Peanut residue biomass charcoal microwave shielding material and preparation method thereof

Abstract

The invention relates to the technical field of microwave shielding materials, in particular to a peanut residue biomass charcoal microwave shielding material which is biomass charcoal with high purity and rich pores prepared from waste peanut residues as a raw material through pyrolysis and sodium hydroxide activation. The method has the advantages that nitrogen, phosphorus, magnesium and other miscellaneous elements can be reduced, generation of magnesium, potassium and other inorganic salts is avoided, and meanwhile, through the coordination effect of'high-temperature cracking + sodium hydroxide dispersion + sodium hydroxide continuous activation ', the number of pores is effectively increased so as to enhance microwave absorption loss. The invention also discloses a method for preparing a microwave loss coating by using the peanut residue biomass charcoal, the prepared biomass charcoal material is mixed with paraffin, epoxy resin or a silicone rubber matrix according to a mixing mass ratio of 1: 1, and the microwave loss of the biomass charcoal material in a range of 2-18 GHz is relatively strong through testing.

Description

Technical Field

[0001] This invention relates to the field of microwave shielding materials technology, and in particular to a microwave high-loss shielding material and method for preparing biochar from waste peanut residue. Background Technology

[0002] With industrial development, the development and utilization of clean energy has become urgent. Biomass energy has become the fourth largest energy source after coal, oil, and natural gas. Biomass refers to all organic matter that directly or indirectly utilizes green plants for photosynthesis, including all plants, animals, microorganisms, and their excrement and metabolites. It is renewable, biodegradable, clean, and diverse, making it a very important renewable energy source. In today's fast-paced life, the amount of waste generated is increasing, posing a challenge to our environment. We should find ways to utilize this waste, turning it into valuable resources to protect the environment. With the continuous development of technology, the number of electronic products in our lives is increasing, and their usage frequency is also rising. This means that the number of sources of interference is constantly increasing. Furthermore, electronic products themselves are sensitive devices, posing a significant challenge to electromagnetic compatibility between products or systems. Excessive electromagnetic radiation can affect people's normal health, causing physiological dysfunction and even threatening life. In the military field, electromagnetic radiation-related information security and data leakage also place higher demands on military defense technologies. Therefore, it is necessary to develop functional materials with high loss and high absorption.

[0003] Therefore, many researchers have proposed using biomass to prepare microwave absorbing materials. Publication (Announcement) No. CN118239780A discloses a method for preparing biomass carbon ultra-wideband microwave absorbing materials. This method employs a hybrid heating technique of microwave / microwave-carbon co-excited plasma, producing biomass carbon with enhanced conduction and polarization losses. Specifically, a cellulose carbon precursor is first obtained through a cellulose-based heating process, and then the cellulose carbon precursor is microwave-heated to finally obtain the biomass carbon. However, this method lacks a precise control mechanism, making it difficult to prepare microwave absorbing materials with the desired specific electromagnetic parameters.

[0004] Fruit-based biomass contains a large amount of protein and oil. If it is used directly as a carbon source, high-temperature pyrolysis will produce a large amount of nitrogen, phosphorus and other heteroatoms, which will reduce the purity of the resulting biochar. It will also make it difficult to accurately control the electromagnetic parameters of the biochar material, which is not conducive to the precise assembly of microwave absorbing materials.

[0005] In the beverage industry, peanut protein milk has gained increasing attention in recent years, especially with the rapid growth of peanut protein beverage production, including peanut milk and peanut yogurt. However, the production of these beverages generates a large amount of peanut residue after grinding peanuts. This residue is typically sold as animal feed at a low price of 0.1 yuan / kg, resulting in low utilization. Similarly, in the edible oil industry, peanut oil is increasingly favored by consumers. The peanut oil production process also produces a significant amount of residue. This residue is either discarded or used as fertilizer, exhibiting extremely low utilization value. Summary of the Invention

[0006] Based on the above problems, the purpose of this invention is to provide a microwave shielding material made from peanut residue biomass char using waste peanut residue. The method for preparing this microwave shielding material comprises the following steps: (1) Collect peanut residue after removing oil and protein, wash the peanut residue with alcohol and deionized water in turn, and put it into an electric constant temperature drying oven for drying. (2) Mix the dried peanut residue with sodium hydroxide powder and grind it quickly to obtain a solid mixture; (3) The solid mixture obtained in step (2) is placed in a tube furnace and subjected to high-temperature pyrolysis under the condition of continuous argon gas to isolate oxygen. (4) After high-temperature pyrolysis, the product is taken out and washed and filtered several times with distilled water until the solution is neutral, and then the filtered wet product is collected. (5) Peanut residue biochar microwave loss material that can be obtained by drying the collected wet products.

