High-efficiency removal and green catalytic degradation methods for microplastics in water

Abstract

The present application belongs to the technical field of water pollutant removal, and particularly relates to a water microplastic efficient removal and green catalytic degradation method. The water microplastic efficient removal and green catalytic degradation method comprises the following steps: preparing a lignin carbon-based magnetic adsorption material; adding the lignin carbon-based magnetic adsorption material to a polluted water body containing microplastics to perform an adsorption reaction; under an inert atmosphere, performing thermal degradation on the lignin carbon-based magnetic adsorption material adsorbing the microplastics to realize in-situ catalytic degradation and recovery of the microplastics and regeneration of the lignin carbon-based magnetic adsorption material. In the in-situ catalytic thermal degradation process of the microplastics, the biochar plays a role of an in-situ catalyst, can promote the in-situ catalytic thermal degradation of the microplastics, generates high-value hydrocarbon byproducts, realizes green thermal degradation and reuse of the microplastics, and regenerates the carbon-based adsorption material.

Description

Technical Field

[0001] This invention belongs to the field of water pollutant removal technology, specifically relating to a method for efficient removal and green catalytic degradation of microplastics in water. Background Technology

[0002] In 2022, my country's water pollution control industry reached a scale of trillions of yuan, with rural water treatment accounting for 320.65 billion yuan. It is worth noting that microplastics (first proposed by Thompson in the journal *Science* in 2004, defined as plastic fibers, particles, or films with a particle size of less than 5 mm) entering the aquatic environment, due to their strong hydrophobicity and large specific surface area, can strongly adsorb other pollutants, affecting the migration, transformation, and bioavailability of pollutants in the aquatic environment, and have been listed as a new global pollutant by the United Nations Environment Programme. Therefore, how to efficiently remove / degrade microplastics in water is of great significance for agricultural water pollution prevention and control.

[0003] Microplastics in aquatic environments can be removed through adsorption, coagulation, filtration, microbial degradation, and advanced oxidation processes. Among these, adsorption is considered one of the most efficient and feasible methods for removing microplastics from water due to its low cost, simple and safe operation, high environmental friendliness, and recyclability. The key is that it is driven by an adsorbent. Adsorbents used for microplastic removal mainly include biochar, activated carbon, and metal-organic framework materials. Biochar, in particular, possesses a well-developed porous structure, rich surface chemical properties, and a low spontaneous desorption rate. Its quality can be further controlled through acid-base activation, coating, and impregnation. In recent years, magnetic biochar has been able to easily and rapidly remove microplastics from aqueous solutions through magnetic separation, providing an effective strategy for addressing the subsequent separation of treated biochar. Therefore, rapid separation of adsorbent materials is a prerequisite for their recycling and reuse.

[0004] Furthermore, the green degradation of microplastics and the recycling of adsorbent materials are crucial aspects of the prevention and control of emerging pollutants. Currently, the recycling of adsorbents is achieved by rinsing with ethanol or water to desorb microplastics, which may lead to secondary pollution as the microplastics are reintroduced into the environment. Therefore, photocatalytic degradation, biodegradation, and thermal degradation methods are widely used for microplastic degradation, with thermal degradation exhibiting unique advantages due to its high degradation efficiency and short process route. Notably, biochar acts as an "in-situ catalyst" in the thermal treatment and recycling of adsorbent materials, potentially promoting the in-situ catalytic thermal degradation of microplastics. Therefore, how to achieve the thermal degradation and recycling of microplastics and the regeneration of carbon-based adsorbent materials is a pressing problem that needs to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide a method for the efficient removal and green catalytic degradation of microplastics in water. This method achieves efficient removal / degradation of microplastics and the recycling of adsorption materials.

[0006] The method for efficient removal and green catalytic degradation of microplastics in water according to the present invention comprises the following steps:

[0007] (1) Modified lignin was prepared using ferric chloride hexahydrate and lignin as raw materials. The modified lignin was then subjected to high-temperature pyrolysis and finally cooled to room temperature for washing to obtain lignin carbon-based magnetic adsorption material.

[0008] (2) The lignin-carbon-based magnetic adsorbent material prepared in step (1) is added to the polluted water containing microplastics for adsorption reaction;

[0009] (3) Under an inert atmosphere, the lignin carbon-based magnetic adsorbent material that adsorbs microplastics is placed in a fixed-bed pyrolysis reactor for thermal degradation, thereby realizing the in-situ catalytic degradation and recovery of microplastics and the regeneration of lignin carbon-based magnetic adsorbent material.

[0010] in:

[0011] The lignin mentioned in step (1) is derived from industrial waste residue from pulping or biogas projects.

