Concept for Increasing Water Recovery by Use of Series Reverse Water-Gas Shift - Sabatier Technology

A novel concept for increasing the water yield from existing Sabatier technology is proposed. Current Sabatier technology on board the ISS uses electrolysis hydrogen and metabolic carbon dioxide to recover water used for electrolysis. The stoichiometry of the Sabatier reaction requires a hydrogen-to-carbon-dioxide-mole-ratio of 4:1. The mass balance of the ISS however, prescribes a feed ratio of approximately 2:1. As a consequence, water is lost in the form of unreacted CO2. By connecting a reverse water-gas shift (RWGS) reactor prior to the Sabatier reactor, the stoichiometric ratio of the net reaction can be shifted below 4:1 and closer to the feed ratio. This way, water recovery can be increased from 50% (Sabatier only) to up to 64% (RWGS-Sabatier) theoretically. The concept is compared to the alternate technology currently under development by NASA - the Plasma Pyrolysis Assembly.