(175b) Fischer-Tropsch Synthesis: Product Distribution, Operating Conditions, Iron Catalyst Deactivation and Catalyst Speciation

Laboratory experiments conducted for long time on stream (TOS: 14 350) provides information on Fischer Tropsch Synthesis (FTS) that is representative of the industrial scale operations. Operation conditions that deliver desirable conversion and product distribution were investigated. Low gas hourly space velocity (GHSV) gave the highest conversion of 20.97 % with the highest C₅₊ selectivity achieved was 59.77%, which was obtained at the highest GHSV level. A one-way ANOVA, followed by a Post- Hoc Test Bonferroni correction, indicated a significant difference in response to GHSV with P(T<=t) two tail values ranging from 1.5 x 10^-4 to 2.7 x 10^-35. The optimum condition for paraffin production is high pressure and low GHSV: in our experiments this corresponded to 20.85 bar (abs): 648 h^-1. Conversely, olefins production is favoured low pressure and low GHSV (1.85 bar (abs): 648 h^-1). C₅₊ production was favoured at high GHSV (2592 h^-1) and was very sensitive to GHSV, as the sensitivity to C₅₊ products dropped sharply when the GHSV decreased to low values (from 1296 h^-1 to 648 h^-1); furthermore, the selectivity to c5+ was found to be independent of pressure. The pressure effect on selectivity is complex and selectivity toward overall gaseous (Paraffin + Olefin) hydrocarbons and C₅₊ does not seem to be significantly affected by variations in pressure. Thermodynamics suggest that the dissociation of CO via the water gas shift (WGS) is more feasible than that of the Boudouard reaction water gas shift (WGS). Our findings may have useful implication for the design of a mobile small-scale biomass/waste to liquid process that would last for period similar to that of an industrial plant.