Preparation method and preparation device of polyamide reverse osmosis membrane

Abstract

The invention discloses a preparation method and a preparation device of a polyamide reverse osmosis membrane, the preparation method of the polyamide reverse osmosis membrane adopts an electrostatic spraying boundary non-interfacial polymerization method to prepare a polyamide composite reverse osmosis membrane, and comprises the following steps: firstly, preparing a P-PES base membrane; a layer of thin PVA is deposited on a PES base film (polyethersulfone base film) through electrostatic spraying, and the PVA modified PES base film is obtained through glutaraldehyde crosslinking and is named as a P-PES base film; and then preparing a polyamide layer on the prepared P-PES base membrane by adopting an electrostatic spraying interface-free polymerization method, and naming the polyamide layer as P-EILP. According to the preparation method, the PVA middle layer is added, the interface stability, the surface structure and the separation performance are enhanced, compared with a polyamide reverse osmosis membrane (CIP) prepared through a traditional interface polymerization method, the water flux is improved by 30%, and the prepared polyamide reverse osmosis membrane is uniform and stable in performance, high in water flux, simple in preparation process, easy to operate, low in production cost and suitable for industrial production. The method is suitable for industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of membrane separation, and particularly relates to a preparation method and a preparation device for a polyamide reverse osmosis membrane. Background Art

[0002] Due to its characteristics such as high efficiency, low energy consumption, and simple operation, membrane separation technology is widely used in drinking water purification and seawater desalination, playing a crucial role in alleviating the water resource crisis. A typical polyamide reverse osmosis membrane is composed of a porous substrate membrane and a dense polyamide separation layer. The polyamide reverse osmosis separation technology is one of the most important membrane separation technologies at present; in recent years, great progress has been made in improving the separation performance of reverse osmosis membranes, but there is still a lack of research on the effective control of the thickness of the polyamide separation layer.

[0003] The main preparation methods of polyamide reverse osmosis membranes in the prior art include interfacial polymerization, phase inversion method, and co-solvent assisted interfacial polymerization method. Interfacial polymerization can provide uniform and stable membrane performance, but the process is relatively complex; the phase inversion method is suitable for large-scale production, but the membrane performance may not be as good as that of interfacial polymerization; the co-solvent assisted interfacial polymerization method can prepare high-performance materials, but the cost is relatively high.

[0004] In order to improve the separation performance of polyamide reverse osmosis membranes and the control of the polyamide structure, adjustments are made from aspects such as surface chemical composition, surface structure, and polyamide layer thickness. For example, thin film nanocomposite (TFN) membranes doped with nanomaterials (such as MoS2, POSS, MOF, aquaporin, and graphene oxide) have been reported, preparing ultrathin defect-free polyamide membranes by interfacial polymerization of free interfaces, an interlayer doping strategy, introducing cadmium hydroxide nanowires, polydopamine, and carbon nanotubes, etc. between the polyamide layer and the substrate membrane as intercalations to improve the permeation performance of the membrane by controlling the thickness of the polyamide separation layer, and preparing ultrathin polyamide membranes by molecular layer-by-layer deposition.

[0005] Existing ultrathin polyamide membrane preparation technologies have problems such as the complexity of molecular layer-by-layer deposition, the vulnerability of interfacial polymerization of the free interface method, uneven dispersion of nanomaterial doping, and the uncontrollability of traditional interfacial polymerization. There is a need to improve the manufacturing technology of the polyamide layer in actual production. In recent years, electrospray interfacial polymerization (EIP) has been applied as a new membrane preparation strategy to prepare ultrathin polyamide layers with a smooth surface. However, due to the large differences in the physical properties (such as dielectric constant and vapor pressure) of water and organic solvents, it is difficult to simultaneously obtain the best spraying state under the same electrospray parameters. In addition, at room temperature, organic solvents volatilize faster than water, and the acyl chloride monomers deposited on the substrate membrane will hydrolyze, reducing the crosslinking degree of the polyamide layer. Summary of the Invention

[0006] Based on the technical problems existing in the prior art, the present invention provides a preparation method and a preparation device for a polyamide reverse osmosis membrane. The present invention uses an electrostatic spray interfaceless polymerization method to prepare the polyamide reverse osmosis membrane, and compared with the traditional interfacial polymerization method for preparing the polyamide reverse osmosis membrane (CIP), the water flux is increased by 30%. The membrane of the present invention has uniform and stable performance, high water flux, simple preparation process, easy operation, and low production cost, and is suitable for industrial production.

[0007] According to the first aspect of the technical solution of the present invention, a preparation method for a polyamide reverse osmosis membrane is provided, and the preparation method includes the following steps: Step S1: Prepare a P-PES base membrane, and electrostatically spray deposit a thin layer of PVA on the polyethersulfone base membrane of the PES base membrane and crosslink it with glutaraldehyde to obtain a PVA-modified PES base membrane; Step S2: Prepare a polyamide layer on the P-PES base membrane obtained in Step S1 by an electrostatic spray interfaceless polymerization method.

[0008] Further, in Step S1, accurately weigh 0.2 g of polyvinyl alcohol 1788 and add it to 99.8 g of ultrapure water, and place it in a constant temperature magnetic stirrer for dissolution. Preferably, the water bath temperature is 80 °C, and it is continuously stirred at 500 rpm for 6 h until completely dissolved.

