High-salinity wastewater freezing-crystallization coupled membrane desalination process
Patent Information
- Application Number
- CN202611305052.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-08-26
- Publication Date
- 2026-09-25
AI Technical Summary
[0004]本发明解决了现有的纳滤膜及其分离技术对高盐废水中硫酸盐和氯盐分离效果较差的问题
[0013]本发明有益的技术效果：利用1,4-二氯甲氧基丁烷对聚醚砜进行氯甲基化处理，经过相转化法成膜，得到聚砜膜，然后氯甲基与3,4-二氨基-3-环丁烯-1,2-二酮的一个氨基进行反应，得到方酰胺聚砜纳滤膜。纳滤膜表面含有的方酰胺结构具有两个N-H氢键供体，被刚性四元芳香环固定，四元环共轭吸电子，与四面体硫酸根负离子相匹配，形成强氢键作用，使聚醚砜纳滤膜对硫酸根负离子呈现选择性吸附作用，经冲洗硫酸根从纳滤膜中洗脱，实现氯化钠和硫酸钠的高效分离，可应用于高盐废水的分离处理中。
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Abstract
Description
Technical Field
[0001] This invention relates to the field of high-salinity wastewater treatment technology, specifically a high-salinity wastewater freeze-crystallization coupled membrane salt separation process. Background Technology
[0002] Zero discharge and resource utilization of high-salinity industrial wastewater have become essential needs for the industry. Currently, high-salinity wastewater generated during the production processes of industries such as coal chemical, fine chemical, and pharmaceutical generally has the characteristics of complex salt composition, large fluctuations in salt content, trace amounts of organic matter and heavy metals, and high water viscosity, making it extremely difficult to treat.
[0003] Nanofiltration membranes exhibit excellent retention of various metal ions, anions, proteins, and pesticides, and are widely used in water treatment, wastewater regeneration, industrial water pretreatment, and seawater desalination. Polyethersulfone (PES) nanofiltration membranes, in particular, are widely used due to their strong chemical resistance, good high-temperature resistance, and high retention and separation efficiency. However, PES nanofiltration membranes show poor selective separation of sodium chloride and sodium sulfate, which limits their practical application in high-salinity wastewater treatment. Summary of the Invention
[0004] This invention solves the problem that existing nanofiltration membranes and their separation technologies have poor separation effects on sulfates and chlorides in high-salt wastewater.
[0005] The technical solution of the present invention is a high-salt wastewater freeze crystallization coupled membrane desalination process, comprising a pretreatment system, a nanofiltration membrane desalination system, a freeze crystallization purification system, and a mother liquor recycling system.
[0006] Furthermore, the pretreatment system consists of the following steps: high-salt wastewater enters a homogenization and equalization tank to stabilize the salt concentration; then, through chemical softening, hardening and silica removal, and flocculation sedimentation processes, metal ions such as calcium and magnesium, suspended particulate matter, etc., are removed from the wastewater; the pretreated wastewater is then filtered through an ultrafiltration membrane to remove fine suspended solids and colloids, ensuring that the influent water quality meets the operating requirements of the nanofiltration membrane system, guaranteeing the stable and long-term operation of the membrane module, and obtaining pretreated wastewater.
[0007] Furthermore, the nanofiltration membrane salt separation system employs an anti-fouling nanofiltration membrane module to separate mixed salts in pretreated wastewater, retaining sulfate ions while allowing chloride ions to permeate. The nanofiltration membrane module is then rinsed to separate the wastewater into high-sulfate wastewater and sodium chloride wastewater. This achieves efficient separation of salt components, avoids the problem of mixed salt coexistence, lays the foundation for subsequent single-salt crystallization and purification, and significantly reduces the processing load and energy consumption of the subsequent crystallization system.
