Electrolysis-fenton oxidation-electrochemical iron reduction system for degrading dimethyl sulfoxide in recycled backwater

Abstract

This invention discloses an electrolysis-Fenton oxidation-electrochemical iron reduction system for degrading and recovering dimethyl sulfoxide (DMSO) in recycled water. The system includes an electrolytic cell, a Fenton oxidation reaction tank, and an electrochemical iron reduction reaction tank. Recycled water from the DMSO distillation recovery system passes through the electrolytic cell. The effluent from the cathode region is directly returned to the storage tank before the DMSO distillation recovery system, while the effluent from the anode region enters the Fenton oxidation reaction tank for the Fenton oxidation reaction. The effluent from the Fenton oxidation reaction tank then enters the electrochemical iron reduction tank, where, through an electrochemical reaction, Fe... 3+ Reduce back to Fe 2+ The effluent from the cathode area is returned to the Fenton oxidation reactor, while the effluent from the anode area is discharged directly after pH adjustment. This invention reduces the amount of acid and alkali used in the dimethyl sulfoxide recovery process. Electrochemical iron reduction eliminates the need for additional packing material, and the entire process does not produce iron sludge or secondary pollution. The treated wastewater can be discharged directly.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of wastewater treatment and relates to an electrolysis-Fenton oxidation-electrochemical iron reduction system for degrading dimethyl sulfoxide in recovered water. BACKGROUND

[0002] Polyacrylonitrile-based carbon fiber is produced by using acrylonitrile monomer as the main raw material and dimethyl sulfoxide (DMSO) as the main solvent through polymerization, spinning, carbonization and other sections to obtain finished carbon fiber. Therefore, dimethyl sulfoxide waste liquid is generated in the production process. Dimethyl sulfoxide has certain toxicity and high permeability, and long-term storage and exposure can easily decompose into toxic or odor substances such as mercaptans and sulfides, causing serious environmental pollution. Recycling of dimethyl sulfoxide waste liquid can effectively reduce the production cost of carbon fiber and reduce environmental pollution. Dimethyl sulfoxide can be effectively recycled and reused by distillation and other methods, but a certain concentration of dimethyl sulfoxide still remains in the discharged wastewater.

[0003] At present, the main treatment methods for organic wastewater are incineration, chlorination, biological treatment and advanced catalytic oxidation, etc. The basis of advanced oxidation technology is to use electricity, light irradiation and catalysts in combination with oxidizing agents to produce highly active free radicals (usually hydroxyl radicals, ·OH) in the reaction, and then through addition, substitution, electron transfer and bond breaking between free radicals and pollutants, the large molecular and difficult-to-degrade organic matter in water is oxidized and degraded into low-toxic or non-toxic small molecular substances, or even directly degraded into CO2 and H2O, close to complete mineralization. Due to the different types of oxidizing agents and catalysts selected in the oxidation process, advanced oxidation technology can be divided into Fenton oxidation method, photochemical (catalytic) oxidation method, ozone oxidation method, wet oxidation method, electrochemical oxidation method and supercritical water catalytic oxidation method, etc. Among them, Fenton oxidation technology can produce ·OH with extremely strong oxidation ability, and the reaction conditions are mild, which is the most promising environmentally friendly water treatment technology at present.

[0004] Fenton reaction is an acid reaction in which Fe 2+ is used as a catalyst to catalyze H2O2 to generate ·OH. The chain reaction between ·OH and pollutants can degrade organic matter and finally generate CO2 and H2O. Fenton reaction has low initial cost, small occupation space and simple and safe operation, but in actual application, it still has the following shortcomings: (1) the reaction pH value range required by the process is relatively narrow, generally 3-4, and the Fenton inlet water needs to be adjusted to neutral by using acid and the outlet water also needs to be adjusted to neutral by using liquid alkali, which will consume a large amount of acid and alkali reagents, and the storage of acid and alkali also has safety hazards; (2) ferrous catalyst needs to be added in the reaction process, and a part of Fe 2+ will be oxidized to Fe 3+, resulting in a decrease in catalytic effect, and iron ions cannot be recycled, resulting in a large amount of Fe 3+ After adjusting the alkali, a large amount of iron sludge is produced, which is a hazardous waste. Patent CN113461235 A discloses an electrolysis-electro-Fenton flocculation composite system without adding acid, alkali and iron salt, which produces less sludge. The electrolysis method is used for pretreatment of wastewater, and the electro-Fenton reaction is carried out after the pH is adjusted. No acid, alkali and iron salt need to be added, which can reduce the cost, but iron sludge is still produced, causing secondary pollution. SUMMARY

[0005] The purpose of the present application is to provide an electrolysis-Fenton oxidation-electrochemical iron reduction system for degrading dimethyl sulfoxide in recycled water, which does not need to adjust the acid and alkali, can effectively reduce the amount of reagent used, reduce the production of iron sludge, and improve the utilization rate of Fe 2+ .

