Environmentally friendly carbon anode for aluminum electrolysis and preparation method thereof

Abstract

This invention discloses an environmentally friendly carbon anode for aluminum electrolysis and its preparation method. The carbon anode is composed of a binder and aggregates, the binder being bioasphalt, and the aggregates comprising biochar and petroleum coke. The weight percentages of the components in the carbon anode are: 15-20% bioasphalt, 10-15% biochar, and 70-75% petroleum coke. The carbon anode is manufactured by crushing, grinding, kneading, molding, calcining, and cooling the binder (bioasphalt) and aggregates (petroleum coke and biochar). Compared to existing technologies, this carbon anode for aluminum electrolysis uses bioasphalt as the binder instead of coal tar. This process eliminates asphalt fumes, improving the construction environment. Furthermore, the bioasphalt and aggregates bond well, reducing gaps between the binder and aggregate, thereby reducing carbon anode consumption in aluminum electrolysis. Biochar replaces part of the petroleum coke, increasing the coking value and improving the quality of the carbon anode.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum electrolysis, in particular to an environmentally friendly carbon anode for aluminum electrolysis and a preparation method thereof. Background Art

[0002] At present, the internationally common aluminum electrolysis technology uses carbon anodes to reduce alumina into primary aluminum in high-temperature molten salt, while emitting CO2. One ton of aluminum consumes about 0.4 tons of carbon anode material.

[0003] Carbon anodes are made of petroleum coke as aggregate and coal tar as binder. The use of petroleum coke and coal tar to prepare carbon anodes has the following disadvantages: (1) During the production process of carbon anodes, coal tar emits gas at high temperature. The more gas is emitted at high temperature, the lower the product yield is, resulting in great waste; (2) The gas emitted by carbonization causes a lot of pores to form in the finished product, and the porosity is high. During the aluminum electrolysis process, as the electrolysis proceeds, the carbon anode aggregate is oxidized and the electrolyte can easily penetrate into the pores, which undoubtedly accelerates the consumption of the anode and increases the production cost of the enterprise; (3) Coal tar emits harmful substances such as SO2 and CO2 at high temperature, which has an adverse effect on the working environment.

[0004] Therefore, how to prepare anodes with long life and environmental protection while ensuring conductive properties has become a top priority for the majority of aluminum metallurgical workers. Summary of the Invention

[0005] In order to address the deficiencies in the prior art, the present invention provides an environmentally friendly carbon anode for aluminum electrolysis and a preparation method thereof. Bio-asphalt is used instead of coal tar, and biochar is used instead of part of petroleum coke. The carbon anode is produced with bio-asphalt, biochar and petroleum coke as the main raw materials, thereby improving the quality of the carbon anode, increasing the service life of the carbon anode, and improving the production environment.

[0006] In order to achieve the above object, the specific scheme adopted by the present invention is:

[0007] An environmentally friendly carbon anode for aluminum electrolysis is composed of a binder and aggregate, wherein the binder is bio-asphalt, and the aggregate includes biochar and petroleum coke. The weight percentage of each component in the carbon anode is: 15-20% bio-asphalt, 10-15% biochar, and 70-75% petroleum coke, and the total mass percentage of all components is 100%.

[0008] As a preferred solution, the bio-asphalt is prepared by high-speed shear mixing of biomass oil and modified asphalt in liquid state.

[0009] As a preferred embodiment, the biomass oil is prepared by solvent-thermal liquefaction of lignocellulosic biomass to form a liquid product, and then vacuum distilling the liquid product.

[0010] As a preferred embodiment, the biochar is prepared by air-drying lignocellulosic biomass and then calcining it at high temperature.

[0011] As a preferred embodiment, the lignocellulosic biomass is one or more of straw, livestock manure, sawdust, waste wood and firewood.

[0012] As a preferred solution, the particle size of the biochar is 1-2 mm, the particle size of the petroleum coke is 2-6 mm, and the particle size of the bio-asphalt is 1-2 mm.

