Quantitative analysis method for concentration of green propellant aqueous solution

Abstract

The application discloses a kind of green propellant aqueous solution concentration quantitative analysis method, after using calibration solution calibration refractive index testing instrument, respectively prepare oxidant, the series standard aqueous solution of combustion agent, measure its refractive index at specified temperature, determine the refractive index concentration coefficient of oxidant and combustion agent by linear regression;While at the same temperature, prepare a series of oxidant and combustion agent concentration change two-component standard aqueous solution, measure the mass and volume of each solution to calculate density, with oxidant concentration and combustion agent concentration as independent variable, determine the density concentration coefficient of oxidant and combustion agent by binary linear regression.Based on the additivity of the refractive index of inorganic aqueous solution, a binary first-order equation with oxidant concentration and combustion agent concentration as independent variables is established, and a system of equations is formed by combining it with the binary linear regression equation of density and oxidant concentration and combustion agent concentration. The target two-component concentration can be obtained by finally solving.

Description

Technical Field

[0001] This invention relates to the field of propellant detection technology, and more specifically, to a quantitative analysis method for the concentration of aqueous solutions of green propellants. Background Technology

[0002] Liquid monocomponent propellants are widely used in attitude and orbit control of spacecraft such as rockets, satellites, and spacecraft, as well as in emergency aircraft propulsion. However, the most widely used propellants, such as hydrazine, generally suffer from high toxicity and severe pollution. With increasing environmental awareness and the urgent need for high-performance propulsion technologies, the development of non-toxic, pollution-free, and green new propellants has become a major direction for the development of space propulsion technology.

[0003] Novel monocomponent propellants are typically formulated by combining oxidizers, fuels, and solvents. Among them, hydroxylamine nitrate (HAN) and ammonium dinitrate (ADN) monocomponent propellants have attracted significant attention due to their unique molecular structures: these propellants simultaneously contain oxidizing and reducing components, forming a complete redox system that can undergo rapid and self-sustaining decomposition reactions upon triggering. These propellants possess excellent energy characteristics such as high energy density, stable decomposition performance, low combustion residue, and high gas production, while also exhibiting high safety and environmental friendliness due to low toxicity and environmentally friendly combustion products. These outstanding advantages have attracted widespread research attention globally. For example, NASA began early research on HAN-based propellants in the 1970s. Related technologies have been continuously validated and developed through missions such as TOMS-EP, TRMM, and MAP. Studies have confirmed that propellant formulations based on HAN / triethanolamine nitrate (TEAN) / water (LP1845, LP1846) have a higher density specific impulse than hydrazine, significantly reducing fuel mass, volume, and tank capacity while meeting the same total impulse requirements for a mission. In 2000, the US Air Force developed the AF-315 series of propellants, using HAN as the oxidizer and hydroxyethyl hydrazine nitrate as the fuel. In the same year, the SHP163 propellant, jointly developed by Japan's JAXA and other organizations, consisted of HAN, methanol, ammonium nitrate (AN), and water, and was successfully applied to the RAPIS-1 satellite in 2019. In 2010, the LMP-103S propellant (using ADN as the oxidizer), developed by the Swedish company ECAPS, was successfully validated in orbit during the PRISMA satellite mission as a green alternative to hydrazine. In addition to the aforementioned mature formulations, as early as 1993, Schmidt EW et al. systematically listed a wide variety of propellant components in their patent on the catalytic decomposition of HAN-based propellants (US05485722A), such as nitrates of a series of hydroxylamine, ammonium, and hydrazine compounds, including dimethyl hydroxylamine nitrate, diethyl hydroxylamine nitrate, TEAN, triethylenediamine nitrate, diethylenetriamine nitrate, ethylenediamine dinitrate, methylammonium nitrate, dimethylammonium nitrate, trimethylammonium nitrate, methylhydrazine nitrate, ethylenedihydrazine dinitrate, and di(hydroxyethyl)hydrazine nitrate. This provided an important foundation for subsequent formulation optimization.

[0004] Existing quantitative detection methods for the oxidant HAN include acid-base titration, diazo-coupled colorimetric spectrophotometry, and ion chromatography. For example, Zou Zhan et al. (Zou Zhan, Zhao Xuqun, Shi Hai. Analytical methods for hydrazine nitrate and hydroxylamine nitrate in nuclear wastewater. Industrial Water and Wastewater, 2019, 50(01):83-87) used acid-base titration to detect the HAN content in the solution. The HAN content was indirectly determined by reacting acetone with acetone to generate acetone oxime and nitric acid, and then titrating the nitric acid content with standard alkaline solution. However, this method has a long reaction time, a complex system, and difficulty in determining the endpoint, making it difficult to achieve automated analysis. Cao Ye et al. (Cao Ye, Zhang Zhi, Hu Wenxiang. Analysis of main components and impurities of hydroxylamine nitrate. Shanghai Aerospace, 2004(05):56-60) used diazo coupling colorimetric spectrophotometry. HAN can be directly oxidized to nitrous acid by iodine, then reacted with p-aminobenzenesulfonic acid to undergo diazotization, and finally coupled with 1-naphthylamine to generate a colored azo compound. The absorbance was measured at 520 nm for quantification. However, this method is cumbersome, involves many steps, and is easily affected by the sample matrix, resulting in numerous sources of error. Zhao Tan et al. (Zhao Tan, Mao Yanan, Zhu Zhenhui, et al. Determination of hydroxylamine nitrate aqueous solution by ion chromatography. Chemical Propellants & Polymer Materials, 2023, 21(01):62-64) optimized the column and mobile phase elution conditions in ion chromatography, and directly detected the hydroxylamine concentration using ion exchange mode, reducing the complexity of sample pretreatment and analytical errors. To determine the HAN concentration, the study hypothesized that HAN in the solution completely dissociates into hydroxylamine and nitrate ions, and performed quantitative analysis based on this hypothesis.

[0005] Quantitative detection methods for the oxidant ADN include ultraviolet spectrophotometry, potentiometric titration, and chromatography. For example, Tang Hong et al. (Tang Hong, Xia Baoqing, Wang Yanqi, et al. Ultraviolet spectrophotometric method for detecting dinitramide ammonium in workplace air. Chinese Journal of Health Laboratory Technology, 2004, 014(002):202-203.) studied an ultraviolet spectrophotometric method for monitoring and detecting ADN in workplace air. The experiment showed that the lowest detection concentration of the method was 0.006 mg / m³. 3When the concentration of RDX (rhexane) coexisting with ADN in the air is greater than 1.66 μg / ml, or the concentration of octogen (octogen) is greater than 3.32 mg / ml, it interferes with the determination. Ma Xingang et al. (Ma Xingang, Lin Xirong. Determination of purity of ADN. Solid Rocket Technology, 2001, 024(004):56-58.) used silver nitrate in a molecular sieve drying solvent (MI) to separate a small amount of ammonium nitrate (AN) impurities mixed in ADN, and determined the purity of ADN by non-aqueous potentiometric titration in MI medium using quaternary ammonium salt as titrant. The standard deviation of the method was 0.0019, and the coefficient of variation was 0.19%. Yang Caining et al. (Yang Caining, Chen Man, Jia Lin, et al. Determination of the purity of dinitramide ammonium by reversed-phase high performance liquid chromatography. Journal of Explosives and Pyrotechnics, 2014, 37(003):74-77.) established a method for determining the purity of ADN by reversed-phase high performance liquid chromatography. The ADN standard solution showed good linearity in the range of 0.0001-0.001 g / ml, with a relative standard deviation of 0.49% and an average recovery rate of 98.33%-99.67%.

