Synthesis method and application of pH reversible switch nonionic surfactant

Abstract

The invention provides a synthetic method of a pH reversible switch nonionic surfactant and regeneration cyclic utilization of the pH reversible switch nonionic surfactant after washing polycyclic aromatic hydrocarbon in soil. The synthetic method comprises the following steps: firstly, reacting polyethylene glycol with paratoluensulfonyl chloride to obtain polyethylene glycol p-toluenesulfonate; then the polyethylene glycol p-toluenesulfonate reacts with p-hydroxybenzaldehyde to obtain 4-polyethylene glycol-benzaldehyde, and the 4-polyethylene glycol-benzaldehyde and octylamine are combined in an alkaline aqueous solution to form the pH switch nonionic surfactant. The method disclosed by the invention has the advantages and beneficial effects that the pH switch nonionic surfactant obtained by the method disclosed by the invention is relatively good in water solubility, relatively high in surface activity and good in solubilizing capacity; the recovery rate of the pH switch nonionic surfactant in the wastewater obtained by washing the polycyclic aromatic hydrocarbon-containing soil with the obtained aqueous solution of the pH switch nonionic surfactant is not lower than 96.5%, and meanwhile, the removal rate of the polycyclic aromatic hydrocarbon in the soil is not lower than 99.9%.

Description

Technical Field

[0001] The invention relates to a method for synthesizing a pH reversible switch nonionic surfactant and the regeneration and recycling of the surfactant after washing polycyclic aromatic hydrocarbons in soil, belonging to the technical field of green chemical industry. Background Art

[0002] In recent years, the switch control of surfactants has attracted widespread attention from chemists, which has led to various types of switch surfactants becoming a research hotspot in the field of green chemical technology. Non-ionic surfactants are a type of fine chemicals with good water solubility, salt resistance and surface activity, but they also bring a problem: it is extremely difficult to recover this type of non-ionic surfactant from the aqueous solution after use. In order to solve this problem, the present invention synthesizes a pH reversible switch non-ionic surfactant using a reversible imine structure as a connecting structure, and its product is a water-soluble liquid at room temperature with good surface activity; the reversible imine structure has unique dynamic stability in water, and can reversibly break and connect under the induction of alkali and acid, respectively, so that the surfactant can be reversibly converted between the active state and the inactive state, and then with the help of its good water solubility, the regeneration and recycling of the pH reversible switch non-ionic surfactant can be achieved. A similar compound has been reported (Journal of Surfactants And Detergents, 2023, 26, 807-815), but the molecular structure and chemical properties of the compound are fundamentally different from those of the imine nonionic surfactant described in the present invention. The most important difference is the synthesis of the precursor polyethylene glycol aromatic aldehyde reported in the literature. Due to the diversity of the molecular structure of the raw material polyethylene glycol itself, there is significant uncertainty in the final product generated by the subsequent nucleophilic substitution reaction. In addition, the above literature does not involve the use of surfactants in washing polycyclic aromatic hydrocarbons in soil and recycling them. The beneficial effects brought by the present invention are that, in addition to effectively reducing the pH window and reducing the adverse effects of acid and alkali, the washing liquid prepared with the pH reversible switch nonionic surfactant obtained by the present invention is used to treat the soil contaminated by hydrophobic organic matter to obtain the washing waste liquid, and the acid is used to induce the imine bond to break, the surfactant is inactivated, and the solubilized pollutants are released and transferred to the oil phase, so that the pollutants and the surfactant in the wastewater after soil washing can be well separated, and the phenanthrene or other polycyclic aromatic hydrocarbon pollutants in the waste liquid are removed at a ratio of not less than 99.9%, and then the pH reversible switch nonionic surfactant is connected by alkali-induced imine bonds to achieve the regeneration of the pH reversible switch nonionic surfactant, and the regeneration ratio is not less than 96.5%. The structural formula of the pH reversible switch nonionic surfactant described in the present invention is shown as follows: . Summary of the invention

[0003] The purpose of the present invention is to provide a method for synthesizing a pH switch nonionic surfactant and regenerating and recycling it after washing polycyclic aromatic hydrocarbons in soil, in view of the current shortcomings of the switch nonionic surfactant in washing pollutants in soil and recycling.

