Hollow ultrafiltration membrane, preparation method and application thereof

Abstract

The application provides a hollow ultrafiltration membrane, a preparation method and application thereof, and the preparation method provided by the application adopts a non-water-soluble ether compound as an opening agent, in a non-solvent induced phase separation (NIPS) process, the casting solution is extruded and then enters a coagulation bath to perform phase separation, the ether compound cannot transfer with water and migrates and stays on the membrane surface and inside, the ether compound is dissolved out through post-treatment, and a hollow fiber ultrafiltration membrane with a composite structure of a sponge body structure in the inside and nano-level openings on the inner and outer surfaces is prepared. In an actual filtration process, the nano-level opening channels on the membrane surface and the sponge body structure in the inside are used to intercept pollutants for multiple times, and the use requirements of high pure water flux and high interception efficiency are met. The obtained hollow ultrafiltration membrane has a rejection rate of not less than 99% for 50nm silicon dioxide particles, and a pure water flux of not less than 600 L / (m2*h*bar) (25 DEG C). The hollow ultrafiltration membrane can provide efficient and stable terminal filtration guarantee for an ultrapure water system.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, and in particular to a hollow fiber ultrafiltration membrane, its preparation method, and its application. Background Technology

[0002] Ultrapure water refers to high-purity water with a resistivity of 18.2 MΩ·cm (25℃), and it is widely used in electronics, semiconductors, pharmaceuticals, and chemicals. In the ultrapure water preparation process, terminal filtration is a crucial step to ensure water quality meets standards. The terminal ultrafiltration membrane, as the core component of terminal filtration, effectively removes micron-sized and even nano-sized particles, colloids, and other impurities from the water, ensuring the purity of the ultrapure water. Therefore, it is required to have a high retention efficiency for minute substances. Simultaneously, during system operation, the ultrafiltration membrane itself needs to have very low impurity content and extremely low soluble substance precipitation to ensure the system meets the stringent water production requirements.

[0003] Most existing terminal ultrafiltration membranes that meet retention requirements have a combination structure of a dense surface layer and internal finger-like pores. This results in relatively low water flux. Therefore, how to overcome the low flux of terminal ultrafiltration membranes while achieving high impurity retention and preventing the precipitation of organic matter is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0004] To address the aforementioned problems in the existing technology, this invention provides a hollow fiber ultrafiltration membrane, its preparation method, and its application, in order to meet the multiple requirements of high water flux, high particulate matter retention efficiency, and low precipitates for terminal ultrafiltration membranes as the core component of terminal filtration.

[0005] The specific details of the invention are as follows:

[0006] In a first aspect, the present invention provides a method for preparing a hollow fiber ultrafiltration membrane, the method comprising:

[0007] Polysulfone resin and pore-opening agent are dissolved in an organic solvent and stirred at a constant temperature until a homogeneous casting solution is formed;

[0008] The casting solution and the core solution are extruded together into a coagulation bath through a dual-channel spinneret. The casting solution is then solidified by non-solvent phase separation to form a membrane precursor.

[0009] The membrane precursor is soaked in ethanol solution and washed with ultrapure water to obtain the hollow fiber ultrafiltration membrane;

[0010] The pore-opening agent is selected from one or more of n-pentyl ether, isopyramyl ether, or dibutyl ether;

[0011] By weight, the homogeneous casting solution contains 15-25 parts of polysulfone resin, 3-10 parts of pore-opening agent, and 55-80 parts of organic solvent.

[0012] Optionally, the organic solvent is selected from one or more of dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

[0013] Optionally, the core fluid is a mixture of water and the organic solvent in a volume ratio of 19:1 to 4:1.

[0014] Optionally, the composition of the coagulation bath is the same as that of the core liquid, and the temperature of the coagulation bath is 25-60 ℃.

[0015] Optionally, the polysulfone resin includes one or more of polysulfone resin, polyethersulfone resin, sulfonated polysulfone resin, and sulfonated polyethersulfone resin; the number average molecular weight of the polysulfone resin is 60,000 to 120,000.

[0016] Optionally, the step of extruding the casting solution and the core solution together into the coagulation bath through a dual-channel spinneret includes: the length of the casting solution exposed to air after extrusion is 1-15 cm, and the time for phase separation of the casting solution in the coagulation bath is 5-20 s.

[0017] Optionally, the concentration of ethanol is not less than 95%, and the soaking time is 2-6 hours.

[0018] In a second aspect, the present invention provides a hollow fiber ultrafiltration membrane, wherein the hollow fiber ultrafiltration membrane is obtained by the preparation method described in the first aspect above;

[0019] The hollow ultrafiltration membrane has nanopores distributed on its inner and outer surfaces, and the pore size of the nanopores is 20-50 nm.

[0020] The porosity of the outer surface of the hollow fiber ultrafiltration membrane is 18-24%.

[0021] Thirdly, the present invention provides an application of a hollow fiber ultrafiltration membrane, wherein the hollow fiber ultrafiltration membrane is obtained by the preparation method described in the first aspect above, and the hollow fiber ultrafiltration membrane is used as a membrane material for terminal ultrafiltration of ultrapure water.

