Pyrolysis of propane for CVI of pyrocarbon Part Ⅲ: Experimental and modeling study of the formation of pyrocarbon

摘要

Carbon/carbon composites synthesis involves the deposition of a matrix of pyrocarbon produced by the pyrolysis of a gaseous hydrocarbon in a preform made of carbon fibers. This work describes an experimental and modeling study of the formation of pyrocarbon obtained by the pyrolysis of propane. The pyrolysis of propane is carried out in a perfectly stirred reactor at low pressure (2.6 kPa) in a wide range of temperature (1173-1298 K) with a residence time of 1 s. During the pyrolysis, the pyrocarbon is quantified by weighing and 29 other products of propane pyrolysis are also analysed by Gas-Chromatography (GC). In order to reproduce the experimental deposit of pyrocarbon but also the gas phase species, an original way of modeling the deposition of pyrocarbon, which contains a homogeneous model completed with lumped heterogeneous reactions, is proposed. This model tries to target which species gives what pyrocarbon although what really happens at the carbon fibers surface remains unknown. Two kinds of reactions of deposition are discussed; those involving small gaseous unsaturated species such as C_2H_2 and those involving large species (≥ C_6). The results of modeling seem to show, in agreement with the literature, that the pyrocarbon deposition could be quantitatively explained by the deposition of small unsaturated species.