A recrystallized silicon carbide honeycomb ceramic membrane for water treatment and a method of making the same

Abstract

The application discloses a recrystallized silicon carbide honeycomb ceramic membrane for water treatment, which comprises a silicon carbide honeycomb ceramic body made by recrystallization sintering, internally provided with through holes arranged along an axis, and adjacent two through holes are alternately blocked at opposite ends, wherein the total air gap rate of the silicon carbide honeycomb ceramic body is 40-50%, the pore size of the intrawall void is 4 nm-20 um, the wall thickness between adjacent through holes is 100-1000 nm, and the maximum tolerable pressure of the silicon carbide honeycomb ceramic body is 30-60 kg pressure; and the silicon carbide honeycomb ceramic body is sintered from the following components by weight: 60-70% silicon carbide powder, 3-6% binder, 5-20% pore former, 4-7% sintering agent and 6-10% lubricant. The recrystallized silicon carbide honeycomb ceramic membrane can realize the functions of microfiltration, ultrafiltration, nanofiltration and even reverse osmosis membrane in the field of water treatment, and has many advantages such as high pressure resistance, strong acid and alkali corrosion resistance and long service life.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of water purification and treatment. In particular, the present application relates to a recrystallized silicon carbide honeycomb ceramic membrane for water treatment and a method for preparing the same. BACKGROUND

[0002] Silicon carbide is an excellent inorganic material, and silicon carbide honeycomb ceramic refers to a honeycomb ceramic mainly composed of silicon carbide (Sic). Compared with other honeycomb ceramics, silicon carbide honeycomb ceramic has the advantages of small thermal expansion coefficient, good thermal stability, large specific surface area, strong oxidation resistance, high porosity, corrosion resistance, etc., and is widely used in the fields of automobile exhaust treatment, power system, construction engineering, petroleum and chemical industry, etc.

[0003] The preparation methods of silicon carbide honeycomb ceramic include silicon bonding method, liquid phase sintering method, recrystallization sintering method, etc. The silicon bonding method refers to mixing silicon carbide powder as raw material with additives and silicon powder, and then performing processes such as pressing and extrusion to obtain the finished product. This method has the advantages of good product quality and high production efficiency, and is the mainstream preparation method of silicon carbide honeycomb ceramic. The sintering method has the problems of poor product quality, complex production process and difficult parameter control, and has not been widely applied at present.

[0004] Honeycomb ceramics are various, and can be divided into cordierite honeycomb ceramic, zircon honeycomb ceramic, aluminum titanate honeycomb ceramic, silicon nitride honeycomb ceramic, silicon carbide honeycomb ceramic, spodumene honeycomb ceramic, mullite honeycomb ceramic, etc. according to different raw materials. In recent years, with the increasing demand for application, the development speed of honeycomb ceramic industry in China has been accelerated. In 2023, the market size of honeycomb ceramic in China reached 6.5 billion yuan, with a growth of more than 10% compared with the previous year. In the future, with the continuous expansion of the market space of honeycomb ceramic, the industry prosperity of silicon carbide honeycomb ceramic as a sub-product will be improved.

[0005] In Chinese patent application CN115532059A, a tubular honeycomb ceramic carrier for water treatment is disclosed, in particular recrystallized silicon carbide, with a bending strength > 50 MPa, a pure water flux greater than 8 m / (mh), and a pH tolerance range of 0-14. However, in its examples (e.g. Example 1), a composite material is prepared, not recrystallized silicon carbide: the dried green body is sintered in a vacuum furnace at 0.02 Pa, with a heating rate of 3.5°C / min, first to about 150°C, holding for 30 min; then to 950°C at a rate of 10°C / min, holding for 100 min; then to 420°C at a rate of 8°C / min, holding for 30 min, and finally naturally cooled to room temperature with the furnace; a multi-channel symmetric structure silicon carbide honeycomb ceramic membrane is obtained, with a membrane characterization filtration pore size of 10 pm, a porosity of 60%, and a pure water filtration flux of 100000 L / m2 / h / bar at a static pressure of 2.5 kg. The reason for this is that the sintering temperature of the silicon carbide is only 950°C, while the sintering temperature of recrystallized silicon carbide is at least 2300°C. Therefore, this document only mentions the use of recrystallized silicon carbide as a honeycomb ceramic filtration carrier for water, but does not prepare a qualified recrystallized honeycomb ceramic silicon carbide filtration carrier.

