Method for carrying out electrochemical oxidation treatment on semi-coke wastewater and coupling cathode to produce hydrogen

Abstract

The invention discloses a method for carrying out electrochemical oxidation treatment on semi-coke wastewater and coupling a cathode to produce hydrogen, and belongs to the field of electrochemical treatment on wastewater. According to the method, a foam nickel-based nickel-iron catalyst is used as an anode, diluted semi-coke wastewater is alkalized and then is used as an anode electrolyte, oxidative degradation of high-COD and high-ammonia-nitrogen semi-coke wastewater is realized under a three-electrode system, and hydrogen is generated by coupling a cathode. According to the method, the conditions are mild, the stability is good, the high removal rate of COD, NH3-N and TOC can be achieved, meanwhile, hydrogen is generated by the cathode, and resource utilization of the wastewater is achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of electrochemical advanced oxidation process wastewater treatment, and particularly relates to a treatment method for high-concentration and refractory coking wastewater. BACKGROUND

[0002] The pollutants in coking wastewater include phenolic substances, tar substances, benzene homologues, aromatic hydrocarbon compounds, ammonia nitrogen compounds, sulfides, cyanides and the like, which are highly toxic and difficult to be biodegraded, and directly discharged into the environment will seriously threaten the ecology and health. Therefore, the treatment of coking wastewater is a great challenge.

[0003] The coking wastewater treatment technologies mainly include physical method, chemical method, biological method and advanced oxidation method. The physical method can efficiently remove high-concentration phenolic substances in wastewater through adsorption, extraction and membrane separation, and is widely used in industrial scale phenol recovery and wastewater purification due to its simple operation and high treatment efficiency. However, the service life of adsorbents, extractants and membrane materials is limited, and they need to be replaced frequently, which increases the operation cost and management difficulty. The chemical method can degrade organic matter in wastewater into small molecular substances, CO2 and H2O through chemical reaction, and has the advantages of fast degradation rate and high pollutant removal rate, and is especially suitable for high-concentration wastewater treatment. However, this method needs to continuously add a large amount of oxidizing agent or coagulant, which leads to the increase of operation cost, and is easy to produce secondary pollutants such as chemical sludge, which needs to be matched with a sludge treatment process. The biological method mainly relies on microbial metabolism, activated sludge system and enzyme catalysis to achieve pollutant degradation, but the toxic organic matter in coking wastewater can easily damage the cell membrane structure of microorganisms and inhibit enzyme activity, which significantly affects the treatment efficiency. In addition, if the residual sludge containing phenolic substances and their metabolites produced in the treatment process is not properly disposed, it will easily cause secondary pollution, which restricts the practical application range of this technology. The advanced oxidation method can realize the deep mineralization of pollutants through the generation of strong oxidizing hydroxyl radicals, and covers various processes such as wet catalytic oxidation, photochemical oxidation and Fenton oxidation, which has the characteristics of mild reaction conditions, flexible operation and no secondary pollution, and has outstanding treatment effect on refractory pollutants. However, due to the high cost of part of the catalytic materials, high energy consumption of equipment and high overall treatment cost, it is difficult to realize large-scale industrial application at present.

[0004] Electrochemical oxidation (electrolysis method) has become a potential technology for wastewater treatment due to its advantages of green and efficient, no secondary pollution and the like, and its in-depth research is of great importance to promote the progress of water treatment technology and environmental safety. For example, patent CN118684312A discloses a microporous SnO2-Sb / Ti@C composite anode and its preparation and application, which shows excellent effect in the treatment of organic simulated wastewater, but it still has limitations such as complex preparation conditions of catalyst, high energy consumption and high cost.

[0005] The essence of hydrogen production by electrolysis of water is to decompose water molecules through electrode reactions (cathode hydrogen evolution and anode oxygen evolution). The kinetics efficiency of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) directly determines the performance of the device. Among them, OER involves a complex 4-electron transfer process (reaction formula: 2H2O → O2+ 4H + + 4e - ), and the kinetic rate is much lower than that of 2-electron transfer HER (2H + + 2e - →H2), resulting in a higher energy barrier for OER (theoretical overpotential 1.23 V). Although Ir / Ru-based noble metal catalysts can improve the OER activity, their high cost and scarcity hinder their large-scale application. More importantly, the low added value (product O2), high overpotential and kinetic lag of OER directly restrict the cathode hydrogen production efficiency.

