Preparation method of low-surface-energy small-pore anti-pollution PTFE-ZrO2 composite membrane

Abstract

The application provides a composite membrane combining polytetrafluoroethylene (PTFE) nanoparticles and zirconium oxide (ZrO2) nanocrystals, the surface energy of the composite membrane is effectively reduced, thereby reducing the microbial adhesion in the fermentation broth. The ZrO2 nanocrystals can form small pores, reducing protein plugging and adsorption, and further relieving membrane pollution in the fermentation broth. This double defense mechanism significantly improves the stable flux of the composite membrane in the ethanol fermentation broth, and widens the application prospect of the composite membrane in fermentation broth clarification and biological product recovery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of ceramic membranes, and particularly relates to a low-surface-energy small-pore anti-pollution PTFE-ZrO2 composite membrane and a preparation method thereof. BACKGROUND

[0002] The biological fermentation liquid system is very complex, and has the characteristics of multi-scale, multi-phase and multi-medium. In addition to the target product, it also contains cell debris, bacteria, proteins, polysaccharides, metabolites, pigments and salt ions. This complexity makes the ceramic membrane prone to problems such as bacterial adhesion, protein adsorption and small molecular debris blocking pores during the filtration process. Microbial contamination accounts for about 45% of membrane pollution in the fermentation liquid system. During operation, the microorganisms in the fermentation liquid will adhere to the membrane surface, deposit and reproduce, and at the same time secrete extracellular polymeric substances (EPS), which further enhance their stable adhesion on the membrane surface. This will lead to the formation of dense biofilm, which seriously affects the performance of the ceramic membrane.

[0003] At present, an effective strategy to slow down microbial contamination in the membrane separation process is to adjust the surface energy of the membrane to reduce the adhesion of bacteria. Surface energy plays a key role in determining the adhesion of microorganisms to the surface of the material. The adjustment of the surface energy of the ceramic membrane can be realized by introducing low-surface-energy substances. The hydrophilic surface of the ceramic membrane has the characteristics of dirt resistance, and can form a hydration layer to slow down membrane pollution. However, during long-term operation, the continuous accumulation of pollutants on the surface may interrupt the function of the hydration layer. The introduction of low-surface-energy organic materials can fundamentally change the surface energy of the ceramic membrane, so that it can continuously resist the adhesion of microorganisms and effectively prevent the formation of biofilm on the membrane surface in long-term operation. Among many low-surface-energy materials, polytetrafluoroethylene (PTFE) is considered to be an ideal material for reducing the surface energy of the ceramic membrane due to its excellent chemical stability and high-temperature resistance.

[0004] The incorporation of PTFE particles into ZrO2 particles to prepare a low-surface-energy ultrafiltration membrane involves an organic-inorganic hybrid process, and faces two key problems. One is the dispersibility of the membrane preparation liquid. Physical mixing of materials with different particle sizes and charges usually leads to particle agglomeration and non-uniformity, resulting in problems such as uneven membrane thickness and surface cracking. The other key problem lies in the sintering process of the membrane. Ceramic membranes usually require high sintering temperatures, while the melting point of PTFE is relatively low, making the composite membrane unsuitable for sintering at high temperatures. Otherwise, the melting of PTFE particles will destroy the integrity and anti-pollution performance of the membrane surface. Therefore, it is necessary to develop a sintering process suitable for the composite membrane.

[0005] In this study, we prepared a PTFE-ZrO2 composite membrane, which can reduce membrane fouling and improve membrane flux in fermentation broth. By taking advantage of the synergistic effect of the hydrophilicity of ZrO2 and the low surface energy of PTFE, the anti-fouling performance of the membrane is enhanced. We studied the dispersion effect and mechanism of dispersants and pH on ZrO2 dispersion and PTFE emulsion to optimize the stable dispersion conditions of PTFE-ZrO2 mixed solution. In addition, the preparation process of the membrane was optimized, and its permeation performance and anti-fouling performance in simulated and real fermentation broth clarification were studied. SUMMARY

[0006] In order to reduce membrane fouling during fermentation broth clarification and improve membrane flux in fermentation broth, the present application provides an anti-fouling PTFE-ZrO2 composite membrane with specific surface energy and its preparation method, which has the characteristics of good anti-fouling performance, stable permeation and high flux.

