Porous carbon and preparation method thereof

Abstract

The invention provides porous carbon and a preparation method thereof, and the preparation method comprises the following steps: sequentially carrying out first drying, crushing and dehydration treatment on plant tissues to obtain an oxygen-enriched matrix; the temperature of the dehydration treatment is 120-320 DEG C; mixing heavy oil, an activating agent and a solvent to obtain a mixed solution; an oxygen-enriched substrate is soaked in the mixed solution for 10 min or longer, then a solvent is removed, and a compound is obtained; and calcining the compound to obtain the porous carbon. The porous carbon with relatively high specific surface area, mesoporous specific surface area, total pore volume, compaction density and particle strength can be obtained.

Description

Technical Field

[0001] The present invention relates to a porous carbon and a preparation method thereof, belonging to the technical field of carbon material preparation. Background Art

[0002] As a new type of functional carbon material, porous carbon has excellent adsorption characteristics due to its rich pore structure, so porous carbon is widely used in many fields including purification, energy storage, and catalysis. With the rapid development of the new energy industry, the demand for various high-efficiency electrical energy storage devices such as supercapacitors, lithium / sodium ion capacitors, and lithium-sulfur batteries is also increasing day by day. These high-efficiency electrical energy storage devices all use porous carbon as the electrode material, so there is an urgent need in the field to develop low-cost and high-quality porous carbon materials.

[0003] Capacitive electrode materials rely on the adsorption / desorption of electrolytes for electrical energy conversion. Therefore, in order to meet the demand for adsorbing electrolyte ions, the porous carbon that can be used as a capacitive electrode material needs to have a large specific surface area and suitable channels for rapid ion transport. However, in the prior art, the interior of activated carbon mostly has a single microporous structure without interconnected pores, and ion transport is blocked during high-rate charge and discharge, resulting in serious capacity attenuation. Therefore, constructing porous carbon with a hierarchical and developed pore structure is very important for improving the capacitance performance of electrode materials.

[0004] In the prior art, porous carbon is usually prepared by an alkaline activation method, and heavy oils such as slurry, petroleum coke, or residue oil are common carbon sources. For example, the patent document with the publication number CN104649267A discloses the preparation of activated carbon by using potassium hydroxide to activate petroleum coke, and the patent document with the publication number CN1186043A discloses the alkaline activation treatment of slurry to obtain multi-porous carbon with a super high specific surface area. However, the dosage of alkaline substances in the above methods is relatively high, and the pore structure of the prepared carbon materials is single, and the rate performance is poor. In order to construct suitable mass transfer pores, most of the prior art uses metal oxides as template agents to improve the pore channels of carbon materials. For example, the patent document with the publication number CN112194112A discloses the use of pyrolysis oil as the carbon source and fibrous magnesium oxide as the template agent to prepare porous carbon with a multi-stage interconnected pore structure. The electrodes made of the above porous carbon show excellent rate performance, but such metal oxide template agents require a complex preparation process, and in the process of preparing porous carbon, they need to be removed by acid washing after carbonization, and the cost is relatively high. In addition, biomass raw materials are also often used as carbon sources for preparing porous carbon. For example, the patent document with the publication number CN107459042A discloses the preparation of biomass-based porous carbon, but such biomass-based porous carbon is a hard carbon material with poor conductivity, a single pore structure, and a problem of low bulk density. Summary of the Invention

[0005] The present invention provides a porous carbon and a preparation method thereof, capable of obtaining a porous carbon that takes into account a relatively high specific surface area, mesoporous specific surface area, total pore volume, tap density, and D50.

[0006] The present invention provides a method for preparing a porous carbon, comprising: sequentially performing first drying, pulverization, and dehydration treatment on plant tissue to obtain an oxygen-rich matrix; the temperature of the dehydration treatment is 120 - 320°C; mixing heavy oil, an activator, and a solvent to obtain a mixed solution; impregnating the oxygen-rich matrix in the mixed solution, the impregnation time ≥ 10 min, and then removing the solvent to obtain a composite; and calcining the composite to obtain the porous carbon.

[0007] Optionally, the plant tissue includes one or more of branches, bamboo, coconut shells, rice husks, cattail fluff, corn cobs, and sugarcane bagasse; and / or, the heavy oil includes one or more of slurry, residue oil, and tar; and / or, the activator includes one or more of potassium hydroxide and sodium hydroxide; and / or, the solvent includes ethanol and / or water; and / or, the temperature of the first drying is 190 - 210°C, and the time of the first drying is 8 - 12 h; and / or, during the pulverization process, the plant tissue after the first drying is pulverized to a particle size D50 of 2 - 1000 μm; and / or, the time of the dehydration treatment is 2 - 6 h.

[0008] Optionally, the mass ratio of the oxygen-rich matrix to the activator is 1:(0.5 - 6); and / or, the mass ratio of the oxygen-rich matrix to the heavy oil is 1:(0.2 - 4).

[0009] Optionally, the impregnation time is 10 - 240 min; and / or, during the impregnation process, one or more of shaking, stirring, and ultrasonic treatment are used for the impregnation; and / or, during the solvent removal process, heating and / or vacuum are used for the solvent removal.

[0010] Optionally, the calcination temperature is 700 - 1100°C, and the calcination time is 60 - 240 min; and / or, during the calcination process, the calcination is carried out in one or more atmospheres of nitrogen, argon, helium, carbon dioxide, and water vapor.

[0011] Optionally, after the composite is sequentially calcined, the composite is washed and second dried to obtain the porous carbon; during the washing process, one or more of water, hydrochloric acid, sulfuric acid, and nitric acid are used for the washing; and / or, the temperature of the second drying is 120 - 150°C, and the time of the second drying is 2 - 12 h.

[0012] Optionally, it further includes: after the second drying, performing ball milling on the obtained product of the second drying to obtain the porous carbon.

[0013] The present invention provides a porous carbon obtained by the preparation method as described above.

[0014] Optionally, the specific surface area of the porous carbon is 500 - 2500 m 2 / g, the proportion of the mesoporous surface area in the total pore surface area is 10% - 35%, the total pore volume is 0.2 - 1.2 cm 3 / g, and the tap density is 0.3 - 0.7 g / cm 3 ; the D50 of the porous carbon is 6 - 10 μm, and the single particle strength is 12 - 20 mN.

