A multi-region microfiltration membrane and its preparation method and application

Abstract

The present invention belongs to the field of membrane separation technology, and specifically relates to a multi-region microfiltration membrane and its preparation method and application. The multi-region microfiltration membrane includes a porous body, and the porous body includes a liquid inlet surface, a liquid outlet surface and a plurality of regions; along the direction from the liquid inlet surface to the liquid outlet surface, the plurality of regions include alternating pore size change regions and pore size tending consistent regions; the pore size change regions include pore size gradually increasing regions and / or pore size gradually decreasing regions; the pore size tending consistent regions in the porous body include a separation layer and a support layer, and the region with the largest average pore size in the plurality of regions is the support layer, and the region with the smallest average pore size is the separation layer. The multi-region microfiltration membrane provided by the present invention is an integrated membrane, and has the properties of fast membrane flux, high loading capacity, and pressure resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of membrane separation, and in particular relates to a multi-region microfiltration membrane and a preparation method and application thereof. Background Art

[0002] The effective pore size of microfiltration membranes ranges from 0.1 to 10 μm and can be used to remove particles such as solid particles, bacteria and microorganisms from liquid flows. It is known in the art that microporous membranes have isotropic (symmetrical) and multi-region structures (asymmetric). The so-called symmetrical membrane refers to a membrane in which the measured value of the micropores does not change substantially in the thickness direction, and the micropore diameters on both sides are substantially the same. The so-called asymmetric membrane refers to a membrane in which the micropore diameter changes continuously or discontinuously in the thickness direction. However, traditional symmetric membranes are no longer suitable for some applications because symmetric membranes provide greater resistance to fluid flow and have a slower flow rate than asymmetric membranes with the same retention.

[0003] Flux and interception performance are becoming increasingly important for filtration applications. There are two ways to increase the flux of filtration membranes without affecting the interception performance: one is to optimize the membrane structure, and the other is to increase the porosity. The prior art discloses a symmetrical microporous membrane, which has the advantages of strong hydrophilicity and temperature resistance. However, in practical applications, in order to ensure the interception of impurities and bacteria in the feed liquid, a large symmetrical structure membrane has a high flux, which is easy to cause bacteria or impurities to pass through. A small symmetrical structure membrane has a reduced flux, which causes large particles of impurities to be concentrated near the liquid inlet surface, resulting in rapid blockage of the membrane pores. The prior art discloses an asymmetric membrane with a gradient structure, in which the pore size increases gradually and continuously from one surface to another; the prior art also discloses an asymmetric membrane, which comprises a skin and a highly porous asymmetric support, the skin containing pores with an average pore size of about 0.005 to about 3.0 microns, and the asymmetric support comprising a mesh structure, which contains pores with an average pore size of about 10 to about 20,000 times the average pore size of the surface, and the structure is often accompanied by the risk of reduced interception effect due to surface scratches; the prior art also discloses an "hourglass" type asymmetric microporous membrane, in which the pore size is distributed in the thickness direction, and the minimum pore layer is arranged in the membrane, which increases the filtration flow and prolongs the life of the filter, but it is necessary to control the amount of non-solvent vapor in contact with the surface of the developing solution and the blowing rate, and the depth of the minimum pore layer and the pore diameter therein are difficult to adjust.

[0004] Membranes with multi-zone structures are more scientifically attractive because each zone can be fine-tuned to achieve overall improved performance. In the method of constructing a multi-zone microfiltration structure, the laminated membrane obtained by stacking multiple conventional single-layer membranes causes the membrane pores between the membranes to become blocked under pressure, resulting in a sharp decrease in the overall flux; and subsequent modification or additional erosion and solvation methods will increase the cost of the membrane. Through the integrated membrane structure, all fibers inside the membrane are connected as a whole, with better permeability, can adapt to more complex environments and have higher flux, and the cost of the membrane can also be controlled accordingly. Asymmetric membranes have obvious pore size changes. In order to achieve better flux, a structure with a large asymmetry will be designed, resulting in a continuous downward trend in the membrane pore size. When high-pressure operation is performed, the membrane is squeezed inside, causing the membrane pores to be compressed and the filtered impurities to accumulate continuously, resulting in a rapid decrease in membrane flux, and the membrane surface is easily damaged. Therefore, a microfiltration membrane with pressure resistance, fast flux and excellent loading capacity is required. Summary of the invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the above-mentioned defects of the asymmetric microfiltration membrane in the prior art, thereby providing a porous area microfiltration membrane and a preparation method and application thereof.

[0006] To this end, the present invention provides the following technical solutions.

[0007] The present invention provides a multi-region microfiltration membrane, comprising a porous body, wherein the porous body comprises a liquid inlet surface, a liquid outlet surface and a plurality of regions; along the direction from the liquid inlet surface to the liquid outlet surface, the plurality of regions comprise pore size variation regions and pore size trending uniform regions arranged alternately; the pore size variation region comprises a pore size gradually increasing region and / or a pore size gradually decreasing region;

[0008] The region with the most consistent pore sizes in the porous body includes a separation layer and a support layer. The region with the largest average pore size among the plurality of regions is the support layer, and the region with the smallest average pore size is the separation layer.

[0009] The asymmetric microfiltration membrane with a multi-region structure in the prior art usually has only the separation layer pore size change trending to be consistent, and the other regions are all asymmetric structures. The outer surface of the microfiltration membrane is generally provided with a large pore size region, which causes the outer surface of the microfiltration membrane to be relatively fragile and prone to damage. The multi-region microfiltration membrane of the present invention is an integrated membrane with the properties of fast membrane flux, high load capacity, and pressure resistance. The average pore size of the support layer is the largest, which can ensure that the microfiltration membrane has a larger space for receiving pollutants and prolongs the clogging time. The average pore size of the separation layer is the smallest in all regions, ensuring the filtering effect. Through the multi-region setting mode, the mechanical strength of the microfiltration membrane as a whole is enhanced, thereby ensuring the strength and integrity of the liquid inlet surface, so that the liquid inlet surface plays a screening role, and large particles are retained on the liquid inlet side, preventing large particles from immersing in the microfiltration membrane, and prolonging the microfiltration membrane clogging time. In the present invention, the pore size of the support layer tends to be consistent, which can play a supporting effect, ensure that the membrane has better pressure resistance, and increase the pollution capacity.

[0010] In the present invention, the pore size tending to be consistent region refers to the region where the gradient coefficient G is lower than 0.005; the pore size changing region refers to the region where the gradient coefficient G is not lower than 0.005.

[0011] The thickness of the support layer is 25-45% of the thickness of the porous body; and / or,

[0012] The average pore size of the support layer is 1-1.5 μm; in the present invention, the support layer can increase the internal space and improve the dirt holding capacity. And / or,

[0013] The average pore size of the separation layer is 0.2-0.45 μm; and / or,

[0014] The thickness of the separation layer is 10-20% of the thickness of the porous body.

[0015] The multi-region microfiltration membrane of the present invention is provided with a plurality of pore size change regions and pore size tending to be consistent regions, so that the microfiltration membrane has two interception zones, namely the screening layer and the separation layer, which are symmetrical structures. The separation layer is arranged inside the microfiltration membrane and is coated by the intermediate layer and the protective layer with a higher pore size, which reduces the risk of the interception effect reduced by scratches on the membrane surface due to external force and the risk of the pores inside the membrane being blocked, thereby increasing the filtration volume and interception efficiency; further, the multi-region microfiltration membrane is an integrated membrane with the properties of fast membrane flux, high load capacity, and pressure resistance. Furthermore, as the filtration time and pressure increase, the membrane microstructure and pore size will change, resulting in a decrease in flux and load capacity. It can be determined from the fact that the microfiltration membrane has good flux and load that the membrane has good pressure resistance. Among them, the separation layer maintains a pore size of 0.2μm to 0.45μm to remove most bacterial microorganisms, and meets the chromatographic requirements for the filtration of conventional samples, mobile phases, etc.

