A freeze-formed high porosity ceramic membrane support and a method of making the same

Abstract

The application discloses a kind of frozen forming high porosity ceramic membrane support and preparation method thereof, it is related to ceramic membrane technical field, slurry raw material is placed into ball mill, ball milling is passed 100 mesh screen, obtain slurry, again slurry is introduced into prepared polytetrafluoroethylene mould, again mould is directly placed into liquid nitrogen pool and frozen forming, then demolding, obtain wet blank, again wet blank is placed into vacuum environment, vacuum freeze-drying, obtain dry blank, then dry blank is placed into kiln, high-temperature sintering, then natural cooling, ceramic membrane support is obtained.The application ceramic membrane support preparation is only 4 process steps, whole process is simple, and raw material component is simple, it is not necessary to add a large number of binder, pore-forming agent to increase porosity, 1-5min can be completed forming, greatly reduce forming time, greatly shorten the sintering cycle of whole support, simultaneously using vacuum freeze-drying, utilize water sublimation drying, the position where water is located can form interstice, greatly improve the porosity of support.

Description

Technical Field

[0001] This invention relates to the field of ceramic membrane technology, and in particular to a freeze-formed high-porosity ceramic membrane support and its preparation method. Background Technology

[0002] Ceramic membranes are important separation materials in the membrane separation industry. They have many advantages, such as good chemical stability, stable membrane separation accuracy, acid and alkali resistance, high temperature resistance, organic solvent resistance, high mechanical strength, and long service life. They are widely used in many fields such as food, beverage, plant (pharmaceutical) deep processing, biomedicine, fermentation, and fine chemicals. Ceramic membranes are generally composed of a separation layer, a transition layer, and a support, and the support plays a decisive role in the strength, flux, fouling resistance, and lifespan of the ceramic membrane.

[0003] Currently, the main process for preparing ceramic membrane supports is extrusion molding. Patent CN115872772A discloses a method for preparing a fly ash-based ceramic membrane support. After treatment, fly ash is mixed with liquid raw materials, kneaded, slurried, aged, extruded, and dried to obtain a green body, which is then sintered at high temperature to obtain the fly ash-based ceramic membrane support. Patent CN111517822A discloses a flat ceramic membrane support and its preparation method, which involves uniformly mixing spherical alumina, binder, sintering aids, and other raw materials, followed by kneading, slurrying, aging, vacuum slurrying, molding, drying, and sintering. Both patents require complex, multi-step processes to produce qualified supports, with complex raw material formulations and diverse raw material types, making the entire process prone to many unstable factors. Furthermore, due to limitations in extrusion molding processes, the porosity of the ceramic membrane support is less than 40%. Existing technologies for increasing the porosity of ceramic membrane supports primarily involve adding large amounts of pore-forming agents, which directly increases the difficulty of the sintering process and causes the ceramic membrane support to fail to meet performance standards in terms of strength and pore size. Therefore, developing a simple and stable method for preparing ceramic membrane supports is of positive significance. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a freeze-formed high-porosity ceramic membrane support and its preparation method, so as to optimize the ceramic membrane support formulation design, simplify and stabilize the process flow, and improve the porosity of the ceramic membrane support.

[0005] In a first aspect, the present invention provides a method for preparing a freeze-formed high-porosity ceramic membrane support, specifically comprising the following steps:

[0006] 1) Slurry preparation: Alumina powder with a diameter of 3-20μm, washed kaolin, sodium carboxymethyl cellulose, sodium tripolyphosphate, water and sintering aid are all put into a ball mill for ball milling, and then passed through a 100-mesh sieve to obtain slurry;

[0007] 2) Freeze-forming: The slurry described in step 1) is poured into the prepared polytetrafluoroethylene mold, and then the mold is directly placed in a liquid nitrogen pool for freeze-forming for 1-5 minutes. Then the mold is demolded to obtain a wet blank.

[0008] 3) Vacuum drying: The wet blank described in step 2) is placed in a vacuum environment at -50°C to -10°C and freeze-dried to obtain a dry blank;

[0009] 4) High-temperature sintering: The dry blank described in step 3) is placed in a kiln and sintered at high temperature, and then cooled naturally to obtain a ceramic film support.

[0010] In conjunction with the first aspect, in some embodiments, the slurry raw materials are formulated in the following weight ratios: 100 parts of alumina powder of 3-20 micrometers, 5-10 parts of washed kaolin, 0.05-0.2 parts of sodium carboxymethyl cellulose, 0.05-0.3 parts of sodium tripolyphosphate, 50-100 parts of water, and 1-3 parts of sintering aid.

