Application of CO2 / N2-responsive Bola surfactant in soil remediation

Abstract

The application discloses a new method for cleaning positively charged soil by using a CO2 / N2-responsive intelligent Bola surfactant, and belongs to the technical field of surfactant science and application. The cleaning process comprises the following steps: after a surfactant aqueous solution is mixed with contaminated soil and CO2 is introduced to react, an oil layer is separated, then solid-liquid separation is performed, N2 is introduced to react in the obtained water phase, and a recyclable surfactant aqueous solution is obtained. In the application, by introducing CO2 / N2, the tertiary amine group in the structure of the surfactant is intelligently converted between 'non-polar' and'strong polarity', namely 'active' and 'inactive'. The method can reduce the oil phase residual rate of the soil to below 0.3%, the deactivated surfactant completely enters the water phase, the quality of the oil phase is not affected, and the amount of the surfactant is small. The method realizes the recycling and recovery of the surfactant solution, and is conducive to achieving the environmental-friendly goals of chemical material reduction and water saving.

Description

Technical Field

[0001] The present invention relates to the preparation of a CO2 / N2 responsive intelligent Bola surfactant pair and its application in soil cleaning, belonging to the field of surfactant science and application technology. Background Art

[0002] The over-exploitation, improper storage and leakage of petroleum resources have posed a major challenge to global soil pollution and have profoundly affected ecological security. Among them, organic pollutants such as mineral oil, aromatic hydrocarbons, polycyclic aromatic hydrocarbons and halogenated hydrocarbons are particularly common. Their difficult-to-degrade properties and long-term environmental retention have not only exacerbated the global ecological crisis, but also directly or indirectly posed a potential threat to human health. Therefore, there is an urgent need for an efficient cleaning technology that can cope with soil contaminated by different types of oil phases. Using surfactants to improve soil cleaning efficiency is one of the more commonly used soil remediation technologies, but it usually involves high surfactant concentrations, large amounts, and secondary soil pollution caused by surfactant adsorption after cleaning. In addition, conventional surfactants usually form an emulsion with the oil phase after cleaning, which not only has the problem of difficult demulsification, but also due to their amphiphilicity, some surfactants will enter the oil phase, resulting in the inability to fully recover the surfactants. They can only be used once, and direct discharge causes waste of resources and environmental pollution.

[0003] Stimuli-responsive surfactants can reversibly switch between "surface-active" and "inactive" states in response to external stimuli. Reported stimulus responses include pH, redox, CO2 / N2, temperature, magnetic fields, and light. This effectively addresses the difficulty in breaking emulsions formed after soil cleaning. However, most stimuli-responsive surfactants, upon deactivation, transform into hydrophobic structures, partially or completely migrating to the oil phase. This increases the difficulty of oil purification and prevents complete recovery of the surfactant molecules. Surfactant recovery and reusability are crucial in soil cleaning.

[0004] Therefore, there is an urgent need to develop an efficient, green and sustainable 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" by regulating hydrophilic groups. The main regulation method is to convert hydrophilic groups (polar groups) into non-polar or weakly polar groups (hydrophobic groups). Therefore, after deactivation, surfactants often become insoluble in water and partially or completely transfer to the oil phase. Especially in the field of soil cleaning, these inactivated surfactants not only increase the difficulty of oil phase purification, but also make the aqueous solution of surfactants unable to be recycled and reused. Direct discharge not only wastes resources, but also increases the burden of environmental pollution.

[0006] In order to solve the problems existing in the prior art, the present invention provides a CO2 / N2-responsive Bola-type surfactant for use in soil cleaning. This surfactant has surface activity when in an amphiphilic state, can be adsorbed at the oil-water interface and reduce interfacial tension. It promotes the desorption of oil droplets from solid particles. The concentration used can be 10-50 times lower than that of conventional surfactants, and the total water consumption does not exceed 200mL / g soil. After the cleaning is completed, a small amount of CO2 is introduced, and the surfactant is converted to a Bola configuration, with significantly improved hydrophilicity. It desorbs from the interface, and the surfactant molecules are completely returned to the water phase. N2 is then introduced, allowing the water phase containing the surfactant to be recycled and reused.

