High-performance desalination precisely-regulated strong alkali-resistant nanofiltration membrane and preparation method thereof

Abstract

The invention relates to a high-performance desalination precisely-regulated strong alkali-resistant nanofiltration membrane and a preparation method thereof, and the nanofiltration membrane is prepared by taking a polyethylene / polypropylene alkyl composite non-woven fabric as a support and polysulfone or polyethersulfone as an ultrafiltration substrate through water / oil phase interface temperature and humidity step regulation interfacial polymerization and gradient ultrasonic post-treatment. The preparation method comprises the steps of preparation of a membrane casting solution, a water phase and an oil phase, preparation of a base membrane and a composite membrane, post-treatment and the like. An SEM graph shows that the microstructure of the film prepared by the gradient temperature and humidity process is better. The nanofiltration membrane has excellent alkali resistance, can accurately desalt, and is good in uniformity and stability and low in pollution. The preparation process is simple and convenient to operate, is suitable for large-scale production, can be widely applied to the fields of printing and dyeing, metallurgical wastewater treatment, drinking water purification and the like, and provides an efficient and reliable solution for a water treatment technology.

Description

Technical Field

[0001] The present invention relates to the technical field of nanofiltration membranes, and particularly relates to a high-performance desalination precisely regulated strongly alkali-resistant nanofiltration membrane and a preparation method thereof. Background Art

[0002] In the current era when industrial development is closely intertwined with environmental protection, the efficient utilization of water resources and wastewater treatment have become key issues. As a highly potential water treatment method, nanofiltration membrane technology is widely used in many fields because it can precisely separate specific molecules and ions, has low energy consumption and is easy to operate. From the deep purification of drinking water, to the recycling of industrial wastewater, and then to the separation and concentration processes in the food and pharmaceutical industries, nanofiltration membranes play an indispensable role.

[0003] Composite nanofiltration membranes are the core components of nanofiltration technology, consisting of a porous support layer and a dense ultrathin separation layer. Among them, the support layer provides mechanical support to ensure the structural stability of the membrane under complex operating conditions; the separation layer determines the key separation performance of the membrane, such as desalination rate, the retention ability for specific substances, etc. Currently, the interfacial polymerization method is the mainstream method for preparing composite nanofiltration membranes. However, there are many bottlenecks in the traditional preparation process.

[0004] In terms of alkali resistance, the functional selective layer of traditional nanofiltration membranes is mostly polyamide. In a strongly alkaline environment, polyamide is prone to hydrolysis reaction. This not only destroys the structure of the separation layer of the membrane, resulting in a decrease in desalination rate, but also significantly shortens the service life of the membrane. In industrial wastewater treatment scenarios such as printing and dyeing and metallurgy, the wastewater often contains high concentrations of alkaline substances, and traditional nanofiltration membranes are difficult to operate stably for a long time. Frequent replacement of membrane modules increases the treatment cost and reduces the production efficiency.

[0005] Although certain progress has been made in existing alkali-resistant nanofiltration membranes, such as alkali-resistant nanofiltration membranes prepared using cyanate esters, melamine, etc. can tolerate high-concentration alkali solutions, there are still problems with performance uniformity and long-term stability. For membranes of different batches and different positions in the same batch, there are obvious differences in permeability and separation performance. This makes it difficult to carry out precise process design based on the performance of the membrane in actual applications, the operating stability of the equipment is poor, and it cannot meet the strict requirements of industrial production for water quality and water volume.

[0006] During the preparation process, the problem of residual monomers in the interfacial polymerization reaction cannot be ignored. Unreacted monomers remain in the membrane and will gradually be released over time, polluting the treated water. Especially in the field of drinking water treatment, this poses a potential threat to human health. Moreover, existing methods for removing residual monomers, such as simple water washing, acid-base washing, etc., have limited effects, are difficult to completely remove residual monomers, and may have a negative impact on the performance of the membrane.

