Micromolecular gel applied to acidic liquid fuel, gel fuel and preparation method of gel fuel

Abstract

The invention relates to the field of fuels, and provides a micromolecular gel applied to an acidic liquid fuel, a gel fuel and a preparation method of the gel fuel. The micromolecular gel has a structure as shown in a formula I or a formula II: # imgabs 0 # or # imgabs 1 #; r1, R2 and R3 are respectively and independently selected from hydrogen, chlorine, bromine or fluorine. The micromolecule gel provided by the invention can effectively gelatinize the acidic liquid fuel and improve the comprehensive performance of the gel fuel, the dosage of the micromolecule gel needing to be added when the gel fuel is formed is small, the gel forming speed is high, and the prepared gel fuel has an excellent shear thinning characteristic.

Description

Technical Field

[0001] The present application relates to the field of fuels, and particularly to small molecule gelling agents, gel fuels for acidic liquid fuels, and preparation methods thereof. Background Art

[0002] The molecular formula of ammonium dinitramide (ADN) is NH4N(NO2)2, which is a green high-energy new oxidizer. As a solid / liquid propellant component, it can not only greatly improve the specific impulse of solid / liquid propellants, but also reduce the characteristic signal and environmental pollution. However, ADN has strong hygroscopicity under high temperature and high humidity conditions, which limits its application in solid composite propellants. Dissolving ADN in water and preparing it into an ADN gel fuel may be an effective strategy for applying ADN.

[0003] In related technologies, most gelling agents are only applicable to the gelation of neutral aqueous solutions or organic solutions, and are not applicable to the gelation of acidic or alkaline solutions, and cannot quickly form a stable gel with good shear thinning properties in acidic or alkaline solutions. In addition, the addition amount 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 with a small dosage that can quickly gel a strong acidic liquid fuel (such as an ADN aqueous solution) to form a gel fuel with stable and excellent shear thinning properties, so as to improve the comprehensive performance of the gel fuel. Summary of the Invention

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

[0006] In the first aspect, an embodiment of the present application provides a small molecule gelling agent for acidic liquid fuels, having the structure shown in Formula I or Formula II: or ; In Formula I and Formula II, R1, R2, and R3 are each independently selected from hydrogen, chlorine, bromine, or fluorine.

[0007] In the second aspect, an embodiment of the present application provides a preparation method of the small molecule gelling agent for acidic liquid fuels in the first aspect, including the following steps: ; In Formula I and Formula III, R1 and R2 are each independently selected from hydrogen, chlorine, bromine, or fluorine; Synthesis of Compound Ⅰ: Dissolve sorbitol in the first solvent to obtain a first solution; Dissolve Compound Ⅲ in the second solvent to obtain a second solution; Add an acidic reagent to the first solution, then add the second solution and stir for reaction, followed by filtration, recrystallization, washing, and drying to obtain a small molecule gelator with the structure of Formula Ⅰ.

[0008] In a third aspect, an embodiment of the present application further provides a preparation method of the small molecule gelator applied to acidic liquid fuel in the first aspect, including the following steps: ; In Formulas Ⅱ and Ⅳ, R2 and R3 each independently selected from hydrogen, chlorine, bromine or fluorine; Synthesis of Compound Ⅰ: Dissolve sorbitol in the first solvent to obtain a first solution; Dissolve Compound Ⅳ in the second solvent to obtain a third solution; Add an acidic reagent to the first solution, then add the third solution and stir for reaction, followed by filtration, recrystallization, washing, and drying to obtain a small molecule gelator with the structure of Formula Ⅱ.

[0009] In a fourth aspect, an embodiment of the present application further provides a preparation method of a gel fuel, including: S1. Add the small molecule gelator applied to acidic liquid fuel in the first aspect to the liquid fuel for mixing, and heat to a first temperature and stir to form a homogeneous mixed solution; S2. Cool the homogeneous mixed solution to a second temperature to cool and crystallize to form a gel fuel.

[0010] In a fifth aspect, an embodiment of the present application further provides a gel fuel, which is prepared by the preparation method of the gel fuel in the third aspect.