[0009] Preferably, after the polyvinyl alcohol 1788 to be dissolved is naturally cooled to room temperature, vacuum filtration is carried out using a 0.45 μm microporous filter membrane to obtain a clarified PVA solution with a mass fraction of 0.2% for standby.

[0010] More preferably, fix the PES base membrane on the receiving roller, remove the excess water on the surface of the PES base membrane with a dust-free paper, and use an electrostatic spray gun to evenly spray the PVA solution on the surface of the PES base membrane.

[0011] Further, the parameters of the electrostatic spray gun: set the total applied voltage to 15 kV; the needle injection rate to 1.8 mL / h; and the electrostatic spray scanning times to two.

[0012] Even more preferably, the parameters of the electrostatic spray gun: the distance between the needle and the roller is 60 mm; the translation rate of the sliding table is 20 mm / min; and the rotation speed of the roller is 80 rpm.

[0013] Preferably, measure 50% glutaraldehyde (GA) mother liquor, dilute it step by step with ultrapure water and adjust the pH to 2.0 ± 0.1 with 0.1 M HCl to prepare a 0.2% (w / v) acidic crosslinking working solution.

[0014] More preferably, immerse the obtained PES base membrane vertically in the crosslinking solution, and place it in a constant temperature water bath shaker (60 ± 1 °C) for dynamic crosslinking at 120 rpm for 120 ± 5 s.

[0015] According to the second aspect of the technical solution of the present invention, there is provided a preparation device for the preparation method of the above polyamide reverse osmosis membrane, which includes a positive and negative high-voltage DC power supply, a precision injection pump and a receiving drum. The positive and negative high-voltage DC power supply provides a stable electric field for jet stretching and droplet atomization. The precision injection pump is equipped with a high-precision stepping motor and supports multi-channel independent programming control to control electrostatic spray interfaceless polymerization. The receiving drum rolls at an appropriate speed to form a polyamide reverse osmosis membrane with a certain thickness.

[0016] Compared with the prior art, the preparation method and preparation device of the polyamide reverse osmosis membrane of the present invention have the following beneficial technical effects: 1. The present invention successfully prepares a polyamide reverse osmosis membrane with a smooth and dense surface and small roughness by electrostatic spray interfaceless polymerization. The polyamide reverse osmosis membrane of the present invention has a PVA intermediate layer, and its desalination rate for a 1000 mg / L sodium chloride aqueous solution under a pressure of 1.0 Mpa reaches 96.7%, and its water flux reaches 32.8 L·m -2 ·h -1 , and the water flux is increased by 30% compared with the polyamide reverse osmosis membrane (CIP) prepared by the traditional interfacial polymerization method.

[0017] 2. The present invention prepares a polyamide composite reverse osmosis membrane by electrostatic spray interfaceless polymerization method. First, a thin layer of PVA is electrostatically spray-deposited on a polyethersulfone (PES) substrate membrane and cross-linked with glutaraldehyde to obtain a PVA-modified PES substrate membrane named P-PES substrate membrane. Then, a polyamide layer named P-EILP is prepared by electrostatic spray interfaceless polymerization on the P-PES substrate membrane. The addition of the PVA intermediate layer helps to enhance the interfacial stability, surface structure and separation performance.

[0018] 3. The present invention prepares a polyamide reverse osmosis membrane by electrostatic spray interfaceless polymerization method. Compared with the polyamide reverse osmosis membrane (CIP) prepared by the traditional interfacial polymerization method, the water flux is increased by 30%. The polyamide reverse osmosis membrane prepared by the present invention has uniform and stable performance, high water flux, simple preparation process, easy operation and low production cost, and is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a schematic process flow diagram of preparing a reverse osmosis membrane by electrostatic spray interfaceless polymerization method according to the present invention; Figure 2 is a schematic diagram of the action mechanism of the PVA-modified PES substrate membrane according to the present invention; Figure 3 is SEM and AFM images of different membrane surfaces and cross-sections according to the present invention; Figure 4a is the Fourier transform infrared spectroscopy diagrams of the P-PES substrate membrane and the PES substrate membrane according to the present invention; Figure 4b Fourier transform infrared spectra of the CIP reverse osmosis membrane, P-EILP reverse osmosis membrane, and EILP reverse osmosis membrane according to the present invention; Figure 5a Schematic diagram of the C1s peak deconvolution of the EILP reverse osmosis membrane according to the present invention; Figure 5b Schematic diagram of the C1s peak deconvolution of the P-EILP reverse osmosis membrane according to the present invention; Figure 5c Schematic diagram of the C1s peak deconvolution of the CIP reverse osmosis membrane according to the present invention; Figure 6a Test diagrams of the water contact angles of different membrane surfaces according to the present invention; Figure 6b Test diagrams of the zeta potentials of different membrane surfaces according to the present invention; Figure 7a Effect of different monomer concentrations on the performance of electrospray interfacelessly polymerized polyamide reverse osmosis membranes according to the present invention. The number of scans shown in the figure is four; Figure 7b Schematic diagram of the effect of different numbers of scans on the reverse osmosis performance of electrospray interfacelessly polymerized polyamide, where the monomer concentration is fixed and MPD:TMC = 0.2%:0.12%; Figure 7c Schematic diagram of the separation performance test of different polyamide reverse osmosis membranes according to the present invention. Detailed implementation manners

[0020] In order to make the technical problems solved by the present invention, the technical solutions adopted, and the beneficial effects obtained more clearly understood, the present invention will be further described in detail below with reference to specific embodiments. The specific embodiments described herein are only used to explain the present invention and do not constitute any limitation to the present invention. Unless otherwise defined, all terms used in the present invention have the same meaning as commonly used in the field to which the present invention belongs.

