Enhanced tubular composite ultrafiltration membrane having network-like pore structure and method for preparing the same

Abstract

The application discloses a reinforced tubular composite ultrafiltration membrane with network pore structure and a preparation method thereof. The tubular composite ultrafiltration membrane comprises a support tube and a polymer membrane layer adhered to the inner wall of the support tube, wherein the polymer membrane layer has a network pore structure, the average pore diameter of the pores is 8nm-200nm, and the porosity is 60%-90%; the support tube is formed into an integrated tubular structure by 2 or more layers of non-woven fabrics. The reinforced tubular composite ultrafiltration membrane with network pore structure has a network pore structure, a pure water flux of 100-2000LHM (0.1MPa pressure operation), and a tensile strength of >400N, so that the surface can withstand a flow rate of 4-6m / s in practical application, and can resist high-concentration COD and SS pollution; and the membrane layer and the non-woven fabric are integrated by adhesion, backwashing negative pressure detection is conducted on the tubular composite ultrafiltration membrane, the backwashing pressure is in the range of 50KPa-100KPa, and the polymer membrane layer and the support tube are not peeled off.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of membrane separation technology, in particular to a reinforced tubular composite ultrafiltration membrane with network-like pore structure for sewage treatment and a preparation method thereof. BACKGROUND

[0002] Membrane separation technology has been widely used in the fields of food, medicine, biology, chemical industry, environmental protection and the like for separation, purification, concentration and the like due to its high efficiency, energy saving, environmental protection, simple operation and easy control. According to the material, the membrane can be divided into organic membrane and inorganic membrane; according to the pore size, the membrane can be divided into microfiltration membrane, ultrafiltration membrane, nanofiltration membrane and reverse osmosis membrane; according to the shape, the membrane can be divided into flat membrane, hollow fiber membrane, tubular membrane and spiral membrane.

[0003] The tubular membrane is a form of membrane module, which is suitable for microfiltration and ultrafiltration membrane separation technology. The tubular membrane has the advantages of wide flow channel, turbulent flow of the feed liquid in the tube, low requirement for the pretreatment accuracy of the feed liquid, easy cleaning, and the ability to use chemical agents for cleaning and mechanical methods for cleaning. The pressure loss of the module is small, so the flow channel is long, the filtration efficiency can be relatively improved, and it is particularly suitable for the treatment of high-content liquid materials such as landfill leachate, sewage containing activated sludge, fruit juice, and crystallization mother liquor, so it is widely used in food and beverage, chemical industry, microelectronics, papermaking and pharmaceutical industry.

[0004] In order to enhance the strength of the membrane and improve the cleaning and backwashing resistance of the membrane, a tubular composite ultrafiltration membrane is provided, which is composed of a support tube and a polymer membrane layer, wherein the polymer membrane layer is formed on the inner wall or the outer wall of the support tube. The separation effect is mainly determined by the polymer membrane layer, and the strength of the membrane is mainly determined by the adhesion between the support tube and the polymer membrane.

[0005] In terms of membrane materials, polyvinylidene fluoride (PVDF), cellulose acetate (CA), polysulfone (PSF), polyether sulfone (PES), polyethylene (PE) and polyvinyl chloride (PVC) and other polymer materials are mainly used. Among them, polyvinylidene fluoride (PVDF) has good mechanical properties, thermal stability, chemical stability and corrosion resistance, so it has become the main membrane material for commercial tubular membranes at home and abroad. The support tube material can be tubular knitted fabric, non-woven fabric or tubular material formed by sintering of high molecular particles.

[0006] The process of membrane separation is a process of separating different components in a feed under pressure driving, and the structure of the polymer membrane layer has a very important influence on the separation performance and the performance of the membrane tube. The polymer membrane layer is generally prepared by a non-solvent induced phase separation method, and is mostly a finger-shaped pore structure or a large pore structure. Although the running resistance is reduced and the permeation performance is improved, the separation performance is reduced (the filtration precision is not high) and the pressure resistance is poor. Under long-term pressure operation, the polymer membrane separation layer is prone to compaction, causing irreversible decay of the flux. The tubular composite ultrafiltration membrane needs hard foreign matter to unblock in the high flow rate cross-flow mode operation and after the pollution blockage. The polymer membrane layer and the support tube are prone to peeling, resulting in failure of the separation performance. In order to prevent the peeling of the polymer membrane layer and the support tube, the combination between the polymer membrane layer and the inner wall of the support tube needs to be enhanced.

