Method for removing heavy metals in waste lubricating oil
By combining the trifunctional adsorption of modified polystyrene chelating resin with a special regenerator, the problems of poor heavy metal removal and short resin life in waste lubricating oil are solved, achieving deep removal and efficient recycling, which is suitable for industrial applications.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-03-05
- Publication Date
- 2026-04-07
AI Technical Summary
Existing resin adsorbents have poor adsorption effect and short lifespan when removing heavy metals from waste lubricating oil, making it difficult to achieve deep removal and efficient recycling.
Modified polystyrene chelating resin is used, and countercurrent adsorption is achieved by grafting aminophosphonic acid, thiazolidinone and Schiff base trifunctional groups. Combined with composite demulsifier and electro-desalination treatment, and with special composite regenerator, the resin is regenerated to achieve deep removal of heavy metals and efficient recycling of the resin.
It significantly improves the adsorption capacity and selectivity for trace and complex heavy metals, extends the resin cycle life, reduces processing costs, and meets the requirements for recycling.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of lubricating oil technology, and more specifically to a method for removing heavy metals from waste lubricating oil. Background Technology
[0002] Waste lubricating oil contains a large amount of heavy metal impurities (such as lead, cadmium, mercury, copper, zinc, etc.). These heavy metals mainly originate from wear debris from engines and mechanical equipment, additive residues, and external pollutants during the use of lubricating oil. If waste lubricating oil is directly recycled or discharged, heavy metals will re-enter the environment with the use of recycled oil, or seep into the soil and water bodies through wastewater and waste residue, seriously endangering the ecological environment and human health.
[0003] Currently, the main methods for removing heavy metals from waste lubricating oil include chemical precipitation, solvent extraction, adsorption, and electrostatic desalination. Among these, adsorption has become a research hotspot due to its simple operation and lack of potential secondary pollution, while resin adsorbents are widely used in the field of heavy metal removal due to their high selectivity and ease of regeneration.
[0004] However, existing resin adsorption and regeneration technologies still face significant bottlenecks: First, most existing modified resins are modified with single or conventional bifunctional groups, resulting in low functional group loading and uneven dispersion. This limits their adsorption capacity for trace and complex heavy metals in waste lubricating oil, making it difficult to achieve deep removal. Second, resin regeneration often uses single acid solutions or simple binary acid solutions, leading to incomplete regeneration. Furthermore, functional groups are easily lost or degraded during the regeneration process, resulting in fewer resin recycling cycles and limiting the resin's adsorption performance and cycle life. Summary of the Invention
[0005] The present invention aims to solve the problems of poor removal effect and short service life of resin when using resin to remove heavy metals from waste lubricating oil.
[0006] To address the above problems, this invention provides a method for removing heavy metals from waste lubricating oil, comprising the following steps: Step 1: The waste lubricating oil is subjected to coarse filtration, fine filtration and dehydration to obtain secondary crude oil; Step 2: Add a compound demulsifier to the crude oil and perform electro-desalting to obtain crude oil; Step 3: Pass the crude oil into an adsorption column filled with modified polystyrene chelating resin for countercurrent adsorption to obtain fine oil; wherein, the modified polystyrene chelating resin is a chloromethylated polystyrene resin grafted with aminophosphonic acid groups, thiazolidinone groups and Schiff base groups.
[0007] The method for removing heavy metals from waste lubricating oil provided by this invention has, but is not limited to, the following beneficial effects compared to existing technologies: This method first removes solid impurities and free water through pretreatment involving coarse filtration, fine filtration, and dehydration, eliminating interference for subsequent processes. A composite demulsifier, combined with electro-desalination, achieves preliminary removal of water-soluble heavy metal impurities. A modified polystyrene chelating resin grafted with trifunctional groups of aminophosphonic acid, thiazolidinone, and Schiff base is used for countercurrent adsorption. The synergistic effect of the trifunctional groups significantly improves the adsorption capacity and selectivity for trace and complex heavy metals, achieving deep removal of heavy metals. The entire process is pollution-free, easy to operate, and solves the core problem of poor resin adsorption and removal efficiency in existing technologies. The heavy metal content of the treated lubricating oil is significantly reduced, meeting the requirements for regeneration.
