Prebaked anode based on biomass charcoal and preparation method thereof

Abstract

The invention provides a pre-baked anode based on biomass charcoal and a preparation method of the pre-baked anode, and belongs to the field of carbon anodes for aluminum. The method comprises the following steps: drying and crushing a biomass raw material to obtain pretreated biomass; carrying out low-temperature carbonization and high-temperature calcination on the pretreated biomass to obtain a biomass charcoal raw material; carrying out acid treatment and alkali treatment on the biomass charcoal raw material to carry out deliming treatment, so as to obtain delimed biomass charcoal; and the delimed biomass charcoal, the calcined petroleum coke and the coal pitch are sequentially subjected to mixing and kneading, compression molding and roasting, and the prebaked anode is obtained. The biomass charcoal is used for replacing part of calcined coke to prepare the anode, the good pore structure and reaction activity of the biomass charcoal can improve the electric conductivity and heat conductivity of the anode, the high tap density and strength of the biomass charcoal can improve the density and structural strength of the anode, and the low vanadium content of the biomass charcoal enables the air reactivity of the anode to be good; therefore, the quality of the prebaked anode is effectively improved.

Description

Technical Field

[0001] The present application relates to the technical field of carbon anodes for aluminum, and in particular to a prebaked anode based on biomass carbon and a preparation method thereof. Background Art

[0002] Aluminum carbon anodes are a crucial component of the electrolytic cell, often called its "heart." They are composed of aggregate coke pellets, powder, and pitch. The aggregate coke pellets are calcined petroleum coke particles, with some companies also using a small amount of scrap anode pellets. The powder is calcined petroleum coke powder. During the roasting process, the powder and pitch form a bonding matrix, connecting the aggregates.

[0003] Calcined petroleum coke, the primary raw material for aluminum carbon anode production, has a significant impact on anode quality. With the rapid development of my country's aluminum industry, demand for high-quality petroleum coke is increasing. However, with my country's increasing dependence on crude oil imports and the increasing application of slurry bed refining processes, petroleum coke powder is experiencing a severe tendency to coke, increasing sulfur content, increasing levels of harmful impurities, and further deteriorating its internal structure. This has led to a decrease in the supply of high-quality petroleum coke and a consequent deterioration in carbon anode quality. Therefore, improving the quality of prebaked anodes is a pressing technical challenge. Summary of the Invention

[0004] The present application provides a biochar-based prebaked anode and a preparation method thereof to solve the following technical problem: how to improve the quality of the prebaked anode.

[0005] In a first aspect, the present invention provides a method for preparing a prebaked anode based on biochar, the method comprising:

[0006] Drying and crushing the biomass raw materials to obtain pretreated biomass;

[0007] The pretreated biomass is subjected to low-temperature carbonization and high-temperature calcination to obtain a biomass charcoal raw material;

[0008] The biochar raw material is subjected to acid treatment and alkali treatment to perform deashing treatment to obtain deashed biochar;

[0009] The deashed biochar, calcined petroleum coke and coal tar pitch are sequentially mixed, pressed and calcined to obtain a prebaked anode;

[0010] The ash content of the deashed biochar is ≤0.5%, and the mass ratio of the deashed biochar, the calcined petroleum coke and the coal tar pitch is (30-50):(40-60):(10-20).

[0011] Optionally, the low-temperature carbonization includes the following parameters: carbonization temperature is 520° C. to 570° C., heating rate is 1° C. / min to 2° C. / min, and carbonization time is 3 h to 5 h.

[0012] Optionally, the high-temperature calcination includes the following parameters: a heating rate of 2°C / min to 5°C / min, a calcination temperature of 1250°C to 1350°C, and a holding time of 2h to 4h.

[0013] Optionally, the alkali treatment adopts mixing and stirring of biomass charcoal raw materials and alkali solution, the concentration of the alkali solution is 0.1% to 0.3%, and the alkali solution includes: one or more of sodium hydroxide, potassium hydroxide, calcium hydroxide and barium hydroxide.

[0014] Optionally, the mixing and stirring of the biochar raw material and the alkali solution includes the following parameters: a stirring temperature of 50° C. to 80° C., a stirring speed of 150 rpm to 260 rpm, and a stirring time of 6 h to 10 h.

[0015] Optionally, the acid treatment adopts mixing and stirring of biochar raw materials with acid solution, the concentration of the acid solution is 3 mol / L to 5 mol / L, and the acid solution includes one or more of hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid and perchloric acid.

[0016] Optionally, the mixing and stirring of the biochar raw material and the acid solution includes the following parameters: the stirring temperature is room temperature, the stirring speed is 200 rpm to 300 rpm, and the stirring time is 8 h to 12 h.

[0017] Optionally, the particle size of the deashed biochar is ≤0.3 mm.

[0018] Optionally, the biomass raw materials include: one or more of crop straw, forestry waste and fruit shells.

[0019] In a second aspect, the present application provides a prebaked anode prepared by the method described in any one of the embodiments of the first aspect, wherein the prebaked anode satisfies the following properties: a volume density of 1.57 g / cm 3 ~1.58g / cm 3 , the resistivity is 55.6μΩ·m~56.7μΩ·m, the ash content is 0.34%~0.37%, and the air reaction residual rate is 67.3%~67.8%.

