Preparation method of polymagnesium-methacrylamide coagulant capable of efficiently removing microplastics

Abstract

The invention belongs to the technical field of water treatment, and provides a preparation method of a polymagnesium-methacrylamide coagulant. And reacting the prepared polyacrylamide with dimethyl sulfate under the conditions that potassium hydroxide is used as an initiator and tetrabutyl ammonium hydroxide is used as a phase transfer catalyst to prepare polymethacrylamide, and then carrying out polymerization and rotary evaporation on the polymethacrylamide and a magnesium sulfate solution to obtain the poly magnesium-methacrylamide (Mg-PMAM) coagulant. Compared with aluminum sulfate and ferric chloride, the coagulant has the advantages of high microplastic removal rate, high floc sedimentation rate and the like. The coagulant for efficiently removing the micro-plastics is prepared, and the micro-plastics in water are effectively removed through adsorption bridging and net catching and sweeping effects.

Description

Technical Field

[0001] The invention belongs to the technical field of water treatment, and specifically relates to a method for preparing a polymagnesium-methacrylamide coagulant for efficiently removing microplastics. Background Art

[0002] Plastic products are being widely used in various industries such as packaging, building materials and daily personal care products due to their excellent physicochemical properties such as easy production, durability, light weight and low cost. The main pathways for plastics to enter the environment involve wastewater and urban runoff. After some larger plastics enter water bodies, they are broken into microplastics with a diameter of less than 1 mm through weathering, biodegradation, photodegradation, thermal degradation and water flow movement. These microplastics are easily swallowed and ingested by organisms and accumulate along the food chain. In addition, due to their hydrophobicity and large specific surface area, microplastics often show high adsorption capacity for a series of pollutants such as persistent organic pollutants (such as polychlorinated biphenyls, organochlorine pesticides, polycyclic aromatic hydrocarbons, dichlorodiphenyltrichloroethane) and heavy metals (such as Zn, Pb and Cu), and therefore play an important role in the fate and migration of pollutants in the environment. Pollutants adsorbed on MPs can desorb and affect metabolic and physiological processes, as well as human and ecological health. Therefore, efficient and feasible methods are urgently needed to remove microplastics from natural water bodies.

[0003] Coagulation is an essential and important part of traditional water purification technology. It is one of the most commonly used treatment methods for removing microplastics in water treatment processes because of its low cost and ease of operation. Since microplastics have small particle sizes and are easily adsorbed by various pollutants, ordinary metal salts are not ideal for their removal. The removal mechanism of metal salts for microplastics is mainly electrical neutralization, and the flocs formed are small and have poor sedimentation performance. Therefore, the present invention proposes a method for preparing a polymagnesium-methacrylamide coagulant, which can effectively "capture" microplastics in the solution through adsorption bridging and winding and sweeping, forming larger flocs and accelerating sedimentation, thereby improving the removal rate of microplastics. Summary of the invention

[0004] The present invention aims at the problem that common metal salt coagulants have low removal efficiency for microplastics and provides a method for preparing a polymagnesium-methacrylamide coagulant which can effectively improve the removal rate of microplastics.

[0005] To achieve the above purpose, the present invention adopts the following scheme.

[0006] (1) Add 80 g of acrylamide (AM), 0.08 g of sodium persulfate and 0.016 g of β-dimethylaminopropionitrile to a 500 mL three-necked flask, and add water to a total weight of 400 g. After nitrogen is passed to deoxygenate, polymerize at 30 °C for 4 hours to obtain polyacrylamide (PAM) colloid; (2) Take 10 g of PAM colloid and place it in a 250 mL three-necked bottle, add dimethyl sulfoxide to swell for 24 h; add 15 g of potassium hydroxide and 3 mL of phase transfer catalyst tetrabutylammonium hydroxide to the three-necked bottle, heat it to 80 °C in a water bath, then add 15 mL of dimethyl sulfate dropwise, control the temperature to 95 °C (add paraffin to prevent evaporation), stir and reflux for 12 h, and obtain macroporous cross-linked poly (N-methyl acrylamide) resin (PNMAM). Rinse the obtained resin with a large amount of water, and finally wash and filter it with anhydrous ethanol, and dry it in a vacuum at below 50 °C for use.

[0007] Preferably, PAM is swollen with dimethyl sulfoxide for 24 hours; Preferably, the phase transfer catalyst is tetrabutylammonium hydroxide.

