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

Abstract

The invention discloses a novel method for cleaning positively charged soil by using a CO2 / N2 response intelligent Bola surfactant, 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, and blowing CO2 for reaction; after an oil layer is separated, solid-liquid separation is carried out, N2 is blown into a water phase obtained through separation for a reaction, and a recyclable surfactant water solution is obtained. According to the surfactant disclosed by the invention, CO2 / N2 is introduced, so that a tertiary amine group in the structure of the surfactant is intelligently converted between'non-polarity 'and'strong polarity', namely'active 'and'inactive'. By means of the method, the soil oil phase residual rate can be reduced to 0.3% or below, the surfactant completely enters the water phase after being inactivated, the quality of the oil phase is not affected, and the using amount of the surfactant is small. Reutilization and recovery of the surfactant solution are achieved, and the environment-friendly targets of emission reduction, water saving and the like of chemical materials are achieved.

Description

Technical Field

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

[0002] Over-exploitation, improper storage and leakage of petroleum resources have become a major challenge of global soil pollution, profoundly affecting ecological security. Among them, organic pollutants such as mineral oil, aromatics, polycyclic aromatic hydrocarbons and halogenated hydrocarbons are particularly common. Their difficult-to-degrade characteristics 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 problems such as high surfactant concentration, large dosage, 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 completely recover the surfactants. They can only be used once, and direct discharge causes waste of resources and environmental pollution.

[0003] Stimulus-responsive surfactants can reversibly switch between "surface active" and "non-surface active" according to external stimuli. The stimulus response modes reported so far include: pH, redox, CO2 / N2, temperature, magnetic field, light, etc. This effectively solves the problem of difficult emulsion demulsification formed after soil cleaning. However, most stimulus-responsive surfactants are "inactivated" and transformed into hydrophobic structures, which are partially or completely transferred to the oil phase, which increases the difficulty of oil purification and makes it impossible to completely recover the surfactant molecules. The recovery and reusability of surfactants are of great significance 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 the hydrophilic group. The main regulation method is to convert the hydrophilic group (polar group) into a non-polar or weakly polar group (hydrophobic group). Therefore, after deactivation, the surfactant often becomes insoluble in water and partially or completely transferred 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 the surfactant unable to be recovered 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, and 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 into a Bola configuration, the hydrophilicity is significantly improved, and it is desorbed from the interface. The surfactant molecules are completely returned to the water phase, and then N2 is introduced, so that 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 Bola surfactant 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 water phase containing the soil is separated into solid and liquid, and the obtained solid phase is washed and dried to obtain the purified soil; the obtained water phase is an aqueous solution containing a surfactant, and N2 is blown into it to adjust the pH value to 9 to 10, so that a recyclable aqueous surfactant solution can be obtained;

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

[0015] Furthermore, the contaminated soil includes contaminated soil and oil 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 the 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 the contaminated soil are stirred at room temperature for 2 to 5 hours, and then CO2 is blown in until the pH of the lower aqueous phase is 4 to 5. After the oil layer is separated, the aqueous phase containing the soil is subjected to solid-liquid separation, and the obtained solid phase is washed and dried to obtain the purified soil; the obtained aqueous phase is the aqueous solution containing the surfactant, and N2 is blown into the aqueous solution to restore the pH value to 9 to 10; the surfactant aqueous solution can be continuously used in the next cleaning process, realizing the recycling of the aqueous phase containing the surfactant. At the same time, the oil phase is also recycled.

[0026] In some embodiments of the present invention, positively charged calcite is used to simulate soil, which is mixed with a surfactant aqueous solution after being soaked in an oil phase; 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 includes 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, thus achieving the goal of green and sustainable circulation.

[0033] 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 is more than 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), with a small amount of surfactant and water used, and 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 on the present application.

[0037] Figure 1 is a CO2 / N2 stimulation-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 4The results of using surfactants to clean calcite 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 calcite 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);

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

[0042] Figure 6 HPLC 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 3 cycles of washing; Figure d is the HPLC of the calcite surface extract after 3 cycles of washing). DETAILED DESCRIPTION

[0043] 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.

[0044] In the embodiment of the present invention, calcite is used to simulate soil, and a variety of different oil phases are used. A surfactant solution is added to the calcite 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 calcite are recovered by simple filtration and centrifugation, the residual oil phase content on the calcite surface and the surfactant content in the recovered water phase are detected, and the cleaning effect of the calcite infiltrated with the oil phase with the circulating water phase is investigated.

