Activated carbon for methane adsorption and method for producing the same

Abstract

This invention discloses activated carbon for methane adsorption and its preparation method, belonging to the field of activated carbon technology. The preparation method includes the following steps: mixing walnut shell powder with phosphoric acid and stirring to obtain a matured material; drying and shaping the matured material sequentially to obtain a carbonized material; performing preliminary activation on the carbonized material using a two-stage heating process, followed by water washing for dephosphorization and drying to obtain a crude product; subjecting the crude product to secondary activation, acid washing, and water washing sequentially to obtain a preliminary product; and modifying the preliminary product with alkali and hydrophobicity to obtain the finished product. The obtained finished product has an average pore size of 2.1 nm and a specific surface area of ​​2000 m². 2 It has a large number of micropores and a capacity of / g or more, which can effectively adsorb methane and is not easily clogged during use.

Description

Technical Field

[0001] This invention belongs to the field of activated carbon technology, specifically relating to an activated carbon for methane adsorption and its preparation method. Background Technology

[0002] Natural gas, as a clean energy source, is closely linked to many human activities. To better transport natural gas from its production sites to various global applications, key storage technologies include compressed natural gas (CNG) storage, liquefied natural gas (LNG) storage, and adsorbed natural gas (ANG) storage. As the applications of natural gas continue to expand, higher demands are being placed on the safe storage and use of natural gas.

[0003] In terms of safety and cost-effectiveness of storage technology, traditional storage and transportation rely on high pressure (20~25MPa) or cryogenic liquefaction (LNG), which has problems such as high cost and low safety. ANG has very obvious technical and cost advantages from the above two perspectives. Based on the technological breakthrough of carbon-based materials for methane adsorption, it can achieve efficient storage and transportation under low pressure, which is an important direction for future natural gas storage and transportation.

[0004] Activated carbon is a porous carbon material with a highly developed pore structure and a large specific surface area. As an excellent adsorbent, it has long been widely used in environmental protection, chemical industry, food industry, hydrometallurgy, and pharmaceutical refining. With the increasing application of activated carbon in new fields such as electrode materials for supercapacitors, catalyst supports, gas separation, and hydrogen and natural gas storage materials, its specific surface area has reached 800–1500 m². 2 Ordinary activated carbon with a specific surface area of ​​2000 m² / g has a limited adsorption capacity, which cannot meet the requirements of its application. Therefore, it is necessary to develop activated carbon with a specific surface area of ​​2000 m² / g. 2 Super activated carbon with a density of / g or higher has become a new hotspot in the research field of porous carbon materials.

[0005] Currently, the prepared surface area has reached 2000 m². 2 Super activated carbon with a specific surface area of ​​2000 m² or higher is mostly produced using the alkaline process, which uses potassium hydroxide as an activating agent. The advantage of this process is that the activated carbon pores are primarily micropores. However, using potassium hydroxide as an activating agent presents problems such as high activation temperatures (700-900℃), strong corrosiveness to reaction equipment, and the inability to recycle the activating agent. This limits the continuous large-scale production of potassium hydroxide to batch production, resulting in low efficiency. While the phosphoric acid process offers advantages such as low activation temperatures (400-600℃), lower corrosivity, and recyclability, the activated carbon produced by this method is predominantly mesopores, making it difficult to achieve a specific surface area of ​​2000 m². 2Super activated carbon of / g and above. Summary of the Invention

[0006] The technical problem to be solved by this invention is: how to prepare a sample with a specific surface area of ​​2000 m² using the phosphoric acid method. 2 Super activated carbon suitable for methane adsorption, with a density of 6g or more and an average pore size of around 2.1nm.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for preparing activated carbon for methane adsorption, comprising the following steps: S1. Mix walnut shell powder with phosphoric acid and stir to mature the material. S2. The calcined material is dried and shaped sequentially to obtain carbonized material; S3. The carbonized material is initially activated by a two-stage heating process to obtain a crude product; S4. The crude product is subjected to high-temperature dephosphorization, secondary activation, acid washing and water washing to obtain the initial product; S5. The initial product is modified by alkali and hydrophobicity to obtain the finished product (activated carbon for methane adsorption).

[0008] Furthermore, the particle size of the walnut shell powder described in S1 is 10-100 mesh.

[0009] Furthermore, in S1, the impregnation ratio of walnut shell powder to phosphoric acid is 1:0.6~1.5; and the concentration of phosphoric acid is 40~85%.

[0010] Furthermore, the ripening temperature in S1 is 100~200℃, and the time is 0.5~3h.

[0011] Furthermore, the first stage of the two-stage heating process involves heating from room temperature to 300°C and holding the temperature at that temperature for 1 hour, while the second stage involves heating from 300°C to 400~600°C. The gas used for preliminary activation is one or more of nitrogen, carbon dioxide, water vapor, and air.

[0012] Furthermore, the secondary activation temperature is 500~900℃, the activation time is 2~8h, and the activator is one or more of nitrogen, carbon dioxide, water vapor, and air.

[0013] Further, the alkali modification is performed by stirring the crude product with 0.1-20 wt% alkali solution at 30-80°C for 1-5 hours, and then rinsing until neutral. The alkaline solution is prepared from deionized water and one or more of ammonium bicarbonate, sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, and ammonia; the solid-liquid ratio of the crude product to the alkaline solution is 1:1~6.