[0021] The following provides specific embodiments to help understand the present invention. However, it should be understood that the embodiments and test examples listed in the present invention are only used to illustrate the present invention, but do not constitute any limitation. The actual protection scope of the present invention is set forth in the claims.

[0022] The present invention provides a method for preparing a polyamide reverse osmosis membrane. The method for preparing the polyamide reverse osmosis membrane of the present invention prepares a polyamide composite reverse osmosis membrane by an electrostatic spraying interfaceless polymerization method. In the present invention, first, a P-PES substrate membrane is prepared. A thin layer of PVA (polyvinyl alcohol 1788) is electrostatically sprayed and deposited on the PES substrate membrane (polyethersulfone substrate membrane) and crosslinked with glutaraldehyde to obtain a PVA-modified PES substrate membrane, and the PES substrate membrane is named the P-PES substrate membrane. Then, a polyamide layer is prepared on the obtained P-PES substrate membrane by an electrostatic spraying interfaceless polymerization method, and the polyamide layer is named P-EILP. Adding a PVA intermediate layer in the present invention helps to enhance the interfacial stability, surface structure and separation performance. Compared with the traditional interfacial polymerization method for preparing polyamide reverse osmosis membranes (CIP), the water flux of the present invention is increased by 30%. The membrane performance of the present invention is uniform and stable, the water flux is high, the preparation process is simple, easy to operate, and the production cost is low, which is suitable for industrial production.

[0023] In the present invention, the polyethersulfone substrate membrane used in the method for preparing the polyamide reverse osmosis membrane is purchased from Chongqing Haitong Environmental Protection Co., Ltd., glutaraldehyde (GA, 50%) is purchased from Aladdin (Shanghai) Biochemical Technology Co., Ltd.; acetone (analytical pure) is purchased from Chongqing Chuandong Chemical (Group) Co., Ltd.; anhydrous sodium chloride (NaCl, 99%) is purchased from Macklin (Shanghai) Biochemical Technology Co., Ltd.; ultrapure water is prepared in the laboratory; other materials are m-phenylenediamine (MPD, 99%), n-hexane (analytical pure), polyvinyl alcohol 1788 (degree of alcoholysis: 87.0 - 89.0%), absolute ethanol (99.7%), trimesoyl chloride (TMC, 98%).

[0024] The following describes the method for preparing the polyamide reverse osmosis membrane of the present invention through multiple examples and in combination with the accompanying drawings.

[0025] Example 1 As Figure 1 and Figure 2 shown, a method for preparing a polyamide reverse osmosis membrane includes the following steps: Step S1: Prepare a P-PES substrate membrane. A thin layer of PVA (polyvinyl alcohol 1788 (preferably, the degree of alcoholysis is 87.0 - 89.0%)) is electrostatically sprayed and deposited on the PES substrate membrane (polyethersulfone substrate membrane) and crosslinked with glutaraldehyde to obtain a PVA-modified PES substrate membrane, and the PES substrate membrane is named the P-PES substrate membrane. Step S1 further includes the following steps: As Figure 1 and Figure 2 shown, a method for preparing a polyamide reverse osmosis membrane includes the following steps: Step S1: Prepare the P-PES base membrane. Electrostatically spray deposit a thin layer of PVA (polyvinyl alcohol 1788 (preferably, the degree of alcoholysis is 87.0 - 89.0%)) on the PES base membrane (polyethersulfone base membrane), and crosslink it with glutaraldehyde to obtain the PVA-modified PES base membrane, which is named the P-PES base membrane.

[0026] Step S1 further includes the following steps: Step S11, accurately weigh 0.2 g of polyvinyl alcohol 1788 (degree of alcoholysis 87.0 - 89.0%) and add it to 99.8 g of ultrapure water, and place it in a constant-temperature magnetic stirrer for dissolution. Control the water bath temperature at any temperature between 70°C and 90°C, preferably the parameter: 80°C, and continuously stir at 500 rpm for 6 h until completely dissolved. After the system (dissolved polyvinyl alcohol 1788) naturally cools to room temperature (25 ± 2°C), vacuum filtration is carried out using a 0.45 μm microporous membrane to obtain a clarified PVA solution with a mass fraction of 0.2% for standby. In the preferred embodiment, this process ensures the full extension of polymer chains through gradient heating and long-time dynamic stirring, and effectively removes undissolved components and mechanical impurities through the terminal filtration process. The obtained clarified PVA solution has good uniformity. Step S12, fix the PES base membrane (polyethersulfone base membrane) on the receiving drum, remove the excess moisture on the surface of the PES base membrane with lint-free paper, and use an electrostatic spray gun to evenly spray the PVA solution on the surface of the PES base membrane. The parameters of the electrostatic spray gun are: set the total applied voltage to 15 kV; the needle injection rate is 1.8 mL / h; the number of electrostatic spray scans is two; the distance between the needle and the drum is 60 mm; the translation rate of the sliding table is 20 mm / min; the rotation speed of the drum is 80 rpm. Electrostatic force will cause the PVA solution to quickly adhere to the PES base membrane, forming a uniform PVA layer.

