2Background and Motivation Heterogeneous CatalysisCharacteristics: different phases for reactants and catalyst (gas/liquid and solid);Processes: porous media flow, chemical reaction, surface chemistry, diffusion, dispersion, etc.;Rate-controlled: reaction rate constants, catalytic active site.Some ApplicationsReactants (gas)+catalyst (solid): nanofibrous carbon (NFC), exhaust treatment, ammonia synthesis, Sulfuric acid synthesis, etc.;Reactants (liquid)+catalyst (solid): margarine production.
3Model descriptionThis example investigates the thermal decomposition of methane over a solid Ni-Al2O3 catalyst. Hydrogen gas and solid carbon are formed as products. Carbon deposits affect the catalyst activity as well as the porosity and fluid flow through the reactor.
4Geometry and Operating Conditions Dimension: 2D;Free channels for inlet and outlet, porous media for middle section;Size: 1 × 0.4 (m).Operating conditionsReaction: atmospheric pressure, temperate between 490—590 oC
5Modeling Processes modeled by COMSOL Processes modeled by COMSOL Carbon decomposition chemical reaction;Catalyst deactivation;Variable porosity and permeability distribution in a porous media;Mass transport of reactants along a reactor;Heat transfer along a reactor;Momentum transfer along a reactor.
6Modeling Interfaces Reaction Engineering Transport of Diluted Species For kinetics investigationTransport of Diluted SpeciesFor mass transport and reactionsFree and Porous Media FlowFor calculating velocity fieldDomain ODEFor calculating varying porosity
7Results from Reaction Engineering Concentration transients of methane, hydrogen and deposited carbon as methane decomposes over a Ni/Al2O3 catalystDeactivation of catalyst during methane decomposition. The activity of catalyst decreases rapidly at the early stage of reaction, then decreases slowly.
8ResultComparison of concentration transients under two conditions of catalyst: 1) deactivation (unlocked) 2) constant activity 1 (locked)
10Result from the coupled model Velocity flow field in the 2D reactor at reacting time s.Distribution of pressure in the reactor for reacting gas passing through a clean catalyst under transient state at reacting time 4000 s.
11Result from the coupled model Concentration distribution of CH4 and H2 along the center line of reactor under fully coupled physics interfaces at different reacting times.Permeability distribution along the center line of reactor at different reacting times