[0011] The beneficial effects of the present application at least include: The small molecule gelator applied to acidic liquid fuel provided by the embodiment of the present application contains structures such as hydroxyl groups and aromatic benzene rings, and can pass through intermolecular non-covalent bond forces, such as van der Waals forces, intermolecular hydrogen bond interactions, Under the combined action of various forces such as key action, strong acidic liquid fuels (such as ADN aqueous solution, etc.) can be rapidly gelled to form a stable gel fuel with excellent shear thinning properties; at the same time, the addition amount of the small molecule gelling agent required for forming the gel fuel is small. Generally, the addition amount of the small molecule gelling agent for making the liquid fuel form a stable gel is less than 3 wt%. This small molecule gelling agent belongs to organic compounds, with a molecular weight less than 500, having a certain flammability and having little influence on the energy density of the gel fuel, which helps to improve the comprehensive performance of the gel fuel. Description of the Drawings

[0012] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0013] Figure 1 It is the nuclear magnetic resonance hydrogen spectrum of the compound GD-1 prepared in Example 1 of the present application; Figure 2 It is the nuclear magnetic resonance carbon spectrum of the compound GD-1 prepared in Example 1 of the present application; Figure 3 It is the nuclear magnetic resonance hydrogen spectrum of the compound GD-2 prepared in Example 2 of the present application; Figure 4 It is the nuclear magnetic resonance carbon spectrum of the compound GD-2 prepared in Example 2 of the present application; Figure 5 It is the SEM scanning electron micrograph of the GD-2 / ADN hydrogel prepared in Example 2 of the present application; Figure 6 It is the physical picture of each group of GD-2 / ADN hydrogels prepared in Example 2 of the present application; Figure 7 It is the result graph of the shear rheological properties of the GD-3 / ADN hydrogel prepared in Example 3 of the present application; Figure 8 It is the comparison graph 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 Embodiments

[0014] In order to make the technical problems to be solved, technical solutions and beneficial effects of the present application clearer, the following further elaborates the present application in combination with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, but the implementation manners of the present application are not limited thereto.

[0015] Unless otherwise defined, the technical terms used in the following examples have the same meanings as commonly understood by those skilled in the art to which this application pertains. The experimental reagents used in the following examples are all conventional biochemical reagents unless otherwise specified; the amounts of the experimental reagents used are the amounts of reagents in conventional experimental operations unless otherwise specified; the experimental methods used are all conventional methods unless otherwise specified.

[0016] The terms "preferably", "more preferably", etc. in this application refer to embodiments of the present invention that can provide certain beneficial effects in certain cases. However, in the same or other cases, other embodiments may also be preferred. In addition, the description of one or more preferred embodiments does not imply that other embodiments are not available, nor is it intended to exclude other embodiments from the scope of the present invention.

[0017] When a numerical range is disclosed in this application, the above range is considered continuous and includes the minimum and maximum values of the range, as well as each value between such minimum and maximum values. Further, when the range refers to integers, it includes each integer between the minimum and maximum values of the range. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed in this application should be understood to include any and all sub-ranges subsumed therein.

[0018] "Room temperature" in this application has the meaning known to those skilled in the art, generally referring to 24~28 °C.

[0019] The molecular formula of ammonium dinitramide (ADN) is NH4N(NO2)2. It is a white crystalline substance that is soluble in water, with a melting point of 90~92 °C. Its density is similar to that of cyclotrimethylenetrinitramine (RDX) (1.81 g / cm 3 ), and it has a relatively low sensitivity, comparable to that of RDX (impact sensitivity 3.7 J, friction sensitivity 373 N). Due to its extremely high nitrogen content in the molecule and no chlorine atoms, ADN has a high energy density, and no HCl gas is produced during the combustion process, with a low smoke generation during combustion, which can meet the usage requirements of green and low-signature propellants. Therefore, ADN is used as a high-energy new oxidizer to replace ammonium perchlorate (AP) or ammonium nitrate (AN) in solid propellants, which can not only greatly improve the energy density of the propellant, but also reduce the signature and environmental pollution. It has gradually been applied in solid and liquid propellants. For example, the theoretical specific impulse of the liquid propellant composed of ADN / water / glycerol is 246.9 s, and the smokeless solid propellant composed of GAP (glycidyl azide polymer) / RDX / ADN can reach a maximum specific impulse of 268.4 s.

