Hollow ultrafiltration membrane as well as preparation method and application thereof

Abstract

The invention provides a hollow ultrafiltration membrane and a preparation method and application thereof.In the preparation method, a non-water-soluble ether compound is adopted as a pore opening agent, in the non-solvent-induced phase separation (NIPS) process, a membrane casting solution enters a coagulating bath for phase separation after being extruded, the ether compound is migrated due to the fact that mass transfer cannot be conducted between the ether compound and water, and the membrane casting solution enters the coagulating bath for phase separation; the ether compound is dissolved out through post-treatment, and the composite structure hollow fiber ultrafiltration membrane with nano-scale open pores in both the inner surface and the outer surface and a sponge body structure in the interior is prepared. In an actual filtering process, pollutants are intercepted for multiple times by virtue of nano-scale open pore channels on the surface of the membrane and an internal sponge body structure, so that the use requirements of high pure water flux and high interception efficiency are met. The retention rate of the obtained hollow ultrafiltration membrane on 50nm silicon dioxide particles is not less than 99%, and the pure water flux is not less than 600L / (m < 2 > hbar) (25 DEG C). And efficient and stable terminal filtering guarantee can be provided for an ultrapure water system.

Description

Technical Field

[0001] The present invention relates to the field of membrane separation technology, and in particular to a hollow ultrafiltration membrane, a preparation method and application thereof. Background Art

[0002] Ultrapure water refers to high-purity water with a resistivity of 18.2 MΩ·cm (25°C), which is widely used in electronics, semiconductors, medicine, chemicals and other fields. In the process of preparing ultrapure water, terminal filtration is a key step to ensure that the water quality meets the standards, and the terminal ultrafiltration membrane, as the core component of terminal filtration, is used to effectively intercept micron-level or even nano-level particles, colloids and other impurities in the water to ensure the purity of ultrapure water. Therefore, it is required to have a high interception efficiency for tiny substances. At the same time, when the system is running, the ultrafiltration membrane itself needs to have a very low impurity content and extremely low soluble substance precipitation to ensure the system's demanding water production requirements.

[0003] Most of the existing terminal ultrafiltration membranes that meet the interception requirements are a combination of a dense surface layer and internal finger-shaped pores. This results in a relatively low water flux. Therefore, how to overcome the low flux of the terminal ultrafiltration membrane while having a high interception effect on impurities and avoiding the precipitation of organic matter is a technical problem that needs to be solved in this field. Summary of the invention

[0004] In view of the above problems existing in the prior art, the present invention provides a hollow ultrafiltration membrane, a preparation method and an application thereof, so as to meet the multiple demands of the terminal ultrafiltration membrane as a core component of terminal filtration, such as high water flux, high particle retention efficiency and low precipitate.

[0005] The specific content of the invention is as follows: In a first aspect, the present invention provides a method for preparing a hollow ultrafiltration membrane, the method comprising: Dissolving polysulfone resin and pore opening agent in an organic solvent, and stirring at a constant temperature to form a homogeneous film casting solution; The casting liquid and the core liquid are co-extruded into a coagulation bath through a double-channel spinneret, and the casting liquid is solidified by non-solvent phase separation to form a membrane precursor; The hollow ultrafiltration membrane is obtained by soaking the membrane precursor in an ethanol solution and washing with ultrapure water; Wherein, the pore opening agent is selected from one or more of n-pentyl ether, isodipentyl ether or dibutyl ether; In terms of weight, in the homogeneous casting solution, the polysulfone resin accounts for 15-25 parts, the pore opening agent accounts for 3-10 parts, and the organic solvent accounts for 55-80 parts.

[0006] Optionally, the organic solvent is selected from one or more of dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone.

[0007] Optionally, the core liquid is formed by mixing water and the organic solvent in a volume ratio of 19:1-4:1.

[0008] 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°C.

[0009] Optionally, the polysulfone resin includes one or more of polysulfone resin, polyethersulfone resin, sulfonated polysulfone resin and sulfonated polyethersulfone resin; and the number average molecular weight of the polysulfone resin is 60,000-120,000.

[0010] Optionally, the extruding the casting liquid and the core liquid together into a coagulation bath through a dual-channel spinneret comprises: the casting liquid is exposed to the air for a length of 1-15 cm after extrusion, and the casting liquid undergoes phase separation in the coagulation bath for a time of 5-20 s.

[0011] Optionally, the concentration of the ethanol is not less than 95%, and the soaking time is 2-6 h.

[0012] In a second aspect, the present invention provides a hollow ultrafiltration membrane, wherein the hollow ultrafiltration membrane is obtained by the preparation method described in the first aspect above; Nanopores are distributed on the inner and outer surfaces of the hollow ultrafiltration membrane, and the pore size of the nanopores is 20-50 nm; The open porosity of the outer surface of the hollow fiber ultrafiltration membrane is 18-24%.

