Preparation and application of high dielectric loss alkali modified foam ceramic three-dimensional catalytic material

Abstract

This invention provides the preparation and application of a high-dielectric-loss alkali metal-modified foam ceramic three-dimensional catalytic material, relating to the field of biomass energy conversion technology. Addressing the technical shortcomings of existing microwave catalytic materials, such as fixed dielectric properties, slow energy response, and separation of microwave absorption and catalysis functions, this invention constructs a three-dimensional porous foam ceramic matrix with a dynamic dielectric response network by doping a silicon-aluminum-magnesium composite ceramic system with alkali metal ions. Furthermore, a molecular sieve and alumina composite catalytic layer are loaded onto this matrix, forming an integrated "energy absorption-thermal conduction-catalysis" material. This material exhibits a dielectric loss coefficient ε″ of 0.134–0.283 at 2.45 GHz, a microwave heating rate of up to 15 °C / s, and can achieve adaptive energy distribution and hotspot migration. When used for microwave catalytic pyrolysis of waste plastics or waste oils, it achieves efficient conversion at 400–600 °C, with the aromatic hydrocarbon content in the liquid product exceeding 96%. This invention solves the problems of low microwave energy utilization and poor catalytic selectivity at the material level.

Description

Technical Field

[0001] This invention relates to the field of biomass energy conversion technology, and in particular to the preparation and application of a high dielectric loss alkali metal modified foam ceramic three-dimensional catalytic material. Background Technology

[0002] The food processing and petrochemical industries generate massive amounts of waste oils and waste plastics annually, and their efficient resource conversion is key to alleviating energy pressure and environmental pollution. Catalytic pyrolysis technology can convert these organic solid wastes into high-value-added fuels or chemicals, but traditional external heating methods suffer from problems such as low heat transfer efficiency, high energy consumption, and uneven temperature distribution, resulting in a wide distribution of pyrolysis products and poor aromatization selectivity.

[0003] In recent years, microwave heating technology has shown great potential in the field of organic solid waste pyrolysis due to its unique internal heating, rapid response and efficient energy transfer characteristics. At present, research and practice in this field mainly rely on foam ceramics with silicon carbide (SiC) or alumina (Al2O3) as the skeleton. These materials are usually used as inert support carriers or passive microwave absorbers. Their dielectric properties (especially dielectric loss) are fixed after preparation, and their functions are singular. They have many inherent defects and shortcomings: (1) Fixed dielectric properties, passive energy response and low efficiency: The dielectric loss characteristics of traditional SiC foam ceramics are determined by their own physicochemical properties and cannot be dynamically adjusted according to microwave field strength or reaction requirements. Their energy absorption and conversion rate is limited, resulting in slow heating and difficulty in achieving rapid start-up and efficient energy utilization; (2) Unable to solve the problem of uneven energy distribution inherent in microwave fields: Microwave heating is prone to generating local "hot spots" and overall temperature gradients. Traditional materials, as passive microwave absorbers, not only fail to alleviate this problem, but may also exacerbate energy concentration, resulting in severe temperature unevenness in the reaction bed, overheating and coking in some areas, while other areas do not react sufficiently, seriously affecting product selectivity and catalyst life; (3) Limited ability to selectively regulate target products (such as aromatics): Due to uneven energy distribution and low efficiency of the “wave absorption-catalysis” interface, traditional microwave catalytic systems have insufficient precision in controlling the aromatization path of pyrolysis products, making it difficult to achieve high selectivity and high yield of high-value chemicals such as single aromatics.

[0004] Therefore, there is an urgent need to provide a solution to improve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing and applying a high-dielectric-loss alkali metal-modified foam ceramic three-dimensional catalytic material. Addressing the technical shortcomings of existing microwave catalytic materials, such as fixed dielectric properties, slow energy response, and separation of microwave absorption and catalysis functions, this invention introduces alkali metal-induced dielectric centers and a multiphase synergistic energy-conducting framework to construct a multifunctional material system capable of self-tuning energy absorption, self-exothermic transfer, and catalytic interface energy gain in a microwave field.

