Application of CO2 / N2 response type multi-head-based surfactant in soil washing

Abstract

The invention relates to application of a CO2 / N2 response type multi-head 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 the polluted soil at room temperature; blowing CO2 until the pH value of the water phase is about 6-7; after an oil layer is separated, N2 is blown into a water phase, the pH value is made to be 9-10, purified soil is obtained after filtering, and the liquid phase is a surfactant water solution; in the soil cleaning process, the surfactant shows an excellent oil displacement effect, the soil oil phase residual rate is reduced to 0.2% or below, and the surfactant completely enters a water phase, does not remain on the soil surface, and can be recovered to a surface active state by introducing nitrogen, so that the surfactant is recycled in the water phase, and the oil displacement efficiency is improved. The repeated utilization and recovery of the surfactant solution are realized; the recovery rate of an oil phase reaches 85% or above, and no surfactant is left in the oil phase; and the environment-friendly targets of emission reduction, water saving and the like of chemical materials can be realized.

Description

Technical Field

[0001] The invention relates to 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 and form 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 problems such as large dosage, high concentration, limited efficiency, and high soil toxicity due to surfactant residues after remediation. In addition, the discharge of aqueous solutions containing surfactants directly leads to resource waste and environmental pollution.

[0003] Stimuli-responsive surfactants generally have a reversibly convertible amphiphilic structure. Under external stimuli (pH, redox, CO2 / N2, temperature, ion pairs, etc.), the surfactant molecular structure can be reversibly converted between "surface active" and "non-surface active". However, most stimuli-responsive surfactants partially or completely dissolve in the oil phase after inactivation, making them difficult to recycle and reuse. The presence of surfactants makes the oil phase turbid and affects the quality and use effect of the oil phase. There are literature reports that after cleaning the soil, by changing the solution temperature, the Krafft point of the surfactant is used to precipitate the surfactant from the system, and then the surfactant is recovered and reused. However, this method may not only increase energy consumption, but also increase the steps of surfactant recovery.

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

[0005] Technical issues: Generally, stimulus-responsive surfactants switch between "active" and "inactive" states by regulating the hydrophilic groups. However, with this regulation method, surfactants often become insoluble in water after being inactivated. Especially in the field of soil cleaning, these inactivated surfactants are often dissolved in the oil phase, which not only causes the loss of surfactants, but also makes the aqueous solutions 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 intelligent surfactant RN-(-(CH2) n -COONa)2, this surfactant has strong surface activity and emulsification ability when in an amphiphilic state, can effectively adsorb on the oil-water interface to reduce interfacial tension, and promote 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, carbon dioxide is blown in, and the surfactant is transformed into a "three-headed" type surfactant, the hydrophilicity is enhanced, and it is desorbed from the interface, and the surfactant is completely returned to the water phase. The water phase containing the surfactant can be recycled and reused.

[0007] The first object of the present invention is to provide an application of a CO2 / N2 responsive multi-head surfactant in soil cleaning, the cleaning process comprising the steps of:

[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 water phase containing the soil to adjust 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 fully mix the surfactant and the contaminated soil 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, and a saturated or unsaturated alkyl group; the alkali metal includes but is not limited to sodium and potassium.

[0016] Furthermore, the contaminated soil includes contaminated soil and oil 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 charge on its surface 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 the contaminated soil are stirred at room temperature for 2 to 5 hours, and then CO2 is bubbled in until the pH of the lower aqueous phase is about 6.5, and after the oil layer is separated, N2 is bubbled into the aqueous phase containing the soil to restore the pH value to 9 to 10, and clean soil is obtained after filtration. The surfactant remains in the aqueous phase and can continue to be used in the next cleaning process, realizing the recycling of the aqueous phase containing the surfactant.

[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 meshes.

[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 includes 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 base with a strong 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 for at least 5 times, thus achieving the goal of green and sustainable circulation.

[0034] The surfactant in the oil phase recovered by the present invention has no residue and can be used as a resource. The surfactant is completely dissolved in water after being inactivated, thus realizing the recovery and reuse of the surfactant; the oil phase recovery rate in the soil reaches more than 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), with a small amount of surfactant and water used, and 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 to the present application.