[0014] Furthermore, the hydrophobic modification is performed by: preparing a DES solution by reacting myristic acid or lauric acid with thymol, stirring the alkali-modified activated carbon with the DES solution at 80 °C for 30 min, and then washing and drying the solution after cooling.

[0015] The present invention also provides activated carbon for methane adsorption prepared by any of the above-described preparation methods.

[0016] Furthermore, the activated carbon used for methane adsorption has a specific surface area greater than 2000 m². 2 / g.

[0017] The beneficial effects of this invention are as follows: the activated carbon provided by this invention for methane adsorption has an average pore size of 2.1 nm and a specific surface area of ​​2000 m². 2 It has a large number of micropores and a capacity for adsorbing methane. It also has the characteristics of being easy to keep out of clogging during use and having a long service life. Attached Figure Description

[0018] Figure 1 This is a pore size distribution diagram of the activated carbon obtained in Example 1 of the present invention; Figure 2 The methane adsorption curve of the activated carbon obtained in Example 1 of this invention; Figure 3 This is a 60x scanning electron microscope image of the activated carbon obtained in Example 1 of the present invention; Figure 4 This is a 300x scanning electron microscope image of the activated carbon obtained in Example 1 of the present invention; Detailed Implementation To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0019] A method for preparing activated carbon for methane adsorption includes the following steps: S1. Mix walnut shell powder with phosphoric acid and stir to mature the material. S2. The calcined material is dried and shaped sequentially to obtain carbonized material; S3. The carbonized material is initially activated by a two-stage heating process to obtain a crude product; S4. The crude product is subjected to high-temperature dephosphorization and secondary activation, and then acid washing and water washing to obtain the initial product; S5. The initial product is modified by alkali and hydrophobicity to obtain activated carbon for methane adsorption.

[0020] As can be seen from the above description, the beneficial effects of the present invention are as follows: The preparation method provided by the present invention uses the phosphoric acid method for activated carbon processing. The specific selection of walnut shells as raw materials can effectively compensate for the defects of hollow carbon produced by the phosphoric acid method. Combined with appropriate processes, activated carbon with micropores can be obtained. In the aging process provided by the present invention, preliminary carbonization is completed first. Before the preliminary activation, the aged material undergoes pre-activation through drying and shaping, generating a certain amount of microporous structure, thus providing a structural basis for subsequent preliminary and secondary activation. Subsequently, in the two-stage heating process of preliminary activation, the first stage ensures uniform heating of the material while preparing for subsequent activation, and the second stage fully activates the material at high temperature. In the secondary activation process, a physical activation agent is used to re-etch the micropores generated in the first activation (pre-activation). Using physical activation agents such as water vapor, the activated carbon with an average pore size of about 1.7 nm is opened to about 2.1 nm, that is, a secondary enhancement of micropores below 1.8 nm is performed, increasing the original pore volume to 0.8 cm³. 3 The activated carbon content was increased from approximately 1.0 cm³ / g. 3 / g or even 1.4cm 3 / g This process greatly enhances the adsorption of methane in micropores. At the same time, the increase in pore size (greater than 2nm) provides channels for methane, improving the adsorption efficiency while ensuring the adsorption capacity. After alkali modification, the acidic oxygen-containing functional groups on the activated carbon surface are reduced, the surface polarity of the activated carbon is lowered, and the adsorption capacity for non-polar methane molecules is enhanced. Finally, hydrophobic modification makes the activated carbon surface hydrophobic, avoiding competitive adsorption of water molecules during the adsorption of methane, which would lead to micropore blockage and significantly increase the service life of the finished product.

[0021] In one or more embodiments, the particle size of the walnut shell powder in S1 is 10-100 mesh. Preferably, it is 10-30 mesh.

[0022] As described above, unlike the general selection of traditional coal-based or other biomass raw materials, this invention specifically selects walnut shell powder, which has the characteristics of high carbon content, low ash content, and high strength. It is more likely to produce micropores rather than mesopores, thus optimizing the quality of the activated carbon precursor and ensuring that the final product can achieve a specific surface area of ​​2000 m². 2 / g or above and with an average pore size of around 2.1nm.

[0023] In one or more embodiments, the impregnation ratio of walnut shell powder to phosphoric acid in S1 is 1:0.6~1.5, preferably 1:0.8~1.2; the concentration of phosphoric acid is 40~85%, preferably 50~70%.

[0024] As described above, the impregnation ratio is the solid-liquid ratio. Using phosphoric acid as the activator differs from traditional methods that primarily use potassium hydroxide as an alkaline activator to prepare super-activated carbon with high specific surface area and low pore size. By precisely controlling the concentration of phosphoric acid and the impregnation ratio, the activation intensity and pore structure can be directionally regulated. Compared to activation processes using a single concentration or ratio, this parameter range allows for targeted adjustment of micropore formation efficiency, ensuring the target specific surface area (around 2000 m² / g) and average pore size (around 2.1 nm). Using phosphoric acid as the activator, a specific surface area of ​​1700 m² / g can be obtained after initial activation. 2 The super activated carbon has a pore size of about 1.8 nm and a final activated carbon microporosity of over 80%, with better ones exceeding 85%. The pore volume is about 1 cm³ / g, with better ones around 1.3 cm³ / g. Its adsorption capacity for methane is 140~170 V / V at 3.4 MPa and 180~220 V / V at 5.4 MPa.

