Polyacrylamide for alkali recovery and preparation method thereof

Abstract

The invention discloses polyacrylamide for alkali recovery. The polyacrylamide is prepared from the following raw materials in parts by weight: 60 to 80 parts of an acrylamide monomer, 5 to 15 parts of a cationic monomer, 10 to 20 parts of an anionic monomer, 2 to 8 parts of a hydrophobic modified monomer, 0.05 to 0.3 part of an initiator, 0.01 to 0.05 part of a chain transfer agent, 0.01 to 0.1 part of a cross-linking agent and 150 to 250 parts of deionized water. The polyacrylamide can efficiently flocculate suspended solid particles in the green liquor under the alkaline condition, the content of suspended solids in the green liquor is remarkably reduced, meanwhile, the dryness of green mud is improved, the size and treatment cost of the green mud are reduced, and the overall efficiency of an alkali recovery system is improved.

Description

Technical Field

[0001] This invention belongs to the field of alkali recovery technology in pulp and paper making, specifically relating to a polyacrylamide for alkali recovery and its preparation method. Background Technology

[0002] In the alkali recovery system of the pulp and paper industry, green liquor filtration is one of the key steps. Green liquor is a solution formed by the dissolution of molten material produced after the combustion of black liquor in water, and its main components include sodium carbonate and sodium sulfate. Green liquor contains a large amount of suspended solids (such as calcium carbonate and magnesium hydroxide), which need to be removed by filtration to obtain clear green liquor for use in the subsequent causticizing process to produce white liquor.

[0003] Currently, the green liquor filtration process commonly used in alkali recovery systems has the following problems: (1) Low filtration efficiency. The suspended solid particles in the green liquor are small and dispersed, and traditional filtration processes are difficult to intercept efficiently, resulting in a high content of suspended solids in the green liquor, which affects the effect of subsequent causticization reactions and product quality; (2) Difficulty in treating green mud. Green mud is a solid waste generated during the filtration process. Its high water content leads to increased transportation and treatment costs. The high water content of green mud also affects the overall efficiency of the alkali recovery system; (3) Poor effect of chemical additives. The existing polyacrylamide flocculants have limited application effects in alkali recovery systems and cannot simultaneously meet the requirements of reducing the content of suspended solids in the green liquor and increasing the dryness of the green mud.

[0004] Therefore, developing a high-efficiency polyacrylamide flocculant suitable for alkali recovery systems is of great practical significance. Summary of the Invention

[0005] One objective of this invention is to address the above-mentioned technical problems by providing a polyacrylamide for alkali recovery. This polyacrylamide can efficiently flocculate suspended solid particles in green liquor under alkaline conditions, significantly reducing the suspended solid content in the green liquor, while simultaneously increasing the dryness of the green mud, reducing the volume and processing cost of the green mud, and improving the overall efficiency of the alkali recovery system.

[0006] Another object of the present invention is to provide a method for preparing the polyacrylamide for alkali recovery.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] In a first aspect, the present invention provides a polyacrylamide for alkali recovery, which is composed of the following raw materials in parts by weight: 60-80 parts of acrylamide monomer, 5-15 parts of cationic monomer, 10-20 parts of anionic monomer, 2-8 parts of hydrophobic modified monomer, 0.05-0.3 parts of initiator, 0.01-0.05 parts of chain transfer agent, 0.01-0.1 parts of crosslinking agent, and 150-250 parts of deionized water.

[0009] Preferably, the polyacrylamide for alkali recovery is composed of the following raw materials in parts by weight: 65-75 parts acrylamide monomer, 8-12 parts cationic monomer, 12-18 parts anionic monomer, 3-6 parts hydrophobic modified monomer, 0.15-0.25 parts initiator, 0.02-0.04 parts chain transfer agent, 0.03-0.07 parts crosslinking agent, and 180-220 parts deionized water.

