Preparation method and preparation device of high-efficiency evaporation membrane

Abstract

The application discloses a preparation method and a preparation device of a high-efficiency evaporation membrane, and belongs to the technical field of surface modification of membrane materials. + The application discloses a preparation method and a preparation device of a high-efficiency evaporation membrane, and belongs to the technical field of surface modification of membrane materials. The application discloses a preparation method and a preparation device of a high-efficiency evaporation membrane, and belongs to the technical field of surface modification of membrane materials. The application discloses a preparation method and a preparation device of a high-efficiency evaporation membrane, and belongs to the technical field of surface modification of membrane materials.

Description

Technical Field

[0001] This invention belongs to the field of membrane material surface modification technology, specifically relating to a method and apparatus for preparing a high-efficiency evaporation membrane. Background Technology

[0002] The scarcity and uneven distribution of freshwater resources are among the major limiting factors hindering sustainable socio-economic development. Obtaining freshwater through desalination of seawater, brackish water, and industrial wastewater is an important way to solve the current freshwater shortage and distribution problems and reduce the environmental impact of wastewater. Currently, there are various water desalination technologies, such as distillation, reverse osmosis (RO), and membrane distillation (MD). Compared with RO, MD technology has the advantages of high desalination rate, requiring only low hydraulic pressure and the ability to treat high-salinity brine. It can also be highly integrated with renewable energy and efficient latent heat recovery systems to reduce energy input; or it can be connected to the high-temperature wastewater effluent system of production processes to directly produce freshwater without energy consumption. Therefore, MD has become the most competitive advanced desalination technology.

[0003] The excellent desalination performance of MD depends on the MD membrane. Industrially used high molecular weight organic polymer membranes include polypropylene (PP), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride (PVDF). These polymer membranes have the inherent hydrophobic advantage of low intrinsic surface energy. As the membrane distillation time increases, the water flux decreases, requiring chemical cleaning. To improve the membrane's anti-fouling properties or water vapor permeation rate, wet chemical modification is usually required on the surface of these commercial polymer membranes. The most common dry treatment is the use of dielectric barrier discharge (DBD) plasma surface treatment technology, which can be divided into atmospheric pressure air discharge or vacuum discharge. However, the former has uneven discharge. For example, Chinese patent 2014105619874 used air discharge plasma dry in-situ polymerization to achieve uniform grafting of functional groups or polymers onto the surface of one-dimensional chemical fibers and the weaving of functional fabrics.

[0004] For two-dimensional membrane materials, achieving uniform surface modification typically requires uniform discharge under vacuum or inert gas protection such as argon. Achieving uniform surface modification under atmospheric pressure air discharge conditions remains a significant challenge. One solution is to continuously increase the discharge voltage to obtain relatively uniform discharge plasma on the surface. However, with increasing operating voltage, random breakdown streamer discharges often occur on the surface of the DBD metal high-voltage electrode, especially in environments with high humidity, leading to malfunctions. Even in dry environments, with prolonged processing time at higher operating voltages, the treated organic membrane material surface is subjected to relatively strong high-energy electron bombardment and plasma oxidation, causing organic polymer decomposition and the formation of water molecules. This still results in random breakdown streamer discharges, leading to membrane surface burn-off defects and a high defect rate. Furthermore, higher operating voltages not only result in higher energy consumption but also generate large amounts of undesirable pollutants such as ozone (O3) under air discharge conditions, polluting the operating environment and impacting human health. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method and apparatus for preparing a high-efficiency evaporation membrane, so as to solve the problems faced in the background art.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A metal mesh electrode, wherein the metal mesh electrode is a discharge electrode, and the discharge electrode is a sintered metal mesh having Ag atom doped on its surface and rich in monovalent cations, consisting of a layered aluminosilicate mineral.

[0008] A method for preparing a metal mesh electrode includes the following steps:

[0009] The metal mesh was washed and dried, and then placed in a plasma processor for discharge surface etching to obtain the metal mesh to be modified.

