Eutectic solvent-mediated fly ash-carbon-based composite catalysts, methods of making and applications thereof

Abstract

This invention relates to a eutectic solvent-mediated fly ash-carbon-based composite catalyst, its preparation method, and its application. The catalyst utilizes a carbon-nitrogen co-doped porous carbon network as a carrier. The active component is derived from highly dispersed metal oxide nanoparticles derived from fly ash, which synergistically interact with the catalytic sites formed by the heteroatom-doped carbon framework, constructing a multi-active-site catalytic system. Using a eutectic solvent as both solvent and reactant, a three-stage graded carbonization process—sulfuric acid carbonization, microwave carbonization, and high-temperature pyrolysis carbonization—effectively encapsulates widely available and low-cost fly ash solid waste into a porous carbon network after activation, forming a loosely structured fly ash-carbon-based composite catalytic material with highly exposed active sites. When applied to CO2-rich liquid desorption, the catalyst enhances the proton-coupled electron transfer effect based on the synergistic effect between different components, promoting the decomposition of carbamates during CO2 desorption and significantly improving the desorption capacity and efficiency.

Description

Technical Field

[0001] This invention relates to a composite catalyst, specifically a fly ash-carbon-based composite catalyst mediated by a eutectic solvent for CO2 catalytic desorption, its preparation method, and its application, belonging to the field of catalyst processing technology. Background Technology

[0002] The massive consumption of fossil fuels in industrial processes has led to a sharp increase in atmospheric CO2 concentration, triggering global climate change and the greenhouse effect. CO2 capture, utilization, and storage (CCUS) technology is one of the effective means to mitigate this problem. Chemical absorption, represented by amine-based absorbents, is currently the most commonly used CO2 capture method, but its high regeneration energy consumption restricts its large-scale commercial application. Catalytic desorption technology can achieve the regeneration of alcoholamines at low temperatures, significantly reducing regeneration energy consumption. Therefore, developing efficient and stable desorption catalysts has become the core technology.

[0003] Solid acid catalysts (such as molecular sieves and metal oxides) are widely used in the desorption process of rich amine solutions due to their abundant Brønsted (B acid) and Lewis (L acid) acid sites. However, traditional solid acid catalysts have two main problems: first, the Brønsted (B acid) sites are prone to strong chemical bonding with the amino groups in alkanolamines, leading to deactivation; second, the metal components are easily dissolved and lost, resulting in poor catalyst cycle stability.

[0004] Recent studies have found that carbon-based catalysts, based on surface electron transfer mechanisms, can significantly improve the catalytic desorption activity and stability of CO2 in amine absorbers. Coupled with metal oxides, they can activate proton-coupled electron transfer capabilities, further enhancing catalytic desorption performance and cycle stability.

[0005] Fly ash (FA) is a major solid waste generated during coal combustion, possessing a high specific surface area and amphoteric acid-base properties. The metal oxides in fly ash can serve as catalytic active sites, and its porous structure facilitates mass transfer, making it a cost-effective catalyst or catalyst support for CO2 desorption. Patent CN115869971A discloses a method for preparing a fly ash-based composite catalyst for desorption of CO2-rich amine solutions. Using fly ash as a support, Zr(SO4)2·4H2O is loaded and subjected to aging and calcination to obtain a composite catalyst. This catalyst exhibits superior desorption performance compared to traditional single metal oxide catalysts in CO2 absorption-desorption cycle experiments and maintains good stability after multiple cycles. This technology provides a feasible path for the resource utilization of fly ash, but it still belongs to the traditional metal-supported modification approach. Summary of the Invention

[0006] The purpose of this invention is to provide a fly ash-carbon-based composite catalyst mediated by a eutectic solvent for CO2 catalytic desorption, its preparation method, and its application. The preparation method is simple, and the catalyst prepared can promote the decomposition of carbamates during CO2 desorption, significantly improve the desorption capacity and desorption efficiency, and reduce the regeneration energy consumption of CO2-rich amine solutions, thereby reducing the cost of CO2 capture by organic amine methods.

