Microwave preparation method of sulfur-free expanded graphite and application thereof

Abstract

This invention discloses a microwave preparation method for sulfur-free expanded graphite and its application, belonging to the field of carbon material preparation technology. The method includes four steps: raw material pretreatment, sulfur-free intercalation treatment, microwave expansion treatment, and post-treatment. This invention selects high-carbon natural flake graphite, which is pretreated by crushing and drying. Then, an intercalation reaction is carried out by adding a sulfur-free oxidant and a composite intercalation solution. Following microwave heating for rapid expansion, the finished sulfur-free expanded graphite is obtained after post-treatment. This invention innovatively adopts a sulfur-free intercalation system, completely eliminating sulfur residue and pollution. Combined with microwave heating technology, energy consumption is reduced by more than 60% compared to traditional processes. The process is simple and the production cycle is short. The obtained product has an expansion volume ≥300mL / g, a sulfur content ≤0.01%, high purity, and stable performance. It can be widely used in multiple fields, solving the problems of sulfur pollution, high energy consumption, complex processes, and limited applications of existing technologies, and has significant economic and environmental benefits.

Description

Technical Field

[0001] This invention relates to the field of carbon material preparation technology, specifically to a microwave preparation method for environmentally friendly sulfur-free expanded graphite. Background Technology

[0002] Expanded graphite is a new type of functional carbon material obtained by intercalation and expansion of natural graphite. It has excellent properties such as loose and porous structure, large specific surface area, high temperature resistance, corrosion resistance and good flexibility. It has broad application prospects in sealing fillers, wastewater treatment, energy storage materials, fire prevention and flame retardancy.

[0003] Currently, the traditional method for preparing expanded graphite in industry mainly adopts a chemical intercalation-high-temperature calcination process. The intercalating agents are often sulfur-containing reagents such as concentrated sulfuric acid and fuming sulfuric acid. This process has significant drawbacks: First, sulfur-containing intercalating agents result in residual sulfur in the product, which not only corrodes equipment and pollutes the environment but also limits its application in high-end sealing, biomedicine, and electronic energy storage fields where high purity is required. Second, the high-temperature calcination process requires raising the temperature to 800-1200℃, resulting in extremely high energy consumption, slow heating rate, and uneven heating, leading to unstable expansion volume and large performance fluctuations in the product. Third, the process is cumbersome, requiring multiple water washings to remove sulfur after intercalation, generating large amounts of acidic wastewater with high treatment costs, which does not align with the trend of green and environmentally friendly industrial development.

[0004] To address sulfur pollution, some sulfur-free preparation techniques have been attempted in existing technologies. These often employ sulfur-free oxidants such as nitric acid and hydrogen peroxide combined with single sulfuric acid-free intercalating agents such as perchloric acid, acetic acid, formic acid, phosphoric acid, and nitric acid. However, these techniques generally suffer from poor intercalation effects, low expansion volume (typically below 200 mL / g), complex processes, and long reaction times. Furthermore, existing sulfur-free preparation processes still largely rely on traditional high-temperature calcination, failing to effectively address the pain points of high energy consumption and unstable product performance. Microwave heating technology offers advantages such as rapid and uniform heating, energy saving, and high efficiency, and has been applied to the preparation of various materials. However, combining it with sulfur-free intercalation systems to achieve a simplified process, reduced energy consumption, and improved product performance for the preparation of sulfur-free expanded graphite lacks a mature technical solution, making it difficult to meet the needs of large-scale industrial production and multi-field applications.

[0005] Therefore, developing a method for preparing expanded graphite that is sulfur-free, environmentally friendly and energy-saving, simple in process, low in cost, produces high-performance products, and has a high expansion volume, in order to break through the limitations of traditional processes and expand its application fields, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] In view of this, the purpose of this invention is to overcome the defects of existing technologies in the preparation of expanded graphite, such as sulfur pollution, high energy consumption, complex processes, unstable product performance, and limited application range. This invention provides a microwave preparation method for sulfur-free expanded graphite. This method does not use sulfur-containing intercalating agents and uses microwave heating to replace traditional high-temperature calcination, achieving sulfur-free, environmentally friendly, simple, energy-saving, and efficient clean production. The resulting sulfur-free expanded graphite has high purity, high expansion volume, and stable performance, and can be widely used in many high-end fields.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A microwave preparation method for sulfur-free expanded graphite includes the following steps: (1) Raw material pretreatment: Crush flake graphite, sieve it to 80-200 mesh, and dry it for later use; (2) Sulfur-free intercalation treatment: The pretreated graphite powder is added to the sulfur-free composite intercalation liquid, heated and stirred at a constant temperature, and then the product is filtered and dried to obtain sulfur-free expandable graphite. The sulfur-free composite intercalation solution consists of an oxidant and an intercalating agent, the latter being obtained by mixing perchloric acid and acetic acid. (3) Microwave expansion treatment: Sulfur-free expandable graphite is placed in a microwave reactor and heated with microwaves at 600-900W for 20-40s. After completion, it is cooled to room temperature to obtain crude sulfur-free expanded graphite. (4) Post-processing: The crude product is crushed and sieved to obtain sulfur-free expanded graphite with an expansion volume ≥300mL / g and a sulfur content ≤0.01%.

