Method for preparing porous carbon by using humin

Abstract

The invention discloses a method for preparing porous carbon by using humin, and belongs to the field of carbon materials. The concentrated sulfuric acid is used for acidizing the humin under the conditions of high temperature and high pressure, so that the humin which is approximately spherical can be obtained, and the humin is pre-carbonized to form a relatively stable spherical structure. According to the invention, by controlling the temperature, on the premise of co-activation of carbon dioxide and water vapor and control of the gas flow rate, the porous carbon spheres with smooth surfaces can be obtained, and the yield can be improved at the same time. The method is simple to operate, the obtained porous carbon can well meet the preparation requirement of the silicon-carbon negative electrode, and the effect of turning waste into wealth is achieved.

Description

Technical Field

[0001] The present invention belongs to the field of carbon materials, and particularly relates to a method for preparing porous carbon by using humin. Background Art

[0002] At present, as the mainstream secondary battery, lithium-ion batteries have been widely used in fields such as mobile devices, electric vehicles, and renewable energy storage systems. Due to the disadvantages of traditional graphite anodes, such as low theoretical capacity, poor cycling performance, and rapid capacity decay, it is difficult to meet the continuously increasing requirements for battery energy density. Compared with traditional carbon materials, silicon can intercalate more lithium ions, so it is expected to improve the energy density of the battery. In addition, silicon resources are abundant, ranking second only to oxygen in the earth's crust, and it is non-toxic, harmless, and environmentally friendly. Therefore, silicon is expected to replace traditional graphite anodes to further improve the energy density of lithium-ion batteries to meet the requirements for the energy density of lithium-ion batteries in the fields of energy storage and electric vehicles.

[0003] However, silicon is a semiconductor material, and its conductivity at room temperature is much lower than that of graphite. When used as an electrode material, it limits the transport of electrons, thus affecting the rate performance of the battery. Moreover, silicon will undergo volume expansion during charge and discharge, causing cracks or even pulverization on the material surface, damaging the electrode structure, and resulting in rapid capacity decay. To solve these problems, carbon materials can be compounded with silicon. After the carbon material and the silicon material are compounded, they exhibit excellent conductivity and structural stability. This composite structure can not only effectively alleviate the volume expansion problem of silicon during charge and discharge, but also significantly improve the transport efficiency of lithium ions and electrons, thereby greatly optimizing its electrochemical performance. In particular, porous carbon with a porous structure is widely used to solve the problems faced by silicon anode materials in the application of lithium-ion batteries, such as volume expansion, poor structural stability, and poor charge transport performance, so as to improve the electrochemical performance of silicon anode materials and the overall performance of the battery, and promote the development of high-energy-density lithium-ion batteries. Moreover, the porous carbon industry is in its infancy and has great development space.

[0004] The commonly used preparation methods of porous carbon are the template method, the activation method, and the sol-gel method. Although the sol-gel method is simple to operate, it will cause the collapse of the pore structure during drying, and the uniformity of the obtained product is not good. The template method can adjust the pores, but impurities may be introduced when removing the template. Patent CN 108069423A discloses a method for preparing porous carbon using marine biomass. Using biomass shrimp and crab shells as raw materials, chitosan is obtained after a series of chemical treatments, and then natural halloysite nanotubes are used as templates to prepare porous carbon by the template method, realizing the secondary utilization of marine biomass waste resources. However, acids and alkalis are introduced many times during the pretreatment and template removal, which will affect the purity of the porous carbon and thus affect the battery performance. At the same time, waste acids and alkalis will also have an impact on the environment. Currently, the preparation of porous carbon mainly uses physical activation with water vapor and chemical activation with alkali. Patent CN119143127A discloses a method for preparing porous carbon by alkali activation. After uniformly mixing a strong alkali as an activator with a carbon source material, high-temperature calcination is carried out under the protection of an inert gas to prepare porous carbon, greatly improving the preparation efficiency of porous carbon. However, it is difficult to control the pore structure, the pores are uneven, and the use of strong acids and strong alkalis not only increases the operation risk but also may cause environmental pollution. Based on this, we use the method of co-activating with carbon dioxide and water vapor to prepare porous carbon.

[0005] The carbon source materials used for porous carbon mainly include synthetic polymers, fossil fuels, and biomass. Among them, the synthesis cost of polymers is relatively high, and there is a greater pressure for mass production. The representative of fossil fuels is asphalt. The Journal of Fuel Chemistry and Technology (Vol. 49, No. 11, 2021, pp. 1648-1655) reported a method for preparing a porous carbon material with a three-dimensional skeleton structure by using coal tar pitch as a raw material, using naphthalene as a pore-forming agent, adding naphthalene to the pitch, oxidizing it in the air to prepare oxidized pitch, and then activating it with water vapor. Using this method, porous carbon with good chemical stability can be obtained under low-cost conditions. However, asphalt will release toxic gases at high temperatures and requires tail gas treatment, which is not friendly to the environment. Biomass has received extensive attention due to its wide source and low cost, but the current process is not yet mature. Patent CN 115784227A discloses a method for preparing porous carbon using agricultural and forestry biomass. The obtained porous carbon has a relatively large specific surface area, but the unreasonable pore size distribution of the biomass-based carbon material makes it difficult to control its pore structure. A large amount of humin is produced during the industrial production of 5-hydroxymethylfurfural and is usually treated as solid waste. Acidifying humin under high temperature and high pressure with concentrated sulfuric acid can obtain spherical humin, which will form a relatively stable spherical structure after pre-carbonization, and then spherical porous carbon can be obtained only by activation. Currently, there is no process for preparing porous carbon using humin. Based on this, we use humin as a carbon source to prepare spherical porous carbon, achieving the effect of turning waste into treasure. Summary of the Invention

