Method for electrochemical oxidation of unsymmetrical dimethylhydrazine wastewater

Abstract

The invention provides a method for electrochemical oxidation of unsymmetrical dimethylhydrazine wastewater. The method comprises the steps that 1, unsymmetrical dimethylhydrazine wastewater to be treated is placed in a middle water tank, an electrolytic bath is arranged in the water tank, and wastewater containing unsymmetrical dimethylhydrazine is introduced into the electrolytic bath; the treatment process comprises a power supply, a reactor, an intermediate water tank and a circulating pump, the reactor is composed of an anode, a cathode, a flow channel, a container and the like, a water pump and the power supply are started, and unsymmetrical dimethylhydrazine wastewater is pressed into the reactor through the water pump; according to the method, persulfate is utilized to cooperate with electrochemical oxidation of unsymmetrical dimethylhydrazine wastewater, only electric energy and persulfate need to be input into the system, the electric energy can activate the persulfate, the activated sulfate free radicals can strengthen the effect of electrochemical oxidation of unsymmetrical dimethylhydrazine, no extra catalyst needs to be added, operation is flexible, starting and stopping are convenient, the oxidation capacity is high, and the method is suitable for industrial production. The treatment period is short.

Description

Technical Field

[0001] The invention relates to the field of environmental science and technology, and in particular to a method for electrochemically oxidizing unsymmetrical dimethylhydrazine wastewater. Background Art

[0002] Unsymmetrical dimethyl hydrazine is a toxic chemical widely used in the production of rocket fuel, plastics and rubber products. However, the wastewater generated during its production and use contains high concentrations of unsymmetrical dimethyl hydrazine, which poses a serious threat to the environment and human health. Unsymmetrical dimethyl hydrazine is the current mainstream conventional propellant. With its high specific impulse and thermal stability, it still has an irreplaceable position in thruster attitude adjustment. High-density launch missions will inevitably bring a large amount of propellant wastewater. Human contact with unsymmetrical dimethyl hydrazine will cause teratogenicity, carcinogenicity and mutagenicity. At present, the main methods for treating unsymmetrical dimethyl hydrazine wastewater are: adsorption, ion exchange, biological treatment, advanced oxidation, etc.

[0003] In Chinese patent CN117101641A, a neodymium-doped titanium dioxide catalyst was synthesized by hydrothermal method for treating unsymmetrical dimethylhydrazine wastewater. 50 g / L of the catalyst was added to 40 mL of low-concentration unsymmetrical dimethylhydrazine wastewater with a content of 100 mg / L. After 12 hours of reaction, the degradation rate was 93.1%. However, the catalyst dosage in this technology is large, the cost of the agent is high, and there is a risk of secondary pollution of nanomaterials, which limits its application and promotion. Therefore, the present invention proposes a method for electrochemical oxidation of unsymmetrical dimethylhydrazine wastewater to solve the problems existing in the prior art. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention proposes a method for electrochemically oxidizing unsymmetrical dimethylhydrazine wastewater. The method for electrochemically oxidizing unsymmetrical dimethylhydrazine wastewater utilizes persulfate to coordinately electrochemically oxidize the unsymmetrical dimethylhydrazine wastewater. Only electrical energy and persulfate need to be input into the system. The electrical energy can activate the persulfate. The activated persulfate free radicals can enhance the effect of the electrochemical oxidation of unsymmetrical dimethylhydrazine. No additional catalyst needs to be added. The method is flexible in operation, easy to start and stop, has strong oxidation ability, and has a short treatment cycle.

[0005] The technical solution of the present invention is achieved as follows: a method for electrochemically oxidizing unsymmetrical dimethylhydrazine wastewater, comprising the following steps;

[0006] Step 1: placing the unsymmetrical dimethylhydrazine wastewater to be treated in an intermediate water tank, in which an electrolytic cell is arranged, and introducing the unsymmetrical dimethylhydrazine-containing wastewater into the electrolytic cell;

[0007] Step 2: Add persulfate. The treatment process includes a power supply, a reactor, an intermediate water tank and a circulation pump. The reactor is composed of an anode, a cathode, a flow channel, a container, etc. Start the water pump and the power supply to press the unsymmetrical dimethylhydrazine wastewater into the reactor through the water pump;

[0008] Step 3: The wastewater is discharged when passing through the flow channel between the graphene-coated titanium electrodes. The treated wastewater returns to the intermediate water tank and the water quality is tested. If it does not meet the standard, it is recycled for treatment. If it meets the standard, it is directly discharged.

