An induction period in the pyrolysis of acetylene

Abstract

Acetylene was pyrolysed in a flow system between 854 and 970 K, at pressures between 27 and 127 Torr and at residence times between 8 and 1520 ms. Both vinylacetylene and benzene were observed to be primary products, but secondary processes removed vinylacetylene and formed benzene. The orders for the steady-state rates of formation of vinylacetylene and benzene were measured to be 1.8 ± 0.1 and 2.4 ± 0.1, respectively. The corresponding rate constants were found to be, ln(k_VA/L mol⁻¹ s⁻¹) = − (165 ± 11) kJ mol⁻¹/RT + (22.7 ± 1.5) and ln(k_B/L^1.4 mol^−1.4 s⁻¹) = − (100 ± 9) kJ mol⁻¹/RT + (15.6 ± 1.1). Induction periods were observed for the first time at these conditions, providing evidence that a free radical process dominates. The order of the initiation reaction was shown to be two. The temperature dependence of the product of the rate constants for the bimolecular, initiation reaction and the termination reaction was determined to be, ln(k_ik_t/L² mol⁻² s⁻²) = − (261 ± 7) kJ mol⁻¹/RT + (53.1 ± 1.0).