Promoter effects on precipitated iron catalysts for Fischer-Tropsch synthesis

Abstract

The effects of potassium and copper promotion on the activity and selectivity of precipitated iron catalysts for Fischer--Tropsch synthesis (FTS) were studied in a fixed bed reactor at 1.48 MPa and 235--265{degrees} C using synthesis gas with a H{sub 2}/CO = 1 molar feed ratio. It was found that both potassium and copper increase the catalyst activity for FTS and the water gas shift reaction. Potassium promotion ({approximately} 0.2--1 wt %) results in an increase in the average molecular weight of hydrocarbon products and suppression of secondary reactions (olefin hydrogenation and isomerization of 1-alkenes to 2-alkenes). Copper promotion ({approximately} 3 wt %) has a similar effect on the hydrocarbon distribution, but it enhances slightly the secondary reactions. The activity of doubly promoted (100 Fe/3 Cu/{ital x}K, {ital x} = 0.2 or 0.5) catalysts was higher than that of singly promoted catalysts and was independent of potassium loading, whereas their selectivity behavior was strongly influenced by their potassium loading. Product selectivities on the 100 Fe/3 Cu/0.2 K catalyst were similar to those of the 100 Fe/3 Cu catalyst, whereas selectivities of the 100 Fe/3 Cu/0.5 K catalyst were similar to those obtained in tests with the 100 Fe/0.5 K catalyst.