[0013] In a third aspect, the present invention provides an application of a hollow ultrafiltration membrane, wherein the hollow ultrafiltration membrane is obtained by the preparation method described in the first aspect, and the hollow ultrafiltration membrane is used as a membrane material for terminal ultrafiltration of ultrapure water.

[0014] Optionally, the pure water flux of the hollow ultrafiltration membrane is not less than 600 L / (㎡•h•bar); The retention efficiency of the hollow ultrafiltration membrane for 50 nm silica particles is not less than 99%.

[0015] Compared with the prior art, the present invention has the following advantages: The present invention provides a method for preparing a hollow ultrafiltration membrane, the method comprising: dissolving a polysulfone resin and a pore opening agent in an organic solvent, stirring at a constant temperature to form a homogeneous casting liquid; co-extruding the casting liquid and the core liquid into a coagulation bath through a double-channel spinneret, and forming a membrane precursor after the casting liquid is solidified; the membrane precursor is soaked in an ethanol solution and washed with ultrapure water to obtain the hollow ultrafiltration membrane; wherein the pore opening agent is selected from one or more of n-pentyl ether, isodipentyl ether or dibutyl ether. In terms of weight, in the homogeneous casting liquid, the polysulfone resin accounts for 15-25 parts, the pore opening agent accounts for 3-10 parts, and the organic solvent accounts for 55-80 parts.

[0016] In the preparation method provided by the present invention, a water-insoluble ether compound is used as a pore-opening agent. In the non-solvent induced phase separation (NIPS) process, the casting liquid is extruded and enters a coagulation bath (non-solvent) for phase separation. Since the ether compound cannot transfer mass with water, it migrates and stays on the outside of the membrane. After post-treatment, the ether compound is dissolved to obtain a composite structure hollow fiber ultrafiltration membrane with nano-scale openings on both the inner and outer surfaces and a sponge structure as the main structure inside; the surface opening rate of the obtained hollow fiber ultrafiltration membrane is 18-24%. In the actual filtration process, the pollutants are intercepted multiple times by means of the nano-scale openings on the membrane surface and the sponge structure inside, meeting the use requirements of high-purity water flux and high interception efficiency. The interception rate of the obtained hollow ultrafiltration membrane for 50nm silica particles is not less than 99%, and the pure water flux is not less than 600 L / (㎡•h•bar)(25℃). It can provide efficient and stable terminal filtration guarantee for ultrapure water systems.

[0017] In addition, the ether compound selected by the present invention as a pore opening agent can greatly improve the pure water flux of the membrane at an addition amount of 3 to 10%, and the molecular weight of the ether compound selected by the present invention is much smaller than that of the traditional pore opening agent, and it can be quickly dissolved when cleaned with ethanol, and then ultrapure water can be used to efficiently remove the residual solvent molecules to obtain a pure ultrafiltration membrane. The traditional pore opening agent requires an addition amount of more than 8%, and the larger molecular weight and chain-like molecular structure require a longer time and more flushing water in the later cleaning. Therefore, the present invention has obvious economic and efficiency advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1A flow chart of a method for preparing a hollow ultrafiltration membrane provided by an embodiment of the present invention is shown; Figure 2 The cross-sectional structure diagram of the hollow ultrafiltration membrane provided in Example 1 of the present invention is shown; Figure 3 The structural diagram of the surface of the hollow ultrafiltration membrane provided in Example 1 of the present invention is shown; Figure 4 The figure shows the calculation diagram of the outer surface porosity of the hollow ultrafiltration membrane provided in Example 1 of the present invention; Figure 5 The cross-sectional structure diagram of the hollow ultrafiltration membrane provided in Comparative Example 1 of the present invention is shown; Figure 6 The structural diagram of the surface of the hollow ultrafiltration membrane provided in Comparative Example 1 of the present invention is shown; Figure 7 A calculation diagram of the porosity of the outer surface of the hollow ultrafiltration membrane provided in Comparative Example 1 of the present invention is shown; Figure 8 The cross-sectional structure diagram of the hollow ultrafiltration membrane provided in Comparative Example 2 of the present invention is shown; Fig. 9 The structural diagram of the surface of the hollow ultrafiltration membrane provided in Comparative Example 2 of the present invention is shown; Fig.10 A calculation diagram of the porosity of the outer surface of the hollow ultrafiltration membrane provided in Comparative Example 2 of the present invention is shown. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means a limitation on the present invention and its application or use. Based on the embodiments of the present invention, any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts falls within the scope of protection of the present invention. In addition, all other embodiments obtained by ordinary technicians in this field without carrying out creative work belong to the scope of protection of the present invention.