[0010] Silver nitrate solution was mixed with a layered mineral nanogel containing monovalent cations of aluminosilicate to obtain Ag-containing... + Ionic aluminosilicate layered mineral nanogel solutions;

[0011] Secondly, the metal mesh to be modified is immersed in a solution containing Ag. + The metal mesh was dipped into a solution of layered mineral nanogels containing ions of aluminosilicates, then dried. After repeated dip-coating and drying, a coated metal mesh was obtained.

[0012] Finally, the coated metal mesh is sintered at high temperature.

[0013] Furthermore, the metal mesh includes stainless steel mesh, titanium mesh, and copper foil.

[0014] Furthermore, the Ag-containing + Ag in a solution of layered mineral nanogels containing ions of aluminosilicates + The ion mass accounts for 1-4%.

[0015] A DBD plasma polymerization reactor.

[0016] A high-efficiency evaporation membrane preparation apparatus includes a winding and unwinding device that rotates synchronously via a belt. A coating device, a plasma polymerization reactor, and a drying device are sequentially arranged between the winding and unwinding devices. A coating material tank is provided below the coating device. The plasma polymerization reactor is connected to a plasma power source via a wire.

[0017] The plasma polymerization reactor includes an electrode support, with quartz plates at both the top and bottom. Two sealing strips are fixed between the two quartz plates, forming a rectangular space between the sealing strips and the quartz plates. The electrode support is located within the rectangular space, and sintered metal mesh and unsintered metal mesh are fixed on the surfaces of the two quartz plates, respectively.

[0018] Application of a DBD plasma polymerization reactor in the preparation of evaporation membranes.

[0019] Further, the method includes the following steps: placing the substrate on a conveyor belt device, moving the substrate to a roller coating device via the conveyor belt, rotating the roller coating device to coat the substrate surface with the modifier in the solution tank, then entering the DBD plasma polymer reactor for polymerization reaction, and finally entering a drying device to dry the substrate after polymerization reaction. The modifier includes an ethanol-water solution, a mixed solution of tridecafluorooctyltrimethoxysilane and γ-(2,3-epoxypropoxy)propyltrimethoxysilane, SiO2 particles, and acetic acid.

[0020] The beneficial effects of this invention are:

[0021] This invention utilizes Na-rich materials with highly dispersed Ag atoms. + A layered aluminosilicate mineral with monovalent cations is sintered at high temperature onto a commonly used metal mesh as a DBD high-voltage discharge electrode. The grounded metal electrode remains unchanged, and this constitutes a DBD plasma membrane material processor. This enables the generation of plasma with large-area uniform discharge at a lower operating voltage, achieving hydrophobic modification of the surface of hydrophilic membranes such as cellulose paper-based membranes. This method and device are used for desalination of saline water and recovery of fresh water, while reducing energy consumption and avoiding O3 generation. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 A schematic diagram of a high-efficiency evaporation membrane preparation device;

[0024] Figure 2 This invention is a schematic diagram of a plasma polymerization reactor structure;

[0025] Figure 3 This invention relates to the discharge of sintered metal mesh discharge electrodes and unmodified metal mesh discharge electrodes. Figure I ;

[0026] Figure 4 This invention relates to the discharge of sintered metal mesh discharge electrodes and unmodified metal mesh discharge electrodes. Figure II ;

[0027] Figure 5 This invention relates to the discharge of sintered metal mesh discharge electrodes and unmodified metal mesh discharge electrodes. Figure III . Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] A method for preparing a high-voltage sintered metal mesh electrode for a DBD plasma processor includes the following steps: First, based on the size and physical and chemical properties of the film material to be treated, select and cut a metal mesh of appropriate size, such as stainless steel mesh or titanium mesh; then wash these metal meshes with deionized water, dry them in an oven at 110 ℃, and then place them in a plasma processor for discharge surface etching to obtain the metal mesh to be modified.

