A design and development of iron ore Fischer Tropsch catalyst

Abstract

The global community has accepted Fischer Tropsch synthesis as one of the sustainable pathways to transportation fuels and chemicals due to the ever-depleting reserves of fossil fuels and its detrimental impact on the environment. However, the high capital investment and operating expenses associated with this technology have hampered its ability to compete with conventional petrochemicals. Some of the operating costs emanate from the choice of catalyst precursors and operational problems, which could lead to plant shutdowns. In recent times, few efforts have been made to explore cheaper FT catalysts to reduce operational costs, but the mechanical strength of solid FT catalysts, especially for pilot-scale fixed bed operations is not well represented in open literature. As a result, there is a high prevalence of mechanical failure of solid FT catalysts in pilot fixed-bed applications. In this study, we propose a scalable, Fischer Tropsch iron ore catalyst that is mechanically suited for fixed bed reactors to help address this issue. The catalyst development of the proposed iron ore catalyst involved the slurry phase impregnation of the precursor with copper and potassium and then shaping into spherical pellets with mass additions of 10%, 15% and 20% of bentonite(binder) on a rotating drum. There afterwards, the mechanical strength of each pelletized catalyst was tested using the single pellet crushing testing method (ASTM D 4179). These results were compared to the crushing strength of commercial spherical alumina to ascertain their suitability for fixed bed reactors. The most robust solid catalyst was the 10% binder iron ore pellets which recorded a single pellet crushing strength of 1833 kPa and was more than three times that of commercial spherical alumina and thus deemed apt for fixed bed reactors. A unique statistical approach was used to study the mechanical strength of the various binder combinations due to scattering in single pellet crushing strength data. The analysis revealed that the 10% binder iron ore pellets were most suited for laboratory FT runs and thus was tested for its catalytic performance. The FT runs revealed that the 10% binder iron ore catalyst had a CO conversion of 72.1 % and comparable to other similar iron-based FT catalysts reported in the literature. The proposed catalyst also showed a CH5+ selectivity of 83.2%, which was comparable the ones reported by other researchers. These findings provide a simple and cost- effect approach to upscale laboratory-scale FT catalyst designs to pre-emp its performance in pilot or industrial scenarios.