A porous polymer membrane, its preparation method and application in turbidity removal pre-filtration

Abstract

The application discloses a kind of polymer porous membrane, its preparation method and application in turbidity removal pre-filtering, belong to the technical field of porous membrane preparation.Its technical scheme includes: when the non-solvent phase separation of film-forming polymer solution occurs and the separation layer is formed on the outer surface of polymer membrane, simultaneously, water-soluble coating layer polymer solution is coated on the surface of separation layer, to obtain polymer porous membrane;Film-forming polymer solution uses polysulfone polymer as film-forming base material, uses water-soluble chloride as porogen, uses nitrogen-containing organic matter as solvent;Coating layer polymer solution has porogen effect, and viscosity is 200-1000 mPa·s.The application is applied to turbidity removal pre-filtering, solves the technical problems that existing non-solvent phase separation technology is difficult to obtain large aperture, surface opening rate is high and easy to appear finger-shaped hole, has the characteristics of large aperture, surface opening rate is high, cross section is sponge hole.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of porous membrane preparation, and particularly relates to a polymer porous membrane, a preparation method thereof and application thereof in turbidity removal pre-filtration. BACKGROUND

[0002] Membrane separation technology is a technology that can achieve deep separation. Sulfur-containing polymers represented by polysulfone are currently widely used in the preparation of porous membranes and in the efficient separation (hereinafter referred to as "turbidity removal pre-filtration") of turbidity-containing systems in the biological field. A larger pore size (pore size of 450 nm, such as efficient retention of colloidal, micro-particle and other suspended liquid systems in water), higher flux and lower protein adsorption are the prerequisite for the practical value of turbidity removal pre-filtration membranes in the biological field. A suitable pore size can efficiently retain substances that cause turbidity in the solution. The lower the filtration resistance, the higher the flux. Giving the membrane certain hydrophilicity can significantly reduce the adsorption of proteins (good post-film surface hydrophilic modification can improve the resistance to proteins, provided that a base film with a suitable pore size and high surface opening rate is prepared). Good membrane pore connectivity and high surface opening rate are the main factors for reducing membrane filtration resistance.

[0003] The non-solvent induced phase technology is the mainstream technology for preparing polysulfone-based polymer porous membranes at present. The principle of the technology is that the polymer, the pore-forming agent and the solvent are formed into a polymer solution at a certain temperature. Due to the concentration gradient, mass transfer occurs between the solvent and the additives and the coagulation bath (usually water). When the water content in the polymer solution reaches a certain level, the amount of remaining solvent is insufficient to dissolve the polymer, the polymer solidifies and precipitates, and the space previously occupied by the solvent and the additives in the polymer solution forms pores.

[0004] The ideal structure of separation membrane is good mechanical property, high surface open porosity, large pore size and through-pore structure. However, the ternary solution of "polymer / porogen / solvent" usually forms instantaneous phase separation due to fast phase separation speed, and finally forms a thick and dense skin layer with finger-like pore structure, which is not suitable for turbidity removal pre-filtration. Literature reports that the reverse thermal induced phase separation technology can prepare polyethersulfone porous membrane with sponge-like pore structure and thin skin layer, but the reverse thermal induced phase separation technology is difficult to form a stable solution at room temperature, but a metastable dispersion system, which is very sensitive to environmental temperature, and the system becomes more unstable when the environmental temperature rises, so the batch repeatability of the microstructure of the prepared membrane is poor. In addition, it is also difficult to obtain hollow fiber membrane with surface 450 nm large pore size by reverse thermal induced phase separation technology. Because the non-solvent induced phase separation technology is relatively simple, the control requirements of process parameters are not very harsh, therefore, in addition to exploring convenient and effective surface hydrophilic modification method, it is particularly necessary to study the preparation of polymer porous membrane for turbidity removal pre-filtration by non-solvent induced phase separation technology, which has good through-pore, thin skin layer, high surface open porosity and pore size up to 450 nm.

[0005] Currently, the methods for improving the pore size of membranes prepared by the non-solvent induced phase separation technique mainly include the following: (1) adding a template agent (such as inorganic nano-particles such as nano calcium carbonate, nano silicon dioxide, etc.) into the casting solution, and then removing the template agent by using a strong alkali or strong acid solution after film formation. However, the prepared membrane has uneven pore size due to the poor compatibility between the inorganic nano-particles and the polymer, and the template agent is difficult to disperse uniformly in the casting solution system. In addition, a certain amount of waste acid or waste alkali solution is generated in the process of removing the template agent, and the improvement degree of the membrane pore size is very limited (the membrane pore size is usually only 50-100 nm), far from the requirement of 450 nm; (2) adding a certain proportion of solvents such as N,N-dimethylacetamide (DMAC) and other polysulfone polymers into the coagulation bath water. The solidification rate of the polymer is reduced due to the presence of the solvent, thereby slowing down the dense skin layer and finger-like pore structure formed due to the rapid solidification of the polymer to a certain extent. However, this method can only reduce the skin layer thickness and improve the surface opening rate and pore size to a certain extent, and the effect of improving the pore size is not significant, and it is difficult to form a pore size of more than 100 nm; (3) reducing the polymer concentration. This method also has difficulty in forming a pore size of more than 100 nm; (4) increasing the air humidity. Before the casting solution enters the coagulation bath, the water vapor in the air adheres to the surface of the casting film, which can greatly slow down the diffusion speed between water and solvents and additives in the subsequent casting solution entering the coagulation bath, thereby reducing the skin layer thickness, eliminating the cross-sectional finger-like pores, and improving the membrane surface opening rate and pore size. However, the air humidity requirement of this process reaches supersaturation, which greatly increases the equipment process, and the control requirement of the humidity is quite high. The water in the supersaturated air will condense and precipitate, thereby changing the humidity of the air, and it is difficult to achieve the required membrane pore size; (5) adding two additives such as calcium chloride and polyvinylpyrrolidone into the polymer solution. However, the improvement degree of the membrane pore size by this method is also limited (the membrane pore size is usually only about 100 nm), far from the requirement of 450 nm; (6) using a three-layer spinneret (from outside to inside, the coating liquid (solvent of the polymer), the polymer solution, and the cavity-forming fluid) to synchronously introduce a solvent as a coating layer outside the polymer solution. This method has similar effects to (2), and the results are that the skin layer thickness of the membrane is reduced, and the surface opening rate is improved to a certain extent. However, the pore size improvement effect is not significant, and it is difficult to form a pore size of more than 100 nm. In addition, since the solvent of the polymer is a small-molecule organic substance with very low viscosity, the solvent as the coating layer is easily broken by the polymer solution with high viscosity during synchronous coating spinning, and the desired effect cannot be achieved. However, since the surface synchronous coating method is simple, efficient, and easy to industrialize, it is an ideal technology for effectively controlling the surface microstructure of the membrane. Therefore, whether the integrity of the coating layer during synchronous coating can be achieved and the pore size of the membrane surface can be significantly improved is the key. SUMMARY

