Application of ethylene glycol alkyl ether aqueous two-phase system in repairing diesel oil polluted soil

Abstract

The invention discloses an application of an ethylene glycol alkyl ether aqueous two-phase system in repairing diesel oil polluted soil, and the ethylene glycol alkyl ether aqueous two-phase system and the diesel oil polluted soil are mixed and react to obtain repaired soil; the method adopts the ethylene glycol alkyl ether aqueous two-phase system for extraction, conforms to the green chemistry principle and is suitable for remediation of the diesel-polluted soil.

Description

Technical Field

[0001] The present invention belongs to the technical field of soil remediation, and particularly relates to the application of an ethylene glycol alkyl ether aqueous two-phase system in the remediation of diesel-contaminated soil. Background Art

[0002] Diesel-contaminated soil is a common accident, mainly occurring during leakage in the processes of oil refining, transportation, storage, and use. Diesel is a low-volatility mixture composed of saturated hydrocarbons (60%-80%) and aromatic hydrocarbons (20%-40%), and has toxicity and carcinogenicity. Due to the complex interaction between diesel and the organic matter in the soil, the natural degradation rate of diesel is prolonged, and the increasing number of diesel pollution accidents poses a serious threat to the ecological environment and human health.

[0003] So far, various technologies have been proposed for the remediation of petroleum hydrocarbon-contaminated soil, from traditional technologies such as solvent extraction and surfactant washing remediation to emerging technologies such as electro-Fenton remediation and foam remediation. Generally speaking, these remediation technologies can be divided into four categories: bioremediation technology, thermal remediation technology, chemical remediation technology, and physicochemical remediation technology. Bioremediation has been successfully applied to the remediation of petroleum-contaminated soil, and this technology can permanently degrade petroleum pollutants into simple non-toxic inorganic compounds. However, bioremediation is a slow remediation process and can only be regarded as a non-emergency solution. Thermal remediation technology can quickly and selectively remove petroleum pollutants. However, compared with other remediation technologies, the excessive energy consumption of thermal remediation remains a challenge. Solvent extraction technology has been proven to be an effective method for the remediation of petroleum-contaminated soil. A recent study shows that using petroleum ether as a solvent can remove 70-90% of the total petroleum hydrocarbons within 20 minutes, indicating that solvent extraction technology has significant advantages in terms of removal efficiency, time, and energy consumption. The use of traditional organic solvents has been on the decline because it easily causes secondary pollution, which reduces the competitiveness of organic solvent remediation compared with other remediation technologies. Summary of the Invention

[0004] The object of the present invention is to provide the application of an ethylene glycol alkyl ether aqueous two-phase system in the remediation of diesel-contaminated soil, aiming to solve the problem that traditional organic solvents easily cause secondary pollution, resulting in low competitiveness of organic solvent remediation compared with other remediation technologies.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] The application of an ethylene glycol alkyl ether aqueous two-phase system in the remediation of diesel-contaminated soil, which comprises mixing the ethylene glycol alkyl ether aqueous two-phase system and diesel-contaminated soil, reacting, and obtaining the remediated soil.

[0007] Furthermore, the ethylene glycol alkyl ether aqueous two-phase system includes an ethylene glycol propyl ether aqueous two-phase system, an ethylene glycol butyl ether aqueous two-phase system, and a triethylene glycol butyl ester aqueous two-phase system.

[0008] Furthermore, the ethylene glycol alkyl ether aqueous two-phase system is an ethylene glycol butyl ether aqueous two-phase system.

[0009] Furthermore, the preparation steps of the ethylene glycol alkyl ether aqueous two-phase system are as follows:

[0010] Step 1: Mix water and alkoxy alcohol in a beaker in proportion;

[0011] Step 2: Add NaCl and dissolve it under sufficient stirring;

[0012] Step 3: After sufficient stirring, the solution becomes turbid. After standing, two homogeneous phases appear. The top phase is rich in ethylene glycol alkyl ether, and the bottom phase is composed of water.

[0013] Furthermore, the temperature of the reaction is 20°C - 80°C; the solid-liquid ratio of the diesel-contaminated soil to the ethylene glycol alkyl ether aqueous two-phase system is 0.1 - 0.5; the stirring speed of the reaction is 200 - 1000 rpm / minute.

[0014] Furthermore, the temperature of the reaction is 20°C - 60°C; the solid-liquid ratio of the diesel-contaminated soil to the ethylene glycol alkyl ether aqueous two-phase system is 0.2; the stirring speed of the reaction is 600 rpm / minute.

[0015] Furthermore, the stirring time of the reaction is 0 - 27 minutes.

[0016] Furthermore, the stirring time of the ethylene glycol butyl ether aqueous two-phase system is 0 - 18 minutes; the stirring time of the ethylene glycol propyl ether aqueous two-phase system is 0 - 21 minutes, and the stirring time of the triethylene glycol butyl ester aqueous two-phase system is 0 - 27 minutes.

[0017] Furthermore, the ethylene glycol alkyl ether aqueous two-phase system can be reused; after being reused 7 times, the removal rate of diesel by the ethylene glycol butyl ether aqueous two-phase system is above 85.17%.

[0018] Furthermore, the germination rate of wheat in the repaired soil reaches 80% after 72 hours.

[0019] Due to the adoption of the above technical solutions, compared with the prior art, the technical progress achieved by the present invention has at least one of the following:

[0020] (1) The ethylene glycol alkyl ether aqueous two-phase system of the present invention can be reused;

[0021] (2) According to the analysis of gas chromatography-mass spectrometry and Fourier transform infrared spectroscopy, the extraction of ethylene glycol alkyl ether aqueous two-phase system can effectively remove diesel hydrocarbons with different carbon chain lengths, and almost no residual organic solvents will be left on the soil surface during the repair process, which has obvious advantages compared with the traditional surfactant washing method and organic solvent extraction method;

[0022] (3) The germination rate of the wheat of the present invention in the repaired soil reaches 80% after 72 hours.

[0023] In summary, the extraction of ethylene glycol alkyl ether aqueous two-phase system adopted by the present invention conforms to the principle of green chemistry and is applicable to the repair of diesel-polluted soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation to the present invention.

