Hydrogenation pretreatment method for waste lubricating oil

Abstract

The present invention relates to a waste lubricating oil hydrogenation pretreatment method, which comprises: contacting waste lubricating oil and a composite extraction agent in an extractive distillation tower to carry out extractive distillation treatment so as to obtain a first mixed solution containing the composite extraction agent from the tower top of the extractive distillation tower, the pretreated waste lubricating oil is obtained from a tower kettle of the extractive distillation tower; wherein the composite extraction agent comprises a first component and a second component, the first component comprises one or more of a pyrrolidone compound, a furan aldehyde compound and an amide compound, and the second component comprises an ester compound. The pretreated waste lubricating oil obtained through the method is low in water content and light hydrocarbon content, the phosphorus content and the sulfur content are both reduced, and it is guaranteed that the hydrofining catalyst has stability and activity for a long time.

Description

Technical Field

[0001] The present disclosure relates to the field of waste lubricating oil regeneration, and in particular, to a method for hydrogenation pretreatment of waste lubricating oil. Background Art

[0002] The fan lubricating oil will deteriorate in long-term use, and the waste lubricating oil produced is waste mineral oil. If the waste lubricating oil is discarded or incinerated, it will cause serious pollution to the environment. Lubricating oil is composed of base oil and additives. Although the properties of waste fan lubricating oil have changed, the main components are still base oil and additives. The degree of deterioration is low and the recycling value is high. It can be recycled or used to produce profitable materials for further use. Waste lubricating oil regeneration not only reduces the consumption of crude oil in lubricating oil production and alleviates the energy crisis, but also helps to improve air quality, land and water pollution in the environment.

[0003] The typical waste oil regeneration process mainly includes: dehydration, removal of light hydrocarbons, fractionation and refining. The waste lubricating oil regeneration treatment technologies include acid-clay method, solvent refining method, hydrofining method, film regeneration, etc. The acid-clay regeneration process will produce a large amount of acid waste residue, alkaline waste residue and sewage during the waste oil regeneration process, which not only causes serious secondary pollution but also has a low waste oil regeneration rate; although the solvent refining process does not use acid solution, its disadvantage is that it produces a large amount of waste chemical reagents and wastewater. At present, the hydrofining method is an important advanced process in the regeneration of waste lubricating oil. It has the advantages of no pollution, high product yield, good quality, good operation flexibility and adaptability to large-scale production. Therefore, it has received widespread attention in waste oil regeneration.

[0004] For high-end lubricating oil products such as fan lubricating oil, which contain special extreme pressure agents, anti-wear agents, antioxidants, demulsifiers and other complex additives, waste fan lubricating oil still contains these additive pollutants mainly polar compounds such as S and P. If the waste fan lubricating oil is directly hydrotreated, the additive pollutants will cause the pores of the hydrogenation catalyst to be blocked, and even cause scaling and blockage of the reactor device, affecting the long-term operation of the device.

[0005] For the pretreatment of waste lubricating oil, the existing process is mainly for mineral oil or semi-synthetic lubricating oil of medium and low viscosity and general quality, in which the impurities are mainly solid particles, water and light hydrocarbons, etc. The pretreatment method is mainly distillation, which is relatively simple; while for high-viscosity fully synthetic lubricating oil products such as fan lubricating oil, which contain special extreme pressure agents, anti-wear agents, antioxidants, demulsifiers and other complex additives, the waste fan oil contains polar additive pollutants such as sulfur and phosphorus.

[0006] Represented by the Kleen and KTI processes, the currently widely used and relatively mature pretreatment method is atmospheric and vacuum distillation. However, for pollutants brought by fan oil additives, direct distillation will cause scaling and blockage problems in the distillation device pipelines, affecting the long-term operation of the device. Represented by the Hylude process, BERC process and domestic patents, mild hydrogenation or light solvent extraction methods can remove some pollutants, but the removal ability for polar additive components is very weak, which will still cause blockage of the hydrogenation catalyst pores and even blockage of the entire bed. Summary of the invention

[0007] The purpose of the present disclosure is to provide a method for hydrogenation pretreatment of waste lubricating oil, wherein the pretreated waste lubricating oil obtained by the method has low water content, low light hydrocarbon content, and reduced phosphorus content and sulfur content, thereby ensuring that the hydrogenation refining catalyst has long-term stability and activity.