[0025] In one or more embodiments, the curing temperature in S2 is 100~200°C and the time is 0.5~3h; preferably 140~180°C and the time is 1~2h.

[0026] As described above, the purpose of ripening is to allow phosphoric acid to be fully stirred into the walnut shell powder at a certain high temperature. At the same time, the combined action of phosphoric acid and temperature at this temperature decomposes the cellulose and other organic substances in the walnut shell, thereby creating micropores and achieving a pre-activation effect.

[0027] In one or more embodiments, the drying temperature is 80~120°C.

[0028] In one or more embodiments, the setting temperature is 120~220°C, the air intake rate is 10~60 L / min, and the setting time is 12~24 h. The air intake rate is preferably 30~60 L / min.

[0029] As described above, air is typically introduced during the shaping process. This process is stress-free, and the oxygen in the air acts as an oxidant to oxidize the organic matter in the walnut shells. The matured walnut shells are then placed in an oven for drying and shaping. During this step, the material undergoes preliminary carbonization, which is also a pre-activation process. This process generates a certain amount of microporous structures, providing a structural basis for subsequent activation.

[0030] In one or more embodiments, the first stage of the two-stage heating process involves heating from room temperature to 100~300℃ and holding the temperature for 1~3 hours, while the second stage continues to heat to 400~600℃. The gas used for preliminary activation is one or more of nitrogen, carbon dioxide, water vapor, and air.

[0031] In one or more embodiments, the heating rate in the two-stage heating process is preferably 5~10℃ / min.

[0032] As can be seen from the above description, an appropriate heating rate can be selected according to the specific equipment and efficiency requirements, and the above is the preferred range.

[0033] As described above, the initial heating rate is relatively fast, which can easily lead to uneven heating. Therefore, it is necessary to maintain the temperature within this range for 1 to 3 hours to ensure uniform heating. After the initial holding time, the heating rate slows down, and uneven heating is unlikely to occur. At the same time, maintaining the temperature for 1 to 3 hours is not a strict requirement, but if it is too short, uneven heating may occur. If the initial holding time is too long, the activated carbon pores that are initially activated may become larger due to the influence of air, thus failing to achieve the purpose of controlling the pore size.

[0034] In one or more embodiments, a gas is introduced at the start of the initial activation heating process. The gas is one or more of nitrogen, carbon dioxide, water vapor, and air, preferably air, carbon dioxide, and nitrogen.

[0035] In one or more embodiments, high-temperature dephosphorization specifically involves placing the pre-activated carbonized material into an atmosphere rotary furnace, setting the heating rate to 5-10°C / min, the dephosphorization temperature to 500-800°C, and the time to 4-10 hours, with water vapor as the introduced gas. The activated carbon activated by the phosphoric acid method has a total phosphorus content between 10,000 and 20,000 ppm. If water washing is used, it can easily cause eutrophication of the water body. However, by decomposing the phosphate at high temperature and removing the phosphorus element with water vapor, the problem of eutrophication of the water body is avoided. At the same time, the total phosphorus content can be reduced from 10,000-20,000 ppm to below 500 ppm. After secondary activation and rinsing, it can be reduced to below 100 ppm, which is far below the national requirements.

[0036] In one or more embodiments, the heating rate of the two-stage heating stage and the heating rate of the high-temperature dephosphorization stage may be the same or different, and can be adjusted according to the equipment used, efficiency requirements, etc.

[0037] In one or more embodiments, the secondary activation is carried out in a rotary kiln at a speed of 30-50 r / min, the temperature of the secondary activation is 500-900℃, the activation time is 2-8 h, and the activating agent is one or more of nitrogen, carbon dioxide, water vapor, and air, preferably carbon dioxide and water vapor.

[0038] In one or more embodiments, high-temperature dephosphorization and secondary activation can be carried out in the same equipment. The atmosphere rotary furnace is first heated to the dephosphorization temperature for dephosphorization. After dephosphorization, the temperature is raised again to the activation temperature to reopen the voids that collapsed during the dephosphorization process. After the experimental process is completed, the total phosphorus and BET index are tested.

[0039] As described above, specific activation gases can be selected for different process stages. For initial activation, air, carbon dioxide, and nitrogen are preferred; for secondary activation, carbon dioxide and water vapor are preferred. By matching the gas type with different process stages, the pore etching efficiency can be enhanced, while excessive ablation can be suppressed, and the specific surface area and pore size distribution can be balanced.

[0040] In one or more embodiments, the secondary activation process further includes acid washing and water washing steps, specifically: washing with inorganic acid, including one or more of phosphoric acid, hydrochloric acid, nitric acid, oxalic acid, and sulfuric acid, with a solid-liquid ratio of 1:3 to 1:5, depending on the specific process; placing the mixture in a heating device and heating and stirring for 0.5 to 3 hours; discharging the waste liquid; adding an equal volume of pure water; and rinsing repeatedly with pure water 2 to 5 times to remove excess acid.

