Detailed Kinetic Modeling of CO2-Based Fischer–Tropsch Synthesis

Abstract

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. However, 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.

Influence of Recycle Operation on the Catalytic Hydrogenation of CO2 to Long-Chain Hydrocarbons

“…Before discussing the experimental results, it must be emphasized that, in principal, it is impossible to differentiate between secondary reactions of recycled products and a shift in the primarily formed products based on the obtained product spectrum. In a previous study, we investigated the change in product composition under once-through conditions for greatly varying residence times . A slight change in the average chain length of the product could be observed for different residence times.…”

“…In a previous study, we investigated the change in product composition under once-through conditions for greatly varying residence times. 27 A slight change in the average chain length of the product could be observed for different residence times. The composition within one carbon number, however, appeared to be relatively independent of the residence time.…”

“…A simple global kinetic model, as well as a detailed, mechanism-based, kinetic model, was recently published by us for Fe–K/γ-Al 2 O 3 –I. , Details about the models are given in the original publications. The simulations of the recycle experiments are based on the detailed, mechanism-based model which allows for the simultaneous prediction of reactant consumption and product distribution.…”

Insights into Fischer–Tropsch catalysis: current perspectives, mechanisms, and emerging trends in energy research

“…In power-to-liquid processes and in biomass-to-liquid approaches, relevant amounts of CO 2 in the FT feed gas typically make a reverse WGS reaction step before the FT reactor mandatory. However, direct CO 2 hydrogenation would eliminate the need for this additional level of complexity (Brübach et al, 2022).…”

Kinetics-Constrained Neural Ordinary Differential Equations: Artificial Neural Network Models tailored for Small Data to boost Kinetic Model Development

“…Recently, a microkinetic approach was applied that allowed obtaining the models successfully describing reagent consumption and products formation as well as hydrocarbon distribution of CO2 hydrogenation that were demonstrated in works. [57,58] From the presented works one can see the complexity of kinetic modeling of CO2 hydrogenation to hydrocarbons. In our work we demonstrated that neural KCNODE could be successfully applied for describing the kinetics of this complicated reaction.…”