THE MECHANISM OF ETHYLENE PYROLYSIS AT SMALL CONVERSIONS

Kinetic modelling is used in conjunction with measurements of product yields to develop a mechanism for the pyrolysis of ethylene at 896 K a nd ethylene pressures ranging from approximately 3 to 78 kPa. An induc tion period was observed for all products except H-2, and was followed by a steady rate, which was of second-order for all products except 1 ,3-C4H6, the most abundant product. The mechanism quantitatively accou nts for the yields of H-2, CH4, C2H6, C3H6, 1-C4H8, and 1,3-C4H6. The reaction is initiated by disproportionation of C2H4 and the product 1, 3-C2H6 results from decomposition of the C4H7 radical, formed by addit ion of C2H3 to C2H4. The other organic products that were measured are formed as a result of reactions involving the C2H5 radical. The hydro gen is produced by abstraction from C2H4 by atomic hydrogen and its ra te is controlled by the reaction C2H5 --> C2H4 + H which is nearly equ ilibrated. The main termination reaction is recombination of C2H5. The auto-acceleration which is evident particularly in the yields of H-2, CH4, C2H6, and C3H6 is accounted for by the decomposition of 1-C4H8. (C) 1996 John Wiley & Sons, Inc.