High-strength internally pressurized composite braided tube film and method of making same

Abstract

The application belongs to the field of membrane separation technology, and particularly relates to a high-strength inner pressure composite braided tube membrane and a preparation method thereof. The high-strength inner pressure composite braided tube membrane comprises a fiber braided support layer and a separation layer which is combined with the inner surface of the fiber braided support layer. The separation layer is formed by a high polymer material and at least partially penetrates into the fiber grid gap of the fiber braided support layer to form mechanical interlocking with the support layer, thereby improving the bonding strength between the separation layer and the support layer. A continuous synchronous braiding and coating process is adopted to continuously form the fiber braided support tube and coat the membrane liquid on the inner surface at the same time. The time for the membrane liquid to enter the coagulation bath is delayed by increasing the air bath, so that the membrane liquid penetrates into the deep layer of the fiber grid, and then the phase inversion is completed through the coagulation bath. The tube membrane prepared in this way has high inner pressure bearing capacity and reverse pressure resistance. Under the action of a reverse water pressure greater than 200 kPa, the flow channel can still be stable, and there is no obvious separation layer bulging, rupture and peeling. The tube membrane can be used for fluid separation, concentration and purification under high-frequency and high-pressure backwashing conditions.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, specifically relating to a high-strength internal pressure composite braided tube membrane and its preparation method. Background Technology

[0002] Tubular composite separation membranes, due to their wide flow channels and strong anti-fouling ability, are widely used in harsh operating conditions such as landfill leachate, zero discharge of high-salinity wastewater, and separation of special materials with high solids content. In order to withstand the high operating pressure during cross-flow filtration, tubular membranes usually use a porous support with certain mechanical strength as the inner lining skeleton, and a polymer separation layer is composited on its surface.

[0003] Traditional tubular membrane supports are mostly formed by winding and welding nonwoven fabrics (such as polyester nonwoven fabric). However, nonwoven fabric-supported tubular membranes have significant structural defects: First, welding defects are prone to occur at the ultrasonic winding weld seams, resulting in low strength. In addition, the dense weld seams prevent the casting solution from penetrating into the nonwoven fabric layer at the weld, resulting in poor adhesion between the membrane layer and the nonwoven fabric after film formation, making it easy to peel off under back pressure. Second, the burst strength of the nonwoven fabric support tube itself is less than 3MPa, making it unsuitable for use in high-pressure environments. Furthermore, the membrane layer is prone to rupture and peeling when exposed to complex industrial fluids and frequent high-pressure pulse backwashing.

[0004] In technologies employing fiber braided tubing as an inner lining support, early fabrication typically involved a two-step, discontinuous process of "braiding first, coating later." For example, US Patent 3,676,193 discloses a molding process for an integrally supported tubular membrane. This process requires first braiding fibers into a tubular support, then inserting it into a larger-diameter support tube to maintain its shape. Finally, a hollow coating mandrel with liquid outlet holes is placed inside the tube, and by moving the mandrel or braided tubing, a polymer solution is extruded and coated onto the inner wall of the braided tubing. This two-step process suffers from significant engineering drawbacks: it requires pre-forming the braided tubing and using an external rigid sleeve for auxiliary support, resulting in low production efficiency and difficulty in achieving continuous industrial production.

[0005] To address the engineering challenge of continuous production in two-step methods, Chinese invention patent CN 103949166 B discloses a method for preparing an internally pressurized fiber-reinforced filter membrane. This technology employs a three-channel spinneret, enabling the hollow braided tube, casting solution, and internal coagulation core solution to be co-extruded simultaneously at the spinneret, thereby achieving a continuous membrane fabrication process.

[0006] This solution addresses the issue of continuous production, but when faced with harsh, highly contaminated operating conditions and the need for large-diameter special separation, the technical approach requires improvement in the following aspects regarding macroscopic structure and microscopic phase transformation kinetics:

[0007] First, the rigidity of the support skeleton is insufficient. The braided fibers used in this process have a fineness of only 30-400 dtex (27-360D, 1 dtex = 0.9D). The support tube woven with such low-density fine fibers has a relatively soft overall skeleton. In actual industrial operation, when the system is subjected to high-pressure backflushing, this soft skeleton cannot provide sufficient radial compressive support, which can easily cause the flow channel to buckle and collapse inward, resulting in severe flattening deformation of the originally perfectly circular flow channel, and thus causing mechanical blockage of the flow channel or failure of the entire membrane tube.

