Composite enhanced organic tubular membrane and preparation method thereof

Abstract

The invention discloses a composite enhanced organic tubular membrane and a preparation method thereof, and belongs to the technical field of membrane separation. Comprising a tubular non-woven fabric supporting layer, a grid fiber skeleton layer arranged on the inner side of the tubular non-woven fabric supporting layer and a polymer membrane separation layer. Wherein the grid fiber skeleton layer and the non-woven fabric supporting layer are fixed into an integrated tubular skeleton through welding; the polymer membrane separation layer is formed by membrane casting liquid through a phase inversion method, completely coats the grid fiber skeleton layer, is in contact with the inner surface of the non-woven fabric supporting layer, and does not permeate into the non-woven fabric supporting layer. According to the invention, the grid fiber skeleton is introduced into the separation layer as a reinforcing structure and is firmly combined with the supporting layer in a welding manner, so that the mechanical strength and anti-stripping performance of the membrane separation layer are greatly improved; meanwhile, the interference of the membrane casting liquid permeating the supporting layer on the phase separation process is avoided, the forming quality and the performance stability of the membrane are ensured, and the problems that a traditional tubular membrane is easy to scratch and delaminate are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of membrane separation technology, and particularly relates to a composite reinforced organic tubular membrane and a preparation method thereof. BACKGROUND

[0002] Membrane separation technology can realize high-efficiency separation of liquid-liquid and solid-liquid. Membrane materials can be divided into hollow fiber membranes, flat sheet membranes and tubular membranes. Tubular membranes are a kind of high-efficiency separation membrane materials, and organic tubular membranes mainly consist of a support structure and a separation layer. The advantages of organic tubular membranes are large packing area, high flux, strong anti-pollution, low requirement on water quality, and the ability to handle materials with high solid content, complex pollutants and a large number of particles. Therefore, in the actual use process, the separation layer is easily damaged when the water contains sharp particles, or the membrane layer is easily damaged when the membrane tube is blocked due to improper operation.

[0003] At present, organic tubular membranes are prepared by a tubular membrane integrated welding and scraping machine, and are formed by synchronously coating a casting solution into a tubular shape through ultrasonic welding of non-woven fabric strips. The non-woven fabric as a support layer not only provides mechanical support for the membrane separation layer, but also has important factors affecting the separation performance of the membrane, such as pore size and surface roughness. Due to the compatibility problem between materials, the bonding strength between the membrane layer and the surface of the non-woven fabric is not high, and the separation problem easily occurs under pressure or high-intensity friction. In the market, the casting solution is permeated into the non-woven fabric to enhance the peeling strength of the membrane layer, which greatly affects the phase separation process of the membrane, causes large defects on the surface of the membrane layer, and results in defective products. Therefore, the problem of membrane defects caused by the permeation of the casting solution and the problem of improving the bonding force between the separation layer and the support layer of the membrane are technical problems to be solved at present. SUMMARY

[0004] The technical problem to be solved by the present application is that the bonding force between the separation layer and the non-woven fabric support layer of the existing organic tubular membrane is insufficient, and the separation layer and the non-woven fabric support layer are easily separated and damaged under fluid pressure or physical cleaning. At the same time, if the method of permeating the casting solution into the support layer is used to enhance the bonding force, the phase separation process of the membrane will be seriously disturbed, defects will be caused on the surface of the membrane, and the filtration performance will be affected. In order to solve the above problems, the technical concept adopted by the present application is that a grid fiber skeleton is introduced into the polymer membrane separation layer as a reinforcing body, and the grid fiber skeleton and the non-woven fabric support layer are pre-fixed into an integrated tubular skeleton by welding. During membrane formation, the casting solution permeates and covers the grid fiber skeleton to form a composite reinforced structure, but does not permeate into the non-woven fabric support layer below. This concept uses physical anchoring (welding) to replace chemical permeation to solve the bonding force problem, which fundamentally eliminates the risk of membrane layer separation and ensures the independence and stability of the phase inversion process of the casting solution, so as to obtain a tubular membrane with high mechanical strength and excellent separation performance.

[0005] A composite reinforced organic tubular membrane includes a tubular nonwoven fabric support layer, a mesh fiber skeleton layer disposed inside the tubular nonwoven fabric support layer, and a polymer membrane separation layer; wherein the mesh fiber skeleton layer and the tubular nonwoven fabric support layer are fixed together as an integrated tubular skeleton by welding at the overlap; the polymer membrane separation layer is formed by phase inversion of a casting solution, and the polymer membrane separation layer covers the mesh fiber skeleton layer and contacts the inner surface of the tubular nonwoven fabric support layer, but does not penetrate into the interior of the tubular nonwoven fabric support layer.

[0006] The tubular nonwoven fabric support layer is composed of a thin nonwoven fabric layer and a thick nonwoven fabric layer stacked sequentially from the inside out, and the mesh fiber skeleton layer is located inside the thin nonwoven fabric layer.

[0007] The integrated tubular skeleton is formed by winding mesh fiber skeleton strips, thin non-woven fabric strips and thick non-woven fabric strips in a cross-spiral overlapping manner. The spiral angle of each material strip relative to the axis of the membrane tube is 20-60°, and the overlap width between two adjacent turns is 1-5mm.

[0008] The material of the mesh fiber skeleton layer is selected from one or more of polyester, polyethylene or polypropylene fibers; the material of the tubular nonwoven fabric support layer is selected from one or more of polyester or polypropylene fibers; the polymer material of the polymer membrane separation layer is selected from one or more of polyvinylidene fluoride, polyethersulfone or polyaryletherketone and their copolymers.

[0009] The basis weight of the mesh fiber skeleton layer is 50-130 g / m². 2 The thickness is 100-250μm, the warp and weft fiber density is 30-60 fibers / cm, and the mesh size is 50-300μm.

[0010] The basis weight of the thin nonwoven fabric layer is 120-150 g / m². 2 The thickness is 150-200μm, and the average pore size is 10-30μm; the basis weight of the thick nonwoven fabric layer is 200-220g / m². 2 The thickness is 240-300μm, and the average pore size is 20-50μm.

[0011] The thickness of the polymer membrane separation layer is 200-350 μm.

[0012] A method for preparing the aforementioned composite-reinforced organic tubular membrane includes the following steps:

[0013] a) Provide mesh fiber skeleton strips, thin nonwoven strips and thick nonwoven strips;

[0014] b) The mesh fiber skeleton strip is placed in the innermost layer, the thin non-woven fabric strip is placed in the middle layer, and the thick non-woven fabric strip is placed in the outermost layer. They are wound together in a cross-spiral overlapping manner, and the overlapping areas of each layer of material are ultrasonically welded to form an integrated tubular skeleton with the mesh fiber skeleton layer on the inner side.

[0015] c) The pre-prepared casting solution is uniformly coated onto the inner surface of the integrated tubular skeleton through a scraping head, so that the casting solution penetrates and coats the mesh fiber skeleton layer, but does not penetrate into the thin nonwoven fabric layer.

[0016] d) The integrated tubular framework coated with casting solution is pre-evaporated and then immersed in a coagulation bath for phase transformation to form the polymer membrane separation layer.

[0017] In step b), the ultrasonic welding frequency is 20-40kHz, the power is 500-1500W, the single-point welding time is 0.05-0.5s, and the distance between adjacent weld points is 2-10mm.

[0018] The viscosity of the casting solution in step c) is 5-10 Pa·s; the casting solution is prepared by mixing a polymer with a mass fraction of 10-25 wt%, a pore-forming agent with a mass fraction of 1-20 wt%, and a solvent with a mass fraction of 50-75 wt%.

[0019] The pore-forming agent is selected from at least one of polyvinylpyrrolidone, polyethylene glycol, sodium dodecyl sulfate, lithium chloride, and adipic acid; the solvent is selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, or dimethyl sulfoxide.

