Method and system for cleaning contaminated lubricating oil
By combining flocculation with membrane separation technology, membrane separation and then flocculation treatment are performed, the problems of low efficiency and oil yield loss in the prior art are solved, and efficient and low-cost lubricant purification and high-yield oil recovery are achieved.
Patent Information
- Application Number
- CN202311235377.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-09-22
- Publication Date
- 2025-03-25
AI Technical Summary
The prior art is inefficient and costly when purifying lubricating oil, and it is difficult to effectively recover "concentrated" oil products with high concentrations of pollutants when using flocculation or membrane separation technology alone, resulting in loss of oil yield.
Using a new process that combines flocculation and membrane separation technology, the first purified lubricant and contaminant-rich lubricant are obtained through membrane separation treatment, and the latter is mixed with the flocculant for flocculation treatment, and finally the floc is separated to obtain the second purified lubricant.
It has achieved efficient purification of lubricating oil, especially suitable for high viscosity lubricating oil, which improves treatment efficiency and oil yield, and has almost no waste oil emissions, achieving the best balance of treatment efficiency and yield.
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Figure CN119685088A_ABST
Abstract
Description
Technical Field
[0001] The present invention generally relates to oil recovery and purification technology, and more particularly to a method and system for purifying contaminated lubricating oil. Background Art
[0002] Lubricating oil plays an important role in lubrication, shock absorption, heat dissipation, rust prevention and mechanical life extension for transportation vehicles, ships, and mechanical processing equipment. Due to the influence of the working environment of mechanical equipment and the life of the lubricating oil itself, after a period of use, various pollutants increase and the oil itself ages, resulting in a decline in various performance indicators, and even failure to meet application requirements.
[0003] These contaminants can affect the performance of lubricants. For example, hard particles can cause damage to machinery or the products they manufacture. In high-temperature environments, contaminated lubricants will condense to form a varnish: these sticky particles can clog pipes and adhere to the surfaces of friction pairs, resulting in increased friction and accelerated wear. Water and metal particle contaminants can induce oxidation reactions, which ultimately lead to the destruction of lubricants. Moreover, when mechanical equipment is lubricated, the lubricating film is sometimes very thin, such as the elastic fluid dynamic lubricating film, which is usually less than 1μm thick. Theoretically, as long as the diameter of the particles in the oil is greater than the thickness of the oil film, it may have a negative impact on the friction pair and cause the friction pair to deteriorate on the surface. At the same time, since the particles in the oil are very small but have a very large specific surface area, they will catalyze the aging of the oil and accelerate the aging of the oil. Therefore, it is of great significance to develop an effective process for purifying lubricants to remove contaminants in the oil as much as possible.
[0004] At present, the main methods for purifying lubricating oil are as follows: online filtration and dehydration; waste oil treatment using distillation and hydrogenation technology; Alfa Laval's flocculation and centrifugal technology, etc.
[0005] However, online filtration and dehydration consume a lot of filter elements and require additional labor costs, which is inefficient. Distillation and hydrogenation technologies require a lot of raw materials, similar to a certain process in the chemical industry. In addition, the investment is large, and it is difficult to find a balance between benefits and costs. Alfa Laval's flocculation and centrifugal technology will lead to the loss of certain additives, affecting the performance of lubricants.
[0006] Therefore, there remains a need to find an improved method and system for purifying contaminated lubricating oil. Summary of the invention
[0007] The present invention is made in view of the above problems existing in the prior art.
[0008] In a first aspect, the present invention provides a method for cleaning contaminated lubricating oil, the method comprising the steps of:
[0009] (1) pre-treating the contaminated lubricating oil to remove part of the contaminants and water to obtain pre-treated lubricating oil, preferably the pre-treatment comprises one or more of centrifugation, dehydration, natural sedimentation and filtration;
[0010] (2) subjecting the pretreated lubricating oil obtained in step (1) to membrane separation treatment to obtain a first purified lubricating oil and a lubricating oil rich in pollutants;
[0011] (3) mixing the contaminant-rich lubricating oil obtained in step (2) with a flocculant and performing flocculation treatment to obtain a mixture; and
[0012] (4) Separating flocculants from the mixture obtained in step (3) to obtain a second purified lubricating oil.
