A polyacrylamide aqueous dispersion, its synthesis method and application

Abstract

The application discloses a kind of polyacrylamide aqueous dispersion and its synthesis method and application, it is related to polyacrylamide synthetic technical field;The synthesis method of polyacrylamide aqueous dispersion includes making the reaction system of acrylamide I, cationic monomer I, inorganic salt, stabilizer and initiator I carries out reaction I, obtains the polyacrylamide aqueous dispersion;Wherein, the stabilizer is the binary mixture of cationic copolymer containing polyacrylamide segment and polyoxyethylene;The polyacrylamide aqueous dispersion prepared in the application has excellent stability, is placed for more than 1 year at room temperature, and no destabilization occurs;It can be stored in above-10 ℃ environment, when temperature recovers to 2-40 ℃, it can continue to keep stable.

Description

Technical Field

[0001] This invention relates to the field of polyacrylamide synthesis technology, specifically to an aqueous polyacrylamide dispersion, its synthesis method, and its applications. Background Technology

[0002] Polyacrylamide possesses excellent water solubility, high-efficiency thickening properties, and unique adsorption characteristics, thus finding wide application in numerous fields such as water treatment, oil extraction, papermaking, and textiles. Aqueous dispersion polymerization is an important method for preparing aqueous dispersions of polyacrylamide.

[0003] Currently, the biggest problem in preparing aqueous polyacrylamide dispersions using aqueous dispersion polymerization is the poor stability of these dispersions. The prepared aqueous polyacrylamide dispersions often exhibit stratification after several weeks to several months of storage. For example, Chinese patent document CN 02627725A discloses a method for synthesizing a cationic polyacrylamide emulsion. The specific preparation method is as follows: a mixed solution of tert-butanol, ammonium sulfate, and water is used as the reaction medium; acrylamide, methacrylamide oxyethyltrimethylammonium chloride, and N-vinylpyrrolidone are used as reaction raw materials; ammonium persulfate and sodium bisulfite are used as reaction initiators; and polyethylene glycol and polymethacrylamide oxyethyltrimethylammonium chloride are used as dispersing stabilizers. The prepared aqueous polyacrylamide dispersion has a relatively low molecular weight, resulting in low viscosity, and stratification occurs within a maximum of two months, rendering it unusable.

[0004] In summary, improving the stability of aqueous polyacrylamide dispersions, especially the stability of high molecular weight aqueous polyacrylamide dispersions, is an urgent problem to be solved in the synthesis of aqueous polyacrylamide dispersions. Summary of the Invention

[0005] This invention addresses the problems existing in the synthesis of aqueous polyacrylamide dispersions in the prior art by preparing aqueous polyacrylamide dispersions through dispersion polymerization. The stabilizer in the dispersion polymerization is a binary mixture of a cationic copolymer containing polyacrylamide segments and polyoxyethylene. Unlike other methods, this invention uses a combination of a cationic copolymer containing polyacrylamide segments and a binary mixture of polyoxyethylene as a stabilizer, which can effectively solve the problem of poor stability of aqueous polyacrylamide dispersions.

[0006] To solve the above-mentioned technical problems, the first aspect of the present invention provides a method for synthesizing an aqueous dispersion of polyacrylamide, comprising reacting a reaction system of acrylamide I, cationic monomer I, inorganic salt, stabilizer and initiator I to obtain the aqueous dispersion of polyacrylamide; wherein the stabilizer is a binary mixture of a cationic copolymer containing polyacrylamide segments and polyoxyethylene.

[0007] According to some embodiments of the present invention, the mass ratio of acrylamide I, cationic monomer I, inorganic salt and stabilizer is 36:(4.32-5.76); 10:(270-275).

[0008] According to some embodiments of the present invention, the amount of initiator I added is 0.1% to 0.5% of the mass of acrylamide I.

[0009] According to some embodiments of the present invention, the cationic monomer I is selected from one or more of acryloyloxyethyltrimethylammonium chloride, methacryloyloxyethyltrimethylammonium chloride, dimethyldiallylammonium chloride, acryloyloxyethyldimethylbenzylammonium chloride, methacryloyloxyethyldimethylbenzylammonium chloride, and 2-acrylamido-2-methylpropyltrimethylammonium chloride.

[0010] According to some embodiments of the present invention, the inorganic salt is selected from ammonium salts; preferably, the ammonium salt is selected from at least one of ammonium sulfate and ammonium persulfate.