[0009] Step 4: setting an anode and a cathode in the electrolytic cell, wherein the anode is an inert electrode material and the cathode is a reducing electrode material;

[0010] Step 5: Pass direct current to generate an electric field between the anode and the cathode;

[0011] Step 6: Under the action of the electric field, UDMH undergoes an oxidation reaction at the anode to generate non-toxic or low-toxic substances;

[0012] Step 7: A reduction reaction occurs at the cathode to generate hydrogen or other reducing substances;

[0013] Step 8: After a certain period of electrolysis treatment, stop the power supply and take out the treated wastewater for subsequent treatment or discharge.

[0014] A further improvement is that in step 1, the UDMH is introduced into the electrolytic cell in the water tank for electrochemical reaction. During this process, an electric field is formed between the anode and cathode in the electrolytic cell, causing the UDMH molecules to undergo oxidation reaction at the anode.

[0015] A further improvement is that in step 2, persulfate, as a strong oxidant, can be activated in the electrochemical reaction to generate sulfate radicals, which are highly reactive species that can effectively oxidize organic pollutants such as unsymmetrical dimethylhydrazine. Starting the water pump can provide the necessary power to transport the unsymmetrical dimethylhydrazine wastewater from the storage tank or other sources to the electrochemical reactor.

[0016] Further improvements are: in step three, the discharge treatment between the graphene-coated titanium electrodes can effectively degrade pollutants such as unsymmetrical dimethyl hydrazine, ensuring that harmful substances in the wastewater are fully removed. The treated wastewater returns to the intermediate water tank and is tested for water quality. If the test results show that the water quality does not meet the standards, the wastewater will be sent back to the reactor for recycling treatment.

[0017] Further improvements are: in step 4, the anode is an inert electrode material; the inert electrode is platinum or its oxides; because these materials have good chemical stability and conductivity, they can withstand strong oxidizing conditions without being corroded; the cathode is a reducing electrode material; the reducing electrode materials are graphite and titanium, which show good performance in the chlor-alkali industry and wastewater treatment.

[0018] A further improvement is that in step 5, in order to drive the electrochemical reaction to achieve the oxidative degradation of UDMH, an oxidation reaction will occur at the anode under the action of the electric field to convert the UDMH molecules, while a reduction reaction will occur at the cathode.

[0019] A further improvement is that in step six, this conversion process helps to remove harmful components in the wastewater, reduce environmental pollution, and ensure that the treated water is safe and meets emission standards.

[0020] Further improvements are as follows: in step seven, at the cathode, water molecules are reduced to generate hydrogen. Hydrogen is a clean energy source that can be collected and utilized, for example, in fuel cells or as an industrial raw material. In addition, the generation of hydrogen also helps to improve the efficiency of the electrochemical reaction because it can promote the migration of ions in the solution, thereby enhancing the overall reaction kinetics. In addition to hydrogen, other reducing substances may be generated at the cathode, such as sulfites, sulfides, etc. These reducing substances can react with oxidants or intermediates in the solution to further promote the degradation of pollutants.

[0021] A further improvement is that in step eight, by setting a certain electrolysis treatment time, it can be ensured that pollutants such as UDMH are effectively degraded and the expected treatment effect is achieved. Stopping the power supply means the end of the electrolysis treatment process, at which time it can be evaluated whether the treatment has reached the environmental protection standard or the predetermined treatment target. If the power supply is continued for electrolysis treatment, it may lead to a waste of energy and may even cause unnecessary chemical changes to the treated wastewater or produce new by-products.

