(22b) Fischer-Tropsch Synthesis Using H2/CO/CO2 Syngas Mixtures: A Comparison of Product Distribution for Iron and Cobalt Based Catalysts

Fischer-Tropsch synthesis (FTS) using H₂/CO/CO₂ syngas mixtures over cobalt- and iron-based catalysts were carried out in a fixed-bed micro reactor. The data show that: (1) For CO₂-rich feeds, most of the products are short chain paraffins with high methane selectivity, and the product distribution follows a typical one-alpha Anderson-Schulz-Flory (ASF) distribution with low alpha values; (2) For CO-rich feeds, the product composition shifts to an FT type product (mainly long chain hydrocarbons), and follows a two-alpha ASF distribution with high alpha values.

The growth factors for paraffin, olefin and oxygenate produced by means of FTS differ. We therefore introduce a new product distribution model entailing a combination of the paraffin and olefin product growth factors to explain the observed two-alpha ASF distribution of FTS. This model shows the likelihood that two-alpha product distribution may be the result of the combination of different product spectrums. We also considered the effect of the vapour-liquid equilibrium (VLE) on the product distribution, and found that our experimental data support the postulate that the double-alpha type plot often encountered in FT results is attributable to VLE.