A method for CO2-promoted hydrothermal liquefaction, demulsification, and separation of steel rolling sludge

Abstract

This invention belongs to the field of hydrothermal liquefaction technology and discloses a method for CO2-promoted hydrothermal liquefaction demulsification and separation of rolling mill sludge. The method involves weighing rolling mill sludge into a high-pressure reactor, adding water, and introducing sufficient carbon dioxide gas to purge air from the reactor. A hydrothermal liquefaction reaction is then carried out, and the liquid phase product in the high-pressure reactor is collected and washed with acetone. The washing liquid and the liquid phase product in the high-pressure reactor are then vacuum filtered together. After washing the filter residue with acetone, a filtrate and a filter residue are obtained. The filter residue is dried to obtain the solid phase product of the reaction. Dichloromethane is added to the filtrate, and after thorough stirring and extraction, the liquid is separated. The upper layer is an aqueous solution, and the lower layer is a mixed solution of acetone, dichloromethane, and bio-oil. Rotary evaporation is used to remove the organic solvent from the oil phase mixture, yielding the oil phase. This invention improves the oil phase separation efficiency and calorific value of rolling mill sludge by using CO2 as a reaction atmosphere during the hydrothermal liquefaction process.

Description

Technical Field

[0001] This invention belongs to the field of hydrothermal liquefaction technology, specifically relating to a method for CO2-promoted hydrothermal liquefaction, demulsification, and separation of steel rolling sludge. Background Technology

[0002] Steel rolling sludge is a typical hazardous industrial waste containing iron and carbon, generated during steel smelting. It is primarily an emulsion composed of three phases: grease, water, and iron filings, and is toxic and flammable. Steel rolling sludge is a high-viscosity, complex emulsion of oil, water, and iron filings, containing 5–60 wt% grease (long-chain fatty acids such as palmitic acid and oleic acid) and 20–90 wt% iron filings (Fe, Fe3O4, and FeOx). Direct discharge not only severely pollutes the environment but also wastes oil and iron resources. Therefore, how to reduce, render harmless, utilize resources, and achieve high-value disposal of steel rolling sludge to achieve synergistic effects in pollution reduction and carbon reduction, as well as the recycling of solid waste resources, has become a major requirement for the green, sustainable, and high-quality development of the steel industry.

[0003] Currently, the main methods for disposing of rolling mill sludge include high-temperature incineration and pyrolysis, medium-temperature distillation, room-temperature organic solvent extraction, acid and alkali cleaning, and microwave radiation. However, these methods have limitations in industrial applications, such as: incineration easily generates secondary pollution, pyrolysis has high energy consumption, distillation requires pre-dehydration, organic solvent extraction has high operating costs, acid and alkali cleaning requires highly corrosion-resistant equipment, and microwave radiation equipment has high investment costs. These limitations severely restrict the resource utilization of oil phase and iron filings in rolling mill sludge. Therefore, there is an urgent need to develop new methods for the efficient, resource-based, and high-value disposal of rolling mill sludge.

[0004] In recent years, researchers have explored ways to fully utilize the moisture in rolling mill sludge by directly placing it in a subcritical / supercritical water environment. Leveraging the low dielectric constant, low hydrogen bonding, and nonpolarity of subcritical / supercritical water, they have achieved demulsification and separation of the rolling mill sludge. Hydrothermal liquefaction separation technology, which uses water directly as a reactant without requiring pre-treatment for raw material dehydration, offers advantages such as high reaction efficiency and strong adaptability to raw materials, attracting significant attention from researchers. However, hydrothermal liquefaction separation of rolling mill sludge typically requires temperatures above 350°C, placing high demands on the equipment. Therefore, improving the efficiency of hydrothermal separation of rolling mill sludge at low temperatures has become a key focus for researchers.