[0027] Step S13, accurately measure the 50% glutaraldehyde (GA) stock solution, gradient dilute it with ultrapure water and adjust the pH to 2.0 ± 0.1 with 0.1 M HCl to prepare a 0.2% (w / v) acidic crosslinking working solution. Immerse the PES base membrane obtained in Step S11 vertically into the crosslinking solution, place it in a constant-temperature water bath shaker (60 ± 1°C) and dynamically crosslink it at 120 rpm for 120 ± 5 s; after the reaction ends, quickly take out the PES base membrane, rinse it three times with pre-cooled ultrapure water to terminate the reaction, and finally place it in a nitrogen-filled sealed container and store it in a low-temperature environment at 4°C. This process realizes the efficient bonding of glutaraldehyde molecules and the active sites on the membrane surface by precisely controlling the acidic environment (pH 2.0) and thermodynamic parameters. The low-temperature storage strategy can effectively inhibit the proliferation of microorganisms and hydrolysis side reactions, and ensure the structural stability of the base membrane.

[0028] Step S2: Prepare a polyamide layer on the P-PES base film prepared in Step S1 via electrostatic spray interfacial polymerization, named P-EILP. Step S2 further includes the following steps: Step S21, prepare MPD solution and TMC solution respectively. Step S21 further includes the following steps: Step S211, measure n-hexane (analytical pure, ≥99.5%) and acetone (analytical pure, ≥99.8%) to prepare a mixed solution according to a volume ratio of 4:1: Measure 400 mL of n-hexane and 100 mL of acetone in sequence. The acetone and n-hexane mixed solution is sealed and placed in an ultrasonic cleaner for ultrasonic acceleration of mixing. This polar mixed solvent system optimizes the physical and chemical properties of the organic solvent by regulating the ratio of non-polar / weakly polar components. After preparation, it needs to be transferred to a brown sealed bottle, marked with the preparation date and component information, and stored in a cool and dark place (validity period is 72 h).

[0029] Step S212, prepare MPD solution by dissolving m-phenylenediamine (MPD, 99%) in absolute ethanol and sonicate for 30 min to fully dissolve. Prepare TMC solution by dissolving trimesoyl chloride (TMC, 98%) in a n-hexane-acetone (4:1) mixed solution and sonicate for 30 min to fully dissolve. The concentration values of the MPD solution and the TMC solution are 0.05%: 0.03%; 0.1%: 0.06%; 0.2%: 0.12%; 0.3%: 0.18%; 0.5%: 0.3%.

[0030] Step S22, fix the P-PES base film prepared in Step S1 on a roller, remove the excess moisture on the film surface with lint-free paper, then use two 10 ml syringes to draw 5 ml of MPD absolute ethanol solution and TMC n-hexane-acetone mixed solution respectively, and fix the two syringes filled with the solution on the propulsion pump of the electrospinning machine. Use the electrospinning machine to simultaneously spray the MPD solution and the TMC solution evenly on the surface of the P-PES base film. The two monomers MPD and TMC undergo a polymerization reaction during flight to form a dense polyamide layer and deposit. Name the dense polyamide layer as the P-EILP film. Parameters of the electrospinning machine: Set the total applied voltage to 11 kV; the injection rates are the same, both 4 mL / h; the distance between the needle and the roller is 25 mm; the translation rate of the sliding table is 20 mm / min; the rotation speed of the roller is 80 rpm; the distance between the needles is 13 mm; the needle gauge is 27G.

[0031] Step S23, take down the P-EILP prepared in Step S22 and rinse the P-EILP film with 50 ml of n-hexane (analytical pure). Put the rinsed P-EILP base film into an oven at 60 °C for heat treatment for 10 min, take it out, rinse it with ultrapure water, and store it in ultrapure water at 4 °C for standby.

[0032] A polyamide reverse osmosis membrane prepared on the surface of a PES base membrane by an electrostatic spraying interfacial polymerization method, and the polyamide reverse osmosis membrane is named EILP (monomer concentration fixed, MPD:TMC = 0.2%:0.12%).

[0033] The polyamide reverse osmosis membrane prepared by the present invention as described above was compared with a polyamide reverse osmosis membrane (CIP) prepared by a conventional interfacial polymerization method and used in a control experiment. The preparation method is as follows: Fix the PES base membrane in a self-made acrylic mold, then slowly pour in a 50 ml aqueous solution of MPD with a concentration of 2%. After five minutes, pour out the excess solution, and gently blow the surface of the base membrane with nitrogen. When there is no residual aqueous solution on the surface of the base membrane, then pour in a certain amount of a 0.15% TMC n-hexane solution, let it stand for one minute, then pour out the excess organic phase solution and rinse the surface of the base membrane with n-hexane. Finally, heat-treat it in an oven at 60 °C for 10 min, take it out, rinse it with ultrapure water, and store it in ultrapure water at 4 °C for standby, and name it CIP membrane.

[0034] Test Example 1: Membrane structure characterization - Characterize the morphological features and surface roughness of the membrane.

[0035] Membrane structure characterization refers to the quantitative and qualitative description and analysis of the structural characteristics of membrane materials through a series of scientific methods and technical means. This includes the characterization of the microstructure, physical properties, chemical composition, etc. of the membrane materials. The instruments used in this example (Test Example 1) are as follows: Scanning electron microscope (SEM, JSM-7800F) purchased from JEOL, Japan; Atomic force microscope (AFM, Dimension EDGE) purchased from Bruker, USA; Fourier transform infrared spectrometer (Cary630) purchased from Agilent, USA; X-ray photoelectron spectrometer (XPS, K-Alpha) purchased from Thermo Scientific, USA; Water contact angle meter (SDC-200S) purchased from Shengding Precision Instruments Co., Ltd., Dongguan; Solid surface Zeta potential tester (SurPASS3) purchased from Anton Paar, Austria.