[0006] In Chinese patent application CN115367931A, a direct drinking water system is disclosed, in which a recrystallized silicon carbide honeycomb ceramic carrier is used, which is purchased from Guizhou Huangdicheli Purifier Co., Ltd. However, the recrystallized silicon carbide honeycomb ceramic filter of this company is mainly used for filtering automobile exhaust, and its performance is poor and not suitable for the field of water treatment.

[0007] Therefore, there is still a need in the art for a recrystallized silicon carbide honeycomb ceramic filtration membrane that can be widely used in the field of water treatment. SUMMARY

[0008] In a first aspect, the present application comprises a recrystallized silicon carbide honeycomb ceramic membrane for water treatment. It comprises a silicon carbide honeycomb ceramic body made by recrystallization sintering, internally provided with through holes arranged along an axis, two adjacent through holes being alternately plugged at opposite ends, wherein the total gas gap rate of the silicon carbide honeycomb ceramic body is 40-50%, preferably 45-50%, the pore size of the wall inner void is 4 nm-20 μm, preferably 8 nm-10 μm, more preferably 20 nm-5 μm, the wall thickness between adjacent through holes is 100-1000 nm, the maximum tolerable pressure of the silicon carbide honeycomb ceramic body is 25-50 kgf, preferably 30-50 kgf; the silicon carbide honeycomb ceramic body is sintered from the following components by weight: silicon carbide powder 70-80%, binder 3-6%, pore former 4-7%, sintering agent 4-7%, lubricant 6-10%. In some preferred embodiments, the silicon carbide honeycomb ceramic membrane is in the shape of a cylinder or a square column. In other embodiments, the shape of the through holes is square, and the width is 1.5-5 mm.

[0009] In the above technical solution, by alternately plugging the holes of the honeycomb ceramic carrier, the thin wall in the ceramic membrane through which the water to be filtered passes can be made, thereby realizing the filtering function. At the same time, by controlling the pore size of the honeycomb ceramic membrane, the particle size of the impurities in the water can be controlled, thereby realizing different water quality filtration.

[0010] In some preferred embodiments, the recrystallization sintering process comprises: placing the green body into a sintering furnace and sintering by temperature rising according to the following procedure: uniform temperature rising to 500°C for 7-8 hours to discharge oil; uniform temperature rising to 1100°C for 8-9 hours; uniform temperature rising to 1500°C for 5-6 hours; uniform temperature rising to 2000°C for 7-8 hours; uniform temperature rising to 2300°C for 25-30 hours to sinter and form.

[0011] In the above technical solution, by uniform temperature rising to 500°C for 7-8 hours, the oil can be discharged. By rising the temperature to 1600-1900 degrees, the glue can be discharged; after 1800, a gas protection tooling is applied. In some embodiments, for example, the protection gas is an inert gas, such as argon or nitrogen.

[0012] In some preferred embodiments, the total gas gap rate of the silicon carbide honeycomb ceramic membrane is 45%, 46%, 47%, 48%, 49% or 50%.

[0013] In some preferred embodiments, the silicon carbide powder is selected from one or both of micron-sized silicon carbide powder and nano-sized silicon carbide powder.

[0014] In some preferred embodiments, the sintering agent is boron carbide.

[0015] Advantages, reduce temperature, improve cost performance, reduce energy consumption.

[0016] In some preferred embodiments, the pore-forming agent is plastic.

[0017] In some preferred embodiments, the binder is selected from hydroxypropyl methylcellulose or a glue solution mixture. In some embodiments, the glue solution mixture comprises nitrile glue, ergo 5011 and 3M DP190.

[0018] In some preferred embodiments, the lubricant is glycerol.

[0019] In a second aspect, the present application provides a method for preparing the silicon carbide honeycomb ceramic membrane according to the aforementioned first aspect, comprising the following steps:

[0020] (1) Weigh the materials in proportion;

[0021] (2) Mix all the materials and then add them to the kneader for kneading for 3-4 hours;

[0022] (3) Extrude the kneaded paste with a mold to obtain a green body with through holes, and dry it at a temperature not higher than 170°C;

[0023] (4) Perform alternating hole plugging on the dried green body, and then dry it again;

[0024] (5) Sinter the alternating hole-plugged green body according to the following temperature rising program: uniformly raise the temperature to 500°C within 7-8 hours; uniformly raise the temperature to 1100°C within 8-9 hours; uniformly raise the temperature to 1500°C within 5-6 hours; uniformly raise the temperature to 2000°C within 7-8 hours; uniformly raise the temperature to 2300°C within 25-30 hours;

[0025] (6) Naturally cool the sintered blank to room temperature and discharge it.

[0026] In some preferred embodiments, in steps (3) and (4), the drying temperature is not higher than 170°C.