[0021] In the embodiment, no specific experimental steps or conditions are indicated, and the operation or conditions of the conventional experimental steps described in the prior art in this field can be carried out. The reagents used and other instruments that do not indicate the manufacturer are conventional reagent products that can be obtained commercially. In addition, the accompanying drawings are only schematic diagrams of the embodiments of the present invention and are not necessarily drawn to scale. The same reference numerals in the figures represent the same or similar parts, and thus their repeated description will be omitted. Some block diagrams shown in the accompanying drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0022] Technologies, methods, and equipment known to ordinary technicians in the relevant field may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered as part of the description of the present invention.

[0023] In the description of the present invention, it should be understood that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present invention.

[0024] In addition, 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.

[0025] Before describing in detail the hollow ultrafiltration membrane, preparation method and application thereof provided by the present invention, it is necessary to describe the related technologies as follows: Patent application number CN202311539734.2, in order to ensure the accuracy of terminal filtration, the inner and outer surfaces of the prepared polysulfone terminal ultrafiltration membrane are very dense, a small number of openings have an aperture between 1-50nm, and the inside of the hollow fiber membrane has a finger-like pore structure. Although such a structure has a guaranteed interception rate, the pure water flux of the membrane is about 360 L / (㎡·h·bar), which is lower than the level of 400-800L L / (㎡·h·bar) of ordinary ultrafiltration. If the surface separation layer has wear defects in the later operation, the interception effect will be reduced. Increasing the surface opening rate to increase the filtration flux is a common technical means; Patent CN201610125548.8 uses polysulfone-polyethylene glycol block copolymer as a pore opening agent to promote the formation of membrane pores, solves the problem of loss of hydrophilic pore opening agents, and gives the membrane permanent hydrophilicity, with high membrane flux and flux recovery rate and good stability. However, this method may result in insufficiently reacted polyethylene glycol remaining inside or on the surface of the membrane, making it more difficult to completely clean it off. This also increases the difficulty of on-site cleaning during actual use, and may even make it impossible to use in an ultrapure water environment.

[0026] Based on this, the present invention has discovered a type of ether-based pore-opening agent that is more suitable for preparing ultrafiltration membranes by non-solvent-induced phase separation through experimental exploration, and uses polysulfone resin as the membrane-forming body to prepare hollow ultrafiltration membranes, which have the advantages of less pore-opening agent usage, less residue, and easy cleaning, and the obtained hollow ultrafiltration membrane has the advantages of both high water flux and high particle retention efficiency. The specific implementation content is as follows: In a first aspect, the present invention provides a method for preparing a hollow ultrafiltration membrane. Figure 1 The flowchart of the method for preparing the hollow ultrafiltration membrane provided by the embodiment of the present invention is shown as follows: Figure 1 As shown, the method includes: S1, dissolving a polysulfone resin and a pore opening agent in an organic solvent, and stirring at a constant temperature to form a homogeneous film casting solution; In the specific implementation, the polysulfone resin is used as the film-forming body and is dissolved in an organic solvent together with a pore-opening agent to form a homogeneous solution. During the dissolution process, the stirring speed of the stirrer is controlled to be 100-1000 rpm, and the dissolution temperature is preferably 60-100°C, preferably 80-90°C; stirring is performed until the polysulfone resin and the pore-opening agent are completely dissolved to form a homogeneous transparent solution.

[0027] In specific implementation, the polysulfone resin is a high molecular polymer with hydrophobicity, which preferentially forms a solid enriched phase when phase separation occurs in a coagulation bath composed of a solvent and a non-solvent; the present invention selects an ether compound as a pore-opening agent, and the ether compound used is a water-insoluble ether compound. In the subsequent phase separation process, the ether compound cannot transfer mass with water and migrates and stays on the surface and inside of the membrane. After the ether compound is dissolved out by post-treatment, pores are formed on the surface of the membrane, and a multi-layer filtration sponge structure is formed inside the membrane; the organic solvent selected by the present invention is a good solvent for the polysulfone resin and the pore-opening agent to maintain the dissolved state of the polysulfone resin and the pore-opening agent. And the selected organic solvent has a high boiling point and is miscible with water, so that the subsequent solvent phase separation process is controllable.

[0028] In specific implementation, by weight, the polysulfone resin constituting the homogeneous casting liquid accounts for 15-25 parts, the pore opening agent accounts for 3-10 parts, and the organic solvent accounts for 55-80 parts; the present invention adopts ether compounds as pore opening agents, and the amount used is not higher than 10% (mass percentage) of the homogeneous casting liquid. Compared with conventional pore opening agents, it has the obvious advantage of small amount, and at the same time reduces the difficulty of subsequent membrane material cleaning, saving cleaning costs.

[0029] In some embodiments, the ether pore opening agent is selected from one or more of n-pentyl ether, isodipentyl 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 pore opening agent is a combination of isodipentyl ether and dibutyl ether (weight ratio 1:1), and the preferred organic solvent is N,N-dimethylacetamide.

[0030] In some embodiments, the polysulfone resin used in the present 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 60,000-120,000.

