Composite porous insulating material in water treatment and application thereof

Abstract

The present application relates to the technical field of water treatment, in particular to a kind of composite porous insulating material and its application in water treatment.The composite porous insulating material includes first functional layer, intermediate migration barrier layer and second functional layer;The raw materials of first functional layer include hydrophilic polymer, inorganic particles and pore-forming agent;The raw materials of intermediate migration barrier layer include hydrophobic polymer, hydrophobic inorganic filler and pore-forming agent;The raw materials of second functional layer include acid-resistant antioxidant polymer and oxidation-resistant inorganic particles.The preparation method includes preparing intermediate migration barrier layer, forming first functional layer and second functional layer on both sides respectively, and forming by hot-pressing composite molding.The material can be arranged between electrolytic water cathode and electrolytic water anode, used for electrochemical treatment of circulating water hardness removal, high-sulfate industrial water, fluorine-containing wastewater or phosphorus-containing wastewater, can regulate and control the nucleation of surface layer of scale-forming components, inhibit ion translayer migration and improve anode side durability.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, specifically to a composite porous insulating material used in water treatment and its application. Background Technology

[0002] Industrial circulating water, cooling water, mining wastewater, metallurgical wastewater, coal chemical wastewater, and some high-salinity wastewater typically contain high concentrations of calcium ions, magnesium ions, bicarbonate ions, sulfate ions, chloride ions, fluoride ions, or phosphate ions. During water concentration and circulation or electrochemical treatment, calcium and magnesium ions readily combine with carbonate ions, hydroxide ions, sulfate ions, fluoride ions, or phosphate ions to form insoluble deposits, leading to scaling on the surfaces of pipes, heat exchangers, electrodes, and insulating materials. Scale formation not only reduces heat exchange efficiency and increases flow resistance but also leads to increased tank pressure, energy consumption, and maintenance frequency in electrochemical water treatment devices.

[0003] Electrochemical water treatment technology generates hydroxide ions at the cathode, causing scale-forming ions such as calcium and magnesium ions to precipitate in a locally alkaline environment, thereby achieving hardness removal or inducing crystallization. Simultaneously, an acidic environment is generated at the anode, forming active chlorine substances in chlorinated water, achieving sterilization, algae suppression, or partial conversion of chlorine-containing components. To reduce ion crosstalk between the anode and cathode, some electrochemical water treatment devices incorporate an isolation layer or porous packing layer between the cathode and anode.

[0004] In existing electrochemical water treatment devices, an isolation layer, a packing layer, or a porous isolation material is typically placed between the cathode and anode to reduce the direct mixing of anode and cathode reaction products and, to some extent, improve energy consumption and ion utilization efficiency during the electrochemical treatment process. These porous isolation materials typically focus on basic properties such as porosity, thickness, pore size, hydrophobicity, or insulation; however, most still employ homogeneous or simple composite structures, making it difficult to differentiate their design for the different chemical environments of the cathode side, the material's interior, and the anode side.

[0005] However, during long-term operation, ordinary homogeneous porous insulating materials still have the following problems: First, the pore area near the cathode side is prone to disordered blockage by deposits such as calcium carbonate, magnesium hydroxide, calcium sulfate, calcium fluoride, or calcium phosphate, leading to a gradual increase in material pressure differential; Second, although ordinary hydrophobic porous layers can inhibit the migration of water and ions, their cathode-side surface lacks control over the nucleation sites of scale-forming ions, and deposits may enter the internal pores of the material instead of remaining in the easily eroded surface area; Third, during long-term operation on the anode side in acidic, oxygen-evolving, and active chlorine environments, ordinary polymer porous layers are prone to surface oxidation, embrittlement, or pore size changes, resulting in a decrease in migration resistance; Fourth, ordinary single-layer materials cannot simultaneously meet the multiple requirements of cathode-side induced crystallization, ion barrier in the intermediate region, and acid and oxidation resistance on the anode side.

[0006] Therefore, it is necessary to provide a new composite porous insulating material that can not only maintain the blocking effect of the intermediate region on ion migration during electrochemical water treatment, but also induce scale-forming ions to nucleate in a directional manner on the cathode side and resist acidic and active chlorine environments on the anode side, thereby improving the long-term operational stability of the material and reducing the rate of increase in tank pressure and the rate of increase in differential pressure. Summary of the Invention

[0007] The purpose of this invention is to provide a composite porous insulating material for water treatment and its application.

[0008] The technical solution of the present invention is as follows: In a first aspect, a composite porous insulating material for water treatment is provided, the composite porous insulating material comprising a first functional layer, an intermediate migration barrier layer, and a second functional layer; the raw materials of the first functional layer include a hydrophilic polymer, inorganic particles, and a pore-forming agent; the raw materials of the intermediate migration barrier layer include a hydrophobic polymer, a hydrophobic inorganic filler, and a pore-forming agent; and the raw materials of the second functional layer include an acid-resistant and antioxidant polymer and an antioxidant inorganic particle.

[0009] Preferably, the composite porous insulating material comprises a first functional layer, an intermediate migration barrier layer, and a second functional layer sequentially laminated along the thickness direction.

[0010] Furthermore, the hydrophilic polymer includes one or more of polyamide, polyethersulfone, polyvinyl alcohol, polyvinyl acetal, hydrophilic modified polyvinylidene fluoride, and hydrophilic modified polyurethane.

[0011] Furthermore, the inorganic particles include one or more of silicon dioxide, aluminum oxide, calcium carbonate, hydroxyapatite, calcium sulfate, and calcium phosphate.