[0041] As described above, the purpose of acid washing is to remove residual iron salts from activated carbon. Taking hydrochloric acid as an example, iron salts, calcium salts, etc., which are inorganic and organic salts, are converted into water-soluble ferric chloride under the action of hydrochloric acid. Calcium chloride is carried away by the solution with each water change, thus ensuring the purity of activated carbon. The temperature during acid washing and water washing with heating and stirring is 80~100℃, and preferably, the temperature of acid washing and water washing is about 100℃ (i.e., heating to boiling).

[0042] In one or more embodiments, the alkali modification is performed by adding 0.1-20 wt% alkali solution to the crude product, stirring at 30-80°C for 1-5 hours, and then rinsing with deionized water until neutral. The alkaline solution is prepared from deionized water and one or more of the following: ammonium bicarbonate, sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, and ammonia; the solid-liquid ratio of the crude product to the alkaline solution is 1:1 to 6.

[0043] As described above, alkali modification can reduce the acidic oxygen-containing functional groups on the surface of activated carbon, lower the surface polarity of activated carbon, and thus enhance the adsorption capacity of activated carbon for non-polar methane molecules.

[0044] In one or more embodiments, hydrophobic modification is performed as follows: a DES solution (melted at 60 °C) is prepared by mixing myristic acid or lauric acid with thymol at a molar ratio of 2:1. The alkali-modified active peptide is then poured into the DES solution and stirred at 80 °C for 30 min. After cooling, the peptide is washed with water and dried. Specifically, deionized water can be used at a solid-liquid ratio of 1:3, and the peptide is washed three times before drying at 80-150 °C.

[0045] As described above, the saturated straight-chain hydrocarbons of myristic acid or lauric acid possess strong hydrophobicity, which can enhance the hydrophobicity of activated carbon. The isopropyl group (-CH(CH3)2) on the side chain of thymol provides steric hindrance, preventing the hydrophobic chains from packing tightly and maintaining pore permeability. After myristic acid or lauric acid (hydrogen bond acceptor) and thymol (hydrogen bond donor) form DES, the melting point of the system drops to 50-70℃. A slight heating is sufficient to achieve a homogeneous liquid-phase reaction, making the operation simple and convenient for surface modification. Hydrophobic modification can endow the activated carbon surface with hydrophobic properties, avoiding competitive adsorption of water molecules during methane adsorption that could lead to micropore blockage, thus significantly increasing the service life of the finished activated carbon. Drying is generally carried out at a temperature between 80-120℃ until the moisture content of the activated carbon is below 2%.

[0046] The activated carbon for methane adsorption prepared by any of the above methods has a specific surface area greater than 2000 m². 2 / g.

[0047] Embodiment 1 of the present invention is: a method for preparing activated carbon for methane adsorption, comprising the following steps: S1. Mix 10*30 mesh walnut shell powder with 70% phosphoric acid at an impregnation ratio of 1:1, and stir and mature at 160℃ for 2 hours in a kneader to obtain matured material. S2. Place the calcined material in an oven and dry it at 120°C for 2 hours. Then place it in a shaping furnace at 180°C for 20 hours to shape it. The air flow rate in the shaping furnace is 40L / min to obtain carbonized material. S3. Place the carbonized material into an atmosphere rotary furnace, introduce air, rotate at 50 r / min, first raise the temperature from room temperature to 300℃, hold for 1 hour, then raise the temperature from 300℃ to 450℃ and hold for 3 hours; the heating rate in S3 is 10℃ / min. S4. The crude product is placed in an atmosphere rotary furnace for high-temperature dephosphorization and secondary activation sequentially. The rotation speed is 50 r / min, the dephosphorization temperature is 600℃, the dephosphorization time is 6 h, the activation temperature is 900℃, the activation time is 6 h, and the activator is water vapor. Then, acid washing is performed. The specific steps are as follows: industrial hydrochloric acid with a concentration of about 31% is added to pure water to prepare a 1:10 hydrochloric acid solution. The solid-liquid ratio of the solution to the crude product is 1:5. The prepared solution and activated carbon are placed in a glass reactor and heated and stirred for 3 h at a temperature of 80℃. After the time is completed, the waste liquid is discharged and an equal volume of pure water is added. The mixture is repeatedly rinsed 5 times to remove excess acid and obtain the initial product. The heating rate in S4 is 10℃ / min. S5. Place the initial product into a glass reactor, add 10wt% ammonium bicarbonate solution, the solid-liquid ratio is 1:3, and stir at 40℃ for 2 hours; then prepare a DES solution by mixing myristic acid and thymol at a molar ratio of 2:1, pour the activated carbon into the DES solution and stir at 80℃ for 30 minutes, cool, wash with deionized water at a solid-liquid ratio of 1:3 3 times, and dry at 100℃ to obtain activated carbon for methane adsorption; Reference Figures 1-4 The performance of the activated carbon obtained in Example 1 for methane adsorption was tested, and the results showed that its specific surface area was 2084 m². 2 / g, average pore size 2.04nm, total pore volume 1.06cm³ 3 The microporosity is 85.13%, and the excess adsorption capacity for methane at 3.4 MPa is 171.7304 cm³. 3 / g, with an excess adsorption capacity of 211.5056 cm⁻¹ at 6 MPa. 3 / g, with an excess adsorption capacity of 226.2339 cm⁻¹ at 10 MPa. 3 / g.