[0004] A method for synthesizing a pH reversible switch nonionic surfactant and its regeneration and recycling after washing polycyclic aromatic hydrocarbons in soil, wherein polyethylene glycol is first reacted with p-toluenesulfonyl chloride to obtain polyethylene glycol p-toluenesulfonate, and then polyethylene glycol p-toluenesulfonate is reacted with p-hydroxybenzaldehyde to obtain 4-polyethylene glycol-benzaldehyde, 4-polyethylene glycol-benzaldehyde and octylamine are combined in an alkaline aqueous solution to form a pH switch nonionic surfactant, a certain concentration of pH switch nonionic surfactant aqueous solution is prepared, soil contaminated with polycyclic aromatic hydrocarbons is washed at room temperature to obtain a soil eluate, and then the soil eluate is adjusted to acidity with hydrochloric acid to crack the pH switch nonionic surfactant into the corresponding 4-polyethylene glycol-benzaldehyde and octylamine hydrochloride to achieve the regeneration and recycling of the pH switch nonionic surfactant. Its reaction formulas (1) to (3) are as follows:

[0005]

[0006] .

[0007] Furthermore, the polyethylene glycol is reacted with p-toluenesulfonyl chloride, the polyethylene glycol is any one of 300, 400 and 500 and a mixture thereof, the reaction temperature is in the range of -10 degrees Celsius to 10 degrees Celsius, the reaction solvent is dichloromethane, the molar ratio of polyethylene glycol to p-toluenesulfonyl chloride is 8:1, the reaction time is 20 to 26 hours, the reaction catalyst is a composition of magnesium oxide and SBA-15 in a mass ratio of 1:1 to 5, and the catalyst is added according to a molar ratio of magnesium oxide to polyethylene glycol of 0.1:1.

[0008] Furthermore, in the polyethylene glycol p-toluenesulfonate, the average polymerization degree of the polyethylene glycol is 10.

[0009] Furthermore, the polyethylene glycol p-toluene sulfonate reacts with p-hydroxybenzaldehyde at a reaction temperature of 90 degrees Celsius to 100 degrees Celsius, the reaction solvent is N,N-dimethylformamide, the molar ratio of polyethylene glycol p-toluene sulfonate to p-hydroxybenzaldehyde is 1:1.1-1.3, and the reaction time is 18-26 hours.

[0010] Furthermore, the 4-polyethylene glycol-benzaldehyde and octylamine are combined in an alkaline aqueous solution to form a pH switch nonionic surfactant, the molar ratio of 4-polyethylene glycol-benzaldehyde to octylamine is 1:1, the reaction temperature is room temperature, the alkaline aqueous solution refers to the aqueous solution whose pH is adjusted to greater than or equal to 10.0 with sodium hydroxide, and the yield of the pH switch nonionic surfactant is not less than 83.3%.

[0011] Furthermore, the provision of a certain concentration of the pH switch nonionic surfactant aqueous solution means that the concentration of the pH switch nonionic surfactant aqueous solution is greater than or equal to the critical micelle concentration of the pH switch nonionic surfactant.

[0012] Furthermore, in the soil eluate obtained by washing the soil contaminated with polycyclic aromatic hydrocarbons under room temperature conditions, the mass ratio of the pH switch non-ionic surfactant aqueous solution to the soil contaminated with polycyclic aromatic hydrocarbons is 4:1, the polycyclic aromatic hydrocarbons are any one of phenanthrene, benzoperylene and benzopyrene and their combinations, the mass ratio of polycyclic aromatic hydrocarbons in the soil is 10 mg to 500 mg per kilogram of soil, and the washing time is 12 hours.

[0013] Furthermore, the step of adjusting the soil eluate to acidity with hydrochloric acid refers to adjusting the pH of the eluate to no greater than 4.0 with hydrochloric acid at room temperature.

[0014] Furthermore, the method of cracking the pH switch nonionic surfactant into corresponding 4-polyethylene glycol-benzaldehyde and octylamine hydrochloride to achieve regeneration and recycling of the pH switch nonionic surfactant means that after adding 1 gram of tetradecane to the eluent, the pH of the eluent is adjusted to no more than 4.0 with hydrochloric acid at room temperature, the recovery rate of 4-polyethylene glycol-benzaldehyde and octylamine hydrochloride in the separated aqueous phase is not less than 96.5%, and then the pH of the obtained aqueous phase is adjusted to no less than 10.0 with sodium hydroxide, and the yield of the pH switch nonionic surfactant is not less than 83.3%.