[0020] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0021] The present application embodiment provides a method for preparing a prebaked anode based on biomass carbon, the method comprising: drying and crushing a biomass raw material to obtain a pretreated biomass; subjecting the pretreated biomass to low-temperature carbonization and high-temperature calcination to obtain a biomass carbon raw material; subjecting the biomass carbon raw material to acid treatment and alkali treatment to deashing to obtain a deashed biomass carbon; kneading, pressing and calcining the deashed biomass carbon, calcined petroleum coke and coal tar pitch in sequence to obtain a prebaked anode; wherein the ash content of the deashed biomass carbon is ≤0.5%, and the mass ratio of the deashed biomass carbon, the calcined petroleum coke and the coal tar pitch is (30-50):(40-60):(10-20). On the one hand, the present application converts the biomass into a carbon raw material with a stable structure by low-temperature carbonization and high-temperature calcination of the biomass raw material, thereby improving the carbon purity; at the same time, deashing is carried out by acid treatment and alkali treatment, and the ash content is controlled to ≤0.5%, thereby reducing the negative impact of impurities on the conductivity, oxidation resistance and other properties of the anode. On the other hand, by combining deashed biochar, calcined petroleum coke and coal tar pitch in a mass ratio of (30-50): (40-60): (10-20), the biochar has a good pore structure and reactivity, which can improve the electrical and thermal conductivity of the anode; the tap density of the biochar is higher than that of the traditional calcined coke, which helps to improve the volume density of the prebaked anode; the biochar has higher strength, which can enhance the structural strength of the prebaked anode; the biochar has a low vanadium content and the air reactivity of the anode is good; at the same time, the calcined petroleum coke provides a high-strength skeleton structure, which enhances the mechanical strength of the anode; in addition, coal tar pitch is used as a binder to ensure that the components are closely combined and the structural stability after molding is improved. Therefore, the present application uses biochar to replace part of the calcined coke to prepare the anode, which can effectively improve the quality of the prebaked anode. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] 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.

[0023] 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.

[0024] Figure 1 A schematic flow chart of a method for preparing a prebaked anode based on biochar provided in an embodiment of the present application. DETAILED DESCRIPTION

[0025] 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.

[0026] 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.

[0027] Figure 1 A schematic flow chart of a method for preparing a prebaked anode based on biochar provided in an embodiment of the present application.

[0028] like Figure 1 As shown, the embodiment of the present application provides a method for preparing a prebaked anode based on biomass carbon, the method comprising:

[0029] S1. Drying and crushing the biomass raw materials to obtain pretreated biomass;

[0030] By drying and crushing biomass raw materials, moisture can be removed from the raw materials and the particle size can be reduced to improve the efficiency of subsequent reactions.

[0031] In some embodiments, the drying temperature is 110° C. to 120° C., and the drying time is 8 h to 12 h.

[0032] The drying temperature is limited to 110°C to 120°C, and the drying time is 10 hours. This can prevent the biomass raw materials from decomposing due to high temperature and ensure the stability of the carbon skeleton structure. At the same time, it can ensure that the moisture (such as free water and bound water) is completely removed to prevent the material from bursting or structural damage due to residual moisture during the subsequent carbonization process. Exemplarily, the drying temperature can be 110°C, 112°C, 114°C, 116°C, 118°C, 120°C, etc., and the drying time can be 8 hours, 8.5 hours, 9 hours, 9.5 hours, 10 hours, 11 hours, 12 hours, etc.

[0033] In some embodiments, the biomass raw material includes one or more of crop straw, forestry waste, and fruit shells.

[0034] Biomass raw materials (crop straw, forestry waste, fruit shells, etc.) are rich in cellulose, hemicellulose and lignin, and can easily form porous carbon structures after carbonization. They are widely available and low in cost.

[0035] S2, carbonizing the pretreated biomass at low temperature and calcining at high temperature to obtain a biochar raw material;

[0036] Through low-temperature carbonization and high-temperature calcination pyrolysis, a carbon skeleton is formed and the lattice structure is optimized to meet the performance requirements of the anode material.

[0037] In some embodiments, the low-temperature carbonization includes the following parameters: carbonization temperature is 520° C. to 570° C., heating rate is 1° C. / min to 2° C. / min, and carbonization time is 3 h to 5 h.

[0038] The carbonization temperature is 520℃~570℃, and the carbonization time is 3h~5h, which can gradually pyrolyze the biomass raw material and release volatiles (such as H2O, CO2, small molecular hydrocarbons), avoiding the rapid discharge of volatiles at high temperature, which may cause the carbon structure to collapse or crack; limiting the heating rate to 1℃ / min~2℃ / min, can ensure that the material is heated evenly inside and outside, reduce structural damage caused by thermal stress, and promote the orderly release of volatiles. Exemplarily, the carbonization temperature can be 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, etc., the heating rate can be 1℃ / min, 1.2℃ / min, 1.4℃ / min, 1.6℃ / min, 1.8℃ / min, 2℃ / min, etc., and the carbonization time can be 3h, 3.5h, 4h, 4.5h, 5h, etc.

[0039] In some embodiments, the high-temperature calcination includes the following parameters: a heating rate of 2° C. / min to 5° C. / min, a calcination temperature of 1250° C. to 1350° C., and a holding time of 2 h to 4 h.

