Small molecule gelling agent for acidic liquid fuel, gelled fuel and method for preparing the same

Abstract

The application relates to the fuel field and provides a small molecule gelling agent applied to acidic liquid fuel, a gelled fuel and a preparation method of the gelled fuel. The small molecule gelling agent has a structure shown in formula I or formula II: or; R1, R2 and R3 are each independently selected from hydrogen, chlorine, bromine or fluorine. The small molecule gelling agent provided in the application can effectively gel the acidic liquid fuel, improves the comprehensive performance of the gelled fuel, requires a small dose of the small molecule gelling agent when the gelled fuel is formed, has a fast gelling speed, and the prepared gelled fuel has excellent shear thinning characteristics.

Description

Technical Field

[0001] The present application relates to the field of fuels, and in particular to a small molecule gelling agent for acidic liquid fuels, a gel fuel and a preparation method thereof. Background Art

[0002] Ammonium dinitramide (ADN), with the molecular formula NH₄N(NO₂)₂, is a new, green, high-energy oxidant. As a component of solid / liquid propellants, its use not only significantly improves their specific impulse but also reduces their signature and environmental pollution. However, ADN's strong hygroscopicity at high temperatures and high humidity limits its application in solid composite propellants. Dissolving ADN in water and preparing it into ADN gel fuel may be an effective strategy for its application.

[0003] Most gelling agents in the prior art are only suitable for gelling neutral aqueous or organic solutions, but not acidic or alkaline solutions. They are unable to rapidly form stable gels with good shear-thinning properties from these solutions. Furthermore, the addition dosage of existing gelling agents is generally higher than 3 wt%.

[0004] Therefore, it is of great significance to research and develop a small molecule gelling agent that can be used in small amounts and can quickly gelate strongly acidic liquid fuels (such as ADN aqueous solutions) to form stable gel fuels with excellent shear-thinning properties, so as to improve the comprehensive performance of gel fuels. Summary of the Invention

[0005] In view of this, the present application provides a small molecule gelling agent, gel fuel and preparation method thereof for acidic liquid fuel. The small molecule gelling agent can effectively gelate the acidic liquid fuel (such as ADN aqueous solution), improve the comprehensive performance of the gel fuel, and the dosage of the small molecule gelling agent required to form the gel fuel is small, the gelling speed is fast, and the prepared gel fuel has excellent shear thinning properties.

[0006] In a first aspect, the embodiments of the present application provide a small molecule gelling agent for acidic liquid fuel, having a structure shown in Formula I or Formula II:

[0007] or ;

[0008] In formula I and formula II, R1, R2 and R3 are each independently selected from hydrogen, chlorine, bromine or fluorine.

[0009] In a second aspect, the present invention provides a method for preparing the small molecule gelling agent for acidic liquid fuel according to the first aspect, comprising the following steps:

[0010] ;

[0011] In formula I and formula III, R1 and R2 are each independently selected from hydrogen, chlorine, bromine or fluorine;

[0012] Synthesis of compound Ⅰ:

[0013] dissolving sorbitol in a first solvent to obtain a first solution;

[0014] dissolving compound III in a second solvent to obtain a second solution;

[0015] An acidic reagent is added to the first solution, and then the second solution is added to carry out stirring reaction, followed by filtering, recrystallization, washing and drying to obtain a small molecule gelling agent having the structure of formula I.

[0016] In a third aspect, the present invention further provides a method for preparing the small molecule gelling agent for acidic liquid fuel according to the first aspect, comprising the following steps:

[0017] ;

[0018] In formula II and formula IV, R2 and R3 are each independently selected from hydrogen, chlorine, bromine or fluorine;

[0019] Synthesis of compound Ⅰ:

[0020] dissolving sorbitol in a first solvent to obtain a first solution;

[0021] dissolving compound IV in a second solvent to obtain a third solution;

[0022] An acidic reagent is added to the first solution, and then the third solution is added to carry out stirring reaction, followed by filtering, recrystallization, washing, and drying to obtain a small molecule gelling agent having a structure of formula II.

