Coal-based activated carbon electrode for removing chlorine through electro-adsorption and preparation method of coal-based activated carbon electrode

Abstract

The invention discloses a coal-based activated carbon electrode for electro-adsorption dechlorination and a preparation method of the coal-based activated carbon electrode. The electrode comprises an active substance and a binder, wherein the active substance comprises sulfur-doped coal-based activated carbon and a biogas slurry derived biomass conductive additive, and the mass ratio of the sulfur-doped coal-based activated carbon to the biogas slurry derived biomass conductive additive is 8: 1. The coal-based activated carbon is subjected to sulfur doping modification, so that the electrochemical activity and the chloride ion adsorption capacity of the material can be improved; a biogas slurry derived biomass conductive additive is introduced as a conductive network construction component and is compounded with sulfur-doped coal-based activated carbon according to a specific mass ratio, so that the obtained electrode can have a good electron conduction path, and meanwhile, an excessive conductive agent can be prevented from blocking channels of an active material; and when the electrode is used for reverse osmosis concentrated water treatment of a coal-fired power plant, the electrode shows excellent chloride ion removal capability and cycling stability.

Description

Technical Field

[0001] This invention belongs to the field of environmental functional materials and capacitive deionization (CDI) technology. Specifically, this invention relates to a coal-based activated carbon electrode for electro-adsorption dechlorination and its preparation method. Background Technology

[0002] Capacitive deionization (CDI) technology has become an important direction for high-salinity wastewater treatment due to its advantages such as low energy consumption, modularity, and mild operation. This technology typically utilizes carbon-based electrodes to adsorb salts from water; however, the conductivity and electrochemical adsorption performance of carbon-based electrodes alone are poor. Therefore, to improve the conductivity and electrochemical adsorption performance of carbon-based electrodes, carbon-based materials can be combined with conductive additives to form the electrode. However, in existing technologies, the conductive additives are mostly ordinary carbon black, which suffers from insufficient conductivity, easy aggregation, and high interfacial impedance with activated carbon. Especially in the treatment of high-salinity wastewater, the charge transport efficiency and cycle stability of the electrode have become key bottlenecks restricting its engineering application.

[0003] In view of this, the present invention is hereby proposed. Summary of the Invention

[0004] The present invention aims to at least partially solve one of the technical problems in the related art.

[0005] Therefore, this invention proposes a coal-based activated carbon electrode for electroadsorption dechlorination and its preparation method. This invention enhances sulfur-doped coal-based activated carbon by employing biomass-derived biomass conductive additives and optimizes the ratio between the two to synergistically improve the adsorption capacity and charge transport efficiency of the resulting electrode.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: In a first aspect, embodiments of the present invention provide a coal-based activated carbon electrode for electro-adsorption dechlorination, the coal-based activated carbon electrode comprising an active material and a binder; wherein the active material comprises sulfur-doped coal-based activated carbon and biomass conductive additives derived from biogas slurry.

[0007] In some embodiments, the mass ratio of the sulfur-doped coal-based activated carbon to the biogas slurry-derived conductive additive is 8:1.

[0008] In some embodiments, the sulfur-doped coal-based activated carbon is prepared by a method comprising the following steps: mixing a coal-based activated carbon precursor with potassium thiosulfate at a mass ratio of 1:2, and then pyrolyzing the mixture in an inert atmosphere at 500-700°C for 1-3 hours to obtain the sulfur-doped coal-based activated carbon.

[0009] In some embodiments, the specific surface area of ​​the sulfur-doped coal-based activated carbon is ≥600 m². 2 / g.

[0010] In some embodiments, the biomass conductive additive derived from biogas slurry is prepared by a method comprising the following steps: a) The concentrated biogas slurry is washed sequentially with distilled water and ethanol, and then vacuum dried, crushed and sieved to obtain biogas slurry solid; b) The biogas slurry solid is soaked in a saturated KCl solution and then dried. c) The sample dried in step b) is subjected to carbonization treatment to obtain carbonized products; d) The carbonized product is acid-washed, then washed with water until the pH of the washing liquid is neutral, and then freeze-dried to obtain the biogas slurry-derived biomass conductive additive.

