Recyclable eutectic solvent microemulsion as well as preparation method and application thereof

Abstract

The invention relates to a recyclable eutectic solvent microemulsion as well as a preparation method and application thereof. The microemulsion is composed of a polar deep-eutectic solvent, a non-polar deep-eutectic solvent and a surfactant, the molar ratio of the polar deep-eutectic solvent to the non-polar deep-eutectic solvent is 1: (3-5), and the surfactant accounts for 1%-10% of the total mass of the deep-eutectic solvent. The preparation method comprises the following steps: respectively heating and stirring a hydrogen bond donor and a hydrogen bond acceptor to prepare polar and non-polar deep-eutectic solvents, mixing the polar and non-polar deep-eutectic solvents with a surfactant according to a ratio, and carrying out ultrasonic treatment to form a stable microemulsion. When the microemulsion is used for oil sludge extraction, alkali is added to adjust the pH value of a system to 10-12 so as to realize high-efficiency separation of an oil phase, and then acid is added and heating dehydration is carried out, so that the microemulsion can be regenerated and recycled. The method has the characteristics of efficient extraction, heavy metal removal and recyclability of the extraction agent, is simple in process, green and economical, and is suitable for resourceful treatment of the oily sludge.

Description

Technical Field

[0001] This invention relates to the field of petroleum pollution control, specifically to a recyclable eutectic solvent microemulsion, its preparation method, and its application. Background Technology

[0002] Oily sludge is an unavoidable hazardous waste in the petroleum industry, generated throughout the entire industrial chain, including crude oil extraction, storage, transportation, and refining. Classified as hazardous waste, oily sludge has a complex composition, typically consisting of a dispersed system of water, hydrocarbons, mechanical impurities, and metals. The mass percentages of the components in oily sludge are as follows: hydrocarbons - 35-58% (by weight); water - 25-31%; mechanical impurities - 25-25%; metals - 3-15%. The hydrocarbon portion contains toxic and harmful substances such as alkanes, aromatic compounds, asphaltenes, anthracene, and pyrene. Untreated discharge and accumulation not only waste petroleum resources but also cause serious environmental pollution.

[0003] Currently, the main methods for treating oily sludge include incineration, solidification, thermal washing, conditioning-mechanical separation, biological methods, and solvent extraction. Incineration generates large amounts of waste gas and has high energy consumption; solidification is only temporary and does not fundamentally solve the problem; biological methods have long treatment cycles and are not suitable for treating oily sludge with high oil content; solvent extraction is a well-known method for extracting oil from oily sludge and oil sands under mild conditions, and it is widely accepted due to its mild reaction conditions and high recovery rate. With the increasing emphasis on green environmental protection, traditional extractants are gradually being replaced by eutectic solvents. However, single eutectic solvent extraction faces several fundamental challenges: poor quality of extracted petroleum products, presence of small amounts of water, inability to remove heavy metals, and high content of residual asphaltenes in the treated solids. Adding surfactants increases the solubility of organic matter, enabling desorbent electrolytic solvents (DES) to desorb organic matter from oily sludge. Simultaneously, since water in oily sludge mainly exists in water-in-oil form, adding surfactants can change its surface tension, making it easier for water to separate from the oil phase and achieving a high water removal rate. The addition of carboxylic acid DES can complex heavy metal ions. At the same time, due to the presence of surfactants, the interfacial tension between oil and solution can be effectively reduced, thereby reducing the free energy of the extracted oil to be removed from the solid surface and achieving efficient separation.

[0004] This invention constructs a recyclable microemulsion based on a polar / nonpolar eutectic solvent (DES). The phase behavior of the microemulsion follows the hydrophilic-lipophilic deviation (HLD) theory. This theory states that salinity is one of the core variables regulating the type of microemulsion: decreasing salinity reduces the HLD value of the system, thereby promoting the formation of O / W type microemulsions; while increasing salinity increases the HLD value, easily leading to W / O type emulsification. In oil sludge treatment, how to easily and cost-effectively separate the microemulsion from the oil phase after efficient extraction and achieve recycling is a key bottleneck restricting its industrialization. Based on this, this invention adds a surfactant and a eutectic solvent with opposite polarity to a single eutectic solvent, separates the oil phase by controlling the pH value, and then ensures the reformation of the microemulsion by adding acid, heating, and drying. Summary of the Invention

[0005] Technical Problem to be Solved: Based on the above analysis, this invention aims to provide a recyclable eutectic solvent microemulsion, its preparation method, and its application, to solve problems such as poor product quality, heavy metal content, poor emulsion stability, and difficulty in phase separation in the treatment of oily sludge. This invention aims to address the problems of difficult extractant recovery, low recycling rate, and poor simultaneous removal of heavy metals in existing oily sludge extraction technologies. The core lies in providing an intelligent and reversible microemulsion system that, through simple acid-base sequence control, can achieve a closed-loop cycle of "high-efficiency extraction → oil phase release → extractant regeneration."

