JPH0423642B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for producing polylactone (hereinafter referred to as PLAC) corresponding to poly-α-hydroxyacrylic acid. PLAC is poly-alpha-hydroxy acrylic acid soda (hereinafter referred to as PHAS), which has uses such as metal sequestering agents, detergent builders, and dyeing aids.
It is an industrially important substance as a precursor of Conventional technology CS Marvel et al. irradiated α-chloroacrylic acid in an organic solvent with light from a mercury lamp to precipitate and isolate poly-α-chloroacrylic acid, then dissolved it in water and boiled it. It was shown that PLAC can be obtained. [J.Amer.Chem.Soc.Volume 62 3495
~3498 pages (1940)] However, these methods of polymerizing α-halogenoacrylic acid in an organic solvent to obtain poly-α-halogenoacrylic acid, isolating it, and heating it in water are The drawback is that the use of organic solvents increases equipment costs, and the resulting PLAC is extremely expensive. In order to improve this drawback, in recent years α
- polymerizing halogenoacrylic acid in water,
A method of directly lactonizing was proposed, and PLAC
It has become a basic manufacturing method. For example, in German Patent Publication No. 2061584 by HenKel, PLAC is obtained by reacting 2,3-dihalogenopropionic acid with a basic substance to convert it into α-halogenoacrylic acid, which is then heated and polymerized. ing. According to patent publication No. 57-39249 by Solvay, α,β-dichloropropionic acid or its alkyl derivative is dehydrochlorinated in the gas phase in the presence of a catalyst such as alumina, and the resulting α-chloroacrylic acid is , PLAC in contact with polymerization catalyst in water
A method has been proposed to obtain the . Also, similarly
According to patent publication No. 54-5839 by Solvay,
An aqueous solution of α,β-dichloropropionic acid was heated to 100°C.
We have proposed a method in which α-chloroacrylic acid is obtained by heating to the above temperature, and a polymerization catalyst is applied to the aqueous solution to obtain PLAC. Further, in Patent Publication No. 57-27882 by Hoechst, a solution of α-chloroacrylic acid is treated with a polymerization catalyst having a radical-forming action, and the resulting poly-α-chloroacrylic acid is heated for 80 hours or more without isolation. By heating to a temperature of ~100℃
A method to obtain PLAC is proposed. Problems to be Solved by the Invention As described above, by polymerizing α-halogenoacrylic acid in water and heating it directly, water-insoluble PLAC can be obtained, and by filtering it, a wet cake can be obtained. You can take out PLAC as
If the final product is to be produced in the form of PHAS, the wet cake can be placed in an aqueous solution of caustic soda and dissolved. However, if it is desired to obtain PLAC as a dried product, a drying process is naturally necessary. In some cases, PLAC as a wet cake is treated as a product as is. In these cases, it is obvious that the moisture content in the wet cake is an economically extremely important factor. However, the moisture content of wet PLAC simply obtained by the conventional method described above is 68
The water content in this wet cake is about ~82%.
Simple measures such as applying pressure during filtration
It is impossible to further reduce the water content. An object of the present invention is to obtain wet PLAC with a low water content when the insoluble polylactone is filtered out after the polymerization reaction is completed. Means for Solving the Problems The present inventors have continued research on the synthesis of PLAC for many years. As a result, they discovered that the hydrogen ion concentration in water during polymerization has a large effect on the water content in the resulting wet PLAC, leading to the completion of the present invention. That is, the present invention provides a method for obtaining PLAC by polymerizing α-halogenoacrylic acid or its salt in water and heating it as it is.
This is a method for producing wet PLAC with a low water content, which is characterized by controlling the PH (hydrogen ion concentration index) in the range of 0.4 to 2.2. As shown later in the Examples and Comparative Examples of the present invention, in order to reduce the moisture content of wet PLAC,
It is necessary to polymerize within a certain pH range, and if the polymerization is carried out outside of that range, the purpose cannot be achieved. When polymerizing α-chloracrylic acid, since it is an acid itself, it will naturally be polymerized on the acidic side, but since hydrolysis and lactonization proceed simultaneously with polymerization, approximately equimolar chlorination Hydrogen is liberated. Therefore, if α-chloroacrylic acid is simply polymerized in water, the PH during polymerization will gradually decrease and the polymerization will proceed in the region of 0.4 or less, making it impossible to achieve the object of the present invention. do not have. Japanese Patent Publication No. 57-27882 states that when α-chloroacrylic acid is polymerized in water, it is advantageous to polymerize it in approximately 20% by weight hydrochloric acid rather than in pure water. In this case, a wet PLAC with a low moisture content, which is the object of the present invention, cannot be obtained. In addition, as in the method of the Special Publication Publication No. 54-5939,
Even in the method of heating α,β-dichloropropionic acid to obtain α-chloroacrylic acid through a dehydrochlorination reaction and polymerizing it, polymerization naturally proceeds at a pH lower than 0.4, so Moisture content wetting
I can't get PLAC. In addition, the Federal Republic of Germany Patent Publication no.
