Atmospheric-pressure microwave plasma reforming of ethane-carbon dioxide mixtures

Atmospheric-pressure microwave plasma reforming of ethane (C₂H₆)–carbon dioxide (CO₂) mixtures was investigated, potentially for plasma dry reforming of large hydrocarbons. The plasma was characterized using optical emission spectroscopy, and the reforming process was analyzed using gas chromatography and thermocouple measurements. The temperature of the plasma region reached approximately 5000 K, regardless of the specific energy input, which was sufficiently high to initiate the reforming reactions. About 90 % of the C₂H₆-CO₂ mixture was reformed into H₂ and CO with selectivities of about 83 %, at a microwave power and mixture flow rate of 2 kW and 10 slpm, respectively, while the mass flow rate of unmeasured species was less than 1 % of the total. An energy efficiency without any heat recovery schemes was determined to be 49 %, which was slightly higher than that for plasma methane dry reforming because the syngas production becomes favored at a lower temperature for ethane dry reforming. A more detailed analysis was performed by developing a reactor network model. The simulation revealed that the reforming process proceeded as the locally heated plasma flow interacts with its relatively cold surrounding flow through heat and mass transfer. Carbon monoxide (CO) was produced mainly through the reaction H + CO₂ → OH + CO, whereas molecular hydrogen (H₂) was mainly produced through hydrogen (H) abstraction reactions of hydrocarbons. Notably, acetylene (C₂H₂) and ethylene (C₂H₄) were the major by-products due to their higher H abstraction energies.