[0012] Furthermore, the pore-forming agent includes one or more of polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol, lithium chloride, sodium chloride, and sodium bicarbonate.

[0013] Furthermore, the hydrophobic polymer includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, polypropylene, polyethylene, polyphenylene sulfide, polyimide, and polybenzimidazole.

[0014] Furthermore, the hydrophobic inorganic filler includes one or more of the following: hydrophobic silica, boron nitride, silicon carbide, zirconium oxide, fluorosilane-modified alumina, and fluorosilane-modified silica.

[0015] Furthermore, the acid-resistant and antioxidant polymer includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, fluorosilicone resin, polyphenylene sulfide, and polyimide.

[0016] Furthermore, the oxidation-resistant inorganic particles include one or more of zirconium oxide, silicon dioxide, aluminum oxide, silicon carbide, and silicon nitride.

[0017] Secondly, a method for preparing the composite porous insulating material for water treatment includes the following steps: A hydrophobic polymer, a hydrophobic inorganic filler, a pore-forming agent and a solvent are mixed to form an intermediate layer casting solution. After the intermediate layer casting solution is formed into a film, phase transformation or thermally induced phase separation is performed to form pores, thereby obtaining an intermediate migration barrier layer. A hydrophilic polymer, inorganic particles, a pore-forming agent, and a solvent are mixed to form a first coating liquid. This first coating liquid is then applied to the first surface of the intermediate migration barrier layer. After pre-drying, solidification to form pores, washing, and drying, a first functional layer is formed. The solvent comprises… Acid-resistant and antioxidant polymer, antioxidant inorganic particles and solvent are mixed to form a second coating liquid. The second coating liquid is coated on the second surface of the intermediate migration barrier layer. After pre-drying and curing, a second functional layer is formed to obtain a layered material. The layered material is hot-pressed to obtain the composite porous insulating material.

[0018] Preferably, the solvent includes one or more of formic acid, N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide.

[0019] Thirdly, the application of a composite porous insulating material in water treatment, wherein the composite porous insulating material is used in an electrochemical water treatment system and is disposed between the electrolytic water cathode and the electrolytic water anode; The first functional layer faces the electrolytic water cathode, and the second functional layer faces the electrolytic water anode; The electrochemical water treatment includes at least one of the following: circulating water hardening treatment, chlorine-containing water electrochemical treatment, high sulfate industrial water crystallization treatment, fluoride-containing wastewater treatment, and phosphorus-containing wastewater treatment.

[0020] It is worth noting that during electrochemical water treatment, hydroxide ions are generated near the cathode of the electrolyzed water, making the local water on the cathode side alkaline. Scale-forming components such as calcium and magnesium ions in the water readily combine with carbonate, hydroxide, sulfate, fluoride, or phosphate ions to form deposits in an alkaline environment. If ordinary porous materials are used, these deposits may randomly adhere to the material surface or enter the internal pores, leading to pore blockage and increased pressure differential. The first functional layer of this invention has a hydrophilic porous structure and contains inorganic particles such as silica, alumina, calcium carbonate, hydroxyapatite, calcium sulfate, or calcium phosphate. These inorganic particles provide solid surfaces and nucleation sites, allowing scale-forming components to preferentially undergo heterogeneous nucleation on the surface or pore area of ​​the first functional layer near the cathode side. Since the crystals are mainly concentrated in the surface or shallow layer, they are more easily detached by water flow shear or backwashing, reducing the risk of deep blockage.

[0021] Meanwhile, the intermediate migration-resistant layer employs a hydrophobic polymer and hydrophobic inorganic filler to form a hydrophobic porous insulating structure, the internal material of which itself does not contain exchangeable ions. This structure, on the one hand, does not provide fixed ion conduction channels similar to ion exchange membranes; on the other hand, it reduces the continuity of the aqueous phase through hydrophobic pore walls, small pore size, and high pore tortuosity, thus inhibiting the migration of hydroxide and hydrogen ions in the thickness direction. Therefore, hydroxide ions generated on the cathode side are less likely to quickly penetrate the material to the anode side to neutralize hydrogen ions, but instead participate more in the precipitation reaction of scale-forming components on the cathode side; hydrogen ions generated on the anode side are also less likely to quickly migrate to the cathode side, weakening local alkalinity. This migration-resistant effect improves the precipitation reaction efficiency on the cathode side and reduces energy loss due to ion crosstalk.

[0022] Furthermore, an acidic environment may form on the anode side during electrochemical water treatment, generating chlorine gas, hypochlorous acid, or other reactive chlorine substances in chlorinated water. If the intermediate migration barrier layer is directly exposed to this environment, the material surface is prone to oxidation, roughening, decreased hydrophobicity, and pore size changes. This invention addresses this by incorporating a second functional layer, allowing acid-resistant and antioxidant polymers and oxidation-resistant inorganic particles to preferentially contact the anode-side reaction environment, thereby forming a protective interface. This protective interface mitigates the erosion of the intermediate migration barrier layer by acids and reactive chlorine, maintaining the stability of the material's pore structure and wettability.

[0023] Therefore, this invention does not improve performance through the replacement of a single material, but rather through the spatial functional division of the first functional layer, the intermediate migration-resistant layer, and the second functional layer, thereby regulating the deposition location of scale-forming components, the migration paths of hydroxide and hydrogen ions, and the anodic oxidation and erosion paths. This multi-layer synergistic effect enables the composite porous insulating material to exhibit high scale-forming component removal efficiency, low tank pressure rise rate, low differential pressure rise rate, and good long-term stability during electrochemical water treatment.

