Method for reversibly regulating and controlling water solubility of long-chain alkyl trimethyl ammonium bromide by using CO2 and N2

Abstract

The invention provides a method for reversibly regulating and controlling the water solubility of long-chain alkyl trimethyl ammonium bromide by using CO2 and N2, 4-nonylcyclohexane ammonium selenite is used as an auxiliary agent, the Krafft temperature of the long-chain alkyl trimethyl ammonium bromide can be reduced to 15 DEG C or below, the water solubility of the long-chain alkyl trimethyl ammonium bromide is promoted to be increased, and the normal surfactant function of the long-chain alkyl trimethyl ammonium bromide is brought into play; the Krafft temperature of the long-chain alkyl trimethyl ammonium bromide is raised to 15 DEG C or above by blowing CO2, and the water solubility of the long-chain alkyl trimethyl ammonium bromide is reduced, so that the long-chain alkyl trimethyl ammonium bromide is crystallized and separated out from the aqueous solution, the separation and recovery of the long-chain alkyl trimethyl ammonium bromide are realized, and the residual aqueous phase after the long-chain alkyl trimethyl ammonium bromide is recovered can be used as a foliar selenium fertilizer for plants. The formation of organic selenium in plant leaf surfaces is promoted.

Description

Technical Field

[0001] This invention belongs to the fields of green environmental protection and daily chemical technology, specifically relating to a method for reversibly controlling the water solubility of long-chain alkyltrimethylammonium bromide using CO2 and N2. Background Technology

[0002] Numerous studies have found that only when the temperature reaches a certain threshold or above can the solubility of ionic surfactants in water reach their critical micelle concentration. This temperature is called the critical micelle temperature of ionic surfactants, also known as the Krafft temperature (K). T , o C). K T The magnitude of K reflects the water solubility of ionic surfactants; therefore, K... T It is one of the important performance parameters of ionic surfactants. Currently, for high-k surfactants... T There are many studies on methods for controlling the water solubility of anionic surfactants, but for high-k... T Research on methods for controlling the water solubility of cationic surfactants is relatively limited. In our previous research, we used sodium benzyl selenide propionate as an auxiliary agent, mixed it with long-chain alkyltrimethylammonium bromide, and dissolved it in water to improve the Kc of the long-chain alkyltrimethylammonium bromide. T Reduced to 10 o C and below, then, by adding the oxidant H2O2, sodium benzylselenopropionate is oxidized to sodium benzylseleoxypropionate, so that the K of the long-chain alkyltrimethylammonium bromide is... T The process increases the water solubility of long-chain alkyltrimethylammonium bromide, thereby causing it to crystallize out of aqueous solution and achieving separation, recovery, and reuse. Considering that the practical applications of cationic surfactants often involve organic pigments, whose molecular structures typically contain unsaturated bonds and conjugated structures, these unsaturated bonds and conjugated structures frequently undergo irreversible chemical reactions with H₂O₂, posing a fatal obstacle to the separation and recovery of cationic surfactants. More importantly, the products of the irreversible chemical reaction between organic compounds, represented by organic pigments, containing unsaturated bonds and conjugated structures, and H₂O₂ are often unidentifiable, not only interfering with the purity of the recovered cationic surfactant but also posing uncontrollable quality risks. Summary of the Invention

[0003] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for reversibly controlling the water solubility of long-chain alkyltrimethylammonium bromide using CO2 and N2, thereby achieving the separation and recovery of long-chain alkyltrimethylammonium bromide. This technology uses 4-nonylcyclohexane selenite as an auxiliary agent and achieves reversible control of the water solubility of long-chain alkyltrimethylammonium bromide solely through the weak acidification effect of CO2 and the CO2 removal effect of N2. It is green and safe, with no uncontrollable side reactions occurring.

