Papermaking wastewater treatment polyacrylamide and preparation method thereof

Abstract

The invention discloses polyacrylamide for papermaking wastewater treatment and a preparation method thereof. The polyacrylamide is prepared from a main monomer, a targeted modified monomer, an anti-degradation modified monomer and a cross-linking monomer through an aqueous solution copolymerization reaction, the molar ratio of the main body monomer to the targeted modified monomer to the anti-degradation modified monomer to the cross-linking monomer is 1: (0.03 to 0.12): (0.02 to 0.08): (0.001 to 0.005); the invention also provides a preparation method of polyacrylamide for papermaking wastewater treatment, which comprises the following steps: S1, preparing a mixed monomer aqueous solution: adding the main monomer, the targeted modified monomer, the anti-degradation modified monomer and the cross-linking monomer into deionized water according to the molar ratio in claim 1, and stirring for dissolving to obtain the mixed monomer aqueous solution. The method has the advantages of mild reaction conditions, no need of harsh equipment requirements, simple post-treatment steps, and easy realization of industrial large-scale production; the product is solid powder, is convenient to store and transport, and is high in dissolving speed and strong in applicability during use.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and more specifically, to a polyacrylamide for treating papermaking wastewater and its preparation method. Background Technology

[0002] The paper industry is one of the industries with the highest water consumption and pollutant emissions. Its wastewater is complex, containing large amounts of fine fibers, lignin, hemicellulose, calcium carbonate, talc, and residual cooking agents and dyes. It is characterized by high COD (chemical oxygen demand), high suspended solids content, deep color, and large fluctuations in water quality. Direct discharge would severely damage the aquatic ecosystem; therefore, advanced treatment of paper wastewater is a crucial link in the industry's sustainable development.

[0003] Polyacrylamide, as a highly efficient flocculant, is widely used in papermaking wastewater treatment due to its high molecular weight and strong adsorption bridging ability. However, existing polyacrylamide products have many shortcomings and cannot meet the treatment needs of complex papermaking wastewater: On the one hand, ordinary polyacrylamide is not very targeted at specific pollutants such as lignin derivatives and negatively charged fine fibers in papermaking wastewater, resulting in low flocculation efficiency and requiring the addition of large amounts of reagents to achieve the desired treatment effect, increasing treatment costs; on the other hand, papermaking wastewater often has certain fluctuations in pH and salinity, and ordinary polyacrylamide is prone to molecular chain coiling under such conditions, resulting in decreased bridging ability and even degradation, affecting treatment stability; in addition, although some modified polyacrylamides have improved individual properties, their preparation processes are complex and the reaction conditions are harsh, making industrial-scale production difficult.

[0004] To address the aforementioned issues, some attempts have been made to modify polyacrylamide for papermaking wastewater in existing technologies. For example, CN109046277A discloses a wastewater treatment agent that can be used for paper industry wastewater treatment, which combines polyacrylamide with bamboo charcoal fiber, titanium dioxide, etc., attempting to improve the treatment effect through the synergistic effect of adsorption and flocculation. However, this scheme is merely a simple physical mixing, with poor synergy between the components, and it does not modify the polyacrylamide itself, making it difficult to fundamentally improve the targeted flocculation ability for pollutants in papermaking wastewater. CN1235613A discloses polyacrylamide polymerization, using ester-based oil as the oil phase to improve the stability of the polymerization system. However, this method mainly focuses on optimizing the preparation process of polyacrylamide and does not involve improving its specific performance in papermaking wastewater treatment. CN106336479A discloses a temperature-resistant, salt-resistant, and oxidation-resistant polyacrylamide and its preparation method, which improves environmental adaptability by introducing various modified structural units. However, this product is mainly aimed at the field of tertiary oil recovery and does not consider the specific pollutant composition of papermaking wastewater, making it insufficiently targeted for papermaking wastewater treatment.

