Reactivation and regeneration
The reactivation or the regeneration of activated carbons involves restoring the adsorptive capacity of saturated activated carbon by desorbing adsorbed contaminants on the activated carbon surface.
Thermal reactivation
The most common regeneration technique employed in industrial processes is thermal reactivation.[47] The thermal regeneration process generally follows three steps:[48]
- Adsorbent drying at approximately 105 °C (221 °F)
- High temperature desorption and decomposition (500–900 °C (932–1,652 °F)) under an inert atmosphere
- Residual organic gasification by an oxidising gas (steam or carbon dioxide) at elevated temperatures (800 °C (1,470 °F))
The heat treatment stage utilises the exothermic nature of adsorption and results in desorption, partial cracking and polymerization of the adsorbed organics. The final step aims to remove charred organic residue formed in the porous structure in the previous stage and re-expose the porous carbon structure regenerating its original surface characteristics. After treatment the adsorption column can be reused. Per adsorption-thermal regeneration cycle between 5–15 wt% of the carbon bed is burnt off resulting in a loss of adsorptive capacity.[49] Thermal regeneration is a high energy process due to the high required temperatures making it both an energetically and commercially expensive process.[48] Plants that rely on thermal regeneration of activated carbon have to be of a certain size before it is economically viable to have regeneration facilities onsite. As a result, it is common for smaller waste treatment sites to ship their activated carbon cores to a specialised facility for regeneration, increasing the process' already significant carbon footprint.[50]
Other regeneration techniques[edit]
Current concerns with the high energy/cost nature of thermal regeneration of activated carbon has encouraged research into alternative regeneration methods to reduce the environmental impact of such processes. Though several of the regeneration techniques cited have remained areas of purely academic research, some alternatives to thermal regeneration systems have been employed in industry. Current alternative regeneration methods are:
- Chemical and solvent regeneration[51]
- Microbial regeneration[52]
- Electrochemical regeneration[53]
- Ultrasonic regeneration[54]
- Wet air oxidation[55]
https://en.wikipedia.org/wiki/Activated_carbon#Reactivation_and_regeneration
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