[0036] Before characterization, rinse the characterization samples with ultrapure water and dry them in a forced-air drying oven at 60 °C for 12 h.

[0037] SEM and AFM were used to characterize the morphological features and surface roughness of the membrane, respectively, as Figure 3 shown. The conventional interfacial polymerization method is a polymerization reaction that occurs between the oil-water interface. The reaction is rapid and can be completed within seconds. At the same time, a large amount of heat is released instantaneously during the reaction, and bubbles overflow, resulting in a typical peak-valley structure on the surface of the CIP membrane, with a relatively large surface roughness of 42.9 nm (as Figure 3as shown in Figures (a) and (c) therein. In contrast, the surface morphology characteristics of the EILP membrane prepared by the electrostatic spraying interfaceless polymerization method are quite different. The surface of the EILP membrane is smooth, no peak-valley structure is observed, and the surface roughness is much smaller than that of the CIP, only 8.57 nm (such as Figure 3 in Figures (d) and (f) therein). The reason is that the electrostatic spraying interfaceless polymerization method uses a lower concentration of monomers to prepare the reverse osmosis membrane and can precisely control the reaction amounts of the two monomers. In addition, under the action of electrostatic spraying, the polyamide layer will polymerize according to the layer-by-layer growth mode, and the polymerization reaction within each layer maintains relative independence, greatly reducing the influence degree of the reaction heat and bubbles on the membrane surface morphology. The finally formed polyamide layer is smoother. By performing electrostatic spraying interfaceless polymerization on the P-PES substrate membrane with a smoother surface, the surface roughness of the prepared polyamide reverse osmosis membrane P-EILP is further reduced, only 5.09 nm (such as Figure 3 in Figures (g) and (i) therein). As can be seen from Figure 3 Figure (m) therein, many micro-nano pores are distributed on the PES substrate membrane, which usually leads to a relatively large water flux of the substrate membrane but a poor rejection rate. By uniformly dispersing PVA on the PES substrate membrane through the electrostatic spraying method and crosslinking with glutaraldehyde, the obtained P-PES substrate membrane has a smaller pore diameter compared with the PES substrate membrane and a lower surface roughness, only 3.47 nm (such as Figure 3 in Figures (j) and (l) therein). The reduction of the substrate membrane pore diameter is beneficial to reducing the probability of defects in the polyamide layer.

[0038] Through Figure 3 the analysis of the SEM cross-sectional images of the membranes therein, it can be obtained that the polyamide reverse osmosis CIP prepared by the traditional interfacial polymerization method has a relatively thick polyamide layer (such as Figure 3 Figure (b) therein), while the polyamide layer prepared by the electrostatic spraying interfaceless polymerization method is very thin, and the boundary with the PES substrate membrane is almost invisible (such as Figure 3 Figures (e) and (h) therein).

[0039] Test Example 2: Membrane Structure Characterization - Physicochemical Properties of Different Membranes Figure 4a and Figure 4b are the Fourier transform infrared spectra of the membranes, Figure 4a is the Fourier transform infrared spectrum of the P-PES substrate membrane and the PES substrate membrane according to the present invention; Figure 4b is the Fourier transform infrared spectrum of the CIP reverse osmosis membrane, the P-EILP reverse osmosis membrane and the EILP reverse osmosis membrane according to the present invention. As shown in Figure 4a and Figure 4b shown, 3500 cm -1 -3200 cm -1 、1663 cm -1 、1609 cm-1 and 1541 cm -1 are the characteristic peaks of the polyamide separation layer, corresponding to N-H stretching vibration, C=O (amide I) stretching, hydrogen-bonded C=O (amide I) stretching, and N-H (amide II) in-plane bending vibration respectively; 1585 cm -1 is one of the characteristic peaks of polyethersulfone, corresponding to the in-plane bending stretching vibration of the benzene ring. From Figure 4a it can be seen that the broad peak between 3500 cm -1 -3200 cm -1 is mainly caused by the alcohol hydroxyl of PVA, and the characteristic peak at 1733 cm -1 comes from the stretching vibration absorption peak of the C=O group of GA, and the intensity of the characteristic peak of polyethersulfone has decreased, indicating that the PVA interlayer has been successfully constructed on the PES substrate membrane. From Figure 4b it can be concluded that all three reverse osmosis membranes have polyamide characteristic peaks, indicating that the polyamide layer has been successfully polymerized on the substrate membrane. By comparison, the polyamide characteristic peaks of the EILP and P-EILP membranes are weaker, and the polyethersulfone characteristic peaks are stronger. The reason is that interfacial polymerization-free occurs during the electrostatic spraying flight process, and the concentrations of the two reactive monomers are lower and the reaction time is very short, resulting in a thinner membrane than traditional interfacial polymerization, and the degree of crosslinking has decreased. At the same time, due to the lower concentration, the polyamide reverse osmosis membrane prepared by the electrostatic spraying interfacial polymerization-free method has a thinner polyamide layer than the polyamide reverse osmosis membrane prepared by the traditional interfacial polymerization method, so as to achieve high water flux.