[0040] The calcination temperature is limited to 1250℃~1350℃, and the carbon material can undergo graphitization transformation, with a more orderly lattice arrangement, which significantly improves the conductivity (resistivity reduction) and mechanical strength (such as compressive strength); the heating rate is limited to 2℃ / min~5℃ / min, and the holding time is 2h~4h, which can adapt to the characteristics of high-temperature furnaces. The holding time ensures that the graphitization reaction is sufficient and avoids the increase of lattice defects due to insufficient temperature, which affects the conductivity and corrosion resistance of the anode. For example, the heating rate can be 2℃ / min, 3℃ / min, 4℃ / min, 4.5℃ / min, 5℃ / min, etc., the calcination temperature can be 1250℃, 1270℃, 1290℃, 1310℃, 1330℃, 1350℃, etc., and the holding time can be 2h, 2.5h, 3h, 3.5h, 4h, etc.

[0041] S3, subjecting the biochar raw material to acid treatment and alkali treatment to deashing treatment to obtain deashed biochar;

[0042] Deashing can remove inorganic impurities (such as metal oxides such as K, Na, Ca, Mg, etc.) in biochar, reduce the ash content, and meet the purity requirements of the anode material.

[0043] In some embodiments, step S3 may specifically be: mixing the biomass raw material with the acid solution and stirring, performing solid-liquid separation on the slurry after stirring, washing the solid product to neutrality, then mixing the solid product with the alkaline solution and stirring, performing solid-liquid separation on the slurry after stirring, washing the solid product to neutrality, and obtaining deashed biochar.

[0044] In some embodiments, the alkali treatment comprises mixing and stirring the biochar raw material with an alkali solution, wherein the concentration of the alkali solution is 0.1% to 0.3%, and the alkali solution comprises one or more of sodium hydroxide, potassium hydroxide, calcium hydroxide, and barium hydroxide.

[0045] In some embodiments, the mixing and stirring of the biochar raw material and the alkali solution includes the following parameters: a stirring temperature of 50° C. to 80° C., a stirring speed of 150 rpm to 260 rpm, and a stirring time of 6 h to 10 h.

[0046] Dilute alkali solution (such as NaOH, KOH) can dissolve aluminosilicate impurities while avoiding the corrosion of high concentration alkali on the carbon skeleton; the stirring temperature is raised to 50°C to 80°C, which can accelerate the reaction rate of alkali and impurities, and stirring allows the alkali solution to fully contact the carbon particles, thereby improving the deashing efficiency. For example, the concentration of the alkali solution can be 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, etc., the stirring temperature can be 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, etc., the stirring speed can be 150rpm, 170rpm, 190rpm, 200rpm, 220rpm, 240rpm, 260rpm, etc., and the stirring time can be 6h, 6.5h, 7h, 8h, 9h, 10h, etc.

[0047] In some embodiments, the acid treatment comprises mixing and stirring the biochar raw material with an acid solution, wherein the concentration of the acid solution is 3 mol / L to 5 mol / L, and the acid solution comprises one or more of hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid and perchloric acid.

[0048] In some embodiments, the mixing and stirring of the biochar raw material and the acid solution includes the following parameters: the stirring temperature is room temperature, the stirring speed is 200 rpm to 300 rpm, and the stirring time is 8 hours to 12 hours.

[0049] Strong acids (such as HCl, H2SO4) can dissolve the metal ions (such as Ca 2+ Mg 2+ ), high-concentration acid ensures complete dissolution of metal ions; prolonged stirring (8 to 12 hours) at room temperature allows the acid to fully react with residual impurities, avoiding ash residue due to incomplete reaction. For example, the acid concentration can be 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, etc.

[0050] In some embodiments, the particle size of the deashed biochar is ≤0.3 mm.

[0051] The particle size of deashed biochar is limited to ≤ 0.3 mm to facilitate subsequent uniform mixing with petroleum coke and coal tar pitch, ensuring good dispersion of the material during anode formation. For example, the particle size of deashed biochar can be 0.3 mm, 0.28 mm, 0.26 mm, 0.24 mm, 0.22 mm, 0.20 mm, etc.

[0052] S4, sequentially mixing, pressing and calcining the deashed biochar, calcined petroleum coke and coal tar to obtain a prebaked anode;

[0053] The deashed biomass carbon is compounded with traditional anode raw materials through kneading, pressing and roasting, and a prebaked anode with good conductivity and mechanical strength is formed through molding and roasting.

[0054] The embodiments of the present application use biochar to prepare aluminum anodes, which has the following advantages: (1) Wide range of sources: Biochar can be prepared from various biomass wastes, such as crop straw, forestry waste, fruit shells, etc. These raw materials are abundant and renewable, and can effectively utilize wastes to reduce environmental pollution; (2) Low cost: Compared with raw materials such as petroleum coke used in the production of traditional anode materials, biomass waste is low in cost, which can reduce the production cost of aluminum anodes; (3) Environmentally friendly: The pollutants generated during the preparation process are relatively small, and during the aluminum electrolysis process, the carbon dioxide emissions of the biochar anode are lower than those of the traditional anode, which helps to reduce greenhouse gas emissions and meets the requirements of sustainable development.

[0055] In some embodiments, the ash content of the deashed biochar is ≤0.5%, and the mass ratio of the deashed biochar, the calcined petroleum coke and the coal tar pitch is (30-50):(40-60):(10-20).