[0008] Furthermore, the antifouling nanofiltration membrane module includes a square amide polysulfone nanofiltration membrane, and the fabrication process of the square amide polysulfone nanofiltration membrane is as follows: (1) Add polyethersulfone to chloroform, stir to dissolve, add 1,4-dichloromethoxybutane and tin tetrachloride; the mass ratio of polyethersulfone, 1,4-dichloromethoxybutane and tin tetrachloride is 100:(110-160):(18-28); stir the reaction at room temperature for 3-4 hours, pour the solution into methanol for precipitation, filter, wash with water and methanol, dry to obtain chloromethyl polysulfone.
[0009] (2) Add chloromethyl polysulfone and polyvinylpyrrolidone in a mass ratio of 100:(20-28) to N,N-dimethylformamide, stir to dissolve, and obtain casting solution; use a film scraper to scrape the casting solution onto the surface of a clean glass plate, place at room temperature for 10-12 hours, then immerse in a deionized water coagulation bath to form a film, remove the film, dry, and obtain chloromethyl polysulfone film.
[0010] (3) Add chloromethyl polysulfone membrane, ethanol solution of 3,4-diaminocyclobut-3-ene-1,2-dione, and potassium carbonate to water in a mass ratio of 100:(18-30):(24-43), heat to 30-50℃, react for 12-18h, remove the membrane, wash with water and ethanol, and dry to obtain square amide polysulfone nanofiltration membrane.
[0011] Furthermore, the freeze crystallization refining system is as follows: high-sulfate wastewater enters the freeze crystallization system, is cooled by low-temperature refrigeration equipment to precipitate sulfate, and is separated by crystallization sedimentation and centrifugal separation equipment. After hot melting and recrystallization, purified sulfate is obtained. The mother liquor after centrifugation is returned to the pretreatment system at the front end for recycling treatment. Chloride wastewater is concentrated by high-pressure membrane and purified by low-temperature assisted crystallization to obtain purified chloride.
[0012] Furthermore, the mother liquor recycling system involves collecting and returning the mother liquor after centrifugal separation to the pretreatment system for recycling treatment, reducing wastewater discharge. The pure water generated during the treatment process meets the industrial production reuse standards and can be directly reused in production processes, equipment cooling, plant area spraying, and other scenarios.
[0013] The beneficial technical effects of this invention are as follows: Polyethersulfone is chloromethylated using 1,4-dichloromethoxybutane, followed by phase inversion to form a polysulfone membrane. Then, the chloromethyl group reacts with one amino group of 3,4-diamino-3-cyclobutene-1,2-dione to obtain a square amide polysulfone nanofiltration membrane. The square amide structure on the nanofiltration membrane surface has two NH hydrogen bond donors, fixed by a rigid four-membered aromatic ring. The four-membered ring conjugately withdraws electrons, matching the tetrahedral sulfate anion to form strong hydrogen bonds. This allows the polyethersulfone nanofiltration membrane to selectively adsorb sulfate anions. After rinsing, sulfate ions are eluted from the nanofiltration membrane, achieving efficient separation of sodium chloride and sodium sulfate. This method can be applied to the separation and treatment of high-salinity wastewater. Detailed Implementation
[0014] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0015] 2.64 g of diethyl squaric acid (CAS No. 5231-87-8) was added to 50 mL of diethyl ether, followed by the dropwise addition of 20 mL of concentrated ammonia. The mixture was stirred at room temperature for 10 h. After filtration, the solid was slowly washed with methanol and dried to obtain 3,4-diamino-3-cyclobutene-1,2-dione with the structural formula [structural formula would be inserted here]. .
[0016] The following polyethersulfone (PES) models are from BASF (PES Ultrason E 2010 MR SW 10111) and Ningbo Rongsu New Materials. Polyvinylpyrrolidone (PVP), CAS No. 9003-39-8, is from Shanghai Hongzhuang Chemical Technology.
[0017] Example 1: A high-salt wastewater cryogenic crystallization coupled membrane desalination process, including a pretreatment system, a nanofiltration membrane desalination system, a cryogenic crystallization purification system, and a mother liquor recycling system.