[0011] Furthermore, in step a), the vacuum drying temperature is 60-100℃, and the drying time is 12-24h; And / or, in step b), the soaking is carried out at room temperature for 12-24 hours; And / or, in step c), the carbonization temperature is 700-900℃ and the carbonization time is 3-6h; And / or, in step d), the pickling solution used is a 0.1M hydrochloric acid solution, and the pickling time is 2-12h; the freeze-drying temperature is -60~-40℃, and the drying time is 12-24h.

[0012] In some embodiments, the adhesive includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, and sodium carboxymethyl cellulose; And / or, the amount of the binder added accounts for 5-15% of the total mass of the active material.

[0013] In some embodiments, when the coal-based activated carbon electrode is used to treat reverse osmosis concentrate from a coal-fired power plant, its adsorption capacity for chloride ions at a voltage of 1.2V is ≥20mg / g.

[0014] Secondly, embodiments of the present invention also provide a method for preparing a coal-based activated carbon electrode for electro-adsorption dechlorination as described in the first aspect, comprising the following steps: (1) The sulfur-doped coal-based activated carbon is mechanically ground and sieved to obtain sulfur-doped coal-based activated carbon powder; at the same time, the biogas slurry-derived biomass conductive additive is dried; and then the dried biogas slurry-derived biomass conductive additive is mixed with the sulfur-doped coal-based activated carbon powder to obtain active material. (2) Add binder and solvent to the active material, stir and mix to obtain slurry; (3) The slurry is coated onto the pretreated current collector and then subjected to gradient drying to obtain the coal-based activated carbon electrode.

[0015] In some embodiments, in step (1), the sieving is done with a 300-400 mesh screen, the drying temperature is 80-100℃, and the drying time is 6-12h; And / or, in step (2), the solvent is N-methylpyrrolidone or deionized water, the stirring speed is 500-1000 r / min, and the mixing time is 2-4 h; And / or, in step (3), after the coating, the thickness of the wet film formed by the slurry on the current collector is 100-200μm; the gradient drying process is as follows: first, vacuum drying at 40-50℃ for 1-2h, and then vacuum drying at 60-80℃ for 4-8h.

[0016] The advantages and beneficial effects of the embodiments of the present invention are as follows: (1) In this embodiment of the invention, sulfur doping is used to introduce sulfur into coal-based activated carbon, which can change the electron distribution of carbon materials, increase active sites, and improve the electrochemical activity and adsorption capacity of chloride ions.

[0017] (2) In this embodiment of the invention, biomass conductive additive KBSA derived from biogas slurry is used as a component for constructing a conductive network. It is combined with sulfur-doped coal-based activated carbon at an optimized mass ratio of 1:8. This ensures that the resulting electrode has a good electronic conduction pathway and avoids excessive conductive agent from clogging the pores of the active material, thus achieving the best balance between conductivity and specific surface area.

[0018] (3) The preparation method of the coal-based activated carbon electrode for electro-adsorption dechlorination in the embodiments of the present invention is simple, the raw material cost is low, the operating conditions are mild, which is conducive to realizing industrial-scale production. Moreover, the electrode prepared exhibits excellent cycle stability and chloride ion removal capacity when treating reverse osmosis concentrate from coal-fired power plants. Attached Figure Description

[0019] Figure 1 This is a SEM image of the coal-based activated carbon electrode prepared in Example 1 of the present invention.

[0020] Figure 2 The electrochemical impedance spectroscopy results are shown for the coal-based activated carbon electrodes prepared in Example 1 and Comparative Examples 1-2 of this invention.

[0021] Figure 3 The graphs show the CDI dechlorination performance test results of the coal-based activated carbon electrodes prepared in Example 1 and Comparative Examples 1-2 of this invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the protection scope of the present invention.

