7 Schematic presentation of a chemical process HeatMain productReactant-purificationReactionProduct-isolationBPsolvent, reactants, catalystProcedure for reactor design1. Stoichiometry und Thermodynamics2. Apparatus and Conditions3. Calculation of Conversion and Reactor Size4. Calculation of Material Flow
8 Steps of Heterogeneous Reaction Diffusion of reactant to catalystTransport of reactant within catalyst poresAdsorption of reactant on catalyst surfaceReactionDesorption of products from catalyst surfaceTransport of products out of catalyst poresDiffusion of products away from catalyst
10 Mass Transport and Heterogeneous Catalysis Principles Surface layerfluid phasecatalystInfluence of mass transport on the temperature dependance of het. catalysisMass transportinfluenceConcentration profile
11 A Dg ~ T1,5 und Dg ~ 1/p Description of pore diffusion 1. Fick`s Law Average free path lengthAverage molecular velocityDg ~ T1, und Dg ~ 1/p
12 DK ~ T0.5 a) Diffusion in pores dp >> l N2, X N2, X =? N2 Wicke-Kallenbach-Experimentporousmaterialb) Knudsen – Diffusion dp = lDK ~ T0.5c) Intermediate range
13 dV Description of simultaneous reaction and pore diffusion temporal change changes of material changes causedof materials within = amount by transport by reactionsvolume elementdVone dimensionalSpherical geometry
14 Mass balance of sperical particle in steady state Solution of mass balance and description of average reaction ratewith r= kcn and n=-1renormalized parameter= Thiele-Modulusradial concentration profilwithin sperical pellet
15 r = rhet Effectiveness factor Reaction without mass transport limitationEffectiveness factoreffectiveness factor
16 Influence of pore diffusion on effective rate constant
21 Three-Phase-Reactors Gas-Liquid-ReactorsGas-Solid-ReactorsThree-Phase-ReactorsGLGLKatalysatorGLGColumnFixed Bed ReactorTrickle Bed ReactorGLK+LK+LGGTank ReactorPacked Bubble ColumnTube Reactor
22 Universal mass balance VRrjAAkk.ReactionTransp.Residence time
23 [-] Damköhler NumberreactionreactorSolution of general mass balance with boundary conditions forDifferent reactions and reactor results in X = f(Da, reactor)
24 . nA q z L . Ideal Tube Reactor (PFTR) steady state (dX/dt=0) LzqnA.steady state (dX/dt=0)no back mixing (plug flow)- Volume of feed is constantno radial concentration gradient (one dimensional system)- characteristic time is definied by: t=VR/V.
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