[0018] The pretreatment system consists of: high-salt wastewater entering a homogenization and equalization tank to stabilize the salt concentration; then, through chemical softening, hardening and silicon removal, and flocculation sedimentation processes, metal ions such as calcium and magnesium, suspended particulate matter, etc., are removed from the wastewater; the pretreated wastewater is then filtered through an ultrafiltration membrane to remove fine suspended solids and colloids, resulting in pretreated wastewater.
[0019] The nanofiltration membrane salt separation system uses an anti-fouling nanofiltration membrane module to separate mixed salts in pretreated wastewater, retain sulfate ions, allow chloride ions to pass through, and rinse the nanofiltration membrane module to separate the wastewater into high-sodium sulfate wastewater and sodium chloride wastewater.
[0020] The antifouling nanofiltration membrane module includes a square amide polysulfone nanofiltration membrane, and the fabrication process of the square amide polysulfone nanofiltration membrane is as follows: (1) Add 100 parts by weight of polyethersulfone to 750 parts by weight of chloroform, stir to dissolve, add 110 parts by weight of 1,4-dichloromethoxybutane and 18 parts by weight of tin tetrachloride, stir to react at room temperature for 3 hours, pour the solution into methanol for precipitation, filter, wash with water and methanol, dry to obtain chloromethyl polysulfone.
[0021] (2) Add 100 parts by weight of chloromethyl polysulfone and 25 parts by weight of polyvinylpyrrolidone to 600 parts by weight of N,N-dimethylformamide, stir and dissolve to obtain casting solution; use a film scraper to scrape the casting solution onto the surface of a clean glass plate, place at room temperature for 12 hours, then immerse in a deionized water coagulation bath to form a film, remove the film, dry it, and obtain chloromethyl polysulfone film.
[0022] (3) Add 100 parts by weight of chloromethyl polysulfone membrane, 18 parts by weight of ethanol solution of 3,4-diaminocyclobut-3-ene-1,2-dione (mass fraction 6%), and 24 parts by weight of potassium carbonate to 2000 parts by weight of water, heat to 40°C, impregnate and react for 12 hours, remove the membrane, wash with water and ethanol, and dry to obtain square amide polysulfone nanofiltration membrane.
[0023] The freeze crystallization refining system works as follows: high-sodium sulfate wastewater enters the freeze crystallization system, is cooled by low-temperature refrigeration equipment to precipitate sodium sulfate, and is separated by crystallization sedimentation and centrifugal separation equipment. After hot melting and recrystallization, purified sodium sulfate is obtained. The mother liquor after centrifugation is returned to the pretreatment system at the front end for recycling. Sodium chloride wastewater is concentrated by high-pressure membrane and purified by low-temperature assisted crystallization to obtain purified sodium chloride.
[0024] The mother liquor recycling system involves collecting and returning the mother liquor after centrifugation to the pretreatment system for recycling, thereby reducing the amount of wastewater discharged.
[0025] Example 2: A high-salt wastewater cryogenic crystallization coupled membrane desalination process, including a pretreatment system, a nanofiltration membrane desalination system, a cryogenic crystallization purification system, and a mother liquor recycling system.
[0026] The pretreatment system consists of: high-salt wastewater entering a homogenization and equalization tank to stabilize the salt concentration; then, through chemical softening, hardening and silicon removal, and flocculation sedimentation processes, metal ions such as calcium and magnesium, suspended particulate matter, etc., are removed from the wastewater; the pretreated wastewater is then filtered through an ultrafiltration membrane to remove fine suspended solids and colloids, resulting in pretreated wastewater.
[0027] The nanofiltration membrane salt separation system uses an anti-fouling nanofiltration membrane module to separate mixed salts in pretreated wastewater, retain sulfate ions, allow chloride ions to pass through, and rinse the nanofiltration membrane module to separate the wastewater into high-sodium sulfate wastewater and sodium chloride wastewater.