[0007] In addition, in terms of the preparation process, the traditional water / oil phase interface temperature mostly adopts constant temperature and humidity control, which cannot accurately regulate the interfacial polymerization reaction process. In the initial stage of the polymerization reaction, the monomers are not evenly distributed and react rapidly, resulting in structural defects in the functional layer; in the later stage of the reaction, the reaction rate is difficult to control, easily causing over-polymerization or uneven growth of the functional layer. This makes it difficult to ensure the thickness and performance uniformity of the functional layer, directly affecting the overall performance of the membrane. In the existing technology, there is also a lack of effective post-treatment means to solve these problems, and it is difficult to achieve all-round optimization of the membrane performance.

[0008] In summary, it is urgent to develop a high-performance alkali-resistant nanofiltration membrane and its preparation method that can overcome the above defects, which is of great significance for promoting the wide application of nanofiltration membrane technology in the fields of complex industrial wastewater treatment, deep purification of drinking water, etc. Summary of the Invention

[0009] For this reason, the present invention provides a high-performance desalination precisely regulated strongly alkali-resistant nanofiltration membrane and its preparation method, which solves the problems that traditional nanofiltration membranes have weak alkali resistance and are prone to hydrolysis in a strong alkali environment; the uniformity and stability of existing alkali-resistant nanofiltration membranes are poor, the performance differences are large among different batches and positions, and the residual monomers during preparation pollute the water body, and the process is difficult to accurately regulate the polymerization reaction.

[0010] In order to achieve the above object, the present invention provides the following technical solution: a high-performance desalination precisely regulated strongly alkali-resistant nanofiltration membrane, using a polyethylene / polypropylene hydrocarbon-based composite non-woven fabric as the support material, and polysulfone or polyethersulfone as the ultrafiltration substrate, and is obtained by stepwise regulating the temperature and humidity of the water / oil phase interface for interfacial polymerization and through gradient ultrasonic post-treatment; the alkali-resistant nanofiltration membrane includes a composite non-woven fabric layer, a polysulfone or polyethersulfone ultrafiltration layer, and an interfacial polymerization layer.

[0011] As a preferred scheme of the high-performance desalination precisely regulated strongly alkali-resistant nanofiltration membrane, the temperature range of the stepwise regulation of the water / oil phase interface temperature and humidity is 20°C - 100°C, and the humidity range is 0 - 100%.

[0012] As a preferred scheme of the high-performance desalination precisely regulated strongly alkali-resistant nanofiltration membrane, the frequency range of the gradient ultrasonic post-treatment is 100 - 500 HZ, and the treatment time is 2 - 20 min.

[0013] As a preferred scheme of the high-performance desalination precisely regulated strongly alkali-resistant nanofiltration membrane, the thickness of the polyethylene / polypropylene hydrocarbon-based composite non-woven fabric is 10 - 200 μm, and the pore size is 0.1 - 2 μm.

[0014] The present invention also provides a preparation method of a high-performance desalination precisely regulated strongly alkali-resistant nanofiltration membrane, including the following steps:

[0015] Preparation of casting solution: Put a set amount of polysulfone or polyethersulfone, additives and solvents into the mixing kettle, heat the mixing kettle to the set temperature, stir and let stand for defoaming to obtain the casting solution;

[0016] Preparation of base membrane: Coat the casting solution on a polyethylene / polypropylene composite non-woven fabric, and prepare the base membrane by phase inversion;

[0017] Preparation of aqueous phase: Add a set amount of amine monomers, crosslinking agents and base membrane pore-preserving agents to pure water, stir to dissolve and let stand to obtain an aqueous phase mixture for standby;

[0018] Preparation of oil phase: Add a set amount of oil phase monomers to a mixed solvent of alkanes, stir and let stand to obtain an oil phase mixture for standby;

[0019] Preparation of composite membrane: Coat the aqueous phase mixture on the base membrane, remove the excess aqueous phase and then coat the oil phase mixture, pass through a temperature and humidity step control platform area, and then dry to obtain a composite alkali-resistant nanofiltration membrane;

[0020] Post-treatment: Put the composite alkali-resistant nanofiltration membrane into an ultrasonic instrument for gradient ultrasonic post-treatment to obtain a high-performance desalination precision control strong alkali-resistant nanofiltration membrane.

