JPH0651754B2 - Method for producing aqueous solution of poly-α-hydroxyacrylic acid or salt thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing poly-α-hydroxyacrylic acid or a salt thereof, and particularly to a method for producing an aqueous solution thereof.

Sodium poly-α-hydroxyacrylate (hereinafter referred to as PHA
Poly-α-hydroxyacrylic acid and salts thereof represented by S) are industrially extremely useful as sequestering agents, stabilizers for peroxides, fiber bleaching aids, detergent builders, etc. is there.

[Conventional technology]

For the production method of poly-α-hydroxyacrylate,
Various methods have already been proposed.

For example, according to JP-B-57-39249, α, β-dihalogenopropionic acid is dehydrochlorinated in the gas phase in the presence of a catalyst such as alumina, and the resulting α-chloroacrylic acid is used as a polymerization catalyst in water. To obtain a lactone type compound of poly-α-hydroxyacrylic acid (hereinafter referred to as PLAC).

Further, according to Japanese Patent Publication No. 54-5839, α-chloroacrylic acid is obtained by heating an aqueous solution of α, β-dichloropropionic acid to a temperature of 100 ° C. or higher, and polymerized with the aqueous solution. A method for obtaining PLAC by acting a catalyst is proposed.

Further, in JP-B-57-27882, a polymerization catalyst having a radical-forming effect is allowed to act on an aqueous solution of α-chloroacrylic acid, and the resulting poly-α-chloroacrylic acid is isolated for 80 hours to 100% for 1 hour or more. It proposes a method of obtaining PLAC by heating to a temperature of ° C.

As described above, in all of the conventional techniques, α-halogenoacrylic acid is polymerized in water and heated as it is to obtain polylactone (PL) insoluble in water.
AC) is obtained, and this is taken out separately. In order to obtain poly-α-hydroxyacrylic acid salt, it is necessary to dissolve this PLAC in an alkaline aqueous solution.

Thus, when an aqueous solution of poly-α-hydroxyacrylic acid salt is to be obtained by the conventional technique, the polymerization-
A multi-step process of over-melting is required, and therefore a device such as a filter vessel and a melting tank is required. Also, it has a drawback of being extremely inefficient in terms of time.

Further, as shown in Examples and Comparative Examples described later, the poly-α-hydroxyacrylate obtained by the conventional method is apt to undergo a depolymerization reaction when heated to a high temperature and has a problem in thermal stability. Have a

[Problems to be solved by the invention]

An object of the present invention is to directly obtain an aqueous solution of poly-α-hydroxyacrylate and to obtain a product having good thermal stability without going through multiple steps of polymerization-over-dissolution.

[Means for solving problems]

The present inventors have, over the years, studied a method for producing an aqueous solution of poly-α-hydroxyacrylate.

As a result, when polymerizing α-halogenoacrylic acid or a salt thereof in water, by controlling the pH during the polymerization, PLAC insoluble in water is not precipitated,
It was discovered that it is possible to directly obtain an aqueous solution of poly-α-hydroxyacrylate. Furthermore, it was surprisingly discovered at the same time that the poly-α-hydroxyacrylates synthesized according to the method of the present invention have better thermal stability than those obtained according to the prior art. The present invention has been completed.

That is, the present invention, when polymerizing α-halogenoacrylic acid or a salt thereof in water, the pH of the polymerization reaction solution, 3.
It is a method for producing an aqueous solution of poly-α-hydroxyacrylic acid or a salt thereof, which is characterized by controlling within a range of 0 to 8.0.

The α-halogenoacrylic acid or a salt thereof used in carrying out the present invention may be separately produced,
Further, as in the method described in Japanese Patent Publication No. 54-5839, α,
Thermally dehydrochlorinating β-dichloropropionic acid to give α
The present invention can also be used in a method of polymerizing while obtaining chloroacrylic acid.

Further, it can be applied to a method in which a basic substance is allowed to act on α, β-dihalogenoacrylic acid or its ester to obtain α-halogenoacrylic acid or its salt, and the resulting compound is polymerized.

