Anti-pollution chlorine-resistant seawater desalination membrane, preparation method and application thereof

Abstract

The present application relates to seawater reverse osmosis membrane technical field, disclose a kind of anti-pollution chlorine-resistant seawater desalination membrane and its preparation method and application.The preparation method is formed aromatic polyamide separation layer by m-phenylenediamine and benzene tricarboxylic acid chloride interfacial polymerization on the surface of porous polymer support layer, the residual n-heptane loading of unit area membrane piece is controlled to be 0.8~2.0g / m 2 After initial liquid removal, then sequentially high n-heptane vapor activity ripening and low n-heptane vapor activity ripening, residual n-heptane tends to be position uniform first and then controlled thinning, and through the second nitrogen flow to complete secondary desolventization, heat treatment and water washing.The method can improve the uniformity of membrane desalination performance, the flux recovery ability after calcium alginate pollution and the salt rejection performance retention rate after chlorine exposure.The prepared membrane is suitable for reverse osmosis desalination of high salinity seawater.

Description

Technical Field

[0001] This invention relates to the field of seawater reverse osmosis membrane technology, and in particular to a fouling-resistant and chlorine-resistant seawater desalination membrane, its preparation method, and its application. Background Technology

[0002] Aromatic polyamide composite reverse osmosis membranes typically use nonwoven fabric and porous polymer layers as support layers. A thin layer of aromatic polyamide with selective separation properties is formed on the support layer surface through interfacial polymerization of aromatic polyamine aqueous monomers and aromatic polyacrylamide organic monomers. This type of membrane has high salt rejection capacity and is widely used in seawater reverse osmosis desalination.

[0003] During the organic phase drainage and solvent removal process after interfacial polymerization, differences can easily exist in the amount of residual organic liquid, the intensity of airflow, and the solvent evaporation rate at different locations on the membrane surface. Locally thin liquid regions may lose their organic phase supply earlier and terminate polymerization prematurely, while locally thick liquid regions may continue to maintain monomer supply for a longer period, resulting in localized low-crosslinking zones, abnormally thickened zones, deep valleys, and areas with weak salt permeability in the aromatic polyamide separation layer. These locational differences are more likely to accumulate in large-area membrane fabrication and continuous roll-to-roll preparation, and may manifest as lateral dispersion in water flux and salt rejection.

[0004] Deep grooves and locally rough areas on the membrane surface easily trap alginate, calcium ion-bridged aggregates, and other seawater organic pollutants, increasing the difficulty of pollutant cleaning. Locally loose or insufficiently cross-linked areas may also become sites of preferential invasion and damage by active chlorine, causing a decline in the membrane's salt rejection performance under fluctuating residual chlorine conditions during disinfection pretreatment. Therefore, it is necessary to implement measurable and repeatable staged control of the residual organic liquid phase after interfacial polymerization. This involves first achieving a more uniform distribution of the residual liquid phase, then thinning it in a controlled manner and uniformly terminating further polymerization, thereby improving the uniformity of membrane formation and operational stability of large-area seawater reverse osmosis membranes. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing and applying a fouling-resistant and chlorine-resistant seawater desalination membrane. By controlling the residual n-heptane loading per unit area of ​​the membrane after interfacial polymerization, and by sequentially setting a high solvent activity curing stage and a low solvent activity curing stage, the residual liquid phase on the membrane surface is first homogenized, then undergoes controlled thinning, and subsequently undergoes uniform solvent removal and shaping. This improves the positional uniformity, fouling resistance, and separation performance retention of the aromatic polyamide separation layer after chlorine exposure.

[0006] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a pollution-resistant and chlorine-resistant seawater desalination membrane, comprising the following steps: S1. A porous polymer support layer is formed on the surface of a nonwoven fabric substrate, and the porous polymer support layer is brought into contact with an aqueous solution containing m-phenylenediamine to remove the flowable aqueous solution from the surface of the porous polymer support layer, thereby obtaining an aqueous treatment membrane. S2. The aqueous phase treatment membrane is brought into contact with an organic phase solution containing trimesoyl chloride and n-heptane, and an aromatic polyamide separation layer is formed on the surface of the porous polymer support layer through interfacial polymerization between the m-phenylenediamine and the trimesoyl chloride. S3. Stop the contact between the aqueous phase treatment membrane and the organic phase solution, drain the free-flowing bulk organic phase solution from the surface of the aromatic polyamide separation layer, and perform an initial dehydration treatment on the surface of the aromatic polyamide separation layer using a first nitrogen flow, so that the residual n-heptane loading per unit area of ​​the membrane after the initial dehydration treatment is 0.8–2.0 g / m². 2 ; S4. The membrane treated in step S3 is passed sequentially through a first solvent vapor maturation zone and a second solvent vapor maturation zone, both of which contain nitrogen gas and n-heptane vapor. The solvent activity of n-heptane vapor in the first solvent vapor ripening zone is 0.70–0.90, the ripening time is 15–45 s, and the membrane surface temperature is 2–7 °C higher than the dew point temperature of n-heptane vapor in the first solvent vapor ripening zone. After treatment in the first solvent vapor ripening zone, the residual n-heptane loading per unit area of ​​the membrane decreases by no more than 25%. The solvent activity of n-heptane vapor in the second solvent vapor ripening zone is 0.30–0.55, the ripening time is 15–60 s, and the membrane surface temperature is 8–25 °C higher than the dew point temperature of n-heptane vapor in the second solvent vapor ripening zone. After treatment in the second solvent vapor ripening zone, the residual n-heptane loading per unit area of ​​the membrane is 0.15–0.60 g / m². 2 ; The solvent activity of n-heptane vapor in the first solvent vapor maturation zone is at least 0.20 higher than that of n-heptane vapor in the second solvent vapor maturation zone; The solvent activity of the n-heptane vapor is the ratio of the actual partial pressure of the n-heptane vapor in the maturation zone to the saturated vapor pressure of n-heptane at the same temperature; S5. The membrane treated in step S4 is subjected to a second nitrogen stream for secondary solvent removal, ensuring that the residual n-heptane loading per unit area of ​​the membrane after the secondary solvent removal is not higher than 0.10 g / m³. 2 ; S6. The membrane treated in step S5 is subjected to heat treatment and water washing in sequence to obtain the anti-fouling and chlorine-resistant seawater desalination membrane.

[0007] The above preparation method does not completely remove n-heptane immediately after interfacial polymerization. Instead, it first controls the residual n-heptane loading per unit area of ​​the membrane to be 0.8–2.0 g / m². 2 This allows the surface of the newly formed aromatic polyamide separation layer to retain a liquid phase environment capable of continuing to support trimesoyl chloride and maintaining interfacial mass transfer. This residual amount can prevent premature disappearance of the liquid phase, which would cause premature termination of the local reaction, and can also reduce the localized prolonged polymerization and film thickening caused by excessive residual liquid, thus providing a more similar basis for subsequent reactions at different locations on the film surface.

[0008] The first solvent vapor maturation zone employs a higher n-heptane vapor activity and maintains a membrane surface temperature slightly above the n-heptane vapor dew point temperature. This reduces the vapor pressure difference between the n-heptane at the membrane surface and the surrounding atmosphere, allowing the n-heptane to maintain a slower net evaporation rate. Under the condition that the residual n-heptane mass reduction rate does not exceed 25%, localized thick and thin liquid areas on the membrane surface will not rapidly solidify. The residual liquid phase can mitigate the volume differences at different locations through surface flow, capillary migration, and concentration diffusion, thereby ensuring a more uniform supply of trimesoyl chloride to different regions of the membrane surface.

[0009] The second solvent vapor ripening zone employs a lower n-heptane vapor activity than the first solvent vapor ripening zone and maintains a greater temperature difference between the membrane surface and the dew point, allowing the already homogenized residual liquid phase to enter a stable thinning stage. This stage gradually reduces the residual n-heptane loading per unit area of ​​the membrane to 0.15–0.60 g / m². 2 This allows the interfacial polymerization at different locations to gradually end at a relatively similar liquid phase thinning rate, reducing local concentration and precipitation of trimesoyl chloride and local overgrowth of the polyamide layer caused by sudden drying.

[0010] The first high-solvent-activity ripening stage and the second low-solvent-activity ripening stage are set sequentially to first homogenize the residual liquid phase and then achieve controlled thinning. These two stages respectively affect the spatial distribution and temporal changes of the residual liquid phase. Subsequently, a second nitrogen flow reduces the residual n-heptane loading per unit area of ​​the membrane to no more than 0.10 g / m². 2 It can uniformly terminate interfacial polymerization when the residual liquid phase is already in a relatively narrow range, reducing the difference in reaction termination time between different film surface positions.

