Preparation method and application of biomass activated carbon

Abstract

The invention belongs to the technical field of activated carbon and gas adsorption, and particularly relates to a preparation method and application of biomass activated carbon. The biomass activated carbon prepared by taking waste biomass as a raw material through a carbonization process, an activation process and a post-treatment process has a highly developed micropore structure, an extremely high micropore volume ratio and a high specific surface area, and the unique pore structure characteristic of the biomass activated carbon provides abundant gas adsorption sites and diffusion channels; the material is endowed with excellent adsorption performance of radon and other gases. The preparation method disclosed by the invention also has the advantages of low cost, environmental friendliness, good economic benefit and the like, resources are saved, and resource utilization of wastes is realized.

Description

Technical Field

[0001] This invention belongs to the field of activated carbon and gas adsorption technology, and in particular relates to a biomass activated carbon adsorbent capable of efficiently removing radioactive radon and its preparation method. Background Technology

[0002] In recent years, radon pollution in enclosed environments has become increasingly prominent. Long-term radon exposure poses a threat to human health and has become one of the most pressing environmental issues. Radon (Rn), as the only inert gas containing only radioactive isotopes under normal conditions, easily escapes from soil and rocks and enters the surrounding air, accumulating to harmful concentrations in poorly ventilated enclosed environments over a long period. When Rn is inhaled, its decay products produce internal radiation in the respiratory tract. Alpha radiation can damage cellular DNA structure, inducing various health problems such as lung cancer, leukemia, and skin cancer. The International Agency for Research on Cancer (IARC) has classified Rn as a Group 1 carcinogen, considering it the second leading cause of lung cancer in humans after smoking. Related studies indicate that 8-25% of lung cancer deaths worldwide can be attributed to radon exposure.

[0003] According to the "Requirements for Indoor Radon and its Progeny Control" (GB / T 16146-2015), my country sets the annual average radon concentration target level for newly constructed buildings at 100 Bq / m³. 3 Meanwhile, the "Standard for Indoor Environmental Pollution Control of Civil Building Engineering" (GB 50325-2020) stipulates that the indoor radon concentration in Class I and Class II civil buildings in my country shall not exceed 150 Bq / m³. 3 These standards have imposed stricter requirements on radon pollution control. Currently, commonly used radon protection methods mainly include ventilation to reduce radon, coating to isolate radon, and adsorption to remove radon. However, ventilation and coating consume a lot of energy and have high process requirements, making them difficult to apply in special working conditions such as underground laboratories and mines. In contrast, adsorption technology is widely used due to its ease of operation and wide applicability. The key to the treatment effect of adsorption technology lies in the selection of adsorption materials. Activated carbon, as a widely used adsorbent, is favored in the field of radioactive inert gas treatment due to its abundant raw material sources, low price, and renewability. However, conventional activated carbon usually exhibits a multi-level pore structure, including micropores, mesopores, and macropores, with a wide and uneven pore size distribution. Radon adsorption mainly relies on the microporous structure that matches its kinetic diameter, resulting in existing activated carbon materials generally having problems such as low adsorption efficiency, limited capacity, and weak selectivity, which restricts its application in the selective adsorption of radon. Therefore, developing new adsorption materials that combine high adsorption performance, good stability, low cost, and environmental friendliness not only has important theoretical and scientific value, but will also provide key technical support for effectively ensuring radiation safety in human living environments and under special working conditions, resulting in significant social and economic benefits.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to explore the adsorption and purification capacity of biomass activated carbon materials for radon through a controllable preparation process, based on biomass raw materials, and to develop a new type of biomass-based activated carbon (BioAC) with uniform pore size, rich micropores and high specific surface area, high adsorption performance, good stability, low cost and environmental friendliness.

[0006] On one hand, the present invention provides a method for preparing biomass activated carbon, characterized by comprising the following steps: S1: Carbonize biomass raw materials to obtain biochar; S2: The biochar and activator are mixed evenly in water and dried, and then activated at high temperature under an inert atmosphere; S3: After washing to remove the activating agent, the activated biochar is dried and cooled to obtain the biomass activated carbon; The activator is selected from one or more of potassium hydroxide, sodium hydroxide, zinc chloride, and potassium oxalate.

[0007] In some embodiments of the present invention, the biomass raw material is a hard nut shell. Preferably, the hard nut shell is selected from one or more of the following: walnut shells, pistachio shells, macadamia nut shells, pine nut shells, hazelnut shells, almond shells, peach kernel shells, and pecan shells. It is understood that other similar hard nut shells are also within the scope of protection of the present invention.

[0008] In some embodiments of the present invention, the biomass raw material is 20-40 mesh particles. In some embodiments, fruit shells are used as raw material; the raw material is cleaned and dried, then crushed and sieved to obtain 20-40 mesh biomass raw material particles.

