Process for treating waste water from the production of epichlorohydrin by direct oxidation

Abstract

The present application provides a process for treating waste water generated in the process of preparing epichlorohydrin by direct oxidation method, which comprises a pretreatment section, a main reaction section and a deep treatment section; the pretreatment section comprises, in sequence, an adjusting unit, a tubular microfiltration unit, a mild wet oxidation unit and a neutralization unit, the main reaction section comprises an electrodialysis unit, an anaerobic biochemical unit, a biological reinforcement unit, an ozone catalysis I unit, a concentration and salt production system and a methane storage unit; the deep treatment section comprises, in sequence, an aerobic biochemical unit, an ozone catalysis II unit and a BAF unit, and the anion exchange membrane of the electrodialysis unit is a modified anion exchange membrane. The present application solves the problem of high toxicity of chlorine-containing organic matter in waste water by coupling mild wet oxidation with electrodialysis, and realizes the separation of organic matter and salt in waste water, wherein the electrodialysis uses a modified anion exchange membrane, and the anti-pollution capacity is greatly increased. The present application realizes zero discharge of waste water, and has the advantages of low operation cost.

Description

Technical Field

[0001] This invention relates to a method for treating wastewater generated during the direct oxidation process of epichlorohydrin, belonging to the field of wastewater treatment technology. Background Technology

[0002] Epichlorohydrin is an important organic chemical raw material with wide applications in the synthesis of various products such as ion exchange resins, pesticides, adhesives, surfactants, and coatings. Currently, the main production methods for epichlorohydrin include direct oxidation, high-temperature chlorination of propylene, glycerol process, and propylene acetate process.

[0003] High-temperature chlorination of propylene is the main method for producing epichlorohydrin, with mature technology and flexible production process. However, it has serious drawbacks, such as numerous byproducts, high energy consumption, severe equipment corrosion, and the generation of large amounts of wastewater containing calcium chloride and organic chlorine compounds, which seriously harm the environment. As described in the claims of patent CN201510737523.9, the total salt content of the epichlorohydrin wastewater produced by the high-temperature chlorination process is as high as 0.6wt% to 5.0wt%, the calcium ion concentration is 2000 to 8000 mg / L, and the COD is 800 to 2500 mg / L. Zhang Yifei of Nanjing University also pointed out in his article "An Example of Epichlorohydrin Production Wastewater Treatment Engineering" that the wastewater generated by the high-temperature chlorination process of propylene is characterized by large volume, high temperature, high pH value, and high salinity, and contains a certain amount of chlorinated organic compounds. During wastewater treatment, the salt and chlorinated organic compounds have an inhibitory effect on the biological system, making treatment difficult.

[0004] Compared with the high-temperature chlorination of propylene, the propylene acetate process reduces material consumption, energy consumption, by-product quantity, and wastewater volume to varying degrees. However, the process is longer, and the problems of equipment corrosion and large amounts of difficult-to-treat wastewater discharge remain unresolved.

[0005] The wastewater generated from the glycerol process for epichlorohydrin production is relatively small, only about 1 / 6 that of the propylene high-temperature chlorination process. However, it has a high salt concentration (up to 12%), a COD of approximately 5000 mg / L, and significant color. As described in the claims of patent CN201310312785.1, the treated epichlorohydrin wastewater from the glycerol process, by weight, contains 9-12% calcium chloride, 0.3-1% calcium hydroxide, 0.25-0.35% glycerol, 0.005-0.01% chlorinated organic matter, a COD of 4800-5000 mg / L, and a pH of 12-13.

[0006] The direct oxidation method uses allyl chloride as a raw material and hydrogen peroxide as an oxidant to catalytically epoxidize and prepare epichlorohydrin. Due to its high atom utilization rate, low wastewater volume, and clean process, it has gradually become a focus of research. Generally, the production of 1 ton of epichlorohydrin generates 0.8–1 ton of wastewater. This wastewater has a very low salt concentration but a high COD (30,000–80,000 mg / L). The main organic matter consists of chlorinated organic compounds such as epichlorohydrin and dichloropropanol, with a pH less than 5. Due to the toxicity of these chlorinated organic compounds, direct biochemical treatment would impact the microbial flora, requiring pretreatment and dilution with large amounts of water. This increases treatment costs and wastewater volume, resulting in resource waste.

[0007] Patent CN201610152853.6 discloses a treatment process for epichlorohydrin production wastewater. Through wet oxidation, ultraviolet-hydrogen peroxide oxidation, and caustic soda preparation, the wastewater is discharged in compliance with standards and the salt in the wastewater is utilized as a resource. Wet oxidation is used as a pretreatment method. The reaction temperature is 150-280℃ and the reaction pressure is 0.5-8MPa. A catalyst is added. Therefore, the equipment materials are required to be high, the investment is large, and the operating cost is high.

[0008] Patent CN201910674505.0 discloses a method for the resource utilization of epichlorohydrin wastewater. It uses a light chlorohydrin removal tower, a hydrolysis reactor, and a dehydration tower for pretreatment to recover allyl chloride and 3-chloro-1,2-propanediol. The operation of the above towers requires heating, and the overall operating cost is considerable. Considering that the allyl chloride content in the wastewater is below 0.5wt%, it does not have obvious recovery value, and the COD of the effluent is still as high as 765mg / L, so further treatment is required.

