A method for preparing low-viscosity anionic polyacrylamide by aqueous solution copolymerization

Abstract

The present invention discloses a method for preparing low-viscosity anionic polyacrylamide by aqueous solution copolymerization, which comprises the following steps: S1: Prepare acrylamide and acrylic acid in proportion, add a viscosity reducer, and adjust the pH of the polymerization solution; S2: Add a complexing agent to the polymerization solution prepared in S1, stir for 0.5 h, then adjust the temperature of the polymerization solution to 15-20 °C, transfer it to a polymerization container, and introduce high-purity nitrogen; S3: After purging oxygen with nitrogen for half an hour, add an inhibitor, an azo initiator, and a chain transfer agent. After continuously introducing nitrogen for 20 min, add a redox initiator and stop introducing nitrogen, and seal the polymerization system; S4: Take out the gel block prepared by the reaction in S3, cut it into pieces, dry, crush, and sieve it to obtain the low-viscosity anionic polyacrylamide. The low-viscosity anionic polyacrylamide prepared by the present invention has a gel block that does not stick to the wall, is easy to granulate, the finished product is easily soluble, and the insoluble matter is low; it can be used for water treatment under special circumstances and will not block the inclined tube and pipeline during the sedimentation process during use, and has a certain application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer polymerization, and specifically relates to a method for preparing low-viscosity anionic polyacrylamide by aqueous solution copolymerization. Background Art

[0002] Anionic polyacrylamide (APAM) is a water-soluble polymer, which is applied to inorganic suspensions with higher concentration and positive charge, as well as suspensions with relatively coarse particles (0.01 - 1 mm) and slightly alkaline pH value. APAM is widely used in the flocculation and sedimentation of industrial wastewater (such as metallurgical plant wastewater, steel plant wastewater, coal washing wastewater, etc.), sewage treatment, sludge dewatering, etc. Since there are a certain amount of polar groups in the molecular chain of APAM, it can adsorb solid particles suspended in water, and through bridging between particles or charge neutralization, the particles are aggregated to form large flocs, accelerating the sedimentation of particles in the suspension, so that APAM has the effects of accelerating the clarification of the solution and promoting filtration.

[0003] However, the APAM used in the prior art has a relatively high viscosity, and there is a situation where the suspension flocs block the pipeline during use. Although reducing the dosage of APAM can reduce the viscosity, this can only be used for the problem of sticky sewage caused by excessive dosage of APAM, and only reduces the proportion of APAM in the sewage. From the actual results, this cannot effectively solve the problem.

[0004] For the above reasons, how to provide a low-viscosity anionic polyacrylamide product, which makes the suspension flocs in sewage more compact and smaller in volume in a specific environment, thereby solving the problem of blocking the inclined tube and pipeline during its sedimentation process, is an important problem that needs to be overcome currently. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a method for preparing low-viscosity anionic polyacrylamide by aqueous solution copolymerization. By adding a viscosity reducer and using an inhibitor during polymerization, the suspension flocs in sewage can be made more compact and smaller in volume, so that they will not block the inclined tube and pipeline during the sedimentation process.

[0006] To achieve the above purpose, the present invention provides the following technical solutions:

[0007] A method for preparing low-viscosity anionic polyacrylamide by aqueous solution copolymerization, comprising the following specific steps:

[0008] S1: Prepare an aqueous solution of acrylamide at 40%-50% by mass percentage; prepare an aqueous solution of the comonomer acrylic acid at 75%-85% by mass ratio; prepare an aqueous solution of sodium hydroxide at 30%-35% by mass ratio; mix the aqueous solution of acrylic acid and the aqueous solution of sodium hydroxide for neutralization treatment, and adjust the pH of the solution to 6.9-7.1, then add water to adjust to an aqueous solution of sodium acrylate with a mass fraction of 30%-40%; mix the aqueous solutions of acrylamide and sodium acrylate at a molar ratio of 0.7-0.8 to form an aqueous solution with a mass fraction of 35%-45%, and at the same time add a viscosity reducer. After complete dissolution, adjust the pH value to 7-8 with liquid alkali or acid to obtain a polymerization solution;

