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Chemical Reactor Design-CHEM-E7135
Yongdan Li
The field that studies the rates and mechanisms of chemical
reactions and the design of the reactors in which they take place
Professor of Industrial ChemistryDepartment of Chemical and Metallurgical EngineeringSchool of Chemical TechnologyAalto UniversityEmail: [email protected] 1, E404
Date/time Place Topic Lecturers
Mon 7th of Jan 10:15-12:00 Ke 5 D 311 Lecture 1: Introduction to the course and basic
kinetics
Yongdan Li
Mon 21th of Jan 10:15-12:00 Ke 5 D 311 Lecture 2: Ideal reactor design Yongdan Li
Mon 28th of Jan 10:15-12:00 Ke 5 D 311 Lecture 3: Non-ideal flow patterns Yongdan Li
Mon 4th of Feb 10:15-12:00 Ke 5 D 311 Assignment 1: Lecture 1-2
Assign the project
Reetta Karinen/Tiia
Viinikainen
Yingnan Zhao/Yongdan Li
Mon 11th of Feb 10:15-12:00 Ke 5 D 311 Lecture 4: Typical catalytic reactors Yongdan Li
Mon 25th of Feb 10:15-12:00 Ke 5 D 311 Assignment 2: Lecture 3-4 Reetta Karinen/Tiia
Viinikainen
Fri 1th of Mar 10:15-12:00 Ke 5 D 311 Lecture 5: Typical non-catalytic reactors Yongdan Li
Mon 4th of March 10:15-12:00 Ke 5 D 311 Lecture 6: Micro-structured reactors Yongdan Li
Fri 8th of March 10:15-12:00 Undetermined Feedback of project Yingnan Zhao/Yongdan Li
Mon 11th of March 10:15-12:00 Ke 5 D 311 Lecture 7: Biochemical reaction systems Yongdan Li
Fri 15th of March 10:15-12:00 Ke 5 D 311 Lecture 8: Reactors with ion transfer through
interfaces
Zhengze Pan/Yongdan LI
Mon 18th of March 10:15-12:00 Ke 5 D 311 Assignment 3: Lecture 5-7 Reetta Karinen/Tiia
Viinikainen
Course Timetable
8 Lectures, 3 Assignments and 1 Project are contained
Professor Yongdan Li
– Office hours whenever office door is open, room E404
University lecturer Reetta Karinen
– Office hours whenever office door is open, room E406
University teacher Tiia Viinikainen
– Office hours whenever office door is open, room E406
3
Contact Information
4
Text Book
Chemical
Reaction
Engineering Third Edition
Octave Levenspiel
Department of Chemical Engineering
Oregon State University
Online version of the textbook available in Aalto University:
https://app.knovel.com/web/toc.v/cid:kpCREE0005/viewerTy
pe:toc/root_slug:viewerType%3Atoc/url_slug:root_slug%3Ac
hemical-reaction-engineering?kpromoter=federation
A teacher will guide you to do assignments
Solution
A. Several examples are demonstrated to teach you how to
calculate the related problems
B. Assignments should be completed by you with the help of
teachers
A. Examples
B. Assignments
5
Assignments
6
Project
Design a Non-catalytic Reactor for Olefins Production by Pyrolysis
Some related materials will be given in Mycourse
Submit a design report: Detailed requirements will be listed after the first
assignment
• Background
• Reactor selection
• Mass balance
• Heat balance
• Flow pattern
• Reactor volume
………
Attention: A feedback about your project should be given before the end of the lectures -
Show introduction and plan of the project
MyCourses is used during the course
– mycourses.aalto.fi/
– General information and time table
– Lecture slides
– Exercises and assignments
– Project materials
7
Handling
Submission of assignments and project in MyCourses
Content Given Accepted DL
First assignment Mon 04th of Feb Thu 14th of Feb
Second assignment Mon 25th of Feb Thu 07th of Mar
Third assignment Mon 18th of Mar Thu 28th of Mar
Project assignment Mon 04th of Feb Mon 01st of Apr
Feedback of project on Fri 8th of Mar, 10:15-12:00
Completed assignments are marked by teachers at the end
Total number of exercises in the assignment is 10
Points distribution Number of exercises to
be completed
20 P (7.5-10]
15 p (5-7.5]
10 p (2.5-5]
5 P [0.5-2.5]
8
Evaluation
Assignment - 20%
Project - 80%
Submitted design project report are evaluated by teachers according to
validity and logicality
9
Overview of Chemical Reactor Design
Typical chemical process
Chemical reaction engineering (or reactor design) is the engineering practice
concerned with the exploitation of chemical reactions on a commercial scale.