[0006] In view of the deficiencies of the prior art, the technical problem to be solved by the present application is to overcome the technical problem that the existing non-solvent induced phase separation technology is difficult to obtain a large pore diameter, high surface opening rate and easy to appear finger-shaped hole, and a polymer porous membrane with large pore diameter, high surface opening rate and cross-section with sponge hole structure characteristics, a preparation method thereof and application in turbidity removal pre-filtration are provided.

[0007] To solve the technical problem, the technical scheme adopted by the present application is:

[0008] The present application provides a preparation method of a polymer porous membrane, comprising: synchronously coating a water-soluble coating layer polymer solution on the surface of the separation layer while the non-solvent induced phase separation of the film-forming polymer solution occurs and the separation layer is formed on the outer surface of the polymer membrane, to obtain a polymer porous membrane; the film-forming polymer solution takes a polysulfone polymer as a film-forming substrate, a water-soluble chloride as a pore-forming agent, and a nitrogen-containing organic matter as a solvent; the coating layer polymer solution has a pore-forming agent effect, and the viscosity is 200-1000 mPa·s.

[0009] In some embodiments, the coating layer polymer solution comprises a hydroxyl-containing polymer and an N-containing polymer; the hydroxyl-containing polymer is polyethylene oxide with a molecular weight of 100-300 kDa, and the N-containing polymer is polyvinylpyrrolidone with a molecular weight of 30-45 kDa.

[0010] In some embodiments, the mass ratio of the polysulfone polymer, the pore-forming agent and the solvent in the film-forming polymer solution is 15-17:2-5:78-82; and the weight average molecular weight of the polysulfone polymer is 55-80 kDa.

[0011] In some embodiments, the solvent is one of N,N-dimethylacetamide and N-methylpyrrolidone, and the pore-forming agent is one of calcium chloride and lithium chloride.

[0012] In some embodiments, the coating layer polymer solution comprises a hydroxyl-containing polymer, an N-containing polymer and a solvent; the mass ratio of the hydroxyl-containing polymer, the N-containing polymer and the solvent is 5-15:3-5:80-92.

[0013] In some embodiments, the polysulfone polymer is polysulfone or polyether sulfone.

[0014] In some embodiments, it comprises:

[0015] S1, uniformly mix the polysulfone polymer, the pore-forming agent and the solvent at 60-70 DEG C, and then vacuum degassing to obtain a film-forming polymer solution for preparing a polymer membrane;

[0016] S2, the hydroxyl-containing water-soluble hydrophilic polymer porogen, the N-containing water-soluble hydrophilic polymer porogen and the organic solvent are mixed at 25 DEG C and then vacuum degassed to obtain a coating layer polymer solution for preparing a coating layer;

[0017] S3, the coating layer polymer solution and the film-forming polymer solution are extruded from the outermost side and the middle side of the spinneret, respectively, at 45-55 DEG C, while deionized water containing 20-30% organic solvent at 30-40 DEG C is introduced into the inner side of the spinneret as a core liquid to form a hollow fiber membrane shape, and then cooled to form a membrane;

[0018] S4, the membrane is immersed and washed with deionized water as an extractant to obtain a polymer porous membrane.

[0019] In some embodiments, the air gap length in S3 is 5-15 cm, the winding speed is 10-20 m / min, and the thickness of the coating layer polymer solution is 0.05-0.10 mm.

[0020] Another aspect of the present application provides a polymer porous membrane prepared by the preparation method of the polymer porous membrane provided in any of the above technical solutions, wherein the polymer porous membrane is a hollow fiber membrane, the outer diameter of the hollow fiber membrane is 1.0-1.4 mm, and the inner diameter is 0.5-0.7 mm.

[0021] The present application also provides the application of the polymer porous membrane provided in the above technical solutions in pre-filtration for removing turbidity.

[0022] Compared with the prior art, the present application has the following advantages:

[0023] The present application provides a preparation method of a polymer porous membrane, which uses a polysulfone-based polymer as a base material and adopts a non-solvent phase separation technology to prepare a polymer hollow fiber membrane. A water-soluble coating layer polymer solution with a certain viscosity and porogen effect is synchronously coated on the surface of the separation layer while the separation layer is formed on the outer surface of the polymer. The contact interface between the porogen polymer chain and the film-forming polymer chain in the process of synchronous extrusion and molding is utilized. The coating layer polymer with a porogenic effect diffuses to the side of the film-forming polymer solution due to the concentration gradient between the coating layer polymer solution and the film-forming polymer solution before solidification, which significantly improves the surface opening rate and pore size of the polymer membrane separation layer. In addition, the coating layer polymer solution has a high viscosity, which hinders the double diffusion mass transfer between the film-forming polymer solution and the coagulation bath, so that the film-forming polymer solution system obviously delays the phase separation, further improves the surface opening rate of the membrane and increases the pore size of the membrane, and eliminates the finger-like pore structure. The problem that it is difficult to obtain a large pore size, high surface opening rate and finger-like pore structure by using the non-solvent phase separation technology is effectively solved. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 Surface topography of the polymer porous membrane provided by Example 1 of the present application;

[0025] Figure 2 Surface topography of the polymer porous membrane provided by Comparative Example 1 of the present application;

[0026] Figure 3 Cross-sectional topography of the polymer porous membrane provided by Example 1 of the present application;

[0027] Figure 4 Cross-sectional topography of the polymer porous membrane provided by Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0028] The technical solutions in the specific embodiments of the present application will be described in detail and completely below. Obviously, the described embodiments are only partial specific embodiments of the general technical solution of the present application, but not all the embodiments. All other embodiments obtained by those skilled in the art based on the general concept of the present application fall within the scope of protection of the present application.

