Application of Zn-based metal organic framework as combustion catalyst in propellant

Abstract

The invention discloses an application of a Zn-based metal organic framework as a combustion catalyst in propellant powder, the Zn-based metal organic framework material is ZIF-8, and the Zn-based metal organic framework material is synthesized by mixing a methanol solution of Zn (NO3) 2 and a methanol solution of 2-methylimidazole and then carrying out hydrothermal reaction. The ZIF-8 and the NC-TEGDN-RDX three-base propellant are evenly mixed through a paper folding method, the ZIF-8 can well wrap the three-base propellant, and the ZIF-8 can serve as a combustion catalyst for promoting thermal decomposition of components of the three-base propellant with a nitrogen-rich heterocyclic compound as an organic connector, a unique molecular structure and high formation heat.

Description

Technical Field

[0001] The present invention relates to the application of Zn-based metal-organic framework materials as combustion catalysts in propellants, belonging to the technical field of propellants. Background Art

[0002] Propellants are important materials used in military equipment such as rockets, missiles, and artillery shells. The mixed ester propellant containing triethylene glycol dinitrate (TEGDN, Taigen) has the characteristics of relatively high energy and good mechanical properties. (Ma Fangsheng, Liao Xin, Wang Zeshan. Influence of catalysts on the combustion performance of Taigen propellant charges [J]. Journal of Ballistics, 2011, 23(01): 9-12+22.). However, in order to meet the new requirements of weapon development for the energy performance of propellants, hexogen (RDX) is often added to Taigen propellant to form NC-TEGDN-RDX triple-base propellant (Xue Huan, He Weidong, Xu Hantao. Study on the thermal decomposition and combustion performance of modified high-energy Taigen propellant [J]. Energetic Materials, 2015, 23(8): 791-795.), which can significantly improve the combustion characteristics of the propellant energy. Among them, the combustion characteristics based on the energy release rate, efficiency, and stability are the key factors affecting the performance of NC-TEGDN-RDX triple-base propellant. However, how to effectively adjust the combustion performance, control the combustion process of the propellant and the law of gas release, and improve the work capacity of the propellant gas, thereby improving the combustion performance [Influence of several metal oxide catalysts on the thermal decomposition performance of double-base propellant], has always been a hot and difficult point in the research of propellants.

[0003] In recent years, the use of combustion catalysts can regulate and improve the thermal and combustion properties of propellants, and can solve the above-mentioned problems (Liu Jinjian, Liu Zuliang, Cheng Jian. Combustion catalytic properties of Ni(II) and Cu(II) energetic complexes of 2,6-diamino-3,5-dinitropyridine-1-oxide [J]. Chinese Journal of Explosives & Propellants, 2015(5): 63-68.). The most common combustion catalysts, such as elemental metals (Qin L, Gong T, Li J, et al. Tuning ignition and energy release properties of Zirconium powder by atomic layer deposited metal oxide coatings [J]. Journal of Hazardous Materials, 2019, 378: 120655.), nano-metal oxides, metal energetic complexes, ferrocene and its derivatives, etc. (Yunfei L, Shaohua J, Hongtao Y, et al. Application of 3D energetic metal-organic frameworks containing Cu as the combustion catalyst to composite solid propellant [J]. Combustion and Flame, 2021, 225: 57-64.) can improve their combustion performance, but most of them are inert catalysts, which reduce the overall energy of the propellant.

[0004] MOFs use nitrogen-rich heterocyclic compounds as organic linkers, and show their application potential as a new generation of combustion catalysts due to their unique molecular structure and high heat of formation. It can not only regulate the combustion performance of propellants, but also improve the energy level of propellants. Summary of the Invention

[0005] The purpose of the present invention is to provide an application of a Zn-based metal-organic framework material ZIF-8 as a combustion catalyst.

[0006] The implementation process of the present invention is as follows: The application of a Zn-based metal-organic framework material as a combustion catalyst in propellants, wherein the Zn-based metal-organic framework material is ZIF-8, which is synthesized by hydrothermal reaction after mixing a methanol solution of Zn(NO3)2 and a methanol solution of 2-methylimidazole.

[0007] Preferably, the hydrothermal reaction temperature is 120 °C and the time is 20 h.