[0009] This invention innovatively employs a sulfur-free composite intercalation system, composed of a sulfur-free oxidant and an organic acid intercalating agent. This completely eliminates traditional sulfur-containing intercalating agents, preventing sulfur residue and acidic wastewater pollution at the source, achieving a green and environmentally friendly preparation process while improving intercalation efficiency and ensuring product purity. Furthermore, this invention organically combines microwave heating technology with the sulfur-free intercalation system, replacing the traditional high-temperature calcination process. Microwave heating is rapid and uniform, reducing energy consumption by more than 60% compared to traditional processes. It also eliminates the need for complex high-temperature heating equipment, significantly simplifying the preparation process and shortening the production cycle. The method of this invention is simple and easy to operate, eliminating the need for multiple water washing desulfurization steps. The raw materials are readily available and inexpensive, enabling direct industrial-scale production. The product is sulfur-free, expanding its applications in high-end sealing, biomedicine, electronic energy storage, and other fields.

[0010] Furthermore, the flake graphite mentioned in step (1) is natural flake graphite; The sieve particle size is 80-200 mesh; The drying temperature is 80-100℃, and the drying time is 2-4 hours.

[0011] Furthermore, in step (2), the mass ratio of graphite powder, oxidant and intercalating agent is 1:(0.1-0.6):(3-7).

[0012] Furthermore, the oxidant is potassium permanganate.

[0013] Furthermore, the volume ratio of perchloric acid to acetic acid in the intercalating agent is (0.5-2):1.

[0014] The perchloric acid has a mass concentration of 70%-72%, and the acetic acid has a mass concentration of ≥99.5%.

[0015] The drying temperature in step (2) is 60-80℃ and the drying time is 1-2h.

[0016] This invention uses a mixture of perchloric acid and acetic acid as an intercalating agent. Compared with using perchloric acid or acetic acid alone, the mixed system exhibits a significant synergistic effect during the intercalation process: perchloric acid provides strong oxidative intercalation ability, while acetic acid improves the wettability and permeability of the intercalation solution, promotes the uniform diffusion of the intercalating agent in the graphite layer, thereby achieving a more complete intercalation effect and providing a basis for subsequent microwave expansion.

[0017] Furthermore, the microwave heating power in step (3) is 600-900W and the heating time is 20-40s.

[0018] This invention optimizes the process parameters of intercalation and microwave expansion, achieving synergistic control of the intercalation and expansion reactions. The resulting sulfur-free expanded graphite has a high expansion volume (≥300mL / g), well-developed pore structure, and stable performance, solving the problems of low expansion volume and large performance fluctuations in existing sulfur-free expanded graphite.

[0019] Furthermore, in step (4), the sieving process involves passing the coarse product through 100-mesh and 300-mesh sieves respectively to obtain the sieve contents, the particle size of which is 100-300 mesh.

[0020] This invention also provides the application of sulfur-free expanded graphite prepared by the above method in the fields of sealing, adsorption, energy storage, environmental protection, fire protection or metallurgy.

[0021] The beneficial effects of this invention are as follows: 1) Sulfur-free and environmentally friendly, pollution-free: This invention adopts a sulfur-free composite intercalation system, does not use any sulfur-containing reagents, does not generate acidic wastewater during the preparation process, and the product has no sulfur residue (sulfur content ≤0.01%). It will not corrode equipment or pollute the environment, which is in line with the green and environmentally friendly industrial policy. At the same time, the product has high purity and can be applied to fields with high purity requirements such as biomedicine and high-end sealing.