[0011] In conjunction with the first aspect, in some embodiments, the sintering aid is one or more of zirconium oxide, magnesium oxide, and yttrium oxide.

[0012] In conjunction with the first aspect, in some embodiments, the ball milling time is 30-120 min, the ball milling speed is 30-90 r / min, and the grinding balls are 3-5 mm high-alumina grinding balls.

[0013] In conjunction with the first aspect, in some embodiments, the vacuum degree of the vacuum freeze-drying is not higher than -0.08 MPa, and the vacuum freeze-drying time is 24-48 h.

[0014] In conjunction with the first aspect, in some embodiments, the heating method for the high-temperature sintering is as follows: first, heat to 200°C over 3-5 hours, then heat to 1190-1350°C over 4-6 hours, and then hold at that temperature for 2-4 hours.

[0015] Secondly, the present invention provides a freeze-formed high-porosity ceramic membrane support, wherein the ceramic membrane support is prepared by the preparation method described above.

[0016] The beneficial effects of this invention are:

[0017] 1. The ceramic membrane support of the present invention has only 4 process steps to prepare. The whole process is simple and the raw materials are simple. It does not require the addition of a large amount of binder and pore-forming agent to increase porosity, which greatly shortens the sintering cycle of the entire support.

[0018] 2. This invention uses freeze molding, which can be completed in 1-5 minutes, greatly reducing the molding time.

[0019] 3. This invention uses vacuum freeze drying, which utilizes the sublimation of water to dry the material. The water in the water can form pores, which greatly increases the porosity of the support to more than 50%.

[0020] 4. This invention uses a polytetrafluoroethylene mold, which improves the smoothness of the support and eliminates the need for oil-based substances for demolding, thus reducing pollution. Attached Figure Description

[0021] Figure 1 The images show the SEM image and pore size distribution of the ceramic membrane support prepared in Example 1 of this invention.

[0022] Figure 2 The images show the SEM image and pore size distribution of the ceramic membrane support prepared in Example 2 of this invention.

[0023] Figure 3 The images show the SEM image and pore size distribution of the ceramic membrane support prepared in Example 3 of this invention. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Unless otherwise specified in the following examples, the conditions are as per standard conditions or the manufacturer's recommendations. Raw materials, equipment, or instruments whose manufacturers are not specified are all commercially available products.

[0026] This invention proposes a freeze-formed high-porosity ceramic membrane support and its preparation method, mainly including four processes: slurry preparation, freeze-forming, vacuum drying, and high-temperature sintering. The process is simple, the raw materials are simple, and there is no need to add a large amount of binder and pore-forming agent to increase porosity, which greatly shortens the sintering cycle of the entire support.

[0027] The present invention provides a method for preparing a freeze-formed high-porosity ceramic membrane support, comprising the following steps:

[0028] 1) Slurry preparation: 100 parts of 3-20 micron alumina powder, 5-10 parts of washed kaolin, 0.05-0.2 parts of sodium carboxymethyl cellulose, 0.05-0.3 parts of sodium tripolyphosphate, 50-100 parts of water, and 1-3 parts of sintering aid (zirconia, magnesium oxide, yttrium oxide, or one or more of these) are all placed in a ball mill for ball milling for 30-120 minutes at a speed of 30-90 r / min. High-alumina ball milling beads of 3-5 mm are used. After ball milling, the slurry is passed through a 100-mesh sieve to obtain the slurry.

[0029] 2) Freeze-forming: The prepared slurry is directly poured into the prepared polytetrafluoroethylene (PTFE) mold, and then the mold is placed directly into a liquid nitrogen bath for freeze-forming for 1-5 minutes. The mold is then demolded to obtain a wet blank. PTFE molds are used because of their excellent demolding performance and resistance to ultra-low temperatures, ensuring stability in subsequent use. Simultaneously, the water forms amorphous ice under rapid cooling, rather than needle-like ice crystals, which also facilitates subsequent demolding and ensures a smooth surface.

[0030] 3) Vacuum drying: The above-formed wet blank is directly placed in an environment of -50℃ to -10℃ for vacuum drying, keeping the vacuum degree no higher than -0.08MPa, and the vacuum freeze drying time is 24-48h, allowing the moisture in the support to sublimate directly, ensuring the dimensional stability of the support and preventing deformation, thus obtaining a dry blank.

