Aluminum electrolysis anode carbon block with gradient biochar-ceramic composite permeable layer and preparation method of aluminum electrolysis anode carbon block

Abstract

The invention discloses an aluminum electrolysis anode carbon block with a gradient biochar-ceramic composite permeable layer and a preparation method of the aluminum electrolysis anode carbon block, and relates to the technical field of anode carbon blocks for electrolysis. Constructing a gradient permeable layer in the primary pores in the surface of the anode carbon block; the gradient permeable layer comprises an Al2O3-biochar composite layer and a graphite-biochar composite layer which are sequentially arranged from the surface of the anode carbon block to the inside, and the Al2O3-biochar composite layer is located within the depth range of 0-5 mm away from the surface of the anode carbon block and comprises 25-30 wt% of silane modified nano Al2O3 with the particle size of 50-100 nm, 15-20 wt% of biochar and the balance of water. The balance is furfural resin derived carbon; the graphite-biochar composite layer is positioned in a depth range of 5-10mm away from the surface of the anode carbon block, and comprises the following components: 50-55wt% of sulfonated graphite, 5-8wt% of biochar and the balance of 0.05-0.2 wt% of nano-diamond modified carbon. The oxidation consumption rate of the carbon material is effectively reduced, the service life of the anode carbon block is prolonged, the period of replacing the anode carbon block is prolonged, and the operation cost of the electrolytic cell is saved.

Description

Technical Field

[0001] The present invention relates to the technical field of anode carbon blocks for electrolysis, and particularly to an aluminum electrolysis anode carbon block with a gradient bio-carbon - ceramic composite penetration layer and a preparation method thereof. Background Art

[0002] In the aluminum electrolysis industry, the anode carbon block is in a high-temperature, strongly corrosive and oxidative environment for a long time. Traditional petroleum coke-based carbon blocks have problems such as poor oxidation resistance, thermal shock cracking, and uneven current distribution. Existing technologies have been improved by using ceramic coatings or gradient pore structures, but the coatings are prone to peeling, the pore connectivity rate is low, and it is difficult to balance conductivity and oxidation resistance. In particular, the interfacial bonding strength between the ceramic layer and the carbon matrix is insufficient, and the mismatch of thermal expansion coefficients leads to interfacial stress concentration, seriously affecting the service life of the anode and the electrolysis efficiency.

[0003] To solve the above problems, existing technologies have tried methods such as supercritical fluid penetration and bio-carbon composite, but there are still defects such as inaccurate control of penetration depth and poor interfacial compatibility between bio-carbon and graphite. For example, the supercritical penetration technology is difficult to precisely control the thickness of the composite layer, resulting in performance fluctuations; although bio-carbon can improve the reaction activity, its bonding force with the graphite matrix is weak, and interlayer peeling is likely to occur. These problems limit the application of anode carbon blocks in high-efficiency aluminum electrolysis, and there is an urgent need to develop new composite structures to improve comprehensive performance. Summary of the Invention

[0004] Aiming at the deficiencies of the above existing technologies, the present invention provides an aluminum electrolysis anode carbon block with a gradient bio-carbon - ceramic composite penetration layer and a preparation method thereof. Through the gradient bio-carbon - ceramic composite penetration layer and an optimized preparation process, a breakthrough improvement in the performance of the anode carbon block is achieved.

[0005] The specific technical solutions are as follows:

[0006] In the first aspect, the present invention discloses an aluminum electrolysis anode carbon block with a gradient bio-carbon - ceramic composite penetration layer, and a gradient penetration layer is constructed in the primary pores on the surface of the anode carbon block; the gradient penetration layer includes an Al2O3 - bio-carbon composite layer and a graphite - bio-carbon composite layer arranged in sequence from the surface of the anode carbon block to the inside, where:

