Thermal hazard analysis for tert-butyl peroxybenzoate contaminated by acid or alkali

Organic peroxide is widely used for initiating free radical polymerization in unsaturated polyester copolymerization reaction, and is thermally unstable in the presence of a single oxygen-oxygen bond, which easily leads to thermal runaway accident, i.e. explosion, when exposed to an external heat source. If any contaminant, such as H⁺ or OH^-, is introduced during production, storage or transport, it may accelerate decomposition under an abnormal situation and result in deterioration. A liquid OP-tert-butyl peroxy benzoate (TBPB) was chosen to mix with NaOH and H₂SO₄ to examine H⁺ or OH^- effects on its thermal hazard using an adiabatic accelerating rate calorimeter. The progresses in thermal decomposition of pure TBPB and mixtures with small amount of NaOH and H₂SO₄ are tracked using single "heat-wait-seek" operation mode and "isothermal age" plus "heat-wait-seek" mode, respectively. In order to characterize the effect of H⁺ and OH^- on TBPB thermal hazard, the parameters of reaction kinetics and their corrected values with thermal inertia factor are determined from their characteristic parameters of thermal decomposition with pseudo inverse matrix method by least square method under the worst condition, and they are the characteristics of intrinsic thermal hazard of TBPB. The time to maximum heating rate (TMR) is predicted by Townsend equation involving reaction mechanism and reactant concentration. Based on the kinetic parameters and Semenov thermal explosion theory, the thermal hazard parameters, such as self accelerating decomposition temperature (SADT), CT, and ET, can be calculated, which are crucial for application in industry. A comparison of the mixtures to pure TBPB shows two exothermic peaks for mixture of TBPB and OH^-. The first is at 60-70℃ and is characterized by very low heating rate and temperature rise, so that reaction heat is not sufficient to sustain the thermal runaway reaction, resulting in higher initial exothermic temperature and reaction kinetic parameters in the second exothermic stage, i.e. main exothermic stage. In contrast, without two peaks for the mixture of TBPB and H⁺, this mixture has lower reaction kinetic parameters, increasing reactivity and thermal hazard. The TMR and SADT data obtained by calculation indicate that the addition of H⁺ contaminant causes appropriately lower warning temperature. When 30 L high density polyethylene barrel packaging is adopted, the SADT of TBPB contaminated by H⁺falls from 65.9 to 62.6℃, indicating that strict temperature control measures are necessary.