[0020] Step c) is carried out under the conditions of ambient temperature of 25-30℃ and relative humidity of 50%-60%; the gap between the outer diameter of the outer tube of the scraping head and the inner diameter of the mesh fiber skeleton layer is 20-100μm.

[0021] In step c), the ratio of the casting solution feed rate to the tube winding speed is controlled to be 1.5-3.0 ml / (min·m / min).

[0022] The pre-evaporation time in step d) is 10-30 s; the temperature of the coagulation bath is 20-30 ℃, and the coagulation bath is selected from deionized water, distilled water, purified water, alcohol solution or aqueous solution of alcohol.

[0023] It also includes a post-treatment step for the membrane tube that has completed the phase inversion: soaking it in pure water, soaking it in a 10-20 wt% glycerol aqueous solution, and then air-drying it.

[0024] The aforementioned online failure detection method for composite-reinforced organic tubular membranes is applied to a liquid filtration system comprising a housing and multiple tubular membrane filter elements disposed within the housing, wherein the tubular membrane is an organic tubular membrane, and the tubular membrane is a composite-reinforced organic tubular membrane. The method includes:

[0025] 1) During filtration operation, the liquid to be treated flows from the inlet side through the tubular membrane filter element under the action of transmembrane pressure difference and is collected into the clean liquid chamber. The filtered liquid is then discharged from the clean liquid chamber through the filter outlet.

[0026] 2) Collect the filtrate quality signal at the filter outlet to obtain the outlet concentration or purity index parameter K. P and the K P As an outlet quality indicator characterizing the integrity of filtration;

[0027] 3) Transient pressure signals during filtration and backwashing processes are collected from multiple pressure sensors arranged axially and / or circumferentially within the clean liquid chamber of the housing, and the data acquisition and processing unit synchronously acquires the K... P With the transient pressure signal;

[0028] 4) The processor executes the stored detection algorithm program:

[0029] Based on the export quality index K P The relationship between feed conditions, total flow rate and transmembrane pressure differential is used to determine whether membrane rupture and leakage exist and to estimate the severity of the leakage.

[0030] When a leak is detected, different tubular membrane filter cartridges are backwashed online in sequence. During each backwashing operation, the multiple pressure sensors are used to collect the transient pressure wave signal of the backwashing, and the location of the pressure wave source is spatially located based on the arrival time difference to determine the tubular membrane filter cartridge that is being backwashed.

[0031] The corresponding outlet quality index K after the backwashing operation P The transient changes are correlated with the pressure wave source location results. When a significant abnormal change in outlet quality is detected within the time window corresponding to a certain backwash filter element group and the pressure wave source location is consistent with the geometric location of the filter element group, it is determined that the tubular membrane corresponding to the filter element group has been damaged or failed to seal.

[0032] In step 2), the export quality index K P With leakage flow Q Leak The relationship between them is derived from the law of conservation of mass:

[0033]

[0034] Among them, C FeedQ represents the impurity concentration or particle number concentration of the feed liquid. Total Given the total flow rate through the filter, the leakage flow rate can be estimated accordingly:

[0035]

[0036] and the Q Leak Compare with a preset leakage flow threshold to determine whether a leak has occurred;

[0037] In step 4), the processor further calculates the leakage flow rate Q based on the orifice outflow model. Leak With equivalent leakage area A L Establishing relationships:

[0038]

[0039] Among them, C d ρ is the flow coefficient, ΔP is the pressure difference across the leak location, and ρ is the flow coefficient. L The density of the liquid is Q; the mass obtained from the law of conservation of mass is... Leak Substituting into the above formula, we obtain the formula for estimating the leakage area:

[0040]

[0041] And according to the A L The size of the leak determines the severity of the leak and classifies it into different levels.

[0042] Before performing step 4), the method further includes: when the tubular filtration system is in a leak-free state, recording the baseline value K of the outlet quality index under a representative stable filtration condition. P,baseline The baseline value is then stored in the processor.

[0043] In step 4), the following formula is used to make a preliminary judgment on the leakage status: K P -K P,baseline >ΔK P,th

[0044] Where ΔK P,th The export quality threshold is set based on system noise and allowable fluctuation range. This threshold is determined when the above inequality holds or the leakage area A... L Greater than the leakage area threshold A L,th At that time, the sequential backwashing and further fault location process is triggered.

[0045] In step 4), during the backwashing and filtration restoration process of each filter element group, the outlet quality index K is monitored. P Extract the steady-state value K corresponding to each backwash event based on the transient change of (t). P,Steady and peak value K P,PeakAnd calculate the peak amplification factor γ:

[0046]

[0047] When γ is greater than or equal to the peak amplification threshold γ th When the corresponding filter element group is considered to have leaked, resulting in the instantaneous release of particles; combined with the time window of the peak occurrence and the pressure wave source location result, the filter element group that has leaked is identified.

[0048] In step 3), the transient pressure wave signal of backwashing is acquired by at least four pressure sensors arranged at different spatial positions in the clean liquid chamber, and in step 4), the time difference of the pressure signal of any sensor pair (i,j) is estimated by the generalized cross-correlation phase transformation method. The time difference estimation process includes:

[0049] 1) Calculate the cross-power spectral density G of the pressure signals acquired by sensor i and sensor j. ij (ω);

[0050] 2) Construct the generalized cross-correlation phase transformation function

[0051]

[0052] 3) Obtain the estimated time difference of arrival through peak finding operation.

[0053]

[0054] And calculate the corresponding propagation distance difference. Where v s Let be the propagation speed of pressure waves in the liquid.

[0055] The beneficial effects of this invention are:

[0056] (1) The composite reinforced organic tubular membrane separation layer of the present invention is composed of a casting solution coating a mesh fiber and then undergoing phase separation. The mesh fiber acts as a steel skeleton, giving the separation layer great mechanical strength. In addition, the separation layer and the support layer are connected by ultrasonic welding of the mesh fiber and non-woven fabric, ensuring that the bonding strength between the membrane separation layer and the support layer will not cause the membrane layer to fall off due to manual membrane passage or scratches on the membrane surface.

[0057] (2) In this invention, the composite reinforced organic tubular membrane support layer is formed by cross-spiral welding of two layers of nonwoven fabric into a tube. During the welding and coating process, the casting solution only coats the mesh fibers and does not penetrate the nonwoven fabric. Therefore, the nonwoven fabric only plays a supporting role and will not affect the membrane phase separation process. Furthermore, the mesh fibers have a relatively small impact on membrane phase separation due to their consistent morphology and structure.

[0058] (3) The online filter diagnostic method proposed in this invention comprehensively utilizes changes in outlet liquid quality, characteristics of backwash transient pressure waves, and arrival time difference positioning technology to achieve real-time identification of minute leaks in the filter, quantitative calculation of the leakage amount, and precise location of faulty membrane tubes. This method can complete the detection without interrupting production, which is superior to traditional methods that rely solely on differential pressure or manual inspection. The method of this invention has a simple structure and is easy to implement. It can be used in conjunction with composite reinforced organic tubular membranes to improve the operational safety, stability, and maintenance efficiency of the filtration system. Attached Figure Description

[0059] Figure 1 This is a schematic diagram of the structure of the tubular membrane prepared according to the present invention.

[0060] Figure 2 The cross-sectional and surface structures of the tubular membrane prepared in Example 1 are shown.

