Method for degrading micro-plastics based on chloride ion and persulfate synergistic thermal activation system

Abstract

The invention relates to a method for degrading micro-plastics based on a chloride ion and persulfate synergistic thermal activation system, which comprises the following steps: adding micro-plastics into a solution of inorganic chlorine salt containing Cl <-> and persulfate, adjusting the pH value of the solution, then carrying out hydrothermal reaction, generating multiple active species by Cl <-> and persulfate under a thermal activation condition so as to attack micro-plastic molecular chains, and further degrading the micro-plastics. And finally, the micro-plastic is mineralized into CO2 and H2O, so that the micro-plastic is oxidized and degraded. The method has the beneficial effects that efficient oxygenolysis of micro-plastics in water is realized by introducing a Cl <-> and PMS / thermal synergistic activation system, the degradation efficiency is improved to 90% or above, a transition metal catalyst is not needed, the reaction condition is mild, the energy consumption is low, degradation products mainly comprise CO2 and H2O, no toxic intermediate products exist, and the method is suitable for industrial production. The method is suitable for various complex water quality environments such as micro-plastics, landfill leachate, seawater and high-salt wastewater, and has remarkable environmental friendliness and industrial application potential.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of environmental pollution control, in particular to a method for degrading microplastics based on a chlorine ion and persulfate synergistic thermal activation system. BACKGROUND

[0002] As a kind of persistent environmental pollutants, microplastics have posed a serious threat to global ecosystems due to their non-biodegradability and bioaccumulation in water environments. Traditional treatment technologies such as photocatalytic degradation and biodegradation have drawbacks such as low quantum efficiency, long cycle time (usually several months), and high cost. Although the advanced oxidation technology based on persulfate (PMS) can generate strong oxidizing free radicals (SO4 - ·, ·OH), the degradation efficiency of microplastics is limited (usually less than 30%) when using PMS alone or only through thermal activation, and complete mineralization is difficult to achieve.

[0003] Existing patent technologies mainly focus on the following directions, such as: patent CN118530504A proposes a method of activating the surface of polyolefin waste plastics through plasma bombardment, combined with metal salt mediation and persulfate hydrothermal reaction, for the degradation and conversion efficiency of polyolefin waste plastics under mild conditions. However, this method requires the introduction of transition metal catalysts, which may cause secondary pollution, and is mainly aimed at macro-plastic recycling rather than micro-plastic degradation. The reaction conditions are harsh (high temperature and high pressure), and the energy consumption is high; patent CN117517178A uses ultraviolet light to activate PMS to accelerate the aging of PVC microplastics, but the core goal is to promote dechlorination and surface modification rather than complete degradation, and may generate intermediate products containing oxygen functional groups, which may not completely eliminate environmental risks; patent CN117566891A proposes to use halide ions in wastewater to activate PMS to degrade micro-pollutants, but its application object is organic pollutants such as drug residues, and does not involve micro-plastic degradation, and does not combine with thermal activation synergy, limiting the oxidation efficiency; patent CN117884087A develops Fe-Gd-Mn oxide catalysts to degrade water microplastics, which requires a complex preparation process and the catalyst is prone to deactivation, making it difficult to achieve large-scale application. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a method for degrading microplastics based on a chlorine ion and persulfate synergistic thermal activation system to overcome the deficiencies in the prior art.

[0005] The technical solution of the present application to solve the above technical problem is as follows: A method for degrading microplastics based on a chlorine ion and persulfate synergistic thermal activation system, comprising the following steps: adding microplastics to a solution containing inorganic chloride salt and persulfate, adjusting the pH value of the solution, and then performing a hydrothermal reaction, - - ​The persulfate generates various active species under thermal activation conditions to attack the molecular chain of microplastics, promote the breaking of the molecular chain and finally mineralize into CO2 and H2O, so as to realize the oxidative degradation of the microplastics.

[0006] Based on the above technical solution, the application can be further improved as follows.

[0007] Further, the concentration of Cl - is 150mmol / L-250mmol / L, and when the concentration is too low, the active species are insufficient, and when the concentration is too high, the activation of PMS can be inhibited.

[0008] Further, the concentration of Cl - is 200mmol / L.

[0009] Further, the inorganic chlorine salt containing Cl - is one or both of NaCl and KCl.

[0010] Further, the dosage of persulfate is 0.5g / L-1.5g / L, and excessive PMS can compete with the active species, reducing the degradation efficiency.

[0011] Further, the dosage of persulfate is 1.0g / L.

[0012] Further, the persulfate is one or both of peroxymonosulfate and peroxodisulfate.

[0013] Further, the hydrothermal temperature is 60℃-120℃, the reaction time is 5d-15d, and the reaction pH is 3-9, and when the temperature is too high, the water may boil, affecting the stability of the experiment, when the time is too short, the degradation is insufficient, and when the time is too long, the economy is reduced.

