Hollow ceramic ultrafiltration membrane and method for preparing the same

Abstract

The application relates to a hollow ceramic ultrafiltration membrane and a preparation method thereof. The ceramic body is internally provided with a fluid passage in the axial direction. The cross section of the passage is shaped in a special shape, so that the inner wall has a circumferential undulating profile. The passage is in the axial direction in a string-bead structure formed by alternating cavities and channels. The cross-sectional area of the cavity is larger than that of the channel. The application induces axial secondary flow to destroy the boundary layer through the special cross-sectional shape, and a backflow area is formed in the cavity through the string-bead structure to generate jet impact. The two are combined to build a three-dimensional turbulent flow field, realize dynamic cleaning of the whole area of the membrane surface, significantly delay the pollution, and the preparation method comprises the following steps: preparing a support body mud; extruding the support body wet blank through a special-shaped variable-diameter extrusion die; immediately vacuum adsorbing and shaping to lock the shape after length cutting; drying and pre-sintering to obtain a porous support body; coating a transition layer and a separation layer on the inner wall in sequence; high-temperature co-sintering to obtain a finished product. The ceramic ultrafiltration membrane prepared by the application has the comprehensive performance of high flux, high precision, anti-pollution and long service life.

Description

Technical Field

[0001] This invention relates to the field of ultrafiltration membranes, and more specifically to hollow ceramic ultrafiltration membranes and their preparation methods. Background Technology

[0002] Tubular hollow ceramic ultrafiltration membranes are widely used in drinking water purification, industrial wastewater treatment, and oil-water separation due to their excellent mechanical strength, chemical stability, and high-temperature resistance. Traditional tubular ceramic membranes are usually prepared by extrusion molding, and their fluid channels are mostly circular, uniform-diameter, straight-through structures.

[0003] However, this traditional structure has inherent drawbacks: in circular channels, the fluid flows in a laminar state, and the velocity and concentration boundary layers continuously thicken along the axial direction, leading to the continuous deposition of particulate matter on the membrane surface, forming a filter cake layer, causing an increase in transmembrane pressure and a decrease in flux. To solve the membrane fouling problem, industry typically increases the cross-flow velocity to enhance the membrane surface shear force, but this not only significantly increases operating energy consumption but also fails to fundamentally destroy the already formed boundary layers. Furthermore, the smooth inner walls of traditional membrane channels mean that fluid disturbance relies solely on the natural development of the turbulent boundary layer, lacking an active disturbance mechanism, resulting in low membrane surface utilization and short cleaning cycles.

[0004] In recent years, researchers have attempted to improve fluid conditions by altering channel shape, such as using non-circular cross-sections or incorporating internal wall protrusions. However, these improvements are limited to single-dimensional perturbation and cannot achieve three-dimensional disruption of the boundary layer. Therefore, developing a ceramic ultrafiltration membrane structure capable of actively perturbing the fluid from multiple dimensions simultaneously, disrupting the boundary layer from all directions, and significantly delaying membrane fouling has become a pressing technical challenge in this field. Summary of the Invention

[0005] The purpose of this invention is to solve the problems in the background art and provide a hollow ceramic ultrafiltration membrane and its preparation method.

[0006] The above-mentioned technical objective of the present invention is achieved through the following technical solution: A hollow ceramic ultrafiltration membrane includes a ceramic body, in which fluid channels are formed along the axial direction. The cross-section of the fluid channels is irregular, giving the inner wall of the channels a circumferentially undulating profile. The fluid channels have a beaded structure along the axial direction, which is composed of several cavities and several channels arranged alternately along the axial direction. The cross-sectional area of ​​the cavities is larger than the cross-sectional area of ​​the channels.

[0007] This invention utilizes an irregularly shaped cross-section design of the fluid channel to create a circumferentially undulating profile on the inner wall of the channel. This induces axial secondary flow during fluid flow, effectively disrupting the laminar boundary layer and enhancing radial mixing, continuously suppressing particle migration to the membrane surface. Furthermore, the channel has a beaded structure along the axial direction. As the fluid flows between the cavities and channels, it undergoes periodic expansion and contraction, forming a stable reflux zone within the cavity. This generates a jet impact on the membrane surface, stripping away deposited contaminants. Through the synergistic effect of the irregular cross-section and the axial beaded structure, a three-dimensional turbulent field is constructed within the channel. The axial vortices induced by the irregular cross-section are periodically interrupted and reorganized by the beaded cavities. The lateral reflux within the cavity is induced by the irregular cross-section to generate secondary disturbances, achieving dynamic cleaning of the entire membrane surface throughout all time periods. This significantly slows down the membrane fouling process, extends the cleaning cycle, and reduces operating energy consumption. Thus, while ensuring high-efficiency filtration performance, it greatly improves the operational stability and service life of the membrane module.