[0007] The present invention aims to provide a CO2 / N2 responsive Bola 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 4-6;

[0010] S3. After the oil layer is separated, the aqueous phase containing the soil is separated into solid and liquid. The solid phase is washed and dried to obtain the purified soil. The aqueous phase obtained is an aqueous solution containing a surfactant. N2 is introduced to adjust the pH to 9 to 10 to obtain a recyclable aqueous surfactant solution.

[0011] The structural formula of the surfactant is:

[0012] In the structural formula, R1 and R2 are C1~C4 alkyl groups; R3 is C8~C 18 An alkyl group; X is an alkali metal.

[0013] 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.

[0014] 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.

[0015] Furthermore, the contaminated soil includes contaminated soil and oily mud sand; the surface of the contaminated soil is positively charged.

[0016] In some embodiments of the present invention, the contaminated soil has a positive charge on its surface and a particle size of 2-100 mesh.

[0017] 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.

[0018] 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.

[0019] In some embodiments of the present invention, the concentration of the surfactant in the mixed solution formed in step S1 is 1.0 to 10 mmol / L;

[0020] In some embodiments of the present invention, the pH value of the mixed solution formed in step S1 is 8-11.

[0021] In some embodiments of the present invention, in step S1, the amount of water used is 1-20 mL / g contaminated soil.

[0022] 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;

[0023] 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;

[0024] Furthermore, the oil content in the contaminated soil is 0.01 to 1 g oil / g soil.

[0025] 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 in until the pH of the lower aqueous phase reaches 4-5. After the oil layer is separated, the soil-containing aqueous phase is subjected to solid-liquid separation, and the resulting solid phase is washed and dried to obtain purified soil. The resulting aqueous phase is the surfactant-containing aqueous solution, and N2 is bubbled into the aqueous solution to restore the pH to 9-10. The surfactant aqueous solution can then be used in the next cleaning process, achieving the recycling of the surfactant-containing aqueous phase. This also allows the oil phase to be recovered and reused.

[0026] In some embodiments of the present invention, positively charged calcite 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 calcite with a mesh size of 3 to 100 meshes.

[0027] Furthermore, the CO2 / N2 introduction time in the present invention is based on the actual pH.

[0028] In one embodiment of the present invention, the soil cleaning time is 1 to 3 hours.

[0029] 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.

[0030] 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.

[0031] Beneficial effects:

[0032] 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 Bola-type 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 three times, achieving the goal of green and sustainable recycling.

[0033] 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 0.3%.

[0034] The present invention can effectively clean contaminated soil at a relatively low concentration (1.0 mM, ≈ 0.06 cmc), uses less surfactant and water, and has high economic benefits;

[0035] 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

[0036] 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.

[0037] Figure 1 2 is a CO2 / N2 stimulus-response performance diagram of the surfactant of Example 1;

[0038] Figure 2 Flow chart for cleaning simulated soil for calcite;

[0039] Figure 3 Interfacial tension between the separated oil phase and the circulating water phase in the soil cleaning cycle in Example 2;

[0040] Figure 4Results of using surfactants to clean calcite contaminated with different oils (Figure a shows the percentage of recovered water after cleaning; Figure b shows the percentage of clean calcite obtained after cleaning; Figure c shows the percentage of recovered oil phases; Figure d shows the percentage of oil phases remaining in the sand).

[0041] Figure 5 Interfacial tension between the separation of other oil phases and pure water during the soil cleaning cycle in Example 3;

[0042] Figure 6 HPLC chromatography of phenanthrene in oil phase and sand after cleaning (Figure a is the absorbance-PHE concentration standard curve; Figure b is the HPLC of the standard sample (0.5g phenanthrene + 15g liquid paraffin); Figure c is the HPLC of the contaminated oil recovered after three cycles of washing; Figure d is the HPLC of the calcite surface extract after three cycles of washing). DETAILED DESCRIPTION

[0043] 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.