[0004] The technical solution of the present invention is as follows: A method for reversibly controlling the water solubility of long-chain alkyltrimethylammonium bromide using CO2 and N2 includes the following steps: 1) Using 4-nonylcyclohexaneselenite as an auxiliary agent, it was mixed with long-chain alkyltrimethylammonium bromide and then added to a 0.1 mol / L tetramethylethylenediamine aqueous solution and stirred to dissolve, thereby lowering the Krafft temperature of the long-chain alkyltrimethylammonium bromide to 15°C. o C and below; 2) By introducing CO2, 4-nonylcyclohexane selenite ammonium is converted to 4-nonylcyclohexane selenite, thereby raising the Krafft temperature of long-chain alkyltrimethylammonium bromide to 15°C. o C and above reduce the water solubility of long-chain alkyltrimethylammonium bromide, causing long-chain alkyltrimethylammonium bromide to crystallize out of aqueous solution; 3) By blowing in N2 and heating to 60°C o C can reduce 4-nonylcyclohexaneselenite to ammonium 4-nonylcyclohexaneselenite, thereby reducing the K+ of long-chain alkyltrimethylammonium bromide. T reduce.

[0005] Furthermore, in step 1), the molar ratio of 4-nonylcyclohexane selenite to long-chain alkyltrimethylammonium bromide is in the range of 0.3 to 6.5.

[0006] Furthermore, the long-chain alkyltrimethylammonium bromide is any one or a mixture of several of hexadecyltrimethylammonium bromide, octadecyltrimethylammonium bromide, and eicosyltrimethylammonium bromide.

[0007] The molecular structural formulas of hexadecyltrimethylammonium bromide, octadecyltrimethylammonium bromide, and eicosyltrimethylammonium bromide described in this invention are as follows: (Hexadecyltrimethylammonium bromide, C16NBr) (Octadecyltrimethylammonium bromide, C18NBr) (eicosyltrimethylammonium bromide, C20NBr) This invention also provides a synthetic process route for 4-nonylcyclohexane selenite ammonium: .

[0008] The specific preparation steps for the 4-nonylcyclohexane selenite ammonium are as follows: 1) Under ice bath conditions and N2 protection, selenium powder is reacted with sodium hydroxide and hydrazine hydrate to obtain disodium selenide (Na2Se2); 2) Disodium diselenide (Na2Se2) reacts with 4-nonyl-1-bromo-cyclohexane to give 4-nonylcyclohexyl diselenide; 3) Under N2 protection, 4-nonylcyclohexyl diselenyl ether is oxidized with nitric acid to obtain 4-nonylcyclohexane selenite; 4) Mix the obtained 4-nonylcyclohexane selenite with tetramethylethylenediamine in equal molar amounts and dissolve in 0.1 mol / L tetramethylethylenediamine aqueous solution to obtain ammonium 4-nonylcyclohexane selenite.

[0009] The separation and recovery of the long-chain alkyltrimethylammonium bromide involves the following steps: after 4-nonylcyclohexaneselenite ammonium is converted to 4-nonylcyclohexaneselenic acid, the long-chain alkyltrimethylammonium bromide precipitates from the system via crystallization. It can then be separated and recovered through conventional filtration, with a recovery rate of no less than 95%. The remaining aqueous solution after recovering the long-chain alkyltrimethylammonium bromide is sprayed once on the leaves of tall fescue at a rate of 170 mg / acre. This application results in an average organic selenium content of 68.3 μg / kg in the dry leaves of tall fescue.

[0010] The method of the present invention has the following advantages over the prior art: 1. The method for reversibly controlling the water solubility of long-chain alkyltrimethylammonium bromide provided by the present invention involves alternating treatment with CO2 and N2 injection and auxiliary heating to reduce the K+ of long-chain alkyltrimethylammonium bromide. T Then it can increase K in the reverse direction. T Conversely, the same applies. Therefore, the method for reversibly controlling the water solubility of long-chain alkyltrimethylammonium bromide using CO2 and N2 provided by this invention is fundamentally different from the traditional method of "increasing the size of the cationic head group and introducing hydrophilic groups." (Controlling K) T The process is highly reversible, with at least 10 reversible adjustments possible.

[0011] 2. The method for reversibly controlling the water solubility of long-chain alkyltrimethylammonium bromide provided by the present invention has a relatively simple process for recovering surfactants, low equipment requirements, low cost, and high recovery rate for various long-chain alkyltrimethylammonium bromide and their mixtures (recovery rate not less than 95%).

