Method for regenerating waste lubricating oil based on membrane separation

Abstract

The invention discloses a method for regenerating waste lubricating oil based on membrane separation, relates to the technical field of waste lubricating oil regeneration, and belongs to the patent classification number B01D71 / 06. Comprising the following steps: standing and settling the waste lubricating oil to remove free water and large mechanical impurities, and then carrying out centrifugal separation to further remove fine solid particles and emulsified water, so as to obtain pretreated waste lubricating oil; preheating the pretreated waste lubricating oil to obtain preheated lubricating oil; the preheated lubricating oil is filtered through an ultrafiltration membrane, filtrate is collected, and regenerated waste lubricating oil is obtained. The waste lubricating oil is recycled and regenerated through a membrane method, and the used ultrafiltration membrane has good flux and anti-pollution performance.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of waste lubricating oil regeneration, belongs to the patent classification B01D71 / 06, and particularly relates to a method for regenerating waste lubricating oil based on membrane separation. BACKGROUND

[0002] Lubricating oil is indispensable in industrial production and mechanical equipment operation, but during long-term use, it will produce carbon black, colloidal particles, asphaltene, organic acid, sulfide and other degradation products and impurities due to oxidation, degradation and external pollution, and finally become waste lubricating oil that loses use performance. According to estimation, the amount of waste lubricating oil generated in China each year can reach several million tons. If it is directly discarded or burned, it will not only seriously pollute the environment, but also cause great waste of oil resources. Therefore, the regeneration and recovery of waste lubricating oil have important environmental protection value and economic significance.

[0003] At present, waste lubricating oil regeneration technologies mainly include physical methods, chemical methods and physical-chemical combined methods. Among them, the physical methods include centrifugal separation, adsorption, conventional filtration and the like, which are simple to operate but have low separation precision and are difficult to effectively remove small colloids and dissolved degradation products; the chemical methods such as acid-base washing and oxidation-reduction can improve the quality of oil, but have problems such as high energy consumption, generation of a large amount of acid-base waste liquid and environmental pollution; the physical-chemical combined methods such as solvent refining and molecular distillation can improve the regeneration effect, but generally have defects such as complex process, large equipment investment and high operation cost, which limit their wide application.

[0004] Membrane separation technology, as a new separation technology developed in the 1950s, provides a new path for waste lubricating oil regeneration. The technology uses a membrane material with selective permeation as a medium and realizes the separation of oil and impurities by using a driving force such as pressure difference, and has the advantages of low energy consumption, simple operation, high separation efficiency, environmental friendliness and no secondary pollution. However, the existing membrane separation technology still has key bottlenecks in the application of waste lubricating oil regeneration. On the one hand, waste lubricating oil has complex composition and high viscosity, and during the filtration process, the concentration polarization phenomenon is easy to occur, which leads to a generally low filtration flux of the membrane and seriously affects the treatment efficiency. On the other hand, the anti-pollution performance of the membrane is insufficient: the impurities in the waste lubricating oil are easy to deposit on the surface of the membrane or block the pores, forming physical pollution. Therefore, how to improve the flux and anti-pollution performance of the membrane has become a core problem for promoting the large-scale application of membrane separation technology in the field of waste lubricating oil regeneration. SUMMARY

[0005] The purpose of the present application is to provide a method for regenerating waste lubricating oil based on membrane separation to solve the technical problems in the background art.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical solutions: A method for regenerating waste lubricating oil based on membrane separation, comprising the following steps: S1, the waste lubricating oil is subjected to static settling to remove free water and large mechanical impurities, and then subjected to centrifugal separation to further remove fine solid particles and emulsified water, to obtain pretreated waste lubricating oil; S2, the pretreated waste lubricating oil is preheated to obtain preheated lubricating oil; S3, the preheated lubricating oil is subjected to ultrafiltration membrane filtration treatment, and the filtrate is collected to obtain regenerated waste lubricating oil.

[0007] Preferably, in step S1, the static settling time is 20-24 h.

[0008] Preferably, in step S2, the preheating temperature is 50-60℃.

[0009] Preferably, in step S3, the preparation method of the ultrafiltration membrane comprises the following steps: S31, the multi-walled carbon nanotubes are subjected to activation treatment to introduce active functional groups on the surface thereof, to obtain activated multi-walled carbon nanotubes; S32, the activated multi-walled carbon nanotubes are dispersed in N,N-dimethylformamide solvent, and an ultrasonic treatment is performed to obtain a dispersion liquid, polyvinylidene fluoride, polyvinylpyrrolidone and polyethylene glycol are added to the dispersion liquid, and stirring and ultrasonic treatment are performed to obtain a uniform casting solution; S33, the casting solution is coated into a film by a doctor blade, and then sequentially immersed in an ethanol coagulation bath and a deionized water bath for phase inversion and solidification, and naturally air-dried to obtain a base film; S34, the base film is subjected to oxygen plasma treatment to obtain a surface-activated base film, and the surface-activated base film is immersed in an acetone solution of 2-bromoisobutyryl bromide for grafting reaction to obtain an initiator immobilized membrane; S35, polyethylene glycol methacrylate and a catalyst are added to a mixed solution of methanol and water, and stirred uniformly to obtain a reaction liquid, the initiator immobilized membrane is immersed in the reaction liquid for surface grafting polymerization reaction, and then subjected to washing and drying to obtain an ultrafiltration membrane.