[0014] Further, the hydrothermal temperature is 80℃, the reaction time is 10d, and the reaction pH is 7.

[0015] Further, NaOH and H2SO4 are used for pH adjustment.

[0016] Further, the active species are SO4 - ·, Cl· and HClO.

[0017] The application has the following beneficial effects: By introducing Cl -The PMS / heat synergistic activation system attacks the molecular chain of microplastics, promotes the breaking of the molecular chain and ultimately mineralizes CO2 and H2O, realizes the efficient oxidation and decomposition of microplastics in water, significantly improves the degradation efficiency of microplastics, and the degradation efficiency is improved to more than 90%. The degradation rate of low-density polyethylene in 10 days reaches 42%, and the system also has high degradation capacity for various microplastics such as polyethylene (PE), polystyrene (PS), polyformaldehyde (POM), low-density polyethylene (LDPE), polypropylene (PP), polyethylene terephthalate (PET) and polylactic acid (PLA). In the method, no transition metal catalyst is needed, the reaction condition is mild, the energy consumption is low, the degradation product is mainly CO2 and H2O, there is no toxic intermediate product, it is suitable for various microplastics and complex water quality environments such as landfill leachate, seawater and high-salt wastewater, has significant environmental friendliness and industrial application potential, fills the technical blank in the field of efficient degradation of microplastics in water environment, and provides a more commercial potential solution for global microplastic pollution control. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The weight loss rate graph of low-density polyethylene degraded by different reaction systems in Example 1; Figure 2 The weight loss rate graph of low-density polyethylene degraded by the Cl - / PMS / heat system at different reaction times in Example 2; Figure 3 The weight loss rate graph of low-density polyethylene degraded by the Cl - / PMS / heat system at different reaction temperatures in Example 3; Figure 4 The weight loss rate graph of low-density polyethylene degraded by the Cl - / PMS / heat system at different pH values in Example 4; Figure 5 The weight loss rate graph of low-density polyethylene degraded by the Cl - / PMS / heat system with different initial concentrations of low-density polyethylene in Example 5; Figure 6 The weight loss rate graph of low-density polyethylene degraded by the Cl - / PMS / heat system at different Cl - concentrations in Example 6; Figure 7 The weight loss rate graph of low-density polyethylene degraded by the Cl - / PMS / heat system at different PMS concentrations in Example 7; Figure 8 The weight loss rate graph of low-density polyethylene degraded by the Cl - / PMS / heat system in different reaction substrates in Example 8; Figure 9 is Cl in Example 9 - / PMS / thermal system degradation of different types of microplastics weight loss rate diagram. DETAILED DESCRIPTION

[0019] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0020] Example 1 like Figure 1 As shown, a method for degrading microplastics based on a synergistic thermal activation system of chloride ions and persulfate comprises the following steps: Low-density polyethylene (LDPE) was selected as the target microplastic pollutant, and the degradation effects of different reaction systems on it were studied. Set up the following 8 reaction systems: Cl - / PMS / thermal system, SO4 2- / PMS / thermal system, PMS / thermal system, Cl - / PMS system, PMS system, Cl - / Thermal system, thermal system and Cl - system; Conditions: Cl - or SO4 2- The concentration was 200 mmol / L, the PMS concentration was 1.0 g / L, the low-density polyethylene concentration was 0.5 g / L, the hydrothermal temperature was 80°C, the reaction time was 10 days, and the pH was 7; Low-density polyethylene was put into the corresponding reaction system respectively. The experimental results showed that Cl - The / PMS / heat system has the best degradation effect on low-density polyethylene. After 10 days, the weight loss rate (degradation rate) of low-density polyethylene reaches 42%, which is significantly higher than that of other systems, indicating that this system has strong catalytic degradation ability.

[0021] Example 2 like Figure 2 As shown, a method for degrading microplastics based on a synergistic thermal activation system of chloride ions and persulfate comprises the following steps: Study the effect of reaction time on Cl - / PMS / The impact of thermal system on degradation of low-density polyethylene; Conditions: Cl - The concentration is 200mmol / L, the PMS concentration is 1.0g / L, the low-density polyethylene concentration is 0.5g / L, the hydrothermal temperature is 80℃, and the pH is 7; Low-density polyethylene was added to Cl -The weight loss rate of low-density polyethylene was measured at 5d, 10d and 15d in the Cl The results show that the degradation efficiency of low-density polyethylene gradually increases with the extension of reaction time, and the weight loss rate of low-density polyethylene is 32.4% after 5d, 42.0% after 10d and 44.4% after 15d. Considering the time cost and degradation efficiency, 10d is finally selected as the optimal reaction time.