[0012] The modified lignin described in step (1) is prepared by placing a mixture of ferric chloride hexahydrate and lignin in deionized water and ultrasonically treating it for 20-40 minutes, then letting it stand for 12 hours, and finally placing the obtained product in an oven and drying it at 100-105℃ for 24 hours; wherein the mass ratio of ferric chloride hexahydrate to lignin is 3-0.33:1.

[0013] The high-temperature pyrolysis described in step (1) involves heating from room temperature to 750-950℃ in a tube furnace at a heating rate of 10℃ / min for 1-3 hours.

[0014] The washing process described in step (1) involves washing three times with ethanol and deionized water, respectively.

[0015] The microplastics mentioned in step (2) are one of polystyrene (PS), polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC) or polyethylene terephthalate (PET).

[0016] In step (2), the amount of lignin-carbon-based magnetic adsorbent material added to the polluted water containing microplastics is 1-5 g / L, the adsorption reaction temperature is 15-40℃, the adsorption reaction time is 12-13 h, and the pH value of the polluted water containing microplastics is controlled to be 6.2-6.8.

[0017] In step (2), the content of microplastics in the polluted water is 10-60 mg / L.

[0018] The inert atmosphere mentioned in step (3) is either nitrogen or argon, and the flow rate of nitrogen or argon is 150-200 mL / min; the thermal degradation temperature is 450-600℃, and the thermal degradation time is 20-40 min.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] (1) The method for efficient removal and green catalytic degradation of microplastics in water described in this invention firstly modifies lignin raw materials by ultrasonic blending and then obtains lignin carbon-based magnetic adsorbent materials through pyrolysis carbonization-in-situ magnetization process; then, it removes different types of microplastics in water by adsorption method to obtain the adsorption capacity of lignin carbon-based magnetic adsorbent materials under complex environmental parameter effects; finally, it places the lignin carbon-based magnetic adsorbent materials that adsorb microplastics in a pyrolysis reactor to realize the in-situ catalytic degradation and recovery of microplastics and the regeneration of lignin carbon-based magnetic adsorbent materials; the parameters of the entire process method are easy to control, the operation is simple, and it is easy to promote and use.

[0021] (2) The method for efficient removal and green catalytic degradation of microplastics in water described in this invention utilizes iron salts to regulate the pore structure and magnetic properties of carbon-based adsorption materials, enhances the adsorption driving force, improves the removal efficiency of microplastics and the separation characteristics of adsorption materials, and utilizes the catalytic properties of biochar to achieve in-situ catalytic thermal degradation of microplastics. This method can realize the recycling of microplastics in water through adsorption-separation-thermal degradation, and has broad application prospects in the field of water environment management.

[0022] (3) The method for efficient removal and green catalytic degradation of microplastics in water described in this invention can achieve simultaneous removal / degradation of novel microplastic pollutants and high-value utilization of lignin resources by coupling the removal of microplastics with lignin carbon-based magnetic adsorption materials and in-situ catalytic thermal degradation of microplastics. Moreover, the preparation process of lignin carbon-based magnetic adsorption materials is simple and low-cost, and has high promotion and utilization value from both economic and environmental perspectives.

[0023] (4) The method for efficient removal and green catalytic degradation of microplastics in water described in this invention uses biochar as an “in-situ catalyst” during the in-situ catalytic thermal degradation of microplastics. This promotes the in-situ catalytic thermal degradation of microplastics and generates high-value hydrocarbon byproducts, thus realizing the green thermal degradation and reuse of microplastics and the regeneration of carbon-based adsorption materials. Detailed Implementation

[0024] The present invention will be further described below with reference to embodiments.

[0025] Example 1

[0026] The method for efficient removal and green catalytic degradation of microplastics in water described in Example 1 consists of the following steps:

[0027] (1) Lignin raw materials were modified using an ultrasonic blending loading method. Ferric chloride hexahydrate (FeCl3·6H2O) and lignin waste from pulping were placed in 100 mL of deionized water at a 1:1 mass ratio and ultrasonically treated for 30 min, then allowed to stand for 12 h. The resulting product was placed in an oven and continuously dried at 105 °C for 24 h to obtain modified lignin. The modified lignin was then pyrolyzed in a tube furnace at a heating rate of 10 °C / min to 850 °C for 2 h using a pyrolysis-carbonization-in-situ magnetization process. Finally, the obtained modified biochar sample was cooled to room temperature and washed three times with ethanol and deionized water to obtain lignin-based carbon magnetic adsorbent material. The specific surface area of ​​the prepared lignin-based carbon magnetic adsorbent material was 410.79 m². 2 / g, pore volume is 0.181cm 3 / g.