[0028] The antifouling nanofiltration membrane module includes a square amide polysulfone nanofiltration membrane, and the fabrication process of the square amide polysulfone nanofiltration membrane is as follows: (1) Add 100 parts by weight of polyethersulfone to 800 parts by weight of chloroform, stir to dissolve, add 140 parts by weight of 1,4-dichloromethoxybutane and 24 parts by weight of tin tetrachloride, stir to react at room temperature for 4 hours, pour the solution into methanol for precipitation, filter, wash with water and methanol, dry to obtain chloromethyl polysulfone.
[0029] (2) Add 100 parts by weight of chloromethyl polysulfone and 28 parts by weight of polyvinylpyrrolidone to 600 parts by weight of N,N-dimethylformamide, stir and dissolve to obtain casting solution; use a film scraper to scrape the casting solution onto the surface of a clean glass plate, place at room temperature for 12 hours, then immerse in a deionized water coagulation bath to form a film, remove the film, dry it, and obtain chloromethyl polysulfone film.
[0030] (3) Add 100 parts by weight of chloromethyl polysulfone membrane, 25 parts by weight of ethanol solution of 3,4-diaminocyclobut-3-ene-1,2-dione (mass fraction 6%), and 32 parts by weight of potassium carbonate to 2000 parts by weight of water, heat to 50°C, impregnate and react for 12 hours, remove the membrane, wash with water and ethanol, and dry to obtain square amide polysulfone nanofiltration membrane.
[0031] The freeze crystallization refining system works as follows: high-sodium sulfate wastewater enters the freeze crystallization system, is cooled by low-temperature refrigeration equipment to precipitate sodium sulfate, and is separated by crystallization sedimentation and centrifugal separation equipment. After hot melting and recrystallization, purified sodium sulfate is obtained. The mother liquor after centrifugation is returned to the pretreatment system at the front end for recycling. Sodium chloride wastewater is concentrated by high-pressure membrane and purified by low-temperature assisted crystallization to obtain purified sodium chloride.
[0032] The mother liquor recycling system involves collecting and returning the mother liquor after centrifugation to the pretreatment system for recycling, thereby reducing the amount of wastewater discharged.
[0033] Example 3: A high-salt wastewater cryogenic crystallization coupled membrane desalination process, including a pretreatment system, a nanofiltration membrane desalination system, a cryogenic crystallization purification system, and a mother liquor recycling system.
[0034] The pretreatment system consists of: high-salt wastewater entering a homogenization and equalization tank to stabilize the salt concentration; then, through chemical softening, hardening and silicon removal, and flocculation sedimentation processes, metal ions such as calcium and magnesium, suspended particulate matter, etc., are removed from the wastewater; the pretreated wastewater is then filtered through an ultrafiltration membrane to remove fine suspended solids and colloids, resulting in pretreated wastewater.
[0035] The nanofiltration membrane salt separation system uses an anti-fouling nanofiltration membrane module to separate mixed salts in pretreated wastewater, retain sulfate ions, allow chloride ions to pass through, and rinse the nanofiltration membrane module to separate the wastewater into high-sodium sulfate wastewater and sodium chloride wastewater.
[0036] The antifouling nanofiltration membrane module includes a square amide polysulfone nanofiltration membrane, and the fabrication process of the square amide polysulfone nanofiltration membrane is as follows: (1) Add 100 parts by weight of polyethersulfone to 800 parts by weight of chloroform, stir to dissolve, add 160 parts by weight of 1,4-dichloromethoxybutane and 28 parts by weight of tin tetrachloride, stir to react at room temperature for 4 hours, pour the solution into methanol for precipitation, filter, wash with water and methanol, dry to obtain chloromethyl polysulfone.
[0037] (2) Add 100 parts by weight of chloromethyl polysulfone and 20 parts by weight of polyvinylpyrrolidone to 650 parts by weight of N,N-dimethylformamide, stir and dissolve to obtain casting solution; use a film scraper to scrape the casting solution onto the surface of a clean glass plate, place at room temperature for 12 hours, then immerse in a deionized water coagulation bath to form a film, remove the film, dry it, and obtain chloromethyl polysulfone film.