[0005] CO2 (carbon dioxide) is a nonpolar gas that dissolves in water to form H2CO3 (carbonic acid). Due to its relatively mild critical point (31.3℃, 7.38 MPa), it easily reaches a supercritical state. In its supercritical state, CO2 exhibits high density, high diffusivity, high solubility, low surface tension, and low viscosity. It more readily dissolves fatty acids, esters, and other organic compounds, and its large reaction interface accelerates the reaction. Given the unique physicochemical properties of supercritical CO2, combining it with hydrothermal liquefaction processes can significantly improve the separation efficiency of oil, water, and solid phases in steel rolling sludge. This not only enables the recovery of oil and iron resources from steel rolling sludge but also reduces its environmental pollution, ultimately achieving the reduction, harmlessness, and resource utilization of steel rolling sludge.

[0006] Although supercritical CO2 extraction has applications, it is a physical process where carbon dioxide acts as a solvent, primarily for dissolution. Supercritical CO2 extraction is inferior to hydrothermal liquefaction in terms of processing time, recovery efficiency, and the calorific value of the recovered oil phase. No research has been found on the application of CO2 in promoting oil phase separation in steel rolling sludge. Summary of the Invention

[0007] In order to improve the oil phase separation efficiency and calorific value of steel rolling sludge in the hydrothermal liquefaction process, this invention uses CO2 as the reaction atmosphere during the hydrothermal liquefaction process of steel rolling sludge to improve the oil phase separation efficiency and calorific value, thereby achieving the purpose of pollution reduction and carbon reduction.

[0008] This invention is achieved through the following technical solution: a method for CO2-promoted hydrothermal liquefaction, demulsification, and separation of rolling mill sludge, comprising the following steps:

[0009] (1) Weigh the steel rolling sludge into the high-pressure reactor, add water, mix evenly, and then seal the high-pressure reactor; open the air inlet valve of the high-pressure reactor, introduce sufficient carbon dioxide gas to expel the air in the reactor, maintain a certain initial pressure in the high-pressure reactor, and then close the air inlet valve.

[0010] (2) Start the high-pressure reactor to carry out hydrothermal liquefaction reaction at a temperature of 250-375°C. After the reaction is completed, turn on the cooling water to cool the high-pressure reactor. After cooling and depressurizing, collect the liquid phase product in the high-pressure reactor and wash the high-pressure reactor body and the stirring paddle with acetone.

[0011] (3) The washing liquid and the liquid product in the high-pressure reactor are vacuum filtered together. After washing the filter residue with acetone, the filtrate and filter residue are obtained. The filter residue is dried to obtain the solid product of the reaction. Dichloromethane is added to the filtrate and the mixture is stirred and extracted. The filtrate is then poured into a separatory funnel for separation. The upper layer is an aqueous solution and the lower layer is a mixed solution of acetone, dichloromethane and bio-oil.

[0012] (4) Rotary evaporation is carried out under the conditions of water bath temperature of 40-50℃ and vacuum degree of 300-700kpa to remove organic solvents from the oil phase mixture solution and obtain oil phase.

[0013] Preferably, in step (1), the mass of the steel rolling sludge is 5-50% of the mass fraction of the mixture, more preferably 5-20%.

[0014] Preferably, in step (1), the initial pressure inside the high-pressure reactor is 0-2 MPa.

[0015] Preferably, in step (2), the stirring speed of the hydrothermal liquefaction reaction is 150-1500 r / min, and the reaction time is 15-60 min.

[0016] Preferably, in step (2), the hydrothermal liquefaction reaction temperature is 300-350℃ and the reaction time is 30min.

[0017] Preferably, in steps (2) and (3), the total amount of acetone used is 1-3 times the amount of water used.

[0018] Preferably, in step (3), the amount of dichloromethane used is 2-3 times the amount of water used.

[0019] Preferably, in step (4), the rotary evaporation time of the organic solvent is 30-45 min.

