A process for treating waste water produced in the process of preparing epichlorohydrin by direct oxidation method

Abstract

A process for treating wastewater generated during the direct oxidation of epichlorohydrin includes a pretreatment section, a main reaction section, and a deep treatment section. The pretreatment section sequentially comprises a conditioning unit, a tubular microfiltration unit, a heat exchange unit, a catalytic dechlorination unit, and a neutralization unit. The main reaction section includes an electrodialysis unit, an anaerobic biological treatment unit, an aerobic biological treatment unit, and a methane storage unit. The deep treatment section sequentially includes an ozone catalytic oxidation unit and a BAF unit. The electrodialysis unit uses a modified anion exchange membrane. This invention solves the problem of high toxicity of chlorinated organic compounds in wastewater by coupling catalytic dechlorination and electrodialysis, and achieves the separation of organic matter and salts in the wastewater. The catalytic dechlorination uses an organic porous copolymer catalyst, which greatly improves the dechlorination efficiency, and the electrodialysis uses a modified anion exchange membrane, which significantly increases its anti-fouling ability. This invention achieves wastewater discharge meeting standards and has the advantage of low operating costs.

Description

Technical Field

[0001] This invention relates to a process for treating wastewater generated during the direct oxidation process for preparing 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. The method employs a light chlorohydrin removal tower, a hydrolysis reactor, and a dehydration tower for pretreatment to recover allyl chloride and 3-chloro-1,2-propanediol. However, all of these towers require heating, resulting in significant overall operating costs. Considering that the allyl chloride content in the wastewater is below 0.5 wt%, it does not possess significant recovery value, and the effluent COD is still as high as 765 mg / L, requiring further treatment.

[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. This method solves the problems of high toxicity and difficulty in treating the wastewater, converts most of the organic matter in the wastewater into methane for resource utilization, achieves compliant discharge, and has low 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 heat exchange unit, a catalytic dechlorination unit, and a neutralization unit. Wastewater is treated by the above units in sequence, and 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, an aerobic biochemical unit, 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 biochemical unit, and the methane gas generated by the anaerobic biochemical unit is stored in the methane storage unit. The effluent from the anaerobic biochemical unit, together with the electrodialysis concentrate, enters the aerobic biochemical unit. The effluent from the aerobic biochemical unit enters the ozone catalytic oxidation unit of the deep treatment section.

[0015] The advanced treatment section includes an ozone catalytic oxidation unit and a BAF unit in sequence, and the effluent from the BAF unit meets the discharge standards; wherein, 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 modified anion exchange membrane is prepared by the following steps:

[0017] Step a: Add polyvinyl alcohol to water to prepare a polyvinyl alcohol aqueous solution. Then add positively charged amine compounds, β-cyclodextrin, and crosslinking agents to the above solution respectively. Add inorganic acid to adjust the pH. After mixing and stirring, the casting solution is obtained.

[0018] Step b: Cast the casting solution obtained in step a onto a horizontal panel, dry it, and obtain the base film;

[0019] Step c: After washing the base membrane obtained in step b, place it in an alkaline solution for alkalization, and then soak it in water to obtain a polyvinyl alcohol anion exchange membrane;

[0020] Step d: Dissolve dopamine in Tris-HCl buffer, adjust the pH with hydrochloric acid to obtain dopamine Tris buffer solution;

[0021] Step e: Place the anion exchange membrane obtained in step c in a dopamine Tris buffer solution and add copper sulfate. Stir the reaction while maintaining air circulation. After the reaction is complete, the modified anion exchange membrane is obtained.

[0022] Furthermore, the positively charged amine compound is selected from one or more of 2,3-epoxypropyltrimethylammonium chloride, polyethyleneimine, polyepoxychloropropaneamine, and quaternized chitosan, preferably 2,3-epoxypropyltrimethylammonium chloride; the mass ratio of the positively charged amine compound to polyvinyl alcohol is 0.1:1 to 0.6:1.

[0023] Furthermore, the mass ratio of β-cyclodextrin to polyvinyl alcohol is 0.02:1 to 0.2:1.

[0024] Furthermore, the crosslinking agent is selected from aldehyde or acid crosslinking agents, preferably glutaraldehyde, and the mass ratio of the crosslinking agent to polyvinyl alcohol is 0.01:1 to 0.1:1.

[0025] Furthermore, the inorganic acid mentioned in step a is sulfuric acid, hydrochloric acid, or nitric acid, and the pH of the solution is adjusted to 4-6.

[0026] Furthermore, in step a, the mass fraction of the polyvinyl alcohol aqueous solution is 5%–15%, and the reaction time with the positively charged amine compound, β-cyclodextrin, and crosslinking agent is 4–16 h.