[0038] (3) Add 100 parts by weight of chloromethyl polysulfone membrane, 30 parts by weight of ethanol solution of 3,4-diaminocyclobut-3-ene-1,2-dione (mass fraction 6%), and 43 parts by weight of potassium carbonate to 2200 parts by weight of water, immerse in water at 30°C for 18 hours, remove the membrane, wash with water and ethanol, and dry to obtain square amide polysulfone nanofiltration membrane.
[0039] The freeze crystallization refining system works as follows: high-sodium sulfate wastewater enters the freeze crystallization system, is cooled by low-temperature refrigeration equipment to precipitate sodium sulfate, and is separated by crystallization sedimentation and centrifugal separation equipment. After hot melting and recrystallization, purified sodium sulfate is obtained. The mother liquor after centrifugation is returned to the pretreatment system at the front end for recycling. Sodium chloride wastewater is concentrated by high-pressure membrane and purified by low-temperature assisted crystallization to obtain purified sodium chloride.
[0040] The mother liquor recycling system involves collecting and returning the mother liquor after centrifugation to the pretreatment system for recycling, thereby reducing the amount of wastewater discharged.
[0041] Comparative Example 1 differs from Example 1 in that polyethersulfone is used instead of chloromethyl polysulfone, and 3,4-diaminocyclobut-3-ene-1,2-dione is not added.
[0042] A high-salt wastewater cryogenic crystallization coupled membrane desalination process includes a pretreatment system, a nanofiltration membrane desalination system, a cryogenic crystallization purification system, and a mother liquor recycling system.
[0043] The pretreatment system consists of: high-salt wastewater entering a homogenization and equalization tank to stabilize the salt concentration; then, through chemical softening, hardening and silicon removal, and flocculation sedimentation processes, metal ions such as calcium and magnesium, suspended particulate matter, etc., are removed from the wastewater; the pretreated wastewater is then filtered through an ultrafiltration membrane to remove fine suspended solids and colloids, resulting in pretreated wastewater.
[0044] The nanofiltration membrane salt separation system uses an antifouling nanofiltration membrane module to separate the mixed salts in the pretreated wastewater. The nanofiltration membrane module is then rinsed to separate the wastewater into sodium sulfate wastewater and sodium chloride wastewater.
[0045] The nanofiltration membrane module includes a polysulfone membrane. The preparation process of the polysulfone membrane is as follows: 100 parts by weight of polyethersulfone and 25 parts by weight of polyvinylpyrrolidone are added to 600 parts by weight of N,N-dimethylformamide and stirred to dissolve, so as to obtain a casting solution; the casting solution is scraped onto the surface of a clean glass plate using a membrane scraper, placed at room temperature for 12 hours, and then immersed in a deionized water coagulation bath to form a membrane. The membrane is then removed, dried, and the polysulfone nanofiltration membrane is obtained.
[0046] The freeze crystallization refining system works as follows: Sodium sulfate wastewater enters the freeze crystallization system, is cooled by low-temperature refrigeration equipment, and solids precipitate out. The solids are then separated by crystallization sedimentation and centrifugal separation equipment. Sodium sulfate is obtained through hot melting and recrystallization. The mother liquor after centrifugation is returned to the pretreatment system at the front end for recycling. Sodium chloride wastewater is concentrated by high-pressure membrane and purified by low-temperature assisted crystallization to obtain solids.
[0047] The mother liquor recycling system involves collecting and returning the mother liquor after centrifugation to the pretreatment system for recycling, thereby reducing the amount of wastewater discharged.
[0048] Comparative Example 2 differs from Example 1 in that polyethersulfone is used instead of chloromethyl polyethersulfone.
[0049] A high-salt wastewater cryogenic crystallization coupled membrane desalination process includes a pretreatment system, a nanofiltration membrane desalination system, a cryogenic crystallization purification system, and a mother liquor recycling system.
