Production process of activated carbon with efficient adsorption performance

Abstract

The invention discloses a production process of activated carbon with efficient adsorption performance, and belongs to the technical field of porous carbon material preparation. The preparation method comprises the following steps: by taking biomass as a raw material, compounding the biomass with a eutectic salt system consisting of zinc chloride and potassium chloride, a nitrogen source precursor and a sacrificial cation source to obtain a homogeneous reaction precursor; the key point is that the precursor is subjected to programmed variable-pressure pyrolysis treatment under the condition that the temperature is far lower than the traditional activation temperature. According to the process, deep infiltration of molten salt is achieved through initial pressurization operation, and then reaction gas is guided to escape orderly through a later programmed pressure reduction process. Through collaborative innovation of the composition and the process, multiple steps of carbonization, activation, pore forming, in-situ functionalization and the like are integrated in a single low-temperature reaction unit, and the technical problems that a traditional method is high in energy consumption and long in flow, and the physical structure and surface chemistry of a material are difficult to synchronously regulate and control are solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of porous carbon material preparation, and particularly relates to a production process of activated carbon with high adsorption performance. BACKGROUND

[0002] As a kind of non-crystalline carbon material with excellent performance, activated carbon plays an indispensable role of adsorbent and catalyst carrier in many fields such as environmental protection, chemical industry, food and medicine, and energy storage, due to its huge specific surface area, developed pore structure and rich surface functional groups. The performance of activated carbon depends largely on its preparation method, and currently, physical and chemical methods are mainly used in industry.

[0003] However, the existing activated carbon preparation technology has some inherent limitations, which jointly restrict the further improvement of product performance and the economy and environmental protection of the production process. Although the traditional chemical activation method is widely used, its core process usually relies on pyrolysis treatment of the mixture of carbon source precursor and chemical activator at high temperature (usually 600-900 DEG C). Such a high reaction temperature not only means huge energy consumption and strict requirements for the high-temperature and corrosion-resistant performance of production equipment, but also often accompanies the problem of difficult accurate control of the reaction process. Severe high-temperature reaction can easily cause the sintering or collapse of the formed pore structure, so that the pore size distribution of the final product is uneven, and it is difficult to realize the ideal multi-level pore structure designed for specific applications.

[0004] In addition, the existing technology also faces the challenges of long process flow and low efficiency in realizing the functionalization of activated carbon. In order to give activated carbon the ability to target adsorb specific substances, such as enhancing the adsorption of acid gases by introducing nitrogen-containing functional groups, it is usually necessary to add one or more independent post-treatment modification steps after preparing the porous skeleton at high temperature. This series process route of "first construction, then modification" not only prolongs the whole production cycle and complicates the operation, but also may cause blockage or damage to the existing pore in the post-treatment process, resulting in the decline of the comprehensive performance of the material. Efficiently integrating the structure construction and surface functionalization of the material into a single process step has always been a technical problem that the field seeks to break through.

[0005] Therefore, developing a new preparation method that can be carried out under mild conditions, simplify the process flow, and realize the synchronous and collaborative regulation of the physical structure and surface chemical properties of activated carbon, is of great practical significance for promoting the technological progress of high-performance activated carbon industry and meeting the growing market demand. SUMMARY

[0006] The technical problem to be solved by the present invention is to provide a new production process and the key intermediates used therein that can overcome the defects of existing activated carbon production processes, such as high energy consumption, complex process, environmental pollution, and limited ability to control the pore structure and surface chemical properties of the product.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0008] The first aspect of this invention provides a production process for activated carbon with high adsorption performance. This process achieves highly efficient integration of carbonization, activation, pore structure construction and surface functionalization of biomass raw materials by designing a unique low-temperature liquid phase reaction system and combining it with programmed physical condition control.

[0009] Specifically, the process includes the following steps:

[0010] Step 1, Preparation of the composite reaction precursor: A homogenized composite reaction precursor is prepared by mixing a biomass carbon source precursor, a eutectic salt mixture of zinc chloride and potassium chloride, a nitrogen source precursor, and a sacrificial cation source. In this step, high-energy mixing methods, such as mechanical ball milling, are used to mix at a speed of 300-500 rpm for 1-3 hours to ensure sufficient and uniform contact of each solid phase component at the microscale. The biomass carbon source precursor is preferably lignin or straw powder. The nitrogen source precursor is preferably urea, and the sacrificial cation source is preferably ferric nitrate.

[0011] Step 2, Activation and Purification: The composite reaction precursor obtained in Step 1 is then subjected to further processing.

[0012] The core of this process lies in the integrated activation stage. The precursor is placed in an inert atmosphere and first heated to a pre-set temperature range (e.g., 280-320°C). At this temperature, the eutectic salt melts to form a low-melting-point liquid-phase reaction medium. Simultaneously, a pressure higher than atmospheric pressure (e.g., 0.2-0.5 MPa) is applied to the system, using physical pressure to force the liquid reaction medium to penetrate deeply and uniformly into the internal fibrous structure of the biomass carbon source precursor, achieving ultimate wetting.

[0013] Subsequently, the temperature is increased to a second preset temperature range (e.g., 400-550°C) to carry out the main reaction. During this stage, the system pressure is programmed and steadily reduced to atmospheric pressure over a period of 45-90 minutes. This programmed pressure change process is one of the key innovations of this invention, and its mechanism is as follows:

[0014] Synergistic catalysis and template construction: In a liquid environment, zinc chloride acts as a Lewis acid to efficiently catalyze the dehydration, cross-linking, and aromatization of biomass, forming a carbon skeleton. At the same time, potassium chloride and zinc chloride ions in the molten salt act as dynamic ionic templates at the nanoscale, occupying space during the carbon skeleton formation process, thereby constructing the initial microporous and mesoporous structures in situ.

[0015] In-situ functionalization and catalytic modification: Within this mild temperature range, nitrogen source precursors (such as urea) decompose, releasing nitrogen-containing active groups that directly react with the newly formed carbon skeleton, achieving in-situ nitrogen doping and endowing the product with specific surface chemical properties. Simultaneously, sacrificial cation sources (such as ferric nitrate) are in-situ reduced to metallic nanoparticles. These nanoparticles micro-regulate the activity of zinc chloride, the main catalyst, and influence the orderliness of the carbon structure.

