Degradable gemini betaine surfactant and preparation method thereof

Abstract

This invention discloses a biodegradable geminate betaine surfactant and its preparation method, comprising: constructing a surfactant-free microemulsion system with a long-chain tertiary amine as the oil phase; then adding sodium 3-chloro-2-hydroxypropanesulfonate dropwise at 70-100℃; after the reaction, removing the solvent and recrystallizing; mixing hydroxypropyl sulfobetaine with maleic anhydride and reacting at 100-180℃ for 4-8 hours under the action of molecular sieves and catalysts; after the reaction, removing the molecular sieves yields the surfactant, with a yield of over 95%. The surfactant of this invention can dissolve rapidly at lower temperatures without any co-solvents; it has stronger self-assembly ability and higher salt tolerance; it can thicken aqueous solutions without any additives, exhibiting good sand-carrying capacity and oil-degrading ability; and it demonstrates excellent high-temperature thickening ability and biodegradability. It can be used in fracturing and plugging operations during oil and gas field development.

Description

Technical Field

[0001] This invention belongs to the field of fine chemicals, specifically relating to a biodegradable gemini betaine surfactant and its preparation method. Background Technology

[0002] Surfactants are important fine chemical products, often referred to as "industrial MSG." With societal development and increasingly prominent environmental issues, the demand for "green, functional, high-quality, and high-value" surfactants is growing stronger. However, surfactants that simultaneously possess multiple functions such as high interfacial activity and biodegradability are still relatively rare.

[0003] Betaine-based surfactants are surfactants based on betaine. Their molecules contain a quaternary ammonium cationic moiety and a zwitterionic moiety consisting of a negatively charged ion. The anionic moiety is typically a carboxylate, sulfonate, sulfate, or phosphate salt. The interaction of the cation and anion charges forms an inner salt. Therefore, within its isoelectric point region, there is no sudden drop in solubility leading to precipitation. The unique structure of betaine surfactants results in excellent properties, such as good resistance to hard water, antibacterial properties, good biocompatibility, low irritation, and good foaming properties. Furthermore, betaine surfactants have good UV resistance, effectively preventing the degradation of organic matter in liquids by ultraviolet light. Their low oil-water interfacial tension is of great value in improving reservoir displacement efficiency in oil extraction. Due to these unique structures and properties, they have wide applications in various fields.

[0004] Compared to traditional single surfactants, gemini surfactants exhibit lower critical micelle concentrations (CMC), better solubilization, lower Krafft points, and excellent anti-deposition and calcium soap dispersibility. Gemini betaine surfactants, on the other hand, combine the superior properties of both gemini and betaine surfactants, possessing high surface activity, excellent synergistic effects, hard water resistance, easy biodegradability, and low toxicity. They hold significant application potential in numerous fields such as seepage recovery and foam drainage.

[0005] However, the synthesis methods and performance of current geminate betaine surfactants still need improvement. Summary of the Invention

[0006] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0007] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0008] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a biodegradable geminate betaine surfactant.

[0009] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a biodegradable gemini betaine surfactant, wherein the structure of the gemini surfactant is shown in formula (1):

[0010]

[0011] Wherein, R1 is a saturated alkyl C n H 2n+1 , saturated alkylamidopropyl C n-1 H 2n-1 CONHCH2CH2CH2, unsaturated alkylamidopropyl C n-1 H 2n-3 Any one of CONHCH2CH2CH2, where n = 10 to 20;

[0012] R2 is any one of methyl, ethyl, or propyl.

[0013] Another object of the present invention is to overcome the shortcomings of the prior art and provide a method for preparing a biodegradable gemini betaine surfactant, comprising,

[0014] Preparation of hydroxypropyl sulfobetaine: Long-chain tertiary amine, deionized water and organic solvent are mixed to form a transparent surfactant-free microemulsion system;

[0015] Then, slowly add 20-30 parts of sodium 3-chloro-2-hydroxypropanesulfonate at 70-100℃ and continue stirring for 2-8 hours. After the reaction is complete, remove the solvent, collect the crude product, wash it three times with acetone, and dry it under vacuum to obtain the hydroxypropyl sulfobetaine surfactant.

