A multi-level pore activated carbon and application thereof, and a method for preparing a multi-level pore activated carbon by using balsa wood

Abstract

The present application belongs to the technical field of waste gas adsorption, and particularly relates to a kind of multi-level pore activated carbon and its application, a kind of method for preparing multi-level pore activated carbon by using balsa wood.The micropore pore size of the activated carbon of the present application includes two intervals of 0.5-0.85 nm and 1-2 nm.The intervals are respectively matched with the molecular dynamics diameter of styrene and the pore size through which a single molecule passes.The pore structure size in the interval of 0.5-0.85 nm makes the styrene adsorbed in the pore size structure single-molecule adsorption, the styrene adsorbed in the pore structure is separated from each other by the pore wall material, prevents the polymerization of the aggregated styrene under the condition of thermal effect, and avoids the problem that the saturated activated carbon is difficult to regenerate.The pore structure size in the interval of 1-2 nm makes the styrene pass in the form of a single molecule, reduces the possibility of the aggregation and polymerization of the styrene when moving and transporting in the pore, and promotes the efficient desorption and regeneration of the styrene.

Description

Technical Field

[0001] This invention belongs to the field of waste gas adsorption technology, specifically relating to a multi-level porous activated carbon and its application, and a method for preparing multi-level porous activated carbon using balsa wood. Background Technology

[0002] Styrene is a common chemical raw material. As an important polymer monomer, it can polymerize on its own or with other monomers, and is widely used in the synthetic resin, synthetic fiber, styrene-butadiene rubber, plastics, and fiberglass industries. Styrene has a saturated vapor pressure of approximately 700 Pa at an ambient temperature of 20°C, classifying it as a volatile organic compound (VOC). Styrene released into the environment can enter the human body through inhalation and skin contact, causing serious harm to red blood cells, the central nervous system, lungs, liver, and kidneys, and may even cause cancer. Therefore, international and domestic environmental protection organizations have strict requirements regarding the styrene content in the environment. Thus, the removal and treatment of styrene in human living and production environments, especially in fiberglass, plastics, and resin production areas, is essential for ensuring environmental safety and maintaining normal production.

[0003] Currently, researchers have developed various methods for treating styrene waste gas in the environment, such as combustion, catalysis, scrubbing, and adsorption. Among these, activated carbon adsorption is the most economical and widely used method for treating styrene waste gas due to its low raw material cost, simple operation, and applicability to environmental protection equipment. However, the adsorption capacity of commercially available activated carbon for styrene is still relatively low, generally between 300 mg / g and 500 mg / g. Therefore, it is necessary to further improve the styrene adsorption capacity of activated carbon. Summary of the Invention

[0004] The purpose of this invention is to provide a hierarchical porous activated carbon and its application, as well as a method for preparing hierarchical porous activated carbon using balsa wood. The hierarchical porous activated carbon prepared by the method provided by this invention has a high adsorption capacity for styrene.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing hierarchical porous activated carbon using balsa wood, comprising the following steps:

[0007] Balsa wood is pre-carbonized, mixed with a pore-forming agent and water, and allowed to stand to obtain a precursor material; the pore-forming agent includes potassium salt, ammonium bicarbonate and melamine; the potassium salt includes at least one of potassium carbonate and potassium bicarbonate;

[0008] The precursor material is carbonized to obtain the hierarchical porous activated carbon.

[0009] Preferably, the particle size of the balsa wood does not exceed 80 mesh; the pre-carbonization temperature is 190-210℃ and the time is 8-16h.

[0010] Preferably, the mass ratio of the potassium salt, ammonium bicarbonate and melamine is 0.5-1.5:0.2-1:0.2-1.

[0011] Preferably, the mass ratio of balsa wood to pore-forming agent is 1:0.9 to 3.5;

[0012] The mass ratio of balsa wood to water is 1:4 to 10.

[0013] Preferably, the settling process is carried out under sealed conditions, and the settling time is 12 to 24 hours.

[0014] Preferably, the carbonization includes performing a first carbonization and a second carbonization sequentially;

[0015] The temperature of the first carbonization is 70-90℃, the heating rate to the temperature of the first carbonization is 5-10℃ / min, and the holding time is 6-12h;

[0016] The second carbonization temperature is 700-800℃, the heating rate to the second carbonization temperature is 1-4℃ / min, and the holding time is 2-4h.

[0017] Preferably, after carbonization, the carbonized material is further subjected to post-processing, which includes: cooling the carbonized material to below 60°C, washing the cooled material with water until neutral, and then acid leaching, and washing the acid-leached material again with water until neutral and then drying.