[0007] The Al2O3 - bio-carbon composite layer is located within a depth range of 0 - 5 mm from the surface of the anode carbon block, and its composition includes: 25 - 30 wt% of silane-modified nano-Al2O3 with a particle size of 50 - 100 nm, 15 - 20 wt% of bio-carbon, and the balance is furfural resin-derived carbon; structural parameters: filling rate 85 - 88%, and the proportion of directionally connected pores with a pore diameter of 5 - 20 μm ≥ 80%;

[0008] The graphite-biochar composite layer is located within a depth range of 5-10 mm from the surface of the anode carbon block, and its composition includes: 50-55 wt% sulfonated graphite, 5-8 wt% biochar, and the balance is 0.05-0.2 wt% nanodiamond-modified carbon; the structural parameters are: the filling rate is 85-90%, and the porosity is 10-15%;

[0009] The interfacial bonding strength between the two layers is ≥15 MPa, and the difference in thermal expansion coefficient is ≤2.5×10 -6 / °C.

[0010] Further in the above solution, the Al2O3-biochar composite layer is formed by supercritical CO2 penetration.

[0011] Further in the above solution, the graphite-biochar composite layer is infiltrated using a CO2-ethanol mixed carrier.

[0012] Further in the above solution, the biochar is derived from the high-temperature pyrolysis product of straw or wood chips, and after ball milling, the particle size distribution is D50 = 1.2 μm and D90 = 3.5 μm.

[0013] In a second aspect, the present invention also discloses a preparation method of an aluminum electrolysis anode carbon block with a gradient biochar-ceramic composite infiltration layer, including:

[0014] Matrix pretreatment, the anode carbon block matrix is sequentially subjected to laser activation treatment and pore expansion treatment;

[0015] Surface infiltration and pre-sintering, injecting the Al2O2-biochar slurry into the pores through a supercritical CO2 carrier at a flow rate of 0.5-1.0 m / s, after maintaining the pressure for 120-180 min, pre-sintering at 500-600 °C for 1-2 h;

[0016] Transition layer infiltration and curing, infiltrating the graphite-biochar slurry using a pulse infiltration process, and curing at 400-500 °C for 1.5-3 h;

[0017] Gradient sintering, keeping the temperature at 800 °C for 2 h to achieve the interfacial bonding between the surface layer and the transition layer; then raising the temperature to 1250 °C and keeping it for 2 h to complete the densification of the composite layer; finally, performing carbon deposition treatment in a CH4 / H2 atmosphere;

[0018] Cooling, when the temperature of the anode carbon block is above 600 °C, the cooling rate is 5-8 °C / min; when the temperature is below 600 °C, the cooling rate is 10-15 °C / min.

[0019] Further in the above solution, the pore expansion treatment is plasma cleaning treatment.

[0020] Further, in the above solution, the pulse penetration process parameters are as follows: a cycle period of pressurization for 10 s / pressure relief for 5 s, repeated 50 times.

[0021] Further, in the above solution, after the plasma reaming treatment, the pore characteristics of the anode carbon block satisfy: the proportion of pores with a pore diameter of 10 - 50 μm is ≥ 40%; the proportion of pores with a pore diameter of 1 - 10 μm is 50 - 70%.

[0022] Further, in the above solution, the supercritical CO2 penetration pressure is 15 - 20 MPa, and the temperature is 40 - 50 °C.

[0023] Further, in the above solution, 0.1 - 0.3 wt% of KH-550 silane coupling agent is added to the graphite - biocarbon slurry, and 0.05 - 0.2 wt% of nanodiamond suspension is injected during the last 5 - 10 pressure cycles. The particle size of the nanodiamond suspension is 20 - 50 nm.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] By setting an Al2O3 - biocarbon composite layer on the surface layer of the anode carbon block, the present invention significantly improves the antioxidant performance of the anode carbon block surface, effectively reduces the oxidation consumption rate of the carbon material, increases the service life of the anode carbon block, extends the period of replacing the anode carbon block, and saves the operation cost of the electrolytic cell.

[0026] By optimizing the matching of the thermal expansion coefficient through the structure of the gradient penetration layer, the present invention greatly improves the thermal shock resistance of the anode and reduces the generation of cracks caused by temperature fluctuations.