[0020] The beneficial effects of this invention are as follows: This invention utilizes CO2 to promote the hydrothermal liquefaction and separation of oil phase resources in steel rolling sludge. Compared with N2 as the reaction atmosphere, the oil phase separation rate and calorific value of bio-oil during the hydrothermal liquefaction process of steel rolling sludge are significantly improved. In this invention, when CO2 is introduced as the reaction atmosphere at a reaction temperature of 300°C and a certain initial pressure is maintained, the oil phase separation rate of steel rolling sludge can be increased by up to 33.023%, and the lower heating value of bio-oil can be increased by up to 7.341%. This is because the carbonic acid formed by CO2 dissolving in water at low temperatures during hydrothermal liquefaction promotes the hydrolysis of steel rolling sludge at low temperatures, while the special physicochemical properties of supercritical CO2 at high temperatures promote the dissolution of the oil phase and the destruction of the emulsion structure in the steel rolling sludge, thereby improving the separation efficiency of the oil phase in the steel rolling sludge. At the same time, Fe in the solid iron filings in the steel rolling sludge reacts with subcritical water to generate H2, promoting the hydrogenation and deoxygenation reaction of the oil phase, thereby increasing the calorific value of the oil phase.

[0021] Unlike supercritical CO2 extraction for treating rolling mill sludge, which uses only carbon dioxide as a solvent to promote the dissolution of the oil phase and achieve separation, this invention introduces CO2 as a reaction atmosphere during hydrothermal liquefaction. This allows for faster processing and more efficient recovery and upgrading of the oil phase, resulting in a higher calorific value oil phase that can be utilized as a potential alternative fuel. Furthermore, no research has been found on the application of CO2 in promoting oil phase separation in rolling mill sludge. Detailed Implementation

[0022] A method for CO2-promoted hydrothermal liquefaction, demulsification, and separation of steel rolling sludge includes the following steps:

[0023] (1) Weigh an appropriate amount of steel rolling sludge into the high-pressure reactor, add water, mix evenly, and then seal the high-pressure reactor; open the air inlet valve of the high-pressure reactor, introduce sufficient carbon dioxide gas to discharge the air in the reactor, maintain a certain initial pressure in the high-pressure reactor, and then close the air inlet valve.

[0024] (2) Set the reaction temperature to 250-375℃, the stirring speed to 150-1500r / min, and the reaction time to 15-60min. Then start the high-pressure reactor to carry out the hydrothermal liquefaction reaction. After the reaction is completed, turn on the cooling water to cool the high-pressure reactor. After the temperature inside the reactor drops to room temperature, open the exhaust valve of the high-pressure reactor to reduce the pressure inside the reactor to atmospheric pressure. Then open the high-pressure reactor, collect the liquid phase product inside the high-pressure reactor, and wash the high-pressure reactor body and the stirring paddle thoroughly with acetone.

[0025] (3) The washing liquid and the liquid product in the high-pressure reactor are vacuum filtered together. After washing the filter residue thoroughly with an appropriate amount of acetone, the filtrate and filter residue are obtained. The filter residue is dried at 105°C for more than 12 hours to obtain the solid product of the reaction. An appropriate amount of dichloromethane is added to the filtrate, and after thorough stirring and extraction, it is poured into a separatory funnel for separation. The upper layer is an aqueous solution, and the lower layer is a mixed solution of acetone, dichloromethane and bio-oil.

[0026] (4) Rotary evaporation is carried out under the conditions of water bath temperature of 40-50℃ and vacuum degree of 300-700kpa to remove organic solvents from the oil phase mixture solution and obtain oil phase.

[0027] Preferably, in step (1), the mass of the steel rolling sludge is 5-50% of the mass fraction of the mixture, and most preferably 5-20%.

[0028] Preferably, in step (1), the initial pressure inside the high-pressure reactor is 0-2 MPa.

[0029] Preferably, in step (2), the hydrothermal liquefaction reaction temperature is 300-350℃ and the reaction time is 30min.

[0030] Preferably, in steps (2) and (3), the total amount of acetone used is 1-3 times the amount of water used.

[0031] Preferably, in step (3), the amount of dichloromethane used is 2-3 times the amount of water used.

[0032] Preferably, in step (4), the rotary evaporation time of the organic solvent is 30-45 min.

