Influence of trace impurities on the risk of thermal runaway

The influence of trace impurities on the risk of undesirable chemical reactions is not frequently the subject of general studies aimed at drawing attention to the subject and drawing conclusions useful for improving the safety of chemical processes . However, the influence of trace impurities is frequently invoked in investigations into accidents in the chemical industry, to explain the unexpected and undesirable occurrence of violent chemical reactions involving thermal decomposition. Contamination of presumably pure chemical substances with trace impurities can considerably alter their thermal stability, leading to unexpected thermal decomposition under otherwise normal process conditions. Representative examples of this phenomenon, which is the cause of numerous accidents, are discussed in this dossier. The examples are taken from our previously published articles, and cover a wide range of process conditions. The contents of this dossier were the subject of a presentation to the French Process Engineering Society (SFGP) in 2001, which encouraged wider publication. A first publication followed in the Journal of Loss Prevention in the Process Industries in 2002 .

The examples considered here in succession are :

• the influence of trace impurities on the thermal stability of organic nitro derivatives ;

• the influence of trace impurities on the thermal stability of reactive monomers, with two examples of reactive monomers, vinyl acetate