Pretreatment effect studies with a precipitated iron Fischer-Tropsch catalyst in a slurry reactor

Effects of pretreatment procedures, using H-2, CO, and syngas (H-2/CO = 2/3 ) as reductants, on the performance (activity, selectivity and stability wi th time) of a precipitated iron catalyst (100 Fe/3 Cu/4 K/16 SiO2 on a mass basis) during Fischer-Tropsch (F-T) synthesis were studied in a stirred ta nk slurry reactor. The catalyst reduced with hydrogen to mag netite only re ached its steady state activity faster than the catalyst partially reduced to metallic iron (2 h versus 4 h). Activity of the catalyst partially reduc ed to metallic iron under mild reduction conditions (250 degrees C for 4 h) was about 40% higher than that of the catalyst reduced at 280 degrees C fo r 8 h. The steady state activities of the catalyst reduced to magnetite onl y (240 degrees C for 2 h and of the unreduced catalyst were the same as tha t of the catalyst partially reduced to metallic iron at 280 degrees C for 8 h. Initial activity of the CO activated catalyst (280 degrees C for 8 h) w as relatively low, and increased with time, reaching a steady state level a t about 50 h on stream. However, its steady state activity was the highest among all the pretreatment procedures used. Methane and gaseous hydrocarbon selectivities on the hydrogen reduced and the unreduced catalyst increased with time before reaching a steady state, whereas the opposite trend was o bserved on the CO and the syngas (280 degrees C for 8 h) activated catalyst s. The catalyst which was initially in an oxide form (unreduced catalyst an d catalyst reduced to magnetite) had lower gaseous hydrocarbon selectivitie s than the catalyst partially reduced to alpha-Fe. The unreduced catalyst h ad the lowest gaseous hydrocarbon selectivity, whereas the syngas activated catalyst had the highest. Total olefin and I-olefin contents decreased in the following order: CO activated approximate to unreduced > syngas > H-2 r educed. (C) 1999 Elsevier Science B.V. All rights reserved.