[0050] The pretreatment system consists of: high-salt wastewater entering a homogenization and equalization tank to stabilize the salt concentration; then, through chemical softening, hardening and silicon removal, and flocculation sedimentation processes, metal ions such as calcium and magnesium, suspended particulate matter, etc., are removed from the wastewater; the pretreated wastewater is then filtered through an ultrafiltration membrane to remove fine suspended solids and colloids, resulting in pretreated wastewater.
[0051] The nanofiltration membrane salt separation system uses an antifouling nanofiltration membrane module to separate the mixed salts in the pretreated wastewater. The nanofiltration membrane module is then rinsed to separate the wastewater into sodium sulfate wastewater and sodium chloride wastewater.
[0052] The antifouling nanofiltration membrane module includes a polysulfone nanofiltration membrane, and the fabrication process of the polysulfone nanofiltration membrane is as follows: (1) Add 100 parts by weight of polysulfone and 25 parts by weight of polyvinylpyrrolidone to 600 parts by weight of N,N-dimethylformamide, stir and dissolve to obtain casting solution; use a film scraper to scrape the casting solution onto the surface of a clean glass plate, place at room temperature for 12 hours, then immerse in a deionized water coagulation bath to form a film, remove the film, dry it, and obtain a polysulfone film.
[0053] (2) Add 100 parts by weight of polysulfone membrane, 18 parts by weight of ethanol solution of 3,4-diaminocyclobut-3-ene-1,2-dione (mass fraction 6%), and 24 parts by weight of potassium carbonate to 2000 parts by weight of water, heat to 40°C, immerse and keep warm for 12 hours, remove the membrane, wash with water and ethanol, and dry to obtain polysulfone nanofiltration membrane.
[0054] The cryogenic crystallization refining system works as follows: Sodium sulfate wastewater enters the cryogenic crystallization system, is cooled by low-temperature refrigeration equipment to precipitate solids, and is separated by crystallization sedimentation and centrifugal separation equipment. After hot melting and recrystallization, solid matter is obtained. The mother liquor after centrifugation is returned to the pretreatment system at the front end for recycling treatment. Sodium chloride wastewater is concentrated by high-pressure membrane and purified by low-temperature assisted crystallization to obtain solid matter.
[0055] The mother liquor recycling system involves collecting and returning the mother liquor after centrifugation to the pretreatment system for recycling, thereby reducing the amount of wastewater discharged.
[0056] Comparative Example 3 differs from Example 1 in that ethylenediamine is used instead of 3,4-diaminocyclobut-3-ene-1,2-dione.
[0057] A high-salt wastewater cryogenic crystallization coupled membrane desalination process includes a pretreatment system, a nanofiltration membrane desalination system, a cryogenic crystallization purification system, and a mother liquor recycling system.
[0058] The pretreatment system consists of: high-salt wastewater entering a homogenization and equalization tank to stabilize the salt concentration; then, through chemical softening, hardening and silicon removal, and flocculation sedimentation processes, metal ions such as calcium and magnesium, suspended particulate matter, etc., are removed from the wastewater; the pretreated wastewater is then filtered through an ultrafiltration membrane to remove fine suspended solids and colloids, resulting in pretreated wastewater.
[0059] The nanofiltration membrane salt separation system uses an antifouling nanofiltration membrane module to separate the mixed salts in the pretreated wastewater. The nanofiltration membrane module is then rinsed to separate the wastewater into sodium sulfate wastewater and sodium chloride wastewater.
[0060] The antifouling nanofiltration membrane module includes a polysulfone nanofiltration membrane, and the fabrication process of the polysulfone nanofiltration membrane is as follows: (1) Add 100 parts by weight of polyethersulfone to 750 parts by weight of chloroform, stir to dissolve, add 110 parts by weight of 1,4-dichloromethoxybutane and 18 parts by weight of tin tetrachloride, stir to react at room temperature for 3 hours, pour the solution into methanol for precipitation, filter, wash with water and methanol, dry to obtain chloromethyl polysulfone.
