Method for preparing high-porosity mesoporous carbon at ultralow temperature

Abstract

The invention relates to the technical field of mesoporous carbon material preparation, and particularly discloses a mesoporous carbon material preparation method, which comprises: S1, mixing a metal halide and an inorganic hydrogen bond donor, and carrying out heating stirring until a solution is clarified to obtain an inorganic eutectic solvent; s2, mixing the inorganic eutectic solvent and a biomass raw material for reaction; and S3, filtering and washing the material obtained in the step S2 to obtain the mesoporous carbon material. According to the preparation method, the inorganic eutectic solvent reacts with the biomass at a relatively low temperature, and the inorganic eutectic solvent swells the biomass and generates the template agent at the same time, so that the material has a pore structure, and high-temperature activation is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of mesoporous carbon material preparation, in particular to a method for preparing high-porosity mesoporous carbon at ultralow temperature. Background Art

[0002] Mesoporous carbon refers to carbon materials with pores concentrated in the range of 2 to 50 nm. It has excellent physical and chemical properties, such as adjustable porosity of the ordered structure, high specific surface area, and high chemical stability, thermal stability, and mechanical stability. This makes it extremely versatile in applications such as catalysis, energy storage, carbon dioxide capture, water purification, and adsorption. Waste biomass is a very promising and sustainable precursor for the preparation of mesoporous carbon materials. Since a large amount of agricultural and forestry waste biomass is generated annually around the world, converting this waste biomass into high-value materials can not only increase the value of these materials, but also solve the environmental problems caused by incineration.

[0003] In recent years, the preparation of mesoporous carbon using biomass as raw materials is mainly done through chemical activation and template methods. Among them, the chemical activation method generally uses KOH, H3PO4 and salts for activation. During the activation process, carbonization and activation are carried out simultaneously. These activations are mainly achieved at high temperatures. For example, the activation temperature using KOH is 700-900°C, the activation temperature using salt reagents is above 500°C, and the activation temperature of the phosphoric acid method is around 500°C. This type of method generally requires high-temperature activation above 500°C. Activation at high temperatures not only causes a large amount of decomposition and volatilization of the reagents, but also the strong corrosiveness of the activator at high temperatures will aggravate the damage to the equipment. Carbon materials prepared by chemical activation generally have a large specific surface area (greater than 1000m 2 / g), but its pore structure is mainly micropores, and the proportion of mesopores is generally less than 50%.

[0004] Another route to preparing mesoporous carbon involves using a template method, where a rigid material such as mesoporous SiO2 is used as a template. The template pores are then filled with a biocarbon precursor and removed to replicate the pore structure. This method requires the preparation of an ordered template, and the subsequent removal of the template requires the use of reagents such as hydrofluoric acid, which carries certain safety risks.

[0005] Therefore, there is an urgent need for a method for preparing biomass mesoporous carbon under low-temperature conditions that is low-cost, green, safe and efficient. Summary of the Invention

[0006] The present invention aims to overcome the shortcomings of existing technologies and provide a method for preparing high-porosity mesoporous carbon at ultralow temperatures. An inorganic deep eutectic solvent is used to react with biomass at relatively low temperatures. The inorganic deep eutectic solvent swells the biomass and simultaneously generates a template, imparting a porous structure to the material while avoiding high-temperature activation.

[0007] The object of the present invention is achieved through the following technical solutions:

[0008] One of the purposes of the present invention is to provide a method for preparing a mesoporous carbon material, comprising the following steps:

[0009] S1: Mixing a metal halide and an inorganic hydrogen bond donor, heating and stirring until the solution is clear to obtain an inorganic deep eutectic solvent;

[0010] S2: mixing the inorganic deep eutectic solvent and the biomass raw material for reaction;

[0011] S3: Filter and wash the material obtained in step S2 to obtain a mesoporous carbon material.

[0012] Furthermore, the metal halide includes at least one of zinc chloride, aluminum chloride, tin chloride and lead chloride.

[0013] Furthermore, the inorganic hydrogen bond donor includes at least one of phosphoric acid, boric acid, and ammonium chloride.

[0014] Furthermore, in step S1, the molar ratio of the metal halide to the inorganic hydrogen bond donor is 1:0.1-10.

