The enclosed report was made relative to NASA plans for a manned mission to Mars, in order to help design a rocket fuel production technology that could be reduced to practice on that planet, and enable a return of Martian explorers back to Earth.
Seriously.
Herein, it's demonstrated that Carbon Dioxide prevalent in the Martian atmosphere can be combined with water from ice in the Martian soil, to make methane and methanol fuel.
Different types of reaction options, including Sabatier and Fischer-Tropsch technologies, were examined; and, a high-efficiency process, "electrochemical reduction", was found by these researchers to be the most efficient for converting Carbon Dioxide, with Hydrogen from water, into methane and methanol.
The complete dissertation, enclosed and accessible via the link, consists of many calculations and formulae that are far beyond our scope.
We'll thus limit our excerpt to the title, revealing introduction, and significant conclusions. Note, especially, the very first statement of:
"Electrochemical Reduction of Carbon Dioxide
Matthew R. Hudson
Department of Chemistry, State University of New York at Potsdam, Potsdam New York 13676
December 9, 2005
The conversion of carbon dioxide into useable hydrocarbons is a process that has been around since the early 1900s. The Sabatier and the Fischer-Tropsch processes are processes that involve the conversion of hydrogen and carbon oxides into hydrocarbons, but especially into hydrocarbons used for fuels. French chemist Paul Sabatier discovered the Sabatier process and he was awarded the Nobel Prize in 1913. His process involves the conversion of CO2 and hydrogen gas into methane and water in the presence of a nickel catalyst at high temperatures and high pressures. The process has been considered in the research of alternative fuels.
Franz Fischer and Hans Tropsch invented the Fischer-Tropsch process in the 1920s. The process involves two steps and is also seen as an alternative fuel source. The first step is the partial oxidation of coal or natural gas fuels into hydrogen gas and carbon dioxide. The carbon oxide and hydrogen are then converted into more useful methanol and methane fuels. Although it is still currently being used, the Fischer-Tropsch process was a major factor in the German effort in World War II, because they did not have an abundance of oil, but did have vast amounts of coal to produce synthetic oil.
Although both these methods are still being pursued today, the electrochemical reduction of carbon dioxide provides a better result than these historical processes. The electrochemical reduction process involves CO2 gas and uses H2 gas or various aqueous electrolytes as the source of the H+. It also produces methane or methanol and environmentally friendly water as products, but can also give a variety of other hydrocarbon products and even O2 gas as a product. Another advantage is better chemical efficiency, the physical yield of product compared to the amount of by-products formed, than the other two processes. Also, depending on the reduction method high Faradaic efficiency, the energy efficiency with which a species is electrolyzed at a given charge, can be accomplished. High Faradaic efficiencies suggest that the process requires lower energy to complete the reaction making the process more feasible. The consideration that this can be achieved at low temperatures is also a benefit when compared to the Sabatier process which involves both high temperature and pressure. The purpose of finding a better method of the reduction of CO2 to methane and methanol fuels includes the use for in situ fuel production for a mission to Mars. This coupled with the possibility of applications on Earth making the electrochemical reduction of CO2 promising.
Finding a better CO2 reduction process is essential for a possible manned mission to Mars. The Martian atmosphere has a composition of 95.3% CO2, as opposed to the 0.03% composition here on Earth. Accounting only for the gaseous CO2 on Mars, this is enough carbon dioxide to make sustainable human life possible if breathable air, water, and especially fuel can be generated in situ. Considering only the fuel production, there are three categories of propellants that could be used: C-free fuels (such as H2 or SiH4), H-free fuels (CO), or C,H-fuels (CH4, CH3OH, C2H2 etc). The electrochemical reduction of CO2 produces a variety of these fuels, especially the hydrocarbon fuel methane.
The necessity of a better process stems directly from the fact that all three methods, Sabatier, Fischer-Tropsch, and electrochemical reduction all require that hydrogen be present in some step of the reaction. Since the atmosphere of Mars contains only a trace of water, subterranean water must be used as an in situ source of hydrogen.
Another consideration is again related to the Martian atmosphere. The Martian atmosphere has a mean temperature of 210 K and a high of 293 K.14. ... the formation of methane is extremely efficient at low temperatures ... .
Methanol was used as a electrolyte solution in the low temperature considerations, but also is a viable fuel. Under “Earth” conditions, the ... production of methanol via reduction ... leads to another fuel source, other than methane, that can be achieved effectively.
In addition to the uses for possible Mars missions, the electrochemical reduction of carbon dioxide could have possible uses here on Earth. With the reduction of fossil fuels occurring at an increasing rate, methane and methanol could serve as possible alternative fuels to crude oil around the world. In addition to fuel production, the electrolysis of carbon dioxide could be extremely important for the lessening of the concentration of green-house gases in the atmosphere. These are possible uses that are proposed.
Conclusions
The electrochemical reduction of CO2 is achieved with high efficiencies at low temperatures ... . These conditions are favorable for the in-situ fuel production on Mars. ... With good Faradaic efficiencies and chemical efficiencies, the electrolysis of CO2 is a better method of obtaining methane and methanol than the Sabatier or Fischer-Tropsch processes alone because it can be achieved at lower energies.
The electrochemical reduction of CO2 is viable for space, but the home applications are of importance here on Earth and need to be considered in the years to come and could even be used here for fuel before the reaching a land far away."
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We'll use the author's own words to sum it all up: "The electrochemical reduction of CO2 is achieved with high efficiencies at low temperatures ... . The electrochemical reduction of CO2 ... could even be used here for fuel."
Could be, should be.
One thing that we think should be taken into account, as well, is that these processes result in the co-production of Oxygen. If you have to have a by-product from an industrial process, that's not a bad one to have, we would suppose.
And, don't forget: "The conversion of carbon dioxide into useable hydrocarbons is a process that has been around since the early 1900s."
Beats the heck out of spending a big bunch of money on CO2, to pipe it all to, and pump it all down, a leaky geologic sequestration rat hole. And, combined with the conversion of coal into liquid fuels, Carbon Dioxide recycling could give us, in the United States, the kind of energy self-sufficiency our astronauts will absolutely need to have on Mars. Although we do bet that some petroleum power would find some way to get a tanker full of oil to our Martian colonists - if the price was right; and, we were willing to pay that price.