[0018] The solvent used for acid leaching is hydrochloric acid solution with a concentration of 1.5 mol / L; the acid leaching time is 6 to 36 hours.

[0019] The present invention also provides a multi-level porous activated carbon prepared by the method described above, wherein the multi-level porous activated carbon includes macroporous structure, mesoporous structure and microporous structure;

[0020] The microporous structure includes a first microporous structure and a second microporous structure;

[0021] The pore size of the first microporous structure is 0.5 to 0.85 nm, and the pore size of the second microporous structure is 1 to 2 nm, excluding 2 nm.

[0022] Preferably, the pore size of the mesoporous structure is 2–10 nm;

[0023] The proportions of the pore volume of the first microporous structure, the second microporous structure, and the mesoporous structure to the total pore volume are 18-25%, 30-41%, and 16-26%, respectively.

[0024] Within the range of 0.5–190 nm, the total pore volume of the hierarchical porous structure is 0.9–1.2 cm³. 3 / g;

[0025] The specific surface area of ​​the multi-level porous activated carbon is 1800–2300 m². 2 / g.

[0026] This invention also provides the application of the multi-level porous activated carbon described in the above technical solution in the adsorption of styrene.

[0027] This invention provides a method for preparing hierarchical porous activated carbon using balsa wood, comprising the following steps: pre-carbonizing balsa wood, mixing it with a pore-forming agent and water, and allowing it to stand to obtain a precursor material; the pore-forming agent includes potassium salt, ammonium bicarbonate and melamine; the potassium salt includes at least one of potassium carbonate and potassium bicarbonate; and carbonizing the precursor material to obtain the hierarchical porous activated carbon.

[0028] This invention utilizes the multi-scale micron-level pore structure and carbon network of balsa wood, combined with the pore-forming effect of a pore-forming agent on balsa wood powder, to prepare activated carbon materials in which the micropore size is mainly distributed in two ranges: 0.5–0.85 nm and 1–2 nm. These two ranges correspond to the molecular dynamic diameter of styrene molecules (0.6 nm) and the pore size (1.1 nm–1.6 nm) through which styrene molecules can pass in single-molecule form, respectively. Within the micropore range, firstly, the pore structure size in the 0.5 nm–0.85 nm range allows styrene molecules adsorbed in this pore structure to be adsorbed as single molecules. In this case, the styrene molecules adsorbed in the pore structure are separated from each other by the pore wall material, preventing the aggregated styrene molecules from polymerizing under thermal effects, thus avoiding the problem of difficult regeneration and reuse of saturated activated carbon materials. Secondly, the pore structure size in the 1 nm–2 nm range allows styrene molecules to pass through in single-molecule form. This pore structure reduces the possibility of aggregation and polymerization of styrene molecules during movement and transport within the pores, promoting efficient desorption and regeneration of styrene molecules.

[0029] Furthermore, balsa wood itself possesses pores at the tens of micrometer scale, arranged along the growth direction of the wood, used for the transport of moisture and inorganic salts, as well as micrometer and submicrometer-scale pores on the pore walls. After carbonization, it can provide a multi-level micrometer-scale pore structure of corresponding scale in the carbon material. This multi-scale micrometer-to-submicrometer macroporous structure facilitates the rapid transport of styrene molecules to adsorption sites within the activated carbon material, as well as the rapid desorption process. Attached Figure Description

[0030] Figure 1 SEM image of balsa wood sawdust material obtained in Example 1;

[0031] Figure 2 Here is a SEM image of the hierarchical porous activated carbon obtained in Example 1;

[0032] Figure 3 The image shows the pore size distribution of the hierarchical porous activated carbon obtained in Example 1.

[0033] Figure 4 The curve shows the change in the amount of styrene adsorbed by the hierarchical porous activated carbon obtained in Example 1. Detailed Implementation

[0034] This invention provides a method for preparing hierarchical porous activated carbon using balsa wood, comprising the following steps:

[0035] Balsa wood is pre-carbonized, mixed with a pore-forming agent and water, and allowed to stand to obtain a precursor material; the pore-forming agent includes potassium salt, ammonium bicarbonate and melamine; the potassium salt includes at least one of potassium carbonate and potassium bicarbonate;

[0036] The precursor material is carbonized to obtain the hierarchical porous activated carbon.

[0037] In this invention, balsa wood is pre-carbonized, mixed with a pore-forming agent and water, and left to stand to obtain a precursor material.