[0023] In a fourth aspect, the present invention also provides a method for preparing a gel fuel, comprising:

[0024] S1, adding the small molecule gelling agent for acidic liquid fuel of the first aspect to the liquid fuel for mixing, heating to a first temperature, and stirring to form a homogeneous mixed solution;

[0025] S2. Cooling the homogeneous mixed solution to a second temperature to cool and crystallize the solution to form a gel fuel.

[0026] In a fifth aspect, an embodiment of the present application further provides a gel fuel, which is prepared by the gel fuel preparation method of the third aspect.

[0027] The beneficial effects of the present application include at least: the small molecule gelling agent for acidic liquid fuel provided by the embodiment of the present application contains structures such as hydroxyl groups and aromatic benzene rings, which can be used through intermolecular non-covalent bond forces such as van der Waals forces, intermolecular hydrogen bonds, The combined action of multiple forces, including bonding, can rapidly gelate strongly acidic liquid fuels (such as ADN aqueous solutions), forming stable gel fuels with excellent shear-thinning properties. Furthermore, the amount of small-molecule gelling agent required to form the gel fuel is small; typically, the amount required to form a stable gel of the liquid fuel is less than 3 wt%. This small-molecule gelling agent is an organic compound with a molecular weight of less than 500 and a certain degree of flammability. It has a minimal impact on the energy density of the gel fuel, thus helping to improve the overall performance of the gel fuel. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments or descriptions of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0029] Figure 1 This is the H NMR spectrum of compound GD-1 prepared in Example 1 of the present application;

[0030] Figure 2 This is the carbon NMR spectrum of compound GD-1 prepared in Example 1 of the present application;

[0031] Figure 3 This is the H NMR spectrum of compound GD-2 prepared in Example 2 of the present application;

[0032] Figure 4 This is the carbon NMR spectrum of compound GD-2 prepared in Example 2 of the present application;

[0033] Figure 5 This is a SEM image of the GD-2 / ADN hydrogel prepared in Example 2 of the present application;

[0034] Figure 6 2 are physical pictures of each group of GD-2 / ADN hydrogels prepared in Example 2 of the present application;

[0035] Figure 7 This is a graph showing the shear rheological properties of the GD-3 / ADN hydrogel prepared in Example 3 of the present application;

[0036] Figure 8This is a comparison chart of the viscosity-shear rate curves of the GD-1 / ADN gel fuel and the agar / ADN gel fuel prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0037] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clearly understood, the following is a further detailed description of this application in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain this application, but the implementation methods of this application are not limited thereto.

[0038] Unless otherwise defined, the technical terms used in the following examples have the same meanings as commonly understood by those skilled in the art. The experimental reagents used in the following examples, unless otherwise specified, are conventional biochemical reagents; the amounts of the experimental reagents used, unless otherwise specified, are the amounts used in routine experimental procedures; and the experimental methods, unless otherwise specified, are conventional methods.

[0039] The terms "preferably," "more preferably," and the like, used herein refer to embodiments of the present invention that may provide certain beneficial effects under certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. Furthermore, the reference to one or more preferred embodiments does not imply that other embodiments are unusable, nor is it intended to exclude other embodiments from the scope of the present invention.

[0040] When a numerical range is disclosed in this application, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed in this application should be understood to include any and all subranges subsumed therein.

[0041] The "room temperature" in this application has a well-known meaning in the art, generally referring to 24-28°C.

[0042] The molecular formula of ammonium dinitramide (ADN) is NH4N(NO2)2. It is a white crystalline substance that is easily soluble in water and has a melting point of 90~92℃. Its density is similar to that of cyclotrimethylene trinitramine (RDX) (1.81g / cm 3), but with a low sensitivity comparable to RDX (impact sensitivity 3.7 J, friction sensitivity 373 N). ADN, due to its extremely high molecular nitrogen content and lack of chlorine atoms, possesses a high energy density. Furthermore, its combustion process produces no HCl gas and low smoke, making it suitable for use as a green, environmentally friendly, and low-signature propellant. Therefore, ADN is being used as a new high-energy oxidizer to replace ammonium perchlorate (AP) or ammonium nitrate (AN) in solid propellants. This not only significantly increases the propellant's energy density, but also reduces its signature and environmental pollution. It has been gradually adopted in both solid and liquid propellants. For example, a liquid propellant composed of ADN / water / glycerol has a theoretical specific impulse of 246.9 s, while a smokeless solid propellant composed of GAP (glycidyl polyazide) / RDX / ADN can achieve a maximum specific impulse of 268.4 s.