[0015] Optionally, the conductivity of the porous carbon is 600 - 1000 S / m, the voltage drop at a current density of 50 A / g is 0.08 - 0.25 V, and the capacity retention rate is 90% - 95%; wherein, the capacity retention rate is the ratio of the capacitance at a current density of 50 A / g to the capacitance at a current density of 1 A / g.

[0016] The porous carbon and its preparation method provided by the present invention can obtain a porous carbon that takes into account a relatively high specific surface area, mesoporous specific surface area, total pore volume, tap density, and particle strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic flow chart of the preparation method of the porous carbon for some embodiments;

[0018] Figure 2 is the nitrogen adsorption / desorption curve of the porous carbon in Example 1 and Comparative Examples 1 - 2 (the ordinate is the volume of the adsorbed gas measured under standard temperature and pressure (Standard Temperature and Pressure, abbreviated as STP) conditions for the porous carbon per unit mass, i.e., Volume@STP);

[0019] Figure 3 is the pore size distribution curve of the porous carbon in Example 1, Comparative Example 1, and Comparative Example 2 (mesoporous part, pore size is 2 - 50 nm, the ordinate is the differential distribution of pore volume / dv(d), unit is cc·nm -1 ·g -1 );

[0020] Figure 4 is the pore size distribution curve of the porous carbon in Example 1, Comparative Example 1, and Comparative Example 2 (microporous part, pore size is 0.5 - 2 nm, the ordinate is the differential distribution of pore volume / dv(d), unit is cc·nm -1 ·g-1 )

[0021] Figure 5 Cyclic voltammogram curves of the electrodes prepared from the porous carbons of Example 1, Comparative Example 1, and Comparative Example 2;

[0022] Figure 6 Charge-discharge curves of the electrodes prepared from the porous carbons of Example 1, Comparative Example 1, and Comparative Example 2;

[0023] Figure 7 Rate performance curves of the electrodes prepared from the porous carbons of Example 1, Comparative Example 1, and Comparative Example 2;

[0024] Figure 8 Impedance spectra curves of the electrodes prepared from the porous carbons of Example 1, Comparative Example 1, and Comparative Example 2. Detailed implementation manners

[0025] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0026] The embodiments of the present invention also provide a method for preparing porous carbon, as Figure 1 shown, including: sequentially performing first drying, pulverization, and dehydration treatment on plant tissues to obtain an oxygen-rich matrix; the temperature of the dehydration treatment is 120-320°C; mixing heavy oil, an activator, and a solvent to obtain a mixed solution; impregnating the oxygen-rich matrix in the mixed solution for a time ≥ 10 min, and then removing the solvent to obtain a composite; and sequentially calcining the composite to obtain porous carbon.

[0027] According to the research and analysis of the inventor: After the plant tissue is first dried and pulverized, dehydration treatment is carried out at 120-320 °C, and the obtained oxygen-rich matrix (or plant tissue) has a large number of naturally formed tubular pore structures (conducting tissues). During the impregnation process, the activator dissolved in the solvent and the heavy oil in liquid state are adsorbed into the conducting tissues of the oxygen-rich matrix through impregnation and capillary action. Then, during the process of removing the solvent, the activator gradually forms microcrystals and adheres to the inner surface of the conducting tissue pipes. At the same time, the heavy oil anchors the microcrystals on the inner surface of the conducting tissue pipes and closes the conducting tissue pipes (pores). Thus, during the subsequent calcination (i.e., activation) process, the activator generates active elementary units (such as potassium atoms) under high temperature. The etching path of the active elementary units is two-way, that is to say, the active elementary units can act on both the oxygen-rich matrix and the heavy oil simultaneously. In addition, the activator is entirely present inside the substances to be activated (oxygen-rich matrix and heavy oil), enabling the activation effect of the active elementary units generated by the activator to proceed from the inside to the outside of the substances to be activated. Therefore, the specific surface area of the porous carbon is effectively increased (that is, when producing porous carbon of a unit mass, the specific surface area of the porous carbon is larger), and the activation efficiency of the activator is improved, while reducing the loss rate of the activator at high temperature (that is, less mass of the activator is required to produce porous carbon with the same specific surface area). This solves the problem in the prior art that during the process of using an activator to treat a single-component carbon source to prepare porous carbon, due to the activation action of the active elementary units proceeding from the outside to the inside of the single-component carbon source, and due to the lack of a sealing effect, the utilization efficiency of the activator is low. At the same time, it solves the problem of low activation efficiency that occurs during the process of first fixing the heavy oil inside the plant tissue and then using the activator to carry out activation with a secondary temperature rise, because the activator acts on the outside of the substances to be activated. This helps to improve economic efficiency; Secondly, a two-component carbon source is adopted, namely plant tissue (the first carbon source) and heavy oil (the second carbon source or sealing agent). Combining the above two-component carbon source has an effect that cannot be achieved by using the plant tissue or heavy oil alone. Specifically, the surface of the conducting tissues of the oxygen-rich matrix (the oxygen-rich matrix formed by the plant tissue) has a large number of oxygen-containing functional groups. After the oxygen-rich matrix is impregnated with heavy oil, during the calcination process, the carbon-hydrogen bonds of carbon-hydrogen compounds such as macromolecular alkanes and aromatics in the heavy oil (such as benzene homologues with more than 3 benzene rings) are broken under the catalytic action of the oxygen-containing functional groups of the oxygen-rich matrix, forming a carbon layer deposited on the pore walls of the oxygen-rich matrix (plant tissue), improving the solid-phase conversion rate of the heavy oil, the conversion rate of the carbon source, and the yield of the porous carbon. This solves the problem that during the process of using heavy oil alone, when the heavy oil is calcined (heat treatment activation), due to the occurrence of thermal cracking-coking reaction behavior of the heavy oil, the heavy oil cracks and separates in the form of a large amount of oil and gas, resulting in a low solid-phase yield of the heavy oil;Furthermore, when the pores in the porous carbon are mesopores (2 - 50 nm), they can provide efficient mass transfer channels and buffer spaces for the adsorption / desorption behaviors of ion-sized adsorption guests (such as potassium ions and hydroxide ions). However, the tubular pore structures of plant tissues or oxygen-rich matrices are all macropores (>200 nm), and such macropores cannot provide efficient mass transfer channels and buffer spaces for the adsorption / desorption behaviors of ion-sized adsorption guests (such as potassium ions and hydroxide ions). Moreover, macropores also mean excessive internal voids, which can lead to problems such as low specific surface area and low volume density of the porous carbon. In the embodiments of the present invention, by filling an activator and heavy oil into the voids of the tubular pore structure (conducting tissue) of the oxygen-rich matrix, the activator is fixed in the voids of the above tubular pore structure (conducting tissue). During the calcination (carbonization) process, through the in-situ activation effect of the activator (that is, the activation motifs generated by the high-temperature action of the activator activate from the inside to the outside of the substance to be activated), mesoporous-scale (sized) pores (such as 5 - 10 nm, 25 - 35 nm) of the porous carbon are formed. Therefore, the porous carbon has a pore structure conducive to ion transport. Further, by using different plant tissues (with different natural structures or conducting tissues), different activators, and changing the addition amounts of the plant tissue, activator, and heavy oil, the pore structure of the porous carbon can be changed, the pore size distribution can be adjusted, and the proportion of mesopores (target pores) can be increased, making the pore structure of the porous carbon gradable and more controllable. Furthermore, the synergistic effect of heavy oil and plant tissue (oxygen-rich matrix) can make the porous carbon have better electrical conductivity. This is because the heavy oil is deposited in the pore walls of the plant tissue (oxygen-rich matrix) and can form thin graphite layers under the induction of the pore walls of the plant tissue (oxygen-rich matrix). The orderliness of these thin graphite layers is relatively high, so the porous carbon has higher electrical conductivity, solving the problem that when only plant tissue is used as the carbon source to form porous carbon, since this porous carbon is a difficult-to-carbonize structure (hard carbon structure) and its internal carbon layer structure is turbulent and disordered, the electrical conductivity is relatively low. It also solves the problem that when only heavy oil is used as the carbon source to form porous carbon, although the orderliness of the heavy oil after carbonization is higher than that of the hard carbon structure, the electrical conductivity of the porous carbon formed is still poor. At the same time, the thin graphite layers formed in the above process have a relatively high modulus of strength and have a good supporting effect, improving the single-particle strength of the porous carbon and solving the problem that the porous carbon particles made of ordinary single biomass carbon source or heavy oil carbon source have poor strength and are prone to collapse and pulverize during the rolling of the electrode. Furthermore, due to the macropores in the plant tissue and the oxygen-rich matrix obtained after its dehydration treatment, there are a large number of unusable spaces (voids) in the porous carbon, which in turn causes the problem of low volume density (such as tapped density and compacted density) of the porous carbon. By filling these voids of the oxygen-rich matrix with heavy oil, these voids can be utilized, which is beneficial to increasing the volume density (density) of the porous carbon;In addition, through the two-component carbon source in-situ activation method in the embodiments of the present invention, it is possible to prevent the activator from only performing single-point activation on heavy oil, and problems such as pore collapse caused by over-activation, only micropores existing inside the porous carbon, and the further development of these micropores into macropores can be avoided.