[0033] The rolling mill sludge in this implementation case comes from the steel rolling process of a large domestic steel company. Table 1 shows the oil, water, and solid phase composition of the rolling mill sludge, with the mass fractions of oil, water, and solid phases being approximately 57.04%, 30.83%, and 12.13%, respectively. Table 2 shows the elemental analysis results of the oil phase in the rolling mill sludge.

[0034] Table 1. Composition of oil, water, and solid phases in steel rolling sludge

[0035]

[0036] Table 2. Elemental analysis results of oil phase in rolling mill sludge

[0037]

[0038] Example 1

[0039] The method for hydrothermal liquefaction, demulsification, and separation of rolling mill sludge under CO2 atmosphere conditions specifically includes the following steps:

[0040] (1) Weigh 8.824g of rolling mill sludge and place it in a high-pressure reactor. Add 50g of distilled water, mix well, and then seal the high-pressure reactor. Open the air inlet valve of the high-pressure reactor, introduce sufficient carbon dioxide gas to expel the air inside the reactor, adjust the pressure inside the high-pressure reactor to atmospheric pressure, and then close the air inlet valve.

[0041] (2) Set the reaction temperature of the high-pressure reactor to 300℃, the stirring speed to 150r / min, and the reaction time to 30min. Start the high-pressure reactor to carry out the hydrothermal liquefaction reaction. After the reaction is completed, turn on the cooling water to cool the high-pressure reactor. After it drops to room temperature, open the exhaust valve of the high-pressure reactor to reduce the pressure inside the reactor to atmospheric pressure. Then open the high-pressure reactor, collect the liquid phase product inside the high-pressure reactor, and take 100ml of acetone solution to thoroughly wash the high-pressure reactor body and the stirring paddle.

[0042] (3) The washing liquid and the liquid product in the reactor are vacuum filtered together. After washing the filter residue thoroughly with 50 ml of acetone, the filtrate and filter residue are obtained. The filter residue is dried at 105°C for more than 12 hours to obtain the solid product of the reaction. 150 ml of the filtrate is added and thoroughly stirred and extracted. The mixture is then poured into a separatory funnel for separation. The upper layer is an aqueous solution and the lower layer is a mixed solution of acetone, dichloromethane and oil.

[0043] (4) Under the conditions of water bath temperature of 50℃ and vacuum degree of 368kpa, the rotary evaporation time is 35min to remove the organic solvent in the oil phase mixed solution and obtain the oil phase.

[0044] Example 2

[0045] (1) Weigh 8.824g of rolling mill sludge and place it in a high-pressure reactor. Add 50g of distilled water, mix well, and then seal the high-pressure reactor. Open the air inlet valve of the high-pressure reactor, introduce sufficient carbon dioxide gas to expel the air inside the reactor, adjust the pressure inside the high-pressure reactor to 1MPa, and then close the air inlet valve.

[0046] (2) Set the reaction temperature of the high-pressure reactor to 300℃, the stirring speed to 150r / min, and the reaction time to 30min. Start the high-pressure reactor to carry out the hydrothermal liquefaction reaction. After the reaction is completed, turn on the cooling water to cool the high-pressure reactor. After it drops to room temperature, open the exhaust valve of the high-pressure reactor to reduce the pressure inside the reactor to atmospheric pressure. Then open the high-pressure reactor, collect the liquid phase product inside the high-pressure reactor, and take 100ml of acetone solution to thoroughly wash the high-pressure reactor body and the stirring paddle.

[0047] (3) The washing liquid and the liquid product in the reactor were vacuum filtered together. The filter residue was thoroughly washed with 50 ml of acetone to obtain the filtrate and the filter residue. The filter residue was dried at 105°C for more than 12 hours to obtain the solid product of the reaction. 150 ml of dichloromethane was added to the filtrate and the mixture was stirred and extracted. The filtrate was then poured into a separatory funnel for separation. The upper layer was an aqueous solution and the lower layer was a mixed solution of acetone, dichloromethane and oil.