[0007] Chinese patent document CN203075853U discloses a backflushing tubular membrane, which comprises, from outside to inside, an outer non-woven support layer, an inner non-woven dense layer and a high polymer membrane separation layer I. Its feature is that a polyester reinforcing layer is arranged between the outer non-woven support layer and the inner non-woven dense layer, and a high polymer membrane separation layer II is further arranged outside the outer non-woven support layer. The patent document is a utility model, and does not disclose the preparation method thereof. The tubular membrane comprises multiple layers, the preparation process is complex, and the produced tubular membrane has thick layers and is difficult to clean after organic pollution.

[0008] Chinese patent document CN101224394A discloses a polymer-fabric composite tubular microporous membrane and a preparation method thereof. The polymer-fabric composite tubular microporous membrane is composed of a circular tubular knitted fabric and a polymer microporous membrane which is immersed and coated on the outer surface layer of the circular tubular knitted fabric. The circular tubular knitted fabric is a support layer, and the polymer microporous membrane is a filtration separation layer, and the surface of the filtration separation layer has uniformly distributed micropores. The preparation method of the polymer-fabric composite tubular microporous membrane comprises the following steps: the circular tubular knitted fabric is sleeved on a forming mold, and then is soaked in a membrane preparation solution for 1-5 minutes; then the forming mold with the sleeved circular tubular knitted fabric is taken out and immersed in deionized water, so that the membrane preparation solution on the circular tubular knitted fabric is solidified to form a membrane, thereby forming the polymer-fabric composite tubular microporous membrane with the circular tubular knitted fabric as the support layer and the polymer microporous membrane as the filtration separation layer. However, the combination between the polymer microporous membrane and the tubular knitted fabric is poor, and the membrane skin layer may fall off during the separation process and the backwashing process, and the durability is poor. SUMMARY

[0009] Therefore, the present application is made to solve the above problems in the prior art. An object of the present application is to provide an enhanced tubular composite ultrafiltration membrane with a network-shaped pore structure, wherein the polymer membrane layer has a network-shaped pore structure, the combination between the polymer membrane layer and the support tube is enhanced, the separation performance is good, and the membrane is resistant to backwashing.

[0010] Another object of the present application is to provide a method for preparing the above-mentioned enhanced tubular composite ultrafiltration membrane having a network-like pore structure.

[0011] According to one aspect of the present application, the enhanced tubular composite ultrafiltration membrane having a network-like pore structure comprises a support tube and a polymer membrane layer adhered to the inner wall of the support tube, wherein the polymer membrane layer has a network-like pore structure with an average pore size of 8 nm to 200 nm and a porosity of 60% to 90%; and the support tube is formed by integrating two or more layers of non-woven fabric into a tubular structure.

[0012] According to another aspect of the present application, the method for preparing the above-mentioned enhanced tubular composite ultrafiltration membrane having a network-like pore structure comprises the following steps:

[0013] Step 1: preparing a casting solution

[0014] At a temperature of 60°C to 70°C, the components are uniformly mixed and dissolved according to the following composition by weight percentage, and then filtered and degassed to prepare a casting solution.

[0015]

[0016] and the sum of the components is 100%,

[0017] wherein the polymer is selected from polyvinylidene fluoride, polyether sulfone, polysulfone, and polyamide;

[0018] The pore-forming agent is selected from one or more of organic pore-forming agents and inorganic pore-forming agents;

[0019] The non-solvent additive is selected from one or more of water, methanol, ethanol, propanol, butanol, octanol, formic acid, acetic acid, and propionic acid;

[0020] The mixed solvent is a mixed solvent of one or more solvents selected from dimethyl sulfoxide (DMSO), dimethylacetamide (DMAC), dimethylformamide (DMF), and N-methyl pyrrolidone, and 1,4-dioxane at a weight ratio of 1 to 9:1;

[0021] Step 2: forming a support tube and a casting solution coating

[0022] At a temperature of 60°C to 70°C, the two or more non-woven fabric strips are spirally wound and welded into an integrated tubular structure to form a support tube, and the casting solution is coated on the inner wall of the support tube to form a casting solution coating, using a tubular membrane integrated film forming machine.