[0007] To achieve the above objectives, the present invention provides a method for preparing a fly ash-carbon-based composite catalyst mediated by a eutectic solvent, comprising the following steps: S1: Weigh glucose and urea according to the preset molar ratio, place them in a magnetic water bath, and stir at the set temperature to form a transparent eutectic solvent (DES solvent). S2: Weigh fly ash according to the preset mass ratio, dry it and then crush it to 100~200 mesh using a pulverizer. Add it to the transparent eutectic solvent in step S1 and stir it thoroughly to form a uniformly mixed slurry. S3: Measure 98% concentrated sulfuric acid according to the preset dosage ratio, add it dropwise to the mixed slurry in step S2, and perform initial carbonization to obtain a black viscous slurry. S4: Transfer the black viscous slurry from step S3 to a microwave reactor and pre-carbonize it at a set power and temperature. After it expands rapidly, a biochar / fly ash composite material precursor with a fluffy structure is obtained. S5: Transfer the precursor from step S4 to a mortar and grind it into powder particles. S6: Place the powdered particles from step S5 into a ceramic boat, transfer it to a tube furnace, introduce inert gas, set the program for high-temperature pyrolysis and carbonization, and finally cool it to room temperature to obtain black solid particles, which are the fly ash-carbon-based composite catalyst mediated by eutectic solvent.

[0008] Preferably, in step S1 of the present invention, the molar ratio of glucose to urea is 1:2, and the water bath temperature is set to 70~90℃.

[0009] Preferably, in step S2 of the present invention, the mass ratio of the eutectic solvent to fly ash is 1.5 to 3.5.

[0010] Preferably, in step S3 of the present invention, the ratio of concentrated sulfuric acid to eutectic solvent is 0.09~0.48 mL / g DES.

[0011] Preferably, in step S4 of the present invention, the set temperature of the microwave reactor is 200~300℃ and the set power is 300~600w.

[0012] Preferably, in step S6 of the present invention, the inert gas introduced is nitrogen; the high-temperature pyrolysis carbonization conditions are: before calcination, nitrogen is used to purge the air in the tubular furnace, and then calcination is carried out at 500~800℃ for 1~5 hours.

[0013] This invention also provides a fly ash-carbon-based composite catalyst mediated by a eutectic solvent, prepared by the above-described preparation method; the structure of the composite catalyst is a porous carbon support doped with S and N elements, on which fly ash-derived metal oxide nanoparticles are embedded; there is an interfacial synergistic effect between the porous carbon support and the fly ash-derived metal oxide nanoparticles, and the porous carbon support can form abundant active acid sites due to the doping of S and N elements.

[0014] This invention also provides an application of a eutectic solvent-mediated fly ash-carbon-based composite catalyst in the catalytic desorption of CO2, the specific application of which includes the following steps: (1) Preparation of rich solution: Prepare a 30wt% MEA (ethanolamine) aqueous solution, and introduce high-purity CO2 into 100g MEA aqueous solution through a conduit at a flow rate of 200mL / min. Continue to absorb at an absorption temperature of 40℃ until the solution is saturated to obtain a rich solution. The CO2 loading in the rich solution is 0.60~0.68mol CO2 / mol MEA. (2) Desorption reaction: Add a fly ash-carbon-based composite catalyst mediated by a eutectic solvent to the rich solution obtained in step (1), and add it to a three-necked flask and stir until it is evenly mixed. Place the three-necked flask in an electric heating mantle and heat it to 90°C to carry out the CO2 desorption reaction. (3) Data recording: When the wet flow meter stops for about 5 minutes, the desorption reaction is determined to be terminated; the desorbed CO2 gas is cooled by the condenser and then enters the wet flow meter, and the cumulative amount of CO2 desorbed is recorded.

[0015] Preferably, in step (2) of the present invention, the amount of fly ash-carbon-based composite catalyst added to the rich liquid is 0.03~0.1wt.

