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

Deactivation Dynamics of a Ni Supported Catalyst during the Steam Reforming of Volatiles from Waste Polyethylene Pyrolysis

by Ochoa, Barbarias, Artetxe, Gayubo, Olazar, Bilbao, Castaño
Appl. Catal. B: Environ. Year: 2017

Abstract

The valorization of waste high density polyethylene (HDPE) for hydrogen production has been studied in a two-step process, comprising pyrolysis and subsequent steam reforming of the volatiles produced in the first step. Particularly, this work focuses on the deterioration mechanisms (sintering and coke deposition) of the Ni commercial catalyst used in the second step, as it conditions the overall process performance. Pyrolysis of HDPE has been performed in a conical spouted bed reactor at 500 °C, and the catalytic steam reforming of the pyrolysis volatiles, in a fluidized bed reactor at 700 °C. Deactivated catalyst samples were recovered at different values of time on stream, and characterized using XRD, N2 adsorption-desorption, SEM and TEM electronic microscopies, temperature programmed oxidation (TPO), Raman, FTIR and LDI-TOF MS spectroscopies. The results show that the deactivation is due to the sintering and encapsulation -by coke- of Ni. The former is inevitable within the current conditions, and the latter can be ascribed to the condensation of adsorbed precursors that evolve over time. Encapsulating coke is partially carbonized into filamentous coke with lower effect on catalytic deactivation and higher economic interest.

Keywords

REF W2C ANW MKM