Method for selectively separating and recovering ammonia nitrogen in sewage based on ultra-microporous carbon electro-adsorption

Abstract

The invention provides a method for selectively separating and recovering ammonia nitrogen in sewage based on ultramicropore carbon electro-adsorption, and belongs to the technical field of sewage treatment and resource recovery. The method aims at solving the problems that in the prior art, ammonia nitrogen selectivity is poor, and resource recycling is difficult. The method comprises the following core steps: S1, preparing an electro-adsorption electrode by using an ultra-microporous carbon material of which the aperture is concentrated within a range of less than 1nm; s2, placing the electrode in ammonia nitrogen-containing sewage to construct an electro-adsorption system; s3, applying a direct-current voltage of 0.6-1.2 V, and realizing selective adsorption and separation of NH4 < + > relative to coexisting ions such as Na < + > and Ca < + > by utilizing aperture screening and surface action of ultra-microporous carbon; and S4, desorbing the enriched NH4 < + > into a small-volume desorption solution through short circuit or reverse electrochemical regeneration to obtain a high-concentration ammonia nitrogen recovery solution, and recycling the electrode. Through the cooperation of the ultramicroporous carbon material with a specific structure and an electro-adsorption process, high-selectivity and high-efficiency separation, enrichment and recovery of ammonia nitrogen in sewage are realized, and the method is low in energy consumption and environment-friendly and has a remarkable resource application prospect.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment and resource recovery technology, specifically relating to a method for selectively separating and recovering ammonia nitrogen (NH4) from wastewater using functionalized electrode materials. + The method. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Ammonia nitrogen is one of the main pollutants causing eutrophication in water bodies, but it is also a valuable nitrogen resource. The efficient separation and recovery of ammonia nitrogen from wastewater is of great significance for water environmental protection and resource recycling. Currently, methods for removing ammonia nitrogen mainly include biological nitrification / denitrification, stripping, breakpoint chlorination, and ion exchange. However, these methods generally suffer from drawbacks such as high energy consumption, easy generation of secondary pollution, poor selectivity, and difficulty in achieving resource recovery of ammonia nitrogen.

[0004] Electroadsorption is an emerging water treatment technology that uses an applied electric field to adsorb ions from a solution onto the surface of a charged electrode, achieving separation. This technology offers potential advantages such as low energy consumption, ease of operation, no secondary pollution, and recyclable electrode materials. However, traditional electroadsorption electrode materials (such as activated carbon) lack selectivity for ion adsorption, especially in solutions containing multiple ions (such as Na+). + K + Ca² + Mg² + NH4 + In complex wastewater systems (such as those containing ammonia nitrogen), it is difficult to achieve efficient and selective separation and enrichment of ammonia nitrogen. Therefore, developing an electrode material with high ammonia nitrogen selectivity and a corresponding electroadsorption process is key to realizing the resource recovery of ammonia nitrogen from wastewater.

[0005] In recent years, metal-organic frameworks (MOFs) have become precursors for the preparation of high-performance porous carbon materials due to their high specific surface area, tunable pore structure, and chemical composition. For example, some studies have carbonized ZIF-8 crystals of different sizes to prepare nanoporous carbon electrodes and investigated their selective electroadsorption performance for hexavalent chromium ions. However, for specific target ions in wastewater (such as NH4+),… + Selective separation of NH4+ requires, in particular, precise matching of pore size and hydrated ion size, and the specific interaction between surface functional groups and target ions. Existing research on MOF-derived carbon materials often overlooks the importance of precisely controlling the carbonization process to obtain specific, uniform ultraporous structures, and rarely systematically explores their effectiveness against NH4+. +Compared to the selective electroadsorption mechanism of other coexisting ions, electroadsorption electrodes prepared from such materials still face challenges in achieving highly selective capture and efficient recovery of ammonia nitrogen in complex wastewater systems. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a method for the selective separation and recovery of ammonia nitrogen from wastewater based on the electroadsorption of ultramicroporous carbon. This method utilizes ultramicroporous carbon with specific pore size distribution and surface chemical properties as the electrode material. By adjusting the electroadsorption operating parameters, it achieves efficient and selective adsorption and enrichment of ammonia nitrogen ions in wastewater. Furthermore, a simple regeneration step enables the recovery of ammonia nitrogen and the recycling of the electrode.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing ultraporous carbon, comprising: NH2-MIL-53(Al) was carbonized at 680℃-720℃ and acid-washed to obtain nitrogen-doped ultraporous carbon materials.

