An interpretation of the hydrogen inhibiting effect on chemical vapor deposition of pyrocarbon

• A kinetic mechanism describing propane pyrolysis and pyrocarbon deposition is used.
• Pyrocarbon is mostly formed by deposition of methyl radicals, acetylene and ethylene.
• Hydrogen has an inhibiting effect on pyrocarbon deposition during propane pyrolysis.
• This inhibiting effect is explained by using the validated mechanism.

A detailed kinetic mechanism, based on elementary steps, modeling both pyrocarbon deposition and gas phase composition obtained by propane pyrolysis on carbon fibers was recently proposed. This model, based on heterogeneous and homogeneous elementary steps was efficient to predict pyrocarbon deposition rate and gas phase composition when the influence of temperature (1173–1323 K), residence time (0.5–4 s), carbon surface fibers, and reactor inlet mixture were studied. In this paper, we discuss experimental and modeling results of hydrogen inhibiting effects on pyrocarbon deposited and gas phase composition during propane/hydrogen pyrolysis (temperature 1273 K, residence time 1 s, surface fibers 3960 cm−1). Simulated results are coherent with experimental data when the pyrocarbon deposition rate is studied. Compared to pure propane chemical vapor deposition, the mole fractions of C2 gas phase species are not affected by an increasing of hydrogen inlet, whereas pyrocarbon deposition rate and mole fractions of C3 and aromatic species decrease. These results also confirm, in accordance with the literature, that hydrogen inhibits highly the formation of pyrocarbon and aromatic species.