How Realistic Is Carbon Capture?

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A few days ago, Elon Musk announced that he’s putting up $100 million for a prize. To win it, one must come up with a better carbon capture technology than the competition. In theory, this could help spur development of the technology, and ultimately help reduce the greenhouse effect that drives climate change.

Am donating $100M towards a prize for best carbon capture technology

— Elon Musk (@elonmusk) January 21, 2021

How SpaceX Could Use Carbon Capture

Beyond caring for the environment, one other motivation he may have is to use the technology for SpaceX. As I covered in another article, pulling carbon dioxide from the atmosphere means it could be converted to rocket fuel for Starship. The CO2 can be combined with water in a Sabatier reaction to make methane, but it requires electricity, which can be derived from renewable sources.

While that doesn’t stop the rocket from emitting CO2 into the atmosphere, the whole launch cycle can be made carbon-neutral by pulling CO2 back out of the atmosphere to make rocket fuel again.

On Mars, this is the only way they can come up with fuel for the return trip. There are no natural gas wells on that planet, and nobody knows if there is even any to drill for. It’s possible, but not something you’d want to stake your life on at the moment. We do know that there’s water in the ice caps and possibly in the soil. Also, there’s plenty of CO2 in the atmosphere that could be used to make methane for launches back to Earth or to other places in the solar system.

It’s A Challenge, Though

The technology could improve and make carbon capture realistic and economically sound, but to do so would require overcoming several obstacles.

Capture

Obviously, one must capture the carbon. But one does not simply capture carbon. This can be done at the source of the emissions, from the surrounding air, or from the atmosphere randomly.

In the case of SpaceX, you’re not going to be able to attack carbon capture devices to the business end of the Raptor engines. It would be like drinking from the fire hose, except the stream of water is fire. Your carbon capture thingy is on fire, you’re on fire, and everything is on fire. That’s just not going to fly. Literally.

Capturing carbon using scrubbers is the most common method today. To pull the CO2 from the air, minerals like quicklime are used. They react with the air, and the carbon joins with the mineral to become a different mineral, like calcium carbonate. The material can then be processed again later to pull the carbon dioxide gas back out. This is often done on site.

Scrubbers are used today in life support systems for spacecraft and submarines. In some cases, the mineral is expendable, and a supply to run the scrubber only for a short mission is taken along. In other cases, the scrubber system could have the capability to reprocess the mineral repeatedly for long missions without running out of the mineral that’s keeping everyone alive.

There are many other methods to remove the CO2 from air, but they all share the problem of costs and if used at large scale, more CO2 might be emitted moving stuff around than was originally removed.

Transportation

Once you have some carbon dioxide gas that you captured either from the atmosphere or from an industrial process that would have emitted into the atmosphere, you need to move it somewhere.

The cheapest and lowest-carbon way to move it would be with pipelines. The only cost/emission activity would be pumping the gas down the pipes, which could be done with renewables. The downside to pipelines is that impurities in the CO2 gas could create acid that would corrode the pipes and make them leak. If the CO2 goes back into the air, the whole thing’s a bust.

Trucks, trains, and tanker ships could move CO2, but those all emit their own CO2 at present, which makes it tough to get beyond breakeven CO2 removal.

Long Term Storage

If you’re SpaceX and you’re going to convert it to methane and burn it again, you don’t need to store the captured CO2. If you’re planning on putting the stuff away somewhere and keeping it out of the atmosphere, then you’ll need a place to put it where that won’t happen.

The most common strategy proposed right now is to put the stuff in the ground. If you can find some gaps in the earth, you could pump the stuff in there and seal up the hole. Hopefully it won’t leak out again anytime soon. If you have the carbon captured in a solid form of some kind, such as when it’s bound to a mineral after scrubbing, you might be able to just bury it.

Oil companies sometimes pump CO2 into oil wells to get more oil to come out, but the gas ends up back in the atmosphere either right away when the oil farts up out of the ground or when any of it trapped in the oil gets burned.

All of these things require energy and emissions to make happen, though. Nothing moves for free. There’s also no guarantee that it will stay stored in the ground, so that’s a problem that must be considered.

For all these reasons, reprocessing the gas to use as fuel again may be the most sane choice. Sure, it’s going into the atmosphere again, but at least you aren’t making the greenhouse problem worse by as much. But there’s no such thing as a lunch, though. Just because you power the process with renewable energy doesn’t mean it’s zero emissions. You still need to make that renewable energy infrastructure, and to build that takes energy.

A Problem Best Avoided

Some people, especially those shilling for oil companies, want us to believe that carbon capture will solve climate change and make it so that we don’t need to adopt cleaner technologies. Just a basic knowledge of the challenges make it pretty clear that it’s something we can only minimally rely on at best, so it won’t work on such large scales. There’s no excuse for continuing to burn fossil fuels like it’s 1955.

The technology can, at best, help mitigate the effects of life-sustaining processes that we can’t realistically convert to run on clean energy. Space launches fall under that category, because mankind has no long-term future without leaving the planet. Eventually something will kill us all off if none of us leave the nest.

There are also a number of other industrial processes, like making steel and concrete, that don’t have any good alternatives right now. Carbon capture can help us with that, and help neutralize those greenhouse gas emissions, but it’s not a cure-all.

Capturing carbon, putting it back into fuel, and burning it again doesn’t make anything truly zero emissions. It’s better than just burning fossil fuels, but nothing happens for free, even in terms of clean energy and impact.

What About Plants?

Plants are the ultimate carbon sequestration machine. They take CO2 from the air, convert it into plant mass, and leave some of it in the ground. It makes sense to use them as much as possible, and some proposed carbon capture technologies use engineered bacteria or algae to capture the CO2, which would be similar to what plants do.

National Geographic has a great piece from 2019 that covers this in great depth. I’d recommend reading it yourself, but I’ll cover some of the main points here.

Plants converting carbon into soils is definitely a key ingredient in the fight against climate change. Improved cropping, better forest management, and other harm reduction techniques can all help increase CO2 uptake into soils. Simply doing less harm would make a difference. Beyond that, reforestation and growing more plants all help increase the uptake of CO2 from the air to the soil. Those efforts are going to be valuable.

Once again, though, the plants can’t make up for continued greenhouse gas emissions. They’re helpful, but there simply aren’t enough of them in any scenario to allow us to keep doing what we did in the 20th and early 21st centuries.

Plants also don’t allow the production of methane and synthetic fuels enough to power industrial processes the way that carbon capture on industrial scales would. This is important to the carbon neutralization of things like space flight.

Thus, improved plant capture is a great complement to industrial carbon capture, but is not a complete replacement for it.

Final Thoughts

I just want to drive the point home again that carbon capture, whether industrially or with plants, is not an excuse for avoidable emissions. The problem can’t be fixed with these technologies. It can only be slowed down and mitigated some. The best thing we can do is take an “all hands on deck” approach to climate change, where carbon capture, plant management, and carbon neutralization all work together with electrification, renewables, and other clean technologies that avoid emitting in the first place.

Capturing enough carbon just to play the part we need it to play will be a big enough challenge on its own, and that’s a challenge worth tackling.

Featured image is of the NET Power facility in Laporte, Texas. Image by NET Power. Licensed under Creative Commons Share Alike 4.0 International License.