Preparation method of lignite-based porous carbon material for styrene adsorption

Abstract

The invention aims to provide a preparation method of a lignite-based porous carbon material for styrene adsorption, and belongs to the technical field of environmental functional materials, lignite is selected as a carbon source, the remarkable advantages of rich carbon and wide sources of the lignite are fully utilized, and the material preparation cost is greatly reduced. Through a process means of synchronous regulation and control of supercritical chemical nitrogen doping and KOH activation, on one hand, a porous structure with rich layers is constructed, and a sufficient pore space is provided for rapid diffusion and mass adsorption of styrene molecules; on the other hand, the supercritical nitrogen doping method can effectively remove oxygen-containing functional groups such as hydroxyl, carboxyl and the like in the lignite, more styrene adsorption active sites are provided, and meanwhile, the hydrophobic property of the material is improved, so that the adsorption selectivity and the adsorption capacity on styrene are remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of environmental functional materials technology, specifically relating to a method for preparing lignite-based porous carbon materials for styrene adsorption. Background Technology

[0002] Styrene, as a typical representative of volatile organic compounds (VOCs), poses significant hazards to production, daily life, and the environment. For human health, it can enter the body through the respiratory tract, damaging the central nervous system and causing headaches and dizziness; irritating the respiratory tract and causing coughing and difficulty breathing; affecting the liver and kidneys and impairing metabolic excretion functions; and also harming the reproductive system. At the environmental level, styrene participates in photochemical reactions to form photochemical smog, reducing atmospheric visibility, promoting ozone formation, exacerbating the greenhouse effect and impacting global climate, and easily forming smog that pollutes the atmosphere.

[0003] Currently, control technologies for styrene emissions from industrial sources mainly include catalytic combustion, adsorption recovery, biodegradation, and low-temperature plasma. Among these, adsorption has become one of the mainstream technologies for styrene pollution control due to its advantages such as flexible operation, low energy consumption, and wide applicability. Existing adsorption materials mainly include various types such as metal-organic frameworks (MOFs), mesoporous silica, activated carbon, and their modified materials. Seung-Ik Kim et al. successfully developed a highly selective styrene adsorbent prepared by incorporating Cu(I) into MIL-100(Fe) metal-organic framework material using a host-guest redox method. This adsorbent exhibits good stability, but the introduction of Cu occupies the pore space of the MOF, leading to a significant decrease in the specific surface area of ​​the material. Furthermore, the high-temperature reduction step required to generate stable Cu(I) during the material synthesis process consumes too much energy, making industrial application difficult. Eva Sanz-Santos et al. successfully prepared high specific surface area activated carbons L-10 and S-10 by ball milling-assisted FeCl3 activation of biomass, demonstrating excellent adsorption performance for polystyrene nanoplastics in water. However, powdered activated carbon materials generate a high pressure drop in fixed-bed adsorption towers, making them unsuitable for direct use. In addition, the granulation process results in a loss of specific surface area, and the reaction conditions are harsh. Jakub Matusik et al. prepared a series of surfactant-modified montmorillonite materials, which exhibit ultra-high adsorption capacity for styrene under suitable humidity conditions, superior to activated carbon. However, this material is sensitive to humidity, and its regeneration is difficult due to styrene polymerization after repeated use, which limits its stability in practical industrial applications.

[0004] Chinese patent document 202211559602.1 discloses a method for preparing an in-situ nitrogen-doped coal-based porous carbon lithium-sulfur battery cathode material. The method involves mixing coal powder with an alkaline activator (alkali-to-carbon mass ratio 1:2~1:6) and activating the mixture at 700~1200℃ to obtain coal-based activated carbon. After alkaline washing, acid washing, deashing, and drying, a purified product with a purity ≥95% is obtained. A nitrogen-containing precursor (preferably dicyandiamide) is dispersed in a solvent (preferably water-ethanol 1:1), and the purified product is added and stirred while drying. The dried product is carbonized in a nitrogen atmosphere at 600~900℃ for 2~4 hours, and after cooling, a composite of graphitic carbon nitride and coal-based activated carbon is obtained, i.e., a sulfur-supported cathode material for lithium-sulfur batteries. Although this patent provides a nitrogen-doped coal-based porous carbon material, it is actually applied to electrode materials. Furthermore, the preparation process involves excessive use of alkaline activator, which can easily cause environmental pollution; the activation temperature is also too high, resulting in high energy consumption.

[0005] It is evident that while various methods exist for synthesizing styrene adsorbents, most of these methods are costly and involve relatively complex processes. Therefore, developing styrene adsorbents that combine high adsorption performance, excellent stability, and low preparation cost has become a research hotspot and challenge in the field of VOCs control.