[0030] At the same time, a silver nitrate solution of a certain concentration is mixed with a certain amount of monovalent cations, such as Na+. + The aluminosilicate layered mineral nanogels were thoroughly mixed to obtain Ag-containing... +A layered mineral nanogel solution of aluminosilicate ions is prepared; next, the metal mesh to be modified is immersed in the gel solution for coating, and then dried in an oven at 110℃. This coating process is repeated multiple times to obtain a uniformly modified metal mesh with the required coating amount; finally, the coated metal mesh is placed in a muffle furnace for high-temperature sintering to obtain a Na-rich metal mesh with highly dispersed Ag atoms doped on its surface. + Sintered metal mesh of layered aluminosilicate minerals with monovalent cations.

[0031] A DBD plasma polymerization reactor and its design method: a sintered metal mesh is firmly bonded to a quartz plate of the required size as a high-voltage discharge electrode; an unsintered metal mesh is bonded to another quartz plate of the same size in the same manner as a grounding electrode.

[0032] When preparing the reactor, select an electrode holder with adjustable electrode plate spacing. Based on the surface characteristics of the membrane to be treated and the discharge requirements, the electrode holder adjusts the distance between the two electrodes using a non-conductive PTFE or PP plastic adjustable shaft. The adjustable range is controlled between 5mm and 15mm. Two sides are sealed with quartz strips of appropriate thickness, while the other two sides are left unsealed, serving as the feed and discharge ports for the membrane substrate. When installing the two electrodes, the sintered high-voltage discharge electrode should face inwards towards the reactor, and the grounding electrode should face outwards (preferably installed at the bottom of the reactor) to facilitate installation and maintenance and to ensure a safe operating environment for high-voltage discharge.

[0033] A high-efficiency evaporation membrane preparation device: In order to achieve continuous surface modification treatment of membrane substrate, the membrane roll to be modified, such as cellulose filter paper hydrophilic membrane roll, roller coating chemical modification, tunnel drying and the above-mentioned plasma reactor are combined with a winding device. This constitutes a new technology and device for continuous and rapid preparation of surface modification of cellulose paper-based hydrophilic membrane roll or membrane substrate, which is used for saline MD desalination and freshwater recovery.

[0034] like Figure 1 As shown, a high-efficiency evaporation membrane preparation apparatus includes a winding and unwinding device 1. The winding and unwinding device 1 rotates synchronously via a belt to wind up the membrane substrate. The substrate is placed on the winding and unwinding device 1. A coating device 3 is arranged between the winding and unwinding devices 1. A coating tank 7 is located below the coating device 3. A plasma polymerization reactor 5 is also arranged on one side of the coating device 3. The plasma polymerization reactor 5 is connected to a plasma power source 4 via wires. A drying device 6 is arranged on one side of the plasma polymerization reactor 5. The membrane substrate 2 is placed between the winding and unwinding devices 1.

[0035] like Figure 2As shown, the plasma polymerization reactor 5 includes an electrode support 5-3. Quartz plates 5-1 are provided at both the top and bottom of the motor support 5-3. Two non-conductive sealing strips 5-5 are fixed between the two quartz plates 5-1, forming a rectangular space between the non-conductive sealing strips 5-5 and the quartz plates 5-1. The electrode support 5-3 is located within this rectangular space. A sintered metal mesh 5-2 is fixedly provided on the bottom surface of the top quartz plate 5-1, serving as a high-voltage discharge electrode. The sintered metal mesh 5-2 is connected to the high-voltage output terminal of the plasma power source 4 via a high-voltage wire. An unsintered metal mesh 5-4 is fixedly provided on the surface of the bottom quartz plate 5-1, serving as a grounding electrode. The unsintered metal mesh 5-4 of the grounding electrode is fixed below the reactor and connected to the grounding electrode of the plasma power source 4 via a wire.