[0008] Preferably, in terms of molar ratio, Zn(NO3)2∶2-methylimidazole = 1∶4.

[0009] Preferably, the mass ratio of ZIF-8 to the propellant is 0.03:0.97.

[0010] Compared with the prior art, the present invention has the following advantages:

[0011] (1) The present invention uses the low-cost and environmentally friendly ZIF-8 metal-organic framework as the catalyst for the propellant. Due to its unique rigid skeleton structure, as well as good thermal stability and mechanical hardness, it is beneficial to reduce the sensitivity of the system to the outside world. At the same time, introducing high-energy components into the skeleton can achieve an effective balance between energy release and low sensitivity.

[0012] (2) The ZIF-8 metal-organic framework of the present invention can well encapsulate the propellant to form a relatively uniform system, and in-situ generate metal oxides during the combustion process. At the same time, MOF also has the ability to catalyze the combustion reaction, and it has high activity in catalyzing the oxidation reactions of organic substances such as alkanes and alkenes, as well as CO. Introducing nitrogen-rich ligands can also effectively improve the energy characteristics of the system and can be used as an excellent oxidant and combustion catalyst in the propellant system. Description of the Drawings

[0013] Figure 1 It is the SEM image of ZIF-8.

[0014] Figure 2 It is the particle size distribution diagram of ZIF-8.

[0015] Figure 3 It is the XRD pattern of ZIF-8.

[0016] Figure 4 It is the FTIR spectrum of ZIF-8.

[0017] Figure 5 It is the thermogravimetric analysis diagram of ZIF-8.

[0018] Figure 6 It is the TG-DSC diagram of ZIF-8@NC-TEGDN-RDX composite propellant and the original propellant at a heating rate of 5 K·min -1 : a: TG-DTG curve of the original propellant, b: DSC-DDSC curve of the original propellant, c: TG-DTG curve of ZIF-8@NC-TEGDN-RDX, d: DSC-DDSC curve of ZIF-8@NC-TEGDN-RDX.

[0019] Figure 7 It is the p-t curve diagram of ZIF-8@NC-TEGDN-RDX composite propellant (c, d) and the original propellant (a, b) at different loading densities. Detailed Embodiments

[0020] In order to better understand the technical content of the present invention, specific embodiments are hereby given and described in conjunction with the accompanying drawings as follows.

[0021] The present invention is illustrated by the following examples, which are only for illustration purposes and should not be construed as limiting the scope of the invention or the method of applying the invention. Unless otherwise specified, the raw materials of the present invention are all commercially available.

[0022] ZIF-8 is a metal-organic framework and a member of zinc-containing MOF materials, CAS: 59061-53-9, molecular formula: C8H 12 N4·Zn, molecular weight: 229.60.

[0023] Example 1 Preparation of ZIF-8 Material

[0024] The specific experimental scheme is as follows: Weigh 1.65 g of 2-methylimidazole and 1.5 g of zinc nitrate hexahydrate respectively. Add the weighed samples to 50 ml of methanol and ultrasonically dissolve for 10 min. Pour the 2-methylimidazole solution into the zinc nitrate hexahydrate solution to obtain a reaction solution with n(Zn 2+ )∶n(mIm) = 1∶4. Ultrasonically treat this solution for 10 min, add the mixed solution to a stainless steel autoclave with a polytetrafluoroethylene liner, and heat at 120 °C for 20 h. After cooling to room temperature, centrifuge the obtained product, wash and purify it with methanol, and then perform vacuum drying to obtain ZIF-8 crystals.

[0025] Example 2 Preparation of ZIF-8@NC-TEGDN-RDX Composite Propellant

[0026] Based on the ZIF-8 material synthesized in Example 1, the origami method was used to prepare a propellant sample containing MOF material with NC-TEGDN-RDX triple-base propellant (referred to as the original propellant, specific composition: nitrocellulose (NC): 64 wt%; cyclotrimethylenetrinitramine (RDX): 17 wt%; triethylene glycol dinitrate (TEGN): 16.50 wt%; stabilizer No. II: 2.00%; ethanol, propanol: 0.50%). Mix 97 wt% of NC-TEGDN-RDX triple-base propellant and 3 wt% of ZIF-8 evenly by the origami method to obtain ZIF-8@NC-TEGDN-RDX composite propellant.