[0024] The beneficial effects of this invention are: First, the composite porous insulating material of this invention adopts an asymmetric layered structure in which a first functional layer, an intermediate migration-resistant layer, and a second functional layer are sequentially composited along the thickness direction. This allows different sides of the material to adapt to the different reaction environments of the cathode and anode sides during electrochemical water treatment. The first functional layer faces the electrolytic cathode and mainly undertakes the functions of water contact, nucleation of scale-forming components, and sediment bearing. The intermediate migration-resistant layer is located inside the material and mainly undertakes the function of inhibiting the translayer migration of hydroxide and hydrogen ions. The second functional layer faces the electrolytic anode and mainly undertakes the functions of acid resistance, oxidation resistance, and resistance to active chlorine corrosion. Thus, this invention adopts a zoned design to meet the functional requirements of different thickness positions during electrochemical water treatment, thereby improving the overall operational stability of the material.

[0025] Second, the first functional layer comprises hydrophilic polymers and inorganic particles, which improve the wettability of the cathode-side surface of the material and provide nucleation sites for scale-forming components such as calcium, magnesium, sulfate, fluoride, or phosphate. This allows deposits to preferentially form on the surface or pore area near the cathode side of the material, rather than randomly entering and growing within the material's internal pores. Consequently, deposits are more easily detached from the material surface during water flushing or backwashing, reducing the risk of irreversible blockage of the internal pores.

[0026] Third, the intermediate migration barrier layer employs a hydrophobic porous insulating structure, and its internal material itself does not contain exchangeable ions, thus avoiding ion conduction relying on fixed ionic groups like ion exchange membranes. This structure reduces the migration rate of hydroxyl ions generated on the cathode side to the anode side, and also reduces the migration rate of hydrogen ions generated on the anode side to the cathode side, minimizing ineffective neutralization of hydroxyl and hydrogen ions within the material or in adjacent regions. Since more hydroxyl ions on the cathode side remain in the aqueous bulk near the cathode, they can participate more fully in the precipitation reaction of calcium and magnesium ions, thereby improving hardness removal efficiency and reducing energy consumption per unit of hardness removal.

[0027] Fourth, the second functional layer comprises acid-resistant and antioxidant polymers and oxidation-resistant inorganic particles, which can improve the material's acid resistance, oxygen evolution environment stability, and active chlorine resistance towards the anode side. In chlorinated water or acidic anode environments, ordinary polymer porous layers are prone to surface whitening, roughening, pore size enlargement, or embrittlement. However, this invention, by setting a second functional layer, prevents the intermediate migration barrier layer from being directly exposed to the strong oxidizing environment on the anode side, thereby slowing down the decrease in hydrophobicity and pore structure damage, and extending the material's service life in electrochemical water treatment systems.

[0028] Fifth, this invention solves the problems of easy scaling and clogging on the cathode side, easy ion crosstalk inside the material, and easy oxidation and aging on the anode side in existing porous isolation materials through the synergistic effect of three layers of materials.

[0029] Sixth, the composite porous insulating material of the present invention is not only suitable for hardening of circulating water, but can also be extended to the treatment of high-sulfate industrial water crystallization, fluoride-containing wastewater, and phosphorus-containing wastewater, depending on the type of inorganic particles in the first functional layer and the water composition. For example, the first functional layer containing calcium sulfate can improve the surface nucleation behavior of calcium sulfate deposits in high-sulfate water; the first functional layer containing hydroxyapatite or alumina can improve the formation site of calcium salts, calcium fluoride, or phosphate deposits in fluoride- or phosphorus-containing water. Therefore, the material of the present invention has strong water quality adaptability. Detailed Implementation

[0030] The present invention will be further described below with reference to embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the raw materials used in the following embodiments are all commercially available, and the listed manufacturers and models are only specific examples for ease of implementation and should not be construed as limiting the scope of protection of the present invention.

[0031] In this invention, the average pore size was measured using a capillary flow aperture gauge, and the test solution was a low surface tension wetting solution. Porosity was determined using the ethanol impregnation method and calculated based on the mass difference before and after impregnation. For finger-shaped macropores or surface open pores present in the first functional layer, their characteristic pore size was determined by analyzing cross-sectional scanning electron microscopy images. Unless otherwise specified, the pore size and porosity in the examples and comparative examples were measured using the same method.

[0032] Cell voltage refers to the operating voltage measured between the terminals of the cathode and anode of water electrolysis under constant current density operating conditions. The cell voltage rise rate is calculated according to the following formula: Cell voltage rise rate = (Cell voltage at the end of operation - Initial cell voltage) / Initial cell voltage × 100%.

[0033] In this invention, pressure difference refers to the difference between the inlet pressure and the outlet pressure of the cathode-side flow channel under constant circulation velocity. It is used to characterize the change in flow resistance caused by the accumulation of deposits on the cathode-side surface and orifice region. The pressure difference rise rate is calculated according to the following formula: Pressure difference rise rate = (Pressure difference at the end of operation - Initial pressure difference) / Initial pressure difference × 100%.

[0034] Deposition removal rate refers to the percentage reduction in the mass of sediment on the cathode side surface and orifice area of ​​the material before and after backwashing, relative to the mass of sediment before backwashing.

[0035] Example 1 This embodiment provides a composite porous insulating material for water treatment.

