A cordierite-based diesel particulate filter and a method of making the same

Abstract

The application relates to the technical field of diesel particulate filters, in particular to a cordierite-based diesel particulate filter and a preparation method thereof. The preparation method comprises the following steps: pre-treating a waste molybdenum silicide heating rod to obtain a mixed powder with molybdenum oxide and amorphous silicon oxide; mixing and grinding coal gangue, magnesium powder and the mixed powder to obtain fine-particle-size material; preparing a freezing medium; mixing the fine-particle-size material and the freezing medium, and then freezing to obtain a frozen sample; performing vacuum freeze drying on the frozen sample to obtain a dried sample; sintering the dried sample under carbon-embedding conditions, and then cooling to obtain the cordierite-based diesel particulate filter; the mass ratio of the mixed powder and the fine-particle-size powder is 0.0938-0.8963; through the synergistic cooperation of the molybdenum oxide formed by the molybdenum silicide and the freezing medium, the cordierite-based diesel particulate filter with a three-dimensional net-like pore structure and high porosity can be synthesized in one step.

Description

Technical Field

[0001] This application relates to the field of diesel particulate filter technology, and in particular to a cordierite-based diesel particulate filter and its preparation method. Background Technology

[0002] Diesel engine exhaust contains a large amount of air pollutants, including ozone, CO, and C. x H y NO x Emissions of particulate matter, including large amounts of particulate matter, pose serious health problems. Currently, diesel particulate filters (DPFs) are used to capture soot particles. These DPFs primarily feature a honeycomb structure, where the collected particulate matter undergoes a high-temperature regeneration process involving the combustion of bituminous coal, reducing the amount of harmful particulate matter released into the atmosphere from diesel engines. Additionally, DPFs are designed with an "active" regeneration function, which utilizes the temperature of fuel injection to increase exhaust temperature, thereby inducing the combustion of soot in the exhaust gas. This regeneration function requires high performance from the DPF in frequent thermal cycling environments, thus necessitating the development of honeycomb ceramic filters with superior structure and higher efficiency.

[0003] Currently, the cordierite structure used in DPFs has a melting point below 1470℃, making it difficult to meet the requirements for regeneration. Silicon carbide (SiC), on the other hand, has a melting point far above 2000℃, and its high-temperature mechanical properties, such as strength and elastic modulus, are superior to cordierite. Therefore, adding silicon carbide to cordierite ceramics can improve its thermomechanical properties, resulting in a longer service life for the prepared DPF. However, to meet the current National VI emission standards for motor vehicles, cordierite-based diesel particulate filters generally require a porosity of around 50%, an inner wall thickness of 8 mil to 10 mil, and a median pore size of 9 μm to 13 μm. Furthermore, existing cordierite-based diesel particulate filters are generally produced using talc, alumina, and kaolin as raw materials, with the addition of a large amount of pore-forming agents. These pore-forming agents typically use sinterable materials such as graphite, starch, and plastic particles. However, the large amount of sinterable materials can cause coking and misfires in cordierite-based DPFs, and also increase the manufacturing cost of the product. In addition, cordierite-based diesel particulate filters can be prepared in the form of honeycomb ceramic filters. However, honeycomb ceramic filters require extrusion molding using molds. When the groove width of the mold is narrow, raw materials with larger particle sizes or wider particle size distributions cannot be extruded into a honeycomb structure. Although cordierite-based diesel particulate filters can seal the inlet and outlet of the ceramic honeycomb channels, and although honeycomb ceramic filters can be made into wall-flow filter bodies to avoid the sealing phenomenon of ceramic honeycomb channels, the open cross-sectional area of ​​the wall-flow filter body is larger, which can reduce the back pressure loss of cordierite-based diesel particulate filters.

[0004] However, current cordierite-based diesel particulate filters generally use cordierite honeycomb ceramic materials as raw materials. In order to promote the formation of cordierite-based diesel particulate filters, a large amount of pore-forming agent needs to be added to the cordierite honeycomb ceramic raw materials to create pores, which undoubtedly increases the preparation cost of cordierite honeycomb ceramics.

[0005] Currently, the general method for preparing cordierite honeycomb ceramics is as follows: using magnesium oxide source, alumina forming source, silicon oxide source, and pore-forming agent containing potato starch, along with liquid carrier and binder, a high-porosity cordierite honeycomb ceramic is prepared. The porosity of the product is greater than 60%, and the median pore size is between 15μm and 30μm. Summary of the Invention

[0006] This application provides a cordierite-based diesel particulate filter and its preparation method to solve the following technical problem: how to reduce the amount of pore-forming agent used in the cordierite-based diesel particulate filter.

[0007] In a first aspect, this application provides a method for preparing a cordierite-based diesel particulate filter, the method comprising: Waste molybdenum silicide heating rods are pretreated to obtain a mixed powder containing molybdenum oxide and amorphous silica. Coal gangue, magnesium powder, and the mixed powder are mixed and ground to obtain fine-particle-size material; Preparation of freezing media; The fine-particle material and the freezing medium are mixed and then frozen to obtain a frozen sample; The frozen sample was subjected to vacuum freeze-drying to obtain a dried sample; The dried sample was sintered under carbon-embedded conditions and then cooled to obtain a cordierite-based diesel particulate filter. The mass ratio of the molybdenum silicide powder to the fine-particle powder is 0.0938 to 0.8963.