[0011] According to some embodiments of the present invention, the initiator I is selected from aqueous initiator I and / or thermal initiator I; preferably, the aqueous initiator I is selected from at least one of V-50 and VA-044; the thermal initiator I is selected from at least two of ammonium persulfate, sodium bisulfite, and potassium persulfate.

[0012] According to some embodiments of the present invention, the conditions for reaction I include: a temperature of 25°C to 45°C and a time of 1 hour to 6 hours.

[0013] According to some embodiments of the present invention, the preparation of the stabilizer includes: mixing cationic monomer II, acrylamide II, and polyoxyethylene in water to obtain a mixed solution under the conditions of initiator II and inactive atmosphere, and reacting II to obtain the stabilizer.

[0014] In this invention, polyoxyethylene does not participate in the polymerization reaction during the preparation of the stabilizer. That is, the cationic copolymer and polyoxyethylene do not react with each other in the binary mixture containing the cationic copolymer of polyacrylamide segments. The role of polyoxyethylene is to stabilize the cationic copolymer.

[0015] According to some embodiments of the present invention, the mass ratio of the cationic monomer II, acrylamide II, polyoxyethylene and water is 72:60:(30-100):(160-260).

[0016] According to some embodiments of the present invention, the amount of initiator II added is 0.1% to 0.5% of the mass of cationic monomer II.

[0017] According to some embodiments of the present invention, the cationic monomer II is selected from one or more of acryloyloxyethyltrimethylammonium chloride, methacryloyloxyethyltrimethylammonium chloride, dimethyldiallylammonium chloride, acryloyloxyethyldimethylbenzylammonium chloride, methacryloyloxyethyldimethylbenzylammonium chloride, and 2-acrylamido-2-methylpropyltrimethylammonium chloride.

[0018] According to some embodiments of the present invention, the polyoxyethylene is selected from polyoxyethylene with or without end capping; preferably, the molecular weight of the polyoxyethylene is 2000 Da to 200000 Da; more preferably, the polyoxyethylene with end capping includes single-end capped polyoxyethylene and double-end capped polyoxyethylene; even more preferably, the single-end capped polyoxyethylene is selected from polyoxyethylene monomethyl ether; the double-end capped polyoxyethylene is selected from polyoxyethylene dimethyl ether; and the polyoxyethylene without end capping is polyethylene glycol.

[0019] According to some embodiments of the present invention, the initiator II is selected from aqueous initiator II and / or thermal initiator II; preferably, the aqueous initiator II is selected from at least one of V-50 and VA-044; the thermal initiator II is selected from at least two of ammonium persulfate, sodium bisulfite, and potassium persulfate.

[0020] According to some embodiments of the present invention, the non-active atmosphere is selected from at least one of nitrogen and argon.

[0021] According to some embodiments of the present invention, the conditions for reaction II include: a temperature of 30°C to 80°C and a reaction time of 5 hours to 10 hours.

[0022] According to some embodiments of the present invention, the reaction II is further followed by dilution; preferably, the stabilizer is cooled to room temperature, and then a certain amount of water is added to dilute the stabilizer to a mass concentration of 5wt% to 10wt%, to obtain an aqueous solution of a binary mixture containing a cationic copolymer of polyacrylamide segments and polyoxyethylene.

[0023] A second aspect of the present invention provides an aqueous polyacrylamide dispersion obtained by the above-described method for synthesizing an aqueous polyacrylamide dispersion.

[0024] A third aspect of the present invention provides the application of the above-mentioned aqueous polyacrylamide dispersion as a flocculant in sewage and / or wastewater treatment.

[0025] Beneficial effects:

[0026] The aqueous polyacrylamide dispersion prepared by this invention has high viscosity and excellent stability. No destabilization was observed after being left at room temperature for more than one year.

[0027] The aqueous dispersion of polyacrylamide prepared by this invention can be stored in an environment above -10°C and can remain stable when the temperature returns to 2-40°C.

[0028] The aqueous polyacrylamide dispersion prepared by this invention can be widely used as a flocculant in environmental protection fields such as wastewater and sewage treatment in industries such as petrochemicals, printing, steelmaking, and papermaking. Detailed Implementation

[0029] The present invention will be further described below with reference to embodiments. However, the present invention is not limited to these embodiments.

[0030] Unless otherwise specified, the three-necked flasks and three-necked bottles used in the embodiments of this invention are all commercially available products.