[0020] Compared with other propellant oxidizers, ADN has strong hygroscopicity under high temperature and high humidity conditions, which limits its application in solid composite propellants. Liquid propellants have safety hazards such as leakage and difficulty in storage. In contrast, gel fuels possess the advantages of both solid fuels and liquid fuels, that is, they maintain a stable gel state during storage and transportation and can turn into a low-viscosity liquid state under the action of external shear force during use. Therefore, gelating an ADN aqueous solution (whose pH value is usually 1-3) to prepare a gel fuel may be an effective strategy for applying ADN.

[0021] In related technologies, most gelling agents are only applicable to the gelation of neutral aqueous solutions or organic solutions, but not to the gelation of acidic or alkaline solutions, and cannot rapidly form a stable gel with good shear-thinning properties in acidic or alkaline solutions. In addition, the addition amount of existing gelling agents is generally higher than 3 wt%.

[0022] In view of this, on the one hand, the embodiments of the present application provide a small molecule gelling agent applied to acidic liquid fuels, having the structures shown in Formula I or Formula II: or ; In Formula I and Formula II, R1, R2 and R3 are each independently selected from hydrogen, chlorine, bromine or fluorine.

[0023] The small molecule gelling agent provided by the embodiments of the present application has good compatibility with the liquid fuel system and has a polyhydroxy structure, an aromatic benzene ring structure, etc. It can form a three-dimensional network structure in the liquid fuel system through the combined action of intermolecular hydrogen bonding, bonding and van der Waals forces and other various forces, so that the strongly acidic liquid fuel can be rapidly gelled to form a gel fuel with stable and excellent shear-thinning properties, and the dosage of the small molecule gelling agent required for forming the gel fuel is small. Generally, the amount of the 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, and the liquid fuel can be formed into a solid and non-flowing gel fuel.

[0024] Due to the relatively weak intermolecular hydrogen bonding, bonding and van der Waals forces, the cross-linked structure formed by adding a gelling agent of a high molecular polymer type is more easily damaged. Therefore, the gel fuel prepared by using the small molecule gelling agent provided by the embodiments of the present application has good rheological properties, and the physical network formed by it has an important thixotropic characteristic, and the viscosity of the gel fuel after liquefaction is small and the structure recovery ability is strong.

[0025] Meanwhile, the small molecule gelling agent provided by the embodiments of the present application belongs to organic compounds, with a molecular weight less than 500, having a certain flammability, having little influence on the energy density of the gel fuel, being able to provide higher energy for the fuel, and helping to improve the comprehensive performance of the gel fuel.

[0026] In some embodiments, the small molecule gelling agent applied to acidic liquid fuel is selected from the following compounds: 。

[0027] Second, the embodiments of the present application also provide a preparation method of the small molecule gelling agent applied to acidic liquid fuel in the first aspect, including the following steps: ; In Formula I and Formula III, R1 and R2 each independently selected from hydrogen, chlorine, bromine or fluorine; Synthesis of Compound I: Dissolve sorbitol in the first solvent to obtain a first solution; Dissolve Compound III in the second solvent to obtain a second solution; Add an acidic reagent to the first solution, then add the second solution and stir for reaction, and then filter, recrystallize, wash and dry to obtain a small molecule gelling agent with the structure of Formula I.

[0028] The preparation method of the small molecule gelling agent provided by the embodiments of the present application has simple preparation steps, short reaction time, mild conditions, easily available raw materials, does not require special synthesis equipment for the reaction, has low cost, and has great popularization and application value.

[0029] In some embodiments, the first solvent includes deionized water. The second solvent includes at least one of methanol and absolute ethanol. The acidic reagent is at least one of concentrated hydrochloric acid, concentrated sulfuric acid or sodium bisulfate.