[0009] Patent CN202110761505.X discloses a method for treating epichlorohydrin wastewater, which uses ozone catalytic oxidation as a pretreatment to catalytically oxidize and decompose epichlorohydrin wastewater into small-molecule, biodegradable organic matter. However, due to the high COD concentration of the wastewater, the operating cost per ton of water for this pretreatment method is very high, making it impractical. Summary of the Invention

[0010] To overcome the shortcomings of existing technologies, this invention provides a process for treating wastewater generated during the direct oxidation process for preparing epichlorohydrin. Using this method, organic matter and salts in the wastewater can be recycled, achieving zero emissions overall and lower operating costs.

[0011] To achieve the above technical objectives, the technical solution adopted by the present invention is as follows:

[0012] This invention provides a process for treating wastewater generated during the direct oxidation process for preparing epichlorohydrin, comprising a pretreatment section, a main reaction section, and a deep treatment section;

[0013] The pretreatment section includes, in sequence, an adjustment unit, a tubular microfiltration unit, a mild wet oxidation unit, and a neutralization unit. The effluent from the neutralization unit enters the electrodialysis unit of the main reaction section.

[0014] The main reaction section includes an electrodialysis unit, an anaerobic biochemical unit, a bio-enhancing unit, an ozone catalysis unit I, a salt concentration system, and a methane storage unit. The effluent from the electrodialysis unit is divided into a concentrate and a desalinated solution. The desalinated solution enters the anaerobic biochemical unit, where the methane gas generated is stored in a methane storage tank. The effluent from the anaerobic biochemical unit enters the aerobic biochemical unit of the advanced treatment section. The electrodialysis concentrate is sequentially processed through the bio-enhancing unit, the ozone catalysis unit I, and the salt concentration system to obtain sodium chloride.

[0015] The advanced treatment section includes, in sequence, an aerobic biochemical unit, an ozone catalytic II unit, and a BAF unit. The effluent from the BAF unit meets the reuse standards and is recycled. The electrodialysis unit is composed of anion and cation exchange membranes, wherein the anion exchange membrane is a modified anion exchange membrane and the cation exchange membrane is a general-purpose cation exchange membrane.

[0016] The modification methods for anion exchange membranes are as follows:

[0017] Step a: Using a commercial anion exchange membrane as the base membrane, rinse it with hydrochloric acid solution and sodium hydroxide solution respectively, and then rinse it with deionized water to remove impurities on the membrane surface, thus obtaining the pretreated base membrane;

[0018] Step b: Dissolve dopamine and β-cyclodextrin in Tris-HCl buffer, adjust the pH to 8-9 with hydrochloric acid, and stir to fully dissolve them to obtain dopamine Tris buffer solution;

[0019] Step c: Place the base membrane obtained in step a in a dopamine Tris buffer solution and add copper sulfate. Stir the reaction while maintaining air circulation. After the reaction is complete, a preliminarily modified anion exchange membrane is obtained.

[0020] Step d: Dissolve the polyanionic modifier and sodium chloride in Tris-HCl buffer, and adjust the pH to 8-9 with hydrochloric acid to obtain the electrodeposition mother solution;

[0021] Step e: Place the anion exchange membrane obtained in step c in the middle of the DC electrodeposition apparatus to form two compartments. Put the electrodeposition mother solution prepared in step d into the compartment on the cathode side, and put water into the compartment on the anode side to carry out the electrodeposition reaction and obtain the final modified anion exchange membrane.

[0022] Those skilled in the art should understand that the anion exchange membrane used before modification is a type of polymer membrane with selective permeability to anions in the prior art, and the substrate is a conventional polymer material for ion exchange membranes such as polyvinyl alcohol, polyethylene, polypropylene, polyvinyl chloride, and polystyrene.

[0023] Furthermore, the concentration of HCl in the hydrochloric acid solution in step a is 0.1–0.3 mol / L, and the concentration of sodium hydroxide in the sodium hydroxide solution is 0.1–0.3 mol / L.

[0024] Furthermore, the concentration of the Tris–HCl buffer solution described in steps b and d is 10–50 mmol / L.

[0025] Furthermore, in step b, the dopamine Tris buffer solution contains dopamine at a concentration of 0.1–2 g / L, preferably 0.5–1 g / L, and β-cyclodextrin at a concentration of 0.1–1.5 g / L, preferably 0.2–0.6 g / L.

[0026] Furthermore, the stirring time in step b is 1 to 10 hours.

[0027] Furthermore, in step c, the concentration of copper sulfate is 1–20 mmol / L, and the stirring reaction time is 1–20 h. The copper sulfate can induce the rapid polymerization of dopamine and utilize the adhesiveness of dopamine to form an electrolyte layer containing β-cyclodextrin and polydopamine on the surface of the anion exchange membrane. After the reaction, a preliminarily modified anion exchange membrane is obtained. This anion exchange membrane not only has a negative surface charge, but also has a significantly increased hydrophilicity.

[0028] Furthermore, the polyanionic modifier mentioned in step d is one or more of sodium poly4-styrene sulfonate, sodium p-styrene sulfonate, sodium polyethylene sulfonate, and sodium polypropylene sulfonate, preferably sodium poly4-styrene sulfonate.

[0029] Furthermore, in step d, the mass concentration of the polyanionic modifier in the electrodeposition mother liquor is 0.5–5 g / L, and the mass concentration of sodium chloride is 3–30 g / L.

[0030] Furthermore, the electrodeposition reaction time in step e is 0.2–2 h, and the current density is 1–50 mA / cm². 2 A polyanionic modifier is deposited a second time on the surface of the anion exchange membrane using an electrodeposition method, which sulfonates and modifies the membrane surface.

