Doped modified carbon anode for inhibiting anode effect as well as preparation method and application of doped modified carbon anode

Abstract

The invention provides a doped modified carbon anode for inhibiting an anode effect as well as a preparation method and application thereof, and belongs to the field of aluminum electrolysis. The doped modified carbon anode comprises the following raw materials: a carbon material, an adhesive and a dopant, the dopant comprises at least one of chloride, fluoride and carbonate, and the mass of the dopant is 5-30% of the total mass of the carbon material and the adhesive. The doping agent is added into the carbon anode, so that the critical current density of the carbon anode can be improved, and the anode effect in the aluminum electrolysis process is inhibited. And moreover, the emission of strong greenhouse gas-perfluorocarbon gas can be reduced, and the green and efficient production of electrolytic aluminum can be realized.

Description

Technical Field

[0001] The present application relates to the technical field of aluminum electrolysis, and in particular to a doped modified carbon anode for suppressing anode effect, a preparation method, and an application thereof. Background Art

[0002] During aluminum electrolysis, when the Al2O3 concentration in the electrolyte drops to a critical value, the carbon anode triggers the anode effect. This anode effect not only reduces the energy efficiency of aluminum electrolysis and shortens the life of the electrolytic cell, but also emits perfluorocarbons (PFCs), potent greenhouse gases. With the advancement of aluminum electrolysis technology, the anode effect has been categorized as either high-voltage or low-voltage, based on PFC emission conditions and cell voltage response. An Alcoa research report indicates that PFCs released by the low-voltage anode effect may account for 81% of total PFC emissions from prebaked aluminum electrolytic cells. Research generally suggests that the low-voltage and high-voltage anode effects, as well as the release of different types of PFCs, share the same mechanism.

[0003] The main research results on the mechanism of anode effect are concentrated in two aspects: (1) PFC covers the gas phase layer to passivate the anode; (2) the solid fluorinated carbon layer (CF x ) passivated anode. In 2012 and 2013, Haverkamp found compounds containing CF bonds that could cause voltage to increase on graphite anodes undergoing the anode effect. In 2022, Gao et al. used a high-temperature transparent electrolytic cell to observe that there was no bubble layer covering the bottom of the anode during the anode effect, which is different from the mechanism of the anode effect caused by the covering gas film blocking the current path. Subsequent studies found that there were complex fluorinated carbons (CF x )Element. CF x The high resistance and insulation properties of CF will inevitably lead to an increase in the cell voltage. When it is generated in large quantities on the surface of the carbon anode, it will block the current path and produce an anode effect. x During the generation process, its low surface energy characteristics will lead to the deterioration of the wettability of the carbon anode surface, causing the bubbles at the bottom of the carbon anode to gather and produce large adhesive bubbles, which will further increase the pressure drop of the anode gas membrane. x Thermal decomposition in high-temperature molten salts releases potent greenhouse gases (PFCs). Therefore, suppressing the anode effect is an important direction for achieving green and efficient electrolytic aluminum production. Summary of the Invention

[0004] The present application provides a doped modified carbon anode for suppressing the anode effect, as well as a preparation method and application thereof, to solve the following technical problem: how to suppress the occurrence of the anode effect during aluminum electrolysis.

[0005] In a first aspect, an embodiment of the present application provides a doped modified carbon anode for suppressing the anode effect, wherein the raw materials of the doped modified carbon anode include: a carbon material, an adhesive and a dopant, wherein the dopant includes: at least one of chloride, fluoride and carbonate, and the mass of the dopant is 5% to 30% of the total mass of the carbon material and the adhesive.

[0006] Optionally, the mass of the dopant is 5% to 25% of the total mass of the carbon material and the adhesive.

[0007] Optionally, the chloride includes at least one of LiCl and NaCl.

[0008] Optionally, the fluoride includes at least one of LiF and NaF.

[0009] Optionally, the carbonate includes at least one of LiCO3 and NaCO3.

[0010] In a second aspect, an embodiment of the present application provides a method for preparing the doped and modified carbon anode according to any one of the embodiments of the first aspect, the method comprising:

[0011] Mixing carbon material, adhesive and dopant to obtain paste;

[0012] shaping the paste to obtain a green body;

[0013] The green body is calcined to obtain a doped modified carbon anode.

