Marspedia - User contributions [en]

User:Rod57

2021-05-12T21:05:45Z

Rod57: intro

User page for Rod57

Hi all - I'm new here, but have been editing Wikipedia for some years under the same user name.
I'm also active on Quora as Rodney Price-7.

I'm assuming Wikipedia type policies and guidelines - except perhaps more "original research" and opinions are acceptable here ?

Please let me know if I do anything that doesn't seem helpful. - [[User:Rod57|Rod57]] ([[User talk:Rod57|talk]]) 22:05, 12 May 2021 (BST)

Talk:Sabatier/Water Electrolysis Process

2021-05-12T20:58:40Z

Rod57: /* Split page - more on Sabatier reactor */ : & say who

==Split page - more on Sabatier reactor==
This page seems to be more about the whole methalox production process that SpaceX might use.

I propose a section here on the Sabatier reactor, that maybe later could be split out into [[Sabatier reactor]].
The Sabatier reactor (it says) is the only part not available 'off-the-self', so we could expand on it here ? - [[User:Rod57|Rod57]] ([[User talk:Rod57|talk]]) 13:56, 12 May 2021 (BST)

:for the other processes we used the expression .... reaction, and Wikipedia mentions the Sabatier reaction. so I suggest we create Sabatier reaction for the chemical aspect, and add a Sabatier reactor section to the Sabatier water electrolysis process page.

:I think splitting out a Sabatier reactor page would be interesting for a detailed design, perhaps there is something available from the ISS system ? Or there may be industrial units from solar to gas grid than could apply.

:The graph seems to be missing the energy rejected from the reaction itself, although that may in the condensation of water part. Would need to be clarified.
: (above by Michel Lamontagne 12 May 2021)

Sabatier/Water Electrolysis Process

2021-05-12T12:59:01Z

Rod57: /* See Also */ == Sabatier reactor == {{empty section|date=May 2021}}

[[File:Propellant production.png|thumb|600x600px|Schematic of Methane production system for a Single SpaceX Starship over a period of two years. Electrolysis and hydrogen storage are off the shelf. Sabatier reactor needs to be developed.]]
The Sabatier reaction and [[Electrolysis|water electrolysis]] are used to convert atmospheric carbon dioxide and water extracted from regolith, or the atmosphere, into propellant. [[Hydrogen]] shipped from [[Earth]] could also be used in certain scenarios to avoid the need for the electrolysis process<ref>Compact and Lightweight Sabatier Reactor for Carbon Dioxide Reduction https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20120016419.pdf</ref>.

The [[Electrolysis|water electrolysis]] separates water into [[hydrogen]] and [[oxygen]]. In is by far the most energy intensive stage in the process. The oxygen is stored for later use in a vehicle propulsion system. The hydrogen is combined with atmospheric CO2 to create [[methane]] and water. The chemical reaction is the following:

:CO2 + 4H2 → CH4 + 2H2O -165 kJ/mol

The reaction takes place in the presence catalysts at a temperature between 300 and 400C. A [[nickel]] [[catalyst]] is the most likely candidate, or a catalyst made out of [[ruthenium]] or [[alumina]] might be used.

The Sabatier process produces a ratio of 4:1 of oxygen to methane, slightly more than the ratio used for propulsion, that is between 3.6 and 3.8 :1. Excess oxygen can be used for the colony atmosphere or stored for future use.

If [[nickel]] is produced in-situ on Mars, additive printing could be used to prepare replacement electrodes for the Sabatier process.

==Detailed process and alternatives==
The illustration shows just one of the possible process arrangements. Compression between the Electrolysis unit and the Sabatier unit might be avoided with other choices of equipment, and the storage tanks might be replaced by metal hydride reservoirs. If dust storms are particularly bad during a synod, the production rate might be too low to complete the refueling of a transportation vehicle. Use of nuclear power rather than solar power would allow for continuous production and reduce the mass of equipment required.