[0008] The present invention has the following advantages: The present invention synthesizes polymethacrylamide by adding dimethyl sulfate to the traditional polyacrylamide synthesis, and then fuses the polymethacrylamide with magnesium sulfate solution to prepare a polymagnesium-methacrylamide coagulant. The organic component of the coagulant is rapidly hydrolyzed in the aqueous solution to form a large floc, which captures small molecular particles in the solution through the net capture and sweeping action; the Mg in the inorganic component is 2+ The organic components act as bridges, thereby attracting the organic components to condense with the small molecular pollutants in the solution, thereby improving the removal rate of small molecular particles. The present invention uses polystyrene microplastics (PS) with a particle size of 5μm as a representative of small molecular particles to explore the advantages of the coagulant in removing small molecular particles. DETAILED DESCRIPTION

[0009] The present invention will be further described below in conjunction with embodiments and drawings, but the present invention is not limited by the following embodiments.

[0010] Example 1 Preparation of polymagnesium-methacrylamide coagulant This case provides a method for synthesizing a polymagnesium-methacrylamide coagulant, comprising the following steps: (1) In a 500 mL three-necked flask, add 80 g of acrylamide (AM), 0.08 g of sodium persulfate and 0.016 g of β-dimethylaminopropionitrile, and add water to a total weight of 400 g.

[0011] (2) Nitrogen was continuously introduced into the three-necked flask in step (1) and polymerization was carried out at 30° C. for 4 hours to obtain polyacrylamide (PAM) colloid.

[0012] (3) Weigh the PAM colloid prepared in step (2), place it in a 250 mL three-necked bottle, and add sufficient dimethyl sulfoxide to swell for 24 h.

[0013] (4) Add 15 g potassium hydroxide and 3 mL tetrabutylammonium hydroxide (phase transfer catalyst) into the three-necked flask in step (3) and heat the mixture to 80°C in a water bath.

[0014] (5) After the water bath is heated to 80°C, add sufficient amount of paraffin wax to the three-necked flask in step (4), and then add 15 mL of dimethyl sulfate dropwise. During this process, the temperature is controlled at 95°C and stirring and refluxing are continued for 12 h.

[0015] (6) After completing step (5), a mixture of polymethacrylamide and other impurities is obtained.

[0016] (7) The mixture obtained in step (6) is rinsed with a large amount of deionized water, then washed with anhydrous ethanol, filtered, and vacuum dried at below 50° C. to obtain polymethacrylamide.

[0017] (8) Take 0.6 g of NaOH and dilute to 100 mL to obtain a 0.15 mol / L NaOH solution.

[0018] (9) Take 10 g of PMAM prepared in step (7) and 12.0368 g of magnesium sulfate and place them in a 500 mL three-necked flask. Add 200 mL of deionized water and heat the mixture to 60 °C in a water bath while stirring continuously.

[0019] (10) Add the NaOH solution in step (8) dropwise to the three-necked flask in step (9). If a white precipitate is formed during the addition, stop adding. Continue adding until the precipitate disappears, until the addition of the NaOH solution is complete.

[0020] (11) The solution obtained in step (10) is placed in a rotary evaporator for rotary evaporation to obtain a solid powder, namely polymagnesium-methacrylamide (Mg-PMAM). BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a scanning electron microscope image of the polymethacrylamide obtained in step (7) of Example 1; Figure 2 is a scanning electron microscope image of polymagnesium-methacrylamide obtained in step (11) of Example 1; Figure 3 This is the coagulation removal effect diagram of PS by polymagnesium-methacrylamide, aluminum sulfate and ferric chloride at different dosages; Figure 4 This is the Zeta potential diagram of the coagulation effluent of PS under different dosages of polymagnesium-methacrylamide, aluminum sulfate and ferric chloride.

[0022] Example 2 Characterization of polymagnesium-methacrylamide (1) Attachment Figure 1This is a scanning electron microscope image of the polymethacrylamide prepared in step (7) of Example 1, showing its lamellar organic polymer structure.

[0023] (2) Attachment Figure 2 This is a scanning electron microscope image of the polymagnesium-methacrylamide prepared in step (11) of Example 1. It can be seen that it has both an inorganic molecule crystal structure and a lamellar organic polymer structure, indicating that polymethacrylamide and magnesium sulfate can be well combined to form polymagnesium-methacrylamide.

[0024] Example 3 Removal of microplastics by polymagnesium-methacrylamide.

[0025] (1) Experimental water preparation: Use a measuring cylinder to measure 15 L of deionized water and 187.5 mL of microplastic mother liquor with a concentration of 400 mg / L to obtain microplastic coagulation raw water with a concentration of 5 mg / L.

[0026] (2) Coagulant: Ferric chloride and aluminum sulfate were selected as traditional metal salt coagulants with dosages of 0.05, 0.1, 0.015, 0.2, 0.25, and 0.3 mmol / L, respectively, calculated as Fe and Al; the dosage of polymagnesium-methacrylamide was 0.16, 0.18, 0.2, 0.22, 0.24, and 0.26 g / L.