[0007] The technical scheme of the present application is:

[0008] A preparation method of a low-surface-energy small-pore anti-fouling PTFE-ZrO2 composite membrane, comprising the following steps:

[0009] Step 1, mixing PTFE emulsion and ZrO2 dispersion to obtain PTFE-ZrO2 dispersion;

[0010] Step 2, coating PTFE-ZrO2 dispersion on the ceramic membrane tube by dip coating;

[0011] Step 3, drying and sintering to obtain PTFE-ZrO2 composite membrane.

[0012] The solid content of the ZrO2 dispersion is 1-5%, the solid content of the PTFE emulsion is 40-70%, and the volume ratio of the PTFE emulsion to the ZrO2 dispersion is 1:9-1:1, preferably 1:2-1:4.

[0013] The pH value of the PTFE emulsion and the ZrO2 dispersion is 9-13.

[0014] The PTFE emulsion and / or ZrO2 dispersion also contains a dispersant, and the dispersant is selected from NH4PAA or AEO-3, NH4PAA is used in the ZrO2 dispersion, and the mass ratio of NH4PAA to ZrO2 is 0.005-0.05, AEO-3 is used in the PTFE emulsion, and the mass ratio of AEO-3 to PTFE is 0.001-0.005.

[0015] The coating time of dip coating is 20-50s.

[0016] The sintering temperature of the step 3 is 300-350℃, preferably 335-345℃.

[0017] The surface roughness Ra of the composite film is 20-30nm, and the surface energy is 25-35mJ·m -2 The thickness of the composite film is 1-2μm.

[0018] Application of low-surface-energy microporous anti-fouling PTFE-ZrO2 composite film in fermentation broth clarification.

[0019] The clarification working conditions of the composite film are: membrane surface flow rate of 0.5-5m / s, transmembrane pressure difference of 0.1-1MPa.

[0020] Beneficial effects

[0021] The application prepares an anti-fouling PTFE-ZrO2 composite film with specific surface energy by mixing polytetrafluoroethylene (PTFE) emulsion into zirconium oxide (ZrO2) dispersion. The film not only reduces protein blockage and adsorption, but also reduces microbial adhesion by adjusting surface energy, thereby alleviating membrane fouling in fermentation broth. At the same time, the composite film of the application realizes the synergistic optimization of the double defense mechanism, improves the anti-fouling performance of the membrane, and has good prospects in fermentation broth clarification application. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 Characterization of ZrO2 dispersion and PTFE emulsion. (a) Zeta potential of ZrO2 dispersion and PTFE emulsion; (b) particle size distribution of ZrO2 dispersion; (c) particle size distribution of PTFE emulsion.

[0023] Figure 2 Schematic diagram of dispersion mechanism of PTFE and ZrO2 particles.

[0024] Figure 3 Effect of dispersant concentration on ZrO2 dispersion and PTFE emulsion under pH 11 conditions. (a) Zeta potential of ZrO2 dispersion; (b) particle size distribution of ZrO2 dispersion; (c) Zeta potential of PTFE emulsion; (d) particle size distribution of PTFE emulsion. Figure 4 Effect of different volume ratios on Zeta potential of PTFE-ZrO2 mixed dispersion.

[0025] Figure 5 Effect of sintering temperature on membrane surface morphology and permeation performance (V PTFE / V ZrO2=1:3). (a) Membrane surface morphology at 320°C; (b) Membrane surface morphology at 340°C; (c) Membrane surface morphology at 360°C; (d) Pure water permeability; (e) Water dynamic contact angle; (f) Diiodomethane dynamic contact angle (the initial static contact angle is shown in the figure).

[0026] Figure 6 Microstructural characterization. (a) Surface morphology of the composite film; (b) Zr distribution on the film surface; (c) F distribution on the film surface; (d) AFM images of the base film and composite film; (e) EDS line scan analysis (red line indicates the line scan trajectory).

