A method for treating and recycling oil sludge in a petrochemical raw material tank

Abstract

The application discloses a treatment and recovery method of oil sludge at the bottom of a petrochemical raw material tank, and relates to the technical field of tank bottom sludge treatment. The modified lignin cleaning agent is prepared by grafting naphthalene ring to alkali lignin and then performing quaternary ammonium modification. Then, the tank bottom sludge is first prepared into slurry, the cleaning agent is added and treated by ball milling, the naphthalene ring of the cleaning agent competes with asphaltene and colloid for adsorption by means of pi-pi stacking, and replaces the heavy oil on the surface of the solid phase; meanwhile, the quaternary ammonium cation neutralizes the negative charge of the particles and destroys the emulsion system, so that the oil droplets are aggregated; then, the pH is adjusted by dilution, and the floating oil and tailings slurry are obtained by flotation separation, the floating oil is impurity-removed to obtain recovered crude oil, and the filtrate of the tailings slurry after pressure filtration and dehydration is recycled. The application has the advantages of high recovery rate of crude oil, low consumption of medicament and water resources, and solves the problem of difficult treatment and recovery of tank bottom sludge.

Description

Technical Field

[0001] This application relates to the field of tank bottom sludge treatment technology, specifically to a method for treating and recycling tank bottom sludge from petrochemical raw material tanks. Background Technology

[0002] With the large-scale development of the petroleum refining and chemical industries, oily sludge, a mixture of oil, water, and solid phases, accumulates at the bottom of various crude oil and heavy feedstock storage tanks over a long period, forming a stable colloidal system of heavy hydrocarbons, clay minerals, and emulsified water. This type of sludge has high viscosity, deep emulsification, and a large proportion of asphaltenes and gums. Conventional hot washing can only remove some of the light oil components, while most of the heavy oil components firmly adhere to the surface of the solid particles. Disposing of this sludge as waste not only results in a serious waste of oil and gas resources but also poses a high environmental risk. Currently, the recycling and treatment of tank bottom sludge mainly adopts mainstream methods such as traditional hot washing, solvent extraction, biological treatment, and pyrolysis. Traditional hot washing methods rely on high-temperature stirring and conventional surfactants to reduce interfacial tension and remove oil. However, they are weak at breaking down the strong adhesion between heavy components such as asphaltenes and gums and the solid phase, making it difficult to meet the oil content requirements of the solid residue. Furthermore, they rely on high-temperature steam heating, resulting in high energy consumption and operating costs. Solvent extraction methods have strong dissolving capabilities for heavy oils, but suffer from high organic solvent loss, high energy consumption during distillation recovery, and pose safety risks of flammability and explosion. Biological treatment methods offer mild reaction conditions but have long processing cycles and extremely low degradation efficiency for heavy polycyclic aromatic hydrocarbons. Pyrolysis can reduce solid waste volume, but requires large equipment investments, involves high reaction temperatures, is prone to localized coking, and produces poor-quality pyrolysis oil. To address these pain points, existing improvement solutions mainly focus on optimizing surfactant formulations and improving hot washing process parameters, such as screening anionic and nonionic composite surfactants and increasing hot washing temperature and stirring shear strength. Chinese invention patent CN115232681B discloses a method for preparing a tank bottom sludge cleaning agent, the cleaning agent, and a tank bottom sludge cleaning process. This scheme uses waste rubber pyrolysis oil, heavy tar, water glass and nonionic surfactants as raw materials to emulsify and disperse them to obtain tank bottom sludge cleaning agent. By mixing the cleaning agent with the sludge, the three-phase micro-separation of the sludge is promoted. Finally, it is combined with other processes to achieve the recycling and treatment of the sludge.