The electrolysis unit uses an electrolyte, into which water is added. An electrical current between two electrodes splits the water molecules into hydrogen and oxygen, with the hydrogen migrating to one electrode and the oxygen to the other.

Heat rejected from the process can be used to melt and heat the input ice, as well as heat the settlement. However, a lot of the heat is at very low temperatures and may have to be rejected into the martian environment.

Another alternative is the use of the [https://doi.org/10.1016/j.ijhydene.2017.09.035 Sulfur Iodine cycle] which uses thermal energy to split water into H2 and O2. This generally requires a [http://www.academia.edu/download/48701931/ACT-RPR-PRO-1107-LS-NTER.pdf turboinductor] to create a sufficiently hot gas stream from the much lower output temperature of a standard nuclear reactor such as a [https://www.nasa.gov/directorates/spacetech/kilopower/ KiloPower]. The primary advantage of this method is that it can more directly use the nuclear energy, reducing the requirement for large scale electricity generation.

A final alternative is the use of ammonia decomposition through [https://pubs.acs.org/doi/pdfplus/10.1021/ja5042836 sodium amide]. This allows for hydrogen to be stored chemically as ammonia, and then decomposed into hydrogen as needed to feed the Sabatier reactor. This also allows for biological processes, such as nitrogen fixing microbes, to provide an alternative path to hydrogen synthesis.

== Sabatier reactor ==
{{empty section|date=May 2021}}

==See Also==

*[[Atmospheric processing]]
*[[Hydrocarbon synthesis|Hydrocarbon Synthesis]]
*[[Bosch process]]
*[[Electrolysis]]

==References==
[[Category:In-situ Resource Utilization]]
<references />

Talk:Sabatier/Water Electrolysis Process

2021-05-12T12:57:05Z

Rod57: split ?

Sabatier/Water Electrolysis Process

2021-05-12T12:44:17Z

Rod57: /* See Also */ *Atmospheric processing

[[File:Propellant production.png|thumb|600x600px|Schematic of Methane production system for a Single SpaceX Starship over a period of two years. Electrolysis and hydrogen storage are off the shelf. Sabatier reactor needs to be developed.]]
The Sabatier reaction and [[Electrolysis|water electrolysis]] are used to convert atmospheric carbon dioxide and water extracted from regolith, or the atmosphere, into propellant. [[Hydrogen]] shipped from [[Earth]] could also be used in certain scenarios to avoid the need for the electrolysis process<ref>Compact and Lightweight Sabatier Reactor for Carbon Dioxide Reduction https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20120016419.pdf</ref>.

The [[Electrolysis|water electrolysis]] separates water into [[hydrogen]] and [[oxygen]]. In is by far the most energy intensive stage in the process. The oxygen is stored for later use in a vehicle propulsion system. The hydrogen is combined with atmospheric CO2 to create [[methane]] and water. The chemical reaction is the following:

:CO2 + 4H2 → CH4 + 2H2O -165 kJ/mol

The reaction takes place in the presence catalysts at a temperature between 300 and 400C. A [[nickel]] [[catalyst]] is the most likely candidate, or a catalyst made out of [[ruthenium]] or [[alumina]] might be used.

The Sabatier process produces a ratio of 4:1 of oxygen to methane, slightly more than the ratio used for propulsion, that is between 3.6 and 3.8 :1. Excess oxygen can be used for the colony atmosphere or stored for future use.

If [[nickel]] is produced in-situ on Mars, additive printing could be used to prepare replacement electrodes for the Sabatier process.

==Detailed process and alternatives==
The illustration shows just one of the possible process arrangements. Compression between the Electrolysis unit and the Sabatier unit might be avoided with other choices of equipment, and the storage tanks might be replaced by metal hydride reservoirs. If dust storms are particularly bad during a synod, the production rate might be too low to complete the refueling of a transportation vehicle. Use of nuclear power rather than solar power would allow for continuous production and reduce the mass of equipment required.