[0022] 2) Simple process, energy saving and high efficiency: This invention uses microwave heating to replace traditional high-temperature roasting, which heats up quickly and evenly, and the heating time is only 20-40 seconds. The energy consumption is reduced by more than 60% compared with the traditional process. There is no need for multiple water washing and desulfurization steps. The whole preparation process is short, simple to operate, requires less equipment investment, can achieve clean production, and significantly reduce production costs.

[0023] 3) Excellent product performance and good stability: By optimizing the intercalation and microwave expansion parameters, the intercalation reaction is sufficient and the expansion volume is high (≥300mL / g), which is far superior to the performance of existing sulfur-free expanded graphite; the product has a well-developed pore structure, large specific surface area, high temperature resistance, corrosion resistance, excellent flexibility and adsorption performance, and small performance fluctuation and stable quality.

[0024] 4) Wide Range of Applications: The sulfur-free expanded graphite prepared by this invention can be widely used in the sealing field, especially in high-performance sealing and gasket materials where an expansion volume ≥ 300 mL / g is required to ensure sealing pressure resistance and compression resilience. It can also be used in adsorption (oily wastewater treatment, heavy metal ion adsorption), energy storage (where, in lithium battery electrode materials and supercapacitors, an expansion volume ≥ 300 mL / g results in a more developed pore structure, which is beneficial for ion transport and volumetric performance improvement), environmental protection (waste gas treatment), fire protection (fire retardant materials), and metallurgy (thermal insulation additives), among other fields. The high-end applications mentioned above all have specific requirements for the expansion volume of expanded graphite (graphite expansion volume ≥ 300 mL / g), and the product of this invention precisely meets this performance threshold, demonstrating broad application prospects. Attached Figure Description

[0025] Figure 1 This is a flowchart of the microwave preparation process of sulfur-free expanded graphite according to the present invention. Detailed Implementation

[0026] 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.

[0027] Example 1 A microwave preparation method for sulfur-free expanded graphite, the specific steps of which are as follows: (1) Raw material pretreatment: Select Xinjiang natural flake graphite with a carbon content of 99.5%, crush it and pass it through a 100-mesh sieve to obtain graphite powder, and dry it at 90℃ for 3 hours for later use.

[0028] (2) Sulfur-free intercalation treatment: Take graphite powder, oxidant and intercalating agent in a mass ratio of 1:0.6:6; the oxidant is potassium permanganate and the intercalating agent is obtained by mixing perchloric acid (concentration 71%) and acetic acid (concentration 99.5%) in a volume ratio of 1:1; add graphite powder to the uniformly mixed sulfur-free composite intercalation solution and stir at 50℃ for 1.5h to carry out the intercalation reaction; after the reaction is completed, filter and collect the solid product, dry it at 70℃ for 1.5h to obtain sulfur-free expandable graphite.

[0029] (3) Microwave expansion treatment: sulfur-free expandable graphite is placed in a microwave reactor, the microwave power is adjusted to 800W, and microwave heating is performed for 30s; after the reaction is completed, it is naturally cooled to room temperature to obtain crude sulfur-free expanded graphite.

[0030] (4) Post-processing: Crush the sulfur-free expanded graphite crude product and sieve it through a double-layer sieve of 100 mesh and 300 mesh to remove impurities and incompletely expanded particles. Take the material in the sieve to obtain the sulfur-free expanded graphite finished product.

[0031] Example 2 A microwave preparation method for sulfur-free expanded graphite, the specific steps of which are as follows: (1) Raw material pretreatment: Select natural flake graphite with a carbon content of 99%, crush it and pass it through an 80-mesh sieve to obtain graphite powder, and dry it at 80℃ for 4 hours for later use.

[0032] (2) Sulfur-free intercalation treatment: Take graphite powder, oxidant and intercalating agent in a mass ratio of 1:0.5:4; the oxidant is potassium permanganate and the intercalating agent is obtained by mixing perchloric acid (concentration 71%) and acetic acid (concentration 99.5%) in a volume ratio of 1.5:1; add graphite powder to the uniformly mixed sulfur-free composite intercalation solution and stir at 40℃ for 2h to carry out the intercalation reaction; after the reaction is completed, filter and collect the solid product, dry it at 60℃ for 2h to obtain sulfur-free expandable graphite.