[0048] (4) Under the conditions of water bath temperature of 50℃ and vacuum degree of 368kpa, the rotary evaporation time is 35min to remove the organic solvent in the oil phase mixed solution and obtain the oil phase.

[0049] Example 3

[0050] (1) Weigh 8.824g of steel rolling sludge and place it in a high-pressure reactor. Add 50g of distilled water, mix well, and then seal the high-pressure reactor. Open the air inlet valve of the high-pressure reactor, introduce sufficient carbon dioxide gas to expel the air inside the reactor, adjust the pressure inside the high-pressure reactor to 2MPa, and then close the air inlet valve.

[0051] (2) Set the reaction temperature of the high-pressure reactor to 300℃, the stirring speed to 150r / min, and the reaction time to 30min. Start the high-pressure reactor to carry out the hydrothermal liquefaction reaction. After the reaction is completed, turn on the cooling water to cool the high-pressure reactor. After it drops to room temperature, open the exhaust valve of the high-pressure reactor to reduce the pressure inside the reactor to atmospheric pressure. Then open the high-pressure reactor, collect the liquid phase product inside the high-pressure reactor, and take 100ml of acetone solution to thoroughly wash the high-pressure reactor body and the stirring paddle.

[0052] (3) The washing liquid and the liquid product in the reactor were vacuum filtered together. The filter residue was thoroughly washed with 50 ml of acetone to obtain the filtrate and the filter residue. The filter residue was dried at 105°C for more than 12 hours to obtain the solid product of the reaction. 150 ml of dichloromethane was added to the filtrate and the mixture was stirred and extracted. The filtrate was then poured into a separatory funnel for separation. The upper layer was an aqueous solution and the lower layer was a mixed solution of acetone, dichloromethane and oil.

[0053] (4) Under the conditions of water bath temperature of 50℃ and vacuum degree of 368kpa, the rotary evaporation time is 35min to remove the organic solvent in the oil phase mixed solution and obtain the oil phase.

[0054] Example 4

[0055] (1) Weigh 8.824g of rolling mill sludge and place it in a high-pressure reactor. Add 50g of distilled water, mix well, and then seal the high-pressure reactor. Open the air inlet valve of the high-pressure reactor, introduce sufficient carbon dioxide gas to expel the air inside the reactor, adjust the pressure inside the high-pressure reactor to 1MPa, and then close the air inlet valve.

[0056] (2) Set the reaction temperature of the high-pressure reactor to 325℃, the stirring speed to 150r / min, and the reaction time to 30min. Start the high-pressure reactor to carry out the hydrothermal liquefaction reaction. After the reaction is completed, turn on the cooling water to cool the high-pressure reactor. After it drops to room temperature, open the exhaust valve of the high-pressure reactor to reduce the pressure inside the reactor to atmospheric pressure. Then open the high-pressure reactor, collect the liquid phase product inside the high-pressure reactor, and take 100ml of acetone solution to thoroughly wash the high-pressure reactor body and the stirring paddle.

[0057] (3) The washing liquid and the liquid product in the reactor were vacuum filtered together. The filter residue was thoroughly washed with 50 ml of acetone to obtain the filtrate and the filter residue. The filter residue was dried at 105°C for more than 12 hours to obtain the solid product of the reaction. 150 ml of dichloromethane was added to the filtrate and the mixture was stirred and extracted. The filtrate was then poured into a separatory funnel for separation. The upper layer was an aqueous solution and the lower layer was a mixed solution of acetone, dichloromethane and oil.

[0058] (4) Under the conditions of water bath temperature of 50℃ and vacuum degree of 368kpa, the rotary evaporation time is 35min to remove the organic solvent in the oil phase mixed solution and obtain the oil phase.

[0059] Example 5

[0060] (1) Weigh 8.824g of rolling mill sludge and place it in a high-pressure reactor. Add 50g of distilled water, mix well, and then seal the high-pressure reactor. Open the air inlet valve of the high-pressure reactor, introduce sufficient carbon dioxide gas to expel the air inside the reactor, adjust the pressure inside the high-pressure reactor to 1MPa, and then close the air inlet valve.