[0028] (2) The polystyrene microplastic stock solution was diluted with deionized water to 20 mg / L, with a pH of approximately 6.4. 0.05 g of lignin-carbon-based magnetic adsorbent and 20 mL of the microplastic solution were added to 50 mL centrifuge tubes, and the mixture was shaken at 200 r / min at 25 °C for 12.5 h. The removal efficiency was calculated by measuring the concentration of residual microplastics in the supernatant using a spectrophotometer. The removal rate of polystyrene was 99.2%, and the adsorption capacity (the removal rate Qe (mg / g) is the weight of microplastics adsorbed by 1 g of biochar adsorbent) was 32.02 mg·g⁻¹. -1 .

[0029] (3) Under a nitrogen atmosphere with a nitrogen flow rate of 170 mL / min, the lignin-based magnetic adsorbent material adsorbing microplastics was placed in a fixed-bed pyrolysis reactor for thermal degradation at a temperature of 550℃ and a time of 40 min, achieving in-situ catalytic degradation and recovery of microplastics and regeneration of the lignin-based magnetic adsorbent material. The relative content of hydrocarbons in the thermal degradation products was 74.6%, achieving green degradation of polystyrene, and the generated hydrocarbons can be used as basic raw materials for polystyrene synthesis; at the same time, the lignin-based magnetic adsorbent material was regenerated, and the regenerated lignin-based magnetic adsorbent material can continue to be used for the removal of microplastics from water bodies without causing secondary pollution.

[0030] Example 2

[0031] The method for efficient removal and green catalytic degradation of microplastics in water described in Example 2 consists of the following steps:

[0032] (1) Lignin raw materials were modified using an ultrasonic blending loading method. Ferric chloride hexahydrate (FeCl3·6H2O) and lignin waste from pulping were placed in 100 mL of deionized water at a mass ratio of 1:3 and ultrasonically treated for 40 min, then allowed to stand for 12 h. The resulting product was placed in an oven and continuously dried at 103 °C for 24 h to obtain modified lignin. The modified lignin was then pyrolyzed in a tube furnace at a heating rate of 10 °C / min to 950 °C for 3 h using a pyrolysis-carbonization-in-situ magnetization process. Finally, the obtained modified biochar sample was cooled to room temperature and washed three times with ethanol and deionized water to obtain lignin-based carbon magnetic adsorbent material. The specific surface area of ​​the prepared lignin-based carbon magnetic adsorbent material was 208.23 m². 2 / g, pore volume is 0.132cm³ 3 / g.

[0033] (2) The polypropylene microplastic stock solution was diluted with deionized water to 60 mg / L, with a pH of approximately 6.8. 0.3 g of lignin-carbon-based magnetic adsorbent and 60 mL of the microplastic solution were added to 100 mL centrifuge tubes, and the mixture was shaken at 200 r / min at 40 °C for 12 h. The removal efficiency was calculated by measuring the concentration of residual microplastics in the supernatant using a spectrophotometer. The removal rate for polypropylene was 98.7%, and the adsorption capacity (the removal rate Qe (mg / g) is the weight of microplastics adsorbed by 1 g of biochar adsorbent) was 29.83 mg·g⁻¹. -1 .

[0034] (3) Under a nitrogen atmosphere with a nitrogen flow rate of 200 mL / min, the lignin-based magnetic adsorbent material adsorbing microplastics was placed in a fixed-bed pyrolysis reactor for thermal degradation at a temperature of 600℃ for 30 min, achieving in-situ catalytic degradation and recovery of microplastics and regeneration of the lignin-based magnetic adsorbent material. The relative content of hydrocarbons in the thermal degradation products was 75.2%, achieving green degradation of polypropylene, and the generated hydrocarbons can be used as basic raw materials for polypropylene synthesis; at the same time, the lignin-based magnetic adsorbent material was regenerated, and the regenerated lignin-based magnetic adsorbent material can continue to be used for the removal of microplastics from water bodies without causing secondary pollution.

[0035] Example 3

[0036] The method for efficient removal and green catalytic degradation of microplastics in water described in Example 3 consists of the following steps:

[0037] (1) Lignin raw materials were modified using an ultrasonic blending loading method. Ferric chloride hexahydrate (FeCl3·6H2O) and lignin waste from pulping were placed in 100 mL of deionized water at a mass ratio of 3:1 and ultrasonically treated for 20 min, then allowed to stand for 12 h. The resulting product was placed in an oven and continuously dried at 100℃ for 24 h to obtain modified lignin. The modified lignin was then pyrolyzed in a tube furnace at a heating rate of 10℃ / min to 750℃ for 1 h using a pyrolysis-carbonization-in-situ magnetization process. Finally, the obtained modified biochar sample was cooled to room temperature and washed three times with ethanol and deionized water to obtain lignin-based carbon magnetic adsorbent material. The specific surface area of ​​the prepared lignin-based carbon magnetic adsorbent material was 863.12 m². 2 / g, pore volume is 0.415cm³ 3 / g.

