Prediction of thermal hazards of chemical reactions

A large number of products of the chemical industry are produced using potentially hazardous reactions. The experimental investigation of the hazards of all reactions involved in production processes would be very expensive. The primary reactions-desired reactions which are part of the process-and the secondary reactions-undesired successive or side reactions-should both be considered. In this paper the methods of prediction of thermodynamic and kinetic properties of reactions are discussed. Thermodynamic data are of eminent practical importance because low heats of reaction may indicate that no further experimental investigations are necessary. For primary reactions, e.g. polymerization, diazotization and hydrogenation reactions, reaction enthalpies have been obtained by experimental methods. Typical data can be found in the public literature for the different reaction classes. When compared with theoretical thermodynamic data estimated by the CHETAH computer program, the agreement is satisfactory. CHETAH implements Benson's second-order group contribution technique (Benson, 1976). For secondary reactions, especially exothermic decomposition reactions, typical heats of reaction-mostly measured by DSC-have been associated with functional groups. Decompositions and other undesired exothermic reactions that proceed from the same functional group, e.g. a nitro group, have about the same heat of reaction. For the estimation using the CHETAH program, decomposition reactions have to be assumed which are typical for the functional group. The reaction yielding the maximum exothermic reaction energy was selected. The comparison of experimental heats of reaction with estimated data shows satisfactory agreement. In principle it is also possible to predict kinetic data of secondary reactions, but sufficient experimental data are missing. (C) 1999 Elsevier Science Ltd. All rights reserved.