[0023] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0024] In this invention, when a value is described as a range, it should be understood that such disclosure includes disclosure of all possible subranges within that range, as well as specific numerical values ​​falling within that range, regardless of whether specific numerical values ​​or specific subranges are explicitly specified.

[0025] In this invention, the terms “comprising” and “including” and their various variations mean that other elements or wholes may be included but are not specifically described.

[0026] In this invention, the term "and / or" is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone.

[0027] In a first aspect, embodiments of the present invention provide a coal-based activated carbon electrode for electro-adsorption dechlorination, the coal-based activated carbon electrode comprising an active material and a binder; wherein the active material comprises sulfur-doped coal-based activated carbon and biomass conductive additives derived from biogas slurry.

[0028] In some embodiments, the mass ratio of the sulfur-doped coal-based activated carbon to the biogas slurry-derived conductive additive is 8:1.

[0029] The inventors discovered through research that if the mass ratio of biogas-derived biomass conductive additive is too low, charge transport will be hindered; however, if the mass ratio is too high, it can easily clog activated carbon pores and obscure active sites, thereby reducing dechlorination capacity and cycle stability, and also causing electron / ion transport mismatch. Therefore, controlling the mass ratio of sulfur-doped coal-based activated carbon to biogas-derived biomass conductive additive at 8:1 is advantageous in this embodiment of the invention.

[0030] In some embodiments, the sulfur-doped coal-based activated carbon is prepared by a method comprising the following steps: mixing a coal-based activated carbon precursor with potassium thiosulfate at a mass ratio of 1:2, and then pyrolyzing the mixture in an inert atmosphere at 500-700°C for 1-3 hours to obtain the sulfur-doped coal-based activated carbon, denoted as S-AC.

[0031] Furthermore, the coal-based activated carbon precursor includes at least one of bituminous coal, lignite, anthracite, and petroleum coke; And / or, the heating rate of the pyrolysis is 2-5 °C / min.

[0032] Sulfur-doped coal-based activated carbon was prepared by using coal-based activated carbon precursors and potassium thiosulfate as raw materials. Potassium thiosulfate serves as both an activator and a sulfur source, which can promote the development of pore structure and introduce sulfur-containing functional groups during pyrolysis, thereby improving the specific surface area and hydrophilicity of the material.

[0033] In some embodiments, the specific surface area of ​​the sulfur-doped coal-based activated carbon is ≥600 m². 2 / g.

[0034] In some embodiments, the biomass conductive additive derived from biogas slurry is prepared by a method comprising the following steps: a) The concentrated biogas slurry is washed sequentially with distilled water and ethanol, and then vacuum dried, crushed and sieved to obtain biogas slurry solid; b) The biogas slurry solid is soaked in a saturated KCl solution and then dried. c) The sample dried in step b) is subjected to carbonization treatment to obtain carbonized products; d) The carbonized product is acid-washed, then washed with water until the pH of the washing liquid is neutral, and then freeze-dried to obtain the biogas slurry-derived biomass conductive additive, denoted as KBSA.

[0035] Furthermore, in step a), the vacuum drying temperature is 60-100℃, and the drying time is 12-24h; And / or, in step b), the soaking is carried out at room temperature for 12-24 hours; And / or, in step c), the carbonization temperature is 700-900℃ and the carbonization time is 3-6h; And / or, in step d), the pickling solution used is a 0.1M hydrochloric acid solution, and the pickling time is 2-12h; the freeze-drying temperature is -60~-40℃, and the drying time is 12-24h.

[0036] The biomass conductive additive KBSA, prepared by using concentrated biogas slurry as raw material and through processes such as saturated KCl pretreatment, high-temperature carbonization, acid washing, and freeze drying, has high conductivity and rich microporous structure; and at the same time, it realizes the resource recovery and utilization of concentrated biogas slurry.