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

[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 The results of using surfactants to clean quartz sand contaminated with different oils (Figure a is the percentage of the total amount of water recovered after cleaning, Figure b is the percentage of clean quartz sand obtained after cleaning; Figure c is the percentage of different oil phases recovered; Figure d is the percentage of different oil phases remaining 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 phenanthrene 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 technical solutions in the embodiments of the present invention are described clearly and completely below. 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 creative work are within the scope of protection of the present invention.

[0046] In the embodiment of the present invention, quartz sand is used to simulate soil, and a variety of different oil phases are used. A surfactant solution is added to the quartz sand pre-infiltrated with the oil phase, and after stirring, the surfactant is intelligently switched between amphiphilicity and strong polarity, that is, "active" and "inactive" by bubbling CO2 / N2. After cleaning, the upper oil phase is recovered, and it is verified whether the surfactant is dissolved in the oil phase. At the same time, the aqueous solution and quartz sand are recovered by simple filtration and centrifugation, the residual oil phase content on the surface of the quartz sand and the surfactant content in the recovered water phase are detected, and the cleaning effect of the quartz sand infiltrated with the oil phase with the circulating water phase is 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 attached drawings) was taken as an example to study its CO2 / N2 stimulation-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), then CO2 (0.5mL / min, 3.5min) and N2 (25mL / min, 30min) were alternately introduced into the solution, the change in pH value was measured, and the cycle was repeated 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 passing CO2 (0.5 mL / min) into a 4 mL (4 mL) COONa)2 solution.

[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. 30g of quartz sand was weighed into a 100mL beaker, 15g of liquid paraffin was added, stirred evenly and allowed to stand for more than 2h to ensure that the oil phase completely infiltrated the quartz sand. 70mL of 0.6mM surfactant aqueous solution (pH=9) was added to the beaker containing the oil phase and quartz sand, a magnet was added and stirred for 2h, and then allowed to stand for 2-5h, CO2 was introduced to make the solution pH=6-7, at which time the oil phase was removed and the interfacial tension between the oil phase and pure water was measured to detect whether there was any surfactant residue. N2 was then introduced and CO2 was removed to restore the solution pH to about 9-10, and 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 supplemented to 70mL, and added to the quartz sand infiltrated in the oil phase for cleaning, and the above steps were repeated for more than 5 cycles.

[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 rate of water phase, oil phase, quartz sand and residual rate of oil phase during the circulation process

[0056]

[0057] Detection of residual surfactant in the 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 In the five cycles, the interfacial tension between the separated oil phase and pure water is almost consistent with the standard value (i.e., the interfacial tension between the fresh oil phase and pure water) (50.2 mN / m), and the interfacial tension between the recovered water phase and the pure oil phase is basically consistent with the initial value, with an error of no more than ±1.0 mN / m, which means that the surfactant can be almost completely recovered after each cycle.

[0058] Example 3: Surfactant used in the recycling and cleaning of sand containing other oil pollution

[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±0.005 g 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 the 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 used for recycling. For dimethyl silicone oil with high viscosity and density, the residual amount after cleaning is only 0.10±0.02g, which is 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 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: Surfactant used for cleaning quartz sand containing phenanthrene mixed oil

[0062] 0.5 g of phenanthrene (PHE) was dispersed in paraffin oil (15 g) as 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 contaminated oil, surfactant aqueous phase and quartz sand were as follows: Figure 6 As shown. 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, 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 7(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 surface of the sand, but in the recovered surfactant solution, almost no ultraviolet absorption peak is detected.

[0063] The contaminated soil cleaning method provided by the present invention uses a surfactant with intelligent conversion in response to CO2 / N2, which can effectively clean oily mud 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, and 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 oily mud and sand can be circulated for cleaning at least 5 times, achieving the goal of green sustainable circulation. The method has a wide range of applications, and the contaminated oil includes 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] The specific embodiments of the present invention are described in detail above, but they are only examples, and the present invention is not limited to the specific embodiments described above. For those skilled in the art, any equivalent modifications and substitutions made to the present invention are also within the scope of the present invention. Therefore, the equalization changes and modifications made without departing from the spirit and scope of the present invention are all 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 about 6-7; S3. After the oil layer is separated, N2 is blown into the water phase containing the soil to adjust 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 but is not limited to 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 contaminated soil surface 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 content of contaminated oil 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, but are not limited to, one or a combination of biphenyl, biphenyls, 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 mixed and 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 required 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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