[0007] Preferably, in step (1), the drying conditions are drying at 160 °C for 10 h.

[0008] Preferably, in step (2), the peanut residue and sodium hydroxide are mixed in a ratio of 1:1 by mass.

[0009] Preferably, in step (3), the high-temperature pyrolysis condition is heating at 700 °C for 2 h.

[0010] This invention also provides a method for preparing a microwave loss coating using peanut residue biochar. The prepared peanut residue biochar material is mixed with a matrix at a mass ratio of 1:1, wherein the matrix is ​​one of paraffin wax, epoxy resin, or silicone rubber.

[0011] Beneficial effects 1. The biomass used in this invention is waste peanut residue. Using it as a carbon source for biomass can turn waste peanut residue into a valuable resource, greatly improving the utilization value of peanut residue.

[0012] 2. Fruit-based biomass contains a large amount of protein and oil. If it is used directly as a carbon source, high-temperature pyrolysis will bring a large amount of nitrogen, phosphorus and other heteroatoms, which will reduce the purity of the resulting biochar. This invention cleverly utilizes the peanut residue left after removing oil and protein, which helps to reduce nitrogen, phosphorus and other impurities, thereby preparing high-purity biochar materials. This is also beneficial for the precise control of the electromagnetic parameters of biochar materials and the precise assembly of microwave absorbing materials.

[0013] 3. Since peanut residue biomass contains small amounts of magnesium and potassium, magnesium carbonate, potassium carbonate, or potassium magnesium carbonate double salts will be formed during high-temperature pyrolysis, affecting the microwave absorption performance of the prepared biochar. This invention adds sodium hydroxide, which intensifies the decomposition reaction of carbonates under high-temperature conditions, reducing the formation of magnesium carbonate, potassium carbonate, or potassium magnesium carbonate double salts. This facilitates precise control of the electromagnetic parameters of the biochar material and forms a richer carbon structure conductive network, which is beneficial for microwave loss.

[0014] 4. The peanut residue raw material has undergone oil and protein removal, and its cellulose has been damaged to a certain extent. The crushed particles are small in size, which is beneficial to the pyrolysis effect during high-temperature pyrolysis.

[0015] 5. Mixing peanut residue with sodium hydroxide allows the sodium hydroxide to embed between the cellulose fibers in the peanut residue, increasing the dispersion of the peanut residue. During high-temperature pyrolysis, this facilitates the formation of porous biochar. Simultaneously, under high-temperature conditions, sodium hydroxide continuously activates the product. Through the coordinated action of "high-temperature pyrolysis + sodium hydroxide dispersion + continuous activation by sodium hydroxide," the pore size and number of pores in the peanut residue biochar are effectively and significantly increased, which is beneficial for improving microwave absorption loss.