[0010] In the technical scheme of the present application, the multi-walled carbon nanotubes treated by activation have good dispersing performance, not only serving as rigid skeleton to improve the mechanical strength of the membrane and prevent the flux attenuation caused by the compaction effect during operation, but also providing preferential transmission channels with extremely low frictional resistance for water molecules and base oil components through the unique nanometer hollow tube cavity and the interface gap formed with the polymer, thus realizing the highway effect at the nanometer level. Meanwhile, the dual porogen system composed of polyvinylpyrrolidone and polyethylene glycol cooperatively constructs a three-dimensional multi-level pore network with high connectivity from the membrane surface to the interior and reasonable pore size gradient distribution through the different compatibility and dissolution rates of the two in the phase inversion process. Such an optimized pore structure greatly reduces the resistance and tortuosity of fluid mass transfer, thus greatly improving the flux of the ultrafiltration membrane. Figure 1 The cross-sectional SEM image of the ultrafiltration membrane prepared in the present application shows that the internal part of the base membrane presents a three-dimensional multi-level pore network structure.

[0011] In addition, the ultrafiltration membrane is endowed with excellent anti-fouling performance through surface chemical grafting modification treatment. Specifically, the polyethylene glycol methacrylate monomer is polymerized on the membrane surface under the condition of atom transfer radical polymerization, and finally forms a high-density and uniform-chain-length polyethylene glycol (PEG) molecular brush. The PEG chain has extremely strong hydrophilicity and can bind water molecules through hydrogen bonding at the membrane-oil interface to form a dense and dynamically flowing hydration layer. This hydration layer produces a double effect: first, the steric hindrance effect, when the macromolecular pollutants such as resins and asphaltenes in the waste lubricating oil approach the membrane surface, a large amount of energy must be consumed to compress or displace this hydration layer, which is extremely unfavorable in thermodynamics, thus being effectively blocked outside; second, the selective screening effect, the PEG brush layer as a soft and dynamic molecular sieve allows the regeneration of base oil components with lower viscosity and smaller molecular size to pass through, while effectively excluding pollutants with larger molecular size and stronger hydrophobicity. This not only significantly improves the purity of the regenerated oil product, but also fundamentally prevents the adsorption and accumulation of pollutants on the membrane surface, ensuring that the membrane can maintain stable and efficient flux during long-term operation.

[0012] As a preferred, in the step S31, the activation treatment method adopts acid soaking treatment.

[0013] As a preferred, in the step S32, the activated multi-walled carbon nanotubes are pretreated, including the following steps: Octyl triethoxysilane is added to a mixed solution of ethanol and water, and hydrolysis is carried out by stirring to obtain a hydrolysis solution. The activated multi-walled carbon nanotubes are added to the hydrolysis solution, heated for reaction, and then subjected to centrifugal separation, washing and drying to obtain the product.

[0014] In the technical scheme of the present application, the inventors have found through in-depth research that the surface of the activated multi-walled carbon nanotube is rich in polar functional groups such as hydroxyl and carboxyl groups, and these functional groups will have a competitive side reaction with the initiator (2-bromoisobutyryl bromide) on the membrane surface in the subsequent atom transfer radical polymerization modification. This not only leads to a large amount of consumption of the initiator, but also causes the PEG molecular brush to grow on the inner wall of the internal pores of the membrane body, thereby blocking the internal pores of the membrane and affecting the flux of the ultrafiltration membrane. In order to further solve this technical problem, the inventors of the present application have pretreated the activated multi-walled carbon nanotube, and reacted the silanol generated by hydrolysis of octyltriethoxysilane with the hydroxyl groups on the surface of the activated carbon nanotube to covalently graft a stable octyl long-chain alkyl on the surface of the activated carbon nanotube, thereby forming an effective inert shielding layer. On the premise of not affecting the dispersibility and strengthening effect of the activated carbon nanotube, the side reaction of the surface functional groups of the activated carbon nanotube with the subsequent initiator is fundamentally blocked, thereby avoiding the blockage of the pore size and improving the flux of the ultrafiltration membrane.

[0015] Preferably, the mass ratio of the activated multi-walled carbon nanotube to octyltriethoxysilane is 10:0.2-0.6.

[0016] Preferably, in the step S34, the concentration of the 2-bromoisobutyryl bromide in the acetone solution is 1-5 wt%.

[0017] Preferably, in the step S35, the catalyst is a mixture of cuprous bromide and pentamethyldiethylenetriamine.

[0018] Preferably, in the step S35, the reaction temperature is 50-60°C, and the reaction time is 8-12 h.

