Runaway Evaluation Of Semi-batch Toluene Mono-nitration

Toluene mono-nitration is one of typical aromatic nitrations and its products are widely used. Because of the high reaction heat generation and the complicated reaction mechanism, it’s generally considered to be of great thermal runaway hazards. Therefore, it’s very important to explore the thermal runaway history and evaluate the thermal runaway risk as well. Then, the research system will be formed, so as to promote the development of inherent safety in chemical industry.Differential scanning calorimeter (DSC), accelerating rate calorimeter (ARC) and reaction calorimeter (RCle) were used to test the thermal stability of materials and investigate the thermal hazards of the reaction. Then, risk matrix method, criticality classes method and extended assessment method were used to evaluate the thermal runaway criticality.Results on the study of materials show that the more concentration the mixed acid is, the lower thermal stability of product is. And the decomposition mechanism is more complicated. ARC results show that the initial decomposition temperature of MNT with mixed acid is 145.6℃, which is 110℃ lower than pure MNT; and the temperature at which the time to maximum rate is 24 hours (TD24) is from 256℃ to 115℃. Therefore, TD24 of the whole product system instead of the pure product should be used to evaluate the thermal hazards.Results on the study of reactions and products demonstrate that high temperature increases reaction heat, supports side reactions and complicates the reaction mechanism. Meanwhile, high dosing rate increases the maximum reaction rate, but also increases the accumulation of toluene which can cause higher thermal hazards. In addition, the results of the reaction kinetics analysis show that the reaction order of nitric acid increases with temperature rising. It further illustrats that the higher temperature, the more side reactions.Under the experimental conditions, the severity of runaway toluene mono-nitration is ’medium’, and the probability of it is’almost impossible’. It’s an’acceptable risk’. The criticality rating of desired reaction is class 2. The thermal risk is low. However, since the accumulation of material is controlled by the feed rate, the risk will belong to class 5 if the feed is not immediately halted when a failure occurs. Moreover, from the perspective of gas release, extended assessment results show that the severity of runaway semi-batch toluene mono-nitration under laboratory scale is’medium’, but under factory scale is’critical’. The probability of loss of control during runaway semi-batch toluene mono-nitration is ’unproblematic’ either under laboratory scale or factory scale.