A high water flux narrow pore size distribution ultrafiltration membrane and a preparation method thereof

Abstract

The application provides a high water flux narrow pore size distribution ultrafiltration membrane and a preparation method thereof. By changing the organic solvent of the polymer and / or adding a non-solvent additive to change the entanglement degree of the polymer coil, the diameter distribution of the polymer aggregate in the membrane liquid is adjusted to be between 50-500 nm, the viscosity of the membrane liquid is between 500-20000 centipoises at 25 DEG C, and the flat plate ultrafiltration membrane and the hollow fiber membrane are prepared by using the non-solvent phase transfer method, so that the pure water flux of the membrane is greater than or equal to 300 L ‑1 m ‑2 h ‑1 bar ‑1 , the average pore flow diameter is between 5-40 nm, and the pore size distribution index is between 0.1-1.0. The method of the application combines the polymer microstructure and the macroscopic membrane structure, the preparation method is simple and easy to operate, can be developed to the application fields of high separation precision such as protein separation, and the preparation of nanofiltration and reverse osmosis composite membrane base film, and is suitable for a wide range of applications.

Description

Technical Field

[0001] This invention belongs to the field of membrane material technology and relates to a high water flux narrow pore size distribution ultrafiltration membrane and its preparation method. Background Technology

[0002] Ultrafiltration (UF) is a pressure-driven membrane separation technology based on pore size sieving. Ultrafiltration membranes typically have pore sizes between 1 and 100 nm, exhibiting high rejection rates and water flux for macromolecules under low pressure. The UF separation process is energy-efficient and highly effective, thus it is widely used in wastewater treatment, food processing, and biomedicine industries. Current UF membranes are mainly prepared using the non-solvent-induced phase separation (NIPS) method, where different types and concentrations of pore-forming agents are added to the polymer solution to control the pore size and pore structure. However, in practical applications, UF technology still faces many challenges: for example, in industries such as monoclonal antibody and vaccine production, and protein separation, the wide pore size distribution of UF membranes limits separation accuracy. Furthermore, a wide pore size distribution leads to severe membrane fouling, requiring multiple cleaning steps and resulting in low treatment efficiency. Therefore, to achieve efficient separation, it is crucial to design the pore size and pore structure of the UF membrane, and preparing an UF membrane with a suitable pore size and narrow pore size distribution is key.

[0003] Numerous patents have been reported on the preparation of ultrafiltration membranes. Some methods propose preparing ultrafiltration membranes with narrow pore size distributions, such as adding pore-forming agents and hydrophilic agents to polymer solutions, or using unsuitable solvents. For example, patent CN111530306A discloses a symmetrical polyethersulfone hollow fiber ultrafiltration membrane and its preparation method. It uses tetraethylene glycol as an unsuitable solvent, polyvinylpyrrolidone as a pore-forming agent, and diethylacetamide or N,N-dimethylformamide as a solvent to prepare a homogeneous casting solution, which is then spun to obtain the hollow fiber ultrafiltration membrane. Patent CN116272448A discloses a method for preparing a high-flux, high-retention asymmetric polyethersulfone ultrafiltration membrane. It uses a conventional good solvent, a volatile unsuitable solvent, and a hydrophilic agent to prepare a casting solution. The solution is first induced to form a pre-phase by air evaporation, and then the membrane solution is immersed in a gel bath to prepare a high-retention, asymmetric ultrafiltration membrane. Patent CN117771983A discloses a polyethersulfone ultrafiltration membrane and its preparation method, which prepares an ultrafiltration membrane capable of effectively separating proteins by adding water-soluble monomer additives, lipid-soluble monomer additives and pore-forming agents.

[0004] However, the preparation methods of the aforementioned patents are mostly based on experience and lack clear and scientific guidance for controlling pore size and distribution, and have not established the relationship between the microstructure of the membrane-forming solution and the macrostructure of the membrane. Therefore, there is an urgent need in the field for an ultrafiltration membrane and its preparation method that achieves high-efficiency separation by optimizing the pore size and distribution of the filter membrane. Summary of the Invention

[0005] This invention addresses the aforementioned problems in existing technologies by proposing a high-flux, narrow-pore-distribution ultrafiltration membrane and its preparation method. The narrow-pore-distribution asymmetric ultrafiltration membrane provided by this invention considers the influence of solvent viscosity on polymer unentanglement and the affinity between the solvent and polymer. By controlling the polymer diameter distribution and the viscosity of the membrane-forming solution, the pore size and distribution of the filter membrane are optimized, thereby obtaining flat-sheet ultrafiltration membranes and hollow fiber membranes with narrow pore distributions, achieving high water separation performance and high rejection rate.

[0006] Specifically, one aspect of the present invention provides a method for preparing an ultrafiltration membrane, the ultrafiltration membrane comprising a flat sheet ultrafiltration membrane and a hollow fiber membrane, the preparation method comprising the following steps:

[0007] (1) The film-forming polymer, solvent and optional non-solvent additives are mixed evenly to prepare a film-forming solution. The diameter of the polymer agglomerates in the film-forming solution is distributed between 50-500 nm, and the viscosity of the film-forming solution at 25°C is between 500-20000 centipoise.

[0008] (2) Pour the film-forming solution prepared in step (1) onto the carrier and coat it to obtain the initial flat sheet membrane; or

[0009] The membrane-forming solution prepared in step (1) is extruded through the outer cavity of the coaxial spinneret to form a membrane, while the core liquid is extruded through the inner cavity of the coaxial spinneret to obtain an initial hollow fiber membrane.

[0010] (3) Quickly immerse the initial flat sheet membrane or initial hollow fiber membrane obtained in step (2) into a gel bath for curing;

[0011] (4) Rinse the solidified flat sheet ultrafiltration membrane or hollow fiber membrane from step (3) to remove solvent and non-solvent, and soak and dry it in glycerol to obtain the final flat sheet ultrafiltration membrane or hollow fiber membrane.

[0012] In one or more embodiments, the standard deviation of the pore size distribution of the ultrafiltration membrane is between 0.1 and 1.0, preferably between 0.1 and 0.8.

[0013] In one or more embodiments, the pure water flux of the ultrafiltration membrane is ≥300 L·m -2 ·h -1 ·bar - 1.

[0014] In one or more embodiments, the average pore diameter of the ultrafiltration membrane is between 5 and 40 nm.

[0015] In one or more embodiments, in step (1), the mass ratio of the film-forming polymer to the solvent is 1:(2-5).

[0016] In one or more embodiments, in step (1), a non-solvent additive is added, and the mass ratio of the film-forming polymer to the non-solvent additive is 1:(0.05-1.5), preferably 1:(0.1-1).

[0017] In one or more embodiments, in step (1), heating is performed during the mixing process at a temperature of 25°C-80°C.

[0018] In one or more embodiments, in step (1), the film-forming polymer is selected from one or more of polysulfone, polyethersulfone, and polyvinylidene fluoride.

[0019] In one or more embodiments, in step (1), the polysulfone has a weight-average molecular weight of 40-100 kDa, the polyethersulfone has a weight-average molecular weight of 40-100 kDa, and the polyvinylidene fluoride has a weight-average molecular weight of 100-1000 kDa.

[0020] In one or more embodiments, in step (1), the solvent is selected from one or more of N-methylpyrrolidone, dipyrrolidone, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, and triethyl phosphate.

[0021] In one or more embodiments, the non-solvent additive is selected from one or more of small molecule non-solvent additives and macromolecule non-solvent additives.

[0022] In one or more embodiments, the non-solvent additive is a small molecule non-solvent additive, or a combination of a small molecule non-solvent additive and a macromolecule non-solvent additive, preferably in a mass ratio of 1:(0.05-1) of the small molecule non-solvent additive and the macromolecule non-solvent additive.

[0023] In one or more embodiments, the small molecule non-solvent additive is selected from one or more of water, ethylene glycol, diethylene glycol, polyethylene glycol, and glycerol.

[0024] In one or more embodiments, the weight-average molecular weight of the small molecule nonsolvent additive is 18-7000 Da.

[0025] In one or more embodiments, the weight-average molecular weight of polyethylene glycol is 200-7000 Da, preferably 200-1000 Da.

[0026] In one or more embodiments, the macromolecular nonsolvent additive is polyvinylpyrrolidone, wherein the weight-average molecular weight of polyvinylpyrrolidone is 10-100 kDa, preferably 30 ± 10 kDa.