[0028] Therefore, the method for preparing porous carbon provided by the embodiments of the present invention helps to improve the yield, specific surface area, mesoporous specific surface area, tap density (product density), electrical conductivity, and particle strength of the porous carbon, can form a hierarchically controllable pore structure beneficial to ion transport inside the porous carbon, and can also improve the activation efficiency of the activator in the preparation process.

[0029] Generally, the above-mentioned plant tissues have conducting tissues, that is, pipeline structures including vascular bundles, vessels, and sieve tubes, and can include one or more of plant roots, stems, leaves, and fruits. For example, it can include one or more of tree branches (wood chips), bamboo, coconut husks, rice husks, cattail fluff, corncobs, and sugarcane bagasse.

[0030] To avoid impurities in the plant tissues (raw materials), generally, the plant tissues can be first subjected to impurity removal treatment, and then first drying, pulverization, and dehydration treatment. During the above-mentioned impurity removal treatment, air flow dust removal and / or water washing can be used to remove impurities from the plant tissues. The process of air flow dust removal can include using air (such as clean air) to blow the plant tissues to remove dust in the plant tissues; the process of water washing can include using water (such as clean water) to soak and rinse the plant tissues to remove impurities such as dust and inorganic salts. Among them, the above-mentioned soaking and rinsing processes can be carried out at least once. In some embodiments, the process of the above-mentioned impurity removal treatment includes: sequentially performing air flow dust removal and water washing on the plant tissues to obtain the impurity-removed plant tissues. After sequentially performing the first drying, pulverization, and dehydration treatment on the impurity-removed plant tissues, an oxygen-rich matrix is obtained.

[0031] In some embodiments, the temperature of the above-mentioned first drying is 150-210°C, for example, it can be 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, or the range composed of any two of them. The time of the first drying is 8-12h, for example, it can be 8, 9, 10, 11, 12h, or the range composed of any two of them. By performing the first drying on the plant tissues, part of the water and part of the volatile components in the plant tissues are removed, facilitating the pulverization treatment of the plant tissues.

[0032] The embodiments of the present invention do not limit the equipment for the above-mentioned first drying. For example, the first drying can be carried out in an oven.

[0033] During the pulverization process, the plant tissue after the first drying is pulverized to a particle size D50 of 2 to 1000 μm, that is, the plant tissue after the first drying is pulverized so that the D50 particle size of the pulverized plant tissue is 2 to 1000 μm. For example, it can be 2, 10, 50, 100, 500, 1000 or the range composed of any two of them.

[0034] The embodiments of the present invention do not limit the above-mentioned pulverization equipment. The above-mentioned pulverization process can be carried out in common pulverization equipment in the field. For example, the above-mentioned pulverization can be carried out in a mechanical pulverizer or a jet mill well-known to those skilled in the art.