[0031] As a preferred combination, the polysulfone resin constituting the homogeneous casting solution can be selected from polysulfone with a weight average molecular weight of 80,000, the pore opening agent is selected from a combination of isodipentyl ether and dibutyl ether (weight ratio of 1:1), and the organic solvent is selected from N-methylpyrrolidone, wherein 18 parts of polysulfone, 5 parts of isodipentyl ether and dibutyl ether each, and 72 parts of N-methylpyrrolidone are taken.

[0032] S2, the casting liquid and the core liquid are co-extruded into a coagulation bath through a double-channel spinneret, and the casting liquid is solidified through non-solvent phase separation to form a membrane precursor.

[0033] In specific implementation, the coagulation bath used in the present invention is prepared by a combination of a solvent (the same as the organic solvent used in the homogeneous casting liquid) and a non-solvent (water). After the casting liquid and the core liquid are co-extruded into the coagulation bath through a double-channel spinneret, the organic solvent in the casting liquid diffuses into the coagulation bath, and the water in the coagulation bath diffuses in the opposite direction. The water-insoluble ether compounds cannot transfer mass with water and migrate and remain inside and on the surface of the membrane. After post-treatment (ethanol soaking, washing) to dissolve the ether compounds, pores are formed on the membrane surface, and a multi-layer filtering sponge structure is formed inside the membrane.

[0034] In some embodiments, the volume ratio of water to organic solvent used to prepare the coagulation bath is 19:1-4:1; 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, so that the driving force for the organic solvent in the casting liquid to diffuse into the coagulation bath is weakened, which is beneficial to slow down the exchange rate of the organic solvent in the casting liquid and ensure the uniformity of the pore size distribution and the porosity requirements.

[0035] In some embodiments, the casting liquid and the core liquid are co-extruded through a dual-channel spinneret, and after passing through an air segment with a length of 1-15 cm (humidity is controlled at 50-80% RH), enter a coagulation bath with a temperature of 25-60°C; the casting liquid stays in the coagulation bath for 5-20 s, and the casting liquid undergoes instantaneous phase separation during this period to form membrane filaments.

[0036] S3. After the membrane precursor is soaked in an ethanol solution and washed with ultrapure water, the hollow ultrafiltration membrane is obtained.

[0037] In specific implementation, the present invention first soaks the membrane precursor with ultrapure water for 24 hours, then selects an ethanol solution with a concentration of not less than 95% to soak the membrane precursor for 2-6 hours, and finally rinses it with ultrapure water for multiple times, with a total rinsing time of not less than 3 hours, to finally obtain a hollow ultrafiltration membrane.

[0038] In the preparation method provided by the present invention, a water-insoluble ether compound is used as a pore-opening agent. In the non-solvent induced phase separation (NIPS) process, the casting liquid is extruded and enters a coagulation bath (non-solvent) for phase separation. Since the water-insoluble ether compound cannot transfer mass with water, it migrates and stays inside and outside the membrane. After post-treatment, the ether compound is dissolved to obtain a membrane with nano-scale openings evenly distributed on the inner and outer surfaces (the opening rate of the outer surface is 18-24%), and a multi-layer filtration sponge structure layer (the overall thickness of the membrane is 150-200μm) is formed inside. In the actual filtration process, the pollutants are intercepted multiple times by means of the opening pores on the membrane surface and the internal sponge structure layer (the average thickness of the sponge structure layer is 80-150μm), thereby realizing the preparation of a terminal ultrafiltration membrane with high pure water flux and high interception efficiency. The obtained hollow ultrafiltration membrane has a retention rate of not less than 99% for 50nm silica particles, and a pure water flux of not less than 600 L / (㎡•h•bar)(25℃). In addition, the ether compound selected as the pore opening agent in the present invention has the advantages of less dosage and easier cleaning compared with traditional pore opening agents.

[0039] In a second aspect, the present invention provides a hollow ultrafiltration membrane, which is obtained by the preparation method described in the first aspect; nanopores are distributed on the inner and outer surfaces of the hollow ultrafiltration membrane, and the pore size of the nanopores is 20-50nm; the porosity of the outer surface of the hollow fiber ultrafiltration membrane is 18-24%.

[0040] In a third aspect, the present invention provides an application of a hollow ultrafiltration membrane, wherein the hollow ultrafiltration membrane is obtained by the preparation method described in the first aspect; the hollow ultrafiltration membrane is used as a membrane material for terminal ultrafiltration of ultrapure water.

[0041] The hollow ultrafiltration membrane provided by the present invention has a pure water flux of not less than 600 L / (㎡•h•bar) and a retention efficiency of not less than 99% for nano-sized particles (50 nm silica particles); it meets the multiple pursuits of high water flux, high particle retention efficiency and low precipitates of the terminal ultrafiltration membrane as the core component of terminal filtration.

[0042] In order to enable those skilled in the art to more clearly understand the present invention, the hollow ultrafiltration membrane, preparation method and application of the present invention are now described in detail through the following examples.