[0019] Compared with the prior art, the present application has the following beneficial effects: 1. By using activated multi-walled carbon nanotubes as a nano-enhanced skeleton and combining a double-pore-forming agent system, a three-dimensional multi-level pore network with highly interconnected and nanoscale rapid channels is constructed in the membrane. This structure greatly reduces the fluid mass transfer resistance, effectively solves the problem of low membrane filtration flux caused by high viscosity of waste lubricating oil, and significantly improves the efficiency of the separation process.

[0020] 2. By surface atom transfer radical polymerization technology, a high-density and uniform polyethylene glycol molecular brush is grafted on the membrane surface. The molecular brush can form a firm dynamic hydration layer, and through strong steric hindrance effect, it actively prevents the adsorption and accumulation of pollutants on the membrane surface, thereby fundamentally solving the membrane pollution problem and ensuring that the membrane can maintain stable and efficient flux and separation performance during long-term operation.

[0021] 3. The activated carbon nanotubes are subjected to silanization pretreatment, and octyl long-chain alkyl is used to shield the surface active functional groups, so as to block the side reaction of the surface active functional groups with initiators in subsequent surface modification, avoid the membrane pore blockage caused by the false growth of PEG brushes, and further improve the ultrafiltration membrane flux. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The cross-sectional SEM image of the ultrafiltration membrane prepared in the application. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the application will be clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0024] Embodiment 1 The method for regenerating waste lubricating oil based on membrane separation comprises the following steps: Step 1: 1 L of waste lubricating oil to be regenerated is taken and left to stand at room temperature for 22 h to separate and settle free water and large mechanical impurities in the waste lubricating oil at the bottom of the container. The upper oil liquid is transferred to a high-speed centrifuge, and centrifugal treatment is performed at a speed of 8000 r / min for 30 min to further remove fine solid particles and emulsified water, and finally clear pretreated waste lubricating oil is obtained.

[0025] Step 2: The pretreated waste lubricating oil is transferred to an electric heating jacket, slowly heated to 58 ℃ and kept at a constant temperature, and gentle stirring is continuously performed during the heating process to ensure uniform oil temperature. The preheated lubricating oil with reduced viscosity and improved flowability is obtained.

[0026] Step 3: The preheated lubricating oil preheated to 55 ℃ is added to a dead-end filtration device, and the ultrafiltration membrane prepared in the above step is used to perform filtration treatment at an operating pressure of 0.4 MPa. The filtrate passing through the membrane is collected, and the regenerated waste lubricating oil is obtained.

[0027] Preparation of the ultrafiltration membrane: Step 1: 2.5 g of multi-walled carbon nanotubes is taken and added to a three-necked flask containing 150 mL of concentrated nitric acid (concentration 68%), and reflux reaction is performed at 80 ℃ oil bath for 6 h. After the reaction is completed, the reaction system is naturally cooled to room temperature, and the product is repeatedly washed with deionized water by suction filtration until the filtrate is neutral. Then, the product is placed in a 80 ℃ vacuum drying oven for drying for 12 h, and activated multi-walled carbon nanotubes are obtained.

[0028] Step 2: 0.10 g of octyltriethoxysilane was added into a mixed solution consisting of 50 mL of anhydrous ethanol and 5 mL of deionized water, and was fully hydrolyzed by magnetic stirring at room temperature for 4 h to obtain a hydrolysis solution. 2.0 g of activated multi-walled carbon nanotubes was added into the hydrolysis solution and reacted at 70°C for 12 h. After the reaction was completed, the solid product was collected by centrifugal separation and washed with ethanol for three times, and finally dried at 80°C to obtain the pretreated carbon nanotubes.

[0029] The pretreated carbon nanotubes were dispersed in 80 mL of N,N-dimethylformamide solvent and ultrasonically treated (power 400 W) for 4 h to obtain a uniform dispersion. Then, 12 g of polyvinylidene fluoride, 2.5 g of polyvinylpyrrolidone and 1.0 g of polyethylene glycol were sequentially added into the dispersion, and were fully dissolved by mechanical stirring at a 60°C water bath for 12 h, and then ultrasonically treated (power 300 W) for 2 h to remove air bubbles, to finally obtain a uniform and stable casting solution.

[0030] Step 3: The casting solution was scraped onto a clean glass plate by a film coater to form a liquid film with a thickness of 200 um, and immediately immersed into a 40 wt% ethanol aqueous solution coagulation bath at a temperature of 25°C together with the glass plate, and soaked for 1 h to complete the initial phase separation and form a nascent membrane. Then, the nascent membrane was transferred into a large amount of deionized water bath and soaked for 5 days to completely replace the residual solvent and porogen, and complete the solidification and membrane forming process. Finally, the membrane was taken out and naturally air-dried at room temperature for 48 h to obtain a base membrane.