[0016] A screening layer is arranged on one side of the porous body close to the liquid inlet surface, and the screening layer is a region where the pore sizes tend to be consistent.

[0017] The thickness of the screening layer is 4-10% of the thickness of the porous body; and / or,

[0018] The average pore size of the screening layer is 0.25-0.55 μm; and / or,

[0019] The total thickness of the screening layer and the separation layer is 14-30% of the thickness of the porous body.

[0020] The multi-region microfiltration membrane is provided with a screening layer on one side of the liquid inlet surface, which can intercept large particles on the other side of the liquid inlet surface and prevent them from penetrating into the microfiltration membrane. The consistent pore size of the screening layer can better adapt to the impact of the initial pressure, slow down the flux attenuation, ensure that the microfiltration membrane has better flux and load, and improve the strength of the liquid inlet surface of the microfiltration membrane to ensure its integrity. The screening layer and separation layer with consistent pore size can play a role in filtering and interception. Setting the screening layer on the outermost side of the microfiltration membrane can isolate larger impurities on the outside of the microfiltration membrane, reduce the risk of clogging of the pores in the membrane, and increase the service life of the membrane. Setting the separation layer inside can prevent it from being damaged by external forces and improve the interception efficiency.

[0021] The aperture change region includes a preparatory layer, an intermediate layer and a protective layer. The preparatory layer, the intermediate layer and the protective layer are the aperture change region, and the asymmetric structure can increase the flux size and meet the application scenarios requiring flux and interception efficiency, and can be used not only for dead-end filtration, but also for tangential flow filtration, etc.

[0022] The thickness of the preparatory layer is 8-15% of the thickness of the porous body; and / or,

[0023] The average pore size of the preparatory layer is 0.75-1.0 μm; and / or,

[0024] The thickness of the intermediate layer is 20-40% of the thickness of the porous body; and / or,

[0025] The average pore size of the intermediate layer is 0.35-0.8 μm; and / or,

[0026] The thickness of the protective layer is 8-15% of the thickness of the porous body; and / or,

[0027] The average pore size of the protective layer is 0.7-1.1 μm; and / or,

[0028] The gradient coefficient of the preparatory layer is 0.05-0.13; and / or,

[0029] The gradient coefficient of the intermediate layer is 0.015-0.05; and / or,

[0030] The gradient coefficient of the protective layer is 0.025-0.07.

[0031] The gradient coefficient G of each region in the multi-region microfiltration membrane is calculated using the following formula:

[0032]

[0033] Among them, D 大孔 is the average pore size of the largest pore size area in each region, in μm; D 小孔 is the average pore size of the smallest pore size area in each area, in μm; L 厚度 It is the distance from the maximum pore area to the minimum pore area, in μm. Taking the preparation layer as an example, the calculation method of the gradient coefficient is: take a thickness of 1 μm on both sides of the preparation layer, that is, the maximum pore area and the minimum pore area, and calculate the ratio of the difference in the average pore size of the areas on both sides of the preparation layer to the thickness of the preparation layer.

[0034] Furthermore, the protective layer has an appropriate thickness to protect the separation layer. External mechanical destructive force often needs to destroy the protective layer first before further destroying the separation layer structure, which greatly reduces the risk of bacterial leakage.

[0035] Optionally, along the direction from the liquid inlet surface to the liquid outlet surface, the porous body includes a screening layer with a consistent pore size, a preparatory layer with a gradually increasing pore size, a supporting layer with a consistent pore size, an intermediate layer with a gradually decreasing pore size, a separation layer with a consistent pore size and a protective layer with a gradually increasing pore size.

[0036] The microfiltration membrane of the present invention is widely used and is sufficient to meet the high requirements for flux and interception in practical applications. It can not only be used for conventional dead-end filtration, but also has a better effect when applied to tangential flow filtration.

[0037] The average pore size of the protective layer is greater than the average pore size of the intermediate layer; and / or,

[0038] The average pore size of the protective layer is larger than the average pore size of the screening layer; and / or,

[0039] The average pore size of the separation layer is smaller than the average pore size of the preparatory layer; and / or,

[0040] The average pore size of the separation layer is smaller than the average pore size of the screening layer; and / or,

[0041] The average pore size of the support layer is greater than the average pore size of the protection layer.

[0042] The average fiber diameter of the screening layer is 0.2-0.5 μm; and / or,

[0043] The ratio of the average pore size of the screening layer to the average fiber diameter thereof is (0.5-2.75):1; and / or,

[0044] The average fiber diameter of the support layer is 0.3-0.7 μm; and / or,

[0045] The ratio of the average pore size of the support layer to the average fiber diameter thereof is (1.4-5):1; and / or,

[0046] The average fiber diameter of the preparatory layer is in the range of 0.35-0.55 μm; and / or,

[0047] The ratio of the average pore size of the preparatory layer to the average fiber diameter thereof is (1.35-2.86):1; and / or,

[0048] The average fiber diameter of the separation layer is 0.08-0.25 μm; and / or,

[0049] The ratio of the average pore size of the separation layer to the average fiber diameter thereof is (0.8-5.65):1; and / or,

[0050] The average fiber diameter of the intermediate layer is 0.12-0.3 μm; and / or,

[0051] The ratio of the average pore size of the intermediate layer to the average fiber diameter thereof is (1.15-6.7):1; and / or,

[0052] The average fiber diameter of the protective layer is 0.4-0.9 μm; and / or,

[0053] The ratio of the average pore size of the protective layer to the average fiber diameter thereof is (0.75-2.75):1; and / or,

[0054] The multi-region microfiltration membrane has a thickness of 95-145 μm; and / or a porosity of 60-80%.

[0055] The ratio of the average pore size of each region to the average fiber diameter thereof refers to the ratio of the pore size of the hole to the diameter of the fiber surrounding the hole.

[0056] The present invention controls the ratio of the average pore size of the protective layer to the average fiber diameter to be (0.75-2.75):1, so that the thicker fibers can protect the separation layer and better withstand pressure, thereby ensuring the smoothness of the immersion or penetration of the feed liquid. The ratio of the average pore size of the separation layer to the average fiber diameter is high, which helps the permeability of the internal structure of the membrane, ensures the retention and ensures the good permeability of the region. The average pore size of the support layer and the average fiber diameter have an appropriate ratio, which can better play the supporting and penetration effects of the support layer.

[0057] The average pore size of the liquid inlet surface is 0.2-0.48 μm; and / or,

[0058] The hole area ratio of the liquid inlet surface is 15-35%; and / or,

[0059] The average pore size of the liquid outlet surface is 0.8-1.5 μm; and / or,

[0060] The hole area ratio of the liquid outlet surface is 12-30%; and / or,

[0061] The primary screening holes are holes in the liquid inlet surface with a pore size lower than the average pore size of the liquid inlet surface, the secondary screening holes are holes in the liquid inlet surface with a pore size higher than 1.2 times the average pore size of the liquid inlet surface, and the area of ​​the primary screening holes on the liquid inlet surface accounts for 3-17%; and / or,

[0062] The ratio of the number of secondary screening holes to the number of primary screening holes is (0.2~0.75):1.

[0063] By controlling the average pore size and hole area ratio of the inlet and outlet surfaces, more liquid can enter in the same period of time, further ensuring the flux of the microfiltration membrane; the main screening holes in the inlet surface can screen the liquid for the first time, relieving the accumulation of large molecular impurities inside the microfiltration membrane, relieving the clogging time of the middle layer and separation layer, and increasing the service life of the microfiltration membrane. The secondary screening holes in the inlet surface are conducive to relieving the initial resistance of the microfiltration membrane to the liquid. Further controlling the hole area ratio can ensure better flux.

