A forward osmosis membrane, its preparation method and application

Abstract

The application discloses a kind of forward osmosis membranes and preparation method and application, a kind of forward osmosis membranes, including sequentially stacked settings base film layer, intermediate layer and separation layer;Base film layer includes the porous hydrophilic polyethylene film of containing hydroxyl group;Intermediate layer includes the hydrophilic layer formed by crosslinking reaction of ethylene-vinyl alcohol copolymer and glutaraldehyde, intermediate layer is anchored to the surface of the base film layer and penetrates into the pore of the base film layer;Fluorine-containing polysulfonamide formed by monomer mixture polymerization, the monomer mixture includes polyamine monomer and poly sulfuryl chloride monomer, polyamine monomer includes fluorine-free polyamine monomer and fluorine-containing rigid amine monomer in it.The surface of the base film layer is modified in the application, while giving it high hydrophilicity, effectively control the pore size of the surface of the base film layer, successfully prepare a kind of forward osmosis membrane with high selectivity, high water permeability, especially excellent acid resistance.

Description

Technical Field

[0001] This invention belongs to the field of forward osmosis membrane technology, and particularly relates to a forward osmosis membrane, its preparation method, and its application. Background Technology

[0002] Forward osmosis (FO) technology relies on the high osmotic pressure generated by a high-concentration draw solution to extract water molecules from a lower-concentration feed solution. Compared to reverse osmosis (RO) technology, this technology utilizes the osmotic pressure difference between the solutions on both sides of the membrane to achieve separation, offering advantages such as high recovery rate, low concentrate discharge, minimal membrane fouling, and no need for external pressure drive. Currently, forward osmosis membrane technology has been applied in various fields, including industrial wastewater and landfill leachate treatment, liquid food processing, seawater desalination, and energy recovery based on pressure-damped osmosis. Furthermore, this technology is also used in life support systems for emergency rescue scenarios to produce drinking water. The phosphate chemical industry (such as phosphoric acid production and phosphate fertilizer manufacturing) generates large amounts of acidic wastewater during production. This wastewater typically contains high concentrations of phosphates, fluorides, and heavy metal ions, has a low pH value, and is highly corrosive. Traditional lime neutralization methods not only consume large amounts of chemical reagents and produce large quantities of difficult-to-dispose chemical sludge, but also waste phosphorus resources. If forward osmosis technology can be used to concentrate such acidic wastewater, it can achieve water reuse and enrich valuable resources such as phosphates, resulting in significant economic and environmental benefits. However, conventional polyamide composite membranes are prone to hydrolysis in strong acid environments, leading to separation layer detachment or a sharp decline in performance, making them unsuitable for such applications. Forward osmosis (FO) technology, with its unique low energy consumption, high recovery rate, and anti-fouling characteristics, consumes very little energy, and membrane fouling during operation is mostly reversible. Membrane flux can be efficiently restored through simple cleaning, effectively extending membrane life. Finally, forward osmosis membranes have excellent retention effects on pollutants such as organic matter and heavy metals, ensuring effluent quality while achieving effective concentration and meeting stringent discharge requirements. Forward osmosis membrane technology faces three main challenges in practical applications: water flux bottleneck and internal concentration polarization occurring within the porous support layer, which is difficult to alleviate through external operating conditions. This significantly reduces the effective osmotic pressure difference, resulting in actual water flux being far lower than the theoretical value. Regarding membrane fouling and cleaning, although the absence of external pressure makes the initial fouling layer relatively loose, biological fouling has strong adhesion and often requires chemical cleaning for effective removal. At the same time, reverse solute diffusion may exacerbate fouling. The limitations of membrane materials are reflected in the fact that an ideal membrane needs to balance high selectivity, high water flux, mechanical strength, and antifouling ability. Currently widely used polyamide thin-layer composite membranes face a contradiction between reducing internal concentration polarization and ensuring mechanical strength in their porous support layer structure.

[0003] Therefore, there is an urgent need to develop a forward osmosis membrane that combines high selectivity, high water permeability, and excellent acid resistance to meet the needs of acidic wastewater treatment and resource utilization. Summary of the Invention

[0004] To address the problems of poor stability and short service life of existing forward osmosis membranes in acidic environments, this invention provides a forward osmosis membrane, its preparation method, and its applications. This invention modifies the surface of the base membrane layer, imparting high hydrophilicity while effectively controlling the pore size of the base membrane layer surface and optimizing the diffusion behavior of monomers during subsequent interfacial polymerization. This allows the monomers to react with sulfonyl chloride monomers in the separation layer, forming a stable chemical cross-linked structure. Consequently, the separation layer becomes denser, thinner, and exhibits significantly improved acid resistance, successfully preparing a forward osmosis membrane with high selectivity, high permeability, and especially excellent acid resistance.

[0005] According to a first aspect of the present invention, a forward osmosis membrane comprises a base membrane layer, an intermediate layer, and a separation layer sequentially stacked thereon; The base film layer comprises a porous hydrophilic polyethylene membrane containing hydroxyl groups; The intermediate layer includes a hydrophilic layer formed by the crosslinking reaction of ethylene-vinyl alcohol copolymer and glutaraldehyde. The intermediate layer is anchored to the surface of the base film layer and penetrates into the pores of the base film layer. The separation layer comprises a fluorinated polysulfonamide formed by polymerization of a monomer mixture, the monomer mixture comprising a polyamine monomer and a polysulfonyl chloride monomer, wherein the polyamine monomer comprises a fluorine-free polyamine monomer and a fluorinated rigid amine monomer; The fluorinated rigid amine monomer includes at least one of 4,4'-diaminooctafluorobiphenyl and 2,2'-di(trifluoromethyl)diaminobiphenyl.

