Process for purifying natural graphite in intermittent rotary furnace

Abstract

The invention discloses a purification process of natural graphite in an intermittent rotary furnace, and relates to the technical field of purification processes of natural graphite, and the purification process comprises the following preparation steps: step A, taking 400-600g of natural crystalline flake graphite, and filling a graphite crucible with the natural crystalline flake graphite; b, putting the graphite crucible into a furnace tube of a rotary furnace; and C, the gas inlet and outlet valve is closed, the vacuum pump is started, the vacuum pump is closed after the pressure in the furnace is pumped to-101 kPa, nitrogen is introduced, and the gas outlet valve is opened when the pressure in the furnace is 0-2 kPa. According to the intermittent rotary furnace natural graphite purification process, by optimizing the heating process, controlling the gas environment and accurately adjusting the heat preservation time and temperature, impurities in natural graphite can be effectively removed, the purity of graphite is improved, and meanwhile energy consumption and production cost are reduced; in addition, by using the high-purity graphite crucible and the high-temperature-resistant alloy furnace tube, the stability of the equipment is improved, and the service life of the equipment is prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of natural graphite purification technology, in particular to a natural graphite purification technology of an intermittent rotary furnace. Background Art

[0002] In the field of natural graphite purification, traditional purification processes mainly include chemical methods and physical methods. Chemical methods usually involve leaching treatment using chemical reagents such as acids, alkalis or chlorides. Although they can effectively remove impurities, they have problems such as complex processes, serious environmental pollution, and high costs. Physical methods mainly use high-temperature calcination or gas phase purification, but traditional high-temperature calcination processes have disadvantages such as inaccurate temperature control, incomplete impurity removal, and high energy consumption.

[0003] In recent years, with the increasing requirements for the purity of natural graphite, especially in the fields of high-end electronic materials, aerospace, etc., the limitations of existing technologies have become increasingly obvious. For example, it is difficult to achieve deep removal of impurities in the traditional high-temperature calcination process. At the same time, in a high-temperature environment, the uniform heating of graphite and the volatilization of impurities are not good, resulting in the purity of the purified graphite being difficult to meet the needs of high-end applications.

[0004] The prior art has the following technical problems:

[0005] 1. Incomplete removal of impurities: Traditional purification processes are difficult to effectively remove trace impurities in natural graphite, resulting in the purity of the purified graphite failing to meet the requirements of high-end applications.

[0006] 2. High energy consumption: The high-temperature calcination process consumes a lot of energy, and the temperature control is not precise, resulting in energy waste.

[0007] 3. Complex process and high cost: The chemical purification process involves complex chemical treatment process, which is not only cumbersome, but also pollutes the environment and increases production costs.

[0008] 4. Insufficient equipment stability: The equipment used in the existing process is prone to wear and tear or instability in high temperature environments, affecting the continuity and reliability of the purification process. Summary of the invention

[0009] The purpose of the present invention is to solve the above problems and provide a process for purifying natural graphite in an intermittent rotary furnace. The process can effectively remove impurities in natural graphite and improve the purity of graphite while reducing energy consumption and production costs by optimizing the heating process, controlling the gas environment, and accurately adjusting the insulation time and temperature. In addition, the present invention also improves the stability and service life of the equipment by using high-purity graphite crucibles and high-temperature resistant alloy furnace tubes.

[0010] To achieve the above object, the technical solution adopted by the present invention is:

[0011] A process for purifying natural graphite in an intermittent rotary furnace comprises the following preparation steps:

[0012] Step A: 400-600 g of natural flake graphite is placed in a graphite crucible;

[0013] Step B: Place the graphite crucible into the rotary furnace tube, and fix the graphite crucible from both ends with plugs, so that it rotates with the rotation of the furnace tube;

[0014] Step C: Close the inlet and outlet valves, start the vacuum pump, pump the pressure in the furnace to -101 kPa, then close the vacuum pump, introduce nitrogen (purity 99.999%), open the outlet valve when the pressure in the furnace reaches 0-2 kPa, and maintain the nitrogen flow rate at 0.5-5 L / min;