[0048] Embodiment 2 of the present invention is as follows: A method for preparing activated carbon for methane adsorption includes the following steps: S1, will 80* 100-mesh walnut shell powder and 50% phosphoric acid are mixed at an impregnation ratio of 1:1.2 and stirred and matured in a kneader at 180°C for 1 hour to obtain matured material; S2. Place the calcined material in an oven and dry it at 100°C. Then place it in a shaping furnace at 160°C for 24 hours to shape it. The air flow rate in the shaping furnace is 40L / min to obtain carbonized material. S3. Place the carbonized material into an atmosphere rotary furnace, introduce air, rotate at 50 r / min, first raise the temperature from room temperature to 100℃, hold for 3 hours, then raise the temperature from 300℃ to 400℃ and hold for 1.5 hours; the heating rate in S3 is 5℃ / min. S4. The crude product is placed in an atmosphere rotary furnace for high-temperature dephosphorization and secondary activation sequentially. The rotation speed is 50 r / min, the dephosphorization temperature is 800℃, the dephosphorization time is 4 h, the activation temperature is 900℃, the activation time is 4 h, and the activator is water vapor. Then, acid washing is performed. The specific steps are as follows: industrial hydrochloric acid with a concentration of about 31% is added to pure water to prepare hydrochloric acid at a ratio of 1:8. The solid-liquid ratio of the solution to the crude product is 1:3. The prepared solution and activated carbon are placed in a glass reactor and heated and stirred for 3 h at a temperature of 100℃. After the time is completed, the waste liquid is discharged and an equal volume of pure water is added. The mixture is rinsed repeatedly 3 times to remove excess acid and obtain the initial product. The heating rate in S4 is 10℃ / min. S5. Place the initial product into a glass reactor, add 5wt% sodium hydroxide solution, the solid-liquid ratio is 1:5, and stir at 30℃ for 1 hour; then prepare a DES solution by mixing myristic acid and thymol at a molar ratio of 2:1, pour the activated carbon into the DES solution and stir at 70℃ for 50 minutes, cool, wash with deionized water at a solid-liquid ratio of 1:5 3 times, and dry at 120℃ to obtain activated carbon for methane adsorption.

[0049] Embodiment 3 of the present invention is as follows: A method for preparing activated carbon for methane adsorption includes the following steps: S1. Mix 10*30 mesh walnut shell powder with 60% phosphoric acid at an impregnation ratio of 1:0.8, and stir and mature in a kneader at 140℃ for 1.5 hours to obtain matured material; S2. Place the calcined material in an oven and dry it at 80°C. Then place it in a shaping furnace at 200°C for 18 hours to shape it. The air flow rate in the shaping furnace is 30L / min to obtain carbonized material. S3. Place the carbonized material into an atmosphere rotary furnace, introduce air, rotate at 45 r / min, first raise the temperature from room temperature to 200℃, hold for 2 hours, then raise the temperature from 300℃ to 500℃ and hold for 2 hours; the heating rate in S3 is 6℃ / min. S4. The crude product is placed in an atmosphere rotary furnace for high-temperature dephosphorization and secondary activation sequentially. The rotation speed is 45 r / min, the dephosphorization temperature is 750℃, the dephosphorization time is 7 h, the activation temperature is 800℃, the activation time is 2 h, and the activator is water vapor. Then, acid washing is performed. The specific steps are as follows: industrial hydrochloric acid with a concentration of about 31% is added to pure water to prepare a 1:10 hydrochloric acid solution. The solid-liquid ratio of the solution to the crude product is 1:5. The prepared solution and activated carbon are placed in a glass reactor and heated and stirred for 3 h at a temperature of 80℃. After the time is completed, the waste liquid is discharged and an equal volume of pure water is added. The mixture is rinsed repeatedly 5 times to remove excess acid and obtain the initial product. The heating rate in S4 is 8℃ / min. S5. Place the initial product into a glass reactor, add 20wt% sodium carbonate solution, the solid-liquid ratio is 1:6, and stir at 40℃ for 2h; then prepare DES solution by mixing myristic acid and thymol at a molar ratio of 2:1, pour activated carbon into the DES solution and stir at 85℃ for 30min, cool, wash three times with deionized water at a solid-liquid ratio of 1:4, and dry at 150℃ to obtain activated carbon for methane adsorption.