[0008] Secondly, the rapid phase transformation limits the penetration depth of the casting solution within the fiber mesh, affecting the anchoring strength of the membrane layer. This process forcibly introduces an inner coagulating core solution into the innermost channel of the spinneret. When the polymer casting solution is extruded from the die and has not yet had sufficient time to penetrate deep into the outer fiber mesh, its inner surface instantly comes into contact with the inner coagulating core solution, triggering a phase transformation. This rapid phase transformation causes the casting solution surface to solidify quickly and lose its fluidity, resulting in the separation layer adhering only superficially to the surface of the braided tube. Due to the lack of deep geometric interlocking that penetrates the fiber support mesh, the interfacial bonding of this membrane layer is extremely weak. In actual high-frequency backwashing, the external backwash fluid can easily penetrate the gaps in the braided tube, lifting the weak separation layer from the fiber skeleton, leading to large-area peeling, bulging, and even tearing, greatly limiting its service life under harsh environments.

[0009] Third, the existing three-channel process is not only exceptionally complex in terms of mechanical structure (requiring a separate assembly design to avoid physical interference, high assembly requirements, and prone to eccentricity leading to uneven coating thickness), but also requires more spindles to produce braided tubes of the same inner diameter due to the small fiber fineness, resulting in high equipment investment, large footprint, and high energy consumption.

[0010] Therefore, how to simplify the coating device, break through the barrier of excessively rapid phase transformation caused by the internal solidification core liquid in the traditional three-channel co-extrusion process, and at the same time realize continuous synchronous weaving of coating in one step, use a pure mechanical physical compaction process to force the casting liquid into the depth of the fiber mesh to prepare a high-strength tubular separation membrane that can maintain the geometric stability of the flow channel and does not delaminate under ultra-high back pressure has become an engineering bottleneck that urgently needs to be solved in the current membrane separation technology field. Summary of the Invention

[0011] To address the shortcomings of existing technologies, the primary objective of this invention is to provide a high-strength, internally pressure-reinforced composite braided tubular membrane. Through deep, three-dimensional interlocking of a high-density fiber skeleton and a polymer separation layer, this significantly improves the engineering challenges of braided tubular membranes, such as easy deformation and membrane peeling under high-pressure backwashing. Another objective of this invention is to provide a method for preparing the aforementioned tubular membrane, overcoming the problems of complex spinneret structures, "internal coagulation of the core liquid" leading to instantaneous phase separation, and weak membrane bonding in traditional three-channel co-extrusion processes. Finally, this invention aims to provide applications of the aforementioned tubular membrane and its components in fluid separation, concentration, and purification.

[0012] This invention is achieved through the following technical solution:

[0013] The first objective of this invention is to provide a high-strength internal pressure composite braided tubular membrane, comprising a fiber braided support layer and a separation layer composited on the inner surface of the fiber braided support layer;

[0014] The fiber-woven support layer is woven from fibers of a single fineness or multiple different finenesses, wherein the fineness of the fibers is 400D~3000D;

[0015] The separation layer is formed of a polymer material and at least partially enters the fiber mesh gaps of the fiber braided support layer, forming a mechanical interlock with the fiber braided support layer;

[0016] The composite braided tubular membrane is an internal pressure type membrane structure, and the composite braided tubular membrane has a back pressure resistance greater than 200 kPa, that is, it can still maintain the stability of the flow channel under the action of reverse water pressure greater than 200 kPa, and reduce the phenomena of separation layer bulging, cracking and peeling.

[0017] Furthermore, the fineness of the fiber is 400D~2500D.

[0018] Furthermore, the fiber material of the fiber braided support layer is selected from one or more of polyester (PET), polypropylene (PP), polyethylene (PE), polyamide (PA), polyetheretherketone (PEEK), polytetrafluoroethylene (PTFE), polylactic acid (PLA), polyphenylene sulfide (PPS), or liquid crystal polyarylate (LCP).

[0019] Furthermore, the polymer material is selected from one or more of phenolphthalein polyaryletherketone (PEK-C), polyvinylidene fluoride (PVDF), polyethersulfone (PES), polysulfone (PSF), polyacrylonitrile (PAN), polyvinyl chloride (PVC), polyamide (PA), cellulose derivatives, or polyetherimide (PEI).

