Process for the purification and recovery of used lubricating oils

Abstract

The application discloses a refining and recycling method of waste lubricating oil, and relates to the technical field of lubricating oil recycling. The method comprises the following steps: firstly, ultrasonic circulation pretreatment is carried out on the waste lubricating oil; secondly, an oil-wet type sulfydryl functionalized cyclodextrin composite material is added for reaction, and the reaction is combined with heat filtration of amino diatomite loaded with nano zinc oxide; thirdly, the filtrate is subjected to hydrogen treatment through a falling film type plasma activation and a magnetic core-shell catalyst; and finally, refined lubricating oil is obtained through vacuum distillation and molecular distillation purification. The method realizes deep removal of colloid and heavy metals, effectively prevents catalyst poisoning, solves the solid-liquid separation problem, and significantly improves the purity and quality of the regenerated oil.

Description

Technical Field

[0001] This invention relates to the field of lubricating oil recycling technology, specifically a method for refining and recycling waste lubricating oil. Background Technology

[0002] Lubricating oil, a key component in industrial production and transportation, is widely used in various mechanical equipment such as engines, gearboxes, and hydraulic systems. Its core function is to reduce friction and wear by forming an oil film, achieve heat dissipation and cooling, prevent rust, and seal, ensuring stable and efficient equipment operation. With the acceleration of global industrialization and the booming development of the transportation industry, the market demand for lubricating oil continues to rise, accompanied by a year-on-year increase in the amount of waste lubricating oil generated. Waste lubricating oil is not entirely unusable waste; its main components are still incompletely degraded base oils. However, during use, it undergoes a series of chemical reactions such as oxidation, cracking, and polymerization due to high-temperature operating conditions and mechanical shearing, generating harmful substances such as gums, asphaltenes, carboxylic acids, and polycyclic aromatic hydrocarbons. Simultaneously, solid impurities such as metal shavings and dust generated during the operation of mechanical equipment, as well as mixed moisture and fuel residues, intertwine with the deterioration products, making the composition of waste lubricating oil extremely complex. If waste lubricating oil is disposed of indiscriminately through dumping or open burning, it will not only cause a huge waste of petroleum resources but also lead to serious ecological and environmental problems. Heavy metal ions in waste lubricating oil can seep into the soil and groundwater, damaging soil structure, polluting drinking water sources, and threatening the growth of plants and animals and human health. During the incineration process, organic matter such as gum and asphalt releases strong carcinogens such as polycyclic aromatic hydrocarbons, exacerbating air pollution.

[0003] The efficient refining and recycling of waste lubricating oil has become a critical industry issue that urgently needs to be addressed. The market has placed higher demands on the purity and performance of recycled lubricating oil, and some high-end machinery even requires recycled oil to meet quality standards comparable to new oil. Summary of the Invention

[0004] The purpose of this invention is to provide a method for refining and recycling waste lubricating oil to solve the technical problems mentioned in the background.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for refining and recycling waste lubricating oil includes the following steps:

[0007] (1) The activated carbon powder and attapulgite clay were acid-washed and activated, and then dried to obtain the activated carrier;

[0008] (2) The activated carrier was dispersed in an ethanol-water mixed solvent, and β-cyclodextrin and mercaptopropyltrimethoxysilane were added. The reaction was first hydrolyzed and then refluxed. The reaction product was washed, dried and pulverized to obtain a lipophilic mercaptofunctionalized cyclodextrin composite material.

[0009] (3) Heat the waste lubricating oil, add demulsifier, and perform pipeline ultrasonic circulation treatment. The treated oil is then centrifuged and filtered to obtain pretreated oil.

[0010] (4) After calcination pretreatment, diatomaceous earth is dispersed in water, zinc source compound is added and the system is adjusted to alkalinity to generate precipitate in situ. After solid-liquid separation, washing and calcination, diatomaceous earth carrier loaded with nano zinc oxide is obtained. Then the carrier is dispersed in alcohol solvent, and aminosilane coupling agent is added to carry out surface functionalization modification reaction. The reaction product is separated, washed and dried to obtain amino diatomaceous earth loaded with nano zinc oxide.

[0011] (5) Under an inert atmosphere, the pretreated oil is heated and the lipophilic thiol-functionalized cyclodextrin composite material is added to react. Before the reaction is completed, amino-modified diatomaceous earth-supported nano zinc oxide is added, and then hot filtration is performed to obtain oil a.

[0012] (6) The oil a is first subjected to falling film dielectric barrier discharge plasma treatment, and then catalytically hydrogenated with hydrogen in the presence of a magnetic core-shell catalyst. After the reaction, the catalyst is separated by magnetic force and filtered to obtain oil b.

[0013] (7) First, the oil b is subjected to vacuum distillation to remove light components, and then molecular distillation is performed to collect the light phase fraction to obtain refined lubricating oil.

[0014] In this invention, purity is improved through the structural characteristics of a lipophilic thiol-functionalized cyclodextrin / carbon / earth composite material. This material, modified with KH-590 silane coupling agent, exhibits excellent lipophilic and hydrophobic properties, allowing it to disperse uniformly in the oil as a sol, avoiding the incomplete purification problems caused by the aggregation and settling of traditional hydrophilic adsorbents. The β-cyclodextrin cavities in the material precisely encapsulate polycyclic aromatic hydrocarbons and colloidal impurities in waste lubricating oil through host-guest molecule recognition. Simultaneously, the high-density thiol groups on the material surface can coordinate with dissolved heavy metal ions such as lead, copper, and cadmium in the oil, generating stable surface complexes. Finally, the adsorbed and chelated impurities are discharged with the filter cake through thermal filtration. This process directly removes over 92% of the colloidal macromolecular impurities from the oil, reducing the heavy metal content to below 5 ppm, significantly reducing the interference of impurities on oil purity, initially improving lubricating oil purity, and eliminating the need for additional insoluble chelating agents, thus avoiding secondary pollution. On the other hand, a synergistic process of plasma activation and catalytic hydrogenation is employed to further enhance purity. A falling film dielectric barrier discharge reactor allows the oil to flow along the pipe wall in a 0.5mm thin film, ensuring that high-energy electrons and free radicals from the plasma penetrate the oil layer, efficiently breaking the C=C double bonds of residual unsaturated hydrocarbons and the C / C bonds of oxides, forming active reaction sites. Then, a magnetic core-shell catalyst is added, utilizing the Ni-Pd bimetallic synergistic effect to completely hydrogenate and saturate the activated unsaturated hydrocarbons under hydrogen pressure, while simultaneously reducing oxides to hydrocarbons. The magnetic core design of the catalyst achieves high catalyst recovery, solving the problem of separating non-magnetic catalysts from viscous oils. This process not only reduces the oil's acid value to below 0.02mgKOH / g but also extends the rotating oxygen bomb test time, significantly improving the oil's oxidation stability. Simultaneously, it thoroughly removes residual polar impurities and unsaturated components. After subsequent molecular distillation purification, a high-purity regenerated lubricating oil is finally obtained.