[0006] The technical solution for achieving the purpose of the present application is as follows:

[0007] The electrolysis-Fenton oxidation-electrochemical iron reduction system for degrading dimethyl sulfoxide in recycled water comprises an electrolytic tank, a Fenton oxidation reaction tank and an electrochemical iron reduction reaction tank. The electrolytic tank is provided with cathode and anode chambers separated by a diaphragm. The Fenton oxidation reaction tank is filled with filler. The electrochemical iron reduction reaction tank is provided with cathode and anode chambers separated by a diaphragm.

[0008] Further, the cathode material of the electrolytic tank is graphite, platinum-ruthenium-iridium-based noble metal electrode or molybdenum-nickel-based transition metal electrode, and the anode material is graphite or titanium mesh, and the diaphragm is Zirfon diaphragm.

[0009] Further, the filler is the filler commonly used in Fenton reaction, such as iron shavings, iron-carbon or Fe-Cu-C composite material.

[0010] Further, the cathode material of the electrochemical iron reduction tank is graphite, platinum-ruthenium-iridium-based noble metal electrode or molybdenum-nickel-based transition metal electrode, and the anode material is graphite or titanium mesh, and the diaphragm is anion exchange membrane.

[0011] The present application also provides a method for degrading dimethyl sulfoxide in recycled water using the above-mentioned electrolysis-Fenton oxidation-electrochemical iron reduction system, comprising the following steps:

[0012] Step 1: The dimethyl sulfoxide distillation recovery system backwater is fed into the electrolytic tank for electrolysis. The cathode chamber effluent is alkaline, and is directly returned to the storage tank before the dimethyl sulfoxide distillation recovery system. Part of the dimethyl sulfoxide in the anode chamber is oxidized, and the anode chamber effluent is acidic. The effluent is fed into the Fenton oxidation reaction tank.

[0013] Step 2, the water from the anode chamber of the electrolytic cell reacts with the filler in the Fenton oxidation reaction tank to continuously generate Fe 2+ , hydrogen peroxide is added, and Fenton oxidation reaction is carried out;

[0014] Step 3, the water from the Fenton oxidation reaction tank enters the electrochemical iron reduction reaction tank, and Fe 3+ is reduced to Fe 2+ in the cathode chamber, the water from the cathode chamber is returned to the Fenton oxidation reaction tank, and Fe 2+ in the water from the cathode chamber continues to catalyze the reaction of H2O2 to generate ·OH, degrades dimethyl sulfoxide, and the water from the anode chamber is adjusted to pH = 7-8 and directly discharged.

[0015] Further, in step 1, the concentration of dimethyl sulfoxide in the water returned by the dimethyl sulfoxide rectification recovery system is 100-2000 mg / L.

[0016] Further, in step 1, the pH of the water from the cathode chamber is 11-12, and the pH of the water from the anode chamber is 3-4.

[0017] Further, in step 1, the current density of the electrolytic cell is 100 mA / cm 2 -1000 mA / cm 2 .

[0018] Further, in step 2, the mass of the filler is 10%-80% of the volume of the water.

[0019] Further, in step 2, the mass fraction of H2O2 in the hydrogen peroxide is 27%, and the amount of hydrogen peroxide is 1‰-6.5‰ of the volume of the wastewater.

[0020] Further, in step 2, the Fenton oxidation reaction time is 0.5-2h.

[0021] Further, in step 3, the power voltage of the electrochemical iron reduction reaction tank is 0.5-3V, and the power time is 0.5-2h.

[0022] Compared with the prior art, the present application has the following advantages:

[0023] (1) Since dimethyl sulfoxide is more stable in alkaline, the water entering the dimethyl sulfoxide rectification recovery system needs to be alkaline, so the conventional method needs to use liquid alkali to adjust the pH of the water to alkaline. In the present application, the water returned by the dimethyl sulfoxide rectification recovery system is first introduced into the electrolytic cell, and the pH of the cathode chamber wastewater is increased during the electrolysis process, so the cathode chamber wastewater is alkaline, and no liquid alkali is needed to adjust the pH value of the water entering the dimethyl sulfoxide rectification recovery system, which can be directly returned to the tank before the dimethyl sulfoxide rectification recovery system, thereby reducing the cost;

[0024] (2) The application sets an electrochemical iron reduction reaction tank after the Fenton oxidation reaction tank, uses electrochemistry to reduce Fe 3+ to Fe 2+ , and returns the solution in the cathode area to the Fenton oxidation reaction tank, without adding fillers again;