[0009] S2: Add a complexing agent to the polymerization solution prepared in S1, stir and complex for 0.4-0.6 h, and at the same time adjust the temperature of the polymerization solution to 15-20 °C, then transfer it to a polymerization container, and introduce high-purity nitrogen with a nitrogen purity ≥ 99.99% to remove oxygen in the solution, and control the nitrogen flow rate at 10-15 L / min;

[0010] S3: Purge oxygen with nitrogen for half an hour. When the oxygen content in the system < 0.01%, add an inhibitor, an azo initiator, and a chain transfer agent in sequence, and then add a redox initiator 20 minutes later under the condition of continuous nitrogen flow. After the polymerization solution reacts, stop passing nitrogen and seal the polymerization system to obtain a rubber block;

[0011] S4: Take out the rubber block prepared in the reaction of S3, cut it into pieces, dry it in an oven at 50-70 °C, crush it, and sieve it through a 20-100 mesh sieve to obtain the low-viscosity anionic polyacrylamide.

[0012] Preferably, the dosage of the viscosity reducer is 15%-25% of the mass of the acrylamide monomer, and it is selected from one or more of sodium sulfate, urea, polyvinyl alcohol, and hydroxyethyl cellulose.

[0013] Preferably, the dosage of the complexing agent is 0.001%-0.01% of the mass of the acrylamide monomer, and it is selected from one or more of disodium ethylenediaminetetraacetate, ethylenediaminetetraacetic acid, and tetrasodium ethylenediaminetetraacetate.

[0014] Preferably, the dosage of the inhibitor is 0.001%-0.005% of the mass of the acrylamide monomer, and it is selected from one or more of p-methoxyphenol and hydroquinone.

[0015] Preferably, the dosage of the chain transfer agent is 0.01%-0.03% of the mass of the acrylamide monomer, and it is selected from one or more of α-methylstyrene dimer, isopropanol, and sodium formate.

[0016] Preferably, the dosage of the azo initiator is 0.15-0.35% of the mass of the acrylamide monomer, and it is selected from one or more of azodiisobutamidine hydrochloride, azodiisobutyronitrile, azodiisoheptonitrile, and dimethyl azodiisobutyrate.

[0017] Preferably, the dosage of the redox initiator is 0.03-0.06% of the mass of the acrylamide monomer, and it is prepared separately with an oxidizing agent and a reducing agent in a mass ratio of 1:(2.0-4.0) for standby use.

[0018] Preferably, the oxidizing agent is selected from one or more of sodium persulfate, ammonium persulfate, hydrogen peroxide, and ferric chloride.

[0019] Preferably, the reducing agent is selected from one or more of sodium bisulfite, sodium metabisulfite, and ferrous chloride.

[0020] Preferably, the molecular weight of the low-viscosity anionic polyacrylamide prepared by this method is 11-14 million, the insoluble matter is ≤0.1%, the apparent viscosity is ≤4.5 mPa·s, and the residual monomer content is ≤1000 ppm.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1. By adding a viscosity reducer, the present invention reconstructs the viscosity of polyacrylamide from aspects such as reaction temperature and polymerization concentration. Compared with the method of reducing the viscosity of APAM products by reducing the dosage later or compounding with inorganic salts, the present invention fundamentally controls the viscosity of APAM products, and has strong practicality and economic value;

[0023] 2. Under the action of a free radical catalyst, acrylamide and sodium acrylate undergo a copolymerization reaction, which includes two steps: first, the redox system initiator releases free radicals, and then the azo initiator releases free radicals under the action of thermal activity. By adding an inhibitor, the present invention intercepts the free radical R· in the polymerization reaction, reduces it to R-H, terminates the free radical chain reaction, and thereby reduces the polymerization rate, resulting in a small molecular weight and low viscosity of the prepared polyacrylamide;

[0024] 3. The polyacrylamide gel block prepared by the present invention does not stick to the wall, is easy to granulate, the finished product is easy to dissolve, has low insoluble matter and low viscosity. Description of the Drawings

[0025] Figure 1 It is the process flow chart of the preparation of the low-viscosity anionic polyacrylamide of the present invention. Detailed Embodiments

