Method for matching thermal expansion coefficient in preparation process of ceramic hollow fiber composite membrane
By doping ceramic powders of different particle sizes into the inner and outer layers of ceramic hollow fiber membranes, the coefficient of thermal expansion is controlled, solving the defect problem caused by the mismatch of the coefficient of thermal expansion of ceramic hollow fiber membranes. This achieves improved permeability and mechanical strength, making it suitable for large-scale production.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-15
- Publication Date
- 2026-03-13
AI Technical Summary
In ceramic hollow fiber membranes, the mismatch in thermal expansion coefficients between the inner and outer layers leads to surface defects and cracks, affecting yield and mechanical strength, and making it difficult to achieve both high permeation flux and mechanical strength simultaneously.
A double-layer ceramic hollow fiber composite membrane was prepared by co-extrusion-co-sintering method, in which small ceramic particles were doped into large ceramic particles in the inner layer and large ceramic particles were doped into small ceramic particles in the outer layer, thereby controlling the matching of the thermal expansion coefficients of the inner and outer layers.
The mechanical strength and yield of ceramic hollow fiber composite membranes have been improved. The pure water flux is 5 times that of traditional membranes, the mechanical strength is 1.5 times that of undoped membranes, and the yield is increased by 30%, making it suitable for large-scale production.
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Figure CN121651867A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for matching the coefficient of thermal expansion during the preparation of ceramic hollow fiber composite membranes, and particularly to a method for preparing defect-free, high-flux, and high-mechanical-strength ceramic hollow fiber composite membranes in one step by controlling different particle size combinations of inner and outer ceramic powders, belonging to the field of membrane separation technology. Background Technology
[0002] Zeolite membrane pervaporation technology is considered an attractive industrial organic solvent dehydration technique due to its high permeation flux and high separation factor. Typically, zeolite membranes are prepared on porous supports to provide the mechanical strength required for industrial processes. Among these supports, ceramic hollow fibers have attracted significant attention due to their high permeation flux and high packing density. Excellent separation performance can be obtained by preparing molecular sieve membranes on ceramic hollow fibers using in-situ or secondary growth methods combined with different seed preparation methods.
[0003] To reduce the mass transfer resistance of molecular sieve membranes, researchers have focused on improving synthesis techniques to obtain thinner, high-flux molecular sieves. However, the performance of the support is equally crucial to the membrane's properties. Large-pore supports exhibit high permeation flux, making them potentially ideal for preparing high-permeation-flux zeolite membranes. However, forming dense zeolite membranes on these supports is quite difficult because their rough surfaces increase the risk of defect formation. Furthermore, the mechanical strength of large-pore supports is generally low, often insufficient for industrial processes. Obtaining ceramic hollow fibers that possess both high permeation flux and mechanical strength, while also being suitable for zeolite membrane synthesis, remains a challenge.
[0004] The bilayer structure design strategy is one option for solving the above problems and has been widely used in membrane preparation. The bilayer structure typically consists of an inner layer with large particles providing high porosity and an outer layer with small particles providing a smooth surface suitable for molecular sieve growth. However, the large-pore structure of the inner layer significantly reduces the mechanical strength of the ceramic hollow fiber. Furthermore, during the sintering process, the difference in thermal expansion coefficients between the large-diameter particles in the inner layer and the small-diameter particles in the outer layer easily leads to defects and cracking in the ceramic hollow fiber. Therefore, improving the matching of thermal expansion coefficients between the inner and outer layers, increasing the mechanical strength of the bilayer ceramic hollow fiber, and ultimately obtaining a ceramic hollow fiber composite membrane with high permeation flux and mechanical strength suitable for molecular sieve growth is one of the urgent problems to be solved. Summary of the Invention
[0005] The technical problem this invention aims to solve is that ceramic hollow fiber membrane materials with a double-layer structure suffer from surface defects and even cracking due to the mismatch in thermal expansion coefficients between the two layers, leading to low yield, reduced mechanical strength, and decreased separation performance. The technical solution of this invention is to prepare a ceramic hollow fiber composite membrane with a double-layer structure in one step using a co-extrusion-co-sintering method. This is achieved by doping a certain proportion of small-particle ceramic powder into the large-particle ceramic powder of the inner layer, and a certain proportion of large-particle ceramic powder into the small-particle ceramic powder of the outer layer, thereby controlling the matching degree of thermal expansion coefficients between the inner and outer layers, and thus improving the mechanical strength and yield of the hollow fiber composite membrane. The inner layer is a support layer with high flux, high porosity, and large pore size; the outer layer is a transition layer with a dense and smooth surface and suitable pore size and surface properties for molecular sieve membrane growth. The specific preparation steps are as follows:
[0006] A method for preparing a ceramic hollow fiber composite membrane includes the following steps:
[0007] a) Prepare the inner spinning solution and the outer spinning solution separately, wherein:
[0008] The inner spinning solution contains a first large-particle-size ceramic powder as the main component and is doped with a first small-particle-size ceramic powder; the outer spinning solution contains a second small-particle-size ceramic powder as the main component and is doped with a second large-particle-size ceramic powder.