[0015] Preferably, in step (1), the mass ratio of activated carbon powder to attapulgite clay is 1:(0.5~1.5).

[0016] Preferably, in step (2), the mass ratio of the activated carrier to β-cyclodextrin is 80:(15-20).

[0017] Preferably, in step (2), the mass ratio of the activated carrier to mercaptopropyltrimethoxysilane is 80:(5-10).

[0018] Preferably, in step (3), a polyether-type demulsifier is selected;

[0019] The amount of demulsifier added is 0.2 to 0.6 wt% of the waste lubricating oil.

[0020] Preferably, in step (5), the amount of lipophilic thiol-functionalized cyclodextrin composite material added is 2 to 5 wt% of the pretreated oil.

[0021] Preferably, in step (5), the amount of aminated diatomaceous earth-supported nano zinc oxide added is 0.5 to 2.0 wt% of the pretreated oil.

[0022] This invention discovered in experiments that while lipophilic thiol-functionalized complexes can deeply remove heavy metals through adsorption-chelation mechanisms, trace amounts of free organic sulfur or incompletely hydrolyzed silane molecules inevitably dissolve in the high-temperature hot oil environment. These dissolved sulfur molecules, after entering subsequent processes with the oil, rapidly undergo strong coordination adsorption with the active centers of expensive nickel / palladium catalysts, leading to irreversible catalyst deactivation due to sulfur poisoning. Simultaneously, the lipophilic modified adsorbent exhibits a highly dispersed submicron-sized sol-like structure, easily penetrating traditional filter cloths to form colloids, causing physical blockage of the downstream plasma reactor. To address this problem, this invention first utilizes the abundant micro / mesopores of diatomaceous earth as a confined reactor. Through precursor impregnation and high-temperature calcination, highly active nano-zinc oxide crystals are forced to grow in situ on the pore walls and firmly sinter, solving both the nanomaterial aggregation problem and preventing the loss of active components. Under low-temperature reflux conditions, chemical modification with KH-550 coupling agent is used to construct a positively charged amino functional layer on its surface. This structure achieves a triple synergistic purification function of chemical capture, electrostatic flocculation, and physical interception: the highly dispersed nano-zinc oxide in the pores utilizes its large specific surface area and forced wall contact effect to instantly convert trace dissolved sulfur in the flowing oil into insoluble solid zinc sulfide (chemical sacrificial capture); the amino groups on the surface utilize the electrostatic attraction generated by the positive Zeta potential to target and adsorb negatively charged micro-adsorbent colloids (charge adsorption); finally, relying on the rigid support of the diatomaceous earth framework, all reaction products and impurities are completely trapped inside the filter cake (physical deep sieving), thus ensuring further improvement in the purity of the regenerated oil and the long-term high-activity operation of the magnetic catalyst.

[0023] Preferably, in step (6), the preparation method of the magnetic core-shell catalyst includes the following steps:

[0024] Iron source was dissolved in ethylene glycol solvent, sodium acetate and dispersant were added, and magnetic microspheres were obtained after solvothermal reaction.

[0025] Magnetic microspheres were dispersed in an alcohol-water mixed solvent, and a silicon source was added in the presence of ammonia to carry out a hydrolysis reaction, thereby coating the surface of the magnetic microspheres with a silica shell to obtain a magnetic composite material.

[0026] The magnetic composite material was dispersed in an alcohol solvent, and an aminosilane coupling agent was added to react and modify the surface of the composite material with amino functional groups to obtain an amino-modified magnetic composite material.

[0027] A mixed solution containing nickel and palladium salts is contacted with an aminated modified magnetic composite material to adsorb metal ions. Then, a reducing agent is added for liquid-phase reduction to reduce the metal ions into nano-metal particles, which are then loaded onto a support. After magnetic separation, washing, and drying, a magnetic core-shell catalyst is obtained.

[0028] Preferably, in step (6), the amount of magnetic core-shell catalyst added is 1 to 3 wt% of oil a.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] 1. By simultaneously adsorbing heavy metals and colloidal impurities through lipophilic thiol-functionalized cyclodextrin composite materials, the purity of the oil is significantly improved without the need for additional chemical agents that may cause secondary pollution.

[0031] 2. The combined process of plasma activation and catalytic hydrogenation effectively breaks down unsaturated hydrocarbons and saturates them with hydrogen, significantly reducing acid value and enhancing oxidation stability, making the recycled oil products close to the standards of new oil.

[0032] 3. The diatomaceous earth-based composite material, which combines chemical capture, electrostatic flocculation, and physical interception, can effectively eliminate trace sulfur impurities in oil (preventing sulfur poisoning and deactivation of downstream precious metal catalysts) and efficiently intercept submicron-sized colloids (avoiding equipment blockage). This ensures the long-term stable operation of the core catalytic process while further purifying the oil. Attached Figure Description

[0033] Figure 1 This is a SEM image of the lipophilic thiol-functionalized cyclodextrin composite material prepared in Example 1 of the present invention.

[0034] Figure 2 This is a SEM image of aminated diatomaceous earth loaded with nano-zinc oxide prepared in Example 1 of the present invention.

[0035] Figure 3 This is a SEM image of the magnetic core-shell catalyst prepared in Example 1 of the present invention. Detailed Implementation

[0036] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0037] Example 1

[0038] A method for refining and recycling waste lubricating oil includes the following steps:

[0039] Step 1: Mix 40 parts by weight of 200-mesh activated carbon powder and 50 parts by weight of attapulgite clay evenly, add 400 parts by weight of 5% hydrochloric acid solution, stir and soak at room temperature for 4 hours to activate, then filter and wash repeatedly with deionized water until the filtrate is neutral, place the filter cake in an oven at 105℃ and dry to constant weight to obtain 80 parts by weight of activated carrier.