[0050] Embodiment four of the present invention is as follows: A method for preparing activated carbon for methane adsorption includes the following steps: S1. Mix 20*40 mesh walnut shell powder with 45% phosphoric acid at an impregnation ratio of 1:1.5, and stir and mature in a kneader at 200℃ for 0.5h to obtain matured material; S2. Place the calcined material in an oven and dry it at 100°C. Then place it in a shaping furnace at 220°C for 12 hours to shape it. The air flow rate in the shaping furnace is 60L / min to obtain carbonized material. S3. Place the carbonized material into an atmosphere rotary furnace, introduce nitrogen gas, rotate at 40 r / min, first raise the temperature from room temperature to 250℃, hold for 1.5 h, then raise the temperature from 300℃ to 600℃ and hold for 2.5 h; the heating rate in S3 is 10℃ / min. S4. The crude product is placed in an atmosphere rotary furnace for high-temperature dephosphorization and secondary activation sequentially. The rotation speed is 40 r / min, the dephosphorization temperature is 500℃, the dephosphorization time is 10 h, the activation temperature is 500℃, the activation time is 8 h, and the activator is water vapor. Then, acid washing is performed. The specific steps are as follows: industrial hydrochloric acid with a concentration of about 31% is added to pure water to prepare a 1:10 hydrochloric acid solution. The solid-liquid ratio of the solution to the crude product is 1:5. The prepared solution and activated carbon are placed in a glass reactor and heated and stirred for 3 h at a temperature of 80℃. After the time is completed, the waste liquid is discharged and an equal volume of pure water is added. The mixture is rinsed repeatedly 5 times to remove excess acid and obtain the initial product. The heating rate in S4 is 5℃ / min. S5. Place the initial product into a glass reactor, add 0.5wt% potassium hydroxide solution, with a solid-liquid ratio of 1:1, and stir at 35℃ for 2 hours; then prepare a DES solution by mixing myristic acid and thymol at a molar ratio of 2:1, pour the activated carbon into the DES solution and stir at 80℃ for 30 minutes, cool, wash with deionized water at a solid-liquid ratio of 1:3 5 times, and dry at 80℃ to obtain activated carbon for methane adsorption.

[0051] Embodiment five of the present invention is as follows: A method for preparing activated carbon for methane adsorption includes the following steps: S1. Mix 30*60 mesh walnut shell powder with 85% phosphoric acid at an impregnation ratio of 1:0.6, and stir and mature at 100℃ for 3 hours in a kneader to obtain matured material. S2. Place the calcined material in an oven and dry it at 90°C. Then place it in a shaping furnace at 150°C for 15 hours to shape it. The air flow rate in the shaping furnace is 50L / min to obtain carbonized material. S3. Place the carbonized material into an atmosphere rotary furnace, introduce carbon dioxide, rotate at 30 r / min, first raise the temperature from room temperature to 150℃, hold for 1.5 h, then raise the temperature from 300℃ to 550℃ and hold for 2 h; the heating rate in S3 is 7℃ / min. S4. The crude product is placed in an atmosphere rotary furnace for high-temperature dephosphorization and secondary activation sequentially. The rotation speed is 30 r / min, the dephosphorization temperature is 700℃, the dephosphorization time is 5 h, the activation temperature is 750℃, the activation time is 7 h, and the activator is water vapor. Then, acid washing is performed. The specific steps are as follows: oxalic acid is used, and the solid-liquid ratio of the solution to the crude product is 1:4. The prepared solution and activated carbon are placed in a glass reactor and heated and stirred for 3 h at 80℃. After the time is completed, the waste liquid is discharged and an equal volume of pure water is added. The mixture is rinsed repeatedly 4 times to remove excess acid and obtain the initial product. The heating rate in S4 is 7℃ / min. S5. Place the initial product into a glass reactor, add 15wt% sodium bicarbonate solution, the solid-liquid ratio is 1:4, and stir at 45℃ for 1.5h; then prepare a DES solution by mixing myristic acid and thymol at a molar ratio of 2:1, pour the activated carbon into the liquid DES solution and stir at 90℃ for 25min, cool, wash with deionized water at a solid-liquid ratio of 1:3 5 times, and dry at 110℃ to obtain activated carbon for methane adsorption.

[0052] Comparative Example 1: 10*30 mesh wood flour and 70% phosphoric acid were mixed at an impregnation ratio of 1:1 and stirred and matured in a kneader at 160°C for 2 hours to obtain matured material; the matured material was placed in an oven and dried at 120°C for 2 hours, and then placed in a setting furnace at 180°C for 20 hours with an air flow rate of 40 L / min to obtain carbonized material; the carbonized material was placed in an atmosphere rotary kiln, air was introduced, and the rotation speed was 50 r / min, first heated from room temperature to 30°C. The temperature was set at 0℃ for 1 hour, then increased from 300℃ to 450℃ and held for 3 hours. The crude product was then placed in an atmosphere rotary furnace for high-temperature dephosphorization and secondary activation, with a rotation speed of 50 r / min, a dephosphorization temperature of 600℃, a dephosphorization time of 6 hours, an activation temperature of 900℃, and an activation time of 6 hours, using water vapor as the activator. After undergoing the same acid washing, rinsing, and alkali modification steps as in Example 1, the resulting wood granular charcoal was obtained. The heating rate in each heating step was the same as in Example 1. That is, the only difference between Comparative Example 1 and Example 1 is that wood powder of the same particle size was used instead of walnut shell powder.

[0053] The specific surface area of ​​the wood pellet charcoal obtained in Comparative Example 1 was 2159.1161 m². 2 The average pore size is 2.5 nm, and the total pore volume is 1.33 cm³ / g. Its pore size exceeds 2.2 nm, and its excess adsorption capacity for methane at 3.4 MPa is 164.0266 cm³ / g. 3 / g, with an excess adsorption capacity of 190.1949 cm⁻¹ at 6 MPa. 3 / g, with an excess adsorption capacity of 199.2242 cm⁻¹ at 10 MPa. 3 / g. Compared with Example 1, it can be seen that the methane adsorption effect is much lower than that of walnut shell activated carbon; in each heating step, the heating rate is 10℃ / min.

