CN113121241B

CN113121241B - High-flux silicon carbide ceramic filter membrane and preparation method thereof

Info

Publication number: CN113121241B
Application number: CN202110448901.7A
Authority: CN
Inventors: 袁林峰; 约翰尼·马切尔; 胡广; 胡飞
Original assignee: Nanjing Ike Carter Emission Technology Co ltd
Current assignee: Nanjing Hanshen Material Technology Co ltd
Priority date: 2021-04-25
Filing date: 2021-04-25
Publication date: 2022-03-22
Anticipated expiration: 2041-04-25
Also published as: CN113121241A

Abstract

The invention provides a high-flux silicon carbide ceramic filter membrane and a preparation method thereof. By optimizing the sintering process and optimizing the formula of the membrane-making solution, fine silicon carbide particles are prevented from entering micropores of the carrier during the coating process due to capillary filtration and membrane formation, a separation layer with the average pore diameter of less than 0.2 mu m can be directly coated on the silicon carbide carrier with the average pore diameter of more than 10 mu m, and the fine silicon carbide particles are effectively prevented from entering the micropores of the carrier during the coating process. Therefore, the defects that multiple coating, namely at least 2 times of coating and 3 times of sintering are needed in the traditional preparation process of the ceramic membrane can be overcome, so that the production cost is reduced, and the product percent of pass is improved. Due to the removal of the middle layer, the flux of the ceramic membrane with the same aperture can be greatly improved.

Description

High-flux silicon carbide ceramic filter membrane and preparation method thereof

Technical Field

The invention relates to the technical field of ceramic filtering membranes, in particular to a high-flux silicon carbide ceramic filtering membrane and a preparation method thereof.

Background

The traditional silicon carbide film preparation is the same as that of a ceramic film, and the structure of the silicon carbide film is also a sandwich structure, namely a supporting layer, a middle layer and a separating layer. The support layer is a carrier of the membrane and mainly ensures the mechanical strength of the membrane. The separating layer plays a role in real filtration and separation. Since the pore size of the support is often at least 25 times greater than the particle size of the separation layer, in prior art processes, an intermediate layer is applied between the support layer and the separation layer to prevent the particles from penetrating into the support layer during the preparation of the separation layer. However, due to the existence of the intermediate layer, the flux is objectively reduced, and the difference among the pore diameters of the micropores of the carrier, the intermediate layer and the separation layer in the traditional process is small and usually varies between 1 and 5 times, so that the flux is low and the improvement difficulty is large.

As shown in fig. 1, the conventional process for preparing silicon carbide film requires at least 3 times of sintering, the preparation process is relatively complex and costly, and the product requires multiple coating, resulting in low yield and low throughput. In the conventional process, after each coating high-temperature sintering (generally sintering under the protection of inert gas such as argon at 2000-2400 ℃), the coating high-temperature sintering is carried out, and then the coating high-temperature sintering is carried out (at 700-1200 ℃) to remove carbon left by the high-temperature sintering, wherein the carbon is derived from green bodies or coating slurry and contains organic matters such as a binder, a dispersing agent and the like. If carbon is not removed, since carbon is a hydrophobic substance, the solvent/water in the slurry is hardly taken into the pores of the carrier by capillary force at the time of coating, and thus a coating film cannot be finally formed.

Therefore, in the conventional process, the product needs to be oxidized after high-temperature sintering. After the carrier is oxidized, the surface is hydrophilic due to the removal of carbon, and the pore size is relatively enlarged, so that the slurry solvent/water enters the pores of the carrier through capillary force to finally form a coating film, but the particle size of the coating particles in the coating film slurry is required to be large enough to prevent the coating particles from entering the carrier through the capillary force.

Disclosure of Invention

The invention aims to provide a preparation method of a high-flux silicon carbide ceramic filter body without removing carbon after a sintering process, namely, a carrier is not oxidized to remove carbon after being sintered, but residual carbon is remained, specifically, membrane layer slurry and a preparation process are optimized to reduce surface tension, so that the membrane layer slurry can still be coated by utilizing capillary force under the condition that the carrier is hydrophobic, and membrane layer fine particles are coated on the carrier with the average pore diameter of more than 10 mu m by utilizing the repulsion action of like charges generated by the like charges on the surface of the carrier and coating particles.