[0008] Specifically, chloromethylated polystyrene resin serves as a rigid porous support. The active sites formed after chloromethylation modification achieve uniform grafting and efficient loading of trifunctional groups, and the porous structure provides ample mass transfer channels for heavy metal ions. Furthermore, the phosphonate and amino groups of the aminophosphonic acid group can interact with Pb. 2+ Cd 2+ The formation of stable five-membered ring chelates by heavy metal ions, and the sulfur and nitrogen coordination sites of the thiazolidinone group for Hg 2+ Exhibiting highly selective complexation, the imine group of the Schiff base can react with Cu. 2+ When transition metal ions form coordination bonds, the trifunctional groups achieve site-specific and synergistic adsorption of typical complex heavy metals in waste lubricating oil, which greatly improves the adsorption capacity and selectivity of the resin for trace heavy metals and solves the problem that existing modified resins have limited adsorption capacity and cannot remove them deeply.
[0009] Preferred options also include: Step 4: The modified polystyrene chelating resin after adsorption is completed is rinsed and activated using a composite regenerator, and the recovered resin is reused in step 3.
[0010] Specifically, by using a special composite regenerator for rinsing and activation, heavy metals adsorbed by the resin can be efficiently desorbed, while avoiding the loss and degradation of resin functional groups. The recycled resin can be reused, significantly improving the resin cycle life, reducing industrial processing costs, and realizing the resource utilization of the adsorbent.
[0011] Preferably, in step 1, the coarse filtration uses a metal filter screen with a pore size of 80-120μm, and the fine filtration uses a cellulose filter membrane with a pore size of 1-5μm; the dehydration treatment conditions are: stirring at a stirring rate of 150-200r / min at a temperature of 80-100℃ for 30-60min, followed by standing for 10-15min.
[0012] Specifically, filter screens and membranes with specific pore sizes can accurately remove solid impurities of different particle sizes, and exclusive dehydration parameters can efficiently remove free water from waste lubricating oil. The pretreatment effect is good, laying a good foundation for subsequent electro-desalination and adsorption processes, and avoiding the impact of impurities and moisture on the subsequent heavy metal removal efficiency.
[0013] Preferably, in step 2, the amount of the composite demulsifier added is 0.3-0.8 wt% of the crude oil mass; the composite demulsifier is a mixture composed of polyoxyethylene polyoxypropylene block copolymer and triethanolamine in a mass ratio of (3-5):1.
[0014] Specifically, this ratio of demulsifier has the best demulsification and desalting effect, effectively breaking down the oil-in-water emulsion in lubricating oil, improving the removal efficiency of water-soluble heavy metals during electro-desalting, and the addition amount is low, so it will not introduce new impurities.
[0015] Preferably, in step 2, the process parameters for the electro-desalination are: electric field strength 15-25 kV / cm, temperature 85-95℃, pressure 0.15-0.25 MPa, and processing time 40-60 min.
[0016] Specifically, under these parameters, the synergistic effect of electric field, temperature, and pressure can achieve efficient removal of water-soluble heavy metal impurities, stable electro-desalination effect, and no side reactions such as lubricating oil cracking or oxidation.
[0017] Preferably, in step 3, the modified polystyrene chelating resin is prepared by the following steps: S1. Polystyrene microspheres were washed sequentially with deionized water and anhydrous ethanol, and then dried under vacuum to obtain clean microspheres. S2. Clean microspheres were added to anhydrous ethanol and dispersed evenly. After cooling in an ice-water bath, chloromethyl methyl ether and anhydrous aluminum trichloride were added dropwise and stirred to react. After the reaction was completed, the mixture was filtered, washed and dried to obtain chloromethylated polystyrene resin. S3. Chloromethylated polystyrene resin is sequentially grafted with aminophosphonic acid groups, thiazolidinone groups, and Schiff base groups. After each grafting step, the resin is washed and dried to obtain modified polystyrene chelated resin.
[0018] Specifically, a three-step method is used to achieve the orderly grafting of three functional groups. After each grafting step, the resin is washed and dried to ensure the grafting rate and dispersibility of the functional groups. The prepared resin has a stable structure and excellent adsorption performance, providing core material support for the deep removal of heavy metals.
[0019] Preferably, the specific operation method of S1 is as follows: add polystyrene microspheres to deionized water, stir at room temperature for 30 minutes, let stand to precipitate, remove the supernatant, wash with anhydrous ethanol 2-3 times, filter and separate, and vacuum dry the filter residue to obtain clean microspheres.
[0020] Specifically, this operation can effectively remove impurities and residual monomers from the surface of microspheres, resulting in clean microspheres and improving the efficiency and uniformity of subsequent chloromethylation and functional group grafting reactions.
