Nanosecond pulsed discharge-driven non-oxidative methane coupling in a plate-to-plate electrode configuration plasma reactor

Abstract

In this work, we establish a set of reactor operation guidelines for efficient non-oxidative methane coupling (i.e., high olefins yield) in nanosecond pulsed discharges and plate-to-plate electrode configuration. The reactor performance analysis suggests that the operating conditions directly affect the bulk gas temperature, which in turn determines the plasma resistance and, subsequently, the energy channeled into the discharge. High performance is attained only at proper load-impedance matching, i.e. when operating in spark regime and applying i) moderate pulse frequencies (≤20 kHz) combined with moderate discharge gaps (≤3.5 mm) or ii) high pulse frequencies (>20 kHz) combined with high discharge gaps (>3.5 mm). Further, the electrode configuration itself significantly affects the reactor performance. When applying same operating conditions, the plate-to-plate configuration attains lower olefin (C2) yield than the co-axial one (~27% vs ~34%, respectively) since lesser energetic discharges are ignited (11 W vs 17 W), but ~20% lower energy is used due to lower electric energy dissipation into gas heating. The plate-to-plate configuration also features significantly higher performance stability and robustness in carbon formation, enabling an order-of-magnitude longer operating periods.