[0008] Preferably, an expansion section and a contraction section are provided between the cavity and the channel. The cross-sectional area of ​​the expansion section and the contraction section gradually changes along the axial direction, realizing a smooth transition of the fluid channel and a gradient evolution of the flow state. In the expansion section, the cross-sectional area gradually increases, the fluid velocity decreases accordingly, and the pressure rises, inducing stable flow separation and pre-recirculation. In the contraction section, the cross-sectional area gradually decreases, the fluid is smoothly accelerated, eliminating dead zones and preventing excessive eddy development. The synergistic effect of the expansion section and the contraction section allows the fluid to expand gradually when entering the cavity, forming an orderly recirculation zone rather than turbulence, and to contract gently when leaving the cavity, avoiding the impact of sudden pressure changes on the membrane structure. This gradual transition design not only ensures the full development and stable existence of the recirculation zone in the cavity, but also eliminates the dead zones and excessive local eddy development that are easily generated by traditional abrupt structures, thus optimizing the overall hydrodynamic performance of the entire beaded structure, further enhancing the uniform scouring effect on the membrane surface, and effectively avoiding the aggravation of local contamination caused by abrupt changes in the flow channel.

[0009] Preferably, the cross-section of the fluid channel is toothed, and the toothed shape is formed by alternating tooth apexes and tooth valleys. The cross-sectional area of ​​the channel is smallest at the tooth apexes and largest at the tooth valleys.

[0010] This invention utilizes the principle that at the tooth tip, the channel cross-sectional area shrinks, and the fluid velocity increases, forming a local high-pressure scouring zone that exerts a strong shearing effect on the membrane surface. At the tooth valley, the channel cross-sectional area expands, and the fluid velocity decreases, inducing a stable axial secondary flow and forming a vortex disturbance zone. The high-speed scouring at the tooth tip and the vortex disturbance in the tooth valley work together to ensure that all areas of the channel inner wall are subjected to periodic dynamic cleaning. The continuous high shear force at the tooth tip prevents particulate matter from adhering, while the secondary flow in the tooth valley draws the deposited particles back into the main flow. The synergistic effect of these two factors ensures that there are no deposition blind spots at any point on the circumference of the membrane surface, significantly improving the membrane's antifouling ability.

[0011] Preferably, the ceramic body has an asymmetric multilayer structure, which includes a separation layer, a transition layer and a porous support from the inside out.

[0012] In this invention, the separation layer, as the innermost layer, directly contacts the fluid. Its dense nanoscale pore size ensures high-precision sieving of suspended solids, colloids, and macromolecules. The transition layer, located between the separation layer and the support layer, has a gradient pore size that prevents nanoparticles from the separation layer from penetrating into the macropores of the support layer and gradually transitions the large pore size of the support layer to the small pore size of the separation layer, eliminating interlayer interface resistance. The porous support, as the outermost main body, provides sufficient mechanical strength for the entire membrane module, enabling it to withstand high-pressure filtration operations without deformation. The three-layer structure, with pore size and thickness increasing layer by layer from the inside out, forms an integrated synergistic system of precise sieving, gradient transition, and strong support. This ensures high filtration accuracy while maintaining low filtration resistance and high permeation flux. At the same time, it allows the irregular cross-section and beaded structure of this invention to be formed on the support and completely transferred to the separation layer, achieving an organic unity of geometric configuration and multilayer structure.

[0013] Transition layer: made of at least one of titanium oxide, zirconium oxide or α-alumina micro powder, and formed by coating and sintering to form a transition layer with an average pore size of 0.05 μm.

[0014] Separation layer: made of zirconium oxide, titanium oxide or γ-alumina sol, with a sol particle size of 50~200 nm, and formed into a dense separation layer with an average pore size of 5~30 nm after coating and sintering.

[0015] The coating of the transition layer and the separation layer can be carried out using the conventional impregnation method in the field of ceramic membranes. Specifically, the pre-sintered porous support is placed vertically or at an angle, and the prepared transition layer slurry is poured into one end of the support to fill the entire fluid channel. After holding for 10 to 60 seconds, the slurry is released to flow out naturally, forming a uniform wet film on the inner wall of the support. After drying, the separation layer sol is coated using the same method.

[0016] Because the fluid channel of the present invention has an axial beaded structure and an irregular cross-section, the viscosity of the slurry and the immersion time can be appropriately adjusted during coating to ensure the uniformity of the coating thickness at the tooth tip and tooth valley, cavity and channel.

[0017] A method for preparing a hollow ceramic ultrafiltration membrane includes the following steps: S1: Preparation of support clay material: ceramic powder is mixed with binder, lubricant and dispersant, and then vacuum kneaded and aged to obtain plastic clay material; S2: Extrusion molding, the support material prepared in S1 is added to the extruder, the material flows through the irregular diameter extrusion die and is extruded to form a support wet blank with an irregular cross section and a beaded structure in the axial direction; S3: Fixed-length cutting and vacuum shaping. The extruded support wet blank is cut to a fixed length to obtain a single blank. The cut single blank is immediately placed into a vacuum shaping mold, and negative pressure is applied to the wet blank for vacuum adsorption shaping. It is kept for 5 to 15 minutes to allow the surface of the wet blank to harden initially, lock the irregular cross section and beaded structure, and then demold and take out the blank. S4: Drying and pre-sintering: The vacuum-formed green body is dried in stages and then pre-sintered at 800-1000℃ to obtain a porous support. S5: Coating a transition layer and a separation layer, the transition layer and the separation layer are sequentially coated on the inner wall of the porous support to form an asymmetric multilayer structure; S6: High-temperature co-sintering, the coated film blank is sintered at a high temperature of 1200-1350℃ to obtain the finished product.