[0015] Step D: Start the rotary kiln for heating, with a heating rate of 2-10°C / min and a furnace tube speed of 0.1-5r / min. After the temperature reaches 800°C, turn off the nitrogen and introduce Freon (R21 / R22 / R123 / R141 / R142) into the furnace tube at a flow rate of 0.5-5L / min;

[0016] Freon is a type of halogenated hydrocarbon compound, mainly used in refrigeration, foaming, cleaning and other fields. According to its chemical composition and the degree of damage to the ozone layer, Freon can be divided into the following categories:

[0017] R21 (dichloromonofluoromethane, CHCl2F) is a hydrochlorofluorocarbon refrigerant (HCFC), mainly used as a refrigerant, which can replace R12 and is widely used in car air conditioning and refrigerator refrigeration.

[0018] R22 (chlorodifluoromethane, CHClF2): commonly used as a raw material for refrigeration equipment and polytetrafluoroethylene resin;

[0019] R123 (difluoromonochloroethane): used for industrial refrigeration;

[0020] R141 (1,1-dichloro-1-fluoroethane, C2H3Cl2F): Mainly used in the field of plastic foam as a foaming agent;

[0021] R142 (1,1-difluoro-1-chloroethane): used as refrigerant and foaming agent;

[0022] Step F: Perform segmented temperature point insulation operation, and cool down after the insulation is completed.

[0023] As a further improvement of the above scheme, the insulation operation 1, in the step F, is carried out at 800°C for 0.5h, 1000°C for 0.5h, 1200°C for 0.5h, 1400°C for 0.5h, 1600°C for 0.5h, 1800°C for 0.5h, 2000°C for 0.5h, and 2200°C for 0.5h, and the temperature is lowered after the insulation is completed.

[0024] As a further improvement of the above scheme, the insulation operation 2, in the step F, is carried out at 800°C for 1 hour, 1000°C for 1 hour, 1200°C for 1 hour, 1400°C for 1 hour, 1600°C for 1 hour, 1800°C for 1 hour, 2000°C for 1 hour, and 2200°C for 1 hour, and the temperature is lowered after the insulation is completed.

[0025] As a further improvement of the above scheme, the insulation operation 3, in the step F, is carried out at 800°C for 1.5h, 1000°C for 1.5h, 1200°C for 1.5h, 1400°C for 1.5h, 1600°C for 1.5h, 1800°C for 1.5h, 2000°C for 1.5h, and 2200°C for 1.5h, and the temperature is lowered after the insulation is completed.

[0026] As a further improvement of the above scheme, in the insulation operation 4, in the step F, the temperature is kept at 800°C for 2 hours, 1000°C for 2 hours, 1200°C for 2 hours, 1400°C for 2 hours, 1600°C for 2 hours, 1800°C for 2 hours, 2000°C for 2 hours, and 2200°C for 2 hours, and the temperature is lowered after the insulation is completed.

[0027] As a further improvement of the above scheme, in step A, the particle size of the natural flake graphite is 0.1-1 mm, and the fixed carbon content of the natural flake graphite is ≥90%.

[0028] As a further improvement of the above scheme, in step A, the graphite crucible is made of high-purity graphite with a purity of ≥99.9%, and the rotary kiln tube is made of a high-temperature resistant alloy that can work normally at a temperature of 2200°C.

[0029] As a further improvement of the above scheme, in step C, the purity of nitrogen is controlled to be 99.999%.

[0030] As a further improvement of the above scheme, the cooling after the insulation is completed is natural cooling, and the cooling rate is 1-5°C / min.

[0031] As a further improvement of the above solution, the fixed carbon content of the purified and prepared natural graphite is ≥99.9%.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] This process can effectively remove impurities in natural graphite and improve the purity of graphite by optimizing the heating process, controlling the gas environment, and accurately adjusting the insulation time and temperature. In addition, the present invention also improves the stability and service life of the equipment by using high-purity graphite crucibles and high-temperature resistant alloy furnace tubes. DETAILED DESCRIPTION

[0034] In order to enable those skilled in the art to better understand the technical solution, the present invention is described in detail below in conjunction with embodiments. The description in this section is only exemplary and explanatory and should not have any limiting effect on the scope of protection of the present invention.