[0025] In the drawings:

[0026] Figure 1a shows the influence of temperature on the diesel removal efficiency of the present invention;

[0027] Figure 1b shows the influence of the solid-liquid ratio on the diesel removal efficiency of the present invention;

[0028] Figure 1c shows the influence of the stirring speed on the diesel removal efficiency of the present invention;

[0029] Figure 1d shows the influence of the stirring time on the diesel removal efficiency of the present invention;

[0030] Figure 1e shows the influence of the molecular structure of ethylene glycol alkyl ether on the diesel removal efficiency of the present invention;

[0031] Figure 2 shows the gas chromatography-mass spectrometry chromatogram of the diesel-polluted soil sample before and after the repair by the ethylene glycol butyl ether aqueous two-phase system of the present invention;

[0032] Figure 3a shows the spectrograms of the diesel-polluted soil, the treated soil (ethylene glycol butyl ether) and the non-polluted soil of the present invention;

[0033] Figure 3b shows the spectrograms of the treated soil (Tritonx-100), the treated soil (toluene) and the treated soil (ethylene glycol butyl ether) of the present invention;

[0034] Figure 4 shows the relationship between the removal efficiency of the ethylene glycol alkyl ether aqueous two-phase system of the present invention and the number of cycle experiments;

[0035] Figure 5 Comparison of aqueous two-phase extraction, Triton X-100 washing and toluene extraction of ethylene glycol alkyl ethers (ethylene glycol butyl ether, ethylene glycol propyl ether, triethylene glycol butyl ester) of the present invention for diesel-contaminated soil remediation;

[0036] Figure 6a Germination of wheat seeds of the present invention in diesel-contaminated soil and uncontaminated soil of ethylene glycol butyl ether (soil after aqueous two-phase extraction of ethylene glycol butyl ether), toluene (soil after toluene extraction), and Triton X-100 (soil after Triton X-100 washing);

[0037] Figure 6b Comparison of the germination rates of wheat seeds of the present invention in soil after aqueous two-phase extraction of ethylene glycol butyl ether, soil after toluene extraction, soil after Triton X-100 washing, and uncontaminated soil within 72 hours in different soil samples. Detailed implementation manners

[0038] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0039] In recent years, with the emergence of emerging green organic solvents, a series of brand-new solvent extraction methods such as supercritical fluid extraction technology, subcritical water extraction technology, and ionic liquid extraction technology have developed rapidly.

[0040] As a new separation technology, aqueous two-phase extraction has attracted wide attention in recent years. When one or more substances are dissolved in water at appropriate concentrations and temperatures, an aqueous two-phase system can be formed, in which the two coexisting phases are both aqueous solutions. Common types of aqueous two-phase systems include polymer-polymer systems (such as polyethylene glycol and dextran), polymer-salt systems, short-chain alcohol-salt systems, and ionic liquid-based systems. Aqueous two-phase systems are widely used in the field of biochemical separation. Thanks to the advantages of high water content and mild environment, aqueous two-phase systems overcome the limitations of low solubility and easy destruction of proteins in organic solvent systems and become the best choice for protein purification. Researchers have effectively separated bovine serum albumin and ampicillin using an aqueous two-phase system composed of polyethylene glycol and potassium dihydrogen phosphate. Since the discovery of triblock copolymers has provided new ideas for the extraction of metal ions, aqueous two-phase systems are also considered a promising metal ion separation system. Copolymers will form micelles containing hydrophobic units at the critical temperature or concentration, thus having the ability to dissolve hydrophobic metal complexes. It is reported that aqueous two-phase systems composed of block polymers can extract and separate different metal ions. Based on a similar mechanism, aqueous two-phase systems are also widely used to extract dyes from textile wastewater and remove aromatic compounds from environmental sediments.

[0041] Our laboratory has studied the newly discovered ethylene glycol alkyl ether aqueous two-phase system. The phase behavior of the ethylene glycol alkyl ether aqueous two-phase system and the influencing factors of the complete phase diagram were discussed in detail. As a small molecule aqueous two-phase system, the ethylene glycol alkyl ether aqueous two-phase system has the advantages of low viscosity and fast phase separation compared with the traditional aqueous two-phase system. To our knowledge, there is no relevant report in the literature on the remediation of diesel-contaminated soil by the ethylene glycol alkyl ether aqueous two-phase system. Therefore, we attempted to apply it to the feasibility of diesel-contaminated soil remediation.

[0042] In this work, the remediation ability of the ethylene glycol alkyl ether aqueous two-phase system on diesel-contaminated soil was studied, and the influencing factors of temperature, stirring speed, stirring time, and solid-liquid ratio on the removal efficiency were studied in detail. The mechanism and characteristics of the removal of diesel hydrocarbons by the aqueous two-phase system were further clarified. In addition, by evaluating the physical and chemical properties of the soil and plant growth, the impact of the ethylene glycol alkyl ether aqueous two-phase system on the soil was determined.

[0043] Example Application of an ethylene glycol alkyl ether aqueous two-phase system in the remediation of diesel-contaminated soil

[0044] Preparation of diesel-contaminated soil: The soil was taken from Shengli Oilfield, with a depth of 20 cm, 0 # Diesel was purchased from the Dongying Gas Station of Sinopec. Table 1 lists the chemical substances related to the preparation of the aqueous two-phase system. NaCl (CAS 7647-14-5, Aladdin, >99.5%), n-hexane (CAS 110-54-3, Sinopharm Chemical Reagent Co., >99.5%), acetone (CAS 67-64-1, Sinopharm Chemical Reagent Co., >99.5%) were used as received without further purification.

[0045] Table 1 Chemical source table

[0046]

[0047]

[0048] Air-dry the soil samples and sieve them through a 2-mm sieve to remove rocks and plant residues. Put 500 g of soil into a beaker, add 300 mL of a n-hexane / acetone (V / V = 1:1) solution containing 8 mL of diesel, and mix well. Then store the beaker in a fume hood and evaporate the organic solvents at room temperature for 48 h. The initial diesel concentration is 12160 mg / kg (expressed as the total petroleum hydrocarbon concentration), which is close to the actual diesel-contaminated soil. Subsequently, mix 500 g of soil and 300 mL of n-hexane / acetone (V / V = 1:1) solution without diesel well and evaporate to obtain uncontaminated soil (uncontaminated soil). All the prepared soil samples are stored in the dark at 4 °C for use.