The invention provides a preparation method of a high-flux silicon carbide ceramic filter body in a first aspect, which comprises the following steps:

(1) preparing a multi-channel tubular blank, and sintering the multi-channel tubular blank at a high temperature to prepare a carrier with a microporous structure with a first mean pore diameter;

(2) erecting a carrier, loading the film layer slurry into a channel from the bottom of the carrier prepared in the step (1), and releasing the film layer slurry in the channel after the film layer slurry reaches the top of the carrier and is kept for a preset time to form a channel film layer; wherein the particles of the film layer slurry carry a charge of the same polarity as the surface of the support;

(3) drying the channel film layer prepared in the step (2);

(4) sintering the channel film layer at high temperature under the protection of inert atmosphere to form a microporous structure with a second mean pore diameter, and manufacturing a separation layer; and

(5) and (4) carrying out high-temperature oxidation sintering on the separation layer obtained in the step (4) to remove residual carbon.

Preferably, the preparation of the support comprises in particular the following processes:

mixing silicon carbide powder with a first particle size mismatching ratio, a first auxiliary agent and water, extruding and molding a multi-channel tubular blank, sintering the blank, and recrystallizing the blank to form a microporous structure with a first mean pore diameter on the wall of a channel to prepare a carrier;

preferably, the silicon carbide powder with the first particle size mismatching ratio comprises silicon carbide powder I and silicon carbide powder II, and the median particle size of the silicon carbide powder I is 5-30 times that of the silicon carbide powder II. More preferably, the median particle diameter of the silicon carbide powder I is between 10 and 30 μm; the median particle diameter of the silicon carbide powder II is between 0.5 and 6 mu m.

Preferably, the first auxiliary agent includes a binder, a plasticizer, and a dispersant. More preferably, the mass ratio of the silicon carbide powder I, the silicon carbide powder II, the binder, the plasticizer, the dispersant and the water is (50-75): (10-20): (4-8): (1-3): (1-3): (10-20).

Preferably, drying the multi-channel tubular body is further included before sintering the body at the high temperature.

Preferably, the film layer slurry is prepared by mixing silicon carbide powder with a second particle size matching ratio, a second auxiliary agent and water, wherein the silicon carbide powder with the second particle size matching ratio comprises silicon carbide powder III and silicon carbide powder IV, and the median particle size of the silicon carbide powder III is 3-8 times that of the silicon carbide powder IV.

Preferably, the median particle size of silicon carbide powder III is 0.5-6 μm, and the median particle size of silicon carbide powder IV is 0.1-3 μm.

Preferably, the second auxiliary agent comprises a binder, a plasticizer, a dispersing agent, an antifoaming agent and a surfactant, wherein the mass ratio of the silicon carbide powder III to the silicon carbide powder IV to the binder to the plasticizer to the dispersing agent to the antifoaming agent to the surfactant to water is (5-15): (5-15): (3-10): (5-15): (0-1.5): (0-1.5): (1-5): (50-80).

Preferably, the pH of the membrane layer slurry is between 6 and 10.

Preferably, the membrane layer slurry is processed by the following pretreatment method and then loaded into the channel:

adding alumina balls with the diameter of 8-10mm, and rolling and grinding for 12-48 hours.

Preferably, the membrane layer slurry enters the channel at a velocity of 20-100 mm/s.

Preferably, in the step (2), the predetermined time is 3 to 15 seconds.

Preferably, the high-temperature sintering of the channel film layer and the high-temperature sintering of the green body comprise degumming treatment. For example, under the protection of argon atmosphere, the temperature is raised to 300-500 ℃, and the temperature is maintained for 2-5 hours, so that the blank and the channel film layer are degummed.

And after degumming, carrying out high-temperature sintering to recrystallize the silicon carbide particles.

Preferably, the sintering temperature for recrystallization of the channel film layer is lower than the sintering temperature for recrystallization of the blank. More preferably, the sintering temperature for recrystallization of the channel film layer is between 1600-2000 ℃, and the sintering temperature for recrystallization of the green body is between 2000-2400 ℃.

Preferably, the particles in the film layer slurry carry a charge of the same nature as the surface of the support.

The second aspect of the present invention also provides a high-throughput silicon carbide ceramic filtration membrane produced by the method for producing a high-throughput silicon carbide ceramic filtration membrane described above, which is composed of a support and a separation layer, and does not include an intermediate layer.

Particularly preferably, the first mean pore size is 10 μm or more, and the second mean pore size is 0.2 μm or less. It is particularly preferred that the second mean pore size is in the range of 0.15 μm to 0.2. mu.m.

The third aspect of the present invention also provides a high-flux silicon carbide ceramic filtration membrane which is composed of a support having micropores and a separation layer having micropores, and which does not include an intermediate layer; wherein the average pore diameter of micropores in the support having micropores is 20 times or more than 20 times the average pore diameter of micropores in the separation layer having micropores.

Preferably, the average pore diameter of micropores in the support having micropores is 10 μm or more, and the average pore diameter of micropores in the separation layer having micropores is 0.2 μm or less.

Preferably, the average pore diameter of the micropores in the separation layer having micropores is between 0.15 μm and 0.2 μm.