[0020] Furthermore, the inner diameter of the composite braided tubular membrane is 3mm to 15mm.

[0021] The second objective of this invention is to provide a method for preparing a high-strength internal pressure composite braided tubing membrane, which includes the following steps:

[0022] (1) While the fiber braiding machine is continuously braiding downwards to form a fiber braided support tube, the inner coating mandrel is coaxially positioned below the braiding convergence point, and the casting liquid is simultaneously coated on the inner surface of the continuously moving fiber braided support tube.

[0023] (2) The coated composite braided tube membrane is passed through an air bath so that the casting solution continues to penetrate radially into the fiber mesh gaps of the fiber braided support tube before entering the coagulation bath to undergo phase transformation;

[0024] (3) The composite braided tube membrane that has passed through the air bath is brought into the coagulation bath for phase transformation, and the casting liquid is solidified to form a separation layer.

[0025] Furthermore, the inner coating mandrel sequentially includes a connecting section, a liquid storage section, and a smoothing section along the axial direction;

[0026] The connecting section is used to connect to the casting liquid conveying pipeline, and the outer diameter of the connecting section is smaller than the inner diameter of the fiber braided support tube.

[0027] The inner coated core rod has an axially extending central flow channel inside, which extends to the liquid storage section.

[0028] The liquid storage section is radially concave, and its outer diameter is smaller than that of the connecting section and the smoothing section, so as to form an annular liquid storage tank between the inner coating core rod and the inner wall of the fiber braided support tube.

[0029] The liquid storage section is provided with a liquid outlet hole in the radial direction that communicates with the central flow channel, so that the casting liquid flows out to the annular liquid storage tank;

[0030] The outer diameter of the smoothing section is larger than the outer diameter of the liquid storage section, and a preset gap is formed between it and the inner diameter of the fiber braided support tube, so as to apply radial extrusion to the casting liquid flowing out of the annular liquid storage tank, so that the casting liquid enters the fiber mesh gap and uniformly coats the separation layer.

[0031] Furthermore, the length of the air bath is 5cm to 30cm.

[0032] A third objective of this invention is to provide a membrane assembly composed of a high-strength internal pressure composite braided tube membrane, comprising a membrane shell and a membrane tube bundle encapsulated inside the membrane shell.

[0033] The membrane bundle is composed of multiple high-strength internal pressure composite braided membrane tubes as described above.

[0034] The two ends of the composite braided tubular membrane are cast, cured and sealed to the two ends of the membrane shell by potting material, thereby forming a physically isolated feed liquid side channel and a product water side channel inside the membrane shell.

[0035] The feed liquid side channel is formed by the inner cavity of the composite braided membrane, and the product water side channel is formed by the annular gap between the outer wall of the composite braided membrane and the inner wall of the membrane shell.

[0036] Furthermore, the membrane module is suitable for backwashing conditions, allowing a backwashing pressure greater than 200 kPa to be applied to the permeate side channel during operation, and the composite braided membrane does not undergo significant flow channel deformation or separation layer peeling; the membrane shell material is selected from one of rigid polyvinyl chloride (UPVC), chlorinated polyvinyl chloride (CPVC), polypropylene (PP), glass fiber reinforced plastic (FRP), 304 stainless steel, 304L stainless steel, 316 stainless steel, 316L stainless steel or 2205 duplex stainless steel.

[0037] A fourth object of the present invention is to provide the application of the tubular membrane or the membrane assembly in fluid separation, concentration and purification.

[0038] Furthermore, the application field is selected from at least one of environmental water treatment, biopharmaceutical processing, food processing, chemical special separation, or industrial fluid treatment.

[0039] Furthermore, the environmental water treatment includes wastewater treatment with high-frequency and high-pressure backwashing conditions. The wastewater treatment is selected from landfill leachate treatment, high-salt wastewater zero-discharge pretreatment, coal chemical ash water treatment, titanium dioxide washing water reuse, iron phosphate synthesis and purification, oilfield produced water treatment, gas field fracturing fluid wastewater treatment, mine water treatment, or electroplating wastewater treatment.

[0040] Furthermore, the biopharmaceutical processing includes clarification of traditional Chinese medicine extracts, purification of enzyme preparations, clarification of plant extracts, clarification of xylose produced by acid hydrolysis of corn cobs, or clarification of bio-fermentation broth; the industrial fluid treatment includes purification of cooling circulating water, preparation of process water, or recycling of wastewater resources.

