Copyright 2023 Robert Clark
ABSTRACT
Proponents of getting propellant from the Moon for spacecraft already in Earth orbit, as for orbital propellant depots, base this on using high power to separate hydrogen and oxygen by electrolysis applied to the water ice in the Moon's south polar region. However, quite surprisingly there may already be free hydrogen at the Moon's south pole or available in far more energy efficient way then by electrolysis. This hydrogen may be so easily obtainable then it may be it can be profitably shipped to Earth for a clean energy economy.
Free Propellant on Mars and the Moon.
In the blog post "Potential Game-Changer for Generating Propellant on Mars," I suggested that getting free oxygen and carbon monoxide from the Martian atmosphere would provide a free means of producing propellant on Mars. This is important since rather than requiring several football fields of solar panels or a nuclear power plant to generate the megawatts of power needed to separate the CO2 or H2O into carbon, oxygen, and hydrogen by electrolysis, we could actually generate megawatts of power after collecting the free CO and O2 in the Martian air then combusting them together:
2CO+O2→2CO2;ΔH=−569kJ/mol
This may may seem odd that we can generate power by collecting the natural resources already there but note this is exactly what we're doing when we collect the coal or petroleum or uranium from the ground on Earth. You get far more potential energy out than what you put in to collect it.
And in fact we could also generate hydrogen in a way that at the same time generates power as well. This comes from the reaction:
1.)CO + H2O → CO2+ H2, ΔH = -41 kJ/mol
The H2O could come from the abundant ice in the Martian soil or in fact from the Martian air as well. The hydrogen(H2) would then come from what is called the water-gas shift reaction:
The water–gas shift reaction (WGSR) describes the reaction of carbon monoxide and water vapor to form carbon dioxide and hydrogen:
- CO + H2O ⇌ CO2 + H2
The water gas shift reaction was discovered by Italian physicist Felice Fontana in 1780. It was not until much later that the industrial value of this reaction was realized. Before the early 20th century, hydrogen was obtained by reacting steam under high pressure with iron to produce iron oxide and hydrogen. With the development of industrial processes that required hydrogen, such as the Haber–Bosch ammonia synthesis, a less expensive and more efficient method of hydrogen production was needed. As a resolution to this problem, the WGSR was combined with the gasification of coal to produce hydrogen. As the idea of hydrogen economy gains popularity, the focus on hydrogen as an energy storage medium when an alternative replacement energy source for hydrocarbons is used.
https://en.wikipedia.org/wiki/Water%E2%80%93gas_shift_reaction
However, it may be this process can also work on the Moon. The LCROSS mission to my mind may have been one of the most significant planetary science missions ever conducted by NASA, as measured in relation to its cost. It was designed as a low cost "Discovery" class mission but what it returned was profoundly important. It had an ingenious design that sent a rocket stage to impact the Moon at the south polar region and observe spectroscopically the material sent up in the impact plume by a second spacecraft..
The mission confirmed what was suspected that there was great amounts of water as ice in the Moon's south polar region. In fact LCROSS found an extensive list of volatiles concentrated at the south pole of the Moon:
Moon Blast Reveals Lunar Surface Rich With Compounds.
Science Oct 21, 2010 2:05 PM EDT.
There is water on the moon … along with a long list of other compounds, including, mercury, gold and silver. That’s according to a more detailed analysis of the chilled lunar soil near the moon’s South Pole, released as six papers by a large team of scientists in the journal, Science Thursday.
https://www.pbs.org/newshour/science/its-confirmed-there-is-water
The amounts of volatiles found by LCROSS was extraordinary:
Lunar Impact Uncovered More Than Just Moon Water.
Oct. 21, 2010: Nearly a year after announcing the discovery of water molecules on the moon, scientists have revealed new data uncovered by NASA's Lunar CRater Observation and Sensing Satellite, or LCROSS, and Lunar Reconnaissance Orbiter, or LRO—and it's more than just water.
In addition to water, the plume contained "volatiles." These are compounds that freeze in the cold lunar craters and vaporize easily when warmed by the sun. The suite of LCROSS and LRO instruments determined as much as 20 percent of the material kicked up by the LCROSS impact was volatiles, including methane, ammonia, hydrogen gas, carbon dioxide and carbon monoxide.
https://science.nasa.gov/science-news/science-at-nasa/2010/21oct_lcross2
These last three are quite important in regards to the lunar propellant issue. If the hydrogen is indeed free then that gives us a ready made source for the clean-energy hydrogen. However, I suspect the hydrogen seen from orbit after the rocket stage impact, was derived from the water-gas shift reaction. This reaction shown in eq. 1.) reacts carbon monoxide and water to produce hydrogen and carbon dioxide and is helped by high temperatures, as would have obtained after the rocket stage impact. So the carbon monoxide could have reacted with the water to generate hydrogen.
Once we have hydrogen then we can send it back to Earth for clean energy. The gravity and required launch speed from the Moon is so low we could use continual launch methods such as railguns or even the space elevator, which is possible with current materials under the Moons low gravity.
