ETH Zurich scientists have developed a one-of-a-kind solar mini-refinery that produces liquid hydrocarbon fuels exclusively from sunlight and air.
Located on the roof of ETH’s Machine Laboratory building, the mini-refinery marks the world’s first demonstration of the entire thermochemical process chain under real field conditions.
The refining process yields a fuel gas mixture called syngas which is subsequently processed into kerosene, methanol or other hydrocarbons.
These drop-in fuels have been touted as environmentally-friendly and could help make the aviation and maritime transportation sectors a lot more sustainable.
“This plant proves that carbon-neutral hydrocarbon fuels can be made from sunlight and air under real field conditions,” explains Zurich professor Aldo Steinfeld.
“The thermochemical process utilizes the entire solar spectrum and proceeds at high temperatures, enabling fast reactions and high efficiency.”
Steinfeld’s group has already founded two spin-offs to advance the same: Synhelion (2016) commercializes the solar fuel production technology, while Climeworks (2010) commercializes the technology for CO2 capture from air.
The technology used by the solar mini-refinery is said to be feasible even under the climate conditions prevalent in Zurich, and is capable of producing one deciliter of fuel per day.
The refinery’s conversion process begins by first extracting CO2 and water from the air. They are then pushed through solar-thermochemical splitting and their subsequent liquefaction into hydrocarbons.
According to the scientists, CO2 and water are extracted directly from ambient air via an adsorption/desorption process. Both are then fed into the solar reactor at the focus of a parabolic reflector.
Solar radiation is concentrated by a factor of 3,000, generating process heat at a temperature of 1,500 degrees Celsius inside the solar reactor.
A ceramic structure made of cerium oxide forms the central core of the solar reactor, and this enables a two-step reaction – the redox cycle – to split water and CO2 into syngas.
The hydrogen and carbon monoxide mixture is then processed into liquid hydrocarbon fuels through conventional methanol or Fischer-Tropsch synthesis.
Steinfeld and his group are already working on a large-scale test of their solar reactor in a solar tower near Madrid.
Their next goal is to scale the technology for industrial implementation and make it economically competitive.
Image and content: Alessandro Della Bella/ETH Zurich