[0027] Furthermore, the polyvinyl alcohol aqueous solution is prepared by stirring at 60–90°C to dissolve the polyvinyl alcohol in water.

[0028] Furthermore, the drying process described in step b involves first drying at room temperature for 2–6 hours, and then continuing to dry under vacuum at 40–80°C for 4–10 hours.

[0029] Furthermore, the washing described in step c involves washing with water until the solution is neutral.

[0030] Furthermore, the alkalization is performed using a 0.5–3 mol / L sodium hydroxide aqueous solution for 12–24 hours.

[0031] Furthermore, the soaking time in step c is 12 to 24 hours.

[0032] Furthermore, the concentration of the Tris–HCl buffer in step d is 10–50 mmol / L.

[0033] Furthermore, in step d, the dopamine concentration is 0.4–4 g / L, and the hydrochloric acid is used to adjust the pH range to 8–9.

[0034] Furthermore, in step e, the concentration of copper sulfate is 1–20 mmol / L, and the stirring reaction time is 1–12 h. Copper sulfate can induce rapid polymerization of dopamine, forming a negatively charged polydopamine electrolyte layer on the surface of the anion exchange membrane, thereby modifying the membrane surface.

[0035] Furthermore, after obtaining the modified anion exchange membrane, it is stored in a sodium chloride solution with a mass concentration of 5–20 g / L.

[0036] 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.

[0037] Furthermore, the adjustment unit adds sodium hydroxide to adjust the pH value to 10-12.

[0038] 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.

[0039] Furthermore, the heat exchange unit is used for temperature regulation of epichlorohydrin wastewater, and is accomplished using a conventional heat exchanger. After heat exchange, the wastewater temperature rises to 40-100℃.

[0040] Furthermore, the catalytic dechlorination unit employs an upflow reactor, with a catalyst bed installed within the reactor shell. The reaction pressure is atmospheric pressure, and the liquid hourly space velocity (LHSV) is 0.2–2 h⁻¹. -1 Air is introduced, with a gas-liquid volume ratio of 1:1 to 10:1, and a small amount of steam is added to maintain the system reaction temperature at 40 to 100°C.

[0041] Furthermore, the catalyst loading volume to reactor volume ratio of the catalytic dechlorination unit is 0.6:1 to 1:1, and the catalyst is an organic porous copolymer solid catalyst containing an active metal and an auxiliary agent; the active metal is selected from one or more of copper, iron, manganese, zinc, aluminum, vanadium, silver and cobalt, and the auxiliary agent is a compound that can form a quaternary phosphonium salt structure, preferably at least one of tributylphosphine and triphenylphosphine; the organic porous copolymer is a polystyrene polymer crosslinked with styrene and divinylbenzene.

[0042] Furthermore, the catalyst, by weight (in 100 wt%), comprises 0.1 wt% to 10 wt% of active metal, 30% to 70% of additives, and 20% to 60% of the organic porous copolymer; the amount of divinylbenzene in the organic porous copolymer is 10% to 20% of the styrene mass; the organic porous copolymer also contains benzoyl peroxide as an initiator, with the amount of benzoyl peroxide being 0.5% to 5% of the styrene mass.

[0043] Furthermore, the catalyst is prepared by the following method: styrene, divinylbenzene, additives, and benzoyl peroxide are added to water for suspension polymerization at a reaction temperature of 50–90°C and a stirring reaction time of 0.5–10 h. Then, water is injected to cool and shape the mixture, and it is dried and solidified below 100°C to obtain a granular solid material. This material is then added to a halide solution of an active metal and the active metal is loaded by impregnation. Finally, it is dried below 100°C to obtain the catalyst.

[0044] Those skilled in the art should understand that, under the aforementioned temperature and catalyst conditions, the catalytic dechlorination reactor can effectively achieve the chemical reaction between epichlorohydrin and alkali, converting chlorinated organic matter into chlorine-free organic matter and sodium chloride, thus achieving the alkali-induced dechlorination effect. Under these conditions, only the elimination reaction of chlorine occurs, and the oxidation reaction of carbon does not occur. Therefore, there is no significant change in COD before and after the reaction, but the salt content of the wastewater increases substantially.

[0045] Furthermore, hydrochloric acid is added to the neutralization unit to adjust the pH value to 6-9.