[0013] In a second aspect, the present invention provides a system for purifying contaminated lubricating oil, the system comprising:
[0014] - a pretreatment unit, which is used to pretreat the contaminated lubricating oil to remove part of the contaminants and water to obtain pretreated lubricating oil, preferably the pretreatment unit comprises one or more of a centrifuge, a dehydration device, a natural sedimentation device and a filtering device;
[0015] a membrane separation unit downstream of the pretreatment unit, comprising a membrane separation device for subjecting the pretreated lubricating oil from the pretreatment unit to a membrane separation treatment to produce a first purified lubricating oil and a lubricating oil enriched with pollutants, a clean oil tank for receiving the first purified lubricating oil, and a concentrated oil tank for receiving the lubricating oil enriched with pollutants;
[0016] a flocculation unit downstream of the membrane separation unit, comprising a storage device for storing a flocculant, a flocculation device for performing a flocculation treatment, a first conduit for supplying the lubricating oil rich in pollutants from the concentrated oil tank to the flocculation device, and a second conduit for supplying the flocculant from the storage device to the flocculation device, the flocculation device for mixing the lubricating oil rich in pollutants from the concentrated oil tank supplied to the flocculation device and the flocculant from the storage device and performing a flocculation treatment; and
[0017] - a separation unit downstream of the flocculation unit for separating the flocs from the mixture coming from the flocculation unit to obtain a second purified lubricating oil.
[0018] When the flocculation technology is used alone to purify lubricating oil, especially high-viscosity lubricating oil, the efficiency of the purification process is very low due to the slow speed of the gravity sedimentation process. When the membrane separation technology is used alone to purify lubricating oil, the oil treated by the membrane separation is divided into two parts, one is the purified oil, and the other is the "concentrated" oil with a higher concentration of dirtier pollutants. For this part of the "concentrated" oil, it is difficult to effectively recycle it in the existing technology, so it is generally discarded, resulting in a loss of oil yield.
[0019] To this end, the present invention proposes to use a new process combining flocculation and membrane separation technology to purify lubricating oil. The applicant has found that by first using membrane separation to purify lubricating oil, and then treating the "concentrated" oil obtained by membrane separation through a flocculation process, a purified oil product with high cleanliness can be obtained, and even for high-viscosity lubricating oil, it can have a high processing efficiency and processing capacity. At the same time, there is almost no waste oil discharge during the processing process, which significantly improves the yield of purified oil products. Therefore, the present invention achieves the best balance between processing efficiency and yield. In some industries where the procurement cost of lubricating oil is very high, the purification method combining flocculation and membrane separation technology according to the present invention has a very broad application prospect.
[0020] In addition, the "concentrated" oil obtained by membrane separation is difficult to be purified by general filtration or membrane separation due to the high concentration of pollutants. The applicant further found that when a flocculant including alkylene glycol, especially ethylene glycol, is used for flocculation treatment, an oil product with improved cleanliness and yield can be obtained compared with other technologies (e.g., filtration or membrane separation technology) or other flocculants. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] In order to more clearly illustrate the technical solution of the present invention, the following will briefly describe the drawings required for describing the embodiments. It should be understood that the drawings are only for the convenience of technicians to understand the present invention more easily, and are not intended to limit the scope of the present invention.
[0022] Figure 1 A method and system for purifying contaminated lubricating oil according to an exemplary embodiment of the present invention is schematically illustrated. DETAILED DESCRIPTION
[0023] In order to make the invention purpose, technical solution and beneficial technical effect of the present application clearer, the present application will be described in detail below. It should be noted that the various aspects, features, implementation methods and advantages described in the present application may be compatible and / or may be combined together.
[0024] Unless otherwise specified, the meanings of the technical terms in this specification are the same as those generally understood by those skilled in the art.
[0025] The present invention relates to a method and system for purifying contaminated lubricating oil.
[0026] The present invention will be described in detail below.