[0022] Further improvements are: the power supply is a DC power supply or a pulse power supply, the positive and negative electrodes are in the form of a flat plate or a tube, the initial pH of the unsymmetrical dimethylhydrazine wastewater is 8-10, the background ion strength of the unsymmetrical dimethylhydrazine wastewater is 30-60mM, the molar ratio of the persulfate to the unsymmetrical dimethylhydrazine is 1-2.5, the persulfate is sodium persulfate or potassium persulfate, the flow rate of the circulating water pump is 100-200mL / min, the concentration of the unsymmetrical dimethylhydrazine wastewater is 100-300mg / L, and the electrochemical treatment time of the unsymmetrical dimethylhydrazine wastewater is 20-40min.

[0023] Compared with the prior art, the present invention has the following advantages: the method utilizes persulfate to coordinate the electrochemical oxidation of unsymmetrical dimethylhydrazine wastewater, and only electric energy and persulfate need to be input into the system. Electric energy can activate persulfate, and the activated sulfate radical can enhance the effect of electrochemical oxidation of unsymmetrical dimethylhydrazine, and no additional catalyst needs to be added. The method is flexible in operation, convenient to start and stop, has strong oxidation ability, short treatment cycle, and is convenient for large-scale amplification of the treatment system. Compared with the traditional hydrogen peroxide, the persulfate solid oxidant is stable in nature, convenient to store, and easy to transport. The redox potential of the sulfate radical is higher than that of the hydroxyl radical, the half-life is long, and the effect of the pH value of the environment is small. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0025] Figure 1 This is a schematic diagram of the structure of the device for degrading unsymmetrical dimethylhydrazine using a persulfate-coupled electrochemical oxidation process;

[0026] Figure 2 Schematic diagram of the electrode arrangement in the reactor. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms installation, connection, and connection should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0029] Example 1

[0030] See also Figure 1 , Figure 2 , the embodiment of the present invention discloses a method for electrochemically oxidizing unsymmetrical dimethylhydrazine wastewater, comprising the following steps;

[0031] Step 1: placing the unsymmetrical dimethylhydrazine wastewater to be treated in an intermediate water tank, in which an electrolytic cell is arranged, and introducing the unsymmetrical dimethylhydrazine-containing wastewater into the electrolytic cell;

[0032] Step 2: Add persulfate, the treatment device includes a power supply, a reactor, an intermediate water tank and a circulation pump, the reactor is composed of an anode, a cathode, a flow channel, a container, etc., start the water pump and the power supply, and press the unsymmetrical dimethylhydrazine wastewater into the reactor by the water pump;

[0033] Step 3: The unsymmetrical dimethylhydrazine wastewater is discharged and treated when passing through the flow channel between the graphene-coated titanium electrodes. The treated wastewater returns to the intermediate water tank and the water quality is tested. If it does not meet the standard, it is recycled for treatment. If it meets the standard, it is directly discharged.

[0034] Step 4: setting an anode and a cathode in the electrolytic cell, wherein the anode is an inert electrode material and the cathode is a reducing electrode material;

[0035] Step 5: Pass direct current to generate an electric field between the anode and the cathode;

[0036] Step 6: Under the action of the electric field, UDMH undergoes an oxidation reaction at the anode to generate non-toxic or low-toxic substances;

[0037] Step 7: A reduction reaction occurs at the cathode to generate hydrogen or other reducing substances;

[0038] Step 8: After a certain period of electrolytic treatment, the power is turned off and the treated wastewater is discharged for subsequent treatment or discharge.

[0039] In step one, UDMH is introduced into the electrolytic cell in the water tank for electrochemical reaction. During this process, an electric field is formed between the anode and cathode in the electrolytic cell, causing the UDMH molecules to undergo oxidation reaction at the anode and be converted into non-toxic or low-toxic substances. At the same time, a reduction reaction occurs at the cathode, which may generate hydrogen or other reducing substances. This series of electrochemical reactions helps to remove UDMH from wastewater and achieve the purpose of purifying water quality.

