Study of the Initiator Mischarging Effect on Runaway Reaction of Styrene Polymerization

Polymerization reactions are prone to runaway risks due to the unstable nature of monomers and complex interactions between reactants. Deviation from a normal recipe or designed operation condition may lead to auto-accelerated temperature and pressure rise, followed by rupture of reaction vessels, fire, and explosion. Mischarging of initiators (radical generators) is one of the most common credible mal-operation cases, which has not been thoroughly investigated. In this study, benzoyl peroxide (BPO) and azobisisobutyronitrile (AIBN) are used as initiators for styrene polymerization at a series of elevated concentrations to mimic the mischarging scenarios. Both screening and adiabatic tests are performed to obtain the most critical safety parameters such as onset temperature, adiabatic temperature rise, and time to maximum rate. To date, we have observed a significant difference in reaction pathways and safety indicators regarding initiator types and concentrations. Uncontrolled initiation reactions not only lead to subsequent faster polymerization but also pose threats to relief valve design due to the generation of non-condensable gas. We anticipate our study to guide polymer manufacturers on the initiator selection and also thermal runaway prevention.