[0015] The method of the present invention has the following advantages over the prior art: 1. The pH switch nonionic surfactant obtained by the present invention has good water solubility, high surface activity and good solubility-enhancing ability.

[0016] 2. The acid-base induced switch cycle conditions of the pH switch nonionic surfactant established by the present invention are mild and well controllable, and the yield of the pH switch nonionic surfactant is not less than 83.3%.

[0017] 3. The recovery rate of the pH switch nonionic surfactant in the wastewater obtained by washing the soil containing polycyclic aromatic hydrocarbons with the pH switch nonionic surfactant aqueous solution obtained by the present invention is not less than 96.5%, and the removal rate of polycyclic aromatic hydrocarbons in the soil is not less than 99.9%. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The hydrogen nuclear magnetic resonance spectrum of 4-polyethylene glycol-benzaldehyde in Example 1 of the present invention is shown in FIG.

[0019] Figure 2 This is the hydrogen nuclear magnetic resonance spectrum of the pH switch non-ionic surfactant in Example 4 of the present invention.

[0020] Figure 3 This is the surface activity diagram of the pH switch non-ionic surfactant in Example 4 of the present invention. DETAILED DESCRIPTION

[0021] The following is a further description of the process for synthesizing 4-polyethylene glycol-benzaldehyde and a pH switch nonionic surfactant according to the present invention, and the effects of regenerating and recycling the pH switch nonionic surfactant after washing polycyclic aromatic hydrocarbons in soil through specific examples.

[0022] Example 1: Synthesis of 4-polyethylene glycol-benzaldehyde Take PEG-400 256.5g (0.64mol), magnesium oxide 2.58g, SBA-15 molecular sieve 2.58g and 150mL dichloromethane and add them to a 1000mL three-necked flask, pass N2, and stir in an ice-water bath at 0 degrees Celsius. Take 9.16g (0.08mol) of p-toluenesulfonyl chloride and dissolve it in 100mL dichloromethane and slowly drop it into the flask. After the addition is completed, continue the reaction for 24h. After the reaction is completed, extract the reaction solution with 1.0 mol / L HCl solution (100mL), deionized water (2×100mL) and saturated brine (2×100mL). After drying the organic phase with anhydrous sodium sulfate, filter and evaporate the solvent to obtain 53.2g of colorless oily crude product polyethylene glycol p-toluenesulfonate.

[0023] Add 12.0g (0.115mol) of p-hydroxybenzaldehyde, 39.8g of potassium carbonate, and 300mL of N,N-dimethylformamide as solvent to a 1000mL three-necked flask, introduce N2, and stir in a 100°C oil bath. Take 53.2g of the crude product of polyethylene glycol p-toluenesulfonate and slowly drop it into the three-necked flask. After the addition is completed, continue the reaction for 24h. After the reaction is completed, remove N,N-dimethylformamide by rotary evaporation and dissolve the residue with ethyl acetate. After filtering and removing the insoluble matter, remove ethyl acetate by rotary evaporation to obtain the crude product of 4-polyethylene glycol-benzaldehyde. Mix dichloromethane and methanol (V二氯甲烷: V 甲醇 =20:1) as the eluent, and silica gel column chromatography was used to separate and purify the crude 4-polyethylene glycol-benzaldehyde to obtain 26.7 g of yellow oily liquid 4-polyethylene glycol-benzaldehyde with a yield of about 47.4%.

[0024] The hydrogen nuclear magnetic resonance spectrum of the product 4-polyethylene glycol-benzaldehyde is shown in Figure 1 ,Depend on Figure 1 It can be seen that the chemical shift of the aldehyde hydrogen signal peak is determined to be 9.87 ppm, and its integrated area is 1 for calculation. 7.86 ppm and 7.14 ppm are H signals on the benzene ring, and 4.54 ppm is the H signal of the terminal hydroxyl group. The integral ratio of the above signal areas is 1:4.08:1.09, which is very close to the theoretical value of the 4-polyethylene glycol-benzaldehyde structure. The polymerization chain length of ethylene glycol in the product 4-polyethylene glycol-benzaldehyde is about 10.