[0016] Pressure gradient guided pore formation: The programmed depressurization process can orderly guide the escape of small molecule gases such as H2O and CO generated during the reaction. This controlled gas release process plays a secondary role in flushing, expanding and sculpting the initial channels formed by the ion template, thereby forming a hierarchical pore structure with better connectivity and more reasonable distribution.

[0017] After the pressure is reduced, the product can be kept at a constant temperature for 1 to 3 hours in the second preset temperature range and at normal pressure to ensure complete reaction.

[0018] After integrated activation, the product is washed and dried. The washing step involves acid washing with 0.5-1.0M hydrochloric acid, followed by washing with deionized water until neutral. The purpose is to completely remove the inorganic salts that serve as templates and catalysts, thereby fully exposing the internally constructed porous structure. Finally, drying yields the final product.

[0019] A second aspect of this invention provides a composite reaction precursor for producing highly efficient activated carbon, which forms the basis for achieving multiple synergistic reactions in the aforementioned process. The precursor is prepared by mixing the following components:

[0020] a. Biomass carbon source precursor, preferably lignin or straw powder;

[0021] b. A eutectic salt mixture of zinc chloride and potassium chloride, wherein the molar ratio of zinc chloride to potassium chloride is (55:45) to (65:35). This ratio ensures that the system has a low melting point and a suitable reaction environment;

[0022] c. A nitrogen source precursor, preferably urea, is prepared in a mass ratio of (8-15):100 to the biomass carbon source precursor. This ratio ensures sufficient surface functionalization.

[0023] d. The sacrificial cation source is preferably ferric nitrate, with a molar ratio of metal cation to zinc chloride of (1-5):100. This ratio is used to achieve effective micro-region control of the main catalyst;

[0024] The total mass ratio of the biomass carbon source precursor to components b, c, and d is 1:(3-5), which ensures sufficient coating of the reaction medium and efficient mass and heat transfer.

[0025] This invention, through the synergistic design of the above-mentioned processes and precursors, couples multiple mechanisms such as catalysis, templating, in-situ functionalization, and pressure gradient physical pore formation into a mild and integrated process flow, solving the inherent contradictions of traditional processes and providing a new, green, and highly controllable technical path for the preparation of high-efficiency adsorption activated carbon.

[0026] In summary, the present invention has at least one of the following beneficial technical effects:

[0027] 1. The activated carbon prepared by this invention possesses excellent adsorption performance and a well-developed hierarchical pore structure. By constructing a low-melting-point salt liquid-phase reaction system composed of zinc chloride and potassium chloride, the traditional solid-phase or gas-solid reaction is transformed into a highly efficient liquid-solid reaction. The ionic template effect of the molten salt is utilized to construct abundant micropores in situ. Simultaneously, a unique programmed pressure-switching process, through a physical method of first pressurizing and wetting followed by depressurizing to guide pore formation, further "carves" and expands the pores formed by the ionic template, efficiently forming a connected mesoporous network. The synergistic effect of these two processes results in a final product with both high specific surface area and well-developed hierarchical pores, enabling the simultaneous and efficient adsorption of target molecules of different sizes.

[0028] 2. This invention achieves precise control and in-situ functionalization of the surface chemical properties of activated carbon. By pre-compositing nitrogen sources such as urea in the precursor, effective nitrogen doping is simultaneously achieved in the mild and low-temperature environment of carbon framework formation. This "integrated" functional modification strategy efficiently and uniformly introduces nitrogen-containing functional groups onto the surface of carbon materials, significantly enhancing the material's targeted adsorption capacity for specific pollutants (such as acidic gases), and avoiding the problems of complex processes and low efficiency caused by traditional multi-step post-processing modification processes.

[0029] 3. The preparation process of this invention is significantly simplified, achieving energy saving, consumption reduction, and clean production. This invention creatively integrates multiple high-temperature steps—such as carbonization, activation, pore structure construction, and surface functionalization—that are independent in traditional processes into a single, continuous low-temperature reaction unit. Thanks to the construction of the eutectic salt system, the entire core reaction can be carried out under mild conditions far below the traditional activation temperature. This fundamentally reduces energy consumption, decreases equipment investment, and, due to the mild and controllable reaction conditions, inhibits the formation of byproducts such as tar, thereby improving production efficiency and environmental friendliness.

[0030] 4. This invention significantly improves the utilization rate of raw materials and the yield of the final product. By introducing a sacrificial cation source into the precursor, highly catalytically active metal nanoparticles are generated in situ during the reaction. These particles produce a synergistic catalytic effect with the molten salt main catalyst, making the conversion pathway from biomass feedstock to the carbon framework more efficient and selective. This meticulously designed composite catalytic system maximizes the fixation of carbon elements from the carbon source into the final product, reducing its loss as small molecule gases, thereby achieving higher product yields while ensuring high product performance.

[0031] 5. This invention achieves efficient and controllable preparation of the pore structure of activated carbon, especially the mesopore structure. Unlike traditional activation methods that have limitations in controlling pore structure, this invention employs a programmed pressure gradient control method, providing a novel physical control mechanism for the precise construction of pore structures. By precisely controlling the depressurization rate and timing, the escape behavior of the generated gases can be effectively regulated, thereby achieving directional "sculpting" of the size and number of mesopores. This high degree of controllability over the pore structure makes it possible to prepare high-performance activated carbon suitable for the adsorption and rapid mass transfer of macromolecules on demand. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the scope of protection of the invention.

[0033] Example 1

[0034] This embodiment provides a method for preparing highly efficient activated carbon, using intermediate parameters within the scope of the claims.

[0035] Preparation of composite reaction precursors

[0036] Weigh 10.0g of lignin powder that has been dried at 105℃ for 12 hours and pulverized through a 100-mesh sieve as a carbon source precursor.

