Carbon dioxide-binding organic liquids (CO₂BOLs) can hold more than twice as much CO₂ as current capture agents, say scientists in North America. The liquids could be used in coal power plants to capture the greenhouse gas from combustion exhaust.

Organic liquids can store almost 3 times the amount of carbon dioxide

David Heldebrant at the Pacific Northwest National Laboratory, Richland, US, and colleagues, made CO₂BOLs from mixtures of organic alcohols and strong organic bases. They found that the CO₂BOLs can store up to 19 per cent of their weight in CO₂, much higher than the maximum of seven per cent achievable with current aqueous amine systems.

'The biggest obstacle in efficient chemical CO₂ capture and release is the cost of stripping CO₂ from the aqueous capture agent due to the high specific heats associated with water,' says Heldebrant. Removing, or stripping, the CO₂ from the capture agent allows the liquid to be recycled and capture more CO₂. With CO₂BOLs, less fluid is needed to capture the same amount of CO₂, and less energy is needed to strip the CO₂, he explains. 'Such a system can potentially offer large energy savings for CO₂ stripping when employed on an industrial scale,' he adds.

In addition, Heldebrant's group found that the CO₂BOLs, which were designed to be a direct replacement for the aqueous amines currently used in coal plants, could go through five cycles of capturing and releasing CO₂ without losing activity or selectivity.

'The release of CO₂ in a controlled fashion is important for permanent sequestration of CO₂ or other applications such as carbonation in the beverage, dry cleaning or chemical industries,' explains Heldebrant. 'Just because CO₂ is a greenhouse gas doesn't mean it has no useful applications or market value.'

Kazunari Ohgaki, from Osaka University, Japan, an expert in carbon capture and storage, sees the potential of the study. 'In the future, these mixtures could replace aqueous amine solutions as a way of removing CO₂ from post-combustion waste gases,' he says.

Heldebrant's team are currently modelling the system to check for any obstacles to implementation and also plan to investigate whether CO₂BOLs could be used to capture CO₂ before the fuel is burned.

Christina Hodkinson