[0054] Comparative Example 2: 10*30 mesh walnut shell powder was mixed with 70% phosphoric acid at an impregnation ratio of 1:1 and stirred and matured in a kneader at 160℃ for 2 hours to obtain matured material. The matured material was placed in an oven and dried at 120℃ for 2 hours, and then placed in a shaping furnace at 180℃ for 20 hours. The air flow rate in the shaping furnace was 40L / min to obtain carbonized material. The carbonized material was placed in an atmosphere rotary furnace, air was introduced, the rotation speed was 50r / min, and the temperature was increased from room temperature to 450℃ at a heating rate of 10℃ / min, and held at the temperature for 3 hours. The crude product was placed in the atmosphere rotary furnace according to... The process involves high-temperature dephosphorization and secondary activation at a rotation speed of 50 r / min, a dephosphorization temperature of 600℃, and a dephosphorization time of 6 h. The activation temperature is 900℃, and the activation time is 6 h, using steam as the activator. Acid washing is then performed. Specifically, industrial hydrochloric acid with a concentration of approximately 31% is added to pure water to prepare a 1:10 hydrochloric acid solution. The solid-liquid ratio of the solution to the crude product is 1:5. The prepared solution and activated carbon are placed in a glass reactor and heated and stirred for 3 h at 80℃. After the time is up, the waste liquid is discharged and an equal volume of pure water is added. The mixture is rinsed repeatedly 5 times to remove excess acid and obtain the initial product. The initial product was placed in a glass reactor, and 10 wt% ammonium bicarbonate solution was added, with a solid-liquid ratio of 1:3. The mixture was stirred at 40°C for 2 hours. Then, myristic acid and thymol were mixed at a molar ratio of 2:1 to prepare a DES solution. Activated carbon was poured into the DES solution and stirred at 80°C for 30 minutes. After cooling, the carbon was washed three times with deionized water at a solid-liquid ratio of 1:3 and then dried at 100°C to obtain activated carbon. The heating rate in each heating step was the same as in Example 1.

[0055] That is, the only difference between Comparative Example 2 and Example 1 is that S3 does not involve segmented heating.

[0056] The specific surface area data of the activated carbon obtained in Comparative Example 2 were similar to those without staged temperature increases. However, the reason why the specific surface area data showed a large distribution range among the multiple samples was particularly evident in large-scale production under the same conditions. The BET data for the five samples were as follows: Sample 1: Specific surface area 2242.47 cm² 3 / g, average pore size 2.04nm, total pore volume 1.14cm³ 3 / g; Sample 2: Specific surface area 1882.16 cm² 3 / g, average pore size 1.97nm, total pore volume 0.93cm³ 3 / g; Sample 3: Specific surface area 1995.11 cm²3 / g, average pore size 1.99nm, total pore volume 0.99cm³ 3 / g; Sample 4: Specific surface area 2029.93 cm² 3 / g, average pore size 2.04nm, total pore volume 1.04cm³ 3 / g; Sample 5: Specific surface area 1955.35 cm² 3 / g, average pore size 2.05nm, total pore volume 1.00cm³ 3 / g; The above five data points all refer to activated carbon produced in the same batch and from the same furnace. It is not difficult to see from the data that the lack of segmented heating will result in significant differences in the BET data. Segmented heating plays a crucial role in the stability of activated carbon preparation.

[0057] Comparative Example 3: 10*30 mesh walnut shell powder and 70% phosphoric acid were mixed at an impregnation ratio of 1:1 and stirred and matured in a kneader at 160°C for 2 hours to obtain matured material. The matured material was placed in an oven and dried at 120°C for 2 hours, and then placed in a shaping furnace at 180°C for 20 hours to obtain carbonized material. The carbonized material was placed in an atmosphere rotary furnace, air was introduced, the rotation speed was 50 r / min, the temperature was first raised from room temperature to 300°C and held for 1 hour, and then the temperature was raised from 300°C to 450°C and held for 3 hours. The crude product was placed in an atmosphere rotary furnace for secondary activation at a speed of 50 r / min, an activation temperature of 900℃, and an activation time of 6 h, using water vapor as the activator. Then, acid washing was performed. The specific steps were as follows: industrial hydrochloric acid with a concentration of about 31% was added to pure water to prepare a 1:10 hydrochloric acid solution. The solid-liquid ratio of the solution to the crude product was 1:5. The prepared solution and activated carbon were placed in a glass reactor and heated and stirred for 3 h at a temperature of 80℃. After the time was completed, the waste liquid was discharged and an equal volume of pure water was added. The mixture was rinsed repeatedly 5 times to remove excess acid.

[0058] The initial product was placed in a glass reactor, and 10 wt% ammonium bicarbonate solution was added, with a solid-liquid ratio of 1:3. The mixture was stirred at 40°C for 2 hours. Then, myristic acid and thymol were mixed at a molar ratio of 2:1 to prepare a DES solution. Activated carbon was poured into the DES solution and stirred at 80°C for 30 minutes. After cooling, the activated carbon was washed three times with deionized water at a solid-liquid ratio of 1:3 and then dried at 100°C to obtain activated carbon. The heating rate in each heating step was the same as in Example 1.

[0059] That is, the only difference between Comparative Example 3 and Example 1 is that high-temperature dephosphorization is not performed, and secondary activation is performed directly.