[0008] Optionally, the mass ratio of the fine-particle material to the freezing medium is 0.7 to 4:1.

[0009] Optionally, the mass ratio of the coal gangue to the fine-particle powder is 0.0918 to 0.8029. The mass ratio of the magnesium powder to the fine-particle powder is 0.0118 to 0.1032.

[0010] Optionally, the particle size of the mixed powder is 10 μm to 12 μm. The particle size of the coal gangue is 10μm to 40μm. The magnesium powder has a particle size of 4μm to 10μm.

[0011] Optionally, the freezing temperature is ≤-18℃, and the freezing time is ≥12h; The vacuum freeze-drying temperature is ≤-18℃, the vacuum freeze-drying time is ≥12h, and the vacuum freeze-drying pressure is ≤10kPa.

[0012] Optionally, the sintering process includes a debinding section, a heating and sintering section, and a cooling section; The temperature of the glue removal section is 550℃~650℃, and the time of the glue removal section is 1.5h~2.5h; The temperature of the heating and sintering section is 1300℃~1400℃, and the heating and sintering time is 2.5h~3.5h; The temperature of the cooling section is 750℃~850℃.

[0013] Optionally, the pretreatment includes crushing, grinding, heat treatment, and heat preservation; The pulverization time is 1.0h to 2.0h; The grinding media used in the grinding process includes zirconium oxide, the particle size of the grinding media is 10 mm to 30 mm, the grinding speed is 850 r / min to 950 r / min, and the grinding time is 2.0 h to 4.0 h. The final temperature of the heat treatment is 450℃~550℃, and the holding time is 12h~36h.

[0014] Optionally, the preparation of the cryogenic medium includes the following steps: Polyvinyl alcohol, carboxymethyl cellulose and deionized water are mixed and then stirred under heating conditions to obtain a freezing medium; wherein the heating temperature is ≥90℃.

[0015] Optionally, by mass fraction, the raw materials of the freezing medium satisfy the following: polyvinyl alcohol: 4%–6%, carboxymethyl cellulose: 0.5%–0.8%, and the remainder being deionized water.

[0016] Secondly, this application provides a cordierite-based diesel particulate filter, which is prepared by the preparation method described in the first aspect, wherein the raw materials of the diesel particulate filter, by mass fraction, satisfy the following: Coal gangue: 14.64%–83.54%, molybdenum silicide: 5.71%–83.47%, and magnesium powder: 1.88%–10.74%; The peak silicon carbide content of the diesel particulate filter and the mass ratio of the diesel particulate filter are 0 to 0.75.

[0017] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a method for preparing a cordierite-based diesel particulate filter. First, waste molybdenum silicide heating rods are pretreated to obtain a mixed powder of molybdenum oxide and amorphous silica. Then, coal gangue, magnesium powder, and the mixed powder are mixed to form fine-particle material. This fine-particle material is then mixed with a freezing medium and subjected to freezing, freeze-drying, and sintering to obtain the cordierite-based diesel particulate filter. This method uses waste molybdenum silicide as the raw material for silicon carbide, and coal gangue as the silicon and aluminum source. During the pretreatment stage, the molybdenum silicide in the waste molybdenum silicide is oxidized to form molybdenum oxide and silica. The formed silica can be reduced by carbon and magnesium powder to generate amorphous silica components through a sintering stage under carbon-burying conditions. Additionally, the mixed powder and fine-particle material... The mass ratio of the powder can be 0.0571 to 0.8347, which can promote the mixed powder to have sufficient molybdenum element, thereby increasing the amount of molybdenum oxide. Sufficient molybdenum oxide can cooperate with the freezing medium and occupy a large number of pores in the cordierite structure in the early stage of the sintering process. In the later stage of sintering, molybdenum oxide and freezing medium can be heated and evaporated, separating from the pores to form a partial pore structure, thereby increasing the porosity of the cordierite-based diesel particulate filter. Compared with the traditional carbothermal reduction method for preparing cordierite-based diesel particulate filters, the preparation method provided in this application only requires the addition of molybdenum silicide and freezing medium, without the need for additional pore-forming agents. This avoids the coking and misfire problems caused by pore-forming agents in sinterable materials, thereby effectively reducing the amount of pore-forming agent used in cordierite-based diesel particulate filters. Attached Figure Description

[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A schematic flowchart illustrating a method for preparing a cordierite-based diesel particulate filter, provided in an embodiment of this application; Figure 2 A detailed flowchart illustrating a method for preparing a cordierite-based diesel particulate filter, as provided in this application embodiment; Figure 3 This is a scanning electron microscope (SEM) schematic diagram of the cordierite-based diesel particulate filter provided in Embodiment 4 of this application; Figure 4A scanning electron microscope schematic diagram of the cordierite-based diesel particulate filter provided in Comparative Example 4 of this application; Figure 5 Comparative graphs showing the changes in flexural strength of cordierite-based diesel particulate filters provided in Example 4 and Comparative Example 4 of this application; Figure 6 Comparative XRD patterns of cordierite-based diesel particulate filters provided in Example 4 and Comparative Example 4 of this application; Figure 7 EDS analysis surface morphology images of cordierite-based diesel particulate filters provided in Example 4 and Comparative Example 4 of this application; Figure 8 EDS total surface spectra of cordierite-based diesel particulate filters provided in Example 4 and Comparative Example 4 of this application; Figure 9 This is a comparison chart showing the porosity analysis results of cordierite-based diesel particulate filters provided in Example 4 and Comparative Example 4 of this application. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0022] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range; for example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range such as 1, 2, 3, 4, 5, and 6, regardless of the range; in addition, whenever a numerical range is indicated herein, it means including any referenced number (fraction or integer) within the indicated range.