[0061] Figure 3 The cross-sectional and surface structures of the tubular membrane prepared in Example 4 are shown. Detailed Implementation

[0062] In the technical solution of this patent, when preparing the composite reinforced organic tubular membrane, a polymer mesh fiber skeleton strip pre-woven into a mesh structure is first provided, along with two thin nonwoven fabric strips and a thick nonwoven fabric strip of the same width. The mesh fiber skeleton strip is located in the innermost layer, the thin nonwoven fabric strip in the middle layer, and the thick nonwoven fabric strip in the outermost layer. The three are wound together on the outer surface of the membrane core shaft and welded into a coaxial tubular skeleton by a cross-helical overlap. From the inside out, a mesh fiber skeleton layer, a thin nonwoven fabric layer, and a thick nonwoven fabric support layer are formed sequentially. The width of the mesh fiber skeleton strip, the thin nonwoven fabric strip, and the thick nonwoven fabric strip is preferably 20-80 mm. Each strip is wound with a helical angle of 20-60° relative to the membrane tube axis, and an overlap width of 1-5 mm is maintained between adjacent turns. After completing one spiral winding, a second layer can be wound in the opposite spiral direction, causing the spiral directions of the inner and outer layers to intersect, thus forming a tubular support structure with intersecting spirals. This gives the membrane tube high mechanical strength in both the axial and circumferential directions. During the winding process, an ultrasonic welding head on an integrated tubular welding and coating machine presses the thick nonwoven fabric from the outside, welding at the spiral overlap areas of each layer. Ultrasonic energy penetrates the thick nonwoven fabric, causing the thick nonwoven fabric, thin nonwoven fabric, and inner mesh fiber skeleton at the overlap to partially melt and fuse, forming welds continuously distributed along the spiral direction. The welds firmly bond adjacent rings and the three layers together, resulting in an integrated tubular skeleton composed of a mesh fiber skeleton layer and a double-layer nonwoven fabric support layer.

[0063] The technical solutions used in some embodiments of this patent are described in detail below:

[0064] A composite reinforced organic tubular membrane includes a polymer membrane separation layer with filtration function, a mesh fiber skeleton that enhances the structure of the membrane separation layer, and a nonwoven fabric support layer that supports the membrane tube. The mesh fiber skeleton layer is composed of polymer fibers woven into a mesh fiber skeleton by warp and weft. The mesh fiber skeleton is wound into a tubular shape by cross-helical overlap and is synchronously welded to the nonwoven fabric support layer at the overlap. The polymer membrane separation layer is formed by phase inversion after the mesh fiber skeleton layer is permeated and coated by casting solution.

[0065] The nonwoven support layer and the mesh fiber skeleton layer are simultaneously welded at the overlap by an integrated tubular welding film scraping machine, preferably by ultrasonic welding; the layer distribution of the tubular structure from the inside out is as follows: a mesh fiber skeleton layer, a thin nonwoven fabric layer and a thick nonwoven fabric layer; the polymer membrane separation layer completely permeates and covers the mesh fiber skeleton layer, and only contacts the surface of the nonwoven support layer without penetrating into the interior of the nonwoven fabric.

[0066] The preferred ultrasonic welding frequency is 20–40 kHz, the welding power is 500–1500 W, the single-point welding time is 0.05–0.5 s, and the spacing between adjacent weld points is 2–10 mm, thereby forming a weld that is basically continuous along the spiral direction.

[0067] The basis weight of the thin nonwoven fabric layer is 120-150 g / m². 2 The thickness is 150-200μm; the basis weight of the thick nonwoven fabric layer is 200-220g / m². 2 The thickness is 240-300 μm; the nonwoven fabric material is made of polyester fiber or polypropylene fiber. The average pore size of the thin nonwoven fabric layer is preferably 10-30 μm, and the average pore size of the thick nonwoven fabric layer is preferably 20-50 μm. The thin nonwoven fabric layer is mainly used for welding and supporting the mesh fiber skeleton layer, while the thick nonwoven fabric layer is mainly used to improve the overall compressive strength and bending resistance of the membrane tube.

[0068] The basis weight of the mesh fiber skeleton layer is 50-130 g / m². 2 The thickness is 100-250μm, the warp and weft fiber densities of the mesh fiber skeleton layer are 30-60 fibers / cm, and the corresponding mesh aperture is preferably 50-300μm; its material is selected from polyester, polyethylene or polypropylene fiber.

[0069] The thickness of the polymer membrane separation layer is 200-350 μm; the polymer material of the polymer membrane separation layer is selected from polyvinylidene fluoride, polyethersulfone, or polyaryletherketone and their copolymers.

[0070] A method for preparing the aforementioned composite-reinforced organic tubular membrane includes the following steps:

[0071] (1) A casting solution with a viscosity of 5-10 Pa·s is prepared by mixing a polymer, a pore-forming agent, and a solvent. This solution has sufficient fluidity to completely wet and fill the voids in the mesh fiber skeleton layer after passing through the scraper head, but the fluidity is not enough to penetrate deeply into the large pores of the nonwoven fabric in a short time. The gap between the outer diameter of the scraper head tube and the inner diameter of the mesh fiber tube is 20-100 μm, and the corresponding wet film thickness is about 200-350 μm. The wet film thickness is slightly greater than the thickness of the mesh skeleton layer, so that the casting solution forms a continuous film on the outside of the mesh skeleton layer. When it comes into contact with the surface of the thin nonwoven fabric, the casting solution is basically restricted by the mesh skeleton layer and only forms a dense skin layer on the surface of the nonwoven fabric, without penetrating into the internal pores of the nonwoven fabric.

[0072] (2) Add the casting liquid to the tubular coating machine, coat and penetrate the inner surface of the mesh fiber evenly through the coating head, and roll it up together with the non-woven support layer. Control the ambient temperature to 25-30℃ and the relative humidity to 50%-60%.

[0073] (3) After pre-evaporation, the membrane is immersed in a coagulation bath to complete the phase transformation, forming a composite reinforced organic tubular membrane. After coating, the membrane is pre-evaporated in air for 10–30 s, causing the casting solution near the nonwoven fabric to begin preliminary phase separation, forming a polymer-rich interface layer. This interface layer acts as a barrier layer, significantly inhibiting the further penetration of the casting solution into the nonwoven fabric. The ratio of the winding speed to the casting solution feeding speed is 1.5–3.0 ml / (min·m / min) to ensure that the thickness of the formed membrane separation layer is within the range of 200–350 μm.

[0074] The specific process in step (1) is as follows:

[0075] The mixing process is carried out at 50-80℃ and stirred at 200-800 rpm for 8-12 hours; after mixing, the mixture is allowed to stand under vacuum to remove bubbles; in the casting solution, the mass fraction of the polymer is 10-25 wt%, the mass fraction of the pore-forming agent is 1-20 wt%, and the mass fraction of the solvent is 50-75 wt%.

[0076] The specific process in step (2) is as follows:

[0077] The feeding rate of the casting solution is 3.5-5.5 ml / min, and the winding speed is 1-3 m / min; the distance between the outer diameter of the outer tube of the scraper head and the inner diameter of the mesh fiber tube is controlled at 20-100 μm; the inner diameter of the selected mesh fiber tube is any one of 6 mm, 8 mm, 10 mm or 12.5 mm.

[0078] The specific process and post-processing in step (3) are as follows:

[0079] The pre-evaporation time is 10-30 seconds, and the coagulation bath temperature is 20-30℃. After the phase transformation is completed, the membrane tube needs to be soaked in pure water for 48 hours and then soaked in a 10-20wt% glycerol aqueous solution for 24 hours, and finally dried.

[0080] The chemical reagents were selected as follows:

[0081] The pore-forming agent is at least one of polyvinylpyrrolidone, polyethylene glycol, sodium dodecyl sulfate, lithium chloride, and adipic acid;

[0082] The solvent is at least one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide or dimethyl sulfoxide;

[0083] The coagulation bath is any one of deionized water, distilled water, purified water, alcohol solution, or aqueous solution of alcohol, wherein the alcohol in the alcohol solution is ethanol or isopropanol.

