Polyamide composite film and preparation method therefor

Abstract

A polyamide composite film and a preparation method therefor. The preparation method comprises the following steps: preparing a base film with a porous structure; applying an aqueous phase solution and an oil phase solution on the base film, wherein the oil phase solution and at least part of the aqueous phase solution are applied on opposite sides of the base film; and forming a polymer layer on the base film by means of an interfacial polymerization reaction of the aqueous phase solution and the oil phase solution, so as to form the polyamide composite film.

Description

A polyamide composite film and its preparation method Technical Field

[0001] This specification relates to the field of membrane separation technology, specifically to a polyamide composite membrane and its preparation method. Background Technology

[0002] Membrane separation technology has experienced rapid development in recent years due to its combined functions of separation, concentration, purification, and refining, as well as its energy-saving, environmentally friendly, simple, and easy-to-control characteristics. Nanofiltration and reverse osmosis membranes, in particular, are widely used in industrial wastewater treatment, food processing, solvent separation, biomedicine, and seawater desalination. Currently, commercially available nanofiltration and reverse osmosis membranes mainly employ aromatic polyamide composite membrane structures. These membranes consist of three parts: a non-woven fabric, a porous support layer, and an aromatic polyamide separation layer on the surface. The traditional preparation method for polyamide composite membranes involves casting a membrane casting solution onto a non-woven fabric layer, obtaining a polysulfone-based membrane through a phase inversion method, immersing the polysulfone-based membrane in an aqueous solution containing amine monomers and other additives, removing it, and removing excess solution using a vacuum pump, hot rollers, and air knife. An oil phase solution containing acyl chloride monomers and other additives is then poured onto the membrane surface, where an interfacial polymerization reaction occurs. Excess oil phase solution is removed by heating in an oven, followed by rinsing and other post-processing steps to obtain the polyamide composite membrane product. However, due to the difficulty in controlling the process parameters of conventional preparation methods, the product yield is low and the product performance and stability are poor.

[0003] Therefore, it is necessary to provide a polyamide composite film and its preparation method to achieve higher yield and better performance of the polyamide composite film.

[0004] Summary of the Invention

[0005] This specification provides a method for preparing a polyamide composite membrane, the method comprising the following steps: preparing a base membrane having a porous structure; coating an aqueous phase solution and an oil phase solution onto the base membrane, wherein the oil phase solution and at least a portion of the aqueous phase solution are coated on opposite sides of the base membrane; and forming a polymer layer on the base membrane by interfacial polymerization of the aqueous phase solution and the oil phase solution to form a polyamide composite membrane.

[0006] In some embodiments, preparing a base film having a porous structure includes: coating a casting solution onto one side surface of a nonwoven fabric to form a support layer; drying the nonwoven fabric coated with the support layer to form the base film; and coating the base film with an aqueous phase solution and an oil phase solution, including: coating the aqueous phase solution onto at least one side surface of the nonwoven fabric opposite to the support layer; and coating the oil phase solution onto the side surface of the support layer opposite to the nonwoven fabric.

[0007] In some embodiments, the porosity of the base membrane is 40%-70%.

[0008] In some embodiments, the aqueous solution is first applied once or multiple times to both sides of the base film (i.e., the side of the nonwoven fabric away from the support layer and the side of the support layer away from the nonwoven fabric), and then the oil phase solution is applied to the side of the support layer away from the nonwoven fabric.

[0009] In some embodiments, the aqueous solution is applied once or multiple times to the surface of the nonwoven fabric facing away from the support layer, while the oil phase solution is applied to the surface of the support layer facing away from the nonwoven fabric.

[0010] In some embodiments, the aqueous solution is first applied once or multiple times to the surface of the nonwoven fabric facing away from the support layer, and then the oil phase solution is applied to the surface of the support layer facing away from the nonwoven fabric.

[0011] In some embodiments, the oil phase solution is first applied to the side surface of the support layer opposite to the nonwoven fabric, and then the aqueous phase solution is applied to the side surface of the nonwoven fabric opposite to the support layer.

[0012] In some embodiments, coating the base film with an aqueous phase solution and an oil phase solution includes: coating the base film with the aqueous phase solution; during the process of coating the aqueous phase solution onto the base film, the tension of the nonwoven fabric is 100N-180N; and / or, coating the base film with the oil phase solution; during the process of coating the oil phase solution onto the base film, the tension of the nonwoven fabric is 100N-180N.

[0013] In some embodiments, the aqueous solution comprises 6-20 parts by mass of an aqueous solute, the aqueous solute comprising an amine monomer, the amine monomer comprising an aromatic amine monomer and / or an aliphatic amine monomer; and the solvent of the aqueous solution is water.

[0014] In some embodiments, the aqueous solution comprises 8-15 parts by weight of an amine monomer.

[0015] In some embodiments, the aromatic amine monomer includes one or more of p-phenylenediamine, m-phenylenediamine, and o-phenylenediamine; and / or, the aliphatic amine monomer includes one or more of ethylenediamine, propylenediamine, butanediamine, pentanediamine, N-(2-hydroxyethyl)ethylenediamine, hexanediamine, 1,2-diaminocyclohexane, 1,3-diaminocyclohexane, 1,4-diaminocyclohexane, piperazine, and 4-aminomethylpiperazine.

[0016] In some embodiments, during the process of coating the base film with an aqueous solution, the temperature of the aqueous solution is 55°C-70°C.

