Iron-containing catalyst prepared from rolling oil sludge and preparation method and application thereof

Abstract

The application discloses a kind of iron-containing catalyst prepared by rolling oil sludge and its preparation method and application, belong to rolling oil sludge recycling and biomass oil extraction technical field, specifically, the method for preparing Fe-Ca-K biochar catalyst using rolling oil sludge and porous biological template, KHCO3, and it is used to promote the bio-oil yield and heavy metal arsenic solidification removal of pteris richardii in the hydrothermal liquefaction process.The Fe-Ca-K biochar material is prepared by calcining at a high temperature above 500 DEG C, has the characteristics of large pore size, high specific surface area, excellent catalytic activity and high heavy metal fixation capacity.The catalyst prepared by the application not only significantly improves the bio-oil yield, but also effectively reduces the migration risk of arsenic in aqueous phase, has the advantages of low cost, excellent catalytic performance, good heavy metal solidification effect and environmental friendliness, and has a wide application prospect in the field of heavy metal contaminated plant remediation and biomass energy conversion.

Description

Technical Field

[0001] This invention belongs to the field of steel rolling sludge recycling and biomass oil extraction technology, specifically relating to an iron-containing catalyst prepared from steel rolling sludge, its preparation method, and its application. Background Technology

[0002] Steel rolling sludge is a byproduct of the steel rolling process, mainly composed of metal oxides, unburned lubricating oil, organic matter, and other impurities. Its iron content can reach 50-70%, and its oil content 10-30%. While possessing high reuse value, it is classified as hazardous waste due to its harmful components, requiring strict adherence to environmental protection requirements during treatment. Common technologies for handling steel rolling sludge include solvent extraction, acid-base cleaning, landfill disposal, hydrothermal liquefaction, and high-temperature incineration. Given the complex composition of steel rolling sludge, conventional extraction methods or direct utilization of this low-grade raw material are often economically impractical. Therefore, promoting the development of resource-based, harmless, and co-processing technologies for steel rolling sludge is of significant practical importance.

[0003] High-temperature calcination of rolling mill sludge using pyrolysis offers advantages such as improved material properties and chemical stability, reduced energy consumption, and lower processing costs. During pyrolysis, adsorbed and bound water are removed first at low temperatures, followed by the gradual volatilization of light hydrocarbons and low-molecular-weight acids. As the temperature rises, tar and aromatic compounds undergo pyrolysis, releasing carbon dioxide gas. At approximately 500°C, organic matter undergoes high-temperature pyrolysis, producing rolling oil, iron powder, slag, and combustible gases. At around 600°C, inorganic compounds such as carbonates and sulfates in the rolling mill sludge further decompose, releasing high-temperature gases.

[0004] Hyperaccumulating plants are widely used in the remediation of contaminated soil and environmental governance due to their efficient absorption and accumulation of heavy metals in soil. Among them, *Pteris vittata*, a highly regarded arsenic hyperaccumulator, not only boasts a large biomass but also exhibits significant tolerance to high concentrations of heavy metals. Studies have shown that its aboveground parts can accumulate up to 23 g / kg of arsenic, far exceeding that of ordinary plants. However, improper disposal of such biomass enriched with heavy metals can easily lead to resource waste and the risk of secondary heavy metal pollution. Therefore, developing eco-friendly and efficient treatment technologies for hyperaccumulating plants is crucial for promoting the industrial application and sustainable development of phytoremediation technology.

[0005] Compared to traditional thermochemical treatment technologies such as incineration, high-temperature pyrolysis, and gasification, hydrothermal liquefaction can be carried out under non-strictly anaerobic and relatively mild temperature conditions, offering advantages such as lower energy consumption, higher bio-oil yield, and no need for pre-drying of biomass feedstock. This process can generate various valuable products, including an oil phase, an aqueous phase, and biochar, while heavy metals are distributed to the aqueous or solid phases at different migration rates depending on their characteristics. In the conventional hydrothermal liquefaction process of *Pteris vittata*, the biomass oil yield is typically only around 21%, and approximately 96% of the arsenic migrates to the aqueous phase, significantly increasing the difficulty and cost of subsequent water treatment. Therefore, developing a biochar material using steel rolling sludge that can solidify and migrate the toxic metal As in *Pteris vittata* is a pressing issue that needs to be addressed. Summary of the Invention

[0006] To promote the efficient utilization of steel rolling sludge and achieve low-cost co-processing, this invention provides a Fe-Ca-K biochar material prepared from steel rolling sludge, its preparation method, and its application. The biochar generated by high-temperature calcination of steel rolling sludge is applied to the hydrothermal liquefaction of enriched plants to achieve the goal of "resource utilization, harmlessness, and co-processing" disposal, thereby improving the resource utilization of solid waste, the yield of biomass oil, and the migration and solidification of heavy metals.

[0007] To achieve the above objectives, the present invention provides a method for preparing an iron-containing catalyst using steel rolling sludge, comprising the following steps: S1. Dry, grind, and sieve the eggshells to prepare a porous biological template; S2. Mix steel rolling sludge, porous biological template and appropriate amount of anhydrous ethanol, stir until ethanol evaporates, and dry at low temperature to obtain mixture; S3. KHCO3 is added to the mixture, and calcination and carbonization are carried out in an inert gas atmosphere to obtain Fe-Ca-K biochar containing iron catalyst.

[0008] As described above, the eggshells are cleaned, dried at 80°C for 24 hours, ground and sieved through a 100-mesh sieve.

[0009] As described above, in the preparation method, the mass fraction of the steel rolling sludge in S2 is 30-80% of the mixture; the low-temperature drying temperature in the oven in S2 is 30-80℃, and the drying time is 48h.

[0010] Preferably, the mass fraction of the steel rolling sludge in S2 is 40-70% of the mass fraction of the mixture.

[0011] In the preparation method described above, the amount of KHCO3 added to S3 is 25-80% of the mixture; the carbonization temperature is 400-900℃, and the time is 1-3h.

[0012] Preferably, the amount of KHCO3 added in S3 is 30-75% of the mixture.

[0013] This invention provides an iron-containing catalyst, wherein the iron-containing catalyst is Fe-Ca-K biochar, that is, a catalyst prepared using the above-described preparation method.

[0014] This invention also provides an application of the iron-containing catalyst Fe-Ca-K biochar for catalyzing the hydrothermal liquefaction reaction of biomass to prepare biomass oil. Specifically, the Fe-Ca-K biochar material obtained by the above preparation method is used as an additive in the hydrothermal liquefaction process of the enrichment plant *Pteris vittata* to improve the biomass oil yield and the solidification and migration of heavy metals. The method involves adding the Fe-Ca-K biochar material, *Pteris vittata*, and water to a high-pressure reactor to achieve increased biomass oil yield and solidification and migration of heavy metals.