[0003] However, existing technologies remain within the framework of reducing interfacial tension and physical shearing, failing to address the adhesion principle between heavy hydrocarbons and the solid phase to achieve chemical desorption. This makes it difficult to simultaneously achieve the goals of low-energy operation, high oil recovery rate, and compliance with solid residue standards. Therefore, there is an urgent need to develop and design a novel tank bottom oil treatment and recovery technology to address these issues. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the primary objective of this application is to provide a method for treating and recovering oil sludge from the bottom of petrochemical feedstock tanks. This method involves modifying alkali lignin by grafting naphthalene ring structures onto the alkali lignin molecules, followed by grafting quaternary ammonium groups onto the lignin molecules to obtain a modified lignin cleaning agent. This cleaning agent is mixed with the tank bottom sludge, and water is added to form a slurry. During ball milling, the naphthalene ring structure of the cleaning agent competes with asphaltenes and gums for adsorption, displacing heavy hydrocarbons on the solid surface and solving the problem of oil phase adhesion to solid surfaces, making separation difficult. Simultaneously, the quaternary ammonium cationic groups on the cleaning agent adsorb onto the negatively charged clay particles, neutralizing the charge and compressing the electric double layer. This causes the desorbed micro-oil droplets to lose electrostatic stability, colliding and agglomerating into larger droplets, facilitating subsequent flotation separation steps. This method offers the advantages of high crude oil recovery rate and low process solid waste production.

[0005] To achieve the above objectives, this application provides the following technical solution:

[0006] This application provides a method for treating and recycling oil sludge at the bottom of petrochemical feedstock tanks, comprising the following steps:

[0007] Add water or filtrate to the oil sludge at the bottom of the tank, stir well, and mix into a slurry;

[0008] Modified lignin cleaning agent was added to the slurry, stirred and dispersed, and then ball-milled to obtain ball-milled slurry;

[0009] Add water to the ball mill slurry to dilute it, stir evenly, adjust the pH value of the system, and obtain the prepared slurry;

[0010] The prepared slurry is subjected to flotation separation to obtain floating oil and tailings slurry;

[0011] Impurities are removed from the floating oil to obtain recovered crude oil. The tailings slurry is dewatered by pressure filtration to obtain filter cake and filtrate. The filtrate is reused in the slurry preparation step and mixed with the oil sludge at the bottom of the tank to prepare a new batch of slurry.

[0012] The modified lignin cleaning agent is obtained by introducing a naphthalene ring structure onto the molecule of alkali lignin and then performing quaternization modification.

[0013] Preferably, the modified lignin cleaning agent is prepared by:

[0014] Alkali lignin and deionized water were added to a reaction vessel. While stirring, solid sodium hydroxide was added to adjust the pH to 11-12. The temperature was raised to 48-52℃ and stirred at a constant temperature for 25-35 min to obtain a homogeneous lignin alkaline solution. A phase transfer catalyst was added and stirred evenly. An ethanol dilution of 1-chloromethylnaphthalene was added dropwise for 28-32 min. The temperature was then raised to 73-77℃ and the reaction was carried out at a constant temperature for 3.5-4.5 h. The pH of the system was maintained at 11-12 during the reaction. After the reaction was completed, the system was cooled to room temperature and the pH was adjusted to 7-8 with 0.5 mol / L dilute hydrochloric acid. Ethanol and some water were removed by vacuum distillation to obtain a naphthyl-modified lignin concentrate with a solid content of 18-22%.

[0015] Add a 20wt% sodium hydroxide solution to the naphthyl-modified lignin concentrate, adjust the pH to 10-11, raise the temperature to 63-67℃, add 3-chloro-2-hydroxypropyltrimethylammonium chloride solution dropwise for 38-42 min, maintain the temperature for 4.5-5.5 h, cool to room temperature, and spray dry to obtain the modified lignin cleaning agent.

[0016] Preferably, the mass ratio of 1-chloromethylnaphthalene to anhydrous ethanol in the ethanol dilution of 1-chloromethylnaphthalene is 1:1; and the concentration of the 3-chloro-2-hydroxypropyltrimethylammonium chloride solution is 65 wt%.

[0017] Preferably, the phase transfer catalyst is either benzyltriethylammonium chloride or tetrabutylammonium bromide.

