Research into sustainable PtL fuel production in the face of electricity fluctuations at Industriepark Höchst Frankfurt/Main

The world’s largest pilot plant for synthetic kerosene in Hesse will demonstrate for the first time how the fluctuating availability of green electricity impacts on the production of CO2-neutral power-to-liquid fuels. The German Federal Ministry of Digital and Transport (BMDV – Bundesministerium für Digitales und Verkehr) has now approved funding of around 3.4 million euros for the RePoSe (Real-time Power Supply for e-fuels) project.

“We have set ourselves the goal of producing at least 200,000 tonnes of sustainable kerosene per year for German air traffic by 2030,” says Oliver Luksic, Parliamentary State Secretary at the Federal Ministry of Digital and Transport Affairs. “We anticipate that the RePoSe project will give a boost to achieving the urgently needed market ramp-up of electricity-based fuels and provide important new insights into the technical conditions that will be necessary to achieve this.”

Pilot plant: Continuous demand meets varying electricity production

The RePoSe project will run from October 2022 to August 2026, with the practical component taking place at the Industriepark Höchst site. Part of the pilot plant planned there will be used in the project to run the Fischer-Tropsch synthesis process to produce PtL fuels – and, for the first time, to do so variably. Fischer-Tropsch synthesis, or the Fischer-Tropsch process, is a large-scale process for converting synthesis gas (CO/H2) into liquid hydrocarbons.

“A key issue for subsequent industrial upscaling is how fluctuations in the supply of electricity from renewable sources can be buffered during the production of the synthetic kerosene. We will investigate this together with our partners from industry and science,” says Bernhard Dietrich, Head of CENA Hessen, the Centre of Competence for Climate, Environment and Noise Protection in Aviation, operated by Hessen Trade & Invest GmbH (HTAI).

Until now, this technology has only been investigated in continuous operation with a continuous supply of hydrogen. However, since power generated by the sun and wind is not continuously available, very large hydrogen storage tanks are needed as buffers. In order to determine exactly how large they need to be, the RePoSe project is calculating and testing these in practical applications. “We expect that this will significantly reduce the size of the hydrogen storage, which means that costs can be optimised in production,” Dietrich said. “It will also be interesting to see what options for flexibilisation lie in the production process itself.”

Alongside the technical testing of the operation, the effects of variable operation on the sustainability of fuel production (by means of a life cycle analysis, among other things) and on the mechanical stress of the Fischer-Tropsch plant are also to be determined.

Carbon neutral fuel from water, electricity and expended CO2

In the PtL process, water is split into hydrogen and oxygen with the help of electricity and the hydrogen produced in this way is used together with CO2 from industrial processes for the synthesis of liquid fuels. If the electricity used for this comes from renewable energies, the CO2 cycle can be completely closed. This means that when such PtL fuels are burnt, only as much CO2 is released as was bound during production. The final product is, for example, CO2-neutral aviation fuel. “We need synthetic fuels to make it possible to achieve the climate goals in all sectors. Every sustainably produced tonne of CO2-neutral fuel is valuable in several ways,” says Dr Rainer Waldschmidt, HTAI Managing Director. “After all, this not only reduces CO2 emissions. Burning it also results in the production of a lower volume of air pollutants.”

Project partners

The RePoSe project is funded by the Federal Ministry of Digital and Transport with a total amount of 3,425,491 euros as part of the renewable fuels overall concept. The PtL fuels development platform is coordinated by NOW GmbH and implemented by the project management organisation VDI/VDE Innovation + Technik GmbH.


The partners in the RePoSe project (in alphabetical order):

  • CENA Hessen
  • Fraunhofer IWKS
  • Fraunhofer LBF
  • Ineratec AG
  • Provadis School of International Management and Technology

CENA Hessen is the project coordinator for RePoSe and is investigating the optimisation of synthesis plant downtimes and the size of the hydrogen storage facility in this project. This includes obtaining and analysing data on the availability of electricity produced from renewable sources, conducting the calculations for optimisation as well as the practical operation of a hydrogen storage facility.

Fraunhofer IWKS will examine the system components replaced at specified intervals and their wear as well as any signs of fatigue (cracking, surface damage) metallographically, structurally and microstructurally and morphologically, as part of the project. This provides the opportunity to perform targeted optimisations on the materials used and to investigate the effects arising from operation in combination with the effects of hydrogen.

Fraunhofer LBF is investigating the reliability of the plant under variable loads. This includes the measurement and evaluation of local stresses on the plant, the derivation of fault-effect relationships for the evaluation of failure scenarios and their effects on the operating time and on plant efficiency and safety. Cyclic analyses of the polymeric and metallic materials used are applied to evaluate the material damage caused by the plant’s contact media.

INERATEC is set to build a pioneering power-to-liquid (PtL) plant for the production of e-fuels at Industriepark Höchst Frankfurt. Up to 3,500 tonnes or 4.6 million litres of INERATEC e-Fuels are to be produced annually from up to 10,000 tonnes of biogenic CO2 and renewable electricity. The pioneer plant is made up of individual, standardised modules. One of these modules is to be incorporated into the RePoSe project in order to test the volatile supply of electricity.

Provadis School of International Management and Technology will prepare a life cycle analysis as part of the RePoSe research project. This will quantify the environmental impacts, such as the carbon footprint and the use of resources, in detail and in relation to each process step. This makes it possible to identify which process steps have a high environmental impact at an early stage, so that measures can be taken to reduce them. Furthermore, it will be possible to determine whether there are ecological advantages compared to continuous processes.


Image source: Jana Kay