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. 1 Chapter 1 Lecture 1 Introduction Definitions General Mole Balance Equation Batch (BR) Continuously Stirred Tank Reactor (CSTR)
Plug Flow Reactor (PFR) Packed Bed Reactor (PBR) 2 Chemical Reaction Engineering Chapter 1 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 3 Chapter 1 4 Chapter 1 Smog (Ch. 1) Wetlands (Ch. 7 DVD-ROM) Hippo Digestion (Ch. 2)
Oil Recovery (Ch. 7) 5 Chemical Plant for Ethylene Glycol (Ch. 5) Lubricant Design (Ch. 9) Cobra Bites (Ch. 8 DVD-ROM) Plant Safety (Ch. 11,12,13)
Materials on the Web and CDROM http://www.umich.edu/~essen/ 6 Chapter 1 Lets 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. 7
Chapter 1 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. 8 Chapter 1 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. Decomposition CH3CH3 H2 + H2C=CH2 2. Combination N2 + O2 2 NO 3. Isomerization 9
C2H5CH=CH2 CH2=C(CH3)2 Chapter 1 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
10 Chapter 1 Reaction Rate Consider the isomerization AB 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 11
Chapter 1 Reaction Rate EXAMPLE: AB If Species B is being formed at a rate of 0.2 moles per decimeter cubed per second, i.e., 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 12
Chapter 1 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 13 Chapter 1 Reaction Rate Consider 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 = kCA2) 14 Chapter 1 Building Block 1: General Mole Balances
System Volume, V Fj0 Gj Molar Flow Rate of Species j in Fj 0 15
mole time Fj Molar Flow Molar Rate Molar Rate Rate of Generation Accumulation Species j out of Species j of Species j dN j
Fj Gj dt mole mole mole
time time time Chapter 1 Building Block 1: General Mole Balances If spatially uniform: G j rjV If NOT spatially uniform:
V1 rj1 G j1 rj1V1 16 V2 rj 2 G j 2 rj 2 V2 Chapter 1 Building Block 1:
General Mole Balances n G j rji Vi i 1 Take limit n G j rji Vi i1 lim V 0 n
17 rj dV Chapter 1 Building Block 1: General Mole Balances System Volume, V FA0 GA
FA General Mole Balance on System Volume V In Out Generation Accumulation dN A FA 0 FA rA dV dt 18 Chapter 1
Batch Reactor - Mole Balances Batch dN A FA0 FA rA dV dt FA0 FA 0 Well-Mixed 19 19 r dV A
rAV dN A rAV dt Chapter 1 Batch Reactor - Mole Balances Integrating when dN A dt rAV
t 0 N A N A0 t t N A N A NA dN A t rAV N A0 Time necessary to reduce the number of moles of A from NA0 to NA. 20 Chapter 1 Batch Reactor - Mole Balances
NA dN A t rAV N A0 NA 21 t Chapter 1 CSTR - Mole Balances
CSTR dN A FA 0 FA rA dV dt Steady State 22 dN A 0 dt Chapter 1
CSTR - Mole Balances Well Mixed r dV r V A A FA 0 FA rAV 0 FA 0 FA V rA
CSTR volume necessary to reduce the molar flow rate from FA0 to FA. 23 Plug Flow Reactor - Mole Balances 24 Chapter 1 Plug Flow Reactor - Mole Balances V
FA 25 V FA V V In Out
Generation 0 at V at V V in V FA V FA V V rA V 0 Chapter 1 Plug Flow Reactor - Mole Balances
Chapter 1 Rearrange and take limit as VV0 lim V 0 FA V V FA V V rA dFA rA
dV This is the volume necessary to reduce the entering molar flow rate (mol/s) from FA0 to the exit molar flow rate of FA. 26 Plug Flow Reactor - Mole Balances PFR dN A FA0 FA rA dV dt Steady State
dN A 0 dt FA0 FA rA dV 0 27 Chapter 1 Alternative Derivation Plug Flow Reactor - Mole