[0006] The present invention has the following significant beneficial effects: This invention successfully solves the problems of poor stability and easy hydrolysis of the separation layer in traditional forward osmosis membranes under strong acidic environments by controllably constructing a hydrophilic EVOH-GA interlayer formed by crosslinking ethylene-vinyl alcohol copolymer (EVOH) and glutaraldehyde (GA) between a hydrophilic polyethylene-based membrane and a fluorinated polysulfonamide separation layer. Specifically, it produces a forward osmosis membrane with high permeability, high selectivity, and excellent acid resistance. Significantly improved structural stability: The EVOH-GA intermediate layer forms a stable three-dimensional network structure through acetalization cross-linking reaction. Its abundant hydroxyl groups can chemically cross-link with the sulfonyl chloride groups in the base film layer and the separation layer, forming a strong covalent bond that runs through the three layers. This greatly enhances the integrity of the multilayer structure and the interfacial bonding strength of the membrane, effectively avoiding interlayer delamination problems.

[0007] Significantly enhanced acid resistance: The EVOH-GA interlayer possesses excellent chemical stability and a dense cross-linked structure, effectively blocking hydrogen ions (H+). +It penetrates into the membrane interior, protecting sensitive groups such as amide bonds that are easily hydrolyzed in the separation layer, thereby enabling the membrane to maintain excellent structural integrity and long-term operational stability even in a strongly acidic environment (pH≈2).

[0008] According to some embodiments of the present invention, the surface pore size of the base film layer is 50~120 nm.

[0009] The intermediate layer not only imparts good hydrophilicity to the base membrane surface, but also, through the synergistic effect of EVOH permeation and filling and the GA crosslinking network, uniformly controls the pore size of the base membrane surface, significantly reducing the average pore size from the original approximately 50-120 nm to 20-40 nm. This effectively limits the excessive diffusion of aqueous monomers, thereby forming a thinner, denser, and defect-free polysulfonamide separation layer on the surface of the intermediate layer, synergistically improving the membrane's water flux and ion rejection rate.

[0010] A second aspect of the present invention provides a method for preparing a forward osmosis membrane, comprising the following steps: S1: The base film layer is placed in a modified liquid containing ethylene-vinyl alcohol copolymer and glutaraldehyde, and heated to react, so that the intermediate layer is anchored to the surface of the base film layer and penetrates into the pores of the base film layer; S2: The surface of the intermediate layer is sequentially reacted with an aqueous solution and an oil solution to form a fluorinated polysulfonamide separation layer on the surface of the intermediate layer through interfacial polymerization, thereby obtaining a composite membrane; The aqueous solution comprises the fluorine-free polyamine monomer and the fluorine-containing rigid amine monomer, and the oil solution comprises one or more of the polysulfonyl chloride monomers. S3: The obtained composite membrane is subjected to heat treatment to obtain a forward osmosis membrane.

[0011] This invention achieves a synergistic effect of base membrane pore size control, interfacial polymerization process optimization, and three-layer structure chemical bonding through steps S1 to S3, fundamentally improving the overall performance of forward osmosis membranes. The specific mechanism is as follows: First, in step S1, EVOH permeates into the pores of the PE base film in a mixed solvent and undergoes an acetalization crosslinking reaction with GA to form a uniform and dense hydrophilic intermediate layer. This process not only significantly reduces and homogenizes the pore size of the base film surface, but also provides a hydrophilic reaction interface with suitable pore size for subsequent interfacial polymerization, effectively suppressing the disordered diffusion of aqueous monomers.

[0012] Secondly, in step S2, the uniform hydrophilic environment on the surface of the intermediate layer allows the polyamine monomers and fluorinated rigid amine monomers to be uniformly adsorbed and slowly diffused, and to undergo a controlled interfacial polymerization reaction with the polysulfonyl chloride monomers in the oil phase at the interface, thereby generating a thinner, more crosslinked fluorinated polysulfonamide separation layer on the surface of the intermediate layer.

[0013] Finally, in step S3, heat treatment promotes further chemical cross-linking between the residual hydroxyl groups in the intermediate layer and the unreacted sulfonyl chloride groups in the separation layer, forming a stable covalent bond network spanning the three layers: the base layer, the intermediate layer, and the separation layer. This chemical bond structure not only significantly enhances the interfacial bonding strength and mechanical stability of the membrane but also constructs a dense "barrier," effectively preventing hydrogen ions from penetrating into the membrane interior, reducing their erosive effect on the separation layer and interlayer interfaces, improving the stability of the membrane layer bonding interfaces, and protecting sensitive groups such as easily hydrolyzed amide bonds in the separation layer. This results in excellent long-term stability of the membrane under strongly acidic conditions. Simultaneously, both the base layer and the intermediate layer are rich in hydroxyl groups (-OH), and the separation layer contains free amino groups (-NH2) and sulfonyl chloride groups (-SO2Cl). Furthermore, the EVOH molecular chain contains ethylene segments with a structure similar to that of the PE base membrane. These ethylene segments exhibit good segment affinity with the polyethylene segments in the PE base membrane. Additionally, non-covalent interactions such as van der Waals forces exist between the EVOH-GA crosslinking network and the pore walls of the PE base membrane, enabling EVOH molecules to spread, adhere, and be fixed uniformly on the base membrane surface and pore walls, thereby promoting the stable construction of the intermediate layer on the PE base membrane. The hydroxyl groups in the intermediate layer undergo chemical crosslinking reactions with the hydroxyl groups in the base membrane layer and the residual sulfonyl chloride groups in the separation layer, forming stable covalent bonds. This ensures a tight bond between the base membrane layer, intermediate layer, and separation layer, significantly improving the overall structural stability and acid resistance of the membrane.

