Carbon dioxide by its very nature is not a bad thing. Humans breathe it out so plants can take it in. Carbon dioxide is what makes your soda bubbly, and it can be used to make rubber, fertilizer and any number of household tools. So, what’s the big deal?
This is a question that brought me to where I am today – a chemist who has been studying carbon dioxide and green energy for the past six years. I was drawn to this subject because I want to help as many people as possible, and carbon dioxide has become quite a problem during the last 70 years.
Carbon dioxide can absorb sunlight, which makes it different from a gas like oxygen. Taking in sunlight causes carbon dioxide to get warm, and the more heated up carbon dioxide is, the warmer the air feels.
The amount of carbon dioxide in the air around you is about 0.04%, which, believe it or not, is actually the highest it has been in the past 800,000 years. In fact, the level didn’t go above 0.03% until 1950.
However, since industrial power plants are burning fossil fuels (mostly carbon) in the presence of oxygen, they are making more carbon dioxide with a percentage of about 10-15%. Some processes, like cement-making, can produce gas streams with up to 30% carbon dioxide. More carbon coming out of the process usually results in a bigger environmental impact (more of that heated-up carbon dioxide gas bopping around). These are some of the best processes to target.
To get to a net carbon neutral society without seriously cutting down on factories, cars and population, carbon capture might be the way. In order to get us there, we will need all the help we can get. Luckily, the science behind the solution is looking promising.
Scientists like myself are currently trying to solve the problem of extra carbon dioxide in the air using a concept that sounds ripped from the mind of a younger scientific dreamer: just grab it out of the air.
Right now, scientists and engineers from around the world are working to achieve “direct air capture,” or pulling carbon dioxide straight out of the air around us, as well as capturing carbon from specific sources, such as a power plant.
Finding a way to capture carbon dioxide straight out of the air isn’t new. In the 1960s, when scientists were attempting to solve the many issues that come with space travel, carbon capture was a subject of concern. NASA funded research in an attempt to find some way to capture the carbon dioxide that the astronauts were breathing out. While researchers were able to find some interesting concepts, nothing worked well enough to send up with Neil Armstrong, Buzz Aldrin and Michael Collins aboard Apollo 11.
As happens with many things that were in style at some point, what’s old is new again. Weather destabilization came more to the forefront of environmental concern, and with it came a renewed interest in carbon capture.
We are able to take carbon dioxide and recycle it. Researchers also are working on processes to make carbon dioxide into materials like methanol and jet fuel. And, if nothing else, we can pump carbon into the ground where it can mineralize. The minerals would be far beneath the Earth’s surface, so the average person wouldn’t really experience much of a change.
So, what’s the problem? What’s taking so long?
Right now, there are companies such as Climeworks in Switzerland that are attempting to make carbon capture a reality. There was even a pilot plant of a carbon capture facility in Texas called Petra Nova, which shut down last year because the facility required so much energy to operate that it needed its own, separate power plant. These plants are capable of carbon capture, but they are using a system that is not going to work for the long haul because they are too expensive to keep up.
The process uses a molecule called an amine that can grab onto the carbon dioxide. However, to get the carbon dioxide, you need to add heat, which requires a lot of energy. Adding so much heat breaks the molecule down, so it needs to be replaced. The process will never be a real solution to carbon capture because it is burdened by too many problems.
Think about the molecules as having an “on/off” switch. When the molecule is “on,” it is ready to attach to carbon dioxide. When the molecule is “off,” it can’t be bothered to think about attaching to carbon dioxide and, in fact, it will readily let it go. The system that is currently in use takes advantage of a molecule that is stuck in the “on” position; turning it off takes a bit more force than is ideal and it ends up causing some issues.
The biggest problem for today’s researchers is finding the holy grail molecule, the goldilocks molecule, the molecule that can turn “on” and “off” on command (and, ideally, without having to touch the thermostat).
To find a molecule like that, we need to think creatively. How are we going to turn the molecule on and off? While heat can be used, another option is to use electrochemistry. That means chemists go in and edit the number of electrons around a molecule in order to change the charge of the molecule.
A carbon dioxide molecule is made up of a carbon atom and two oxygen atoms. While it is very symmetrical in appearance, there is a slight difference in charge between the atoms, making the carbon ever so slightly positive and the oxygens ever so slightly negative. This slight change makes a big difference when it comes to finding that holy grail molecule.
Right now, there are two really interesting systems that seem to have almost answered our prayers. One has been around for a while, and the other is quite new.
The older of the two systems uses a molecule called a quinone. This system was most extensively studied by the chemist Dr. Daniel Dubois. He worked with his colleagues at Pacific Northwest National Lab to develop a greater understanding of exactly what makes this molecule so effective at capturing carbon.
Quinones are made up of a ring of carbons with two oxygen atoms hanging off. They are commonly used in all types of chemistry, specifically in anti-cancer drugs. The most fascinating part of them is that they have a great sense of balance; when electrons are thrown at them, they can juggle the change in charge without falling apart. This results in a molecule that is quite attractive for electrochemical reduction, or giving electrons to the molecule in order to change the charge of the molecule.
When the quinone is given extra electrons, it rebalances itself into a molecule that has a slightly negative charge, and that charge rests on the oxygen atoms. In this state, the quinone is “on.” The negative oxygen atoms act as bait for the carbon dioxide, whose carbon is ever so slightly positively charged. Opposites attract, and the quinone can grab onto the carbon dioxide. We have capture!
How do we get release? How do we “turn off” the quinone? We have to do the opposite reaction.
If giving more electrons turned it off, we need to take those extra electrons away through a process called electrochemical oxidation. Once the quinone loses those bonus electrons, it rebalances itself and finds that the oxygen atoms no longer have a strong enough negative charge. No attractive charge means the magic is lost for carbon dioxide, and it sees itself out.
Using electrochemistry for carbon capture is an appealing option for researchers since it allows for more control of the “on/off” switch of the molecule. Systems such as the quinone allow you to directly switch the molecule off with electrons.
Researcher T. Alan Hatton and his team have been toying with a way to turn “on” and “off” the amines that seemed stuck in the “on” position using electrochemistry and metals.
This method presents a fascinating idea of taking what technology researchers already know and love and cutting the less-than-ideal part out. If they are able to figure out a way to make the amines turn “on” and “off” more easily on a large scale, this could lead to the amine method becoming much more energy efficient and perhaps more likely to be implemented on an industrial scale.
However, with all of these interesting methods, there is a catch: Oxygen is inescapable. It’s in the air around us at all times. Every molecule that’s been looked at does not play well with oxygen; in fact, the presence of oxygen makes them break down.
Nevertheless, we are trying to find a way around the oxygen. There are some molecules out there that could work with oxygen around. There also are ways of filtering out the oxygen out before it becomes problematic.
If we can find a practical way to get carbon dioxide out of the air, we could see wonderful results. Some possibilities:
- Having an energetically efficient way to capture carbon out of a power plant could result in a hugely reduced carbon footprint for industrial plants.
- Finding a way to plug a carbon capture device onto your car’s exhaust could mean less smog.
- Perhaps those carbon dioxide tanks that are used to make your favorite beers or power your soda stream could come from recycled carbon dioxide.
For the world at large, it would mean the possibility of less extreme weather, healthier air quality, and perhaps even new economic opportunities. Once that carbon is out of the air, there’s plenty it can be used for.
Every day, we grow closer to finding a more efficient way to grab carbon out of the air. With more researchers working on it than ever before, you and I can look forward to a net carbon neutral future – with the help of carbon capture, that is.
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