[0021] Preferably, the specific operation method of S2 is as follows: clean microspheres are added to anhydrous ethanol, dispersed evenly, and then placed in an ice-water bath. Chloromethyl ether is added dropwise first, and then anhydrous aluminum trichloride is added in small amounts several times. The reaction is stirred and the reaction is terminated by adding deionized water after the reaction is completed. The reaction product is filtered, washed, and dried to obtain chloromethylated polystyrene resin. The ratio of the amount of clean microspheres, chloromethyl ether and anhydrous aluminum trichloride is 100g:(50-70)mL:(6-9).
[0022] Specifically, this formulation results in high chloromethylation efficiency and moderate chloromethylation degree in the resin, providing ample reaction sites for subsequent functional group grafting. The low-temperature reaction in an ice-water bath avoids resin cross-linking and degradation, ensuring the integrity of the resin structure.
[0023] Preferably, the specific operation method of S3 is as follows: S31. Chloromethylated polystyrene resin, deionized water and diethylenetriamine methylphosphonic acid are mixed and stirred evenly. Sodium hydroxide solution is added dropwise to adjust the pH to 8-9, and then the temperature is raised to carry out the reaction. After the reaction is completed, the reaction product is filtered, washed and dried to obtain chloromethylated polystyrene resin grafted with aminophosphonic acid groups; wherein, the mass ratio of diethylenetriamine methylphosphonic acid to clean microspheres is (2-3):5. S32. Chloromethylated polystyrene resin grafted with aminophosphonic acid groups, anhydrous ethanol, and 2-mercapto-2-imidazolinone are mixed and stirred evenly. Hydrochloric acid solution is added dropwise to adjust the pH to 5-6, and then the mixture is heated to carry out the reaction. After the reaction is complete, the resulting reaction product is filtered, washed, and dried to obtain chloromethylated polystyrene resin grafted with aminophosphonic acid groups and thiazolidinone groups; wherein the mass ratio of 2-mercapto-2-imidazolinone to clean microspheres is (30-45):100. S33. Chloromethylated polystyrene resin grafted with aminophosphonic acid groups and thiazolidinone groups, anhydrous ethanol and salicylaldehyde are mixed and stirred evenly, and then heated to react. After the reaction is completed, the reaction product is cooled to room temperature, filtered, washed and dried to obtain chloromethylated polystyrene resin grafted with aminophosphonic acid groups, thiazolidinone groups and Schiff base groups, i.e. modified polystyrene chelate resin; wherein the mass ratio of salicylaldehyde to clean microspheres is (25-35):100.
[0024] Specifically, by adjusting pH, reaction temperature, and material ratio, efficient and orderly grafting of trifunctional groups onto the resin surface is achieved. The trifunctional groups synergistically enhance the resin's adsorption performance for heavy metals, and the grafted resin structure is stable with strong adsorption selectivity.
[0025] Preferably, in S2, the composite regenerant is a mixture of aminotrimethylene phosphoric acid, dilute sulfuric acid, and citric acid in a mass ratio of (4-6):1:1.
[0026] Specifically, this formulation of regenerant can efficiently desorb heavy metals without damaging the resin functional groups, significantly improving resin regeneration efficiency and recycling performance. Dilute sulfuric acid provides H+ ions to compete with heavy metal ions for resin adsorption sites, achieving efficient desorption. Citric acid, as a complexing agent, forms stable water-soluble complexes with the desorbed heavy metal ions, preventing them from re-adsorbing onto the resin surface and ensuring thorough regeneration. Aminotrimethylene phosphoric acid effectively protects the chelating and coordinating functional groups on the resin surface, preventing hydrolysis, loss, and degradation of functional groups caused by acid. The combination of these three components achieves efficient resin regeneration, significantly improving the resin's cyclic adsorption capacity retention rate and solving the problems of incomplete regeneration and short resin life associated with existing single-acid regeneration methods. Detailed Implementation
[0027] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.
[0028] The terminology used in the embodiments of this application is for the purpose of describing particular implementations only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the implementations of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.
[0029] It should be understood that in the various embodiments of this application, the sequence number of each process does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the implementation regulations of this application.
[0030] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass described in the embodiments of this application can be a mass unit known in the chemical industry, such as μg, mg, g, or kg.
[0031] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.
