Poly-alpha-hydroxy acrylic acid as well as preparation method and application thereof

Abstract

The invention belongs to the field of macromolecules, and discloses a preparation method of poly-alpha-hydroxy acrylic acid, which comprises the following steps: step 1, adding water, alpha-chloroacrylic acid and an oxidant into a reaction container in an inert atmosphere, and keeping the temperature at 20-40 DEG C; 2, alpha-chloroacrylic acid and a reducing agent are added into the reaction container in a dropwise adding mode within 30-60 min, and stirring is assisted; 3, after dropwise adding is completed, a constant-temperature reaction is conducted for 30-60 min, then the temperature is increased to 80-90 DEG C, a peroxidation initiator is added to eliminate alpha-chloroacrylic acid which is not completely reacted, and the constant temperature is kept at 80-90 DEG C for 1-2 h; 4, filtering after the reaction is stopped, and collecting a polymer solid; and step 5, adding the polymer solid into alkali liquor, and fully hydrolyzing to obtain the poly-alpha-hydroxy acrylic acid. The poly-alpha-hydroxy acrylic acid is moderate in molecular weight and narrow in molecular weight distribution, serious intermolecular lactonization is not prone to being formed in the production process, and the gelation phenomenon can be remarkably delayed and relieved. Meanwhile, the invention also discloses application of the polymer.

Description

Technical Field

[0001] The present invention relates to the field of polymers, and in particular to poly-α-hydroxy acrylic acid and a preparation method and application thereof. Background Art

[0002] In the papermaking industry, bleaching with hydrogen peroxide is a very common process. In production, an important factor affecting the stability of hydrogen peroxide is metal ions. Therefore, in order to reduce the amount of hydrogen peroxide used, people have proposed various hydrogen peroxide stabilizers, which can be divided into adsorption stabilizers, chelation stabilizers, and adsorption-chelation mixed stabilizers.

[0003] In papermaking enterprises, chelating stabilizers are now more commonly used. Chelating stabilizers can be roughly divided into organic phosphonic acid chelating agents and polymer chelating agents. From an environmental protection perspective, polymer chelating agents such as polyacrylic acid and poly-α-hydroxyacrylic acid are more commonly used polymers.

[0004] The preparation method of poly-α-hydroxy acrylic acid can be referred to:

[0005] Publication No. US3984439A is a method for producing polylactone derived from poly-α-hydroxy acrylic acid. The main process route is: converting α, β-dichloropropionic acid into α-chloroacrylic acid, then polymerizing and hydrolyzing it.

[0006] This is the most commonly used process path in this field.

[0007] Poly-α-hydroxyacrylic acid produced using this process is susceptible to lactonization during production, leading to gel formation. This affects production and makes the molecular weight of the product uncontrollable. The causes of this apparent lactonization are under investigation in the industry. For example, certain metal ions can promote lactonization, as can increasing levels of chelation.

[0008] Therefore, the problem to be solved in this case is: how to suppress the gelation phenomenon caused by the rapid lactonization of poly-α-hydroxy acrylic acid during the production process and effectively control the molecular weight of poly-α-hydroxy acrylic acid. Summary of the Invention

[0009] The present invention aims to provide a method for preparing poly-α-hydroxy acrylic acid. The method adopts a monomer dropwise addition method and a low-temperature initiation method to prepare poly-α-chloroacrylic acid, then hydrolyzes and lactonizes the poly-α-chloroacrylic acid at elevated temperature to form lactonized poly-α-hydroxy acrylic acid, and finally hydrolyzes the poly-α-hydroxy acrylic acid under alkaline conditions to obtain the poly-α-hydroxy acrylic acid. The poly-α-hydroxy acrylic acid has a moderate molecular weight and a narrow molecular weight distribution. During the production process, serious intermolecular lactonization is not easily formed, and gelation can be significantly delayed and alleviated.

[0010] At the same time, the invention also provides application of the polymer.

[0011] To achieve the above object, the present application discloses a method for preparing poly-α-hydroxy acrylic acid, comprising the following steps:

[0012] Step 1: Add water, α-chloroacrylic acid, and an oxidant to a reaction vessel under an inert atmosphere and maintain a constant temperature of 20-40°C;

[0013] Step 2: Add α-chloroacrylic acid and a reducing agent dropwise into a reaction vessel over 30 to 60 minutes while stirring;

[0014] Step 3: After the addition is completed, the reaction is carried out at a constant temperature for 30 to 60 minutes, then the temperature is raised to 80 to 90°C and a peroxide initiator is added to eliminate the unreacted α-chloroacrylic acid, and the temperature is kept at 80 to 90°C for 1 to 2 hours;

[0015] Step 4: Stop the reaction and filter to collect the polymer solid;

[0016] Step 5: adding the polymer solid to an alkaline solution for full hydrolysis to obtain poly-α-hydroxy acrylic acid;

[0017] The weight ratio of α-chloroacrylic acid in step 1 to that in step 2 is 1:2-4.