[0061] (2) Set the reaction temperature of the high-pressure reactor to 350℃, the stirring speed to 150r / min, and the reaction time to 30min. Start the high-pressure reactor to carry out the hydrothermal liquefaction reaction. After the reaction is completed, turn on the cooling water to cool the high-pressure reactor. After it drops to room temperature, open the exhaust valve of the high-pressure reactor to reduce the pressure inside the reactor to atmospheric pressure. Then open the high-pressure reactor, collect the liquid phase product inside the high-pressure reactor, and take 100ml of acetone solution to thoroughly wash the high-pressure reactor body and the stirring paddle.

[0062] (3) The washing liquid and the liquid product in the reactor were vacuum filtered together. The filter residue was thoroughly washed with 50 ml of acetone to obtain the filtrate and the filter residue. The filter residue was dried at 105°C for more than 12 hours to obtain the solid product of the reaction. 150 ml of dichloromethane was added to the filtrate and the mixture was stirred and extracted. The filtrate was then poured into a separatory funnel for separation. The upper layer was an aqueous solution and the lower layer was a mixed solution of acetone, dichloromethane and oil.

[0063] (4) Under the conditions of water bath temperature of 50℃ and vacuum degree of 368kpa, the rotary evaporation time is 35min to remove the organic solvent in the oil phase mixture solution and obtain bio-oil.

[0064] Comparative Example 1

[0065] (1) Weigh 8.824g of steel rolling sludge and place it in a high-pressure reactor. Add 50g of distilled water, mix well, and then seal the high-pressure reactor. Open the gas inlet valve of the high-pressure reactor, introduce sufficient nitrogen gas to expel the air inside the reactor, adjust the pressure inside the high-pressure reactor to atmospheric pressure, and then close the gas inlet valve.

[0066] (2) Set the reaction temperature of the high-pressure reactor to 350℃, the stirring speed to 150r / min, and the reaction time to 30min. Start the high-pressure reactor to carry out the hydrothermal liquefaction reaction. After the reaction is completed, turn on the cooling water to cool the high-pressure reactor. After it drops to room temperature, open the exhaust valve of the high-pressure reactor to reduce the pressure inside the reactor to atmospheric pressure. Then open the high-pressure reactor, collect the liquid phase product inside the high-pressure reactor, and take 100ml of acetone solution to thoroughly wash the high-pressure reactor body and the stirring paddle.

[0067] (3) The washing liquid and the liquid product in the reactor were vacuum filtered together. The filter residue was thoroughly washed with 50 ml of acetone to obtain the filtrate and the filter residue. The filter residue was dried at 105°C for more than 12 hours to obtain the solid product of the reaction. 150 ml of dichloromethane was added to the filtrate and the mixture was stirred and extracted. The filtrate was then poured into a separatory funnel for separation. The upper layer was an aqueous solution and the lower layer was a mixed solution of acetone, dichloromethane and oil.

[0068] (4) Under the conditions of water bath temperature of 50℃ and vacuum degree of 368kpa, the rotary evaporation time is 35min to remove the organic solvent in the oil phase mixed solution and obtain the oil phase.

[0069] Comparative Example 2

[0070] (1) Weigh 8.824g of steel rolling sludge and place it in a high-pressure reactor. Add 50g of distilled water, mix well, and then seal the high-pressure reactor. Open the air inlet valve of the high-pressure reactor, introduce sufficient nitrogen gas to expel the air inside the reactor, adjust the pressure inside the high-pressure reactor to 1MPa, and then close the air inlet valve.

[0071] (2) Set the reaction temperature of the high-pressure reactor to 325℃, the stirring speed to 150r / min, and the reaction time to 30min. Start the high-pressure reactor to carry out the hydrothermal liquefaction reaction. After the reaction is completed, turn on the cooling water to cool the high-pressure reactor. After it drops to room temperature, open the exhaust valve of the high-pressure reactor to reduce the pressure inside the reactor to atmospheric pressure. Then open the high-pressure reactor, collect the liquid phase product inside the high-pressure reactor, and take 100ml of acetone solution to thoroughly wash the high-pressure reactor body and the stirring paddle.

