The Sabatier process

The Sabatier process produces water and methane through a reaction of hydrogen with carbon dioxide. It is being used on the International Space Station (ISS) to produce clean, drinkable water and to retrieve the oxygen contained in the CO2.

A vital feature of the Sabatier process is that it’s nearly a closed loop: the water generated can be split again and pumped back into the reaction to continue generating more oxygen and fuel.

How does it work?
Carbon dioxide is the natural result of respiration and its density will gradually increase in the air of the ISS with time. Too much and you can no longer breath and are asphyxiated. What is needed is a process where the CO2 is removed from the air faster than the oxygen. That can be achieved using zeolites, a porous alumino-silicate that can be formed during volcanic eruptions, can float in huge rafts on the sea and is called pumice. This rock can now be man made into molecular sieves, and the best for collecting CO2 from the air is 13x which allows atoms and molecules smaller than 1 nanometre to pass into the zeolite and be adsorbed.

The Sabatier process uses a couple of processes to separate water into hydrogen and oxygen.

One method is to pass an electric current through water to separate the H20 into hydrogen at the negative cathode and oxygen at the positive anode. These gases can then be collected separately. But pure water does not conduct electricity at all well so strong acids such as sulphuric acid (H2SO4), and strong bases such as potassium hydroxide (KOH), and sodium hydroxide (NaOH) are frequently used as electrolytes due to their strong conducting abilities. However, these acids and bases are very strong and can quickly lead to corrosion problems.

By mixing the hydrogen gas with carbon dioxide at a high temperature and flowing the mixture across an appropriate catalyst, the Sabatier process generates drinkable water and methane. On the ISS, the methane is vented to space as the astronauts are primarily interested  in recycling the water and oxygen. However, on earth and on the Moon the methane can be used for heating and rocket propellant.

Why Is the Sabatier process important to humanity’s future?
While the Sabatier process is being used on the ISS, it may also provide solutions to essential questions back on Earth and help get humans out to Mars.

  • Synthetic natural gas. The methanation of carbon dioxide is a key stepping stone to the production of synthetic natural gas. The Sabatier process can supplement a power-to-gas method to help create a renewable energy system, alongside wind energy, solar panels that create solar energy, and water energy. The methane created by the Sabatier reaction can be injected directly into a country’s existing gas network. As climate change impacts the planet further, the need for an energy system that is less reliant on fossil fuels will be essential. Instead of using the methane from fossil fuels, the Sabatier processes allows us to just recirculate what is already in the atmosphere and not add to the CO2 pollution. Large scale CO2 removal from the atmosphere is possible using a variety of capture technologies, including zeolites, followed by the Sabatier process to generate methane and subsequently methanol, which, as a fluid, is very simple to transport and can be used instead of petrol in internal combustion engines.
  • Future space travel. As future missions of space exploration take us deeper into our solar system, the Sabatier process may be a key component in making missions to Mars and beyond feasible through in-situ resource utilisation. The Sabatier methanation reaction can theoretically be tweaked to produce methane from the raw materials in the Martian atmosphere. Tests have shown that using a reverse water gas shift reaction to reduce carbon dioxide to carbon monoxide, the Sabatier methanation process can be used for methane rocket propellant production at nearly 100 per cent conversion rate. The process of such conversion efficiency creates a functionally effective renewable energy system that could be used to help propel a Mars spacecraft back home. The first rocket fired from the Woomera Rocket Range in South Australia used methane as a fuel, as does the huge rocket Starship developed by SpaceX.