[0006] Electrochemical advanced oxidation processes (EAOPs) replace traditional OER, and innovatively use coking wastewater alkali as anode reactants, replacing the oxygen evolution process through organic pollutant oxidation reactions (such as organic matter → small molecule organic matter, CO2 and H2O, NH3 → N2 and H2O). Its advantages are that the oxidation overpotential of organic matter is significantly lower than that of OER, reducing power consumption; toxic ingredients in wastewater are degraded at the anode (mineralized into small molecule acid / CO2 / N2), and hydrogen is produced synchronously at the cathode; avoid the dependence on noble metal catalysts, reduce system cost. This coupling technology realizes the double optimization of wastewater treatment and green hydrogen production. For example, ZhenHai Wen et al. (10.1002 / anie.202407079) prepared a Ni9S8-Ni 15 O 16 / NF catalyst to oxidize phenol to prepare p-benzoquinone in an H-type electrolytic cell, using phenol oxidation instead of OER to reduce the overpotential of the oxidation end. However, this foam nickel-based catalyst also has the problems of complex preparation process, harsh preparation conditions, and high preparation cost, which to some extent limits its practical application. SUMMARY

[0007] In view of this, the purpose of the present application is to provide a method for electrocatalytic oxidation treatment of coking wastewater and coupling cathode hydrogen production, which uses a foam nickel-iron catalyst as an anode to oxidize and degrade coking wastewater while accelerating the hydrogen production efficiency at the cathode, achieving efficient removal of organic pollutants in coking wastewater.

[0008] To solve the above problems, the technical scheme adopted by the present application consists of the following steps:

[0009] Step 1: Preparation of foam nickel-based nickel-iron catalyst

[0010] Method one: the pretreated nickel foam is immersed in an aqueous ethanol solution containing a nickel source and an iron source, and is soaked at 25-130℃ for 24-60 h, and is washed with distilled water and dried to obtain a nickel foam-based nickel-iron catalyst.

[0011] Method two: the pretreated nickel foam is immersed in an aqueous ethanol solution containing a nickel source and an iron source, and is soaked at 25-130℃ for 24-60 h, and is then immersed in a sodium borohydride N,N-dimethylformamide solution, and is reduced at 100-130℃ for 1-3 h under airtight conditions, and is washed with distilled water and dried to obtain a nickel foam-based nickel-iron catalyst.

[0012] Step 2: electrocatalytic oxidation of coking wastewater coupled with hydrogen production

[0013] An H-type electrolytic cell is used, the nickel foam-based nickel-iron catalyst obtained in step 1 is used as the anode, a Hg / HgO electrode is used as the reference electrode, a platinum electrode is used as the cathode, and the diluted coking wastewater is alkalized with KOH and used as the anode electrolyte, and 1 mol / L KOH aqueous solution is used as the cathode electrolyte, the concentration of KOH in the anode electrolyte is 1 mol / L, and the coking wastewater is electrocatalytically oxidized and degraded, and hydrogen is produced at the cathode.

[0014] Further, in the above step 1, the pretreated nickel foam is preferably immersed in an aqueous ethanol solution containing a nickel source and an iron source, and is soaked at 100-120℃ for 48 h.

[0015] Further, in the above step 1, the iron source is preferably ferrous sulfate or ferric nitrate, and the nickel source is preferably nickel nitrate or nickel sulfite.

[0016] Further, in the above step 1, the molar ratio of the iron source to the nickel source is preferably 1:6-1:12.

[0017] Further, in the above step 1, the total concentration of nickel ions and iron ions in the aqueous ethanol solution containing a nickel source and an iron source is preferably 0.2-1 mol / L.

[0018] Further, in the above step 1, the volume ratio of water to anhydrous ethanol in the aqueous ethanol solution is preferably 1:5-1:1.

[0019] Further, in the above step 1, the concentration of sodium borohydride in the sodium borohydride N,N-dimethylformamide solution is preferably 0.1-2 mol / L, and more preferably the concentration of sodium borohydride in the sodium borohydride N,N-dimethylformamide solution is 1-1.5 mol / L.

[0020] Further, in the step 2, the COD content of the semi-coke wastewater is 45000-55000 mg / L, the NH3-N content is 4000-5000 mg / L, and the TOC content is 7000-8500 mg / L, and after being diluted by 5-100 times of deionized water, the semi-coke wastewater is alkalinized by KOH to be used as an anode electrolyte.