[0017] In some embodiments, the oil phase solution comprises 0.1-0.5 parts by mass of an oil phase solute, the oil phase solute comprising an acyl chloride monomer, the acyl chloride monomer comprising aromatic acyl chlorides and / or fatty acyl chlorides; the solvent of the oil phase solution comprises one or more of the following: aliphatic hydrocarbons containing 4 to 10 carbon atoms, cyclic aliphatic hydrocarbons containing 4 to 10 carbon atoms, and aromatic hydrocarbons containing 4 to 10 carbon atoms.

[0018] In some embodiments, the oil phase solution comprises 0.1-0.4 parts by weight of acyl chloride monomer.

[0019] In some embodiments, the aromatic acyl chloride includes one or more of terephthaloyl chloride, phthaloyl chloride, isophthaloyl chloride, biphenyl dichloroyl chloride, benzene disulfonyl chloride, and trimesoyl chloride; and / or, the fatty acyl chloride includes one or more of succinyl chloride, glutaryl chloride, adipicoyl chloride, sebacyl chloride, cyclobutane dichloroyl chloride, and cyclopentane dichloroyl chloride.

[0020] In some embodiments, during the process of coating the base film with the oil phase solution, the temperature of the oil phase solution is 55°C-75°C.

[0021] In some embodiments, the interfacial polymerization reaction occurs once, and the polyamide composite film has uniform density.

[0022] This specification also provides a polyamide composite film prepared by the method described in any of the above embodiments. Attached Figure Description

[0023] Figure 1 is a flowchart of the preparation methods of some embodiments of this specification;

[0024] Figure 2 is a schematic diagram of the structure of the polyamide composite film prepared in some embodiments of this specification;

[0025] Figure 3 is a flowchart of the preparation of the base film in some embodiments of this specification;

[0026] Figure 4 is a flowchart of the preparation method of some embodiments of this specification, in which the aqueous phase solution and the oil phase solution are coated;

[0027] Figure 5 is a schematic diagram of the structure of the support layer and polymer layer of the polyamide composite film prepared in some embodiments of this specification;

[0028] Figure 6 is a schematic diagram of the polymer layer structure of the polyamide composite film prepared in some embodiments of this specification. Detailed Implementation

[0029] To more clearly illustrate the technical solutions of the embodiments in this specification, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are merely some examples or embodiments of this specification. For those skilled in the art, these drawings can be applied to other similar scenarios without creative effort. It should be understood that these exemplary embodiments are given merely to enable those skilled in the art to better understand and implement this specification, and are not intended to limit the scope of this specification in any way. Unless obvious from the linguistic context or otherwise, the same reference numerals in the figures represent the same structures or operations.

[0030] As indicated in this specification and claims, unless the context clearly indicates otherwise, the words "a," "an," "an," and / or "the" are not specifically singular and may include the plural. Generally speaking, the terms "comprising" and "including" only indicate the inclusion of explicitly identified steps and elements, which do not constitute an exclusive list, and the method or apparatus may also include other steps or elements.

[0031] This specification provides a polyamide composite film and its preparation method. The polyamide composite film includes a base film and a polymer layer formed on the base film through an interfacial polymerization reaction. The method described in this specification prepares the polyamide composite film by coating, which allows the aqueous and oil phase solutions required for the interfacial polymerization reaction to adhere to the base film. This improves the utilization rate of raw materials, reduces process steps, and shortens the preparation time of the polyamide composite film. Therefore, this method for preparing the polyamide composite film has a high yield.

[0032] Figure 1 is a flowchart illustrating the preparation method shown in some embodiments of this specification. Figure 2 is a schematic structural diagram of the polyamide composite film prepared in some embodiments of this specification. The structure of the polyamide composite film and its preparation method are described below with reference to Figures 1 and 2. As shown in Figure 1, the preparation method 100 of the polyamide composite film includes the following steps:

[0033] Step 110: Prepare a base membrane 200 with a porous structure.

[0034] The base membrane 200 can serve as a carrier for reactions (such as the interfacial polymerization reaction described herein) and support other membrane layers of the polyamide composite membrane (such as the polymer layer 300 formed by the interfacial polymerization reaction described herein). The structure of the base membrane 200 is shown in Figure 2. The porous structure on the base membrane 200 can be understood as a sponge-like structure. In some embodiments, the base membrane 200 may include a nonwoven fabric 201 and a support layer 202 formed on the nonwoven fabric 201. The support layer 202 may be a polysulfone layer.

[0035] In some embodiments, the porosity of the base film 200 is 40%-70%. In some embodiments, the porosity of the base film 200 can be 45%-65%. Understandably, the porosity of the base film 200 is related to the material composition of the support layer 202. Therefore, the porosity of the support layer 202 can be adjusted based on the adjustment of the material composition of the base film 200 (e.g., the support layer 202). Table 1 below is a comparison table of the performance of polyamide composite films obtained from various embodiments with different base film porosities:

[0036] Table 1

[0037] As shown in Table 1, when the base membrane porosity is too high (e.g., 80% in Table 1), although the permeate flux is large, the desalination rate is very low; when the base membrane porosity is too low (e.g., 30% in Table 1), although the desalination rate is not low, the permeate flux is too low. When the base membrane porosity is within the range mentioned above (40%-70%), the desalination rate and permeate flux of the polyamide composite membrane are both ideal, and the overall performance of the polyamide composite membrane is better.