[0027] Figure 7 Effect of PTFE doping level on surface energy and permeability. (a) Contact angle and surface free energy; (b) Pure water permeability of base film, ZrO2 film, and composite film.

[0028] Figure 8 Filtration tests in simulated ethanol fermentation broth. (a) Flux of the base membrane, ZrO2, and composite membrane in simulated ethanol fermentation broth; (b) Flux recovery rates (FRR) of the base membrane, ZrO2, and composite membrane after pure water and chemical cleaning.

[0029] Figure 9 : Cyclic antifouling test of membrane in simulated fermentation broth.

[0030] Figure 10 Filtration tests in ethanol fermentation broth. (a) Flux of the base membrane, ZrO2, and composite membrane in actual ethanol fermentation broth; (b) Flux recovery rates (FRR) of the base membrane, ZrO2, and composite membrane after pure water and chemical cleaning. DETAILED DESCRIPTION

[0031] Preparation of PTFE-ZrO2 dispersion and composite membrane

[0032] First, a ZrO2 dispersion (solid content 2%) and a PTFE emulsion (solid content 60%) were ultrasonically treated for 30 minutes. Subsequently, the pH values ​​of the ZrO2 dispersion and PTFE emulsion were adjusted with nitric acid or ammonia water, respectively. The corresponding dispersant was then added to each dispersion: fatty alcohol polyoxyethylene ether (AEO-3) was used to disperse PTFE particles, while ammonium polyacrylate (NH4PAA) was used to disperse ZrO2 particles. The two were mixed and stirred continuously for 30 minutes, maintaining a constant pH value throughout the process. After stirring, the PTFE-ZrO2 dispersion was obtained by ultrasonic treatment for 5 minutes, and then the composite membrane was prepared by dip coating. The base membrane used was an alumina microfiltration membrane with an average pore size of 100nm, and the coating time was 30s.

[0033] Due to the presence of PTFE emulsion and dispersant, the dispersion exhibits a certain degree of viscosity, so no additional thickening agent is added during preparation. The resulting composite membranes are named according to the volume ratio of PTFE and Zr02dispersion, for example, P1Z2 represents the volume ratio of PTFE and Zr02is 1:2.

[0034] Subsequently, the membrane tubes were dried at 25 °C for 12 h, and then transferred to an oven for drying at 70 °C and 110 °C for 12 h, respectively. Finally, the membrane tubes were placed in a muffle furnace for sintering at a specific temperature, with the sintering time controlled at 2 h. By controlling the solid content of the PTFE-Zr02mixed dispersion, adjusting the volume ratio of PTFE to Zr02, and changing the coating time, different composite membranes were prepared. In order to compare the performance of the composite membranes, a batch of Zr02membranes was prepared using Zr02dispersion under the same conditions.

[0035] Characterization of membranes

[0036] The wettability of the membranes was characterized by measuring the contact angle (OCA-25, Dataphysics, Germany). The droplet volume for testing was 3 μL, and three points were measured for each membrane tube to obtain the average value as the result. The surface free energy of the membrane was calculated using the Owens-Wendt-Kaelble equation by calculating the static water contact angle (WCA) and diiodomethane contact angle (DCA) of the membrane surface:

[0037]

[0038] where γ is the total surface free energy, γ D is the dispersive surface free energy, γ P is the polar surface free energy, θ is the static contact angle, and L and S represent the liquid and solid phases, respectively.

[0039] Simulation of fermentation broth filtration performance test

[0040] In order to study the anti-fouling performance of the prepared composite membranes, a simulated fermentation broth containing 5 g·L -1 of yeast, 8 wt% of ethanol, 10 g·L -1 of glucose, and 5 g·L -1 of sucrose was prepared for flux measurement in the simulated system.