[0027] In one or more embodiments, in step (1), the mass fraction of the film-forming polymer in the film-forming solution is 10 wt%-30 wt%.

[0028] In one or more embodiments, in step (1), the mass ratio of the non-solvent additive to the solvent in the film-forming solution is (0-1):1.

[0029] In one or more embodiments, in step (2), the carrier is a non-woven fabric, the thickness of the film-forming liquid coated on the carrier is 150-300μm, the ambient temperature for scraping the initial flat film is 20℃-35℃, and the ambient relative humidity is in the range of 20%-80%, preferably 30%-60%.

[0030] In one or more embodiments, in step (2), the core liquid introduced into the inner cavity of the coaxial spinneret during the preparation of the initial hollow fiber membrane is a mixture of water and solvent, wherein the solvent is preferably selected from one or more of N-methylpyrrolidone, dipyrrolidone, dimethylformamide, dimethylacetamide, dimethyl sulfoxide and triethyl phosphate; the mass ratio of solvent to water in the core liquid is preferably 1:(1-9).

[0031] In one or more embodiments, before the initial hollow fiber membrane enters the gel bath, it passes through an air section with a temperature of 20°C-60°C, a relative humidity of 40%-100%, and a height of 5-30cm.

[0032] In one or more embodiments, in step (3), the initial flat sheet membrane or initial hollow fiber membrane obtained in step (2) is immersed in a gel bath and rapidly cured, and the time interval between the preparation of the initial flat sheet membrane or initial hollow fiber membrane and its entry into the gel bath is ≤5 seconds.

[0033] In one or more embodiments, in step (3), the medium of the gel bath is water or a mixture of water and a solvent, wherein the solvent is preferably selected from one or more of N-methylpyrrolidone, dipyrrolidone, dimethylformamide, dimethylacetamide, dimethyl sulfoxide and triethyl phosphate; when the medium of the gel bath is a mixture of water and a solvent, the solvent accounts for ≤80wt% of the mixture by mass, for example 1wt%-80wt%, preferably ≤50wt% of the mixture by mass, for example 1wt%-50wt%.

[0034] In one or more embodiments, in step (3), the temperature of the gel bath is 10°C-95°C, preferably 20°C-80°C.

[0035] In one or more embodiments, the phase transition time of the flat sheet membrane or hollow fiber membrane in the gel bath is 1-20 min.

[0036] In one or more embodiments, the film-forming solution uses polysulfone with a weight-average molecular weight of 67-72 kDa as the film-forming polymer and dipyrrolidone as the solvent, with a mass ratio of polysulfone to dipyrrolidone of 1:(3-5), for example 1:4.

[0037] In one or more embodiments, the film-forming solution uses polyethersulfone with a weight-average molecular weight of 49-52 kDa as the film-forming polymer, glycerol as a small molecule non-solvent additive, and N-methylpyrrolidone as the solvent. The mass ratio of polyethersulfone to glycerol is 1:(0.5-1), for example 1:0.75, and the mass ratio of polyethersulfone to N-methylpyrrolidone is 1:(2.5-4), for example 1:3.25.

[0038] In one or more embodiments, the film-forming solution uses polyvinylidene fluoride (PVDF) with a weight-average molecular weight of 200-250 kDa as the film-forming polymer, diethylene glycol as a small-molecule non-solvent additive, polyvinylpyrrolidone (PVP) as a large-molecule non-solvent additive, and dimethylacetamide as the solvent. The mass ratio of PVDF to diethylene glycol is 1:(0.25-1), for example, 1:0.5; the mass ratio of PVDF to PPV is 1:(0.1-0.5), for example, 1:0.25; and the mass ratio of PVDF to dimethylacetamide is 1:(2.5-4), for example, 1:3.25.

[0039] In one or more embodiments, the film-forming solution uses polyethersulfone with a weight-average molecular weight of 78-84 kDa as the film-forming polymer, diethylene glycol as a small molecule non-solvent additive, polyvinylpyrrolidone with a weight-average molecular weight of 30 kDa as a large molecule non-solvent additive, and N-methylpyrrolidone as the solvent. The mass ratio of polyethersulfone to diethylene glycol is 1:(0.25-1), for example 1:0.5; the mass ratio of polyethersulfone to polyvinylpyrrolidone is 1:(0.1-0.5), for example 1:0.25; and the mass ratio of polyethersulfone to N-methylpyrrolidone is 1:(2.5-4), for example 1:3.25.

[0040] The ultrafiltration membrane of the present invention can be prepared by the method described in any of the embodiments herein. Attached Figure Description

[0041] Figure 1 The pore size distribution curves are the standard deviations of the peaks for different pore size distributions.

[0042] Figure 2 The diameter distribution curves of polymer aggregates in different dilute polymer solution systems are shown.

[0043] Figure 3 The pore size distribution curve is shown for the wide pore size distribution ultrafiltration membrane prepared in Comparative Example 4 of this invention.

[0044] Figure 4 The pore size distribution curve is shown for the narrow pore size distribution ultrafiltration membrane prepared in Example 1 of the present invention. Detailed Implementation

[0045] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used herein are explained and defined in general terms below. Unless otherwise specified, all technical and scientific terms used herein have the common meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0046] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0047] In this document, the terms “contains,” “includes,” “containing,” and similar terms encompass the meanings of “basically composed of” and “composed of.” For example, when this document discloses “A contains B and C,” “A is basically composed of B and C” and “A is composed of B and C” should be considered as having been disclosed in this document.

[0048] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0049] Unless otherwise specified, percentages refer to mass percentages and proportions refer to mass ratios in this article.

[0050] In this article, the sum of the percentages of all components in the composition is 100%.

[0051] In this document, when describing embodiments or examples, it should be understood that it is not intended to limit the invention to those embodiments or examples. Rather, all alternatives, modifications, and equivalents of the methods and materials described herein are covered within the scope of this invention.

[0052] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0053] The purpose of this invention is to optimize the pore size and distribution of the filter membrane by controlling the polymer diameter distribution between 50-500 nm and the viscosity of the membrane-forming solution between 500-20000 centipoise, thereby obtaining flat sheet ultrafiltration membranes and hollow fiber membranes with narrow pore size distributions. The standard deviation of the membrane pore size distribution is between 0.1 and 1.0, achieving high water flux (≥300 L). -1 m -2 h - 1 bar -1 ) and high retention rate.

[0054] This invention discovers that the viscosity of the solvent and the affinity between the solvent and the polymer have a significant impact on the unentanglement and swelling of the polymer, thereby affecting the pore-forming effect when the film-forming solution comes into contact with a poor solvent.

[0055] Polymer dissolution is the process by which solvent diffuses into the polymer, causing swelling and disentanglement of polymer chains. When the solvent's solubility decreases, such as with the use of high-viscosity solvents, the addition of non-solvent additives, or the interaction between solvent groups and polymer chain groups, the interactions between chain segments increase, leading to increased polymer chain entanglement in the membrane-forming solution. Therefore, differences in the interaction between the solvent and the polymer, as well as the addition of non-solvent additives, all affect the morphology of the polymer in solution. Generally, in a good solvent system, the weaker the interaction between polymers, the greater the distance between polymer chains, and the lower the degree of entanglement. Conversely, in a poor solvent system, the higher the degree of entanglement between polymer chains, the higher the viscosity of the membrane-forming solution, which in turn affects the phase separation process, ultimately resulting in significant differences in membrane morphology between the two solution systems. Furthermore, during phase separation, the solvent and gel bath diffuse into each other, while the movement of the polymer chains is significantly restricted due to their high degree of entanglement. After phase separation, the polymer chains form an interconnected ultrafiltration membrane with a narrow pore size distribution, ultimately achieving high water flux.

[0056] Specifically, a method for preparing an ultrafiltration membrane, the ultrafiltration membrane comprising a flat sheet ultrafiltration membrane and a hollow fiber membrane, the preparation method comprising the following steps:

[0057] (1) The film-forming polymer, solvent and optional non-solvent additives are mixed evenly to prepare a film-forming solution. The diameter of the polymer aggregates in the film-forming solution is distributed between 50-500 nm, and the viscosity of the film-forming solution at 25°C is between 500-20000 centipoise.