[0049] The ethylene glycol alkyl ether aqueous two-phase system was prepared according to the alkoxy alcohol phase diagram reported by Wang et al., and the ratio of alkoxy alcohol, water, and NaCl should be in the two-phase region. Three ethylene glycol alkyl ethers (C n E m , n = 1 - 4, m = 1 - 3), ethylene glycol propyl ether (C3E1), ethylene glycol butyl ether (C4E1), and triethylene glycol butyl ester (C4E3) were studied in this laboratory. The preparation process of the ethylene glycol alkyl ether aqueous two-phase system is as follows: Mix water and alkoxy alcohol at a volume ratio of 1:1, and then add NaCl to dissolve with sufficient stirring. After sufficient stirring, the solution becomes turbid, and two homogeneous phases appear after standing for a period of time. The prepared aqueous two-phase system is transparent, the interface between the two phases is clear, the top phase is rich in ethylene glycol alkyl ether, and the bottom phase is mainly composed of water.

[0050] The remediation process of the ethylene glycol alkyl ether aqueous two-phase system for diesel-contaminated soil is as follows:

[0051] Mix 2 g of diesel-contaminated soil and 20 mL of the ethylene glycol propyl ether aqueous two-phase system in a beaker, and then stir in a water bath at a temperature of 20 °C - 80 °C, with a stirring speed of 200 - 1000 rpm and a stirring time of 0 - 21 minutes to extract the diesel in the contaminated soil. After the extraction is completed, centrifuge the mixed solution to achieve solid-liquid separation, and dry the obtained soil sample for further analysis.

[0052] Mix 2 g of diesel-contaminated soil and 20 mL of the ethylene glycol butyl ether aqueous two-phase system in a beaker, and then stir in a water bath at a temperature of 20 °C - 80 °C, with a stirring speed of 200 - 1000 rpm and a stirring time of 0 - 18 minutes to extract the diesel in the contaminated soil. After the extraction is completed, centrifuge the mixed solution to achieve solid-liquid separation, and dry the obtained soil sample for further analysis.

[0053] Mix 2 grams of diesel - contaminated soil and 20 milliliters of the triethylene glycol dibutyl phthalate aqueous two - phase system in a beaker, and then stir in a water bath at a temperature of 20°C - 80°C with a stirring speed of 200 - 1000 rpm for 0 - 27 minutes to extract the diesel in the contaminated soil. After extraction, centrifuge the mixed solution to achieve solid - liquid separation, and dry the obtained soil sample for further analysis.

[0054] 1 It is concluded from the analysis of the remediation of diesel - contaminated soil by the above - mentioned three aqueous two - phase systems that:

[0055] 1.1 Influence of temperature on the removal efficiency

[0056] The extraction and remediation of diesel - contaminated soil by the aqueous two - phase system is carried out in the temperature range of 20°C to 80°C. The influence of temperature on the diesel removal rate is as Figure 1a shown. As the temperature increases, the removal efficiency increases sharply, especially in the range of 20°C to 50°C. Subsequently, when the temperature is higher than 60°C, the growth of the diesel removal efficiency slows down and tends to be stable. It is worth noting that during the whole remediation process, the removal efficiency of the ethylene glycol monobutyl ether aqueous two - phase system for diesel is always higher than that of the ethylene glycol n - propyl ether aqueous two - phase system and the triethylene glycol dibutyl phthalate aqueous two - phase system. During the removal process of diesel, both desorption and dissolution are temperature - dependent processes. On the one hand, the increase in temperature can increase the dissolved amount of diesel in the aqueous two - phase system. On the other hand, the interaction between diesel and the soil surface gradually weakens with the increase in temperature, which will promote the stripping of diesel from the soil surface. In addition, according to the phase equilibrium data of the ternary (water + octane + 2 - butoxy - ethanol) system, the amount of alkane dissolved in the ethylene glycol monobutyl ether phase increases with the increase in temperature. The increase in temperature can effectively remove diesel from the soil, which is consistent with the previous research conclusions. However, higher temperatures may damage the soil structure and microbial environment. Therefore, the optimal temperature needs to be determined from the aspects of removal efficiency and influence on the soil.

[0057] 1.2 Influence of the solid - liquid ratio on the removal efficiency

[0058] The ratio of diesel - contaminated soil to the aqueous two - phase system is considered an important factor in soil remediation because it determines the diesel removal rate and the cost of soil remediation. The influence of the solid - liquid ratio (diesel - contaminated soil - aqueous two - phase system) (0.1 - 0.5) on the removal efficiency was studied by changing the solid - liquid ratio, and the results are as Figure 1bAs shown, the removal efficiency of diesel remains at a relatively high level when the initial ratio is less than 0.2. As the ratio increases, a downward trend begins to emerge. A lower solid-liquid ratio is beneficial for improving the removal efficiency of diesel through washing with the aqueous two-phase system. On the one hand, the soil can effectively contact the aqueous two-phase system; on the other hand, the desorbed diesel can be completely dissolved in the aqueous two-phase system. However, a lower solid-liquid ratio results in higher energy consumption and larger water consumption during the actual remediation process. In this experiment, a solid-liquid ratio of 0.2 can be considered an appropriate proportion. The removal efficiency decreases with the increase of the solid-liquid ratio, which can be attributed to the fact that it is difficult for excessive soil to effectively contact the aqueous two-phase system, resulting in insufficient dissolution of diesel in the aqueous two-phase system.