[0031] Unless otherwise specified, the methacryloyloxyethyltrimethylammonium chloride, acryloyloxyethyltrimethylammonium chloride, acrylamide, polyethylene glycol, VA-044 initiator, ammonium sulfate, ammonium persulfate, and sodium bisulfite in this invention are all commercially available reagents.

[0032] Unless otherwise specified, the room temperature mentioned in the embodiments of the present invention is 25°C.

[0033] Example 1

[0034] This embodiment provides a binary mixture containing a cationic copolymer and polyoxyethylene.

[0035] In a three-necked flask, 60g of an 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 30g of an 80% aqueous solution of acryloyloxyethyltrimethylammonium chloride, 60g of acrylamide, 30g of polyethylene glycol (PEG20000, molecular weight 20000 Da), 0.10g of VA-044 initiator, and 160g of water were added sequentially. After degassing and deoxygenation, nitrogen gas was introduced, and the reaction was carried out at 45℃ for 7 hours. Then, the mixture was cooled to room temperature, and 2900g of water was added to dilute it into a 5% aqueous solution containing a mixture of cationic copolymer and polyoxyethylene, i.e., stabilizer A1.

[0036] This embodiment further provides an aqueous dispersion of polyacrylamide.

[0037] At room temperature, 36g of acrylamide, 5.4g of 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 270g of the above stabilizer A1 (a 5% aqueous solution containing a cationic copolymer and a binary mixture of polyoxyethylene) and 10g of ammonium sulfate were added to a three-necked flask equipped with a stirrer. The mixture was stirred until all the additives were completely dissolved. Then, after degassing and deoxygenation, nitrogen gas was introduced and the temperature was raised to 45°C. 1mL of degassed and deoxygenated VA-044 aqueous solution (the concentration of VA-044 aqueous solution was 40mg / mL) was added, and the reaction was continued for 6 hours. The heating source was removed, and the reaction was stopped to obtain polyacrylamide aqueous dispersion B1.

[0038] Example 2

[0039] This embodiment provides a binary mixture containing a cationic copolymer and polyoxyethylene.

[0040] In a three-necked flask, 60g of an 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 30g of an 80% aqueous solution of acryloyloxyethyltrimethylammonium chloride, 60g of acrylamide, 30g of polyethylene glycol (PEG20000, molecular weight 20000 Da), 0.10g of VA-044 initiator, and 160g of water were added sequentially. After degassing and deoxygenation, nitrogen gas was introduced, and the reaction was carried out at 45℃ for 7 hours. After cooling to room temperature, 2900g of water was added to dilute the solution into a 5% aqueous solution containing a binary mixture of cationic copolymer and polyoxyethylene, i.e., stabilizer A1.

[0041] This embodiment further provides an aqueous dispersion of polyacrylamide.

[0042] At room temperature, 36 g of acrylamide, 5.4 g of 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 270 g of stabilizer A1 (a 5% aqueous solution containing a cationic copolymer and a binary mixture of polyoxyethylene) and 10 g of ammonium sulfate were added to a three-necked flask equipped with a stirrer. The mixture was stirred until all the added substances were completely dissolved. Then, after degassing and deoxygenation, nitrogen gas was introduced, and the temperature was raised to 30°C. 0.60 mL of degassed and deoxygenated aqueous solution of ammonium persulfate (concentration of ammonium persulfate was 40 mg / mL) and 0.40 mL of aqueous solution of sodium bisulfite (concentration of sodium bisulfite was 40 mg / mL) were added respectively. The reaction was continued for 6 hours, the heating source was removed, and the reaction was stopped to obtain aqueous dispersion of polyacrylamide B2.

[0043] Example 3

[0044] This embodiment provides a binary mixture containing a cationic copolymer and polyoxyethylene.

[0045] In a three-necked flask, 90g of an 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 60g of acrylamide, 100g of polyethylene glycol (PEG20000, molecular weight 20000 Da), 0.10g of VA-044 initiator, and 260g of water were added sequentially. After degassing and deoxygenation, nitrogen gas was introduced, and the mixture was reacted at 45°C for 7 hours. After cooling to room temperature, 4130g of water was added to dilute the mixture into a 5% aqueous solution containing a binary mixture of cationic copolymer and polyoxyethylene, i.e., stabilizer A2.

[0046] This embodiment further provides an aqueous dispersion of polyacrylamide.