[0006] In a first aspect, the present invention provides a method for preparing a high dielectric loss alkali metal modified foam ceramic three-dimensional catalytic material, comprising: mixing and stirring a silicon source, an aluminum source, a magnesium source, a binder, an alkali metal source, and a medium to form a uniform slurry; impregnating a porous foam template in the slurry and forming it; drying and sintering the template sequentially to obtain an alkali metal-doped three-dimensional foam ceramic matrix; and then loading an active component onto the surface of the matrix and performing heat treatment to obtain a high dielectric loss alkali metal modified foam ceramic three-dimensional catalytic material.

[0007] Optionally, the silicon source includes one or more of silicon carbide and silica sol.

[0008] Optionally, the aluminum source includes boehmite.

[0009] Optionally, the magnesium source includes magnesium oxide.

[0010] Optionally, the binder includes sodium carboxymethyl cellulose.

[0011] Optionally, the alkali metal source includes an alkali metal hydroxide; the alkali metal hydroxide includes one of sodium hydroxide, potassium hydroxide, or lithium hydroxide monohydrate.

[0012] Optionally, the medium includes deionized water.

[0013] Optionally, the porous foam template comprises spherical polyurethane foam; the average pore size of the spherical polyurethane foam is 5mm-15mm.

[0014] Optionally, by mass fraction, the slurry contains 75-85 parts of silicon source, 10-13 parts of aluminum source, 7-10 parts of magnesium source, 0.5-2 parts of binder, 4-6 parts of alkali metal source, and 42-47 parts of medium.

[0015] Optionally, the total loading of the active components accounts for 25%-35% of the total mass of the three-dimensional catalytic material.

[0016] Optionally, the sintering process includes a staged heating process: first, the temperature is increased from room temperature to 200°C at a heating rate of 2°C / min, then increased to 500°C at a heating rate of 1°C / min and held for 1-2 hours to remove the template; subsequently, the temperature is increased to 1300°C-1400°C at a heating rate of 2°C / min and held for 1.5-2.5 hours for high-temperature sintering.

[0017] Optionally, the active component includes a composite active component of ZSM-5 molecular sieve and pseudoboehmite.

[0018] Optionally, the temperature of the heat treatment is 500℃-600℃.

[0019] Secondly, the present invention also provides a three-dimensional catalytic material prepared by any of the above-mentioned optional preparation methods, wherein the dielectric loss coefficient ε″ of the three-dimensional catalytic material is 0.134-0.283 at 2.45 GHz; and the self-heating rate of the three-dimensional catalytic material in a microwave field can reach 15 °C / s.

[0020] Thirdly, the present invention also provides an application of a three-dimensional catalytic material prepared by any of the above-mentioned optional preparation methods in the catalytic conversion of organic matter under a microwave energy field.

[0021] Optionally, the organic matter includes one or more of waste plastics, waste oils, or biomass.

[0022] Optionally, the application is as follows: under microwave radiation, the organic matter is brought into contact with the three-dimensional catalytic material and a rapid catalytic pyrolysis and aromatization reaction occurs; the reaction is carried out in a temperature range of 400℃-600℃; the total aromatic content in the liquid product produced by the reaction is ≥96%.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The three-dimensional catalytic material provided by the present invention introduces alkali metal ions to dope the Si-Al-Mg-O composite ceramic matrix in a directional manner. The alkali metal ions are substituted in situ in the lattice to construct a three-dimensional energy-conducting network with "micro-mesoelectronic domain". The "energy traps" and "local electric field nodes" inside the material can be dynamically adjusted with the external microwave frequency, so that the microwave energy can be orderly migrated and locally amplified in the framework, thereby realizing active ultrafast thermal response.

[0025] (2) The three-dimensional catalytic material provided by the present invention has its dielectric loss coefficient (ε″) increased to 0.134-0.283 (2.45GHz) through alkali metal modification, exhibiting a rapid heating rate of about 15℃ / s in a microwave field, and its energy absorption and conversion efficiency is about 2-3 times higher than that of traditional SiC foam ceramics;

[0026] (3) The three-dimensional catalytic material provided by the present invention has a multi-scale polarization lattice formed inside it, which can realize the self-distribution of energy and the "hot spot migration" effect, effectively avoiding the problem of local overheating in the microwave heating process, and significantly improving the temperature uniformity and stability of the catalytic reaction.