[0059] 1.3 Effect of stirring speed on removal efficiency

[0060] The stirring speed also plays an important role in the experiment. It affects the diesel removal rate by changing the adequacy and effectiveness of the contact between the soil and the aqueous two-phase system. Figure 1C shows the effect of the stirring speed (200 - 1000 rpm) on diesel removal. In the initial stage, as the stirring speed increases, the removal efficiency increases significantly and then decreases after reaching the maximum value. Taking the ethylene glycol monobutyl ether aqueous two-phase system as an example, as the stirring speed increases, the removal efficiency rises sharply, and the maximum removal rate of diesel is 600 rpm. However, as the stirring speed increases to 800 rpm, the removal efficiency decreases slightly, and as the stirring speed increases to 1000 rpm, the removal efficiency decreases significantly. The three ethylene glycol alkyl ether aqueous two-phase systems with different molecular structures all show the same trend. The increase in the stirring speed can promote the full contact between the aqueous two-phase system and the soil. In addition, the collision between soil particles will become stronger, which helps to remove pollutants. Although this does not mean that a faster stirring speed can achieve a higher removal efficiency. At an excessively fast stirring speed, the soil will adhere to and accumulate on the beaker wall, which will significantly reduce the effective contact between the soil and the aqueous two-phase system, resulting in a decrease in the removal efficiency. In addition, a further increase in the stirring speed will cause the slurry to move in a bulk form with relatively little relative movement, which will reduce collisions and lead to a decrease in the removal efficiency. Therefore, the best removal efficiency is observed at 600 - 800 rpm, and further research was carried out at this stirring speed.

[0061] 1.4 Effect of stirring time on removal efficiency

[0062] The stirring time has always been a key factor affecting the soil remediation efficiency. Through extraction experiments at different time intervals, the effect of the stirring time on diesel removal was determined. The results are as Figure 1dAs shown, the removal efficiency of diesel by the ethylene glycol butyl ether aqueous two-phase system increases rapidly within 0 - 15 minutes, then slows down, and gradually reaches equilibrium at about 18 minutes. The removal efficiency of the ethylene glycol propyl ether aqueous two-phase system and the triethylene glycol butyl ester aqueous two-phase system increases significantly within 0 - 20 minutes, and then the ethylene glycol propyl ether aqueous two-phase system reaches stability at 21 ± 1 minutes and the triethylene glycol butyl ester aqueous two-phase system reaches stability at 27 ± 1 minutes. The removal efficiency of diesel is relatively fast in the initial stage and then gradually slows down. From a kinetic perspective, the large concentration difference in the initial stage provides a strong mass transfer driving force. As the concentration gradient gradually decreases, the mass transfer rate will gradually slow down. In addition, the initial removal efficiency is faster because the desorption process of light hydrocarbons is easier, while the desorption process of heavy hydrocarbons from the soil surface is more complex, resulting in a slowdown in the growth of the removal efficiency.

[0063] 1.5 Influence of the Molecular Structure of Ethylene Glycol Alkyl Ethers on the Remediation of Diesel-Contaminated Soil

[0064] Ethylene glycol alkyl ethers are very interesting solvents because alcohols, ethers, and hydrocarbon chains coexist in the same molecule. To study the influence of the molecular structure on the diesel removal efficiency, three ethylene glycol alkyl ethers (ethylene glycol butyl ether, ethylene glycol propyl ether, triethylene glycol butyl ester) were selected for the diesel-contaminated soil remediation experiment. Ethylene glycol butyl ether and ethylene glycol propyl ether contain the same ethylene glycol group in their structures but different alkyl groups. Ethylene glycol butyl ether and triethylene glycol butyl ester contain the same butyl group but different ether parts. Therefore, although their molecular structures are similar, there are also certain differences in their solubility and molecular polarity. As Figure 1e shown, under the optimized experimental conditions, diesel in diesel-contaminated soil can be effectively removed (Table 2), and the diesel content decreases from 12160 mg / kg to 342.91 mg / kg (ethylene glycol butyl ether aqueous two-phase system), 1810.62 mg / kg (ethylene glycol propyl ether aqueous two-phase system), and 3498.43 mg / kg (triethylene glycol butyl ester aqueous two-phase system). That is to say, the removal rates of diesel by the ethylene glycol butyl ether aqueous two-phase system, the ethylene glycol propyl ether aqueous two-phase system, and the triethylene glycol butyl ester aqueous two-phase system reach 97.18%, 85.11%, and 71.23% respectively. Compared with triethylene glycol butyl ester and ethylene glycol propyl ether, ethylene glycol butyl ether contains a shorter ethylene oxide chain and a longer alkyl chain, which makes it show relatively strong hydrophobicity, so it shows obvious advantages in the diesel remediation process. Therefore, the ethylene glycol butyl ether aqueous two-phase system has the best removal efficiency, and the diesel content in the treated soil is lower than the relevant standards in many countries and regions (such as the Chinese risk screening level standard of 826 mg / kg and the French total petroleum hydrocarbon content threshold of 500 mg / kg).

[0065] Table 2 Optimal Experimental Conditions and Diesel Removal Results Using Different Ethylene Glycol Alkyl Ethers

[0066]

[0067]

[0068] rpm: revolutions per minute;

[0069] 2. Analytical methods for soil remediation

[0070] 2.1 The content of residual diesel hydrocarbons in the treated soil after the remediation of the aqueous two-phase system was measured using a Fourier transform infrared oil spectrometer (SYT700, Sun Yang Technology, Beijing, China). In an ultrasonic ice bath, 2 g of the treated soil was extracted in 15 mL of CCl4 for 45 minutes, and then centrifuged at 8000 rpm for 15 minutes to remove solid particles. The extract was passed through a column containing anhydrous Na2SO4 to remove water, and then the volume was adjusted to 50 mL for further analysis. The removal efficiency (%) of diesel was calculated according to Equation (1).

[0071]

[0072] where C i (mg / kg) is the initial concentration of diesel in the soil, and C r (mg / kg) is the residual concentration of diesel in the soil.

[0073] The pH value and electrical conductivity of the soil were analyzed using a conductivity / pH multiparameter meter (KL-2266, Keland Instrument Technology, Shanghai, China). According to the national environmental protection standard of the People's Republic of China (HJ658-2013), the combustion oxidation titration method was used to determine the soil organic carbon content. The soil particle size distribution was analyzed using a laser particle size analyzer (LT3600, Linkoptik Instrument, Zhuhai, China).

