An induction period in the pyrolysis of acetylene

Acetylene was pyrolysed in a flow system between 854 and 970 K, at pressure s between 27 and 127 Torr and at residence times between 8 and 1520 ms. Bot h vinylacetylene and benzene were observed to be primary products, but seco ndary processes removed vinylacetylene and formed benzene. The orders for t he steady-state rates of formation of vinylacetylene and benzene were measu red to be 1.8 +/- 0.1 and 2.4 +/- 0.1, respectively. The corresponding rate constants were found to be, 1n(k(VA)/L mol(-1) s(-1)) = -(165 +/- 11) kJ m ol(-1)/RT + (22.7 +/- 1.5) and 1n(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 pro cess dominates. The order of the initiation reaction was shown to be two. T he temperature dependence of the product of the rate constants for the bimo lecular, initiation reaction and the termination reaction was determined to be, 1n(k(i)k(t)/L-2 mol(-2) s(-2))= -(261 +/- 7) kJ mol(-1)/RT + (53.1 +/- 1.0).