[0013] A method for preparing an environmentally friendly carbon anode for aluminum electrolysis mainly comprises the following steps:

[0014] S1. preparing bio-asphalt;

[0015] S2. Preparation of biochar

[0016] S21, air-drying the lignocellulosic biomass;

[0017] S22, calcining the air-dried lignocellulosic biomass at 700°C for 2 h to obtain biochar;

[0018] S3, crushing and grinding the bio-asphalt, biochar and petroleum coke to target particle sizes respectively;

[0019] S4. Preparation of anode

[0020] S41. Weigh bioasphalt, biochar, and petroleum coke according to the above proportions, dry-mix the biochar and petroleum coke to obtain a mixture, and preheat the mixture and bioasphalt separately;

[0021] S42, placing the preheated mixture and bio-asphalt in a Sigma-type double-blade kneader and kneading into a paste;

[0022] S43, taking the paste out of the pot, cooling it to the forming temperature, and pressing it into a green body;

[0023] S44. The green body embedded in the middle of the metallurgical coke powder is roasted and cooled to obtain a carbon anode.

[0024] As a preferred solution, in step S1, the specific method for preparing bio-asphalt is:

[0025] S11, placing lignocellulosic biomass into a reactor filled with an ethanol-ethylene glycol mixed solvent, adding 98% concentrated sulfuric acid as a catalyst, and heating the reactor to 475° C. at a heating rate of 5° C. / min to obtain a liquid product; vacuum filtering the liquid product, and performing reduced pressure distillation on the liquid product at a distillation temperature of 200° C. to separate the light component organic phase to obtain biomass oil;

[0026] S12, baking the modified asphalt at 155° C. to a fluid state, and keeping it at this temperature for later use;

[0027] S13. Keep the biomass oil at 165°C for 1 h, add the biomass oil to the beaker containing the modified asphalt, shear at high speed in an oil bath at 155°C for 30 min, and cool to room temperature to obtain bio-asphalt.

[0028] As a preferred embodiment, in step S44, the specific parameters of roasting are: heating to 110°C at a heating rate of 3.5°C / min, heating to 160°C at a heating rate of 1.7°C / min, heating to 200°C at a heating rate of 1.3°C / min, heating to 550°C at a heating rate of 0.15°C / min, heating to 620°C at a heating rate of 0.3°C / min, heating to 720°C at a heating rate of 0.8°C / min, heating to 1050°C at a heating rate of 1.25°C / min, and keeping warm at 1050°C for 1 hour.

[0029] As a preferred solution, in step S44, the specific cooling parameters are: cooling to 800°C at a cooling rate of 0.8°C / min, then cooling naturally, and when the temperature drops to 250-350°C, taking it out of the furnace and cooling it to room temperature.

[0030] Beneficial effects:

[0031] 1) The carbon anode of the present invention incorporates biochar during its preparation. Biochar has high C / H and C / O ratios, increases the quinoline-insoluble content and coking value of the carbon anode, reduces the porosity of the carbon anode, increases the density of the carbon anode, and improves the quality of the carbon anode. Furthermore, biochar partially replaces petroleum coke, a previous raw material for carbon anodes, reducing my country's oil import pressure and alleviating the oil shortage crisis caused by rapid industrial development. This effectively utilizes agricultural byproducts and reduces the cost of aluminum electrolysis.

[0032] 2) Bio-asphalt offers advantages such as sustainable renewable production, minimal environmental pollution during production, and improved performance of coal tar. This invention uses bio-asphalt instead of coal tar. Because bio-asphalt better wets petroleum coke and adheres to it, it reduces the porosity of the carbon anode, increases its density, and improves its quality. Replacing coal tar with bio-asphalt eliminates asphalt fumes during carbon anode production, improving the production environment.

[0033] 3) The present invention reduces the porosity of the carbon anode by using biochar and bioasphalt, thereby achieving the purpose of reducing the consumption of the carbon anode in the aluminum electrolysis process and correspondingly extending the service life of the anode.