[0018] Preferably, the mass ratio of the alkali lignin, deionized water, phase transfer catalyst, 1-chloromethylnaphthalene ethanol dilution and 3-chloro-2-hydroxypropyltrimethylammonium chloride solution is 10:(80-110):(0.05-0.1):(0.8-1):(9-11).

[0019] Preferably, the slurry prepared by adding water or filtrate to the bottom sludge of the tank has a solid content of 20-25%.

[0020] Preferably, the modified lignin cleaning agent is added at an amount of 1-1.5% of the mass of the sludge at the bottom of the tank.

[0021] Preferably, the specific parameters of the ball milling process are as follows: the grinding media are zirconia ceramic balls with a particle size of 5 mm and 10 mm, with a quantity ratio of 1:1, a ball-to-material mass ratio of 5:(0.9-1.2), a ball milling speed of 350-400 rpm, a ball milling time of 25-30 min, a discharge particle size of ≤75 μm, and a discharge temperature of ≤40℃.

[0022] It should be noted that the high-frequency collisions and shear forces of the grinding media break down solid particles, peel off the oil film covering the particle surface, and disrupt the oil-solid-water emulsion network, exposing the solid surface and allowing the cleaning agent to be adsorbed onto the solid particle surface. Simultaneously, the mechanical energy of ball milling lowers the interfacial reaction energy barrier, accelerating the diffusion and penetration of cleaning agent molecules to the solid-oil interface. The naphthalene ring groups rapidly form π-π stacks with the asphaltenes and gums on the solid surface, competitively displacing the heavier components and improving desorption efficiency.

[0023] Preferably, the solid content of the slurry after dilution with water added to the ball mill slurry is 8-10%; the pH value of the system is adjusted to 8-8.5 using a 10wt% sodium hydroxide solution.

[0024] It should be noted that by diluting the slurry, the concentration and viscosity of the slurry can be reduced, avoiding the entrainment of fine mud and the inability of bubbles to rise effectively under high solid content, thus ensuring the stability of the flotation flow. Adjusting the pH value allows the interfacial activity of the cleaning agent to reach the optimal range, maximizing the hydrophobicity of the oil droplet surface and improving the flotation adhesion efficiency.

[0025] Preferably, the parameters for the flotation separation process are: aeration rate of 0.25-0.35 m³ / h. 3 / (m 2 (·min), flotation time 12-15min, flotation temperature 30-40℃, foam layer thickness 15-20cm.

[0026] It should be noted that the surface of the desorbed oil droplets is strongly hydrophobic, and after colliding with microbubbles, they can stably adhere to the surface of the bubbles and float with them; while the clay particles become more hydrophilic after being adsorbed by the cleaning agent, and cannot stably adhere to the bubbles, and sink with the aqueous phase, thus achieving selective separation of oil and solids.

[0027] Preferably, the specific method for removing impurities from the floating oil is as follows: the floating oil is sent to a settling tank, heated to 55-65℃, and allowed to stand for dehydration for 1.5-2.5 hours to separate the bottom water and solid impurities, thereby obtaining recovered crude oil; the specific method for pressure filtration and dehydration is as follows: the tailings slurry is sent to a plate and frame filter press, the filtration pressure is 0.6-0.8MPa, and after filtration is completed, filter cake and filtrate are obtained, with the filter cake having a moisture content ≤30%.

[0028] It should be noted that the filtrate used for recycling contains cleaning agents, which can reduce the amount of cleaning agents needed after reuse, effectively reducing the cost of chemicals and the consumption of water resources. After multiple cycles, if there are too many impurities in the filtrate, the chemicals can be recovered by acid precipitation, and the remaining effluent can be discharged after meeting the standards.