[0040] Figure 5a 、 Figure 5b and Figure 5c are the C1s deconvolution spectra of different reverse osmosis membranes, Figure 5a is the C1s deconvolution spectrum of the EILP reverse osmosis membrane according to the present invention, Figure 5b is the C1s deconvolution spectrum of the P-EILP reverse osmosis membrane according to the present invention, Figure 5c is the C1s deconvolution spectrum of the CIP reverse osmosis membrane according to the present invention. The surface elemental composition of the reverse osmosis membrane is characterized by XPS. As Figure 5a 、 Figure 5b and Figure 5cAs shown, the results further confirm the conclusion of the present invention. All three membranes show characteristic peaks of the polyamide structure at approximately 288.0 eV (O=C-N / O=C-O) and 285.8 eV (C-N), indicating that regardless of the preparation method used, a polyamide layer can be successfully prepared. The proportion of the peak areas of the three membranes is different, which reflects the different degrees of crosslinking of the polyamide layer. At around 288.0 eV, the area content of the O=C-N / O=C-O peak is CIP (12.2%) > P-EILP (10.86%) > EILP (10.59%), indicating that compared with traditional interfacial polymerization, due to the reaction occurring between two liquid phases and the long reaction time, the interfacial polymerization reaction is sufficient, resulting in a higher degree of crosslinking between the polyamide molecular chains. In contrast, the proportion of the amide bond and ester bond areas in the EILP and P-EILP membranes prepared by the electrospray interfaceless polymerization method is smaller. This may be because the monomer concentration used in the electrospray interfaceless polymerization process is lower, and the dynamic deposition process significantly shortens the contact time of the reactants during a single scan, resulting in the covalent bonds between the polyamide segments being difficult to form, thus reducing the degree of crosslinking.

[0041] Test Example 3: Membrane Structure Characterization - Contact Angle and Zeta Potential of Membranes Figure 6a and Figure 6b are the water contact angles and Zeta potentials of different membrane surfaces. The water contact angles and Zeta potentials of different membrane surfaces were measured to test the hydrophilicity and hydrophobicity of different membrane surfaces. The test results are as Figure 6a shown. The size of the contact angle is directly related to the hydrophilicity and hydrophobicity of the membrane surface. The smaller the contact angle, the more hydrophilic the membrane. Among the three reverse osmosis membranes, the water contact angle of the CIP membrane is the smallest at 55.4°. The reason is that the surface of the CIP membrane is rougher and the residual TMC monomers after interfacial polymerization are hydrolyzed to obtain hydrophilic carboxylic acid groups. The water contact angle of the P-EILP membrane is 72.6°, which is larger than that of the EILP (62.9°). The reason is that the surface roughness of the P-EILP is smaller and the acyl chloride of the TMC that did not participate in the polymerization reaction on the membrane surface can undergo an in-situ polymerization reaction with the hydroxyl groups in the PVA, reducing the number of unreacted TMC molecules and weakening the hydrophilicity of the polyamide layer surface. The contact angle of the P-PES-based membrane is 46.1°, which is lower than that of the PES-based membrane (58.5°). The reason is that PVA is a hydrophilic polymer containing a large number of hydrophilic -OH groups, endowing the base membrane with more hydrophilic properties.

[0042] The charged groups on the surface of the polyamide membrane play a crucial role in the separation performance of the membrane, especially the rejection rate and anti-fouling performance. The zeta potential of different polyamide reverse osmosis membranes was measured, and the results are as Figure 6bAs shown. Compared with the pH of the isoelectric point (3.60) of the polyamide reverse osmosis membrane prepared by interfacial polymerization, electrospray has a lower isoelectric point (3.40 and 3.49). The reason is that the reaction time of the two monomers in the preparation of the polyamide reverse osmosis membrane by electrospray is short, and the cross-linking mainly occurs during the electrospray flight process, resulting in a higher content of free carboxyl groups. In contrast, the reaction time of the two monomers in the preparation of the polyamide reverse osmosis membrane by interfacial polymerization is long and the cross-linking is more sufficient, so the content of free carboxyl groups is lower. In addition, P-EILP has a lower isoelectric point pH than EILP, indicating that the P-PES substrate membrane is more hydrophilic than the PES substrate membrane and can carry more water molecules. The water molecules enhance the hydrolysis of TMC, resulting in more carboxylic acid groups remaining on the membrane surface.

[0043] Test Example 4: Comparison of Membrane Separation Performance In this example (Test Example 4), the separation performance of the membrane was tested using a FlowMem0021-HP type triple high-pressure flat membrane pilot test machine from Fumei Technology Co., Ltd., Xiamen, China. The effective test area of each membrane cell is 64.6 cm 2 , the circulation volume is 1000 ml, the test pressure is 10 bar, and a constant temperature device is used to keep the feed liquid at a constant temperature during the test to ensure that the temperature during operation is stable at 25 ± 1 °C. The intercepted substance is NaCl (1000 mg / L). Before the test, the membrane needs to be operated at a pressure of 18 bar for 1 hour to ensure that the separation performance of the membrane reaches stability. Each separation performance test is carried out in three parallel experiments and the average value is taken.

[0044] The water flux refers to the volume of the permeated liquid passing through the unit effective membrane area per unit time, and the calculation formula is shown in (1): (1) where J is the water flux of the membrane (L·m -2 ·h -1 ), V represents the volume of the permeate (L), Δt is the permeation time (h), and S is the effective area of the membrane (m 2 ).

