Antifouling piezoelectric ceramic membrane and preparation method thereof

Abstract

The invention discloses an anti-fouling piezoelectric ceramic membrane which comprises a support body, a coil and a piezoelectric ceramic separation layer, the support body is made of porous ceramic with a through hole in the middle; the coil is a closed loop composed of a lead coil and a crystal oscillator; the piezoelectric separation layer is coated on the inner wall of the through hole of the support body; and the coil is arranged between the support body and the piezoelectric ceramic separation layer. When a medium containing electrolyte passes through a membrane hole, the coil generates induction direct current, the direct current is converted into positive wave pulse current through the oscillator, the wound and overlapped piezoelectric ceramic membrane separation layer is excited, ultrasonic vibration is generated, and therefore the membrane dirt blocking condition is reduced, the use efficiency of the ceramic membrane is improved, and the maintenance and use cost is reduced.

Description

Technical Field

[0001] This invention relates to ceramic membranes, and more particularly to a process for a self-generating ultrasonic anti-fouling piezoelectric ceramic membrane structure. Background Technology

[0002] Membrane separation technology uses selectively permeable membranes as the separation medium. By applying pressure across the membrane, components on the feed side selectively permeate through the membrane to achieve separation and purification. For example, the currently mainstream cross-flow membrane filtration method offers advantages such as no phase change, low energy consumption, high efficiency, and simple process. Ceramic membranes possess advantages such as resistance to acid and alkali corrosion, organic solvents, and high temperature and pressure, thus having a very broad application prospect. However, membrane fouling is a common problem faced by membrane separation technology in practical applications. Pollutants accumulate on the membrane surface or within the membrane pores, causing membrane fouling. This not only severely reduces membrane filtration flux and energy efficiency but also affects the membrane's retention performance of the separated substances, directly impacting the economy and reliability of the membrane separation process.

[0003] Piezoelectric materials are crystalline materials that exhibit a voltage across their terminals when subjected to pressure. After high-voltage polarization, the previously randomly oriented grains within a piezoelectric material will align with the applied electric field under a DC voltage, maintaining a state of separation between the positive and negative electrodes after the electric field is removed. Applying an AC or pulsed DC electric field to its terminals can induce mechanical vibration in the piezoelectric material. Based on the characteristic that piezoelectric materials can convert AC current into mechanical vibration, they can be fabricated as separation layers in ceramic membranes. This allows the membrane material to act as an in-situ ultrasonic emission source, generating mechanical vibration during the separation process, thereby mitigating or even preventing membrane fouling.

[0004] Currently, reports on the preparation of antifouling separation membranes using piezoelectric materials mainly include: Darestani (J Membrane Sci, 2013, 435: 226-232) prepared a symmetrical PVDF organic vibrating membrane with a pore size of 220 nm and a thickness of 123 μm using PVDF as raw material; Qiu (J Membrane Sci, 2015, 44: 120-135) prepared a symmetrical PZT electroceramic vibrating membrane with a pore size of 365 nm using lead zirconate titanate ceramic as raw material; and Nanjing University of Technology, a non-symmetrical in-situ ultrasonic antifouling membrane and its preparation method. These in-situ ultrasonic membranes all exhibit good antifouling, permeation, and separation performance. However, these advantages are mainly in terms of material technology; there are no specific methods or results on how to solve the problem of generating ultrasonic mechanical vibration when the membrane element is connected to a power source during preparation and use. Therefore, antifouling piezoelectric ceramic membrane elements with a self-powered structure are of great significance in actual industrial production. Summary of the Invention

[0005] The problem this invention aims to solve is to address the shortcomings of the prior art by proposing an innovative solution. This solution utilizes a structure in which a closed coil and piezoelectric material are intertwined and overlapped within the membrane element. During use, as the flowing medium passes through the ceramic membrane, an induced current is generated in the closed coil within the ceramic membrane element. Under the inverse piezoelectric effect, the piezoelectric material in the membrane element's separation layer is excited to generate mechanical vibration, achieving an electrical-to-mechanical energy conversion. This results in micron-level ultrasonic vibration generated in the piezoelectric ceramic separation layer. Simultaneously, the low-voltage pulse current in the coil also has a certain electrolytic effect on fouling substances in the water, thereby reducing or even preventing membrane fouling.

