(513bo) Plasma-Assisted Non-Oxidative Methane Coupling to Olefins

Methane to olefins, specifically to ethylene, by means of non-thermal plasma (NTP) technologies gained much attention over the past years. NTP can work on renewable electricity that is mainly consumed in producing energetic electrons, instead of gas heating, for reagents activation, thereby overcoming the disadvantages of high pyrolytic temperatures. A new NTP technology in the field of chemical processing, namely the nanosecond pulsed discharge (NPD) allows for exploration of new operating windows far from thermodynamic equilibrium. By applying short voltage pulses, electric to chemical energy conversion is favored, limiting the thermal effect. The NPDs application for methane-to-ethylene valorization has been assessed through a multifaceted approach, aiming at addressing scientific, engineering and economic aspects of the process.

Novel plasma reactor systems employing NPDs are investigated and optimized at lab scale. We found that direct plasma-assisted non-oxidative methane coupling to ethylene is possible at elevated pressures (ethylene yield ~20% per pass, consuming 2020 kJ/molC₂H₄; Figure 1a and Figure 1b). Alternatively, hybrid plasma-catalytic reactor systems operating at ambient pressure can enable low energy-cost methane conversion to ethylene (ethylene yield ~26% per pass, consuming 1642 kJ/molC₂H₄; Figure 1c). Catalyst pretreatment by means of NPD in the dielectric barrier discharge regime can enhance active metal dispersion on the catalyst surface, thereby its activity, reducing further the total energy cost of the process. Methane fragmentation patterns and the main C₂ formation pathways as function of operating conditions and discharge regime have also been mechanistically explored. Further, plantwide process models of both the hybrid plasma-catalytic and direct ethylene formation processes have been developed to define the economically preferable operating window and assess the economic potential of such electrified processes. Break-even electricity prices have been calculated and compared to the current electricity prices (Figure 1d). Finally, aspects of process decoking, performance stability and reactor up-scaling are discussed.