[0014] In a third aspect, an embodiment of the present application provides an application of a doped modified carbon anode as described in any one of the embodiments of the first aspect, wherein the doped modified carbon anode is used for aluminum electrolysis to suppress the generation of anode effect during aluminum electrolysis.

[0015] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0016] The embodiment of the present application provides a doped modified carbon anode for suppressing the anode effect, wherein the raw materials of the doped modified carbon anode include: a carbon material, an adhesive and a dopant, wherein the dopant includes: at least one of chloride, fluoride and carbonate, and the mass of the dopant is 5% to 30% of the total mass of the carbon material and the adhesive. By adding chloride, fluoride or carbonate as a dopant in the carbon anode, the critical current density can be synergistically improved through multiple mechanisms. The three types of dopants can all improve the electrochemical reaction stability of the anode at high current density from the dimensions of electrolyte property regulation, interface reaction optimization or anode surface modification, and avoid the anode effect caused by potential surge. As a result, the dopant can increase the critical current density of the carbon anode and suppress the generation of the anode effect during aluminum electrolysis. It can also reduce the emission of perfluorocarbon gas, a strong greenhouse gas, and help to achieve green and efficient production of electrolytic aluminum. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0018] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0019] Figure 1 A schematic flow chart of a method for preparing a doped and modified carbon anode provided in an embodiment of the present application;

[0020] Figure 2 Typical cyclic voltammetry test diagram of the carbon anode provided in Example 1 and Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0021] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0022] The range descriptions described in this article, such as numerical ranges, ratio ranges, etc., include all possible sub-ranges and single numerical values ​​within the range. For example, the range description of "1 to 6" or "1~6" covers all sub-ranges from 1 to 6 (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6). Unless otherwise specified, the terms "including", "comprising", etc. used in this article mean "including but not limited to"; relational terms such as "first" and "second" are only used to distinguish different entities or operations, and do not imply an actual sequence or association relationship; "and / or" means that multiple situations can exist alone or at the same time; expressions such as "at least one", "multiple", and "at least one" refer to any combination of corresponding objects, including a combination of single or multiple objects. The proportional relationships involved in the article, such as mass ratios, molar ratios, etc., should be understood as the corresponding relationship between the first and second terms of the proportional formula in the order of description. The raw materials, reagents, instruments and equipment used in this article can be purchased on the market or prepared by existing methods.

[0023] An embodiment of the present application provides a doped modified carbon anode for suppressing the anode effect. The raw materials of the doped modified carbon anode include: a carbon material, an adhesive and a dopant. The dopant includes: at least one of chloride, fluoride and carbonate. The mass of the dopant is 5% to 30% of the total mass of the carbon material and the adhesive.

[0024] Dopants can increase the critical current density of carbon anodes, inhibit the generation of anode effects during aluminum electrolysis, and may also inhibit the deterioration of carbon anode wettability and the high resistance insulating carbon fluoride (CF x ) will help achieve green and efficient production of electrolytic aluminum.

[0025] The mass of the dopant is limited to 5% to 30% of the total mass of the doped modified carbon anode. The dopant can effectively improve the electrolyte performance and anode reaction activity, thereby suppressing the anode effect. If the dopant accounts for more than 30%, its effect on improving the critical current density is not obvious. For example, the mass of the dopant can be 5%, 10%, 12%, 15%, 17%, 20%, 22%, 25%, 28%, 30%, etc. of the total mass of the doped modified carbon anode.

[0026] In some embodiments, the mass of the dopant is 5% to 25% of the total mass of the carbon material and the adhesive.

[0027] Limiting the mass of the dopant to 5% to 25% of the total mass of the doped modified carbon anode can significantly improve the performance of the electrolyte and the reaction activity of the anode, thereby suppressing the anode effect and reducing PFC emissions.

[0028] It should be noted that critical current density is a key parameter for measuring a carbon anode's resistance to the anodic effect. A higher critical current density indicates the anode can withstand a higher current density without experiencing the anodic effect, and thus, higher electrolysis efficiency. Dopants increase the critical current density of the anode through multiple mechanisms, such as improving electrolyte conductivity, reducing interfacial resistance, and promoting gas evolution, thereby suppressing the anodic effect.

