Single-Stage Fischer–Tropsch Synthesis and Hydroprocessing: The Hydroprocessing Performance of Ni/ZSM-5/γ-Al₂O₃ under Fischer–Tropsch Conditions

The single-stage combination of Fischer–Tropsch synthesis and hydroprocessing without intermediate product fractionation has been studied using Co/Al2O3 as FT and Ni/ZSM-5/γ-Al2O3 as HP catalysts either in dual-layer arrangement or in physical mixture. Furthermore, the performance of the hydroprocessing catalyst under Fischer–Tropsch conditions was investigated in more detail in the gas phase hydroprocessing of n-dodecane in the presence of CO and H2O vapor, mimicking 69.4% Fischer–Tropsch conversion. All experiments were conducted at 10 bar and varying temperatures and residence times. In the gas phase hydroconversion of n-dodecane, CO and H2O showed a strongly inhibiting effect. The disturbance of the hydrogenation function by CO is most detrimental because enduring deactivation by coke formation is initiated. In combined single-stage experiments, the formation of a liquid hydrocarbon film in the FT reactions reduces the impact of the inhibitors to a large extent. Here, the hydroprocessing performance is mostly determined by the ratio H2/hydrocarbons. In both single-stage configurations, lower C numbers and larger isomer fractions as compared to the FT reference evidenced the activity of the HP catalyst. In physical mixture configuration, however, the HP catalyst benefits from the higher H2/hydrocarbon ratios along the complete catalyst bed, resulting in a more efficient reduction of C21+ hydrocarbons and high isomer fractions in a broader range of carbon numbers.