[0006] In view of the above deficiencies of the prior art, the present invention provides a method for preparing porous carbon using humin. The present invention uses humin as a carbon source, and under the co-activation of carbon dioxide and water vapor, by controlling the flow rate, spherical porous carbon is prepared.

[0007] The method for preparing porous carbon using humin of the present invention includes the following steps:

[0008] Put the carbon source into a tubular furnace, first perform pre-carbonization treatment, then raise the temperature of the tubular furnace to 900°C - 1000°C, and input a gas activator into the tubular furnace for activation and pore formation to obtain spherical porous carbon.

[0009] The pre-carbonization is carried out under the protection of an inert gas. The pre-carbonization temperature is 500°C and the time is 2 h. The inert gas is selected from one or more of helium, neon, argon, krypton, and nitrogen.

[0010] The gas activator is selected from one or more of carbon dioxide, air, and water vapor. The flow rate of the gas activator is controlled to be 0.1 mL / min - 50 mL / min.

[0011] Further preferably, the gas activator is carbon dioxide and water vapor.

[0012] Even more preferably, the flow rate of carbon dioxide is controlled to be 30 - 50 mL / min, and the flow rate of water vapor is controlled to be 0.1 - 0.5 mL / min.

[0013] The time for activation and pore formation is 1 h.

[0014] The carbon source is selected from one or more of spherical humin, coal tar pitch, glucose, and phenolic resin.

[0015] The spherical humin is obtained by the following method:

[0016] Dissolve an appropriate amount of humin and concentrated sulfuric acid in deionized water at a certain mass ratio, react in a high-pressure reaction kettle, and obtain spherical humin after filtration, washing, and drying.

[0017] Furthermore, the mass ratio of humin to concentrated sulfuric acid is 200:1.

[0018] Furthermore, the reaction temperature is 180°C and the reaction time is 3 h.

[0019] A large amount of humin is produced during the industrial production of 5-hydroxymethylfurfural, which is usually treated as solid waste. In the present invention, concentrated sulfuric acid is used to acidify humin under high temperature and high pressure conditions, and spherical humin can be obtained. After pre-carbonization, a relatively stable spherical structure will be formed. By controlling the temperature, co-activating with carbon dioxide and water vapor, and controlling the gas flow rate, carbon spheres with multiple pores and smooth surfaces can be obtained while increasing the yield. This method is simple to operate, and the obtained porous carbon can better meet the preparation requirements of silicon-carbon anodes, achieving the effect of turning waste into treasure. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a process flow chart for the preparation of the present invention.

[0021] Figure 2 It is a schematic diagram of the preparation process of the present invention.

[0022] Figure 3 It is a scanning electron microscope photograph of the porous carbon 1 prepared in Example 1.

[0023] Figure 4 It is a nitrogen isothermal adsorption-desorption curve of the porous carbon material prepared in Example 1.

[0024] Figure 5 It is a pore volume-pore size distribution diagram of the porous carbon material prepared in Example 1.

[0025] Figure 6 It is a scanning electron microscope photograph of the porous carbon 2 prepared in Example 2.

[0026] Figure 7 It is a scanning electron microscope photograph of the porous carbon 3 prepared in Example 3.

[0027] Figure 8 It is a scanning electron microscope photograph of the porous carbon 4 prepared in Example 4.

[0028] Figure 9 It is a scanning electron microscope photograph of the porous carbon 5 prepared in Example 5.

[0029] Figure 10 It is a scanning electron microscope photograph of the porous carbon 6 prepared in Comparative Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] The technical solution of the present invention will be further analyzed and described through specific embodiments below.

[0031] Example 1:

[0032] Dissolve 10 g of humin and 0.05 g of concentrated sulfuric acid (mass ratio of 200:1) in deionized water to prepare a 50 mL solution. Put the solution into a high-pressure reactor and react at 180 °C for 3 h. After filtration, washing, and drying, spherical humin is obtained. Use 2 g of spherical humin as the carbon source and perform a 2 h pre-carbonization treatment at 500 °C under nitrogen protection. Then, heat the tubular furnace to 900 °C and stop the input of nitrogen. Replace the input gas with carbon dioxide at a flow rate of 50 mL / min. At the same time, use a syringe to add deionized water to the tubular furnace at a flow rate of 0.5 mL / min. After the deionized water enters the tubular furnace, it evaporates into water vapor under the action of high temperature and flows together with carbon dioxide to the pre-carbonized spherical humin, and perform 1 h of activation to create pores to obtain spherical porous carbon 1.