[0016] 5. This invention integrates the activation step into the high-temperature pyrolysis process, enabling the preparation of activated biochar materials in one step. The operation is simple and suitable for large-scale production applications. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 The images show the XRD patterns of peanut residue biochar prepared in Example 1 and Comparative Example 1 of this invention. Figure 2SEM images of peanut residue biochar prepared in Example 1 and Comparative Example 1 of the present invention (a: unactivated; b: activated). Figure 3 Linear scanning SEM image of activated peanut residue biochar prepared in Example 1 of this invention; Figure 4 Line scan elemental distribution map of activated peanut residue biochar prepared in Example 1 of this invention; Figure 5 The image shows the total carbon spectrum of activated peanut residue prepared in Example 1 of this invention. Figure 6 The graph shows the real and imaginary parts of the dielectric constant and the dielectric loss tangent of the peanut residue biochar prepared in Example 1 and Comparative Example 1 of the present invention. Figure 7 The graph shows the real and imaginary parts of the magnetic permeability and the tangent of the magnetic loss angle of the peanut residue biochar prepared in Example 1 and Comparative Example 1 of the present invention. Figure 8 The attenuation constant diagrams are shown for the peanut residue biochar prepared in Example 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1 Take an appropriate amount of peanut residue from an oil mill. The peanut residue refers to the residue remaining after frying. Soak the peanut residue in alcohol, crush it, and then filter it thoroughly to remove the oil. Soak it in water and filter it again to remove the protein components. Then, put it into an electric constant temperature forced-air drying oven for drying at 160 ℃ for 10 h. Pour the dried peanut residue and sodium hydroxide powder into a grinding jar at a mass ratio of 1:1 and grind and mix them quickly. After thorough mixing, put it into a tube furnace and continuously pass argon gas to isolate oxygen. Then, heat it for high-temperature pyrolysis at 700 ℃ for 2 h. After high-temperature pyrolysis, take out the product and wash it several times with distilled water until the solution is neutral. Then, collect the filtered wet product. Dry the collected wet product to obtain peanut residue biochar microwave loss material.

[0021] Comparative Example 1 Take an appropriate amount of peanut residue from an oil mill. The peanut residue refers to the residue remaining after frying. Soak the peanut residue in alcohol, crush it, and then filter it thoroughly to remove the oil. Soak it in water and filter it again to remove the protein components. Then put it into an electric constant temperature forced-air drying oven for drying at 160 ℃ for 10 h. Place the dried peanut residue in a tube furnace and continuously pass argon gas to isolate oxygen. Then heat it for high-temperature pyrolysis at 700 ℃ for 2 h. After high-temperature pyrolysis, take out the product and wash it with distilled water and filter it several times until the solution is neutral. Then collect the filtered wet product. Dry the collected wet product to obtain peanut residue biochar microwave loss material.

[0022] To further analyze the biochar prepared in Example 1 and Comparative Example 1, the structure of the biochar was analyzed by X-ray diffraction (XRD), the morphology of the biochar was analyzed by scanning electron microscopy, and the electromagnetic parameters of the biochar were tested using the transmission reflection method with an Agilent 8722ES vector network analyzer.

[0023] XRD analysis: The peanut residue biochar materials prepared in Example 1 and Comparative Example 1 were tested using an X-ray diffractometer. The test results are as follows: Figure 1 As shown, through Figure 1 It can be seen that a diffraction peak packet appeared in the samples around 2θ=25°, which represents the (002) crystal plane in the graphite structure. The half-peak width of the activated peanut residue biomass char was slightly larger than that of the unactivated peanut residue biomass char. This is attributed to the activation etching by sodium hydroxide, which reduced the order of the obtained char material. In the low-angle range, the diffraction peak intensity of the activated peanut residue biomass char was significantly enhanced, indicating that a certain amount of micropores were generated in the activated peanut residue biomass char material. In addition, there were some small impurity peaks between 28° and 35° of the unactivated peanut residue biomass. This is because the unactivated peanut residue biomass itself contains a small amount of magnesium and potassium elements, which will form magnesium carbonate, potassium carbonate, potassium magnesium carbonate double salt and other substances during high-temperature pyrolysis. This indicates that the unactivated peanut residue biomass is easily affected by other impurities. This characteristic is not conducive to the precise preparation of biomass char composition and the precise control of electromagnetic parameters, thus affecting the microwave loss efficiency. The activated peanut residue biochar did not have inorganic salt impurities. This is because by adding sodium hydroxide, under high temperature conditions, sodium hydroxide will intensify the decomposition reaction of carbonates and reduce the formation of substances such as magnesium carbonate, potassium carbonate, or potassium magnesium carbonate double salt. This method is beneficial for preparing high-purity biochar materials and for the precise control of the electromagnetic parameters of biochar materials.