[0009] b) After degassing the inner and outer spinning solutions, they are co-extruded through a double-layer spinneret under pressure, and after passing through an air gap, they enter a coagulation bath for phase transformation to form a hollow fiber composite membrane preform.
[0010] c) The hollow fiber composite membrane green body is dried and calcined at high temperature to obtain the ceramic hollow fiber composite membrane.
[0011] The particle size range of the first large-particle-size ceramic powder is 5-20 μm, and the particle size range of the second small-particle-size ceramic powder is 1-5 μm.
[0012] The particle size range of the first small-diameter doped ceramic powder is 1-5 μm; the particle size range of the second large-diameter doped ceramic powder is 3-20 μm.
[0013] The first small-diameter ceramic powder in the inner spinning solution is one or more ceramic powders with different particle sizes; and / or, the second large-diameter ceramic powder in the outer spinning solution is one or more ceramic powders with different particle sizes.
[0014] The high-temperature calcination temperature in step c) is 1000-1800℃, and the holding time is 1-20 hours.
[0015] The preferred temperature for the high-temperature calcination is 1300-1600℃, and the preferred holding time is 5-10 hours; the heating rate and cooling rate during the calcination process are both 1-5℃ / min.
[0016] The length of the air gap in step b) is 3-50 cm; the co-extrusion process also utilizes an internal coagulation bath with a flow rate of 1-300 ml / min.
[0017] The preferred length of the air gap is 10-30 cm; the preferred flow rate of the internal coagulation bath is 5-40 ml / min.
[0018] The ceramic powder in the inner spinning solution is selected from one or more of alumina, zirconium oxide, silicon carbide, and kaolin; the ceramic powder in the outer spinning solution is selected from one or more of alumina, zirconium oxide, and mullite.
[0019] The inner and outer spinning solutions also contain polymers, organic solvents, and dispersants;
[0020] The polymer is selected from one or more of polyvinyl chloride, polyethersulfone, polyethyleneimine, cellulose acetate, or polyvinylidene fluoride;
[0021] The organic solvent is selected from one or more of dimethyl sulfoxide, N-methylpyrrolidone, dimethylacetamide, or chloroform;
[0022] The dispersant is selected from one or more of polyethylene glycol, polyvinylpyrrolidone, ethyl cellulose, polyoxyethylene, or polymethacrylic acid.
[0023] The beneficial effects of this invention are: the ceramic hollow fiber composite membrane prepared by this invention has a smooth and defect-free surface and excellent performance: a porosity as high as 58%, an average pore size of 0.35-0.50 μm, and a pure water flux of 40-55 m³ / h. 3 ·m -2 ·h -1 ·bar -1The mechanical strength is 40-60 N. The innovation of this invention lies in matching the thermal expansion coefficients of the inner and outer layers by doping a certain proportion of small ceramic particles into the inner layer of large-particle ceramic powder and a certain proportion of large-particle ceramic powder into the outer layer of small-particle ceramic powder. This solves the problem of defects that easily occur when preparing ceramic hollow fiber composite membranes with a double-layer structure, increasing its mechanical strength and yield. Furthermore, this method is simple to operate, easy to control, has low energy consumption, and is suitable for large-scale preparation. Under the same effective pore size conditions, the ceramic hollow fiber composite membrane prepared by this invention has a pure water flux that is 5 times higher than that of traditional single-layer hollow fiber ceramic membranes; compared with ceramic hollow fiber composite membranes without different particle size doping, its mechanical strength is 1.5 times higher and its yield is 30% higher. NaA molecular sieve membranes were synthesized on the ceramic hollow fiber composite membrane prepared using the method of this invention and used for the separation of 90 wt.% ethanol / water at 110℃, with a water permeation flux of 28 kg / (m²). 2 The separation factor reached 1×10 (·h). 4 The above. Based on this, a molecular sieve membrane module was synthesized and used at 110℃ for the separation of 90 wt.% ethanol / water, with a water permeation flux of 11 kg / (m²). 2 The separation factor reached 1×10 (·h). 4 above. Attached Figure Description
[0024] Figure 1 This is a SEM image of the cross-section of the ceramic hollow fiber composite membrane prepared in Example 1.