[0027] In summary, the product and method provided according to the present application have at least the following advantages:

[0028] 1. The recrystallized silicon carbide honeycomb ceramic membrane prepared by the method of the present application has nanoscale intrawall voids and can withstand a pressure of up to 25 kilograms or more, so it can be successfully applied to primary and secondary filtration of various water sources (including domestic water, industrial water, process wastewater, seawater, etc.), realizing the reuse of water resources;

[0029] 2. The recrystallized silicon carbide honeycomb ceramic membrane provided by the present application can realize the functions of microfiltration, ultrafiltration, nanofiltration and even reverse osmosis membrane in water treatment field, and has many advantages such as high pressure resistance, strong acid and alkali corrosion resistance and long service life. BRIEF DESCRIPTION OF DRAWINGS

[0030] The preferred features, embodiments and variations of the present application can be seen from the following detailed description, which provides sufficient information for those skilled in the art to implement the present application. The detailed description should not be regarded as limiting the scope of the foregoing summary in any way. The detailed description will be described with reference to the following multiple drawings.

[0031] Figure 1 and 2 is the appearance of sintered recrystallized silicon carbide honeycomb ceramic.

[0032] Figure 3 is the metallographic structure diagram of the recrystallized silicon carbide honeycomb ceramic carrier obtained by observing the recrystallized silicon carbide honeycomb ceramic carrier obtained by Examples 1 and 2 under a microscope.

[0033] Figure 4 is the photo of the extrusion failure caused by improper proportioning in Comparative Example 1.

[0034] Figure 5 is the photo of the surface cracks caused by too fast heating rate in Comparative Example 2.

[0035] Figure 6 is the photo of the cracks after sintering in Comparative Example 3.

[0036] Figure 7 is the photo of the insufficient crystallization effect, unobvious crystal grains and voids and insufficient strength in Comparative Example 4.

[0037] Figure 8 is the photo of the insufficient crystallization effect caused by improper temperature control in Comparative Example 5.

[0038] Figure 9 is the water filter device made of the recrystallized silicon carbide honeycomb ceramic carrier prepared by Example 2.

[0039] Figure 10 is the result diagram of the recrystallized silicon carbide honeycomb ceramic filter carrier in Comparative Example 1 tested under 25 kg water pressure by using the device shown in Figure 9 DETAILED DESCRIPTION

[0040] The detailed description of the present application is described below with reference to the drawings. Where possible, the same reference numbers will be used in the entire drawings and the following description to refer to the same and similar parts. The size of some parts shown in the drawings can be modified and / or enlarged for the purpose of clarity or illustration.​

[0041] ‌Silicon carbide honeycomb ceramics have a wide range of applications in various fields, including automotive exhaust treatment, power systems, construction engineering, and petroleum chemical industry. In the field of automotive exhaust treatment, silicon carbide honeycomb ceramics as catalyst carriers can effectively treat harmful substances in automobile exhaust and reduce air pollution. In addition, silicon carbide honeycomb ceramics also have good thermal stability, strong oxidation resistance, corrosion resistance and other advantages, making them widely used in power systems, construction engineering and petroleum chemical industry. However, there is currently no report on the application of silicon carbide honeycomb ceramics in water treatment.

[0042] Although there are currently patent applications for using silicon carbide honeycomb ceramics for water treatment, such as CN115532059 A, the compressive strength of the honeycomb ceramic silicon carbide material produced by this application is low, and cannot truly achieve the required compressive strength for nanoscale gap water filtration. For example, in Comparative Example 1, the silicon carbide honeycomb ceramic filter prepared by this method cracked when the water pressure reached 25 kgf, and could not be used.

[0043] In addition, a method for preparing a composite silicon carbide honeycomb ceramic carrier for water treatment is disclosed in patent application CN113321512A, but the strength of the composite silicon carbide honeycomb ceramic carrier prepared according to this method is also relatively low, and cannot be used for small pore size water filtration under high water pressure.

[0044] Therefore, there is still a need in the art for a honeycomb ceramic filtration carrier with high pressure resistance. In view of this, the inventors of the present application have improved the firing process of recrystallized silicon carbide honeycomb ceramic carriers through extensive practical work, thereby obtaining a recrystallized silicon carbide honeycomb ceramic carrier with high pressure resistance and good porosity distribution. The carrier can be used to filter various water sources in the nanoscale range, thereby realizing the water treatment application of recrystallized silicon carbide.