[0046] 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 undergoes catalytic dechlorination, organic chlorine is converted into inorganic chlorine, significantly reducing the wastewater's biotoxicity. However, this also leads to a substantial increase in sodium chloride content, which is detrimental to biochemical reactions, especially anaerobic biochemical reactions. After pH adjustment, most organic matter in the catalytic dechlorination effluent becomes 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. This modification effectively inhibits the migration of large negatively charged organic molecules while maintaining a high chloride ion permeability, thereby significantly improving the anion exchange membrane's antifouling ability and ultimately achieving the separation of organic matter and salts.

[0047] 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.

[0048] Furthermore, the aerobic biochemical unit uses salt-tolerant bacteria, and the process uses one of the aerobic processes such as BAF, MBR, contact oxidation tank, and MBBR, with a residence time of 12–96 h.

[0049] Furthermore, the ozone dosage of the ozone catalytic oxidation unit 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.

[0050] Furthermore, the BAF unit uses salt-tolerant bacteria and has a residence time of 2–24 hours.

[0051] Furthermore, the methane storage unit has a methane purity greater than 96%, and its methane can be used as fuel for gas-fired boilers to achieve resource utilization through steam production or power generation.

[0052] Compared with the prior art, the present invention has the following advantages:

[0053] (1) This invention solves the problem of high toxicity of chlorinated organic matter in wastewater by coupling catalytic dechlorination with electrodialysis, and achieves the separation of organic matter and salt in wastewater. The catalytic dechlorination uses an organic porous copolymer catalyst, which greatly improves the dechlorination efficiency. The electrodialysis uses a modified anion exchange membrane, which greatly increases the anti-pollution ability.

[0054] (2) This invention achieves efficient resource utilization of organic matter in epichlorohydrin wastewater. Specifically, by controlling reaction conditions and using a specific catalyst, catalytic dechlorination is made to only involve the elimination of chlorine without the oxidation of carbon. Then, pH is adjusted to keep most of the organic matter electrically neutral, and the organic matter is stripped off through electrodialysis. The stripped organic matter is then converted into methane through an anaerobic reaction, thereby achieving resource utilization.

[0055] (3) This invention achieves wastewater discharge compliance and has the advantage of low operating cost. Specifically, compared with pretreatment methods such as wet oxidation, ozone catalytic oxidation, and Fenton oxidation, the catalytic dechlorination process has milder reaction conditions and lower operating costs. Moreover, the low-temperature heat required for catalytic dechlorination is obtained through heat exchange, resulting in very low operating costs, even to the point of zero cost. The electrodialysis process has lower voltage and current, thus lower power consumption. Furthermore, the electrodialysis process of this invention only separates and does not concentrate, resulting in short operating time and low operating costs. Anaerobic biochemical treatment can realize the utilization of methane resources, which can further offset costs. With the help of halophilic bacteria, aerobic biochemical treatment and BAF unit remove most of the organic matter from the anaerobic biochemical effluent, so that the ozone catalytic oxidation unit only needs to add a small amount of ozone to improve the biodegradability of the wastewater, resulting in lower operating costs and ultimately achieving wastewater discharge compliance (regardless of salt content).

[0056] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0057] Figure 1 Flowchart of epichlorohydrin wastewater treatment in Example 1. Detailed Implementation

[0058] 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.

[0059] Example 1

[0060] The process flow diagram for treating wastewater generated during the direct oxidation process for epichlorohydrin is as follows: Figure 1As shown, epichlorohydrin wastewater sequentially enters an equalization tank, a tubular microfiltration system, a heat exchanger, a catalytic dechlorination 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, and the methane gas produced by the anaerobic biological treatment system is stored in a methane storage tank. The effluent from the anaerobic biological treatment system, together with the electrodialysis concentrate, enters an aerobic biological treatment system. The aerobic biological treatment effluent is then sequentially treated by ozone catalysis and BAF (biochemical oxygen demand) before being discharged in compliance with standards.

[0061] The process method of this invention is used to treat epichlorohydrin wastewater:

[0062] 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 41500 mg / L, sulfate concentration is 16 mg / L, chloride concentration is 1400 mg / L, a small amount of heavy metals are introduced due to catalyst loss during the direct oxidation process, with a concentration of 85 mg / L in the wastewater, total salt content is 2000 mg / L, pH is 1.8, and influent flow rate is 20 t / h.

[0063] 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).

[0064] The modified anion exchange membrane described above was prepared by the following method:

[0065] Step a: Add polyvinyl alcohol to deionized water to prepare a 10% aqueous solution. Stir at 80°C to dissolve it. Then add 2,3-epoxypropyltrimethylammonium chloride, β-cyclodextrin, and glutaraldehyde to the water. The mass ratio of 2,3-epoxypropyltrimethylammonium chloride to polyvinyl alcohol is 0.5:1, the mass ratio of β-cyclodextrin to polyvinyl alcohol is 0.1:1, and the mass ratio of glutaraldehyde to polyvinyl alcohol is 0.05:1. Adjust the pH to 5 with hydrochloric acid and react for 9 hours to obtain a viscous liquid, which is the casting solution.