[0047] At room temperature, 36 g of acrylamide, 5.4 g of 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 270 g of stabilizer A2 (a 5% aqueous solution containing a cationic copolymer and a binary mixture of polyoxyethylene) and 10 g of ammonium sulfate were added to a three-necked flask equipped with a stirrer. The mixture was stirred until all the additives were completely dissolved. Then, after degassing and deoxygenation, nitrogen gas was introduced, and the temperature was raised to 45°C. 1 mL of degassed and deoxygenated VA-044 aqueous solution (the concentration of VA-044 aqueous solution was 40 mg / mL) was added, and the reaction was continued for 6 hours. The heating source was removed, and the reaction was stopped to obtain polyacrylamide aqueous dispersion B3.

[0048] Example 4

[0049] This embodiment provides a binary mixture containing a cationic copolymer and polyoxyethylene.

[0050] In a three-necked flask, 90g of an 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 60g of acrylamide, 100g of polyethylene glycol (PEG20000, molecular weight 20000 Da), 0.10g of VA-044 initiator, and 260g of water were added sequentially. After degassing and deoxygenation, nitrogen gas was introduced, and the mixture was reacted at 45°C for 7 hours. After cooling to room temperature, 4130g of water was added to dilute the mixture into a 5% aqueous solution containing a binary mixture of cationic copolymer and polyoxyethylene, i.e., stabilizer A2.

[0051] This embodiment further provides an aqueous dispersion of polyacrylamide.

[0052] At room temperature, 36 g of acrylamide, 7.2 g of 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 275 g of stabilizer A2 (a 5% aqueous solution containing a cationic copolymer and a binary mixture of polyoxyethylene) and 10 g of ammonium sulfate were added to a three-necked flask equipped with a stirrer. The mixture was stirred until all the added substances were completely dissolved. Then, after degassing and deoxygenation, nitrogen gas was introduced, and the temperature was raised to 30°C. 0.60 mL of degassed aqueous solution of ammonium persulfate (concentration of ammonium persulfate was 40 mg / mL) and 0.40 mL of aqueous solution of sodium bisulfite (concentration of sodium bisulfite was 40 mg / mL) were added respectively. The reaction was continued for 6 hours, the heating source was removed, and the reaction was stopped to obtain aqueous dispersion of polyacrylamide B4.

[0053] Example 5

[0054] This embodiment provides a binary mixture containing a cationic copolymer and polyoxyethylene.

[0055] In a three-necked flask, 90g of an 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 60g of acrylamide, 200g of polyethylene glycol (PEG20000, molecular weight 20000 Da), 0.10g of VA-044 initiator, and 260g of water were added sequentially. After degassing and deoxygenation, nitrogen gas was introduced, and the reaction was carried out at 45°C for 7 hours. After cooling to room temperature, 6362g of water was added to dilute the solution into a 5% aqueous solution containing a mixture of cationic copolymer and polyoxyethylene, i.e., stabilizer A3.

[0056] This embodiment further provides an aqueous dispersion of polyacrylamide.

[0057] At room temperature, 36 g of acrylamide, 5.4 g of 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 270 g of stabilizer A3 (a 5% aqueous solution containing a cationic copolymer and a binary mixture of polyoxyethylene) and 10 g of ammonium sulfate were added to a three-necked flask equipped with a stirrer. The mixture was stirred until all the additives were completely dissolved. Then, after degassing and deoxygenation, nitrogen gas was introduced, and the temperature was raised to 45°C. 1 mL of degassed and deoxygenated VA-044 aqueous solution (the concentration of VA-044 aqueous solution was 40 mg / mL) was added, and the reaction was continued for 6 hours. The heating source was removed, and the reaction was stopped to obtain polyacrylamide aqueous dispersion B5.

[0058] Example 6

[0059] This embodiment provides a binary mixture containing a cationic copolymer and polyoxyethylene.

[0060] In a three-necked flask, 90g of an 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 60g of acrylamide, 200g of polyethylene glycol (PEG20000, molecular weight 20000 Da), 0.10g of VA-044 initiator, and 260g of water were added sequentially. After degassing and deoxygenation, nitrogen gas was introduced, and the reaction was carried out at 45°C for 7 hours. After cooling to room temperature, 6362g of water was added to dilute the solution into a 5% aqueous solution containing a mixture of cationic copolymer and polyoxyethylene, i.e., stabilizer A3.

[0061] This embodiment further provides an aqueous dispersion of polyacrylamide.