[0061] (2) Add 100 parts by weight of chloromethyl polysulfone and 25 parts by weight of polyvinylpyrrolidone to 600 parts by weight of N,N-dimethylformamide, stir and dissolve to obtain casting solution; use a film scraper to scrape the casting solution onto the surface of a clean glass plate, place at room temperature for 12 hours, then immerse in a deionized water coagulation bath to form a film, remove the film, dry it, and obtain chloromethyl polysulfone film.
[0062] (3) Add 100 parts by weight of chloromethyl polysulfone membrane, 18 parts by weight of ethanol solution of ethylenediamine (mass fraction 6%), and 24 parts by weight of potassium carbonate to 2000 parts by weight of water, heat to 40°C, impregnate for 12 hours, remove the membrane, wash with water and ethanol, and dry to obtain polysulfone nanofiltration membrane.
[0063] The freeze crystallization refining system works as follows: Sodium sulfate wastewater enters the freeze crystallization system, is cooled by low-temperature refrigeration equipment to precipitate solids, and is separated by crystallization sedimentation and centrifugal separation equipment. After hot melting and recrystallization, solids are obtained. The mother liquor after centrifugation is returned to the pretreatment system at the front end for recycling. Sodium chloride wastewater is concentrated by high-pressure membrane and purified by low-temperature assisted crystallization to obtain solids.
[0064] The mother liquor recycling system involves collecting and returning the mother liquor after centrifugation to the pretreatment system for recycling, thereby reducing the amount of wastewater discharged.
[0065] Wastewater separation simulation experiment: 1g of sodium chloride and 1g of sodium sulfate were added to 1L of distilled water to prepare simulated wastewater. The simulated wastewater was filtered and separated using a polysulfone nanofiltration membrane, and the filtrate was collected. Then, the polysulfone nanofiltration membrane was rinsed with 1L of deionized water, and the rinsing solution was collected. The concentrations of chloride and sulfate ions in the filtrate were determined by ion chromatography and converted to the concentrations of sodium chloride and sodium sulfate. The concentrations of chloride and sulfate ions in the rinsing solution were also determined by ion chromatography and converted to the concentrations of sodium chloride and sodium sulfate.
[0066] Table 1
[0067] After testing, compared with Comparative Example 1, the polyethersulfone nanofiltration membranes prepared in each embodiment separated aqueous solutions containing sodium chloride and sodium sulfate, selectively adsorbed sulfate ions, and efficiently permeated chloride ions. This was mainly because the nanofiltration membrane surface contained a square amide structure ( Two NH hydrogen bond donors are fixed by a rigid four-membered aromatic ring. The four-membered ring conjugate electron-withdrawing function matches the tetrahedral sulfate anion, forming a strong hydrogen bond. This enables the polyethersulfone nanofiltration membrane to selectively adsorb sulfate anions. After rinsing, sulfate ions are eluted from the nanofiltration membrane, achieving efficient separation of sodium chloride and sodium sulfate.
[0068] The polysulfone membrane in Comparative Example 2 does not contain chloromethyl groups and cannot react with the amino groups of 3,4-diaminocyclobut-3-ene-1,2-dione. It does not introduce a square amide structure on the surface of the polyethersulfone nanofiltration membrane and does not have selective adsorption for sulfate anions, making it difficult to separate sodium chloride and sodium sulfate.
[0069] Comparative Example 3 utilizes the reaction of chloromethyl polyethersulfone with ethylenediamine. However, it does not introduce a square amide structure onto the surface of the polyethersulfone nanofiltration membrane, thus lacking selective adsorption of sulfate anions and failing to effectively separate sodium chloride and sodium sulfate.
Claims
1. A high-salinity wastewater cryogenic crystallization coupled membrane separation process, characterized in that, The high-salt wastewater freeze crystallization coupled membrane desalination process includes a pretreatment system, a nanofiltration membrane desalination system, a freeze crystallization purification system, and a mother liquor recycling system. The nanofiltration membrane salt separation system includes an antifouling nanofiltration membrane module containing a squaramide polyethersulfone nanofiltration membrane.
