In Germany, various technologies such as fuel cells, batteries or renewable fuels are available to minimize CO₂ emissions in the transport sector.

Electromobility alone is not enough to make transport climate-neutral. Existing fleets and applications that are difficult to electrify, such as in shipping and aviation, will continue to require renewable fuels in large quantities for a long time to come.

Renewable fuels thought holistically

In the production of e-fuels, i.e. synthetic fuels produced using renewable electricity and CO₂, there are still challenges in the sustainable provision of carbon - as there are in advanced biofuels produced from biogenic residues. These are inefficient in their use of carbon because up to 50 percent of the carbon available in biomass is lost as CO₂ when converted to fuels. This increases the demand for raw materials.

In the new collaborative project »Synergy Fuels« researchers aim to overcome these challenges by interconnecting e-fuels with biofuel-producing demonstration plants. »Material and energy integration of e-fuels and biofuels syntheses creates synergies: Using renewable electricity to convert CO₂ to liquid fuels increases the carbon efficiency of the biotech processes. In addition, the long-term carbon sequestration in the form of the by-product plant carbon even enables negative CO₂ emissions, i.e. a net carbon sequestration from the atmosphere,« says project coordinator Prof. Dr.-Ing. Jakob Burger, Professor of Chemical and Thermal Process Engineering at the TUM Campus Straubing for Biotechnology and Sustainability.

For example, Verbund uses waste heat from the (thermo-)chemical syntheses (e.g. methanol synthesis) for product processing. The provision of biogenic CO₂ for methanol synthesis and of biogenic hydrogen through the thermochemical conversion of biomass residues is also essential. This circumvents the use of fossil CO₂ sources, for example by burning coal or natural gas, or a costly CO₂ capture from the atmosphere. 

In the project, Fraunhofer UMSICHT is optimizing thermochemical conversion processes for the utilization of biogenic residues (including Thermo-Catalytic Reforming TCR) and adapting it for coupling with Power-to-X processes. This includes the improvement of the product quality of bio-oil, as well as the processing and separation of biogenic synthesis gases or biogenic hydrogen. Furthermore, the input material possibilities for the thermochemical conversion processes are to be increased, so that a market introduction is facilitated.

Dr. Ing. Robert Daschner of Fraunhofer UMSICHT at the institute branch in Sulzbach-Rosenberg: »At UMSICHT, we are working intensively on the further development of thermochemical conversion processes for the utilization of biogenic residues in the project. This enables us to provide both bio-oil as an intermediate for sustainable fuels and hydrogen and carbon dioxide as a co-product for the power-to-X route«.

Rapid market introduction of the fuels produced

»We need highly efficient processes to produce sustainable drop-in fuels in industrial quantities at reasonable prices. Our Verbund is piloting these processes to ensure a rapid market introduction of the new fuels,« says Prof. Burger. Drop-in means that the fuels can be seamlessly blended into the existing fuel pool, replacing fossil fuels without technically modifying the engines.

Nine synthesis plants in eastern Bavaria will be integrated into the refinery network over the next four years, including existing ones in Straubing and Sulzbach-Rosenberg. These plants produce a wide range of renewable fuels on a ton scale. Those involved in the project are testing their physical properties, such as lubricity or cold behavior. Application partners from the fields of aviation and shipping as well as vehicles and mobile machinery are demonstrating the suitability of the fuels in real-world operation.

In addition to the TUM and the Fraunhofer Institute for Environmental, Safety and Energy Technology (UMSICHT), the Technology and Support Center (TFZ), the Fraunhofer Institute for Interfacial Engineering and Biotechnology (IGB), and the industrial companies Clariant Produkte GmbH, Martech GmbH, and Volkswagen AG are participating in the project »Synergies through the Integration of Biomass Utilization and Power-to-X in the Production of Renewable Fuels (Synergy Fuels)«.

The German Federal Ministry of Digital Affairs and Transport (BMDV) is funding the project through the »Measures for the Development of Renewable Fuels« funding line with a total of 13.6 million euros.