[0084] Example 1

[0085] (1) Formulation: polyvinylidene fluoride (PVDF, 19wt%), polyvinylpyrrolidone (PVPK30, 8wt%), polyethylene glycol (PEG-400, 6wt%), N,N-dimethylacetamide (DMAc, 67wt%); viscosity: 8.2 Pa·s.

[0086] (2) Heat DMAc to 70°C, add PVDF powder, and stir at 600 rpm for 6 hours; add PVPK30 and PEG-400, and continue stirring at 80°C and 400 rpm for 4 hours until the solution is transparent.

[0087] (3) Filter the casting solution with a stainless steel filter screen and degas the filtrate under vacuum to obtain the casting solution for coating.

[0088] (4) The casting solution was coated onto the inner layer with a thickness of 180μm and a basis weight of 86g / m using a tubular integrated membrane forming machine. 2 The outer layer consists of two layers of PET nonwoven fabric (thin layer, 140g / m²) on a PET mesh fiber skeleton. 2 Thick layer 216g / m 2 The feeding speed is controlled at 4.2 ml / min, and the tube winding speed is controlled at 1.8 m / min.

[0089] (5) After coating, pre-evaporate for 15 seconds, then immerse in a 20°C pure water coagulation bath for 1 hour to obtain a wet tubular membrane.

[0090] (6) Soak in pure water for 48 hours (change the water every 24 hours), soak in 20% glycerol aqueous solution for 24 hours and then air dry to obtain dry tubular membrane.

[0091] Example 2 and Example 3

[0092] Referring to Example 1, the inner PET mesh fiber skeleton uses a weight of 60 g / m². 2 Thickness 120μm, and weight 100g / m 2 Thickness 192μm.

[0093] Example 4

[0094] (1) Formulation: Polymer: Polyethersulfone (PES, 22wt%), Pore-forming agent: Polyvinylpyrrolidone (PVPK30, 8wt%) + Lithium chloride (LiCl, 2wt%), Solvent: N-methylpyrrolidone (NMP, 68wt%), Viscosity: 6.8Pa·s.

[0095] (2) Heat NMP to 60°C, add PES powder, stir at 500 rpm for 8 hours until completely dissolved, add PVPK30 and LiCl, keep at 65°C and stir at 300 rpm for 6 hours to obtain a transparent casting solution.

[0096] (3) Filter the casting solution with a stainless steel filter screen, and degas the filtrate under vacuum to obtain the casting solution for coating.

[0097] (4) The casting solution for coating is coated onto the inner wall of the membrane tube using a tubular integrated membrane forming machine. The membrane tube is 180μm thick and has a basis weight of 86g / m³. 2 The outer layer consists of two layers of PET nonwoven fabric (thin layer, 140g / m²) on a PET mesh fiber skeleton. 2 Thick layer 216g / m 2 The film scraping gap is controlled at 25μm, the feeding speed at 4.2ml / min, and the tube winding speed at 1.8m / min.

[0098] (5) Then the membrane tube was pre-evaporated in the air for 20 seconds and then immersed in a 28°C pure water coagulation bath. After that, it was soaked in pure water for 48 hours, treated with 15% glycerol for 24 hours, and then dried.

[0099] Examples 5 and 6

[0100] Referring to Example 4, Example 5 controlled the scraping gap to be 15 μm and the feeding rate to be 2.6 ml / min, and Example 6 controlled the scraping gap to be 30 μm and the feeding rate to be 5.1 ml / min.

[0101] Example 7

[0102] (1) Formulation: polyaryletherketone (PAEK, 15wt%), sodium dodecyl sulfate (SDS, 5wt%), adipic acid (3wt%), dimethyl sulfoxide (DMSO, 77wt%); viscosity: 9.1 Pa·s.

[0103] (2) Preheat DMSO to 80°C, add PAEK granules, and stir at 700 rpm for 10 h under nitrogen protection; add SDS and adipic acid, and stir at 400 rpm for 4 h at 75°C until the solution is clear.

[0104] (3) Filter the casting solution with a stainless steel filter screen, and degas the filtrate under vacuum to obtain the casting solution for coating.

[0105] (4) The casting solution for coating is coated onto the inner wall of the membrane tube using a tubular integrated membrane forming machine. The membrane tube is made of PP mesh (110 g / m²). 2 ) and PP nonwoven fabric (thin layer 130g / m 2 Thick layer 200g / m 2 The combination controls the feeding speed at 5.0 ml / min, the tube winding speed at 2.5 m / min, and the ambient humidity at 55%.

[0106] (5) After pre-evaporating in the air for 25 seconds, the membrane is transferred to a 20% ethanol aqueous solution coagulation bath for 1 hour; then soaked in pure water for 48 hours (changing the water every 24 hours), and then soaked in a 20% glycerol aqueous solution for 24 hours before being air-dried. Finally, the wet tubular membrane is removed and air-dried at room temperature to obtain a dry tubular membrane.

[0107] Comparative Example 1

[0108] (1) Formulation (polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP, 20wt%); porogen: polyethylene glycol (PEG-400, 10wt%); solvent: N,N-dimethylformamide (DMF, 70wt%); viscosity: 7.5 Pa·s)

[0109] (2) Add PVDF-HFP and PEG-400 to DMF in sequence, and stir at 70℃ for 12h until the solution is clear;

[0110] (3) Filter the casting solution with a stainless steel filter screen, and degas the filtrate under vacuum to obtain the casting solution for coating.

[0111] (4) The casting liquid for coating is coated onto the inner 100μm thick PET nonwoven fabric support layer and the outer 200μm thick PET nonwoven fabric using a tubular membrane integrated film forming machine. Then the membrane tube is immersed in a 20℃ pure water coagulation bath to solidify and form a wet tubular membrane.

[0112] (5) Pre-evaporate in air for 15 seconds, immerse in a 25°C deionized water coagulation bath for 1 hour; soak in pure water for 48 hours (change the water every 24 hours), soak in 20% glycerol aqueous solution for 24 hours, and then air dry. Finally, remove the wet tubular membrane and air dry it naturally at room temperature to obtain the dry tubular membrane.

[0113] Comparative Example 2

[0114] With only a single layer of nonwoven fabric support, under the same casting solution formulation and process conditions as in Example 1, only a thick layer of 216 g / m2 PET nonwoven fabric was used for tube forming, without setting a mesh fiber skeleton and a thin nonwoven fabric layer, and the other conditions were the same.

[0115] (1) Formulation: Same as in Example 1. Polyvinylidene fluoride (PVDF, 19 wt%), polyvinylpyrrolidone (PVPK30, 8 wt%), polyethylene glycol (PEG-400, 6 wt%), N,N-dimethylacetamide (DMAc, 67 wt%); viscosity: 8.2 Pa·s.

[0116] (2) Preparation of casting solution: Same as in Example 1. DMAc was heated to 70°C, PVDF powder was added, and the mixture was stirred at 600 rpm for 6 h; PVPK30 and PEG-400 were added, and the mixture was stirred at 80°C and 400 rpm for 4 h until the solution became clear.

[0117] (3) Filtration and degassing: Same as in Example 1. The casting solution was filtered with a stainless steel filter screen, and the filtrate was degassed under vacuum to obtain the casting solution for coating.

[0118] (4) Coating and forming: The casting solution prepared in step (3) is directly coated onto a single layer of PET nonwoven fabric (216 g / m²) using a tubular integrated film forming machine. 2 The material is then rolled into a tube on the support layer. The feeding speed is controlled at 4.2 ml / min, and the tube rolling speed is 1.8 m / min.

[0119] (5) Phase transformation: Same as in Example 1. After coating, pre-evaporate for 15s, then immerse in a 20°C pure water coagulation bath for 1h to obtain a wet tubular membrane.