[0005] Therefore, developing a polyacrylamide product that has strong targeted adsorption capacity for pollutants in papermaking wastewater, high stability in complex water quality environments, excellent flocculation efficiency, and simple preparation process that is easy to industrialize is of great practical significance and application value. Summary of the Invention

[0006] In order to overcome the above-mentioned defects of the prior art, the embodiments of the present invention provide a high-risk operation indicator device for thermal power plants. The technical problem to be solved by the present invention is that after the worker finishes using the safety belt, it needs to be placed correctly to avoid being squeezed by other heavy objects, which would cause deformation of the internal structure. In particular, the metal parts of the safety belt may be bent or damaged, affecting its strength and performance.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A polyacrylamide for treating papermaking wastewater is prepared by copolymerization of a main monomer, a targeted modifying monomer, an anti-degradation modifying monomer, and a crosslinking monomer in an aqueous solution.

[0009] The molar ratio of each monomer is: main monomer : targeted modified monomer : anti-degradation modified monomer : crosslinking monomer = 1 : (0.03-0.12) : (0.02-0.08) : (0.001-0.005);

[0010] The main monomer is acrylamide;

[0011] The targeted modification monomer is N-(2-hydroxyethyl)-3-phenylacrylamide;

[0012] The anti-degradation modifying monomer is 2-acrylamide-2-methylpropanesulfonic acid;

[0013] The crosslinking monomer is N,N'-methylenebisacrylamide;

[0014] The polyacrylamide has a number-average molecular weight of 18 million to 25 million, a degree of hydrolysis of 25% to 35%, and an intrinsic viscosity of 1200 to 1800 mL / g within a pH range of 3 to 11.

[0015] In a preferred embodiment, the molar ratio of each monomer is: host monomer : targeted modified monomer : anti-degradation modified monomer : crosslinking monomer = 1 : (0.05-0.08) : (0.03-0.05) : (0.002-0.003).

[0016] In a preferred embodiment, the polyacrylamide has a number-average molecular weight of 22 million to 24 million and a degree of hydrolysis of 30% to 33%.

[0017] This invention also proposes a method for preparing polyacrylamide for treating papermaking wastewater, comprising the following steps: S1. Preparing a mixed monomer aqueous solution: adding the main monomer, targeted modified monomer, anti-degradation modified monomer, and crosslinking monomer to deionized water according to the molar ratio described in claim 1, stirring to dissolve, and obtaining a mixed monomer aqueous solution; controlling the mass concentration of the mixed monomer aqueous solution to be 20%-30%; adding a pH adjuster to the mixed monomer aqueous solution to adjust the pH of the system to 6.5-7.5;

[0018] S2. Deoxygenation treatment: Transfer the mixed monomer aqueous solution prepared in step S1 into the polymerization reactor, and introduce high-purity nitrogen into the reactor at a flow rate of 0.8-1.2 L / min for 30-40 min.

[0019] S3. Segmented temperature-controlled polymerization: Maintain a nitrogen atmosphere, add a composite initiator to the reactor, first control the reaction temperature at 35-45℃, react for 1.5-2.5h, then raise the temperature to 55-65℃ and continue the reaction for 2-3h to obtain polyacrylamide gel.

[0020] S4. Post-processing: Take out the polyacrylamide gel obtained in step S3, granulate it to obtain gel particles with a particle size of 2-5 mm; place the gel particles in a vacuum drying oven at 60-70℃ and dry them to constant weight for 8-12 hours; crush the dried particles and pass them through an 80-mesh sieve to obtain the finished polyacrylamide product for papermaking wastewater treatment.

[0021] In a preferred embodiment, in step S1, the pH adjuster is a mixed aqueous solution of sodium carbonate and sodium bicarbonate, with a mass ratio of 1:2, and the amount of pH adjuster added is 0.5%-1.0% of the mass of the mixed monomer aqueous solution.

[0022] In a preferred embodiment, in step S3, the composite initiator is composed of an oxidizing initiator, a reducing initiator, and an azo initiator, with a mass ratio of 2:1:0.5.

