Thermal hazards analysis of styrene in contact with impurities

Styrene is a reactive monomer commonly used to produce polystyrene and other copolymers. Unintended thermal runaway polymerization reactions of styrene keep reoccurring and have led to catastrophic consequences. One of the possible causes of these runaway incidents involves the contamination of the styrene monomer by incompatible species, which was not adequately investigated and documented. This study focuses on the quantification of thermal runaway hazards of styrene in contact with a series of contamination substances by adopting calorimetric analysis. Both Differential Scanning Calorimeter (DSC) and Advanced Reactive System Screening Tool (ARSST) were employed to examine the exothermic characteristics of styrene mixed with contaminating substances at different concentration levels and mixing conditions. Key safety parameters of the exothermic reaction, such as the onset temperature, the overall heat release, the maximum self-heating rate, as well as the activation energy, were obtained. The results indicated that the thermal runaway polymerization of purified styrene was significantly altered by the presence of contaminant species. Water effectively retarded and quenched the runaway polymerization at a higher temperature range. Alkaline had no substantial effect on the thermal runaway characteristics. The presence of acid solution under both static contact and vigorous mixing condition significantly promoted the thermal polymerization of styrene. A trace amount of concentrated acid initiated violent exothermic activity even at room temperature; and the severity of the reaction was profoundly impacted by the mass-transfer. Our study demonstrates significant implications in the prevention of runaway incidents during transportation and storage of styrene.