Compared with the prior art, the preparation process of the ceramic filter membrane is adjusted and optimized, the intermediate layer and the preparation process of the intermediate layer in the traditional process are removed, the formula of the membrane slurry is optimized, oxidation and carbon removal are not carried out after the carrier is sintered and prepared, residual carbon is utilized to play a certain role in blocking the micropores of the carrier, so that the probability that silicon carbide small particles of a separation layer enter the pores of the carrier is reduced, and meanwhile, the like charge repulsion effect of the particles of the membrane slurry and the surface of the carrier is combined, so that the membrane slurry is prevented from entering the micropores of the carrier due to fine particles in the processes of capillary filtration and film formation during coating.

Through the process optimization of the invention, the silicon carbide carrier with the average pore diameter of more than 10 mu m can be directly coated with the silicon carbide film separation layer with the average pore diameter of 150nm, so that the silicon carbide film can be sintered for 2 times on the ultrafiltration application level to complete the preparation of the filter film, the defects that the traditional ceramic film needs a multilayer structure (the carrier, the intermediate layer and the separation layer) and is sintered for at least 3 times are avoided, the preparation of the intermediate layer is reduced, the production cost is greatly reduced, and the qualification rate of the product is improved.

Meanwhile, the ceramic filter membrane prepared by the invention only consists of the silicon carbide carrier and the separation layer, the preparation of the separation layer with high-magnification aperture on the large-aperture carrier is realized, the middle layer is not included, and compared with the existing filter membrane product with the same aperture specification, the flux of the ceramic filter membrane prepared by the invention can be greatly improved, and the flux after testing is improved by more than 30%.

It should be understood that all combinations of the foregoing concepts and additional concepts described in greater detail below can be considered as part of the inventive subject matter of this disclosure unless such concepts are mutually inconsistent. In addition, all combinations of claimed subject matter are considered a part of the presently disclosed subject matter.

Drawings

In the drawings, each identical or nearly identical component that is illustrated in various figures may be represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. Embodiments of various aspects of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a process route diagram for preparing a ceramic filtering membrane by adopting three-step sintering and oxidation in the conventional process.

FIG. 2 is a process scheme for preparing a ceramic filtration membrane with the removal of the intermediate layer according to an exemplary embodiment of the present invention.

Fig. 3 is a production process example of a ceramic filtration membrane according to an exemplary embodiment of the present invention.

Fig. 4 is an example of a process for preparing a silicon carbide support in the process for preparing a ceramic filtration membrane according to an exemplary embodiment of the present invention.

Fig. 5 is an example of a separation layer preparation and decarbonization process in the ceramic filtration membrane preparation process according to an exemplary embodiment of the present invention.

FIG. 6 is a schematic representation of a ceramic body comprising a support, an intermediate and a separating layer prepared using the conventional process shown in FIG. 1.

FIG. 7 is a schematic view of a silicon carbide ceramic membrane obtained by the ceramic filtration membrane production method of example 1, which does not include an intermediate layer.

FIG. 8 is a graph showing pore size measurements of a silicon carbide ceramic membrane prepared by the method for preparing a ceramic filtration membrane according to example 1, wherein the mean pore size of the support is 10.5. mu.m.

FIG. 9 is a graph showing a pore size test of a separation layer of a silicon carbide ceramic membrane obtained by the ceramic filtration membrane preparation method of example 1, wherein the mean value of the pore size of the separation layer was 0.15. mu.m.

FIG. 10 is a pore size diagram of a support of a silicon carbide ceramic membrane obtained by the ceramic filtration membrane preparation method of example 2, which does not include an intermediate layer and has a mean pore size of 15 μm.

FIG. 11 is a graph showing a pore size test of a separation layer of a silicon carbide ceramic membrane obtained by the ceramic filtration membrane preparation method of example 2, wherein the mean value of the pore size of the separation layer was 0.2. mu.m.

Detailed Description

In order to better understand the technical content of the present invention, specific embodiments are described below with reference to the accompanying drawings.

In this disclosure, aspects of the present invention are described with reference to the accompanying drawings, in which a number of illustrative embodiments are shown. Embodiments of the present disclosure are not necessarily intended to encompass all aspects of the invention. It should be appreciated that the various concepts and embodiments described above, as well as those described in greater detail below, may be implemented in any of numerous ways, as the disclosed concepts and embodiments are not limited to any one implementation. In addition, some aspects of the present disclosure may be used alone, or in any suitable combination with other aspects of the present disclosure.