[0023] In a preferred embodiment, the oxidation initiator is ammonium persulfate, the reduction initiator is sodium bisulfite, and the azo initiator is azobisisobutyramidine hydrochloride.

[0024] In a preferred embodiment, the amount of the composite initiator added is 0.05%-0.15% of the total mass of the mixed monomers.

[0025] In a preferred embodiment, in step S3, after the temperature rises to 55-65°C, the stirring speed is controlled to be 30-50 r / min.

[0026] In a preferred embodiment, in step S1, the mass concentration of the mixed monomer aqueous solution is 24%-26%; in step S2, the nitrogen flow rate is 1.0-1.2 L / min, and nitrogen is continuously purged for 30-35 min; in step S3, the reaction temperature is first controlled at 40-45℃, and after reacting for 1.5-2 h, the temperature is raised to 60-65℃, and the reaction continues for 2-2.5 h.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] The polyacrylamide of this invention achieves precise targeted adsorption of pollutants in papermaking wastewater by introducing the targeted modified monomer N-(2-hydroxyethyl)-3-phenylacrylamide: the phenyl group in its molecular structure can undergo π-π stacking with lignin derivatives in papermaking wastewater, and the hydroxyl group can form hydrogen bonds with the hydroxyl groups on the surface of fine fibers, which significantly improves the adsorption capacity for specific pollutants. Compared with ordinary polyacrylamide, the flocculation efficiency is increased by more than 30%, and the dosage of the reagent can be reduced by 25%-35%, effectively reducing the treatment cost.

[0029] By introducing the anti-degradation modified monomer 2-acrylamide-2-methylpropanesulfonic acid, polyacrylamide is endowed with excellent environmental stability: the sulfonic acid group introduced into this monomer has strong hydrophilicity and salt resistance, which can prevent the molecular chain from curling under the acid-base fluctuation and salinity environment of papermaking wastewater; at the same time, the electronic effect of the sulfonic acid group can enhance the antioxidant capacity of the molecular chain, reduce the degradation effect of pharmaceutical residues or oxidants in wastewater on polyacrylamide, and maintain stable flocculation performance in the pH range of 3-11.

[0030] A segmented temperature-controlled polymerization process, combined with a composite initiator system, was adopted to achieve stable polymerization: the low-temperature stage initiated the reaction slowly, avoiding excessively vigorous local reactions that could lead to uneven molecular weight distribution; the high-temperature stage promoted complete reaction and improved monomer conversion rate; the synergistic effect of the composite initiator could reduce the initiation temperature and broaden the reaction temperature range, enabling the monomer conversion rate to reach over 98%, and the product to have a uniform molecular weight distribution with a stable number-average molecular weight of 18 million to 25 million, ensuring excellent bridging and flocculation capabilities.

[0031] The reaction conditions of this invention are 35-65℃ and normal pressure, requiring no stringent equipment requirements, and the post-processing steps are simple, making it easy to achieve large-scale industrial production. The product is a solid powder, which is easy to store and transport, dissolves quickly during use, and has strong applicability. Detailed Implementation

[0032] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0033] Example 1

[0034] A polyacrylamide for treating papermaking wastewater is prepared by copolymerization of monomers in the following molar ratio: acrylamide : N-(2-hydroxyethyl)-3-phenylacrylamide : 2-acrylamide-2-methylpropanesulfonic acid : N,N'-methylenebisacrylamide = 1 : 0.05 : 0.03 : 0.002.

[0035] Its preparation method includes the following steps:

[0036] S1. Preparation of mixed monomer aqueous solution: Weigh 100g (1.408mol) of acrylamide, 11.2g (0.0704mol) of N-(2-hydroxyethyl)-3-phenylacrylamide, 7.8g (0.0422mol) of 2-acrylamide-2-methylpropanesulfonic acid, and 0.5g (0.0032mol) of N,N'-methylenebisacrylamide, add them to deionized water, stir and dissolve to obtain 500g of mixed monomer aqueous solution (mass concentration 24.3%); add 3g of a mixed aqueous solution of sodium carbonate and sodium bicarbonate (mass ratio 1:2) to the mixed monomer aqueous solution, and adjust the pH of the system to 7.0.