[0012] 3. This invention is green, safe, and produces no waste. It is low-cost and easy to operate, and can effectively remove K from hexadecanetrimethylammonium bromide. TReduced to 15 o C and below, and can also be used to make long-chain alkyltrimethylammonium bromide (including octadecyltrimethylammonium bromide and eicosyltrimethylammonium bromide) with longer carbon chains. T Reduced to 15 o The good results were achieved with C and below, and the recovery rate of the above long-chain alkyltrimethylammonium bromide was not less than 95%.

[0013] 4. The method proposed in this invention for reversibly regulating the water solubility of the cationic surfactant long-chain alkyltrimethylammonium bromide using CO2 and N2, after recovering the long-chain alkyltrimethylammonium bromide, the remaining aqueous solution can be treated with conventional activated carbon and ion exchange resin to reduce its chemical oxygen demand (COD) to about 18 mg O2 / L, and can also be used as a foliar selenium fertilizer for tall fescue, with an average organic selenium content of up to 68.3 μg / kg in the dry leaves of tall fescue. Attached Figure Description

[0014] Figure 1 The 4-nonylcyclohexaneselenoic acid obtained in Example 1 of this invention 13 C10 NMR spectrum.

[0015] Figure 2 In Examples 2, 3, and 4 of this invention, 4NCHSeOAm was used to regulate the K of hexadecyltrimethylammonium bromide (C16NBr), octadecyltrimethylammonium bromide (C18NBr), and eicosyltrimethylammonium bromide (C20NBr), respectively. T The rendered image.

[0016] Figure 3 The Ki of CO2 and N2 in Example 5 of this invention is the effect of CO2 and N2 on C16NBr-4NCHSeOAm, C18NBr-4NCHSeOAm, and C20NBr-4NCHSeOAm. T The effect of reversible regulation. Detailed Implementation

[0017] The following detailed embodiments and accompanying drawings further illustrate the method and effects of reversibly controlling the water solubility of long-chain alkyltrimethylammonium bromide using CO2 and N2 provided by the present invention.

[0018] Unless otherwise specified, all raw materials used in the embodiments of this invention are commercially available.

[0019] Example 1: Synthesis method of 4-nonylcyclohexane selenite ammonium (4NCHSeOAm) This embodiment mainly illustrates the synthesis method of 4-nonylcyclohexane selenite (4NCHSeOAm). The specific reaction process is as follows: Under ice bath conditions and N2 protection, 24.3 g of selenium powder, 14.5 g of sodium hydroxide, and 150 mL of tetrahydrofuran were mixed in a 250 mL round-bottom flask. After stirring for 10 minutes, 6.7 g of hydrazine hydrate was added dropwise, and the reaction was allowed to proceed for 0.5 hours after the addition was complete. Then, 96.7 g of 4-nonyl-1-bromo-cyclohexane was added dropwise, and the reaction was allowed to proceed for 12 hours at room temperature after the addition was complete. The organic phase was extracted with dichloromethane, dehydrated, and the solvent was evaporated. The residue was recrystallized three times with ethyl acetate to give a yellow 4-nonylcyclohexyl diselenoether in 88.3% yield.

[0020] Under nitrogen protection, 57.9 g of 4-nonylcyclohexyl diselenide was added to a 500 mL round-bottom flask, followed by 75 mL each of tetrahydrofuran and deionized water. The flask was placed in an ice-water bath, and concentrated nitric acid was added dropwise while stirring. After the addition was complete, the reaction was continued in the ice-water bath for 2 hours. Then, 10 g of ice-water solution was added to the system, and after thorough stirring, the mixture was repeatedly extracted with dichloromethane. The dichloromethane extract was repeatedly washed with saturated sodium chloride solution, and then washed with deionized water until the deionized water was neutral. After removing the solvent, 4-nonylcyclohexane selenite (4NCHSeOH) was obtained with a yield of 98.7%. Figure 1 4NCHSeOH 13 C10 NMR spectrum.