[0038] It should be noted that the porosity of the base membrane can be tested using the gas adsorption method.

[0039] By using a base membrane 200 with the aforementioned porosity, the aqueous monomers of the subsequently coated aqueous solution can diffuse more easily on the base membrane 200, thus facilitating the preparation of a polyamide composite membrane with fewer defects, higher flux, and higher desalination rate. For details regarding the aqueous solution, aqueous monomers, etc., please refer to the relevant explanation in step 120 below. The desalination rate refers to the percentage of soluble impurities removed from the feed liquid by the polyamide composite membrane during separation. Therefore, the desalination rate = (1 - salt content of the separated liquid / salt content of the feed liquid) × 100%. Generally, the higher the density of the polymer layer 300 of the polyamide composite membrane (see the relevant explanation in step 130 for details), the higher the desalination rate. The permeate flux reflects the permeability of the polyamide composite membrane; flux can refer to the amount of liquid permeating through the polyamide composite membrane per unit time. Furthermore, by limiting the surface porosity of the support layer 202 within the aforementioned range, it is beneficial to reduce the lateral water transport resistance, thereby facilitating the formation of a more permeable polyamide composite membrane.

[0040] It should be noted that permeate flux (or water flux) and desalination rate are two of the most basic and important indicators for evaluating polyamide composite membranes. Cross-flow permeation experiments can be used to evaluate the permeation and separation performance of polyamide composite membranes, allowing for the measurement of their water flux and desalination rate. In this specification, the measurement conditions for the polyamide composite membrane are as follows: 1000 ppm NaCl as the test solution, an applied pressure of 1.05 MPa, and an aqueous solution temperature of 25°C.

[0041] Figure 3 is a flowchart of the preparation of a base membrane in some embodiments of this specification. In some embodiments, as shown in Figure 3, preparing a base membrane 200 having a porous structure may include the following steps:

[0042] Step 111: Apply the casting solution to one side surface of the nonwoven fabric 201 to form a support layer 202.

[0043] The casting solution can be absorbed into the nonwoven fabric 201, forming a support layer 202 on one side of the nonwoven fabric 201. The support layer 202 and the nonwoven fabric 201 together form the base film 200. In some embodiments, the support layer 202 can be a polysulfone layer. The surface of the nonwoven fabric 201 facing away from the support layer 202 can be understood as the back side of the base film 200, and the surface of the support layer 202 facing away from the nonwoven fabric 201 can be understood as the front side of the base film 200. In some embodiments, the thickness of the nonwoven fabric 201 can be 50 μm-200 μm. In some embodiments, the basis weight of the nonwoven fabric 201 can be 20-100 g / m³. 3 .

[0044] In some embodiments, the casting solution can be obtained by adding a certain mass of solute to a certain mass of solvent and stirring until homogeneous. The solute in the casting solution may include: 10-20 mass of polysulfone, 0-5 mass of a pore-forming agent, and one or more of polyvinylpyrrolidone / polyethylene glycol / water. That is, the solute in the casting solution may include polysulfone, a pore-forming agent, and other raw materials, which may be one or more of polyvinylpyrrolidone, polyethylene glycol, and water. Polysulfone materials have excellent mechanical properties, high rigidity, wear resistance, and high strength, and maintain excellent mechanical properties even at high temperatures. The pore-forming agent is a substance used to form pores during the manufacturing process of the support layer 202. In some embodiments, the pore-forming agent may include polyvinylpyrrolidone and / or polyethylene glycol, etc. Other raw materials may be substances that can play a role in binding, solubilizing, and coagulating. In some embodiments, the solvent of the casting solution includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide. The solvent content of the casting solution can be 70-80 parts by mass. The specific content of polysulfone and pore-forming agent will affect the mechanical properties (such as mechanical strength) and structural properties (such as internal pore parameters, surface pore parameters, etc.) of the support layer 202. By preparing the support layer 202 according to the above raw material composition and ratio, the prepared base film 200 will also have relatively ideal mechanical and structural properties.

[0045] In some embodiments, the temperature of the casting solution is 20°C-50°C during the coating process on the nonwoven fabric 201. In some preferred embodiments, the temperature of the casting solution is 23°C-33°C during the coating process on the nonwoven fabric 201. By setting the temperature of the casting solution within the above-mentioned temperature range, it is possible to ensure that the formed support layer 202 has good mechanical and structural properties and is stably attached to the nonwoven fabric 201. In particular, when the temperature of the casting solution is limited to 23°C-33°C, the mechanical and structural properties of the formed support layer 202 are even better.

[0046] Step 112: Dry the nonwoven fabric 201 coated with the support layer 202 to form a base film 200.

[0047] In some embodiments, during the drying process of the nonwoven fabric 201 coated with the support layer 202, the drying temperature can be 20°C-50°C. In some embodiments, the drying temperature can not exceed 35°C. For example, the drying temperature can be 20°C-25°C. In some embodiments, the drying time is 30s-150s. In some embodiments, the nonwoven fabric 201 coated with the support layer 202 can be dried by air drying at room temperature. Through the drying operation, excess liquid on the support layer 202 and the nonwoven fabric 201 is avoided from affecting subsequent reactions. At the same time, by operating according to the above-mentioned drying temperature (not exceeding 35°C) and time, complete drying is ensured without affecting the moisture content inside the base film 200 due to excessively high drying temperature or excessively long drying time, thus ensuring the good performance of the base film 200.

