Thermal analysis and fire and explosion hazards of selected amino-containing organic compounds

Introduction. Explosions and fires involving organic compound dusts continue to be a pressing issue in the field of industrial safety. The aim of this study is to conduct a comprehensive investigation into the fire and explosion hazard properties and thermal decomposition of 3,3’,5,5’-tetramethylbenzidine, its dihydrochloride and 2-diethyl­aminoethyl chloride hydrochloride, with a view to incorporating the findings into the scientific and technical documentation of manufacturing enterprises and subsequently reducing the number of incidents involving explosions and fires at production facilities.

Methods. The fire and explosion hazard properties were investigated in accordance with GOST 12.1.044–2018; specimens with a particle size of less than 100 μm were used to prepare dust–air mixtures. The thermal behaviour of the compounds was studied using thermogravimetric analysis and differential thermal analysis (TG-DTA). Kinetic parameters were determined in accordance with GOST R 57951–2017, and the decomposition mechanism was investigated using infrared spectroscopy.

Thermal analysis. The general thermal behaviour of the compounds was established, and the temperatures corresponding to the onset of intensive thermal decomposition were determined.

Fire and explosion hazard parameters. For all the investigated compounds, the ignition and autoignition temperatures and the lower flammability limit were experimentally determined, while the heats of combustion were calculated.

Kinetic parameters of the initial stage of thermal decomposition. The activation energies of the initial stage of thermal degradation were calculated using the Ozawa – Flynn – Wall method, and the thermal stability of the investigated compounds was evaluated.

Mechanism of the initial stage of thermal decomposition. It was established that the decomposition of the primary amine bond is characteristic of tetramethylbenzidine (TMB), whereas for TMB dihydrochloride (TMB-d) and 2-diethylaminoethyl chloride hydrochloride (DAH) the most probable process is elimination of the hydrogen chloride moiety.

Results. The thermochemical and fire and explosion hazard characteristics of the investigated compounds were determined, including the temperatures of the onset of intensive thermal decomposition, ignition, and autoignition, and the activation energies of the initial stage of thermal degradation were calculated. Based on the results of thermal analysis and infrared spectroscopy, mechanisms for the initial stage of thermal decomposition of the investigated compounds were proposed.

Conclusions. All the substances studied belong to the class of flammable compounds, their dust-air mixtures are flammable and explosive and exhibit a relatively high thermal stability. Of the three compounds studied, 2-diethylaminoethyl chloride hydrochloride is the most flammable, with a flash point of 185 °C.

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