[0021] The 4-nonylcyclohexane selenite ammonium (4NCHSeOAm) of this invention can be obtained by mixing 4NCHSeOH and tetramethylethylenediamine in equimolar amounts and dissolving them in a 0.1 mol / L tetramethylethylenediamine aqueous solution.

[0022] Example 2: 4NCHSeOAm reduces the K of C16NBr T The molar ratio of 4NCHSeOAm to C16NBr ( n 4NCHSeOAm / n Surf Within the range of 0–6.0, a 4NCHSeOAm-C16NBr aqueous solution was prepared using a 0.1 mol / L tetramethylethylenediamine aqueous solution as the solvent, with the mass percentage of C16NBr in the resulting solution controlled to 1.0%. The sample was then placed in a refrigerator to cool until crystals precipitated, and then stored at a constant temperature for 12 hours. Finally, its K was determined by visual temperature increase method. T Each sample was measured three times, and the average value was taken. The experimental results are shown in [the table below]. Figure 2 .Depend on Figure 2 The results show that when the molar ratio of 4NCHSeOAm to C16NBr is ( n 4NCHSeOAm / n SurfWhen the K of C16NBr is in the range of 0~0.25, T From approximately 25 o C continued to decrease to 15 o Near C; K of C16NBr T Reduced to 15 o Below C, the required amount of 4NCHSeOAm is approximately 0.3 to 2.0 times that of C16NBr. That is, when the molar ratio of 4NCHSeOAm to C16NBr is in the range of 0.3 to 2.0, the Kc of C16NBr is... T Between 2.5 and 15 o Within the range of C.

[0023] Example 3: 4NCHSeOAm reduces the K of C18NBr T The molar ratio of 4NCHSeOAm to C18NBr ( n 4NCHSeOAm / n Surf Within the range of 0 to 6.0, a 4NCHSeOAm-C18NBr aqueous solution was prepared using a 0.1 mol / L tetramethylethylenediamine aqueous solution as the solvent, with the mass percentage of C18NBr in the resulting solution controlled at 0.5%. The sample was placed in a refrigerator to cool until crystals precipitated, then kept at a constant temperature for 12 hours. Finally, its K was determined by visual temperature increase method. T Each sample was measured three times, and the average value was taken. The experimental results are shown in [the table below]. Figure 2 .Depend on Figure 2 The results show that when the molar ratio of 4NCHSeOAm to C18NBr is in the range of 0~6.1, the K of C18NBr is... T From approximately 36 o C continued to decrease to 5.2 o Near C; K of C18NBr T Reduced to 15 o For C18 and below, the required amount of 4NCHSeOAm is approximately 1.1 to 3.1 times that of C18NBr. That is, when the molar ratio of 4NCHSeOAm to C18NBr is in the range of 1.1 to 3.1, the Kc of C18NBr is... T Between 5.2 and 15 o Within the range of C.

[0024] Example 4: 4NCHSeOAm reduces the K of C20NBr T The molar ratio of 4NCHSeOAm to C20NBr ( n 4NCHSeOAm / n SurfWithin the range of 0 to 6.0, a 4NCHSeOAm-C20NBr aqueous solution was prepared using a 0.1 mol / L tetramethylethylenediamine aqueous solution as the solvent, with the mass percentage of C20NBr in the resulting solution controlled at 0.2%. The sample was placed in a refrigerator to cool until crystals precipitated, then stored at a constant temperature for 12 hours. Finally, its K was determined by visual temperature increase method. T Each sample was measured three times, and the average value was taken. The experimental results are shown in [the table below]. Figure 2 .Depend on Figure 2 The results show that when the molar ratio of 4NCHSeOAm to C20NBr is ( n 4NCHSeOAm / n Surf When the K of C20NBr is in the range of 0~6.5, T From approximately 45.6 o C continued to decrease to 10.1 o Near C; K of C20NBr T Reduced to 15 o For C and below, the required amount of 4NCHSeOAm is approximately 1.9 to 6.5 times that of C20NBr. That is, when the molar ratio of 4NCHSeOAm to C20NBr is in the range of 1.9 to 6.5, the Kc of C20NBr is... T Between 10 and 15 o Within the range of C.