[0014] According to some embodiments of the present invention, the modified liquid contains 0.3-5.0% by mass of ethylene-vinyl alcohol copolymer and 0.5-2.0% by volume of glutaraldehyde.

[0015] According to some embodiments of the present invention, the mass fraction of the ethylene-vinyl alcohol copolymer in the modified liquid is 0.3 to 5.0 wt%. The mass fraction of the ethylene-vinyl alcohol copolymer can be, for example, 0.3 wt%, 0.6 wt%, 0.9 wt%, 1.5 wt%, 2.0 wt%, 3.0 wt%, 4.0 wt%, or 5.0 wt%, or any value between 0.3 and 5.0 wt%.

[0016] The volume fraction of glutaraldehyde in the modified solution is 0.5~2.0 v / v%. The volume fraction of glutaraldehyde can be, for example, 0.5 v / v%, 0.8 v / v%, 1.0 v / v%, 1.2 v / v%, 1.5 v / v%, 1.8 v / v%, or 2.0 v / v%, or any value between 0.5 and 2.0 v / v%.

[0017] According to some embodiments of the present invention, the concentration of ethylene-vinyl alcohol copolymer is preferably 0.3~0.9 wt%, and the concentration of glutaraldehyde is preferably 0.5~1.5 v / v%, at which point a middle layer with uniform pore size distribution, good hydrophilicity and stable crosslinking can be obtained.

[0018] The concentration of EVOH in the modification solution was controlled at 0.3-5.0 wt%, and the concentration of glutaraldehyde (GA) was controlled at 0.5-2.0 v / v%. As the main hydrophilic modifier, EVOH suffers from insufficient hydrophilicity and weak pore size control if its concentration is too low, while excessive concentration can easily lead to excessive pore blockage. GA, as a crosslinking agent, can effectively fix the EVOH molecular chains into a stable three-dimensional network through acetal reaction within this range, ensuring both the hydrophilicity and pore size uniformity of the intermediate layer, while avoiding a decrease in membrane flux caused by an excessively thick intermediate layer.

[0019] In summary, by synergistically optimizing the concentrations of EVOH / GA modified solution, aqueous monomer, and oil sulfonyl chloride, this invention achieves a balance between intermediate layer pore size control, separation layer densification, and acid resistance, significantly improving the overall performance of the forward osmosis membrane.

[0020] According to some embodiments of the present invention, in step S1, the temperature of the heating reaction is 40~80°C and the reaction time is 2~10h.

[0021] According to some embodiments of the present invention, in step S1, the solvent of the modified liquid includes a mixture of isopropanol and water, wherein the volume ratio of isopropanol to water is 7:2 to 7:5.

[0022] In this invention, under the above conditions, the hydrophilic intermediate layer can regulate the pore size and hydrophilicity of the base film surface.

[0023] First, EVOH molecules contain both hydrophilic hydroxyl groups (-OH) and ethylene segments similar to the main chain structure of polyethylene (PE). In a mixed solvent of isopropanol and water (volume ratio 7:2 to 7:5), they exhibit good interfacial compatibility and can effectively penetrate into the porous structure of the PE base film, partially filling the pore walls and coating the pore surface, thereby significantly reducing the average pore size of the base film and making the originally unevenly distributed pores more uniform.

[0024] Secondly, glutaraldehyde (GA) was introduced as a crosslinking agent during the modification process, connecting the EVOH molecular chains through an acetal reaction to form a stable three-dimensional crosslinked network. This crosslinked network not only further immobilizes the EVOH molecules that permeate into the pores, but also finely controls the size and shape of the pores.

[0025] According to some embodiments of the present invention, in step S2, the aqueous solution contains a mixture of fluorine-free polyamine monomers and fluorine-containing rigid amine monomers with a total concentration of 1.0 to 3.0 wt%.

[0026] According to some embodiments of the present invention, in step S2, the total concentration of the fluorine-free polyamine monomer and the fluorine-containing rigid amine monomer in the aqueous solution is 1.0~3.0 wt%. The total concentration can be, for example, 1.0 wt%, 1.2 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, or 3.0 wt%, or any value between 1.0 and 3.0 wt%.

[0027] According to some embodiments of the present invention, the total concentration of fluorine-free polyamine monomers and fluorine-containing rigid amine monomers in the aqueous solution is controlled at 1.0~3.0 wt%, wherein the preferred mass ratio of m-phenylenediamine (MPD) to 2,2'-bis(trifluoromethyl)diaminobiphenyl (TFMB) is 0.6:0.4. This ratio ensures that the polymerization reaction proceeds fully while introducing a rigid fluorine-containing structure, effectively improving the free volume and acid resistance of the separation layer.

[0028] According to some embodiments of the present invention, in step S2, the concentration of the polysulfonyl chloride monomer in the oil phase solution is 0.1~0.2 wt%. The concentration can be, for example, 0.1 wt%, 0.12 wt%, 0.15 wt%, 0.18 wt%, or 0.2 wt%, or any value between 0.1 and 0.2 wt%.

[0029] In some embodiments, the polysulfonyl chloride monomer is selected from one or more of 1,3,5-benzenetrisulfonyl chloride, 1,3,6-naphthalenetrisulfonyl chloride, or isophenylene disulfonyl chloride. In some embodiments, the oil phase solution preferably contains 1,3,5-benzenetrisulfonyl chloride (BTSC), and its concentration is preferably 0.05-0.20 wt%, more preferably 0.075-0.15 wt%.