[0022] Optionally, the pure water flux of the hollow fiber ultrafiltration membrane is not less than 600 L / (㎡•h•bar);

[0023] The hollow fiber ultrafiltration membrane has a rejection efficiency of no less than 99% for 50nm silica particles.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] This invention provides a method for preparing a hollow fiber ultrafiltration membrane. The method includes: dissolving a polysulfone resin and a pore-opening agent in an organic solvent, and stirring at a constant temperature to form a homogeneous casting solution; extruding the casting solution and core solution together through a dual-channel spinneret into a coagulation bath, whereby the casting solution solidifies to form a membrane precursor; and immersing the membrane precursor in an ethanol solution and washing with ultrapure water to obtain the hollow fiber ultrafiltration membrane. The pore-opening agent is selected from one or more of n-pentyl ether, isoprene ether, or dibutyl ether. By weight, the homogeneous casting solution contains 15-25 parts of polysulfone resin, 3-10 parts of the pore-opening agent, and 55-80 parts of the organic solvent.

[0026] In the preparation method provided by this invention, a non-water-soluble ether compound is used as an opening agent. During non-solvent-induced phase separation (NIPS), the casting solution, after extrusion, enters a coagulation bath (non-solvent) for phase separation. Because the ether compound cannot transfer mass with water, it migrates and remains on the outer side of the membrane. After post-treatment, the ether compound is dissolved, resulting in a composite hollow fiber ultrafiltration membrane with nanoscale openings on both the inner and outer surfaces and a sponge-like internal structure. The surface porosity of the obtained hollow fiber ultrafiltration membrane is 18-24%. In actual filtration, the nanoscale openings on the membrane surface and the internal sponge structure effectively trap pollutants multiple times, meeting the requirements for high-purity water flux and high retention efficiency. The obtained hollow fiber ultrafiltration membrane has a retention rate of no less than 99% for 50nm silica particles and a pure water flux of no less than 600 L / (㎡•h•bar) (25℃). It can provide efficient and stable terminal filtration for ultrapure water systems.

[0027] Furthermore, the ether compounds selected in this invention, as pore-opening agents, can significantly improve the pure water flux of the membrane at an addition level of 3-10%. The molecular weight of the ether compounds used in this invention is much smaller than that of traditional pore-opening agents, allowing for rapid dissolution during ethanol cleaning. Subsequent ultrapure water efficiently removes residual solvent molecules, resulting in a pure ultrafiltration membrane. Traditional pore-opening agents, on the other hand, require an addition level of over 8%, and their larger molecular weight and chain-like molecular structure necessitate longer cleaning times and larger rinsing water volumes. Therefore, this invention offers significant economic and efficiency advantages. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1A flowchart illustrating the preparation method of the hollow fiber ultrafiltration membrane provided in an embodiment of the present invention is shown;

[0030] Figure 2 A cross-sectional structural diagram of the hollow fiber ultrafiltration membrane provided in Embodiment 1 of the present invention is shown;

[0031] Figure 3 A structural diagram of the surface of the hollow fiber ultrafiltration membrane provided in Embodiment 1 of the present invention is shown;

[0032] Figure 4 This diagram illustrates the calculation of the porosity of the outer surface of the hollow fiber ultrafiltration membrane provided in Embodiment 1 of the present invention.

[0033] Figure 5 A cross-sectional structural diagram of the hollow fiber ultrafiltration membrane provided in Comparative Example 1 of the present invention is shown.

[0034] Figure 6 A structural diagram of the hollow fiber ultrafiltration membrane surface provided in Comparative Example 1 of the present invention is shown;

[0035] Figure 7 The diagram showing the calculation of the porosity of the hollow fiber ultrafiltration membrane on the outer surface provided in Comparative Example 1 of the present invention is illustrated.

[0036] Figure 8 A cross-sectional structural diagram of the hollow fiber ultrafiltration membrane provided in Comparative Example 2 of the present invention is shown;

[0037] Figure 9 A structural diagram of the hollow fiber ultrafiltration membrane surface provided in Comparative Example 2 of the present invention is shown;

[0038] Figure 10 A diagram showing the calculation of the porosity of the outer surface of the hollow ultrafiltration membrane provided in Comparative Example 2 of the present invention is shown. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, any product identical or similar to the present invention derived by anyone under the guidance of the present invention or by combining the features of the present invention with other prior art falls within the protection scope of the present invention. Furthermore, all other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of the present invention.

[0040] Specific experimental steps or conditions are not specified in the embodiments; they can be performed according to the conventional experimental steps or conditions described in the prior art. Reagents and other instruments used, unless otherwise specified, are all commercially available conventional reagent products. Furthermore, the accompanying drawings are merely illustrative diagrams of the embodiments of the present invention and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore, repeated descriptions of them will be omitted. Some block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0041] Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of this specification.