[0027] Method for purifying contaminated lubricating oil
[0028] The method for purifying contaminated lubricating oil according to the first aspect of the present invention comprises a pretreatment step, a membrane separation step, a flocculation step and a separation step in sequence. Specifically, the present invention relates to a method for purifying contaminated lubricating oil, the method comprising the following steps:
[0029] (1) pre-treating the contaminated lubricating oil to remove part of the contaminants and water to obtain pre-treated lubricating oil, preferably the pre-treatment comprises one or more of centrifugation, dehydration, natural sedimentation and filtration;
[0030] (2) subjecting the pretreated lubricating oil obtained in step (1) to membrane separation treatment to obtain a first purified lubricating oil and a lubricating oil rich in pollutants;
[0031] (3) mixing the contaminant-rich lubricating oil obtained in step (2) with a flocculant and performing flocculation treatment to obtain a mixture; and
[0032] (4) Separating flocculants from the mixture obtained in step (3) to obtain a second purified lubricating oil.
[0033] Each step is described in detail below.
[0034] Step (1)
[0035] In step (1), the contaminated lubricating oil is pretreated to remove part of the contaminants and water to obtain pretreated lubricating oil. The pretreatment step can remove larger particles and most of the water in the contaminated oil, reducing the load of the subsequent membrane separation and flocculation process.
[0036] In one or more embodiments, the pretreatment includes subjecting the contaminated lubricating oil to one or more treatments selected from the group consisting of: centrifugation, dehydration, natural sedimentation, and filtration.
[0037] In a preferred embodiment, the pretreatment includes filtering the contaminated lubricating oil through a metal sintered filter element (coarse filtration).
[0038] In a preferred embodiment, the pretreatment comprises centrifuging and dehydrating the contaminated lubricating oil, preferably the pretreatment comprises centrifuging and vacuum dehydrating the contaminated lubricating oil.
[0039] The method according to the present invention has no particular restrictions on the type and source of the contaminated lubricating oil in principle, and those skilled in the art can select it according to actual needs. For example, the contaminated lubricating oil can be selected from one or more of super refined oil, hydraulic oil, refrigeration compressor oil, gear oil, lithium battery diaphragm white oil, vacuum pump fluorine oil, quenching oil and metal rolling oil, especially super refined oil.
[0040] The method according to the present invention can be used to treat lubricating oils with a wide viscosity range, and is particularly suitable for treating lubricating oils with high viscosity. In particular, the kinematic viscosity of the contaminated lubricating oil at 40°C can be 2-10 centistokes (cst), for example, 2, 3, 4, 5, 6, 7, 8, 9, 10 cst or a range defined by any two of the above values.
[0041] In one or more embodiments, the lubricating oil in the contaminated lubricating oil is a superfine oil having a kinematic viscosity at 40° C. of 2-10 cst, such as 4-5 cst.
[0042] The contaminated lubricating oil may contain various possible contaminant particles. For example, the contaminants in the contaminated lubricating oil may include one or more selected from dust, grit, metal and rust.
[0043] The pretreatment step may remove a portion of the contaminants contained in the contaminated lubricating oil, in particular up to 95% by weight, such as up to 90% by weight, up to 85% by weight, up to 80% by weight, up to 75% by weight, up to 70% by weight, up to 65% by weight, up to 60% by weight, up to 55% by weight, up to 50% by weight, up to 45% by weight, up to 40% by weight, up to 35% by weight or up to 30% by weight of the contaminants contained in the contaminated lubricating oil. The pretreatment step may remove contaminant particles of larger size, such as contaminant particles having a diameter greater than 4 μm, in particular contaminant particles having a diameter greater than 6 μm, more particularly contaminant particles having a diameter greater than 14 μm.
[0044] This pretreatment step may remove a portion of the water contained in the contaminated lubricating oil, in particular may remove up to 95 wt.-%, for example up to 90 wt.-%, up to 85 wt.-%, up to 80 wt.-%, up to 75 wt.-%, up to 70 wt.-%, up to 65 wt.-%, up to 60 wt.-%, up to 55 wt.-%, up to 50 wt.-%, up to 45 wt.-%, up to 40 wt.-%, up to 35 wt.-% or up to 30 wt.-% of the water contained in the contaminated lubricating oil.
[0045] Step (2)
[0046] In step (2), the pretreated lubricating oil obtained in step (1) is subjected to membrane separation treatment to obtain a first purified lubricating oil and a lubricating oil rich in pollutants. The membrane separation step can be performed continuously. Through the membrane separation step, most of the lubricating oil is purified, leaving only a small portion of the lubricating oil rich in pollutants, thereby ensuring a high purification efficiency.