[0030] In some embodiments, by controlling the concentration of polysulfonyl chloride monomers in the oil phase solution within the above-mentioned range, the interfacial polymerization reaction rate and the degree of crosslinking of the separation layer can be precisely controlled, so that the separation layer has a moderate thickness and a dense structure, which not only ensures a high water flux, but also effectively reduces the reverse salt permeation flux.

[0031] The concentration of poly(sulfonyl chloride) monomers in the oil phase solution is preferably controlled between 0.05 and 0.2 wt%. This concentration precisely regulates the interfacial polymerization rate and the crosslinking density of the separation layer: too low a concentration leads to a loose separation layer structure, while too high a concentration results in an excessively thick separation layer and increased resistance. At 0.075 wt%, the membrane's water flux reaches its peak, while the reverse salt flux decreases to its minimum, resulting in optimal overall separation performance.

[0032] According to some embodiments of the present invention, in step S2, the solvent of the oil phase solution includes n-hexane.

[0033] According to some embodiments of the present invention, in step S2, the contact time between the surface of the intermediate layer and the aqueous solution is 1-5 min, and the contact time with the oil solution is 0.5-3 min.

[0034] According to some embodiments of the present invention, the fluorine-free polyamine monomer includes at least one of m-phenylenediamine, polyethyleneimine, and polyacrylamine; The fluorinated rigid amine monomer includes at least one of 4,4'-diaminooctafluorobiphenyl and 2,2'-di(trifluoromethyl)diaminobiphenyl.

[0035] According to some embodiments of the present invention, the fluorinated rigid amine monomer further includes ω-perfluoroalkyl substituted biphenyl diamine derivatives.

[0036] According to some embodiments of the present invention, the ω-perfluoroalkyl-substituted biphenyl diamine derivatives include at least one of formulas I to V: Equation I is: Equation II is: Equation III is: Equation IV is: Equation V is: .

[0037] According to some embodiments of the present invention, the polysulfonyl chloride monomer includes at least one selected from 1,3,5-benzenetrisulfonyl chloride, 1,3,6-naphthalenetrisulfonyl chloride, and isobenzenedisulfonyl chloride.

[0038] According to some embodiments of the present invention, the heat treatment temperature in step S3 is 80~100℃ and the time is 5~15min.

[0039] A third aspect of the present invention proposes the application of a forward osmosis membrane in the concentration and separation of acidic materials.

[0040] The acid-resistant forward osmosis membrane prepared by this invention is particularly suitable for the concentration and resource recovery of low-pH, highly corrosive acidic materials such as phosphate chemical wastewater and pickling waste liquid, providing efficient and reliable technical support for the enrichment and utilization of valuable resources such as phosphate and the green treatment of acidic industrial wastewater.

[0041] According to some embodiments of the present invention, the acidic material includes acidic wastewater, which includes phosphate chemical wastewater, phosphoric acid-containing wastewater, and pickling waste liquid.

[0042] In this invention, to address the problem of poor stability and easy hydrolysis of existing forward osmosis membranes under strongly acidic environments, a hydrophilic EVOH-GA interlayer formed by crosslinking ethylene-vinyl alcohol copolymer (EVOH) and glutaraldehyde (GA) is introduced between the base membrane layer and the separation layer. This interlayer not only optimizes the surface properties of the base membrane and regulates monomer diffusion during interfacial polymerization, thus forming a thinner, denser, defect-free separation layer, but more importantly, its stable chemical crosslinking network and abundant reactive hydroxyl groups (-OH) can chemically crosslink with the hydroxyl groups in the base membrane layer and the sulfonyl chloride groups (-SO2Cl) in the separation layer, forming a strong covalent bond structure that runs through all three layers. This constructs an effective barrier, significantly delaying the erosion of the membrane functional layer by acid, thereby greatly improving the membrane's acid resistance.

[0043] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0044] Figure 1 Infrared spectra (ATR-FTIR) of the hydrophilic PE base membrane, the EVOH-GA supported interlayer base membrane, and the polysulfonamide acid-resistant forward osmosis membrane provided by the present invention; Figure 2 The surface morphology of the hydrophilic PE-based film; Figure 3 Morphology of the EVOH-GA loaded intermediate layer substrate film; Figure 4 This is a morphology diagram of a polysulfonamide acid-resistant forward osmosis membrane. Detailed Implementation

[0045] The embodiments of the present invention are described in detail below, with examples of the embodiments shown below, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The following examples are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Unless otherwise specified, specific conditions in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all conventional products that can be purchased commercially.

[0046] Example 1 This embodiment provides a forward osmosis membrane and its preparation method, including the following steps: S1: A porous hydrophilic polyethylene membrane containing hydroxyl groups was used as the base membrane and placed in a mixed solution of isopropanol / water (volume ratio 7:3) containing 0.6 wt% ethylene-vinyl alcohol copolymer (EVOH) and 1.0 v / v% glutaraldehyde (GA). The mixture was heated at 40°C for 6 h. After removal, it was thoroughly rinsed 3 times with deionized water and stored in deionized water for later use, thus obtaining a base membrane loaded with an intermediate layer. S2: Fix the base film with intermediate layer obtained in step S1, first contact it with the aqueous solution for 2 min, then remove the excess aqueous solution with a rubber roller, and then contact it with the oil solution for 1 min. Through interfacial polymerization, a fluorinated polysulfonamide separation layer is formed on the surface of the intermediate layer to obtain a composite film. The aqueous solution was prepared by dissolving m-phenylenediamine (MPD) and 2,2'-bis(trifluoromethyl)diaminobiphenyl (TFMB) in deionized water to prepare an aqueous solution with a total concentration of 1.0 wt%, wherein the concentration of MPD was 0.6 wt% and the concentration of TFMB was 0.4 wt%. Preparation of oil phase solution: Dissolve 1,3,5-benzenetrisulfonyl chloride (BTSC) in n-hexane to prepare an oil phase solution with a concentration of 0.075 wt%. S3: The composite membrane obtained in step S2 is subjected to heat treatment by heating at 80°C for 10 min to obtain the acid-resistant forward osmosis membrane.