[0038] In this invention, the particle size of the balsa wood is preferably no more than 80 mesh, and more preferably 40-80 mesh. In this invention, the balsa wood is preferably sawdust generated during the cutting and processing of balsa wood material for wind turbine blade cores, and the undersize material obtained by sieving through a 40-80 mesh sieve. Using balsa wood sawdust from the core material processing as raw material in this invention has the following three advantages: First, it eliminates the wood crushing process, reducing process steps and saving energy and equipment; second, balsa wood sawdust is a waste material from wind turbine blade core material processing plants, and its low price helps reduce the price of the prepared activated carbon, improving the product's market competitiveness; third, the use of balsa wood sawdust waste material also solves the waste disposal problem of wind turbine blade core material processing plants, which is conducive to the construction of a zero-waste factory.

[0039] In this invention, the pre-carbonization temperature is preferably 190–210°C, specifically 190°C, 200°C, or 210°C, and the time is preferably 8–16 hours, specifically 8 hours, 10 hours, 12 hours, 14 hours, or 16 hours. In this invention, the pre-carbonization method is preferably electric heating baking. In this invention, pre-carbonization can remove moisture and some water-repellent oily substances from the wood flour material, so that the treated wood flour can fully adsorb the pore-forming agent aqueous solution, improving the dispersibility of the pore-forming agent material in the treated wood flour.

[0040] In this invention, the potassium salt includes at least one of potassium carbonate and potassium bicarbonate; the preferred mass ratio of the potassium salt, ammonium bicarbonate, and melamine is 0.5–1.5:0.2–1:0.2–1. In this invention, the preferred mass ratio of balsa wood to the pore-forming agent is 1:0.9–3.5; the preferred mass ratio of balsa wood to water is 1:4–10.

[0041] In this invention, the mixing is preferably carried out under stirring conditions, and the stirring time is preferably 30 minutes. In this invention, the settling is preferably carried out under sealed conditions, and the settling time is preferably 12–24 hours. In this invention, during the settling process, potassium ions (K+) in the potassium salt... + ) can be adsorbed into wood flour, K + The theoretical radius of the ions is 0.36 nm, which is favorable for constructing microporous structures of 0.5–0.85 nm during the carbonization of wood flour. Potassium ions in potassium salts react with NH3·H2O produced when ammonium bicarbonate dissolves in water to form potassium amide (KNH2·NH3). Potassium ions in potassium salts can also react with melamine molecules dissolved in water to form potassium melamine (K(C3N6H5)). The long axis dimension of the unit cell in potassium amide crystals is approximately 1.1 nm, which is favorable for constructing microporous structures of 1–2 nm. The long axis dimension of the unit cell in potassium melamine crystals is approximately 1.9 nm, which is favorable for constructing mesoporous structures >2 nm. Furthermore, potassium amide molecules release ammonia gas during heating, and potassium melamine molecules release hydrogen gas during heating; these gas molecules generated during heating are beneficial for constructing mesoporous and macroporous structures.

[0042] After the settling period, the present invention preferably does not perform any post-processing and directly proceeds to subsequent carbonization.

[0043] After obtaining the precursor material, the present invention carbonizes the precursor material to obtain the multi-level porous activated carbon.

[0044] In this invention, the carbonization is preferably carried out under a protective atmosphere, preferably high-purity nitrogen or high-purity argon. In this invention, the carbonization preferably includes sequentially performing a first carbonization and a second carbonization; the temperature of the first carbonization is preferably 70–90°C, specifically 70°C, 80°C, or 90°C; the heating rate to the first carbonization temperature is preferably 5–10°C / min, specifically 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, or 10°C / min; the holding time is preferably 6–12 hours, specifically 6 hours, 8 hours, 10 hours, or 12 hours; during the first carbonization process, on the one hand, moisture in the raw material slurry is removed; on the other hand, while removing moisture, the pore-forming agent derived from the pore-forming agent is transformed from a free state to a molecular state and bound to the wood flour-based raw material, facilitating pore-forming during the second carbonization process.

