Graphite anode plate for electrolysis

Abstract

The invention introduces a graphite anode plate for electrolysis, which adopts needle coke particles, carbonaceous short fibers and asphalt as main raw materials and a small amount of one or more of graphite scraps, a solvent and a lubricant, and is manufactured into the graphite anode plate with a composite material structure through the working procedures of kneading, profiling, roasting, dipping, graphitizing, machining and the like. The graphite anode plate has the needle coke particles, the carbon whiskers growing on the needle coke particles, the asphalt carbonized matrix and the composite material formed by three carbon components, has mechanical properties of specific strength and specific rigidity superior to those of a traditional graphite anode, and also has higher electric conductivity and heat conductivity coefficient.

Description

Technical Field

[0001] The present invention relates to a manufacturing technology for a graphite anode plate and its forming process. Background Art

[0002] The graphite anode plate is a plate-shaped graphite anode made from materials such as low-ash coke, asphalt, and additives through processes including crushing, kneading, molding, roasting, impregnation, graphitization, and then mechanical finishing. The graphite anode plate is usually used as an electrolysis electrode for aqueous solutions or salt solutions.

[0003] Common carbon fiber composites are composites formed with carbon fiber-reinforced resin as the matrix. For example, wind turbine blades, rackets, etc. are all resin-based carbon fibers. The matrix of C / C composites is carbon, and the reinforcing material is also carbon fiber. Since it is almost entirely composed of elemental carbon, such as carbon-carbon friction plates, it has extremely excellent high-temperature resistance and at the same time has strong mechanical properties of carbon fiber, and has been partially industrialized in the fields of national defense and aircraft braking systems.

[0004] The invention with application number 202310800635.9 proposes a carbon composite anode plate and its preparation method. The carbon composite anode plate provided by the present invention uses a graphite plate as the matrix, and a preparation method of modulating carbon black, graphene, and carbon nanotube composites with a surfactant and depositing a reinforcing film, making the deposition of the composite material on the surface of the graphite plate more uniform, enhancing the adhesion and dispersion of the composite material on the substrate surface, which is beneficial to improving the conductivity of the graphite anode plate, but the mechanical strength is not improved much.

[0005] The comprehensive review article "Fibrous Graphite Crystal Materials: Graphite Whiskers, Graphite Cones, and Graphite Polyhedral Crystals" published in the 38th volume, issue 1, pages 18 - 39 of New Carbon Materials in 2023 introduced the unique appearance structure, high degree of graphite microcrystal regularity, extremely high mechanical and electrical conductivity, complex growth mechanism, rich and diverse preparation methods, and potential application prospects of fibrous graphite crystal materials. However, graphite whiskers, which are different from carbon fibers (VGCFs) and carbon nanotubes (CNTs), have not been widely studied and summarized. The graphite whiskers therein can be used for reference in the present invention. Summary of the Invention

[0006] Object of the Invention: To provide a graphite anode plate for electrolysis of a composite material type with high carbon content, high conductivity, and higher mechanical strength by adding carbon fiber or the forming process of adding carbon fiber to the raw materials of the traditional graphite anode plate.

[0007] Technical Solution: The graphite anode plate for electrolysis of the present invention uses needle coke particles with a mass percentage of 30-40%, 1-20% of carbonaceous short fibers (chopped carbon fibers, chopped graphite fibers, carbon whiskers or graphite whiskers; the length is on the order of the length of the needle coke, which not only enhances the mechanical strength but also does not cause difficulty in molding due to entanglement), 30-45% of asphalt resin as the main raw materials, and a small amount of additives (one or several of graphite powder, graphite fragments, solvents, iron oxide powder fillers, stearic acid lubricants). It is manufactured through processes such as kneading, pressing, roasting, impregnation (roasting and impregnation can be repeated 2-4 times), graphitization, and machining to form a graphite anode plate with a composite material structure composed of three carbonaceous materials (needle coke, carbonaceous short fibers, and carbonized asphalt after roasting).

[0008] Preferably, carbon whiskers or graphite whiskers are used.

[0009] Deepseek search for "carbon whiskers" or "graphite whiskers" Carbon whiskers generally refer to fibrous structures composed of sp² hybridized carbon, which may include graphitized structures.

[0010] Carbon whiskers vs. carbon fibers: Whiskers are finer and closer to single crystals, and are mostly used in high-performance composite materials; carbon fibers focus on macroscopic mechanical properties.

[0011] Carbon whiskers vs. carbon nanotubes: The latter has a tubular structure and more unique electrical properties, but the cost is higher.

[0012] Due to its unique structure and properties, carbon whiskers have important potential in the field of advanced materials. Its performance in making composite materials is superior to that of carbon fibers or graphite fibers and carbon nanotubes, and it may play a role in more high-tech applications in the future.

