Effect of potassium promoter on reaction performance of iron-based catalyst for Fischer-Tropsch synthesis in slurry reactor

The potassium-promoted precipitated Fe/Cu/K/SiO2 catalysts with K/Fe mass ratio of 0.010similar to0.058 for Fischer-Tropsch synthesis (FTS) in a slurry reactor were prepared by the combination of continuous co-precipitation and spray-drying technology. The catalyst exhibits good spherical morphology of about 14 mum in average diameter. The surface area decreases and the pore size and pore volume increase with the increase in potassium content in the as-prepared catalyst, but when the potassium content further increases to K/Fe = 0.058, the surface area of the as-prepared catalyst increases and its pore size and pore volume decrease due to the possible interaction between potassium and SiO2 binder. The overall reaction performance of the catalyst for FTS was investigated in a stirred tank slurry reactor under reaction conditions (523 similar to 533 K, 1.5 MPa, H-2/CO = 0.67) representative of industrial practice using CO-rich synthesis gas. The addition of potassium promoter can improve the FTS activity, enhance the product selectivity for C5+, oxygenates and total olefins, promote water-gas-shift reaction and increase CO2 selectivity, but excessive addition of potassium promoter results in an acceleration of the deactivation rate. The FTS product selectivity and the reaction activity for water-gas-shift over the iron-based catalyst with K/Fe 0.045 changes in some extent compared with the other two catalysts with higher potassium content of K/Fe 0.030 and 0.058 due to the catalyst textural properties, especially pore size, besides the dominant chemical effect of the potassium promoter. The potassium-promoted iron-based catalyst with K/Fe = 0.030 shows high FTS activity and C5+ selectivity, preferable product distribution and perfect run stability in 660 h time on stream. The catalyst also exhibits high attrition resistance by the observation of the morphology of the unloaded catalyst used for 660 h.