[0036] The ingredients are as follows: Polyvinylidene fluoride (PVDF): Arkema, Kynar 761 powder; Hydrophobic fumed silica: Evonik, AEROSIL R 812 S; Aqueous dispersion of polytetrafluoroethylene (PTFE): Chemours, Teflon PTFE DISP 30; Zirconia powder: Tosoh, TZ series zirconia powder; Polyamide PA6: BASF, Ultramid B3S; Silica micro powder: Evonik, AEROSIL 200; Hydroxyapatite powder: Sigma-Aldrich; Polyvinylpyrrolidone (PVP): BASF, Luvitec K30; Solvent: N,N-dimethylacetamide, analytical grade; Formic acid: purity ≥96%; Non-solvent: Deionized water.

[0037] The preparation process is as follows: S1, Preparation of the intermediate migration barrier layer. 18g of PVDF, 3g of hydrophobic fumed silica, 6g of PVP, and 73g of N,N-dimethylacetamide were weighed and placed in a mechanically stirred reactor. The mixture was stirred at 60℃ for 6 hours to obtain a uniform casting solution. After vacuum degassing the casting solution for 30 minutes, a film was scraped onto a clean glass plate using a doctor blade, resulting in a wet film thickness of 1.0 mm. The wet film was left in air for 60 seconds and then immersed in a 25℃ deionized water coagulation bath for 30 minutes. Subsequently, it was replaced with deionized water for 24 hours to obtain the intermediate migration barrier layer. The obtained intermediate migration barrier layer had a thickness of 0.72 mm, an average pore size of 1.8 μm, a porosity of 61%, a water contact angle of 132°, and a volume resistivity of 3.5 × 10^9 Ω·cm.

[0038] S2, Preparation of the first functional layer coating solution. 8g of PA6, 2g of silica micropowder, 1g of hydroxyapatite powder, 5g of PVP, and 84g of formic acid were weighed and stirred at room temperature for 4 hours to obtain the first coating solution. The first coating solution was coated onto the first surface of the intermediate migration barrier layer, with a wet film thickness of 0.25mm. After pre-drying at 40℃ for 5 minutes, it was immersed in a 25℃ deionized water coagulation bath for 30 minutes to allow solvent exchange between the formic acid and water, causing PA6 to precipitate and form a film. Simultaneously, PVP was partially eluted during subsequent water washing, forming a porous structure. The film was then washed and replaced with deionized water for 24 hours, and dried at 60℃ for 2 hours to form the first functional layer. The thickness of the first functional layer was 0.18mm, and the characteristic pore size of the surface open pores or finger-like macropores in the first functional layer was approximately 45μm.

[0039] S3. Preparation of the second functional layer coating solution. Weigh 20g of PTFE aqueous dispersion, 5g of PVDF, 3g of zirconium oxide powder, and 72g of N,N-dimethylacetamide, and stir until homogeneous to obtain the second coating solution. The amount of PTFE aqueous dispersion used is based on the mass of the commercial dispersion concentrate. Apply the second coating solution to the second surface of the intermediate migration barrier layer, with a wet film thickness of 0.20mm. Pre-dry at 80℃ for 10min, then cure at 120℃ for 30min to form the second functional layer. The second functional layer has a thickness of 0.15mm, an average pore size of 18μm, and a water contact angle of 112°.

[0040] S4, Hot-pressing composite. The three-layer material obtained in step S3 is placed in a hot press and hot-pressed for 5 minutes at 105℃ and 0.8MPa to obtain a composite porous insulating material. The total thickness of the obtained material is 1.05mm. Interlayer bonding transition zones are formed between the first functional layer and the intermediate migration barrier layer, and between the intermediate migration barrier layer and the second functional layer, respectively. These interlayer bonding transition zones are formed by local penetration, encapsulation, or mechanical interlocking of adjacent layers during coating, pre-drying, and hot-pressing processes. They are used to improve the bonding strength between adjacent functional layers and reduce the risk of delamination under long-term water flow erosion conditions.

[0041] The composite porous insulating material was used in an electrochemical circulating water hardness removal test. In the test apparatus, the composite porous insulating material was placed between the electrolytic water cathode and the electrolytic water anode, with the first functional layer facing the electrolytic water cathode and the second functional layer facing the electrolytic water anode. The calcium and magnesium hardness of the raw water (calculated as calcium carbonate) was 1000 mg / L, the chloride ion concentration was 500 mg / L, and the current density was 200 A / m. 2 It operates in constant current mode with an initial tank voltage of approximately 4.5V, a circulation flow rate of 0.4m / s, and continuous operation for 72 hours.

[0042] The results showed that the calcium and magnesium hardness removal rate was 93.8%, the 72-hour tank pressure rise rate was 6.7%, the differential pressure rise rate was 8.5%, and the deposits formed on the surface of the first functional layer were mainly surface flaky and granular crystals. The deposit removal rate after backwashing was 91.2%.

[0043] Example 2 This embodiment provides a composite porous insulating material for water treatment, which differs from Embodiment 1 in that the formulation of the first functional layer is different.

[0044] Specifically, the first functional layer coating solution consists of 8g PA6, 2g calcium sulfate powder, 1g alumina micro powder, 5g PVP, and 84g formic acid. The remaining preparation conditions are the same as in Example 1. The calcium sulfate powder is Sigma-Aldrich, with a purity ≥99.99%.

[0045] The resulting composite porous insulating material has a total thickness of 1.08 mm. The characteristic pore size of the surface open pores or finger-shaped macropores in the first functional layer is about 52 μm, the average pore size of the intermediate migration barrier layer is 1.9 μm, and the average pore size of the second functional layer is 20 μm.