[0008] This application incidentally discovered that direct calcination of NH2-MIL-53(Al) at 700℃ can yield ultraporous carbon. Increasing the temperature to 800℃ and 900℃ respectively widens the pore size, resulting in a multi-layered carbon material composed of ultraporous and microporous composites. Further research shows that, based on the micropore size of specific MOF materials, the ultraporous structure constructed at a specific temperature (700℃) can achieve highly efficient and selective separation and enrichment of ammonia nitrogen.

[0009] A second aspect of the present invention provides a method for preparing an ultraporous carbon electrode, comprising: After the above-mentioned microporous carbon, electrolytic carbon black and binder are mixed evenly, they are coated on a titanium mesh current collector and dried to obtain a microporous carbon electrode.

[0010] A third aspect of the present invention provides an ultraporous carbon electrode prepared by the above method.

[0011] A fourth aspect of the present invention provides an ultramicroporous carbon electroadsorption module, comprising: electrically connecting at least one of the above-described ultramicroporous carbon electrodes to an external power supply and a switch.

[0012] A fifth aspect of the present invention provides a method for selectively separating and recovering ammonia nitrogen from wastewater based on ultraporous carbon electroadsorption, comprising: The above-mentioned microporous carbon electroadsorption module is placed in a wastewater solution containing ammonia nitrogen, and a DC voltage is applied to the electrode for adsorption. After adsorption saturation, the voltage is removed or reversed to obtain the final product.

[0013] The ultraporous carbon prepared by this invention exhibits specific adsorption for ammonium ions in a mixed solution (NaCl, NH4Cl), which may be due to its adsorption to the abundant Na+ present in wastewater. + In comparison, NH4 + The hydrated ionic radius is lower, which makes NH4+... + It is well-suited for insertion into slit-like micropores, thereby achieving specific adsorption.

[0014] A sixth aspect of the present invention provides a wastewater treatment system comprising: at least one of the above-described microporous carbon electroadsorption modules for performing the above-described method.

[0015] Beneficial effects of the present invention (1) High selectivity: This invention is the first to discover that ultraporous carbon has a specific separation effect on ammonia nitrogen, utilizing the pore size of ultraporous carbon and NH4 + The size matching effect of (hydrated) ions enabled the control of NH4+. + Compared to other common cations (such as Na) + K + Ca² + Highly selective adsorption.

[0016] (2) High efficiency and energy saving: The electro-adsorption process is carried out under low pressure, and the energy consumption is much lower than that of membrane separation and thermal drive processes; and the electrode regeneration is easy and does not require expensive chemicals.

[0017] (3) Resource recovery: This method not only removes ammonia nitrogen from wastewater, but also enriches and recovers it into a high-concentration ammonium salt solution, which can be used directly or after simple processing as liquid fertilizer or chemical raw material, thus realizing "turning waste into treasure".

[0018] (4) Environmentally friendly: No sludge is generated during the process, there is no secondary pollution, the electrode materials are stable and recyclable, which is in line with the concept of green and sustainable development. (5) Flexible operation: The process is simple, the equipment is highly modular, and it is easy to couple with other water treatment processes. It is suitable for deep treatment and recovery of ammonia nitrogen in various scenarios such as municipal sewage, aquaculture wastewater, and industrial wastewater. Attached Figure Description

[0019] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. Exemplary embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0020] Figure 1 This is a process flow diagram of the selective separation and recovery of ammonia nitrogen using the electroadsorption system described in this invention.