[0023] In this document, terms including "comprising" and the like mean "including but not limited to". Relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. "At least one" means one or more, and "more than one" means two or more; "at least one", "at least one of the following", or similar expressions refer to any combination of these items, including any combination of single or plural items; for example, "at least one of a, b, or c", or "at least one of a, b, and c", can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple. Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in this application are commercially available or can be prepared by existing methods.

[0024] It should be noted that, based on the background information in the existing technology, the inventors have discovered that current cordierite-based diesel particulate filters require the addition of a large amount of pore-forming agent to cordierite honeycomb ceramic raw materials to create pores, which undoubtedly increases the preparation cost of cordierite honeycomb ceramics.

[0025] Therefore, in the selection of raw materials for cordierite honeycomb ceramics, since coal gangue contains more than 50% SiO2 and Al2O3, it can be used as the silicon and aluminum source for cordierite honeycomb ceramics. Furthermore, in the selection of silicon carbide raw materials, waste molybdenum silicide heating rods can be selected as silicon carbide raw materials. Molybdenum silicide can both increase porosity and produce amorphous silica to synthesize silicon carbide. Therefore, these raw materials can be reused to manufacture cordierite-silicon carbide composite materials, rather than being ultimately treated as waste, thus reducing the preparation cost of cordierite honeycomb ceramics.

[0026] Figure 1 An exemplary schematic diagram of a method for preparing a cordierite-based diesel particulate filter according to an embodiment of this application is shown; like Figure 1 As shown in the embodiment of this application, a method for preparing a cordierite-based diesel particulate filter is provided, the method comprising: S1. Pre-treat the waste molybdenum silicide heating rod to obtain a mixed powder containing molybdenum oxide and amorphous silicon oxide; S2. The coal gangue, magnesium powder and the mixed powder are mixed and ground to obtain fine-particle-size material; S3. Prepare the freezing medium; S4. The fine-particle material and the freezing medium are mixed and then frozen to obtain a frozen sample; S5. The frozen sample is subjected to vacuum freeze-drying to obtain a dried sample; S6. The dried sample is sintered under carbon-embedded conditions and then cooled to obtain a cordierite-based diesel particulate filter. The mass ratio of the mixed powder to the fine-particle-size powder is 0.0938 to 0.8963. The mass ratio of the mixed powder to the fine-particle powder can be 0.0938, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, or 0.8963.

[0027] It should be noted that the chemical reactions that occur in these raw materials during the sintering stage include: SiO2(s) + 3C(s) = SiC(g) + 2CO(g), reaction conditions: T≥1150℃ (1) SiO2(s) + C(s) = SiO(g) + CO(g), reaction conditions: T≥1150 ℃; (2) SiO(g) + 2C(s) = SiC(s) + CO(g), reaction conditions: T≥1150℃; (3) SiO(g) + 3CO(g) = SiC(s) + 2CO2(g), reaction conditions: T≥1150℃; (4) CO2(g) + C(s) = 2CO(g), reaction conditions: T≥400℃; (5) 2MoSi2(s) + 7O2(g) = 2MoO3(s) + 4SiO2(s), reaction conditions: T = 500℃; (6) 2Mg + SiO2 → 2MgO + Si, reaction conditions: T≥600℃; (7) Si+C→SiC, reaction conditions: T ≥600℃; (8) SiO2 + Si → SiC, reaction conditions: carbon embedded, T ≥ 1200℃; (9) 2MgO+2Al2O3+5SiO2=Mg2Al4Si5O 18 Reaction conditions: T≥1150℃; (10) In the above chemical reaction process, the specific process is as follows: In the initial stage of the carbothermic reduction reaction, CO2 in the air reacts with C particles in chemical reaction formula (5) to generate CO. Then, molybdenum silicide reacts with oxygen in the air in chemical reaction formula (6) to generate MoO3 and amorphous SiO2. A portion of the amorphous SiO2 reacts with chemical reaction formulas (7) and (8) to generate SiC. Another portion of the amorphous SiO2 is very close to the SiO2 in the coal gangue and the carbon particles under the carbon burial conditions. At this time, chemical reaction formula (2) is generated to produce SiO(g). The generated SiO(g) then continues to react with C particles in chemical reaction formula (3) to form SiC particles. As the reaction proceeds, the SiC generated on the surface of C particles gradually thickens, hindering the diffusion process of solid C particles and gaseous SiO. Therefore, the reactions of chemical reaction formulas (2) and (3) gradually slow down and eventually stop. This will lead to the incomplete reaction of C particles. The incompletely reacted C particles will exhibit the phenomenon of "carbon nuclei" inside the SiC particles. This "carbon core" phenomenon is particularly pronounced when the size of the C particles is large. Subsequently, SiC can be generated through a gas-gas reaction between gaseous SiO and gaseous CO, as shown in chemical reaction formula (4); in addition, SiC can also be generated in situ at the location of SiO2 through a solid-solid reaction mechanism (SS).

