Supercritical phase Fischer—Tropsch synthesis reaction: 3. Extraction capability of supercritical fluids

Abstract

A Fischer-Tropsch (FT) synthesis reaction was conducted in supercritical fluid media using conventional FT catalysts such as cobalt, ruthenium and iron catalysts. Waxy products were effectively extracted in situ from the catalyst bed. Among several supercritical solvents, n-hexane gave the highest extraction capability and the highest reaction rate. It was found that only 2 wt% of the total hydrocarbon product remained on the catalyst in the supercritical phase reaction, while 10–25 wt% of the product remained in the gas phase reaction. The partial pressure of the solvents could be reduced to one-third of the critical pressure while maintaining effective extraction capability for wax in the case of n-hexane solvent. It was also found that the olefin content in the hydrocarbon was highest for supercritical phase reaction in three reaction phases (gas, liquid and supercritical). This was attributed to the well-balanced extraction of primary product olefins from the catalyst and their quick diffusion.