[0021] Figure 2The nitrogen adsorption-desorption isotherm and pore size distribution diagram of the ultramicroporous carbon material used in Example 1 are shown.

[0022] Figure 3 The ultramicroporous carbon electrode in Example 1 for NH4 + and Na + Selective adsorption performance diagram. Detailed Implementation

[0023] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of skill in the art. The reagents and raw materials used in this invention are readily available through conventional means, and unless otherwise specified, they are used in accordance with conventional methods in the art or product instructions. Similarly, unless otherwise specified, the test methods of this invention are performed in accordance with conventional methods in the art or industry-standard methods or practices. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to the methods of this invention. The preferred embodiments and materials described herein are for illustrative purposes only.

[0025] Terminology Explanation: NH2-MIL-53(Al) is a commercially available product, CAS NO.: 1134360-62-5.

[0026] This invention provides a method for preparing ultraporous carbon, comprising: NH2-MIL-53(Al) was carbonized at 680℃-720℃ and acid-washed to obtain nitrogen-doped ultraporous carbon materials.

[0027] This invention has accidentally discovered that direct calcination of NH2-MIL-53(Al) at 700℃ can obtain ultraporous carbon. When the temperature is increased to 800℃ and 900℃, the pore size becomes wider, and the obtained carbon material is a multi-level carbon composed of ultraporous-microporous composites. Ultraporous carbon can significantly improve the selective separation and enrichment of ammonia nitrogen. Therefore, the preferred carbonization temperature is 700℃ to obtain ultraporous carbon.

[0028] This invention explored different types of MOF materials, such as ZIF-8 and Cu-MOF, with the carbon materials obtained by direct carbonization exhibiting a wider pore size distribution. Only when NH2-MIL-53(Al) was used as a precursor, the carbon material obtained by carbonization at 700℃ had a pore size relatively concentrated in the ultramicroporous range. Therefore, this invention also provides ultramicroporous carbon prepared by the above method, with a pore size distribution concentrated in the 0.6-0.8 nm range.

[0029] It should be noted that ultraporous carbon can also be modified by physical or chemical activation methods or doping methods to control its pore size distribution and surface chemical properties.

[0030] This invention also provides a method for preparing an ultraporous carbon electrode, comprising: After the above-mentioned microporous carbon, electrolytic carbon black and binder are mixed evenly, they are coated on a titanium mesh current collector and dried to obtain a microporous carbon electrode.

[0031] The amount of microporous carbon used affects the selective separation and enrichment of ammonia nitrogen. Therefore, this invention studies the mass ratio of microporous carbon, electrolytic carbon black, and binder. Preferably, the mass ratio of microporous carbon, electrolytic carbon black, and binder is 8-10:1:1 to obtain better selective separation and enrichment of ammonia nitrogen.

[0032] The coating thickness of the microporous carbon electrode also affects the selective separation and enrichment of ammonia nitrogen. Therefore, this invention studies the thickness of the microporous carbon electrode. Preferably, the thickness of the microporous carbon electrode is 180-220 μm, and more preferably, it is 200 μm, in order to obtain a better selective separation and enrichment effect of ammonia nitrogen.

[0033] This invention also provides a method for selectively separating and recovering ammonia nitrogen from wastewater based on ultraporous carbon electroadsorption, comprising: The above-mentioned microporous carbon electroadsorption module is placed in a wastewater solution containing ammonia nitrogen, and a DC voltage is applied to the electrode for adsorption. After adsorption saturation, the voltage is removed or reversed to obtain the final product.

[0034] The magnitude of voltage affects the rate and effect of electroadsorption. Therefore, this invention studies the range of DC voltage. Preferably, the DC voltage is 0.6 V to 1.2 V to effectively improve the rate and effect of electroadsorption.

