Expandable graphite without waste acid discharge as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of graphite preparation, and particularly relates to expandable graphite without waste acid discharge as well as a preparation method and application thereof. The preparation method comprises the following steps: stirring and mixing a graphite raw material and recycled sulfuric acid for pretreatment, then adding hydrogen peroxide into the mixture, and carrying out oxidation intercalation reaction at room temperature to obtain a reaction product; carrying out solid-liquid separation on the reaction product to obtain filtrate and a solid product; filtrate is used as recycled sulfuric acid for a pretreatment process; the solid product is sequentially subjected to washing, drying and high-temperature expansion treatment, and the expandable graphite is prepared. According to the method, the core problems of high consumption of sulfuric acid and serious waste acid pollution in the production of the expandable graphite are solved from the source, the raw material and wastewater treatment cost is remarkably reduced through efficient resource recycling, and an economical, feasible and environment-friendly green production process path is provided for the industry.

Description

Technical Field

[0001] This invention belongs to the field of graphite preparation technology, specifically relating to an expandable graphite with zero waste acid emissions, its preparation method, and its application. Background Technology

[0002] Expanded graphite is a functional carbon material produced by the oxidation intercalation reaction of natural flake graphite. It exhibits a worm-like porous structure, possessing high specific surface area, excellent thermal and electrical conductivity, and stable chemical properties. Based on these characteristics, expanded graphite is widely used in sealing applications in industries such as petroleum, chemical, and metallurgy, and also shows significant application potential in electrode materials, electromagnetic shielding, thermal interface materials, and composite material reinforcement.

[0003] Currently, the chemical intercalation method is widely used in industry to prepare expandable graphite. This method typically requires the sequential addition of concentrated sulfuric acid, hydrogen peroxide, and natural flake graphite under specific temperature conditions, involving multiple processes such as reaction, washing, filtration, and drying to finally obtain the product. However, this process uses a large amount of concentrated sulfuric acid, and the waste acid generated after the reaction is difficult to effectively recover and reuse. This not only leads to a serious waste of sulfuric acid resources but also causes environmental pollution problems and significantly increases the cost of subsequent wastewater treatment.

[0004] To alleviate the aforementioned problems, existing technologies recycle and reuse the waste acid generated during the preparation process. However, in practice, the large amount of washing water introduced during processes such as washing and filtration leads to severe dilution of the waste acid, resulting in a sulfuric acid concentration far below the high concentration required for the initial intercalation reaction. To reuse this low-concentration waste acid in production, it must first undergo energy-intensive concentration and purification. However, currently feasible concentration technologies (such as evaporation concentration and membrane separation) generally suffer from high equipment investment and enormous energy consumption, making them uneconomical. Furthermore, these recycling processes themselves may generate new solid hazardous waste or secondary wastewater, failing to fundamentally achieve the production goal of "zero waste acid discharge." Summary of the Invention

[0005] The purpose of this invention is to provide an expandable graphite with zero waste acid discharge, its preparation method and application, thereby overcoming the shortcomings of the prior art. A new process with a 100% waste acid recovery utilization rate has been developed, which can prepare highly expandable graphite using recycled sulfuric acid without adding other metal ion oxidants, completely solving the waste acid discharge problem and achieving green, efficient and low-cost production.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: In a first aspect, the present invention provides a method for preparing expandable graphite without waste acid emissions, comprising the following steps: The graphite raw material was pretreated by mixing it with recycled sulfuric acid. Then hydrogen peroxide was added to the mixture, and an oxidation intercalation reaction was carried out at room temperature to obtain the reaction product. The reaction products were subjected to solid-liquid separation to obtain filtrate and solid product; the filtrate was used as recovered sulfuric acid for the pretreatment process; the solid product was successively washed, dried and subjected to high-temperature expansion treatment to obtain expandable graphite.

[0007] In some other embodiments, the mass ratio of the recovered sulfuric acid to the graphite raw material is (2-4):1, and the mass fraction of the recovered sulfuric acid is 84-92%.

[0008] The mass ratio of the recovered sulfuric acid to the graphite raw material is 2:1, 2.8:1, 3:1 or 4:1.

[0009] In some other embodiments, the temperature of the intercalation pretreatment reaction is 45-60 °C and the time is 30-60 min.

[0010] In some other embodiments, the amount of hydrogen peroxide added is 8%-15% of the mass of the graphite raw material.

[0011] Specifically, the amount of hydrogen peroxide added is 8%, 10%, 13% or 15% of the mass of the graphite raw material.