[0016] Compared with existing technologies, this invention introduces eutectic solvent (DES) into the preparation of fly ash carbon-based composite catalysts for the first time. Utilizing DES as a solvent, carbon source, heteroatom source, and structure directing agent simultaneously, a composite structure of S and N co-doped porous carbon encapsulating fly ash particles is constructed in situ through a three-step method of "sulfuric acid carbonization-microwave pre-carbonization-high-temperature pyrolysis." In the fly ash-carbon-based composite catalyst prepared by this invention, fly ash particles are encapsulated and embedded in a porous carbon framework doped with heteroatoms. This structure, based on the encapsulation effect of porous carbon, effectively inhibits the leaching and loss of metal components in fly ash, solving the problem of poor cycle stability of traditional solid acids and existing fly ash-based catalysts. This invention enhances the synergistic effect of heteroatom-doped porous carbon and metal oxides in fly ash. This invention enhances the electron and proton transfer capabilities of the interface, thereby strengthening the activation of the proton-coupled electron transfer effect in the CO2 desorption process. It is more advantageous than existing technologies that rely on a single metal oxide to provide acid sites, significantly improving desorption reaction kinetics, thus drastically shortening desorption time, increasing system efficiency, and reducing the regeneration energy consumption of CO2-rich amine solutions, thereby lowering the cost of CO2 capture via organic amine methods. This invention combines the high-value utilization of industrial solid waste fly ash with the application of green eutectic solvents (DES). The catalyst preparation process has a short cycle and can be synthesized on a large scale, opening up a new path for "carbon control through waste." While reducing catalyst costs, it achieves the dual goals of resource utilization and carbon emission reduction, possessing both environmental benefits and engineering application potential. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the CO2 absorption-desorption performance evaluation device of the present invention; Figure 2 This is a SEM image of the fly ash-carbon-based composite catalyst with a porous structure obtained in the embodiments of the present invention. Figure 3 This is a TEM image of the fly ash-carbon-based composite catalyst encapsulated with fly ash particles obtained in an embodiment of the present invention. Figure 4 The graph shows a comparison of the desorption amounts of the catalysts prepared in the blank experiment, the examples of the present invention, and comparative examples 1-5 when added to the rich solution. Figure 5 The graphs show the desorption rate curves of the catalysts prepared in the blank experiment, the examples of the present invention, and comparative examples 1-5, respectively, when added to the rich solution. Figure 6 The catalyst in this embodiment of the invention has a stability curve after 20 cycles of desorption rate. Figure 7 This is a TEM image of the fly ash-carbon-based composite catalyst encapsulated with fly ash particles obtained in Example 1 of the present invention. Figure 8This is a TEM image of the fly ash-carbon-based composite catalyst encapsulated with fly ash particles obtained in Example 2 of the present invention. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to specific embodiments.

[0019] Example A method for preparing a fly ash-carbon-based composite catalyst mediated by a eutectic solvent includes the following steps: S1: Weigh 6.6g of glucose (monohydrate) and 4g of urea at a molar ratio of 1:2, place them in a magnetic water bath, set the water bath temperature to 90℃, the rotation speed to 300r / min, and stir for 20min to form a transparent eutectic solvent (DES solvent). S2: Weigh 4g of fly ash, dry it, and then crush it to 150 mesh using a pulverizer. Add it to the transparent eutectic solvent in step S1 and stir thoroughly for 30 minutes to obtain a mixed slurry. S3: Measure 2.12 mL of concentrated sulfuric acid with a mass concentration of 98% according to the ratio of concentrated sulfuric acid to DES solvent of 0.20 mL / g DES. Slowly add the concentrated sulfuric acid dropwise to the mixed slurry while stirring. After the addition is complete, continue stirring for 40 min to carry out the initial carbonization and obtain a black viscous slurry. S4: Transfer the black viscous slurry from step S3 to a microwave reactor, adjust the temperature to 200 ℃ and the power to 500W, and observe the solution rapidly expand into a solid through the display screen to obtain a biochar / fly ash composite material precursor with a fluffy structure. S5: Transfer the precursor from step S4 to a mortar and grind it into powder particles. S6: Place the powdered particles from step S5 into a ceramic boat, transfer it to a tube furnace, purge the air from the tube furnace with nitrogen, calcine at 600℃ for 2 hours under nitrogen atmosphere protection, and finally cool to room temperature to obtain a fly ash-carbon-based composite catalyst mediated by a eutectic solvent. The prepared catalyst is labeled as FA@(N,S)-C.