[0015] The preparation method for biomass oil using Fe-Ca-K biochar catalyzed hydrothermal liquefaction reaction of biomass is as follows: R1. Dry the centipede grass, grind it, and sieve it. R2. Grind Fe-Ca-K biochar, mix it with centipede grass, put it into a high-pressure reactor, and add an appropriate amount of water. R3. Seal the reactor, remove the air from the high-pressure reactor under a nitrogen atmosphere, heat the high-pressure reactor under stirring to carry out the hydrothermal liquefaction reaction, and after the reaction is completed, cool the high-pressure reactor to room temperature in a water bath to obtain the hydrothermal liquefaction mixture. R4: Filter the hydrothermal liquefaction mixture, wash the solid phase with an organic solvent, and collect the liquid phase for separation. R5, the organic solvent is removed by rotary evaporation of the oil phase to obtain the biomass oil phase.

[0016] As described above, in R1, centipede grass (with some leaves removed) is dried in an oven at 105°C for 48 hours, ground, sieved, and passed through a 100-mesh sieve.

[0017] In the application described above, the amount of biochar added in R2 is 10-70% of the mass of centipede grass; the amount of water added is 20-45 ml.

[0018] As described above, the heating conditions for hydrothermal liquefaction reaction in the high-pressure reactor of R3 are 220~300℃, and the time is 10~45min.

[0019] In the application described above, the organic solvent used in R4 is ethyl acetate, and the amount of ethyl acetate used is 4 to 9 times that of water.

[0020] As described above, in R4, the collected liquid phase is separated in a separatory funnel, with the upper layer being a mixture of organic solvent and oil phase, and the lower layer being an aqueous solution.

[0021] As described above, in R5, ethyl acetate is removed by rotary evaporation of the oil phase. The rotary evaporation time is 15-35 min, the rotary evaporation temperature is 40-55℃, and the vacuum degree is 180-280 kPa.

[0022] Compared with the prior art, the technical effects achieved by the present invention are as follows: This invention utilizes steel rolling sludge to prepare Fe-Ca-K biochar material. The biochar is prepared by drying followed by pyrolysis. First, the moisture on the surface of the steel rolling sludge is dried, and then porous biotemplate / KHCO3 is added to reduce its viscosity. Then, high-temperature pyrolysis is performed to open its pore size and increase its specific surface area, thereby improving the performance of the biochar.

[0023] In the process of converting rolling mill sludge into biochar through pyrolysis, traditional methods typically use strongly alkaline substances such as KOH as activators, but these methods are not environmentally friendly. This application selects weakly alkaline potassium bicarbonate (KHCO3) as an alternative activator, supplemented with a porous biological template. This composite system combines environmental friendliness and low cost, helping to increase the specific surface area of ​​biochar and optimize its pore structure during pyrolysis. This method is a low-cost, low-consumption, and simple preparation method with green and environmentally friendly advantages, and can realize the resource utilization of rolling mill sludge to a certain extent; it is simple to operate, low in cost, and conducive to industrial production.

[0024] Introducing biochar prepared from steel rolling sludge as a catalyst can effectively improve bio-oil yield and promote the fixation of heavy metals in the solid phase, thereby reducing the concentration of arsenic in the aqueous phase and alleviating the burden on secondary water treatment, thanks to its high specific surface area, well-developed pore structure, and abundant alkali metal content. Therefore, steel rolling sludge biochar can serve as an excellent additive for the hydrothermal liquefaction of Centipede Grass, promoting the resource-based, harmless, and synergistic treatment of this process.

[0025] The Fe-Ca-K biochar material prepared by this invention can be used as a catalyst for the hydrothermal liquefaction of Centipede Grass. The iron species such as Fe, Fe3O4, and Fe2O3 present in the material can effectively promote the conversion of organic matter into bio-oil and increase the oil yield. At the same time, the alkali metal components (such as Fe and Ca) in the material synergistically enhance the solidification and stabilization of toxic heavy metal arsenic, achieving its efficient recovery in the solid phase.

[0026] Therefore, the Fe-Ca-K biochar material prepared by this invention not only has a rich pore size distribution and specific surface area, but also achieves the goals of resource utilization, harmlessness and synergistic treatment in the hydrothermal liquefaction process, thereby improving the resource utilization of solid waste, the yield of biomass oil and the migration and solidification of heavy metals. Attached Figure Description

[0027] Figure 1 This is a graph showing the biomass oil yield and solid-phase arsenic migration rate produced by hydrothermal reaction with different amounts of biochar added. Figure 2 This is a graph showing the biomass oil yield and solid-phase arsenic migration rate produced by hydrothermal reactions at different reaction temperatures. Figure 3 This is a graph showing the biomass oil yield and solid-phase arsenic migration rate using different catalysts in hydrothermal reactions; Figure 4 The following are elemental analysis diagrams of the biomass oils from the hydrothermal reactions in the examples and comparative examples; Figure 5 The graphs show the phenol and acid content analysis of the bio-oils from the hydrothermal reactions in the examples and comparative examples. Figure 6 The specific surface area and average pore size of the four biochars prepared in the examples and comparative examples are shown. Figure 7 These are SEM images of the four types of biochar prepared in the examples and comparative examples; Figure 8 These are XRD patterns of four types of biochar prepared in the examples and comparative examples; Figure 9 It is an X-ray photoelectron spectroscopy (XPS) of the change in the valence state of Fe before and after the hydrothermal liquefaction reaction of Fe-Ca-K biochar. Figure 10 The graphs show the hysteresis regression curves of the four types of biochar prepared in the examples and comparative examples. Figure 11 The distribution of As content in the magnetic and non-magnetic solid phases after magnetic separation of four types of biochar is shown. Detailed Implementation

[0028] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] The steel rolling sludge used in this embodiment is all cold rolling sludge.

[0030] Example 1 Eggshells were washed, dried at 80℃ for 24 hours, ground, and sieved to prepare a porous biotemplate. A steel rolling sludge sample, the porous biotemplate (mass ratio of steel rolling sludge sample to porous biotemplate 1:1), and an appropriate amount of anhydrous ethanol were mixed and stirred until the ethanol evaporated. The mixture was then dried in an oven at a low temperature of 30-80℃ for 48 hours to obtain a mixture. KHCO3 (the same amount as the steel rolling sludge sample) was added to the mixture, and it was placed in a tube furnace for calcination and carbonization under a N2 atmosphere (calcination temperature 500℃, calcination time 1 hour) to obtain Fe-Ca-K biochar. The biochar was ground into powder and packaged for later use. The experimental conditions for preparing the centipede grass sample in the hydrothermal liquefaction reaction were as follows: centipede grass (with some leaves removed) was dried at 105℃ and pulverized, then passed through a 100-mesh sieve to obtain the centipede grass sample.

[0031] (1) Take 0.5g of Fe-Ca-K biochar, 1.5g of centipede grass sample and 55ml of distilled water, add them to a container and stir evenly to obtain a mixture; (2) Place the mixture into a high-pressure reactor and add a magnetic stir bar. Use nitrogen to purge the air from the reactor. Control the hydrothermal liquefaction temperature at 275°C for 15 minutes and the stirring speed at 550 rpm. After the reaction, cool the reactor to room temperature in a water bath. Filter the mixture after the reaction through vacuum filter paper to separate the solid and liquid phases. At the same time, wash the filter residue with ethyl acetate solution to obtain a mixture containing organic solvent. (3) Pour the mixture containing organic solvent into a separatory funnel for separation. The lower layer is an aqueous solution and the upper layer is a mixture of ethyl acetate and oil phase. (4) The mixture of the upper ethyl acetate and the oil phase was rotary evaporated at 50°C for 15-35 min to remove the ethyl acetate and obtain biomass oil; the filter residue after filtration was dried at 105°C to obtain the solid phase.

