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: yongdan.li@aalto.fiKemistintie 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

– yongdan.li@aalto.fi

University lecturer Reetta Karinen

– reetta.karinen@aalto.fi

University teacher Tiia Viinikainen

– tiia.viinikainen@aalto.fi

Contact Information

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

Assignments

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

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]

Evaluation

Assignment - 20%

Project - 80%

Submitted design project report are evaluated by teachers according to

validity and logicality

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

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)

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.

Classification of chemical reactions useful in reactor design

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

𝑑𝑁𝑖

𝑑𝑡=

𝑚𝑜𝑙𝑒 𝑖 𝑓𝑜𝑟𝑚𝑒𝑑

(𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑓𝑙𝑢𝑖𝑑)(𝑡𝑖𝑚𝑒)

Based on unit mass of solid in fluid-solid systems,

𝑟𝑖′ =

𝑑𝑁𝑖

𝑑𝑡=

(𝑚𝑎𝑠𝑠 𝑜𝑓 𝑠𝑜𝑙𝑖𝑑)(𝑡𝑖𝑚𝑒)(3)

Based on unit volume of solid in gas-solid systems,

𝑟𝑖′′′ =

𝑉𝑠

𝑑𝑁𝑖

𝑑𝑡=

(𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑠𝑜𝑙𝑖𝑑)(𝑡𝑖𝑚𝑒)(5)

Based on unit interfacial surface in two-fluid systems or

based on unit surface of solid in gas-solid systems,

𝑟𝑖′′ =

𝑑𝑁𝑖

𝑑𝑡=

(𝑠𝑢𝑟𝑓𝑎𝑐𝑒)(𝑡𝑖𝑚𝑒)(4)

Based on unit volume of reactor, if different from the rate based on unit

volume of fluid,

𝑟𝑖′′′′ =

𝑉𝑟

𝑑𝑁𝑖

𝑑𝑡=

(𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑟𝑒𝑎𝑐𝑡𝑜𝑟)(𝑡𝑖𝑚𝑒)(6)

Reaction rate is the key issue

Relationship between these definitions:

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.

Broad classification of reactor types

(a) The batch reactor. (b) The steady-state flow reactor. (c), (d), and (e) Various forms of the

semibatch reactor

Broad classification of reactor types

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.

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

Ammonia Synthesis

Example II: Fluid Catalytic Cracking (FCC)

Heavier fractions are converted into naphtha and middle distillates

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

Catalyst

20% Zeolite Y

80% Matrix

The catalyst

and coke

Coke was burned,

and the catalyst was

heated

The hot catalyst

Fluid Catalytic Cracking (FCC)

Example III: Hydrocarbon Thermal Cracking

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 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

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

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

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

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

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,

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.

aA + bB cC + dD

CAa=-rA CB

Mass interaction law

For an elementary reaction:

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

However,

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

Br2 → 2Br ·

Br · + H2 → HBr + H ·

H · + Br2 → HBr + Br ·

Br · and H ·

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

Kinetic Model Development

Type 1

Type 2

For unseen and unmeasured intermediate X

Pseudo-steady-state approximation

Quasi-equilibrium approximation

A X X B

=-rX 0

A + B C : A + B X X C

X C is rate-determining step

A + B X K=k1/k2=[X]/([A][B])k1

Kinetic Model Example

(10) (11)

Type 1, steady-state

approximation

Michaelis-Menten

d[X]/dt ≈ 0

Temperature Dependency from Arrhenius' Law

Arrhenius’ Law

Frequency factor

Activation energy

Same concentration

Actually,Mask pre-

exponential termsensitiveCollision and transition

state theories

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.

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

The Conversion

XA: the conversion of A

Irreversible Unimolecular-Type First-Order Reactions

Suppose the first-order rate equation,

Separating and integrating,

In terms of conversion ( Eqs. 17 and 18) and the rate equation Eq. 20,

Rearranging and integrating,

Fig 1.2 Test for the first-order rate equation

21 or 22

Irreversible Bimolecular-Type Second-Order Reactions

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

After breakdown into partial fractions, integration, and rearrangement, the final result in

a number of different forms is

Fig 1.3 Test for the bimolecular mechanism A + B → R with CA0 ≠ CB0

CA0 CB0

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

On integration it yields

Rate Equations of nth Order reaction

When the mechanism of reaction is not known

On separation and integration it yields

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

Zero-Order Reactions high

concentration

Integrating and noting that CA can never become negative

concentration

independent

radiation intensity,

available surface

Fig 1.4 Test for a zero-order reaction

Overall Order of Irreversible Reactions from the Half-Life t1/2

If CB0/CA0 = β/α…, at any time CB/CA = β/α…

Integrating for n ≠ 1 gives

Half-Life t1/2 (Time needed for CA /CA0 =1/2) is

Irreversible Reactions in Parallel

Eq. 33, which is of simple first order, is integrated to give

dividing Eq. 34 by Eq. 35 we obtain the following

Fig 1.6 Plotting for Eqs. 36, 37 Fig 1.7 Concentration-time curves for Parallel reactions

Irreversible Reactions in Series

First consider consecutive unimolecular type first-order reactions

Start with a concentration CA0 of A, no R or S present. Integrate Eq. 38,

Substitute CA in Eq. 39

(42) (43)

Because there is no change in total number of moles,

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)

Fig 1.8 Typical concentration-time curves for consecutive first-order reactions

Evaluate k1 and k2

First-Order Reversible Reactions

Irreversible reactions can be considered as reversible ones with large equilibrium constants.

Starting with M = CR0/CA0

equilibrium constant

Now at equilibrium dCA/dt = 0, Hence

Combining the above three equations (48, 49, 50)

(49) (50)

Reversible

Irreversible

special case CAe=0 or

XAe=1 or

KC= ∞

Fig 1.9 Test for the unimolecular type reversible (i) and irreversible (ii) reactions

Second-Order Reversible Reactions

For the bimolecular-type second-order reactions

When CA0=CB0 and CR0=CS0=0

Fig 1.10 Test for the reversible bimolecular reactions

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

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

Noting that (56)

On combining with Eq. 54

(isothermal varying-volume systems)

In general

Replace V (Eq. 54) and NA (Eq. 56)

in terms of volume (Eq. 54)

Zero-Order Reactions

First-Order Reactions

Replace XA by V from Eq. 54 and integrate it gives

Second-Order Reactions

Yongdan LiProfessor of Industrial ChemistryDepartment of Chemical and Metallurgical EngineeringSchool of Chemical TechnologyAalto UniversityEmail: yongdan.li@aalto.fiKemistintie 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

Chemical Reactor Design-CHEM-E7135

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