[0066] Step b: Cast the casting solution onto a horizontal glass plate and dry it at room temperature for 3 hours. Then, continue to dry the formed film under vacuum at 60°C for 6 hours to obtain the base film.

[0067] Step c: Wash the base membrane obtained in step b with deionized water until neutral, then place it in a 1 mol / L sodium hydroxide aqueous solution for alkalization for 16 h, and then soak it in deionized water for 16 h to obtain a polyvinyl alcohol anion exchange membrane.

[0068] Step d: Dissolve dopamine in 20 mmol / L Tris–HCl buffer, adjust the pH to 8.5 with hydrochloric acid to obtain a dopamine Tris buffer solution with a dopamine mass concentration of 0.8 g / L.

[0069] Step e: Place the polyvinyl alcohol anion exchange membrane to be modified in a dopamine Tris buffer solution and add 4 mmol / L copper sulfate. Stir and react for 5 hours. Keep the air circulating during the reaction. Copper sulfate can induce rapid polymerization of dopamine and form a negatively charged polydopamine electrolyte layer on the surface of the anion exchange membrane. After the reaction is completed, the modified anion exchange membrane is obtained.

[0070] Step f: Remove the modified anion exchange membrane and place it in a sodium chloride solution with a mass concentration of 10 g / L for later use.

[0071] The specific operating parameters for treating epichlorohydrin wastewater are as follows:

[0072] Wastewater first enters an equalization tank, where sodium hydroxide is added to adjust the pH to 10.6, resulting in a small amount of precipitation. After passing through a tubular microfiltration system, the heavy metal concentration is reduced to below 5 mg / L. The tubular microfiltration membrane has a pore size of 0.6 micrometers. The effluent is then heated to 85°C via a heat exchanger before entering the catalytic dechlorination process. The catalytic dechlorination uses an upflow reactor with a catalyst bed inside the reactor shell. The catalyst loading volume to shell volume ratio is 0.8:1. The catalyst for catalytic dechlorination is a solid organic porous copolymer catalyst containing an active metal and an additive. The active metal is zinc, and the additive is tributylphosphine. The catalyst weight is 100 wt%, the active metal weight content is 4 wt%, the additive weight content is 51%, and the organic porous copolymer weight content is 45%. The organic porous copolymer is a styrene and divinylbenzene copolymer, also containing the initiator benzoyl peroxide. The amount of divinylbenzene is 14% of the styrene mass, and the amount of benzoyl peroxide is 2% of the styrene mass.

[0073] The catalyst was prepared by the following method: styrene, divinylbenzene, tributylphosphine, and benzoyl peroxide were added to water for suspension polymerization at 75°C for 5 hours. The mixture was then cooled and shaped by water injection, dried and solidified at 90°C to obtain granular solid material. This material was then added to a zinc chloride solution to impregnate it with the active metal, and finally dried at 95°C to obtain the catalyst. The catalytic dechlorination unit was operated at atmospheric pressure with a liquid hourly space velocity (LHSV) of 0.7 h⁻¹. -1Air was introduced at a gas-liquid volume ratio of 4:1, and a small amount of steam was added to maintain the system reaction temperature at 85°C. The effluent contained 0.02 wt% epichlorohydrin and 0.01 wt% dichloropropanol, with a COD of 41368 mg / L, showing no significant change. The sulfate concentration was 16 mg / L, the chloride concentration was 12412 mg / L, and the wastewater salt content increased to 22167 mg / L, while the glycerol content increased to 1.8 wt%, indicating that most of the epichlorohydrin and dichloropropanol had undergone dechlorination. Hydrochloric acid was added to the neutralization tank to adjust the pH to 8, and the wastewater salt content increased to 23560 mg / L. The effluent then entered electrodialysis.