[0016] The structural formula of the hydroxypropyl sulfobetaine is shown in formula (2):

[0017]

[0018]

[0019] Preparation of gemini-type betaine surfactant: Hydroxypropyl sulfobetaine was mixed with maleic anhydride and reacted at 100–180 °C for 4–8 hours in the presence of molecular sieves and catalysts.

[0020] After the reaction is complete, the molecular sieve is removed by filtration to obtain the geminate betaine surfactant.

[0021] The yield, as determined by acid value analysis, can reach over 95%.

[0022] As a preferred embodiment of the preparation method described in this invention, the preparation of hydroxypropyl sulfonate betaine comprises, by weight percentage, 20 parts of long-chain tertiary amine, 20 parts of deionized water, and 40 parts of organic solvent.

[0023] Among them, long-chain tertiary amines, water and organic solvents can form surfactant-free microemulsions containing abundant nanodroplets, providing a huge reaction interface for the reaction of tertiary amines with sodium 3-chloro-2-hydroxypropanesulfonate.

[0024] As a preferred embodiment of the preparation method described in this invention, the preparation of hydroxypropyl sulfonate betaine includes one or more of ethanol, isopropanol, hexanediol, pentanediol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, and diethylene glycol monoethyl ether.

[0025] As a preferred embodiment of the preparation method described in this invention, the preparation of a gemini-type betaine surfactant involves a molar ratio of hydroxypropyl sulfobetaine to maleic anhydride of 2 to 3:1.

[0026] In a preferred embodiment of the preparation method described in this invention, the molar ratio of hydroxypropyl sulfobetaine to maleic anhydride is 2.2:1.

[0027] As a preferred embodiment of the preparation method described in this invention, the preparation of a gemini-type betaine surfactant is wherein the molecular sieve is a 4A or 5A molecular sieve.

[0028] As a preferred embodiment of the preparation method described in this invention, the preparation of a gemini-type betaine surfactant includes a catalyst selected from p-toluenesulfonic acid, concentrated sulfuric acid, glacial acetic acid, sodium acetate, and sodium bisulfite, or a combination thereof.

[0029] As a preferred embodiment of the preparation method described in this invention, the preparation of the gemini betaine surfactant involves using a catalyst at an amount of 0.2 to 1.0% of the mass of maleic anhydride.

[0030] As a preferred embodiment of the preparation method described in this invention, the gemini betaine surfactant has excellent high-temperature thickening ability and oil-induced gel breaking ability, and is used as a clean fracturing fluid for oil and gas field development.

[0031] Beneficial effects of this invention:

[0032] (1) In the preparation of hydroxypropyl sulfobetaine, the present invention uses a water-in-oil microemulsion droplet with a long-chain tertiary amine as the oil phase as the reaction medium. By adding another reactant, sodium 3-chloro-2-hydroxypropanesulfonate, the two reactants meet at the flexible interface of the non-surface-active microemulsion droplet. Due to the interfacial effect of the nanodroplet, the collision frequency between molecules increases, the reaction rate increases, and the yield increases.

[0033] (2) In the preparation of the gemini betaine surfactant, the present invention introduces a molecular sieve, which can act as a water-binding agent to capture the water produced by the esterification reaction of hydroxypropyl sulfobetaine and maleic anhydride, and promote the reaction to proceed to the product; it can also provide a confined reaction space for the esterification reaction of hydroxypropyl sulfobetaine and maleic anhydride, and the two reactants meet in the molecular sieve channel. Under the nano-confining effect, the yield is significantly improved.

[0034] (3) The gemini betaine surfactant of the present invention can dissolve rapidly at a lower temperature without any co-solvent, making it convenient to prepare on-site and simple to operate. The gemini betaine surfactant prepared by the present invention has stronger self-assembly ability and higher salt resistance compared with traditional gemini surfactants. It can thicken aqueous solutions without any additives, exhibiting good sand-carrying ability and oil-breaking ability. It also exhibits excellent high-temperature thickening ability and biodegradability.

