Two-stage decomposition of 2-hydroxyethylhydrazinium nitrate (HEHN)

Abstract

The hydrazine-derived ionic liquid 2-hydroxyethylhydrazinium nitrate (HEHN) is a promising fuel component of green monopropellants. For successful implementation of these propellants, it is necessary to understand the kinetics and mechanism of HEHN decomposition, but the available data are scarce. The objective of the present work was to investigate the kinetics of HEHN thermal decomposition using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) as well as to identify the evolved gas products with mass spectrometry (MS) and Fourier-transform infrared (FTIR) spectroscopy. Both TGA and DSC have revealed that the decomposition of high-purity HEHN has two distinct stages. The effective kinetic parameters of both stages were determined using the Ozawa-Wall-Flynn, Kissinger, and model-based methods. The model-based analysis has shown autocatalytic behaviour of the involved reactions and produced apparent activation energies of 113.7 ± 1.7 kJ/mol at the first stage and 123.6 ± 2.5 kJ/mol at the second stage, close to the literature data (124.8 kJ/mol) on the autocatalytic reaction between HEHN and HNO3. The evolved gas analysis has shown that the first stage generates H2O, N2, NH3, NO, N2O, and NO2, while the second stage also generates HNO3 and CO2. The observed existence of two stages in the thermal decomposition of HEHN could be explained by the formation of a condensed by product, which, in turn, decomposes via a highly activated reaction during the second (high-temperature) stage.