[0032] Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in this application are commercially available or can be prepared using existing methods. For example, the specific sources and types of raw materials involved in the following preparation examples, embodiments, and comparative examples are as follows: Polystyrene microspheres: particle size 0.4-0.6 mm, specific surface area 100-150 m² 2 / g, crosslinking degree 8%, model PS-800, Shanghai Maclean Biochemical Technology Co., Ltd., analytical grade; Chloromethyl methyl ether: 98% purity, model CM-98, Sinopharm Chemical Reagent Co., Ltd., analytical grade; Anhydrous aluminum trichloride: 99% purity, model AlCl3-AR, Tianjin Kemei Chemical Reagent Co., Ltd., analytical grade; Diethylenetriaminemethylphosphonic acid: 97% purity, model DTPMP-97, Shandong Taihe Water Treatment Technology Co., Ltd., industrial grade; 2-Mercapto-2-imidazolinone: 98% purity, model MIO-98, Shanghai Aladdin Biochemical Technology Co., Ltd., analytical grade; Salicylaldehyde: 99% purity, model SA-99, Sinopharm Chemical Reagent Co., Ltd., analytical grade; Dilute sulfuric acid: 0.8 mol / L, prepared by diluting 98% concentrated sulfuric acid (Sinopharm Group, analytical grade); Citric acid: 99.5% purity, CA-AR grade, Tianjin Guangfu Fine Chemical Research Institute, analytical grade; Aminotrimethylenephosphonic acid (ATMP): 95% purity, model ATMP-95, Shandong Scale Inhibitor Chemical Co., Ltd., industrial grade; Sodium hydroxide: 96% purity, model NaOH-AR, Tianjin Kemei Chemical Reagent Co., Ltd., analytical grade; Hydrochloric acid: purity 36-38%, type HCl-AR, Sinopharm Chemical Reagent Co., Ltd., analytical grade; Anhydrous ethanol: 99.7% purity, EtOH-AR, Tianjin Fuyu Fine Chemical Co., Ltd., analytical grade; Composite demulsifier: a compound of polyoxyethylene-polyoxypropylene block copolymer (model L64, BASF Chemical, industrial grade) and triethanolamine (purity 99%, Sinopharm Group, analytical grade); Waste automotive lubricating oil: 15W-40 type, taken from the waste engine oil recycling pool of an auto repair shop, with initial heavy metal content meeting the requirements of each embodiment; Industrial waste lubricating oil: taken from waste gearbox oil in a machine processing plant, the initial heavy metal content meets the requirements of Example 2; Aminophosphonic acid monoligand modified polystyrene resin: particle size 0.4-0.6 mm, specific surface area 120 m² 2 / g, single ligand loading 2.5mmol / g, model D401, Tianjin Nankai Resin Factory, industrial grade; Cellulose filter membrane: pore size 1-5μm, model CF-1, Shanghai Filter Membrane Factory, industrial grade; Metal filter screen: pore size 80-120μm, 304 stainless steel, Anping County Screen Factory.
[0033] Preparation Example 1
[0034] The modified polystyrene chelating resin was prepared by following these steps: S1, Preprocessing Take 110g of polystyrene microspheres, add them to 200mL of deionized water, stir at 130r / min at room temperature for 30min, let them stand to precipitate and remove the supernatant; wash twice with anhydrous ethanol, stirring for 10min after each wash, filter and separate; put the filter residue into a vacuum drying oven and dry at 65℃ and 0.09MPa for 2.5h to obtain clean microspheres for later use; S2, chloromethylation 100g of clean microspheres were placed in a three-necked flask, and 80mL of anhydrous ethanol was added. The mixture was stirred at 110r / min for 30min to disperse the microspheres evenly. The three-necked flask was placed in an ice-water bath to cool to 3℃, and 60mL of chloromethyl methyl ether was slowly added dropwise (dropping time 35min). After the addition was completed, 1.5g of anhydrous aluminum trichloride was added every 10min, for a total of 7.5g. The mixture was stirred at 3℃ for 5h. After the reaction was completed, 50mL of deionized water was slowly added to terminate the reaction, and the