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

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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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