[0029] Figure 1 A schematic flow chart of a method for preparing a doped and modified carbon anode provided in an embodiment of the present application.

[0030] Based on a general inventive concept, such as Figure 1 As shown, the embodiment of the present application provides a method for preparing the doped modified carbon anode described in any one of the above embodiments, the method comprising:

[0031] S1. Mixing the carbon material, adhesive and dopant to obtain a paste;

[0032] S2, shaping the paste to obtain a green body;

[0033] S3, calcining the green body to obtain a doped modified carbon anode.

[0034] Based on a general inventive concept, an embodiment of the present application provides an application of a doped modified carbon anode as described in any one of the above embodiments, wherein the doped modified carbon anode is used for aluminum electrolysis to suppress the generation of anode effect during aluminum electrolysis.

[0035] Therefore, in the aluminum electrolysis process, suppressing the anode effect, reducing PFC emissions and improving anode wettability are key to ensuring production efficiency and environmental benefits. The core mechanisms are as follows:

[0036] Suppressing the anode effect: By adding dopants such as LiCl and LiF to the carbon anode, the critical current density (the maximum current the anode can withstand without triggering the anode effect) is increased. When the actual current density is below the critical value, the electrochemical reaction on the anode surface can proceed smoothly, avoiding sudden potential increases and thus suppressing the anode effect.

[0037] Reducing PFC emissions: When the anode effect occurs, perfluorocarbons (PFCs) such as CF4 and C2F6 are generated. These compounds have extremely high greenhouse gas potential. By inhibiting the anode effect, the generation of high-temperature arcs can be directly reduced, curbing the generation of PFC gases at the source and helping the electrolytic aluminum industry achieve green and low-carbon production.

[0038] Improved anode wettability: Dopants can adjust the viscosity and surface tension of the electrolyte, reducing the interfacial tension between it and the carbon anode. This not only maintains good conductivity on the anode surface but also further reduces the risk of anode effect, resulting in multiple synergistic optimization effects.

[0039] In summary, the doped modified carbon anode and its preparation method and application provided in this application achieve anode effect suppression and green production in the aluminum electrolysis process through multi-dimensional innovation. Its advantages are mainly reflected in the following aspects:

[0040] (1) Significant environmental benefits: It inhibits the occurrence of anode effect, reduces PFC gases such as CF4 and C2F6 (GWP value reaches 6500-12000) from the source, helps the electrolytic aluminum industry reduce greenhouse gas emissions, and meets green production requirements.

[0041] (2) The process is simple and compatible with traditional production lines: It is compatible with the traditional production process of prebaked carbon anodes, does not require major equipment modifications, and has low industrial conversion costs.

[0042] (3) The core path to suppress the anode effect: dopants lower the electrolyte's crystallization temperature, improve conductivity, increase critical current density, and avoid potential surges, forming a closed-loop mechanism of "material modification-performance improvement-effect suppression", which significantly extends the stable operation time of the electrolytic cell compared to traditional carbon anodes.

[0043] (4) Optimization of interface performance and reaction kinetics: Adjusting electrolyte viscosity and surface tension, reducing interfacial tension → improving wettability → reducing CF x The insulating layer is formed, and at the same time, the escape of anode gas (CO2 / CO) is promoted, which reduces the increase in polarization potential caused by gas retention and causes fluorine ion discharge.

[0044] The present application will be further described below in conjunction with specific examples. It should be understood that these examples are intended to illustrate the present application only and are not intended to limit the scope of the present application. The experimental methods in the following examples where specific conditions are not specified are generally measured according to industry standards. If there are no corresponding industry standards, then the methods are carried out according to general international standards, conventional conditions, or the conditions recommended by the manufacturer.

[0045] Example 1

[0046] This embodiment provides a doped modified carbon anode for suppressing the anode effect. The raw materials of the doped modified carbon anode include: carbon material, adhesive and dopant;

[0047] Wherein, the dopant is LiCl, and the mass of the dopant is 5% of the total mass of the carbon material and the adhesive.

[0048] It should be noted that for the specific preparation method of the doped modified carbon anode, the specific type and amount of carbon materials, and the specific type and amount of adhesives, please refer to the following literature: Lang Guanghui, Jiang Yujing. Carbon Material Technology and Process for Aluminum Electrolysis [M]. Beijing: Metallurgical Industry Press, 2021, PP: 50-53.