[0037] In a dry environment, anhydrous zinc chloride (ZnCl2) and anhydrous potassium chloride (KCl) were weighed and mixed to a molar ratio of 60:40; urea was weighed to a mass ratio of 11.5:100 with lignin; and ferric nitrate nonahydrate (Fe(NO3)3·9H2O) was weighed to a molar ratio of 3:100 with zinc chloride. These three substances were then mixed thoroughly to obtain a composite reaction medium.

[0038] Weigh 40.0g of the above composite reaction medium (making the mass ratio of carbon source precursor to composite reaction medium 1:4), and place it together with 10.0g of lignin powder in a planetary ball mill. Ball mill and mix them at 400rpm for 2 hours under nitrogen atmosphere to obtain a homogeneous composite reaction precursor.

[0039] Programmable transformer activation

[0040] The aforementioned precursor was placed in a high-pressure reactor, sealed, and the air inside the reactor was purged with nitrogen. The temperature was programmed to increase at a rate of 6°C / min. When the temperature reached 300°C, nitrogen was added to the reactor to stabilize the pressure at 0.35 MPa, and the temperature was maintained at this condition for 30 minutes.

[0041] Subsequently, the temperature was increased to 475°C at a rate of 6°C / min. Upon reaching 475°C, while maintaining a constant temperature, the pressure inside the reactor was linearly reduced to atmospheric pressure (0.1 MPa) over 60 minutes. The reactor was then aged at 475°C and atmospheric pressure for another 2 hours. After the reaction was complete, it was allowed to cool naturally to room temperature.

[0042] Product purification and drying

[0043] The product was removed and placed in a 0.75M hydrochloric acid solution, and stirred at room temperature for 4 hours. Subsequently, it was repeatedly filtered and washed with deionized water until the pH of the filtrate reached 7.0. The washed product was then dried in a vacuum drying oven at 110°C for 12 hours to obtain the final product.

[0044] Example 2

[0045] This embodiment provides a method for preparing highly efficient activated carbon, using parameters within the lower limit of the claims.

[0046] Preparation of composite reaction precursors

[0047] Weigh 10.0g of straw powder that has been dried at 105℃ for 12 hours and pulverized through a 100-mesh sieve as a carbon source precursor.

[0048] In a dry environment, anhydrous zinc chloride (ZnCl2) and anhydrous potassium chloride (KCl) were weighed and mixed to a molar ratio of 55:45; urea was weighed to a mass ratio of 8:100 with straw powder; and ferric nitrate nonahydrate (Fe(NO3)3·9H2O) was weighed to a molar ratio of 1:100 with zinc chloride. These three substances were then mixed thoroughly to obtain a composite reaction medium.

[0049] Weigh 30.0g of the above composite reaction medium (making the mass ratio of carbon source precursor to composite reaction medium 1:3), and place it together with 10.0g of straw powder in a planetary ball mill. Ball mill and mix them at 300rpm for 1 hour under nitrogen atmosphere to obtain a homogeneous composite reaction precursor.

[0050] Programmable transformer activation

[0051] The aforementioned precursor was placed in a high-pressure reactor, sealed, and the air inside the reactor was purged with nitrogen. The temperature was programmed to increase at a rate of 3°C / min. When the temperature reached 280°C, nitrogen was added to the reactor to stabilize the pressure at 0.2 MPa, and the temperature was maintained at this level for 20 minutes.

[0052] Subsequently, the temperature was increased to 400°C at a rate of 3°C / min. Upon reaching 400°C, while maintaining a constant temperature, the pressure inside the reactor was linearly reduced to atmospheric pressure (0.1 MPa) over 45 minutes. The reactor was then aged at 400°C and atmospheric pressure for another hour. After the reaction was complete, it was allowed to cool naturally to room temperature.

[0053] Product purification and drying

[0054] The product was removed and placed in a 0.5M hydrochloric acid solution, and stirred at room temperature for 2 hours. Subsequently, it was repeatedly filtered and washed with deionized water until the pH of the filtrate reached 7.0. The washed product was then dried in a vacuum drying oven at 105°C for 8 hours to obtain the final product.

[0055] Example 3

[0056] This embodiment provides a method for preparing highly efficient activated carbon, using parameters at the upper limit of the claims.

[0057] Preparation of composite reaction precursors

[0058] Weigh 10.0g of lignin powder that has been dried at 105℃ for 12 hours and pulverized through a 100-mesh sieve as a carbon source precursor.

[0059] In a dry environment, anhydrous zinc chloride (ZnCl2) and anhydrous potassium chloride (KCl) were weighed and mixed to a molar ratio of 65:35; urea was weighed to a mass ratio of 15:100 with lignin; and ferric nitrate nonahydrate (Fe(NO3)3·9H2O) was weighed to a molar ratio of 5:100 with zinc chloride. These three substances were then mixed thoroughly to obtain a composite reaction medium.

[0060] Weigh out 50.0g of the above composite reaction medium (making the mass ratio of carbon source precursor to composite reaction medium 1:5), and place it together with 10.0g of lignin powder in a planetary ball mill. Ball mill and mix at 500rpm for 3 hours under nitrogen atmosphere to obtain homogeneous composite reaction precursor Euros.

[0061] Programmable transformer activation

[0062] The aforementioned precursor was placed in a high-pressure reactor, sealed, and the air inside the reactor was purged with nitrogen. The temperature was programmed to increase at a rate of 10°C / min. When the temperature reached 320°C, nitrogen was added to the reactor to stabilize the pressure at 0.5 MPa, and the temperature was maintained at this level for 40 minutes.

[0063] Subsequently, the temperature was increased to 550°C at a rate of 10°C / min. Upon reaching 550°C, while maintaining a constant temperature, the pressure inside the reactor was linearly reduced to atmospheric pressure (0.1 MPa) over 90 minutes. The reactor was then aged at 550°C and atmospheric pressure for another 3 hours. After the reaction was complete, the reactor was allowed to cool naturally to room temperature.

[0064] Product purification and drying

[0065] The product was removed and placed in a 1.0M hydrochloric acid solution, and stirred at room temperature for 6 hours. Subsequently, it was repeatedly filtered and washed with deionized water until the pH of the filtrate reached 7.0. The washed product was then dried in a vacuum drying oven at 120°C for 16 hours to obtain the final product.