[0011] Through the above continuous control, it is beneficial to reduce the film formation difference at different locations on the membrane surface, make the separation performance of the aromatic polyamide separation layer more uniform at different locations, and improve the membrane's antifouling performance and separation performance retention after chlorine exposure.

[0012] Preferably, the porous polymer support layer is formed of polysulfone or polyethersulfone; The porous polymer support layer is disposed on the surface of the polyester nonwoven fabric substrate. The wet thickness of the porous polymer support layer is 35–60 μm, and the pure water flux at 25°C and 0.10 MPa is 500–900 L·m. -2 ·h -1 .

[0013] Polyester nonwoven fabric provides the mechanical support required for continuous processing and high-pressure operation of the membrane, while the porous polymer support layer formed by polysulfone or polyethersulfone provides a smooth film-forming interface with aqueous phase storage capacity for the aromatic polyamide separation layer. By controlling the wet thickness and pure water flux within the specified range, the pore connectivity, surface stability, and compressive strength of the support layer can be balanced, reducing the interference of mass transfer resistance and local pore structure differences in the support layer on the uniformity of interfacial polymerization.

[0014] Preferably, in step S1, the aqueous solution comprises the following components by mass percentage: 1.8%–2.8% m-phenylenediamine, 0.05%–0.30% triethylamine, 0.05%–0.30% camphor sulfonic acid, 0.005%–0.030% sodium dodecyl sulfate, and the balance being water; the pH of the aqueous solution at 25°C is 10.0–10.8, and the contact time between the porous polymer support layer and the aqueous solution is 30–180 s.

[0015] Within the specified concentration and contact time, m-phenylenediamine can fully penetrate the pores of the porous polymer support layer and form a stable aqueous reaction layer on the membrane surface. Triethylamine and camphor sulfonic acid work together to regulate the acid-base environment of the aqueous phase and the acidic byproducts during interfacial polymerization, ensuring that m-phenylenediamine maintains suitable reactivity. Sodium dodecyl sulfate reduces the interfacial tension between the aqueous phase and the support layer, improving the spreading and wetting uniformity of the aqueous phase on the membrane surface. The specified pH range can reduce film formation fluctuations caused by excessive protonation or overly rapid reaction of m-phenylenediamine.

[0016] Preferably, in step S2, the mass fraction of pyromellitic chloroformyl chloride in the organic phase solution is 0.06% to 0.20%, with the remainder being n-heptane; the contact temperature between the aqueous phase treatment membrane and the organic phase solution is 20 to 35°C, and the contact time is 15 to 90 seconds.

[0017] The initial nucleation density and initial crosslinking degree of the aromatic polyamide separation layer are jointly determined by the pyromellitic trimethylol chloride content, contact temperature, and contact time. This range allows for the formation of a continuous aromatic polyamide network at the interface while retaining a certain amount of incompletely reacted pyromellitic trimethylol chloride, providing adjustable reaction space for the subsequent two-stage solvent vapor maturation. Heptane has a well-defined vapor pressure and gas-liquid equilibrium relationship, facilitating quantitative control of the residual liquid phase volatilization process through solvent activity and dew point difference.

[0018] Preferably, in step S3, after the main organic phase solution is discharged, the membrane surface is kept at 60° to 90° relative to the horizontal plane, and the liquid is drained by gravity for 5 to 30 seconds. Then, the first nitrogen gas flow is used for the initial desolvation treatment. The average flow velocity of the first nitrogen gas at a distance of 5 mm from the membrane surface is 0.3 to 1.5 m / s, the angle between the first nitrogen gas flow and the membrane surface is 10° to 40°, and the treatment time of the first nitrogen gas flow is 2 to 15 seconds.

[0019] Gravity-driven drainage first removes the free-flowing bulk organic phase from the membrane surface, reducing the impact of large droplets and localized liquid accumulation on the distribution of the residual liquid phase. Subsequently, a low-speed, low-angle initial nitrogen flow is used for primary dehydration along the membrane surface, which preferentially weakens locally thick liquid regions without completely removing residual n-heptane from the membrane surface. The coordinated control of airflow velocity, angle, and treatment time ensures the formation of a thin layer of residual liquid on the membrane surface suitable for subsequent steam curing, and reduces localized disturbances caused by strong airflow directly impacting the nascent polyamide layer.

[0020] Preferably, in step S4, the temperatures of the first solvent vapor maturation zone and the second solvent vapor maturation zone are 20-35°C, the airflow velocity at a distance of 50 mm from the membrane surface in the first solvent vapor maturation zone and the second solvent vapor maturation zone is not higher than 0.30 m / s, the oxygen volume fraction in the first solvent vapor maturation zone and the second solvent vapor maturation zone is not higher than 2.0%, and the absolute pressure is 98-105 kPa.

[0021] A lower gas flow velocity in the aging zone reduces localized volatilization differences at the membrane surface caused by boundary layer fluctuations, making solvent activity the primary factor controlling mass transfer of n-heptane. Maintaining temperature and absolute pressure within these ranges helps stabilize the gas-liquid equilibrium of n-heptane and improves the accuracy of solvent activity control. A low-oxygen, low-nitrogen environment also reduces the risk of n-heptane vapor forming a flammable mixture with air, while minimizing the interference of aging atmosphere composition fluctuations on the volatilization process at the membrane surface.

[0022] Preferably, a first sealed transition channel is provided between the outlet of the first nitrogen gas flow and the inlet of the first solvent vapor maturation zone, the residence time of the membrane in the first sealed transition channel does not exceed 2 seconds, and the solvent activity of n-heptane vapor in the first sealed transition channel is 0.70 to 0.90; a second sealed transition channel is provided between the first solvent vapor maturation zone and the second solvent vapor maturation zone, the solvent activity of n-heptane vapor in the second sealed transition channel is 0.30 to 0.55, the residence time of the membrane in the second sealed transition channel does not exceed 2 seconds, and the residence time is included in the maturation time of the second solvent vapor maturation zone.

[0023] The first closed transition channel prevents the membrane, after initial dehydration, from being exposed to an uncontrolled low-solvent concentration atmosphere before entering the high-activity curing zone, thus preventing residual n-heptane from prematurely and rapidly volatilizing during short-distance transport. The second closed transition channel employs a low-activity atmosphere corresponding to the second curing stage, and incorporates the residence time into the second stage, making the transition of the membrane from a high-activity state to a low-activity state more continuous and reducing process deviations caused by atmospheric crosstalk between the two curing zones and untimed volatilization.

[0024] Preferably, the n-heptane vapor in the first solvent vapor maturation zone and the second solvent vapor maturation zone are formed by the following methods: a first portion of nitrogen gas is passed through a constant-temperature n-heptane saturator to obtain a first mixed gas containing n-heptane vapor; the first mixed gas is mixed with a second portion of nitrogen gas that does not pass through the constant-temperature n-heptane saturator, and the solvent activity of the n-heptane vapor in the first solvent vapor maturation zone and the second solvent vapor maturation zone is controlled by adjusting the flow ratio of the first portion of nitrogen gas to the second portion of nitrogen gas; the actual partial pressure of the n-heptane vapor at the outlet of the constant-temperature n-heptane saturator is not lower than 90% of the saturated vapor pressure of n-heptane at the temperature of the constant-temperature n-heptane saturator.

[0025] By quantitatively mixing saturated nitrogen and dry nitrogen, a stable n-heptane vapor environment can be established without directly injecting liquid n-heptane into the aging chamber. The actual partial pressure of n-heptane can be continuously changed by adjusting the flow rate ratio of the two nitrogen streams, allowing the two aging zones to achieve independent and repeatable solvent activities. Reaching near-saturation at the saturator outlet facilitates establishing a clear correlation between gas flow rate ratios and target solvent activities, improving process control and the operability of continuous scale-up.

[0026] Preferably, in step S5, the average flow velocity of the second nitrogen gas at a distance of 5 mm from the membrane surface is 2-8 m / s, and the secondary desolvation treatment time is 5-30 s; in step S6, the heat treatment temperature is 60-90℃, and the heat treatment time is 2-8 min; after heat treatment, the membrane is washed with water at a temperature of 20-50℃ for 5-20 min, and then treated with a 0.2%-1.0% glycerol aqueous solution for 5-20 min.

