Hazard evolution in liquid dinitrogen tetroxide-isopropanol cleaning systems: thermal runaway and gas release
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Updated: Nov 4, 2026

Utilization of Stop-flow Micro-tubing Reactors for the Development of Organic Transformations
Published on: January 4, 2018
Shichun Weng1, Jing Ye Li2, Jinyao Hu1
1School of Safety Science and Engineering, Nanjing University of Science and Technology, Nanjing, Jiangsu 210094, China.
Abstract:
Liquid dinitrogen tetroxide (N₂O₄, NTO) can pose severe hazards when contacting incompatible cleaning agents. A vessel rupture accident involving NTO and an isopropanol-containing cleaning agent was investigated using accident reconstruction, chemical analysis, online Raman monitoring, calorimetry and field validation. Temperature-pressure records supported chemically driven thermal runaway. Blank tests showed vigorous gas evolution but limited heat accumulation during NTO hydrolysis and neutralization. HPLC/HPLC-MS supported acetone formation and tentative assignments to isonitrosoacetone, nitrolic-acid- and isoxazoline-type products. Raman monitoring revealed attenuation of NTO-related bands and transient spectral features tentatively associated with oxime/N-OH and cyano-containing species, while quantum-chemical calculations assessed the proposed nitrile-oxide-mediated pathway. Gas analysis tentatively indicated N₂O and carbon oxides without establishing their formation pathways. DSC revealed exothermic decomposition at approximately 60-90°C under the tested conditions, while ARC demonstrated rapid self-heating and pressure rise. Comparative experiments showed greater runaway severity at lower initial temperatures, consistent with liquid NTO retention and enhanced liquid-liquid contact. Higher temperatures reduced heat accumulation under the tested conditions but promoted volatilization, while toxic-gas release remained a concern. These findings highlight thermal runaway and gas-release hazards, with secondary decomposition of unstable intermediates as a possible contributor, and inform safer residual oxidizer cleaning and off-gas management.
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