[0025] Example 5: Reversible regulation of K in long-chain alkyltrimethylammonium bromide T This embodiment mainly illustrates the use of CO2 and N2 (and heating to 60°C) to induce CO2 and N2. o C) The measure causes the interconversion between 4NCHSeOAm and 4NCHSeOH, thereby reversibly altering the K of the long-chain alkyltrimethylammonium bromide. T The technical process and effects are described below. The cases for the three long-chain alkyl trimethylammonium bromide compounds, C16NBr, C18NBr, and C20NBr, are described separately as follows: For a C16NBr aqueous solution with a mass percentage of 1.0% prepared according to the method of Example 2, the concentration was fixed. n 4NCHSeOAm / n Surf The ratio is 0.5:1, at which point the K0 of C16NBr is measured. T Approximately 8.1 o C; After CO2 is introduced to convert 4NCHSeOAm to 4NCHSeOH, the K of C16NBr is measured. T Approximately 25.1 o C ( Figure 3 Based on this, N2 was continued to be bubbled in and the system was heated to 60°C.o At C, 4NCHSeOH is reduced to 4NCHSeOAm, and the K of C16NBr is measured. T It dropped again to 8.1 o Near C, thus achieving K in C16NBr T The reversible regulation of the cycle can reach at least 10 cycles, as shown in the results. Figure 3 .

[0026] For a C18NBr aqueous solution with a mass percentage of 0.5% prepared according to the method of Example 3, the concentration was fixed. n 4NCHSeOAm / n Surf The ratio is 3:1, at which point the K of C18NBr is measured. T Approximately 5.2 o C; After CO2 is introduced to convert 4NCHSeOAm to 4NCHSeOH, the K of C18NBr is measured. T Approximately 36.1 o C; Based on this, continue to introduce N2 and heat the system to 60°C. o At C, 4NCHSeOH is reduced to 4NCHSeOAm, and the K of C18NBr is measured. T It decreased again to 5.2. o Near C, it can be seen that K can be reversibly regulated in C18NBr. T It is also achievable, and the K of C18NBr T The reversible regulation of the cycle can reach at least 10 cycles.

[0027] For a C20NBr aqueous solution with a mass percentage of 0.2% prepared according to the method of Example 4, the concentration was fixed. n 4NCHSeOAm / n Surf The ratio is 4:1, at which point the K20 of CNBr is measured. T Approximately 10.3 o C; After CO2 is introduced to convert 4NCHSeOAm to 4NCHSeOH, the K of C20NBr is measured. T Approximately 46.1 o C; Based on this, continue to introduce N2 and heat the system to 60°C. o At C, 4NCHSeOH is reduced to 4NCHSeOAm, and the K of C20NBr is measured. T It decreased again to 10.2 o Near C, it can be seen that K can be reversibly controlled in C20NBr. T It is also achievable, and the K of C20NBr T The reversible regulation of the cycle can reach at least 10 cycles.

[0028] Example 6: Recovery of long-chain alkyltrimethylammonium bromide A 1.0% (w / w) C16NBr aqueous solution was prepared according to the method in Example 2, and the concentration was fixed. n 4NCHSeOAm / n Surf The ratio is 1:1, and the solution is at 15°C. o Under C conditions, the solution is clear and transparent; upon bubbling in CO2, it reacts with 4NCHSeOAm, causing the solution to become cloudy within 15 minutes. This is due to the K+ in C16NBr. T Greater than 15 o C (approximately 25) o C, Figure 3 The precipitation was caused by precipitation from the aqueous solution. After the precipitate was fully separated, it was filtered, washed with cold water, and then dried under vacuum to obtain white crystalline C16NBr with a recovery rate of 95.2 ± 0.2%.