Its goal is the successful design and operation of chemical reactors.
Thermodynamics Chemical kinetics Fluid mechanics
Heat transferMass transfer Economics
10
Input Output
Performance equation
relates input to output
Contacting pattern or how materials
flow through and contact each other in
the reactor, how early or late they mix,
their clumpiness or state of aggregation.
By their very nature some materials are
very clumpy, for instance, solids and
noncoalescing liquid droplets.
Kinetics or how fast things happen. If
very fast, then equilibrium tells what
will leave the reactor. If not so fast, then
the rate of chemical reaction, and maybe
heat and mass transfer too, will
determine what will happen.
Information needed to predict what a reactor can do
Output = f [input, kinetics, contacting] (1)
Overview of Chemical Reactor Design
11
Develop appropriate performance equations by reaction types
It depends on how we choose to treat them, and this in turn depends on which
description we think is more useful.
Overview of Chemical Reactor Design
Classification of chemical reactions useful in reactor design
12
Reaction rate is the key issue
If the rate of change in number of moles of component i due to reaction is
dNi/dt, the rate of reaction is defined as follows.
Based on unit volume of reacting fluid,
𝑟𝑖 =1
𝑉
𝑑𝑁𝑖
𝑑𝑡=
𝑚𝑜𝑙𝑒 𝑖 𝑓𝑜𝑟𝑚𝑒𝑑
(𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑓𝑙𝑢𝑖𝑑)(𝑡𝑖𝑚𝑒)
(2)
Overview of Chemical Reactor Design
Based on unit mass of solid in fluid-solid systems,
𝑟𝑖′ =
1
𝑊
𝑑𝑁𝑖
𝑑𝑡=
𝑚𝑜𝑙𝑒 𝑖 𝑓𝑜𝑟𝑚𝑒𝑑
(𝑚𝑎𝑠𝑠 𝑜𝑓 𝑠𝑜𝑙𝑖𝑑)(𝑡𝑖𝑚𝑒)(3)
13
Based on unit volume of solid in gas-solid systems,
𝑟𝑖′′′ =
1
𝑉𝑠
𝑑𝑁𝑖
𝑑𝑡=
𝑚𝑜𝑙𝑒 𝑖 𝑓𝑜𝑟𝑚𝑒𝑑
(𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑠𝑜𝑙𝑖𝑑)(𝑡𝑖𝑚𝑒)(5)
Overview of Chemical Reactor Design
Based on unit interfacial surface in two-fluid systems or
based on unit surface of solid in gas-solid systems,
𝑟𝑖′′ =
1
𝑆
𝑑𝑁𝑖
𝑑𝑡=
𝑚𝑜𝑙𝑒 𝑖 𝑓𝑜𝑟𝑚𝑒𝑑
(𝑠𝑢𝑟𝑓𝑎𝑐𝑒)(𝑡𝑖𝑚𝑒)(4)
Based on unit volume of reactor, if different from the rate based on unit
volume of fluid,
𝑟𝑖′′′′ =
1
𝑉𝑟
𝑑𝑁𝑖
𝑑𝑡=
𝑚𝑜𝑙𝑒 𝑖 𝑓𝑜𝑟𝑚𝑒𝑑
(𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑟𝑒𝑎𝑐𝑡𝑜𝑟)(𝑡𝑖𝑚𝑒)(6)
Reaction rate is the key issue
14
Relationship between these definitions:
Overview of Chemical Reactor Design
Variables Affecting the Rate of Reaction
In homogeneous systems the temperature, pressure, and composition are
obvious variables.
Heat and mass transfer may play important roles in determining the rates
of heterogeneous reactions.
15
Broad classification of reactor types
Overview of Chemical Reactor Design
(a) The batch reactor. (b) The steady-state flow reactor. (c), (d), and (e) Various forms of the
semibatch reactor
16
Broad classification of reactor types
Overview of Chemical Reactor Design
Batch Ideal for small-scale experimental studies on reaction kinetics
or small amounts of material are to be treated industrially.
Steady-state flow
Ideal for industrial purposes when large quantity of materials
is to be processed and when the rate of reaction is fairly high
to extremely high. Good product quality control can be obtai-
ned (oil industry).