[0043] Compared to other propellant oxidizers, ADN is highly hygroscopic under high-temperature and high-humidity conditions, limiting its application in solid composite propellants. Liquid propellants, on the other hand, pose safety risks such as leakage and storage difficulties. In contrast, gel fuel combines the advantages of both solid and liquid fuels: it maintains a stable gel state during storage and transportation, and can transform into a low-viscosity liquid state upon application under external shear forces. Therefore, gelling ADN aqueous solutions (typically with a pH of 1–3) to prepare gel fuels may be an effective strategy for ADN applications.

[0044] Most gelling agents in the prior art are only suitable for gelling neutral aqueous or organic solutions, but not acidic or alkaline solutions. They are unable to rapidly form stable gels with good shear-thinning properties from these solutions. Furthermore, the addition dosage of existing gelling agents is generally higher than 3 wt%.

[0045] In view of this, in a first aspect, the embodiments of the present application provide a small molecule gelling agent for acidic liquid fuel, having a structure shown in Formula I or Formula II:

[0046] or ;

[0047] In formula I and formula II, R1, R2 and R3 are each independently selected from hydrogen, chlorine, bromine or fluorine.

[0048] The small molecule gelling agent provided in the embodiment of the present application has good compatibility with the liquid fuel system and has a polyhydroxy structure, an aromatic benzene ring structure, etc., which can be formed by intermolecular hydrogen bonding, The combined action of multiple forces such as bonding and van der Waals forces forms a three-dimensional network structure in the liquid fuel system, which enables the strong acidic liquid fuel to gel rapidly, forming a stable gel fuel with excellent shear-thinning properties. In addition, the dosage of small molecule gelling agent required to form the gel fuel is small. Under normal circumstances, the amount of small molecule gelling agent required to form a stable gel of the liquid fuel is 0.5 wt%~2 wt% (less than 3 wt%) of the total mass of the liquid fuel and the gelling agent, which can make the liquid fuel form a solid, non-flowing gel fuel.

[0049] Due to intermolecular hydrogen bonding, Bonding forces such as bonding and van der Waals forces are relatively weak, making the cross-linked structure formed by adding polymer-based gelling agents more easily disrupted. Therefore, the gel fuel prepared using the small molecule gelling agent provided in the examples of this application has good rheological properties, the physical network it forms has important thixotropic characteristics, and the gel fuel has a low viscosity after liquefaction and strong structural recovery ability.

[0050] At the same time, the small molecule gelling agent provided in the embodiment of the present application is an organic compound with a molecular weight of less than 500 and a certain flammability. It has little effect on the energy density of the gel fuel, can provide higher energy for the fuel, and helps to improve the overall performance of the gel fuel.

[0051] In some embodiments, the small molecule gelling agent used in acidic liquid fuel is selected from the following compounds:

[0052] .

[0053] In a second aspect, the present application also provides a method for preparing the small molecule gelling agent for acidic liquid fuel according to the first aspect, comprising the following steps:

[0054] ;

[0055] In formula I and formula III, R1 and R2 are each independently selected from hydrogen, chlorine, bromine or fluorine;

[0056] Synthesis of compound Ⅰ:

[0057] dissolving sorbitol in a first solvent to obtain a first solution;

[0058] dissolving compound III in a second solvent to obtain a second solution;

[0059] An acidic reagent is added to the first solution, and then the second solution is added to carry out stirring reaction, followed by filtering, recrystallization, washing and drying to obtain a small molecule gelling agent having the structure of formula I.