[0009] In some embodiments of the present invention, the carbonization in step S1 is performed at 450-550 °C for 1-2 hours. Preferably, the carbonization is carried out under an inert atmosphere. Preferably, the heating rate of the carbonization is 5 °C / min.

[0010] In some embodiments of the present invention, the mass ratio of the activator to the biochar in step S2 is 0.75-1.25:1, for example, it can be 0:75:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, or 1.25:1. Preferably, the ratio is 1-1.15:1. Preferably, the activator includes potassium hydroxide and / or sodium hydroxide.

[0011] In some embodiments of the present invention, in step S2, the biochar and the activator are mixed uniformly by ultrasonic treatment. Preferably, the ultrasonic treatment time is 1-1.5 h.

[0012] In some embodiments of the present invention, the drying in step S2 is performed at 90-120 °C. In some embodiments, after mechanical stirring at 90-95 °C until the moisture evaporates, the product is transferred to an oven and dried overnight at 100-110 °C.

[0013] In some embodiments of the present invention, the high-temperature activation temperature is 600-900 °C, for example, 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, 850 °C, or 900 °C. Preferably, the high-temperature activation temperature is 700-900 °C, more preferably 750-850 °C.

[0014] In some embodiments of the present invention, the high-temperature activation time is 1-2 hours.

[0015] In some embodiments of the present invention, the inert atmosphere gas in steps S1 and S2 is selected from nitrogen or argon. Preferably, the inert atmosphere is a high-purity nitrogen atmosphere or a high-purity argon atmosphere. In some embodiments, before carbonization / high-temperature activation, an inert gas is introduced into the carbonization device / activation device to purge residual air from the device. In some embodiments, during the carbonization or high-temperature activation process, an inert gas is continuously injected at a rate of 300 ml / min as a protective gas. In some embodiments, the carbonization device / activation device is kept under positive pressure during the carbonization / high-temperature activation process.

[0016] In some embodiments of the present invention, the drying temperature in step S3 is 90-120 °C, preferably 100-110 °C. In some embodiments, the drying time is 24-48 h. In some embodiments, in step S3, the activated biochar is soaked in an acidic solution to remove the activator. Preferably, the acidic solution is a hydrochloric acid solution. Preferably, the concentration of the hydrochloric acid solution is 5-15 wt%. In some embodiments, after soaking the biochar in the acidic solution, it is repeatedly washed with water until the pH of the solution remains constant.

[0017] On the other hand, the present invention also provides biomass activated carbon obtained by the above preparation method.

[0018] On the other hand, the present invention also provides the application of the above-mentioned biomass activated carbon in the adsorption of radioactive inert gases.

[0019] Compared with the prior art, the present invention has at least the following beneficial effects: 1. Microporous activated carbon is considered the preferred material for radon adsorption due to its high adsorption capacity and excellent selectivity. The biomass activated carbon prepared in this study not only has a high BET specific surface area and suitable pore structure, but its microporous structure is also highly developed and predominant, which plays a dominant role in radon adsorption, thus enabling the material to exhibit excellent radon removal performance.

[0020] 2. The radon adsorption coefficient of the biomass activated carbon of this invention is higher than that of existing traditional activated carbon, and it has a better radon adsorption capacity. More importantly, it is easy to combine with traditional radon removal processes. Therefore, the use of biomass activated carbon for radon adsorption can fully take into account the actual factors of radon removal processes, thereby achieving the goal of solving emergency pollution problems and saving resources.

[0021] 3. This invention uses biomass waste as a precursor to prepare a biomass activated carbon suitable for radon adsorption. It boasts advantages such as low cost, environmental friendliness, and good economic benefits, while also conserving resources and realizing the resource utilization of waste. This method not only significantly reduces raw material costs but also aligns with the principles of green and sustainable development, demonstrating the dual environmental and economic benefits of "treating waste with waste." Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the specific embodiments of this disclosure or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0023] Figure 1 The flowchart shows the preparation method of biomass activated carbon of the present invention, and the nitrogen adsorption-desorption isotherms of biomass activated carbon KBC-600-1, KBC-700-1 and KBC-800-1 obtained under different activation temperatures in the examples. Figure 2 The pore size distribution and nitrogen adsorption-desorption isotherms of biomass activated carbons KBC-600-0.75, KBC-600-1, and KBC-600-1.25 obtained in Example 1 at an activation temperature of 600 °C are shown. Figure 3 The pore size distribution and nitrogen adsorption-desorption isotherms of biomass activated carbons KBC-700-0.75, KBC-700-1, and KBC-700-1.25 obtained in Example 2 at an activation temperature of 700 °C are shown. Detailed Implementation

[0024] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0025] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form includes the plural form unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used herein, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof. Unless otherwise stated, all parts, percentages, and ratios used herein are based on mass meters.