[0023] Step 3: forming a tubular composite ultrafiltration membrane

[0024] The support tube coated with the casting solution in the above step 2 is dipped in a coagulation solution forming at a temperature of 20-50°C; and then soaked in water at a temperature of 10-50°C for 12-24 hours, and then soaked in a glycerol-water mixture containing 10-20wt% glycerol for 12-24 hours, and then dried to obtain a tubular composite ultrafiltration membrane with a network pore structure,

[0025] The coagulation solution is a mixture of one or more solvents selected from dimethyl sulfoxide (DMSO), dimethyl acetamide (DMAC), dimethyl formamide (DMF) and N-methyl pyrrolidone and water in a weight ratio of 0-50%: 100-50%.

[0026] The enhanced tubular composite ultrafiltration membrane with a network pore structure and the preparation method thereof will be described in more details as follows.

[0027] The enhanced tubular composite ultrafiltration membrane with a network pore structure comprises a support tube and a polymer membrane layer adhered to the inner wall of the support tube, wherein the polymer membrane layer has a network pore structure, the average pore size of the pores is 8-200 nm, and the porosity is 60-90%; the support tube is formed into an integrated tubular structure by 2 or more layers of non-woven fabric.

[0028] The polymer membrane layer is a membrane layer formed by a polymer selected from polyvinylidene fluoride, polyether sulfone, polysulfone or polyamide, and preferably a membrane layer formed by polyvinylidene fluoride. The polymer membrane layer has a network pore structure, as shown in the microscope picture of the cross-section of the polymer membrane layer (magnification 500) of the present application, Figure 1 Figure 2 The microscope picture of the surface of the polymer membrane layer (magnification 5000) of the present application clearly shows that the polymer membrane layer has a network pore structure, the average pore size of the pores is 8-200 nm, and preferably 30-60 nm; the porosity is 60-90%, and preferably 80-90%; the thickness of the polymer membrane layer is 10-100 μm, and preferably 50-75 μm.

[0029] The support tube is formed into an integrated tubular structure by 2 or more layers of non-woven fabric, the inner diameter of the support tube is 5-25 mm, and preferably 5-20 mm; the thickness is 300-500 μm, or 300-400 μm. The support tube is preferably formed into an integrated tubular structure by 2 layers of non-woven fabric, specifically, a first non-woven fabric is spirally wound to form an inner layer of the support tube, and a second non-woven fabric is spirally wound on the inner layer to form an outer layer of the support tube, and each joint is welded and combined to form an integrated tubular structure, as shown in Figure 3

[0030] ​​The nonwoven fabric can be a nonwoven fabric formed of a polymer selected from polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE), and a propylene / ethylene copolymer (PP / PE), and has a nonwoven fabric unit area mass of, for example, 100 to 300 g / m 2 , or 150 to 200 g / m 2 ; a longitudinal breaking strength and a transverse breaking strength of, for example, 500 to 1000 N, or 800 to 1000 N, respectively; and a thickness of, for example, 150 to 250 μm, or 180 to 250 μm.

[0031] Here, it should be noted that the ordinal numbers such as "first", "second", and the like are used only for the purpose of distinguishing one component from another component, and are not limited by the ordinal numbers.

[0032] The tubular composite ultrafiltration membrane according to the present application has a pure water flux of 100 to 2000 LHM (0.1 MPa pressure operation), a tensile strength of > 400 N, for example, 450 N to 800 N, and a backwashing negative pressure detection of a backwashing pressure in a range of 50 KPa to 100 KPa, and the polymer membrane layer and the support tube are not peeled off.

[0033] According to another aspect of the present application, in the preparation method of the enhanced tubular composite ultrafiltration membrane with a network pore structure provided by the present application, in the step 1 of preparing the casting solution, the polymer is selected from polyvinylidene fluoride, polyether sulfone, polysulfone, and polyamide, and is preferably polyvinylidene fluoride.

[0034] The pore-forming agent is selected from one or more of an organic pore-forming agent and an inorganic pore-forming agent, the organic pore-forming agent is, for example, polyvinylpyrrolidone with a molecular weight of 10 to 1300 KDa, and polyethylene glycol with a molecular weight of 0.2 to 20 KDa; and the inorganic pore-forming agent is selected from one or more of lithium chloride, silicon oxide, and calcium chloride.