[0048] The morphology and chemical properties of the base film 200 will affect the distribution of the aqueous solution and aqueous monomers on the surface of the base film 200 and the diffusion process of the aqueous monomers into the oil solution in subsequent operations, thereby affecting the structure and performance of the final polyamide composite film. By preparing the base film 200 according to the above embodiments, the base film 200 has ideal mechanical and structural properties, which is conducive to the diffusion of aqueous monomers in the subsequent interfacial polymerization reaction, and thus conducive to the preparation of a polyamide composite film with better performance.

[0049] Step 120: Coat the base film 200 with an aqueous phase solution and an oil phase solution.

[0050] Aqueous solutions are formed by dissolving aqueous monomers in an aqueous solvent. Oil solutions are formed by dissolving organic monomers in an organic solvent. Aqueous solutions can be solutions containing amine monomers (such as aromatic amine monomers), while oil solutions can be solutions containing acyl chloride monomers (such as aromatic acyl chloride monomers).

[0051] When coating the base film 200 with an aqueous solution and an oil solution, the oil solution and at least a portion of the aqueous solution are coated on opposite sides of the base film 200. For example, the aqueous solution may be coated on one side of the base film 200 (e.g., the back side of the base film 200), while the oil solution may be coated on the other side of the base film 200 (e.g., the front side of the base film 200); or, for another example, the aqueous solution may be coated on both sides of the base film 200 (e.g., the front and back sides of the base film 200), while the oil solution may be coated on one side of the base film 200 (e.g., the front side of the base film 200). When coating the base film 200 with the aqueous solution and the oil solution, the oil solution and at least a portion of the aqueous solution may be coated simultaneously or sequentially. For example, an aqueous phase solution can be coated on one side of the base film 200 (such as the back side of the base film 200), while an oil phase solution is coated on the other side of the base film 200 (such as the front side of the base film 200); or, for example, an aqueous phase solution can be coated on one side of the base film 200 (such as the back side of the base film 200) first, and then an oil phase solution can be coated on the other side of the base film 200 (such as the front side of the base film 200); or, for example, an aqueous phase solution can be coated on both sides of the base film 200 (such as the front and back sides of the base film 200), and then an oil phase solution can be coated on one side of the base film 200 (such as the front side of the base film 200).

[0052] Figure 4 is a flowchart illustrating the coating of an aqueous phase solution and an oil phase solution in the preparation methods of some embodiments of this specification. In some embodiments, as shown in Figure 4, the process of coating an aqueous phase solution and an oil phase solution on the base film 200 may specifically include the following steps:

[0053] Step 121: Apply an aqueous solution to at least one side of the nonwoven fabric 201 that is away from the support layer 202.

[0054] In some embodiments, the base membrane 200 can be immersed in an aqueous solution to allow the aqueous solution to adhere to the base membrane 200. However, this method consumes a large amount of aqueous solution. Furthermore, excess aqueous solution needs to be removed by heating or other methods, increasing the number of steps and making it difficult to control the amount of aqueous monomers adhering to the base membrane 200. In some embodiments, the aqueous solution can be coated onto the base membrane 200. Compared to immersion, coating significantly reduces the consumption of aqueous solution, increases yield, and allows for more precise control of the amount of aqueous monomers adhering to the base membrane 200 (a suitable aqueous solution concentration is greater than 200 mg / m³). 2 ).

[0055] In some embodiments, during the coating of the aqueous solution onto the base film 200, the tension of the nonwoven fabric 201 is 100N-180N. Table 2 below is a comparison table of the performance of polyamide composite films obtained in various embodiments with different nonwoven fabric tensions:

[0056] Table 2

[0057] The tension of the nonwoven fabric 201 affects the uniformity of the polymer layer formed by the polymerization reaction. As shown in Table 2, if the tension of the nonwoven fabric is too low (e.g., 50N in Table 2), the aqueous solution may not reach the front side of the base membrane 200, leading to an uneven polymer layer formed by the interfacial polymerization reaction. If the tension of the nonwoven fabric is too high (e.g., 200N in Table 2), the aqueous solution may not be able to coat the nonwoven fabric 201, also leading to an uneven polyamide layer formed by the interfacial polymerization reaction. Both of these factors contribute to a decrease in desalination rate and permeate flux. Therefore, when the tension of the nonwoven fabric is within the above-mentioned range (100N-180N), both the desalination rate and permeate flux are relatively ideal, resulting in better overall performance of the polyamide composite membrane.

[0058] In some embodiments, the nonwoven fabric 201 can be tensioned by a tensioning mechanism. The tension of the nonwoven fabric can be adjusted in real time based on parameters related to the aqueous solution coating.

[0059] In some embodiments, in step 121, an aqueous solution is coated on the surface of the support layer 202 facing away from the nonwoven fabric 201. In other embodiments, to improve the flux and desalination rate of the polyamide composite membrane, in step 121, the aqueous solution may be coated on the surface of the nonwoven fabric 201 facing away from the support layer 202, or the aqueous solution may be coated on both sides of the base membrane 200 (the front and back sides of the base membrane 200). Table 5 below is a comparison table of the performance of the polyamide composite membranes obtained by coating the front side of the base membrane 200 with an aqueous solution, coating the back side of the base membrane 200 with an aqueous solution, and coating both the front and back sides of the base membrane 200 with an aqueous solution.