[0035] To ensure the adsorption effect, sufficient electro-adsorption time is required to reach the equilibrium adsorption capacity. Therefore, this invention studies the electro-adsorption time. Preferably, the applied DC voltage is a constant voltage or a pulse voltage, and the electro-adsorption time is 10 to 180 min to improve the adsorption effect.

[0036] After adsorption saturation, remove or reverse the voltage, and simultaneously place the electrode in a low ionic strength or acidic desorption solution to allow the NH4+ enriched within the electrode to be absorbed. + It is rapidly released to obtain a high-concentration ammonia nitrogen recovery solution. Preferably, the reverse voltage is -0.6 V to -1.2 V to facilitate the release of NH4. + Rapid release.

[0037] Preferably, the pH value of the wastewater is in the range of 6 to 8, within which NH4+ is present. + Its primary form of existence is...

[0038] Preferably, the step of placing the electrode in the desorption solution allows NH4 to accumulate within the electrode. + It is rapidly released, resulting in a high-concentration ammonia nitrogen recovery solution and regenerated electrodes; Preferably, the desorption solution is a dilute hydrochloric acid, dilute sulfuric acid solution, or water, used to receive the desorbed NH4. + This forms concentrated solutions of ammonium sulfate, ammonium chloride, etc., which can be used as fertilizers.

[0039] More specifically, including: S1. Electrode preparation: An electroadsorption electrode is prepared using carbon material with abundant micropores (pore size less than 1 nm) as the active material; the specific surface area of ​​the microporous carbon is greater than 1000 m² / g. S2. Construct an electro-adsorption system: Arrange one or more pairs of electrodes in parallel and place them in a complex wastewater solution containing ammonia nitrogen and interfering ions to form an electro-adsorption module; connect an external power supply, switch and monitoring equipment. S3. Selective Electroadsorption: A DC voltage is applied to the electrodes, controlled within the range of 0.6 V to 1.2 V, to remove NH4+ from the wastewater to be treated. + Driven by an electric field, ions preferentially enter and adsorb within the micropores of the ultraporous carbon electrode, achieving selective separation and enrichment of ammonia nitrogen; during the adsorption process, the NH4+ in the solution can be monitored. + Changes in the concentration of interfering ions were used to determine the adsorption endpoint; S4. Electrode Regeneration and Ammonia Nitrogen Recovery: After adsorption saturation, remove or reverse the voltage (0 V or apply a reverse voltage to -0.6 V to -1.2 V), and simultaneously place the electrode in a low ionic strength or acidic desorption solution to allow the NH4+ enriched in the electrode to be absorbed. + The ammonia nitrogen is rapidly released, resulting in a high-concentration ammonia nitrogen recovery solution; the regenerated electrode can be reused in the electroadsorption process of step S3.

[0040] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are explanations of the present invention and not limitations thereof.

[0041] Example 1 Example 1 S1, Electrode Preparation: A metal-organic framework NH2-MIL-53(Al) was selected as the precursor. After carbonization at 700 °C, acid washing, and drying, nitrogen-doped ultraporous carbon material was obtained. Its BET specific surface area was 1447 m² / g, and the pore size distribution was concentrated in the range of 0.6-0.8 nm. Figure 2 The material, conductive carbon black, and polyvinylidene fluoride (PVDF) binder were mixed in a mass ratio of 8:1:1, ground evenly, and then coated onto a titanium mesh current collector. The mixture was then vacuum dried at 80°C for 12 hours to prepare the working electrode (approximately 200 μm thick). S2. System Construction: Two identical electrodes (effective area 9 cm²) were placed parallel to each other, with a spacing of 3.5 mm, in a reaction tank containing 100 mL of simulated wastewater. The simulated wastewater contained NH₄Cl (corresponding to NH₄⁺). + -N concentration of 50 mg / L) and NaCl (corresponding to Na + (Concentration 50 mg / L). Connect a DC power supply and a conductivity meter. S3, Selective Electroadsorption: Apply a constant voltage of 1.0 V for 120 min. During adsorption, the ion concentration in the solution continuously decreases. After adsorption, take a sample to determine the NH4+ concentration in the solution. + -N concentration decreased to 38.2 mg / L, while Na + The concentration decreased to 47.5 mg / L ( Figure 3 ). Calculations show that NH4 + / Na + The selectivity coefficient is close to 5. S4, Regeneration and Recovery: Remove the adsorbed electrode and place it in a recovery tank containing 10 mL of 0.01 M HCl solution. Short-circuit the electrode and let it stand for 60 min. Detect NH4 in the recovered solution. + The ammonia nitrogen concentration reached approximately 110 mg / L, achieving an enrichment rate of about 2.2 times. After the electrode was cleaned with deionized water, it underwent another adsorption cycle. After five consecutive cycles, the ammonia nitrogen removal rate remained above 80%.

