Kinetic-free safe optimization of a semibatch runaway reaction: Nitration of 4-chloro benzotrifluoride

In this work the general Ψ number criterion for the safe operation of semibatch runaway reactions has been applied to the optimization of a nitration process of primary importance in the agrochemical industry, that is the nitration through mixed acids of 4-chloro benzotrifluoride to produce a widely employed class of fluorinated herbicides. Such a reaction, as is the case for almost all the organic nitrations, belongs to the most critical class of exothermic reaction processes, for which the maximum temperature of the synthesis reaction under adiabatic conditions overcomes the decomposition temperature of the system, without any tempering effect due to a solvent evaporation. It has been verified that higher productivity operating conditions can be easily implemented through the general Ψ number criterion, even without a kinetic characterization of the system, but just elaborating information already available at the laboratory scale, where the chemical recipe is developed. The results obtained have been further validated through the boundary and temperature diagrams criterion, which however requires a previous estimation of the reaction kinetic parameters, with a much higher experimental effort.