Modified activated carbon and preparation method and application thereof

Abstract

This invention relates to the field of activated carbon preparation technology, and discloses a modified activated carbon, its preparation method, and its application. The modified activated carbon preparation method includes the following steps: (1) subjecting biomass raw materials to a first high-temperature activation treatment under an inert atmosphere, followed by a second high-temperature activation treatment under a carbon dioxide atmosphere, and then cooling under an inert atmosphere to obtain carbon dioxide-activated activated carbon; (2) immersing the carbon dioxide-activated activated carbon in a metal salt solution, subjecting the immersed activated carbon material to a first drying, water washing, and a second drying process, and then subjecting the obtained activated carbon material to a third high-temperature activation treatment under an inert atmosphere. The modified activated carbon prepared according to the method of this invention exhibits a significantly higher dynamic methane adsorption capacity.

Description

Technical Field

[0001] This invention relates to the field of activated carbon preparation technology, specifically to a modified activated carbon, its preparation method, and its application. Background Technology

[0002] Every year, a large amount of low-concentration methane gas is directly released into the atmosphere in my country, wasting significant resources and causing serious environmental impacts. Methane's greenhouse effect is 21 times that of carbon dioxide, and its ability to damage the ozone layer is 7 times that of carbon dioxide. Furthermore, methane is a clean energy source with high calorific value, low price, and energy efficiency; therefore, the collection and reuse of low-concentration methane is of great significance to my country's energy development and environmental protection. However, due to the large flow rate, low concentration, low enrichment efficiency, and potential safety hazards associated with low-concentration methane gas, enrichment technology for low-concentration methane presents significant challenges.

[0003] Adsorption is one of the main methods for gas adsorption enrichment and separation, and the adsorbent is the key to adsorption separation technology. Generally, adsorbents with high specific surface area and large micropore size are excellent adsorbents for methane. However, relying solely on the microporous structure of activated carbon makes it difficult to achieve a high methane / nitrogen separation ratio. Activated carbon is a commonly used gas adsorbent in industry due to its advantages such as a variety of active groups on its surface, large specific surface area, well-developed pore structure, large adsorption capacity, good stability, and low price. Its adsorption performance is determined by its surface physical structure and chemical properties. The difficulty in adsorbing and enriching low-concentration methane gas lies in the fact that the molecular dynamic diameters of methane and nitrogen are very similar, making simple pore-based physical adsorption difficult for separation. Summary of the Invention

[0004] The purpose of this invention is to overcome the problem of poor adsorption performance of activated carbon for low concentrations of methane in existing technologies, and to provide a modified activated carbon, its preparation method, and its applications. The modified activated carbon of this invention exhibits a high dynamic breakthrough adsorption capacity for methane and can be used for efficient adsorption and treatment of methane.

[0005] To achieve the above objectives, the present invention provides a method for preparing modified activated carbon, the method comprising the following steps:

[0006] (1) The biomass raw material is first subjected to a first high-temperature activation treatment under an inert atmosphere, then subjected to a second high-temperature activation treatment under a carbon dioxide atmosphere, and then cooled under an inert atmosphere to obtain activated carbon dioxide activated carbon.

[0007] (2) The activated carbon activated by carbon dioxide is immersed in a metal salt solution, and the immersed activated carbon material is dried once, washed with water and dried twice in sequence. Then the obtained activated carbon material is subjected to a third high-temperature activation treatment under an inert atmosphere.

[0008] Preferably, in step (1), the temperature of the first high-temperature activation treatment is 700-950℃, and more preferably 800-900℃.

[0009] Preferably, in the first high-temperature activation process in step (1), the heating rate to the target temperature is 2-12℃ / min, the gas flow rate is 0.2-1.5L / min, and the activation time is 1-5h.

[0010] Preferably, in step (1), the temperature of the second high-temperature activation treatment is 700-950℃, and more preferably 800-900℃.

[0011] Preferably, in the second high-temperature activation process of step (1), the gas flow rate is 0.2-1.5 L / min and the activation time is 1-5 h.

[0012] Preferably, the biomass raw material is coconut shell.

[0013] Preferably, the method further includes: grinding, milling and sieving the coconut shell raw material in sequence, collecting coconut shell powder with a particle size of 40-100 mesh, and drying the coconut shell powder.

