Page - 156 - in Advanced Chemical Kinetics
Image of the Page - 156 -
Text of the Page - 156 -
The linearity obtained in the plot of t/qt versus t results in k2 value (as the intercept) and qe
valueas theequilibriumadsorptioncapacity (fromtheslope).Similar to thepseudo-firstorder
kinetics, k2decreasesas the concentrationof initialMOincreases forbothprocesses (Table3).
Althoughhigh correlation coefficients are obtained, calculated qe values are not closer to the
experimental values.Moreover, thepredicted chemical adsorption cannot be applicable since
onlyphysical interactionsaresuggestedbetweenMOmoleculesandthesupportedcatalystvia
D-Rmodel.
Elovich equation:The Elovich equation is based on the adsorption capacity and expressed as
follows [46–48]:
dqt
dt ¼αexp �βqt (14)
whereβ is the initialadsorptionrate (mgg�1min�1)andα is thedesorptionconstant (gmg�1).
The linearizedformofEq. (14)withboundaryconditionsofqt=0at t=0andqt=qtat t= t isas
follows
qt¼ 1=β ln αβ � 1=β lnt (15)
Elovichparameters are given inTable 3. Theplot of qt versus ln t yields a linear relationship
with a slope of 1/ β and an intercept of (1/β) ln (α β). The high correlation coefficients
indicate suitability of the model for the evaluation of the adsorption process. The limited
number of vacant-available sites on the supported catalyst may decrease the possibility of
chemical adsorptionprocess through increments inMOconcentration.This eventually results
insmallerβvalues inbothdecolorizationanddegradationprocesses. Simultaneously,desorp-
tions from the surfacemay be enhanced via less strong physical attractions and increase α
values.
Interparticlediffusionmodel:Theadsorbatespeciesareprobablytransportedfromthebulkof the
solution into the solid phase through intraparticle diffusion/transport process. Themodel is
expressedby the followingequation:
qt¼Kdifft1=2þC (16)
where C (mg g�1) is the intercept and Kdiff is the intraparticle diffusion rate constant (in
mgg�1min1/2).Kdiff canbeevaluatedby the linear correlationofqt versus t 1/2 (Table3).Asa
general trend,Kdiffvalues increasewith increaseof initialMOconcentrationbutfor thehighest
concentrations there seems to be a constancy. Thismay point out the existence of restricted
diffusion for theexternalmass.AlthoughCvaluessupplies informationabout the thicknessof
the boundary layer, experimental data do not exhibit neither an increasing nor a decreasing
trend.Thus, theadsorptionmechanismcannotbeexplainedbyusing thismodelowing to the
complexstructureof thesupportedcatalyst.
Advanced Chemical
Kinetics156
back to the
book Advanced Chemical Kinetics"
Advanced Chemical Kinetics
- Title
- Advanced Chemical Kinetics
- Author
- Muhammad Akhyar Farrukh
- Editor
- InTech
- Location
- Rijeka
- Date
- 2018
- Language
- English
- License
- CC BY 4.0
- ISBN
- 978-953-51-3816-7
- Size
- 18.0 x 26.0 cm
- Pages
- 226
- Keywords
- Engineering and Technology, Chemistry, Physical Chemistry, Chemical Kinetics
- Categories
- Naturwissenschaften Chemie