[0040] Step 2: Disperse 80 parts by weight of the activated carrier in 400 parts by weight of an ethanol-water mixed solvent with a volume ratio of 9:1 and mechanically stir to form a suspension; add 18 parts by weight of β-cyclodextrin and 9 parts by weight of mercaptopropyltrimethoxysilane (KH-590) in sequence, first stir at 50°C to carry out hydrolysis reaction for 2 h, then heat the system to 85°C and reflux for 6 h; after the reaction is completed, the product is washed 3 times with anhydrous ethanol, dried in a vacuum drying oven at 120°C for 2 h, and finally pulverized by an air jet mill to obtain a lipophilic mercaptofunctionalized cyclodextrin composite material.

[0041] Step 3: Pump waste lubricating oil into a pretreatment vessel with a heating jacket and heat it to 80°C. Add 0.5 wt% polyether demulsifier to the waste lubricating oil. Turn on the pipeline high-power ultrasonic circulation system, set the ultrasonic frequency to 20 kHz and the total power to 24 kW, and circulate the oil in the pipeline for 2 hours. After treatment, send the oil to a disc centrifuge with a speed of 6000 r / min to remove the settled water and large particulate impurities. The supernatant is further filtered through a ceramic membrane with a pore size of 1 μm to obtain the pretreated oil.

[0042] Step 4: 100 parts by weight of diatomaceous earth were calcined in a muffle furnace at 450℃ for 2 hours for pretreatment. After cooling, the precipitate was dispersed in 400 parts by weight of deionized water. 15 parts by weight of zinc acetate dihydrate were added and stirred for 1 hour to allow zinc ions to wet the pores. Then, sodium hydroxide solution was slowly added dropwise to adjust the pH to 10, resulting in a precipitate. After filtration and washing with water, the solid was placed in a muffle furnace and calcined at 350℃ for 2 hours to obtain a diatomaceous earth carrier loaded with nano-zinc oxide. The carrier was dispersed in 500 parts by weight of 95% ethanol solution, and 3 parts by weight of γ-aminopropyltriethoxysilane (KH-550) were added. The mixture was heated to 75℃ and refluxed for 4 hours. The reaction product was filtered and washed twice with anhydrous ethanol, dried in a forced-air drying oven at 105℃ for 2 hours, and then ground to obtain aminated diatomaceous earth loaded with nano-zinc oxide.

[0043] Step 5: Under the protection of inert nitrogen gas, the pretreated oil obtained in step (3) is heated to 140°C, and 4 wt% of the lipophilic thiol-functionalized cyclodextrin composite material of the pretreated oil is added. The stirring rate is adjusted to 300 r / min, and the reaction is carried out at a constant temperature for 3.5 h. 20 min before the end of the reaction, 1.5 wt% of the aminated diatomaceous earth-supported nano zinc oxide of the pretreated oil is added to the system, and the mixture is stirred and dispersed. After the reaction is completed, the high-temperature suspension is pumped into a closed plate and frame filter press lined with 300-mesh filter cloth for hot filtration separation to obtain oil a.

[0044] Step 6: Dissolve 5 parts by weight of ferric chloride hexahydrate in 100 parts by weight of ethylene glycol, add 15 parts by weight of anhydrous sodium acetate and 2 parts by weight of polyethylene glycol, and react in a high-pressure reactor at 200℃ for 10 h to obtain magnetic microspheres; disperse 10 parts by weight of magnetic microspheres in 200 parts by weight of ethanol-water solution, and add 3 parts by weight of tetraethyl orthosilicate dropwise in the presence of 5 parts by weight of concentrated ammonia water for 6 h to coat a silica shell; disperse the obtained magnetic composite material in 200 parts by weight of ethanol, add 2 parts by weight of KH-550 and reflux for 4 h to modify the amino group; finally, impregnate it in a mixed solution containing 0.7 parts by weight of nickel nitrate and 0.05 parts by weight of palladium dichloride dissolved with dilute hydrochloric acid, reduce it by adding sodium borohydride solution dropwise under ice bath, and obtain a magnetic core-shell catalyst after magnetic separation, washing and drying at 60℃.

[0045] Oil solution a was fed into a falling film dielectric barrier discharge plasma reactor and circulated through the discharge zone three times in an argon atmosphere and at a discharge voltage of 12 kV. Then, the oil solution was fed into a hydrogenation reactor and 2.5 wt% of a magnetic core-shell catalyst was added. The reaction was carried out at 230 °C and 3.0 MPa hydrogen pressure for 4 hours. After the reaction was completed, the catalyst was separated by an electromagnetic chuck and filtered through a 0.1 μm precision filter to obtain oil solution b.

[0046] Step 7: Send oil b into a vacuum flash distillation tower to remove solvent and light components at 180℃ and 3kPa. The bottom material is sent into a multi-stage short-path molecular distillation unit. Set the evaporation surface temperature to 230℃, the scraper speed to 350r / min, and the ultimate vacuum to 2Pa. Collect the light phase fraction flowing out of the condensation surface and the heavy phase residue flowing down the wall. The obtained light phase fraction is the refined lubricating oil.

[0047] Example 2

[0048] A method for refining and recycling waste lubricating oil includes the following steps:

[0049] Step 1: Mix 40 parts by weight of 200-mesh activated carbon powder and 30 parts by weight of attapulgite clay evenly, add 400 parts by weight of 5% hydrochloric acid solution, stir and soak at room temperature for 4 hours to activate, then filter and wash repeatedly with deionized water until the filtrate is neutral, place the filter cake in an oven at 105℃ and dry to constant weight to obtain 80 parts by weight of activated carrier.

[0050] Step 2: 80 parts by weight of the activated carrier were dispersed in 400 parts by weight of an ethanol-water mixed solvent with a volume ratio of 9:1 and mechanically stirred to form a suspension; 16 parts by weight of β-cyclodextrin and 6 parts by weight of mercaptopropyltrimethoxysilane (KH-590) were added sequentially, and the mixture was first stirred at 50°C for 2 hours for hydrolysis, and then the system was heated to 85°C for reflux reaction for 6 hours; after the reaction was completed, the product was washed three times with anhydrous ethanol, dried in a vacuum drying oven at 120°C for 2 hours, and finally pulverized by an air jet mill to obtain an oleophilic mercaptofunctionalized cyclodextrin composite material.

