Chemical vapor infiltration of pyrocarbon from methane pyrolysis: kinetic modeling with texture formation

甲烷化学气相沉积不同织构热解碳的动力学分析（英文）

A complete mechanism of methane pyrolysis is proposed for chemical vapor infiltration of pyrocarbon with different textures, which contains a detailed homogeneous mechanism for gas reactions and a lumped heterogeneous mechanism for pyrocarbon deposition. This model is easily applied to simulate gas compositions and pyrocarbon deposition in a vertical hot-wall flow reactor in the temperature range of 1,323–1,398 K without any adjusting parameters and presents better results than previous mechanisms. Results have shown that the consumption of methane and the production of hydrogen are well enhanced due to pyrocarbon deposition. Pyrocarbon deposition prevents the continuously increasing of acetylene composition and leads to the reduction in the mole fraction of benzene at long residence times in the gas phase. The carbon growth with active sites on the surface is the controlling mechanism of pyrocarbon deposition. C1 species is the precursor of pyrocarbon deposition at 1,323 K,and the primary source over the whole temperature range. As temperature increases, gas phase becomes more mature and depositions from acetylene, benzene and polyaromatic hydrocarbons become more prevalent. A general pyrocarbon formation mechanism is derived with the specific precursors and illustrates that the maturation of gas compositions is beneficial to forming planar structures with hexagonal rings or pentagon-heptagon pairs, namely, high textured pyrocarbon. The results are in well agreement with experiments.

本文建立了一种甲烷化学气相沉积不同织构热解碳的动力学模型.该模型包括甲烷气相热解的详细基元反应及热解碳沉积的集总表面反应,模拟了1323–1398 K立式热壁反应炉中热解碳沉积过程中不同气体的组分浓度及热解碳的沉积速率,且模拟结果优于已有报道的模型、与实验结果吻合良好.结果表明,热解碳的主要沉积机理为碳源气体在表面活性位的生长机理,其中C_1物质为主要碳源气体.随着温度升高,甲烷热解混合气体趋于成熟,乙炔、苯和多环芳香烃逐渐成为重要的碳源气体.基于以上碳源气体的热解碳形成机理分析指出热解混合气体的成熟有利于形成由六元环及五元环-七元环组合而成的高定向平面结构,即高织构热解碳,与实验结论吻合良好.