The present invention is essentially to control the pH during the polymerization to be 3.0 to 8.0, but it is not always necessary to maintain a constant pH, and it is possible to temporarily deviate from the range of 3.0 to 8.0 during the polymerization reaction. Absent. However, of the total time required for polymerization, at least 2
It is necessary to maintain the pH range for 5% or more.

The pH during the polymerization is preferably in the range of 3.0 to 8.0, but it is particularly preferable to control it within the range of 4.0 to 6.0.

When the polymerization is carried out in the region where the pH is lower than 3.0, it is difficult to carry out the polymerization as it is, and especially at pH 2.0 or less, the solid matter (PLAC) is always deposited.

When polymerized in a region where pH is higher than 8.0, PH
This is disadvantageous because it causes a decrease in AS yield.

In order to maintain the pH, it is common to add an appropriate amount of acid or alkali while directly monitoring the pH with a pH meter.

As the acid used for pH adjustment, inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid and perchloric acid, and organic acids such as formic acid and acetic acid can be used, but hydrochloric acid is generally used.

As the alkali, sodium hydroxide, potassium hydroxide, sodium carbonate, sodium acetate or the like can be used, but sodium hydroxide is generally used.

The method of the present invention can be used in both batch reaction and continuous reaction.

The catalyst used for the polymerization should be a commonly used catalyst having a radical action such as persulfuric acid, hydrogen peroxide, azobisisobutyronitonyl, azobiscyanovaleric acid, benzoyl peroxide, etc. You can

The temperature at the time of polymerization may be 80 to 120 ° C, but generally 90 to
98 ℃ is good.

The poly-α-hydroxyacrylate aqueous solution obtained by the method of the present invention contains chlorides such as NaCl as a by-product, but the chlorides have a direct adverse effect on the general application. Is few. When it is necessary to remove chloride, it is also possible to remove low molecular weight substances by using an ultrafiltration membrane.

[Action]

The mechanism of action in the present invention has not been clarified yet, but can be presumed as follows.

That is, α-halogenoacrylic acid is polymerized in water.
And first polymerized in the form of poly-α-halogenoacrylic acid,
Since chlorine in the polymer skeleton is active, H
₂Cl reacts with O molecule Desorbs in the form of
It changes to poly-α-hydroxyacrylic acid. That
When the pH in water is 2.5 or less, poly-α-hydro
Xyacrylic acid undergoes lactonization reaction and is insoluble in water
It will be deposited as PLAC. pH is above 3.0
If so, PLAC formation does not proceed, and water-soluble poly-α-hydro
Xyacrylic acid or its salt.

When the polymerization is carried out at a pH of 8.5 or more, the α-halogenoacrylic acid salt is hydrolyzed before the polymerization and is transformed into a substance such as pyruvic acid, which is extremely disadvantageous in terms of yield.

The cause of the poor thermal stability of the poly-α-hydroxyacrylates produced using PLACs obtained according to the prior art as compared to those according to the process of the invention is unknown, but probably The conventional reaction is that P
It is conceivable that there are many branches and crosslinks in the polymer because the growth reaction of the polymerization occurs while LAC is precipitated as a solid form, and the branched portion is thermally weak.

In the method of the present invention, since the liquid is uniform throughout the polymerization during the polymerization, it is presumed that the polymer grows linearly and is therefore thermally stable, and the molecular weight does not decrease so much by heating. .

〔The invention's effect〕

According to the present invention, the poly-α
-It is possible to produce an aqueous solution of hydroxy acrylate, and the product obtained by this method has excellent properties as compared with the conventional method, and the present invention is industrially applicable. It is significant.

〔Example〕

 Examples of the method of the present invention are shown below.

Examples 1 to 6 and Comparative Example 1 A 500 ml five-necked flask was equipped with a stirring blade, pH electrode, thermometer, and cooler, and the flask was charged with 53.3 g (0.5 mol) of α-chloroalkyl acid and 300 ml of water. Put in and dissolve.