[0120] (6) Post-processing: Same as in Example 1. Soak in pure water for 48 hours (change water every 24 hours), soak in 20% glycerol aqueous solution for 24 hours, and then air dry to obtain a dry tubular membrane.

[0121] Comparative Example 3

[0122] Using the impregnation nonwoven fabric process, based on Example 1, the viscosity of the casting solution was adjusted to 3.5 Pa·s, the scraping gap was increased to 120 μm, and the pre-evaporation time was shortened to 5 s, so that the casting solution could be significantly penetrated into the internal pores of the thin nonwoven fabric and even partially penetrated into the thick nonwoven fabric, thus obtaining the membrane tube structure of the traditional impregnation nonwoven fabric.

[0123] (1) Formulation: To obtain a lower viscosity, the formulation was adjusted to: polyvinylidene fluoride (PVDF, 15wt%), polyvinylpyrrolidone (PVPK30, 5wt%), polyethylene glycol (PEG-400, 4wt%), N,N-dimethylacetamide (DMAc, 76wt%); the viscosity of the casting solution was adjusted to 3.5 Pa·s.

[0124] (2) Preparation of casting solution: Heat DMAc to 70°C, add PVDF powder, and stir at 600 rpm for 6 h; add PVPK30 and PEG-400, and continue stirring at 80°C and 400 rpm for 4 h until the solution is transparent.

[0125] (3) Filtration and degassing: The casting solution is filtered with a stainless steel filter screen and the filtrate is degassed under vacuum to obtain the casting solution for coating.

[0126] (4) Coating and forming: The low-viscosity casting liquid prepared in step (3) is coated onto the same composite support structure as in Example 1 using a tubular integrated film forming machine (the inner layer is 180 μm thick and has a basis weight of 86 g / m²). 2 The PET mesh fiber skeleton is used, and the outer layer consists of two layers of PET nonwoven fabric. The scraping gap is increased to 120μm, and the feeding speed is controlled at 4.2ml / min and the winding speed at 1.8m / min to promote the penetration of the casting solution into the nonwoven fabric.

[0127] (5) Phase transformation: After coating, the pre-evaporation time is shortened to 5s, and then the film is immersed in a 20℃ pure water coagulation bath for 1h to obtain a wet tubular membrane in which the casting liquid has penetrated into the nonwoven fabric.

[0128] (6) Post-treatment: Soak in pure water for 48 hours (changing the water every 24 hours), then soak in a 20% glycerol aqueous solution for 24 hours and air dry to obtain a dry tubular membrane. Experimental Example 1: Mechanical property testing of the tubular membrane (burst pressure + axial tension)

[0129] Sample A is a PVDF / PVP / PEG tubular membrane prepared according to Example 1. Sample B is prepared according to Comparative Example 1. Sample C is prepared according to Comparative Example 2. The effective inner diameter of the membrane tubes of all three samples is controlled at about 8 mm, and the membrane separation layer thickness is about 230–260 μm.

[0130] The burst pressure test method is as follows: randomly cut 5 samples with a length of 300 mm from each type of membrane tube, use a special pressure resistance test device for tubular membranes, seal and fix the two ends of the membrane tube with stainless steel joints, use deionized water as the medium, gradually increase the pressure from the inside of the membrane tube at a rate of 0.05 MPa / min until the membrane tube ruptures or leaks and fails, record the burst pressure value, and take the average value of 5 parallel samples of each type of sample to obtain the average burst pressure.

[0131] The procedure for axial tensile property testing is as follows: Cut a 100mm long segment from each type of membrane tube, slit it axially, flatten it, and prepare a 10mm wide strip specimen. Prepare five parallel specimens for each type. Use a universal testing machine with a clamp spacing of 50mm and a tensile speed of 50mm / min. Record the stress-strain curves, calculate the tensile strength and elongation at break of the specimens, and average the test results of the five parallel specimens.

[0132] Table 1. Circumferential burst pressure and axial tensile properties of different samples

[0133] Sample Bursting pressure / MPa Axial tensile strength / MPa Elongation at break / % A 0.86 43 18 B 0.52 25 12 C 0.60 30 14

[0134] As shown in Table 1, under the same casting formulation and film thickness conditions, the burst pressure of sample A of this invention is 0.86 MPa, which is significantly higher than that of sample B in Comparative Example 1 (0.52 MPa) and sample C in Comparative Example 2 (0.60 MPa). The axial tensile strength also increased from 25 MPa in Comparative Example 1 and 30 MPa in Comparative Example 2 to 43 MPa, with increases of approximately 72% and 43%, respectively. This indicates that by introducing a warp and weft woven mesh fiber skeleton inside the nonwoven support layer and simultaneously welding it with the double-layer nonwoven fabric to form a composite skeleton structure, the overall mechanical strength of the tubular membrane in both the circumferential and axial directions can be significantly improved, which is beneficial for the long-term stable operation of the membrane tube under high-pressure operation and frequent backflush conditions.

[0135] Experimental Example 2: Peel Strength Test of the Separation Layer / Support Layer Interface

[0136] The three samples from Experiment 1 were still selected.

[0137] The peel strength test procedure is as follows: Cut a 150mm sample from each type of membrane tube; carefully cut the interface between the separating layer and the support layer axially at one end with a scalpel, separating a free end approximately 20mm wide and 50mm long; attach one side of the separating layer to the upper clamping plate and the other side of the non-woven support layer to the lower clamping plate, ensuring a peel angle of 180°. Using a universal testing machine, with a peel speed of 50mm / min, record the peel force-displacement curve during the stable peel stage (ignoring the initial stage), calculate the average peel force F (N) during the stable stage, and divide it by the sample width w (cm) to obtain the peel strength F / w (N·cm). -1 For each sample, three parallel samples were tested, and the average value was taken.

[0138] Table 2. Peel strength and damage morphology of the separation layer / support layer for different samples.

[0139]

[0140] As shown in Table 2, the interfacial peel strength of sample A of the present invention is approximately 5.2 N·cm. -1The strength of the membrane layer was approximately four times that of sample B in Comparative Example 1 and approximately 2.6 times that of sample C in Comparative Example 2. After peeling, sample A showed simultaneous destruction of both the separation layer fragments and the mesh fibers, indicating that the interfacial bonding strength was close to that of the separation layer itself. In contrast, Comparative Examples 1 and 2 showed that the entire separation layer detached from the nonwoven support layer, with a smooth interface, indicating that the mechanical interlocking effect formed by the traditional method of casting solution permeating the nonwoven fabric is still prone to delamination under pressure or friction. This demonstrates that the present invention, through the integrated welded structure of the mesh fiber skeleton and the double-layer nonwoven fabric, can significantly improve the interfacial bonding strength between the separation layer and the support layer, preventing the entire membrane layer from detaching when manually applied or scratched by particles.

[0141] Experiment Example 3: Filtration Performance and Anti-fouling Test

[0142] Samples A and B are the same as in Example 1 and Comparative Example 1; Sample D is Comparative Example 3.

[0143] Three membrane tubes of each sample, each 300 mm in length, were placed in a stainless steel housing to form a single membrane module. An internal pressure operation mode was adopted, with feed inside the membrane and water effluent from the housing side. A 1.0 g / L bovine serum albumin (BSA) aqueous solution was prepared as a simulated contaminant solution. The module was operated at 0.1 MPa for 60 min, and the steady-state flux J was recorded. p The concentrations of BSA in the influent and product water were determined using a UV-Vis spectrophotometer. in With C out Calculate the retention rate R = (1 - C) out / C in )×100%. After BSA filtration, the solution was first rinsed with deionized water at 0.1 MPa for 10 min in the forward direction, and then rinsed with deionized water at 0.2 MPa for 10 min in the reverse direction; the pure water flux J was measured again. w,clean Calculate flux recovery rate FRR = (J w,clean / J w )×100%.