[0051] Step 3: Pump waste lubricating oil into a pretreatment vessel with a heating jacket and heat it to 80°C. Add 0.3wt% polyether demulsifier to the waste lubricating oil. Turn on the pipeline high-power ultrasonic circulation system, set the ultrasonic frequency to 20kHz and the total power to 24kW, and circulate the oil in the pipeline for 2 hours. After treatment, send the oil to a disc centrifuge with a speed of 6000r / min to remove the settled water and large particulate impurities. The supernatant is further filtered through a ceramic membrane with a pore size of 1μm to obtain the pretreated oil.

[0052] Step 4: 100 parts by weight of diatomaceous earth were calcined in a muffle furnace at 450℃ for 2 hours for pretreatment. After cooling, the precipitate was dispersed in 400 parts by weight of deionized water. 15 parts by weight of zinc acetate dihydrate were added and stirred for 1 hour to allow zinc ions to wet the pores. Then, sodium hydroxide solution was slowly added dropwise to adjust the pH to 10, resulting in a precipitate. After filtration and washing with water, the solid was placed in a muffle furnace and calcined at 350℃ for 2 hours to obtain a diatomaceous earth carrier loaded with nano-zinc oxide. The carrier was dispersed in 500 parts by weight of 95% ethanol solution, and 3 parts by weight of γ-aminopropyltriethoxysilane (KH-550) were added. The mixture was heated to 75℃ and refluxed for 4 hours. The reaction product was filtered and washed twice with anhydrous ethanol, dried in a forced-air drying oven at 105℃ for 2 hours, and then ground to obtain aminated diatomaceous earth loaded with nano-zinc oxide.

[0053] Step 5: Under the protection of inert nitrogen gas, the pretreated oil obtained in step (3) is heated to 140°C, and 3wt% of the lipophilic thiol-functionalized cyclodextrin composite material of the pretreated oil is added. The stirring rate is adjusted to 300 r / min, and the reaction is carried out at a constant temperature for 3.5 h. 20 min before the end of the reaction, 0.8wt% of the aminated diatomaceous earth-supported nano zinc oxide of the pretreated oil is added to the system, and the mixture is stirred and dispersed. After the reaction is completed, the high-temperature suspension is pumped into a closed plate and frame filter press lined with 300-mesh filter cloth for hot filtration separation to obtain oil a.

[0054] Step 6: Dissolve 5 parts by weight of ferric chloride hexahydrate in 100 parts by weight of ethylene glycol, add 15 parts by weight of anhydrous sodium acetate and 2 parts by weight of polyethylene glycol, and react in a high-pressure reactor at 200℃ for 10 h to obtain magnetic microspheres; disperse 10 parts by weight of magnetic microspheres in 200 parts by weight of ethanol-water solution, and add 3 parts by weight of tetraethyl orthosilicate dropwise in the presence of 5 parts by weight of concentrated ammonia water for 6 h to coat a silica shell; disperse the obtained magnetic composite material in 200 parts by weight of ethanol, add 2 parts by weight of KH-550 and reflux for 4 h to modify the amino group; finally, impregnate it in a mixed solution containing 0.7 parts by weight of nickel nitrate and 0.05 parts by weight of palladium dichloride dissolved with dilute hydrochloric acid, reduce it by adding sodium borohydride solution dropwise under ice bath, and obtain a magnetic core-shell catalyst after magnetic separation, washing and drying at 60℃.

[0055] Oil solution a was fed into a falling film dielectric barrier discharge plasma reactor and circulated through the discharge zone three times in an argon atmosphere and at a discharge voltage of 12 kV. Then, the oil solution was fed into a hydrogenation reactor and 1.5 wt% of a magnetic core-shell catalyst was added. The reaction was carried out at 230 °C and 3.0 MPa hydrogen pressure for 4 hours. After the reaction was completed, the catalyst was separated by an electromagnetic chuck and filtered through a 0.1 μm precision filter to obtain oil solution b.

[0056] Step 7: Send oil b into a vacuum flash distillation tower to remove solvent and light components at 180℃ and 3kPa. The bottom material is sent into a multi-stage short-path molecular distillation unit. Set the evaporation surface temperature to 230℃, the scraper speed to 350r / min, and the ultimate vacuum to 2Pa. Collect the light phase fraction flowing out of the condensation surface and the heavy phase residue flowing down the wall. The obtained light phase fraction is the refined lubricating oil.

[0057] Example 3

[0058] A method for refining and recycling waste lubricating oil includes the following steps:

[0059] Step 1: Mix 40 parts by weight of 200-mesh activated carbon powder and 40 parts by weight of attapulgite clay evenly, add 400 parts by weight of 5% hydrochloric acid solution, stir and soak at room temperature for 4 hours to activate, then filter and wash repeatedly with deionized water until the filtrate is neutral, place the filter cake in an oven at 105℃ and dry to constant weight to obtain 80 parts by weight of activated carrier.

[0060] Step 2: 80 parts by weight of the activated carrier were dispersed in 400 parts by weight of an ethanol-water mixed solvent with a volume ratio of 9:1 and mechanically stirred to form a suspension; 17 parts by weight of β-cyclodextrin and 7 parts by weight of mercaptopropyltrimethoxysilane (KH-590) were added sequentially, and the mixture was first stirred at 50°C for 2 hours for hydrolysis, and then the system was heated to 85°C for reflux reaction for 6 hours; after the reaction was completed, the product was washed three times with anhydrous ethanol, dried in a vacuum drying oven at 120°C for 2 hours, and finally pulverized by an air jet mill to obtain an oleophilic mercaptofunctionalized cyclodextrin composite material.

[0061] Step 3: Pump waste lubricating oil into a pretreatment vessel with a heating jacket and heat it to 80°C. Add 0.4 wt% polyether demulsifier to the waste lubricating oil. Turn on the pipeline high-power ultrasonic circulation system, set the ultrasonic frequency to 20 kHz and the total power to 24 kW, and circulate the oil in the pipeline for 2 hours. After treatment, send the oil to a disc centrifuge with a speed of 6000 r / min to remove the settled water and large particulate impurities. The supernatant is further filtered through a ceramic membrane with a pore size of 1 μm to obtain the pretreated oil.

