Activated carbon regeneration

The removal of volatile organic compounds (VOC) from air is most often accompHshed by TSA. Air streams needing treatment can be found in most chemical and manufacturing plants, especially those using solvents. At concentrations from 500 to 15,000 ppm, recovery of the VOC from steam used to regenerate activated carbon adsorbent thermally is economically justified. Concentrations above 15,000 ppm ate typically in the explosive range and... 

Solvent recovery with adsorption is most feasible when the reusable solvent is valuable and is readily separated from the regeneration agent. When steam-regenerated activated-carbon adsorption is employed, the solvent should be immiscible with water. If more than one compound is to be recycled, the compounds should be easily separated or reused as a mixture. Only very large solvent users can afford the cost of solvent purification by distillation. ... 

Krupa NE. Characterization of the pore structure of thermally regenerated activated carbon using adsorbates of varying molecular dimensions. M.S. thesis, Penn.sylva-nia State University, 1994. 

Gonzalez-Martin, M.L., Gonzalez-Garcia, C.M., Gonzalez, J.F., et al. (2002). Thermodynamic characterization of a regenerated activated carbon surface. Appl. Surf. Sci., 191, 166-70. 

Usually, thermal processes using CO2 or steam are employed for the regeneration of this field-spent activated carbon at temperatures that commonly exceed 700° C. However, the quality of regenerated activated carbon for organics removal may be negatively affected by the presence of these metal hydroxides. 

Figure 8.1 Schematic diagram of an apparatus used for regenerating activated carbon with a supercritical fluid solvent.

Electromagnetic induction heating has been recently studied to regenerate activated carbon filters without any contact between the heat source and the adsm-benL Foucault s currents induced by an alternative magnetic field nerate the heat production. 

Comparative characteristics of a fresh and thermally regenerated activated carbon... 

Warner Nicholson Engmeering Consultants, Thermally Regenerated Activated Carbon Technology, http //www.vaporcontrol.com/tracdescrip.htm (last retrieved 16.11.2004). 

For adsorption to activated carbon, the exhaust gas flows tiirough a carbon bed. Upon saturation, the carbon is thermally regenerated. Activated carbon has a very high adsorption (and abatement) efficiency. For benzene, the efficiency is >99 %. Nevertheless, it has the following disadvantages ... 

First, the temperature of the activated carbon is increased to approx. 100°C. This temperature increase reduces the equilibrium load of the activated carbon. Further reduction of the residual load is obtained by the flushing effect of the steam and the declining toluene partial pressure. The load difference between spent and regenerated activated carbon - the working capacity - is then available for the next adsorption cycle. 

Off-site reactivation Transportation of the spent carbon to a reactivation plant. Partial gasification at 800-900°C with steam in a reactivation reactor. Reuse of the regenerated activated carbon - low inlet concentration - odor control application - solvents with boiling points above 200 °C - polymerization of solvents... 

The water content of the activated carbon after desorption may constitute another problem. The purification efficiency of each activated carbon is the better the less water is present after desorption. Unfortunately, the desorbed activated carbon in the vicinity of the adsorber walls usually contains high proportions of water (approx. 10 to 20%). With such a high water content it is difficult to remove all the water even when drying with hot-air over longer periods. The wet and poorly-regenerated activated carbons in these zones frequently lead to higher solvent concentrations in the purified air, and this is even at the beginning of the adsorption cycle. Some proposals for improvement include ... 

W.N. Tuttle, Recent developments in vacuum regenerated activated carbon based hydrocarbon vapour recovery systems. Port Technology International, 1, pp. 143-146,1995. 

The inert gases from the absorber are saturated with CCI4, which must be removed before they can be released. The standard technique for this is the use of regenerable activated carbon beds. Passing the gases through a bed in the adsorption mode removes the CCla, and the adsorbed material is recovered by steaming out a bed in the recovery mode. This was a troublesome operation. 

McLaughlin, H.S., Regenerate activated carbon using organic solvents, Chem. Eng. Prog., 91(7), 45-53 (1995). 

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