The electrolysis unit uses an electrolyte, into which water is added. An electrical current between two electrodes splits the water molecules into hydrogen and oxygen, with the hydrogen migrating to one electrode and the oxygen to the other.

Heat rejected from the process can be used to melt and heat the input ice, as well as heat the settlement. However, a lot of the heat is at very low temperatures and may have to be rejected into the martian environment.

Another alternative is the use of the [https://doi.org/10.1016/j.ijhydene.2017.09.035 Sulfur Iodine cycle] which uses thermal energy to split water into H2 and O2. This generally requires a [http://www.academia.edu/download/48701931/ACT-RPR-PRO-1107-LS-NTER.pdf turboinductor] to create a sufficiently hot gas stream from the much lower output temperature of a standard nuclear reactor such as a [https://www.nasa.gov/directorates/spacetech/kilopower/ KiloPower]. The primary advantage of this method is that it can more directly use the nuclear energy, reducing the requirement for large scale electricity generation.

A final alternative is the use of ammonia decomposition through [https://pubs.acs.org/doi/pdfplus/10.1021/ja5042836 sodium amide]. This allows for hydrogen to be stored chemically as ammonia, and then decomposed into hydrogen as needed to feed the Sabatier reactor. This also allows for biological processes, such as nitrogen fixing microbes, to provide an alternative path to hydrogen synthesis.

==See Also==

*[[Atmospheric processing]]
*[[Hydrocarbon synthesis|Hydrocarbon Synthesis]]
*[[Bosch process]]
*[[Electrolysis]]

==References==
[[Category:In-situ Resource Utilization]]
<references />

Atmospheric processing

2021-05-12T12:36:49Z

Rod57: /* Oxygen */ [[

[[File:Marspedia-Martian_atmospheric_processing_(1).png|alt=|500x500px|thumb|Schematic of a possible Martian mechanical compression atmospheric processing system]]
__NOTOC__

'''Atmospheric processing''' describes the extraction of substances out of the Martian [[atmosphere]] and the usage as raw material for further processing. Unlike surface and sub-surface mining, the atmospheric mining does not require the movement of large amounts of [[regolith]] or rock with heavy machinery, nor is expensive transport per [[rover]] or [[railroad]] necessary. The atmosphere can simply be sucked in through a pipe at every location, and the processing is done inside of [[building]]s. Also, the maintenance of all the atmospheric mining machinery could be in-house, which would be a major safety advantage.

==Collection of Atmosphere==
There are a number of ways the martian atmosphere can be processed to separate it into its individual components for process use. Mechanical compression is one of the main possibilities for large scale operations

In mechanical compression systems, a fan collects martian atmosphere and passes it through filters to separate out the dust. Then a compressor increases the pressure of the atmosphere to reach a point when water can be condensed out. Then a second compressor increases the pressure to the liquefaction point of CO2. The liquid CO2 is removed, and the leftover gases can be cooled further, to condense out into their liquid phases. Alternatively, using ionic liquids<ref>https://pubs.acs.org/doi/full/10.1021/ja017593d</ref>, the CO2 can be removed at atmospheric pressure, requiring only the N2 and Ar fractions to be compressed.

==Process==
[[File:Atmospheric Production.jpg|thumb|500x500px|A view of a large atmospheric production unit, based on the process schematic, capable of treating 1 kg (50 m3) of Martian atmosphere per second, or 30 000 tonnes per year.]]

===Filtering===
The martian atmosphere contains 1.8*10-7 kg of dust per m3, on average<ref>https://pdfs.semanticscholar.org/418a/88f31b87f3d615a1f6116d31a078cfde8802.pdf</ref>. This dust must be removed to avoid process problems in subsequent steps. [[Dust collector|Dust collectors]] or electrostatic precipitation will be required<ref>Chepko, Ariane, Michael Swanwick, Paul Sorensen, and Darius Modarress. "Two-Stage Dust Removal System for Mars In-Situ Resource Utilization Systems: System Sizing and Trade-offs." 48th International Conference on Environmental Systems, 2018.</ref>.