[0025] Figure 2 This is a SEM image of the cross-section of the ceramic hollow fiber composite membrane prepared in Example 2.
[0026] Figure 3 This is a SEM image of the cross-section of the ceramic hollow fiber composite membrane prepared in Example 3.
[0027] Figure 4 This is a SEM image of the cross-section of the ceramic hollow fiber composite membrane prepared in Example 4.
[0028] Figure 5 This is a SEM image of the cross-section of the ceramic hollow fiber composite membrane prepared in Example 5.
[0029] Figure 6 This is a SEM image of the cross-section of the ceramic hollow fiber composite membrane prepared in Example 6.
[0030] Figure 7 This is a SEM image of the surface of the ceramic hollow fiber composite membrane prepared in Example 6.
[0031] Figure 8This is a SEM image of the cross-section of the ceramic hollow fiber composite membrane prepared in Comparative Example 1 at the defect location.
[0032] Figure 9 This is a diagram showing the continuous dehydration performance of the composite membrane.
[0033] Figure 10 This is a diagram showing the continuous dehydration performance of the composite membrane module.
[0034] Figure 11 This is a comparison chart showing the performance of a composite membrane module prepared using the method of this invention and an undoped membrane module. Detailed Implementation
[0035] This invention involves uniformly mixing polymer binders, organic solvents, dispersants, etc., to prepare a homogeneous and stable solution. Then, large-particle ceramic powder is first added to the inner layer solution, followed by small-particle ceramic powder of different particle sizes in batches. In the outer layer solution, small-particle ceramic powder is first added, followed by small-particle ceramic powder of different particle sizes in batches. The mixtures are stirred separately to obtain the inner and outer spinning solutions.
[0036] Degassing technology is used to remove air bubbles from the spinning solution. Under pressure, the inner and outer spinning solutions are simultaneously extruded from a double-layer spinneret, pass through an air gap, and enter an external coagulation bath to stand until the phase transformation is complete, thus obtaining a double-layer ceramic hollow fiber composite membrane green body. The prepared green body is thoroughly dried at room temperature and then calcined at a high temperature of 1000℃~1800℃ for a controlled holding time of 1~20h to produce a ceramic hollow fiber composite membrane.
[0037] In some preferred embodiments, the technical solutions employed are detailed below:
[0038] (1) Solution preparation: Dissolve the polymer and dispersant in an organic solvent in a certain proportion to form a stable solution.
[0039] (2) Preparation of spinning solution: First, add large ceramic powder particles to the inner layer solution, and then add small ceramic powder particles of different particle sizes in batches; first, add small ceramic powder particles to the outer layer solution, and then add small ceramic powder particles of different particle sizes in batches. Stir and mix them separately to obtain the inner and outer spinning solutions.
[0040] (3) Debubbling: Debubbling technology is used to remove air bubbles from the spinning solution;
[0041] (4) Co-extrusion molding: The inner and outer spinning solutions are extruded simultaneously from the double-layer spinneret under pressure, pass through an air gap, enter the outer coagulation bath and stand until the phase transformation is fully completed to prepare a ceramic hollow fiber composite membrane green body.
[0042] (5) Drying: Take out the ceramic hollow fiber composite membrane green body and air dry it at room temperature;
[0043] (6) High-temperature calcination: The ceramic hollow fiber composite membrane green body is placed in a high-temperature furnace and calcined according to the heating program.