[0037] In some embodiments, the adhesive includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, and sodium carboxymethyl cellulose; And / or, the amount of the binder added accounts for 5-15% of the total mass of the active material.

[0038] In some embodiments, when the coal-based activated carbon electrode is used to treat reverse osmosis concentrate from a coal-fired power plant, its adsorption capacity for chloride ions at a voltage of 1.2V is ≥20mg / g.

[0039] Secondly, embodiments of the present invention also provide a method for preparing a coal-based activated carbon electrode for electro-adsorption dechlorination as described in the first aspect, comprising the following steps: (1) The sulfur-doped coal-based activated carbon is mechanically ground and sieved to obtain sulfur-doped coal-based activated carbon powder; at the same time, the biogas slurry-derived biomass conductive additive is dried to remove moisture; then the dried biogas slurry-derived biomass conductive additive is mixed with the sulfur-doped coal-based activated carbon powder to obtain active material. (2) Add binder and solvent to the active material, stir and mix to obtain slurry; (3) The slurry is coated onto the pretreated current collector and then subjected to gradient drying to obtain the coal-based activated carbon electrode.

[0040] In some embodiments, in step (1), the sieving is done with a 300-400 mesh screen, the drying temperature is 80-100℃, and the drying time is 6-12h; And / or, in step (2), the solvent is N-methylpyrrolidone or deionized water, the stirring speed is 500-1000 r / min, and the mixing time is 2-4 h; And / or, in step (3), after the coating, the thickness of the wet film formed by the slurry on the current collector is 100-200μm; the gradient drying process is as follows: first, vacuum drying at 40-50℃ for 1-2h, and then vacuum drying at 60-80℃ for 4-8h; through gradient drying, the solvent is completely removed.

[0041] Furthermore, in step (3), the pretreatment process of the current collector includes cleaning, drying and other processes; and it should be noted that the type of current collector is not particularly limited, and those skilled in the art can select it according to actual needs. For example, the current collector can be a carbon current collector, or more specifically, carbon paper, graphite felt, etc.

[0042] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. Unless otherwise stated, all raw materials used in the embodiments and comparative examples are conventional commercially available products, or can be prepared by known methods; and the experimental methods in the embodiments that do not specify specific conditions are conventional methods and conditions well known in the art.

[0043] Example 1 This embodiment provides a coal-based activated carbon electrode for electro-adsorption dechlorination. The coal-based activated carbon electrode includes an active material and a binder. The active material includes sulfur-doped coal-based activated carbon and biogas slurry-derived conductive additives in a mass ratio of 8:1. The binder is polyvinylidene fluoride, and the amount of binder added accounts for 10% of the total mass of the active material.

[0044] In this embodiment, sulfur-doped coal-based activated carbon is prepared by a method comprising the following steps: Bituminous coal and potassium thiosulfate were thoroughly ground and mixed in a mortar at a mass ratio of 1:2. The mixture was then placed in a tube furnace and heated to 600°C at a rate of 3°C / min under a nitrogen atmosphere, and held at this temperature for 2 hours for pyrolysis activation and sulfur doping. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, and the product was removed, washed with deionized water until neutral, and then dried to obtain sulfur-doped coal-based activated carbon, denoted as S-AC. The specific surface area of ​​S-AC was 677.66 m². 2 / g.

[0045] In this embodiment, the biomass conductive additive derived from biogas slurry is prepared by a method including the following steps: a) Take the concentrated biogas slurry and rinse it with distilled water and ethanol in sequence to remove soluble impurities and some organic residues; then place the rinsed concentrated biogas slurry in a vacuum oven at 100°C and dry it for 16 hours to obtain loose biogas slurry solid powder, and then crush and sieve the obtained biogas slurry solid powder appropriately. b) Immerse the dried and sieved biogas slurry solid powder in 50 mL of saturated KCl solution and let it stand at room temperature for 24 h. Then take out the sample and vacuum dry it at 50 °C. c) Place the dried sample from step b) in a vacuum tube furnace and carbonize it at 800°C for 4 hours to obtain the carbonized product; d) The carbonized product was soaked in 0.1M hydrochloric acid solution for acid washing to remove inorganic impurities and some metal ions. After soaking for 4 hours, the acid-washed sample was repeatedly washed with distilled water until the pH of the washing solution was 7. Finally, the neutral sample was placed in a freeze dryer and freeze-dried at -60℃ for 24 hours to obtain biomass conductive additive derived from biogas slurry, denoted as KBSA.