[0035] The specific scheme of this embodiment is: a purification process of natural graphite in an intermittent rotary furnace, comprising the following preparation steps:

[0036] Step A: 400-600 g of natural flake graphite is placed in a graphite crucible;

[0037] Step B: Place the graphite crucible into the rotary furnace tube, and fix the graphite crucible from both ends with plugs, so that it rotates with the rotation of the furnace tube;

[0038] Step C: Close the inlet and outlet valves, start the vacuum pump, pump the pressure in the furnace to -101 kPa, then close the vacuum pump, introduce nitrogen (purity 99.999%), open the outlet valve when the pressure in the furnace reaches 0-2 kPa, and maintain the nitrogen flow rate at 0.5-5 L / min;

[0039] Step D: Start the rotary kiln for heating, with a heating rate of 2-10°C / min and a furnace tube speed of 0.1-5r / min. After the temperature reaches 800°C, turn off the nitrogen and introduce Freon (R21 / R22 / R123 / R141 / R142) into the furnace tube at a flow rate of 0.5-5L / min;

[0040] Freon is a type of halogenated hydrocarbon compound, mainly used in refrigeration, foaming, cleaning and other fields. According to its chemical composition and the degree of damage to the ozone layer, Freon can be divided into the following categories:

[0041] R21 (dichloromonofluoromethane, CHCl2F) is a hydrochlorofluorocarbon refrigerant (HCFC), mainly used as a refrigerant, which can replace R12 and is widely used in car air conditioning and refrigerator refrigeration.

[0042] R22 (chlorodifluoromethane, CHClF2): commonly used as a raw material for refrigeration equipment and polytetrafluoroethylene resin;

[0043] R123 (difluoromonochloroethane): used for industrial refrigeration;

[0044] R141 (1,1-dichloro-1-fluoroethane, C2H3Cl2F): Mainly used in the field of plastic foam as a foaming agent;

[0045] R142 (1,1-difluoro-1-chloroethane): used as refrigerant and foaming agent;

[0046] Step F: Perform segmented temperature point insulation operation, and cool down after the insulation is completed.

[0047] Further, as a preferred mode of the above embodiment, in the insulation operation 1, in step F, the temperature is kept at 800°C for 0.5h, 1000°C for 0.5h, 1200°C for 0.5h, 1400°C for 0.5h, 1600°C for 0.5h, 1800°C for 0.5h, 2000°C for 0.5h, and 2200°C for 0.5h, and the temperature is lowered after the insulation is completed.

[0048] Further, as a preferred mode of the above embodiment, in the insulation operation 2, in step F, the temperature is kept at 800°C for 1 hour, 1000°C for 1 hour, 1200°C for 1 hour, 1400°C for 1 hour, 1600°C for 1 hour, 1800°C for 1 hour, 2000°C for 1 hour, and 2200°C for 1 hour, and the temperature is lowered after the insulation is completed.

[0049] Further, as a preferred mode of the above embodiment, in the insulation operation 3, in step F, the temperature is kept at 800°C for 1.5 h, 1000°C for 1.5 h, 1200°C for 1.5 h, 1400°C for 1.5 h, 1600°C for 1.5 h, 1800°C for 1.5 h, 2000°C for 1.5 h, and 2200°C for 1.5 h, and the temperature is lowered after the insulation is completed.

[0050] Further, as a preferred mode of the above embodiment, in the insulation operation 4, in step F, the temperature is kept at 800°C for 2 hours, 1000°C for 2 hours, 1200°C for 2 hours, 1400°C for 2 hours, 1600°C for 2 hours, 1800°C for 2 hours, 2000°C for 2 hours, and 2200°C for 2 hours, and the temperature is lowered after the insulation is completed.

[0051] More specifically, the beneficial effects produced by the above embodiment are:

[0052] The present invention can effectively remove impurities in natural graphite and improve the purity of graphite by accurately controlling the heating temperature, holding time and gas flow rate, while ensuring the stability and repeatability of the process. In addition, the process also has the advantages of simple operation, low energy consumption and environmental friendliness.