[0035] (4) The gemini betaine surfactant prepared by this invention has a stronger self-assembly ability, a lower Craft temperature, a higher biodegradability, and a stronger thickening ability compared with traditional single-chain betaine surfactants. Attached Figure Description

[0036] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0037] Figure 1 The hydrogen nuclear magnetic resonance spectrum of U18HB-M-U18HB in this embodiment of the invention is shown.

[0038] Figure 2 The Fourier infrared spectrum of U22HB-M-U22HB in this embodiment of the invention is shown.

[0039] Figure 3 This is a graph showing the sand-carrying performance of the U22HB-M-U22HB aqueous solution (1% by mass) at 85°C in an embodiment of the present invention.

[0040] Figure 4 The hydrogen nuclear magnetic resonance spectrum of 16HB-M-16HB in this embodiment of the invention is shown.

[0041] Figure 5 The hydrogen nuclear magnetic resonance spectrum of 12HB-M-12HB in this embodiment of the invention is shown. Detailed Implementation

[0042] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0043] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0044] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0045] The chemical reaction equation for the preparation method of the selenium-containing spacer-group gemini surfactant of the present invention is shown below:

[0046]

[0047] Wherein, R1 is a saturated alkyl C n H 2n+1 , saturated alkylamidopropyl C n-1 H 2n-1 CONHCH2CH2CH2, unsaturated alkylamidopropyl C n-1 H 2n-3 Any one of CONHCH2CH2CH2, where n = 10 to 20;

[0048] R2 is any one of methyl, ethyl, or propyl.

[0049] Example 1

[0050] 20 parts of N,N-dimethyloleamide propyl tertiary amine, 20 parts of deionized water and 40 parts of ethanol were mixed to form a transparent water-in-oil type surfactant-free microemulsion system with a droplet size of 12 nm.

[0051] Then, slowly add 21 parts of sodium 3-chloro-2-hydroxypropanesulfonate at 70°C and continue stirring for 4 hours.

[0052] After the reaction is complete, the solvent is removed, the crude product is collected, washed three times with acetone, and dried under vacuum to obtain the oleamide propyl hydroxypropyl sulfobetaine surfactant U18HB.

[0053] The yield was determined to be 95% by high performance liquid chromatography.

[0054] Mix 42 parts of U18HB with 20 parts of maleic anhydride, add 1 part of molecular sieve and 0.25 parts of p-toluenesulfonic acid, and stir at 160°C for 8 hours.

[0055] After the reaction, filtration to remove the 4A molecular sieve yields the gemini betaine surfactant U18HB-M-U18HB. Acid value analysis showed a yield of up to 97%, and proton nuclear magnetic resonance spectroscopy confirmed its molecular structure. Figure 1 The molecular structure of U18HB-M-U18HB is shown in equation (3):

[0056]

[0057] Example 2

[0058] 20 parts of N,N-dimethylmuscarinamide propyl tertiary amine, 20 parts of deionized water and 40 parts of isopropanol were mixed to form a transparent water-in-oil type surfactant-free microemulsion system with a droplet size of 10 nm.

[0059] Then, slowly add 20 parts of sodium 3-chloro-2-hydroxypropanesulfonate at 90°C and continue stirring for 6 hours.

[0060] After the reaction was complete, the solvent was removed, the crude product was collected, washed three times with acetone, and dried under vacuum to obtain the erucamide propyl hydroxypropyl sulfobetaine surfactant U22HB. The yield was determined to be 94% by high-performance liquid chromatography.

[0061] Mix 60 parts of U22HB with 30 parts of maleic anhydride, add 1 part of 5A molecular sieve and 0.3 parts of concentrated sulfuric acid, and stir at 150°C for 6 hours.