[0027] After the two-stage curing process, the second nitrogen flow rapidly reduces the residual n-heptane loading at a high flow rate, causing interfacial polymerization at different locations to end at approximately the same time point. At this point, the residual n-heptane has already undergone homogenization and controlled thinning, making high-speed solvent removal less likely to cause significant positional differences. Subsequent heat treatment further stabilizes the aromatic polyamide network, water washing removes residual m-phenylenediamine, hydrolysis products of trimesoyl chloride, and soluble additives, while glycerol treatment helps maintain the wet pore structure and membrane performance stability during storage.

[0028] A second aspect of the present invention provides a pollution-resistant and chlorine-resistant seawater desalination membrane, wherein the pollution-resistant and chlorine-resistant seawater desalination membrane is prepared by the preparation method described above.

[0029] The anti-fouling and chlorine-resistant seawater desalination membrane, by controlling the loading of residual n-heptane after interfacial polymerization and the staged maturation process, helps to reduce the membrane formation differences at different locations on the membrane, so that different locations on the membrane have more consistent water flux and salt rejection performance, and improves the membrane's ability to maintain performance under calcium alginate pollution and chlorine exposure conditions.

[0030] The third aspect of the present invention provides a method for seawater reverse osmosis desalination, wherein a fouling-resistant and chlorine-resistant seawater desalination membrane prepared by the preparation method described above is made into a spiral-wound reverse osmosis membrane element, and seawater to be treated with a total dissolved solids content of 25-45 g / L is flowed through the spiral-wound reverse osmosis membrane element and reverse osmosis separation is performed at an operating pressure of 4.5-7.0 MPa.

[0031] Fabricating the seawater desalination membrane into a spiral-wound reverse osmosis membrane element allows for the utilization of the high positional uniformity of the aromatic polyamide separation layer, maintaining a more consistent permeate and salt rejection state across different flow channels of the membrane element, thus reducing the concentrated deposition of pollutants caused by localized high-flux areas. The reduction in weak salt permeation areas and chlorination-sensitive areas within the membrane sheet also helps maintain the operational stability of the spiral-wound membrane element under conditions of fluctuating residual chlorine during saline seawater treatment and disinfection pretreatment.

[0032] The present invention, by adopting the above technical solution, has the following beneficial effects: 1. This invention controls the residual n-heptane loading per unit area of ​​the membrane to 0.8–2.0 g / m² through initial dehydration. 2 This ensures continuous and adjustable liquid phase conditions for subsequent interfacial polymerization. This residual liquid range prevents premature disappearance of the liquid phase, which could lead to early termination of localized reactions, and also reduces prolonged localized reactions caused by excessive residual liquid. This ensures that different locations on the membrane surface have a relatively consistent supply of trimesoyl chloride when entering the ripening stage.

[0033] 2. This invention sequentially incorporates high solvent activity aging and low solvent activity aging. The first stage suppresses rapid volatilization of n-heptane through a smaller vapor pressure difference, resulting in a more uniform distribution of residual liquid at different locations. The second stage reduces solvent activity and increases the dew point difference, causing the homogenized residual liquid to thin synchronously. These two stages operate continuously in a specific order, enabling control over the spatial distribution and temporal changes of the residual liquid.

[0034] 3. In this invention, a second nitrogen stream is used for unified solvent removal after the two-stage curing process, reducing the residual n-heptane loading per unit area membrane to no more than 0.10 g / m². 2The aromatic polyamide network is stabilized and solidified through subsequent heat treatment and water washing. This reduces localized low-crosslinking areas, abnormally thickened areas, and areas with weak salt permeation, thereby improving the uniformity of water flux and NaCl rejection rate at different locations on the membrane.

[0035] 4. By improving the film formation uniformity at different locations on the membrane, this invention can reduce the uneven deposition of pollutants in local areas of the membrane surface and improve the cleaning and recovery ability after contamination; at the same time, it helps to reduce the sensitivity of local weak areas of the membrane to the action of active chlorine and improve the salt interception performance retention rate after chlorine exposure.

[0036] 5. This invention uses the actual partial pressure of n-heptane vapor, dew point difference, residual n-heptane loading per unit area of ​​membrane, and its reduction rate as process control parameters, enabling quantitative detection and repeated implementation of the maturation process after interfacial polymerization. The closed transition channel, two-stage vapor maturation zone, and mixed supply method of saturated nitrogen and dry nitrogen also facilitate continuous roll-to-roll production and process scale-up. Detailed Implementation

[0037] The specific embodiments of the present invention will be described in detail below. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0038] Unless otherwise defined, all scientific and technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art.

[0039] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Other implementation methods obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0040] Unless otherwise specified, all materials, reagents, and equipment used in the following examples are commercially available. Unless otherwise specified, all raw materials used are industrial grade or analytical grade, and the water is deionized water with a conductivity not exceeding 10 μS / cm. All percentages are by mass.

[0041] The polyester nonwoven fabric used in the examples and comparative examples had a surface density of 75 g / m². 2 The thickness is 90μm; the number average molecular weight of polysulfone is 75000; the number average molecular weight of polyethersulfone is 65000; the polyvinylpyrrolidone is K30 grade; the purity of N-methylpyrrolidone is not less than 99.5%; the purity of m-phenylenediamine is not less than 99.0%; the purity of trimesoyl chloride is not less than 98.0%; and the purity of n-heptane is not less than 99.0%.

[0042] The first nitrogen flow, the second nitrogen flow, the first solvent vapor maturation zone, and the second solvent vapor maturation zone all use nitrogen with a purity of not less than 99.9%. Both the first and second solvent vapor maturation zones are closed maturation chambers, equipped with a gas distribution plate, a temperature sensor, a n-heptane vapor sampling port, an oxygen concentration detector, and a solvent recovery device. Before operation, the chambers are purged with nitrogen. During operation, the oxygen volume fraction within the chambers does not exceed 2.0%, and the absolute pressure of the chambers is 101±2 kPa.

[0043] The membrane surface airflow velocity refers to the airflow velocity measured at a distance of 5 mm from the membrane surface using a thermal anemometer. For intermittent membrane sheets, 5 measuring points are evenly arranged along the width direction of the air knife; for continuous membrane rolls, 9 measuring points are evenly arranged along the width direction. The membrane surface airflow velocity is taken as the arithmetic mean of the measured values ​​at each measuring point.

[0044] The solvent activity of n-heptane vapor is calculated using the following formula: Solvent activity = Actual partial pressure of n-heptane vapor in the aging chamber ÷ Saturated vapor pressure of n-heptane at the same temperature.

[0045] Gas samples were taken from 50 mm above the membrane in the curing chamber. The volume fraction of n-heptane was determined using a gas chromatograph calibrated with n-heptane standard gas, and the actual partial pressure of n-heptane vapor was calculated based on the total pressure of the chamber. The saturated vapor pressure of n-heptane was calculated using the Antoine equation for n-heptane at the corresponding temperature.

[0046] The intermittent aging chamber has sampling ports at the inlet, middle, and outlet; the continuous aging chamber also has sampling ports on the left, middle, and right sides along the membrane width. When the solvent activity measurement value varies by no more than ±0.02 for three consecutive measurements with an interval of 1 minute, the aging environment is considered to have reached a stable state. The solvent activity described in the examples is the arithmetic mean of the measurements at each sampling point under stable conditions.

[0047] Heptane vapor is formed through a constant-temperature saturator. A first portion of nitrogen gas is introduced into the liquid heptane from the bottom of the saturator, and after gas-liquid contact, it exits from the top of the saturator. The temperature of the saturator is the same as the temperature of the corresponding aging chamber. The gas flow rate and gas-liquid contact time are controlled to ensure that the actual partial pressure of the heptane vapor at the saturator outlet is not lower than 92% of the saturated vapor pressure of heptane at that temperature. The first portion of nitrogen gas containing heptane vapor is mixed with a second portion of nitrogen gas that does not pass through the saturator. The solvent activity in the aging zone is controlled by adjusting the flow rate ratio of the two portions of nitrogen gas.

[0048] The residual n-heptane loading per unit area of ​​the membrane was determined by headspace gas chromatography. For each process node to be tested, three accompanying test membranes were prepared and subjected to the same treatment as the main membrane. Each accompanying test membrane had an area of ​​0.0100 m². 2After the corresponding processing steps are completed, the accompanying test membrane is placed into a sealed headspace vial within 3 seconds, equilibrated at 60°C for 20 minutes, and the n-heptane content is determined using headspace-gas chromatography with a flame ionization detector.