[0062] At room temperature, 36 g of acrylamide, 7.2 g of 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 275 g of stabilizer A3 (a 5% aqueous solution containing a cationic copolymer and a binary mixture of polyoxyethylene) and 10 g of ammonium sulfate were added to a three-necked flask equipped with a stirrer. The mixture was stirred until all the added substances were completely dissolved. Then, after degassing and deoxygenation, nitrogen gas was introduced, and the temperature was raised to 30°C. 0.60 mL of degassed aqueous solution of ammonium persulfate (concentration of ammonium persulfate was 40 mg / mL) and 0.40 mL of aqueous solution of sodium bisulfite (concentration of sodium bisulfite was 40 mg / mL) were added respectively. The reaction was continued for 6 hours, the heating source was removed, and the reaction was stopped to obtain aqueous dispersion of polyacrylamide B6.

[0063] Comparative Example 1

[0064] This comparative example provides a cationic copolymer.

[0065] The procedure was carried out according to the method described in Example 2, except that PEG20000 was not added to the raw materials; the details are as follows:

[0066] In a three-necked flask, 90g of an 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 60g of acrylamide, 0.10g of VA-044 initiator, and 160g of water were added sequentially. After degassing and deoxygenation, nitrogen gas was introduced, and the reaction was carried out at 45°C for 7 hours. After cooling to room temperature, 2330g of water was added to dilute the solution into an aqueous solution of a 5% cationic copolymer, i.e., stabilizer A4.

[0067] This comparative example further provides an aqueous dispersion of polyacrylamide.

[0068] At room temperature, 36 g of acrylamide, 5.4 g of 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 270 g of stabilizer A4 (5% aqueous solution of cationic copolymer) and 10 g of ammonium sulfate were added to a three-necked flask equipped with a stirrer. The mixture was stirred until all the additives were completely dissolved. Then, after degassing and deoxygenation, nitrogen gas was introduced and the temperature was raised to 45°C. 1 mL of degassed and deoxygenated VA-044 aqueous solution (concentration of VA-044 aqueous solution was 40 mg / mL) was added, and the reaction was continued for 6 hours. The heating source was removed, and the reaction was stopped to obtain polyacrylamide aqueous dispersion B7.

[0069] Comparative Example 2

[0070] This comparative example provides a cationic copolymer.

[0071] The procedure was carried out according to the method described in Example 2, except that PEG20000 was not added to the raw materials; the details are as follows:

[0072] In a three-necked flask, 90g of an 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 60g of acrylamide, 0.10g of VA-044 initiator, and 160g of water were added sequentially. After degassing and deoxygenation, nitrogen gas was introduced, and the reaction was carried out at 45°C for 7 hours. After cooling to room temperature, 2330g of water was added to dilute the solution into a 5% aqueous solution of the cationic copolymer, i.e., stabilizer A4.

[0073] This comparative example further provides an aqueous dispersion of polyacrylamide.

[0074] At room temperature, 36 g of acrylamide, 7.2 g of 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 280 g of stabilizer A4 (5% aqueous solution of cationic copolymer), and 10 g of ammonium sulfate were added to a three-necked flask equipped with a stirrer. The mixture was stirred until all the additives were completely dissolved. Then, after degassing and deoxygenation, nitrogen gas was introduced, and the temperature was raised to 30°C. 0.60 mL of degassed and deoxygenated aqueous solution of ammonium persulfate (concentration of ammonium persulfate was 40 mg / mL) and 0.40 mL of aqueous solution of sodium bisulfite (concentration of sodium bisulfite was 40 mg / mL) were added respectively. The reaction was continued for 6 hours, the heating source was removed, and the reaction was stopped to obtain aqueous dispersion B8 of polyacrylamide.

[0075] Comparative Example 3

[0076] This comparative example uses a 5% (w / w) aqueous solution of polyoxyethylene (PEG20000) as stabilizer A5.

[0077] This comparative example further provides an aqueous dispersion of polyacrylamide.

[0078] At room temperature, 36 g of acrylamide, 5.4 g of 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 270 g of stabilizer A5 (5% aqueous solution of polyoxyethylene), and 10 g of ammonium sulfate were added to a three-necked flask equipped with a stirrer. The mixture was stirred until all the additives were completely dissolved. Then, after degassing and deoxygenation, nitrogen gas was introduced, and the temperature was raised to 45°C. 1 mL of degassed and deoxygenated VA-044 aqueous solution (concentration of VA-044 aqueous solution was 40 mg / mL) was added, and the reaction was continued for 6 hours. The heating source was removed, and the reaction was stopped to obtain polyacrylamide aqueous dispersion B9.