[0029] The beneficial effects of this application are:

[0030] This application utilizes naphthyl groups grafted onto alkali lignin molecules and the introduction of quaternary ammonium cations. The naphthyl groups can form π-π stacking interactions with asphaltenes and resins, competitively displacing heavy hydrocarbons on the surface of solid particles. This breaks the strong adhesion between heavy oil and clay at the molecular level. Simultaneously, the quaternary ammonium cations neutralize the negative charges on the surfaces of oil droplets and solid particles, compress the electric double layer of clay particles, and disrupt the electrostatic stability of the three-phase emulsion system, causing the desorbed micro-oil droplets to rapidly aggregate and grow. Desorption and demulsification are completed in one step, avoiding re-emulsification and dispersion of desorbed oil droplets, ensuring efficient oil recovery. Furthermore, the high-frequency shearing of wet ball milling breaks up the oil sludge agglomerates, exposing a fresh oil-solid interface, significantly shortening the diffusion and mass transfer path of cleaning agent molecules, and maximizing the desorption effect. This allows for the treatment and recovery of crude oil from oil sludge at room temperature. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This application provides a flowchart of a method for treating and recovering oil sludge from the bottom of a petrochemical feedstock tank. Detailed Implementation

[0033] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the specific embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0034] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0035] The following specific embodiments further illustrate this point:

[0036] Example 1

[0037] like Figure 1 As shown in the figure, this embodiment provides a method for treating and recycling oil sludge at the bottom of petrochemical feedstock tanks:

[0038] 1. Alkali lignin and deionized water were added to a reaction vessel. While stirring, solid sodium hydroxide was added to adjust the pH to 11.5. The temperature was raised to 50°C and stirred at this temperature for 30 minutes to obtain a homogeneous lignin alkaline solution. A phase transfer catalyst, benzyltriethylammonium chloride, was added and stirred until homogeneous. An ethanol dilution of 1-chloromethylnaphthalene diluted at a mass ratio of 1:1 to anhydrous ethanol was added dropwise over 30 minutes. The temperature was then raised to 75°C and the reaction was maintained at this temperature for 4 hours. The pH of the system was maintained at 11.5 throughout the reaction. After the reaction was complete, the mixture was cooled to room temperature, and the pH was adjusted to 7.5 with 0.5 mol / L dilute hydrochloric acid. The ethanol was removed by vacuum distillation. A 20% solids content naphthyl-modified lignin concentrate was obtained by adding some water. A 20wt% sodium hydroxide solution was added to the naphthyl-modified lignin concentrate to adjust the pH to 10.5. The temperature was raised to 65℃, and a 65wt% 3-chloro-2-hydroxypropyltrimethylammonium chloride solution was added dropwise over 40 minutes. The mixture was kept at a constant temperature for 5 hours, cooled to room temperature, and spray-dried to obtain a modified lignin cleaning agent. The mass ratio of the alkali lignin, deionized water, phase transfer catalyst, 1-chloromethylnaphthalene ethanol dilution, and 3-chloro-2-hydroxypropyltrimethylammonium chloride solution was 10:100:0.08:0.9:10.

[0039] 2. Add water to the sludge at the bottom of the tank, stir evenly, and adjust to a slurry with a solid content of 23%; add 1.2% of the modified lignin cleaning agent by weight of the sludge at the bottom of the tank to the slurry, stir and disperse, and use zirconia ceramic balls with a particle size of 5 mm and 10 mm as grinding media, with a ratio of 1:1 between the two particle sizes of grinding media and a ball-to-material mass ratio of 5:1, a ball milling speed of 380 rpm, ball milling treatment for 28 min, discharge particle size ≤75 μm, discharge temperature ≤40℃, to obtain ball milled slurry.

[0040] 3. Add water to the ball mill slurry to dilute it to a solid content of 9%, stir well, and adjust the pH of the system to 8.3 using a 10wt% sodium hydroxide solution to obtain the prepared slurry.

[0041] 4. The prepared slurry was subjected to flotation separation at 35℃ for 13 minutes, with a flotation aeration rate of 0.3 m³ / min. 3 / (m 2 (min), with a foam layer thickness of 18cm, to obtain floating oil and tailings slurry.