[0047] The method according to the present invention has no particular limitation on the membrane used in the membrane separation process in principle, and those skilled in the art can select any known membrane that can be used for oil separation process according to actual needs. For example, the membrane used for membrane separation process can be selected from one or more of a ceramic membrane, a silicon carbide membrane and a graphene membrane, preferably a graphene membrane.
[0048] The membrane separation treatment may be carried out at a temperature of 20° C. to 80° C., preferably 25° C. to 50° C. For example, the temperature of the membrane separation treatment may be 20° C., 25° C., 30° C., 35° C., 40° C., 45° C., 50° C., 55° C., 60° C., 65° C., 70° C., 75° C., 80° C., or a range defined by any two of the above values.
[0049] Membrane separation can be carried out at 0.5-6.0kg / cm 2 , preferably 1.0-3.0kg / cm 2 For example, the operating pressure of the membrane separation process can be 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0 kg / cm 2 Or a range defined by any two of the above values.
[0050] The first purified lubricating oil can achieve a higher cleanliness level. In particular, for a waste oil with a cleanliness level of 27 / 26 / 21 according to ISO 4406, the first purified lubricating oil can achieve a cleanliness level according to ISO 4406 of, for example, 15 / 12 / 10.
[0051] Step (3)
[0052] In step (3), the lubricating oil rich in pollutants obtained in step (2) is mixed with a flocculant and subjected to flocculation treatment to obtain a mixture.
[0053] The flocculant may include one or more selected from polyalkylene glycol, polyacrylamide and polyacrylic acid. In a preferred embodiment, the flocculant may include polyalkylene glycol, such as polyethylene glycol, polypropylene glycol, etc., preferably polyethylene glycol.
[0054] In step (3), the mixing mass ratio of the pollutant-rich lubricating oil to the flocculant may be 500:1 to 1000:1, for example, 500:1, 600:1, 700:1, 800:1, 900:1, 1000:1 or a range defined by any two of the above values.
[0055] The flocculation treatment may include mixing the contaminant-rich lubricating oil obtained in step (2) with a flocculant and then subjecting it to sedimentation. In one or more embodiments, the sedimentation time is 1-30 hours, more preferably 3-20 hours. For example, the sedimentation time may be 1, 5, 10, 15, 20, 25, 30 hours or a range defined by any two of the above values. The applicant has found that the method according to the present invention can greatly shorten the treatment time, especially the sedimentation time required in the flocculation process, by combining membrane separation with flocculation technology. However, if the contaminated lubricating oil is treated only by a single flocculation process (i.e., without previous membrane separation treatment), for the same treatment volume, it usually takes several times more time than the present invention.
[0056] The present invention first uses pretreatment and membrane separation technology to purify lubricating oil, and then flocculates the lubricating oil containing pollutants obtained by membrane separation. Since most of the contaminated lubricating oil has been purified by membrane separation technology, compared with the purification of lubricating oil by flocculation process alone, the amount of lubricating oil rich in pollutants that needs to be flocculated in the flocculation process of the method according to the present invention is significantly reduced, so that the required sedimentation time can be greatly shortened, so even the treatment of high-viscosity lubricating oil can be completed in a shorter time. In addition, in the method according to the present invention, the concentrated oil product obtained by membrane separation is treated by the flocculation process, and the oil in the concentrated oil product can be recovered, thereby improving the overall oil yield. In particular, the purification method according to the present invention can achieve a yield of at least 97% of the purified oil, and the flocculation process can capture almost all sizes of particles in the concentrate, especially submicron and nanometer-scale particles, so as to obtain a purified oil product with an excellent cleanliness level.
[0057] Step (4)
[0058] In step (4), floccules are separated from the mixture obtained in step (3) to obtain a second purified lubricating oil.
[0059] In principle, there is no particular limitation on the specific separation method, and those skilled in the art can select any separation method that can be used to separate floccules.
[0060] In one or more embodiments, in step (4), the separation comprises filtering the mixture obtained in step (3), for example, one or more selected from cellulose filtration, cartridge filtration, electrostatic filtration and centrifugal filtration. In one or more embodiments, in step (4), the separation comprises cellulose filtration.