[0020] Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses were performed on the prepared catalyst FA@(N,S)-C. The results showed that the material had a uniform porous structure, with fly ash particles uniformly encapsulated within the carbon material and no obvious agglomeration. Figure 2 and Figure 3 As shown; at the same time, it was found that N and S elements were successfully doped into the catalyst, forming abundant active acid sites.

[0021] The application of catalysts in catalytic CO2 desorption includes the following specific steps: (1) Preparation of rich solution: Prepare a 30wt% MEA (ethanolamine) aqueous solution, and introduce high-purity CO2 into 100g MEA aqueous solution through a conduit at a flow rate of 200mL / min. Continue to absorb at an absorption temperature of 40℃ until the solution is saturated to obtain rich solution. (2) Desorption reaction: Add 0.05g of fly ash-carbon-based composite catalyst FA@(N,S)-C mediated by eutectic solvent to the rich solution obtained in step (1), and add it to a three-necked flask and stir until it is evenly mixed. Place the three-necked flask in an electric heating mantle and heat it to 90℃ to carry out CO2 desorption reaction. (3) Data recording: When the wet flow meter stops for about 5 minutes, the desorption reaction is determined to be terminated; the desorbed CO2 gas is cooled by the condenser and then enters the wet flow meter, and the cumulative amount of CO2 desorbed is recorded.

[0022] Preferably, the CO2 loading in the rich solution in step (1) of the present invention is 0.60~0.68 mol CO2 / mol MEA.

[0023] Blank experiment: The rich solution was heated to 90°C and desorption was performed.

[0024] Comparative Example 1 Weigh out the same mass of fly ash as in the embodiment of the present invention, calcine it at 600°C for 2 hours under nitrogen atmosphere protection, and the resulting catalyst is labeled FA. Use it as a catalyst for CO2 desorption experiments. Take 0.05g of catalyst sample FA to test its CO2 desorption performance, and test the same conditions as in the embodiment of the present invention.

[0025] Comparative Example 2 Without adding fly ash, the eutectic solvent was treated with sulfuric acid carbonization, microwave pre-carbonization, and high-temperature pyrolysis carbonization, with the remaining conditions the same as in the embodiment of the present invention, to obtain pure DES-derived porous carbon material. The catalyst sample was labeled as (N,S)-C. Similarly, 0.05g of catalyst sample (N,S)-C was taken for CO2 desorption performance testing, and the testing conditions were the same as in the embodiment of the present invention.

[0026] Comparative Example 3 After mixing fly ash with a eutectic solvent, without adding sulfuric acid, microwave carbonization and high-temperature pyrolysis carbonization were directly performed. The remaining conditions were the same as in the embodiment of the present invention. The prepared catalyst was labeled as FA@(N)-C. No sulfur element was doped in the carbon support. 0.05g of catalyst FA@(N)-C was taken to test the CO2 catalytic desorption performance. The test conditions were the same as in the embodiment of the present invention.

[0027] Comparative Example 4 After mixing fly ash with a eutectic solvent, without performing a microwave pre-carbonization step, carbonization with concentrated sulfuric acid is performed, followed by direct high-temperature pyrolysis carbonization. The remaining conditions are the same as in the embodiment of the present invention. The prepared catalyst is labeled as FA@(N,S)-C(0). 0.05g of catalyst FA@(N,S)-C(0) is taken for CO2 desorption performance testing, and the testing conditions are the same as in the embodiment of the present invention.