[0079] Test case

[0080] (I) Stabilizer Parameters

[0081] The basic parameters of stabilizers A1-A3 prepared in Examples 1-6 of this invention are shown in Table 1.

[0082] In Examples 1-6, the binary mixtures containing cationic copolymers and polyethylene oxide, namely stabilizers A1, A2, and A3, were prepared and used. The weight ratio of cationic copolymers to polyethylene oxide varied. In A1, the ratio was 4.4 / 1 ((mass of cationic monomer II in the raw material + mass of acrylamide) / mass of PEG20000), indicating that the cationic copolymer was the main component. In A2, the content of polyethylene oxide increased, and the ratio was 1.3 / 1. In A3, the content of polyethylene oxide further increased, and the ratio was 0.66 / 1, indicating that PEG20000 was the main component.

[0083] Comparative Examples 1-3 were prepared and used with a single cationic copolymer aqueous solution or PEG20000 aqueous solution as a stabilizer.

[0084] In Table 1, the appearance, solid content, and viscosity of stabilizers A1-A3 were tested in accordance with GB / T 11175-2002;

[0085] The viscosity testing instrument was a Brookfield DV1 viscometer, and the viscosity was measured directly at a temperature of 25°C.

[0086] Table 1 Comparison of basic parameters of the stabilizers prepared in Examples 1-6 and the stabilizers described in Comparative Examples 1-2

[0087]

[0088]

[0089] In Table 1, the PEG content (taking Example 1 as an example) is: 30g / (60g+30g+60g+30g+160g+2900g)×100%=0.92%.

[0090] The results in Table 1 show that, compared with the cationic copolymer stabilizer A4 prepared in Comparative Examples 1-2, the stabilizers A1, A2 and A3 prepared in Examples 1-6 have slightly lower viscosity due to the presence of the nonionic polymer PEG. The viscosity of stabilizers A1, A2 and A3 prepared in Examples 1-6 decreases with increasing PEG20000 content.

[0091] (II) Parameters of Aqueous Polyacrylamide Dispersions

[0092] The basic parameters of the polyacrylamide aqueous dispersions prepared in Examples 1-6 and Comparative Examples 1-3 of this invention are shown in Table 2.

[0093] The polymer concentration measurement method is as follows: the weight of C1 of the polyacrylamide aqueous dispersion is diluted with water to a concentration of 1% of the polyacrylamide aqueous dispersion, placed in a dialysis bag (molecular weight cutoff: 1000 Da) and dialyzed in water for three days. Then the sample is freeze-dried to obtain the weight of the dried sample C2. The polymer concentration is the percentage of the ratio of C2 to C1.

[0094] The apparent viscosity is the viscosity of the polyacrylamide aqueous dispersions prepared in Examples 1-6 and Comparative Examples 1-3 without dilution with water; the viscosity of the polymer solution with a mass concentration of 1% refers to the viscosity of the solution when the polyacrylamide aqueous dispersion is diluted with water to a mass concentration of 1% for polyacrylamide and its copolymers.

[0095] Among them, the stability of the polyacrylamide aqueous dispersions prepared in Examples 1-6 and Comparative Examples 1-3 at room temperature is determined by visual observation. If the dispersion does not separate into layers, it is considered stable; if it separates into layers, it is considered unstable.

[0096] Freeze-thaw stability: 50 mL of polyacrylamide dispersion was placed in a low-temperature chamber at -5±2℃. After 18 hours, it was taken out and placed at 23±2℃ for 6 hours. The operation was repeated to observe whether there was any precipitation.

[0097] Table 2. Parameters of the polyacrylamide aqueous dispersions prepared in Examples 1-6 and Comparative Examples 1-3 of the present invention.

[0098]

[0099]

[0100] The results in Table 2 show that the polyacrylamide aqueous dispersions prepared in Examples 1-6 have suitable apparent viscosity and high viscosity of a 1% polymer solution, with stability exceeding 6 months, even reaching 1 year; while the polyacrylamide aqueous dispersions prepared in Comparative Examples 1-3 have significantly lower viscosity of a 1% polymer solution, and their stability is less than 1 month. This indicates that the present invention, using cationic copolymers and polyoxyethylene binary polymers as stabilizers in dispersion polymerization, is an effective method for preparing highly stable, high-viscosity polyacrylamide aqueous dispersions.