[0064] Furthermore, when the feed liquid passes through the small holes, it is easy to generate resistance due to the existence of surface tension. The feed liquid is compressed and twisted in the small holes. The generated resistance will cause the flux of the microfiltration membrane to decrease. Distributing a certain number of secondary screening holes in the liquid inlet surface is helpful to alleviate the initial resistance of the microfiltration membrane to the feed liquid; the main screening holes perform the first wave of screening on the feed liquid, which alleviates the accumulation rate of large molecular impurities inside the membrane and improves the service life of the membrane. The overall design helps the filter membrane to have better flux and retention effect.

[0065] The present invention also provides a method for preparing the multi-region microfiltration membrane, comprising the following steps:

[0066] (1) dissolving a polymer in a solvent to prepare a casting solution; wherein the polymer in the casting solution comprises a hydrophobic polymer and a hydrophilic polymer;

[0067] (2) The casting solution forms a primary film on the surface of the carrier and is left to stand to obtain a wet film;

[0068] (3) Immersing the wet membrane obtained in step (2) into a first coagulation bath and a second coagulation bath to obtain a multi-region microfiltration membrane; wherein the immersion time of the wet membrane in the first coagulation bath is 5 to 100 seconds.

[0069] The temperature of the carrier is at least 15° C. higher than the temperature of the first coagulation bath and / or the second coagulation bath; and / or,

[0070] The temperature of the carrier is 35-80° C.; and / or,

[0071] The hydrophobic polymer is an aromatic sulfone polymer; and / or,

[0072] The hydrophilic polymer is a sulfonated aromatic sulfone polymer; and / or,

[0073] The average molecular weight of the hydrophilic polymer is at least 10,000 Daltons greater than the average molecular weight of the hydrophobic polymer; and / or,

[0074] The mass ratio of polymer, solvent and additive in the casting solution is (15-22):(40-70):(20-35).

[0075] Specifically, the hydrophobic polymer is polysulfone and / or polyethersulfone;

[0076] The hydrophilic polymer is sulfonated polysulfone and / or sulfonated polyethersulfone.

[0077] The speed at which the wet film is immersed in the second coagulation bath is at least 1.2 times the speed at which the wet film is immersed in the first coagulation bath; and / or,

[0078] The solvent of the first coagulation bath is a mixture of aprotic polar solvent and water; and / or,

[0079] The volume proportion of the aprotic polar solvent in the first coagulation bath is 20-80%; and / or,

[0080] The solvent of the second coagulation bath is at least one polar protic solvent.

[0081] The preparation method of the multi-region microfiltration membrane provided by the present invention combines the traditional wet phase conversion and the thermal phase separation method or the steam induced phase separation method to prepare an integrated membrane with the properties of fast membrane flux, high loading capacity, pressure resistance and the like.

[0082] By adjusting the parameters in the process, such as the immersion time in the first coagulation bath, the coagulation bath temperature, the carrier temperature, the type of polymer, etc., the continuous diffusion of water vapor on the surface of the native membrane can be used in a high humidity environment to promote the phase separation of the membrane and the air interface to form a macroporous region. After immersion in the coagulation bath, two-way diffusion between the solvent and the non-solvent occurs, which promotes the appearance of a small pore selection layer. Before the phase conversion is completed, the membrane is transferred to the second coagulation bath (with a smaller surface tension), and rapid two-way diffusion occurs on one side of the membrane and the carrier interface, so that the membrane structure at this location also tends to be a dense structure, thereby obtaining a multi-region microfiltration membrane with a special structure of the present invention.

[0083] The method for preparing the multi-region microfiltration membrane specifically comprises:

[0084] (1) A polymer, a solvent and an additive are mixed to obtain a casting solution; wherein the mass ratio of the polymer, the solvent and the additive is (15-22):(40-70):(20-35); the polymer comprises a hydrophilic polymer and a hydrophobic polymer in a mass ratio of 1:(4-30), the hydrophobic polymer is polysulfone and / or polyethersulfone, and the hydrophilic polymer is sulfonated polysulfone and / or sulfonated polyethersulfone.

[0085] The solvent in step (1) is at least one of dimethylformamide, dimethylacetamide, methyl lactate, ethyl lactate, butyl lactate, N-methylpyrrolidone, triethyl phosphate, chloroform, caprolactam, dimethyl sulfoxide and γ-butyrolactone.

[0086] The additives in step (1) include at least one of a porogen and a hydrophilic additive. The porogen is selected from one or more of polyethylene glycol, polyvinyl alcohol, polyvinyl pyrrolidone, alcohols, salts, etc.; polyethylene glycol such as PEG-200, PEG-800; polyvinyl pyrrolidone such as PVP-K30, PVP-K60; alcohols such as tripropylene glycol, triethylene glycol, diethylene glycol, n-butanol, tert-amyl alcohol, triethylene glycol; salts such as lithium chloride, potassium dihydrogen phosphate, potassium bicarbonate, sodium bicarbonate. The hydrophilic additive is selected from one or more of acrylamide monomers and their derivatives.

[0087] Viscosity of casting liquid: The viscosity at 25°C is 5000~22000mPa.s.

[0088] (2) The carrier is adjusted to a predetermined temperature so that the casting liquid forms a primary film on the surface of the carrier, and is placed in a specific environment for a period of time to obtain a wet film.

[0089] In step (2), the specific environment can be a high humidity environment or an air flow environment, and the placement time is 10-120 seconds; the high humidity can be a humidity of 60-90% RH; the air flow can be: at room temperature, the air flow rate is set to 0.3-1 m / s, and an air flow is formed on the membrane. The temperature of the carrier is 35-80°C.

[0090] (3) The wet membrane is immersed in the first coagulation bath at a first speed v1 for preliminary phase separation, and then immersed in the second coagulation bath at a second speed v2 for complete phase separation, solidification, and formation of a membrane structure to obtain a multi-region microfiltration membrane. The immersion time of the wet membrane in the first coagulation bath is 5 to 100 seconds, and the process refers to the wet membrane from the beginning of immersion in the first coagulation bath until it completely leaves the first coagulation bath.

[0091] In step (3), the first coagulation bath is at least one of a non-protonic polar solvent and water; wherein the non-protonic polar solvent may be, but is not limited to, acetonitrile, dimethylformamide, dimethyl sulfoxide, hexamethylphosphoric triamide, dimethylacetamide (DMAc), etc. The second coagulation bath is at least one polar protic solvent, such as at least one of water, isopropanol, ethanol, acetone, etc., and may also be an isopropanol aqueous solution, an acetone aqueous solution, etc. The ratio of v2 to v1 in step (3) is not less than 1.2.

[0092] The present invention also provides an application of the multi-region microfiltration membrane or the multi-region microfiltration membrane prepared by the preparation method in removing insoluble particles or microbial impurities from a liquid flow.

[0093] The technical solution of the present invention has the following advantages:

[0094] 1. The multi-region microfiltration membrane provided by the present invention comprises a porous body, wherein the porous body comprises a liquid inlet surface, a liquid outlet surface and several regions; along the direction from the liquid inlet surface to the liquid outlet surface, the several regions comprise alternating pore size change regions and pore size tending to be consistent regions; the pore size change regions comprise regions with gradually increasing pore size and / or regions with gradually decreasing pore size; the pore size tending to be consistent regions in the porous body comprise a separation layer and a support layer, wherein the region with the largest average pore size among the several regions is the support layer, and the region with the smallest average pore size is the separation layer. The multi-region microfiltration membrane provided by the present invention is an integrated membrane having the properties of fast membrane flux, high load capacity, and pressure resistance. The multi-region microfiltration membrane alternately arranges pore size change regions and pore size tending to be consistent regions, wherein the pore size tending to be consistent regions comprise a separation layer and a support layer, and the average pore size of the support layer is the largest among all regions, which can ensure that the microfiltration membrane has a larger pollution receiving space and prolong the clogging time, and the average pore size of the separation layer is the smallest among all regions, thus ensuring the filtering effect. Through the above-mentioned multi-zone setting method, the overall mechanical strength of the microfiltration membrane is enhanced, thereby ensuring the strength and integrity of the liquid inlet surface, so that the liquid inlet surface plays a screening role, intercepting large particles on the liquid inlet side, preventing large particles from penetrating into the microfiltration membrane and prolonging the clogging time of the microfiltration membrane.

