An electrochemical method for preparing expanded graphite

Abstract

The application discloses an electrochemical preparation method of expanded graphite, which comprises the following steps: S1, preparing an electrolyte, uniformly coating a mixture of graphite powder and the electrolyte on the surface of an anode of an electrochemical reactor; S2, laying a porous membrane on the mixture layer of the graphite powder and the electrolyte; S3, pressing a cathode on the polypropylene cloth layer, and performing electrolysis; S4, after the electrolysis process is completed, separating a solid phase from a solution, then adding ammonia water into the solid phase until the solution is alkaline; S5, adding disodium ethylenediaminetetraacetate solution, heating the prepared mixture to 50-100 DEG C, and heating for 1-2 hours, then filtering out the solution, washing the filter residue with deionized water, adding ammonium hydrogen fluoride-hydrochloric acid solution, and keeping the temperature at 55-75 DEG C for 5-10 hours, and washing with deionized water until no chlorine ion exists; and S6, separating the filter residue from the solution, drying, and heat treating at a temperature of 800-1200 DEG C. The method can effectively improve the purity of the expanded graphite and generates good economic benefits.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of material preparation, and particularly relates to an electrochemical preparation method of expanded graphite. BACKGROUND

[0002] Expanded graphite, as an intermediate product for manufacturing flexible graphite, is a loose and porous vermicular substance obtained by oxidizing, acidizing intercalation, washing, drying and high-temperature expansion of natural flake graphite. The expanded graphite not only has the excellent properties of natural graphite, such as heat resistance, corrosion resistance, electrical conductivity, thermal conductivity, self-lubrication and the like, but also has the properties of natural graphite, such as light weight, softness, compressibility and resilience. At present, the expanded graphite is widely used in petroleum, chemical industry, electric power, metallurgy, machinery, aerospace and nuclear industry.

[0003] A preparation method of expanded graphite is disclosed in the prior art. Dispersed graphite with a weight of 100-200 grams is mixed with a sulfuric acid aqueous solution with a concentration of 50-57% at a ratio of 750-850 cubic centimeters of the sulfuric acid aqueous solution per 1 kilogram of the graphite. The obtained mixture is loaded into a reaction container and is smoothed, and a separator sheet and a cathode with a cover are placed on the top of the mixture. After the separator sheet is soaked with an electrolyte, the current is turned on, and the treatment is performed in a constant current mode. After the anode treatment at 80 Ah / kg, the graphite mixture is squeezed into a filter, and sulfuric acid and ammonium bifluoride are added at a ratio of 10 grams of the ammonium bifluoride per 100 grams of the graphite. The reaction temperature is 20-70 DEG C, and the reaction time is 2-12 hours. The solid is washed with acid, dried, and heated in a quartz reactor of a shaft furnace at a temperature of 1000 DEG C. The purity of the obtained expanded graphite is 98.5-99.3%. The above preparation method mainly comprises the following steps: adding a sulfuric acid solution into natural dispersed graphite, electrochemical treatment, removing a liquid phase, washing with water, treating with an acid solution of ammonium bifluoride, removing a liquid phase, drying and heat treatment. However, the method has the following problems: the purity of the prepared expanded graphite is low. SUMMARY

[0004] In order to solve the above technical problems, the inventors have developed an electrochemical preparation method of expanded graphite based on their experience in the field.

[0005] The technical scheme adopted by the present application is as follows:

[0006] An electrochemical preparation method of expanded graphite comprises the following steps: S1: preparing sulfuric acid with a concentration of 30-94% as an electrolyte, and uniformly coating the surface of an anode of an electrochemical reactor with a mixture of graphite powder and the electrolyte with a thickness of 4-10 millimeters;

[0007] S2: laying a porous film made of a chemical corrosion resistant polypropylene cloth on the surface of the mixture of the graphite powder and the electrolyte;

[0008] S3: Press the cathode onto the polypropylene cloth layer to ensure electrical contact with the graphite powder, then connect the graphite to a direct current source for electrolysis at a current density of 0.5-55 mA / cm². 2 The power consumption is 90-120 A·h / kg;

[0009] S4: After the electrolysis process is completed, the solid phase is separated from the solution, and then ammonia is added to the solid phase until the solution becomes alkaline.

[0010] S5: Add disodium ethylenediaminetetraacetate solution, heat the prepared mixture to 50-100℃ for 1-2 hours, then filter out the solution, wash the filter residue with deionized water, add ammonium fluoride-hydrochloric acid solution, keep warm at 55-75℃ for 5-10 hours, and wash with deionized water until no chloride ions are present.

