Method for recycling waste lubricating oil

Abstract

The invention provides a method for recycling waste lubricating oil, and the core process comprises the following steps: pretreating waste lubricating oil, mixing the pretreated waste lubricating oil with glycerol and water in proportion, and introducing a nickel-based catalyst. Through an in-situ catalytic hydrofining technology, the reaction is carried out under a specific temperature condition, so that the synergistic conversion of the waste lubricating oil and glycerol is effectively promoted. The process not only realizes efficient separation of oil and water, but also successfully regenerates lubricating oil, and synchronously converts glycerol into a high value-added product lactic acid. According to the method, resources of the waste lubricating oil and glycerol are creatively combined, value-added utilization of low-value wastes is realized, an effective path is provided for resource cyclic utilization of the waste lubricating oil, and dual improvement of environmental protection and economic benefits is promoted. The whole process is simple and efficient, and the method has the remarkable characteristics of environmental friendliness and resource conservation.

Description

Technical Field

[0001] This invention belongs to the field of resource recycling technology, specifically relating to a method for the recycling of waste lubricating oil. Background Technology

[0002] Lubricating oil is widely used in industries such as machining and equipment manufacturing. As its usage increases, so does the amount of waste lubricating oil generated. Statistics show that my country generates approximately 10 million tons of waste lubricating oil annually. Waste lubricating oil is explicitly classified as hazardous waste in the "National Hazardous Waste List" (HW08 Waste Mineral Oil and Mineral Oil-Containing Waste), making its harmless treatment and recycling a hot topic of concern.

[0003] Lubricating oil is composed of base oil (70%–99%) and additives. During use, on the one hand, metal powder from friction parts, moisture, and external dust contaminate the lubricating oil; on the other hand, due to high temperatures and oxidation from air, the lubricating oil also ages and deteriorates, producing organic acids, gums, and asphalt-like substances. This worsens the lubricating oil's viscosity-temperature ratio and oxidation stability, increases its corrosiveness, and causes it to darken in color. The regeneration of waste lubricating oil removes these external impurities and deteriorated components, obtaining a new oil product that meets the required standards.

[0004] The main methods for regenerating waste lubricating oil include acid washing, distillation, solvent extraction, adsorption, and hydrorefining. Acid washing uses sulfuric acid as the cleaning medium, but the quality of the regenerated product is low, the yield is low, and it generates a large amount of acidic wastewater and other pollutants; therefore, it has been largely phased out. Distillation is divided into atmospheric distillation and vacuum distillation. The former is mainly used to remove water, gasoline, or diesel from waste oil, while the latter is mainly used to remove asphaltenes, gums, additives, metal salts, etc., or to cut base oil fractions. Distillation requires high investment and attention must be paid to equipment corrosion prevention and scale prevention within the distillation column. Solvent extraction requires selecting a suitable solvent based on the characteristics of the base oil to dissolve the base oil without dissolving impurities; the separation of the extracted base oil requires significant energy consumption. Adsorption utilizes adsorbents to selectively remove gums, asphaltenes, sulfur compounds, acids, and other polar substances and solvents from waste lubricating oil. Cost control of the adsorbent and regeneration of the adsorbent bed are challenges facing this technology. Hydrorefining differs from the aforementioned methods in that it reduces the content of heteroatom compounds such as O, S, and N in waste oil through hydrogenation treatment, saturating aromatic substances and thereby improving the viscosity-temperature and oxidation stability of lubricating oil. This method fundamentally improves the quality of waste lubricating oil and is the most promising base oil regeneration technology.

[0005] Currently, in the field of waste lubricating oil regeneration, most patented technologies focus on traditional treatment methods, such as distillation, adsorption, and extraction, as seen in patents CN202410668814.6, CN202410603115.3, CN202310555295.8, CN202311252174.2, CN202311038141.8, and CN202211088172.X. While these methods each have their advantages, they still have limitations in improving the quality of regenerated lubricating oil. In contrast, patents employing hydrogenation regeneration technology are relatively few, but they demonstrate significant potential in improving the quality of waste lubricating oil. For example, patent CN202410413331.1 proposes a waste lubricating oil hydrogenation catalyst and its application in waste lubricating oil regeneration base oil. This technology improves oil quality by removing sulfur, nitrogen, and other heteroatoms from waste lubricating oil through catalytic hydrogenation. Patent CN202210888975.7 discloses a method for hydrogenation regeneration of waste lubricating oil in a suspended bed, using a specific heterogeneous catalyst and high-purity hydrogen as the hydrogen source to achieve efficient regeneration of waste lubricating oil. However, while these hydrogenation regeneration technologies are effective, they all rely on high-purity hydrogen, which requires high-pressure cylinders for storage and transportation. This not only increases safety risks during operation but also leads to additional energy consumption, becoming a major challenge for the widespread application of current hydrogenation regeneration technologies.