[0040] In step 2, persulfate, as a strong oxidant, can be activated in the electrochemical reaction to generate sulfate free radicals, which is a highly reactive species that can effectively oxidize organic pollutants such as unsymmetrical dimethyl hydrazine. Starting the water pump can provide the necessary power to transport the unsymmetrical dimethyl hydrazine wastewater from the electrolytic cell to the electrochemical reactor, ensuring that the wastewater is in full contact with the electrode surface, thereby improving the reaction efficiency. After starting the power supply, an electric field will be generated between the anode and cathode in the electrolytic cell, prompting the persulfate to decompose at the anode to generate sulfate free radicals. At the same time, hydrogen generation or other reduction reactions may occur at the cathode.

[0041] In step three, the discharge treatment between the graphene-coated titanium electrodes can effectively degrade pollutants such as unsymmetrical dimethylhydrazine, ensuring that harmful substances in the wastewater are fully removed. The treated wastewater returns to the intermediate water tank and is tested for water quality. If the test results show that the water quality does not meet the standards, the wastewater will be sent back to the reactor for recycling treatment until the water quality meets the standards. This can ensure the thoroughness and reliability of wastewater treatment. Through strict water quality testing and recycling treatment, it can be ensured that the final discharged wastewater meets environmental protection standards, reduces pollution to the environment, and protects the ecological environment.

[0042] In step four, the anode is an inert electrode material; the inert electrode is platinum or their oxides; because these materials have good chemical stability and conductivity, they can withstand strong oxidizing conditions without being corroded, and the cathode is a reducing electrode material; the reducing electrode materials are graphite and titanium. Graphite and titanium can be used as anode materials and can also be used as reducing electrode materials. They show good performance in the chlor-alkali industry and wastewater treatment. These materials can effectively promote the occurrence of reduction reactions. The anode and cathode are set so that when direct current passes through the electrolytic cell, an oxidation reaction will occur on the anode, and a reduction reaction will occur on the cathode. For the treatment of unsymmetrical dimethylhydrazine wastewater, the oxidation reaction on the anode can oxidize the unsymmetrical dimethylhydrazine into non-toxic or low-toxic products, while the reduction reaction on the cathode may involve the generation of hydrogen or other beneficial side reactions. In this way, the electrochemical method can effectively remove unsymmetrical dimethylhydrazine in the wastewater and achieve wastewater purification.

[0043] In step five, in order to drive the electrochemical reaction and thus realize the oxidative degradation of UDMH, an oxidation reaction will occur at the anode under the action of the electric field to convert the UDMH molecules, while a reduction reaction will occur at the cathode, which may generate hydrogen or other reducing substances. This process helps to remove UDMH from wastewater and achieve the purpose of purifying water quality.

[0044] In step six, this conversion process helps remove harmful components in the wastewater, reduce environmental pollution, and ensure that the treated water is safe and meets emission standards. Through electrochemical reactions, the UDMH molecules are oxidized, destroying their harmful structures, thereby achieving wastewater purification.

[0045] In step seven, at the cathode, water molecules are reduced to generate hydrogen. Hydrogen is a clean energy source that can be collected and used, for example, in fuel cells or as an industrial raw material. In addition, the generation of hydrogen also helps to improve the efficiency of the electrochemical reaction because it can promote ion migration in the solution, thereby enhancing the overall reaction kinetics. In addition to hydrogen, other reducing substances may be generated at the cathode, such as sulfites, sulfides, etc. These reducing substances can react with oxidants or intermediates in the solution to further promote the degradation of pollutants. For example, they can react with oxidized unsymmetrical dimethyl hydrazine to help it further convert into non-toxic or low-toxic substances. In the electrochemical reaction, the reduction reaction at the cathode helps to balance the positive charge generated by the oxidation reaction at the anode and maintain the charge balance in the electrolytic cell, which is crucial to maintaining the stability and sustainability of the electrochemical reaction. The reduction reaction at the cathode works synergistically with the oxidation reaction at the anode to improve the efficiency of the entire electrochemical treatment system. By optimizing the cathode reaction, the entire treatment process can be better controlled and regulated, thereby improving the removal rate and treatment speed of unsymmetrical dimethyl hydrazine.