[0015] Preferably, the molar ratio of the metal halide to the hydrogen bond donor is 0.3:1.

[0016] Furthermore, in step S1, the temperature of the heating and stirring is 60-140°C.

[0017] Preferably, the temperature of the heating and stirring is 90°C.

[0018] Furthermore, in step S2, the biomass raw material is at least one of native biomass and biomass separation and decomposition products.

[0019] Furthermore, the primary biomass includes at least one of bamboo, straw and sawdust; and the biomass separation and decomposition products include at least one of glucose, cellulose and lignin.

[0020] Furthermore, in step S2, the solid-liquid ratio of the biomass raw material and the inorganic deep eutectic solvent is 1 g:1-30 mL.

[0021] Preferably, the solid-to-liquid ratio of the biomass raw material to the deep eutectic solvent is 1 g:5 mL.

[0022] Furthermore, in step S2, the reaction temperature of the mixed reaction is 100-400° C.; and the reaction time of the mixed reaction is 0.5-30 h.

[0023] Preferably, the reaction temperature is 300° C.; and the reaction time of the mixing reaction is 2 h.

[0024] Furthermore, in step S3: the deep eutectic solvent washed out during the washing can be returned to step S2 for reuse as a raw material.

[0025] The second object of the present invention is to provide a method for preparing biomass mesoporous carbon without activation, which, based on steps S1 to S3, further comprises the following steps:

[0026] S4: Carbonizing the material obtained in step S3 in a high-temperature inert atmosphere to obtain high-temperature mesoporous carbon.

[0027] Furthermore, in step S4, the carbonization temperature is 450-1200° C.; and the carbonization time is 0.5-30 h.

[0028] Preferably, in step S4, the carbonization temperature is 800° C. and the carbonization time is 2 h.

[0029] A third object of the present invention is to provide a method for preparing biomass-based high-performance capacitor carbon, which, based on steps S1 to S3, further comprises the following steps:

[0030] S5: adding an activator to the material obtained in step S3 and activating it in a high-temperature inert gas to obtain a biomass-based high-performance capacitor carbon.

[0031] Preferably, in step S5, the activator includes at least one of potassium hydroxide, potassium carbonate or sodium carbonate.

[0032] Preferably, in step S5, the weight ratio of the material obtained in step S3 to the activating agent is 1:1 to 3.

[0033] It is worth noting that in the present invention, IDES (inorganic deep eutectic solvent) composed of metal halides and hydrogen bond donors has a developed hydrogen bond network, which allows the biomass to swell at 10-30°C. At lower temperatures (100-400°C), IDES reacts when heated to generate fine metal salt templates inside the biomass, so that the obtained carbon material has a huge mesoporous volume.

[0034] The beneficial effects of the present invention are:

[0035] 1) The method of the present invention directly uses the lowest-value lignocellulosic biomass such as straw, bamboo and sawdust as raw materials, without the need to separate the components of the lignocellulosic biomass, and can achieve high-value utilization of bulk low-value lignocellulosic biomass.

[0036] 2) The method of the present invention has a simple process, mild conditions, does not require the use of an activator at high temperature, has a high product yield, and the IDES used can be recycled and dissolved after forming a template.

[0037] 3) The biomass mesoporous carbon prepared by the method of the present invention has a large mesoporous volume and a high specific surface area. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a simplified process flow diagram of the present invention;

[0039] Figure 2 This is a scanning electron microscope image of the mesoporous carbon material in Example 1;

[0040] Figure 3 This is the SEM image of the carbon material in Comparative Example 4. DETAILED DESCRIPTION

[0041] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings, but the protection scope of the present invention is not limited to the following.

[0042] Example 1

[0043] A mesoporous carbon material is prepared by the following method:

[0044] Zinc chloride powder and solid phosphoric acid were mixed (heated to melt) at a molar ratio of 0.4:1, then stirred and heated at 90°C until the solution clarified to produce IDES. 30g of sawdust (a biomass raw material) was added to a crucible and mixed with 100mL of IDES. After stirring, the mixture was heated at 300°C for 2 hours. After the reaction, the resulting solid-liquid mixture was cooled to room temperature, filtered, and the solids were washed with hydrochloric acid and then water to a constant pH. The mesoporous carbon material was obtained after drying.

