Sabatier reaction
Encyclopedia
The Sabatier reaction or Sabatier process involves the reaction of hydrogen
with carbon dioxide
at elevated temperatures and pressures in the presence of a nickel
catalyst to produce methane
and water. Optionally ruthenium
on alumina (aluminum oxide) makes a more efficient catalyst. It is described by the following reaction:
It was discovered by the French
chemist
Paul Sabatier
.
produce oxygen from water using electrolysis
and dump the hydrogen produced overboard. As astronauts consume oxygen, carbon dioxide is produced which must then be removed from the air and discarded as well. This approach requires 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 currently investigating the use of the Sabatier reaction to recover water from exhaled carbon dioxide, for use on the International Space Station and future missions. (In April 2010, Sabatier hardware was delivered to the International Space Station
on the STS-131
shuttle mission.) The other resulting chemical, methane, would most likely be dumped overboard. As half of the input hydrogen becomes wasted as methane, additional hydrogen would need to be supplied from Earth to make up the difference. 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.
Ignoring other results of respiration, this cycle would look like:
The loop could be completely closed if the waste methane was pyrolyzed into its component parts:
The released hydrogen would then be recycled back into the Sabatier reactor, leaving an easily removed deposit of pyrolytic graphite
. The reactor would be little more than a steel pipe, and could be periodically serviced by an astronaut where the deposit is chiselled out.
The Bosch reaction
is also being investigated for this purpose. Though the Bosch reaction would present a completely closed hydrogen and oxygen cycle which only produces atomic carbon as waste, difficulties maintaining its higher required temperature and properly handling carbon deposits mean significantly more research will be required before a Bosch reactor could become a reality. One problem is that the production of elemental carbon tends to foul the catalyst's surface, which is detrimental to the reaction's efficiency.
) through In-Situ Resource Utilization
. Hydrogen is combined with CO2 from the atmosphere, with methane then becoming a storable fuel and the water side product yielding oxygen to be liquefied for the oxidizer and hydrogen to be recycled back into the reactor. The original amount of hydrogen could be transported from Earth or separated from martian sources of water.
The stoichiometric ratio of oxidizer and fuel is 3.5:1, for an oxygen:methane engine, however one pass through the Sabatier reactor produces a ratio of only 2:1. More oxygen may be produced by running the water gas shift reaction
in reverse. When the water is split, the extra oxygen needed is obtained.
Another option is to make more methane than needed and pyrolyze the excess of it into carbon and hydrogen (see above section) where the hydrogen is recycled back into the reactor to produce further methane and water. In an automated system, the carbon deposit may be removed by blasting with hot Martian CO2, oxidizing the carbon into carbon monoxide, which is vented.
A fourth solution to the stoichiometry
problem would be to combine the Sabatier reaction with the reverse water gas-shift reaction in a single reactor as follows:
3CO2 + 6H2 → CH4 + 2CO + 4H2O
This reaction is slightly exothermic, and when the water is electrolyzed, an oxygen to methane ratio of 4:1 is obtained, resulting in a large backup supply of oxygen. With only the light hydrogen transported from Earth, and the heavy oxygen and carbon extracted locally, a mass leveraging of 18:1 is afforded with this scheme. This in-situ resource utilization
would result in massive weight and cost savings to any proposed manned Mars or sample return missions.
The methane can be injected into the existing gas network which in many countries has one or two years of gas stockage capacity. The methane can then be used on demand to generate electricty (and heat - combined heat and power) overcoming low points of renewable energy production. The process is hydrolis of water by electricity to creat hydrogen (which can partly be used directly in fuel cells) and the addition of carbon dioxyde CO2 (Sabatier process) to create methane.
CO2 + 4H2 → CH4 + 2H2O
The CO2 can be extracted from the air or fossil fuel waste gases by the amine process amongst many others. It is a low CO2 system and has similar efficiencies of todays energy system.
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
with carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
at elevated temperatures and pressures in the presence of a nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
catalyst to produce methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
and water. Optionally ruthenium
Ruthenium
Ruthenium is a chemical element with symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is inert to most chemicals. The Russian scientist Karl Ernst Claus discovered the element...
on alumina (aluminum oxide) makes a more efficient catalyst. It is described by the following reaction:
- CO2 + 4H2 → CH4 + 2H2O
It was discovered by the French
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
chemist
Chemist
A chemist is a scientist trained in the study of chemistry. Chemists study the composition of matter and its properties such as density and acidity. Chemists carefully describe the properties they study in terms of quantities, with detail on the level of molecules and their component atoms...
Paul Sabatier
Paul Sabatier (chemist)
Paul Sabatier FRS was a French chemist, born at Carcassonne. He taught science classes most of his life before he became Dean of the Faculty of Science at the University of Toulouse in 1905....
.