[0074] The content of each hydrocarbon component before and after diesel extraction was determined by gas chromatography-mass spectrometry (7890B-7000C, Agilent, DB-5ms), and the removal characteristics of diesel were evaluated by aqueous two-phase extraction. As described above, diesel in the diesel-contaminated soil and the treated soil was extracted with CCl4, and then 1 μL of the sample was injected into the inlet at a temperature of 250 °C. Helium was used as the carrier gas, and the flow rate was maintained at 1.0 mL / min. The programmed temperature range was from 60 °C to 300 °C, with a flow rate of 10 °C / min and held for 8 minutes. The total running time was 32 minutes. The correspondence between diesel hydrocarbon components and characteristic peaks was determined by the National Institute of Standards and Technology library of the United States. The removal efficiency (%) of a single hydrocarbon was calculated based on the change in the characteristic peak area shown in Equation (2).

[0075]

[0076] where A i is the initial peak area of diesel hydrocarbons in the diesel-contaminated soil, and Ar The peak area of diesel hydrocarbon residues in the treated soil.

[0077] Fourier transform infrared spectroscopy (FTLR-8400S, Shimadzu, Japan) was used to qualitatively analyze the residues of diesel and organic solvents in the treated soil. By comparing the characteristic peaks of functional groups, it was possible to infer whether there were residual diesel and organic solvents in the soil.

[0078] 2.2 Analysis and characterization of soil samples

[0079] 2.2.1 Gas chromatography-mass spectrometry was used to analyze the changes in the content and distribution of diesel hydrocarbons before and after aqueous two-phase extraction remediation. The results are as Figure 2 shown in Table 3. A significant high-intensity peak appeared at a retention time of 14.693, indicating that the main component of diesel in this experiment was C 15 H 32 (pentadecane). Most of the peaks corresponding to hydrocarbons (C 12 -C 28 ) disappeared or weakened after remediation. According to the diesel hydrocarbon data in Table 3, the removal efficiency of light hydrocarbon components (C 12 -C 20 ) in diesel reached over 97%, and for a few light hydrocarbons, it even reached 100%. The removal efficiency of relatively heavier hydrocarbons (C 21 -C 28 ) exceeded 80%, and for a few heavier hydrocarbons, it even reached 90%. Overall, aqueous two-phase extraction remediation could effectively remove diesel hydrocarbons with different carbon chain lengths in diesel-contaminated soil, and the removal efficiency of some heavy hydrocarbons was weaker than that of light hydrocarbons. The gas chromatography-mass spectrometry chromatogram proved that, from another perspective, the desorption process of heavy hydrocarbons was more complex and difficult than that of light hydrocarbons, which was consistent with previous reports in the literature.

[0080] Table 3 Gas chromatography-mass spectrometry analysis data of diesel-contaminated soil samples before and after remediation with ethylene glycol monobutyl ether aqueous two-phase system

[0081]

[0082]

[0083] 2.2.2 Fourier transform infrared spectroscopy analysis

[0084] Fourier transform infrared spectroscopy was used to determine the functional groups of diesel hydrocarbons and organic solvents on the soil surface, which helped to further study the characteristics of different remediation methods. Figure 3a shows 2853 cm in the spectrum of diesel-contaminated soil -1 and 2925 cm -1Apparent peaks in the vicinity, which are attributed to the symmetric and asymmetric C-H stretching vibrations of diesel hydrocarbons. The characteristic peaks of diesel hydrocarbons in the spectrum of the treated soil (ethylene glycol monobutyl ether) disappeared, and no obvious new characteristic peaks appeared compared with the spectrum of the uncontaminated soil, indicating that aqueous two-phase extraction can effectively remove diesel hydrocarbons and hardly leave organic solvents on the soil surface. Gas chromatography-mass spectrometry analysis also confirmed this characteristic. Figure 3b Shows that each of the three remediation techniques has its own characteristics. The spectrum of the treated soil (Triton X-100) still has characteristic peaks of diesel hydrocarbons at 2853 cm -1 and 2925 cm -1 , indicating that there is still a small amount of diesel residue in the soil. The characteristic peaks of diesel hydrocarbons (2853 cm -1 and 2925 cm -1 ) in the spectrum of the treated soil (toluene) disappeared, and a new peak appeared at 1639 cm -1 , which is caused by the C-C stretching vibration at the junction of aromatic hydrocarbons and methyl groups. This means that although toluene can effectively remove diesel hydrocarbons from the soil, it will produce residual toluene in the soil, resulting in secondary pollution.

[0085] 2.2.3 Characteristics of soil samples

[0086] Aqueous two-phase extraction shows a high removal ability in the remediation of diesel-contaminated soil. To comprehensively evaluate the feasibility of this remediation method, the physicochemical properties of the soil were further studied. The results are shown in Table 4. The pH value of the soil after aqueous two-phase extraction has no significant difference from that of the uncontaminated soil and remains weakly alkaline. This is because the high water content of the aqueous two-phase system creates a mild extraction environment for the soil remediation process, which is also an obvious advantage of the aqueous two-phase system compared with other organic solvent systems. After aqueous two-phase extraction, the conductivity of the diesel-contaminated soil increased from 62.5 uS / cm to 81.9 uS / cm, slightly higher than 78.9 uS / cm of the uncontaminated soil. This is due to the small amount of Na + and Cl - in the aqueous two-phase system remaining in the soil after aqueous two-phase extraction. Due to the presence of diesel in the soil, the soil organic carbon of the diesel-contaminated soil reaches 2.56%, much higher than that of the uncontaminated soil. The soil organic carbon content of the treated soil (ethylene glycol monobutyl ether) is lower than that of the uncontaminated soil, indicating that diesel hydrocarbons are effectively removed, and a small amount of organic matter in the soil is carried away under the action of aqueous two-phase extraction. Soil particle size distribution analysis shows that there is no significant difference among the three soil samples, indicating that aqueous two-phase extraction does not affect the soil structure and particle size distribution. Generally speaking, there is no significant difference in the physicochemical properties of the three soil samples, indicating that aqueous two-phase extraction hardly affects the physicochemical characteristics of the soil.

[0087] Table 4 Physicochemical properties of different soil samples

[0088]

[0089] 2.3 Discussion on the Recycling of Aqueous Two-Phase Systems

[0090] Reusability is an important criterion for evaluating new extraction systems related to organic solvent consumption and the cost of the extraction process.

