Ionic liquids for carbon capture

Materials World magazine
,
1 May 2009

Ionic liquids could boost the efficiency of removing impurities from natural gas and have potential for capturing carbon from coal-fired plants, say researchers at a US university spin-out company.

Impurities within natural gas – such as CO2 and hydrogen sulphide – are commonly removed using an aqueous amine solution. Ion Engineering, a spin-off from The University of Colorado, proposes replacing water with a ‘tailored’ ionic liquid. The company estimates a saving of around one-third in energy costs by an increase in reaction rates.

Ionic liquids are polar solvents that consist of two ‘organic ions’. Chief Technical Officer Jason Bara explains, ‘These are tunable structures – so you can alter their properties by adding different functional groups’. The company is concentrating on imidazolium-based ionic liquids.

A number of research teams have looked at these substances to capture CO2 because the gas is very soluble in them. But nobody has yet suggested combining ionic liquids with established amine technology, says Bara.

He explains that this method combines the strengths of the two systems – ionic liquids are non-volatile, non-flammable and have high acid gas solubility, and amines are a proven technology and highly reactive with acid gases. Carbon dioxide reacts with amines to form carbamate salts.

Ion Engineering claims that ionic liquids help to boost the reaction rates of amines, compared with an aqueous solution, but is unable to reveal more detail at this stage.

Switching from aqueous to ionic liquid amines also enables the process to be carried out on smaller equipment, because of the higher reaction rate and more gas being captured per volume
of solution. This helps to reduce the cost of the process, says the company, and makes it economically viable to open up ‘sour’ gas fields, which are currently seen as too expensive to develop.

Furthermore, because ionic liquids have very low vapour pressures, they do not evaporate, reducing the risk of atmospheric pollution and energy wasted.

However, they are still toxic, which the company is looking to address, along with the issue
of disposal.

Using technology partnerships and venture capital, Ion Engineering aims to raise US$5m to develop the technology for natural gas cleaning – but knows it will need around US$40m to do the same for carbon capture.

This year, it will start field trials for both applications. The company says it could remove CO2 for as little as US$20/t – around 65% cheaper than current ‘industry best performance’ – though it admits this is a ‘preliminary estimate’.

Further information: Ion Engineering