含能离子液体自燃过程的热效应及机理研究

Hypergolic propellant as the key power of missile, rocket, and space aircraft, is one of important securities for the development of aeronautics and astronautics. As the derivatives of hydrazine (the main components of hypergols) are volatile and highly carcinogenic substances with low volumetric energy density, the research shows the environmental and strategic importance in replacing the derivatives of hydrazine with energetic ionic liquids. However, there are still two problems to solve: (1) the relationship between structures of ionic liquids and the thermal effct of hypergolic reactions; (2) the mechnism of hpergolic reactions. Based on the current problems, this project is proposed to design and synthesize three series of energic hypergolic ionic liquids, and then finish the investigations as follows: The ionic liquids are studied by thermal and kinetic analyses to obtain the relationship between the ionic liquid structures and the reaction enthalpies and impulses. By using in-situ Fourier Transform Infrared (FTIR) measurements, the hypergolic reactions between ionic liquids and oxidizers are monitored to get the information of the intermediate phases. The mechanism of hypergolic reactions is proposed based on the experiments and ab initio/DFT calculations. With the above knowledge, hypergolic ionic liquids are optimized to possess better properties so as to achieve the goal of replacing hydrazine derivatives with ionic liquids as hypergolic propellant.

自燃推进剂作为火箭和太空飞行器的动力核心，是航空航天领域发展的重要保障。鉴于该类推进剂的主要组分是易挥发、强致癌和低容积能量密度的肼类化合物，开发含能离子液体替代肼类物质用作绿色自燃推进剂具有重要的环保和战略意义。但是，目前该研究还迫切需要解决两个关键问题：（1）离子液体结构与自燃反应热效应的构效关系；（2）离子液体自燃反应的机理。针对存在的问题，本项目拟设计合成三个系列含能自燃离子液体，通过离子液体自燃反应的热力学和动力学研究，获得离子液体结构与反应生成焓及推进效率之间的变化规律。采用原位红外测试技术，在线测定含能离子液体的自燃反应过程，并辅助量子化学模拟计算，解析离子液体自燃反应的过渡态及阴、阳离子协同作用对自燃过程的影响，揭示离子液体自燃反应的内在规律，指导合成新的综合性能良好的含能自燃离子液体，实现离子液体替代肼类物质用作航空航天推进剂。

自燃推进剂作为一类化学点火的双组元液体推进剂，可简化发动机设计、实现万次无故障点火，是火箭及太空飞行器的动力核心。目前自燃推进剂燃料广泛应用易挥发、剧毒的肼类化合物，亟待研发绿色替代产品。离子液体普遍具有低蒸汽压、低毒、高稳定性的特点，同时部分离子液体还具有良好的“自燃”特性，成为极具潜力的新型推进剂绿色燃料。本项目旨在开发新型自燃离子液体推进剂，并利用量化计算揭示离子液体结构与自燃反应之间的内在关系，获得离子液体自燃点火的热效应及规律。主要创新性成果如下：（1）以四甲基乙二胺和三甲胺硼烷络合物为反应底物，设计合成了4种四甲基乙二胺类和10种双（R-基咪唑）硼烷类自燃离子液体。通过1H和13C NMR、IR和元素分析（或高分辨质谱）综合表征，确认了所得离子液体的结构。通过密度、粘度、热稳定性、点火性能测试及相关计算，着重考察阳离子基团与自燃离子液体物性之间的关系。四甲基乙二胺类离子液体热稳定性好，分解温度200-230 °C，生成焓85.1-154.4 kJ·mol-1。双（R-基咪唑）硼烷类离子液体分解温度154-221 °C，密度1.04-1.27 g·cm-3，生成焓12.4-484.9 kJ·mol-1，分解活化能74.72-130.82 kJ·mol-1，比冲 161.9-202.1 s，点火延迟时间18-122 s。（2）提出了多环化和增加重原子的思想，进一步提高自燃离子液体能量。设计合成了三个系列自燃离子液体，包括1-氮-双环[2,2,2]辛烷类、1,4-二氮-双环[2,2,2]辛烷类和5,7-二甲基-1,3-二氮金刚烷类。测试结果表明：分解温度 208-322 °C，密度1.06-1.31 g·cm-3，比冲260.5-266.2 s，生成焓7.8-537.5 kJ·mol-1，点火延迟时间14-1053 ms。实验与计算结果均证明，同对应的单环同分异构体相比，三类多环离子液体在能量上均有提高，从而为自燃离子液体能量提高提供了新方法。