Separately, 0.5 g of potassium persulfate was dissolved in 20 ml of water,
The reactor was heated, and an aqueous potassium persulfate solution was added dropwise at 90 to 95 ° C. over 2 hours. Meanwhile, the pH was controlled by adding 20% NaOH so as to maintain the predetermined value shown in Table 1. After dropping potassium persulfate, keep it at a predetermined pH,
Stirring was continued at 90-95 ° C for an additional hour.

After that, the reaction solution was cooled to room temperature, an appropriate amount of 20% NaOH was added to adjust the pH to 13.0, and pure water was added to adjust the total solution weight to 500 g to prepare a PHAS solution.

Taking a part of the PHAS solution in the examples, pouring it into methanol to precipitate the polymer, separating it, and refining it by repeating this to make a dried sample, and taking an infrared spectrum, Description (Japanese Patent Publication No. Sho 54-20995)
It was in good agreement with the PHAS obtained by the method described in Japanese patent publication).

The PHAS obtained in the examples was analyzed for average molecular weight and PHAS concentration by GPC (gel permeation chromatography). In GPC, the column used was a series of Toyo Soda G500OPW and G300OPW, and the eluent was phosphate buffer (pH 6.86). For detection, an RI (differential diffractometer) and a light scatterometer were used in series to perform simultaneous measurement. The molecular weight was determined by a light scattering meter, and the PHAS concentration was determined from the area ratio by RI. The standard for obtaining the PHAS concentration is P obtained according to the method of Japanese Patent Publication No. 54-20995.
A purified HAS was used.

〔performance test〕

The obtained PHAS liquid was used to test the stabilizing performance of H ₂ O ₂ . The conditions were as follows, and the residual ratio of H ₂ O ₂ after heating at 95 ° C. for 1 hour was determined by KMnO ₄ titration and used as the stability.

(conditions) Further, a part of the liquid after the test was taken and the average molecular weight was measured by GPC. The results are shown in Table-1.

[Thermal stability test]

The obtained PHAS aqueous solution was heated at 100 ° C. for 5 hours, and then the average molecular weight was measured by GPC. Table of the obtained results
Shown in 1.

Comparative Example 2 The reaction was carried out in exactly the same manner as in Example except that the PH adjustment during polymerization was as shown in Table 1. The pH during polymerization is
Initially it was 1.0 and finally it was 0.2. In this case, a solid substance is precipitated in the form of PLAC, so after the reaction, this is separated, the cake obtained is returned to the 500 ml reactor again, and 350 ml of water is added to disperse it. %
NaOH was added and dissolved, and the pH was adjusted to 13.0. The analysis and the like were exactly the same as in the example.

The obtained results are shown in Table-1.

Comparative Examples 3 to 4 The reaction was carried out in exactly the same manner as in the Example except that the pH during the polymerization was set to 1.5 or 1.0. After completion of the reaction, 20% NaOH was added to dissolve the precipitated PLAC as it was, and the pH was adjusted to 13.0. After that, the same treatment as in the example was performed.

The obtained results are shown in Table-1.

Comparative Example 5 According to Example 2 of JP-B-57-27882, 188 g of PL was used.
AC was obtained. 38g of this (PLAC lactonization degree is 2/3
Assuming that the molecular weight unit is 76, it is equivalent to 0.5mole) and put it in a 500ml reaction flask, and add water 30
While adding 0 ml and dispersing, 20% NaOH was added and dissolved to adjust the pH to 13.0. After adding water so that the total liquid weight would be 500 g, the same treatment as in Example was carried out.

The obtained results are shown in Table-1.

Claims (2)

[Claims] 1. When polymerizing α-halogenoacrylic acid or a salt thereof in water, the pH of the polymerization reaction liquid is controlled to be within the range of 3.0 to 8.0, and poly-α-hydroxyacrylic acid or a salt thereof is characterized. A method for producing an aqueous solution. 2. The time during which the pH of the polymerization reaction solution should be maintained within the range of 3.0 to 8.0 is at least 25 out of the total time required for the polymerization.
% Or more, The manufacturing method of Claim 1 characterized by the above-mentioned.