[0027] Characterization and Testing:

[0028] (I) Structure and Morphology Analysis of ZIF-8 Material

[0029] For the morphology analysis of ZIF-8 material, the microscopic morphology of the material was first characterized by scanning electron microscopy (SEM). As Figure 1As shown, ZIF-8 presents a typical standard dodecahedron, and the particles are about 240 nm and evenly distributed. The sample was characterized by X-ray diffraction (XRD) morphology. The characteristic diffraction peaks of the prepared ZIF-8 sample are consistent with the standard sample in the published literature. Diffraction peaks at 2θ of 7.30, 10.38, 12.70, and 17.98° can be observed, corresponding to the (011), (002), (112), and (222) planes of standard ZIF-8, respectively. And near 2θ = 7.2°, a very strong diffraction peak appears in the catalyst sample, proving that the prepared ZIF-8 has good crystallinity and no other crystalline phases are formed in the ZIF-8 sample. Figure 4 The FTIR spectrum of the synthesized ZIF-8 is shown. As can be seen from the figure, several characteristic spectral bands of ZIF-8 can be found, at 3134 and 2929 cm -1 The bands at are the C-H stretching vibrations of methyl and imidazole rings, respectively. The band at 1585 cm-1 can be attributed to the C=N stretching vibration. At 1144 and 1309 cm -1 The peaks at correspond to the bending signals of the imidazole ring. At 1417 and 1585 cm -1 The peaks at are the stretching vibrations of the imidazole ring. Similarly, at 994 and 758 cm -1 The peaks at can be attributed to the bending vibrations of C-N and C-H. In addition, at 693 cm -1 The peak at is the out-of-plane bending change of the imidazole ring. Based on the above data, we can infer that a single-phase ZIF-8 crystal framework with good crystallinity has been synthesized.

[0030] (II) Thermogravimetric analysis of ZIF-8 material

[0031] TG and DSC were applied to the ZIF-8 material test under a high-purity argon atmosphere, and the obtained thermogravimetric curve is as Figure 5 shown. ZIF-8 nanoparticles have high thermal stability, with a small weight loss of 16.74% in the range of 200 °C to 615 °C. During the first weight loss process, it may be due to the vaporization of moisture and the volatilization of imidazole ligands (boiling point: 267 - 268 °C). As the temperature further increases, the ZIF-8 framework begins to collapse and rapid decomposition occurs. When the temperature reaches 650 °C, the MOF framework is completely destroyed, indicating that ZIF-8 has high thermal stability from the thermogravimetric curve. Zinc oxide (ZnO) can be formed as the final calcination product of ZIF-8.

[0032] (III) Catalytic performance study of ZIF-8 material on propellant

[0033] Figure 6(a) and (b) in the figure are the TG-DTG and DSC-DDSC thermal decomposition diagrams of the as-received propellant, respectively. There are clearly two weight loss steps in the TG curve. During the first-stage decomposition process, approximately 54.65% of the weight is lost, and during the second-stage decomposition process, approximately 3.85% of the weight is lost. On the DSC curve, there is an obvious exothermic peak from 197.2 °C to 250.2 °C, with the starting peak value at 197.2 °C, the maximum peak value at 216.7 °C, and the heat release of 811 J / g. During the second-stage decomposition process, there is a small exothermic peak between 250.2 °C and 263.2 °C, with its maximum peak value at 256.9 °C.

[0034] Figure 6 (c) and (d) in the figure are the TG-DTG and DSC-DDSC thermal decomposition diagrams of the ZIF-8@NC-TEGDN-RDX composite propellant, respectively. It can be found that the thermal decomposition behavior of the ZIF-8@NC-TEGDN-RDX composite propellant is very similar to that of the as-received propellant. The difference is that the decomposition peak in the second stage of the ZIF-8@NC-TEGDN-RDX composite propellant on the TG curve is not very obvious, and the reaction advances to the first-stage decomposition. During this stage of the decomposition process, 55.64% of the weight is lost. On the DSC curve, the starting peak value of the ZIF-8@NC-TEGDN-RDX composite propellant is 191.4 °C, the maximum peak value is 210.3 °C, and the heat release is 1102 J / g. Its starting peak value and maximum peak value are 6 °C and 6.4 °C earlier than those of the NC-TEGDN-RDX triple-base propellant, respectively, and the heat release also increases by 35.88% compared with the as-received propellant. During the second-stage decomposition process, it can be seen that its maximum peak value is 244.6 °C, which is 12.3 °C earlier than the maximum peak temperature of the NC-TEGDN-RDX triple-base propellant.