[0006] Lignite, with its naturally occurring porous precursor structure and abundant surface functional groups, readily forms a well-developed pore structure and high specific surface area after appropriate activation treatment, demonstrating its great potential as a precursor for high-performance adsorbent materials. Utilizing lignite to prepare high-value-added porous carbon materials can not only significantly reduce the production cost of adsorbents but also provide a new technological approach for the efficient and clean utilization of lignite resources. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing lignite-based porous carbon materials for styrene adsorption. The method described in this invention is simple, environmentally friendly, and uses readily available raw materials, providing a promising technical solution for the efficient adsorption and resource-based treatment of styrene in industrial VOCs.

[0008] The present invention adopts the following technical solution: A method for preparing a lignite-based porous carbon material for styrene adsorption includes the following steps: S1. Mix lignite, supercritical fluid, activator and nitrogen-containing material in a certain proportion and carry out a solvothermal reaction to obtain the precursor; S2. The precursor is subjected to pyrolysis, alkali leaching, high-temperature activation, acid washing, water washing to neutral, drying and grinding, tableting and granulation and sieving in sequence to finally obtain 40-60 mesh lignite-based porous carbon material.

[0009] Furthermore, the supercritical fluid includes one or both of methanol and ethanol, preferably methanol.

[0010] Furthermore, the activator includes one or more of NaOH, KOH, and K2CO3; preferably KOH.

[0011] Furthermore, the nitrogen-containing material includes one or more of urea, melamine, and ammonia; melamine is preferred.

[0012] Furthermore, the ratio of lignite, supercritical fluid, activator, and nitrogen-containing material is 10g:20mL:1g:1-5g.

[0013] Furthermore, the solvothermal reaction temperature is 200-320℃, preferably 240℃; the reaction time is 1h.

[0014] Furthermore, the pyrolysis treatment temperature is 500℃, and the pyrolysis time is 2h.

[0015] Furthermore, the alkaline leaching treatment involves mixing the pyrolysis product with KOH at a mass ratio of 1:1 and leaching for 12 hours.

[0016] Furthermore, the high-temperature activation treatment conditions are as follows: under a nitrogen atmosphere, the activation temperature is 700°C, and the activation time is 2 hours.

[0017] The principle of this invention is as follows: This invention innovatively selects inexpensive lignite as a carbon source, fully utilizing its significant advantages of abundant carbon and wide availability, thereby greatly reducing the material preparation cost. Through a process of simultaneous control of supercritical chemical nitrogen doping and KOH activation, on the one hand, a multi-layered porous structure is constructed, providing sufficient pore space for the rapid diffusion and large-scale adsorption of styrene molecules; on the other hand, the supercritical nitrogen doping method can effectively remove oxygen-containing functional groups such as hydroxyl (-OH) and carboxyl (-COOH) groups in lignite, providing more active sites for styrene adsorption, while improving the hydrophobic properties of the material, thereby significantly improving the adsorption selectivity and adsorption capacity for styrene.

[0018] The beneficial effects of this invention are as follows: 1. Significantly reduced raw material costs: Using abundant and inexpensive lignite as the main carbon source, replacing the high-quality coal or biomass raw materials used in the traditional activated carbon preparation, significantly reducing material production costs and providing economic feasibility for industrial-scale application; 2. Excellent adsorption performance: Through the synergistic effect of supercritical nitrogen doping and KOH activation, a multi-level pore structure with micropores as the main component and mesopores as the auxiliary component is constructed in the material. At the same time, nitrogen-containing functional groups are introduced as specific adsorption sites to achieve efficient capture and firm binding of styrene molecules. The adsorption capacity is as high as 1663 mg / g, which far exceeds that of commercial activated carbon (usually less than 500 mg / g). 3. High adsorption selectivity: Supercritical nitrogen doping can effectively remove oxygen-containing functional groups such as hydroxyl (-OH) and carboxyl (-COOH) in lignite, providing more active sites for styrene adsorption; in addition, the benzene ring structure of styrene has significant hydrophobicity, and the removed hydrophilic oxygen-containing functional groups can remove some water, enhance the hydrophobic properties of the material, and make the material more likely to adsorb styrene, thereby improving the selective adsorption capacity of styrene in complex VOCs systems; 4. Good structural stability: The carbon skeleton formed by high-temperature activation of lignite as a precursor has good mechanical strength and thermal stability, making it suitable for industrial operating environments such as fixed-bed adsorption. 5. The preparation process is green and efficient: the method is simple, the reaction conditions are mild, the chemical reagents used are environmentally friendly, and the overall process is easy to scale up and implement, with good prospects for industrial promotion. Attached Figure Description

[0019] Figure 1 This is a pore size distribution diagram of the products prepared at different hydrothermal temperatures according to the present invention.