In the conventional process for preparing a ceramic membrane with a sandwich structure as shown in fig. 1, at least 3 times of sintering are required in the preparation process, and after each time of coating and high-temperature sintering, the ceramic membrane needs to be subjected to high-temperature oxidation to remove carbon remained in the high-temperature sintering, because the preparation process is relatively complicated and high in cost, and because the ceramic membrane needs to be coated for multiple times, the yield is low. Fig. 6 is a diagram showing an example of a ceramic membrane having a typical sandwich structure prepared according to a conventional sintering process, which has a typical structure of a support, an intermediate layer and a separation layer, and the pore size mean of the intermediate layer is about 2 times that of the separation layer, and flux is affected to some extent due to the presence of the intermediate layer and the low-fold size of the pore size of the intermediate layer and the separation layer.

As shown in FIG. 2, the invention aims to provide an improved preparation method of a ceramic filter membrane, which is used for removing an intermediate layer and a preparation process thereof, and adopts a process of directly coating a separation layer on the basis of a carrier once, namely, after the carrier is sintered, the separation layer is directly coated, and carbon removal is carried out after sintering. By optimizing the sintering process and optimizing the formula of the membrane-making solution, fine silicon carbide particles are prevented from entering the microporous structure of the carrier during the coating process due to capillary filtration and membrane formation, a separating layer with micropores of 150nm in average pore diameter can be directly coated on the silicon carbide carrier with the average pore diameter of more than 10 mu m, and the fine silicon carbide particles of membrane slurry are effectively prevented from entering the pores of the carrier during the coating process. Therefore, the defects that multiple coating, namely at least 2 times of coating (firstly coating the intermediate layer on the carrier and then coating the separation layer on the intermediate layer) and 3 times of sintering are needed in the traditional preparation process of the ceramic membrane can be avoided, so that the production cost is reduced, and the product percent of pass is improved. Due to the removal of the middle layer, the flux of the ceramic membrane with the same aperture can be greatly improved.

The preparation method of the present invention is particularly suitable for preparing a ceramic filtration membrane of a separation layer having a pore size difference of a microporous structure of 20 times or more on the basis of a large pore size support, and the prepared ceramic filtration membrane structure is composed of only the large pore size support and the separation layer attached to the surface of the support, and particularly, the average pore size value (first pore size D1) of the pores of the support is 20 times or more of the average pore size value (second pore size D2) of the pores of the separation layer, and in the following examples, we further explain by taking as an example that the separation layer having a microporous structure with an average pore size of less than 0.2 μm is directly coated on a silicon carbide support having a microporous structure with an average pore size of 10 μm or more.

As shown in the drawings, we illustrate more specifically exemplary implementations of the preparation method of the present invention.

The preparation process shown in fig. 3 comprises the following steps: preparing a multi-channel tubular blank, and sintering the multi-channel tubular blank at a high temperature to prepare a carrier with a microporous structure with a first mean pore diameter; erecting a carrier, loading the film layer slurry into a channel from the bottom of the prepared carrier, and releasing the film layer slurry in the channel to form a channel film layer after the film layer slurry reaches the top of the carrier and is kept for a preset time; wherein the particles of the film layer slurry carry a charge of the same polarity as the surface of the support; drying the channel film layer; sintering the channel film layer at high temperature under the protection of inert atmosphere to form a microporous structure with a second mean pore diameter, and manufacturing a separation layer; and carrying out high-temperature oxidation sintering on the separation layer to remove residual carbon.

As a specific example of the invention, the preparation of the high-flux low-cost silicon carbide ceramic filter membrane is taken as an example, and the process comprises the following steps:

mixing silicon carbide powder with a first particle size mismatching ratio, a first auxiliary agent and water, extruding and molding a multi-channel tubular blank, sintering the blank at a high temperature, and recrystallizing the blank to form a microporous structure with a first mean pore diameter on the wall of a channel to prepare a carrier;

erecting a carrier, loading the film layer slurry into each channel from the bottom of the carrier, and releasing the film layer slurry in the channel after the film layer slurry reaches the top of the carrier and keeping for a preset time to form a channel film layer; the film layer slurry is prepared by mixing silicon carbide powder with a second particle size mismatching ratio, a second auxiliary agent and water, and the pH value of the slurry is controlled to be 6-10;

drying the channel film layer;

forming a microporous structure with a second mean pore diameter by sintering the channel membrane layer at a high temperature under the atmosphere protection condition, and manufacturing a separation layer; and

and carrying out high-temperature oxidation sintering on the separation layer to remove residual carbon in the separation layer.

It is particularly desirable to include drying of the multi-channel tubular body prior to recrystallization of the body. For example, the multi-channel tubular blank is dried in a drying chamber for 24-48 hours, and the environmental conditions controlled in the drying chamber are as follows: relative humidity 20-60%, temperature 25-50 deg.C. In the drying process, hot air is introduced into the green body channel at the flow rate of 0.5-2 m/s.