Balances Differientiate with respect to V dFA rA dV dFA 0 rA dV FA The integral form is:
28 dFA V rA FA 0 This is the volume necessary to reduce the entering molar flow rate (mol/s) from FA0 to the exit molar flow rate of FA. Chapter 1 Packed Bed Reactor - Mole
Chapter 1 Balances W PBR FA FA W 29
W W dN A FA W FA W W rAW dt dN A Steady State 0 dt FA W W FA W lim rA W 0 W
Packed Bed Reactor - Mole Chapter 1 Balances Rearrange: dFA rA dW The integral form to find the catalyst weight is:
FA dFA W rA F A0 PBR catalyst weight necessary to reduce the entering molar flow rate FA0 to molar flow rate FA. 30 Reactor Mole Balances Summary Chapter 1
The GMBE applied to the four major reactor types (and the general reaction AB) Reactor Batch Differential PBR 31 dN A t rV
N A0 A V dFA rA dV dFA rA dW Integral NA dN A rAV
dt CSTR PFR Algebraic FA 0 FA rA FA V FA 0 FA
dFA drA dFA W rA F NA t FA V FA A0
W Reactors with Heat Effects Chapter 11 Fast Forward to the 10th Week of the Course EXAMPLE: Production of Propylene Glycol in an Adiabatic CSTR Propylene glycol is produced by the hydrolysis of propylene oxide:
H SO 2 CH2 CH CH3 H 2O 4 CH2 CH CH3 O 32 OH OH Fast Forward to the 10th Week of the Course Chapter 11
v0 Propylene Glycol What are the exit conversion X and exit temperature T? Solution Let the reaction be represented by A+BC 33 Chapter 11 34 Chapter 11
35 Chapter 11 Parameter Evaluation (CA0, i, ): The total liquid volumetric flow rate entering the reactor is 36 Chapter 11 Evaluate mole balance terms: The conversion calculated from the mole balance, XMB, is found form Equation (E88.5). 37
Chapter 11 38 Chapter 11 Evaluate energy balance terms 39 Chapter 11 40 Chapter 11
41 Chapter 11 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 A+BC X=0.84 T=614 R
42 Algorithm Keeping Up 43 Algorithm Separations Filtration Distillation
Adsorption These topics do not build upon one another. 44 Algorithm Reaction Engineering Mole Balance Rate Laws Stoichiometry
These topics build upon one another. 45 Algorithm Heat Effects Isothermal Design Stoichiometry Rate Laws Mole Balance CRE Algorithm 46 Algorithm
Rate Laws Mole Balance Be careful not to cut corners on any of the CRE building blocks while learning this material! 47 Algorithm Heat Effects Isothermal Design Stoichiometry
Rate Laws Mole Balance Otherwise, your Algorithm becomes unstable. 48 End of Lecture 1 49 Supplemental Slides Additional Applications of CRE 50 Supplemental Slides
Additional Applications of CRE 51 Supplemental Slides Additional Applications of CRE 52 Supplemental Slides Additional Applications of CRE Hippo Digestion (Ch. 2) 53
Supplemental Slides Additional Applications of CRE 54 Supplemental Slides Additional Applications of CRE 55 Supplemental Slides Additional Applications of CRE Smog (Ch. 1) 56
Supplemental Slides Additional Applications of CRE Chemical Plant for Ethylene Glycol (Ch. 5) 57 Supplemental Slides Additional Applications of CRE Wetlands (Ch. 7 DVD-ROM) 58 Oil Recovery (Ch. 7)
Supplemental Slides Additional Applications of CRE Cobra Bites (Ch. 8 DVD-ROM) 59 Supplemental Slides Additional Applications of CRE Lubricant Design (Ch. 9) 60 Supplemental Slides
Additional Applications of CRE Plant Safety (Ch. 11,12,13) 61
