PH switch microemulsion capable of enhancing reversibility of acid-base switch and preparation method thereof

Abstract

The invention provides a pH switch microemulsion capable of enhancing the reversibility of an acid-base switch, which is characterized in that the microemulsion is a quaternary system formed by compounding an anionic surfactant and long-chain dimethyl tertiary amine which are combined according to an equal molar ratio to serve as a main surfactant, a short-chain fatty alcohol serving as a cosurfactant, alkane serving as an oil phase and water. Chemical reagents involved in the formula and the switch circulation process of the microemulsion for constructing the pH switch are commercially available reagents, extra synthesis is not needed, special equipment is not needed in the construction process, extra heating is not needed, the construction process is carried out at room temperature, and the cost is low. According to the creative strategy for increasing the cation size in the byproduct salt provided by the invention, the pH switch cycle reversibility of the O / W type microemulsion can be further greatly improved under the alternate action of hydrochloric acid and choline hydroxide; and W / O and B.C. Type micro-emulsions which cannot be reversibly switched and circulated under the alternate action of hydrochloric acid and sodium hydroxide can be switched and circulated.

Description

Technical Field

[0001] The invention relates to a method for constructing a switch microemulsion, in particular to a method for realizing a switch microemulsion by changing pH by acid and alkali and enhancing the reversibility of the acid-base switch process, belonging to the technical field of green chemical industry. Background Art

[0002] Microemulsion, also known as microemulsion, is a thermodynamically stable liquid phase mixed system composed of emulsifier, oil phase and water phase with a transparent or translucent appearance. Generally, a combination of ionic surfactants and short-chain alcohols is often used as an emulsifier for microemulsion. Compared with conventional emulsions, the content of surfactant in microemulsions is relatively high, and the adsorption film of emulsifiers on the oil-water interface is relatively soft, and its curvature can be positive, negative or equal to zero. Therefore, microemulsions have O / W type, bicontinuous type (BC type) and W / O type, while emulsions do not have BC type. In addition, the demulsification process of microemulsions is also more difficult than that of conventional emulsions. Microemulsions can solubilize both water-soluble substances and oil-soluble substances, and can also solubilize both water-soluble and oil-soluble substances at the same time. From the perspective of solubilization capacity, the solubilization capacity of microemulsions is greater than that of micelles. In summary, microemulsions have a wide range of important uses in industrial and agricultural production and daily life. However, after the effectiveness of microemulsions is fully exerted in the actual process, especially after the application related to the solubilizing properties of microemulsions is completed, people always hope to have a simple method to achieve the demulsification of microemulsions, so as to separate the solubilized substances therefrom. In addition, from the perspective of sustainable development, after the solubilized substances are separated from the demulsified microemulsions, if the remaining surfactants, oil phases and water phases can be efficiently recovered and reused, it is undoubtedly an important embodiment of saving resources and reducing environmental emissions. For this reason, scholars at home and abroad have proposed the concept of switch microemulsions. The so-called switch microemulsion is a microemulsion that can reversibly realize the demulsification and re-microemulsification cycle conversion of microemulsions under the action of certain environmental or internal factors. The switch microemulsions reported in the literature mainly include switch microemulsions under the action of chemical and / or physical factors such as CO2 / N2, redox, light, heat and physical magnetic fields. In fact, reversibly changing the pH of the system under the alternating action of acid and alkali is a low-cost, rapid switching process and wide application of chemical means. However, there has been no literature report on a microemulsion that can achieve microemulsion switching by reversibly changing pH based on the alternating action of acid and alkali. In view of this situation, the present invention provides a method for constructing a pH switch microemulsion and enhancing the reversibility of the acid-base switch, using an equimolar combination of anionic surfactants and long-chain dimethyl tertiary amines as the main surfactant, short-chain fatty alcohols as the co-surfactant, alkanes as the oil phase, and water to form a quaternary system, systematically studying its phase diagram structure, obtaining the phase diagram region of the pH switch microemulsion, and then using hydrochloric acid to reduce the pH of the microemulsion to achieve rapid demulsification, and then using sodium hydroxide to increase the pH of the demulsification system to achieve rapid recovery of the microemulsion, and then carefully analyzing the main factors that hinder the cyclic reversibility of the pH switch of the microemulsion obtained by the present invention, it is found that the byproduct salt NaCl formed by the alternating action of hydrochloric acid and sodium hydroxide is the most important hindering factor, and a strategy of increasing the size of the cations in the byproduct salt is creatively proposed to achieve further substantial improvement in the cyclic reversibility of the pH switch of the microemulsion obtained by the present invention. Summary of the invention

[0003] The purpose of the present invention is to provide a method for constructing a pH switch microemulsion and enhancing the reversibility of the acid-base switch in view of the current technical status that there is no literature report on microemulsions based on the reversible change of pH by alternating acid and base to achieve microemulsion switching.