[0028] Amorphous SiO2 has poor stability and will gradually soften and melt at high temperatures. Under this mechanism, the carbon phase of the outer coating gradually diffuses into the slag, thereby undergoing a solid-solid reaction with SiO2 as shown in chemical reaction formula (1), so that SiC is gradually generated in situ in the sample. As the process proceeds, the carbon in the outer layer continues to diffuse inward and continues to react with SiO2 according to chemical reaction formula (9). SiC particles nucleate and gradually grow until SiO2 is completely reacted. The cordierite-based diesel particulate filter is finally obtained through the reaction of chemical reaction formula (10) during the sintering process.

[0029] Furthermore, the fibrous morphology of SiC and the porosity characteristics resulting from the fibrous morphology of SiC mainly depend on the porous structure of the carbon components in the initial C and SiO2 materials, as well as the number of contact areas between SiO2 and the carbon phase. However, the number of contact areas between SiO2 and the carbon phase is determined by their specific surface area. Therefore, thanks to the good specific surface area of ​​amorphous SiO2, amorphous SiO2 formed by the reduction reaction of molybdenum silicide can not only produce needle-shaped SiC, but also increase the contact area between SiO2 and C, thereby accelerating the reaction rate of these reactions.

[0030] It should be noted that the mixing of the fine-particle material and the freezing medium can be carried out by grinding. The grinding medium can be zirconium oxide, the particle size of the grinding medium can be 10 mm to 30 mm, the grinding speed can be 900 r / min, and the grinding time can be 6 h.

[0031] It should be noted that the mass of the mixed powder is 1.71 times the mass of the molybdenum silicide powder formed by crushing waste molybdenum silicide heating rods.

[0032] In some optional embodiments, the mass ratio of the fine-particle material to the freezing medium is 0.7 to 4:1; In these embodiments, the mass ratio of fine-particle material to refrigerant can be 0.7 to 4:1, which can promote the refrigerant to be fully dispersed in the fine-particle material, thereby promoting the refrigerant to fully occupy the pore size of the fine-particle material, so as to facilitate subsequent sintering to obtain cordierite-based diesel particulate filters with good porosity.

[0033] The mass ratio of the fine-particle material to the freezing medium can be 0.7:1, 0.8:1, 0.9:1, 1.0:1, 2.0:1, 3.0:1, or 4.0:1.

[0034] In some optional embodiments, the mass ratio of the coal gangue to the fine-particle powder is 0.0918 to 0.8029. The mass ratio of the magnesium powder to the fine-particle-size powder is 0.0118 to 0.1032; In these embodiments, the mass ratio of coal gangue to fine-particle powder can be 0.0918 to 0.8029, and the mass ratio of magnesium powder to fine-particle powder can be 0.0118 to 0.1032. This ensures that the fine-particle powder contains sufficient amounts of coal gangue and magnesium powder. Sufficient coal gangue can provide sufficient SiO2 and Al2O3 components. Sufficient SiO2 can form sufficient SiC components during the sintering stage, while sufficient Al2O3 components can serve as the aluminum source for the cordierite-based diesel particulate filter. In addition, sufficient magnesium powder can provide sufficient Mg components, which can not only act as a reducing agent to reduce SiO2 to form sufficient SiC components during the sintering stage, but also serve as the magnesium source for the cordierite-based diesel particulate filter.

[0035] The mass ratio of coal gangue to fine-grained powder can be 0.0918, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, or 0.8029.

[0036] The mass ratio of magnesium powder to fine-particle powder can be 0.0118, 0.020, 0.030, 0.040, 0.050, 0.060, 0.070, 0.080, 0.090, 0.100, or 0.1032.

[0037] In some optional embodiments, the particle size of the mixed powder is 10 μm to 12 μm. The particle size of the coal gangue is 10μm to 40μm. The particle size of the magnesium powder is 4μm to 10μm; In these embodiments, the particle size of the mixed powder can be 10 μm to 12 μm, the particle size of the coal gangue can be 10 μm to 40 μm, and the particle size of the magnesium powder can be 4 μm to 10 μm. This promotes thorough mixing of the mixed powder, coal gangue, and magnesium powder, thereby obtaining fine-particle materials with uniform particle size distribution. This facilitates the subsequent filling of voids by the refrigerant, ultimately improving the porosity of the cordierite-based diesel particulate filter and avoiding the use of pore-forming agents.

[0038] The preset particle size can be 10μm, 11μm or 12μm.

[0039] The particle size of the coal gangue can be 10μm, 20μm or 40μm.

[0040] The particle size of the magnesium powder can be 4μm, 7μm or 10μm.