[0024] SEM and EDS analysis: SEM analysis was performed on the peanut residue biochar materials prepared in Example 1 and Comparative Example 1, such as... Figure 2 As shown, unactivated biochar is blocky with fine particles of about 2-4 μm on its surface, while activated biochar has pores of about 0.5-1 μm in diameter on its surface. These pores are well-developed and numerous. This is because mixing peanut residue with sodium hydroxide allows the sodium hydroxide to embed between the cellulose fibers in the peanut residue, increasing the dispersion of the peanut residue. During high-temperature pyrolysis, this promotes the formation of a porous structure in the biochar. Simultaneously, under high-temperature conditions, sodium hydroxide continuously activates the product. Through the coordinated action of "high-temperature pyrolysis + sodium hydroxide dispersion + continuous sodium hydroxide activation," the formation of a porous structure in the biochar is effectively facilitated. The results will be: firstly, a lower density in the prepared biochar, making the material lighter; secondly, the porous structure will cause repeated microwave reflection loss and interfacial polarization, thereby improving the microwave loss capability of the biochar and facilitating the assembly of high-performance shielding materials.

[0025] pass Figure 3 , Figure 4 and Figure 5 It can be seen that the peanut residue biochar prepared by sodium hydroxide activation mainly contains carbon and a small amount of oxygen. No magnesium, potassium and other elements were detected by energy dispersive spectroscopy analysis, which is consistent with the XRD analysis results. This further indicates that the peanut residue biochar prepared by sodium hydroxide activation has high purity.

[0026] Electromagnetic parameters and loss angle analysis: The peanut residue biochar materials prepared in Example 1 and Comparative Example 1 were mixed with paraffin wax at a mass ratio of 1:1 to prepare coaxial rings with an inner diameter of 3.04 mm, an outer diameter of 7.0 mm, and a thickness of 2 mm. The dielectric constant (ε) of the materials in the frequency range of 2-18 GHz was measured using the coaxial method. r , εr=ε'-jε") and permeability (μ r , ε r =μ'-jμ").

[0027] Figure 6 Let ε' be the real part (ε′) and imaginary part (ε″) of the dielectric constant of peanut residue biochar, and tanδ be the dielectric loss tangent. εAs shown in the figure, in the low to mid-frequency range, the ε′ values ​​of both unactivated and activated peanut residue biochar decrease with increasing frequency. This can be attributed to frequency dispersion behavior; at high frequencies, the dipole polarization of biochar cannot follow the alternating field. In the 2-18 GHz range, the ε′ values ​​of unactivated biochar are higher than those of activated biochar. ε′ represents the material's ability to store electrical energy, indicating that activated peanut residue biochar has a better capacity for storing electrical energy. The ε" value of activated peanut residue biochar is relatively large at low frequencies, reaching as high as 66 at 2 GHz. Subsequently, the ε" value gradually decreases by 10 with increasing frequency (at 8 GHz). In contrast, the ε" value of unactivated peanut residue biochar shows little fluctuation in the 2-18 GHz range, remaining around 5-10. The higher ε" value of activated peanut residue biochar is attributed to its abundant porosity, which significantly increases the specific surface area and interface, thus affecting the dielectric constant and benefiting microwave loss. The tanδε value of both activated and unactivated biochar shows a similar trend to the ε" value: the tanδε value of activated peanut residue biochar gradually decreases with increasing frequency, while the tanδε value of unactivated peanut residue biochar shows little variation in the 2-18 GHz range. In the S-band, C-band, and X-band, the tanδε value of activated peanut residue biochar is much larger than that of unactivated peanut residue biochar. This result is consistent with the analysis results of ε′ and ε″ values.

[0028] tanδ ε Based on the comprehensive analysis of the dielectric loss capacity of the reaction material, the above analysis shows that under high temperature conditions, sodium hydroxide continuously etches the product to form a porous structure, which promotes the repeated reflection and absorption of microwaves, thereby improving the microwave dielectric loss capacity of biochar.

[0029] Figure 7 The real part (μ′) and imaginary part (μ″) of the magnetic permeability and the magnetic loss tangent (tanδ) of peanut residue biochar are given. μ )picture, Regarding the variation of μ′ values, the μ′ values ​​of unactivated peanut residue biochar fluctuated within the range of 0.83 to 1.17, while those of activated peanut residue biochar fluctuated within the range of 0.91 to 1.31. Specifically, in the 4–17 GHz range, the μ′ values ​​of activated biochar were higher than those of unactivated biochar, but in other GHz bands, the μ′ values ​​of activated biochar were lower than those of unactivated biochar.

