Poly-alpha-hydroxyacrylic acid, its preparation and use

Abstract

The application belongs to the field of high polymers, and discloses a preparation method of poly-alpha-hydroxy acrylic acid, which comprises the following steps: step 1: adding water, alpha-chloro acrylic acid and an oxidizing agent into a reaction container in an inert atmosphere, and keeping the temperature at 20-40 DEG C; step 2: adding the alpha-chloro acrylic acid and a reducing agent into the reaction container by dropwise adding within 30-60 min and stirring; step 3: after the dropwise adding is completed, keeping the temperature at 20-40 DEG C for 30-60 min, then increasing the temperature to 80-90 DEG C, adding a peroxide initiator to eliminate the alpha-chloro acrylic acid which is not completely reacted, and keeping the temperature at 80-90 DEG C for 1-2 h; step 4: after the reaction is stopped, filtering and collecting the polymer solid; and step 5: adding the polymer solid into a lye to hydrolyze sufficiently, and obtaining poly-alpha-hydroxy acrylic acid. The poly-alpha-hydroxy acrylic acid has moderate molecular weight and narrow molecular weight distribution, and is not easy to form serious intermolecular lactonization in the production process, so that the gelation phenomenon can be significantly delayed and reduced. Meanwhile, the application also discloses the application of the polymer.

Description

A poly-α-hydroxyacrylic acid, its preparation method and application Technical Field

[0001] This invention relates to the field of polymers, and more particularly to a poly-α-hydroxyacrylic acid, its preparation method, and its applications. Background Technology

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

[0003] In paper manufacturing companies, chelating stabilizers are currently the most commonly used. Chelating stabilizers can be broadly classified into organophosphonic acid chelating agents and polymeric chelating agents. From an environmental perspective, polymeric chelating agents such as polyacrylic acid and poly-α-hydroxyacrylic acid are commonly used polymers.

[0004] For the preparation method of poly-α-hydroxyacrylic acid, please refer to:

[0005] Publication number US3984439A, subject to a method for manufacturing polylactones derived from poly-α-hydroxyacrylic acid, the main process route of which is: converting α,β-dichloropropionic acid into α-chloroacrylic acid, then polymerizing and hydrolyzing it.

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

[0007] The poly-α-hydroxyacrylic acid prepared using this process is prone to lactone formation during production, leading to gelation and affecting production while making the molecular weight of the resulting product uncontrollable. The reasons for this pronounced lactone formation have been under investigation in the industry; for example, certain metal ions and the increasing degree of chelation can promote lactone formation.

[0008] Therefore, the problem to be solved in this case is: how to suppress the gelation phenomenon caused by the excessively rapid lactone formation of poly-α-hydroxyacrylic acid during the production process, so as to effectively control the molecular weight of poly-α-hydroxyacrylic acid. Summary of the Invention

[0009] The purpose of this invention is to provide a method for preparing poly-α-hydroxyacrylic acid. This method uses a monomer dropwise addition method and a low-temperature initiation method to prepare poly-α-chloroacrylic acid. Then, it is heated to hydrolyze and lactone-form lactone-formed poly-α-hydroxyacrylic acid. Finally, it is hydrolyzed under alkaline conditions to obtain poly-α-hydroxyacrylic acid with a moderate molecular weight and narrow molecular weight distribution. During the production process, it is not easy to form severe intermolecular lactone formation, which can significantly delay and reduce gelation.

[0010] In addition, the present invention also provides applications of this polymer.

[0011] To achieve the above objectives, this application discloses a method for preparing poly-α-hydroxyacrylic acid, comprising the following steps:

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

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

[0014] Step 3: After the addition is complete, keep the temperature constant for 30-60 minutes, then raise the temperature to 80-90℃ and add peroxide initiator to eliminate unreacted α-chloroacrylic acid, and keep the temperature constant at 80-90℃ for 1-2 hours;

[0015] Step 4: After stopping the reaction, filter and collect the polymer solid;

[0016] Step 5: Add the polymer solid to the alkaline solution for complete hydrolysis to obtain poly-α-hydroxyacrylic acid;

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

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

[0019] In the above preparation method, the oxidant 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% to 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 of 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, step 2 further contains an unsaturated monomer with an amide group; the amount of the unsaturated monomer with the 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 amide groups is N-vinylformamide or N-vinylacetamide.

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

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

[0026] Meanwhile, the present invention also discloses a poly-α-hydroxyacrylic acid, which is prepared by any of the methods described above; its molecular weight is 10,000 to 300,000 and its molecular weight distribution is 2 to 10.

[0027] Furthermore, the present invention also discloses the use of the above-mentioned poly-α-hydroxyacrylic acid in the preparation of hydrogen peroxide stabilizers.

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

[0029] (1) The poly-α-hydroxyacrylic 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 severe intermolecular lactone formation, which can significantly delay and reduce the gelation phenomenon.

