Multi-stage deep deashing method for coal-based porous carbon under assistance of external field
By employing a multi-stage acid washing process that combines mechanical ball milling and ultrasonic cavitation, the problem of ash removal from porous carbon after high-temperature activation was solved, achieving low-damage and highly efficient deep deashing and improving the electrochemical performance of the electrode material.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-26
- Publication Date
- 2026-04-10
AI Technical Summary
Existing technologies are unable to effectively remove the inorganic ash remaining in porous carbon after high-temperature activation, leading to a decline in electrochemical performance. Furthermore, traditional deashing methods are costly and environmentally burdensome.
A multi-stage pickling process combining mechanical ball milling and ultrasonic cavitation is adopted to physically break down the ash encapsulation structure and enhance the mass transfer process of chemical reagents in multi-stage channels, combined with low-concentration pickling solution for deep deashing.
This method achieves low-damage and efficient reduction of the ash content of porous carbon to below 0.5%, while maintaining the material's high specific surface area and pore structure, thus improving the electrochemical performance of the electrode material.
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Abstract
Description
TECHNICAL FIELD
[0001] The present application belongs to the technical field of porous carbon material preparation and electrochemical energy storage, and relates to a method for removing ash from coal-based porous carbon, in particular to a method for deeply removing inorganic ash from high-ash coal-based supercapacitor activated carbon by using physical external field (mechanical ball milling combined with ultrasonic cavitation) in cooperation with graded chemical cleaning. BACKGROUND
[0002] With the iteration and upgrading of green energy and advanced energy storage technology, supercapacitors have established their core position in the field of electrochemical energy storage due to their excellent power characteristics, extremely fast charge and discharge rate, and outstanding cycle stability. Currently, porous carbon is the most commercially available electrode active material, and coal, with its low cost and natural carbon-rich cross-linked network structure, has become an ideal precursor for preparing such high-performance electrodes. For the preparation of coal-based porous carbon, mature physical or chemical activation processes have been developed, i.e., using oxidizing atmospheres (such as CO2, water vapor) or chemical reagents (such as KOH, NaOH) to etch the carbon matrix, so as to build a high specific surface area of pore network, thereby improving the energy density of the device. However, the inherent mineral components such as alkali metals, alkaline earth metals, and silicate in raw coal are difficult to strip, and after undergoing thermal chemical conversion, they will remain in the material in the form of ash in a significant proportion. These ashes will induce irreversible side reactions during electrochemical operation, leading to the attenuation of coulombic efficiency; at the same time, they may catalyze the decomposition of electrolyte, and the deposits produced will block the pores, seriously hindering ion transport and storage, thereby degrading the comprehensive performance of the electrode material.
[0003] Currently, the mainstream of industrial deashing methods includes physical deashing and chemical deashing. Physical deashing methods (such as gravity separation, magnetic separation, flotation, etc.) mainly rely on the differences in density, magnetism or surface properties of coal and mineral matter for separation. However, such methods are mainly suitable for the preliminary purification of raw coal, and for porous carbon with high temperature activation, the separation efficiency is very low, which is difficult to meet the strict requirements of electrode materials for ash content (usually less than 0.5%). Chemical deashing method is to use inorganic acid or alkali solution to react with impurities to generate soluble salt and remove it. Although this method can effectively reduce the ash content, due to the developed pore structure of porous carbon, its deep deashing capacity still faces significant bottleneck: on the one hand, the complex internal topology of porous carbon hinders the full infiltration and diffusion of chemical reagents, making it difficult to effectively dissolve the impurities in the deep pores; on the other hand, part of the ash is densely wrapped by the carbon microcrystals reconstructed during high temperature activation, making it difficult for conventional liquid phase cleaning to reach. If the acid / alkali concentration, temperature or time is increased to achieve deep deashing effect, not only the reagent consumption and process cost will be greatly increased, but also the carbon structure will be damaged and the environmental burden will be serious. Therefore, developing a new process that can balance deashing effect, deashing efficiency, economy and environmental friendliness is of great significance to promote the practical application of coal-based high-performance electrode materials. SUMMARY
[0004] For natural coal-based precursors with high ash content, the present application provides a multi-stage deep deashing method for coal-based porous carbon assisted by external field. With the synergistic effect of physical external field (mechanical ball milling and ultrasonic cavitation), the ash wrapping structure is effectively broken and the mass transfer process of chemical reagents in multi-stage pores is strengthened without excessive damage to the carbon skeleton, thereby realizing deep and efficient deashing of high specific surface area coal-based porous carbon, meeting the strict requirements of supercapacitor electrode materials for ultra-low ash content, ensuring that the ash content of activated porous carbon is less than 0.5%, and avoiding the economic and environmental burden caused by single dependence on high-strength chemical cleaning.
