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Comment by xnx | Hacker News Reader

I've never understood synthetic fuel. We've got plenty of petroleum in the ground, but too much carbon in the air. Better to come up with a good sequestration strategy to put some of that carbon back in the ground.

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"Carbon is extracted from the air in the form of CO2 and combined with the hydrogen in a process called synthesis."

It seems like at least re-burning the carbon that's already in the air is better than burning new dug up carbon? This is at least not net atmospheric carbon positive. You can do sequestration too...

There’s no possible way the process for carbon sequestration and fuel synthesis would use less e-fuel.

I am by no means a chemist (beyond a secondary school level), but burning CO2 doesn’t seem possible. Doesn’t burning through application of some energy split the bonds of complicated stable molecules into less complicated, but stable molecules (by adding oxygen), thus releasing energy.

In this case; how do they recombine the CO2 into more complicated hydrocarbons? And if it’s energy negative, is it better to do this, or to use it to capture carbon?

> In this case; how do they recombine the CO2 into more complicated hydrocarbons?

Fischer–Tropsch process.

> And if it’s energy negative, is it better to do this, or to use it to capture carbon?

It's obviously "energy negative", as it would be a violation of thermodynamics for it not to be, entropy being how it is. As far as doing it over carbon capture, I would be more interested in hearing your thoughts on why carbon capture would be a better alternative.

"In this case; how do they recombine..." that is exactly what the article is about. E-fuels are atmospheric carbon dioxide that is electrolyzed using renewable sources and combined with additional hydrogen in order to produce octane. So, my original parent is saying the process we should focus on is sequestration (Atmospheric carbon dioxide -> electrolyze to carbon and oxygen [this is the energy intensive step] -> bury the carbon and leave the oxygen -> harvest natural hydrocarbons / oil -> distill into various weights -> burn the octane). I propose achieving similar atmospheric carbon balance with similar energy inputs with the cycle (Atmospheric carbon dioxide -> electrolyze to carbon and oxygen [same energy per carbon] -> hydogenate the carbon to octane for portability and compatibility reasons -> burn the octane). The only point in doing all of this of course is the huge installed user base for engines that burn octane, a portable and stable fuel.

Synthetic fuels are generally cleaner in that they have significantly less sulfur and a decent bit less aromatics. There’s a great picture on Wikipedia that illustrates the difference.

Synthetic fuels done right are carbon neutral, a much better option than burning petroleum and adding more carbon to the system.

Formula 1 plans to move to synthetic fuel in 2026:

https://www.bbc.com/sport/formula1/61942876

The problem here is leaks.

Burning and recapturing is a carbon positive process without separately trying to recapture carbon out of the rest of the air.

The air at large has a very low concentration of CO2, so the capture is unfavourable. Your apparatus is only going to touch so many CO2 particles to recapture them, asides from CO2 being energetically favourable

And, once you have sequestered them, the sequestration also has to worry about leaks.

If you're using a synthetic fuel, those leaks move you from -100% net release towards 0% net release.

If you're using newly mined fuel, the leaks move you from 0% release towards 100% release

This doesn't account for the energy requirements to create the fuel

Doesn't sequestration also capture the things that the carbon is bonded with? Which is oxygen.

trees?

The marketing blurb for this fuel can say: we only kill birds! (Because wind turbines)

Turbines kill fewer birds per kWh than a coal plant.

Imagine being as stupid as this

sadly, the number is much greater than 1

> we only kill birds!

Bats too. They don't even need to hit the bats to kill them. The difference in air pressure around the blades is enough to rupture bat lungs:

https://www.newscientist.com/article/dn14593-wind-turbines-m...

https://www.scientificamerican.com/article/bat-killings-by-w...

Which is interesting, but non-windturbine power is also responsible for mass bat deaths because the heat got too high

https://www.nrdc.org/stories/heat-wave-australia-killed-2300....

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