Introduction to Chemical Reaction Engineering
CHBE 424:
Chemical Reaction Engineering
Introduction & Lecture 1
Understanding how chemical reactors work lies at the heart of
almost every chemical processing operation.
Design of the reactor is no routine matter, and many
alternatives can be proposed for a process. Reactor design
uses information, knowledge and experience from a variety of
areas - thermodynamics, chemical kinetics, fluid mechanics,
heat and mass transfer, and economics.
CRE is the synthesis of all these factors with the aim of
properly designing and understanding the chemical reactor.
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Type & size
Maximize the space-time yield of the desired product
(productivity lb/hr/ft
3
)
Stoichiometry
Kinetics
Basic molar balances
Fluid dynamics
Reactor volume
Use a lab-scale reactor to determine the kinetics!
Reactor Design
Reaction
Stoichiometry
Kinetics: elementary vs non-elementary
Single vs multiple reactions
Reactor
Isothermal vs non-isothermal
Ideal vs nonideal
Steady-state vs nonsteady-state
What type of reactor(s) to use?
C
ontinuously
S
tirred
T
ank
R
eactor (CSTR)
Well-mixed batch reactor
Plug flow reactor (PFR)
What size reactor(s) to use?
Answers to this questions are based on the desired
conversion, selectivity and kinetics
Reactor type
&
size
Conversion
&
selectivity
Chemical Reaction
•
A detectable number of molecules have
lost their identity
and assumed a new form by a change in the kind or number
of atoms in the compound and/or by a change in the atoms’
configuration
•
Decomposition
•
Combination
•
Isomerization
•
Rate of reaction
–
How fast a number of moles of one chemical species are
being consumed to form another chemical species
Rate Law for
r
j
•
r
A
: the rate of
formation
of species A per unit volume [e.g., mol/m
3•
s
]
•
-r
A
: the rate of a
consumption
of species A per unit volume
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1
st
order in A, 1
st
order in B, 2
nd
order overall
n
th
order in A
Michaelis-Menton: common in enzymatic reactions
Basic Molar Balance (BMB)
combine
N
j
: moles j in
system at time t
Basic Molar Balance (BMB)
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:
Non-Uniform Generation
V
If r
j
varies with position (because
the temperature or concentration
varies) then r
j1
at location 1 is
surrounded by a small subvolume
V within which the rate is uniform
Rate is r
j1
within this
volume
V
Rate is r
j2
within this
volume
1
1
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x
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system
Basic Molar Balance Equations
Next time: Apply BME to ideal batch, CSTR, & PFR reactors
Review of Frequently Encountered
Math Concepts
Solve for X:
Basic Math Review
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For n≠1:
For n=1:
Review of Basic Integration
Solve
for t:
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A
:
0
Solve for c:
ε
is a
constant
Chemical Reaction Engineering (CRE) is crucial for understanding how chemical reactors operate in various processing operations. This field involves reactor design by integrating factors such as thermodynamics, kinetics, fluid mechanics, heat transfer, and economics. CRE aims to effectively design and comprehend chemical reactors through the synthesis of diverse knowledge and experiences. The design process covers aspects like reactor type and size, maximizing productivity, stoichiometry, kinetics, fluid dynamics, and reactor volume determination. Various reactor types, such as Continuously Stirred Tank Reactors (CSTR) and Plug Flow Reactors (PFR), are designed based on factors like desired conversion, selectivity, and kinetics.
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Presentation Transcript
L1-1 CHBE 424: Chemical Reaction Engineering Introduction & Lecture 1 Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
L1-2 What is Chemical Reaction Engineering (CRE) ? Understanding how chemical reactors work lies at the heart of almost every chemical processing operation. Raw material Separation Process Chemical process Separation Process Products By-products Design of the reactor is no routine matter, and many alternatives can be proposed for a process. Reactor design uses information, knowledge and experience from a variety of areas - thermodynamics, chemical kinetics, fluid mechanics, heat and mass transfer, and economics. CRE is the synthesis of all these factors with the aim of properly designing and understanding the chemical reactor. Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
L1-3 How do we design a chemical reactor? Type & size Maximize the space-time yield of the desired product (productivity lb/hr/ft3) Stoichiometry Kinetics Basic molar balances Fluid dynamics Reactor volume Use a lab-scale reactor to determine the kinetics! Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
