Methane pyrolysis in packed bed reactors: Kinetic modeling, numerical simulations, and experimental insights

Pyrolysis of hydrocarbon feeds such as methane (CH$_4$) and natural gas emerges as a pivotal carbon dioxide-free
large-scale hydrogen (H$_2$) production process combined with capturing the carbon as solid material. For
fundamental understanding and upscaling, the complex kinetics and dynamics of this process in technically
relevant reactors such as packed and moving beds still need to be explored, particularly concerning carbon
formation and its impact on reactor performance. This study integrates kinetic modeling, numerical simulations,
and experimental findings to comprehensively understand CH$_4$ pyrolysis under industrially relevant conditions
and its implications for efficient H$_2$ production and carbon capture. The investigation covers temperatures from
1273 K to 1873 K, H$_2$ addition with H$_2$:CH$_4$ ratios of 0 to 4, and hot zone residence time of 1 to 7 s. Two distinct
pathways lead to carbon formation: soot formation and carbon deposition. Each pathway originates from
different gas-phase precursors. An elementary-step-based gas-phase reaction mechanism is coupled with a soot
formation model from polycyclic aromatic hydrocarbon and a newly developed deposition model from light
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hydrocarbons. Numerical simulations are performed in a packed bed reactor model, incorporating a method of
moments for soot formation and a model for carbon deposition. The model is evaluated against experiments and
predicts the effects of operating conditions on gas-phase product distribution and carbon formation. It also es-
timates the change in bed-voidage over operational time. The study reveals that at the temperature 1673 K, CH$_4$
conversion exceeds 94 %, while both H$_2$ and solid carbon yields surpass 96 %. The sophisticated modeling and
simulation framework presented herein thus provides an enhanced understanding of the CH$_4$ pyrolysis process
and presents a valuable tool for optimizing this process.