Synthesis and testing of mixed magnetite and iron carbide nanocatalysts for enhanced slurry phase fischer tropsch synthesis.
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2018
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Abstract
This study focused on the preparation and performance testing of iron-based nanocatalysts. The performance evaluation for slurry phase Fischer – Tropsch reaction was carried out in a bench-scale compact reactor. The investigation was focused on determining whether the product yield and hydrocarbons distribution from the processing of syngas can be significantly improved through the coupled use of unsupported magnetite and preformed iron carbide nanocatalysts. Iron oxides and iron carbide nanoparticles (NPs) are believed to be the active phases in the Fischer–Tropsch reaction. In this work, effects of nanoscale magnetite and iron carbide particles on the rate, yield, selectivity and product distribution of the Fischer–Tropsch Synthesis (FTS) were investigated in a bench scale slurry phase reactor. Nanoparticles were prepared separately and mixed in different proportions to obtain the required catalysts mixtures. Magnetite catalysts were prepared using a modified solvothermal synthesis route while Iron carbide nanocatalysts were prepared using three (3) different biopolymer routes in which an iron precursor was suspended in the biopolymer matrix. The resulting product was subsequently exposed to a thermal degradation step in a box furnace under a constant flow of nitrogen to form carbides. Structural characterization of the catalysts was performed by TEM, SEM, EDX and XRD analyses. Particle sizes of both magnetite and iron carbide nanoparticles as determined from XRD patterns (Scherrer equation) and TEM images was about 8.07 and 13 nm, respectively. Catalyst evaluation was conducted in a 600ml slurry phase stainless steel Parr reactor and the system performance was classified according to methane selectivity, C2-C4 selectivity and the yield of C5+ hydrocarbons. The results revealed that, the addition of preformed iron carbide nanocatalysts resulted in better yields of higher range hydrocarbons. A C5+ hydrocarbons selectivity of 82% was recorded with a catalysts mixture containing 50% iron carbides. This was accompanied by a minimum methane selectivity of 6.9%.
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Masters Degree (Chemical Engineering). University of KwaZulu-Natal. Durban, 2018.