[0035] (IV) Study on the combustion performance of ZIF-8 materials on propellants

[0036] The ZIF-8 catalyst is used to study its influence on the combustion process of the propellant. The p-t curve of the propellant can most intuitively reflect the law of the change of the combustion gas with time (five shots are carried out for each sample at different loading densities to determine its repeatability).

[0037] Figure 7 (a) and (b) in the figure are the P-t curves of the as-received propellant at different loading densities (0.012 g·cm -3 and 0.02 g·cm -3 ); Figure 7 (c) and (d) in the figure are the P-t curves of the ZIF-8@NC-TEGDN-RDX composite propellant at different loading densities (0.012 g·cm -3 and 0.02 g·cm -3)P-t curve. And the following characteristic quantities are obtained, including the average maximum pressure, average combustion time, and average pressure rise rate, as recorded in Table 1. As Figure 7 shown, as the propellant burns, the pressure gradually rises to the maximum pressure (P max ). At a loading density of 0.02 g·cm -3 , the maximum pressure of the original propellant gradually rises to 15.19 MPa, and its combustion time (Δt), which is the time from ignition to reaching the maximum pressure, is 0.05 s; the average pressure rise rate is obtained as 303.8 MPa / s. At a loading density of 0.012 g·cm -3 , the maximum pressure of the propellant gradually rises to 9.31 MPa, and its combustion time (Δt) is 0.07 s; the average pressure rise rate is obtained as 121.28 MPa / s. At a loading density of 0.02 g·cm -3 , the maximum pressure of the ZIF-8@NC-TEGDN-RDX composite propellant compared to the original propellant rises from 15.19 MPa to 15.49 MPa. At a loading density of 0.012 g·cm -3 , the maximum pressure of the ZIF-8@NC-TEGDN-RDX composite propellant compared to the original propellant rises from 9.31 MPa to 10.04 MPa; while the combustion time of the ZIF-8@C-TEGDN-RDX triple-base propellant shortens to 0.04 s after ignition, shortening by 0.03 s compared to the propellant combustion time.

[0038] Table 1 Gas generation combustion characteristic quantities of the original propellant and ZIF-8@NC-TEGDN-RDX propellant

[0039]

[0040] At a loading density of 0.012 g·cm -3 , the average Pmax of the propellant is 8.78 MPa, and the average time used is 0.0724 s, thus obtaining a pressure rise rate of 121.28 MPa / s. The average pressure of the ZIF-8@NC-TEGDN-RDX composite propellant is 9.06 MPa, and the average combustion time is 0.0692 s. Its pressure rise rate is 20.2 MPa / s faster than that of the original propellant. At a loading density of 0.02 g·cm -3 , the average maximum pressure of the ZIF-8@NC-TEGDN-RDX composite propellant is 15.24 MPa, and the average combustion time is 0.053 s. The average pressure rate rises from 258.24 MPa / s to 288.02 MPa / s, which is 29.78 MPa / s faster than the original propellant.

[0041] The above data indicate that the MOF material ZIF-8 can shorten the combustion time of the original propellant in a closed bomb, increase the maximum pressure of the propellant, and thus improve the pressure rise rate of the propellant.

Claims

1. Application of a Zn-based metal-organic framework material as a combustion catalyst in propellant, characterized in that The Zn-based metal-organic framework material is ZIF-8, which is synthesized by hydrothermal reaction after mixing a methanol solution of Zn(NO3)2 and a methanol solution of 2-methylimidazole.

2. The application according to claim 1, characterized in that, The hydrothermal reaction temperature is 120 °C and the time is 20 h.

3. The application according to claim 1, characterized in that In terms of molar ratio, Zn(NO3)2∶2-methylimidazole = 1∶4.

4. The application according to claim 1, characterized in that, The mass ratio of ZIF-8 to the propellant is 0.03:0.

97.

5. The application according to claim 1, wherein The propellant is an NC-TEGDN-RDX triple-base propellant.

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