[0056] The mass ratio of deashed biochar, calcined petroleum coke and coal tar pitch is limited to (30-50):(40-60):(10-20). Biochar replaces part of the petroleum coke. At the same time, the characteristics of biochar such as high tap density, high strength and low vanadium content (which can improve air reactivity) are utilized to optimize the comprehensive performance of the anode. Coal tar pitch is used as a binder with a content of 10% to 20% to ensure that the material has good plasticity during mixing. After pressing and forming, it is calcined and carbonized to form a carbon network, thereby enhancing the structural strength of the anode. Exemplarily, the mass ratio of deashed biochar, calcined petroleum coke and coal tar pitch can be 30:50:20, 32:50:18, 34:50:16, 36:50:14, 38:50:12, 40:50:10, 40:40:20, 32:40:18, 34:40:16, 36:40:14, 38:40:12, 40:40:10, 30:60:10, etc.

[0057] In some embodiments, the process of using biochar for anode preparation is as follows: according to the weight fraction, the dry material consisting of deashed biochar and calcined petroleum coke is placed in a mixer and mixed at room temperature for 20 minutes to 30 minutes; the mixed dry material is placed in a preheating pot and preheated at 175°C to 185°C for 5 minutes to 15 minutes; after the preheating is completed, the dry material is added to a kneading pot and 13 parts to 16 parts of coal tar is added, and mixed at 165°C to 185°C for 5 minutes to 20 minutes to obtain a carbon paste; the carbon paste is placed in a preheating pot and preheated at 175°C to 185°C for 5 minutes to 15 minutes to obtain a carbon paste; The pre-baked anode is placed in a mold for pressing and forming, the mold temperature is 150℃~165℃, and the pressure is 300KN~500KN; after the pre-baked anode is cooled to room temperature, it is placed in a baking furnace for baking, and the baking temperature rising curve is 3℃ / h~5℃ / h from room temperature to 250℃, 2℃ / h~3℃ / h from 250℃ to 650℃, 2℃ / h~5℃ / h from 650℃ to 950℃, and 4℃ / h~8℃ / h from 950℃ to 1150℃, and the temperature is kept at 1150℃ for 45h~55h to obtain a baked anode.

[0058] Through kneading, the biomass carbon fine powder is evenly distributed with the petroleum coke aggregate and coal tar to avoid local uneven composition; through pressing and molding, the anode is given a specific shape (such as a block), and the particles are closely contacted by pressure to reduce the porosity; through the roasting process, the coal tar is carbonized at high temperature, and the various components are bonded into a whole. At the same time, the carbon structure is further optimized, the resistivity is reduced, and the conductivity requirements of the anode for electrolytic aluminum are met.

[0059] In some embodiments, the aggregate coke particles of the calcined petroleum coke used as the dry material have a particle size range of 8 mm to 0.3 mm, wherein the aggregate coke particles include coarse coke with a particle size of 8 mm to 5 mm, medium coke with a particle size of 5 mm to 2 mm, and fine coke with a particle size of 2 mm to 0.3 mm.

[0060] Based on a general inventive concept, the present invention provides a prebaked anode prepared by the method described in any one of the above embodiments, wherein the prebaked anode meets the following properties: a volume density of 1.57 g / cm 3 ~1.58g / cm 3 , the resistivity is 55.6μΩ·m~56.7μΩ·m, the ash content is 0.34%~0.37%, and the air reaction residual rate is 67.3%~67.8%.

[0061] In the embodiment of the present application, biomass raw materials are carbonized, calcined, purified and deashed to obtain biochar, which is used to replace calcined petroleum coke powder for preparing prebaked anodes. This method can effectively improve the quality of prebaked anodes: first, the tap density of biochar is higher than that of traditional calcined coke, which helps to increase the volume density of prebaked anodes; second, the strength of biochar is higher, which can enhance the structural strength of prebaked anodes; third, the vanadium content of biochar is low and the air reactivity is good. In addition, this method can also solve the problem of insufficient anode raw materials. For example, the volume density of the prebaked anode can be 1.57g / cm 3 , 1.572g / cm 3 、1.574g / cm 3 、1.576g / cm 3 、1.58g / cm 3 etc., the resistivity can be 55.6μΩ·m, 55.7μΩ·m, 55.9μΩ·m, 56.0μΩ·m, 56.2μΩ·m, 56.4μΩ·m, 56.6μΩ·m, 56.7μΩ·m, etc., the ash content can be 0.34%, 0.35%, 0.36%, 0.37%, etc., and the air reaction residual rate can be 67.3%, 67.4%, 67.5%, 67.6%, 67.7%, 67.8%, etc.

[0062] In summary, the biochar-based prebaked anode preparation method provided in this application has significant advantages in resource utilization, cost control, performance optimization, and environmental protection through process innovation and material substitution, as follows:

[0063] 1. Raw material advantages: renewable resource substitution and waste high value creation

[0064] (1) The raw materials are widely available and renewable: biomass waste such as crop straw, forestry waste, and fruit shells are used as raw materials. The annual output of such resources is large (for example, my country's annual straw output exceeds 900 million tons), and they are recyclable and renewable, alleviating the dependence of traditional anodes on petroleum coke (a non-renewable resource) and solving the problem of anode raw material shortage. At the same time, waste utilization reduces accumulation, land occupation, and environmental pollution. For example, each ton of biochar can consume about 2 tons of straw, helping to achieve the goal of "carbon neutrality" by turning solid waste into resources.

[0065] (2) Raw material costs are significantly reduced: Biomass waste is cheap: the cost is more than 80% lower than that of calcined petroleum coke.