[0029] The present application provides, in one aspect, a preparation method of a polymer porous membrane, comprising: synchronously coating a water-soluble coating layer polymer solution on the surface of a separation layer while the non-solvent induced phase separation of a film-forming polymer solution occurs and the separation layer is formed on the outer surface of the polymer membrane, to obtain the polymer porous membrane; the film-forming polymer solution takes a polysulfone polymer as a film-forming base material, a water-soluble chloride as a porogen, and a nitrogen-containing organic substance as a solvent; the coating layer polymer solution has a porogenic effect and a viscosity of 200-1000 mPa·s.

[0030] The above preparation method utilizes the contact interface between the porogenic polymer chains and the film-forming polymer chains in the synchronous extrusion molding process of the coating layer polymer solution and the film-forming polymer solution to make a relatively sufficient contact before solidification. The coating layer polymer with a porogenic effect diffuses to the side of the film-forming polymer solution due to the concentration gradient between the coating layer polymer solution and the film-forming polymer solution, thereby significantly improving the surface opening rate and pore size of the separation layer of the polymer membrane. In addition, the coating layer polymer has a high viscosity to hinder the double diffusion mass transfer between the film-forming polymer solution and the coagulation bath, so that the film-forming polymer solution system obviously delays the phase separation, further improves the surface opening rate of the membrane, increases the pore size of the membrane, and eliminates the finger-like pore structure, and finally obtains a polymer porous membrane with large pore size and high surface opening rate, which can be used for turbidity removal and pre-filtration.

[0031] The ternary solution of the common "polymer / pore-forming agent / solvent" forms an instantaneous phase separation when the non-solvent induced phase separation process occurs, and the skin layer is thick and dense, and the cross-section is a non-compressive finger-shaped hole structure. The above preparation method provided by the present application solves the above problems. Specifically, the principle of the present application is as follows:

[0032] A thin layer (referred to as a coating layer) of a polymer solution with a certain viscosity and pore-forming agent effect at the same temperature as the polymer solution is coated outside the film-forming polymer solution. Since the coating layer polymer solution has a certain viscosity and can form a barrier between the coagulation bath and the film-forming polymer solution, it can greatly slow down the double diffusion mass transfer between the coagulation bath and the film-forming polymer solution, and greatly slow down the solidification and film formation of the polymer in the film-forming polymer solution, thereby forming a porous skin layer structure without forming a dense thick skin layer, and without the problem of being broken by the film-forming polymer solution with a certain pressure during the spinning process. Especially, since the contact interface between the two polymer chains of the film-forming polymer solution and the coating layer polymer solution is fully contacted before solidification during the synchronous extrusion molding process, and there is a concentration gradient between the coating layer polymer solution and the film-forming polymer solution, the coating layer polymer with pore-forming effect diffuses to the side of the film-forming polymer solution, which significantly improves the surface opening rate and pore size of the polymer membrane separation layer, and the nominal pore size of the membrane reaches 450nm, which is very suitable for biological field turbidity removal and pre-filtration operation.

[0033] In some embodiments, the coating layer polymer solution includes a hydroxyl-containing polymer and an N-containing polymer; the hydroxyl-containing polymer is polyethylene oxide with a molecular weight of 100-300kDa, and the N-containing polymer is polyvinylpyrrolidone with a molecular weight of 30-45kDa.

[0034] The coating layer polymer solution has a certain viscosity and pore-forming agent effect, and the components include a hydroxyl-containing polymer and an N-containing polymer, the hydroxyl-containing polymer, the N-containing polymer and the solvent (the same as the solvent used in the film-forming polymer solution) are prepared in a certain mass ratio, the viscosity of the formed coating layer polymer solution is 200-1000 mPa·s, and the types and molecular weights of the hydroxyl-containing polymer and the N-containing polymer are limited, because when a polyethylene oxide with a molecular weight of 20-100 kDa is used, although the viscosity can be ensured not to be broken by the film-forming polymer solution with a certain pressure extruded from the spinneret, the pore size of the membrane can only reach 200 nm, and still cannot reach 450 nm, and further cooperation with the N-containing polymer pore-forming agent is required to further improve the pore size of the membrane; when a polyethylene oxide with a molecular weight exceeding 300 kDa is used, the viscosity is too high at the spinning temperature, the diffusion rate of the film-forming polymer solution is reduced, and it is not easy to form the required pore size. In addition, if a solvent of a polysulfone polymer without pore-forming effect is used as a coating liquid, the skin layer thickness can only be reduced to a certain extent, and the effect of improving the pore size is not significant.

[0035] In some embodiments, the mass ratio of the polysulfone polymer, the pore-forming agent and the solvent in the film-forming polymer solution is 15-17:2-5:78-82; and the weight average molecular weight of the polysulfone polymer is 55-80 kDa.

[0036] If the weight average molecular weight of the polysulfone polymer is too low or the content of the polysulfone polymer in the film-forming polymer solution is too low, the viscosity of the film-forming polymer solution is too low, the formability is poor, and the strength is low; if the weight average molecular weight of the polysulfone polymer is too high or the content of the polysulfone polymer in the film-forming polymer solution is too high, the viscosity of the film-forming polymer solution is too large and not easy to process, and the pore size is too small, which cannot meet the pore size requirement of the turbidity removal pre-filter. It can be understood that the weight average molecular weight of the polysulfone polymer can also be 60 kDa, 65 kDa, 70 kDa, 75 kDa and any point value within the range.

[0037] In some embodiments, the solvent is one of N,N-dimethylacetamide and N-methyl pyrrolidone, and the pore-forming agent is one of calcium chloride and lithium chloride.