[0032] Example 2 The difference between this embodiment and Example 1 is that the amount of porous biochar template added during biochar preparation is 0.5 times that in Example 1. The specific method is as follows: Eggshells are washed, dried at 80℃ for 24 hours, ground, and sieved to prepare a porous biochar template; a steel rolling sludge sample, the porous biochar template (mass ratio of steel rolling sludge sample to porous biochar template is 2:1), and an appropriate amount of anhydrous ethanol are mixed and stirred until the ethanol evaporates. The mixture is then dried in an oven at a low temperature of 30-80℃ for 48 hours to obtain a mixture; KHCO3 is added to the mixture (the amount added is the same as that for the steel rolling sludge sample), and the mixture is placed in a tube furnace for calcination and carbonization under a N2 atmosphere (calcination temperature is 500℃, calcination time is 1 hour) to obtain Fe-0.5Ca-K biochar.

[0033] (1) Take 0.5g of Fe-0.5Ca-K biochar, 1.5g of centipede grass sample and 55ml of distilled water, add them to a container and stir evenly to obtain a mixture; (2) Place the mixture into a high-pressure reactor and add a magnetic stir bar. Use nitrogen to purge the air from the reactor. Control the hydrothermal liquefaction temperature at 275°C for 15 minutes and the stirring speed at 550 rpm. After the reaction, cool the reactor to room temperature in a water bath. Filter the mixture after the reaction through vacuum filter paper to separate the solid and liquid phases. At the same time, wash the filter residue with ethyl acetate solution to obtain a mixture containing organic solvent. (3) Pour the mixture containing organic solvent into a separatory funnel for separation. The lower layer is an aqueous solution and the upper layer is a mixture of ethyl acetate and oil phase. (4) The mixture of the upper ethyl acetate and the oil phase was rotary evaporated at 50°C for 15-35 min to remove the ethyl acetate and obtain biomass oil; the filter residue after filtration was dried at 105°C to obtain the solid phase.

[0034] Example 3 The difference between this embodiment and Example 1 is that the amount of porous biochar template added during biochar preparation is 1.5 times that in Example 1. The specific method is as follows: Eggshells are washed, dried at 80℃ for 24 hours, ground, and sieved to prepare a porous biochar template; a steel rolling sludge sample, the porous biochar template (mass ratio of steel rolling sludge sample to porous biochar template is 2:3), and an appropriate amount of anhydrous ethanol are mixed and stirred until the ethanol evaporates. The mixture is then dried in an oven at a low temperature of 30-80℃ for 48 hours to obtain a mixture; KHCO3 is added to the mixture (the amount added is the same as that for the steel rolling sludge sample), and the mixture is placed in a tube furnace for calcination and carbonization under a N2 atmosphere (calcination temperature is 500℃, calcination time is 1 hour) to obtain Fe-1.5Ca-K biochar.

[0035] (1) Take 0.5g of Fe-1.5Ca-K biochar, 1.5g of centipede grass sample and 55ml of distilled water, add them to a container and stir evenly to obtain a mixture; (2) Place the mixture into a high-pressure reactor and add a magnetic stir bar. Use nitrogen to purge the air from the reactor. Control the hydrothermal liquefaction temperature at 275°C for 15 minutes and the stirring speed at 550 rpm. After the reaction, cool the reactor to room temperature in a water bath. Filter the mixture after the reaction through vacuum filter paper to separate the solid and liquid phases. At the same time, wash the filter residue with ethyl acetate solution to obtain a mixture containing organic solvent. (3) Pour the mixture containing organic solvent into a separatory funnel for separation. The lower layer is an aqueous solution and the upper layer is a mixture of ethyl acetate and oil phase. (4) The mixture of the upper ethyl acetate and the oil phase was rotary evaporated at 50°C for 15-35 min to remove the ethyl acetate and obtain biomass oil; the filter residue after filtration was dried at 105°C to obtain the solid phase.

[0036] Example 4 The difference between this embodiment and Example 1 is that the amount of KHCO3 added during biochar preparation is 0.5 times that in Example 1. The specific method is as follows: Eggshells are washed, dried at 80℃ for 24 hours, ground, and sieved to prepare a porous biotemplate; a steel rolling sludge sample, the porous biotemplate (the ratio of steel rolling sludge sample to porous biotemplate is 1:1), and an appropriate amount of anhydrous ethanol are mixed and stirred until the ethanol evaporates. The mixture is then dried in an oven at a low temperature of 30-80℃ for 48 hours to obtain a mixture; KHCO3 (0.5 times the amount of the steel rolling sludge sample) is added to the mixture, and the mixture is placed in a tube furnace for calcination and carbonization under a N2 atmosphere (calcination temperature is 500℃, calcination time is 1 hour) to obtain Fe-Ca-0.5K biochar.

[0037] (1) Take 0.5g of Fe-Ca-0.5K biochar, 1.5g of centipede grass sample and 55ml of distilled water, add them to a container and stir evenly to obtain a mixture; (2) Place the mixture into a high-pressure reactor and add a magnetic stir bar. Use nitrogen to purge the air from the reactor. Control the hydrothermal liquefaction temperature at 275°C for 15 minutes and the stirring speed at 550 rpm. After the reaction, cool the reactor to room temperature in a water bath. Filter the mixture after the reaction through vacuum filter paper to separate the solid and liquid phases. At the same time, wash the filter residue with ethyl acetate solution to obtain a mixture containing organic solvent. (3) Pour the mixture containing organic solvent into a separatory funnel for separation. The lower layer is an aqueous solution and the upper layer is a mixture of ethyl acetate and oil phase. (4) The mixture of the upper ethyl acetate and the oil phase was rotary evaporated at 50°C for 15-35 min to remove the ethyl acetate and obtain biomass oil; the filter residue after filtration was dried at 105°C to obtain the solid phase.

[0038] Example 5 The difference between this embodiment and Example 1 is that the amount of KHCO3 added during biochar preparation is 1.5 times that in Example 1. The specific method is as follows: Eggshells are washed, dried at 80℃ for 24 hours, ground, and sieved to prepare a porous biotemplate; a steel rolling sludge sample, the porous biotemplate (mass ratio of steel rolling sludge sample to porous biotemplate 1:1), and an appropriate amount of anhydrous ethanol are mixed and stirred until the ethanol evaporates. The mixture is then dried in an oven at a low temperature of 30-80℃ for 48 hours to obtain a mixture; KHCO3 (1.5 times the amount used in the steel rolling sludge sample) is added to the mixture, and the mixture is placed in a tube furnace for calcination and carbonization under a N2 atmosphere (calcination temperature 500℃, calcination time 1 hour) to obtain Fe-Ca-1.5K biochar.