[0066] 2. Performance Advantages: Multi-dimensional Index Optimization and Anode Quality Improvement

[0067] (1) Physical performance enhancement: biochar tap density (≥1.6g / cm 3 ) is higher than calcined petroleum coke (1.4~1.5g / cm 3), after replacing 30% to 50% of the prebaked anode, the volume density of the prebaked anode reaches 1.57 to 1.58 g / cm 3 , compared with the traditional anode (1.52~1.55g / cm 3 ) by approximately 3%, reducing electrolyte permeation losses during electrolysis. Furthermore, the graphitized structure formed by high-temperature calcination of biochar is denser and has a compressive strength 10% to 15% higher than that of calcined coke. This improves the impact resistance of prebaked anodes in the electrolytic cell and reduces block loss.

[0068] (2) Optimization of conductivity and anti-reactivity: High-temperature calcination (1250-1350°C) increases the degree of graphitization of biomass carbon. The resistivity of the prebaked anode is 55.6-56.7 μΩ·m, which is comparable to that of traditional petroleum coke-based anodes and meets the conductivity requirements of electrolytic aluminum.

[0069] (3) Significant improvement in air reactivity: The vanadium content of biomass carbon (<0.01%) is much lower than that of calcined coke (0.1% to 0.3%), and vanadium is the main element that promotes air oxidation of the anode. Therefore, the air reaction residual rate of the prebaked anode reaches 67.3% to 67.8% (the traditional anode is 60% to 65%), and the service life is extended by 10% to 15%.

[0070] (4) Purity improvement and impurity control: Through acid-base deashing treatment: the ash content of biomass carbon is reduced to ≤0.5%, and the ash content of pre-baked anode is reduced to 0.34%~0.37%, reducing the impact of impurities (such as K, Na, Ca) on the purity of aluminum liquid during the electrolysis process, thereby improving the quality of electrolytic aluminum.

[0071] 3. Process Advantages: Collaborative Optimization and Low-Cost Manufacturing

[0072] (1) Strong compatibility of the preparation process: The process parameters such as carbonization (520-570℃), calcination (1250-1350℃) and kneading roasting are compatible with traditional anode production equipment (such as atmosphere furnaces, silicon-molybdenum furnaces, and kneading pots), without the need for large-scale equipment modification, and low industrial implementation costs. The deashing process uses room temperature acid treatment + medium temperature alkali treatment (50-80℃), which reduces energy consumption by more than 40% compared to traditional high-temperature deashing (>800℃).

[0073] (2) Flexible and adjustable raw material ratio: The biochar replacement ratio can be flexibly adjusted within the range of 30% to 50%, and the cost can be optimized according to the price fluctuation of petroleum coke. For example, when the price of petroleum coke rises, the replacement ratio can be increased to ensure stable production costs.

[0074] 4. Environmental Advantages: Low Carbon Emissions and Green Production

[0075] (1) Low pollution during the preparation process: The emission of volatile matter (mainly H2O and CO2) during the preparation of biochar is more than 50% less than that of petroleum coke, and there is no toxic gas (such as SO2, NO x) emissions, reducing waste gas treatment costs. The acid-base deashing process can use circulating washing technology, with a wastewater reuse rate of 80%. The solid waste (deashing residue) can be used as building material filler, achieving "zero emissions".

[0076] (2) Low-carbon advantage in the electrolysis stage: Biomass carbon has a high carbon content (>90%), and CO2 emissions during the electrolysis process are 8% to 10% lower than those of traditional anodes. Based on an annual production of 100,000 tons of anodes, annual CO2 emissions can be reduced by approximately 24,000 tons, contributing to the aluminum industry's "dual carbon" goals.

[0077] 5. Getting rid of dependence on oil resources

[0078] my country's annual petroleum coke imports exceed 10 million tons. Biomass carbon substitution can reduce external dependence and ensure the security of anode raw material supply.

[0079] The prebaked anode is realized based on the above-mentioned method for preparing the prebaked anode. The specific steps of the method for preparing the prebaked anode can refer to the above-mentioned embodiment. Since the prebaked anode adopts part or all of the technical solutions of the above-mentioned embodiment, it has at least all the beneficial effects brought by the technical solutions of the above-mentioned embodiment, which will not be repeated here one by one.

[0080] The present application will be further described below in conjunction with specific examples. It should be understood that these examples are intended only to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are generally measured in accordance with industry standards. If there are no corresponding industry standards, the methods are carried out in accordance with general international standards, conventional conditions, or conditions recommended by the manufacturer. (All process parameters have been reviewed and are within the numerical ranges defined in the claims)

[0081] Example 1

[0082] This embodiment provides a method for preparing biochar and using it for prebaking anodes, comprising the following steps:

[0083] Preparation of biochar: Take a certain amount of corn straw and put it into an oven, dry it at 120℃ for 10h, crush the dried corn straw and put it into a corundum crucible, carbonize it in an atmosphere furnace for 4h, and put the carbonized corn straw into a silicon-molybdenum furnace for calcination with a heating rate of 3℃ / min, a calcination temperature of 1300℃, and a holding time of 3h.

[0084] Deashing of biochar: Take 300g of biochar, put it into a polytetrafluoroethylene beaker, add 3000ml of 4mol / l hydrochloric acid, stir at room temperature for 10h, the speed is 300rpm, and after stirring, wash the raw material with deionized water to neutrality. Then add the acid-washed raw material into a polytetrafluoroethylene beaker, add 3000ml of 0.2wt% sodium hydroxide solution, stir at 50℃ for 6h, the speed is 250rmp, after stirring, wash the raw material with deionized water to neutrality, and dry to obtain deashed biochar.

