Sabatier reaction

Methanation reactions over different metal catalysts including Ni,[4] Ru[5] and Rh[6] have been widely investigated for the production of CH4 from syngas and other power to gas initiatives.

[8] The Sabatier reaction has been used in renewable-energy-dominated energy systems to use the excess electricity generated by wind, solar photovoltaic, hydro, marine current, etc.

[9][10] In contrast to a direct usage of hydrogen for transport or energy storage applications,[11] the methane can be injected into the existing gas network.

This approach required copious amounts of water to be regularly transported to the space station for oxygen generation in addition to that used for human consumption, hygiene, and other uses—a luxury that will not be available to future long-duration missions beyond low Earth orbit.

NASA is using the Sabatier reaction to recover water from exhaled carbon dioxide and the hydrogen previously discarded from electrolysis on the International Space Station and possibly for future missions.

However, this creates a nearly-closed cycle between water, oxygen, and carbon dioxide which only requires a relatively modest amount of imported hydrogen to maintain.

The loop could be further closed if the waste methane was separated into its component parts by pyrolysis, the high efficiency (up to 95% conversion) of which can be achieved at 1200 °C:[19] The released hydrogen would then be recycled back into the Sabatier reactor, leaving an easily removed deposit of pyrolytic graphite.

[citation needed] Alternatively, the loop could be partially closed (75% of H2 from CH4 recovered) by incomplete pyrolysis of the waste methane while keeping the carbon locked up in gaseous form as acetylene:[20] The Bosch reaction is also being investigated by NASA for this purpose, which is:[21] The Bosch reaction would present a completely closed hydrogen and oxygen cycle which only produces atomic carbon as waste.

However, difficulties maintaining its temperature of up to 600 °C and properly handling carbon deposits mean significantly more research will be required before a Bosch reactor could become a reality.

This kind of in situ resource utilization would result in massive weight and cost savings to any proposed crewed Mars or sample-return missions.