[0041] In the cyclic anti-fouling test, a simulated fermentation broth containing 1 g·L -1 of bovine serum albumin (BSA), 5 g·L -1 of yeast, 8 wt% of ethanol, 10 g·L -1 of glucose, and 5 g·L -1A simulated ethanol fermentation broth of sucrose was used to accurately simulate the substances produced in the metabolic activities of microorganisms. During the test, the membrane tube was first tested with pure water for 60 minutes, and then filtered with the simulated fermentation broth for 60 minutes. This process was repeated three times, and then the membrane tube was washed with pure water for another 60 minutes. When cleaning the membrane tube, the membrane tube was washed with pure water for the first 30 minutes, while the permeation side was kept closed. Subsequently, the permeation side was opened, and the membrane tube was washed with pure water for another 30 minutes. The pure water flux of the membrane was then measured to determine the recovery rate of the pure water cleaning. Next, the membrane was chemically cleaned using 1.0 wt% NaOH and 1.0 wt% NaClO solutions for 1 hour, and then its pure water flux was tested. The entire process was repeated to obtain the flux recovery rate of different membranes after chemical cleaning.

[0042] Ethanol fermentation broth filtration performance test

[0043] Ethanol fermentation broth filtration experiments were conducted to evaluate the anti-fouling performance of different membranes in actual fermentation environments. The ethanol fermentation broth was obtained from Shougang Langze Technology Co., Ltd. The solid content of the fermentation broth was measured to be 3.6 wt%, and the protein content was 6.40 g·L -1 , determined using the Coomassie Brilliant Blue staining method.

[0044] Dispersion of PTFE-ZrO2 mixture

[0045] In order to obtain a composite membrane with excellent performance and integrity, it is necessary to obtain a well-dispersed PTFE-ZrO2 mixture. In solutions of different pH values, the surface charge of nanoparticles changes, which in turn affects their dispersion performance. Figure 1 It is shown that the isoelectric point of the ZrO2 dispersion is about 6.67, and it exhibits uniform particle size distribution (about 60-70 nm) under acidic and basic conditions. In contrast, the PTFE emulsion shows a negative Zeta potential in the pH range of 3-11, and the particle size remains around 200 nm with uniform distribution. Since the initial pH of the ZrO2 dispersion is about 3, and the pH of the PTFE emulsion is about 8, they have opposite charges, and direct mixing will cause particle aggregation due to mutual attraction. Adjusting the pH of the two dispersions to alkaline conditions above 9 will help to disperse the mixture, as they both exhibit negative Zeta potentials at this time.

[0046] In addition to the electrostatic effect under alkaline conditions, the dispersion is further optimized by introducing a dispersant to enhance the steric repulsion. Figure 2The dispersion mechanism of PTFE and Zr02 particles under alkaline conditions is shown in the schematic diagram. NH4PAA, as an anionic polyelectrolyte, is easily adsorbed onto the surface of Zr02 particles through chemical adsorption and ionized under alkaline conditions to form negatively charged carboxyl groups, which enhances the electrostatic repulsion between Zr02 particles. The dispersion of PTFE particles is attributed to the steric hindrance effect. The oxygen atoms (green circles in the figure) in the ether bond of the EO chain can form hydrogen bonds with water molecules, thereby forming a stable and thick hydration layer on the outer surface of the PTFE particles. This hydration layer can effectively prevent other particles from approaching, thereby promoting the stability of the two particles in the suspension.

[0047] Optimizing the dispersant concentration can achieve the best dispersion stability of the dispersion. As shown in a of FIG. Figure 3 When NH4PAA is added under the condition of pH 11, the absolute value of the Zeta potential of the Zr02 dispersion increases significantly, and the average particle size decreases. When the mass ratio of added NH4PAA to Zr02 is 0.01, the Zeta potential of the dispersion rises, and the particle size distribution becomes narrower (b of FIG. Figure 3 At the same time, it is found that the average particle size of Zr02 particles under pH 11 is significantly smaller than that under pH 9, and the particle size distribution is narrower. Figure 3 The Zeta potential of the PTFE emulsion in c of FIG. also shows an upward trend under pH 11 with the addition of AEO-3. The particle size distribution of PTFE particles under the condition of pH 11 is narrower and more concentrated than that under pH 9, and the average particle size is smaller when the mass ratio of AEO-3 is 0.0025 or 0.005 (d of FIG. Figure 3 Based on the above results, and considering that as little dispersant as possible should be added during dispersion, it is considered that when the mass ratio of NH4PAA to Zr02 is 0.01 and the mass ratio of AEO-3 to PTFE is 0.0025 under the condition of pH 11, the dispersion of the two dispersions is the most stable; this condition is used to prepare the composite membrane in the subsequent preparation process.