[0026] The present invention will be described clearly and completely in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0027] Please refer to Figure 1 , the present invention provides a technical solution:

[0028] Example 1

[0029] A method for preparing low-viscosity anionic polyacrylamide by aqueous solution copolymerization, comprising the following steps:

[0030] S101: Take 400 g of acrylamide and prepare an aqueous solution with a mass ratio of 40%; neutralize 115 g of acrylic acid with 23 g of water and 30% sodium hydroxide and prepare an aqueous solution of sodium acrylate with a mass fraction of 36%; mix the two, add 90 g of urea, stir and dissolve, then adjust the pH to 7.5 with sodium hydroxide liquor or phosphoric acid, and finally make up the volume to 1500 ml to obtain a polymerization solution.

[0031] S102: Add 0.0058 g of the complexing agent disodium ethylenediaminetetraacetate to the prepared 1500 ml of polymerization solution, stir and complex for 0.5 h, at the same time adjust the temperature of the polymerization solution to 15 °C, then transfer it to a polymerization container, and introduce high-purity nitrogen (nitrogen purity ≥ 99.99%) to remove oxygen in the solution, and control the nitrogen flow rate at 12 L / min.

[0032] S103: Prepare azo initiator dimethyl 2,2'-azobis(2-methylpropionate), chain transfer agent α-methylstyrene dimer, and redox initiator respectively as required. The redox initiator is prepared from oxidant sodium persulfate and reductant sodium bisulfite according to a mass ratio of 1:2. Each of the above initiators is prepared and ready for use.

[0033] S104: After purging oxygen with nitrogen for half an hour, when the oxygen content in the system < 0.01%, sequentially add 0.66 g of azo initiator dimethyl 2,2'-azobis(2-methylpropionate) and 0.10 g of chain transfer agent α-methylstyrene dimer, then under the condition of continuous nitrogen introduction, wait for 20 minutes and then add 0.028 g of oxidant sodium persulfate, and add 0.056 g of reductant sodium bisulfite after 1 minute. After the polymerization solution reacts, stop introducing nitrogen and seal the polymerization system. After the reaction is completed, keep warm for 4 - 6 hours to obtain a rubber block.

[0034] S105: Take out the rubber block obtained by the reaction, cut it into pieces, dry it in an oven at 65 °C, crush it with a pulverizer and sieve it to obtain the low-viscosity anionic polyacrylamide.

[0035] Example 2

[0036] A method for preparing low-viscosity anionic polyacrylamide by aqueous solution copolymerization, comprising the following steps:

[0037] S201: Take 370 g of acrylamide and make an aqueous solution with a mass ratio of 43%; neutralize 160.8 g of acrylic acid with 32 g of water and 30% sodium hydroxide and make an aqueous solution of sodium acrylate with a mass fraction of 36.5%; mix the two, add 34 g of urea, stir and dissolve, then adjust the pH to 7.7 with sodium hydroxide liquor or phosphoric acid, and finally make up the volume to 1500 ml to obtain a polymerization solution.

[0038] S202: Add 0.0075 g of complexing agent ethylenediaminetetraacetic acid to the prepared 1500 ml polymerization solution, stir and complex for 0.5 h, at the same time adjust the temperature of the polymerization solution to 16 °C, then transfer it to a polymerization container, introduce high-purity nitrogen (nitrogen purity ≥ 99.99%) to remove oxygen in the solution, and control the nitrogen flow rate at 10 L / min.

[0039] S203: Prepare inhibitor p-methoxy phenol, azo initiator 2,2'-azobisisoheptonitrile, chain transfer agent sodium formate, and redox initiator respectively as required. The redox initiator is prepared from oxidant hydrogen peroxide and reductant sodium metabisulfite according to a mass ratio of 1:3. The above initiators are prepared and ready for use.

