Atmospheric pressure microwave plasma for selective acetylene production

Microwave plasmas have demonstrated potential for selective conversion of methane into acetylene. The high temperatures in the plasma drive fast kinetics, producing acetylene, ethylene, as well as unwanted byproducts. A key aspect in maximizing the C₂ selectivity is gaining control over residence time, which changes with pressure. While most experiments in literature are performed at sub-atmospheric pressure, industry favors processes at elevated pressures to increase cost-effectiveness. Residence times are even more critical at these higher pressures, because reaction rates are increased on one hand, and volumetric flow rates are reduced on the other.

In this contribution we build upon our previous work at 100 mbar and 1 kW to expand the operational space to 1 bar. Multiple swirl geometries are tested to minimize carbon deposition in the reactor zone, in combination with central flow injection to control plasma residence time. Additionally, mixing ratios of methane and hydrogen are optimized in view of C₂ selectivity. Reactor performance is quantified by gas chromatography and plasma imagining is used to characterize power deposition and plasma stability.