===Compression===
[[Compression]] from the initial atmospheric pressure of 600 Pa to 0,1 bar (10 kPa, or 1/10 Earth atmosphere) heats the atmosphere to 100°C but also creates adequate conditions for the condensation of water when it is cooled to about 40°C. It can then be collected at the bottom of a pressure vessel and removed. A second compressor increases the gas pressure to a bit above 5,1 bar (520 kPa) but also boosts the temperature to over 800°C. 520 kPa is the lowest pressure at which CO2 can change from a gas to a liquid (at lower pressures it turns directly into a solid), at about -57°C. The liquid carbon dioxide can then be separated by gravity from the other gasses. The total compression ratio from 600 to 520 000 Pa is about 860 times.

An exit temperature for a compressor of 800°C is extremely high. Intermediate cooling with isobaric compression (change of volume with constant pressure) will be required to reduce the exit temperatures of the compressors.

===Condensation===
The change from a gas phase to a liquid phase is condensation. The compressors create a pressure environment where cooling the gas condensates one of the fractions of the atmosphere. The first gas to condensate out is water, at 40°C for 10 kPa pressure. After an increase in pressure, the hot dry gas is cooled further to condense the CO2 , at -57°C for 520 kPa. The condensed liquid CO2 can be removed by gravity. Nitrogen at 510 kPa will liquefy at -170°C, and Argon at about the same temperature, so care must be taken if we want to keep these two gases separate. The next gas to condense out is Oxygen. All of the cooled gas may be used for process purposes, or some of the gases may be released back into the atmosphere. The expansion of the gas back to atmospheric pressure produces a cooling effect that can be used in the process to help condensate out the atmospheric gases.

===Desiccation (adsorption) and scrubbers===
Desiccation might be used as an alternative to compression for water removal. A desiccant bed, or a desiccant coated wheel, can be inserted into the gas stream, after filtration. The desiccant captures the water, that is later removed from the desiccant using heat in a regenerative process. This might use the heat from the secondary compression, that is significant at 520 kPa, rather than mechanical work. Similar systems can be used for CO2, N2 and Argon separation as well. For example, amines are used to remove CO2 from the atmosphere of submarines<ref>http://web.mit.edu/12.000/www/m2005/a2/8/pdf1.pdf</ref> and of the ISS. Various types of [[Carbon Dioxide Scrubbers|carbon dioxide scrubbers]] exist or are under development<ref>https://en.wikipedia.org/wiki/Carbon_dioxide_scrubber</ref>. Adsorption of nitrogen is an existing industrial [[w:Nitrogen_generator|process]] that should use less energy than compression/condensation systems. Ionic liquids<ref>https://pubs.acs.org/doi/full/10.1021/ja017593d</ref><ref>https://ttu-ir.tdl.org/bitstream/handle/2346/74045/ICES_2018_31.pdf?sequence=1</ref> are an interesting development in scrubbers, as unlike amine scrubbers they have no vapor pressure. As such they can extract CO2 from the Martian atmosphere at atmospheric pressure. This then makes compression more efficient, as it's only compressing the N2 and Ar fractions.

==Process outputs==
===Dust===
The Martian [[atmosphere]] contains variable amounts of [[dust]], which consists of [[minerals]] lifted by wind from the surface [[regolith]]. Electrostatic filters, cyclonic separators or dust collectors with fabric filters will be used to remove the dust to prevent it from damaging the equipment.

===Water===
The 0.03 % [[water]] vapor (H2O) is equivalent to about 10 % air humidity after adiabatic compression and cooling to around 1°C. A device similar to an air dehumidifier can be used to extract this water.