[0006] Therefore, developing safer and lower-cost hydrogenation regeneration technology for waste lubricating oil is a research hotspot and challenge in this field. Summary of the Invention

[0007] In view of this, the purpose of the present invention is to provide a method for the recycling of waste lubricating oil. This method can not only achieve efficient recycling of waste lubricating oil, but also promote the value-added utilization of glycerin, thereby improving the economy and applicability of waste lubricating oil resource utilization, and promoting the development of environmental protection and circular economy.

[0008] Specifically, the present invention provides a method for recycling waste lubricating oil, comprising the following steps:

[0009] S1. The collected waste lubricating oil is adjusted with alkali to make the pH value within the range of 10≤pH<12, and then it is subjected to precipitation and filtration treatment to achieve the purpose of purification and impurity removal;

[0010] S2. Add glycerin, water and nickel-based catalyst to the purified and impurity-removed waste lubricating oil, and mix and blend.

[0011] S3. Catalytic hydrogenation refining of the mixed and blended waste lubricating oil;

[0012] S4. After catalytic hydrogenation refining, the mixture of waste lubricating oil is subjected to oil-water separation. After separation, the oil phase is further dehydrated and refined to obtain regenerated lubricating oil, and the aqueous phase is enriched and separated to obtain lactic acid.

[0013] In some specific embodiments of the present invention, the alkali is an inorganic alkali.

[0014] In some specific embodiments of the present invention, the inorganic base is one or more of sodium hydroxide, potassium hydroxide, and calcium hydroxide.

[0015] In some specific embodiments of the present invention, the sedimentation is carried out by gravity sedimentation or centrifugal separation; the filtration is carried out by precision filter screen filtration.

[0016] In some specific embodiments of the present invention, the catalyst is a Ni catalyst supported on activated carbon, wherein the Ni loading is 5-15 wt%.

[0017] In some specific embodiments of the present invention, the activated carbon-supported Ni catalyst is prepared by impregnation, with a Ni loading of 5-15 wt%, and the activated carbon can be derived from biomass carbonization products such as straw and coconut shells.

[0018] In some specific embodiments of the present invention, the addition of glycerol, water and catalyst to the purified waste lubricating oil in step S2 follows the following ratio: the molar ratio of waste lubricating oil, glycerol, water and catalyst is 1:(0.5~2):(1~3):(0.01~0.05).

[0019] In some specific embodiments of the present invention, the reaction vessel for catalytic hydrogenation refining in S3 is a high-pressure hydrogenation reactor, and the reaction parameters are: reaction temperature of 250-350°C and pressure of 5-20 MPa.

[0020] In some specific embodiments of the present invention, the reaction time for catalytic hydrogenation purification in S3 is 2 to 6 hours.

[0021] In some specific embodiments of the present invention, the aqueous phase enrichment and separation method is electrodialysis enrichment and separation.

[0022] The main innovation of this invention lies in utilizing glycerol, a byproduct of biodiesel processing, as a hydrogen source. Hydrogen is produced through catalytic decomposition in an alkaline environment, and then hydrogenated in situ to modify waste lubricating oil. The hydrogen generated in situ from glycerol is highly reactive and can replace traditional high-pressure, high-purity hydrogen, reducing the safety risks associated with hydrogen storage, transportation, and operation. Simultaneously, lactic acid, a product of glycerol conversion, is a raw material for easily biodegradable plastics, enabling the value-added utilization of low-value products.

[0023] The present invention has the following significant advantages and effects compared with the prior art:

[0024] 1. Achieved in-situ co-conversion of waste lubricating oil and glycerin: Through this innovative method, waste lubricating oil and glycerin, two substances that might otherwise be considered low-value or waste, are effectively combined and transformed into high-value hydrogenated recycled lubricating oil and lactic acid. This not only improves resource utilization but also realizes the transformation from waste to high-value products.

[0025] 2. Avoids the use of traditional high-pressure, high-purity hydrogen: Traditional waste lubricating oil hydrogenation regeneration technology usually requires high-pressure, high-purity hydrogen as a hydrogen source, which not only increases production costs but also poses safety hazards. This invention utilizes glycerol as a hydrogen source and achieves hydrogenation and upgrading of waste lubricating oil through in-situ catalysis, thereby avoiding the use of high-pressure, high-purity hydrogen and making the entire process safer and less carbon-intensive.

[0026] 3. Highly efficient nickel-based catalyst: The nickel-based catalyst used in this invention not only has a good catalytic hydrogenation effect and can efficiently promote the conversion of waste lubricating oil and glycerol, but also facilitates separation, recovery and recycling.