[0058] (2) Pour the film-forming solution prepared in step (1) onto the carrier and coat it to obtain the initial flat sheet membrane; or

[0059] The membrane-forming solution prepared in step (1) is extruded through the outer cavity of the coaxial spinneret to form a membrane, while the core liquid is extruded through the inner cavity of the coaxial spinneret to obtain an initial hollow fiber membrane.

[0060] (3) Quickly immerse the initial flat sheet membrane or initial hollow fiber membrane obtained in step (2) into a gel bath for curing;

[0061] (4) Rinse the solidified flat sheet ultrafiltration membrane or hollow fiber membrane from step (3) to remove solvent and non-solvent, and soak and dry it in glycerol to obtain the final flat sheet ultrafiltration membrane or hollow fiber membrane.

[0062] In some embodiments, in step (1), the film-forming polymer is selected from one or more of polysulfone, polyethersulfone, and polyvinylidene fluoride, or a mixture thereof.

[0063] In some implementations, the weight-average molecular weight of polysulfone is 40-100 kDa, such as 40 kDa, 45 kDa, 50 kDa, 55 kDa, 60 kDa, 65 kDa, 67-72 kDa, 70 kDa, 75 kDa, and 80 kDa.

[0064] In some implementations, the weight-average molecular weight of polyethersulfone is 40-100 kDa, such as 40 kDa, 45 kDa, 49-52 kDa, 50 kDa, 55 kDa, 60 kDa, 65 kDa, 70 kDa, 75 kDa, 78-84 kDa, 80 kDa, 85 kDa, 90 kDa, 95 kDa, and 100 kDa.

[0065] In some implementations, the weight-average molecular weight of polyvinylidene fluoride is 100-1000 kDa, such as 100 kDa, 150 kDa, 200 kDa, 200-250 kDa, 250 kDa, 300 kDa, 350 kDa, 400 kDa, 450 kDa, 500 kDa, 600 kDa, 700 kDa, 800 kDa, 900 kDa, 950 kDa, and 1000 kDa.

[0066] In some embodiments, in step (1), the solvent of the film-forming solution is selected from one or more of N-methylpyrrolidone, dipyrrolidone, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, and triethyl phosphate.

[0067] The degree of entanglement of polymer coils (i.e., cluster diameter distribution) and the viscosity of the film-forming solution can be adjusted by changing the organic solvent of the polymer and / or adding non-solvent additives.

[0068] In some implementations, the non-solvent additive is selected from one or more of small molecule non-solvent additives and large molecule non-solvent additives.

[0069] In some embodiments, the non-solvent additive is a small molecule non-solvent additive, or a combination of a small molecule non-solvent additive and a large molecule non-solvent additive, preferably in a mass ratio of 1:(0.05-1), such as 1:0.05, 1:0.1, 1:0.2, 1:0.25, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.75, 1:0.8, 1:0.9, or 1:1.

[0070] In some implementations, the small molecule non-solvent additive is selected from one or more of water, ethylene glycol, diethylene glycol, polyethylene glycol, and glycerol.

[0071] In some implementations, the weight-average molecular weight of the small molecule non-solvent additive is 18-7000 Da, such as 18 Da, 50 Da, 80 Da, 100 Da, 120 Da, 150 Da, 180 Da, 200 Da, 250 Da, 300 Da, 350 Da, 380 Da, 400 Da, 450 Da, 500 Da, 550 Da, 580 Da, 600 Da, 650 Da, 700 Da, 750 Da, 800 Da, 850 Da, 900 Da, 950 Da, 1000 Da, 1500 Da, 2000 Da, 3000 Da, 4000 Da, and 6000 Da.

[0072] In some implementations, the weight-average molecular weight of polyethylene glycol is 200-7000 Da, preferably 200-1000 Da, such as 200 Da, 300 Da, 400 Da, 600 Da, 800 Da, and 1000 Da.

[0073] In some embodiments, the macromolecular nonsolvent additive is polyvinylpyrrolidone, with a weight-average molecular weight of 10-100 kDa, preferably 30 ± 10 kDa, such as 20 kDa, 25 kDa, 30 kDa, 35 kDa, or 40 kDa.

[0074] In some implementations, the diameter distribution of the polymer agglomerates in the film-forming solution is between 50-500 nm, such as 50-100 nm, 58-96 nm, 50-200 nm, 50-300 nm, 50-400 nm, 50-450 nm, 72-205 nm, 78-266 nm, 90-150 nm, 90-200 nm, 90-300 nm, 90-400 nm, 90-450 nm, 90-500 nm. m, 100-200nm, 100-300nm, 100-400nm, 100-450nm, 100-500nm, 200-250nm, 200-300nm, 200-400nm , 200-450nm, 200-500nm, 300-400nm, 300-450nm, 300-500nm, 400-450nm, 400-500nm, 450-500nm.

[0075] In some implementations, in step (1), the mass ratio of the film-forming polymer to the solvent is 1:(2-5), such as 1:2, 1:2.25, 1:2.5, 1:2.75, 1:3, 1:3.25, 1:3.5, 1:3.75, 1:4, 1:4.25, 1:4.5, 1:4.75, and 1:5.

[0076] In some implementations, in step (1), a non-solvent additive is added, and the mass ratio of the film-forming polymer to the non-solvent additive is 1:(0.05-1.5), preferably 1:(0.1-1), such as 1:0.1, 1:0.15, 1:0.2, 1:0.25, 1:0.3, 1:0.35, 1:0.4, 1:0.45, 1:0.5, 1:0.55, 1:0.6, 1:0.65, 1:0.7, 1:0.75, 1:0.8, 1:0.85, 1:0.9, 1:0.95, 1:1.

[0077] In some implementations, in step (1), heating is performed during the mixing process at a temperature of 25°C-80°C, such as 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, and 80°C.

[0078] In some implementations, in step (1), the mass fraction of the film-forming polymer in the film-forming solution is 10wt%-30wt%, such as 10wt%, 12wt%, 14wt%, 15wt%, 16wt%, 18wt%, 20wt%, 22wt%, 24wt%, 25wt%, 26wt%, 28wt%, or 30wt%.

[0079] The diameter distribution of polymer aggregates and the viscosity of the film-forming solution can be achieved by changing the type of solvent and adjusting the mass ratio of non-solvent additives to solvent.

[0080] In some implementations, in step (1), the mass ratio of the non-solvent additive to the solvent is (0-1):1, such as 0:1, 0.1:1, 0.2:1, 0.23:1, 0.25:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.75:1, 0.8:1, 0.9:1, 1:1.

[0081] This invention proposes a strategy to regulate the pore size and pore size distribution of ultrafiltration membrane by controlling the diameter distribution of polymer agglomerates and the viscosity of the solution in the membrane-forming solution. Unexpectedly, this method was found to be a key and scientific means to achieve the preparation of ultrafiltration membranes with narrow pore size distribution.

[0082] The present invention also found that the solvent in the film-forming solution can affect the diameter distribution and viscosity of the polymer agglomerates in the film-forming solution, mainly for three reasons: the viscosity of the solvent, the solubility of the solvent in the polymer, and the interaction force between the solvent and the polymer.

[0083] Different solvents have varying viscosities and different solvents have different solubilities for polymers, resulting in different viscosities in the film-forming solution, which in turn affects the diameter distribution of polymer agglomerates in the solution. For example, the viscosity of the solvent dipyrrolidone (2-PD) (13.3 centipoise) is higher than that of dimethylacetamide (0.92 centipoise) and N-methylpyrrolidone (1.65 centipoise). According to Hansen solubility parameters, 2-PD has weaker solubility for polymers such as polysulfone and polyethersulfone than for dimethylacetamide and N-methylpyrrolidone. Therefore, when using the same mass ratio of polymers, the viscosity of the film-forming solution prepared with 2-PD is higher than that prepared with dimethylacetamide or N-methylpyrrolidone.

[0084] On the other hand, the viscosity of the film-forming solution is also related to the affinity of the solvent for the polymer. This affinity affects the viscosity by influencing the shape and arrangement of polymer molecules in the solvent. For example, the formation of hydrogen bonds between the amide groups of 2-PD and the sulfonyl groups on the polymer chains of polysulfone and polyethersulfone, as well as the formation of hydrogen bonds between 2-PD molecules, will also increase the viscosity of the film-forming solution.