[0039] (1) Take 0.5g of Fe-Ca-1.5K biochar, 1.5g of centipede grass sample and 55ml of distilled water, add them to a container and stir evenly to obtain a mixture; (2) Place the mixture into a high-pressure reactor and add a magnetic stir bar. Use nitrogen to purge the air from the reactor. Control the hydrothermal liquefaction temperature at 275°C for 15 minutes and the stirring speed at 550 rpm. After the reaction, cool the reactor to room temperature in a water bath. Filter the mixture after the reaction through vacuum filter paper to separate the solid and liquid phases. At the same time, wash the filter residue with ethyl acetate solution to obtain a mixture containing organic solvent. (3) Pour the mixture containing organic solvent into a separatory funnel for separation. The lower layer is an aqueous solution and the upper layer is a mixture of ethyl acetate and oil phase. (4) The mixture of the upper ethyl acetate and the oil phase was rotary evaporated at 50°C for 15-35 min to remove the ethyl acetate and obtain biomass oil; the filter residue after filtration was dried at 105°C to obtain the solid phase.

[0040] The biochar used in Examples 6-10 was the biochar prepared in Example 1.

[0041] Example 6 (1) Take 0.2g of Fe-Ca-K biochar, 1.5g of centipede grass sample and 55ml of distilled water, add them to a container and stir evenly to obtain a mixture; (2) Place the mixture into a high-pressure reactor and add a magnetic stir bar. Use nitrogen to purge the air from the reactor. Control the hydrothermal liquefaction temperature at 275°C for 15 minutes and the stirring speed at 550 rpm. After the reaction, cool the reactor to room temperature in a water bath. Filter the mixture after the reaction through vacuum filter paper to separate the solid and liquid phases. At the same time, wash the filter residue with ethyl acetate solution to obtain a mixture containing organic solvent. (3) Pour the mixture containing organic solvent into a separatory funnel for separation. The lower layer is an aqueous solution and the upper layer is a mixture of ethyl acetate and oil phase. (4) The mixture of the upper ethyl acetate and the oil phase was rotary evaporated at 50°C for 15-35 min to remove the ethyl acetate and obtain biomass oil; the filter residue after filtration was dried at 105°C to obtain the solid phase.

[0042] Example 7 (1) Take 0.8g of Fe-Ca-K biochar, 1.5g of centipede grass sample and 55ml of distilled water, add them to a container and stir evenly to obtain a mixture; (2) Place the mixture into a high-pressure reactor and add a magnetic stir bar. Use nitrogen to purge the air from the reactor. Control the hydrothermal liquefaction temperature at 275°C for 15 minutes and the stirring speed at 550 rpm. After the reaction, cool the reactor to room temperature in a water bath. Filter the mixture after the reaction through vacuum filter paper to separate the solid and liquid phases. At the same time, wash the filter residue with ethyl acetate solution to obtain a mixture containing organic solvent. (3) Pour the mixture containing organic solvent into a separatory funnel for separation. The lower layer is an aqueous solution and the upper layer is a mixture of ethyl acetate and oil phase. (4) The mixture of the upper ethyl acetate and the oil phase was rotary evaporated at 50°C for 15-35 min to remove the ethyl acetate and obtain biomass oil; the filter residue after filtration was dried at 105°C to obtain the solid phase.

[0043] Example 8 (1) Take 1.0g of Fe-Ca-K biochar, 1.5g of centipede grass sample and 55ml of distilled water, add them to a container and stir evenly to obtain a mixture; (2) Place the mixture into a high-pressure reactor and add a magnetic stir bar. Use nitrogen to purge the air from the reactor. Control the hydrothermal liquefaction temperature at 275°C for 15 minutes and the stirring speed at 550 rpm. After the reaction, cool the reactor to room temperature in a water bath. Filter the mixture after the reaction through vacuum filter paper to separate the solid and liquid phases. At the same time, wash the filter residue with ethyl acetate solution to obtain a mixture containing organic solvent. (3) Pour the mixture containing organic solvent into a separatory funnel for separation. The lower layer is an aqueous solution and the upper layer is a mixture of ethyl acetate and oil phase. (4) The mixture of the upper ethyl acetate and the oil phase is rotary evaporated at 50°C for 15-35 min to remove the ethyl acetate and obtain biomass oil; the filter residue after filtration is dried at 105°C to obtain the solid phase.

[0044] Example 9 (1) Take 0.5g of Fe-Ca-K biochar, 1.5g of centipede grass sample and 55ml of distilled water, add them to a container and stir evenly to obtain a mixture; (2) Place the mixture into a high-pressure reactor and add a magnetic stir bar. Use nitrogen to purge the air from the reactor. Control the hydrothermal liquefaction temperature at 225°C for 15 minutes and the stirring speed at 550 rpm. After the reaction, cool the reactor to room temperature in a water bath. Filter the mixture after the reaction through vacuum filter paper to separate the solid and liquid phases. At the same time, wash the filter residue with ethyl acetate solution to obtain a mixture containing organic solvent. (3) Pour the mixture containing organic solvent into a separatory funnel for separation. The lower layer is an aqueous solution and the upper layer is a mixture of ethyl acetate and oil phase. (4) The mixture of the upper ethyl acetate and the oil phase was rotary evaporated at 50°C for 15-35 min to remove the ethyl acetate and obtain biomass oil; the filter residue after filtration was dried at 105°C to obtain the solid phase.

[0045] Example 10 (1) Take 0.5g of Fe-Ca-K biochar, 1.5g of centipede grass sample and 55ml of distilled water, add them to a container and stir evenly to obtain a mixture; (2) Place the mixture into a high-pressure reactor and add a magnetic stir bar. Use nitrogen to purge the air from the reactor. Control the hydrothermal liquefaction temperature at 250°C for 15 minutes and the stirring speed at 550 rpm. After the reaction, cool the reactor to room temperature in a water bath. Filter the mixture after the reaction through vacuum filter paper to separate the solid and liquid phases. At the same time, wash the filter residue with ethyl acetate solution to obtain a mixture containing organic solvent. (3) Pour the mixture containing organic solvent into a separatory funnel for separation. The lower layer is an aqueous solution and the upper layer is a mixture of ethyl acetate and oil phase. (4) The mixture of the upper ethyl acetate and the oil phase was rotary evaporated at 50°C for 15-35 min to remove the ethyl acetate and obtain biomass oil; the filter residue after filtration was dried at 105°C to obtain the solid phase.

[0046] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that Fe-Ca-K biochar is not added during the hydrothermal liquefaction process.

[0047] (1) Take 1.5g of centipede grass sample and 55ml of distilled water, add them to a container and stir well to obtain a mixture; (2) Place the mixture into a high-pressure reactor and add a magnetic stir bar. Use nitrogen to purge the air from the reactor. Control the hydrothermal liquefaction temperature at 275°C for 15 minutes and the stirring speed at 550 rpm. After the reaction, cool the reactor to room temperature in a water bath. Filter the mixture after the reaction through vacuum filter paper to separate the solid and liquid phases. At the same time, wash the filter residue with ethyl acetate solution to obtain a mixture containing organic solvent. (3) Pour the mixture containing organic solvent into a separatory funnel for separation. The lower layer is an aqueous solution and the upper layer is a mixture of ethyl acetate and oil phase. (4) The mixture of the upper ethyl acetate and the oil phase is rotary evaporated at 50°C for 15-35 min to remove the ethyl acetate and obtain biomass oil; the filter residue after filtration is dried at 105°C to obtain the solid phase.