Preferably, the silicon carbide powder with the first particle size mismatching ratio comprises silicon carbide powder I and silicon carbide powder II, and the median particle size of the silicon carbide powder I is 5-30 times that of the silicon carbide powder II. Particularly, the median particle diameter of the silicon carbide powder I is between 10 and 30 mu m; the median particle diameter of the silicon carbide powder II is between 0.5 and 6 mu m.

Exemplary first adjuvants include binders, plasticizers, and dispersants. Particularly preferably, the mass ratio of the silicon carbide powder I, the silicon carbide powder II, the adhesive, the plasticizer, the dispersing agent and the water is (50-75): (10-20): (4-8): (1-3): (1-3): (10-20).

Preferably, the binder is selected from methyl hydroxyethyl cellulose or polyvinyl alcohol, the plasticizer is polyethylene glycol or phthalate, and the dispersant is acrylic polymer.

Preferably, the silicon carbide powder with the second particle size mismatching ratio comprises silicon carbide powder III and silicon carbide powder IV, and the median particle size of the silicon carbide powder III is 3-8 times that of the silicon carbide powder IV. Particularly, the median particle size of silicon carbide powder III is 0.5-6 μm, and the median particle size of silicon carbide powder IV is 0.1-3 μm.

Particularly preferably, the median particle diameters of the silicon carbide powder III and the silicon carbide powder IV are controlled to be between 0.1 and 1.5 μm, so as to effectively prepare a microporous structure with the pore diameter of less than 200 μm.

It is to be understood that the median particle diameter, also referred to as the median particle size, of the examples of the present invention.

The second auxiliary agent comprises a binder, a plasticizer, a dispersing agent, an antifoaming agent and a surfactant, wherein the mass ratio of the silicon carbide powder III to the silicon carbide powder IV to the binder to the plasticizer to the dispersing agent to the antifoaming agent to the surfactant to water is (5-15): (5-15): (3-10): (5-15): (0-1.5): (0-1.5): (1-5): (50-80).

Preferably, the carbon binder may be at least one of methylhydroxyethyl cellulose or polyvinyl alcohol. The plasticizer adopts polyethylene glycol or phthalate; the dispersing agent adopts acrylic polymer; the defoaming agent adopts siloxane polyether and the surfactant adopts alcohol.

The film layer slurry which is uniformly mixed according to the mass ratio is treated by the following pretreatment method and then loaded into a channel:

Preferably, in some embodiments of the present invention, the film layer slurry is controlled to be loaded into the channel at a speed of 20-100 mm/s. More preferably, the film layer slurry is held for 3-15 seconds after it reaches the top of the carrier to achieve effective coating and form the film layer by capillary action.

Therefore, through optimization of the formula of the membrane slurry, after the carrier is sintered and prepared, oxidation decarbonization is not carried out, residual carbon is utilized to play a certain role in blocking micropores of the carrier, so that the probability that the silicon carbide particles of the separation layer enter the pores of the carrier is reduced, and meanwhile, the like charge repulsion of the particles of the membrane slurry and the surface of the carrier is combined, so that the membrane slurry is prevented from entering the micropores of the carrier due to fine particles in the processes of capillary filtration and film formation during coating.

Alternatively, the configuration of the film slurry can be adjusted in various ways to make the particles (silicon carbide particles) and the surface of the carrier carry the same charges, for example, by fluid (slurry) property adjustment, pH adjustment, etc., which can be implemented by one of them, or by a combination of more than 2 means.

For example, in a separation layer film slurry prepared by mixing silicon carbide powder with a second particle size mismatching ratio, a second auxiliary agent and water, the pH value of the slurry can be controlled to be 6-10, so that the particles in the film slurry and the surface of the carrier carry charges with the same polarity, and the particles in the film slurry are prevented from entering the pore size of the carrier through the repulsion action of the charges with the same polarity.

In some embodiments of the present invention, the high-temperature sintering of the channel film and the high-temperature sintering of the green body include a degumming process, as shown in fig. 4 and 5. For example, under the protection of argon atmosphere, heating to 300-.

After degumming, heating again to the heat preservation range of recrystallization, and recrystallizing. And finally, cooling to room temperature along with the furnace.

In the specific implementation process, the sintering temperature of the recrystallization of the channel film layer is lower than that of the recrystallization of the blank. Preferably, the sintering temperature for recrystallization of the channel film layer is between 1600-2000 ℃, and the sintering temperature for recrystallization of the green body is between 2000-2400 ℃.

The raw materials for the green body and the slurry are commercially available. Preferably, the purity of silicon carbide powder I is greater than 98%, and the purity of silicon carbide powder II is greater than 99%. The purities of the silicon carbide powder III and the silicon carbide powder IV are more than 99 percent.

