The disclosure relates to methods, systems, and apparatus arranged and designed for converting non-methane hydrocarbon gases into multiple product gas streams including a predominately hydrogen gas stream and a predominately methane gas steam. Hydrocarbon gas streams are reformed, cracked, or converted into a synthesis gas stream and methane gas stream by receiving a volume of flare gas or other hydrocarbon liquid or gas feed, where the volume of hydrocarbon feed includes a volume of methane and a volume of non-methane hydrocarbons. The hydrogen contained in the syngas may be separated into a pure hydrogen gas stream. A corresponding gas conversion system can include a super heater to provide a hydrocarbon feed/steam mixture, a heavy hydrocarbon reactor for synthesis gas formation, and a hydrogen separator to recover the hydrogen portion of the synthesis gas. The gas conversion system can have a modal design such that it can operate to form hydrogen gas or alternatively operate to form synthetic natural gas with the same unit operation components.