[0038] In some embodiments, the coating layer polymer solution includes a hydroxyl-containing polymer, an N-containing polymer and a solvent; and the mass ratio of the hydroxyl-containing polymer, the N-containing polymer and the solvent is 5-15:3-5:80-92.

[0039] In some embodiments, the polysulfone polymer is polysulfone or polyether sulfone.

[0040] In some embodiments, the method includes:

[0041] S1, mixing the polysulfone polymer, the pore-forming agent and the solvent at 60-70°C, vacuum degassing to obtain a film-forming polymer solution for preparing the polymer membrane;

[0042] S2, mixing the hydroxyl-containing water-soluble hydrophilic polymer pore-forming agent, the N-containing water-soluble hydrophilic polymer pore-forming agent and the organic solvent at 25°C, vacuum degassing to obtain a coating layer polymer solution for preparing the coating layer;

[0043] S3, extruding the coating layer polymer solution and the film-forming polymer solution from the outermost side and the middle side of the spinneret at 45-55°C, respectively, while passing the 30-40°C deionized water containing 20-30% organic solvent as the core liquid in the inner side of the spinneret to form the shape of the hollow fiber membrane, and cooling to form the membrane;

[0044] S4, immersing the membrane in deionized water as the extractant for washing to obtain the polymer porous membrane.

[0045] The above-mentioned membrane preparation process synchronously extrudes the coating layer polymer solution and the film-forming polymer solution, which has the following characteristics: (1) simple preparation process. Only a slight improvement of the spinneret (adding a polymer solution channel), using the existing commercial non-solvent phase separation technology operation steps and adding a kettle containing the coating material which can be heated and a metering pump can prepare the required structure of the hollow fiber membrane. (2) significantly improve the effect of the membrane surface pore size and the method is simple. By the way of synchronous extrusion of surface coating and polymer film formation, the separation layer is formed on the outer surface of the polymer membrane at the same time, and the water-soluble binary polymer containing multiple hydroxyl and N elements with high viscosity and pore-forming effect is coated on the surface of the separation layer at the same temperature as the spinning temperature. The contact interface between the two polymer chains of the polymer solution of the separation layer and the polymer solution of the coating layer is fully contacted before solidification. The coating layer polymer with pore-forming effect diffuses to the side of the film-forming polymer solution due to the concentration gradient between the coating layer polymer solution and the film-forming polymer solution, which significantly improves the surface opening rate and pore size of the polymer membrane separation layer. In addition, the coating layer polymer has high viscosity, which hinders the double diffusion mass transfer between the film-forming polymer solution and the coagulation bath, so that the film-forming polymer solution system occurs obvious delayed phase separation, further improves the membrane surface opening rate, increases the membrane pore size and eliminates the finger-like pore structure, and finally obtains the polymer porous membrane with large pore size and high surface opening rate. (3) adjustment of the membrane pore size. By adjusting the composition of the coating layer and the composition of the film-forming polymer layer and the membrane preparation process parameters, the film-forming process can be effectively adjusted, which finally improves the membrane pore connectivity, effectively reduces the skin layer thickness, improves the membrane surface opening rate and realizes larger pore size, thereby realizing the adjustment of the membrane microstructure, especially the pore size.

[0046] In some embodiments, the air gap length in S3 is 5-15 cm, the winding rate is 10-20 m / min, and the thickness of the coating layer polymer solution is 0.05-0.10 mm.

[0047] Since the coating layer polymer solution and the film-forming polymer solution enter the coagulation bath together, first, double diffusion mass transfer between the coating layer polymer solution and the coagulation bath and double diffusion mass transfer between the coating layer polymer solution and the film-forming polymer solution occur, respectively. Therefore, the contact interface between the coating layer polymer solution and the film-forming polymer solution needs to be completed within the time of the air gap before the coating layer polymer solution enters the coagulation bath, so that the chain entanglement is completed and the coating layer and the film-forming polymer solution are integrated, and the pore-forming agent polymer of the coating layer fully penetrates the surface of the film-forming polymer under the action of the concentration difference, thereby improving the pore diameter of the membrane surface due to the strong pore-forming effect. In addition, after the coating layer polymer solution enters the coagulation bath, the double diffusion between water in the coagulation bath and the film-forming polymer solution is effectively hindered, and the significant delay of phase separation of the film-forming polymer solution further improves the pore diameter of the membrane surface, and finally forms a pore diameter that can remove turbidity and pre-filter.

[0048] The time of the polymer solution in the air is closely related to the air gap length, the winding rate, and the membrane liquid thickness. Experimental tests show that for a hollow fiber membrane with an outer diameter of 1.0-1.4 mm and an inner diameter of 0.5-0.7 mm, the air gap length (traveling distance in the air) is 5-15 cm, the winding rate is 10-20 m / min, and the thickness of the coating layer polymer solution is 0.05-0.10 mm to achieve the above purpose. If the air gap length is too short or the thickness of the coating layer polymer solution is too thin, it is difficult to ensure the effective diffusion of the double-component pore-forming agent in the coating layer polymer solution layer towards the film-forming polymer solution layer, and the required size of the pore diameter cannot be obtained. If the air gap length is too long or the thickness of the coating layer polymer solution is too thick, the pore diameter of the membrane is too large, the spinnability of the film-forming polymer solution is poor, and the strength is reduced.