[0010] Preferably, the cationic monomer is methacryloyloxyethyltrimethylammonium chloride (DMC) or dimethyl diallyl ammonium chloride (DMDAAC).

[0011] Preferably, the anionic monomer is acrylic acid (AA) or 2-acrylamide-2-methylpropanesulfonic acid (AMPS).

[0012] Preferably, the hydrophobic modifying monomer is methyl methacrylate (MMA) or styrene.

[0013] Preferably, the initiator is ammonium persulfate or azobisisobutyronitrile.

[0014] Preferably, the chain transfer agent is isopropanol or mercaptoethanol.

[0015] Preferably, the crosslinking agent is N,N'-methylenebisacrylamide or polyethylene glycol diacrylate.

[0016] Secondly, the present invention provides a method for preparing the aforementioned polyacrylamide for alkali recovery, comprising the following steps:

[0017] S1. Add deionized water to the reactor, and under stirring conditions, add acrylamide monomer, cationic monomer, anionic monomer and hydrophobic modified monomer in sequence, and stir until completely dissolved.

[0018] S2. Adjust the pH of the solution to 8.5-9.5, add the chain transfer agent and cross-linking agent, and continue stirring for 15-30 minutes;

[0019] S3. Introduce nitrogen gas to remove oxygen for 20-40 minutes, and raise the temperature of the reactor to 35-45℃;

[0020] S4. Prepare an aqueous solution of the initiator and add it dropwise to the reaction vessel over a period of 40-90 minutes.

[0021] S5. After the addition is complete, keep the reaction at the temperature for 6-8 hours to obtain a gel-like product;

[0022] S6. Granulate, dry, and pulverize the gel-like product to obtain a powdered polyacrylamide product.

[0023] Preferably, in step S6, the drying temperature is 60-90℃, more preferably 70-80℃, and the drying time is 3-6 hours, more preferably 4-5 hours.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] (1) High efficiency in reducing the content of suspended solids in green liquor: By introducing cationic and anionic monomers, the present invention enables polyacrylamide to have an amphoteric structure, which can effectively neutralize the surface charge of suspended particles in green liquor under alkaline conditions, and form large and dense flocs through adsorption bridging, significantly improving filtration efficiency and reducing the content of suspended solids in green liquor to below 50 mg / L.

[0026] (2) Improve the dryness of green mud: The introduction of hydrophobic modified monomers enhances the hydrophobicity of flocs, reduces the water encapsulation in green mud, and increases the dryness of green mud to 40%-50%, thereby reducing the volume and treatment cost of green mud.

[0027] (3) Strong alkali resistance: The polyacrylamide of the present invention has good stability and flocculation performance in the green liquor environment with high pH value (usually 10-12), is not easily hydrolyzed and degraded, and can maintain a high efficiency of flocculation effect for a long time.

[0028] (4) Low dosage and low cost: Compared with traditional flocculants, the dosage of polyacrylamide in this invention can be reduced by 20%-40%, which reduces the cost of the agent and improves the operating efficiency of the alkali recovery system. Detailed Implementation

[0029] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0030] Unless otherwise specified, the instruments or reagents used in the examples are all conventional instruments or reagents in the art and are commercially available products. Unless otherwise specified, the specific experimental operations involved in the text are all understandable or known to those skilled in the art based on their common knowledge or conventional technical means, and will not be described in detail here.

[0031] Example 1

[0032] 1. Raw material ratio (by weight): Acrylamide 70 parts, DMC 10 parts, AMPS 15 parts, MMA 5 parts, ammonium persulfate 0.15 parts, isopropanol 0.03 parts, N,N'-methylenebisacrylamide 0.05 parts, deionized water 200 parts.

[0033] 2. Preparation process

[0034] (1) Add deionized water to the reactor, and add acrylamide, DMC, AMPS and MMA in sequence under stirring. Stir for 40 minutes until completely dissolved.