[0043] Embodiment 1: (1) Preparation of casting liquid, core liquid and coagulation bath Preparation of casting solution: Polysulfone resin: polysulfone (weight average molecular weight 80,000) 18 parts; ether pore opener: n-pentyl ether 3 parts; organic solvent: N,N-dimethylacetamide 79 parts.

[0044] The polysulfone and n-pentyl ether were dissolved in N,N-dimethylacetamide and stirred in a constant temperature stirrer (speed 100 rpm, temperature 80°C) for 12 hours until they were completely dissolved to form a uniform transparent solution.

[0045] Core liquid and coagulation bath preparation: Water and N,N-dimethylacetamide were mixed in a volume ratio of 15:1 and stirred for more than 30 minutes to ensure uniformity. The coagulation bath had the same composition as the core liquid.

[0046] (2) Film making process Non-solvent phase separation membrane preparation: The casting liquid and the core liquid are co-extruded through a double-channel spinneret with an air section length of 1.5 cm (humidity 65% ​​RH); the non-solvent phase separation is carried out in a coagulation bath to form a membrane precursor; the coagulation bath temperature used is 30°C, and the phase separation time is 15 seconds.

[0047] Post-treatment: The membrane precursor was first soaked in ultrapure water for 24 h, then soaked in 95% ethanol for 4 h, and finally soaked in ultrapure water for 3 times, each time for 1 h.

[0048] Figure 2 The cross-sectional structure diagram of the hollow ultrafiltration membrane provided in Example 1 of the present invention is shown, wherein: Figure 2 The upper left is the structural diagram of the overall cross section of the hollow ultrafiltration membrane. Figure 2 The upper right is a structural diagram of a partial cross section of a hollow ultrafiltration membrane. Figure 2 The lower left is the structural diagram of the outer side of the hollow ultrafiltration membrane cross section. Figure 2 The lower right side is a structural diagram of the inner side of the hollow ultrafiltration membrane cross section.

[0049] Figure 3 The structure diagram of the surface of the hollow ultrafiltration membrane provided by Example 1 of the present invention is shown, wherein: Figure 3 The left is the outer surface structure of the hollow ultrafiltration membrane. Figure 3 The right side shows the inner surface structure of the hollow ultrafiltration membrane. As can be seen from the figure, the membrane surface has good pore opening effect, uniform pore size distribution, and the pore size is 20-50nm.

[0050] like Figure 2 , Figure 3 As shown, the overall thickness of the hollow ultrafiltration membrane is 200μm, and the average thickness of the sponge structure layer is 150μm; the inner and outer surfaces of the ultrafiltration membrane have nano-scale openings, and the inside of the membrane has a multi-layer filtering sponge structure layer to meet the structural requirements of efficient retention of nano-scale particles and high-purity water flux.

[0051] Embodiment 2: (1) Preparation of casting liquid, core liquid and coagulation bath Preparation of casting solution: Polysulfone resin: polysulfone (weight average molecular weight 80,000) 18 parts; isodipentyl ether and dibutyl ether mixed (weight ratio 1:1) 5 parts; organic solvent: N-methylpyrrolidone 77 parts.

[0052] Dissolve polysulfone and n-pentyl ether in N-methylpyrrolidone and stir in a constant temperature stirrer (speed 100 rpm, temperature 80°C) for 12 hours until they are completely dissolved to form a uniform transparent solution; Core liquid and coagulation bath preparation: Water and N-methylpyrrolidone were mixed in a volume ratio of 9:1 and stirred for more than 30 minutes to ensure uniformity. The coagulation bath had the same composition as the core liquid.

[0053] 2) Film making process Non-solvent phase separation membrane: Same as Example 1.

[0054] Post-processing: Same as Example 1.

[0055] The cross-section and surface structure diagram of the hollow ultrafiltration membrane prepared in Example 2 are similar to those provided in Example 1 and are not repeated here. The hollow ultrafiltration membrane prepared in Example 2 has good membrane surface opening effect, uniform pore size distribution, and a pore size of 20-50nm.

[0056] Embodiment 3: (1) Preparation of casting liquid, core liquid and coagulation bath Preparation of casting solution: Polysulfone resin: polysulfone (weight average molecular weight 80,000) 18 parts; dibutyl ether 8 parts; organic solvent: dimethyl sulfoxide 74 parts.

[0057] Dissolve polysulfone and dibutyl ether in dimethyl sulfoxide and stir in a constant temperature stirrer (speed 100 rpm, temperature 80°C) for 12 hours until they are completely dissolved to form a uniform transparent solution; Preparation of core liquid and coagulation bath: Water and dimethyl sulfoxide were mixed in a volume ratio of 15:1 and stirred for more than 30 minutes to ensure uniformity. The coagulation bath had the same composition as the core liquid.