[0048] The key to enhancing the anti-fouling performance of the composite membrane is to adjust the surface energy to an appropriate range by controlling the proportion of PTFE. Figure 4 The change of Zeta potential of PTFE-Zr02 mixed solution with different volume ratios under pH 9 and 11 after adding the optimal concentration of dispersant is shown. Under the condition of pH 11, the Zeta potential value of each PTFE-Zr02 dispersion mixture is about -45 mV, and the absolute value of the Zeta potential is significantly higher than that under the condition of pH 9, indicating that after adding a certain amount of optimal dispersant under the condition of pH 11, the PTFE-Zr02 mixed solution is more stable.

[0049] Effect of sintering temperature on the surface morphology of the composite membrane

[0050] Figure 5 The surface morphology of composite membranes with a PTFE to ZrO2 volume ratio of 1:3 at different sintering temperatures is shown. TG-DSC curves show that the PTFE particles begin to melt at approximately 320°C and rapidly decompose above 500°C. Therefore, sintering temperatures of 320°C, 340°C, and 360°C were selected. The composite membranes sintered at 320°C and 340°C exhibit relatively intact surfaces. The membrane surface exhibits a slit-like pore structure, which is attributed to the irregular shape of the PTFE particles and the size difference between the two types of particles. As the temperature increases to 340°C, the slit-like pore structure narrows due to the tighter connection between the particles. However, when the temperature is further increased to 360°C, the PTFE particles remain molten, resulting in a large number of irregular pores on the membrane surface. Figure 5 It is further shown that the pure water permeability of the composite membrane sintered at 360℃ is significantly higher than that of the membranes sintered at 320℃ and 340℃. Figure 5 Figures e and f show that the dynamic contact angles of water and diiodomethane decrease faster. The permeability performance of the composite membranes sintered at 320℃ and 340℃ is not significantly different. The final sintering temperature is 340℃.

[0051] The effects of solid content and coating time on the integrity of the composite membrane were also investigated. The composite membrane obtained under the conditions of solid content of 0.9 wt% and coating time of 30 s showed better integrity and no obvious cracking. Figure 6 As shown in Figure a, under the optimized preparation conditions, the surface of the composite membrane is intact and has no obvious defects. Figure 6 The uniform distribution of Zr and F elements on the membrane surface in b and c of 6 indicates that PTFE exists in the membrane layer, proving that the composite membrane was successfully prepared. The FTIR spectrum further confirms this. Compared with the base membrane, the hybrid membrane has a -1 and 1150cm -1 Two new peaks appeared at , which were attributed to the -CF2- stretching vibration of PTFE molecules. Figure 6 The d shows that the surface roughness of the composite membrane is lower than that of the base membrane. Low surface roughness can reduce the attachment and accumulation of microorganisms on the membrane surface, thereby enhancing the anti-fouling performance of the composite membrane. Figure 6 From the EDS line scan analysis of the composite membrane cross section, it can be seen that the thickness of the composite membrane is about 1.2μm. F and Zr elements are mainly concentrated in the composite membrane layer, and the signal value decreases with increasing depth. On the contrary, the signal value of Al element increases with increasing depth. These results show that PTFE and ZrO2 particles are evenly distributed in the composite membrane layer, and there is a clear boundary between the composite membrane layer and the base membrane.

[0052] The antifouling performance is strongly dependent on the surface characteristics of the composite membrane. By adjusting the PTFE content in the zirconia membrane, compact ultrafiltration (UF) membranes with different surface energies can be prepared. The surface energy of each membrane is determined by calculating the static contact angle, such as Figure 7 As shown in a. The increase of PTFE content leads to an increase in the contact angle of the composite membrane and a decrease in the surface energy. With the gradual increase of PTFE content, the surface energy of the membrane increases from 73.82 mJ·m -2 and 76.72 mJ·m -2 The lowest value was 17.94 mJ·m -2 .