[0034] 4) The binder of the carbon anode uses bio-asphalt instead of coal tar, and bio-char replaces part of the petroleum coke, which greatly improves the physical properties of the finished carbon anode. The volume density of the finished carbon anode is increased from the original 1.56g / cm 3 Increased to 1.68g / cm 3 The compressive strength increased from the original 31Mpa to about 36Mpa; the resistivity dropped from the original 68.26μΩ•m to 55.6μΩ•m. All indicators reached the national secondary standard, and most indicators reached the national first-level standard. DETAILED DESCRIPTION

[0035] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0036] An environmentally friendly carbon anode for aluminum electrolysis, comprising a binder and aggregate. The binder is bio-asphalt, and the aggregate comprises biochar and petroleum coke. The weight percentages of the components in the carbon anode are: 15-20% bio-asphalt, 10-15% biochar, and 70-75% petroleum coke, with the total weight percentage of all components being 100%. The biochar has a particle size of 1-2 mm, the petroleum coke has a particle size of 2-6 mm, and the bio-asphalt has a particle size of 1-2 mm.

[0037] The bio-asphalt is prepared by high-speed shear mixing of biomass oil and modified asphalt in liquid state, and the biomass oil is prepared by solvent thermal liquefaction of lignocellulosic biomass into a liquid product and then vacuum distillation of the liquid product.

[0038] The present invention uses bio-asphalt instead of coal tar, effectively avoiding the pollution of asphalt smoke to the working environment of aluminum electrolysis, realizing the rational utilization of waste biomass resources, saving non-renewable fossil resources, and conforming to the concept of low-carbon green metallurgy.

[0039] The biochar is prepared by air-drying lignocellulose biomass and then calcining it at high temperature.

[0040] In detail, the lignocellulosic biomass is one or more of straw, livestock manure, sawdust, waste wood and firewood.

[0041] The preparation method of the carbon anode mainly includes the following steps:

[0042] S1. Preparation of bio-asphalt

[0043] S11, placing lignocellulosic biomass into a reactor filled with an ethanol-ethylene glycol mixed solvent, adding 98% concentrated sulfuric acid as a catalyst, and heating the reactor to 475° C. at a heating rate of 5° C. / min to obtain a liquid product; vacuum filtering the liquid product, and performing reduced pressure distillation on the liquid product at a distillation temperature of 200° C. to separate the light component organic phase to obtain biomass oil;

[0044] S12, baking the modified asphalt at 155° C. to a fluid state, and keeping it at this temperature for later use;

[0045] S13, placing the biomass oil in an oven (165°C) for 1 hour, adding the biomass oil to a beaker containing the modified asphalt, high-speed shearing in an oil bath at 155°C for 30 minutes, and cooling to room temperature to obtain bio-asphalt;

[0046] S2. Preparation of biochar

[0047] S21, air-drying the lignocellulosic biomass;

[0048] S22, calcining the air-dried lignocellulosic biomass at 700°C for 2 h to obtain biochar;

[0049] S3, respectively crushing the bio-asphalt, bio-char and petroleum coke on a crusher and grinding them on a grinder to the particle size required for producing carbon anodes;

[0050] S4. Prepare a certain amount of aggregate (biochar and petroleum coke) according to the formula and particle size requirements, place them in a three-dimensional mixer and mix for 1 hour, then place them in a constant temperature oven and preheat them at 150°C for 10 hours, heat the binder to 170°C, and knead the dry material and binder in a Sigma-shaped double-blade kneader for 15-20 minutes at a kneading temperature of 155±5°C; take the hot paste out of the kneader, cool it to the molding temperature of 40~50°C, and use an oil press at a pressure of 8~10MPa to make a green body. The dried green sample was buried in a corundum crucible with at least 10 mm of filler (metallurgical coke powder) around the sample, and then placed in a muffle furnace for calcination in the following stages: 25-110 ° C, with a heating rate of 3.5 ° C / min. This stage is mainly to remove excess adsorbed water. At the same time, the bio-asphalt melts and migrates violently under the action of gravity, which can easily cause uneven distribution of the bio-asphalt in the sample. Therefore, the heating rate should be fast; 110-160 ° C, with a heating rate of 1.7 ° C / min n; 160℃-200℃, heating rate is 1.3℃ / min, 200℃-550℃, heating rate is 0.15℃ / min; 550℃-620℃, heating rate is 0.3℃ / min; 620℃-720℃, heating rate is 0.8℃ / min; adopting a smaller heating rate at 200℃-720℃ is conducive to the discharge of volatile matter in the raw materials; 720℃-1050℃, heating rate is 1.25℃ / min, and keep at 1050℃ for 1h. Cooling stage: cool to 800℃ at a cooling rate of 0.8℃ / min. The cooling speed should not be too fast to avoid cracks in the sample. Then cool naturally. When the temperature drops to 250-350℃, take it out of the furnace and cool it to room temperature to obtain the finished product.

