OK, I know that when Cal and Stanford come to mind, it’s hard not to think of this:
(Not that Stanford hasn’t had great finishes in this series, too!)
Whoever you were pulling for there, we’ll need a similarly dramatic finish if we’re to avoid the worst consequences of climate change. While renewables are obviously a huge part of that, the less-glamorous — but just as important — aspect is carbon capture. There are a number of industries and processes for which there’s no straightforward way to stop emitting CO2, like the production of chemicals, steel, and concrete, so we also need to deal with that fact.
The Inflation Reduction Act of 2022, which should be law within a few days (yay!!), acknowledges this by granting a lot more tax credits and broader eligibility for facilities that successfully cut carbon emissions, to the tune of $85 per ton. The trouble right now is that carbon capture is still expensive and energy-intensive, so it’s not widely used.
Enter Cal and Stanford. They’re both such great academic institutions, so imagine what can happen when they work together. Well, that’s exactly what they’ve done to create an incredible material that can rip 90% of the CO2 out of flue gas in less than 60 seconds, and it’s easily made from cheap and plentiful components. You can read all about it in the August 3 edition of Science Advances (open access).
Right now the main approach for pulling CO2 out of flue gas is amine scrubbing. It certainly works well, but unfortunately it consumes a lot of energy. The first part is simple enough. We bubble our flue gas through cool water that contains one or more amines:
Amine scrubbing to remove CO2 from flue gas. Amines are molecules with a nitrogen atom (N) attached to three things, as long as all three are not H, because that would be ammonia (NH3)
Here we show a pretty simple amine (ethanolamine, in black) for, well, simplicity. The CO2 (in green) and the amine each grab their favorite piece of water (in red and blue), and so the CO2 turns into bicarbonate (HCO3—). CO2 would much rather be a gas, but bicarbonate is perfectly happy when it’s dissolved in water. So, great! We’ve managed to get CO2 out of the gas and prevent it from going back. Mission accomplished, right?
Sort of, but what now? We can’t just stop here. We have to regenerate the amine so we can use it again, and that means getting the CO2 back out of there, into its own pure gas or compressed liquid stream we can use for something else. But that’s where we have a big issue, because to do that we’re going to have to heat the water up to boiling, and that’s a LOT of extra heat we need to add. (Plus, then we’ll have to cool it back down again to do this over. Yoi! Double yoi!)
Wouldn’t it be way better if we could do this without all that extra water somehow?
Yes indeed, and that’s what makes this new material so great. We’re still going to use amines, but we’re going to attach them to a solid porous surface so lots of them are exposed:
Structure of the CO2 adsorption material. The blue part is made up of melamine and cyanuric acid, and the orange pendants are diethylenetriamine (DETA)
We can make this stuff out of the common and cheap starting materials melamine and formaldehyde, along with a bit of cyanuric acid and diethylenetriamine (DETA). You might remember melamine from its unfortunate role in the 2008 scandal in China where it was mixed into baby formula and passed off as real. That happened because melamine costs $40 a ton, or about 2 cents a pound. Cyanuric acid goes into swimming pools to help stabilize chlorine bleach in sunlight, and DETA is used for a bunch of things, including, somewhat ironically, an additive to oilfield drilling fluids. So these chemicals aren’t exactly hard to get.
We make a polymer (or network molecule) out of 92.5% melamine and 7.5% cyanuric acid, along with a shot of DETA, and we get a nice flaky and porous material that will give us lots of surface area to work with:
Transmission electron microscope image of the new material
The authors show clearly that this new network molecule can pull CO2 out of industrial gases in two ways. One, CO2 can physically stick to it by associating with the holes in the structure, but CO2 can also chemically react directly with the amine groups, instead of needing water as the middleman.
Two ways CO2 can associate with the molecular network, by physical (center) and chemical (left) adsorption. CO2 reacting with an amine is just an acid reacting with a base — the birds and the bees
One kilogram of this material can pull about 80 grams — nearly a fifth of a pound — of CO2 out of flue gas — moisture and all, which is very important — in less than a minute. It does this at temperatures typical of factory effluent flue gas, around 100°F.
We can release CO2 from the material by heating its surface to just 180°F, not even hot enough to boil water. But of course we don’t have to boil water anymore! All we have to do is heat air, which is around 3,000 times easier. The authors went through ten cycles without the material losing significant ability to adsorb CO2.
After this process, we’re left with a stream of pure CO2. Sequestering it underground shouldn’t have significant negative impacts. But even better would be to use solar energy, etc., to convert the CO2 to useful products, the kind we used to get from petroleum.
Others are working on materials like this from different angles, too, like Cornell University’s May 2022 report of carbon capture using bundles of sugar molecules treated with alkali salts.
It’s all tied together as part of the new carbon-neutral economy, which we can achieve, and the Inflation Reduction Act — thanks to Joe Biden and Democrats in Congress — is finally going to amp up the momentum on several fronts. It took long enough, but here we are. Now we’ve got to pick it up and throw it into shape.
Let’s get to work.
