The rates of pyrolysis of cyclopropane in nitrogen have been determined using a wall-less reactor at temperatures of 600-740 "C and a total pressure of 1 atm. In the presence of oxidized stainless steel. quartz, o r carbon coated steel rods the rate of conversion to propylene is 1.9 times the rate under homogeneous conditions. A maximum in surface effect was observed at S / V = 0.6 a n -' . A small but increased amount of methane and ethene are formed under surface conditions as compared to homogeneous conditions. Several possible mechanisms for the rate enhancement by surface are discussed. The most likely possibility is surface interaction with the cyclopropane molecule to form the diradical followed by its surface promoted conversion to propene. The importance of determining surface effects by comparing surface rates with totally homogeneous rates is emphasized.On a evalue les differentes vitesses de pyrolyse dans I'azote du cyclopropane en utilisant un reacteur sans paroi a des temperatures de 600 a 740 "C et a une pression totale d'un atmosphere. En presence de tiges d'acier recouvertes de quartz, de carbone ou d'acier inoxydable oxyde, la vitesse de transformation en propylene est superieure par un facteur de 1.9 a celle enregistree dans des conditions hornogenes. On a observe a S / V = 0.6 cm-' un effet de surface maximum. D e m&me, uneltgtre augmentation d e la quantite produite de methane et d'ethane a Ctt enregistree dans les conditions impliquant une surface par rapport aux conditions homogenes. On discute de plusieurs mecanismes probables tenant compte de I'augmentation de vitesse due a une interaction surface-cyclopropane conduisant i u n biradical puis a s a transformation, favorisee par la surface, en propene. On discute aussi de I'importance d'evaluer les effets de surface par comparaison entre les vitesses observtes lors de la presence d'une surface et celles obtenues dans des conditions parfaitement homogenes.[Traduit p a r le journal]Can.
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