High-Temperature\nFe-Based Fischer–Tropsch Synthesis:\nExperimentally Validated Kinetic Models Implemented at Pellet and\nReactor Scales

Pellet- and reactor-scale models for Fischer–Tropsch\nsynthesis\n(FTS) with a Fe–K/silica catalyst were developed to investigate\nthe sensitivity of the hydrocarbon products and carbon dioxide selectivity\nto process conditions and feed composition at high temperature (350–400\n°C), moderate pressure (1–10 bar), and a range of H<sub>2</sub>/CO ratios (3–1). The major objective of this paper\nis to develop, validate, and evaluate a high-temperature FTS model\nthat is then used to assess the feasibility of process integration\nwith syngas production. Since there is limited kinetic data available,\nin literature at these conditions, bench-scale reactor tests were\nconducted to obtain operational data for parameter fitting of kinetic\nexpressions used in the model. This resulting kinetic model demonstrated\nagreement with the experimental data with an <i>R</i><sup>2</sup> of 0.97 to the testing data set and, thus, was feasible to\napply at pellet and reactor scales. Multiple pellet sizes were modeled\nto detail the role of transport limitations as the sphere’s\ndiameter approached and exceeded 1 mm. Application of the reactor\nmodel indicated that hydrocarbon selectivity depended strongly on\ntemperature, whereas the ratio of olefin to paraffin products decreased\nwith increasing temperature, pressure, and H<sub>2</sub>/CO ratio.\nProduct selectivity was not sensitive to the conversion of carbon\nmonoxide. Furthermore, the roles of the pressure and H<sub>2</sub>/CO ratio were closely coupled. At a H<sub>2</sub>/CO ratio of 3,\nonly slight variations in selectivity occurred over a pressure range\nof 1–20 bar, whereas at a ratio of 1, selectivity could vary\nby as much as 30% over the same pressure range. At pressures below\n5 bar and temperatures above 350 °C, minimal selectivity to heavy\nhydrocarbons (C<sub>12+</sub>) is obtained, and selectivity to midrange\nproducts (C<sub>5–11</sub>) rapidly declined as pressure dropped\nbelow 5 bar, which indicated that an operational pressure of at least\n5 bar is needed to achieve reasonable yields in this temperature range.\nThese results, while tentative, provide guidelines for further experimentation\nand evaluation of integrated FTS processes.