===Carbon Dioxide===
96% of the Martian atmosphere is [[Carbon dioxide]]. It can be used for [[hydrocarbon synthesis]], including the production of [[methane]] based [[fuel]]. It can also be used to produce [[Oxygen]] through splitting of the H2O produced during [[hydrocarbon synthesis]], or during the production of [[Carbon]] through the [https://en.wikipedia.org/wiki/Bosch_reaction Bosch process]. Alternatively, it can also be electrolysed in a [[Carbon_Dioxide_Scrubbers|MOXIE]], producing CO and O2 or used in [[farming]].

===Nitrogen===
The balance of the remaining gas after carbon dioxide condensation contains mostly [[nitrogen]] and [[argon]]. This mixture can serve as a buffer for oxygen to produce a breathable atmosphere. Remaining traces of Carbon monoxide must be removed if the gas is to be used for the settlement atmosphere.

[[Nitrogen]] can be used to create [[ammonia]] and nitrates in [[fertilizer]] and as nitric acid in industry. A process such as an optimized low pressure<ref>https://www.ammoniaenergy.org/wp-content/uploads/2019/11/20191112.1043-Ammonia-Talk-NH3-Fuel.pdf</ref> low temperature <ref>https://www.ammoniaenergy.org/wp-content/uploads/2019/08/20191114.0826-AIChE_CSM_Final.pdf</ref> Haber reactor would allow for simplified industrial production, and the use of nitrogen fixing microbes would allow for the biological production of both ammonia and nitrates.

===Argon===
[[Argon]] is useful for industrial processes that must be performed in an inert atmosphere. It can also be used for electric rocket propulsion. It may be used as a complement for nitrogen in a martian settlement if it proves to be safe for that purpose.

===Oxygen===
[[Oxygen]] is used for the creation of the settlement atmosphere or for a large number of industrial processes. Oxygen can be produced through the splitting of water directly, via CO2 chemically, or via [[farming|photosynthesis]].
A chemical method for the production of O2 from CO2 is:

:CO2 + H2 → CO + H2O (The [[Reverse_Water-Gas_Shift_Reaction|Reverse Water-Gas Shift Reaction]])
:2H2O → 2H2 + O2

Where the H2 is recycled from reaction 2 to reaction 1, forming a loop, resulting in an overall reaction equivalent to:

:2CO2 → 2CO + O2

The splitting of water may be obtained either through [[electrolysis]], or thermochemically with something like the Sulfur/Iodine cycle<ref>https://doi.org/10.1016/j.enconman.2006.02.010</ref>.

==See also==

*[[Sabatier/Water Electrolysis Process]]
*[[Mining]]
*[[Farming]]

==References==
[[Category:In-situ Resource Utilization]]
<references />

Atmospheric processing

2021-05-12T12:36:12Z

Rod57: /* See also */ *Sabatier/Water Electrolysis Process

[[File:Marspedia-Martian_atmospheric_processing_(1).png|alt=|500x500px|thumb|Schematic of a possible Martian mechanical compression atmospheric processing system]]
__NOTOC__

'''Atmospheric processing''' describes the extraction of substances out of the Martian [[atmosphere]] and the usage as raw material for further processing. Unlike surface and sub-surface mining, the atmospheric mining does not require the movement of large amounts of [[regolith]] or rock with heavy machinery, nor is expensive transport per [[rover]] or [[railroad]] necessary. The atmosphere can simply be sucked in through a pipe at every location, and the processing is done inside of [[building]]s. Also, the maintenance of all the atmospheric mining machinery could be in-house, which would be a major safety advantage.

==Collection of Atmosphere==
There are a number of ways the martian atmosphere can be processed to separate it into its individual components for process use. Mechanical compression is one of the main possibilities for large scale operations

In mechanical compression systems, a fan collects martian atmosphere and passes it through filters to separate out the dust. Then a compressor increases the pressure of the atmosphere to reach a point when water can be condensed out. Then a second compressor increases the pressure to the liquefaction point of CO2. The liquid CO2 is removed, and the leftover gases can be cooled further, to condense out into their liquid phases. Alternatively, using ionic liquids<ref>https://pubs.acs.org/doi/full/10.1021/ja017593d</ref>, the CO2 can be removed at atmospheric pressure, requiring only the N2 and Ar fractions to be compressed.