[0018] This invention directly forms a wet blank of a support with an irregular cross-section and an axial beaded structure using an irregularly shaped variable-diameter extrusion die. Combined with vacuum adsorption shaping, it can precisely lock the complex channel contour at the wet blank stage, effectively preventing deformation and ensuring the structural accuracy of the fluid channel. On this basis, a transition layer and a separation layer are sequentially coated on the support with a complex inner wall. Combined with high-temperature co-sintering in step S6, not only is an asymmetric multilayer structure with a reasonable pore size gradient and strong bonding formed to ensure ultrafiltration accuracy, but the special structure of the support channel also makes the separation layer adhere more uniformly and stably, further ensuring the integrity of the filtration performance. Finally, through the synergistic process from the precise forming of the support to the coating and sintering of the functional layer, the ceramic ultrafiltration membrane prepared by the method of this invention simultaneously achieves a comprehensive improvement in performance, including high throughput, high precision, anti-fouling, and long lifespan, significantly reducing operation and maintenance costs and demonstrating outstanding industrial application value.

[0019] Preferably, the irregular diameter extrusion die includes a die housing disposed at the discharge end of the extruder barrel and an irregular diameter mandrel disposed inside the die housing. A clay extrusion space is formed between the die housing and the irregular diameter mandrel. Through the coordinated cooperation of the inner and outer dies, the irregular diameter profile of the mandrel directly imparts a complex channel structure with an irregular cross-section and an axial beaded shape to the clay.

[0020] Preferably, the irregularly shaped variable-diameter mandrel includes a support disk, a tooth-forming assembly, and a tooth-shaped transition support assembly. The tooth-forming assembly is disposed on the front side of the support disk, and the tooth-shaped transition support assembly is disposed on the back side of the support disk. The tooth-forming assembly includes a first support bar and a first rotating disk, and the tooth-shaped transition support assembly includes a second support bar and a second rotating disk. The front side of the support disk has a plurality of first limiting grooves along the circumferential direction, and the back side of the support disk has a plurality of second limiting grooves along the circumferential direction. Both the first limiting grooves and the second limiting grooves are arranged along the radial direction of the support disk. Furthermore, a second limiting groove is correspondingly provided between two adjacent first limiting grooves. The first support bar is slidably disposed in the first limiting groove, and the second support bar is slidably disposed in the second limiting groove. Limiting posts are fixed on the upper surfaces of the first and second support bars. Arc-shaped linkage grooves are provided on the first and second rotating disks, and the limiting posts are slidably disposed in the corresponding arc-shaped linkage grooves. A toothed forming block is provided at the end of the first support bar, and an arc-shaped support piece is provided at the end of the second support bar. The outer surface of the arc-shaped support piece is in contact with the inner surface of the adjacent toothed forming block.

[0021] This invention utilizes the rotation of a first rotating disk and the cooperation between its arc-shaped linkage groove and the limiting post to drive the first support bar to slide radially along the first limiting groove, thereby precisely adjusting the radial position of the tooth-forming block at the end of the first support bar to form the tooth tip. Simultaneously, by rotating a second rotating disk, the second support bar is driven to slide radially along the second limiting groove, precisely adjusting the radial position of the arc-shaped support piece at the end of the second support bar to form the tooth valley. The radial dimensions of the tooth tip and tooth valley are precisely adjusted. Since the first and second limiting grooves are staggered along the circumferential direction, the tooth tip and tooth valley form an alternating and continuous irregular cross-sectional profile on the inner wall of the fluid channel, enabling rapid switching of different specifications of irregular cross-sections and realizing the porous support structure of this invention.

[0022] Preferably, a rotating shaft is fixed in the middle of the second rotating disk, the first rotating disk is fixed on the side wall of the rotating shaft, the side wall of the first rotating disk is rotatably connected to the support disk through a rotating bearing, a rotating motor is fixed at the end of the rotating shaft, a fixed cylinder is fixed on the back of the support disk, a fixed rod is provided inside the die head housing, fixed strips are provided on opposite sides of the fixed rod, the fixed strips are fixed to the inner side wall of the die head housing, the fixed cylinder is fixed on the fixed rod, an elastic sealing layer is provided on the outer wall of the toothed forming block and the arc-shaped support piece, the right side of the elastic sealing layer extends and is fixed to the fixed cylinder, and the left side seals and wraps the left side of the irregular diameter mandrel.

[0023] The support plate of this invention is fastened to the fixing rod inside the mold head housing through the fixing cylinder on the back, and the fixing rod is firmly engaged with the inner wall of the mold head housing through the fixing strips on both sides, thereby forming a rigid integral fixation between the support plate of the entire rotating plate assembly and the mold head housing. Then, the rotating shaft is driven by a rotary motor to drive the first rotating plate and the second rotating plate to rotate synchronously, so that the outer surface of the arc-shaped support plate and the inner surface of the adjacent tooth-forming block can always remain in contact. Liquid silicone rubber can be used.

[0024] This invention provides an elastic sealing layer on the outer wall of the toothed forming block and the arc-shaped support plate. The right side of the elastic sealing layer is fixed to the fixed cylinder, and the left side seals and wraps the irregularly shaped variable diameter mandrel. The elastic sealing layer can effectively fill and seal any tiny gaps that may exist at the splicing surface of the toothed and arc-shaped parts using the elasticity of the material itself. This prevents mud from seeping into the movement gap of the rotating mechanism under high pressure and affecting the normal operation of the irregularly shaped variable diameter mandrel. At the same time, thanks to the good deformation capacity of the elastic sealing layer, sufficient space can be provided for the radial movement of the first and second support bars while ensuring the sealing effect, ensuring that their movement is smooth and uninterrupted.