[0144] Table 3 Filtration performance and antifouling performance of different samples

[0145]

[0146] It can be seen that the standardized pure water flux of sample A in this invention at 0.1 MPa is approximately 430 L·m. -2 ·h-1·bar -1 The result was comparable to that of Comparative Example 1, Sample B, and significantly higher than the 360 ​​L·m of Comparative Example 3, Sample D, where the casting solution penetrated deeply into the nonwoven fabric. -2 ·h-1·bar -1This indicates that coating the mesh fibers with the casting solution without penetrating the nonwoven fabric does not reduce flux; on the contrary, it is beneficial for obtaining a more uniform finger-like pore structure. Sample A's BSA rejection rate was 96.5%, higher than sample D's 90.2%, indicating that excessive penetration into the nonwoven fabric would disrupt the phase separation process, leading to increased membrane surface defects. After BSA contamination and cleaning, the flux recovery rate (FRR) of sample A was approximately 93%, significantly higher than Comparative Example 1's 82% and Comparative Example 3's 78%, indicating that the membrane surface structure of this invention is more compact, the pore size distribution is more uniform, and its performance is more easily restored after contamination through simple water washing and backflushing.

[0147] Example 4

[0148] When the composite-reinforced organic tubular membrane of this invention is used in the filtration of materials containing a large number of suspended particles and at risk of scratching, local damage to the membrane tubes or failure of the end seals may still occur due to violent backwashing or sharp particle erosion. To achieve online identification and location of membrane tube damage, this invention further proposes an online integrity detection method based on filtrate quality analysis and the propagation of transient pressure waves during backwashing. A typical system includes: multiple tubular organic membrane filter elements, preferably the aforementioned composite-reinforced organic tubular membrane filter elements, packed into several groups (G1 to G5, etc.), and equipped with online backwashing valves for group control; an online liquid particle counter or turbidity meter is installed on the filter outlet main pipe as an outlet quality monitoring unit to obtain the filtrate purity index K in real time. P At least four high-frequency dynamic pressure sensors are arranged axially and circumferentially on the inner wall of the clean liquid chamber shell as transient pressure wave monitoring units to collect transient pressure wave signals excited by the backwashing operation; a high-speed data acquisition system is used to synchronously acquire pressure signals and K... P The signal serves as a data acquisition and processing unit, and the processor executes the leak diagnosis algorithm of this invention. The online detection method of this invention includes two complementary mathematical models: Model 1 is a leak determination and quantification model based on the quality of the filtrate, utilizing the mass conservation relationship to determine the outlet concentration K. P With leakage flow Q Leak and leakage area A L A quantitative relationship is established to estimate the severity of the leak. Model 2 is a fault location model based on the transient pressure wave of backwashing. It uses the transient pressure wave generated during backwashing, along with the arrival time difference of multi-point pressure sensors and a spherical intersection algorithm, to calculate the three-dimensional position of the pressure wave source within the clean liquid chamber, thereby locating the filter cartridge currently being backwashed. When the filter uses the aforementioned composite-reinforced organic tubular membrane, the membrane module's high mechanical strength and repeatable backwashing capability make it easier to generate a clear transient pressure wave response during the backwashing stage, which is beneficial for the stable implementation of Model 2. Simultaneously, the membrane's high rejection rate results in an extremely low baseline value for the outlet concentration, facilitating sensitive detection of even minor leaks by Model 1.

[0149] Model 1 is a leakage detection and quantification model, considering the total system flow as Q. Total The concentration of impurities in the feed liquid is C Feed When at least one tubular membrane ruptures, it is considered as a leakage path, with a leakage flow rate of Q. Leak This invention makes the following assumptions: the outlet impurity concentration of a healthy membrane filter element is negligible; the liquid passing through the leakage channel is unfiltered, and its impurity concentration is equal to C. Feed The mixture in the clean liquid chamber is rapid, and the outlet concentration is equal to the average concentration in the clean liquid chamber.

[0150] The flow rate of leaked impurities entering the clean liquid chamber. It can be approximated as Equation (1):

[0151]

[0152] The concentration of impurities C in the filtered liquid at the outlet of the clean liquid chamber Effluent That is, the purity index K P It approximately satisfies equation (2):

[0153]

[0154] Therefore, the leakage flow estimation formula (3) is obtained:

[0155]

[0156] Given the feed concentration and total flow rate, the outlet concentration K P With leakage flow Q Leak The values ​​are directly proportional, which can be used to determine whether a leak has occurred and the severity of the leak.

[0157] To further correlate the severity of leakage with the physical size of the damage, this invention uses an orifice outflow model to describe the relationship between leakage flow rate and transmembrane pressure difference ΔP, equation (4):

[0158]

[0159] Where: C d A is the flow coefficient; L ρ is the equivalent leakage area. L The density is the liquid density.

[0160] Substituting equation (3) into equation (4), we can obtain the estimation expression (5) for the leakage area:

[0161]

[0162] In systems employing the aforementioned composite-reinforced organic tubular membranes, by adjusting C... Feed QTotal ΔP and K P Online measurements can be used to estimate the leak area A in real time. L This enables online quantification of the severity of membrane damage.

[0163] When an online backwash is performed on a leaking filter assembly, the reverse fluid impacts the contaminants accumulated near the rupture point, causing a large amount of impurities to be released instantaneously into the clean liquid chamber. When the system resumes filtration, the outlet concentration K will be high for a short period of time. P Peak-like (6) patterns will appear:

[0164] K P,Peak =γ·K P,Steady (6)

[0165] Where: K P,Steady The peak value represents the steady-state outlet concentration during stable operation of the leak; γ is the peak amplification factor, with a typical value of approximately γ≈2.5 in experiments. This transient peak value is a key feature that links the leak event to a specific backflushing operation time window, providing a time reference for fault location.

[0166] Model 2 is a fault location model based on backwash transient pressure waves. In a multi-core tubular membrane filtration system, when a filter cartridge is backwashed, the rapid opening and closing of the backwash valve and the sudden change in the flow field will generate transient pressure waves. These pressure waves travel at the speed of sound v. s It spreads in liquids.

[0167] Let the coordinates of the filter cartridge assembly (pressure wave source) undergoing backwashing in three-dimensional space be P = (x p ,y p ,z p The coordinates of the (i)th pressure sensor are S. i =(x i ,y i ,z i If the distance between the two is R, then the distance between them is R. i For equation (7):

[0168]

[0169] The time for the pressure wave to reach sensors (i) and (j) are t and t, respectively. i t j Then the time difference Δt ij Equation (8):

[0170]

[0171] As long as the arrival time difference Δt of several pairs of sensors is determined ij The nonlinear equation system can be constructed based on equations (7) and (8) to solve for the location P of the pressure wave source.

[0172] In actual measurements, pressure signals contain noise and reflected signals. This invention employs a generalized cross-correlation phase transform method to robustly estimate the time difference. Let the cross-power spectral density of the pressure signals from sensors (i) and (j) be G. ij (ω), then the generalized cross-correlation phase transformation method function Φ ij (τ) is defined as in equation (9):

[0173]

[0174] Time difference estimate To maximize Φ*ij(τ), use equation (10):

[0175]

[0176] Further, the distance difference estimate is obtained.