[0030] In some embodiments, in the synthesis step of Compound I, the molar mass ratio of sorbitol to Compound III is 1 - 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, etc. The stirring reaction time is 6 - 12 h. For example, the stirring time can be 6 h, 7 h, 8 h, 9 h, 10 h, 11 h or 12 h, etc. The stirring rate is 250 - 350 rpm. For example, the stirring rate can be 250 rpm, 280 rpm, 300 rpm, 320 rpm or 350 rpm, etc. The drying temperature is 60 - 75 °C. For example, the drying temperature can be 60 °C, 65 °C, 70 °C or 75 °C, etc.

[0031] In a third aspect, the embodiments of the present application further provide a preparation method of the small molecule gelling agent for acidic liquid fuel according to the first aspect, including the following steps: ; In Formula II and Formula IV, R2 and R3 are each independently selected from hydrogen, chlorine, bromine or fluorine; Synthesis of Compound I: Dissolve sorbitol in a first solvent to obtain a first solution; Dissolve Compound IV in a second solvent to obtain a third solution; Add an acidic reagent to the first solution, then add the third solution and stir for reaction, followed by filtration, recrystallization, washing and drying to obtain a small molecule gelling agent with the structure of Formula II.

[0032] In a fourth aspect, the embodiments of the present application further provide a preparation method of a gel fuel, including: S1. Add the small molecule gelling agent for acidic liquid fuel according to the first aspect to a liquid fuel for mixing, and heat to a first temperature, then stir to form a homogeneous mixed solution; S2. Cool the homogeneous mixed solution to a second temperature to cause it to cool and crystallize to form a gel fuel.

[0033] In some embodiments, the liquid fuel is an ammonium dinitramide solution (ADN aqueous solution), the pH value of the ammonium dinitramide solution is 1-3, for example, it can be pH = 1, 2 or 3, etc.; the addition 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.

[0034] In a fifth aspect, the embodiments of the present application further provide a gel fuel, which is prepared by the preparation method of the gel fuel according to the third aspect.

[0035] In the process of preparing the ADN gel fuel, by introducing a small molecule gelling agent as shown in Formula I or Formula II above that can meet the strong acidic environment system of the ADN solution, the ADN solution can be quickly gelled to form an ADN gel fuel with stability and excellent shear thinning characteristics, thereby improving the use performance of the ADN gel fuel.

[0036] The present application has been tested many times. Now, some test results are cited as a reference to further describe the invention in detail. The following will be described in detail with specific embodiments.

[0037] The synthesis route of Compound I is as follows: ; In Formula I and Formula III, R1 and R2 are each independently selected from hydrogen, chlorine, bromine or fluorine.

[0038] Example 1 (1)Preparation of compound GD-1 (2,4-(3,4-dichlorobenzylidene)-D-sorbitol): At room temperature, 7.0 g (38.5 mmol) of sorbitol and 8.0 g of deionized water were successively added to a 100 mL four-necked flask equipped with a mechanical stirring paddle, a thermometer and a dropping funnel, and stirred until all the sorbitol was dissolved to obtain a first solution. 4.8 g (27.5 mmol) of 3,4-dichlorobenzaldehyde was dissolved in 15 mL of methanol to obtain a second solution. 10.0 g of concentrated hydrochloric acid was added to the first solution, and the second solution was added dropwise thereto at a temperature of 15 °C. After the addition was completed, the reaction was stirred at this temperature for 6 h. After the reaction was completed, 20 mL of water was added to the four-necked flask, stirred for 10 min and then filtered. The filter cake was recrystallized with 75 mL of a 2-3% aqueous sodium bicarbonate solution. After recrystallization, the solid was washed 2-3 times with ethyl acetate, and then dried to constant weight at 60 °C to obtain 2.4 g of a white powder product, namely compound GD-1, with a yield of 36%.

[0039] (2)Preparation of ADN gel fuel (GD-1 / ADN hydrogel): The compound GD-1 prepared in the above step (1) was added to an aqueous ADN solution (pH = 2) with stirring for mixing, wherein the addition amount of the compound GD-1 was 1 wt%, and the temperature was raised to 85 °C, and stirring was continued for 15 min to form a homogeneous mixed solution; the homogeneous mixed solution was cooled to 5 °C, allowed to cool and crystallize, and left standing for 30 min to form a solid ADN gel fuel that was solid and non-flowing.