[0046] In step eight, by setting a certain electrolysis treatment time, it can be ensured that pollutants such as unsymmetrical dimethyl hydrazine are effectively degraded and the expected treatment effect is achieved. Stopping the power supply means the end of the electrolysis treatment process. At this time, it can be evaluated whether the treatment has reached the environmental protection standards or the predetermined treatment goals. If the power supply continues to be turned on for electrolysis treatment, it may lead to a waste of energy and may even cause unnecessary chemical changes to the treated wastewater or produce new by-products. Stopping the power supply in time can avoid excessive treatment. The treated wastewater needs further testing to determine whether it meets the emission standards. If the test results show that the wastewater still does not meet the standards, further treatment is required; if it meets the standards, it can be directly discharged or used in the next step. This process ensures the compliance and safety of wastewater treatment. Stopping the power supply in time can save energy and reduce treatment costs. This is particularly important for industrial applications because it directly affects the economy and sustainability of the treatment process.

[0047] The power supply is a DC power supply or a pulse power supply, the positive and negative electrodes are in the form of a flat plate or a tube, the initial pH of the UDMH wastewater is 8-10, the background ion strength of the UDMH wastewater is 30-60 mM, the molar ratio of persulfate to UDMH is 1-2.5, the persulfate is sodium persulfate or potassium persulfate, the flow rate of the circulating water pump is 100-200 mL / min, the concentration of the UDMH wastewater is 100-300 mg / L, and the electrochemical treatment time of the UDMH wastewater is 20-40 min.

[0048] Example 2

[0049] Prepare 500mL-100mg / L UDMH solution in a 1L beaker, adjust the initial pH with NaOH and H2SO4, add NaCl to adjust the initial background ion strength, and transfer the solution to the intermediate water tank. Add sodium persulfate to the intermediate water tank according to the molar ratio of persulfate to UDMH, start the peristaltic pump and power supply, and maintain the current density at 50, 80, and 100 mA / cm 2 , samples were taken at 0, 5, 10, 15, 20, 25, 35, and 45 min of reaction, the power was turned off before sampling, and the reaction was terminated with 0.1 mL of anhydrous ethanol after sampling. The concentration of UDMH in the solution was obtained by the sodium aminoferrocyanide spectrophotometry method according to GB / T14376-1993.

[0050] As shown in Table 1, when the device is not powered on, only relying on the direct oxidation of persulfate, 73.8% of UDMH can be degraded after 45 minutes. As the current density increases (0→80 mA / cm2), the time for UDMH degradation to achieve basic stability becomes shorter and shorter, and the degradation rate of UDMH after stabilization also increases. However, when the current density exceeds 80 mA / cm 2 After that, the degradation rate of UDMH decreased instead of increasing with the increase of current. 2 When the reaction time was 45 minutes, the removal rate of UDMH was 83.5%.

[0051] Table 1 Variation trend of UDMH removal rate over time when current density changes

[0052]

[0053] The effect of initial pH on the degradation of unsymmetrical dimethylhydrazine by persulfate-coupled electrochemical oxidation process was detected.

[0054] Prepare 500mL of 100mg / L UDMH solution in a 1L beaker, adjust the initial pH to 4, 6, 8, and 10 with NaOH and H2SO4, add NaCl to adjust the initial background ion strength, and transfer the solution to the intermediate water tank. Add sodium persulfate to the intermediate water tank according to the molar ratio of persulfate to UDMH, start the peristaltic pump and power supply, and maintain the current density at 80mA / cm 2 Sampling was performed at 0, 5, 10, 15, 20, 25, 35, and 45 min of reaction. The power was turned off before sampling. After sampling, the reaction was terminated with 0.1 mL of anhydrous ethanol. The concentration of UDMH in the solution was obtained by the sodium aminoferrocyanide spectrophotometry method according to GB / T14376-1993.

[0055] As shown in Table 2, within the initial pH range of 4-8, as the initial pH increases, the time for the degradation of unsymmetrical dimethylhydrazine to achieve basic stability gradually shortens, and the degradation rate of unsymmetrical dimethylhydrazine gradually increases after stabilization; after the initial pH exceeds 8, the alkalinity of the solution continues to increase. Although the time for the degradation of unsymmetrical dimethylhydrazine to achieve basic stability remains unchanged (15 minutes), the final removal rate of unsymmetrical dimethylhydrazine is slightly reduced. The weakly alkaline environment with a better degradation rate is close to the natural pH of unsymmetrical dimethylhydrazine wastewater, so the amount of medicine required for acid-base adjustment in this method is small.

