Spectroscopy of Hydrothermal Reactions III: The Water—Gas Reaction, “Hot Spots”, and Formation of Volatile Salts of NCO− from Aqueous [NH3(CH2)nNH3]NO3 (n = 2, 3) at 720 K and 276 Bar by T-Jump/FT-IR Spectroscopy

Abstract

Strongly exothermic reactions raise fundamental and practical questions about the use of hydrothermal reactions to destroy hazardous materials. The decomposition products of ethylenediammonium dinitrate, which is close to oxygen balance, are compared by IR spectroscopy after flash heating under 69–276 bar in Ar and in the presence of excess H₂O and H₂. The occurrence of the water–gas shift reaction was confirmed by changes in the CO/CO₂ ratio. This reaction sets the final CO/CO₂ ratio at the “freeze-out” temperature, whose magnitude (1300–1470 K) raises concern about potential formation of “hot spots” in the reaction stream should solid particles of the explosive exit. IR absorbances at 2168 and 2193 cm⁻¹ are also observed when flash decomposition of the propylene homolog occurs in the presence of H₂O. These absorbances lie in the range of the explosive fulminate group. It was found, however, that these absorbances result instead from vaporized H₃O⁺NCO⁻and NH₄⁺NCO⁻ aggregates. Consequently, in addition to contributing to the water–gas shift reaction, H₂O opens an isocyanate decomposition channel which has a minimal role without H₂O.