[0012] In some other embodiments, the oxidation intercalation reaction takes 60-120 min.

[0013] In some other embodiments, the drying temperature is 40-50 °C and the drying time is 10-15 h; The temperature for high-temperature expansion is 900-1000 ℃, and the expansion time is 5-10 s.

[0014] In some other embodiments, when the mass fraction of the recovered sulfuric acid is <90%, before stirring and mixing the graphite raw material and the recovered sulfuric acid, the recovered sulfuric acid is further mixed with concentrated sulfuric acid with a mass fraction of 98%, so that the mass fraction of the recovered sulfuric acid after mixing is 90%-94%.

[0015] In some other embodiments, the graphite raw material has a mesh size of 50-80 mesh; The expansion ratio of expandable graphite is 133-230 mL / g, preferably 200-230 mL / g.

[0016] In a second aspect, the present invention provides expandable graphite prepared by the method for preparing expandable graphite with no waste acid emissions as described in the first aspect.

[0017] Thirdly, the present invention provides the application of the expandable graphite described in the second aspect in adsorption, sealing, flame retardant and shielding materials for environmental pollution.

[0018] The beneficial effects of this invention are: (1) Through the optimized design of the process, the present invention can almost completely recover the sulfuric acid in the reaction mother liquor and directly use it for a new round of production. The utilization rate of the recovered acid is high, which fundamentally eliminates the external discharge of waste acid and completely solves the environmental pollution and high treatment cost problems caused by it.

[0019] (2) This invention does not require the addition of heavy metals to the existing sulfuric acid-hydrogen peroxide intercalation system. It can stably prepare expandable graphite products with high expansion ratios by recycling the recovered acid and at a low acid concentration (about 92%), thus ensuring product performance while maintaining the purity and environmental friendliness of the system.

[0020] (3) The technical solution of the present invention can be directly integrated into the traditional production process without major modifications to the existing reaction and filtration equipment, achieving efficient and stable production under low concentration acid recovery conditions, which greatly improves the feasibility and economy of technology promotion.

[0021] In summary, compared with existing technologies, this invention not only solves the core problems of high sulfuric acid consumption and serious waste acid pollution in the production of expandable graphite from the source, but also significantly reduces the cost of raw materials and wastewater treatment through efficient resource recycling, providing the industry with an economical, feasible, and environmentally friendly green production process. Attached Figure Description

[0022] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0023] Figure 1 This is a SEM image of the expanded graphite prepared in Example 1 of the present invention; Figure 2 This is a SEM image of the expanded graphite prepared in Example 2 of the present invention; Figure 3 This is a SEM image of the expanded graphite prepared in Example 6 of the present invention; Figure 4 The images show the XRD patterns of the expanded graphite prepared in Examples 1-2 and Example 6 of this invention. Detailed Implementation

[0024] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0025] As mentioned earlier, existing waste acid recycling processes suffer from problems such as low utilization rate of sulfuric acid raw materials, environmental pollution caused by waste acid emissions, high subsequent treatment costs, and difficulty in achieving low-cost, high-efficiency recycling of waste acid within existing production systems. These problems severely restrict the green and sustainable development of expandable graphite production.

[0026] Example 1 An expandable graphite and its preparation method, comprising the following steps: Add 6 g of 80-mesh graphite raw material and 20 g of 98% concentrated sulfuric acid to a beaker, stir well, and then slowly add 0.8 g of hydrogen peroxide. Maintain mechanical stirring (200 r / min) throughout the process. After the oxidation and intercalation reaction for 30 min, filter the solution and recover the filtrate to a recovery tank. Wash the product with deionized water until neutral and dry at 45 ℃ for 6 h to obtain expanded graphite. Take 0.5 g of expandable graphite and expand it in a muffle furnace at 950 ℃ for 7 s to obtain expanded graphite. Measure its volume using the 200 mL beaker method and calculate the expansion ratio to be 220 mL / g. The concentration of the filtrate recovered in the recovery tank is approximately 92%–93%.

[0027] Figure 1 This is a SEM image of the expanded graphite prepared in Example 1 of this invention. Figure 1 It can be seen that the expanded graphite is a loose and porous worm-like carbon material. Each "worm" is a graphite sheet that forms a highly porous network structure that expands dramatically along the thickness direction, but the layers are still partially connected.

