Mechanistic insights into the suppression of p-nitrotoluene explosions by a novel urea–NH4H2PO4 modified dry water powder

A novel urea-NH₄H₂PO₄ modified dry water powder (UN MDW powder) was developed to mitigate dust explosions induced by p-nitrotoluene. The explosion suppression performance of the UN MDW powder was assessed using both experiments and numerical simulations. Suppression experiments were conducted in a 120 L explosion vessel with p-nitrotoluene powder. Results showed that a concentration of 500 g/m³ of UN MDW powder could completely suppress the explosion. ReaxFF molecular dynamics and reaction kinetics simulations demonstrated that UN MDW powder suppressed the rapid cleavage of nitro and methyl groups in p-nitrotoluene molecules. It also suppressed oxidative ring-opening pathways in the benzene ring. This disruption weakened the chain reaction mechanism underlying the decomposition of p-nitrotoluene. The decomposition products of UN MDW powder effectively scavenged key radicals involved in the explosion process. Through catalytic cyclic reactions (PO⇔HPO, PO₂⇔HOPO, PO₃⇔HPO₃, and HPO₃⇔PO(OH)₂), these products continuously quenched radicals that sustain flame propagation or converted them into stable species such as CO₂ and H₂O. The UN MDW powder exhibited significant suppression effects on p-nitrotoluene dust explosions. The findings offer important implications for enhancing the elimination and mitigation of combustion and explosion risks associated with nitro-containing hazardous chemicals during their production, storage, transportation, and disposal.