[0004] A method for constructing a pH switch microemulsion and enhancing the reversibility of an acid-base switch comprises the following steps: using an anionic surfactant and a long-chain dimethyl tertiary amine in an equimolar ratio as a main surfactant, using a short-chain fatty alcohol as a co-surfactant, using an alkane as an oil phase, and then compounding with water to form a quaternary system, systematically studying its phase diagram structure, obtaining the phase diagram region of the pH switch microemulsion, and then using hydrochloric acid to reduce the pH of the microemulsion to achieve rapid demulsification, and then using sodium hydroxide to increase the pH of the demulsification system to achieve rapid recovery of the microemulsion, and then carefully analyzing the main factors hindering the cyclic reversibility of the pH switch of the microemulsion obtained by the present invention, finding that the byproduct salt NaCl formed by the alternating action of hydrochloric acid and sodium hydroxide is the most important hindering factor, and creatively proposing a strategy of increasing the size of cations in the byproduct salt, so as to achieve further substantial improvement in the cyclic reversibility of the pH switch of the microemulsion obtained by the present invention.

[0005] Furthermore, the anionic surfactant and the long-chain dimethyl tertiary amine are used as the main surfactant in an equimolar ratio, the anionic surfactant refers to sodium dodecyl sulfate (SDS), and the long-chain dimethyl tertiary amine refers to N,N-dimethyl-N-dodecyl tertiary amine (C 12 A).

[0006] Furthermore, the short-chain fatty alcohol is used as a co-surfactant and the alkane is used as the oil phase, the short-chain fatty alcohol is any one of n-butanol, n-pentanol and n-hexanol, and the alkane refers to n-heptane.

[0007] Furthermore, the system studies its phase diagram structure, which refers to the phase diagram of SDS and C 12 A composition in an equal molar ratio (denoted as SDS-C 12 A) A pseudo-ternary phase diagram formed by a composition of any one of n-butanol, n-pentanol and n-hexanol in a mass ratio of 1:2 as an emulsifier (denoted as Em), n-heptane as an oil phase and H2O.

[0008] Furthermore, the step of lowering the pH of the microemulsion with hydrochloric acid to achieve rapid demulsification, and then raising the pH of the demulsified system with sodium hydroxide to achieve rapid recovery of the microemulsion means lowering the pH of the obtained microemulsion to 7.0 with hydrochloric acid to achieve complete separation of the oil-water phase within 5 minutes, and raising the pH of the demulsified system to 10.5 with sodium hydroxide to achieve the re-formation of a single-phase microemulsion within 5 minutes.

[0009] Furthermore, the detailed analysis of the main factors hindering the cyclic reversibility of the microemulsion pH switch obtained in the present invention is to analyze the influence of the percentage of water and salt in the single-phase microemulsion system on the size of the microemulsion droplets and the influence of the type of salt on the proportion of the single-phase microemulsion region area in the total area of ​​the pseudo-ternary phase diagram.

[0010] Furthermore, the strategy of creatively proposing to increase the size of cations in the by-product salt to further substantially improve the pH switch cycle reversibility of the microemulsion obtained by the present invention means replacing sodium hydroxide with choline hydroxide. The number of reversible "demulsification-re-microemulsification" switch cycles of the microemulsion obtained by the present invention under the alternating action of hydrochloric acid and choline hydroxide is significantly increased compared with the number of reversible "demulsification-re-microemulsification" switch cycles under the alternating action of hydrochloric acid and sodium hydroxide.

[0011] Furthermore, the strategy of creatively proposing to increase the size of cations in the by-product salt is used to further substantially improve the pH switch cycle reversibility of the microemulsion obtained by the present invention, which means that choline hydroxide is used instead of sodium hydroxide. The microemulsion obtained by the present invention can reversibly switch the "demulsification-re-microemulsification" switch cycle under the alternating action of hydrochloric acid and choline hydroxide to fully cover the types of microemulsions including W / O type, BC type and O / W type.

[0012] The method of the present invention has the following advantages over the prior art: 1. The chemical reagents involved in the construction of the pH switch microemulsion formula provided by the present invention are all commercially available reagents, and no special additional synthesis is required. The construction process does not require special equipment or additional heating, and can be carried out at room temperature, which is relatively low in cost.