[0006] Technical solution: A recyclable eutectic solvent microemulsion, comprising a polar eutectic solvent, a non-polar eutectic solvent, and a surfactant; wherein the molar ratio of the polar eutectic solvent to the non-polar eutectic solvent is 1:(3~5); and the ratio of the total mass of the surfactant to the total mass of the polar eutectic solvent and the non-polar eutectic solvent is 1:(0.01~0.1).

[0007] Preferably, the above-mentioned polar eutectic solvent is composed of a hydrogen bond donor and a hydrogen bond acceptor in a molar ratio of 1:(1~4); the hydrogen bond donor is selected from carboxylic acid compounds; and the hydrogen bond acceptor is selected from at least one of choline chloride or a metal salt.

[0008] Preferably, the above-mentioned nonpolar eutectic solvent is composed of a hydrogen bond donor and a hydrogen bond acceptor in a molar ratio of 1:(1~5); the hydrogen bond donor is selected from at least one of long-chain carboxylic acids, terpenoids, phenols or long-chain alcohols; the hydrogen bond acceptor is selected from at least one of quaternary ammonium compounds, terpenoids, ketones or long-chain organic salts.

[0009] Preferably, the surfactant is a nonionic surfactant or an ionic surfactant; the nonionic surfactant is selected from the Brij series, Tween series or Span series surfactants; the ionic surfactant is selected from quaternary ammonium salt surfactants or anionic surfactants.

[0010] The preparation method of the above-mentioned recyclable eutectic solvent microemulsion includes the following steps: S1. Preparing a polar eutectic solvent: mixing a hydrogen bond donor and a hydrogen bond acceptor under stirring conditions of 60~100℃ and 200~400 r / min for 30~50 min to form a homogeneous liquid; S2. Preparing a nonpolar eutectic solvent: mixing a hydrogen bond donor and a hydrogen bond acceptor under stirring conditions of 60~100℃ and 200~400 r / min for 30~50 min to form a homogeneous liquid; S3. Constructing a microemulsion: The polar eutectic solvent obtained in step S1 and the non-polar eutectic solvent obtained in step S2 are mixed with a surfactant, wherein the molar ratio of the polar eutectic solvent to the non-polar eutectic solvent is 1:(3~5), and the ratio of the total mass of the surfactant to the total mass of the polar eutectic solvent and the non-polar eutectic solvent is 1:(0.01~0.1); then, the mixture is ultrasonically treated at 30~60℃ and 2000~3000 Hz for 10~20 min to form a stable microemulsion system.

[0011] In step S1, the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1:(1~4); the hydrogen bond donor is selected from carboxylic acid compounds; and the hydrogen bond acceptor is selected from at least one of choline chloride or metal salts.

[0012] In step S2, the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1:(1~5); the hydrogen bond donor is selected from at least one of long-chain carboxylic acids, terpenoids, phenols, or long-chain alcohols; and the hydrogen bond acceptor is selected from at least one of quaternary ammonium compounds, terpenoids, ketones, or long-chain organic salts.

[0013] The application of the above-mentioned recyclable eutectic solvent microemulsion in oil sludge extraction includes the following steps: A. Extraction and oil phase separation: The microemulsion is mixed with oily sludge at a mass ratio of 1:(3~10), and an alkaline solution with a concentration of 1~5 mol / L is added to adjust the pH of the system to 10-12. The mixture is allowed to stand or centrifuged to separate the oil phase, and the upper oil phase is collected; B. Microemulsion regeneration: An acid with a concentration of 2~6 mol / L is added to the liquid phase remaining after the oil phase separation in step A to adjust the pH of the system to 2-4. The system is then heated and stirred at 70~90℃ until the water content of the system decreases and a homogeneous and stable microemulsion system is re-formed.

[0014] In step A, the alkaline solution is sodium hydroxide solution or ammonia water; in step B, the acid is hydrochloric acid or sulfuric acid.

[0015] In step A, the centrifugation speed is 3000-5000 r / min and the time is 15-45 min; or the settling time is 12 h.

