A polyamide thin layer composite film and its preparation method

Abstract

The present invention discloses a polyamide thin-layer composite membrane and a preparation method thereof. The preparation method comprises: adding a polyamine and a small molecule acid-binding agent to a lithium magnesium silicate nanoclay sol, stirring and dispersing the mixture, and allowing the mixture to stand to form a hydrogel stock solution of the polyamine; coating the hydrogel stock solution into a hydrogel thin layer; spraying an alkane solution of a polyacyl chloride onto the hydrogel thin layer, and allowing the polyacyl chloride and the polyamine to undergo an interfacial polymerization reaction on the surface of the hydrogel thin layer to form a polyamide film. The preparation method of the present invention has the characteristics of controllable reaction, environmental friendliness, and high efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of thin film synthesis and membrane separation, in particular to a polyamide thin layer composite membrane and a preparation method thereof. Background Art

[0002] The shortage of fresh water resources is one of the great challenges facing the sustainable development of today's society. Thin-layer composite nanofiltration membranes and reverse osmosis membranes have played a huge role in the fields of household water purification, drinking water softening, brackish water desalination and seawater desalination. At present, the preparation of thin-layer composite membranes in industry mainly adopts the method of interfacial polymerization, that is, the polyamine monomers in the aqueous solution and the polyacyl chloride monomers in the organic solution form a dense cross-linked polyamide film on the surface of the polymer porous base membrane as a selective separation layer (such as patent documents US006162358A and US009555378B2). However, due to the balance effect between water permeation flux and water-salt selectivity caused by the structural characteristics of the polyamide selective separation layer in this type of membrane material, it is difficult to further improve the comprehensive performance of the membrane material.

[0003] Nanomaterials have attracted considerable attention because they can significantly enhance the separation performance of polyamide-based thin-layer composite membranes by regulating interfacial polymerization reactions or altering the cross-linking structure of polyamides by influencing monomer distribution during reactions, limiting the diffusion of polyamine monomers to a certain extent, and blending them into the polyamide separation layer. For example, as reported in J. Membr. Sci. 2007, 294, 1-7, Science, 2015, 348, 1347-1351, J. Membr. Sci. 2016, 515, 238-244, Desalination, 2018, 441, 77-86, and patents such as CN112452164A, CN110585931A, CN113578070A, and CN113559725A, various nanomaterials can be used to form a nanomaterial intermediate layer or a nanomaterial-doped polyamide layer on the surface of a base membrane through vacuum filtration or blending with reactive monomers. However, it is worth noting that the nanomaterials currently reported for use in the preparation of thin-layer composite membranes are usually complex to synthesize, have high preparation costs, and are difficult to recycle; when forming an intermediate layer, the composite strength with the base membrane that has not been specially treated is often insufficient, and the long-term stability is lacking; some nanomaterials (such as cadmium hydroxide nanowires, metal-organic framework materials, etc.) also have potential heavy metal pollution problems when used for drinking water purification. Moreover, when nanomaterials are loaded on porous base membranes using methods such as vacuum filtration, it is difficult to combine them with traditional roll-to-roll membrane production methods. Therefore, there is an urgent need to find a new interfacial polymerization method that can more efficiently utilize the advantages of nanomaterials in regulating reactions, while achieving green preparation and adjustable structural properties of polyamide films. Summary of the Invention

[0004] The invention provides a method for preparing a polyamide thin-layer composite membrane, which has the characteristics of controllable reaction, greenness and high efficiency.

[0005] The technical solutions of the present invention are as follows:

[0006] A method for preparing a polyamide thin layer composite film, comprising:

[0007] Adding polyamine and a small molecule acid-binding agent to the lithium magnesium silicate nanoclay sol, stirring and dispersing the mixture, and allowing it to stand to form a polyamine hydrogel stock solution;

[0008] The hydrogel stock solution is coated into a hydrogel thin layer, and the alkane solution of polyacyl chloride is sprayed onto the hydrogel thin layer. The polyacyl chloride and polyamine undergo interfacial polymerization reaction on the surface of the hydrogel thin layer to form a polyamide film.

