Ert 316 reaction engineering chapter 1 mole balances
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ERT 316: REACTION ENGINEERING CHAPTER 1 MOLE BALANCES. Lecturer: Miss Anis Atikah Ahmad Email: [email protected] Tel: +604-976 3245. OUTLINE. Introduction Chemical Species Chemical Reaction Rate of Reaction General Mole Balance Equation Batch Reactor Continuous-Flow Reactors

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ERT 316: REACTION ENGINEERING CHAPTER 1 MOLE BALANCES

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Ert 316 reaction engineering chapter 1 mole balances

ERT 316: REACTION ENGINEERINGCHAPTER 1MOLE BALANCES

Lecturer: Miss Anis Atikah Ahmad

Email: [email protected]

Tel: +604-976 3245


Outline

OUTLINE

  • Introduction

  • Chemical Species

  • Chemical Reaction

  • Rate of Reaction

  • General Mole Balance Equation

  • Batch Reactor

  • Continuous-Flow Reactors

  • Industrial Reactors


Introduction

Introduction

  • Application of Chemical Reaction Engineering


1 chemical species

1. Chemical species

What are chemical species?

  • Any chemical component or element with a given identity.

  • Identity of a chemical species is determined by the kind, number, and configuration of that species’ atoms.

  • Kind of species- methane, butene, butane

  • Number of atoms- eg: CH4: 1 C, 4 H

  • Configuration of atoms- arrangement of the atoms


Ert 316 reaction engineering chapter 1 mole balances

Can they be considered as different SPECIES?

Kind: Same (Butene)

Number of atoms: Same (C4H8)

Configuration: Different arrangement

ANSWER: Yes. We consider them as two different species because they have different configurations.


2 chemical reaction

2. Chemical reaction

  • Chemical reaction is any reaction when one or more species lost their identity and produce a new form by a change in the kind or number of atoms in the compound, and/or by a change in structure or configuration of these atoms.

    HOW????


2 chemical reaction1

2. Chemical reaction

  • Species may lose its chemical identity by:

    1) Decomposition (by breaking down the

    molecule into smaller molecule)

    Eg: C ⇌ A + B

    2) Combination (reverse of decomposition)

    3) Isomerization ( neither add other molecule nor

    breaks into smaller molecule)


3 rate of reaction

It tells how fast a number of moles of one chemical species to form anotherchemical species.

3. Rate of Reaction,

,the rate of reaction: is the number of moles of A reacting (disappearing) per unit time per unit volume ( ).

, is the rate of formation (generation) of species A.

, is a heterogeneous reaction rate: the no of moles of A reacting per unit time per unit mass of catalyst ( catalyst)


4 the general mole balance equation

4. The General Mole Balance Equation

  • A mole balance of species j at any instant time:

Rate of accumulation of j within the system (moles/time)

Rate of generation of j by chemical reaction within the system (moles/time)

Rate of flow of j into the system (moles/time)

Rate of flow of j out of the system (moles/time)

In - Out + Generation = Accumulation

Fj0 - Fj + Gj =

Fj0 - Fj + =


4 the general mole balance equation1

4. The General Mole Balance Equation

Consider a system volume :

System volume

Fj0

Gj

Fj

General mole balance:

Fj0 - Fj + Gj = dNj/dt

In - Out + Generation = Accumulation


The general mole balance equation

The General Mole Balance Equation

Condition 1:

  • If all the the system variables (eg: T, C) are spatially uniform throughout a system volume:

    Gj = rj.V


The general mole balance equation1

The General Mole Balance Equation

Condition 2:

  • If the rate of formation, rjof a species j for the reaction varies with position in the system volume:

  • The rate of generation ∆Gj1:

    ∆Gj1=rj1∆V1

∆V1

rj1

rj2

∆V2

Fj0

Fj


4 the general mole balance equation2

4. The General Mole Balance Equation

  • The total rate of generation within the system volume is the sum of all rates of generation in each of the subvolumes.