[0042] In the description of this invention, it should be understood that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0043] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0044] Before providing a detailed description of the hollow fiber ultrafiltration membrane, its preparation method, and its applications provided by this invention, it is necessary to explain the relevant technologies as follows:

[0045] Patent application CN202311539734.2 describes a polysulfone terminal ultrafiltration membrane with a highly dense inner and outer surface to ensure the precision of terminal filtration. The membrane has a small number of pores with diameters between 1-50 nm, and the hollow fiber membrane has a finger-like pore structure. While this structure ensures a high rejection rate, the pure water flux is approximately 360 L / (m²·h·bar), lower than the 400-800 L / (m²·h·bar) of ordinary ultrafiltration. If wear defects occur in the surface separation layer during later operation, the rejection effect will decrease. Increasing the surface porosity to improve filtration flux is a common technique. Patent CN201610125548.8 utilizes a polysulfone-polyethylene glycol block copolymer as an opening agent to promote pore formation, solving the problem of hydrophilic opening agent loss and giving the membrane permanent hydrophilicity. This results in higher membrane flux, flux recovery rate, and better stability. However, this method may leave unreacted polyethylene glycol residue inside or on the surface of the membrane, making it more difficult to clean completely. This increases the difficulty of on-site cleaning during actual use and may even prevent its application in ultrapure water environments.

[0046] Based on this, through experimental exploration, this invention discovered a class of ether-based pore-opening agents more suitable for the preparation of ultrafiltration membranes using non-solvent-induced phase separation. Using polysulfone resin as the membrane-forming host, hollow fiber ultrafiltration membranes are prepared, exhibiting advantages such as low pore-opening agent dosage, low residue, and easy cleaning. Furthermore, the resulting hollow fiber ultrafiltration membranes possess both high water flux and high particulate matter retention efficiency. Specific implementation details are as follows:

[0047] In a first aspect, the present invention provides a method for preparing a hollow fiber ultrafiltration membrane. Figure 1 A flowchart illustrating the preparation method of the hollow fiber ultrafiltration membrane provided in an embodiment of the present invention is shown, as follows: Figure 1 As shown, the method includes:

[0048] S1. Dissolve polysulfone resin and pore-opening agent in an organic solvent and stir at a constant temperature until a homogeneous casting solution is formed;

[0049] In practice, polysulfone resin, as the main film-forming agent, is dissolved together with the pore-opening agent in an organic solvent to form a homogeneous solution. During the dissolution process, the stirring speed is controlled at 100-1000 rpm, and the dissolution temperature is preferably 60-100℃, with 80-90℃ being the most desirable. Stirring continues until the polysulfone resin and the pore-opening agent are completely dissolved, forming a homogeneous and transparent solution.

[0050] In specific implementation, polysulfone resins are hydrophobic polymers that preferentially form a solid enriched phase during phase separation in a coagulation bath composed of solvent and non-solvent components. This invention uses ether compounds as pore-opening agents. These ether compounds are water-insoluble and migrate and remain on the membrane surface and inside the membrane during subsequent phase separation because they cannot transfer mass with water. After post-treatment to dissolve the ether compounds, channels are formed on the membrane surface, and a multi-layered filtration sponge structure is formed inside the membrane. The organic solvent used in this invention is a good solvent for both the polysulfone resin and the pore-opening agent, maintaining their dissolved state. Furthermore, the selected organic solvent has a high boiling point and is miscible with water, making the subsequent solvent phase separation process controllable.

[0051] In specific implementation, by weight, the polysulfone resin comprising the homogeneous casting solution accounts for 15-25 parts, the pore-opening agent accounts for 3-10 parts, and the organic solvent accounts for 55-80 parts. This invention uses ether compounds as pore-opening agents, with a dosage not exceeding 10% (by mass) of the homogeneous casting solution. Compared with conventional pore-opening agents, this has the significant advantage of requiring less dosage, while also reducing the difficulty of subsequent membrane material cleaning and saving cleaning costs.

[0052] In some embodiments, the ether-based pore-opening agent is selected from one or more of n-pentyl ether, isoprene ether, or dibutyl ether; the organic solvent is selected from one or more of dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone; the preferred ether-based pore-opening agent is a combination of isoprene ether and dibutyl ether (weight ratio 1:1), and the preferred organic solvent is N,N-dimethylacetamide.

[0053] In some embodiments, the polysulfone resin used in this invention is selected from one or more of polysulfone resin, polyethersulfone resin, sulfonated polysulfone resin, and sulfonated polyethersulfone resin; the number average molecular weight of the polysulfone resin is 60,000 to 120,000.

[0054] As a preferred combination, the polysulfone resin constituting the homogeneous casting solution may be selected from polysulfone with a weight average molecular weight of 80,000, the pore-opening agent is selected from a combination of isopentyl ether and dibutyl ether (weight ratio 1:1), and the organic solvent is selected from N-methylpyrrolidone, wherein 18 parts of polysulfone, 5 parts each of isopentyl ether and dibutyl ether, and 72 parts of N-methylpyrrolidone are used.

[0055] S2. The casting solution and the core solution are extruded together into the coagulation bath through a dual-channel spinneret. The casting solution is solidified after non-solvent phase separation to form a membrane precursor.