[0066] Comparative Example

[0067] Comparative Example 1:

[0068] Compared to Example 1, the difference lies in that: in step 1, "Preparation of the composite reaction precursor," potassium chloride (KCl) is not added, and the mass of zinc chloride (ZnCl2) used in the composite reaction medium is the same as the total mass of zinc chloride and potassium chloride in Example 1. All other aspects are the same.

[0069] Comparative Example 2:

[0070] The difference from Example 1 is that urea is not added in step 1, "Preparation of the composite reaction precursor". Everything else is the same.

[0071] Comparative Example 3:

[0072] The difference from Example 1 is that ferric nitrate nonahydrate (Fe(NO3)3·9H2O) is not added in step 1, “Preparation of the composite reaction precursor”. All other steps are the same.

[0073] Comparative Example 4:

[0074] Compared to Example 1, the difference lies in that: in step 2, "programmed transformer-integrated activation," the entire heating and isothermal curing process is carried out at atmospheric pressure (0.1 MPa), and the step of increasing the pressure to 0.35 MPa and maintaining the isothermal temperature after heating to 300°C is not performed. All other steps are the same.

[0075] Comparative Example 5:

[0076] Compared to Example 1, the difference lies in the following: In step 2, "Programmed Variable Pressure Integrated Activation," after the temperature is raised to 475°C, the pressure is maintained at 0.35 MPa, and isothermal curing is performed at this pressure for 2 hours. The step of programmatically reducing the pressure to atmospheric pressure is not performed. All other steps are the same.

[0077] Comparative Example 6:

[0078] Compared with Example 1, the difference lies in that in step 1, "Preparation of Composite Reaction Precursor", the mass ratio of the carbon source precursor (lignin) to the composite reaction medium is adjusted to 1:2, which is outside the range of 1:(3-5) defined in the claims. All other aspects are the same.

[0079] Comparative Example 7:

[0080] The difference from Example 1 is that in step 1, "Preparation of the composite reaction precursor," the molar ratio of zinc chloride (ZnCl2) to potassium chloride (KCl) is adjusted to 80:20, which is outside the range of (55:45) to (65:35) defined in the claims. All other aspects are the same.

[0081] Test Example 1: Verification of the Role of the Eutectic Salt System

[0082] Experimental steps

[0083] Sample pretreatment:

[0084] Approximately 0.2 g each of the dried sample S1 prepared in Example 1 and the dried sample D1 prepared in Comparative Example 1 were placed in the sample tubes of a physical adsorption analyzer. The samples were degassed at 200°C under vacuum for 6 hours to remove impurities and small molecules adsorbed on their surface and within their pores.

[0085] Nitrogen adsorption-desorption test:

[0086] The pretreated sample tubes were mounted on a fully automated physical adsorption analyzer. Using high-purity nitrogen as the adsorbate at liquid nitrogen temperature (77 K), the nitrogen adsorption-desorption isotherms of the samples were measured within a relative pressure range (P / P0) from 0.005 to 0.995. After the test, the specific surface area of ​​the samples was calculated using the multi-point BET (Brunauer-Emmett-Teller) method based on the adsorption data; the micropore volume was calculated using the t-plot method; and the total pore volume was calculated based on the amount of nitrogen adsorbed at a relative pressure P / P0≈0.99.

[0087] Iodine adsorption value test:

[0088] The procedure was performed according to GB / T 12496.8-2015. Accurately weigh 0.5 g of dried samples S1 and D1 and place them separately in stoppered conical flasks. Accurately add 50.0 mL of 0.1 mol / L iodine standard solution to each flask, tighten the stopper, and shake in a constant-temperature shaker for 15 minutes. After standing, filter rapidly. Accurately pipette 25.0 mL of the filtrate and titrate with 0.1 mol / L sodium thiosulfate standard solution. Near the endpoint, add starch solution as an indicator and continue titrating until the blue color disappears. Record the volume of sodium thiosulfate standard solution consumed and calculate the iodine adsorption value according to the following formula.

[0089] Experimental data

[0090] Table 1: Comparison of performance test data of Samples from Example 1 and Comparative Example 1

[0091]

[0092] Experiment Summary

[0093] As shown in Table 1, the sample S1 prepared using the process of Example 1 has significantly higher specific surface area, micropore volume, total pore volume, and iodine adsorption value than sample D1 prepared using the process of Comparative Example 1. This result strongly demonstrates that the eutectic salt system composed of zinc chloride and potassium chloride plays an irreplaceable key role in the process of this invention. Without the potassium chloride component, even with all other conditions remaining consistent, the porous structure and adsorption performance of the product show a fundamental decline.

[0094] The underlying mechanism lies in the fact that this invention constructs a eutectic system by precisely proportioning zinc chloride and potassium chloride. This system can form a homogeneous and stable liquid-phase reaction environment at temperatures far below the melting point of zinc chloride alone. This low-temperature liquid-phase platform not only serves as a highly efficient reaction solvent, ensuring sufficient wetting and efficient mass transfer of the catalyst and carbon source precursor, but more importantly, it allows molten ions (K... +In the formation of the carbon framework, ions (such as Cl-) act as dynamic nanotemplates, constructing rich microporous structures in situ by occupying space. In Comparative Example 1, due to the lack of potassium chloride, zinc chloride alone has a higher melting point and more intense reaction conditions, making it difficult to form an effective ionic template effect. It may even lead to sintering and collapse of the already formed pore structure, ultimately resulting in a product with a small specific surface area and low pore volume.

[0095] Therefore, the innovative introduction of potassium chloride and zinc chloride into a eutectic system is the foundation for successfully constructing a mild and efficient liquid-phase reaction platform. This platform is a prerequisite for achieving high specific surface area and well-developed microporous structure (as indicated by high iodine adsorption value). This strategy based on eutectic salt phase transition fundamentally optimizes the reaction pathway, which is the core difference between this invention and the traditional high-temperature activation method, and the key to obtaining products with excellent adsorption performance, highlighting the significant innovation of this invention in composition design.