[0040] Identification of the white powder product prepared in the above step (1): The nuclear magnetic resonance hydrogen spectrum ( 1 H NMR) spectrum of the white powder product is as shown in Figure 1 the following, 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). The nuclear magnetic resonance carbon spectrum ( 13 C NMR) spectrum is as shown in Figure 2 the following, 1313C 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. The GD-1 / ADN hydrogel prepared in the above step (2) was placed in a normal temperature environment, sealed and stored for more than 6 months, and no gel destruction occurred. It can be seen that the GD-1 / ADN hydrogel prepared in the embodiment of the present application has good storage stability and is convenient for storage and transportation.

[0041] Example 2 (1) Preparation of compound GD-2 (2,4-(3-chloro-4-bromobenzylidene)-D-sorbitol): At room temperature, 7.0 g (38.5 mmol) of sorbitol and 8.0 g of deionized water were successively added to a 250 mL four-necked flask equipped with a mechanical stirring paddle, a thermometer and a dropping funnel, and stirred until all the sorbitol was dissolved to obtain a first solution. 6 g (27.5 mmol) of 3-chloro-4-bromobenzaldehyde was dissolved in 70 mL of absolute ethanol to obtain a second solution. 10.0 g of concentrated hydrochloric acid was added to the first solution, and the second solution was added dropwise thereto at a temperature of 15 °C. After the addition was completed, the reaction was stirred at this temperature for 8 h. After the reaction was completed, 20 mL of water was added to the four-necked flask, stirred for 12 min and then filtered. The filter cake was recrystallized with 75 mL of an aqueous sodium bicarbonate solution with a mass concentration of 2%-3%. After recrystallization, the solid was washed twice with 30 mL of dichloromethane and then dried to constant weight at 70 °C to obtain a white powder product, that is, compound GD-2, with a yield of 39%.

[0042] (2) Preparation of ADN gel fuel (GD-2 / ADN hydrogel): The compound GD-2 prepared in the above step (1) was added to an ADN aqueous solution (pH = 1) with stirring for mixing, wherein the addition amount of the compound GD-2 was 2 wt%, and the temperature was raised to 90 °C, and stirring was continued for 15 min to form a homogeneous mixed solution; the homogeneous mixed solution was cooled to 3 °C, allowed to cool and crystallize, and left standing for 20 min to form a solid ADN gel fuel that was solid and non-flowing.

[0043] Identification of the white powder product prepared in the above step (1): The nuclear magnetic resonance hydrogen spectrum ( 1 1H NMR) spectrum of the white powder product is as Figure 3 shown, 11H 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). 13C nuclear magnetic resonance ( 13 13C NMR) spectra are as follows Figure 4 shown 13 13C 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. The SEM scanning electron micrograph of the GD-2 / ADN hydrogel prepared in the above step (2) is as follows Figure 5 shown

[0044] Based on the above Example 2, only the addition amounts of compound GD-2 in step (2) of Example 2 were changed to 1.5 wt%, 2 wt%, and 2.5 wt% respectively, and the remaining steps and preparation conditions remained unchanged. The physical pictures of the prepared GD-2 / ADN hydrogels in each group are as follows Figure 6 shown

[0045] It can be seen from Figure 6 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

[0046] Example 3 (1) Preparation of compound GD-3 (2,4-(3-bromo-4-chlorobenzylidene)-D-sorbitol): At room temperature, 7.0 g (38.5 mmol) of sorbitol and 8.0 g of deionized water were successively added to a 250 mL four-necked flask equipped with a mechanical stirring paddle, a thermometer and a dropping funnel. The mixture was stirred until all the sorbitol was dissolved to obtain a first solution. 6 g (27.5 mmol) of 3-bromo-4-chlorobenzaldehyde was dissolved in 70 mL of absolute ethanol to obtain a second solution. 10.0 g of concentrated hydrochloric acid was added to the first solution, and the second solution was added dropwise thereto at a temperature of 15 °C. After the addition was completed, the reaction was stirred at this temperature for 12 h. After the reaction was completed, 20 mL of water was added to the four-necked flask, and the mixture was stirred for 15 min and then filtered. The filter cake was recrystallized with 75 mL of an aqueous sodium bicarbonate solution with a mass concentration of 2%-3%. After recrystallization, the solid was washed twice with dichloromethane and then dried at 70 °C to constant weight to obtain a white powder product, namely compound GD-3, with a yield of 48%.