[0091] The recycling process of the ethylene glycol propyl ether aqueous two-phase system for the remediation of diesel-contaminated soil is as follows:

[0092] First time: Mix 2 g of diesel-contaminated soil and 20 mL of the ethylene glycol propyl ether aqueous two-phase system in a beaker, then stir in a water bath at a temperature of 20°C - 80°C with a stirring speed of 200 - 1000 rpm for 0 - 21 minutes to extract the diesel in the contaminated soil. After the extraction is completed, centrifuge the mixed solution to achieve solid-liquid separation, dry the obtained soil sample for further analysis, and collect the ethylene glycol propyl ether aqueous two-phase system for the first time for standby.

[0093] Second time: Mix 2 g of diesel-contaminated soil and 20 mL of the ethylene glycol propyl ether aqueous two-phase system collected for the first time in a beaker, with other conditions unchanged, and collect the ethylene glycol propyl ether aqueous two-phase system for the second time for standby.

[0094] Third time: Mix 2 g of diesel-contaminated soil and 20 mL of the ethylene glycol propyl ether aqueous two-phase system collected for the second time in a beaker, with other conditions unchanged, and collect the ethylene glycol propyl ether aqueous two-phase system for the third time for standby.

[0095] Fourth time: Mix 2 g of diesel-contaminated soil and 20 mL of the ethylene glycol propyl ether aqueous two-phase system collected for the third time in a beaker, with other conditions unchanged, and collect the ethylene glycol propyl ether aqueous two-phase system for the fourth time for standby.

[0096] Fifth time: Mix 2 g of diesel-contaminated soil and 20 mL of the ethylene glycol propyl ether aqueous two-phase system collected for the fourth time in a beaker, with other conditions unchanged, and collect the ethylene glycol propyl ether aqueous two-phase system for the fifth time for standby.

[0097] Sixth time: Mix 2 g of diesel-contaminated soil and 20 mL of the ethylene glycol propyl ether aqueous two-phase system collected for the fifth time in a beaker, with other conditions unchanged, and collect the ethylene glycol propyl ether aqueous two-phase system for the sixth time for standby.

[0098] Seventh time: Mix 2 g of diesel-contaminated soil and 20 mL of the ethylene glycol propyl ether aqueous two-phase system collected for the sixth time in a beaker, with other conditions unchanged, and collect the ethylene glycol propyl ether aqueous two-phase system for the seventh time for standby.

[0099] The eighth time: Mix 2 grams of diesel - contaminated soil and 20 mL of the ethylene glycol propyl ether aqueous two - phase system collected in the seventh time in a beaker, with other conditions remaining unchanged.

[0100] The reuse process of the ethylene glycol butyl ether aqueous two - phase system for the remediation of diesel - contaminated soil is as follows:

[0101] The first time: Mix 2 grams of diesel - contaminated soil and 20 mL of the ethylene glycol butyl ether aqueous two - phase system in a beaker, then stir in a water bath at a temperature of 20°C - 80°C, with a stirring speed of 200 - 1000 rpm and a stirring time of 0 - 18 minutes to extract the diesel in the contaminated soil. After extraction, centrifuge the mixed solution to achieve solid - liquid separation, dry the obtained soil sample for further analysis, and collect the ethylene glycol butyl ether aqueous two - phase system for the first time for standby.

[0102] The second time: Mix 2 grams of diesel - contaminated soil and 20 mL of the ethylene glycol butyl ether aqueous two - phase system collected in the first time in a beaker, with other conditions remaining unchanged, and collect the ethylene glycol butyl ether aqueous two - phase system for the second time for standby.

[0103] The third time: Mix 2 grams of diesel - contaminated soil and 20 mL of the ethylene glycol butyl ether aqueous two - phase system collected in the second time in a beaker, with other conditions remaining unchanged, and collect the ethylene glycol butyl ether aqueous two - phase system for the third time for standby.

[0104] The fourth time: Mix 2 grams of diesel - contaminated soil and 20 mL of the ethylene glycol butyl ether aqueous two - phase system collected in the third time in a beaker, with other conditions remaining unchanged, and collect the ethylene glycol butyl ether aqueous two - phase system for the fourth time for standby.

[0105] The fifth time: Mix 2 grams of diesel - contaminated soil and 20 mL of the ethylene glycol butyl ether aqueous two - phase system collected in the fourth time in a beaker, with other conditions remaining unchanged, and collect the ethylene glycol butyl ether aqueous two - phase system for the fifth time for standby.

[0106] The sixth time: Mix 2 grams of diesel - contaminated soil and 20 mL of the ethylene glycol butyl ether aqueous two - phase system collected in the fifth time in a beaker, with other conditions remaining unchanged, and collect the ethylene glycol butyl ether aqueous two - phase system for the sixth time for standby.

[0107] The seventh time: Mix 2 grams of diesel - contaminated soil and 20 mL of the ethylene glycol butyl ether aqueous two - phase system collected in the sixth time in a beaker, with other conditions remaining unchanged, and collect the ethylene glycol butyl ether aqueous two - phase system for the seventh time for standby.

[0108] The eighth time: Mix 2 grams of diesel - contaminated soil and 20 mL of the ethylene glycol butyl alcohol aqueous two - phase system collected in the seventh time in a beaker, with other conditions remaining unchanged.

[0109] The reuse process of the triethylene glycol butyl ester aqueous two - phase system for the remediation of diesel - contaminated soil is as follows:

[0110] First time: Mix 2 g of diesel-contaminated soil and 20 mL of the triethylene glycol dibutyrate aqueous two-phase system in a beaker, then stir in a water bath at a temperature of 20°C - 80°C with a stirring speed of 200 - 1000 rpm for 0 - 27 minutes to extract the diesel in the contaminated soil. After the extraction is completed, centrifuge the mixed solution to achieve solid-liquid separation, dry the obtained soil sample for further analysis, and collect the triethylene glycol dibutyrate aqueous two-phase system for the first time for standby.

[0111] Second time: Mix 2 g of diesel-contaminated soil and 20 mL of the triethylene glycol dibutyrate aqueous two-phase system collected for the first time in a beaker, with other conditions remaining unchanged, and collect the triethylene glycol dibutyrate aqueous two-phase system for the second time for standby.

