Description
1. The following equilibrium data for phenol adsorption on a special clay has been
obtained at 30°C. Here, c is the concentration in equilibrium in the liquid in mg/l and
q is the uptake in mg/g of adsorbent.
Which isotherm model among Freundlich and
Langmuir best fits the data and what are the isotherm parameters.
c (mg/L) q (mg/g)
3.9 9.6
6.8 11.6
9.9 14.9
12.0 17.6
16.0 21.0
23.0 25.6
35.7 32.1
61.8 38.2
80.2 40.1
2. 10 litres of water containing 3.5 mg/L of an organic compound is to be treated with
charcoal to reduce the final concentration to 0.1 mg/L. The average particle diameter
of the charcoal used is 2 mm and the specific surface area is 5m2
/kg.
The adsorption
equilibrium at 25°C is represented by q=50c0.32 where q is mg of the organic
compound per gram of charcoal and c is mg of organic compound per litre of solution.
The adsorption is mass transfer controlled with the Sherwood number determined to
be 30 and the binary diffusivity estimated to be 1.5×10-5
cm2
/s.
a) What is the minimum amount of adsorbent required?
b) Using twice the minimum amount of adsorbent required, estimate the batch time
required for the desired final concentration of the solution to be attained.
3. Adsorption breakthrough of methyl ethyl ketone (MEK) from air on a zeolite based
packed bed adsorber was studied at 20°C and atmospheric pressure. The length of the
bed for this experiment was 0.2 m and the superficial gas velocity was 0.29 m/s and
the bed density was 700 kg/m3
. The concentration in the feed ci was 0.11 gmol/m3
.
The following breakthrough data was obtained.
Time (min) 9.5 19 21 25.7 34.3 39 42 46.7 51.4 56.2
c/ci 0 0.018 0.037 0.083 0.287 0.435 0.491 0.62 0.713 0.768
64.7 68.6 72.4 77.1 84.8 97.1 104.7 108.6
0.852 0.935 0.952 0.963 0.97 0.981 0.991 1
a) If the maximum permissible concentration of MEK in the effluent gas is specified
as c/ci=0.03, determine the breakthrough time and the length of the mass transfer
zone.
b) Using the above data, design a bed for treating 3000 m3
/h of the same gas if an
adsorption cycle of 8 hours is allowed. What is the average loading of the bed at
the breakthrough time? Calculate the maximum solute loading at the given inlet
concentration of MEK in the gas.