Pyrolysis of vinylacetylene between 300 and 450°C

Abstract

AbstractVinylacetylene was pyrolyzed at 300–450°C in a packed and an unpacked static reactor with a pinhole bleed to a quadrupole mass spectrometer. The reactant and C8H8 products were monitored continuously during a reaction by mass spectrometry. In some runs, the products were also analyzed by gas chromatography after the run. In these runs CH4, C2H6, C3H6, and C2H4 were also detected.The reaction for vinylacetylene removal and C8H8 formation is homogeneous, second order in reactant, and independent of the presence of a large excess of N2 or He. However, C8H8 formation is about half‐suppressed by the addition of the free‐radical scavengers NO or O2. The rate coefficient for total vinylacetylene removal is 1.7 × 106 exp(−79 ± 13 kJ/mol RT) L/mol · s. The major reaction for C4H4 removal is polymerization. In addition four C8H8 isomers, carbon, and small hydrocarbons are formed. The three major C8H8 isomers are styrene, cyclooctatetraene (COT), and 1,5dihydropentalene (DHP).The C8H8 compounds are formed by both molecular and free‐radical processes in a second‐order process with an overall k ≃ 3 × 108 exp(−122 kJ/mol RT) L/mol · s (average of packed and unpacked cell results). The molecular process occurs with an overall k = 8.5 × 107 exp (−118 kJ/mol RT) L/mol · s. The COT, DHP, and an unidentified isomer (d), are formed exclusively in molecular processes with respective rate coefficients of 4.4 × 104 exp(−77 kJ/mol RT), 1.7 × 105 exp(−89 kJ/mol RT), and 3.1 × 109 exp(− 148 kJ/mol RT) L/mol · s. The styrene is formed both by a direct free‐radical process and by isomerization of COT.