[0061] Optional recycle step
[0062] The second purified lubricating oil obtained in step (4) can also be recycled. In particular, the method for purifying contaminated lubricating oil according to the present invention can also include recycling the second purified lubricating oil to step (1) (i.e., the pretreatment step) to perform secondary purification on the second purified lubricating oil. This recycling process can further improve the cleanliness of the obtained purified oil product and help improve the yield and purification efficiency.
[0063] Systems for purifying contaminated lubricating oils
[0064] The system for purifying contaminated lubricating oil according to the second aspect of the present invention comprises a pretreatment unit, a membrane separation unit, a flocculation unit and a separation unit in sequence. Specifically, the system for purifying contaminated lubricating oil according to the present invention comprises:
[0065] - a pretreatment unit, which is used to pretreat the contaminated lubricating oil to remove part of the contaminants and water to obtain pretreated lubricating oil, preferably the pretreatment unit comprises one or more selected from a centrifuge, a dehydration device, a natural sedimentation device and a filtering device;
[0066] a membrane separation unit downstream of the pretreatment unit, comprising a membrane separation device for subjecting the pretreated lubricating oil from the pretreatment unit to a membrane separation treatment to produce a first purified lubricating oil and a lubricating oil enriched with pollutants, a clean oil tank for receiving the first purified lubricating oil, and a concentrated oil tank for receiving the lubricating oil enriched with pollutants;
[0067] a flocculation unit downstream of the membrane separation unit, comprising a storage device for storing a flocculant, a flocculation device for performing a flocculation treatment, a first conduit for supplying the lubricating oil rich in pollutants from the concentrated oil tank to the flocculation device, and a second conduit for supplying the flocculant from the storage device to the flocculation device, the flocculation device for mixing the lubricating oil rich in pollutants from the concentrated oil tank supplied to the flocculation device and the flocculant from the storage device and performing a flocculation treatment; and
[0068] - a separation unit downstream of the flocculation unit for separating the flocs from the mixture coming from the flocculation unit to obtain a second purified lubricating oil.
[0069] Each unit will be described in detail below.
[0070] Preprocessing unit
[0071] The pretreatment unit is configured to pretreat the contaminated lubricating oil to remove part of the contaminants and water to obtain pretreated lubricating oil. The pretreatment unit can remove large particles and most of the water in the contaminated oil, reducing the load of subsequent membrane separation and flocculation processes.
[0072] In one or more embodiments, the pretreatment unit includes one or more of the following devices: a centrifuge, a dehydration device, a natural sedimentation device, and a filtering device. In a preferred embodiment, the pretreatment unit includes a metal sintered filter element filtering (coarse filtering) device. In a preferred embodiment, the pretreatment unit includes a combination of a centrifuge and a dehydration device, preferably a combination of a centrifuge and a vacuum dehydration device.
[0073] Membrane separation unit
[0074] The membrane separation unit is arranged downstream of the pretreatment unit, and is configured to perform membrane separation treatment on the pretreated lubricating oil.
[0075] The membrane separation unit may include a membrane separation device for subjecting the pretreated lubricating oil from the pretreatment unit to membrane separation treatment to produce a first purified lubricating oil and a lubricating oil rich in pollutants, a clean oil tank for receiving the first purified lubricating oil, and a concentrated oil tank for receiving the lubricating oil rich in pollutants.
[0076] In one or more embodiments, the concentrated oil tank may have a stirring device for stirring the lubricating oil rich in pollutants to be uniform for transportation.
[0077] Flocculation unit
[0078] The flocculation unit is arranged downstream of the membrane separation unit and is configured to perform flocculation treatment on the lubricating oil rich in pollutants from the concentrated oil tank.
[0079] The flocculation unit may include a storage device for storing a flocculant, a flocculation device for performing a flocculation process, a first conduit for supplying the lubricating oil rich in pollutants from the concentrated oil tank to the flocculation device, and a second conduit for supplying the flocculant from the storage device to the flocculation device. The flocculation device may be used to mix the lubricating oil rich in pollutants from the concentrated oil tank supplied to the flocculation device and the flocculant from the storage device and perform a flocculation process.
[0080] Separation unit
[0081] A separation unit is arranged downstream of the flocculation unit and is configured to separate flocs from the mixture from the flocculation unit to obtain a second purified lubricating oil.