[0047] Figure 1 The ATR-FTIR infrared spectra of the hydrophilic PE-based membrane, the EVOH-GA-loaded interlayer membrane, and the polysulfonamide acid-resistant forward osmosis membrane provided by this invention are shown in the figure. The figure plots wavenumber on the x-axis and transmittance on the y-axis, displaying three curves from top to bottom: the hydrophilic porous polyethylene-based membrane (hydrophilic PE-based membrane), the interlayer membrane formed by crosslinking ethylene-vinyl alcohol copolymer (EVOH) and glutaraldehyde (GA), and the final fluorinated polysulfonamide acid-resistant forward osmosis membrane.

[0048] The changes in characteristic functional groups in each layer can be clearly seen from the infrared spectrum. 3300 cm⁻¹ -1 The broad peak at 2920 cm⁻¹ corresponds to the -OH stretching vibration, and all three curves show significant absorption, indicating that the hydrophilic PE-based film itself has introduced hydroxyl groups, and the introduction of the EVOH-GA interlayer further enhances the hydroxyl content, providing sufficient reaction sites for subsequent chemical crosslinking with sulfonyl chloride groups. -1 The peak at 1720 cm⁻¹ is due to the -CH₂- antisymmetric stretching vibration, a typical characteristic peak of PE-based films. The peak shape changes slightly after loading the interlayer, confirming the good compatibility between the ethylene segments in the EVOH molecular chain and the PE-based film segments. -1The C=O stretching vibration peak at this point mainly appears in the red curve, originating from the ester / aldehyde groups formed after the acetalization crosslinking reaction of glutaraldehyde and EVOH. This fully demonstrates that the intermediate layer has been successfully constructed and a stable three-dimensional crosslinked network has been formed. (1660 cm⁻¹) -1 The amide I band (C=O stretching) at the point is significantly enhanced in the blue curve, indicating that the polyamine (m-phenylenediamine, fluorinated rigid amine monomers such as TFMB) and polysulfonyl chloride monomers (BTSC, etc.) have successfully undergone interfacial polymerization on the surface of the intermediate layer, generating a dense fluorinated polysulfonamide separation layer.

[0049] SEM (scanning electron microscope) images of the hydrophilic PE base membrane, the EVOH-GA supported interlayer base membrane, and the polysulfonamide acid-resistant forward osmosis membrane provided by the present invention show that the surface of the hydrophilic PE base membrane exhibits a porous structure. Figure 2 The pores are relatively large and unevenly distributed, with an average pore size of approximately 50–120 nm; after loading the EVOH-GA interlayer, the surface becomes smooth and flat. Figure 3 The pore size is significantly reduced and the distribution is uniform (the average pore size in Example 1 is approximately 30 ± 3 nm); finally, the surface of the polysulfonamide acid-resistant forward osmosis membrane becomes more uniform and dense, with almost no obvious large pores, and it is completely covered by a thin and continuous defect-free separation layer. Figure 4 The cross-sectional structure diagram shows that the hydrophilic PE base film has a clear, interconnected porous support layer; the intermediate layer is not only coated on the surface of the base film, but also penetrates into the pores to form an anchoring structure, and the pores are partially filled; finally, an extremely thin (usually tens to two hundred nanometers) dense separation layer can be seen above the intermediate layer of the composite film, which is tightly bonded to the intermediate layer and the base film, with no obvious peeling interface.

[0050] Example 2 Example 2 discloses a forward osmosis membrane and its preparation method. The difference between Example 2 and Example 1 is that the EVOH concentration of the modified solution in step S1 is adjusted to 0.3 wt%; the other conditions are exactly the same as in Example 1.

[0051] Example 3 Example 3 discloses a forward osmosis membrane and its preparation method. The difference between Example 3 and Example 1 is that the EVOH concentration in step S1 is 0.9 wt%, and the other conditions are exactly the same as in Example 1.

[0052] Example 4 Example 4 discloses a forward osmosis membrane and its preparation method. The difference between Example 4 and Example 1 is that the GA concentration in the modified solution in step S1 is 0.5 v / v%, and the other conditions are the same as in Example 1.

[0053] Example 5 Example 5 discloses a forward osmosis membrane and its preparation method. The difference between Example 5 and Example 1 is that the GA concentration in the modified solution in step S1 is 1.5 v / v%, and the other preparation conditions are the same as in Example 1.

[0054] Example 6 Example 6 discloses a forward osmosis membrane and its preparation method. The difference between Example 6 and Example 1 is that the concentration of 1,3,5-benzenetrisulfonyl chloride (BTSC) in the oil phase in step S2 is 0.05 wt%, and the other conditions are the same as in Example 1.

[0055] Example 7 Example 7 discloses a forward osmosis membrane and its preparation method. The difference between Example 7 and Example 1 is that the BTSC concentration in the oil phase in step S2 is 0.15 wt%, and the other conditions are the same as in Example 1.