[0027] (4) The present invention uses an impregnation-sintering-loading process to load the catalytic active component (ZSM-5 / pseudo-boehmite) onto the skeleton of a three-dimensional foam ceramic matrix in the form of a micro-thin layer. Because the loading layer is thin, the conduction distance is shortened. After the ceramic matrix skeleton responds quickly and heats up instantaneously, it can be efficiently and almost losslessly transferred to the active sites tightly bound to the surface, thus solving the defects of low interface efficiency and temperature mismatch between the reaction zone and the catalytic zone in the prior art.

[0028] (5) This invention realizes the integrated function of "wave absorption-heat conduction-catalysis". The material itself has the triple functions of efficient microwave absorber, heat conduction medium and catalytic active carrier. There is no need to add additional wave absorbing filler or complex carrier structure, which simplifies the design of reaction system.

[0029] (6) The three-dimensional catalytic material prepared by the present invention exhibits extremely high aromatization selectivity for the catalytic pyrolysis of waste plastics and waste oils under microwave radiation. The aromatic content in the liquid product can exceed 96%, and it is mainly composed of high-value monocyclic aromatic hydrocarbons, thus realizing the high-value transformation of resources. Attached Figure Description

[0030] Figure 1 The images shown are photographs of the materials obtained in different steps of Example 1 of the present invention; wherein, (A) is the dried green body after drying and before programmed sintering in step S3 of Example 1; (B) is the three-dimensional foam ceramic matrix after programmed sintering in step S3 of Example 1; and (C) is the three-dimensional catalytic material obtained in step S4 of Example 1.

[0031] Figure 2 This is a photograph of the actual product after the high dielectric loss lithium-modified foam ceramic three-dimensional catalytic material used in Application Example 1 of this invention has undergone a catalytic reaction. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by those skilled in the art to which this invention pertains.

[0033] This invention provides a method for preparing a high dielectric loss alkali metal modified foam ceramic three-dimensional catalytic material, comprising: mixing and stirring a silicon source, an aluminum source, a magnesium source, a binder, an alkali metal source, and a medium to form a uniform slurry; impregnating a porous foam template in the slurry and forming it; drying and sintering the template sequentially to obtain an alkali metal-doped three-dimensional foam ceramic matrix; and then loading an active component onto the surface of the matrix and performing heat treatment to obtain the high dielectric loss alkali metal modified foam ceramic three-dimensional catalytic material.

[0034] In fact, by doping and modifying the silicon-aluminum-magnesium composite ceramic system with alkali metal ions, a three-dimensional porous foam ceramic matrix with a dynamic dielectric response network was constructed. Furthermore, a molecular sieve and alumina composite catalytic layer were loaded onto this matrix, forming an integrated "energy absorption-thermal conduction-catalysis" material. This material exhibits a dielectric loss coefficient ε″ of 0.134-0.283 at 2.45 GHz, a microwave heating rate of up to 15 °C / s, and can achieve adaptive energy distribution and hotspot migration. When used for microwave catalytic pyrolysis of waste plastics or waste oils, it can achieve highly efficient conversion at 400-600 °C, with the aromatic hydrocarbon content in the liquid product exceeding 96%. This invention solves the problems of low microwave energy utilization and poor catalytic selectivity at the material level.

[0035] In some embodiments, the silicon source used includes one or more of silicon carbide and silica sol.

[0036] In some embodiments, the aluminum source used includes boehmite.

[0037] In some embodiments, the magnesium source used includes magnesium oxide.

[0038] In some embodiments, the binder used includes sodium carboxymethyl cellulose.

[0039] In some embodiments, the alkali metal source used includes an alkali metal hydroxide; the alkali metal hydroxide includes one of sodium hydroxide, potassium hydroxide, or lithium hydroxide monohydrate.

[0040] In fact, the framework of the high dielectric loss alkali metal modified foam ceramic three-dimensional catalytic material prepared by this invention is composed of Si, Al, Mg and O-based composite phases. After alkali metal directional doping, multiple "micro-dielectronic domains" that can respond to electromagnetic fields are formed, thereby enabling the material to generate self-excited energy amplification and spatial hot spot migration phenomena under microwave action.