[0009] Lithium magnesium silicate nanoclay is a non-toxic, odorless, and non-irritating sheet silicate. It is often added as a functional additive to various water-based formulations to improve viscosity, thixotropy, and leveling properties. Lithium magnesium silicate nanoclay easily disperses in water, resulting in a high viscosity dispersion. After a period of stagnant time, the nanosheets spontaneously assemble into a regular house-of-cards structure due to electrostatic interactions between the nanosheets, forming a gel. Therefore, using this inorganic hydrogel to store water-soluble amine monomers can significantly inhibit the diffusion of the amine monomers and regulate interfacial polymerization reactions. Furthermore, the addition of small molecule amines and alkaline acid-binding agents accelerates the gelation process of the nanoclay dispersion, shortening the preparation process. Furthermore, the excellent thixotropy of the nanoclay hydrogel allows it to spread evenly across a variety of surfaces under shear forces, such as doctor blade coating, enabling large-scale preparation. For example, by utilizing the high viscosity and film-forming properties of nanoclay gel, a uniform and stable hydrogel layer containing amine monomers can be formed by scraping on a conveyor belt. By combining a spraying device with an organic phase acyl chloride monomer to carry out an interfacial polymerization reaction, the continuous and large-scale preparation of polyamide nanofilms can be achieved at the alkane / hydrogel interface. Importantly, after the reaction, the nanoclay hydrogel can be recycled and reused, that is, it can be redispersed and supplemented with amine monomers under high-speed shear, thereby achieving the recycling of the nanoclay. Compared with traditional methods, this greatly reduces the amount of nanomaterials used and the potential safety risks, achieving the green synthesis of polyamide films and their composite films.

[0010] The present invention can be produced continuously using continuous production equipment. The continuous production equipment includes: a conveying device, a feeding device, a spraying device, a unwinding device, a drying device and a winding device;

[0011] The feeding device is arranged above the conveying device and is used to scrape the hydrogel stock solution containing polyamine onto the surface of the conveying device to form a thin layer of hydrogel;

[0012] The spraying device is arranged downstream of the feeding mechanism and is used to spray the alkane solution of polyacyl chloride onto the hydrogel thin layer, so that the polyacyl chloride and the polyamine undergo interfacial polymerization reaction on the surface of the hydrogel thin layer to form a polyamide film;

[0013] The unwinding device is used to contact and composite the polymer porous base film with the polyamide film on the conveying device to form a polyamide thin layer composite film;

[0014] The polyamide thin layer composite enters the drying device for drying and heat treatment, and is finally wound up by the winding device to form a roll film product.

[0015] Preferably, a method for preparing a polyamide thin layer composite membrane comprises:

[0016] (1) adding a polyamine and a small molecule acid-binding agent to a lithium magnesium silicate nanoclay sol, stirring and dispersing the mixture, and allowing the mixture to stand to form a polyamine hydrogel stock solution;

[0017] (2) applying the hydrogel stock solution to the surface of the continuously moving forward conveying device to form a uniform and stable hydrogel thin layer;

[0018] (3) spraying an alkane solution of polyacyl chloride onto the hydrogel thin layer, and the polyacyl chloride and polyamine undergo interfacial polymerization reaction on the surface of the hydrogel thin layer to form a polyamide film;

[0019] (4) contacting the polymer porous base film unwinding device with the polyamide film on the conveying device, transferring the polyamide film from the surface of the hydrogel thin layer to the polymer porous base film to form a polyamide thin layer composite membrane;

[0020] (5) After the reaction is completed, the thin layer of hydrogel is peeled off by a scraper and transported to the hydrogel stock solution, and then stirred evenly after adding polyamine to achieve the recovery and reuse of the remaining reaction monomers and lithium magnesium silicate nanoclay;

[0021] (6) The polyamide thin layer composite enters a drying device for drying and heat treatment, and is finally wound up by a winding device to form a roll membrane product. Preferably, the polyamine is piperazine or m-phenylenediamine. Piperazine is used to prepare nanofiltration polyamide thin layer composite membranes, and m-phenylenediamine is used to prepare reverse osmosis polyamide thin layer composite membranes.

[0022] As the concentration of the polyamine in the hydrogel stock solution increases, the water permeation flux of the prepared polyamide thin layer composite membrane gradually decreases, and the desalination rate gradually increases to more than 99%.