[0056] Table 2 Changes of UDMH removal rate over time when initial pH changes

[0057]

[0058] The effect of NaCl concentration on the degradation of unsymmetrical dimethylhydrazine by persulfate-coupled electrochemical oxidation process was detected.

[0059] Prepare 500mL of 100mg / L UDMH solution in a 1L beaker, adjust the initial pH to 8 with NaOH and H2SO4, add NaCl to adjust the initial background ion strength to 0-60mM, and transfer the solution to the intermediate water tank. Add sodium persulfate to the intermediate water tank according to the molar ratio of persulfate to UDMH, start the peristaltic pump and power supply, and maintain the current density at 80mA / cm 2 , samples were taken at 0, 5, 10, 15, 20, 25, 35, and 45 min of reaction, the power was turned off before sampling, and the reaction was terminated with 0.1 mL of anhydrous ethanol after sampling. The concentration of UDMH in the solution was obtained by the sodium aminoferrocyanide spectrophotometry method according to GB / T14376-1993.

[0060] As shown in Table 3, when the NaCl background ion strength is 0mM, the 10-minute degradation curve is basically stable, and the removal rate of UDMH in 45 minutes is 38.5%. Increasing the NaCl background ion strength to 30mM, the removal rate of UDMH in 45 minutes is increased to 83.5%. Further increasing the NaCl background ion strength to 60mM, the removal rate of UDMH in 45 minutes is 92.9%. - Addition of ·OH and ·SO4 - The reaction produces HOCl and OCl - , ·Cl, ·Cl 2- These chlorine-containing active free radicals can attack electron-rich organic matter, thereby improving the removal rate of unsymmetrical dimethylhydrazine.

[0061] Table 3 Changes of UDMH removal rate over time when NaCl concentration changes

[0062]

[0063] Effect of sodium persulfate molar ratio on degradation of unsymmetrical dimethylhydrazine by persulfate-coupled electrochemical oxidation process

[0064] Prepare 500mL of 100mg / L UDMH solution in a 1L beaker, adjust the initial pH to 8 with NaOH and H2SO4, add NaCl to adjust the initial background ion strength to 30mM, transfer the solution to the intermediate water tank, add sodium persulfate to the intermediate water tank according to the molar ratio of persulfate to UDMH of 0-2.5, start the peristaltic pump and power supply, and maintain the current density at 80mA / cm2. Take samples at 0, 5, 10, 15, 20, 25, 35, and 45min of reaction, turn off the power supply before sampling, and terminate the reaction with 0.1mL of anhydrous ethanol after sampling. Obtain the concentration of UDMH in the solution by the sodium aminoferrocyanide spectrophotometry method of GB / T14376-1993.

[0065] As shown in Table 4, when Na2S2O8 is not added, 49.9% of UDMH is removed after 45 minutes of reaction. When Na2S2O8 / UDMH (mol / mol) = 0.5, 62.6% of UDMH can be removed within 10 minutes. When the reaction time is increased to 15 minutes, the removal rate of UDMH reaches 65.3%, and the curve of removal rate changing with time tends to be flat. Continue to increase Na2S2O8 / UDMH (mol / mol) to 1.0, 72.4% of UDMH can be degraded within 10 minutes. When Na2S2O8 / UDMH (mol / mol) = 2.0, the degradation rate of UDMH is increased to 93.8% compared with Na2S2O8 / UDMH (mol / mol) = 1.5. Continuing to increase the Na2S2O8 / UDMH (mol / mol), the reaction rate continued to increase, but the addition of persulfate exceeding the reaction requirement led to self-quenching.

[0066] Table 4 Changes in removal rate of UDMH over time when the molar ratio of persulfate to UDMH is changed

[0067]

[0068] Effect of circulation flow rate on degradation of unsymmetrical dimethylhydrazine by persulfate-coupled electrochemical oxidation process.

