Alumina-supported iron catalyst - long-term study of the light product distribution in Fischer-Tropsch synthesis

Several models have been proposed to describe the carbon number product distribution and mechanism in Fischer-Tropsch synthesis (FTS). However, these models have not fully explained the product distribution and mechanism owing to the wide range and complexity of hydrocarbons in FTS. This study was conducted based on the Yao and Anderson-Schulz-Flory (ASF) carbon number product distribution models for light (C₁–C₆) hydrocarbon products of a Fe/Al₂O₃ catalyst. The product distribution based on the molar ratio of olefin to paraffin (O/P) and the neighboring olefins was also studied in order to better understand the mechanism in FTS and C₂ olefin deviation during FTS. Two sets of experiments (A and B) with different reaction conditions were conducted in microtubular fixed-bed reactors on the Fe/Al₂O₃ catalyst for 2249 h and 360 h, respectively. We found that the α values from the Yao and ASF carbon number product distribution models are relatively similar. The α values from the Yao carbon number product distribution plots are relatively constant, irrespective of the reaction conditions. Interestingly, it was also found that the secondary reactions of the C₂ olefin by re-adsorption to produce paraffins and long-chain olefins are dependent on the CO conversion and the reaction temperature during the FTS. Also, the product distribution of the neighboring olefins during the reduction condition gave a similar trend to what was observed for other reaction conditions. This result confirmed what was observed in the Yao and ASF carbon number product distribution of the olefins.