[0006] To solve the above problems, the present invention adopts the following solution: an anti-fouling piezoelectric ceramic membrane, characterized in that it comprises a support, a coil, and a piezoelectric ceramic separation layer; the support is a porous ceramic with a through hole in the middle; the coil is a closed loop composed of a conductive coil and a crystal oscillator; the piezoelectric ceramic separation layer contains abundant pores and is coated on the inner wall of the through hole of the support, and the coil of the closed loop is sandwiched between the piezoelectric ceramic separation layer and the support. The conductive coil is spirally coiled in a spring-like shape, with its ends connected by wires, and the crystal oscillator is connected therein.

[0007] Furthermore, the antifouling piezoelectric ceramic membrane is characterized in that the support is a sheet-like or tubular porous ceramic structure, with the through holes of the tubular porous ceramic structure disposed at its center, and the through holes of the sheet-like porous ceramic structure disposed side by side inside its interior.

[0008] Furthermore, the anti-fouling piezoelectric ceramic membrane is characterized in that the thickness of the piezoelectric ceramic separation layer is 20-200 μm, and it completely covers the coil.

[0009] Furthermore, the antifouling piezoelectric ceramic membrane is characterized in that the piezoelectric ceramic separation layer is made of a piezoelectric crystal material pore-forming agent.

[0010] Furthermore, the antifouling piezoelectric ceramic membrane is characterized in that the piezoelectric crystal material includes one or more of silicon oxide, zirconium oxide, titanium oxide, oxidant, and quartz; and the pore-forming agent is NH4HCO3, NH4Cl, carbon powder, coal powder, starch, sawdust, polyvinyl alcohol, or polyvinyl chloride.

[0011] A method for preparing an antifouling piezoelectric ceramic membrane, characterized by comprising the following steps:

[0012] A. Pre-set the slot for the crystal oscillator component in the support mold, demold the ceramic blank, calcine and shape it to form a sheet or tubular support with through holes.

[0013] B. Use a wire winder to wind the metal wire into the through hole to form a coil, embed the crystal oscillator in the preset position, and spot weld the crystal oscillator to the beginning and end of the coil.

[0014] C. Disperse the piezoelectric crystal material and pore-forming agent for preparing the piezoelectric ceramic separation layer in deionized water until uniformly dispersed.

[0015] Film-forming solution;

[0016] D. Spin-coating the film-forming liquid into the through-hole of the support, drying to form a film, then calcining at low temperature to make the film porous, and finally cooling naturally to obtain an inorganic porous membrane.

[0017] F. Polarization is performed under a high-voltage electric field to transform the inorganic porous membrane into a piezoelectric ceramic separation layer with piezoelectric properties, resulting in the finished antifouling piezoelectric ceramic membrane.

[0018] Furthermore, the method for preparing the antifouling piezoelectric ceramic membrane is characterized by repeating steps C and D 1-4 times to prepare a piezoelectric ceramic separation layer with a smaller pore size.

[0019] Working Principle: When filtering high-salt leachate wastewater using a single-pore tubular ceramic membrane, water enters through the central through-hole, increasing the pressure of the central circulating water. Water permeates through the outer layer of the ceramic membrane and separates, resulting in a gradual increase in COD concentration in the central effluent. During this filtration process, the leachate containing electrolytes passes through the central coil. As the water flows unidirectionally through the central annular coil, a magnetic field change occurs, inducing an electromotive force in the coil through electromagnetic effects, forming direct current. This direct current is converted into a positive-wave pulsed current by the crystal oscillator on the coil. The voltage is proportional to the electrolyte concentration, flow rate, and flow volume in the leachate, while the current is proportional to the number of coil turns and the coil conductivity. The current is conducted within the coil, passing through the piezoelectric ceramic separation layer wound and stacked on the coil. This piezoelectric ceramic separation layer generates ultrasonic vibrations, and the pulsed current also has a certain electrolytic effect, resulting in a significantly better anti-fouling effect than ordinary ceramic membranes.