[0013] The article "Production Principle and Several Typical Production Processes of Coal-based Needle Coke" in the 2023 Zhongke Huamei WeChat app introduced the forming process of needle coke: The production process of coal-based needle coke is mainly divided into three parts. The first part is pretreatment, where the coal tar or its fractionated oil raw materials are purified to obtain qualified intermediate raw materials. The second part is that the qualified intermediate raw materials obtained from the pretreatment are converted into needle coke green coke through delayed coking, and at the same time, some light component oils are separated. The third part is that the needle coke green coke is calcined to remove volatile components and moisture to obtain needle coke products that meet the standards.

[0014] Among them, the second part is the delayed coking process. The raw material is heated to the temperature required for coke formation and then enters the coke drum, where various complex pyrolysis reactions occur. First, low-molecular-weight alkanes and olefin light fractions in the coking drum gasify and escape from the top of the drum; second, some components undergo intense pyrolysis, dehydrogenation, and aromatization reactions, simultaneously generating a small amount of hydrogen and low-molecular-weight aromatic light fractions, which escape from the top of the drum in the form of oil and gas; the third stage is mainly a polycondensation reaction process, where carbonized solids begin to form, and at the same time, a small amount of hydrogen, low-molecular-weight alkanes, olefins, and aromatic light fractions are also generated and escape from the top of the drum in the form of oil and gas; in the fourth stage, the semi-coke solids generated further dehydrogenate and dealkylate to completely form coke, producing needle coke products; during the carbonization process of pitch, it usually undergoes changes such as the generation, growth, and fusion of mesophase spheres, making the layered stacking of the condensed carbon network orderly, that is, a wide-area streamline layered mesophase, and finally forming a three-dimensional ordered and easily graphitizable needle coke.

[0015] In the third part, the green coke is calcined at a high temperature (1000 - 1500 °C) to become needle coke. Calcination can remove the moisture and volatile components in the green coke. During this process, the volume of the green coke shrinks sufficiently, the density further increases, and as the volatile components are released, the aromatic compounds undergo decomposition and polycondensation reactions, the molecular structure changes, the volume of the green coke continuously shrinks, and the density and mechanical strength of the green coke are greatly improved.

[0016] Deepseek search, preparation method of carbon whiskers: Chemical vapor deposition (CVD): Using hydrocarbon gases as the carbon source, under the action of metal catalysts (such as Fe, Co, Ni), it decomposes at high temperature to grow into carbon whiskers.

[0017] Arc discharge method: The electrodes arc discharge in an inert gas (such as He, Ar), and at high temperature, carbon evaporates to produce carbon vapor, which condenses on the cathode or in the gas phase to form carbon whiskers.

[0018] Template method: Using a porous template (such as Al2O3) to restrict the directional growth of carbon to obtain carbon whiskers with uniform size.

[0019] In the present invention, a forming method similar to that of "fibrous graphite crystal materials: graphite whiskers, graphite cones, and graphite polyhedral crystals" in the background art can be adopted to obtain graphite whiskers. The conductive needle coke is contacted with an electrode and undergoes DC arc discharge. Under high pressure (about 92 atmospheres), the extremely high temperature (about 3900 K) generated by the arc discharge at the discharge end face causes carbon to gasify and gradually deposit on the end face of the needle coke (the surface and the nearby area of the discharge place), and finally carbon whiskers or graphite whiskers are grown (high temperature and high pressure may cause partial graphitization of some carbon whiskers), with a length of about 1 - 3 cm and a diameter of 1 - 5 μm.

[0020] In the present invention, the preferred forming method is as follows: during the calcination of needle coke, chemical vapor deposition (CVD) is used. Hydrocarbon gases (low-molecular-weight alkanes and olefin light fractions in the coking tower, which are easy to decompose, have pure components, and make full use of the carbon resources in the system of the present invention) are used as carbon sources. Under the action of a metal catalyst (such as Fe, Co, or Ni), they are decomposed at low pressure and high temperature, and carbon whiskers are epitaxially grown (with a mass of about 1-10% of the needle coke and accounting for 0.3-4% in the formed graphite anode plate). After cooling, they are deposited on the needle coke to form carbon whiskers connected to the needle coke (in the subsequent graphitization process, they become graphite whiskers, making the conductivity and thermal conductivity of the product higher). There is a strong bonding strength between the two.

[0021] Beneficial effects: In the graphite anode plate of the present invention, there is a composite material formed by needle coke particles, carbon whiskers, and a carbonized matrix of enhanced pitch resin, which has mechanical properties of specific strength and specific rigidity superior to those of traditional graphite anodes.

[0022] Moreover, the carbon whiskers epitaxially formed on the needle coke result in a good bonding force between the needle coke particles and the carbon whiskers, making the graphite anode plate not only not easily break, but also have a higher conductivity and thermal conductivity.