[0036] Example 1: A DBD plasma surface hydrophobic treatment (or modification) method for cellulose paper-based hydrophilic membranes used in saline MD desalination is used as an example:

[0037] First, based on the size and physical and chemical properties of the membrane material to be treated, a metal mesh of appropriate size, such as stainless steel mesh or titanium mesh, is cut. It is then washed with deionized water, dried in an oven at 110℃, and surface etched using a plasma processor for 10 minutes to obtain the metal mesh to be modified. Simultaneously, a certain volume of solution containing 1-4% Ag is prepared. + Monovalent cations (such as Na) + Aluminosilicate layered mineral nanogels (such as those containing silicate aluminate) are placed in an electrode immersion bath.

[0038] Then, the metal mesh to be modified is immersed in the gel solution for coating, and then dried in an oven at 110 ℃. This dipping and coating process is repeated multiple times to obtain a uniformly modified metal mesh with the required coating amount, which accounts for 3-5% of the metal mesh mass. Finally, the coated metal mesh is placed in a muffle furnace for high-temperature sintering. The sintering control procedure is to first pre-sinter at 350 ℃ for 2 hours, then raise the temperature to 650 ℃ for 6 hours, and then allow it to cool naturally to room temperature to obtain a Na-rich metal mesh with highly dispersed Ag atoms doped on the surface. + A sintered metal mesh of layered aluminosilicate minerals with monovalent cations. The sintered metal mesh is firmly bonded to a quartz plate of the required size as a high-voltage discharge electrode; an unsintered metal mesh is bonded to another quartz plate of the same size in the same manner as a grounding electrode.

[0039] The reactor is then installed and adjusted. Based on the membrane material, its thickness, and the required processing conditions, a cuboid electrode holder with adjustable electrode plate spacing is selected. Taking a cuboid as an example, the electrode holder is a non-conductive PTFE or PP plastic adjustable holder. The distance between the two electrodes is adjusted, with an adjustable range of 5mm-15mm. Both sides are sealed with quartz strips or acrylic transparent material of appropriate thickness, serving as support for the electrode plates and controlling the spacing. The other two sides are left unsealed, acting as the inlet and outlet ports for the substrate to be modified. When installing the two electrodes, the sintering high-voltage discharge electrode should face inwards towards the reactor, and the grounding electrode should face outwards (preferably at the bottom of the reactor) to facilitate installation and maintenance and ensure a safe operating environment for high-voltage discharge.

[0040] Next, a DBD plasma online polymerization reactor 5 is installed and commissioned. This reactor includes a plasma power source 4 with a specific power output to meet production capacity requirements, the aforementioned plasma polymerization reactor 5, a coating tank 7, a drying device 6, a winding / unwinding device 1, and power lines. The power source's grounding terminal is properly connected to the earth using a wire. The DBD plasma polymerization reactor 5 includes a sintered metal mesh 5-2 (such as stainless steel or titanium mesh) discharge electrode and an unsintered metal mesh 5-4 grounding electrode. The sintered metal mesh 5-2 of the discharge electrode is connected to the high-voltage output terminal of the plasma power source 4 using a high-voltage wire. The unsintered metal mesh 5-4 of the grounding electrode is fixed below the reactor and connected to the grounding electrode of the plasma power source 4 using a wire.

[0041] According to the modification procedure of the membrane substrate to be treated, a reagent coating device 3 or drying device 6 of appropriate width is set in front of the DBD plasma reactor. The purpose is to load the raw materials and auxiliary materials by adsorbing the modifier to be coated on the membrane substrate when it passes through the device. Then, it enters the DBD plasma reactor for polymerization reaction to complete the reagent plasma-induced polymerization and deposition modification of the membrane substrate, so as to change the specific molecular properties and membrane pore structure on the surface of the membrane substrate and to use it for desalination and freshwater recovery in saline MD.

[0042] Taking the hydrophobic modification of hydrophilic cellulose filter paper roll as an example, the modifier preparation method is as follows: a certain volume of a mixed solution containing 0.1 mol / L tridecafluorooctyltrimethoxysilane and 0.02 mol / L γ-(2,3-epoxypropoxy)propyltrimethoxysilane is prepared with 50% ethanol-water solution and placed in a mixing tank. 1.5 g / L 200±5 nm SiO2 particles and a small amount of acetic acid are added to it. The mixture is stirred at 1500 rpm for 12 h to obtain the matured modifier.

