Experimental and Theoretical Studies of HAN and HEHN Pyrolysis at Low Pressure

Nitro-based ionic liquids are promising green propellants that have been studied as substitutes for hydrazine. An in-depth study of their thermal decomposition mechanism is important to further improve their combustion efficiency. In this work, pyrolysis experiments of hydroxylamine nitrate (HAN) and 2-hydroxyethylhydrazinium nitrate (HEHN) were carried out by using a flow reactor combined with synchrotron vacuum ultraviolet photoionization mass spectrometry. The mole fraction distribution of the pyrolysis products was quantitatively measured. In addition, to further understand the decomposition mechanism of nitro-based ionic liquids, we performed quantum chemical calculations on 2-hydroxyethylhydrazine (HEH), the initial decomposition product of HEHN, at the CCSD(T)/BH&HLYP/6-311++G(d,p) level. The calculation results show that bond fission and hydrogen migration are potential driving forces in the overall pyrolysis process. In particular, nitric acid plays an important role in the autocatalytic decomposition behavior of HEH. These results on the thermal decomposition of these two ionic liquids provide valuable references for the future kinetic modeling of nitro-based ionic liquids.