[0006] Propellants can be classified according to their molecular characteristics, including nitrates of amines, ammonium compounds, and hydrazine compounds. Currently, the main detection methods for amine nitrates include spectrophotometry and chromatography. For example, Xiao Songtao et al. (Xiao Songtao, Ouyang Yinggen. Indirect spectrophotometric determination of monomethylhydrazine and dimethylhydroxylamine [J]. China Nuclear Science and Technology Report, 2008, (01): 68-72.) proposed an indirect spectrophotometric method for determining trace amounts of hydroxylamine and monomethylhydrazine based on the absorption peak at 510 nm formed by the reduction of Fe(III) to Fe(II) in a weakly acidic medium and the resulting complex with o-phenanthroline. This method provides accurate measurements, is easy to operate, and is suitable for the analysis of trace amounts of hydroxylamine, monomethylhydrazine, and their inorganic salts under normal conditions. Luo Yangu et al. (Luo Yangu, Cao Chao. A method for determining the content of triethylamine salts. Chongqing Ziguang International Chemical Co., Ltd., Chongqing, 2015-07-01.) found that converting triethylamine salts in samples to triethylamine before determining them by gas chromatography is simpler and faster. This method is suitable for determining the content of triethylamine salts in reaction liquids, mother liquors, intermediates, waste residues, and waste liquids in organic chemical production processes. It is of great significance for monitoring triethylamine-related chemical reaction processes, recovering and utilizing triethylamine, and treating waste residues and wastewater. Experimental data showed that the relative standard deviation (RSD) of the sample determination was 0.59 (%n=6), and the spiked recovery rate was 96.87%-99.36%.

[0007] The main detection methods for ammonium nitrates include potentiometric titration and conductivity method. For example, Zou Zhan et al. (Zou Zhan, Zhao Xuqun, Shi Hai. Detection of ammonium nitrate by potentiometric titration. China Testing, 2019, 45(1):60-63) used potentiometric titration to titrate the concentration of AN in aqueous solution, and conducted linearity, precision, and accuracy tests on the method. The method was also compared with the detection method in GB / T 659-2011 "Chemical Reagents Ammonium Nitrate". The experimental results showed that potentiometric titration can be used to detect the concentration of AN. Within the linear range of 0.05~1.50 mol / L, R 2 The value was 0.9999, and the relative standard deviation was 0.409%. When the volume of titrant consumed was maintained between 4 and 13 mL, the relative error of the experiment was less than 1%. At the same time, there was no significant difference from the determination results of the chemical titration method in GB / T 659-2011. Huang Yinsheng et al. (Huang Yinsheng, Liu Jie, Zeng Zhichao. Rapid detection method for concentration of ammonium nitrate aqueous solution. Explosive Materials, 2011, 40(1):16-18.) measured the conductivity of AN aqueous solution of known concentration at different temperatures and made a standard curve of temperature-conductivity-concentration of AN aqueous solution. The conductivity and temperature of the AN aqueous solution to be tested were measured and compared with the above standard curve to obtain the concentration of the AN aqueous solution to be tested. The standard curve data was imported into the production online monitoring system, and the measurement signals of conductivity and temperature of the AN aqueous solution to be tested were connected to the computer through the transmission line to realize the online rapid detection of the concentration of AN aqueous solution.

[0008] The main detection methods for hydrazine nitrates include chromatography and capillary electrophoresis. Xu Linnan et al. (Xu Linnan, Zhang Xuejun, Zhao Tan, Li Jun, Fang Tao. Hydrophilic chromatography-mass spectrometry analysis of hydroxyethylhydrazine nitrate content. Energetic Materials, 2020, 28(9):936-941.) developed a hydrophilic interaction-based chromatography-mass spectrometry method for the analysis of hydroxyethylhydrazine nitrate. The effects of mobile phase composition, mass spectrometry determination, and other analytical conditions on separation effect, analysis time, and detection sensitivity were investigated, and optimized liquid chromatography-mass spectrometry analysis conditions suitable for the analysis of hydroxyethylhydrazine nitrate were obtained. The established analytical method is effective in the range of 0.01–0.1 µg·mL⁻¹. -1 The correlation coefficient R within the sample concentration range 2 =0.9991, detection limit is 1.2 ng·mL -1 The method exhibits good accuracy and precision for concentrations of 0.0250 and 0.0900 µg·mL. -1The recoveries of HAN and hydroxyethylhydrazine nitrate in the hydroxylamine nitrate solution were 98.1% and 97.7%, respectively, with relative standard deviations ≤1.6%. Wang Yabin et al. (Wang Yabin, Li Guangyi, Xia Liangen, et al. A method for determining the content of HAN and hydroxyethylhydrazine nitrate in a hydroxylamine nitrate propellant: 202411818608[P]) provide a capillary electrophoresis internal standard method for determining the content of HAN and hydroxyethylhydrazine nitrate in non-toxic propellants. The internal standard used is an aminoguanidine salt compound. The separation conditions for capillary electrophoresis are: a total length of quartz capillary ranging from 40 to 100 cm, and an inner diameter of the column ranging from 50 to 100 μm. The capillary electrophoresis voltage used in this invention is 15-45 kV. The capillary electrophoresis of this invention uses pressure injection, with an injection pressure ranging from 0.1 to 1.0 psi and an injection time of 1 to 10 seconds. The detection wavelength used in this invention is ultraviolet 180-220 nm. The buffer solution is a commercially available cation exchange kit.

[0009] Ammonia (an aqueous solution of ammonia) is a relatively special liquid propellant. Given its significant differences in physicochemical properties compared to the aforementioned nitrates, its detection method needs further investigation. Currently, quantitative analysis methods for ammonia include infrared analysis, density methods, and ultrasonic methods. For example, Wei Na et al. (Wei Na, Pang Yike, Wang Yeting, et al. Research on the method of determining ammonia concentration using NIRS. China New Technologies & New Products, 2022(23):70-72.) explored a method for determining ammonia concentration based on near-infrared spectroscopy (NIRS), improving upon the shortcomings of traditional analytical methods which take too long. They measured the near-infrared spectrum and chemical analysis values ​​of the samples, and established a mathematical relationship between the two using chemometrics. After evaluating and validating the model, the samples were scanned, and the concentrations were measured. The results were compared with the national standard method using range normality tests and two-sample t-tests. The results showed that the near-infrared measurement system had good stability. Furthermore, compared with the national standard method, the range was controlled within 0.30%. Li Mei (Li Mei. Design exploration of a density meter in ammonia concentration monitoring system [J]. China Petroleum and Chemical Standards and Quality, 2024(21):118-120+123.), based on the relationship between liquid density and concentration, calculates the concentration of liquid ammonia by measuring the density of the solution; at the same time, taking the ammonia density monitoring system of a certain liquid ammonia absorption section as an example, she compared and analyzed multiple design schemes for ammonia concentration detection, and listed the precautions in the design process, in order to serve as a reference for similar projects. Huang Xiaohong et al. (Huang Xiaohong, Fan Xiaozhi, Jia Moyi. Design of ultrasonic ammonia concentration online analyzer. Journal of Hebei Polytechnic University, 2003, 25(4):129-133) designed an intelligent ammonia concentration online analyzer by combining ultrasonic detection technology with microcontroller technology. With the powerful processing function and computing power of the single-chip microcomputer, it successfully realized the real-time online analysis of ammonia concentration that cannot be completed by hardware alone, solving a long-standing problem in the production of small and medium-sized nitrogen fertilizer plants.

