The Fischer-Tropsch (FT) process yields high-quality hydrocarbon products, including hard waxes used in adhesives, polymer processing, cosmetics, and pharmaceutical applications. Sasol commercially produces these hard waxes using precipitated iron-based catalysts, which are cost-effective compared to cobalt catalysts. With proper chemical promotion, these iron catalysts can produce a high-alpha (C25–40 = 0.95) product slate, suitable for hard wax production. However, iron catalysts are characterised by short reactor lifetimes, waste generation during production, sensitivity to high water partial pressures, and high CO2 production. These issues can be mitigated by using cobalt slurry catalysts. However, cobalt’s limited responsiveness to chemical promotion poses a significant obstacle, making it challenging to achieve hard wax selectivity under the same conditions. This study aims to enhance hard wax selectivity by tuning the active sites of a supported cobalt catalyst for stable operation at high per pass conversion. During activation and FT synthesis, nanoparticulate cobalt mainly exists in two phases: hexagonal close-packed (HCP) and face-centred cubic (FCC). Theoretical simulations indicated that the HCP phase has superior activity due to a greater variety of site arrangements. A reduction-carbiding-reduction (RCR) technique was developed to prepare HCP-rich cobalt catalysts. The performance of HCP-rich and FCC-HCP mixed catalysts (the latter produced by standard H2 activation) were assessed via in-situ magnetometry and lab-scale FT testing. The catalyst preparation and activation methods were scaled up to a pilot level and tested in a 2-inch slurry bubble column to evaluate catalyst hard wax yield, and to generate samples for application testing.
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