The single-stage combination of FischerÀTropsch synthesis and hydroprocessing without intermediate product fractionation has been studied using Co/Al 2 O 3 as FT and Ni/ZSM-5/γ-Al 2 O 3 as HP catalysts either in dual-layer arrangement or in physical mixture. Furthermore, the performance of the hydroprocessing catalyst under FischerÀTropsch conditions was investigated in more detail in the gas phase hydroprocessing of n-dodecane in the presence of CO and H 2 O vapor, mimicking 69.4% FischerÀTropsch conversion. All experiments were conducted at 10 bar and varying temperatures and residence times. In the gas phase hydroconversion of n-dodecane, CO and H 2 O 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 H 2 /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 H 2 /hydrocarbon ratios along the complete catalyst bed, resulting in a more efficient reduction of C 21+ hydrocarbons and high isomer fractions in a broader range of carbon numbers.

According to various published process studies, efficiencies of biomass-to-liquid conversion may be expected in the range of 30−50% for chemical energy and 25−45% for carbon recovered in hydrocarbon products. Strategies for improving carbon conversion efficiency include minimizing O2 consumption in gasification and increasing synthesis selectivities and CO2 conversion during synthesis with hydrogen added from external sources. CO2 conversion during Fischer−Tropsch (FT) synthesis is possible with a CO/CO2 shift-active catalyst, if sufficient H2 is available. A combined experimental and modeling study has shown that equilibrium and kinetic limitations involved can be decreased by means of a membrane, which allows for in situ removal of H2O from the catalyst bed. The results help to quantify the effects of H2O permeability, permselectivities, and reaction conditions and help to indicate directions for further membrane development. This paper collects yield and efficiency estimates for FT synfuel production from biomass feedstocks. Limiting factors for the heating value output are discussed, and a conceptual/experimental study is presented that addresses in situ H2O removal by a hydrophilic membrane, aiming at maximizing carbon efficiency.

No abstract