[0045] Example 1 Preparation of recrystallized silicon carbide honeycomb ceramic carrier with pore size 5-10 microns

[0046] (1) Take 70 kg of micron-sized silicon carbide, 4 kg of hydroxypropyl methylcellulose, 5 kg of plastic, 13 kg of boron carbide, and 8 kg of glycerol;

[0047] (2) Mix all the materials to obtain a mixture, divide the mixture into two parts, one with a total mass of 80 kg and the other with a total mass of 20 kg, then add the first part of the mixture to the kneading machine and knead for 4 hours;

[0048] (3) Extrude the kneaded paste with a mold to obtain a green body with through holes, and place it in an oven, increasing the temperature to 160°C at a rate of 10°C / min and maintaining it for 2 hours;

[0049] (4) The dried green body is alternately plugged with the second mixture, and then dried again;

[0050] (5) The green body alternately plugged is sintered according to the following temperature rising procedure: uniformly rising to 500°C in 8 hours; uniformly rising to 1100°C in 8 hours; uniformly rising to 1500°C in 6 hours; uniformly rising to 2000°C in 8 hours; uniformly rising to 2300°C in 28 hours;

[0051] The sintered body is naturally cooled to room temperature and discharged.

[0052] The appearance of the obtained recrystallized silicon carbide honeycomb ceramic is shown in Figure 1 The average pore diameter is 7.3 microns measured by mercury method.

[0053] Preparation of recrystallized silicon carbide honeycomb ceramic carrier with pore diameter of 0.1-1 micron

[0054] (1) 70 kg of micron-sized silicon carbide, 5 kg of special glue (602 of 1 kg; ergo 5011 of 2 kg; DP190 of 3M of 2 kg), 14 kg of boron carbide, 5 kg of plastic, and 6 kg of glycerol are weighed;

[0055] (2) All the materials are mixed to obtain a mixture, which is divided into two parts, one with a total mass of 80 kg and the other with a total mass of 20 kg, and then the first part of the mixture is added to the kneading machine for kneading for 4 hours;

[0056] (3) The kneaded paste is extruded with a mold to obtain a green body with through holes, which is placed in an oven and raised to 160°C at a rate of 10°C / min, and kept for 2 hours;

[0057] (4) The dried green body is alternately plugged with the second mixture, and then dried again;

[0058] (5) The green body alternately plugged is sintered according to the following temperature rising procedure: uniformly rising to 500°C in 8 hours; uniformly rising to 1100°C in 9 hours; uniformly rising to 1500°C in 6 hours; uniformly rising to 2000°C in 8 hours; uniformly rising to 2300°C in 30 hours;

[0059] The sintered body is naturally cooled to room temperature and discharged.

[0060] The appearance of the obtained recrystallized silicon carbide honeycomb ceramic is shown in Figure 2 Meanwhile, the metallographic structure of the recrystallized silicon carbide honeycomb ceramic carriers obtained in Examples 1 and 2 is observed by microscope, as shown in Figure 3The average pore diameter of the recrystallized silicon carbide honeycomb ceramic membrane prepared in Example 2 was measured to be 280 nm by mercury method.

[0061] Comparative Example 1

[0062] The difference from Example 1 is that the material ratio is different: micron-sized silicon carbide 78 kg, hydroxypropyl methylcellulose 4 kg, plastic 5 kg, boron carbide 5 kg, and glycerol 8 kg. The extrusion failed, see Figure 4 .

[0063] Comparative Example 2

[0064] The difference from Example 1 is that the temperature is raised at a rate of 40°C / hour in step (3). Due to the too fast temperature rising rate, cracks appear on the surface, see Figure 5 .

[0065] Comparative Example 3

[0066] The difference from Example 2 is that a common cellulose binder is used. Cracks appear after sintering, see Figure 6 .

[0067] Comparative Example 4

[0068] The difference from Example 1 is that the sintering process is different. The temperature is raised uniformly to 500°C within 7-8 hours, to 1100°C within 8-9 hours, to 1300°C within 5-6 hours, to 2000°C within 7-8 hours, and to 2300°C within 25-30 hours. This results in poor crystallization effect, and the grains and voids are not obvious, leading to insufficient strength. See Figure 7 .

[0069] Comparative Example 5

[0070] The difference from Example 2 is that the sintering process is different. The temperature is raised uniformly to 500°C within 7-8 hours, to 1500°C within 8-9 hours, to 2000°C within 7-8 hours, and to 2300°C within 25-30 hours. This results in poor crystallization effect, and the grains and voids are not obvious, leading to insufficient strength. See Figure 8 .