[0026] Furthermore, it should be understood that the one or more method steps mentioned in this invention do not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated; moreover, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or limiting the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered as within the scope of the invention.

[0027] This invention uses waste biomass as raw material and, through a carbonization process, a gas activation process, and a post-treatment process, obtains biomass activated carbon with high adsorption activity for radioactive inert gases such as radon. In some embodiments, the preparation method of the biomass activated carbon of this invention includes the following steps: (1) Pretreatment: Using biomass as raw material, the raw material is washed with deionized water to remove surface ash and peel, and excess moisture is dried in an oven. Then it is crushed and screened, and finally particles of appropriate size are selected for use.

[0028] (2) Carbonization process: The sieved particles are placed in a crucible and placed in a tube furnace. Carbonization is carried out under an inert atmosphere at 500 °C, with a heating rate of 5 °C / min and a carbonization time of 1.5 h.

[0029] (3) Activation process: A certain mass of biochar and activator were mixed in deionized water in a certain proportion, ultrasonically treated for 0.5 h, and then mechanically stirred at 90 ℃ until the water in the solution evaporated. Then it was transferred to an oven and dried at 105 ℃ overnight. After that, it was transferred to a tube furnace and activated under an inert atmosphere at 600-900 ℃, with a heating temperature of 5 ℃ / min and an activation time of 1.5 h.

[0030] (4) Post-treatment process: The activated sample was immersed in 10wt% HCl to remove excess KOH, and then washed repeatedly with deionized water until the pH of the solution remained unchanged. It was dried at 105 °C for 24 hours to remove moisture, and then placed in a desiccator to cool before use. The obtained material is biomass activated carbon (BioAC).

[0031] The biomass in step (1) includes at least one of the common biomass such as walnut shells, pistachio shells, and macadamia nut shells.

[0032] The biomass particles in step (1) are approximately 20-40 mesh.

[0033] Before heating, a certain amount of inert gas should be introduced into the tubular furnace in steps (2) and (3) to exhaust the residual air in the tube.

[0034] In steps (2) and (3), an inert gas of 300 ml / min should be continuously injected as a protective gas during the heating process.

[0035] The inert atmosphere gas in steps (2) and (3) is selected from high-purity nitrogen or argon.

[0036] The activator in step (3) is at least one of potassium hydroxide, sodium hydroxide, zinc chloride, and potassium oxalate.

[0037] The ratio of the activator dosage to the biomass material in step (3) is 0.75-1.25:1; The activation process in step (3) must ensure that the activation furnace is under positive pressure.

[0038] The biomass activated carbon (BioAC) prepared by this invention using biomass as raw material has a highly developed microporous structure, an extremely high micropore volume ratio, and a high specific surface area. This unique pore structure provides abundant gas adsorption sites and diffusion channels, thereby endowing the material with excellent adsorption performance for gases such as radon.

[0039] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Unless otherwise stated, all reagents used in the examples are commercially available or synthesized using conventional methods and are ready for use without further processing, as are the instruments used in the examples.

[0041] Example 1 Waste pistachio shells (20-40 mesh) were used as raw material and carbonized at 500 °C for 1.5 h under a high-purity nitrogen atmosphere. The resulting biochar was then activated using a chemical activation method. The biochar was mixed with solid KOH in deionized water at mass ratios of 0.75, 1, and 1.25, respectively. After ultrasonic mixing, the mixture was mechanically stirred at 90 °C until dry. After drying overnight, it was placed in a tube furnace for high-temperature activation under a high-purity nitrogen atmosphere at a gas flow rate of 300 ml / min and a heating rate of 5 °C / min. The temperature was maintained at 600 °C for 1.5 h before automatic cooling. After cooling to room temperature, the solution was repeatedly washed with hydrochloric acid and deionized water until the pH remained constant. The solution was then dried at 105 °C for 24 h to remove moisture, yielding biomass activated carbons KBC-600-0.75, KBC-600-1, and KBC-600-1.25, which were cooled in a desiccator for later use.

[0042] Example 2 Waste pistachio shells (20-40 mesh) were used as raw material and carbonized at 500 °C for 1.5 h under a high-purity nitrogen atmosphere. The resulting biochar was then activated using a chemical activation method: the biochar was mixed with solid KOH in deionized water, with the mass ratios of KOH to biochar being 0.75, 1, and 1.25, respectively. After ultrasonic mixing, the mixture was mechanically stirred at 90 °C until dry. After drying overnight, it was placed in a tube furnace for high-temperature activation under a high-purity nitrogen atmosphere at a gas flow rate of 300 ml / min and a heating rate of 5 °C / min. After reaching 700 °C, it was maintained at this temperature for 1.5 h and then automatically cooled. After cooling to room temperature, the solution was repeatedly washed with hydrochloric acid and deionized water until the pH remained constant. The solution was then dried at 105 °C for 24 h to remove moisture, yielding biomass activated carbons KBC-700-0.75, KBC-700-1, and KBC-700-1.25, which were cooled in a desiccator for later use.

