syimi-topic 9 week 13
TRANSCRIPT
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Credit to Ms Nor Faeqah IdrusReference: Fogler and Levenspiel
TOPIC 9
Solid Catalyzed Reactions
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Solid Catalyzed Reaction
Reaction rates are usually expressed in terms ofmass of catalyst loading.
The design equations can be derived in a mannersimilar to those for homogeneous reactors - by using
mass (w) instead of volume (V).
Examples of solid catalyzed reactions:
Steam Methane Reforming (SMR) for HYDROGEN production Conversion of NOx and CO in automobile catalytic converter
Styrene production
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in mol/timemass of catalyst)( 'Ar
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Reactors for Heterogeneous
Reactions Packed bed reactor
Fluidized bed (FCC)
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Packed Bed Reactor
Similar to PFR, but reactor is packed with catalyst Heterogeneous reactionredefine rate of reaction
as Number of moles reacting per unit time per unit
mass of catalyst.
Mole Balance: [flow in] - [flow out] + [generation] = [accumulation]
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j
jW F
F r
dFWdW
j
j'
0 0
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Applications of PBR When is it used?
Heterogeneous reactions
E.g.catalytic converter
Advantages
Easy to maintain (no moving parts) High conversion per mass of catalyst
Disadvantages
Difficult to control temperature
Can get channeling of packed bed Catalyst is difficult to replace
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Stirred Batch Reactor
Catalyst dispersed as slurry There is good contact between the catalysts
and reactants.
However, if the catalyst decays, the activity and
selectivity will vary during the course of datacollection.
Since the system is well mixed, its isothermalityis good.
Sampling can be problematic, because thecatalyst may go along with the sample.
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Differential Reactor
It is a tube containing a small amount of catalyst
arranged in the form of a thin wafer or disk. Conversion in the reactor is extremely small and
hence, it is called a differential reactor.
The concentration in the reactor is assumed to be
uniform in the catalyst bed. Heat release per unit volume is low, and hence the
reactor behaves isothermally.
Channeling must be avoided
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FA0 FAe
Catalyst Bed
Inert Filling
Catalyst weight =W
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Differential Reactor
Mole Balance
For constant volumetric flow rates
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0)(0 WrFF AAeA
W
FFr AeAA
0)(
W
CvCvr AeAoA
0)(
W
F
W
XFr
pAA
0)(
W
Cv
W
CCvr
poAeAoA
][)( 0
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References Fogler, H.S. (2006). Elements of Chemical Reaction
Engineering, 4thEdition, New Jersey: Prentice Hall.
Levenspiel, O. (1999). Chemical Reaction
Engineering, 3rdEdition, New York: John Wiley.
Schmidt, L.D. (2005). The Engineering of ChemicalReactions, 2ndedition, New York: Oxford University
Press.
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BACK UP
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General Mole Balance for Packed Bed
Reactors
Input - Output + Gen =
Accumulation
w w+w
0)( '
wrFFAwwAwA
)( 'AwwAwA r
w
FF
)( 'AAO r
dw
dXF
wAF wwAF
Mass of catalyst = w
XX
X A
A
r
dXFw
0
'0
)(
)( 'AA rdw
dF