[0037] S2. Deoxygenation treatment: Transfer the mixed monomer aqueous solution into the polymerization reactor, and introduce high-purity nitrogen into the reactor at a flow rate of 1.0 L / min for 35 min.

[0038] S3. Segmented temperature-controlled polymerization: Maintain a nitrogen atmosphere and add a composite initiator (0.4g ammonium persulfate, 0.2g sodium bisulfite, and 0.1g azobisisobutyramidine hydrochloride) to the reactor. First, control the reaction temperature at 40℃. After reacting for 2 hours, raise the temperature to 60℃ and continue the reaction for 2.5 hours to obtain polyacrylamide gel.

[0039] S4. Post-processing: The polyacrylamide gel is removed and granulated to obtain gel particles with a particle size of 2-5 mm; the gel particles are placed in a vacuum drying oven at 65℃ and dried for 10 hours to constant weight; the dried particles are crushed and passed through an 80-mesh sieve to obtain the finished polyacrylamide product for papermaking wastewater treatment.

[0040] Testing revealed that the product has a number-average molecular weight of 22 million, a degree of hydrolysis of 30%, and an intrinsic viscosity of 1580 mL / g at pH 5. When used to treat wastewater from the middle stage of papermaking (COD = 2800 mg / L, suspended solids = 3200 mg / L, color = 500 times), at a dosage of 10 mg / L, the COD removal rate is 85%, the suspended solids removal rate is 98%, and the color removal rate is 92%.

[0041] Example 2

[0042] A polyacrylamide for treating papermaking wastewater is prepared by copolymerization of monomers in the following molar ratio: acrylamide : N-(2-hydroxyethyl)-3-phenylacrylamide : 2-acrylamide-2-methylpropanesulfonic acid : N,N'-methylenebisacrylamide = 1 : 0.08 : 0.05 : 0.003.

[0043] Its preparation method includes the following steps:

[0044] S1. Preparation of mixed monomer aqueous solution: Weigh 100g (1.408mol) of acrylamide, 17.9g (0.1126mol) of N-(2-hydroxyethyl)-3-phenylacrylamide, 13.0g (0.0704mol) of 2-acrylamide-2-methylpropanesulfonic acid, and 0.75g (0.0048mol) of N,N'-methylenebisacrylamide, add them to deionized water, stir and dissolve to obtain 520g of mixed monomer aqueous solution (mass concentration 25.4%); add 4g of a mixed aqueous solution of sodium carbonate and sodium bicarbonate (mass ratio 1:2) to the mixed monomer aqueous solution, and adjust the pH of the system to 7.2.

[0045] S2. Deoxygenation treatment: Transfer the mixed monomer aqueous solution into the polymerization reactor, and introduce high-purity nitrogen into the reactor at a flow rate of 1.2 L / min for 30 min.

[0046] S3. Segmented temperature-controlled polymerization: Maintain a nitrogen atmosphere and add a composite initiator (0.5g ammonium persulfate, 0.25g sodium bisulfite, and 0.125g azobisisobutyramidine hydrochloride) to the reactor. First, control the reaction temperature at 45℃. After reacting for 1.5h, raise the temperature to 65℃ and continue the reaction for 2h to obtain polyacrylamide gel.

[0047] S4. Post-processing: The polyacrylamide gel is removed and granulated to obtain gel particles with a particle size of 2-5 mm; the gel particles are placed in a vacuum drying oven at 70℃ and dried for 8 hours until constant weight; the dried particles are crushed and passed through an 80-mesh sieve to obtain the finished polyacrylamide product for papermaking wastewater treatment.

[0048] Testing revealed that the product has a number-average molecular weight of 24 million, a degree of hydrolysis of 33%, and an intrinsic viscosity of 1650 mL / g at pH=10. When used to treat pretreated wastewater from papermaking black liquor (COD=5600 mg / L, suspended solids=4500 mg / L, color=800 times), a dosage of 15 mg / L resulted in a COD removal rate of 82%, a suspended solids removal rate of 99%, and a color removal rate of 95%.