[0040] S204: After purging with nitrogen to remove oxygen for half an hour, when the oxygen content in the system < 0.01%, add 0.005 g of inhibitor p-methoxy phenol, 0.88 g of azo initiator 2,2'-azobisisoheptonitrile, 0.11 g of chain transfer agent sodium formate in sequence, then under the condition of continuous nitrogen flow, wait for 20 minutes and add 0.032 g of oxidant hydrogen peroxide, and add 0.096 g of reductant sodium bisulfite after 1 minute. After the polymerization solution reacts, stop purging with nitrogen and seal the polymerization system. After the reaction ends, keep warm for 4 - 6 hours to obtain a rubber block.

[0041] S205: Take out the rubber block obtained by the reaction, cut it into pieces, dry it in an oven at 60 °C, crush it with a pulverizer and sieve it to obtain the low-viscosity anionic polyacrylamide.

[0042] Example 3

[0043] A method for preparing low-viscosity anionic polyacrylamide by aqueous solution copolymerization, comprising the following steps:

[0044] S301: Take 395 g of acrylamide and make it into an aqueous solution with a mass ratio of 42%; neutralize 148.15 g of acrylic acid with 30 g of water and 30% sodium hydroxide and make it into an aqueous solution of sodium acrylate with a mass fraction of 36.2%; mix the two, add 80 g of urea, stir to dissolve, then adjust the pH to 7.4 with sodium hydroxide liquor or phosphoric acid, and finally make the volume constant at 1500 ml to obtain the polymerization solution.

[0045] S302: Add 0.0051 g of the complexing agent sodium ethylenediaminetetraacetate to the prepared 1500 ml of polymerization solution, stir and complex for 0.5 h, at the same time adjust the temperature of the polymerization solution to 18 °C, then transfer it to the polymerization container, introduce high-purity nitrogen (nitrogen purity ≥ 99.99%) to remove the oxygen in the solution, and control the nitrogen flow rate at 10 L / min.

[0046] S303: Prepare the inhibitor hydroquinone, the azo initiator azobisisobutyronitrile, the chain transfer agent isopropanol, and the redox initiator respectively according to the requirements. The redox initiator is prepared from the oxidant ammonium persulfate and the reductant ferrous chloride in a mass ratio of 1:4. The above initiators are prepared and ready for use.

[0047] S304: After purging oxygen with nitrogen for half an hour, when the oxygen content in the system < 0.01%, add 0.0045 g of the inhibitor hydroquinone, 1.02 g of the azo initiator azobisisobutyronitrile, and 0.10 g of the chain transfer agent isopropanol in sequence. Then, under the condition of continuously introducing nitrogen, wait for 20 minutes and add 0.029 g of the oxidant ammonium persulfate, and add 0.116 g of the reductant ferrous chloride after 1 minute. Stop introducing nitrogen and seal the polymerization system after the polymerization solution reacts. After the reaction ends, keep warm for 4 - 6 hours to obtain the rubber block.

[0048] S305: Take out the rubber block obtained by the reaction, cut it into pieces, dry it in an oven at 70 °C, crush it with a pulverizer and sieve it to obtain the low-viscosity anionic polyacrylamide.

[0049] Example 4

[0050] A method for preparing low-viscosity anionic polyacrylamide by aqueous solution copolymerization, comprising the following steps:

[0051] S401: Take 410 g of acrylamide and make it into an aqueous solution with a mass ratio of 44%; neutralize 146.08 g of acrylic acid with 29.2 g of water and 30% sodium hydroxide and make it into an aqueous solution of sodium acrylate with a mass fraction of 36.4%; mix the two, add 39 g of urea and 39 g of hydroxyethyl cellulose, stir to dissolve, then adjust the pH to 7.6 with sodium hydroxide liquor or phosphoric acid, and finally make the volume constant at 1500 ml to obtain the polymerization solution.

[0052] S402: Add 0.015 g of chelating agent disodium ethylenediaminetetraacetate to the prepared 1500 ml of polymerization solution, stir and complex for 0.5 h. At the same time, adjust the temperature of the polymerization solution to 17 °C, then transfer it to a polymerization container, and introduce high-purity nitrogen (nitrogen purity ≥ 99.99%) to remove the oxygen in the solution, and control the nitrogen flow rate at 10 L / min.