[0014] Preferably, in step (2), the concentration of the metal salt solution is 0.01-0.3 mol / L, more preferably 0.05-0.2 mol / L; the ratio of the activated carbon activated by carbon dioxide to the metal salt solution is 1 g:(1-5 mL), more preferably 1 g:(1.5-4 mL).

[0015] Preferably, in step (2), the metal in the metal salt is at least one of Li, Na, K, Mg, Ca, Sr, Ba, Ni, Pb, Pt, Pd, Co, Rh, Fe, Ru, and Al, and the anion of the metal salt is at least one of chloride ion, nitrate ion, and sulfate ion.

[0016] Preferably, in step (2), the impregnation process includes: ultrasonic treatment for 0.5-5 hours, followed by static impregnation for 2-48 hours.

[0017] Preferably, in step (2), the temperature of the third high-temperature activation treatment is 500-900℃, and more preferably 600-700℃.

[0018] Preferably, in the third high-temperature activation process in step (2), the heating rate to the target temperature is 2-8℃ / min, the gas flow rate is 0.5-1L / min, and the activation time is 0.1-3h.

[0019] A second aspect of the present invention provides modified activated carbon prepared by the method described above.

[0020] A third aspect of the present invention provides the application of the modified activated carbon described above in the methane adsorption process.

[0021] According to the method for preparing modified activated carbon described in this invention, by first activating the biomass raw material with carbon dioxide and then modifying it with metal ions, the chemical properties of the activated carbon pore surface can be changed, increasing the active sites for methane adsorption within the activated carbon pores and enhancing the interaction between activated carbon and methane molecules. This results in the prepared modified activated carbon having a high dynamic methane penetration adsorption capacity. Specifically, the dynamic methane penetration adsorption capacity of the modified activated carbon prepared according to the method of this invention can reach up to 75 cm⁻¹. 3 / g. Attached Figure Description

[0022] Figure 1 This is the nitrogen adsorption isotherm of the modified activated carbon prepared in Example 1. Detailed Implementation

[0023] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0024] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0025] The method for preparing modified activated carbon according to the present invention includes the following steps:

[0026] (1) The biomass raw material is first subjected to a first high-temperature activation treatment under an inert atmosphere, and then subjected to a second high-temperature activation treatment under a carbon dioxide atmosphere, and then cooled under an inert atmosphere to obtain activated carbon activated by carbon dioxide.

[0027] (2) The activated carbon activated by carbon dioxide is immersed in a metal salt solution, and the immersed activated carbon material is dried once, washed with water and dried twice in sequence. Then the obtained activated carbon material is subjected to a third high-temperature activation treatment under an inert atmosphere.

[0028] In step (1), the temperature of the first high-temperature activation treatment can be 700-950℃, preferably 800-900℃. Specifically, it can be, for example, 800℃, 810℃, 820℃, 830℃, 840℃, 850℃, 860℃, 870℃, 880℃, 890℃, or 900℃. When the temperature of the first high-temperature activation treatment is within the above-mentioned preferred range, the prepared modified activated carbon has better methane adsorption performance.

[0029] More preferably, in the first high-temperature activation treatment in step (1), the heating rate to the target temperature is 2-12℃ / min, the gas flow rate is 0.2-1.5L / min, and the activation time is 1-5h. More preferably, in the first high-temperature activation treatment in step (1), the heating rate to the target temperature is 3-8℃ / min, the gas flow rate is 0.4-1L / min, and the activation time is 2-3h. Even more preferably, in the first high-temperature activation treatment in step (1), the heating rate to the target temperature is 4-6℃ / min, the gas flow rate is 0.6-0.9L / min, and the activation time is 2-2.5h.

[0030] In step (1), the temperature of the second high-temperature activation treatment can be 700-950℃, preferably 800-900℃. Specifically, it can be, for example, 800℃, 810℃, 820℃, 830℃, 840℃, 850℃, 860℃, 870℃, 880℃, 890℃, or 900℃. When the temperature of the second high-temperature activation treatment is within the above-mentioned preferred range, the prepared modified activated carbon has better methane adsorption performance.

[0031] In the method described in this invention, the temperature of the first high-temperature activation treatment and the temperature of the second high-temperature activation treatment may be the same or different. Preferably, the temperature of the first high-temperature activation treatment and the temperature of the second high-temperature activation treatment are the same.