[0053] More specifically, the working principle of the above embodiment scheme is:

[0054] The present invention utilizes the high temperature heating of the rotary kiln and the gas protection environment, and through the process of gradual heating, heat preservation and cooling, the impurities in the natural graphite are volatilized or removed at high temperature, thereby achieving high purification of the graphite. At the same time, by controlling the rotation speed of the furnace tube and the gas flow rate, the graphite is ensured to be evenly heated and reacted in the high temperature environment.

[0055] Further, as a preferred embodiment of the above embodiment, in step A, the particle size of the natural flake graphite is 0.1-1 mm, and the fixed carbon content of the natural flake graphite is ≥90%.

[0056] More specifically, the beneficial effects produced by the above embodiment are:

[0057] Optimize the purification process of natural graphite and improve the purification efficiency and product quality by controlling the particle size of natural flake graphite.

[0058] More specifically, the working principle of the above embodiment scheme is:

[0059] By controlling the particle size of natural flake graphite, the graphite can be heated more evenly during high-temperature treatment, thereby improving the removal efficiency of impurities and further improving the purity of the graphite and product quality.

[0060] Furthermore, as a preferred embodiment of the above embodiment, in step A, the graphite crucible is made of high-purity graphite with a purity of ≥99.9%, and the rotary kiln tube is made of a high-temperature resistant alloy that can work normally at a temperature of 2200°C.

[0061] More specifically, the beneficial effects produced by the above embodiment are:

[0062] Using high-temperature resistant alloy as the furnace tube material can ensure the structural stability and safety of the furnace tube in a high-temperature environment, avoid deformation or damage caused by high temperature, thereby extending the service life of the furnace tube and improving the reliability of the purification process.

[0063] More specifically, the working principle of the above embodiment scheme is:

[0064] High-temperature resistant alloys have excellent high-temperature strength and oxidation resistance, and can maintain stable structure and performance in a high-temperature environment of 2200°C, providing reliable physical support for the purification of natural graphite.

[0065] Furthermore, as a preferred embodiment of the above embodiment, in step C, the purity of nitrogen is controlled to be 99.999%.

[0066] Furthermore, as a preferred embodiment of the above embodiment, the cooling after the heat preservation is completed is natural cooling, and the cooling rate is 1-5°C / min.

[0067] In the purification process of natural graphite, the control of the cooling process is crucial to the final quality of graphite and the stability of the process. In the prior art, rapid cooling may increase the internal stress of graphite and affect its structural integrity, while uncontrolled natural cooling may lead to a long cooling time and reduce production efficiency. Therefore, a cooling method that can both ensure the quality of graphite and improve production efficiency is needed.

[0068] More specifically, the beneficial effects produced by the above embodiment are:

[0069] 1. Ensure graphite quality: By controlling the cooling rate within the range of 1-5℃ / min, the increase in internal stress of graphite caused by rapid cooling can be effectively avoided, thereby ensuring the structural integrity and quality stability of graphite.

[0070] 2. Improve production efficiency: Compared with uncontrolled natural cooling, limiting the cooling rate can shorten the cooling time, reduce the production cycle and improve production efficiency.

[0071] 3. Energy saving and environmental protection: The natural cooling method does not require additional cooling equipment or energy consumption, which reduces production costs and reduces the impact on the environment.

[0072] More specifically, the working principle of the above embodiment scheme is:

[0073] After the high-temperature purification process is completed, the graphite needs to be cooled down gradually to avoid damage to its structure caused by thermal stress. Natural cooling controls the slow decrease of the ambient temperature to evenly dissipate the heat inside the graphite, thereby avoiding internal stress concentration caused by rapid cooling. At the same time, the cooling rate is limited to 1-5℃ / min, which can shorten the cooling time as much as possible and improve production efficiency while ensuring the quality of graphite; this cooling method combines the economy of natural cooling and the stability of controllable cooling, and is an optimized cooling strategy.

[0074] Furthermore, as a preferred embodiment of the above embodiment, the fixed carbon content of the purified natural graphite is ≥ 99.9%.