[0027] By means of the graphite - biocarbon composite layer, the present invention ensures good electrical conductivity. At the same time, the introduction of nanodiamonds further reduces the contact resistance and realizes uniform current distribution; as a result, the service life of the anode carbon block in a large - current electrolytic cell with 500 - 800 kA is significantly extended, the consumption rate is reduced, and the number of thermal shock cycles is increased. Description of the Drawings

[0028] Figure 1 is a schematic diagram of the structure of the gradient biocarbon - ceramic composite penetration layer of the present invention;

[0029] Figure 2 is the process flow of the preparation method of the present invention. Detailed Embodiments

[0030] The following further describes the embodiments of the invention in detail with reference to the accompanying drawings of the specification, so as to more clearly present the purpose, technical solution and technical effect of the present invention.

[0031] As Figure 1As shown in the figure, the present invention discloses an aluminum electrolysis anode carbon block with a gradient biochar-ceramic composite permeable layer, and a gradient permeable layer is constructed in the primary pores on the surface of the anode carbon block 1; the gradient permeable layer includes an Al2O3-biochar composite layer 2 and a graphite-biochar composite layer 3 arranged in sequence from the surface of the anode carbon block to the inside, where: the Al2O3-biochar composite layer 2 is located within a depth range of 0-5 mm from the surface of the anode carbon block 1, and its composition includes: 25-30 wt% of silane-modified nano-Al2O3 with a particle size of 50-100 nm, 15-20 wt% of biochar, and the balance is furfural resin-derived carbon; structural parameters: filling rate 85-88%, the proportion of oriented connected pores with a pore diameter of 5-20 μm ≥ 80%. The graphite-biochar composite layer 3 is located within a depth range of 5-10 mm from the surface of the anode carbon block 1, and its composition includes: 50-55 wt% of sulfonated graphite, 5-8 wt% of biochar, and the balance is 0.05-0.2 wt% of nano-diamond modified carbon; structural parameters: filling rate 85-90%, porosity 10-15%. The interfacial bonding strength between the two layers ≥ 15 MPa, and the difference in thermal expansion coefficient ≤ 2.5×10 -6 / °C.

[0032] In the above solution, a composite permeable layer that gradually changes from the outside to the inside is constructed on the surface of the anode carbon block. The outer layer is mainly composed of Al2O3-biochar to provide antioxidant protection, and the inner layer is mainly composed of graphite-biochar to ensure electrical conductivity. Through the synergistic effect of silane-modified nano-Al2O3 and biochar with a specific particle size, dense filling and pore connection of the composite layer are achieved. The introduction of the nano-SiC transition layer effectively regulates the difference in thermal expansion coefficient between different material layers and ensures the interfacial bonding strength.

[0033] Specifically, the Al2O3-biochar composite layer is located within the depth range of 0 - 5 mm from the surface of the anode carbon block. In the composition of this composite layer, 25 - 30 wt% of silane-modified nano-Al2O3 with a particle size of 50 - 100 nm plays a key role. Silane modification can improve the compatibility of nano-Al2O3 with other components, and its nano-scale particle size endows it with a large specific surface area, which can effectively enhance the mechanical properties and chemical stability of the composite layer. 15 - 20 wt% of biochar is derived from the high-temperature pyrolysis products of straw or wood chips, and after ball milling, its particle size distribution is D50 = 1.2 μm and D90 = 3.5 μm. Biochar has good electrical conductivity and certain flexibility, which can improve the electrical conductivity of the composite layer, and its unique microstructure helps to form pore channels in the composite layer. The balance is furfural resin-derived carbon, which acts as a binder to firmly bind nano-Al2O3 and biochar together to form a stable composite structure. In terms of the structural parameters of this composite layer, a filling rate of 85 - 88% ensures a high density of the composite layer and reduces pore defects; the proportion of oriented connected pores with a pore size of 5 - 20 μm is ≥80%. These oriented connected pores are conducive to the discharge of gas during the aluminum electrolysis process, preventing the accumulation of gas inside the anode carbon block and resulting in increased pressure, thereby improving the stability of the anode carbon block. At the same time, it also helps the penetration of the electrolyte and promotes the progress of the electrochemical reaction. This composite layer is formed by supercritical CO2 penetration. Supercritical CO2 has the characteristics of high density of liquid, high diffusivity and low viscosity of gas, and can carry the Al2O3-biochar slurry to uniformly penetrate into the pores of the anode carbon block, ensuring the uniformity and integrity of the composite layer.