[0049] A calibration curve was established by adding a known mass of n-heptane to a blank membrane of the same specifications and aqueous state. The measured mass of n-heptane was divided by the effective area of ​​the accompanying test membrane to obtain the residual n-heptane loading per unit area of ​​the membrane, expressed in g / m². 2 The detection limit for residual n-heptane loading using this method is 0.005 g / m³. 2 The residual n-heptane loading at each process node is the arithmetic mean of the values ​​measured on three accompanying test membranes. After the accompanying test membranes are tested, they will not be used in subsequent membrane fabrication processes.

[0050] The rate of reduction in the mass of residual n-heptane in the first solvent vapor maturation zone is calculated using the following formula: Mass reduction rate = (Residual n-heptane load before entering the first solvent vapor maturation zone - Residual n-heptane load after leaving the first solvent vapor maturation zone) ÷ Residual n-heptane load before entering the first solvent vapor maturation zone × 100%.

[0051] In the first solvent vapor maturation zone, the membrane surface temperature is controlled to be 2–7°C higher than the dew point temperature of n-heptane vapor; in the second solvent vapor maturation zone, the membrane surface temperature is controlled to be 8–25°C higher than the dew point temperature of n-heptane vapor. The first solvent vapor maturation zone inhibits the rapid volatilization of n-heptane and avoids condensation on the membrane surface by keeping the membrane surface temperature close to but higher than the dew point temperature; the second solvent vapor maturation zone reduces the activity of n-heptane vapor and increases the difference between the membrane surface temperature and the dew point temperature, thereby steadily reducing the residual n-heptane loading per unit area of ​​the membrane.

[0052] The wet polysulfone layer thickness of the porous polysulfone support used in the examples and comparative examples was 45±2 μm, and the pure water flux at 25°C and 0.10 MPa was 685±28 L·m. -2 ·h -1 In Example 4, the wet polyethersulfone porous support layer had a thickness of 47±2 μm and a pure water flux of 718±31 L·m at 25°C and 0.10 MPa. -2 ·h -1 Except for Example 4, all examples and comparative examples used the same batch of polysulfone porous support membrane.

[0053] Example 1

[0054] This embodiment discloses a method for preparing a pollution-resistant and chlorine-resistant seawater desalination membrane, including the following steps.

[0055] S1. Prepare a porous polysulfone support layer.

[0056] According to the mass percentage, 16.5% polysulfone, 2.0% polyvinylpyrrolidone, 3.0% polyethylene glycol 400 and 78.5% N-methylpyrrolidone were mixed, stirred at 60°C for 8 hours, and allowed to stand for degassing for 12 hours to obtain a uniform casting solution.

[0057] The casting solution temperature was adjusted to 25℃, and the casting solution was coated onto the surface of a polyester nonwoven fabric using a doctor blade with a gap of 130μm. After coating, the film was left to stand in air at 25℃ and 50% relative humidity for 8 seconds, and then immersed in a deionized water coagulation bath at 25℃ for 10 minutes to solidify. The formed polysulfone porous support membrane was then transferred to flowing deionized water for washing for 24 hours to obtain a polysulfone porous support layer.

[0058] Cut the cleaned support membrane into 300mm×300mm sheets and keep the surface of the sheets moist.

[0059] Prepare an aqueous solution. The aqueous solution consists of 2.20% m-phenylenediamine, 0.12% triethylamine, 0.18% camphor sulfonic acid, 0.015% sodium dodecyl sulfate, and the balance deionized water. The pH of the aqueous solution at 25°C is 10.42.

[0060] The polysulfone porous support layer was contacted with an aqueous solution at 25°C for 90 seconds to allow the aqueous solution to wet the surface of the support layer. The membrane was then removed from the aqueous solution and rolled once in the same direction using silicone rubber rollers with a Shore hardness of 60A at a linear load of 18 N / mm and a rolling speed of 0.10 m / s to remove the flowable aqueous solution from the membrane surface, thus obtaining the aqueous treatment membrane.

[0061] S2, forming an aromatic polyamide separation layer.

[0062] Prepare the organic phase solution. The organic phase solution consists of 0.12% trimesoyl chloride and 99.88% n-heptane, and should be kept at 25°C before use.

[0063] The aqueous phase treatment membrane is placed horizontally so that the organic phase solution can uniformly cover the membrane surface. It is then contacted at 25°C for 35 seconds to allow m-phenylenediamine and trimesoyl chloride to undergo interfacial polymerization at the interface between the aqueous and organic phases, forming a new aromatic polyamide separation layer.

[0064] S3. Perform initial dehydration treatment.

[0065] After the organic phase contact is completed, the bulk organic phase solution that is not attached to the membrane surface is drained, and the membrane is kept at a 75° angle relative to the horizontal plane for gravity drainage for 15 seconds.

[0066] The initial liquid removal process was performed using a first nitrogen flow along the membrane surface. The flow velocity of the first nitrogen flow on the membrane surface was 0.80 m / s, the angle between the first nitrogen flow and the membrane surface was 25°, the distance between the air knife nozzle and the membrane surface was 35 mm, and the initial liquid removal time was 6 s.

[0067] According to the accompanying membrane test, the residual n-heptane loading per unit area of ​​the membrane after the initial dehydration treatment was 1.24 g / m². 2 .

[0068] S4. Perform two-stage solvent vapor curing.

[0069] The main membrane processed in step S3 is fed into the first solvent vapor ripening zone within 2 seconds. A sealed transition channel is provided between the first nitrogen gas outlet and the inlet of the first solvent vapor ripening zone. The activity of n-heptane vapor in the transition channel is 0.76, and the transition time is 1.6 seconds.

[0070] The temperature in the first solvent vapor ripening zone is 28℃, the activity of n-heptane vapor is 0.82, the airflow velocity inside the chamber is 0.12 m / s, and the membrane surface temperature is 28℃. Based on the actual partial pressure of n-heptane vapor, the membrane surface temperature is approximately 4.0℃ higher than the dew point temperature of n-heptane vapor. The ripening time for the first stage is 30 s.

[0071] According to the accompanying membrane test, the residual n-heptane loading per unit area of ​​the membrane was 1.07 g / m² when leaving the first solvent vapor ripening zone. 2 The mass reduction rate of residual n-heptane in the first solvent vapor maturation zone was 13.7%.

[0072] A sealed transition section is provided between the first solvent vapor maturation zone and the second solvent vapor maturation zone. The activity of n-heptane vapor in the sealed transition section is 0.42, and the residence time is 1.0s. The residence time is included in the second solvent vapor maturation stage.

[0073] The temperature in the second solvent vapor ripening zone is 28℃, the activity of n-heptane vapor is 0.42, the airflow velocity inside the chamber is 0.18 m / s, and the membrane surface temperature is 28℃. Based on the actual partial pressure of n-heptane vapor, the membrane surface temperature is approximately 16.1℃ higher than the dew point temperature of n-heptane vapor. The total ripening time of the second stage, including the gas seal transition section, is 40 s.

[0074] According to the accompanying membrane test, the residual n-heptane loading per unit area of ​​the membrane was 0.34 g / m² when leaving the second solvent vapor ripening zone. 2 .

[0075] S5. Perform a secondary solvent removal process.

[0076] A second nitrogen flow was used to perform secondary desolvation on the membrane surface. The flow rate of the second nitrogen flow on the membrane surface was 4.5 m / s, the angle between the flow and the membrane surface was 30°, the distance between the air knife nozzle and the membrane surface was 40 mm, and the treatment time was 12 s.

[0077] According to the accompanying membrane test, the residual n-heptane loading per unit area of ​​the membrane after secondary solvent removal was 0.058 g / m². 2 .

[0078] S6. Perform heat treatment and water washing.

[0079] The membrane treated in step S5 was heat-treated in a hot air environment at 78°C for 5 minutes. After heat treatment, the membrane was immersed in flowing deionized water at 35°C for 10 minutes, and then immersed in a 0.50% glycerol aqueous solution for 10 minutes. After removal, it was sealed and stored to obtain a fouling-resistant and chlorine-resistant seawater desalination membrane.

[0080] Example 2

[0081] This embodiment discloses a method for preparing a pollution-resistant and chlorine-resistant seawater desalination membrane. The difference compared to Example 1 is: In step S3, the gravity drainage time is 20 s, the flow rate of the first nitrogen gas on the membrane surface is 0.55 m / s, the treatment time is 5 s, and the residual n-heptane loading per unit area of ​​the membrane after the initial dehydration is 0.91 g / m². 2 .

