CHEN 4460 – Process Synthesis, Simulation and Optimization

Dr. Mario Richard EdenDepartment of Chemical Engineering

Auburn University

Lab Lecture No. 3 – Sequencing of Azeotropic Distillation ColumnsOctober 4, 2011

Contains Material Developed by Dr. Daniel R. Lewin, Technion, Israel

Azeotropic Distillation

Introduction• When two or more components differ in boiling by

less than approximately 50C and form a nonideal liquid solution, the relative volatility may be below 1.10.

• Then ordinary distillation may be uneconomic, and if an azeotrope forms even impossible.

• In that event, the following separation techniques, referred as enhanced distillation by Stichlmair, Fair, and Bravo, should be explored:– Extractive distillation– Salt distillation– Pressure-swing distillation– Homogeneous azeotropic distillation– Heterogeneous azeotropic distillation– Reactive distillation

Example 1• Given that methyl acetate (1), which boils at

57.8C, methanol (2), which boils at 64.7C and n-hexane (3), which boils at 68.7C.

A. Sketch any boundaries across which the residue curves cannot traverse.

B. Sketch the residue curves for three feed compositions:

Mole FractionsComponent I II III

1 0.70 0.15 0.152 0.15 0.70 0.153 0.15 0.15 0.7

Example 1• Note the existence of four azeotropes, where

compositions are in mol %:

Azeotrope T oCMethyl acetate (65%), methanol (35%) Binary 53.5Methanol (51%), n-hexane (49%) Binary 50.0Methyl acetate (60%), n-hexane (40%) Binary 51.8Methyl acetate (31%), n-hexane (40%), methanol (29%) Ternary

49.0

Example 1 – Solution

1

0.8

0.6

0.4

0.2

0

0

0.2

0.4

0.6

0.8

1

10.80.60.40.2 0

B

C A 1

0.8

0.6

0.4

0.2

0

0

0.2

0.4

0.6

0.8

1

10.80.60.40.2 0

<< Methanol (2)

(2) 64.7oC

<<

Hexa

ne (3

)

(3) 68.7oC

MA (1) >>

(1) 57.8oC 1

0.8

0.6

0.4

0.2

0

0

0.2

0.4

0.6

0.8

1

10.80.60.40.2 0

<< Methanol (2)

(2) 64.7oC

<<

Hexa

ne (3

)

(3) 68.7oC

MA (1) >>

(1) 57.8oC

53.5oC

51.8oC

50oC

49oC

1

0.8

0.6

0.4

0.2

0

0

0.2

0.4

0.6

0.8

1

10.80.60.40.2 0

<< Methanol (2)

(2) 64.7oC

<<

Hexa

ne (3

)

(3) 68.7oC

MA (1) >>

(1) 57.8oC

53.5oC

51.8oC

50oC

49oC

Plot pure components on vertices with Tb

Plot all azeotropes on diagram with Tb

Plot the residue curves connecting all azeotropes, azeotropes & vertices, and finally vertices & vertices with arrow heads pointing towards increasing boiling point temperatures

Example 1 – Solution Plot pure components

on vertices with Tb

Plot all azeotropes on diagram with Tb

Plot the residue curves connecting all azeotropes, azeotropes & vertices, and finally vertices & vertices with arrow heads pointing towards increasing boiling point temperatures

Plot additional residue curves that “arch” towards intermediate temperatures on the way to the end point

1

0.8

0.6

0.4

0.2

0

0

0.2

0.4

0.6

0.8

1

10.80.60.40.2 0

<< Methanol (2)

(2) 64.7oC

<<

Hexa

ne (3

)

(3) 68.7oC

MA (1) >>

(1) 57.8oC

53.5oC

51.8oC

50oC

49oC

Feed I

Example 1 – Solution Plot pure components

on vertices with Tb

Plot all azeotropes on diagram with Tb

Plot the residue curves connecting all azeotropes, azeotropes & vertices, and finally vertices & vertices with arrow heads pointing towards increasing boiling point temperatures

Plot additional residue curves that “arch” towards intermediate temperatures on the way to the end point

1

0.8

0.6

0.4

0.2

0

0

0.2

0.4

0.6

0.8

1

10.80.60.40.2 0

<< Methanol (2)

(2) 64.7oC

<<

Hexa

ne (3

)

(3) 68.7oC

MA (1) >>

(1) 57.8oC

53.5oC

51.8oC

50oC

49oC

Feed IFeed III

Example 1 – Solution Plot pure components

on vertices with Tb

Plot all azeotropes on diagram with Tb

Plot the residue curves connecting all azeotropes, azeotropes & vertices, and finally vertices & vertices with arrow heads pointing towards increasing boiling point temperatures

Plot additional residue curves that “arch” towards intermediate temperatures on the way to the end point

1

0.8

0.6

0.4

0.2

0

0

0.2

0.4

0.6

0.8

1

10.80.60.40.2 0

<< Methanol (2)

(2) 64.7oC

<<

Hexa

ne (3

)

(3) 68.7oC

MA (1) >>

(1) 57.8oC

53.5oC

51.8oC

50oC

49oC

Feed IFeed III

Feed II

Example 1 – Solution Plot pure components

on vertices with Tb

Plot all azeotropes on diagram with Tb

Plot the residue curves connecting all azeotropes, azeotropes & vertices, and finally vertices & vertices with arrow heads pointing towards increasing boiling point temperatures

Plot additional residue curves that “arch” towards intermediate temperatures on the way to the end point

Example 2• A stream consisting of a mixture of A, an organic

component, and water, B, which forms an azeotrope. A separation process is to be designed to obtain pure products A and B. The plant manager suggests that you investigate the possibility of using component C as MSA. Componen

tBoiling Temperature (K)

A 360B 400C 370

F Azeotrope I

Azeotrope II

Azeotrope III

Azeotrope IV

A 40% 50% 55% 30% B 60% 55% 45% 45% C 50% 45% 25%

Temp 350 K 360 K 330 K 315 K

Example 2

• Indicate the location of the azeotropes on a ternary diagram, as well as representative residue curves.

• Suggest a process for the separation of A and B into pure products and show its operating lines on the ternary diagram.

• Draw a PFD for your process. Indicate flow rates of all internal and external streams as multiples of the flow rate of F.

Example 2 – Solution

C

I, 350 KIII, 330 K

II, 360 K

IV, 315 K

360 K

370 K400 K

Example 2 – Solution

C

I, 350 KIII, 330 K

II, 360 K

IV, 315 K

360 K

370 K400 K

D2

B2

S1

F

B1

M1

S2

D1M2

B2B1

D2D1F M1 S1

S2

M2