日本ゼオライト学会　刊行物 Publication of Japan Zeolite Association

Fischer-Tropsh Synthesis (FTS) is an effective method to produce liquid fuels from syngas. The liquid fuels contain principally normal paraffins, which are suitable for diesel fuels, but not for gasoline. In general, cetane number of the normal paraffins is high, but their octane number is low. On the other hand, isoparaffins have high octane number. Thus it is desired to produce isoparaffines from syngas at one step.

In order to produce isoparaffin at one step, an FTS catalyst Co/SiO₂ was hybridized with zeolite ZSM-5. It is expected that since the wax produced on the FTS catalysts will be in situ decomposed by the zeolite in the hybrid catalysts, the lifetime of hybrid FTS catalysts becomes extremely longer. CO conversions of both FTS and hybrid catalysts were 100%. The FTS products from the hybrid catalyst were mainly isoparaffins, and became very lighter that those from conventional FTS catalysts. Hydrocarbons with over C13 disappeared. In order to activate hybrid FTS catalyst further, Pd/SiO₂ was added to the hybrid catalyst. The lifetime of this kind of three-component hybrid catalyst, Co/SiO₂+ZSM-5+Pd/SiO₂ became much longer. Even after 100 h, the catalysts were not deactivated and the hydrocarbon distributions were the same. The distributions of the hydrocarbons concentrared much more on Co/SiO₂+ZSM-5+Pd/SiO₂, indicating acidity of the zeolite was strengthened by spillover hydrogen form Pd/SiO₂. In addition, two-stage reaction was conducted. At the first stage FTS was carried out using hybrid catalyst Co/SiO₂ +ZSM-5 and at the second stage the FTS products were hydrogenated, hydrocracked and isomerized with additional hydrogen. The obtained hydrocarbons contained lighter isoparaffins under C8.

These results indicate that the hybrid catalysts containing ZSM-5 have good peformance for the production of isoparaffin directly.