[0022] Example 3 As shown in Figure 3 A method for degrading microplastics based on a chlorion and persulfate synergistic thermal activation system, comprising the following steps: The effect of reaction temperature on the degradation of low-density polyethylene by the Cl - / PMS / thermal system was investigated. The conditions are as follows: the concentration of Cl - is 200mmol / L, the concentration of PMS is 1.0g / L, the concentration of low-density polyethylene is 0.5g / L, the reaction time is 10d, and the pH is 7. The low-density polyethylene was put into the Cl - / PMS / thermal system, and experiments were carried out at 60℃, 80℃, 100℃ and 120℃, respectively. The results show that the degradation effect of low-density polyethylene gradually increases with the increase of reaction temperature, and the maximum weight loss rate is 49.0% at 120℃. However, considering the influence of water boiling point on the stability of the experiment, 80℃ is selected as the optimal temperature, and the weight loss rate of low-density polyethylene is 42.0%.

[0023] Example 4 As shown in Figure 4 A method for degrading microplastics based on a chlorion and persulfate synergistic thermal activation system, comprising the following steps: The effect of different pH conditions on the degradation of low-density polyethylene by the Cl - / PMS / thermal system was investigated. The conditions are as follows: the concentration of Cl - is 200mmol / L, the concentration of PMS is 1.0g / L, the concentration of low-density polyethylene is 0.5g / L, the hydrothermal temperature is 80℃, and the reaction time is 10d. The initial pH value of the solution was adjusted to 3, 5, 7, 9 and 11 by diluting NaOH and H2SO4, respectively. The low-density polyethylene was put into the Cl - / PMS / thermal system, and the results show that the system has good degradation effect in the pH range of 3-11.

[0024] Example 5 As shown in Figure 5 A method for degrading microplastics based on a chlorine ion and persulfate synergistic thermal activation system, comprising the following steps: The effect of the initial concentration of low-density polyethylene on the degradation efficiency of the Cl - / PMS / thermal system was studied. The conditions were: the concentration of Cl - was 200 mmol / L, the concentration of PMS was 1.0 g / L, the hydrothermal temperature was 80°C, the reaction time was 10 days, and the pH was 7. Low-density polyethylene was put into the Cl - / PMS / thermal system, and the initial concentrations of low-density polyethylene were 0.1 g / L, 0.3 g / L, 0.5 g / L, 0.7 g / L, and 0.9 g / L, respectively. The results showed that when the initial concentration of low-density polyethylene was in the range of 0.1 g / L to 0.5 g / L, the degradation rate was stable at about 42%. Therefore, under the reaction conditions, the optimal initial concentration of low-density polyethylene was determined to be 0.5 g / L, and the efficiency of 0.1 g / L and 0.5 g / L was not much different. In the same system, it is better to be able to treat more pollutants, so 0.5 g / L was selected.

[0025] Example 6 As shown in Figure 6 A method for degrading microplastics based on a chlorine ion and persulfate synergistic thermal activation system, comprising the following steps: The effect of the initial concentration of Cl - on the degradation efficiency of the Cl - / PMS / thermal system was studied. The conditions were: the initial concentration of Cl - was 150 mmol / L, 200 mmol / L, and 250 mmol / L, the concentration of PMS was 1.0 g / L, the hydrothermal temperature was 80°C, the reaction time was 10 days, and the pH was 7. Low-density polyethylene was put into the Cl - / PMS / thermal system, and the degradation of microplastics with an initial concentration of 0.5 g / L was investigated. The results showed that when the concentration of Cl - increased from 150 mmol / L to 200 mmol / L, the weight loss of low-density polyethylene increased from 24.2% to 42.0%; when the concentration of Cl - was further increased to 250 mmol / L, the degradation effect did not improve significantly. Therefore, under the reaction conditions, the optimal concentration of Cl - was determined to be 200 mmol / L.

[0026] Example 7 As shown inFigure 7 As shown, a method for degrading microplastics based on a synergistic thermal activation system of chloride ions and persulfate comprises the following steps: The effect of initial PMS concentration on Cl - / PMS / The influence of thermal system degradation efficiency; Conditions: Cl - The concentration was 200 mmol / L, the initial PMS concentrations were 0.5 g / L, 1.0 g / L, and 1.5 g / L, respectively, the hydrothermal temperature was 80 °C, the reaction time was 10 days, and the pH was 7; Low-density polyethylene was added to Cl - In the / PMS / heat system, the degradation of microplastics with an initial concentration of 0.5 g / L was investigated; The results showed that with the increase of PMS concentration, the weight loss of low-density polyethylene increased significantly. When the PMS concentration increased to 1.0 g / L, the weight loss of low-density polyethylene reached 42% within 10 days. When the PMS concentration was increased to 1.5 g / L, the weight loss of low-density polyethylene did not increase further significantly. This may be because too many PMS molecules will compete with active species and affect the removal of low-density polyethylene.