[0035] The non-solvent additive is selected from one or more of water, methanol, ethanol, propanol, butanol, octanol, formic acid, acetic acid, and propionic acid.

[0036] The mixed solvent is a mixed solvent of one or more solvents selected from dimethyl sulfoxide (DMSO), dimethylacetamide (DMAC), dimethylformamide (DMF), and N-methyl pyrrolidone, and 1,4-dioxane in a weight ratio of 1 to 9:1, and is preferably a mixed solvent in a weight ratio of 2 to 5:1.

[0037] In the preparation of the casting solution, 1,4-dioxane is added as a poor solvent, and a non-solvent additive is added to prepare a homogeneous casting solution. The addition of 1,4-dioxane reduces the solubility of the mixed solvent, making the system prone to delayed phase separation. The addition of the non-solvent additive facilitates the formation of a porous structure, and the system is prone to delayed phase separation. Under suitable process conditions, a high network pore structure separation layer is formed.

[0038] In the step 2 of forming the support tube and the casting solution coating, at a temperature of 60-70°C, a tubular membrane integrated film forming machine is used to spiral wrap and weld two or more non-woven fabric strips into an integrated tubular structure support tube, and at the same time, the above-mentioned casting solution is coated on the inner wall of the support tube to form a casting solution coating.

[0039] As an example, a tubular membrane integrated film forming machine is used to spiral wrap and weld two non-woven fabric strips into an integrated tubular structure support tube. Specifically, the first non-woven fabric strip is spirally wrapped to form the inner layer of the support tube, and the second non-woven fabric strip is spirally wrapped on the inner layer to form the outer layer of the support tube, and the interfaces are welded (e.g. ultrasonic welding) to form an integrated tubular structure, as shown in Figure 3 At the same time, a metal coating rod is used to coat the above-mentioned casting solution on the inner wall of the support tube to form a casting solution coating.

[0040] The mixed solvent containing 1,4-dioxane has a certain swelling effect on the non-woven fabric at 60-70°C, which makes the casting solution and the non-woven fabric adhere together as a whole, thereby improving the adhesion between the membrane separation layer and the non-woven fabric interface.

[0041] In the step 3 of forming the tubular composite ultrafiltration membrane, the support tube with the casting solution coating obtained in step 2 is immersed in a coagulation liquid at a temperature of 20-50°C; then, it is soaked in water at a temperature of 10-50°C for 12-24 hours to remove the solvents, non-solvent additives and pore-forming agents in the system, and then soaked in a glycerol-water mixture containing 10wt%-20wt% glycerol for 12-24 hours, and after drying, an enhanced tubular composite ultrafiltration membrane with a network pore structure is obtained.

[0042] Advantages

[0043] The enhanced tubular composite ultrafiltration membrane with a network pore structure of the present application has the following advantages:

[0044] In the present application, 1,4-dioxane is added as a poor solvent in the preparation of casting solution, and a non-solvent additive is added to prepare a homogeneous casting solution. The addition of 1,4-dioxane reduces the solubility of the mixed solvent, and the system is prone to delayed phase separation. The addition of the non-solvent additive is prone to produce a porous structure, and the system is prone to delayed phase separation. Under suitable process conditions, a high network pore structure separation layer is formed.

[0045] In the step 2 of forming the support tube and the casting solution coating, the mixed solvent containing 1,4-dioxane has a certain swelling effect on the non-woven fabric at 60-70°C, so that the casting solution is integrally bonded with the non-woven fabric, thereby improving the bonding force between the membrane separation layer and the non-woven fabric interface.

[0046] The enhanced tubular composite ultrafiltration membrane with network pore structure of the present application has a network pore structure, the membrane pores have good connectivity, the membrane permeability, precision and pressure resistance are improved, specifically, the tubular composite ultrafiltration membrane of the present application has a pure water flux of 100-2000 LHM (0.1 MPa pressure operation), and a tensile strength of >400 N, so that the surface can withstand a flow rate of 4-6 m / s in actual application, and can resist high concentration COD and SS pollution; and the membrane layer and the non-woven fabric are integrally bonded, the tubular composite ultrafiltration membrane is subjected to backwashing negative pressure detection, the backwashing pressure is in the range of 50 KPa-100 KPa, and the polymer membrane layer and the support tube are not peeled off. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 is a microscope picture (magnification 500) of the cross-sectional direction of the polymer membrane layer of the tubular composite ultrafiltration membrane prepared in Example 1 of the present application;