[0031] Step 4: The base membrane was placed in an oxygen plasma processor and treated at a power of 80 W for 5 min to obtain a surface-activated base membrane. It was immersed into a 2-bromoisobutyryl bromide acetone solution with a concentration of 4 wt%, and reacted in a 30°C constant temperature water bath for 4 h. After the reaction was completed, the membrane surface was washed with anhydrous acetone to remove the physically adsorbed initiator, and then vacuum dried to obtain an initiator immobilized membrane.

[0032] Step 5: 15 g of polyethylene glycol methacrylate (Mn=500), 0.05 g of cuprous bromide and 0.12 g of pentamethyldiethylenetriamine were weighed and added into a mixed solvent consisting of 30 mL of methanol and 20 mL of deionized water, and nitrogen was bubbled for 30 min to remove oxygen. The initiator immobilized membrane was placed into a reactor, and the above deoxygenated reaction solution was injected, and reacted at a 55°C oil bath under nitrogen protection for 10 h. After the reaction was completed, the membrane was taken out, and repeatedly washed with methanol and deionized water, and dried in a 40°C vacuum drying oven for 6 h to obtain a membrane.

[0033] Example 2 The method for regenerating waste lubricating oil based on membrane separation comprises the following steps: Step 1: Take 1 L of waste lubricating oil to be regenerated, and let it stand for 22 h at room temperature to allow the free water and large mechanical impurities to separate and settle at the bottom of the container. Transfer the upper layer of oil to a high-speed centrifuge and centrifuge at a speed of 8000 r / min for 30 min to further remove fine solid particles and emulsified water, and finally obtain clear pretreated waste lubricating oil.

[0034] Step 2: Transfer the pretreated waste lubricating oil to an electric heating jacket, slowly heat to 52°C and maintain the temperature, and continuously stir gently to ensure uniform oil temperature. Obtain preheated lubricating oil with reduced viscosity and improved flowability.

[0035] Step 3: Add the preheated lubricating oil preheated to 55°C to a dead-end filtration device, and use the ultrafiltration membrane prepared above to filter at an operating pressure of 0.4 MPa. Collect the filtrate that passes through the membrane, and you can get the regenerated waste lubricating oil.

[0036] Preparation of ultrafiltration membrane: Step 1: Weigh 2.5 g of multi-walled carbon nanotubes and add them to a three-necked flask containing 150 mL of concentrated nitric acid (concentration 68%) and reflux at 80°C for 6 h. After the reaction is completed, cool it to room temperature naturally, and wash it repeatedly with deionized water by suction filtration until the filtrate is neutral. Then, dry the product in a vacuum drying oven at 80°C for 12 h to obtain activated multi-walled carbon nanotubes.

[0037] Step 2: Add 0.06 g of octyl triethoxysilane to a mixed solution composed of 50 mL of anhydrous ethanol and 5 mL of deionized water, and magnetically stir it at room temperature for 4 h to allow it to hydrolyze completely, obtaining a hydrolysis solution. Add 2.0 g of activated multi-walled carbon nanotubes to the hydrolysis solution and react at 70°C for 12 h. After the reaction is completed, collect the solid product by centrifugal separation and wash it with ethanol three times, and finally dry it at 80°C to obtain pretreated carbon nanotubes.

[0038] Disperse the pretreated carbon nanotubes in 80 mL of N,N-dimethylformamide solvent and ultrasonicate (power 400 W) for 4 h to obtain a uniform dispersion. Then, add 12 g of polyvinylidene fluoride, 2.5 g of polyvinylpyrrolidone, and 1.0 g of polyethylene glycol to the dispersion in sequence, and mechanically stir it in a 60°C water bath for 12 h to allow it to dissolve completely. Then, ultrasonicate (power 300 W) for 2 h to remove air bubbles, and finally obtain a uniform and stable casting solution.

[0039] Step 3: The casting solution was cast on a clean glass plate using a knife coater to form a liquid film with a thickness of 200 um, and then immediately immersed in a 40 wt% ethanol aqueous solution coagulation bath at 25℃ to complete the initial phase separation and form a nascent membrane. Then the nascent membrane was transferred to a large amount of deionized water bath and soaked for 5 days to completely replace the residual solvent and porogen, and complete the solidification process. Finally, the membrane was taken out and naturally air-dried at room temperature for 48 h to obtain the base membrane.

[0040] Step 4: The base membrane was placed in an oxygen plasma processor and treated at a power of 80 W for 5 min to obtain a surface-activated base membrane. It was immersed in a 2 wt% 2-bromoisobutyryl bromide acetone solution and reacted in a 30℃ constant temperature water bath for 4 h. After the reaction was completed, the membrane surface was washed with anhydrous acetone to remove the physically adsorbed initiator, and then vacuum dried to obtain the initiator immobilized membrane.

[0041] Step 5: 15 g of polyethylene glycol methacrylate (Mn=500), 0.05 g of cuprous bromide and 0.12 g of pentamethyldiethylenetriamine were weighed and added to a mixed solvent composed of 30 mL of methanol and 20 mL of deionized water, and nitrogen was bubbled for 30 min to remove oxygen. The initiator immobilized membrane was placed in the reactor, and the above deoxygenated reaction solution was injected, and the reaction was carried out in a 55℃ oil bath under nitrogen protection for 9 h. After the reaction was completed, the membrane was taken out and washed with methanol and deionized water in turn, and dried in a 40℃ vacuum drying oven for 6 h to obtain the product.