[0027] Example 8 like Figure 8 As shown, a method for degrading microplastics based on a synergistic thermal activation system of chloride ions and persulfate comprises the following steps: Research Cl - / PMS / thermal system’s ability to degrade LDPE in different water quality environments; Conditions: Cl - The concentration was 200 mmol / L, the PMS concentration was 1.0 g / L, the low-density polyethylene concentration was 0.5 g / L, the hydrothermal temperature was 80°C, the reaction time was 10 days, and the pH was 7; The experiments were conducted using landfill leachate, seawater and high-salt wastewater. Low-density polyethylene was added to the Cl - / PMS / in thermal system; The results showed that the weight loss rates of low-density polyethylene in these water quality environments were 27.2%, 25.4% and 25.0%, respectively. The experimental results showed that this system is suitable for the removal of microplastics in complex and diverse water bodies.

[0028] Example 9 like Figure 9 As shown, a method for degrading microplastics based on a synergistic thermal activation system of chloride ions and persulfate comprises the following steps: Research Cl - / PMS / thermal system degradation effect on different types of microplastics; Conditions: Cl - The concentration of the microplastics was 0.5 g / L, the concentration of PMS was 1.0 g / L, the concentration of H2O2 was 200 mmol / L, the hydrothermal temperature was 80℃, the reaction time was 10 days, and the pH was 7. The selected microplastics included polyethylene (PE), polystyrene (PS), polyoxymethylene (POM), low-density polyethylene (LDPE), polypropylene (PP), polyethylene terephthalate (PET), and polylactic acid (PLA). The polyethylene (PE), polystyrene (PS), polyoxymethylene (POM), low-density polyethylene (LDPE), polypropylene (PP), polyethylene terephthalate (PET), and polylactic acid (PLA) were each put into the Cl - / PMS / thermal system. The results showed that the system was suitable for degrading polyethylene (PE), polystyrene (PS), polyoxymethylene (POM), low-density polyethylene (LDPE), polypropylene (PP), polyethylene terephthalate (PET), and polylactic acid (PLA) and other microplastics.

[0029] Although the embodiments of the present application have been shown and described above, it should be understood that the above-described embodiments are exemplary and should not be construed as limiting the present application, and those of ordinary skill in the art can make changes, modifications, replacements, and variations to the above-described embodiments within the scope of the present application.

Claims

1. A method for degrading microplastics based on a synergistic thermal activation system of chloride ions and persulfate, characterized in that: The steps include: Towards Cl - Add microplastics to the solution of inorganic chloride salt and persulfate, adjust the pH value of the solution, and then perform hydrothermal reaction. - Under thermal activation conditions, various active species are generated with persulfate to attack the molecular chains of microplastics, causing them to break and eventually mineralize into CO2 and H2O to achieve oxidative degradation of microplastics.

2. The method for degrading microplastics based on a chloride ion and persulfate synergistic thermal activation system according to claim 1, characterized in that: Cl - The concentration is 150mmol / L~250mmol / L.

3. A method for degrading microplastics based on a chloride ion and persulfate synergistic thermal activation system according to claim 1 or 2, characterized in that, Cl - The concentration is 200mmol / L.

4. The method for degrading microplastics based on a chloride ion and persulfate synergistic thermal activation system according to any one of claims 1 to 3, characterized in that: Contains Cl - The inorganic chloride salt is one or two of NaCl and KCl.

5. The method for degrading microplastics based on a chloride ion and persulfate synergistic thermal activation system according to claim 1, characterized in that: The dosage of persulfate is 0.5g / L~1.5g / L.

6. The method for degrading microplastics based on a chloride ion and persulfate synergistic thermal activation system according to claim 5, characterized in that: The dosage of persulfate was 1.0 g / L.

7. A method for degrading microplastics based on a chloride ion and persulfate synergistic thermal activation system according to claim 1, 5 or 6, characterized in that: The persulfate is one or both of peroxymonosulfate and peroxydisulfate.

8. The method for degrading microplastics based on a chloride ion and persulfate synergistic thermal activation system according to claim 1, characterized in that: The hydrothermal temperature is 60°C to 120°C, the reaction time is 5d to 15d, and the reaction pH is 3 to 9.

9. The method for degrading microplastics based on a chloride ion and persulfate synergistic thermal activation system according to claim 8, characterized in that: The hydrothermal temperature was 80°C, the reaction time was 10 days, and the reaction pH was 7.

10. The method for degrading microplastics based on a chloride ion and persulfate synergistic thermal activation system according to claim 1, characterized in that: The pH was adjusted using NaOH and H2SO4.

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