[0056] In specific implementation, the coagulation bath used in this invention is prepared by combining a solvent (the same organic solvent used in the homogeneous casting solution) and a non-solvent (water). After the casting solution and the core solution are extruded into the coagulation bath through a dual-channel spinneret, the organic solvent in the casting solution diffuses into the coagulation bath, and the water in the coagulation bath diffuses in the opposite direction. The non-water-soluble ether compounds migrate and remain inside and on the surface of the membrane because they cannot transfer mass with water. After post-treatment (ethanol soaking and washing) to dissolve the ether compounds, pores are formed on the membrane surface, and a multi-layered filtration sponge structure is formed inside the membrane.

[0057] In some embodiments, the volume ratio of water to organic solvent in the coagulation bath is 19:1 to 4:1; the composition of the core liquid is the same as that of the coagulation bath; the coagulation bath contains a certain amount of organic solvent, which weakens the driving force for the diffusion of organic solvent in the casting solution into the coagulation bath, which helps to slow down the exchange rate of organic solvent in the casting solution and ensure the uniformity of pore size distribution and the required porosity.

[0058] In some embodiments, the casting solution and the core solution are extruded together through a dual-channel spinneret. After passing through an air section of 1-15 cm in length (with humidity controlled at 50-80%RH), the casting solution enters a coagulation bath at a temperature of 25-60°C. The casting solution remains in the coagulation bath for 5-20 seconds, during which time transient phase separation occurs, forming film filaments.

[0059] S3. The membrane precursor is soaked in ethanol solution and washed with ultrapure water to obtain the hollow fiber ultrafiltration membrane.

[0060] In specific implementation, the present invention first soaks the membrane precursor in ultrapure water for 24 hours, then soaks the membrane precursor in an ethanol solution with a concentration of not less than 95% for 2-6 hours, and finally rinses it multiple times with ultrapure water for a total rinsing time of not less than 3 hours, and finally obtains a hollow fiber ultrafiltration membrane.

[0061] In the preparation method provided by this invention, insoluble ether compounds are used as pore-opening agents. During non-solvent-induced phase separation (NIPS), the casting solution, after extrusion, enters a coagulation bath (non-solvent) for phase separation. Because the insoluble ether compounds cannot transfer mass with water, they migrate and remain inside and outside the membrane. Post-treatment dissolves the ether compounds, resulting in a membrane with uniformly distributed nanoscale pores on both the inner and outer surfaces (an opening rate of 18-24% on the outer surface) and a multi-layered sponge structure (overall membrane thickness of 150-200 μm) forming internally. In actual filtration, pollutants are repeatedly retained by the surface pores and the internal sponge structure (average thickness of 80-150 μm), thus achieving the fabrication of a high-purity water flux and high retention efficiency terminal ultrafiltration membrane. The resulting hollow fiber ultrafiltration membrane has a rejection rate of no less than 99% for 50nm silica particles and a pure water flux of no less than 600 L / (㎡•h•bar) (25℃). Furthermore, the ether compounds selected in this invention as pore-opening agents have the advantages of requiring less dosage and being easier to clean compared to traditional pore-opening agents.

[0062] In a second aspect, the present invention provides a hollow fiber ultrafiltration membrane, which is obtained by the preparation method described in the first aspect above; the inner and outer surfaces of the hollow fiber ultrafiltration membrane are distributed with nanopores, the pore size of the nanopores being 20-50 nm; and the porosity of the outer surface of the hollow fiber ultrafiltration membrane is 18-24%.

[0063] Thirdly, the present invention provides an application of a hollow fiber ultrafiltration membrane, wherein the hollow fiber ultrafiltration membrane is obtained by the preparation method described in the first aspect above; the hollow fiber ultrafiltration membrane is used as a membrane material for terminal ultrafiltration of ultrapure water.

[0064] The hollow fiber ultrafiltration membrane provided by this invention has a pure water flux of not less than 600 L / (㎡•h•bar) and a rejection efficiency of not less than 99% for nano-sized particles (50 nm silica particles); it meets the multiple requirements of terminal ultrafiltration membrane as the core component of terminal filtration, namely high water flux, high particle rejection efficiency and low precipitate.

[0065] To enable those skilled in the art to more clearly understand the present invention, the following embodiments will be used to provide a detailed description of a hollow fiber ultrafiltration membrane, its preparation method, and its application.

[0066] Example 1:

[0067] (1) Preparation of casting solution, core solution and coagulation bath

[0068] Preparation of casting solution:

[0069] Polysulfone resin: 18 parts polysulfone (weight average molecular weight 80,000); ether pore-opening agent: 3 parts n-pentyl ether; organic solvent: 79 parts N,N-dimethylacetamide.

[0070] Polysulfone and n-pentyl ether were dissolved in N,N-dimethylacetamide and stirred in a constant temperature stirrer (100 rpm, 80°C) for 12 hours until completely dissolved, forming a homogeneous and transparent solution.

[0071] Preparation of core fluid and coagulation bath:

[0072] Water and N,N-dimethylacetamide were mixed at a volume ratio of 15:1 and stirred for at least 30 minutes to ensure homogeneity. The coagulation bath had the same composition as the core solution.

