chemical reaction engineering

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SABIC Chair in Catalysis at K SABIC Chair in Catalysis at K AU AU Chemical Chemical Reaction Reaction Engineering Engineering Dr. Yahia Alhamed Dr. Yahia Alhamed

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Chemical Reaction Engineering. Dr. Yahia Alhamed. Kinetics and Reaction Rate. What is reaction rate? It is the rate at which a species looses its chemical identity per unit volume. The rate of a reaction can be expressed as:- - The rate of disappearance of a reactant or - PowerPoint PPT Presentation

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Page 1: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

ChemicalChemical Reaction Reaction EngineeringEngineering

Dr. Yahia AlhamedDr. Yahia Alhamed

Page 2: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

What is reaction rate?

It is the rate at which a species looses its chemical identity per unit volume.

The rate of a reaction can be expressed as:-

- The rate of disappearance of a reactant or

- The rate of appearance of a product.

Kinetics and Reaction RateKinetics and Reaction Rate

Page 3: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

Reaction RateReaction RateConsider species A:

-rA = the rate of formation of species A per unit volume

rB = the rate of formation of species B per unit volume

EXAMPLE: If B is being formed at 0.2 moles per decimeter cubed per second, ie, rB = 0.2 mole/dm3/s

Then A is disappearing at the same rate:-rA= 0.2 mole/dm3/sThe rate of formation (generation of A) is rA= -0.2 mole/dm3/s

Page 4: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

Reaction RateReaction RateConsider species j:

• rj is the rate of formation of species j per unit volume [e.g. mol/dm3*s]

• rj is a function of concentration, temperature, pressure, and the type of catalyst (if any)

• rj is independent of the type of reaction system (batch, plug flow, etc.)

• rj is an algebraic equation, not a differential equation

Page 5: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

Rate Law BasicsRate Law Basics

• A rate law describes the behavior of a reaction. The rate of a reaction is a function of temperature (through the rate constant) and concentration.

Page 6: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

Reaction Rate for solid catalytic reactionsReaction Rate for solid catalytic reactions

• For a catalytic reaction, we refer to -rA', which is the rate of disappearance of species A on a per mass of catalyst basis.

• -r'A = rA/bulk density of the catalyst (ρb)

Page 7: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

Rate Law BasicsRate Law Basics• A rate law describes the behavior of a reaction. The rate

of a reaction is a function of temperature (through the rate constant) and concentration.

• Power Law Modelk is the specific reaction rate (constant)

k is given by the Arrhenius Equation:

Where:E = activation energy (cal/mol)

– R = gas constant (cal/mol*K)

– T = temperature (K)

– A = frequency factor (units of A, and k, depend on overall reaction order)

Page 8: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

General General MoleMole Balance Balance

Page 9: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

Batch Reactor Mole BalanceBatch Reactor Mole Balance

Page 10: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

Constantly Stirred Tank Reactor Mole BalanceConstantly Stirred Tank Reactor Mole BalanceCSTR or MFRCSTR or MFR

Page 11: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

Plug Flow Reactor (PFR) Mole BalancePlug Flow Reactor (PFR) Mole Balance

V dFArAFA 0

FAThe integral form is:

This is the volume necessary to reduce the entering molar flow rate (mol/s) from FA0 to the exit molar flow rate of FA.

Page 12: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

Packed Bed Reactor Mole Packed Bed Reactor Mole BalanceBalance

PBR

The integral form to find the catalyst weight is:

W dFA

r AFA 0

FA

FA0 FA r AdW dNA

dt

Page 13: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

Space time and space velocitySpace time and space velocity FA0 = CAo vo

θ = is called space time (s) = V/vo

Space velocity = 1/θ, where;FA0 = Molar feed rate of key reactant A (mol/s)

CAo= Concentration of key reactant A in the feed (mol/m3)

vo=Volumetric flow rate of feed to the reactor (m3/s)

V = volume of the reactor

For constant volume systems v = vo where v is volumetric flow rate leaving the reactor