[0018] In the above preparation method, the ratio of the total amount of α-chloroacrylic acid to the total amount of water in step 1 and step 2 is 1:5-10.

[0019] In the above preparation method, the oxidizing agent in step 1 and the reducing agent in step 2 are redox initiators; the redox initiator is a combination of persulfate and sulfite or a combination of hydrogen peroxide and ascorbic acid;

[0020] The redox initiator is equivalent to 0.2-3% of the total weight of α-chloroacrylic acid.

[0021] In the above preparation method, the peroxidation initiator in step 3 is one or more selected from ammonium persulfate, potassium persulfate, and sodium persulfate; the peroxidation initiator is equivalent to 0.02 to 0.05% of the total weight of α-chloroacrylic acid.

[0022] In the above preparation method, the step 2 further contains an unsaturated monomer with an amide group; the amount of the unsaturated monomer with an amide group is equivalent to 2 to 10% of the total weight of α-chloroacrylic acid.

[0023] In the above preparation method, the unsaturated monomer containing an amide group is N-vinylformamide or N-vinylacetamide.

[0024] In the above preparation method, the concentration of the alkaline solution in step 5 is 1 to 2 mol / L.

[0025] In the above preparation method, the hydrolysis temperature in step 5 is 70-90°C.

[0026] At the same time, the present invention also discloses a poly-α-hydroxy acrylic acid, which is prepared by any of the above methods; the molecular weight is 10,000 to 300,000, and the molecular weight distribution is 2 to 10.

[0027] In addition, the present invention also discloses the use of the poly-α-hydroxy acrylic acid in preparing a hydrogen peroxide stabilizer.

[0028] The present invention has the following advantages and effects compared to the prior art:

[0029] (1) The poly-α-hydroxy acrylic acid of the present invention has a moderate molecular weight and a narrow molecular weight distribution. During the production process, it is not easy to form serious intermolecular lactone, which can significantly delay and alleviate the gelation phenomenon.

[0030] (2) In the preferred embodiment, by introducing an unsaturated monomer containing an amide group, the amide group will dissociate into an amino group when hydrolyzed under alkaline conditions. The amino group also has a chelating effect, which can enrich the types of chelating groups on the polymer chain segments, and the final manifestation is that the gelation phenomenon can be further delayed and alleviated. The possible reasons for this result are: the types of chelating groups are richer, which can avoid the lactonization phenomenon when the metal ion chelation saturation is high. At the same time, the amidation of amino and carboxyl groups is more difficult, and the amino group can act as a steric hindering group to inhibit the lactonization phenomenon to a certain extent. DETAILED DESCRIPTION

[0031] The present invention will be described clearly and completely below in conjunction with the examples of the present invention. In the description of the present invention, it should be noted that, where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer were used. Reagents or instruments used where the manufacturer is not specified are conventional products that can be purchased commercially.

[0032] Example 1

[0033] A method for preparing poly-α-hydroxy acrylic acid comprises the following steps:

[0034] Step 1: Add 300 g of water, 25 g of α-chloroacrylic acid, and 1.31 g of sodium persulfate to a reaction vessel under an inert atmosphere and maintain the temperature at 30°C;

[0035] Step 2: 75 g of α-chloroacrylic acid, 0.69 g of sodium sulfite, and 200 g of water were added dropwise to the reaction vessel over 60 min with stirring;

[0036] Step 3: After the addition is completed, the mixture is kept at a constant temperature for 30 minutes, then the temperature is raised to 80°C and 0.05g of sodium persulfate is added to eliminate the unreacted α-chloroacrylic acid, and the temperature is kept at 80°C for 1 hour;

[0037] Step 4: Stop the reaction and filter to collect the polymer solid;

[0038] Step 5: The polymer solid is added into a 1 mol / L aqueous solution of sodium hydroxide and fully hydrolyzed at a temperature of 80° C. to obtain poly-α-hydroxy acrylic acid.