[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 attached figures) was taken 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, and then CO2 (25 mL / min, 30 min) and N2 (50 mL / min, 50 min) were alternately introduced into the solution, and the change in pH was measured. The cycle was repeated 6 times. Figure 1 Shown.

[0049] Example 2 Cleaning of positively charged soil (calcite) with surfactant aqueous solution

[0050] The experimental process is as follows Figure 2 As shown, 2-10 mesh calcite was selected to simulate soil. 30g calcite was weighed into a 100mL beaker, 15g liquid paraffin was added, stirred evenly and allowed to stand for more than 2h to ensure that the oil phase completely infiltrated the calcite. 70mL of 1.0mM surfactant (DUMa) aqueous solution (pH=9.5) was added to the beaker containing the oil phase and calcite, a magnet was added and stirred for 2h, and then allowed to stand for 2-5h, CO2 was introduced to make the solution pH=4-6, 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. The calcite and the aqueous phase containing the surfactant were separated by filtration and centrifugation, N2 was blown into the aqueous phase and CO2 was removed, the pH of the solution was restored to about 9-10, the aqueous phase was collected and the surfactant aqueous solution was supplemented to 70mL, and added to the calcite infiltrated in the oil phase for cleaning, and the above steps were repeated, which could be cycled more than 3 times.

[0051] The residual rate of oil phase in calcite, the recovery rate of water phase, the recovery rate of oil phase and the recovery rate of calcite 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 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 three 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.

[0055] Example 3: Surfactant used in the recycling and cleaning of sand containing other oil pollution

[0056] Select 10-20 mesh calcite, the oil phases are paraffin oil, toluene and dimethyl silicone oil, and the cleaning process is referenced 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 the 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 used for recycling. For dimethyl silicone oil with high viscosity and density, the residual amount after cleaning is only 0.11±0.09g, which is 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 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: Surfactant used for cleaning calcite soil containing phenanthrene mixed oil

[0059] 0.5 g of phenanthrene (PHE) was dispersed in paraffin oil (15 g) as 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. After the cleaning, the recovery rates of contaminated oil, surfactant aqueous phase and calcite sand were shown in Table 2 and Figure 6 The PHE content in the recovered oil and calcite was determined by high performance liquid chromatography, as shown in Figure 6 shown. Figure 6 (ad) are the HPLC chromatograms of the standard sample, the recovered oil after washing, and the calcite surface extract and the corresponding standard curve, based on which the recovery rate of PHE can be calculated (Table 2). About 88.0% of the simulated mixed contaminated oil was recovered, more than 93.0% of PHE was recovered together with the paraffin oil, and the residual rate of PHE in the sand after washing was 2.9-5.8%.

[0060] Table 2. DUMa remediation results for 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 Bola-type surfactant that responds to CO2 / N2, which can effectively clean positively charged oil sludge sand at a relatively low concentration (1.0mM, ≈0.06cmc), with a small amount of surfactant, and can achieve efficient removal of oil pollution in the soil. After a small amount of CO2 is injected, the surfactant molecules are transformed into a Bola-type strong hydrophilic configuration, the surfactant is desorbed from the oil pollution surface and transferred to the water phase, and after removing the oil phase and CO2, the surfactant solution can be recycled and reused, and the oil sludge sand can be circulated and cleaned at least 3 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 thereof, and the above-mentioned oil phase containing polycyclic aromatic hydrocarbons. The oil phase recovery rate can reach more than 85%, the residual rate is reduced to less than 0.3%, and the water phase recovery rate is more than 90%. The surfactant in the present invention, by introducing CO2 / N2, makes the tertiary amine group in the surfactant structure intelligently switch between "non-polar" and "strong polarity", that is, "active" and "inactive". After the surfactant is deactivated, it completely enters the water phase without affecting the quality of the oil phase. This enables the reuse and recycling of the surfactant solution, which is beneficial to achieving environmentally friendly goals such as reducing the emission of chemical materials and saving water.

[0063] 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 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 about 4-6; S3. After the oil layer is separated, the water phase containing the soil is separated into solid and liquid, and the obtained solid phase is washed and dried to obtain the purified soil; the obtained water phase is an aqueous solution containing a surfactant, and N2 is blown into it to adjust the pH value to 9 to 10, so that a recyclable aqueous surfactant solution can be obtained; 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.

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 but is not limited to 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 soil includes contaminated soil and oil sludge sand; And / or, the contaminated soil surface is positively charged.

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

10. 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; 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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