[0025] Preferably, the vacuum forming mold includes a lower mold and an upper mold. The surfaces of the lower mold and the upper mold are provided with undulating grooves that match the shape of the outer wall of the ceramic body. Vacuum suction holes are evenly distributed in the undulating grooves. The vacuum suction holes are connected to a pre-set vacuum channel inside the mold. By providing undulating grooves that match the shape of the outer wall of the ceramic body on the surfaces of the lower mold and the uniformly distributed vacuum suction holes in the grooves, and connecting the vacuum suction holes to the pre-set vacuum channel inside the mold, a conformal suction vacuum forming system is constructed. When the extruded ceramic body passes through the vacuum forming mold, the vacuum negative pressure passes through the uniformly distributed... Distributed vacuum suction holes act on the outer wall of the ceramic body, making it fit tightly against the inner wall of the undulating grooves. This effectively constrains the external dimensions of the ceramic body, preventing deformation due to gravity or internal stress before it is fully hardened. At the same time, the evenly distributed vacuum suction holes ensure the circumferential balance of the adsorption force, avoiding surface indentations or collapses caused by excessive local adsorption, and significantly improving the accuracy and consistency of the ceramic body's external dimensions. In addition, vacuum adsorption helps the ceramic body to make close contact with the mold wall, improving heat transfer efficiency, accelerating the shaping process, and providing a stable and dimensionally accurate blank foundation for subsequent processes.

[0026] In summary, the beneficial effects of this invention are as follows: 1. This invention utilizes the synergistic effect of an irregular cross-sectional design of the fluid channel and an axial beaded structure to construct a three-dimensional turbulent flow field within the channel. The axial secondary flow induced by the irregular cross-section continuously disrupts the laminar boundary layer and inhibits particle migration to the membrane surface. The periodic expansion and contraction of the beaded structure forms a stable reflux zone within the cavity, generating a jet impact on the membrane surface to peel off deposited pollutants. The coupling of these two elements ensures that the entire membrane surface is subjected to periodic dynamic cleaning. High-speed shearing at the tooth tips prevents particle adhesion, while vortex disturbance at the tooth valleys entrains and absorbs deposits. The reflux within the cavity enhances the flushing effect, significantly slowing down the membrane fouling process, extending the cleaning cycle, and reducing operating energy consumption. While ensuring high-efficiency filtration, this invention greatly improves the operational stability and service life of the membrane module.

[0027] 2. In this invention, an expansion section and a contraction section are preferably set between the cavity and the channel to achieve a smooth transition of the fluid channel and a gradient evolution of the flow state. The expansion section induces an ordered recirculation zone in a gradual manner rather than turbulent flow, while the contraction section gently accelerates the elimination of dead zones and prevents excessive development of eddies. This gradual design not only ensures the full and stable existence of the recirculation zone in the cavity, but also eliminates the local eddy excessiveness and flow dead zones that are easily generated by traditional abrupt structures. This optimizes the overall hydrodynamic performance of the entire beaded structure, further enhances the uniform scouring effect on the membrane surface, and effectively avoids the problem of increased local contamination caused by abrupt changes in the flow channel.

[0028] 3. This invention, by rotating the first rotating disk and utilizing the cooperation between the arc-shaped linkage groove and the limiting post, drives the first support bar to slide radially along the first limiting groove, thereby precisely adjusting the radial position of the tooth-forming block at the end of the first support bar to form the tooth tip; simultaneously, by rotating the second rotating disk, the second support bar is driven to slide radially along the second limiting groove, precisely adjusting the radial position of the arc-shaped support piece at the end of the second support bar to form the tooth valley, and precisely adjusting the radial dimensions of the tooth tip and tooth valley. Since the first limiting groove and the second limiting groove are staggered along the circumferential direction, the tooth tip and tooth valley form an alternating continuous irregular cross-sectional profile on the inner wall of the fluid channel, which can realize the rapid switching of different specifications of irregular cross-sections, realizing the porous support structure of this invention.

[0029] 4. This invention provides an elastic sealing layer on the outer wall of the toothed forming block and the arc-shaped support plate, and extends and fixes the right side of the elastic sealing layer to the fixed cylinder, while sealing and wrapping the irregularly shaped variable diameter mandrel on the left side. The elastic sealing layer can effectively fill and seal any tiny gaps that may exist at the splicing surface of the toothed and arc-shaped parts using the elasticity of the material itself, thereby preventing mud from seeping into the movement gap of the rotating mechanism under high pressure and affecting the normal operation of the irregularly shaped variable diameter mandrel. At the same time, thanks to the good deformation capacity of the elastic sealing layer, sufficient space can be provided for the radial movement of the first and second support bars while ensuring the sealing effect, ensuring that their movement is smooth and uninterrupted. Attached Figure Description