[0023] Preferably, the concentration of the polyamine in the hydrogel stock solution is 0.5-3 g / L.

[0024] Preferably, the small molecule acid binding agent is at least one of sodium hydroxide, sodium bicarbonate, sodium carbonate, triethylamine, triethanolamine, N,N-dimethylaniline and pyridine.

[0025] The amount of small molecule acid binding agent added needs to be adjusted according to the concentration of the polyamine, and preferably the molar ratio of small molecule acid binding agent to polyamine is maintained at 1:0.5-2.

[0026] Preferably, the concentration of lithium magnesium silicate nanoclay in the hydrogel stock solution is 1-2.5 wt%.

[0027] As the amount of lithium magnesium silicate nanoclay added to the hydrogel stock solution increases, the nanofiltration performance of the resulting polyamide nanofilm gradually improves and stabilizes. At lower nanoclay content, the viscosity of the hydrogel stock solution is low, significantly affected by the movement of the conveyor belt or the purge of the spraying device. This prevents the hydrogel from providing a stable interface during the reaction, which can lead to defects in the polyamide nanofilm and a low desalination rate. Furthermore, at lower nanoclay concentrations, the diffusion inhibition effect on the polyamine monomer is less pronounced, resulting in thicker polyamide nanofilms and reduced water permeation flux.

[0028] Preferably, the thickness of the hydrogel layer is 50 to 500 μm.

[0029] When the thickness of the hydrogel layer is too thin, a stable liquid film cannot be formed; when the gel layer is too thick, the effective composite of the polyamide film and the porous base membrane is affected.

[0030] The transmission device is a roller or a conveyor belt. The surface of the transmission device is a dense smooth surface or a frosted surface, so that the nanoclay hydrogel can form a stable thin layer thereon.

[0031] Preferably, the material of the delivery device is polyurethane, epoxy resin, nylon, ceramic, glass, or stainless steel.

[0032] In step (3), the alkane solution of the polyacyl chloride can be sprayed onto the hydrogel thin layer by a spraying device. The spraying device is pneumatically controlled, the driving gas is dry compressed air or high-purity nitrogen; the driving gas pressure is 0.05 to 1.0 MPa; and the diameter of the spray head is 0.1 to 1.0 mm.

[0033] Preferably, the polyacyl chloride is at least one of phthaloyl chloride, isophthaloyl chloride, terephthaloyl chloride, and trimesoyl chloride; and the solvent of the alkane solution is at least one of n-hexane, n-heptane, n-dodecane, Isopar G, Isopar H, Isopar L, and Isopar M.

[0034] With the increase of the concentration of trimesoyl chloride in the alkane solution of polyacid chloride, the water permeation flux of the prepared polyamide thin layer composite membrane increased and the salt rejection rate decreased slightly.

[0035] Preferably, in the alkane solution of the polyacyl chloride, the concentration of the polyacyl chloride is 1-4 g / L.

[0036] During spraying, the amount of alkane solution sprayed is sufficient to allow the organic phase liquid film formed to completely cover the hydrogel layer to synthesize a uniform and complete polyamide film. After the organic phase liquid film completely covers the hydrogel layer, further increasing the spray amount has little effect on the synthesized polyamide film.

[0037] The polymer porous base membrane can be selected according to the application scenario. Preferably, the polymer porous base membrane is a microfiltration membrane or ultrafiltration membrane of polysulfone, polyethersulfone, polyimide, polyetherimide, nylon, polyacrylonitrile, cellulose acetate, polyvinylidene fluoride, or polyethylene.

[0038] Preferably, the drying and heat treatment temperature is 50-80° C.; and the drying and heat treatment time is 5-20 min.

[0039] The present invention also provides a polyamide thin layer composite membrane prepared by the above preparation method.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] (1) Taking advantage of the good thixotropy of lithium magnesium silicate nanoclay hydrogel, a thin layer of hydrogel is quickly formed by scraping, which can remain stable in the air for a long time; after the reaction, it can be recovered and redispersed into a hydrogel reserve solution for repeated use, which greatly saves raw materials, reduces costs, and realizes green synthesis.