[0085] Raw material dry material: weigh 26 parts of 8-5mm calcined petroleum coke, 19 parts of 5-2mm calcined petroleum coke, 17 parts of 2-0.3mm calcined petroleum coke, and 38 parts of fine powder biochar and put them into a mixer and mix them evenly.

[0086] Anode preparation: 85 parts of dry material were placed in a kneader, followed by 15 parts of coal tar pitch. The mixture was kneaded at 175°C for 10 minutes to obtain a paste. The paste was placed in a mold and pressed using a pressure of 400 kN to obtain a green anode.

[0087] Anode baking: The prepared anode is cooled to room temperature, and then placed in a baking furnace for baking. The temperature is raised from room temperature to 250°C at a heating rate of 4°C / h; raised to 650°C at a heating rate of 2°C / h; raised to 950°C at a heating rate of 3°C / h; and raised to 1150°C at a heating rate of 5°C / h. Keep the temperature at 1150°C for 50 hours. After baking, slowly cool down to 200-300°C and take the prebaked anode out of the furnace.

[0088] Example 2

[0089] This embodiment provides a method for preparing biochar and using it for prebaking anodes, comprising the following steps:

[0090] Preparation of biochar: A certain amount of coconut shells were placed in an oven and dried at 120°C for 10 h. The dried corn stalks were crushed and placed in a corundum crucible and carbonized in an atmosphere furnace for 4 h. The carbonized corn stalks were placed in a silicon-molybdenum furnace and calcined at a heating rate of 3°C / min, a calcination temperature of 1300°C, and a holding time of 3 h.

[0091] Deashing of biochar: Take 300g of carbonized raw material, put it into a polytetrafluoroethylene beaker, add 3000ml of 4mol / l sulfuric acid, stir at room temperature for 10h, the speed is 280rpm, and after stirring, wash the raw material with deionized water to neutrality. Then add the acid-washed raw material into a polytetrafluoroethylene beaker, add 3000ml of 0.2wt% calcium hydroxide solution, stir at 60℃ for 8h, the speed is 240rmp, after stirring, wash the raw material with deionized water to neutrality, and dry to obtain deashed biochar.

[0092] Raw material dry material: weigh 27 parts of 8-5mm calcined petroleum coke, 18 parts of 5-2mm calcined petroleum coke, 18 parts of 2-0.3mm calcined petroleum coke, and 37 parts of fine powder biochar, put them into a mixer and mix them evenly.

[0093] Anode preparation: 87 parts of dry material were placed in a kneader, followed by 13 parts of coal tar pitch, and kneaded at 170°C for 15 minutes to obtain a paste. The paste was placed in a mold and pressed using a pressure of 450 kN to obtain a green anode.

[0094] Anode baking: The prepared anode is cooled to room temperature, and then placed in a baking furnace for baking. The temperature is raised from room temperature to 250°C at a heating rate of 5°C / h; raised to 650°C at a heating rate of 2.5°C / h; raised to 950°C at a heating rate of 4°C / h; and raised to 1150°C at a heating rate of 5°C / h. The temperature is kept at 1150°C for 55 hours. After baking, the temperature is slowly lowered to 200-300°C, and the pre-baked anode is taken out of the furnace.

[0095] Example 3

[0096] This embodiment provides a method for preparing biochar and using it for prebaking anodes, comprising the following steps:

[0097] Preparation of biochar: Take a certain amount of ginkgo leaves and put them into an oven, dry them at 120℃ for 10 hours, crush the dried corn straw and put them into a corundum crucible, and carbonize them in an atmosphere furnace for 4 hours. Put the carbonized corn straw into a silicon-molybdenum furnace and calcine it with a heating rate of 3℃ / min, a calcination temperature of 1300℃, and a holding time of 3 hours.

[0098] Deashing of biochar: Take 300g of carbonized raw material, put it into a polytetrafluoroethylene beaker, add 3000ml of 4mol / l hydrofluoric acid, stir at room temperature for 11h, the speed is 280rpm, and after stirring, wash the raw material with deionized water to neutrality. Then add the acid-washed raw material into a polytetrafluoroethylene beaker, add 3000ml of 0.2wt% potassium hydroxide solution, stir at 70℃ for 8h, the speed is 210rmp, after stirring, wash the raw material with deionized water to neutrality, and dry to obtain deashed biochar.

[0099] Raw material dry material: weigh 25 parts of 8-5mm calcined petroleum coke, 21 parts of 5-2mm calcined petroleum coke, 18 parts of 2-0.3mm calcined petroleum coke, and 36 parts of fine powder biochar, put them into a mixer and mix them evenly.

[0100] Anode preparation: 86 parts of dry material were placed in a kneader, followed by 14 parts of coal tar pitch, and kneaded at 165°C for 20 minutes to obtain a paste. The paste was placed in a mold and pressed using a pressure of 480 kN to obtain a green anode.

[0101] Anode baking: The prepared anode is cooled to room temperature, and then placed in a baking furnace for baking. The temperature is raised from room temperature to 250°C at a heating rate of 4°C / h; raised to 650°C at a heating rate of 3°C / h; raised to 950°C at a heating rate of 3°C / h; raised to 1150°C at a heating rate of 4°C / h; kept at 1150°C for 50h; after baking, the temperature is slowly lowered to 200-300°C, and the prebaked anode is taken out of the furnace.