[0075] More specifically, the test results of the four segmented temperature point insulation operation in the present invention are shown in the following table:

[0076]

[0077]

[0078] Analyze the above data:

[0079] Process optimization and high temperature purification:

[0080] The high-temperature method is currently one of the important methods that can effectively purify natural flake graphite to a high purity. The high-temperature method heats the graphite to about 2500°C, causing the impurities to gasify and escape, thereby significantly improving the purity of the graphite.

[0081] In the insulation operation 2, insulation operation 3, and insulation operation 4 processes, the temperature is gradually increased to 2200°C, and multiple multi-stage temperature point insulation treatments are carried out. This high-temperature insulation process helps to fully volatilize impurities, thereby significantly reducing the impurity content.

[0082] 2. Significant reduction in ash and impurity content:

[0083] Ash content (Ash%): Ash is one of the main sources of impurities in graphite. In the insulation operation 2, insulation operation 3, and insulation operation 4 processes, the ash content dropped to 0.0092%, 0.0074%, and 0.0067%, respectively, which is much lower than 0.0133% in the insulation operation 1 process. This shows that the high-temperature purification process effectively removes the ash in the graphite.

[0084] Magnetic material: The content of magnetic material was also significantly reduced in the insulation operation 2, insulation operation 3, and insulation operation 4 processes, which were 0.731%, 0.344%, and 0.092%, respectively, which was much lower than 2.653% in the insulation operation 1 process.

[0085] Other impurity elements: The contents of impurity elements such as Al, Ca, Fe, and Mg were also greatly reduced in the insulation operation 2, insulation operation 3, and insulation operation 4 processes; for example, the Fe content dropped from 11.059% in the insulation operation 1 process to 1.211% in the insulation operation 4 process, indicating that the high-temperature process effectively removed these impurities.

[0086] 3. The role of high temperature Freon purification technology:

[0087] High temperature decomposition of Freon (such as R22): At high temperatures, the fluorine and chlorine gases produced by the decomposition of Freon have strong oxidizing properties and can remove impurities such as boron, silicon, iron, calcium, and magnesium in graphite.

[0088] Impurity removal effect: Studies have shown that after using high-temperature Freon purification technology, the impurity content in graphite can be as low as 1×10 -6 Below, it is shown that the high temperature Freon technology used in the insulation operation 2, insulation operation 3, and insulation operation 4 processes can effectively remove trace impurities in graphite.

[0089] 4. Optimization of process parameters:

[0090] Insulation time and temperature: In the insulation operation 2, insulation operation 3, and insulation operation 4 processes, the insulation time is gradually increased and the temperature is gradually increased, so that impurities have more time to volatilize at high temperature.

[0091] Cooling rate: Control of the natural cooling rate (1-5℃ / min) helps to avoid the increase of internal stress in the graphite and ensure that impurities will not be redeposited during the cooling process.

[0092] 5. Comprehensive purification effect:

[0093] Fixed carbon content: Through the combination of the above-mentioned high-temperature purification and Freon purification technology, the fixed carbon content of graphite is significantly improved. In the insulation operation 2, insulation operation 3, and insulation operation 4 processes, the purity of graphite can reach more than 99.99%.

[0094] Comparative analysis: Although the insulation operation 1 process can also achieve a higher purity, the ash and impurity content is still higher than that of the insulation operation 2, insulation operation 3, and insulation operation 4 processes, so the latter has a higher purity.

[0095] In summary, through high-temperature purification, Freon purification technology and optimized process parameters, insulation operation 2, insulation operation 3, and insulation operation 4 processes can significantly reduce the ash and impurity content in graphite, thereby achieving high-purity graphite with a fixed carbon content ≥ 99.99%.

[0096] It should be noted that, in this article, the terms include, contain or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. Specific examples are used in this article to illustrate the principle and implementation of the technical solution of the present invention. The above examples are only used to help understand the method of the present invention and its core idea. The above is only a preferred implementation of the present invention. It should be pointed out that due to the limitations of textual expression and the objective existence of infinite specific structures, for ordinary technicians in this technical field, without departing from the principle of the present invention, several improvements, modifications or changes can be made, and the above technical features can also be combined in an appropriate manner; these improvements, modifications, changes or combinations, or the direct application of the concept and technical solution of the invention to other occasions without improvement, should be regarded as the protection scope of the present invention.

