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Lecture 1. Chemical Reaction Engineering (CRE) is the field that studies the rates and mechanisms of chemical reactions and the design of the reactors in which they take place. Today’s lecture. Introduction Definitions General Mole Balance Equation Batch (BR) - PowerPoint PPT Presentation
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Chemical Reaction Engineering (CRE) is the field that studies the rates and mechanisms of
chemical reactions and the design of the reactors in which they take place.
Lecture 1
1
Today’s lecture Introduction Definitions General Mole Balance Equation
Batch (BR) Continuously Stirred Tank Reactor
(CSTR) Plug Flow Reactor (PFR) Packed Bed Reactor (PBR)
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Chemical Reaction EngineeringChemical reaction engineering is at the heart of virtually every chemical process. It separates the chemical engineer from other engineers.Industries that Draw Heavily on Chemical Reaction Engineering (CRE) are:
CPI (Chemical Process Industries)Examples like Dow, DuPont, Amoco,
Chevron
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Chemical Plant for Ethylene Glycol (Ch. 5)
Smog (Ch. 1)
Plant Safety(Ch.
11,12,13)
Lubricant Design (Ch.
9)
Cobra Bites (Ch. 6 DVD-
ROM)
Oil Recovery (Ch. 7)
Wetlands (Ch. 7 DVD-ROM)
Hippo Digestion (Ch. 2)
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http://www.umich.edu/~ess
en/
Materials on the Web and CD-ROM
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Let’s Begin CREChemical Reaction Engineering (CRE) is
the field that studies the rates and mechanisms of chemical reactions and the design of the reactors in which they take place.
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Chemical IdentityA chemical species is said to have reacted
when it has lost its chemical identity.The identity of a chemical species is
determined by the kind, number, and configuration of that species’ atoms.
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Chemical IdentityA chemical species is said to have reacted
when it has lost its chemical identity. There are three ways for a species to loose its identity:
1. Decomposition CH3CH3 H2 + H2C=CH2
2. Combination N2 + O2 2 NO3. Isomerization C2H5CH=CH2
CH2=C(CH3)2
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Reaction RateThe reaction rate is the rate at which a species
looses its chemical identity per unit volume.
The rate of a reaction (mol/dm3/s) can be expressed as either:
The rate of Disappearance of reactant: -rA
or asThe rate of Formation (Generation) of
product: rP
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Reaction RateConsider the isomerization
A BrA = the rate of formation of species A
per unit volume -rA = the rate of a disappearance of
species A per unit volume rB = the rate of formation of species B
per unit volume
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Reaction RateEXAMPLE: AB
If Species B is being formed at a rate of 0.2 moles per decimeter cubed per second, ie, rB = 0.2 mole/dm3/s
Then A is disappearing at the same rate:-rA= 0.2 mole/dm3/s
The rate of formation (generation of A) is rA= -0.2 mole/dm3/s
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Reaction RateFor a catalytic reaction, we refer to -rA',
which is the rate of disappearance of species A on a per mass of catalyst basis. (mol/gcat/s)
NOTE: dCA/dt is not the rate of reaction
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Reaction RateConsider species j: 1. rj is the rate of formation of species j
per unit volume [e.g. mol/dm3s]2. rj is a function of concentration,
temperature, pressure, and the type of catalyst (if any)
3. rj is independent of the type of reaction system (batch, plug flow, etc.)
4. rj is an algebraic equation, not a differential equation
(e.g. = -rA = kCA or -rA = kCA
2)14
General Mole Balance
timemole
timemole
timemole
timemole
dtdN
GFF
jSpeciesofonAccumulati
RateMolar
jSpeciesofGeneration
RateMolar
outjSpeciesofRate
FlowMolar
injSpeciesofRate
FlowMolar
jjjj
0
Fj0 FjGj
System Volume, V
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General Mole BalanceIf spatially uniform
G j rjV
If NOT spatially uniform
2V
rj 2
G j1 rj1V1
G j 2 rj 2V2
1V
rj1
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General Mole Balance
G j rjiVii1
W
G j lim V 0 n
rjiVii1
n
rjdV
Take limit
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General Mole Balance
General Mole Balance on System Volume V
In Out Generation Accumulation
FA 0 FA rA dV dNA
dt
FA
0
FAGA
System Volume, V
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Batch Reactor Mole Balance
FA 0 FA rA dV dNA
dtFA 0 FA 0
dNA
dtrAV
Batch
VrdVr AA Well Mixed
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Batch Reactor Mole Balance
dt dNA
rAVIntegrating
Time necessary to reduce number of moles of A from NA0 to NA.