[0048] Figure 2 is a microscope picture (magnification 5000) of the surface of the polymer membrane layer of the tubular composite ultrafiltration membrane prepared in Example 1 of the present application;

[0049] Figure 3 is a shape diagram of the support tube of the integrated tubular structure formed by the non-woven fabric of the present application;

[0050] Figure 4 shows the peeling phenomenon of the tubular composite ultrafiltration membrane of Comparative Example 1 after being assembled into a membrane module in actual application under negative pressure of 100 KPa backwashing. DETAILED DESCRIPTION

[0051] In the following, the enhanced tubular composite ultrafiltration membrane with network pore structure and the preparation method thereof of the present application will be described more specifically by examples, but the protection scope of the present application is not limited to these examples.

[0052] Example 1

[0053] Step 1: Preparation of casting solution

[0054] At a temperature of about 70°C, the components were uniformly mixed and dissolved in the following proportions by weight, and after filtration and degassing, a casting solution was prepared;

[0055]

[0056] Step 2: Forming support tube and casting solution coating

[0057] Using a tubular membrane integrated film forming machine, at a temperature of about 70°C, two PET non-woven fabric belts (unit area mass 180 g / m 2 , longitudinal and transverse breaking strength 1000 N, thickness 200 μm) were spirally wound and welded into an integrated tubular structure support tube (inner diameter 8 mm, thickness 400 μm, welding speed 3 m / min), and a metal coating rod coated the above-mentioned casting solution on the inner wall of the support tube to form a casting solution coating;

[0058] Step 3: Forming tubular composite ultrafiltration membrane

[0059] The support tube with casting solution coating obtained in Step 2 was immersed in a coagulation liquid (temperature 50°C, composition: mixture of dimethylacetamide (DMAC) and water in a weight ratio of 1:1) to form, and then soaked in water (temperature 50°C) for 24 hours, and then soaked in a glycerol-water mixture containing 20 wt% glycerol (temperature 50°C) for 24 hours, and after air drying, a reinforced tubular composite ultrafiltration membrane with network-like pore structure was obtained.

[0060] Figure 1 is a microscope picture (magnification 500) of a cross-sectional direction of a section of the polymer membrane layer of the tubular composite ultrafiltration membrane prepared in Example 1 of the present application, Figure 2 is a microscope picture (magnification 5000) of the surface of the polymer membrane layer of the tubular composite ultrafiltration membrane prepared in Example 1 of the present application, clearly showing that the polymer membrane layer has a network-like pore structure.

[0061] The average pore size of the polymer membrane layer was 30 nm, the porosity was 70%, and the membrane thickness was 60 μm;

[0062] The pure water flux of the tubular composite ultrafiltration membrane was 1000 L / h·m2 (static pressure method), and the tensile strength was 500 N (measured using a tensile strength tester);

[0063] The outer side of the membrane tube can withstand repeated backwashing, and the maximum negative pressure is 100 KPa.

[0064] Example 2

[0065] Step 1: Preparation of casting solution

[0066] At a temperature of about 70°C, the components were uniformly mixed and dissolved in the following proportions by weight, and after filtration and degassing, a casting solution was prepared;

[0067]

[0068] Step 2: Forming a support tube and a casting solution coating

[0069] Using a tubular membrane integrated film forming machine, two PET non-woven fabric belts (unit area mass 180 g / m 2 , longitudinal and transverse breaking strengths of 1000 N, and thickness of 200 μm) were spirally wound and welded into an integrated tubular structure support tube (inner diameter of 12.5 mm, thickness of 400 μm, welding speed of 2.5 m / min), and a metal coating rod coated the above casting solution on the inner wall of the support tube to form a casting solution coating;

[0070] Step 3: Forming a tubular composite ultrafiltration membrane

[0071] The support tube with the casting solution coating obtained in Step 2 above was immersed in a coagulation solution (temperature of 40°C, composition of a mixture of dimethylacetamide (DMAC) and water at a weight ratio of 1:1) to form, and then soaked in water (temperature of 50°C) for 24 hours, and then soaked in a glycerol-water mixture (temperature of 50°C) containing 20 wt% glycerol for 24 hours, and after air drying, a reinforced tubular composite ultrafiltration membrane with a network-like pore structure was obtained.