[0058] (2) Film making process Non-solvent phase separation membrane preparation: The casting liquid and the core liquid are co-extruded through a double-channel spinneret with an air section length of 10 cm (humidity 50% RH); the non-solvent phase separation is carried out in a coagulation bath to form a membrane precursor; the coagulation bath temperature used is 25°C, and the phase separation time is 20 seconds.

[0059] Post-treatment: The membrane precursor was first soaked in ultrapure water for 24 h, then soaked in 95% ethanol for 4 h, and finally soaked in ultrapure water for 3 times, each time for 1 h.

[0060] The cross-section and surface structure diagram of the hollow ultrafiltration membrane prepared in Example 3 are similar to those provided in Example 1 and are not repeated here. The hollow ultrafiltration membrane prepared in Example 3 has good membrane surface opening effect, uniform surface opening, uniform pore size distribution, and a pore size of 20-50nm.

[0061] Embodiment 4: (1) Preparation of casting liquid, core liquid and coagulation bath Preparation of casting solution: Polysulfone resin: a mixture of polysulfone and sulfonated polysulfone (weight ratio 2:1, total weight 18 parts); ether pore opener: a mixture of n-pentyl ether and isodipentyl ether (weight ratio 3:1) 10 parts; organic solvent: dimethylformamide 72 parts.

[0062] The three types of substances were mixed and stirred in a constant temperature stirrer (speed 100 rpm, temperature 80°C) for 12 hours until they were completely dissolved to form a uniform transparent solution.

[0063] Core liquid and coagulation bath preparation: Water and dimethylformamide were mixed in a volume ratio of 15:1 and stirred for more than 30 minutes to ensure uniformity. The coagulation bath had the same composition as the core liquid.

[0064] (2) Film making process Non-solvent phase separation membrane: Same as Example 1.

[0065] Post-processing: Same as Example 1.

[0066] The cross-section and surface structure diagram of the hollow ultrafiltration membrane prepared in Example 4 are similar to those provided in Example 1 and are not repeated here. The hollow ultrafiltration membrane prepared in Example 4 has good membrane surface opening effect, uniform pore size distribution, and a pore size of 20-50nm.

[0067] Comparative Example 1: (1) Preparation of casting solution, core solution and coagulation bath: Preparation of casting solution: Polysulfone resin: 18 parts of polysulfone; organic solvent: 82 parts of N,N-dimethylacetamide.

[0068] The polysulfone and N,N-dimethylacetamide were mixed, and stirred in a thermostatic stirrer (speed 100 rpm, temperature 80°C) for 12 hours until they were completely dissolved to form a uniform transparent solution; Core liquid preparation: Mix water and dimethylacetamide in a volume ratio of 15:1, and stir for more than 30 minutes to ensure uniformity. The coagulation bath has the same composition as the core liquid.

[0069] (2) Film making process Non-solvent phase separation membrane preparation: Same as Example 1.

[0070] Post-processing: Wash with ultrapure water for 48 hours.

[0071] Figure 5 The cross-sectional structure diagram of the hollow ultrafiltration membrane provided in Comparative Example 1 of the present invention is shown, wherein: Figure 5 The left is a structural diagram of a partial cross section of a hollow ultrafiltration membrane. Figure 5 The middle is the structural diagram of the outer side of the hollow ultrafiltration membrane section. Figure 5 The right side is a structural diagram of the inner side of the hollow ultrafiltration membrane cross section.

[0072] Figure 6 The structural diagram of the surface of the hollow ultrafiltration membrane provided by Example 1 of the present invention is shown, wherein: Figure 6 The left is the outer surface structure of the hollow ultrafiltration membrane. Figure 6 The right is a diagram of the inner surface structure of the hollow ultrafiltration membrane.

[0073] like Figure 6 As shown, Comparative Example 1 is an ultrafiltration membrane structure made without adding a pore-opening agent. Due to the lack of the pore-opening effect of the pore-opening agent (such as PEG, PVP, etc.), the exchange rate between the solvent and the non-solvent is slow, resulting in rapid solidification of the polymer on the surface, forming a denser cortex, and the surface may have only a small number of nano-scale pores, or even no pores. In the cross-sectional structure, due to the slow exchange rate, the non-solvent cannot quickly penetrate into the casting liquid, resulting in a reduction in the finger-like pore structure, forming a dense small pore structure in the middle, and reducing the flux.

[0074] Comparative Example 2: (1) Preparation of casting liquid, core liquid and coagulation bath Preparation of casting solution: Polysulfone resin: 18 parts of sulfone polymer; additive: 12 parts of polyethylene glycol; organic solvent: 70 parts of N,N-dimethylacetamide.

[0075] The three types of substances were mixed and stirred in a constant temperature stirrer (speed 100 rpm, temperature 80°C) for 12 hours until they were completely dissolved to form a uniform transparent solution; Core liquid preparation: Mix water and N,N-dimethylacetamide in a volume ratio of 15:1 and stir for more than 30 minutes to ensure uniformity. The coagulation bath has the same composition as the core liquid.