[0042] 5. The floating oil is sent to a settling tank, heated to 60°C, and allowed to stand for 2 hours to remove water and solid impurities from the bottom, thus obtaining recovered crude oil. The tailings slurry is sent to a plate and frame filter press at a filtration pressure of 0.7 MPa. After filtration is completed, filter cake and filtrate are obtained, with the filter cake having a moisture content of ≤30%.

[0043] Example 2

[0044] like Figure 1As shown in the figure, this embodiment provides a method for treating and recycling oil sludge at the bottom of petrochemical feedstock tanks:

[0045] 1. Alkali lignin and deionized water were added to a reaction vessel. While stirring, solid sodium hydroxide was added to adjust the pH to 11. The temperature was raised to 48℃ and stirred at this temperature for 25 min to obtain a homogeneous lignin alkaline solution. Tetrabutylammonium bromide, a phase transfer catalyst, was added and stirred until homogeneous. An ethanol dilution of 1-chloromethylnaphthalene diluted at a mass ratio of 1:1 to anhydrous ethanol was added dropwise over 28 min. The temperature was then raised to 73℃ and the reaction was maintained at this temperature for 3.5 h. The pH of the system was maintained at 11 throughout the reaction. After the reaction was complete, the mixture was cooled to room temperature, and the pH was adjusted to 7 with 0.5 mol / L dilute hydrochloric acid. Ethanol and some other components were removed by vacuum distillation. The water content was removed to obtain a naphthyl-modified lignin concentrate with a solid content of 18%. A 20wt% sodium hydroxide solution was added to the naphthyl-modified lignin concentrate to adjust the pH to 10. The temperature was raised to 63℃, and a 65wt% 3-chloro-2-hydroxypropyltrimethylammonium chloride solution was added dropwise for 38 min. The reaction was carried out at a constant temperature for 4.5 h, cooled to room temperature, and spray-dried to obtain a modified lignin cleaning agent. The mass ratio of the alkali lignin, deionized water, phase transfer catalyst, 1-chloromethylnaphthalene ethanol dilution, and 3-chloro-2-hydroxypropyltrimethylammonium chloride solution was 10:80:0.05:0.8:9.

[0046] 2. Add filtrate to the bottom sludge of the tank, stir evenly, and adjust to a slurry with a solid content of 20%; add 1% modified lignin cleaning agent by weight of the bottom sludge of the tank to the slurry, stir and disperse, and use zirconia ceramic balls with a particle size of 5 mm and 10 mm as grinding media, with a ratio of the two particle size grinding media quantity to 1:1 and a ball-to-material mass ratio of 5:0.9, ball milling speed of 350 rpm, ball milling treatment for 25 min, discharge particle size ≤75 μm, discharge temperature ≤40℃, to obtain ball milled slurry.

[0047] 3. Add water to the ball mill slurry to dilute it to a solid content of 8%, stir well, and adjust the pH of the system to 8 using a 10wt% sodium hydroxide solution to obtain the prepared slurry.

[0048] 4. The prepared slurry was subjected to flotation separation at 30℃ for 12 minutes, with a flotation aeration rate of 0.25 m³ / min. 3 / (m 2 (min), with a foam layer thickness of 15cm, to obtain floating oil and tailings slurry.

[0049] 5. The floating oil is sent to a settling tank, heated to 55°C, and allowed to stand for 1.5 hours to remove bottom water and solid impurities, thus obtaining recovered crude oil. The tailings slurry is sent to a plate and frame filter press at a filtration pressure of 0.6 MPa. After filtration is completed, filter cake and filtrate are obtained, with the filter cake having a moisture content of ≤30%.