[0044] The ceramic powder contained in the inner spinning solution described in step 1 is one or two of alumina, zirconium oxide, silicon carbide, and kaolin. Preferably, the ceramic powder is one of alumina, zirconium oxide, and kaolin.
[0045] The ceramic powder contained in the inner spinning solution described in step 1 has a particle size of several selected from 5μm, 10μm, 12μm, 15μm, and 20μm. Preferably, the particle size is several selected from 10μm, 12μm, 15μm, and 20μm.
[0046] The ceramic powder contained in the outer spinning solution described in step 1 is one or two of alumina, zirconium oxide, and mullite. Preferably, the ceramic powder is one of alumina and mullite.
[0047] The ceramic powder contained in the outer spinning solution described in step 1 has a particle size of several selected from 1μm, 2μm, 3μm, 4μm, and 5μm. Preferably, the particle size is selected from several selected from 1μm, 2μm, 3μm, and 4μm.
[0048] The polymer contained in the inner or outer spinning solution described in step 1 is one or two of polyvinyl chloride, polyethersulfone, polyethyleneimine, cellulose acetate, or polyvinylidene fluoride. Preferably, the polymer is one of polyimide, polyethersulfone, or polyethyleneimine.
[0049] The organic solvent mentioned in step 1 is one or two of dimethyl sulfoxide, N-methylpyrrolidone, dimethylacetamide, or chloroform. Preferably, the organic solvent is one of dimethyl sulfoxide or N-methylpyrrolidone.
[0050] The dispersant mentioned in step 1 is one or two of polyethylene glycol, polyvinylpyrrolidone, ethyl cellulose, polyoxyethylene, and polymethacrylic acid. Preferably, the dispersant is one of polyethylene glycol and polyvinylpyrrolidone.
[0051] During the stirring process of the spinning solution in step 3, the temperature is set to 10–200°C. Preferably, the temperature is 100–200°C.
[0052] During the spinning process described in step 3, the air gap is 3–50 cm. Preferably, the air gap is 10–30 cm.
[0053] The inner coagulation bath in step 3, which contacts the inner spinning solution, and the outer coagulation bath, which contacts the outer spinning solution; the outer coagulation bath is one or two of water, ethanol, or N-methylpyrrolidone, and the inner coagulation bath is one or two of water, ethanol, dimethylacetamide, or N-methylpyrrolidone. The temperature of both the inner and outer coagulation baths is 0–90°C, and the flow rate of the inner coagulation bath is 1–300 ml / min. Preferably, both the inner and outer coagulation baths are water or ethanol, and preferably the flow rate of the inner coagulation bath is 5–40 ml / min.
[0054] In the sintering process described in step 5, the sintering procedure is as follows: first, heat to 1000–1800°C at a heating rate of 1–5°C / min and hold for 1–20 hours; then cool to 100–300°C at a cooling rate of 1–5°C / min; finally, allow to cool naturally to room temperature. Preferably, the heating rate is 2–4°C / min, the holding temperature is 1300–1600°C, the holding time is 5–10 hours, and the cooling rate is 1–3°C / min.
[0055] Examples 1-6 below compare the effects of different particle size combinations of inner layer ceramic powder on the preparation of ceramic hollow fiber composite membranes.
[0056] Example 1
[0057] Polyethersulfone (PES) and polyvinylpyrrolidone (PVP) were dissolved in N-methylpyrrolidone solvent under a 150°C water bath and stirred until the polymer was completely dissolved. Then, ceramic powder was added in batches, and stirring continued for 24 hours to prepare a uniformly dispersed spinning suspension. The inner layer spinning solution had a composition ratio of kaolin:PES:NMP:PVP = 60:10:29:1, using kaolin as the ceramic powder and 30% wt. of 1μm small ceramic powder mixed with 13μm large ceramic powder particles. The outer layer spinning solution had a composition ratio of Al2O3:PEI:NMP:PVP = 56:9:33:2, using Al2O3 as the ceramic powder and 1μm small ceramic powder particles. Centrifugation was used to remove air bubbles. The inner and outer spinning solutions are extruded from a specially designed double-layer spinneret under pneumatic pressure (0.15 MPa), with a flow rate of 25 ml / min for the deionized water in the inner coagulation bath. The air gap is 10 cm. After soaking in ethanol in the outer coagulation bath for 24 hours, the membrane is removed and dried to obtain a hollow fiber composite membrane green body. The prepared green body is placed in a high-temperature electric furnace and calcined in air atmosphere, reaching 1600℃ at a heating rate of 2℃ / min, and held at 1600℃ for 5 hours. It is then cooled to room temperature at a rate of 2℃ / min to obtain the ceramic hollow fiber composite membrane.
