Yeah, with the addition that if you're going to go the synthetic hydrocarbon route you might as well go all the way to a fuel which is a liquid at normal operating temperatures to simplify logistics (and which isn't a massive GHG when it accidentally leaks like methane).
Advantage of shorter carbohydrates (like propane) is that they're made up of less carbon relative to the hydrogen (compared to longer chains), so for the same amount of energy stored, you need to capture less CO2 from the atmosphere or from wherever you're taking it.
Propane can relatively easily be compressed to be liquefied at room temperature. Takes just a few bars of pressure.
By my calculation, you need to capture 0.9176 carbon atoms from the air to make propane whose energy content is the same as octane made from 1.0000 captured carbon atoms.
I used the "Std enthalpy of combustion (?cH?298)" of the 2 fuels from Wikipedia in my calculation.
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