[0021] As a preferred scheme of the preparation method of the high-performance desalination precision control strong alkali-resistant nanofiltration membrane, the concentration of polysulfone or polyethersulfone in the casting solution is 15-20 wt.%, the additive content is 0-3%, and the additives are at least one of pure water, small molecule ketones, small molecule alcohols, polyvinyl alcohol with a specified molecular weight, polyvinylpyrrolidone with a specified molecular weight, sulfonated polysulfone or sulfonated polyethersulfone with different sulfonation degrees; the solvent is at least one of dimethylformamide, dimethylacetamide, and dimethyl sulfoxide.

[0022] As a preferred scheme of the preparation method of the high-performance desalination precision control strong alkali-resistant nanofiltration membrane, in the step of preparing the aqueous phase, the amine monomer is at least one of polyethyleneimine, polyallylamine, polyvinylamine, poly(piperidine) and poly(diallylamine); the crosslinking agent is at least one of polyvinyl alcohol and chitosan; the base membrane pore-preserving agent is at least one of triethylamine hydrochloride, camphorsulfonic acid sodium, sodium chloride, and sodium citrate;

[0023] The content of the amine monomer is 1-5 wt.%, the content of the crosslinking agent is 0.1-1 wt.%, and the content of the base membrane pore-preserving agent is 0.5-1.5 wt.%.

[0024] As a preferred scheme of the preparation method of the high-performance desalination precision control strong alkali-resistant nanofiltration membrane, in the step of preparing the oil phase, the mixed solvent of alkanes is at least one of IsoparG, IsoparE, IsoparM, pentane and alkanes with more carbon atoms;

[0025] The oil-phase monomer uses cyanuric chloride and its derivatives, sulfonic acid, benzenesulfonic acid and its derivatives, and the concentration of the oil-phase monomer is 0.2-2 wt.%.

[0026] As an optimized scheme for the preparation method of a high-performance desalination precision control strongly alkali-resistant nanofiltration membrane, in the composite membrane preparation step, the temperature range of the temperature and humidity step control platform area is 20°C-100°C, and the humidity range is 0-100%; the temperature gradient is 10°C, and the humidity gradient is 10%.

[0027] The synergistic regulation strategy of temperature and humidity step control includes:

[0028] In the initial stage of the reaction, the temperature is controlled at 20°C-30°C and the humidity is controlled at 0-30%, slowing down the monomer diffusion and reaction rate, and promoting the uniform distribution of the monomer.

[0029] In the middle stage of the reaction, the temperature is increased to 40°C-70°C and the humidity is increased to 40%-70%, accelerating the reaction to make the functional layer grow rapidly, and using humidity to promote the reaction to increase the crosslinking degree.

[0030] In the later stage of the reaction, the temperature is maintained at 80°C-100°C and the humidity is kept at 80%-100%, promoting the monomer reaction.

[0031] As an optimized scheme for the preparation method of a high-performance desalination precision control strongly alkali-resistant nanofiltration membrane, in the post-treatment step, the ultrasonic frequency range is 100-500 HZ, and the ultrasonic frequency gradient is 100 HZ.

[0032] The beneficial effects of the present invention are as follows:

[0033] First, by selecting polyolefin composite non-woven fabrics such as polyethylene / polypropylene and alkali-resistant materials such as polysulfone or polyethersulfone, combined with the interfacial polymerization process of temperature and humidity step regulation at the water / oil interface, the membrane structure is more stable, and it can effectively resist the erosion of alkaline substances. In a high-concentration alkali solution environment, the hydrolysis rate of the membrane is significantly reduced, greatly extending the service life of the membrane. It can be widely used in the treatment of strongly alkaline wastewater in fields such as printing and dyeing and metallurgy, reducing equipment maintenance and replacement costs, and improving production efficiency.

[0034] Second, the precisely regulated interfacial polymerization process and the optimized membrane structure enable the membrane to have high selectivity for different ions and molecules. In terms of desalination, precise control can be achieved, with a high rejection rate for specific salts and effective removal of impurity ions in water. In practical applications, the performance of the membrane can be precisely adjusted according to different treatment requirements to ensure that the treated water quality meets high standards and meets the requirements of various scenarios such as drinking water purification and industrial pure water preparation.