[0034] Specifically, the graphite-biochar composite layer is in the depth range of 5 - 10 mm from the surface of the anode carbon block. In its composition, 50 - 55 wt% is sulfonated graphite. Sulfonation treatment increases the hydrophilicity and reactivity of graphite, enabling it to better play the roles of electrical conduction and lubrication in the composite layer, reducing resistance and improving the current efficiency during the aluminum electrolysis process. 5 - 8 wt% of biochar further enhances the electrical conductivity and flexibility of the composite layer, synergistically acting with the biochar in the Al2O3-biochar composite layer. The balance is 0.05 - 0.2 wt% of nano-diamond modified carbon. Nano-diamond has extremely high hardness and wear resistance, and after modifying the carbon, it can significantly improve the wear resistance of the composite layer and extend the service life of the anode carbon block. The filling rate of this composite layer is 85 - 90%, ensuring the tightness of the structure, and the porosity is 10 - 15%. An appropriate porosity helps to store a certain amount of electrolyte and maintain the continuous progress of the electrochemical reaction. This composite layer is formed by CO2-ethanol mixed carrier penetration. The mixed system of CO2 and ethanol can adjust the viscosity and surface tension of the slurry, enabling the graphite-biochar slurry to more smoothly penetrate into the pores at the specified depth.

[0035] As Figure 2As shown in the figure, the present invention also discloses a preparation method of an aluminum electrolysis anode carbon block with a gradient biochar-ceramic composite permeable layer, including:

[0036] Matrix pretreatment stage: Select a specific anode carbon block matrix, first perform laser activation treatment on it, irradiate the surface of the anode carbon block with a high-energy laser beam to enable surface atoms to obtain sufficient energy to form active sites, enhancing the bonding force between the material and the infiltration slurry during subsequent processing. Immediately afterwards, pore expansion treatment is carried out. Here, a plasma cleaning treatment method is adopted. Place the anode carbon block in a plasma cleaning device, and the plasma in the device undergoes physical and chemical reactions with the impurities on the surface and inside the pores of the anode carbon block, removing impurities while expanding the pores. After plasma pore expansion treatment, the pore characteristics of the anode carbon block need to meet the standards of a pore diameter of 10 - 50μm with a pore proportion ≥ 40% and a pore diameter of 1 - 10μm with a pore proportion of 50 - 70%, creating suitable pore conditions for the effective infiltration of the subsequent slurry.

[0037] Surface layer infiltration and pre-sintering stage: After matrix pretreatment, enter the surface layer infiltration and pre-sintering link. Use supercritical CO2 as a carrier, fully mix supercritical CO2 with the Al2O3-biochar slurry, and inject the mixed slurry into the pores of the anode carbon block at a flow rate of 0.5 - 1.0m / s through a conveying device. The pressure during the supercritical CO2 infiltration process needs to be maintained at 15 - 20MPa, and the temperature is controlled at 40 - 50°C. Under this condition, keep the pressure for 120 - 180min to ensure that the Al2O3-biochar slurry uniformly and fully infiltrates into the pores. After the pressure holding ends, transfer the anode carbon block into a sintering furnace and pre-sinter it for 1 - 2h in the temperature range of 500 - 600°C to preliminarily solidify and form the Al2O3-biochar composite layer, enhancing the bonding stability between the composite layer and the anode carbon block matrix.

