Catalytic and thermal decomposition of ionic liquid monopropellants using a dynamic reactor: Comparison of powder and sphere-shaped catalysts

A dynamic reactor with mass spectroscopy online product analysis has been used to study the thermal and catalytic decompositions of ionic liquid HAN-based monopropellants. The activity of different catalysts has been evaluated by determining qualitatively and quantitatively the reaction products. A careful calibration of the expected products detected by the mass spectrometer (MS) (N2, O2, N2O, NO and NO2) has been performed. The analytical results have been supplemented by Raman spectroscopy of the aqueous solutions trapped after the reactor. The thermal and catalytic decomposition of water–HAN (80 wt.%, hydroxylammonium nitrate NH3OH+NO3−) mixture gave primary products (major N2, medium NO) and secondary products (medium N2O and traces NO2). From the data, a reaction mass balance could be proposed, based on the combination of two parallel competitive reactions:6NH3OHNO3(aq) = 3N2(g) + 2NO(g) + 10H2O(g) + 4HNO3(g), ΔrH° = −117.8 kJ HAN mol−16NH3OHNO3(aq) = 2N2(g) + 2N2O(g) + 10H2O(g) + 4HNO3(g), ΔrH° = −121.0 kJ HAN mol−1 The influence of the catalyst shape (powder or spheres) has been followed. The isothermal tests at 50 °C display the best activity for the powder catalyst with a complete decomposition of the HAN solution, due to a good contact between catalyst bed and monopropellant. On the other hand, the sphere-shaped catalyst leads only to a partial HAN decomposition, due to preferential paths through the catalyst bed. The thermal decomposition at 200 °C, leads also to a partial reaction.