Hydrogen production by microwave plasma CH4 pyrolysis: Characterization via optical emission spectroscopy and response surface methodology
Gregory G. Facas, Gianmarco Calabrese, Nora Schüller, Daniel Schreiber, Markus Zennegg, Marilena Radoiu, Panayotis Dimopoulos Eggenschwiler
Abstract
Microwave plasma pyrolysis of methane (CH 4 ) is a route for hydrogen (H 2 ) production with low CO 2 emissions. This study utilizes Optical Emission Spectroscopy and Design of Experiments to characterize plasma pyrolysis of CH 4 using a 2.45 GHz microwave-based plasma reactor operated at atmospheric pressure with N 2 as the plasmagen gas. Measured characteristic plasma temperatures include electron temperatures of 15,000 ± 1500 K, rotational temperatures of 7500 ± 1000 K, and vibrational temperatures of 6000 ± 1000 K, with little variation across microwave power (1–3 kW) and flowrate (15–50 L/min). Electron microscopy shows the pyrolysis carbon exhibits carbon black-like morphology. CH 4 conversion, H 2 selectivity, C 2 H 2 selectivity, HCN selectivity and specific energy consumption are modelled using Response Surface Methodology. Results indicate a trade-off between reactivity and energy efficiency. Complete CH 4 conversion is possible but requires high energy input, while the lowest energy use (60 kWh/kg H 2 ) occurs at ∼50 % CH 4 conversion.