[0076] (2) Film making process Non-solvent phase separation membrane: Same as Example 1.

[0077] Post-processing process: Wash with ultrapure water for 48 hours.

[0078] Figure 8 The cross-sectional structure diagram of the hollow ultrafiltration membrane provided in Comparative Example 2 of the present invention is shown, wherein: Figure 8 The upper left is the structural diagram of the overall cross section of the hollow ultrafiltration membrane. Figure 8 The upper right is a structural diagram of a partial cross section of a hollow ultrafiltration membrane. Figure 8 The lower left is the structural diagram of the outer side of the hollow ultrafiltration membrane cross section. Figure 8 The lower right side is a structural diagram of the inner side of the hollow ultrafiltration membrane cross section.

[0079] Fig. 9 The structural diagram of the surface of the hollow ultrafiltration membrane provided by the comparative example 2 of the present invention is shown, wherein: Fig. 9 The left is the outer surface structure of the hollow ultrafiltration membrane. Fig. 9 The right is a diagram of the inner surface structure of the hollow ultrafiltration membrane.

[0080] like Figure 8 , 9 As shown, it can be seen that the surface of comparative example 2 is a dense structure with a small number of openings. The surface opening rate is slightly increased compared with the comparative example, but it is still low. A larger and longer finger-like pore structure is generated inside the ultrafiltration membrane. The finger-like pore structure reduces the mass transfer resistance and improves the water production flux to a certain extent. At this time, the retention performance of the membrane is completely dependent on the surface layer of the membrane. In the actual operation process, if the surface dense layer is worn, the retention performance will be seriously reduced. In addition, due to the presence of the water-soluble pore opening agent polyethylene glycol, the time and difficulty of on-site flushing will also be increased.

[0081] The hollow ultrafiltration membranes provided in the above Examples 1-4 and Comparative Examples 1-3 were subjected to performance tests, and the test items were as follows: (1) Surface opening rate: Take the dried hollow fiber membrane sprayed with gold and then inspect it with a scanning electron microscope. Take a photo of the surface at 20,000 times, and then use ImageJ software to calculate the surface open porosity. The implementation steps of ImageJ software are as follows: a. Set the software scale according to the scale of the electron microscope photo. b. Convert the image to 8-bit. c. Use the rectangular selection tool to select the photo. At this time, the selected area is the total area. d. Adjust the threshold and select the pores. At this time, the software calculates and reads the open area. Click Measure to calculate.

[0082] Opening rate (%) = opening area / selected area × 100% (2) Hollow fiber membrane pure water flux: A 30 cm long hollow fiber membrane was completely wetted and sealed in a test container. A filtration test was performed in a 25 ℃ environment using 25 ℃ pure water. The operating pressure was 0.1 MPa. After 10 min of stable operation, the water production was collected for 5 min and the pure water flux was determined using the following formula.

[0083] Pure water flux [L / ㎡ / h (LMH)] = 60 × (permeable water volume [L]) / {π × (membrane outer diameter [m]) × (membrane effective length [m]) × (measurement time [min])} (3) Tensile strength and elongation at break of hollow fiber membrane: The test was conducted using an electronic universal testing machine at a test speed of 25 mm / min, at room temperature, and with a spacing of 50 mm between the upper and lower fixtures. The formula for calculating the strength of the membrane is: Tensile strength [MPa] = tension [N] / cross-sectional area of ​​hollow fiber membrane [㎡]; Elongation at break [%] = 100 × (total length at break [mm] - initial length [mm]) / initial length [mm] (4) 50nmSiO 2 Retention rate: The 0.5㎡ completely wetted hollow fiber ultrafiltration membrane was encapsulated in a test container with a length of 50cm, and a sodium dodecyl sulfate mixed solution with a concentration of 0.2wt% was prepared. It was filtered by external pressure, with an operating pressure of 0.1MPa. After stable filtration for 10min, a 20ppm (0.02g / L) mixed solution was prepared with 50nm silica and 0.2wt% sodium dodecyl sulfate solution. After mixing evenly, it was also filtered by external pressure, with an operating pressure of 0.1MPa. After stable filtration for 15min, the permeate and raw liquid were collected. The Si element concentration in the permeate and raw liquid was measured by ICP (inductively coupled plasma spectrometer), and the silica particle retention rate was calculated according to the formula: 50nmSiO 2 Retention rate [%] = [1- (Si element concentration in permeate water / Si element concentration in raw water)] × 100% (5) Permeate water ΔTOC: ΔTOC is used to characterize the amount of residual organic matter in the ultrafiltration membrane. Take 0.5㎡ of the completely wetted hollow ultrafiltration membrane and encapsulate it into the test container. Rinse it with ultrapure water for 12 hours, and use 25℃ test water with TOC of 1-2ppb in a 25℃ environment to continuously pass the membrane. The operating pressure is 0.1MPa and the filtration is stable for 10 minutes. After filtration, the permeate water is collected, and the TOC concentration in the raw water and the permeate water is tested with a TOC tester, and the growth value of TOC in the permeate water is tested.

