A project combing all four steps required to produce synthetic fuel from air and green power has taken place at a test facility on the premises of Karlsruhe Institute of Technology (KIT).
The synthetic fuels produced are both carbon-neutral and function as a storage for surplus renewable energy. The first litres of fuel were produced from air-captured carbon dioxide and green power.
The project combines technologies which promise optimal use of carbon dioxide and maximum energy efficiency, as mass and energy flows are recycled internally. Project partners include Climeworks, Ineratec, Sunfire and KIT.
At present, the test facility can produce approximately ten litres of fuel per day. The second phase of the project is planned to develop a plant with a capacity of 200 litres per day, and in time, a pre-industrial demonstration plant in the megawatt range, i.e. with a production capacity of 1500 to 2000 litres per day will be designed.
Four steps to fuel
The first step of the technology sees the plant capture carbon dioxide from ambient air in a cyclic process. The direct air capture (DAC) technology by Climeworks uses a specifically treated filter material for this purpose.
Air then passes across the filters which absorb the carbon dioxide molecules. Under vacuum and at 95°C, the captured carbon dioxide releases from the surface and is pumped out.
Secondly, the electrolytic splitting of carbon dioxide and water vapour takes place simultaneously. The co-electrolysis technology commercialised by Sunfire produces hydrogen and carbon monoxide in a single process step.
The mixture can be applied as synthesis gas for a number of processes in chemical industry. Co-electrolysis has a high efficiency and theoretically binds in the synthesis gas 80% of the green energy used in chemical form.
In the third step, the Fischer-Tropsch synthesis is used to convert the synthesis gas into long-chain hydrocarbon molecules. For this, Ineratec, a spin-off of KIT, contributes a micro-structured reactor.
In the final step, hydrocracking takes place – a process in which the quality of the fuel and yield are optimised. Under a hydrogen atmosphere, the long hydrocarbon chains are partly cracked in the presence of a platinum-zeolite catalyst and shift the product spectrum towards more directly usable fuels.
The process may be installed decentralised at locations where solar, wind or waterpower is available.