Decomposition and combustion of ionic liquid compound synthesized from N'N'N',N'-tetramethylethylenediamine and nitric acid

A nitrate-based ionic liquid compound, TMEDA.8HNO₃, was synthesized from hypergolic bipropellants N,N,N',N'-tetramethylethylenediamine (TMEDA) and nitric acid by premixing them carefully at a stoichiometric molar ratio of 1:8. The overall ignition and combustion behaviors of this liquid propellant were examined by using a high-pressure strand burner with optical access, coupled with a high-speed video camera for capturing and analyzing the liquid- and gas-phase processes as well as measuring the regression rates of the liquid strands. TMEDA.8HNO₃ has a pressure deflagration limit (PDL) of approximately 300 psi, below which the liquid strand regresses without a luminous flame. Burn rates of this liquid propellant were measured from 400 to 1000 psi. Thermal decomposition of TMEDA.8HNO₃ was investigated by a confined rapid thermolysis setup with heating rates on the order of 2,000 K/s coupled to rapid-scan Fourier transform infrared (FTIR) spectroscopy of the evolved gases. Over the temperature range from 50 to 80°C, the major IR-active gaseous species evolved from the condensed-phase decomposition are HNO₃, NO₂, H₂O, CO₂, HCOOH, and glyoxylic acid (HOCCOOH). At higher temperatures, additional species such as CH₂O, (CH3)2NNO, NO and N₂O also evolved. Possible decomposition pathways of TMEDA.8HNO₃ are discussed based on the rapid thermolysis studies.