[0051] Example 1

[0052] A carbon anode, wherein the weight percentages of the components in the carbon anode are: 17% bio-asphalt, 13% bio-char, and 70% petroleum coke.

[0053] The preparation method of the carbon anode mainly includes the following steps:

[0054] S1. Preparation of bio-asphalt

[0055] S11, taking an appropriate amount of sawdust and placing it in a reactor filled with an ethanol-ethylene glycol mixed solvent, adding 98% concentrated sulfuric acid as a catalyst, heating the reactor to 475° C. at a heating rate of 5° C. / min to obtain a liquid product, vacuum filtering the liquid product, and performing reduced pressure distillation on the liquid product at a distillation temperature of 200° C. to separate the light component organic phase to obtain biomass oil;

[0056] S12, drying the modified asphalt at 155°C until it is fluidized, and keeping it at this temperature for later use, keeping the biomass oil in the lower oven at 165°C for 1 hour, adding the biomass oil to the beaker containing the modified asphalt, shearing at high speed in an oil bath at 155°C for 30 minutes, and cooling to room temperature to produce bio-asphalt (the mass percentage concentrations of modified asphalt and biomass oil in the bio-asphalt are 18% biomass oil and 82% modified asphalt, respectively);

[0057] S2. Take a batch of sawdust and air-dry it under natural conditions for 1-2 weeks, calcine it in a muffle furnace at 700℃ for 2 hours, and cool it to room temperature to produce biochar;

[0058] S3, crushing the bio-asphalt, bio-char and petroleum coke on a crusher and grinding them on a grinder to 1-2 mm, 1-2 mm and 2-6 mm respectively;

[0059] S4. Take biochar and petroleum coke and mix them in a three-dimensional mixer for 1 hour. Then preheat the aggregate in a constant temperature oven at 150℃ for 10 hours, heat the binder to 170℃, and knead the aggregate and binder in a Sigma-shaped double-knife mixer for 20 minutes at a kneading temperature of 160℃. Take the hot paste out of the mixer and cool it to the molding temperature of 40℃. Use an oil press at a pressure of 8~10MPa to make a green body. Bury the dried green body sample in a metallurgical coke oven to ensure that there is at least 10mm of metallurgical coke around the sample. The powdered corundum crucible is placed in a muffle furnace and calcined in the following stages: 25-110°C, a heating rate of 3.5°C / min; 110°C-160°C, a heating rate of 1.7°C / min; 160°C-200°C, a heating rate of 1.3°C / min, 200°C-550°C, a heating rate of 0.15°C / min; 550°C-620°C, a heating rate of 0.3°C / min; 620°C-720°C, a heating rate of 0.8°C / min, 720°C-1050°C, a heating rate of 1.25°C / min, and kept at 1050°C for 1 hour. In the cooling stage, the temperature is cooled to 800°C at a cooling rate of 0.8°C / min, and then cooled naturally. When the temperature drops to 250-350°C, the product is taken out of the furnace and cooled to room temperature to obtain the product.

[0060] The carbon anode prepared by the present invention has the following indicators: resistivity 55.6μΩ•m, volume density 1.68×10 3 kg / m 3 , true density 2.06×10 3 kg / m 3 , ash content 0.76%, compressive strength 36Mpa, compared with the previous carbon anode indicators have been improved, and the cost is greatly reduced.