[0008] In order to achieve the above object, the present disclosure provides a method for hydrogenation pretreatment of waste lubricating oil, the method comprising: The waste lubricating oil and the composite extractant are contacted in an extractive distillation tower for extractive distillation treatment, a first mixed liquid containing the composite extractant is obtained from the top of the extractive distillation tower, and the pretreated waste lubricating oil is obtained from the bottom of the extractive distillation tower; The composite extractant comprises a first component and a second component, wherein the first component comprises one or more of pyrrolidone compounds, furan aldehyde compounds and amide compounds, and the second component comprises an ester compound.

[0009] Optionally, based on the weight of the composite extractant, the weight content of the first component is 65-99wt%, preferably 80-90wt%, and the weight content of the second component is 1-35wt%, preferably 10-20wt%.

[0010] Optionally, the furan aldehyde compound includes one or more of furfural and 2-furanacetaldehyde, preferably furfural; the amide compound includes N,N-dimethylformamide and / or N,N-dimethylacetamide; the pyrrolidone compound includes one or more of N-methylpyrrolidone, α-pyrrolidone and N-vinylpyrrolidone; the ester compound includes one or more of 1,4-butyrolactone and ethylene glycol carbonate.

[0011] Optionally, the conditions of the extractive distillation treatment include: a pressure of -0.01 to -0.08 MPa, preferably -0.05 to -0.08 MPa; the number of theoretical plates of the extractive distillation tower is 10 to 50, preferably 20 to 40; the reflux ratio is 0.1 to 2, preferably 0.5 to 1; the bottom temperature is 180 to 200°C, and the top temperature is 140 to 160°C.

[0012] Optionally, the weight ratio of the composite extractant to the waste lubricating oil is 0.25-4:1, preferably 1-2:1.

[0013] Optionally, the method further comprises: The first mixed liquid is fed into a first distillation tower for a first distillation treatment, and then the top mixed liquid of the first distillation tower is fed into a second distillation tower for a second distillation treatment, a circulating water stream is obtained from the top of the second distillation tower, and a regenerated extractant is obtained from the bottom of the second distillation tower; The regenerated extractant is returned to the extractive distillation tower for continued use.

[0014] Optionally, the conditions of the first distillation treatment include: a pressure of -0.01 to -0.08 MPa, preferably -0.05 to -0.08 MPa; the number of theoretical plates of the first distillation tower is 10 to 50, preferably 20 to 40; the reflux ratio is 3 to 7, the bottom temperature is 130 to 150°C, and the top temperature is 90 to 110°C.

[0015] Optionally, the conditions of the second distillation treatment include: being carried out under normal pressure, the normal pressure is 0.1~0.2MPa, the number of theoretical plates of the second distillation tower is 10~50, preferably 20~40; the reflux ratio is 0.1~1, the bottom temperature is 105~115°C, and the top temperature is 90~100°C.

[0016] Optionally, the method further comprises filtering the waste lubricating oil before entering the extractive distillation tower; The waste lubricating oil has a water content of 0-10wt%, a light hydrocarbon content of 0-10wt%, a phosphorus content of 0-0.1wt%, a sulfur content of 0-1.0wt%, and a kinematic viscosity of 100°C of 10-320mm. 2 / s.

[0017] Optionally, the water content in the pretreated waste lubricating oil is less than 1 ppm, the light hydrocarbon content is less than 1 ppm, the phosphorus content is less than 50 ppm, and the sulfur content is less than 200 ppm.

[0018] Through the above technical scheme, the present invention uses a composite extractant to perform extractive distillation treatment on waste lubricating oil, which can remove pollutants such as water, light hydrocarbons and polar additives in the waste lubricating oil in one step, avoiding the pollutants in the waste fan lubricating oil from clogging the hydrotreating catalyst and the entire reactor bed, thereby enabling the hydrotreating process to operate stably for a long time. The pretreated waste lubricating oil obtained by the method disclosed in the present invention has low water content, low light hydrocarbon content, and reduced phosphorus content and sulfur content, ensuring the long-term stability and activity of the hydrotreating catalyst.

[0019] Other features and advantages of the present disclosure will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings are used to provide a further understanding of the present disclosure and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present disclosure but do not constitute a limitation of the present disclosure. In the accompanying drawings: Figure 1 It is a process flow chart of the pretreatment method of the embodiment of the present disclosure.