[0030] Figure 1 This is a three-dimensional schematic diagram of the hollow ceramic ultrafiltration membrane of the present invention; Figure 2 This is a cross-sectional schematic diagram of the hollow ceramic ultrafiltration membrane of the present invention; Figure 3 This is a schematic cross-sectional view of the hollow ceramic ultrafiltration membrane of the present invention. Figure 4 This is a cross-sectional schematic diagram of the irregularly shaped variable diameter extrusion die of the present invention; Figure 5 This is an overall schematic diagram of the irregularly shaped variable diameter mandrel of the present invention; Figure 6 This is a front view of the irregularly shaped variable diameter mandrel of the present invention; Figure 7 This is a schematic diagram of the back side of the irregularly shaped variable diameter mandrel of the present invention; Figure 8 This is a cross-sectional schematic diagram of the irregularly shaped variable-diameter mandrel of the present invention; Figure 9 This is a three-dimensional schematic diagram of the support plate of the present invention; Figure 10 This is a schematic diagram of the tooth-forming block of the present invention; Figure 11 This is a schematic diagram of the arc-shaped support sheet of the present invention; Figure 12 This is a schematic diagram of the vacuum shaping mold of the present invention; Figure 13 This is a schematic diagram of the lower mold of the present invention; In the diagram, the markings are: 1-ceramic body; 2-fluid channel; 3-beaded structure; 31-cavity; 32-channel; 33-expansion section; 34-contraction section; 210-tooth shape; 211-tooth tip; 212-tooth valley. 13-Separation layer; 12-Transition layer; 11-Porous support; 4-Irregularly shaped variable diameter extrusion die; 5-Vacuum forming mold; 41-Die housing; 42-Irregularly shaped variable diameter mandrel; 43-Slurry extrusion space; 421-Support plate; 422-Toothed forming assembly; 423-Toothed transition support assembly; 4221-First support bar; 4222-First rotating disk; 4231-Second support bar; 4232-Second rotating disk; 4211-First limiting groove; 4212-Second limiting groove; 4223-Limiting post; 4224-Arc-shaped linkage groove; 425-Toothed forming block; 426-Arc-shaped support piece; 4210-Rotating shaft; 4213-Rotating bearing; 424-Rotating motor; 427-Fixed cylinder; 411-Fixed rod; 412-Fixed strip; 428-Elastic sealing layer; 51-Lower mold; 52-Upper mold; 511-Irregular groove; 512-Vacuum suction hole. Detailed Implementation

[0031] The following specific embodiments are merely illustrative of the present invention and are not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to these embodiments without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of the present invention.

[0032] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0033] Example

[0034] according to Figures 1-3 As shown, a hollow ceramic ultrafiltration membrane includes a ceramic body 1. A fluid channel 2 is formed axially within the ceramic body 1. The cross-section of the fluid channel 2 is irregular, giving the inner wall of the channel a circumferentially undulating profile. The fluid channel 2 has a beaded structure 3 axially, composed of several cavities 31 and several channels 32 arranged alternately axially. The cross-sectional area of ​​the cavities 31 is larger than that of the channels 32. An expansion section 33 and a contraction section 34 are provided between the cavities 31 and the channels 32. The cross-sectional areas of the expansion section 33 and the contraction section 34 gradually change axially. The cross-section of the fluid channel 2 is toothed 210, composed of several tooth tips 211 and tooth valleys 212 alternately connected. The channel cross-sectional area is smallest at the tooth tip 211 and largest at the tooth valley 212. The ceramic body 1 has an asymmetric multilayer structure, comprising a separation layer 13, a transition layer 12, and a porous support 11 from the inside out.

[0035] A method for preparing a hollow ceramic ultrafiltration membrane includes the following steps: S1: Prepare the support clay material. Using a conventional formula in this field, mix 100 parts of α-alumina powder, 5-15 parts of pore-forming agent, 3-8 parts of binder, 1-3 parts of lubricant and 15-25 parts of water. After vacuum kneading and aging, obtain a plastic clay material.

[0036] S2: Extrusion molding, the support material prepared in S1 is added to the extruder, the material flows through the irregular diameter extrusion die 4 and is extruded to form a support wet blank with an irregular cross section and a beaded structure in the axial direction; S3: Fixed-length cutting and vacuum shaping. The extruded support wet blank is cut to a fixed length to obtain a single blank. The cut single blank is immediately placed into the vacuum shaping mold 5. Negative pressure is applied to the wet blank for vacuum adsorption shaping. It is kept for 5 to 15 minutes to allow the surface of the wet blank to harden initially, lock the irregular cross section and beaded structure, and then demold and take out the blank. The cutting can be performed using a piano wire cutting device, in which the piano wire moves vertically downward during cutting. The piano wire is driven by a servo motor to move back and forth and maintain constant tension. S4: Drying and pre-sintering. The vacuum-shaped green body is dried in stages. First stage: air-drying for 24 hours in an environment with room temperature of 25℃ and relative humidity of 95%. Second stage: Transfer to a constant temperature and humidity chamber, temperature 45℃, relative humidity 85%, dry for 18 hours; Third stage: Dry in an oven at 80℃ for 12 hours until constant weight, with a final moisture content of <1%; The dried green body was placed in a sintering furnace and heated to 900℃ at 1.5℃ / min. It was held for 2 hours for pre-sintering and then cooled with the furnace to obtain a porous support (11). S5: Coating transition layer and separation layer, the transition layer 12 and separation layer 13 are sequentially coated on the inner wall of the porous support 11 to form an asymmetric multilayer structure; S6: High-temperature co-sintering, the coated film blank is sintered at a high temperature of 1200-1350℃ to obtain the finished product.