[0023] Due to the complete crystal of the whiskers, the carbon whiskers do not contain defects such as holes, dislocations, and grain boundaries existing in ordinary carbon fibers. The atomic arrangement is highly ordered, and its density and strength are close to the theoretical values of ideal crystals, having extremely high strength and elastic modulus (see the table), which are superior to carbon fibers. Description of the drawings

[0024] Figure 1 is a schematic structural diagram of a part (needle coke and carbon whiskers) of the present invention; Figure 2 is another schematic partial structure diagram of the present invention; Figure 3 is a schematic diagram of the material composition of the present invention; In the figure, 1 - needle coke particles (small balls or amorphous), 2 - chopped carbon fibers, 3 - carbon whiskers, 4 - pitch matrix. Specific embodiments

[0025] Example 1: As Figure 3 shown in the electrolytic graphite anode plate, needle coke particles 1, pitch, and 10-20% carbonaceous short fibers are used as the main raw materials, and there is also one or several of a small amount of graphite fragments, solvents, and lubricants. It is manufactured through processes such as kneading, pressing, roasting, impregnation, graphitization, and machining. The three carbonaceous materials together form a graphite anode plate with a composite material structure; the carbonaceous short fibers are chopped carbon fibers 2, which are randomly mixed in it.

[0026] Example 2: As Figure 1 shown, it is a schematic diagram of the internal partial structure of a graphite anode plate for electrolysis. The main raw materials are needle coke particles 1 with a mass ratio of 30 - 35%, pitch with a mass ratio of 30 - 35%, and carbon whiskers 3 with a mass ratio of 5 - 10% (which can grow during the green coke stage of needle coke and then be calcined into needle coke). There is also one or several of a small amount of graphite fines, solvents, and lubricants. It is manufactured through processes of kneading, molding, roasting, impregnation, graphitization, and machining. The three carbonaceous materials together form a graphite anode plate with a composite material structure.

[0027] The carbon whiskers 3 are carbon whiskers that are epitaxially grown on green coke by using hydrocarbon gas as a carbon source and decomposing at high temperature under the action of a metal catalyst, adopting the process of chemical vapor deposition, and are transformed into graphite whiskers after subsequent calcination and graphitization processes. The hydrocarbon gas is the light fraction of low-molecular-weight alkanes and alkenes discharged from the coking tower used in the production of amorphous needle coke 1, making full use of the useful resources in the system and reducing carbon emissions.

[0028] Example 3: As Figure 2 shown, it is a schematic diagram of the internal partial structure of a graphite anode plate for electrolysis. The main raw materials are needle coke particles 1 with a mass ratio of 35 - 40%, pitch with a mass ratio of 33 - 36%, and carbon whiskers 3 with a mass ratio of 2 - 5%. There is also one or several of a small amount of graphite fines, solvents, and lubricants. It is manufactured through processes of kneading, molding, roasting, impregnation, graphitization, and machining. The three carbonaceous materials together form a graphite anode plate with a composite material structure.

[0029] The carbon whiskers 3 are grown epitaxially on needle coke with a length of 1 - 3 cm and a diameter of 1 - 5 μm by using the arc discharge method (using needle coke as one electrode and a metal molybdenum or tungsten rod as the other electrode, and performing arc discharge under a high-pressure environment of 70 - 100 atm).

Claims

1. A graphite anode plate for electrolysis is made from needle coke particles (1) with a mass ratio of 30 - 40%, 30 - 45% of asphalt resin as the main raw materials, and one or several of a small amount of graphite fines, solvents, and lubricants through processes such as kneading, molding, roasting, impregnation, graphitization, and machining. It is characterized in that: The main raw material is additionally added with 1-20% carbonaceous short fibers, and the three carbonaceous materials together form a graphite anode plate with a composite material structure; the carbonaceous short fibers are one or several of chopped carbon fibers (2), chopped graphite fibers, carbon whiskers (3), or graphite whiskers.

2. The graphite anode plate for electrolysis according to claim 1, characterized in that: The carbon whiskers (3) or graphite whiskers in the carbonaceous short fibers grow on the surface of the needle coke particles.

3. The graphite anode plate for electrolysis according to claim 1 or 2, characterized in that: Contact a conductive needle coke with an electrode and pass a direct current arc discharge, which causes carbon gasification and gradually deposits on the end face of the needle coke particles, and finally forms carbon whiskers (3) or graphite whiskers connected to the needle coke.

4. The graphite anode plate for electrolysis according to claim 1 or 2, characterized in that: The carbonaceous short fibers are carbon whiskers (3) grown epitaxially on needle coke by chemical vapor deposition: using hydrocarbon gas as a carbon source and decomposing at high temperature under the action of a metal catalyst.

5. The graphite anode plate for electrolysis according to claim 4, characterized in that: The hydrocarbon gas is the low molecular weight alkane and olefin light fractions discharged from the coking tower used in the production of needle coke.

6. The graphite anode plate for electrolysis according to claim 4 or 5, characterized in that: After the graphite anode plate for electrolysis is graphitized, the carbon whiskers (3) are converted into graphite whiskers.

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