[0005] The purpose of the present application is realized by the following technical scheme:
[0006] A multi-stage deep deashing method for coal-based porous carbon assisted by external field, comprising the following steps:
[0007] Step (1) water washing pretreatment: the coal-based porous carbon obtained after activation is water washed, wherein: the coal-based porous carbon is activated carbon for supercapacitors prepared by KOH, CO2 or steam (H2O2) activation method; deionized water is used for water washing, and stirring is carried out at room temperature until the washing liquid is neutral;
[0008] Step (2) ultrasonic-assisted primary acid washing: the water-washed coal-based porous carbon is mixed with an acid washing solution in a proportion, and is subjected to primary washing treatment under ultrasonic conditions, wherein: the acid washing solution adopts one or more combinations of nitric acid (HNO3), hydrochloric acid (HCl) or hydrofluoric acid (HF), the concentration of HNO3 is 2-5 mol L -1 , the concentration of HCl is 1-5 mol L -1 , and the mass fraction of HF is 1-10 wt.%; the frequency of ultrasonic is 20-40 kHz, the power density is 0.2-1.0 W cm -2 ; the washing temperature is 25-80℃, the washing time is 1-12 h, and the solid-liquid ratio is 1 g:20 ml;
[0009] Step (3) intermediate mechanical ball milling: the material after acid washing is subjected to short-time mechanical ball milling, wherein: the mechanical ball milling adopts a planetary ball mill, the ball-to-material mass ratio is 10:1-30:1, the rotating speed is 300-500 rpm, and the ball milling time is 5-60 min;
[0010] Step (4) ultrasonic-assisted deep acid washing: the material after ball milling is mixed with an acid washing solution again, and is subjected to second deep acid washing treatment under ultrasonic conditions, wherein: the acid washing solution adopts one or more combinations of nitric acid (HNO3), hydrochloric acid (HCl) or hydrofluoric acid (HF), the concentration of HNO3 is 2-5 mol L -1 , the concentration of HCl is 1-5 mol L -1 , the mass fraction of HF is 1-10 wt.%, and the solid-liquid ratio is 1 g:20 ml; the frequency of ultrasonic is 20-40 kHz, the power density is 0.2-1.0 W cm -2 ; the washing temperature is 25-80℃, and the washing time is 1-12 h;
[0011] Step (5) post-treatment: the solid-phase product after washing is fully washed with water to neutral, and then is dried to obtain a coal-based porous carbon material, wherein: the drying temperature is 80-120℃, and the drying time is 6-12 h.
[0012] Compared with the prior art, the present application has the following advantages:
[0013] (1) The present application proposes a multi-stage collaborative degreasing process of “ultrasonic acid washing-ball milling breaking-ultrasonic acid washing”, which realizes deep, efficient and low-damage purification of the coal-based porous carbon. The strong cavitation and vibration effect generated by ultrasonic treatment enhances the penetration and mass transfer efficiency of the acid washing solution in the complex pore channel, effectively removing most of the soluble ash on the surface and in the pore channel. The short-time mechanical ball milling step introduced in the middle can break the deep wrapping of the ash by the carbon layer through physical action, opening the closed pores blocked, and creating channels for subsequent deep cleaning.
[0014] (2) The present application significantly improves the efficiency of deashing, and is economical and environmentally friendly. Compared with the traditional single dependence on high-strength and long-time chemical deashing process, the present application can deeply remove the ash content of porous carbon to below 0.5% in lower pickling liquid concentration and shorter overall processing time through the synergistic reinforcement of coupling physical external field (ultrasound, ball milling). This greatly reduces the amount of chemical reagents used, energy consumption, and the cost of subsequent high-concentration waste liquid treatment, making the process more green and economical.