[0028] Comparative Example 5 6.6 g of glucose monohydrate was dissolved in 10 mL of water to form a glucose aqueous solution without adding urea. Then, fly ash was added and stirred evenly. The solution was then subjected to a three-step carbonization process: sulfuric acid carbonization, microwave pre-carbonization, and high-temperature pyrolysis carbonization. The remaining conditions were the same as in the embodiment of the present invention. The resulting catalyst was labeled FA@(S)-C. The carbon support was not doped with nitrogen. 0.05 g of the catalyst FA@(S)-C was used to test the CO2 catalytic desorption performance under the same conditions as in the embodiment of the present invention.

[0029] To simulate actual decarbonization processes, a CO2 absorption and desorption device is constructed, such as... Figure 1 As shown, a mass flow controller is installed at the front end of the device to control the CO2 flow rate. The main absorption and desorption part is a 250mL three-necked flask. The left neck is sealed with a glass stopper, and the central neck is connected to a reflux condenser to prevent amine loss due to evaporation during high-temperature desorption. A wet flow meter is connected after the condenser to monitor the cumulative CO2 desorption in the amine solution in real time. A thermocouple is installed at the right neck to monitor the temperature change of the amine solution in real time. The heating of the amine solution is achieved by an electric heating mantle, and a rotor stirrer is used for low-speed stirring to ensure that the catalyst and amine solution are fully mixed. This desorption device is a conventional experimental apparatus, and its structure will not be described in detail here.

[0030] In the experiment, high-purity CO2 was introduced into 100g of a 30% MEA aqueous solution at a flow rate of 200mL / min via a conduit. Absorption was carried out at an absorption temperature of 40℃ until the solution was saturated, with the CO2 loading in the rich solution ranging from 0.60 to 0.68 mol CO2 / mol MEA. Subsequently, different catalysts were added to the rich solution at a rate of 0.05g each. The three-necked flask was placed in an electric heating mantle and heated to 90℃ for desorption reaction. Desorption was considered terminated when the wet scrubber stopped for approximately 5 minutes. The desorbed CO2 gas entered the wet scrubber through a condenser, and the cumulative desorption amount was recorded.

[0031] Under identical experimental conditions, the desorption results of the amine solution without catalyst were defined as a "blank experiment," while the CO2 desorption amount and desorption rate after adding catalyst in the embodiments of this invention are shown in Table 1. The experimental results show that the eutectic solvent-mediated fly ash-carbon-based composite catalyst of this invention can achieve a desorption amount and desorption rate of 148 mmol CO2 / molMEA and 0.394 mmol CO2 / (mol MEA s), respectively, representing increases of 35.8% and 133.1% compared to the blank experiment.

[0032] Table 1 shows the increase in desorption amount and desorption rate of the catalysts in Examples 1-5 compared to the blank experiment. The eutectic solvent-mediated fly ash-carbon-based composite catalyst prepared in the embodiments of the present invention and the catalysts prepared in Comparative Examples 1-5 were respectively added to a CO2-rich MEA solution, with the amount of catalyst added in the embodiments of the present invention and Comparative Examples 1-5 being 0.05 g. The temperature was raised to 90 °C, and other experimental conditions were the same for catalytic-desorption experiments. The comparison chart of catalytic desorption amount between the embodiments of the present invention and the blank experiment and Comparative Examples 1-5 is shown in the figure. Figure 4 The catalytic rate curve is shown in the figure. Figure 5 The catalyst underwent 20 absorption-desorption cycle experiments, and the desorption rate remained essentially unchanged, indicating good catalyst stability. The cycle stability curves of the catalyst are shown below. Figure 6 .

[0033] Ethanolamine (MEA) is a commonly used organic amine for CO2 capture, and its carbamate product has a stable structure. Traditional desorption processes require high temperatures to break the CN bonds, which is the main reason for the high energy consumption required for amine regeneration and also serves as a standard for evaluating the performance of the catalyst in this invention. An electric heating mantle provides the heat required for MEA regeneration, a wet flow meter monitors the CO2 desorption amount, and the regeneration energy consumption of the blank system and the catalytic system is compared by calculating the desorption amount and rate at the same desorption temperature to verify the catalyst's effectiveness.