[0096] Test Example 2: Verification of In-situ Nitrogen Doping

[0097] Experimental steps

[0098] Elemental analysis:

[0099] Approximately 2.0 mg of thoroughly dried samples S1 and D1 were accurately weighed and wrapped in tin foil. The samples were then burned at high temperature in an oxygen-rich environment using an elemental analyzer. The signals of the combustion products (N2, CO2, H2O) were detected by a thermal conductivity detector (TCD). After instrument calibration, the mass fraction of nitrogen (N) in the samples was calculated.

[0100] Carbon dioxide (CO2) adsorption performance test:

[0101] Approximately 0.2 g of dried samples S1 and D1 were placed in sample tubes of a physical adsorption analyzer and degassed under vacuum at 200 °C for 6 hours. Afterward, the sample tubes were placed in a thermostatic mantle at 298 K (25 °C). Using high-purity carbon dioxide as the adsorbate, the CO2 adsorption isotherm of the samples was measured within a pressure range of 0 to 1 bar. The saturated adsorption capacity at 1 bar was recorded.

[0102] Experimental data

[0103] Table 2: Comparison of performance test data of Samples from Example 1 and Comparative Example 2

[0104] Sample No. Mass fraction of nitrogen element (%) 1 0.0002 2 0.0002 3 0. CO2adsorption capacity (mmol / g) S1 4.17 3.92 D2 0.23 2.14

[0105] Experiment Summary

[0106] According to the test results shown in Table 2, sample S1 prepared in Example 1 contained up to 4.17% nitrogen, while sample D2 of Comparative Example 1 without urea contained only 0.23% trace nitrogen. This directly confirms that the present invention successfully achieved nitrogen doping of the final activated carbon product by introducing a nitrogen source into the precursor. Corresponding to the difference in elemental composition, sample S1 achieved an adsorption capacity of 3.92 mmol / g for carbon dioxide, which is much higher than that of sample D2 (2.14 mmol / g), indicating that the introduction of nitrogen significantly improved the adsorption performance of the material for acidic gases.

[0107] This performance difference stems from the unique in-situ functionalization mechanism of this invention. In the low-temperature liquid-phase reaction system constructed in this invention, the formation of the carbon skeleton and the decomposition of the nitrogen source precursor (urea) occur simultaneously within the same mild temperature range. The nitrogen-containing active groups generated by the decomposition can be instantly captured by the highly active dangling bonds and edge sites on the newly formed carbon skeleton, and stably embedded into the six-membered ring structure of carbon through chemical bonding, forming basic functional groups such as pyridine nitrogen and pyrrole nitrogen. This "in-situ doping" strategy ensures the efficient and uniform introduction of nitrogen into the material.

[0108] Therefore, the nitrogen-containing functional groups enriched on the surface of sample S1 act as effective Lewis basic sites, generating strong interactions with Lewis acidic CO2 molecules, thus significantly enhancing its adsorption capacity. In contrast, sample D2, lacking these active sites, relies primarily on weaker van der Waals forces for CO2 adsorption. The innovation of this invention lies in its ingenious integration of material structure construction and surface chemical modification into a single reaction step through pre-designed precursors. This achieves simultaneous construction of the material's bulk structure and surface function, fully demonstrating the advanced nature of this invention in process integration and material functional design.

[0109] Test Example 3: Verification of In-situ Modification Effect of Sacrificial Cations

[0110] Experimental steps

[0111] Product yield calculation:

[0112] Accurately weigh the dry weight of the biomass precursors (lignin or straw powder) used before the reaction in Example 1 and Comparative Example 3, respectively, and record it as m_raw material. After the respective preparation processes are completed, the final activated carbon products are vacuum dried at 110°C to constant weight, and their mass is accurately weighed and recorded as m_product. Calculate the product yield using the following formula:

[0113] Yield (%) = (m_product / m_raw material) × 100%

[0114] Nitrogen adsorption-desorption test:

[0115] Approximately 0.2 g of dried samples S1 and D3 were placed in sample tubes of a physical adsorption analyzer and degassed at 200 °C under vacuum for 6 hours. Subsequently, at liquid nitrogen temperature (77 K), using high-purity nitrogen as the adsorbate, and at relative pressures (P / P0.005) ranging from 0.005 to 0.995, the samples were analyzed. o The nitrogen adsorption-desorption isotherm of the sample was determined within a certain range. Based on the test data, the specific surface area of ​​the sample was calculated using the BET method, the micropore volume was calculated using the t-plot method, and the total pore volume was calculated based on the adsorption amount at P / P0≈0.99.

[0116] Experimental data

[0117] Table 3: Comparison of performance test data of Samples from Example 1 and Comparative Example 3

[0118]

[0119] Experiment Summary

[0120] As can be seen from the test data in Table 3, compared with Comparative Example 3 sample D3 (which does not contain ferric nitrate), Sample S1 of Example 1 shows significant advantages in both product yield and porous structure parameters. Sample S1 has a higher yield, and its specific surface area, micropore volume, and total pore volume are also superior to those of Sample D3. This indicates that introducing a sacrificial cation source into the precursor has a crucial positive impact on the overall efficiency of the process and the structural properties of the final product.

[0121] This comprehensive performance improvement is attributed to the unique in-situ catalytic modification mechanism of this invention. Ferric nitrate, pre-introduced into the precursor, is reduced in situ during low-temperature activation, forming highly dispersed metal nanoparticles. These newly formed nanoparticles are not inert components, but rather act as highly efficient co-catalysts or micro-region regulators, synergistically interacting with the zinc chloride molten salt system, which serves as the main catalyst. This synergistic effect makes the conversion of biomass feedstock into a carbon skeleton more efficient and thorough, reducing the loss of carbon elements in the form of small molecule gases, thereby directly increasing product yield.

[0122] More importantly, these in-situ generated catalytic modification sites can precisely regulate the formation of the carbon framework and the pore-forming process of the ionic template, guiding the generation of richer and more regular porous structures. Therefore, the innovation of this invention lies not only in introducing a functional component, but also in using the "in-situ generation" strategy to create a dynamically optimized, multi-center synergistic catalytic environment at the moment the reaction occurs. This design concept of achieving self-optimization of the reaction process through precursor pre-setting is the key to simultaneously improving yield and porous structure, profoundly demonstrating the originality of this invention in constructing complex functional integrated reaction systems.