[0041] In some optional embodiments, the freezing temperature is ≤-18°C, and the freezing time is ≥12h; The vacuum freeze-drying temperature is ≤-18℃, the vacuum freeze-drying time is ≥12h, and the vacuum freeze-drying pressure is ≤10kPa; In these embodiments, the freezing temperature can be ≤-18℃ and the freezing time can be ≥12h, which can promote sufficient freezing so that the freezing medium is frozen and fixed in the fine-particle material, facilitating the subsequent vacuum freeze-drying and sintering, ultimately improving the porosity of the cordierite-based diesel particulate filter and avoiding the use of pore-forming agents. In addition, the vacuum freeze-drying temperature can be ≤-18℃, the vacuum freeze-drying time can be ≥12h, and the vacuum freeze-drying pressure can be ≤10kPa. Vacuum drying can be used to ensure that the moisture in the fine-particle material is fully dried, so that the freezing medium is more uniformly dispersed in the fine-particle material, ultimately improving the porosity of the cordierite-based diesel particulate filter and thus avoiding the use of pore-forming agents.

[0042] In some alternative embodiments, the sintering includes a debinding section, a heating sintering section, and a cooling section; The temperature of the glue removal section is 550℃~650℃, and the time of the glue removal section is 1.5h~2.5h; The temperature of the heating and sintering section is 1300℃~1400℃, and the heating and sintering time is 2.5h~3.5h; The temperature of the cooling section is 750℃~850℃; In these embodiments, sintering may include a glue removal section, a heating sintering section, and a cooling section. The temperature of the glue removal section may be 550°C to 650°C, and the duration of the glue removal section may be 1.5h to 2.5h, which can ensure that the glue removal process is fully carried out, thereby ultimately increasing the porosity of the cordierite-based diesel particulate filter and avoiding the use of pore-forming agents. Similarly, the temperature of the heating sintering section may be 1300°C to 1400°C, and the duration of the heating sintering section may be 2.5h to 3.5h, which can ensure that the heating process is fully carried out, thereby ultimately increasing the porosity of the cordierite-based diesel particulate filter and avoiding the use of pore-forming agents. Finally, the temperature of the cooling section may be 750°C to 850°C, which can ensure that the cooling process is fully carried out, thereby ultimately increasing the porosity of the cordierite-based diesel particulate filter and avoiding the use of pore-forming agents.

[0043] The temperature of the dispensing section can be 550℃, 560℃, 570℃, 580℃, 590℃, 600℃, 610℃, 620℃, 630℃, 640℃ or 650℃.

[0044] The duration of the glue removal segment can be 1.5h, 1.6h, 1.7h, 1.8h, 1.9h, 2.0h, 2.1h, 2.2h, 2.3h, 2.4h, or 2.5h.

[0045] The temperature of the heating and sintering section can be 1300℃, 1310℃, 1320℃, 1330℃, 1340℃, 1350℃, 1360℃, 1370℃, 1380℃, 1390℃ or 1400℃.

[0046] The heating and sintering time can be 2.5h, 2.6h, 2.7h, 2.8h, 2.9h, 3.0h, 3.1h, 3.2h, 3.3h, 3.4h or 3.5h.

[0047] The temperature of this cooling section can be 750℃, 760℃, 770℃, 780℃, 790℃, 800℃, 810℃, 820℃, 830℃, 840℃ or 850℃.

[0048] In some alternative embodiments, the pretreatment includes crushing, grinding, heat treatment, and heat preservation; The pulverization time is 1.0h to 2.0h; The grinding media used in the grinding process includes zirconium oxide, the particle size of the grinding media is 10 mm to 30 mm, the grinding speed is 850 r / min to 950 r / min, and the grinding time is 2.0 h to 4.0 h. The final temperature of the heat treatment is 450℃~550℃, and the holding time is 12h~36h; In these embodiments, the pulverization time can be 1.0h to 2.0h, which can ensure that the waste molybdenum silicide heating rod is fully crushed; in addition, the particle size of the grinding medium used for grinding can be 10mm to 30mm, the grinding speed can be 850r / min to 950r / min, and the grinding time can be 2.0h to 4.0h, which can be used to fully grind the crushed waste molybdenum silicide heating rod into fine particles to initially obtain molybdenum silicide powder with a preset particle size; in addition, the final temperature of the heat treatment can be 450℃ to 550℃, and the holding time can be 12h to 36h, which can be used to ensure that the molybdenum silicide powder is oxidized to amorphous silicon oxide and molybdenum oxide at a sufficient temperature to finally obtain a mixed powder with amorphous silicon oxide and molybdenum oxide.

[0049] The pulverization time can be 1.0h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h or 2.0h.

[0050] The particle size of the grinding media used in this grinding process can be 10mm, 15mm, 20mm, 25mm or 30mm.

[0051] The grinding speed can be 850 r / min, 860 r / min, 870 r / min, 880 r / min, 890 r / min, 900 r / min, 910 r / min, 920 r / min, 930 r / min, 940 r / min or 950 r / min.

[0052] The grinding time can be 2.0h, 2.5h, 3.0h, 3.5h or 4.0h.

[0053] The key temperature for this heat treatment can be 450℃, 460℃, 470℃, 480℃, 490℃, 500℃, 510℃, 520℃, 530℃, 540℃, or 550℃.

[0054] The insulation time can be 12h, 14h, 16h, 18h, 20h, 22h, 24h, 26h, 28h, 30h, 32h, 34h or 36h.