[0049] Comparative Example 1

[0050] Using a common acrylamide homopolymer (number average molecular weight 20 million, degree of hydrolysis 30%), the same papermaking mid-stage wastewater was treated under the treatment conditions of Example 1. When the dosage was 10 mg / L, the COD removal rate was 52%, the suspended solids removal rate was 75%, and the color removal rate was 60%.

[0051] Comparative Example 2

[0052] A polyacrylamide with a monomer molar ratio of acrylamide : 2-acrylamide-2-methylpropanesulfonic acid : N,N'-methylenebisacrylamide = 1 : 0.05 : 0.003 (without added targeted modified monomers) was prepared using the same method as in Example 2. When used to treat the papermaking black liquor pretreatment wastewater in Example 2, at a dosage of 15 mg / L, the COD removal rate was 65%, the suspended solids removal rate was 88%, and the color removal rate was 72%.

[0053] The experimental parameters and treatment effects of Examples 1 and 2 and Comparative Examples 1 and 2 are compared in the table below:

[0054] Case types Polyacrylamide formulation characteristics Wastewater Treatment Types and Parameters Dosage of the agent (mg / L) Key product performance indicators (number average molecular weight / 10,000, degree of hydrolysis / %) COD removal rate (%) Suspended solids removal rate (%) Color removal rate (%) Example 1 Acrylamide : N-(2-hydroxyethyl)-3-phenylacrylamide : 2-acrylamide-2-methylpropanesulfonic acid : N,N'-methylenebisacrylamide = 1 : 0.05 : 0.03 : 0.002 Wastewater from the middle stage of papermaking; COD = 2800 mg / L, suspended solids = 3200 mg / L, color = 500 times. 10 2200，30 85 98 92 Example 2 Acrylamide : N-(2-hydroxyethyl)-3-phenylacrylamide : 2-acrylamide-2-methylpropanesulfonic acid : N,N'-methylenebisacrylamide = 1 : 0.08 : 0.05 : 0.003 Paper mill black liquor pretreatment wastewater; COD=5600mg / L, suspended solids=4500mg / L, color=800 times. 15 2400，33 82 99 95 Comparative Example 1 Ordinary acrylamide homopolymer, without modified monomers Wastewater from the middle stage of papermaking; COD = 2800 mg / L, suspended solids = 3200 mg / L, color = 500 times. 10 2000，30 52 75 60 Comparative Example 2 Acrylamide : 2-Acrylamido-2-methylpropanesulfonic acid : N,N'-methylenebisacrylamide = 1 : 0.05 : 0.003, without targeted modification monomers. Paper mill black liquor pretreatment wastewater; COD=5600mg / L, suspended solids=4500mg / L, color=800 times. 15 / 65 88 72

[0055] As can be seen from the comparison results in the table above, the polyacrylamide of the present invention, due to the introduction of targeted modified monomers and anti-degradation modified monomers, has a significantly better removal effect on pollutants in papermaking wastewater than ordinary polyacrylamide and polyacrylamide without the introduction of targeted modified monomers, demonstrating excellent targeted flocculation ability and environmental stability.

[0056] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing tables and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A polyacrylamide for treating papermaking wastewater, characterized in that: It is prepared by copolymerization of main monomer, targeted modified monomer, anti-degradation modified monomer and crosslinking monomer through aqueous solution; The molar ratio of each monomer is: main monomer : targeted modified monomer : anti-degradation modified monomer : crosslinking monomer = 1 : (0.03-0.12) : (0.02-0.08) : (0.001-0.005); The main monomer is acrylamide; The targeted modification monomer is N-(2-hydroxyethyl)-3-phenylacrylamide; The anti-degradation modifying monomer is 2-acrylamide-2-methylpropanesulfonic acid; The crosslinking monomer is N,N'-methylenebisacrylamide; The polyacrylamide has a number-average molecular weight of 18 million to 25 million, a degree of hydrolysis of 25% to 35%, and an intrinsic viscosity of 1200 to 1800 mL / g within a pH range of 3 to 11.

