Method for removing low concentration ammonia nitrogen by catalytic oxidation of peroxyacetic acid

Abstract

The application relates to a method for removing low-concentration ammonia nitrogen by catalytic oxidation, and relates to a method for removing low-concentration ammonia nitrogen by catalytic oxidation. The application aims to solve the technical problems of the existing ammonia nitrogen removal method, such as strict reaction conditions, high energy consumption and cost, and low practical application feasibility. The porous carbon-nitrogen-coated FeMn bimetallic catalyst prepared by the application has a large specific surface area and a porous structure, which is helpful for the rapid occurrence of a catalytic reaction. Meanwhile, the Fe / Mn bimetal and the nitrogen element doping can adjust the electronic structure and the electron density distribution of the material, greatly increase the number of active sites, and improve the catalytic activity. The porous carbon structure on the surface of the material provides a stable chemical structure for the catalyst, which is helpful for the material to resist corrosion and change under different reaction conditions, so that the material can be used repeatedly. The ammonia nitrogen removal rate is more than 90% within 30 minutes.

Description

Technical Field

[0001] This invention relates to a method for removing low concentrations of ammonia nitrogen by catalytic oxidation. Background Technology

[0002] Common methods for removing ammonia nitrogen from surface water include biological and physicochemical methods. Biological methods mainly include activated sludge processes, biofilm processes, and biological contact oxidation, which utilize microorganisms to degrade ammonia nitrogen in water. However, these microorganisms are greatly affected by external factors, and the reactions require a large land area. Physicochemical methods mainly include adsorption, precipitation, ion exchange, and advanced oxidation processes. Adsorption can achieve highly efficient ammonia nitrogen removal using suitable adsorbents, but adsorbent clogging leads to high investment and operating costs. Precipitation and ion exchange methods have high treatment efficiency, but they are greatly affected by water quality and are not suitable for large-scale use. Advanced oxidation processes oxidize pollutants into a gaseous state by generating free radicals with high oxidation potential, achieving complete mineralization of pollutants. They are applicable to many scenarios and are currently a popular technology favored by engineers. Existing advanced oxidation technologies include Fenton reaction, wet oxidation, electrochemical oxidation, photocatalytic oxidation, and catalytic ozone oxidation. Among these, the Fenton reaction utilizes Fe under acidic conditions... 2+ Catalytic oxidation of H₂O₂ to generate highly oxidizing hydroxyl radicals (·OH) achieves efficient mineralization of pollutants; however, its reaction conditions are harsh and it easily produces large amounts of iron sludge. Wet oxidation oxidizes pollutants under high temperature and pressure conditions with oxygen and air; electrochemical oxidation is a method based on electrochemical reactions to generate strong oxidants to oxidize pollutants; photocatalytic oxidation uses photoexcitation to induce redox reactions to decompose pollutants in water; ozone catalytic oxidation uses the strong oxidizing power of ozone to remove pollutants from water. However, all of these methods suffer from harsh reaction conditions, high energy consumption and cost, and low feasibility in practical applications.

[0003] Peracetic acid (PAA) is an organic peroxyacid with a high redox potential. Upon activation, it can generate reactive oxygen species such as ·OH and CH3C(O)OO· to ​​degrade pollutants. Compared to hydrogen peroxide and persulfate, commonly used in advanced oxidation processes, PAA requires less dosage and produces less secondary pollution. Furthermore, PAA's oxidation capacity can be enhanced with the aid of catalysts.

[0004] Metal-organic frameworks (MOFs) are hybrid porous crystalline materials constructed by coordination between organic matter and inorganic metal clusters. Their structural diversity, large specific area, and abundant active sites make them a research hotspot in catalytic materials. Meanwhile, their derivatives are widely used in the field of catalytic oxidation due to their high chemical stability and strong catalytic activity. Summary of the Invention

[0005] The present invention aims to address the technical problems of existing ammonia nitrogen removal methods, such as harsh reaction conditions, high energy consumption and cost, and low practical application feasibility, and provides a method for removing low concentrations of ammonia nitrogen by catalytic oxidation of peracetic acid.