[0055] Figure 2A detailed flowchart illustrating a method for preparing a cordierite-based diesel particulate filter according to an embodiment of this application is shown as an example. like Figure 2 As shown, in some optional embodiments, the preparation of the cryogenic medium includes the following steps: S301. Polyvinyl alcohol, carboxymethyl cellulose and deionized water are mixed and then stirred under heating conditions to obtain a freezing medium; wherein the heating temperature is ≥90℃.

[0056] In these embodiments, the heating temperature can be ≥90°C, which can effectively increase the solubility of polyvinyl alcohol and carboxymethyl cellulose in deionized water, thereby obtaining a clear cryogenic medium solution.

[0057] In some alternative embodiments, the raw materials of the freezing medium, by mass fraction, satisfy the following: polyvinyl alcohol: 4%–6%, carboxymethyl cellulose: 0.5%–0.8%, and the remainder being deionized water.

[0058] In these embodiments, the mass fraction of polyvinyl alcohol can be 4% to 6%, which promotes the uniform dispersion of polyvinyl alcohol within the fine-particle material, facilitating subsequent freezing and vacuum freeze-drying, thereby ultimately increasing the porosity of the cordierite-based diesel particulate filter and avoiding the use of pore-forming agents. Additionally, the mass fraction of carboxymethyl cellulose can be 0.5% to 0.8%, allowing hydroxymethyl cellulose to act as a binder, effectively dispersing and fixing the polyvinyl alcohol within the gaps of the fine-particle material. During subsequent freezing and vacuum freeze-drying, the freezing medium can interact with the fine-particle material, forming a good pore structure within it, ultimately increasing the porosity of the cordierite-based diesel particulate filter and avoiding the use of pore-forming agents.

[0059] Based on a general inventive concept, this application provides a cordierite-based diesel particulate filter, which is prepared by the aforementioned preparation method. The raw materials of the diesel particulate filter, by mass fraction, satisfy the following: Coal gangue: 14.64%–83.54%, molybdenum silicide: 5.71%–83.47%, and magnesium powder: 1.88%–10.74%; The peak silicon carbide content of the diesel particulate filter and the mass ratio of the diesel particulate filter are 0 to 0.75.

[0060] The diesel particulate filter is made based on the above preparation method. The specific steps of the preparation method can be referred to the above embodiments. Since the diesel particulate filter adopts some or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be repeated here.

[0061] It should be noted that the mass fraction of coal gangue can be 14.64% to 83.54%. Coal gangue can provide sufficient SiO2 and Al2O3 content, which can be used as the silicon and aluminum source for cordierite-based diesel particulate filters. In addition, the mass fraction of molybdenum silicide can be 5.71% to 83.47%. Molybdenum silicide can be used to provide sufficient SiO2 and MoO3 for the sintering stage after pretreatment, so as to finally obtain cordierite-based diesel particulate filters with good porosity. In addition, the mass fraction of magnesium powder can be 1.88% to 10.74%. It can be used as the magnesium source for cordierite diesel particulate filters, and can also act as a reducing agent to reduce SiO2, so as to form sufficient SiC content in the sintering stage, so that the peak silicon carbide content of the final diesel particulate filter is 0.75%.

[0062] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to industry standards; if no corresponding industry standard exists, they are performed according to general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0063] Example 1

[0064] like Figure 2 As shown, a method for preparing a cordierite-based diesel particulate filter includes: S1. The waste molybdenum silicide heating rods are pretreated to obtain a mixed powder containing molybdenum oxide and amorphous silicon oxide; S2. Coal gangue, magnesium powder and mixed powder are mixed and ground to obtain fine-particle-size materials; S301. Polyvinyl alcohol, carboxymethyl cellulose and deionized water are mixed and then stirred under heating conditions to obtain a freezing medium; wherein the heating temperature is ≥90℃; S4. Fine-particle materials and freezing media are mixed in a rectangular mold of 6cm×2cm×2cm and then frozen to obtain a frozen sample; S5. Perform vacuum freeze-drying on the frozen sample to obtain a dried sample; S6. The dried sample was sintered under carbon-embedded conditions and then cooled to obtain a cordierite-based diesel particulate filter. The mass ratio of molybdenum silicide powder to fine-particle powder is 0.0571.

[0065] The mass ratio of fine-particle material to freezing medium is 7:3.

[0066] The mass ratio of coal gangue to fine-grained powder is 0.8354. The mass ratio of magnesium powder to fine-particle powder is 0.1074.

[0067] The preset particle size is ≤12μm, the particle size of coal gangue is ≤40μm, and the particle size of magnesium powder is ≤10μm.

[0068] Freezing temperature ≤ -18℃, freezing time ≥ 12h; The temperature for vacuum freeze drying is ≤-18℃, the time for vacuum freeze drying is ≥12h, and the pressure for vacuum freeze drying is ≤10kPa.

[0069] Sintering includes a debinding section, a heating and sintering section, and a cooling section; The temperature of the glue removal section is 600℃, the time of the glue removal section is 2.0h, and the heating rate of the glue removal section is 3°C / min; After the glue removal section, the temperature is increased to 1000℃ at a rate of 5°C / min, and then held for 1 hour; the temperature of the heating and sintering section is 1370℃, the heating and sintering time is 3.0 hours, and the heating and sintering rate is 2°C / min. The temperature of the cooling section is 800℃.

