Alkaline hydrolysis of 1,3,5-trichloro-2,4,6-trinitrobenzene (TCTNB) during spent sulfuric acid neutralization using lime

1,3,5-trichloro-2,4,6-trinitrobenzene (TCTNB) is the main byproduct of synthesizing an insensitive explosive 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) and requires environmental management and safe handling during disposal. This study introduces a lime neutralization method for treating TCTNB-containing spent sulfuric acid and systematically investigates the underlying hydrolysis mechanism using mass spectroscopy, Fourier transform infrared spectroscopy (FTIR) and Density functional theory (DFT) calculations. Our results demonstrated that TCTNB hydrolysis was significantly accelerated by increasing the pH from 10 to 12 and the temperature from 22 to 95 °C. The hydrolysis reactions proceeded via nucleophilic aromatic substitution, with preference for targeting the chlorine (Cl) groups of TCTNB over the nitro (NO₂) groups due to the higher electrophilicity of Cl-attached carbon atoms. DFT calculations indicated 15 thermodynamically favorable substitution products; however, kinetic limitations caused by deprotonation of intermediates led to the formation of mono- and di-substituted products. Hirshfeld charge analysis and pKa calculations revealed that deprotonation decreased the electrophilicity of the benzene ring, increased energy barriers, and thus hindered further hydrolysis. Additionally, hydrolysis significantly reduced the ecotoxicity of TCTNB by weakening the electrophilicity of the benzene ring. Field tests confirmed that TCTNB in spent acid could be successfully treated with lime to produce non-hazardous and recyclable gypsum. These findings offer theoretical guidance for the safe disposal of TCTNB-containing spent acid and underscore alkaline hydrolysis with lime as a promising treatment strategy.