[0048] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that only steel rolling sludge was used for high-temperature calcination in the preparation of biochar. The specific method is as follows: An appropriate amount of anhydrous ethanol was added to the steel rolling sludge sample and mixed. The mixture was stirred until the ethanol evaporated, then dried in an oven at a low temperature of 30-80°C for 48 hours to obtain a mixture. This mixture was then placed in a tube furnace and calcined and carbonized under a N2 atmosphere (calcination temperature: 500°C, calcination time: 1 hour) to obtain biochar, which was named Fe biochar.

[0049] (1) Take 0.5g of Fe biochar, 1.5g of centipede grass sample and 55ml of distilled water, add them to a container and stir evenly to obtain a mixture; (2) Place the mixture into a high-pressure reactor and add a magnetic stir bar. Use nitrogen to purge the air from the reactor. Control the hydrothermal liquefaction temperature at 275°C for 15 minutes and the stirring speed at 550 rpm. After the reaction, cool the reactor to room temperature in a water bath. Filter the mixture after the reaction through vacuum filter paper to separate the solid and liquid phases. At the same time, wash the filter residue with ethyl acetate solution to obtain a mixture containing organic solvent. (3) Pour the mixture containing organic solvent into a separatory funnel for separation. The lower layer is an aqueous solution and the upper layer is a mixture of ethyl acetate and oil phase. (4) The mixture of the upper ethyl acetate and the oil phase was rotary evaporated at 50°C for 15-35 min to remove the ethyl acetate and obtain biomass oil; the filter residue after filtration was dried at 105°C to obtain the solid phase.

[0050] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that no porous biological template was added during the calcination process to prepare the biochar. The specific method is as follows: An appropriate amount of anhydrous ethanol was added to the steel rolling sludge sample and mixed. The mixture was stirred until the ethanol evaporated, and then dried in an oven at a low temperature of 30-80°C for 48 hours to obtain a mixture. KHCO3 (the same amount as the steel rolling sludge sample) was added to the mixture, and the mixture was placed in a tube furnace and calcined and carbonized under a N2 atmosphere (calcination temperature 500°C, calcination time 1 hour) to obtain biochar, which was named Fe-K biochar.

[0051] (4) Take 0.5g of Fe-K biochar, 1.5g of centipede grass sample and 55ml of distilled water, add them to a container and stir well to obtain a mixture; (5) Place the mixture into a high-pressure reactor and add a magnetic stir bar. Use nitrogen to purge the air from the reactor. Control the hydrothermal liquefaction temperature at 275°C for 15 minutes and the stirring speed at 550 rpm. After the reaction, cool the reactor to room temperature in a water bath. Filter the mixture after the reaction through vacuum filter paper to separate the solid and liquid phases. At the same time, wash the filter residue with ethyl acetate solution to obtain a mixture containing organic solvent. (6) Pour the mixture containing organic solvent into a separatory funnel for separation. The lower layer is an aqueous solution and the upper layer is a mixture of ethyl acetate and oil phase. (4) The mixture of the upper ethyl acetate and the oil phase is rotary evaporated at 50°C for 15-35 min to remove the ethyl acetate and obtain biomass oil; the filter residue after filtration is dried at 105°C to obtain the solid phase.

[0052] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that KHCO3 was not added during the calcination process to prepare biochar. The specific method is as follows: Eggshells were washed, dried at 80°C for 24 hours, ground, and sieved to prepare a porous biotemplate; a steel rolling sludge sample, the porous biotemplate (the same amount added as the steel rolling sludge sample), and an appropriate amount of anhydrous ethanol were mixed and stirred until the ethanol evaporated. The mixture was then dried in an oven at a low temperature of 30-80°C for 48 hours to obtain a mixture; the mixture was placed in a tube furnace and calcined and carbonized under a N2 atmosphere (calcination temperature 500°C, calcination time 1 hour) to obtain Fe-Ca biochar.

[0053] (1) Take 0.5g of Fe-Ca biochar, 1.5g of centipede grass sample and 55ml of distilled water, add them to a container and stir evenly to obtain a mixture; (2) Place the mixture into a high-pressure reactor and add a magnetic stir bar. Use nitrogen to purge the air from the reactor. Control the hydrothermal liquefaction temperature at 275°C for 15 minutes and the stirring speed at 550 rpm. After the reaction, cool the reactor to room temperature in a water bath. Filter the mixture after the reaction through vacuum filter paper to separate the solid and liquid phases. At the same time, wash the filter residue with ethyl acetate solution to obtain a mixture containing organic solvent. (3) Pour the mixture containing organic solvent into a separatory funnel for separation. The lower layer is an aqueous solution and the upper layer is a mixture of ethyl acetate and oil phase. The ethyl acetate was removed by rotary evaporation at 50°C for 15-35 min to obtain biomass oil; the filter residue after filtration was dried at 105°C to obtain the solid phase.

[0054] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that shell powder was added as a biological template during the calcination process to prepare biochar. The specific method is as follows: the shells were cleaned, dried at 80℃ for 24 hours, ground, and sieved to prepare a shell biological template; the steel rolling sludge sample, the shell biological template (mass ratio of steel rolling sludge sample to shell biological template 1:1), and an appropriate amount of anhydrous ethanol were mixed and stirred until the ethanol evaporated. The mixture was then dried in an oven at a low temperature of 30-80℃ for 48 hours to obtain a mixture; KHCO3 (the same amount as the steel rolling sludge sample) was added to the mixture, and the mixture was placed in a tube furnace for calcination and carbonization under a N2 atmosphere (calcination temperature 500℃, calcination time 1 hour) to obtain shell biochar.

[0055] (1) Take 0.5g of shell biochar, 1.5g of centipede grass sample and 55ml of distilled water, add them to a container and stir evenly to obtain a mixture; (2) Place the mixture into a high-pressure reactor and add a magnetic stir bar. Use nitrogen to purge the air from the reactor. Control the hydrothermal liquefaction temperature at 275°C for 15 minutes and the stirring speed at 550 rpm. After the reaction, cool the reactor to room temperature in a water bath. Filter the mixture after the reaction through vacuum filter paper to separate the solid and liquid phases. At the same time, wash the filter residue with ethyl acetate solution to obtain a mixture containing organic solvent. (3) Pour the mixture containing organic solvent into a separatory funnel for separation. The lower layer is an aqueous solution and the upper layer is a mixture of ethyl acetate and oil phase. The ethyl acetate was removed by rotary evaporation at 50°C for 15-35 min to obtain biomass oil; the filter residue after filtration was dried at 105°C to obtain the solid phase.