[0044] In the present embodiment, calcite was used to simulate soil. Using various oil phases, a surfactant solution was added to the oil-soaked calcite. After stirring, CO2 / N2 was 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 was recovered, and the surfactant's dissolution in the oil phase was verified. Simultaneously, the aqueous solution and calcite were recovered through simple filtration and centrifugation. The residual oil content on the calcite surface and the surfactant content in the recovered aqueous phase were measured. The effectiveness of using recycled water to clean the oil-soaked calcite was also examined.

[0045] The appearance photos during the cleaning process are taken with a digital camera or mobile phone; the test temperature is controlled at 25℃.

[0046] Example 1: CO2 / N2 Stimulus-Response Performance of Surfactants

[0047] With 0.6mM (CH3)2N-(CH2) 10 -COONa (hereinafter referred to as DUMa in the accompanying drawings) was used as an example to study its CO2 / N2 stimulus-response performance.

[0048] In a 25 mL glass bottle, 10 mL of 0.6 mM DUMa aqueous solution (pH = 9.50) was prepared. CO2 (25 mL / min, 30 min) and N2 (50 mL / min, 50 min) were then alternately introduced into the solution. The pH change was measured and the cycle was repeated 6 times. Figure 1 Shown.

[0049] Example 2 Cleaning of Positively Charged Soil (Calcite) with an Aqueous Surfactant Solution

[0050] The experimental process is as follows Figure 2 As shown, a 2-10 mesh calcite simulated soil was selected. 30 g of calcite 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 calcite. 70 mL of a 1.0 mM surfactant (DUMa) aqueous solution (pH = 9.5) was added to the beaker containing the oil phase and calcite. A magnetic rod was added and stirred for 2 hours. The mixture was then allowed to stand for 2-5 hours. CO₂ was then introduced to bring the solution pH to 4-6. 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. The calcite and surfactant-containing aqueous phase were separated by filtration and centrifugation. N₂ was then bubbled through the aqueous phase to remove the CO₂, restoring the solution pH to approximately 9-10. The aqueous phase was then collected and the surfactant aqueous solution was added to 70 mL. This was then added to the calcite soaked in the oil phase for cleaning. This step could be repeated three or more times.

[0051] The oil phase residual rate in calcite, water phase recovery rate, oil phase recovery rate and calcite recovery rate are shown in Table 1.

[0052] Table 1 Recovery rates of water phase, oil phase, calcite and residual oil phase during the cycle

[0053]

[0054] 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 As shown in the figure, the interfacial tension between the separated oil phase and pure water during the three cycles was almost identical to the standard value (i.e., the interfacial tension between the fresh oil phase and pure water) (50.2 mN / m). The interfacial tension between the recovered water phase and the pure oil phase was essentially identical to 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.

[0055] Example 3: Surfactants are used in the recycling and cleaning of sand containing other oils

[0056] Select 10-20 mesh calcite, the oil phase is paraffin oil, toluene and dimethyl silicone oil, the cleaning process refers to Example 2. The cleaning results are as follows Figure 4 For low viscosity oils (such as paraffin oil and toluene), the residual oil phase in the sand was reduced to an average of 0.015±0.008g in three cycles of cleaning, equivalent to a residual rate of 0.10±0.05% ( Figure 4 d). At the same time, the recovery rate of calcite reached more than 98.0±1.0% ( Figure 4 b), the recovery rate of contaminated oil phase reached 88.1±0.6% ( Figure 4 c), and the recovery rate of DUMa aqueous solution each time reached 90.6±0.6% ( Figure 4 a) can be recycled. For dimethyl silicone oil with high viscosity and density, the residual amount after cleaning is only 0.11±0.09g, equivalent to a residual rate of 0.71±0.06%, and the silicone oil recovery rate can reach 78.5±0.4%.

[0057] like Figure 5 As shown in the figure, in the three cycles, the interfacial tension between the separated oil phase (paraffin oil, 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.