[0072] The average pore size of the polymer membrane layer was 50 nm, the porosity was about 70%, and the membrane thickness was 60 μm;

[0073] The pure water flux of the tubular composite ultrafiltration membrane was 1200 L / h·m

[0074] The membrane tube outside could withstand repeated backwashing, and the maximum negative pressure was 100 KPa.

[0075] Example 3

[0076] Step 1: Preparation of a casting solution

[0077] At a temperature of about 70°C, the components were uniformly mixed and dissolved in the following proportions by weight, and after filtration and degassing, a casting solution was prepared;

[0078]

[0079] Step 2: Forming a support tube and a casting solution coating

[0080] Two PET non-woven fabric belts (mass per unit area 180 g / m 2 , longitudinal breaking strength and transverse breaking strength 1000 N respectively, thickness 180 μm) were spirally wound and welded into a support tube (inner diameter 8 mm, thickness 360 μm, welding speed 2.5 m / min) of integrated tubular structure at a temperature of about 60°C, and a metal coating rod coated the casting solution on the inner wall of the support tube to form a casting solution coating;

[0081] Step 3: forming a tubular composite ultrafiltration membrane

[0082] The support tube with the casting solution coating obtained in Step 2 was immersed in a coagulation liquid (temperature 30°C, composition: a mixture of dimethylacetamide (DMAC) and water at a weight ratio of 45:55) to form, and then soaked in water (temperature 50°C) for 24 hours, and then soaked in a glycerol-water mixture (temperature 50°C) containing 20 wt% glycerol for 24 hours, and then air-dried to obtain a reinforced tubular composite ultrafiltration membrane with a network-like pore structure.

[0083] The average pore size of the polymer membrane layer was 10 nm, the porosity was 80%, and the membrane thickness was 50 μm;

[0084] The pure water flux of the tubular composite ultrafiltration membrane was 400 L / h·m2 (static pressure method), and the tensile strength was 500 N (measured by a tensile strength tester).

[0085] The outer side of the membrane tube can withstand repeated backwashing, and the maximum negative pressure is 100 KPa.

[0086] Example 4

[0087] Step 1: preparing a casting solution

[0088] At a temperature of about 70°C, the components were uniformly mixed and dissolved in the following proportions by weight, and after filtration and degassing, a casting solution was prepared;

[0089]

[0090] Step 2: forming a support tube and a casting solution coating

[0091] Two PP / PE non-woven fabric belts (mass per unit area 180 g / m 2 , longitudinal breaking strength and transverse breaking strength 1000 N respectively, thickness 190 μm) were spirally wound and welded into a support tube (inner diameter 5 mm, thickness 380 μm, welding speed 2.5 m / min) of integrated tubular structure at a temperature of about 70°C, and a metal coating rod coated the casting solution on the inner wall of the support tube to form a casting solution coating;

[0092] Step 3: Forming the tubular composite ultrafiltration membrane

[0093] The support tube coated with the casting solution obtained in Step 2 above was immersed in a coagulation solution (temperature 40°C, composition: a mixture of dimethylacetamide (DMAC) and water at a weight ratio of 45:55) to form, and then soaked in water (temperature 50°C) for 24 hours, and then soaked in a glycerol-water mixture (temperature 50°C) containing 20 wt% glycerol for 24 hours, and then air-dried to obtain a reinforced tubular composite ultrafiltration membrane having a network-like pore structure.

[0094] The polymer membrane layer had an average pore size of 80 nm, a porosity of 60%, and a thickness of 50 μm;

[0095] The tubular composite ultrafiltration membrane had a pure water flux of 1200 L / h-m2 (static pressure method) and a tensile strength of 450 N (measured using a tensile strength tester).

[0096] The outer side of the membrane tube could withstand repeated backwashing, and the maximum negative pressure was 100 KPa.

[0097] Comparative Example 1

[0098] A tubular composite ultrafiltration membrane was prepared by the same method as in Example 1, except that the casting solution did not contain 1,4-dioxane, and the composition of the casting solution was as follows:

[0099]

[0100] The polymer membrane layer had an average pore size of 30 nm, a porosity of 75%, and a thickness of 30 μm;

[0101] The tubular composite ultrafiltration membrane had a pure water flux of 1000 L / h-m2 (static pressure method) and a tensile strength of 400 N (measured using a tensile strength tester).