[0042] Example 3 The method for regenerating waste lubricating oil based on membrane separation comprises the following steps: Step 1: Take 1 L of waste lubricating oil to be regenerated, and let it stand at room temperature for 22 h to separate and settle the free water and large mechanical impurities in the oil. The upper layer of oil is transferred to a high-speed centrifuge and centrifuged at a speed of 8000 r / min for 30 min to further remove fine solid particles and emulsified water, and finally obtain clear pretreated waste lubricating oil.

[0043] Step 2: The pretreated waste lubricating oil is transferred to an electric heating jacket and slowly heated to 55℃ and maintained at a constant temperature, and the temperature is continuously stirred to ensure uniform oil temperature. The preheated lubricating oil with reduced viscosity and improved flowability is obtained.

[0044] Step 3: The preheated lubricating oil at 55℃ is added to a dead-end filtration device, and the ultrafiltration membrane prepared above is used to filter at an operating pressure of 0.4 MPa. The filtrate passing through the membrane is collected, and the regenerated waste lubricating oil is obtained.

[0045] Preparation of ultrafiltration membrane: Step 1: 2.5 g of multi-walled carbon nanotubes were weighed into a three-necked flask containing 150 mL of concentrated nitric acid (68% concentration) and refluxed at 80 °C for 6 h. After the reaction, the mixture was allowed to cool to room temperature and washed repeatedly with deionized water until the filtrate was neutral. The product was then dried in a vacuum oven at 80 °C for 12 h to obtain activated multi-walled carbon nanotubes.

[0046] Step 2: 0.08 g of octyltriethoxysilane was added to a mixture of 50 mL of absolute ethanol and 5 mL of deionized water and stirred magnetically at room temperature for 4 h to obtain a hydrolyzate. 2.0 g of activated multi-walled carbon nanotubes were added to the hydrolyzate and reacted at 70 °C for 12 h. After the reaction, the solid product was collected by centrifugation and washed with ethanol three times, and finally dried at 80 °C to obtain pre-treated carbon nanotubes.

[0047] The pre-treated carbon nanotubes were dispersed in 80 mL of N,N-dimethylformamide solvent and ultrasonicated (power 400 W) for 4 h to obtain a uniform dispersion. Then, 12 g of polyvinylidene fluoride, 2.5 g of polyvinylpyrrolidone, and 1.0 g of polyethylene glycol were sequentially added to the dispersion, and completely dissolved by mechanical stirring at 60 °C for 12 h. After that, the dispersion was ultrasonicated (power 300 W) for 2 h to remove air bubbles, and finally a uniform and stable casting solution was obtained.

[0048] Step 3: The casting solution was cast onto a clean glass plate using a film doctor blade to form a liquid film with a thickness of 200 um. The glass plate with the liquid film was immediately immersed in a 40 wt% ethanol aqueous solution coagulation bath at 25 °C for 1 h to complete the initial phase separation and form a nascent membrane. Then, the nascent membrane was transferred to a large amount of deionized water bath and soaked for 5 days to completely replace the residual solvent and porogen, and the membrane formation process was completed. Finally, the membrane was taken out and naturally air-dried at room temperature for 48 h to obtain a base membrane.

[0049] Step 4: The base membrane was placed in an oxygen plasma processor and treated at a power of 80 W for 5 min to obtain a surface-activated base membrane. The base membrane was immersed in a 3 wt% 2-bromoisobutyryl bromide solution in acetone and reacted in a 30 °C constant temperature water bath for 4 h. After the reaction, the membrane surface was washed with absolute acetone to remove the physically adsorbed initiator, and then vacuum dried to obtain an initiator-immobilized membrane.

[0050] Step 5: 15 g of polyethylene glycol methacrylate (Mn=500), 0.05 g of cuprous bromide and 0.12 g of pentamethyldiethylenetriamine were weighed and added to a mixed solvent composed of 30 mL of methanol and 20 mL of deionized water, and nitrogen was bubbled for 30 min to remove oxygen. The initiator immobilized membrane was placed in a reactor, the above-mentioned deoxygenated reaction solution was injected, and the reaction was carried out in a 55°C oil bath under nitrogen protection for 10 h. After the reaction was completed, the membrane was taken out and washed repeatedly with methanol and deionized water, and dried in a vacuum drying oven at 40°C for 6 h to obtain the product.

[0051] Example 4 The method for regenerating waste lubricating oil based on membrane separation comprises the following steps: Step 1: 1 L of waste lubricating oil to be regenerated was taken and allowed to stand for 24 h at room temperature to separate and settle free water and large mechanical impurities in the container bottom. The upper oil liquid was transferred to a high-speed centrifuge, and centrifuged at a speed of 8000 r / min for 30 min to further remove fine solid particles and emulsified water, and finally obtain clear pretreated waste lubricating oil.