[0085] Polymer dissolution is the process by which solvent diffuses into the polymer, causing swelling and disentanglement of the polymer chains. As solvent solubility decreases, solution viscosity increases, and the interactions between polymer chain segments strengthen, resulting in greater polymer chain entanglement in the membrane-forming solution. In solvent systems with strong solubility, the interaction between solvent molecules and polymers is even stronger, leading to a higher degree of disentanglement of polymer chain segments. The state of polymer entanglement can be quantitatively determined by analyzing the viscoelasticity of the membrane-forming solution. The interaction between solvent and polymer is also reflected in the size of polymer clusters: the weaker the solvent's solubility, the less solvent enters the polymer chain, the stronger the interactions between chain segments, the higher the degree of polymer chain entanglement, and therefore the larger the diameter of the polymer aggregates. High polymer entanglement in a solvent system with a certain solubility may be one of the important reasons for the formation of the interconnected pore structure of ultrafiltration membranes.

[0086] Based on the above analysis, it can be seen that the differences in the rheological properties of the membrane-forming solution, such as viscosity, degree of polymer entanglement, and agglomerate diameter distribution, affect the phase separation process in the preparation of ultrafiltration membranes, thereby affecting the pore structure and water permeability of ultrafiltration membranes.

[0087] Therefore, by using a suitable membrane-forming solution, such as a membrane-forming solution with polymer aggregates having a diameter distribution between 50-500 nm and a viscosity between 500-20000 centipoise at 25°C, the standard deviation of the pore size distribution of the prepared ultrafiltration membrane can be between 0.1-0.8. This allows the membrane to form a connected pore structure, and the membrane cross-section to resemble a sponge with interconnected pores, thus creating a relatively uniform pore structure and achieving high water flux.

[0088] In some implementations, in step (1), the viscosity of the film-forming solution at 25°C is between 500 and 20,000 centipoise, for example, 500 centipoise, 600 centipoise, 700 centipoise, 800 centipoise, 900 centipoise, 1000 centipoise, 1328 centipoise, 1500 centipoise, 2000 centipoise, 3000 centipoise, 4000 centipoise, 5000 centipoise, 5267 centipoise, 5500 centipoise, 5 739 centipoise, 6000 centipoise, 7000 centipoise, 8000 centipoise, 9000 centipoise, 10000 centipoise, 11000 centipoise, 12000 centipoise, 13000 centipoise, 14000 centipoise, 14275 centipoise, 14500 centipoise, 15000 centipoise, 16000 centipoise, 17000 centipoise, 18000 centipoise, 19000 centipoise, 20000 centipoise.

[0089] In some implementations, the standard deviation of the pore size distribution of the ultrafiltration membrane is between 0.1 and 1.0, preferably between 0.1 and 0.8, such as 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.67, 0.69, 0.7, 0.72, 0.76, 0.79, and 0.8.

[0090] In some implementations, the pure water flux of the ultrafiltration membrane is ≥300 L·m -2 ·h -1 ·bar -1 For example, 300 L·m -2 ·h -1 ·bar -1 323 L·m -2 ·h -1 ·bar -1 350L·m -2 ·h -1 ·bar -1 400L·m -2 ·h -1 ·bar -1 450L·m -2 ·h -1 ·bar -1 460L·m -2 ·h -1 ·bar -1 497 L·m -2 ·h -1 ·bar -1 500L·m -2 ·h -1 ·bar -1 550L·m -2 ·h -1 ·bar -1 590 L·m -2 ·h -1 ·bar -1 600L·m -2 ·h -1 ·bar -1 650L·m -2 ·h -1 ·bar -1 700L·m -2 ·h -1 ·bar -1 750L·m -2 ·h -1 ·bar -1 800L·m -2 ·h -1 ·bar-1 、850L·m -2 ·h -1 ·bar -1 、890L·m -2 ·h -1 ·bar -1 、900L·m -2 ·h -1 ·bar -1 、950L·m -2 ·h -1 ·bar -1 、1000L·m -2 ·h -1 ·bar -1 、1050L·m -2 ·h -1 ·bar -1 、1100L·m -2 ·h -1 ·bar -1 、1150L·m -2 ·h -1 ·bar -1 、1200L·m -2 ·h -1 ·bar -1 、1250L·m -2 ·h -1 ·bar -1 、1275L·m -2 ·h -1 ·bar -1 、1300L·m -2 ·h -1 ·bar -1 、1400L·m -2 ·h -1 ·bar -1 、1500L·m -2 ·h -1 ·bar -1 、1600L·m -2 ·h -1 ·bar -1 、1700L·m -2 ·h -1 ·bar -1 、1760L·m -2 ·h -1 ·bar -1 、1800L·m -2 ·h -1 ·bar -1 、1900L·m -2 ·h -1 ·bar-1 2000L·m -2 ·h -1 ·bar -1 2100L·m -2 ·h -1 ·bar -1 wait.

[0091] In some implementations, the average pore diameter of the ultrafiltration membrane is between 5 and 40 nm, such as 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm, 21 nm, 22 nm, 23 nm, 24 nm, 25 nm, 26 nm, 27 nm, 28 nm, 29 nm, 30 nm, 31 nm, 32 nm, 33 nm, 34 nm, 35 nm, 36 nm, 37 nm, 38 nm, 39 nm, and 40 nm.

[0092] In some implementations, in step (2), the carrier for scraping the initial flat film is a nonwoven fabric, and the thickness of the film-forming liquid coated on the carrier is 150-300μm, such as 150μm, 200μm, 250μm, or 300μm.

[0093] In some implementations, in step (2), the ambient temperature for scraping the initial flat film is 20°C-35°C, such as 20°C, 22°C, 25°C, 28°C, 30°C, 32°C, or 35°C.

[0094] In some implementations, in step (2), the relative humidity of the environment for scraping the initial flat film is in the range of 20%-80%, preferably 30%-60%, such as 30%, 35%, 40%, 45%, 50%, 55%, and 60%.

[0095] In some embodiments, in step (2), the core fluid introduced into the inner cavity of the coaxial spinneret during the preparation of the initial hollow fiber membrane is a mixture of water and solvent, preferably selected from one or more of N-methylpyrrolidone, dipyrrolidone, dimethylformamide, dimethylacetamide, dimethyl sulfoxide and triethyl phosphate.

[0096] In some implementations, the mass ratio of solvent to water in the core fluid in step (2) is preferably 1:(1-9), such as 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9.

[0097] In some implementations, in step (2), before the initial hollow fiber membrane enters the gel bath, it first passes through an air section with a temperature of 20°C-60°C, such as 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, and 60°C.

[0098] In some implementations, in step (2), the relative humidity of the initial hollow fiber membrane passing through the air section is 40%-100%, such as 40%, 50%, 60%, 70%, 80%, 90%, 100%.

[0099] In some implementations, in step (2), the height of the initial hollow fiber membrane through the air section is preferably 5-30cm, such as 5cm, 10cm, 15cm, 20cm, 25cm, or 30cm.

[0100] In some implementations, in step (3), the initial flat sheet membrane or initial hollow fiber membrane obtained in step (2) is immersed in a gel bath and rapidly cured. The time interval between the preparation of the initial flat sheet membrane or initial hollow fiber membrane and its entry into the gel bath is ≤5 seconds, such as 0 seconds, 1 second, 2 seconds, 3 seconds, 4 seconds, or 5 seconds.

[0101] In some implementations, in step (3), the medium of the gel bath is water or a mixture of water and solvent.

[0102] In some embodiments, in step (3), when the medium of the gel bath is a mixture of water and solvent, the solvent is preferably selected from one or more of N-methylpyrrolidone, dipyrrolidone, dimethylformamide, dimethylacetamide, dimethyl sulfoxide and triethyl phosphate.

[0103] In some embodiments, in step (3), the solvent in the gel bath accounts for ≤80 wt% of the mixture by mass, for example, 1 wt%-80 wt%, preferably ≤50 wt% of the mixture by mass, for example, 1 wt%-50 wt%, 1 wt%, 2 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%.

[0104] In some embodiments, the temperature of the gel bath is 10°C-95°C, preferably 20°C-80°C, such as 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, and 80°C.

[0105] In some implementations, the phase transition time of the flat sheet membrane or hollow fiber membrane in the gel bath is 1-20 min, such as 1 min, 2 min, 3 min, 4 min, 5 min, 8 min, 10 min, 12 min, 15 min, 18 min, and 20 min.