[0031] Furthermore, the modified anion exchange membrane is then stored in a sodium chloride solution with a mass concentration of 5–20 g / L.

[0032] Furthermore, the epichlorohydrin wastewater has a COD of 30,000–80,000 mg / L, a pH of less than 5, and a salt content of less than 4,000 mg / L.

[0033] Furthermore, the adjustment unit adds sodium hydroxide to adjust the pH value to 10-12.

[0034] Furthermore, the pore size of the tubular microfiltration unit is in the range of 0.1 to 1.0 micrometers, which can filter suspended solids, colloids, and hydroxide precipitates of heavy metals.

[0035] Furthermore, the mild wet oxidation unit employs a bubbling flow internal circulation reactor, with a reaction temperature of 50–100°C, a reaction pressure of 0.3 MPa–1 MPa, and a liquid hourly space velocity of 0.25–4 h⁻¹. -1 The gas-liquid volume ratio is 2:1 to 20:1. Those skilled in the art should understand that, under the above temperature and pressure conditions, the mild wet oxidation unit can effectively achieve the chemical reaction between epichlorohydrin and alkali, converting chlorinated organic matter into chlorine-free organic matter and sodium chloride, achieving an alkali-based decomposition effect. Under the above conditions, only the elimination reaction of chlorine occurs, and the oxidation reaction of carbon does not occur; therefore, the COD does not change significantly, but the salt content of the wastewater increases substantially.

[0036] Furthermore, hydrochloric acid is added to the neutralization unit to adjust the pH value to 6-9.

[0037] Furthermore, the electrodialysis unit has a treatment time of 0.1–2 hours and a current density of 1–80 mA / cm². 2 Those skilled in the art should understand that after epichlorohydrin wastewater is treated by a moderate wet oxidation unit, organic chlorine is converted into inorganic chlorine, significantly reducing the wastewater's biotoxicity. However, at the same time, the sodium chloride content increases significantly, which is also detrimental to biochemical reactions, especially anaerobic biochemical reactions. After pH adjustment, most organic matter in the effluent from the moderate wet oxidation unit is electrically neutral. However, to prevent a small amount of negatively charged organic matter from contaminating the anion exchange membrane of the electrodialysis unit, this invention modifies the surface of the anion exchange membrane. While maintaining a high chloride ion permeability, it effectively inhibits the migration of large negatively charged organic molecules, thereby significantly improving the antifouling ability of the anion exchange membrane and ultimately achieving the separation of organic matter and salts.

[0038] Furthermore, the dissolved oxygen in the anaerobic biochemical unit is controlled below 0.2 mg / L, the wastewater retention time is 6–120 h, the temperature is 25–35 °C, the bacterial strains are conventional anaerobic strains, and the process uses one of the following anaerobic processes: AFB, UASB, IC, EGSB, etc.

[0039] Furthermore, the biological strains in the biochemical enhancement unit are salt-tolerant strains, and the process uses one of the aerobic processes such as BAF, MBR, contact oxidation tank, and MBBR, with a residence time of 12 to 144 hours.

[0040] Furthermore, the aerobic biochemical unit uses conventional aerobic bacteria, and the process is selected from one of the aerobic processes such as BAF, MBR, contact oxidation tank, MBBR, or A / O, SBR, etc., which are mainly aerobic processes, with a residence time of 12 to 60 hours.

[0041] Furthermore, the ozone dosage in the ozone catalytic oxidation unit I and ozone catalytic oxidation unit II is 0.1 to 2 times the amount of oxidant required based on the COD value of the wastewater, the reaction time is 10 to 120 minutes, and the catalyst is a conventional solid supported metal catalyst.

[0042] Furthermore, the BAF unit uses conventional aerobic bacteria, with a residence time of 2–12 hours.

[0043] Furthermore, the salt concentration system described herein is a conventional membrane concentration, evaporation concentration and salt crystallization process, which does not involve salt separation and can produce sodium chloride with an initial purity greater than 98%.

[0044] Furthermore, the methane storage unit has a methane purity greater than 96%, and its methane can be used as fuel for a gas-fired boiler. The steam generated is used for steam tracing in the evaporation and crystallization unit and the mild wet oxidation unit of the salt concentration system, thereby maximizing resource utilization and reducing overall process operating costs.

[0045] Compared with the prior art, the present invention has the following advantages:

[0046] (1) This invention solves the problem of high toxicity of chlorinated organic matter in wastewater by coupling mild wet oxidation with electrodialysis, and achieves the separation of organic matter and salt in wastewater. The electrodialysis uses a modified anion exchange membrane, which greatly increases the anti-pollution ability.

[0047] (2) This invention achieves efficient resource utilization of organic matter in epichlorohydrin wastewater. Specifically, by controlling the reaction conditions, the mild wet oxidation unit only undergoes the chlorine elimination reaction and no carbon oxidation reaction occurs. Then, by adjusting the pH, most of the organic matter is kept electrically neutral, and the organic matter is stripped off through electrodialysis. The stripped organic matter is converted into methane through anaerobic reaction, thereby achieving resource utilization.

[0048] (3) This invention realizes the efficient resource utilization of salt in epichlorohydrin wastewater. Specifically, the conditioning and neutralization units use sodium hydroxide and hydrochloric acid to regulate the salt and ensure the purity of the subsequent sodium chloride product; the electrodialysis unit removes the salt; the bio-enhancing unit and ozone catalysis unit I refine the salt and finally obtain a high-purity sodium chloride product through concentration, evaporation and crystallization.