[0053] S403: Prepare inhibitor hydroquinone, azo initiator azodiisobutyramidine hydrochloride, chain transfer agent sodium formate, and redox initiator respectively according to requirements. The redox initiator is prepared from oxidant sodium persulfate and reductant sodium metabisulfite in a mass ratio of 1:2.5. Each of the above initiators is prepared and ready for use.

[0054] S404: After purging oxygen with nitrogen for half an hour, when the oxygen content in the system < 0.01%, add 0.0060 g of inhibitor hydroquinone, 1.2 g of azo initiator azodiisobutyramidine hydrochloride, and 0.12 g of chain transfer sodium formate in sequence. Then, under the condition of continuous nitrogen flow, wait for 20 minutes and add 0.040 g of oxidant sodium persulfate, and add 0.100 g of reductant sodium metabisulfite after 1 minute. After the polymerization solution reacts, stop purging nitrogen and seal the polymerization system. After the reaction is completed, keep warm for 4 - 6 hours to obtain a rubber block.

[0055] S405: Take out the rubber block obtained by the reaction, cut it into pieces, dry it in an oven at 67 °C, crush it with a pulverizer and sieve it to obtain the low-viscosity anionic polyacrylamide.

[0056] Comparative example:

[0057] The differences between the comparative example and the example are as follows. The only difference is that in the comparative example, steps S1 and S4 originally existing in the example are omitted, so the addition of viscosity reducer and inhibitor is cancelled, and the mass of acrylamide and acrylic acid and the dosage of chain transfer agent are also less. The remaining steps are exactly the same in the comparative example and the example. The specific preparation method of the comparative example is as follows:

[0058] Comparative example 1:

[0059] S501: Take 272 g of acrylamide and make an aqueous solution with a mass ratio of 26%; neutralize 102.33 g of acrylic acid with 25 g of water and 30% sodium hydroxide and make an aqueous solution of sodium acrylate with a mass fraction of 36.4%; mix the two, stir evenly, and adjust the PH to 7.5 with sodium hydroxide liquid alkali or phosphoric acid, and finally make the volume constant at 1500 ml to obtain a polymerization solution.

[0060] S502: Add 0.0058 g of the complexing agent disodium ethylenediaminetetraacetate to the prepared 1500 ml of the polymerization solution, stir and complex for 0.5 h. At the same time, adjust the temperature of the polymerization solution to 15 °C, then transfer it to a polymerization container, and introduce high-purity nitrogen (nitrogen purity ≥ 99.99%) to remove the oxygen in the solution, and control the nitrogen flow rate at 10 L / min.

[0061] S503: Prepare azo initiator dimethyl 2,2'-azobisisobutyrate, chain transfer agent α-methylstyrene dimer, and redox initiator respectively as required. The redox initiator is prepared from oxidant sodium persulfate and reductant sodium bisulfite in a mass ratio of 1:2. Each of the above initiators is prepared and ready for use.

[0062] S504: After purging oxygen with nitrogen for half an hour, when the oxygen content in the system < 0.01%, add 0.66 g of azo initiator dimethyl 2,2'-azobisisobutyrate and 0.04 g of chain transfer agent α-methylstyrene dimer in sequence. Then, under the condition of continuous nitrogen flow, wait for 20 minutes and add 0.028 g of oxidant sodium persulfate, and add 0.056 g of reductant sodium bisulfite after 1 minute. Stop purging nitrogen and seal the polymerization system after the polymerization solution reacts. After the reaction is completed, keep warm for 4 - 6 hours to obtain a rubber block.

[0063] S505: Take out the rubber block obtained by the reaction, cut it into pieces, dry it in an oven at 65 °C, crush it with a pulverizer and sieve it to obtain the low-viscosity anionic polyacrylamide.

[0064] Comparative Example 2:

[0065] S601: Dissolve 272 g of acrylamide to form an aqueous solution with a mass ratio of 26%; neutralize 102.33 g of acrylic acid with 25 g of water and 30% sodium hydroxide and prepare an aqueous solution of sodium acrylate with a mass fraction of 36.4%. Mix the two, stir evenly, and adjust the pH to 7.5 with sodium hydroxide liquid alkali or phosphoric acid, and finally make up the volume to 1500 ml to obtain the polymerization solution.