[0073] (2) Film-making process

[0074] Non-solvent phase separation membrane formation: The casting solution and core solution are co-extruded through a dual-channel spinneret with an air section length of 1.5 cm (65% RH); they are then introduced into a coagulation bath for non-solvent phase separation to form the membrane precursor; the coagulation bath temperature is 30℃ and the phase separation time is 15 seconds.

[0075] Post-processing: First, soak the membrane precursor in ultrapure water for 24 hours, then soak it in 95% ethanol for 4 hours, and finally soak it in ultrapure water 3 times for 1 hour each time.

[0076] Figure 2 A cross-sectional structural diagram of the hollow fiber ultrafiltration membrane provided in Embodiment 1 of the present invention is shown, wherein, Figure 2 The top left is a structural diagram of the overall cross-section of the hollow fiber ultrafiltration membrane. Figure 2 The upper right corner shows a partial cross-sectional view of the hollow fiber ultrafiltration membrane. Figure 2 The lower left is a structural diagram of the outer side of the hollow fiber ultrafiltration membrane cross-section. Figure 2 The bottom right corner shows the internal structure of the hollow fiber ultrafiltration membrane cross-section.

[0077] Figure 3 A structural diagram of the surface of the hollow fiber ultrafiltration membrane provided in Embodiment 1 of the present invention is shown, wherein, Figure 3 The left image shows the outer surface structure of a hollow fiber ultrafiltration membrane. Figure 3The image on the right shows the internal surface structure of the hollow fiber ultrafiltration membrane. As can be seen from the image, the membrane surface has good pore size distribution, with a pore size of 20-50 nm.

[0078] like Figure 2 , Figure 3 As shown, the overall thickness of the hollow fiber ultrafiltration membrane is 200 μm, and the average thickness of the sponge structure layer is 150 μm. The inner and outer surfaces of the ultrafiltration membrane have nanoscale openings, and the membrane has a multi-layered sponge structure layer for filtration, in order to meet the structural requirements of efficient interception of nanoscale particles and high-purity water flux.

[0079] Example 2:

[0080] (1) Preparation of casting solution, core solution and coagulation bath

[0081] Preparation of casting solution:

[0082] Polysulfone resin: 18 parts polysulfone (weight average molecular weight 80,000); 5 parts of a mixture of isopentyl ether and dibutyl ether (weight ratio 1:1); organic solvent: 77 parts N-methylpyrrolidone.

[0083] Polysulfone and n-pentyl ether were dissolved in N-methylpyrrolidone and stirred in a constant temperature stirrer (100 rpm, 80°C) for 12 hours until completely dissolved to form a homogeneous and transparent solution.

[0084] Preparation of core fluid and coagulation bath:

[0085] Water and N-methylpyrrolidone were mixed at a volume ratio of 9:1 and stirred for at least 30 minutes to ensure homogeneity. The coagulation bath had the same composition as the core solution.

[0086] 2) Film-forming process

[0087] Non-solvent phase separation membrane fabrication:

[0088] Same as Example 1.

[0089] Post-processing:

[0090] Same as Example 1.

[0091] The cross-sectional and surface structure diagrams of the hollow fiber ultrafiltration membrane prepared in Example 2 are similar to those provided in Example 1, and will not be repeated here. The hollow fiber ultrafiltration membrane prepared in Example 2 has good pore opening effect on the membrane surface, uniform pore size distribution, and pore size of 20-50 nm.

[0092] Example 3:

[0093] (1) Preparation of casting solution, core solution and coagulation bath

[0094] Preparation of casting solution:

[0095] Polysulfone resin: 18 parts polysulfone (weight average molecular weight 80,000); 8 parts dibutyl ether; organic solvent: 74 parts dimethyl sulfoxide.

[0096] Polysulfone and dibutyl ether were dissolved in dimethyl sulfoxide and stirred in a constant temperature stirrer (100 rpm, 80°C) for 12 hours until completely dissolved to form a homogeneous and transparent solution.

[0097] Core fluid and coagulation bath preparation:

[0098] Water and dimethyl sulfoxide are mixed at a volume ratio of 15:1 and stirred for at least 30 minutes to ensure homogeneity. The coagulation bath has the same composition as the core solution.

[0099] (2) Film-making process

[0100] Non-solvent phase separation membrane formation: The casting solution and core solution are co-extruded through a dual-channel spinneret with an air section length of 10 cm (50% RH); they are then introduced into a coagulation bath for non-solvent phase separation to form the membrane precursor; the coagulation bath temperature is 25℃ and the phase separation time is 20 seconds.

[0101] Post-processing: First, soak the membrane precursor in ultrapure water for 24 hours, then soak it in 95% ethanol for 4 hours, and finally soak it in ultrapure water 3 times for 1 hour each time.

[0102] The cross-sectional and surface structure diagrams of the hollow fiber ultrafiltration membrane prepared in Example 3 are similar to those provided in Example 1, and will not be repeated here. The hollow fiber ultrafiltration membrane prepared in Example 3 has good surface opening effect, uniform surface opening, uniform pore size distribution, and pore size of 20-50 nm.