[0069] Prepare 500mL of 100mg / L UDMH solution in a 1L beaker, adjust the initial pH to 8 with NaOH and H2SO4, add NaCl to adjust the initial background ion strength to 30mM, and transfer the solution to the intermediate water tank. Add sodium persulfate to the intermediate water tank at a molar ratio of persulfate to UDMH of 2.0, start the peristaltic pump and power supply, adjust the circulation flow rate to 100-200mL / min, and maintain the current density at 80mA / cm 2Samples were taken at 0, 5, 10, 15, 20, 25, 35, and 45 minutes of reaction. The power was turned off before sampling. After sampling, the reaction was terminated with 0.1 mL of anhydrous ethanol. The concentration of UDMH in the solution was obtained by the sodium aminoferrocyanide spectrophotometry method according to GB / T14376-1993.

[0070] As shown in Table 5, with the increase of circulation flow rate, the removal rate of unsymmetrical dimethyl hydrazine shows a trend of first increasing and then decreasing. The optimal value appears when the circulation flow rate is 150 mL / min. At low circulation flow rate, the increase in flow rate promotes the removal of unsymmetrical dimethyl hydrazine, but excessive flow rate converts the flow state between the inner and outer pipe walls into a mixed flow of bubbles and water, which is not conducive to the production of active substances and produces an inhibitory effect.

[0071] Table 5 Changes of UDMH removal rate over time when the circulation flow rate changes

[0072]

[0073] Effect of UDMH concentration on degradation of UDMH by persulfate-coupled electrochemical oxidation process.

[0074] Prepare 500mL of 100-500mg / L UDMH solution in a 1L beaker, adjust the initial pH to 8 with NaOH and H2SO4, add NaCl to adjust the initial background ion strength to 30mM, and transfer the solution to the intermediate water tank. Add sodium persulfate to the intermediate water tank at a molar ratio of persulfate to UDMH of 2.0, start the peristaltic pump and power supply, adjust the circulation flow rate to 150mL / min, and maintain the current density at 80mA / cm2. Take samples at 0, 5, 10, 15, 20, 25, 35, and 45min of reaction, turn off the power supply before sampling, and terminate the reaction with 0.1mL of anhydrous ethanol after sampling. Obtain the concentration of UDMH in the solution by the sodium aminoferrocyanide spectrophotometry method of GB / T14376-1993.

[0075] As shown in Table 6, when the initial concentration of UDMH was in the range of 100-500 mg / L, as the initial concentration of UDMH increased, although the degradation rate and final degradation rate of UDMH decreased slightly, the removal rate of UDMH was basically the same, indicating that the plasma activated persulfate process can adapt to the change of the initial UDMH concentration and has good stability.

[0076] Table 6 Changes in removal rate of UDMH over time when the initial concentration of UDMH changes

[0077]

[0078] When the method of electrochemical oxidation of unsymmetrical dimethylhydrazine wastewater is used, an electrolytic cell is prepared, and an anode and a cathode are arranged therein, the anode is an inert electrode material; the inert electrode is platinum or its oxides; because these materials have good chemical stability and conductivity, they can withstand strong oxidizing conditions without being corroded, and the cathode is a reducing electrode material; the reducing electrode materials are graphite and titanium, which can be used as anode materials and can also be used as reducing electrode materials. Both graphite and titanium can be used as anodes or cathodes, depending on their roles in electrochemical reactions and the electrochemical environments in which they are located. They show good performance in the chlor-alkali industry and wastewater treatment. Wastewater containing unsymmetrical dimethylhydrazine is introduced into the electrolytic cell, an oxidant is added, and persulfate is added to the electrolytic cell as an oxidant to enhance the oxidation effect. The water pump is started to press the wastewater into the flow channel in the reactor, and a straight line is connected. A current source is provided to generate an electric field between the anode and the cathode. Under the action of the electric field, UDMH undergoes an oxidation reaction at the anode to generate non-toxic or low-toxic substances, and undergoes a reduction reaction at the cathode to generate hydrogen or other reducing substances. After a certain period of electrolytic treatment, the power is stopped, the treated wastewater is taken out, and the water quality is tested. If the test results show that the water quality does not meet the standards, the wastewater is returned to the electrolytic cell for circulation treatment. If the water quality meets the standards, the treated wastewater can be discharged or used for other purposes. The electrolytic cell, electrodes, water pumps and other equipment are regularly inspected and maintained to ensure their normal operation. Key parameters in the treatment process, such as current, voltage, treatment time, etc., are recorded to monitor the treatment effect and ensure that the treated wastewater meets environmental protection standards. Through the above steps, the electrochemical method can be effectively used to treat wastewater containing UDMH to achieve wastewater purification and pollutant removal.