[0046] The material was tested for use in the treatment of industrial circulating water with high sulfate concentrations. The raw water had a sulfate concentration of 1800 mg / L, a calcium ion concentration of 650 mg / L, a magnesium ion concentration of 180 mg / L, and a current density of 220 A / m. 2 The initial tank pressure was approximately 4.8V, the circulation flow rate was 0.5m / s, and it ran continuously for 72 hours.

[0047] The results showed that the sulfate removal rate was 67.5%, the calcium and magnesium hardness removal rate was 88.4%, the 72-hour cell pressure rise rate was 7.9%, and the differential pressure rise rate was 10.3%. Numerous calcium sulfate crystals were observed on the surface of the first functional layer, mainly located on the cathode side surface and in the shallow pore area.

[0048] Example 3 This embodiment provides a composite porous insulating material for water treatment.

[0049] The formulation is different compared to Example 1.

[0050] The raw material formulations are as follows: The intermediate migration barrier layer contains 18g PVDF, 2.5g boron nitride, 6g PVP, and 73.5g N,N-dimethylacetamide; the first functional layer contains 8g polyethersulfone, 2g hydroxyapatite, 1g alumina, 5g PVP, and 84g N,N-dimethylacetamide; the second functional layer contains 18g PTFE aqueous dispersion, 6g PVDF, 3g zirconium oxide, and 73g N,N-dimethylacetamide. Each layer was prepared using the same coating, coagulation, pore-forming, drying, and hot-pressing conditions as in Example 1.

[0051] The resulting composite porous insulating material has a total thickness of 0.96 mm, a porosity of 55%, a water contact angle of 128° for the intermediate migration barrier layer, a water contact angle of 42° for the first functional layer, and a water contact angle of 115° for the second functional layer.

[0052] This material was used for the electrochemical treatment of fluoride-containing wastewater. The raw water had a fluoride ion concentration of 50 mg / L, a calcium ion concentration of 300 mg / L, and a current density of 180 A / m. 2 The initial tank pressure was approximately 4.2V, the circulation flow rate was 0.35m / s, and it ran continuously for 48 hours.

[0053] The operating results were as follows: fluoride ion removal rate was 82.6%, calcium ion removal rate was 71.3%, tank pressure rise rate was 5.8% after 48 hours, and differential pressure rise rate was 7.4%.

[0054] Example 4 This embodiment provides a composite porous insulating material for water treatment.

[0055] The formulation of the second functional layer differs from that of Example 1. The coating solution for the second functional layer consists of 18g of PTFE aqueous dispersion, 4g of PVDF, 3g of fluorosilicone resin, 3g of zirconium oxide powder, and 72g of N,N-dimethylacetamide. The remaining steps are the same as in Example 1.

[0056] The second functional layer of the obtained material was placed facing an aqueous solution containing active chlorine, and an accelerated immersion test was conducted. The test solution had a pH of 3.0, an effective chlorine concentration of 200 mg / L, a temperature of 35°C, and was immersed for 168 hours.

[0057] The test results showed that the material mass retention rate was 98.6%, the water contact angle of the second functional layer changed from 118° to 113°, and the volume resistivity of the intermediate anti-migration layer remained above 1×10^9 Ω·cm. This indicates that the second functional layer can improve the durability of the composite porous insulating material in a chlorine-containing anolyte environment.

[0058] Comparative Example 1 This comparative example demonstrates the preparation of PVDF porous insulating material. The specific preparation process is as follows: 20g of PVDF, 8g of PVP, and 72g of N,N-dimethylacetamide were weighed and stirred at 60℃ for 6h to form a uniform casting solution. After vacuum degassing for 30min, a film was formed using a doctor blade, with a wet film thickness of 1.0mm. The wet film was left in air for 60s and then immersed in a 25℃ deionized water coagulation bath for phase transformation and pore formation. After coagulation for 30min, the film was removed, washed with deionized water and replaced for 24h, and then dried at 60℃ to obtain PVDF porous insulating material.

[0059] The resulting material has a thickness of 1.02 mm, an average pore size of 3.5 μm, a porosity of 60%, a water contact angle of 126°, and a volume resistivity of 3.2 × 10^9 Ω·cm.

[0060] The material was installed between the cathode and anode of the water electrolysis system in the same manner as in Example 1, and evaluated under the same circulating water hardness removal test conditions as in Example 1. The calcium and magnesium hardness in the raw water was 1000 mg / L (calculated as calcium carbonate), the chloride ion concentration was 500 mg / L, the current density was 200 A / m², the initial cell voltage was approximately 4.5 V, the circulation flow rate was 0.4 m / s, and the system operated continuously for 72 hours.

[0061] Test results show that the calcium and magnesium hardness removal rate is 85.1%, the 72-hour tank pressure rise rate is 18.6%, and the differential pressure rise rate is 24.8%.

[0062] After operation, disassembly and observation revealed that a large amount of calcium carbonate and magnesium hydroxide deposits not only adhered to the surface near the cathode side but also extended into the material's interior along the pores. Some pores were completely blocked by deposits, forming obvious internal scaling areas. Due to the lack of induced crystallization function, crystals randomly nucleated and grew on the material's surface and inside, making it difficult for deposits to concentrate in easily eroded areas. At the same time, because the material has a homogeneous structure, it is impossible to differentiate the design for the cathode and anode environments. Therefore, the pressure difference increased significantly faster than in Example 1 during long-term operation.

[0063] Further testing revealed that after 72 hours of operation, the effective porosity of the material decreased by approximately 21%, and a significant amount of sediment remained in the internal channels after backwashing, with a sediment removal rate of only 63.4%. This indicates that ordinary PVDF porous materials are prone to irreversible blockage.