[0045] In this invention, the preferred temperature for the second carbonization is 700–800°C, specifically 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, 760°C, 770°C, 780°C, 790°C, or 800°C. The preferred heating rate to the second carbonization temperature is 1–4°C / min, specifically 1°C / min, 2°C / min, 3°C / min, or 4°C / min. The preferred holding time is 2–4 hours, specifically 2 hours, 3 hours, or 4 hours. h; During the second carbonization process, the carbon-containing wood components (mainly cellulose, hemicellulose and lignin) in balsa wood powder undergo carbonization through dehydrogenation, deoxygenation and other reactions during high-temperature heating to generate carbon materials; at the same time, during the heating and carbonization process, pore-forming materials (such as potassium ions, KNH2·NH3 and K(C3N6H5)) undergo thermal decomposition reactions to generate solid compounds of potassium element and gas molecules such as NH3 and H2, which produce a pore-forming effect and generate porous carbon materials with multiple pore sizes.

[0046] In this invention, the carbonization is preferably carried out in an atmosphere-protected furnace.

[0047] In this invention, after carbonization, it is preferable to further include post-processing the obtained carbonized material. The post-processing preferably includes: cooling the carbonized material to below 60°C, washing the cooled material with water until neutral, then acid leaching, washing the acid-leached material again with water until neutral, and then drying. The solvent used for acid leaching is preferably hydrochloric acid solution, and the concentration of the hydrochloric acid solution is preferably 1.5 mol / L. The acid leaching time is preferably 6 to 36 hours.

[0048] In a specific embodiment of the present invention, the carbonization process is as follows: the precursor material is loaded into a corundum sagger with a lid, and the filling volume is 60-80% of the sagger volume; after the sagger lid is closed, the sagger containing the material is placed in a protective atmosphere furnace, and the first carbonization and the second carbonization are carried out sequentially under the protective atmosphere; then it is cooled, and the cooled carbonized material is washed with water until neutral and then acid-leached; then it is washed with water again until neutral; finally, the obtained product is placed in a drying oven to dry, and multi-level porous activated carbon is obtained.

[0049] The present invention also provides a hierarchical porous activated carbon prepared by the method described above, wherein the hierarchical porous activated carbon includes a macroporous structure, a mesoporous structure and a microporous structure; the microporous structure includes a first microporous structure and a second microporous structure;

[0050] The pore size of the first microporous structure is 0.5 to 0.85 nm, and the pore size of the second microporous structure is 1 to 2 nm, excluding 2 nm.

[0051] In this invention, the pore size of the mesoporous structure is preferably 2–10 nm; the pore volumes of the first microporous structure, the second microporous structure, and the mesoporous structure account for 18–25%, 30–41%, and 16–26% of the total pore volume, respectively. In this invention, within the range of 0.5–190 nm, the total pore volume of the hierarchical pore structure is 0.9–1.2 cm³. 3 / g. In this invention, the specific surface area of ​​the hierarchical porous activated carbon is preferably 1800-2300 m². 2 / g.

[0052] This invention also provides the application of the hierarchical porous activated carbon described in the above technical solution in the adsorption of styrene. The present invention does not specifically limit the implementation method of the application; any method well known to those skilled in the art can be used. In this invention, the initial adsorption capacity of the hierarchical porous activated carbon for styrene is 900–1200 mg / g, and it is regenerable. After five regenerations, the styrene adsorption capacity is 700–1000 mg / g.

[0053] Unless otherwise specified, the materials and equipment used in this invention are all commercially available products in the field.

[0054] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0055] Example 1

[0056] The sawdust produced by Jiangxi Aorison New Energy Technology Co., Ltd. in the process of processing balsa wood (originating from Papua New Guinea) into wind turbine blade core material was sieved through a 60-mesh sieve, and the undersize material was recorded as balsa wood sawdust material.

[0057] The obtained balsa wood sawdust material was pre-carbonized by electric heating at 200℃ for 8 hours. Then, the pre-carbonized balsa wood, potassium bicarbonate, ammonium bicarbonate, and melamine were added to water and mechanically stirred for 30 minutes. The weight ratio of balsa wood sawdust material, potassium bicarbonate, ammonium bicarbonate, melamine, and water was 1:1:0.5:0.5:8. The stirred and mixed material was placed in a plastic sealed container, sealed and stored for 20 hours, and then dried to obtain the precursor material.

[0058] The precursor material was loaded into a corundum sagger with a lid, filling the sagger to 80% of its volume. After covering the sagger, the sagger containing the material was placed in a protective atmosphere furnace. Under the protection of a high-purity argon atmosphere, the temperature was first increased to 80°C at a rate of 5°C / min and held for 10 hours. Then, the temperature was increased to 780°C at a rate of 3°C / min and held for 3 hours. After cooling to 40°C, the cooled carbonized material was washed with water until neutral and then placed in a 1.5 mol / L hydrochloric acid aqueous solution for acid leaching for 24 hours. It was then washed with water again until neutral. Finally, the obtained product was dried in a drying oven to obtain multi-level porous activated carbon.