==Process==
[[File:Atmospheric Production.jpg|thumb|500x500px|A view of a large atmospheric production unit, based on the process schematic, capable of treating 1 kg (50 m3) of Martian atmosphere per second, or 30 000 tonnes per year.]]

===Filtering===
The martian atmosphere contains 1.8*10-7 kg of dust per m3, on average<ref>https://pdfs.semanticscholar.org/418a/88f31b87f3d615a1f6116d31a078cfde8802.pdf</ref>. This dust must be removed to avoid process problems in subsequent steps. [[Dust collector|Dust collectors]] or electrostatic precipitation will be required<ref>Chepko, Ariane, Michael Swanwick, Paul Sorensen, and Darius Modarress. "Two-Stage Dust Removal System for Mars In-Situ Resource Utilization Systems: System Sizing and Trade-offs." 48th International Conference on Environmental Systems, 2018.</ref>.

===Compression===
[[Compression]] from the initial atmospheric pressure of 600 Pa to 0,1 bar (10 kPa, or 1/10 Earth atmosphere) heats the atmosphere to 100°C but also creates adequate conditions for the condensation of water when it is cooled to about 40°C. It can then be collected at the bottom of a pressure vessel and removed. A second compressor increases the gas pressure to a bit above 5,1 bar (520 kPa) but also boosts the temperature to over 800°C. 520 kPa is the lowest pressure at which CO2 can change from a gas to a liquid (at lower pressures it turns directly into a solid), at about -57°C. The liquid carbon dioxide can then be separated by gravity from the other gasses. The total compression ratio from 600 to 520 000 Pa is about 860 times.

An exit temperature for a compressor of 800°C is extremely high. Intermediate cooling with isobaric compression (change of volume with constant pressure) will be required to reduce the exit temperatures of the compressors.

===Condensation===
The change from a gas phase to a liquid phase is condensation. The compressors create a pressure environment where cooling the gas condensates one of the fractions of the atmosphere. The first gas to condensate out is water, at 40°C for 10 kPa pressure. After an increase in pressure, the hot dry gas is cooled further to condense the CO2 , at -57°C for 520 kPa. The condensed liquid CO2 can be removed by gravity. Nitrogen at 510 kPa will liquefy at -170°C, and Argon at about the same temperature, so care must be taken if we want to keep these two gases separate. The next gas to condense out is Oxygen. All of the cooled gas may be used for process purposes, or some of the gases may be released back into the atmosphere. The expansion of the gas back to atmospheric pressure produces a cooling effect that can be used in the process to help condensate out the atmospheric gases.

===Desiccation (adsorption) and scrubbers===
Desiccation might be used as an alternative to compression for water removal. A desiccant bed, or a desiccant coated wheel, can be inserted into the gas stream, after filtration. The desiccant captures the water, that is later removed from the desiccant using heat in a regenerative process. This might use the heat from the secondary compression, that is significant at 520 kPa, rather than mechanical work. Similar systems can be used for CO2, N2 and Argon separation as well. For example, amines are used to remove CO2 from the atmosphere of submarines<ref>http://web.mit.edu/12.000/www/m2005/a2/8/pdf1.pdf</ref> and of the ISS. Various types of [[Carbon Dioxide Scrubbers|carbon dioxide scrubbers]] exist or are under development<ref>https://en.wikipedia.org/wiki/Carbon_dioxide_scrubber</ref>. Adsorption of nitrogen is an existing industrial [[w:Nitrogen_generator|process]] that should use less energy than compression/condensation systems. Ionic liquids<ref>https://pubs.acs.org/doi/full/10.1021/ja017593d</ref><ref>https://ttu-ir.tdl.org/bitstream/handle/2346/74045/ICES_2018_31.pdf?sequence=1</ref> are an interesting development in scrubbers, as unlike amine scrubbers they have no vapor pressure. As such they can extract CO2 from the Martian atmosphere at atmospheric pressure. This then makes compression more efficient, as it's only compressing the N2 and Ar fractions.