[0037] according to Figure 4 As shown, the irregular diameter extrusion die 4 includes a die housing 41 disposed at the discharge end of the extruder barrel and an irregular diameter mandrel 42 disposed inside the die housing 41. A mud extrusion space 43 is formed between the die housing 41 and the irregular diameter mandrel 42.

[0038] according to Figures 5-10As shown, the irregularly shaped variable diameter mandrel 42 includes a support disk 421, a toothed forming assembly 422, and a toothed transition support assembly 423. The toothed forming assembly 422 is disposed on the front side of the support disk 421, and the toothed transition support assembly 423 is disposed on the back side of the support disk 421. The toothed forming assembly 422 includes a first support bar 4221 and a first rotating disk 4222. The toothed transition support assembly 423 includes a second support bar 4231 and a second rotating disk 4232. The front side of the support disk 421 is provided with a plurality of first limiting grooves 4211 along the circumferential direction, and the back side of the support disk 421 is provided with a plurality of first limiting grooves 4211 along the circumferential direction. A plurality of second limiting grooves 4212 are provided in the circumferential direction. The first limiting grooves 4211 and the second limiting grooves 4212 are both arranged in the radial direction of the support disk 421, and a second limiting groove 4212 is provided between two adjacent first limiting grooves 4211. The first support bar 4221 is slidably disposed in the first limiting groove 4211, and the second support bar 4231 is slidably disposed in the second limiting groove 4212. Limiting posts 4223 are fixed on the upper surfaces of the first support bar 4221 and the second support bar 4231. Both the first rotating disk 4222 and the second rotating disk 4232 are provided with An arc-shaped linkage groove 4224 is provided, and a limiting post 4223 is slidably disposed within the corresponding arc-shaped linkage groove 4224; the end of the first support bar 4221 is provided with a tooth-forming block 425, and the end of the second support bar 4231 is provided with an arc-shaped support piece 426, the outer surface of the arc-shaped support piece 426 is in contact with the inner surface of the adjacent tooth-forming block 425, a rotating shaft 4210 is fixed in the middle of the second rotating disk 4232, the first rotating disk 4222 is fixed on the side wall of the rotating shaft 4210, and the side wall of the first rotating disk 4222 and the support disk 421 are rotated by a rotating bearing 4213. The rotating shaft 4210 is connected to a rotating motor 424 at its end. A fixed cylinder 427 is fixed to the back of the support plate 421. A fixed rod 411 is provided inside the mold head housing 41. Fixed strips 412 are provided on opposite sides of the fixed rod 411. The fixed strips 412 are fixed to the inner side wall of the mold head housing 41. The fixed cylinder 427 is fixed to the fixed rod 411. An elastic sealing layer 428 is provided on the outer wall of the tooth forming block 425 and the arc-shaped support plate 426. The right side of the elastic sealing layer 428 extends and is fixed to the fixed cylinder 427. The left side seals and wraps the left side of the irregular diameter mandrel 42.

[0039] according to Figures 11-12 As shown, the vacuum forming mold 5 includes a lower mold 51 and an upper mold 52. The surfaces of the lower mold 51 and the upper mold 52 are provided with undulating grooves 511 that match the shape of the outer wall of the ceramic body 1. Vacuum suction holes 512 are evenly distributed in the undulating grooves 511.