International Space Station life support
Currently, oxygen generators onboard the International Space StationInternational Space Station
The International Space Station is a habitable, artificial satellite in low Earth orbit. The ISS follows the Salyut, Almaz, Cosmos, Skylab, and Mir space stations, as the 11th space station launched, not including the Genesis I and II prototypes...
produce oxygen from water using electrolysis
Electrolysis of water
Electrolysis of water is the decomposition of water into oxygen and hydrogen gas due to an electric current being passed through the water.-Principle:...
and dump the hydrogen produced overboard. As astronauts consume oxygen, carbon dioxide is produced which must then be removed from the air and discarded as well. This approach requires 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
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
is currently investigating the use of the Sabatier reaction to recover water from exhaled carbon dioxide, for use on the International Space Station and future missions. (In April 2010, Sabatier hardware was delivered to the International Space Station
International Space Station
The International Space Station is a habitable, artificial satellite in low Earth orbit. The ISS follows the Salyut, Almaz, Cosmos, Skylab, and Mir space stations, as the 11th space station launched, not including the Genesis I and II prototypes...
on the STS-131
STS-131
STS-131 was a NASA Space Shuttle mission to the International Space Station . launched on 5 April 2010 at 6:22 am from Kennedy Space Center's launch pad 39A, and landed at 9:08 am on 20 April 2010 on runway 33 at the Kennedy Space Center's Shuttle Landing Facility...
shuttle mission.) The other resulting chemical, methane, would most likely be dumped overboard. As half of the input hydrogen becomes wasted as methane, additional hydrogen would need to be supplied from Earth to make up the difference. 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.
Ignoring other results of respiration, this cycle would look like:
- 2H2O → O2 + 2H2 → (respiration) → CO2 + 2H2 + 2H2 (added) → 2H2O + CH4 (discarded)
The loop could be completely closed if the waste methane was pyrolyzed into its component parts:
- CH4 + heat → C + 2H2
The released hydrogen would then be recycled back into the Sabatier reactor, leaving an easily removed deposit of pyrolytic graphite
Pyrolytic carbon
Pyrolytic carbon is a material similar to graphite, but with some covalent bonding between its graphene sheets as a result of imperfections in its production....
. The reactor would be little more than a steel pipe, and could be periodically serviced by an astronaut where the deposit is chiselled out.
The Bosch reaction
Bosch reaction
The Bosch reaction is a chemical reaction between carbon dioxide and hydrogen that produces elemental carbon , water and a 10% return of invested heat...
is also being investigated for this purpose. Though the Bosch reaction would present a completely closed hydrogen and oxygen cycle which only produces atomic carbon as waste, difficulties maintaining its higher required temperature and properly handling carbon deposits mean significantly more research will be required before a Bosch reactor could become a reality. One problem is that the production of elemental carbon tends to foul the catalyst's surface, which is detrimental to the reaction's efficiency.
Manufacturing propellant on Mars
The Sabatier reaction has been proposed as a key step in reducing the cost of manned exploration of Mars (Mars DirectMars Direct
Mars Direct is a proposal for a manned mission to Mars. Proponents of the scheme have claimed it to be both cost-effective and that it can be conducted with current technology. It was originally detailed in a research paper by NASA engineers Robert Zubrin and David Baker in 1990, and later expanded...
) through In-Situ Resource Utilization
In-Situ Resource Utilization
In space exploration, in-situ resource utilization describes the proposed use of resources found or manufactured on other astronomical objects to further the goals of a space mission....
. Hydrogen is combined with CO2 from the atmosphere, with methane then becoming a storable fuel and the water side product yielding oxygen to be liquefied for the oxidizer and hydrogen to be recycled back into the reactor. The original amount of hydrogen could be transported from Earth or separated from martian sources of water.
The stoichiometric ratio of oxidizer and fuel is 3.5:1, for an oxygen:methane engine, however one pass through the Sabatier reactor produces a ratio of only 2:1. More oxygen may be produced by running the water gas shift reaction
Water gas shift reaction
The water-gas shift reaction is a chemical reaction in which carbon monoxide reacts with water vapor to form carbon dioxide and hydrogen:The water-gas shift reaction is an important industrial reaction. It is often used in conjunction with steam reforming of methane or other hydrocarbons, which is...
in reverse. When the water is split, the extra oxygen needed is obtained.
Another option is to make more methane than needed and pyrolyze the excess of it into carbon and hydrogen (see above section) where the hydrogen is recycled back into the reactor to produce further methane and water. In an automated system, the carbon deposit may be removed by blasting with hot Martian CO2, oxidizing the carbon into carbon monoxide, which is vented.
A fourth solution to the stoichiometry
Stoichiometry
Stoichiometry is a branch of chemistry that deals with the relative quantities of reactants and products in chemical reactions. In a balanced chemical reaction, the relations among quantities of reactants and products typically form a ratio of whole numbers...
problem would be to combine the Sabatier reaction with the reverse water gas-shift reaction in a single reactor as follows:
3CO2 + 6H2 → CH4 + 2CO + 4H2O
This reaction is slightly exothermic, and when the water is electrolyzed, an oxygen to methane ratio of 4:1 is obtained, resulting in a large backup supply of oxygen. With only the light hydrogen transported from Earth, and the heavy oxygen and carbon extracted locally, a mass leveraging of 18:1 is afforded with this scheme. This in-situ resource utilization
In-Situ Resource Utilization
In space exploration, in-situ resource utilization describes the proposed use of resources found or manufactured on other astronomical objects to further the goals of a space mission....
would result in massive weight and cost savings to any proposed manned Mars or sample return missions.
Energy Storage
It has been proposed in a renewable energy dominated energy system to use the excess electricity generated by wind, solar photovoltaic, hydro, marine current, etc to make methane (natural gas).,The methane can be injected into the existing gas network which in many countries has one or two years of gas stockage capacity. The methane can then be used on demand to generate electricty (and heat - combined heat and power) overcoming low points of renewable energy production. The process is hydrolis of water by electricity to creat hydrogen (which can partly be used directly in fuel cells) and the addition of carbon dioxyde CO2 (Sabatier process) to create methane.
CO2 + 4H2 → CH4 + 2H2O
The CO2 can be extracted from the air or fossil fuel waste gases by the amine process amongst many others. It is a low CO2 system and has similar efficiencies of todays energy system.