[0043] Finally, the modified membrane material was subjected to a desalination test in saline solution using an MD desalination testing device to evaluate the effect of modification on desalination efficiency and permeability and to optimize the modification conditions.

[0044] 1. Contains Ag and Na + A comparison of ion-sintered metal mesh electrodes with traditional metal mesh electrodes (titanium mesh, stainless steel mesh, etc.) discharge plasma, their hydrophobic modification of the surface of hydrophilic filter paper substrates, and MD desalination performance.

[0045] Contains Ag and Na + For a comparison of the discharge characteristics of ion-bearing sintered metal mesh electrodes with those of traditional metal mesh electrodes (titanium mesh, stainless steel mesh, etc.) and their hydrophobic modification of the surface of hydrophilic filter paper substrates and their MD desalination performance, please refer to [reference needed]. Figure 3 and Table 1. From Figure 3 As can be seen, under the same operating discharge voltage (24V), the content of Ag and Na... + The pulse peak voltage of the sintered metal mesh discharge electrode with ions is nearly 2.5 times higher than that of the electrode pair consisting of the unmodified metal mesh discharge electrode and the ground electrode. Table 1 shows that after 1 minute of discharge plasma treatment with the sintered metal mesh electrode at an operating voltage of 24V, better hydrophobic modification of the filter paper surface is achieved, with uniform discharge and modification, resulting in a relatively higher MD desalination rate for the modified filter paper. Based on the treatment time of the two electrodes in Table 1, the electrodes containing Ag and Na... + The processing time of the sintered metal mesh discharge electrode for ions is greatly shortened, which indicates that its processing efficiency is increased by 4 times; at the same time, the concentration of O3 by-product generated by discharge is significantly reduced, and the concentration of tail gas is reduced by about 96.0%.

[0046] Table 1 Contains Ag and Na + Comparison of discharge and treatment effects between sintered metal mesh electrodes and traditional metal mesh electrodes (titanium mesh, stainless steel mesh, etc.)

[0047]

[0048] 2. Contains Ag and K + A comparison of discharge plasma of ion-sintered metal mesh electrodes with those of traditional metal mesh electrodes (titanium mesh, stainless steel mesh, etc.) and their hydrophobic modification of the surface of hydrophilic filter paper substrates, as well as their MD desalination performance.

[0049] Contains Ag and K + For a comparison of the discharge characteristics of ion-sintered metal mesh electrodes with those of traditional metal mesh electrodes (titanium mesh, stainless steel mesh, etc.), their hydrophobic modification of the filter paper hydrophilic substrate surface, and their MD desalination performance, please refer to [reference needed]. Figure 4 and Table 2. From Figure 4 As can be seen, under the same operating discharge voltage (24V), the content of Ag and K... +The pulse peak voltage of the sintered metal mesh discharge electrode with ions was nearly 2.5 times higher than that of the electrode pair consisting of the unmodified metal mesh discharge electrode and the ground electrode. Table 2 shows that after 1 minute of discharge plasma treatment with the sintered metal mesh electrode at an operating voltage of 24V, better hydrophobic modification of the filter paper surface was achieved, with uniform discharge and modification, resulting in a relatively higher MD desalination rate for the modified filter paper. Looking at the treatment time of the two electrodes in Table 2, the electrodes containing Ag and K... + The processing time of the sintered metal mesh discharge electrode for ions is greatly shortened, which indicates that its processing efficiency is increased by 4 times; at the same time, the concentration of O3 by-product generated by discharge is significantly reduced, and the concentration of tail gas is reduced by about 95.6%.

[0050] Table 2 contains Ag and K + Comparison of discharge and treatment effects between sintered metal mesh electrodes and traditional metal mesh electrodes (titanium mesh, stainless steel mesh, etc.)