[0010] In summary, current quantitative analysis and detection schemes for oxidizers and propellants involve a wide variety of analytical methods and instruments, and the lack of consistency between detection methods for different types of oxidizers and propellants makes the detection process for two-component systems particularly complex. Existing methods suffer from several common limitations: for example, titration methods are cumbersome, endpoint determination is not sensitive enough, they are easily affected by coexisting substances, and their sensitivity is limited; spectrophotometry suffers from insufficient selectivity, is easily affected by other propellants, and its colorimetric reaction is extremely sensitive to conditions such as pH, temperature, and time, often requiring derivatization steps, which is time-consuming; while chromatographic analysis has high separation capabilities, its instruments are expensive, its operation requires high technical skills, it consumes a lot of mobile phase, and its analysis cycle is long, limiting its widespread application. Therefore, there is an urgent need to develop a novel, green, single-component propellant quantitative detection strategy that combines high sensitivity, simple and rapid operation, low cost, and strong anti-interference capabilities to meet the growing demand for accurate analysis and rapid response challenges. This has become a key technical problem that urgently needs to be solved in this field.

[0011] To address the aforementioned issues, this invention provides a rapid concentration determination method based on the linear relationship between refractive index, density, and concentration, which are inherent properties of the substance itself. Currently, the application of refractive index in industrial process monitoring is widespread, but these methods are all based on the detection of a single concentration index. For example, GB 5009.5-2016, "National Food Safety Standard - Determination of Protein in Food," uses the Kjeldahl method as its primary method. The principle is to measure the nitrogen content in the sample and then multiply it by a protein conversion factor. All other rapid methods (including the refractive index method) require calibration and verification based on this method. The core of the refractive index method for protein determination is a set of industry-recognized practices. Its accuracy relies entirely on establishing and calibrating the refractometer readings using the classical standard method (i.e., the Kjeldahl method), and it is mainly concentrated in specific systems with relatively stable components, such as human blood proteins, silk fibroin in the textile industry, or whey or skim milk in the dairy industry. For example, Fan Jing et al. (Fan Jing, Wang Xueqian; Rapid quality control of human hemoglobin concentration using a refractometer; Proceedings of the 4th National Congress of the Chinese Blood Transfusion Association; Tianjin Blood Center; 2006: 186.) established a modified refractometer method for rapid determination of hemoglobin concentration and compared the results of the Coulter method with those of the refractometer method. The results of the refractometer method and the Coulter method were basically consistent. Li Jigong et al. (Li Jigong, Zhu Jingxin, Shao Huili et al.; Method for rapid determination of regenerated silk fibroin aqueous solution concentration using refractive index; Liaoning Silk; 2006, (03): 4-6.) obtained the curve of regenerated silk fibroin aqueous solution concentration C-refractometer index n by measuring the refractive index of regenerated silk fibroin aqueous solution in different concentration ranges (2%-45%) using an Abbe refractometer, and fitted it with mathematical tools to obtain the equation characterizing this curve. Although the early and typical commercial cases of the refractometer method in solution concentration detection are concentrated on organic matter, it also has important teaching and practical value in the field of inorganic matter detection. In university physics experiments, the refractive index method is often used to measure the concentration of NaCl aqueous solution. For example, Ji Mingyi et al. (Ji Mingyi, Ma Xi, Wang Wei; Measurement of the refractive index of liquids; Science and Technology Innovation and Application, 2017(31): 83-85) used two methods, grazing incidence and Newton's rings method, to measure the refractive index of salt water of different concentrations. Through data analysis and comparison of the two methods, they concluded that the grazing incidence method is more accurate than the Newton's rings method.

[0012] The above applications fully demonstrate the significant value of the refractive index method as a rapid screening tool in teaching demonstrations and conventional industrial fields. It also shows considerable potential in the rapid detection of special chemicals such as monocomponent propellants. Studies have shown that at a specified temperature, the refractive index of a monocomponent propellant solution exhibits a good linear relationship with its concentration (R²>0.99), and this relationship remains valid in its mixed solutions, with the refractive index approximately satisfying the linear additive property of the refractive indices of each component. However, this rule holds true only if the physicochemical properties of the components in the mixture are similar (e.g., they are all inorganic substances). If it is necessary to determine the specific concentration of each component in a two-component or multi-component system, other physical parameters such as density and conductivity need to be introduced for joint modeling to compensate for the insufficient information provided by a single refractive index parameter. Summary of the Invention

[0013] The purpose of this invention is to overcome the above-mentioned defects in the prior art and provide a quantitative analysis method for the concentration of green propellant aqueous solution.

[0014] This invention establishes a quantitative analysis method for the concentration of green propellant aqueous solutions based on the synergistic measurement of density and refractive index. This aqueous solution system mainly consists of an oxidant (such as HAN, ADN), a propellant (such as ammonia; nitrates of amines, ammonium compounds, and hydrazine compounds), and water as a solvent. Studies show that the concentration and density of a single component exhibit a good linear relationship within a specific range. Taking Example 4 as an example, the concentration-density linear correlation coefficient R between the oxidant HAN and the propellant TEAN is... 2 The effective concentrations reached 0.9917 and 0.9965, respectively, with effective concentration ranges of 5.07–69.37 wt.% and 1.35–96.53 wt.%. It is noteworthy that the density-concentration relationship of the two-component mixture cannot be obtained by simply superimposing the single-component relationships. This is because the interactions between the components disrupt the strict linear superposition property. Therefore, a binary linear regression method is required to fit a linear model from the experimental data. The parameters of this model are optimized using the least squares method to minimize prediction errors. These regression coefficients are flexible, capturing the overall trend in the data and even absorbing nonlinear effects caused by interactions. In other words, the regression coefficients are empirical, and their values ​​integrate the intrinsic contributions of the components with the influence of interactions. For this reason, compared to the ideal linear superposition assumption, the data-driven binary linear regression model shows higher fitting accuracy. Based on this, according to the binary linear regression fitting, the equation for the concentration and density of the HAN-TEAN solution can be obtained, namely y = 0.005899x1 + 0.004514x2 + 0.989709, where x1 is the HAN concentration (range 5.07 ≤ x1 ≤ 69.37) and x2 is the TEAN concentration (range 1.35 ≤ x2 ≤ 96.53), R0. 2=0.9917; The equation for the concentration and density of the HAN-AN solution was obtained by binary linear regression fitting, namely y = 0.006073x1 + 0.006616x2 + 0.976815, where x1 is the HAN concentration (range 5.07 ≤ x1 ≤ 69.37) and x2 is the AN concentration (range 1.05 ≤ x2 ≤ 50.31), R0 2 =0.9899; In Example 5, the equation for the concentration and density of the ADN-NH3·H2O solution was obtained by binary linear regression fitting, namely y=0.006224x1-0.004360x2+0.979765, where x1 is the ADN concentration (range 5.05≤x2≤72.40) and x2 is the NH3·H2O concentration (range 1.30≤x2≤25.00), R 2 =0.9928. This invention achieves simultaneous solution of the concentrations of each component under known coexisting conditions by using density as the second parameter and simultaneously establishing a system of two linear equations with respect to refractive index. It should be noted that when the propellant is methanol-based organic compounds, the refractive index of the solution after mixing with the oxidant deviates from the linear assumption, making the linear equations in this method unsuitable for solution. For details on related nonlinearities, please refer to the discussion in Example 3 and Comparative Example 1.

