Coupling the high-temperature Fischer–Tropsch synthesis and the skeletal isomerization reaction at optimal operation conditions in the Power-to-Fuels process route for the production of sustainable aviation gasoline

Abstract

In this study we presented a concept process route for the production of sustainable aviation gasoline and investigated experimentally the high-temperature Fischer–Tropsch (HTFT) synthesis and the first upgrading step, the skeletal isomerization reaction, both independently and coupled. The influence of the side products of the HTFT synthesis on the stability of the isomerization catalyst and the product distribution represents the main challenges of the coupled operation. While the individual steps of Power-to-Fuels processes are well investigated, there are not many studies on their coupled operation. In this work, the operating conditions of both reactions were firstly optimized independently from each other. Targeting the maximisation of the C₃–C₅ olefin fraction, especially butene, preferably at high CO conversion, the optimal operating parameters for HTFT synthesis were 300 °C, 20 bar(g), H₂ : CO = 2 and high GHSV. Targeting high isobutene selectivity at high 1-butene conversion, the optimal operating parameters for the isomerization reaction were 400 °C and atmospheric pressure. To investigate the coupling of both reactions, the gasous HTFT products together with the unconverted feed were separated from the liquid and solid products and fed into the isomerization reactor. The feed was diluted with N₂ at 35.7 vol% and 8 vol% and the temperature of the isomerization reaction was increased from 300 °C to 400 °C. The coupling was run in steady-state at 400 °C and both 35.7 vol% and 8 vol% N₂ dilution up to 65 h, while an operation temperature of 300 °C led to catalyst deactivation within the first hours.