[0021] Description of Reference Numerals 1: waste lubricating oil; 2: composite extractant; 3: pretreated waste lubricating oil; 4: first mixed liquid; 5: third mixed liquid; 6: second mixed liquid; 7: regenerated extractant; 8: circulating water; A: extractive distillation tower; E: first distillation tower; I: second distillation tower. DETAILED DESCRIPTION

[0022] The specific implementation of the present disclosure is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described herein is only used to illustrate and explain the present disclosure, and is not used to limit the present disclosure.

[0023] The present disclosure provides a method for hydrogenation pretreatment of waste lubricating oil, the method comprising: The waste lubricating oil and the composite extractant are contacted in an extractive distillation tower for extractive distillation treatment, a first mixed liquid containing the composite extractant is obtained from the top of the extractive distillation tower, and the pretreated waste lubricating oil is obtained from the bottom of the extractive distillation tower; The composite extractant comprises a first component and a second component, the first component comprises one or more of pyrrolidone compounds, furan aldehyde compounds and amide compounds, and the solute component comprises an ester compound.

[0024] The present invention uses a composite extractant to perform extractive distillation treatment on waste lubricating oil, which can remove pollutants such as water, light hydrocarbons and polar additives in the waste lubricating oil in one step, avoiding the pollutants in the waste fan lubricating oil from clogging the hydrotreating catalyst and the entire reactor bed, thereby enabling the hydrotreating process to operate stably for a long time. The pretreated waste lubricating oil obtained by the method disclosed in the present invention has low water content, low light hydrocarbon content, and reduced phosphorus content and sulfur content, ensuring the long-term stability and activity of the hydrotreating catalyst.

[0025] According to an embodiment of the present disclosure, based on the weight of the composite extractant, the weight content of the first component is 65-99wt%, preferably 80-90wt%, and the weight content of the second component is 1-35wt%, preferably 10-20wt%. The above embodiment is conducive to removing pollutants such as water, light hydrocarbons and polar additives from waste lubricating oil in one step, and is conducive to reducing the water content, light hydrocarbon content, phosphorus content and sulfur content in waste lubricating oil.

[0026] According to an embodiment of the present disclosure, the furan aldehyde compound can be a furan aldehyde with a carbon number of 4 to 6, for example, it can include one or more of furfural and 2-furanacetaldehyde, preferably furfural. The above embodiment is conducive to removing pollutants such as water, light hydrocarbons and polar additives from waste lubricating oil in one step, and is conducive to reducing the water content, light hydrocarbon content, phosphorus content and sulfur content in waste lubricating oil.

[0027] According to one embodiment of the present disclosure, the amide compound may be an amide with a carbon number of 3 to 6, for example, N,N-dimethylformamide and / or N,N-dimethylacetamide. The above embodiment is conducive to removing pollutants such as water, light hydrocarbons and polar additives from waste lubricating oil in one step, and is conducive to reducing the water content, light hydrocarbon content, phosphorus content and sulfur content in waste lubricating oil.

[0028] According to an embodiment of the present disclosure, the pyrrolidone compound may be a pyrrolidone with a carbon number of 5 to 6, for example, may include one or more of N-methylpyrrolidone and N-vinylpyrrolidone. The above embodiment is conducive to removing pollutants such as water, light hydrocarbons and polar additives from waste lubricating oil in one step, and is conducive to reducing the water content, light hydrocarbon content, phosphorus content and sulfur content in waste lubricating oil.

[0029] According to an embodiment of the present disclosure, the ester compound may be an ester with a carbon number of 3 to 6, and may include one or more of 1,4-butyrolactone and ethylene glycol carbonate, preferably 1,4-butyrolactone. The above embodiment is conducive to removing pollutants such as water, light hydrocarbons and polar additives from waste lubricating oil in one step, and is conducive to reducing the water content, light hydrocarbon content, phosphorus content and sulfur content in waste lubricating oil.

[0030] According to an embodiment of the present disclosure, the conditions of the extractive distillation treatment include: pressure of -0.01 to -0.08 MPa, preferably -0.05 to -0.08 MPa; the number of theoretical plates of the extractive distillation tower is 10 to 50, preferably 20 to 40; the reflux ratio is 0.1 to 2, preferably 0.5 to 1; the tower bottom temperature is 180 to 200°C, and the tower top temperature is 140 to 160°C. The above embodiment is conducive to removing pollutants such as water, light hydrocarbons and polar additives from waste lubricating oil in one step, and is conducive to reducing the water content, light hydrocarbon content, phosphorus content and sulfur content in waste lubricating oil.