[0013] 2. The acid and base involved in the switching process of the pH switch microemulsion provided by the present invention are all commercially available reagents, and no special additional synthesis is required. The switching process does not require special equipment or additional heating, and is carried out at room temperature. The switching response process is extremely rapid (the switching response process does not exceed 5 minutes), so the cost is relatively low.

[0014] 3. The creative strategy of increasing the size of cations in the by-product salt provided by the present invention can not only achieve a further substantial improvement in the reversibility of the pH switch cycle of the obtained O / W type microemulsion by alternating hydrochloric acid and choline hydroxide, but also can achieve the switch cycle of W / O and BC type microemulsions that cannot be reversibly switched by alternating hydrochloric acid and sodium hydroxide, both of which can be carried out at room temperature and with extremely rapid response speed (the switching response process does not exceed 5 minutes).

[0015] 4. The pH switch microemulsion provided by the present invention has a very thorough demulsification degree. After the demulsification, the chemical oxygen demand value of the wastewater obtained after conventional treatment with ion exchange resin and activated carbon does not exceed 14.1 mg O2 / L. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 SDS-C for Example 1 of the present invention 12 A-Pseudo-ternary phase diagram of n-butanol-n-heptane-H2O system.

[0017] Figure 2 SDS-C for Example 1 of the present invention 12 A- n-butanol-n-heptane-H2O microemulsion along the dilution line with a mass ratio of Em to heptane of 9:1, and the conductivity of the microemulsion was measured ( κ , mS / cm) and H2O mass percentage ( F W ,%).

[0018] Figure 3 SDS-C for Example 2 of the present invention 12 A-Pseudo-ternary phase diagram of n-pentanol-n-heptane-H2O system.

[0019] Figure 4 SDS-C for Example 2 of the present invention 12 A-Pseudo-ternary phase diagram of n-hexanol-n-heptane-H2O system.

[0020] Figure 5 Example 3 SDS-C of the present invention 12 A-n-Butanol-n-heptane-H2O microemulsion (sample III) (A) The volume percentage of the upper oil phase precipitated at different pH values ​​and the actual appearance at pH=10.5 (B) and pH=7.0 (C).

[0021] Figure 6 Example 3 SDS-C of the present invention 12 A- Cryo-TEM images of the upper oil phase (B) and lower water phase (C) of n-butanol-n-heptane-H2O microemulsion (sample III) after demulsification at pH = 10.5 (A) and when the pH was adjusted to 7.0 with hydrochloric acid, and the microemulsion droplets when the pH was adjusted to 10.5 again with sodium hydroxide (D).

[0022] Figure 7 Example 3 SDS-C of the present invention 12 A- Droplet size of n-butanol-n-heptane-H2O microemulsion (sample III) during the microemulsion switching process under the alternating action of hydrochloric acid and sodium hydroxide.

[0023] Figure 8 Example 5 SDS-C 12 A- Droplet size of n-butanol-n-heptane-H2O microemulsion (sample III) during the microemulsion switching process under the alternating action of hydrochloric acid and choline hydroxide, respectively.

[0024] Fig. 9 Example 5 SDS-C 12 A-n-Butanol-n-heptane-H2O-NaCl system (A) and SDS-C 12 A- Pseudo-ternary phase diagram of the n-butanol-n-heptane-H2O-choline chloride (ChCl) system (B). DETAILED DESCRIPTION

[0025] The pseudo-ternary phase diagram of the quaternary system of the present invention, the microemulsion pH switch, the reversibility of the microemulsion pH switch, the microemulsion droplet size during the switching process and the wastewater treatment effect are further described below through specific examples.

[0026] Example 1: SDS-C 12 A-n-Butanol-n-heptane-H2O system SDS-C 12 Composition A is the main surfactant, n-butanol is the auxiliary surfactant, and SDS-C 12 The composition of composition A and n-butanol in a mass ratio of 1:2 is the emulsifier (Em), n-heptane (heptane) is the oil phase, H2O is the water phase, and the pseudo-ternary phase diagram is constructed according to the Shah method. The results are shown in Figure 1 . Figure 1 The middle oblique line area is the single-phase microemulsion area, accounting for 41.2% of the total area of ​​the pseudo-ternary phase diagram. Figure 1 The dilution line with a mass ratio of Em to heptane of 9:1 was used to measure the conductivity of the microemulsion ( κ , mS / cm) and H2O mass percentage ( F W , %), the results are shown in Figure 2 .Depend on Figure 2 It can be seen that F W In the range of 7.4% to 44.1%, microemulsion belongs to W / O type. F W In the range of 44.1% to 63.2%, microemulsions belong to BC type. F W In the range of 63.2% to 99.1%, microemulsions belonged to the O / W type. Figure 1 and Figure 2 The data points marked in the figure are recorded as samples I to III, which are the corresponding types of microemulsions, and their specific compositions are shown in Table 1.

