6.8. Absorption of acetone from air.

Ninety-five percent of the acetone vapor in an 85 vol air stream

is to be absorbed by countercurrent contact with pure water in a

valve-tray column with an expected overall tray efficiency of 50%.

The column will operate at 20°C and 101 kPa. Equilibrium data for

acetone-water at these conditions are as follows:

Acetone in water, mol

3.30

7.20 11.7 17.1

Acetone partial pressure in air, torr 30.00 62.80 85.4 103.0

Calculate (a) the minimum value of L'/V", the ratio mol H₂O/mol air:

(b) the total number of equilibrium stages using a value of

L'/V' of 1.25 times the minimum; and (c) the concentration of

acetone in the exit water.

From Table 5.3 for N connected equilibrium stages, there are 2N+

2C+5 degrees of freedom. The following values are specified in this

problem:

Stage pressures (101 kPa)

Stage temperatures (20°C)

Feed stream composition

Water stream composition

Feed stream, T. P

Water stream, T. P

Acetone recovery

L/V

|xx J Juma

1

2N+2C+4

One more specification is needed. Take the gas feed rate at

100 kmol/h.