[0016] Beneficial Effects: This invention achieves efficient extraction of oil sludge and recycling of the extractant through the synergistic combination of polar eutectic solvents, non-polar eutectic solvents, and surfactants, combined with pH-responsive control. Compared to a single eutectic solvent, this microemulsion system significantly improves oil phase removal efficiency and water removal. Simultaneously, its selective extraction capability substantially reduces the content of heavy components and asphaltenes in the recovered oil, effectively improving oil quality. The carboxylic acid components in the system can complex and remove heavy metal ions from the oil phase, achieving oil purification. Particularly noteworthy is that through a simple "alkali-acid" sequential operation, oil phase release and microemulsion regeneration can be achieved under mild conditions, forming a highly efficient, green, and recyclable complete process that significantly reduces processing costs. Attached Figure Description

[0017] Figure 1 Extraction rates and components of oil sludge with different solvents.

[0018] Figure 2 shows the components of oil recovered from different solvents.

[0019] Figure 3 To recover the main heavy metal content in the oil. Detailed Implementation

[0020] The present invention will be described in detail below through embodiments, but the scope of protection of the present invention is not limited thereto. The oily sludge used in the following examples all comes from Yangzi Petrochemical.

[0021] Comparative Example 1 (1) Preparation of hydrophobic DES: tertiary amine group and thymol are mixed in a molar ratio of 1:1 and stirred at 60°C for 2 hours to obtain transparent liquid A.

[0022] (2) Oil sludge treatment: Transparent liquid A and oily sludge (oil content 35%) are mixed at a mass ratio of 10:1. 2 mol / L NaOH solution is added to the mixture while stirring until the pH of the system reaches 11. Stirring is stopped, and the mixture is allowed to stand for 4 hours. A dark oil phase is observed precipitated in the upper layer, an emulsion layer in the middle layer, and an aqueous and solid phase in the lower layer. The upper oil phase is collected, and the mixture of the lower and middle layers is taken. 4 mol / L HCl solution is added while stirring to adjust the pH of the system to 3. The system is then transferred to an 80°C water bath, stirred, and dried until the volume shrinks by approximately 80%. Heating is stopped, and the mixture is cooled to room temperature. The system reverts to a homogeneous and stable milky white liquid, i.e., the regenerated microemulsion.

[0023] (3) Analysis and Calculation: The oil content of the oily sludge, the distribution of the four phases of the recovered oil, and LIBS spectral analysis were calculated. The oil removal rate was 70%, and the water removal rate was 96%. The proportions of saturated hydrocarbons, aromatic hydrocarbons, gums, and asphaltenes in the recovered oil were 50.5%, 13.7%, 14.4%, and 21.4%, respectively. The contents of the main heavy metals copper, zinc, chromium, and nickel in the recovered oil were 0.4284 wt.%, 0.4106 wt.%, 0.4475 wt.%, and 0.4960 wt.%, respectively.

[0024] Example 1 (1) Preparation of polar DES: choline chloride and urea are mixed at a molar ratio of 1:2 and stirred at 80°C for 1 hour to obtain transparent liquid A.

[0025] (2) Preparation of nonpolar DES: Oleic acid and methyltrioctylammonium chloride are mixed in a molar ratio of 3:1 and stirred at 90°C for 2 hours to obtain transparent liquid B.

[0026] (3) Construction of extract: Take 20g of transparent liquid A, 80g of transparent liquid B and 0.3g of Brij-35, and ultrasonically emulsify at 50℃ for 20min to obtain extract C.

[0027] (4) Oil sludge extraction: Extract C was mixed with oily sludge (35% oil content) at a mass ratio of 10:1. The pH was adjusted to 10 with NaOH, stirring was stopped, and the mixture was allowed to stand for 4 hours. A dark oil phase was observed to precipitate in the upper layer, an emulsion layer in the middle layer, and an aqueous and solid phase in the lower layer. The upper oil phase was collected, and the mixed liquid phase of the lower and middle layers was taken. A 4 mol / L HCl solution was added while stirring to adjust the pH of the system to 3. The system was then transferred to an 80°C water bath, stirred, and dried until the volume decreased by about 80%. Heating was stopped, and the system was cooled to room temperature. The system was transformed back into a homogeneous and stable milky white liquid, i.e., the regenerated microemulsion.

[0028] (5) Analysis and Calculation: The oil content of the oily sludge, the four-phase component distribution of the recovered oil, and LIBS spectral analysis were calculated. The oil removal rate was 80.8%, and the water removal rate was 99.1%. The proportions of saturated hydrocarbons, aromatic hydrocarbons, gums, and asphaltenes in the recovered oil were 70.3%, 13.9%, 9.4%, and 6.4%, respectively. The contents of the main heavy metals copper, zinc, chromium, and nickel in the recovered oil were 0.1684 wt.%, 0.1506 wt.%, 0.1875 wt.%, and 0.2360 wt.%, respectively.

