The fixed-bed catalytic reactors at the heart of most processes are a key element of process engineering. However achieving optimal reactor design and efficient operation can be very challenging because of the complexity involved.

Traditional modelling approaches oversimplify the reactor, and thus have limited scope. True digital design requires a high-fidelity model that can be used from R&D through to industrial operation.

Siemens’ gPROMS Advanced Model Library for Fixed-Bed Catalytic Reactors (AML:FBCR) provides high-fidelity, first-principles reactor models that can be used throughout the process development lifecycle.


This library captures PSE’s extensive experience in reaction engineering, and can be used to validate reaction kinetics and optimize new catalyst designs, to scale-up new reactor designs, to optimize or troubleshoot reactor operation and to monitor or control plant operation.

Models handle gas or liquid single-phase flow in many different fixed-bed configurations from tubular, to multitubular or radial flow reactors.


The AML:FBCR has a been proven in many industry applications:

  • Development and validation of reaction kinetics
  • Optimizing catalyst design
  • Industrial reactor design and scale up
  • Optimization of both reaction and separation sections
  • Troubleshooting reactor operation
  • Control and monitoring of plant operations


There are many benefits to applying the AML:FBCR high-fidelity models. These can be summarised as:

  • Reduced model development time. Detailed models can be constructed in weeks rather than months.
  • Improved reactor design. Predictive models can be used to optimize many aspects of geometry to ensure uniform operation.
  • Improved operations. Similar models can be used to optimize operating conditions and thus enhance catalyst life.
  • Realistic “catalyst test bed”. Model simulations can be used for designing, screening and ranking catalyst.
  • Engineering focus. Support for process development and scale-up, catalyst development and general innovation, as part of a model-based engineering programme.

Scope and features

The AML:FBCR aims to make life easier for reaction engineers by providing a packaged tool that embodies many years’ research and development into physics and chemistry representation and modelling techniques.

It includes high-fidelity first-principles models that represent reactor complexity at different scales from the catalyst pellet to the fixed-bed and the cooling jacket or shell of the reactor.

It also includes typical correlations used in industry to account for the non-idealities in the fixed-bed heat transfer parameters. Chemical kinetics can be configured for virtually any process. These can be easily validated via the gPROMS standard parameter estimation and model validation features.

Here are some of the key features of the library.

Modular library allowing for different reactor designs:

  • Single pellet or basket laboratory scale reactors
  • Traditional tubular reactors
  • Multiple tube-in-tube arrangement designs, with reaction and catalyst in the concentric annular sections
  • Varied heat transfer options from simpler adiabatic or cooling jacket designs to multitubular or boiling coolant shell compartments
  • Gas cooled bed, a multitubular arrangement with catalyst on the shell side and fluid in the tubes
  • Radial flow reactors with centrifugal or centripetal flow configuration, adiabatic or internally cooled
  • Gas or liquid phase reactors. (Reactors with two-phase flow over a fixed-bed of catalyst can be modelled with the AML:TBR)

Multiple model complexity options:

  • Fixed-bed models predicting the radial and axial profiles (2-D) or simplified to radial averaged axial profiles (1-D), including different levels of complexity in the bed mass and heat transfer phenomena
  • Catalyst pellet model solving the intraparticle multicomponent diffusion-reaction problem, or using an effectiveness factor
  • Different pellet 1D model geometry options to solve the intraparticle diffusion problem: infinite slab, infinite cylinder, sphere, infinite hollow cylinder, non-ideal geometry
  • Some phenomena, like axial conduction, can be enabled or disabled for optimum solution accuracy and speed

Usability and flexibility:

  • Easily configure a reactor model by configuring reactor specifications and by choosing correlations from a pre-defined list
  • Provide reaction kinetics via a drag-and-drop model and dialog
  • Or create a custom kinetics model for more complex reaction systems
  • Quickly extend the list of existing correlations by adding your own heat transfer or pressure drop equation
  • Change between the different complexity options to check model assumptions and optimise solution speed

Advanced features:

  • Consider up to three different types of catalyst in the reactor, each with its own reaction kinetics
  • Account for non-uniformity in the fixed-bed packing by specifying a non-uniform bed porosity
  • Add catalyst deactivation to custom kinetics
  • Interface with CFD to incorporate the shell-side cooling hydrodynamics using PSE’s Hybrid gPROMS—CFD Multitubular option

Typical results

Typical results are temperature and concentration profiles through catalyst, tube and shell, accurately calculated from validated first-principles models, for example:

Concentration of main reactant in catalyst pellet showing radial variation

Concentration of main product in catalyst pellet showing radial variation

Temperature profile through catalytic tube bed in axial and radial direction

Methanol reactor catalyst deactivation after 100 days

Multitubular reactor – Comparison of predicted vs. experimental tube centre temperature

Coolant temperature profiles showing hot-spot (taken from linked CFD model of shell side fluid)


The AML:FBCR and Hybrid gPROMS-CFD Multitubular interface are supplied as options to gPROMS Process. They are not available under PSE’s Academic Programme.

More Information
The gPROMS AML:FBCR allows us to improve the performance of industrial reactors using our catalysts significantly

Multitubular reactor design variables. Catalyst design decisions can also be included

Why use the AML:FBCR?

The AML:FBCR allows you to focus on engineeering, not modelling:

  • reduce development time from months to weeks
  • avoid reinventing models
  • free up time for engineering analysis
  • quality-assured, project-proven models with reduced potential for error
  • universal applicability quickly apply to different projects
  • overall enhanced productivity and better results

The AML:FBCR palette

Advanced reactor models in other environments

Complex reactor models built in gPROMS can be inserted into CAPE-OPEN compliant flowsheet simulators, using PSE’s gO:CAPE-OPEN unit operation plug.