[0011] S6: Separate the filter residue from the solution, dry it, and heat-treat it at a temperature of 800-1200℃.

[0012] Furthermore, in step S5, 5-40 grams of disodium ethylenediaminetetraacetate are added to the disodium ethylenediaminetetraacetate solution for every 100 grams of graphite.

[0013] Furthermore, in step S5, the amount of ammonium bifluoride-hydrochloric acid solution added is 10-20 grams of ammonium bifluoride per 100 grams of natural graphite.

[0014] Furthermore, the ammonium bifluoride content in the ammonium bifluoride-hydrochloric acid solution is 2-4 wt%.

[0015] The preparation method of this invention uses the following materials:

[0016] The flotation enrichment graphite produced by the Xiangyang Company in China has a carbon content of 94%.

[0017] The GT-2 grade flotation enriched graphite with a carbon content of 96.4% from the Zavalyevskiy Graphite Complex GOST 17022-81.

[0018] The flotation enrichment graphite produced by the Qingdao Company in China has a carbon content of 94.7%.

[0019] The flotation-enriched graphite produced by Titan Metals and Minerals Limited in India has a carbon content of 97%.

[0020] Sulfuric acid, DSTU GOST 2184:2018 Industrial Sulfuric Acid; wherein concentrated sulfuric acid, anhydrous sulfuric acid, fuming sulfuric acid, etc. can be used. The concentration of this sulfuric acid is usually above 95%, preferably above 98%. The sulfuric acid content in the treatment solution is above 90%, preferably above 95%, and especially preferably above 97%. If it is less than 90%, the reaction rate may decrease significantly. In addition, as mentioned above, since water plays a role in lowering the thermal expansion initiation temperature of thermally expandable graphite, the water concentration in the treatment solution should be minimized as much as possible.

[0021] Ammonium bifluoride (GOST 4518-75) has the molecular formula NH4HF2 and a relative molecular mass of 57.05. It is a white or colorless transparent orthorhombic crystal with a relative density of 1.52 (25℃), a melting point of 125.6℃, and a boiling point of 239.5℃. Ammonium bifluoride can be used as a glass etchant, corrosion inhibitor, solvent for the production of metallic beryllium from beryllium oxide, chemical reagent, cleaning agent for boiler feedwater and steam generation systems, disinfectant in fermentation industries, surface treatment agent for silicon steel plates, oxidant in the manufacture of ceramics and aluminum-magnesium alloys, fluorinating agent in organic synthesis, electroplating solution, solvent for extracting rare elements, surface treatment agent for silicon steel plates, etchant in the surface treatment of aluminum profiles, and acidification agent for oilfield sand and gravel.

[0022] Potassium dichromate (GOST 4220-75), with the molecular formula K₂Cr₂O₇, is an important chromium chemical product. It is mainly used to prepare chromium salts such as chromium trioxide, potassium chromium sulfate, and chrome yellow pigment. It is also used in the manufacture of matches, explosives, electroplating additives, mordants, tanning agents, pharmaceuticals, oxidizing agents, synthetic fragrances, enamel glaze powder, metal passivating agents, printing inks, and welding electrodes.

[0023] Ammonia solution, purchased commercially; ammonia water, also known as ammonia solution, is mainly composed of NH3·H2O. It is an aqueous solution of ammonia, colorless and transparent with a pungent odor. Ammonia has a melting point of -77.773℃, a boiling point of -33.34℃, and a density of 0.91 g / cm³. 3 Ammonia is readily soluble in water and ethanol. It is volatile and exhibits some of the general properties of alkalis. Ammonia water is prepared by passing ammonia gas into water. Ammonia is toxic and irritating and corrosive to the eyes, nose, and skin; it can cause suffocation. The maximum permissible concentration in air is 30 mg / m³. It is mainly used as a fertilizer.

[0024] Industrial ammonia solution is an aqueous solution containing 25%–28% ammonia. Only a small portion of the ammonia molecules in the solution react with water to form ammonia monohydrate, making it a weak base present only in ammonia solution. The freezing point of ammonia solution is related to its concentration; a commonly used 20% (wt) concentration has a freezing point of approximately -35°C. It generates heat when neutralized with acids. It poses a flammable and explosive hazard. Its specific heat capacity is 4.3 × 10⁻⁶. 3 J / kg·℃ (10% ammonia solution)

[0025] Disodium EDTA (GOST 10652-73), ethylenediaminetetraacetic acid (EDTA), is an important complexing agent. It is used in solutions for electroless copper plating, gold plating, lead-tin alloy plating, electrochemical polishing of steel parts, and silver plating of copper parts. EDTA-Na can also be used as a substitute. It is also used in detergents, liquid soaps, shampoos, agricultural chemical sprays, bleaching and fixing solutions for color photosensitive materials, water purification agents, pH adjusters, and coagulant inhibitors. In the chemical reduction initiation system for styrene-butadiene rubber polymerization, disodium EDTA, as a component of the activator, is mainly used to complex ferrous ions and control the polymerization rate.

