Topic 6: Heterogeneous reactions

Topic 6: Heterogeneous reactions‣ Gas-solid catalytic reactions‣ Gas-solid noncatalytic reactions‣ Gas-liquid reactionsIndian Institute of Science

Heterogeneous catalysisIndian Institute of Science

Heterogeneous catalysisIndian Institute of Science

Concentration and temperature profilesconcentrationtemperaturec AbTic AiT bpositionpositionIndian Institute of Science

External transportIndian Institute of Science

Bulk/Molecular diffusionBinary (1 1)1.86× 10 T +M MMulti-component−3 3/212( )1/2= ⎡⎤PσΩ⎣ ⎦1 2−1 −5 2D12 gases:10 ; liquids:10cm s2N =−D C ∇ y + y N + N1 12 T 1 1 1 2N =−D C ∇ y + y N D =N∑j jm T j j k jm Nk = 11−y ∑ jNk Njk=11D⎛NN∑kyk− y⎜jk≠j jkNj⎝⎞⎟⎠Indian Institute of Science

Characterization of catalyst pelletSVρεggppf()rdrsurfacearea/gmcatalystvoidvolume/gmcatalystgmcatalyst/pelletvolumevoid fractionvoidvolumedistributionIndian Institute of Science

Transport in poreBulk Knudson ViscousN1 1N( )jyj⎛ PB0⎞− ∇ pj = ∑ yNk j− yNj k+ + PRT k≠j Djk DKj D⎜ ∇KjRT µ⎟⎝ ⎠DKj2 ⎛ 8RT⎞= r3 ⎜πM⎟⎝ j ⎠12Indian Institute of Science

Transport in pelletdCjNj=−DjmdzFlowdCjNj=−DejdzFlowDej=ετDjmIndian Institute of Science

Reaction and diffusion A→Bbulk phasecAbLcatalystDiffusionAReactiondzz+dz zzAccumulation C Adz − C AdzA gt+dtA gdCAIn DeAA dtdzz+dzdc A0dz = dCAOut DeAA dtdzzGenerated −rAdzdt∂ ∂( )⎛ ∂CA⎞εpCA = ⎜DeA⎟−r∂t ∂z⎝∂z⎠tIndian Institute of Science

Concentration profilesIndian Institute of Science

Effectiveness factorIndian Institute of Science

Effect of geometryIndian Institute of Science

Nonlinear kineticsIndian Institute of Science

Falsification of the kineticsIndian Institute of Science

Falsification of the kineticsIndian Institute of Science

Multiple reactionsIndian Institute of Science

Nonisothermal pelletIndian Institute of Science

Nonisothermal pelletraterate1.00.80.60.40.20.00.0 0.2 0.4 0.6 0.8 1.01.00.5β=0β= -0.6concentration0.00.0 0.2 0.4 0.6 0.8 1.0concentrationraterate1401201004.03.53.02.52.01.51.00.5β=0.20.00.0 0.2 0.4 0.6 0.8 1.0806040200concentration0.0 0.2 0.4 0.6 0.8 1.0concentrationβ= 0.6Indian Institute of Science

External and internal energy transfer limitationsIndian Institute of Science

Multiple steady states and hystersis300250β= 0.6G(T * )/(T * -1)2001501005001.0 1.2 1.4 1.6TemperatureIndian Institute of Science