[0049] The present application provides a preparation method of a polymer hollow fiber membrane which can be used in the field of biology to achieve efficient turbidity removal and pre-filtration. The method has lower requirements for the preparation temperature of the membrane, can reduce the thickness of the product skin layer and improve the opening rate of the skin layer, and the nominal pore diameter reaches 450 nm with good permeability, thereby overcoming the shortcomings of the prior art. At the same time, the membrane forming and the improvement of the surface pore diameter are carried out synchronously without additional process for the preparation of the membrane. The specific implementation means include:

[0050] (1) For the polymer membrane layer, a water solution containing a certain concentration of polymer solvent is used as the cavity-forming fluid, a polysulfone-based polymer is used as the film-forming substrate, a water-soluble chloride is used as the pore-forming agent, and a nitrogen-containing organic compound is used as the solvent, and a polymer porous membrane with large pore size and high surface opening rate is prepared by using the non-solvent induced phase separation technology; (2) For the coating layer, a water-soluble polymer solution with a certain viscosity and pore-forming effect is simultaneously coated on the surface of the separation layer formed on the outer surface of the polymer membrane, and a polymer porous membrane with large surface pore size and high opening rate is obtained; (3) Film formation and surface coating are carried out simultaneously. Specifically, the following steps are included:

[0051] 1) Preparation of polymer solution:

[0052] Preparation of film-forming polymer solution: 16-20 parts of polysulfone-based polymer with a weight average molecular weight of 55-80 kDa after drying, 2-5 parts of pore-forming agent after drying, and 75-82 parts of solvent are mixed uniformly in a kettle stirrer at 60-70°C for 8 h to form a polymer solution, and then vacuum degassing for 2 h to obtain a film-forming polymer solution for preparing a polymer membrane;

[0053] Preparation of coating layer polymer solution: a water-soluble and pore-forming hydroxyl-containing polymer, a N-containing polymer, and a solvent are added to a kettle stirrer in a mass ratio of 5-15:3-5:80-92, mixed uniformly at 25°C for 4 h to form a polymer solution, and then vacuum degassed for 2 h to obtain a coating layer polymer solution for preparing a coating layer, with a viscosity range of 200-1000 mPa·s;

[0054] 2) Spinning into hollow fiber membrane:

[0055] A three-layer spinneret is used, from outside to inside, the coating layer polymer solution for forming the coating layer, the film-forming polymer solution for forming the membrane, and the cavity-forming fluid. The coating layer polymer solution and the film-forming polymer solution obtained in step 1) are simultaneously extruded through the outermost channel and the middle channel of the spinneret at 45-55°C, while the inner channel of the spinneret is introduced with 30-40°C deionized water containing 20-30% solvent as the cavity-forming fluid. The flow rate of the coating layer polymer solution is 0.3-0.6 L / h, the flow rate of the film-forming polymer solution is 0.9-1.2 L / h, and the flow rate of the cavity-forming fluid is 0.5-0.7 L / h. The coating layer polymer solution and the film-forming polymer solution, as well as the cavity-forming fluid, pass through an air gap with a length of 5-15 cm and then enter a room temperature quenching bath composed of deionized water. The resulting nascent membrane is cooled and wound into a silk by deionized water. The obtained hollow fiber membrane product has an outer diameter of 1.2-1.4 mm, an inner diameter of 0.6-0.8 mm, a pore size of 450 nm, and meets the use requirements.

[0056] The solvent in the film-forming polymer solution in step 1) is one of N,N-dimethylacetamide and N-methylpyrrolidone; the pore-forming agent is one of calcium chloride and lithium chloride;

[0057] The solvent in the coating layer polymer solution in step 1) is the same as that in the film-forming polymer solution; the pore-forming agent in the coating layer polymer solution is both a hydroxyl-containing polymer and an N-containing polymer, the hydroxyl-containing polymer is polyethylene oxide with a molecular weight of 100-300 kDa, and the N-containing polymer is polyvinylpyrrolidone with a molecular weight of 30-45 kDa;

[0058] The winding speed in the spinning process in step 2) is 10-20 m / min.

[0059] Compared with the prior art, the application uses a binary mixed water-soluble polymer containing hydroxyl and N elements with pore-forming effect and high viscosity as the coating layer polymer solution, forms a separation layer on the outer surface of the polymer membrane at the same time, and synchronously coats the above coating layer polymer solution on the surface of the separation layer to obtain a polymer hollow fiber membrane with the required structure, and by selecting a polymer with a suitable weight average molecular weight and content, a solvent, and an inorganic pore-forming agent, the structure with a thin and porous outer skin layer and a nominal pore size of up to 450 nm can be easily obtained or controlled by a non-solvent phase inversion membrane forming technology.

[0060] Compared with the prior art, the present application is different in coating method, used coating polymer, coating temperature, film forming effect, obtained film structure and air gap length. In the present application, the temperature of the coating polymer solution (which has two main functions: hindering the double diffusion between the coagulation bath and the film forming polymer solution to greatly delay the phase separation process of the film forming polymer solution, and the polymer in the coating polymer solution with pore-forming effect diffuses to the side of the film forming polymer solution, finally significantly increasing the surface opening rate and pore size of the polymer membrane separation layer) and the film forming polymer solution is the same, the film forming polymer film solution layer undergoes non-solvent induced phase separation, and the polymer film forming and film surface coating are carried out synchronously (step-by-step coating cannot form large pores on the surface), which is different from the step-by-step coating (first film forming and then coating polymer on the film surface-coating polymer is not washed away, which is a method to realize the shrinkage of the film) and the homogeneous composite (the coating layer and the film are the same polymer, the coating layer undergoes non-solvent induced phase separation, and the separation layer undergoes thermal induced phase separation-coating polymer is not washed away, which is a method to realize the shrinkage of the film) reported in the literature and patents, and the method of improving the surface opening rate (coating an aqueous solution containing a certain concentration of organic solvent on the surface of the polymer solution film formed by non-solvent induced phase separation technology, which increases the possibility of being washed away by the polymer solution due to the low viscosity of the organic solvent aqueous solution, resulting in poor spinning effect and the method has no obvious effect on improving the surface pore size, far from reaching the standard of forming a 450nm nominal pore size), and the effect obtained by synchronous coating with styrene-maleic anhydride copolymer (styrene-maleic anhydride copolymer has poor film forming property, poor adhesion with the polymer film, and is used to realize surface functional modification instead of being washed away later) is also different, and the effect achieved is also different.

[0061] In the present application, two polymer additives with high viscosity, solubility in ethanol or water and pore-forming effect are used in the coating layer, which are washed away during the subsequent membrane extraction and washing process to obtain a large-pore polymer membrane with a nominal pore size of up to 450nm, and substances such as tannic acid dissolved in water used for coating have low viscosity, which not only has no obvious pore-forming effect, but also has the possibility of being washed away by the polymer solution. The membrane obtained by the present application has a large surface pore size (the nominal pore size can reach 450nm), while the purpose of the coating technology reported in the literature and patents is to reduce the skin layer thickness or realize surface functional modification. In summary, the present application has good adaptability, is simple and easy to implement, has a wide source of materials, low cost, good effect, only needs to update part of the equipment, is easy to popularize, and has good industrialization prospect. In addition, the pore-forming agent is easily dissolved in water and can be easily washed away by water. The present application has the characteristics of simple preparation process, good membrane pore connectivity, large pore size and high surface opening rate.