[0029] A 1.0% (w / w) C18NBr aqueous solution was prepared according to the method in Example 3, and the solution was fixed. n 4NCHSeOAm / n Surf The ratio is 2:1, and the solution is at 25°C. o Under C conditions, it is clear and transparent because the K of C18NBr is high at this time. T Approximately 7.2 o C; CO2 is bubbled in and reacts with 4NCHSeOAm, causing the solution to become cloudy within 12 minutes. This is due to the K+ of C18NBr. T Higher (approximately 36) o C) The precipitation from the aqueous solution was observed. After the precipitate was fully separated, it was filtered, washed with cold water, and then vacuum dried to obtain a pale grayish-white crystalline C18NBr with a recovery rate of 96.6 ± 0.5%. The C18NBr aqueous solution prepared above was stained with water-soluble pigment methylene blue (methylene blue concentration of 0.5%). The solution was clear and transparent with a blue color at 25 °C. The KT of C18NBr was measured to remain around 7.2 °C. After CO2 was bubbled in and the reaction was completed, a white solid precipitate was precipitated in the solution. After the precipitate was fully separated, it was filtered, washed with cold water, and then vacuum dried to obtain a pale grayish-white crystalline C18NBr with a recovery rate of 96.7 ± 0.4%, which was roughly equivalent to the case without methylene blue staining.

[0030] A 0.5% (w / w) C20NBr aqueous solution was prepared according to the method in Example 4, and the solution was fixed. n 4NCHSeOAm / n Surf The ratio is 2:1, and the solution is at 25°C. oUnder C conditions, it is clear and transparent because the K of C20NBr is high at this time. T Approximately 14.2 o C; CO2 is bubbled in and reacts with 4NCHSeOAm, causing the solution to become cloudy within 5 minutes. This is due to the K+ of C20NBr. T Relatively high (approximately 45.7) o C) The precipitation was caused by precipitation from the aqueous solution. After the precipitate was fully separated, it was filtered, washed with cold water, and dried under vacuum to obtain white crystalline C20NBr with a recovery rate of 98.8±0.1%.

[0031] The purity of the long-chain alkyltrimethylammonium bromide recovered in this embodiment was not less than 99.1% when analyzed by two-phase titration. It can be seen that the technology described in this invention can obtain long-chain alkyltrimethylammonium bromide with high purity.

[0032] To further highlight the advantages of this invention, a 1.0% (w / w) C18NBr aqueous solution was prepared, with sodium benzyl selenate (PhSePNa) as an auxiliary agent, and the solution was fixed. n PhSePNa / n Surf The ratio is 2:1, and the solution is at 25°C. o Under conditions C, the solution is clear and transparent; upon further staining with the water-soluble pigment methylene blue (methylene blue concentration 0.5%), the solution remains clear and transparent and appears blue. The K0 of C18NBr at this point is measured. T Approximately 10.5 o C; H2O2 was then added to react with PhSePNa. The solution became turbid within 1 minute, and a significant change in blue color was observed. The solution also became slightly turbid. After the precipitate had settled and precipitated, it was filtered, washed with cold water, and then vacuum dried to obtain gray-blue C18NBr. The recovery rate was 90.1±0.4%. The purity of C18NBr obtained by two-phase titration was approximately 97.9%.

[0033] Example 7: Reversible control of K in mixed long-chain alkyl trimethylammonium bromide T and recycling Three long-chain alkyltrimethylammonium bromides, C16NBr, C18NBr, and C20NBr, were mixed in a molar ratio of 1:1:1 to obtain a mixed long-chain alkyltrimethylammonium bromide. A 1.0% (w / w) aqueous solution of the mixed long-chain alkyltrimethylammonium bromide was prepared using the solvents described in Examples 2-3. At this point, most of the mixed long-chain alkyltrimethylammonium bromide in the solution was insoluble. 4NCHSeOAm was added at a molar ratio of 2:1 to the mixed long-chain alkyltrimethylammonium bromide. After a slight shaking, the mixed long-chain alkyltrimethylammonium bromide was completely dissolved. CO2 was then bubbled in to react with 4NCHSeOAm. The solution became turbid within 5 minutes. After the precipitate was fully separated, it was filtered, washed with cold water, and then vacuum dried to obtain a recovery rate of 97.4 ± 0.4% for the long-chain alkyltrimethylammonium bromide.