[0032] More preferably, in the second high-temperature activation process of step (1), the gas flow rate is 0.2-1.5 L / min, and the activation time is 1-5 h. More preferably, in the second high-temperature activation process of step (1), the gas flow rate is 0.4-1 L / min, and the activation time is 2-3 h. Even more preferably, in the second high-temperature activation process of step (1), the gas flow rate is 0.6-0.9 L / min, and the activation time is 2-2.5 h.

[0033] In the method described in this invention, the biomass raw material can be any type of biomass raw material conventionally used in the art. In a preferred embodiment, the biomass raw material is coconut shell. According to this preferred embodiment, the dynamic methane penetration adsorption capacity of the prepared modified activated carbon can be further improved.

[0034] More preferably, when coconut shell is used as a biomass raw material, the method for preparing modified activated carbon of the present invention further includes: grinding, milling and sieving the coconut shell raw material in sequence, collecting coconut shell powder with a particle size of 40-100 mesh, and drying the coconut shell powder.

[0035] In the method described in this invention, the first high-temperature activation process and the second high-temperature activation process in step (1) can be carried out in various conventional reaction apparatuses. In some embodiments, the biomass raw material (such as coconut shell powder) is placed in a crucible, placed in a tube furnace, and then heated to the target activation temperature for activation treatment.

[0036] In step (2), the concentration of the metal salt solution can be 0.01-0.3 mol / L, preferably 0.05-0.2 mol / L, specifically, for example, 0.05 mol / L, 0.08 mol / L, 0.1 mol / L, 0.12 mol / L, 0.14 mol / L, 0.15 mol / L, 0.16 mol / L, 0.18 mol / L or 0.2 mol / L; the ratio of the activated carbon activated by carbon dioxide to the metal salt solution can be 1 g:(1-5 mL), preferably 1 g:(1.5-4 mL), specifically, for example, 1 g:1.5 mL, 1 g:1.8 mL, 1 g:2 mL, 1 g:2.5 mL, 1 g:2.8 mL, 1 g:3 mL, 1 g:3.5 mL, 1 g:3.8 mL or 1 g:4 mL.

[0037] In step (2), the metal in the metal salt can be at least one selected from Li, Na, K, Mg, Ca, Sr, Ba, Ni, Pb, Pt, Pd, Co, Rh, Fe, Ru, and Al, and the anion of the metal salt can be at least one selected from chloride, nitrate, and sulfate ions. In the most preferred embodiment, the metal salt is palladium chloride. According to this most preferred embodiment, the prepared modified activated carbon has significantly improved methane adsorption performance.

[0038] In step (2), in a preferred embodiment, the impregnation process includes: ultrasonic treatment for 0.1-5 hours (preferably 0.5-3 hours), followed by static impregnation for 2-48 hours (preferably 5-30 hours). The frequency of the ultrasonic treatment can be 20-80 kHz, preferably 30-60 kHz, and more preferably 35-55 kHz.

[0039] In step (2), the conditions for the primary drying may include: a temperature of 100-120℃ and a time of 8-24 hours. The primary drying process can be carried out in an oven.

[0040] In step (2), the water washing process after the first drying is to remove the metal salts precipitated on the surface of the material. The water washing can be carried out in accordance with conventional water washing methods.

[0041] In step (2), the conditions for secondary drying may include: a temperature of 100-120℃ and a time of 8-24 hours. The secondary drying process can be carried out in an oven.

[0042] In this invention, the conditions for the primary drying and the secondary drying can be the same or different, but preferably the same.

[0043] In step (2), the temperature of the third high-temperature activation treatment can be 500-900℃, preferably 600-700℃. Specifically, it can be, for example, 600℃, 610℃, 620℃, 630℃, 640℃, 650℃, 660℃, 670℃, 680℃, 690℃, or 700℃. When the temperature of the third high-temperature activation treatment is within the above-mentioned preferred range, the prepared modified activated carbon has better methane adsorption performance.

[0044] More preferably, in the third high-temperature activation treatment in step (2), the heating rate to the target temperature is 2-8℃ / min, the gas flow rate is 0.5-1L / min, and the activation time is 0.1-3h. More preferably, in the third high-temperature activation treatment in step (2), the heating rate to the target temperature is 3-7℃ / min, the gas flow rate is 0.6-0.9L / min, and the activation time is 0.2-2h. Even more preferably, in the third high-temperature activation treatment in step (2), the heating rate to the target temperature is 4-6℃ / min, the gas flow rate is 0.7-0.8L / min, and the activation time is 0.5-1.5h.