[0056] Example 8 Example 8 discloses a forward osmosis membrane and its preparation method. The difference between Example 8 and Example 1 is that the concentration of 1,3,5-benzenetrisulfonyl chloride (BTSC) in the oil phase in step S2 is 0.20 wt%, and the other conditions are the same as in Example 1.

[0057] Comparative Example 1 Comparative Example 1 discloses a forward osmosis membrane and its preparation method. The difference between Comparative Example 1 and Example 1 is that the EVOH-GA intermediate layer construction step is omitted, and a hydrophilic polyethylene-based membrane is used directly; the MPD concentration in the aqueous phase solution is 0.6 wt%, the TFMB concentration is 0.4 wt%, the BTSC concentration in the oil phase solution is 0.075 wt%, and the other conditions are the same as in Example 1.

[0058] Comparative Example 2 Comparative Example 2 discloses a forward osmosis membrane and its preparation method. The difference between Comparative Example 2 and Example 1 is that the modified solution does not contain glutaraldehyde (GA) and only contains 0.6 wt% EVOH; the other conditions are the same as those in Example 1.

[0059] Comparative Example 3 Comparative Example 3 discloses a forward osmosis membrane and its preparation method. The difference between Comparative Example 3 and Example 1 is that the aqueous phase contains only 1.0 wt% MPD and does not contain TFMB. The other conditions are the same as those in Example 1.

[0060] Comparative Example 4 Comparative Example 4 discloses a forward osmosis membrane and its preparation method. The difference between Comparative Example 4 and Example 1 is that the oil phase monomer is trimesoyl chloride (TMC) with a concentration of 0.075 wt%; the other conditions are the same as in Example 1.

[0061] Comparative Example 5 Comparative Example 5 discloses a forward osmosis membrane and its preparation method, which differs from Example 1 in that: the EVOH-GA intermediate layer construction step is omitted, and a hydrophilic polyethylene base membrane is used directly; the aqueous phase solution in step S2 contains only 1.0 wt% m-phenylenediamine (MPD) and does not contain TFMB; the concentration of 1,3,5-benzenetrisulfonyl chloride (BTSC) in the oil phase solution is halved; and the remaining conditions are the same as in Example 1.

[0062] Test Example 1 The separation performance of the forward osmosis membranes prepared in Examples 1-8 and Comparative Examples 1-5 was tested. The draw solution was 1 mol / L NaCl, and the feed solution was deionized water. The test results are shown in Table 1.

[0063] Test conditions: Forward osmosis performance evaluation: A laboratory cross-flow FO test system was used in AL-FS mode. The draw solution was 1 mol / L NaCl, and the feed solution was deionized water or simulated phosphoric acid wastewater. The temperature was 25±1℃. The water flux and reverse salt flux of the membrane were tested.

[0064] Acid resistance evaluation: The membrane was immersed in H2SO4 solution with pH=2 and left to stand at 25℃ for 7 days. After removal, it was thoroughly cleaned, and its FO performance was tested again (using deionized water as feed solution). The changes in water flux retention rate and rejection rate were calculated.

[0065] Simulated phosphoric acid wastewater treatment: A simulated phosphoric acid wastewater was prepared based on the composition of typical phosphoric acid chemical wastewater, as shown in Table 2. Using this as the feed solution, the system was continuously operated in AL-FS mode for 48 h. Water flux decay was monitored, and the enrichment factor of phosphate in the concentrate was analyzed.

[0066] Pore ​​size testing of the base film and the base film containing the intermediate layer: A capillary flow pore size analyzer (CFP-1500A, PMIInc., USA) was used. The test liquid was Galwick (surface tension 15.9 dyn / cm). Samples were immersed in isopropanol for 10 min before testing. The test pressure range was 0–500 psi. Three different locations were tested for each sample group, and the average value was taken.

[0067] In this invention, the separation performance of the forward osmosis membrane was measured using a laboratory-made apparatus. To ensure a stable permeate flux, the forward osmosis membrane was first pre-run for 1 hour, and then the permeate volume was collected at regular intervals under the same conditions. The testing of the forward osmosis membrane was conducted in two modes: separation layer facing the draw solution side (AL-DS) mode and separation layer facing the feed solution side (AL-FS) mode.

[0068] The formula for calculating water flux is as follows: Where Jw represents water flux, in L·m -2 ·h -1 V is the volume of permeate during the operating time, in liters; t is the operating time, in hours; A is the effective membrane area, in square meters.

[0069] The formula for calculating the reverse salt permeation flux Js is as follows: Js unit g·m -2 ·h -1 Ct(g·L) -1 V(L) and Vt(L) are the concentration and volume of the feed solution at time t, respectively. t(h) is the actual test time. C0 is the concentration of the solute in the feed solution at the initial moment; The retention rate R is calculated using the following formula: .

[0070] C0 represents the initial solute concentration. C f This represents the initial concentration of the solute in the feed solution; Table 1: Separation performance test results The pore size data were measured using a capillary flow pore size analyzer (CFP). The values ​​in the table represent the "mean ± standard deviation". Each sample was tested three times. As shown in Table 1, the forward osmosis membranes prepared in Examples 1-8 all exhibited high water flux and salt rejection rates, with Example 1 showing the best overall performance; the water flux in AL-DS mode was 42.8 L·m⁻¹. - ²·h - ¹, The reverse salt osmotic flux is 2.0 g·m - ²·h - ¹, the retention rate was 99.8%; the water flux in AL-FS mode was 35.6 L·m - ²·h - ¹, The reverse salt osmotic flux is 2.5 g·m - ²·h -¹, the rejection rate was 99.8%. This indicates that when the EVOH concentration was 0.6 wt%, the GA concentration was 1.0 v / v%, and the BTSC concentration was 0.075 wt%, the pore size control of the interlayer and the interfacial polymerization process were suitable, and the resulting membrane achieved an optimal balance between flux, reverse salt permeation, and rejection performance. Compared with the comparative example, the overall performance of the membrane decreased when the EVOH-GA interlayer, GA crosslinking agent, TFMB fluorinated monomer, or BTSC was replaced by TMC, indicating a synergistic effect between the EVOH-GA interlayer, TFMB, and BTSC.