L1-4 Reactor Design Reaction Stoichiometry Kinetics: elementary vs non-elementary Single vs multiple reactions Reactor Isothermal vs non-isothermal Ideal vs nonideal Steady-state vs nonsteady-state Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
L1-5 What type of reactor(s) to use? in Continuously Stirred Tank Reactor (CSTR) out Plug flow reactor (PFR) Well-mixed batch reactor Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
L1-6 What size reactor(s) to use? Answers to this questions are based on the desired conversion, selectivity and kinetics Kinetics Reactor type & size Conversion & selectivity Material & energy balances Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
L1-7 Chemical Reaction A detectable number of molecules have lost their identity and assumed a new form by a change in the kind or number of atoms in the compound and/or by a change in the atoms configuration Decomposition Combination Isomerization Rate of reaction How fast a number of moles of one chemical species are being consumed to form another chemical species Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
L1-8 Rate Law for rj rA: the rate of formation of species A per unit volume [e.g., mol/m3 s] -rA: the rate of a consumption of species A per unit volume + A= r kC C A B products A B 1st order in A, 1st order in B, 2nd order overall n A= r kC nth order in A A k + C 1 k A C = r Michaelis-Menton: common in enzymatic reactions A 1 2 A rj depends on concentration and temperature: E a RT = -r Ae A: pre-exponential factor E R :ideal gas constant T:temperature C Arrhenius dependence on temperature :activation energy A A A Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
L1-9 Basic Molar Balance (BMB) Fj0 Fj Gj System volume Rate of flow of j into system Rate of flow of j out of system Rate of generation of j by chemical rxn Rate of decomposition of j Rate of accumulation - + - = combine Nj: moles j in system at time t dN j + = F F G 0j j j dt mol mol mol d ( ) mol s s s dt generation = accumulation out in - + Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
L1-10 Basic Molar Balance (BMB) Rate of flow of j into system system rxn Rate of flow of j out of Rate of generation of j by chemical Rate of decomposition of j Rate of accumulation - + - = dN j + = F F G 0j j j dt mol mol mol d ( ) mol s s s dt If the system is uniform throughout its entire volume, then: j= G r V j Moles Moles j generated per unit time (mol/s) generated per unit time and volume (mol/s m3) Volume (m3) = Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
L1-11 Non-Uniform Generation system If rj varies with position (because the temperature or concentration varies) then rj1 at location 1 is surrounded by a small subvolume V within which the rate is uniform V Rate is rj1 within this volume Rate is rj2 within this volume V V m = = G lim m V 0 r V r dV = i j j j 1 z 1 1 1 1 ( z , y , x ) = then G r dx dy dz 0 0 j j 0 y 1 Plug in rj and integrate over x, y, and z 1 x Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
L1-12 Basic Molar Balance Equations Fj0 Fj Gj System volume In Out - +Generation =Accumulation dN dt j + = F F G j0 j j dN dt dN dt j r V + = F F uniform rate n V i j0 j j V j + = F F r dV nonuniform rate in V j0 j j Next time: Apply BME to ideal batch, CSTR, & PFR reactors Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
L1-13 Review of Frequently Encountered Math Concepts Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
L1-14 Basic Math Review 1 x p n x = ( ) q ln a e p q = a x x n = ( ) y x ( ) ( ) = ln y ( ) ( ) ( ) ( ) y = + = ln x yln x ln x ln ln x ln y ln xy Example: Problems that Contain Natural Logs aln bt b ( ) ( ) ( ) + = 1 ln x ln y Solve for X: ) ( aln bt 1 b x y a b ( ) ( ) ( ) n y l ( ) + = + = ln x ln bt 1 ln ( ) x y x y a b ( ) a b + = bt 1 ( ) ln a b ( ) + ln bt 1 e + = y bt 1 x = e Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
L1-15 Review of Basic Integration 1 x p n x = q p q x x n = ) ( ( n 1 + n 1 + b b b 1dx x b + a + ) n 1 + n x n 1 + x dx = For n 1: n 1 n 1 n a a a b 1dx x b a b a ( ) ( ) ( ) ln x = ln b ln a = = ln a For n=1: n 5 1 5 1 1 c d 5 t 1 x c d dx x c d t 0 t 0 Solve for t: = t dt = = 1 0 2 1 = c d c c d 0.8 t 0.8 t = 0.2 1 t + = d Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
L1-16 k dc dt k dc c c = dt = Solve for c: 1 k t + 1 k t + d d t c t c 1 k k dc c c 1 dc k k dt dt = = 0 0 0 0 Do NOT move t or c outside of the integral 1 1 t t + + c c d d x x x 0 x is a constant From dx + + 1ln 1 dx 1ln 1 x ( ( ) ) = = + + x Appendix A: 1 1 x x 0 0 0 t 1 c c0 ( ) ( ) + = k ln 1 k t ln c d k d 0 1 1 ( ) ( ) ( ) ( ) + + = k ln 1 k t ln 1 k 0 ln c l n c d d 0 k k 0 d d kln k t k c ( ) ( ) ( ) ( ) + = 1 ln c ln c + = ln k t 1 ln d 0 d k k c d d 0 kln k t 1 kd c kln k t 1 kd k ( ) ( ) ( ) + + + ln ln k t 1 d d d c c k 0 = d e = = e e c e c 0 c 0 Slides courtesy of Prof M L Kraft, Chemical & Biomolecular Engr Dept, University of Illinois, Urbana-Champaign.
