Methods and systems are provided for converting methane in a feed stream to acetylene. The hydrocarbon stream is introduced into a supersonic reactor and pyrolyzed to convert at least a portion of the methane to acetylene. The reactor effluent stream may be treated to convert acetylene to a process stream having aromatic compounds. The acetylene stream can be reacted to generate larger hydrocarbon compounds, which are passed to a cyclization and aromatization reactor to generate aromatics. The method according to certain aspects includes controlling the level of carbon oxides in the hydrocarbon stream.