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Comment by rmcginnis | Hacker News Reader

Hi, Rob from Prometheus here! Most of the skepticism about CO2 removal from the air is focused on "carbon sequestration and storage" or CSS, which is mitigation of emissions from fossil fuel by putting CO2 into the ground, for example. Turning CO2 from the air into useful products like fuels and building materials is much more capable of scaling because these products have value independently from regulations or carbon taxes/credits. If you can be the low cost producer of a commodity like gasoline or polyethylene, it's possible to grow zero or negative carbon capture very quickly to very large scale. If all transportation fuels, heating fuels, and plastics were from atmospheric CO2 capture, this would be more than 10 GT of CO2 a year, which is hugely significant.

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>Most of the skepticism about CO2 removal from the air is focused on "carbon sequestration and storage" or CSS, which is mitigation of emissions from fossil fuel by putting CO2 into the ground

That is false! Most of the skepticism about CO2 removal from the air is focused on the difficulty of said removal, compared with the relative ease of removing CO2 from eg power plant exhaust.

> Turning CO2 from the air into useful products like fuels and building materials

You mean something like DME synthesis from CO2 and H2? Isn't atmospheric CO2 capture sort of expensive at 400 ppm? Obe would obtain one kilogram of CO2 from 2500 kgs of air.

Turning atmospheric carbon to building materials is already being done with plant based fiber mixtures such as hempcrete or fiber cement.

Hi Rob! Is it possible to produce gasoline through atmospheric CO2 capture for less than traditional methods? Will CO2 capture be competitive in real costs?

I cannot see how you could take CO2 and make gasoline out of it using less energy than what the gasoline contains. At best, you will need to supply that energy via something like solar panels. Then it becomes a question of efficiency: how many Watts of gasoline can you produce per Watt of electricity you have? My guess is, not many.

It can still be competitive with things like tar-sand extraction, which takes more energy than you get out of the oil. It's only economically viable because energy in gasoline/oil form is more valuable than the energy content itself, due to it's ease of transfer. Air sequestration might be a viable fuel source in regions where import costs of fuel are high, but energy is cheap.

I did not know that! Thanks.

I am less concerned about economic efficiency and more about environmental efficiency. The process to set up carbon sequestration facilities will itself produce CO2. If you produce a paltry amount of gasoline because all your energy is going towards that conversion, it might take you years or decades to actually reduce atmospheric CO2.

Even more important is the fact that the gas you produce and sell will go right back into the air as CO2, further reducing your net impact. You would basically need to produce gasoline faster than people can use it. Do you think a private company can do this process and outpace the consumption of Asia and Africa? It’s a catch 22: either your process is so inefficient that you pollute more than you clean up, or it’s efficient enough that you just drop the prices of gasoline, putting CO2 right back into the air. Their option is that you produce so much gasoline that you cannot sell it fast enough. Ironically that will tank your profits.

I think doing something other than gasoline is the answer. Make fertilizer: it will help grow the ecosystem while not immediately winding up as CO2.

This is false, the net energy is positive for tar sands it is just less than for conventional oil extraction.

The ideal method would be CRISPRing up some algae to synthesize gasoline, but we're pretty far from that.

you cannot. That would be a perpetuum mobile

very exciting! Do we know yet if gasoline is the most efficient hydrocarbon to make from CO2 for a given amount of electricity? I would think there are a whole range of oil like things that could be produced. I always dreamed about using nuclear power to do all kinds of terraforming type things that would otherwise be energy inefficient.

It’s not thermodynamically possible to recapture carbon from the air without using more energy than was obtained by burning it the first place.

Thermodynamically, no. But is that the question?

We're a long way away from consuming so much energy we thermodynamically scorch the Earth, right?

It seems like they want to know if you can be mostly carbon neutral and generate existing fuels.

If that's the case, then if you have access to a cheap form of renewable energy -- huge amounts of geothermal, tidal, or solar -- you could generate a ton of something-like-gasoline, reduce carbon, and come out nearly neutral when re-burning it.

Theoretically, you can profit if the renewable source of energy is cheaper than the cost of generating and distributing the fuels.

I'm skeptical this is possible. But if it is, I'm optimistic it will actually happen.

It is the question. You need to break up the CO2 molecule and reconstitute it as gasoline. That will take more energy than the gasoline had initially. So you have a process where you take say solar energy and convert it into gasoline chemical bonds. Great, what is your efficiency of this process? Because if it is close to 100%, great. But chances are it is much closer to 0, at which point you’d be better off just using that electricity for something else.

True, many people don't realize this. But carbon capture solutions don't necessarily need to be efficient - we are not doing it to make more energy, we are doing it to clean up the many decades of mess we already made in the atmosphere. So yes, we will have to spend energy, to clean that up, naturally. The most important part is that none of these solutions is exclusive and shouldn't be pictured as exclusive. We need to offset fossil fuels, lower our energy use, and suck CO2 from the atmosphere. All three of them.

>But chances are it is much closer to 0, at which point you’d be better off just using that electricity for something else.

Unless your ultimate goal is not just to use energy efficiently, but to recapture carbon dioxide.

Solar panels take energy to produce, transport, and install. Mining the lithium needed to produce them is pretty harmful to the environment. Other parts of the process are pretty bad too. If your efficiency is too low, if you install a gigawatt power plant and produce a half gallon of gasoline a month, you will take way too long to get an emissions ROI. Just recapturing CO2 requires less energy than recapturing and reconstituting it as gasoline. Sure you can sell the gasoline and maybe make some $$ but will that actually in the end be a net negative for the atmospheric CO2? The answer will 100% depend on efficiency.

As an aside, we're not that far from boiling the oceans at the current rate of growth in energy usage. Maybe 400 years, IIRC.

Hydrocarbons are better energy stores than batteries. If we can “charge your car” by pumping hydrocarbons into it, that is better than lugging around heavy batteries (maybe.) so, in a way, co2 -> gasoline via solar power (or nuke) is an overall win.

I personally doubt the energy cost for the conversion is so low that it makes sense, but would like to see that demonstrated. Then you are still burning hydrocarbons, which is a big health problem.

I imagine the goal is to use renewables for the energy required for capture.

The esoteric read on this, then, is it is a bet on fusion.

And before that?

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