Scale up of Hazardous Chemistry
with thermal runaway potential
Chemical reactions involving potentially unstable chemicals or indeed even quite standard reactions which are exothermic, are an accepted part of the chemical industry. When there is no alternative to the selected route, it is vital that the process is subjected to modern methods of experimental and analytical investigation so that the potential hazard is properly quantified and a protection strategy based on scalable results developed, before even pilot scale operation is anticipated.
This paper will describe, with examples, why it is virtually impossible for even experienced chemists to “spot” hazardous reactions without some measurement and how reactions that might have been safely performed for many years can lead to disaster unless the risk is understood. This is now quite simple to do with a range of experimental methods available. With the correct equipment, it is possible even to experimentally simulate a thermal runaway accident in order to fully understand the potential hazard, using less than a 100ml of sample.
Successful scale up of exothermic chemical reactions relies critically on the data and understanding developed during process development. Too often however, chemists develop processes while focusing very narrowly on the synthesis steps they ideally need to undertake with little or no attention to deviations in operation, especially if something goes wrong. Also, severity of the exothermic hazard is often not measured, relying instead on the chemist’s visual observations to decide when there might be a potential problem and hence when heat generation data might be warranted.
The problem with focusing only on the normal (often called “desired”) operation is that it ignores the real world situation where things do go wrong and where the process will go into “undesired” situations.
Expecting chemists to “notice” potentially exothermic problems is also fraught with problems as in practice this is near impossible to do as small scale reaction flasks or vessels will give little clue as to the heat being generated. This is basically a scale effect where the natural heat loss from small vessels is so large that they hav ...