[0038] Transition layer infiltration and curing stage: Select a graphite-biochar slurry, add 0.1 - 0.3wt% of KH-550 silane coupling agent to it, and make it uniformly dispersed in the slurry by stirring and other methods. The silane coupling agent can improve the bonding performance between the graphite-biochar slurry and the pore wall. Use a pulse infiltration process to infiltrate this slurry. The specific parameters of the pulse infiltration process are a cycle period of pressurization for 10s / relief for 5s, and repeat this cycle 50 times. During the last 5 - 10 pressure cycles, inject a 0.05 - 0.2wt% nanodiamond suspension with a particle size of 20 - 50nm, and evenly distribute the nanodiamonds in the graphite-biochar composite layer by means of pulse pressure. After infiltration is completed, place the anode carbon block in a heating device and cure it at a temperature of 400 - 500°C for 1.5 - 3h to promote the curing and forming of the graphite-biochar composite layer and form a stable transition layer structure.

[0039] Gradient sintering stage: The anodic carbon block that has undergone the previous treatment is placed in a high-temperature sintering furnace. First, it is kept at a temperature of 800 °C for 2 h. During this process, physical and chemical processes such as atomic diffusion occur between the Al2O3-biochar composite layer on the surface and the graphite-biochar composite layer in the transition layer, realizing the interfacial bonding between the two and enhancing the bonding strength between the two layers. Then, the temperature of the sintering furnace is raised to 1250 °C and kept for 2 h. At this high temperature, the atoms inside the composite layer further diffuse and migrate, and the pores gradually decrease, completing the densification process of the composite layer and improving the overall density and strength of the material. Finally, the anodic carbon block is placed in a CH4 / H2 atmosphere for carbon deposition treatment. CH4 and H2 decompose at high temperature, and carbon atoms are deposited on the surface of the anodic carbon block and in the pores of the composite layer, further optimizing the microstructure and properties of the material.

[0040] Entering the cooling stage: The temperature of the anodic carbon block is monitored. When the temperature of the anodic carbon block is in the range above 600 °C, by controlling the flow rate of the cooling medium of the cooling equipment and other means, the cooling rate is maintained at 5 - 8 °C / min, and the temperature of the anodic carbon block is slowly reduced to avoid cracking of the material due to thermal stress caused by too rapid cooling. When the temperature of the anodic carbon block drops to the range below 600 °C, the cooling rate is appropriately increased, and the cooling rate is controlled at 10 - 15 °C / min until the anodic carbon block is cooled to room temperature, obtaining the finished product of the aluminum electrolysis anodic carbon block with a gradient biochar-ceramic composite penetration layer.

[0041] In practical applications, the anodic carbon block of the present invention has been successfully applied to 500 kA large aluminum electrolysis cells. Compared with traditional anodes, the voltage fluctuation range has been reduced by more than 10%, and the anode replacement cycle has been extended by 2 days. In continuous operation tests, the anode shows excellent thermal shock resistance. In addition, due to the introduction of biochar materials, this technology also has the advantages of wide raw material sources and controllable production costs, providing a new technical option for energy conservation and emission reduction in the aluminum electrolysis industry.

[0042] The above are only preferred and feasible embodiments of the present invention, and are not used to limit the scope of the patent application of the present invention. Any equivalent changes, equivalent substitutions or modification changes completed within the technical spirit and principles disclosed by the present invention shall be included within the scope of patent protection covered by the present invention.