[0035] Third, the temperature and humidity gradient control and gradient ultrasonic post-treatment processes ensure uniform monomer distribution and uniform functional layer thickness during membrane preparation. This results in minimal performance differences between membranes of different batches and different positions within the same batch, improving product uniformity. At the same time, the gradient ultrasonic treatment repairs defects in the functional layer, enhancing membrane stability. During long-term operation, the membrane's permeability and separation performance remain stable, reducing process adjustments and production interruptions caused by membrane performance fluctuations and enhancing the reliability of the entire system.

[0036] Fourth, the gradient ultrasonic post-treatment can thoroughly wash away residual monomers and solvents, significantly reducing the content of organic pollutants in the membrane. This not only reduces the risk of secondary pollution to the treated water body, ensuring drinking water safety, but also meets environmental protection requirements and reduces the impact on the environment. In an era where water resource protection is increasingly important, the nanofiltration membrane of the present invention provides strong support for sustainable water treatment technologies.

[0037] Fifth, compared with the complex preparation process of traditional special alkali-resistant membranes, the preparation method of the present invention is simple to operate and easy to control. Each step cooperates with each other to form an efficient preparation system. Processes such as temperature and humidity gradient control and gradient ultrasonic treatment do not require complex equipment and harsh conditions, have good technical scalability and operability, are suitable for large-scale industrial production, can meet the market demand for high-performance alkali-resistant nanofiltration membranes, and promote the wide application of nanofiltration membrane technology in the industrial field. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings described below are merely exemplary, and those of ordinary skill in the art can also obtain other implementation drawings based on the provided drawings without creative efforts.

[0039] Figure 1 SEM structure comparison of cross-sections of composite membranes prepared by different processes provided in the embodiments of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present invention, not all of them. All other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments of the present invention belong to the scope of protection of the present invention.

[0041] Example 1

[0042] Example 1 of the present invention provides a high-performance desalination precisely regulated strongly alkali-resistant nanofiltration membrane, and the preparation process is as follows:

[0043] Preparation of casting solution: Add 18 wt.% polysulfone, 1 wt.% polyvinylpyrrolidone (K30), and 81 wt.% dimethylformamide (DMF) into a mixing kettle. Heat the mixing kettle to the set temperature, stir at a certain stirring speed for 8 h, stir rapidly at 50 Hz within the first 10 min, and then stir slowly under negative pressure at 10 Hz for 6 h. After the material temperature reaches 25 °C, let it stand for defoaming for 12 h to obtain the casting solution.

[0044] Preparation of base membrane: Uniformly coat the prepared casting solution on a polyethylene / polypropylene hydrocarbon-based composite non-woven fabric with a thickness of 50 μm and a pore size of 0.3 μm, and prepare the base membrane by the phase inversion method.

[0045] Preparation of aqueous phase: Add 2 wt.% polyethyleneimine, 0.5 wt.% polyvinyl alcohol, and 1 wt.% triethylamine hydrochloride into pure water, stir at 30 °C for 2 h to fully dissolve it, and then let it stand for 1 h to obtain the aqueous phase mixture for standby.

[0046] Preparation of oil phase: Add 0.5 wt.% cyanuric chloride into IsoparG solvent, stir at room temperature for 1 hour, and then let it stand for 1 hour to obtain the oil phase mixture for standby.

[0047] Preparation of composite membrane: Uniformly coat the aqueous phase mixture on the base membrane, and remove the excess aqueous phase on the surface with a pressure roller and an air knife after 1 minute. Then coat the oil phase mixture to make its thickness reach 80 μm, and then enter the temperature and humidity step control platform area. In the initial stage of the reaction, control the temperature at 25 °C and the humidity at 20%, and keep it for 3 min; in the middle stage of the reaction, raise the temperature to 50 °C and increase the humidity to 50%, and maintain it for 6 min; in the later stage of the reaction, maintain the temperature at 90 °C and the humidity at 90%, and continue for 3 min. Finally, dry it in an oven at 80 °C to obtain the composite alkali-resistant nanofiltration membrane.

[0048] Post-treatment: Put the composite alkali-resistant nanofiltration membrane into an ultrasonic instrument, first perform ultrasonic treatment at a frequency of 100 HZ for 1 min, and then perform ultrasonic treatment at a frequency of 200 HZ for 1 min to complete the gradient ultrasonic post-treatment, and obtain the high-performance desalination precisely regulated strongly alkali-resistant nanofiltration membrane.

