Process converts CO2 and water into fuels

RESEARCHERS at the University of Texas at Arlington (UTA) have discovered a one-step method for converting CO₂ and water into liquid hydrocarbon fuels using concentrated light, heat, and high pressures.

The single stage process can be achieved using concentrated light to start a photochemical reaction which splits the CO₂ and H₂O molecules into high-energy intermediates in a “photothermochemical flow reactor” that operates at 180–200^oC and pressures up to 6 bar.

The high temperature and pressure then drives a thermochemical reaction, which links the split carbon and hydrogen intermediates together, forming hydrocarbon chains, suitable for fuel usage without further processing. The process produces oxygen as a by-product, which is funnelled back into the reactor.

Brian Dennis, professor of mechanical and aerospace engineering at UTA said, “We are the first to use both light and heat to synthesise liquid hydrocarbons in a single-stage reactor from carbon dioxide and water.”

The team says the process creates sustainable hydrocarbon fuels that can be used in current combustion engine vehicles.

Frederick MacDonnell, interim chair of chemistry and biochemistry at UTA, said, “Our process has an important advantage over battery or gaseous-hydrogen powered vehicle technologies as many of the hydrocarbon products from our reaction are exactly what we use in cars, trucks and planes. There would be no need to change the current fuel distribution system.'

The team used a photochemical and thermochemical catalyst based on TiO₂, a white powder which cannot absorb the entire visible light spectrum.

The next step for the team is to develop a better photocatalyst, one which can absorb the entire solar light spectrum. The team is working on these photocatalysts for hydrogen generation purposes, with the goal of creating an “artificial photosynthetic system,” which uses solar energy to split water molecules into hydrogen and oxygen.

MacDonnell said if the team were to use a better photocatalyst, 'we could more effectively use the entire spectrum of incident light to work towards the overall goal of a sustainable solar liquid fuel.'

The team is also working on using parabolic mirrors to concentrate sunlight on the catalyst bed, providing both heat and photo-excitation for the reaction, and claim that the excess heat from this reaction could be used for related operations for a solar fuels facility, including product separations and water purification.

The researchers have received over US$2.6m in corporate funding for their projects over the last four years, and aim to continue scaling up their process to deliver cleanly made fuels on an industrial scale.

Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1516945113