FISCHER-TROPSCH SYNTHESIS IN A SLURRY REACTOR - PRETREATMENT EFFECT STUDIES

Effects of pretreatment procedures, using H-2, CO, and syngas (H-2/CO = 0.7) as reductants, on the performance (activity, selectivity, and s tability with time) of a precipitated iron catalyst (100 Fe/5 Cu/4.2 K /16 SiO2 on a mass basis) during Fischer-Tropsch (FT) synthesis were s tudied in a stirred tank slurry reactor. The syngas conversion varied between 70 and 87% during the first 300 h on stream at baseline proces s conditions (260 degrees C, 1.48 MPa, 1.5 L(STP)/g-cat/h, H-2/CO = 0. 67), and the catalyst deactivation rate was less than 1% per day in al l three tests, The catalyst selectivity did not vary markedly with tim e on stream. The reactor space-time-yield increased by 32-47% in all t hree tests, upon increasing the reaction pressure and gas space veloci ty to 2.17 MPa and 2.2 L(STP)/g-cat/h, respectively. The catalyst deac tivation rate increased and the water-gas-shift (WGS) activity decreas ed during testing at the higher reaction pressure. This resulted in a slight decrease of secondary olefin hydrogenation and isomerization re actions in all three tests, and in a shift of hydrocarbon distribution toward higher molecular weight products (CO pretreated catalyst). Tot al olefin content decreased in the following order with the pretreatme nt conditions: CO > syngas > H-2, whereas the olefin isomerization act ivity was essentially independent of the pretreatment conditions emplo yed, Methane selectivity varied with the pretreatment conditions in th e following order: CO < H-2 < syngas.