[0049] Performance testing

[0050] Filter the membrane prepared in Example 1 with a 2000 ppm MgSO4 solution under a pressure of 1 MPa. Record the relevant data and compare it with a conventional nanofiltration membrane. The results are shown in Table 1:

[0051]

[0052]

[0053] Table 1 Comparison between the membrane prepared in Example 1 and the conventional nanofiltration membrane

[0054] The membrane was immersed in 10% NaOH solution for 30 days, rinsed with pure water and then tested again. The data are shown in Table 2:

[0055]

[0056] Table 2 Comparison between the membrane prepared in Example 1 and the conventional nanofiltration membrane after soaking for 30 days

[0057] From the data in Table 1 and Table 2 above, it can be seen that:

[0058] Flux comparison: When not soaked in alkali solution, the MgSO4 flux of the membrane prepared in Example 1 was 45 LMH, and that of the conventional nanofiltration membrane was 35 LMH. The former had a higher flux, indicating that this membrane could process more solution per unit time and had a better filtration efficiency than the conventional membrane. After soaking in 10% NaOH solution for 30 days, the flux of the membrane in Example 1 decreased to 43 LMH, while that of the conventional nanofiltration membrane decreased to 30 LMH, indicating that the membrane in Example 1 had a relatively smaller flux attenuation amplitude in an alkaline environment and could better maintain the filtration efficiency.

[0059] Desalination rate comparison: When not soaked in alkali solution, the MgSO4 desalination rate of the membrane in Example 1 reached 98.5%, and that of the conventional nanofiltration membrane was 96.0%, indicating that the membrane in Example 1 had a stronger retention ability for MgSO4 and could desalinate more precisely. After soaking for 30 days, the desalination rate of the membrane in Example 1 was 98.2%, and that of the conventional nanofiltration membrane was 93.0%, demonstrating that the membrane in Example 1 had more stable desalination performance in a strong alkaline environment.

[0060] Deviation comparison: In terms of flux deviation and desalination deviation, the deviation values of the membrane prepared in Example 1 were smaller than those of the conventional nanofiltration membrane before and after soaking in alkali solution, indicating that this membrane had better performance consistency and higher stability under different working conditions.

[0061] Example 2

[0062] Example 2 of the present invention provides a high-performance desalination and precise regulation strong alkali-resistant nanofiltration membrane, and the preparation process is as follows:

[0063] Preparation of casting solution: Take 16 wt.% of polyethersulfone, 2 wt.% of small molecule alcohol additives (such as ethanol) and 82 wt.% of dimethylacetamide (DMAc) and place them in a mixing kettle. Heat the mixing kettle and stir for 7 h at a preset stirring speed. The stirring method is the same as that in Example 1, and let it stand for defoaming for 10 h to obtain the casting solution.

[0064] Preparation of the base membrane: Coat the casting solution on a polyethylene / polypropylene hydrocarbon-based composite non-woven fabric with a thickness of 80 μm and a pore size of 0.5 μm, and form the base membrane by phase inversion.

[0065] Aqueous phase preparation: Add 3 wt.% polyaldehyde propyleneamine, 0.8 wt.% chitosan, and 0.8 wt.% sodium camphorsulfonate to pure water, stir at 25 °C for 2.5 h, and let stand for 1.5 h to obtain an aqueous phase mixture.

[0066] Oil phase preparation: Add 1 wt.% benzenesulfonic acid derivative to a mixed solvent of Isopar E and pentane (volume ratio 1:1), stir at room temperature for 1.5 hours, and let stand for 1.5 hours to obtain an oil phase mixture.

[0067] Composite membrane preparation: Coat the aqueous phase mixture on the base membrane, remove the excess aqueous phase, and then coat an oil phase mixture with a thickness of 120 μm. In the temperature and humidity step control platform area, the temperature is 22 °C and the humidity is 10% at the initial stage of the reaction, and it is maintained for 4 min; the temperature is 45 °C and the humidity is 40% in the middle stage of the reaction, and it is maintained for 7 min; the temperature is 85 °C and the humidity is 85% in the later stage of the reaction, and it lasts for 4 min. Then dry it in an oven at 75 °C to obtain a composite alkali-resistant nanofiltration membrane.