[0064] Comparative Example 2 This comparative example prepares a porous insulating material without fabricating a second functional layer. The specific preparation process is as follows: An intermediate migration barrier layer was prepared according to the method in Example 1. 18g of PVDF, 3g of hydrophobic fumed silica, 6g of PVP and 73g of N,N-dimethylacetamide were weighed and a hydrophobic porous insulating layer with a thickness of about 0.75mm was prepared by phase inversion.

[0065] Subsequently, a first functional layer was formed on one side according to the method of Example 1. The coating solution of the first functional layer consisted of 68g of PA, 2g of silica micro powder, 1g of hydroxyapatite powder, 5g of PVP and 84g of formic acid. After coating, phase transformation to form pores and drying, a hydrophilic induced crystallization layer with a thickness of about 0.18mm was formed.

[0066] Finally, the two-layer materials were hot-pressed together to obtain a two-layer composite porous insulating material. The total thickness of the obtained material was 0.95 mm, the characteristic pore size of the surface open pores or finger-like macropores in the first functional layer was approximately 46 μm, and the average pore size of the intermediate migration barrier layer was 1.8 μm.

[0067] The material was used in the same circulating water hardening test as in Example 1.

[0068] Test results show that the calcium and magnesium hardness removal rate is 91.7%, the 72-hour tank pressure rise rate is 13.2%, and the differential pressure rise rate is 13.5%.

[0069] Compared with Comparative Example 1, Comparative Example 2 has a higher hardness removal rate and a lower pressure difference growth rate because it has a hydrophilic induced crystallization layer, which causes the deposits to be more concentrated on the cathode side surface area.

[0070] However, due to the direct exposure of the anode side to the acidic environment, oxygen evolution environment, and active chlorine environment, the intermediate migration barrier layer is subject to long-term oxidation. After 72 hours of operation, a slight whitening phenomenon was observed on the anode side surface, and local pore walls became rough; after further operation for 168 hours, some areas showed pore size enlargement and surface embrittlement.

[0071] After conducting accelerated chlorine resistance tests on the material (pH 3.0, available chlorine 200 mg / L, 35°C, 168 h), it was found that the material's mass retention rate was 94.8%, which was significantly lower than that of the acid-resistant and antioxidant structure in Example 4. The surface contact angle of the intermediate migration barrier layer decreased from 132° to 118°, indicating that the hydrophobicity of the material surface was damaged to a certain extent.

[0072] The above results indicate that although using only the induced crystallization layer and the migration-resistant layer can improve scaling behavior, the long-term stability of the anode side is still insufficient when a dedicated acid-resistant and antioxidant layer is lacking.

[0073] Comparative Example 3 The porous insulating material prepared in this comparative example has a different formulation for the first functional layer compared to Example 1.

[0074] The specific preparation process is as follows: The intermediate migration barrier layer and the second functional layer were both prepared according to the method of Example 1.

[0075] The first functional layer coating solution consists of 9g PA6, 5g PVP, and 86g formic acid, without the addition of silica micropowder, hydroxyapatite, calcium carbonate, or other induced crystallization particles. This coating solution is applied to the surface of the intermediate migration barrier layer, with a wet film thickness of 0.25mm. After pre-drying at 40℃ for 5 minutes, it is immersed in a 25℃ deionized water coagulation bath for 30 minutes to allow solvent exchange between the formic acid and water, causing PA6 to precipitate and form a film. Simultaneously, PVP is partially eluted during subsequent water washing, forming a porous structure. The layer is then washed and replaced with deionized water for 24 hours, and dried at 60℃ for 2 hours to form the first functional layer free of induced crystallization particles.

[0076] The total thickness of the resulting material is 1.03 mm. The characteristic pore size of the surface open pores or finger-like macropores in the first functional layer is approximately 43 μm, the average pore size of the intermediate migration barrier layer is 1.8 μm, and the average pore size of the second functional layer is 18 μm. The water contact angle of the first functional layer is 51°.

[0077] The material was used in a hardness removal test of circulating water under the same conditions as in Example 1.

[0078] Test results show that the calcium and magnesium hardness removal rate is 88.9%, the 72-hour tank pressure rise rate is 11.5%, and the differential pressure rise rate is 17.2%.

[0079] Scanning electron microscopy observation of the material after operation revealed that although the deposits mainly formed in the cathode-side region, the crystal size distribution was relatively wide, and the nucleation sites were quite random. Some small crystals grew inward along the pores of the first functional layer and gradually entered the entrance region of the intermediate migration barrier layer.

[0080] Compared to Example 1, the absence of hydroxyapatite, silica, and other induced crystallization particles significantly reduced the number of heterogeneous nucleation sites on the material surface, making it easier for crystals to form inside the pores. Statistical results showed that only 61% of the deposits were located within the surface 100 μm layer, while in Example 1, this figure exceeded 87%.

[0081] The backwash test results showed that the sediment removal rate of Comparative Example 3 was 74.6%, significantly lower than the 91.2% of Example 1. This indicates that in the absence of induced crystallization particles, although the material still has a certain hardening ability, it is difficult to achieve surface directional crystallization and rapid desorption, and pore blockage is more likely to occur during long-term operation.

[0082] Comparative Example 4 This comparative example prepares a porous insulating material. This comparative example adopts a three-layer structure, but the hydrophobic design in the middle migration barrier layer is eliminated, making the middle layer a normal hydrophilic porous layer.