Semibatch
It offers good control of reaction speed because the reaction
proceeds as reactants are added. It was used from the calor-
imetric titrations in the laboratory to the large open hearth
furnaces for steel production.
17
Batch
Rea
ctor
Flo
w R
eacto
r
Overview of Chemical Reactor Design
18
Example I: Ammonia Synthesis
20~35 MPa
470~520 oC
Ammonia is the initial chemical material for a variety of industries. Ammonia synthesis
is therefore a very important process in chemical world.
The reaction features
High temperature
High pressure
Exothermic process
The reactor must bear high temperature and high pressure
The heat generated by the reaction must be removed in time
The requirements for reactors
N2 + 3H2 2NH3
N2 and H2
The reactor shell bare
the high pressure
The core layer of the reactor
bare the high temperature
The heat generated by the reaction
was removed by the cool N2 and H2,
and the feeding N2 and H2was
preheated
NH3
Ammonia Synthesis
19
Example II: Fluid Catalytic Cracking (FCC)
Heavier fractions are converted into naphtha and middle distillates
AlCl3
Earthly 20th century
Acid-treated clay
1930 1940
silica-alumina Zeolites
1963-Nowadays
FCC is an endothermic process
Coke deposits on the catalyst,
so the catalyst easily deactivates
The reaction features
Catalyst
20% Zeolite Y
80% Matrix
20
The catalyst
and coke
Coke was burned,
and the catalyst was
heated
The hot catalyst
Fluid Catalytic Cracking (FCC)
21
Example III: Hydrocarbon Thermal Cracking
22
The raw material is heated to 750-900 oC for pyrolysis without catalyst
Naphtha oil, but natural gas, refinery gas, light oil, diesel, heavy oil
etc. are also occasionally used
Raw Material
Ethylene, propylene, butadieneProducts
The reaction features
The reaction is strongly endothermic. Increasing the temperature is advantageous for
the formation of olefins
The residence time of the feedstock in the reactor should be as short as possible. If
reaction reaches equilibrium, large amounts of hydrogen and carbon will be formed.
Reducing the pressure helps to improve the ethylene balance composition and
inhibit the coking reaction
Hydrocarbon Thermal Cracking
23
Tubular reactor
The reactor is placed at the center of the furnace and the heat is adsorbed in the flame.
Diameter 75 ~ 133 mm
length: 80~90 m
Wall temperature 1050 ~1100 oC
Flow rate 277 m/s
Residence time 0.09s
Outlet gas temperature 875 oC
Using high temperature resistant alloy steel: HP-40 ( Ni-Cr alloy steel )
Hydrocarbon Thermal Cracking
24
The volume of gas in the tube increases greatly. The pressure drop caused by small
diameter is obvious
The conversion of the reaction becomes high, and the demand for heat is
moderated
The coking is serious and the large diameter can reduce the risk of coke blockage
Variable diameter
(increase)
At the later period of the reaction
1. Kinetics of Chemical Reactions
26
Lecture 1.1 Basis of Kinetics
The Rate Equation
Suppose a single-phase reaction:
The most useful measure of reaction rate for reactant A is
The rates of reaction of all molecules are related by
Experience shows that the rate of reaction is influenced by the composition and energy
of the material.
Temperature
27
Lecture 1.1 Basis of Kinetics
The Rate Equation
Suppose a single-phase reaction:
The most useful measure of reaction rate for reactant A is
The rates of reaction of all molecules are related by
Experience shows that the rate of reaction is influenced by the composition and energy
of the material.
Temperature
28
Single and Multiple Reactions
When a single stoichiometric equation and single rate equation are chosen
to represent the progress of the reaction, we have a single reaction.
When more than one stoichiometric equation is chosen to represent the
observed changes, then more than one kinetic expression is needed to
follow the changing composition of all the reaction components, and we
have multiple reactions.
Series reactions,
Parallel reactions,
more complicated,
Lecture 1.1 Basis of Kinetics
29
Elementary and Nonelementary Reactions
The rate-controlling
mechanism involves
the collision or
interaction of a A
molecules with b B
molecules
The number of
collisions of molecules
A with B is proportional
to the rate of reaction
The number of collisions
is proportional to the
concentration of
reactants in the mixture
(T constant)
Such reactions are called elementary reactions.
Otherwise, the ones are called nonelementary reactions.