[0021] Further, in the step 2, the current density for electrocatalytic oxidation degradation of the semi-coke wastewater is preferably 50-200 mA·cm -2 .

[0022] The beneficial effects of the present application are as follows:

[0023] 1. The present application uses foamed nickel as a catalyst substrate, and a dense nickel-iron catalyst layer is grown in situ after simple impregnation, and the catalyst surface is further treated by hydrothermal reduction of sodium borohydride to prepare a high-performance transition metal catalyst with extremely low cost. The catalyst exhibits excellent corrosion resistance in alkaline semi-coke wastewater, and the catalyst stability is extremely strong when the electrochemical oxidation method is used for long-term oxidation.

[0024] 2. The present application dilutes and alkalinizes high-COD and high-ammonia-nitrogen semi-coke wastewater to be used as an anode electrolyte, and foamed nickel-based nickel-iron catalyst is used as an anode to oxidize and degrade semi-coke wastewater in a three-electrode system, which can reduce the anode oxidation voltage, and simultaneously couple hydrogen production at the cathode to remove organic pollutants in the semi-coke wastewater efficiently, thereby realizing resource utilization of the wastewater. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 Figure 1 is a SEM image of the foamed nickel-based nickel-iron catalyst prepared in Example 1.

[0026] Figure 2 Figure 2 is an electrochemical characterization image of the foamed nickel-based nickel-iron catalyst prepared in Example 1.

[0027] Figure 3 Figure 3 is a COD change curve of the foamed nickel-based nickel-iron catalyst prepared in Examples 1-4 in the electrocatalytic oxidation of semi-coke wastewater in an H-type electrolytic cell.

[0028] Figure 4 Figure 4 is an NH3-N change curve of the foamed nickel-based nickel-iron catalyst prepared in Examples 1-4 in the electrocatalytic oxidation of semi-coke wastewater in an H-type electrolytic cell.

[0029] Figure 5 Figure 5 is a TOC change curve of the foamed nickel-based nickel-iron catalyst prepared in Examples 1-4 in the electrocatalytic oxidation of semi-coke wastewater in an H-type electrolytic cell.

[0030] Figure 6are i-t curves of electrolysis of the foamed nickel-based nickel-iron catalyst prepared in Example 1 on the diluted 10 times coking waste water (AOPs) containing 1 mol / L KOH and 1 mol / L KOH aqueous solution (OER) respectively at 0.7 V voltage for 5 min. DETAILED DESCRIPTION

[0031] The application will be further described in detail below in conjunction with the drawings and examples, but the protection scope of the application is not limited to these examples.

[0032] Example 1

[0033] Step 1: Preparation of foamed nickel-based nickel-iron catalyst

[0034] 1.11 g (4 mmol) of FeSO4·7H2O and 10.44 g (36 mmol) of Ni(NO)3·6H2O were mixed and dissolved in 25 mL of deionized water, and after being fully dissolved, the solution was slowly poured into 25 mL of anhydrous ethanol, and a nickel-iron mixed solution was obtained by fully stirring. A 1 cm×2 cm foamed nickel was sequentially ultrasonically treated in 1 mol / L HCl aqueous solution, acetone and deionized water for 30 min each, and after being dried, it was placed in the nickel-iron mixed solution and immersed at 120℃ for 48 h to obtain a dark green foamed nickel. The dark green foamed nickel was immersed in a 1 mol / L sodium borohydride DMF solution and reduced at 120℃ for 2 h in a polytetrafluoroethylene-lined high-pressure reaction kettle to obtain a foamed nickel-based nickel-iron catalyst. The foamed nickel-based nickel-iron catalyst was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Figure 1 It can be seen that the surface of the foamed nickel presents a dense and irregularly arranged sheet structure, and its unique surface morphology can provide a large specific surface area, thereby providing abundant active sites for the reaction and significantly improving the catalytic reaction activity.