[0046] This embodiment also provides a method for preparing the above-mentioned coal-based activated carbon electrode for electroadsorption dechlorination, including the following steps: (1) The sulfur-doped coal-based activated carbon was mechanically ground and passed through a 325-mesh sieve to obtain sulfur-doped coal-based activated carbon powder; at the same time, the biogas slurry-derived biomass conductive additive was dried in a vacuum drying oven at 90℃ for 8 hours; then 1.0g of the dried biogas slurry-derived biomass conductive additive was mixed with 8.0g of sulfur-doped coal-based activated carbon powder to obtain active material. (2) Add polyvinylidene fluoride (PVDF, and the amount added accounts for 10% of the total mass of the active material) to the above active material, and add an appropriate amount of N-methylpyrrolidone (NMP) as a solvent. Stir in a mechanical mixer at 1000 r / min for 3 h to obtain a uniform slurry. (3) The above slurry is coated on the pretreated graphite felt current collector, the wet film thickness is controlled to be 100 μm, and then it is pre-dried at 50℃ for 1 h and then vacuum dried at 70℃ for 6 h to obtain the coal-based activated carbon electrode, denoted as S-AC / KBSA-8:1.

[0047] Figure 1 The image shows the SEM image of the coal-based activated carbon electrode prepared in this embodiment. As can be seen from the image, when the mass ratio of sulfur-doped coal-based activated carbon (S-AC) to biogas slurry-derived conductive additive (KBSA) is 8:1, KBSA can be uniformly distributed between S-AC particles, forming a continuous conductive path without significantly blocking the pores, thus achieving a good balance between conductivity and specific surface area.

[0048] Comparative Example 1 This comparative example is basically the same as Example 1, except that the active material of the coal-based activated carbon electrode in this comparative example does not include biogas slurry-derived biomass conductive additives, that is, the mass ratio of sulfur-doped coal-based activated carbon to biogas slurry-derived biomass conductive additives is 8:0.

[0049] Comparative Example 2 This comparative example is basically the same as Example 1, except that the mass ratio of sulfur-doped coal-based activated carbon to biomass conductive additives derived from biogas slurry in the active material of the coal-based activated carbon electrode in this comparative example is 8:2.

[0050] Figure 2The figures show the electrochemical impedance spectroscopy (EIS) of the coal-based activated carbon electrodes prepared in Example 1 and Comparative Examples 1-2 of this invention. As can be seen from the figures, compared to Comparative Examples 1-2, the coal-based activated carbon electrode (S-AC / KBSA-8:1) prepared in Example 1 of this invention has the lowest charge transfer impedance. This is mainly because the constructed KBSA conductive network can significantly reduce the interfacial impedance.

[0051] Figure 3 The figures show the CDI dechlorination performance test results of the coal-based activated carbon electrodes prepared in Example 1 and Comparative Examples 1-2 of this invention. As can be seen from the figures, compared with Comparative Examples 1-2, the coal-based activated carbon electrode (S-AC / KBSA-8:1) prepared in Example 1 of this invention has the highest dechlorination capacity, which is attributed to the combined effect of the additional capacity provided by sulfur doping and the optimized conductive network.

[0052] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0053] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A coal-based activated carbon electrode for electroadsorption dechlorination, characterized in that, The coal-based activated carbon electrode includes an active material and a binder; wherein the active material includes sulfur-doped coal-based activated carbon and biomass conductive additives derived from biogas slurry.

