Thermodynamic analysis and experimental verification of bi-reforming of industrial off-gases as a pre-step for e-fuel generation

Abstract

E-fuels are highly necessary to decarbonize transportation, especially in sectors such as heavy-duty transportation or aviation, which require high energy density fuels. Fischer–Tropsch (FT) synthesis can be used to produce these carbon-neutral fuels, using syngas as the feedstock. Instead of utilizing carbon dioxide produced by direct air capture facilities in extremely low amounts and in an energy-intensive manner, it is more favorable to extract it from industrial processes and other off-gases, where it is available in high amounts. An innovative solution for the conversion of off-gases to syngas is high-temperature solid oxide electrolysis (SOE) in co-electrolysis mode. However, off-gases can contain hydrocarbons, which can reduce the lifetime of cells in electrolyzers. To overcome this problem, bi-reforming is employed as a preliminary stage to convert hydrocarbons into syngas. This study considers three pathways for production of e-fuels from off-gases: (1) bi-reforming, co-electrolysis, FT synthesis, (2) bi-reforming, FT synthesis, and (3) direct application of syngas as fuel from bi-reforming. The reliability and lifetime of reforming reactors depend on specific operating conditions, which vary according to the path in question. The objective of this study is to analyze the thermodynamics of the reforming processes in order to identify optimal operating parameters and to prevent undesired reactor degradation. Accordingly, an equilibrium-based calculation method was developed and experimentally confirmed in a reforming reactor utilizing distinct catalysts. To mitigate the risk of carbon deposition and, consequently, extend the catalyst’s lifespan, the formation of graphite and carbon nanofibers is considered in equilibrium calculations.