[0041] Furthermore, the food processing includes dairy product sterilization, fruit juice clarification, or brewing wastewater recovery; the chemical special separation includes catalyst recovery, product purification, or mother liquor separation.

[0042] The present invention has the following advantages over the prior art:

[0043] 1. Excellent resistance to high pressure and deformation: This invention abandons conventional small-fiber fibers and uses large-fiber fibers of 400D to 3000D to weave the support layer, which can withstand filtration pressure of more than 5MPa, while greatly improving the deformation resistance of the support tube under back pressure.

[0044] 2. Extremely strong resistance to membrane peeling (deep three-dimensional interlocking): This invention uses a mandrel for internal coating. The mandrel is inside the braided tube, and the casting solution has a certain extrusion pressure to better penetrate into the braided layer. At the same time, an air bath is combined to ensure the penetration depth of the casting solution. The separation layer continuously penetrates and is anchored in the fiber mesh gaps of the fiber braided support layer, forming an extremely strong mechanical and physical anchoring and geometric interlocking effect, thereby significantly reducing the delamination and peeling of the membrane under high-pressure backwashing.

[0045] 3. Highly stable continuous production: This invention seamlessly combines downward fiber weaving with single-channel coaxial coating through a specific one-step process. By eliminating the need for complex fluid (core fluid) pressure control and complex spinneret assembly requirements, the difficulty of equipment setup is greatly reduced, improving the yield rate and dimensional consistency of continuous mass production.

[0046] 4. Superior separation performance: The tubular membrane prepared using the same formula and process has a higher flux than traditional nonwoven tubular membranes.

[0047] 5. Wide adaptability to challenging working conditions: The tubular membrane of this invention is not only suitable for conventional water treatment, but also maintains the stability of the flow channel shape and the integrity of the membrane layer under frequent high-pressure backwashing conditions of high temperature (below 90℃), high solid content, and high viscosity materials. This solves the engineering pain points of traditional non-woven tubular membranes, such as easy delamination and short lifespan in fields such as biopharmaceutical extraction and special chemical separation.

[0048] 6. The equipment of this invention has low investment, small footprint, and low energy consumption. Attached Figure Description

[0049] Figure 1 Here is a scanning electron microscope image of Example 1;

[0050] Figure 2 This is a scanning electron microscope image of Example 2;

[0051] Figure 3 Here is a scanning electron microscope image of Example 3;

[0052] Figure 4 Here is a scanning electron microscope image of Example 4;

[0053] Figure 5 Here is a scanning electron microscope image of Example 5;

[0054] Figure 6 Here is a scanning electron microscope image of Example 6;

[0055] Figure 7 This is a scanning electron microscope image of Example 7;

[0056] Figure 8 This is a scanning electron microscope image of Comparative Example 2;

[0057] Figure 9 Comparison of 0.45 g / L humic acid (HA) flux between Example 1 and Comparative Example 3;

[0058] Figure 10 For comparison of the throughput of 1 g / L bovine serum albumin (BSA) in Example 1 and Comparative Example 3;

[0059] Figure 11 This is a schematic diagram of the equipment for the single-channel continuous synchronous braiding coating process of the present invention;

[0060] Figure 12 This is a diagram of the mandrel structure;

[0061] In the diagram: 1. Smoothing section; 2. Liquid storage section; 3. Connecting section; 4. Casting liquid tank; 5. Precision metering pump; 6. Mandrel; 7. Braiding machine; 8. Water pipe; 9. Coagulation bath. Detailed Implementation

[0062] The present invention will be further described in detail below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0063] like Figure 11 As shown, this invention employs a continuous synchronous braiding coating process. The mechanism is as follows: the prepared casting solution is stored in the casting solution tank 4, and after being precisely metered by the precision metering pump 5, it is delivered to the interior of the inner coating mandrel 6, which is coaxially positioned below the braiding convergence point of the braiding machine 7. Simultaneously, the fiber braiding machine continuously braids downwards to form a fiber braided support tube.