[0082] In one or more embodiments, the separation unit may include a filtration device. In one or more embodiments, the separation unit may include a cellulose filtration device.
[0083] In addition to the above-described units, the system for purifying contaminated lubricating oil according to the present invention may further include a pipeline downstream of the separation unit for recycling the second purified lubricating oil from the separation unit to the pretreatment unit.
[0084] The following will be combined Figure 1 A method and system for purifying contaminated lubricating oil according to an exemplary embodiment of the present invention is described.
[0085] exist Figure 1 In the method, the contaminated lubricating oil to be treated is first transported from the dirty oil tank 1 to the pretreatment device 3 through the pump 2. The pretreatment device 3 may be a combination of a centrifuge and a vacuum dehydration device, which is mainly used to remove large particles and most of the water in the dirty oil. Then, the pretreated lubricating oil is supplied to the membrane separation device 4 for treatment to obtain two parts of oil, wherein the clean oil is supplied to the clean oil tank 5, and the other part of the oil rich in pollutants is supplied to the concentrated oil tank 6. The concentrated oil tank 6 may be provided with a stirring paddle, which stirs the oil rich in pollutants evenly for transportation. Then, on the one hand, the oil rich in pollutants is transported from the concentrated oil tank 6 to the flocculation device 10 through the pump 7. On the other hand, the flocculant stored in the storage device 8 is transported to the flocculation device 10 through the pump 9. A metering pump can be used to accurately transport the flocculant. In the flocculation device 10, the flocculant is dispersed in the oil rich in pollutants to flocculate and settle the oil to obtain a flocculated mixture. Finally, the obtained mixture is transported to the separation device 11 to separate the flocculants and obtain clean oil.
[0086] Example
[0087] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.
[0088] Hereinafter, unless otherwise specified, the contents or concentrations mentioned are all based on mass.
[0089] Materials used
[0090] The materials used in the following examples are as follows:
[0091] Raw material waste oil to be treated: super refined oil, whose kinematic viscosity at 40°C is 4.2 cst, and which has the following cleanliness:
[0092] Unprocessed ISO 4406 27 / 26 / 21 >4μm(c) 992098 >6μm(c) 392572 >14μm(c) 14792
[0093] Membrane used for membrane separation treatment: graphene membrane (purchased from Weihai Suotong Energy Saving Technology Co., Ltd.);
[0094] Flocculant used: Product ORL01 from SKF, which comprises polyethylene glycol.
[0095] Purification process
[0096] The total weight of 9.6 kg of the raw waste oil to be treated was supplied to a 50 micron coarse filter for filtration for pretreatment. The coarsely filtered oil was then supplied to a membrane separation device (operating temperature: 25°C, operating pressure: 1 bar) for membrane separation treatment for 0.5 hours to obtain purified oil (8.4 kg) and a concentrate containing a large amount of impurities (1.2 kg). The concentrate was transported to the dirty oil tank, and the purified oil obtained by membrane separation was transported to the clean oil tank. Then the concentrate was transported from the dirty oil tank to the DST Proof of Concept (POC), serial number: 1010-1990, obtained from SKF), and the flocculant was transported from the storage tank to the flocculation device, the concentrate and the flocculant were mixed and flocculated in the flocculation device at a mass ratio of 1000:1 for 1 hour, and settled for 4 hours, and then the mixture obtained by flocculation treatment was transported to the separation device of the above-mentioned DST experimental equipment to separate the flocculants (operating temperature: 25°C, operating pressure: 0.1 bar), and finally 0.98 kg of oil was recovered and returned to the pretreatment process for circulation and purification, and the single yield of the purified oil obtained was 1-(1.2-0.98) / 9.6=97.71%. The cleanliness level of the oil at each stage according to ISO 4406 is shown in Table 1 below:
[0097] Table 1 Cleanliness level of oil at each stage of purification process
[0098]
[0099] As can be seen from the table above, the concentration of pollutants of various particle sizes in the concentrate obtained by membrane separation treatment increases sharply compared with the untreated oil and the pretreated oil. Such concentrate is considered to have no recycling value in the prior art, so it is usually directly discarded. However, as can be seen from the table above, by flocculating such concentrate, the cleanliness level of the obtained purified oil has reached a level that is close to the cleanliness level of the purified oil obtained by membrane separation treatment. By recycling the purified oil obtained by flocculation treatment to the pretreatment step, its cleanliness level can be further improved.