[0035] In some embodiments, the process of obtaining an oxygen-rich matrix by dehydrating the pulverized plant tissue (heat treatment) includes: dehydrating the pulverized plant tissue at 120 to 320 °C for 0.5 to 6 h to obtain an oxygen-rich matrix. Exemplarily, the temperature of the above-mentioned dehydration treatment can be 120 °C, 150 °C, 200 °C, 250 °C, 300 °C, 320 °C or the range composed of any two of them, preferably 150 to 300 °C; the time of the above-mentioned dehydration treatment can be 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h or the range composed of any two of them.

[0036] To ensure the effect of the dehydration treatment, the above-mentioned dehydration treatment can be carried out in air or an inert atmosphere. For example, the dehydration treatment can be carried out in a nitrogen atmosphere calcination furnace.

[0037] It can be understood that since the particle size of the pulverized plant tissue satisfies D50 of 2 to 1000 μm, therefore, the particle size of the above-mentioned oxygen-rich matrix also basically satisfies its particle size D50 of 2 to 1000 μm.

[0038] The particle size of the above-mentioned oxygen-rich matrix satisfies D50 of 2 to 1000 μm, preferably 20 μm to 500 μm, which helps to improve the impregnation effect of the oxygen-rich matrix in the mixed liquid. The reason is analyzed as follows: if the particle size of the oxygen-rich matrix is too small, there is a problem that the oxygen-rich matrix is not easily recovered after the impregnation; if the particle size of the oxygen-rich matrix is too large, the impregnation effect is poor. Therefore, the particle size of the oxygen-rich matrix satisfies D50 of 2 to 1000 μm, preferably 20 μm to 500 μm, which helps to ensure the impregnation effect, and then improve the specific surface area, yield, electrical conductivity and product density of the porous carbon, improve the activation efficiency of the activator in the preparation process, and form a multi-stage controllable pore structure conducive to ion transport.

[0039] During the process of mixing heavy oil, activator and solvent, one or more of shaking, stirring, and ultrasonic waves can be used for mixing to make them evenly dispersed, obtaining a mixed liquid (dispersion). For example, after adding heavy oil, activator and solvent into a reaction kettle, a stirring paddle is used for stirring and mixing, and at the same time an ultrasonic device is used to assist in mixing to obtain a mixed liquid (dispersion).

[0040] The heavy oil in the embodiments of the present invention may include liquid hydrocarbons well-known in the fields of petroleum processing, coal processing, etc., such as various heavy distillate oils, reaction separation oils or crude oils involved in the process of petroleum processing or coal processing. Specifically, it includes one or more of slurry oil, residue oil, and tar. For example, it may include one or more of catalytic slurry oil produced by a refinery fluid catalytic cracking unit, vacuum residue in the process of crude oil distillation, atmospheric residue in the process of crude oil distillation, coal tar, and ethylene tar (ethylene pyrolysis oil).

[0041] In some embodiments, the mass ratio of the oxygen-rich matrix to the heavy oil is 1:(0.2 - 4). For example, it can be 1:0.2, 1:1, 1:2, 1:3, 1:4 or the range composed of any two of them. Preferably 1:(0.5 - 3), which is beneficial to improving the utilization rate of the oxygen-rich matrix and heavy oil, increasing the specific surface area, yield, electrical conductivity and product density of the porous carbon, improving the activation efficiency of the activator in the preparation process, and forming a multi-stage controllable pore structure beneficial to ion transport.

[0042] The activator in the embodiments of the present invention may include alkaline substances. For example, it may include one or more of potassium hydroxide, sodium hydroxide, sodium carbonate, and potassium carbonate.

[0043] In some embodiments, the mass ratio of the oxygen-rich matrix to the activator is 1:(0.5 - 6). For example, it can be 1:0.5, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6 or the range composed of any two of them. Preferably 1:(1 - 4), which is beneficial to improving the utilization rate of the oxygen-rich matrix and activator, increasing the specific surface area, yield, electrical conductivity and product density of the porous carbon, improving the activation efficiency of the activator in the preparation process, and forming a multi-stage controllable pore structure beneficial to ion transport.

[0044] The solvent in the embodiments of the present invention may include ethanol and / or water, and its dosage needs to meet the requirement of fully dissolving the activator.

[0045] To improve the impregnation effect, during the process of impregnating the oxygen-rich matrix into the mixed solution, one or more of shaking, stirring, and ultrasonic treatment can be used for impregnation to enhance the impregnation effect. Among them, ultrasonic-assisted impregnation can remove the gas in the oxygen-rich matrix (plant tissue), which helps to enhance the impregnation effect. In some embodiments, the process of impregnating the oxygen-rich matrix into the mixed solution includes: impregnating the oxygen-rich matrix into the mixed solution, using a stirring paddle for stirring, and simultaneously applying ultrasonic treatment to enhance the impregnation effect.

[0046] The above impregnation time is ≥ 10 min. For example, it can be 10 min, 30 min, 50 min, 100 min, 120 min, 150 min, 200 min, 240 min, or the range composed of any two of them. Preferably, it is 30 - 120 min, which can ensure the impregnation effect, is beneficial to improving the specific surface area, yield, electrical conductivity, and product density of the porous carbon, improving the activation efficiency of the activator in the preparation process, and can form a multi-level controllable pore structure conducive to ion transport.

[0047] After the above impregnation is completed, during the process of removing the solvent, one or more of the single heating method, single decompression method (vacuum method), and vacuum heating method can be used to remove the solvent to obtain a composite. For example, after the impregnation is completed, the impregnation material including the mixed solution and the oxygen-rich matrix can be transferred to a rotary evaporator, and the solvent can be efficiently removed (evaporated) by rotary heating in a vacuum environment to obtain a composite; a rotary dryer can also be used to replace the above rotary evaporator to remove the solvent to obtain a composite (oxygen-rich matrix loaded with heavy oil).

[0048] In some embodiments, the composite is calcined at 700 - 1100 °C to carbonize the oxygen-rich matrix and the heavy oil, and at the same time, the activator undergoes an activation effect, thereby obtaining porous carbon. Exemplarily, the above calcination temperature can be 700 °C, 800 °C, 850 °C, 900 °C, 1000 °C, 1100 °C, or the range composed of any two of them. Preferably, it is 700 - 1000 °C, and more preferably 750 - 900 °C.