[0015] Compared with existing methods for detecting green monocomponent propellants, this method offers significant advantages in terms of portability and simplified sample pretreatment procedures, resulting in a substantial reduction in detection time. This invention is applicable to the detection of two-component concentrations in green monocomponent propellants with known components (one of the following: oxidant is HAN or ADN; propellant is NH3·H2O, dimethylhydroxylamine nitrate, diethylhydroxylamine nitrate, TEAN, triethylenediamine nitrate, diethylenetriamine nitrate, ethylenediamine dinitrate, AN, methylammonium nitrate, dimethylammonium nitrate, trimethylammonium nitrate, methylhydrazine nitrate, dimethylhydrazine nitrate, ethylenedihydrazine dinitrate, hydroxyethylhydrazine nitrate, and di(hydroxyethyl)hydrazine nitrate). It provides a reliable and efficient analytical tool for quality control during production, storage stability assessment, and safe application, and has significant practical value for promoting the standardized production and widespread application of this type of propellant.

[0016] To achieve the above objectives, the technical solution of the present invention is as follows: A method for quantitative analysis of the concentration of a green propellant aqueous solution, wherein the green propellant aqueous solution is composed of an oxidant, a combustion agent, and a solvent water; The method utilizes the linear relationship between refractive index and density and concentration to determine the concentration of green propellant aqueous solution. It mainly consists of four steps: calibration, standard curve plotting, measurement, and calculation. The steps include: S1. Calibration steps: Calibrate the refractive index testing instrument using a standard solution at a specified temperature; S2. Steps for drawing a standard curve: A series of single-component standard aqueous solutions of the oxidant and the combustion agent were prepared separately, and their refractive indices were measured at the specified temperature. The refractive index concentration coefficient α of the oxidant was determined by linear regression. o and the refractive index concentration coefficient a of the propellant r The refractive index and concentration of the oxidizer and the propellant are respectively expressed as follows: n o =a o × C o + n w ; n r =a r × C r + n w ; Where, n o n is the refractive index of the standard aqueous solution of the oxidant. r n is the refractive index of the standard aqueous solution of the combustion agent. w C is the refractive index of water at a specified temperature. o and C r The concentrations of the oxidizer and the propellant are respectively, a o and a r For the coefficients obtained through linear regression of the standard curve, when the temperature and type of substance are determined, a o and a r It is a constant; At the specified temperature, a series of two-component standard aqueous solutions with varying concentrations of the oxidant and the propellant were prepared, and the mass and volume of each solution were measured to calculate the density ρ. m With oxidant concentration C o and propellant concentration C r Using a binary linear regression method with the oxidant as the independent variable, the density concentration coefficient k of the oxidant was determined. o and the density concentration coefficient k of the combustion agent r The relationship between oxidizer concentration and propellant concentration and density is as follows: ρ m =k o × C o + k r × C r + ρ w ; Where, ρ m The density of the green propellant aqueous solution is ρ. w C is the intercept in bivariate linear regression. o and C r The concentrations of the oxidizer and the propellant, respectively, are k. o and k rThe coefficients for the oxidizer and the propellant, respectively, are obtained through binary linear regression. When the temperature and the type of substance are determined, k... o and k r It is a constant; S3. Measure the refractive index n of the aqueous solution of the green propellant to be tested at the specified temperature. a and density ρ a ; S4. When the concentration of either the oxidant or the propellant in the solution to be tested is zero, the refractive index concentration coefficient and the measured refractive index n are used. a According to the linear equation n a =a x × C x + n w Calculate the concentration C of the target component. x； Where, n a Let a be the refractive index of the solution to be tested. x The refractive index concentration coefficient a of the oxidant o Or the refractive index concentration coefficient a of the propellant r n w The refractive index of water at a specified temperature; S5. When the concentrations of both the oxidant and the propellant in the test solution are not zero, based on the additive property of the refractive index of inorganic aqueous solutions, a two-variable linear equation with two independent variables, namely refractive index and oxidant concentration and propellant concentration, is established. This equation is then combined with a two-variable linear regression equation with density and oxidant concentration and propellant concentration to establish the following system of equations: n a =a o × C o + a r × C r + n w ; ρ a =k o × C o + k r × C r + ρ w ; Where, n a Let ρ be the refractive index of the solution to be tested. a Let a be the density of the solution to be tested. o Let a be the refractive index concentration coefficient of the oxidant. r Let n be the refractive index concentration coefficient of the propellant. w Let ρ be the refractive index of water at a specified temperature. w k is the intercept in bivariate linear regression. o and k rThese are the coefficients obtained through binary linear regression for the oxidizer and the propellant, respectively. When the temperature and type of substance are determined, a... o and a r k is a constant. o and k r The oxidant concentration C is a constant; solving the system of equations yields the oxidant concentration C. o and propellant concentration C r .

[0017] Optionally, the oxidant is selected from hydroxylamine nitrate and dinitramide ammonium.

[0018] Optionally, the propellant is selected from ammonia, dimethylhydroxylamine nitrate, diethylhydroxylamine nitrate, triethanolamine nitrate, triethylenediamine nitrate, diethylenetriamine nitrate, ethylenediamine dinitrate, ammonium nitrate, methylammonium nitrate, dimethylammonium nitrate, trimethylammonium nitrate, methylhydrazine nitrate, dimethylhydrazine nitrate, ethylenedihydrazine dinitrate, hydroxyethylhydrazine nitrate, and di(hydroxyethyl)hydrazine nitrate.

[0019] Optionally, the method is applicable to concentrations of 9-70 wt.% oxidant and 10-90 wt.% combustor.

[0020] Optionally, the specified temperature range is 10-50°C.

[0021] Optionally, the specified temperature range is 10-40°C.

[0022] Optionally, the standard solution is water or bromonaphthalene.

[0023] Implementing the embodiments of the present invention will have the following beneficial effects: This invention provides a quantitative analysis method for the concentration of aqueous solutions of green propellants. Refractive index measurement is convenient and quick; using an Abbe refractometer as an example, only 1-2 drops of sample (approximately 0.05-0.1 ml) are needed for each measurement, and the test time is only a few seconds. Density measurement, if using a precision pipette in conjunction with an electronic balance, requires approximately 1-2 mL of sample and takes approximately 1-2 minutes. Therefore, this method is characterized by high efficiency, small sample volume, no need for standard samples, and continuous repeatability. Attached Figure Description

[0024] Figure 1 This is the standard curve of the concentration of HAN aqueous solution versus the refractive index of HAN aqueous solution in Example 1.

[0025] Figure 2 This is a standard curve of the concentration and density of the HAN aqueous solution in Example 4. Detailed Implementation

[0026] The present invention will be further described below with reference to specific embodiments, but this does not limit the present invention in any way.

[0027] Example 1 Prepare a 90 wt.% HAN aqueous solution stock solution. The concentration of the HAN aqueous solution stock solution is determined by the current national standard method HG / T 6320-2024 for the concentration of the HAN sample solution. The detection principle is based on the reducing property of hydroxylamine ions in HAN. Specifically, it utilizes Fe... 3+ The oxidizing property of the hydroxylamine ion undergoes a redox reaction, oxidizing the hydroxylamine ion and simultaneously generating Fe. 2+ Subsequently, the generated Fe was analyzed using a potassium permanganate standard solution. 2+ A back titration was performed, and the hydroxylamine ion content was calculated by measuring the amount of potassium permanganate consumed. Since the concentration of HAN is directly proportional to the amount of hydroxylamine ions it contains, the measured hydroxylamine content can be regarded as the overall concentration of HAN.