[0034] The test results of Comparative Examples 1-5 show that, compared to the blank MEA, the addition of the catalyst significantly reduced the desorption amount and rate of the amine solvent. Compared to Comparative Examples 1-5, the fly ash-carbon-based composite catalyst prepared by a eutectic solvent-mediated, three-step carbonization method significantly improved the catalytic CO2 desorption performance, increasing the desorption amount by 35.8% and the maximum instantaneous catalytic desorption rate by 133.1%. In contrast, fly ash, single DES carbon materials, conventional aqueous solutions, and omitting key steps cannot achieve the technical effects of this invention. By using DES as the solvent, carbon source, and heteroatom source, and by encapsulating and embedding fly ash particles in situ within an S- and N-doped porous carbon framework through a three-step carbonization method, the synergistic enhancement of the metal active sites of fly ash and the electronic conductivity of the carbon-based material is achieved, thereby significantly improving the catalytic desorption activity and cycle stability.

[0035] The present invention provides two more embodiments to verify the preparation method and application of the eutectic solvent-mediated fly ash-carbon-based composite catalyst of the present invention, namely, Example 1 and Example 2. Example 1

[0036] A method for preparing a fly ash-carbon-based composite catalyst mediated by a eutectic solvent and its application in catalytic desorption includes the following steps: S1: Weigh 6.6g of glucose (monohydrate) and 4g of urea at a molar ratio of 1:2, place them in a magnetic water bath, set the water bath temperature to 90℃, the rotation speed to 300r / min, and stir for 20min to form a transparent eutectic solvent (DES). S2: Weigh 6g of fly ash, dry it, and then crush it to 150 mesh using a pulverizer. Add it to the transparent eutectic solvent in step S1 and stir thoroughly for 30 minutes to obtain a mixed slurry. S3: Measure 4.24 mL of concentrated sulfuric acid with a mass concentration of 98% according to the ratio of concentrated sulfuric acid to DES solvent of 0.40 mL / g DES. Slowly add the concentrated sulfuric acid dropwise to the mixed slurry while stirring. After the addition is complete, continue stirring for 40 min to carry out the initial carbonization and obtain a black viscous slurry. S4: Transfer the black viscous slurry from step S3 to a microwave reactor, adjust the temperature to 200 ℃ and the power to 500W, and observe the solution rapidly expand into a solid through the display screen to obtain a biochar / fly ash composite material precursor with a fluffy structure. S5: Transfer the precursor from step S4 to a mortar and grind it into powder particles. S6: Place the powdered particles from step S5 into a ceramic boat, transfer it to a tube furnace, purge the air from the tube furnace with nitrogen, calcine at 600℃ for 2 hours under nitrogen atmosphere protection, and finally cool to room temperature to obtain a fly ash-carbon-based composite catalyst mediated by a eutectic solvent. The prepared catalyst is labeled as FA@(N,S)-C-1. S7: Take 0.1 wt% (0.1 g) of catalyst FA@(N,S)-C-1 for CO2 desorption performance testing. Other test conditions are the same as those in the above embodiments of the present invention.

[0037] The prepared catalyst FA@(N,S)-C-1 was analyzed by transmission electron microscopy (TEM), such as... Figure 7 As shown in the figure, the results indicate that the material has a uniform porous structure, with fly ash particles uniformly encapsulated in the carbon material without obvious agglomeration. Simultaneously, detection revealed successful N and S doping in the catalyst, forming abundant active acid sites. The catalytic desorption experiment evaluation is shown in Table 2. The results show that FA@(N,S)-C-1 can achieve a desorption capacity and desorption rate of 150 mmol CO2 / mol MEA and 0.402 mmol CO2 / (mol MEA s), respectively, representing increases of 37.6% and 137.8% compared to the blank experiment. Example 2