[0038] (2) The polyvinyl chloride (PVC) microplastic stock solution was diluted with deionized water to 10 mg / L, with a pH of approximately 6.2. 0.01 g of lignin-carbon-based magnetic adsorbent and 10 ml of the microplastic solution were added to 30 mL centrifuge tubes, and the mixture was shaken at 200 r / min at 15 °C for 13 h. The removal efficiency was calculated by measuring the concentration of residual microplastics in the supernatant using a spectrophotometer. The removal rate for PVC was 99.1%, and the adsorption capacity (Qe (mg / g) is the weight of microplastics adsorbed by 1 g of biochar adsorbent) was 36.43 mg·g⁻¹. -1 .

[0039] (3) Under a nitrogen atmosphere with a nitrogen flow rate of 150 mL / min, the lignin-based magnetic adsorbent material adsorbing microplastics was placed in a fixed-bed pyrolysis reactor for thermal degradation at a temperature of 450℃ for 20 min, achieving in-situ catalytic degradation and recovery of microplastics and regeneration of the lignin-based magnetic adsorbent material. The relative content of hydrocarbons in the thermal degradation products was 73.2%, achieving green degradation of polyvinyl chloride (PVC), and the generated hydrocarbons can be used as basic raw materials for PVC synthesis. Simultaneously, the lignin-based magnetic adsorbent material was regenerated, and the regenerated material can continue to be used for the removal of microplastics from water bodies without causing secondary pollution.

[0040] Comparative Example 1

[0041] The method for removing and catalytically degrading microplastics in water described in Comparative Example 1 is the same as that in Example 1. The only difference is that the thermal degradation method is no longer used in step (3). The lignin-carbon-based magnetic adsorbent material with microplastics adsorbed in step (2) is washed three times with ethanol and deionized water respectively. The microplastic resolution rate is measured to be 99.1%. Then, the lignin-carbon-based magnetic adsorbent material is placed in a 105°C oven and dried continuously for 12 hours for later use. Microplastics cannot be degraded and reused, and the wastewater containing microplastics will cause secondary pollution.

Claims

1. A method for efficient removal and green catalytic degradation of microplastics in water bodies, characterized by: Comprise the following steps: (1) The modified lignin is prepared by using ferric chloride hexahydrate and lignin as raw materials, then the modified lignin is pyrolyzed at high temperature, and finally washed after cooling to room temperature to prepare the lignin carbon-based magnetic adsorption material; (2) The lignin carbon-based magnetic adsorption material prepared in step (1) is added to the polluted water body containing microplastics to carry out adsorption reaction; (3) The lignin carbon-based magnetic adsorption material adsorbed with microplastics is placed in a fixed bed pyrolysis reactor for thermal degradation under an inert atmosphere to realize in-situ catalytic degradation and recovery of microplastics and regeneration of the lignin carbon-based magnetic adsorption material; Wherein: In step (1), the preparation of the modified lignin is to place the mixture of ferric chloride hexahydrate and lignin in deionized water for ultrasonic treatment for 20-40 min, then stand for 12 h, and finally put the obtained product into an oven for drying at 100-105℃ for 24 h; wherein the mass ratio of ferric chloride hexahydrate to lignin is 3-0.33:1; In step (1), the high temperature pyrolysis is to pyrolyze at a heating rate of 10℃ / min from room temperature to 750-950℃ for 1-3 h in a tube furnace.

2. The method for efficient removal and green catalytic degradation of microplastics in water bodies according to claim 1, characterized in that: In step (1), the lignin is derived from industrial waste residues of pulp-making or biogas engineering.

3. The method for efficient removal and green catalytic degradation of microplastics in water bodies according to claim 1, characterized in that: In step (1), the washing is to wash with ethanol and deionized water for 3 times respectively.

4. The method for efficient removal and green catalytic degradation of microplastics in water bodies according to claim 1, characterized in that: In step (2), the microplastics are one of polystyrene, polyethylene, polypropylene, polyvinyl chloride or polyethylene terephthalate.

5. The method for efficient removal and green catalytic degradation of microplastics in water bodies according to claim 1, characterized in that: In step (2), the addition amount of the lignin carbon-based magnetic adsorption material in the polluted water body containing microplastics is 1-5 g / L, the adsorption reaction temperature is 15-40℃, the adsorption reaction time is 12-13 h, and the pH value of the polluted water body containing microplastics is controlled to be 6.2-6.

8.

6. The method for efficient removal and green catalytic degradation of microplastics in water bodies according to claim 1, characterized in that: In step (2), the content of microplastics in the polluted water body is 10-60 mg / L.

7. The method of claim 1, wherein the method is characterized by: In step (3), the inert atmosphere is one of nitrogen or argon, the flow rate of nitrogen or argon is 150-200 mL / min; the thermal degradation temperature is 450-600℃, and the thermal degradation time is 20-40 min.