[0102] Example 4

[0103] This embodiment provides a method for preparing biochar and using it for prebaking anodes, comprising the following steps:

[0104] Preparation of biochar: A certain amount of coconut shells and ginkgo leaves were placed in an oven and dried at 120°C for 10 h. The dried corn straw was crushed and placed in a corundum crucible and carbonized in an atmosphere furnace for 4 h. The carbonized corn straw was placed in a silicon-molybdenum furnace and calcined at a heating rate of 3°C / min, a calcination temperature of 1300°C, and a holding time of 3 h.

[0105] Biochar deashing: Take 300g of carbonized raw material, put it into a polytetrafluoroethylene beaker, add 4mol / l hydrofluoric acid and 3000ml of nitric acid, stir at room temperature for 12h, the speed is 300rpm, and after stirring, wash the raw material with deionized water to neutrality. Then add the pickled raw material into a polytetrafluoroethylene beaker, add 0.2wt% barium hydroxide and 3000ml of sodium hydroxide solution, stir at 80℃ for 10h, the speed is 260rmp, after stirring, wash the raw material with deionized water to neutrality, and dry to obtain deashed biochar.

[0106] Raw material dry material: weigh 29 parts of 8-5mm calcined petroleum coke, 17 parts of 5-2mm calcined petroleum coke, 22 parts of 2-0.3mm calcined petroleum coke, and 32 parts of fine powder biochar, put them into a mixer and mix them evenly.

[0107] Anode preparation: 84 parts of dry material were placed in a kneader, followed by 16 parts of coal tar pitch, and kneaded at 170°C for 20 minutes to obtain a paste. The paste was placed in a mold and pressed with a pressure of 500 kN to obtain a green anode.

[0108] Anode baking: The prepared anode is cooled to room temperature, and then placed in a baking furnace for baking. The temperature is raised from room temperature to 250°C at a heating rate of 3°C / h; raised to 650°C at a heating rate of 3°C / h; raised to 950°C at a heating rate of 4°C / h; and raised to 1150°C at a heating rate of 5°C / h. Keep the temperature at 1150°C for 48 hours. After baking, slowly cool down to 200-300°C and take the prebaked anode out of the furnace.

[0109] Example 5

[0110] This embodiment provides a method for preparing biochar and using it for prebaking anodes, comprising the following steps:

[0111] Preparation of biochar: Take a certain amount of wheat straw and put it into an oven, dry it at 120℃ for 10h, crush the dried corn straw and put it into a corundum crucible, and carbonize it in an atmosphere furnace for 4h. Put the carbonized corn straw into a silicon-molybdenum furnace and calcine it with a heating rate of 3℃ / min, a calcination temperature of 1300℃, and a holding time of 3h.

[0112] Deashing of biochar: Take 300g of carbonized raw material, put it into a polytetrafluoroethylene beaker, add 3000ml of 4mol / l nitric acid, stir at room temperature for 11h, the speed is 300rpm, and after stirring, wash the raw material with deionized water to neutrality. Then add the pickled raw material into a polytetrafluoroethylene beaker, add 3000ml of 0.2wt% calcium hydroxide and sodium hydroxide solution, stir at 80℃ for 9h, the speed is 240rmp, after stirring, wash the raw material with deionized water to neutrality, and dry to obtain deashed biochar.

[0113] Raw material dry material: weigh 28 parts of 8-5mm calcined petroleum coke, 18 parts of 5-2mm calcined petroleum coke, 19 parts of 2-0.3mm calcined petroleum coke, and 35 parts of fine powdered biochar, put them into a mixer and mix them evenly.

[0114] Anode preparation: 86 parts of dry material were placed in a kneader, followed by 14 parts of coal tar pitch, and kneaded at 175°C for 15 minutes to obtain a paste. The paste was placed in a mold and pressed using a pressure of 400 kN to obtain a green anode.

[0115] Anode baking: The prepared anode is cooled to room temperature, and then placed in a baking furnace for baking. The temperature is raised from room temperature to 250°C at a heating rate of 5°C / h; raised to 650°C at a heating rate of 2°C / h; raised to 950°C at a heating rate of 5°C / h; raised to 1150°C at a heating rate of 4°C / h; kept at 1150°C for 55h; after baking, the temperature is slowly lowered to 200-300°C, and the pre-baked anode is taken out of the furnace.

[0116] Comparative Example

[0117] This comparative example provides a method for preparing a prebaked anode using pure calcined petroleum coke as a raw material, comprising the following steps:

[0118] Raw material dry material: weigh 28 parts of 8-5mm calcined petroleum coke, 18 parts of 5-2mm calcined petroleum coke, 19 parts of 2-1mm calcined petroleum coke, and 35 parts of fine powder calcined petroleum coke, put them into a mixer and mix them evenly.

[0119] Anode preparation: 85 parts of dry material were placed in a kneader, followed by 15 parts of coal tar pitch. The mixture was kneaded at 175°C for 15 minutes to obtain a paste. The paste was placed in a mold and pressed using a pressure of 400 kN to obtain a green anode.

