Thermal isomerization and decomposition of 1,2‐butadiene in shock waves

Abstract

Abstract1,2‐Butadiene diluted with Ar was heated behind reflected shock waves over the temperature and the total density range of 1100–1600 K and 1.36 × 10−5 − 1.75 × 10−5 mol/cm3. The major products were 1,3‐butadiene, 1‐butyne, 2‐butyne, vinylacetylene, diacetylene, allene, propyne, C2H6, C2H4, CH4, and benzene, which were analyzed by gas chromatography. The UV kinetic absorption spectroscopy at 230 nm showed that 1,2‐butadiene rapidly isomerizes to 1,3‐butadiene from the initial stage of the reaction above 1200 K. In order to interpret the formation of 1,3‐butadiene, 1‐butyne, and 2‐butyne, it was necessary to include the parallel isomerizations of 1,2‐butadiene to these isomers. The present data were successfuly modeled with a 82 reaction mechanism. From the modeling, rate constant expressions were derived for the isomerization 1,2‐butadiene = 1,3‐butadiene to be k3 = 2.5 × 1013 exp(−63 kcal/RT) s−1 and for the decomposition 1,2‐butadiene = C3H3 + CH3 to be k6 = 2.0 × 1015 exp(−75 kcal/RT) s−1, where the activation energies, 63 kcal/mol and 75 kcal/mol, were assumed. These rate constants are only applicable under the present experimental conditions, 1100–1600 K and 1.23–2.30 atm. © 1995 John Wiley & Sons, Inc.