[0066] S602: Add 0.0075 g of the complexing agent ethylenediaminetetraacetic acid to the prepared 1500 ml of the polymerization solution, stir and complex for 0.5 h. At the same time, adjust the temperature of the polymerization solution to 16 °C, then transfer it to a polymerization container, and introduce high-purity nitrogen (nitrogen purity ≥ 99.99%) to remove the oxygen in the solution, and control the nitrogen flow rate at 10 L / min.

[0067] S603: Prepare azo initiator 2,2'-azobisisoheptonitrile, chain transfer agent sodium formate, and redox initiator respectively as required. The redox initiator is prepared from oxidant hydrogen peroxide and reductant sodium metabisulfite in a mass ratio of 1:3. Each of the above initiators is prepared and ready for use.

[0068] S604: After purging with nitrogen and removing oxygen for half an hour, when the oxygen content in the system is < 0.01%, 0.88 g of azo initiator 2,2'-azobisisoheptonitrile and 0.055 g of chain transfer agent sodium formate are added in sequence. Then, under the condition of continuous nitrogen purging, after 20 minutes, 0.032 g of oxidant hydrogen peroxide is added, and 1 minute later, 0.096 g of reductant sodium bisulfite is added. After the polymerization solution reacts, stop purging with nitrogen and seal the polymerization system. After the reaction ends, keep warm for 4 - 6 hours to obtain the rubber block.

[0069] S605: Take out the rubber block obtained from the reaction, cut it into pieces, dry it in an oven at 60 °C, crush it with a pulverizer and perform sieving treatment to obtain the low-viscosity anionic polyacrylamide.

[0070] Comparative Example 3:

[0071] S701: Dissolve 272 g of acrylamide to form an aqueous solution with a mass ratio of 26%; neutralize 102.33 g of acrylic acid with 25 g of water and 30% sodium hydroxide and prepare an aqueous solution of sodium acrylate with a mass fraction of 36.4%; mix the two, stir evenly, and adjust the pH to 7.5 with sodium hydroxide liquid alkali or phosphoric acid, and finally make up the volume to 1500 ml to obtain the polymerization solution.

[0072] S702: Add 0.0051 g of complexing agent ethylenediaminetetraacetic acid tetrasodium salt to the prepared 1500 ml polymerization solution, stir and complex for 0.5 h, and at the same time adjust the temperature of the polymerization solution to 18 °C, then transfer it to a polymerization container, introduce high-purity nitrogen (nitrogen purity ≥ 99.99%) to remove oxygen in the solution, and control the nitrogen flow rate at 10 L / min.

[0073] S703: Prepare azo initiator 2,2'-azobisisobutyronitrile, chain transfer agent isopropanol, and redox initiator as required. The redox initiator is prepared from oxidant ammonium persulfate and reductant ferrous chloride in a mass ratio of 1:4. The above initiators are prepared and ready for use.

[0074] S704: After purging with nitrogen and removing oxygen for half an hour, when the oxygen content in the system is < 0.01%, 1.02 g of azo initiator 2,2'-azobisisobutyronitrile and 0.05 g of chain transfer agent isopropanol are added in sequence. Then, under the condition of continuous nitrogen purging, after 20 minutes, 0.029 g of oxidant ammonium persulfate is added, and 1 minute later, 0.116 g of reductant ferrous chloride is added. After the polymerization solution reacts, stop purging with nitrogen and seal the polymerization system. After the reaction ends, keep warm for 4 - 6 hours to obtain the rubber block.

[0075] S705: Take out the rubber block obtained from the reaction, cut it into pieces, dry it in an oven at 70 °C, crush it with a pulverizer and perform sieving treatment to obtain the low-viscosity anionic polyacrylamide.

[0076] Comparative Example 4:

[0077] S801: Weigh 272 g of acrylamide and make it into an aqueous solution with a mass ratio of 26%. Neutralize 102.33 g of acrylic acid with 25 g of water and 30% sodium hydroxide, and make it into an aqueous solution of sodium acrylate with a mass fraction of 36.4%. Mix the two, stir evenly, and then adjust the pH to 7.5 with sodium hydroxide liquor or phosphoric acid. Finally, make up the volume to 1500 ml to obtain the polymerization solution.