[0049] Furthermore, the above calcination time can be 30 - 360 min. For example, it can be 30 min, 60 min, 80 min, 100 min, 120 min, 150 min, 200 min, 240 min, 300 min, 360 min, or the range composed of any two of them. Preferably, it is 60 - 240 min.

[0050] It can be understood that during the above calcination process, calcination can be carried out in an anaerobic atmosphere. For example, it can be carried out in one or more of the atmospheres of nitrogen, argon, helium, carbon dioxide, and water vapor.

[0051] During the above-mentioned calcination process, the calcination can be carried out under an absolute pressure of 0.05 MPa to 0.2 MPa, such as 0.05, 0.1, 0.15, 0.2 or a range composed of any two of them, or the calcination can also be carried out under normal pressure.

[0052] The embodiments of the present invention do not limit the above-mentioned calcination equipment, and conventional calcination equipment in the art can be used. For example, the calcination can be carried out in a calcination furnace.

[0053] In some embodiments, after the composite is calcined, the calcined composite is washed and secondarily dried to obtain porous carbon.

[0054] During the above-mentioned washing process, the calcined composite can be washed by water washing and / or acid washing. Specifically, water, hydrochloric acid, sulfuric acid, nitric acid or one or more of them can be used for washing to remove the residual activator (alkali) and the salts generated by the reaction. For example, the calcined composite can be first washed with water to remove most of the residual activator in the calcined composite; then acid washing is used to neutralize the remaining activator; finally, water washing is used again to remove the salts generated during the acid washing process (neutralization reaction). The embodiments of the present invention do not limit the number of times of the above-mentioned water washing and acid washing. For example, the number of times of water washing and acid washing can be 1 time, 2 times, 3 times, 4 times respectively.

[0055] In some embodiments, the temperature of the above-mentioned second drying is 120 - 210 °C, such as 120 °C, 130 °C, 140 °C, 150 °C, 160 °C, 170 °C, 180 °C, 190 °C, 200 °C, 210 °C or a range composed of any two of them, and the time of the second drying is 2 - 12 h, such as 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h or a range composed of any two of them, which helps to remove the moisture in the composite.

[0056] In some embodiments, the process of the second drying includes: filtering the washed composite (such as suction filtration), and then carrying out the second drying at 120 - 210 °C for 8 - 12 h to obtain porous carbon.

[0057] During the above-mentioned second drying process, the second drying can be carried out by means of separate heating or vacuum heating.

[0058] The embodiments of the present invention do not limit the equipment for the second drying. For example, the second drying can be carried out in a vacuum drying oven.

[0059] In some embodiments, after the second drying, the obtained second drying product is ball-milled and screened to obtain porous carbon with a D50 of 6 - 10 μm (8 ± 2 μm), and this porous carbon can be used for preparing an electrode.

[0060] An embodiment of the present invention also provides a porous carbon, which is obtained by the above preparation method. The porous carbon has a relatively high specific surface area, yield, electrical conductivity and product density, and the pore structure of the porous carbon is multi-level controllable, which is beneficial to ion transport.

[0061] According to the research and analysis of the inventors: the above-mentioned porous carbon takes into account a relatively high specific surface area, mesoporous specific surface area, total pore volume, tap density and particle strength, meets the requirements for preparing electrode materials, and can be used to prepare electrode materials for electric double layer capacitors, lithium ion capacitors, sodium ion capacitors, potassium ion capacitors, lithium ion batteries, sodium ion batteries, potassium ion batteries, zinc-air batteries and lithium-sulfur batteries. It can also be used as a high-strength carbon skeleton (porous carbon) used in the preparation of silicon-carbon anode materials by the silane method vapor deposition, and has a wide range of applications.

[0062] In some embodiments, the specific surface area of the porous carbon is 500-2500 m 2 / g, the proportion of the mesoporous surface area in the total pore surface area is 10%-35%, the total pore volume is 0.2-1.2 cm 3 / g, and the tap density is 0.3-0.7 g / cm 3 ; the D50 of the porous carbon is 6-10 μm, and the single particle strength is 12-20 mN.

[0063] In the embodiments of the present invention, the single particle strength is detected according to the method described in GB / T 43091-2023.

[0064] In some embodiments, the electrical conductivity of the above-mentioned porous carbon is 600-1000 S / m, the voltage drop at a current density of 50 A / g is 0.08-0.25 V, and the capacity retention rate is 90%-95%; wherein, the above-mentioned capacity retention rate is the ratio of the capacitance at a current density of 50 A / g to the capacitance at a current density of 1 A / g. The porous carbon has good electrical conductivity and meets the requirements for preparing electrode materials.

[0065] Hereinafter, the present invention will be introduced in more detail through specific examples and comparative examples.

[0066] The sources of the materials used in the examples and comparative examples are as follows:

[0067] The rice husk is natural rice husk and is purchased through Alibaba (e-commerce);

[0068] The wood chips are purchased through Alibaba (e-commerce);

[0069] The corncob is purchased through Alibaba (e-commerce);

[0070] The catalytic slurry is taken from the refinery of PetroChina Lanzhou Branch and has been subjected to solid removal treatment, and the solid (waste catalyst) content < 100 ppm;

[0071] Atmospheric residue, taken from PetroChina Daqing Petrochemical Company;

[0072] Ethylene tar, taken from PetroChina Daqing Petrochemical Company;

[0073] Coal tar, taken from Shenhua Group;

[0074] Potassium hydroxide, analytical pure, purchased from Sinopharm Chemical Reagent Co., Ltd.;

[0075] Sodium hydroxide, analytical pure, purchased from Sinopharm Chemical Reagent Co., Ltd.