[0042] (2) High-viscosity inorganic nanoclay hydrogels used to store amine monomers can significantly reduce the diffusion rate of amine monomers and improve the controllability of interfacial polymerization; the uniform and flat hydrogel surface improves the stability of the reaction interface and is conducive to the formation of thin and uniform polyamide films.

[0043] (3) Polyamide nanofilms are generated at the free interface of alkane / hydrogel without relying on traditional polymer porous support substrates. After the reaction, they can be composited to various porous base membranes with hydrophilic or hydrophobic surfaces, greatly expanding the selection of thin-layer composite membrane base membranes. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 A schematic diagram of a method and process for preparing a polyamide composite membrane by inorganic nanoclay hydrogel-assisted interfacial polymerization according to a preferred embodiment;

[0045] Figure 2A schematic diagram of a method and process for preparing a polyamide composite membrane by inorganic nanoclay hydrogel-assisted interfacial polymerization according to another preferred embodiment;

[0046] Figure 3 These are scanning electron microscope images of the front (a) and back (b) of the polyamide film prepared in Example 1. DETAILED DESCRIPTION

[0047] The present invention will be described in more detail below with reference to the accompanying drawings and examples, but the examples do not limit the present invention.

[0048] The method for synthesizing a polyamide film at an alkane / hydrogel interface disclosed by the present invention can be used for large-scale preparation using a continuous production device.

[0049] A continuous large-scale production equipment includes a distributing device 1, a spraying device 2, a conveying device 3, a reeling device 4, a laminating device 5, a drying device 6 and a reeling device 7.

[0050] In one embodiment, the structure of the continuous mass production equipment is as follows: Figure 1 As shown, the distributing device 1 includes a liquid cylinder 11 with a stirrer and a scraper 12. The liquid cylinder 11 is arranged in front of the scraper 12, and the gap between the scraper 12 and the conveying device 3 can be adjusted. As the conveying device 3 continuously moves forward, the nanoclay hydrogel reserve solution containing polyamine reaction monomers in the liquid cylinder 11 is evenly released onto the conveying device and scraped to form a hydrogel layer 8.

[0051] The spraying device 2 is disposed downstream of the distributing device 1. When the hydrogel layer 8 passes through the spraying device 2, an isoparaffin solution of polyacyl chloride is applied by spraying, so that a complete liquid film is formed on the hydrogel layer 8. The polyamine and polyacyl chloride undergo interfacial polymerization to form a self-supporting polyamide film 9.

[0052] The unwinding device 4 and the laminating device 5 are arranged below the entire conveying device 3 to load the polymer porous supporting base film 10 and transport the base film forward at the same operating speed as the conveying device 3. The position of the laminating device 5 can be fine-tuned to ensure that the polyamide film is transferred with appropriate pressure;

[0053] The composite polyamide thin layer composite film enters the drying device 6 for heat treatment and is finally wound up by the winding device 7.

[0054] In the above-mentioned device for continuous large-scale preparation of polyamide films and composite films thereof, the liquid output of the distributing device 1 is adjustable, and the position of the scraper 12 is adjustable; the mist surface and mist amount of the spraying device 2 are adjustable; the speed of the conveying device 3 is adjustable; the speed of the unwinding device 4 is adjustable; the position of the laminating device 5 is adjustable; the temperature of the drying device 6 is adjustable; and the speed of the winding device 7 is adjustable.

[0055] Another embodiment of the continuous macro-production device structure is as follows Figure 2 The conveying device 3 is a roller, and one rotation of the roller constitutes a working cycle, which is divided into preparation section I, reaction section II, lamination section III and end section IV;

[0056] The dispensing device 1 includes a liquid tank 11 with an agitator and a scraper 12. The gap between the scraper 12 and the conveyor 3 is adjustable. During preparation stage I, as the conveyor 3 continuously moves forward, the nanoclay hydrogel stock solution containing polyamine reactive monomers in the liquid tank 11 is evenly released onto the rollers by scraping to form a hydrogel layer 8.

[0057] The spraying device 2 is disposed downstream of the distributing device 1. In reaction section II, an isoparaffin solution of polyacyl chloride is sprayed onto the hydrogel layer 8 as it passes through the spraying device 2, thereby forming a complete liquid film on the hydrogel layer 8. The polyamine and polyacyl chloride undergo interfacial polymerization to form a self-supporting polyamide film 9.