[0078] S802: Add 0.015 g of the complexing agent disodium ethylenediaminetetraacetate to the prepared 1500 ml of polymerization solution, stir and complex for 0.5 h. At the same time, adjust the temperature of the polymerization solution to 17 °C, then transfer it to a polymerization container, and introduce high-purity nitrogen (nitrogen purity ≥ 99.99%) to remove the oxygen in the solution, and control the nitrogen flow rate at 10 L / min.

[0079] S803: Prepare the azo initiator 2,2'-azobis(2-methylpropionamidine) dihydrochloride, the chain transfer agent sodium formate, and the redox initiator respectively as required. The redox initiator is prepared from the oxidant sodium persulfate and the reductant sodium metabisulfite according to a mass ratio of 1:2.5. The above initiators are prepared and ready for use.

[0080] S804: After purging oxygen with nitrogen for half an hour, when the oxygen content in the system < 0.01%, add 1.2 g of the azo initiator 2,2'-azobis(2-methylpropionamidine) dihydrochloride and 0.05 g of the chain transfer agent sodium formate in sequence. Then, under the condition of continuous nitrogen flow, wait for 20 minutes and add 0.040 g of the oxidant sodium persulfate, and add 0.100 g of the reductant sodium metabisulfite after 1 minute. Stop purging nitrogen and seal the polymerization system after the polymerization solution reacts. After the reaction is completed, keep warm for 4 - 6 hours to obtain the rubber block.

[0081] S805: Take out the rubber block obtained by the reaction, cut it into pieces, dry it in an oven at 67 °C, crush it with a pulverizer, and sieve it to obtain the said conventional polyacrylamide.

[0082] For the polyacrylamide prepared in Examples 1 - 4 and Comparative Examples 1 - 4 according to Q / ATH01 - 2017 "Enterprise Standard of Anhui Tianrun Chemical Industry Co., Ltd. Non-ionic and Anionic Polyacrylamide", test the molecular weight, insoluble matter, and AM residue; test the apparent viscosity. The specific method is as follows:

[0083] 1. Weigh 100 ml of pure water with a 500 ml beaker, stir at 500 r / min, add 0.5617 g of the sample and stir for 5 min;

[0084] 2. Add 100 ml of pure water, and then add 100 ml of pure water every 5 min (until there is 490 ml of pure water in the beaker), and continue to stir for 5 min.

[0085] 3. Add 29.25 g of NaCl and then stop stirring after 5 min.

[0086] Note: UL viscosity at 25 °C, rotor No. 0, 60 gears + 16 ml.

[0087] The product test results are shown in Table 1:

[0088] Table 1 Product Test Results

[0089]

[0090] As can be seen from Table 1, in the case of Examples 1-4 improving the quality of acrylamide and acrylic acid and adding a viscosity reducer or inhibitor, they are significantly superior to Comparative Examples 1-4 in terms of apparent viscosity, insoluble matter, AM residue, etc. Therefore, the low-viscosity anionic polyacrylamide prepared by the method based on the present invention is reliable; through the relevant performance test parameters in the table, it shows that the low-viscosity anionic polyacrylamide prepared by the method based on the present invention basically does not have the situation of affecting granulation due to the softness of the rubber block, and its apparent viscosity is lower than that of the conventional polyacrylamide described in Comparative Example 1, which can meet the use requirements in special cases.

[0091] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those skilled in the art, additional modifications can be easily made. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to specific details.