[0050] Example 3

[0051] like Figure 1 As shown in the figure, this embodiment provides a method for treating and recycling oil sludge at the bottom of petrochemical feedstock tanks:

[0052] 1. Alkali lignin and deionized water were added to a reaction vessel. While stirring, solid sodium hydroxide was added to adjust the pH to 12. The temperature was raised to 52℃ and stirred at this temperature for 35 min to obtain a homogeneous lignin alkaline solution. Tetrabutylammonium bromide, a phase transfer catalyst, was added and stirred until homogeneous. An ethanol dilution of 1-chloromethylnaphthalene diluted at a mass ratio of 1:1 to anhydrous ethanol was added dropwise over 32 min. The temperature was then raised to 77℃ and the reaction was maintained at this temperature for 4.5 h. The pH of the system was maintained at 12 throughout the reaction. After the reaction was complete, the mixture was cooled to room temperature, and the pH was adjusted to 8 with 0.5 mol / L dilute hydrochloric acid. Ethanol and other components were removed by vacuum distillation. A portion of the water was removed to obtain a naphthyl-modified lignin concentrate with a solid content of 22%. A 20wt% sodium hydroxide solution was added to the naphthyl-modified lignin concentrate to adjust the pH to 11. The temperature was raised to 67℃, and a 65wt% 3-chloro-2-hydroxypropyltrimethylammonium chloride solution was added dropwise over 42 minutes. The mixture was kept at a constant temperature for 5.5 hours, cooled to room temperature, and spray-dried to obtain a modified lignin cleaning agent. The mass ratio of the alkali lignin, deionized water, phase transfer catalyst, 1-chloromethylnaphthalene ethanol dilution, and 3-chloro-2-hydroxypropyltrimethylammonium chloride solution was 10:110:0.1:1:11.

[0053] 2. Add water to the bottom sludge of the tank, stir evenly, and adjust to a slurry with a solid content of 25%; add 1.5% modified lignin cleaning agent by weight of the bottom sludge of the tank to the slurry, stir and disperse, and use zirconia ceramic balls with a particle size of 5 mm and 10 mm as grinding media, with a ratio of the two particle size grinding media quantity to 1:1 and a ball-to-material mass ratio of 5:1.2, ball milling speed of 400 rpm, ball milling treatment for 30 min, discharge particle size ≤75 μm, discharge temperature ≤40℃, to obtain ball milling slurry.

[0054] 3. Add water to the ball mill slurry to dilute it to a solid content of 10%, stir evenly, and adjust the pH of the system to 8.5 using a 10wt% sodium hydroxide solution to obtain the prepared slurry.

[0055] 4. The prepared slurry was subjected to flotation separation at 40℃ for 15 minutes, with a flotation aeration rate of 0.35 m³ / min. 3 / (m 2 (min), with a foam layer thickness of 20cm, to obtain floating oil and tailings slurry.

[0056] 5. The floating oil is sent to a settling tank, heated to 65°C, and allowed to stand for 2.5 hours to remove bottom water and solid impurities, thus obtaining recovered crude oil. The tailings slurry is sent to a plate and frame filter press at a filtration pressure of 0.8 MPa. After filtration is completed, filter cake and filtrate are obtained, with the filter cake having a moisture content of ≤30%.

[0057] Comparative Example 1

[0058] This comparative example provides a method for treating and recycling oil sludge at the bottom of petrochemical raw material tanks. The difference from Example 1 is that the modified lignin cleaning agent is replaced with sodium dodecylbenzene sulfonate. The remaining steps are the same as in Example 1 and will not be repeated here.

[0059] Comparative Example 2

[0060] This comparative example provides a method for treating and recycling oil sludge at the bottom of petrochemical raw material tanks. The difference from Example 1 is that no alkali lignin is modified and it is used directly as a cleaning agent. The remaining steps are the same as in Example 1 and will not be repeated here.

[0061] Comparative Example 3

[0062] This comparative example provides a method for treating and recycling oil sludge at the bottom of petrochemical raw material tanks. The difference from Example 1 is that ball milling is not used in the treatment process. The remaining steps are the same as in Example 1 and will not be repeated here.

[0063] To demonstrate the beneficial effects of the proposed solution, the following performance tests were conducted on Examples 1-3 and Comparative Examples 1-3:

[0064] Crude oil recovery rate test: The material balance weight method is used. Homogeneous sludge from the bottom of the tank of the same batch is taken and the total oil content per unit mass of sludge is determined by Soxhlet extraction. The total crude oil mass of the sample sludge is then calculated. The mass of recovered crude oil is weighed. The ratio of the mass of recovered crude oil to the total mass of raw crude oil is the crude oil recovery rate.

