Regeneration of spent activated carbon

The spent activated carbons from water treatment systems or decolorization of sugar-beet juice are troublesome because of the presence of wide variety of organic substances. The 

Comparative characteristics of a fresh and thermally regenerated activated carbon 

Murayama, N. Moriyama, H. Mitobe, H. Mukai, Y. Takase, K. Shimizu, and Y. Kitayama, Chemosphere, 52 (2003) 825. 

Swietlik, U. Raczyk-Stenislawiak, S. Bilozor, W. Ilecki, and J. Nawrocki, Water Res., 36 (2002) 2328. 

Clark and B.K. Boutin (eds.) United States Environmental Protection Agency Document EPA/600/R-01/110, 2001. 

---

Facilities are available for disposal and regeneration of spent activated carbon, and the vendor can coordinate transportation and on-site exchange requirements. 

In the cases above, a two-parameter model well represents the data. A model with more parameters would be more flexible, but by using a partition constant, K, or a desorption rate constant ka and k, , for the mass-transfer coefficients, the data are well described (see Figs. 3.4-15 and 3.4-13). While K would be a value experimentally determined, kp can be estimated from eqn. (3.4-97) with the external mass-transfer coefficient, km, estimated from the correlation of Stiiber et al. [25] or from that of Tan et al. [27], and the effective diffusivity from the Wakao Smith model [36], Typical values of kp obtained by fitting the data of Tan and Liou are shown in Fig. 3.4-16. As expected, they are below the usual mass-transfer correlations, because internal resistance diminishes the global mass transfer coefficient. These data correspond to the regeneration of spent activated carbon loaded with ethyl acetate, using high-pressure carbon dioxide, published by Tan and Liou [45]. 

Another potential application of the packed fluidized bed is in the regeneration of spent activated carbon after its use in municipal waste water treatments and in the removal of odors from waste gases (Kato et al. 1980). The adsorption capacity of the regenerated catalyst as measured by the iodine number was found to agree well with the values predicted by the model described above. 

Thermal Regeneration of Spent Activated Carbon from Water Treatment... 

The main mechanism by which activated carbon removes impurities is one of physical adsorption, this being a reversible process. Consequently one can expect that desorption of the impurities will render the carbon surface available again for adsorption. Regeneration of spent activated carbon is not only important from the point of view of restoring the adsorption capacity of the carbon, but also because in many cases the recovery of the adsorbed species is important. If the adsorption is of chemical type (chemisorption), the formation of a bond between the carbon and the adsorbate makes the process non-reversible, and even if desorption is possible the desorbed species will be different to those originally adsorbed. Additionally, adsorption (especially in liquid phase) is often accompanied by precipitation of species which cannot be removed by simple desorption. 

Regeneration of spent activated carbon can be accomplished by heating carbon to 950°C in a steam-air atmosphere. This process oxidizes adsorbed organics and regenerates the carbon surface, with an approximately 10% loss of carbon. 

---