[0031] 4) High-temperature sintering: The dried blank is placed in the kiln and heated as follows: first, it is heated to 200℃ in 3-5 hours, then heated to 1190-1350℃ in 4-6 hours, and then held at that temperature for 2-4 hours and allowed to cool naturally to obtain the ceramic film support.

[0032] The following examples 1-6 provide a detailed description of a freeze-formed high-porosity ceramic membrane support and its preparation method according to the present invention.

[0033] Example 1

[0034] This embodiment provides a method for preparing a freeze-formed high-porosity ceramic membrane support, the steps of which are as follows:

[0035] 1) Slurry preparation: 1000g of 3-micron alumina powder, 50g of washed kaolin, 0.5g of sodium carboxymethyl cellulose, 0.5g of sodium tripolyphosphate, 500g of water, and 10g of zirconium oxide were all put into a ball mill for ball milling for 30 minutes at a speed of 300 r / min. 3mm high-alumina ball milling beads were used. After ball milling, the slurry was passed through a 100-mesh sieve to obtain the slurry.

[0036] 2) Freeze-forming: The slurry prepared above is directly poured into the prepared polytetrafluoroethylene mold, and then the mold is directly placed in the liquid nitrogen pool for freeze-forming for 1 minute. Then it is demolded and taken out to obtain a wet blank.

[0037] 3) Vacuum drying: The above-formed wet blank is placed directly into an environment of -50°C for vacuum drying, maintaining a vacuum degree of -0.12MPa, and the vacuum freeze drying time is 24h, allowing the moisture in the support to sublimate directly to obtain a dry blank.

[0038] 4) High-temperature sintering: The dried support is placed in the kiln and heated as follows: first, it is heated to 200℃ in 3 hours, then to 1190℃ in 4 hours, and then held at that temperature for 2 hours and allowed to cool naturally to obtain the ceramic film support.

[0039] Example 2

[0040] This embodiment provides a method for preparing a freeze-formed high-porosity ceramic membrane support, the steps of which are as follows:

[0041] 1) Slurry preparation: 1000g of 10-micron alumina powder, 70g of washed kaolin, 1g of sodium carboxymethyl cellulose, 2g of sodium tripolyphosphate, 700g of water, and 20g of zirconium oxide were all put into a ball mill for ball milling. The ball milling time was 90min and the ball milling speed was 60r / min. 4mm high-alumina ball milling beads were used. After ball milling, the slurry was completely passed through a 100-mesh sieve to obtain the slurry.

[0042] 2) Freeze-forming: The slurry prepared above is directly poured into the prepared polytetrafluoroethylene mold, and then the mold is directly placed in the liquid nitrogen pool for freeze-forming for 2 minutes. Then it is demolded and taken out to obtain a wet blank.

[0043] 3) Vacuum drying: The formed wet blank is directly placed in an environment of -20°C for vacuum drying, maintaining a vacuum degree of -0.10MPa, and the vacuum freeze-drying time is 36 minutes.

[0044] 4) High-temperature sintering: The dried support is placed in the kiln and heated as follows: first, it is heated to 200℃ in 4 hours, then to 1250℃ in 5 hours, and then held at that temperature for 3 hours and allowed to cool naturally to obtain the ceramic film support.

[0045] Example 3

[0046] This embodiment provides a method for preparing a freeze-formed high-porosity ceramic membrane support, the steps of which are as follows:

[0047] 1) Put 1000g of 20-micron alumina powder, 100g of washed kaolin, 2g of sodium carboxymethyl cellulose, 3g of sodium tripolyphosphate, 1000g of water, and 30g of zirconium oxide into a ball mill for ball milling. The ball milling time is 120min and the ball milling speed is 90r / min. 5mm high-alumina ball milling beads are used. After ball milling, the slurry is completely passed through a 100-mesh sieve to obtain the slurry.

[0048] 2) Freeze-forming: The slurry prepared above is directly poured into the prepared polytetrafluoroethylene mold, and then the mold is directly placed in the liquid nitrogen pool for freeze-forming for 5 minutes. Then it is demolded and taken out to obtain a wet blank.

[0049] 3) Vacuum drying: The above-formed support is placed directly into an environment of -10°C for vacuum drying, maintaining a vacuum degree of -0.08MPa, and the vacuum freeze drying time is 48h, allowing the moisture in the support to sublimate directly to obtain a dry blank.

[0050] 4) High-temperature sintering: The dried support is placed in the kiln and heated as follows: first, it is heated to 200℃ in 5 hours, then heated to 1350℃ in 6 hours, and then held at -4 hours and cooled naturally to obtain the ceramic film support.