[0045] The obtained mesoporous carbon material was subjected to SEM detection, as shown in Figure 2 shown.

[0046] Example 2

[0047] Zinc chloride powder and 85wt% phosphoric acid solution were mixed in a 0.4:1 molar ratio and heated at 90°C with stirring until the solution became clear. Heating and stirring were continued for 12 hours to remove excess water from the raw materials, yielding IDES. 40g of bamboo powder, a biomass raw material, was added to a crucible and mixed with 100mL of IDES. After stirring, the mixture was heated at 230°C for 2 hours. After the reaction, the resulting solid-liquid mixture was cooled to room temperature and filtered. The solids were then washed with hydrochloric acid and then water until the pH was constant. The mesoporous carbon material was obtained after drying.

[0048] Example 3

[0049] Tin chloride powder, solid phosphoric acid, and boric acid powder were mixed (heated and melted) in a molar ratio of 0.6:1:0.2, then stirred and heated at 90°C until the solution clarified to produce IDES. 20g of wheat straw (a biomass raw material) was added to a crucible and mixed with 100mL of IDES. After stirring, the mixture was heated at 350°C for 2 hours. After the reaction, the resulting solid-liquid mixture was cooled to room temperature and filtered. The solid material was then washed with hydrochloric acid and then water to a constant pH. The mesoporous carbon material was obtained after drying.

[0050] Example 4

[0051] A high-temperature mesoporous carbon material is prepared by the following method:

[0052] Zinc chloride powder and 85wt% phosphoric acid solution were mixed in a 0.4:1 molar ratio and then heated with stirring at 90°C until the solution became clear. Heating and stirring were continued for 12 hours to remove excess water from the raw materials to obtain IDES. 40g of bamboo powder, a biomass raw material, was added to a crucible and mixed with 100mL of IDES. After stirring, the mixture was heated at 300°C for 2 hours. After the reaction, the resulting solid-liquid mixture was cooled to room temperature and filtered. The solid matter was then washed with an acidic solution and then with water to a constant pH. After drying, the mesoporous carbon material was obtained. The dried mesoporous carbon was placed in a crucible and carbonized at 800°C in a nitrogen atmosphere for 2 hours to obtain high-temperature biomass mesoporous carbon.

[0053] Example 5

[0054] Prepare a capacitor carbon, the specific method is as follows:

[0055] Tin chloride powder, solid phosphoric acid, and boric acid powder were mixed (heated to melt) in a molar ratio of 0.6:1:0.2 and then stirred and heated at 90°C until the solution clarified to produce IDES. 20g of wheat straw (a biomass raw material) was added to a crucible and mixed with 100mL of IDES. After stirring, the mixture was heated at 300°C for 2 hours. After the reaction, the resulting solid-liquid mixture was cooled to room temperature and filtered. The solids were then washed with an acidic solution and then with water to a constant pH. After drying, the mesoporous carbon material was obtained. The dried mesoporous carbon material was placed in a crucible and mixed with 10g of KOH, 2g of K2CO3, and 2g of Na2CO3. The mixture was carbonized at 800°C under a nitrogen atmosphere for 2 hours to produce capacitive carbon.

[0056] Comparative Example 1

[0057] A carbon material was prepared using biomass as a raw material. Unlike Example 1, phosphoric acid was omitted and zinc chloride was used alone. The specific method was as follows: 30 g of sawdust (a biomass raw material) was mixed with 100 g of zinc chloride and reacted at 300°C for 2 hours. After the reaction, the resulting solid-liquid mixture was cooled to room temperature and filtered. The solids were then washed with acid and then water until the pH was constant. The carbon material was then dried.

[0058] Comparative Example 2

[0059] A carbon material was prepared using biomass as a raw material. Unlike Example 2, zinc chloride powder was omitted and only phosphoric acid solution was used. The specific method was as follows: 40 g of the biomass raw material, sawdust, and 100 mL of 85% wt phosphoric acid were added to a crucible, mixed, stirred, and then heated at 300°C for 2 hours. After the reaction, the resulting solid-liquid mixture was cooled to room temperature and filtered. The solid material was then washed with acid and then water to a constant pH, and dried. The dried material was placed in a crucible and carbonized at 800°C under a nitrogen atmosphere for 2 hours to obtain the carbon material.

