Activated alumina water adsorption isotherm

In some systems, three stages of adsorption may be discerned. In the activated alumina-air-water vapour system at normal temperature, the isotherm is found to be of Type IV. This consists of two regions which are concave to the gas concentration axis separated by a region which is convex. The concave region that occurs at low gas concentrations is usually associated with the formation of a single layer of adsorbate molecules over the... 

All zeolites have a highly hydrophilic surface and are very efficient desiccants. Contrary to other nonzeolitic desiccants such as silica gel and activated alumina, zeolite adsorbents have type I adsorption isotherms for water—i.e., a high water adsorption capacity at a low concentration of water. To obtain extremely dry gases and liquids, therefore, zeolite adsorbents are strongly preferred over amorphous desiccants. The 3A mo-... 

The adsorption coefficients of the substances present during the dehydration of ethyl alcohol (i.e., water, ethylene, and ethanol) over alumina were determined kinetically and from the adsorption isotherms. The values of these adsorption coefficients are listed in Table IV. The values of the adsorption coefficients determined from the adsorption isotherms greatly exceed those calculated from the kinetic data thus the catalytically active centers are characterized by a smaller adsorption capacity for the reaction product, water, than other sections of the surface. Antipina and Frost, therefore, assert that the dehydration of ethyl alcohol occurs on sections possessing a smaller adsorption for water than those upon which water vapor alone is adsorbed. 

The isotherms for adsorption of pure water vapour on activated aluminas are typically Type I (microporous) or Type IV (mesoporous) in shape according to the Brunauer classification [6]. Figure 1 shows several examples. Alcoa F-1 alumina has a type I shape while Alcan AA-300 and Alcoa H-156 exhibit type IV shapes. The plots represent the specific amount of water vapour adsorbed (n, g/g) as functions of the relative vapour pressure of water (x = P/P ) at 30°C. P(atm) is the water vapour pressure over the adsorbent... 

The surface excess isotherm [nj(xi)] of trace water (xi 1) from a mixture on activated alumina can have types I and IV shapes analogous to those for adsorption of pure water vapour [20,21],... 

Generally, low solubility favors adsorption. The dramatic effects of the solute-solvent interaction on adsorption may be illusffated by adsorption of aqueous solutions of thiolane and its derivative, sulfolane. Sulfolane is of interest because it has been used for more than 40 years for solvent extraction in a number of industrial processes (e.g., the Sulfinol process for CO2 removal, the UOP Sulfolane process for recovery of aromatics from hydrocarbons, processes for extraction of fatty acids, etc.). It has now become a serious pollutant for ground water, however. The structures of sulfolane and thiolane are shown in Figure 5.10. The adsorption isotherms of their aqueous solutions on a clay sorbent are given in Figure 5.11 (Kim et al 1999). The clay had a cation exchange capacity of 0.3 meq/g, and its surface was relatively polar (more polar than carbon but less polar than silica gel and activated alumina). 

Fig 2 6 Typical examples of adsorption isotherms of water vapor on Silica gel type A and B and active alumina... 

Active alumina is also used as a drying agent and the typical adsorption isotherm of water vapor is included in Fig. 2.6. It is also employed for removal of polar gases from hydrocarbon streams. 

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