Multiscale kinetic modeling in catalysis ⇒ from microkinetics to computational fluid dynamics and process simulations

Problem statement

We envision multiscale modeling as critical enablers of reaction understanding, catalyst and reactor design, scale-up, and process optimization. The framework includes predicting the molecular reaction mechanism at the molecular level to the process optimization stage. As catalytic processes occur at the multiscale, we address these issues individually and collectively.

At the microkinetic level, our models resolve the rates of the individual elementary steps, rate-determining step (RDS), adsorption, and desorption mechanisms. We use quantum chemical calculations (density functional theory, DFT) to support our assumed kinetic pathways, original parameter estimations, and adsorption-desorption energies.

We incorporate thermodynamic constraints into our models. Once developed, the microkinetic model could guide the catalyst and reactor design. We also have experience developing Langmuir-Hinshelwood and Eley-Rideal types of kinetic models.

At the macrokineitc level, we develop lump-based and empirical models which, in some cases, are very robust and, together with other models, can be used to extract information such as mechanism change, optimize conditions, or for reactor pre-design.

We couple hydrodynamics, heat transfer, and reaction kinetics at the reactor level in computational fluid dynamic (CFD) simulations. Together with optimization algorithms, we aim to improve operating scenarios, develop innovative reactor prototypes, and predict process behaviors at the industrial scale.

Goals

  • Microkinetics I ⇒ key thermodynamic relationships
  • Microkinetics II ⇒ fitting, training, and optimization
  • Microkinetics III ⇒ ab initio kinetic modeling
  • Macrokinetics ⇒ complex reaction networks and population balances
  • CPFD ⇒ reactor modeling and scale-up
  • CFD ⇒ reactor modeling and optimization
  • CFD II ⇒ modeling operando reactors
  • Process system engineering ⇒ gPROMS

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Related Publications

Operating Ranges of Coupled–Decoupled Counter-current Downer and Riser Reactors

by Cui, Alfilfil, Morales-Osorio, Almajnouni, Gascon, Castaño
ACS Eng. Au Year: 2025 DOI: https://doi.org/10.1021/acsengineeringau.4c00041

Abstract

The counter-current downers have the potential to combine the hydrodynamic characteristics of co-current risers and downers with less back-mixing and improved solid holdup. However, flooding may occur when particles suspend or reverse the flowing direction under increasing superficial gas velocity or solid mass flux. Here, we evaluate transported bed configurations by coupling the counter-current downer with a riser reactor to take advantage of the flooding behaviors. We analyze the theoretical hydrodynamics in risers and co- and counter-current downers from particle mechanics to cluster development. By validation with experimental results from the literature, we determine the proper simulation strategy for counter-current downers using computational particle fluid dynamics by replacing the particle size with empirically calculated cluster size. We investigate the effects of superficial gas velocity and solid mass flux with Geldart group A particles until beyond the flooding point of the counter-current downer. The coupled riser–counter-current downer reactor configuration offers more uniform axial and dynamic radial solid distribution while keeping a relatively high solid holdup to better utilize the reactor volume for enhanced gas–solid contact. The fluidization regime diagram by the Richardson–Zaki equation fails to capture the counter-current operation, so we provide a separate graph to mark the limitation of the coupled and decoupled riser and counter-current downer reactor configurations.

Keywords

C2C FCC CRE MKM