[0047] (2)Preparation of ADN gel fuel (GD-3 / ADN hydrogel): The compound GD-3 prepared in the above step (1) was added to an aqueous ADN solution (pH = 2) with stirring for mixing. Among them, 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 min to form a homogeneous mixed solution; the homogeneous mixed solution was cooled to 8 °C to cool and crystallize, and allowed to stand for 10 min to form a solid ADN gel fuel that was solid and non-flowing.

[0048] The shear rheological properties of the GD-3 / ADN hydrogel prepared in Example 3 were tested, and the test results are as Figure 7 shown.

[0049] From Figure 7 it can be seen that the viscosity of the GD-3 / ADN hydrogel prepared in Example 3 decreases with the increase of the shear rate, which indicates that the prepared GD-3 / ADN hydrogel has excellent shear thinning properties.

[0050] Example 4 The synthetic route of compound II is as follows: ; In Formula II and Formula IV, R2 and R3 are each independently selected from hydrogen, chlorine, bromine or fluorine; (1)Preparation of compound GD-4 (2,4-(3,5-dichlorobenzylidene)-D-sorbitol): At room temperature, 7.0 g (38.5 mmol) of sorbitol and 8.0 g of deionized water were successively added to a 100 mL four-necked flask equipped with a mechanical stirring paddle, a thermometer and a dropping funnel. The mixture was stirred until all the sorbitol was dissolved to obtain a first solution. 4.8 g (27.5 mmol) of 3,5-dichlorobenzaldehyde was dissolved in 70 mL of absolute ethanol to obtain a second solution. 10.0 g of concentrated hydrochloric acid was added to the first solution, and the second solution was added dropwise thereto at a temperature of 15 °C. After the addition was completed, the reaction was stirred at this temperature for 6 h. After the reaction was completed, 20 mL of water was added to the four-necked flask, and the mixture was stirred for 10 min and then filtered. The filter cake was recrystallized with 75 mL of a 2% aqueous sodium bicarbonate solution. After recrystallization, it was washed with ethyl acetate 2-3 times, and then dried at 60 °C to constant weight to obtain 2.4 g of a white powder product, namely compound GD-4, with a yield of 36%.

[0051] (2) Preparation of ADN gel fuel (GD-4 / ADN hydrogel): The compound GD-4 prepared in the above step (1) was added to an aqueous ADN solution (pH = 1) with stirring for mixing. 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 min to form a homogeneous mixed solution; the homogeneous mixed solution was cooled to 5 °C to cool and crystallize, and left standing for 30 min to form a solid ADN gel fuel that was solid and non-flowing.

[0052] In the process of synthesizing compounds GD1-GD-4, in the recrystallization step, if the pH value of the reaction system is less than 7, the situation of non-crystallization may occur. Therefore, it is necessary to pay attention to adjusting the mass fraction of the aqueous sodium bicarbonate solution and try to control the pH value of the reaction system between 7 and 9 to achieve a higher yield.

[0053] Example 5 Referring to step (2) of Example 1 above, GD-1 / ADN gel fuel with an addition amount of 2 wt% of compound GD-1 was prepared; and agar / ADN gel fuel with an addition amount of 2 wt% of agar (a polymer gelling agent) was prepared.

[0054] Test the viscosity changes of the above-prepared GD-1 / ADN gel fuel and agar / ADN gel fuel in the range of shear rate from 1 s -1 ~100 s -1 range, and draw a viscosity-shear rate curve, as Figure 8 shown.