[0042] Example 2 The difference from Example 1 is that the carbonization temperature of NH2-MIL-53(Al) was 680 °C. The BET specific surface area and pore size distribution of the obtained material were almost identical to those of the carbon material obtained at a carbonization temperature of 700 °C.

[0043] Example 3 The difference from Example 1 is that the carbonization temperature of NH2-MIL-53(Al) was 720 °C. The BET specific surface area and pore size distribution of the obtained material were almost identical to those of the carbon material obtained at a carbonization temperature of 700 °C.

[0044] Comparative Example 1 (Homologous but Different Structures: Control of Pore Size Structure) To verify the importance of one of the core technical features of this invention—the pore size being concentrated in the ultramicropore range (<1 nm)—this comparative example uses the exact same precursor (NH2-MIL-53(Al)) as Example 1, but prepares carbon materials with different pore structures using a higher carbonization temperature. S1, Electrode Preparation: The NH2-MIL-53(Al) precursor was carbonized at 900℃ in an inert atmosphere, and after the same acid washing and drying treatment, nitrogen-doped microporous carbon materials were obtained. Its BET specific surface area was 1770 m² / g, and the pore size distribution was significantly broadened, mainly distributed between 0.5-3 nm. Electrodes were prepared according to the same formulation (8:1:1) and process. S2, System Construction: Exactly the same as Example 1. S3, Selective Electroadsorption: Run under the same conditions (1.0 V, 120 min). After adsorption, NH4+ in the solution... + -N concentration decreased to 40.5 mg / L, Na + The concentration decreased to 43.3 mg / L. The calculated NH4+... + / Na + The selectivity coefficient is approximately 1.4. S4, Regeneration and Recovery: Regenerate using the same method, recovering NH4 from the liquid. + -N concentration was approximately 80 mg / L, with an enrichment factor of approximately 1.6-fold.

[0045] Comparative Example 2 (Commercial Materials: Performance Benchmark Comparison of General-Purpose Materials) To compare the performance differences between the present invention and commonly used materials in existing electroadsorption technologies, this comparative example uses commercially available high specific surface area activated carbon as the electrode material. S1. Electrode Preparation: The aforementioned commercial activated carbon, with a BET specific surface area of ​​approximately 2588 m² / g and a pore size distribution mainly concentrated between 0.7-2.2 nm, was selected and prepared using the same formulation and process. S2. System Construction: Completely identical to Example 1. S3. Selective Electroadsorption: Run under the same conditions (1.0 V, 120 min). After adsorption, the NH₄⁺ in the solution... + -N concentration decreased to 39.7 mg / L, Na + The concentration decreased to 42.1 mg / L. The calculated NH4+... + / Na + The selectivity coefficient is approximately 1.3. S4. Regeneration and Recovery: Regenerate using the same method; the recovered solution contains NH4+. + The -N concentration was approximately 85 mg / L, with an enrichment factor of approximately 1.7 times.

[0046] Comparative Example 3 The difference from Example 1 is that ZIF-8 was used instead of NH2-MIL-53(Al). The obtained material has a BET specific surface area of ​​674.4 m² / g and a significantly broadened pore size distribution, mainly distributed in the range of 0.6-2 nm.

