Thermodynamic and Ecological Preselection of Synthetic Fuel Intermediates from Biogas at Farm Sites

Background: Synthetic fuels based on renewable hydrogen and CO2 are a currently highly discussed piece of the puzzle to defossilize the transport sector. In this regard, CO2 can play a positive role in shaping a sustainable future. Large potentials are available as a product of biogas production, however occurring in small scales and in thin spatial distributions. This work aims to evaluate suitable synthetic fuel products to be produced at farm sites.
Methods: A thermodynamic analysis to assess the energetic efficiency of synthesis pathways and a qualitative assessment of product handling issues is carried out.
Results: Regarding the technical and safety-related advantages in storage, liquid products are the superior option for fuel production at decentralized sites. Due to the economy of scale, multi-stage synthesis processes lose economic performance with rising complexity. A method was shown which covers a principle sketch of all necessary reaction, separation steps, and all compression and heat exchanger units. The figures showed that methanol and butanol are the most suitable candidates in contrast to OME3-5 for implementation in existing transportation and fuel systems. These results were underpin by a Gibbs energy analysis.
Conclusions: As long as safety regulations are met and the farm can guarantee safe storage and transport, farm-site production for all intermediates can be realized technically. Ultimately, this work points out that the process must be kept as simple as possible, favoring methanol production at farm site and its further processing to more complicated fuels in large units for several fuel pathways.