[0060] The preparation method of the small molecule gelator provided in the embodiment of the present application has simple preparation steps, short reaction time, mild conditions, and readily available raw materials. The reaction does not require special synthesis equipment, the cost is low, and it has great promotion and application value.

[0061] In some embodiments, the first solvent comprises deionized water, the second solvent comprises at least one of methanol and anhydrous ethanol, and the acidic reagent is at least one of concentrated hydrochloric acid, concentrated sulfuric acid, or sodium bisulfate.

[0062] In some embodiments, in the synthesis step of Compound I, the molar mass ratio of sorbitol to Compound III is 1 to 1.5:1, for example, the molar mass ratio of sorbitol to Compound III can be 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, or 1.5:1. The stirring reaction time is 6 to 12 hours, for example, the stirring time can be 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, or 12 hours. The stirring rate is 250 to 350 rpm, for example, the stirring rate can be 250 rpm, 280 rpm, 300 rpm, 320 rpm, or 350 rpm. The drying temperature is 60 to 75°C, for example, the drying temperature can be 60°C, 65°C, 70°C, or 75°C.

[0063] In a third aspect, the present invention further provides a method for preparing the small molecule gelling agent for acidic liquid fuel according to the first aspect, comprising the following steps:

[0064] ;

[0065] In formula II and formula IV, R2 and R3 are each independently selected from hydrogen, chlorine, bromine or fluorine;

[0066] Synthesis of compound Ⅰ:

[0067] dissolving sorbitol in a first solvent to obtain a first solution;

[0068] dissolving compound IV in a second solvent to obtain a third solution;

[0069] An acidic reagent is added to the first solution, and then the third solution is added to carry out stirring reaction, followed by filtering, recrystallization, washing, and drying to obtain a small molecule gelling agent having a structure of formula II.

[0070] In a fourth aspect, the present invention also provides a method for preparing a gel fuel, comprising:

[0071] S1, adding the small molecule gelling agent for acidic liquid fuel of the first aspect to the liquid fuel for mixing, heating to a first temperature, and stirring to form a homogeneous mixed solution;

[0072] S2. Cooling the homogeneous mixed solution to a second temperature to cool and crystallize the solution to form a gel fuel.

[0073] In some embodiments, the liquid fuel is an ammonium dinitramide solution (ADN aqueous solution), and the pH value of the ammonium dinitramide solution is 1~3, for example, it can be pH=1, 2 or 3, etc.; the added amount of the small molecule gelling agent is 0.5%~2.5% of the mass of the liquid fuel, for example, it can be 0.5%, 1%, 2% or 2.5%, etc.

[0074] In a fifth aspect, an embodiment of the present application further provides a gel fuel, which is prepared by the gel fuel preparation method of the third aspect.

[0075] In the process of preparing ADN gel fuel, by introducing a small molecule gelling agent as shown in the above-mentioned formula I or formula II structure that can meet the strong acidic environment system of the ADN solution, the ADN solution can be quickly gelled to form a stable ADN gel fuel with excellent shear thinning properties, thereby improving the performance of the ADN gel fuel.

[0076] The present application has been subjected to multiple tests, and part of the test results are cited as a reference to further describe the invention in detail, which will be described in detail in conjunction with specific embodiments.

[0077] The synthetic route of compound I is as follows:

[0078] ;

[0079] In formula I and formula III, R1 and R2 are each independently selected from hydrogen, chlorine, bromine or fluorine.

[0080] Example 1

[0081] (1) Preparation of compound GD-1 (2,4-(3,4-dichlorobenzylidene)-D-sorbitol):

[0082] To a 100 mL four-necked flask equipped with a mechanical stirrer, thermometer, and dropping funnel, 7.0 g (38.5 mmol) of sorbitol and 8.0 g of deionized water were added sequentially at room temperature and stirred until the sorbitol was completely dissolved to obtain the first solution. 4.8 g (27.5 mmol) of 3,4-dichlorobenzaldehyde was dissolved in 15 mL of methanol to obtain the second solution. 10.0 g of concentrated hydrochloric acid was added to the first solution, and the second solution was added dropwise at 15°C. After the addition was complete, the reaction was stirred at this temperature for 6 h. After the reaction was complete, 20 mL of water was added to the four-necked flask, stirred for 10 min, and filtered. The filter cake was recrystallized from 75 mL of 2-3% sodium bicarbonate aqueous solution. After recrystallization, the solid was washed two to three times with ethyl acetate and then dried at 60°C to constant weight, yielding 2.4 g of white powder, compound GD-1, in a 36% yield.

