Effect Of Promoters And Reaction Conditions On Fe_1-xo-based Iron Catalysts For Fischer-tropsch Synthesis

As the coal is abundant in china, but the oil resource is short, presently, it is very significant to convert coal into liquid hydrocarbon by catalytic reaction.In this paper, the catalytic performances of Fe_1-xO-based fused iron catalyst in fixed bed reactor, as well as influences of promoters on Fischer-Tropsch synthesis have been studied. The influences of CO₂ in Syngas and reaction temperature, pressure, space velocity, H₂/CO ratio were investigated. These catalysts are characterized by means of H₂-TPR, CO-TPD-MS, CO₂-TPD-MS, XRD and so on. Main results from this are as follows:(1) With increasing of MnO dopped into the catalyst, the Syngas (CO+H₂ )conversion and the selectivity of methane decreased, while the selectivity of C₅₊ products and the selectivity of light olefins increased. Also, the lattice parameter of Fe_1-xO increased, distored lattices were formed and changed catalytic performance of the catalysts.(2)The new phase formed on the Fe_1-xO-based catalysts with the addition of Sm₂O₃. It was SmCaAl₃O₇ solid solution, which may cover part ofα-Fe surface and K. It was found that a suitable addition of Sm₂O₃ could suppress the formation of methane and improve the C₅₊ selectivity and obviously increase the olefin/paraffin ratio of C₂-C₄ cut.(3)The strength and amount of basic on the catalyst surface were measured by temperature programmed desorption of carbon dioxide(CO₂-TPD).The results showed the density of basic sites on the catalyst with MnO or Sm₂O₃ was higher than on the catalyst without MnO or Sm₂O₃.(4) The promoter CoO can strengthen the hydrogenation ability of catalyst, and subsequently decreased the olefin/paraffin ratio of C₂-C₄ cut. Compared with other promoters, the effect of CoO on the catalytic performances for Fischer-Tropsch synthesis is not very obvious.(5)It was found that the content of CO₂ in syngas have great effect on syngas conversion, yield and product distributions. When the content of CO₂ in the syngas isn't more than 18.6 mol%, the Syngas (CO+H₂)conversion, the methane and CO₂ selectivity decreased however, the C₅₊ products and WSO selectivity and the yield of C₅₊ products and the olefin/paraffin ratio of C₂-C₄ cut increased. But when the content of CO₂ in Syngas is 23.9mol%, because of equilibrium between CO₂ and CO, little changes were found for the water gas shift reaction. The syngas conversion decreased greatly, the hydrocarbon yield decreased, to some extent the methane selectivity increased and the olefin/paraffin ratio of C₂-C₄ cut decreased. It is one of the effective ways to suppress the methane by introducing CO₂ into the syngas.(6) It showed that lowering the reaction temperature, H₂/CO ratio of feed gas and gas hourly space velocity (GHSV) can reduce the selectivity of methane and increase selectivity of the C₅₊ hydrocarbon. With the increasing of pressure, the methane selectivity firstly decreased, but with the further increasing of pressure the methane selectivity increased, whereas, in the case of C₅₊ hydrocarbon selectivity the change tread is contrary to the methane selectivity. Under the reaction conditions of 583k, 2.0MPa, H₂/CO=1.6, 8600h^-1, the methane and C₅₊ hydrocarbon selectivity are 16.51 and 45.31% respectively, while C₁₊ hydrocarbon yield is 125.53g/m³.