when t = 0 NA=NA0t = t NA=NA
A
A
N
N A
A
VrdNt
0
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Batch Reactor Mole Balance
A
A
N
N A
A
VrdNt
0
NA
t21
CSTR Mole Balance
FA 0 FA rA dV dNA
dt
dNA
dt0Steady State
CSTR
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FA 0 FA rAV 0
V FA 0 FA
rA
VrdVr AA Well Mixed
CSTR volume necessary to reduce the molar flow rate from FA0 to FA.
CSTR Mole Balance
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Plug Flow Reactor
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Plug Flow Reactor Mole Balance
V
V VV
FA
FA
0
0
VrFF
VinGeneration
VVatOut
VatIn
AVVAVA25
limV 0
FA V V FA V
VrA
Rearrange and take limit as ΔV0
dFA
dVrA
Plug Flow Reactor Mole Balance
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This is the volume necessary to reduce the entering molar flow rate (mol/s) from FA0 to the exit molar flow rate of FA.
Alternative Derivation – Plug Flow Reactor Mole Balance
0 0 dVrFF AAA
0dt
dN ASteady State
dtdNdVrFF A
AAA 0
PFR
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dFA
dVrA
0 dFA
dV rA
Differientiate with respect to V
A
A
F
F A
A
rdFV
0
The integral form is:
This is the volume necessary to reduce the entering molar flow rate (mol/s) from FA0 to the exit molar flow rate of FA.
Alternative Derivation –Plug Flow Reactor Mole Balance
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dt
dNWrWWFWF AAAA
AWAWWA
Wr
WFF
0lim
0dt
dN ASteady State
PBR
Packed Bed Reactor Mole Balance
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Packed Bed Reactor Mole Balance
dFA
dW r A
Rearrange:
PBR catalyst weight necessary to reduce the entering molar flow rate FA0 to molar flow rate FA.
A
A
F
F A
A
rdFW
0
The integral form to find the catalyst weight is:
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Reactor Mole Balance SummaryReactor
Differential Algebraic Integral
V FA 0 FA
rA
CSTR
Vrdt
dNA
A 0
A
A
N
N A
A
VrdNtBatch
NA
t
dFA
dVrA
A
A
F
F A
A
drdFV
0
PFRFA
V31
Reactors with Heat EffectsEXAMPLE: Production of Propylene Glycol in
an Adiabatic CSTR
Propylene glycol is produced by the hydrolysis of propylene oxide:
CH2 CH CH3 H2OH2SO4 CH2 CH CH3
O
OH
OH
Fast Forward 10 weeks from now:
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What are the exit conversion X and exit temperature T?SolutionLet the reaction be represented by
A+BC
v0
Propylene Glycol
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Evaluate energy balance terms
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AnalysisWe have applied our CRE algorithm to calculate the Conversion (X=0.84) and Temperature (T=614 °R) in a 300 gallon CSTR operated adiabatically.
X=0.84T=614 °R
T=535 °R
A+BC
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KEEPING UP
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Separations
These topics do not build upon one another
Filtration Distillation Adsorption
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Reaction Engineering
Mole Balance Rate Laws Stoichiometry
These topics build upon one another
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Mole BalanceRate Laws
StoichiometryIsothermal Design
Heat Effects
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Mole Balance Rate Laws
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Mole Balance
Rate LawsStoichiometry
Isothermal DesignHeat Effects
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End of Lecture 1
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Additional Applications of CRE
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Supplemental Slides
Additional Applications of CRE
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Compartments for perfusion
Perfusion interactions between compartments are shown by arrows.
VG, VL, VC, and VM are -tissue water volumes for the gastrointestinal, liver, central and muscle compartments, respectively.
VS is the stomach contents volume.
StomachVG = 2.4 l
GastrointestinalVG = 2.4 ltG = 2.67 min
Liver
Alcohol
VL = 2.4 l tL = 2.4 min
CentralVC = 15.3 l tC = 0.9 min
Muscle & FatVM = 22.0 l tM = 27 min
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