[0031] According to one embodiment of the present disclosure, the weight ratio of the composite extractant to the waste lubricating oil is 0.25-4:1, preferably 1-2:1. The above embodiment is conducive to removing pollutants such as water, light hydrocarbons and polar additives in the waste lubricating oil in one step, and is conducive to reducing the water content, light hydrocarbon content, phosphorus content and sulfur content in the waste lubricating oil.

[0032] According to an embodiment of the present disclosure, the method further includes: allowing the first mixed liquid to enter a first distillation tower for a first distillation treatment, then allowing the top mixed liquid of the first distillation tower to enter a second distillation tower for a second distillation treatment, obtaining a circulating water flow from the top of the second distillation tower, and obtaining a regenerated extractant from the bottom of the second distillation tower; and returning the regenerated extractant to the extractive distillation tower for continued use. The above embodiment is conducive to obtaining circulating water and regenerated extractant, reducing process energy consumption, and reducing raw material costs.

[0033] In one embodiment, a third mixed liquid containing light hydrocarbons and polar additives is obtained from the bottom of the first distillation tower, and those skilled in the art can further separate the light hydrocarbons and polar additives according to conventional techniques.

[0034] According to an embodiment of the present disclosure, the conditions of the first distillation treatment include: pressure of -0.01 to -0.08 MPa, preferably -0.05 to -0.08 MPa; the number of theoretical plates of the first distillation tower is 10 to 50, preferably 20 to 40; the reflux ratio is 3 to 7, the tower bottom temperature is 130 to 150° C., and the tower top temperature is 90 to 110° C. The above embodiment is conducive to further obtaining a circulating water flow, further regenerating the composite extractant, and reducing the cost of raw materials.

[0035] According to an embodiment of the present disclosure, the conditions of the second distillation treatment include: being carried out under normal pressure, the normal pressure is 0.1-0.2 MPa, the number of theoretical plates of the second distillation tower is 10-50, preferably 20-40; the reflux ratio is 0.1-1, the tower bottom temperature is 105-115° C., and the tower top temperature is 90-100° C. The above embodiment is conducive to further obtaining a circulating water flow and regenerating an extractant, and is conducive to reducing raw material costs.

[0036] According to an embodiment of the present disclosure, the method further includes filtering the waste lubricating oil before entering the extractive distillation tower, wherein the waste lubricating oil after filtering has a water content of 0-10wt%, a light hydrocarbon content of 0-10wt%, a phosphorus content of 0-0.1wt%, and a sulfur content of 0-1.0wt%.

[0037] According to one embodiment of the present disclosure, the water content in the pretreated waste lubricating oil is less than 1 ppm, the light hydrocarbon content is less than 1 ppm, the phosphorus content is less than 50 ppm, and the sulfur content is less than 200 ppm. In a further embodiment, the pretreated waste lubricating oil enters a hydrogenation process, and the pretreated waste lubricating oil obtained in the present disclosure has low water content, low light hydrocarbon content, and reduced phosphorus content and sulfur content, ensuring that the hydrorefining catalyst has long-term stability and activity.

[0038] The present disclosure is further illustrated below by way of examples, but the present disclosure is not limited thereby.

[0039] Unless otherwise specified, the other chemical reagents used in the examples are commercially available products.

[0040] In the present disclosure, the properties of the pretreated waste fan lubricating oil are measured through the full index and conventional index analysis of GB / T 33540.3-2017.

[0041] Example 1 The waste fan lubricating oil used in this embodiment 1 has a water content of 2 wt%, a light hydrocarbon content of 10 wt%, a phosphorus content of 450 ppm, and a sulfur content of 2350 ppm; the composite extractant used in this embodiment 1 includes 50 wt% N-methylpyrrolidone, 35 wt% furfural, and 15 wt% 1,4-butyrolactone; the weight ratio of the composite extractant to the waste fan lubricating oil is 0.6:1; like Figure 1 As shown, the method for hydrogenation pretreatment of waste lubricating oil includes: (1) waste lubricating oil 1 and composite extractant 2 are contacted in an extractive distillation tower A for extractive distillation treatment, a first mixed liquid 4 containing the composite extractant is obtained from the top of the extractive distillation tower A, and pretreated waste lubricating oil 3 is obtained from the bottom of the extractive distillation tower; (2) The first mixed liquid 4 is introduced into a first distillation tower E for a first distillation treatment, and a second mixed liquid 6 containing water and an extractant is obtained at the top of the first distillation tower, and a third mixed liquid 5 containing light hydrocarbons and a polar additive is obtained at the bottom of the tower; then, the second mixed liquid 6 at the top of the first distillation tower E is introduced into a second distillation tower I for a second distillation treatment, and a circulating water stream 8 is obtained from the top of the second distillation tower I, and a regenerated extractant is obtained from the bottom of the second distillation tower I; the regenerated extractant 7 is returned to the extractive distillation tower for continued use; the specific operating conditions are shown in Table 1.