[0064] The casting solution is transported to the storage section 2 through the central flow channel inside the inner coated mandrel 6. It then flows out through radially arranged outlet holes in the storage section 2 into the annular storage tank. Driven by the continuous downward movement of the braided support tube, it flows downward along the annular gap between the mandrel 6 and the inner wall of the braided tube. When it flows through the smoothing section 1, the smoothing section 1 applies radial extrusion force to the casting solution, forcing it into the fiber mesh gaps of the fiber braided support tube.

[0065] The coated composite braided membrane continues to move downwards, first passing through an air bath of 5cm to 30cm in length. Within this air bath section, the casting solution has not yet undergone phase transformation and remains in a flowing state, allowing it to continue to penetrate radially into the fiber mesh gaps, so that the casting solution can fully fill and penetrate the fiber mesh.

[0066] Subsequently, the composite braided membrane, after passing through an air bath, enters coagulation bath 9. The casting solution undergoes a complete phase transformation and solidifies in coagulation bath 9, forming a separation layer. Since the separation layer has deeply penetrated and permeated the fiber mesh gaps before solidification, it forms a mechanical interlocking structure with the fiber braided support layer after solidification, thereby achieving a high-strength bond between the separation layer and the support layer.

[0067] Example 1:

[0068] 1) Preparation of casting solution: Prepare 500g of casting solution according to the following mass fractions: 18% PEK-C, 3% PVP-K15, 2% F-127, 5% PEG400, and 72% DMAC. Stir and dissolve at 60℃ for 6 hours, and after vacuum degassing, obtain the PEK-C casting solution.

[0069] 2) Continuous synchronous braided coating: A 56-spindle high-speed braiding machine is used, and PET fibers with a fineness of 1200D are selected as raw materials. The braiding machine braids downwards, and a 6mm diameter mandrel is coaxially fixed below the braiding point. The casting solution is synchronously coated onto the inner surface of the continuously moving fiber braided support tube.

[0070] 3) Physical Compaction and Molding: The PEK-C casting solution is injected into a single-channel mandrel using a precision metering pump. After being extruded from the mandrel, the casting solution is forcibly pressed into the fiber mesh. The coated membrane undergoes leveling and deep penetration via a 15cm air bath.

[0071] 4) Solidification phase transformation: The composite braided tubular membrane after air bath is directly placed into a pure water solidification bath at 25°C to undergo full phase transformation. After rinsing, treatment with 20% glycerol aqueous solution, and drying, a PEK-C internal pressure composite braided tubular membrane with an inner diameter of 6 mm is obtained.

[0072] Example 2:

[0073] Other conditions are the same as in Example 1, except that PET fibers with a fineness of 2000D are used for weaving, and an 8mm core rod is used.

[0074] Example 3:

[0075] Other conditions are the same as in Example 1, except that aramid fibers (aromatic polyamide) with a fineness of 1000D are used for weaving, and a 6mm mandrel is used.

[0076] Example 4:

[0077] Other conditions are the same as in Example 1, except that LCP fibers with a fineness of 400D are used for weaving, and a 4mm core rod is used.

[0078] Example 5:

[0079] 1) The casting solution is the same as in Example 1.

[0080] 2) Continuous synchronous braided coating: A 108-spindle high-speed braiding machine is used, and PET fibers with a fineness of 500D are selected as raw materials. The braiding machine braids downwards, and an 8mm diameter mandrel is coaxially fixed below the braiding point. The casting solution is synchronously coated onto the inner surface of the continuously moving fiber braided support tube.

[0081] 3) Physical Compaction and Molding: The PEK-C casting solution is injected into a single-channel mandrel using a precision metering pump. After being extruded from the mandrel, the casting solution is forcibly pressed into the fiber mesh. The coated membrane undergoes a 10cm air bath for leveling and deep penetration.

[0082] 4) Solidification phase transformation: The composite braided tubular membrane after air bath is directly placed into a pure water solidification bath at 25°C to undergo full phase transformation. After rinsing, treatment with 20% glycerol aqueous solution, and drying, a PEK-C internal pressure composite braided tubular membrane with an inner diameter of 8 mm is obtained.

[0083] Example 6:

[0084] 1) Preparation of casting solution: Prepare 500g of casting solution according to the following mass fractions: 20% PES, 3% PVP-K60, 5% PEG6000, and 72% DMAC. Stir and dissolve at 70℃ for 4 hours, and after vacuum degassing, obtain the PES casting solution.

[0085] 2) Subsequent processes are the same as in Example 5.