[0040] Working principle: According to Figures 1 to 13As shown, S1 prepares the support clay: ceramic powder is mixed with binder and lubricant, and after vacuum kneading and aging, a plastic clay is obtained; S2 extrusion molding: the support clay prepared in S1 is added to an extruder, and the clay flows through the irregular diameter extrusion die 4 for extrusion. During the extrusion process, the mandrel is fixed, and the clay naturally forms cavities 31 and channels 32 that match the contour of the mandrel as it flows through the mandrel, thereby forming a support wet blank with an irregular cross-section and a beaded structure 3 in the axial direction; during the extrusion process, a clay extrusion space 43 is formed between the die shell 41 of the irregular diameter extrusion die 4 and the irregular diameter mandrel 42, and the rotating shaft 4210 is driven to rotate by the rotary motor 424, driving the first A rotating disk 4222 and a second rotating disk 4232 rotate synchronously. The arc-shaped linkage groove 4224 on the first rotating disk 4222 drives the first support bar 4221 to slide radially along the first limiting groove 4211 on the front of the support disk 421 via the limiting post 4223, thereby precisely adjusting the radial position of the tooth-forming block 425 at the end of the first support bar 4221 to form the tooth tip 211. At the same time, the arc-shaped linkage groove 4224 on the second rotating disk 4232 drives the second support bar 4231 to slide radially along the second limiting groove 4212 on the back of the support disk 421 via the limiting post 4223, thereby precisely adjusting the radial position of the arc-shaped support piece 426 at the end of the second support bar 4231 to form the tooth valley. 212, because the first limiting groove 4211 and the second limiting groove 4212 are staggered along the circumferential direction, the tooth tip 211 and tooth valley 212 form an alternating continuous irregular cross-sectional profile on the inner wall of the fluid channel 2. At the same time, through the axial diameter change profile of the irregular diameter mandrel 42, the fluid channel 2 forms a bead-like structure 3 along the axial direction, which is composed of alternating cavities 31 and channels 32; S3 Fixed-length cutting and vacuum shaping: the extruded support wet blank is cut into a single blank at a fixed length. The cut single blank is immediately placed into the vacuum shaping mold 5. The surfaces of the lower mold 51 and the upper mold 52 are provided with undulating grooves 511 that match the shape of the outer wall of the ceramic body 1. The undulating grooves 511 are evenly distributed in the vacuum. The suction hole 512 is connected to the vacuum channel preset inside the mold. Negative pressure is applied to the wet blank for vacuum adsorption and shaping. It is maintained for 5 to 15 minutes. The vacuum negative pressure is applied to the outer wall of the ceramic body 1 through the uniformly distributed vacuum suction hole 512, so that it fits tightly against the inner wall of the undulating groove 511. This effectively constrains the external dimensions of the ceramic body 1 and prevents it from deforming due to gravity or internal stress before it is fully hardened. This allows the surface of the wet blank to be initially hardened and lock the irregular cross section and beaded structure 3. Then the blank is demolded and taken out. S4 Drying and pre-sintering: The blank after vacuum shaping is dried in a step-by-step manner to completely remove the residual moisture in the blank. Then it is pre-sintered at 800 to 1000℃ to obtain the porous support 11.S5 Coating of Transition and Separation Layers: A transition layer 12 and a separation layer 13 are sequentially coated onto the inner wall of the porous support 11 using an impregnation method. The pre-sintered porous support 11 is placed vertically or at an angle. The prepared transition layer slurry is poured into the support from one end, filling the entire fluid channel 2. After holding for 10–60 seconds, the slurry is allowed to flow out naturally, forming a uniform wet film on the inner wall of the support. After drying, the separation layer sol is coated using the same method. Due to the axial beaded structure 3 and irregular cross-section of the fluid channel 2, appropriate coating techniques are used. Adjust the slurry viscosity and impregnation time to ensure the uniformity of coating thickness at the tooth top 211 and tooth valley 212, cavity 31 and pore 32; S6 High-temperature co-sintering: The coated membrane blank is sintered at a high temperature of 1200-1350℃ to make the transition layer 12 and separation layer 13 firmly bonded to the porous support 11, forming an asymmetric multilayer structure from the inside out, consisting of separation layer 13, transition layer 12 and porous support 11, and finally obtaining a hollow ceramic ultrafiltration membrane product with comprehensive performance of high flux, high precision, anti-fouling and long life. The feed liquid to be treated enters the ceramic body 1 from one end of the membrane module through a fluid channel 2 opened along the axial direction. Due to the irregular cross-section of the fluid channel 2, the inner wall of the channel has a circumferentially undulating profile. During the flow, the fluid is induced to generate axial secondary flow, which effectively destroys the laminar boundary layer and enhances radial mixing, continuously inhibiting the migration of particles to the membrane surface. At the same time, since the fluid channel 2 has a beaded structure 3 along the axial direction, which is composed of several cavities 31 and several channels 32 arranged alternately along the axial direction, and the cross-sectional area of ​​the cavities 31 is larger than that of the channels 32, the fluid undergoes periodic expansion and contraction when flowing between the cavities 31 and the channels 32, forming a stable reflux zone in the cavity 31, which generates a jet impact on the membrane surface to peel off the deposited pollutants. Through the synergistic effect of the irregular cross-section and the axial beaded structure 3, a three-dimensional turbulent field is constructed in the flow channel, realizing dynamic cleaning of the entire area of ​​the membrane surface at all times. When the cross-section of the fluid channel 2 is preferably toothed 210 and is composed of several tooth tips 211 and tooth valleys 212 connected alternately, the fluid velocity increases at the tooth tips 211 due to the contraction of the channel cross-sectional area, forming a local high-pressure scouring zone that exerts a strong shearing effect on the membrane surface. At the tooth valleys 212, the fluid velocity decreases due to the expansion of the channel cross-sectional area, inducing a stable axial secondary flow that forms a vortex disturbance zone. The high-speed scouring of the tooth tips 211 and the vortex disturbance of the tooth valleys 212 work together to make each area of ​​the inner wall of the channel undergo periodic dynamic cleaning. When the cavity 31 and the channel 32 are preferably provided with an expansion section 33 and a contraction section 34, and the cross-sectional area of ​​the expansion section 33 and the contraction section 34 gradually changes along the axial direction, the fluid expands in the expansion section 33 in a progressive manner to form an orderly backflow zone, and contracts in the contraction section 34 in a gentle manner to eliminate the flow dead zone and prevent excessive development of vortices, so that the overall fluid dynamic performance of the entire beaded structure 3 is optimized.

Claims

1. A hollow ceramic ultrafiltration membrane, characterized in that, The system includes a ceramic body (1), in which a fluid channel (2) is provided along the axial direction. The cross-section of the fluid channel (2) is irregular, giving the inner wall of the channel a circumferentially undulating profile. The fluid channel (2) has a beaded structure (3) along the axial direction. The beaded structure (3) is composed of several cavities (31) and several channels (32) arranged alternately along the axial direction. The cross-sectional area of ​​the cavity (31) is larger than the cross-sectional area of ​​the channel (32).

2. The hollow ceramic ultrafiltration membrane according to claim 1, characterized in that, An expansion section (33) and a contraction section (34) are provided between the cavity (31) and the channel (32), and the cross-sectional area of ​​the expansion section (33) and the contraction section (34) gradually changes along the axial direction.