[0020] The technical effects of this invention are as follows:

[0021] 1) In this invention, piezoelectric ceramic materials made from silicon dioxide, zirconium oxide, titanium oxide, lead oxide, etc. are used to prepare the main separation layer of the ceramic membrane. The thickness of a single layer is about 20 to 200 μm, so that the membrane material becomes an in-situ ultrasonic emission source, generating ultrasonic mechanical vibration during the filtration and separation process, thereby alleviating or even avoiding membrane fouling.

[0022] 2) In this invention, the induced current generated by the membrane filter medium through a closed conductive metal coil is used as the system power source, which solves the problem of the external power source required for the vibration of the piezoelectric ceramic membrane.

[0023] 3) In this invention, an electronic component with a crystal oscillator mounted on an induction coil is used to convert direct current into pulse current. The closed coil overlaps the piezoelectric ceramic filter layer and the current conductive separation layer. At the same time, the pulse current also has a certain electrolytic effect on the organic matter that is fouling the membrane separation layer. The dual effect of vibration and electrolysis improves the stability of membrane flux, reduces the fouling rate, thereby reducing the overall system maintenance cost and improving the efficiency of use. Attached Figure Description

[0024] Figure 1 This is a perspective view of an antifouling piezoelectric ceramic membrane structure with a tubular porous ceramic structure.

[0025] Figure 2 This is a schematic diagram of an antifouling piezoelectric ceramic membrane with a tubular porous ceramic structure.

[0026] Figure 3 This is a schematic diagram of a cross-section of an antifouling piezoelectric ceramic membrane with a tubular porous ceramic structure.

[0027] Figure 4 This is a schematic diagram of an antifouling piezoelectric ceramic membrane structure with a sheet-like porous ceramic structure.

[0028] Figure 5 This example compares the membrane flux of an antifouling piezoelectric ceramic membrane with that of an existing ordinary piezoelectric ceramic membrane.

[0029] Among them, 1. support body, 2. closed-loop coil, 3. crystal oscillator, and 4. piezoelectric ceramic separation layer. Detailed Implementation

[0030] The present invention will now be described in further detail with reference to the accompanying drawings.

[0031] like Figure 1 , Figure 2 , Figure 3 As shown, an antifouling piezoelectric ceramic membrane has an outer support made of porous ceramic and an inner separation layer made of porous piezoelectric ceramic. The support has an average pore size distribution of 100-3000 nm, and the separation layer has an average pore size distribution of 1-1000 nm. The inorganic material used to prepare the porous piezoelectric ceramic is a mixture of silicon oxide, zirconium oxide, and titanium oxide; the particle size of the inorganic material is 10-1000 nm. The support is a tubular ceramic membrane structure; the separation layer has 5 layers, each 200 μm thick, completely covering the coil. The resonant frequency of the piezoelectric ceramic membrane in the separation layer is 50 kHz. A closed conductive metal coil, made of pure copper with high conductivity and a diameter of 200 μm, is sandwiched between the support and the piezoelectric ceramic separation layer. The coil is connected at both ends, and an electronic component of a crystal oscillator is connected to the circuit. The oscillator frequency is 50 kHz, the same as the frequency of the polarized piezoelectric ceramic membrane. The antifouling piezoelectric ceramic membrane with a sheet-like porous ceramic structure is shown below. Figure 4 As shown, it has multiple through holes arranged side by side in the support body.