[0060] Table 3

[0061] As shown in Table 3, compared to the embodiment where the aqueous solution is coated on the front side of the base film 200 (the side of the support layer 202 facing away from the nonwoven fabric 201), the embodiments where the aqueous solution is coated on the back side of the base film 200 (i.e., the side of the nonwoven fabric 201 facing away from the support layer 202), and the embodiments where the aqueous solution is coated on both the front and back sides of the base film 200, result in polyamide composite membranes with higher flux, higher desalination rates, and better overall performance. It should be noted that the only difference between the three embodiments in Table 3 is the coating position of the aqueous solution; all other parameters and processes are identical.

[0062] It should also be noted that during the process of coating the nonwoven fabric 201 with the aqueous solution, the coating operation can be performed once or multiple times, regardless of which side of the nonwoven fabric 201 is coated with the aqueous solution.

[0063] In some embodiments, the aqueous phase solution may be formed by dissolving an aqueous monomer (i.e., an aqueous solute) in an aqueous solution (i.e., an aqueous solvent). In some embodiments, the aqueous phase solution comprises 6-20 parts by mass of the aqueous solute, which includes an amine monomer, comprising aromatic amine monomers and / or aliphatic amine monomers. In some preferred embodiments, the aqueous phase solution comprises 5-15 parts by mass of the aqueous solute. In some preferred embodiments, the aqueous phase solution comprises 8-15 parts by mass of the aqueous solute. In some embodiments, the aromatic amine may include one or more of p-phenylenediamine, m-phenylenediamine, and o-phenylenediamine. In some embodiments, the aliphatic amine is one or more of ethylenediamine, propylenediamine, butanediamine, pentanediamine, N-(2-hydroxyethyl)ethylenediamine, hexamethylenediamine, 1,2-diaminocyclohexane, 1,3-diaminocyclohexane, 1,4-diaminocyclohexane, piperazine, and 4-aminomethylpiperazine. The solvent of the aqueous phase solution is water.

[0064] The concentration of amine monomers in the aqueous solution affects the performance of the polyamide composite membrane. Table 4 below compares the performance of the polyamide composite membranes obtained from various examples with different concentrations of amine monomers in the aqueous solution:

[0065] Table 4

[0066] As shown in Table 4, when the concentration of the aqueous solution is too low (i.e., the concentration of amine monomers is too low, such as 2 wt% in Table 4), insufficient amine monomers diffuse to the front side of the substrate membrane, leading to poor film formation, pore formation in the substrate membrane, and thus a decrease in permeate flux. When the aqueous solution concentration is too high (such as 25 wt% in Table 4), there will be an excess of amine monomers (such as m-phenylenediamine, also known as MPD), which will also reduce the permeate flux.

[0067] In some embodiments, the aqueous phase solution may further include additives. Additives may be surfactants, pH adjusters, inorganic salts, etc. In some embodiments, surfactants may include one or more of sodium dodecyl sulfate, sodium dodecyl sulfonate, sodium dodecylbenzene sulfonate, and sodium stearate. pH adjusters may include sodium hydroxide, sodium carbonate, carbamic acid, etc. In some embodiments, inorganic salts may include sodium chloride.

[0068] In some embodiments, during the coating of the aqueous solution onto the base film 200, the temperature of the aqueous solution is 55°C-70°C. For example, 55°C, 62°C, 70°C, etc. In some embodiments, during the coating of the aqueous solution onto the base film 200, the temperature of the aqueous solution is 55°C-65°C. For example, 56°C, 63°C, 65°C, etc. In some embodiments, during the coating of the aqueous solution onto the base film 200, the temperature of the aqueous solution is 55°C-60°C. For example, 57°C, 59°C, etc. By limiting the temperature of the aqueous solution to the above ranges during the coating process, it is ensured that the aqueous solution can diffuse well into the base film 200, ensuring the subsequent interfacial polymerization reaction. Table 5 below is a comparison table of the performance of polyamide composite films obtained in various embodiments with different aqueous solution temperatures:

[0069] Table 5

[0070] As shown in Table 5, if the temperature of the aqueous solution is too low (e.g., 30℃ in Table 5), insufficient permeation of the aqueous solution will result in poor membrane formation. Consequently, during the drying of the aqueous solution, pores will form in the base membrane, leading to low water flux of the polyamide composite membrane.

[0071] Step 122: Apply an oil phase solution to the surface of the support layer 202 on the side facing away from the nonwoven fabric 201.

[0072] In some embodiments, the oil phase solution can be poured onto the base membrane 200 to allow it to adhere. However, this method consumes a large amount of oil phase solution, and the amount of organic monomers in the oil phase solution adhering to the base membrane 200 is difficult to control. In some embodiments, the oil phase solution can be coated onto the base membrane 200. Compared to pouring onto the base membrane 200, coating can significantly reduce the consumption of oil phase solution, increase the yield, and allow for more precise control of the amount of organic monomers adhering to the base membrane 200 (a suitable oil phase solution dosage is greater than 400 mg / m³). 2 ).

[0073] In some embodiments, an oil phase solution may be coated onto the base film. In some embodiments, the tension of the nonwoven fabric 201 is 100N-180N during the coating of the oil phase solution onto the base film. When coating the base film 200 with the oil phase solution, the method (such as the tension of the nonwoven fabric 201, etc.) can be similar to the coating method of the aqueous phase solution; for details, please refer to the relevant description of the coating method of the aqueous phase solution.