[0035] Step 2: Electro-catalytic oxidation of coking waste water coupled with hydrogen production

[0036] The coking waste water generated by a chemical plant was used, which had a COD content of 50000 mg / L, an NH3-N content of 4500 mg / L and a TOC content of 7500 mg / L. After the coking waste water was diluted 10 times with deionized water, KOH was added to prepare a coking waste water solution containing 1 mol / L KOH as the anode electrolyte, 1 mol / L KOH aqueous solution as the cathode electrolyte, platinum sheet electrode as the cathode, Hg / HgO electrode as the reference electrode, and the foamed nickel-based nickel-iron catalyst obtained in step 1 as the anode. A three-electrode workstation and an H-type electrolytic cell were used, and the current density was 100 mA·cm -2The electrocatalytic oxidation degradation of the coking wastewater was carried out at the same time, and hydrogen was generated at the cathode. The COD, NH3-N and TOC of the wastewater were detected every 6 h. After 36 h of degradation, it was measured that the COD content in the wastewater solution was reduced by 83.93%, the NH3-N content was reduced by 96.47%, and the TOC content was reduced by 88.32%.

[0037] From Figure 2 It can be seen that the oxygen evolution activity of the catalyst reached 230 mV vs. RHE (90% IR compensation) at 100 mA·cm -2 , showing extremely high oxygen evolution activity.

[0038] Example 2

[0039] Step 1: Preparation of a foam nickel-based nickel-iron catalyst

[0040] 1.11 g (4 mmol) of FeSO4·7H2O and 10.44 g (36 mmol) of Ni(NO)3·6H2O were dissolved in 25 mL of deionized water, and after being fully dissolved, the solution was slowly poured into 25 mL of anhydrous ethanol, and a nickel-iron mixed solution was obtained by fully stirring. A 1 cm x 2 cm foam nickel was sequentially treated in 1 mol / L HCl aqueous solution, acetone, and deionized water for 30 min each, and after drying, it was placed in the nickel-iron mixed solution and immersed at 120°C for 48 h to obtain a foam nickel-based nickel-iron catalyst.

[0041] Step 2: Electro-catalytic oxidation of coking wastewater coupled with hydrogen production

[0042] This step is the same as step 2 of example 1. After 36 h of degradation, it was measured that the COD content in the wastewater solution was reduced by 79.65%, the NH3-N content was reduced by 91.56%, and the TOC content was reduced by 78.02%.

[0043] Example 3

[0044] Step 1: Preparation of a foam nickel-based nickel-iron catalyst

[0045] This step is the same as step 1 of example 1.

[0046] Step 2: Electro-catalytic oxidation of coking wastewater coupled with hydrogen production

[0047] In this step, the electro-catalytic oxidation degradation of the coking wastewater was carried out at a current density of 150 mA·cm -2 , and the other steps were the same as step 2 of example 1. After 36 h of degradation, it was measured that the COD content in the wastewater solution was reduced by 86.52%, the NH3-N content was reduced by 96.47%, and the TOC content was reduced by 89.74%.

[0048] Example 4

[0049] Step 1: Preparation of foamed nickel-based nickel-iron catalyst

[0050] This step is the same as step 1 in Example 1.

[0051] Step 2: Electrocatalytic oxidation of semi-coke wastewater coupled with hydrogen production

[0052] In this step, the current density is 200 mA·cm. -2 The semi-coke wastewater was then subjected to electrocatalytic oxidation degradation, with other steps being the same as step 2 in Example 1. After 36 hours of degradation, the COD content in the wastewater was measured to have decreased by 85.08%, the NH3-N content by 96.76%, and the TOC content by 91.34%.

[0053] Depend on Figures 3 to 5 The results show that when the catalyst is reduced with sodium borohydride to create oxygen vacancies, the high concentration of sodium borohydride enhances the catalyst's oxidation performance, promoting the oxidation of COD, ammonia nitrogen, and TOC in semi-coke wastewater. Increasing the current density also demonstrates extremely high catalytic oxidation efficiency for COD, NH3-N, and TOC in semi-coke wastewater. These experimental results indicate that the electrochemical oxidation method using the foamed nickel-based nickel-iron catalyst of this invention for treating semi-coke wastewater can generate hydroxyl radicals, efficiently oxidizing pollutants in the wastewater, while simultaneously generating hydrogen gas at the cathode.

[0054] Furthermore, using the foamed nickel-based nickel-iron catalyst prepared in Example 1 as the anode, a platinum sheet electrode as the cathode, and an Hg / HgO electrode as the reference electrode, a three-electrode workstation and an H-type electrolytic cell were used to electrolyze 10-fold diluted semi-coke wastewater (AOPs) containing 1 mol / L KOH and 1 mol / L KOH aqueous solution (OER) for 5 min at 0.7 V. Figure 6 As shown, using the foamed nickel-based nickel-iron catalyst prepared in Example 1 to electrolyze semi-coke wastewater and pure water under the same voltage and KOH concentration, it can be clearly seen that the current generated by the semi-coke wastewater is greater. Using a drainage method to collect the hydrogen generated during the 5-minute electrolysis process, the hydrogen yield increased by 19.32%. Therefore, this invention achieves the cross-integration of water treatment technology and renewable energy hydrogen production technology, providing a new approach to producing high-value clean energy from waste resources.