[0123] Test Example 4: Verification of the Function of Programmed Transformer Process

[0124] Experimental steps

[0125] Nitrogen adsorption-desorption test:

[0126] Approximately 0.2 g of dried samples S1, D4, and D5 were placed in sample tubes of a physical adsorption analyzer and degassed at 200 °C under vacuum for 6 hours. Subsequently, nitrogen adsorption-desorption isotherms were measured at liquid nitrogen temperature (77 K) using high-purity nitrogen as the adsorbate, within a relative pressure (P / P0) range of 0.005 to 0.995. Based on the test data, the specific surface area of ​​the samples was calculated using the BET method, the micropore volume was calculated using the t-plot method, and the total pore volume was calculated based on the adsorption amount at P / P0≈0.99. The difference between the total pore volume and the micropore volume was taken as the mesopore volume.

[0127] Methylene blue adsorption value test:

[0128] The procedure was performed according to GB / T 12496.10-2015. Accurately weigh 0.1 g of dried samples S1, D4, and D5 into stoppered conical flasks. Accurately add 50.0 mL of a 1.0 g / L methylene blue standard solution to each flask. Tightly seal the flasks and shake in a constant-temperature shaker for 30 minutes. After standing, filter rapidly. Pipette an appropriate amount of the filtrate and measure its absorbance at 664 nm using a UV-Vis spectrophotometer. Calculate the remaining concentration of methylene blue in the filtrate based on the standard curve, and then calculate the mass of methylene blue adsorbed per gram of sample.

[0129] Experimental data

[0130] Table 4: Comparison of performance test data of samples prepared under different pressure programs

[0131]

[0132] Experiment Summary

[0133] Table 4 clearly shows that the sample S1 prepared using the programmed pressure swing process in Example 1 exhibits significantly superior porous structure parameters, particularly the methylene blue adsorption value reflecting the macromolecular channel capacity, compared to samples prepared under constant atmospheric pressure (D4) or constant high pressure (D5). Sample S1 not only possesses the highest specific surface area, but its well-developed mesoporous structure also enables it to adsorb macromolecular dyes at a rate more than 2.5 times that of the other two. This fully demonstrates the originality and crucial role of the programmed pressure control in the process of this invention.

[0134] This significant difference in performance stems from the invention's profound understanding and precise control of the physical conditions during the reaction process. Compared to Comparative Example 4, which operates at constant atmospheric pressure, this invention applies pressure in the first stage. Its core mechanism lies in utilizing physical force to enable the molten liquid-phase salt system to overcome mass transfer resistance and deeply penetrate every microscopic corner of the biomass precursor, achieving ultimate wetting and a uniform catalytic reaction. The D4 sample, lacking this step, only undergoes surface activation, its internal structure cannot be effectively developed, resulting in an underdeveloped overall pore structure.

[0135] A more crucial innovation lies in the comparison with Comparative Example 5, which uses constant high pressure. The programmed depressurization step in the second stage of this invention operates on the mechanism of a "pressure gradient-guided pore carving" process. Orderly reducing the pressure during the main reaction stage allows for the smooth and controllable escape of a large amount of small-molecule gas generated by the reaction. This directional gas flow acts as a secondary flushing, expansion, and interconnection mechanism for the pores initially formed by the ion template, thereby efficiently constructing a continuous mesoporous network. In contrast, in D5, the continuous high pressure inhibits the effective release of gas, leading to pore blockage or the inability to form a connected network. Therefore, even if the micropore volume is acceptable, the mesoporous structure and accessibility to macromolecules are extremely poor, resulting in a correspondingly low methylene blue adsorption value. This invention achieves precise construction of the multi-level pore structure of the material through this combined process of "first pressurizing and then depressurizing for carving," representing a core technological innovation for obtaining high-performance adsorbent materials.

[0136] Test Example 5: Verification of Key Group Allocation Ratio Range

[0137] Experimental steps

[0138] Nitrogen adsorption-desorption test:

[0139] Approximately 0.2 g of dried samples S1, D6, and D7 were placed in sample tubes of a physical adsorption analyzer. The samples were degassed at 200 °C under vacuum for 6 hours. Subsequently, nitrogen adsorption-desorption isotherms were measured at liquid nitrogen temperature (77 K) using high-purity nitrogen as the adsorbate, within a relative pressure (P / P0) range of 0.005 to 0.995. Based on the test data, the specific surface area of ​​the samples was calculated using the BET method, the micropore volume was calculated using the t-plot method, and the total pore volume was calculated based on the adsorption amount at P / P0≈0.99.

[0140] Methylene blue adsorption value test:

[0141] The procedure was performed according to GB / T 12496.10-2015. Accurately weigh 0.1 g of dried samples S1, D6, and D7 into stoppered conical flasks. Accurately add 50.0 mL of a 1.0 g / L methylene blue standard solution to each flask. Tightly seal the flasks and shake in a constant-temperature shaker for 30 minutes. After standing, filter rapidly. Pipette an appropriate amount of the filtrate and measure its absorbance at 664 nm using a UV-Vis spectrophotometer. Calculate the remaining concentration of methylene blue in the filtrate based on the standard curve, and then calculate the mass of methylene blue adsorbed per gram of sample.

[0142] Experimental data

[0143] Table 5: Comparison of Performance Test Data for Samples with Different Composition Ratios

[0144]

[0145] Experiment Summary

[0146] The test data in Table 5 clearly show that only sample S1 prepared within a specific component ratio range exhibits the best adsorption performance. When either the ratio of carbon source to reaction medium (D6) or the ratio between eutectic salt components (D7) deviates from this specific range, the specific surface area, pore volume, and adsorption capacity for macromolecules of the final product all decrease significantly. This indicates that the component ratio range determined in this invention is a necessary condition for achieving the technical effect, and is both non-arbitrary and crucial.