[0027] Table 1 Figure 1 and Figure 2 Specific material composition of samples I to III

[0028] Example 2: SDS-C12 A-n-pentanol-n-heptane-H2O and SDS-C 12 A-n-hexanol-n-heptane-H2O system SDS-C 12 Composition A is the main surfactant, n-pentanol is the auxiliary surfactant, and SDS-C 12 The composition of composition A and n-pentanol in a mass ratio of 1:2 is the emulsifier (Em), n-heptane (heptane) is the oil phase, H2O is the water phase, and the pseudo-ternary phase diagram is constructed according to the Shah method. The results are shown in Figure 3 . Figure 3 The middle oblique line area is the single-phase microemulsion area, accounting for 29.7% of the total area of ​​the pseudo-ternary phase diagram.

[0029] SDS-C 12 Composition A is the main surfactant, n-hexanol is the auxiliary surfactant, and SDS-C 12 The composition of composition A and n-hexanol in a mass ratio of 1:2 is the emulsifier (Em), n-heptane (heptane) is the oil phase, H2O is the water phase, and the pseudo-ternary phase diagram is constructed according to the Shah method. The results are shown in Figure 4 . Figure 4 The middle oblique line area is the single-phase microemulsion area, which accounts for 22.3% of the total area of ​​the pseudo-ternary phase diagram.

[0030] The pseudo-ternary phase diagram obtained from Example 1 and Example 2 ( Figure 1 , Figure 3 and Figure 4 ) The results show that SDS-C 12 A- Area of ​​n-butanol-n-heptane-H2O microemulsion region ( Figure 1 , 41.2%), SDS-C 12 The area of ​​A-n-pentanol-n-heptane-H2O microemulsion region is second ( Figure 3 , 29.7%), while SDS-C 12 A- Area of ​​n-hexanol-n-heptane-H2O microemulsion region ( Figure 4 , 22.3%) minimum. Description SDS-C 12 The compositions of the A equal molar ratio and n-butanol, n-pentanol and n-hexanol in a mass ratio of 1:2 all showed good microemulsification properties and were able to emulsify the mixture of n-heptane and H2O to form a single-phase microemulsion. 12 A-n-butanol-n-heptane-H2O microemulsion has the largest area ( Figure 1 , 41.2%), and the subsequent examples were all analyzed by SDS-C 12The three types of microemulsion samples corresponding to A-n-butanol-n-heptane-H2O microemulsion (samples I to III, Table 1) are specific microemulsion examples, and specific descriptions of pH switch, switch reversible cycle, switch reversibility enhancement and wastewater treatment effect are carried out.

[0031] Example 3: SDS-C 12 A-pH Switch Response of n-Butanol-n-Heptane-H2O Microemulsion SDS-C 12 Taking sample III of A-n-butanol-n-heptane-H2O microemulsion as an example (scale 25 g), the pH of sample III was adjusted with hydrochloric acid to observe the demulsification of sample III, and the volume percentage of the upper oil phase precipitated at different pH values ​​was calculated ( F up ,%), the results are shown in Figure 5 A. By Figure 5 A shows that sample III starts to demulsify at pH about 10.5 and completely demulsifies at pH about 7.0. Therefore, pH values ​​of 10.5 and 7.0 are selected as the window values ​​of the microemulsion pH switch cycle to investigate the switch response of sample III at pH 10.5 and 7.0. Sodium hydroxide is used to adjust the pH of sample III after demulsification to 10.5 to observe whether microemulsion is formed. The results are shown in Figure 5 B and Figure 5 C. By Figure 5 B and Figure 5 C shows that the clear and transparent sample III ( Figure 5 B) After adjusting the pH to 7.0 with hydrochloric acid, the emulsion demulsified within 2 minutes ( Figure 5 C, and then adjust the pH to 10.5 with sodium hydroxide and restore to a clear and transparent microemulsion within 1.5 minutes ( Figure 5 B), thereby achieving a reversible switch of demulsification and recovery.