[0006] The method for removing low concentrations of ammonia nitrogen by catalytic oxidation of peracetic acid according to the present invention is carried out according to the following steps:

[0007] I. Porous carbon-nitrogen coated FeMn bimetallic catalyst (Fe x Mn@N y Preparation of PC-T:

[0008] FeCl3·6H2O, MnCl2·4H2O, and terephthalic acid (H2BDC) in a molar ratio of (1-5):1:1 were added to N,N-dimethylformamide (DMF) and stirred for 15-20 minutes to ensure complete dissolution and homogeneity. The mixture was then transferred to a reaction vessel lined with polytetrafluoroethylene and kept at 110-120°C for 20-22 hours, followed by cooling to room temperature. The solid obtained from the above reaction was collected by filtration and washed three to four times alternately with anhydrous ethanol and DMF at 60°C. The solid was then placed in a vacuum drying oven at 60-70°C and kept at that temperature for 9-10 hours to obtain the bimetallic MOF precursor.

[0009] The molar ratio of FeCl3·6H2O to the volume ratio of DMF is (7mmol~7.5mmol):45mL;

[0010] The obtained bimetallic MOF precursor and urea were placed together in a tube furnace, with urea and the bimetallic MOF precursor placed at opposite ends of the furnace. Argon gas was introduced, with the argon gas inlet located at the urea end. Under argon protection, the temperature was increased to 500℃~800℃ at a heating rate of 5℃ / min~10℃ / min and held for 4h~4.5h to obtain a porous carbon-nitrogen coated FeMn bimetallic catalyst (Fe x Mn@N y PC-T), where x is the molar ratio of Fe to Mn, y is the mass ratio of urea to bimetallic MOF precursor, and T is the calcination temperature; the mass ratio of the bimetallic MOF precursor to urea is 1:(9-12).

[0011] 2. The porous carbon-nitrogen-coated FeMn bimetallic catalyst prepared in step one is added to the wastewater to be treated. PAA is added and mixed evenly with the wastewater sample before stirring to carry out catalytic oxidation treatment. Under the catalysis of the porous carbon-nitrogen-coated FeMn bimetallic catalyst, PAA generates hydroxyl radicals (·OH) and singlet oxygen (·OH). 1 Oxygen-active species such as O2 oxidize ammonia nitrogen into nitrogen gas;

[0012] The wastewater to be treated is river water containing low concentrations of ammonia nitrogen, with the ammonia nitrogen concentration being less than 10 ppm.

[0013] Advantages of this invention:

[0014] 1. The porous carbon-nitrogen-coated FeMn bimetallic catalyst (Fe) prepared in this invention x Mn@N y PC-T has a large specific surface area and porous structure, which helps the catalytic reaction to occur quickly. At the same time, the doping of Fe / Mn bimetal and nitrogen can adjust the electronic structure and electron density distribution of the material, greatly increasing the number of active sites and improving catalytic activity. Its porous carbon structure provides a stable chemical structure for the catalyst, which helps the material resist corrosion and changes under different reaction conditions, allowing the material to be recycled multiple times.

[0015] 2. The porous carbon-nitrogen-coated FeMn bimetallic catalyst (Fe) prepared in this invention x Mn@N y The mechanism of PC-T activation of PAA: There is an electron transfer process between Fe-NC and Mn-NC in the material and PAA. Fe-NC and Mn-NC are the reaction sites for PAA activation, exciting PAA to generate hydroxyl radicals (OH·) and singlet oxygen (OH·). 1 Active species such as O2 are used to oxidize and remove ammonia nitrogen in water together with non-free radicals and free radicals, ultimately achieving an ammonia nitrogen removal rate of over 90% within 30 minutes. Attached Figure Description

[0016] Figure 1 The porous carbon-nitrogen-coated FeMn bimetallic catalyst Fe4Mn@N prepared in step one of Experiment 1. 10 SEM image of PC-700;

[0017] Figure 2 for Figure 1 Enlarged view within the dashed box. Detailed Implementation

[0018] Specific Implementation Method 1: This implementation method is a method for removing low-concentration ammonia nitrogen by catalytic oxidation of peracetic acid, specifically carried out according to the following steps:

[0019] I. Porous carbon-nitrogen coated FeMn bimetallic catalyst (Fe x Mn@N y Preparation of PC-T:

[0020] FeCl3·6H2O, MnCl2·4H2O, and terephthalic acid in a molar ratio of (1-5):1:1 were added to N,N-dimethylformamide and stirred for 15-20 minutes to ensure complete dissolution and homogeneity. The mixture was then transferred to a reaction vessel lined with polytetrafluoroethylene and kept at 110-120°C for 20-22 hours, followed by cooling to room temperature. The solid obtained from the above reaction was collected by filtration and washed three to four times alternately with anhydrous ethanol and DMF at 60-65°C. The solid was then placed in a vacuum drying oven at 60-70°C and kept at that temperature for 9-10 hours to obtain the bimetallic MOF precursor.