mixture was stirred for 10min. The mixture was filtered and separated, and repeatedly washed with deionized water until the pH of the washing solution was 7. Then it was washed once with anhydrous ethanol and dried under vacuum at 60℃ for 3h to obtain chloromethylated polystyrene resin for later use. S3, Grafting S31. Place the chloromethylated polystyrene resin in a three-necked flask, add 100 mL of deionized water and 50 g of diethylenetriaminemethylphosphonic acid, stir at 90 r / min for 30 min, and adjust the pH to 8.8 with a 30% sodium hydroxide solution. Place the three-necked flask in an oil bath, heat to 65 °C, and stir at a constant temperature for 9 h. After the reaction is complete, cool to room temperature, filter and separate, wash with deionized water until pH=7, and vacuum dry at 65 °C for 2 h to obtain chloromethylated polystyrene resin grafted with aminophosphonic acid groups for later use. S32. Place the chloromethylated polystyrene resin grafted with aminophosphonic acid groups into a three-necked flask, add 80 mL of anhydrous ethanol and 38 g of 2-mercapto-2-imidazolinone, stir at 100 r / min for 30 min, adjust the pH to 5.8 with 30% hydrochloric acid solution; heat to 55℃ in an oil bath and stir at this temperature for 7 h; filter to separate, wash twice with anhydrous ethanol, then wash with deionized water until pH=7, and vacuum dry at 60℃ for 2 h to obtain chloromethylated polystyrene resin grafted with aminophosphonic acid and thiazolidinone groups, for later use. S33. The chloromethylated polystyrene resin grafted with aminophosphonic acid groups and thiazolidinone groups was added to a three-necked flask, along with 90 mL of anhydrous ethanol and 30 g of salicylaldehyde. The mixture was stirred at 110 r / min for 30 min, heated in an oil bath to 75 °C, and stirred at this temperature for 6 h. After cooling to room temperature, the mixture was filtered and separated. It was washed twice with anhydrous ethanol, then washed with deionized water until pH=7, and dried under vacuum at 70 °C for 4 h. The chloromethylated polystyrene resin grafted with aminophosphonic acid groups, thiazolidinone groups, and Schiff base groups was obtained, i.e., modified polystyrene chelate resin. Finally, the resin was sieved and classified, and the modified polystyrene chelate resin with a particle size of 0.4-0.6 mm was selected for later use.
[0035] Preparation Example 2
[0036] The preparation steps and conditions for the modified polystyrene chelating resin differ from those in Preparation Example 1 only in that: 1. In S2, the amount of chloromethyl methyl ether added is 50 mL, the amount of anhydrous aluminum trichloride added is 6 g, and the reaction time is 4 h; 2. In S31, the amount of diethylenetriaminemethylphosphonic acid added is 40g, and the reaction time is 8h; 3. In S31, the amount of 2-mercapto-2-imidazolinone added is 30g, and the reaction time is 6h; 4. In S31, the amount of salicylaldehyde added is 25g, and the reaction time is 5h; Keeping all other steps and conditions exactly the same, the modified polystyrene chelate resin with a particle size of 0.4-0.6 mm was finally obtained.
[0037] Preparation Example 3
[0038] The preparation steps and conditions for the modified polystyrene chelating resin differ from those in Preparation Example 1 only in that: 1. In S2, the amount of chloromethyl ether added is 70 mL, the amount of anhydrous aluminum trichloride added is 9 g, and the reaction time is 6 h; 2. In S31, the amount of diethylenetriaminemethylphosphonic acid added is 60g, and the reaction time is 10h; 3. In S31, the amount of 2-mercapto-2-imidazolinone added is 45g, and the reaction time is 8h; 4. In S31, the amount of salicylaldehyde added is 35g, and the reaction time is 7h; Keeping all other steps and conditions exactly the same, the modified polystyrene chelate resin with a particle size of 0.4-0.6 mm was finally obtained.