[0039] Example 2

[0040] A method for preparing poly-α-hydroxy acrylic acid comprises the following steps:

[0041] Step 1: Add 400 g of water, 20 g of α-chloroacrylic acid, and 0.98 g of sodium persulfate to a reaction vessel under an inert atmosphere and maintain the temperature at 40°C;

[0042] Step 2: 80 g of α-chloroacrylic acid, 0.52 g of sodium sulfite, and 300 g of water were added dropwise to the reaction vessel over 40 minutes with stirring;

[0043] Step 3: After the addition is completed, the mixture is kept at a constant temperature for 40 minutes, then the temperature is raised to 85°C and 0.04g of sodium persulfate is added to eliminate the unreacted α-chloroacrylic acid, and the temperature is kept at 85°C for 1.5 hours;

[0044] Step 4: Stop the reaction and filter to collect the polymer solid;

[0045] Step 5: The polymer solid was added into a 1.5 mol / L aqueous solution of sodium hydroxide and fully hydrolyzed at a temperature of 80° C. to obtain poly-α-hydroxy acrylic acid.

[0046] Example 3

[0047] A method for preparing poly-α-hydroxy acrylic acid comprises the following steps:

[0048] Step 1: Add 600 g of water, 35 g of α-chloroacrylic acid, and 0.33 g of sodium persulfate to a reaction vessel under an inert atmosphere and maintain the temperature at 20°C;

[0049] Step 2: 65 g of α-chloroacrylic acid, 0.17 g of sodium sulfite, and 400 g of water were added dropwise to the reaction vessel over 30 minutes with stirring;

[0050] Step 3: After the addition is completed, the mixture is kept at a constant temperature for 60 minutes, then the temperature is raised to 90°C and 0.02g of sodium persulfate is added to eliminate the unreacted α-chloroacrylic acid, and the temperature is kept at 90°C for 2 hours;

[0051] Step 4: Stop the reaction and filter to collect the polymer solid;

[0052] Step 5: The polymer solid is added into a 2 mol / L aqueous solution of sodium hydroxide and fully hydrolyzed at a temperature of 80° C. to obtain poly-α-hydroxy acrylic acid.

[0053] Example 4

[0054] The process is substantially the same as Example 2, except that 2 g of N-vinylformamide is further included in step 2.

[0055] Example 5

[0056] The process is substantially the same as Example 2, except that, in step 2, 10 g of N-vinylformamide is further included.

[0057] Example 6

[0058] The process is substantially the same as Example 2, except that 5 g of N-vinyl acetamide is further included in step 2.

[0059] Comparative Example 1

[0060] A method for preparing poly-α-hydroxy acrylic acid comprises the following steps:

[0061] Step 1: Add 400 g of water, 20 g of α-chloroacrylic acid, and 0.3 g of sodium persulfate to a reaction vessel under an inert atmosphere and maintain the temperature at 80°C;

[0062] Step 2: 80 g of α-chloroacrylic acid, 1.2 g of sodium persulfate, and 300 g of water were added dropwise to the reaction vessel over 40 minutes with stirring;

[0063] Step 3: After the addition is completed, the reaction is kept at constant temperature for 2 hours;

[0064] Step 4: Stop the reaction and filter to collect the polymer solid;

[0065] Step 5: The polymer solid was added into a 1.5 mol / L aqueous solution of sodium hydroxide and fully hydrolyzed at a temperature of 80° C. to obtain poly-α-hydroxy acrylic acid.

[0066] Comparative Example 2

[0067] A method for preparing poly-α-hydroxy acrylic acid comprises the following steps:

[0068] Step 1: Add 700 g of water, 100 g of α-chloroacrylic acid, and 1.5 g of sodium persulfate to a reaction vessel under an inert atmosphere, and react at a constant temperature of 80° C. for 3 h while stirring;

[0069] Step 2: Stop the reaction and filter to collect the polymer solid;

[0070] Step 3: The polymer solid was added into a 1.5 mol / L sodium hydroxide aqueous solution and fully hydrolyzed at a temperature of 80° C. to obtain poly-α-hydroxy acrylic acid.