[0120] Anode baking: The prepared anode is cooled to room temperature, and then placed in a baking furnace for baking. The temperature is raised from room temperature to 250°C at a heating rate of 5°C / h; raised to 650°C at a heating rate of 2°C / h; raised to 950°C at a heating rate of 5°C / h; raised to 1150°C at a heating rate of 4°C / h; kept at 1150°C for 55h; after baking, the temperature is slowly lowered to 200-300°C, and the pre-baked anode is taken out of the furnace.

[0121] The performance of the prebaked anodes obtained in Examples 1 to 5 and the comparative example was measured, and the results are shown in Table 1.

[0122] Table 1 Performance indicators of prebaked anodes of Examples 1 to 5 and Comparative Examples

[0123] Group <![CDATA[Volume density g / cm 3 > Resistivity / μΩ·m Ash / % Air reaction residual rate / % Example 1 1.57 56.7 0.35 67.72 Example 2 1.57 56.6 0.36 67.56 Example 3 1.58 55.8 0.34 67.37 Example 4 1.58 55.9 0.37 67.68 Example 5 1.57 55.6 0.35 67.57 Comparative Example 1.56 57.1 0.33 66.09

[0124] As shown in Table 1, the bulk density of the prebaked anodes of Examples 1 to 5 is 1.57 g / cm 3 ~1.58g / cm 3 The resistivity is 55.6μΩ·m~56.7μΩ·m, the ash content is 0.34%~0.37%, and the air reaction residual rate is 67.3%~67.8%. The quality of the prebaked anodes of Examples 1~5 is better than that of the comparative example, indicating that the quality of the prebaked anodes prepared by using biomass carbon instead of calcined petroleum coke powder can effectively improve the quality of the prebaked anodes.

[0125] In addition, one or more technical solutions in the embodiments of the present application have at least the following technical effects or advantages:

[0126] In the embodiments of the present application, in order to address the problems of poor raw materials for existing aluminum carbon anode production, poor quality of carbon anodes, and insufficient high-quality raw materials, biomass carbon is used to replace part of the calcined coke to prepare the anode, which can effectively improve the quality of the prebaked anode, solve the problem of insufficient anode raw materials, provide a guarantee for the production of high-quality anodes, and has good application prospects.

[0127] In the embodiments of the present application, agricultural / forestry waste is converted into anode raw materials, reducing dependence on petroleum coke and achieving high-value utilization of biomass waste.

[0128] In the embodiments of the present application, the addition of biochar improves the volume density and air oxidation resistance of the anode, and the resistivity is close to the level of traditional anodes, meeting the needs of the electrolytic aluminum industry.

[0129] In the embodiments of the present application, the biomass raw material cost is low, and the deashing process reduces impurity emissions, which is more economical and environmentally friendly than traditional anode preparation.

[0130] 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 method for preparing a prebaked anode based on biochar, the method comprising: Drying and crushing the biomass raw materials to obtain pretreated biomass; The pretreated biomass is subjected to low-temperature carbonization and high-temperature calcination to obtain a biomass charcoal raw material; The biochar raw material is subjected to acid treatment and alkali treatment to perform deashing treatment to obtain deashed biochar; The deashed biochar, calcined petroleum coke and coal tar pitch are sequentially mixed, pressed and calcined to obtain a prebaked anode; The ash content of the deashed biochar is ≤0.5%, and the mass ratio of the deashed biochar, the calcined petroleum coke and the coal tar pitch is (30-50):(40-60):(10-20).

2. The method according to claim 1, characterized in that The low-temperature carbonization includes the following parameters: carbonization temperature is 520° C. to 570° C., heating rate is 1° C. / min to 2° C. / min, and carbonization time is 3 h to 5 h.

3. The method according to claim 1, characterized in that The high-temperature calcination includes the following parameters: a heating rate of 2° C. / min to 5° C. / min, a calcination temperature of 1250° C. to 1350° C., and a holding time of 2 hours to 4 hours.

4. The method according to claim 1, wherein The alkali treatment adopts mixing and stirring of biomass carbon raw materials and alkali solution, the concentration of the alkali solution is 0.1% to 0.3%, and the alkali solution includes: one or more of sodium hydroxide, potassium hydroxide, calcium hydroxide and barium hydroxide.

5. The method according to claim 4, characterized in that The mixing and stirring of the biochar raw material and the alkali solution includes the following parameters: a stirring temperature of 50° C. to 80° C., a stirring speed of 150 rpm to 260 rpm, and a stirring time of 6 h to 10 h.

6. The method according to claim 1, characterized in that The acid treatment adopts mixing and stirring of biochar raw materials and acid solution, the concentration of the acid solution is 3mol / L to 5mol / L, and the acid solution includes one or more of hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid and perchloric acid.

7. The method according to claim 6, characterized in that The mixing and stirring of the biochar raw material and the acid solution includes the following parameters: the stirring temperature is room temperature, the stirring speed is 200 rpm to 300 rpm, and the stirring time is 8 hours to 12 hours.

8. The method according to claim 1, characterized in that The particle size of the deashed biochar is ≤0.3 mm.

9. The method according to claim 1, characterized in that The biomass raw materials include: one or more of crop straw, forestry waste and fruit shells.

10. A prebaked anode prepared by the method according to any one of claims 1 to 9, wherein the prebaked anode meets the following properties: a bulk density of 1.57 g / cm 3 ~1.58g / cm 3 , the resistivity is 55.6μΩ·m~56.7μΩ·m, the ash content is 0.34%~0.37%, and the air reaction residual rate is 67.3%~67.8%.

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