[0039] Example 1
[0040] This embodiment discloses a method for removing heavy metals from waste lubricating oil, comprising the following steps: Step 1: Take 1000mL of waste automotive lubricating oil, first filter it through an 80μm metal mesh for coarse filtration, and then filter it through a 1μm cellulose membrane for fine filtration; send the filtered waste lubricating oil into a heated reaction vessel, stir at 150r / min for 30min, then heat it to 80℃, stir at a constant temperature for 30min, let it stand for 10min, and drain the bottom sediment to obtain the secondary crude oil. Step 2: Send the crude oil into the electrostatic desalting tank, add 3g of composite demulsifier (a mixture of polyoxyethylene polyoxypropylene block copolymer and triethanolamine in a mass ratio of 3:1), stir evenly and let stand for 5 minutes; adjust the electric field strength to 15kV / cm, temperature to 85℃, and pressure to 0.15MPa, and treat for 40 minutes; drain the bottom aqueous phase to obtain the electrostatically desalted crude oil; Step 3: The crude oil is fed into an adsorption column filled with 100g of the modified polystyrene chelating resin of Preparation Example 1. The flow rate is controlled at 1 BV / h, the adsorption temperature at 70℃, and the adsorption time at 2h. Countercurrent adsorption is used to collect the fine oil. Step 4: After adsorption is complete, prepare a composite regenerator (mix 0.8 mol / L dilute sulfuric acid, 0.2 mol / L citric acid and 0.1 mol / L aminotrimethylenephosphonic acid in a mass ratio of 4:1:1 and stir until homogeneous). Heat to 50°C, and first pass the regenerator into the adsorption column at a flow rate of 2 BV / h to rinse and regenerate the modified polystyrene chelating resin for 0.5 h; then increase the flow rate to 3 BV / h to rinse and regenerate for 1.5 h; after regeneration, rinse with deionized water until pH=6.5, then pass a 0.5% sodium hydroxide solution at a flow rate of 1 BV / h to rinse for 10 min, and finally rinse with deionized water until neutral to complete the rinsing and activation; the regenerated resin can be reused in the adsorption process of step 3.
[0041] Example 2
[0042] This embodiment discloses a method for removing heavy metals from waste lubricating oil. Compared with Embodiment 1, the only difference is that in step 3, the flow rate is 2 BV / h, the adsorption temperature is 78℃, and the adsorption time is 3h; other steps and conditions remain the same.
[0043] Example 3
[0044] This embodiment discloses a method for removing heavy metals from waste lubricating oil. Compared with Embodiment 1, the only difference is that in step 3, the flow rate is 3 BV / h, the adsorption temperature is 85℃, and the adsorption time is 4h; other steps and conditions remain the same.
[0045] Example 4
[0046] This embodiment discloses a method for removing heavy metals from waste lubricating oil. Compared with Example 1, the only difference is that in step 3, the modified polystyrene chelating resin of Preparation Example 1 is replaced with the modified polystyrene chelating resin of Preparation Example 2; the other steps and conditions remain the same.
[0047] Example 5
[0048] This embodiment discloses a method for removing heavy metals from waste lubricating oil. Compared with Example 1, the only difference is that in step 3, the modified polystyrene chelating resin of Preparation Example 1 is replaced with the modified polystyrene chelating resin of Preparation Example 3; the other steps and conditions remain the same.
[0049] Comparative Example 1
[0050] This comparative example discloses a method for removing heavy metals from waste lubricating oil. Compared with Example 1, the only difference is that in step 3, the modified polystyrene chelating resin of Preparation Example 1 is replaced with a commercially available aminophosphonic acid monoligand modified polystyrene resin; the other steps and conditions remain the same.
[0051] Comparative Example 2
[0052] This comparative example discloses a method for removing heavy metals from waste lubricating oil. Compared with Example 1, the only difference is that in step 4, the composite regenerator is replaced with dilute sulfuric acid with a concentration of 0.8 mol / mL; the other steps and conditions remain the same.
[0053] The heavy metal removal rate of the fine oil collected in step 3 of Examples 1-5 and Comparative Examples 1-2 was tested, and the recycling performance of the resin was also tested. The specific testing methods are as follows: Heavy metal removal rate: Take 5.000g each of crude oil before adsorption and fine oil after adsorption, place them in a 50mL polytetrafluoroethylene digestion vessel, add 10mL of nitric acid + 5mL of perchloric acid (volume ratio 2:1) mixed digestion solution, cover and place in a microwave digester, set the digestion program: 120℃ for 10min, 160℃ for 20min, 190℃ for 30min; after digestion, cool to room temperature, transfer the digestion solution to a 50mL volumetric flask, dilute to the mark with deionized water, shake well and let stand for later use; the blank sample is a solution of an equal volume of deionized water treated with the same digestion program; adjust the atomic absorption spectrophotometer to the optimal working state, set the detection wavelengths of lead (283.3nm), cadmium (228.8nm), mercury (253.7nm), and copper (324.8nm), respectively, and use the standard curve method to determine the mass concentration of each heavy metal in the sample digestion solution. Each sample is measured in parallel 3 times and the average value is taken. Total heavy metal removal rate = (total mass of four heavy metals in crude oil before adsorption - total mass of four heavy metals in fine oil after adsorption) / total mass of four heavy metals in crude oil before adsorption × 100%; where, heavy metal mass = mass concentration × constant volume / sample mass.