[0074] In some embodiments, the oil phase solution may be formed by dissolving an organic phase monomer (i.e., the oil phase solute) in an organic solution (i.e., the oil phase solvent). The oil phase solution comprises 0.1-0.5 parts by mass of the oil phase solute, which includes an acyl chloride monomer, comprising aromatic acyl chlorides and / or fatty acyl chlorides. In some embodiments, the oil phase solution comprises 0.1-0.4 parts by mass of the oil phase solute. In some embodiments, the aromatic acyl chloride may include one or more of terephthaloyl chloride, phthaloyl chloride, isophthaloyl chloride, biphenyl dicarboxylate chloride, benzene disulfonyl chloride, and trimesoyl chloride. In some embodiments, the fatty acyl chloride may include one or more of succinic acid chloride, glutaryl chloride, adipyl chloride, sebacyl chloride, cyclobutane diacyl chloride, and cyclopentane diacyl chloride.

[0075] In some embodiments, the solvent of the oil phase solution includes one or more of the following: aliphatic hydrocarbons containing 4 to 10 carbon atoms, cyclic aliphatic hydrocarbons containing 4 to 10 carbon atoms, and aromatic hydrocarbons containing 4 to 10 carbon atoms.

[0076] In some embodiments, during the coating of the oil phase solution onto the base film 200, the temperature of the oil phase solution is 55°C-75°C. For example, 55°C, 61°C, 75°C, etc. In some embodiments, during the coating of the oil phase solution onto the base film 200, the temperature of the oil phase solution is 55°C-70°C. For example, 56°C, 62°C, 70°C, etc. In some embodiments, during the coating of the oil phase solution onto the base film 200, the temperature of the oil phase solution is 60°C-70°C. For example, 60°C, 65°C, 69°C, etc. By limiting the temperature of the oil phase solution to the above range (i.e., 55°C-75°C) during the coating process, the reaction time in the interfacial polymerization reaction can be shortened, improving the formation efficiency of the polymer layer 300 and the performance of the polyamide composite film. Table 6 below is a comparison table of the performance of the polyamide composite films obtained in various embodiments with different oil phase solution temperatures:

[0077] Table 6

[0078] As shown in Table 6, if the temperature of the oil phase solution is too low (e.g., 30℃ in Table 6), the permeate flux will be very low. If the temperature of the oil phase solution is too high (e.g., 80℃ in Table 6), the permeate flux will also be very low.

[0079] In some embodiments, step 122 may be performed before step 121. Since both the nonwoven fabric 201 and the support layer 202 are hydrophobic, to ensure better absorption of the aqueous solution by the base film 200, step 122 is performed after step 121, or simultaneously with step 121, thereby ensuring the smooth progress of the interfacial polymerization reaction. When step 122 is performed after step 121, the performance of the polyamide composite film can be improved.

[0080] Specifically, the coating order of the aqueous and oil phase solutions can vary. In some embodiments, the aqueous phase solution can be coated once or multiple times on the surface of the nonwoven fabric facing away from the support layer, while the oil phase solution is coated on the surface of the support layer facing away from the nonwoven fabric. In other embodiments, the oil phase solution can be coated first on the surface of the support layer facing away from the nonwoven fabric, and then the aqueous phase solution can be coated once or twice on the surface of the nonwoven fabric facing away from the support layer. In some preferred embodiments, the aqueous phase solution can be coated first on the surface of the nonwoven fabric facing away from the support layer, and then the oil phase solution can be coated on the surface of the support layer facing away from the nonwoven fabric, thus obtaining a polyamide composite film with better performance. Table 7 below is a comparison table of the performance of polyamide composite films obtained from various embodiments with different coating orders of aqueous and oil phase solutions:

[0081] Table 7

[0082] As can be seen from Table 7, the desalination rate and water flux of the technical schemes that first coat the oil phase solution and then coat the aqueous phase solution, as well as the technical schemes that simultaneously coat the oil phase solution and the aqueous phase solution, are both relatively low.

[0083] Step 130: The aqueous solution and the oil solution undergo an interfacial polymerization reaction to form a polymer layer 300 on the base film 200, thereby forming a polyamide composite film.

[0084] Interfacial polymerization refers to a polymerization reaction that occurs at the interface of two immiscible molecules, where the aqueous monomer is dissolved in the aqueous solution and the organic monomer is dissolved in the oil solution. By contacting the aqueous and oil solutions, these two monomers polymerize at the interface, thereby forming a dense polymer layer 300 on the support layer 202. This polymer layer 300 can be a dense layer of aromatic polyamide (also called a polyamide layer, which includes polyamide and polyimide). Referring to Figures 5 and 6, Figure 5 is a schematic diagram of the structure of the support layer and polymer layer of the polyamide composite film prepared in some embodiments of this specification, and Figure 6 is a schematic diagram of the structure of the polymer layer of the polyamide composite film prepared in some embodiments of this specification. Figure 5 shows the structure of the polymer layer 300 and the base film 200 (support layer 202), and Figure 6 is an enlarged schematic diagram of Figure 5, showing the structure of the polymer layer 300.

[0085] The polymer layer 300, together with the support layer 202 and the nonwoven fabric 201, forms a polyamide composite film. Because the solubility of aqueous monomers in organic solutions is greater than that of organic monomers in aqueous solutions, this asymmetric solubility causes the interfacial polymerization reaction to primarily occur on the organic phase side. When the formation of the cross-linked polymer film hinders the contact between monomers, interfacial polymerization slows down or even stops. This is the self-inhibiting characteristic of interfacial polymerization, and it also explains the ultrathin thickness of the resulting polymer film.