[0082] In step S4, the temperature of the first solvent vapor ripening zone is 26°C, the activity of n-heptane vapor is 0.72, the membrane surface temperature is approximately 6.1°C higher than the dew point temperature of n-heptane vapor, and the ripening time is 20 seconds. After treatment in the first solvent vapor ripening zone, the residual n-heptane loading per unit area of ​​the membrane is 0.76 g / m². 2 The quality reduction rate was 16.5%.

[0083] The temperature in the second solvent vapor ripening zone was 26℃, the activity of n-heptane vapor was 0.34, and the membrane surface temperature was approximately 19.4℃ higher than the n-heptane vapor dew point temperature. The total ripening time was 30 s. After treatment in the second solvent vapor ripening zone, the residual n-heptane loading per unit area of ​​the membrane was 0.21 g / m². 2 .

[0084] In step S5, the flow rate of the second nitrogen gas on the membrane surface is 3.0 m / s, the treatment time is 15 s, and the residual n-heptane loading per unit area of ​​the membrane after the second solvent removal is 0.046 g / m². 2 .

[0085] In step S6, the heat treatment temperature is 72℃ and the heat treatment time is 6 minutes.

[0086] Other formulations and process parameters are the same as in Example 1.

[0087] Example 3

[0088] This embodiment discloses a method for preparing a pollution-resistant and chlorine-resistant seawater desalination membrane. The difference compared to Example 1 is: In step S3, the gravity drainage time is 8 s, the flow rate of the first nitrogen gas on the membrane surface is 1.10 m / s, the treatment time is 4 s, and the residual n-heptane loading per unit area of ​​the membrane after the initial dehydration is 1.78 g / m². 2 .

[0089] In step S4, the temperature of the first solvent vapor ripening zone is 30°C, the activity of n-heptane vapor is 0.88, the membrane surface temperature is approximately 2.6°C higher than the dew point temperature of n-heptane vapor, and the ripening time is 40 seconds. After treatment in the first solvent vapor ripening zone, the residual n-heptane loading per unit area of ​​the membrane is 1.51 g / m². 2 The quality reduction rate was 15.2%.

[0090] The temperature in the second solvent vapor ripening zone was 30℃, the activity of n-heptane vapor was 0.52, and the membrane surface temperature was approximately 12.5℃ higher than the n-heptane vapor dew point temperature. The total ripening time was 55 s. After treatment in the second solvent vapor ripening zone, the residual n-heptane loading per unit area of ​​the membrane was 0.56 g / m². 2 .

[0091] In step S5, the flow rate of the second nitrogen gas on the membrane surface is 6.5 m / s, the treatment time is 10 s, and the residual n-heptane loading per unit area of ​​the membrane after the second solvent removal is 0.074 g / m². 2 .

[0092] In step S6, the heat treatment temperature is 85℃ and the heat treatment time is 3 minutes.

[0093] Other formulations and process parameters are the same as in Example 1.

[0094] Example 4

[0095] This embodiment discloses a method for preparing a pollution-resistant and chlorine-resistant seawater desalination membrane using a polyethersulfone porous support layer.

[0096] The following ingredients were mixed by mass percentage: 17.0% polyethersulfone, 1.5% polyvinylpyrrolidone, 2.5% polyethylene glycol 400, and 79.0% N-methylpyrrolidone. The mixture was stirred at 65°C for 8 hours and allowed to stand for 12 hours to remove bubbles, thus obtaining the casting solution.

[0097] The casting solution was applied to the surface of the polyester nonwoven fabric using a doctor blade with a gap of 125 μm. After being left in the air for 6 seconds, it was immersed in deionized water at 23°C to solidify. The preparation steps for other support layers were the same as in Example 1.

[0098] The aqueous solution consists of 2.50% m-phenylenediamine, 0.15% triethylamine, 0.20% camphor sulfonic acid, 0.020% sodium dodecyl sulfate, and the balance deionized water. The pH of the aqueous solution at 25°C is 10.48. The polyethersulfone support layer is in contact with the aqueous solution for 75 seconds.

[0099] The organic phase solution consisted of 0.10% trimesoyl chloride and 99.90% n-heptane, with an organic phase contact time of 45 s.

[0100] In step S3, gravity drainage is performed at a 70° tilt angle for 12 seconds. The flow rate of the first nitrogen gas on the membrane surface is 0.70 m / s, and the treatment time is 8 seconds. After the initial liquid removal, the residual n-heptane loading per unit area of ​​the membrane is 1.36 g / m². 2 .

[0101] The temperature in the first solvent vapor ripening zone was 27℃, the activity of n-heptane vapor was 0.78, the membrane surface temperature was approximately 4.6℃ higher than the dew point temperature of n-heptane vapor, and the ripening time was 35s. After treatment, the residual n-heptane loading per unit area of ​​the membrane was 1.13 g / m². 2 The quality reduction rate was 16.9%.

[0102] The temperature in the second solvent vapor ripening zone was 27℃, the activity of n-heptane vapor was 0.38, the membrane surface temperature was approximately 17.7℃ higher than the dew point temperature of n-heptane vapor, and the total ripening time was 45s. The residual n-heptane loading per unit area of ​​the membrane after treatment was 0.31 g / m². 2 .

[0103] The second nitrogen flow rate on the membrane surface was 5.0 m / s, the treatment time was 14 s, and the residual n-heptane loading per unit area of ​​the membrane after the second solvent removal was 0.051 g / m². 2 .

[0104] The membrane was heat-treated at 80℃ for 4 minutes, and then washed with deionized water at 30℃ for 12 minutes. After washing, the membrane was immersed in a 0.50% glycerol aqueous solution for 10 minutes, then removed and sealed for storage to obtain a fouling-resistant and chlorine-resistant seawater desalination membrane.

[0105] This embodiment is only used to illustrate that the two-stage solvent vapor curing process of the present invention can be applied to polyethersulfone porous support layers, and is not used to evaluate the performance differences between polysulfone support layers and polyethersulfone support layers.

[0106] Example 5

[0107] This embodiment discloses a method for continuous preparation of anti-fouling and chlorine-resistant seawater desalination membranes.

[0108] A 500mm wide polysulfone porous support membrane was used as a continuous roll material, and the film feeding speed was 0.80m / min. The aqueous phase solution, organic phase solution, and their concentrations were the same as in Example 1.

[0109] The effective contact length of the polysulfone porous support membrane through the aqueous phase tank is 1.20m, and the aqueous phase contact time is 90s. After the excess aqueous phase is removed by the squeezing roller, the membrane roll enters the organic phase coating area, and the organic phase contact time is 35s.

[0110] After the organic phase contact is completed, the membrane roll passes through a 0.20m long gravity drainage section at a 75° angle for 15s, and then passes through a first nitrogen gas knife. The average flow velocity of the first nitrogen gas on the membrane surface is 0.85m / s, and the treatment time is 7s.

[0111] The residual n-heptane loading per unit area of ​​the membrane was measured using accompanying test membranes positioned on the left, center, and right along the membrane width direction. 2 1.27g / m 2 and 1.22g / m 2 The average value is 1.23 g / m 2 .

[0112] A sealed transition channel with a length of 0.020 m is set between the outlet of the first nitrogen gas knife and the inlet of the first solvent vapor maturation zone. The transition time is 1.5 s, and the activity of n-heptane vapor in the transition channel is 0.74.

[0113] The effective length of the first solvent vapor ripening zone is 0.40 m, the temperature is 28 °C, the activity of n-heptane vapor is 0.80, the gas flow velocity above the membrane surface is 0.15 m / s, and the ripening time is 30 s. After treatment in the first solvent vapor ripening zone, the average residual n-heptane loading per unit area of ​​the membrane is 1.04 g / m². 2 The quality reduction rate was 15.4%.

[0114] A sealed gas-sealed transition section with a length of 0.015 m is set between the first solvent vapor maturation zone and the second solvent vapor maturation zone, with a residence time of 1.1 s. The activity of n-heptane vapor in the gas-sealed transition section is 0.40, and its residence time is included in the second stage maturation time.

[0115] The effective length of the second solvent vapor ripening zone is 0.52 m, the temperature is 28 °C, the activity of n-heptane vapor is 0.40, and the total ripening time in the second stage is 40.1 s. After treatment in the second solvent vapor ripening zone, the average residual n-heptane loading per unit area of ​​the membrane is 0.32 g / m². 2 .

[0116] A second nitrogen gas knife was then used for secondary solvent removal. The average flow velocity of the second nitrogen gas on the membrane surface was 4.8 m / s, and the treatment time was 12 s. After the second solvent removal, the average residual n-heptane loading per unit area of ​​the membrane was 0.055 g / m². 2 .