[0059] Example 2

[0060] The sawdust produced by Jiangxi Aorison New Energy Technology Co., Ltd. in the process of processing balsa wood (originating from Papua New Guinea) into wind turbine blade core material was sieved through an 80-mesh sieve, and the undersize material was recorded as balsa wood sawdust material.

[0061] The obtained balsa wood sawdust material was pre-carbonized by electric heating at 210℃ for 6 hours. Then, the pre-carbonized balsa wood, potassium bicarbonate, ammonium bicarbonate, and melamine were added to water and mechanically stirred for 30 minutes. The weight ratio of balsa wood sawdust material, potassium bicarbonate, ammonium bicarbonate, melamine, and water was 1:1.5:1:1:10. The stirred and mixed material was placed in a plastic sealed container, sealed and stored for 16 hours, and then dried to obtain the precursor material.

[0062] The precursor material was loaded into a corundum sagger with a lid, filling the sagger to 80% of its volume. After covering the sagger, the sagger containing the material was placed in a protective atmosphere furnace. Under the protection of a high-purity argon atmosphere, the temperature was first raised to 90°C at a rate of 8°C / min and held for 12 hours. Then, the temperature was raised to 750°C at a rate of 2°C / min and held for 4 hours. After cooling to room temperature, the cooled carbonized material was washed with water until neutral and then placed in a 1.2 mol / L hydrochloric acid aqueous solution for acid leaching for 20 hours. It was then washed with water again until neutral. Finally, the obtained product was dried in a drying oven to obtain multi-level porous activated carbon.

[0063] Example 3

[0064] The sawdust produced by Jiangxi Aoruisen New Energy Technology Co., Ltd. in the process of processing balsa wood (originating from Papua New Guinea) into wind turbine blade core material was sieved through a 40-mesh sieve, and the material that passed through the sieve was recorded as balsa wood sawdust material.

[0065] The obtained balsa wood sawdust material was pre-carbonized by electric heating at 190℃ for 15 hours. Then, the pre-carbonized balsa wood, potassium bicarbonate, ammonium bicarbonate, and melamine were added to water and mechanically stirred for 30 minutes. The weight ratio of balsa wood sawdust material, potassium bicarbonate, ammonium bicarbonate, melamine, and water was 1:0.5:0.2:0.2:4. The stirred and mixed material was placed in a plastic sealed container, sealed and stored for 12 hours, and then dried to obtain the precursor material.

[0066] The precursor material was loaded into a covered corundum crucible, filling it to 80% of its volume. After covering the crucible, the crucible containing the material was placed in a protective atmosphere furnace. Under the protection of a high-purity argon atmosphere, the temperature was first increased to 70°C at a rate of 10°C / min and held for 6 hours. Then, the temperature was increased to 700°C at a rate of 1°C / min and held for 2 hours. After cooling to 60°C, the cooled carbonized material was washed with water until neutral and then placed in a 1.0 mol / L hydrochloric acid aqueous solution for acid leaching for 12 hours. It was then washed with water again until neutral. Finally, the obtained product was dried in a drying oven to obtain multi-level porous activated carbon.

[0067] Example 4

[0068] The sawdust produced by Jiangxi Aoruisen New Energy Technology Co., Ltd. in the process of processing balsa wood (originating from Papua New Guinea) into wind turbine blade core material was sieved through a 40-mesh sieve, and the material that passed through the sieve was recorded as balsa wood sawdust material.

[0069] The obtained balsa wood sawdust material was pre-carbonized by electric heating at 200℃ for 12 hours. Then, the pre-carbonized balsa wood, potassium bicarbonate, ammonium bicarbonate, and melamine were added to water and mechanically stirred for 20 minutes. The weight ratio of balsa wood sawdust material, potassium bicarbonate, ammonium bicarbonate, melamine, and water was 1:1:0.7:0.3:6. The stirred and mixed material was placed in a plastic sealed container, sealed and stored for 24 hours, and dried to obtain the precursor material.

