Catalytic Decomposition of Hydroxylammonium Nitrate Ionic Liquid: Enhancement of NO Formation

Abstract

Hydroxylammonium nitrate (HAN) is a promising candidate to replace highly toxic hydrazine in monopropellant thruster space applications. The reactivity of HAN aerosols on heated copper and iridium targets was investigated using tunable vacuum ultraviolet photoionization time-of-flight aerosol mass spectrometry. The reaction products were identified by their mass-to-charge ratios and their ionization energies. Products include NH, HO, NO, hydroxylamine (HA), HNO, and a small amount of NO at high temperature. No NO was detected under these experimental conditions, despite the fact that NO is one of the expected products according to the generally accepted thermal decomposition mechanism of HAN. Upon introduction of iridium catalyst, a significant enhancement of the NO/HA ratio was observed. This observation indicates that the formation of NO via decomposition of HA is an important pathway in the catalytic decomposition of HAN.

Kinetics and Mechanism of Thermal and Catalytic Decomposition of Hydroxylammonium Nitrate (HAN) Monopropellant

“…Simulated curves of thermal and catalysed decomposition with f =3.5 and 3 rd order Savitzky‐Golay smoothing does fall on the raw TG data as shown in Figure 3, validating the approach followed in optimization of smoothing parameter f . Interestingly, the Ea profile extracted from the smoothed data matches with the reported values in the literature [17, 18, 25, 26, 35, 48, 49]. The Ea values computed at different conversion ranges for the three systems studied are shown in Figure 4a.…”

“…[23] and Chambreau et al . [49]. As per given reports [23, 49], this decomposition of HNO 3 close to peak temperature mostly lead to formation of NO 2 since beyond α 0.75 NH 2 OH is over and leftover HONO end up reacting with HNO 3 reaction step VIII.…”

“…The decomposition rate, as reflected in higher slope of TG thermograms, is faster due to high frequency factor i. e. 2.6×10 16 s −1 . The decomposition practically ends at α 0.6 according to activation energy profile of Figure 4a, since Ir as a catalyst is capable of decomposing HNO 3 only marginally [17, 18, 36, 49]. Hence, once NH 2 OH is consumed completely decomposition stops and produced HNO 3 starts vaporizing due to energy at the expense of exothermic decomposition.…”

“…HNO 3 decomposition in absence of HONO has activation energy ranging from 1422 kJ/mol (decomposition to ionic species) to 209 kJ/mol (decomposition to free radicals) depending on the mechanism followed [17], which makes HNO 3 decomposition practically impossible without HONO in current case. Since HNO 3 cannot decompose, it evaporates [17, 49] due high temperature and do not contribute anything to the overall exothermicity required in a catalytic combustion chamber.…”

Cerium oxide based active catalyst for hydroxylammonium nitrate (HAN) fueled monopropellant thrusters

“…6,37 Nitric acid and its products with hydroxylamine like nitrous acid play a critical role as intermediate products in the overall decomposition mechanism of HAN. The relation between NO 2 and HNO 3 is quite subtle as per mechanisms reported in literature; 16,37,38 The proposed dissociation is as follows…”