Use of a co2 / n2-responsive multi-tailed surfactant in soil washing

Abstract

The application relates to application of a CO2 / N2 response type multi-head base intelligent conversion surfactant in soil cleaning, and belongs to the technical field of surfactant science and application. The cleaning process comprises the following steps: mixing a surfactant aqueous solution with contaminated soil at room temperature; then blowing in CO2 until the pH of the water phase is about 6-7; separating an oil layer, blowing in N2 into the water phase, making the pH value reach 9-10, filtering to obtain purified soil, and the liquid phase is a surfactant aqueous solution; in the soil cleaning process, the surfactant shows excellent oil displacement effect, the oil phase residual rate of the soil is reduced to below 0.2%, the surfactant completely enters the water phase, is not left on the surface of the soil, and can be restored to a surface active state by blowing in nitrogen, so that the surfactant is recycled in the water phase, the surfactant solution is reused and recovered, the oil phase recovery rate reaches above 85%, and no surfactant is left in the oil phase; and the application is beneficial to realization of environmental friendly targets such as chemical material reduction and water saving.

Description

Technical Field

[0001] The present invention relates to the application of a CO2 / N2 responsive multi-headed group intelligent conversion surfactant in soil cleaning, belonging to the field of surfactant science and application technology. Background Art

[0002] The increase in oil extraction and commercialization has brought more environmental problems. Improper storage and accidental leakage of oil products have caused large-scale soil and marine pollution. Mineral oil, aromatic hydrocarbons, polycyclic aromatic hydrocarbons, halogenated hydrocarbons, etc. are harmful pollutants commonly found in contaminated soil. Due to the hydrophobic nature of oil products, they are easily absorbed by soil organic matter, forming persistent pollutants in the environment, posing a potential threat to human health directly or indirectly. Therefore, there is an urgent need for a method that can effectively clean soil contaminated by oil phase. The cleaning methods reported in recent years for removing oil pollutants based on surfactant technology usually involve large dosages, high concentrations, limited efficiency, and high soil toxicity due to residual surfactants after remediation. In addition, the discharge of aqueous solutions containing surfactants directly leads to resource waste and environmental pollution.

[0003] Stimuli-responsive surfactants generally possess reversibly convertible amphiphilic structures. Under external stimuli (e.g., pH, redox, CO₂ / N₂, temperature, ion pairs), the surfactant's molecular structure can reversibly switch between "surfactant" and "inactive" states. However, most stimuli-responsive surfactants partially or completely dissolve in the oil phase after inactivation, making them difficult to recycle and reuse. Furthermore, the presence of the surfactants can cause the oil phase to become turbid, affecting its quality and effectiveness. Literature reports that after soil cleaning, by changing the solution temperature and exploiting the Krafft point of the surfactant, the surfactant can be precipitated from the system, allowing for further recovery and reuse. However, this approach can increase energy consumption and require additional steps for surfactant recovery.

[0004] Therefore, there is an urgent need to develop an efficient, environmentally friendly and energy-saving soil cleaning method that can also recycle and reuse oil and surfactants. Summary of the Invention

[0005] Technical issues: Generally, stimulus-responsive surfactants switch between "active" and "inactive" states by regulating hydrophilic groups. However, with this regulation method, surfactants often become insoluble in water after inactivation. Especially in the field of soil cleaning, these inactivated surfactants often dissolve in the oil phase, which not only causes the loss of surfactants, but also makes the aqueous solution containing surfactants difficult to recover and reuse, causing certain environmental pollution problems.

[0006] In order to solve the problems existing in the prior art, the present invention provides a CO2 / N2 responsive smart surfactant RN-(-(CH2) n -COONa)2, a surfactant with strong surface activity and emulsifying ability in its amphiphilic state, can effectively adsorb at the oil-water interface, reducing interfacial tension and promoting the desorption of oil droplets from solid particles. Its usage concentration can be 10-50 times lower than that of conventional surfactants, and the total water consumption does not exceed 200mL / g of soil. After cleaning, carbon dioxide is bubbled in, transforming the surfactant into a "tri-headed" surfactant, increasing its hydrophilicity. It then desorbs from the interface and returns entirely to the aqueous phase, allowing the aqueous phase containing the surfactant to be recycled and reused.