[0054] Cyclic performance: 10.000 g of dried modified polystyrene chelating resin was placed in an adsorption column and adsorbed according to the corresponding example / comparative example process. After adsorption, the heavy metals adsorbed by the resin were completely desorbed with 0.1 mol / L nitric acid solution. After adjusting the volume, the total mass of heavy metals in the desorbate was determined by atomic absorption spectrophotometry. Initial adsorption capacity (mg / g) = total mass of heavy metals / mass of resin. The adsorbed resin was then regenerated according to the corresponding example / comparative example process, and the adsorption-regeneration operation was repeated. After a total of 20 cycles, the adsorption capacity of the resin was determined according to the above method. Adsorption capacity retention rate = adsorption capacity after 20 cycles / initial adsorption capacity × 100%.
[0055] The test results are listed in Table 1, as follows: Table 1
[0056] Analyzing the data in Table 1, we can find that:
[0057] 1. The heavy metal removal rates of Examples 1-5 are all ≥98.5%, which is much higher than the 85.2% of Comparative Example 1. This indicates that the modified polystyrene chelating resin with grafted trifunctional groups prepared in this invention has a much better adsorption performance for trace and complex heavy metals in waste lubricating oil than conventional commercially available monoligand aminophosphonic acid modified polystyrene resin. The trifunctional groups of aminophosphonic acid, thiazolidinone, and Schiff base can form stable chelates with different heavy metal ions, thereby improving the adsorption capacity and selectivity of the resin and achieving deep removal of heavy metals.
[0058] 2. Examples 1-5 all showed an adsorption capacity retention rate of ≥92.7%, and maintained high adsorption performance after 20 cycles, indicating that the composite regenerator of the present invention can efficiently desorb heavy metals without damaging the functional groups and structure of the resin, and the resin has excellent cycle stability. Among them, Example 5 adopted the resin preparation process of Example 3, and the retention rate reached the highest of 94.5%, indicating that the optimized resin preparation parameters can further improve the cycle performance of the resin.
[0059] 3. The heavy metal removal rate of Comparative Example 1 was significantly low. It used a single-ligand aminophosphonic acid modified resin. The single functional group has limited adsorption selectivity and capacity for complex heavy metals, and cannot achieve deep removal. This verifies the significant progress of the modified polystyrene chelating resin of the present invention.
[0060] 4. The removal rate of Comparative Example 2 is similar to that of Example 1, but the adsorption capacity retention rate is only 61.3%. This indicates that although the single dilute sulfuric acid regenerator can achieve heavy metal desorption, the regeneration is incomplete and will cause the loss and degradation of resin functional groups, resulting in a significant decrease in resin cycle performance. This verifies that the composite regenerator formulation of the present invention can effectively improve the cycle life of the resin.
[0061] 5. Overall, the process of this invention achieves the dual effects of deep removal of heavy metals and efficient recycling of resin. The process has good stability, and the data fluctuations between examples are small, making it suitable for industrial-scale application.
[0062] The foregoing has described several embodiments of the present invention in detail, but these descriptions are merely preferred embodiments and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.
Claims
1. A method for removing heavy metals from waste lubricating oil, characterized in that, Includes the following steps: Step 1: The waste lubricating oil is subjected to coarse filtration, fine filtration and dehydration to obtain secondary crude oil; Step 2: Add a compound demulsifier to the crude oil and perform electro-desalting to obtain crude oil; Step 3: Pass the crude oil into an adsorption column filled with modified polystyrene chelating resin for countercurrent adsorption to obtain fine oil; wherein, the modified polystyrene chelating resin is a chloromethylated polystyrene resin grafted with aminophosphonic acid groups, thiazolidinone groups and Schiff base groups.
2. The method for removing heavy metals from waste lubricating oil according to claim 1, characterized in that, Also includes: Step 4: The modified polystyrene chelating resin after adsorption is completed is rinsed and activated using a composite regenerator, and the recovered resin is reused in step 3.
3. The method for removing heavy metals from waste lubricating oil according to claim 1, characterized in that, In step 1, the coarse filtration uses a metal filter screen with a pore size of 80-120μm, and the fine filtration uses a cellulose filter membrane with a pore size of 1-5μm. The dehydration treatment conditions are as follows: stirring at a stirring rate of 150-200r / min at a temperature of 80-100℃ for 30-60min, followed by standing for 10-15min.