2. The high-salinity wastewater freeze-crystallization coupled membrane salt separation process according to claim 1, characterized in that, The pretreatment system consists of: high-salt wastewater entering a homogenization and equalization tank to stabilize the salt concentration; then, through chemical softening, hardening and silica removal, and flocculation sedimentation processes, the pretreated wastewater is filtered through an ultrafiltration membrane to remove fine suspended solids and colloids, thus obtaining pretreated wastewater.
3. The high-salinity wastewater freeze-crystallization coupled membrane salt separation process according to claim 1, characterized in that, The nanofiltration membrane salt separation system employs an anti-fouling nanofiltration membrane module to separate mixed salts in pretreated wastewater, retain sulfate ions, allow chloride ions to pass through, and rinse the nanofiltration membrane module to separate the wastewater into high-sulfate wastewater and sodium chloride wastewater.
4. The high-salinity wastewater freeze-crystallization coupled membrane salt separation process according to claim 1, characterized in that, The freeze crystallization refining system is as follows: high-sulfate wastewater enters the freeze crystallization system, is cooled by low-temperature refrigeration equipment to precipitate sulfate, and is separated by crystallization sedimentation and centrifugal separation equipment. After hot melting and recrystallization, purified sulfate is obtained. The mother liquor after centrifugation is returned to the pretreatment system at the front end for recycling. Chloride wastewater is concentrated by high-pressure membrane and then purified by low-temperature assisted crystallization to obtain purified chloride.
5. The high-salinity wastewater freeze-crystallization coupled membrane salt separation process according to claim 1, characterized in that, The mother liquor recycling system is as follows: the mother liquor after centrifugation is collected and returned to the pretreatment system for recycling treatment, thereby reducing the discharge of wastewater.
6. The high-salinity wastewater freeze-crystallization coupled membrane salt separation process according to claim 1, characterized in that, The antifouling nanofiltration membrane module includes a square amide polysulfone nanofiltration membrane, and the preparation process of the square amide polysulfone nanofiltration membrane is as follows: (1) Add polyethersulfone to chloroform, stir to dissolve, add 1,4-dichloromethoxybutane and tin tetrachloride, stir to react at room temperature for 3-4 h, pour the solution into methanol to precipitate, filter, wash and dry to obtain chloromethyl polysulfone; (2) Add chloromethyl polysulfone and polyvinylpyrrolidone to N,N-dimethylformamide, stir to dissolve, and obtain casting solution; use a film scraper to scrape the casting solution onto the surface of a clean glass plate, place at room temperature for 10-12 hours, then immerse in a deionized water coagulation bath to form a film, remove the film, dry, and obtain chloromethyl polysulfone film. (3) Add chloromethyl polysulfone membrane, ethanol solution of 3,4-diaminocyclobut-3-ene-1,2-dione and potassium carbonate to water, heat to 30-50℃, impregnate for 12-18h, remove the membrane, wash and dry to obtain square amide polysulfone nanofiltration membrane.
7. The high-salinity wastewater freeze-crystallization coupled membrane salt separation process according to claim 6, characterized in that, The mass ratio of polyethersulfone, 1,4-dichloromethoxybutane and tin tetrachloride in (1) is 100:(110-160):(18-28).
8. The high-salinity wastewater cryogenic crystallization coupled membrane salt separation process according to claim 6, characterized in that, In (2), the mass ratio of chloromethyl polysulfone to polyvinylpyrrolidone is 100:(20-28).
9. The high-salinity wastewater cryogenic crystallization coupled membrane salt separation process according to claim 6, characterized in that, The mass ratio of chloromethyl polysulfone membrane, 3,4-diaminocyclobut-3-ene-1,2-dione and inorganic alkali compound in (3) is 100:(18-30):(24-43).