[0068] Post-treatment: Put the composite alkali-resistant nanofiltration membrane into an ultrasonic instrument, and ultrasonically treat it for 1 min at frequencies of 200 HZ, 300 HZ, and 400 HZ in sequence to complete the gradient ultrasonic post-treatment, and obtain a high-performance desalination and precision regulation strong alkali-resistant nanofiltration membrane.

[0069] Performance testing

[0070] Under the same test conditions, the performance of the membrane prepared in Example 2 was tested, and the comparison data with the nanofiltration membrane prepared by the conventional process are shown in Table 3:

[0071]

[0072] Table 3 Comparison between the membrane prepared in Example 2 and the conventional nanofiltration membrane After soaking in 15% NaOH solution for 20 days and rinsing with pure water, the test results are shown in Table 4:

[0073]

[0074] Table 4 Comparison between the membrane prepared in Example 2 and the conventional nanofiltration membrane after soaking for 20 days

[0075] From the data in Table 3 and Table 4 above, it can be seen that:

[0076] Flux comparison: In the initial state, the MgSO4 flux of the membrane prepared in Example 2 is 42 LMH, which is higher than 38 LMH of the membrane prepared by the conventional process, indicating that its filtration performance is better. After soaking in 15% NaOH solution for 20 days, the membrane flux of Example 2 becomes 40 LMH, and the membrane prepared by the conventional process drops to 32 LMH, indicating that the membrane in Example 2 has stronger flux retention ability in an alkaline environment.

[0077] Desalination rate comparison: When not affected by the lye, the MgSO4 desalination rate of the membrane in Example 2 was 98.8%, and that of the membrane prepared by the conventional process was 97.0%, indicating that the membrane in Example 2 had a better desalination effect. After soaking for 20 days, the desalination rate of the membrane in Example 2 was 98.6%, and that of the membrane prepared by the conventional process was 95.0%, showing that the membrane in Example 2 had better desalination stability under alkaline conditions.

[0078] Deviation comparison: Similar to Example 1, the membranes prepared in Example 2 had smaller flux deviation and desalination deviation than those prepared by the conventional process, demonstrating better performance stability and uniformity.

[0079] Example 3

[0080] Example 3 of the present invention provides a high-performance desalination precision-controlled strong alkali-resistant nanofiltration membrane, and the preparation process is as follows:

[0081] Preparation of the casting solution: 20 wt.% of polysulfone, 1.5 wt.% of sulfonated polysulfone with different sulfonation degrees, and 78.5 wt.% of dimethyl sulfoxide (DMSO) were added to the mixing kettle. Stir for 9 h according to the set temperature and stirring procedure, and let it stand for 15 h to remove bubbles, obtaining the casting solution.

[0082] Preparation of the base membrane: The casting solution was coated on a polyethylene / polypropylene hydrocarbon-based composite non-woven fabric with a thickness of 30 μm and a pore size of 0.2 μm, and the base membrane was prepared by phase inversion.

[0083] Preparation of the aqueous phase: 1.5 wt.% of polyvinylamine, 0.3 wt.% of polyvinyl alcohol, and 1.2 wt.% of sodium chloride were added to pure water, stirred at 35 °C for 1.5 h, and let it stand for 1 h to obtain the aqueous phase mixture.

[0084] Preparation of the oil phase: 1.5 wt.% of cyanuric chloride derivative was added to the Isopar M solvent, stirred at room temperature for 1.2 hours, and let it stand for 1.2 hours to obtain the oil phase mixture.

[0085] Preparation of the composite membrane: The aqueous phase mixture was coated on the base membrane, and after removing the excess aqueous phase, a 150-μm-thick oil phase mixture was coated. In the temperature and humidity step control platform area, the temperature was 30 °C and the humidity was 30% at the initial stage of the reaction, maintained for 2 min; the temperature was 60 °C and the humidity was 60% in the middle stage of the reaction, maintained for 5 min; the temperature was 100 °C and the humidity was 100% in the later stage of the reaction, continued for 2 min. Finally, it was dried in an oven at 90 °C to obtain the composite alkali-resistant nanofiltration membrane.