[0062] Step 4: 100 parts by weight of diatomaceous earth were calcined in a muffle furnace at 450℃ for 2 hours for pretreatment. After cooling, the precipitate was dispersed in 400 parts by weight of deionized water. 15 parts by weight of zinc acetate dihydrate were added and stirred for 1 hour to allow zinc ions to wet the pores. Then, sodium hydroxide solution was slowly added dropwise to adjust the pH to 10, resulting in a precipitate. After filtration and washing with water, the solid was placed in a muffle furnace and calcined at 350℃ for 2 hours to obtain a diatomaceous earth carrier loaded with nano-zinc oxide. The carrier was dispersed in 500 parts by weight of 95% ethanol solution, and 3 parts by weight of γ-aminopropyltriethoxysilane (KH-550) were added. The mixture was heated to 75℃ and refluxed for 4 hours. The reaction product was filtered and washed twice with anhydrous ethanol, dried in a forced-air drying oven at 105℃ for 2 hours, and then ground to obtain aminated diatomaceous earth loaded with nano-zinc oxide.

[0063] Step 5: Under the protection of inert nitrogen gas, the pretreated oil obtained in step (3) is heated to 140°C, and 3.5 wt% of the lipophilic thiol-functionalized cyclodextrin composite material of the pretreated oil is added. The stirring rate is adjusted to 300 r / min, and the reaction is carried out at a constant temperature for 3.5 h. 20 min before the end of the reaction, 1.0 wt% of the amino-modified diatomaceous earth-supported nano zinc oxide of the pretreated oil is added to the system, and the mixture is stirred and dispersed. After the reaction is completed, the high-temperature suspension is pumped into a closed plate and frame filter press lined with 300-mesh filter cloth for hot filtration separation to obtain oil a.

[0064] Step 6: Dissolve 5 parts by weight of ferric chloride hexahydrate in 100 parts by weight of ethylene glycol, add 15 parts by weight of anhydrous sodium acetate and 2 parts by weight of polyethylene glycol, and react in a high-pressure reactor at 200℃ for 10 h to obtain magnetic microspheres; disperse 10 parts by weight of magnetic microspheres in 200 parts by weight of ethanol-water solution, and add 3 parts by weight of tetraethyl orthosilicate dropwise in the presence of 5 parts by weight of concentrated ammonia water for 6 h to coat a silica shell; disperse the obtained magnetic composite material in 200 parts by weight of ethanol, add 2 parts by weight of KH-550 and reflux for 4 h to modify the amino group; finally, impregnate it in a mixed solution containing 0.7 parts by weight of nickel nitrate and 0.05 parts by weight of palladium dichloride dissolved with dilute hydrochloric acid, reduce it by adding sodium borohydride solution dropwise under ice bath, and obtain a magnetic core-shell catalyst after magnetic separation, washing and drying at 60℃.

[0065] Oil solution a was fed into a falling film dielectric barrier discharge plasma reactor and circulated through the discharge zone three times in an argon atmosphere and at a discharge voltage of 12 kV. Then, the oil solution was fed into a hydrogenation reactor and 2 wt% of a magnetic core-shell catalyst was added. The reaction was carried out at 230 °C and 3.0 MPa hydrogen pressure for 4 hours. After the reaction was completed, the catalyst was separated by an electromagnetic chuck and filtered through a 0.1 μm precision filter to obtain oil solution b.

[0066] Step 7: Send oil b into a vacuum flash distillation tower to remove solvent and light components at 180℃ and 3kPa. The bottom material is sent into a multi-stage short-path molecular distillation unit. Set the evaporation surface temperature to 230℃, the scraper speed to 350r / min, and the ultimate vacuum to 2Pa. Collect the light phase fraction flowing out of the condensation surface and the heavy phase residue flowing down the wall. The obtained light phase fraction is the refined lubricating oil.

[0067] Example 4

[0068] A method for refining and recycling waste lubricating oil includes the following steps:

[0069] Step 1: Mix 40 parts by weight of 200-mesh activated carbon powder and 60 parts by weight of attapulgite clay evenly, add 400 parts by weight of 5% hydrochloric acid solution, stir and soak at room temperature for 4 hours to activate, then filter and wash repeatedly with deionized water until the filtrate is neutral, place the filter cake in an oven at 105℃ and dry to constant weight to obtain 80 parts by weight of activated carrier.

[0070] Step 2: 80 parts by weight of the activated carrier were dispersed in 400 parts by weight of an ethanol-water mixed solvent with a volume ratio of 9:1 and mechanically stirred to form a suspension; 20 parts by weight of β-cyclodextrin and 10 parts by weight of mercaptopropyltrimethoxysilane (KH-590) were added sequentially, and the mixture was first stirred at 50°C for 2 hours for hydrolysis, and then the system was heated to 85°C for reflux reaction for 6 hours; after the reaction was completed, the product was washed three times with anhydrous ethanol, dried in a vacuum drying oven at 120°C for 2 hours, and finally pulverized by an air jet mill to obtain an oleophilic mercaptofunctionalized cyclodextrin composite material.

[0071] Step 3: Pump waste lubricating oil into a pretreatment vessel with a heating jacket and heat it to 80°C. Add 0.6 wt% polyether demulsifier to the waste lubricating oil. Turn on the pipeline high-power ultrasonic circulation system, set the ultrasonic frequency to 20 kHz and the total power to 24 kW, and circulate the oil in the pipeline for 2 hours. After treatment, send the oil to a disc centrifuge with a speed of 6000 r / min to remove the settled water and large particulate impurities. The supernatant is further filtered through a ceramic membrane with a pore size of 1 μm to obtain the pretreated oil.

[0072] Step 4: 100 parts by weight of diatomaceous earth were calcined in a muffle furnace at 450℃ for 2 hours for pretreatment. After cooling, the precipitate was dispersed in 400 parts by weight of deionized water. 15 parts by weight of zinc acetate dihydrate were added and stirred for 1 hour to allow zinc ions to wet the pores. Then, sodium hydroxide solution was slowly added dropwise to adjust the pH to 10, resulting in a precipitate. After filtration and washing with water, the solid was placed in a muffle furnace and calcined at 350℃ for 2 hours to obtain a diatomaceous earth carrier loaded with nano-zinc oxide. The carrier was dispersed in 500 parts by weight of 95% ethanol solution, and 3 parts by weight of γ-aminopropyltriethoxysilane (KH-550) were added. The mixture was heated to 75℃ and refluxed for 4 hours. The reaction product was filtered and washed twice with anhydrous ethanol, dried in a forced-air drying oven at 105℃ for 2 hours, and then ground to obtain aminated diatomaceous earth loaded with nano-zinc oxide.