[0032] The specific steps of the above-mentioned method for manufacturing the antifouling piezoelectric ceramic membrane are as follows: A. A pre-set slot for a crystal oscillator element is placed in the mold of the support body. The ceramic preform is demolded and calcined to form a sheet-like or tubular porous piezoelectric ceramic support body; B. A wire winder is used to wind a metal wire into a coil inside the hole, and the oscillator is embedded in the pre-set position. The ends are then spot-welded together; C. The inorganic material and pore-forming agent for preparing the piezoelectric ceramic separation layer are dispersed in deionized water and evenly dispersed to prepare a film-forming solution; D. The film-forming solution is spin-coated into the pores of the porous ceramic support body and dried to form a separation membrane layer; E. Low-temperature calcination forms pores in the separation layer, and natural cooling yields a porous ceramic membrane; F. Steps C and D can be repeated 1-4 times to prepare a porous ceramic membrane with a smaller pore size; G. The prepared inorganic porous membrane is polarized under a high-voltage electric field to give the piezoelectric ceramic membrane piezoelectric properties, resulting in the finished antifouling piezoelectric ceramic membrane.

[0033] Table 1: Comparison of membrane flux between the antifouling piezoelectric ceramic membrane of the example and existing ordinary piezoelectric ceramic membranes. See appendix for details. Figure 5 .

[0034] Table 2: Membrane flux after 36 hours.

[0035] project Membrane flux after 36 hours Ordinary piezoelectric ceramic membrane 26.44％ Example: Antifouling piezoelectric ceramic membrane 55.62％

[0036] It can be seen that the flux decrease of the antifouling piezoelectric ceramic membrane after 36 hours is significantly less than that of the ordinary ceramic membrane.

Claims

1. An anti-fouling piezoelectric ceramic membrane, characterized in that, It includes a support, a coil, and a piezoelectric ceramic separation layer; the support is a porous ceramic with a through hole in the middle; the coil is a closed circuit composed of a conductive coil and a crystal oscillator; the piezoelectric ceramic separation layer contains abundant pores, the piezoelectric ceramic separation layer is coated on the inner wall of the through hole of the support, and the coil of the closed circuit is sandwiched between the piezoelectric ceramic separation layer and the support.

2. The antifouling piezoelectric ceramic membrane according to claim 1, characterized in that, The support is a sheet-like or tubular porous ceramic structure, with through holes in the tubular porous ceramic structure located at its center, and through holes in the sheet-like porous ceramic structure arranged side by side inside its interior.

3. The antifouling piezoelectric ceramic membrane according to claim 1, characterized in that, The piezoelectric ceramic separation layer has a thickness of 20~200um and completely covers the coil.

4. The antifouling piezoelectric ceramic membrane according to claim 1, characterized in that, The piezoelectric ceramic separation layer is made of piezoelectric crystal material and pore-forming agent.

5. The antifouling piezoelectric ceramic membrane according to claim 4, characterized in that, The piezoelectric crystal material includes one or more of silicon oxide, zirconium oxide, titanium oxide, oxide, and quartz; the pore-forming agent is NH4HCO3, NH4Cl, carbon powder, coal powder, starch, sawdust, polyvinyl alcohol, or polyvinyl chloride.

6. A method for preparing an antifouling piezoelectric ceramic membrane according to any one of claims 1 to 5, characterized in that, Includes the following steps: A. Pre-set the slot for the crystal oscillator component in the support mold, demold the ceramic blank, calcine and shape it to form a sheet or tubular support with through holes. B. Use a wire winder to wind the metal wire into the through hole to form a coil, embed the crystal oscillator in the preset position, and spot weld the crystal oscillator to the beginning and end of the coil. C. Disperse the piezoelectric crystal material and pore-forming agent for preparing the piezoelectric ceramic separation layer in deionized water and prepare a film-forming solution by uniform dispersion. D. Spin-coating the film-forming liquid into the through-hole of the support, drying to form a film, then calcining at low temperature to make the film porous, and finally cooling naturally to obtain an inorganic porous membrane. F. Polarization is performed under a high-voltage electric field to transform the inorganic porous membrane into a piezoelectric ceramic separation layer with piezoelectric properties, resulting in the finished antifouling piezoelectric ceramic membrane.

7. The method for preparing the antifouling piezoelectric ceramic membrane according to claim 6, characterized in that, Repeat steps C and D 1-4 times to prepare a piezoelectric ceramic separation layer with a smaller pore size.

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