[0086] Post-treatment: The composite alkali-resistant nanofiltration membrane was placed in an ultrasonic instrument, ultrasonically treated at a frequency of 300 HZ for 1 min, and then ultrasonically treated at a frequency of 400 HZ for 1 min to obtain the high-performance desalination precision-controlled strong alkali-resistant nanofiltration membrane.

[0087] Performance testing

[0088] The performance of this membrane was tested. Under the conditions of a pressure of 1 MPa and a 2000 ppm MgSO4 solution, the test data was compared with that of a conventional nanofiltration membrane as shown in Table 5:

[0089]

[0090]

[0091] Table 5 Comparison between the membrane prepared in Example 3 and a conventional nanofiltration membrane. After soaking in 20% NaOH solution for 10 days and rinsing with pure water, the test was carried out, and the data comparison is shown in Table 6:

[0092]

[0093] Table 6 Comparison between the membrane prepared in Example 2 and a conventional nanofiltration membrane after soaking for 10 days

[0094] It can be seen from the comparison of Table 5 and Table 6 that:

[0095] Flux comparison: Under the initial test conditions, the MgSO4 flux of the membrane prepared in Example 3 was 48 LMH, higher than 40 LMH of the conventional nanofiltration membrane, indicating that its filtration efficiency is higher. After soaking in 20% NaOH solution for 10 days, the membrane flux of Example 3 was 46 LMH, and the conventional nanofiltration membrane decreased to 35 LMH, indicating that the membrane of Example 3 has better flux retention performance in a strong alkaline environment.

[0096] Desalination rate comparison: When not soaking in alkali solution, the MgSO4 desalination rate of the membrane in Example 3 was 98.2%, higher than 96.5% of the conventional nanofiltration membrane, and the desalination ability was stronger. After soaking for 10 days, the desalination rate of the membrane in Example 3 was 98.0%, and that of the conventional nanofiltration membrane was 94.0%, indicating that the membrane of Example 3 has better desalination accuracy and stability in an alkaline environment.

[0097] Deviation comparison: The membrane prepared in Example 3 also had smaller flux deviation and desalination deviation than the conventional nanofiltration membrane, indicating that the performance of this membrane fluctuates less under different conditions and has better stability.

[0098] Generally speaking, the high-performance desalination-precision-regulated and strongly alkali-resistant nanofiltration membranes prepared in Examples 1, 2, and 3 are superior to the conventional nanofiltration membranes or the membranes prepared by conventional processes in terms of flux, desalination rate, and performance stability, demonstrating the significant advantages of the present invention in improving the performance of nanofiltration membranes.

[0099] Although the present invention has been described in detail with general descriptions and specific examples above, based on the present invention, some modifications or improvements can be made, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection required by the present invention.

Claims

1. A high-performance desalination precisely regulated strongly alkali-resistant nanofiltration membrane, characterized in that, Using polyethylene / polypropylene hydrocarbon-based composite non-woven fabric as the support material, polysulfone or polyethersulfone as the ultrafiltration substrate, interfacial polymerization is carried out through the temperature and humidity step regulation of the water / oil phase interface, and then gradient ultrasonic post-treatment is carried out to obtain; the alkali-resistant nanofiltration membrane includes a composite non-woven fabric layer, a polysulfone or polyethersulfone ultrafiltration layer and an interfacial polymerization layer.

2. The high-performance desalination precisely regulated strong alkali-resistant nanofiltration membrane according to claim 1, wherein The temperature range of the temperature and humidity step regulation in the water / oil phase interface platform area is 20°C - 100°C, and the humidity range is 0 - 100%.

3. The high-performance desalination precisely regulated strong alkali-resistant nanofiltration membrane according to claim 1, wherein The frequency range of the gradient ultrasonic post-treatment is 100 - 500 HZ, and the treatment time is 2 - 20 min.

4. A high-performance desalination precisely regulated strongly alkali-resistant nanofiltration membrane according to claim 1, characterized in that, The thickness of the polyethylene / polypropylene hydrocarbon-based composite non-woven fabric is 10 - 200 μm, and the pore size is 0.1 - 2 μm.