[0177] To facilitate the solution, one of the sensors, S0, is selected as the reference sensor and set as the origin of the coordinate system, S0 = (0,0,0). T Let the distance from the pressure wave source to the reference sensor be R0 = |P|, and the distance to the (i)th sensor can be expressed as (Equation (11)):

[0178] R i =R0+ΔR i0

[0179] Based on geometric relationships, squaring equation (7) and substituting it into equation (11) yields equations (12), (13), and (14):

[0180]

[0181] Summarized as follows:

[0182] 2S*i T P = |S*i| 2 -ΔR*i0 2 -2R0ΔR*i0

[0183] For all i = 1, ..., N sensors, the matrix form is expressed as (15):

[0184] (AP = B - R0D)

[0185] in:

[0186]

[0187] The least squares method is used, utilizing the pseudo-inverse matrix A. + =(A T A) -1 A TThe relationship between P and R0 can be formally obtained as equation (16):

[0188] P = A + (B-R0D)

[0189] And because of geometric constraints Substituting equation (16) into the equation, we obtain quadratic equations (17) and (18) in R0:

[0190]

[0191] The coefficients a, b, and c can be explicitly given through matrix operations. Solving for the positive real roots of this quadratic equation yields R0, which, when substituted into equation (16), gives the pressure wave source location P, i.e., the center position of the filter cartridge assembly undergoing backwashing.

[0192] To verify the effectiveness of the online fault diagnosis method for tubular filters based on effluent quality analysis and backwash transient pressure wave propagation proposed in this invention, this embodiment uses a multi-core filtration system constructed with a composite-reinforced organic tubular membrane as the experimental platform. The platform includes a stainless steel vertical filter housing. Inside the housing, 15 composite-reinforced organic tubular membrane filter elements are arranged concentrically along the axial direction. Each filter element consists of a mesh fiber skeleton layer, a thin non-woven fabric layer, a thick non-woven fabric layer, and a polymer membrane separation layer covering the mesh fiber skeleton, with a structure consistent with the aforementioned composite-reinforced organic tubular membrane. The 15 filter elements are divided into 5 independent control groups, denoted as G1 to G5, according to the process piping. Each group contains 3 tubular membrane filter elements. The inlet side of each group is connected to a separately configured high-speed solenoid valve with a response time of less than 50ms. Online backwashing of that group is achieved by rapidly switching the valve, while other groups maintain normal filtration. This facilitates backwashing of each group of filter elements without stopping the system. The experimental medium was a simulated liquid containing 1% CaCO3 suspended particles. The total flow rate of the filtration system was set to approximately 5 m³ / h, with a transmembrane pressure difference of approximately 0.3 MPa. A high-sensitivity online liquid particle counter (LPC) was installed on the filter outlet main line to monitor the particle concentration or equivalent purity index (KP) of the filtered liquid in real time, with a sampling frequency of 2 Hz. Four high-frequency dynamic pressure sensors (HDPS-1 to HDPS-4) were evenly installed circumferentially and axially on the inner wall of the clean liquid chamber of the filter housing, with a frequency response of not less than 50 kHz, to collect transient pressure wave signals caused by backwashing. A high-speed data acquisition system was used to simultaneously acquire the signals from each pressure sensor at a sampling rate of approximately 100 kHz, while simultaneously recording the KP of the LPC. P Signals and total flow rate, transmembrane pressure difference, etc. Equivalent leakage holes are pre-fabricated on the membrane separation layer of the filter element. Specifically, in some filter elements, holes are precisely drilled from the separation layer side at the middle position of the membrane tube, forming a known equivalent leakage area A. LThe leak channels are designed while maintaining the integrity of the mesh skeleton and non-woven fabric support layer structure to simulate a working condition where only the separation layer fails but the support structure remains stable. The prefabricated leak levels are as follows: L1 level: equivalent leak pore diameter approximately 0.5 mm, leak area approximately 0.196 mm². 2 Level L2: Equivalent leak orifice diameter approximately 1.0 mm, leak area approximately 0.785 mm². 2 Level L3: Equivalent leak orifice diameter approximately 2.0 mm, leak area approximately 3.142 mm². 2 The aforementioned leakage holes are directly formed in the separation layer region of the composite reinforced organic tubular membrane, and the pores are kept to penetrate the separation layer, allowing unfiltered feed liquid to directly enter the clean liquid chamber through the leakage holes, thereby providing controllable fault samples for the online diagnostic method of this invention.

[0193] The estimated leakage area A is obtained. L,Est The result is: the estimated area for level L1 is approximately 0.203 mm. 2 The error is 3.6%; the calculated area for L2 level is approximately 0.769 mm². 2 The error is 2.0%; the estimated area for L3 level is approximately 3.167 mm². 2 The error is 0.8%. The results show that in systems using composite reinforced organic tubular membrane filter cartridges, the method of this invention can clearly distinguish minute leaks at the 0.5 mm level, and its estimated leak area is highly consistent with the actual leak area.

[0194] Under leak-free conditions, the spatial positioning accuracy of the fault location model based on the time difference of arrival (TDOA) of the backwash transient pressure wave and the spherical intersection algorithm was verified. Taking groups G1, G3, and G5 as examples, the comparison results show that the spatial error between the positioning point of group G1 and the actual group center is approximately 14.3 mm; the spatial error of group G3 is approximately 11.4 mm; and the spatial error of group G5 is approximately 11.8 mm. This indicates that the positioning model proposed in this invention also has high spatial resolution in tubular filtration systems using composite reinforced organic tubular membranes, and can reliably identify the position of the filter element group currently undergoing backwashing, providing a geometric basis for subsequent leak unit location.

[0195] In the backwash transient concentration characteristic test, a composite reinforced organic tubular membrane filter cartridge with an L2-level leak hole was installed in group G1, while the remaining filter cartridges were intact and leak-free. The system was then stabilized to obtain the steady-state outlet concentration K when a leak was present. P,Steady The concentration was approximately 0.360 mg / L in the experiment. The automatic backwashing program was initiated, and each filter element group was backwashed sequentially in the order of G1→G2→G3→G4→G5. Throughout the process, the K output from the LPC was collected at 2 Hz. P (t) curve. When backwashing is performed on the healthy filter cartridges (G2~G5), the outlet concentration K P(t) Only slight fluctuations were observed, with no obvious peaks; when backwashing was performed on group G1 with L2 leakage, a significant transient peak in the outlet concentration appeared at the moment filtration was restored, with a peak value of approximately 0.90 mg / L. The calculated peak amplification factor was approximately 2.5, indicating that the leaking filter group would produce a significant transient concentration peak signal when filtration was restored after backwashing, while the undamaged filter group would not produce a similar peak.

Claims

1. A composite reinforced organic tubular membrane, characterized in that, The device includes a tubular nonwoven fabric support layer, a mesh fiber skeleton layer disposed inside the tubular nonwoven fabric support layer, and a polymer membrane separation layer; wherein the mesh fiber skeleton layer and the tubular nonwoven fabric support layer are fixed together as an integrated tubular skeleton by welding at the overlap; the polymer membrane separation layer is formed by phase inversion of the casting solution, and the polymer membrane separation layer covers the mesh fiber skeleton layer and contacts the inner surface of the tubular nonwoven fabric support layer, but does not penetrate into the interior of the tubular nonwoven fabric support layer.

2. The composite reinforced organic tubular membrane according to claim 1, characterized in that, The tubular nonwoven fabric support layer is composed of a thin nonwoven fabric layer and a thick nonwoven fabric layer stacked sequentially from the inside to the outside, and the mesh fiber skeleton layer is located inside the thin nonwoven fabric layer. The integrated tubular skeleton is made of mesh fiber skeleton strips, thin non-woven fabric strips and thick non-woven fabric strips wound together in a cross spiral overlap manner. The spiral angle of each material strip relative to the axis of the membrane tube is 20-60°, and the overlap width between two adjacent turns is 1-5mm. The material of the mesh fiber skeleton layer is selected from one or more of polyester, polyethylene, or polypropylene fibers; the material of the tubular nonwoven fabric support layer is selected from one or more of polyester or polypropylene fibers; and the polymer material of the polymer membrane separation layer is selected from one or more of polyvinylidene fluoride, polyethersulfone, or polyaryletherketone and their copolymers. The basis weight of the mesh fiber skeleton layer is 50-130 g / m². 2 The thickness is 100-250μm, the warp and weft fiber density is 30-60 fibers / cm, and the mesh size is 50-300μm; The basis weight of the thin nonwoven fabric layer is 120-150 g / m². 2 The thickness is 150-200μm, and the average pore size is 10-30μm; the basis weight of the thick nonwoven fabric layer is 200-220g / m². 2 The thickness is 240-300μm, and the average pore size is 20-50μm; The thickness of the polymer membrane separation layer is 200-350 μm.