[0100] From the above results, it can be seen that the method according to the present invention obtains clean oil products with a higher cleanliness level by using a combination of membrane separation and flocculation processes, and from a comprehensive perspective of yield and processing time, compared with single membrane separation treatment or single flocculation treatment, the method according to the present invention takes advantage of the respective advantages of the two processes and achieves the best balance between yield and purification efficiency.
Claims
1. A method for purifying contaminated lubricating oil, the method comprising the following steps: (1) pre-treating the contaminated lubricating oil to remove part of the contaminants and water to obtain pre-treated lubricating oil, preferably the pre-treatment comprises one or more of centrifugation, dehydration, natural sedimentation and filtration; (2) subjecting the pretreated lubricating oil obtained in step (1) to membrane separation treatment to obtain a first purified lubricating oil and a lubricating oil rich in pollutants; (3) mixing the contaminant-rich lubricating oil obtained in step (2) with a flocculant and performing flocculation treatment to obtain a mixture; and (4) Separating flocculants from the mixture obtained in step (3) to obtain a second purified lubricating oil.
2. The method according to claim 1, further comprising recycling the second purified lubricating oil to step (1) to perform secondary purification on the second purified lubricating oil.
3. The method according to claim 1 or 2, wherein The membrane separation treatment is carried out at a temperature of 20°C to 80°C, preferably 25°C to 50°C, and / or the membrane separation treatment is carried out at a pressure of 0.5 to 6.0 kg / cm 2 , preferably 1.0-3.0kg / cm 2 under operating pressure.
4. The method according to claim 1 or 2, wherein The flocculant comprises a polyalkylene glycol, preferably polyethylene glycol.
5. The method according to claim 1 or 2, wherein In step (3), the mixing mass ratio of the pollutant-rich lubricating oil to the flocculant is 500:1 to 1000:
1.
6. The method according to claim 1 or 2, wherein: The flocculation treatment comprises mixing the pollutant-rich lubricating oil obtained in step (2) with a flocculant and then subjecting the mixture to sedimentation. Preferably, the sedimentation time is 1-30 hours, more preferably 3-20 hours.
7. The method according to claim 1 or 2, wherein: The contaminants in the contaminated lubricating oil include one or more selected from the group consisting of dust, grit, metal and rust.
8. The method according to claim 1 or 2, wherein: The lubricating oil in the contaminated lubricating oil is a super-fine oil, for example, whose kinematic viscosity at 40° C. is 2-10 cst.
9. A system for purifying contaminated lubricating oil, the system comprising: - a pretreatment unit, which is used to pretreat the contaminated lubricating oil to remove part of the contaminants and water to obtain pretreated lubricating oil, preferably the pretreatment unit comprises one or more of a centrifuge, a dehydration device, a natural sedimentation device and a filtering device; a membrane separation unit downstream of the pretreatment unit, comprising a membrane separation device (4) for subjecting the pretreated lubricating oil from the pretreatment unit to membrane separation treatment to produce a first purified lubricating oil and a lubricating oil rich in pollutants, a clean oil tank (5) for receiving the first purified lubricating oil, and a concentrated oil tank (6) for receiving the lubricating oil rich in pollutants; - a flocculation unit downstream of the membrane separation unit, comprising a storage device (8) for storing a flocculant, a flocculation device (10) for performing a flocculation treatment, a first pipeline for supplying the lubricating oil rich in pollutants from the concentrated oil tank (6) to the flocculation device (10), and a second pipeline for supplying the flocculant from the storage device (8) to the flocculation device (10), the flocculation device (10) being used to mix the lubricating oil rich in pollutants from the concentrated oil tank (6) supplied to the flocculation device (10) and the flocculant from the storage device (8) and perform a flocculation treatment; and - a separation unit downstream of the flocculation unit for separating the flocs from the mixture coming from the flocculation unit to obtain a second purified lubricating oil.
10. The system according to claim 9, wherein: The system also includes a conduit downstream of the separation unit for recycling the second purified lubricating oil from the separation unit to the pretreatment unit.