Prediction of thermal hazards of chemical reactions

A large number of products of the chemical industry are produced using pote ntially 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 t he secondary reactions-undesired successive or side reactions-should both b e 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 nece ssary. For primary reactions, e.g. polymerization, diazotization and hydrog enation reactions, reaction enthalpies have been obtained by experimental m ethods. Typical data can be found in the public literature for the differen t reaction classes. When compared with theoretical thermodynamic data estim ated 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, typ ical heats of reaction-mostly measured by DSC-have been associated with fun ctional groups. Decompositions and other undesired exothermic reactions tha t proceed from the same functional group, e.g. a nitro group, have about th e same heat of reaction. For the estimation using the CHETAH program, decomposition reactions have t o be assumed which are typical for the functional group. The reaction yield ing the maximum exothermic reaction energy was selected. The comparison of experimental heats of reaction with estimated data shows satisfactory agree ment. In principle it is also possible to predict kinetic data of secondary react ions, but sufficient experimental data are missing. (C) 1999 Elsevier Scien ce Ltd. All rights reserved.