[0083] (2) Preparation of ADN gel fuel (GD-1 / ADN hydrogel):

[0084] The compound GD-1 prepared in the above step (1) was added to an ADN aqueous solution (pH = 2) under stirring and mixed, wherein the addition amount of the compound GD-1 was 1 wt%, and the temperature was raised to 85°C and stirred for 15 minutes to form a homogeneous mixed solution; the homogeneous mixed solution was cooled to 5°C, allowed to cool and crystallize, and allowed to stand for 30 minutes to form a solid, non-flowing solid ADN gel fuel.

[0085] The white powder product obtained in step (1) above was identified as follows:

[0086] The H NMR spectrum of the white powder product ( 1 H NMR) spectrum as shown Figure 1 As shown, 1 H NMR (400 MHz, DMSO-d6)δ: 7.90-7.44 (m, 4H), 5.58 (s, 1H), 4.73-4.67 (m, 2H), 4.48 (d, J= 8.4 Hz, 1H), 4.41 (t, J= 5.8 Hz, 1H), 3.81 (t, 1H), 3.70-3.53 (m, 6H), 3.43-3.38 (m,1H).

[0087] C NMR spectroscopy ( 13 C NMR) spectrum as shown Figure 2 As shown, 13C NMR (101 MHz, DMSO) δ: 139.54,131.18, 130.79, 130.26, 128.61, 126.92, 98.41, 81.07, 79.42, 69.02, 62.64,61.60, 60.97,39.52.

[0088] The GD-1 / ADN hydrogel prepared in step (2) was placed in a sealed container at room temperature for more than 6 months without any gel damage. This indicates that the GD-1 / ADN hydrogel prepared in this embodiment of the present application has good storage stability and is easy to store and transport.

[0089] Example 2

[0090] (1) Preparation of compound GD-2 (2,4-(3-chloro-4-bromobenzylidene)-D-sorbitol):

[0091] To a 250 mL four-necked flask equipped with a mechanical stirrer, thermometer, and dropping funnel, 7.0 g (38.5 mmol) of sorbitol and 8.0 g of deionized water were added sequentially at room temperature and stirred until the sorbitol was completely dissolved to obtain the first solution. 6 g (27.5 mmol) of 3-chloro-4-bromobenzaldehyde was dissolved in 70 mL of anhydrous ethanol to obtain the second solution. 10.0 g of concentrated hydrochloric acid was added to the first solution, and the second solution was added dropwise at 15°C. After the addition was complete, the reaction was stirred at this temperature for 8 h. After the reaction was complete, 20 mL of water was added to the four-necked flask, stirred for 12 min, and filtered. The filter cake was recrystallized from 75 mL of a 2%-3% sodium bicarbonate aqueous solution. After recrystallization, the solid was washed twice with 30 mL of dichloromethane and then dried at 70°C to constant weight to obtain a white powder product, compound GD-2, in a yield of 39%.

[0092] (2) Preparation of ADN gel fuel (GD-2 / ADN hydrogel):

[0093] The compound GD-2 prepared in the above step (1) was added to an ADN aqueous solution (pH = 1) under stirring and mixed, wherein the addition amount of the compound GD-2 was 2 wt%, and the temperature was raised to 90 ° C, and the stirring was continued for 15 minutes to form a homogeneous mixed solution; the homogeneous mixed solution was cooled to 3 ° C, allowed to cool and crystallize, and allowed to stand for 20 minutes to form a solid, non-flowing solid ADN gel fuel.