[0074] The electrodialysis treatment time was 0.8 hours, and the current density was 25 mA / cm². 2 After treatment, the COD concentration of the electrodialysis desalination solution was 61861 mg / L, the total salt content was 3081 mg / L, and the flow rate was 13 t / h. The COD concentration of the concentrate was 3310 mg / L, the total salt content was 61592 mg / L, and the flow rate was 7 t / h. The chloride ion selective permeability was 91.5%, and the organic matter rejection rate was 97.2%. The electrodialysis desalination solution then entered anaerobic biological treatment, with dissolved oxygen controlled below 0.15 mg / L, the temperature at 30℃, and conventional anaerobic bacteria, including organic acidifying bacteria and methanogenic bacteria. The wastewater retention time was 72 h. The effluent... The COD was reduced to 1025 mg / L, and the generated methane gas was stored in a methane storage tank with a purity of 97.2%. The methane can be used as fuel in the company's gas-fired boiler to produce steam or generate electricity. The anaerobic biological treatment effluent entered the aerobic biological treatment process, along with the electrodialysis concentrate. After mixing, the COD concentration of the aerobic biological treatment influent was 1825 mg / L, and the total salt content was 23432 mg / L. The aerobic biological treatment adopted the MBBR process, adding salt-tolerant bacteria, specifically the salt-tolerant bacteria GXNYJ-DL-1 disclosed in patent CN114686391A, with accession number CGMCC. No. 20350, with a residence time of 60h, the effluent COD was reduced to 165mg / L; the ozone concentration for ozone catalysis was 70mg / L, the reaction time was 30min, and the effluent COD was 81mg / L; the salt-tolerant bacteria added to BAF were the same as those added to MBBR, with a residence time of 8h, the effluent COD was 55mg / L, and the total salt content was 23646mg / L, meeting the GB31571 discharge standard.

[0075] As demonstrated in this embodiment, the present invention can effectively treat epichlorohydrin wastewater. Catalytic dechlorination solves the problem of high toxicity of chlorinated organic matter in the wastewater, and the modified electrodialysis achieves the separation of organic matter and salts in the wastewater. Most of the organic matter is converted into methane and recycled, and the wastewater ultimately meets the discharge standards. Due to the low reaction conditions of catalytic dechlorination and the heat and electricity compensation brought by methane recycling, the overall operating cost of the wastewater treatment remains at a low level.

[0076] Example 2

[0077] use Figure 1 The process shown is for treating epichlorohydrin wastewater.

[0078] 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 56642 mg / L, sulfate concentration is 28 mg / L, chloride concentration is 2115 mg / L, a small amount of heavy metals (110 mg / L) are lost due to catalyst loss during the direct oxidation process, the total salt content is 2680 mg / L, pH is 2.1, and the influent flow rate is 20 t / h.

[0079] 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). In the preparation of the modified anion exchange membrane, except that in step a, the positively charged amine compound is polyethyleneimine, the mass ratio of polyethyleneimine to polyvinyl alcohol is 0.5:1, the mass ratio of β-cyclodextrin to polyvinyl alcohol is 0.13:1, the mass ratio of glutaraldehyde to polyvinyl alcohol is 0.06:1, and the reaction time in step a is 10 hours, everything else is the same as in Example 1.

[0080] The specific operating parameters for treating epichlorohydrin wastewater are as follows:

[0081] Wastewater first enters an equalization tank, where sodium hydroxide is added to adjust the pH to 10.9, resulting in a small amount of precipitation. After passing through a tubular microfiltration system, the heavy metal concentration is reduced to below 5 mg / L. The tubular microfiltration membrane has a pore size of 0.7 micrometers. The effluent is then heated to 88°C via a heat exchanger before entering the catalytic dechlorination process. The catalytic dechlorination uses an upflow reactor with a catalyst bed inside the reactor shell. The catalyst loading volume to shell volume ratio is 0.85:1. The catalyst for catalytic dechlorination is a solid organic porous copolymer catalyst containing active metals and additives. The metal is an iron-copper composite metal, with an iron-copper mass ratio of 5:1 (elemental basis). The additive is triphenylphosphine. The catalyst is 100 wt% by weight. The active metal content is 5 wt% by weight, the additive content is 55% by weight, and the organic porous copolymer content is 40% by weight. The organic porous copolymer is a styrene-divinylbenzene copolymer, and also contains the initiator benzoyl peroxide. The amount of divinylbenzene is 15% of the mass of styrene, and the amount of benzoyl peroxide is 1.8% of the mass of styrene.