==Process outputs==
===Dust===
The Martian [[atmosphere]] contains variable amounts of [[dust]], which consists of [[minerals]] lifted by wind from the surface [[regolith]]. Electrostatic filters, cyclonic separators or dust collectors with fabric filters will be used to remove the dust to prevent it from damaging the equipment.

===Water===
The 0.03 % [[water]] vapor (H2O) is equivalent to about 10 % air humidity after adiabatic compression and cooling to around 1°C. A device similar to an air dehumidifier can be used to extract this water.

===Carbon Dioxide===
96% of the Martian atmosphere is [[Carbon dioxide]]. It can be used for [[hydrocarbon synthesis]], including the production of [[methane]] based [[fuel]]. It can also be used to produce [[Oxygen]] through splitting of the H2O produced during [[hydrocarbon synthesis]], or during the production of [[Carbon]] through the [https://en.wikipedia.org/wiki/Bosch_reaction Bosch process]. Alternatively, it can also be electrolysed in a [[Carbon_Dioxide_Scrubbers|MOXIE]], producing CO and O2 or used in [[farming]].

===Nitrogen===
The balance of the remaining gas after carbon dioxide condensation contains mostly [[nitrogen]] and [[argon]]. This mixture can serve as a buffer for oxygen to produce a breathable atmosphere. Remaining traces of Carbon monoxide must be removed if the gas is to be used for the settlement atmosphere.

[[Nitrogen]] can be used to create [[ammonia]] and nitrates in [[fertilizer]] and as nitric acid in industry. A process such as an optimized low pressure<ref>https://www.ammoniaenergy.org/wp-content/uploads/2019/11/20191112.1043-Ammonia-Talk-NH3-Fuel.pdf</ref> low temperature <ref>https://www.ammoniaenergy.org/wp-content/uploads/2019/08/20191114.0826-AIChE_CSM_Final.pdf</ref> Haber reactor would allow for simplified industrial production, and the use of nitrogen fixing microbes would allow for the biological production of both ammonia and nitrates.

===Argon===
[[Argon]] is useful for industrial processes that must be performed in an inert atmosphere. It can also be used for electric rocket propulsion. It may be used as a complement for nitrogen in a martian settlement if it proves to be safe for that purpose.

===Oxygen===
[[Oxygen]] is used for the creation of the settlement atmosphere or for a large number of industrial processes. Oxygen can be produced through the splitting of water directly, via CO2 chemically, or via [[farming|photosynthesis]].
A chemical method for the production of O2 from CO2 is:

:CO2 + H2 → CO + H2O (The [[Reverse_Water-Gas_Shift_Reaction|Reverse Water-Gas Shift Reaction]])
:2H2O → 2H2 + O2

Where the H2 is recycled from reaction 2 to reaction 1, forming a loop, resulting in an overall reaction equivalent to:

:2CO2 → 2CO + O2

The splitting of water may be obtained either through electrolysis, or thermochemically with something like the Sulfur/Iodine cycle<ref>https://doi.org/10.1016/j.enconman.2006.02.010</ref>.