[0071] Comparative Example 3

[0072] A method for preparing poly-α-hydroxy acrylic acid comprises the following steps:

[0073] Step 1: Add 650 g of water, 100 g of α-chloroacrylic acid, and 0.98 g of sodium persulfate to a reaction vessel under an inert atmosphere and maintain the temperature at 40°C;

[0074] Step 2: 0.52 g of sodium sulfite and 50 g of water were added dropwise to the reaction vessel over 40 min with stirring;

[0075] Step 3: After the addition is completed, the mixture is kept at a constant temperature for 40 minutes, then the temperature is raised to 85°C and 0.04g of sodium persulfate is added to eliminate the unreacted α-chloroacrylic acid, and the temperature is kept at 85°C for 1.5 hours;

[0076] Step 4: Stop the reaction and filter to collect the polymer solid;

[0077] Step 5: The polymer solid was added into a 1.5 mol / L aqueous solution of sodium hydroxide and fully hydrolyzed at a temperature of 80° C. to obtain poly-α-hydroxy acrylic acid.

[0078] Performance Testing

[0079] 1. Molecular weight and molecular weight distribution are tested by dynamic light scattering method;

[0080] 2. Metal ion chelation performance test, using the method of determination of chelating capacity of textile printing and dyeing auxiliaries GB / T21884-2008;

[0081] 3. Artificial gel phenomenon test, the test method is as follows:

[0082] (1) Take 12% of the alkali recovery from a pulp mill;

[0083] (2) Take 30g of the stabilizer to be tested in a 500ml beaker and slowly add 270g of the above-mentioned recovered alkali;

[0084] (3) Observe the gel agglomeration phenomenon in the solution, record the amount of recovery alkali added when gel agglomeration occurs, observe after the recovery alkali is added, and record the time when the gel agglomeration disappears

[0085] The test results of molecular weight and molecular weight distribution are shown in Table 1 below;

[0086] Table 1 Molecular weight test data of poly-α-hydroxy acrylic acid synthesized in Examples 1-6 and Comparative Examples 1-3

[0087] Molecular weight Molecular weight distribution Example 1 258936 2.6 Example 2 214570 2.3 Example 3 286479 4.7 Example 4 227652 2.4 Example 5 249345 3.6 Example 6 222651 2.8 Comparative Example 1 153120 6.9 Comparative Example 2 163459 7.8 Comparative Example 3 231528 5.2

[0088] Result analysis:

[0089] (1) Comparison of the data of Examples 1-6 and Comparative Examples 1-3 shows that the molecular weight of α-chloroacrylic acid obtained by polymerization at low temperature is higher and the molecular weight distribution is narrower. This is because the use of this low-temperature polymerization method can avoid premature lactonization of poly-α-hydroxyacrylic acid during the reaction process and its precipitation from the reaction system, thereby terminating the growth of the free radical chain. As a result, the molecular weight of the final product is lower and the molecular weight distribution is wider.

[0090] (2) Comparison of Example 2 and Comparative Example 4 shows that the method in which all the α-chloroacrylic acid monomers are in the base liquid has a wider molecular weight distribution than the method in which part of the α-chloroacrylic acid monomers are in the base liquid and part of the α-chloroacrylic acid monomers are added dropwise with the chain transfer agent. This indicates that in this solution free radical polymerization, maintaining uniform monomer concentration is more conducive to obtaining poly-α-hydroxypropionic acid with a narrower molecular weight distribution.

[0091] (3) Comparative Examples 2, 4, 5, and 6 show that when an unsaturated monomer containing an amide group is introduced, the molecular weight distribution coefficient of the polymer gradually increases with the increase in the amount of the introduced unsaturated monomer containing an amide group. This is due to the different reactivity rates of the unsaturated monomer containing an amide group and α-chloroacrylic acid. When a certain amount of the unsaturated monomer containing an amide group is introduced, the molecular weight distribution of the polymer is not significantly affected.

[0092] The metal ion chelation performance results can be found in Table 2;

[0093] Table 2 Metal ion chelating properties of poly-α-hydroxy acrylic acid synthesized in Examples 1-6 and Comparative Examples 1-3

[0094] Calcium chelation value Iron chelation value Example 1 73.28 43.17 Example 2 75.32 46.93 Example 3 73.42 45.19 Example 4 76.28 54.26 Example 5 70.21 58.92 Example 6 74.29 56.19 Comparative Example 1 68.9 41.37 Comparative Example 2 67.21 42.85 Comparative Example 3 72.19 43.25

[0095] Result analysis:

[0096] (1) Comparison of the data of Examples 1-6 and Comparative Examples 1-3 shows that the metal ion chelating performance of the poly-α-hydroxy acrylic acid obtained by the low-temperature polymerization method proposed in the present invention is improved. This beneficial effect is that the low-temperature polymerization method effectively reduces the production of α-hydroxy acrylic acid oligomers in the system, and this oligomer has no effect on the metal ion chelating performance of the product.