[0033] (3) Microwave expansion treatment: sulfur-free expandable graphite is placed in a microwave reactor, the microwave power is adjusted to 600W, and microwave heating is performed for 40s; after the reaction is completed, it is naturally cooled to room temperature to obtain crude sulfur-free expanded graphite.

[0034] (4) Post-processing: Crush the sulfur-free expanded graphite crude product and sieve it through a double-layer sieve of 100 mesh and 300 mesh to remove impurities and incompletely expanded particles. Take the material in the sieve to obtain the sulfur-free expanded graphite finished product.

[0035] Example 3 A microwave preparation method for sulfur-free expanded graphite, the specific steps of which are as follows: (1) Raw material pretreatment: Select natural flake graphite with a carbon content of 99.8%, crush it and pass it through a 200-mesh sieve to obtain graphite powder, and dry it at 100℃ for 2 hours for later use.

[0036] (2) Sulfur-free intercalation treatment: Take graphite powder, oxidant and intercalating agent in a mass ratio of 1:0.8:5; the oxidant is potassium permanganate, and the intercalating agent is obtained by mixing (concentration 71%) and acetic acid (concentration 99.5%) in a volume ratio of 2:1; add graphite powder to the uniformly mixed sulfur-free composite intercalation solution, stir at 60℃ for 1h to carry out the intercalation reaction; after the reaction is completed, filter and collect the solid product, dry at 80℃ for 1h to obtain sulfur-free expandable graphite.

[0037] (3) Microwave expansion treatment: sulfur-free expandable graphite is placed in a microwave reactor, the microwave power is adjusted to 900W, and microwave heating is performed for 20s; after the reaction is completed, it is naturally cooled to room temperature, and the contents of the sieve are taken to obtain crude sulfur-free expanded graphite.

[0038] (4) Post-processing: The sulfur-free expanded graphite crude product is crushed and sieved through a double-layer sieve of 100 mesh and 300 mesh to remove impurities and incompletely expanded particles, and sulfur-free expanded graphite finished product is obtained.

[0039] Comparative Example 1 Expanded graphite was prepared using a traditional sulfur-containing intercalation-high-temperature calcination process, with the following specific steps: (1) Raw material pretreatment: Same as in Example 1; (2) Sulfur-containing intercalation treatment: Take graphite powder, oxidant and intercalating agent in a mass ratio of 1:0.6:6; the oxidant is potassium permanganate, and the intercalating agent is made by mixing 97% concentrated sulfuric acid and 67% nitric acid in a volume ratio of 5:1. Add graphite powder to the mixed intercalation solution of concentrated sulfuric acid and nitric acid, stir at 50°C for 1.5h, filter, wash with water until neutral, and dry to obtain sulfur-containing expandable graphite. (3) High-temperature calcination: Sulfur-containing expandable graphite is placed in a muffle furnace and calcined at 900°C for 2 minutes. After cooling to room temperature, sulfur-containing expandable graphite is obtained. (4) Post-processing: Same as in Example 1.

[0040] Comparative Example 2 Expanded graphite was prepared using a traditional sulfur-containing intercalation-high-temperature calcination process, with the following specific steps: (1) Raw material pretreatment: Same as in Example 1; (2) Sulfur-containing intercalation treatment: Take graphite powder, oxidant and intercalating agent in a mass ratio of 1:0.6:6; wherein the oxidant is potassium permanganate and the intercalating agent is 97% concentrated sulfuric acid. Add graphite powder to the intercalation solution of concentrated sulfuric acid, stir at 50°C for 1.5h, filter, wash with water until neutral, and dry to obtain sulfur-containing expandable graphite. (3) High-temperature calcination: Sulfur-containing expandable graphite is placed in a muffle furnace and calcined at 900°C for 2 minutes. After cooling to room temperature, sulfur-containing expandable graphite is obtained. (4) Post-processing: Same as in Example 1.

[0041] Comparative Example 3 (Perchloric Acid Alone) Using perchloric acid as a single intercalating agent, the specific steps are as follows: Raw material pretreatment: Same as in Example 1; Sulfur-free intercalation treatment: Graphite powder, oxidant, and intercalating agent were prepared in a mass ratio of 1:0.6:6; the oxidant was potassium permanganate, and the intercalating agent was perchloric acid (mass fraction 71%). The graphite powder was added to the perchloric acid solution and stirred at 50°C for 1.5 h to carry out the intercalation reaction. After the reaction was completed, the solid product was collected by filtration and dried at 70°C for 1.5 h to obtain sulfur-free expandable graphite.