[0015] (3) The present application realizes deep deashing while effectively preserving the high specific surface area and hierarchical pore structure of the porous carbon material. By precisely controlling the strength and time of ball milling (such as rotation speed, ball-to-material ratio, and ball milling time), the mechanical damage to the carbon skeleton itself is minimized while effectively breaking up the ash inclusions. Therefore, the specific surface area retention rate of the treated material is ≥85%, and the total pore volume retention rate is ≥80%, ensuring the abundant active sites and efficient ion transport paths necessary for the material as an electrode material.
[0016] (4) The low-ash coal-based porous carbon obtained by the present application has a comprehensive and significant improvement in electrochemical performance. The extremely low ash content fundamentally eliminates problems such as side reactions, electrolyte decomposition, and pore blockage caused by inorganic impurities, thereby greatly reducing the ion diffusion resistance of the electrode. When used as a supercapacitor electrode, the material exhibits higher mass specific capacitance (≥110 F g -1 ) and ionic conductivity, thereby maintaining a higher capacitance retention rate at high current density, providing a key material basis for constructing high-performance and long-life energy storage devices. BRIEF DESCRIPTION OF DRAWINGS
[0017] Figure 1 is a schematic diagram of a multi-stage deep deashing method for coal-based porous carbon under the assistance of an external field;
[0018] Figure 2 is a comparison chart of deashing effects of coal-based porous carbon of Examples 1, 2 and Comparative Examples 1-5 and a water washing method only;
[0019] Figure 3 is a constant current charge-discharge curve of an organic supercapacitor constructed by the sample of Example 1;
[0020] Figure 4 is a Nyquist plot of an organic supercapacitor constructed by the sample of Example 1;
[0021] Figure 5 is the specific surface area of Examples 1 and Comparative Examples 1 and 2. DETAILED DESCRIPTION
[0022] The technical solutions of the present application are further described below with reference to the drawings, but are not limited thereto, and any modification or equivalent replacement of the technical solutions of the present application without departing from the spirit and scope of the present application shall be covered in the protection scope of the present application.
[0023] The present application provides a multi-stage deep deashing method for coal-based porous carbon under external field assistance, which innovatively combines mechanical ball milling with ultrasonic-assisted chemical cleaning, constructs a multi-stage synergistic process of "ultrasonic acid washing-ball milling-crushing-ultrasonic acid washing" based on mechanical treatment in the intermediate stage of acid washing, as shown in Figure 1 , specifically comprising the following steps:
[0024] Step (1) water washing pretreatment: water washing the coal-based porous carbon obtained after activation to remove a large amount of soluble alkaline substances on the surface, wherein: the coal-based porous carbon is activated carbon for supercapacitors prepared by KOH, CO2 or steam (H2O2) activation method, with a specific surface area ≥1000 m 2 g -1 ; deionized water is used for water washing, which is stirred at room temperature until the washing liquid is neutral.
[0025] Step (2) ultrasonic-assisted primary acid washing: mixing 1 g of coal-based porous carbon after water washing with 20 ml of acid washing solution and performing primary washing treatment under ultrasonic conditions, which preliminarily dissolves and removes most of the acid-soluble ash, wherein: the acid washing solution uses one or more combinations of nitric acid (HNO3), hydrochloric acid (HCl) or hydrofluoric acid (HF), the concentration of HNO3 is 2~5 mol L -1 , the concentration of HCl is 1~5 mol L -1 , and the mass fraction of HF is 1~10 wt.%; the frequency of ultrasonic cavitation treatment is 20~40 kHz, and the power density is 0.2~1.0 W cm -2 ; the washing temperature is 25~80℃, and the washing time is 1~12 h.
[0026] Step (3) intermediate mechanical ball milling: short-time mechanical ball milling of the material after acid washing to break the ash wrapped by carbon microcrystals and open the closed pores, wherein: the planetary ball mill is used for mechanical ball milling, the ball-to-material mass ratio is 10:1~30:1, the rotation speed is 300~500 rpm, and the ball milling time is 5~60 min.