[0030] (2) In the preferred embodiment, by introducing an unsaturated monomer containing amide groups, hydrolysis is performed under alkaline conditions. The amide groups will dissociate into amino groups, which also have a chelating effect. This can enrich the types of chelating groups on the polymer chain segments. Ultimately, this can further delay and reduce the gelation phenomenon. The possible reason for this result is that the types of chelating groups are richer, which can avoid the lactone phenomenon when the chelation saturation of metal ions is high. At the same time, the amidation of amino and carboxyl groups is more difficult, and amino groups can play the role of steric hindrance groups to inhibit the lactone phenomenon to a certain extent. Detailed Implementation

[0031] The present invention will now be clearly and completely described in conjunction with embodiments thereof. It should be noted that, unless specific conditions are specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0032] Example 1

[0033] A method for preparing poly-α-hydroxyacrylic acid includes the following steps:

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

[0035] Step 2: Add 75g of α-chloroacrylic acid, 0.69g of sodium sulfite, and 200g of water dropwise into the reaction vessel over 60 minutes while stirring.

[0036] Step 3: After the addition is complete, keep the temperature constant for 30 minutes, then raise the temperature to 80℃ and add 0.05g of sodium persulfate to eliminate unreacted α-chloroacrylic acid, and keep the temperature constant at 80℃ for 1 hour;

[0037] Step 4: After stopping the reaction, filter and collect the polymer solid;

[0038] Step 5: Add the polymer solid to a 1 mol / L sodium hydroxide aqueous solution and hydrolyze it completely at 80°C to obtain poly-α-hydroxyacrylic acid.

[0039] Example 2

[0040] A method for preparing poly-α-hydroxyacrylic acid includes the following steps:

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

[0042] Step 2: Add 80g of α-chloroacrylic acid, 0.52g of sodium sulfite, and 300g of water dropwise into the reaction vessel over 40 minutes while stirring.

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

[0044] Step 4: After stopping the reaction, filter and collect the polymer solid;

[0045] Step 5: Add the polymer solid to a 1.5 mol / L sodium hydroxide aqueous solution and hydrolyze it completely at 80°C to obtain poly-α-hydroxyacrylic acid.

[0046] Example 3

[0047] A method for preparing poly-α-hydroxyacrylic acid includes the following steps:

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

[0049] Step 2: Add 65g of α-chloroacrylic acid, 0.17g of sodium sulfite, and 400g of water dropwise into the reaction vessel over 30 minutes while stirring.

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

[0051] Step 4: After stopping the reaction, filter and collect the polymer solid;

[0052] Step 5: Add the polymer solid to a 2 mol / L sodium hydroxide aqueous solution and hydrolyze it completely at 80°C to obtain poly-α-hydroxyacrylic acid.

[0053] Example 4

[0054] The process is largely the same as in Example 2, except that step 2 also includes 2g of N-vinylformamide.

[0055] Example 5

[0056] The method is largely the same as in Example 2, except that step 2 also includes 10g of N-vinylformamide.

[0057] Example 6

[0058] The process is largely the same as in Example 2, except that step 2 includes 5g of N-vinylacetamide.

[0059] Comparative Example 1

[0060] A method for preparing poly-α-hydroxyacrylic acid includes the following steps:

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

[0062] Step 2: Add 80g of α-chloroacrylic acid, 1.2g of sodium persulfate, and 300g of water dropwise into the reaction vessel over 40 minutes while stirring.

[0063] Step 3: After the addition is complete, maintain the temperature for 2 hours to allow the reaction to continue.

[0064] Step 4: After stopping the reaction, filter and collect the polymer solid;

[0065] Step 5: Add the polymer solid to a 1.5 mol / L sodium hydroxide aqueous solution and hydrolyze it completely at 80°C to obtain poly-α-hydroxyacrylic acid.

[0066] Comparative Example 2

[0067] A method for preparing poly-α-hydroxyacrylic acid includes the following steps:

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

[0069] Step 2: After stopping the reaction, filter and collect the polymer solid;

[0070] Step 3: Add the polymer solid to a 1.5 mol / L sodium hydroxide aqueous solution and hydrolyze it completely at 80°C to obtain poly-α-hydroxyacrylic acid.

[0071] Comparative Example 3

[0072] A method for preparing poly-α-hydroxyacrylic acid includes the following steps:

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

[0074] Step 2: Add 0.52g sodium sulfite and 50g water dropwise into the reaction vessel over 40 minutes while stirring.

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

[0076] Step 4: After stopping the reaction, filter and collect the polymer solid;

[0077] Step 5: Add the polymer solid to a 1.5 mol / L sodium hydroxide aqueous solution and hydrolyze it completely at 80°C to obtain poly-α-hydroxyacrylic acid.

[0078] Performance testing

[0079] 1. Molecular weight and molecular weight distribution were determined using dynamic light scattering method;

[0080] 2. Metal ion chelating performance test: The chelating ability of chelating agents in textile printing and dyeing auxiliaries was determined using the method in GB / T21884-2008.

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

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

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

[0084] (3) Observe the gelation phenomenon in the solution, record the amount of recycled alkali added when gelation occurs, and observe the solution after the recycled alkali is added and let it stand. Record the time it takes for the gelation to disappear.