[0086] In some embodiments, multiple interfacial polymerization reactions can be performed to form multiple polymer layers 300. The density of the multiple polymer layers 300 prepared in this way increases layer by layer from the inside to the outside. However, this greatly increases the complexity of the process, reduces the preparation efficiency, and the performance of the polyurethane composite film is also poor because it is difficult to control the multiple reactions.

[0087] In some embodiments, by using the raw materials described above and preparing the aqueous and oil phase solutions according to the above proportions, and limiting the temperature during the coating process of the aqueous and oil phase solutions to the above temperature range, the aqueous and oil phase solutions do not need to undergo multiple interfacial polymerization reactions; only one interfacial polymerization reaction is required to prepare a uniform and dense polyamide layer. This greatly improves the preparation efficiency of the polyamide composite membrane and simplifies the process. Furthermore, by limiting the raw material composition, proportions, and temperatures of the aqueous and oil phase solutions in the above embodiments, even with only one interfacial polymerization reaction, a polyamide composite membrane with high flux and high desalination rate can be prepared. For example, when the aqueous phase solution includes 8-15 parts by mass of amine monomers and the oil phase solution includes 0.1-0.4 parts by mass of acyl chloride monomers, and during the coating process, the temperature of the aqueous phase solution is 55℃-70℃ and the temperature of the oil phase solution is 55℃-75℃, even with only one interfacial polymerization reaction, the flux of the prepared polyamide composite membrane can be higher than 100 GFD and the desalination rate higher than 99%. The polymer layer 300 prepared in this way is a layer structure with uniform density. Uniform density can be understood as the density at various locations in the polymer layer being basically the same (e.g., the difference is less than 5%). Table 8 below is a comparison table of the performance of polyamide composite films obtained by examples with different numbers of interfacial polymerization reactions: first, an aqueous phase solution is coated on the side of the nonwoven fabric away from the support layer, and then an oil phase solution is coated on the side of the support layer away from the nonwoven fabric.

[0088] Table 8

[0089] As can be seen from Table 8, when both methods involve coating the aqueous phase solution first and then the oil phase solution, the polyamide composite membrane obtained by performing one interfacial polymerization reaction has a higher desalination rate and water flux than that obtained by performing multiple reactions (such as the two reactions shown in Table 8).

[0090] In some embodiments, the method for preparing a polyamide composite film may include a removal step. The removal step may be used to remove excess oil phase solution. Here, excess oil phase solution refers to oil phase solution that has not undergone interfacial polymerization.

[0091] In some embodiments, the method for preparing the polyamide composite membrane may further include a drying step. The drying step involves drying the polyamide composite membrane (e.g., both sides of the polyamide composite membrane) after removing excess oil phase solution. The drying step can improve the cleaning effect of subsequent cleaning steps.

[0092] In some embodiments, the preparation method of the polyamide composite membrane may further include a cleaning step. The cleaning step can be used to further remove residual excess oil phase solution and aqueous phase solution to ensure the performance of the polyamide composite membrane. It should be noted that, in this specification, excess oil phase solution refers to oil phase solution that has not undergone interfacial polymerization, and excess aqueous phase solution refers to aqueous phase solution that has not undergone interfacial polymerization.

[0093] The preparation method of the polyamide composite film provided in this specification will be described below with reference to a specific embodiment. In one specific embodiment, the preparation method of the amide composite film may include the following steps:

[0094] Step S1: Preparation of casting solution: Mix 16 parts by mass of polysulfone, 81 parts by mass of N,N-dimethylformamide and 3 parts by mass of polyvinylpyrrolidone, and stir at 25°C and 500 r / min to form a homogeneous solution; let the above homogeneous solution stand and degas to obtain the casting solution.

[0095] Step S2: The casting solution is evenly sprayed onto the nonwoven fabric through a slit coating head. After coating, it is allowed to stand, and then placed in pure water at 10°C to solidify into a film. After drying, a polysulfone-based film is obtained. The porosity of the obtained polysulfone-based film is 65%. Steps S1 and S2 correspond to step 110 above.

[0096] Step S3: Prepare an aqueous solution: Add 15 parts by mass of m-phenylenediamine, 8 parts by mass of dimethyl sulfoxide, 0.2 parts by mass of sodium dodecyl sulfonate and 0.5 parts by mass of sodium hydroxide to 76.3 parts by mass of pure water, stir to dissolve and obtain an aqueous solution.

[0097] Step S4: Prepare the oil phase solution: Dissolve 0.3 parts by mass of trimesoyl chloride in 99.7 parts by mass of isoparaffin to obtain the oil phase solution.

[0098] Step S5: Preparation of the polymer layer: The aqueous solution is heated to 55°C and uniformly sprayed onto the surface of the polysulfone-based nonwoven fabric away from the support layer using a slit coating head. The tension of the nonwoven fabric is controlled at 135N. Subsequently, the oil phase solution is heated to 70°C and uniformly sprayed onto the surface of the polysulfone-based film support layer away from the nonwoven fabric using a slit coating head. The tension of the nonwoven fabric is controlled at 135N. The oil phase solution and the aqueous phase solution undergo a polymerization reaction to obtain a composite layer film. The composite layer film is then dried, washed with pure water, and dried again to obtain a polyamide composite film. Steps S3-S5 correspond to steps 120 and 130 above.

