Resins comparison with activated carbon

The adsorption process, in principle, is an anion-exchange process which is restricted only to the surface of the activated charcoal. This fact makes the loading or the exchange capacity of activated charcoal to be relatively smaller in comparison with ion-exchange resins, and it is for this reason that charcoals are quite often treated suitably to improve their loading capacities. The surface and the pore structure characteristics of activated carbon are the important factors upon which its industrial applications depend. 

An excellent early review of the properties of the various XAD resins, along with comparisons with EXP-500 and activated carbon, can be found in Gustafson and Paleos [38]. 

The polymeric resins and the carbonaceous polymers are significantly more hydrophobic than activated carbon. A comparison of water vapor isotherms is shown in Figure 9.25. With such highly hydrophobic surfaces, it is not clear whether the micropores are indeed wetted upon the pretreatment described above. 

Figure 9.26. Comparison of isotherms in aqueous soiution between activated carbon (Caigon F-400) and resin (XAD-4). Lines are D-R equation fits (Weber and van Viiet, 1981b, with permission).

Rexwinkel et al. (1999) studied the adsorption of a number of chlorinated hydrocarbons from aqueous solution on different resins, an activated carbon and carbonized resins. The comparisons are exemplified by adsorption of dichloromethane, shown in Figure 9.27. Again, the carbonized resins showed the highest capacities (by >5X compared with other sorbents) at dilute concentrations. 

Polymers Instead of being limited to styrene-divinylbenzene, polymer adsorbents are also made from polymethacrylate, divinylbenzene/ethylvinylbenzene, or vinylpyridine and are sometimes sulfonated or chloromethylated, much as are ion exchange resins. As a result, some are sufficiently hydrophilic to be used as desiccants, while others are quite hydrophobic. The effective surface area is usually smaller than for activated carbon, e.g., 5-800 mVg. Pore diameters range from about 0.3 to 200 mn. The range of application is somewhat restricted due to a higher price in comparison with other adsorbents. Currently, the main application includes removing VOCs from off-gas. 

Despite the number of papers published on natural adsorbents for pollutants uptake from contaminated water, there is yet little literature containing a wholesome study comparing various sorbents. Infact, the data obtained from the biopolymer derivatives have not been compared systematically with commercial activated carbon or synthetic ion exchange resins, which showed high removal efficiencies, except in recent publi-catiorrs. In additiorr, comparisons of different sorbents are difficult because of inconsistencies in the data presentation. Thus, much work is necessary to better understand adsorption and the possible technologies in the industrial scale. 

In a related study, Khedr (2013) assessed the removal of radium, U, as uranyl cation, or carbonate complexes, and radon by reverse osmosis (RO) and nanofiltration (NF) in comparison with the conventional methods of ion exchange resins (lERs), chemical precipitation/softening, coagulation, and adsorption on surface active media. lERs and chemical softening achieved radionuclide rejection from 32 to 95%, but with loss of process efficiency due to undesired... 

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