[0062] After the reaction, filtration to remove the molecular sieve yields the geminal betaine surfactant U22HB-M-U22HB. Acid value analysis showed a yield of up to 98%, and Fourier transform infrared spectroscopy confirmed its molecular structure. Figure 2 The molecular structure of U22HB-M-U22HB is shown in equation (4):

[0063]

[0064] The sand-carrying capacity diagram of the aqueous solution (1% by mass) at 85°C in Example 2 of this invention is shown in the figure. Figure 3As can be seen, the sedimentation of quartz sand in the aqueous solution (1%) of the gemini-type betaine surfactant exemplified in the embodiments of the present invention is very slow, indicating that the aqueous solution (1%) of the gemini-type betaine surfactant exemplified in the embodiments of the present invention has very good suspension performance for quartz sand, which meets the requirements for fracturing fluid in the "General Technical Conditions for Fracturing Fluids".

[0065] Example 3

[0066] 20 parts of N,N-diethylhexadecyl tertiary amine, 20 parts of deionized water and 40 parts of ethylene glycol monomethyl ether were mixed to form a transparent water-in-oil type surfactant-free microemulsion system with a droplet size of 15 nm.

[0067] Then, slowly add 22 parts of sodium 3-chloro-2-hydroxypropanesulfonate at 70°C and continue stirring for 8 hours.

[0068] After the reaction was complete, the solvent was removed, the crude product was collected, washed three times with acetone, and dried under vacuum to obtain the cetylhydroxypropyl sulfobetaine surfactant 16HB. The yield was determined to be 97% by high-performance liquid chromatography.

[0069] Mix 50 parts of 16HB and 26 parts of maleic anhydride, add 1 part of 5A molecular sieve and 0.5 parts of glacial acetic acid, and stir at 130°C for 8 hours.

[0070] After the reaction, the molecular sieve was removed by filtration to obtain the gemini-type betaine surfactant 16HB-M-16HB. Acid value analysis showed a yield of up to 95%, and proton nuclear magnetic resonance spectroscopy confirmed its molecular structure. Figure 4 The molecular structure of 16HB-M-16HB is shown in equation (5):

[0071]

[0072] Example 4

[0073] 20 parts of N,N-diethyldodecyl tertiary amine, 20 parts of deionized water and 40 parts of hexanediol were mixed to form a transparent water-in-oil type surfactant-free microemulsion system with a droplet size of 20 nm.

[0074] Then, slowly add 22 parts of sodium 3-chloro-2-hydroxypropanesulfonate at 90°C and continue stirring for 8 hours.

[0075] After the reaction was complete, the solvent was removed, the crude product was collected, washed three times with acetone, and dried under vacuum to obtain the dodecylhydroxypropyl sulfobetaine surfactant 12HB. The yield was determined to be 95% by high-performance liquid chromatography.

[0076] 50 parts of 12HB and 26 parts of maleic anhydride were mixed, and 1 part of 4A molecular sieve and 0.5 parts of glacial acetic acid were added. The mixture was stirred at 170°C for 4 hours. After the reaction, the molecular sieve was removed by filtration to obtain the gemini-type betaine surfactant 12HB-M-12HB. The yield was 96% as determined by acid value analysis, and its molecular structure was confirmed by proton nuclear magnetic resonance spectroscopy. Figure 5 The molecular structure of 12HB-M-12HB is shown in equation (6):

[0077]

[0078] Example 5

[0079] Mix 20 parts of N,N-dimethylsorcinamide propyl tertiary amine, 40 parts of deionized water and 20 parts of isopropanol to form a transparent true solution with no microemulsion structure.

[0080] Then, slowly add 20 parts of sodium 3-chloro-2-hydroxypropanesulfonate at 90°C and continue stirring for 6 hours.

[0081] After the reaction was complete, the solvent was removed, the crude product was collected, washed three times with acetone, and dried under vacuum to obtain the erucamide propyl hydroxypropyl sulfobetaine surfactant U22HB. The yield was determined to be 85% by high-performance liquid chromatography.