[0117] The membrane roll is passed through a 4.0m long heat treatment channel at 78℃ for 5 minutes, followed by a 35℃ flowing water washing tank for 10 minutes. After washing, the membrane roll is treated in a 0.50% glycerol aqueous solution treatment tank for 10 minutes, then removed, sealed, and rolled up to obtain a pollution-resistant and chlorine-resistant seawater desalination membrane roll.

[0118] Sampling was performed 30 minutes after the continuous production equipment had been running stably. Within 10 minutes prior to sampling, the film flow rate fluctuation should not exceed ±0.02 m / min, the temperature fluctuation in the two curing zones should not exceed ±0.5℃, and the n-heptane vapor activity fluctuation at each sampling point should not exceed ±0.02.

[0119] The n-heptane vapor activities at the left, center, and right positions in the first solvent vapor maturation zone are 0.79, 0.81, and 0.80, respectively; the n-heptane vapor activities at the corresponding positions in the second solvent vapor maturation zone are 0.39, 0.41, and 0.40, respectively.

[0120] Comparative Example 1 This comparative example discloses a method for preparing a seawater desalination membrane using a single high-speed nitrogen desolvation process. The difference compared to Example 1 is: After the organic phase contact ended and gravity drainage was completed for 15 seconds, controlled initial desolvation was not performed using the first nitrogen flow, nor was the membrane subjected to the first or second solvent vapor maturation zones. Instead, the membrane was directly treated with nitrogen at a flow rate of 4.5 m / s for 18 seconds, reducing the residual n-heptane loading per unit area of ​​the membrane to 0.061 g / m². 2 .

[0121] The other formulations and process parameters are the same as in Example 1. This comparative example is used to reflect the overall performance of a conventional one-step high-speed solvent removal process and is not used to evaluate the effect of any single process parameter.

[0122] Comparative Example 2 This comparative example discloses a method for preparing a seawater desalination membrane without solvent vapor aging. The difference compared to Example 1 is: The initial dehydration was performed according to step S3 of Example 1, resulting in a residual n-heptane loading of 1.22 g / m² per unit area of ​​the membrane after the initial dehydration. 2After the initial solvent removal, the membrane was treated directly with a second nitrogen flow at a velocity of 4.5 m / s for 12 s without passing through two solvent vapor maturation zones. After the second solvent removal, the residual n-heptane loading per unit area of ​​the membrane was 0.063 g / m². 2 .

[0123] Other formulations and process parameters are the same as in Example 1.

[0124] Comparative Example 3 This comparative example discloses a method for preparing a seawater desalination membrane that only undergoes high solvent activity aging. The difference compared to Example 1 is: After step S3, the residual n-heptane loading per unit area of ​​the membrane is 1.25 g / m². 2 The membrane was only treated for 70 seconds in a ripening zone at 28°C with a n-heptane vapor activity of 0.82, and was not subjected to a ripening zone with low solvent activity. After high-activity ripening, the residual n-heptane loading per unit area of ​​the membrane was 0.98 g / m². 2 .

[0125] Subsequently, the membrane was treated with a second nitrogen flow at a flow rate of 4.5 m / s for 12 s. After the second solvent removal, the residual n-heptane loading per unit area of ​​the membrane was 0.072 g / m². 2 .

[0126] Other formulations and process parameters are the same as in Example 1.

[0127] Comparative Example 4 This comparative example discloses a method for preparing a seawater desalination membrane that only undergoes low solvent activity aging. The difference compared to Example 1 is: After step S3, the residual n-heptane loading per unit area of ​​the membrane was 1.23 g / m³. 2 The membrane was only subjected to a 70-second curing zone at 28°C with a n-heptane vapor activity of 0.42, without passing through a high-solvent-activity curing zone. After curing, the residual n-heptane loading per unit area of ​​the membrane was 0.26 g / m². 2 .

[0128] Subsequently, the membrane was treated with a second nitrogen flow at a flow rate of 4.5 m / s for 12 s. After the second solvent removal, the residual n-heptane loading per unit area of ​​the membrane was 0.049 g / m². 2 .

[0129] Other formulations and process parameters are the same as in Example 1.

[0130] Comparative Example 5 This comparative example discloses a method for preparing seawater desalination membranes by first ripening with low solvent activity and then ripening with high solvent activity. The difference compared to Example 1 is: After step S3, the residual n-heptane loading per unit area of ​​the membrane is 1.24 g / m². 2 .

[0131] The membrane was first subjected to a curing zone at 28°C with a n-heptane vapor activity of 0.42 for 40 seconds. After treatment, the residual n-heptane loading per unit area of ​​the membrane was 0.39 g / m². 2 Subsequently, it was treated in a maturation zone at 28℃ with a n-heptane vapor activity of 0.82 for 30 seconds. After treatment, the residual n-heptane loading per unit area of ​​the membrane was 0.34 g / m². 2 .

[0132] Subsequently, the membrane was treated with a second nitrogen flow at a flow rate of 4.5 m / s for 12 s. After the second solvent removal, the residual n-heptane loading per unit area of ​​the membrane was 0.057 g / m². 2 .

[0133] Other formulations and process parameters are the same as in Example 1. This comparative example has the same two n-heptane vapor activities, the same total aging time, the same second nitrogen flow treatment conditions, and similar initial and final residual n-heptane loadings as Example 1. The main difference is the order of the two aging stages.

[0134] Comparative Example 6 This comparative example discloses a method for preparing a seawater desalination membrane with excessively low residual n-heptane loading after initial desolvation. The difference compared to Example 1 is: In step S3, the flow rate of the first nitrogen gas on the membrane surface is 2.2 m / s, and the treatment time is 12 s, so that the residual n-heptane loading per unit area of ​​the membrane after the initial desolvation is 0.36 g / m². 2 .

[0135] Subsequently, the membrane was treated according to the first solvent vapor curing zone and the second solvent vapor curing zone of Example 1. After treatment in the first solvent vapor curing zone, the residual n-heptane loading per unit area of ​​the membrane was 0.31 g / m². 2 The residual n-heptane loading per unit area of ​​the membrane after treatment in the second solvent vapor maturation zone is 0.12 g / m². 2 .

[0136] After treatment with a second nitrogen flow at a flow rate of 4.5 m / s for 12 s, the residual n-heptane loading per unit area of ​​the membrane after secondary solvent removal was 0.027 g / m². 2 .

[0137] This comparative example is used to illustrate that when the initial liquid removal amount is too low, the subsequent aging and secondary desolventizing processes deviate from the controlled state defined by this invention as a whole, and is not used alone to prove the role of the initial residual n-heptane loading.

[0138] Comparative Example 7 This comparative example discloses a method for preparing a seawater desalination membrane with excessively high residual n-heptane loading after initial desolvation. The difference compared to Example 1 is: After the organic phase contact, gravity drainage was performed for only 5 seconds without initial nitrogen flow for dehydration. The residual n-heptane loading per unit area of ​​the membrane after the initial dehydration was 2.73 g / m². 2 .

[0139] Subsequently, the membrane was treated according to the first solvent vapor curing zone and the second solvent vapor curing zone of Example 1. After treatment in the first solvent vapor curing zone, the residual n-heptane loading per unit area of ​​the membrane was 2.39 g / m². 2 The residual n-heptane loading per unit area of ​​the membrane after treatment in the second solvent vapor maturation zone is 0.81 g / m². 2 .

[0140] The membrane was treated with a second nitrogen flow rate of 4.5 m / s, the same as in Example 1, for 12 s. After the second solvent removal, the residual n-heptane loading per unit area of ​​the membrane was 0.126 g / m². 2 .

[0141] This comparative example is used to illustrate that if the initial liquid removal amount is too high, the subsequent aging and secondary desolventizing processes are difficult to stably reach the controlled state defined by this invention, and is not used alone to prove the role of the initial residual n-heptane loading.

[0142] Comparative Example 8 This comparative example discloses a method for preparing a seawater desalination membrane with low n-heptane vapor activity and excessive volatilization during the first ripening stage. The difference from Example 1 is: After step S3, the residual n-heptane loading per unit area of ​​the membrane is 1.26 g / m². 2 .

[0143] The temperature in the first solvent vapor ripening zone was 28℃, the activity of n-heptane vapor was 0.55, and the ripening time remained at 30 s. After treatment in the first solvent vapor ripening zone, the residual n-heptane loading per unit area of ​​the membrane was 0.82 g / m². 2 The quality reduction rate was 34.9%.