The foregoing production method will be described below with reference to specific examples.

Example 1

1) Shaping and sintering of silicon carbide bodies

Selecting raw materials: silicon carbide powder I, silicon carbide powder II, methyl hydroxyethyl cellulose, polyethylene glycol, acrylic polymer and water, wherein the mass ratio of the silicon carbide powder I to the silicon carbide powder II is 60: 18: 6: 2: 2: 12 selecting for standby.

The median particle diameter of the silicon carbide powder I is 20 times of that of the silicon carbide powder II. Median particle diameter of silicon carbide powder I: 20 μm, purity greater than 98%, median particle size of silicon carbide powder II: 1 μm, purity more than 99%.

Mixing raw materials: the raw materials selected according to the proportion are mixed at room temperature (20-25 ℃) to form a uniform mixture according to the sequence of adding liquid and adding powder.

Molding: and putting the obtained mixture into an extrusion molding machine, and molding into a multi-channel tubular blank under the extrusion pressure of 120 MPa.

And (3) drying: the extruded green body was dried in a drying chamber for 24 hours at relative humidity: 50-60 percent, the temperature is 25-30 ℃, hot air is introduced into the green body channel, and the flow rate is 2 m/s.

High-temperature sintering recrystallization: and sintering the dried blank at high temperature under the protection of argon atmosphere. Heating to 500 ℃, preserving heat for 2 hours, and degumming the blank body. After degumming, heating to 2400 ℃, sintering for 18 hours, recrystallizing and sintering the blank, keeping the temperature for 5 hours, and finally cooling to room temperature along with the furnace.

2) Coating of silicon carbide film

Preparing slurry: silicon carbide powder III, silicon carbide powder IV, methyl hydroxyethyl cellulose, phthalate, an acrylic polymer dispersing agent, a siloxane polyether defoaming agent, an alcohol surfactant PEG and water, wherein the mass ratio of the components is 15: 10: 5: 8: 1.5: 1.5: 3: 56, uniformly mixing, controlling the pH value to be 8-9, adding alumina balls with the diameter of 8-10mm, and rolling and grinding for 48 hours to prepare film slurry;

the median particle diameter of silicon carbide powder III is 5 times of that of silicon carbide powder IV.

Median particle diameter of silicon carbide powder III: 1.5 μm, purity more than 99%, median diameter of silicon carbide powder IV: 0.3 μm and purity more than 99%.

Coating a film layer: and (3) vertically standing the carrier, enabling the film layer slurry to enter the carrier channel from the bottom at the speed of 80mm/s, stopping for 4 seconds when the film layer slurry reaches the top of the carrier, finally releasing the film layer slurry in the carrier channel, and forming a film layer by utilizing the capillary action.

And (3) drying the film layer: the prepared silicon carbide film was dried in a drying chamber for 24 hours at relative humidity: 50-60 percent, the temperature is 25-30 ℃, hot air is introduced into the green body channel, and the flow rate is 2 m/s.

High-temperature sintering recrystallization: and (4) sintering the dried silicon carbide film at high temperature under the protection of argon atmosphere. Heating to 500 ℃, and preserving heat for 2 hours to degum the silicon carbide film. After degumming, heating to 1600 ℃, recrystallizing and sintering, keeping the temperature for 5 hours, and finally cooling to room temperature along with the furnace. And the sintering temperature rise process is carried out for 20 hours.

Oxidizing and sintering: the obtained silicon carbide film was subjected to oxidation sintering at 800 ℃ under air-supply to remove residual carbon and improve the mechanical strength of the film, and the obtained product was a 100% recrystallized silicon carbide film, as shown in FIG. 7, having a separation layer thickness of about 47.9 μm, attached to the surface of the support and containing no intermediate layer.

Through detection, the average pore diameter of the microporous structure of the prepared ceramic membrane carrier is 10.5 microns (shown in figure 8), the average pore diameter of the microporous structure of the separation layer is 0.15 microns (shown in figure 9), the preparation of the large-pore-diameter carrier is realized, and the coating and the preparation of the separation layer with the small average pore diameter (0.15 microns) are realized on the basis of the preparation, so that the water quality of filtered water is ensured, and meanwhile, the high flux is ensured based on the large-pore-diameter carrier.

Example 2

1) Shaping and sintering of silicon carbide bodies

Selecting raw materials: silicon carbide powder I, silicon carbide powder II, methyl hydroxyethyl cellulose, polyethylene glycol, acrylic polymer and water, wherein the mass ratio of the silicon carbide powder I to the silicon carbide powder II to the methyl hydroxyethyl cellulose to the polyethylene glycol is 65: 15: 5: 1: 1: 13 to select for standby.