[0073] Step 5: Under the protection of inert nitrogen gas, the pretreated oil obtained in step (3) is heated to 140°C, and 5 wt% of the lipophilic thiol-functionalized cyclodextrin composite material of the pretreated oil is added. The stirring rate is adjusted to 300 r / min, and the reaction is carried out at a constant temperature for 3.5 h. 20 min before the end of the reaction, 2.0 wt% of the aminated diatomaceous earth-supported nano zinc oxide of the pretreated oil is added to the system, and the mixture is stirred and dispersed. After the reaction is completed, the high-temperature suspension is pumped into a closed plate and frame filter press lined with 300-mesh filter cloth for hot filtration separation to obtain oil a.

[0074] Step 6: Dissolve 5 parts by weight of ferric chloride hexahydrate in 100 parts by weight of ethylene glycol, add 15 parts by weight of anhydrous sodium acetate and 2 parts by weight of polyethylene glycol, and react in a high-pressure reactor at 200℃ for 10 h to obtain magnetic microspheres; disperse 10 parts by weight of magnetic microspheres in 200 parts by weight of ethanol-water solution, and add 3 parts by weight of tetraethyl orthosilicate dropwise in the presence of 5 parts by weight of concentrated ammonia water for 6 h to coat a silica shell; disperse the obtained magnetic composite material in 200 parts by weight of ethanol, add 2 parts by weight of KH-550 and reflux for 4 h to modify the amino group; finally, impregnate it in a mixed solution containing 0.7 parts by weight of nickel nitrate and 0.05 parts by weight of palladium dichloride dissolved with dilute hydrochloric acid, reduce it by adding sodium borohydride solution dropwise under ice bath, and obtain a magnetic core-shell catalyst after magnetic separation, washing and drying at 60℃.

[0075] Oil solution a was fed into a falling film dielectric barrier discharge plasma reactor and circulated through the discharge zone three times in an argon atmosphere and at a discharge voltage of 12 kV. Then, the oil solution was fed into a hydrogenation reactor and 3 wt% of a magnetic core-shell catalyst was added. The reaction was carried out at 230 °C and 3.0 MPa hydrogen pressure for 4 hours. After the reaction was completed, the catalyst was separated by an electromagnetic chuck and filtered through a 0.1 μm precision filter to obtain oil solution b.

[0076] Step 7: Send oil b into a vacuum flash distillation tower to remove solvent and light components at 180℃ and 3kPa. The bottom material is sent into a multi-stage short-path molecular distillation unit. Set the evaporation surface temperature to 230℃, the scraper speed to 350r / min, and the ultimate vacuum to 2Pa. Collect the light phase fraction flowing out of the condensation surface and the heavy phase residue flowing down the wall. The obtained light phase fraction is the refined lubricating oil.

[0077] Example 5

[0078] A method for refining and recycling waste lubricating oil includes the following steps:

[0079] Step 1: Mix 40 parts by weight of 200-mesh activated carbon powder and 20 parts by weight of attapulgite clay evenly, add 400 parts by weight of 5% hydrochloric acid solution, stir and soak at room temperature for 4 hours to activate, then filter and wash repeatedly with deionized water until the filtrate is neutral, place the filter cake in an oven at 105℃ and dry to constant weight to obtain 80 parts by weight of activated carrier.

[0080] Step 2: 80 parts by weight of the activated carrier were dispersed in 400 parts by weight of an ethanol-water mixed solvent with a volume ratio of 9:1 and mechanically stirred to form a suspension; 15 parts by weight of β-cyclodextrin and 5 parts by weight of mercaptopropyltrimethoxysilane (KH-590) were added sequentially, and the mixture was first stirred at 50°C for 2 hours for hydrolysis, and then the system was heated to 85°C for reflux reaction for 6 hours; after the reaction was completed, the product was washed three times with anhydrous ethanol, dried in a vacuum drying oven at 120°C for 2 hours, and finally pulverized by an air jet mill to obtain an oleophilic mercaptofunctionalized cyclodextrin composite material.

[0081] Step 3: Pump waste lubricating oil into a pretreatment vessel with a heating jacket and heat it to 80°C. Add 0.2 wt% polyether demulsifier to the waste lubricating oil. Turn on the pipeline high-power ultrasonic circulation system, set the ultrasonic frequency to 20 kHz and the total power to 24 kW, and circulate the oil in the pipeline for 2 hours. After treatment, send the oil to a disc centrifuge with a speed of 6000 r / min to remove the settled water and large particulate impurities. The supernatant is further filtered through a ceramic membrane with a pore size of 1 μm to obtain the pretreated oil.

[0082] Step 4: 100 parts by weight of diatomaceous earth were calcined in a muffle furnace at 450℃ for 2 hours for pretreatment. After cooling, the precipitate was dispersed in 400 parts by weight of deionized water. 15 parts by weight of zinc acetate dihydrate were added and stirred for 1 hour to allow zinc ions to wet the pores. Then, sodium hydroxide solution was slowly added dropwise to adjust the pH to 10, resulting in a precipitate. After filtration and washing with water, the solid was placed in a muffle furnace and calcined at 350℃ for 2 hours to obtain a diatomaceous earth carrier loaded with nano-zinc oxide. The carrier was dispersed in 500 parts by weight of 95% ethanol solution, and 3 parts by weight of γ-aminopropyltriethoxysilane (KH-550) were added. The mixture was heated to 75℃ and refluxed for 4 hours. The reaction product was filtered and washed twice with anhydrous ethanol, dried in a forced-air drying oven at 105℃ for 2 hours, and then ground to obtain aminated diatomaceous earth loaded with nano-zinc oxide.

[0083] Step 5: Under the protection of inert nitrogen gas, the pretreated oil obtained in step (3) is heated to 140°C, and 2wt% of the lipophilic thiol-functionalized cyclodextrin composite material of the pretreated oil is added. The stirring rate is adjusted to 300 r / min, and the reaction is carried out at a constant temperature for 3.5 h. 20 min before the end of the reaction, 0.5wt% of the aminated diatomaceous earth-supported nano zinc oxide of the pretreated oil is added to the system, and the mixture is stirred and dispersed. After the reaction is completed, the high-temperature suspension is pumped into a closed plate and frame filter press lined with 300-mesh filter cloth for hot filtration separation to obtain oil a.