[0027] Step (4) ultrasonic-assisted deep acid washing: the ball-milled material is mixed with acid washing solution again, and is subjected to a second deep acid washing treatment under ultrasonic conditions to remove residual ash exposed due to the destruction of the encapsulation structure, wherein: the acid washing solution uses one or more combinations of nitric acid (HNO3), hydrochloric acid (HCl) or hydrofluoric acid (HF), the concentration of HNO3 is 2-5 mol / L -1 , the concentration of HCl is 1-5 mol / L -1 , and the mass fraction of HF is 1-10 wt.%; the frequency of ultrasonic cavitation treatment is 20-40 kHz, and the power density is 0.2-1.0 W / cm -2 ; the washing temperature is 25-80°C, and the washing time is 1-12 h.
[0028] Step (5) post-treatment: the washed solid-phase product is washed with water until neutral, and then is dried to obtain a coal-based porous carbon material with extremely low ash content, wherein: the drying temperature is 80-120°C, and the drying time is 6-12 h.
[0029] The low-ash coal-based porous carbon material obtained by the above-mentioned multi-stage deep deashing method assisted by external fields has the following characteristics:
[0030] (1) Extremely low ash content: after the treatment by the method of the present application, the total ash content of the porous carbon is reduced to below 0.5%, and preferably reaches 0.1%-0.3%.
[0031] (2) Good structure retention: while achieving deep deashing, the pore structure and high specific surface area characteristics of the porous carbon skeleton can be effectively maintained. Compared with traditional treatment processes, the specific surface area retention rate is ≥85%.
[0032] (3) Excellent electrochemical performance: when the low-ash coal-based porous carbon is applied to supercapacitor electrode materials, the mass specific capacitance is ≥100 F / g -1 ; compared with high-ash porous carbon, the ion diffusion impedance is significantly reduced, thereby exhibiting more excellent rate performance.
[0033] Example 1:
[0034] First, water washing pretreatment is performed. The alkali-containing coal-based porous carbon material obtained after chemical activation is stirred and washed with a sufficient amount of deionized water at room temperature until the filtrate is neutral, and the preliminary purified product AC-1 is obtained after solid-liquid separation.
[0035] Subsequently, ultrasonic-assisted primary acid washing is performed. 10 g of AC-1 is transferred into a beaker containing a mixed acid solution of 200 mL of HCl (5 mol / L -1 ) and HF (10 wt.%), and is subjected to ultrasonic cavitation treatment at a frequency of 40 kHz and a power density of 0.5 W / cm -2Under ultrasonic conditions, the mixture was treated in a constant temperature water bath at 60℃ for 3 hours. After the treatment, the mixture was centrifuged and the collected solid material was recorded as AC-2.
[0036] Next, intermediate mechanical ball milling was performed. AC-2 was transferred into a planetary ball mill, using zirconia balls as grinding balls, with a ball-to-material mass ratio of 20:1, and ball milled at 400 rpm for 20 min to obtain product AC-3.
[0037] Then, ultrasonic-assisted deep acid washing was performed. AC-3 was immersed again in an HCl-HF mixed acid solution, with all treatment conditions the same as the primary acid washing step, to thoroughly remove the residual ash newly exposed due to the destruction of the encapsulation structure, yielding product AC-4.
[0038] Finally, post-processing was performed. The deeply acid-washed AC-4 was repeatedly washed with deionized water with stirring until the filtrate was neutral to completely remove residual acid and soluble ions. The washed material was then dried in a drying oven at 100°C for 10 hours to obtain the final low-ash coal-based porous carbon sample, denoted as LA-AC-1.
[0039] through Figures 2-5 Tests showed that the ash content of LA-AC-1 decreased to 0.18%, and the specific surface area was 1752 m². 2 g -1 When used as an electrode in an organic supercapacitor, at 1 A·g -1 The following value is 127.4 F·g -1 It has a higher specific capacitance and a lower ion diffusion impedance.
[0040] Example 2:
[0041] The difference between this embodiment and Embodiment 1 is that only the pickling solution system was adjusted to 200 mL and 5 mol / L. -1 The low-ash coal-based porous carbon sample was obtained by using an HCl solution with other parameters remaining unchanged. The final sample was denoted as LA-AC-2.
[0042] through Figure 2 The tests showed that the ash content of LA-AC-2 was 0.21%. Compared with LA-AC-1 obtained in Example 1 (using HCl-HF mixed acid), its ash content was slightly higher. This was attributed to the absence of HF in the pickling solution, resulting in relatively insufficient removal capacity for aluminosilicate ash.