2061584, by reacting α,β-dihalogenoacrylic acid with an alkaline substance, α-
When obtaining chloroacrylic acid or its salt and polymerizing it, depending on the amount of alkali used, polymerization may proceed through the PH range of 0.4 to 2.2, but the optimum PH range Wet PLAC with low moisture content cannot be obtained because the soaking time is not sufficient. The α-halogenoacrylic acid or its salt used in carrying out the present invention may be separately produced, or α,β-dichloropropionic acid can be The present invention can also be used in a method in which α-chloroacrylic acid is polymerized while being thermally dehydrochlorinated to obtain α-chloroacrylic acid. Furthermore, a basic substance is applied to α,β-dihalogenoacrylic acid or its ester,
Obtain α-halogenoacrylic acid or a salt thereof,
It can also be applied to methods of polymerizing it. In this case, since a slightly excess basic substance is generally used, it has the ability to neutralize hydrogen chloride produced as a by-product during polymerization, which has the advantage of making it easier to control the pH. The essence of the present invention is to control the PH during polymerization to a range of 4.0 to 2.2, but it is not necessary to maintain a constant PH at all times, and it is not necessary to maintain a constant PH of 0.4 to 2.2 for a while during the polymerization reaction.
However, in that case, at least 25% of the total time required for polymerization must be exceeded.
% or more time should be kept in the range of 0.4 to 2.2. However, if you want to keep the water content as low as possible, it is better to keep the pH constant during polymerization, especially
It is best to keep it in the range of 1.0 to 1.7. To maintain the pH, it is best to use a method generally used in the chemical industry, in which acid or alkali is added while monitoring the pH with a PH meter. As the acid used, 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, etc. can be used, but sodium hydroxide is generally used. The method of the present invention can be used in both batch-type reactions and continuous-type reactions; however, in batch-type reactions, it is preferable to prepare α
- Better results are obtained if the halogenoacrylic acid solution is brought into contact with the polymerization catalyst while being fed into the reactor sequentially. As the catalyst used for polymerization, commonly used catalysts having a radical action such as persulfate, azobisisobutynitrile, and benzoyl peroxide can be used. The temperature during polymerization may be 80 to 120°C, as in known methods, but 90 to 98°C is generally preferred. When α-chloroacrylic acid or its salt is supplied to the polymerization reactor, the supply method may be continuous or intermittent. Generally, it is best to feed the entire amount over 1 to 6 hours. Effect The present inventors variously changed the pH during polymerization.
It was discovered that in order to obtain PLAC and a wet cake with low water content, it is necessary to control the reaction solution within a certain pH range. i.e. PH is 2.5
Above, solid PLAC cannot be obtained, and below 2.5
As the pH is lowered, the moisture content in the cake gradually decreases, reaching a minimum around PH = 1.3. When the pH drops below 1.3, the moisture content increases again. It is not clear by what mechanism the pH during polymerization affects the moisture content in the cake. However, in order to undergo lactonization and solidification, acidity of pH 2.5 or lower is required. Therefore, as the pH decreases below 2.5, lactonization occurs more frequently and free COOH and OH groups decrease. It is presumed that the moisture content decreases because of this. On the other hand, the polymerization rate of acrylic acid is generally
It is known that the lower the value, the faster the reaction time, and the case of α-halogenoacrylic acid is no exception. Therefore, when the pH is 1.3 or less, both the polymerization rate and the lactonization rate increase, so it is presumed that branching and crosslinking occur in the polymer, which causes it to grow into a water-absorbing polymer. Effects of the Invention Wet PLAC produced by conventional methods had a moisture content of 68 to 82%. According to the present invention, it is possible to reduce the water content to 50% or less even when simply suction filtration is performed. This is extremely advantageous in terms of energy when drying, and also has great advantages when transporting wet bodies. Furthermore, there is also the advantage that a more concentrated solution can be obtained when converting PLAC to PHAS, and the present invention has great industrial significance. Examples Examples 1 to 7 and Comparative Examples 1 to 3 42.6 g (0.4 mol) of α-chloroacrylic acid was added to water.
The solution was dissolved in 300 ml and immediately neutralized with 20% NaOH solution to prepare an aqueous solution with a pH of 7.5. Attach a stirring blade, PH electrode, condenser, and thermometer to a 500ml five-necked flask, and place inside the flask.
Add 100ml of water. The above aqueous solution of α-chloroacrylate is continuously supplied to the reactor using a metering pump so that the entire amount can be supplied over 2 hours. At the same time, 0.54 g of potassium persulfate dissolved in 13.5 g of water was injected into the reactor over a period of 2 hours.