[0028] The specific operating procedure is as follows: accurately weigh 0.10~0.12 g of sample (accurate to 0.0002 g) and place it in a clean 250 mL Erlenmeyer flask. Add 25 mL of ferric ammonium sulfate solution (200 g / L) to the flask, and then add 10 mL of sulfuric acid solution (1+9) along the wall. Boil for 5 min, and then titrate the solution with potassium permanganate standard titration solution (0.1 mol / L) until the solution turns pink, which is the endpoint.

[0029] Except for the absence of a sample, the blank test solution contained the same types and amounts of reagents as the test solution (excluding the standard titration solution). The HAN concentration test results are shown in Table 1.

[0030] Table 1. HAN Concentration Detected by National Standard Method

[0031] The HAN aqueous solution stock solution was diluted to obtain six portions of HAN aqueous solution with different concentrations: 1 wt.%, 10 wt.%, 30 wt.%, 50 wt.%, 70 wt.%, and 90 wt.%. Before the formal measurement, the refractive index measuring instrument needs to be calibrated using water as the calibration liquid, with a refractive index of 1.3330. After calibration, 1-2 drops from each diluted HAN aqueous solution stock solution were placed on the light-gathering prism of the refractive index measuring instrument. o The refractive index was read by C, and three parallel measurements were taken to obtain the average value. The specific data are shown in Table 2.

[0032] Table 2. Refractive index of HAN aqueous solution stock solutions of different concentrations measured by refractive index testing instrument.

[0033] Based on the data in Table 2, standard curves were plotted for HAN aqueous solutions of different concentrations and their corresponding refractive indices. The fitted equation is y = 0.001526x + 1.3330, where x is the concentration of the HAN aqueous solution and y is the refractive index of the HAN aqueous solution. See [link to table]. Figure 1 .

[0034] Take 1-2 drops of the aqueous solution of hydroxylamine nitrate to be tested and place it on the optical prism of the refractive index testing instrument. 20 o The refractive index was read by C, and the average value was taken for three parallel measurements. The HAN content was calculated using the standard curve plotted. The specific data are shown in Table 3.

[0035] Table 3. Specific concentrations of HAN aqueous solution obtained by measuring with a refractive index testing instrument.

[0036] Test solutions 1, 2, 3, 4, 5, and 6 were measured in triplicate. The relative standard deviations (RSDs) of the measured values ​​for test solutions 1, 2, 3, 4, 5, and 6 were 1.63%, 0.11%, 0.13%, 0.03%, 0.03%, and 0.01%, respectively. This data indicates good precision, minimal fluctuation, and good repeatability. In the low concentration range, the instrument's signal-to-noise ratio is relatively low, and small fluctuations in the absolute measured values ​​are amplified, leading to a significant increase in the calculated RSD.

[0037] The accuracy of the method was verified by measuring the spiked recovery rate of the samples. Two high-concentration standard solutions were added to samples with known concentrations at a mass ratio of 1:1. The refractive index was then measured using a refractive index measuring instrument according to the above method, and the recovery rate was calculated. The results are shown in Table 4.

[0038] Table 4. Spiking recovery rate of HAN content in aqueous solution determined by refractive index test.

[0039] Table 4 shows that the spiked recovery rate of HAN is 99%, indicating that the method has high accuracy and can meet the requirements of quantitative analysis. The precision and spiked recovery experiments above demonstrate that the method for detecting HAN content in aqueous solution using the refractive index method described in this invention is convenient and feasible. This method has high precision and good spiked recovery rate, enabling accurate and reliable quantitative detection of HAN.

[0040] Example 2 Using a refractive index measuring instrument at different specified temperatures, 10 ± 1 o C, 30 ± 1 o C, 40 ± 1 o C, 50 ±1o C. The refractive index of test solutions 1, 2, 3, 4, and 5 in Example 1 was measured. Before the formal measurement, the refractive index testing instrument needed to be calibrated using water as the calibration liquid, with a calibration value of 10 ± 1. o C, 30 ± 1 o C, 40 ± 1 o C, 50 ± 1 o The refractive indices of C are 1.3337, 1.3319, 1.3306, and 1.3290, respectively. After calibration, 1-2 drops of the diluted HAN aqueous solution stock solution from Example 1 were taken and dropped onto the light-gathering prism of the refractive index testing instrument. The refractive index was read, and the average value was taken for three parallel measurements. The specific data are shown in Table 5.

[0041] Table 5. Refractive index of HAN aqueous solution stock solution of different concentrations measured by refractive index testing instrument at different temperatures.

[0042] Based on the data in Table 5, standard curves were plotted for HAN aqueous solutions of different concentrations at different temperatures and their corresponding refractive indices using the refractive index testing instrument. The fitting equations are shown in Table 6.

[0043] Table 6. Linear fitting equations for HAN aqueous solution concentration-refractive index at different temperatures

[0044] As shown in Table 6, 10 o C≤Specified Temperature≤40 o At temperature C, the refractive index data measured for the HAN aqueous solution stock solution are almost on a straight line, but at 50°C... o The refractive index data measured at time C deviated from a straight line after fitting, and the linear correlation coefficient R 2 The low value is due to the evaporation of water from the aqueous solution of hydroxylamine nitrate at high temperatures.

[0045] Take 1-2 drops of the aqueous solutions of hydroxylamine nitrate to be tested 1, 2, 3, 4, 5 and 6 in Example 1 respectively, drop them onto the light-gathering prism of the refractive index testing instrument, read the refractive index at different specified temperatures, take the average value of three parallel measurements, and calculate the HAN content using the standard curve plotted. The specific data are shown in Table 7.

[0046] Table 7. Specific concentrations of HAN aqueous solution obtained by refractive index testing instrument at different specified temperatures.

[0047] As shown in Table 7, the specified temperature is 50. oAt temperature C, the overall HAN content of the test solution is too high. This is because the HAN aqueous solution evaporates quickly at high temperatures, resulting in a larger overall measurement error.

[0048] Based on this, the above data was integrated, and the linear fitting equation was further extended to obtain a two-dimensional temperature-concentration-refractive index table. This table excludes values ​​at a specified temperature of 50°C. o The detection data at time C is shown in Table 8. The values ​​in the table are the average values ​​obtained after three parallel tests.

[0049] Table 8. Refractive index of HAN aqueous solutions of different concentrations at different temperatures

[0050] To verify the universality of this method, refractive indexes of aqueous solutions of various substances were selected for measurement, including ADN, methanol (MeOH), triethanolamine nitrate (TEAN), ammonium nitrate (AN), and ammonia (NH3·H2O). The refractive indexes were measured using a refractive index measuring instrument at a temperature of 20 ± 1°C. Before the formal measurement, the refractive index measuring instrument needed to be calibrated using water as the calibration liquid, with a refractive index of 1.3330. After calibration, 1-2 drops of the test aqueous solution were placed on the optical prism of the instrument, and the refractive index was measured. Each group of samples was measured in triplicate, and the average value was taken as the final result. Specific data are shown in Table 9.

[0051] Table 9. Refractive index of aqueous stock solutions with different concentrations measured by refractive index testing instruments.

[0052] Based on the data in Table 9, standard curves were plotted for different concentrations of aqueous solutions of different substances and their corresponding refractive indices obtained by measuring the refractive index at 20 ± 1°C using a refractive index measuring instrument. The fitting equations are shown in Table 10.

[0053] Table 10 Linear fitting equations for aqueous solution concentration-refractive index at different temperatures

[0054] Table 10 shows that the standard curves plotted from the aqueous solutions of different substances at different concentrations and their corresponding refractive indices obtained at 20 ± 1°C have a linear correlation coefficient R0. 2 >0.99.

