A Novel Metod And Catalyst For Controlling Fischer-Tropsch Synthesis Products Distribution

Fischer-Tropsch synthesis (FTS), directly converting a mixture of carbon monoxide and hydrogen into hydrocarbons and oxy-compound, has attracted much attention because of hydrocarbons can be obtained from coal, natural gas and biomass instead of crude petroleum, and the hydrocarbons from FTS are more environmental friendly. In general, product obtained FTS is a mixed hydrocarbons, which is a broad molecular weigh distribution following the Anderson-Schultz-Flory (ASF) distribution. Consequently, it is important for FTS to control the products selectivity. Published efforts manipulate the FTS products distribution towards light hydrocarbons has mainly focused on the improvement of the secondary reactions by new modified catalysts and process intensification resulting in a narrow product distribution. Therefore, our studies mainly focused on the development of efficient Co/MnOx catalysts favoring light olefins (C2--C4-). In order to investigate the effects of pretreatment, preparation methods, experiment conditions and Zr promoter on catalytic performance of Co/MnOx catalysts for FTS, the obtained catalysts were characterized by XRD, BET-PSD, TG/DSC, SEM, TEM, TPR, DRIFTS and XPS.The Co/MnOx catalysts were developed by modified coprecipitation, which applied different solvent for pretreating cobalt and manganese precursors. In order to study the effects of morphological properties, reducibility and electronic states on catalytic performance for FTS, the obtained Co/MnOx catalysts were characterized by XRD, BET-PSD, TG/DSC, SEM, TEM, TPR, DRIFTS and XPS. According to the results, the structure properties for Co/MnOx-BDO catalyst featured narrow pore distribution, spherical morphology with a clear hierarchy, smaller cobalt particle and homogenous particle distribution, higher electron density for Co compared with that of Co/MnOx-H2O catalyst. The selectivity of light olefins for catalyst prepared by1,4-butyl glycol (BDO) pretreatment is42.2%, which is much higher than26.5%of Co/MnOx-H2O catalyst without pretreatment, and the O/P (olefin/paraffin ratio in C2-C4products) is2.38, which is2times higher than that of Co/MnOx-H2O catalyst.The Co/MnOx catalyst was also prepared by impregnation for purpose of studying the effects of preparation methods on catalytic performance for FTS. On the basis of XRD and TPR results, the catalyst prepared by impregnation is less interaction between Co and Mn as a result of higher electron density for Co, which may improve the effect of Mn in FTS. Therefore, the selectivity of C2=-C4=for Co/MnOx-Imp catalyst is51.6%and O/P is reached3.88, which is2times and4times higher than these of Co/MnOx-Cop catalyst prepared by coprecipitation.The optimal calcination temperature for Co/MnOx catalysts is673K by investigating the effects of preparation methods on catalytic performance for FTS, as well as the CO conversion rate is52.0%, the selectivity of C2=～C4=is43.1%and O/P reached3.04for Co/MnOx-Imp catalyst at the reaction condition (T=523K, P=2.0MPa).The Co/ZrO2/MnOx catalysts were also prepared by coprecipitation method. The effects of Zr promoter on catalytic performance of Co/MnOx catalysts in FTS were investigate. It is found that Zr promoter change the reduction behavior of catalysts, and obviously adjust the FTS product distribution on account of the synergistic effect between cobalt and manganese. Though the FTS products distribution towards heavy hydrocarbons and the CO conversions decrease along with increase ZrO2of content, hydrogenation reaction is suppressed as a result of significant increasing the selectivity of C2=～C4=and O/P. Consequently, the O/P reached as high as3.46for Co/20ZrO2/MnOx catalyst.