A kinetic model based on the most important free radical reaction steps has been developed for propane pyrolysis. The kinetic and product distribution data were obtained over a wide range of conversions at temperatures from 700 to 850°C. and with various amounts of steam or other diluents. The results of the investigation clarify the important reaction steps and the effect of the critical operating variables.Although the pyrolysis of propane is used for large-scale production of ethylene and propylene, the kinetics and mechanism for the reaction are not yet completely understood. The rate of propane pyrolysis has frequently been reported to be first order relative to propane concentrations, especially at lower conversions of 40% or less ( 4 , 11 ) . Both Crynes and Albright ( 3 ) and Buekens and Froment ( 1 ) have recently shown however that the overall rate is not well described by either first-order or other simple-order equations.Pyrolysis reactions of propane and other light hydrocarbons always involve a complicated series of consecutive and simultaneous free radical steps (7 to 9, 13, 14, 19).At low conversions, approximately equal moles of ethylene, propylene, methane, and hydrogen are produced when propane is pyrolyzed (3, 5, 1 0 ) . Several of the primary products and especially propylene are relatively unstable. As propane conversions increase, yields of ethylene and methane increase relative to those of propylene and hydrogen (1, 3 ) . Ethane, butenes, butadiene, aromatics, heavier components, and acetylene are always produced to at least a small extent. The surface of the reactor is also known to effect the pyrolysis reactions to at least some degree ( 3 , 12, 1 8 ) .Because of the complexity of the reaction mechanism, it is not surprising that simple order kinetic equations are not applicable. Considerable questions still exist though as to just which free radical steps are important in the overal! processes for the various light paraffins. Many previous pyrolysis investigations have been at operating conditions quite different than those used commercially. Temperatures and pressures employed have often been relatively low, and the rates of pyrolysis were then much less than those in commercial units. Although steam is apparently employed exclusively as a diluent commercially, it has been employed only to a very limited extent in kinetic investigations reported to date. however, since the kinetic data available for ethane pyrolysis do not appear to be completely consistent. Furthermore, the model does not contain terms for some less important reaction steps. Current literature does not contain adequate kinetic data for propane pyrolysis in order to develop a similar mechanistic approach. Such data have now been obtained in the present investigation. A mechanistic model that represents the kinetics of the reaction and predicts product composition has also been developed. E X P E R I M E N T A L DETAILSThe equipment used in this investigation was the same as that used by Crynes and Albright