[0083] The specific preparation process is as follows: The intermediate layer was prepared using 15g of polyethersulfone (PES), 8g of PVP, and 77g of N,N-dimethylacetamide. Specifically, the above components were stirred at 60°C for 6 hours to form a uniform casting solution. After vacuum degassing, the solution was coated onto a wet film with a thickness of 1.0 mm. The wet film was then immersed in a deionized water coagulation bath at 25°C for 30 minutes to allow solvent exchange between N,N-dimethylacetamide and water, causing PES to precipitate and form a film. Simultaneously, PVP was partially washed away during water washing, forming pores. After replacement with deionized water for 24 hours and drying at 60°C, a hydrophilic porous layer with an average pore size of approximately 4.2 μm and a water contact angle of 68° was obtained.

[0084] The first and second functional layers were prepared according to the method of Example 1 and formed into a three-layer structure by hot pressing.

[0085] The resulting material has a total thickness of 1.06 mm and a porosity of 62%.

[0086] The material was used in a hardness removal test of circulating water under the same conditions as in Example 1.

[0087] Test results show that the calcium and magnesium hardness removal rate is 87.6%, the 72-hour tank pressure rise rate is 14.8%, and the differential pressure rise rate is 15.9%.

[0088] Analysis of water samples from the cathode and anode sides revealed that the pH increase on the anode side was significantly greater than that in Example 1, while the local alkalinity on the cathode side was lower than that in Example 1. This indicates that hydroxide ions and hydrogen ions are more likely to migrate and neutralize through the intermediate layer.

[0089] Further measurements revealed that, under the same current density conditions, the power consumption per unit hardness removal of this material system was approximately 17.5% higher than that of Example 1. This indicates that when the intermediate layer lacks a hydrophobic migration barrier structure, the utilization efficiency of hydroxyl radicals generated at the cathode decreases, thus affecting the electrochemical hardening effect.

[0090] The above results indicate that the hydrophobic structure of the intermediate migration barrier layer plays an important role in suppressing ion crosstalk, improving hydroxide ion utilization, and reducing operating energy consumption.

[0091] The results from Example 1 and Comparative Example 1 show that, in Example 1, after using a three-layer composite porous insulating material formed by sequentially combining a first functional layer, an intermediate migration-resistant layer, and a second functional layer, the calcium and magnesium hardness removal rate increased from 85.1% in Comparative Example 1 to 93.8%, the 72-hour tank pressure rise rate decreased from 18.6% to 6.7%, the differential pressure rise rate decreased from 24.8% to 8.5%, and the deposit removal rate after backwashing increased from 63.4% to 91.2%. This indicates that, compared with ordinary PVDF porous materials, the asymmetric three-layer structure of the present invention allows the cathode-side deposits to concentrate more on the surface of the first functional layer or in the shallow pore area, reducing the extension of deposits into the deep pores inside the material, thereby reducing irreversible blockage and flow resistance growth.

[0092] The results from Example 1 and Comparative Example 2 show that although Comparative Example 2 incorporated a first functional layer and an intermediate migration barrier layer, which improved the crystallization position on the cathode side to some extent, the absence of a second functional layer meant that the intermediate migration barrier layer on the anode side was directly exposed to the acidic, oxygen-evolving, and active chlorine environments. This resulted in surface whitening, pore wall roughening, decreased contact angle, and localized pore size enlargement after long-term operation. In contrast, Examples 1 and 4, by incorporating a second functional layer, allowed the acid-resistant and antioxidant polymers and oxidation-resistant inorganic particles to preferentially contact the anode-side environment, thereby reducing the impact of anode-side oxidation corrosion on the intermediate migration barrier layer and improving the material's stability in chlorinated acidic environments.

[0093] The results from Example 1 and Comparative Example 3 show that, in the presence of all three layers, the presence or absence of inorganic particles in the first functional layer significantly affects the deposition location and desorption performance. In Comparative Example 3, the first functional layer does not contain inorganic particles such as silica, hydroxyapatite, calcium carbonate, calcium sulfate, or calcium phosphate; only 61% of the deposits are located within the surface 100 μm region, and the deposition removal rate after backwashing is 74.6%. In contrast, in Example 1, the proportion of deposits located within the surface 100 μm region exceeds 87%, and the deposition removal rate after backwashing is 91.2%. This indicates that inorganic particles in the first functional layer can provide heterogeneous nucleation sites, allowing fouling components to preferentially form deposits on the surface of the material near the cathode or in the shallow pore area, thereby improving the washability of the deposits and reducing the risk of pore blockage.

[0094] The results from Example 1 and Comparative Example 4 show that, in the case of a three-layer structure, the hydrophobicity of the intermediate layer plays a crucial role in suppressing ion crosstalk and improving electrochemical treatment efficiency. In Comparative Example 4, the intermediate layer is a common hydrophilic porous layer. During the test, the pH increase on the anode side was significantly greater than in Example 1, while the local alkalinity on the cathode side was lower than in Example 1, indicating that hydroxide and hydrogen ions migrate and neutralize more easily through the hydrophilic intermediate layer. Compared to Example 1, Comparative Example 4 showed a decrease in calcium and magnesium hardness removal rate, an increase in the 72-hour cell pressure rise rate and differential pressure rise rate, and an increase in power consumption per unit of hardness removal. This indicates that the intermediate anti-migration layer, with its hydrophobic porous insulating structure and lack of exchangeable ions, can reduce the cross-layer migration of hydroxide and hydrogen ions, decrease ineffective neutralization, and improve the utilization rate of hydroxide on the cathode side.