[0095] 2. The multi-region microfiltration membrane provided by the present invention has a screening layer on one side of the liquid inlet surface, which can intercept large particles on the other side of the liquid inlet surface to prevent them from penetrating into the microfiltration membrane. The screening layer has a consistent pore size, which can better adapt to the impact of the initial pressure, slow down the flux attenuation, and ensure that the microfiltration membrane has better flux and load. A support layer with a consistent pore size is provided inside the microfiltration membrane, which can play a supporting effect, ensure that the membrane has better pressure resistance, and increase the pollution holding capacity. The multi-region microfiltration membrane is provided with multiple pore size change areas and pore size consistent areas, so that the microfiltration membrane has two interception areas, namely the screening layer and the separation layer. The separation layer is arranged inside the microfiltration membrane and is coated by an intermediate layer and a protective layer with a higher pore size, which reduces the risk of scratches on the membrane surface due to external force, reducing the interception effect, and the risk of pores inside the membrane being blocked, thereby increasing the filtration volume. The screening layer and separation layer with consistent pore sizes can play a role in filtering and interception. Setting the screening layer on the outermost side of the microfiltration membrane can isolate larger impurities on the outside of the microfiltration membrane, reduce the risk of clogging of pores in the membrane, and increase the service life of the membrane. Setting the separation layer inside can prevent it from being damaged by external forces and improve the interception efficiency. The preparatory layer, intermediate layer and protective layer are pore size change areas with an asymmetric structure, which can increase the flux and meet the application scenarios with requirements for flux and interception efficiency. It can be used not only for dead-end filtration, but also for tangential flow filtration, etc.

[0096] 3. The multi-region microfiltration membrane provided by the present invention controls the average pore size and hole area ratio of the liquid inlet surface and the liquid outlet surface, and can allow more liquid to enter in the same time period, further ensuring the flux of the microfiltration membrane. The main screening holes in the liquid inlet surface can perform the first screening of the liquid, alleviate the accumulation of macromolecular impurities inside the microfiltration membrane, alleviate the clogging time of the intermediate layer and the separation layer, and increase the service life of the microfiltration membrane. The secondary screening holes in the liquid inlet surface are conducive to alleviating the initial resistance of the microfiltration membrane to the liquid.

[0097] 4. The method for preparing a multi-region microfiltration membrane provided by the present invention combines the traditional wet phase conversion and the thermally induced phase separation method or the steam-induced phase separation method to produce an integrated membrane having the above-mentioned effect.

[0098] Furthermore, by adjusting the parameters in the process, such as the immersion time in the first coagulation bath, the coagulation bath temperature, the carrier temperature, the type of polymer, etc., the continuous diffusion of water vapor on the surface of the native membrane can be used in a high humidity environment to promote the phase separation of the membrane and the air interface to form a macroporous region, and after immersion in the coagulation bath, a two-way diffusion between the solvent and the non-solvent occurs, which promotes the appearance of a small pore selection layer. Before the phase transformation is completed, the membrane is transferred to the second coagulation bath (with a smaller surface tension), and rapid two-way diffusion occurs on one side of the membrane and the carrier interface, so that the membrane structure at this location also tends to be a dense structure, thereby obtaining a multi-region microfiltration membrane with a special structure of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0099] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0100] Figure 1 is a scanning electron microscope image of a cross section of a microfiltration membrane provided in Example 1 of the present invention, with a magnification of 600×;

[0101] Figure 2 is a scanning electron microscope image of a cross section of a screening layer of a microfiltration membrane provided in Example 1 of the present invention, with a magnification of 5000×;

[0102] Figure 3 is a scanning electron microscope image of the liquid inlet surface of the microfiltration membrane provided in Example 1 of the present invention, with a magnification of 5000×;

[0103] Figure 4 This is a scanning electron microscope image of the liquid outlet surface of the microfiltration membrane provided in Example 1 of the present invention, with a magnification of 5000×. DETAILED DESCRIPTION

[0104] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope 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 shall fall within the protection scope of the present invention.

[0105] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0106] Example 1

[0107] The present embodiment provides a multi-zone microfiltration membrane, including a porous body, the porous body including a liquid inlet surface and a liquid outlet surface, and along the direction from the liquid inlet surface to the liquid outlet surface, the porous body also includes a screening layer, a preparatory layer, a support layer, an intermediate layer, a separation layer and a protective layer.

[0108] The method for preparing the multi-region microfiltration membrane comprises the following steps:

[0109] (1) Dissolve 3 parts of sulfonated polyethersulfone (Mw=130000) and 17 parts of polyethersulfone (Mw=58000) resin in 58 parts of solvent, adjust the temperature to 60℃ and stir for 1h. Then, add 5 parts of polyvinyl pyrrolidone (PVP K30), stir to make it evenly dispersed, and remove most of the oxygen in the container by passing nitrogen. Then raise the temperature to 80℃, slowly add 17 parts of diethylene glycol, continue stirring for 3h, then cool to 40℃, vacuum degas, and obtain a casting solution for use. The solvent is a mixture of dimethylformamide and methyl lactate, and the mass ratio of dimethylformamide to methyl lactate is 50:8.

[0110] (2) The carrier temperature was adjusted to 60°C, and a 40°C casting solution was poured onto the carrier surface to form a primary film with a thickness of about 120 μm. The primary film was transferred to an environment with a relative humidity of 75% RH and stayed in the air section for 10 s to obtain a wet film.

[0111] (3) The wet membrane was immersed in a first coagulation bath at 25°C (DMF aqueous solution with a volume percentage of 50%) at a speed of 0.1 m / s. The wet membrane was immersed in the first coagulation bath for 10 s. After being taken out, it was quickly immersed in a second coagulation bath at 40°C (acetone aqueous solution with a volume percentage of 5%) at a speed of 0.15 m / s for phase separation. After washing with pure water, a multi-region microfiltration membrane was obtained, which was recorded as a.

[0112] The cross section of the multi-region microfiltration membrane in the thickness direction was characterized by SEM, such as Figure 1As shown in the figure, the trends of pore size from the liquid inlet surface to the liquid outlet surface are as follows: ① the pore size tends to be consistent, ② the pore size gradually increases to the maximum, ③ the pore size tends to be consistent, ④ the pore size gradually decreases to the minimum; ⑤ the pore size tends to be consistent; ⑥ the pore size gradually increases; the thickness of the microfiltration membrane is 110μm.

[0113] Example 2

[0114] The present embodiment provides a multi-zone microfiltration membrane, including a porous body, the porous body including a liquid inlet surface and a liquid outlet surface, and along the direction from the liquid inlet surface to the liquid outlet surface, the porous body includes a screening layer, a preparatory layer, a support layer, an intermediate layer, a separation layer and a protective layer.