[0082] 60 parts of U22HB and 30 parts of maleic anhydride were mixed, and 0.3 parts of concentrated sulfuric acid were added. The mixture was stirred at 150°C for 6 hours. After the reaction was completed, the molecular sieve was removed by filtration to obtain the geminal betaine surfactant U22HB-M-U22HB. The yield was determined to be 80% by acid value analysis.

[0083] Test example:

[0084] 1. Surface properties of Gemini surfactants:

[0085] The equilibrium surface tension and critical micelle concentration of the gemini-type betaine surfactant aqueous solutions prepared in Examples 1-4 at 25°C were determined using the dip plate method, with conventional gemini surfactants 12-2-12·2Br- and U22HB as control samples. The results are shown in Table 1.

[0086] As can be seen from the test data in Table 1, the aqueous solutions of the four gemini-type betaine surfactants exemplified in the embodiments of the present invention have lower equilibrium surface tensions at 25°C, and are lower than those of the comparative example; the critical micelle concentration is at least lower than that of the comparative example 12-2-12·2Br - It is 2-3 orders of magnitude lower than the control sample U22HB, and even reaches the micromolar level.

[0087] Table 1

[0088]

[0089]

[0090] Note: Pure U22HB cannot be dissolved at room temperature, therefore its surface tension, critical micelle concentration and biodegradation rate are all test results of 500 mmol / L NaCl aqueous solution.

[0091] 2. Biodegradability of Gemini Surfactants

[0092] Each of the 15 mg / mL betaine surfactants prepared in Examples 1-5 was used to prepare 500 mL of nutrient solution. 1.0 mL of soil bacterial suspension was then inoculated into each solution. The solutions were placed on a shaker at 20°C for 28 days, and the biodegradation rate was monitored by measuring the chemical oxygen demand (COD). A sample without surfactant was used as a blank sample. The same concentration of 12-2-12·2Br was used as the biodegradation solution. - U22HB was used as a control example in the insecticidal experiment. The test results are shown in Table 1.

[0093] As can be seen from the test data in Table 1, the biodegradation rates of the four geminal betaine surfactants exemplified in the embodiments of the present invention all reached over 95% after 28 days, which is higher than the 92% of the comparative example U22HB, while the comparative example 12-2-12·2Br - The biodegradation rate was only 75% after 28 days, which shows that the gemini betaine surfactant of the present invention has good biodegradability and is an environmentally friendly surfactant.

[0094] 3. Measurement of Kraft temperature

[0095] The Crafts temperatures of the surfactants prepared in Examples 1-4 were determined by visual observation, with each solution containing 1% by mass. The sample solution was first heated in a water bath until clear and transparent, then cooled until crystals precipitated. The solution was then slowly heated again until all crystals completely dissolved; the temperature at this point was the Crafts temperature. This measurement was repeated three times, and the average value was taken. (The text then abruptly shifts to a different topic: 12-2-12·2Br...) - U22HB was used as the control sample. The results are shown in Table 1.

[0096] As can be seen from Table 1, the gemini-type betaine surfactants prepared in Examples 1-4 are similar to those in Control Example 12-2-12·2Br -Similarly, it has a low Crafts temperature and dissolves very easily, which is beneficial for on-site preparation. In contrast, the control sample U22HB cannot dissolve even at 80°C and requires the addition of an additional solubilizer. This indicates that the gemini structure does not lead to enhanced hydrophobicity of the surfactant described in this invention, but rather enhances water solubility, resulting in a significant decrease in the Crafts temperature of the surfactant compared to the control sample U22HB.

[0097] 4. Rheological properties:

[0098] The surfactants obtained in Examples 1-7 were prepared into 1% (w / w) aqueous solutions, allowed to stand at 35°C for 48 hours, and then the apparent viscosity of the solution at a shear rate of 170 s⁻¹ was measured using a rotational rheometer. I²⁻²⁻¹²·2Br⁻ and U²⁻²HB were used as control samples. The results are shown in Table 2.