[0106] In some preferred embodiments, when preparing the film-forming solution, polysulfone with a weight-average molecular weight of 67-72 kDa is used as the film-forming polymer, and dipyrrolidone is used as the solvent, with a mass ratio of polysulfone to dipyrrolidone of 1:4.

[0107] In some preferred embodiments, when preparing the film-forming solution, polyethersulfone with a weight-average molecular weight of 49-52 kDa is used as the film-forming polymer, glycerol is used as a small molecule non-solvent additive, and N-methylpyrrolidone is used as the solvent. The mass ratio of polyethersulfone to glycerol is 1:0.75, and the mass ratio of polyethersulfone to N-methylpyrrolidone is 1:3.25.

[0108] In some preferred embodiments, when preparing the film-forming solution, polyvinylidene fluoride with a weight-average molecular weight of 200-250 kDa is used as the film-forming polymer, diethylene glycol is used as a small-molecule non-solvent additive, polyvinylpyrrolidone is used as a large-molecule non-solvent additive, and dimethylacetamide is used as the solvent. The mass ratio of polyvinylidene fluoride to diethylene glycol is 1:(0.25-1), for example 1:0.5, the mass ratio of polyvinylidene fluoride to polyvinylpyrrolidone is 1:(0.1-0.5), for example 1:0.25, and the mass ratio of polyvinylidene fluoride to dimethylacetamide is 1:3.25.

[0109] In some preferred embodiments, when preparing the film-forming solution, polyethersulfone with a weight-average molecular weight of 78-84 kDa is used as the film-forming polymer, diethylene glycol is used as a small molecule non-solvent additive, polyvinylpyrrolidone with a weight-average molecular weight of 30 kDa is used as a large molecule non-solvent additive, N-methylpyrrolidone is used as the solvent, the mass ratio of polyethersulfone to diethylene glycol is 1:(0.25-1), for example 1:0.5, the mass ratio of polyethersulfone to polyvinylpyrrolidone is 1:(0.1-0.5), for example 1:0.25, and the mass ratio of polyethersulfone to N-methylpyrrolidone is 1:3.25.

[0110] The present invention has the following beneficial effects:

[0111] 1. By linking the microstructure of polymers with the macroscopic morphology of membranes, the degree of entanglement of polymer coils (i.e., cluster diameter distribution) can be changed by altering the organic solvent of the polymer and / or adding non-solvent additives, thereby achieving scientific control of membrane pore size.

[0112] 2. The ultrafiltration membrane prepared by the method of this invention has a narrow pore size distribution with a standard deviation between 0.1 and 0.8, and a water flux of up to 300 L. -1 m -2 h -1 bar -1 The average orifice diameter is between 5 and 40 nm.

[0113] 3. The method for preparing the high water flux narrow pore size distribution ultrafiltration membrane provided by the present invention is simple and easy to operate, and is suitable for applications with high separation precision such as protein separation, as well as the preparation of nanofiltration and reverse osmosis composite membrane bases, with a wide range of applications.

[0114] The present invention will be described below by way of specific embodiments. It should be understood that these embodiments are merely illustrative and are not intended to limit the scope of the invention. The methods, reagents, and materials used in the embodiments and comparative examples are conventional methods, reagents, and materials in the art, unless otherwise stated. The starting material compounds in the embodiments and comparative examples are all commercially available.

[0115] In this invention, the film-forming solution is diluted to a polymer concentration of 0.1 wt%, and the diameter distribution of polymer aggregates in the solution is measured using dynamic light scattering.

[0116] Test method for pure water flux of ultrafiltration membrane

[0117] The membrane testing apparatus was operated using dead-end filtration. The test water temperature was stabilized at 25.0℃±0.5℃, and the inlet pressure was slowly adjusted to 0.150MPa±0.005MPa for 30 minutes of pre-pressurization. The test pressure was then slowly reduced to 0.100MPa±0.005MPa and stabilized for 10 minutes. A certain volume of filtered water was collected using a graduated cylinder, and the time taken was recorded using a stopwatch. Parallel experiments were conducted following the above steps, testing three membrane samples of the same specifications. The results were taken as the average of the three parallel experiments.

[0118] The pure water flux of the ultrafiltration membrane is calculated using the following formula, and the result is the average of three parallel experiments:

[0119]

[0120] Where P is the pure water transmittance, expressed in liters per square hour (L·m). -2 ·h -1 V represents the pure water permeate flow rate, in liters (L); S represents the effective filtration area of ​​the membrane, in square meters (m²). 2 ); t is the time taken for pure water of volume V to pass through, in hours (h).

[0121] Test method for average orifice diameter

[0122] The average pore diameter of the ultrafiltration membrane was measured using a capillary flow meter. The average pore diameter was defined as the pore size at 50% of the total flow rate, and the unit was nanometers (nm).

[0123] Test methods for pore size and distribution of ultrafiltration membranes

[0124] The molecular weight cutoff was obtained by testing the separation performance of ultrafiltration membranes on mixed solutions of dextran with different molecular weights. The molecular weights of the dextran were 10 kDa, 40 kDa, 70 kDa, and 500 kDa, with corresponding concentrations of 0.25 wt%, 0.10 wt%, 0.15 wt%, and 0.20 wt%. The filtration pressure during the test was 0.1 MPa. The organic matter concentrations in the feed liquid and permeate were determined by gel permeation chromatography. The organic matter rejection rate R was calculated using formula (2):

[0125]

[0126] Among them, C permeance and C feed These are the concentrations of dextran in the filtrate and the feed solution, respectively.

[0127] Furthermore, by plotting the molecular weight of the organic solute on the x-axis and the membrane's retention rate on the y-axis, a curve and corresponding equation were obtained through fitting. The molecular weight corresponding to a 90% retention rate in the fitted curve is the membrane's molecular weight cutoff. Additionally, the molecular weight M corresponding to a 50% retention rate was also calculated. w Substituting into the empirical equation (3) for calculation, the corresponding r is obtained. s That is, the average diameter of the solute, μ s :

[0128] log 10 r s = -1.3363 + 0.395log 10 M w (3) σ g (μ s The geometric standard deviation is given by the two r values ​​corresponding to the cutoff rates of 84.13% and 50%. s The ratio was determined, and the molecular weight M corresponding to the 84.13% retention rate was calculated. w Substituting into the empirical equation (3) for calculation, the corresponding r is obtained. s Divide by μ s That is, σ is obtained g When the spatial and hydrodynamic effects between the solute and pore size are neglected, the median pore size (μ) p ) and geometric standard deviation (σ p ) respectively with μ s and σ gThe same. Therefore, the aperture distribution can be represented by the probability density function (4) of the log-normal distribution. The log-normal distribution refers to the aperture r p The logarithm of follows a normal distribution, i.e., ln(r) p ) follows a mean of ln(μ) p ) and standard deviation is ln(σ) p The normal distribution of ).

[0129]

[0130] The width of the aperture distribution peak is defined by the standard deviation (5) of the log-normal distribution:

[0131]

[0132] like Figure 1 As shown, the standard deviations of the two pore size distribution peaks are 1.00 and 2.00, respectively. This invention defines "narrow pore size distribution ultrafiltration membrane" as an ultrafiltration membrane with a pore size distribution standard deviation between 0.1 and 1.0, preferably between 0.1 and 0.8.

[0133] Example 1

[0134] Preparation of film-forming solution: Dissolve 20g of polysulfone (film-forming polymer, 67-72kDa) in 80g of dipyrrolidone (solvent) under thorough stirring at 60℃. After the polymer is completely dissolved, filter through a stainless steel wire mesh with a pore size of 40 microns, and allow to stand in a 30℃ oven to remove bubbles before using as the film-forming solution.

[0135] The viscosity of the film-forming solution at room temperature was 14275 centipoise. The film-forming solution was diluted to a polymer concentration of 0.1 wt%, and the diameter distribution of the polymer aggregates in the solution was measured to be 90-450 nm using dynamic light scattering.

[0136] The film-forming solution was scraped onto the nonwoven fabric using an automatic film-forming machine at an ambient temperature of 25°C and a relative humidity of 30%. The thickness of the film-forming solution coated on the nonwoven fabric was 200 micrometers. Then, the initial flat sheet membrane was immersed in a coagulation bath for 3 minutes within 3 seconds to separate the phases and obtain a polymer flat sheet membrane.

[0137] The membrane thickness was measured to be 0.63 mm, and the pure water flux was 323 L. -1 m -2 h -1 bar -1 The average pore diameter of the membrane is 10 nm, and the standard deviation of the pore size distribution is 0.76.

