Lab-Scale Demonstration of By-Product Utilization in an Integrated Power-to-Liquid Process Applying Co-Electrolysis

High-temperature electrolysis has been shown to be a promising technology for the so-called Power-to-Liquid processes. However, to reach the full potential of high-temperature electrolysis regarding process efficiency, by-product recirculation and heat utilization are of vital importance. Herein, the possibility to perform internal reforming of by-products within the electrolyzer to again obtain syngas can be advantageous. This mode of operation is demonstrated in electrolysis lab tests on cell and stack level, showing the ability to convert methane. However, the recycled gaseous product stream from a Fischer-Tropsch synthesis is much broader in its composition and longer-chained hydrocarbons may lead to issues such as carbon formation, thermal stress, and catalytic stability. Herein, the Power-to-Liquid process, consisting of high-temperature co-electrolysis and Fischer-Tropsch synthesis, is implemented in a laboratory-scale plant to study the possibility of internally reforming by-products within the electrolyzer. Herein, the importance of by-product recirculation is highlighted by the results of the investigation, as it allows for a significant increase in carbon efficiency and subsequently in energetic efficiency, but especially the potential of high-temperature electrolysis for integrated process concepts applying internal reforming.