2. The polyacrylamide for treating papermaking wastewater according to claim 1, characterized in that: The molar ratio of each monomer is: main monomer : targeted modified monomer : anti-degradation modified monomer : crosslinking monomer = 1 : (0.05-0.08) : (0.03-0.05) : (0.002-0.003).

3. The polyacrylamide for treating papermaking wastewater according to claim 2, characterized in that: The polyacrylamide has a number average molecular weight of 22 million to 24 million and a degree of hydrolysis of 30% to 33%.

4. A method for preparing polyacrylamide for treating papermaking wastewater, characterized in that: The process includes the following steps: S1. Preparing a mixed monomer aqueous solution: The main monomer, the targeted modified monomer, the anti-degradation modified monomer, and the crosslinking monomer are added to deionized water according to the molar ratio described in claim 1, and stirred to dissolve, thereby obtaining a mixed monomer aqueous solution; the mass concentration of the mixed monomer aqueous solution is controlled to be 20%-30%; a pH adjuster is added to the mixed monomer aqueous solution to adjust the pH of the system to 6.5-7.5; S2. Deoxygenation treatment: Transfer the mixed monomer aqueous solution prepared in step S1 into the polymerization reactor, and introduce high-purity nitrogen into the reactor at a flow rate of 0.8-1.2 L / min for 30-40 min. S3. Segmented temperature-controlled polymerization: Maintain a nitrogen atmosphere, add a composite initiator to the reactor, first control the reaction temperature at 35-45℃, react for 1.5-2.5h, then raise the temperature to 55-65℃ and continue the reaction for 2-3h to obtain polyacrylamide gel. S4. Post-processing: Take out the polyacrylamide gel obtained in step S3, granulate it to obtain gel particles with a particle size of 2-5 mm; place the gel particles in a vacuum drying oven at 60-70℃ and dry them to constant weight for 8-12 hours; crush the dried particles and pass them through an 80-mesh sieve to obtain the finished polyacrylamide product for papermaking wastewater treatment.

5. The method for preparing polyacrylamide for treating papermaking wastewater according to claim 4, characterized in that: In step S1, the pH adjuster is a mixed aqueous solution of sodium carbonate and sodium bicarbonate, with a mass ratio of 1:2, and the amount of pH adjuster added is 0.5%-1.0% of the mass of the mixed monomer aqueous solution.

6. The method for preparing polyacrylamide for papermaking wastewater treatment according to claim 4, characterized in that: In step S3, the composite initiator is composed of an oxidizing initiator, a reducing initiator, and an azo initiator, with a mass ratio of 2:1:0.

5.

7. The method for preparing polyacrylamide for treating papermaking wastewater according to claim 4, characterized in that: The oxidation initiator is ammonium persulfate, the reduction initiator is sodium bisulfite, and the azo initiator is azobisisobutyramidine hydrochloride.

8. The method for preparing polyacrylamide for treating papermaking wastewater according to claim 4, characterized in that: The amount of the composite initiator added is 0.05%-0.15% of the total mass of the mixed monomers.

9. The method for preparing polyacrylamide for papermaking wastewater treatment according to claim 4, characterized in that: In step S3, when the temperature rises to 55-65℃, the stirring speed is controlled to be 30-50 r / min.

10. The method for preparing polyacrylamide for treating papermaking wastewater according to claim 4, characterized in that: In step S1, the mass concentration of the mixed monomer aqueous solution is 24%-26%; in step S2, the nitrogen flow rate is 1.0-1.2 L / min, and nitrogen is continuously purged for 30-35 min; in step S3, the reaction temperature is first controlled at 40-45℃, and after reacting for 1.5-2 h, the temperature is raised to 60-65℃, and the reaction continues for 2-2.5 h.