[0045] In the method described in this invention, the third high-temperature activation process in step (2) can be carried out in various conventional reaction apparatuses. In some embodiments, the secondary dried activated carbon material is placed in a crucible, placed in a tube furnace, and then heated to the target activation temperature for activation treatment.

[0046] In the method described in this invention, the inert atmosphere may be provided by nitrogen and / or an inert gas (such as argon). Preferably, the inert atmosphere is provided by nitrogen.

[0047] The present invention also provides a modified activated carbon prepared by the above method. This modified activated carbon has a high specific surface area and abundant micropores, exhibiting high dynamic penetration adsorption capacity for small methane molecules under low-concentration methane gas conditions, and good adsorption selectivity for methane and nitrogen, thus achieving highly selective adsorption and separation of methane and nitrogen.

[0048] This invention also provides the application of the modified activated carbon in the methane adsorption process. In practical applications, at room temperature, the dynamic methane adsorption capacity of the modified activated carbon can reach up to 75 cm³ / h. 3 / g.

[0049] The modified activated carbon, its preparation method, and its application according to the present invention are further illustrated below through examples. These examples are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of the present invention is not limited to the following examples.

[0050] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available.

[0051] In the following examples and comparative examples, the relevant parameters of the modified activated carbon were tested according to the following methods:

[0052] Specific surface area and pore size analysis: The specific surface area and pore size of the samples were analyzed using a Bestech BSD-PM2 specific surface area and micropore analyzer. Before testing, the samples underwent activation pretreatment at 150℃ in a vacuum for 6 hours, followed by N2 adsorption isotherm testing at 77K. The BET and Langmuir specific surface areas of the materials were calculated using the BET and Langmuir equations, respectively. The pore volume (<2nm) of the micropores was calculated using the t-plot model, and the pore size within the micropore range was calculated using the HK equation.

[0053] Atmospheric pressure adsorption breakthrough test of methane on activated carbon: The dynamic adsorption performance of activated carbon for methane was tested using a BSD-MAB adsorption breakthrough analyzer. Built-in analytical methods and breakthrough adsorption curves of the activated carbon were analyzed. A breakthrough column with an inner diameter of 1 cm was used. Approximately 2 g of activated carbon sample was weighed and mixed with silica wool to reduce the pressure drop. Before testing, the sample was dried at 120℃ and degassed under vacuum for 10 min, followed by the introduction of methane gas (CH4:N2 = 1:1) using nitrogen as the carrier gas. The gas flow rate was 8 mL / min, and the concentration of the effluent gas at the outlet was analyzed using an online mass spectrometer. The adsorption curve was obtained, and the dynamic adsorption capacity of the material was calculated (the breakthrough point was recorded when the methane concentration in the tail gas reached 5% of the inlet concentration; the amount of methane adsorbed by the activated carbon at this point is the breakthrough adsorption capacity).

[0054] Example 1

[0055] (1) After grinding, pulverizing and sieving the coconut shell raw material, collect the coconut shell powder (80 mesh) and place it in an oven to dry.

[0056] (2) Place the dried coconut shell powder in a crucible, place it in a tube furnace, introduce nitrogen gas at a flow rate of 0.8 L / min, heat it to 850 °C at a heating rate of 5 °C / min, and continue the activation treatment for 2.5 h; then switch the nitrogen gas to carbon dioxide gas at a flow rate of 0.8 L / min, and activate it at 850 °C for 2.5 h; then switch the carbon dioxide gas back to nitrogen gas until the tube furnace cools down to room temperature, and obtain activated carbon dioxide activated carbon.

[0057] (3) Weigh 10g of the activated carbon activated by carbon dioxide and place it in 20mL of palladium chloride solution with a concentration of 0.15mol / L. Sonicate for 1h at a frequency of 40kHz. After sonication, let it stand for 24h.

[0058] (4) Place the impregnated activated carbon in an oven and dry it at 120°C for 8 hours. Then wash it with water to remove the metal salts precipitated on the surface, and then place it in an oven and dry it at 120°C for 8 hours.

[0059] (5) Place the dried activated carbon in a tube furnace, introduce nitrogen gas at a flow rate of 0.8 L / min, and heat it to 650°C at a heating rate of 6°C / min, and continue the activation treatment for 1.5 h. After the activation time is completed, allow the tube furnace to cool to room temperature to obtain the modified activated carbon A1 of the present invention.