[0065] Oil content test of filter cake: Soxhlet extraction gravimetric method was used, with petroleum ether (boiling range 60~90℃) as the extraction solvent; 5g of the crushed filter cake after pressure filtration was taken, dehydrated with anhydrous sodium sulfate, and then placed into a constant weight degreased filter paper tube for continuous reflux extraction for 6h; the extract was subjected to rotary evaporation to remove the solvent, vacuum dried, and weighed to obtain the oil content; the solid phase after extraction was dried at 105℃ to constant weight to obtain the dry solid phase mass, and the oil content on a dry basis was calculated.

[0066] Table 1. Crude oil recovery rate and filter cake oil content test results of Examples 1-3 and Comparative Examples 1-3

[0067]

[0068] As can be seen from the data in Table 1, the crude oil recovery rate and filter cake oil content of the treatment methods in Examples 1-3 are significantly better than those in Comparative Examples 1-3. This indicates that the improvements in this scheme can effectively enhance the treatment effect of tank bottom sludge. In Comparative Example 1, the modified lignin cleaning agent in this scheme was replaced with sodium dodecylbenzenesulfonate, which mainly removes light oil by reducing interfacial tension, but cannot break the strong π-π adhesion between heavy hydrocarbons and clay. Therefore, its crude oil recovery rate and filter cake oil content are not as good as those in Examples 1-3. In Comparative Example 2, the alkaline lignin was not treated with naphthyl grafting and quaternary ammonium cation modification, which greatly reduced the cleaning agent's effect of removing heavy hydrocarbons, thus reducing its test performance. In Comparative Example 3, ball milling was not used, which made the original oil-solid separation difficult. The cleaning agent molecules could not effectively diffuse to the oil-solid interface and generate competitive adsorption, thereby removing oily substances. Therefore, its test performance decreased.

[0069] In summary, the proposed solution combines modified lignin cleaning agent with ball milling, which effectively achieves oil-solid separation, improves crude oil recovery rate, reduces waste, and conserves petroleum resources. It is suitable for treating oil sludge at the bottom of tanks or inside pipelines in petrochemical plants.

[0070] It should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the spirit and scope of the technical solutions of this application, and all such modifications and substitutions should be covered within the scope of the claims of this application.

Claims

1. A method for treating and recovering oil sludge from the bottom of petrochemical feedstock tanks, characterized in that, Includes the following steps: Add water or filtrate to the oil sludge at the bottom of the tank, stir well, and mix into a slurry; Modified lignin cleaning agent was added to the slurry, stirred and dispersed, and then ball-milled to obtain ball-milled slurry; Add water to the ball mill slurry to dilute it, stir evenly, adjust the pH value of the system, and obtain the prepared slurry; The prepared slurry is subjected to flotation separation to obtain floating oil and tailings slurry; Impurities are removed from the floating oil to obtain recovered crude oil. The tailings slurry is dewatered by pressure filtration to obtain filter cake and filtrate. The filtrate is reused in the slurry preparation step and mixed with the oil sludge at the bottom of the tank to prepare a new batch of slurry. The modified lignin cleaning agent is obtained by introducing a naphthalene ring structure onto the molecule of alkali lignin and then performing quaternization modification.