[0055] Example 3 Furthermore, a mixed aqueous solution of HAN and TEAN was prepared, and the refractive index of the system was measured. Each group of samples was measured in parallel three times, and the average value was taken as the final result. The specific data are shown in Table 11.

[0056] Table 11 Refractive index of mixed solutions of HAN and TEAN at different concentrations

[0057] It is worth noting that the refractive index of the above mixed solution can be obtained by superimposing the linear equations fitted in Tables 2 and 10. For example, in measurement sequence 1 in Table 11, the concentrations of HAN and TEAN are both 10 wt.%, so the theoretical refractive index is equal to (0.0014×10+0.0014×10+1.3330) = 1.3610. The theoretical refractive index calculations are performed on the above sequences, and the specific values ​​are shown in Table 12.

[0058] Table 12 Comparison of theoretical and measured refractive indices of mixed solutions of HAN and TEAN at different concentrations

[0059] As shown in Table 12, the absolute errors of measurement sequences 1-8 are -0.0003, -0.0007, -0.0004, -0.0009, -0.0007, -0.0006, -0.0004, and -0.0006, respectively. Further analysis of the above data shows that the relative errors of measurement sequences 1-8 are -0.02%, -0.05%, -0.02%, -0.06%, -0.04%, -0.04%, -0.03%, and 0.04%, respectively, indicating that the overall error is relatively small.

[0060] Relative error is an analytical tool used to evaluate the proportion of error at a single point. To assess the overall error among the multiple data points, the root mean square error (RMSE) is used for further data analysis. The analysis above shows an RMSE of 0.06%. Given that the measured and theoretical values ​​range from approximately 1.36 to 1.46, the data magnitude is approximately 10^- ... 0 (Single digit), the data range is about 0.1, and the RMSE accounts for about 0.6% of the data range, indicating that the theoretical value and the measured value are in good agreement.

[0061] Furthermore, HAN-AN mixed aqueous solution, HAN-MeOH mixed aqueous solution, ADN-MeOH mixed aqueous solution, and ADN-NH3·H2O mixed aqueous solution were prepared, and the refractive index of their mixed systems was measured. Each group of samples was measured in parallel three times, and the average value was taken as the final result. The specific data are shown in Table 13. Table 13 Refractive index detection of mixed solutions of different substances at different concentrations

[0062] As shown in Table 13, when inorganic substances are mixed, the measured refractive index and the theoretical refractive index are relatively close, with an absolute error of -0.0008 ≤ -0.0005. However, when the mixed solution contains organic substances, the measured refractive index and the theoretical refractive index are relatively close, with an absolute error of -0.0090 ≤ -0.0030. The detection range of refractive index is generally 1.3000-1.7000, with a variation range of only 0.4000. As can be seen from the above detection, the detection range of refractive index of the screened known substances is 1.333-1.4800, with a variation range of only 0.1470. Therefore, an error of 0.0090 may lead to a concentration judgment error of more than 6.12 wt.%. In quantitative analysis and quality control, this error is too large and is only suitable for preliminary screening or rapid on-site detection, which is barely acceptable. An error of 0.0008 may lead to a relative error in concentration judgment of less than 0.5 wt.%. This error is acceptable in scientific research experiments, industrial testing, and process control.

[0063] The total concentration of the mixed solution is the sum of the concentrations of each component. When all solutes are inorganic, each component has a good linear fit to the relationship between refractive index and concentration. Furthermore, under the premise of no significant interaction, the refractive index can be calculated by summing according to the weight of each component.

[0064] Example 4 Room temperature 20 o At time C, prepare HAN-TEAN two-component standard aqueous solution, and use a precision analytical balance and volumetric instruments to measure the mass and volume of each solution to calculate the density. The specific values ​​are shown in Table 14.

[0065] Table 14 Densities of aqueous solutions containing different substances at different concentrations and mixtures of different substances

[0066] A linear fit was performed on the data sequences 1-7 above, and the fitted equation is y = 0.005513x + 1.0000, R0. 2 =0.9917, where x is the concentration of the HAN aqueous solution and y is the density of the HAN aqueous solution. See details... Figure 2 Linear fitting was performed on the above data sequences 1 and 8-13, and the fitted equation is y = 0.004446x + 1.0000, R0. 2=0.9965, where x is the concentration of the HAN aqueous solution and y is the density of the TEAN aqueous solution. Assuming the concentration-density coefficients of the HAN-HEHN mixed solution can be simply superimposed using a linear relationship, we obtain the linear equation: y = 0.005513x1 + 0.004446x2 + 1.0000, where x1 is the HAN concentration and x2 is the TEAN concentration. Substituting the concentration of sequence 15 into the above linear equation, we find that the theoretical density should be 1.2361, and the actual density is 1.2260. Substituting the concentration of sequence 16 into the above linear equation, we find that the theoretical density should be 1.3407, and the actual density is 1.3565. The relative errors of the two sets of data reach -0.82% and +1.18%, respectively, which are higher than the generally acceptable accuracy range (<0.5%) in density measurements, highlighting the room for optimization in the current fitting process.

[0067] Based on this, a binary linear regression fitting was performed on the above data, resulting in equation (1): y = 0.005899x1 + 0.004514x2 + 0.989709, where x1 is the HAN concentration (range 5.07 ≤ x1 ≤ 69.37) and x2 is the TEAN concentration (range 1.35 ≤ x2 ≤ 96.53). R 2 =0.9917, Equation (1) and the refractive index equation (2) y=0.001526x1+0.001392x2+1.3330 are combined, and the target binary component concentration can be obtained by solving the equation.

[0068] The refractive index and density of HAN-TEAN mixed solutions with different ratios and unknown concentrations were measured, and the specific values ​​are shown in Table 15.

[0069] Table 15 Refractive index and density of the HAN-TEAN test solution

[0070] Based on the data in Table 15, we can obtain the system of two linear equations in two variables: (3), (4), (5), (6), and (7):

[0071] Solving the system of equations (3), (4), (5), (6), and (7) yields x1 and x2. The obtained x1 and x2 are then compared and analyzed with the theoretical values, as shown in Table 16.

[0072] Table 16 Measured and theoretical values ​​of solutions to equations (3), (4), (5), (6), and (7)

[0073] Based on the data analysis in Table 16, there is a significant difference between the solved values ​​of Equation 3 and the actual theoretical values, while the differences in Equations 4, 5, 6, and 7 are relatively smaller. Specifically, the percentage error of x2 in Equation 3 is as high as 49.00%, indicating that under the conditions of Equation 3, the theoretical model of the x2 variable may be significantly inconsistent with the actual measurement. Further comparison using Euclidean distance error shows that the error value of Equation 3 is 3.47. The percentage errors of x1 and x2 in Equations 4, 5, 6, and 7 are 1.23%, 4.08%, 4.61%, 1.82%, 2.81%, 0.45%, 3.96%, and 0.32%, respectively. In summary, Equation 3 has a significant error in the low concentration region (x2 ≤ 5.02 wt.%), while the calculation errors of Equations 4, 5, 6, and 7 are ≤ 5%. To ensure measurement accuracy, this paper corrects the effective concentration range of the TEAN component in the HAN-TEAN two-component system to 9.57 ≤ x2 ≤ 96.53 wt.%.

[0074] Furthermore, at room temperature 20 o At time C, prepare a HAN-AN two-component standard aqueous solution. Use precision analytical and volumetric instruments to measure the mass and volume of each solution to calculate the density. The specific values ​​are shown in Table 17.