[0045] The calculation formula for the water permeability coefficient is shown in (2): (2) where A is the water permeability coefficient of the membrane (L·m -2 ·h -1 ·bar -1 ), and ΔP is the pressure difference (bar).

[0046] The rejection rate of the membrane refers to the percentage of the amount of the intercepted solute in the raw liquid after filtration to the mass of the solute in the raw liquid, and the calculation formula is shown in (3): (3) Wherein R is the rejection rate (%), Cf is the solute concentration of the stock solution, and Cp is the solute concentration of the permeate solution.

[0047] Such as Figure 7a , Figure 7b and Figure 7c shown, Figure 7a shows the influence of different monomer concentrations on the performance of the electrospray interfacelessly polymerized polyamide reverse osmosis membrane according to the present invention, with the number of scans being four times; Figure 7b shows the influence of different numbers of scans on the reverse osmosis performance of electrospray interfacelessly polymerized polyamide according to the present invention, with the monomer concentration fixed, MPD:TMC = 0.2%:0.12%; Figure 7c is the separation performance test chart of different polyamide reverse osmosis membranes according to the present invention. Under the same electrospray conditions, a series of polyamide reverse osmosis membranes were prepared by adjusting the monomer concentration, and their separation performance was tested. The results are shown in Figure 7a . As MPD increased from 0.05% to 0.5%, the membrane water flux decreased from 84.1 L·m -2 ·h -1 to 16.8 L·m -2 ·h -1 . On the contrary, due to the existence of the trade-off effect, the rejection rate of the polyamide membrane for sodium chloride increased from 28.5% to 96.7%. The results show that when the monomer concentration is too low, the number of reactive monomers is insufficient, resulting in the formation of a thin and low-crosslinked polyamide layer, increasing the possibility of defects in the polyamide reverse osmosis membrane, and making the membrane exhibit a large water permeation flux and a low rejection rate. When the monomer concentration is too high, the membrane thickness increases, increasing the mass transfer resistance of water, and making the membrane exhibit a low water permeability coefficient and a stable rejection rate. When the MPD concentration is 0.2%, the membrane performance is the best, with a water flux of 32.8 L·m -2 ·h -1 and a rejection rate of 96.7% for sodium chloride.

[0048] The influence of electrospray time on the performance of polyamide reverse osmosis membrane was studied. The results are as shown in Figure 7b . As the number of electrospray scans increased from two to eight, the polyamide membrane flux gradually decreased from 54.2 L·m -2 ·h -1 to 12.8 L·m -2 ·h -1 . At the same time, the rejection rate of sodium chloride increased from 87.2% at two scans to 96.7% at four scans and tended to be stable after four scans. The results show that the optimal number of electrospray scans is four times. Continuing to increase the number of electrospray scans will only increase the thickness of the polyamide layer and reduce the water flux of the polyamide membrane.

[0049] Figure 7cFor the separation performance of different membranes, the water permeability coefficient of the P-EILP membrane has been greatly improved (3.28 L·m -2 ·h -1 ·bar -1 ). Compared with the water permeability coefficient of the CIP membrane, it has increased significantly by 30%, and compared with the water permeability coefficient of the commercial reverse osmosis membrane SW30 (Dow), it has increased by 13.5%. The significant improvement in the water permeability coefficient is mainly due to the reduction in the thickness of the polyamide layer, which reduces the resistance during the water transfer process. The rejection rate of the P-EILP membrane is slightly lower than that of the CIP membrane because the traditional interfacial polymerization cross-linking reaction is more complete. The performance of the CIP membrane is not as good as that of the commercial BW30 because the commercial formulation of the polyamide reverse osmosis membrane has been highly optimized in terms of monomer concentration and additives used for interfacial polymerization. Compared with the EILP membrane, the P-EILP membrane has a higher rejection rate and a smaller water permeability coefficient because the P-EILP membrane is prepared on a P-PES-based membrane modified with PVA. The presence of the PVA intermediate layer increases the mass transfer resistance of water and reduces the pore diameter of the PES-based membrane, thereby reducing the probability of defects appearing around the pores on the base membrane during electrospray interfaceless polymerization.

[0050] In summary, polyamide reverse osmosis membranes were successfully prepared by electrospray interfaceless polymerization using MPD and TMC as polymerization monomers. The thickness of the polyamide membrane was controlled by changing the number of electrospray scans; through SEM and AFM characterization, it was found that compared with the CIP membrane, the polyamide layer of the EILP membrane was thinner, the surface was smoother, and the roughness was smaller. FTIR and XPS were used to analyze the cross-linking of the membrane and found that the degree of cross-linking of the polyamide reverse osmosis membrane prepared by electrospray interfaceless polymerization was less than that of the traditional interfacial polymerization method, resulting in a lower rejection rate of the EILP membrane than that of the CIP membrane. Through contact angle and Zeta potential, it was found that the electrospray interfaceless polymerization method had a more hydrophobic surface and a lower isoelectric point, and this characteristic endowed the EILP membrane with better anti-anion fouling performance. At the same time, the surface roughness of the membrane and the pore diameter of the base membrane surface were further reduced in the presence of the PVA intermediate layer.