Lecture 1.1 Basis of Kinetics
aA + bB cC + dD
CAa=-rA CB
bk
Mass interaction law
For an elementary reaction:
30
Representation of an Elementary Reaction
the order unchanged, but k different
any measure equiva-
lent to concentration
AMBIGUITY:
correct -r expression?
k1 refers to ?
1) write the stoichiometric
equation followed by the
complete rate expression.
2) give the units of the rate
constant
I
II
However,
Lecture 1.1 Basis of Kinetics
31
Representation of a Nonelementary Reaction
Stoichiometry: Rate:
Develop a multistep reaction model to explain the kinetics
unobserved intermediates
Determined by experiments
Suggested by chemistry of the materials
Lecture 1.1 Basis of Kinetics
Br2 → 2Br ·
Br · + H2 → HBr + H ·
H · + Br2 → HBr + Br ·
Br · and H ·
32
Molecularity and Order of Reaction
The molecularity of an elementary reaction (must be an elementary reaction)
is the number of molecules taking part in the reaction.
This has been found to have the values of one, two, or occasionally three.
For non-elementary reaction: a, b, . . . , d are not necessarily related to the
stoichiometric coefficients.
We call the powers to which the concentrations are raised the order of the Reaction.
Must be integer
A fractional value
is allowable
ath order with respect to A bth order with respect to B nth order overall
k: rate constant, (time)-1(concentration)1-n
Lecture 1.1 Basis of Kinetics
33
Kinetic Model Development
Type 1
Type 2
For unseen and unmeasured intermediate X
Pseudo-steady-state approximation
Quasi-equilibrium approximation
Lecture 1.1 Basis of Kinetics
A X X B
=-rX 0
A B :
A + B C : A + B X X C
X C is rate-determining step
A + B X K=k1/k2=[X]/([A][B])k1
k2
34
Kinetic Model Example
Lecture 1.1 Basis of Kinetics
(8)
(9)
(10) (11)
Type 1, steady-state
approximation
(13)
(14)
(12)
Michaelis-Menten
type
d[X]/dt ≈ 0
35
Temperature Dependency from Arrhenius' Law
Arrhenius’ Law
Frequency factor
Activation energy
J/mol
Same concentration
Actually,Mask pre-
exponential termsensitiveCollision and transition
state theories
Lecture 1.1 Basis of Kinetics
36
Activation Energy and Temperature Dependency
Fig 1.1 Sketch showing temperature dependency of the reaction rate
1, Reactions with high activationenergies are very temperature-sensitive.
2, Reactions are much moretemperature-sensitive in lowtemperature range than in ahigh temperature range.
Lecture 1.1 Basis of Kinetics
37
Constant-VolumeConstant-density
reaction system
Constant-Volume
of reaction mixture
Most liquid-phase reactions and all gas-phase
reactions occurring in a constant-volume bomb
For gas reactions with
changing numbers of moles
ri is to follow the change
in total pressure π
(15) (16)
Lecture 1.2 Constant-Volume Batch Reactor
38
The Conversion
XA: the conversion of A
(17)
(18)
Irreversible Unimolecular-Type First-Order Reactions
(19)
Suppose the first-order rate equation,
(20)
Lecture 1.2 Constant-Volume Batch Reactor
39
Separating and integrating,
(21)
In terms of conversion ( Eqs. 17 and 18) and the rate equation Eq. 20,
(22)
Rearranging and integrating,
Fig 1.2 Test for the first-order rate equation
Lecture 1.2 Constant-Volume Batch Reactor
21 or 22
40
Irreversible Bimolecular-Type Second-Order Reactions
(23)
Note: The reacted amounts of A and B at any time t are equal, i.e., CA0XA= CB0XB,
Let M = CB0/CA0 be the initial molar ratio of reactants,
After separation and integration it becomes
Lecture 1.2 Constant-Volume Batch Reactor
41
After breakdown into partial fractions, integration, and rearrangement, the final result in
a number of different forms is
(24)
Fig 1.3 Test for the bimolecular mechanism A + B → R with CA0 ≠ CB0
CA0 CB0
Lecture 1.2 Constant-Volume Batch Reactor
42
Reactants are introduced in their stoichiometric ratio
go back to the original diff-
erential rate expression
For a second-order reaction with equal initial CA0 and CB0 or for the reaction
the defining second-order differential equation becomes
(25)
On integration it yields
(26)