[0029] Example 2 (1) Preparation of polar DES: Glycerol / choline chloride were mixed in a molar ratio of 2:1 and stirred at 70°C for 1.5 h to obtain transparent liquid A.

[0030] (2) Preparation of nonpolar DES: Lauric acid / hexadecyltrimethylammonium bromide are mixed in a molar ratio of 2:1 and stirred at 85°C for 2 hours to obtain transparent liquid B.

[0031] (3) Preparation of extract: 15g of transparent liquid A, 85g of transparent liquid B, and 0.2g of Tween-80 were ultrasonicated at 55℃ for 15min to obtain extract C.

[0032] (4) Oil sludge treatment: Extract C was mixed with oily sludge at a mass ratio of 8:1, and the pH was adjusted to 10 with NaOH. The mixture was allowed to stand for 4 hours. A dark oil phase was observed to precipitate in the upper layer, an emulsion layer in the middle layer, and an aqueous and solid phase in the lower layer. The upper oil phase was collected, and the mixed liquid phase of the lower and middle layers was taken. A 4 mol / L HCl solution was added while stirring to adjust the pH of the system to 3. The system was then transferred to an 80°C water bath, stirred, and dried until the volume decreased by about 40%. Heating was stopped, and the system was cooled to room temperature. The system was transformed back into a homogeneous and stable milky white liquid, i.e., the regenerated microemulsion.

[0033] (5) Analysis and Calculation: The oil content of the oily sludge, the four-phase component distribution of the recovered oil, and LIBS spectral analysis were calculated. The oil removal rate was 83.9%, and the water removal rate was 99.6%. The proportions of saturated hydrocarbons, aromatic hydrocarbons, gums, and asphaltenes in the recovered oil were 73.3%, 18.9%, 8.7%, and 5.7%, respectively. The contents of the main heavy metals copper, zinc, chromium, and nickel in the recovered oil were 0.1584 wt.%, 0.1406 wt.%, 0.1775 wt.%, and 0.2260 wt.%, respectively.

[0034] Example 3 (1) Preparation of polar DES: benzenesulfonic acid / choline chloride are mixed in a molar ratio of 2:1 and stirred at 70°C for 1.5 h to obtain transparent liquid A.

[0035] (2) Preparation of nonpolar DES: Lauric acid / thymol are mixed in a molar ratio of 2:1 and stirred at 85°C for 2 hours to obtain transparent liquid B.

[0036] (3) Preparation of extract: 15g of transparent liquid A, 85g of transparent liquid B, and 0.2g of Tween-80 were ultrasonicated at 55℃ for 15min to obtain extract C.

[0037] (4) Oil sludge treatment: Extract C and oily sludge were mixed at a mass ratio of 10:1. The pH was adjusted to 8.5 with NaOH, and then the mixture was allowed to stand for 4 hours after adjusting the pH to 10. A dark oil phase was observed to precipitate in the upper layer, an emulsion layer in the middle layer, and an aqueous and solid phase in the lower layer. The upper oil phase was collected, and the mixed liquid phase of the lower and middle layers was taken. A 4 mol / L HCl solution was added while stirring to adjust the pH of the system to 3. The system was then transferred to an 80°C water bath, stirred, and dried until the volume decreased by about 80%. Heating was stopped, and the system was cooled to room temperature. The system was transformed back into a homogeneous and stable milky white liquid, i.e., the regenerated microemulsion.

[0038] (5) Analysis and Calculation: The oil content of the oily sludge, the four-phase component distribution of the recovered oil, and LIBS spectral analysis were calculated. The oil removal rate was 88.1%, and the water removal rate was 99.8%. The proportions of saturated hydrocarbons, aromatic hydrocarbons, gums, and asphaltenes in the recovered oil were 75.1%, 12.9%, 7.7%, and 5.3%, respectively. The contents of the main heavy metals copper, zinc, chromium, and nickel in the recovered oil were 0.1288 wt.%, 0.1209 wt.%, 0.1577 wt.%, and 0.1860 wt.%, respectively.

[0039] The initial oil content of the oily sludge used in the above embodiments was determined by distillation to be 67.34%, solid content 24.69%, and water content 7.97%.

[0040] The above embodiments correspond to the accompanying drawings. Figure 1 The total oil removal rate of Comparative Example 1 was compared with that of Examples 1, 2, and 3, directly demonstrating that the overall oil phase removal efficiency can be significantly improved compared to a single DES microemulsion system. Figure 2 This demonstrates that the microemulsion system does not simply "dissolve" sludge, but rather preferentially extracts light components while discarding asphaltenes, thereby fundamentally improving the quality of recovered oil. Figure 3 The microemulsion system (example) was demonstrated to have a stronger heavy metal removal capability than DES alone (comparative example).