[0051]

[0052] 3. No Ag, contains Na + or K + Comparison of discharge plasma of sintered metal mesh electrodes and traditional metal mesh electrodes (titanium mesh, stainless steel mesh, etc.) and their hydrophobic modification of the surface of hydrophilic filter paper substrates and MD desalination performance.

[0053] No Ag, contains Na + or K + For a comparison of the discharge characteristics of ion-sintered metal mesh electrodes with those of traditional metal mesh electrodes (titanium mesh, stainless steel mesh, etc.), their hydrophobic modification of the filter paper hydrophilic substrate surface, and their MD desalination performance, please refer to [reference needed]. Figure 5 and Table 3. From Figure 5 As can be seen, under the same operating discharge voltage (24 V), Na-containing Na without Ag... + or K + The peak pulse voltages of the sintered metal mesh discharge electrode and the electrode pair consisting of the unmodified metal mesh discharge electrode and the ground electrode are not significantly different. Table 3 shows that only after 5 minutes of discharge plasma treatment with the sintered metal mesh electrode at an operating voltage of 24 V can a good hydrophobic modification of the filter paper surface be achieved, and the discharge is also uneven, resulting in a relatively low MD desalination rate of the modified filter paper. Looking at the treatment times of the two electrodes in Table 3, only those containing Na... + or K + The processing time for the sintered metal mesh discharge electrode of ions still requires 5 minutes; the concentration of O3 byproduct generated by discharge is slightly reduced, and the ozone concentration in the exhaust gas is reduced by only about 26.0%.

[0054] Table 3. No Ag, Contains Na + or K +Comparison of discharge and treatment effects between sintered metal mesh electrodes and traditional metal mesh electrodes (titanium mesh, stainless steel mesh, etc.)

[0055]

[0056] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0057] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A DBD plasma polymerization reactor characterized in that, The metal mesh electrode is a discharge electrode, and the discharge electrode is a sintered metal mesh of a monovalent cation-rich silicate layer mineral with Ag atom doping on the surface; The preparation method of the metal mesh electrode comprises the following steps: First, the metal mesh is washed and dried, and then is placed into a plasma processor for discharge surface etching to obtain a metal mesh to be modified; Mixing silver nitrate solution with silicate-aluminate layered mineral nanogel containing monovalent cation Na + or K + , to obtain silicate-aluminate layered mineral nanogel solution containing Ag + ion Secondly, the metal mesh to be modified is immersed in a solution containing Ag + ions, and then dried, and the immersion and drying are repeated to obtain an immersed metal mesh; Finally, the metal mesh after immersion coating is sintered at high temperature, and the sintering is pre-sintering at 350 DEG C for 2 hours, then sintering at 650 DEG C for 6 hours, and then natural cooling to room temperature.

2. The DBD plasma polymerization reactor according to claim 1, characterized in that The metal mesh comprises a stainless steel mesh or a titanium mesh.

3. The DBD plasma polymerization reactor according to claim 1, characterized in that The immersion coating amount of the metal mesh after immersion coating accounts for 3-5% of the mass of the metal mesh.

4. A DBD plasma polymerization reactor according to claim 1, wherein the Ag + ion mass accounts for 1-4% in the solution of the silico-aluminate layered mineral nanogel. + ion mass accounts for 1-4% in the solution of the silico-aluminate layered mineral nanogel.

5. The application of the DBD plasma polymerization reactor in claim 1 in the preparation of an evaporation membrane.

6. Use according to claim 5, characterized in that, The method comprises the following steps: placing a substrate on a conveying belt device, moving the substrate to a pair of roller coating devices through the conveying belt, rotating the pair of roller coating devices to coat a modifier in a solution tank to the surface of the substrate, then entering a DBD plasma polymerization reactor for polymerization reaction, and finally entering a drying device to dry the substrate after polymerization reaction, wherein the modifier comprises an ethanol-water solution, a tridecafluorooctyltrimethoxysilane, a mixed solution of γ-(2, 3-epoxypropoxy) propyltrimethoxysilane, SiO2 particles and acetic acid.

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