[0038] A method for preparing a fly ash-carbon-based composite catalyst mediated by a eutectic solvent and its application in catalytic desorption includes the following steps: S1: Weigh 6.6g of glucose (monohydrate) and 4g of urea at a molar ratio of 1:2, place them in a magnetic water bath, set the water bath temperature to 90℃, the rotation speed to 300r / min, and stir for 20min to form a transparent eutectic solvent (DES solvent). S2: Weigh 3.5g of fly ash, dry it, and then crush it to 150 mesh using a pulverizer. Add it to the transparent eutectic solvent in step S1 and stir thoroughly for 30 minutes to obtain a mixed slurry. S3: Measure 98% concentrated sulfuric acid. According to the ratio of concentrated sulfuric acid to DES solvent of 0.10 mL / g DES, measure 1.06 mL of concentrated sulfuric acid and slowly add it dropwise to the mixed slurry while stirring. After the addition is complete, continue stirring for 40 min to carry out the initial carbonization and obtain a black viscous slurry. S4: Transfer the black viscous slurry from step S3 to a microwave reactor, adjust the temperature to 200 ℃ and the power to 500W, and observe the solution rapidly expand into a solid through the display screen to obtain a biochar / fly ash composite material precursor with a fluffy structure. S5: Transfer the precursor from step S4 to a mortar and grind it into powder particles. S6: Place the powdered particles from step S5 into a ceramic boat, transfer it to a tube furnace, purge the air from the tube furnace with nitrogen, calcine at 600℃ for 2 hours under nitrogen atmosphere protection, and finally cool to room temperature to obtain a fly ash-carbon-based composite catalyst mediated by a eutectic solvent. The prepared catalyst is labeled as FA@(N,S)-C-2. S7: Take 0.03wt% (0.03g) of catalyst FA@(N,S)-C-2 for CO2 desorption performance testing. Other test conditions are the same as those in the above embodiments of the present invention.

[0039] The prepared catalyst FA@(N,S)-C-2 was analyzed by transmission electron microscopy (TEM), such as... Figure 8 As shown in the figure, the results indicate that the material has a uniform porous structure, with fly ash particles uniformly encapsulated in the carbon material without obvious agglomeration. Simultaneously, detection revealed successful N and S doping in the catalyst, forming abundant active acid sites. The catalytic desorption experiment evaluation is shown in Table 2. The results show that FA@(N,S)-C-2 can achieve a desorption capacity and desorption rate of 145 mmol CO2 / mol MEA and 0.385 mmol CO2 / (mol MEA s), respectively, representing increases of 33.0% and 127.8% compared to the blank experiment.

[0040] Table 2 shows the increase in desorption capacity and desorption rate of the catalysts prepared in Examples 1 and 2 compared to the blank experiment. This invention is specifically designed for the catalytic desorption of CO2 in the capture process of alkanolamine solutions. The catalyst uses a carbon-nitrogen co-doped porous carbon network as a carrier, with the active component derived from highly dispersed metal oxide nanoparticles derived from fly ash. These nanoparticles synergistically interact with the catalytic sites formed by the heteroatom-doped carbon framework, constructing a multi-active-site catalytic system. This invention utilizes a eutectic solvent as both solvent and reactant, employing a three-stage graded carbonization process—sulfuric acid carbonization, microwave carbonization, and high-temperature pyrolysis carbonization—to effectively encapsulate widely available and low-cost fly ash solid waste into a porous carbon network after activation, forming a loosely structured fly ash-carbon-based composite catalytic material with highly exposed active sites. When applied to the CO2 desorption process of a 30wt% MEA solution, this catalyst significantly promotes the desorption reaction efficiency, significantly increasing the CO2 desorption rate and amount compared to traditional non-catalyst systems. This invention not only achieves high-value and resource utilization of fly ash but also provides a novel CO2 desorption catalytic material with low cost and excellent catalytic performance, offering a feasible approach to reducing the overall cost of the alkanolamine carbon capture process.