[0035] (2) Adjust the pH to 9 with sodium hydroxide solution, add isopropanol and N,N'-methylenebisacrylamide, and continue stirring for 20 minutes;

[0036] (3) Purge with nitrogen gas to remove oxygen for 30 minutes, then raise the temperature to 40°C;

[0037] (4) Prepare a 5% aqueous solution of ammonium persulfate and slowly add it dropwise to the reaction vessel over a period of 40 minutes;

[0038] (5) After the addition is complete, keep the reaction at the temperature for 7 hours to obtain a gel-like product;

[0039] (6) Granulation, drying at 75℃ for 4 hours, and pulverization are performed to obtain polyacrylamide product PAM-1 for alkali recovery.

[0040] Example 2

[0041] 1. Raw material ratio (by weight): Acrylamide 65 parts, DMDAAC 8 parts, AA 12 parts, styrene 3 parts, azobisisobutyronitrile 0.2 parts, mercaptoethanol 0.02 parts, polyethylene glycol diacrylate 0.03 parts, deionized water 180 parts.

[0042] 2. Preparation process

[0043] (1) Add deionized water to the reactor, and add acrylamide, DMC, AMPS and MMA in sequence under stirring. Stir for 40 minutes until completely dissolved.

[0044] (2) Adjust the pH to 8.5 with sodium hydroxide solution, add isopropanol and N,N'-methylenebisacrylamide, and continue stirring for 15 minutes;

[0045] (3) Purge with nitrogen gas to remove oxygen for 20 minutes, then raise the temperature to 35°C;

[0046] (4) Prepare a 5% aqueous solution of ammonium persulfate and slowly add it dropwise to the reaction vessel over a period of 60 minutes;

[0047] (5) After the addition is complete, keep the reaction at the temperature for 8 hours to obtain a gel-like product;

[0048] (6) Granulation, drying at 80℃ for 4 hours, and pulverization are performed to obtain polyacrylamide product PAM-2 for alkali recovery.

[0049] Example 3

[0050] 1. Raw material ratio (by weight): Acrylamide 75 parts, DMC 12 parts, AMPS 18 parts, MMA 6 parts, ammonium persulfate 0.25 parts, isopropanol 0.04 parts, N,N'-methylenebisacrylamide 0.07 parts, deionized water 220 parts.

[0051] 2. Preparation process

[0052] (1) Add deionized water to the reactor, and add acrylamide, DMC, AMPS and MMA in sequence under stirring. Stir for 40 minutes until completely dissolved.

[0053] (2) Adjust the pH to 9.5 with sodium hydroxide solution, add isopropanol and N,N'-methylenebisacrylamide, and continue stirring for 30 minutes;

[0054] (3) Purge with nitrogen gas to remove oxygen for 40 minutes, then raise the temperature to 45°C;

[0055] (4) Prepare a 5% aqueous solution of ammonium persulfate and slowly add it dropwise to the reaction vessel over a period of 90 minutes;

[0056] (5) After the addition is complete, keep the reaction at the temperature for 6 hours to obtain a gel-like product;

[0057] (6) Granulation, drying at 70℃ for 5 hours, and pulverization are performed to obtain polyacrylamide product PAM-3 for alkali recovery.

[0058] Performance testing

[0059] The green liquor from the alkali recovery system of a paper mill was selected for testing, and the results are shown in Table 1 below.

[0060] Table 1. Results of Green Liquid Detection

[0061]

[0062] The test results show that the polyacrylamide prepared by this invention is significantly superior to commercially available products in reducing the suspended solids content of green liquor, increasing the dryness of green mud, and improving filtration speed. This invention, tailored to the characteristics of alkali recovery systems, significantly improves the flocculation effect of polyacrylamide in green liquor filtration and the dewatering performance of green mud by introducing hydrophobically modified monomers and optimizing the molecular structure.