  • Taking the limit M∞, and ∆V0 and integrating,


Type of reactors

TYPE OF REACTORS

in

out

Batch

REACTORS

Continuous

Flow


5 batch reactors

5. Batch Reactors

  • The reactants are first placed inside the reactor and then allowed to react over time.

  • Closed system: no material enters or leaves the reactor during the time the reaction takes place.

  • Operate under unsteady state condition.

  • Advantage: high conversion

the conditions inside the reactor (eg: concentration, temperature) changes over time


5 batch reactors derivation

5. Batch Reactors: Derivation

  • Batch reactor has neither inflow nor outflow of reactants or products while the reaction is carried out:

    FA0 = FA = 0

  • General Mole Balance on System Volume V

FA0 - FA+ =


5 batch reactors derivation1

5. Batch Reactors: Derivation

  • Assumption: Well mixed so that no variation in the rate of reaction throughout the reactor volume:

  • Rearranging;

  • Integrating with limit at t=0, NA=NA0

    & at t=t1, NA=NA1,


6 continuous flow reactors steady state

6. Continuous-Flow Reactors: steady state

1. Continuous-Stirred Tank Reactor (Backmix/ vat)

  • open system: material is free to enter

    or exit the reactor

    • reactants are fed continuously into the

      reactor.

    • products are removed continuously.

  • operate under steady state condition

  • perfectly mixed: have identical

    properties (T, C) everywhere within the vessel.

  • used for liquid phase reaction


6 1 continuous stirred tank reactor

6.1 Continuous-Stirred Tank Reactor

DERIVATION

  • General Mole Balance:

  • Assumption:

    1.steady state:

    2. well mixed:

  • Mole balance: FA - FA + = 0

FA0 - FA+ =

design equation

for CSTR


6 continuous flow reactors steady state1

6. Continuous-Flow Reactors: steady state

2. Plug Flow/Tubular Reactor

  • Consist of cylindrical hollow pipe.

  • Reactants are continuously

    consumed as they flow down the

    length of the reactor.

  • Operate under steady state cond.

  • No radial variation in velocity, conc,

    temp, reaction rate.

  • Usually used for gas phase reaction


6 2 plug flow reactor

6.2 Plug Flow Reactor

DERIVATION

  • General Mole Balance:

  • Assumption:

    1.steady state:

  • Differentiate with respect to V:

FA0 - FA+ =

FA0 - FA+ = 0


6 2 plug flow reactor1

6.2 Plug Flow Reactor

DERIVATION

  • Rearranging and integrating between   V = 0, FA = FA0   V = V1, FA = FA1


6 continuous flow reactors steady state2

6. Continuous-Flow Reactors: steady state

3. Packed-Bed Reactor

(fixed bed reactor)

  • Often used for catalytic process

  • Heterogeneous reaction system

    (fluid-solid)

  • Reaction takes place on the surface

    of the catalyst.

  • No radial variation in velocity,

    conc, temp, reaction rate


6 3 packed bed reactor

6.3 Packed Bed Reactor

DERIVATION

  • General Mole Balance:

  • Assumption:

    1.steady state:

  • Differentiate with respect to W:

the reaction rate is based on mass of solid catalyst, W, rather than reactor volume

FA0 - FA+ =

FA0 - FA+ = 0


6 2 packed bed reactor

6.2 Packed Bed Reactor

DERIVATION

  • Rearranging and integrating betweenW = 0, FA = FA0   W = W1, FA = FA1


Summary of reactor mole balance

Summary of Reactor Mole Balance


Industrial reactors

Industrial Reactors

Packed-Bed Reactor at Sasol Limited Chemical


Industrial reactors1

Industrial Reactors

Fixed-Bed Reactor at British Petroleum (BP): using a colbalt-molybednum catalyst to convert SO2 to H2S


Industrial reactors2

Industrial Reactors

Fluidized Catalytic Cracker at British Petroleum (BP): using H2SO4 as a catalyst to bond butanes and iso-butanes to make high octane gas


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