Supercritical phase process for direct synthesis of middle iso-paraffins from modified Fischer–Tropsch reaction

A new concept on the direct synthesis of middle iso-paraffins through the modified supercritical Fischer–Tropsch (FT) reaction was proposed and experimentally demonstrated with the combination of Co/SiO2 and palladium-supported β zeolite (Pd/β) catalysts both in one-stage and two-stage fixed-bed reaction systems. Depending on the reaction conditions, the selectivity of C4+ iso-paraffins mostly in gasoline range was 60–80% due to hydrocracking and hydro-isomerization function of Pd/β. Irrespective of reaction conditions, the hydrocarbons produced from FT reaction were preferentially hydro-converted over Pd/β catalyst while the supercritical solvent of n-hexane could only be slightly hydro-converted under severe conditions. The production of iso-paraffin in two-stage process was tested for 100 h without observable deactivation by feeding additional hydrogen in lower reactor, which is ascribed to the inhibition of coke deposition over Pd/β as revealed from TG analysis of the used catalysts.