[0071] Simulated phosphoric acid wastewater treatment test: A simulated phosphoric acid wastewater was prepared based on the composition of typical phosphoric acid chemical wastewater, as shown in Table 2. Using this as the feed solution, the system was continuously operated in AL-FS mode for 48 h. The water flux decay was monitored, and the enrichment factor of phosphate in the concentrate was analyzed, as shown in Table 2.

[0072] Table 2: Composition of Simulated Phosphoric Acid Wastewater Experiments were conducted using forward osmosis membrane modules. The simulated phosphoric acid wastewater shown in Table 2 was used as the feed solution, and sodium chloride solution was used as the draw solution. The pH value was approximately 2, simulating the main ionic composition and weakly acidic environment of real phosphate chemical wastewater. A 1 mol / L NaCl solution was used as the draw solution, the operating temperature was 20–25 °C, and the experimental time was 2–6 h. Comparative experiments were conducted using the forward osmosis membrane modules prepared in Example 1 (best performance) and Comparative Examples 1–5, with each experiment lasting 4 hours.

[0073] The test results are recorded in Table 3: Table 3: Initial separation performance of different membranes (AL-FS mode) To investigate the actual acid resistance of the membranes, the membranes from Example 1 and Comparative Examples 1-5 were immersed in an H2SO4 solution at pH=2 for 7 days at 25°C. After removal, they were thoroughly cleaned, and their basic performance in the deionized water / NaCl system (AL-DS) was retested. The results are shown in Table 4.

[0074] Table 4: Acid resistance of the membrane (after immersion in H2SO4 for 7 days at pH=2) Table 5: Simulated phosphoric acid wastewater treatment performance (after 48 hours of operation) Note: Flux decay rate = (Initial flux - Flux at 48 hours) / Initial flux × 100% Results analysis: 1. Separation performance: As shown in Table 3, the membrane prepared in this embodiment of the invention maintains a high rejection rate while achieving the highest water flux (34.8 L·m). -2 ·h -1 The reverse salt flux was the lowest (2.6 g·m). -2 ·h -1 The NaCl rejection rate reached 99.8%, indicating that it possesses both high water transport capacity and excellent salt barrier performance. In contrast, Comparative Example 1 did not construct an EVOH-GA interlayer, Comparative Example 2 did not add GA crosslinking agent, Comparative Example 3 did not introduce TFMB fluorinated monomer, Comparative Example 4 used TMC instead of BTSC, and Comparative Example 5 lacked both the EVOH-GA interlayer and TFMB. All of these examples showed lower water flux than Example 1 and higher reverse salt permeation flux. These results indicate that the EVOH-GA crosslinking interlayer can optimize the pore size of the base membrane surface and the interfacial polymerization environment, the TFMB fluorinated rigid amine monomer can improve the structural stability of the separation layer, and the polysulfonamide separation layer constructed with BTSC is more beneficial to improving the selective separation performance of the membrane than the ordinary TMC polyamide layer. The synergistic effect of these three factors allows the resulting membrane to achieve an optimal balance between flux, reverse salt permeation, and rejection performance.

[0075] 2. Acid Resistance and Stability: Table 4 shows that the membrane of Example 1 exhibits the least performance degradation after strong acid immersion, with a water flux retention rate as high as 95.1% and a retention rate that only slightly decreases from 99.8% to 99.5%, demonstrating excellent acid resistance. This is attributed to the chemical stability of the EVOH-GA crosslinking interlayer and its "barrier" effect, effectively protecting the upper polysulfonamide separation layer. In contrast, Comparative Examples 1 and 5, lacking the EVOH-GA interlayer, showed significantly reduced water flux retention rates after acid immersion; Comparative Example 2, without the introduction of GA crosslinking agent, suffered from insufficient interlayer stability; Comparative Example 3, without the introduction of TFMB, and Comparative Example 4, using TMC instead of BTSC, also showed lower performance retention after acid treatment compared to Example 1. This indicates that the EVOH-GA crosslinking interlayer can serve as a stable interfacial bonding layer and barrier, mitigating the erosion of the membrane's functional layers by acid; simultaneously, the fluorinated polysulfonamide separation layer formed by TFMB and BTSC further enhances the membrane's acid resistance and stability.

[0076] 3. Simulated Wastewater Treatment: The results in Table 5 show that, when treating simulated phosphoric acid wastewater, the membrane in Example 1 of this invention exhibited the best long-term operational stability and concentration effect, with a flux decay rate of only 8.8% after 48 hours. It effectively concentrated phosphate by approximately 6.5 times, with only a slight decrease in the rejection rate, demonstrating excellent chemical corrosion resistance. In contrast, Comparative Examples 1 and 5, lacking the EVOH-GA interlayer, showed significant membrane performance degradation and lower phosphate enrichment factors during operation. Comparative Example 2 did not add GA, Comparative Example 3 did not introduce TFMB, and Comparative Example 4 used TMC instead of BTSC; their operational stability and enrichment effect were all weaker than Example 1. This directly proves that by constructing an EVOH-GA crosslinked interlayer and introducing a TFMB / BTSC fluorinated polysulfonamide separation layer, this invention can effectively improve the membrane's resistance to decay, chemical corrosion, and continuous concentration performance in acidic phosphoric acid wastewater systems, demonstrating promising application prospects for acidic material concentration and resource recovery.