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

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

[0087] Molecular weight distribution. Example 1: 2589362.6; Example 2: 2145702.3; Example 3: 2864794.7; Example 4: 2276522.4; Example 5: 2493453.6; Example 6: 2226512.8; Comparative Example 1: 1531206.9; Comparative Example 2: 1634597.8; Comparative Example 3: 2315285.2 surface

[0088] Results analysis:

[0089] (1) Comparing the data of Examples 1-6 and Comparative Examples 1-3, it can be seen that the molecular weight of α-chloroacrylic acid polymerized at low temperature is higher and the molecular weight distribution is narrower. This is because the low-temperature polymerization method can avoid premature lactone formation of poly-α-hydroxyacrylic acid during the reaction process, which will precipitate out of the reaction system and terminate the free radical chain growth. The final product has a lower molecular weight and a wider molecular weight distribution.

[0090] (2) Comparing Example 2 and Comparative Example 4, it can be seen that the method of having all the α-chloroacrylic acid monomers in the bottom solution is more effective than the method of having some in the bottom solution and some added dropwise with the chain transfer agent. This indicates that in this solution free radical polymerization, maintaining the uniformity of monomer concentration is more conducive to obtaining poly-α-hydroxypropionic acid with a narrower molecular weight distribution.

[0091] (3) Comparing Examples 2, 4, 5 and 6, when introducing unsaturated monomers containing amide groups, the molecular weight distribution coefficient of the polymer gradually increases with the increase of the amount of unsaturated monomers containing amide groups. This is due to the different polymerization rates of unsaturated monomers containing amide groups and α-chloroacrylic acid. Introducing a certain amount of unsaturated monomers containing amide groups has little effect on the molecular weight distribution of the polymer.

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

[0093] Table 2. Metal ion chelating properties of poly-α-hydroxyacrylate 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: 168.94, 1.37; Comparative Example 2: 267.21, 42.85; Comparative Example 3: 372.19, 43.25 surface

[0095] Results analysis:

[0096] (1) Comparing the data of Examples 1-6 and Comparative Examples 1-3, it can be seen that the metal ion chelating performance of poly-α-hydroxyacrylic acid obtained by the low-temperature polymerization method proposed in this invention is improved. The beneficial effect is that the low-temperature polymerization method effectively reduces the generation of α-hydroxyacrylic acid oligomers in the system. These oligomers have no effect on the metal ion chelating performance of the product.

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

[0098] The test results for the artificial gel phenomenon can be found in Table 3.

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

[0100]

[0101] Results analysis:

[0102] (1) Comparing Examples 1-6 and Comparative Examples 1-3, the higher the molecular weight of poly-α-hydroxyacrylic 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 indicates that the lactone formation of poly-α-hydroxyacrylic acid is not solely caused by the alkali. The recovered metal ion content of a certain pulping plant used in the experiment is relatively high. Metal ions will promote the lactone formation of poly-α-hydroxyacrylic acid. Example 2 has better metal ion chelation performance, which may be the reason for its good alkali resistance.

[0103] (2) As can be seen from Examples 4 and 6, introducing amide groups into the poly-α-hydroxyacrylic acid molecular chain can effectively improve the lactone formation phenomenon caused by the combined action of alkali and metal ions in poly-α-hydroxyacrylic acid.

Claims

1. A method for preparing poly-α-hydroxyacrylic acid, characterized in that, The reaction includes the following steps: Step 1: Add water, α-chloroacrylic acid, and an oxidizing agent to a reaction vessel under an inert atmosphere, and maintain the temperature at 20-40°C; Step 2: Add α-chloroacrylic acid and a reducing agent dropwise to the reaction vessel over 30-60 minutes while stirring; Step 3: After the dropwise addition, maintain the temperature for 30-60 minutes, then raise the temperature to 80-90°C and add a peroxidation initiator to eliminate unreacted α-chloroacrylic acid, and maintain the temperature at 80-90°C for 1-2 hours; Step 4: After stopping the reaction, filter and collect the polymer solid; Step 5: Add the polymer solid to an alkaline solution for complete hydrolysis to obtain poly-α-hydroxyacrylic acid; The weight ratio of α-chloroacrylic acid in Step 1 and Step 2 is 1:2-4; 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; The redox initiator is equivalent to 0.2-3% of the total weight of α-chloroacrylic acid.

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 steps 1 and 2 is 1:5~10.

3. The preparation method according to claim 1, characterized in that, The peroxidation initiator in step 3 is one or more of 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.

4. The preparation method according to claim 1, characterized in that, Step 2 also contains unsaturated monomers with amide groups; the amount of the unsaturated monomers with amide groups is equivalent to 2 to 10% of the total weight of α-chloroacrylic acid.

5. The preparation method according to claim 4, characterized in that, The unsaturated monomer containing amide groups is N-vinylformamide or N-vinylacetamide.

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

7. The preparation method according to claim 6, characterized in that, The hydrolysis temperature in step 5 is 70~90℃.

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