[0061] Therefore, the raw material for this carbon anode for aluminum electrolysis uses bio-asphalt as a binder instead of asphalt. This eliminates asphalt fumes during operation, improving the production environment. Furthermore, the bio-asphalt maintains a good bond with the aggregate, reducing gaps between the binder and the aggregate, thereby reducing carbon anode consumption during aluminum electrolysis. Biochar replaces some petroleum coke, increasing the coking value and improving the quality of the carbon anode for aluminum electrolysis.

[0062] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any equivalent changes or modifications made based on the essence of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing an environmentally friendly carbon anode for aluminum electrolysis, wherein the environmentally friendly carbon anode is composed of a binder and an aggregate, characterized in that: The binder is bio-asphalt, and the aggregate includes biochar and petroleum coke; the weight percentage of each component in the carbon anode is: bio-asphalt 15-20%, biochar 10-15%, petroleum coke 70-75%, and the total weight percentage of all components is 100%; The preparation method of the environmentally friendly carbon anode mainly includes the following steps: S1. preparing bio-asphalt; S11, placing the lignocellulosic biomass into a reactor filled with an ethanol-ethylene glycol mixed solvent, adding 98% concentrated sulfuric acid as a catalyst, and heating the reactor to 475° C. at a heating rate of 5° C. / min to obtain a liquid product; The liquid product is vacuum filtered and subjected to reduced pressure distillation at a distillation temperature of 200° C. to separate the light component organic phase to obtain biomass oil; S12, baking the modified asphalt at 155° C. to a fluid state, and keeping it at this temperature for later use; S13, keeping the biomass oil at 165°C for 1 hour, adding the biomass oil to the beaker containing the modified asphalt, high-speed shearing for 30 minutes in an oil bath at 155°C, and cooling to room temperature to obtain bio-asphalt; S2. Preparation of biochar S21, air-drying the lignocellulosic biomass; S22, calcining the air-dried lignocellulosic biomass at 700°C for 2 h to obtain biochar; S3, crushing and grinding the bio-asphalt, biochar and petroleum coke to target particle sizes respectively; S4. Preparation of anode S41. Weigh bioasphalt, biochar, and petroleum coke in proportion, dry-mix the biochar and petroleum coke to obtain a mixture, and preheat the mixture and bioasphalt separately; S42, placing the preheated mixture and bio-asphalt in a Sigma-type double-blade kneader and kneading into a paste; S43, taking the paste out of the pot, cooling it to the forming temperature, and pressing it into a green body; S44, calcining and cooling the green body embedded in the middle of the metallurgical coke powder to obtain a carbon anode; Among them, in step S44, the specific parameters of roasting are: heating to 110°C at a heating rate of 3.5°C / min, heating to 160°C at a heating rate of 1.7°C / min, heating to 200°C at a heating rate of 1.3°C / min, heating to 550°C at a heating rate of 0.15°C / min, heating to 620°C at a heating rate of 0.3°C / min, heating to 720°C at a heating rate of 0.8°C / min, heating to 1050°C at a heating rate of 1.25°C / min, and keeping at 1050°C for 1h.

2. The method for preparing an environmentally friendly carbon anode for aluminum electrolysis according to claim 1, characterized in that: The lignocellulosic biomass is one or more of straw, sawdust, and waste wood.

3. The method for preparing an environmentally friendly carbon anode for aluminum electrolysis according to claim 1, characterized in that: The particle size of the biochar is 1-2 mm, the particle size of the petroleum coke is 2-6 mm, and the particle size of the bio-asphalt is 1-2 mm.

4. The method for preparing an environmentally friendly carbon anode for aluminum electrolysis according to claim 1, characterized in that: In step S44, the specific parameters of cooling are: cooling to 800°C at a cooling rate of 0.8°C / min, then cooling naturally, and when the temperature drops to 250-350°C, taking it out of the furnace and cooling it to room temperature.