SAJJAD KHUDHUR ABBASCeo , Founder & Head of SHacademyChemical Engineering , Al-Muthanna University, IraqOil & Gas Safety and Health Professional – OSHACADEMYTrainer of Trainers (TOT) - Canadian Center of Human Development

Episode 56 : Simulation for design and analysis

Simulation for design and analysis (I)Separation of an azeotropic mixture

• Mixture analysisIdentification of an azeotrope.

• Possible separation techniques Pressure swing. Extractive/azeotropic distillation.

• Solvent identification and validation

• Flowsheet configuration

Mixture analysisWhenever you have the problem of separating a mixture, a good starting point is always to do a mixture anaysis.This can include both pure component and mixture properties.The mixture analysis will imediately give information both intuitively and to a computer aided system on what kind of separation is possible.

Binary Azeotrope:A binary azeotrope is when a 2 component, 2 phase system of gas and liquid in chemical equilibrium has the same composition in both phases.

Gas phase, composition: ya, yb

Liquid phase, composition: xa, xb

Azeotropic condition: xa = ya, xb = yb

Identification of an azeotropeAzeotropes is found by VLE (Vapor-Liquid Equilibria) mixture analysis.

This can be either database lookup for VLE datapoints or the datapoints can be calculated with a thermodynamic model.

0 10

Comp A 1

x

y

Comp A

By the definition of an azeo- trope, in a x-y plot the curve crosses the diagonal, at the azeotrope composition.

Acetone - chloroform

0

10

3054

20

40

50

0

CHCl3

20 40 60mole

%

80 100ACETONECHCl

3

CH

Cl

3m

ole

%A

CE

TON

E

7060

60

80

90

100

VLE-PhaseDiagram: Pres.=

1.00 atm

ACETONE

50

52

56

58

62

64

0

CHCl3

20 40 60

ACETONE

80 100

VLE-PhaseDiagram: Pres.=

1.00 atm

Tem

pera

ture

(°C

)

Azeotrope ~ 38 mole% acetone, 64.5 °C, maximum boiling

Possible separation techniquesConventional distillation not possible, if 2 pure products are desired.

Possible solutions to this problem:

• Use separation techniques which are not exploiting differences in vapor vs. liquid phases, i.e. membranes or liquid- liquid extraction.

• Pressure swing.

• Extractive / azeotropic distillation.

Pressure swingPressure swing distillation is exploiting the fact that for some azeotropes the composition changes with pressure

0

20

40

60

80

100

0

METHANOL

20METHA

NOL

40 60 80CH3- ACETA

TE

100

VLE- PhaseDiagram: Pres.=

1.00 atm

mole %

ME

THA

NO

Lm

ole

%C

H3-

AC

ETA

CH3-ACETATE

0

20

40

60

80

100

0

METHANOL

20METHANOL

40 60mole %

80100

CH3-ACETATE

VLE-PhaseDiagram: Pres.=

6.00 atm

ME

THA

NO

Lm

ole

%C

H3-

AC

ETA

CH3-ACETATE

Extractive distillation

70

60

50

40

30

20

10

0

90

100

The addition of a third component (solvent/entrainer) to the binary system in order to facilitate the separation by distillation.

VLE-PhaseDiagram: Pres.= 1.00 atm solvent mole %

0

CHCl3

20 40 60 80 100

Vapour

Diagonal

Vapour 60.0

CHCl3 mole % ACETONE

CH

Cl3

mol

e %

AC

ETO

NE

ACETONE

Solvent identification (I)The solvent can be found in a solvent database or by the use of a computer tool.

The computer tool must be able to solve the following problem:Given:

Needed:A set of desired properties (pure and mixture) Description of compounds with these properties

Computer Aided Molecular Design (CAMD) programs can solve this.

General functionality:1. Combine molecular fragments to describe complete

molecules2. Predict the properties of the molecular descriptions3. Reject descriptions with undesired properties

Solvent identification (II)Desired properties for the entrainer:

1.If it is a minimum boiling azeotrope the boiling point of the entrainer should be lower than the azeotropic temperature and vice versa.

2.The boiling point should not be to high in order to have small energy consumption.3. Should not be harmful to the environment.

4. Should not form azeotropes with any of the two compounds.

5. High selectivety: S

6. Low solvent loss: S7. ...

iS

jSs

sJsv.L

1

Solvent validation (I)

( 331.0 K) 0.0 0.1 0.2 0.3 0.4

328.1 K

0.5 0.6 0.7 0.8 0.9 1.0( 338.0 K)METHYL-ACETATE METHANOL

1-PROPANAL ( 321.5 K)

1.0

0.9A

zeotrope0

.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

Solvent validation (II)

0.0

( 331.0 K) 0.0

0.3

0.2

0.1

0.1 0.2 0.3 0.4

328.1 K

0.4

0.5

0.5 0.6 0.7 0.8 0.9

0.9Azeotrope0.8

0.7

0.6

1.0

1.0( 338.0 K)

1-PROPANAL ( 321.5 K)

METHYL-ACETATE METHANOL

Feed 1

D1, Feed 2

B1

D2

B2

Flowsheet configuration

B

A, B, Solvent

A

Solvent

A, Solvent

The flowsheet is fixed, and consists of to columns to allow solvent recycle.

Thanks for Watching Please follow me / SAJJAD KHUDHUR ABBAS