Combining Fischer-Tropsch (FT) and Hydrocarbon Reactions under FT Reaction Conditions -- Catalyst and Reactor Studies with Co or Fe and Pt/ZSM-5

Abstract

Fischer-Tropsch synthesis (FTS) offers the potential to produce high-value transportation fuels or petrochemicals from biomass (``2nd generation biofuels"). Primary synthesis products contain mainly n-alkanes and n-alkenes, ranging from methane to high molecular weight waxes. Bifunctional catalysts, as used in petroleum refining, are capable of modifying hydrocarbon molecules. They are characterized by the presence of acidic sites, which provide the hydrocracking and isomerization functions, as well as metal sites, which provide hydro-/dehydrogenation functions, and thus avoid the formation of carbon. The present study addresses the combination of FT synthesis (with Co or Fe catalysts) and hydrocarbon modification reactions. Experimental results obtained in a dual layer configuration with Fe and Co catalysts and Pt/ZSM-5 indicate i) an increase of branched hydrocarbons in the gasoline range (C5-C10), ii) a decrease of alkene and alcohol yields, iii) partial hydrocracking of long chain hydrocarbon molecules leading to higher yields of gasoline and distillates, iv) nearly constant methane selectivity in comparison with the FT catalyst alone, and v) no significant catalyst deactivation. In addition, studies with 1-octene as the model compound were carried out, being mixed with synthesis gas H2/CO or with H2/Ar. The presence of CO decreases reaction rates of hydrogenation and hydrocracking, although all reactions still occur to a significant extent. For the conditions used in this study (1 MPa, 200-300 °C, 4000 kg s/m3), a significant change of hydrocarbon product composition with hydroprocessing catalyst functions added can be observed.