[0075] Table 17 Densities of aqueous solutions containing different substances at different concentrations and mixtures of different substances

[0076] A binary linear regression was performed on the above data to obtain equation (8): y = 0.006073x1 + 0.006616x2 + 0.976815, where x1 is the HAN concentration (range 5.07 ≤ x1 ≤ 69.37) and x2 is the AN concentration (range 1.05 ≤ x2 ≤ 50.31). R 2 =0.9899, ​​equation (8) and refractive index equation (9) y=0.001526x1+0.001309x2+1.3330 are combined, and the target two-component concentration can be obtained by solving the equation. The refractive index and density of HAN-AN mixed solutions with different ratios and unknown concentrations are detected. The specific values ​​are shown in Table 18.

[0077] Table 18 Refractive index and density of the HAN-AN test solution

[0078] Based on the data in Table 18, we can obtain the system of two linear equations in two variables (10) and (11):

[0079] Solving the system of equations (10) and (11) yields x1 and x2. The obtained x1 and x2 are then compared and analyzed with the theoretical values, as shown in Table 19.

[0080] Table 19 Measured and theoretical values ​​of the solutions to equations (10) and (11)

[0081] Table 19 shows that the solutions to equations 10 and 11 exhibit some differences: for equation 10, x1 is 0.46 larger and x2 is 0.12 smaller; for equation 11, x1 is 0.97 larger and x2 is only 0.03 smaller. Percentage error analysis shows that the errors for x1 and x2 in equation 10 are 4.33% and 0.49%, respectively, while those in equation 11 are 1.65% and 0.65%. The overall deviations, measured by Euclidean distance, are 0.48 and 0.97, respectively. The results indicate that the current data accuracy still meets the requirements for solving simultaneous equations with high-precision refractive index data.

[0082] Further tests were conducted on known two-component aqueous solutions of HAN and different combustion agents using the methods described above. The specific test results are shown in Table 20.

[0083] Table 20 Measured and theoretical values ​​for oxidizer HAN and different combustion agents

[0084] Table 20 shows that, from 1 to 14, the absolute deviations between the theoretical and measured values ​​of HAN are 0.49, 1.28, 1.52, 1.52, 1.53, 1.54, 1.18, 1.59, 0.92, 1.02, 1.22, 1.56, 1.38, and 1.69, respectively, and their relative deviations are 1.61%, 4.18%, 4.95%, 4.98%, 4.99%, 4.99%, 3.92%, 5.14%, 3.02%, 3.35%, 3.96%, 5.05%, 4.40%, and 5.25%, respectively. The absolute deviations between the theoretical and measured values ​​of different propellants from 1 to 14 are... The values ​​are 0.68, 0.88, 1.13, 1.16, 1.40, 1.14, 1.52, 0.71, 1.52, 1.24, 1.52, 1.29, 1.34, and 1.20, respectively, with relative deviations of 6.65%, 5.74%, 7.12%, 5.71%, 6.59%, 4.89%, 6.19%, 3.33%, 6.45%, 5.55%, 6.01%, 4.27%, 4.45%, and 4.74%. Considering that simultaneous solution algorithms typically have a tolerance of less than 5% to 10% for errors in the input data, the current accuracy level of the data is sufficient to ensure the reliability of the solution results.

[0085] Example 5 Room temperature 20 o At time C, a two-component standard aqueous solution of ADN-NH3·H2O was prepared. The mass and volume of each solution were measured using a precision analytical balance and volumetric instruments to calculate the density. The specific values ​​are shown in Table 21.

[0086] Table 21 Densities of aqueous solutions containing different substances at different concentrations and mixtures of different substances

[0087] A binary linear regression fit was performed on the above data, resulting in equation (12): y = 0.006224x1 - 0.004360x2 + 0.979765, where x1 is the ADN concentration (range 5.05 ≤ x2 ≤ 72.40) and x2 is the NH3·H2O concentration (range 1.30 ≤ x2 ≤ 25.00), R 2 =0.9928, equation (12) and refractive index equation (13) y=0.001968x1+0.0004009x2+1.3330 are combined, and the target two-component concentration can be obtained by solving the equation. The refractive index and density of ADN-NH3·H2O mixed solutions with different ratios and unknown concentrations are detected. The specific values ​​are shown in Table 22.

[0088] Table 22 Refractive index and density of the ADN-NH3·H2O solution to be tested

[0089] Based on the data in Table 22, we can obtain the system of two linear equations in two variables: (14), (15), (16), and (17).

[0090] Solving equations (14), (15), (16), and (17) yields x1 and x2. Substituting the obtained x1 and x2 back into the equations yields the theoretical values ​​of refractive index and density, as shown in Table 23.

[0091] Table 23 Measured and theoretical values ​​of the solutions to equations (14), (15), (16), and (17)

[0092] Based on the data in Table 23, a difference analysis was performed on equation sets 14, 15, 16, and 17. The results show that for equation set 14, x1 is too large by 0.55 and x2 is too small by 0.73; for equation set 15, x1 is too small by 1.90 and x2 is too small by 0.83; for equation set 16, x1 is too small by 0.26 and x2 is too small by 0.61; and for equation set 17, x1 is too small by 0.12 and x2 is too small by 0.19. In the percentage error analysis, the x1 error for equation set 14 is 5.34% and the x2 error is 3.59%; for equation set 15, the x1 error is 4.00% and the x2 error is 11.43%; for equation set 16, the x1 error is 0.45% and the x2 error is 12.50%; and for equation set 17, the x1 error is 0.17% and the x2 error is 2.59%. The overall deviation is measured by Euclidean distance, with values ​​of 0.91, 2.07, 0.66, and 0.22 for equations 12, 13, 14, and 15, respectively.

[0093] In summary, at low concentrations, there is a significant deviation between the theoretical model and the measured values, especially in the x2 (ammonia) dimension; although deviations exist, the numerical results are still within an acceptable range. As the system concentration increases, the solution accuracy improves significantly, and the measured values ​​agree closely with the theoretical values. These results demonstrate that this method possesses good accuracy and precision in a high concentration range, enabling quantitative analysis of known two-component aqueous solutions of green propellants.

[0094] Further, ADN and known two-component aqueous solutions with different combustion agents were tested using the above method. The specific test results are shown in Table 24.

[0095] Table 24 Measured and theoretical values ​​for oxidizer ADN and different combustion agents

[0096] Table 24 shows that, from 1 to 15, the absolute deviations between the theoretical and measured values ​​of ADN are 0.60, 0.66, 0.75, 0.48, 0.78, 1.05, 0.48, 1.35, 1.42, 1.82, 1.47, 1.06, 1.53, 1.20, and 1.15, respectively, and their relative deviations are 2.37%, 2.50%, 3.08%, 1.82%, 2.85%, 4.07%, 1.76%, 5.06%, 5.11%, 6.31%, 5.06%, 3.77%, 5.55%, 4.24%, and 3.83%, respectively. The absolute deviations between the theoretical and measured values ​​of different propellants from 1 to 15 are... The values ​​are 0.56, 0.78, 0.60, 0.62, 0.34, 0.45, 0.55, 1.91, 1.62, 1.09, 1.23, 1.03, 1.43, 1.13, and 1.52, respectively, with relative deviations of 2.75%, 3.93%, 2.55%, 2.53%, 1.46%, 2.11%, 2.44%, 8.36%, 6.88%, 4.66%, 5.01%, 4.12%, 6.39%, 5.03%, and 7.36%. Considering that simultaneous solution algorithms typically have a tolerance of less than 5% to 10% for errors in the input data, the current accuracy level of the data is sufficient to ensure the reliability of the solution results.