[0025] Example 2: Synthesis of 4-polyethylene glycol-benzaldehyde Take PEG-300 72.1g (0.24mol), magnesium oxide 0.97g, SBA-15 molecular sieve 4.83g and 50mL dichloromethane and add them to a 1000mL three-necked flask, pass N2, and stir at -10~-5 degrees Celsius. Take another 3.44g (0.03mol) p-toluenesulfonyl chloride and dissolve it in 100mL dichloromethane and slowly drop it into the flask. After the addition is completed, continue the reaction for 20h. After the reaction is completed, extract the reaction solution with 1.0 mol / L HCl solution (100mL), deionized water (2×100mL) and saturated brine (2×100mL). After drying the organic phase with anhydrous sodium sulfate, filter and evaporate to remove the solvent to obtain 55.6g of colorless oily crude product polyethylene glycol p-toluenesulfonate.

[0026] Add 12.0g (0.115mol) of p-hydroxybenzaldehyde, 39.8g of potassium carbonate, and 300mL of N,N-dimethylformamide as solvent to a 1000mL three-necked flask, introduce N2, and stir in a 90°C oil bath. Take 53.2g of the crude product of polyethylene glycol p-toluenesulfonate and slowly drop it into the three-necked flask. After the addition is completed, continue the reaction for 18h. After the reaction is completed, remove N,N-dimethylformamide by rotary evaporation and dissolve the residue with ethyl acetate. After filtering to remove the insoluble matter, remove ethyl acetate by rotary evaporation to obtain the crude product of 4-polyethylene glycol-benzaldehyde. Mix dichloromethane and methanol (V 二氯甲烷: V 甲醇 =20:1) was used as the eluent, and the crude 4-polyethylene glycol-benzaldehyde product was separated and purified by silica gel column chromatography to obtain 23.7 g of yellow oily liquid 4-polyethylene glycol-benzaldehyde with a yield of about 41.3%.

[0027] The H NMR spectrum of the product 4-polyethylene glycol-benzaldehyde is Figure 1 Exactly the same, the polymer chain length of ethylene glycol in the product 4-polyethylene glycol-benzaldehyde is about 10.

[0028] Example 3: Synthesis of 4-polyethylene glycol-benzaldehyde Take PEG-500 180.2g (0.36mol), magnesium oxide 1.45g, SBA-15 molecular sieve 6.67g and 175mL dichloromethane and add them to a 1000mL three-necked flask, pass N2, and stir at 0-10 degrees Celsius. Take another 3.44g (0.03mol) of p-toluenesulfonyl chloride, dissolve it in 100mL dichloromethane and slowly drop it into the flask. After the addition is completed, continue the reaction until the total reaction time is 26 hours. After the reaction is completed, the reaction solution is extracted with 1.0 mol / L HCl solution (100mL), deionized water (2×100mL) and saturated brine (2×100mL). After drying the organic phase with anhydrous sodium sulfate, filter and evaporate the solvent to obtain 135.9g of colorless oily crude product polyethylene glycol p-toluenesulfonate.

[0029] Add 12.0g (0.115mol) of p-hydroxybenzaldehyde, 39.8g of potassium carbonate, and 300mL of N,N-dimethylformamide as solvent to a 1000mL three-necked flask, introduce N2, and stir in a 90°C oil bath. Take 53.2g of the crude product of polyethylene glycol p-toluenesulfonate and slowly drop it into the three-necked flask. After the addition is completed, continue the reaction for 26 hours. After the reaction is completed, remove N,N-dimethylformamide by rotary evaporation and dissolve the residue with ethyl acetate. After filtering to remove the insoluble matter, remove ethyl acetate by rotary evaporation to obtain the crude product of 4-polyethylene glycol-benzaldehyde. Mix dichloromethane and methanol (V 二氯甲烷: V 甲醇 =20:1) as the eluent, and silica gel column chromatography was used to separate and purify the crude 4-polyethylene glycol-benzaldehyde to obtain 27.5 g of yellow oily liquid 4-polyethylene glycol-benzaldehyde with a yield of about 48.9%.

[0030] The H NMR spectrum of the product 4-polyethylene glycol-benzaldehyde is Figure 1 Exactly the same, the polymer chain length of ethylene glycol in the product 4-polyethylene glycol-benzaldehyde is about 10.

