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Comment by guy_c | Hacker News Reader

Not sure how accurate but napkin maths and quick google suggest barrel of oil produces 118 kg of co2. So about 9 barrels to produce a ton. Barrel is $67. So cost of capture might add 15% to 38% to cost of oil.

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This is not correct. A barrel of oil is 118kg of pure carbon but when burning this translate to roughly 450kg of CO2 (because carbon combines with heavier oxygen to form CO2)

This is without taking into account the CO2 that is emitted to extract the oil from the ground.

Yes, the simple "rule of thumb" is "the resulting CO2 is 3 times heavier than the gasoline burned." Because chemistry. H weights "almost nothing" (in the engineering approximation sense, to the first order of magnitude) in hydrocarbons, and the weight of a single CO2 molecule (made of two oxygen atoms, one carbon atom) is roughly 3 times the weight of C atom alone (again as a good enough simple approximation, it's a little more, but C alone is a little lighter than O, so all together with the starting H, everything comes to 3).

https://www.scientificamerican.com/article/experts-weight-ra...

For those who like more exact calculation: one molecule of C8H18 (octane) weights approx 8 * 12+18=114 masses of H, only that one molecule will produce when burnt 8 CO2 molecules, which weight 8 * 12+2 * 8 * 16=352, and 352/114 ~ 2.98 ~ 3

the ~$100 per ton of CO2 is only to capture CO2 to the form of K2CO3, the energy cost to convert this to fuel will be much more!

I believe what the poster was implying is that in a future scheme, the cost of carbon capture would be directly added to the cost of the fuel. This is in line with other extraction industries, e.g. logging, where the loggers must plant replacement trees. The cost of that replacement is incorporated into that of the lumber, wood pulp, etc.

In the future (where all fuel is manufactured by energy from renewables), the price of carbon fuel would simply be the price of manufacture: capturing CO2 and energizing it into fuel. Or are we celebratinng the fact that some people learned about objective energetic cost today? Capturing CO2 has never been hard, and to make the analogy with the loggers planting trees more complete, the price component due to capture would be almost nothing compared to the price component of turning CO2 into fuel which would make up the majority of the price of this future fuel.

And how do you get enough substrates, plus how expensive and energy intensive they are?

I looked up how much volume a tonne of CO2 takes at average temp/pressure.

A sphere with a diameter of 10M.

That's an insane volume when you think about it.

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