Abstract: Pyrolysis systems and methods of generating hydrogen gas from a hydrocarbon gas. The pyrolysis systems include a solar thermal reactor configured to heat a gaseous hydrocarbon stream, such as methane, to its dissociation temperature. A supersonic turbomachine disposed in a housing receives resulting carbon particles and hydrogen gas from the solar thermal reactor and prevents dissociated carbon from forming deposits on an interior wall of the housing. A particulate separator is located downstream of the supersonic turbomachine to separate the carbon particles from the remaining hydrogen gas.