[0058] In the laminating section III, the unwinding device 4 and the laminating device 5 are arranged below the roller to load the polymer porous supporting base film 10 and transport the base film forward at a running speed matching the roller to ensure that the polyamide film is transferred with appropriate pressure;

[0059] At the end of section IV, the composite polyamide thin layer composite film enters the drying device 6 for heat treatment and is finally wound up by the winding device 7.

[0060] The polyamide film prepared by the present invention can be used as a selective separation layer to form a thin composite nanofiltration membrane or reverse osmosis membrane. In the case of desalination applications, the salt rejection rate and water permeation flux of the composite membrane are important parameters for evaluating the performance of the composite membrane. The salt rejection rate is defined as:

[0061] R=(1-C p / C f )×100%

[0062] Among them, C f is the salt ion concentration of the feed brine, C p is the salt ion concentration of the filtrate.

[0063] The definition of water permeation flux is: the volume of water filtered through a unit effective membrane area under a certain operating pressure per unit time:

[0064] F=V / At

[0065] Where F is the water permeation flux, in L / m 2 h; V is the volume of filtrate, in L; A is the effective membrane area, in m 2; t is time, unit is h.

[0066] Example 1

[0067] Piperazine was dissolved as a polyamine monomer in a pre-dispersed aqueous solution of lithium magnesium silicate nanoclay. Triethylamine was then added and stirred rapidly to form a hydrogel stock solution. The piperazine concentration was 2.0 g / L, the triethylamine concentration was 4.7 g / L, and the lithium magnesium silicate nanoclay concentration was 2.0 wt%. Trimesoyl chloride was used as a polyacyl chloride monomer and dissolved in isoparaffin at a concentration of 3.0 g / L.

[0068] Use a scraper with a slit of 200 μm to apply a layer of the above-mentioned hydrogel stock solution on the surface of the continuously running matte polyurethane conveyor belt. Then enter the spraying device, and evenly spray the isoparaffin solution of trimesoyl chloride on the surface of the hydrogel layer to carry out interfacial polymerization reaction. The conveyor belt continues to move forward to the unwinding device, so that the polyamide nanofilm generated on the surface of the hydrogel layer is transferred and bonded to the polyethersulfone microporous membrane loaded by the unwinding device to form a thin layer of composite membrane. The time for the conveyor belt to leave the spraying device and run to the bonding device is controlled to be 120s. The thin layer of composite membrane moves forward to the heating and drying device, heat-treated at 70°C for 5 minutes, and finally wound by the winding device to obtain the finished composite nanofiltration membrane. The desalination performance of the composite nanofiltration membrane prepared in this embodiment is shown in Table 1. The scanning electron microscope images of the front and back of the polyamide nanofilm are shown in Table 1. Figure 3 shown.

[0069] Examples 2-6

[0070] The piperazine contents in the hydrogel stock solution were adjusted to 0.5 g / L, 1.0 g / L, 1.5 g / L, 2.5 g / L, and 3.0 g / L, respectively. Other conditions were the same as in Example 1.

[0071] Test Example 1

[0072] The polyamide nanofilms prepared in Examples 1-6 were tested for salt rejection and water permeation flux. The nanofiltration performance of the composite membrane samples was tested by placing them in a cross-flow filtration apparatus and pre-pressing them for 1 hour at 25°C and an operating pressure of 0.2 MPa. A 2000 ppm Na₂SO₄ solution was used as the feed solution. The results are shown in Table 1.

[0073] Table 1 Salt rejection and water permeation flux of the polyamide nanofilm described in Examples 1 to 6

[0074]

[0075] It can be seen from the data in Table 1 that as the concentration of piperazine monomer in the hydrogel stock solution increases, the water permeation flux of the prepared polyamide nanofilm gradually decreases, and the salt rejection rate gradually increases to more than 99%.

[0076] Examples 7 to 9

[0077] The concentrations of the sprayed trimesoyl chloride solution were adjusted to 1 g / L, 2 g / L, and 4 g / L, respectively, and the other conditions were the same as in Example 1.