[0021] The molar ratio of FeCl3·6H2O to the volume ratio of DMF is (7mmol~7.5mmol):45mL;

[0022] The obtained bimetallic MOF precursor and urea were placed together in a tube furnace, with urea and the bimetallic MOF precursor placed at opposite ends of the tube furnace. Argon gas was introduced, with the argon gas inlet located at the urea end. Under argon protection, the temperature was increased to 500℃~800℃ at a heating rate of 5℃ / min~10℃ / min and held for 4h~4.5h to obtain a porous carbon-nitrogen coated FeMn bimetallic catalyst. The mass ratio of the bimetallic MOF precursor to urea was 1:(9~12).

[0023] 2. Add the porous carbon-nitrogen-coated FeMn bimetallic catalyst prepared in step 1 to the wastewater to be treated, add PAA and mix it evenly with the water sample to be treated, and then start stirring to carry out catalytic oxidation treatment.

[0024] The wastewater to be treated is river water containing low concentrations of ammonia nitrogen, with the ammonia nitrogen concentration being less than 10 ppm.

[0025] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the molar ratio of FeCl3·6H2O to the volume ratio of DMF in step one is 7.35 mmol: 45 mL. Everything else is the same as in Specific Implementation Method One.

[0026] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that: in step 1, the sample is kept at 110℃ for 20 hours and then cooled to room temperature before being taken out. Everything else is the same as in Specific Implementation Method 1 or 2.

[0027] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that: in step one, the precursor is placed in a 60°C vacuum drying oven and kept at that temperature for 9 hours to obtain the bimetallic MOF precursor. Everything else is the same as in Specific Implementation Methods One to Three.

[0028] Specific Implementation Method Five: This implementation method differs from Specific Implementation Method Four in that the mass ratio of the bimetallic MOF precursor to urea in step one is 1:10. Everything else is the same as in Specific Implementation Method Four.

[0029] Specific Implementation Method Six: This implementation method differs from Specific Implementation Method Five in that: in step two, the concentration of the porous carbon-nitrogen-coated FeMn bimetallic catalyst in the wastewater to be treated is 0.15 g / L, the concentration of PAA is 0.2 mM, and the system undergoes catalytic oxidation treatment at pH 6. Everything else is the same as in Specific Implementation Method Five.

[0030] The invention was verified using the following experiments:

[0031] Experiment 1: This experiment demonstrates a method for removing low concentrations of ammonia nitrogen through the catalytic oxidation of peracetic acid, and was conducted according to the following steps:

[0032] I. Porous carbon-nitrogen coated FeMn bimetallic catalyst (Fe x Mn@N y Preparation of PC-T:

[0033] FeCl3·6H2O, MnCl2·4H2O, and terephthalic acid (H2BDC) in a molar ratio of 4:1:1 were added to N,N-dimethylformamide (DMF) and stirred for 15 min to ensure complete dissolution and homogeneity. The mixture was then transferred to a reaction vessel lined with polytetrafluoroethylene and kept at 110 °C for 20 h. After cooling to room temperature, the solid obtained from the above reaction was collected by vacuum filtration and washed three to four times alternately with anhydrous ethanol and DMF at 60 °C. The solid was then placed in a vacuum drying oven at 60 °C for 9 h to obtain the bimetallic MOF precursor.

[0034] The molar ratio of FeCl3·6H2O to the volume ratio of DMF is 7.35 mmol: 45 mL;

[0035] The obtained bimetallic MOF precursor and urea were placed together in a tube furnace, with urea and the bimetallic MOF precursor placed at opposite ends of the furnace. Argon gas was introduced, with the argon gas inlet located at the urea end. Under argon protection, the temperature was increased to 700℃ at a rate of 5℃ / min and held for 4 hours to obtain the porous carbon-nitrogen coated FeMn bimetallic catalyst Fe4Mn@N. 10 PC-700; The mass ratio of the bimetallic MOF precursor to urea is 1:10;

[0036] II. The porous carbon-nitrogen-coated FeMn bimetallic catalyst Fe4Mn@N prepared in step one 10PC-700 was added to the wastewater to be treated, PAA was added, and the mixture was stirred and stirred to carry out catalytic oxidation treatment. The concentration of porous carbon-nitrogen-coated FeMn bimetallic catalyst in the wastewater to be treated was 0.15 g / L, and the concentration of PAA was 0.2 mM. The system was subjected to catalytic oxidation treatment at pH 6. Under the catalysis of the porous carbon-nitrogen-coated FeMn bimetallic catalyst, PAA generated hydroxyl radicals (·OH) and singlet oxygen (·OH). 1 Oxygen-active species such as O2 oxidize ammonia nitrogen into nitrogen gas, achieving an ammonia nitrogen removal rate of over 90% within 30 minutes;

[0037] The wastewater to be treated is river water containing low concentrations of ammonia nitrogen, with the ammonia nitrogen concentration being less than 10 ppm.