[0042] Microwave expansion treatment: Same as in Example 1.

[0043] Post-processing: Same as in Example 1.

[0044] Comparative Example 4 (Single Acetic Acid) Using acetic acid as an intercalating agent, the specific steps are as follows: Raw material pretreatment: Same as in Example 1; Sulfur-free intercalation treatment: Graphite powder, oxidant, and intercalating agent were prepared in a mass ratio of 1:0.6:6; the oxidant was potassium permanganate, and the intercalating agent was acetic acid with a mass fraction of 99.5%; the graphite powder was added to the acetic acid solution and stirred at 50°C for 1.5 h to carry out the intercalation reaction; after the reaction was completed, the solid product was collected by filtration and dried at 70°C for 1.5 h to obtain sulfur-free expandable graphite.

[0045] Microwave expansion treatment: Same as in Example 1.

[0046] Post-processing: Same as in Example 1.

[0047] Test case The sulfur-free expanded graphite prepared in Examples 1-3 and the sulfur-containing expanded graphite prepared in Comparative Examples 1-4 were tested, and the results are shown in Table 1.

[0048] Table 1 Comparison of performance of different expanded graphite products

[0049] The comparison results of Examples 1-3 and Comparative Examples 1-4 show that the sulfur-free expanded graphite prepared by the present invention has no sulfur residue, higher expansion volume (expansion volume > 300 mL / g, while single perchloric acid intercalation is only 230 mL / g and single acetic acid intercalation is only 190 mL / g), more stable performance, and the preparation process is environmentally friendly, energy-saving, simple, and has lower production cost. It is significantly better than the traditional sulfur-containing preparation process and is more suitable for industrial-scale production and multi-field applications.

[0050] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A microwave preparation method for sulfur-free expanded graphite, characterized in that, Includes the following steps: (1) Raw material pretreatment: Crush flake graphite, sieve it to 80-200 mesh, and dry it for later use; (2) Sulfur-free intercalation treatment: The pretreated graphite powder is added to the sulfur-free composite intercalation liquid, heated and stirred at a constant temperature, and then the product is filtered and dried to obtain sulfur-free expandable graphite. The sulfur-free composite intercalation solution consists of an oxidant and an intercalating agent, the latter being obtained by mixing perchloric acid and acetic acid. (3) Microwave expansion treatment: Sulfur-free expandable graphite is placed in a microwave reactor and heated with microwaves at 600-900W for 20-40s. After completion, it is cooled to room temperature to obtain crude sulfur-free expanded graphite. (4) Post-processing: The crude product is crushed and sieved to obtain sulfur-free expanded graphite with an expansion volume ≥300mL / g and a sulfur content ≤0.01%.

2. The microwave preparation method for sulfur-free expanded graphite according to claim 1, characterized in that, The flake graphite mentioned in step (1) is natural flake graphite; The sieve particle size is 80-200 mesh; The drying temperature is 80-100℃, and the drying time is 2-4 hours.

3. The microwave preparation method for sulfur-free expanded graphite according to claim 1, characterized in that, In step (2), the mass ratio of graphite powder, oxidant and intercalating agent is 1:(0.1-0.6):(3-7).

4. The microwave preparation method for sulfur-free expanded graphite according to claim 1 or 3, characterized in that, The oxidant is potassium permanganate.

5. The microwave preparation method for sulfur-free expanded graphite according to claim 1 or 3, characterized in that, The intercalating agent contains perchloric acid and acetic acid in a volume ratio of (0.5-2):

1.

6. The microwave preparation method for sulfur-free expanded graphite according to claim 1, characterized in that, The drying temperature in step (2) is 60-80℃ and the drying time is 1-2h.

7. The microwave preparation method for sulfur-free expanded graphite according to claim 1, characterized in that, The microwave heating power in step (3) is 600-900W and the heating time is 20-40s.

8. The microwave preparation method for sulfur-free expanded graphite according to claim 1, characterized in that, The sieving process mentioned in step (4) involves passing the coarse product through 100-mesh and 300-mesh sieves respectively to obtain the sieve contents with a particle size of 100-300 mesh.

9. The application of sulfur-free expanded graphite prepared by the method of any one of claims 1-8 in the fields of sealing, adsorption, energy storage, environmental protection, fire protection or metallurgy.

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