[0115] The method for preparing the multi-region microfiltration membrane comprises the following steps:

[0116] (1) Dissolve 1.5 parts of sulfonated polyethersulfone (Mw=130000) and 18.5 parts of polyethersulfone (Mw=58000) resin in 58 parts of solvent, adjust the temperature to 60°C and stir for 1 hour. Then, add 5 parts of polyvinyl pyrrolidone (PVP K30), stir to make it evenly dispersed, and remove most of the oxygen in the container by passing nitrogen. Then raise the temperature to 80°C, slowly add 17 parts of diethylene glycol, continue stirring for 3 hours, cool to 40°C, vacuum degas, and obtain a casting solution for use. The solvent is a mixture of dimethylformamide and methyl lactate, and the mass ratio of dimethylformamide to methyl lactate is 50:8.

[0117] (2) The temperature of the carrier was adjusted to 60°C, and a 40°C casting solution was poured onto the surface of the carrier to form a primary film with a thickness of about 120 μm. The primary film was transferred to an environment with a relative humidity of 75% RH and stayed in the air section for 10 seconds to obtain a wet film.

[0118] (3) The wet membrane was immersed in a first coagulation bath (50 vol% DMF aqueous solution) at 25 °C at a speed of 0.1 m / s. The wet membrane was immersed in the first coagulation bath for 10 s. After being taken out, it was quickly immersed in a second coagulation bath (5 vol% acetone aqueous solution) at 40 °C at a speed of 0.15 m / s for phase separation. After washing with pure water, a multi-region microfiltration membrane was obtained, which was recorded as b.

[0119] Example 3

[0120] The present embodiment provides a multi-zone microfiltration membrane, including a porous body, the porous body including a liquid inlet surface and a liquid outlet surface, and along the direction from the liquid inlet surface to the liquid outlet surface, the porous body includes a screening layer, a preparatory layer, a support layer, an intermediate layer, a separation layer and a protective layer.

[0121] The method for preparing the multi-region microfiltration membrane comprises the following steps:

[0122] (1) Dissolve 1.5 parts of sulfonated polysulfone (Mw=200000) and 18.5 parts of polyethersulfone (Mw=72000) resin in 57 parts of solvent, adjust the temperature to 60°C and stir for 1 hour. Then, add 5 parts of polyvinyl pyrrolidone (PVP K17), stir to make it evenly dispersed, and remove most of the oxygen in the container by passing nitrogen. Then raise the temperature to 80°C, slowly add 18 parts of polyethylene glycol 200, and continue stirring for 3 hours. Then cool to 50°C, vacuum degas, and obtain a casting solution for use. The solvent is a mixture of dimethylacetamide and ethyl lactate, and the mass ratio of dimethylacetamide to ethyl lactate is 50:8.

[0123] (2) The temperature of the carrier is adjusted to 65°C, and a 50°C casting solution is poured onto the surface of the carrier to form a primary film with a thickness of about 120 μm. The primary film is then transferred to an environment with a relative humidity of 65% RH and allowed to stay in the air section for 15 seconds to obtain a wet film.

[0124] (3) The wet membrane was immersed in the first coagulation bath (50 vol% DMAc aqueous solution) at 25°C at a speed of 0.1 m / s. The wet membrane was immersed in the first coagulation bath for 30 s. After being taken out, it was quickly immersed in the second coagulation bath (5 vol% isopropyl ketone aqueous solution) at 35°C at 0.2 m / s for phase separation. After washing with pure water, a multi-region microfiltration membrane was obtained, which was recorded as c.

[0125] Example 4

[0126] The present embodiment provides a multi-zone microfiltration membrane, including a porous body, the porous body including a liquid inlet surface and a liquid outlet surface, and along the direction from the liquid inlet surface to the liquid outlet surface, the porous body includes a screening layer, a preparatory layer, a support layer, an intermediate layer, a separation layer and a protective layer.

[0127] The method for preparing the multi-region microfiltration membrane comprises the following steps:

[0128] (1) Dissolve 1.5 parts of sulfonated polyethersulfone (Mw=130000) and 18.5 parts of polyethersulfone (Mw=72000) resin in 55 parts of solvent, adjust the temperature to 60°C and stir for 1 hour. Then, add 8 parts of polyvinyl pyrrolidone (PVP K30), stir to make it evenly dispersed, and remove most of the oxygen in the container by passing nitrogen. Then raise the temperature to 80°C, slowly add 17 parts of polyvinyl alcohol, and continue stirring for 3 hours. Then cool to 40°C, vacuum degas, and obtain a casting solution for use. The solvent is a mixture of caprolactam and γ-butyrolactone, and the mass ratio of caprolactam to γ-butyrolactone is 10:45.

[0129] (2) The temperature of the carrier was adjusted to 60°C, and a 40°C casting solution was poured onto the surface of the carrier to form a primary film with a thickness of about 120 μm. The primary film was transferred to an environment with a relative humidity of 80% RH and stayed in the air section for 8 seconds to obtain a wet film.

[0130] (3) The wet membrane was immersed in the first coagulation bath (70 vol% DMF aqueous solution) at 25°C at a speed of 0.1 m / s. The wet membrane was immersed in the first coagulation bath for 60 s. After being taken out, it was quickly immersed in the second coagulation bath (5 vol% acetone aqueous solution) at 40°C at a speed of 0.15 m / s for phase separation. After washing, a multi-region microfiltration membrane was obtained, which was recorded as d.

[0131] Example 5

[0132] The present embodiment provides a multi-zone microfiltration membrane, including a porous body, the porous body including a liquid inlet surface and a liquid outlet surface, and along the direction from the liquid inlet surface to the liquid outlet surface, the porous body includes a screening layer, a preparatory layer, a support layer, an intermediate layer, a separation layer and a protective layer.

[0133] The method for preparing the multi-region microfiltration membrane comprises the following steps:

[0134] (1) Dissolve 3 parts of sulfonated polyethersulfone (Mw=130000) and 18 parts of polyethersulfone (Mw=50000) resin in 55 parts of solvent, adjust the temperature to 60℃ and stir for 1h. Then, add 5 parts of polyvinylpyrrolidone (PVP K30) and 2 parts of acrylamide, stir to make the dispersion uniform, and remove most of the oxygen in the container by passing nitrogen. Then raise the temperature to 80℃, slowly add 17 parts of polyethylene glycol 400, and continue stirring for 3h. Then cool to 45℃, vacuum degas, and obtain the casting solution for use. The solvent is a mixture of dimethylformamide and N-methylpyrrolidone, and the mass ratio of dimethylformamide to N-methylpyrrolidone is 40:15.

[0135] (2) The temperature of the carrier was adjusted to 70°C, and a casting solution at 45°C was poured onto the surface of the carrier to form a primary film with a thickness of about 120 μm. The primary film was transferred to an environment with a relative humidity of 80% RH and stayed in the air section for 5 seconds to obtain a wet film.

[0136] (3) The wet membrane was immersed in the first coagulation bath (75 vol% NMP aqueous solution) at 25°C at a speed of 0.1 m / s. The wet membrane was immersed in the first coagulation bath for 10 s. After being taken out, it was quickly immersed in the second coagulation bath (15 vol% ethanol aqueous solution) at 40°C at a speed of 0.2 m / s for phase separation. After washing, a multi-region microfiltration membrane was obtained, which was recorded as e.

[0137] Example 6

[0138] The present embodiment provides a multi-zone microfiltration membrane, including a porous body, the porous body including a liquid inlet surface and a liquid outlet surface, and along the direction from the liquid inlet surface to the liquid outlet surface, the porous body includes a screening layer, a preparatory layer, a support layer, an intermediate layer, a separation layer and a protective layer.