[0049] (4) This invention achieves zero wastewater discharge and has the advantage of low operating costs. Specifically, in addition to realizing the resource utilization of organic matter and salt, the effluent from the anaerobic biological treatment unit, after treatment by the aerobic biological treatment unit, the ozone catalytic II unit, and the BAF unit, can easily achieve the target of COD less than 60 mg / L and salt content less than 2000 mg / L, and can be completely reused without the aid of dual membranes (ultrafiltration and reverse osmosis). The wet oxidation unit of this invention has low energy consumption due to its low reaction temperature and pressure. In addition, the methane produced by anaerobic biological treatment can be used as fuel to enter the gas boiler to produce steam or generate electricity, which can effectively offset the steam consumption of the wet oxidation and salt evaporation crystallization system and the power consumption of electrical equipment, thereby keeping the overall operating cost of wastewater at a low level.

[0050] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0051] Figure 1 Flowchart of epichlorohydrin wastewater treatment in Example 1.

[0052] Figure 2 Schematic diagram of anion exchange membrane electrodeposition modification in Example 1. Detailed Implementation

[0053] The present invention will be further described in detail below with reference to specific embodiments. These embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0054] Example 1

[0055] The process flow diagram for treating wastewater generated during the direct oxidation process for epichlorohydrin is as follows: Figure 1 As shown, epichlorohydrin wastewater sequentially enters an equalization tank, a tubular microfiltration system, a mild wet oxidation system, and a neutralization tank. The effluent from the neutralization tank enters an electrodialysis system. The electrodialysis effluent is divided into a concentrate and a desalinated solution. The desalinated solution enters an anaerobic biological treatment system, where the methane gas produced is collected and stored in a methane storage tank. The anaerobic biological treatment effluent is then sequentially treated by an aerobic biological treatment system, an ozone catalytic II system, and a BAF system to meet reuse standards. The electrodialysis concentrate is sequentially treated by a biological enhancement system, an ozone catalytic I system, and a concentration and salt production system to obtain sodium chloride.

[0056] The process method of this invention is used to treat epichlorohydrin wastewater.

[0057] The wastewater generated during a direct oxidation process for preparing epichlorohydrin has the following characteristics: epichlorohydrin content is 1.5 wt%, dichloropropanol content is 1.0 wt%, glycerol content is 0.2 wt%, COD concentration is 41200 mg / L, sulfate concentration is 15 mg / L, chloride concentration is 1500 mg / L, a small amount of heavy metals are introduced from the catalyst loss during the direct oxidation process, with a concentration of 80 mg / L in the wastewater, total salt content is 2100 mg / L, pH is 1.5, and influent flow rate is 20 t / h.

[0058] The electrodialysis provided in this embodiment is a modified electrodialysis, wherein the anion exchange membrane is a modified anion exchange membrane with strong anti-fouling ability and high ion permeability, and the cation exchange membrane is a general-purpose cation exchange membrane (Hefei Capgemini Polymer Co., Ltd., China, model CJ-MC-3).

[0059] The modified anion exchange membrane described above was prepared by the following method:

[0060] Step a: Using a commercial anion exchange membrane (product of Asahi Glass Co., Ltd., Japan, SELEMION AMV) as the base membrane, rinse it with 0.2 mol / L hydrochloric acid solution and 0.2 mol / L sodium hydroxide solution respectively, and then rinse it with deionized water to remove impurities on the membrane surface, thus obtaining the pretreated base membrane;

[0061] Step b: Prepare a 20 mmol / L Tris–HCl buffer solution, adjust the pH to 8.5 with hydrochloric acid, add dopamine and β-cyclodextrin, stir for 4 h to fully dissolve them, and obtain a dopamine Tris buffer solution. The dopamine Tris buffer solution has a dopamine mass concentration of 0.5 g / L and a β-cyclodextrin mass concentration of 0.3 g / L.

[0062] Step c: Place the base membrane obtained in step a in dopamine Tris buffer solution and add 4 mmol / L copper sulfate. Stir the reaction for 7 h while keeping the air circulating during the reaction. After the reaction is completed, an anion exchange membrane with preliminary surface modification is obtained.

[0063] Step d: Dissolve the polyanionic modifier and sodium chloride in 20 mmol / L Tris–HCl buffer, adjust the pH to 8.5 with hydrochloric acid, the mass concentration of the polyanionic modifier is 1.5 g / L, the mass concentration of sodium chloride is 10 g / L, and the polyanionic modifier is sodium poly4-styrene sulfonate, to obtain the electrodeposition mother liquor.

[0064] Step e: Surface sulfonation and modification are performed using electrodeposition methods, such as... Figure 2As shown, the anion exchange membrane obtained in step c is placed in the middle of a DC electrodeposition apparatus to form two compartments. The electrodeposition mother solution prepared in step d is placed in the compartment on the cathode side, and water is placed in the compartment on the anode side. The electrodeposition time is 0.6 h, and the current density is 20 mA / cm². 2 The final modified anion exchange membrane was obtained.

[0065] Step f: Take out the modified anion exchange membrane obtained in step e and place it in a sodium chloride solution with a mass concentration of 10 g / L for later use.