[0103] Example 4:

[0104] (1) Preparation of casting solution, core solution and coagulation bath

[0105] Preparation of casting solution:

[0106] Polysulfone resin: a mixture of polysulfone and sulfonated polysulfone (weight ratio 2:1, total weight 18 parts); Ether pore-opening agent: a mixture of n-pentyl ether and isopramyl ether (weight ratio 3:1) 10 parts; Organic solvent: dimethylformamide 72 parts.

[0107] The three substances were mixed and stirred in a constant temperature stirrer (100 rpm, 80°C) for 12 hours until completely dissolved, forming a homogeneous and transparent solution.

[0108] Preparation of core fluid and coagulation bath:

[0109] Water and dimethylformamide are mixed at a volume ratio of 15:1 and stirred for at least 30 minutes to ensure homogeneity. The coagulation bath has the same composition as the core solution.

[0110] (2) Film-making process

[0111] Non-solvent phase separation membrane fabrication:

[0112] Same as Example 1.

[0113] Post-processing:

[0114] Same as Example 1.

[0115] The cross-sectional and surface structure diagrams of the hollow fiber ultrafiltration membrane prepared in Example 4 are similar to those provided in Example 1, and will not be repeated here. The hollow fiber ultrafiltration membrane prepared in Example 4 has good pore opening effect on the membrane surface, uniform pore size distribution, and pore size of 20-50 nm.

[0116] Comparative Example 1:

[0117] (1) Preparation of casting solution, core solution and coagulation bath:

[0118] Preparation of casting solution:

[0119] Polysulfone resin: 18 parts polysulfone; organic solvent: 82 parts N,N-dimethylacetamide.

[0120] The above polysulfone was mixed with N,N-dimethylacetamide and stirred in a constant temperature stirrer (100 rpm, 80°C) for 12 hours until completely dissolved to form a homogeneous and transparent solution.

[0121] Core solution preparation: Mix water and dimethylacetamide at a volume ratio of 15:1 and stir for at least 30 minutes to ensure homogeneity. The coagulation bath has the same composition as the core solution.

[0122] (2) Film-making process

[0123] Non-solvent phase separation membrane preparation: Same as Example 1.

[0124] Post-processing:

[0125] Cleaned with ultrapure water for 48 hours.

[0126] Figure 5 A cross-sectional structural diagram of the hollow fiber ultrafiltration membrane provided in Comparative Example 1 of the present invention is shown, wherein, Figure 5 The left image shows a partial cross-sectional view of a hollow fiber ultrafiltration membrane. Figure 5 The middle section shows the structural diagram of the outer side of the hollow fiber ultrafiltration membrane cross-section. Figure 5 The right side shows the structural diagram of the inner side of the hollow fiber ultrafiltration membrane cross section.

[0127] Figure 6 A structural diagram of the surface of the hollow fiber ultrafiltration membrane provided in Comparative Example 1 of the present invention is shown, wherein, Figure 6 The left image shows the outer surface structure of a hollow fiber ultrafiltration membrane. Figure 6 The diagram on the right shows the internal surface structure of a hollow fiber ultrafiltration membrane.

[0128] like Figure 6 As shown, Comparative Example 1 shows an ultrafiltration membrane structure made without the addition of an opening agent. Due to the lack of an opening agent (such as PEG, PVP, etc.), the exchange rate between solvent and non-solvent is slow, causing the polymer to solidify rapidly on the surface, forming a dense skin layer. The surface layer may only have a few nanoscale pores, or even be non-porous. In terms of cross-sectional structure, due to the slowed exchange rate, the non-solvent cannot quickly penetrate into the casting solution, resulting in a reduction in finger-like pore structures and the formation of a dense micropore structure in the middle, thus reducing flux.

[0129] Comparative Example 2:

[0130] (1) Preparation of casting solution, core solution and coagulation bath

[0131] Preparation of casting solution:

[0132] Polysulfone resin: 18 parts of sulfone polymer; Additive: 12 parts of polyethylene glycol; Organic solvent: 70 parts of N,N-dimethylacetamide.

[0133] The three substances were mixed and stirred in a constant temperature stirrer (100 rpm, 80°C) for 12 hours until completely dissolved, forming a homogeneous and transparent solution.

[0134] Core solution preparation: Mix water and N,N-dimethylacetamide at a volume ratio of 15:1 and stir for at least 30 minutes to ensure homogeneity. The coagulation bath has the same composition as the core solution.

[0135] (2) Film-making process

[0136] Non-solvent phase separation membrane fabrication:

[0137] Same as Example 1.

[0138] Post-processing:

[0139] Cleaned with ultrapure water for 48 hours.

[0140] Figure 8 A cross-sectional structural diagram of the hollow fiber ultrafiltration membrane provided in Comparative Example 2 of the present invention is shown, wherein, Figure 8 The top left is a structural diagram of the overall cross-section of the hollow fiber ultrafiltration membrane. Figure 8 The upper right corner shows a partial cross-sectional view of the hollow fiber ultrafiltration membrane. Figure 8 The lower left is a structural diagram of the outer side of the hollow fiber ultrafiltration membrane cross-section. Figure 8 The bottom right corner shows the internal structure of the hollow fiber ultrafiltration membrane cross-section.