[0071] Application Example 1

[0072] The recrystallized silicon carbide honeycomb ceramic carrier prepared in Example 2 is made into a water filter, and tested under a pressure of 25 kg. The device is shown in Figure 9which includes a driving motor, a water inlet pipe, a water filter (with built-in recrystallized silicon carbide honeycomb ceramic membrane), a water outlet pipe, a control valve and other components. The recrystallized silicon carbide honeycomb ceramic carrier remains intact after the test and can be reused after cleaning.

[0073] Application Comparative Example 1

[0074] In this comparative example, a recrystallized silicon carbide honeycomb ceramic carrier was prepared according to the material ratio of Example 24 and the firing process of Example 35 of Chinese Patent No. CN100569700C. The pore size was measured by mercury method, and the average diameter of the voids was 21 microns. The average porosity was 34.9%. Then, the recrystallized silicon carbide honeycomb ceramic carrier was tested in the device shown in Figure 9 at a pressure of 25 kilograms, and the result was that the sidewall of the honeycomb ceramic carrier cracked. See Figure 10 .

[0075] The present application can be well obtained further advantages and improvements without departing from the scope of the present application. Although the present application has been shown and described in what is considered to be the most practical and preferred embodiment, it is recognized that departures can be made within the scope of the present application, which is not limited to the details disclosed herein, but is intended to be afforded the full scope of the claims to include any and all equivalent devices and apparatuses. Any discussion of the prior art throughout the specification should not be considered as an admission that such prior art is widely known or forms part of the common general knowledge of the art.

Claims

1. A recrystallized silicon carbide honeycomb ceramic membrane for water treatment, characterized in that... The silicon carbide honeycomb ceramic body, manufactured by recrystallization sintering, has through-holes arranged along an axis inside, with adjacent through-holes alternately blocked at opposite ends. The overall air gap of the silicon carbide honeycomb ceramic body is 40%-50%, the pore size of the internal voids is 4nm-20µm, the wall thickness between adjacent through-holes is 100-1000nm, and the maximum pressure resistance of the silicon carbide honeycomb ceramic body is 25-60 kg / min. By weight, the silicon carbide honeycomb ceramic body is fired from the following components: silicon carbide powder 6... The composition is 0-70%, binder 3-6%, pore-forming agent 5-20%, sintering agent 4-7%, lubricant 6-10%. The recrystallization sintering process includes: placing the green body into a sintering furnace and sintering according to the following procedure: uniformly heating to 500℃ within 7-8 hours; uniformly heating to 1100℃ within 8-9 hours; uniformly heating to 1500℃ within 5-6 hours; uniformly heating to 2000℃ within 7-8 hours; uniformly heating to 2300℃ within 25-30 hours; and introducing inert gas at 1800℃.

2. The recrystallized silicon carbide honeycomb ceramic membrane according to claim 1, characterized in that, The silicon carbide honeycomb ceramic membrane is cylindrical or square.

3. The recrystallized silicon carbide honeycomb ceramic membrane according to claim 1, characterized in that, The through holes are square, hexagonal, or octagonal.

4. The recrystallized silicon carbide honeycomb ceramic membrane according to claim 1, characterized in that, The sintering agent is boron carbide.

5. The recrystallized silicon carbide honeycomb ceramic membrane according to claim 1, characterized in that, The pore-forming agent is a plastic.

6. The recrystallized silicon carbide honeycomb ceramic membrane according to claim 1, characterized in that, The adhesive is selected from hydroxypropyl methylcellulose or a mixture of adhesives.

7. The recrystallized silicon carbide honeycomb ceramic membrane according to claim 1, characterized in that, The lubricant is glycerin.

8. A method for preparing a recrystallized silicon carbide honeycomb ceramic membrane according to any one of claims 1-7, characterized in that... Includes the following steps: Step (1): Weigh the materials according to the proportion; Step (2): Mix all the materials together and then add them to a kneader and knead for 3-4 hours; Step (3): Extrude the kneaded paste using a mold to obtain a green body with through holes, and dry it at a temperature not exceeding 170°C; Step (4): Alternately plug the holes in the dried green body, and then dry it again; Step (5): Sinter the green blanks with alternating plugs according to the following heating program: heat up to 500℃ at a constant rate over 7-8 hours; heat up to 1100℃ at a constant rate over 8-9 hours; heat up to 1500℃ at a constant rate over 5-6 hours; heat up to 2000℃ at a constant rate over 7-8 hours; heat up to 2300℃ at a constant rate over 25-30 hours. Step (6): Allow the fired blanks to cool naturally to room temperature before unloading.

9. The method according to claim 8, characterized in that, In steps (3) and (4), the drying temperature does not exceed 170°C.

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