2. The coal-based activated carbon electrode for electro-adsorption dechlorination according to claim 1, characterized in that, The mass ratio of the sulfur-doped coal-based activated carbon to the biogas slurry-derived conductive additive is 8:

1.

3. The coal-based activated carbon electrode for electro-adsorption dechlorination according to claim 1, characterized in that, The sulfur-doped coal-based activated carbon is prepared by a method comprising the following steps: mixing a coal-based activated carbon precursor with potassium thiosulfate at a mass ratio of 1:2, and then pyrolyzing the mixture in an inert atmosphere at 500-700°C for 1-3 hours to obtain the sulfur-doped coal-based activated carbon.

4. The coal-based activated carbon electrode for electro-adsorption dechlorination according to any one of claims 1-3, characterized in that, The specific surface area of ​​the sulfur-doped coal-based activated carbon is ≥600 m². 2 / g.

5. The coal-based activated carbon electrode for electro-adsorption dechlorination according to claim 1, characterized in that, The biomass conductive additive derived from biogas slurry is prepared by a method including the following steps: a) The concentrated biogas slurry is washed sequentially with distilled water and ethanol, and then vacuum dried, crushed and sieved to obtain biogas slurry solid; b) The biogas slurry solid is soaked in a saturated KCl solution and then dried. c) The sample dried in step b) is subjected to carbonization treatment to obtain carbonized products; d) The carbonized product is acid-washed, then washed with water until the pH of the washing liquid is neutral, and then freeze-dried to obtain the biogas slurry-derived biomass conductive additive.

6. The coal-based activated carbon electrode for electro-adsorption dechlorination according to claim 5, characterized in that, In step a), the vacuum drying temperature is 60-100℃ and the drying time is 12-24h. And / or, in step b), the soaking is carried out at room temperature for 12-24 hours; And / or, in step c), the carbonization temperature is 700-900℃ and the carbonization time is 3-6h; And / or, in step d), the pickling solution used is a 0.1M hydrochloric acid solution, and the pickling time is 2-12h; the freeze-drying temperature is -60~-40℃, and the drying time is 12-24h.

7. The coal-based activated carbon electrode for electro-adsorption dechlorination according to claim 1, characterized in that, The adhesive includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, and sodium carboxymethyl cellulose. And / or, the amount of the binder added accounts for 5-15% of the total mass of the active material.

8. The coal-based activated carbon electrode for electro-adsorption dechlorination according to any one of claims 1-7, characterized in that, When the coal-based activated carbon electrode is used to treat reverse osmosis concentrate from a coal-fired power plant, its adsorption capacity for chloride ions at a voltage of 1.2V is ≥20mg / g.

9. A method for preparing a coal-based activated carbon electrode for electroadsorption dechlorination as described in any one of claims 1-8, characterized in that, Includes the following steps: (1) The sulfur-doped coal-based activated carbon is mechanically ground and sieved to obtain sulfur-doped coal-based activated carbon powder; at the same time, the biogas slurry-derived biomass conductive additive is dried; and then the dried biogas slurry-derived biomass conductive additive is mixed with the sulfur-doped coal-based activated carbon powder to obtain active material. (2) Add binder and solvent to the active material, stir and mix to obtain slurry; (3) The slurry is coated onto the pretreated current collector and then subjected to gradient drying to obtain the coal-based activated carbon electrode.

10. The method for preparing a coal-based activated carbon electrode for electro-adsorption dechlorination according to claim 9, characterized in that, In step (1), the sieving process uses a 300-400 mesh screen, the drying temperature is 80-100℃, and the drying time is 6-12h. And / or, in step (2), the solvent is N-methylpyrrolidone or deionized water, the stirring speed is 500-1000 r / min, and the mixing time is 2-4 h; And / or, in step (3), after the coating, the thickness of the wet film formed by the slurry on the current collector is 100-200μm; the gradient drying process is as follows: first, vacuum drying at 40-50℃ for 1-2h, and then vacuum drying at 60-80℃ for 4-8h.

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