Claims

1. An aluminum electrolysis anode carbon block with a gradient biochar-ceramic composite permeable layer, characterized in that: Construct a gradient penetration layer in the native pores on the surface of the anode carbon block; the gradient penetration layer includes an Al2O3-biochar composite layer and a graphite-biochar composite layer sequentially arranged from the surface of the anode carbon block to the inside, where: The Al2O3-biochar composite layer is located within a depth range of 0-5 mm from the surface of the anode carbon block, and its composition includes: 25-30 wt% of silane-modified nano-Al2O3 with a particle size of 50-100 nm, 15-20 wt% of biochar, and the balance is furfural resin-derived carbon; structural parameters: filling rate 85-88%, and the proportion of directionally connected pores with a pore size of 5-20 μm is ≥80%; The graphite-biochar composite layer is located within a depth range of 5-10 mm from the surface of the anode carbon block, and its composition includes: 50-55 wt% of sulfonated graphite, 5-8 wt% of biochar, and the balance is 0.05-0.2 wt% of nano-diamond modified carbon; structural parameters: filling rate 85-90%, and porosity 10-15%; The interfacial bonding strength between the two composite layers is ≥ 15 MPa, and the difference in coefficient of thermal expansion is ≤ 2.5×10 -6 / °C.

2. The aluminum electrolysis anode carbon block with a gradient biochar-ceramic composite permeable layer according to claim 1, characterized in that: The Al2O3-biochar composite layer is formed by supercritical CO2 penetration.

3. The aluminum electrolysis anode carbon block with a gradient bio-carbon-ceramic composite permeable layer according to claim 1, characterized in that: The graphite-biochar composite layer is infiltrated with a CO2-ethanol mixed carrier.

4. The aluminum electrolysis anode carbon block with a gradient biochar-ceramic composite permeable layer according to claim 1, characterized in that: The biochar is derived from the high-temperature pyrolysis product of straw or wood chips, and after ball milling, the particle size distribution is D50 = 1.2 μm and D90 = 3.5 μm.

5. A preparation method of an aluminum electrolysis anode carbon block with a gradient biochar-ceramic composite penetration layer, characterized in that: Matrix pretreatment, sequentially performing laser activation treatment and pore expansion treatment on the anode carbon block matrix; Surface layer infiltration and pre-sintering, injecting the Al2O2-biochar slurry into the pores at a flow rate of 0.5-1.0 m / s through a supercritical CO2 carrier, after maintaining the pressure for 120-180 min, pre-sintering at 500-600 °C for 1-2 h; Transition layer infiltration and curing, infiltrating the graphite-biochar slurry using a pulse infiltration process, and curing at 400-500 °C for 1.5-3 h; Gradient sintering, holding at 800 °C for 2 h to achieve the interfacial bonding between the surface layer and the transition layer; Then raise the temperature to 1250 °C and hold for 2 h to complete the densification of the composite layer; finally, perform carbon deposition treatment in a CH4 / H2 atmosphere; Cooling, when the temperature of the anode carbon block is above 600 °C, the cooling rate is 5-8 °C / min; when the temperature is below 600 °C, the cooling rate is 10-15 °C / min.

6. The preparation method of an aluminum electrolysis anode carbon block with a gradient biochar-ceramic composite permeable layer according to claim 5, characterized in that: The pore expansion treatment is plasma cleaning treatment.

7. The preparation method of an aluminum electrolysis anode carbon block with a gradient bio-carbon-ceramic composite permeable layer according to claim 5, characterized in that: The pulse infiltration process parameters are a cyclic period of pressurization for 10 s / depressurization for 5 s, repeated 50 times.

8. The preparation method of an aluminum electrolysis anode carbon block with a gradient biochar-ceramic composite permeable layer according to claim 5, characterized in that: After the plasma pore expansion treatment, the pore characteristics of the anode carbon block satisfy: the proportion of pores with a pore size of 10-50 μm is ≥40%; the proportion of pores with a pore size of 1-10 μm is 50-70%.

9. The preparation method of an aluminum electrolysis anode carbon block with a gradient biochar-ceramic composite permeable layer according to claim 5, characterized in that: The supercritical CO2 penetration pressure is 15-20 MPa, and the temperature is 40-50 °C.

10. The preparation method of an aluminum electrolysis anode carbon block with a gradient biochar-ceramic composite permeable layer according to claim 5, characterized in that: 0.1-0.3 wt% of KH-550 silane coupling agent is added to the graphite-biochar slurry, and a 0.05-0.2 wt% nano-diamond suspension with a particle size of 20-50 nm is injected during the last 5-10 pressure cycles.

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