[doctorwho42]

So it acts like a reusable CO2 trap, then releases said CO2 at the cost of heating it up to 140F. Which then releases it.

It doesn't really talk about how you would sequester the gaseous CO2 other than "put it underground."... But if you put a gas underground it will eventually leak out. Even a liquid is prone to leak out eventually due to plate techtonics, but a liquid doesn't immediately turn into gaseous CO2.

So though a crucial technology, I don't see how effective it would be in a long term solution.

[BizarroLand]

If you can extract ~100% pure CO2 from the powder, then it might be feasible to develop a process that can convert very dense CO2 into Carbon and Oxygen.

Carbon is about 3/8ths of the total weight of a CO2 molecule and is solid and relatively inert at room temperature and pressure.

Of course, if there were a convenient way to simply strip carbon off of a CO2 molecule to begin with that would be the ideal system, but I'm sure that can be figured out given enough opportunity.

Plants do it, after all. It's not impossible.

[gus_massa]

> Plants do it, after all. It's not impossible.

The problem is that to reverse CO2 -> C + O2 you need the same amount of energy that you get burning coal C + O2 -> CO2.

But burning coal, like half of the energy is lost as unuseful heat.

The reaction of plants is different, but plants only has a 2% of efficiency. The chemical reaction of plants is more complicated, so let's be optimistic and assume this reaction has a 10% of efficiency.

If they use a coal plant to power the CO2 -> C + O2 conversion, they will release like 20 times the amount of CO2 absorbed.

If they use a renewable source, it's better to close the absortion plant and also 20 coal plants.

Until we close all the coal plants and we get very cheep carbon-free energy, it's bad for the environment to try a CO2 -> C + O2 conversion.

[jjk166]

There are reasons you would want to use fossil fuels and use renewables to reverse the process. Fossil fuels have high energy density, can be transported and stored with minimal losses, and consumed anywhere anytime. There are lots of things that are difficult to directly electrify like say planes. You can't simply stick a bunch of batteries on a plane to replace a jet engine and its fuel tanks. But building an excess of solar panels on the ground to mop up the CO2 equivalent of the jet engine's exhaust is simply a matter of cost. E-fuels are basically just really dense chemical batteries.

[gus_massa]

I agree. I'd prefer using something like biodiesel in planes, but I'm not sure if there is a technical limitation.

[BizarroLand]

Seems like the chemical process has been a solved equation for a while. Rather than directly splitting the molecule, they use high pressure and heat to incorporate a hydrogen atom into it, converting it into Methane which can then be broken down with high heat to carbon and hydrogen.

From the page https://chemistry.stackexchange.com/questions/915/how-can-ca...

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React carbon-dioxide with hydrogen in the Sabatier (https://en.wikipedia.org/wiki/Sabatier_reaction) process to get methane. 400 °C, high pressure and Nickel catalyst needed. The process is slightly exothermic so it can keep going on its own:

CO2+4H2→CH4+2H2O

This process have been proposed to generate fuel on Mars, and used on the ISS to process exhaled carbon-dioxide.

Split the resulting water (use electrolysis or some other thermochemical cycle) take the oxygen, bring the hydrogen back to Step 1:

2H2O→2H2+O2

Electricity for this may come off solar panels.

Methane decomposes at high temperatures. The process goes to completion around 1200°C. Collect the condensed carbon, bring the hydrogen back to step 1.

CH4→C+2H2

This process is proposed as an emissions free alternative to produce hydrogen from natural gas. Heat may come from concentrated solar light.

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The missing ingredients are excess CO2 from the atmosphere and a machine system to do the full process with, and of course the math about economies of scale regarding how fast a machine that uses this method combined with the powder in the article can actually strip carbon from CO2 in the atmosphere.

It likely would neither be cheap nor fast, but since it uses nickle as a catalyst at least it is not fancy rarefied expensive hard to find materials, just more an issue of getting all of the parts together and making the whole machine run as efficiently and effectively as possible.

Also, if the methane is generated from CO2, then burning it is nearly carbon neutral, so in places where fossil fuels are the ideal energy source it would allow us to use Green energy to make transportable low-carbon fossil fuels for them to use.

[jiggawatts]

Plants do it using the energy from the sun.

All of these “can’t we just unburn burnt things” forget that the reason we burnt the carbon in the first place was to get that energy.

Unburning it would need to return that energy and more because of inefficiencies.

If you have energy to spare, you don’t need to burn the carbon in the first place.

With global fossil fuel usage still rising, we clearly don’t have any to spare.

[glial]

It's not so clear to me -- the MIT Technology Review is already wringing its hands about energy being so cheap it causes problems with economics.

[1] https://www.technologyreview.com/2021/07/14/1028461/solar-va...

[doctorwho42]

Energy can be economically cheap in the current paradigm, while also being insufficiently cheap or insufficient quantities of clean energy to make the above comments suggestion work.

[jjk166]

Many common minerals like olivine react with CO2 at high concentrations to form carbonates which are geologically stable. The issue is getting the high carbon concentrations to make this process fast. Concentrating CO2 is the major technical hurdle of carbon sequestration.

[floxy]

>how you would sequester the gaseous CO2 other than "put it underground."

I wonder if there is a reason you couldn't just sequester the powder. Probably too expensive? Or not volume efficient?

>to leak out eventually due to plate techtonics

This might seem shortsighted, but I'm OK pushing the problem out by 50 million years or so.

[BizarroLand]

Since the powder is reusable, it likely wouldn't make sense to sequester it with the CO2 either materially or financially.

[entropicdrifter]

This. The powder is more efficiently used as a way to move the CO2 around than as a means to keep it sequestered.

[Woodi]

Still, tree produce oxygen from that CO_2. And do not need energy from grid for that :)

Threating CO_2 like radioactive waste, putting it underground etc - that what I call not self-sustained :>

[7speter]

What I'm about to say may sound absurd and an attempt to be funny, but I'm being serious.

The other day I was wondering how people always talk about sending undesirable material (garbage, spent radioactive fuel, etc.) on a one way trip to the sun. Why not send things to the surface of Venus? It has an ultra dense atmosphere that pulverizes anything that reaches the surface. In the case of this material, it's just more C02, which is what the atmosphere of Venus is already primarily composed of. We aren't going to ever explore the surface of Venus, or at least we won't for thousands, if not millions of years, barring we can easily convert co2 into energy, so is this a bad idea?

[defrost]

Let's take the 2020 figures for annual human carbon dioxide emmissions.

35 billion metric tons.

What's your back of the envelope energy figure for extracting that weight of a gas from the atmosphere, pressurising it, and lifting it to orbit and sending it to Venus?

Got a rough notion of the number of trips, fuel and resources that would need every single year?