[0026] Deionized water, quality standard MOL-LUB 09619;

[0027] Deionized water refers to pure water after impurities in ionic form have been removed. The International Organization for Standardization (ISO) / TC 147 defines "deionized" water as: "water that has completely or incompletely removed ionic substances, primarily referring to treatment methods using ion exchange resins." Current processes mainly utilize RO (reverse osmosis) to produce deionized water. While ion exchange resins remove anions and cations from water, soluble organic matter still exists, which can contaminate the ion exchange column and reduce its effectiveness. Furthermore, deionized water is prone to bacterial growth after storage.

[0028] A membrane made of polypropylene fabric.

[0029] Polypropylene fabric is a well-structured crystalline polymer, a white granular or powdery, odorless, non-toxic, and lightweight thermoplastic resin. It possesses advantages such as easy processing, high impact strength, good flexibility, and excellent electrical insulation, and has wide applications in the automotive industry, home appliances, electronics, packaging, building materials, and furniture. The polypropylene film used in this invention has a longitudinal tensile modulus of over 3.49 GPa, a transverse tensile modulus of over 5.32 GPa, a longitudinal tensile strength of over 72 MPa, and a transverse tensile strength of over 105 MPa.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] This invention, through steps such as electrochemical treatment, liquid-solid phase separation, washing, drying, and expansion, can effectively solve the problem of low purity, improve the purity of expanded graphite, meet current market demands, and generate good economic benefits. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to the embodiments.

[0033] Example 1

[0034] An electrochemical preparation method for expanded graphite includes the following steps: 800 grams of natural flotation-enriched graphite (94% carbon content) produced by a company in Xiangyang, China, is selected and mixed with a 30% sulfuric acid solution at a ratio of 100 grams of graphite to 100 cubic centimeters of electrolyte. A 10 mm thick mixture of graphite powder and electrolyte is uniformly coated onto the anode surface of the electrochemical reactor. A porous membrane made of chemically resistant polypropylene cloth is then laid on top of the graphite powder and electrolyte mixture layer; this membrane provides good diaphragm properties, low ion movement resistance, and sufficient thickness. A cathode is pressed onto the polypropylene cloth layer to ensure electrical contact with the graphite powder. Then, a direct current is applied to the graphite at a current density of 0.5 mA / cm². 2 The power consumption was 90 A·h / kg. After the electrolysis process, the solid phase was separated from the solution, and then ammonia was added to the solid phase until the solution became alkaline. A sodium ethylenediaminetetraacetate solution was added at a ratio of 40 g of disodium ethylenediaminetetraacetate per 100 g of graphite. The prepared mixture was heated to 100°C for 1 hour, then the solution was filtered off. The filter residue was washed with deionized water, and an ammonium bifluoride-hydrochloric acid solution (ammonium bifluoride content 4 wt%) was added at a ratio of 20 g of ammonium bifluoride per 100 g of natural graphite. The mixture was kept at 75°C for 5 hours, washed with deionized water until no chloride ions were present, and the solid phase was separated from the solution, dried, and heat-treated at 800°C. The purity of the obtained expanded graphite was 99.93%.

[0035] Example 2

[0036] An electrochemical preparation method for expanded graphite includes the following steps: 1000g of GT-2 grade flotation-enriched graphite (96.4% carbon content) from the Zavalyevskiy Graphite Plant (GOST 17022-81) is selected and mixed with a 50% sulfuric acid solution at a ratio of 80 cubic centimeters of electrolyte per 100g of graphite. A 6mm thick mixture of graphite powder and electrolyte is uniformly coated onto the anode surface of the electrochemical reactor. A porous membrane made of chemically resistant polypropylene cloth is then laid on top of the graphite powder and electrolyte mixture layer; this membrane provides good diaphragm properties, low ion movement resistance, and sufficient thickness. A cathode is pressed onto the polypropylene cloth layer to ensure electrical contact with the graphite powder. Then, a direct current is applied to the graphite at a current density of 10mA / cm². 2The power consumption was 95 A·h / kg. After the electrolysis process, the solid phase was separated from the solution, and then ammonia was added to the solid phase until the solution became alkaline. Disodium ethylenediaminetetraacetate solution was added at a ratio of 30 g of disodium ethylenediaminetetraacetate per 100 g of graphite. The prepared mixture was heated to 80°C for 2 hours, then the solution was filtered off, and the filter residue was washed with deionized water. An ammonium bifluoride-hydrochloric acid solution (ammonium bifluoride content 4 wt%) was added at a ratio of 15 g of ammonium bifluoride per 100 g of natural graphite. The mixture was kept at 70°C for 6 hours, washed with deionized water until no chloride ions were present, and the solid phase was separated from the solution, dried, and heat-treated at 1100°C. The purity of the obtained expanded graphite was 99.91%.