[0007] The present invention aims to provide a CO2 / N2 responsive multi-head surfactant for use in soil cleaning, wherein the cleaning process comprises the following steps:

[0008] S1. The surfactant aqueous solution is mixed with the contaminated soil at room temperature;

[0009] S2. Then, CO2 is introduced until the pH of the aqueous phase is about 6-7;

[0010] S3. After the oil layer is separated, N2 is blown into the aqueous phase containing the soil to bring the pH value to 9-10. The solid phase after filtration is the purified soil, and the liquid phase is recovered to obtain an aqueous surfactant solution;

[0011] The structural formula of the surfactant is:

[0012]

[0013] In the structural formula, R1 is C1~C 12 R2 and R3 are C8~C 18 An alkyl group; X is an alkali metal.

[0014] Furthermore, in step S1, the mixture is stirred at room temperature for 2 to 5 hours to allow the surfactant and the contaminated soil to be fully mixed and react with the oil therein.

[0015] Furthermore, in the structural formula, the alkyl group includes a straight-chain alkyl group, a branched-chain alkyl group, an alkyl group containing an aromatic ring, a saturated or unsaturated alkyl group; and the alkali metal includes but is not limited to sodium and potassium.

[0016] Furthermore, the contaminated soil includes contaminated soil and oily mud sand; the surface of the contaminated soil is negatively charged.

[0017] In some embodiments of the present invention, the contaminated soil has a negative surface charge and a particle size of 3-100 mesh.

[0018] Furthermore, the pollutants in the contaminated soil are contaminated oils, which include a mixture of one or more of alkanes, aromatic hydrocarbons, silicone oils, and ester compounds.

[0019] Furthermore, the aromatic hydrocarbons include polycyclic aromatic hydrocarbons; the polycyclic aromatic hydrocarbons include but are not limited to one or a combination of biphenyl, biphenyls, polyphenylated aliphatic hydrocarbons, and condensed-ring aromatic hydrocarbons.

[0020] In some embodiments of the present invention, the concentration of the surfactant in the mixed solution formed in step S1 is 0.3 to 10 mmol / L;

[0021] In some embodiments of the present invention, the pH value of the mixed solution formed in step S1 is 8-11.

[0022] In some embodiments of the present invention, in step S1, the amount of water used is 1-20 mL / g contaminated soil.

[0023] In some embodiments of the present invention, in step S2, the CO2 introduced is pure CO2 gas or a mixture of CO2 and an inert gas;

[0024] In some embodiments of the present invention, in step S3, the N2 introduced is pure N2 gas or a mixture of N2 and an inert gas;

[0025] Furthermore, the oil content in the contaminated soil is 0.01 to 1 g oil / g soil.

[0026] In one embodiment of the present invention, the contaminated soil cleaning process is as follows: the surfactant aqueous solution and contaminated soil are stirred at room temperature for 2-5 hours, then CO2 is bubbled through the lower aqueous phase until the pH reaches approximately 6.5. After the oil layer is separated, N2 is bubbled through the soil-containing aqueous phase to restore the pH to 9-10. The soil is then filtered to obtain clean soil. The surfactant remains in the aqueous phase and can be reused in the next cleaning process, enabling the recycling of the surfactant-containing aqueous phase.

[0027] In some embodiments of the present invention, negatively charged quartz sand is used to simulate soil, which is soaked in the oil phase and then mixed with the surfactant aqueous solution; the soil is simulated by quartz sand with a mesh size of 3 to 100.

[0028] Furthermore, the CO2 / N2 introduction time in the present invention is based on the actual pH.

[0029] In one embodiment of the present invention, the soil cleaning time is 1 to 3 hours.

[0030] In one embodiment of the present invention, the oil phase comprises a mixture of one or more of liquid paraffin, n-hexadecane, toluene, isopropyl myristate, and dimethicone.

[0031] Another object of the present invention is to apply the above-mentioned CO2 / N2 responsive intelligent conversion surfactant to the fields of oil transportation, emulsion polymerization, nanomaterial synthesis and heterogeneous catalysis.

[0032] Beneficial effects:

[0033] The contaminated soil cleaning method provided by the present invention is simple and easy to operate. It utilizes the CO2 / N2 response characteristics of the surfactant. After the CO2 is injected, the surfactant molecules are transformed into a three-headed, strongly hydrophilic configuration. The surfactant is desorbed from the oily surface and transferred to the water phase. After the oil phase and CO2 are removed, the surfactant can be circulated to clean the oily mud and sand at least five times, achieving the goal of green and sustainable recycling.