[0049] Example 2

[0050] This embodiment is modified as follows based on the disclosure of embodiment 1:

[0051] The dopant is LiCl, and the mass of the dopant is 25% of the total mass of the carbon material and the adhesive.

[0052] Example 3

[0053] This embodiment is modified as follows based on the disclosure of embodiment 1:

[0054] The dopant is LiCl, and the mass of the dopant is 30% of the total mass of the carbon material and the adhesive.

[0055] Example 4

[0056] This embodiment is modified as follows based on the disclosure of embodiment 1:

[0057] The dopant is LiF, and the mass of the dopant is 5% of the total mass of the carbon material and the adhesive.

[0058] Example 5

[0059] This embodiment is modified as follows based on the disclosure of embodiment 1:

[0060] The dopant is LiCO3, and the mass of the dopant is 5% of the total mass of the carbon material and the adhesive.

[0061] Example 6

[0062] This embodiment is modified as follows based on the disclosure of embodiment 1:

[0063] The dopant is LiCl, and the mass of the dopant is 15% of the total mass of the carbon material and the adhesive.

[0064] Comparative Example 1:

[0065] The carbon anode used in this comparative example is a traditional industrial carbon anode used in the normal production process of an aluminum electrolysis plant.

[0066] The critical current density of the carbon anodes in the examples and comparative examples was determined by the following method:

[0067] Using cyclic voltammetry, Al / Al3+ The effect of suppressing the anodic effect during aluminum electrolysis was investigated using a doped / undoped carbon anode and cryolite-alumina molten salt as a reference electrode. To gain a deeper understanding of the anodic effect, the researchers introduced the concept of critical current density. This critical current density is an important parameter for the onset of the anodic effect and is defined as the maximum current density at which the anodic reaction can proceed smoothly. Therefore, in this experiment, the inhibitory effect of dopants on the anodic effect was investigated by analyzing the critical current density. During the cyclic voltammetry tests, it was assumed that electrolysis parameters such as alumina concentration and interelectrode distance remained unchanged.

[0068] The test shows that when the carbon anode of Comparative Example 1 is subjected to cyclic voltammetry test in a cryolite system with an alumina concentration of 4 wt%, the critical current density is about 0.95 A / cm 2 .

[0069] When the carbon anode of Comparative Example 1 was subjected to cyclic voltammetry in a cryolite system with an alumina concentration of 1.5 wt%, the critical current density was about 0.68 A / cm 2 .

[0070] When the carbon anode of Comparative Example 1 was subjected to cyclic voltammetry test in a pure cryolite system, the critical current density did not exceed 0.15 A / cm 2 .

[0071] When the doped modified carbon anode of Example 1 was subjected to cyclic voltammetry test in a cryolite system with an alumina concentration of 4 wt%, the critical current density was about 2.55 A / cm 2 Under the same conditions, the critical current density is increased by 3 times compared with that of comparative example 1.

[0072] When the doped modified carbon anode of Example 1 was subjected to cyclic voltammetry test in a cryolite system with an alumina concentration of 1.5 wt%, the critical current density was about 1.57 A / cm 2 Under the same conditions, the critical current density is increased by 2.3 times compared with that of comparative example 1.

[0073] When the doped modified carbon anode of Example 1 was subjected to cyclic voltammetry test in a pure cryolite system, the doped modified carbon anode was 2 Even at a current density of 1.5 Å, no anode effect was observed.

[0074] When the doped modified carbon anode of Example 2 was subjected to cyclic voltammetry in a cryolite system with an alumina concentration of 1.5 wt%, the critical current density was about 1.92 A / cm 2 Under the same conditions, the critical current density is increased by 2.8 times compared with that of comparative example 1.

[0075] When the doped modified carbon anode of Example 3 was subjected to cyclic voltammetry test in a cryolite system with an alumina concentration of 1.5 wt%, the critical current density was about 1.93 A / cm 2 Under the same conditions, the critical current density is increased by 2.8 times compared with that of comparative example 1, which is not a significant improvement in the critical current density.