[0052] Step 2: The pretreated waste lubricating oil was transferred to an electric heating jacket, slowly heated to 60°C and maintained at a constant temperature, and continuously stirred gently during the period to ensure uniform oil temperature, to obtain preheated lubricating oil with reduced viscosity and improved flowability.

[0053] Step 3: The preheated lubricating oil preheated to 55°C was added to a dead-end filtration device, and the above-prepared ultrafiltration membrane was used for filtration treatment at an operating pressure of 0.4 MPa. The filtrate passing through the membrane was collected, and the regenerated waste lubricating oil was obtained.

[0054] Preparation of ultrafiltration membrane: Step 1: 2.5 g of multi-walled carbon nanotubes was added to a three-necked flask containing 150 mL of concentrated nitric acid (concentration 68%), and refluxed at 80°C for 6 h. After the reaction was completed, it was naturally cooled to room temperature, washed repeatedly with deionized water by suction filtration until the filtrate was neutral, and then the product was dried in a vacuum drying oven at 80°C for 12 h to obtain activated multi-walled carbon nanotubes.

[0055] Step 2: 0.12 g of octyltriethoxysilane was added to a mixed solution composed of 50 mL of anhydrous ethanol and 5 mL of deionized water, and magnetically stirred at room temperature for 4 h to obtain a hydrolysis solution. 2.0 g of activated multi-walled carbon nanotubes was added to the hydrolysis solution and reacted at 70°C for 12 h. After the reaction was completed, the solid product was collected by centrifugal separation and washed with ethanol three times, and finally dried at 80°C to obtain pretreated carbon nanotubes.

[0056] The pretreated carbon nanotubes were dispersed in 80 mL of N,N-dimethylformamide solvent and ultrasonically treated (400 W) for 4 h to obtain a uniform dispersion. Then 12 g of polyvinylidene fluoride, 2.5 g of polyvinylpyrrolidone and 1.0 g of polyethylene glycol were sequentially added to the dispersion, and the mixture was completely dissolved by mechanical stirring at 60°C for 12 h in a water bath, followed by ultrasonic treatment (300 W) for 2 h to remove air bubbles, and finally a uniform and stable casting solution was obtained.

[0057] Step 3: The casting solution was cast on a clean glass plate using a film doctor blade to form a liquid film with a thickness of 200 um, and then immediately immersed in a 40 wt% ethanol aqueous solution coagulation bath at 25°C to complete the initial phase separation and form a nascent membrane after 1 h. Then the nascent membrane was transferred to a large amount of deionized water bath and soaked for 5 days to completely replace the residual solvent and porogen, and the solidification process was completed. Finally, the membrane was taken out and naturally air-dried at room temperature for 48 h to obtain the base membrane.

[0058] Step 4: The base membrane was placed in an oxygen plasma processor and treated at a power of 80 W for 5 min to obtain a surface-activated base membrane. It was immersed in a 5 wt% 2-bromoisobutyryl bromide solution in acetone and reacted in a 30°C constant temperature water bath for 4 h. After the reaction was completed, the membrane surface was washed with anhydrous acetone to remove the physically adsorbed initiator, and then vacuum dried to obtain the initiator-immobilized membrane.

[0059] Step 5: 15 g of polyethylene glycol methacrylate (Mn=500), 0.05 g of cuprous bromide and 0.12 g of pentamethyldiethylenetriamine were weighed and added to a mixed solvent composed of 30 mL of methanol and 20 mL of deionized water, and nitrogen was bubbled for 30 min to remove oxygen. The initiator-immobilized membrane was placed in a reactor, and the above deoxygenated reaction solution was injected, and the reaction was carried out at 60°C in a nitrogen atmosphere for 12 h. After the reaction was completed, the membrane was taken out and washed with methanol and deionized water in turn, and dried in a vacuum drying oven at 40°C for 6 h to obtain the product.

[0060] Example 5 The method for regenerating waste lubricating oil based on membrane separation comprises the following steps: Step 1: Take 1 L of waste lubricating oil to be regenerated, and let it stand at room temperature for 20 h to allow the free water and large mechanical impurities to separate and settle at the bottom of the container. The upper layer of oil is transferred to a high-speed centrifuge and centrifuged at a speed of 8000 r / min for 30 min to further remove fine solid particles and emulsified water, and finally a clear pretreated waste lubricating oil is obtained.

[0061] Step 2: The pretreated waste lubricating oil was transferred to an electric heating jacket, slowly heated to 50°C and maintained at a constant temperature, and gentle stirring was continued during the process to ensure uniform oil temperature, obtaining preheated lubricating oil with reduced viscosity and improved flowability.

[0062] Step 3: The preheated lubricating oil at 55°C was added to a dead-end filtration device, and filtration treatment was carried out using the ultrafiltration membrane prepared above at an operating pressure of 0.4 MPa. The filtrate that passed through the membrane was collected, and the regenerated waste lubricating oil was obtained.