[0084] ΔTOC = permeate water TOC - raw water TOC The above performance test indicators of the ultrafiltration membranes provided in Examples 1-4 and Comparative Examples 1-2 are shown in Table 1: Table 1 Ultrafiltration membrane performance indicators

[0085] Figure 4 The figure shows the calculation diagram of the outer surface porosity of the hollow ultrafiltration membrane provided in Example 1 of the present invention. Figure 7 The figure shows the calculation diagram of the outer surface porosity of the hollow ultrafiltration membrane provided in Comparative Example 1 of the present invention. Fig.10 The calculation diagram of the outer surface porosity of the hollow ultrafiltration membrane provided by the comparative example 2 of the present invention is shown. Combined with Table 1, the outer surface porosity of the ultrafiltration membrane provided by Examples 1-4 is 19.27-22.05%. Compared with Comparative Example 1 (no pore opening agent) and Comparative Example 2 (additive is water-soluble polyethylene glycol), the outer surface porosity of the ultrafiltration membrane provided by Examples 1-4 is greatly improved, and the pure water flux is significantly improved. Because the surface pore size is uniform and the internal sponge structure is, nano-scale particles (50nm silica particles) can be effectively retained.

[0086] At the same time, the ultrafiltration membrane provided by Examples 1-4 can also maintain relatively good tensile strength and elongation at break. The pure water flux of the hollow ultrafiltration membrane provided by the present invention is 643-750L / (㎡•h•bar), the interception efficiency is greater than 99%, the tensile strength is 4.15-5.95MPa, the elongation at break is 49.5-71.2%, and the TOC increase of the permeate water is 0.2-0.4 ppb. Its pure water flux is not less than 600 L / (㎡•h•bar), and the interception efficiency of nano-scale particles (50 nm silica particles) is not less than 99%; and the tensile strength and elongation at break are maintained well. In terms of TOC of permeate water, due to the easy-to-clean characteristics of small molecules of ether compounds, under the same test flushing conditions, the test results of Examples 1-4 are 0.2-0.4ppb, which is significantly lower than 0.9ppb of Comparative Example 2. Therefore, the hollow ultrafiltration membrane provided by the present invention meets the multiple pursuits of high water flux, high particle retention efficiency and low precipitate of the terminal ultrafiltration membrane as a core component of terminal filtration.

[0087] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification.

[0088] For the method embodiments, for the sake of simplicity, they are all described as a series of action combinations, but those skilled in the art should know that the present invention is not limited by the order of the actions described, because according to the present invention, some steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also know that the embodiments described in the specification are all preferred embodiments, and the actions and components involved are not necessarily required by the present invention.

[0089] The hollow ultrafiltration membrane, preparation method and application thereof provided by the present invention are introduced in detail above. Specific examples are used in this article to illustrate the principle and implementation mode of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation mode and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. A method for preparing a hollow ultrafiltration membrane, characterized in that: The method comprises: Dissolving polysulfone resin and pore opening agent in an organic solvent, and stirring at a constant temperature to form a homogeneous film casting solution; The casting liquid and the core liquid are co-extruded into a coagulation bath through a double-channel spinneret, and the casting liquid is solidified by non-solvent phase separation to form a membrane precursor; The hollow ultrafiltration membrane is obtained by soaking the membrane precursor in an ethanol solution and washing with ultrapure water; Wherein, the pore opening agent is selected from one or more of n-pentyl ether, isodipentyl ether or dibutyl ether; In terms of weight, in the homogeneous casting solution, the polysulfone resin accounts for 15-25 parts, the pore opening agent accounts for 3-10 parts, and the organic solvent accounts for 55-80 parts.

2. The method for preparing the hollow 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 ultrafiltration membrane according to claim 1, characterized in that: The core liquid is formed by mixing water and the organic solvent in a volume ratio of 19:1-4:

1.

4. The method for preparing the hollow 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°C.

5. The method for preparing the hollow 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 60,000-120,000.

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

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

8. A hollow ultrafiltration membrane, characterized in that: The hollow ultrafiltration membrane is obtained by the preparation method described in any one of claims 1 to 7 above; Nanopores are distributed on the inner and outer surfaces of the hollow ultrafiltration membrane, and the pore size of the nanopores is 20-50 nm; The open porosity of the outer surface of the hollow fiber ultrafiltration membrane is 18-24%.

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

10. The use according to claim 9, characterized in that: The pure water flux of the hollow ultrafiltration membrane is not less than 600 L / (㎡•h•bar); The retention efficiency of the hollow ultrafiltration membrane for 50 nm silica particles is not less than 99%.

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