[0042] The waste fan lubricating oil obtained from the bottom of the extractive distillation tower A has the following properties: water content is less than 1 ppm, light hydrocarbons are less than 1 ppm, phosphorus content is 13 ppm, sulfur content is 63 ppm, polar additive removal rate is more than 95%, and oil recovery rate is more than 85%.

[0043] Example 2 This embodiment adopts the same method as that of embodiment 1, except that: the properties of the waste fan lubricating oil used in this embodiment 2 are: 3 wt% water content, 6 wt% light hydrocarbon content, 251 ppm phosphorus content, and 4870 ppm sulfur content; the composite extractant used in this embodiment 2 includes 55 wt% N,N-dimethylformamide, 35 wt% furfural, and 10 wt% 1,4-butyrolactone; the weight ratio of the composite extractant to the waste fan lubricating oil is 1:1; the specific operating conditions are shown in Table 1; The properties of the pretreated waste fan lubricating oil obtained in Example 2 are as follows: the water content is less than 1 ppm, the light hydrocarbons are less than 1 ppm, the phosphorus content is 4 ppm, and the sulfur content is 98 ppm.

[0044] Example 3 This example uses the same method as Example 1, except that: the properties of the waste fan lubricating oil used in this Example 3 are: water content is 4 wt%, light hydrocarbon content is 4 wt%, phosphorus content is 403 ppm, and sulfur content is 3780 ppm; the composite extractant used in this example is 85 wt% NN-dimethylformamide and 15 wt% 1,4-butyrolactone; the weight ratio of the composite extractant to the waste fan lubricating oil is 1.5:1; the specific operating conditions are shown in Table 1; The properties of the waste fan lubricating oil obtained in this example are: water content is less than 1 ppm, light hydrocarbons are less than 1 ppm, phosphorus content is 11 ppm, and sulfur content is 69 ppm.

[0045] Example 4 This Example 4 is the same as Example 1, except that the composite extractant used in this Example includes 10 wt % N-methylpyrrolidone, 85 wt % furfural and 5 wt % 1,4-butyrolactone; the specific operating conditions are shown in Table 1.

[0046] The waste fan lubricating oil obtained from the bottom of the extractive distillation tower A has the following properties: water content is less than 1 ppm, light hydrocarbons are less than 1 ppm, phosphorus content is 45 ppm, and sulfur content is 150 ppm.

[0047] Example 5 This embodiment 5 is the same as embodiment 1, except that the conditions of the extractive distillation treatment are different from those of embodiment 1. The specific operating conditions are shown in Table 1; The waste fan lubricating oil obtained from the bottom of the extractive distillation tower A has the following properties: water content is less than 1 ppm, light hydrocarbons are less than 1 ppm, phosphorus content is 50 ppm, and sulfur content is 180 ppm.

[0048] Comparative Example 1 The method of this comparative example 1 is the same as that of Example 1, except that the extractant used in this comparative example is furfural; the specific operating conditions are shown in Table 1.

[0049] The waste fan lubricating oil obtained from the bottom of the extractive distillation tower A has the following properties: water content is less than 1 ppm, light hydrocarbons are less than 1 ppm, phosphorus content is 230 ppm, and sulfur content is 1150 ppm.

[0050] Comparative Example 2 The method of this comparative example 2 is the same as that of Example 1, except that the extractant used in this comparative example is 1,4-butyrolactone; the specific operating conditions are shown in Table 1.

[0051] The waste fan lubricating oil obtained from the bottom of the extractive distillation tower A has the following properties: water content is less than 1 ppm, light hydrocarbons are less than 1 ppm, phosphorus content is 180 ppm, and sulfur content is 100 ppm.