[0041] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for preparing a eutectic solvent-mediated fly ash-carbon-based composite catalyst, characterized in that, Includes the following steps: S1: Weigh glucose and urea according to the preset molar ratio, place them in a magnetic water bath, and stir at the set temperature to form a transparent eutectic solvent. S2: Weigh fly ash according to the preset mass ratio, dry it and crush it to 100~200 mesh, add it to the transparent eutectic solvent in step S1 and stir it evenly to form a mixed slurry; S3: Measure 98% concentrated sulfuric acid according to the preset dosage ratio, add it dropwise to the mixed slurry in step S2, and perform initial carbonization to obtain a black viscous slurry. S4: Transfer the black viscous slurry from step S3 to a microwave reactor and pre-carbonize it at a set power and temperature. After it expands rapidly, a biochar / fly ash composite material precursor with a fluffy structure is obtained. S5: Grind the precursor from step S4 into powder particles; S6: Place the powdered particles from step S5 into a ceramic boat, transfer it to a tube furnace, introduce inert gas, set the program for high-temperature pyrolysis and carbonization, and finally cool it to room temperature to obtain black solid particles, which are the fly ash-carbon-based composite catalyst mediated by eutectic solvent.

2. The method for preparing a eutectic solvent-mediated fly ash-carbon-based composite catalyst according to claim 1, characterized in that, In step S1, the molar ratio of glucose to urea is 1:2, and the water bath temperature is set to 70~90℃.

3. The method for preparing a eutectic solvent-mediated fly ash-carbon-based composite catalyst according to claim 2, characterized in that, In step S2, the mass ratio of the eutectic solvent to fly ash is 1.5 to 3.

5.

4. The method for preparing a eutectic solvent-mediated fly ash-carbon-based composite catalyst according to claim 2, characterized in that, In step S3, the ratio of concentrated sulfuric acid to eutectic solvent is 0.09~0.48 mL / g DES.

5. The method for preparing a eutectic solvent-mediated fly ash-carbon-based composite catalyst according to claim 4, characterized in that, In step S4, the microwave reactor is set to a temperature of 200~300℃ and a power of 300~600W.

6. The method for preparing a eutectic solvent-mediated fly ash-carbon-based composite catalyst according to claim 4, characterized in that, In step S6, the inert gas introduced is nitrogen; the high-temperature pyrolysis carbonization conditions are: before calcination, nitrogen is used to purge the air from the tubular furnace, and then calcination is carried out at 500~800℃ for 1~5 hours.

7. A eutectic solvent-mediated fly ash-carbon-based composite catalyst, characterized in that, The composite catalyst is prepared by any one of the preparation methods described in claims 1-6; the structure of the composite catalyst is a porous carbon support doped with S and N elements with fly ash-derived metal oxide nanoparticles embedded on it; there is an interfacial synergistic effect between the porous carbon support and the fly ash-derived metal oxide nanoparticles, and the porous carbon support can form abundant active acid sites due to the doping of S and N elements.

8. The application of the eutectic solvent-mediated fly ash-carbon-based composite catalyst according to claim 7 in the catalytic desorption of CO2, characterized in that, The specific solution for the application includes the following steps: (1) Preparation of rich solution: Prepare a 30wt% MEA aqueous solution, and introduce high-purity CO2 into 100g MEA aqueous solution through a conduit at a flow rate of 200mL / min. Continue to absorb at an absorption temperature of 40℃ until the solution is saturated to obtain a rich solution. The CO2 loading in the rich solution is 0.60~0.68mol CO2 / mol MEA. (2) Desorption reaction: Add a fly ash-carbon-based composite catalyst mediated by a eutectic solvent to the rich solution obtained in step (1), and add it to a three-necked flask and stir until it is evenly mixed. Place the three-necked flask in an electric heating mantle and heat it to 90°C to carry out the CO2 desorption reaction. (3) Data recording: When the wet flow meter stops for about 5 minutes, the desorption reaction is determined to be terminated; the desorbed CO2 gas is cooled by the condenser and then enters the wet flow meter, and the cumulative amount of CO2 desorbed is recorded.

9. The application of the eutectic solvent-mediated fly ash-carbon-based composite catalyst according to claim 8 in the catalytic desorption of CO2, characterized in that, In step (2), the amount of fly ash-carbon-based composite catalyst added to the rich solution is 0.03~0.1wt.

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