[0041] In some embodiments, the medium used includes deionized water.

[0042] In some embodiments, the porous foam template used includes spherical polyurethane foam; the average pore size of the spherical polyurethane foam is 5mm-15mm.

[0043] In some embodiments, the slurry contains, by weight, 75-85 parts of silicon source, 10-13 parts of aluminum source, 7-10 parts of magnesium source, 0.5-2 parts of binder, 4-6 parts of alkali metal source, and 42-47 parts of medium.

[0044] In some embodiments, the total loading of the active components used accounts for 25%-35% of the total mass of the three-dimensional catalytic material.

[0045] In some embodiments, the sintering process includes a staged heating process: first, the temperature is increased from room temperature to 200°C at a heating rate of 2°C / min, then increased to 500°C at a heating rate of 1°C / min and held for 1-2 hours to remove the template; subsequently, the temperature is increased to 1300°C-1400°C at a heating rate of 2°C / min and held for 1.5-2.5 hours for high-temperature sintering.

[0046] In some embodiments, the active components used include a composite active component of ZSM-5 molecular sieve and pseudoboehmite.

[0047] In fact, by further loading molecular sieves and pseudoboehmite active components onto the surface of a three-dimensional foam ceramic matrix, an integrated interface of "energy absorption-thermal conduction-catalysis" can be formed, thereby enabling transient thermal decomposition and aromatization transformation of organic macromolecules.

[0048] In some embodiments, the heat treatment temperature used is 500°C-600°C.

[0049] The present invention also provides a three-dimensional catalytic material prepared using any of the above embodiments, wherein the dielectric loss coefficient ε″ of the three-dimensional catalytic material is 0.134-0.283 at 2.45 GHz; and the self-heating rate of the three-dimensional catalytic material in a microwave field can reach 15 °C / s.

[0050] The present invention also provides an application of the three-dimensional catalytic material prepared in any of the above embodiments for the catalytic conversion of organic matter under a microwave energy field.

[0051] In some embodiments, the selected organic materials include one or more of waste plastics, waste oils, or biomass. Specifically, waste plastics include waste low-density polyethylene plastics; waste oils include waste soybean oil used for frying.

[0052] In fact, under microwave radiation, the alkali metal modified phase in the three-dimensional catalytic material forms a dynamic electric field-induced region, realizing a "self-absorption-re-radiation-synergistic catalysis" process for energy. A nonlinear resonance is formed between the microwave field and the dielectric loss point, allowing the local temperature to rise in milliseconds, achieving efficient pyrolysis and aromatization of waste plastics and oils.

[0053] In some embodiments, the specific application is as follows: under microwave radiation, organic matter is brought into contact with a three-dimensional catalytic material and a rapid catalytic pyrolysis and aromatization reaction occurs; the reaction is carried out in a temperature range of 400℃-600℃; the total aromatic content in the liquid product produced by the reaction is ≥96%. Example 1

[0054] This embodiment 1 provides a method for preparing a high dielectric loss lithium-modified foam ceramic three-dimensional catalytic material, comprising the following steps:

[0055] S1. Weigh 80 parts of silicon carbide powder, 11.43 parts of boehmite, 8.57 parts of MgO, and 1 part of sodium carboxymethyl cellulose, mix and ball mill for 4 hours to obtain a mixture;

[0056] S2. Add 2 parts of alkaline silica sol, 5 parts of alkali metal hydroxide LiOH·H2O and 45 parts of deionized water to the mixture obtained in step S1 and stir to form a slurry;

[0057] S3. Immerse a 5mm diameter polyurethane foam into the slurry prepared in step S2. After drying, perform a programmed sintering process: increase the temperature from room temperature to 200℃ at 2℃ / min, then increase it to 500℃ at 1℃ / min and hold for 1 hour, and then increase it to 1350℃ at 2℃ / min and hold for 2 hours to obtain a three-dimensional foam ceramic matrix with a honeycomb structure.