3. A hollow ceramic ultrafiltration membrane according to claim 1, characterized in that, The cross-section of the fluid channel (2) is toothed (210), which is composed of several tooth tips (211) and tooth valleys (212) connected alternately. The cross-sectional area of ​​the channel is smallest at the tooth tip (211) and largest at the tooth valley (212).

4. The hollow ceramic ultrafiltration membrane according to claim 1, characterized in that, The ceramic body (1) has an asymmetric multilayer structure, which includes a separation layer (13), a transition layer (12) and a porous support (11) from the inside to the outside.

5. A method for preparing a hollow ceramic ultrafiltration membrane, characterized in that, Includes the following steps: S1: Prepare the support clay by mixing ceramic powder with binder and lubricant to obtain a plastic clay. S2: Extrusion molding, the support clay prepared in S1 is added to the extruder, the clay flows through the irregular diameter extrusion die (4) and is extruded to form a support wet blank with an irregular cross section and a beaded structure in the axial direction; S3: Fixed-length cutting and vacuum shaping. The extruded support wet blank is cut to a fixed length to obtain a single blank. The cut single blank is immediately placed into the vacuum shaping mold (5). Negative pressure is applied to the wet blank for vacuum adsorption shaping. It is kept for 5 to 15 minutes to allow the surface of the wet blank to harden initially, lock the irregular cross section and beaded structure, and then demold and take out the blank. S4: Drying and pre-sintering: The blank after vacuum shaping is dried in a stepwise manner, and then pre-sintered at 800-1000℃ to obtain a porous support (11). S5: Coating transition layer and separation layer, coating transition layer (12) and separation layer (13) sequentially on the inner wall of the porous support (11) to form an asymmetric multilayer structure; S6: High-temperature co-sintering, the coated film blank is sintered at a high temperature of 1200-1350℃ to obtain the finished product.

6. The method for preparing a hollow ceramic ultrafiltration membrane according to claim 5, characterized in that, The irregular diameter extrusion die (4) includes a die housing (41) disposed at the discharge end of the extruder barrel and an irregular diameter mandrel (42) disposed inside the die housing (41), and a mud extrusion space (43) is formed between the die housing (41) and the irregular diameter mandrel (42).

7. The method for preparing a hollow ceramic ultrafiltration membrane according to claim 5, characterized in that, The irregular diameter mandrel (42) includes a support disk (421), a toothed forming component (422), and a toothed transition support component (423). The toothed forming component (422) is disposed on the front side of the support disk (421), and the toothed transition support component (423) is disposed on the back side of the support disk (421).

8. The method for preparing a hollow ceramic ultrafiltration membrane according to claim 7, characterized in that, The tooth-forming assembly (422) includes a first support bar (4221) and a first rotating disk (4222). The tooth-shaped transition support assembly (423) includes a second support bar (4231) and a second rotating disk (4232). The front side of the support disk (421) is provided with a plurality of first limiting grooves (4211) along the circumferential direction, and the back side of the support disk (421) is provided with a plurality of second limiting grooves (4212) along the circumferential direction. The first limiting grooves (4211) and the second limiting grooves (4212) are both arranged along the radial direction of the support disk (421), and a second limiting groove (4212) is provided between two adjacent first limiting grooves (4211). The first support bar (4221) is slidably disposed on the first limiting groove. Inside the groove (4211), the second support bar (4231) is slidably disposed in the second limiting groove (4212); the upper surfaces of the first support bar (4221) and the second support bar (4231) are both fixed with limiting posts (4223), and the first rotating disk (4222) and the second rotating disk (4232) are both provided with arc-shaped linkage grooves (4224), and the limiting posts (4223) are slidably disposed in the corresponding arc-shaped linkage grooves (4224); the end of the first support bar (4221) is provided with a tooth-forming block (425), and the end of the second support bar (4231) is provided with an arc-shaped support piece (426), and the outer surface of the arc-shaped support piece (426) is in contact with the inner surface of the adjacent tooth-forming block (425).

9. The method for preparing a hollow ceramic ultrafiltration membrane according to claim 8, characterized in that, A rotating shaft (4210) is fixed in the middle of the second rotating disk (4232). The first rotating disk (4222) is fixed on the side wall of the rotating shaft (4210). The side wall of the first rotating disk (4222) is rotatably connected to the support disk (421) through a rotating bearing (4213). A rotating motor (424) is fixed at the end of the rotating shaft (4210). A fixing cylinder (427) is fixed on the back of the support disk (421). A fixing rod is provided inside the mold head housing (41). 411), the fixing rod (411) has fixing strips (412) on opposite sides. The fixing strips (412) are fixed to the inner wall of the mold head housing (41). The fixing cylinder (427) is fixed on the fixing rod (411). The outer wall of the tooth forming block (425) and the arc support plate (426) is provided with an elastic sealing layer (428). The right side of the elastic sealing layer (428) extends and is fixed on the fixing cylinder (427). The left side seals and wraps the left side of the irregular diameter mandrel (42).

10. The method for preparing a hollow ceramic ultrafiltration membrane according to claim 5, characterized in that, The vacuum forming mold (5) includes a lower mold (51) and an upper mold (52). The surfaces of the lower mold (51) and the upper mold (52) are provided with undulating grooves (511) that match the shape of the outer wall of the ceramic body (1). Vacuum suction holes (512) are evenly distributed in the undulating grooves (511).

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