==See also==

*[[Sabatier/Water Electrolysis Process]]
*[[Mining]]
*[[Farming]]

==References==
[[Category:In-situ Resource Utilization]]
<references />

Reverse Water-Gas Shift Reaction

2021-05-12T12:35:18Z

Rod57: [[Sabatier/Water Electrolysis Process|

The '''Reverse Water-Gas Shift Reaction''' (RWGS reaction) was discovered in the 19th century as a method of producing [[water]] from [[carbon dioxide]] and [[hydrogen]], with [[carbon monoxide]] as a side product. In the context of [[manned mission|human missions]] to [[Mars]], it has been proposed as a complement to the [[Sabatier/Water Electrolysis Process|Sabatier/water electrolysis (SE) process]] to produce [[methane]] and [[oxygen]] from hydrogen and carbon dioxide on the surface. Alternatively, it can be used with water [[electrolysis]] to generate carbon monoxide and oxygen. The oxygen is used for breathing or as oxidizer, while the carbon monoxide can be used as a moderate specific-impulse fuel (with oxygen as the oxidizer) or as a feedstock to [[hydrocarbon synthesis|generate]] higher [[hydrocarbons]] (see [[Fischer-Tropsch reaction]]) 
Whether one would use the RWGS reaction or the [[Bosch reaction]] depends largely on whether carbon monoxide or elemental [[carbon]] is the preferred by-product.

==Process==

In the presence of a suitable catalyst, the reaction takes place according to this equation:

CO2 + H2 → CO + H2O (deltaH = +9 kcal/mole)

The reactor itself is very similar to a Sabatier unit; a simple steel pipe filled with catalyst. According to experiments done by Pioneer Astronautics in Lakewood, Colorado, the best catalyst at low temperature for this reaction is silica consisting of 5% copper by weight and a smaller amount of [[nickel]]. This catalyst is exclusively selective to CO (i.e., it only produces carbon monoxide) with 60% conversion of CO2 to CO at 350o C, 20 kPa (150 torr)(0,2 Bar), and a CO2/H2 feed ratio of 1/4.

==Applications==
===Production of oxygen===
The RWGS reaction’s chief attribute is that it, when used alongside water electrolysis, can generate any amount of oxygen from the equivalent amount of carbon dioxide with only a tiny amount of hydrogen. The hydrogen is recovered from the water via electrolysis and recycled back into the reactor’s feed end. When used with the Sabatier and water electrolysis reactions, the RWGS can provide an oxidizer/fuel (O/F) ratio of 3.5:1 (3.5 units of oxygen to 1 unit of methane) compared with 2:1 for the SE process alone. This is advantageous because a methane/oxygen engine reaches its highest specific impulse at this ratio.

However, the RWGS can be used in conjunction with water-electrolysis as an "infinite-leverage oxygen machine" to generate oxygen from carbon dioxide via a small amount of hydrogen.

===Production of carbon monoxide===
The side product carbon monoxide can be used to synthesize [[methane]], [[methanol]], and higher hydrocarbons such as ethylene and propylene, which are usable to produce further [[synthetic materials‎]] and for [[energy storage]]. The higher hydrocarbons are manufactured via the Fischer-Tropsch reactions, which use carbon monoxide and hydrogen as feedstocks.

==Advantages==

For the purposes of CO2 separation, the RWGS is far more efficient and requires a fraction of the power, compared to solid-oxide or molten carbonate electrolysis. It is also more rugged and reliable because it uses a simple steel pipe instead of multiple brittle tubes. For the same reason, a RWGS reactor can be scaled up (by adding more catalyst-filled pipes) to support a robotic sample return or human mission.

==Disadvantages==

This reaction has an low equilibrium constant even at temperatures of 400o C , so it must be fed with either a hydrogen-rich or a carbon dioxide-rich mixture to ensure satisfactory results, or you have to increase the operating temperature (equilibrium constant is 0.5 only at 750°C). Excess hydrogen (or excess carbon dioxide) is captured from the exhaust with a filtering membrane and fed back into the reactor. The effective catalyst depends on the operating temperature : Corean used ZnO-Al catalysts for the Camere Process at 600°C but also ZnO-Cr can be used above 600°C. The activity of both catalysts is however too low below this temperature.

==References==

R. Zubrin, The Case for Mars, pp. 153

[[Category:In-situ Resource Utilization]]