[0053] Pure water permeability of base film, ZrO2 film and composite film Figure 7 (b) Due to the smaller pore size and lower surface energy of the composite membrane, its permeability is lower than that of the base membrane. Furthermore, as the PTFE content in the membrane increases, permeability initially increases and then decreases. This initial increase in permeability is likely due to the increase in PTFE particles, which increases the pore size of the composite membrane. The subsequent decrease in permeability is likely due to the further increase in PTFE content, which weakens the hydrophilicity of the composite membrane.

[0054] The PTFE content in the hybrid membrane was further optimized by simulating fermentation broth filtration experiments. In the test, the temperature was maintained at 25°C and the membrane surface flow rate was 2 m·s -1 , the transmembrane pressure difference is 0.2MPa, the results are as follows Figure 8 The simulated fermentation broth caused serious contamination of the bottom membrane, resulting in a decrease in the flux from 323.0 L·m in 15 minutes. -2 ·h -1 Rapidly dropped to only 66.4L·m -2 ·h -1 After 90 minutes of operation, the flux of the bottom membrane stabilized at about 21 L·m -2 ·h -1 In contrast, the flux of the ZrO2 membrane and the composite membrane also decreased, but to a lesser extent than that of the base membrane. After 90 minutes of testing, the ZrO2 membrane achieved a higher stable flux of approximately 31 L·m -2 ·h -1 Among all the hybrid membranes tested, the P1Z3 composite membrane performed best, with the highest stable flux of 62.9 L·m -2 ·h -1 , while the stable flux of other composite membranes is mainly between 30-40 L·m -2 ·h -1 This is almost three times the stable flux of the bottom membrane and twice that of the ZrO2 membrane. Figure 8Figure b shows that effective chemical cleaning can remove most of the contaminants on the membrane surface. After pure water rinsing and chemical cleaning, the flux recovery rate (FRR) of the bottom membrane remained below 70%. All composite membranes exceeded 85%, with the P1Z3 composite membrane achieving an FRR as high as 96.9%. These results highlight the excellent anti-fouling properties of the composite membranes. Considering the pure water flux and application results in simulated fermentation broth, the P1Z3 composite membrane performed the best among all composite membranes.

[0055] The high stable flux and flux recovery rate (FRR) of the composite membrane can be attributed to two aspects. First, the -CF2- groups of the PTFE particles in the composite membrane provide low surface energy characteristics, which effectively weaken the interfacial bonding between the pollutants and the membrane surface. Under appropriate shear stress, the pollutants can be easily removed from the membrane surface. Although many studies have shown that in the surface energy range of 20-30mJ·m -2 Microbial attachment was minimized when the membrane was exposed to water, but these findings were primarily based on research into developing anti-fouling coating materials. In this study, the composite membrane had a rich porous structure. The presence of the porous structure and ZrO2 particles, as well as the difference in roughness, resulted in a decrease in the measured contact angle. Therefore, although the surface energy of the optimized composite membrane was higher than 20-30 mJ·m -2 Despite its high flux and FRR in the fermentation broth, the membrane's surface demonstrates its effective resistance to biofouling. Secondly, the composite membrane is primarily composed of ZrO2 particles. The presence of these ZrO2 particles imparts small pores to the composite membrane, significantly reducing pore blockage and fouling caused by small molecules in the fermentation broth.

