钾助剂对F-T合成铁基催化剂浆态床反应性能的影响

Effect of Potassium Promoter on Reaction Performance of Iron-Based Catalyst for Fischer-Tropsch Synthesis in Slurry Reactor

采用连续共沉淀与喷雾干燥成型技术相结合的方法制备了不同K助剂含量的系列微球形Fe/Cu/K/SiO2 催化剂 (K/Fe质量比为 0 0 10～ 0 0 5 8) ,采用低H2 /CO比的合成气于典型的工业反应条件下 (5 2 3～ 5 33K ,1 5MPa,H2 /CO =0 6 7)进行了长期的浆态相F T合成 (FTS)反应性能评价 .结果表明 :K助剂的添加可增大催化剂活性 ,提高C5+ 、总的烯烃、有机含氧化合物及CO2 的选择性 ,并促进水煤气变换反应 ,但过高的K含量易使催化剂反应稳定性变差 .适中的K含量为K/Fe =0 0 30 ,该K含量催化剂的 6 6 0h浆态床FTS反应性能评价结果显示 ,该催化剂具有较高的催化活性和C5+ 选择性 ,产物分布较合理 ,长期运行稳定性好 ,反应后卸载下的催化剂形貌观测表明该催化剂还具有较好的抗磨损性能 .除K助剂的化学效应起主导作用外 ,催化剂的织构性质尤其是孔结构可能对催化剂的催化性能也有一定的影响 ,并引起K/Fe =0 0 4 5时铁基催化剂对FTS产物选择性和水煤气变换反应活性的部分调变 .

The potassium-promoted precipitated Fe/Cu/K/SiO 2 catalysts with K/Fe mass ratio of 0.010～0.058 for Fischer-Tropsch synthesis (FTS) in a slurry reactor were prepared by the combination of continuous co-precipitation and spray-drying technology. The catalyst exhibits good spherical morphology of about 14 μm in average diameter. The surface area decreases and the pore size and pore volume increase with the increase in potassium content in the as-prepared catalyst, but when the potassium content further increases to K/Fe=0.058, the surface area of the as-prepared catalyst increases and its pore size and pore volume decrease due to the possible interaction between potassium and SiO 2 binder. The overall reaction performance of the catalyst for FTS was investigated in a stirred tank slurry reactor under reaction conditions (523～533 K, 1.5 MPa, H 2/CO=0.67) representative of industrial practice using CO-rich synthesis gas. The addition of potassium promoter can improve the FTS activity, enhance the product selectivity for C 5+ , oxygenates and total olefins, promote water-gas-shift reaction and increase CO 2 selectivity, but excessive addition of potassium promoter results in an acceleration of the deactivation rate. The FTS product selectivity and the reaction activity for water-gas-shift over the iron-based catalyst with K/Fe=0.045 changes in some extent compared with the other two catalysts with higher potassium content of K/Fe=0.030 and 0.058 due to the catalyst textural properties, especially pore size, besides the dominant chemical effect of the potassium promoter. The potassium-promoted iron-based catalyst with K/Fe=0.030 shows high FTS activity and C 5+ selectivity, preferable product distribution and perfect run stability in 660 h time on stream. The catalyst also exhibits high attrition resistance by the observation of the morphology of the unloaded catalyst used for 660 h.