[0060] The modified activated carbon A1, as measured by a physical adsorption analyzer, has a BET specific surface area of ​​1834 m². 2 / g; The dynamic breakthrough adsorption capacity of methane was determined and calculated using the normal pressure breakthrough curve, and was 75 cm⁻¹. 3 / g.

[0061] Example 2

[0062] (1) After grinding, pulverizing and sieving the coconut shell raw material, collect the coconut shell powder (40 mesh) and place it in an oven to dry.

[0063] (2) Place the dried coconut shell powder in a crucible, place it in a tube furnace, introduce nitrogen gas at a flow rate of 0.6 L / min, heat it to 900 °C at a heating rate of 6 °C / min, and continue the activation treatment for 2 h; then switch the nitrogen gas to carbon dioxide gas at a flow rate of 0.6 L / min, and activate it at 900 °C for 2 h; then switch the carbon dioxide gas back to nitrogen gas until the tube furnace cools down to room temperature, and obtain activated carbon activated by carbon dioxide.

[0064] (3) Weigh 10g of the activated carbon activated by carbon dioxide and place it in 40mL of 0.2mol / L palladium chloride solution. Sonicate for 3h at a frequency of 35kHz. After sonication, let it stand for 5h.

[0065] (4) Place the impregnated activated carbon in an oven and dry it at 120°C for 8 hours. Then wash it with water to remove the metal salts precipitated on the surface, and then place it in an oven and dry it at 120°C for 8 hours.

[0066] (5) Place the dried activated carbon in a tube furnace, introduce nitrogen gas at a flow rate of 0.75 L / min, and heat it to 700°C at a heating rate of 4°C / min, and continue the activation treatment for 1 hour. After the activation time is completed, allow the tube furnace to cool to room temperature to obtain the modified activated carbon A2 of the present invention.

[0067] The modified activated carbon A2, as measured by a physical adsorption analyzer, has a BET specific surface area of ​​1828 m². 2 / g; The dynamic breakthrough adsorption capacity of methane was determined and calculated using the normal pressure breakthrough curve, and was 73 cm⁻¹. 3 / g.

[0068] Example 3

[0069] (1) After grinding, pulverizing and sieving the coconut shell raw material, collect the coconut shell powder (100 mesh) and place it in an oven to dry.

[0070] (2) Place the dried coconut shell powder in a crucible, place it in a tube furnace, introduce nitrogen gas at a flow rate of 0.9 L / min, heat it to 800 °C at a heating rate of 4 °C / min, and continue the activation treatment for 2.3 h; then switch the nitrogen gas to carbon dioxide gas at a flow rate of 0.9 L / min, and activate it at 800 °C for 2.3 h; then switch the carbon dioxide gas back to nitrogen gas until the tube furnace cools down to room temperature, and obtain activated carbon dioxide activated carbon.

[0071] (3) Weigh 10g of the activated carbon activated by carbon dioxide and place it in 15mL of palladium chloride solution with a concentration of 0.05mol / L. Sonicate for 0.5h at a frequency of 55kHz. After sonication, let it stand and soak for 30h.

[0072] (4) Place the impregnated activated carbon in an oven and dry it at 120°C for 8 hours. Then wash it with water to remove the metal salts precipitated on the surface, and then place it in an oven and dry it at 120°C for 8 hours.

[0073] (5) Place the dried activated carbon in a tube furnace, introduce nitrogen gas at a flow rate of 0.7 L / min, and heat it to 600°C at a rate of 5°C / min, continuing the activation treatment for 0.5 h. After the activation time is completed, allow the tube furnace to cool to room temperature to obtain the modified activated carbon A3 of the present invention.

[0074] The modified activated carbon A3, as measured by a physical adsorption analyzer, has a BET specific surface area of ​​1805 m². 2 / g; The dynamic breakthrough adsorption capacity of methane was determined and calculated using the normal pressure breakthrough curve, and was 70 cm⁻¹. 3 / g.

[0075] Example 4

[0076] Modified activated carbon was prepared according to the method of Example 1, except that in step (3), the concentration of palladium chloride solution used was 0.03 mol / L, and finally modified activated carbon A4 was obtained.