[0072] (3) The washing liquid and the liquid product in the reactor were vacuum filtered together. The filter residue was thoroughly washed with 50 ml of acetone to obtain the filtrate and the filter residue. The filter residue was dried at 105°C for more than 12 hours to obtain the solid product of the reaction. 150 ml of dichloromethane was added to the filtrate and the mixture was stirred and extracted. The filtrate was then poured into a separatory funnel for separation. The upper layer was an aqueous solution and the lower layer was a mixed solution of acetone, dichloromethane and oil.

[0073] (4) Under the conditions of water bath temperature of 50℃ and vacuum degree of 368kpa, the rotary evaporation time is 35min to remove the organic solvent in the oil phase mixed solution and obtain the oil phase.

[0074] Comparative Example 3

[0075] (1) Weigh 8.824g of steel rolling sludge and place it in a high-pressure reactor. Add 50g of distilled water, mix well, and then seal the high-pressure reactor. Open the air inlet valve of the high-pressure reactor, introduce sufficient nitrogen gas to expel the air inside the reactor, adjust the pressure inside the high-pressure reactor to 1MPa, and then close the air inlet valve.

[0076] (2) Set the reaction temperature of the high-pressure reactor to 350℃, the stirring speed to 150r / min, and the reaction time to 30min. Start the high-pressure reactor to carry out the hydrothermal liquefaction reaction. After the reaction is completed, turn on the cooling water to cool the high-pressure reactor. After it drops to room temperature, open the exhaust valve of the high-pressure reactor to reduce the pressure inside the reactor to atmospheric pressure. Then open the high-pressure reactor, collect the liquid phase product inside the high-pressure reactor, and take 100ml of acetone solution to thoroughly wash the high-pressure reactor body and the stirring paddle.

[0077] (3) The washing liquid and the liquid product in the reactor were vacuum filtered together. The filter residue was thoroughly washed with 50 ml of acetone to obtain the filtrate and the filter residue. The filter residue was dried at 105°C for more than 12 hours to obtain the solid product of the reaction. 150 ml of dichloromethane was added to the filtrate and the mixture was stirred and extracted. The filtrate was then poured into a separatory funnel for separation. The upper layer was an aqueous solution and the lower layer was a mixed solution of acetone, dichloromethane and oil.

[0078] (4) Under the conditions of water bath temperature of 50℃ and vacuum degree of 368kpa, the rotary evaporation time is 35min to remove the organic solvent in the oil phase mixed solution and obtain the oil phase.

[0079]

[0080] A comparison of Examples 1, 2, and 3 with Comparative Example 1 shows that when the reaction temperature is 300℃, CO2, compared to N2, significantly improves the oil-phase separation rate of rolling mill sludge during hydrothermal liquefaction. The oil-phase separation rate reaches its highest level when the initial CO2 pressure is 2 MPa, representing a 33.023% increase compared to Comparative Example 1. Furthermore, the lower heating value of the oil phase is highest when the initial CO2 pressure is 1 MPa, increasing by 7.341% compared to Comparative Example 1. Therefore, introducing CO2 as the reaction atmosphere during the hydrothermal liquefaction of rolling mill sludge can improve the oil phase recovery rate and calorific value.

[0081] As can be seen from the comparison of Examples 4 and 5 and Comparative Examples 2 and 3, when the reaction temperature is increased, even if the initial pressure of the reaction atmosphere is the same, the oil phase separation rate of the rolling mill sludge can be improved by 17.583% and 8.903% respectively compared with N2 as the reaction atmosphere and CO2 as the reaction atmosphere.