[0056] Comparative Example 6 The difference between Comparative Example 6 and Example 1 is that CaCO3 was added as a template during the calcination process to prepare the biochar. Specifically, the following steps were taken: A steel rolling sludge sample, a CaCO3 template (the amount of steel rolling sludge sample and CaCO3 template was the same), and an appropriate amount of anhydrous ethanol were mixed and stirred until the ethanol evaporated. The mixture was then dried in an oven at a low temperature of 30-80°C for 48 hours to obtain a mixture. KHCO3 (the amount added was the same as the mass of the steel rolling sludge sample) was added to the mixture, and the mixture was placed in a tube furnace for calcination and carbonization under a N2 atmosphere (calcination temperature was 500°C, calcination time was 1 hour) to obtain CaCO3 biochar.

[0057] (1) Take 0.5g of CaCO3 biochar, 1.5g of centipede grass sample and 55ml of distilled water, add them to a container and stir evenly to obtain a mixture; (2) Place the mixture into a high-pressure reactor and add a magnetic stir bar. Use nitrogen to purge the air from the reactor. Control the hydrothermal liquefaction temperature at 275°C for 15 minutes and the stirring speed at 550 rpm. After the reaction, cool the reactor to room temperature in a water bath. Filter the mixture after the reaction through vacuum filter paper to separate the solid and liquid phases. At the same time, wash the filter residue with ethyl acetate solution to obtain a mixture containing organic solvent. (3) Pour the mixture containing organic solvent into a separatory funnel for separation. The lower layer is an aqueous solution and the upper layer is a mixture of ethyl acetate and oil phase. The ethyl acetate was removed by rotary evaporation at 50°C for 15-35 min to obtain biomass oil; the filter residue after filtration was dried at 105°C to obtain the solid phase.

[0058]

[0059] A comparison of Examples 1-5 shows that adding an appropriate amount of porous biotemplate or KHCO3 during biochar preparation is necessary to maximize the efficiency of biomass oil and heavy metal As in the hydrothermal liquefaction of Centipede Grass. Excessive solid calcium carbonate particles may physically adsorb onto the surface of biomass or catalyst, hindering the reaction. Furthermore, excessive catalyst may over-catalyze the decomposition of biomass, causing intermediate products to further react and generate large amounts of gases such as carbon dioxide. When calcium carbonate is in excess, the Ca in the solution... 2+ Excessive concentration may cause arsenic to form soluble complexes with arsenate ions, or redissolve existing calcium arsenate precipitates, thus promoting the migration of arsenic into the liquid phase. Carbonate (CO3) 2- ) and bicarbonate (HCO3) - It will compete with arsenate ions for adsorption sites on the solid surface, directly reducing the adsorbed arsenic and causing more of it to remain in the liquid phase.

[0060] A comparison of Examples 6-8 with Example 1 shows that, at the same hydrothermal liquefaction reaction temperature, different Fe-Ca-K biochar preparation ratios and addition amounts result in significant differences in biomass oil yield after hydrothermal liquefaction. The results are as follows: Figure 1 As shown, when the ratio of all substances in the biochar preparation process is 1:1:1 and the Fe-Ca-K addition is 0.5g, the biomass oil yield reaches its highest level of 40.5%. With the increase of Fe-Ca-K biochar addition, the biomass oil yield gradually decreases. When the addition amount increases to 1.0g, the biomass oil yield is lower than that when the addition amount is 0.2g, while at this point, the proportion of heavy metal arsenic (As) migrating to the solid phase reaches its highest level of 99.83%. Figure 2 The results show that, compared with Example 1, Examples 9 and 10 reveal that when the reaction temperature is varied while keeping the amount of added biochar constant, the yield of bio-oil and the migration rate of heavy metal As increase from 225°C to 275°C. This indicates that at a reaction temperature of 275°C, the yield of bio-oil from hydrothermal liquefaction using 0.5g Fe-Ca-K biochar reaches its optimal level; and the solidification effect is optimal with an added amount of 1.0g As. As shown in Example 1 and Comparative Example 1, the addition of Fe-Ca-K biochar doubled the yield of bio-oil from hydrothermal liquefaction of Centipede Grass, and increased the distribution ratio of As in the solid phase by 11 times. This demonstrates that the addition of Fe-Ca-K biochar significantly promotes the yield of bio-oil from hydrothermal liquefaction of Centipede Grass, achieving optimal results while simultaneously promoting the migration and distribution of arsenic into the solid phase product. Figure 3 It can be seen from the comparison between Comparative Example 1 and Comparative Examples 2-4 that the biochar prepared by steel rolling sludge has a significant promoting effect on the yield of hydrothermal liquefaction biomass oil from Centipede Grass and has a significant solidification effect on As. It can be seen from the comparison between Example 1 and Comparative Examples 2-4 that when KHCO3 or porous biotemplate is not added during the preparation of biochar by steel rolling sludge, the promoting effect on the yield of hydrothermal liquefaction biomass oil from Centipede Grass cannot reach the optimal state.

[0061] Comparison Examples 5-6 with the remaining examples and comparative examples show that the biochar prepared from shell powder or CaCO3 has a lower migration rate of heavy metals (As) to the solid phase and a lower bio-oil yield than the remaining examples and comparative examples. Therefore, Comparison Examples 5 and 6 will not be further characterized.

[0062] In summary, when steel rolling sludge, KHCO3, and porous biotemplate are used simultaneously for preparation, the synergistic effect of the generated Fe-Ca-K biochar achieves the best oil production effect from hydrothermal liquefaction of Centipede Grass biomass.

[0063] like Figure 4As shown, elemental characterization of bio-oil under different catalyst conditions revealed that the addition of catalysts significantly increased the hydrogenation and deoxygenation of the bio-oil. In Comparative Example 1, the hydrogen content of the bio-oil was 6.013%. In Comparative Example 2, the addition of Fe catalyst increased the hydrogen content to 6.115%. In Comparative Example 3, the addition of Fe-K catalyst or Comparative Example 4, the hydrogen content of the bio-oil decreased. In Example 2, Fe-Ca-K biochar significantly increased the hydrogen content of the bio-oil. This is because oxygen-containing compounds (such as phenols and carboxylic acids) in bio-oil are usually negatively charged. CaCO3 preferentially and strongly adsorbs these polar oxygen-containing molecules due to strong electrostatic attraction, directly hindering the contact between oxygen-containing molecules and the iron catalyst, cutting off the hydrogenation pathway, and causing the hydrogen content to decrease instead of increase. Furthermore, the extremely strong alkalinity of K2CO3 removes hydrogen substances and may excessively damage the carbon skeleton of biomass. The generated hydrogen is not effectively used for hydrogenation but instead produces a large amount of methane and other gases. Simultaneously, the products are prone to polymerization reactions to form coke, which coats the surface of the iron catalyst, deactivating it. When all three coexist in a hydrothermal system, iron and calcium carbonate form highly efficient active structures such as calcium ferrite. These catalysts can dissociate water molecules (H2O) to produce active hydrogen atoms (H·). 2+ and K + The competition for carbonate ions leads to the conversion of some potassium carbonate into calcium carbonate, consuming the excess alkalinity of K₂CO₃ (generated from the high-temperature decomposition of KHCO₃). This synergistic division of labor allows more hydrogen atoms to be precisely used in the hydrogenation reaction, significantly increasing the hydrogen content of bio-oil and producing a "1+1+1>3" effect. Furthermore, the addition of Fe-Ca-K biochar in Example 2 significantly reduced the oxygen content of the bio-oil. This is because potassium carbonate has strong alkalinity, which can break down biomolecules and efficiently promote decarboxylation (removal of carboxyl groups) and dehydration (removal of hydroxyl groups) deoxygenation reactions. CaCO₃ reacts with Fe to form Ca-Fe composite oxides (Ca-Fe-O), a highly efficient active phase that provides optimal reaction sites for hydrogen. Through synergy between catalysts, the strongest hydrodeoxygenation effect is achieved, significantly improving the calorific value, storage, and thermal stability of the bio-oil, resulting in a high-quality renewable fuel with lower viscosity and corrosivity, better flowability, and easier processing and application.

