adsorbent A solid surface on which gas or liquid molecules condense to form a film.
adsorption The physical process that occurs when gas or liquid molecules are brought into contact with a solid surface and condense on the surface.
adsorption isotherm The mathematical or experimental relation between the amount a single component adsorbed (the adsorbate) on the adsorbent, and the bulk amount of the adsorbate in a different phase expressed in terms of the partial pressure in the gas phase, or the concentration in the liquid phase, at some temperature.
chemisorption Adsorption when interaction between the solid and the condensed molecules is relatively strong as contrasted with physical adsorption.
Freundlich isotherm Mathematical relation for adsorption that takes place at equilibrium.
Langmuir isotherm Mathematical relation for adsorption that takes place at equilibrium.
Supplementary References
Basmadjian, D. The Little Adsorption Book: A Practical Guide for Engineers and Scientists, CRC Press, Boca Raton, FL (1996).
De Nevers, N. Physical and Chemical Equilibrium for Chemical Engineers, Wiley-Interscience, New York (2002).
Masel, R. I. Principles of Adsorption and Reaction on Solid Surfaces, Wiley-Interscience, New York (1996).
Thomas, W. J. Adsorption Technology and Design, Butterworth-Heinemann, Oxford, UK (1998).
Toth, J. Adsorption, Marcel Dekker, New York (2002).
Problems
* 13.1 The adsorption of sulfur dioxide by polymer pellets at 0°C is listed below. Using these data, determine the Langmuir constants and the Freundlich constants.
| pso2 (mm Hg) | Uptake (mg mol/g) |
|---|---|
| 5 | 1.75 |
| 10 | 2.20 |
| 15 | 2.40 |
| 20 | 2.62 |
| 30 | 2.75 |
| 40 | 2.85 |
| 50 | 3.00 |
| 60 | 3.05 |
| 70 | 3.12 |
Do these two isotherms fit the data well?
* 13.2 Emmett studied the adsorption of argon on 0.606 g of silica gel at − 183°C. From the following data, calculate the Freundlich and Langmuir constants:
| p (mm Hg) | Uptake (cm3 at S.C.) |
|---|---|
| 78.46 | 55.03 |
| 176.92 | 72.73 |
| 224.62 | 80.00 |
| 378.46 | 106.67 |
| 432.31 | 117.58 |
| 513.38 | 138.18 |
| 584.62 | 166.06 |
Do these two isotherms fit the data well?
* 13.3 The adsorption of ethane on 5A molecular sieves was studied by Glessner and Myers (1969) at 35°C. Using the data given below, determine (a) if the Langmuir equation can be used to model the data and (b) if the Freundlich equation can be used to model the data.
| p (mm Hg) | Uptake (cm3 at S.C./g) |
|---|---|
| 0.17 | 0.059 |
| 0.95 | 0.318 |
| 5.57 | 1.638 |
| 12.09 | 3.613 |
| 111.32 | 24.236 |
| 220.87 | 34.278 |
| 300.05 | 38.340 |
| 401.25 | 41.779 |
| 500.18 | 44.037 |
| 602.74 | 45.693 |
* 13.4 In the isothermal adsorption of a mixture of butanol-2 (component 1) and t-amyl alcohol (component 2) on porous activated carbon, the following relation represented the data within an accuracy of ±2%:
cs1=1.06cf11.217cf10.812+0.626cf20.764
where cs = concentration of solute in the solid phase, g/cm3
cf = concentration of the solute in the fluid phase, g/cm3
What would the Freundlich equation be for butanol-2 as a pure liquid?
* 13.5 A solution containing a trace amount of chloroform (12 mg/L) is to be reduced to 1 μg/L of CCl4 using activated charcoal as the adsorbent. The Freundlich equation that applies to this system is y = k Cn where C is in milligrams adsorbate per liter of solution after processing, and y is the cumulative milligrams of adsorbate per gram of adsorbent. k = 100 and n = 0.30 at the temperature of the process. How much activated charcoal is required per liter of solution?
** 13.6 One hundred pounds per minute of moist air that includes 1 lb of water vapor flow through a dehumidifier. Dry silica is fed to the process and flows counter-current to the air. The water content of the exit air is reduced to 10−3 lb of water per pound of dry air. The water in the exit silica gel is in equilibrium with the water in the entering air. What is the required flow rate of the silica gel per minute? The equilibrium relation that applies to this process is y = 0.0375p0.65 where y is the grams of water per gram of silica gel and p is the partial pressure of the water in the entering air in millimeters of Hg.
** 13.7 The compound 1, 1-dichloroethane (DE) in air at 40°C and with a dew point of 12°C is to be removed with 2 kg/min of activated carbon. The entering activated carbon contains 50 g DE per kilogram of DE-free activated carbon and leaves the process with a DE content of 300 g of DE per kilogram of DE-free activated carbon. Calculate the concentration of DE in the exit air, assuming that the DE in the exit air is in equilibrium with the exit activated carbon. The barometer is 770 mm of Hg. The equilibrium relation for the DE is y = 0.089p0.51 where y is the grams of DE adsorbed per gram of activated charcoal, and p is the partial pressure in the gas phase of the DE in millimeters of Hg. How many gram moles of bone-dry air pass through the process per minute?
* 13.8 The partition of a compound between soil and water can be estimated by using a soil adsorption coefficient KOC
KOC= Mass of compound adsorbed in μg Mass of organic carbon in the soil in g Mass of compound in the liquid in μg Volume of the liquid in mL
Values of KOC for low adsorption are in the range 2.5 > log10 (KOC) > 1.5.
How much nitrobenzene will be adsorbed at equilibrium from 1 L of a saturated solution in water at 20°C by 1 kg of soil that has a carbon content of 11%? Data: The solubility of nitrobenzene in water is 0.19 g/100 g water at 20°C, and log10 (KOC) = 2.27.
Leave a Reply