[0043] Comparative Example 1: Changing the intermediate ball milling time
[0044] First, a water washing pretreatment is performed. The alkali-containing coal-based porous carbon material obtained after chemical activation is washed with sufficient deionized water at room temperature until the filtrate is neutral. After solid-liquid separation, a preliminary purified product is obtained.
[0045] Subsequently, a primary acid washing with ultrasonic assistance was performed. The above 10 g of the primary purified product was transferred into a beaker containing a mixed acid solution of 200 mL of HCl (5 mol L -1 ) and HF (10 wt.%), and was treated in an ultrasonic condition of a frequency of 40 kHz and a power density of 0.5 W cm -2 at 60°C in a constant temperature water bath for 3 h. After the end of the treatment, the mixture was centrifuged, and the solid material was collected.
[0046] Next, an intermediate mechanical ball milling treatment was performed. The above solid material obtained after the primary acid washing was transferred into a planetary ball mill, and was ball milled at a rotation speed of 400 rpm for 10 min with a ball-to-material mass ratio of 20:1 using zirconia balls as the milling balls, to obtain a broken solid material.
[0047] Then, a deep acid washing with ultrasonic assistance was performed. The broken solid material was again immersed in the HCl-HF mixed acid solution, and all the treatment conditions were the same as those in the primary acid washing step, to completely remove the residual ash newly exposed due to the destruction of the encapsulation structure, to obtain a deep acid washed product.
[0048] Finally, a post-treatment was performed. The deep acid washed product was repeatedly washed with stirring using deionized water until the filtrate was neutral. The washed material was dried in a drying oven at 100°C for 10 h, to obtain a final medium-ash coal-based porous carbon sample, which was recorded as MA-AC-1.
[0049] The tests of Figure 2 and Figure 5 showed that the ash content of MA-AC-1 was 0.43%, and the specific surface area was 1754 m 2 g -1 .
[0050] Comparative Example 2: Change of the intermediate ball milling treatment time
[0051] The difference between this comparative example and Comparative Example 1 was that only the intermediate ball milling time was adjusted to 5 min, and the other parameters were kept unchanged. A final medium-ash coal-based porous carbon sample was obtained, which was recorded as MA-AC-2.
[0052] The tests of Figure 2 and Figure 5 showed that the ash content of MA-AC-2 was 0.57%, and the specific surface area was 1769 m 2 g -1 .
[0053] Comparative Example 3: No intermediate ball milling treatment
[0054] First, a water washing pretreatment is performed. The alkali-containing coal-based porous carbon material obtained after chemical activation is washed with sufficient deionized water at room temperature until the filtrate is neutral. After solid-liquid separation, a preliminary purified product is obtained.
[0055] Subsequently, an ultrasonic-assisted primary acid wash was performed. The 10 g of the preliminarily purified product was transferred to 200 mL of HCl (5 mol / L). -1 In a beaker, a mixed acid solution of HF (10 wt.%) and HF was prepared at a frequency of 40 kHz and a power density of 0.5 W / cm². -2 Under ultrasonic conditions, the mixture was treated in a constant temperature water bath at 60℃ for 6 hours; after the treatment, the mixture was centrifuged and the solid material was collected.
[0056] Then, post-processing was performed. The above solid material was repeatedly washed with deionized water by stirring until the filtrate was neutral. The washed material was placed in a drying oven at 100°C and dried for 10 hours to obtain the final high-ash coal-based porous carbon sample, denoted as HA-AC-1.
[0057] through Figure 2 The test results show that the ash content of HA-AC-1 is 1.41%.
[0058] Comparative Example 4: No intermediate ball milling and ultrasonic treatment performed.
[0059] The difference between this comparative example and comparative example 3 is that only the ultrasonic conditions were not used, while the other parameters remained unchanged. The high-ash coal-based porous carbon sample obtained was denoted as HA-AC-2.
[0060] through Figure 2 The test results show that the ash content of HA-AC-2 is 2.04%.
[0061] Comparative Example 5: No primary pickling treatment performed.
[0062] First, a water washing pretreatment is performed. The alkali-containing coal-based porous carbon material obtained after chemical activation is washed with sufficient deionized water at room temperature until the filtrate is neutral. After solid-liquid separation, a preliminary purified product is obtained.