[0055] It can be seen from Figure 8 that when the shear rate is 1 s -1At this time, the viscosity of the GD-1 / ADN gel fuel is , significantly lower than that of the agar / ADN gel fuel . As the shear rate gradually increases, the viscosities of the GD-1 / ADN gel fuel and the agar / ADN gel fuel slowly decrease. During this process, the viscosity of the GD-1 / ADN gel fuel is continuously less than that of the agar / ADN gel fuel. When the shear rate increases to 100 s -1 , the viscosity of the GD-1 / ADN gel fuel drops to , approaching the viscosity of pure water. It can be seen that under the condition of the same dosage of the gelling agent, the GD-1 / ADN gel fuel prepared with the small molecule gelling agent of the embodiment of the present application has lower viscosity and better shear thinning characteristics, which is beneficial to the subsequent more complete atomization combustion of the gel fuel.

[0056] In summary, the small molecule gelling agent prepared in the embodiment of the present application can rapidly gelate a strongly acidic liquid fuel (such as an ADN aqueous solution with a pH value of 1-3, etc.), forming a gel fuel with stable and excellent shear thinning characteristics, and the dosage of the small molecule gelling agent required for forming the gel fuel is small.

[0057] 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 foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A small molecule gelling agent applied to acidic liquid fuel, characterized in that, It has the structure shown in Formula I or Formula II: 、 ； In Formula I and Formula II, R1, R2 and R3 are each independently selected from hydrogen, chlorine, bromine or fluorine.

2. The small molecule gelling agent applied to acidic liquid fuel according to claim 1, wherein The small molecule gelator is selected from the following compounds: 。 3. The preparation method of the small molecule gelling agent applied to acidic liquid fuel according to claim 1 or 2, characterized in that, It includes the following steps: ； In Formula I and Formula III, R1 and R2 are each independently selected from hydrogen, chlorine, bromine or fluorine; Synthesis of Compound I: Dissolve sorbitol in a first solvent to obtain a first solution; Dissolve Compound III in a second solvent to obtain a second solution; Add an acidic reagent to the first solution, then add the second solution and stir for reaction, followed by filtration, recrystallization, washing and drying to obtain a small molecule gelator with the structure of Formula I.

4. The preparation method of the small molecule gelling agent applied to acidic liquid fuel according to claim 3, characterized in that, The first solvent includes deionized water; the second solvent includes at least one of methanol and absolute ethanol; the acidic reagent is at least one of concentrated hydrochloric acid, concentrated sulfuric acid or sodium bisulfate.

5. The preparation method of the small molecule gelling agent applied to acidic liquid fuel according to claim 3, characterized in that, The molar mass ratio of sorbitol to Compound III is 1 - 1.5:1; the stirring reaction time is 6 - 12 h, the stirring rate is 250 - 350 rpm; the drying temperature is 60 - 75 °C.

6. The preparation method of the small molecule gelling agent applied to acidic liquid fuel according to claim 1 or 2, characterized in that It includes the following steps: ； In Formula II and Formula IV, R2 and R3 are each independently selected from hydrogen, chlorine, bromine or fluorine; Synthesis of Compound I: Dissolve sorbitol in a first solvent to obtain a first solution; Dissolve Compound IV in a second solvent to obtain a third solution; Add an acidic reagent to the first solution, then add the third solution and stir for reaction, followed by filtration, recrystallization, washing and drying to obtain a small molecule gelator with the structure of Formula II.

7. A preparation method of a gel fuel, characterized in that It includes: S1. Add the small molecule gelator applied to acidic liquid fuel as described in Claim 1 or 2 into the liquid fuel for mixing, and heat up to a first temperature, then stir to form a homogeneous mixed solution; S2. Cool the homogeneous mixed solution to a second temperature to make it cool and crystallize to form a gel fuel.

8. The preparation method of the gel fuel according to claim 7, characterized in that, The liquid fuel is an ammonium dinitramide solution with a pH value of 1 - 3; The addition amount of the small molecule gelator is 0.5% - 2.5% of the total mass of the liquid fuel and the small molecule gelator.

9. The preparation method of the gel fuel according to claim 7, wherein, In step S1, the first temperature is 85 - 95 °C, and the stirring time is 10 - 30 min; In step S2, the second temperature is 3 - 10 °C.

10. A gel fuel, characterized in that, The gel fuel is prepared by the preparation method of the gel fuel described in any one of Claims 7 - 9.

Images