Claims

1. A process for purifying natural graphite in an intermittent rotary furnace, characterized in that: The method comprises the following preparation steps: Step A: 400-600 g of natural flake graphite is placed in a graphite crucible; Step B: Place the graphite crucible into the rotary furnace tube, and fix the graphite crucible from both ends with plugs, so that it rotates with the rotation of the furnace tube; Step C: close the inlet and outlet valves, start the vacuum pump, pump the pressure in the furnace to -101kPa, then close the vacuum pump, introduce nitrogen, open the outlet valve when the pressure in the furnace reaches 0-2kPa, and maintain the nitrogen flow rate at 0.5-5L / min; Step D: start the rotary kiln for heating, with a heating rate of 2-10℃ / min and a furnace tube speed of 0.1-5r / min. After the temperature rises to 800℃, close the nitrogen and introduce Freon into the furnace tube at a flow rate of 0.5-5L / min; Step F: Perform segmented temperature point insulation operation, and cool down after the insulation is completed.

2. The process for purifying natural graphite in an intermittent rotary kiln according to claim 1, characterized in that: In the step F, the temperature is kept at 800° C. for 0.5 h, 1000° C. for 0.5 h, 1200° C. for 0.5 h, 1400° C. for 0.5 h, 1600° C. for 0.5 h, 1800° C. for 0.5 h, 2000° C. for 0.5 h, and 2200° C. for 0.5 h, and the temperature is lowered after the temperature is kept.

3. The process for purifying natural graphite in an intermittent rotary kiln according to claim 1, characterized in that: In the step F, the temperature is kept at 800° C. for 1 hour, 1000° C. for 1 hour, 1200° C. for 1 hour, 1400° C. for 1 hour, 1600° C. for 1 hour, 1800° C. for 1 hour, 2000° C. for 1 hour, and 2200° C. for 1 hour, and the temperature is lowered after the temperature is kept.

4. The process for purifying natural graphite in an intermittent rotary kiln according to claim 1, characterized in that: In the step F, the temperature is kept at 800° C. for 1.5 h, 1000° C. for 1.5 h, 1200° C. for 1.5 h, 1400° C. for 1.5 h, 1600° C. for 1.5 h, 1800° C. for 1.5 h, 2000° C. for 1.5 h, and 2200° C. for 1.5 h, and the temperature is lowered after the temperature is kept.

5. The process for purifying natural graphite in an intermittent rotary kiln according to claim 1, characterized in that: In the step F, the temperature is kept at 800° C. for 2 h, 1000° C. for 2 h, 1200° C. for 2 h, 1400° C. for 2 h, 1600° C. for 2 h, 1800° C. for 2 h, 2000° C. for 2 h, and 2200° C. for 2 h, and the temperature is lowered after the temperature is kept.

6. The process for purifying natural graphite in an intermittent rotary kiln according to claim 1, characterized in that: In step A, the particle size of the natural flake graphite is 0.1-1 mm, and the fixed carbon content of the natural flake graphite is ≥90%.

7. The process for purifying natural graphite in an intermittent rotary kiln according to claim 1, characterized in that: In step A, the graphite crucible is made of high-purity graphite with a purity of ≥99.9%, and the rotary kiln tube is made of a high-temperature resistant alloy that can work normally at a temperature of 2200°C.

8. The process for purifying natural graphite in an intermittent rotary furnace according to claim 1, characterized in that: In step C, the purity of nitrogen is controlled to be 99.999%.

9. A process for purifying natural graphite in an intermittent rotary furnace according to any one of claims 1 to 5, characterized in that: After the heat preservation is completed, the temperature is lowered naturally, and the cooling rate is 1-5°C / min.

10. A process for purifying natural graphite in an intermittent rotary furnace according to any one of claims 3, 4 and 5, characterized in that: The fixed carbon content of the purified natural graphite is ≥99.9%.

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