[0070] Pretreatment includes crushing and grinding in a vibratory mill, heat treatment and holding in a muffle furnace; The grinding time is 1.5 hours; The grinding media used for grinding include zirconium oxide, the particle size of the grinding media is 10mm to 30mm, the grinding speed is 900r / min, and the grinding time is 3.0h. The final temperature of the heat treatment was 500℃, and the holding time was 24 hours.

[0071] By mass fraction, the raw materials of the refrigerant are: polyvinyl alcohol: 5%, carboxymethyl cellulose: 0.6%, and the remainder is deionized water.

[0072] like Figure 3 As shown, a cordierite-based diesel particulate filter is prepared by the method of the first aspect, wherein the raw materials of the diesel particulate filter satisfy the following conditions by mass fraction: Coal gangue: 83.54%, molybdenum silicide: 5.71%, and magnesium powder: 10.74%, with the remainder being unavoidable impurities.

[0073] Example 2

[0074] Based on the content disclosed in Example 1, the following modifications are made: By mass fraction, the raw material for diesel particulate filters meets the following requirements: Coal gangue: 56.75%, molybdenum silicide: 35.94%, and magnesium powder: 7.3%, with the remainder being unavoidable impurities.

[0075] Example 3

[0076] Based on the content disclosed in Example 1, the following modifications are made: By mass fraction, the raw material for diesel particulate filters meets the following requirements: Coal gangue: 33.02%, molybdenum silicide: 62.73%, and magnesium powder: 4.24%, with the remainder being unavoidable impurities.

[0077] Example 4

[0078] Based on the content disclosed in Example 1, the following modifications are made: By mass fraction, the raw material for diesel particulate filters meets the following requirements: Coal gangue: 14.64%, molybdenum silicide: 83.47%, and magnesium powder: 1.88%, with the remainder being unavoidable impurities.

[0079] Comparative Example 1 Based on the content disclosed in Example 1, the following modifications are made: By mass fraction, the raw material for diesel particulate filters meets the following requirements: Coal gangue: 80.91%, silica powder: 8.68%, and magnesium powder: 10.40%, with the remainder being unavoidable impurities.

[0080] Comparative Example 2 Based on the content disclosed in Example 1, the following modifications are made: By mass fraction, the raw material for diesel particulate filters meets the following requirements: Coal gangue: 61.52%, silica powder: 30.56%, and magnesium powder: 7.91%, with the remainder being unavoidable impurities.

[0081] Comparative Example 3 Based on the content disclosed in Example 1, the following modifications are made: By mass fraction, the raw material for diesel particulate filters meets the following requirements: Coal gangue: 38.18%, silica powder: 56.90%, and magnesium powder: 4.91%, with the remainder being unavoidable impurities.

[0082] Comparative Example 4 Based on the content disclosed in Example 1, the following modifications are made: By mass fraction, the raw material for diesel particulate filters meets the following requirements: Coal gangue: 17.85%, silica powder: 79.84%, and magnesium powder: 2.30%, with the remainder being unavoidable impurities.

[0083] Relevant experimental and effect data: 1. Performance tests were conducted on the cordierite-based diesel filters obtained from each embodiment and comparative example. In addition, the silicon carbide content produced in the cordierite-based diesel filters was calculated based on each raw material. The results are shown in Table 1.

[0084] Table 1 Performance results of cordierite-based diesel filters obtained from various embodiments and comparative examples

[0085] As shown in Table 1, the method for preparing a cordierite-based diesel particulate filter provided in this application embodiment can synthesize a cordierite-based diesel particulate filter product with high porosity and a three-dimensional network pore structure in one step through the synergistic effect of molybdenum oxide formed by molybdenum silicide and the freezing medium.

[0086] 2. The scanning electron microscope (SEM) images of the cordierite-based diesel particulate filters obtained in Example 4 and Comparative Example 4 were analyzed separately. The results are as follows: Figure 3 and Figure 4 As shown, the results indicate that silicon carbide generated using molybdenum silicide as the silicon source exhibits a needle-like morphology, and the needle-like silicon carbide structures interweave to form a structure that refines the microstructure of the cordierite-based diesel particulate filter, thereby improving the material's mechanical strength. However, cordierite-based diesel particulate filter materials prepared using ordinary silicon sources have looser particles, and the microstructure is mostly granular, which weakens the material strength of the cordierite-based diesel particulate filter.

[0087] 3. Based on the bending strength of the cordierite-based diesel particulate filter obtained in Example 4 and Comparative Example 4, the results are as follows: Figure 5 As shown, the results indicate that the flexural strength of the composite material increases with increasing silicon carbide doping, and the addition of silicon carbide has a significant positive effect on flexural strength. Furthermore, the molybdenum silicide in this application produces needle-like and rod-shaped SiC, which is consistent with... Figure 2 and Figure 3 The analysis results match.