[0082] The comparisons between Examples 1, 2, 3, and Comparative Example 1, and between Examples 4, 5, and Comparative Examples 2 and 3, show that when the reaction temperature is 300°C, CO2 as the reaction atmosphere significantly improves the oil-middle phase separation rate and lower heating value of the rolling mill sludge. Therefore, at lower hydrothermal liquefaction temperatures, introducing CO2 as the reaction atmosphere into the high-pressure reactor and maintaining a certain initial pressure can further improve the oil-middle phase recovery rate and calorific value of the rolling mill sludge.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for CO2-promoted hydrothermal liquefaction, demulsification, and separation of rolling mill sludge, characterized in that, Includes the following steps: (1) Steel rolling sludge is a high-viscosity emulsion composed of oil, water and iron filings, containing 5~60wt% grease and 20~90wt% iron filings. Weigh the steel rolling sludge into a high-pressure reactor, add water, mix evenly, and then seal the high-pressure reactor. Open the air inlet valve of the high-pressure reactor, introduce sufficient carbon dioxide gas to expel the air in the reactor, maintain a certain initial pressure in the high-pressure reactor, and then close the air inlet valve. (2) Start the high-pressure reactor to carry out hydrothermal liquefaction reaction. The reaction temperature is 250~375℃. After the reaction is completed, turn on the cooling water to cool the high-pressure reactor. After the temperature and pressure are reduced, collect the liquid phase product in the high-pressure reactor and wash the high-pressure reactor body and the stirring paddle with acetone. (3) The washing liquid and the liquid product in the high-pressure reactor are vacuum filtered together. After washing the filter residue with acetone, the filtrate and filter residue are obtained. The filter residue is dried to obtain the solid product of the reaction. Dichloromethane is added to the filtrate and the mixture is stirred and extracted. The filtrate is then poured into a separatory funnel for separation. The upper layer is an aqueous solution and the lower layer is an oil-phase mixture of acetone and dichloromethane. (4) Rotary evaporation is carried out under the conditions of water bath temperature of 40-50℃ and vacuum degree of 300-700kpa to remove organic solvents from the oil phase mixture solution and obtain oil phase.

2. The method for CO2-promoted hydrothermal liquefaction, demulsification, and separation of rolling mill sludge according to claim 1, characterized in that, In step (1), the mass of the steel rolling sludge is 5-50% of the mass fraction of the mixture.

3. The method for CO2-promoted hydrothermal liquefaction, demulsification, and separation of rolling mill sludge according to claim 1, characterized in that, In step (1), the initial pressure inside the high-pressure reactor is 0-2 MPa.

4. The method for CO2-promoted hydrothermal liquefaction, demulsification, and separation of rolling mill sludge according to claim 1, characterized in that, In step (2), the stirring speed of the hydrothermal liquefaction reaction is 150~1500 r / min, and the reaction time is 15-60 min.

5. The method for CO2-promoted hydrothermal liquefaction, demulsification, and separation of rolling mill sludge according to claim 1, characterized in that, In step (2), the hydrothermal liquefaction reaction temperature is 300-350℃ and the reaction time is 30min.

6. The method for CO2-promoted hydrothermal liquefaction, demulsification, and separation of rolling mill sludge according to claim 1, characterized in that, In steps (2) and (3), the total amount of acetone used is 1-3 times the amount of water used.

7. The method for CO2-promoted hydrothermal liquefaction, demulsification, and separation of rolling mill sludge according to claim 1, characterized in that, In step (3), the amount of dichloromethane used is 2-3 times the amount of water used.

8. The method for CO2-promoted hydrothermal liquefaction, demulsification, and separation of rolling mill sludge according to claim 1, characterized in that, In step (4), the rotary evaporation time of the organic solvent is 30-45 min.

9. The method for CO2-promoted hydrothermal liquefaction, demulsification, and separation of rolling mill sludge according to claim 1, characterized in that, The filter residue is dried at 105℃ for more than 12 hours.

10. The method for CO2-promoted hydrothermal liquefaction, demulsification, and separation of rolling mill sludge according to claim 1, characterized in that, The cooling and depressurization refers to: after the temperature inside the reactor drops to room temperature, opening the exhaust valve of the high-pressure reactor to reduce the pressure inside the reactor to atmospheric pressure.

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