[0076] When the doped modified carbon anode of Example 4 was subjected to cyclic voltammetry test in a cryolite system with an alumina concentration of 1.5 wt%, the critical current density was about 1.75 A / cm 2 Under the same conditions, the critical current density is increased by 2.6 times compared with that of comparative example 1.

[0077] When the doped modified carbon anode of Example 5 was subjected to cyclic voltammetry test in a cryolite system with an alumina concentration of 1.5 wt%, the critical current density was about 1.81 A / cm 2 Under the same conditions, the critical current density is increased by 2.7 times compared with that of comparative example 1.

[0078] When the doped modified carbon anode of Example 6 was subjected to cyclic voltammetry test in a cryolite system with an alumina concentration of 1.5 wt%, the critical current density was about 1.71 A / cm 2 Under the same conditions, the critical current density is increased by 2.5 times compared with that of comparative example 1.

[0079] The critical current densities of Examples 1 to 6 and Comparative Example 1 are summarized, and the results are shown in Table 1.

[0080] Table 1 Critical current density of Examples 1 to 6 and Comparative Example 1

[0081] Group <![CDATA[The alumina concentration is 4 wt% (A / cm 2 )]]> <![CDATA[The alumina concentration is 1.5 wt% (A / cm 2 )]]> <![CDATA[Pure cryolite (A / cm 2 )]]> Example 1 2.55 1.57 >2 Example 2 -- 1.92 -- Example 3 -- 1.93 -- Example 4 -- 1.75 -- Example 5 -- 1.81 -- Example 6 -- 1.71 -- Comparative Example 1 0.95 0.68 ≤0.15

[0082] Figure 2 Typical cyclic voltammetry test diagram of the carbon anode provided in Example 1 and Comparative Example 1 of the present application.

[0083] Depend on Figure 2 It can be seen that the cyclic voltammetry curve of the doped anode of Example 1 shows a higher critical current density than that of the undoped anode of Comparative Example 1.

[0084] In addition, one or more technical solutions in the embodiments of the present application have at least the following technical effects or advantages:

[0085] In the embodiments of the present application, 5%-25% of chlorides such as LiCl and NaCl or fluorides such as LiF and NaF or carbonates such as LiCO3 and NaCO3 are doped during the preparation of the carbon anode. This can not only increase the critical current density during the aluminum electrolysis process, thereby suppressing the anode effect, but also reduce the emission of perfluorocarbon (PFC) gas, a strong greenhouse gas, and contribute to the green and efficient production of electrolytic aluminum.

[0086] The aluminum electrolysis process is a high-temperature electrochemical process, and its reaction system is affected by a variety of dynamic factors, such as temperature stability, electrolyte composition uniformity, and electrode interface state. It is normal for test data to fluctuate during actual experiments. However, it should be noted that these fluctuating data were measured within the experimental parameter range, operating conditions, and technical solution framework defined in this application, and the fluctuation amplitude is within a reasonable error range, which can truly reflect the actual effect of the technical solution of this application. Therefore, they are all valid data within the scope of protection of this application.

[0087] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.

Claims

1. A doped modified carbon anode for suppressing anode effect, the raw materials of the doped modified carbon anode comprising: A carbon material, an adhesive and a dopant, wherein the dopant comprises at least one of chloride, fluoride and carbonate, and the mass of the dopant is 5% to 30% of the total mass of the carbon material and the adhesive.

2. The doped modified carbon anode according to claim 1, characterized in that: The mass of the dopant is 5% to 25% of the total mass of the carbon material and the adhesive.

3. The doped modified carbon anode according to claim 1, characterized in that: The chloride includes at least one of LiCl and NaCl.

4. The doped modified carbon anode according to claim 1, characterized in that: The fluoride includes at least one of LiF and NaF.

5. The doped modified carbon anode according to claim 1, characterized in that: The carbonate includes at least one of LiCO3 and NaCO3.

6. A method for preparing the doped and modified carbon anode according to any one of claims 1 to 5, comprising: Mixing carbon material, adhesive and dopant to obtain paste; shaping the paste to obtain a green body; The green body is calcined to obtain a doped modified carbon anode.

7. Use of the doped modified carbon anode according to any one of claims 1 to 5, wherein the doped modified carbon anode is used in aluminum electrolysis to suppress the generation of anode effect during aluminum electrolysis.

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