Yield, morphology and maturity of carbon black made by methane pyrolysis in a shock tube

Carbon black (CB) is a high-volume industrial nanomaterial used primarily as a reinforcing filler in rubber, especially tires. Global production exceeds 10 million tons per year, with a market value above $20 billion annually. Direct methane (CH₄) decomposition via thermal plasma is a low-emission, high-yield method for CB production. Achieving specific CB grades for targeted applications requires precise control of the synthesis process.

Controlling CB synthesis remains challenging due to limited understanding of CB formation during methane pyrolysis, despite extensive studies on pyrolysis kinetics [1]. This limitation arises from incomplete knowledge of CB inception pathways and uncertainties in existing kinetic mechanisms. Uncertainty in early CH₄ dissociation propagates through key intermediates such as ethylene (C₂H₄) and acetylene (C₂H₂) and becomes amplified during the formation of polycyclic aromatic hydrocarbons (PAHs), which are major CB precursors.

There is a scarcity of benchmark data that simultaneously quantify gas-phase species and CB evolution under high-temperature conditions relevant to CB synthesis. Such coupled measurements are necessary to quantify carbon flux to CB and to constrain kinetic mechanisms together with CB inception and surface growth rates using time-resolved diagnostics.

Here, we report time-resolved CH₄, C₂H₄, and C₂H₂ mole fractions measured by laser absorption spectroscopy and CB volume fraction, quantified by multi-wavelength extinction [2]. Transmission electron microscopy (TEM) images of collected samples provide the primary particle diameter. The CB maturity inferred extinction ratio, demonstrated strong correspondence with the predicted H/C ratio, indicating a quantitative, time-resolved probe of CB maturity directly linked to reactive surface chemistry.