Lecture 1.2 Constant-Volume Batch Reactor
43
Rate Equations of nth Order reaction
When the mechanism of reaction is not known
(27)
On separation and integration it yields
(28)
Trial-and-error solution select a value for n and calculate k. The value of n which minimizes
the variation in k is the desired value of n
Curious features
the reaction never goes to completion
the reactant concentration will fall to zero and
then become negative
n > 1
n < 1
Lecture 1.2 Constant-Volume Batch Reactor
44
Zero-Order Reactions high
concentration
(29)
Integrating and noting that CA can never become negative
(30)
concentration
independent
radiation intensity,
available surface
Fig 1.4 Test for a zero-order reaction
Lecture 1.2 Constant-Volume Batch Reactor
30
30
45
Overall Order of Irreversible Reactions from the Half-Life t1/2
If CB0/CA0 = β/α…, at any time CB/CA = β/α…
(31)
Integrating for n ≠ 1 gives
Half-Life t1/2 (Time needed for CA /CA0 =1/2) is
(32a)
Lecture 1.2 Constant-Volume Batch Reactor
32a
46
Irreversible Reactions in Parallel
(33)
(34)
(35)
Eq. 33, which is of simple first order, is integrated to give
(36)
dividing Eq. 34 by Eq. 35 we obtain the following
(37)
Lecture 1.2 Constant-Volume Batch Reactor
47
Fig 1.6 Plotting for Eqs. 36, 37 Fig 1.7 Concentration-time curves for Parallel reactions
Lecture 1.2 Constant-Volume Batch Reactor
3637
48
Irreversible Reactions in Series
First consider consecutive unimolecular type first-order reactions
(38)
(39)
(40)
Start with a concentration CA0 of A, no R or S present. Integrate Eq. 38,
(41)
Substitute CA in Eq. 39
(42) (43)
Lecture 1.2 Constant-Volume Batch Reactor
49
Because there is no change in total number of moles,
(44)
In general, for any number of reactions in series it is the slowest
step that has the greatest influence on the overall reaction rate
Differentiate Eq. 43 and set dCR/dt = 0, CR, max occurs
(45) (46)
Lecture 1.2 Constant-Volume Batch Reactor
50
Fig 1.8 Typical concentration-time curves for consecutive first-order reactions
Evaluate k1 and k2
Lecture 1.2 Constant-Volume Batch Reactor
43
41
44
46
45
51
First-Order Reversible Reactions
Irreversible reactions can be considered as reversible ones with large equilibrium constants.
(47)
Starting with M = CR0/CA0
equilibrium constant
(48)
Now at equilibrium dCA/dt = 0, Hence
and
Combining the above three equations (48, 49, 50)
Lecture 1.2 Constant-Volume Batch Reactor
(49) (50)
(51)
52
(51)
(21)
Reversible
Irreversible
(22)
special case CAe=0 or
XAe=1 or
KC= ∞
i
ii
Fig 1.9 Test for the unimolecular type reversible (i) and irreversible (ii) reactions
Lecture 1.2 Constant-Volume Batch Reactor
51
21-22
53
Second-Order Reversible Reactions
For the bimolecular-type second-order reactions
(52a)
(52b)
(52c)
(52d)
When CA0=CB0 and CR0=CS0=0
(53)
Fig 1.10 Test for the reversible bimolecular reactions
Lecture 1.2 Constant-Volume Batch Reactor
53
54
Lecture 1.3 Varying-Volume Batch Reactor
Fig 1.11 A varying-volume batch reactor
The progress of the reaction is followed
by noting the movement of the bead with
time
Isothermal constant
pressure operations
Volume is linearly related
to the conversion (54)
(55)Fractional change in volume of the system between no
conversion and complete conversion of reactant A
Examplepure A 50% A
50% Ar
55
Noting that (56)
On combining with Eq. 54
(57)
(isothermal varying-volume systems)
In general
Replace V (Eq. 54) and NA (Eq. 56)
in terms of volume (Eq. 54)
(58)
(59)
Lecture 1.3 Varying-Volume Batch Reactor
56
Zero-Order Reactions
(60)
Lecture 1.3 Varying-Volume Batch Reactor
First-Order Reactions
Replace XA by V from Eq. 54 and integrate it gives
(61)
Second-Order Reactions
or
(62)
Yongdan LiProfessor of Industrial ChemistryDepartment of Chemical and Metallurgical EngineeringSchool of Chemical TechnologyAalto UniversityEmail: [email protected] 1, E404
Chemical Reactor Design
The field that studies the rates and mechanisms of chemical
reactions and the design of the reactors in which they take place