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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Comparative analysis of counter-current and co-current downer reactors using particle image velocimetry and computational particle-fluid dynamics

by Aldugman, Cui, Alzailaie, Alhareth, Langley, Alfilfil, Almajnouni, Gascon, Thoroddsen, Castaño
Chem. Eng. J. Adv. Year: 2025 DOI: https://doi.org/10.1016/j.ceja.2024.100687

Abstract

We investigated the hydrodynamics in co- and counter-current downer operations using particle image velocimetry (PIV) and computational particle fluid dynamics simulations (CPFD). Pilot-scale experiments were conducted for fluid catalytic cracking (FCC) catalysts and sand, which verified the system stability and provided the validation basis for the simulation strategy. We compared the reactor characteristics of counter-current and co-current downers under different operating modes and conditions using PIV experiments and CPFD simulations. PIV experiments showed that the counter-current downer exhibits a more uniform particle velocity profile, with a gradient of only 8 % of the maximum velocity, compared to the co-current operation, which shows a significantly steeper gradient of 39.5 % from the maximum. Simulations confirmed that the counter-current downer reactor has 69 % higher solid holdup and 98 % longer residence time than the co-current operation. Thus, the counter-current downer reactor demonstrated intermediate behavior between the classical co-current downer and riser reactors, offering flexibility for industrial applications.

Keywords

C2C FCC MKM CRE