2. The method for treating and recovering oil sludge at the bottom of petrochemical feedstock tanks according to claim 1, characterized in that, The modified lignin cleaning agent is prepared by: Alkali lignin and deionized water were added to a reaction vessel. While stirring, solid sodium hydroxide was added to adjust the pH to 11-12. The temperature was raised to 48-52℃ and stirred at a constant temperature for 25-35 min to obtain a homogeneous lignin alkaline solution. A phase transfer catalyst was added and stirred evenly. An ethanol dilution of 1-chloromethylnaphthalene was added dropwise for 28-32 min. The temperature was then raised to 73-77℃ and the reaction was carried out at a constant temperature for 3.5-4.5 h. The pH of the system was maintained at 11-12 during the reaction. After the reaction was completed, the system was cooled to room temperature and the pH was adjusted to 7-8 with 0.5 mol / L dilute hydrochloric acid. Ethanol and some water were removed by vacuum distillation to obtain a naphthyl-modified lignin concentrate with a solid content of 18-22%. Add a 20wt% sodium hydroxide solution to the naphthyl-modified lignin concentrate, adjust the pH to 10-11, raise the temperature to 63-67℃, add 3-chloro-2-hydroxypropyltrimethylammonium chloride solution dropwise for 38-42 min, maintain the temperature for 4.5-5.5 h, cool to room temperature, and spray dry to obtain the modified lignin cleaning agent.

3. The method for treating and recovering oil sludge at the bottom of petrochemical raw material tanks according to claim 2, characterized in that, The ethanol dilution of 1-chloromethylnaphthalene has a mass ratio of 1-chloromethylnaphthalene to anhydrous ethanol of 1:1; the concentration of the 3-chloro-2-hydroxypropyltrimethylammonium chloride solution is 65 wt%.

4. The method for treating and recovering oil sludge at the bottom of petrochemical feedstock tanks according to claim 2, characterized in that, The phase transfer catalyst is either benzyltriethylammonium chloride or tetrabutylammonium bromide.

5. The method for treating and recovering oil sludge at the bottom of petrochemical feedstock tanks according to claim 2, characterized in that, The mass ratio of the alkali lignin, deionized water, phase transfer catalyst, 1-chloromethylnaphthalene ethanol dilution and 3-chloro-2-hydroxypropyltrimethylammonium chloride solution is 10:(80-110):(0.05-0.1):(0.8-1):(9-11).

6. The method for treating and recovering oil sludge at the bottom of petrochemical raw material tanks according to claim 1, characterized in that, The slurry made by adding water or filtrate to the bottom sludge of the tank has a solid content of 20-25%.

7. The method for treating and recovering oil sludge at the bottom of petrochemical raw material tanks according to claim 1, characterized in that, The modified lignin cleaning agent is added at a rate of 1-1.5% of the mass of the sludge at the bottom of the tank.

8. The method for treating and recovering oil sludge at the bottom of petrochemical raw material tanks according to claim 1, characterized in that, The specific parameters of the ball milling process are as follows: the grinding media are zirconia ceramic balls with a particle size of 5 mm and 10 mm, the ball-to-material mass ratio is 5:(0.9-1.2), the ball milling speed is 350-400 rpm, the ball milling time is 25-30 min, the output particle size is ≤75 μm, and the output temperature is ≤40℃.

9. The method for treating and recovering oil sludge at the bottom of petrochemical raw material tanks according to claim 1, characterized in that, The solid content of the slurry after dilution with water is 8-10%; the pH of the system is adjusted to 8-8.5 using a 10wt% sodium hydroxide solution.

10. The method for treating and recovering oil sludge at the bottom of petrochemical feedstock tanks according to claim 1, characterized in that, The parameters for the flotation separation process are: aeration rate of 0.25-0.35 m³ / h. 3 / (m 2 (·min), flotation time 12-15min, flotation temperature 30-40℃, foam layer thickness 15-20cm.

11. The method for treating and recovering oil sludge at the bottom of petrochemical feedstock tanks according to claim 1, characterized in that, The specific method for removing impurities from the floating oil is as follows: the floating oil is sent to a settling tank, heated to 55-65℃, and allowed to stand for dehydration for 1.5-2.5 hours to separate the bottom water and solid impurities, thus obtaining recovered crude oil; the specific method for pressure filtration and dehydration is as follows: the tailings slurry is sent to a plate and frame filter press, the filtration pressure is 0.6-0.8MPa, and after filtration is completed, filter cake and filtrate are obtained, with the filter cake having a moisture content of ≤30%.

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