[0094] The white powder product obtained in step (1) above was identified as follows:

[0095] The H NMR spectrum of the white powder product (1 H NMR) spectrum as shown Figure 3 As shown, 1 H NMR (400 MHz, DMSO-d6)δ: 7.82-7.74 (m, 2H), 7.37 (dd, J= 8.3, 2.0 Hz, 1H), 5.57 (s, 1H), 4.47 (d,J= 29.4 Hz, 2H), 3.84 -3.50 (m, 9H), 3.42-3.37 (m, 2H).

[0096] C NMR spectroscopy ( 13 C NMR) spectrum as shown Figure 4 As shown, 13 C NMR (101 MHz, DMSO-d6) δ: 139.55, 133.15, 131.79, 130.10, 127.53, 121.07, 98.33, 81.09, 79.42, 68.97, 62.63, 61.52, 60.9.

[0097] The SEM scanning electron microscopy image of the GD-2 / ADN hydrogel prepared in the above step (2) is as follows: Figure 5 shown.

[0098] On the basis of the above Example 2, only the addition amount of compound GD-2 in step (2) of Example 2 was changed to 1.5 wt%, 2 wt%, and 2.5 wt%, respectively, and the other steps and preparation conditions remained unchanged. The actual pictures of the prepared GD-2 / ADN hydrogels are shown in the following figure: Figure 6 shown.

[0099] Depend on Figure 6 It can be seen that when the addition amount of compound GD-2 is 1.5 wt%~2.5 wt%, the ADN aqueous solution can be effectively gelled to form a stable GD-2 / ADN hydrogel.

[0100] Example 3

[0101] (1) Preparation of compound GD-3 (2,4-(3-bromo-4-chlorobenzylidene)-D-sorbitol):

[0102] To a 250 mL four-necked flask equipped with a mechanical stirrer, thermometer, and dropping funnel, 7.0 g (38.5 mmol) of sorbitol and 8.0 g of deionized water were added sequentially at room temperature and stirred until the sorbitol was completely dissolved to obtain the first solution. 6 g (27.5 mmol) of 3-bromo-4-chlorobenzaldehyde was dissolved in 70 mL of anhydrous ethanol to obtain the second solution. 10.0 g of concentrated hydrochloric acid was added to the first solution, and the second solution was added dropwise at 15°C. After the addition was complete, the reaction was stirred at this temperature for 12 h. After the reaction was complete, 20 mL of water was added to the four-necked flask, stirred for 15 min, and filtered. The filter cake was recrystallized from 75 mL of 2%-3% sodium bicarbonate aqueous solution. After recrystallization, the solid was washed twice with dichloromethane and then dried at 70°C to constant weight to obtain a white powder product, compound GD-3, in a yield of 48%.

[0103] (2) Preparation of ADN gel fuel (GD-3 / ADN hydrogel):

[0104] The compound GD-3 prepared in the above step (1) was added to an ADN aqueous solution (pH = 2) under stirring and mixed, wherein the addition amount of the compound GD-3 was 2.5 wt%, and the temperature was raised to 90 ° C, and stirring was continued for 15 minutes to form a homogeneous mixed solution; the homogeneous mixed solution was cooled to 8 ° C, allowed to cool and crystallize, and allowed to stand for 10 minutes to form a solid, non-flowing solid ADN gel fuel.

[0105] The shear rheological properties of the GD-3 / ADN hydrogel prepared in Example 3 were tested, and the test results are as follows: Figure 7 shown.

[0106] from Figure 7 It can be seen that the viscosity of the GD-3 / ADN hydrogel prepared in Example 3 decreases with increasing shear rate, which indicates that the prepared GD-3 / ADN hydrogel has excellent shear thinning properties.