[0086] Example 7:

[0087] 1) Preparation of casting solution: Prepare 500g of casting solution according to the following mass fractions: 15% PVDF, 1% PEG6000, 3% F-127, 8% PVP-K12, 1% LiCl, and 72% DMAC. Stir and dissolve at 60℃ for 6 hours, and after vacuum degassing, obtain the PVDF casting solution.

[0088] 2) Continuous synchronous braided coating: A 56-spindle high-speed braiding machine is used, and PET fibers with a fineness of 1200D are selected as raw materials. The braiding machine braids downwards, and a 6mm diameter mandrel is coaxially fixed below the braiding point. The casting solution is synchronously coated onto the inner surface of the continuously moving fiber braided support tube.

[0089] 3) Physical Compaction and Molding: The PVDF casting solution is injected into a single-channel mandrel using a precision metering pump. After being extruded from the mandrel, the casting solution is forcibly pressed into the fiber mesh. The coated membrane undergoes leveling and deep penetration via a 20cm air bath.

[0090] 4) Solidification phase transformation: The composite braided tubular membrane after air bath is directly placed into a pure water solidification bath at 25°C to undergo full phase transformation. After rinsing, treatment with 20% glycerol aqueous solution, and drying, a PVDF internal pressure composite braided tubular membrane with an inner diameter of 6 mm is obtained.

[0091] Comparative Example 1: Fine Denier Fiber Support Process

[0092] A 108-spindle high-speed braiding machine was used, and the same PEK-C casting solution system and process as in Example 1 were selected.

[0093] By replacing the support layer fiber with 300D low-density polyester fiber, a composite braided tube membrane with an inner diameter of 6mm was produced using controlled equipment.

[0094] Comparative Example 2: Instantaneous phase separation after coating

[0095] The same PEK-C casting solution system and process as in Example 5 were used, and the film was immediately placed in the coagulation bath after coating.

[0096] Comparative Example 3: Nonwoven Tube Membrane

[0097] The casting solution is the same as in Example 1. The nonwoven fabric is welded into a tube by ultrasonic welding using a tubular membrane integral forming machine, and the casting solution is simultaneously coated into the inside of the nonwoven fabric tube. After the coated nonwoven fabric tube membrane is passed through a 15cm air bath, it is placed in a 25°C pure water coagulation bath to undergo a full phase transformation. After rinsing, treatment with a 20% glycerol aqueous solution, and drying, a PEK-C internal pressure nonwoven fabric tube membrane with an inner diameter of 6mm is obtained.

[0098] Performance evaluation and testing

[0099] The tubular membranes produced in Examples 1-7 and Comparative Examples 1-3 were subjected to cross-sectional scanning electron microscopy and high-pressure backwashing tests (test conditions: reverse water pressure was applied to the permeate side of the tubular membrane, and the water pressure was gradually increased until the membrane tube deformed or the membrane layer bulged, ruptured and peeled off. The pressure at this time was defined as the upper limit of the membrane tube's back pressure resistance). The test results are shown in Table 1 below:

[0100] Table 1

[0101] Example 1 1200D PET PEK-C 6 15 250 greater than 8MPa Example 2 2000D PET PEK-C 8 15 220 greater than 8MPa Example 3 1000D Aramid PEK-C 6 15 400 greater than 8MPa Example 4 400D LCP PEK-C 4 15 260 greater than 8MPa Example 5 500D PET PEK-C 8 10 230 greater than 8MPa Example 6 500D PET PES 8 10 220 greater than 8MPa Example 7 1200D PET PVDF 6 20 210 greater than 8MPa Comparative Example 1 300D PET PEK-C 6 15 120 greater than 8MPa Comparative Example 2 500D PET PEK-C 8 0 not applicable greater than 8MPa Comparative Example 3 PET nonwoven fabric PEK-C 6 15 120 2MPa

[0102] Figure 1-7 These are scanning electron microscope (SEM) images of embodiments 1-7 of the present invention. The images show that the membrane material penetrates and is anchored within the fiber mesh gaps of the fiber-woven support layer. The membrane layer and the fiber support layer are well bonded, and no membrane separation occurs. However, as... Figure 8 Comparative Example 2, as shown, exhibits significant membrane separation.