[0028] Example 2 An expandable graphite with zero waste acid emission and its preparation method, comprising the following steps: Add 6 g of 80-mesh graphite raw material and 20 g of sulfuric acid (concentration approximately 92%) recovered in Example 1 to a beaker. After stirring evenly, transfer the beaker to a 50 °C water bath and let it stand for 60 min. Then, transfer the beaker to room temperature and stir, slowly adding 0.8 g of hydrogen peroxide. Mechanically stir at 200 r / min for 60 min of oxidative intercalation reaction. Filter and recover the filtrate to a recovery tank. Wash the product with deionized water until neutral and dry at 45 °C for 12 h to obtain expanded graphite. Take 0.5 g of expandable graphite and expand it at 950 °C in a muffle furnace for 7 s to obtain expanded graphite. Measure its volume using the 200 mL beaker method and calculate the expansion ratio as 210 mL / g.

[0029] Figure 2 This is a SEM image of the expanded graphite prepared in Example 2 of the present invention. Figure 2 It can be seen that the expanded graphite is also a loose and porous worm-like carbon material. Each "worm," that is, each graphite sheet, forms a highly porous network structure that expands dramatically along the thickness direction, but the layers are still partially connected. From the scanning image, the degree of expansion is similar to that of concentrated acid, indicating that the heating process ensures the intercalation effect.

[0030] Example 3 An expandable graphite with zero waste acid emission and its preparation method, comprising the following steps: Take 10g of the recovered acid from Example 2, add 10g of 98% concentrated sulfuric acid to obtain 20g of a compound acid with a concentration of approximately 92%. Add 6g of 80-mesh graphite raw material, stir evenly, transfer the beaker to a 50℃ water bath and let it stand for 60 min. Then transfer the beaker to room temperature and stir, slowly add 0.8g of hydrogen peroxide, mechanically stir (200r / min), and perform an oxidation intercalation reaction for 60 min. Filter and recover the filtrate to a recovery tank. Wash the product with deionized water until neutral, and dry at 45℃ for 12 h to obtain expanded graphite. Take 0.5g of expandable graphite and expand it at a high temperature of 950℃ in a muffle furnace for 7 s to obtain expanded graphite. Measure its volume using the 200 mL beaker method and calculate the expansion ratio to be 210 mL / g.

[0031] Example 4 Unlike Example 2, the water bath temperature was 60 °C, but the other preparation steps were the same as in Example 2. The final expansion ratio of the obtained expanded graphite was 200 mL / g.

[0032] Example 5 Unlike Example 2, the amount of graphite added was 4 g, while the other preparation steps were the same as in Example 2. The final expansion ratio of the obtained expanded graphite was 230 mL / g.

[0033] Example 6 Unlike Example 2, the graphite raw material used in this example had a mesh size of 50, while the other preparation steps were the same as in Example 2. The final expansion ratio of the obtained expanded graphite was 200 mL / g.

[0034] Example 7 Add 6 g of 80-mesh graphite raw material and 20 g of sulfuric acid (concentration approximately 92%) recovered in Example 1 to a beaker. After stirring evenly, slowly add 0.8 g of hydrogen peroxide and mechanically stir at 200 r / min for 60 min of oxidative intercalation. Then, transfer the beaker to a 50 ℃ water bath and let it stand for 60 min. Subsequently, filter the mixture and recover the filtrate to a recovery tank. Wash the product with deionized water until neutral and dry it at 45 ℃ for 12 h to obtain expanded graphite. Take 0.5 g of expandable graphite and expand it at a high temperature of 950 ℃ in a muffle furnace for 7 s to obtain expanded graphite. Measure its volume using the 200 mL beaker method and calculate the expansion ratio as 215 mL / g.

[0035] Comparative Example 1 Unlike Example 2, the water bath temperature was 40 °C, but the other preparation steps were the same as in Example 2. The final expansion ratio of the obtained expanded graphite was 133 mL / g.

[0036] Comparative Example 2 Unlike Example 2, the water bath temperature was 70 °C, but the other preparation steps were the same as in Example 2. The final expansion ratio of the obtained expanded graphite was 188 mL / g.

[0037] Comparative Example 3 Unlike Example 2, the water bath temperature was 80 °C, but the other preparation steps were the same as in Example 2. The final expansion ratio of the obtained expanded graphite was 176 mL / g.

[0038] Comparative Example 4 Unlike Example 2, the water bath temperature was 90 °C, but the other preparation steps were the same as in Example 2. The final expansion ratio of the obtained expanded graphite was 166 mL / g.

[0039] Comparative Example 5 Unlike Example 2, the amount of hydrogen peroxide added was 0.64 g, while the other preparation steps were the same as in Example 2. The final expansion ratio of the obtained expanded graphite was 166 mL / g.

[0040] Comparative Example 6 Unlike Example 2, the amount of hydrogen peroxide added was 0.96 g, while the other preparation steps were the same as in Example 2. The final expansion ratio of the obtained expanded graphite was 177 mL / g.

[0041] Comparative Example 7 Unlike Example 2, the oxidation intercalation time was 60 min, while the other preparation steps were the same as in Example 2. The final expansion ratio of the obtained expanded graphite was 166 mL / g.

[0042] Comparative Example 8 Unlike Example 2, the oxidation intercalation time was 180 min, while the other preparation steps were the same as in Example 2. The final expansion ratio of the obtained expanded graphite was 188 mL / g.

[0043] Comparative Example 9 Unlike Example 2, the amount of graphite added was 8 g, while the other preparation steps were the same as in Example 2. The final expansion ratio of the obtained expanded graphite was 175 mL / g.

[0044] Figure 3 This is a SEM image of the expanded graphite prepared in Example 6 of the present invention. Figure 3 It is known that the expanded graphite is also a loose and porous worm-like carbon material, but the 50-mesh sheet has a larger particle size. Each "worm" is a graphite sheet that forms a highly porous network structure that expands dramatically along the thickness direction, but the sheets are still partially connected.

[0045] Figure 4 The images show the XRD patterns of expanded graphite prepared in Examples 1, 2, and 6 of this invention. Figure 4 It can be seen that the expanded graphite has obvious (002) carbon diffraction peaks, indicating that the expansion treatment did not destroy its basic graphite crystal phase and layered framework.

[0046] The results from the above embodiments show that the process of preparing expandable graphite using the method of the present invention can prepare high-expansion graphite (expansion ratio ≥ 200 mL / g) using recycled sulfuric acid without adding other metal ion oxidants. It has the advantages of low sulfuric acid consumption, low production cost, high expansion ratio, and low environmental pollution. The highest expansion ratio can reach 230 mL / g. Moreover, the reaction device is simple, low-cost, pollution-free, easy to operate, and can be used for large-scale production.

[0047] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing expandable graphite with no waste acid emissions, characterized in that, Includes the following steps: The graphite raw material was pretreated by mixing it with recycled sulfuric acid. Then hydrogen peroxide was added to the mixture, and an oxidation intercalation reaction was carried out at room temperature to obtain the reaction product. The reaction products are subjected to solid-liquid separation to obtain filtrate and solid product; the filtrate is used as recovered sulfuric acid in the pretreatment process. The solid product is sequentially washed, dried, and subjected to high-temperature expansion treatment to obtain expandable graphite.

2. The method for preparing expandable graphite with no waste acid emission according to claim 1, characterized in that, The mass ratio of the recovered sulfuric acid to the graphite raw material is (2-4):1, and the mass fraction of the recovered sulfuric acid is 84%-92%.

3. The method for preparing expandable graphite with no waste acid emission according to claim 1, characterized in that, The pretreatment temperature is 45-60 ℃ and the time is 30-60 min.

4. The method for preparing expandable graphite with no waste acid emission according to claim 1, characterized in that, The amount of hydrogen peroxide added is 8%-15% of the mass of the graphite raw material; The graphite raw material is natural flocculent graphite.

5. The method for preparing expandable graphite with no waste acid emission according to claim 1, characterized in that, The oxidation intercalation reaction takes 60-120 minutes.

6. The method for preparing expandable graphite with no waste acid emission according to claim 1, characterized in that, The drying temperature is 40-50 ℃, and the drying time is 10-15 h; The high-temperature expansion treatment is performed at a temperature of 900-1000 ℃ for a time of 5-10 s.

7. The method for preparing expandable graphite with no waste acid emission according to claim 1, characterized in that, When the mass fraction of the recovered sulfuric acid is less than 90%, before mixing the graphite raw material and the recovered sulfuric acid, the recovered sulfuric acid is also mixed with concentrated acid with a mass fraction of 98%, so that the mass fraction of the recovered sulfuric acid after mixing is 90%-94%.

8. The method for preparing expandable graphite with no waste acid emission according to claim 1, characterized in that, The graphite raw material has a mesh size of 50-80 mesh; The expandable graphite has an expansion ratio of 200-230 mL / g.

9. Expandable graphite prepared by the method of any one of claims 1-8, which produces expandable graphite without waste acid emissions.

10. The application of the expandable graphite of claim 9 in the adsorption, sealing, flame retardant and shielding materials for environmental pollution.

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