Methane conversion to C2 hydrocarbons and hydrogen in atmospheric non-thermal plasmas generated by different electric discharge techniques

Methane conversion to C-2 hydrocarbons and hydrogen has been investigated in a needle-to-plate reactor by pulsed streamer and pulsed spark discharges and in a wire-to-cylinder dielectric barrier discharge (DBD) reactor by pulsed DC DBD and AC DBD at atmospheric pressure and ambient temperature. In the former two electric discharge processes, acetylene is the dominating C-2 products. Pulsed spark discharges gives the highest acetylene yield (54%) and H-2 yield (51%) with 69% of methane conversion in a pure methane system and at 10 SCCM of flow rate and 12 Wof discharge power. In the two DBD processes, ethane is the major C-2 products and pulsed DC DBD provides the highest ethane yield. Of the four electric discharge techniques, ethylene yield is less than 2%. Energy costs for methane conversion, acetylene or ethane (for DBD processes) formation, and H-2 formation increase with methane conversion percentage, and were found to be: in pulsed spark discharges (methane conversion 18-69%), 14-25, 35-65 and 10-17 eV/molecule; in pulsed streamer discharges (methane conversion 19-41%), 17-21, 38-59, and 12-19 eV/molecule; in pulsed DBD (methane conversion 6-13%), 38-57, 137-227 and 47-75 eV/molecule; in AC DBD (methane conversion 5-8%), 116-175, 446-637, and 151-205 eV/molecule, respectively. The immersion of the gamma-Al2O3 pellets in the pulsed streamer discharges, or in the pulsed DC DBD, or in the AC DBD has a positive effect on increasing methane conversion and C-2 yield. (C) 2004 Elsevier B.V. All rights reserved.