[0058] Example 4: Use of surfactants to clean calcite soil containing phenanthrene mixed oil

[0059] 0.5 g of phenanthrene (PHE) was dispersed in paraffin oil (15 g) as a simulated contaminated oil and used to infiltrate calcite sand (2-10 mesh) to prepare simulated contaminated soil. The cleaning process was referred to Example 2. The recovery rates of contaminated oil, surfactant aqueous phase, and calcite sand after cleaning are shown in Table 2 and Figure 6 The PHE content in the recovered oil and calcite was determined by HPLC, as shown in Figure 6 shown. Figure 6 (a, b) are the HPLC chromatograms of the standard sample, the recovered oil after washing, and the calcite surface extract, and the corresponding calibration curves, respectively. The PHE recovery rate was calculated based on these curves (Table 2). Approximately 88.0% of the simulated mixed contaminated oil was recovered, and over 93.0% of the PHE was recovered along with the paraffin oil. The residual PHE in the washed sand ranged from 2.9% to 5.8%.

[0060] Table 2 DUMa remediation results on calcite soil (2-10 mesh) containing mixed oil (PHE / paraffin oil)

[0061]

[0062] The contaminated soil cleaning method provided by the present invention uses a CO2 / N2-responsive Bola-type surfactant, which can effectively clean positively charged oily sludge and sand at a relatively low concentration (1.0mM, ≈0.06cmc). The surfactant dosage is small, and the oily soil can be efficiently removed. After a small amount of CO2 is introduced, the surfactant molecules are transformed into a Bola-type strongly hydrophilic configuration, and the surfactant is desorbed from the oily surface and transferred to the aqueous phase. After removing the oil phase and CO2, the surfactant solution can be recycled and reused, and the oily sludge and sand can be recycled and cleaned at least three times, achieving the goal of green and sustainable recycling. The method has a wide range of applications, and the contaminated oils include alkanes, aromatic hydrocarbons, silicone oils, ester compounds, and mixtures thereof, as well as the above-mentioned oil phases containing polycyclic aromatic hydrocarbons. The oil phase recovery rate can reach over 85%, the residual rate is reduced to below 0.3%, and the aqueous phase recovery rate is over 90%. The surfactant in the present invention, by introducing CO2 / N2, intelligently switches the tertiary amine groups in the surfactant structure between "non-polar" and "strongly polar," that is, "active" and "inactive." After deactivation, the surfactant completely enters the water phase without affecting the quality of the oil phase. This enables the reuse and recycling of the surfactant solution, contributing to environmentally friendly goals such as reducing chemical emissions and saving water.

[0063] 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 Bola-type 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 4-6; S3. After the oil layer is separated, the aqueous phase containing the soil is separated into solid and liquid, and the solid phase is washed and dried to obtain the purified soil; the aqueous phase obtained is an aqueous solution containing a surfactant, and N2 is introduced to bring the pH value to 9~10 to obtain a recyclable aqueous surfactant solution; The structural formula of the surfactant is: ; Wherein R1 and R2 are C1~C4 alkyl groups; R3 is C8~C 18 An alkyl group; X is an alkali metal; The contaminated soil includes contaminated soil and oily mud sand; the surface of the contaminated soil is positively charged; The contaminated oil content in the contaminated soil is 0.01-1 g / g soil.

2. The use of the CO2 / N2 responsive Bola-type 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 Bola-type 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.

4. The use of the CO2 / N2 responsive Bola-type surfactant in soil cleaning according to claim 3, 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.

5. The use of the CO2 / N2 responsive Bola-type 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.

6. The use of the CO2 / N2 responsive Bola-type surfactant in soil cleaning according to claim 1, characterized in that: The surfactant concentration in the mixed solution formed in step S1 is 1.0-10 mmol / L.

7. The use of the CO2 / N2 responsive Bola-type surfactant in soil cleaning according to claim 1, characterized in that: The pH value of the mixed solution formed in step S1 is 8-11.

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

9. The use of the CO2 / N2 responsive Bola-type 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.

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

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