[0099] Table 2

[0100]

[0101] As can be seen from the test data in Table 2, the four gemini betaine surfactants exemplified in the embodiments of the present invention, at a shear rate of 170 s... -1 All samples exhibited high apparent viscosity. Even at 130°C, the apparent shear viscosity of Examples 1-3 remained above 70 mPa·s, demonstrating excellent temperature-resistant thickening ability. In contrast, the control sample 12-2-12·2Br - Its apparent viscosity is less than 5 mPa·s.

[0102] 5. Salt resistance:

[0103] The surfactants obtained in Examples 1-4 were prepared into 1% (w / w) aqueous solutions and allowed to stand at 35°C for 48 hours. Sodium chloride and calcium chloride were then added to the samples respectively until the samples changed from clear to turbid. The salt content in the samples was recorded. (The last part, "12-2-12·2Br", appears to be a separate, unrelated instruction and is left untranslated.) - U22HB served as the control sample. The results are shown in Table 2.

[0104] As shown in Table 2, the four geminal betaine surfactants exemplified in the embodiments of this invention maintained good solubility in aqueous solutions of 200,000 mg / L sodium chloride and 100,000 mg / L calcium chloride, indicating that the geminal structure did not compromise the salt tolerance of traditional betaine surfactants. In contrast, the control sample 12-2-12·2Br - Its tolerance to sodium chloride is 50,000 mg / L, and its tolerance to calcium chloride is 20,000 mg / L.

[0105] 6. Sand-carrying capacity and gel-breaking performance

[0106] The surfactants obtained in Examples 1-4 were prepared into an aqueous solution with a mass concentration of 1%. 30-50 mesh quartz sand was added at a solid-liquid mass ratio of 2:8 and stirred to disperse it evenly. The evenly distributed suspension was then placed in a 100 mL graduated cylinder and allowed to stand at a constant temperature. The sedimentation of the proppant was observed and recorded.

[0107] Methods for calculating settlement rate:

[0108] Settlement rate = Settlement distance / Settlement time

[0109] With 12-2-12·2Br - U22HB was used as the control sample. The results are shown in Table 3.

[0110] The breaking performance of surfactant-based viscoelastic fluids was evaluated using the breaking time. The surfactants prepared in Examples 1-4 were formulated into 1% (w / w) aqueous solutions. After adding a certain amount of alkane, the time required for the system viscosity to decrease to 5 mPa·s was determined as the time required for complete breaking. (The text then abruptly shifts to a different topic: 12-2-12·2Br...) - U22HB was used as the control sample. The results are shown in Table 3.

[0111] Table 3

[0112]

[0113] As shown in Table 3, the settling rate of quartz sand in the aqueous solutions (1%) of the four gemini-type betaine surfactants exemplified in the embodiments of this invention is lower than the standard of 0.5 cm / min specified in SY / T 6376-2008 "General Technical Conditions for Fracturing Fluids", with the best results observed in the systems of Examples 1-3, where the quartz sand showed the lowest settling rate. However, after the addition of octane and toluene, the viscosity of the system can rapidly decrease to 5 mPa·s within 1 hour, indicating that the gemini-type betaine surfactant prepared in this invention not only has excellent sand-carrying capacity but also can rapidly break down alkanes. In contrast, the control sample 1% 12-2-12·2Br - It basically has no ability to carry sand.

[0114] In the preparation of hydroxypropyl sulfobetaine, this invention utilizes a surface-inactive microemulsion droplet as the reaction medium, allowing the two reactants to meet at the interface of the nanodroplets. This increases the collision probability of the two reactions, resulting in a significant improvement in the reaction yield. The surface-inactive microemulsion droplet formed in this invention is an oil-in-water microemulsion with one of the reactants, a long-chain tertiary amine, as the oil phase. When the other reactant, sodium 3-chloro-2-hydroxypropanesulfonate, is added to the system, the two reactants meet at the flexible interface of the surface-inactive microemulsion droplet. Due to the interfacial effect of the nanodroplet, the collision frequency between molecules increases, thereby increasing the reaction rate and yield.