[0099] The polyamide composite membrane prepared according to the above method was tested and found to have a water flux of 65.7 LMH and a desalination rate of 99.8%, which are high.

[0100] It should be noted that, in order to simplify the descriptions disclosed herein and thus aid in the understanding of one or more embodiments of the invention, the foregoing description of embodiments of this specification may sometimes combine multiple features into a single embodiment, drawing, or description thereof. However, this method of disclosure does not imply that the subject matter of this specification requires more features than those mentioned in the claims. In fact, the embodiments contain fewer features than all the features of a single embodiment disclosed above.

[0101] Finally, it should be understood that the embodiments described in this specification are merely illustrative of the principles of the embodiments described herein. Other variations may also fall within the scope of this specification. Therefore, alternative configurations of the embodiments described herein are intended to be illustrative rather than limiting, and should be considered consistent with the teachings of this specification. Accordingly, the embodiments described herein are not limited to those explicitly introduced and described herein.

Claims

1. A method for producing a polyamide composite film, wherein, The preparation method includes the following steps: Preparation of a base membrane with a porous structure; An aqueous phase solution and an oil phase solution are coated on the base film, wherein the oil phase solution and at least a portion of the aqueous phase solution are coated on opposite sides of the base film; The aqueous solution and the oil solution undergo interfacial polymerization to form a polymer layer on the base film, thereby forming a polyamide composite film.

2. The production method according to claim 1, wherein The preparation of a base film with a porous structure includes: The casting solution is applied to one side surface of the nonwoven fabric to form a support layer; The nonwoven fabric coated with the support layer is dried to form the base film; Coating the base film with an aqueous phase solution and an oil phase solution includes: The aqueous solution is applied to at least one surface of the nonwoven fabric opposite to the support layer. The oil phase solution is coated on the surface of the support layer opposite to the nonwoven fabric.

3. The production method according to claim 1, wherein The aqueous solution comprises 6-20 parts by mass of an aqueous solute, the aqueous solute comprising amine monomers, the amine monomers comprising aromatic amine monomers and / or aliphatic amine monomers; The solvent for the aqueous solution is water.

4. The production method according to claim 3, wherein The aqueous solution comprises 8-15 parts by mass of amine monomers.

5. The production method according to claim 3, wherein The aromatic amine monomer includes one or more of p-phenylenediamine, m-phenylenediamine, and o-phenylenediamine; and / or, The fatty amine monomers include one or more of ethylenediamine, propylenediamine, butanediamine, pentanediamine, N-(2-hydroxyethyl)ethylenediamine, hexanediamine, 1,2-diaminocyclohexane, 1,3-diaminocyclohexane, 1,4-diaminocyclohexane, piperazine, and 4-aminomethylpiperazine.

6. The production method according to claim 3, wherein During the process of coating the base film with an aqueous solution, the temperature of the aqueous solution is 55℃-70℃.

7. The production method according to claim 2, wherein The aqueous solution is applied once or multiple times to the surface of the nonwoven fabric facing away from the support layer, while the oil phase solution is applied to the surface of the support layer facing away from the nonwoven fabric. or, First, the aqueous solution is applied to both sides of the base film in one or more applications, and then the oil solution is applied to the side of the support layer facing away from the nonwoven fabric.

8. The production method according to claim 2, wherein First, the aqueous solution is applied to the surface of the nonwoven fabric opposite to the support layer, and then the oil solution is applied to the surface of the support layer opposite to the nonwoven fabric.

9. The production method as claimed in claim 2, wherein, Coating the base film with an aqueous phase solution and an oil phase solution includes: During the process of coating the aqueous solution onto the base film, the tension of the nonwoven fabric is 100N-180N; and / or, During the process of coating the oil phase solution onto the base film, the tension of the nonwoven fabric is 100N-180N.

10. The production method as claimed in claim 1, wherein, The oil phase solution comprises 0.1-0.5 parts by mass of an oil phase solute, wherein the oil phase solute comprises an acyl chloride monomer, and the acyl chloride monomer comprises aromatic acyl chloride and / or fatty acyl chloride; The solvent of the oil phase solution includes one or more of the following: aliphatic hydrocarbons containing 4 to 10 carbon atoms, cyclic aliphatic hydrocarbons containing 4 to 10 carbon atoms, and aromatic hydrocarbons containing 4 to 10 carbon atoms.

11. The production method according to claim 10, wherein The oil phase solution comprises 0.1-0.4 parts by mass of acyl chloride monomer.

12. The production method according to claim 10, wherein The aromatic acyl chloride includes one or more of terephthaloyl chloride, phthaloyl chloride, isophthaloyl chloride, biphenyl acyl chloride, benzenesulfonyl chloride, and trimesoyl chloride; and / or, The fatty acyl chlorides include one or more of succinyl chloride, glutaryl chloride, adipicoyl chloride, sebacyl chloride, cyclobutane diacyl chloride, and cyclopentane diacyl chloride.

13. The production method according to claim 10, wherein During the process of coating the base film with the oil phase solution, the temperature of the oil phase solution is 55℃-75℃.

14. The production method according to claim 1, wherein The porosity of the base membrane is 40%-70%.

15. The production method according to claim 1, wherein The interfacial polymerization reaction occurs once, and the polyamide composite film has uniform density.

16. A polyamide composite film prepared by any one of claims 1-15.

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