The median particle diameter of the silicon carbide powder I is 15 times of that of the silicon carbide powder II. Median particle diameter of silicon carbide powder I: 30 μm, purity greater than 98%, median diameter of silicon carbide powder II: 2 μm, purity over 99%.

High-temperature sintering recrystallization: and sintering the dried blank at high temperature under the protection of argon atmosphere. Heating to 500 ℃, preserving heat for 2 hours, and degumming the blank body. After degumming, heating to 2400 ℃, sintering for 25 hours, recrystallizing and sintering the blank, keeping the temperature for 5 hours, and finally cooling to room temperature along with the furnace.

2) Coating of silicon carbide film

Preparing slurry: silicon carbide powder III, silicon carbide powder IV, methyl hydroxyethyl cellulose, phthalate, an acrylic polymer dispersing agent, a siloxane polyether defoaming agent, an alcohol surfactant PEG and water, wherein the mass ratio of the components is 15: 15: 6: 6: 1.5: 1.5: 4: 51, uniformly mixing, controlling the pH value to be 7-8, adding alumina balls with the diameter of 8-10mm, and rolling and grinding for 48 hours to prepare film slurry;

Coating a film layer: vertically standing the carrier, allowing the film layer slurry to enter the carrier channel from the bottom at the speed of 80mm/s, stopping for 3 seconds when the film layer slurry reaches the top of the carrier, and finally releasing the film layer slurry in the carrier channel to form a film layer by utilizing the capillary action.

High-temperature sintering recrystallization: and (4) sintering the dried silicon carbide film at high temperature under the protection of argon atmosphere. Heating to 500 ℃, and preserving heat for 2 hours to degum the silicon carbide film. After degumming, heating to 1800 ℃, carrying out recrystallization sintering in a sintering heating process for 25 hours, keeping the temperature for 5 hours, and finally cooling to room temperature along with the furnace.

Oxidizing and sintering: and (3) carrying out 800 ℃ oxidation sintering on the obtained silicon carbide film under the condition of introducing air, thereby removing residual carbon and improving the mechanical strength of the film, wherein the obtained product is a 100% recrystallized silicon carbide film.

The prepared ceramic membrane support was examined to have a pore size mean of the microporous structure of 15 μm (see fig. 10), a pore size mean of the microporous structure of the separation layer of 0.2 μm (see fig. 11), and no intermediate layer was included.

The ceramic membranes prepared according to the above examples were tested on the ceramic membranes prepared according to examples 1 and 2, and it can be seen from the test results that the average pore size of the microporous structure of the support of the prepared ceramic membrane is above 10 μm (as shown in fig. 8 and 10), and the average pore size of the microporous structure of the separation layer is below 0.2 μm (as shown in fig. 9 and 11), so as to realize the preparation of the support with large pore size and the coating and preparation of the separation layer with small pore size on the basis of the above, and the technology of the present invention particularly realizes the preparation of the ceramic filtration membrane with the difference between the pore size of the micropores of the separation layer and the pore size of the micropores of the support being up to 20 times or more than 20 times. Through the raw materials and the preparation process in the embodiment, the preparation of the silicon carbide ceramic membrane with the mean pore diameter of the micropores of the carrier being more than 10 microns and the mean pore diameter of the micropores of the separation layer being less than 0.2 microns can be realized, particularly preferably, the mean pore diameter of the micropores of the separation layer can be controlled within the range of 0.15-0.2 microns, and the preparation of the ceramic filter membrane with low cost and high flux can be realized.

The silicon carbide ceramic membrane prepared in the embodiment 1 of the invention is tested, and meanwhile, the ceramic membrane with the traditional sandwich structure and the ceramic membrane prepared by the invention have similar average pore diameter (0.15 mu m), so that the pure water flux of the traditional silicon carbide membrane (sandwich structure) is compared with that of the novel silicon carbide membrane (middle layer removed): 3000LMH/bar vs 4000LMH/bar, the flux of the ceramic membrane prepared by the process is obviously improved by more than 30%. Meanwhile, in a pore test result, the porosity of the ceramic body prepared by the method reaches over 42 percent, and high-flux filtration is realized.

The strength of the film layer structure of the ceramic film prepared in this example 1 was tested, and the separation layer (i.e., the film) obtained as a result of the test had a high mechanical strength, and the flexural strength was 25MPa or more. The test results of the membranes passing multiple sets of tests can be maintained at about 35 MPa.

Although the present invention has been described with reference to the preferred embodiments, it is not intended to be limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, the protection scope of the present invention should be determined by the appended claims.