[0058] Example 2
[0059] Polyethersulfone (PES) and polyvinylpyrrolidone (PVP) were dissolved in N-methylpyrrolidone solvent under a 150°C water bath and stirred until the polymer was completely dissolved. Then, ceramic powder was added in batches, and stirring continued for 24 hours to prepare a spinning solution with uniform powder dispersion. The inner layer spinning solution had a composition ratio of kaolin:PES:NMP:PVP = 60:10:29:1, using kaolin as the ceramic powder, with 30% wt. of 3μm small ceramic powder added to the large ceramic powder with an average particle size of 13μm. The outer layer spinning solution had a composition ratio of Al2O3:PES:NMP:PVP = 56:9:33:2, using Al2O3 as the ceramic powder, with small ceramic powder with an average particle size of 1μm. Centrifugation was used to remove air bubbles. The inner and outer spinning solutions are extruded from a specially designed double-layer spinneret under pneumatic pressure (0.15 MPa), with a flow rate of 25 ml / min for the deionized water in the inner coagulation bath. The air gap is 10 cm. After soaking in ethanol in the outer coagulation bath for 24 hours, the membrane is removed and dried to obtain a hollow fiber composite membrane green body. The prepared green body is placed in a high-temperature electric furnace and calcined in air atmosphere, reaching 1600℃ at a heating rate of 2℃ / min, and held at 1600℃ for 5 hours. It is then cooled to room temperature at a rate of 2℃ / min to obtain the ceramic hollow fiber composite membrane.
[0060] Example 3
[0061] Polyethersulfone (PES) and polyvinylpyrrolidone (PVP) were dissolved in N-methylpyrrolidone solvent under a 150°C water bath and stirred until the polymer was completely dissolved. Then, ceramic powder was added in batches, and stirring continued for 24 hours to prepare a spinning solution with uniform powder dispersion. The inner layer spinning solution had a composition ratio of kaolin:PES:NMP:PVP = 60:10:29:1, using kaolin as the ceramic powder, with 30% wt. of 5μm small ceramic powder added to large ceramic powder with an average particle size of 13μm. The outer layer spinning solution had a composition ratio of Al2O3:PES:NMP:PVP = 56:9:33:2, using Al2O3 as the ceramic powder, with small ceramic powder having an average particle size of 1μm. Centrifugation was used to remove air bubbles. The inner and outer spinning solutions are extruded from a specially designed double-layer spinneret under pneumatic pressure (0.15 MPa), with a flow rate of 25 ml / min for the deionized water in the inner coagulation bath. The air gap is 10 cm. After soaking in ethanol in the outer coagulation bath for 24 hours, the membrane is removed and dried to obtain a hollow fiber composite membrane green body. The prepared green body is placed in a high-temperature electric furnace and calcined in air atmosphere, reaching 1600℃ at a heating rate of 2℃ / min, and held at 1600℃ for 5 hours. It is then cooled to room temperature at a rate of 2℃ / min to obtain the ceramic hollow fiber composite membrane.
[0062] Example 4
[0063] Polyethersulfone (PES) and polyvinylpyrrolidone (PVP) were dissolved in N-methylpyrrolidone solvent under a 150°C water bath and stirred until the polymer was completely dissolved. Then, ceramic powder was added in batches, and stirring continued for 24 hours to prepare a spinning solution with uniform powder dispersion. The inner layer spinning solution had a composition ratio of kaolin:PES:NMP:PVP = 60:10:29:1, using kaolin as the ceramic powder, with large particles of kaolin having an average particle size of 13 μm. The outer layer spinning solution had a composition ratio of Al2O3:PES:NMP:PVP = 56:9:33:2, using Al2O3 as the ceramic powder, with small particles of 1 μm on average mixed with 30% wt. of large particles of 3 μm. Ultrasonic degassing was used to remove air bubbles. The inner and outer spinning solutions are extruded from a specially designed double-layer spinneret under pneumatic pressure (0.15 MPa), with a flow rate of 25 ml / min for the deionized water in the inner coagulation bath. The air gap is 10 cm. After soaking in ethanol in the outer coagulation bath for 24 hours, the membrane is removed and dried to obtain a hollow fiber composite membrane green body. The prepared green body is placed in a high-temperature electric furnace and calcined in air atmosphere, reaching 1600℃ at a heating rate of 2℃ / min, and held at 1600℃ for 5 hours. It is then cooled to room temperature at a rate of 2℃ / min to obtain the ceramic hollow fiber composite membrane.