[0147] The imbalance in the ratio of carbon source to reaction medium in Comparative Example 6 stems from the disruption of the physical environment of the reaction system. The liquid-phase reaction system designed in this invention requires a sufficient amount of molten salt as both a "solvent" and a "template" to fully coat, wet, and disperse the carbon source precursor particles. When the amount of reaction medium is too small, a continuous liquid-phase environment cannot be formed, resulting in the reaction occurring only in a localized, non-uniform solid or semi-solid phase. This leads to extremely low mass and heat transfer efficiency, and the catalytic and templating effects cannot be effectively utilized. Consequently, the resulting product, D6, exhibits severely underdeveloped pore structure, and all performance indicators are at low levels.

[0148] The imbalance in the ratio of zinc chloride to potassium chloride in Comparative Example 7 fundamentally weakened the technical effect by creating an unsuitable chemical reaction environment. This invention selects a specific molar ratio of zinc chloride and potassium chloride to construct a system with the lowest eutectic point, thereby ensuring the initiation of an efficient liquid-phase reaction within an optimal, mild low-temperature range. Deviating from this optimal eutectic point leads to an increase in the melting point of the mixed salt, preventing the reaction from proceeding smoothly within the preset low-temperature window, or requiring higher temperatures to form a liquid phase. This not only undermines the low-temperature advantage of the process but also alters the physicochemical properties of the molten salt, weakening its ability to form pores as a dynamic ionic template. Ultimately, while product D7 outperforms D6, it is far inferior to S1 prepared in the optimal reaction platform. This fully demonstrates that the precise design at the composition level is the cornerstone of the invention's technological advancement.

[0149] Test Example 6: Comparative Verification with Traditional High-Temperature Activation Process

[0150] For this test, a separate control sample, D8, was prepared. This sample was prepared using a traditional single-activator high-temperature pyrolysis method: 10.0 g of lignin powder was mixed with 30.0 g of zinc chloride and impregnated in water. After evaporating the water, the mixture was heated to 700 °C in a muffle furnace under a nitrogen atmosphere at a rate of 10 °C / min and activated at this temperature for 2 hours. The product was purified and dried using the same acid washing and water washing steps to obtain sample D8.

[0151] Experimental steps

[0152] Elemental analysis:

[0153] Approximately 2.0 mg of thoroughly dried samples S1 and D8 were accurately weighed and wrapped in tin foil. The mass fraction of nitrogen (N) in the samples was determined and calculated using an elemental analyzer in high-temperature combustion and thermal conductivity detection modes.

[0154] Nitrogen adsorption-desorption test:

[0155] Approximately 0.2 g of dried samples S1 and D8 were placed in sample tubes of a physical adsorption analyzer and degassed at 200 °C under vacuum for 6 hours. Subsequently, nitrogen adsorption-desorption isotherms were measured at liquid nitrogen temperature (77 K) using high-purity nitrogen as the adsorbate, within a relative pressure (P / P0) range of 0.005 to 0.995. Based on the test data, the specific surface area of ​​the samples was calculated using the BET method, and the total pore volume was calculated based on the adsorption amount at P / P0≈0.99.

[0156] Carbon dioxide (CO2) adsorption performance test:

[0157] Approximately 0.2 g of dried samples S1 and D8 were taken and subjected to the same degassing pretreatment in a physical adsorption analyzer. Afterward, the sample tubes were placed in a constant-temperature mantle at 298 K (25 °C). Using high-purity carbon dioxide as the adsorbate, the CO2 adsorption isotherm of the samples was measured within a pressure range of 0 to 1 bar, and the saturated adsorption capacity at 1 bar was recorded.

[0158] Experimental data

[0159] Table 6: Comparison of Performance Test Data of Samples from the Invention Process and the Traditional Process

[0160]

[0161] Experiment Summary

[0162] The comparative data in Table 6 irrefutably demonstrate, from multiple dimensions, the significant superiority of the process of this invention over the traditional high-temperature activation method. Under the premise of significantly reducing the reaction temperature (475℃ vs 700℃), the physical structural parameters of sample S1 prepared by this invention, such as specific surface area and total pore volume, far exceed those of sample D8 prepared by the traditional method. More notably, the nitrogen content and CO2 adsorption capacity of sample S1 are more than ten times and more than twice that of sample D8, respectively, demonstrating the breakthrough progress of this invention in the functionalization of material surfaces.

[0163] This comprehensive performance improvement stems from the revolutionary low-temperature liquid-phase reaction system of this invention. Traditional high-temperature gas-solid activation methods (such as the preparation of sample D8) are violent and difficult to control, often leading to over-etching and pore collapse, thus limiting further improvement in specific surface area. In contrast, the multi-component eutectic salt liquid-phase platform constructed in this invention transforms the reaction into a mild and homogeneous liquid-solid mode. Utilizing the ion template effect, it can efficiently and orderly construct rich porous structures at lower temperatures, thereby achieving superior physical structures while saving energy.

[0164] One of the core innovations of this invention lies in the one-step integration of material structure construction and surface functionalization through the pre-design of the precursor. The significant nitrogen content and excellent CO2 adsorption performance of sample S1 are precisely due to the in-situ doping of the nitrogen source during the formation of the carbon framework. This strategy endows the material with specific surface chemical properties. Traditional methods, to achieve similar functions, must add a separate, energy-intensive post-processing modification step after high-temperature activation. Therefore, this invention, through its unique composition and process synergistic design, not only simplifies the process and reduces energy consumption but also achieves simultaneous optimization of physical structure and surface function, providing a new and efficient pathway for the preparation of high-performance activated carbon.

[0165] Test Example 7: Validation of the Synergistic Effect of Innovative Compositions and Innovative Processes

[0166] To conduct this test, a comparative sample D9 was prepared separately. This sample used the exact same composite reaction precursor as in Example 1, but was treated with a conventional high-temperature activation process: the homogeneous composite reaction precursor prepared in Example 1 was placed in a muffle furnace and heated to 700°C at a rate of 10°C / min under a nitrogen atmosphere, and activated at this temperature for 2 hours. The product was purified and dried using the same acid washing and water washing steps to obtain sample D9.