[0034] Example 8: Aqueous solution after recovery of long-chain alkyltrimethylammonium bromide The aqueous solutions remaining after recovering long-chain alkyltrimethylammonium bromide in Examples 2 to 7 were combined and adjusted with deionized water to a selenium content of 8.5 mg / L. The solution was then sprayed on the leaves of tall fescue once at a rate of 170 mg / acre (approximately 20 liters of aqueous solution). The leaves of tall fescue were harvested 2.5 months later. Analysis showed that the average organic selenium content in the dry leaves of tall fescue reached 68.3 μg / kg (average of 23 measurements).

[0035] The aqueous solutions remaining after the recovery of long-chain alkyltrimethylammonium bromide in Examples 2 to 7 were combined and treated three times with ion exchange resin (wet resin to aqueous phase mass ratio of 1:1) and activated carbon (activated carbon mass to aqueous phase volume ratio of 5 g per 50 ml). The chemical oxygen demand (COD) of the aqueous phase was approximately 18 mg O2 / L, which met the standard for direct discharge.

[0036] The present invention has been disclosed above by way of embodiments, but it is not intended to limit the technical solution of the present invention. Anyone skilled in the art can make various modifications and alterations after the disclosure of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A method for reversibly controlling the water solubility of long-chain alkyltrimethylammonium bromide using CO2 and N2, characterized in that, Includes the following steps: 1) Using 4-nonylcyclohexaneselenite as an auxiliary agent, it was mixed with long-chain alkyltrimethylammonium bromide and then added to a 0.1 mol / L tetramethylethylenediamine aqueous solution and stirred to dissolve, thereby lowering the Krafft temperature of the long-chain alkyltrimethylammonium bromide to 15°C. o C and below; 2) By introducing CO2, 4-nonylcyclohexane selenite ammonium is converted to 4-nonylcyclohexane selenite, thereby raising the Krafft temperature of long-chain alkyltrimethylammonium bromide to 15°C. o C and above reduce the water solubility of long-chain alkyltrimethylammonium bromide, causing long-chain alkyltrimethylammonium bromide to crystallize out of aqueous solution; 3) By blowing in N2 and heating to 60°C o C can reduce 4-nonylcyclohexaneselenite to ammonium 4-nonylcyclohexaneselenite, thereby reducing the K+ of long-chain alkyltrimethylammonium bromide. T reduce.

2. The method for reversibly controlling the water solubility of long-chain alkyltrimethylammonium bromide according to claim 1, characterized in that, The molar ratio of the 4-nonylcyclohexane selenite to the long-chain alkyltrimethylammonium bromide is in the range of 0.3 to 6.

5.

3. The method for reversibly controlling the water solubility of long-chain alkyltrimethylammonium bromide according to claim 1, characterized in that, The long-chain alkyltrimethylammonium bromide is any one or a mixture of several of hexadecyltrimethylammonium bromide, octadecyltrimethylammonium bromide, and eicosyltrimethylammonium bromide.

4. The method for reversibly controlling the water solubility of long-chain alkyltrimethylammonium bromide according to claim 1, characterized in that, The synthesis route of the ammonium 4-nonylcyclohexane selenite is as follows: 。 5. The method for reversibly controlling the water solubility of long-chain alkyltrimethylammonium bromide according to claim 4, characterized in that, The specific preparation steps for the 4-nonylcyclohexane selenite ammonium are as follows: 1) Under ice bath conditions and N2 protection, selenium powder is reacted with sodium hydroxide and hydrazine hydrate to obtain disodium selenide (Na2Se2); 2) Disodium diselenide (Na2Se2) reacts with 4-nonyl-1-bromo-cyclohexane to give 4-nonylcyclohexyl diselenide; 3) Under N2 protection, 4-nonylcyclohexyl diselenyl ether is oxidized with nitric acid to obtain 4-nonylcyclohexane selenite; 4) The obtained 4-nonylcyclohexane selenite is mixed with tetramethylethylenediamine in equimolar amounts and dissolved in a solvent to obtain ammonium 4-nonylcyclohexane selenite.

6. The method for reversibly controlling the water solubility of long-chain alkyltrimethylammonium bromide according to claim 5, characterized in that, The solvent in step 4) is a 0.1 mol / L aqueous solution of tetramethylethylenediamine.

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