Claims

1. A preparation method of a high-flux silicon carbide ceramic filter membrane is characterized by comprising the following steps:

(1) preparing a multi-channel tubular blank, sintering the multi-channel tubular blank at a high temperature, and preparing a carrier with a microporous structure with a first mean pore size through recrystallization;

(3) drying the channel film layer prepared in the step (2);

2. The method for preparing a high flux silicon carbide ceramic filter membrane according to claim 1, wherein the preparation of the support of the step (1) comprises the steps of:

mixing the silicon carbide powder with the first particle size mismatching ratio, a first auxiliary agent and water, extruding and molding a multi-channel tubular blank, sintering the blank, and recrystallizing the blank to form a microporous structure with a first mean pore diameter on the wall of a channel to obtain the silicon carbide composite material.

3. The method for preparing the high-flux silicon carbide ceramic filter membrane according to claim 2, wherein the silicon carbide powder with the first particle size mismatching ratio comprises silicon carbide powder I and silicon carbide powder II, and the median particle size of the silicon carbide powder I is 5-30 times that of the silicon carbide powder II.

4. The preparation method of the high-flux silicon carbide ceramic filter membrane according to claim 3, wherein the median particle size of the silicon carbide powder I is between 10 and 30 μm; the median particle diameter of the silicon carbide powder II is between 0.5 and 6 mu m.

5. The method for preparing a high flux silicon carbide ceramic filtration membrane according to claim 3, wherein the first auxiliary agent comprises a binder, a plasticizer, and a dispersant.

6. The preparation method of the high-flux silicon carbide ceramic filter membrane according to claim 5, wherein the mass ratio of the silicon carbide powder I, the silicon carbide powder II, the binder, the plasticizer, the dispersant and the water is (50-75): (10-20): (4-8): (1-3): (1-3): (10-20).

7. The method for preparing the high-flux silicon carbide ceramic filter membrane according to claim 1, wherein the step (1) further comprises drying the multi-channel tubular blank before sintering the multi-channel tubular blank at high temperature.

8. The method for preparing the high-flux silicon carbide ceramic filter membrane according to claim 1, wherein in the step (2), the membrane layer slurry is prepared by mixing silicon carbide powder with a second particle size mismatching ratio, a second auxiliary agent and water, the silicon carbide powder with the second particle size mismatching ratio comprises silicon carbide powder III and silicon carbide powder IV, and the median particle size of the silicon carbide powder III is 3-8 times that of the silicon carbide powder IV.

9. The preparation method of the high-flux silicon carbide ceramic filter membrane according to claim 8, wherein the median particle size of the silicon carbide powder III is 0.5-6 μm, and the median particle size of the silicon carbide powder IV is 0.1-3 μm.

10. The method for preparing the high-flux silicon carbide ceramic filter membrane according to claim 8, wherein the second auxiliary agent comprises a binder, a plasticizer, a dispersant, an antifoaming agent and a surfactant, and the mass ratio of the silicon carbide powder III, the silicon carbide powder IV, the binder, the plasticizer, the dispersant, the antifoaming agent, the surfactant and the water is (5-15): (5-15): (3-10): (5-15): (0-1.5): (0-1.5): (1-5): (50-80).

11. The method for preparing a high flux silicon carbide ceramic filtration membrane according to any one of claims 8 to 10, wherein the pH of the membrane slurry is between 6 and 10.

12. The method for preparing a high flux silicon carbide ceramic filtration membrane according to any one of claims 8 to 10, wherein the membrane slurry is first pretreated and then loaded into the channel by:

13. The method for preparing a high flux silicon carbide ceramic filtration membrane according to claim 1, wherein the membrane slurry is loaded into the channel at a speed of 20-100 mm/s.

14. The method for preparing a high flux silicon carbide ceramic filtration membrane according to claim 1, wherein the predetermined time is 3 to 15 seconds in the step (2).

15. The preparation method of the high-flux silicon carbide ceramic filter membrane according to claim 1, wherein in the step (1) or (4), the high-temperature sintering process of the green body and the high-temperature sintering process of the channel further comprise a degumming treatment.

16. The method for preparing the high-flux silicon carbide ceramic filter membrane according to claim 1, wherein the temperature for sintering the green body at high temperature in the step (1) is between 2000 ℃ and 2400 ℃.

17. The method for preparing the high-flux silicon carbide ceramic filter membrane as claimed in claim 1, wherein the temperature in the high-temperature sintered channel membrane layer is between 1600 ℃ and 2000 ℃.

18. A high flux silicon carbide ceramic filtration membrane prepared by the method for preparing a high flux silicon carbide ceramic filtration membrane according to any one of claims 1 to 17.

19. The high flux silicon carbide ceramic filtration membrane according to claim 18, wherein the first mean pore size is 10 μm or more and the second mean pore size is 0.15 μm to 0.2 μm.