In Spain, they not only fight against excess carbon dioxide, but also convert it into useful fuel. A thermal solar tower has been built here that uses CO2, water, and sunlight as raw materials to produce carbon-neutral diesel and jet fuel. Research was published in the journal Joule.
Why is this important?
Fossil fuel can be replaced by electricity or hydrogen in cars, both passenger and truck. Clean aviation technologies still do not exist, so airlines are looking for carbon-neutral fuels to reduce emissions.
Carbon-neutral fuel is a replacement for modern Jet-A jet fuel. The difference is that instead of burning fossil carbon, this fuel contains carbon from other sources. It will still enter the atmosphere, but before that, it will do useful work.
There are several ways to produce carbon-neutral fuel. Biofuels made from specially grown corn create emissions from fertilizers and farm machinery, and take up land that could feed people.
There are also attempts to turn garbage or old cooking oil into jet fuel, but this process requires a lot of energy and often requires additional, also energy-intensive, cleaning. It is much better for the environment to capture carbon from other sources of emissions and process it with renewable energy.
How does the tower work in Spain?
The installation consists of a tower and 169 mirror panels placed on the ground. The panels reflect sunlight and direct it into a 16cm hole to the solar reactor at the top of the tower. In this way, the reactor receives about 50 kW of solar thermal energy.
Heat is used to control the redox cycle, in which water and carbon dioxide are converted into hydrogen and synthesis gas. By adjusting the amount of water and CO2, the composition of the gas can be controlled.
In the lower part of the tower, the synthesis gas is converted into a liquid phase containing 16% kerosene and 40% diesel fuel, and a paraffin phase containing 7% kerosene and 40% diesel fuel. This proves that a solar reactor can produce syngas that is clean enough to convert into fuel.
What are the prospects for technology?
Researchers worked with the setup for nine days, making 6-8 cycles each day. During this time, the installation produced about 5,191 liters of synthesis gas. For example, a Boeing 787 Dreamliner can contain up to 126,372 liters of fuel, which will let it fly 14,140 km from New York to Vietnam. This is just one plane out of thousands that fly every day.
However, synthetic fuels do not necessarily have to completely replace fossil fuels. It can be mixed with conventional, which will still reduce overall emissions.
Although the efficiency of the system was only about 4%, the researchers have a plan to increase it to 20%. Scientists emphasize that they were able to demonstrate the entire chain of conversion of water and carbon dioxide into fuel, and their development can be implemented on an industrial scale.