[0030] Regarding the variation of μ" value, the μ" value of unactivated biochar shows a relatively smooth variation across other frequency ranges, except for a significant peak at 4.95 GHz (peak value of 0.35). In contrast, the μ" value of unactivated biochar remains around 0 in the 2-9 GHz range, but increases significantly and fluctuates considerably in the 9-18 GHz range (fluctuation range of 0-0.63).

[0031] For tanδ μ The change curve of the tanδ value is similar to that of the μ' value. This is mainly because the μ' value of both biochars fluctuates around 1, leading to the change in tanδ. μ The main factor affecting the magnitude of the value is the difference in the μ" value.

[0032] In addition, compare the tanδ of biochar. ε Value and tanδ μ From the value, we can know tanδ ε The value is significantly higher than tanδ μ The value indicates that this material is mainly characterized by dielectric loss.

[0033] Attenuation constant analysis: Dielectric losses mainly occur through three mechanisms: conductive loss, dipole polarization, and interfacial polarization. These various loss mechanisms have varying degrees of impact on the microwave absorption performance of materials. However, it is difficult to determine a material's overall microwave absorption capability solely based on these losses. Therefore, an attenuation constant (α) is introduced to measure a material's overall microwave absorption capability. In a lossy medium, the complex propagation constant... (Usually expressed as γ = α + jβ, where α is the attenuation constant and β is the phase constant). The larger the attenuation constant of the material, the greater the loss intensity of the incident electromagnetic wave.

[0034] Back-calculation is possible

[0035] Where f is the frequency, in Hz, and c is the speed of light, in m / s.

[0036] like Figure 8As shown, the α values ​​of both unactivated and activated biochar generally increase with increasing frequency. Specifically, the α value of activated biochar increases from 196.05 at 2 GHz to 613.77 at 18 GHz, while the α value of unactivated biochar increases from 39.33 at 2 GHz to 378.92 at 18 GHz. Comparing the α values ​​of unactivated and activated biochar, it can be seen that in the 2–18 GHz band, the α value of activated peanut residue biochar is significantly greater than that of unactivated peanut residue biochar. This further indicates that using peanut residue as raw material and activating it with sodium hydroxide can improve the purity of the carbon material, while simultaneously forming a rich porous structure, generating multiple reflections, and ultimately improving the microwave loss capability of the material.

[0037] The above-disclosed embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the invention. Those skilled in the art will understand that implementing all or part of the above-described embodiments and making equivalent changes in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A microwave shielding material made from peanut residue biochar, characterized in that, The preparation method of this peanut residue biochar microwave shielding material includes the following steps: (1) Collect peanut residue after removing oil and protein, wash the peanut residue with alcohol and deionized water in turn, and put it into an electric constant temperature drying oven for drying. (2) Mix the dried peanut residue with sodium hydroxide powder and grind it quickly to obtain a solid mixture; (3) The solid mixture obtained in step (2) is placed in a tube furnace and subjected to high-temperature pyrolysis under the condition of continuous argon gas to isolate oxygen. (4) After high-temperature pyrolysis, the product is taken out and washed and filtered several times with distilled water until the solution is neutral, and then the filtered wet product is collected. (5) Biochar microwave loss material that can be obtained by drying the collected wet products.

2. The peanut residue biochar microwave shielding material as described in claim 1, characterized in that, The drying conditions in step (1) are drying at 160 °C for 10 h.

3. The peanut residue biochar microwave shielding material as described in claim 2, characterized in that, In step (2), the mixing ratio of peanut residue and sodium hydroxide is 1:1 by mass.

4. The peanut residue biochar microwave shielding material as described in claim 3, characterized in that, The high-temperature pyrolysis condition in step (3) is heating at 700 °C for 2 h.

5. A method for preparing a microwave loss layer using the peanut residue biochar microwave shielding material as described in claim 4, characterized in that, The prepared peanut residue biochar is mixed with a matrix at a mass ratio of 1:

1. The matrix is ​​one of paraffin, epoxy resin, or silicone rubber.

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