4. The method for removing heavy metals from waste lubricating oil according to claim 1, characterized in that, In step 2, the amount of the composite demulsifier added is 0.3-0.8 wt% of the crude oil mass; the composite demulsifier is a mixture composed of polyoxyethylene polyoxypropylene block copolymer and triethanolamine in a mass ratio of (3-5):
1.
5. The method for removing heavy metals from waste lubricating oil according to claim 1, characterized in that, In step 2, the process parameters for the electro-desalination are: electric field strength 15-25kV / cm, temperature 85-95℃, pressure 0.15-0.25MPa, and processing time 40-60min.
6. The method for removing heavy metals from waste lubricating oil according to claim 1, characterized in that, In step 3, the modified polystyrene chelating resin is prepared through the following steps: S1. Polystyrene microspheres were washed sequentially with deionized water and anhydrous ethanol, and then dried under vacuum to obtain clean microspheres. S2. Clean microspheres were added to anhydrous ethanol and dispersed evenly. After cooling in an ice-water bath, chloromethyl methyl ether and anhydrous aluminum trichloride were added dropwise and stirred to react. After the reaction was completed, the mixture was filtered, washed and dried to obtain chloromethylated polystyrene resin. S3. Chloromethylated polystyrene resin is sequentially grafted with aminophosphonic acid groups, thiazolidinone groups, and Schiff base groups. After each grafting step, the resin is washed and dried to obtain modified polystyrene chelated resin.
7. The method for removing heavy metals from waste lubricating oil according to claim 6, characterized in that, The specific operation method of S1 is as follows: add polystyrene microspheres to deionized water, stir at room temperature for 30 minutes, let stand to precipitate, remove the supernatant, wash with anhydrous ethanol 2-3 times, filter and separate, and vacuum dry the filter residue to obtain clean microspheres.
8. The method for removing heavy metals from waste lubricating oil according to claim 6, characterized in that, The specific operation method of S2 is as follows: clean microspheres are added to anhydrous ethanol, dispersed evenly, and then placed in an ice-water bath. Chloromethyl ether is added dropwise first, and then anhydrous aluminum trichloride is added in small amounts several times. The reaction is stirred and the reaction is terminated by adding deionized water after the reaction is completed. The reaction product is filtered, washed, and dried to obtain chloromethylated polystyrene resin. The ratio of the amount of clean microspheres, chloromethyl ether and anhydrous aluminum trichloride is 100g:(50-70)mL:(6-9)g.
9. The method for removing heavy metals from waste lubricating oil according to claim 6, characterized in that, The specific operation method of S3 is as follows: S31. Chloromethylated polystyrene resin, deionized water and diethylenetriamine methylphosphonic acid are mixed and stirred evenly. Sodium hydroxide solution is added dropwise to adjust the pH to 8-9, and then the temperature is raised to carry out the reaction. After the reaction is completed, the reaction product is filtered, washed and dried to obtain chloromethylated polystyrene resin grafted with aminophosphonic acid groups; wherein, the mass ratio of diethylenetriamine methylphosphonic acid to clean microspheres is (2-3):
5. S32. Chloromethylated polystyrene resin grafted with aminophosphonic acid groups, anhydrous ethanol, and 2-mercapto-2-imidazolinone are mixed and stirred evenly. Hydrochloric acid solution is added dropwise to adjust the pH to 5-6, and then the mixture is heated to carry out the reaction. After the reaction is complete, the resulting reaction product is filtered, washed, and dried to obtain chloromethylated polystyrene resin grafted with aminophosphonic acid groups and thiazolidinone groups; wherein the mass ratio of 2-mercapto-2-imidazolinone to clean microspheres is (30-45):
100. S33. Chloromethylated polystyrene resin grafted with aminophosphonic acid groups and thiazolidinone groups, anhydrous ethanol and salicylaldehyde are mixed and stirred evenly, and then heated to react. After the reaction is completed, the reaction product is cooled to room temperature, filtered, washed and dried to obtain chloromethylated polystyrene resin grafted with aminophosphonic acid groups, thiazolidinone groups and Schiff base groups, i.e. modified polystyrene chelate resin; wherein the mass ratio of salicylaldehyde to clean microspheres is (25-35):
100.
10. The method for removing heavy metals from waste lubricating oil according to claim 2, characterized in that, In S2, the composite regenerator is a mixture of aminotrimethylene phosphoric acid, dilute sulfuric acid, and citric acid in a mass ratio of (4-6):1:1.