[0063] Preparation of ultrafiltration membrane: Step 1: 2.5 g of multi-walled carbon nanotubes were weighed and added to a three-necked flask containing 150 mL of concentrated nitric acid (concentration 68%), and refluxed at 80°C oil bath for 6 h. After the reaction was completed, it was naturally cooled to room temperature, washed repeatedly with deionized water by suction filtration until the filtrate was neutral, and then the product was dried in a 80°C vacuum drying oven for 12 h to obtain activated multi-walled carbon nanotubes.

[0064] Step 2: 0.04 g of octyl triethoxysilane was added to a mixed solution composed of 50 mL of anhydrous ethanol and 5 mL of deionized water, and magnetically stirred at room temperature for 4 h to fully hydrolyze, obtaining a hydrolysis solution. 2.0 g of activated multi-walled carbon nanotubes were added to the hydrolysis solution and reacted at 70°C for 12 h. After the reaction was completed, the solid product was collected by centrifugal separation and washed with ethanol three times, and finally dried at 80°C to obtain pretreated carbon nanotubes.

[0065] The pretreated carbon nanotubes were dispersed in 80 mL of N,N-dimethylformamide solvent and ultrasonically treated (power 400 W) for 4 h to obtain a uniform dispersion. Then 12 g of polyvinylidene fluoride, 2.5 g of polyvinylpyrrolidone, and 1.0 g of polyethylene glycol were sequentially added to the dispersion, and mechanically stirred at 60°C water bath for 12 h to completely dissolve, and then ultrasonically treated (power 300 W) for 2 h to remove bubbles, finally obtaining a uniform and stable casting solution.

[0066] Step 3: The casting solution was scraped onto a clean glass plate using a film coater to form a liquid film with a thickness of 200 um, and immediately immersed in a 40 wt% ethanol aqueous solution coagulation bath at a temperature of 25°C, and soaked for 1 h to complete the initial phase separation and form a nascent membrane. Then the nascent membrane was transferred to a large amount of deionized water bath and soaked for 5 days to completely replace the residual solvent and porogen, and the solidification and membrane formation process was completed. Finally, the membrane was taken out and naturally air-dried at room temperature for 48 h to obtain the base membrane.

[0067] Step 4: The base membrane was placed in an oxygen plasma treater and treated at a power of 80 W for 5 min to obtain a surface-activated base membrane. The membrane was immersed in an acetone solution of 2-bromoisobutyryl bromide with a concentration of 1 wt% and reacted in a constant-temperature water bath at 30 °C for 4 h. After the reaction was completed, the membrane surface was washed with anhydrous acetone to remove the physically adsorbed initiator, and then vacuum dried to obtain the initiator-immobilized membrane.

[0068] Step 5: 15 g of polyethylene glycol methacrylate (Mn=500), 0.05 g of cuprous bromide and 0.12 g of pentamethyldiethylenetriamine were weighed and added to a mixed solvent composed of 30 mL of methanol and 20 mL of deionized water, and nitrogen was bubbled for 30 min to remove oxygen. The initiator-immobilized membrane was placed in the reactor, and the above-mentioned deoxygenated reaction solution was injected, and the reaction was carried out in a 50 °C oil bath under nitrogen protection for 8 h. After the reaction was completed, the membrane was taken out and washed with methanol and deionized water in turn, and dried in a vacuum drying oven at 40 °C for 6 h to obtain the product.

[0069] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that no pretreated carbon nanotubes are added to the casting solution in step 2 of the preparation of the ultrafiltration membrane.

[0070] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that the pretreated carbon nanotubes are replaced by activated multi-walled carbon nanotubes in step 2 of the preparation of the ultrafiltration membrane, i.e. without pretreatment.

[0071] Comparative Example 3: The difference between Comparative Example 3 and Example 1 is that steps 4 and 5 are omitted in the preparation of the ultrafiltration membrane, i.e. no polyethylene glycol methacrylate is grafted onto the surface of the ultrafiltration membrane.

[0072] Performance test: 1. Regenerated oil kinematic viscosity recovery rate test: Kinematic viscosity is a core indicator for measuring the performance of lubricating oil. The difference in viscosity between the regenerated oil and the new lubricating oil is tested to evaluate the regeneration effect. The 40 °C kinematic viscosity of the feed waste lubricating oil (initial viscosity), the regenerated oil of each example / comparative example (post-regeneration viscosity) and the new lubricating oil of the same type (standard viscosity) were measured respectively. According to the formula: viscosity recovery rate (%) = [(standard viscosity - initial viscosity) - (standard viscosity - post-regeneration viscosity)] / (standard viscosity - initial viscosity) x 100%, the higher the recovery rate, the closer the performance of the regenerated oil to that of the new oil. The test results are shown in Table 1.