Claims

1. A method for electrochemical oxidation of coking wastewater and coupled cathodic hydrogen production, characterized in that The method comprises the following steps: Step 1: Preparation of a foamed nickel-based nickel-iron catalyst Method one: the pretreated foamed nickel is immersed in an ethanol aqueous solution containing a nickel source and an iron source, and is soaked at 25-130 DEG C for 24-60 hours; after being washed with distilled water and dried, a foamed nickel-based nickel-iron catalyst is obtained; Method two: the pretreated foamed nickel is immersed in an ethanol aqueous solution containing a nickel source and an iron source, and is soaked at 25-130 DEG C for 24-60 hours; then it is immersed in a sodium borohydride N,N-dimethylformamide solution, and is reduced at 100-130 DEG C for 1-3 hours under a sealed condition; after being washed with distilled water and dried, a foamed nickel-based nickel-iron catalyst is obtained; Step 2: Electro-catalytic oxidation of coking waste water coupled with hydrogen production In a H-type electrolytic cell, the foamed nickel-based nickel-iron catalyst obtained in step 1 is used as an anode, a Hg / HgO electrode is used as a reference electrode, a platinum electrode is used as a cathode, and diluted coking waste water is alkalized with KOH and used as an anode electrolyte, and 1 mol / L KOH aqueous solution is used as a cathode electrolyte; the concentration of KOH in the anode electrolyte is 1 mol / L; electro-catalytic oxidation degradation of the coking waste water is carried out, and hydrogen is produced at the cathode.

2. The method for electrochemical oxidation treatment of coking wastewater and coupled cathodic hydrogen production according to claim 1, characterized in that: In step 1, the pretreated foamed nickel is immersed in an ethanol aqueous solution containing a nickel source and an iron source, and is soaked at 100-120 DEG C for 48 hours.

3. The method for electrochemical oxidation treatment of coking wastewater and coupled cathodic hydrogen production according to claim 1 or 2, characterized in that: In step 1, the iron source is ferrous sulfate or ferric nitrate, and the nickel source is nickel nitrate or nickel sulfite.

4. The method for electrochemical oxidation treatment of coking wastewater and coupled cathodic hydrogen production according to claim 1 or 2, characterized in that: In step 1, the molar ratio of the iron source to the nickel source is 1:6-1:

12.

5. The method for electrochemical oxidation treatment of coking wastewater and coupled cathodic hydrogen production according to claim 1 or 2, characterized in that: In step 1, the total concentration of nickel ions and iron ions in the ethanol aqueous solution containing a nickel source and an iron source is 0.2-1 mol / L.

6. The method for electrochemical oxidation treatment of coking wastewater and coupled cathodic hydrogen production according to claim 1 or 2, characterized in that: In step 1, the volume ratio of water to anhydrous ethanol in the ethanol aqueous solution is 1:5-1:

1.

7. The method for electrochemical oxidation of coking wastewater and coupled cathodic hydrogen production according to claim 1, characterized in that: In step 1, the concentration of sodium borohydride in the sodium borohydride N,N-dimethylformamide solution is 0.1-2 mol / L.

8. The method for electrochemical oxidation of coking wastewater and coupled cathodic hydrogen production according to claim 1, characterized in that: In step 1, the concentration of sodium borohydride in the sodium borohydride N,N-dimethylformamide solution is 1-1.5 mol / L.

9. The method for electrochemical oxidation of coking wastewater and coupled cathodic hydrogen production according to claim 1, characterized in that: In step 2, the COD content of the coking waste water is 45,000-55,000 mg / L, the NH3-N content is 4,000-5,000 mg / L, and the TOC content is 7,000-8,500 mg / L; after being diluted 5-100 times with deionized water, the coking waste water is alkalized with KOH and used as an anode electrolyte.

10. The method for electrochemical oxidation of coking wastewater and coupled cathodic hydrogen production according to claim 1, characterized in that: In step 2, the current density for electrocatalytic oxidative degradation of the lignite coal wastewater is 50-200 mA·cm -2 .

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