[0051] Example 4

[0052] The difference between this embodiment and Embodiment 1 is that the sintering aid used in this embodiment is magnesium oxide.

[0053] Example 5

[0054] The difference between this embodiment and Embodiment 1 is that the sintering aid used in this embodiment is yttrium oxide.

[0055] Example 6

[0056] The difference between this embodiment and Embodiment 1 is that the sintering aid used in this embodiment is a mixture of zirconium oxide, magnesium oxide and yttrium oxide in a mass ratio of 1:1:1.

[0057] The ceramic membrane supports obtained in Examples 1 to 3 were tested. Porosity was measured using a vacuum immersion water method, average pore size was measured using the immersion pressure method, flexural strength was measured using the three-point bending strength method, and pure water flux was measured using the flow rate of pure water passing through at 1 bar. The microstructure of the ceramic membrane supports was observed using scanning electron microscopy. The test results are shown in Table 1 and... Figure 1 , 2 As shown in Figure 3:

[0058] Table 1

[0059]

[0060] As shown in Table 1, the ceramic membrane supports prepared in Examples 1-3 have a porosity of over 50%, a flexural strength of over 40 MPa, an average pore size of over 0.1 μm, and a pure water flux of 3.2 m³ / s. 3 / (m 2 The properties of the ceramic membrane support, measured in *h*bar and above, are significantly superior to those of existing ceramic membrane supports on the market. Furthermore, the preparation of this ceramic membrane support involves only four process steps, making the entire process simple and using readily available raw materials. It eliminates the need for large amounts of binders and pore-forming agents to increase porosity, and molding can be completed in 1-5 minutes, greatly reducing molding time and the sintering cycle of the entire support. Simultaneously, vacuum freeze-drying, utilizing the sublimation of water, creates voids where water is present, significantly increasing the porosity of the support. Therefore, the method of this invention for preparing ceramic membrane supports not only offers simple and controllable raw materials and processes, but also produces performance indicators such as porosity and flexural strength that far exceed existing technologies. This method has a positive impact on the development of ceramic membranes and is worthy of widespread application.

[0061] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention. Technologies not described in detail in this invention are known technologies.

Claims

1. A method for preparing a freeze-formed high-porosity ceramic membrane support, characterized in that, Specifically, the following steps are included: 1) Slurry preparation: Alumina powder with a diameter of 3-20μm, washed kaolin, sodium carboxymethyl cellulose, sodium tripolyphosphate, water and sintering aid are all put into a ball mill for ball milling, and then passed through a 100-mesh sieve to obtain slurry; 2) Freeze-forming: The slurry described in step 1) is poured into the prepared polytetrafluoroethylene mold, and then the mold is directly placed in a liquid nitrogen pool for freeze-forming for 1-5 minutes. Then the mold is demolded to obtain a wet blank. 3) Vacuum drying: The wet blank described in step 2) is placed in a vacuum environment at -50°C to -10°C and freeze-dried to obtain a dry blank; 4) High-temperature sintering: The dry blank described in step 3) is placed in a kiln and sintered at high temperature, and then cooled naturally to obtain a ceramic film support. The slurry raw materials are formulated in the following weight ratios: 100 parts of alumina powder with a diameter of 3-20 micrometers, 5-10 parts of washed kaolin, 0.05-0.2 parts of sodium carboxymethyl cellulose, 0.05-0.3 parts of sodium tripolyphosphate, 50-100 parts of water, and 1-3 parts of sintering aid.

2. The preparation method according to claim 1, characterized in that, The sintering aid is one or more of zirconium oxide, magnesium oxide, and yttrium oxide.

3. The preparation method according to claim 2, characterized in that, The ball milling time is 30-120 min, the ball milling speed is 30-90 r / min, and the ball milling beads are 3-5 mm high alumina ball milling beads.

4. The preparation method according to claim 3, characterized in that, The vacuum degree of the vacuum freeze-drying is not higher than -0.08 MPa, and the vacuum freeze-drying time is 24-48 h.

5. The preparation method according to claim 4, characterized in that, The heating method for the high-temperature sintering is as follows: first, heat to 200℃ in 3-5 hours, then heat to 1190-1350℃ in 4-6 hours, and then hold at that temperature for 2-4 hours.

6. A freeze-formed high-porosity ceramic membrane support, characterized in that, The ceramic membrane support is prepared by any one of the preparation methods described in claims 1-5.

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