[0032] Then, cryo-TEM was used to observe the size of microemulsion droplets. From the perspective of the size of microemulsion droplets, the reversibility of the switching response process of sample III under pH induction was investigated. Figure 6 .Depend on Figure 6 A shows that the radius of the oil droplets in sample III is approximately around 18.7 nm, and the upper oil phase after demulsification ( Figure 6 B) and the lower aqueous phase ( Figure 6 C) showed no droplets or aggregates, indicating that sample III was completely demulsified when the pH was adjusted to 7.0 with hydrochloric acid. When the pH was adjusted to 10.5 with sodium hydroxide, the radius of the microemulsion droplets obtained after one switching cycle was about 21.4 nm ( Figure 6 D). It can be seen that from the perspective of the size of the microemulsion droplets, the reversibility of the pH switch cycle of the microemulsion (sample III) in this embodiment is very good. In addition, the number of switch cycles in this embodiment can reach 4 times ( Figure 7 ).Depend on Figure 7 It can be seen that as the number of cycles increases, the size of the microemulsion droplets also increases, and a single-phase microemulsion cannot be obtained in the fifth cycle. The reason for the increase in the size of the microemulsion droplets is the formation and accumulation of byproduct water and byproduct NaCl during the acid-base alternation process. The effect of the formation and accumulation of NaCl on the increase in the size of the microemulsion droplets is more obvious than the formation and accumulation of byproduct water. Therefore, it is inferred that the accumulation of byproduct salts is the main obstacle to the limited number of cycles of the microemulsion pH switch.

[0033] Similarly, in the case of switching cycles triggered by the alternating action of hydrochloric acid and sodium hydroxide, both sample I (scale 25 g) and sample II (scale 25 g) could achieve complete demulsification within 3 min at pH = 7.0, but single-phase microemulsions could not be obtained when the pH was adjusted to 10.5 with sodium hydroxide.

[0034] Example 4: SDS-C 12 A-pH Switch Response of n-Butanol-n-Heptane-H2O Microemulsion SDS-C 12 Taking samples I to III of A-n-butanol-n-heptane-H2O microemulsion as an example, the pH was adjusted to 7.0 and 10.5 with hydrochloric acid and sodium hydroxide, and the demulsification and recovery of the microemulsion were observed. The experimental results of different scales are statistically shown in Table 2.

[0035] Table 2 Results of on-off cycles of samples I to III of different scales triggered by hydrochloric acid and sodium hydroxide

[0036] Example 5: SDS-C 12 A-pH Switch Response of n-Butanol-n-Heptane-H2O Microemulsion SDS-C 12 Taking sample III of A-n-butanol-n-heptane-H2O microemulsion as an example (scale 25 g), hydrochloric acid and choline hydroxide were used to adjust the pH to 7.0 and 10.5, and the demulsification and recovery of the microemulsion were observed. The demulsification time and microemulsion recovery time were very similar to those of sample III of the same scale when the pH was adjusted by hydrochloric acid and sodium hydroxide, and the demulsification and microemulsion recovery time did not exceed 5 minutes. In addition, the number of pH switching cycles of sample III increased sharply to 11, and the results are shown in Figure 8 It can be seen that the creative strategy of increasing the size of cations in the by-product salt provided by the present invention has a significant effect on improving the reversibility of the pH switch cycle of the microemulsion.

[0037] To avoid the limitation of single sample (Sample III) test, SDS-C 12 A-n-Butanol-n-heptane-H2O-NaCl and SDS-C12 A- Pseudo-ternary phase diagram of n-butanol-n-heptane-H2O-choline chloride (ChCl) system, the results are shown in Fig. 9 .Depend on Fig. 9 It can be seen that SDS-C 12 A-n-Butanol-n-heptane-H2O-NaCl and SDS-C 12 A-n-butanol-n-heptane-H2O-ChCl system can form a single-phase microemulsion, among which SDS-C 12 The area of ​​the A-n-butanol-n-heptane-H2O-NaCl single-phase microemulsion region accounts for about 1.7% of the total area of ​​the ternary phase diagram, while the SDS-C 12 The area of ​​the A-n-butanol-n-heptane-H2O-ChCl single-phase microemulsion region accounts for about 14.3% of the total area of ​​the ternary phase diagram, which further reveals the scientific connotation of the creative strategy provided by the present invention to increase the size of cations in the byproduct salt to improve the reversibility of the microemulsion pH switch cycle. Fig. 9 The results also suggest that sample I and sample II can also switch reversibly to a certain extent under the alternating action of hydrochloric acid and choline hydroxide. The experimental results show that the number of switching cycles of sample I under the alternating action of hydrochloric acid and choline hydroxide is 1, while the number of switching cycles of sample II under the alternating action of hydrochloric acid and choline hydroxide is 4. This result not only further reveals that the creative strategy of increasing the size of cations in the byproduct salt to enhance the reversibility of the microemulsion pH switch cycle provided by the present invention is applicable to O / W type microemulsions, but also to W / O type and BC type microemulsions, thereby achieving full coverage of the reversible pH switch cycles of the three types of microemulsions.