[0064] like Figure 5As shown in the graph, the phenol and acid content of bio-oil under different catalyst conditions are analyzed. The results show that the addition of catalyst significantly increased the phenol content in bio-oil and greatly reduced the acid content. Comparing Comparative Examples 1-4, the phenol content of bio-oil increased from 40.10% to 49.31%, while the acid content decreased from 20.57% to 13.33%. The addition of catalyst achieved the deacidification of phenol-rich bio-oil. In Example 1, the phenol content of bio-oil increased to the highest of 51.33%, an increase of 11.23% compared to Comparative Example 1, while the acid content reached the lowest of 13.15%. This is because under hydrothermal conditions, the extremely strong alkalinity of K2CO3 greatly promotes the depolymerization and dissolution of lignin, efficiently breaking the ether bonds in lignin and releasing a large number of molecules rich in phenolic functional groups. It can also rapidly undergo acid-base neutralization reactions with organic acids (such as acetic acid) produced by biomass pyrolysis, generating corresponding potassium salts and water, directly "removing" free carboxylic acids in the liquid phase. CaCO3 first undergoes a neutralization reaction with organic acids to produce calcium fatty acids. Subsequently, at high temperatures, these calcium fatty acid salts undergo thermal decomposition, losing a molecule of CO2 and efficiently converting into low-oxygen substances – ketones, thus achieving the system's deoxygenation reaction. Iron, on the other hand, is responsible for "opening up" the hydrogenation and decarboxylation pathway. Through its catalytic activity, it promotes the hydrogenation of carboxylic acids while they lose a molecule of CO2, converting them into saturated alkanes or other non-acidic substances, eliminating acidity at its source. The efficient synergy of these three components not only directionally "synthesizes" phenolic compounds but also efficiently "eliminates" carboxylic acids, enhancing the antioxidant and anti-aging capabilities of bio-oils, reducing corrosiveness, and improving the calorific value and stability of bio-oils, resulting in high-value, high-quality bio-oil products.

[0065] like Figure 6 As shown, the BET specific surface area and average pore size of the four biochars were analyzed. The results showed that the specific surface area of ​​the catalysts was all in the range of 0-50 m². 2 Within the range of / g. Specific surface area of ​​Fe-Ca-K biochar (10.58 m²) 2 / g) is higher than Fe (1.88 m 2 / g), Fe-K (4.78 m 2 / g) and Fe-Ca (5.20 m 2 / g). The average pore size of the catalysts ranged from 0 to 50 nm. The average pore size of Fe-Ca-K biochar (40.01 nm) was significantly better than that of Fe (14.01 nm), Fe-K (30.09 nm), and Fe-Ca (10.21 nm). This indicates that the Fe-Ca-K ternary active component system, formed by simultaneously introducing porous biological templates and KHCO3 (chemical activator), synergistically creates a superior pore structure, significantly improving the specific surface area and pore structure uniformity of the catalyst. This ensures the effective diffusion of metal ions during the reaction, promotes the decomposition of biomass, and provides sufficient active sites, thereby achieving the enrichment of heavy metals in the solid phase and improving the yield of bio-oil. The synergistic effect is far greater than the combined effect of individual factors.

[0066] like Figure 7 As shown, scanning electron microscopy (SEM) characterization results of the four biochars revealed that the solid products generated by the Fe catalyst system exhibited pores of varying sizes and significant differences in channel dimensions, indicating an incomplete overall pore structure. In the Fe-K system, K... + At high temperatures, carbon skeletons can be embedded, and etching significantly increases the specific surface area and microporous structure of biochar, resulting in a relatively uniform pore size distribution, although some pores remain incompletely open. The Fe-Ca system forms a relatively uniform pore layer on the product surface, but internal pore development is insufficient, with pores mainly concentrated on the surface. In contrast, the Fe-Ca-K system, due to the synergistic effect of Fe, KHCO3, and CaCO3, results in a more ideal pore structure in the solid product: uniform pore size distribution, with pores penetrating both the surface and interior of the material, forming a deep pore network. This structure facilitates the diffusion and transport of reactant molecules, providing a structural basis for optimizing bio-oil yield.

[0067] like Figure 8As shown, X-ray diffraction (XRD) analysis was performed on the four types of biochar prepared. The results showed that: Fe biochar only showed diffraction peaks for iron species (Fe, Fe3O4, Fe2O3); Fe-K biochar showed K2CO3 (generated by high-temperature decomposition of KHCO3) in addition to iron species peaks; Fe-Ca biochar showed CaCO3, the main porous biotemplate, in addition to iron species peaks. The Fe-Ca-K biochar generated by pyrolysis is a carbon skeleton system formed by the pyrolysis of steel rolling sludge and eggshells. K2CO3 and CaCO3 were detected, and three iron diffraction peaks such as Fe, Fe3O4, and Fe2O3 were also found. The large specific surface area formed by the abundant iron source provides a large number of active sites for the reaction, which can form stable inner surface complexes (such as Fe-O-As) with arsenic (As(V) and As(III)). This chemical bond is very strong and can effectively prevent the re-release of arsenic. Furthermore, the aqueous phase generated by the hydrothermal liquefaction reaction of Centipede Grass is acidic. In this acidic environment, the iron oxide surface carries a positive charge, while arsenic mainly exists as negatively charged oxygen-containing anions (such as H2AsO4). - ,HAsO4 2- It exists in the form of CaCO3, and therefore can be efficiently adsorbed through electrostatic attraction; the Ca precipitated from CaCO3 2+ It can react with arsenate ions (AsO4) 3- The reaction produces chemically stable calcium-arsenic precipitates (such as Ca3(AsO4)2). The abundant K+ on the surface of Fe-Ca-K biochar... + Arsenic can undergo ion exchange with arsenate ions in solution, fixing arsenic onto the carbon surface. Therefore, Fe-Ca-K biochar efficiently fixes arsenic through a three-pronged mechanism of "carrier-adsorption-precipitation": Fe chemically binds arsenic; Ca converts arsenic into insoluble minerals through precipitation; and K enhances the adsorption capacity of the carrier through physical activation. The results show that the arsenic (As) fixation effect of Fe-Ca-K biochar is significantly higher than the combined effect of Fe, Fe-Ca, and Fe-K alone.