[0060] Compared with Example 1, the total phosphorus content of activated carbon that has not undergone high-temperature dephosphorization is difficult to control. Direct activation will also remove total phosphorus during the activation process, but since it has not been tested, it is unknown whether its phosphorus content meets safety standards, which will cause trouble for subsequent rinsing. During the high-temperature dephosphorization process, the activated carbon structure will be fixed, and the strength of activated carbon after high-temperature dephosphorization will be higher than that of activated carbon that has not undergone high-temperature dephosphorization, thus extending the service life of activated carbon.

[0061] Comparative Example 4: 10*30 mesh walnut shell powder and 70% phosphoric acid were mixed at an impregnation ratio of 1:1 and stirred and matured in a kneader at 160°C for 2 hours to obtain matured material. The matured material was placed in an oven and dried at 120°C for 2 hours, and then placed in a shaping furnace at 180°C for 20 hours to obtain carbonized material. The carbonized material was placed in an atmosphere rotary furnace, air was introduced, the rotation speed was 50 r / min, the temperature was first raised from room temperature to 300°C and held for 1 hour, and then the temperature was raised from 300°C to 450°C and held for 3 hours. The crude product was placed in an atmosphere rotary furnace for high-temperature dephosphorization and secondary activation sequentially. The rotation speed was 50 r / min, the dephosphorization temperature was 600℃, and the dephosphorization time was 6 h. The activation temperature was 900℃, and the activation time was 6 h. The activator was water vapor. Then, acid washing was performed. Specifically, industrial hydrochloric acid with a concentration of about 31% was added to pure water to prepare a 1:10 hydrochloric acid solution. The solid-liquid ratio of the solution to the crude product was 1:5. The prepared solution and activated carbon were placed in a glass reactor and heated and stirred for 3 h at a temperature of 80℃. After the time was completed, the waste liquid was discharged and an equal volume of pure water was added. The mixture was rinsed repeatedly 5 times to remove excess acid. The activated carbon was then dried at 100℃. The heating rate in each heating step was the same as in Example 1.

[0062] That is, the only difference between Comparative Example 4 and Example 1 is that hydrophobic modification is not performed.

[0063] The performance of the activated carbon obtained in Comparative Example 4 was tested, and the results showed that its specific surface area was 2060 m². 2 / g, average pore size 2.04nm, total pore volume 1.05cm³ 3 The microporosity is 84.21%, and the excess adsorption capacity for methane at 3.4 MPa is 162.7404 cm³. 3 / g, with an excess adsorption capacity of 201.2036 cm⁻¹ at 6 MPa. 3 / g, with an excess adsorption capacity of 215.2145 cm⁻¹ at 10 MPa. 3 / g. After multiple experiments, the adsorption capacity of the unmodified activated carbon for methane adsorption was significantly lower than that of the hydrophobically modified activated carbon in Example 1, with a difference of approximately 10 cm⁻¹. 3 The difference is around / g, and it will be smaller when the adsorption amount is low.

[0064] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification and drawings, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing activated carbon for methane adsorption, characterized in that, Includes the following steps: S1. Mix walnut shell powder with phosphoric acid and stir to mature the material. S2. The calcined material is dried and shaped sequentially to obtain carbonized material; S3. The carbonized material is initially activated by a two-stage heating process to obtain a crude product; S4. The crude product is subjected to high-temperature dephosphorization, secondary activation, acid washing and water washing to obtain the initial product; S5. The initial product is modified by alkali and hydrophobicity to obtain activated carbon for methane adsorption.

2. The preparation method according to claim 1, characterized in that, The walnut shell powder described in S1 has a particle size of 10-100 mesh.

3. The preparation method according to claim 1, characterized in that, The impregnation ratio of walnut shell powder to phosphoric acid in S1 is 1:0.6~1.5; the concentration of phosphoric acid is 40~85%.

4. The preparation method according to claim 1, characterized in that, The ripening temperature in S1 is 100~200℃, and the time is 0.5~3h.

5. The preparation method according to claim 1, characterized in that, The first stage of the two-stage heating process involves heating from room temperature to 300℃ and holding the temperature at that temperature for 1 hour. The second stage involves heating from 300℃ to 400~600℃. The gas used for preliminary activation is one or more of nitrogen, carbon dioxide, water vapor, and air.

6. The preparation method according to claim 1, characterized in that, The secondary activation temperature is 500~900℃, the activation time is 2~8h, and the activator is one or more of nitrogen, carbon dioxide, water vapor, and air.

7. The preparation method according to claim 1, characterized in that, The alkali modification is performed by stirring the crude product with 0.1-20 wt% alkali solution at 30-80°C for 1-5 hours, and then rinsing until neutral. The alkaline solution is prepared from deionized water and one or more of ammonium bicarbonate, sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, and ammonia; the solid-liquid ratio of the crude product to the alkaline solution is 1:1~6.

8. The preparation method according to claim 1, characterized in that, The hydrophobic modification is as follows: myristic acid or lauric acid and thymol are used to prepare a DES solution, and alkali-modified activated carbon is stirred with the DES solution at 80 °C for 30 min. After cooling, the mixture is washed with water and dried.

9. Activated carbon for methane adsorption prepared by the preparation method according to any one of claims 1 to 8.

10. The activated carbon for methane adsorption according to claim 9, characterized in that, The activated carbon used for methane adsorption has a specific surface area greater than 2000 m². 2 / g.

Images