[0139] The method for preparing the multi-region microfiltration membrane comprises the following steps:

[0140] (1) Dissolve 3 parts of sulfonated polysulfone (Mw=130000) and 18 parts of polysulfone (Mw=48000) resin in 55 parts of solvent, adjust the temperature to 60℃ and stir for 1h. Then, add 5 parts of polyvinyl pyrrolidone (PVP K30) and 2 parts of acrylamide, stir to make the dispersion uniform, and remove most of the oxygen in the container by passing nitrogen. Then raise the temperature to 80℃, slowly add 17 parts of triethylene glycol, continue stirring for 3 hours, cool to 45℃, vacuum degas, and obtain the casting solution for use. The solvent is a mixture of dimethylformamide and methyl lactate, and the ratio of dimethylformamide to methyl lactate is 45:10.

[0141] (2) The temperature of the carrier was adjusted to 70°C, and a casting solution at 45°C was poured onto the surface of the carrier to form a primary film with a thickness of about 120 μm. The primary film was transferred to an environment with a relative humidity of 80% RH and stayed in the air section for 10 seconds to obtain a wet film.

[0142] (3) The wet membrane was immersed in the first coagulation bath (75 vol% NMP aqueous solution) at 25°C at a speed of 0.1 m / s. The wet membrane was immersed in the first coagulation bath for 70 s. After being taken out, it was immersed in the second coagulation bath (15 vol% ethanol aqueous solution) at 40°C at a speed of 0.2 m / s for complete phase separation. After being washed with pure water, a multi-region microfiltration membrane was obtained, which was recorded as f.

[0143] Example 7

[0144] The present embodiment provides a multi-zone microfiltration membrane, including a porous body, the porous body including a liquid inlet surface and a liquid outlet surface, and along the direction from the liquid inlet surface to the liquid outlet surface, the porous body includes a screening layer, a preparatory layer, a support layer, an intermediate layer, a separation layer and a protective layer.

[0145] The method for preparing the multi-region microfiltration membrane comprises the following steps:

[0146] (1) Dissolve 5 parts of sulfonated polyethersulfone (Mw=95000) and 16 parts of polyethersulfone (Mw=48000) resin in 60 parts of solvent, adjust the temperature to 60℃ and stir for 1h. Then, add 8 parts of polyvinyl pyrrolidone (PVP K30) and 1 part of hydroxyethyl acrylamide, stir to make them evenly dispersed, and remove most of the oxygen in the container by passing nitrogen. Then raise the temperature to 80℃, slowly add 10 parts of triethylene glycol, and continue stirring for 3h. Then cool to 25℃, vacuum degas, and obtain the casting solution for use. The solvent is a mixture of N-methylpyrrolidone and methyl lactate, and the mass ratio of N-methylpyrrolidone to methyl lactate is 55:5.

[0147] (2) The temperature of the carrier was adjusted to 60°C, and a casting solution at 25°C was poured onto the surface of the carrier to form a primary film with a thickness of about 120 μm. The primary film was transferred to an environment with a relative humidity of 70% RH and stayed in the air section for 10 seconds to obtain a wet film.

[0148] (3) The wet membrane was immersed in the first coagulation bath (75 vol% NMP aqueous solution) at 45°C at a speed of 0.1 m / s. The wet membrane was immersed in the first coagulation bath for 15 s. After being taken out, it was quickly immersed in the second coagulation bath (5 vol% hexafluoroisopropanol aqueous solution) at 40°C at a speed of 0.2 m / s for complete phase separation. After washing, a multi-region microfiltration membrane was obtained, which was recorded as g.

[0149] Example 8

[0150] The present embodiment provides a multi-zone microfiltration membrane, including a porous body, the porous body including a liquid inlet surface and a liquid outlet surface, and along the direction from the liquid inlet surface to the liquid outlet surface, the porous body includes a screening layer, a preparatory layer, a support layer, an intermediate layer, a separation layer and a protective layer.

[0151] The method for preparing the multi-region microfiltration membrane comprises the following steps:

[0152] (1) Dissolve 17 parts of sulfonated polyethersulfone (Mw=130000) and 3 parts of polyethersulfone (Mw=48000) resin in 58 parts of solvent, adjust the temperature to 60°C and stir for 1 hour. Then, add 5 parts of polyvinyl pyrrolidone (PVP K60), stir to make it evenly dispersed, and remove most of the oxygen in the container by passing nitrogen. Then raise the temperature to 80°C, slowly add 17 parts of diethylene glycol, and continue stirring for 3 hours. Then cool to 40°C, vacuum degas, and obtain a casting solution for use. The solvent is a mixture of dimethylformamide and methyl lactate, and the mass ratio of dimethylformamide to methyl lactate is 50:8.

[0153] (2) The temperature of the carrier was adjusted to 60°C, and a 40°C casting solution was poured onto the surface of the carrier to form a primary film with a thickness of about 120 μm. The primary film was transferred to an environment with a relative humidity of 75% RH and stayed in the air section for 10 seconds to obtain a wet film.

[0154] (3) The wet membrane was immersed in the first coagulation bath (50 vol% DMF aqueous solution) at 25°C at a speed of 0.1 m / s. The wet membrane was immersed in the first coagulation bath for 10 s. After being taken out, it was quickly immersed in the second coagulation bath (5 vol% acetone aqueous solution) at 40°C at a speed of 0.15 m / s for complete phase separation. After washing, a multi-region microfiltration membrane was obtained, which was recorded as h.

[0155] Comparative Example 1

[0156] This comparative example provides a method for preparing a multi-region microfiltration membrane, comprising the following steps:

[0157] (1) Dissolve 20 parts of polyethersulfone (Mw=58000) resin in 58 parts of solvent, adjust the temperature to 60℃ and stir for 1h. Then, add 5 parts of polyvinyl pyrrolidone (PVP K30), stir to make it evenly dispersed, and remove most of the oxygen in the container by passing nitrogen. Then raise the temperature to 80℃, slowly add 17 parts of diethylene glycol, continue stirring for 3 hours, then cool to 40℃, vacuum degas, and obtain a casting solution for use. The solvent is a mixture of dimethylformamide and methyl lactate, and the ratio of dimethylformamide to methyl lactate is 50:8.

[0158] (2) The temperature of the carrier was adjusted to 60°C, and a 40°C casting solution was poured onto the surface of the carrier to form a primary film with a thickness of about 120 μm. The primary film was transferred to an environment with a relative humidity of 75% RH and stayed in the air section for 10 seconds to obtain a wet film.

[0159] (3) Immerse in the first coagulation bath (50 vol% DMF aqueous solution) at 25°C at an initial speed of 0.1 m / s. The wet membrane is immersed in the first coagulation bath for 10 s. After being taken out, it is quickly immersed in the second coagulation bath (5 vol% acetone aqueous solution) at 40°C at a speed of 0.15 m / s for complete phase separation. After washing with pure water, a multi-region microfiltration membrane is obtained, which is denoted as i.

[0160] Comparative Example 2

[0161] This comparative example provides a method for preparing a multi-region microfiltration membrane, comprising the following steps:

[0162] (1) Dissolve 3 parts of sulfonated polyethersulfone (Mw=130000) and 17 parts of polyethersulfone (Mw=58000) resin in 58 parts of solvent, adjust the temperature to 60℃ and stir for 1h. Then, add 5 parts of polyvinyl pyrrolidone (PVP K30), stir to make it dispersed evenly, and remove most of the oxygen in the container by passing nitrogen. Then raise the temperature to 80℃, slowly add 17 parts of diethylene glycol, continue stirring for 3h, then cool to 40℃, vacuum degas, and obtain a casting solution for use. The solvent is a mixture of dimethylformamide and methyl lactate, and the ratio of dimethylformamide to methyl lactate is 50:8.

[0163] (2) The carrier temperature was adjusted to 60°C, and a 40°C casting solution was poured onto the carrier surface to form a primary film with a thickness of about 120 μm. The primary film was transferred to an environment with a relative humidity of 75% RH and stayed in the air section for 10 seconds to obtain a wet film.