[0144] The temperature in the second solvent vapor ripening zone was 28℃, the activity of n-heptane vapor was 0.42, and the ripening time remained at 40 s. After treatment in the second solvent vapor ripening zone, the residual n-heptane loading per unit area of ​​the membrane was 0.31 g / m². 2 .

[0145] After treatment with a second nitrogen flow at a flow rate of 4.5 m / s for 12 s, the residual n-heptane loading per unit area of ​​the membrane after secondary solvent removal was 0.054 g / m². 2 .

[0146] Other formulations and process parameters are the same as in Example 1.

[0147] Performance testing Each embodiment and comparative example was prepared in three independent film-forming batches. Except for continuous embodiment 5, each batch produced one 300mm×300mm film sheet.

[0148] Nine sampling centers for each membrane were located at the intersections of points 50 mm, 150 mm, and 250 mm from the left edge of the membrane and 50 mm, 150 mm, and 250 mm from the front edge of the membrane. A circular sample with a diameter of 40 mm was cut from each sampling location, ensuring no overlap between samples, resulting in an effective test area of ​​12.56 cm². 2 .

[0149] In the continuous embodiment 5, three 500mm×500mm membrane sheets were cut at 2m intervals along the membrane walking direction during the stable operation of the equipment, and each membrane sheet was sampled in the same nine-point manner.

[0150] Before each performance test, the membrane was removed from the glycerol protective solution, rinsed with running deionized water for 30 minutes, and then soaked in deionized water for 12 hours to remove the glycerol from the membrane. After soaking, the corresponding tests were performed.

[0151] Each circular sample was first used for basic desalination performance testing. For Examples 1, 5, Comparative Examples 1, 2, and 5, after completing the basic desalination performance testing for each independent film-forming batch, three independent samples were selected from the nine circular samples for antifouling performance testing, and another three independent samples were selected for chlorine resistance performance testing. The remaining samples were used for backup or retesting. The same sample was not used for both antifouling performance testing and chlorine resistance performance testing simultaneously.

[0152] The data in each table are the arithmetic mean of the results obtained from three independent film-forming batches. For the nine-point homogeneity index, the coefficient of variation and range of the nine-point data for each independent film sheet were first calculated, and then the arithmetic mean of the results obtained from the three independent film-forming batches was taken. The coefficient of variation was calculated by dividing the sample standard deviation of the measured values ​​at each sampling location by the arithmetic mean and then multiplying by 100%; the range was calculated by the difference between the maximum and minimum values ​​among the measured values ​​at each sampling location.

[0153] I. Basic Desalination Performance and Membrane Uniformity Testing: Testing was conducted according to GB / T 32373-2025 "Reverse Osmosis Membrane Test Method". The test solution was a 35.0 g / L sodium chloride aqueous solution, the temperature was 25±0.5℃, the pH was 7.0±0.2, the operating pressure was 5.5 MPa, and the membrane crossflow velocity was 0.20 m / s. After pre-pressurizing and stabilizing each sample at the test pressure for 60 min, the water flux and NaCl rejection rate were recorded.

[0154] Water flux is calculated as the volume of product water passing through a unit effective membrane area per unit time. NaCl rejection rate is calculated using the following formula: NaCl rejection rate = (1 - NaCl concentration in product water ÷ NaCl concentration in feed water) × 100%.

[0155] Table 1. Basic desalination performance and membrane uniformity

[0156] As shown in Table 1, the coefficient of variation of water flux and the range of NaCl rejection rate in Examples 1-5 were significantly lower than those in the comparative examples. This indicates that retaining a limited amount of n-heptane after the initial desolvation and sequentially performing high solvent activity aging and low solvent activity aging are beneficial to reducing the differences in film formation at different locations on the membrane.

[0157] Example 1 and Comparative Example 5 have similar initial residual n-heptane loading, the same two n-heptane vapor activities, and the same total aging time. However, Comparative Example 5 reversed the two aging stages, and its water flux variation coefficient and NaCl rejection rate range increased significantly, indicating that the order of the two aging stages cannot be interchanged.

[0158] II. Effect of maturation sequence on the uniformity of residual n-heptane position: In Example 1 and Comparative Example 5, after the initial dehydration and the first curing stage, accompanying test membranes were placed on the left, middle, and right sides of the membrane, respectively. The residual n-heptane loading per unit area of ​​the membrane was measured, and the positional variation coefficient was calculated. To eliminate the influence of differences in the initial dehydration state on the comparison results, in each independent membrane preparation batch, the accompanying test membranes used in Example 1 and Comparative Example 5 were obtained from the same batch of membranes that had completed step S3, and were respectively entered into the corresponding curing treatment path. Therefore, the residual n-heptane loading on the left, middle, and right sides after the initial dehydration of both examples used the same initial measurement value.

[0159] Table 2. Location distribution of residual n-heptane under different maturation sequences

[0160] As shown in Table 2, after the first high-activity ripening stage, the coefficient of variation of the residual n-heptane position in Example 1 decreased from 8.7% to 4.1%, indicating that the high-activity environment inhibits rapid volatilization while making the residual n-heptane state at different positions more uniform.

[0161] In Comparative Example 5, after entering a low-activity aging environment, the coefficient of variation of the position of the residual n-heptane increased to 23.5%; even after entering a high-activity environment, the coefficient of variation was still 15.6%, indicating that after the thin liquid region rapidly thinned in the first stage, the subsequent high-activity treatment could not fully restore the positional differences that had already formed.

[0162] III. Anti-pollution performance: A sodium alginate contamination system containing calcium was used for detection. Sodium alginate was first fully dissolved in a 35.0 g / L sodium chloride aqueous solution. Then, calcium chloride was added before the contamination test to achieve a sodium alginate concentration of 20 mg / L and a calcium chloride concentration of 2 mmol / L in the contaminated solution. After adding calcium chloride, the solution was stirred for 10 min, and the contamination test began within 30 min. The pH of the contaminated solution was 8.0 ± 0.2, and the temperature was 25 ± 0.5℃.

[0163] By adjusting the operating pressure of each sample before the first contamination, the initial stable water flux was made to be 25.0 ± 1.0 L·m. -2 ·h -1 Once the test pressure is determined, the same pressure is maintained for three consecutive contamination-cleaning cycles without readjustment.

[0164] Each sample was first stabilized for 60 min using a 35.0 g / L sodium chloride aqueous solution without sodium alginate and calcium chloride, and the initial stable flux J0 before the first contamination was recorded. Then, it was switched to the contaminated solution and run for 12 h, and the flux Jf,i at the end of the i-th contamination was recorded. Then, it was washed with a 35.0 g / L sodium chloride aqueous solution without contaminants at the same cross-flow rate for 30 min, and the flux Jr,i at the end of the i-th wash was recorded, where i is 1, 2 or 3.

[0165] The flux decline rate and flux recovery rate for each cycle are calculated relative to J0 before the first pollution: Flux decline rate of cycle i = (J0 - Jf,i) ÷ J0 × 100%; Flux recovery rate of cycle i = Jr,i ÷ J0 × 100%.

[0166] Table 3. Results of Anti-pollution Performance Tests

[0167] As shown in Table 3, the flux decline rate of Examples 1 and 5 in the first and third contamination-cleaning cycles was lower than that of the comparative examples, and the flux recovery rate was higher than that of the comparative examples. This indicates that the membrane prepared by the process of the present invention has good anti-fouling and cleaning recovery performance under the calcium-containing alginate contamination conditions.

[0168] IV. Chlorine resistance test: Refer to the basic principles of GB / T 38908-2020 "Test method for chlorine resistance of household reverse osmosis and nanofiltration membrane elements" and set the following test conditions according to seawater reverse osmosis flat sheet membrane.

[0169] The membrane was immersed in an aqueous solution of sodium hypochlorite containing 100 mg / L free chlorine, with a pH of 7.0 ± 0.2 and a temperature of 25 ± 1 °C, and treated in the dark for 10 hours. Samples were taken every 2 hours, and the test solution was diluted with chlorine-free water to the linear detection range of the DPD method. The free chlorine concentration was then measured, and sodium hypochlorite was added according to the measurement results to maintain the free chlorine concentration in the original solution at 95–105 mg / L.

[0170] The cumulative chlorine exposure is calculated by summing the products of the average free chlorine concentration and the corresponding time for each time period. The actual cumulative chlorine exposure is 998–1015 mg·h / L.

[0171] After chlorine exposure, the membrane was quickly drained and immersed in a 200 mg / L sodium bisulfite aqueous solution for 10 min. After confirming that the free chlorine in the stop solution was below the detection limit using the DPD method, it was thoroughly rinsed with deionized water.