[0062] In another aspect of the present application, the polymer porous membrane prepared by the method for preparing the polymer porous membrane provided by any of the above technical solutions is provided, and the polymer porous membrane is a hollow fiber membrane; the outer diameter of the hollow fiber membrane is 1.0-1.4 mm, and the inner diameter is 0.5-0.7 mm.

[0063] The present application also provides the application of the polymer porous membrane provided by the above technical solutions in pre-filtration for removing turbidity.

[0064] In order to more clearly and specifically introduce the polymer porous membrane, the method for preparing the same and the application of the same in pre-filtration for removing turbidity provided by the embodiments of the present application, the following will be described in combination with specific embodiments.

[0065] Embodiment 1

[0066] 1) Preparation of polymer solution:

[0067] Preparation of film-forming polymer solution: 16 parts of polyether sulfone with a weight average molecular weight of 55 kDa after drying, 2 parts of calcium chloride after drying and 82 parts of N,N-dimethylacetamide were mixed uniformly in a kettle stirrer at 60°C for 8 h to form a polymer solution, and then vacuum degassing was performed for 2 h to obtain a film-forming polymer solution for preparing a polymer membrane;

[0068] Preparation of coating layer polymer solution: 5 parts of polyethylene oxide with a molecular weight of 100 kDa, 3 parts of polyvinylpyrrolidone with a molecular weight of 30 kDa and 92 parts of N,N-dimethylacetamide were mixed uniformly in a kettle stirrer at 25°C for 4 h to form a polymer solution, and then vacuum degassing was performed for 2 h to obtain a coating layer polymer solution for preparing a coating layer;

[0069] 2) Preparation of hollow fiber membrane: a three-layer spinneret was used, and the coating layer polymer solution, the film-forming polymer solution and the lumen-forming fluid were sequentially arranged from the outside to the inside. The coating layer polymer solution and the film-forming polymer solution obtained in step 1) were extruded through the outermost side and the middle side of the spinneret, respectively, at 45°C. Meanwhile, 20% N,N-dimethylacetamide deionized water at 30°C was introduced into the inner side of the spinneret as the lumen-forming fluid, the flow rate of the coating layer polymer solution was 0.3 L / h, the flow rate of the film-forming polymer solution was 0.9 L / h, and the flow rate of the lumen-forming fluid was 0.5 L / h; the spinning speed was 10 m / min, and after passing through an air gap with a length of 5 cm, the obtained nascent membrane was introduced into a coagulation bath composed of room temperature deionized water, and then the nascent membrane was wound into a yarn through double diffusion of substances between the deionized water and the nascent membrane. The obtained yarn was extracted with deionized water at 25°C to extract the solvent and the pore-forming agent, and after two extractions, a hollow fiber membrane product with an outer diameter of 1.0 mm and an inner diameter of 0.5 mm was obtained.

[0070] The surface morphology of the membrane is as shown in Figure 1As shown, the membrane pore size was determined to be 465 nm (test method: GB / T 32361-2015 "Separation membrane pore size test method - bubble point and average flow rate method"), as shown in Figure 3 As shown, the cross-section is a sponge hole, and the membrane pore size without a coating layer is 78 nm, and the cross-section is a finger hole.

[0071] Example 2

[0072] 1) Preparation of polymer solution:

[0073] Preparation of film-forming polymer solution: 20 parts of polyether sulfone with a weight average molecular weight of 80 kDa after drying and 5 parts of calcium chloride after drying and 75 parts of N,N-dimethylacetamide were mixed uniformly in a kettle stirrer at 70°C for 8 h to form a polymer solution, and then vacuum degassing was performed for 2 h to obtain a film-forming polymer solution for preparing a polymer film;

[0074] Preparation of coating layer polymer solution: 100 kDa polyethylene oxide and 30 kDa polyvinylpyrrolidone, N,N-dimethylacetamide were mixed uniformly in a kettle stirrer at 25°C for 4 h to form a polymer solution at a mass ratio of 15:5:80, and then vacuum degassing was performed for 2 h to obtain a coating layer polymer solution for preparing a coating layer;

[0075] 2) Hollow fiber membrane preparation: a three-layer structure spinneret was used, and the coating layer polymer solution, the film-forming polymer solution and the cavity-forming fluid were sequentially arranged from the outside to the inside. The coating layer polymer solution and the film-forming polymer solution in step 1) were extruded through the outermost side and the middle side of the spinneret, respectively, at 55°C. At the same time, 30% N,N-dimethylacetamide deionized water at 40°C was introduced into the inner side of the spinneret as the cavity-forming fluid, the flow rate of the coating layer polymer solution was 0.3 L / h, the flow rate of the polymer solution was 0.9 L / h, and the flow rate of the cavity-forming fluid was 0.5 L / h; the spinning speed was 10 m / min, and after passing through an air gap with a length of 5 cm, it entered a coagulation bath composed of room temperature deionized water, and then the obtained primary membrane was wound into a silk through double diffusion of substances between the deionized water. After 2 extractions of the solvent and the pore-forming agent at 25°C using deionized water, a hollow fiber membrane product with an outer diameter of 1.0 mm and an inner diameter of 0.5 mm was obtained.

[0076] The membrane pore size was determined to be 460 nm (test method: GB / T 32361-2015 "Separation membrane pore size test method - bubble point and average flow rate method"), and the cross-section was a sponge hole; the membrane pore size without a coating layer was 71 nm, and the cross-section was a finger hole.