[0041] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. For those skilled in the art, after learning the contents described in the present invention, several equivalent changes and substitutions can be made without departing from the principle of the present invention. These equivalent changes and substitutions should also be considered to fall within the protection scope of the present invention.

Claims

1. A recyclable eutectic solvent microemulsion, characterized in that, It is composed of a polar eutectic solvent, a non-polar eutectic solvent and a surfactant; wherein the molar ratio of the polar eutectic solvent to the non-polar eutectic solvent is 1:(3~5); and the ratio of the total mass of the surfactant to the total mass of the polar eutectic solvent and the non-polar eutectic solvent is 1:(0.01~0.1).

2. The recyclable eutectic solvent microemulsion according to claim 1, characterized in that, The polar eutectic solvent is composed of a hydrogen bond donor and a hydrogen bond acceptor in a molar ratio of 1:(1~4); the hydrogen bond donor is selected from carboxylic acid compounds; and the hydrogen bond acceptor is selected from at least one of choline chloride or a metal salt.

3. The recyclable eutectic solvent microemulsion according to claim 1, characterized in that, The nonpolar eutectic solvent is composed of a hydrogen bond donor and a hydrogen bond acceptor in a molar ratio of 1:(1~5); the hydrogen bond donor is selected from at least one of long-chain carboxylic acids, terpenoids, phenols or long-chain alcohols; the hydrogen bond acceptor is selected from at least one of quaternary ammonium compounds, terpenoids, ketones or long-chain organic salts.

4. The recyclable eutectic solvent microemulsion according to claim 1, characterized in that, The surfactant is a nonionic surfactant or an ionic surfactant; the nonionic surfactant is selected from the Brij series, Tween series or Span series surfactants; the ionic surfactant is selected from quaternary ammonium salt surfactants or anionic surfactants.

5. The method for preparing the recyclable eutectic solvent microemulsion according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Preparation of polar eutectic solvent: The hydrogen bond donor and the hydrogen bond acceptor are mixed at 60~100℃ and 200~400 r / min for 30~50 min to form a homogeneous liquid; S2. Preparation of nonpolar eutectic solvent: The hydrogen bond donor and the hydrogen bond acceptor are mixed at 60~100℃ and 200~400 r / min for 30~50 min to form a homogeneous liquid; S3. Constructing a microemulsion: The polar eutectic solvent obtained in step S1 and the non-polar eutectic solvent obtained in step S2 are mixed with a surfactant, wherein the molar ratio of the polar eutectic solvent to the non-polar eutectic solvent is 1:(3~5), and the ratio of the total mass of the surfactant to the total mass of the polar eutectic solvent and the non-polar eutectic solvent is 1:(0.01~0.1); then, the mixture is ultrasonically treated at 30~60℃ and 2000~3000 Hz for 10~20 min to form a stable microemulsion system.

6. The preparation method according to claim 5, characterized in that, In step S1, the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1:(1~4); the hydrogen bond donor is selected from carboxylic acid compounds; and the hydrogen bond acceptor is selected from at least one of choline chloride or metal salts.

7. The preparation method according to claim 5, characterized in that, In step S2, the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1:(1~5); the hydrogen bond donor is selected from at least one of long-chain carboxylic acids, terpenoids, phenols, or long-chain alcohols; and the hydrogen bond acceptor is selected from at least one of quaternary ammonium compounds, terpenoids, ketones, or long-chain organic salts.

8. The application of the recyclable eutectic solvent microemulsion according to any one of claims 1-4 in sludge extraction, characterized in that, Includes the following steps: A. Extraction and oil phase separation: The microemulsion and oily sludge are mixed at a mass ratio of 1:(3~10), and an alkaline solution with a concentration of 1~5 mol / L is added to adjust the pH of the system to 10-12. The mixture is allowed to stand or centrifuged to separate the upper oil phase. B. Microemulsion regeneration: Add acid with a concentration of 2-6 mol / L to the liquid phase remaining after separating the oil phase in step A, adjust the pH of the system to 2-4, and then heat and stir at 70-90℃ until the water content of the system is reduced and a homogeneous and stable microemulsion system is formed again.

9. The application according to claim 8, characterized in that, In step A, the alkaline solution is sodium hydroxide solution or ammonia water; in step B, the acid is hydrochloric acid or sulfuric acid.

10. The application according to claim 8, characterized in that, In step A, the centrifugation speed is 3000-5000 r / min and the time is 15-45 min; or the settling time is 12 h.

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