[0058] S4. The composite active layer of ZSM-5 molecular sieve and pseudoboehmite loaded on the surface of the three-dimensional foam ceramic matrix obtained in step S3 (62.10g of three-dimensional foam ceramic matrix loaded with 20g of ZSM-5 and pseudoboehmite) is obtained by calcination at 550℃ to obtain a three-dimensional catalytic material of high dielectric loss alkali metal modified foam ceramic. Example 2

[0059] This embodiment 2 provides a method for preparing a high dielectric loss sodium-modified foam ceramic three-dimensional catalytic material. The difference from embodiment 1 is that in step S2, the added alkali metal hydroxide is changed to NaOH; in step S3, the diameter of the polyurethane foam is changed to 15 mm; and in step S4, 67.06 g of three-dimensional foam ceramic matrix is ​​loaded with 20 g of ZSM-5 and pseudoboehmite. Example 3

[0060] This embodiment 3 provides a method for preparing a high dielectric loss potassium-modified foam ceramic three-dimensional catalytic material. The difference from embodiment 1 is that in step S2, the added alkali metal hydroxide is changed to KOH; in step S3, the diameter of the polyurethane foam is changed to 8 mm; and in step S4, 65.84 g of three-dimensional foam ceramic matrix is ​​loaded with 20 g of ZSM-5 and pseudoboehmite.

[0061] Comparative Example 1

[0062] Comparative Example 1 provides a silicon carbide powder.

[0063] The silicon carbide powder used in Examples 1 to 3 and Comparative Example 1 above was all commercially available silicon carbide powder from McLean.

[0064] The dielectric properties of the three-dimensional catalytic materials prepared in Examples 1 to 3 and the commercial silicon carbide powder of Comparative Example 1 were characterized using a vector network analyzer (P5000A, Keysight Technologies, Co, Ltd, USA) at a microwave frequency of 2.45 GHz. The test results are shown in Table 1.

[0065] Table 1: Dielectric property data of materials from Examples 1 to 3 and Comparative Example 1

[0066]

[0067] Note: ε′ represents the real part of the dielectric constant; ε″ represents the imaginary part of the dielectric loss factor; tan δ = ε″ / ε′ represents the loss tangent.

[0068] As can be seen from the data in Table 1, the three-dimensional catalytic materials prepared in Examples 1 to 3 have higher dielectric constants and dielectric losses compared with Comparative Example 1. In particular, the dielectric loss can be increased to 0.134-0.283, which is 13-28 times higher than that of the Comparative Example (0.010). This directly proves the effect of alkali metal doping modification, and it is also the basis for the three-dimensional catalytic materials to achieve rapid heating and efficient wave absorption.

[0069] Application Example 1

[0070] 550g of silicon carbide spheres were placed in the pyrolysis bed, and the high dielectric loss lithium-modified foam ceramic three-dimensional catalytic material prepared in Example 1 was placed in the catalytic bed, and then loaded into quartz tubes according to the loading order. 600g of fried waste soybean oil was continuously fed using a liquid injection pump at a feed rate of 5g per minute for microwave rapid catalytic pyrolysis. The microwave pyrolysis bed temperature was controlled at 500℃ and the microwave catalytic bed temperature at 450℃ using microwave heating. The resulting pyrolysis gas was catalytically reformed and condensed using a composite catalytic material supported on ZSM-5 and pseudoboehmite to obtain bio-oil. Non-condensable gases were collected through a gas bag. The bio-oil obtained after condensation through this catalyst was 527.8g, with an aromatic content exceeding 96% and a monocyclic aromatic hydrocarbon yield exceeding 86%.

[0071] Application Example 2

[0072] 650g of silicon carbide spheres were placed in the pyrolysis bed, and the high dielectric loss sodium-modified foam ceramic three-dimensional catalytic material prepared in Example 2 was placed in the catalytic bed, and then loaded into quartz tubes according to the loading order. 600g of fried waste soybean oil was continuously fed into the microwave catalytic pyrolysis bed at a feed rate of 5g per minute using a liquid injection pump. The microwave pyrolysis bed temperature was controlled at 450℃ and the microwave catalytic bed temperature at 400℃ using microwave heating. The resulting pyrolysis gas was catalytically reformed and condensed using a composite catalytic material supported on ZSM-5 and boehmite to obtain bio-oil. Non-condensable gases were collected through a gas bag. The bio-oil obtained after condensation through this catalyst was 500.2g, with an aromatic content exceeding 97% and a monocyclic aromatic hydrocarbon yield exceeding 90%.