[0034] The recovered oil phase of the present invention leaves no surfactant residue and can be recycled as a resource. After deactivation, the surfactant is completely dissolved in water, enabling the recovery and reuse of the surfactant. The oil phase recovery rate in the soil reaches over 85%, and the residual rate is reduced to less than 0.2%.

[0035] The present invention can effectively clean contaminated soil at a relatively low concentration (0.6 mM, ≈ 0.04 cmc), uses less surfactant and water, and has high economic benefits;

[0036] The method provided by the present invention has a wide range of applications and is applicable to soils contaminated by alkanes, aromatic hydrocarbons, silicone oils, ester compounds, polycyclic aromatic hydrocarbons and mixtures thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The accompanying drawings are used to provide a further understanding of the present application and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the present application and do not constitute a limitation of the present application.

[0038] Figure 1 For surfactant RN-(-(CH2) 10 -COONa)2 CO2 / N2 stimulus-response performance diagram;

[0039] Figure 2 Cleaning flow chart for quartz sand simulated soil;

[0040] Figure 3 interfacial tension between the separated oil phase and the circulating water phase in the soil washing cycle;

[0041] Figure 4 Results of using surfactants to clean quartz sand contaminated with different oils (Figure a shows the percentage of recovered aqueous phase after cleaning; Figure b shows the percentage of clean quartz sand obtained after cleaning; Figure c shows the percentage of recovered oil phases; Figure d shows the percentage of residual oil phases in the sand).

[0042] Figure 5 Interfacial tension between the separated other oil phases and pure water during the soil washing cycle;

[0043] Figure 6 The results of using surfactants to clean mud and sand containing philanthropy oil;

[0044] Figure 7 UV spectra of phenanthrene in oil phase, sand and water phase after cleaning (Figure a is the absorbance-PHE concentration annotation curve; Figure b is the UV spectra of the standard sample (0.5g phenanthrene + 15g liquid paraffin) and the contaminated oil recovered after 3 cycles of washing, Figure c is the UV spectrum of the quartz sand surface extract after 3 cycles of washing, and Figure d is the UV spectrum of the surfactant aqueous solution recovered after 3 cycles of washing). DETAILED DESCRIPTION

[0045] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0046] In this embodiment of the present invention, quartz sand is used to simulate soil. Using various oil phases, a surfactant solution is added to the oil-soaked quartz sand. After stirring, CO2 / N2 is bubbled through the system to intelligently switch the surfactant between amphiphilic and highly polar properties, i.e., "active" and "inactive." After cleaning, the upper oil phase is recovered, and the surfactant's dissolution in the oil phase is verified. Simultaneously, the aqueous solution and quartz sand are recovered through simple filtration and centrifugation. The residual oil phase content on the quartz sand surface and the surfactant content in the recovered aqueous phase are measured. The effectiveness of using recycled water to clean the oil-soaked quartz sand is also examined.

[0047] The appearance photos during the cleaning process are taken with a digital camera or mobile phone; the test temperature is controlled at 25℃.

[0048] Example 1: CO2 / N2 Stimulus-Response Performance of Surfactants

[0049] With 0.01mM CH3CH2CH2-N-(-(CH2) 10 -COONa)2 (hereinafter referred to as di-UAPAba and in the accompanying drawings) was taken as an example to study its CO2 / N2 stimulus-response performance.

[0050] Figure 1 (a) shows the preparation of 4 mL of 0.01 mM CH3CH2CH2-N-(-(CH2) 10-COONa)2 aqueous solution (pH = 10.50), and then alternately introduce CO2 (0.5mL / min, 3.5min) and N2 (25mL / min, 30min) into the solution, measure the change of pH value, and repeat the cycle 6 times.

[0051] Figure 1 (b) shows the preparation of different concentrations of CH3CH2CH2-N-(-(CH2) 10 The time required for the pH to reach the desired value (6.4) was calculated by bubbling CO2 (0.5 mL / min) into a 4 mL solution of 1-COONa).