[0164] (3) The wet membrane was immersed in a first coagulation bath (50 vol% DMF aqueous solution) at 25 °C at a speed of 0.1 m / s. The wet membrane was immersed in the first coagulation bath for 180 s. After being taken out, it was immersed in a second coagulation bath (5 vol% acetone aqueous solution) at 40 °C at a speed of 0.15 m / s for phase separation. After washing with pure water, a multi-region microfiltration membrane was obtained, which was recorded as j.

[0165] Comparative Example 3

[0166] This comparative example provides a method for preparing a multi-region microfiltration membrane, comprising the following steps:

[0167] (1) 36 parts of PES (Mw = 48000) were dissolved in a mixed solvent of 100 parts of NMP and 8 parts of tetrahydrofuran, and then 10 parts of N-hydroxymethyl acrylamide, 1 part of lithium chloride and 50 parts of polyethylene glycol 200 were added, mixed, and stirred at 60°C until clear to obtain a homogeneous casting solution.

[0168] (2) The scraper thickness was adjusted to 250 μm, the carrier was heated to 80 °C, and then the casting solution was cast onto the carrier. Then, the carrier was kept in the air section for 25 seconds under a relative humidity of 80% RH, and then immersed in the first coagulation bath (3 wt% isopropanol). The wet membrane was immersed in the first coagulation bath for 2 seconds, taken out and immediately transferred to the second coagulation bath (5 wt% trifluoroethanol) for complete phase separation. After washing with pure water, a multi-region microfiltration membrane was obtained, which was recorded as k.

[0169] Test example

[0170] This test example provides the performance of the multi-region microfiltration membrane of each embodiment and comparative example.

[0171] (1) The parameters of the multi-region microfiltration membranes of various embodiments and comparative examples are shown in Tables 1 to 4; wherein the average pore size, layer thickness, pore ratio, etc. are obtained by characterizing the membrane structure morphology by scanning electron microscopy (SEM), and then the average value is calculated by computer software (such as NIS-Elements and Matlab in sequence), and the parts with obviously smaller or larger sizes are not taken into consideration.

[0172] Table 1 Parameters related to the liquid inlet and outlet surfaces of the multi-region microfiltration membranes of various embodiments and comparative examples

[0173]

[0174] Table 2 Parameters of the screening layer and preparatory layer of the multi-region microfiltration membrane of each embodiment and comparative example

[0175]

[0176] Table 3 Related parameters of the support layer and intermediate layer of the multi-region microfiltration membrane of each embodiment and comparative example

[0177]

[0178] Table 4 Separation layer and protective layer related parameters of the multi-region microfiltration membrane of each embodiment and comparative example

[0179]

[0180] Note: “ / ” in the table means that the data does not exist.

[0181] (2) Performance test of multi-region microfiltration membranes of various embodiments and comparative examples

[0182] Test method for microfiltration membrane flux: Water flux is the amount of water passing through a membrane sample within a given time. The microfiltration membrane is cut into a disc with a diameter of 47 mm and pre-wetted with MilliQ grade water. The sample is placed in an Amicon8050 stirring unit holder (EMDMillipore 5122), with a support disk at the bottom (3MBLA020 grade nylon microfiltration membrane, purchased from 3M Company). Stirring is applied by a magnetic stirring plate (Corning PC-420D), and pressure is applied to the indoor air by a regulator (Ingersoll-Rand R37121-100). At 20psi (138kPa), water flux tests were performed under stirring of>200rpm, and the results are shown in Table 5.

[0183] Logarithmic reduction value (LRV) test of microfiltration membrane: The filter membranes prepared in each embodiment and comparative example were used as samples to conduct bacterial retention challenge experiments; wherein, the detection method refers to the guidance document TR26 issued by PDA. During the test, Pseudomonas diminuta (ATCC 19146) with a bacterial diameter of 0.3-0.4 μm was used as the retained bacteria, and the bacterial retention experiment was conducted on the sample according to the standard ASTM F838-2015 ae1 to test the LRV value of the filter membrane.

[0184] Test method for microfiltration membrane loading: Take the microfiltration membrane prepared in each embodiment and comparative example as a sample, cut the sample (membrane to be tested) into a membrane sheet with a diameter of 22.5 mm; clamp the sample in a membrane filter, with the liquid inlet surface as the liquid inlet side, and equip it in a pressure vessel. The device is equipped with a pressure regulating valve, and the effective filtration area is 3.5 cm 2, pour the test liquid into the pressure vessel and adjust the pressure to 30psi. The test liquid is 0.1% BSA protein solution; place the liquid collection container on the electronic balance and peel it, open the valve of the pressure vessel, and immediately start the automatic counting device; record the change value of the membrane filtration quality as the filtration time increases. Record once every 10s in the first minute, record once every 30s from the second minute to the tenth minute, and record once every 1 minute after 10 minutes. Stop filtration when the material filtration flow rate decays to 90%. Record the change value of the membrane filtration quality over time, and convert the filtration volume of the test liquid through the density of the test liquid.

[0185] Testing method for viscosity of casting liquid: keep the casting liquid in a constant temperature water bath at 25°C for 24 hours, and measure the viscosity of the casting liquid using a rotational viscometer.

[0186] Test method for contact angle of the inlet and outlet surfaces of the microfiltration membrane: Use DropMeter A-100P contact angle / surface tension tester to measure water contact angle. Cut a 2cm×2cm microfiltration membrane, fix it on a glass slide with tape, and place it on the sample stage for testing. Record the initial contact angle when the water drop falls on the membrane surface, repeat the experiment 5 times, and take the average value.

[0187] Table 5 Performance of multi-region microfiltration membranes in various embodiments and comparative examples

[0188]

[0189] Figures 1 to 4 It can be seen that the microfiltration membrane prepared in Example 1 has a multi-region structure. Figure 1 The upper surface is the liquid inlet surface, and the lower surface is the liquid outlet surface. From the liquid inlet surface to the liquid outlet surface, there are respectively a screening layer with a consistent pore size, a preparatory layer with a gradually increasing pore size, a support layer with a consistent pore size, an intermediate layer with a gradually decreasing pore size, a separation layer with a consistent pore size, and a protective layer with a gradually increasing pore size. Among them, the support layer has the largest average pore size, accounting for 30.5% of the thickness, and because the pore size remains basically consistent, the strength of the support layer is further improved on the basis of having a larger pollution-receiving space. The separation layer has the smallest average pore size and plays the main role in filtration and separation. It accounts for 14% of the thickness, which ensures the filtration effect. The protective layer set between the separation layer and the liquid outlet surface allows the separation layer to be set inside the microfiltration membrane to prevent leakage caused by external damage to the separation layer. Reference Figure 2 Further magnification of the screening layer shows that there is a screening layer with a consistent pore size at the liquid inlet surface. The average pore size of the screening layer is 0.41 μm, and the thickness accounts for 4.5%. It not only improves the strength of the liquid inlet surface of the microfiltration membrane and ensures its integrity, but also plays a screening role, intercepting large particles on the liquid inlet side, preventing them from entering the microfiltration membrane, and prolonging the clogging time of the microfiltration membrane. Figure 3From the electron microscope image of the middle liquid surface, it can be seen that the pore area ratio is 21.7%, and the setting of secondary screening holes can help alleviate the initial resistance of the filter membrane to the feed liquid and achieve better flux and retention effects.