As in the case of the getting hydrogen or other propellants on Mars discussed in the prior blog post, we would need low energy separation methods. A new method sounds quite promising:
Mechanochemical breakthrough unlocks cheap, safe, powdered hydrogen
By Loz Blain July 18, 2022
Australian scientists say they've made a "eureka moment" breakthrough in gas separation and storage that could radically reduce energy use in the petrochemical industry, while making hydrogen much easier and safer to store and transport in a powder.
https://newatlas.com/energy/mechanochemical-breakthrough-unlocks-cheap-safe-powdered-hydrogen/
This proposed solution for low energy gas separation though still needs to be confirmed by other researchers.
Hydrogen on the Moon Cheaper and Cleaner than on Earth?
7.1. WHY HYDROGEN?
Clean hydrogen is of the greatest interest in addressing the climate crisis, with the recognition that hydrogen could play a crucial role in economy-wide decarbonization, particularly in the transportation and industrial sectors including sustainable fuels, iron & steel, ammonia and chemicals, and more.1 Hydrogen is an extremely clean energy carrier, as its consumption produces only water; it also has a high energy density by mass. Hydrogen can be used to power fuel cells or combusted in a hydrogen turbine to generate electricity, and could also serve as clean transportation fuel.
The first Energy Earthshot, the Hydrogen Shot launched in 2021, seeks to reduce the cost of clean hydrogen by 80% to $1 per kilogram in 1 decade. This is an ambitious initiative, since current costs of clean hydrogen are much higher. For example, electrolytic generation of hydrogen using renewable electricity costs at least $6 per kilogram.
Worldwide, about half of all hydrogen production is from reforming of natural gas (mainly steam methane reforming or SMR), with the remainder deriving from gasification of liquid and solid feedstocks such as coal, petcoke, and petroleum residuals, from oil as a byproduct, and with a few percent from electrolysis. Syngas from gasification already contains a significant amount of hydrogen, which can be increased through water gas shift (WGS) and separated into a pure hydrogen product meeting industry product quality standards. There are several conventional hydrogen separation processes, with the well-proven and moderate cost pressure swing adsorption (PSA) methods commonly chosen. PSA has the ability to produce high purity (99.9%) hydrogen at near feed pressure; however, relatively high hydrogen concentration in feed gases is required for its economics to remain favorable.
For either natural gas reforming or gasification routes, hydrogen production costs are lower than the electrolytic route, but the challenge is that the carbon footprint of conventional hydrogen production is large, as shown in the following table:
| Hydrogen product (kg/h) | CO2 product (kg/h) | CO2 emitted in stack gas (kg/h) | Carbon intensity kg CO2/kg H2 |
|---|---|---|---|---|
SMR w/ 90% capture | 25,700 | 227,600 | 25,300 | 1.0 |
Coal gasification w/ 90% capture | 25,700 | 456,700 | 49,300 | 1.9 |
Carbon Intensities of SMR and Coal Gasification-based Hydrogen Production (with 90% capture)
If all CO2 produced in these processes is emitted, and CO2 footprint ranges from about 10 to 20 times the mass of the hydrogen produced. Only 0.7% of fossil fuel-based hydrogen production is currently performed in conjunction with carbon capture and storage.2
The gasification route to hydrogen presents an opportunity to use low-cost and liability feedstocks including biomass, solid wastes, and waste coal, which could help reduce the environmental costs and liabilities of solid waste disposal and legacy waste impoundments. Carbon-neutral biomass feedstocks significant reduce the carbon footprint of gasification, and combined with high levels of carbon capture facilitated by high syngas concentrations of CO2 and hydrogen characteristic of efficient gasification processes, production of clean hydrogen from gasification could be a compelling option in the emerging decarbonized economy.
__________________________________________________________________
https://www.netl.doe.gov/research/Coal/energy-systems/gasification/gasifipedia/hydrogen
Note then on the Moon, either the hydrogen is already free, or it can be obtained by the water-gas shift reaction that obtains for the low cost chemical production methods used on Earth. But now this can be considered clean production, at least in regards to Earth, in that the CO2 released would be on the Moon.
As for energy generation actually solar or nuclear generation would not be needed. The materials for energy generation would be available in the Moon's regolith, according to the LCROSS results. See here:.
You see there are abundances listed for H2 and H2O and CO and CO2 but nothing for O2 for combustion. Oxygen could be obtained from high temperature burning of lunar rocks, but this is energy intensive. We want an energy production method that does not require high energy input in the first place.
One possibility might be to use the free magnesium Mg seen in the LCROSS data. Magnesium can burn in CO2 without requiring oxygen:
Another possibility would be to use the free sodium Na seen by LCROSS. Sodium reacts explosively with water releasing heat and also hydrogen, so this might provide an additional method of producing hydrogen.
Robert Clark
2 comments:
There may be an even cheaper source of hydrogen at the lunar poles in the form of methanol. Methanol has already been detected from the polar impact debris. And heating methanol to produce hydrogen and CO2 is relatively easy-- even using waste heat.
Separating out trace or low-percentage gases from an atmosphere is not as easy as it sounds, or we would already be doing it "big time" to reduce atmospheric CO2 here on Earth. In a thin atmosphere, it seems to me that this would be even more difficult. -- GW
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