[0070] The precursor material was loaded into a corundum sagger with a lid, filling the sagger to 60% of its volume. After covering the sagger, the sagger containing the material was placed in a protective atmosphere furnace. Under the protection of a high-purity argon atmosphere, the temperature was first raised to 85°C at a rate of 6°C / min and held for 8 hours. Then, the temperature was raised to 800°C at a rate of 4°C / min and held for 2.5 hours. After cooling to 30°C, the cooled carbonized material was washed with water until neutral and then placed in a 2.0 mol / L hydrochloric acid aqueous solution for acid leaching for 16 hours. It was then washed with water again until neutral. Finally, the obtained product was dried in a drying oven to obtain multi-level porous activated carbon.

[0071] Example 5

[0072] The sawdust produced by Jiangxi Aorison New Energy Technology Co., Ltd. in the process of processing balsa wood (originating from Papua New Guinea) into wind turbine blade core material was sieved through a 60-mesh sieve, and the undersize material was recorded as balsa wood sawdust material.

[0073] The obtained balsa wood sawdust material was pre-carbonized by electric heating at 200℃ for 8 hours. Then, the pre-carbonized balsa wood, potassium carbonate, ammonium bicarbonate, and melamine were added to water and mechanically stirred for 30 minutes. The weight ratio of balsa wood sawdust material, potassium carbonate, ammonium bicarbonate, melamine, and water was 1:1:0.5:0.5:8. The stirred and mixed material was placed in a plastic sealed container, sealed and stored for 20 hours, and then dried to obtain the precursor material.

[0074] The precursor material was loaded into a corundum sagger with a lid, filling the sagger to 80% of its volume. After covering the sagger, the sagger containing the material was placed in a protective atmosphere furnace. Under the protection of a high-purity argon atmosphere, the temperature was first increased to 80°C at a rate of 5°C / min and held for 10 hours. Then, the temperature was increased to 780°C at a rate of 3°C / min and held for 3 hours. After cooling to 40°C, the cooled carbonized material was washed with water until neutral and then placed in a 1.5 mol / L hydrochloric acid aqueous solution for acid leaching for 24 hours. It was then washed with water again until neutral. Finally, the obtained product was dried in a drying oven to obtain multi-level porous activated carbon.

[0075] Comparative Example 1

[0076] The sawdust produced by Jiangxi Aorison New Energy Technology Co., Ltd. in the process of processing balsa wood (originating from Papua New Guinea) into wind turbine blade core material was sieved through a 60-mesh sieve, and the undersize material was recorded as balsa wood sawdust material.

[0077] The obtained balsa wood sawdust material was pre-carbonized by electric heating at 200℃ for 8 hours. Then, the pre-carbonized balsa wood, potassium bicarbonate, and melamine were added to water and mechanically stirred for 30 minutes. The weight ratio of balsa wood sawdust material, potassium bicarbonate, melamine, and water was 1:1:0.5:8. The stirred and mixed material was placed in a plastic sealed container, sealed and stored for 20 hours, and then dried to obtain the precursor material.

[0078] The precursor material was loaded into a covered corundum crucible, filling it to 80% of its volume. After covering the crucible, the crucible containing the material was placed in a protective atmosphere furnace. Under the protection of a high-purity argon atmosphere, the temperature was first increased to 80°C at a rate of 6°C / min and held for 10 hours. Then, the temperature was increased to 780°C at a rate of 3°C / min and held for 3 hours. After cooling to room temperature, the cooled carbonized material was washed with water until neutral and then placed in a 2.0 mol / L hydrochloric acid aqueous solution for acid leaching for 18 hours. It was then washed with water again until neutral. Finally, the obtained product was dried in a drying oven to obtain multi-level porous activated carbon.

[0079] Performance testing

[0080] Test Example 1

[0081] The appearance morphology of the balsa wood sawdust material and the final activated carbon obtained in the examples was characterized using scanning electron microscopy, and the elemental composition of the obtained activated carbon was analyzed using energy dispersive spectroscopy.

[0082] Figure 1 This is a SEM image of the balsa wood sawdust material obtained in Example 1. Figure 2 SEM image of the hierarchical porous activated carbon obtained in Example 1; from Figure 1 As can be seen, balsa wood sawdust sieved through a 60-mesh sieve contains nearly parallel channels with a diameter of about ten micrometers. The channel walls contain micrometer and submicrometer pore structures, which are generally the wood's own pore structures used to transport moisture and inorganic salts. Figure 2 As can be seen, the obtained multi-level porous activated carbon has micron-scale pore structure and pit structure on its surface, and the pore walls and pits also contain a large number of submicron-scale pore structures.

[0083] The elemental energy dispersive spectroscopy (EDS) data of the activated carbon obtained in Example 1 are shown in Table 1.