[0020] Figure 2 for Figure 1 A magnified view of a portion of the image.

[0021] Figure 3 This diagram shows the styrene adsorption capacity and specific surface area of ​​the products prepared at different hydrothermal temperatures according to the present invention.

[0022] Figure 4 This is a pore size distribution diagram of the products prepared with different nitrogen doping amounts according to the present invention.

[0023] Figure 5 for Figure 4 A magnified view of a portion of the image.

[0024] Figure 6 This diagram shows the styrene adsorption capacity and specific surface area of ​​the products prepared with different nitrogen doping amounts according to the present invention.

[0025] Figure 7 Water contact angle diagram of the sample prepared by the direct nitrogen doping method.

[0026] Figure 8 This is a water contact angle diagram of the sample prepared in Example 1 of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, specific embodiments of the invention are described in detail, but are not limited thereto. Unless otherwise specified, the raw materials used in the embodiments are all commercially available products; and unless otherwise specified, the methods used are methods commonly used in the art.

[0028] Example 1 A method for preparing a lignite-based porous carbon material for styrene adsorption includes the following steps: S1. Accurately weigh 10g of lignite, 20ml of methanol, 1g of KOH and 4g of melamine, place them in a hydrothermal reactor and mix them evenly. React at 240℃ for 1 hour, and after cooling, obtain a black precursor. S2. The precursor is transferred to a tube furnace and pyrolyzed at 500℃ for 2 hours under nitrogen protection. The pyrolysis product is mixed with an equal mass of KOH, and an appropriate amount of distilled water is added and stirred for 12 hours, followed by drying. The dried sample is ground into powder and activated at 700℃ under nitrogen atmosphere for 2 hours. After grinding, the activated product is adjusted to pH≈4 (pH paper turns purple) with 2 mol / L hydrochloric acid solution and magnetically stirred for 5 hours to remove ash and residual alkali metals. After acid washing, the sample is filtered and washed with distilled water until the filtrate is neutral. It is then dried at 105℃ for 12 hours. The resulting powder is granulated by pressing and sieved to obtain 40~60 mesh particles, which is the finished product of lignite-based porous carbon material.

[0029] Example 2 This embodiment investigates the effect of hydrothermal reaction temperature on the material structure and adsorption performance: the preparation steps are the same as in Example 1, except that the hydrothermal reaction temperature in Example 1 is adjusted to 200℃, 280℃ and 320℃ respectively, and the other conditions remain unchanged.

[0030] Figure 1 and Figure 2 The figures show the pore size distribution of the samples prepared in Examples 1 and 2. As can be seen from the figures, there are significant differences in the pore size distribution of the samples prepared at different temperatures. When the hydrothermal temperature is 240℃, the sample exhibits the optimal pore size distribution and the largest pore volume in the microporous region, corresponding to a styrene adsorption capacity of 1663 mg / g. This indicates that a suitable hydrothermal temperature is conducive to the formation of a microporous dominant structure that facilitates styrene adsorption.

[0031] Figure 3 The graphs show the styrene adsorption capacity and specific surface area of ​​the products prepared at different hydrothermal temperatures, derived from... Figure 3 It can be seen that as the temperature increases, the styrene adsorption capacity of the product first increases and then decreases, while the specific surface area shows a decreasing trend. The adsorption performance is optimal at 240℃.

[0032] Example 3 This embodiment examines the effect of nitrogen doping on material properties: the preparation steps are the same as in Example 1, except that the amount of melamine in step S1 is adjusted to 0g, 1.5g, 2.5g and 5g respectively, while the other conditions remain unchanged.

[0033] Figure 4 and Figure 5The figures show the pore size distribution of the samples prepared in Examples 1 and 3. As can be seen from the figures, with the increase of melamine dosage, the pore volume and specific surface area in the microporous region of the material show a trend of first increasing and then decreasing. When the melamine dosage is 4g, the sample has the highest peak pore volume and the largest specific surface area in the microporous region, and its styrene adsorption capacity reaches 1663mg / g. This indicates that an appropriate nitrogen doping amount can effectively optimize the pore structure and surface chemical properties of the material, thereby maximizing its adsorption performance.