[0073] 2. Initial flux test: The initial separation efficiency of the membrane was evaluated based on the volume of oil permeated per unit membrane area per unit time. The ultrafiltration membranes of each example and the comparative example were installed in a dead-end filtration device, and the operating pressure was kept stable at 0.4 MPa, the temperature of the feed oil was 55℃, and the pretreated waste lubricating oil was injected into the device. The volume of permeate liquid was recorded within 0-30 min after the start of filtration, and the average permeate volume within 30 min was recorded every 5 min. The average permeate volume was calculated according to the formula: initial flux (LMH) = permeate volume (L) / [membrane effective area (m 2 ) × time (h) ], and the membrane effective area was uniformly 0.01 m 2 . The test results are shown in Table 1.

[0074] 3. Anti-pollution performance test: The actual long-term use scenario of the membrane was simulated to evaluate the influence of the anti-pollution ability on the flux decay. The test conditions were consistent with the initial flux, and the continuous filtration was performed for 12 h. The instantaneous fluxes at 1 h, 3 h, 6 h, 9 h, and 12 h were recorded, respectively, and the ratio of the flux after 12 h to the initial flux (i.e., the flux retention rate) was calculated. The higher the ratio, the stronger the anti-pollution performance of the membrane and the better the long-term operation stability. After the test, the membrane surface was washed with deionized water for 10 min, and the flux within 30 min was tested again (recorded as “cleaning flux”). The cleaning flux recovery rate (cleaning flux / initial flux × 100%) was calculated to evaluate the cleanability of the membrane. The test results are shown in Table 1.

[0075] Table 1: Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments or make equivalent replacements to some technical features, and any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for regenerating used lubricating oil based on membrane separation, characterized in that, The method comprises the following steps: S1, removing free water and large mechanical impurities from waste lubricating oil through static settling, and further removing fine solid particles and emulsified water through centrifugal separation to obtain pretreated waste lubricating oil; S2, preheating the pretreated waste lubricating oil to obtain preheated lubricating oil; S3, filtering the preheated lubricating oil through an ultrafiltration membrane to collect a filtrate to obtain regenerated waste lubricating oil.

2. A method for regenerating used lubricating oil based on membrane separation according to claim 1, characterized in that, In the step S1, the static settling time is 20-24 h.

3. A method for regenerating used lubricating oil based on membrane separation according to claim 1, characterized in that, In the step S2, the preheating temperature is 50-60 DEG C.

4. The method for regenerating waste lubricating oil based on membrane separation according to claim 1, characterized in that, The preparation method of the ultrafiltration membrane comprises the following steps: S31, activating the multi-walled carbon nanotubes to introduce active functional groups on the surface of the multi-walled carbon nanotubes to obtain activated multi-walled carbon nanotubes; S32, dispersing the activated multi-walled carbon nanotubes in N, N-dimethylformamide solvent, and obtaining a dispersion liquid through ultrasonic treatment, adding polyvinylidene fluoride, polyvinylpyrrolidone and polyethylene glycol into the dispersion liquid, and obtaining a uniform casting solution through stirring and ultrasonic treatment; S33, coating the casting solution into a film through a doctor blade, and then sequentially immersing into an ethanol coagulation bath and a deionized water bath for phase inversion and solidification, and naturally air-drying to obtain a base film; S34, performing oxygen plasma treatment on the base film to obtain a surface-activated base film, immersing the surface-activated base film into an acetone solution of 2-bromoisobutyryl bromide for grafting reaction to obtain an initiator immobilized membrane; S35, adding polyethylene glycol methacrylate and a catalyst into a mixed solution of methanol and water, stirring uniformly to obtain a reaction liquid, immersing the initiator immobilized membrane into the reaction liquid for surface grafting polymerization reaction, and then washing and drying to obtain the ultrafiltration membrane.

5. A method for regenerating used lubricating oil based on membrane separation according to claim 4, characterized in that, In the step S31, the activation treatment method adopts acid soaking treatment.

6. A process for the regeneration of used lubricating oil based on membrane separation as claimed in claim 4 wherein, In the step S32, the activated multi-walled carbon nanotubes are pretreated, which comprises the following steps: adding octyl triethoxysilane into a mixed solution of ethanol and water, stirring for hydrolysis to obtain a hydrolysis liquid, adding the activated multi-walled carbon nanotubes into the hydrolysis liquid, and heating for reaction, and then performing centrifugal separation, washing and drying.

7. A process for the regeneration of used lubricating oil based on membrane separation as claimed in claim 4 wherein, The mass ratio of the activated multi-walled carbon nanotubes to octyl triethoxysilane is 10:0.2-0.

6.

8. A method for regenerating used lubricating oil based on membrane separation according to claim 4, characterized in that, In the step S34, the concentration of the acetone solution of 2-bromoisobutyryl bromide is 1-5 wt%.

9. A method for regenerating used lubricating oil based on membrane separation according to claim 4, characterized in that, In the step S35, the catalyst is a mixture of cuprous bromide and pentamethyldiethylenetriamine.

10. A method for regenerating used lubricating oil based on membrane separation according to claim 4, characterized in that, In the step S35, the reaction temperature is 50-60 DEG C, and the reaction time is 8-12 h.

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