[0064] Example 5
[0065] Polyethersulfone (PES) and polyvinylpyrrolidone (PVP) were dissolved in N-methylpyrrolidone solvent under a 150°C water bath and stirred until the polymer was completely dissolved. Then, ceramic powder was added in batches, and stirring continued for 24 hours to prepare a spinning solution with uniform powder dispersion. The inner layer spinning solution had a composition ratio of kaolin:PES:NMP:PVP = 60:10:29:1, using kaolin as the ceramic powder, with large particles of kaolin having an average particle size of 13 μm. The outer layer spinning solution had a composition ratio of Al2O3:PES:NMP:PVP = 56:9:33:2, using Al2O3 as the ceramic powder, with small particles of kaolin having an average particle size of 1 μm and 30% wt. of large particles of 5 μm added. Ultrasonic degassing was used to remove air bubbles. The inner and outer spinning solutions are extruded from a specially designed double-layer spinneret under pneumatic pressure (0.15 MPa), with a flow rate of 25 ml / min for the deionized water in the inner coagulation bath. The air gap is 10 cm. After soaking in ethanol in the outer coagulation bath for 24 hours, the membrane is removed and dried to obtain a hollow fiber composite membrane green body. The prepared green body is placed in a high-temperature electric furnace and calcined in air atmosphere, reaching 1600℃ at a heating rate of 2℃ / min, and held at 1600℃ for 5 hours. It is then cooled to room temperature at a rate of 2℃ / min to obtain the ceramic hollow fiber composite membrane.
[0066] Example 6
[0067] Polyethersulfone (PES) and polyvinylpyrrolidone (PVP) were dissolved in N-methylpyrrolidone solvent under a 150°C water bath and stirred until the polymer was completely dissolved. Then, ceramic powder was added in batches, and stirring continued for 24 hours to prepare a spinning solution with uniform powder dispersion. The inner layer spinning solution has a composition ratio of kaolin:PES:NMP:PVP = 60:10:29:1, using kaolin as the ceramic powder and incorporating 10% wt. of 1μm, 10% wt. of 3μm, and 10% wt. of 5μm large-particle ceramic powder with an average particle size of 13μm. The outer layer spinning solution has a composition ratio of Al2O3:PES:NMP:PVP = 56:9:33:2, using Al2O3 as the ceramic powder and incorporating 15% wt. of 3μm and 15% wt. of 5μm large-particle ceramic powder with an average particle size of 1μm. Ultrasonic degassing is used to remove air bubbles. The inner and outer spinning solutions are extruded from a specially designed double-layer spinneret under pneumatic pressure (0.15 MPa), with a flow rate of 25 ml / min for the deionized water in the inner coagulation bath. The air gap is 10 cm. After soaking in ethanol in the outer coagulation bath for 24 hours, the membrane is removed and dried to obtain a hollow fiber composite membrane green body. The prepared green body is placed in a high-temperature electric furnace and calcined in air atmosphere, reaching 1600℃ at a heating rate of 2℃ / min, and held at 1600℃ for 5 hours. It is then cooled to room temperature at a rate of 2℃ / min to obtain the ceramic hollow fiber composite membrane.