[0038] Figure 1 The porous carbon-nitrogen-coated FeMn bimetallic catalyst Fe4Mn@N prepared in step one of Experiment 1. 10 SEM image of PC-700 Figure 2 for Figure 1 The magnified image within the dashed box shows its large specific surface area and porous structure. This structure facilitates the rapid occurrence of catalytic reactions. Furthermore, the doping of Fe / Mn bimetallic elements and nitrogen can adjust the electronic structure and electron density distribution of the material, greatly increasing the number of active sites and improving catalytic activity. The porous carbon structure on its surface provides a stable chemical structure for the catalyst, helping the material resist corrosion and changes under different reaction conditions, allowing the material to be recycled multiple times.

Claims

1. A method for removing low-concentration ammonia nitrogen by catalytic oxidation of peracetic acid, characterized in that... The method for removing low concentrations of ammonia nitrogen by catalytic oxidation of peracetic acid is carried out according to the following steps: I. Preparation of porous carbon-nitrogen coated FeMn bimetallic catalysts: FeCl3•6H2O, MnCl2•4H2O, and terephthalic acid in a molar ratio of (1~5):1:1 were added to N,N-dimethylformamide and stirred for 15-20 minutes to ensure complete dissolution and homogeneity. The mixture was then transferred to a reaction vessel lined with polytetrafluoroethylene and kept at 110-120°C for 20-22 hours, followed by cooling to room temperature. The solid obtained from the above reaction was collected by filtration and washed three to four times alternately with anhydrous ethanol and DMF at 60-65°C. The solid was then placed in a vacuum drying oven at 60-70°C for 9-10 hours to obtain the bimetallic MOF precursor. The molar ratio of FeCl3•6H2O to the volume ratio of DMF is (7mmol~7.5mmol):45mL; The obtained bimetallic MOF precursor and urea were placed together in a tube furnace, with urea and the bimetallic MOF precursor placed at opposite ends of the tube furnace. Argon gas was introduced, with the argon gas inlet located at the urea end. Under argon protection, the temperature was increased to 500℃~800℃ at a heating rate of 5℃ / min~10℃ / min and held for 4h~4.5h to obtain a porous carbon-nitrogen coated FeMn bimetallic catalyst. The mass ratio of the bimetallic MOF precursor to urea was 1:(9~12).

2. Add the porous carbon-nitrogen-coated FeMn bimetallic catalyst prepared in step 1 to the wastewater to be treated, add PAA and mix it evenly with the water sample to be treated, and then start stirring to carry out catalytic oxidation treatment. The wastewater to be treated is river water containing low concentrations of ammonia nitrogen, with the ammonia nitrogen concentration being less than 10 ppm.

2. The method for removing low-concentration ammonia nitrogen by catalytic oxidation of peracetic acid according to claim 1, characterized in that... The molar ratio of FeCl3•6H2O to DMF in step one is 7.35 mmol: 45 mL.

3. The method for removing low-concentration ammonia nitrogen by catalytic oxidation of peracetic acid according to claim 1, characterized in that... After being kept at 110℃ for 20 hours in step one, the product is cooled to room temperature and then removed.

4. The method for removing low-concentration ammonia nitrogen by catalytic oxidation of peracetic acid according to claim 1, characterized in that... In step one, the sample was placed in a 60℃ vacuum drying oven and kept at that temperature for 9 hours to obtain a bimetallic MOF precursor.

5. The method for removing low-concentration ammonia nitrogen by catalytic oxidation of peracetic acid according to claim 1, characterized in that... The mass ratio of the bimetallic MOF precursor to urea in step one is 1:

10.

6. The method for removing low-concentration ammonia nitrogen by catalytic oxidation of peracetic acid according to claim 1, characterized in that... In step two, the concentration of the porous carbon-nitrogen coated FeMn bimetallic catalyst in the wastewater to be treated is 0.15 g / L, the concentration of PAA is 0.2 mM, and the system is subjected to catalytic oxidation treatment at pH 6.

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