In order to achieve the Federal Government's high CO2 avoidance targets by 2050, increased efforts to introduce renewable energy sources are also needed in the transport sector, which currently accounts for just under 20% of direct CO2 emissions. The potential of renewable biofuels is limited, among other things, because of land scarcity and competition with food production, so "e-fuels" are also considered, which are accessible on the basis of hydrogen from renewable energy fed electrolysis and renewable carbon sources. CO2 can also be used as a feedstock, which can come from industrial plants (e. g. steel or cement industry), biomass (e. g. biogas) or directly from the atmosphere. Liquid synthetic hydrocarbons as fuels offer the advantage that they are compatible with the existing infrastructure for storage, distribution and enjoy high consumer acceptance. This can be used in the syntheses (catalysts, process conditions) to develop tailor-made "designer-fuels" which, in addition to reduced CO2 footprint, also have lower pollutant emissions (NOx, particles, etc.) and better application properties than the established crude oil-based fuels. Platform chemicals with a high tonnage can also be synthesized from CO2 and regenerative electricity which will make a significant contribution to achieving the CO2 avoidance targets.
An important aspect of the conversion of renewable electricity into chemical products is the ability to store and utilize large amounts of energy. For example, 100000 m3 of diesel have an energy content (heating value) of about 1 TWh. The total electricity yield from wind power and photovoltaics in Germany in 2013 was 83 TWh. This was offset by a fuel consumption equivalent to 709 TWh. The German steel industry emits approx. 65 million tonnes of CO2 per year, which means that 21 million tonnes of pure stoichiometric fuel could be synthesised (~250 TWh). In addition, there are large quantities of CO2 from other industrial processes (e. g. 18 million t/a from cement production) as well as from biogas (approx. 8 million t/a) and other decentralised sources and finally CO2 from the atmosphere. The figures show that e-fuels made from CO2 have great potential in terms of quantity to reduce CO2 emissions by substituting fossil fuels. However, the cost-effectiveness of the conversion chain from electricity and CO2 to fuels based on established technologies is not given today. Other challenges include the efficiency of converting electrical energy into chemical energy and the long-term stability or compliance with the required product quality under dynamic operating conditions.
IMVT plans to set up an integrated P2X process chain using the example of the production of synthetic kerosene and diesel as a self-sufficient plant based on new Fischer-Tropsch technologies as part of work package 1 in cluster B2. This involves the direct material and thermal combination of CO2 capture from the atmosphere, high-temperature co-electrolysis, Fischer-Tropsch synthesis and hydrogenating cleavage or isomerization. The CO2 capture process is adjusted to the subsequent steps (cycle times, intermediate buffering, energy input into the desorption process) to optimize system efficiency and dynamic capability. At the end of the first funding phase, 25-100 l of product are to be made available for distillation or engine tests.
Together with the Engler Bunte Institute (EBI) at KIT, cluster B2 is also focusing on the development of an integrated condensing concept for small-scale plants for methanization in decentralized LNG production and the energetic evaluation of the process chain using simulations. Parts of the process chain are being set up as part of the Energy Lab 2.0 investment project. In addition to a pilot plant for methanisation, this includes a PEM electrolysis plant with a hydrogen pressure tank as intermediate storage for hydrogen supply and, as a carbon source, optionally biogenic synthesis gas from the bioliq plant or CO2 from a pressure tank. Work package 2 in the framework of the Kopernikus project P2X / Cluster B2 is therefore limited to the validation of new reactor concepts for methanization on pilot plant scale (TRL 5) and the assessment of the integrated liquefaction using simulations based on experimental data on methanization. After 30 months, benchmarking is carried out in comparison with conventional methanisation reactors and a concept evaluation of decentralised LNG production. IMVT is developing a reactor for 50 m3/h H2/CO2 feed with evaporation cooling. The process steam can be used in the future for an upstream high-temperature electrolysis.
Researchers from the Institute for Micro Process Engineering at KIT have developed together with the partners INERATEC GmbH, sunfire GmbH, Climeworks AG and German Aerospace Center (DLR) within the Kopernikus-Project "Power-to-X" a concept for an integrated plant which can generate synthetic hydrocarbons as easily storable chemical energy carriers from renewable power and carbon dioxide captured from the ambient air. Target product are kerosene fractions for use in aviation. The aim is a reduction of the carbon dioxide emissions in this important sector.