[0066] The specific operating parameters for treating epichlorohydrin wastewater are as follows:

[0067] Wastewater first enters an equalization tank, where sodium hydroxide is added to adjust the pH to 10.5, resulting in a small amount of precipitation. After passing through a tubular microfiltration membrane with a pore size of 0.6 micrometers, the heavy metal concentration is reduced to below 5 mg / L. The effluent then enters a mild wet oxidation process. The mild wet oxidation reaction temperature is 80℃, the reaction pressure is 0.55 MPa, and the liquid hourly space velocity (LHSV) is 1 h⁻¹. -1 The gas-liquid volume ratio was 10:1. The effluent contained 0.03 wt% epichlorohydrin and 0.02 wt% dichloropropanol. The COD was 41,130 mg / L, showing no significant change. The sulfate concentration was 15 mg / L, the chloride concentration was 12,500 mg / L, and the salt content of the wastewater increased to 22,350 mg / L. In addition, the glycerol content increased to 2.4 wt%, indicating that most of the epichlorohydrin and dichloropropanol were converted into glycerol. Hydrochloric acid was added to the neutralization tank to adjust the pH to 8, and the salt content of the wastewater increased to 23,830 mg / L. The effluent then entered electrodialysis.

[0068] The electrodialysis treatment time was 1 hour, and the current density was 30 mA / cm². 2 After treatment, the COD concentration of the electrodialysis desalination solution was 66356 mg / L, the total salt content was 1787 mg / L, and the flow rate was 12 t / h. The COD concentration of the concentrate was 3290 mg / L, the total salt content was 56894 mg / L, and the flow rate was 8 t / h. The chloride ion selective permeability was 95.5%, and the organic matter rejection rate was 96.8%. The electrodialysis concentrate entered the bio-enhancing unit, which adopted a contact oxidation process and added salt-tolerant bacteria. The salt-tolerant bacteria GXNYJ-DL-1 disclosed in patent CN114686391A, with accession number CGMCC, was selected. No. 20350, with a residence time of 72 hours, produces effluent COD as low as 255 mg / L; ozone dosage for ozone catalysis I is 100 mg / L, reaction time is 40 minutes, effluent COD is 125 mg / L, and total salt content is 56355 mg / L; the effluent from ozone catalysis I enters the concentration and salt production system, which uses a multi-effect evaporator and salt crystallizer to finally obtain sodium chloride product with a purity of 99.2%, and the steam condensate is reused;

[0069] The electrodialysis desalination solution enters the anaerobic biological treatment process, with dissolved oxygen controlled below 0.15 mg / L, temperature at 30℃, and conventional anaerobic bacteria, including organic acidifying bacteria and methanogenic bacteria. The wastewater retention time is 72 h, and the effluent COD is reduced to 656 mg / L. The generated methane gas is stored in a methane storage tank with a purity of 97.4%. The methane can be used as fuel in the enterprise's gas-fired boiler to produce steam or generate electricity, effectively offsetting the steam consumption of the wet oxidation and salt evaporation crystallization systems and the power consumption of electrical equipment. The aerobic biological treatment adopts the MBBR process, adding conventional aerobic bacteria, with a retention time of 24 h, and the effluent COD is reduced to 145 mg / L. The ozone concentration of ozone catalysis II is 60 mg / L, the reaction time is 30 min, and the effluent COD is 71 mg / L. The BAF uses conventional aerobic bacteria, with a retention time of 4 h, and the effluent COD is 45 mg / L, with a total salt content of 1755 mg / L, meeting the reuse standards.

[0070] As demonstrated in this embodiment, the present invention can effectively treat epichlorohydrin wastewater. The moderate wet oxidation process solves the problem of high toxicity of chlorinated organic matter in the wastewater. The modified electrodialysis achieves the separation of organic matter and salts in the wastewater, ultimately realizing resource utilization. Specifically, the salts are converted into high-purity sodium chloride, and most of the organic matter is converted into methane, achieving zero wastewater discharge. Due to the lower reaction conditions of the moderate wet oxidation process and the heat and electricity compensation from methane resource utilization, the overall operating cost of the wastewater treatment remains at a low level.

[0071] Example 2

[0072] use Figure 1 The process shown is for treating epichlorohydrin wastewater.

[0073] The wastewater generated during a direct oxidation process for preparing epichlorohydrin has the following characteristics: epichlorohydrin content is 1.8 wt%, dichloropropanol content is 1.3 wt%, glycerol content is 0.3 wt%, COD concentration is 56500 mg / L, sulfate concentration is 30 mg / L, chloride concentration is 2100 mg / L, a small amount of heavy metals (100 mg / L) are introduced from the catalyst loss during the direct oxidation process, the total salt content is 2650 mg / L, pH is 2, and the influent flow rate is 20 t / h.

[0074] The process route is the same as in Example 1, involving modified electrodialysis. The anion exchange membrane is a modified anion exchange membrane, and the cation exchange membrane is a general-purpose cation exchange membrane (Hefei Kaijie Polymer Co., Ltd., China, model CJ-MC-3). During the preparation of the modified anion exchange membrane, except that in step b (dopamine Tris buffer solution, dopamine concentration is 0.6 g / L), in step c (copper sulfate addition is 4.5 mmol / L, and stirring time is 9 h), in step d (polyanion modifier concentration is 1.7 g / L), and in step e (e (electrodeposition time is 0.7 h), all other procedures are the same as in Example 1.