[0077] The modified activated carbon A4, as measured by a physical adsorption analyzer, has a BET specific surface area of ​​1880 m². 2 / g; The dynamic breakthrough adsorption capacity of methane was determined and calculated using the normal pressure breakthrough curve, and was 55 cm⁻¹. 3 / g.

[0078] Example 5

[0079] Modified activated carbon was prepared according to the method of Example 1, except that in step (3), the concentration of palladium chloride solution used was 0.3 mol / L, and finally modified activated carbon A5 was obtained.

[0080] The modified activated carbon A5, as measured by a physical adsorption analyzer, has a BET specific surface area of ​​1812 m². 2 / g; The dynamic breakthrough adsorption capacity of methane was determined and calculated using the normal pressure breakthrough curve, and was 60 cm⁻¹. 3 / g.

[0081] Example 6

[0082] Modified activated carbon was prepared according to the method of Example 1, except that in step (5), the activation treatment time was adjusted to 0.3h, and finally modified activated carbon A6 was obtained.

[0083] The modified activated carbon A6, as measured by a physical adsorption analyzer, has a BET specific surface area of ​​1742 m². 2 / g; The dynamic breakthrough adsorption capacity of methane was determined and calculated based on the breakthrough curve under normal pressure: 59 cm⁻¹. 3 / g.

[0084] Example 7

[0085] Modified activated carbon was prepared according to the method of Example 1, except that in step (5), the activation treatment time was adjusted to 2h, and finally modified activated carbon A7 was obtained.

[0086] The modified activated carbon A7, as measured by a physical adsorption analyzer, has a BET specific surface area of ​​1799 m². 2 / g; The dynamic breakthrough adsorption capacity of methane was determined and calculated using the normal pressure breakthrough curve, and was 66 cm⁻¹. 3 / g.

[0087] Example 8

[0088] Modified activated carbon was prepared according to the method of Example 1, except that in step (5), the activation temperature was adjusted to 550°C, and finally modified activated carbon A8 was obtained.

[0089] The modified activated carbon A8, as measured by a physical adsorption analyzer, has a BET specific surface area of ​​1738 m². 2 / g; The dynamic breakthrough adsorption capacity of methane was determined and calculated using the normal pressure breakthrough curve, and was 57 cm⁻¹. 3 / g.

[0090] Example 9

[0091] Modified activated carbon was prepared according to the method of Example 1, except that in step (5), the activation temperature was 750°C, and finally modified activated carbon A9 was obtained.

[0092] The modified activated carbon A9, as measured by a physical adsorption analyzer, has a BET specific surface area of ​​1647 m². 2 / g; The dynamic breakthrough adsorption capacity of methane was determined and calculated using the normal pressure breakthrough curve, and was 51 cm⁻¹. 3 / g.

[0093] Comparative Example 1

[0094] Activated carbon was prepared according to the method of Example 1, except that in step (3), deionized water was used instead of the palladium chloride solution, that is, no metal salt modification was performed, and finally activated carbon D1 was obtained.

[0095] The modified activated carbon D1, as measured by a physical adsorption analyzer, has a BET specific surface area of ​​2012 m². 2 / g; The dynamic breakthrough adsorption capacity of methane was determined and calculated based on the breakthrough curve under normal pressure, and was 21 cm⁻¹. 3 / g.

[0096] Comparative Example 2

[0097] Activated carbon was prepared according to the method of Example 1, except that in step (2), the activation process under carbon dioxide atmosphere was not carried out, and nitrogen was used instead of carbon dioxide, and finally activated carbon D2 was obtained.

[0098] The modified activated carbon D2, as measured by a physical adsorption analyzer, has a BET specific surface area of ​​1362 m². 2 / g; The dynamic breakthrough adsorption capacity of methane was determined and calculated based on the breakthrough curve under normal pressure, which was 24 cm⁻¹. 3 / g.

[0099] Comparative Example 3

[0100] The steps for preparing a high-performance coconut shell activated carbon adsorbent for separating methane / nitrogen, according to the existing technology (CN108057420B), are as follows:

[0101] (1) Crush the coconut shell to about 3mm in length, place it in a tube furnace, heat it to 600℃ at a rate of 10℃ / min, and keep it at that temperature for 30min.

