonitrile, and as solid crystals in the reaction liquid dispersed, acrylamide alkanesulfonic acid powder, and filtered, it is to separate acquisition.
This basic technical idea can be rephrased as follows.
That is, the present invention distills an aqueous solution of crude acrylamide alkanesulfonic acid in the presence of acrylonitrile to azeotropically distill acrylonitrile and water to remove moisture, and the crystals of acrylamide alkanesulfonic acid are in acrylonitrile. This is a method for purifying acrylamide alkanesulfonic acid, which has a step of filtering the dispersion after obtaining a dispersion dispersed therein.
The azeotropy employed in the present invention means that when a mixture of two or more liquids is distilled under a constant pressure, the boiling point is reached at a certain temperature, and the composition of the mixture and the composition of the vapor coincide with each other. It is a phenomenon that behaves as if it is a single substance (this is called an azeotrope).
The function that this azeotropic phenomenon is responsible for in the present invention is:

It is.
Hereinafter, the present invention will be described in more detail.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
First, the crude acrylamide alkanesulfonic acid to be purified in the present invention will be outlined. The crude acrylamide alkanesulfonic acid in the present invention is not particularly limited. Of course, although not limited by the production method, since acrylamide alkanesulfonic acid is produced by the method described below on an industrial scale, the crude acrylamide alkanesulfonic acid obtained by such a method is used in the present invention. This is a representative example of the purification target.
[0008]
As described above, acrylamide alkanesulfonic acid is produced by addition reaction of acrylonitrile, sulfuric acid and olefin. As olefin, isobutylene, ethylene, propene, butene, pentene, hexene and the like can be used, and the chemical structure of the alkane portion in the acrylamide alkanesulfonic acid obtained is determined depending on the type of olefin used. The preferred olefin is isobutylene and the acrylamide alkane sulfonic acid obtained when it is used is 2-acrylamido-2-methylpropane sulfonic acid or ATBS.
[0009]
The above addition reaction is an equimolar reaction with each other. Acrylonitrile serves as a reaction solvent and is used in large amounts for that purpose. In this reaction, if water is present in the system, it may cause a side reaction, which is not preferable. It is desirable that none of the raw materials contain moisture. Moreover, as a sulfuric acid to be used, general concentrated sulfuric acid or fuming sulfuric acid is preferable, but a mixture thereof is more preferable because it does not contain moisture and is easy to handle. It is desirable that the iron content in sulfuric acid is as low as possible. When the iron content exceeds 20 ppm, there is a problem that the resulting acrylamide alkanesulfonic acid is colored.
[0010]
As the reaction proceeds, a slurry in which solid crystalline acrylamide alkanesulfonic acid is dispersed in acrylonitrile is obtained, and the acrylamide alkanesulfonic acid powder can be taken out by filtering the slurry. Generally, as the slurry, a slurry having a solid content concentration of about 15 to 25% by mass is obtained.
[0011]
By subjecting such slurry to filtration or filtration / washing / filtration, a crude acrylamide alkanesulfonic acid cake is obtained. The cake is subsequently dried to obtain crude acrylamide alkanesulfonic acid crystals. In the present invention, the crude acrylamide alkanesulfonic acid powder obtained in this way is the subject of purification.
[0012]
Next, the purification process according to the gist of the present invention will be described.
The crude acrylamide alkanesulfonic acid obtained in the solid state dissolves it in water. By making it into an aqueous solution, impurities contained in the solid crude acrylamide alkanesulfonic acid are also dissolved in the aqueous solution. The amount of water used for dissolving the crude acrylamide alkanesulfonic acid is preferably as small as possible from the viewpoint of easy removal of water by distillation, specifically, the solid content concentration is 40 to 60% by mass. Amount (near saturated aqueous ATBS concentration) is preferred.
[0013]
In the present invention, an aqueous solution of crude acrylamide alkanesulfonic acid is distilled in the presence of an organic solvent that azeotropes with water (hereinafter sometimes referred to as an azeotropic solvent), and water is removed by the process. The system pressure during distillation may be normal pressure or reduced pressure. The organic solvent preferably has a low solubility in acrylamide alkanesulfonic acid in addition to having an azeotropic property with water, and examples of the organic solvent include acrylonitrile, benzene, toluene, xylene, and methacrylonitrile. It is done. Acrylonitrile is preferred in that no new impurities are added to the acrylamide alkanesulfonic acid.