[0088] 4. XRD analysis was performed on the cordierite-based diesel particulate filters obtained in Example 4 and Comparative Example 4, respectively. The results are as follows: Figure 6 As shown, the results indicate that, under the premise of using molybdenum silicide as the silicon source, the diffraction peak intensity of silicon carbide formed by molybdenum silicide is much higher than that of cordierite-based diesel particulate filters using ordinary silica. In addition, the diffraction peak intensity of silica in the cordierite-based diesel particulate filter sample formed by molybdenum silicide is much lower than that of the cordierite-based diesel particulate filter sample using ordinary silica. This is because the silicon carbide produced by the reaction is not complete when using ordinary silica as the source.

[0089] 5. Surface EDS analysis was performed on the cordierite-based diesel particulate filters obtained in Example 4 and Comparative Example 4, respectively. The results are as follows: Figure 7 , Figure 8 As shown in Table 2, the surface scan total spectrum of the cordierite-based diesel particulate filter obtained in Comparative Example 4 is also shown in Table 2.

[0090] Table 2. Surface scan total spectra of the cordierite-based diesel particulate filter obtained in Comparative Example 4.

[0091] From Table 2 and Figure 7 and Figure 8 As shown, the results indicate that the surface EDS analysis of the sample using ordinary silica as the silicon source shows that the cordierite-based diesel particulate filter has a high content of Si and O atoms, which is consistent with the proportion of silica. Therefore, it can be confirmed that some silica in the raw material did not participate in the reaction.

[0092] 6. The porosity of the cordierite-based diesel particulate filters obtained in Example 4 and Comparative Example 4 was analyzed using the Archimedes method, and the results are as follows: Figure 9 As shown, the results indicate that the porosity of cordierite-based diesel particulate filter samples prepared using molybdenum silicide as the silicon source is between 46% and 57%, while the porosity of cordierite-based diesel particulate filter samples prepared using ordinary silica as the silicon source is between 46% and 50%. This is because during the sintering process of the cordierite-based diesel particulate filter samples, molybdenum silicide generates MoO3 and SiO2. During sintering, MoO3 evaporates, creating additional pores, and the generated SiO2 forms SiC. The overall porosity of the cordierite-based diesel particulate filter increases with the increase of silicon carbide fraction during the sintering stage. This may be due to the reduction of the cordierite phase, leading to a decrease in the liquid phase during sintering. Furthermore, when using molybdenum silicide as the silicon source, the rate of increase in porosity of the cordierite-based diesel particulate filter is much higher than that of ordinary silica. This is mainly caused by the increase in the amount of pore-forming materials (MoO3) formed during the sintering stage as the molybdenum silicide content increases.

[0093] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed in this application.

Claims

1. A method for preparing a cordierite-based diesel particulate filter, characterized in that, The preparation method includes: Waste molybdenum silicide heating rods are pretreated to obtain a mixed powder containing molybdenum oxide and amorphous silica. Coal gangue, magnesium powder, and the mixed powder are mixed and ground to obtain fine-particle-size material; Preparation of freezing media; The fine-particle material and the freezing medium are mixed and then frozen to obtain a frozen sample; The frozen sample was subjected to vacuum freeze-drying to obtain a dried sample; The dried sample was sintered under carbon-embedded conditions and then cooled to obtain a cordierite-based diesel particulate filter. The mass ratio of the mixed powder to the fine-particle material is 0.3594 to 0.8347. The mass ratio of the fine-particle material to the freezing medium is 0.7 to 4:1; The mass ratio of the coal gangue to the fine-particle material is 0.1464 to 0.5675; The mass ratio of the magnesium powder to the fine-particle material is 0.0188 to 0.0730; By mass fraction, the raw materials of the freezing medium satisfy the following: polyvinyl alcohol: 4%–6%, carboxymethyl cellulose: 0.5%–0.8%, and the remainder being deionized water; The sintering process includes a debinding section, a heating and sintering section, and a cooling section. The temperature of the glue removal section is 550℃~650℃, and the time of the glue removal section is 1.5h~2.5h; The temperature of the heating and sintering section is 1300℃~1400℃, and the heating and sintering time is 2.5h~3.5h; The temperature of the cooling section is 750℃~850℃.

2. The preparation method according to claim 1, characterized in that, The particle size of the mixed powder is 10μm to 12μm; The particle size of the coal gangue is 10μm to 40μm; The magnesium powder has a particle size of 4μm to 10μm.

3. The preparation method according to claim 1, characterized in that, The freezing temperature is ≤-18℃, and the freezing time is ≥12h; The vacuum freeze-drying temperature is ≤-18℃, the vacuum freeze-drying time is ≥12h, and the vacuum freeze-drying pressure is ≤10kPa.

4. The preparation method according to claim 1, characterized in that, The pretreatment includes crushing, grinding, heat treatment, and heat preservation; The pulverization time is 1.0h to 2.0h; The grinding media used in the grinding process includes zirconium oxide, the particle size of the grinding media is 10 mm to 30 mm, the grinding speed is 850 r / min to 950 r / min, and the grinding time is 2.0 h to 4.0 h. The final temperature of the heat treatment is 450℃~550℃, and the holding time is 12h~36h.

5. The preparation method according to claim 1, characterized in that, The preparation of the cryogenic medium includes the following steps: Polyvinyl alcohol, carboxymethyl cellulose and deionized water are mixed and then stirred under heating conditions to obtain a freezing medium; wherein the heating temperature is ≥90℃.

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