5. The preparation method of the high-performance desalination precisely regulated and strongly alkali-resistant nanofiltration membrane according to any one of claims 1-4, characterized in that, Including the following steps: Preparation of casting solution: Put a set amount of polysulfone or polyethersulfone, additives and solvents into the mixing kettle, heat the mixing kettle to the set temperature, stir and stand for defoaming to obtain the casting solution; Preparation of the base membrane: Coat the casting solution on the polyethylene / polypropylene-based composite non-woven fabric, and prepare the base membrane by phase inversion; Preparation of the aqueous phase: Add a set amount of amine monomers, cross-linking agents and base membrane pore-preserving agents to pure water, stir to dissolve and stand to obtain an aqueous phase mixture for standby; Preparation of the oil phase: Add a set amount of oil phase monomers to the mixed solvent of alkanes, stir and stand to obtain an oil phase mixture for standby; Preparation of the composite membrane: Coat the aqueous phase mixture on the base membrane, remove the excess aqueous phase and then coat the oil phase mixture, pass through the temperature and humidity step control platform area, and then dry to obtain the composite alkali-resistant nanofiltration membrane; Post-treatment: Put the composite alkali-resistant nanofiltration membrane into an ultrasonic instrument for gradient ultrasonic post-treatment to obtain a high-performance desalination precision control and strong alkali-resistant nanofiltration membrane.

6. The preparation method of the high-performance desalination precision control strongly alkali-resistant nanofiltration membrane according to claim 5, characterized in that, The concentration of polysulfone or polyethersulfone in the casting solution is 15 - 20 wt.%, the additive content is 0 - 3%, and the additives are at least one of pure water, small molecule ketones, small molecule alcohols, polyvinyl alcohol with a specified molecular weight, polyvinylpyrrolidone with a specified molecular weight, sulfonated polysulfone or sulfonated polyethersulfone with different sulfonation degrees; the solvent is at least one of dimethylformamide, dimethylacetamide, and dimethyl sulfoxide.

7. The preparation method of the high-performance desalination precisely regulated strong alkali-resistant nanofiltration membrane according to claim 5, characterized in that, In the aqueous phase preparation step, the amine monomers are at least one of polyethyleneimine, polyallylamine, polyvinylamine, poly(piperidine), and poly(diallylamine); the cross-linking agents are at least one of polyvinyl alcohol and chitosan; the base membrane pore-preserving agents are at least one of triethylamine hydrochloride, sodium camphorsulfonate, sodium chloride, and sodium citrate; The content of amine monomers is 1 - 5 wt.%, the content of cross-linking agents is 0.1 - 1 wt.%, and the content of base membrane pore-preserving agents is 0.5 - 1.5 wt.%.

8. The preparation method of the high-performance desalination precisely regulated strong alkali-resistant nanofiltration membrane according to claim 5, characterized in that, In the oil phase preparation step, the mixed solvent of alkanes is at least one of IsoparG, IsoparE, IsoparM, pentane and alkanes with more carbon atoms; The oil phase monomers are cyanuric chloride and its derivatives, sulfonic acid, benzenesulfonic acid and its derivatives, and the concentration of the oil phase monomers is 0.2 - 2 wt.%.

9. The preparation method of the high-performance desalination precision control strong alkali-resistant nanofiltration membrane according to claim 5, characterized in that In the composite membrane preparation step, the temperature range of the temperature and humidity step control platform area is 20°C - 100°C, and the humidity range is 0 - 100%; the temperature gradient is 10°C and the humidity gradient is 10%; The synergistic regulation strategy of temperature and humidity step control includes: In the initial stage of the reaction, the temperature is controlled at 20°C - 30°C and the humidity is controlled at 0 - 30% to slow down the monomer diffusion and reaction rate and promote the uniform distribution of the monomers; In the middle stage of the reaction, the temperature is increased to 40°C - 70°C and the humidity is increased to 40% - 70% to accelerate the reaction for rapid growth of the functional layer and promote the reaction with humidity to increase the crosslinking degree; In the later stage of the reaction, the temperature is maintained at 80°C - 100°C and the humidity is maintained at 80% - 100% to promote the monomer reaction.

10. The preparation method of the high-performance desalination precision-controlled strong alkali-resistant nanofiltration membrane according to claim 5, characterized in that, In the post-treatment step, the ultrasonic frequency range is 100 - 500 HZ and the ultrasonic frequency gradient is 100 HZ.

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