[0082] The catalyst was prepared by the following method: styrene, divinylbenzene, triphenylphosphine, and benzoyl peroxide were added to water for suspension polymerization at 80°C for 5 hours. The mixture was then cooled and solidified with water at 88°C to obtain granular solid material. This material was then impregnated with a solution of ferric chloride and copper sulfate to load the active metal, and finally dried at 94°C to obtain the catalyst. The catalytic dechlorination unit was operated at atmospheric pressure with a liquid hourly space velocity (LHSV) of 0.5 h⁻¹. -1 Air was introduced at a gas-liquid volume ratio of 5:1, and a small amount of steam was added to maintain the system reaction temperature at 88℃. The effluent contained 0.03 wt% epichlorohydrin and 0.02 wt% dichloropropanol, with a COD of 56233 mg / L, showing no significant change. The sulfate concentration was 28 mg / L, the chloride concentration was 16237 mg / L, and the wastewater salt content increased to 29540 mg / L, while the glycerol content increased to 2.4 wt%, indicating that most of the epichlorohydrin and dichloropropanol had undergone dechlorination. Hydrochloric acid was added to the neutralization tank to adjust the pH to 7.8, and the wastewater salt content increased to 31556 mg / L. The effluent then entered electrodialysis.

[0083] 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 98970 mg / L, the total salt content was 3327 mg / L, and the flow rate was 11 t / h. The concentrated solution had a COD concentration of 3998 mg / L, a total salt content of 66058 mg / L, and a flow rate of 9 t / h. The chloride ion selective permeability was 94.2%, and the organic matter rejection rate was 96.8%. The electrodialysis desalination solution then entered an anaerobic biological treatment process, with dissolved oxygen controlled below 0.15 mg / L, a temperature of 31℃, and conventional anaerobic bacteria, including organic acidifying bacteria and methanogens. The wastewater retention time was 96 h, and the effluent C... The COD concentration was reduced to 1538 mg / L, and the generated methane gas was stored in a methane storage tank. The methane purity was 97.6%. The methane can be used as fuel in the company's gas-fired boiler to produce steam or generate electricity. The anaerobic biological treatment effluent entered the aerobic biological treatment process, along with the electrodialysis concentrate. After mixing, the COD concentration of the aerobic biological treatment influent was 2645 mg / L, and the total salt content was 31386 mg / L. The aerobic biological treatment adopted a contact oxidation tank process, and salt-tolerant bacteria were added. The salt-tolerant bacteria GXNYJ-DL-1 disclosed in patent CN114686391A, with accession number CGMCC, was selected. No. 20350, with a residence time of 72h, the effluent COD decreased to 188mg / L; the ozone concentration for ozone catalysis was 100mg / L, the reaction time was 30min, and the effluent COD was 75mg / L; the salt-tolerant bacteria added to the BAF were the same as those in the contact oxidation tank, with a residence time of 7h, the effluent COD was 51mg / L, and the total salt content was 31553mg / L, meeting the GB31571 emission standard.

[0084] As can be seen from this embodiment, the present invention can effectively treat epichlorohydrin wastewater of different concentrations, and the organic matter in the wastewater is recycled in the form of methane, and the effluent finally meets the discharge standards.

[0085] Comparative Example 1

[0086] 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).

[0087] Specifically, as in Example 1, the wastewater was treated in an equalization tank, tubular microfiltration, heat exchanger, catalytic dechlorination, and neutralization tank before entering electrodialysis. The effluent from the neutralization tank had a salt content of 23560 mg / L, a COD of 41368 mg / L, and a pH of 8. The electrodialysis treatment time was 0.8 h, and the current density was 25 mA / cm². 2 After treatment, the COD concentration of the electrodialysis desalination solution was 56163 mg / L, the total salt content was 7430 mg / L, and the flow rate was 13 t / h. The COD concentration of the concentrate was 13891 mg / L, the total salt content was 53516 mg / L, and the flow rate was 7 t / h. The chloride ion selective permeability was 79.5%, and the organic matter rejection rate was 88.2%. The electrodialysis desalination solution then entered an anaerobic biological treatment process, with dissolved oxygen controlled below 0.15 mg / L, the temperature at 30℃, and conventional anaerobic bacteria, including organic acidifying bacteria and methanogenic bacteria. The wastewater retention time was... The retention time was extended to 96 hours, and the high salt concentration of 7430 mg / L affected the COD removal efficiency, with the effluent COD being 21533 mg / L. The anaerobic biological effluent entered the aerobic biological treatment, along with the electrodialysis concentrate. After mixing, the COD concentration of the aerobic biological influent was 18858 mg / L, and the total salt content was 23128 mg / L. The aerobic biological treatment used the same process and added salt-tolerant bacteria as in Example 1, with the retention time extended to 96 hours. However, due to the treatment load of the aerobic biological treatment, the effluent COD was still as high as 10455 mg / L.