[0115] In the preparation of gemini-type betaine surfactants, this invention introduces a molecular sieve, which can act as a water-binding agent to capture the water produced by the esterification reaction of hydroxypropyl sulfobetaine and maleic anhydride, promoting the reaction towards the product; it can also provide a confined reaction space for the esterification reaction of hydroxypropyl sulfobetaine and maleic anhydride, allowing the two reactants to meet within the molecular sieve channels. Under the effect of nano-confinement, the yield is significantly improved.

[0116] The gemini betaine surfactant of the present invention can dissolve rapidly at a low temperature without any co-solvent, making it convenient for on-site preparation and simple to operate.

[0117] The invented gemini betaine surfactant has stronger self-assembly ability and higher salt resistance compared to traditional gemini surfactants. It can thicken aqueous solutions without any additives, exhibits good sand-carrying ability and oil-breaking ability, and also shows excellent high-temperature thickening ability and biodegradability.

[0118] The invented gemini-type betaine surfactant has stronger self-assembly ability, lower Craft temperature, higher biodegradability, and stronger thickening ability compared to traditional single-chain betaine surfactants.

[0119] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the present invention.

Claims

1. A method for preparing a biodegradable gemini-type betaine surfactant, characterized in that: include, Preparation of hydroxypropyl sulfonate betaine: A long-chain tertiary amine, deionized water, and an organic solvent are mixed to form a transparent, surfactant-free microemulsion system. The long-chain tertiary amine, deionized water, and organic solvent are, by mass percentage, 20 parts by mass and 40 parts by mass. The long-chain tertiary amine, deionized water, and organic solvent form a surfactant-free microemulsion containing abundant nanodroplets, providing a large reaction interface for the reaction of the tertiary amine with sodium 3-chloro-2-hydroxypropanesulfonate. The organic solvent is one or more of ethanol, isopropanol, hexanediol, pentanediol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, and diethylene glycol monoethyl ether. Then, slowly add 20-30 parts of sodium 3-chloro-2-hydroxypropanesulfonate at 70-100℃ and continue stirring for 2-8 hours. After the reaction is complete, remove the solvent, collect the crude product, wash it three times with acetone, and dry it under vacuum to obtain the hydroxypropyl sulfobetaine surfactant. The structural formula of the hydroxypropyl sulfonobetaine is shown below: Preparation of gemini-type betaine surfactant: Hydroxypropyl sulfobetaine is mixed with maleic anhydride and stirred at 100-180°C for 4-8 hours in the presence of a molecular sieve and a catalyst. The molecular sieve is 4A or 5A molecular sieve, and the catalyst is one or more of p-toluenesulfonic acid, concentrated sulfuric acid, glacial acetic acid, sodium acetate, and sodium bisulfite. After the reaction is complete, the molecular sieve is removed by filtration to obtain the geminate betaine surfactant. The structure of the gemini surfactant is shown in the following formula: Wherein, R1 is a saturated alkyl C n H 2n+1 , saturated alkylamidopropyl C n-1 H 2n-1 CONHCH2CH2CH2, unsaturated alkylamidopropyl C n-1 H 2n-3 Any one of CONHCH2CH2CH2, where n = 10 to 20; R2 is any one of methyl, ethyl, or propyl.

2. The method for preparing the biodegradable gemini betaine surfactant as described in claim 1, characterized in that: The molar ratio of hydroxypropyl sulfobetaine to maleic anhydride is 2–3:

1.

3. The method for preparing the biodegradable gemini betaine surfactant as described in claim 2, characterized in that: The molar ratio of hydroxypropyl sulfobetaine to maleic anhydride is 2.2:

1.

4. The method for preparing the biodegradable gemini betaine surfactant as described in claim 1, characterized in that: The amount of catalyst used is 0.2 to 1.0% of the mass of maleic anhydride.

5. The method for preparing the biodegradable gemini betaine surfactant according to any one of claims 1 to 4, characterized in that: The described gemini betaine surfactant has excellent high-temperature thickening ability and oil-induced gel breaking ability, and is used as a clean fracturing fluid for oil and gas field development.

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