[0060] Comparative Example 3

[0061] Boric acid powder and 85wt% phosphoric acid solution were mixed in a molar ratio of 0.2:1, then stirred and heated at 90°C until the solution became clear. Heating and stirring were continued for 12 hours to remove excess water from the raw materials to obtain a mixture (because it did not contain metal halide salts, IDES could not be formed). 40g of biomass raw material sawdust and 100mL of the mixture were added to a crucible, mixed, and stirred evenly before being heated at 300°C for 2 hours. After the reaction, the resulting solid-liquid mixture was cooled to room temperature, filtered, and the solid matter was washed with acid and water to a constant pH, and then dried. The dried material was placed in a crucible and carbonized at 800°C under a nitrogen atmosphere for 2 hours to obtain a carbon material.

[0062] Comparative Example 4

[0063] Using DES as a comparison, choline chloride powder and lactic acid were mixed in a 1:1 molar ratio and heated at 90°C with stirring until the solution clarified. 30g of biomass straw powder and 100mL of DES were added to a crucible, mixed, stirred, and then heated at 300°C for 2 hours. After the reaction, the resulting solid-liquid mixture was cooled to room temperature, filtered, and the solids were washed with an acidic solution and then with water to a constant pH. The carbon material was then dried.

[0064] Experimental example

[0065] The carbon materials or high-temperature mesoporous carbon materials of Examples 1-3 and Comparative Examples 1-4 were tested using nitrogen adsorption-desorption method to calculate the specific surface area, pore volume, and mesoporous ratio. A blank control was also set up. The results are shown in the following table:

[0066] Blank control

[0067] 30 g of bamboo powder was placed in a crucible and heated at 300° C. for 2 h. The obtained biochar was washed with acid and water and dried to obtain a carbon material.

[0068] Table 1

[0069]

[0070] As shown in the table above, the mesoporous carbon materials prepared using sawdust, bamboo powder, and wheat straw as biomass feedstocks in Examples 1-3 all achieved a mesopore ratio exceeding 70%. Compared to carbon materials prepared without the addition of metal halides, inorganic hydrogen bond donors, or using other deep eutectic solvents, the specific surface area, pore volume, and mesopore ratio were more than doubled, demonstrating improved adsorption and storage capabilities.

[0071] The foregoing description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the form disclosed herein and should not be construed as excluding other embodiments. Rather, the present invention can be used in various other combinations, modifications, and environments and can be modified within the scope of the concept described herein through the above teachings or techniques or knowledge in the relevant field. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention are intended to be protected by the appended claims.

Claims

1. A method for preparing a mesoporous carbon material, characterized in that: The following steps are involved: S1: Mixing a metal halide and an inorganic hydrogen bond donor, heating and stirring until the solution is clear to obtain an inorganic deep eutectic solvent; S2: mixing the inorganic deep eutectic solvent and the biomass raw material for reaction; S3: Filter and wash the material obtained in step S2 to obtain a mesoporous carbon material.

2. The preparation method according to claim 1, wherein: The metal halide includes at least one of zinc chloride, aluminum chloride, tin chloride and lead chloride.

3. The preparation method according to claim 1, wherein: The inorganic hydrogen bond donor includes at least one of phosphoric acid, boric acid, and ammonium chloride.

4. The preparation method according to claim 1, wherein: In step S1, the molar ratio of the metal halide to the inorganic hydrogen bond donor is 1:0.1-10.

5. The preparation method according to claim 1, wherein: In step S2, the biomass raw material is at least one of primary biomass and biomass separation and decomposition products.

6. The preparation method according to claim 1, wherein: In step S2, the solid-liquid ratio of the biomass raw material to the inorganic deep eutectic solvent is 1:1-30.

7. The preparation method according to claim 1, wherein: In step S2, the reaction temperature of the mixed reaction is 100-400° C.; the reaction time of the mixed reaction is 0.5-30 h.

8. The mesoporous carbon material obtained by the preparation method according to any one of claims 1 to 7.

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