Carbon capture and storage remains a thorny engineering problem. Most policymakers and technologists agree that it will be needed as a stopgap during a long-term transition to lower carbon electricity generation, whatever form that takes, but it has still not been demonstrated anywhere at a scale large enough for deployment and its effect on the cost of energy production remains uncertain. But a discovery by the School of Life Sciences at Dundee University may hold the key to a previously-unexplored route to carbon capture.
Working with the UK subsidiary of Saudi state petrochemicals firm Sasol, which operates chemical technology laboratories in St Andrews, and Scottish biotechnology company Ingenza, Prof Frank Sargent and colleagues have developed a process which exploits a natural trait of the bacterium Escherichia Coli to convert gaseous carbon dioxide into liquid formic acid.
“Reducing carbon dioxide emissions will require a basket of different solutions and nature offers some exciting options,” Sargent said. “Microscopic, single-celled bacteria are used to living in extreme environments and often perform chemical reactions that plants and animals cannot do. For example, the E. coli bacterium can grow in the complete absence of oxygen. When it does this it makes a special metal-containing enzyme, called formate hydrogenalase (FHL), which can interconvert gaseous carbon dioxide with liquid formic acid. This could provide an opportunity to capture carbon dioxide into a manageable product that is easily stored, controlled or even used to make other things.”
The trouble is, Sargent added, that normally this process is slow and can be unreliable. In a paper in the journal Current Biology the team explains that the bacterium normally uses FHL to oxidise formic acid into carbon dioxide and couples that reaction directly to the reduction of protons to molecular hydrogen; so their task was to drive that reaction backwards.
The paper describes how placing the bacteria containing the FHL enzyme under pressurised carbon dioxide and hydrogen gas mixtures — up to 10 atmospheres of pressure — converts 100 per cent of the carbon dioxide to formic acid. The reaction happens quickly, over a few hours, and at ambient temperatures.
"This could be an important breakthrough in biotechnology,” Sargent said, noting that formic acid is stable, easily stored and already has industrial applications, such as a preservative and antibacterial agent in livestock feed, a coagulant in the production of rubber, and, in salt form, a de-icer for airport runways . “It should be possible to optimise the system still further and finally develop a `microbial cell factory' that could be used to mop up carbon dioxide from many different types of industry,” he said.
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