[0078] Test Example 2

[0079] The polyamide nanofilms prepared in Examples 7-9 were tested for salt rejection and water permeation flux. The nanofiltration performance of the composite membrane samples was tested by placing them in a cross-flow filtration apparatus and pre-pressing them for 1 hour at 25°C and an operating pressure of 0.2 MPa. A 2000 ppm Na₂SO₄ solution was used as the feed solution. The results are shown in Table 2.

[0080] Table 2 Salt rejection and water permeation flux of the polyamide nanofilm described in Examples 7 to 9

[0081]

[0082] It can be seen from the data in Table 2 that with the increase of the concentration of trimesoyl chloride in the sprayed isoparaffin solution, the water permeation flux of the polyamide nanofilm increases and the salt rejection rate decreases slightly.

[0083] Examples 10 to 13

[0084] The addition amount of lithium magnesium silicate nanoclay in the hydrogel stock solution was adjusted to 1.0 wt %, 1.5 wt %, 2.25 wt % and 2.5 wt %, and other conditions were the same as in Example 1.

[0085] Test Example 3

[0086] The polyamide nanofilms prepared in Examples 10-13 were tested for salt rejection and water permeation flux. The nanofiltration performance of the composite membrane samples was tested by placing them in a cross-flow filtration apparatus and pre-pressing them for 1 hour at 25°C and an operating pressure of 0.2 MPa. A 2000 ppm Na₂SO₄ solution was used as the feed solution. The results are shown in Table 3.

[0087] Table 3 Salt rejection and water permeation flux of the polyamide nanofilms described in Examples 10 to 13

[0088]

[0089] As can be seen from the data in Table 3, as the amount of lithium magnesium silicate nanoclay added to the hydrogel stock solution increases, the nanofiltration performance of the prepared polyamide nanofilm gradually improves and tends to stabilize. When the nanoclay content is low, the viscosity of the hydrogel stock solution is low and is greatly affected by the movement of the conveyor belt or the purging of the spraying device. It cannot provide a stable interface during the reaction, which can easily cause defects in the polyamide nanofilm and lead to a low desalination rate. In addition, when the nanoclay concentration is low, the diffusion inhibition effect on the polyamine monomer is not obvious enough, so the thickness of the obtained polyamide nanofilm is also thicker, and the water permeation flux decreases. When the lithium magnesium silicate nanoclay content is above 2.0wt%, a stable hydrogel layer can be formed. However, when the mass concentration is greater than 2.5wt%, the viscosity increases significantly, making it difficult to disperse evenly. Therefore, the nanoclay addition amount is preferably 2.0-2.5wt%.

[0090] Examples 14 to 18

[0091] The size of the scraper slit was adjusted so that the thickness of the formed nanoclay hydrogel layer was 50, 100, 200, 300, and 500 μm. Other conditions were the same as those in Example 1.

[0092] Test Example 4

[0093] The polyamide nanofilms prepared in Examples 14-18 were tested for salt rejection and water permeation flux. The nanofiltration performance of the composite membrane samples was tested by placing them in a cross-flow filtration apparatus and pre-pressing them for 1 hour at 25°C and an operating pressure of 0.2 MPa. A 2000 ppm Na₂SO₄ solution was used as the feed solution. The results are shown in Table 4.

[0094] Table 4 Salt rejection and water permeation flux of the polyamide nanofilms described in Examples 14 to 18

[0095]

[0096] As shown in Table 4, the nanoclay hydrogel layer formed by doctor blade coating is not well spread evenly on the substrate surface when the thickness is too thin, resulting in defects in the synthesized polyamide film. Properly increasing the thickness of the hydrogel layer can form a more stable hydrogel layer, but an excessively thick hydrogel layer will affect the subsequent lamination process of the polyamide film and the base film. The preferred thickness of the nanoclay hydrogel layer is 100 to 300 μm.

[0097] Examples 19 to 23

[0098] The heat treatment temperature in the heating and drying stage was adjusted to 50° C., 60° C., and 80° C., and the heat treatment time was adjusted to 5 min, 10 min, and 20 min. Other conditions were the same as in Example 1.

[0099] Test Example 5

[0100] The polyamide nanofilms prepared in Examples 19-23 were tested for salt rejection and water permeation flux. The nanofiltration performance of the composite membrane samples was tested by placing them in a cross-flow filtration apparatus and pre-pressing them for 1 hour at 25°C and an operating pressure of 0.2 MPa. A 2000 ppm Na₂SO₄ solution was used as the feed solution. The results are shown in Table 5.