[0031] Example 4: pH switch nonionic surfactant and its properties Take 55.2g (0.1mol) of 4-polyethylene glycol-benzaldehyde and 12.92g of octylamine and add them to 250mL of water. Use sodium hydroxide to adjust the pH to 10.3 and make the volume to 500mL. Take a small amount of the resulting solution and use heavy water at a volume ratio of 1:100 to prepare a sample for hydrogen nuclear magnetic resonance measurement. Then use the corresponding concentration of 4-polyethylene glycol-benzaldehyde as a reference. The results are shown in the figure. Figure 2 ,Depend on Figure 2 The yield of pH switch nonionic surfactant was calculated by integration to be about 83.3%. Then the surface tension (γ, mN / m) and concentration logarithm (lgc) curves and interfacial tension (IFT, mN / m) and concentration logarithm (lgc) curves of pH switch nonionic surfactant were measured respectively. The results are shown in Figure 3 .Depend on Figure 3 The results show that the critical micelle concentration of the pH switch nonionic surfactant is about 1.01×10 -3 mol / L.

[0032] Take 44.16g (0.08mol) of 4-polyethylene glycol-benzaldehyde and 10.34g of octylamine and add them to 200mL of water, adjust the pH to 10.0 with sodium hydroxide and make the volume to 250mL. The obtained H NMR spectrum results are similar to Figure 2 Similarly, the yield of the pH-switching nonionic surfactant was calculated to be about 83.5%.

[0033] Take 16.56g (0.03mol) of 4-polyethylene glycol-benzaldehyde and 3.88g of octylamine and add them to 50mL of water, adjust the pH to 10.0 with sodium hydroxide and make the volume to 100mL. The obtained H NMR spectrum results are similar to Figure 2 Similarly, the yield of pH-switching nonionic surfactant was calculated to be about 83.3%.

[0034] Example 5: Recovery of pH switch nonionic surfactant This example uses the washing wastewater obtained by washing soil contaminated with phenanthrene (280 mg phenanthrene / kg soil) with a micellar aqueous solution of a pH switch nonionic surfactant as an example. 5.0 g of contaminated soil and 20.1 g of an aqueous solution of a pH switch nonionic surfactant (5.0×10 -3 mol / L, pH=10.0) was mechanically stirred at room temperature for 12 h, the soil was filtered to separate the soil eluate, 1 g of tetradecane was added to the filtrate and shaken evenly, then HCl was added to make the pH of the filtrate not higher than 4.0, and the oil and water phases were completely separated after standing for 12 h. The residual rate of phenanthrene was less than 0.02% by UV and fluorescence spectroscopy tests on the aqueous phase, and the recovery rates of 4-polyethylene glycol-benzaldehyde and octylamine hydrochloride were calculated to be 96.5%. The pH of the aqueous phase was adjusted to 10.0 with NaOH, and the yield of the pH switch non-ionic surfactant was detected to be 83.6%.

[0035] Example 6: Recovery of pH switch nonionic surfactant This example uses the washing wastewater obtained by washing soil contaminated with benzoperylene (500 mg benzoperylene / kg soil) with a micellar aqueous solution of a pH switch nonionic surfactant as an example. 10.0 g of contaminated soil and 40.3 g of an aqueous solution of a pH switch nonionic surfactant (8.4×10 -3 mol / L, pH=10.0) was mechanically stirred at room temperature for 12 h, the soil was filtered to separate the soil eluate, 1 g of tetradecane was added to the filtrate and shaken evenly, then HCl was added to make the pH of the filtrate not higher than 4.0, and the oil and water phases were completely separated after standing for 12 h. The residual rate of benzoperylene was lower than the detection limit by UV and fluorescence spectroscopy tests on the aqueous phase, and the recovery rates of 4-polyethylene glycol-benzaldehyde and octylamine hydrochloride were calculated to be 97.8%. The pH of the aqueous phase was adjusted to 10.0 with NaOH, and the yield of the pH switch non-ionic surfactant was detected to be 83.4%.

[0036] Example 7: Recovery of pH switch nonionic surfactant This example uses the washing wastewater obtained by washing soil contaminated with benzopyrene (10 mg benzopyrene / kg soil) with a micellar aqueous solution of a pH switch nonionic surfactant as an example. 5.0 g of contaminated soil and 20.3 g of an aqueous solution of a pH switch nonionic surfactant (6.8×10 -3 mol / L, pH=10.0) was mechanically stirred at room temperature for 12 h, the soil was filtered to separate the soil eluate, 1 g of tetradecane was added to the filtrate and shaken evenly, then HCl was added to adjust the pH of the filtrate to no more than 4.0, and the oil and water phases were completely separated after standing for 12 h. The residual rate of benzopyrene was lower than the detection limit by UV and fluorescence spectroscopy tests on the aqueous phase, and the recovery rates of 4-polyethylene glycol-benzaldehyde and octylamine hydrochloride were calculated to be 98.2%. The pH of the aqueous phase was adjusted to 10.0 with NaOH, and the yield of the pH switch non-ionic surfactant was detected to be 83.9%.