[0097] (2) Comparing 2, 4, 5, and 6, when unsaturated monomers containing amide groups are introduced, the iron ion chelating performance of poly-α-hydroxy acrylic acid can be improved. However, as the amount of unsaturated monomers containing amide groups introduced increases, the iron chelating performance of poly-α-hydroxy acrylic acid improves, while the calcium ion chelating performance shows a downward trend. This is because when amide groups are introduced into the molecular chain of poly-α-hydroxy acrylic acid, the amino group can coordinate and complex with iron ions, but has no effect on calcium ions.

[0098] The test results of artificial gel phenomenon can be found in Table 3;

[0099] Table 3 Alkali resistance test of poly-α-hydroxy acrylic acid

[0100]

[0101] Result analysis:

[0102] (1) Comparing Examples 1-6 and Comparative Examples 1-3, the higher the molecular weight of poly-α-hydroxy acrylic acid, the worse the alkali resistance. However, although the molecular weight of Example 2 is higher than that of Comparative Examples 1 and 2, its alkali resistance is better than that of Comparative Examples 1 and 2. This situation shows that the lactonization of poly-α-hydroxy acrylic acid is not caused by the effect of alkali alone. The recovered metal ion content of a pulping plant used in the experiment is relatively high. Metal ions will promote the lactonization of poly-α-hydroxy acrylic acid. Example 2 has better metal ion chelating performance, which may be the reason for its good alkali resistance.

[0103] (2) From Examples 4 and 6, it can be seen that the introduction of amide groups into the poly-α-hydroxy acrylic acid molecular chain can effectively improve the lactonization phenomenon of poly-α-hydroxy acrylic acid caused by the combined action of alkali and metal ions.

Claims

1. A method for preparing poly-α-hydroxy acrylic acid, characterized in that: The steps include: Step 1: Add water, α-chloroacrylic acid, and an oxidant to a reaction vessel under an inert atmosphere and maintain a constant temperature of 20-40°C; Step 2: Add α-chloroacrylic acid and a reducing agent dropwise into a reaction vessel over 30 to 60 minutes while stirring; Step 3: After the addition is completed, the reaction is carried out at a constant temperature for 30 to 60 minutes, then the temperature is raised to 80 to 90°C and a peroxide initiator is added to eliminate the unreacted α-chloroacrylic acid, and the temperature is kept at 80 to 90°C for 1 to 2 hours; Step 4: Stop the reaction and filter to collect the polymer solid; Step 5: adding the polymer solid to an alkaline solution for full hydrolysis to obtain poly-α-hydroxy acrylic acid; The weight ratio of α-chloroacrylic acid in step 1 to that in step 2 is 1:2-4.

2. The preparation method according to claim 1, characterized in that The ratio of the total amount of α-chloroacrylic acid to the total amount of water in step 1 and step 2 is 1:5-10.

3. The preparation method according to claim 1, characterized in that The oxidizing agent in step 1 and the reducing agent in step 2 are redox initiators; the redox initiator is a combination of persulfate and sulfite or a combination of hydrogen peroxide and ascorbic acid; The redox initiator is equivalent to 0.2-3% of the total weight of α-chloroacrylic acid.

4. The preparation method according to claim 1, characterized in that The peroxidation initiator in step 3 is one or more selected from ammonium persulfate, potassium persulfate, and sodium persulfate; the peroxidation initiator is equivalent to 0.02-0.05% of the total weight of α-chloroacrylic acid.

5. The preparation method according to claim 1, characterized in that The step 2 further comprises an unsaturated monomer having an amide group; the amount of the unsaturated monomer having an amide group is equivalent to 2-10% of the total weight of α-chloroacrylic acid.

6. The preparation method according to claim 5, characterized in that The unsaturated monomer containing an amide group is N-vinylformamide or N-vinylacetamide.

7. The preparation method according to claim 1, characterized in that The alkaline solution in step 5 has a concentration of 1 to 2 mol / L.

8. The preparation method according to claim 7, characterized in that The hydrolysis temperature in step 5 is 70-90°C.

9. A poly-α-hydroxy acrylic acid, characterized in that The polyol is prepared by the method according to any one of claims 1 to 8; its molecular weight is 10,000 to 300,000, and its molecular weight distribution is 2 to 10.

10. Use of the poly-α-hydroxy acrylic acid according to claim 9 in the preparation of a hydrogen peroxide stabilizer.

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