Regeneration of exhausted activated carbons

This is one of the most frequent methods used in the regeneration of exhausted activated carbons. It consists in heating the carbon at temperatures between 873 - 1273 K in different types of furnace such as a rotary kiln, a multiple hearth, a fluidized bed, etc. so that... 

Zhang HP (2002) Regeneration of exhausted activated carbon by electrochtanical method. Chem Eng J 85(l) 81-85... 

Moreno-Castilla, C., Rivera-Utrilla, J., Joly, J.P., et al. (1995). Thermal regeneration of an activated carbon exhausted with different substituted phenols. Carbon, 33, 1417-23. 

Activated carbon adsorption is mainly a waste concentration method. The exhausted carbon must be regenerated or disposed of as hazardous waste. For GAC consumptions larger than 2000 Ib/day, onsite regeneration may be economically justified [7]. Thermal regeneration is the most common method for GAC reactivation, although other methods such as washing the exhausted GAC with acid, alkaline, solvent, or steam are sometimes practiced for specific applications [17]. 

Ferro-Garcia, M.A., Utrera-Hidalgo, E., Rivera-UtriUa, et al. (1993). Regeneration of activated carbons exhausted with chlorophenols. Carbon, 31, 857-63. 

Bone char, the forefather of activated carbon, has long been in the forefront of adsorbents for sugar refining. The granular char is placed in columns through which the hot syrups percolate until the char is exhausted, as evidenced by the appearance of color in the filtrate. The bone char is then regenerated by thermal means for re-use.3... 

Due to its high temperature, thermal regeneration is usually not conducted in situ but requires shipment of the spent activated carbon to special regeneration units such as multiple hearth furnaces or rotary kilns. The design of the reactivation system is dependent on the carbon loading, in mg g and on the carbon usage in the adsorber i.e. the mass of carbon exhausted per unit time, in kg d [43]. 

Thermal and chemical regeneration of activated carbons exhausted with various aromatic compounds have been compared [76]. Whereas thermal treatment is independent on the characteristics of the adsorbate, the efficiency of the chemical treatment, which varies from 15.2 to 96.8 %, is a function of the properties of adsorbate and the choice of chemical... 

Another part of the sulfur formed by the reaction between the carbon surface and SO2 gets bonded to the carbon surface in the form of stable carbon-sulfur surface compounds that can be neither desorbed by extraction with a solvent nor by heat treatment. These surface compounds can only be desorbed as H2S on heat treatment in hydrogen gas, as mentioned earlier. The formation of these carbon-sulfur surface compounds reduces the availability of the carbon surface for any further adsorption, making the regeneration of the sulfurized activated carbon difficult. The proportion of these three forms in which SO2 is adsorbed on the carbon surface depends upon the temperature and composition of the exhaust gases and the nature of the carbon surface. It, therefore, indicates that the experimental conditions for using activated carbon adsorption technique for the recovery of SO2 should be such that there is... 

For the exhausted adsorbents from gas phase adsorption, regeneration by thermal desorption is most commonly used. For example, activated carbon used to prevent contamination of air by organic solvents of low concentrations, and silica gel, activated alumina or zeolite used for dehumidification of gases are regenerated by high temperature steam, air or inert gases. In the case of organic adsorbates... 

Apart from the usual adsorptive dryer station, additional adsorption steps can serve to remove trace components (e.g. sulphur compounds, alcohols, aldehydes, ketones, ester, other odorants, aromatics, etc.). All molsieves and all types of activated carbon are used as adsorbents, but also zinc and ferric oxides which, in contrast to the dryers, are usually not regenerated in situ but have to be replaced by fresh adsorbents after saturation. According to the quantity of the component(s) to be removed, adsorption occurs in single adsorbers or in series-connected twin-adsorbers. This series-connection (also called Lead/Lag configuration) is designed in such a way that the container with the unloaded adsorbent follows the active one during normal operation of the plant. When the adsorption capacity of the active adsorber is exhausted, it is taken out of operation and the vessel with the fresh adsorbent is turned into the active one. The loaded adsorbent can be replaced by a fresh one while the plant is kept in operation. 

---