5.3 The equilibrium partial pressure of water vapor in contact with a certain silica gel on which
water is adsorbed is, at 25°C, as follows:
Partial pressure
of water, mmHg
Ib water/100 lb
dry gel = kg/100 kg
0 2.14
0
5
4.74
10
7.13
15
9.05 10.9 12.6 14.3 16.7
20
25
30
35
40
(a) Plot the equilibrium data as = partial pressure of water vapor against xwt fraction
water in the gel.
(6) Plot the equilibrium data as X = mol water/mass dry gel, Y = mol water vapor/mol dry
air, for a total pressure of 1 std atm.
(c) When 10 lb (4.54 kg) of silica gel containing 5 wt% adsorbed water is placed in a flowing
airstream containing a partial pressure of water vapor 12 mmHg, the total pressure is 1 std atm
and the temperature 25°C. When equilibrium is reached, what mass of additional water will the gel
have adsorbed? Air is not adsorbed.
(d) One pound mass (0.454 kg) of silica gel containing 5 wt% adsorbed water is placed in a
vessel in which there are 400 ft (11.33 m²) moist air whose partial pressure of water is 15 mmHg.
The total pressure and temperature are kept at 1 std atm and 25°C, respectively. At equilibrium,
what will be the moisture content of the air and gel and the mass of water adsorbed by the gel? Ans.:
0.0605 kg water.
(e) Write the equation of the operating line for part (d) in terms of X and Y. Convert this into
an equation in terms of p and x, and plot the operating curve on 5, x coordinates.
If 1 lb (0.454 kg) of silica gel containing 18% adsorbed water is placed in a vessel containing
500 ft³ (14.16 m²) dry air and the temperature and pressure are maintained at 25°C and 1 std atm,
respectively, what will be the final equilibrium moisture content of the air and the gel.