[0034] Figure 6 The graph shows the styrene adsorption capacity and specific surface area of ​​the products prepared with different nitrogen doping amounts. Figure 6 It can be seen that as the nitrogen doping amount increases, the styrene adsorption capacity of the product first increases and then decreases, while the specific surface area generally shows an upward trend. The adsorption performance is optimal when the nitrogen doping amount is 4g.

[0035] Comparative Example 1 This comparative study investigates the effect of supercritical nitrogen doping on the adsorption performance of the material: Accurately weigh 10g of lignite, 20ml of methanol, 1g of KOH, and 4g of melamine. Mix the above reagents and place them in a tube furnace. Pyrolyze at 500℃ for 2 hours under nitrogen protection. Mix the pyrolysis product with an equal mass of KOH, add an appropriate amount of distilled water, stir and soak for 12 hours, and then dry. Grind the dried sample into powder and activate it at 700℃ under nitrogen atmosphere for 2 hours. After grinding the activated product, adjust the pH to ≈4 (pH paper turns purple) with 2 mol / L hydrochloric acid solution and stir magnetically for 5 hours to remove ash and residual alkali metals. After acid washing, filter the sample with distilled water until the filtrate is neutral, and dry it at 105℃ for 12 hours. The obtained powder is pressed into tablets and granulated, and sieved to obtain 40-60 mesh particles to obtain the finished product of directly nitrogen-doped lignite-based porous carbon material, that is, lignite-based porous carbon material without supercritical nitrogen doping.

[0036] Figure 7 and Figure 8 The figures show the water contact angles of samples prepared by the direct nitrogen doping method and the supercritical nitrogen doping method of Example 1. The water contact angle of the sample prepared by the direct nitrogen doping method is 123.5°, while that of the sample prepared by the supercritical nitrogen doping method in Example 1 is 137.9°. Analysis shows that the sample prepared by the supercritical nitrogen doping method has a larger contact angle, indicating improved hydrophobicity. Since the benzene ring structure of styrene is hydrophobic, hydrophobic materials more readily adsorb styrene. Therefore, the supercritical nitrogen doping method has a greater adsorption advantage than the direct nitrogen doping method.

[0037] Comparative Example 2 Using existing technology, the method in the patent with application number 202211559602.1, the porous carbon prepared for styrene adsorption has a styrene adsorption capacity of less than 800 mg / g. The reason is that during the preparation process, the amount of activator potassium hydroxide is large and highly corrosive, which leads to the collapse of micropores.

[0038] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The above embodiments only illustrate several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those skilled in the art, several modifications and improvements can be made without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for the preparation of lignite-based porous carbon material for styrene adsorption, characterized by: The method comprises the following steps: S1, mixing lignite, supercritical fluid, activator and nitrogen-containing material in proportion to carry out solvothermal reaction to obtain a precursor; S2, sequentially carrying out pyrolysis treatment, alkali leaching treatment, high-temperature activation treatment, acid pickling treatment, water washing to neutral, drying and grinding, tabletting and granulating, and screening to finally obtain lignite-based porous carbon material with 40-60 mesh.

2. A process for the preparation of lignite based porous carbon material for styrene adsorption as claimed in claim 1, wherein: The supercritical fluid comprises one or both of methanol and ethanol.

3. A process for the preparation of lignite based porous carbon material for styrene adsorption as claimed in claim 1, wherein: The activator comprises one or more of NaOH, KOH and K2CO3.

4. The process for the preparation of lignite based porous carbon material for styrene adsorption as claimed in claim 1 wherein: The nitrogen-containing material comprises one or more of urea, melamine and ammonia.

5. The process for the preparation of lignite based porous carbon material for styrene adsorption as claimed in claim 1 wherein: The use amount ratio of the lignite, supercritical fluid, activator and nitrogen-containing material is 10g:20mL:1g:1-5g.

6. The process for the preparation of lignite based porous carbon material for styrene adsorption as claimed in claim 1 wherein: The solvothermal reaction temperature is 200-320 DEG C, and the reaction time is 1h.

7. The process as claimed in claim 1, wherein the process for the preparation of lignite based porous carbon material for styrene adsorption is characterized by: The pyrolysis temperature is 500 DEG C, and the pyrolysis time is 2h.

8. The process for the preparation of lignite based porous carbon material for styrene adsorption as claimed in claim 1 wherein: The alkali leaching treatment is that the pyrolysis product is mixed with KOH in a mass ratio of 1:1 for impregnation for 12h.

9. The process as claimed in claim 1, wherein the lignite based porous carbon material for styrene adsorption is prepared by: The high-temperature activation treatment condition is that the activation temperature is 700 DEG C under nitrogen atmosphere, and the activation time is 2h.

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