[0084] Table 1. Elemental energy dispersive spectroscopy (EDS) data of activated carbon obtained in Example 1.

[0085]

[0086] As can be seen from Table 1, the main component of the obtained activated carbon is carbon (C), with carbon accounting for 95.89% of the material by weight. It also contains small amounts of oxygen, nitrogen, and other elements.

[0087] Test Example 2

[0088] The surface area and pore size distribution of the activated carbon obtained in the examples and comparative examples were tested using a specific surface area and pore size analyzer.

[0089] from Figure 3 As can be seen, the micropore size of the prepared hierarchical activated carbon is mainly distributed in two ranges: 0.5 nm to 0.85 nm and 1 nm to 2 nm; it also contains some mesoporous structures, and the pore size of the mesoporous structures is mainly distributed in the smaller range of 2 to 10 nm.

[0090] The specific surface area and pore volume data of the obtained activated carbon are shown in Table 2;

[0091] Table 2. Specific surface area and pore volume of activated carbon obtained from the examples and comparative examples.

[0092]

[0093] As can be seen from Table 2, the specific surface area of ​​the activated carbon material obtained in Example 1 is 2159 m². 2 / g, the pore volume in the 0.5nm to 0.85nm pore size range is 0.207cm³. 3 / g, the pore volume in the 1nm to 2nm pore size range is 0.450cm³. 3 / g, the pore volume in the 2nm to 10nm pore size range is 0.267cm³. 3 / g.

[0094] The specific surface area of ​​the activated carbon obtained in Example 2 was 2297 m². 2 / g, the ratio of pore volume distributed in the pore size ranges of 0.5nm~0.85nm, 1nm~2nm and 2nm~10nm is approximately 1:2.1:1.2.

[0095] The specific surface area of ​​the activated carbon obtained in Example 3 was 1843 m². 2 / g, with a pore volume of 0.198 cm³ distributed in the pore size range of 0.5 nm to 0.85 nm. 3 / g, the pore volume in the 1nm to 2nm pore size range is 0.361cm³. 3 / g, the pore volume in the 2nm to 10nm pore size range is 0.162cm³. 3 / g.

[0096] The specific surface area of ​​the activated carbon obtained in Example 4 was 2013 m². 2 / g, the ratio of pore volume distributed in the pore size ranges of 0.5nm~0.85nm, 1nm~2nm and 2nm~10nm is approximately 1:2.1:1.2.

[0097] The specific surface area of ​​the activated carbon obtained in Example 5 was 2084 m². 2 / g, the micropore volumes distributed in the 0.5nm–0.85nm and 1nm–2nm pore size ranges are 0.268cm³, respectively. 3 / g, 0.346cm 3 / g, the mesopore volume distributed in the pore size range of 2nm to 10nm is 0.286cm³. 3 / g.

[0098] The specific surface area of ​​the activated carbon obtained in Comparative Example 1 was 871 m². 2 / g, the pore capacity of the pore structure distributed in the 1nm to 2nm pore size range is relatively low, with a pore capacity of 0.068m. 3 / g, pore capacity in the pore size range of 0.5nm to 0.85nm.

[0099] Test Example 3

[0100] Static styrene gas adsorption tests were conducted on the multi-level porous activated carbon obtained in the examples and comparative examples. After adsorption saturation, the saturated activated carbon material was placed in a 160℃ forced-air drying oven for desorption for 12 hours. After desorption, the activated carbon was subjected to static styrene gas adsorption tests again. The adsorption tests were repeated 5 times, and the styrene gas adsorption data obtained are shown in Table 3.

[0101] Table 3 shows the adsorption test results of activated carbon obtained in the examples and comparative examples.

[0102]

[0103] Figure 4 The curve showing the change in the amount of styrene adsorbed by activated carbon obtained in Example 1; from Figure 4 It can be seen that the initial adsorption capacity of the obtained activated carbon for styrene gas can reach 1150 mg / g. During the adsorption-desorption cycle, the decreasing trend of styrene adsorption gradually slows down, and the styrene adsorption capacity in the fifth cycle is about 930 mg / g, indicating that the obtained activated carbon material can be regenerated and used.

[0104] As can be seen from Table 3, the activated carbon obtained in Example 2 can adsorb styrene gas up to 1203 mg / g initially. In the adsorption-desorption cycle, the styrene adsorption capacity in the fifth cycle is 992 mg / g, indicating that the obtained activated carbon material can be regenerated and used.