[0167] Experimental steps

[0168] Elemental analysis:

[0169] Approximately 2.0 mg of thoroughly dried samples S1 and D9 were accurately weighed and wrapped in tin foil. The mass fraction of nitrogen (N) in the samples was determined and calculated using an elemental analyzer through high-temperature combustion and thermal conductivity detection.

[0170] Nitrogen adsorption-desorption test:

[0171] Approximately 0.2 g of dried samples S1 and D9 were placed in sample tubes of a physical adsorption analyzer and degassed at 200 °C under vacuum for 6 hours. Subsequently, the nitrogen adsorption-desorption isotherms of the samples were measured at liquid nitrogen temperature (77 K) using high-purity nitrogen as the adsorbate, within a relative pressure (P / P0) range of 0.005 to 0.995. Based on the test data, the specific surface area of ​​the samples was calculated using the BET method, and the difference between the total pore volume and the micropore volume was taken as the mesopore volume.

[0172] Methylene blue adsorption value test:

[0173] The procedure was performed according to GB / T 12496.10-2015. Accurately weigh 0.1 g of dried samples S1 and D9 into stoppered conical flasks. Accurately add 50.0 mL of 1.0 g / L methylene blue standard solution to each flask. Tightly seal the flasks and shake in a constant-temperature shaker for 30 minutes. After standing, filter rapidly. Pipette an appropriate amount of the filtrate and measure its absorbance at 664 nm using a UV-Vis spectrophotometer. Calculate the remaining concentration of methylene blue in the filtrate based on the standard curve, and then calculate the mass of methylene blue adsorbed per gram of sample.

[0174] Experimental data

[0175] Table 7: Performance Comparison of the Invention Process and the Traditional Process for the Same Precursor

[0176]

[0177] Experiment Summary

[0178] The data in Table 7 powerfully reveal a core fact: even when using the innovative, functionally integrated precursor designed according to this invention, its final performance is far inferior to that of sample S1 prepared using the complete process of this invention, if it is treated under conventional, mismatched high-temperature processes (such as sample D9). Sample S1 exhibits overwhelming advantages in specific surface area, mesoporous structure (characterized by mesopore volume and methylene blue adsorption value), and degree of surface functionalization (characterized by nitrogen mass fraction), which eloquently demonstrates the inseparable and profound synergistic effect between the innovative process and the innovative composition of this invention.

[0179] The fundamental mechanism lies in the fact that the composition of this invention is designed for a specific low-temperature liquid-phase reaction environment. The high temperature of 700°C experienced by sample D9 completely destroyed this ingenious synergistic mechanism. First, the high-temperature environment eliminated the mild catalysis and template effect of the eutectic salt system, and the violent gas-solid reaction replaced the mild liquid-solid reaction, leading to the disordered growth and thermodynamic collapse of the pore structure. Therefore, its specific surface area and mesopore volume were much lower than those of S1. Second, the high temperature caused nitrogen source precursors such as urea to decompose and escape violently before the carbon skeleton was stably formed, and nitrogen-containing groups could not be effectively captured and fixed, resulting in extremely low nitrogen doping efficiency.

[0180] Therefore, the true innovative power of this invention lies not merely in the design of the composition or the improvement of the process flow, but in the perfect coupling of the two. The precursor composition of this invention can only maximize its potential for multifunctional integration on the "stage" of low-temperature programmed transformer technology; conversely, the process flow of this invention can only precisely guide the reaction path and achieve the simultaneous construction of pore structure and surface chemical properties when applied to this pre-designed multifunctional reactive precursor. This "tailor-made" composition-process synergy is the fundamental reason why this invention can break through traditional technical bottlenecks and achieve a leap in performance.

Claims

1. A process for producing activated carbon with high adsorption performance, characterized in that, The method comprises the following steps: Step one, preparation of composite reaction precursor: mixing biomass carbon source precursor, eutectic salt mixture of zinc chloride and potassium chloride, nitrogen source precursor and sacrificial cation source to prepare composite reaction precursor; Step two, activation and purification: treating the composite reaction precursor prepared in step one, which comprises: carrying out integrated activation under inert atmosphere, which comprises: increasing temperature to a first preset temperature interval and applying pressure higher than normal pressure, then continuing to increase temperature to a second preset temperature interval and during or after this process, programmatic reducing pressure to normal pressure; washing and drying the product obtained by the integrated activation to obtain the activated carbon with high adsorption performance.

2. A composite reaction precursor for producing highly efficient activated carbon, characterized in that, The following components are mixed to prepare: a, biomass carbon source precursor; b, eutectic salt mixture of zinc chloride and potassium chloride, wherein the molar ratio of zinc chloride to potassium chloride is (55:45) to (65:35); c, nitrogen source precursor, the mass ratio of the nitrogen source precursor to the biomass carbon source precursor is (8-15):100; d, sacrificial cation source, the molar ratio of metal cation in the sacrificial cation source to the zinc chloride is (1-5):100; wherein the total mass ratio of the biomass carbon source precursor to components b, c and d is 1:(3-5).

3. The process of claim 1, wherein, In step one, the composite reaction precursor is prepared by mixing the components at a rotation speed of 300-500 rpm for 1-3 hours by mechanical ball milling.

4. The process of claim 1, wherein, In the integrated activation of step two, the first preset temperature interval is 280-320℃, and the pressure higher than normal pressure is 0.2-0.5 MPa.

5. The process of claim 1, wherein, In the integrated activation of step two, the second preset temperature interval is 400-550℃, and the programmatic reduction of pressure is completed within 45-90 minutes.

6. The process of claim 1, wherein, After the pressure reduction process in the integrated activation of step two, a maturation step of keeping constant temperature for 1-3 hours at the second preset temperature interval and normal pressure is further included.

7. The process of claim 1, wherein, The nitrogen source precursor is urea, and the sacrificial cation source is ferric nitrate.

8. The precursor of claim 2, wherein, The biomass carbon source precursor is lignin or straw powder.

9. The precursor of claim 2, wherein, The nitrogen source precursor is urea, and the sacrificial cation source is ferric nitrate.

10. The process of claim 1, wherein, The washing in step two comprises: acid washing using 0.5-1.0 M hydrochloric acid, and washing with deionized water until neutral.

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