[0025] (3) The concentration of dimethyl sulfoxide in the wastewater in the anode area of the electrochemical iron reduction reaction tank is obviously reduced, the removal rate of dimethyl sulfoxide reaches more than 97%, the pH is adjusted to 7-8, and the wastewater can be directly discharged, the whole process does not produce iron sludge, does not need to set a sedimentation tank, and does not cause secondary pollution. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a schematic diagram and process flow chart of an electrolysis-Fenton oxidation-electrochemical iron reduction system for degrading and recycling dimethyl sulfoxide in wastewater. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical scheme and advantages of the application clearer, the application is further described in detail below with examples. It should be understood that the specific examples described herein are only used to explain the application, and are not used to limit the application.

[0028] In the following examples, the diaphragm used in the electrolytic tank is Zirfon high-performance ion exchange membrane, which can be commercially purchased, with a density of 1±0.2 g / cm 3 , a thickness of 500±50 μm, a porosity of 60±5%, and composed of an open mesh polyphenylene sulfide fabric, which is uniformly coated with a mixture of polymer and zirconium oxide, with high temperature stability, high pressure resistance, excellent electrical conductivity and good chemical stability. The diaphragm used in the electrochemical iron reduction reaction tank is an anion exchange membrane, which can be commercially purchased, with a thickness of 25±2 μm, an ion exchange capacity of 2.50±0.05 mmol / g, an ion conductivity of 140±10 ms / cm@80℃, a suitable temperature of R.T.-95℃, a suitable pH range of 0-14, a tensile strength of 33±3 MPa@R.T., alkali resistance stability, no degradation of the main chain after soaking in 1M NaOH solution at 80℃ for 5000h, and cation degradation of less than 5%.

[0029] Example 1

[0030] The wastewater from the dimethyl sulfoxide rectification recovery system was detected by liquid phase, and the concentration of dimethyl sulfoxide was 610 mg / L. The wastewater first entered the electrolytic tank, the anode material of the electrolytic tank was graphite, the cathode material was titanium mesh coated with noble metal iridium, the diaphragm was Zirfon high-performance ion exchange membrane, and the current density was 500 mA / cm 2The influent flow rate is 100 mL / min, the pH of the cathode chamber effluent is 12, and the wastewater is recycled to the storage tank of the dimethyl sulfoxide distillation and recovery system. The pH of the anode chamber effluent is 3, and the wastewater enters the subsequent Fenton oxidation reaction tank with a volume of 5 L. Iron shavings are used as packing material, with a mass of 0.5 kg. 15 mL of H2O2 solution is added, and after reacting for 1 h, the effluent enters the cathode area of ​​the electrochemical iron reduction reaction tank. The anode material of the reaction tank is graphite, the cathode material is a titanium mesh coated with Ni-Mo alloy, and the diaphragm is an anion exchange membrane. The energizing voltage is 1 V, and the energizing time is 1 h. The solution in the cathode area is recycled to the Fenton oxidation reaction tank. The pH of the solution in the anode area is adjusted to 7-8. The dimethyl sulfoxide concentration is measured to be 18 mg / L by liquid chromatography, and the dimethyl sulfoxide removal rate is 97%. No additional packing material is needed, and it can operate continuously for a long time. No iron sludge is generated during the entire process.

[0031] Example 2

[0032] The reflux water from the dimethyl sulfoxide distillation and recovery system, analyzed by liquid chromatography, had a dimethyl sulfoxide concentration of 1351 mg / L. This wastewater first enters an electrolytic cell. The anode material of the electrolytic cell is a titanium mesh, the cathode material is an IrO2-C composite material, the diaphragm is a Zirfon high-performance ion exchange membrane, and the current density is 1000 mA / cm². 2 The influent flow rate is 100 mL / min. The pH of the effluent from the cathode chamber is 12. The wastewater is recycled to the storage tank before the distillation system. The pH of the effluent from the anode chamber is 3. The wastewater enters the subsequent Fenton oxidation reaction tank with a volume of 5 L. Iron-carbon filler is used, with a mass of 1.5 kg. 25 mL of H2O2 solution is added. After reacting for 2 hours, the effluent enters the cathode area of ​​the electrochemical iron reduction reaction tank. The anode material of the reaction tank is graphite, and the cathode material is a Ni-Mo2C-C coated composite material. The diaphragm is an anion exchange membrane. The energizing voltage is 3 V, and the energizing time is 2 hours. The solution in the cathode area is recycled to the Fenton oxidation reaction tank. The pH of the solution in the anode area is adjusted to 7-8. The concentration of dimethyl sulfoxide is measured to be 26 mg / L by liquid chromatography, and the dimethyl sulfoxide removal rate is 98%. No additional filler is needed. It can operate continuously for a long time, and no iron sludge is generated during the entire process.