During this time, the reaction temperature was maintained at 90 to 95°C and the pH was maintained under predetermined conditions. PH control is 10% HCl
and 10% NaOH were prepared and controlled by injecting them into the reactor while watching the PH meter. After the supply of the solution of α-chloroacrylate and potassium persulfate was completed, the mixture was stirred for another hour while maintaining the temperature at 90 to 95°C. Thereafter, the reaction solution was cooled down to 40° C., filtered with suction on a Nutsuchie filter, and washed with 200 ml of water. The moisture content in the wet cake was measured using an infrared lamp type moisture meter at 75°C for 45 minutes. in the cake
Cl ^- was determined by potentiometric titration using a silver electrode using silver nitrate, and the analytical value was calculated as NaCl. The purity of PLAC is determined by subtracting the water and NaCl content. The results obtained are shown in Table 1.

[Table] Comparative Example 4 Aqueous solution 1 containing 1 mole of α,β-dichloropropionic acid was placed in a 4-volume enameling autoclave according to Example 2 described in Japanese Patent Publication No. 54-5839.
I put it in. This mixture was heated to reflux and potassium persulfate was added.
0.05 mol was added and the temperature was maintained at 102-103°C for 8 hours. The wet PLAC obtained weighed 135 g and had a moisture content of 69%. The PH during polymerization was initially 0.95, but as the reaction progressed, the PH decreased and remained below 0.4 for most of the reaction time. Comparative Example 5 42.6 g of α-chloroacrylic acid was dissolved in 400 g of water and heated to 95°C. Potassium persulfate in 13.5g of water
A solution of 0.54 g was added dropwise over 2 hours while stirring while maintaining the temperature at 95°C. After dropping potassium persulfate, the reaction was further carried out at 95°C for 1 hour. The pH of the reaction solution was initially 1.3, but it quickly decreased to below 0.4, and the reaction was progressing at a pH of approximately 0.3 to 0.0. After the reaction, the obtained wet PLAC was cooled and filtered, weighing 43.1 g and having a water content of 65%. Comparative Example 6 A 500ml five-necked flask, a stirrer, a condenser,
Attach a thermometer and PH electrode, and place α, β in the flask.
- 57.2 g (0.4 mol) of dichloropropionic acid was added, and 300 g of water was added to dissolve it. A solution of 17.6 g (0.44 mol) of NaOH in 100 g of water was added and the reaction solution was heated to 90-95°C. A solution of 0.54 g of potassium persulfate dissolved in 13.5 g of water was added dropwise over 3 hours, and the mixture was stirred while maintaining the temperature at 90 to 95°C. Thereafter, the reaction was further carried out at 90 to 95°C for 1 hour, and after cooling, the mixture was filtered to obtain PLAC. Immediately after the start of the reaction, the pH was 7.5. As the reaction progresses, the pH gradually decreases and reaches 1.0 after 2 hours.
It went down to After that, it hardly changed from 1.0. The obtained wet PLAC weighed 79.4 g and had a moisture content of 79.5%. Example 8 852 g (8.0 mole) of α-chloroacrylic acid was added to water.
Dissolve in 6000g, immediately neutralize with 20% NaOH solution,
An aqueous solution with pH 6.0 was obtained. Attach a stirring blade, PH electrode, condenser, and thermometer to a 101-volume five-necked flask, and place 1600 g of water in the flask. While keeping the reaction temperature at 90-95℃,
The above aqueous solution of sodium α-chloroacrylate is continuously supplied to the reactor using a metering pump so that the entire amount can be supplied over 3 hours. At the same time, a solution of 10.8 g of potassium persulfate dissolved in 210 g of water was fed into the reactor over the same period of 3 hours, during which time 35% HCl and 10
% NaOH aqueous solution was used to maintain the pH at 1.0. After the supply of α-chloroacrylate and potassium persulfate was completed, the mixture was further stirred at 90 to 95°C for 1 hour.
Thereafter, it was cooled to 40°C, filtered using a centrifuge, and washed with 6000 g of water. The gravity in centrifugal filtration was 1354G. The total weight of the wet PLAC obtained was 849 g, with a moisture content of 33.9% and a NaCl content of 0.8.
%, and the purity of PLAC was 65.3%.

Claims (1)

[Claims] 1. In the step of polymerizing α-halogenoacrylic acid or its salt to obtain a polylactone corresponding to poly-α-hydroxyacrylic acid, the pH during polymerization is controlled within the range of 0.4 to 2.2. A method for producing wet polylactone with a low water content. 2. The method according to claim 1, characterized in that α-halogenoacrylic acid or its salt is sequentially supplied to a polymerization reactor and brought into contact with a polymerization catalyst. 3. Claims 1 or 2, characterized in that the time during polymerization to maintain the pH in the range of 0.4 to 2.2 occupies at least 25% or more of the total time required for polymerization. Method.