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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)

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Lecture 1

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
Today’s lecture

  • Introduction

  • Definitions

  • General Mole Balance Equation

    • Batch (BR)

    • Continuously Stirred Tank Reactor (CSTR)

    • Plug Flow Reactor (PFR)

    • Packed Bed Reactor (PBR)


Chemical reaction engineering
Chemical Reaction Engineering

Chemical 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


Smog (Ch. 1)

Wetlands (Ch. 7 DVD-ROM)

Hippo Digestion (Ch. 2)

Cobra Bites

(Ch. 6 DVD-ROM)

Oil Recovery (Ch. 7)

Plant Safety

(Ch. 11,12,13)

Lubricant Design (Ch. 9)

Chemical Plant for Ethylene Glycol (Ch. 5)


Materials on the web and cd rom

Materials on the Web and CD-ROM

http://www.umich.edu/~essen/


Let s begin cre
Let’s Begin CRE

  • 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.


Chemical identity
Chemical Identity

  • A 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.


Chemical identity1
Chemical Identity

  • A 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. DecompositionCH3CH3 H2 + H2C=CH2

    2. Combination N2 + O2 2 NO

    3. Isomerization C2H5CH=CH2 CH2=C(CH3)2


Reaction rate
Reaction Rate

  • The 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 as

    • The rate of Formation (Generation) of product: rP


Reaction rate1
Reaction Rate

Consider the isomerization

A  B

rA = 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


Reaction rate2
Reaction Rate

EXAMPLE: AB

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


Reaction rate3
Reaction Rate

  • For 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


Reaction rate4
Reaction Rate

Consider species j:

  • rj is the rate of formation of species j per unit volume [e.g. mol/dm3s]

  • rj is a function of concentration, temperature, pressure, and the type of catalyst (if any)

  • rj is independent of the type of reaction system (batch, plug flow, etc.)

  • rj is an algebraic equation, not a differential equation

    (e.g. = -rA = kCA or -rA = kCA2)


General mole balance
General MoleBalance

System Volume, V

Fj0

Fj

Gj


General mole balance1
General MoleBalance

Ifspatially uniform

If NOT spatially uniform


General mole balance2
General MoleBalance

Take limit


General mole balance3
General MoleBalance

System Volume, V

General MoleBalance on System Volume V

FA0

FA

GA


Batch reactor mole balance
Batch Reactor Mole Balance

Batch

Well Mixed


Batch reactor mole balance1
Batch Reactor Mole Balance

when t = 0 NA=NA0

t = t NA=NA

Integrating

Time necessary to reducenumber of moles of A from NA0 to NA.



Cstr mole balance
CSTR Mole Balance

CSTR

Steady State


Cstr mole balance1
CSTR Mole Balance

Well Mixed

CSTR volumenecessary to reduce the molar flow rate from FA0 to FA.




Plug flow reactor mole balance1
Plug Flow Reactor Mole Balance

Rearrange and take limit as ΔV0

This is the volumenecessary 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
Alternative Derivation – Plug Flow Reactor Mole Balance

PFR

Steady State


Alternative derivation plug flow reactor mole balance1
Alternative Derivation –Plug Flow Reactor Mole Balance

Differientiate with respect to V

The integral form is:

This is the volumenecessary to reduce the entering molar flow rate (mol/s) from FA0 to the exit molar flow rate of FA.



Packed bed reactor mole balance1
Packed Bed Reactor Mole Balance

Rearrange:

The integral form to find the catalyst weight is:

PBR catalyst weight necessary to reduce the entering molar flow rate FA0 to molar flow rate FA.


Reactor mole balance summary
Reactor Mole Balance Summary

NA

FA

t

V

Batch

CSTR

PFR


Reactors with heat effects

Fast Forward 10 weeks from now:

Reactors with Heat Effects

  • EXAMPLE: Production of Propylene Glycol in an Adiabatic CSTR

  • Propyleneglycol is produced by the hydrolysis of propyleneoxide:


v0

Propylene Glycol

What are the exit conversion X and exit temperature T?

Solution

Let the reaction be represented by

A+BC



Analysis
Analysis

We have applied our CRE algorithm to calculate the Conversion (X=0.84) and Temperature (T=614 °R) in a 300 gallon CSTR operated adiabatically.

T=535 °R

X=0.84

A+BC

T=614 °R



Separations
Separations

Filtration

Distillation

Adsorption

These topics do not build upon one another


Reaction engineering
Reaction Engineering

Mole Balance

Rate Laws

Stoichiometry

These topics build upon one another


Heat Effects

Isothermal Design

Stoichiometry

Rate Laws

Mole Balance


Mole Balance

Rate Laws


Isothermal Design

Heat Effects

Rate Laws

Stoichiometry

Mole Balance


End of lecture 1
End of Lecture 1


Additional applications of cre

SupplementalSlides

Additional Applications of CRE



Compartments for perfusion

Gastrointestinal

VG = 2.4 l

tG = 2.67 min

Alcohol

Stomach

VG = 2.4 l

Liver

VL = 2.4 l

tL = 2.4 min

Central

VC = 15.3 l

tC = 0.9 min

Muscle & Fat

VM = 22.0 l

tM = 27 min

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.


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