[0052] Example 2 Cleaning of Negatively Charged Soil (Quartz Sand) with Surfactant Aqueous Solution

[0053] The experimental process is as follows Figure 2 As shown, 3-10 mesh quartz sand was selected to simulate soil. 30 g of quartz sand was weighed into a 100 mL beaker, and 15 g of liquid paraffin was added. The mixture was stirred evenly and allowed to stand for at least 2 hours to ensure that the oil phase completely soaked the quartz sand. 70 mL of a 0.6 mM surfactant aqueous solution (pH = 9) was added to the beaker containing the oil phase and quartz sand. A magnetic rod was added and the mixture was stirred for 2 hours. The mixture was then allowed to stand for 2-5 hours. CO₂ was introduced to reduce the solution pH to 6-7. The oil phase was then removed, and the presence of residual surfactant was determined by measuring the interfacial tension between the oil phase and pure water. N₂ was then introduced and the CO₂ removed to restore the solution pH to approximately 9-10. The quartz sand and the aqueous phase containing the surfactant were separated by filtration and centrifugation. The aqueous phase was collected and the surfactant aqueous solution was added to 70 mL. This was then added to the quartz sand soaked in the oil phase for cleaning. This step could be repeated at least five times.

[0054] The residual rate of oil phase in quartz sand, water phase recovery rate, oil phase recovery rate and quartz sand recovery rate are shown in Table 1.

[0055] Table 1 Recovery rates of water phase, oil phase, quartz sand and residual oil phase during the cycle

[0056]

[0057] Detection of residual surfactant in oil phase: Collect the oil phase separated in each cycle and measure the interfacial tension between it and ultrapure water. The test results are as follows: Figure 3 Over the five cycles, the interfacial tension between the separated oil phase and pure water was nearly identical to the standard value (50.2 mN / m) (i.e., the interfacial tension between the fresh oil phase and pure water). The interfacial tension between the recovered water phase and the pure oil phase also matched the initial value, with an error of no more than ±1.0 mN / m. This indicates that the surfactant was almost completely recovered after each cycle.

[0058] Example 3: Surfactants are used in the recycling and cleaning of sand containing other oils

[0059] Select 8-16 mesh quartz sand, replace the oil phase with n-hexadecane, toluene and dimethyl silicone oil respectively, and refer to Example 2 for the cleaning process. The cleaning results are as follows: Figure 4 For low viscosity oils (such as n-hexadecane and toluene), the residual oil phase in the sand was reduced to an average of 0.012±0.005g in three cycles of cleaning, equivalent to a residual rate of 0.08±0.03% ( Figure 4 d). At the same time, the recovery rate of quartz sand reaches more than 98% ( Figure 4 b), the recovery rate of contaminated oil phase reached 87.4±1.0% ( Figure 4 c), and the recovery rate of di-UAPAba aqueous solution each time reached 90.6±0.5% ( Figure 4 a) can be recycled. For dimethyl silicone oil with high viscosity and density, the residual amount after cleaning is only 0.10±0.02g, equivalent to a residual rate of 0.67±0.11%, and the silicone oil recovery rate can reach 77.9±0.5%.

[0060] like Figure 5 As shown in the figure, in the five cycles, the interfacial tension between the separated oil phase (n-hexadecane, toluene and dimethyl silicone oil) and pure water is almost consistent with the standard value, which means that the surfactant can be almost completely recovered after each cycle, that is, there is almost no surfactant in the oil phase.

[0061] Example 4: Use of surfactants to clean quartz sand containing phenanthrene mixed oil

[0062] 0.5 g of phenanthrene (PHE) was dispersed in 15 g of paraffin oil as a simulated contaminated oil and used to infiltrate quartz sand (3-10 mesh) to prepare simulated contaminated soil. The cleaning process was referred to Example 2. After the cleaning, the recovery rates of the contaminated oil, surfactant aqueous phase, and quartz sand were as follows: Figure 6 As shown in Figure 2, about 89.0% of the simulated contaminated oil was recovered. Since phenanthrene has a strong absorption peak at a wavelength of about 290-295nm ( Figure 7 (b), based on which the absorbance-phenanthrene concentration standard curve can be obtained ( Figure 7 a), the UV absorbance of phenanthrene in the recovered oil phase after cleaning is slightly lower than that of the original contaminated oil standard sample ( Figure 7 b, cycle 1), according to the standard curve calculation, it can be calculated that 93.9% of PHE is recovered along with the paraffin oil. The absorbance of the recovered quartz sand extract and di-UAPAba solution was detected respectively, and the results are as follows Figure 7As shown in (b, c), the surface extract of the cleaned quartz sand has a small absorption peak at a wavelength of 280-300 nm, indicating that a small amount of PHE remains on the sand surface. However, in the recovered surfactant solution, almost no UV absorption peak was detected.