[0101] Table 5 Salt rejection and water permeation flux of the polyamide nanofilm described in Examples 19 to 23

[0102]

[0103] The data in Table 5 show that as the heat treatment temperature during the drying and heating phase increases, the salt rejection rate of the resulting polyamide nanofilm increases significantly, while the water permeation flux decreases. When the heat treatment temperature is above 70°C, the effect on the water permeation flux and salt rejection rate is no longer significant. Extending the heat treatment time at 70°C slightly increases the salt rejection rate and slightly decreases the water permeation flux. This indicates that heat treatment at 70°C for more than 5 minutes can completely dry out the residual isoparaffins on the surface of the polyamide nanofilm, resulting in a polyamide nanofilm with a moderate degree of crosslinking. From the perspectives of production efficiency and energy conservation, the heat treatment temperature and time are preferably 70°C and 5 minutes.

[0104] Examples 24 to 29

[0105] The material of the polymer porous supporting base membrane is adjusted to be nylon, polyvinylidene fluoride, cellulose acetate, mixed cellulose, polypropylene, or polytetrafluoroethylene. Other conditions are the same as those in Example 1.

[0106] Test Example 6

[0107] The polyamide nanofilms prepared in Examples 24-29 were tested for salt rejection and water permeation flux. The nanofiltration performance of the composite membrane samples was tested by placing them in a cross-flow filtration apparatus and pre-pressing them for 1 hour at 25°C and an operating pressure of 0.2 MPa. A 2000 ppm Na₂SO₄ solution was used as the feed solution. The results are shown in Table 6.

[0108] Table 6 Salt rejection and water permeation flux of the polyamide nanofilm described in Examples 24 to 29

[0109]

[0110] The data in Table 6 show that different polymer porous support substrates can be used to transfer-bond polyamide nanofilms to form thin-layer composite nanofiltration membranes. Separation performance varies slightly depending on the properties of the porous substrates. In practical applications, different polymer porous substrates can be selected for transfer-bonding with polyamide films based on the separation performance requirements of the application scenario.

[0111] Examples 30 to 35

[0112] After completing one preparation cycle according to the above Example 1, the nanoclay hydrogel layer is not removed, and multiple production cycles are continued, with other conditions being the same as in Example 1.

[0113] Test Example 7

[0114] The polyamide nanofilms prepared in Examples 30-35 were tested for salt rejection and water permeation flux. The nanofiltration performance of the composite membrane samples was tested by placing them in a cross-flow filtration apparatus and pre-pressing them for 1 hour at 25°C and an operating pressure of 0.2 MPa. A 2000 ppm Na₂SO₄ solution was used as the feed solution. The results are shown in Table 7.

[0115] Table 7 Salt rejection and water permeation flux of the polyamide nanofilm described in Examples 30 to 35

[0116]

[0117] From the data in Table 7, it can be seen that the inorganic nanoclay hydrogel layer with a thickness of about 200 μm can be recycled for more than 3 times while maintaining the stable separation performance of the prepared thin-layer composite membrane. However, when it is recycled for more than 4 times, the total amount of amine monomers is insufficient, resulting in a decrease in the separation performance of the composite membrane.

[0118] Examples 36 to 40

[0119] Under the conditions of Examples 1 and 32 above, the hydrogel layer was recovered and redispersed after completing three preparation cycles, and then re-coated on the conveyor belt and continued for three production cycles. The thin layer composite films prepared after each re-coating of the hydrogel layer were taken as Examples 36 to 40, and the other conditions were the same as in Example 1.

[0120] Test Example 8

[0121] The polyamide nanofilms prepared in Examples 36-40 were tested for salt rejection and water permeation flux. The nanofiltration performance of the composite membrane samples was tested by placing them in a cross-flow filtration apparatus and pre-pressing them for 1 hour at 25°C and an operating pressure of 0.2 MPa. A 2000 ppm Na₂SO₄ solution was used as the feed solution. The results are shown in Table 8.

