1

Tutorial 3 Solution

1. (a) In VLE, when the pressure reduces as shown in below figure, bubble point is when the

first bubble appears, dew point is when the last drop of liquid disappears.

(b) (i) Calculate the saturated pressure for acetone and water at temperature 298K.

P

x1, y1

L

V

Bubble point, x1

Dew point, y1

P1sat @ x1=1

P2sat @ x1=0

0 1

Refer Table B.2 for the Antoine constants, A, B and C

L+V

2

Example: x1=0.2, so x2=0.8

P=x1P1sat+x2P2

sat

=0.2(30.686)+0.8(3.1877)=8.687 kPa

Y1=x1P1sat/P

=0.2(30.686)/8.687=0.707

P

Pxy

sat

11

1

P

x1, y1

Composition of liquid for acetone, x1

y1

3.187

30.686

3

y = 386.64x - 69.932

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

0 5 10 15 20 25

(iii) From the graph, the composition for acetone at 15kPa is x1=0.42, y1 = 0.9.

2 (a)

H=386.64 x 105 mmHg ( )

10354.51028.18

2000700055

Gradient

xco x 105

Pco (mmHg)

4101.74101.68510386.64

6500HcoP

H

Pcoycox

4

3(a) Azeotrope is a mixture of two or more liquids whose proportions cannot be altered by

simple distillation. This happens because, when an azeotrope is boiled, the vapor has the same

proportions of constituents as the unboiled mixture (x1=y1).

(b) Benzene(1)/ethanol (2) system:

5

6

7

8

X2, y2

P ( bar)