[0051] At the same time, the introduction of the PVA intermediate layer structure not only further reduced the pore diameter of the base membrane surface, effectively reducing the probability of defects in the polyamide layer, but also significantly reduced the surface roughness of the membrane. These improvements jointly promoted the improvement of the rejection performance of the P-EILP membrane. The separation performance test results showed that when the number of scans was four and the MPD monomer concentration was 0.2%, the performance of the P-EILP membrane was the best. At a pressure of 1.0 Mpa, the desalination rate for a 1000 mg / L aqueous sodium chloride solution was 96.7%, and its water flux was 32.8 L·m -2 ·h -1, the water flux is increased by 30% compared with the CIP membrane. The polyamide reverse osmosis membrane prepared by electrostatic spraying interfacial polymerization method shows great development potential due to its simple operation and high controllability.

[0052] Example 2: The present invention provides a preparation device for polyamide reverse osmosis membrane, which includes a positive and negative high-voltage DC power supply, a precision injection pump and a receiving drum; wherein, the positive and negative high-voltage DC power supply provides a stable electric field for jet stretching and droplet atomization, and the precision injection pump is equipped with a high-precision stepping motor and supports multi-channel independent programming control to control electrostatic spraying interfacial polymerization; the receiving drum rolls at an appropriate speed to form a polyamide reverse osmosis membrane with a certain thickness. Further, the output range of the positive and negative high-voltage DC power supply is usually 0-50 kV and -30-0 kV (adjustable accuracy ±0.1 kV), and it has short-circuit protection and overload alarm functions, providing a stable electric field for jet stretching and droplet atomization.

[0053] The precision injection pump is equipped with a high-precision stepping motor, the flow resolution of the precision injection pump is ≤0.1 μL / min, and the precision injection pump supports multi-channel independent programming control.

[0054] The rotation speed of the receiving drum is adjustable from 0 to 3000 rpm (driven by a servo motor). By adjusting the rotation speed of the receiving drum, it is beneficial to the formation of a dense and defect-free polyamide layer.

[0055] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept scope of the present invention, various simple modifications can be made to the technical solutions of the present invention. These simple modifications all belong to the protection scope of the present invention.

[0056] In addition, it should be noted that, in the above specific embodiments, the various specific technical features described can be combined in any way without conflict. To avoid unnecessary repetition, the present invention does not separately describe various possible combination methods. In addition, any combination can be made between different embodiments of the present invention, as long as it does not violate the idea of the present invention, it should also be regarded as the content disclosed by the present invention.

Claims

1. A method for preparing a polyamide reverse osmosis membrane, characterized in that: The preparation method comprises the following steps: Step S1: preparing a P-PES base membrane, depositing a thin layer of PVA on a PES base membrane polyethersulfone base membrane by electrostatic spraying, and cross-linking with glutaraldehyde to obtain a PVA-modified PES base membrane; Step S2: preparing a polyamide layer on the P-PES base membrane prepared in step S1 via electrostatic spray non-interfacial polymerization.

2. The method for preparing a polyamide reverse osmosis membrane according to claim 1, wherein In step S1, 0.2 g of polyvinyl alcohol 1788 was accurately weighed and added into 99.8 g of ultrapure water, and the mixture was placed in a constant temperature magnetic stirrer for dissolution.

3. The method for preparing a polyamide reverse osmosis membrane according to claim 2, characterized in that: The water bath temperature was 80°C and stirring was continued at 500 rpm for 6 h until complete dissolution.

4. The method for preparing a polyamide reverse osmosis membrane according to claim 2, wherein After the dissolved polyvinyl alcohol 1788 is naturally cooled to room temperature, it is vacuum filtered using a 0.45 μm microporous filter membrane to obtain a clear PVA solution with a mass fraction of 0.2% for use.

5. The method for preparing a polyamide reverse osmosis membrane according to claim 4, characterized in that: The PES base film is fixed on the receiving roller, excess moisture on the surface of the PES base film is removed with dust-free paper, and the PVA solution is evenly sprayed on the surface of the PES base film using an electrostatic spray gun.

6. The method for preparing a polyamide reverse osmosis membrane according to claim 5, characterized in that: Parameters of the electrostatic spray gun: set the total applied voltage to 15 kV; the needle injection rate to 1.8 mL / h; and the number of electrostatic spray scans to two times.

7. The method for preparing a polyamide reverse osmosis membrane according to claim 5, characterized in that: Parameters of the electrostatic spray gun: the distance between the needle and the roller is 60 mm; the sliding table translation rate is 20 mm / min; the roller speed is 80 rpm.

8. The method for preparing a polyamide reverse osmosis membrane according to claim 4, characterized in that: 50% glutaraldehyde (GA) stock solution was measured, gradiently diluted with ultrapure water and supplemented with 0.1 M HCl to adjust the pH to 2.0 ± 0.1 to prepare 0.2% (w / v) acidic cross-linking working solution.

9. The method for preparing a polyamide reverse osmosis membrane according to claim 4, characterized in that: The obtained PES-based membrane was vertically immersed in the cross-linking solution and placed in a constant temperature water bath shaker (60±1°C) for dynamic cross-linking at 120 rpm for 120±5 s.

10. A preparation device for the preparation method of the polyamide reverse osmosis membrane according to claim 1, comprising positive and negative high-voltage DC power supplies, a precision injection pump and a receiving roller, wherein the positive and negative high-voltage DC power supplies provide a stable electric field for jet stretching and droplet atomization, the precision injection pump is equipped with a high-precision stepper motor and supports multi-channel independent programming control to control electrostatic spray interface-free polymerization; the receiving roller rolls at an appropriate speed to form a polyamide reverse osmosis membrane of a certain thickness.

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