Kinetic Modeling Analysis of the Pyrolysis of Vinyl Bromide

A kinetic model has been developed for the thermal decomposition of vinyl bromide at temperatures below approximately 750 K. The decomposition is initiated by two channels, a pressure dependent molecular channel, C<INF>2</INF>H<INF>3</INF>Br + M → C<INF>2</INF>H<INF>2</INF> + HBr + M, and a free radical channel, 2 C<INF>2</INF>H<INF>3</INF>Br → C<INF>2</INF>H<INF>3</INF> + C<INF>2</INF>H<INF>3</INF>Br<INF>2</INF>. The molecular channel is second-order overall at all the temperatures and pressures investigated. The temperature dependence of the rate constant for this reaction when vinyl bromide is M is given by ln(k<INF>1a</INF>) = 35.7 ± 5.4−29.8 × 10³(±12%)/T. This leads to a preexponential factor of 3 × 10¹⁵ L mol^-1 s^-1 and an activation energy of 248 kJ mol^-1. When M is argon, the preexponential factor is 2 × 10⁸ L mol^-1 s^-1 and the activation energy is 153 kJ mol^-1 ± 23%. The temperature dependence of the free radical decomposition step is given by ln(k<INF>2</INF>) = 17.3 ± 3.2 − (17.3 × 10³ ±13%)/T, giving a preexponential factor of 3 × 10⁷ L mol^-1 s^-1 and an activation energy of 144 kJ mol^-1. The model also provides kinetic data for the abstraction of hydrogen from vinyl bromide by C<INF>2</INF>H<INF>3</INF> radicals, C<INF>2</INF>H<INF>3</INF> + C<INF>2</INF>H<INF>3</INF>Br → C<INF>2</INF>H<INF>4</INF> + C<INF>2</INF>H<INF>2</INF>Br. The temperature dependence of this reaction is given by ln(k<INF>3</INF>) = 28.7 ± 3.1−9.7 × 10³(± 22%)/T, leading to a preexponential factor of 3 × 10¹² L mol^-1 s^-1 and an activation energy of 81 kJ mol^-1.