[0063] The beneficial effects of this invention are as follows:

[0064] (1) High efficiency in reducing the content of suspended solids in green liquor: By introducing cationic and anionic monomers, the present invention enables polyacrylamide to have an amphoteric structure, which can effectively neutralize the surface charge of suspended particles in green liquor under alkaline conditions, and form large and dense flocs through adsorption bridging, significantly improving filtration efficiency and reducing the content of suspended solids in green liquor to below 50 mg / L.

[0065] (2) Improve the dryness of green mud: The introduction of hydrophobic modified monomers enhances the hydrophobicity of flocs, reduces the water encapsulation in green mud, and increases the dryness of green mud to 40%-50%, thereby reducing the volume and treatment cost of green mud.

[0066] (3) Strong alkali resistance: The polyacrylamide of the present invention has good stability and flocculation performance in the high pH (usually 10-12) green liquor environment, is not easily hydrolyzed and degraded, and can maintain a high efficiency of flocculation effect for a long time.

[0067] (4) Low dosage and low cost: Compared with traditional flocculants, the dosage of polyacrylamide in this invention can be reduced by 20%-40%, which reduces the cost of the agent and improves the operating efficiency of the alkali recovery system.

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A polyacrylamide for alkali recovery, characterized in that, It is composed of the following raw materials in parts by weight: 60-80 parts acrylamide monomer, 5-15 parts cationic monomer, 10-20 parts anionic monomer, 2-8 parts hydrophobic modified monomer, 0.05-0.3 parts initiator, 0.01-0.05 parts chain transfer agent, 0.01-0.1 parts crosslinking agent, and 150-250 parts deionized water.

2. The polyacrylamide for alkali recovery according to claim 1, characterized in that, The polyacrylamide for alkali recovery is composed of the following raw materials in parts by weight: 65-75 parts acrylamide monomer, 8-12 parts cationic monomer, 12-18 parts anionic monomer, 3-6 parts hydrophobic modified monomer, 0.15-0.25 parts initiator, 0.02-0.04 parts chain transfer agent, 0.03-0.07 parts crosslinking agent, and 180-220 parts deionized water.

3. The polyacrylamide for alkali recovery according to claim 1 or 2, characterized in that, The cationic monomer is methacryloyloxyethyltrimethylammonium chloride or dimethyldiallylammonium chloride.

4. The polyacrylamide for alkali recovery according to claim 1 or 2, characterized in that, The anionic monomer is acrylic acid or 2-acrylamide-2-methylpropanesulfonic acid.

5. The polyacrylamide for alkali recovery according to claim 1 or 2, characterized in that, The hydrophobic modifying monomer is methyl methacrylate or styrene.

6. The polyacrylamide for alkali recovery according to claim 1 or 2, characterized in that, The initiator is ammonium persulfate or azobisisobutyronitrile.

7. The polyacrylamide for alkali recovery according to claim 1 or 2, characterized in that, The chain transfer agent is isopropanol or mercaptoethanol.

8. The polyacrylamide for alkali recovery according to claim 1 or 2, characterized in that, The crosslinking agent is N,N'-methylenebisacrylamide or polyethylene glycol diacrylate.

9. A method for preparing low-ionicity polyacrylamide as described in any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Add deionized water to the reactor, and under stirring conditions, add acrylamide monomer, cationic monomer, anionic monomer and hydrophobic modified monomer in sequence, and stir until completely dissolved. S2. Adjust the pH of the solution to 8.5-9.5, add the chain transfer agent and cross-linking agent, and continue stirring for 15-30 minutes; S3. Introduce nitrogen gas to remove oxygen for 20-40 minutes, and raise the temperature of the reactor to 35-45℃; S4. Prepare an aqueous solution of the initiator and add it dropwise to the reaction vessel over a period of 40-90 minutes. S5. After the addition is complete, keep the reaction at the temperature for 5-10 hours to obtain a gel-like product; S6. Granulate, dry, and pulverize the gel-like product to obtain a powdered polyacrylamide product.

10. The method according to claim 9, characterized in that: In step S6, the drying temperature is 60-90℃ and the drying time is 3-6 hours.

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