[0141] Figure 9 The diagram shows the structural features of the hollow fiber ultrafiltration membrane surfaces provided in the two comparative examples of the present invention. Figure 9 The left image shows the outer surface structure of a hollow fiber ultrafiltration membrane. Figure 9The diagram on the right shows the internal surface structure of a hollow fiber ultrafiltration membrane.

[0142] like Figure 8 , 9 As shown, Comparative Example 2 has a dense surface structure with fewer openings, and its surface porosity is slightly higher than that of the comparative example, but still relatively low. The ultrafiltration membrane contains larger and longer finger-like pores, which reduce mass transfer resistance and increase permeate flux to some extent. However, the membrane's retention performance depends entirely on the membrane surface. In actual operation, if the dense surface layer wears down, a significant decrease in retention performance will occur. Furthermore, the presence of the water-soluble pore-opening agent polyethylene glycol will increase the time and difficulty of on-site flushing.

[0143] The hollow fiber ultrafiltration membranes provided in Examples 1-4 and Comparative Examples 1-2 were subjected to performance tests, and the test items are as follows:

[0144] (1) Surface porosity:

[0145] After gold sputtering and preparation of a dried hollow fiber membrane, scanning electron microscopy (SEM) was performed to examine the surface. A 20,000x magnification image was taken, and the surface porosity was calculated using ImageJ software. The ImageJ software implementation steps were as follows: a. Set the software scale according to the scale of the electron microscope image. b. Convert the image to 8-bit. c. Use the rectangular selection tool to select the image; the selected area represents the total area. d. Adjust the threshold, select the pores, and the software will calculate and read the open area. Click "Measure" to perform the calculation.

[0146] Open area ratio (%) = Open area / Selected area × 100%

[0147] (2) Pure water flux of hollow fiber membrane fibers:

[0148] After completely wetting a 30 cm long hollow fiber membrane, it was sealed in a test container and filtered using pure water at 25 ℃ in an environment of 25 ℃. The operating pressure was 0.1 MPa. After running stably for 10 min, the permeate flow rate for 5 min was collected, and the pure water flux was determined using the following formula.

[0149] Pure water flux [L / m² / h (LMH)] = 60 × (permeate flow [L]) / {π × (membrane outer diameter [m]) × (effective membrane length [m]) × (measurement time [min])}

[0150] (3) Tensile strength and elongation at break of hollow fiber membrane filaments:

[0151] The test was conducted using an electronic universal testing machine at a speed of 25 mm / min and at room temperature, with a 50 mm gap between the upper and lower clamps. The formula for calculating the membrane fiber strength is:

[0152] Tensile strength [MPa] = Tensile force [N] / Cross-sectional area of ​​hollow fiber membrane [㎡];

[0153] Elongation at break [%] = 100 × (Total length at break [mm] - Initial length [mm]) / Initial length [mm]

[0154] (4) 50nm SiO2 rejection rate:

[0155] A 0.5 m² fully wetted hollow fiber ultrafiltration membrane was encapsulated in a 50 cm long test container. A 0.2 wt% sodium dodecyl sulfate solution was prepared and filtered under external pressure at 0.1 MPa for 10 min. Then, a 20 ppm (0.02 g / L) solution was prepared using 50 nm silica and the 0.2 wt% sodium dodecyl sulfate solution. After thorough mixing, the membrane was filtered under external pressure at 0.1 MPa for 15 min. The permeate and feed solution were then collected. The Si concentration in both solutions was measured using ICP (Inductively Coupled Plasma Spectrometry). The silica particle rejection rate was calculated using the following formula:

[0156] 50nm SiO2 rejection rate [%] = [1 - (Si element concentration in permeated water / Si element concentration in raw water)] × 100%

[0157] (5) ΔTOC permeable to water:

[0158] ΔTOC is used to characterize the amount of residual organic matter in ultrafiltration membranes. A 0.5 m² fully wetted hollow fiber ultrafiltration membrane is packaged into a test container and rinsed with ultrapure water for 12 h. Continuous membrane filtration is performed in an environment of 25 °C using test water with a TOC of 1-2 ppb. The operating pressure is 0.1 MPa and the filtration is stable for 10 min. After filtration, the permeate water is collected, and the TOC concentration in the raw water and permeate water is measured using a TOC analyzer. The increase in TOC in the permeate water is measured.

[0159] ΔTOC = TOC of permeate water - TOC of raw water

[0160] The performance test indicators of the ultrafiltration membranes provided in Examples 1-4 and Comparative Examples 1-2 are shown in Table 1:

[0161] Table 1 Performance Indicators of Ultrafiltration Membranes

[0162]

[0163] Figure 4 This diagram illustrates the calculation of the porosity of the outer surface of the hollow fiber ultrafiltration membrane provided in Embodiment 1 of the present invention. Figure 7This diagram illustrates the calculation of the porosity of the hollow fiber ultrafiltration membrane's outer surface provided in Comparative Example 1 of the present invention. Figure 10 The diagram shows the calculation of the porosity of the hollow fiber ultrafiltration membrane provided in Comparative Example 2 of the present invention. Referring to Table 1, the porosity of the ultrafiltration membranes provided in Examples 1-4 ranges from 19.27% ​​to 22.05%. Compared with Comparative Example 1 (without porosilicate agent) and Comparative Example 2 (additive is water-soluble polyethylene glycol), the porosity of the ultrafiltration membranes provided in Examples 1-4 is significantly improved, resulting in a marked increase in pure water flux. Due to the uniform surface pore size and the sponge-like internal structure, it can effectively retain nanoscale particles (50nm silica particles).