[0079] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for electrochemically oxidizing unsymmetrical dimethylhydrazine wastewater, characterized in that: The steps include: Step 1: placing the unsymmetrical dimethylhydrazine wastewater to be treated in an intermediate water tank, in which an electrolytic cell is arranged, and introducing the unsymmetrical dimethylhydrazine-containing wastewater into the electrolytic cell; Step 2: Add persulfate into the electrolytic cell; the treatment device includes a power supply, a reactor, an intermediate water tank and a circulation pump; the reactor is composed of an anode, a cathode, a flow channel and a container, the water pump and the power supply are started, and the unsymmetrical dimethylhydrazine wastewater is pressed into the reactor by the water pump; Step 3: The unsymmetrical dimethylhydrazine wastewater is discharged and treated when passing through the flow channel between the graphene-coated titanium electrodes. The treated wastewater returns to the intermediate water tank and the water quality is tested. If it does not meet the standard, it is recycled for treatment. If it meets the standard, it is directly discharged. Step 4: setting an anode and a cathode in the electrolytic cell, wherein the anode is an inert electrode material and the cathode is a reducing electrode material; Step 5: Pass direct current to generate an electric field between the anode and the cathode; Step 6: Under the action of the electric field, UDMH undergoes an oxidation reaction at the anode to generate non-toxic or low-toxic substances; Step 7: A reduction reaction occurs at the cathode to generate hydrogen or other reducing substances; Step 8: After a certain period of electrolysis treatment, stop the power supply and take out the treated wastewater for subsequent treatment or discharge.

2. A method for electrochemically oxidizing unsymmetrical dimethylhydrazine wastewater according to claim 1, characterized in that: In step 4, the anode is an inert electrode material; the inert electrode is platinum or its oxides, the platinum oxide is platinum dioxide, which is a black solid with high conductivity and chemical stability; the cathode is a reducing electrode material; the reducing electrode material is graphite and titanium.

3. A method for electrochemically oxidizing unsymmetrical dimethylhydrazine wastewater according to claim 1, characterized in that: In step five, an electrochemical reaction is driven to achieve oxidative degradation of UDMH; under the action of the electric field, an oxidation reaction occurs on the anode to convert the UDMH molecules.

4. The method for electrochemically oxidizing unsymmetrical dimethylhydrazine wastewater according to claim 1, characterized in that: The power source is a direct current power source or a pulse power source, and the positive and negative electrodes are in the form of a flat plate or a tube.

5. The method for electrochemically oxidizing unsymmetrical dimethylhydrazine wastewater according to claim 1, characterized in that: The initial pH of the unsymmetrical dimethylhydrazine wastewater is 8-10, and the background ion strength of the unsymmetrical dimethylhydrazine wastewater is 30-60 mM.

6. The method for electrochemically oxidizing unsymmetrical dimethylhydrazine wastewater according to claim 1, characterized in that: The molar ratio of the persulfate to unsymmetrical dimethylhydrazine is 1-2.5, and the persulfate is sodium persulfate or potassium persulfate.

7. The method for electrochemically oxidizing unsymmetrical dimethylhydrazine wastewater according to claim 1, characterized in that: The flow rate of the circulating water pump is 100-200 mL / min, the concentration of the unsymmetrical dimethylhydrazine wastewater is 100-300 mg / L, and the electrochemical treatment time of the unsymmetrical dimethylhydrazine wastewater is 20-40 min.

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