[0073] Application Example 3

[0074] 750g of silicon carbide spheres were placed in the pyrolysis bed, and the high dielectric loss potassium-modified foam ceramic three-dimensional catalytic material prepared in Example 3 was placed in the catalytic bed, and then loaded into quartz tubes according to the loading order. 600g of waste low-density polyethylene plastic was continuously fed into the catalytic bed using a solid feeder at a feed rate of 5g per minute for microwave rapid catalytic pyrolysis. The microwave pyrolysis bed temperature was controlled at 500℃ and the microwave catalytic bed temperature at 450℃ using microwave heating. The resulting pyrolysis gas was catalytically reformed and condensed using a composite catalytic material supported on ZSM-5 and pseudoboehmite to obtain bio-oil. Non-condensable gases were collected through a gas bag. The bio-oil obtained after condensation through this catalyst was 294.7g, with an aromatic content exceeding 99% and a monocyclic aromatic hydrocarbon yield exceeding 85%.

[0075] While embodiments of the present invention have been described in detail above, it will be apparent to those skilled in the art that various modifications and variations can be made to these embodiments. However, it should be understood that such modifications and variations fall within the scope and spirit of the invention as set forth in the claims. Furthermore, the invention described herein may have other embodiments and can be implemented or carried out in various ways.

Claims

1. A method for preparing a high dielectric loss alkali metal modified foam ceramic three-dimensional catalytic material, characterized in that, include: A homogeneous slurry is formed by mixing silicon, aluminum, magnesium, binder, alkali metal source, and a medium. A porous foam template is impregnated into the slurry and shaped. The mixture is then dried and sintered sequentially to obtain an alkali metal-doped three-dimensional foam ceramic matrix. Subsequently, an active component is loaded onto the matrix surface and heat-treated to obtain a high-dielectric-loss alkali metal-modified foam ceramic three-dimensional catalytic material. The sintering process includes a staged heating process: first, the temperature is increased from room temperature to 200°C at a rate of 2°C / min, then increased to 500°C at a rate of 1°C / min and held for 1-2 hours to remove the template; then, the temperature is increased to 1300°C-1400°C at a rate of 2°C / min and held for 1.5-2.5 hours for high-temperature sintering. The heat treatment temperature is 500°C-600°C. The alkali metal source includes an alkali metal hydroxide, which includes sodium hydroxide, potassium hydroxide, or lithium hydroxide monohydrate. The porous foam template comprises spherical polyurethane foam; the average pore size of the spherical polyurethane foam is 5mm-15mm; the active component comprises a composite active component of ZSM-5 molecular sieve and boehmite; by mass fraction, the slurry contains 75-85 parts of silicon source, 10-13 parts of aluminum source, 7-10 parts of magnesium source, 0.5-2 parts of binder, 4-6 parts of alkali metal source, and 42-47 parts of medium; the total loading of the active component accounts for 25%-35% of the total mass of the three-dimensional catalytic material; the silicon source includes one or more of silicon carbide and silica sol; the aluminum source includes boehmite; the magnesium source includes magnesium oxide; the binder includes sodium carboxymethyl cellulose; the medium includes deionized water; the dielectric loss coefficient ε″ of the three-dimensional catalytic material at 2.45GHz is 0.134-0.283; the self-heating rate of the three-dimensional catalytic material in a microwave field can reach 15℃ / s.

2. The application of a three-dimensional catalytic material prepared by the method described in claim 1 in the catalytic conversion of organic matter under a microwave energy field.

3. The application according to claim 2, characterized in that, The organic matter includes one or more of waste plastics and waste oils.

4. The application according to claim 2, characterized in that, The application is as follows: under microwave radiation, the organic matter is brought into contact with the three-dimensional catalytic material and a rapid catalytic pyrolysis and aromatization reaction occurs; the reaction is carried out in a temperature range of 400℃-600℃; the total aromatic content in the liquid product produced by the reaction is ≥96%.

Images