[0068] like Figure 9 As shown, X-ray photoelectron spectroscopy (XPS) characterization results of the changes in the valence states of Fe and As before and after the hydrothermal liquefaction (HTL) reaction of Fe-Ca-K biochar show that before the reaction, Fe-Ca-K biochar contained a small amount of elemental iron, accounting for 6.06%. After the hydrothermal liquefaction (HTL) reaction, the valence states of iron species changed significantly, and the content of elemental iron decreased to 0.18%. 2+ From 7.20% to 11.74%, Fe 3+The toxicity of As increased from 80.74% to 88.08%, an increase of 1.34%. Before the reaction, the proportion of As(III), which has higher valence state and is more toxic, was 91.19%, while As(V) accounted for 8.81%, indicating that the overall toxicity of Centipede Grass biomass was relatively high. After the Fe-Ca-K biochar was added to the hydrothermal liquefaction system, the detoxification effect of As was significant. The proportion of As(III), which has higher toxicity, was reduced to only 12.33% after oxidation, while the proportion of As(V) increased to 87.67%. Due to the graphitized structure of biochar having a certain degree of conductivity, it may participate in the electron transfer process between iron and arsenic. Fe in situ exists in the hydrothermal system. 0 As a strong reducing electron donor, it undergoes an interfacial corrosion reaction with solvent water or dissolved oxygen under high-temperature hydrothermal conditions, releasing electrons to generate Fe. 2+ Subsequently, Fe 2+ It is further oxidized to Fe via a Fenton-like reaction. 3+ The reactive oxygen species generated during this process can oxidize As(III) to As(V), which is less toxic and easily fixed. It is worth emphasizing that the newly formed Fe... 3+ It is not an inert end product; it can react with residual Fe. 0 Contact reduction and regeneration occur to Fe 2+ Fe can also be achieved by utilizing the electrons provided by the graphitized structure of biochar. 3+ →Fe 2+ The reverse regeneration of Fe maintains 2+ / Fe 3+ The efficient redox cycle is crucial. Changes in iron valence state promote significant oxidative detoxification of arsenic while also affecting bio-oil yield. Furthermore, the presence of K₂CO₃ effectively catalyzes the breakage of biomass macromolecules to produce smaller reactive intermediates and inhibits the repolymerization of these intermediates to form hydrothermal char, providing a favorable foundation for bio-oil production and thus increasing its yield. Therefore, Fe-Ca-K biochar further promotes bio-oil yield through the efficient synergistic effect of regulating iron and arsenic valence states and its dual mechanism of "promoting depolymerization and inhibiting polymerization" in *Pteris vittata*.

[0069] like Figure 10 As shown, magnetic separation was performed on the solid phases after hydrothermal liquefaction of four catalysts (Fe-c, Fe-Kc, Fe-Ca-c, and Fe-Ca-Kc represent magnetic solid phases; Fe, Fe-K, Fe-Ca, and Fe-Ca-K represent non-magnetic solid phases). The hysteresis regression curves show that the non-magnetic data is close to zero, indicating a significant magnetic separation effect. The Fe-c and Fe-Kc solid phases exhibited stronger magnetic properties, while the relatively weaker magnetic data for Fe-Ca-c and Fe-Ca-Kc are attributed to the higher Fe content in these two catalysts. The addition of CaCO3 reduced the proportion of Fe in the solid phase, while the non-magnetic calcium ions (Ca... 2+When ions enter the iron oxide lattice, they will replace some of the iron ions (Fe). 3+ The position of the magnetic dilution effect is formed.

[0070] like Figure 11 As shown, the distribution of As content in the magnetic and non-magnetic solid phases after magnetic separation was investigated. The results showed that the As content was highest in the Fe-K magnetic system (67.95%), followed by the Fe-Ca magnetic system (86.92%). In the non-magnetic system, the As content of Fe-Ca-K (2.7%) was significantly lower than that of the Fe system (9.35%), indicating that over 60% of the As in these four systems was distributed in the magnetic system, with the Fe-Ca-K system showing a particularly significant difference. Therefore, magnetic separation can be performed on the solid phase after hydrothermal liquefaction to recover heavy metals, significantly reducing the total volume of As-containing solid phases and environmental risks, which aligns with the "stabilization-separation-recovery" principle in heavy metal pollution control.

Claims

1. A method for preparing an iron-containing catalyst using steel rolling sludge, characterized in that, Includes the following steps: S1. Dry, grind, and sieve the eggshells to prepare a porous biological template; S2. Mix steel rolling sludge, porous biological template and appropriate amount of anhydrous ethanol, stir until ethanol evaporates, and dry at low temperature to obtain mixture; S3. KHCO3 is added to the mixture, and calcination and carbonization are carried out in an inert gas atmosphere to obtain Fe-Ca-K biochar containing iron catalyst.

2. The method for preparing an iron-containing catalyst using steel rolling sludge according to claim 1, characterized in that: The mass fraction of the steel rolling sludge in S2 is 30-80% of the mixture; the low-temperature drying temperature in the oven in S2 is 30-80℃.

3. The method for preparing an iron-containing catalyst using steel rolling sludge according to claim 1, characterized in that: The amount of KHCO3 added to S3 is 25-80% of the mixture; the carbonization temperature is 400-900℃, and the time is 1-3h.

4. An iron-containing catalyst, characterized in that: The catalyst is prepared using the preparation method described in any one of claims 1 to 3.

5. The application of the catalyst prepared by the method according to any one of claims 1 to 3, characterized in that: Used to catalyze the hydrothermal liquefaction reaction of biomass to produce biomass oil.

6. The application according to claim 5, characterized in that: The preparation method for biomass oil by catalyst-catalyzed hydrothermal liquefaction reaction of biomass is as follows: R1. Dry the centipede grass, grind it, and sieve it. R2. Grind Fe-Ca-K biochar, mix it with centipede grass, put it into a high-pressure reactor, and add an appropriate amount of water. R3. Seal the reactor, remove the air from the high-pressure reactor under a nitrogen atmosphere, heat the high-pressure reactor under stirring to carry out the hydrothermal liquefaction reaction, and after the reaction is completed, cool the high-pressure reactor to room temperature in a water bath to obtain the hydrothermal liquefaction mixture. R4: Filter the hydrothermal liquefaction mixture, wash the solid phase with an organic solvent, and collect the liquid phase for separation. R5, the organic solvent is removed by rotary evaporation of the oil phase to obtain the biomass oil phase.

7. The application according to claim 6, characterized in that: In R2, the amount of biochar added is 10-70% of the mass of centipede grass; the amount of water added is 20-45 ml.

8. The application according to claim 6, characterized in that: The heating conditions for hydrothermal liquefaction in the high-pressure reactor of R3 are 220~300℃ and the time is 10~45min.

9. The application according to claim 6, characterized in that: The organic solvent used in R4 is ethyl acetate, and the amount of ethyl acetate used is 4 to 9 times that of water.

10. The application according to claim 6, characterized in that: Ethyl acetate was removed by rotary evaporation in R5, with a evaporation time of 15-35 min, a evaporation temperature of 40-55℃, and a vacuum degree of 180-280 kPa.

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