[0103] The back pressure test results show that: Comparative Example 1, despite using low-fiber fibers and increasing the number of woven fibers, still exhibited poor resistance to deformation of the supporting skeleton; while Comparative Example 2, even using high-fiber fibers, suffered from extremely poor casting solution penetration due to the use of zero air gaps (equivalent to the instantaneous phase separation effect of existing patent CN 103949166 B). Before the actual test, scanning electron microscopy revealed significant separation between the membrane layer and the fiber support layer, thus failing to meet the basic conditions for back pressure resistance testing and was therefore deemed unsuitable.

[0104] For Comparative Example 3, which uses conventional nonwoven fabric as the support layer, although the formulation and coating process are completely identical to Example 1, its burst pressure and back pressure resistance are significantly lower than those of the braided composite membrane of the present invention. Furthermore, parallel tests on the separation performance of various materials revealed that the present invention exhibits unexpected technical effects in separation flux: the HA (humic acid) flux of the braided membrane in Example 1 is approximately 22% higher than that of the nonwoven membrane, and the BSA (bovine serum albumin) flux is approximately 70% higher. Figure 9 , Figure 10 ).

[0105] In summary, only by combining appropriate fiber fineness with coating processes can membranes that meet the corresponding pressure resistance and separation performance requirements be prepared.

[0106] Typical industrial applications and advantages of the tubular membrane of this invention

[0107] Based on the synergistic structural design of the high-density fiber braided support layer and the separation layer with deep physical anchoring, the high-strength internal pressure composite braided tubular membrane of this invention has both excellent mechanical load-bearing capacity and chemical stability. Its typical industrial application scenarios and implementation advantages are as follows:

[0108] (1) High-frequency high-pressure backwashing wastewater treatment

[0109] For wastewaters with a high tendency to fouling, such as titanium dioxide washing water reuse, ferric phosphate synthesis and purification, oilfield produced water, gas field fracturing fluid, coal chemical ash water, and landfill leachate, traditional non-woven tubular membranes are often limited to backwash pressure below 100 kPa due to insufficient support burst strength. This results in incomplete cleaning, rapid membrane flux decline, and frequent chemical cleaning. The tubular membrane of this invention has a backwash pressure resistance greater than 200 kPa and can withstand high-frequency pulsed hydraulic backwashing. In practical engineering, it achieves long-term stable operation, and the chemical cleaning cycle is significantly extended compared to traditional tubular membranes, significantly reducing operation and maintenance costs and downtime frequency.

[0110] (2) Clarification and concentration of high-viscosity, high-solids materials

[0111] In systems involving the clarification of plant extracts, the acid hydrolysis of corn cobs to produce xylose, the separation of bio-fermentation broths, and the purification of traditional Chinese medicine extracts, the materials often have high viscosity and high solid content, and operation at 40-60°C is frequently required to maintain fluidity. The high-fiber braided support layer of the tubular membrane of this invention provides ample radial support. Combined with heat-resistant separation layer materials such as PEK-C and PVDF, it can operate continuously at temperatures below 90°C without thermal deformation or membrane peeling. Its temperature resistance is significantly superior to traditional polyester nonwoven tubular membranes (typically limited to 50-60°C).

[0112] (3) Complete replacement of conventional tubular membrane applications

[0113] In conventional tubular membrane applications such as cooling circulating water purification, process water preparation, wastewater resource reuse, and municipal greywater reuse, the tubular membrane of this invention, with its higher structural strength and longer service life, can be used to replace traditional non-woven fabric-based tubular membranes without changing the existing membrane module packaging form and system piping design, achieving plug-and-play upgrades.

[0114] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-strength internal pressure composite braided tubular membrane, characterized in that, It includes a fiber braided support layer and a separation layer composited on the inner surface of the fiber braided support layer; The fiber-woven support layer is formed by weaving fibers with a fineness of 400D to 3000D; The separation layer is formed of a polymer material and at least partially enters the fiber mesh gaps of the fiber braided support layer, forming a mechanical interlock with the fiber braided support layer; The composite braided tubular membrane is an internal pressure type membrane structure, and its back pressure resistance is greater than 200 kPa. That is, it can still maintain the stability of the flow channel under reverse water pressure greater than 200 kPa, without obvious separation layer bulging, cracking and peeling.

