How 'Ionic Liquids' Could Keep Factories from Belching Carbon Dioxide

Researchers are developing a new method of carbon capture using liquids with unique properties.

Jul 7 2014, 5:55pm
Image: YouTube

If we don't put a lid on our fossil fuel-burning spree, the outlook for climate change will only get worse. A key course of action is to reduce the use of combustibles like oil and gas, but weaning the world off of fossil fuels is a tall order. Thankfully, it's possible to look at the problem—and potential solutions—from a different perspective, too. 

Scientists from Queen's University Ionic Liquids Laboratory (QUILL) in Belfast are working to use new-generation, customised solvents known as "ionic liquids" to filter carbon dioxide out of the flue gas of factories and power plants. The idea is that the stacks, though still churning out smoke, would then puff out far less polluting emissions. 

I spoke to QUILL's researchers, captained by professor Ken Seddon, during an exhibit at London's Royal Society. They declined to give too many specifics about this CO2-capturing application of the technology, the details of which they're keeping pretty secret for now, but the basic idea is pretty simple to grasp. 

Ionic liquids are, essentially, lab-made salts. All the components of the liquid carry an electrical charge, which means they behave very differently from other liquids, such as having a lowered melting point that keeps them in a liquid state at room temperature.

They also have an extremely low vapour pressure, which means that they virtually cannot evaporate. That means they don't pollute the atmosphere, and also burn or explode with extreme difficulty. They can be manipulated and reinvented to perform specific tasks, and the number of ionic liquids that could potentially be created is mind-blowing—"about a trillion," according to Seddon.

In the pollution-fighting application, the researchers will channel flue gas into twisting pipes similar to a "water-park structure," as one researcher put it, where it will pass through filters containing a solution of water and ionic liquid. This solution is specifically designed to bond with carbon dioxide, which gets trapped inside it. 

It's not the first time people have tried to shave CO2 off flue gases. "Post-combustion carbon capture" has been around for decades, but it's usually done by means of chemical solvents called amine solutions. The trouble is, amines can be pretty toxic and volatile, which ultimately means they could wind up contaminating air and water, ironically compounding the whole environmental conundrum. That's where ionic liquids could make the difference.

"Ionic liquids are totally recyclable. You can always heat them, separate them from the carbon dioxide, and re-use them again"

Minimal evaporation gives ionic liquids the edge over amines: since their molecules cannot evaporate, they won't be able to pollute the atmosphere as amines do. In addition, Seddon underlined that, "Unlike amines, ionic liquids are totally recyclable. You can always heat them, separate them from the carbon dioxide, and re-use them again."   

His hope is that something similar could happen with the CO2 capture technology. In fact, the team just launched a pilot project that uses ionic liquids to filter carbon dioxide, but were not able to reveal where the site was, nor which particular ionic liquid was being used in the process. 

The competition to discover the best way to tap into the ionic liquids' potential is apparently huge, so they prefer to keep quiet. It all sounds wonderful, until money comes into play. Despite all their qualities, ionic liquids are more expensive than amines to manufacture and work with. 

But Seddon said that "cost is just the last thing to think about when looking for a solution to such important issues." He pointed out that when QUILL recently discovered a way to remove mercury from natural gas using ionic liquids, they made it commercially viable within few years.