[0172] A blank immersion control was set up with no sodium hypochlorite and other immersion conditions being the same. The change in NaCl rejection rate before and after the blank immersion was no more than 0.03 percentage points.

[0173] After chlorine exposure, water flux and NaCl rejection rate were retested under the basic desalination performance testing conditions, and the decrease in NaCl rejection rate and the increase in water flux were calculated. The decrease in NaCl rejection rate was calculated as the difference between the NaCl rejection rate before and after chlorine exposure; the increase in water flux after chlorine exposure was calculated by dividing the difference between the water flux after and before chlorine exposure by the water flux before chlorine exposure, and then multiplying by 100%.

[0174] Table 4 Chlorine resistance test results

[0175] As shown in Table 4, after cumulative exposure to approximately 1000 mg·h / L chlorine in Examples 1 and 5, the decrease in NaCl rejection rate and the increase in water flux were both lower than those in the comparative examples, indicating that the membranes prepared by the process of the present invention have good separation performance retention capabilities under the chlorine exposure conditions.

[0176] In summary, the membranes prepared in Examples 1-5 generally outperformed the comparative examples in terms of basic desalination performance and membrane uniformity. The representative examples also demonstrated good flux recovery and separation performance retention in tests involving calcium alginate contamination and chlorine exposure. These results indicate that sequential high solvent activity curing, low solvent activity curing, and secondary solvent removal are beneficial for improving the uniformity of seawater desalination membrane formation and enhancing its antifouling properties and performance stability after chlorine exposure.

[0177] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principle of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a pollution-resistant and chlorine-resistant seawater desalination membrane, characterized in that, Includes the following steps: S1. A porous polymer support layer is formed on the surface of a nonwoven fabric substrate, and the porous polymer support layer is brought into contact with an aqueous solution containing m-phenylenediamine to remove the flowable aqueous solution from the surface of the porous polymer support layer, thereby obtaining an aqueous treatment membrane. S2. The aqueous phase treatment membrane is brought into contact with an organic phase solution containing trimesoyl chloride and n-heptane, and an aromatic polyamide separation layer is formed on the surface of the porous polymer support layer through interfacial polymerization between the m-phenylenediamine and the trimesoyl chloride. S3. Stop the contact between the aqueous phase treatment membrane and the organic phase solution, drain the free-flowing bulk organic phase solution from the surface of the aromatic polyamide separation layer, and perform an initial dehydration treatment on the surface of the aromatic polyamide separation layer using a first nitrogen flow, so that the residual n-heptane loading per unit area of ​​the membrane after the initial dehydration treatment is 0.8–2.0 g / m². 2 ; S4. The membrane treated in step S3 is passed sequentially through a first solvent vapor maturation zone and a second solvent vapor maturation zone, both of which contain nitrogen gas and n-heptane vapor. The solvent activity of n-heptane vapor in the first solvent vapor ripening zone is 0.70–0.90, the ripening time is 15–45 s, and the membrane surface temperature is 2–7 °C higher than the dew point temperature of n-heptane vapor in the first solvent vapor ripening zone. After treatment in the first solvent vapor ripening zone, the residual n-heptane loading per unit area of ​​the membrane decreases by no more than 25%. The solvent activity of n-heptane vapor in the second solvent vapor ripening zone is 0.30–0.55, the ripening time is 15–60 s, and the membrane surface temperature is 8–25 °C higher than the dew point temperature of n-heptane vapor in the second solvent vapor ripening zone. After treatment in the second solvent vapor ripening zone, the residual n-heptane loading per unit area of ​​the membrane is 0.15–0.60 g / m². 2 ; The solvent activity of n-heptane vapor in the first solvent vapor maturation zone is at least 0.20 higher than that of n-heptane vapor in the second solvent vapor maturation zone; The solvent activity of the n-heptane vapor is the ratio of the actual partial pressure of the n-heptane vapor in the maturation zone to the saturated vapor pressure of n-heptane at the same temperature; S5. The membrane treated in step S4 is subjected to a second nitrogen stream for secondary solvent removal, ensuring that the residual n-heptane loading per unit area of ​​the membrane after the secondary solvent removal is not higher than 0.10 g / m³. 2 ; S6. The membrane treated in step S5 is subjected to heat treatment and water washing in sequence to obtain the anti-fouling and chlorine-resistant seawater desalination membrane.

2. The preparation method according to claim 1, characterized in that, The porous polymer support layer is formed of polysulfone or polyethersulfone; The porous polymer support layer is disposed on the surface of the polyester nonwoven fabric substrate. The wet thickness of the porous polymer support layer is 35–60 μm, and the pure water flux at 25°C and 0.10 MPa is 500–900 L·m. -2 ·h -1 .

3. The preparation method according to claim 1, characterized in that, In step S1, the aqueous solution comprises the following components by mass percentage: m-Phenylated diamine 1.8%–2.8%; Triethylamine 0.05%–0.30%; Camphor sulfonic acid 0.05%–0.30%; Sodium dodecyl sulfate 0.005%–0.030%; The remainder is water; The aqueous solution has a pH of 10.0 to 10.8 at 25°C, and the contact time between the porous polymer support layer and the aqueous solution is 30 to 180 seconds.

4. The preparation method according to claim 1, characterized in that, In step S2, the mass fraction of pyromellitic methyl chloride in the organic phase solution is 0.06% to 0.20%, with the remainder being n-heptane; The contact temperature between the aqueous phase treatment membrane and the organic phase solution is 20–35°C, and the contact time is 15–90 seconds.

5. The preparation method according to claim 1, characterized in that, In step S3, after the main organic phase solution is discharged, the membrane surface is kept at 60° to 90° relative to the horizontal plane, and the liquid is discharged by gravity for 5 to 30 seconds. Then, the first nitrogen flow is used for the initial liquid removal treatment. The average flow velocity of the first nitrogen gas at a distance of 5 mm from the membrane surface is 0.3 to 1.5 m / s, the angle between the first nitrogen gas flow and the membrane surface is 10° to 40°, and the treatment time of the first nitrogen gas flow is 2 to 15 s.

6. The preparation method according to claim 1, characterized in that, A first sealed transition channel is provided between the outlet of the first nitrogen gas flow and the inlet of the first solvent vapor maturation zone. The residence time of the membrane in the first sealed transition channel does not exceed 2 seconds. The solvent activity of n-heptane vapor in the first sealed transition channel is 0.70 to 0.

90. A second sealed transition channel is provided between the first solvent vapor maturation zone and the second solvent vapor maturation zone. The solvent activity of n-heptane vapor in the second sealed transition channel is 0.30 to 0.

55. The residence time of the membrane in the second sealed transition channel does not exceed 2 seconds, and the residence time is included in the maturation time of the second solvent vapor maturation zone.

7. The preparation method according to claim 1, characterized in that, The n-heptane vapor in the first solvent vapor maturation zone and the second solvent vapor maturation zone are formed in the following ways: The first part of the nitrogen flow is passed through a constant-temperature n-heptane saturator to obtain a first mixed gas containing n-heptane vapor; The first mixed gas is mixed with a second portion of nitrogen gas that does not pass through the constant-temperature n-heptane saturator, and the solvent activity of n-heptane vapor in the first solvent vapor ripening zone and the second solvent vapor ripening zone is controlled by adjusting the flow ratio of the first portion of nitrogen gas to the second portion of nitrogen gas. The actual partial pressure of n-heptane vapor at the outlet of the constant-temperature n-heptane saturator is not less than 90% of the saturated vapor pressure of n-heptane at the temperature of the constant-temperature n-heptane saturator.

8. The preparation method according to claim 1, characterized in that, In step S5, the average flow velocity of the second nitrogen gas at a distance of 5 mm from the membrane surface is 2 to 8 m / s, and the secondary desolvation treatment time is 5 to 30 s; In step S6, the heat treatment temperature is 60-90℃ and the heat treatment time is 2-8 min; after heat treatment, the water is washed at a temperature of 20-50℃ for 5-20 min, and then treated with a 0.2%-1.0% glycerol aqueous solution for 5-20 min.

9. A pollution-resistant and chlorine-resistant seawater desalination membrane, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 8.

10. A method for seawater reverse osmosis desalination, characterized in that, The antifouling and chlorine-resistant seawater desalination membrane of claim 9 is made into a spiral-wound reverse osmosis membrane element, and seawater to be treated with a total dissolved solids content of 25-45 g / L flows through the spiral-wound reverse osmosis membrane element and reverse osmosis separation is carried out at an operating pressure of 4.5-7.0 MPa.

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