[0068] Comparative Example 1
[0069] Polyethersulfone (PES) and polyvinylpyrrolidone (PVP) were dissolved in N-methylpyrrolidone solvent under a 150°C water bath and stirred until the polymer was completely dissolved. Ceramic powder was then added in batches, and stirring continued for 24 hours to prepare a uniformly dispersed spinning suspension. The inner layer spinning solution had a composition ratio of kaolin:PES:NMP:PVP:TiO2 = 60:10:29:1, using kaolin with large particles of 13 μm. The outer layer spinning solution had a composition ratio of Al2O3:PES:NMP:PVP = 56:9:33:2, using Al2O3 with small particles of 1 μm. Vacuum degassing was used to remove air bubbles. The inner and outer spinning solutions were extruded from a specially designed double-layer spinneret under pneumatic pressure (0.15 MPa), with a deionized water flow rate of 25 ml / min in the inner coagulation bath. With an air gap of 10 cm, the membrane was soaked in tap water in an external coagulation bath for 24 hours and then dried to obtain a hollow fiber composite membrane green body. The prepared green body was placed in a high-temperature electric furnace and calcined at high temperature in an air atmosphere, with the temperature increased to 1600℃ at a heating rate of 2℃ / min, held at 1600℃ for 5 hours, and then cooled to room temperature at a rate of 2℃ / min to obtain a defective ceramic hollow fiber composite membrane.
[0070] In the following tests, the yield rate refers to the percentage of 200 hollow fiber composite membranes produced simultaneously, with no obvious defects on the membrane surface and good bonding between the inner and outer layers. Strength refers to the average value measured using the three-point pressure method from 100 qualified samples. The average pore size also refers to the average value from the 100 qualified samples.
[0071]
[0072]
[0073] Comparing Examples 1 to 3, it can be seen that, with the same inner layer doping ratio of 30 wt.%, as the particle size of the doped particles increases from 1 μm to 5 μm, the pure water flux of the membrane shows a significant upward trend, increasing from 30.67 m... 3 ·m -2 • h-1 increased to 38.38m 3 ·m -2However, the mechanical strength decreased accordingly, from 47.28 N to 34.98 N. This indicates that while doping with excessively small particle sizes, such as 1 μm, can maximize the filling of voids between large particles and thus significantly improve strength, it can also excessively clog pores, leading to flux loss. Conversely, while doping with excessively large particle sizes, such as 5 μm, maintains high flux, its contribution to increasing packing density is limited, resulting in a less significant strength gain compared to smaller particle sizes. Therefore, in Example 2, a medium particle size of 3 μm was selected for doping, maintaining a high mechanical strength of 44.50 N while achieving a flux of 35.12 m. 3 ·m -2 The h-1 layer was not severely damaged, achieving a good performance balance. Examples 4 and 5 mainly investigated the effect of doping with larger particles of different sizes in the outer layer. Comparative data shows that Example 5, with its outer layer doped with larger 5μm particles, increased the pure water flux to 43.26m compared to Example 4, which had smaller 3μm particles. 3 ·m -2 The mechanical strength remained above 40 N without significant decrease, exhibiting a value of h⁻¹. This indicates that the fine-tuning of the outer layer structure primarily contributes to reducing transmembrane mass transfer resistance. Furthermore, due to the thinner outer layer, its negative impact on overall mechanical strength is relatively small, outperforming the effect of adjusting only a single part of the inner layer. Example 6 employed a multi-level particle size mixing doping strategy. Compared with Examples 1 to 5, which used single-size doping, Example 6 had a mechanical strength of 41.33 N, slightly lower than Example 1's 47.28 N, and a slightly higher limiting flux than Example 3. Furthermore, its yield reached a maximum of 98%. This further confirms that while single-size doping can improve the matching of thermal expansion coefficients, it easily leads to localized stress concentrations or accumulation defects. In contrast, multi-level particle size gradient doping forms a tightly packed structure similar to concrete gradation. This continuous particle size distribution not only more effectively alleviates thermal stress mismatch during sintering at the microscopic level and eliminates macroscopic defects such as cracks, but also ensures the uniformity of pore size distribution, with an average pore size stable at 0.42 μm. This is a key path to achieving high-yield industrial-scale preparation. Comparative Example 1, without any particle size doping, exhibited a mechanical strength of only 38.20 N and a yield as low as 75%. Considering the improved performance of the embodiments, it can be inferred that the low performance of Comparative Example 1 is not due to insufficient strength of the material itself, but rather to the drastic difference in thermal expansion coefficients caused by the difference in the single particle size between the inner and outer layers (13 μm and 1 μm), resulting in numerous microcracks during sintering and cooling. These microcracks may artificially inflate the flux value to 39.28 m. 3 ·m -2 •h-1, but it damages the membrane integrity and separation selectivity.