[0077] in conclusion: This invention provides an EVOH-modified polyethylene-based acid-resistant forward osmosis membrane and its preparation method. By controllably constructing an EVOH-GA crosslinked interlayer on a hydrophilic PE-based membrane, the following was successfully achieved: 1. Membrane structure optimization: The intermediate layer homogenizes the pore size of the base membrane surface and finely controls the diffusion rate and distribution of monomers during interfacial polymerization, thereby forming a thinner, denser and defect-free polysulfonamide separation layer.

[0078] 2. Significantly improved performance: The prepared membrane also features high water flux (up to 42.8 L·m). -2 ·h -1 (above), low reverse salt flux (as low as 2.0 g·m³) -2 ·h -1 It has a high rejection rate (>99.7%) and excellent overall separation performance.

[0079] 3. Excellent acid resistance: The chemical stability and barrier function of the EVOH-GA intermediate layer enable the membrane to maintain structural integrity and stable performance in a strong acid environment (pH=2) for a long time, with low flux decay rate and high rejection rate.

[0080] 4. Broad application prospects: This membrane is particularly suitable for forward osmosis applications that have stringent requirements for membrane acid resistance, such as the recovery of phosphorus chemical wastewater and acidic industrial wastewater. It provides an effective solution to the key problems of poor acid resistance and rapid performance degradation of existing forward osmosis membranes in complex acidic environments.

[0081] In summary, this invention introduces a chemically cross-linked hydrophilic EVOH-GA interlayer between the base membrane and the separation layer. This interlayer not only optimizes the surface properties of the base membrane and regulates the interfacial polymerization process to form a separation layer with a superior structure, but more importantly, its stable chemical cross-linking network and abundant reactive hydroxyl groups can form strong chemical bonds with the separation layer and the base membrane, thereby constructing a "barrier" that effectively delays the erosion of the membrane's functional layers by acid.

[0082] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope of the claims of the present invention.

Claims

1. A forward osmosis membrane, characterized in that, The forward osmosis membrane comprises a base membrane layer, an intermediate layer, and a separation layer stacked sequentially. The base film layer comprises a porous hydrophilic polyethylene membrane containing hydroxyl groups; The intermediate layer includes a hydrophilic layer formed by the crosslinking reaction of ethylene-vinyl alcohol copolymer and glutaraldehyde. The intermediate layer is anchored to the surface of the base film layer and penetrates into the pores of the base film layer. The separation layer comprises a fluorinated polysulfonamide formed by polymerization of a monomer mixture, the monomer mixture comprising a polyamine monomer and a polysulfonyl chloride monomer, wherein the polyamine monomer comprises a fluorine-free polyamine monomer and a fluorinated rigid amine monomer; The fluorinated rigid amine monomer includes at least one of 4,4'-diaminooctafluorobiphenyl and 2,2'-di(trifluoromethyl)diaminobiphenyl.

2. The forward osmosis membrane according to claim 1, characterized in that, The pore size of the base film layer is 50~120 nm.

3. A method for preparing a forward osmosis membrane as described in claim 1 or 2, characterized in that, Includes the following steps: S1: The base film layer is placed in a modified liquid containing ethylene-vinyl alcohol copolymer and glutaraldehyde, and heated to react, so that the intermediate layer is anchored to the surface of the base film layer and penetrates into the pores of the base film layer; S2: The surface of the intermediate layer is sequentially reacted with an aqueous solution and an oil solution to form a fluorinated polysulfonamide separation layer on the surface of the intermediate layer through interfacial polymerization, thereby obtaining a composite membrane; The aqueous solution comprises the fluorine-free polyamine monomer and the fluorine-containing rigid amine monomer, and the oil solution comprises one or more of the polysulfonyl chloride monomers. S3: The obtained composite membrane is subjected to heat treatment to obtain a forward osmosis membrane.

4. The method for preparing a forward osmosis membrane according to claim 3, characterized in that, In the modified liquid, the mass fraction of the ethylene-vinyl alcohol copolymer is 0.3-5.0%; and the volume fraction of the glutaraldehyde is 0.5-2.0%.

5. The method for preparing a forward osmosis membrane according to claim 3, characterized in that, In step S1, the heating reaction temperature is 40~80℃ and the reaction time is 2~10h.

6. The method for preparing a forward osmosis membrane according to claim 3, characterized in that, In step S1, the solvent of the modified liquid includes a mixture of isopropanol and water, wherein the volume ratio of isopropanol to water is 7:2 to 5.

7. The method for preparing a forward osmosis membrane according to claim 3, characterized in that, The fluorine-free polyamine monomer includes at least one of m-phenylenediamine, polyethyleneimine, and polyacrylamine.

8. The method for preparing a forward osmosis membrane according to claim 3, characterized in that, The polysulfonyl chloride monomer includes at least one of 1,3,5-benzenetrisulfonyl chloride, 1,3,6-naphthalenetrisulfonyl chloride, and isobenzenedisulfonyl chloride.

9. The application of a forward osmosis membrane as described in claim 1 or 2 in the concentration and separation of acidic materials.

10. The application according to claim 9, characterized in that, The acidic material includes acidic wastewater, which includes phosphate chemical wastewater, phosphoric acid-containing wastewater, and pickling waste liquid.

Images