[0052] Table 1

[0053] According to the properties of the pretreated waste lubricating oil obtained from the embodiments and comparative examples of the present disclosure, it can be seen that the composite extractant used in the present disclosure performs extractive distillation treatment on the waste lubricating oil, which can remove pollutants such as moisture, light hydrocarbons and polar additives in the waste lubricating oil in one step, and the pretreated waste lubricating oil obtained has low water content, low light hydrocarbon content, and reduced phosphorus content and sulfur content, ensuring that the hydrofining catalyst has long-term stability and activity. By comparing Example 1 with Example 4, it can be seen that within the component content range of the preferred composite extractant of the present disclosure, the composite extractant has a better removal effect on the waste lubricating oil. By comparing Example 1 with Example 5, it can be seen that within the conditions of the preferred extractive distillation treatment of the present disclosure, the composite extractant has a better removal effect on the waste lubricating oil.

[0054] The preferred embodiments of the present disclosure are described in detail above in conjunction with the accompanying drawings; however, the present disclosure is not limited to the specific details in the above embodiments. Within the technical concept of the present disclosure, a variety of simple modifications can be made to the technical solution of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure.

[0055] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

[0056] In addition, various embodiments of the present disclosure may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the contents disclosed by the present disclosure.

Claims

1. A method for hydrogenation pretreatment of waste lubricating oil, characterized in that: The method comprises: The waste lubricating oil and the composite extractant are contacted in an extractive distillation tower for extractive distillation treatment, a first mixed liquid containing the composite extractant is obtained from the top of the extractive distillation tower, and the pretreated waste lubricating oil is obtained from the bottom of the extractive distillation tower; The composite extractant comprises a first component and a second component, wherein the first component comprises one or more of pyrrolidone compounds, furan aldehyde compounds and amide compounds, and the second component comprises an ester compound.

2. The method according to claim 1, wherein: Based on the weight of the composite extractant, the weight content of the first component is 65-99wt%, preferably 80-90wt%, and the weight content of the second component is 1-35wt%, preferably 10-20wt%.

3. The method according to claim 1, wherein: The furan aldehyde compounds include one or more of furfural and 2-furanacetaldehyde, preferably furfural; the amide compounds include N,N-dimethylformamide and / or N,N-dimethylacetamide; the pyrrolidone compounds include one or more of N-methylpyrrolidone, α-pyrrolidone and N-vinylpyrrolidone; the ester compounds include one or more of 1,4-butyrolactone and ethylene glycol carbonate.

4. The method according to claim 1, wherein: The conditions of the extractive distillation treatment include: a pressure of -0.01 to -0.08 MPa, preferably -0.05 to -0.08 MPa; the number of theoretical plates of the extractive distillation tower is 10 to 50, preferably 20 to 40; the reflux ratio is 0.1 to 2, preferably 0.5 to 1; the bottom temperature is 180 to 200°C, and the top temperature is 140 to 160°C.

5. The method according to claim 1, wherein: The weight ratio of the composite extractant to the waste lubricating oil is 0.25-4:1, preferably 1-2:

1.

6. The method according to claim 1, wherein: The method further comprises: The first mixed liquid is fed into a first distillation tower for a first distillation treatment, and then the top mixed liquid of the first distillation tower is fed into a second distillation tower for a second distillation treatment, a circulating water stream is obtained from the top of the second distillation tower, and a regenerated extractant is obtained from the bottom of the second distillation tower; The regenerated extractant is returned to the extractive distillation tower for continued use.

7. The method according to claim 6, wherein: The conditions of the first distillation treatment include: a pressure of -0.01 to -0.08 MPa, preferably -0.05 to -0.08 MPa; the number of theoretical plates of the first distillation tower is 10 to 50, preferably 20 to 40; the reflux ratio is 3 to 7, the bottom temperature is 130 to 150°C, and the top temperature is 90 to 110°C.

8. The method according to claim 6, wherein: The conditions of the second distillation treatment include: being carried out under normal pressure, the normal pressure is 0.1~0.2MPa, the number of theoretical plates of the second distillation tower is 10~50, preferably 20~40; the reflux ratio is 0.1~1, the bottom temperature is 105~115°C, and the top temperature is 90~100°C.

9. The method according to claim 1, wherein: The method further comprises filtering the waste lubricating oil before entering the extractive distillation tower; The waste lubricating oil has a water content of 0-10wt%, a light hydrocarbon content of 0-10wt%, a phosphorus content of 0-0.1wt%, a sulfur content of 0-1.0wt%, and a kinematic viscosity of 100°C of 10-320mm. 2 / s.

10. The method according to claim 1, wherein: The water content of the pretreated waste lubricating oil is less than 1 ppm, the light hydrocarbon content is less than 1 ppm, the phosphorus content is less than 50 ppm, and the sulfur content is less than 200 ppm.

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