Comment by mapontosevenths
2 days ago
I hadn't heard of Fischer-Tropsch. Looks like it usually works based on gassification of biomass or existing fossil fuels, so it seems at first glance that it has the same negative externalities as just burning the source material doesn't it?
The Sabatier process looks like it might have much less of that! Very cool stuff. I would love to see a future in which we use uninhabitable, non-arable, desert land to generate cheap synfuel that we can ship wherever needed.
FT can work with pretty much any source of carbon and hydrogen.
The latter might come from an existing hydrocarbon (as with so-called "blue", "grey", "black", or "brown" hydrogen), or from electrolysis, which is not carbon-neutral. If the latter is powered by a carbon-neutral source (surplus renewables, nuclear), it's "green", and carbon-neutral.
CO2 can also be obtained from numerous sources. One prospect suggested when US peak oil was a concern, in the 1960s, was limestone. More recently, the US Naval Research Lab, as well as Google's Project Foghorn, looked at separating CO2 (in the form of carbonic and carbolic acid) from seawater, which is far less energy intensive than direct removal from the atmosphere. I'd looked up the history of research and industrial applications circa 2014, noted here:
<https://web.archive.org/web/20170719101136/https://www.reddi...>
<https://web.archive.org/web/20230601122020/https://old.reddi...>
The US Navy has an interest largely for its carrier fleet. Whilst the carriers themselves are nuclear powered, their aircraft are not, and fuel provisioning for the aircraft fleets is a major logistical hurdle as well as a strategic vulnerability. No need to target the carriers themselves (heavily defended) if the supply tankers can be sunk, something present US adversaries might consider. One prospect would be to effectively recommission older carriers as fuel-synthesis platforms, capable of producing aviation fuel from seawater in situ and not having to transit between fuel depots and the fleet itself. Given the additional costs of transit and strategic significance, the economics should be somewhat more favourable than for civilian use. This was the subject of a number of papers published in the 2010s by the US Naval Research Laboratory (listed above). Earlier research based on other carbon sources was performed at MIT and Brookhaven National Laboratory in the 1970s and 1960s, respectively.
Fischer-Tropsch is based on the reaction of carbon monoxide with dihydrogen (free hydrogen). This mixture is known as syngas.
While now the cheapest way is to make syngas from methane or from coal, it is possible to make syngas from carbon dioxide that reacts with electrolytic hydrogen.
It is also possible to make equivalent precursors of synthetic hydrocarbons by the electrolysis of carbon dioxide in water.
For these 2 methods, you do not need any fossil fuels, but only electrical energy for electrolysis.
Where the energetic efficiency is still very low is when you want to use clean air as the source of CO2, instead of using a concentrated source of CO2. With very cheap energy, i.e. solar energy that is used at the point of capture, it should still be possible to devise a method of capture for CO2 from the air. Many such methods are known, their only problem being a high energy consumption per the amount of captured CO2, so they are impractical with energy that must be bought from the grid, but I do not see why they could not work when coupled directly with solar panels.