[0014]
During the distillation, the ratio of the aqueous solution of the crude acrylamide alkanesulfonic acid and the azeotropic solvent is not particularly limited, but basically, the azeotropic solvent is always present in the distillation can during the distillation period. Is preferred and rather necessary. The preferred initial charge of the azeotropic solvent is 0.5 to 10 times the volume of the aqueous solution.
[0015]
Since the amount of the azeotropic solvent in the can liquid gradually decreases with the azeotropic distillation, it is usually necessary to add the azeotropic solvent to the can liquid during the distillation. At this time, it is economical to return the azeotropic solvent distilled together with water to the can and reuse it, and it is more preferable to continuously return the azeotropic solvent to the can.
When acrylonitrile is used as the azeotropic solvent, the stoichiometric composition of the azeotrope with water is 13% water and 87% acrylonitrile, and its boiling point at atmospheric pressure is 71 ° C.
[0016]
In the distillation, for the purpose of preventing the polymerization of acrylamide alkanesulfonic acid, it is desirable to maintain a certain amount of dissolved oxygen by an operation such as blowing air into the distillation can.
It is also preferable to use a polymerization inhibitor in combination, and examples of the polymerization inhibitor include hydroquinone, t-butyl hydroquinone and hydroquinone monomethyl ether, among which hydroquinone monomethyl ether is particularly preferable. A preferable addition amount of the polymerization inhibitor is 500 ppm or less, more preferably 100 ppm or less, based on acrylamide alkanesulfonic acid. When it exceeds 500 ppm, there is a problem that the polymerization inhibiting effect is improved and the polymerizability of the obtained acrylamide alkanesulfonic acid is lowered.
[0017]
As described above, water is gradually removed from the can liquid as the distillation proceeds. Distillation is stopped when at least 90% of the water in the can is removed, preferably when the water is substantially zero. By doing so, the can liquid is converted into a dispersion liquid in which acrylamide alkanesulfonic acid powder is dispersed in an azeotropic solvent. By filtering the dispersion thus obtained using a known filtration means, it is possible to obtain a high-purity acrylamide alkanesulfonic acid powder from which impurities are removed on the filtrate side. The purified acrylamide alkanesulfonic acid has high polymerizability, and is suitably used as a polymer flocculant by copolymerizing such acrylamide alkanesulfonic acid or its sodium salt with acrylamide or the like. A high molecular weight water-soluble copolymer can be obtained.
[0018]
As a means for evaluating the polymerizability of the acrylamide alkanesulfonic acid powder, after converting it to a sodium salt, the sodium salt and acrylamide are copolymerized in an aqueous solution, and the aqueous solution viscosity of the resulting polymer (for example, Brookfield) A method of measuring an aqueous solution viscosity measured using a type viscometer is simple. When the viscosity is measured under certain conditions, the higher the viscosity obtained, the higher the molecular weight of the polymer dissolved in the solution. Furthermore, it can be evaluated that acrylamide alkane sulfonic acid that gives a polymer having such a large molecular weight is highly polymerizable. The measurement conditions of the Brookfield viscometer are that the rotor rotational speed is 60 rpm and the temperature is about 25 ° C.
[0019]
Such purified acrylamide alkanesulfonic acid can also be obtained by other purification methods, for example, a recrystallization method using an acetic acid addition method, a recrystallization method using a difference in solubility in water, and the present invention is as follows. There is a remarkably superior effect that surpasses these conventional methods.
I. First, the operation is extremely simple.
B. High yield.
C. Good reproducibility.
[0020]
Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. In the following description, “%” is “% by mass”.
The crude ATBS used in each example was synthesized by the following operation.
[0021]
Crude ATBS synthesis process (hereinafter sometimes referred to as pre-process)
Two reactors equipped with a stirrer, an inlet pipe and an outlet pipe are connected, acrylonitrile and fuming sulfuric acid are introduced into the first reactor under the following conditions, acrylonitrile and fuming sulfuric acid are mixed, and this mixture To the second reactor. Isobutylene gas was continuously introduced into the second reactor to carry out the reaction continuously.
[0022]
The amount of acrylonitrile supplied per mole of fuming sulfuric acid (sulfur trioxide content: 9%) was 11 mol, and the amount of isobutylene supplied was 0.9 mol. The temperature of the first reactor was maintained at -5 to -15 ° C, the residence time was 10 minutes, the temperature of the second reactor was maintained at 30 to 50 ° C, and the residence time was 40 minutes.
[0023]
The ATBS slurry produced by the above process was filtered through a glass filter, and the crude ATBS cake on the filter was washed by flowing down twice the amount of acrylonitrile. The solid obtained through these steps was dried to obtain crude ATBS.