[0164] Meanwhile, the ultrafiltration membranes provided in Examples 1-4 also maintain relatively good tensile strength and elongation at break. The hollow fiber ultrafiltration membranes provided by this invention have a pure water flux of 643-750 L / (㎡•h•bar), a rejection efficiency greater than 99%, a tensile strength of 4.15-5.95 MPa, an elongation at break of 49.5-71.2%, and a TOC increase in permeated water of 0.2-0.4 ppb. Their pure water flux is not less than 600 L / (㎡•h•bar), and the rejection efficiency for nanoscale particles (50 nm silica particles) is not less than 99%; moreover, the tensile strength and elongation at break are well maintained. Regarding TOC in permeated water, due to the easy-to-wash characteristics of small molecules of ether compounds, under the same test rinsing conditions, the test results of Examples 1-4 are 0.2-0.4 ppb, significantly lower than the 0.9 ppb of Comparative Example 2. Therefore, the hollow fiber ultrafiltration membrane provided by this invention satisfies the multiple requirements of terminal ultrafiltration membranes as core components of terminal filtration, namely high water flux, high particulate matter retention efficiency, and low precipitates.

[0165] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0166] For the sake of simplicity, the method embodiments are described as a series of actions. However, those skilled in the art should understand that the present invention is not limited to the described order of actions, as some steps can be performed in other orders or simultaneously according to the present invention. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and components involved are not necessarily essential to the present invention.

[0167] The hollow fiber ultrafiltration membrane, its preparation method, and its application provided by the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for preparing a hollow fiber ultrafiltration membrane, characterized in that, The method includes: Polysulfone resin and pore-opening agent are dissolved in an organic solvent and stirred at a constant temperature until a homogeneous casting solution is formed; The casting solution and the core solution are extruded together into a coagulation bath through a dual-channel spinneret. The casting solution is then solidified by non-solvent phase separation to form a membrane precursor. The membrane precursor is soaked in ethanol solution and washed with ultrapure water to obtain the hollow fiber ultrafiltration membrane; The pore-opening agent is selected from one or more of n-pentyl ether, isopyramyl ether, or dibutyl ether; By weight, the homogeneous casting solution contains 15-25 parts of polysulfone resin, 3-10 parts of pore-opening agent, and 55-80 parts of organic solvent.

2. The method for preparing the hollow fiber ultrafiltration membrane according to claim 1, characterized in that, The organic solvent is selected from one or more of dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone.

3. The method for preparing the hollow fiber ultrafiltration membrane according to claim 1, characterized in that, The core fluid is a mixture of water and organic solvent in a volume ratio of 19:1 to 4:

1.

4. The method for preparing the hollow fiber ultrafiltration membrane according to claim 1, characterized in that, The composition of the coagulation bath is the same as that of the core liquid, and the temperature of the coagulation bath is 25-60℃.

5. The method for preparing the hollow fiber ultrafiltration membrane according to claim 1, characterized in that, The polysulfone resin includes one or more of polysulfone resin, polyethersulfone resin, sulfonated polysulfone resin, and sulfonated polyethersulfone resin; the number average molecular weight of the polysulfone resin is 60,000 to 120,000.

6. The method for preparing the hollow fiber ultrafiltration membrane according to claim 1, characterized in that, The step of extruding the casting solution and the core solution together into the coagulation bath through a dual-channel spinneret includes: the length of the casting solution exposed to air after extrusion is 1-15 cm, and the phase separation time of the casting solution in the coagulation bath is 5-20 s.

7. The method for preparing the hollow fiber ultrafiltration membrane according to claim 1, characterized in that, The concentration of the ethanol solution is not less than 95%, and the soaking time is 2-6 hours.

8. A hollow fiber ultrafiltration membrane, characterized in that, The hollow fiber ultrafiltration membrane is obtained by any of the preparation methods described in claims 1-7; The hollow ultrafiltration membrane has nanopores distributed on its inner and outer surfaces, and the pore size of the nanopores is 20-50 nm. The porosity of the outer surface of the hollow ultrafiltration membrane is 18-24%.

9. An application of a hollow fiber ultrafiltration membrane, characterized in that, The hollow fiber ultrafiltration membrane is obtained by any of the preparation methods described in claims 1-7, and the hollow fiber ultrafiltration membrane is used as a membrane material for terminal ultrafiltration of ultrapure water.

10. The application according to claim 9, characterized in that, The pure water flux of the hollow fiber ultrafiltration membrane is not less than 600 L / (m³). 2 •h•bar); The hollow fiber ultrafiltration membrane has a rejection efficiency of no less than 99% for 50 nm silica particles.

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