[0037] Example 3

[0038] An electrochemical preparation method for expanded graphite includes the following steps: 1200 grams of natural graphite produced by a company in Qingdao, China, with a carbon content of 94.7%, is mixed with a 40% sulfuric acid solution at a ratio of 90 cubic centimeters of electrolyte per 100 grams of graphite. A 4 mm thick mixture of graphite powder and electrolyte is uniformly coated onto the anode surface of the electrochemical reactor. A porous membrane made of chemically resistant polypropylene cloth is then laid on top of the graphite powder and electrolyte mixture layer; this serves as an excellent diaphragm with low ion movement resistance and sufficient thickness. A cathode is pressed onto the polypropylene cloth layer to ensure electrical contact with the graphite powder. Then, a direct current is applied to the graphite at a current density of 30 mA / cm². 2 The power consumption was 100 A·h / kg. After the electrolysis process, the solid phase was separated from the solution, and then ammonia was added to the solid phase until the solution became alkaline. Disodium ethylenediaminetetraacetate solution was added at a ratio of 35 g of disodium ethylenediaminetetraacetate per 100 g of graphite. The prepared mixture was heated to 90°C for 1 hour, then the solution was filtered off, and the filter residue was washed with deionized water. Ammonium bifluoride-hydrochloric acid solution (ammonium bifluoride content 4 wt%) was added at a ratio of 20 g of ammonium bifluoride per 100 g of natural graphite. The mixture was kept at 55°C for 10 hours, washed with deionized water until no chloride ions were present, and the solid phase was separated from the solution, dried, and heat-treated at 1000°C. The purity of the obtained expanded graphite was 99.95%.

[0039] Example 4

[0040] An electrochemical preparation method for expanded graphite includes the following steps: 1500 grams of flotation enrichment stone (97.0% carbon content) produced by Titan Metals and Minerals Limited, India, is selected and mixed with 94% sulfuric acid solution at a ratio of 50 cubic centimeters of electrolyte per 100 grams of graphite. An 8 mm thick mixture of graphite powder and electrolyte is uniformly coated onto the anode surface of the electrochemical reactor. A porous membrane made of chemically resistant polypropylene cloth is then laid on top of the graphite powder and electrolyte mixture layer; this membrane provides good diaphragm properties, low ion movement resistance, and sufficient thickness. A cathode is pressed onto the polypropylene cloth layer to ensure electrical contact with the graphite powder. Then, a direct current is applied to the graphite at a current density of 55 mA / cm². 2 The power consumption was 120 A·h / kg. After the electrolysis process, the solid phase was separated from the solution, and then ammonia was added to the solid phase until the solution became alkaline. Disodium ethylenediaminetetraacetate solution was added at a ratio of 5 grams of disodium ethylenediaminetetraacetate per 100 grams of graphite. The prepared mixture was heated to 50°C for 2 hours, then the solution was filtered off, and the filter residue was washed with deionized water. An ammonium bifluoride-hydrochloric acid solution (ammonium bifluoride content 4 wt%) was added at a ratio of 10 grams of ammonium bifluoride per 100 grams of natural graphite. The mixture was kept at 60°C for 7 hours, washed with deionized water until no chloride ions were present, and the solid phase was separated from the solution, dried, and heat-treated at 1200°C. The purity of the obtained expanded graphite was 99.96%.