[0088] As shown in this comparative example, electrodialysis uses unmodified anion and cation exchange membranes. Anion exchange membranes are easily fouled by organic matter, resulting in poor separation of organic matter and salts. The final salt concentration of the desalinated liquid is as high as 7430 mg / L, which affects the treatment efficiency of anaerobic biological treatment. As a result, the COD of the anaerobic biological effluent is as high as 21533 mg / L. The subsequent aerobic biological treatment prolongs the residence time, but the COD of the effluent is still as high as 10455 mg / L. The treatment in the ozone catalytic unit is meaningless, and the wastewater cannot be treated to meet the discharge standards.

[0089] Comparative Example 2

[0090] The treatment of epichlorohydrin wastewater was the same as in Example 1, except that the wastewater, after being treated in an equalization tank, tubular microfiltration, and neutralization tank, directly entered the anaerobic biological treatment unit without pretreatment methods such as catalytic dechlorination or electrodialysis. The influent COD concentration of the anaerobic biological treatment unit was 41500 mg / L, and the total salt content of the wastewater was 3010 mg / L. Similar to 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 effluent COD was 35934 mg / L, with a COD removal rate of only 13.4%. The reason for this was that the toxicity of chlorinated organic matter affected the biological activity of the anaerobic bacteria.

[0091] Comparative Example 3

[0092] 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 no catalyst is used for catalytic dechlorination.

[0093] Specifically, as in Example 1, the wastewater is treated in an equalization tank, a tubular microfiltration system, and a heat exchanger before entering the dechlorination reactor. The dechlorination reactor is an upflow reactor with no catalyst bed, and the reaction pressure is atmospheric pressure with a liquid hourly space velocity of 0.7 h⁻¹. -1 Air was introduced, with a gas-liquid volume ratio of 4:1. A small amount of steam was added to maintain the system reaction temperature at 85°C. The effluent contained 1.22 wt% epichlorohydrin, 0.81 wt% dichloropropanol, and 41335 mg / L COD, showing no significant change. The sulfate concentration was 16 mg / L, the chloride concentration was 3493 mg / L, the wastewater salt content increased to 5881 mg / L, and the glycerol content increased to 0.65 wt%.

[0094] As can be seen from this comparative example, compared with Example 1, when the catalytic dechlorination was changed to a dechlorination reactor without a catalyst, the dechlorination rate was less than 20% as calculated, while the dechlorination rate of the catalytic dechlorination unit in Example 1 was greater than 98% as calculated.

Claims

1. A process for treating wastewater generated during the direct oxidation process for preparing epichlorohydrin, comprising 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 heat exchange unit, a catalytic dechlorination unit, and a neutralization unit. Wastewater is treated by the above units in sequence, and 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, an aerobic biochemical unit, 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 biochemical unit, and the methane gas generated by the anaerobic biochemical unit is stored in the methane storage unit. The effluent from the anaerobic biochemical unit, together with the electrodialysis concentrate, enters the aerobic biochemical unit. The effluent from the aerobic biochemical unit enters the ozone catalytic oxidation unit of the deep treatment section. The advanced treatment section includes an ozone catalytic oxidation unit and a BAF unit in sequence, and the effluent from the BAF unit meets the discharge standards. in, 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 modified anion exchange membrane is prepared by the following steps: Step a: Polyvinyl alcohol is added to water to prepare a polyvinyl alcohol aqueous solution. Then, a positively charged amine compound, β-cyclodextrin, and a crosslinking agent are added to the above solution respectively. An inorganic acid is added to adjust the pH. After mixing and stirring, a casting solution is obtained. The positively charged amine compound is selected from one or more of 2,3-epoxypropyltrimethylammonium chloride, polyethyleneimine, polyepoxychloropropaneamine, and quaternized chitosan. Step b: Cast the casting solution obtained in step a onto a horizontal panel, dry it, and obtain the base film; Step c: After washing the base membrane obtained in step b, place it in an alkaline solution for alkalization, and then soak it in water to obtain a polyvinyl alcohol anion exchange membrane; Step d: Dissolve dopamine in Tris-HCl buffer, adjust the pH with hydrochloric acid to obtain dopamine Tris buffer solution; Step e: Place the anion exchange membrane obtained in step c in a dopamine Tris buffer solution and add copper sulfate. Stir the reaction while maintaining air circulation. After the reaction is complete, the modified anion exchange membrane is obtained.

2. The process method according to claim 1, characterized in that, In the preparation of the modified anion exchange membrane, the mass ratio of the positively charged amine compound to polyvinyl alcohol is 0.1:1 to 0.6:1; the mass ratio of the β-cyclodextrin to polyvinyl alcohol is 0.02:1 to 0.2:1; the crosslinking agent is selected from aldehyde or acid crosslinking agents, and the mass ratio of the crosslinking agent to polyvinyl alcohol is 0.01:1 to 0.1:

1.