[0063] The contaminated soil cleaning method provided by the present invention uses a surfactant with intelligent conversion that responds to CO2 / N2, which can effectively clean oil sludge and sand at a relatively low concentration (0.6mM, ≈0.04cmc). The amount of surfactant used is small, and the oil pollution in the soil can be efficiently removed. After a small amount of CO2 is injected, the surfactant molecules are transformed into a three-headed group with a strong hydrophilic configuration. The surfactant is desorbed from the surface of the oil pollution and transferred to the water phase. After removing the oil phase and CO2, the surfactant solution can be recycled and reused, and the oil sludge and sand can be circulated for at least 5 times, achieving the goal of green sustainable recycling. The method has a wide range of applications, and the contaminated oils include alkanes, aromatic hydrocarbons, silicone oils, ester compounds, and mixtures formed therefrom, and the above-mentioned oil phases containing polycyclic aromatic hydrocarbons. The oil phase recovery rate can reach more than 85%, the residual rate is reduced to less than 0.2%, and the water phase recovery rate is more than 90%.

[0064] While the specific embodiments of the present invention have been described in detail above, these are merely exemplary and the present invention is not limited thereto. It will be apparent to those skilled in the art that any equivalent modifications and substitutions to the present invention fall within the scope of the present invention. Therefore, any equivalent changes and modifications made without departing from the spirit and scope of the present invention are encompassed within the scope of the present invention.

Claims

1. Application of a CO2 / N2 responsive multi-head surfactant in soil cleaning, characterized in that: The cleaning process includes the following steps: S1. The surfactant aqueous solution is mixed with the contaminated soil at room temperature; S2. Then, CO2 is introduced until the pH of the aqueous phase is 6-7; S3. After the oil layer is separated, N2 is blown into the aqueous phase containing the soil to bring the pH value to 9-10. The solid phase after filtration is the purified soil, and the liquid phase is recovered to obtain an aqueous surfactant solution; The structural formula of the surfactant is: Where R1 is C1~C 12 R2 and R3 are C8~C 18 An alkyl group; X is an alkali metal.

2. The use of the CO2 / N2 responsive multi-head surfactant in soil cleaning according to claim 1, characterized in that: The alkyl group includes a straight-chain alkyl group, a branched-chain alkyl group, an alkyl group containing an aromatic ring, and a saturated or unsaturated alkyl group; And / or, the alkali metal includes sodium and potassium.

3. The use of the CO2 / N2 responsive multi-head surfactant in soil cleaning according to claim 1, characterized in that: The contaminated soil includes contaminated soil and oil sludge sand; And / or, the surface of the contaminated soil is negatively charged.

4. The use of the CO2 / N2 responsive multi-head surfactant in soil cleaning according to claim 1, characterized in that: The contaminated oil content in the contaminated soil is 0.01-1 g / g soil.

5. The use of the CO2 / N2 responsive multi-head surfactant in soil cleaning according to claim 1, characterized in that: The contaminated oil includes a mixture of one or more of alkanes, aromatic hydrocarbons, silicone oils, and ester compounds.

6. The use of the CO2 / N2 responsive multi-head surfactant in soil cleaning according to claim 5, characterized in that: The aromatic hydrocarbons include polycyclic aromatic hydrocarbons; The polycyclic aromatic hydrocarbons include one or a combination of biphenyl, bipolyphenyls, polyphenylated aliphatic hydrocarbons, and condensed ring aromatic hydrocarbons.

7. The use of the CO2 / N2 responsive multi-head surfactant in soil cleaning according to claim 1, characterized in that: In step S1, the mixture is stirred at room temperature for 2 to 5 hours.

8. The use of the CO2 / N2 responsive multi-head surfactant in soil cleaning according to claim 1, characterized in that: The surfactant concentration in the mixed solution formed in step S1 is 0.3-10 mmol / L; And / or, the pH value of the mixed solution formed in step S1 is 8-11.

9. The use of the CO2 / N2 responsive multi-head surfactant in soil cleaning according to claim 1, characterized in that: In step S1, the amount of water used is 1-20 mL / g of contaminated soil.

10. The use of the CO2 / N2 responsive multi-head surfactant in soil cleaning according to claim 1, characterized in that: In step S2, the CO2 introduced is pure CO2 gas or a mixture of CO2 and inert gas; And / or, in step S3, the N2 introduced is pure N2 gas or a mixture of N2 and an inert gas.

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