A kinetic modeling study of ethylene pyrolysis

A kinetic model is presented for the pyrolysis of ethylene at pressures ran ging from 0.8 to 27 kPa and temperatures from 774 to 1023 K. The model is b ased on experimental measurements of C2H2, C2H6, C3H6, 1-C4H8, and 1,3-C4H6 . in this temperature range the reaction is initiated by the disproportiona tion of C2H2 and the observed products result from reactions of the C2H3 an d C2H5 radicals produced in this process. The C2H2 and 1,3-C4H6 result from reactions of C2H3 while C2H6, C3H6, and 1-C4H8 result from reactions of C2 H5. C2H2 is produced exclusively by the decomposition of the C2H3 radical. This process is in its falloff region throughout the range of experimental conditions examined and the yield of C2H2 provides a measure of the degree of falloff. The production of 1,3-C4H6 is controlled by the reaction C4H7 - -> C4H6 + H. The rate constants for this reaction were independent of press ure and are given as a function of temperature by k = 2.2 x 10(13) exp (-19 .6 x 10(3)/T). Production of C2H6 is controlled by the reaction C2H5 + C2H4 --> C2H6 + C2H3. The rate constant for this reaction is given as a functio n of temperature by k = 5.83 x 10(11) exp (-14.6 x 10(3)/T). C3H6 is produc ed by decomposition of 2-C4H9 and is controlled kinetically by the isomeriz ation reaction 1-C4H9 --> 2-C4H9. The temperature dependence of the rate co nstants obtained for this reaction leads to a preexponential factor of appr oximately 3 x 10(16) and an activation energy of approximately 200 kJ mol(- 1). The yield of 1-C4H8 is controlled by 1-C4H9 --> 1-C4H8 + H. The rate co nstants fur this reaction were independent of pressure and are given as a f unction of temperature by k = 2.97 x 10(12) exp (-17.1 x 10(3)/T).