[0084] Step 6: Dissolve 5 parts by weight of ferric chloride hexahydrate in 100 parts by weight of ethylene glycol, add 15 parts by weight of anhydrous sodium acetate and 2 parts by weight of polyethylene glycol, and react in a high-pressure reactor at 200℃ for 10 h to obtain magnetic microspheres; disperse 10 parts by weight of magnetic microspheres in 200 parts by weight of ethanol-water solution, and add 3 parts by weight of tetraethyl orthosilicate dropwise in the presence of 5 parts by weight of concentrated ammonia water for 6 h to coat a silica shell; disperse the obtained magnetic composite material in 200 parts by weight of ethanol, add 2 parts by weight of KH-550 and reflux for 4 h to modify the amino group; finally, impregnate it in a mixed solution containing 0.7 parts by weight of nickel nitrate and 0.05 parts by weight of palladium dichloride dissolved with dilute hydrochloric acid, reduce it by adding sodium borohydride solution dropwise under ice bath, and obtain a magnetic core-shell catalyst after magnetic separation, washing and drying at 60℃.

[0085] Oil solution a was fed into a falling film dielectric barrier discharge plasma reactor and circulated through the discharge zone three times in an argon atmosphere and at a discharge voltage of 12 kV. Then, the oil solution was fed into a hydrogenation reactor and 1 wt% of a magnetic core-shell catalyst was added. The reaction was carried out at 230 °C and 3.0 MPa hydrogen pressure for 4 hours. After the reaction was completed, the catalyst was separated by an electromagnetic chuck and filtered through a 0.1 μm precision filter to obtain oil solution b.

[0086] Step 7: Send oil b into a vacuum flash distillation tower to remove solvent and light components at 180℃ and 3kPa. The bottom material is sent into a multi-stage short-path molecular distillation unit. Set the evaporation surface temperature to 230℃, the scraper speed to 350r / min, and the ultimate vacuum to 2Pa. Collect the light phase fraction flowing out of the condensation surface and the heavy phase residue flowing down the wall. The obtained light phase fraction is the refined lubricating oil.

[0087] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that step 2 is omitted, and the lipophilic thiol-functionalized cyclodextrin composite material in step 5 is replaced with an equal mass of the activated carrier prepared in step 1.

[0088] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that step 6 is omitted and oil b in step 7 is replaced with oil a.

[0089] Comparative Example 3: The difference between Comparative Example 3 and Example 1 is that step 4 is omitted and amino-modified diatomaceous earth-supported nano-zinc oxide is not added in step 5.

[0090] Comparative Example 4: The difference between Comparative Example 4 and Example 1 is that step 4 is omitted, and the aminated diatomaceous earth-supported nano zinc oxide that appears in step 5 is replaced with an equal mass of diatomaceous earth and zinc oxide mixture (mass ratio of the two is 1:1).

[0091] Performance testing:

[0092] 1. Lubricating oil purity test: According to GB / T 11132-2022 "Determination of Hydrocarbons in Liquid Petroleum Products - Fluorescent Indicator Adsorption Method", an appropriate amount of refined lubricating oil sample was weighed, a fluorescent indicator was added, and the sample was filled into an adsorption column. Different hydrocarbon components were separated by adsorption, and the content of each component was determined using a spectrophotometer. The percentage of base oil components was calculated as the lubricating oil purity. The test results are shown in Table 1.

[0093] 2. Heavy Metal Content Test: According to GB / T 17476-2023 "Determination of Additive Elements, Wear Metals and Contaminants in Used Lubricating Oils and Certain Elements in Base Oils by Inductively Coupled Plasma Atomic Emission Spectrometry", the samples were ashed and digested. The concentrations of heavy metal ions such as lead, copper, and cadmium were then determined using an inductively coupled plasma atomic emission spectrometer. The sum of the contents of each heavy metal was taken as the total heavy metal content. The test results are shown in Table 1.

[0094] 3. Acid Value Test: According to GB / T 7304-2014 "Determination of Acid Value of Petroleum Products - Potentiometric Titration Method", the refined lubricating oil sample was dissolved in a toluene-isopropanol mixed solution. Potentiometric titration was then performed using a potassium hydroxide-isopropanol standard solution. The volume of standard solution consumed at the titration endpoint was recorded, and the acid value of the lubricating oil was calculated in mgKOH / g. The test results are shown in Table 1.

[0095] 4. Rotating Oxygen Bomb Test: According to GB / T 12581-2006 "Determination of Oxidation Characteristics of Mineral Oils with Inhibitors", the refined lubricating oil sample was placed in an oxygen bomb, a copper catalyst coil was added, and oxygen was introduced to a pressure of 620 kPa. The oxygen bomb was placed in a constant temperature bath at 150°C and kept rotating. The time required for the pressure inside the oxygen bomb to drop by 175 kPa was recorded, which is the rotating oxygen bomb test duration. The test results are shown in Table 1.

[0096] 5. Kinematic Viscosity Test: According to GB / T 265-1988 "Determination of Kinematic Viscosity and Calculation of Dynamic Viscosity of Petroleum Products", the refined lubricating oil sample is placed in a capillary viscometer and kept at a constant temperature of 100℃. The time required for the sample to flow through a specified volume in the capillary is measured. The kinematic viscosity is calculated using the viscometer constant, and the unit is mm. 2 / s. The test results are shown in Table 1.

[0097] 6. Colorimetric Value Test: In accordance with GB / T 6540-2025 "Determination of Color of Petroleum Products", a Cépotentiometer was used. The refined lubricating oil sample was placed in a colorimetric tube and visually compared with the standard color scale to determine the Cépotenti value of the sample. The test results are shown in Table 1.

[0098] Table 1:

[0099]

[0100] The lubricating oils in Examples 1-5 all achieved a purity of over 99.80% (the highest being 99.88% in Example 4), while the purity of Comparative Example 1 (omitting the lipophilic thiol-functionalized cyclodextrin composite material) was only 92.16%, and the purity of Comparative Example 2 (omitting the plasma-catalytic hydrogenation step) was 95.53%. This difference confirms the synergistic effect of lipophilic supramolecular adsorption, chelation, plasma activation, and catalytic hydrogenation in the technical solution: the lipophilic composite material initially improves purity by encapsulating gums through cyclodextrin cavities and chelating impurities with thiol groups; the subsequent plasma-hydrogenation step deeply decomposes oxides and unsaturated hydrocarbons, ultimately achieving high purity retention of the base oil components.

[0101] The total heavy metal content in all examples was controlled to be below 1.7 ppm (as low as 0.8 ppm in Example 4), while the heavy metal content in Comparative Example 1 (using a common activated carrier instead of the oleophilic composite material) was as high as 45.2 ppm.