[0075] The specific operating parameters for treating epichlorohydrin wastewater are as follows:

[0076] Wastewater first enters an equalization tank, where sodium hydroxide is added to adjust the pH to 10.8, resulting in a small amount of precipitate. After passing through a tubular microfiltration membrane with a pore size of 0.7 micrometers, the heavy metal concentration is reduced to below 5 mg / L. The effluent then enters a mild wet oxidation process. The mild wet oxidation reaction temperature is 75℃, the reaction pressure is 0.6 MPa, and the liquid hourly space velocity (LHSV) is 1 h⁻¹. -1 The gas-liquid volume ratio was 12:1. The effluent contained 0.04 wt% epichlorohydrin and 0.03 wt% dichloropropanol. The COD was 56430 mg / L, showing no significant change. The sulfate concentration was 30 mg / L, the chloride concentration was 16119 mg / L, and the salt content of the wastewater increased to 29450 mg / L. In addition, the glycerol content increased to 3.0 wt%, indicating that most of the epichlorohydrin and dichloropropanol were converted into glycerol. Hydrochloric acid was added to the neutralization tank to adjust the pH to 7.5, and the salt content of the wastewater increased to 31223 mg / L. The effluent then entered electrodialysis.

[0077] The electrodialysis treatment time was 1.1 hours, and the current density was 35 mA / cm². 2After treatment, the COD concentration of the electrodialysis desalination solution was 109022 mg / L, the total salt content was 1950 mg / L, and the flow rate was 10 t / h. The COD concentration of the concentrate was 3838 mg / L, the total salt content was 60510 mg / L, and the flow rate was 10 t / h. The chloride ion selective permeability was 96.9%, and the organic matter rejection rate was 96.6%. The electrodialysis concentrate entered the bio-enhancing unit, which adopted the MBBR process and added salt-tolerant bacteria. The salt-tolerant bacteria GXNYJ-DL-1 disclosed in patent CN114686391A, with accession number CGMCC, was selected. No. 20350, with a residence time of 96 hours, produces effluent COD as low as 276 mg / L; the ozone dosage concentration for ozone catalysis I is 120 mg / L, the reaction time is 40 minutes, and the effluent COD is 112 mg / L with a total salt content of 60437 mg / L; the effluent from ozone catalysis I enters the concentration and salt production system, which uses a multi-effect evaporator and a salt crystallizer to finally obtain sodium chloride product with a purity of 99.4%, and the steam condensate is reused;

[0078] The electrodialysis desalination solution enters the anaerobic biological treatment process, with dissolved oxygen controlled below 0.15 mg / L and the temperature at 31℃. The bacterial strains used are conventional anaerobic bacteria, including organic acidifying bacteria and methanogenic bacteria. The wastewater retention time is 96 hours, and the effluent COD is reduced to 883 mg / L. The generated methane gas is stored in a methane storage tank with a purity of 98.1%. The methane can be used as fuel in the enterprise's gas-fired boiler to produce steam or generate electricity, effectively offsetting the steam consumption of the wet oxidation and salt evaporation crystallization systems, as well as the power consumption of electrical equipment. The aerobic biological treatment uses an A / O process, adding conventional biological strains, with a retention time of 30 hours, including a 24-hour aerobic retention time and a 6-hour anoxic retention time, resulting in an effluent COD of 195 mg / L. The ozone catalysis II process uses an ozone concentration of 70 mg / L, reacts for 30 minutes, and produces an effluent COD of 104 mg / L. The BAF process uses conventional aerobic strains, with a retention time of 6 hours, resulting in an effluent COD of 56 mg / L and a total salt content of 1823 mg / L, meeting reuse standards.

[0079] As can be seen from this embodiment, the present invention can effectively treat epichlorohydrin wastewater of different concentrations. The organic matter and salt in the wastewater can be utilized as resources, the effluent meets the reuse standards, and the whole process achieves zero discharge.

[0080] Comparative Example 1

[0081] The treatment of epichlorohydrin wastewater was the same as in Example 1, and the process route and implementation steps were also the same as in Example 1. The difference was that the anion and cation exchange membranes and bipolar membranes used in the electrodialysis were both general-purpose membranes. The anion exchange membrane was a product of Asahi Glass Co., Ltd. of Japan (SELEMION AMV), and the cation exchange membrane was a product of Hefei Kaijie Polymer Co., Ltd. of China (model CJ-MC-3).

[0082] Specifically, as in Example 1, the wastewater was treated in an equalization tank, tubular microfiltration, mild wet oxidation, and neutralization tank before entering electrodialysis. The effluent from the neutralization tank had a salt content of 23830 mg / L, a COD of 41130 mg / L, and a pH of 8. The electrodialysis treatment time was 1 hour, and the current density was 30 mA / cm². 2 After treatment, the COD concentration of the electrodialysis desalination solution was 59296 mg / L, the total salt content was 7864 mg / L, and the flow rate was 12 t / h. The COD concentration of the concentrate was 13881 mg / L, the total salt content was 47779 mg / L, and the flow rate was 8 t / h. The chloride ion selective permeability was 80.2%, and the organic matter rejection rate was 86.5%. The electrodialysis concentrate entered the bio-enhancing unit, which adopted a contact oxidation process and added salt-tolerant bacteria. The salt-tolerant bacteria GXNYJ-DL-1 disclosed in patent CN114686391A, with accession number CGMCC, was selected. For No. 20350, the retention time was extended to 120 hours. Due to the treatment load of the contact oxidation tank, the effluent COD was still as high as 7430 mg / L. The electrodialysis desalination liquid entered the anaerobic biological treatment, with dissolved oxygen controlled below 0.15 mg / L, temperature at 30℃, and conventional anaerobic bacteria, including organic acidifying bacteria and methanogens. The wastewater retention time was extended to 96 hours. The salt concentration as high as 7864 mg / L affected the COD removal efficiency, and the final effluent COD was 23460 mg / L.