[0122] Table 8 Salt rejection and water permeation flux of the polyamide nanofilm described in Examples 31 to 35

[0123]

[0124] From the data in Table 8, it can be seen that the inorganic nanoclay hydrogel layer with a thickness of about 200 μm is recycled and replenished with monomers after being recycled three times. The thin layer composite membrane prepared by continuing to scrape the gel layer and performing interfacial polymerization on it has stable separation performance, which can realize the recycling and reuse of inorganic nanoclay.

[0125] The embodiments described above provide a detailed description of the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a polyamide thin layer composite membrane, characterized in that: include: Adding polyamine and a small molecule acid-binding agent to the lithium magnesium silicate nanoclay sol, stirring and dispersing the mixture, and allowing it to stand to form a polyamine hydrogel stock solution; The hydrogel stock solution is coated into a hydrogel thin layer, and the alkane solution of polyacyl chloride is sprayed onto the hydrogel thin layer. The polyacyl chloride and polyamine undergo interfacial polymerization reaction on the surface of the hydrogel thin layer to form a polyamide film.

2. The method for preparing a polyamide thin layer composite membrane according to claim 1, wherein: include: (1) Adding polyamine and small molecule acid-binding agent to lithium magnesium silicate nanoclay sol, stirring and dispersing the mixture, and allowing it to stand to form a polyamine hydrogel stock solution; (2) applying the hydrogel stock solution onto the surface of the continuously moving forward conveying device to form a uniform and stable hydrogel thin layer; (3) Spraying an alkane solution of polyacyl chloride onto the hydrogel thin layer, the polyacyl chloride and polyamine undergo interfacial polymerization reaction on the surface of the hydrogel thin layer to form a polyamide film; (4) The polymer porous base film is brought into contact with the polyamide film on the conveying device through the unwinding device, and the polyamide film is transferred from the surface of the hydrogel thin layer to the polymer porous base film to form a polyamide thin layer composite membrane; (5) After the reaction is completed, the thin layer of hydrogel is peeled off by a scraper and transported to the hydrogel reserve solution, and then the polyamine is added and stirred evenly to achieve the recovery and reuse of the remaining reaction monomers and lithium magnesium silicate nanoclay; (6) The polyamide thin layer composite enters the drying device for drying and heat treatment, and is finally wound up by the winding device to form a roll film product.

3. The method for preparing a polyamide thin layer composite membrane according to claim 1, wherein: The polyamine is piperazine or m-phenylenediamine; and the concentration of the polyamine in the hydrogel stock solution is 0.5-3 g / L.

4. The method for preparing a polyamide thin layer composite membrane according to claim 1, wherein: The small molecule acid binding agent is at least one of sodium hydroxide, sodium bicarbonate, sodium carbonate, triethylamine, triethanolamine, N,N-dimethylaniline and pyridine.

5. The method for preparing a polyamide thin layer composite membrane according to claim 1, characterized in that: In the hydrogel stock solution, the concentration of lithium magnesium silicate nanoclay is 1-2.5wt%.

6. The method for preparing a polyamide thin layer composite membrane according to claim 1, characterized in that: The thickness of the hydrogel layer is 50~500 μm.

7. The method for preparing a polyamide thin layer composite membrane according to claim 1, characterized in that: The alkane solution of polyacyl chloride is sprayed onto the hydrogel thin layer through a spraying device; the spraying device is pneumatically controlled, and the driving gas is dry compressed air or high-purity nitrogen; the pressure of the driving gas is 0.05~1.0 MPa; the diameter of the spray head of the spraying device is 0.1~1.0 mm.

8. The method for preparing a polyamide thin layer composite membrane according to claim 1, characterized in that: The polybasic acid chloride is at least one of phthaloyl chloride, isophthaloyl chloride, terephthaloyl chloride, and trimesoyl chloride; the solvent of the alkane solution is at least one of n-hexane, n-heptane, n-dodecane, Isopar G, Isopar H, Isopar L, and Isopar M.

9. The method for preparing a polyamide thin layer composite membrane according to claim 1 or 8, characterized in that: In the alkane solution of the polybasic acid chloride, the concentration of the polybasic acid chloride is 1-4 g / L.

10. A polyamide thin layer composite membrane prepared by the preparation method according to any one of claims 1 to 9.

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