[0102] (2) After the carbonized coconut shell raw material is cooled and removed, it is ground into powder to 95% by ball mill and passed through a 200-mesh sieve. Then it is mixed evenly with water and binder (phenolic resin and bentonite mixed in a 1:1 ratio) (the mass ratio of coconut shell powder to water is 10:1, and the mass ratio of coconut shell powder to binder is 10:3). It is then shaped on a four-column press to obtain a 4mm cylindrical strip.

[0103] (3) After the material strips are naturally air-dried, they are subjected to secondary carbonization. The temperature is increased to 600℃ at a rate of 5℃ / min and kept constant for 1h. Then, they are immersed in a 15wt% K2CO3 alkaline solution for 6h. After drying at 120℃, they are subjected to physical activation with steam. The mass ratio of steam to secondary carbonized material is 1:1. The material is activated at 900℃ for 90min.

[0104] (4) After natural cooling, wash with water until neutral and then dry to obtain activated carbon sample D3.

[0105] The BET specific surface area of ​​activated carbon sample D3 was determined to be 1128 m² using a physical adsorption analyzer. 2 / g; The dynamic breakthrough adsorption capacity of methane was determined and calculated using the normal pressure breakthrough curve, and was 35 cm⁻¹. 3 / g.

[0106] The corresponding operating conditions and performance parameters of the activated carbon samples in the above embodiments and comparative examples are shown in Table 1 below.

[0107] Table 1

[0108]

[0109] As can be seen from the results in Table 1, the modified activated carbon prepared according to the method described in this invention has a significantly higher dynamic methane breakthrough adsorption capacity.

[0110] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing modified activated carbon, characterized in that, The method includes the following steps: (1) The biomass raw material is first subjected to a first high-temperature activation treatment under an inert atmosphere, and then subjected to a second high-temperature activation treatment under a carbon dioxide atmosphere, and then cooled under an inert atmosphere to obtain activated carbon activated by carbon dioxide. (2) The activated carbon activated by carbon dioxide is immersed in a metal salt solution, and the immersed activated carbon material is dried once, washed with water and dried twice in sequence. Then the obtained activated carbon material is subjected to a third high-temperature activation treatment under an inert atmosphere.

2. The method according to claim 1, characterized in that, In step (1), the temperature of the first high-temperature activation treatment is 700-950℃, preferably 800-900℃.

3. The method according to claim 1 or 2, characterized in that, In the first high-temperature activation process in step (1), the heating rate to the target temperature is 2-12℃ / min, the gas flow rate is 0.2-1.5L / min, and the activation time is 1-5h.

4. The method according to claim 1, characterized in that, In step (1), the temperature of the second high-temperature activation treatment is 700-950℃, preferably 800-900℃.

5. The method according to claim 1 or 4, characterized in that, In the second high-temperature activation process in step (1), the gas flow rate is 0.2-1.5 L / min and the activation time is 1-5 h.

6. The method according to any one of claims 1-5, characterized in that, The biomass raw material is coconut shell; Preferably, the method further includes: grinding, milling and sieving the coconut shell raw material in sequence, collecting coconut shell powder with a particle size of 40-100 mesh, and drying the coconut shell powder.

7. The method according to claim 1, characterized in that, In step (2), the concentration of the metal salt solution is 0.01-0.3 mol / L, preferably 0.05-0.2 mol / L; the ratio of the activated carbon activated by carbon dioxide to the metal salt solution is 1 g:(1-5 mL), preferably 1 g:(1.5-4 mL).

8. The method according to claim 1 or 7, characterized in that, In step (2), the metal in the metal salt is at least one of Li, Na, K, Mg, Ca, Sr, Ba, Ni, Pb, Pt, Pd, Co, Rh, Fe, Ru and Al, and the anion of the metal salt is at least one of chloride ion, nitrate ion and sulfate ion.

9. The method according to claim 1, 7 or 8, characterized in that, In step (2), the impregnation process includes: first ultrasonic treatment for 0.5-5 hours, and then static impregnation for 2-48 hours.

10. The method according to claim 1, characterized in that, In step (2), the temperature of the third high-temperature activation treatment is 500-900℃, preferably 600-700℃.

11. The method according to claim 1 or 10, characterized in that, In the third high-temperature activation process in step (2), the heating rate to the target temperature is 2-8℃ / min, the gas flow rate is 0.5-1L / min, and the activation time is 0.1-3h.

12. Modified activated carbon prepared by the method according to any one of claims 1-11.

13. The application of the modified activated carbon according to claim 12 in the methane adsorption process.

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