[0076] Example 1

[0077] The preparation method of the porous carbon in this example includes:

[0078] After blowing air through rice husks, soak and wash the rice husks with water twice, then perform the first drying on the washed rice husks at 200 °C for 12 h; crush the rice husks after the first drying so that the D50 of the crushed rice husks is 100 ± 20 μm; place the crushed rice husks in a nitrogen atmosphere for dehydration treatment at a temperature of 300 °C for 2 h to obtain an oxygen-rich matrix;

[0079] Mix 10 g of catalytic slurry, 10 g of potassium hydroxide, and 40 g of ethanol. During this mixing process, use stirring and ultrasonic assistance for mixing to obtain a mixed solution;

[0080] Immerse 10 g of the above oxygen-rich matrix in the above mixed solution, use stirring and ultrasonic assistance for impregnation for 60 min, and then remove ethanol (solvent) from the impregnated material (including the above oxygen-rich matrix and mixed solution) at a temperature of 120 °C and a pressure of -0.8 MPa to obtain a composite;

[0081] Transfer the composite to be calcined at 850 °C for 120 min in a nitrogen atmosphere, cool the calcined product, wash the cooled product with water twice, then add hydrochloric acid (the concentration of HCl in the hydrochloric acid is 0.1 mol / L) to wash once, and then wash with water twice again. Filter by suction to collect the washed composite and perform the second drying at 150 °C for 120 min;

[0082] After the second drying, perform ball milling on the obtained product of the second drying so that its D50 is 6 - 10 μm (8 ± 2 μm) to obtain porous carbon.

[0083] Comparative Example 3

[0084] The preparation method of the porous carbon in this comparative example includes:

[0085] After blowing the rice husks with air, the rice husks were soaked and washed with water twice, and then the washed rice husks were dried for the first time at 200 °C for 12 h; the rice husks after the first drying were crushed so that the D50 of the crushed rice husks was 100 ± 20 μm; the crushed rice husks were placed in a nitrogen atmosphere for dehydration treatment, the temperature of the dehydration treatment was 300 °C, and the time of the dehydration treatment was 2 h, to obtain an oxygen-rich matrix;

[0086] 10 g of the above oxygen-rich matrix was impregnated in 10 g of catalytic slurry oil, and stirring and ultrasonic assistance were used for impregnation for 60 min to obtain a composite;

[0087] The composite was calcined at 350 °C for 120 min under a nitrogen atmosphere to obtain a calcined product;

[0088] The above calcined product was mixed with 10 g of potassium hydroxide and 40 g of ethanol. During this mixing process, stirring and ultrasonic assistance were used for impregnation. Subsequently, the impregnated material (oxygen-rich matrix a and the mixed solution) was de-ethanolized (solvent) at a temperature of 120 °C and a pressure of -0.8 MPa;

[0089] The product after de-ethanolizing (solvent) was calcined at 850 °C for 120 min under a nitrogen atmosphere to obtain a calcined product. After the calcined product was cooled, it was washed with water twice, then washed with hydrochloric acid (the concentration of HCl in the hydrochloric acid was 0.1 mol / L) once, then washed with water twice again, and the washed product was collected by suction filtration, and then dried for the second time at 150 °C for 120 min;

[0090] After the second drying, the obtained product after the second drying was subjected to ball milling treatment so that its D50 was 6 - 10 μm (8 ± 2 μm) to obtain porous carbon.

[0091] Referring to the process of Example 1, the preparation of porous carbon for Examples 2 - 9 and Comparative Examples 1, 2, 4 - 6 was carried out respectively. The types of plant tissues, the mass of the oxygen-rich matrix, the types and masses of heavy oils, the types and masses of activators, the types and masses of solvents, the mass ratio of the oxygen-rich matrix to the heavy oil, the mass ratio of the oxygen-rich matrix to the activator, etc. for Examples 2 - 9 and Comparative Examples 1, 2, 4 - 6 are summarized in Table 1; the methods of impurity removal treatment, the temperature and time of the first drying, the particle size (D50) of the crushed plant tissues, the temperature and time of the dehydration treatment, the methods and time of the impregnation process, the temperature and pressure of solvent removal, the atmosphere, temperature and time of the calcination process, the methods of washing, the temperature and time of the second drying, the particle size (D50) of the porous carbon after ball milling treatment, etc. for Examples 2 - 9 and Comparative Examples 1, 2, 4 - 6 are summarized in Table 2.

[0092] Comparative Example 7

[0093] Prepare 10 g of catalytic slurry, 10 g of oxygen-rich matrix identical to that in Example 1, 20 g of potassium hydroxide, and 80 g of ethanol as raw materials (i.e., the raw material composition is the same as that in Example 8). The difference between this comparative example and Example 8 is that 10 g of oxygen-rich matrix, 10 g of potassium hydroxide, and 40 g of ethanol are taken respectively, and product a is prepared according to the method of Comparative Example 5 (i.e., activating the oxygen-rich matrix alone), then 10 g of catalytic slurry, 10 g of potassium hydroxide, and 40 g of ethanol are used to prepare product b according to the method of Comparative Example 6 (i.e., activating heavy oil alone), and a and b are directly mixed to obtain mixture c as the final product of Comparative Example 7.

[0094] Table 1

[0095]

[0096]

[0097] Table 2

[0098]

[0099]

[0100] Test Example

[0101] 1. Detect the following parameters of the porous carbon in the above examples and comparative examples:

[0102] 1) Particle size test: Measured by laser particle size method. The specific detection process can refer to the method described in GB / T 19077-2016. For example, use a Mastersizer 3000 laser particle size analyzer from Malvern Panalytical, USA for measurement. In the implementation of the present invention, the particle size is uniformly measured by the D50 diameter.

[0103] 2) Yield of porous carbon: The yield is calculated according to the following formula, w3 / (w1 + w2) * 100, where w1 is the mass of the oxygen-rich matrix, w2 is the mass of heavy oil, and w3 is the mass of the product porous carbon. The calculation results of the yield are shown in Table 3 and Table 4;

[0104] 3) Specific surface area, mesoporous specific surface area, and average pore diameter of porous carbon: Detected by the multi-point Brunauer-Emmett-Teller adsorption method (multi-point BET adsorption method). The specific detection process refers to the method described in GB / T 19587. Use an Autosorb iQ specific surface area and pore size analyzer from Quantachrome Instruments, USA (Autosorb iQ instrument) to complete the detection; and calculate according to the ratio of the mesoporous specific surface area to the specific surface area of porous carbon to obtain the mesoporous specific surface area contribution; the specific surface area, mesoporous specific surface area, and mesoporous specific surface area contribution values of the porous carbon in each example and comparative example are shown in Table 3 and Table 4;