[0041] Example 5

[0042] An electrochemical preparation method for expanded graphite includes the following steps: 1200g of GT-2 grade flotation-enriched graphite (97.9% carbon content) from the Zavalyevskiy Graphite Plant (GOST 17022-81) is selected and mixed with a 50% sulfuric acid solution at a ratio of 80 cubic centimeters of electrolyte per 100g of graphite. A 7mm thick mixture of graphite powder and electrolyte is uniformly coated onto the anode surface of the electrochemical reactor. A porous membrane made of chemically resistant polypropylene cloth is then laid on top of the graphite powder and electrolyte mixture layer; this membrane provides good diaphragm properties, low ion movement resistance, and sufficient thickness. A cathode is pressed onto the polypropylene cloth layer to ensure electrical contact with the graphite powder. A direct current is then applied to the graphite at a current density of 10mA / cm². 2The power consumption was 95 A·h / kg. After the electrolysis process, the solid phase was separated from the solution, and then ammonia was added to the solid phase until the solution became alkaline. Disodium ethylenediaminetetraacetate solution was added at a ratio of 30 g of disodium ethylenediaminetetraacetate per 100 g of graphite. The prepared mixture was heated to 100°C for 3 hours, then the solution was filtered off, and the filter residue was washed with deionized water. An ammonium bifluoride-hydrochloric acid solution (ammonium bifluoride content 4 wt%) was added at a ratio of 18 g of ammonium bifluoride per 100 g of natural graphite. The mixture was kept at 80°C for 6 hours, washed with deionized water until no chloride ions were present, and the solid phase was separated from the solution, dried, and heat-treated at 1100°C. The purity of the obtained expanded graphite was 99.80%.

[0043] Example 6

[0044] An electrochemical preparation method for expanded graphite includes the following steps: 1000 grams of natural graphite produced by a company in Qingdao, China, with a carbon content of 95.5%, is mixed with a 40% sulfuric acid solution at a ratio of 90 cubic centimeters of electrolyte per 100 grams of graphite. A 4 mm thick mixture of graphite powder and electrolyte is uniformly coated onto the anode surface of the electrochemical reactor. A porous membrane made of chemically resistant polypropylene cloth is then laid on top of the graphite powder and electrolyte mixture layer; this serves as an excellent diaphragm with low ion movement resistance and sufficient thickness. A cathode is pressed onto the polypropylene cloth layer to ensure electrical contact with the graphite powder. Then, a direct current is applied to the graphite at a current density of 30 mA / cm². 2 The power consumption was 100 A·h / kg. After the electrolysis process, the solid phase was separated from the solution, and then ammonia was added to the solid phase until the solution became alkaline. Disodium ethylenediaminetetraacetate solution was added at a ratio of 38 g of disodium ethylenediaminetetraacetate per 100 g of graphite. The prepared mixture was heated to 100°C for 1.5 hours, then the solution was filtered off, and the filter residue was washed with deionized water. An ammonium bifluoride-hydrochloric acid solution (ammonium bifluoride content 4 wt%) was added at a ratio of 18 g of ammonium bifluoride per 100 g of natural graphite. The mixture was kept at 68°C for 11 hours, washed with deionized water until no chloride ions were present, and the solid phase was separated from the solution, dried, and heat-treated at 1100°C. The purity of the obtained expanded graphite was 99.82%.

[0045] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. An electrochemical preparation method for expanded graphite, characterized in that: Includes the following steps: S1: Prepare sulfuric acid with a concentration of 30-94% as an electrolyte, and uniformly coat the anode surface of the electrochemical reactor with a mixture of graphite powder and electrolyte with a thickness of 4-10 mm; S2: A porous membrane made of chemically resistant polypropylene cloth is laid on top of the mixture of graphite powder and electrolyte; S3: Press the cathode onto the polypropylene cloth layer to ensure electrical contact with the graphite powder, then connect the graphite to a direct current source for electrolysis at a current density of 0.5-55 mA / cm². 2 The power consumption is 90-120 A·h / kg; S4: After the electrolysis process is completed, the solid phase is separated from the solution, and then ammonia is added to the solid phase until the solution becomes alkaline. S5: Add disodium ethylenediaminetetraacetate solution, heat the prepared mixture to 50-100℃ for 1-2 hours, then filter out the solution, wash the filter residue with deionized water, add ammonium fluoride-hydrochloric acid solution, keep warm at 55-75℃ for 5-10 hours, and wash with deionized water until no chloride ions are present. S6: Separate the filter residue from the solution, dry it, and heat-treat it at a temperature of 800-1200℃.

2. The electrochemical preparation method of expanded graphite according to claim 1, characterized in that: In step S5, 5-40 grams of disodium ethylenediaminetetraacetate are added to the disodium ethylenediaminetetraacetate solution for every 100 grams of graphite.

3. The electrochemical preparation method of expanded graphite according to claim 1, characterized in that: In step S5, the amount of ammonium bifluoride-hydrochloric acid solution added is 10-20 grams of ammonium bifluoride per 100 grams of natural graphite.

4. The electrochemical preparation method of expanded graphite according to claim 1, characterized in that: The ammonium fluoride content in the ammonium fluoride-hydrochloric acid solution is 2-4 wt%.