[0112] Third time: Mix 2 g of diesel-contaminated soil and 20 mL of the triethylene glycol dibutyrate aqueous two-phase system collected for the second time in a beaker, with other conditions remaining unchanged, and collect the triethylene glycol dibutyrate aqueous two-phase system for the third time for standby.

[0113] Fourth time: Mix 2 g of diesel-contaminated soil and 20 mL of the triethylene glycol dibutyrate aqueous two-phase system collected for the third time in a beaker, with other conditions remaining unchanged, and collect the triethylene glycol dibutyrate aqueous two-phase system for the fourth time for standby.

[0114] Fifth time: Mix 2 g of diesel-contaminated soil and 20 mL of the triethylene glycol dibutyrate aqueous two-phase system collected for the fourth time in a beaker, with other conditions remaining unchanged, and collect the triethylene glycol dibutyrate aqueous two-phase system for the fifth time for standby.

[0115] Sixth time: Mix 2 g of diesel-contaminated soil and 20 mL of the triethylene glycol dibutyrate aqueous two-phase system collected for the fifth time in a beaker, with other conditions remaining unchanged, and collect the triethylene glycol dibutyrate aqueous two-phase system for the sixth time for standby.

[0116] Seventh time: Mix 2 g of diesel-contaminated soil and 20 mL of the triethylene glycol dibutyrate aqueous two-phase system collected for the sixth time in a beaker, with other conditions remaining unchanged, and collect the triethylene glycol dibutyrate aqueous two-phase system for the seventh time for standby.

[0117] Eighth time: Mix 2 g of diesel-contaminated soil and 20 mL of the triethylene glycol dibutyrate aqueous two-phase system collected for the seventh time in a beaker, with other conditions remaining unchanged.

[0118] The aqueous two-phase system is repeatedly used for the remediation of diesel-contaminated soil, and the results are as Figure 4As shown, with the increase in the number of repetitions, the removal efficiency of diesel by aqueous two-phase extraction shows a slow downward trend. After 7 repetitions, the removal rate of diesel by the ethylene glycol monobutyl ether aqueous two-phase system decreases from 97.18% to 85.17%, that of the ethylene glycol monopropyl ether aqueous two-phase system decreases from 85.11% to 68.26%, and that of the triethylene glycol monobutyl ester aqueous two-phase system decreases from 71.23% to 46.33%. On the one hand, since the top phase of the aqueous two-phase system contains some diesel, the mass transfer driving force of diesel from the soil to the aqueous two-phase system decreases. On the other hand, the loss of the aqueous two-phase system during the laboratory recycling operation is inevitable. It is estimated that about 2.5% (by weight) of the aqueous two-phase system is lost each time, which actually inhibits the removal rate of diesel by increasing the solid-liquid ratio. The removal rate of diesel by the ethylene glycol monobutyl ether aqueous two-phase system can still remain above 85.17% after 7 repetitions, which is still higher than that of traditional surfactant detergents and thermal remediation technologies. By supplementing a small amount of the top phase of the aqueous two-phase system into the aqueous two-phase system, the removal efficiency of diesel by aqueous two-phase extraction can be maintained. In this way, the removal efficiency of diesel by aqueous two-phase extraction always remains at a high level while reducing the water consumption.

[0119] 2.4 Remediation mechanism of aqueous two-phase extraction and its comparison with Triton X-100 washing and toluene extraction

[0120] Ethylene glycol alkyl ethers are amphiphilic because they contain a hydrocarbon group, an ether bond, and a hydroxyl group in the same molecule. On the one hand, the non-polar alkyl chain makes it show lipophilicity. On the other hand, the ether bond and the hydroxyl group can form hydrogen bonds with water, making ethylene glycol alkyl ethers hydrophilic. Ethylene glycol alkyl ethers can dissolve most organic compounds and are miscible with water. An aqueous solution of ethylene glycol alkyl ether mixed with an appropriate amount of salt can form two phases. Ethylene glycol alkyl ethers are mainly concentrated in the top phase, while the bottom phase is rich in water.

[0121] When the aqueous two-phase system is mixed with diesel-contaminated soil, with the increase in the stirring speed, they may come into complete contact. The interaction between ethylene glycol alkyl ether and diesel on the soil surface gradually increases. With the increase in temperature, the adhesion of diesel on the soil surface decreases, and the solubility of diesel in the aqueous two-phase system increases. Under the combined action of these two factors, the attached diesel is finally stripped from the soil surface. As Figure 5 shown, diesel is dissolved in the top phase of the aqueous two-phase system and is hardly soluble in the bottom phase. The bottom phase acts as a barrier to prevent the desorbed oil from adsorbing on the soil again. The soil sinks to the bottom, forming a three-phase coexistence system. Therefore, by soaking in the bottom phase, the residual ethylene glycol alkyl ether on the soil surface can be significantly reduced. The apparent color of the ethylene glycol monobutyl ether aqueous two-phase system is darker than that of the ethylene glycol monopropyl ether aqueous two-phase system and the triethylene glycol monobutyl ester aqueous two-phase system (as Figure 5As shown, it indicates that the ethylene glycol monobutyl ether aqueous two-phase system can dissolve more diesel hydrocarbons than the other two aqueous two-phase systems. The ethylene glycol monobutyl ether aqueous two-phase system shows a higher removal efficiency because the ethylene glycol monobutyl ether molecule contains more lipophilic alkyl groups than ethylene glycol propyl ether and fewer hydrophilic ether bonds than triethylene glycol monobutyl ether.

[0122] The removal rate of diesel by Triton X-100 washing reached 52%, and the solution was still turbid and opaque after centrifugation. This is because Triton X-100 has a specific adsorption capacity for soil, which makes the micro soil particles suspended in the solution. In addition, the emulsified oil droplets in the solution will have the opportunity to contact the soil, where it is easily adsorbed again. The toluene solution was clear and transparent after centrifugation. Toluene has strong solubility and can easily remove diesel hydrocarbons from the soil. Although the removal efficiency of toluene extraction for diesel is close to 100%, the subsequent secondary pollution seriously hinders its application in actual industry.