[0105] The activated carbon obtained in Example 3 had an initial adsorption capacity of 918 mg / g for styrene. During the adsorption-desorption cycle, the styrene adsorption capacity was 746 mg / g in the fifth cycle. The obtained activated carbon material can be regenerated and reused.

[0106] The activated carbon obtained in Example 4 had an initial adsorption capacity of 1086 mg / g for styrene. During the adsorption-desorption cycle, the styrene adsorption capacity was 894 mg / g in the fifth cycle. The obtained activated carbon material can be regenerated and reused.

[0107] The activated carbon obtained in Example 5 had an initial adsorption capacity of 971 mg / g for styrene. During the adsorption-desorption cycle, the adsorption capacity for styrene in the fifth cycle was 785 mg / g. The obtained activated carbon material can be regenerated and reused.

[0108] The activated carbon obtained in Comparative Example 1 had an initial adsorption capacity of 583 mg / g for styrene, and in the adsorption-desorption cycle, the adsorption capacity for styrene in the fifth cycle was 277 mg / g.

[0109] As can be seen from Tables 2 and 3, the styrene adsorption capacity of activated carbon materials is positively correlated with the sum of the pore volumes of the corresponding activated carbon micropores with a pore size of 0.5–0.85 nm and pore sizes of 1–2 nm. That is, the larger the sum of the pore volumes, the greater the corresponding styrene adsorption capacity.

[0110] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing hierarchical porous activated carbon using balsa wood, characterized in that, Includes the following steps: Balsa wood is pre-carbonized, mixed with a pore-forming agent and water, and allowed to stand to obtain a precursor material. The pore-forming agent includes potassium salt, ammonium bicarbonate, and melamine. The potassium salt includes at least one of potassium carbonate and potassium bicarbonate. The mass ratio of the potassium salt, ammonium bicarbonate, and melamine is 0.5–1.5:0.2–1:0.2–1. The mass ratio of balsa wood to the pore-forming agent is 1:0.9–3.

5. The precursor material is carbonized to obtain the multi-level porous activated carbon; the carbonization includes sequentially performing a first carbonization and a second carbonization; the temperature of the first carbonization is 70-90℃, the heating rate to the first carbonization temperature is 5-10℃ / min, and the holding time is 6-12h; the temperature of the second carbonization is 700-800℃, the heating rate to the second carbonization temperature is 1-4℃ / min, and the holding time is 2-4h. The multi-level porous activated carbon includes macroporous structure, mesoporous structure and microporous structure; the microporous structure includes a first microporous structure and a second microporous structure; the pore size of the first microporous structure is 0.5 to 0.85 nm, and the pore size of the second microporous structure is 1 to 2 nm, excluding 2 nm; The multi-level porous activated carbon is used to adsorb styrene.

2. The method according to claim 1, characterized in that, The particle size of the balsa wood does not exceed 80 mesh; the pre-carbonization temperature is 190-210℃ and the time is 8-16h.

3. The method according to claim 1, characterized in that, The mass ratio of balsa wood to water is 1:4 to 10.

4. The method according to claim 1, characterized in that, The settling process is carried out under sealed conditions, and the settling time is 12 to 24 hours.

5. The method according to claim 1, characterized in that, After carbonization, the process further includes post-processing the carbonized material, which includes: cooling the carbonized material to below 60°C, washing the cooled material with water until neutral, then acid leaching, and washing the acid-leached material again with water until neutral before drying. The solvent used for acid leaching is hydrochloric acid solution with a concentration of 1.5 mol / L; the acid leaching time is 6 to 36 hours.

6. The multi-level porous activated carbon prepared by the method according to any one of claims 1 to 5, characterized in that, The multi-level porous activated carbon includes macroporous, mesoporous, and microporous structures. The microporous structure includes a first microporous structure and a second microporous structure; The pore size of the first microporous structure is 0.5 to 0.85 nm, and the pore size of the second microporous structure is 1 to 2 nm, excluding 2 nm.

7. The multi-level porous activated carbon according to claim 6, characterized in that, The pore size of the mesoporous structure is 2–10 nm; The proportions of the pore volume of the first microporous structure, the second microporous structure, and the mesoporous structure to the total pore volume are 18-25%, 30-41%, and 16-26%, respectively. Within the range of 0.5–190 nm, the total pore volume of the hierarchical porous structure is 0.9–1.2 cm³. 3 / g; The specific surface area of ​​the multi-level porous activated carbon is 1800–2300 m². 2 / g.

8. The application of the hierarchical porous activated carbon according to claim 6 or 7 in the adsorption of styrene.

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