[0138] The membrane obtained in this embodiment was subjected to a protein retention test. The test procedure was as follows: 100 ppm bovine serum albumin solution was filtered through the obtained membrane for 30 minutes, and the water flux during the filtration process was tested. The test temperature was stabilized at 25.0℃ ± 0.5℃, the test pressure was stabilized at 0.100 MPa ± 0.005 MPa, and the water flux of the membrane was 226 L. -1 m -2 h -1 bar -1 The retention rate of bovine serum albumin was 92%.

[0139] Comparative Example 1

[0140] The solvent in the formulation of Example 1 was replaced with dimethylacetamide, while the polymer mass and solvent mass remained unchanged. The mixture was stirred thoroughly at 60°C until homogeneous. After the polymer was completely dissolved, it was filtered through a stainless steel wire mesh with a pore size of 40 micrometers and allowed to stand in a 30°C oven to remove bubbles, thus becoming the film-forming solution.

[0141] The film-forming solution was scraped onto the nonwoven fabric using an automatic film-forming machine at an ambient temperature of 25°C and a relative humidity of 50%. The thickness of the film-forming solution coated on the nonwoven fabric was 200 micrometers. Then, the initial flat sheet membrane was immersed in a coagulation bath for 2 minutes within 3 seconds to separate the phases and obtain a polymer flat sheet membrane.

[0142] The viscosity of the film-forming solution was 192 centipoise. The film-forming solution was diluted to a polymer concentration of 0.1 wt%. The diameter distribution of the polymer aggregates in the solution was measured to be 8-22 nm using dynamic light scattering.

[0143] The membrane thickness was measured to be 0.65 mm, and the pure water flux was 158 L. -1 m -2 h -1 bar -1 The average pore diameter of the membrane is 23 nm, and the standard deviation of the pore size distribution is 0.84.

[0144] The membrane obtained in this comparative example was used for a protein retention test. The procedure was as follows: 100 ppm bovine serum albumin solution was filtered through the obtained membrane for 30 minutes, and the water flux during the filtration process was measured. The test temperature was stabilized at 25.0℃ ± 0.5℃, the test pressure was stabilized at 0.100 MPa ± 0.005 MPa, and the membrane water flux was 10³ L. -1 m -2 h -1 bar -1 The retention rate of bovine serum albumin was 79%.

[0145] Comparative Example 2

[0146] The solvent in the formulation of Example 1 was changed to N-methylpyrrolidone, while the polymer mass and solvent mass remained unchanged. The mixture was stirred thoroughly at 60°C until homogeneous. After the polymer was completely dissolved, it was filtered through a stainless steel wire mesh with a pore size of 40 micrometers and allowed to stand in a 30°C oven to remove bubbles, which was then used as the film-forming solution.

[0147] The film-forming solution was scraped onto the nonwoven fabric using an automatic film-forming machine at an ambient temperature of 25°C and a relative humidity of 50%. The thickness of the film-forming solution coated on the nonwoven fabric was 200 micrometers. Then, the initial flat sheet membrane was immersed in a coagulation bath for 2 minutes within 3 seconds to separate the phases and obtain a polymer flat sheet membrane.

[0148] The viscosity of the film-forming solution was 154 centipoise. The film-forming solution was diluted to a polymer concentration of 0.1 wt%. The diameter distribution of the polymer aggregates in the solution was measured to be 10-25 nm using dynamic light scattering.

[0149] The membrane thickness was measured to be 0.59 mm, and the pure water flux was 124 L. -1 m -2 h -1 bar -1 The average pore diameter of the membrane is 25 nm, and the standard deviation of the pore size distribution is 0.9.

[0150] The membrane obtained in this comparative example was subjected to a protein retention test. The procedure was as follows: 100 ppm bovine serum albumin solution was filtered through the obtained membrane for 30 minutes, and the water flux during the filtration process was measured. The test temperature was stabilized at 25.0℃ ± 0.5℃, the test pressure was stabilized at 0.100 MPa ± 0.005 MPa, and the membrane water flux was 86 L. -1 m -2 h -1 bar -1 The retention rate of bovine serum albumin was 75%.

[0151] Example 2

[0152] Preparation of the film-forming solution: 20g of polyethersulfone (film-forming polymer, 49-52kDa), 15g of glycerol (small molecule non-solvent additive), dissolved in 65g of N-methylpyrrolidone (solvent) under thorough stirring at 60℃. After the polymer is completely dissolved, filter through a stainless steel wire mesh with a pore size of 40 microns, and allow to stand in a 50℃ oven to remove bubbles, then use as the film-forming solution.

[0153] The film-forming solution was scraped onto the nonwoven fabric using an automatic film-forming machine. The ambient temperature was 30°C and the relative humidity was 50%. The thickness of the film-forming solution coated on the nonwoven fabric was 200 micrometers. Then, the initial flat sheet membrane was immersed in a coagulation bath for 3 seconds to separate the phases for 3 minutes, thus obtaining a polymer flat sheet membrane.

[0154] The viscosity of the film-forming solution was 1328 centipoise. The film-forming solution was diluted to a polymer concentration of 0.1 wt%. The diameter distribution of the polymer aggregates in the solution was measured to be 58-96 nm using dynamic light scattering.

[0155] The membrane thickness was measured to be 0.65 mm, and the pure water flux was 460 L. -1 m -2 h -1 bar -1 The average pore diameter of the membrane is 15 nm, and the standard deviation of the pore size distribution is 0.67.

[0156] The membrane obtained in this embodiment was subjected to a protein retention test. The test procedure was as follows: 100 ppm bovine serum albumin solution was filtered through the obtained membrane for 30 minutes, and the water flux during the filtration process was tested. The test temperature was stabilized at 25.0℃ ± 0.5℃, the test pressure was stabilized at 0.100 MPa ± 0.005 MPa, and the membrane water flux was 375 L. -1 m -2 h -1 bar -1 The retention rate of bovine serum albumin was 90%.

[0157] Comparative Example 3

[0158] In Example 2, the small-molecule non-solvent additive glycerol was replaced with an equal mass of the solvent N-methylpyrrolidone, while keeping the polymer mass and the original solvent mass unchanged. The mixture was thoroughly stirred at 60°C until homogeneous. After the polymer was completely dissolved, it was filtered through a stainless steel wire mesh with a 40-micron pore size and allowed to stand in a 30°C oven to remove bubbles, thus becoming the film-forming solution.

[0159] The film-forming solution was scraped onto the nonwoven fabric using an automatic film-forming machine. The ambient temperature was 30°C and the relative humidity was 50%. The thickness of the film-forming solution coated on the nonwoven fabric was 200 micrometers. Then, the initial flat sheet membrane was immersed in a coagulation bath for 3 seconds to separate the phases for 3 minutes, thus obtaining a polymer flat sheet membrane.

[0160] The viscosity of the film-forming solution was 207 centipoise. The film-forming solution was diluted to a polymer concentration of 0.1 wt%. The diameter distribution of the polymer aggregates in the solution was measured to be 14-25 nm using dynamic light scattering.

[0161] The membrane thickness was measured to be 0.62 mm, and the pure water flux was 179 L. -1 m -2 h -1 bar -1 The average pore diameter of the membrane is 29 nm, and the standard deviation of the pore size distribution is 1.37.

[0162] The membrane obtained in this comparative example was subjected to a protein retention test. The procedure was as follows: 100 ppm bovine serum albumin solution was filtered through the obtained membrane for 30 minutes, and the water flux during the filtration process was measured. The test temperature was stabilized at 25.0℃ ± 0.5℃, the test pressure was stabilized at 0.100 MPa ± 0.005 MPa, and the membrane water flux was 126 L. -1 m -2 h -1 bar -1 The retention rate of bovine serum albumin was 64%.

[0163] Example 3

[0164] Preparation of the film-forming solution: 20g of polyvinylidene fluoride (film-forming polymer, 200-250kDa), 10g of diethylene glycol (small molecule non-solvent additive), and 5g of polyvinylpyrrolidone (large molecule non-solvent additive) are dissolved in 65g of dimethylacetamide (solvent) under thorough stirring at 60℃. After the polymer is completely dissolved, the solution is filtered through a stainless steel wire mesh with a pore size of 40 micrometers and allowed to stand in a 50℃ oven to remove bubbles, thus obtaining the film-forming solution.