2. The high-strength internal pressure composite braided tubular membrane according to claim 1, characterized in that, The fiber material of the fiber braided support layer is selected from one or more of polyester, polypropylene, polyethylene, polyamide, polyetheretherketone, polytetrafluoroethylene, polylactic acid, polyphenylene sulfide, or liquid crystal polyarylate.

3. The high-strength internal pressure composite braided tubular membrane according to claim 1 or 2, characterized in that, The polymer material is selected from one or more of phenolphthalein polyaryletherketone, polyvinylidene fluoride, polyethersulfone, polysulfone, polyacrylonitrile, polyvinyl chloride, polyamide, cellulose derivatives or polyetherimide.

4. The high-strength internal pressure composite braided tubular membrane according to claim 3, characterized in that, The inner diameter of the composite braided tubular membrane is 3mm to 15mm.

5. A method for preparing a high-strength internal pressure composite braided tubular membrane, characterized in that, The method for preparing the high-strength internal pressure composite braided tubular membrane according to any one of claims 1 to 4 comprises the following steps: (1) While the fiber braiding machine is continuously braiding downwards to form a fiber braided support tube, the inner coating mandrel is coaxially positioned below the braiding convergence point, and the casting liquid is simultaneously coated on the inner surface of the continuously moving fiber braided support tube. (2) The coated composite braided tube membrane is passed through an air bath so that the casting solution continues to penetrate radially into the fiber mesh gaps of the fiber braided support tube before entering the coagulation bath to undergo phase transformation; (3) The composite braided tube membrane that has passed through the air bath is brought into the coagulation bath for phase transformation, and the casting liquid is solidified to form a separation layer.

6. The method for preparing the high-strength internal pressure composite braided tubular membrane according to claim 5, characterized in that, The inner coating core rod includes, along the axial direction, a connecting section (3), a liquid storage section (2), and a smoothing section (1). The connecting section (3) is used to connect with the casting liquid conveying pipeline, and the outer diameter of the connecting section (3) is smaller than the inner diameter of the fiber braided support tube; The inner coated core rod has an axially extending central flow channel inside, which extends to the liquid storage section. The liquid storage section (2) is radially concave, and its outer diameter is smaller than that of the connecting section (3) and the smoothing section (1) to form an annular liquid storage tank between the inner coating core rod and the inner wall of the fiber braided support tube. The liquid storage section (2) is provided with a liquid outlet hole in the radial direction that communicates with the central flow channel so that the casting liquid flows out to the annular liquid storage tank; The outer diameter of the smoothing section (1) is larger than the outer diameter of the liquid storage section (2), and a preset gap is formed between it and the inner diameter of the fiber braided support tube, so as to apply radial extrusion to the casting liquid flowing out of the annular liquid storage tank, so that the casting liquid enters the fiber mesh gap and uniformly coats the separation layer.

7. The method for preparing a high-strength internal pressure composite braided tubular membrane according to claim 5 or 6, characterized in that, The length of the air bath is 5cm to 30cm.

8. A membrane module composed of a high-strength internal pressure composite braided tube membrane, characterized in that, Includes a membrane housing and a membrane tube bundle encapsulated inside the membrane housing; The membrane bundle is composed of multiple high-strength internal pressure composite braided tubular membranes as described in any one of claims 1 to 4; The two ends of the composite braided tubular membrane are cast, cured and sealed to the two ends of the membrane shell by potting material, thereby forming a physically isolated feed liquid side channel and a product water side channel inside the membrane shell. The feed liquid side channel is formed by the inner cavity of the composite braided membrane, and the product water side channel is formed by the annular gap between the outer wall of the composite braided membrane and the inner wall of the membrane shell.

9. The membrane module composed of a high-strength internal pressure composite braided tube membrane according to claim 8, characterized in that, The membrane module is suitable for backwashing conditions, and during operation, a backwashing pressure greater than 200 kPa is allowed to be applied to the permeate side channel, and the composite braided tube membrane does not undergo significant flow channel deformation or separation layer peeling; the membrane shell material is selected from one of rigid polyvinyl chloride, chlorinated polyvinyl chloride, polypropylene, glass fiber reinforced plastic, 304 stainless steel, 304L stainless steel, 316 stainless steel, 316L stainless steel or 2205 duplex stainless steel.

10. The use of the tubular membrane according to any one of claims 1 to 4 or the membrane module according to any one of claims 8 to 9 in fluid separation, concentration and purification.

Images