[0097] Comparative Example 1 Room temperature 20 o At time C, prepare a two-component standard aqueous solution of HAN-MeOH. Use a precision analytical balance and volumetric instruments to measure the mass and volume of each solution to calculate the density. The specific values ​​are shown in Table 25.

[0098] Table 25 Densities of aqueous solutions containing different substances at different concentrations and mixtures of different substances

[0099] A binary linear regression was performed on the above data to obtain the equation (18) y=0.005666x1-0.001960x2+0.99275, where x1 is the HAN concentration (range 5.07≤x1≤69.37) and x2 is the MeOH concentration (range 5.30≤x2≤100), R 2 =0.9951, Equation (18) and the refractive index equation (19) y=0.001526x1-0.0002340x2+1.3330 (0≤x2≤30 wt. %) are combined, and the target binary concentration can be obtained by solving the equation. It is worth noting that the linear range of refractive index-concentration of MeOH is 0-30 wt. %, based on this, the range of x2 is the intersection of equations (18) and (19), that is, 0≤x2≤30 wt. %.

[0100] The refractive index and density of HAN-MeOH mixed solutions with different ratios and unknown concentrations were measured, and the specific values ​​are shown in Table 26.

[0101] Table 26 Refractive index and density of the HAN-MeOH test solution

[0102] Based on the data in Table 26, we can obtain the system of two linear equations in two variables (20) and (21):

[0103] Solving the system of equations (20) and (21) yields x1 and x2. The obtained x1 and x2 are compared and analyzed with the theoretical values, as shown in Table 27.

[0104] Table 27 Measured and theoretical values ​​of the solutions to equations (20) and (21)

[0105] According to the data in Table 27, the actual values ​​of x1 and x2 obtained from equations (20) and (21) deviate significantly from the theoretical values, and x2 even shows a negative value. This is because the refractive index equation in one of these equations is based on the premise that "the refractive index contributions of each component are additive," a premise that usually holds true when the solute is inorganic and there are no significant interactions. However, this premise fails in the HAN-MeOH mixed solution, causing the relationship between its refractive index and concentration to deviate from the linear additive law. Therefore, the equations established based on the incorrect premise are inherently inaccurate, and their solutions inevitably deviate significantly from the theoretical concentration.

[0106] The method of this invention significantly improves detection efficiency while ensuring high accuracy and good reproducibility. It is simple to operate and easy to implement, effectively filling the gap in the current lack of rapid methods for determining the content of each component in aqueous solutions of green single-component propellants. Compared with existing technologies, this invention has significant advantages in speed, accuracy, and practicality, demonstrating good prospects for industrial application. The above embodiments and comparative examples are used to explain and illustrate this invention, not to limit it. Those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

[0107] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for quantitative analysis of the concentration of a green propellant aqueous solution, characterized in that, The green propellant aqueous solution is composed of an oxidant, a combustion agent, and a solvent, water. The method includes the following steps: S1. Calibration steps: Calibrate the refractive index testing instrument using a standard solution at a specified temperature; S2. Steps for drawing a standard curve: A series of single-component standard aqueous solutions of the oxidant and the combustion agent were prepared separately, and their refractive indices were measured at the specified temperature. The refractive index concentration coefficient α of the oxidant was determined by linear regression. o and the refractive index concentration coefficient a of the propellant r The refractive index and concentration of the oxidizer and the propellant are respectively expressed as follows: n o =a o × C o + n w ; n r =a r × C r + n w ; Where, n o n is the refractive index of the standard aqueous solution of the oxidant. r n is the refractive index of the standard aqueous solution of the combustion agent. w C is the refractive index of water at a specified temperature. o and C r The concentrations of the oxidizer and the propellant are respectively, a o and a r For the coefficients obtained through linear regression of the standard curve, when the temperature and type of substance are determined, a o and a r It is a constant; At the specified temperature, a series of two-component standard aqueous solutions with varying concentrations of the oxidant and the propellant were prepared, and the mass and volume of each solution were measured to calculate the density ρ. m With oxidant concentration C o and propellant concentration C r Using a binary linear regression method with the oxidant as the independent variable, the density concentration coefficient k of the oxidant was determined. o and the density concentration coefficient k of the combustion agent r The relationship between oxidizer concentration and propellant concentration and density is as follows: r m =k o × C o + k r × C r + p w ; Where, ρ m The density of the green propellant aqueous solution is ρ. w C is the intercept in bivariate linear regression. o and C r The concentrations of the oxidizer and the propellant, respectively, are k. o and k r The coefficients for the oxidizer and the propellant, respectively, are obtained through binary linear regression. When the temperature and the type of substance are determined, k... o and k r It is a constant; S3. Measure the refractive index n of the aqueous solution of the green propellant to be tested at the specified temperature. a and density ρ a ; S4. When the concentration of either the oxidant or the propellant in the solution to be tested is zero, the refractive index concentration coefficient and the measured refractive index n are used. a According to the linear equation n a =a x × C x + n w Calculate the concentration C of the target component. x； Where, n a Let a be the refractive index of the solution to be tested. x The refractive index concentration coefficient a of the oxidant o Or the refractive index concentration coefficient a of the propellant r n w The refractive index of water at a specified temperature; S5. When the concentrations of both the oxidant and the propellant in the test solution are not zero, establish the following system of equations: n a =a o × C o + a r × C r + n w ; r a =k o × C o + k r × C r + p w ; Where, n a Let ρ be the refractive index of the solution to be tested. a Let a be the density of the solution to be tested. o Let a be the refractive index concentration coefficient of the oxidant. r Let n be the refractive index concentration coefficient of the propellant. w Let ρ be the refractive index of water at a specified temperature. w k is the intercept in bivariate linear regression. o and k r These are the coefficients obtained through binary linear regression for the oxidizer and the propellant, respectively. When the temperature and type of substance are determined, a... o and a r k is a constant. o and k r The oxidant concentration C is a constant; solving the system of equations yields the oxidant concentration C. o and propellant concentration C r .

2. The method for quantitative analysis of the concentration of green propellant aqueous solution according to claim 1, characterized in that, The oxidant is selected from hydroxylamine nitrate and dinitramide ammonium.

3. The method for quantitative analysis of the concentration of green propellant aqueous solution according to claim 1, characterized in that, The propellant is selected from one of the following: ammonia, dimethylhydroxylamine nitrate, diethylhydroxylamine nitrate, triethanolamine nitrate, triethylenediamine nitrate, diethylenetriamine nitrate, ethylenediamine dinitrate, ammonium nitrate, methylammonium nitrate, dimethylammonium nitrate, trimethylammonium nitrate, methylhydrazine nitrate, dimethylhydrazine nitrate, ethylenedihydrazine dinitrate, hydroxyethylhydrazine nitrate, and di(hydroxyethyl)hydrazine nitrate.

4. The method for quantitative analysis of the concentration of green propellant aqueous solution according to claim 1, characterized in that, The method is applicable to concentration ranges of 9-70 wt.% for oxidants and 10-90 wt.% for combustors.

5. The method for quantitative analysis of the concentration of green propellant aqueous solution according to claim 1, characterized in that, The specified temperature range is 10-50°C.

6. The method for quantitative analysis of the concentration of green propellant aqueous solution according to claim 1, characterized in that, The specified temperature range is 10-40°C.

7. The method for quantitative analysis of the concentration of green propellant aqueous solution according to claim 1, characterized in that, The standard solution is water or bromonaphthalene.

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