[0037] Example 8: Recovery of pH switch nonionic surfactant In this example, the washing wastewater obtained by washing soil contaminated by a mixture of phenanthrene, benzopyrene and benzoperylene (339 mg of a mixture of phenanthrene, benzopyrene and benzoperylene / kg of soil) with a micellar aqueous solution of a pH switch nonionic surfactant is used as an example. 5.0 g of the contaminated soil and 20.3 g of an aqueous solution of a pH switch nonionic surfactant (6.8×10 -3mol / L, pH=10.0) was mechanically stirred at room temperature for 12 h, the soil was filtered to separate the soil eluate, 1 g of tetradecane was added to the filtrate and shaken evenly, then HCl was added to adjust the pH of the filtrate to no more than 4.0, and the oil and water phases were completely separated after standing for 12 h. The residual rate of the mixture of phenanthrene, benzopyrene and benzoperylene was lower than the detection limit by UV and fluorescence spectroscopy tests on the aqueous phase. The recovery rate of 4-polyethylene glycol-benzaldehyde and octylamine hydrochloride was calculated to be 98.7%, the pH of the aqueous phase was adjusted to 10.0 with NaOH, and the yield of the pH switch non-ionic surfactant was detected to be 83.7%.

[0038] The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention. Any person familiar with the present invention can easily change or replace the components after the present invention is disclosed, and all technical improvements that do not depart from the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for synthesizing a pH reversible switch nonionic surfactant, characterized in that: First, polyethylene glycol is reacted with p-toluenesulfonyl chloride to obtain polyethylene glycol p-toluenesulfonate, and then polyethylene glycol p-toluenesulfonate is reacted with p-hydroxybenzaldehyde to obtain 4-polyethylene glycol-benzaldehyde. Finally, 4-polyethylene glycol-benzaldehyde is combined with octylamine in an alkaline aqueous solution to form a pH reversible switch nonionic surfactant.

2. The method for synthesizing the pH reversible switch nonionic surfactant according to claim 1, characterized in that: The structural formula of pH reversible switch nonionic surfactant is as follows 。 3. The method for synthesizing the pH reversible switch nonionic surfactant according to claim 1, characterized in that: The polyethylene glycol is any one of 300, 400 and 500 and a mixture thereof with an average molecular weight; the reaction temperature of the polyethylene glycol and p-toluenesulfonyl chloride is in the range of -10°C to 10°C; the reaction solvent is dichloromethane; the molar ratio of the polyethylene glycol to p-toluenesulfonyl chloride is 8:1; the reaction time is 20 to 26 hours; the reaction catalyst is a composition of magnesium oxide and SBA-15 in a mass ratio of 1:1 to 5; and the molar ratio of the magnesium oxide to the polyethylene glycol is 0.1:

1.

4. The method for synthesizing the pH reversible switch nonionic surfactant according to claim 1, characterized in that: The average polymerization degree of polyethylene glycol in the polyethylene glycol p-toluenesulfonate is 10.

5. The method for synthesizing the pH reversible switch nonionic surfactant according to claim 1, characterized in that: The polyethylene glycol p-toluene sulfonate reacts with p-hydroxybenzaldehyde at a reaction temperature of 90 degrees Celsius to 100 degrees Celsius, the reaction solvent is N,N-dimethylformamide, the molar ratio of polyethylene glycol p-toluene sulfonate to p-hydroxybenzaldehyde is 1:1.1-1.3, and the reaction time is 18-26 hours.

6. The method for synthesizing the pH reversible switch nonionic surfactant according to claim 1, characterized in that: The molar ratio of 4-polyethylene glycol-benzaldehyde to octylamine is 1:1, the reaction temperature is room temperature, and the alkaline aqueous solution refers to adjusting the pH of the aqueous solution to be greater than or equal to 10.0 using sodium hydroxide.

7. Use of the pH reversible switch nonionic surfactant according to any one of claims 1 to 6 in the regeneration cycle of polycyclic aromatic hydrocarbons in soil washing.

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