[0083] This comparative example shows that electrodialysis using unmodified cation and anion exchange membranes is prone to fouling by organic matter, resulting in poor separation of organic matter and salts. The final desalination solution has a salt concentration as high as 7864 mg / L, affecting the treatment efficiency of anaerobic biological treatment. This leads to a COD of 23460 mg / L in the anaerobic biological effluent, exceeding the treatment capacity of aerobic biological treatment and ozone catalysis II, making the wastewater unsuitable for reuse. Simultaneously, the concentrated solution has a COD concentration as high as 13881 mg / L, also exceeding the treatment capacity of biological enhancement and ozone catalysis I, ultimately failing to yield a qualified sodium chloride product.

[0084] Comparative Example 2

[0085] The treatment of epichlorohydrin wastewater is the same as in Example 1, and the process route and implementation steps are also basically the same as in Example 1. The difference is that the mild wet oxidation is replaced by high temperature and high pressure wet oxidation.

[0086] Specifically, as in Example 1, the wastewater is treated in a regulating tank before entering a high-temperature, high-pressure wet oxidation process; the high-temperature, high-pressure wet oxidation reaction temperature is 210°C, the reaction pressure is 3.5 MPa, and the liquid hourly space velocity is 1 h⁻¹. -1The gas-liquid volume ratio was 40:1. The main organic compounds in the effluent were sodium propionate, glycerol, sodium acetate, and methanol. Epichlorohydrin and dichloropropanol were barely detectable. The COD was 12460 mg / L, with a COD removal rate of 69.7%. The sulfate concentration was 15 mg / L, and the chloride concentration was 12733 mg / L, resulting in a salt content of 22488 mg / L. The effluent from the high-temperature, high-pressure wet oxidation process entered a neutralization tank. Hydrochloric acid was added to the neutralization tank to adjust the pH to 8, increasing the salt content to 24046 mg / L. The effluent then entered electrodialysis. The electrodialysis treatment time was 1 hour, and the current density was 30 mA / cm³. 2 After treatment, the COD concentration of the electrodialysis desalination solution was 10840 mg / L, the total salt content was 9899 mg / L, and the flow rate was 12 t / h. The COD concentration of the concentrate was 14890 mg / L, the total salt content was 45266 mg / L, and the flow rate was 8 t / h. The chloride ion selective permeability was 75.3%, and the organic matter rejection rate was 52.2%.

[0087] As shown in this comparative example, compared with Example 1, when the mild wet oxidation was changed to high temperature and high pressure wet oxidation, the COD removal rate increased from 0 to 69.7%, corresponding to the conversion of chlorinated organic matter into sodium propionate, glycerol, sodium acetate, methanol, carbon dioxide, water, etc. Due to the deep conversion of chlorinated organic matter, propionic acid, acetic acid, etc. in the electrodialysis feed water are negatively charged organic matter, resulting in an electrodialysis organic matter rejection rate of only 52.2%. The passage of a large number of negatively charged organic matter easily causes anion membrane fouling and membrane blockage, leading to a decrease in chloride ion selective permeability to 75.3%. Finally, the total salt content of the electrodialysis desalination solution is as high as 9899 mg / L, and the COD concentration of the electrodialysis concentrate is as high as 14890 mg / L, making it difficult to obtain qualified sodium chloride products and achieve wastewater reuse that meets standards. In addition, the cost per ton of water treated by the high-temperature and high-pressure wet oxidation in this comparative example is 5 to 10 times that of the moderate wet oxidation treatment in Example 1. The equipment investment of the wet oxidation reactor is 2 to 4 times that of the wet oxidation reactor in Example 1. Furthermore, since most of the organic matter is converted into carbon dioxide, the thermal and electrical energy compensation brought about by methane resource utilization is greatly reduced, further increasing the overall operating cost of wastewater treatment.

[0088] Comparative Example 3

[0089] The treatment of epichlorohydrin wastewater was the same as in Example 1, except that the wastewater was directly introduced into the anaerobic biological treatment unit after the pH was adjusted to 7 in the equalization tank, without the use of pretreatment methods such as slow wet oxidation or electrodialysis. The COD concentration of the influent to the anaerobic biological treatment unit was 41200 mg / L, and the total salt content of the wastewater was 2400 mg / L. As in Example 1, dissolved oxygen was controlled below 0.15 mg / L, the temperature was 30℃, and the bacterial strains used were conventional anaerobic bacteria, including organic acidifying bacteria and methanogens. The wastewater retention time was 72 h, and the COD of the effluent was 35463 mg / L, with a COD removal rate of only 13.9%. The reason for this was that the toxicity of chlorinated organic matter affected the biological activity of the anaerobic bacteria.

