Methane reforming to valuable products by an atmospheric pressure direct current discharge

Conventionally, syngas produced by steam reforming is used to convert methane into methanol and other valuable products. In this work, methane reforming in a glow electrical discharge is studied under highly non-thermal conditions. The gas temperature at the core of the discharge depends on gas pressure and discharge current, and ranges between 1500 and 2000 K. The underlying chemistry and important reaction pathways of non-thermal plasma methane reforming are unravelled using a batch reactor coupled with a mass spectrometer and gas chromatography system. Rate of production analysis supports the hypothesis of predominantly methane dissociation reactions into methyl free radicals recombine to form ethane, with a selectivity of more than 94% on carbon basis. Ethylene and acetylene are identified as secondary products with a C-based selectivity of less than 5.2%. This plasma approach can provide a global selectivity of 63% for methane reforming directly to ethane which is higher than reported values for other electrical discharges of typically 30–40%. The lowest energy cost achievable in the glow discharge for ethane formation is estimated to be 8.8 MJ/mol which is highly competitive with a barrier discharge performance of 17.4 MJ/mol. Moreover, glow discharge has an advantage of a negligible soot production which is a major drawback of many plasma-assisted processes reported. However, a comparison between investment costs and the gross margin indicates that methane reforming using glow discharge is economically profitable only for very long time scales due to the low profit margins. To make plasma assisted gas reforming feasible for industrial scale additional optimization of the process is required