[0101] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for synthesizing an aqueous dispersion of polyacrylamide, characterized in that, The reaction system comprising acrylamide I, cationic monomer I, inorganic salt, stabilizer and initiator I is subjected to reaction I to obtain the aqueous dispersion of polyacrylamide; wherein the stabilizer is an aqueous solution of a binary mixture of a cationic copolymer containing polyacrylamide segments and polyoxyethylene at a mass concentration of 5wt% to 10wt%. The preparation of the stabilizer includes: mixing cationic monomer II, acrylamide II, and polyoxyethylene in water under the conditions of initiator II and inactive atmosphere, and carrying out reaction II to obtain the stabilizer; The mass ratio of acrylamide I, cationic monomer I, inorganic salt, and stabilizer is 36:(4.32-5.76); 10:(270-275). The mass ratio of the cationic monomer II, acrylamide II, polyethylene oxide and water is 72:60:(30-100):(160-260).

2. The synthesis method according to claim 1, characterized in that, The amount of initiator I added is 0.1% to 0.5% of the mass of acrylamide I.

3. The synthesis method according to claim 1, characterized in that, The cationic monomer I is selected from one or more of acryloyloxyethyltrimethylammonium chloride, methacryloyloxyethyltrimethylammonium chloride, dimethyldiallylammonium chloride, acryloyloxyethyldimethylbenzylammonium chloride, methacryloyloxyethyldimethylbenzylammonium chloride, and 2-acrylamido-2-methylpropyltrimethylammonium chloride; And / or, the inorganic salt is selected from ammonium salts; And / or, the initiator I is selected from aqueous initiator I and / or thermal initiator I.

4. The synthesis method according to claim 3, characterized in that, The ammonium salt is selected from ammonium sulfate; And / or, the aqueous initiator I is selected from at least one of V-50 and VA-044; and / or, the thermal initiator I is selected from at least two of ammonium persulfate, sodium bisulfite, and potassium persulfate.

5. The synthesis method according to any one of claims 1-4, characterized in that, The conditions for reaction I include: a temperature of 25°C to 45°C and a time of 1 hour to 6 hours.

6. The synthesis method according to any one of claims 1-4, characterized in that, The amount of initiator II added is 0.1% to 0.5% of the mass of cationic monomer II.

7. The synthesis method according to any one of claims 1-4, characterized in that, The cationic monomer II is selected from one or more of acryloyloxyethyltrimethylammonium chloride, methacryloyloxyethyltrimethylammonium chloride, dimethyl diallyl ammonium chloride, acryloyloxyethyldimethylbenzylammonium chloride, methacryloyloxyethyldimethylbenzylammonium chloride, and 2-acrylamido-2-methylpropyltrimethylammonium chloride; And / or, the polyoxyethylene is selected from polyoxyethylene with or without end caps; And / or, the initiator II is selected from aqueous initiator II and / or thermal initiator II; And / or, the inactive atmosphere is selected from at least one of nitrogen and argon.

8. The synthesis method according to claim 7, characterized in that, The molecular weight of the polyoxyethylene is 2000 Da to 200000 Da; And / or, the aqueous initiator II is selected from at least one of V-50 and VA-044; and / or, the thermal initiator II is selected from at least two of ammonium persulfate, sodium bisulfite, and potassium persulfate.

9. The synthesis method according to claim 7, characterized in that, The terminated polyethylene oxide includes single-terminated polyethylene oxide and double-terminated polyethylene oxide.

10. The synthesis method according to claim 9, characterized in that, The single-terminated polyoxyethylene is selected from polyoxyethylene monomethyl ether; and / or, the double-terminated polyoxyethylene is selected from polyoxyethylene dimethyl ether.

11. The synthesis method according to any one of claims 1-4, characterized in that, The conditions for reaction II include: a temperature of 30°C to 80°C and a reaction time of 5 to 10 hours. And / or, the reaction II may be followed by dilution.

12. An aqueous dispersion of polyacrylamide obtained by the synthesis method according to any one of claims 1-11.

13. The use of an aqueous polyacrylamide dispersion obtained by any one of the synthesis methods of claims 1-11 or the aqueous polyacrylamide dispersion of claim 12 as a flocculant in wastewater and / or sewage treatment.

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