[0063] Subsequently, intermediate mechanical ball milling was performed. The pre-purified product was transferred to a planetary ball mill, using zirconia balls as grinding balls, with a ball-to-material mass ratio of 20:1, and ball milled at 400 rpm for 10 min to obtain the crushed solid material.
[0064] Then, ultrasonic-assisted acid washing was performed. The 10 g of crushed solid material was transferred into a container containing 200 mL of HCl (5 mol / L). -1 In a beaker, a mixed acid solution of HF (10 wt.%) and HF was prepared at a frequency of 40 kHz and a power density of 0.5 W / cm².-2 Under ultrasonic conditions, the mixture was treated in a constant temperature water bath at 60℃ for 6 hours; after the treatment, the mixture was centrifuged and the solid material was collected.
[0065] Finally, post-processing was performed. The above solid material was repeatedly washed with deionized water by stirring until the filtrate was neutral. The washed material was then dried in a drying oven at 100 °C for 10 h to obtain the final high-ash coal-based porous carbon sample, denoted as HA-AC-3.
[0066] through Figure 2 The test results showed that the ash content of HA-AC-3 was 2.26%. The increase in ash content instead of a decrease is attributed to the agglomeration effect between powders caused by ball milling, which resulted in some surface inorganic components being secondary-encapsulated, making them difficult to remove by acid washing.
[0067]
Claims
1. A method for multistage deep de-ashing of coal-based porous carbon under external field assistance, characterized by The method comprises the following steps: Step (1) water washing pretreatment: the coal-based porous carbon obtained after activation is water washed; Step (2) ultrasonic-assisted primary acid washing: the water-washed coal-based porous carbon is mixed with an acid washing solution in a certain proportion, and primary washing treatment is carried out under ultrasonic conditions; Step (3) intermediate mechanical ball milling: the acid-washed material is subjected to short-time mechanical ball milling; Step (4) ultrasonic-assisted deep acid washing: the ball-milled material is mixed with an acid washing solution again, and second deep acid washing treatment is carried out under ultrasonic conditions; Step (5) post-treatment: the washed solid-phase product is thoroughly water washed to neutral, and then dried to obtain a low-ash coal-based porous carbon material.
2. The externally field-assisted multi-stage deep de-ashing method of coal-based porous carbon according to claim 1, characterized in that In the step (1), the coal-based porous carbon is supercapacitor active carbon prepared by a KOH, CO2 or steam activation method.
3. The externally field-assisted multi-stage deep de-ashing method of coal-based porous carbon according to claim 1, characterized in that In the step (1), the water washing is carried out by stirring at room temperature until the washing liquid is neutral.
4. The externally field-assisted multi-stage deep de-ashing method of coal-based porous carbon according to claim 1, characterized in that In the step (2) and step (4), the pickling solution adopts one or more combinations of nitric acid, hydrochloric acid or hydrofluoric acid, the concentration of HNO3 is 2-5 mol / L -1 , the concentration of HCl is 1-5 mol / L -1 , the mass fraction of HF is 1-10 wt.%, and the ratio of the material liquid is 1g:20ml.
5. The externally field-assisted multi-stage deep de-ashing method of coal-based porous carbon according to claim 1, characterized in that The frequency of the ultrasound in the steps (2) and (4) is 20-40 kHz, and the power density is 0.2-1.0 W cm -2 .
6. The externally field-assisted multi-stage deep de-ashing method of coal-based porous carbon according to claim 1, characterized in that In the steps (2) and (4), the washing temperature is 25-80℃, and the washing time is 1-12 h.
7. The externally field-assisted multi-stage deep de-ashing method of coal-based porous carbon according to claim 1, characterized in that In the step (3), the mechanical ball milling is carried out by using a planetary ball mill, the ball-to-material mass ratio is 10:1-30:1, the rotation speed is 300-500 rpm, and the ball milling time is 5-60 min.
8. The externally field-assisted multi-stage deep de-ashing method of coal-based porous carbon according to claim 1, characterized in that In the step (5), the drying temperature is 80-120℃, and the drying time is 6-12 h.
9. A coal-based porous carbon material prepared by the method of any one of claims 1-8.
10. Application of the coal-based porous carbon material prepared by the method of any one of claims 1-8 in a supercapacitor electrode material.