Claims

1. A process for treating wastewater generated during the direct oxidation process for preparing epichlorohydrin, including a pretreatment section, a main reaction section, and an advanced treatment section; The pretreatment section includes, in sequence, an adjustment unit, a tubular microfiltration unit, a mild wet oxidation unit, and a neutralization unit. The effluent from the neutralization unit enters the electrodialysis unit of the main reaction section. The main reaction section includes an electrodialysis unit, an anaerobic biochemical unit, a biofortification unit, an ozone catalysis unit I, a salt concentration system, and a methane storage unit; The effluent from the electrodialysis unit is divided into a concentrate and a desalination solution. The desalination solution enters the anaerobic biological treatment unit, and the methane gas generated in the anaerobic biological treatment unit is stored in a methane storage tank. The effluent from the anaerobic biological treatment unit enters the aerobic biological treatment unit in the deep treatment section. The electrodialysis concentrate is then processed sequentially through a bio-enhancing unit, an ozone catalysis unit I, and a concentration and salt production system to obtain sodium chloride product. The advanced treatment section includes, in sequence, an aerobic biochemical unit, an ozone catalytic II unit, and a BAF unit. The effluent from the BAF unit meets the reuse standards and is recycled. The electrodialysis unit is composed of anion and cation exchange membranes, wherein the anion exchange membrane is a modified anion exchange membrane and the cation exchange membrane is a general-purpose cation exchange membrane. The modification methods for anion exchange membranes are as follows: Step a: Using a commercial anion exchange membrane as the base membrane, rinse it with hydrochloric acid solution and sodium hydroxide solution respectively, and then rinse it with deionized water to remove impurities on the membrane surface, thus obtaining the pretreated base membrane; Step b: Dissolve dopamine and β-cyclodextrin in Tris-HCl buffer, adjust the pH to 8-9 with hydrochloric acid, and stir to fully dissolve them to obtain dopamine Tris buffer solution; Step c: Place the base membrane obtained in step a in a dopamine Tris buffer solution and add copper sulfate. Stir the reaction while maintaining air circulation. After the reaction is complete, a preliminarily modified anion exchange membrane is obtained. Step d: Dissolve the polyanionic modifier and sodium chloride in Tris-HCl buffer, and adjust the pH to 8-9 with hydrochloric acid to obtain the electrodeposition mother solution; Step e: Place the anion exchange membrane obtained in step c in the middle of the DC electrodeposition apparatus to form two compartments. Put the electrodeposition mother solution prepared in step d into the compartment on the cathode side, and put water into the compartment on the anode side to carry out the electrodeposition reaction and obtain the final modified anion exchange membrane.

2. The process method according to claim 1, characterized in that, In the modification method of the anion exchange membrane, the concentration of HCl in the hydrochloric acid solution in step a is 0.1–0.3 mol / L, and the concentration of sodium hydroxide in the sodium hydroxide solution is 0.1–0.3 mol / L; the concentration of the Tris–HCl buffer solution in steps b and d is 10–50 mmol / L; the dopamine Tris buffer solution in step b has a dopamine mass concentration of 0.1–2 g / L and a β-cyclodextrin mass concentration of 0.1–1.5 g / L.

3. The process method according to claim 1, characterized in that, In the modification method of anion exchange membrane, the stirring time in step b is 1-10 h; in step c, the concentration of copper sulfate is 1-20 mmol / L, and the stirring reaction time is 1-20 h.

4. The process method according to claim 1, characterized in that, In the modification method of anion exchange membrane, the polyanion modifier in step d is one or more of sodium poly4-styrene sulfonate, sodium p-styrene sulfonate, sodium polyethylene sulfonate, and sodium polypropylene sulfonate; the mass concentration of the polyanion modifier in the electrodeposition mother liquor of step d is 0.5-5 g / L, and the mass concentration of sodium chloride is 3-30 g / L.

5. The process method according to claim 1, characterized in that, In the modification method of anion exchange membranes, the electrodeposition reaction time in step e is 0.2–2 h, and the current density is 1–50 mA / cm². 2 .

6. The process method according to claim 1, characterized in that, The adjustment unit adds sodium hydroxide to adjust the pH value to 10-12; the filter membrane pore size of the tubular microfiltration unit is in the range of 0.1-1.0 micrometers.

7. The process method according to claim 1, characterized in that, The aforementioned mild wet oxidation unit employs a bubbling flow internal circulation reactor, with a reaction temperature of 50–100℃, a reaction pressure of 0.3 MPa–1 MPa, and a liquid hourly space velocity of 0.25–4 h⁻¹. -1 The gas-liquid volume ratio is 2:1 to 20:

1.

8. The process method according to claim 1, characterized in that, The electrodialysis unit has a treatment time of 0.1–2 hours and a current density of 1–80 mA / cm². 2 .

9. The process method according to claim 1, characterized in that, The dissolved oxygen in the anaerobic biochemical unit is controlled below 0.2 mg / L, the wastewater retention time is 6–120 h, the temperature is 25–35 °C, the bacterial strains are conventional anaerobic strains, and the process uses one of the following anaerobic processes: AFB, UASB, IC, and EGSB.

10. The process method according to claim 1, characterized in that, The biochemical enhancement unit uses one of the following aerobic processes: BAF, MBR, contact oxidation tank, and MBBR, with a residence time of 12–144 h and salt-tolerant bacteria. The aerobic biochemical unit uses one of the following aerobic processes: BAF, MBR, contact oxidation tank, and MBBR, or one of the following processes: A / O or SBR, which are mainly aerobic, with a residence time of 12–60 h and conventional aerobic bacteria.

11. The process method according to claim 1, characterized in that, The ozone dosage in the ozone catalytic oxidation unit I and ozone catalytic oxidation unit II is 0.1 to 2 times the amount of oxidant required based on the COD value of the wastewater, the reaction time is 10 to 120 minutes, and the catalyst is a conventional solid supported metal catalyst.

12. The process method according to claim 1, characterized in that, The BAF unit residence time is 2-12 hours, and the biological strains used are conventional aerobic strains.

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