Detailed Kinetic Modeling of CO₂-Based Fischer–Tropsch Synthesis

The direct hydrogenation of CO₂ to long-chain hydrocarbons, so called CO₂-based Fischer–Tropsch synthesis (FTS), is a viable future production route for various hydrocarbons used in the chemical industry or fuel applications. The detailed modeling of the reactant consumption and product distribution is very important for further process improvements but has gained only limited attention so far. We adapted proven modeling approaches from the traditional FTS and developed a detailed kinetic model for the CO₂-FTS based on experiments with an Fe based catalyst in a lab-scale tubular reactor. The model is based on a direct CO₂ dissociation mechanism for the reverse water gas shift and the alkyl mechanism with an H-assisted CO dissociation step for the FTS. The model is able to predict the reactant consumption, as well as the hydrocarbon distribution, reliably within the experimental range studied (10 bar, 280–320 °C, 900–120,000 mLN h−1 g−1 and H₂/CO₂ molar inlet ratios of 2–4) and demonstrates the applicability of traditional FTS models for the CO₂-based synthesis. Peculiarities of the fractions of individual hydrocarbon classes (1-alkenes, n-alkanes, and iso-alkenes) are accounted for with chain-length-dependent kinetic parameters for branching and dissociative desorption. ... mehrHowever, the reliable modeling of class fractions for high carbon number products (>C₁₂) remains a challenge not only from a modeling perspective but also from product collection and analysis.