[0077] Example 3

[0078] 1) Preparation of polymer solution:

[0079] Preparation of the coating layer polymer solution: 15 parts of polyethylene oxide with a molecular weight of 100 kDa and 5 parts of polyvinylpyrrolidone with a molecular weight of 30 kDa, and 80 parts of N,N-dimethylacetamide were mixed uniformly in a kettle stirrer at 25°C for 4 h to form a polymer solution, which was then vacuum degassed for 2 h to obtain a coating layer polymer solution for preparing the coating layer;

[0080] Preparation of the coating layer polymer solution: 15 parts of polyethylene oxide with a molecular weight of 100 kDa and 5 parts of polyvinylpyrrolidone with a molecular weight of 30 kDa, and 80 parts of N,N-dimethylacetamide were mixed uniformly in a kettle stirrer at 25°C for 4 h to form a polymer solution, which was then vacuum degassed for 2 h to obtain a coating layer polymer solution for preparing the coating layer;

[0081] 2) Hollow fiber membrane preparation: a three-layer spinneret was used, and the coating layer polymer solution, the membrane-forming polymer solution, and the lumen-forming fluid were sequentially arranged from the outside to the inside. The coating layer polymer solution and the membrane-forming polymer solution obtained in step 1) were simultaneously extruded through the outermost and middle channels of the spinneret at 55°C. At the same time, 30% N,N-dimethylacetamide deionized water at 40°C was introduced into the inner channel of the spinneret as the lumen-forming fluid. The flow rates of the coating layer polymer solution, the polymer solution, and the lumen-forming fluid were 0.6 L / h, 1.2 L / h, and 0.7 L / h, respectively. The spinning speed was 10 m / min, and after passing through an air gap with a length of 5 cm, the nascent membrane filaments were introduced into a coagulation bath composed of room temperature deionized water. The obtained membrane filaments were extracted with deionized water at 25°C to remove the solvent and the pore-forming agent. After two extractions, a hollow fiber membrane product with an outer diameter of 1.4 mm and an inner diameter of 0.7 mm was obtained.

[0082] It was determined that the membrane pore size was 462 nm (the test method was GB / T 32361-2015 "Separation membrane pore size test method - bubble point and average flow rate method"), and the cross-section was a sponge hole. The pore size of the membrane without a coating layer was 72 nm, and the cross-section was a finger-shaped hole.

[0083] Example 4

[0084] 1) Preparation of the polymer solution:

[0085] Preparation of the coating layer polymer solution: 15 parts of polyethylene oxide with a molecular weight of 100 kDa and 5 parts of polyvinylpyrrolidone with a molecular weight of 30 kDa, and 80 parts of N,N-dimethylacetamide were mixed uniformly in a kettle stirrer at 25°C for 4 h to form a polymer solution, which was then vacuum degassed for 2 h to obtain a coating layer polymer solution for preparing the coating layer;

[0086] Preparation of the coating layer polymer solution: 10 parts of polyethylene oxide with a molecular weight of 100 kDa, 5 parts of polyvinylpyrrolidone with a molecular weight of 45 kDa, and 85 parts of N-methylpyrrolidone were mixed uniformly at 25°C for 4 h in a kettle stirrer to obtain a polymer solution, which was then vacuum degassed for 2 h to obtain the coating layer polymer solution for preparing the coating layer;

[0087] 2) Hollow fiber membrane preparation: a spinneret with a three-layer structure was used, and the coating layer polymer solution, the membrane-forming polymer solution, and the lumen-forming fluid were sequentially arranged from the outside to the inside. The coating layer polymer solution and the membrane-forming polymer solution in step 1) were extruded through the outermost and middle channels of the spinneret, respectively, at 55°C. At the same time, 30% N-methylpyrrolidone deionized water at 40°C was introduced into the inner channel of the spinneret as the lumen-forming fluid. The flow rates of the coating layer polymer solution, the polymer solution, and the lumen-forming fluid were 0.6 L / h, 1.2 L / h, and 0.7 L / h, respectively. The spinning speed was 20 m / min. After passing through an air gap with a length of 15 cm, the nascent membrane filaments were introduced into a coagulation bath composed of room temperature deionized water, and then were wound into filaments through double diffusion mass exchange between the deionized water. After being extracted with deionized water at 25°C to remove the solvent and the pore-forming agent for 2 times, a hollow fiber membrane product with an outer diameter of 1.3 mm and an inner diameter of 0.7 mm was obtained.

[0088] It was determined that the membrane pore size was 447 nm (the test method was GB / T 32361-2015 “Separation membrane pore size test method - bubble point and average flow rate method”), and the cross-section was a sponge hole. The pore size of the membrane without a coating layer was 69 nm, and the cross-section was a finger-shaped hole.

[0089] Example 5

[0090] 1) Preparation of the polymer solution:

[0091] Preparation of the membrane-forming polymer solution: 20 parts of oven-dried polysulfone with a weight average molecular weight of 79 kDa, 5 parts of oven-dried lithium chloride, and 75 parts of N-methylpyrrolidone were mixed uniformly at 70°C for 8 h in a kettle stirrer to obtain a polymer solution, which was then vacuum degassed for 2 h to obtain the membrane-forming polymer solution for preparing the polymer membrane;

[0092] Preparation of the coating layer polymer solution: 10 parts of polyethylene oxide with a molecular weight of 100 kDa, 5 parts of polyvinylpyrrolidone with a molecular weight of 45 kDa, and 85 parts of N-methylpyrrolidone were mixed uniformly at 25°C for 4 h in a kettle stirrer to obtain a polymer solution, which was then vacuum degassed for 2 h to obtain the coating layer polymer solution for preparing the coating layer;

[0093] 2) Hollow fiber membrane preparation: use a spinneret with a three-layer structure, from outside to inside, coating layer polymer solution, film-forming polymer solution and cavity-forming fluid. The coating layer polymer solution and film-forming polymer solution obtained in step 1) are extruded through the outermost and middle channels of the spinneret at 55°C, respectively. At the same time, 30% N-methylpyrrolidone in deionized water at 40°C is introduced into the inner channel of the spinneret as the cavity-forming fluid. The flow rate of the coating layer polymer solution is 0.5 L / h, the flow rate of the polymer solution is 1.0 L / h, and the flow rate of the cavity-forming fluid is 0.7 L / h. The spinning speed is 15 m / min, and after passing through an air gap of 15 cm, it enters a coagulation bath composed of room temperature deionized water. The resulting nascent membrane filaments are extracted with deionized water at 25°C to remove the solvent and pore-forming agent. After two extractions, a hollow fiber membrane product with an outer diameter of 1.2 mm and an inner diameter of 0.7 mm is obtained.