[0043] Example 3 Waste pistachio shells (20-40 mesh) were used as raw material and carbonized at 500 °C for 1.5 h under a high-purity nitrogen atmosphere. The resulting biochar was then activated using a chemical activation method: the biochar was mixed with solid KOH in deionized water, with the mass ratios of KOH to biochar being 0.75, 1, and 1.25, respectively. After ultrasonic mixing, the mixture was mechanically stirred at 90 °C until dry. After drying overnight, it was placed in a tube furnace for high-temperature activation under a high-purity nitrogen atmosphere at a gas flow rate of 300 ml / min and a heating rate of 5 °C / min. After reaching 800 °C, it was maintained at this temperature for 1.5 h and then automatically cooled. After cooling to room temperature, the solution was repeatedly washed with hydrochloric acid and deionized water until the pH remained constant. It was then dried at 105 °C for 24 h to remove moisture, yielding biomass activated carbons KBC-800-0.75, KBC-800-1, and KBC-800-1.25, which were cooled in a desiccator for later use.

[0044] Example 4 Waste pistachio shells (20-40 mesh) were used as raw material and carbonized at 500℃ for 1.5 h under a high-purity nitrogen atmosphere. The resulting biochar was then activated using a chemical activation method: the biochar and KOH solid were mixed in deionized water, with the mass ratios of KOH to biochar being 0.75, 1, and 1.25, respectively. After ultrasonic treatment and homogenization, the mixture was mechanically stirred at 90℃ until dry. After drying overnight, it was placed in a tube furnace for high-temperature activation under a high-purity nitrogen inert atmosphere at a gas flow rate of 300 ml / min and a heating rate of 5℃ / min. After reaching 900℃, it was maintained at this temperature for 1.5 h and then automatically cooled. After cooling to room temperature, the solution was repeatedly washed with hydrochloric acid and deionized water until the pH remained constant. It was then dried at 105℃ for 24 h to remove moisture, yielding biomass activated carbons KBC-900-0.75, KBC-900-1, and KBC-900-1.25, which were cooled in a desiccator for later use.

[0045] Experimental Example The biomass activated carbon prepared in the examples was tested, and its nitrogen adsorption-desorption isotherms were measured respectively. Figure 1-3 The total specific surface area of ​​different activated carbons was calculated using the BET equation (Table 1). The micropore size distribution of activated carbon was characterized using the HK method. The pore volume, specific surface area, and pore size distribution of mesopores were calculated and described using the BJH model. The results are as follows: Figure 2-3 See Table 1.

[0046] The radon adsorption coefficient of the biomass activated carbon prepared in the example was tested using the static adsorption method. The test method was specifically referred to in the literature (Xie Lifei, Qiu Shoukang, Tang Quan, et al. Study on static adsorption coefficient measurement of radon by activated carbon adsorption. Nuclear Electronics & Detection Technology, 2019, 39(3): 255-259). The radon concentration was detected by the scintillation chamber method. The detection results are shown in Table 1.

[0047] Table 1. Pore structure and radon adsorption test results of biomass activated carbon

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing biomass activated carbon, characterized in that, Includes the following steps: S1: Carbonize biomass raw materials to obtain biochar; S2: The biochar and activator are mixed evenly in water and dried, and then activated at high temperature under an inert atmosphere; S3: After washing to remove the activating agent, the activated biochar is dried and cooled to obtain the biomass activated carbon; The activator is selected from one or more of potassium hydroxide, sodium hydroxide, zinc chloride, and potassium oxalate.

2. The preparation method according to claim 1, characterized in that, The biomass raw material is a hard nut shell.

3. The preparation method according to claim 1, characterized in that, The biomass raw material is 20-40 mesh particles.

4. The preparation method according to claim 1, characterized in that, The carbonization is carried out under an inert atmosphere.

5. The preparation method according to claim 1, characterized in that, The mass ratio of the activator to the biochar in step S2 is 0.75-1.25:

1.

6. The preparation method according to claim 1, characterized in that, The high-temperature activation temperature is 600-900 ℃.

7. The preparation method according to claim 1, characterized in that, The high-temperature activation time is 1-2 hours.

8. The preparation method according to claim 1, characterized in that, The inert atmosphere gas is selected from nitrogen or argon.

9. Biomass activated carbon obtained by the preparation method according to any one of claims 1-8.

10. The application of the biomass activated carbon according to claim 9 in the adsorption of radioactive inert gases.

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