Activation studies with an iron Fischer-Tropsch catalyst in fixed bed and stirred tank slurry reactors

A precipitated iron catalyst (100 Fe/5 Cu/4.2 K/25 SiO2 on a mass basis) was tested in a fixed bed reactor and a stirred tank slurry reactor under the same process conditions (250 degrees C, 1.48 MPa, 2 L(STP)/gcat . h, H-2:CO=2:3). Two different pretreatment procedures were employed (hydrogen reduction at 220 degrees C and carbon monoxide activation at 280 degrees C) in each of the two reactor types. In the stirred tank slurry reactor tests the activity (based on an apparent first order reaction rate constant) of the carbon monoxide pretreated catalyst was about 25% higher than that of hydrogen reduced catalyst, due to incomplete reduction of the latter. In all tests the catalyst selectivity changed slowly with time on stream. Hydrocarbon distribution shifted toward lower molar mass products, and secondary reactions (l-olefin hydrogenation, isomerization and readsorption) increased with time. The secondary reactions were the most pronounced on the hydrogen reduced catalyst in the fixed bed reactor.