[0027] This invention provides a novel, efficient, safe, and low-carbon method that integrates waste lubricating oil regeneration with the high-value utilization of glycerin. It not only solves the resource utilization problem of waste lubricating oil but also achieves value-added utilization of glycerin, resulting in significant economic and environmental benefits. Through the achievement of these technical effects, this invention demonstrates its broad application prospects and practical value in the field of waste lubricating oil regeneration. Attached Figure Description

[0028] Appendix Figure 1 This is a schematic diagram of the waste lubricating oil recycling method proposed in this invention. Detailed Implementation

[0029] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined in this application.

[0030] Example 1: Recycling of waste engine oil collected by a solid waste treatment company

[0031] According to the appendix Figure 1The flowchart shown illustrates the recycling process for waste engine oil: Step 1: The collected waste engine oil is initially filtered to remove suspended solids; sodium hydroxide is added to adjust the pH to 11, mechanically stirred for 15 minutes, and then allowed to stand for 1 hour to separate the bottom precipitate. The solution is then filtered through a 200-mesh precision filter to achieve purification. Step 2: Glycerin, water, and a catalyst are added to the purified waste engine oil and stirred until homogeneous. Glycerin can be derived from a byproduct of biodiesel refining, and is inexpensive and readily available. The catalyst is a Ni catalyst supported on activated carbon, prepared by impregnation. It is obtained by impregnating 40-60 mesh activated carbon in a nickel nitrate solution and calcining at 600℃, with a Ni loading of 10%. The molar ratio of waste engine oil, glycerin, water, and catalyst is 1:1:2:0.02. Step 3: The prepared mixture is placed in a hydrogenation reactor and reacted at 320℃ and 15 MPa for 4 hours. In the fourth step, the hydrogenated mixture is separated into oil and water by a separator. The oil phase is further dehydrated and refined to obtain hydrogenated regenerated lubricating oil (see Table 1 for oil products). The aqueous phase is enriched by electrodialysis to obtain a lactic acid solution of about 15%.

[0032] Taking the regeneration of 100g of waste engine oil as an example, it consumes about 80g of glycerin and produces about 70g of regenerated oil and 60g of lactic acid (equivalent to 100% purity), resulting in significant product added value.

[0033] Table 1 shows the physicochemical properties of waste engine oil before and after regeneration, including color, density, viscosity, mechanical impurities, flash point, pour point, acid value, sulfur content, ash content, and carbon residue. The comparison shows that the regenerated engine oil changes from brownish-black to light yellow, its density decreases slightly, and its viscosity, mechanical impurities, sulfur content, ash content, carbon residue, and pour point significantly decrease, while its flash point increases markedly, indicating an improvement in engine oil quality.

[0034] Table 1 Comparison of physicochemical properties of waste engine oil before and after regeneration.

[0035]

Claims

1. A method for recycling waste lubricating oil, characterized in that: The following steps are involved: S1. The collected waste lubricating oil is adjusted with alkali to a pH value within the range of 10≤pH<12, and then precipitated and filtered to achieve the purpose of purification and impurity removal; S2. Add glycerol, water and a nickel-based catalyst to the purified waste lubricating oil and mix and prepare; S3. catalytic hydrotreating of the mixed waste lubricating oil; S4. After catalytic hydrogenation refining, the mixed liquid of the waste lubricating oil is separated into oil and water. After separation, the oil phase is further dehydrated and refined to obtain regenerated lubricating oil, and the water phase is enriched and separated to obtain lactic acid.

2. The method for recycling waste lubricating oil according to claim 1, characterized in that: The base is an inorganic base.

3. The method for recycling waste lubricating oil according to claim 2, characterized in that: The inorganic base is one or more of sodium hydroxide, potassium hydroxide and calcium hydroxide.

4. The method for recycling waste lubricating oil according to claim 1, characterized in that: The precipitation method is gravity sedimentation or centrifugal separation; the filtration adopts precision filter filtration.

5. The method for recycling waste lubricating oil according to claim 1, characterized in that: The catalyst is an activated carbon-supported Ni catalyst, wherein the Ni loading is 5-15 wt %.

6. The method for recycling waste lubricating oil according to claim 1, characterized in that: In S2, glycerol, water and a catalyst are added to the purified and impurity-removed waste lubricating oil in the following proportion: the molar ratio of the waste lubricating oil, glycerol, water and the catalyst is 1:(0.5-2):(1-3):(0.01-0.05).

7. The method for recycling waste lubricating oil according to claim 1, characterized in that: The reaction vessel for the catalytic hydrogenation refining in S3 is a high-pressure hydrogenation reactor, and the reaction parameters are: reaction temperature of 250-350° C. and pressure of 5-20 MPa.

8. The method for recycling waste lubricating oil according to claim 7, characterized in that: The reaction time of the catalytic hydrotreating in S3 is 2 to 6 hours.

9. The method for recycling waste lubricating oil according to claim 1, characterized in that: The water phase enrichment and separation method is electrodialysis enrichment and separation.

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