[0047] The key role of pore size structure in Examples 1 (700℃ ultraporous carbon), Comparative Example 1 (900℃ microporous carbon), and Comparative Example 2 (commercial activated carbon) of this invention is highlighted: Example 1 (ultraporous carbon) achieved the highest selectivity coefficient (~5.0) and enrichment factor (~1.8). Comparative Example 1 shows that even using the same precursor, different carbonization processes leading to increased pore size and loss of the ultraporous dominant structure significantly reduce selectivity and enrichment. Comparative Example 2 further demonstrates that traditional activated carbon, due to its wider pore size distribution, exhibits lower selectivity and enrichment.

[0048] The above examples and comparative examples fully demonstrate that the electro-adsorption method based on specific ultraporous carbon provided by the present invention can efficiently and selectively separate and recover ammonia nitrogen from water containing complex coexisting ions, and has significant application advantages and innovations in the field of wastewater resource utilization.

[0049] The inventive aspect of this invention lies in its specific use of carbon materials with predominantly micropores smaller than 1 nm, rather than simply porous carbon. This particular structural feature, synergistically with the electroadsorption process, produces high ammonia nitrogen selectivity and high enrichment efficiency, solving the technical problems of poor selectivity and low resource recovery efficiency inherent in traditional electroadsorption materials. Comparative experiments strongly demonstrate that even with homologous precursors or commercially available materials with higher specific surface areas, deviating from this core feature will not yield the superior performance of this invention.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing ultramicroporous carbon, characterized by, Comprising: Carburizing NH2-MIL-53(Al) at 680-720℃, acid washing to obtain a nitrogen-doped ultramicroporous carbon material.

2. The method for preparing ultramicro-porous carbon according to claim 1, characterized in that, The carbonization temperature is 700℃.

3. The ultramicroporous carbon produced by the method of any one of claims 1 or 2, characterized in that, The pore size distribution is concentrated at 0.6-0.8 nm.

4. A method for preparing an ultramicroporous carbon electrode, characterized by, Comprising: Mixing the ultramicroporous carbon of claim 3, electric carbon black and binder uniformly, coating on a titanium mesh current collector, drying to obtain an ultramicroporous carbon electrode.

5. The method of claim 4, wherein the carbon electrode is an ultramicro porous carbon electrode. The mass ratio of the ultramicroporous carbon, electric carbon black and binder is 8-10:1:1; Or, the thickness of the ultramicroporous carbon electrode is 180-220μm or 200μm.

6. The ultramicroporous carbon electrode prepared by the method of claim 4 or 5.

7. An ultra-microporous carbon electrosorption module, characterized by, Comprising: Electrically connecting at least one ultramicroporous carbon electrode of claim 6 with an external power source and a switch.

8. A method for selectively separating and recovering ammonia nitrogen in sewage based on ultra-microporous carbon electrosorption, characterized in that, Comprising: Placing the ultramicroporous carbon electrode adsorption module of claim 7 in a sewage solution containing ammonia nitrogen, applying a direct current voltage to the electrode for adsorption, and after saturation, removing or reversing the voltage to obtain the product.

9. The method for selectively separating and recovering ammonia nitrogen in sewage based on ultra-microporous carbon electrosorption according to claim 8, characterized in that, The direct current voltage is 0.6 V~1.2 V; Or, the applied direct current voltage is a constant voltage or a pulse voltage, and the electrode adsorption time is 10~180 min; Or, the reverse voltage is -0.6 V~-1.2 V; Or, the pH value of the sewage is 6~8; or, the electrode is placed in the desorption solution, NH4 + is rapidly released, obtaining a high-concentration ammonia nitrogen recovery solution and a regenerated electrode; Or, the desorption solution is dilute hydrochloric acid, dilute sulfuric acid solution or water.

10. A sewage treatment system characterised in that, Comprising: At least one ultramicroporous carbon electrode adsorption module of claim 7 is used to perform the method of claim 8 or 9.

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