Claims

1. A method for preparing low-viscosity anionic polyacrylamide by aqueous solution copolymerization, characterized in that, It includes the following specific steps: S1: Prepare an aqueous solution of acrylamide with a mass percentage of 40%-50%; prepare an aqueous solution of the comonomer acrylic acid with a mass ratio of 75%-85%; prepare an aqueous solution of sodium hydroxide with a mass ratio of 30%-35%; mix the aqueous solution of acrylic acid and the aqueous solution of sodium hydroxide for neutralization treatment, and adjust the pH of the solution to 6.9-7.1, then add water to adjust to an aqueous solution of sodium acrylate with a mass fraction of 30%-40%; mix the aqueous solutions of acrylamide and sodium acrylate at a molar ratio of 0.7-0.8 to form an aqueous solution with a mass fraction of 35%-45%, and at the same time add a viscosity reducer. After complete dissolution, adjust the HpH value to 7-8 with liquid alkali or acid to obtain a polymerization solution; The dosage of the viscosity reducer is 15%-25% of the mass of the acrylamide monomer, and the viscosity reducer is selected from urea; S2: Add a complexing agent to the polymerization solution prepared in S1, stir and complex for 0.4-0.6 h, and at the same time adjust the temperature of the polymerization solution to 15-20 °C, then transfer it to a polymerization container, and introduce high-purity nitrogen with a nitrogen purity ≥ 99.99% to remove the oxygen in the solution, and control the nitrogen flow rate at 10-15 L / min; S3: Purge oxygen with nitrogen for half an hour. When the oxygen content in the system < 0.01%, add a polymerization inhibitor, an azo initiator, and a chain transfer agent in sequence, and then add a redox initiator 20 minutes later under the condition of continuous nitrogen passing. After the polymerization solution reacts, stop passing nitrogen and seal the polymerization system to obtain a rubber block; The dosage of the polymerization inhibitor is 0.001%-0.005% of the mass of the acrylamide monomer, and it is selected from one of p-methoxyphenol and hydroquinone; S4: Take out the rubber block prepared in the reaction of S3, cut it into pieces, dry it in an oven at 50-70 °C, pulverize it, and sieve it through a 20-100 mesh sieve to obtain the low-viscosity anionic polyacrylamide.

2. The method for preparing low-viscosity anionic polyacrylamide by aqueous solution copolymerization according to claim 1, characterized in that: The dosage of the complexing agent is 0.001%-0.01% of the mass of the acrylamide monomer, and it is selected from one or more of disodium ethylenediaminetetraacetate, ethylenediaminetetraacetic acid, and tetrasodium ethylenediaminetetraacetate; 3. The method for preparing low-viscosity anionic polyacrylamide by aqueous solution copolymerization according to claim 1, characterized in that: The dosage of the chain transfer agent is 0.01%-0.03% of the mass of the acrylamide monomer, and it is selected from one or more of α-methylstyrene dimer, isopropanol, and sodium formate; 4. The method for preparing low-viscosity anionic polyacrylamide by aqueous solution copolymerization according to claim 1, characterized in that: The dosage of the azo initiator is 0.15%-0.35% of the mass of the acrylamide monomer, and it is selected from one or more of azodiisobutyramidine hydrochloride, azodiisobutyronitrile, azodiisooctanenitrile, and dimethyl azodiisobutyrate; 5. The method for preparing low-viscosity anionic polyacrylamide by aqueous solution copolymerization according to claim 1, characterized in that: The dosage of the redox initiator is 0.03%-0.06% of the mass of the acrylamide monomer, and it is prepared separately with an oxidizing agent and a reducing agent in a mass ratio of 1:(2.0-4.0) for standby; 6. The method for preparing low-viscosity anionic polyacrylamide by aqueous solution copolymerization according to claim 5, characterized in that: The oxidizing agent is selected from one or more of sodium persulfate, ammonium persulfate, hydrogen peroxide, and ferric chloride; 7. The method for preparing low-viscosity anionic polyacrylamide by aqueous solution copolymerization according to claim 5, characterized in that: The reducing agent is selected from one or more of sodium bisulfite, sodium metabisulfite, and ferrous chloride; 8. A method for preparing low-viscosity anionic polyacrylamide by aqueous solution copolymerization according to any one of claims 1-7, characterized in that: The molecular weight of the low-viscosity anionic polyacrylamide prepared by this method is 11-14 million, the insoluble matter ≤ 0.1%, the apparent viscosity ≤ 4.5 mPa·s, and the residual monomer content ≤ 1000 ppm.

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