[0102] The outer side of the membrane layer could not be backwashed, as shown in Figure 4 When the membrane module assembled from the tubular composite ultrafiltration membrane of Comparative Example 1 was used in practice, and backwashing was required, peeling occurred when backwashing at a negative pressure of 100 KPa.

[0103] Comparative Example 2

[0104] A tubular composite ultrafiltration membrane was prepared by the same method as in Example 1, except that the casting solution did not contain octanol, and the composition of the casting solution was as follows:

[0105] Polyvinylidene fluoride resin 15%,

[0106] Polyvinylpyrrolidone (molecular weight 40 KDa) 5%,

[0107] Dimethylacetamide / 1,4-dioxane (2.3:1) 80%,

[0108] Polymer film layer average pore size 50 nm, porosity 60%, film thickness 25 μm;

[0109] Tubular composite ultrafiltration membrane pure water flux 800 L / h.m2(static pressure method), tensile strength 400 N (measured by tensile strength tester).

[0110] The membrane layer outside cannot be backwashed, and backwashing under negative pressure of 100 KPa will cause the membrane layer to fall off.

Claims

1. A method for preparing an enhanced tubular composite ultrafiltration membrane with a network-like pore structure, comprising the following steps: Step 1: Prepare the casting solution At a temperature of 60℃~70℃, the components are uniformly mixed and dissolved according to the following composition by weight percentage, and after filtration and degassing, a casting solution is prepared. Polymer 15%–30%, Pore-forming agent 1%–12%, Non-solvent additives 1%–5%, Mixed solvent 53%–83%, And the sum of all components is 100%. in, The polymer is selected from one or more of polyvinylidene fluoride, polyethersulfone, polysulfone, and polyamide; The pore-forming agent is selected from one or more of organic and inorganic pore-forming agents; The non-solvent additive is selected from one or more of water, methanol, ethanol, propanol, butanol, octanol, formic acid, acetic acid, and propionic acid; The mixed solvent is a mixture of one or more solvents selected from dimethyl sulfoxide (DMSO), dimethylacetamide (DMAC), dimethylformamide (DMF) and N-methylpyrrolidone with 1,4-dioxane in a weight ratio of 1 to 9:

1. Step 2: Forming the support tube and casting solution coating At a temperature of 60℃~70℃, a tubular integrated film forming machine is used to spirally wind and weld two or more non-woven fabric tapes into an integrated tubular support tube, while the above-mentioned casting liquid is coated on the inner wall of the support tube to form a casting liquid coating. Step 3: Forming a tubular composite ultrafiltration membrane The support tube with the casting solution coating obtained in step 2 above is immersed in a coagulation solution at a temperature of 20℃ to 50℃ to form a membrane. Then, it is soaked in water at a temperature of 10℃ to 50℃ for 12 to 24 hours, and then soaked in a glycerol-water mixture containing 10wt% to 20wt% glycerol for 12 to 24 hours. After drying, a tubular composite ultrafiltration membrane with a network pore structure is obtained. The coagulation solution is a mixture of one or more solvents selected from dimethyl sulfoxide (DMSO), dimethylacetamide (DMAC), dimethylformamide (DMF) and N-methylpyrrolidone with water in a weight ratio of 0% to 50%: 100% to 50%.

2. The method for preparing the enhanced tubular composite ultrafiltration membrane with a network pore structure according to claim 1, characterized in that, The organic pore-forming agent is polyvinylpyrrolidone with a molecular weight of 10-1300 kDa, polyethylene glycol with a molecular weight of 0.2-20 kDa, or a mixture thereof; the inorganic pore-forming agent is one or more selected from lithium chloride, silicon oxide, and calcium chloride.

3. The method for preparing the enhanced tubular composite ultrafiltration membrane with a network pore structure according to claim 1, characterized in that, The mixed solvent is a mixture of one or more solvents selected from dimethyl sulfoxide (DMSO), dimethylacetamide (DMAC), dimethylformamide (DMF) and N-methylpyrrolidone with 1,4-dioxane in a weight ratio of 2 to 5:

1.