[0033] Comparative Example 1

[0034] The backwater of dimethyl sulfoxide rectification recovery system was detected by liquid phase, and the dimethyl sulfoxide concentration was 580 mg / L. The wastewater only underwent two steps of electrolysis and Fenton oxidation, and the specific steps were the same as those in Example 1. The effluent after Fenton oxidation was directly adjusted to pH 7-8, and discharged after passing through a sedimentation tank. The dimethyl sulfoxide concentration of the effluent was 22 mg / L, and the dimethyl sulfoxide removal rate was 96.2%. After continuous operation for 7 days, the dimethyl sulfoxide removal rate decreased to 70%, and after continuous operation for 15 days, the dimethyl sulfoxide removal rate decreased to 23%. After adding 0.5 kg of filler again, the dimethyl sulfoxide removal rate returned to 97%, and there was a large amount of iron sludge in the sedimentation tank, which needed to be periodically pressed, dried and stored in a hazardous waste warehouse for outsourcing treatment.

Claims

1. Process for the degradation of dimethyl sulfoxide in reclaimed water using an electrolysis-Fenton oxidation-electrochemical iron reduction system, characterized in that, It comprises the following steps: Step 1, the water from the dimethyl sulfoxide rectification recovery system is introduced into the electrolytic cell for electrolysis, the water from the cathode chamber is alkaline and is directly returned to the tank before the dimethyl sulfoxide rectification recovery system, part of the dimethyl sulfoxide in the anode chamber is oxidized, the water from the anode chamber is acidic and is introduced into the Fenton oxidation reaction tank; Step 2, the water from the anode chamber of the electrolytic cell reacts with the filler in the Fenton oxidation reaction tank to continuously produce Fe 2+ , add hydrogen peroxide, and carry out Fenton oxidation reaction; Step 3, the effluent from the Fenton oxidation reaction tank enters the electrochemical iron reduction reaction tank. In the cathode chamber, Fe 3+ is reduced to Fe 2+ . The effluent from the cathode chamber flows back to the Fenton oxidation reaction tank. Fe 2+ in the effluent from the cathode chamber continues to catalyze the reaction of H2O2 to generate ·OH, and degrades dimethyl sulfoxide. The effluent from the anode chamber is directly discharged after being adjusted to pH = 7-8. The electrolysis-Fenton oxidation-electrochemical iron reduction system comprises an electrolytic cell, a Fenton oxidation reaction tank and an electrochemical iron reduction reaction tank; the electrolytic cell is provided with cathode and anode chambers which are separated by a diaphragm, the Fenton oxidation reaction tank is filled with fillers, and the electrochemical iron reduction reaction tank is provided with cathode and anode chambers which are separated by a diaphragm.

2. The method of claim 1, wherein, In the electrolytic cell, the cathode material is graphite, or the cathode is a platinum-ruthenium-iridium-based noble metal electrode or a molybdenum-nickel-based transition metal electrode, the anode material is graphite or titanium mesh, and the diaphragm is a Zirfon diaphragm.

3. The method of claim 1, wherein, The fillers are iron shavings, iron-carbon or Fe-Cu-C composite materials.

4. The method of claim 1, wherein, In the electrochemical iron reduction reaction tank, the cathode material is graphite, or the cathode is a platinum-ruthenium-iridium-based noble metal electrode or a molybdenum-nickel-based transition metal electrode, the anode material is graphite or titanium mesh, and the diaphragm is an anion exchange membrane.

5. The method of claim 1, wherein, In step 1, the concentration of dimethyl sulfoxide in the water from the dimethyl sulfoxide rectification recovery system is 100-2000 mg / L.

6. The method of claim 1, wherein, In step 1, the pH of the water from the cathode chamber is 11-12, and the pH of the water from the anode chamber is 3-4.

7. The method of claim 1, wherein, In step 1, the current density of the electrolytic cell was 100 mA / cm 2 - 1000 mA / cm 2 .

8. The method of claim 1, wherein, In step 2, the mass of the fillers is 10%-80% of the volume of the water, the mass fraction of H2O2 in the hydrogen peroxide is 27%, the dosage of the hydrogen peroxide is 1‰-6.5‰ of the volume of the wastewater, and the Fenton oxidation reaction time is 0.5-2 h.

9. The method of claim 1, wherein, In step 3, the voltage of the electrochemical iron reduction reaction tank is 0.5-3 V, and the power-on time is 0.5-2 h.

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