[0102] This is because the thiol group of the lipophilic thiol functionalized cyclodextrin composite material in the technical solution can form a stable coordination complex with heavy metal ions, thereby achieving directional removal; while the ordinary activated carrier in Comparative Example 1 only has physical adsorption capacity and cannot efficiently capture dissolved heavy metals.

[0103] The acid values ​​of all examples were below 0.014 mg KOH / g (as low as 0.008 mg KOH / g in Example 4), while the acid value of Comparative Example 2 (omitting the plasma-catalytic hydrogenation step) reached 0.153 mg KOH / g. The core reason for the difference in acid values ​​is that the examples used falling film plasma to break down the functional groups of oxides and catalytic hydrogenation to reduce acidic carboxylic acids to hydrocarbons; while Comparative Example 2 did not perform this step, and the residual deteriorated carboxylic acid products in the waste oil directly led to a higher acid value.

[0104] The rotating oxygen bomb test duration in all examples exceeded 228 minutes (Example 4 reached 238 minutes), while Comparative Example 2 (without hydrogenation step) only took 56 minutes. This indicator reflects the anti-oxidation performance of the lubricating oil: the catalytic hydrogenation step in the examples completely saturates the unsaturated hydrocarbons, eliminating easily oxidized active sites; while Comparative Example 2 has a large amount of residual unsaturated hydrocarbons, which are rapidly oxidized in a high-temperature and aerobic environment, resulting in a significant reduction in test duration.

[0105] The color intensity of the examples all reached +27 to +30, which is considered a water-white and transparent level; the color intensity of Comparative Example 1 (non-oleophilic composite material) was only +10, and the color was darker. This result corresponds to the inclusion and removal of gums and asphaltenes by the oleophilic composite material in the technical solution, as well as the reduction of dark oxides by catalytic hydrogenation. The deep removal of these two types of impurities gives the recycled oil a high-quality water-white appearance.

[0106] The kinematic viscosity (100°C) of both the examples and the comparative examples remained stable at 5.78–5.95 mm. 2 The viscosity range was within a certain range, with no significant fluctuations. This indicates that the refining process of this invention (adsorption, plasma, hydrogenation, and distillation) only specifically removes impurities without damaging the molecular chain structure of the base oil, thus maintaining the core viscosity characteristics of the lubricating oil.

[0107] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for refining and recycling waste lubricating oil, characterized in that, Includes the following steps: (1) The activated carbon powder and attapulgite clay were acid-washed and activated, and then dried to obtain the activated carrier; (2) The activated carrier was dispersed in an ethanol-water mixed solvent, and β-cyclodextrin and mercaptopropyltrimethoxysilane were added. The reaction was first hydrolyzed and then refluxed. The reaction product was washed, dried and pulverized to obtain a lipophilic mercaptofunctionalized cyclodextrin composite material. (3) Heat the waste lubricating oil, add demulsifier, and perform pipeline ultrasonic circulation treatment. The treated oil is then centrifuged and filtered to obtain pretreated oil. (4) After calcination pretreatment, diatomaceous earth is dispersed in water, zinc source compound is added and the system is adjusted to alkalinity to generate precipitate in situ. After solid-liquid separation, washing and calcination, diatomaceous earth carrier loaded with nano zinc oxide is obtained. Then the carrier is dispersed in alcohol solvent, and aminosilane coupling agent is added to carry out surface functionalization modification reaction. The reaction product is separated, washed and dried to obtain amino diatomaceous earth loaded with nano zinc oxide. (5) Under an inert atmosphere, the pretreated oil is heated and the lipophilic thiol-functionalized cyclodextrin composite material is added to react. Before the reaction is completed, amino-modified diatomaceous earth-supported nano zinc oxide is added, and then hot filtration is performed to obtain oil a. (6) The oil a is first subjected to falling film dielectric barrier discharge plasma treatment, and then catalytically hydrogenated with hydrogen in the presence of a magnetic core-shell catalyst. After the reaction, the catalyst is separated by magnetic force and filtered to obtain oil b. (7) First, the oil b is subjected to vacuum distillation to remove light components, and then molecular distillation is performed to collect the light phase fraction to obtain refined lubricating oil.

2. The method for refining and recycling waste lubricating oil according to claim 1, characterized in that, In step (1), the mass ratio of activated carbon powder to attapulgite clay is 1:(0.5~1.5).

3. The method for refining and recycling waste lubricating oil according to claim 1, characterized in that, In step (2), the mass ratio of the activated carrier to β-cyclodextrin is 80:(15-20).

4. The method for refining and recycling waste lubricating oil according to claim 1, characterized in that, In step (2), the mass ratio of the activated carrier to mercaptopropyltrimethoxysilane is 80:(5-10).

5. The method for refining and recycling waste lubricating oil according to claim 1, characterized in that, In step (3), a polyether-type demulsifier is selected as the demulsifier; The amount of demulsifier added is 0.2 to 0.6 wt% of the waste lubricating oil.

6. The method for refining and recycling waste lubricating oil according to claim 1, characterized in that, In step (5), the amount of lipophilic thiol-functionalized cyclodextrin composite material added is 2 to 5 wt% of the pretreated oil.

7. The method for refining and recycling waste lubricating oil according to claim 1, characterized in that, In step (5), the amount of aminated diatomaceous earth-supported nano zinc oxide added is 0.5 to 2.0 wt% of the pretreated oil.

8. The method for refining and recycling waste lubricating oil according to claim 1, characterized in that, In step (6), the preparation method of the magnetic core-shell catalyst includes the following steps: Iron source was dissolved in ethylene glycol solvent, sodium acetate and dispersant were added, and magnetic microspheres were obtained after solvothermal reaction. Magnetic microspheres were dispersed in an alcohol-water mixed solvent, and a silicon source was added in the presence of ammonia to carry out a hydrolysis reaction, thereby coating the surface of the magnetic microspheres with a silica shell to obtain a magnetic composite material. The magnetic composite material was dispersed in an alcohol solvent, and an aminosilane coupling agent was added to react and modify the surface of the composite material with amino functional groups to obtain an amino-modified magnetic composite material. A mixed solution containing nickel and palladium salts is contacted with an aminated modified magnetic composite material to adsorb metal ions. Then, a reducing agent is added for liquid-phase reduction to reduce the metal ions into nano-metal particles, which are then loaded onto a support. After magnetic separation, washing, and drying, a magnetic core-shell catalyst is obtained.

9. The method for refining and recycling waste lubricating oil according to claim 1, characterized in that, In step (6), the amount of magnetic core-shell catalyst added is 1 to 3 wt% of oil a.

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