[0165] The film-forming solution was scraped onto the nonwoven fabric using an automatic film-forming machine. The ambient temperature was 30°C and the relative humidity was 40%. The thickness of the film-forming solution coated on the nonwoven fabric was 200 micrometers. Then, the initial flat sheet membrane was immersed in a coagulation bath for 3 minutes within 3 seconds to separate the phases and obtain a polymer flat sheet membrane.

[0166] The viscosity of the film-forming solution was 5267 centipoise. The film-forming solution was diluted to a polymer concentration of 0.1 wt%. The diameter distribution of the polymer aggregates in the solution was measured to be 72-205 nm using dynamic light scattering.

[0167] The membrane thickness was measured to be 0.63 mm, and the pure water flux was 590 L. -1 m -2 h -1 bar -1 The average pore diameter of the membrane is 13 nm, and the standard deviation of the pore size distribution is 0.79.

[0168] The membrane obtained in this embodiment was subjected to a protein retention test. The test procedure was as follows: 100 ppm bovine serum albumin solution was filtered through the obtained membrane for 30 minutes, and the water flux during the filtration process was tested. The test temperature was stabilized at 25.0℃ ± 0.5℃, the test pressure was stabilized at 0.100 MPa ± 0.005 MPa, and the membrane water flux was 447 L. -1 m -2 h -1 bar -1 The retention rate of bovine serum albumin was 90%.

[0169] Comparative Example 4

[0170] In Example 3, the macromolecular non-solvent additive polyvinylpyrrolidone was replaced with an equal mass of dimethylacetamide, and 5g of the small-molecule non-solvent additive diethylene glycol was replaced with an equal mass of dimethylacetamide. The mass of the film-forming polymer and the original solvent remained unchanged. The mixture was thoroughly stirred at 60°C until homogeneous. After the polymer was completely dissolved, it was filtered through a stainless steel wire mesh with a 40-micron pore size and allowed to stand in a 50°C oven to remove bubbles, thus obtaining the film-forming solution.

[0171] The film-forming solution was scraped onto the nonwoven fabric using an automatic film-forming machine. The ambient temperature was 30°C and the relative humidity was 40%. The thickness of the film-forming solution coated on the nonwoven fabric was 200 micrometers. Then, the initial flat sheet membrane was immersed in a coagulation bath for 3 minutes within 3 seconds to separate the phases and obtain a polymer flat sheet membrane.

[0172] The viscosity of the film-forming solution was 415 centipoise. The film-forming solution was diluted to a polymer concentration of 0.1 wt%. The diameter distribution of the polymer aggregates in the solution was measured to be 43-78 nm using dynamic light scattering.

[0173] The membrane thickness was measured to be 0.64 mm, and the pure water flux was 340 L. -1 m -2 h -1 bar -1 The average pore diameter of the membrane is 28 nm, and the standard deviation of the pore size distribution is 1.67.

[0174] The membrane obtained in this comparative example was subjected to a protein retention test. The procedure was as follows: 100 ppm bovine serum albumin solution was filtered through the obtained membrane for 30 minutes, and the water flux during the filtration process was measured. The test temperature was stabilized at 25.0℃ ± 0.5℃, the test pressure was stabilized at 0.100 MPa ± 0.005 MPa, and the membrane water flux was 253 L. -1 m -2 h -1 bar -1 The retention rate of bovine serum albumin was 73%.

[0175] Example 4

[0176] Preparation of the film-forming solution: 20g of polyethersulfone (film-forming polymer, 78-84kDa), 10g of diethylene glycol (small molecule non-solvent additive), and 5g of polyvinylpyrrolidone (large molecule non-solvent additive, weight average molecular weight 30kDa) are dissolved in 65g of N-methylpyrrolidone (solvent) under thorough stirring at 60℃. After the polymer is completely dissolved, the solution is filtered through a stainless steel wire mesh with a pore size of 40 micrometers and allowed to stand in a 50℃ oven to remove bubbles, thus obtaining the film-forming solution.

[0177] Hollow fiber membrane fibers were spun using a hollow fiber spinning device. The core liquid was a mixed solution of water and N-methylpyrrolidone (solvent) with a solvent-to-water mass ratio of 1:3. The membrane-forming liquid was extruded from the spinneret and then immersed in a 40°C gel bath after passing through an air section with a height of 10 cm. After 3 seconds in the air section, the membrane entered the gel bath and was completely separated into phases after 3 minutes. The membrane was then collected by winding the fibers together to obtain the hollow fiber membrane.

[0178] The viscosity of the film-forming solution was 5739 centipoise. The film-forming solution was diluted to a polymer concentration of 0.1 wt%. The diameter distribution of the polymer aggregates in the solution was measured to be 78-266 nm using dynamic light scattering.

[0179] The hollow fiber membrane was measured to have an inner diameter of 0.90 mm, an outer diameter of 1.33 mm, a wall thickness of 0.21 mm, and a pure water flux of 497 L. -1 m -2 h -1 bar -1 The average pore diameter of the membrane is 8 nm, and the standard deviation of the pore size distribution is 0.69.

[0180] The membrane obtained in this embodiment was subjected to a protein retention test. The test procedure was as follows: 100 ppm bovine serum albumin solution was filtered through the obtained membrane for 30 minutes, and the water flux during the filtration process was tested. The test temperature was stabilized at 25.0℃ ± 0.5℃, the test pressure was stabilized at 0.100 MPa ± 0.005 MPa, and the membrane water flux was 438 L. -1 m -2 h -1 bar -1 The retention rate of bovine serum albumin was 96%.

[0181] The filtration performance of the flat sheet ultrafiltration membranes and hollow fiber membranes prepared in the examples and comparative examples is listed in Table 1.

[0182] Table 1. Properties of ultrafiltration membranes and hollow fiber membranes prepared in the examples and comparative examples.

[0183]

[0184] The difference between Example 1 and Comparative Examples 1-2 lies in the use of different solvents. Example 1 uses dipyrrolidone, which has a viscosity of 13.3 centipoise, higher than the two solvents in Comparative Examples 1 and 2 (dimethylacetamide: 0.92 centipoise, N-methylpyrrolidone: 1.65 centipoise). Furthermore, the amide groups of dipyrrolidone form hydrogen bonds with the sulfonyl groups on the polyethersulfone molecular chain, and hydrogen bonds also form between dipyrrolidone molecules. Therefore, the viscosity of the membrane-forming solution in Example 1 (14275 centipoise) is greater than that of the membrane-forming solutions in Comparative Examples 1 and 2 (192 centipoise, 154 centipoise, respectively). The diameter distribution of the polymer aggregates in Example 1 is 90-450 nm, also greater than the diameter distributions in Comparative Examples 1 and 2 (8-22 nm and 10-25 nm, respectively). Ultimately, the flat-sheet ultrafiltration membrane prepared in Example 1 has interwoven channels and a rich pore structure, with a pure water flux of 323 L. -1 m -2 h -1 bar -1 This is far higher than the pure water flux (158L) of Comparative Examples 1 and 2. -1 m -2 h -1 bar -1 and 124L -1 m -2 h -1 bar -1 )

[0185] Compared to Comparative Example 3, Example 2 added glycerol, a small molecule non-solvent additive, which reduced the solvent content. As a result, the solubility of polyethersulfone in the membrane-forming solution was reduced, making the viscosity of the membrane-forming solution in Example 2 higher than that in Comparative Example 3. The diameter distribution of polymer agglomerates in the membrane-forming solution of Example 2 was also larger (58-96 nm), resulting in higher connectivity between membrane pores and higher pure water flux.

[0186] Compared to Comparative Example 4, Example 3 added an appropriate amount of non-solvent additives and reduced the amount of solvent, thus lowering the solubility of the film-forming polymer. Therefore, the polymer aggregate diameter distribution and viscosity in the membrane-forming solution of Example 3 were greater than those of Comparative Example 4. The standard deviation of the flat-sheet ultrafiltration membrane prepared in Example 3 was 0.79, exhibiting a narrow pore size distribution, significantly lower than the standard deviation of 1.67 of the flat-sheet ultrafiltration membrane in Comparative Example 4. Therefore, the flat-sheet ultrafiltration membrane of Example 3 had uniform pore size and a pure water flux of 590 L. -1 m -2 h -1 bar -1 It significantly outperforms the ultrafiltration performance of Comparative Example 4 (340L). -1 m -2 h -1 bar -1 ).