[0107] Example 4

[0108] The synthetic route of compound II is as follows:

[0109] ;

[0110] In formula II and formula IV, R2 and R3 are each independently selected from hydrogen, chlorine, bromine or fluorine;

[0111] (1) Preparation of compound GD-4 (2,4-(3,5-dichlorobenzylidene)-D-sorbitol):

[0112] At room temperature, 7.0 g (38.5 mmol) of sorbitol and 8.0 g of deionized water were added sequentially to a 100 mL four-necked flask equipped with a mechanical stirrer, a thermometer, and a dropping funnel. Stirring was performed until the sorbitol was completely dissolved to obtain the first solution. 4.8 g (27.5 mmol) of 3,5-dichlorobenzaldehyde was dissolved in 70 mL of anhydrous ethanol to obtain the second solution. 10.0 g of concentrated hydrochloric acid was added to the first solution, and the second solution was added dropwise at 15°C. After the addition was complete, the reaction was stirred at this temperature for 6 h. After the reaction was complete, 20 mL of water was added to the four-necked flask, stirred for 10 min, and filtered. The filter cake was recrystallized from 75 mL of 2% sodium bicarbonate aqueous solution. After recrystallization, the product was washed with ethyl acetate 2–3 times and then dried at 60°C to constant weight. 2.4 g of white powder product, compound GD-4, was obtained in a 36% yield.

[0113] (2) Preparation of ADN gel fuel (GD-4 / ADN hydrogel):

[0114] The compound GD-4 prepared in the above step (1) was added to an ADN aqueous solution (pH = 1) under stirring and mixed, wherein the addition amount of the compound GD-4 was 1 wt%, and the temperature was raised to 85 ° C. and stirring was continued for 15 minutes to form a homogeneous mixed solution; the homogeneous mixed solution was cooled to 5 ° C, allowed to cool and crystallize, and allowed to stand for 30 minutes to form a solid, non-flowing solid ADN gel fuel.

[0115] During the synthesis of compounds GD1-GD-4, if the pH of the reaction system is less than 7 during the recrystallization step, crystallization may not occur. Therefore, it is necessary to adjust the mass fraction of the sodium bicarbonate aqueous solution and try to control the pH of the reaction system between 7 and 9 to achieve a higher yield.

[0116] Example 5

[0117] Referring to step (2) of Example 1 above, a GD-1 / ADN gel fuel containing 2 wt% of compound GD-1 was prepared; and an agar / ADN gel fuel containing 2 wt% of agar (a polymer gelling agent) was prepared.

[0118] The GD-1 / ADN gel fuel and agar / ADN gel fuel prepared above were tested at a shear rate of 1 s -1 ~100s -1 The viscosity changes within the range and the viscosity-shear rate curve are drawn, such as Figure 8 shown.

[0119] Depend on Figure 8 It can be seen that when the shear rate is 1 s-1 When the viscosity of GD-1 / ADN gel fuel is , significantly lower than the viscosity of agar / ADN gel fuel As the shear rate gradually increased, the viscosity of GD-1 / ADN gel fuel and agar / ADN gel fuel slowly decreased. During this process, the viscosity of GD-1 / ADN gel fuel was continuously lower than that of agar / ADN gel fuel. When the shear rate increased to 100 s -1 When the viscosity of GD-1 / ADN gel fuel drops to , close to the viscosity of pure water. It can be seen that, with the same amount of gelling agent added, the GD-1 / ADN gel fuel prepared using the small molecule gelling agent of the embodiment of the present application has lower viscosity and better shear thinning properties, which is conducive to more complete atomization and combustion of the gel fuel.

[0120] In summary, the small molecule gelling agent prepared in the embodiments of the present application can rapidly gelate a strongly acidic liquid fuel (such as an ADN aqueous solution with a pH value of 1 to 3), forming a stable gel fuel with excellent shear-thinning properties, and the dosage of the small molecule gelling agent required to form the gel fuel is small.

[0121] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present application, and should all be included in the scope of protection of the present application.

Claims

1. A method for preparing ammonium dinitramide gel fuel, characterized in that: The steps of the method are as follows: A small molecule gelling agent is added to an aqueous solution of ammonium dinitramide with a pH value of 2 under stirring and mixed, wherein the addition amount of the small molecule gelling agent is 2.5 wt%, and the temperature is raised to 90°C and stirred for 15 minutes to form a homogeneous mixed solution; the homogeneous mixed solution is cooled to 8°C, cooled and crystallized, and allowed to stand for 10 minutes to form a solid, non-flowing solid ammonium dinitramide gel fuel. The structural formula of the small molecule gelling agent is as follows: .

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