3. The process method according to claim 1, characterized in that, In the preparation of the modified anion exchange membrane, the inorganic acid in step a is sulfuric acid, hydrochloric acid or nitric acid, and the pH of the solution is adjusted to 4-6; the mass fraction of the polyvinyl alcohol aqueous solution is 5%-15%, and the reaction time with the positively charged amine compound, β-cyclodextrin and crosslinking agent is 4-16 h.

4. The process method according to claim 1, characterized in that, In the preparation of the modified anion exchange membrane, the drying in step b is to first dry at room temperature for 2-6 hours, and then continue drying under vacuum at 40-80°C for 4-10 hours; the washing in step c is to wash with water until neutral; the alkalization uses a 0.5-3 mol / L sodium hydroxide aqueous solution for 12-24 hours; and the soaking time is 12-24 hours.

5. The process method according to claim 1, characterized in that, In the preparation of the modified anion exchange membrane, the concentration of Tris–HCl buffer in step d is 10–50 mmol / L, the mass concentration of dopamine is 0.4–4 g / L, and the pH range of hydrochloric acid is adjusted to 8–9; the concentration of copper sulfate in step e is 1–20 mmol / L, and the stirring reaction time is 1–12 h.

6. The process method according to claim 1, characterized in that, After the modified anion exchange membrane is prepared, it is stored in a sodium chloride solution with a mass concentration of 5–20 g / L.

7. The process method according to claim 1, characterized in that, The COD of epichlorohydrin wastewater is 30,000–80,000 mg / L, pH is less than 5, and salt content is less than 4,000 mg / L.

8. The process method according to claim 1, characterized in that, The regulating unit adds sodium hydroxide to adjust the pH value to 10-12; the filter membrane of the tubular microfiltration unit has a pore size range of 0.1-1.0 micrometers; the heat exchange unit is used for temperature regulation of epichlorohydrin wastewater, and the wastewater temperature rises to 40-100℃ after heat exchange.

9. The process method according to claim 1, characterized in that, The catalytic dechlorination unit employs an upflow reactor with a catalyst bed inside the reactor shell. The reaction pressure is atmospheric pressure, and the liquid hourly space velocity (LHSV) is 0.2–2 h⁻¹. -1 Air is introduced, with a gas-liquid volume ratio of 1:1 to 10:1, and a small amount of steam is added to maintain the system reaction temperature at 40 to 100°C.

10. The process method according to claim 1, characterized in that, The catalyst loading volume to reactor volume ratio of the catalytic dechlorination unit is 0.6:1 to 1:

1. The catalyst is an organic porous copolymer solid catalyst containing an active metal and an additive. The active metal is selected from one or more of copper, iron, manganese, zinc, aluminum, vanadium, silver and cobalt. The additive is a compound that can form a quaternary phosphonium salt structure. The organic porous copolymer is a polystyrene polymer crosslinked with styrene and divinylbenzene.

11. The process method according to claim 10, characterized in that, The catalyst, by weight (100 wt%), comprises 0.1 wt% to 10 wt% of active metal, 30% to 70% of additives, and 20% to 60% of organic porous copolymer. The amount of divinylbenzene in the organic porous copolymer is 10% to 20% of the styrene mass. The organic porous copolymer also contains benzoyl peroxide as an initiator, with the amount of benzoyl peroxide being 0.5% to 5% of the styrene mass.

12. The process method according to claim 11, characterized in that, The catalyst is prepared by the following method: styrene, divinylbenzene, additives, and benzoyl peroxide are added to water for suspension polymerization at a reaction temperature of 50–90°C and a stirring reaction time of 0.5–10 h. Then, water is added to cool and shape the mixture, and it is dried and solidified below 100°C to obtain a granular solid material. This material is then added to a halide solution of an active metal and the active metal is loaded by impregnation. Finally, it is dried below 100°C to obtain the catalyst.

13. The process method according to claim 1, characterized in that, The neutralization unit adds hydrochloric acid to adjust the pH to 6-9; the electrodialysis unit has a treatment time of 0.1-2 hours and a current density of 1-80 mA / cm². 2 .

14. 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.

15. The process method according to claim 1, characterized in that, The aerobic biochemical unit uses salt-tolerant bacteria, and the process uses one of the following aerobic processes: BAF, MBR, contact oxidation tank, and MBBR, with a residence time of 12–96 h.

16. The process method according to claim 1, characterized in that, The ozone dosage of the ozone catalytic oxidation unit is 0.1 to 2 times the amount of oxidant required based on the COD value of the wastewater, and the reaction time is 10 to 120 minutes.

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