4. The method for preparing the enhanced tubular composite ultrafiltration membrane with a network pore structure according to claim 1, characterized in that, in At a temperature of 60℃~70℃, a tubular integrated film forming machine is used to spirally wind and weld two non-woven fabric tapes into an integrated tubular support tube. The first non-woven fabric tape spirally winds to form the inner layer of the support tube, and the second non-woven fabric tape spirally winds on the inner layer to form the outer layer of the support tube. The joints are welded together to form an integrated tubular structure. At the same time, a metal coating rod coats the casting liquid onto the inner wall of the support tube to form a casting liquid coating.

5. The method for preparing the enhanced tubular composite ultrafiltration membrane with a network pore structure according to claim 1, characterized in that, The tubular composite ultrafiltration membrane with a network pore structure includes: a support tube and a polymer membrane layer bonded to the inner wall of the support tube, wherein the polymer membrane layer has a network pore structure, the average pore diameter of the pores is 8nm to 200nm, and the porosity is 60% to 90%; the support tube is an integrated tubular structure formed by two or more layers of nonwoven fabric.

6. The method for preparing the enhanced tubular composite ultrafiltration membrane with a network pore structure according to claim 5, characterized in that, The thickness of the polymer film is 10–100 mm. m.

7. The method for preparing the enhanced tubular composite ultrafiltration membrane with a network pore structure according to claim 5, characterized in that, The inner diameter of the support tube is 5mm to 25mm, and the thickness is 300 to 500mm. m.

8. The method for preparing the enhanced tubular composite ultrafiltration membrane with a network pore structure according to claim 1, characterized in that, The nonwoven fabric is made from polymers selected from polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE), and propylene / ethylene copolymer (PP / PE), and has a unit area mass of 100-300 g / m². 2 The longitudinal and transverse breaking strengths are 500–1000 N, and the thickness is 150–200 mm. m.

9. The method for preparing the enhanced tubular composite ultrafiltration membrane with a network pore structure according to claim 1, characterized in that, The tubular composite ultrafiltration membrane has a pure water flux of 100-2000 LHM and a tensile strength of >400 N. When the tubular composite ultrafiltration membrane is subjected to backwash negative pressure testing, the polymer membrane layer does not peel off from the support tube when the backwash pressure is in the range of 50 kPa to 100 kPa.

10. An enhanced tubular composite ultrafiltration membrane with a network pore structure, prepared by the preparation method described in claim 1.

11. The enhanced tubular composite ultrafiltration membrane with a network pore structure according to claim 10, characterized in that, The tubular composite ultrafiltration membrane includes: a support tube and a polymer membrane layer bonded to the inner wall of the support tube, wherein the polymer membrane layer has a network-like pore structure, the average pore diameter of the pores is 8nm to 200nm, and the porosity is 60% to 90%; the support tube is an integrated tubular structure formed by two or more layers of nonwoven fabric.

12. The enhanced tubular composite ultrafiltration membrane with a network pore structure according to claim 11, characterized in that, The thickness of the polymer film is 10–100 mm. m.

13. The enhanced tubular composite ultrafiltration membrane with a network pore structure according to claim 11, characterized in that, The inner diameter of the support tube is 5mm to 25mm, and the thickness is 300 to 500mm. m.

14. The enhanced tubular composite ultrafiltration membrane with a network pore structure according to claim 11, characterized in that, The support tube is an integrated tubular structure formed by two layers of non-woven fabric. The first non-woven fabric tape is spirally wound to form the inner layer of the support tube, and the second non-woven fabric tape is spirally wound on the inner layer to form the outer layer of the support tube. The joints are welded together to form an integrated tubular structure.

15. The enhanced tubular composite ultrafiltration membrane with a network pore structure according to claim 11, characterized in that, The nonwoven fabric is made from polymers selected from polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE), and propylene / ethylene copolymer (PP / PE), and has a unit area mass of 100-300 g / m². 2 The longitudinal and transverse breaking strengths are 500–1000 N, and the thickness is 150–200 mm. m.

16. The enhanced tubular composite ultrafiltration membrane with a network pore structure according to claim 10, characterized in that, The tubular composite ultrafiltration membrane has a pure water flux of 100-2000 LHM and a tensile strength of >400 N. When the tubular composite ultrafiltration membrane is subjected to backwash negative pressure testing, the polymer membrane layer does not peel off from the support tube when the backwash pressure is in the range of 50 kPa to 100 kPa.

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