[0056] Application of composite membrane in fermentation broth

[0057] The actual ethanol fermentation broth from Shougang Langze Technology Co., Ltd. was then tested. Under constant conditions (temperature: 25°C, cross flow velocity: 3.0 m·s -1 , transmembrane pressure: 0.2MPa) clarification experiments were carried out using bottom membrane, ZrO2 membrane and P1Z3 composite membrane, such as Figure 10 As shown in Figure a, the flux of the composite membrane remained stable throughout the filtration process, while the base membrane and ZrO2 membrane reached a plateau after 5 minutes. This phenomenon may be attributed to the complex composition and diverse contaminants in the actual fermentation broth, which led to the rapid formation of a complete gel layer on the membrane surface. The ZrO2 nanocrystals in the composite membrane have the properties of resisting protein adsorption and preventing pore clogging. By adjusting the surface energy through the addition of PTFE, this synergistic effect effectively alleviated microbial contamination. Therefore, the stable flux of the composite membrane in actual ethanol fermentation broth was nearly 2.1 times that of the base membrane and approximately 1.5 times that of the ZrO2 membrane. Figure 10 The pictures in a represent the original ethanol fermentation liquid, the permeate of the composite membrane, the permeate of the ZrO2 membrane and the permeate of the bottom membrane from left to right.

[0058] After the three membranes were washed in sequence, the results were as follows: Figure 10 The results are shown in b. The results are similar to those obtained in the simulated fermentation broth. However, the degree of membrane fouling in the actual fermentation broth is significantly higher. In the simulated fermentation broth without protein, the flux recovery rates (FRR) of the base membrane, ZrO2 membrane and composite membrane after pure water rinsing were 35.6%, 52.3% and 69.7%, respectively. In the actual fermentation broth, these values ​​dropped to only 11.2%, 26.0% and 31.8%, respectively. After chemical cleaning, the FRR of the base membrane, ZrO2 membrane and composite membrane were 41.1%, 78.8% and 95.5%, respectively. This further demonstrates that the composite membrane developed in this study can effectively combine the functions of anti-protein pore blocking and surface energy regulation to reduce microbial adsorption, thereby exhibiting excellent anti-fouling performance in actual ethanol fermentation broth.

Claims

1. A method for preparing a small-pore, anti-pollution PTFE-ZrO2 composite membrane with low surface energy, characterized in that: The steps include: Step 1, mixing PTFE emulsion and ZrO2 dispersion to obtain PTFE-ZrO2 dispersion; Step 2, coating the ceramic membrane tube with a PTFE-ZrO2 dispersion by dip coating; Step 3, drying and sintering to obtain a PTFE-ZrO2 composite membrane; The pH range of PTFE emulsion and ZrO2 dispersion is 9-13; The PTFE emulsion and ZrO2 dispersion also contain a dispersant, which is selected from NH4PAA or AEO-3. When NH4PAA is used in the ZrO2 dispersion, the mass ratio of NH4PAA to ZrO2 is 0.005-0.05, and when AEO-3 is used in the PTFE emulsion, the mass ratio of AEO-3 to PTFE is 0.001-0.

005.

2. The method for preparing a small-pore anti-pollution PTFE-ZrO2 composite membrane with low surface energy according to claim 1, characterized in that: The solid content of the ZrO2 dispersion is 1-5%, the solid content of the PTFE emulsion is 40-70%, and the volume ratio of the PTFE emulsion to the ZrO2 dispersion is 1:9-1:

1.

3. The method for preparing a small-pore anti-pollution PTFE-ZrO2 composite membrane with low surface energy according to claim 1, characterized in that: The coating time of dip coating is 20-50s.

4. The method for preparing a small-pore anti-pollution PTFE-ZrO2 composite membrane with low surface energy according to claim 1, characterized in that: The sintering temperature in step 3 is 300°C-350°C.

5. A PTFE-ZrO2 composite membrane prepared by the method for preparing a small-pore, anti-pollution PTFE-ZrO2 composite membrane with low surface energy according to any one of claims 1 to 4, characterized in that: The surface roughness Ra of the composite film is 20-30nm, and the surface energy is 25-35mJ·m -2 , the composite film thickness is 1-2μm.

6. Use of the PTFE-ZrO2 composite membrane according to claim 5 in filtration and clarification of fermentation broth.

7. The use according to claim 6, characterized in that The clarification working conditions of the composite membrane are: membrane surface flow rate of 0.5-5m / s and transmembrane pressure difference of 0.1-1MPa.

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