Aviation industry aims at reducing the carbon footprint by 50% by 2050 as compared to that in 2005. Currently, aviation fuel is produced with the help of fossil fuels .
Aviation fuel is a blend of hydrocarbons, namely kerosene type (Aviation fuel A) and naptha type (Aviation fuel B), to name a few. The composition of the aviation fuel depends on the performance specification. In order to shift from fossil fuels to renewable energy sources, Power-to-Liquid (PtL) technology can facilitate this transition. For the production of aviation fuel using PtL pathway, two main pathways are available, namely Fisher-Trospsh (FT) synthesis and Methanol (MeOH) synthesis [1,2].
Power-to-Liquid technology uses excess electricity to produce chemicals. For instance, excess wind energy in Denmark can be sent to an electrolysis cell where water is electrolyzed to produce hydrogen. To produce aviation fuel, a mixture of syngas (CO+hydrogen) is needed. For this, hydrogen produced could be mixed with carbon dioxide thereby producing aviation fuel by downstream processing.
The PtL conversion pathway consists of producing hydrogen through electrolysis of water along with availability of renewable carbon dioxide and conversion in order to subsequently convert the mixture so obtained into aviation fuel.
Figure 1: Schematic of PtL pathway for Aviation fuel production
One of the prospective PtL technologies is Solid Oxide Electrolysis Cells (SOECs), wherein carbon dioxide and hydrogen can be converted simultaneously to produce syngas at temperatures around 700-750 C. In addition, based on the operating parameters aviation fuel and/or methane/methanol can be produced already in the SOEC. This technology is promising owing to its very high efficiency and flexibility of fuels being produced.
The reactions taking place in the SOEC are as follows:
Figure 2: An electrolysis cell in operation
During co-electrolysis, a mixture of steam and carbon dioxide is fed to the fuel electrode of the SOEC and a mixture of hydrogen and CO is obtained. Downstream conversion into hydrocarbons such as methane requires lowering of temperature along with a pressurized system. In addition, SOECs are accompanied with the advantage of high levels of waste heat which can be integrated in the system. On the other hand, long-term stability of the materials due to degradation is a drawback of such cells. Demonstration projects have been carried out previously on co-electrolysis using SOECs and using FT synthesis after syngas production is expected to attain a system efficiency of 66% by 2050 .
Conversion of syngas into chemicals for transportation
Figure 3: Schematic of methane production using SOEC
One of the important chemicals in the context of transportation is methanol which is used for the production of olefins, dimethyl ether and liquid fuels . Additionally, it is a liquid energy carrier. Methanol can be produced via syngas as:
Another important chemical produced visa Power-to-X is methane which contributes overall to heat, electricity and further chemical production. It is accompanied by the ability to lower Green House Gas emission . Methanation can be described using the following reaction:
Furthermore, aviation fuel,which is mainly kerosene or naphtha, can be produced using syngas visa Fishcher-Tropsch synthesis. The following reactions can be optimized depending on the desired hydrocarbon production .
In summary, production of hydrocarbons and aviation fuel using syngas produced by SOECs can lower the carbon dioxide footprint and can be integrated in the existing infrastructure.
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Schmidt, P. & Weindorf, W. Power-to-Liquids: Potentials and Perspectives for the Future Supply of Renewable Aviation Fuel. 1–36 (2016).
Fateh, S. Master of Science Thesis Exergy evaluation of jet fuel and ammonia as fuel alternatives Sana Fateh. (2015).
Power-to-x technologies are available – Global Alliance Powerfuels.
de Vasconcelos, B. R. & Lavoie, J. M. Recent advances in power-to-X technology for the production of fuels and chemicals. Front. Chem. 7, 1–24 (2019).
Yde, L., Rabbani, A., Wenzel, H. & Ras, K. D. Sustainable Transportation in a future 100 % Renewable Danish Energy System. (2018).