[0074] The above comparisons demonstrate that by doping a certain proportion of small ceramic particles into the inner layer of large ceramic particles and a certain proportion of large particles into the outer layer of small particles, the combination and distribution of particle sizes effectively suppresses membrane defects and increases the yield of the membrane material. The prepared ceramic hollow fiber composite membrane maintains a high porosity and pure water flux compared to the undoped version, while also improving overall mechanical strength. Furthermore, the membrane material possesses a smooth surface suitable for molecular sieve growth.
[0075] The optimal doping ratio is as follows: the inner layer consists of 13μm large-particle ceramic powder doped with 10% wt. of 1μm large-particle ceramic powder, 10% wt. of 3μm large-particle ceramic powder, and 10% wt. of 5μm large-particle ceramic powder; the outer layer consists of 1μm small-particle ceramic powder doped with 15% wt. of 3μm large-particle ceramic powder and 15% wt. of 5μm large-particle ceramic powder. For example... Figure 11 As shown, the yield of molecular sieve membranes prepared on ceramic hollow fiber composite membranes without different particle doping is low, resulting in lower separation performance of the membrane modules compared to those with doping.
Claims
1. A method for preparing a ceramic hollow fiber composite membrane, characterized in that, Includes the following steps: a) Prepare the inner spinning solution and the outer spinning solution separately, wherein: The inner spinning solution contains a first large-particle-size ceramic powder as the main component, and is doped with a first small-particle-size ceramic powder. The outer spinning solution contains ceramic powder with a second small particle size as the main component, and is also doped with ceramic powder with a second large particle size. b) After degassing the inner and outer spinning solutions, they are co-extruded through a double-layer spinneret under pressure, and after passing through an air gap, they enter a coagulation bath for phase transformation to form a hollow fiber composite membrane preform. c) The hollow fiber composite membrane green body is dried and calcined at high temperature to obtain the ceramic hollow fiber composite membrane.
2. The method according to claim 1, characterized in that, The particle size range of the first large-particle-size ceramic powder is 5-20 μm, and the particle size range of the second small-particle-size ceramic powder is 1-5 μm.
3. The method according to claim 1 or 2, characterized in that, The particle size range of the first small-diameter doped ceramic powder is 1-5 μm; the particle size range of the second large-diameter doped ceramic powder is 3-20 μm.
4. The method according to claim 1, characterized in that, The first small-diameter ceramic powder in the inner spinning solution is one or more ceramic powders with different particle sizes; and / or, the second large-diameter ceramic powder in the outer spinning solution is one or more ceramic powders with different particle sizes.
5. The method according to claim 1, characterized in that, The high-temperature calcination temperature in step c) is 1000-1800℃, and the holding time is 1-20 hours.
6. The method according to claim 5, characterized in that, The preferred temperature for the high-temperature calcination is 1300-1600℃, and the preferred holding time is 5-10 hours; the heating rate and cooling rate during the calcination process are both 1-5℃ / min.
7. The method according to claim 1, characterized in that, The length of the air gap in step b) is 3-50 cm; the co-extrusion process also utilizes an internal coagulation bath with a flow rate of 1-300 ml / min.
8. The method according to claim 7, characterized in that, The preferred length of the air gap is 10-30 cm; the preferred flow rate of the internal coagulation bath is 5-40 ml / min.
9. The method according to claim 1, characterized in that, The ceramic powder in the inner spinning solution is selected from one or more of alumina, zirconium oxide, silicon carbide, and kaolin; the ceramic powder in the outer spinning solution is selected from one or more of alumina, zirconium oxide, and mullite.
10. The method according to claim 1, characterized in that, The inner and outer spinning solutions also contain polymers, organic solvents, and dispersants; The polymer is selected from one or more of polyvinyl chloride, polyethersulfone, polyethyleneimine, cellulose acetate, or polyvinylidene fluoride; The organic solvent is selected from one or more of dimethyl sulfoxide, N-methylpyrrolidone, dimethylacetamide, or chloroform; The dispersant is selected from one or more of polyethylene glycol, polyvinylpyrrolidone, ethyl cellulose, polyoxyethylene, or polymethacrylic acid.