Effects of heating rate, temperature and iron catalysis on the thermal behaviour and decompostion of 2-nitrobenzoyl chloride

Runaway reactions arising from the decomposition of thermally unstable materials are a concern in industry due to the potentially devastating effects that they yield. Studies into the occurrence of thermal runaway incidents have shown the most likely cause to be a result of an inadequate investigation of the process prior to its operation on a large-scale. The chlorination of ortho-nitrated carboxylic acids is an industrially important reaction in the fine and agrochemical industries. The products of these reactions, ortho-nitrated acid chlorides, have been involved in runaway incidents that have resulted in violent explosions; hence, their thermal stability must be studied. Previous studies [S.D. Lever, M. Papadaki, Study of condition-dependent decomposition reactions: the thermal behaviour and decompostion of 2-nitrobenzoyl chloride, Part I, J. Hazard. Mater. 115 (2004) 91–100] showed that the decomposition of the parent molecule, 2-nitrobenzoyl chloride, is highly condition-dependent with the sample heating rate and temperature of decomposition playing a preponderant role in the course of the decomposition. Here, we present the results of studies of the decomposition of 2-nitrobenzoyl chloride, when the sample is subjected to various heating treatments, temperatures and in the presence of iron. As the temperature of decomposition was increased from 150 to 162 °C, the heat of decomposition was reduced from −215 to −90 kJ/mol. As the heat up rate applied in bringing the sample to the decomposition temperature increased, the heat of decomposition also increased. An increase in the heat up rate from 2 to 7.5 °C/min resulted in an increase in the heat of decomposition from −90 to −215 kJ/mol. The presence of iron and silver was observed to lower the heat of decomposition from −185 to −160 and −110 kJ/mol, respectively. Under most conditions investigated, the temperature at which gas flow was initiated was 147–150 °C. The presence of iron reduced this temperature to 140 °C. Decomposition was observed to take place over two stages, where the sample was heated directly from 40 °C at the required heat up rate. Where the sample was heated in stages and where calibrations had been carried out preceding decomposition, the decomposition took place in one stage alone.