[0024]
Next, polymerization evaluation of the crude ATBS obtained by the above method was performed. First, 63.2 g of ATBS was slowly added to 76.4 g of 16% sodium hydroxide aqueous solution and dissolved, and then pure water was added to adjust the total weight to 200 g, thereby obtaining a 35% ATBS sodium aqueous solution. 136.5 g of this solution and 55.6 g of 40% acrylamide aqueous solution were mixed, and 5.2 g of water was further added.
[0025]
After replacing the above aqueous solution with nitrogen, 0.7 g of 1% ammonium persulfate water, 0.7 g of 1% sodium sulfite water, 0.6 g of an aqueous copper chloride solution containing 10 ppm of copper ions, and V-50 (Wako Pure Chemical Industries, Ltd.) 0.7 g of a 10% aqueous solution of diazo radical polymerization initiator (manufactured by Co., Ltd.) was added, polymerization was started at 30 ° C., and a copolymer was produced in 2 hours.
[0026]
When 1.15 g of the obtained copolymer was dissolved in 393 g of water and the viscosity was measured under the following conditions, the viscosity was 3.1 mPa · s. The measurement conditions are as follows.
Viscometer used: Brookfield digital viscometer rotor rotation speed: 60 rpm
Temperature of aqueous solution: 25 ° C
[0027]
【Example】
A stirrer, a nitrogen / oxygen mixed gas supply pipe, and a condenser were set in a 1 liter round bottom flask. 100 g of crude ATBS obtained by the above operation and 82 g of pure water were added to a flask, and solid crude ATBS was dissolved to produce an ATBS aqueous solution. Acrylonitrile (500 g) and hydroquinone monomethyl ether (50 mg) were added, and stirring was started. Nitrogen / oxygen mixed gas supply was started, the bath temperature was set to 60 ° C., the degree of vacuum was set to 160 mmHg, and azeotropic distillation was started. During the distillation, the flask was replenished with 500 g of acrylonitrile every 20 minutes. The fraction was allowed to stand, the amount of water removed from the reactor was weighed, and distillation was terminated when 80 g of water was recovered. The time required for distillation was 90 minutes.
[0028]
The obtained ATBS / acrylonitrile slurry was filtered, washed with acrylonitrile and dried in the same manner as in the previous step to obtain 93 g of ATBS with a yield of 93%. As a result of evaluating the polymerizability in the same manner, the solution viscosity was 3.9 mPa · s.
[0029]
Since the solution viscosity of unpurified ATBS measured under the same conditions was 3.1 mPa · s as described above, it was clear that the polymerizability of ATBS obtained by purification using this example was improved. It is.
[0030]
[Comparative example]
Methyl alcohol (749 g) was added to the crude ATBS (157 g) obtained in the previous step and heated to 50 ° C. to dissolve the crude ATBS. The resulting solution was slowly cooled to room temperature and then left in the refrigerator overnight.
The obtained crystals were filtered through a glass filter, washed with cooled methyl alcohol at the same magnification as the crystals, suction filtered again, and dried under reduced pressure to obtain purified ATBS. The yield was 55%. As a result of evaluating the polymerizability of the obtained purified ATBS, the solution viscosity was 4.0 mPa · s.
[0031]
As is clear from the comparison between the above examples and comparative examples, according to the comparative example which is a prior art, purified ATBS having excellent polymerizability can be obtained, but the yield is significantly inferior to that of the present invention. .
[0032]
【The invention's effect】
According to the present invention, acrylamide alkanesulfonic acid having a small content of impurities that inhibit polymerization can be obtained by a simple operation and with a high yield. When the purified acrylamide alkanesulfonic acid obtained by the present invention (or a salt thereof) is copolymerized with another water-soluble monomer such as acrylamide, a polymer having an extremely large molecular weight can be obtained. It can be preferably used as a polymer flocculant or the like.

Claims (2)

By distilling an aqueous solution of crude acrylamide alkanesulfonic acid in the presence of acrylonitrile,
Acrylonitrile and water are azeotropically distilled to remove moisture,
After obtaining a dispersion in which crystals of acrylamide alkanesulfonic acid are dispersed in acrylonitrile,
A method for purifying acrylamide alkanesulfonic acid, comprising filtering the dispersion . 2. The method for purifying acrylamide alkanesulfonic acid according to claim 1 , wherein acrylonitrile evaporated and distilled with water in the distillation step is returned to the distillation apparatus and repeatedly used as an azeotropic solvent with water. .