[0094] It is determined that the membrane pore size is 450 nm (test method is GB / T 32361-2015 "Separation membrane pore size test method - bubble point and average flow method"), and the cross section is a sponge hole; the pore size of the membrane without a coating layer is 68 nm, and the cross section is a finger-shaped hole.

[0095] Comparative Example 1

[0096] The same as Example 1, except that no synchronous coating is performed, as follows:

[0097] 1) Preparation of polymer solution:

[0098] Preparation of film-forming polymer solution: 16 parts of polyether sulfone with a weight average molecular weight of 55 kDa after drying, 2 parts of calcium chloride after drying, and 82 parts of N,N-dimethylacetamide are mixed uniformly in a kettle stirrer at 60°C for 8 h to form a polymer solution, and then vacuum degassing for 2 h to obtain a film-forming polymer solution for preparing a polymer membrane;

[0099] 2) Hollow fiber membrane preparation: use a spinneret with a two-layer structure, from outside to inside, film-forming polymer solution and cavity-forming fluid. The film-forming polymer solution obtained in step 1) is extruded through the outer channel at 45°C, and at the same time, 20% N,N-dimethylacetamide in deionized water at 30°C is introduced into the cavity channel of the spinneret as the cavity-forming fluid. The flow rate of the film-forming polymer solution is 0.9 L / h, and the flow rate of the cavity-forming fluid is 0.5 L / h. The spinning speed is 10 m / min, and after passing through an air gap of 5 cm, it enters a coagulation bath composed of room temperature deionized water. The resulting nascent membrane filaments are extracted with deionized water at 25°C to remove the solvent and pore-forming agent. After two extractions, a hollow fiber membrane product with an outer diameter of 1.0 mm and an inner diameter of 0.5 mm is obtained.

[0100] Membrane surface morphology such as Figure 2 As shown, the pore size of the uncoated film is 78 nm. Figure 4 As shown, the cross-section is a finger-shaped hole.

[0101] It is particularly important to note that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in the spirit, scope, and content of this invention. Examples include changes to the type of coating material, polymer or diluent, spinning temperature, type and temperature of the quenching bath, temperature and length of the air gap, different membrane shapes such as rolls, hollow fibers, and tubular membranes, and composite membranes scraped onto high-temperature resistant nonwoven fabrics.

[0102] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the content of the present invention specification, or any direct or indirect application of other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for producing a polymer porous membrane, characterized by, The application relates to a method for preparing a polymer porous membrane. The method comprises the following steps: when a film-forming polymer solution is subjected to non-solvent induced phase separation and a separation layer is formed on the outer surface of the polymer film, a water-soluble coating layer polymer solution is synchronously coated on the surface of the separation layer to obtain a polymer porous membrane; the film-forming polymer solution takes a polysulfone polymer as a film-forming base material, a water-soluble chloride as a pore-forming agent and a nitrogen-containing organic substance as a solvent; the coating layer polymer solution has a pore-forming effect and the viscosity is 200-1000 mPa.s; The coating layer polymer solution comprises a hydroxyl-containing polymer and an N-containing polymer; the hydroxyl-containing polymer is polyethylene oxide with a molecular weight of 100-300 kDa, and the N-containing polymer is polyvinylpyrrolidone with a molecular weight of 30-45 kDa.

2. The method for producing a polymer porous membrane according to claim 1, characterized by, The mass ratio of the polysulfone polymer, the pore-forming agent and the solvent in the film-forming polymer solution is 15-17:2-5:78-82; the weight average molecular weight of the polysulfone polymer is 55-80 kDa.

3. The method of claim 1, wherein the polymer porous membrane is prepared by a process comprising: The solvent is one of N,N-dimethylacetamide and N-methylpyrrolidone, and the pore-forming agent is one of calcium chloride and lithium chloride.

4. The method of claim 1, wherein the polymer porous membrane is prepared by a process comprising: The coating layer polymer solution comprises a hydroxyl-containing polymer, an N-containing polymer and the solvent; the mass ratio of the hydroxyl-containing polymer, the N-containing polymer and the solvent is 5-15:3-5:80-92.

5. The method of claim 1, wherein the polymer porous membrane is prepared by a process comprising: The polysulfone polymer is polysulfone or polyether sulfone.

6. The method of claim 1, wherein the polymer porous membrane is prepared by a process comprising: The method comprises the following steps: S1, uniformly mixing the polysulfone polymer, the pore-forming agent and the solvent at 60-70 DEG C, and then vacuum degassing to obtain the film-forming polymer solution for preparing a polymer membrane; S2, uniformly mixing a hydroxyl-containing water-soluble hydrophilic polymer pore-forming agent, an N-containing water-soluble hydrophilic polymer pore-forming agent and an organic solvent at 25 DEG C, and then vacuum degassing to obtain the coating layer polymer solution for preparing a coating layer; S3, extruding the coating layer polymer solution and the film-forming polymer solution from the outermost side and the middle side of a spinneret respectively at 45-55 DEG C, simultaneously introducing 30-40 DEG C deionized water containing 20-30% organic solvent as a core liquid into the inner side of the spinneret to form a hollow fiber membrane shape, and cooling to form a membrane; S4, immersing and washing the membrane in deionized water as an extractant to obtain the polymer porous membrane.

7. The method of claim 6, wherein the polymer porous membrane is prepared by a process comprising: The air gap length in S3 is 5-15 cm, the winding speed is 10-20 m / min, and the thickness of the coating layer polymer solution is 0.05-0.10 mm.

8. The porous polymer membrane prepared according to the method of any one of claims 1-7, wherein, The polymer porous membrane is a hollow fiber membrane; the outer diameter of the hollow fiber membrane is 1.0-1.4 mm, and the inner diameter is 0.5-0.7 mm.

9. The polymer porous membrane according to claim 8 is applied in turbidity removal pre-filtration.

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