Page 14: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

Reactor Mole Balance SummaryReactor Mole Balance Summary

Page 15: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

Reactor Mole Balance Reactor Mole Balance SummarySummary

Page 16: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

Reactor Mole Balance Reactor Mole Balance SummarySummary

Page 17: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

Reactor Mole Balance Reactor Mole Balance SummarySummary

Page 18: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

Reactor Mole Balance Reactor Mole Balance SummarySummary

Page 19: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

ConversionConversion

Consider the general reaction: aA + bB -cC + dDWe will choose A as bases of calculation (i.e. Key reactant)The limiting reactant is usually taken as the key reactant Then: A + (b/a)B (c/a)C + (d/a)DXA = moles reacted/moles fed

Page 20: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

Batch Reactor ConversionBatch Reactor Conversion

dN Adt

rAV

Page 21: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

CSTR ConversionCSTR Conversion

Algebraic Form:

There is no differential or integral form for a CSTR.

Page 22: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

PFR ConversionPFR Conversion

PFR

dFAdV

rA

FA FA0 1 X

Differential Form:

Integral Form:

Page 23: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

Design EquationsDesign Equations

V

Page 24: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

Reactor Sizing (CSTR)Reactor Sizing (CSTR)

• Given -rA as a function of conversion, -rA=f(X), one can size any type of reactor.

• We do this by constructing a Levenspiel plot.

• Here we plot either as a function of X.

• volume of a CSTR is:

FA0 rA

or 1 rA

VFA0 X 0 rA EXIT

Page 25: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

Reactor Sizing (PFR)Reactor Sizing (PFR)

VPFR FA 0

rA0

X

dX

For PFR th evolume of the reactor needed is given by the area under the curve

=area

Page 26: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

SummarySummary

Page 27: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

Rate Law BasicsRate Law Basics

• A rate law describes the behavior of a reaction. The rate of a reaction is a function of temperature (through the rate constant) and concentration.

• Power Law Model

k is the specific reaction rate (constant)

Page 28: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

Examples of Rate LawsExamples of Rate Laws

62HCA

24262

kCr

HHCHC

T

1

1000

1

mol

82kcal1e0.072sk

• First Order Reactions

(1) Homogeneous irreversible elementary gas phase reaction

with

Page 29: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

• First Order Reactions

(1) Homogeneous irreversible elementary gas phase reaction

with

(2) Homogeneous reversible elementary reaction

with and

Examples of Rate LawsExamples of Rate Laws

104104 HCiHCn

CiCnCn KCCkr44

360T

360T790631.1expk

333T

333T830.33.03expKC

62HCA

24262

kCr

HHCHC

T

1

1000

1

mol

82kcal1e0.072sk

Page 30: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

• First Order Reactions

(1) Homogeneous irreversible elementary gas phase reaction

with

(2) Homogeneous reversible elementary reaction

with and

• Second Order Reactions

(1) Homogeneous irreversible non-elementary reaction

with and

This is first order in ONCB, first order in ammonia and overall second order.

Examples of Rate LawsExamples of Rate Laws

104104 HCiHCn

CiCnCn KCCkr44

360T

360T790631.1expk

333T

333T830.33.03expKC

62HCA

24262

kCr

HHCHC

T

1

1000

1

mol

82kcal1e0.072sk

3NHONCBA CkCr

kmol.min

m0.0017k

3

mol

cal11273E At 188˚C

Page 31: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

Examples of Rate LawsExamples of Rate Laws

2323 NCNHBrCHNHCHCNBr

23NHCHCNBrA CkCr s.mol

2.2dmk

3

with

• Second Order Reactions

(2) Homogeneous irreversible elementary reaction

Page 32: Chemical  Reaction Engineering

SABIC Chair in Catalysis at KAUSABIC Chair in Catalysis at KAU

Examples of Rate LawsExamples of Rate Laws

with2323 NCNHBrCHNHCHCNBr

23NHCHCNBrA CkCr s.mol

2.2dmk

3

• Second Order Reactions

(2) Homogeneous irreversible elementary reaction

This reaction is first order in CNBr, first order in CH3NH2 and overall second order.

(3) Heterogeneous catalytic reaction: The following reaction takes place over a solid catalyst: