Method for preparing and recycling expanded graphite from graphite and prepared expanded graphite

Abstract

The invention provides a method for preparing and recycling expanded graphite from graphite and the prepared expanded graphite, and belongs to the technical field of expanded graphite. The preparation method comprises the following steps: performing electrochemical intercalation swelling reaction on graphite to obtain expandable graphite; the preparation method comprises the following steps: preparing an electrochemical intercalation swelling reaction, then carrying out expansion treatment on the expandable graphite to obtain the expanded graphite, an electrolyte for the electrochemical intercalation swelling reaction comprises a carbonate solution of perchlorate and water, the mass ratio of the graphite to the electrolyte is 1: (10-20), the electrochemical intercalation swelling reaction is a direct current constant voltage reaction, and the direct current constant voltage is 5-30V. The expanded graphite is prepared by adopting an electrochemical method, the mixed solution of water, perchlorate and carbonate is used as the electrolyte, the dosage of the used oxidant is very small, the electrolyte is non-toxic and harmless and can be recycled, and the electrochemical intercalation swelling reaction can be carried out at normal temperature and normal pressure; and the intercalator of the prepared expanded graphite is uniformly distributed among layers, and the volume can be up to 150mL / g.

Description

Technical Field

[0001] The invention relates to the technical field of expanded graphite, and in particular to a method for preparing expanded graphite from graphite and recycling the expanded graphite prepared therefrom. Background Art

[0002] Graphite is a crystalline material with a layered structure. Atoms, ions, and molecules are inserted between the layers of graphite to form graphite intercalation compounds. Some of these graphite intercalation compounds (expandable graphite) can expand rapidly under high temperature or microwave irradiation to form expanded graphite, which is worm-like after expansion. Expanded graphite is widely used in sealing materials, adsorption materials, dielectric materials, energy storage materials, catalyst carriers, etc., and has great market application prospects.

[0003] The traditional process for preparing expanded graphite requires the use of a large amount of strong acids such as concentrated sulfuric acid, concentrated nitric acid, concentrated perchloric acid, and strong oxidants such as potassium permanganate, potassium dichromate, potassium ferrate, etc., and sometimes phosphoric acid or perchloric acid is also used; or direct current electrochemical intercalation is performed in a sulfuric acid solution to prepare intercalated graphite or pre-oxidized graphite. These intercalation or pre-oxidation methods consume a large amount of strong oxidizing and corrosive chemicals and discharge a large amount of waste acid and strong oxidants. For example, the chemical oxidation method uses sulfuric acid as an intercalation agent, and there will be sulfur residue in the product. Sulfur is corrosive, which affects its application in the sealing field. Whether it is expanded by microwave or high-temperature furnace, during the expansion process, the exhaust gas contains difficult-to-handle nitrogen oxides and heavy metal oxides, which produces a lot of smoke and pollutes the environment. With the environmental protection requirements and regulations, the oxidation method using concentrated sulfuric acid in the existing technology cannot pass the requirements of the environmental protection department, and many places that produce or use graphite (worm graphite) are forced to close.

[0004] On the other hand, a large amount of waste graphite will be generated during the production, processing and use of graphite. Various graphite products have a certain service life, and eventually they are scrapped due to performance degradation, mechanical fatigue or overall wear and tear, resulting in a large amount of waste graphite. These waste materials pollute the environment and waste resources. For example: graphite sealing rings have a wide range of irreplaceable applications in engines and high-temperature seals, and are mainly made of graphite materials. It has the advantages of high temperature resistance, corrosion resistance and wear resistance, and is widely used in chemical, petroleum, metallurgy, electricity, aviation, aerospace and other industries. However, graphite materials are usually made of natural flake graphite as the source material, which is obtained through expansion and processing, but it is rare to recycle retired graphite sealing materials, and there is a lack of means for re-expansion. At present, the recycling of waste graphite has made certain progress, but the technology is still in the laboratory stage, the operation is complicated, and industrial production cannot be achieved. Therefore, it is of great significance to study a method for preparing expanded graphite and recycling graphite and the prepared expanded graphite to realize the reuse of waste graphite. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing expanded graphite from graphite and recycling the expanded graphite prepared thereby, so as to solve the problem in the prior art that waste graphite cannot be recycled.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing expanded graphite from graphite and recycling the same, comprising the following steps:

[0008] (1) subjecting graphite to an electrochemical intercalation swelling reaction to obtain expandable graphite;

[0009] (2) expanding the expandable graphite to obtain expanded graphite;

[0010] The electrolyte for the electrochemical intercalation swelling reaction comprises a carbonate solution of perchlorate and water;

[0011] The mass ratio of graphite to electrolyte is 1:10-20;

[0012] The electrochemical intercalation swelling reaction is a direct current constant voltage reaction, wherein the direct current constant voltage is 5 to 30V.

[0013] Preferably, in step (1), the graphite comprises one or more of waste graphite, natural graphite and artificial graphite, wherein the waste graphite comprises one or more of waste graphite battery materials, waste graphite refractory materials, waste graphite electrode materials, waste graphite sealing materials, waste graphite equipment, waste graphite containers and waste graphite blocks.

[0014] Preferably, the perchlorate is one or more of sodium perchlorate, lithium perchlorate, potassium perchlorate, ammonium perchlorate, calcium perchlorate, magnesium perchlorate and silver perchlorate; and the concentration of the perchlorate in the carbonate solution of the perchlorate is 0.001 to 100 g / L.

[0015] Preferably, the amount of water added is 0.1 to 10 wt.% of the electrolyte mass.

[0016] Preferably, the carbonate comprises one or more of dimethyl carbonate, diethyl carbonate, diphenyl carbonate, propylene carbonate, ethylene carbonate and ethyl methyl carbonate.

[0017] Preferably, in step (1), the anode of the electrochemical intercalation swelling reaction is a composite anode, wherein the composite anode is formed by pressing graphite powder and shaped graphite; the shaped graphite comprises a graphite plate, a graphite strip, a graphite paper or a graphite rod; and the cathode of the electrochemical intercalation swelling reaction comprises a graphite plate, a graphite strip, a graphite paper or a graphite rod.

[0018] Preferably, the cathode of the electrochemical intercalation swelling reaction adopts a double cathode mode, wherein the double cathodes are respectively placed on both sides of the anode, and the distance between the anode and each cathode is independently 0.5 to 3 cm.

[0019] Preferably, the electrochemical intercalation swelling reaction time is 0.5 to 60 hours.

[0020] Preferably, in step (2), the puffing treatment temperature is 250 to 1000° C., and the puffing treatment time is 0.1 to 10 min.

[0021] The present invention provides expanded graphite obtained by the above-mentioned method for preparing expanded graphite and recycling graphite, wherein the volume of the expanded graphite is 80-150 mL / g.

[0022] Beneficial effects of the present invention:

[0023] (1) The present invention adopts an electrochemical method to prepare expanded graphite, operates at room temperature and pressure, has a simple device, and the electrolyte can be recycled. The present invention uses intermittent renewable electricity to achieve electrochemical intercalation swelling of waste graphite. The electrolyte is non-toxic and harmless, and no waste liquid is generated, thereby avoiding the generation of hazardous waste from the source and fundamentally eliminating environmental hazards. In the process of preparing expanded graphite by the electrochemical method, the amount of oxidant required is very small, and after the electrochemical intercalation swelling reaction, the intercalant is evenly distributed between the graphite layers, so that the expandability of the product tends to be stable.

[0024] (2) The present invention uses a mixed solution of water, perchlorate and carbonate as an electrolyte. The free radicals generated by the electrolytic aqueous solution oxidize the edges of the graphite sheets, and the voltage drives the solvated perchlorate ions to intercalate and swell the graphite. High-temperature heating causes the solvated ions to instantly decompose and produce a large amount of gas, increasing the distance between graphite layers to obtain expanded graphite. The solid product of electrolytic decomposition in the present invention is mainly chloride, which is easy to remove by washing with water. Therefore, the electrolyte in the present invention can be recycled and does not contain strong oxidants such as heavy metals. During the preparation process, no pollutants such as sulfur dioxide and nitrogen oxides are generated. The generated carbon dioxide and oxygen are less harmful to the human body, and the operation is safe, which fundamentally eliminates the harm to the environment.

[0025] (3) The expanded graphite product prepared by the present invention does not contain sulfur, which improves the corrosion resistance of the expanded graphite. In addition, during the high-temperature expansion process of the sulfur-free expandable graphite, no smoke or irritating gas escapes, and the expanded volume of the prepared expanded graphite can reach 80 to 150 mL / g, which has broad application prospects.

[0026] (4) The tail gas generated during the expansion process of the expandable graphite in the present invention is recycled and treated in an environmentally friendly manner, thereby reducing the emission of greenhouse gases and achieving the recycling of resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A scanning electron microscope image of the waste graphite used in Example 1;

[0028] Figure 2 This is a scanning electron microscope image of the expanded graphite obtained in Example 1. DETAILED DESCRIPTION

[0029] The present invention provides a method for preparing expanded graphite from graphite and recycling the same, comprising the following steps:

[0030] (1) subjecting graphite to an electrochemical intercalation swelling reaction to obtain expandable graphite;

[0031] (2) expanding the expandable graphite to obtain expanded graphite;

[0032] The electrolyte for the electrochemical intercalation swelling reaction comprises a carbonate solution of perchlorate and water;

[0033] The mass ratio of graphite to electrolyte is 1:10-20;

[0034] The electrochemical intercalation swelling reaction is a direct current constant voltage reaction, wherein the direct current constant voltage is 5 to 30V.

[0035] In the present invention, the DC constant voltage is preferably 5V, 6V, 7V, 9V, 11V, 13V, 15V, 20V, 21V, 24V, 30V, and more preferably 9V, 11V, 15V, 30V.

[0036] In the present invention, the mass ratio of the graphite to the electrolyte is preferably 1:12-18, and more preferably 1:14-16.

[0037] In the present invention, in step (1), the graphite comprises one or more of waste graphite, natural graphite and artificial graphite, preferably waste graphite and / or natural graphite, and more preferably waste graphite.

[0038] In the present invention, the waste graphite comprises one or more of waste graphite battery materials, waste graphite refractory materials, waste graphite electrode materials, waste graphite sealing materials, waste graphite equipment, waste graphite containers and waste graphite blocks, preferably one or more of waste graphite electrode materials, waste graphite sealing materials and waste graphite blocks, and further preferably waste graphite electrodes and / or waste graphite sealing materials.

[0039] In the present invention, when waste graphite is used to prepare expandable graphite, the waste graphite needs to be crushed and pre-treated to obtain graphite powder, and then the composite anode is prepared.

[0040] In the present invention, the natural graphite is natural flake graphite.

[0041] In the present invention, the carbon content of the natural graphite and artificial graphite is 60-99.9%, preferably 60%, 80%, 85%, 94%, 99.9%, and more preferably 85%, 94%, 99.9%.

[0042] In the present invention, the particle size of the natural graphite and the artificial graphite is 20 to 150 meshes, preferably 40 to 120 meshes, and more preferably 50 to 100 meshes.

[0043] In the present invention, the perchlorate is one or more of sodium perchlorate, lithium perchlorate, potassium perchlorate, ammonium perchlorate, calcium perchlorate, magnesium perchlorate and silver perchlorate, preferably one or more of sodium perchlorate, lithium perchlorate and potassium perchlorate, and more preferably sodium perchlorate and / or lithium perchlorate; the concentration of the perchlorate in the carbonate solution of the perchlorate is 0.001 to 100 g / L, preferably 1 to 70 g / L, and more preferably 5 to 50 g / L.

[0044] In the present invention, the amount of water added is 0.1 to 10 wt.%, preferably 1 to 7.5 wt.%, and more preferably 3.7 to 5 wt.% of the mass of the electrolyte.

[0045] In the present invention, the carbonate comprises one or more of dimethyl carbonate, diethyl carbonate, diphenyl carbonate, propylene carbonate, ethylene carbonate and ethyl methyl carbonate, preferably a mixture of dimethyl carbonate and ethylene carbonate, a mixture of propylene carbonate and dimethyl carbonate, a mixture of propylene carbonate and diethyl carbonate, a mixture of propylene carbonate, diphenyl carbonate and ethyl methyl carbonate, a mixture of propylene carbonate and diphenyl carbonate, a mixture of propylene carbonate and ethyl methyl carbonate, a mixture of propylene carbonate, ethyl methyl carbonate, diethyl carbonate and dimethyl carbonate, further preferably a mixture of propylene carbonate and dimethyl carbonate, a mixture of propylene carbonate and diethyl carbonate, or a mixture of propylene carbonate, diphenyl carbonate and ethyl methyl carbonate.

[0046] In the present invention, in the step (1), the anode of the electrochemical intercalation swelling reaction is a composite anode, wherein the composite anode is formed by pressing graphite powder and shaped graphite; the shaped graphite comprises a graphite plate, a graphite strip, a graphite paper or a graphite rod, preferably a graphite rod or a graphite strip; the cathode of the electrochemical intercalation swelling reaction comprises a graphite plate, a graphite strip, a graphite paper or a graphite rod, preferably a graphite rod or a graphite strip, and more preferably a graphite rod.

[0047] In the present invention, the cathode of the electrochemical intercalation swelling reaction adopts a dual cathode mode, wherein the dual cathodes are respectively placed on both sides of the anode, and the distance between the anode and each cathode is independently 0.5 to 3 cm, preferably 1 to 2.5 cm, and further preferably 1 cm, 1.5 cm, 2 cm, 2.5 cm.

[0048] In the present invention, the time of the electrochemical intercalation swelling reaction is 0.5 to 60 h, preferably 40 min, 2 h, 15 h, 22 h, 37 h, 45 h, 48 h, 50 h, 55 h, 60 h, and more preferably 40 min, 2 h, 15 h, 22 h, 55 h.

[0049] In the present invention, the solid product generated during the electrochemical intercalation swelling reaction is chloride, which can be easily removed by hydrolysis.

[0050] In the present invention, in the step (2), the temperature of the puffing treatment is 250-1000°C, preferably 300-900°C, and more preferably 550°C, 650°C, 750°C, 850°C, and 900°C; the time of the puffing treatment is 0.1-10 min, preferably 10s, 30s, 50s, 1min, 1.5min, 2min, and 3min, and more preferably 10s, 1min, and 2min.

[0051] In the present invention, the tail gas generated when the expandable graphite is expanded is mainly composed of carbon dioxide and oxygen, and no nitrogen oxides are detected. Therefore, the tail gas is treated by adsorbing with an adsorbent, and the adsorbent includes one or more of a calcium-based adsorbent, an organic liquid amine, ammonia water, an inorganic base, and a solid amine adsorbent, preferably one or more of a calcium-based adsorbent, ammonia water, and an inorganic base, and more preferably a calcium-based adsorbent and / or an organic base. The present invention does not specifically limit the specific model of the calcium-based adsorbent, and any calcium-based adsorbent that can adsorb tail gas known in the art can be used.

[0052] The inorganic base used in the present invention comprises one or more of sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, lithium hydroxide aqueous solution, and magnesium hydroxide aqueous solution, preferably one or more of sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, and lithium hydroxide aqueous solution, and more preferably sodium hydroxide aqueous solution and / or potassium hydroxide aqueous solution.

[0053] The present invention provides expanded graphite prepared by the method for preparing expanded graphite from graphite and recycling the graphite, wherein the volume of the expanded graphite is 20 to 150 mL / g, preferably 70 mL / g, 80 mL / g, 85 mL / g, 95 mL / g, 100 mL / g, 105 mL / g, 120 mL / g, 150 mL / g, and further preferably 95 mL / g, 100 mL / g, 105 mL / g, 120 mL / g, 150 mL / g.

[0054] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0055] Example 1

[0056] Sodium perchlorate, dimethyl carbonate and ethylene carbonate are mixed to obtain a sodium perchlorate carbonate solution, wherein the volume ratio of dimethyl carbonate to ethylene carbonate is 5:1, and the concentration of sodium perchlorate in the sodium perchlorate carbonate solution is 100 g / L, and then 0.1 wt.% of water is added to obtain an electrolyte.

[0057] The waste graphite battery material is crushed and pretreated into graphite powder (particle size is 80 mesh), 100g of graphite powder is weighed, and then the graphite powder and graphite plate are pressed into strip composite electrodes, wherein the mass ratio of graphite powder to graphite plate is 10:1, the length of the graphite plate is 21 cm, the width is 12 cm, and the thickness is 5 mm. It is packed in a PP bag and put into an electrolyte (where the mass ratio of graphite powder to electrolyte is 1:15), and then two graphite plate cathodes (the size of the cathode graphite plate is the same as that of the anode) are placed on both sides of the anode, and the distance between each cathode and the anode is 0.5 cm. Constant voltage electrolysis is carried out for 60 hours under the condition of an electrolysis voltage of 5V to obtain expandable graphite.

[0058] Finally, the expandable graphite is expanded at 650°C for 3 minutes, then washed with deionized water and anhydrous ethanol until the pH value of the filtrate is 6, and finally filtered and dried at 80°C to obtain expanded graphite with a volume of 80 mL / g. The tail gas generated during the expansion process can be absorbed by a calcium-based absorbent.

[0059] Figure 1 This is an electron microscope image of the waste graphite used in Example 1. Figure 2 The electron microscope image of the expanded graphite obtained in Example 1 is shown in FIG. Figure 1 and Figure 2 It can be seen that the waste graphite raw materials are in the form of flakes, with a small amount of shorter graphite worms; the prepared expanded graphite worms are mostly over 1000 microns in length and are accordion-shaped.

[0060] Example 2

[0061] Lithium perchlorate, propylene carbonate and dimethyl carbonate are mixed to obtain a lithium perchlorate carbonate solution, wherein the volume ratio of propylene carbonate to dimethyl carbonate is 4:1, and the concentration of lithium perchlorate in the lithium perchlorate carbonate solution is 75 g / L, and then 10 wt.% of water is added to obtain an electrolyte.

[0062] The waste graphite refractory material is crushed and pretreated into graphite powder (particle size is 70 mesh), 100 grams of graphite powder is weighed, and then the graphite powder and graphite paper are pressed into a block composite electrode, wherein the mass ratio of graphite powder to graphite paper is 20:1, and the graphite paper is 21 cm long, 10 cm wide and 2 mm thick. It is packed in a PE bag and put into an electrolyte (wherein the mass ratio of graphite powder to electrolyte is 1:20), and then two graphite paper cathodes (the size of the cathode graphite paper is the same as that of the anode) are placed on both sides of the anode, and the distance between each cathode and the anode is 1.5 cm. Constant voltage electrolysis is carried out for 45 hours under the condition of an electrolysis voltage of 15 V to obtain expandable graphite.

[0063] Finally, the expandable graphite is expanded at 750°C for 1 min, then washed with deionized water and ethanol until the pH value of the filtrate is 6, and finally filtered and dried at 80°C to obtain expanded graphite with a volume of 100 mL / g. The tail gas generated during the expansion process can be absorbed by diethanolamine.

[0064] Example 3

[0065] Lithium perchlorate, propylene carbonate and diethyl carbonate are mixed to obtain a lithium perchlorate carbonate solution, wherein the volume ratio of propylene carbonate to diethyl carbonate is 3:1, and the concentration of lithium perchlorate in the lithium perchlorate carbonate solution is 50 g / L, and then 5 wt.% of water is added to obtain an electrolyte.

[0066] The waste graphite electrode material was crushed and pretreated into graphite powder (particle size of 90 mesh), 100 grams of graphite powder was weighed, and then the graphite powder and graphite rod were pressed into a rod-shaped composite electrode, wherein the mass ratio of graphite powder to graphite rod was 15:1, the length of the graphite rod was 15 cm, and the diameter was 1 cm. It was packed in a PE bag and put into an electrolyte (where the mass ratio of graphite powder to electrolyte was 1:10), and then two graphite rod cathodes (the size of the cathode graphite rod was the same as that of the anode) were placed on both sides of the anode, and the distance between each cathode and anode was 2.5 cm. Constant voltage electrolysis was carried out for 40 minutes under the condition of an electrolysis voltage of 30 V to obtain expandable graphite.

[0067] Finally, the expandable graphite is expanded at 900°C for 10s, then washed with deionized water and ethanol until the pH value of the filtrate is 7, and finally filtered and dried at 80°C to obtain expanded graphite with a volume of 150mL / g. The tail gas generated during the expansion process can be absorbed by ammonia water with a concentration of 25wt%.

[0068] Example 4

[0069] Lithium perchlorate, propylene carbonate, diphenyl carbonate and ethyl methyl carbonate are mixed to obtain a carbonate solution of lithium perchlorate, wherein the volume ratio of propylene carbonate, diphenyl carbonate and ethyl methyl carbonate is 1:1:1, and the concentration of lithium perchlorate in the carbonate solution of lithium perchlorate is 1 g / L, and then 7.5 wt.% of water is added to obtain an electrolyte.

[0070] The waste graphite sealing material was crushed and pretreated into graphite powder (particle size of 100 mesh), 100 grams of graphite powder was weighed, and then the graphite powder and graphite strips were pressed into a porous composite electrode, wherein the mass ratio of graphite powder to graphite strip was 5:1, and the graphite strip was 18 cm long, 15 cm wide and 3 mm thick. It was packed in a PP bag and put into an electrolyte (where the mass ratio of graphite powder to electrolyte was 1:13), and then two graphite strip cathodes (the size of the cathode graphite strip was the same as that of the anode) were placed on both sides of the anode, with a distance of 2.5 cm between each cathode and anode, and constant voltage electrolysis was performed for 22 hours at an electrolysis voltage of 20 V to obtain expandable graphite.

[0071] Finally, the expandable graphite is expanded at 850°C for 2 minutes, then washed with deionized water and ethanol until the pH value of the filtrate is 7, and finally filtered and dried at 80°C to obtain expanded graphite with a volume of 120 mL / g. The tail gas generated during the expansion process can be absorbed by a calcium-based absorbent.

[0072] Example 5

[0073] Lithium perchlorate, propylene carbonate and diphenyl carbonate are mixed to obtain a lithium perchlorate carbonate solution, wherein the volume ratio of propylene carbonate to diphenyl carbonate is 1:2, and the concentration of lithium perchlorate in the lithium perchlorate carbonate solution is 27 g / L, and then 3 wt.% of water is added to obtain an electrolyte.

[0074] The waste graphite equipment was crushed and pretreated into graphite powder (particle size of 85 mesh), 100 grams of graphite powder was weighed, and then the graphite powder and graphite strips were pressed into a porous composite electrode, wherein the mass ratio of graphite powder to graphite strip was 8:1, and the graphite strip was 30 cm long, 10 cm wide and 5 mm thick. It was packed in a PP bag and put into an electrolyte (where the mass ratio of graphite powder to electrolyte was 1:17), and then two graphite strip cathodes (the size of the cathode graphite strip was the same as that of the anode) were placed on both sides of the anode, with a distance of 1.0 cm between each cathode and anode, and constant voltage electrolysis was performed for 50 hours under an electrolysis voltage of 13 V to obtain expandable graphite.

[0075] Finally, the expandable graphite is expanded at 700°C for 2 minutes, then washed with deionized water and ethanol until the pH value of the filtrate is 7, and finally filtered and dried at 80°C to obtain expanded graphite with a volume of 90 mL / g. The tail gas generated during the expansion process can be absorbed by a potassium hydroxide aqueous solution (concentration of 0.5 mol / L).

[0076] Example 6

[0077] Lithium perchlorate, propylene carbonate and ethyl methyl carbonate are mixed to obtain a carbonate solution of lithium perchlorate, wherein the volume ratio of propylene carbonate to ethyl methyl carbonate is 1:1, and the concentration of lithium perchlorate in the carbonate solution of lithium perchlorate is 13 g / L, and then 4.7 wt.% of water is added to obtain an electrolyte.

[0078] The waste graphite container was crushed and pretreated into graphite powder (particle size of 75 mesh), 100 grams of graphite powder was weighed, and then the graphite powder and graphite strips were pressed into a sheet-like composite electrode, wherein the mass ratio of graphite powder to graphite strip was 5:1, and the graphite strip was 25 cm long, 15 cm wide and 1 cm thick. It was packed in a PE bag and put into an electrolyte (where the mass ratio of graphite powder to electrolyte was 1:15), and then two graphite strip cathodes (the size of the cathode graphite strip was the same as that of the anode) were placed on both sides of the anode, with a distance of 1.0 cm between each cathode and anode, and constant voltage electrolysis was performed for 37 hours under an electrolysis voltage of 24 V to obtain expandable graphite.

[0079] Finally, the expandable graphite is expanded at 450°C for 1.5 min, then washed with deionized water and ethanol until the pH value of the filtrate is 7, and finally filtered and dried at 80°C to obtain expanded graphite with a volume of 95 mL / g. The tail gas generated during the expansion process can be absorbed by a sodium hydroxide aqueous solution (concentration of 0.5 mol / L).

[0080] Example 7

[0081] Lithium perchlorate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate and dimethyl carbonate are mixed to obtain a carbonate solution of lithium perchlorate, wherein the volume ratio of propylene carbonate, ethyl methyl carbonate, diethyl carbonate and dimethyl carbonate is 1:2:4:7, and the concentration of lithium perchlorate in the carbonate solution of lithium perchlorate is 5 g / L, and then 1.7 wt.% of water is added to obtain an electrolyte.

[0082] The waste graphite blocks were crushed and pretreated into graphite powder (particle size of 60 mesh), 100 grams of graphite powder were weighed, and then the graphite powder and graphite strips were pressed into sheet-like composite electrodes, wherein the mass ratio of graphite powder to graphite strip was 10:1, and the graphite strips were 20 cm long, 10 cm wide and 5 mm thick. They were packed in PE bags and placed in electrolyte (where the mass ratio of graphite powder to electrolyte was 1:14), and then two graphite strip cathodes (the size of the cathode graphite strips was the same as that of the anode) were placed on both sides of the anode, with a distance of 1.5 cm between each cathode and anode, and constant voltage electrolysis was performed for 2 h at an electrolysis voltage of 11 V to obtain expandable graphite.

[0083] Finally, the expandable graphite is expanded at 750°C for 1.5 min, then washed with deionized water and ethanol until the pH value of the filtrate is 7, and finally filtered and dried at 80°C to obtain expanded graphite with a volume of 105 mL / g. The tail gas generated during the expansion process can be absorbed by tetraethylene pentamine.

[0084] Example 8

[0085] Lithium perchlorate and propylene carbonate are mixed to obtain a lithium perchlorate carbonate solution, wherein the concentration of lithium perchlorate in the lithium perchlorate carbonate solution is 5 g / L, and then 6 wt.% of water is added to obtain an electrolyte.

[0086] Natural flake graphite powder and graphite strips with a particle size of 50 mesh and a carbon content of 99.9% are pressed into strip-shaped composite electrodes. 100 grams of graphite powder are weighed, wherein the mass ratio of graphite powder to graphite strip is 15:1, and the graphite strip is 23 cm long, 7 cm wide and 2 mm thick. It is packed in a PE bag and placed in an electrolyte (where the mass ratio of graphite powder to electrolyte is 1:16). Then, two graphite strips (the size of the cathode graphite strip is the same as that of the anode) are placed on both sides of the anode, and the distance between each cathode and the anode is 1.0 cm. Constant voltage electrolysis is performed for 15 hours under the condition of an electrolysis voltage of 21 V to obtain expandable graphite.

[0087] Finally, the expandable graphite is expanded at 850°C for 1.5 min, then washed with deionized water and ethanol until the pH value of the filtrate is 7, and finally filtered and dried at 80°C to obtain expanded graphite with a volume of 95 mL / g. The tail gas generated during the expansion process can be absorbed by ammonia water with a concentration of 25wt%.

[0088] Example 9

[0089] Lithium perchlorate and dimethyl carbonate are mixed to obtain a lithium perchlorate carbonate solution, wherein the concentration of lithium perchlorate in the lithium perchlorate carbonate solution is 80 g / L, and then 1 wt.% of water is added to obtain an electrolyte.

[0090] Artificial graphite powder and graphite strips with a particle size of 80 mesh and a carbon content of 94% are pressed into a sheet-like composite electrode. 100 grams of graphite powder are weighed, wherein the mass ratio of graphite powder to graphite strip is 10:1, and the graphite strip is 20 cm long, 8 cm wide and 5 mm thick. The powder is placed in a PE bag and put into an electrolyte (where the mass ratio of graphite powder to electrolyte is 1:15). Two graphite strip cathodes (the size of the cathode graphite strip is the same as that of the anode) are placed on both sides of the anode, and the distance between each cathode and the anode is 1 cm. Constant voltage electrolysis is performed for 50 hours under an electrolysis voltage of 21 V to obtain expandable graphite.

[0091] Finally, the expandable graphite is expanded at 750°C for 1.5 min, then washed with deionized water and ethanol until the pH value of the filtrate is 7, and finally filtered and dried at 80°C to obtain expanded graphite with a volume of 85 mL / g. The tail gas generated during the expansion process can be absorbed by a lithium hydroxide solution.

[0092] Example 10

[0093] Lithium perchlorate and dimethyl carbonate are mixed to obtain a lithium perchlorate carbonate solution, wherein the concentration of lithium perchlorate in the lithium perchlorate carbonate solution is 80 g / L, and then 0.5 wt.% of water is added to obtain an electrolyte.

[0094] Natural flake graphite powder with a particle size of 40 mesh and a carbon content of 85% and a graphite plate are pressed into a strip composite electrode. 100 grams of graphite powder are weighed, wherein the mass ratio of graphite powder to graphite plate is 10:1, and the graphite plate is 23 cm long, 12 cm wide and 5 mm thick. It is packed in a PE bag and put into an electrolyte (where the mass ratio of graphite powder to electrolyte is 1:13). Two graphite plate cathodes (the size of the cathode graphite plate is the same as that of the anode) are placed on both sides of the anode, and the distance between each cathode and the anode is 1 cm. Constant voltage electrolysis is carried out for 40 minutes under the condition of an electrolysis voltage of 30 V to obtain expandable graphite.

[0095] Finally, the expandable graphite is expanded at 450°C for 1.5 min, then washed with deionized water and ethanol until the pH value of the filtrate is 7, and finally filtered and dried at 80°C to obtain expanded graphite with a volume of 80 mL / g. The tail gas generated during the expansion process can be absorbed by a calcium-based absorbent.

[0096] Embodiment 11

[0097] Lithium perchlorate and propylene carbonate are mixed to obtain a lithium perchlorate carbonate solution, wherein the concentration of lithium perchlorate in the lithium perchlorate carbonate solution is 70 g / L, and then 3.7 wt.% of water is added to obtain an electrolyte.

[0098] Artificial graphite powder and graphite strips with a particle size of 40 mesh and a carbon content of 99.9% are pressed into a sheet-like composite electrode. 100 grams of graphite powder are weighed, wherein the mass ratio of graphite powder to graphite strip is 10:1, and the graphite strip is 23 cm long, 10 cm wide and 5 mm thick. It is packed in a PE bag and placed in an electrolyte (where the mass ratio of graphite powder to electrolyte is 1:12). Two graphite strip cathodes (the size of the cathode graphite strip is the same as that of the anode) are placed on both sides of the anode, and the distance between each cathode and the anode is 1.5 cm. Constant voltage electrolysis is performed for 55 hours under the condition of an electrolysis voltage of 9 V to obtain expandable graphite.

[0099] Finally, the expandable graphite is expanded at 550°C for 1 min, then washed with deionized water and ethanol until the pH value of the filtrate is 7, and finally filtered and dried at 80°C to obtain expanded graphite with a volume of 105 mL / g. The tail gas generated during the expansion process can be absorbed by a sodium hydroxide solution (concentration of 0.5 mol / L).

[0100] from Figure 1 and Figure 2 It can be seen that the waste graphite raw materials are in the form of flakes, with a small amount of shorter graphite worms; the prepared expanded graphite worms are mostly over 1000 microns in length and are accordion-shaped.

[0101] As can be seen from the above embodiments, the present invention provides a method for preparing expanded graphite and recycling graphite and the prepared expanded graphite. The present invention firstly performs an electrochemical intercalation swelling reaction on graphite to obtain expandable graphite; then the expandable graphite is subjected to an expansion treatment to obtain expanded graphite, wherein the electrolyte of the electrochemical intercalation swelling reaction comprises a carbonate solution of perchlorate and water, the mass ratio of graphite to the electrolyte is 1:10-20, and the electrochemical intercalation swelling reaction is a DC constant voltage reaction, wherein the DC constant voltage is 5-30V. The present invention adopts an electrochemical method to prepare expanded graphite using waste graphite as a raw material, adopts a mixed solution of water, perchlorate and carbonate as an electrolyte, uses a small amount of oxidant, and the electrolyte is non-toxic and harmless and can be recycled, the electrochemical intercalation swelling reaction can be carried out at room temperature and pressure, the device is simple, and the inserts of the prepared expanded graphite are evenly distributed between layers, and the volume can be as high as 150mL / g.

[0102] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing expanded graphite from graphite and recycling it, characterized in that: The following steps are included: (1) subjecting graphite to an electrochemical intercalation swelling reaction to obtain expandable graphite; (2) expanding the expandable graphite to obtain expanded graphite; The electrolyte for the electrochemical intercalation swelling reaction comprises a carbonate solution of perchlorate and water; The mass ratio of graphite to electrolyte is 1:10-20; The electrochemical intercalation swelling reaction is a direct current constant voltage reaction, wherein the direct current constant voltage is 5 to 30V.

2. The method for preparing expanded graphite and recycling graphite according to claim 1, characterized in that: In the step (1), the graphite comprises one or more of waste graphite, natural graphite and artificial graphite, wherein the waste graphite comprises one or more of waste graphite battery materials, waste graphite refractory materials, waste graphite electrode materials, waste graphite sealing materials, waste graphite equipment, waste graphite containers and waste graphite blocks.

3. The method for preparing expanded graphite and recycling graphite according to claim 1 or 2, characterized in that: The perchlorate is one or more of sodium perchlorate, lithium perchlorate, potassium perchlorate, ammonium perchlorate, calcium perchlorate, magnesium perchlorate and silver perchlorate; the concentration of the perchlorate in the carbonate solution of the perchlorate is 0.001-100 g / L.

4. The method for preparing expanded graphite and recycling graphite according to claim 3, characterized in that: The amount of water added is 0.1-10 wt.% of the electrolyte mass.

5. The method for preparing expanded graphite and recycling graphite from graphite according to claim 1, 2 or 4, characterized in that: The carbonate comprises one or more of dimethyl carbonate, diethyl carbonate, diphenyl carbonate, propylene carbonate, ethylene carbonate and ethyl methyl carbonate.

6. The method for preparing expanded graphite and recycling graphite according to claim 5, characterized in that: In the step (1), the anode of the electrochemical intercalation swelling reaction is a composite anode, wherein the composite anode is formed by pressing graphite powder and shaped graphite; the shaped graphite comprises a graphite plate, a graphite strip, a graphite paper or a graphite rod; and the cathode of the electrochemical intercalation swelling reaction comprises a graphite plate, a graphite strip, a graphite paper or a graphite rod.

7. The method for preparing expanded graphite and recycling graphite according to claim 6, characterized in that: The cathode of the electrochemical intercalation swelling reaction adopts a double cathode mode, wherein the double cathodes are respectively placed on both sides of the anode, and the distance between the anode and each cathode is independently 0.5 to 3 cm.

8. The method for preparing expanded graphite and recycling graphite from graphite according to claim 1, 2, 4 or 7, characterized in that: The electrochemical intercalation swelling reaction time is 0.5 to 60 hours.

9. The method for preparing expanded graphite and recycling graphite according to claim 8, characterized in that: In the step (2), the temperature of the puffing treatment is 250 to 1000° C., and the time of the puffing treatment is 0.1 to 10 minutes.

10. Expanded graphite obtained by the method for preparing expanded graphite and recycling graphite according to any one of claims 1 to 9, characterized in that: The volume of the expanded graphite is 80-150 mL / g.

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