[0187] The membrane-forming solution in Example 4 had a viscosity of 5739 centipoise, and the diameter distribution of the polymer aggregates in the solution ranged from 78 to 266 nm. The resulting hollow fiber membrane had a narrow pore size distribution with a standard deviation of 0.69. Therefore, the hollow fiber membrane exhibited a high pure water flux of 497 L / min. -1 m -2 h -1 bar -1 The average pore diameter of the membrane is 8 nm.

Claims

1. A method for preparing an ultrafiltration membrane, characterized in that, The ultrafiltration membrane includes a flat sheet ultrafiltration membrane and a hollow fiber membrane, and the preparation method includes the following steps: (1) The film-forming polymer, solvent and optional non-solvent additives are mixed evenly to prepare a film-forming solution. The diameter of the polymer agglomerates in the film-forming solution is distributed between 50-500 nm, and the viscosity of the film-forming solution at 25°C is between 500-20000 centipoise. (2) Pour the film-forming solution prepared in step (1) onto the carrier and coat it to obtain the initial flat sheet membrane; or The membrane-forming solution prepared in step (1) is extruded through the outer cavity of the coaxial spinneret to form a membrane, while the core liquid is extruded through the inner cavity of the coaxial spinneret to obtain an initial hollow fiber membrane. (3) Quickly immerse the initial flat sheet membrane or initial hollow fiber membrane obtained in step (2) into a gel bath for curing; (4) Rinse the solidified flat sheet ultrafiltration membrane or hollow fiber membrane from step (3) to remove solvent and non-solvent, and soak and dry it in glycerol to obtain the final flat sheet ultrafiltration membrane or hollow fiber membrane.

2. The preparation method according to claim 1, characterized in that, The ultrafiltration membrane has one or more of the following characteristics: The standard deviation of the pore size distribution of the ultrafiltration membrane is between 0.1 and 1.0, preferably between 0.1 and 0.8; The ultrafiltration membrane has a pure water flux ≥ 300 L·m -2 ·h -1 ·bar -1 ; The average pore diameter of the ultrafiltration membrane is between 5 and 40 nm.

3. The preparation method according to claim 1, characterized in that, The preparation method has one or more of the following characteristics: In step (1), the mass ratio of the film-forming polymer to the solvent is 1:(2-5); In step (1), a non-solvent additive is added, and the mass ratio of the film-forming polymer to the non-solvent additive is 1:(0.05-1.5), preferably 1:(0.1-1); In step (1), heating is carried out during the mixing process, and the heating temperature is 25℃-80℃; In step (1), the film-forming polymer is selected from one or more of polysulfone, polyethersulfone and polyvinylidene fluoride; preferably, the weight-average molecular weight of the polysulfone is 40-100 kDa, the weight-average molecular weight of the polyethersulfone is 40-100 kDa, and the weight-average molecular weight of the polyvinylidene fluoride is 100-1000 kDa. In step (1), the solvent is selected from one or more of N-methylpyrrolidone, dipyrrolidone, dimethylformamide, dimethylacetamide, dimethyl sulfoxide and triethyl phosphate.

4. The preparation method according to claim 1, characterized in that, The non-solvent additive is selected from one or more of small molecule non-solvent additives and macromolecule non-solvent additives; Preferably, the non-solvent additive is a small molecule non-solvent additive, or a combination of a small molecule non-solvent additive and a macromolecule non-solvent additive, preferably in a mass ratio of 1:(0.05-1). Preferably, the small molecule non-solvent additive is selected from one or more of water, ethylene glycol, diethylene glycol, polyethylene glycol, and glycerol; Preferably, the weight-average molecular weight of the small molecule non-solvent additive is 18-7000 Da; Preferably, the weight-average molecular weight of polyethylene glycol is 200-7000 Da, and more preferably 200-1000 Da; Preferably, the macromolecular nonsolvent additive is polyvinylpyrrolidone, and the weight-average molecular weight of polyvinylpyrrolidone is 10-100 kDa, preferably 30±10 kDa.

5. The preparation method according to claim 1, characterized in that, In step (1), the mass fraction of the film-forming polymer in the film-forming solution is 10 wt%-30 wt.%; and / or In step (1), the mass ratio of the non-solvent additive to the solvent in the film-forming solution is (0-1):

1.

6. The preparation method according to claim 1, characterized in that, In step (2), the carrier is a non-woven fabric, the thickness of the film-forming liquid coated on the carrier is 150-300μm, the ambient temperature for scraping the initial flat film is 20℃-35℃, and the ambient relative humidity is 20%-80%, preferably 30%-60%. In step (2), the core liquid introduced into the inner cavity of the coaxial spinneret during the preparation of the initial hollow fiber membrane is a mixture of water and solvent. The solvent is preferably selected from one or more of N-methylpyrrolidone, dipyrrolidone, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, and triethyl phosphate. The mass ratio of solvent to water in the core liquid is preferably 1:(1-9). Before entering the gel bath, the initial hollow fiber membrane passes through an air section. The temperature of the air section is 20℃-60℃, the relative humidity of the air section is 40%-100%, and the height of the air section is preferably 5-30cm.

7. The preparation method according to claim 1, characterized in that, In step (3), the initial flat sheet membrane or initial hollow fiber membrane obtained in step (2) is immersed in the gel bath and rapidly solidified. The time interval between the preparation of the initial flat sheet membrane or initial hollow fiber membrane and its entry into the gel bath is ≤5 seconds.

8. The preparation method according to claim 1, characterized in that, In step (3), the medium of the gel bath is water or a mixture of water and solvent. The solvent is preferably selected from one or more of N-methylpyrrolidone, dipyrrolidone, dimethylformamide, dimethylacetamide, dimethyl sulfoxide and triethyl phosphate. When the medium of the gel bath is a mixture of water and solvent, the solvent accounts for ≤80wt% of the mixture by mass, for example 1wt%-80wt%, and preferably ≤50wt% of the mixture by mass, for example 1wt%-50wt%. The temperature of the gel bath is 10℃-95℃, preferably 20℃-80℃; The phase transition time of the flat sheet membrane or hollow fiber membrane in the gel bath is 1-20 min.

9. The preparation method according to claim 1, characterized in that, The preparation method includes: In the film-forming solution, polysulfone with a weight-average molecular weight of 67-72 kDa is used as the film-forming polymer, and dipyrrolidone is used as the solvent. The mass ratio of polysulfone to dipyrrolidone is 1:(3-5), for example, 1:4; or In the film-forming solution, polyethersulfone with a weight-average molecular weight of 49-52 kDa is used as the film-forming polymer, glycerol is used as a small-molecule non-solvent additive, and N-methylpyrrolidone is used as the solvent. The mass ratio of polyethersulfone to glycerol is 1:(0.5-1), for example 1:0.75, and the mass ratio of polyethersulfone to N-methylpyrrolidone is 1:(2.5-4), for example 1:3.25; or In the film-forming solution, polyvinylidene fluoride (PVDF) with a weight-average molecular weight of 200-250 kDa is used as the film-forming polymer, diethylene glycol is used as a small-molecule non-solvent additive, polyvinylpyrrolidone (PVP) is used as a large-molecule non-solvent additive, and dimethylacetamide is used as the solvent. The mass ratio of PVDF to diethylene glycol is 1:(0.25-1), for example 1:0.5; the mass ratio of PVDF to PPV is 1:(0.1-0.5), for example 1:0.25; and the mass ratio of PVDF to dimethylacetamide is 1:(2.5-4), for example 1:3.25; or In the film-forming solution, polyethersulfone with a weight-average molecular weight of 78-84 kDa is used as the film-forming polymer, diethylene glycol is used as a small molecule non-solvent additive, polyvinylpyrrolidone with a weight-average molecular weight of 30 kDa is used as a large molecule non-solvent additive, and N-methylpyrrolidone is used as the solvent. The mass ratio of polyethersulfone to diethylene glycol is 1:(0.25-1), for example 1:0.5; the mass ratio of polyethersulfone to polyvinylpyrrolidone is 1:(0.1-0.5), for example 1:0.25; and the mass ratio of polyethersulfone to N-methylpyrrolidone is 1:(2.5-4), for example 1:3.

25.

10. An ultrafiltration membrane prepared by any one of claims 1-9.

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