[0027] (3) Coagulation experiment: rapid stirring for 30 s (200 rpm), dosing, rapid stirring for 90 s (200 rpm), slow stirring for 15 min (40 rpm), and sedimentation for 30 min.

[0028] (4) Experimental phenomena: By the attached Figure 1 It can be seen that in the range of 0.05-0.2mmol / L, the removal rate of aluminum sulfate for PS gradually increases. When the dosage of aluminum sulfate is 0.2mmol / L, the removal effect of aluminum sulfate on PS is the best, and the removal rate reaches about 68%; in the range of 0.2-0.3mmol / L, with the increase of the dosage, the removal rate of PS decreases. This is because the excessive dosage of aluminum sulfate will cause the flocs to become smaller and the sedimentation performance to weaken, resulting in a decrease in the PS removal rate. With the increase of the dosage of ferric chloride, the removal rate of PS also gradually increases, and its optimal removal rate is about 75%, which is greater than the optimal removal rate of aluminum sulfate. This may be because the flocs formed by ferric chloride are larger than aluminum sulfate. The removal rate of polymagnesium-methacrylamide for PS is above 95%, and the optimal removal rate is about 98.5%, which shows that the removal effect of polymagnesium-methacrylamide on PS is much higher than that of traditional coagulants such as aluminum sulfate and ferric chloride.

[0029] By the attached Figure 2It can be seen that the Zeta potential of the coagulated raw water is around -12mV, indicating that the PS solution is in a stable state and is not easy to become unstable. With the increase in the dosage of aluminum sulfate and ferric chloride, the Zeta potential of the solution gradually increases, indicating that the removal methods of these two coagulants for PS contain charge neutralization. However, the Zeta potential of the solution has reached a positive value when the dosage of aluminum sulfate is 0.1mmol / L, while the Zeta potential of the solution is greater than 0 when the dosage of ferric chloride is 0.25mmol / L. This shows that aluminum sulfate mainly relies on charge neutralization to remove PS, while charge neutralization is not the main mechanism for ferric chloride to remove PS. On the other hand, the Zeta potential of the solution of polymagnesium-methacrylamide does not rise with the increase in the dosage, but decreases, and always remains at a negative value. This shows that the mechanism of polymagnesium-methacrylamide to remove PS does not have a charge neutralization effect. Its removal mechanism should be adsorption bridging effect and net capture and sweeping effect, which separates PS from the solution by continuously aggregating PS particles to form large flocs, thereby effectively removing PS.

Claims

1. A method for preparing a polymagnesium-methacrylamide coagulant for efficiently removing microplastics, characterized in that: The following steps are involved: (1) Add 80 g of acrylamide (AM), 0.08 g of sodium persulfate and 0.016 g of β-dimethylaminopropionitrile to a 500 mL three-necked flask, and add water to a total weight of 400 g. After nitrogen is passed through to deoxygenate, polymerize at 30 °C for 4 hours to obtain polyacrylamide (PAM) colloid; (2) Take 10 g of PAM colloid and place it in a 250 mL three-necked bottle, add dimethyl sulfoxide to swell for 24 h; add 15 g of potassium hydroxide and 3 mL of phase transfer catalyst tetrabutylammonium hydroxide to the three-necked bottle, heat it to 80 °C in a water bath, then add 15 mL of dimethyl sulfate dropwise, control the temperature to 95 °C (add paraffin to prevent evaporation), stir and reflux for 12 h, and obtain macroporous cross-linked poly (N-methyl acrylamide) resin (PNMAM). Rinse the obtained resin with a large amount of water, and finally wash and filter it with anhydrous ethanol, and dry it in a vacuum at below 50 °C for use.

2. (3) Take 0.6g NaOH and dilute to 100mL to obtain a 0.15mol / L NaOH solution. Take 10g PMAM and 12.0368g magnesium sulfate and place them in a 500mL three-necked flask. Add 200mL deionized water. Heat the water bath to 60°C and stir continuously. Then add the NaOH solution dropwise. Observe the process of adding. If a white precipitate is generated, stop adding. Continue adding until the precipitate disappears. Add the NaOH solution until the addition is complete. Place the resulting solution in a rotary evaporator for rotary evaporation. Finally, obtain a solid powder, which is polymagnesium-methyl acrylamide (Mg-PMAM).

3. The preparation method according to claim 1, characterized in that PAM colloid needs to be swollen with dimethyl sulfoxide for 24 hours.

4. The preparation method according to claim 1, characterized in that The phase catalyst selected was tetrabutylammonium hydroxide, and the reaction temperature was 80°C.

5. The preparation method according to claim 1, characterized in that When adding dimethyl sulfate dropwise, the temperature should be controlled at 95°C and paraffin should be added to prevent evaporation.

6. The preparation method according to claim 1, characterized in that Alkalinity [OH - ]:[Mg 2+ ]=1.5.

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