Carbon-neutral fuel derived from sunlight and air – ScienceDaily

Carbon-neutral fuels are essential for making air and sea transport sustainable. ETH researchers have developed a solar power plant to produce synthetic liquid fuels that release as much CO₂ during their combustion as previously extracted from the air for their production. CO₂ and water are extracted directly from the ambient air and split up with the help of solar energy. This process produces synthesis gas, a mixture of hydrogen and carbon monoxide, which is then converted into kerosene, methanol or other hydrocarbons. These booster fuels are ready to be used in the existing global transportation infrastructure.

Aldo Steinfeld, professor of renewable energy carrier at ETH Zurich, and his research group have developed the technology. "This plant proves that carbon-neutral hydrocarbon fuels can be made from sunlight and air under real-world conditions," he said. "The thermochemical process uses the entire solar spectrum and takes place at high temperatures, which allows for fast reactions and high efficiency." The research facility in the heart of Zurich is advancing the ETH research on sustainable fuels.

A small demonstration unit with high potential

The solar mini-refinery installed on the roof of ETH Zurich proves that this technology is achievable, even in the climatic conditions prevailing in Zurich. It produces about one deciliter of fuel a day. Steinfeld and his group are already working on a large-scale test of their solar reactor in a solar tower near Madrid, which is being carried out as part of the European sun-to-liquid project. The solar tower plant is presented to the public in Madrid at the same time as the Zurich mini-refinery.

The next objective of the project is to adapt the technology to industrial implementation and make it economically competitive. "A solar power plant with an area of ​​one square kilometer could produce 20,000 liters of kerosene a day," said Philipp Furler, director (CTO) of Synhelion and former PhD student of the Steinfeld group. "Theoretically, a plant the size of Switzerland – or a third of California's Mojave desert – could cover the kerosene needs of the entire aviation sector." Our goal for the future is to efficiently produce sustainable fuels with our technology and CO₂ emissions. "

Two benefits already

Aldo Steinfeld's research group has already developed two derivatives: Synhelion, founded in 2016, markets solar fuel production technology. Climeworks, founded in 2010, markets technology for CO₂ capture air.

BOX How the new solar mini-refinery works

The process chain of the new system combines three thermochemical conversion processes: first, the extraction of CO₂ and water from the air. Second, the solar thermochemical split of CO₂ and water. Third, their subsequent liquefaction in hydrocarbons. CO₂ and water are extracted directly from the ambient air via an adsorption / desorption process. Both are then introduced into the solar reactor in the center of a parabolic reflector. The solar radiation is 3000 times more concentrated, which generates heat at a temperature of 1500 degrees Celsius in the solar reactor. At the heart of the solar reactor is a ceramic cerium oxide structure, which allows a two-step reaction – the redox cycle – to split water and CO₂ in synthesis gas. This mixture of hydrogen and carbon monoxide can then be converted into liquid hydrocarbon fuels by the conventional synthesis of methanol or Fischer-Tropsch.

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