[0123] 2.5 Wheat germination test

[0124] Wheat seed germination is usually selected as an indicator to evaluate the repaired soil samples. In this work, germination experiments were carried out on 5 representative soil samples, and there were significant differences in the germination rate and growth of wheat. Figure 6 shows the growth of wheat within 72 hours and the relationship between the germination rate and time. Diesel pollution seriously affected the germination rate of wheat seeds, resulting in a germination rate of only 2% for wheat in diesel-polluted soil, and the growth of germinated wheat was poor. In contrast, the germination rates of wheat in the soil samples treated with aqueous two-phase extraction and Triton X-100 washing technology reached 80% and 50% respectively, and the growth conditions were good. However, in the toluene-treated soil, the germination rate of wheat was only 20%, which was due to the highly toxic residual toluene in the soil severely inhibiting the germination and growth of wheat. Similar results have also been reported in previous studies. Water, as the main component of the two phases of the aqueous two-phase system, provides a mild environment for the remediation of diesel-polluted soil. The germination rate and growth of wheat in the soil after aqueous two-phase extraction remediation further confirm that the aqueous two-phase system can effectively protect the ecological stability of the soil.

[0125] In summary, the ethylene glycol alkyl ether aqueous two-phase system is applied to the remediation of diesel-contaminated soil, showing ideal removal efficiency and soil protection performance. The aqueous two-phase extraction with ethylene glycol butyl ether can rapidly and effectively remediate diesel-contaminated soil within 18 minutes at a stirring speed of 600 rpm at 60 °C. The maximum removal efficiency of diesel can reach 97.18%, close to that of extraction with organic solvents (toluene) (about 100%), and significantly higher than that of washing with surfactants (such as Triton X-100) (52%). According to gas chromatography-mass spectrometry analysis, most of the peaks corresponding to hydrocarbons disappear or weaken after remediation, which means that the aqueous two-phase extraction can also effectively remove petroleum hydrocarbons with different carbon chain lengths, even heavy components. Fourier transform infrared spectroscopy analysis shows that based on the slight difference between the spectra of the treated soil (ethylene glycol butyl ether) and the uncontaminated soil, the aqueous two-phase extraction hardly leaves residual organic solvents on the soil surface. Soil physical and chemical property analysis shows that the aqueous two-phase extraction can effectively maintain the ecological stability of the treated soil. Although the soil organic carbon content in the treated soil decreases slightly, it hardly affects the germination and growth of wheat. The germination rate of wheat in the treated soil (ethylene glycol butyl ether) reaches 80% after 72 hours, close to that of the uncontaminated soil, and higher than the 50% germination rate of washing with Triton X-100 and the 20% germination rate of remediation by toluene extraction. The aqueous two-phase extraction of ethylene glycol alkyl ether conforms to the principles of green chemistry.

[0126] The parts not detailed in the present invention belong to the common general knowledge of those skilled in the art.

[0127] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent substitution on some of the technical features. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. Application of an ethylene glycol alkyl ether aqueous two-phase system in repairing diesel-contaminated soil, characterized in that: Mix the ethylene glycol alkyl ether aqueous two-phase system with diesel-contaminated soil, and react to obtain the repaired soil.

2. Use of the ethylene glycol alkyl ether aqueous two-phase system according to claim 1 in the remediation of diesel-contaminated soil, characterized in that: The ethylene glycol alkyl ether aqueous two-phase system includes an ethylene glycol propyl ether aqueous two-phase system, an ethylene glycol butyl ether aqueous two-phase system, and a triethylene glycol butyl ester aqueous two-phase system.

3. Use of the ethylene glycol alkyl ether aqueous two-phase system according to claim 2 in the remediation of diesel-contaminated soil, characterized in that: The ethylene glycol alkyl ether aqueous two-phase system is an ethylene glycol butyl ether aqueous two-phase system.

4. Use of the ethylene glycol alkyl ether aqueous two-phase system according to claim 1 in the remediation of diesel-contaminated soil, characterized in that: The preparation steps of the ethylene glycol alkyl ether aqueous two-phase system are as follows: Step 1: Mix water and alkoxy alcohol in a beaker in proportion. Step 2: Add NaCl and dissolve it under sufficient stirring. Step 3: After sufficient stirring, the solution becomes turbid. After standing, two homogeneous phases appear. The top phase is rich in ethylene glycol alkyl ether, and the bottom phase is composed of water.

5. Use of the ethylene glycol alkyl ether aqueous two-phase system according to claim 1 in the remediation of diesel oil-contaminated soil, characterized in that: The temperature of the reaction is 20°C - 80°C; the solid-liquid ratio of the diesel-contaminated soil to the ethylene glycol alkyl ether aqueous two-phase system is 0.1 - 0.5; the stirring speed of the reaction is 200 - 1000 rpm / minute.

6. Use of the ethylene glycol alkyl ether aqueous two-phase system according to claim 5 in the remediation of diesel-contaminated soil, characterized in that: The temperature of the reaction is 20°C - 60°C; the solid-liquid ratio of the diesel-contaminated soil to the ethylene glycol alkyl ether aqueous two-phase system is 0.2; the stirring speed of the reaction is 600 rpm / minute.

7. Use of the ethylene glycol alkyl ether aqueous two-phase system according to claim 2 in the remediation of diesel-contaminated soil, characterized in that: The stirring time of the reaction is 0 - 27 minutes.

8. Use of the ethylene glycol alkyl ether aqueous two-phase system according to claim 7 in the remediation of diesel-contaminated soil, characterized in that: The stirring time of the ethylene glycol butyl ether aqueous two-phase system is 0 - 18 minutes; the stirring time of the ethylene glycol propyl ether aqueous two-phase system is 0 - 21 minutes, and the stirring time of the triethylene glycol butyl ester aqueous two-phase system is 0 - 27 minutes.

9. Use of the ethylene glycol alkyl ether aqueous two-phase system according to claim 2 in the remediation of diesel-contaminated soil, characterized in that: The ethylene glycol alkyl ether aqueous two-phase system can be reused; after being reused 7 times, the removal rate of diesel by the ethylene glycol butyl ether aqueous two-phase system is above 85.17%.

10. Use of the ethylene glycol alkyl ether aqueous two-phase system according to claim 1 in the remediation of diesel-contaminated soil, characterized in that: The germination rate of wheat in the repaired soil reaches 80% after 72 hours.

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