Porous Catalyst
Use this feature to model adsorption, desorption, and heterogeneous reactions, as a gas or liquid is moving through the interstices of a catalytic porous medium. The mass transfer in the fluid inside the porous matrix is treated using the Linear Driving Force model and a lumped mass transfer coefficient.
A catalyst is a substance that increases the rate of a reaction without itself being consumed. The catalytic process usually consists of the following steps:
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The adsorbate transfers across the fluid-adsorbent boundary layer to the adsorbent surface
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The adsorbate is adsorbed on the adsorbent surface
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Chemical reactions on the surface involving the adsorbate
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Desorption of reaction products (adsorbate) from the adsorbent surface into the fluid-adsorbent boundary layer
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Adsorbate transfers across the boundary layer to the bulk fluid.
Species transport through a porous medium is affected both by properties of the fluid phase, as well as by properties of the solid matrix. These properties are defined in the Fluid and Porous Matrix subnodes respectively.
Add an Adsorption or a Surface Reaction subfeature to the Porous Catalyst to model adsorption or heterogeneous reactions. To model volumetric reactions in the fluid phase (bulk), add a Reactions subnode under Fluid.
Model Input
Specify the temperature to be used in the catalyst. The temperature will be used for the adsorption isotherms and the rate of surface reactions.
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By default, the Common model input option corresponds to the minput.T variable, set to 293.15 K by default. To edit the minput.T variable, click the Go to Source button (), and in the Default Model Inputs node under Global Definitions, set a value for the Temperature in the Expression for remaining selection section.
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Select User defined to enter a value or an expression for the temperature (SI unit: K). This input is always available.
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If available, select a temperature defined by a Heat Transfer interface present in the model. For example, select Temperature (ht) to use the temperature defined by the Heat Transfer in Porous Media interface using the Name ht.
reactive specific surface area
Enter a specific surface area for the adsorption and surface reaction processes. The default value is 1·107 1/m.
concentration input
Select a Concentration input — Molar concentration (mol/(m2)) (the default) or Amount per solid mass (mol/kg). This parameter determines the unit for initial values of adsorbed species and user-defined surface species.
adsorbed species
Specify which of the bulk species that can be adsorbed to the catalyst (adsorbent). The surface concentrations (SI unit: mol/m2) of the adsorbed species, named cads_j corresponding to bulk species j, are solved for. The rate of adsorption is defined in the Adsorption subnode. With an adsorbed species being selected, its initial value field is activated. Enter the initial value in accordance with the Concentration input.
surface species
There could be extra surface species besides the adsorbed bulk species and their corresponding adsorbed sites on adsorbent surface. These additional surface species could take part in catalytic reactions. The surface reaction rate is defined in the Surface Reaction subnode.
Add a user-defined surface species in the Surface species table by clicking the Add button under the table. The concentration (SI unit: mol/m2) of all surface species added are solved for. To define the surface reaction kinetics add a Surface Reaction subnode.
When using the Transport of Concentrated Species interface, the molar mass of each surface species is required to convert between molar and mass basis. For a surface species already defined in a Chemistry interface, say O2(ads), select Molar mass for O2(ads) for the corresponding surface species (using a the column Molar mass from). Select User defined to instead enter a constant or expression in the column Molar mass (kg/mol).