[0033] The porous carbon 1 in Example 1 was characterized by scanning electron microscopy, and the results are as Figure 3 shown. It can be seen that the prepared porous carbon material is a smooth spherical shape. And the specific surface area of porous carbon 1 was analyzed to judge the pore-forming effect, specifically as Figure 4 、 5 shown. Figure 4 This is the nitrogen isothermal adsorption-desorption curve of the porous carbon material. It can be seen from the figure that there is a microporous structure. Figure 5 This is the pore volume-pore diameter distribution diagram of the porous carbon material. It can be seen from the figure that the main pores are micropores with a pore diameter of about 1 nm, and there are also some mesopores with a diameter of 2-5 nm, indicating that porous carbon has been prepared. When preparing the silicon-carbon negative electrode, the micropores can provide enough space for silicon to buffer its volume expansion during the lithium intercalation process, and at the same time help to increase the deposition amount of silicon. The mesoporous structure can further accommodate the volume change of silicon particles and provide channels for the diffusion of lithium ions, thereby improving the cycle stability and rate performance of the battery. The specific surface area of the obtained porous carbon is about 1700 m 2 / g, and the pore volume is about 0.85 cm 3 / g. Theoretically, it can significantly improve the reversible specific capacity and charge-discharge efficiency of the silicon-carbon negative electrode.

[0034] Example 2:

[0035] Porous carbon 2 was prepared by the same method as in Example 1, with the only difference being that: the spherical humin was not pre-carbonized and was directly activated. The scanning electron microscopy (SEM) image of the prepared porous carbon 2 is as Figure 6 shown. It can be seen from the figure that without pre-carbonization to stabilize the spherical morphology and directly performing high-temperature activation, the spherical structure will be damaged, affecting its pore structure.

[0036] Example 3:

[0037] Porous carbon 3 was prepared by the same method as in Example 1, with the only difference being that the activation temperature was increased from 900 °C to 1000 °C. The scanning electron microscope (SEM) image of the prepared porous carbon 3 is as shown in Figure 7 It can be seen from the figure that after the temperature was increased to 1000 °C, spherical porous carbon was prepared. When the temperature was relatively high (above 900 °C), the porous carbon spheres were severely bonded, destroying the pore structure. At the same time, due to the bonding of the porous carbon spheres, the specific surface area decreased significantly.

[0038] Example 4:

[0039] Porous carbon 4 was prepared by the same method as in Example 1, with the only difference being that deionized water was not input during activation. The scanning electron microscope (SEM) image of the prepared porous carbon 4 is as shown in Figure 8 It can be seen from the figure that without the pore-forming effect of water vapor, spherical porous carbon was also prepared, but the surface was relatively rough and there were more impurities.

[0040] Example 5:

[0041] Porous carbon 5 was prepared by the same method as in Example 1, with the only difference being that the flow rate of the syringe was increased from 0.5 mL / min to 1 mL / min. The scanning electron microscope (SEM) image of the prepared porous carbon 5 is as shown in Figure 9 It can be seen from the figure that when the flow rate increased, spherical porous carbon could be prepared, but the yield of the porous carbon decreased due to the increase in the gas flow rate.

[0042] Comparative Example 1:

[0043] Using coal tar pitch as the carbon source material, porous carbon 6 was prepared by the same method as in Example 1. The scanning electron microscope (SEM) image of the prepared porous carbon 6 is as shown in Figure 10 It can be seen that when coal tar pitch was used as the carbon source material, the prepared product did not have a definite morphology.

Claims

1. A method for preparing porous carbon using humin, characterized in that The steps include: The carbon source is placed in a tubular furnace and pre-carbonized. The tubular furnace is then heated to 900°C-1000°C, and a gas activator is introduced into the tubular furnace for activation and pore formation to obtain spherical porous carbon.

2. The method according to claim 1, characterized in that: The pre-carbonization is carried out under the protection of inert gas, the pre-carbonization temperature is 500° C., and the time is 2 hours.

3. The method according to claim 2, characterized in that: The inert gas is selected from one or more of helium, neon, argon, krypton and nitrogen.

4. The method according to claim 1, characterized in that: The gas activating agent is selected from one or more of carbon dioxide, air and water vapor.

5. The method according to claim 4, characterized in that: The flow rate of the gas activator is controlled to be 0.1 mL / min-50 mL / min.

6. The method according to claim 4, characterized in that: The gas activating agents are carbon dioxide and water vapor.

7. The method according to claim 6, characterized in that: The flow rate of carbon dioxide was controlled at 30-50 mL / min, and the flow rate of water vapor was controlled at 0.1-0.5 mL / min.

8. The method according to claim 1, characterized in that: The activation pore-forming time is 1 h.

9. The method according to claim 1, characterized in that: The carbon source is selected from one or more of spherical humin, coal tar pitch, glucose, and phenolic resin.

10. The method according to claim 9, characterized in that The spherical humin is prepared by the following method: Humin and concentrated sulfuric acid are dissolved in deionized water at a mass ratio of 200:1, reacted in a high-pressure reactor, and spherical humin is obtained after filtering, washing and drying.

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