[0095] Examples 2 and 3 further illustrate that the composite porous insulating material of the present invention is not limited to ordinary circulating water hardening scenarios. By adjusting the types of inorganic particles in the first functional layer, the present invention can be applied to the treatment of high-sulfate industrial circulating water and fluoride-containing wastewater. In Example 2, after the first functional layer contains calcium sulfate inorganic particles, the calcium sulfate crystals are mainly located on the cathode side surface and shallow pore area of ​​the material, and the sulfate removal rate reaches 67.5%. In Example 3, after the first functional layer contains hydroxyapatite and alumina, the fluoride ion removal rate in fluoride-containing wastewater reaches 82.6%. The above results show that the present invention can select appropriate inorganic particles according to the main scale-forming components in the water to be treated, thereby improving the nucleation site and desorption performance of sediments under different water quality conditions.

[0096] In summary, the results of the embodiments and comparative examples together demonstrate that the technical effect of the present invention is not achieved by replacing a single material or adjusting a single pore size, but rather by the combined functional division of the first functional layer, the intermediate migration-resistant layer, and the second functional layer in the thickness direction. Specifically, the first functional layer regulates the heterogeneous nucleation sites of scale-forming components through its hydrophilic porous structure and inorganic particles; the intermediate migration-resistant layer inhibits the translayer migration of hydroxide and hydrogen ions through its hydrophobic porous insulating structure; and the second functional layer improves stability in the anodic environment through its acid-resistant and oxidation-resistant structure. The synergistic effect of these three elements enables the composite porous insulating material to simultaneously exhibit high pollutant or scale-forming component removal efficiency, low tank pressure rise rate, low differential pressure rise rate, and good backwash recovery performance and durability during electrochemical water treatment.

[0097] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A composite porous insulating material for water treatment, characterized in that, The composite porous insulating material includes a first functional layer, an intermediate migration barrier layer, and a second functional layer; the raw materials of the first functional layer include a hydrophilic polymer, inorganic particles, and a pore-forming agent; the raw materials of the intermediate migration barrier layer include a hydrophobic polymer, a hydrophobic inorganic filler, and a pore-forming agent; and the raw materials of the second functional layer include an acid-resistant and antioxidant polymer and an antioxidant inorganic particle.

2. The composite porous insulating material for water treatment according to claim 1, characterized in that, The hydrophilic polymer includes one or more of polyamide, polyethersulfone, polyvinyl alcohol, polyvinyl acetal, hydrophilic modified polyvinylidene fluoride, and hydrophilic modified polyurethane.

3. The composite porous insulating material for water treatment according to claim 1, characterized in that, The inorganic particles include one or more of silicon dioxide, aluminum oxide, calcium carbonate, hydroxyapatite, calcium sulfate, and calcium phosphate.

4. The composite porous insulating material for water treatment according to claim 1, characterized in that, The pore-forming agent includes one or more of polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol, lithium chloride, sodium chloride, and sodium bicarbonate.

5. The composite porous insulating material for water treatment according to claim 1, characterized in that, The hydrophobic polymer includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, polypropylene, polyethylene, polyphenylene sulfide, polyimide, and polybenzimidazole.

6. The composite porous insulating material for water treatment according to claim 1, characterized in that, The hydrophobic inorganic filler includes one or more of the following: hydrophobic silica, boron nitride, silicon carbide, zirconium oxide, fluorosilane-modified alumina, and fluorosilane-modified silica.

7. The composite porous insulating material for water treatment according to claim 1, characterized in that, The acid-resistant and antioxidant polymers include one or more of polyvinylidene fluoride, polytetrafluoroethylene, fluorosilicone resin, polyphenylene sulfide, and polyimide.

8. The composite porous insulating material for water treatment according to claim 1, characterized in that, The oxidation-resistant inorganic particles include one or more of zirconium oxide, silicon dioxide, aluminum oxide, silicon carbide, and silicon nitride.

9. The composite porous insulating material for water treatment according to any one of claims 1-8, characterized in that, The preparation method of the composite porous insulating material includes the following steps: A hydrophobic polymer, a hydrophobic inorganic filler, a pore-forming agent and a solvent are mixed to form an intermediate layer casting solution. After the intermediate layer casting solution is formed into a film, phase transformation or thermally induced phase separation is performed to form pores, thereby obtaining an intermediate migration barrier layer. A first coating liquid is formed by mixing a hydrophilic polymer, inorganic particles, a pore-forming agent and a solvent. The first coating liquid is then coated onto the first surface of the intermediate migration barrier layer. After pre-drying, solidification to form pores, washing and drying, a first functional layer is formed. Acid-resistant and antioxidant polymer, antioxidant inorganic particles and solvent are mixed to form a second coating liquid. The second coating liquid is coated on the second surface of the intermediate migration barrier layer. After pre-drying and curing, a second functional layer is formed to obtain a layered material. The layered material is hot-pressed to obtain the composite porous insulating material.

10. The application of a composite porous insulating material in water treatment according to any one of claims 1-8, characterized in that, The composite porous insulating material is used in an electrochemical water treatment system and is disposed between the electrolytic water cathode and the electrolytic water anode. The first functional layer faces the electrolytic water cathode, and the second functional layer faces the electrolytic water anode; The electrochemical water treatment includes at least one of the following: circulating water hardening treatment, chlorine-containing water electrochemical treatment, high sulfate industrial water crystallization treatment, fluoride-containing wastewater treatment, and phosphorus-containing wastewater treatment.