[0038] Example 6: SDS-C 12 pH switch response of A-n-butanol-n-heptane-H2O microemulsion under the action of hydrochloric acid and choline hydroxide SDS-C 12 Taking samples I to III of A-n-butanol-n-heptane-H2O microemulsion as an example, the pH was adjusted to 7.0 and 10.5 with hydrochloric acid and choline hydroxide, and the demulsification and recovery of the microemulsion were observed. The experimental results of different scales are statistically summarized in Table 3.

[0039] Table 3 Results of on-off cycles of samples I to III of different scales triggered by hydrochloric acid and choline hydroxide

[0040] Example 7: SDS-C 12 A-Effect of pH switch response on wastewater treatment of n-butanol-n-heptane-H2O microemulsion In this example, the effects of the water phase treatment obtained after the samples were demulsified in Example 4 and Example 6 were randomly selected. 10 grams of the water phase was taken and treated with anion exchange resin and activated carbon respectively, wherein the mass ratio of the water phase to the resin was 1:1, and the mass ratio of the water phase to the activated carbon was 1:0.5. The treatment time was 0.5 hour and 1 hour respectively. After the treatment, the chemical oxygen demand value of the water was measured. The results are shown in Table 4.

[0041] Table 4 Chemical oxygen demand results of water phase treatment obtained from different batches of microemulsion switches

[0042] The results in Table 4 further illustrate that the demulsification degree of the pH switch microemulsion provided by the present invention is very thorough, and the chemical oxygen demand value of the wastewater obtained after demulsification does not exceed 14.1 mg O2 / L after conventional treatment with ion exchange resin and activated carbon, indicating that the method for constructing a pH switch microemulsion and enhancing the reversibility of the acid-base switch provided by the present invention is very effective and has the advantages of being green and sustainable.

[0043] 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 pH switch microemulsion capable of enhancing the reversibility of acid-base switching, characterized in that: The microemulsion is a quaternary system formed by combining anionic surfactant and long-chain dimethyl tertiary amine in an equimolar ratio as the main surfactant, short-chain fatty alcohol as the auxiliary surfactant, alkane as the oil phase, and water.

2. The pH switch microemulsion according to claim 1, characterized in that: The anionic surfactant is sodium lauryl sulfate, and the long-chain dimethyl tertiary amine is N,N-dimethyl-N-dodecyl tertiary amine.

3. The pH switch microemulsion according to claim 1, characterized in that: The short-chain fatty alcohol is any one of n-butanol, n-pentanol and n-hexanol.

4. The pH switch microemulsion according to claim 1, characterized in that: The alkane refers to n-heptane.

5. A method for preparing a pH switch microemulsion capable of enhancing the reversibility of an acid-base switch, characterized in that: The method comprises preparing a main surfactant and an auxiliary surfactant into an emulsifier in a mass ratio of 1:2, taking alkanes as an oil phase and water as an aqueous phase, and constructing a pseudo-ternary phase diagram.

6. The pH switch microemulsion according to any one of claims 1 to 5, characterized in that: The pH switch microemulsion can realize a reversible switch of demulsification and re-restoration.

7. The pH switch microemulsion according to claim 6, characterized in that: Acid is used to lower the pH of the pH switch microemulsion to achieve rapid demulsification, and then alkali is used to increase the pH of the demulsification system to achieve rapid recovery of the microemulsion. The acid is hydrochloric acid, and the alkali is sodium hydroxide or choline hydroxide.

8. The pH switch microemulsion according to claim 7, characterized in that: The rapid demulsification refers to lowering the pH of the obtained microemulsion to 7.0 with hydrochloric acid to achieve complete separation of the oil-water two phases within 5 minutes, and the rapid recovery refers to raising the pH of the demulsified system to 10.5 with sodium hydroxide to achieve the re-formation of a single-phase microemulsion within 5 minutes.

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