“Beyond-thermal-equilibrium” conversion of methane to acetylene and hydrogen under pulsed corona discharge

Abstract

At ambient temperature and pressure, C₂H₂ and H₂ are the dominating products from pure methane conversion under pulsed corona discharge (PCD). When the energy density of 194-1788 kJ/mol was applied, 7%-30% of C₂H₂ yield and 6%-35% of H₂ yield per pass have been obtained. These results are higher than the maximum thermodynamic yield of C₂H₂ (5.1%) and H₂ (3.8%) at 100 kPa and 1100 K, respectively. Thereby, pulsed corona discharge is a very effective tool for “beyond-thermal-equilibrium” conversion of methane to C₂H₂ and H₂ at ambient temperature and pressure. In the PCD energy density range of 339-822 kJ/mol, the carbon distribution of the methane conversion products is found to be: C₂H₂ 86%-89%, C₂H₂ 4%-6%, C₂H₄ 4%-6%, C₃ ∼2%, C₄ ∼1%. Through comparison of the product from pure methane, ethane and ethylene conversion at the same discharge conditions, it can be concluded that three pathways may be responsible for the C₂H₂ formation via CH_X radicals produced from the collisions of CH₄ molecules with energized electrons in the PCD plasma: (i) C₂H₂ is formed directly from free radical reactions, (ii) C₂H₂ is formed through the dehydrogenation of C₂H₄, which is formed via free radical reactions primarily, and (iii) C₂H₆ is the primary product and then dehydrogenates to C₂H₄ (secondary product) and followed by C₂H₄ dehydrogenation to C₂H₂.