Fuel from air and sunlight

Demonstration plant demonstrates practical feasibility of sun-to-liquid technology

This solar panel provides the energy for the conversion of CO2 and water from the air to synthesis gas. © ETH Zurich / Alessandro Della Bella
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It only requires sunlight and air: on the roof of ETH Zurich, a solar refinery produces high-energy synthesis gas only from sunlight and air - and demonstrates the practical feasibility of this "sun-to-liquid" technology. The system separates CO2 and water from the air and converts it into hydrogen and carbon monoxide in a multi-step thermochemical process chain. Kerosene can then be produced from this syngas.

You kill two birds with one stone: if you were to capture the CO2 from the air and convert it into fuel, you could slow down climate change and at the same time save fossil fuels. The first systems for CO2 capture from power plant exhaust gases, but also directly from ambient air, are already available. On the drawing board, on the other hand, there is the idea of ​​converting air-conditioning systems to capture CO2 from the air and produce fuel from it.

One deciliter of kerosene a day

Now a demonstration facility on the roof of ETH Zurich shows that fuel can only be produced from air and sunlight. The solar mini-refinery produces synthesis gas - the precursor of kerosene and other liquid fuels - with the help of solar heat and draws the required raw materials - air and CO2 directly from the ambient air via air capture.

"With this plant we prove that the production of sustainable fuel from sunlight and air also works under real conditions, " explains project leader Aldo Steinfeld from ETH Zurich. It was the first time that the entire thermochemical process chain was demonstrated under real conditions. Even under the rather sun-poor conditions of Zurich, the small plant already produces so much syngas that it can produce one deciliter of kerosene per day.

From CO2 to syngas in three steps

The new plant integrates three thermochemical conversion processes. The first is the separation of CO2 and water from the air by a chemical adsorption-desorption process. The parabolic mirror of the system then provides the necessary heat and energy for the subsequent steps: It concentrates the sunlight by a factor of 3000, thus creating a temperature of 1, 500 degrees Celsius inside the reactor. display

At the heart of the reactor is a special ceramic structure made of cerium oxide. There, in a two-stage reaction the so-called redox cycle water and CO2 are split and syngas is produced. This mixture of hydrogen and carbon monoxide can then be further processed by conventional methanol or Fischer-Tropsch synthesis in liquid fuels.

"The thermochemical process uses the entire solar spectrum and runs off at high temperatures, " explains Steinfeld. "This allows fast reaction speeds and high efficiency."

This is how the Z richer solar refinery works. ETH Zurich

One square kilometer is sufficient for 20, 000 liters of kerosene

While the plant in Zurich demonstrates the fundamental feasibility, researchers are already testing such a solar reactor on a large scale near Madrid. The next goal is then to scale the technology to industrial size and achieve competitiveness. "The goal is to use our technology to efficiently produce sustainable fuels in the future and thus contribute to reducing global CO2 emissions, " says Philipp Furler from Synhelion, a spin-off of ETH Zurich.

According to the researchers, a solar system of one square kilometer per day could produce 20, 000 liters of kerosene. "Theoretically, an installation on the Swiss territory or one-third of the Mojave desert in California can meet the kerosene needs of the entire aviation industry, " says Furler.

Source: Swiss Federal Institute of Technology Z rich (ETH Zurich)

- Nadja Podbregar