[0105] Using isotherm data simulation, the pore size distribution curves of the porous carbons of Example 1, Comparative Example 1, and Comparative Example 2 (mesoporous part, pore size 2 - 50 nm) are shown in Figure 3 , and the pore size distribution curves of the porous carbons of Example 1, Comparative Example 1, and Comparative Example 2 (microporous part, pore size 0.5 - 2 nm) are shown in Figure 4 ; where Figure 3 and Figure 4 the ordinate of both is the differential distribution of pore volume / dv(d), with the unit of cc·nm -1 ·g -1 ;

[0106] 4) Apparent density of the porous carbon: The apparent density of the porous carbon was detected using the FT-301A powder resistivity / apparent density tester from Ningbo Ruike Micro Intelligence Co., Ltd., and the results are shown in Table 3 and Table 4;

[0107] 5) Electrical conductivity of the porous carbon: It was detected by the powder resistivity method. The electrical conductivity of the porous carbon was detected using the FT-301A powder resistivity / apparent density tester from Ningbo Ruike Micro Intelligence Co., Ltd., and the results are shown in Table 3 and Table 4;

[0108] 6) Single particle strength of the porous carbon: The detection process can refer to the method described in GB / T 43091-2023. For example, it was measured using the SPFT1000 single particle mechanical tester from Fujian Yuaneng Technology Co., Ltd., and the results are shown in Table 3 and Table 4;

[0109] 7) Electrochemical performance analysis of the porous carbon:

[0110] Device assembly: The electrochemical performance was evaluated using a symmetric two-electrode capacitor. The masses of the active materials loaded on the two symmetric electrodes used were the same. A 6 mol / L potassium hydroxide solution was used as the electrolyte, and the separator was glass fiber (Whatman, GF / D1823-047). A CR2032 button cell case was used to assemble the capacitor;

[0111] The cyclic voltammetry test, specific capacitance test, and AC impedance test all refer to the methods described in IEC 62391-1-2015;

[0112] Among them, the calculation of the specific capacitance (C) is based on the mass of the electrode and follows the following formula:

[0113]

[0114] In the above formula, I(A) is the discharge current; Δt(s) is the discharge time; m(g) is the mass of the activated carbon in the electrode; ΔV(V) is the voltage window after removing the voltage drop in the discharge interval; The cyclic voltammetry (cv) curves of the electrodes prepared from the porous carbons of Example 1, Comparative Example 1, and Comparative Example 2 are shown in Figure 5; The charge-discharge curves of the electrodes prepared using the porous carbons of Example 1, Comparative Example 1, and Comparative Example 2 are shown in Figure 6 ; The rate performance curves of the electrodes prepared using the porous carbons of Example 1, Comparative Example 1, and Comparative Example 2 are shown in Figure 7 ; The impedance spectrum curves of the electrodes prepared using the porous carbons of Example 1, Comparative Example 1, and Comparative Example 2 are shown in Figure 8 ; The voltage drops and capacity retention rates of the electrodes prepared using the porous carbons of each example and comparative example are shown in Tables 3 and 4;

[0115] 8) Nitrogen adsorption / desorption curve (nitrogen adsorption / desorption isotherm) of the porous carbon: Record the change in the adsorption amount of the probe molecule (nitrogen) per unit mass of the porous carbon at different relative pressures, as shown in Figure 2 .

[0116] 2. Test results

[0117] Table 3. Yields, specific surface areas, mesoporous specific surface areas, mesoporous specific surface area contributions, tap densities, conductivities, single particle strengths, voltage drops, and capacity retention rates of the porous carbons of Examples 1 to 5, Comparative Examples 1 to 3, and 7

[0118]

[0119]

[0120] Table 4. Yields, specific surface areas, mesoporous specific surface areas, mesoporous specific surface area contributions, tap densities, conductivities, single particle strengths, voltage drops, and capacity retention rates of the porous carbons of Examples 6 to 9 and Comparative Examples 4 to 6

[0121]

[0122]

[0123] Data analysis:

[0124] 1) Data analysis of Tables 3 and 4:

[0125] The method of the embodiments of the present invention helps to improve the yield, specific surface area, mesoporous specific surface area, tap density (product density), single particle strength, and electrical conductivity of the porous carbon, can form a multi-stage controllable pore structure beneficial to ion transport inside the porous carbon, and can also improve the activation efficiency of the activator in the preparation process.

[0126] 2) Analysis Figure 2 The pore structure of the porous carbon can be obtained from the morphology of the nitrogen adsorption / desorption curve (nitrogen adsorption / desorption isotherm) of the porous carbon. Specifically, the nitrogen adsorption / desorption curve of the porous carbon of Example 1 presents a combination of Type I and Type IV, with an obvious hysteresis loop (Figure 2 In Example 1, the nitrogen adsorption / desorption curve of the porous carbon showed a separation phenomenon, indicating that the porous carbon in Example 1 contained abundant mesopores; the nitrogen adsorption / desorption curve of the porous carbon in Comparative Example 1 presented a quasi-I type, indicating that micropores (pore diameter < 2 nm) dominated in the pore structure of the porous carbon in Comparative Example 1; the nitrogen adsorption / desorption curve of the porous carbon in Comparative Example 2 presented a type-II, indicating that the pore size distribution of micropores in the pore structure of the porous carbon in Comparative Example 2 was slightly wider than that of the porous carbon in Comparative Example 1, containing a small amount of mesopores with a narrower pore size distribution, but still dominated by micropores overall; combined with Figure 3 and Figure 4 it can also be seen the distribution of mesopores and micropores in the porous carbons of Example 1, Comparative Example 1 and Comparative Example 2;

[0127] 3) Figure 5 The cyclic voltammetry (CV) curve of the electrodes prepared using the porous carbons of Example 1, Comparative Example 1 and Comparative Example 2 can be used to judge the performance of the capacitor. Specifically, the area enclosed by the cyclic voltammetry curve is positively correlated with the capacitance of the capacitor. The cyclic voltammetry (CV) curve of an ideal capacitor is rectangular, that is, the closer the shape of the cyclic voltammetry (CV) curve is to a rectangle, the better its capacitance formation mechanism. That is, the closer the cyclic voltammetry (CV) curve in the 0 - 0.05 V region is to the vertical axis, the better its rate performance. It can be seen that compared with Comparative Example 1 and Comparative Example 2, the shape of the cyclic voltammetry (CV) curve of the electrode prepared using the porous carbon of Example 1 is closer to a rectangle, has a larger area, and the cyclic voltammetry (CV) curve in the 0 - 0.05 V region is closer to the vertical axis. Therefore, the electrode prepared using the porous carbon of Example 1 has a higher capacitance, a better capacitance formation mechanism, and a better rate performance;

