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CHEMICAL REACTION ENGINEERING-IISolid Catalyzed Reactions - Heat Effects During Reaction
B.Manikandan
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Introduction
Introduction
When reaction is so fast that the heat released (or absorbed) in the pelletcannot be removed rapidly enough to keep the pellet close to thetemperature of the fluid, then nonisothermal effects intrude.
In such a situation two different kinds of temperature effects may beencountered:
Within-particle ∆T. There may be a temperature variation within thepellet. Film ∆T. The pellet may be hotter (or colder) than the surroundingfluid.
Thus present research on catalysts is strongly centered on the surfacestructure of solids.
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Introduction
Introduction
For Film ∆T we equate the rate of heat removal through the film with therate heat generation by reaction within the pellet. ThusQ generated = (V pellet ) (−r ”
A ,obs ) (−∆Hr )
Q removed = h S pellet (T g − T s )and on combining we find
∆T film =(T g − T s ) =where L is the characteristic size of the pellet.
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Introduction
Introduction
For within-particle ∆T the simple analysis by Prater (1958) for anyparticle geometry and kinetics gives the desired expression.
Since the temperature and concentration within the particle arerepresented by the same form of differential equation (Laplace equation)
Prater showed that the T and C A distributions must have the same shape;thus at any point in the pellet x
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Introduction
Introduction
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Introduction
PERFORMANCE EQUATIONS FOR REACTORS
CONTAINING POROUS CATALYST PARTICLESFor Plug Flow
Take a thin slice of the PFR.
Then following the analysis for homogeneous reactions we have thesituation shown in following Fig.
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I d i
7/23/2019 CREIIUnit4heateffectsduringrxn
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Introduction
PERFORMANCE EQUATIONS FOR REACTORS
CONTAINING POROUS CATALYST PARTICLESFor Plug Flow
At steady state a material balance for reactant A gives
input = output + accumulation . . .
molA
s
F A0 − F A0X Ain = F A0 − F A0X Aout + (−r
A ) ∆W
In differential form ,F A0dX A = (−r
A ) dW = (−r ”
A ) dV S
Integrating over the whole reactor gives
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I t d ti
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Introduction
PERFORMANCE EQUATIONS FOR REACTORS
CONTAINING POROUS CATALYST PARTICLESFor Plug Flow
B.Manikandan CHEMICAL REACTION ENGINEERING-II 8 / 9
Introduction
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Introduction
PERFORMANCE EQUATIONS FOR REACTORS
CONTAINING POROUS CATALYST PARTICLESFor Mixed Flow
B.Manikandan CHEMICAL REACTION ENGINEERING-II 9 / 9