3. A method for preparing the composite reinforced organic tubular membrane as described in any one of claims 1-4, characterized in that, Includes the following steps: a) Provide mesh fiber skeleton strips, thin nonwoven strips and thick nonwoven strips; b) The mesh fiber skeleton strip is placed in the innermost layer, the thin non-woven fabric strip is placed in the middle layer, and the thick non-woven fabric strip is placed in the outermost layer. They are wound together in a cross-spiral overlapping manner, and the overlapping areas of each layer of material are ultrasonically welded to form an integrated tubular skeleton with the mesh fiber skeleton layer on the inner side. c) The pre-prepared casting solution is uniformly coated onto the inner surface of the integrated tubular skeleton through a scraping head, so that the casting solution penetrates and coats the mesh fiber skeleton layer, but does not penetrate into the thin nonwoven fabric layer. d) The integrated tubular framework coated with casting solution is pre-evaporated and then immersed in a coagulation bath for phase transformation to form the polymer membrane separation layer.

4. The method according to claim 3, characterized in that, The ultrasonic welding in step b) has a frequency of 20-40 kHz, a power of 500-1500 W, a single-point welding time of 0.05-0.5 s, and a spacing of 2-10 mm between adjacent weld points; the casting solution in step c) has a viscosity of 5-10 Pa·s; the casting solution is prepared by mixing a polymer with a mass fraction of 10-25 wt%, a pore-forming agent with a mass fraction of 1-20 wt%, and a solvent with a mass fraction of 50-75 wt%. The pore-forming agent is selected from at least one of polyvinylpyrrolidone, polyethylene glycol, sodium dodecyl sulfate, lithium chloride, and adipic acid; the solvent is selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, or dimethyl sulfoxide.

5. The method according to claim 3, characterized in that, Step c) is carried out under the conditions of ambient temperature 25-30℃ and relative humidity 50%-60%; the gap between the outer diameter of the outer tube of the scraping head and the inner diameter of the mesh fiber skeleton layer is 20-100μm; in step c), the ratio of the feeding speed of the casting solution to the winding speed is controlled to be 1.5-3.0ml / (min·m / min). The pre-evaporation time in step d) is 10-30 s; the temperature of the coagulation bath is 20-30 ℃, and the coagulation bath is selected from deionized water, distilled water, purified water, alcohol solution or aqueous solution of alcohol; It also includes a post-treatment step for the membrane tube that has completed the phase inversion: soaking it in pure water, soaking it in a 10-20 wt% glycerol aqueous solution, and then air-drying it.

6. The online failure detection method for the composite-reinforced organic tubular membrane according to claim 1, applied to a liquid filtration system including a housing and multiple tubular membrane filter elements disposed within the housing, wherein the tubular membrane is an organic tubular membrane, and the tubular membrane is a composite-reinforced organic tubular membrane, characterized in that... The method includes: 1) During filtration operation, the liquid to be treated flows from the inlet side through the tubular membrane filter element under the action of transmembrane pressure difference and is collected into the clean liquid chamber. The filtered liquid is then discharged from the clean liquid chamber through the filter outlet. 2) Collect the filtrate quality signal at the filter outlet to obtain the outlet concentration or purity index parameter K. P and the K P As an outlet quality indicator characterizing the integrity of filtration; 3) Transient pressure signals during filtration and backwashing processes are collected from multiple pressure sensors arranged axially and / or circumferentially within the clean liquid chamber of the housing, and the data acquisition and processing unit synchronously acquires the K... P With the transient pressure signal; 4) The processor executes the stored detection algorithm program: Based on the export quality index K P The relationship between feed conditions, total flow rate and transmembrane pressure differential is used to determine whether membrane rupture and leakage exist and to estimate the severity of the leakage. When a leak is detected, different tubular membrane filter cartridges are backwashed online in sequence. During each backwashing operation, the multiple pressure sensors are used to collect the transient pressure wave signal of the backwashing, and the location of the pressure wave source is spatially located based on the arrival time difference to determine the tubular membrane filter cartridge that is being backwashed. The corresponding outlet quality index K after the backwashing operation P The transient changes are correlated with the pressure wave source location results. When a significant abnormal change in outlet quality is detected within the time window corresponding to a certain backwash filter element group and the pressure wave source location is consistent with the geometric location of the filter element group, it is determined that the tubular membrane corresponding to the filter element group has been damaged or failed to seal.

7. The line detection method according to claim 6, characterized in that, In step 2), the export quality index K P With leakage flow Q Leak The relationship between them is derived from the law of conservation of mass: Among them, C Feed Q represents the impurity concentration or particle number concentration of the feed liquid. Total The total flow rate through the filter is used to estimate the leakage flow rate: and the Q Leak Compare with a preset leakage flow threshold to determine whether a leak has occurred; In step 4), the processor further calculates the leakage flow rate Q based on the orifice outflow model. Leak With equivalent leakage area A L Establishing relationships: Among them, C d ρ is the flow coefficient, ΔP is the pressure difference across the leak location, and ρ is the flow coefficient. L The density of the liquid; Q, obtained from the law of conservation of mass. Leak Substituting into the above formula, we obtain the formula for estimating the leakage area: And according to the A L The size of the leak determines the severity of the leak and classifies it into different levels.

8. The online detection method according to claim 6, characterized in that, Before performing step 4), the method further includes: when the tubular filtration system is in a leak-free state, recording the baseline value K of the outlet quality index under a representative stable filtration condition. P,baseline The baseline value is then stored in the processor. In step 4), the following formula is used to make a preliminary judgment on the leakage status: K P -K P,baseline >ΔK P,th Where ΔK P,th The export quality threshold is set based on system noise and allowable fluctuation range. This threshold is determined when the above inequality holds or the leakage area A... L Greater than the leakage area threshold A L,th At that time, the sequential backwashing and further fault location process is triggered.

9. The line detection method according to claim 6, characterized in that, In step 4), during the backwashing and filtration restoration process of each filter element group, the outlet quality index K is monitored. P Extract the steady-state value K corresponding to each backwash event based on the transient change of (t). P,Steady and peak value K P,Peak And calculate the peak amplification factor γ: When γ is greater than or equal to the peak amplification threshold γ th When the corresponding filter element group is considered to have leaked, resulting in the instantaneous release of particles; combined with the time window of the peak occurrence and the pressure wave source location result, the filter element group that has leaked is identified.

10. The line detection method according to claim 6, characterized in that, In step 3), the transient pressure wave signal of backwashing is acquired by at least four pressure sensors arranged at different spatial positions in the clean liquid chamber, and in step 4), the time difference of the pressure signal of any sensor pair (i,j) is estimated by the generalized cross-correlation phase transformation method. The time difference estimation process includes: 1) Calculate the cross-power spectral density G of the pressure signals acquired by sensor i and sensor j. ij (ω); 2) Construct the generalized cross-correlation phase transformation function 3) Obtain the estimated time difference of arrival through peak finding operation. And calculate the corresponding propagation distance difference. Where v s Let be the propagation speed of pressure waves in the liquid.

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