[0128] 4) From Figure 6 it can be seen that the voltage drop of Example 1 is significantly smaller than that of Comparative Example 1 and Comparative Example 2, indicating that the internal ion transport resistance of the porous carbon in Example 1 is smaller than that of Comparative Example 1 and Comparative Example 2;

[0129] 5) As the current density increases, that is, the charge-discharge speed increases. For example, 50 A / g is 50 times that of 1 A / g, that is, the charge-discharge speed is increased by 50 times. Figure 7 It describes the attenuation of the performance (capacitance) of the capacitor when the charge-discharge speed is increased (corresponding to the capacitance retention rate in Tables 3 and 4 (capacitance at 50 A g -1 / capacitance at 1 A g -1 ), %), specifically, from Figure 7 it can be seen that as the charge-discharge speed increases, the influence of the pore structure on the capacitance becomes more and more obvious. Due to the large ion diffusion resistance, the specific capacitance of the porous carbons in Comparative Example 1 and Comparative Example 2 (microporous materials) decreases significantly;

[0130] 6) Figure 8 The slopes of the impedance spectrum curves of Example 1, Comparative Example 1, and Comparative Example 2 decrease in sequence, indicating that the ion diffusion resistance of the porous carbon in Example 1, Comparative Example 1, and Comparative Example 2 increases in sequence, and the electrostatic ion adsorption ability becomes worse in sequence. That is, the porous carbon in Example 1 has a smaller ion diffusion resistance and the best electrostatic ion adsorption ability, which is most conducive to improving the capacitance performance. At the same time, the smaller the value at the intersection of the impedance spectrum curve of the electrode prepared from the porous carbon in Example 1 and the x-axis, the smaller the contact resistance of the porous carbon in Example 1;

[0131] 7) The dehydration temperature of Comparative Example 4 is too high, resulting in the loss of oxygen-containing groups, which is not conducive to the attachment of heavy oil;

[0132] 8) Comparing Example 8 and Comparative Example 7, the raw material compositions of the two groups are the same. In Comparative Example 7, the oxygen-rich matrix and heavy oil are respectively treated first, and then the obtained materials are mixed to obtain a mixture (the product of Comparative Example 7). All the performances exhibited by the product of Comparative Example 7 are lower than those of the material obtained by simultaneous action (the product of Example 8). This proves that the technical effects produced by the examples come from the common reaction of the oxygen-rich matrix, heavy oil, and activator, and the effects are not obtained by the direct combination of the prior art.

[0133] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing porous carbon, characterized in that, Comprising: Successively subjecting the plant tissue to first drying, pulverization, and dehydration treatment to obtain an oxygen-rich matrix; The temperature of the dehydration treatment is 120 - 320 °C; Mixing heavy oil, an activator, and a solvent to obtain a mixed solution; Impregnating the oxygen-rich matrix in the mixed solution, the impregnation time ≥ 10 min, and then removing the solvent to obtain a composite; Calcining the composite to obtain the porous carbon.

2. The preparation method according to claim 1, characterized in that The plant tissue includes one or more of branches, bamboo, coconut shell, rice husk, cattail fluff, corncob, bagasse; And / or, the heavy oil includes one or more of slurry, residue oil, tar; And / or, the activator includes one or more of potassium hydroxide, sodium hydroxide; And / or, the solvent includes ethanol and / or water; And / or, the temperature of the first drying is 190 - 210 °C, and the time of the first drying is 8 - 12 h; And / or, during the pulverization process, the plant tissue after the first drying is pulverized to a particle size D50 of 2 - 1000 μm; And / or, the time of the dehydration treatment is 2 - 6 h.

3. The preparation method according to claim 1, characterized in that The mass ratio of the oxygen-rich matrix to the activator is 1:(0.5 - 6); And / or, the mass ratio of the oxygen-rich matrix to the heavy oil is 1:(0.2 - 4).

4. The preparation method according to any one of claims 1 - 3, characterized in that The impregnation time is 10 - 240 min; And / or, during the impregnation process, one or more of shaking, stirring, ultrasonic wave is used for the impregnation; And / or, during the process of removing the solvent, heating and / or vacuum is used for removing the solvent.

5. The preparation method according to any one of claims 1 - 3, characterized in that The temperature of the calcination is 700 - 1100 °C, and the time of the calcination is 60 - 240 min; And / or, during the calcination process, the calcination is carried out in one or more atmospheres of nitrogen, argon, helium, carbon dioxide, water vapor.

6. The preparation method according to any one of claims 1 - 3, characterized in that After successively calcining the composite, washing and second drying the composite to obtain the porous carbon; During the washing process, one or more of water, hydrochloric acid, sulfuric acid, nitric acid is used for the washing; And / or, the temperature of the second drying is 120 - 150 °C, and the time of the second drying is 2 - 12 h.

7. The preparation method according to claim 6, characterized in that, Also comprising: After the second drying, subjecting the obtained product of the second drying to ball milling treatment to obtain the porous carbon.

8. A porous carbon, characterized in that, The porous carbon is obtained according to the preparation method of any one of claims 1 - 7.

9. The porous carbon according to claim 8, wherein, The specific surface area of the porous carbon is 500-2500 m 2 / g, the proportion of the mesoporous surface area in the total pore surface area is 10%-35%, and the total pore volume is 0.2-1.2 cm 3 / g, and the bulk density is 0.3-0.7 g / cm 3 ; the D50 of the porous carbon is 6-10 μm, and the single particle strength is 12-20 mN.

10. The porous carbon according to claim 8, characterized in that, The conductivity of the porous carbon is 600-1000 S / m, the voltage drop at a current density of 50 A / g is 0.08-0.25 V, and the capacity retention rate is 90%-95%; wherein, the capacity retention rate is the ratio of the capacitance at a current density of 50 A / g to the capacitance at a current density of 1 A / g.

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