[0190] According to the results of Tables 1 to 4 and 5, the multi-region microfiltration membrane prepared in Comparative Examples 1-3 has no screening layer and preparatory layer, the average pore size of the support layer and the protective layer is relatively close, and the ratio of the average pore size of the support layer to the average fiber diameter thereof is too small. Comparing Comparative Example 1 with Example 1, it can be seen that the addition of sulfonated polymers in the preparation of the microfiltration membrane of the present invention can form a multi-region microfiltration membrane with a specific structure, which helps to improve the flux and load of the microfiltration membrane, and reduces the risk of bacterial leakage. It can also be seen from the contact angle that the multi-region microfiltration membrane of Example 1 of the present invention has better hydrophilicity. Comparative Examples 2-3 illustrate that the immersion time of the wet membrane in the first coagulation bath is too long or too short, which is not conducive to the formation of a multi-region microfiltration membrane with a specific structure; combined with the results of the examples, when the immersion time of the wet membrane in the first coagulation bath is 5 to 100 seconds, an integrated membrane with fast membrane flux, high load, pressure resistance and other properties can be obtained.

[0191] Furthermore, as the filtration time and pressure increase, the structure and pore size of the microfiltration membrane will change, resulting in a downward trend in flux and load. The multi-region microfiltration membrane prepared in the embodiment of the present invention has a higher flux and load, which can prove that the microfiltration membrane has good pressure resistance.

[0192] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the scope of protection of the invention.

Claims

1. A multi-zone microfiltration membrane, characterized in that: The porous body comprises a liquid inlet surface, a liquid outlet surface and a plurality of regions; along the direction from the liquid inlet surface to the liquid outlet surface, the porous body comprises a screening layer with a uniform pore size, a preparatory layer with a gradually increasing pore size, a supporting layer with a uniform pore size, an intermediate layer with a gradually decreasing pore size, a separation layer with a uniform pore size and a protective layer with a gradually increasing pore size; The region with the largest average pore size among the several regions is the support layer, and the region with the smallest average pore size is the separation layer; A screening layer is provided on a side of the porous body close to the liquid inlet surface; The thickness of the screening layer is 4-10% of the thickness of the porous body; The average pore size of the screening layer is 0.25-0.55 μm.

2. The multi-zone microfiltration membrane according to claim 1, characterized in that: The thickness of the support layer is 25-45% of the thickness of the porous body; and / or, The average pore size of the support layer is 1-1.5 μm; and / or, The average pore size of the separation layer is 0.2-0.45 μm; and / or, The thickness of the separation layer is 10-20% of the thickness of the porous body.

3. The multi-zone microfiltration membrane according to claim 1, characterized in that: The total thickness of the screening layer and the separation layer is 14-30% of the thickness of the porous body.

4. The multi-zone microfiltration membrane according to claim 1, characterized in that: The aperture variation region includes a preparation layer, an intermediate layer and a protection layer.

5. The multi-zone microfiltration membrane according to claim 4, characterized in that: The thickness of the preparatory layer is 8-15% of the thickness of the porous body; and / or, The average pore size of the preparatory layer is 0.75-1.0 μm; and / or, The thickness of the intermediate layer is 20-40% of the thickness of the porous body; and / or, The average pore size of the intermediate layer is 0.35-0.8 μm; and / or, The thickness of the protective layer is 8-15% of the thickness of the porous body; and / or, The average pore size of the protective layer is 0.7-1.1 μm; and / or, The gradient coefficient of the preparatory layer is 0.05-0.13; and / or, The gradient coefficient of the intermediate layer is 0.015-0.05; and / or, The gradient coefficient of the protective layer is 0.025-0.

07.

6. The multi-zone microfiltration membrane according to claim 1, characterized in that: The average pore size of the protective layer is greater than the average pore size of the intermediate layer; and / or, The average pore size of the protective layer is larger than the average pore size of the screening layer; and / or, The average pore size of the separation layer is smaller than the average pore size of the preparatory layer; and / or, The average pore size of the separation layer is smaller than the average pore size of the screening layer; and / or, The average pore size of the support layer is greater than the average pore size of the protection layer.

7. The multi-zone microfiltration membrane according to claim 1, characterized in that: The average fiber diameter of the screening layer is 0.2-0.5 μm; and / or, The ratio of the average pore size of the screening layer to the average fiber diameter thereof is (0.5-2.75):1; and / or, The average fiber diameter of the support layer is 0.3-0.7 μm; and / or, The ratio of the average pore size of the support layer to the average fiber diameter thereof is (1.4-5):1; and / or, The average fiber diameter of the preparatory layer is in the range of 0.35-0.55 μm; and / or, The ratio of the average pore size of the preparatory layer to the average fiber diameter thereof is (1.35-2.86):1; and / or, The average fiber diameter of the separation layer is 0.08-0.25 μm; and / or, The ratio of the average pore size of the separation layer to the average fiber diameter thereof is (0.8-5.65):1; and / or, The average fiber diameter of the intermediate layer is 0.12-0.3 μm; and / or, The ratio of the average pore size of the intermediate layer to the average fiber diameter thereof is (1.15-6.7):1; and / or, The average fiber diameter of the protective layer is 0.4-0.9 μm; and / or, The ratio of the average pore size of the protective layer to the average fiber diameter thereof is (0.75-2.75):1; and / or, The multi-region microfiltration membrane has a thickness of 95-145 μm; and / or a porosity of 60-80%.

8. The multi-zone microfiltration membrane according to claim 1, characterized in that: The average pore size of the liquid inlet surface is 0.2-0.48 μm; and / or, The hole area ratio of the liquid inlet surface is 15-35%; and / or, The average pore size of the liquid outlet surface is 0.8-1.5 μm; and / or, The hole area ratio of the liquid outlet surface is 12-30%; and / or, The primary screening holes are holes in the liquid inlet surface with a pore size lower than the average pore size of the liquid inlet surface, the secondary screening holes are holes in the liquid inlet surface with a pore size higher than 1.2 times the average pore size of the liquid inlet surface, and the area of ​​the primary screening holes on the liquid inlet surface accounts for 3-17%; and / or, The ratio of the number of secondary screening holes to the number of primary screening holes is (0.2~0.75):

1.

9. A method for preparing a multi-region microfiltration membrane according to any one of claims 1 to 8, characterized in that: The following steps are involved: (1) dissolving a polymer in a solvent to prepare a casting solution; wherein the polymer in the casting solution comprises a hydrophobic polymer and a hydrophilic polymer; (2) The casting solution forms a primary film on the surface of the carrier and is left to stand to obtain a wet film; (3) Immersing the wet membrane obtained in step (2) into a first coagulation bath and a second coagulation bath to obtain a multi-region microfiltration membrane; wherein the immersion time of the wet membrane in the first coagulation bath is 5 to 100 seconds; and the speed of immersing the wet membrane in the second coagulation bath is at least 1.2 times the speed of immersing the wet membrane in the first coagulation bath.

10. The preparation method according to claim 9, characterized in that: The temperature of the carrier is at least 15° C. higher than the temperature of the first coagulation bath and / or the second coagulation bath; and / or, The temperature of the carrier is 35-80° C.; and / or, The hydrophobic polymer is an aromatic sulfone polymer; and / or, The hydrophilic polymer is a sulfonated aromatic sulfone polymer; and / or, The average molecular weight of the hydrophilic polymer is at least 10,000 Daltons greater than the average molecular weight of the hydrophobic polymer; and / or, The mass ratio of polymer, solvent and additive in the casting solution is (15-22):(40-70):(20-35).

11. The preparation method according to claim 9 or 10, characterized in that: The solvent of the first coagulation bath is a mixture of aprotic polar solvent and water; and / or, The volume proportion of the aprotic polar solvent in the first coagulation bath is 20-80%; and / or, The solvent of the second coagulation bath is at least one polar protic solvent.

12. Use of the multi-region microfiltration membrane according to any one of claims 1 to 8 or the multi-region microfiltration membrane prepared by the preparation method according to any one of claims 9 to 11 in removing insoluble particles or microbial impurities from a liquid flow.

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