The chemical regeneration and subsequent volatilization of exhausted activated carbon

Abstract

Following experimental research studies carried out at the University of Birmingham, UK, this paper presents data on the application of heat subsequent to chemical regeneration of exhausted activated carbon. Earlier studies by the authors have shown that chemical regeneration can be successful for a wide range of organic adsorbates using organic regenerants with solubilising powers; in those studies, a water rinsing phase subsequent to the regeneration phase was employed so that water-soluble organic regenerants could be washed out of the carbon pores. Residual regenerant can reduce the adsorption capacity per unit weight of carbon for a subsequent application of pollutant. Experiments have shown, however, that contamination of the re-exhaustion phase with residual regenerant is still possible, even for a regenerant with infinite solubility in water. Thus, the application of heat subsequent to chemical regeneration was evaluated. Acetone, methanol, ethanol and formic acid were used as regenerants for carbon exhausted with nitrobenzene. It was found that thermal volatilization removed the regenerants more completely than did the application of a hot water rinsing operation. Recovery of adsorptive capacity was generally superior when using a thermal volatilization phase compared with using a hot water rinsing phase. Regeneration efficiency values generally increased as temperatures increased within the temperature range studied (50-380°C). Carbon weight losses and gains were both observed. Weight gains may be attributed to residual adsorbate and regenerant in the carbon pores; they may also arise form the formation of pyrolysis products in the pores. Weight losses were recorded for all samples heated at 380°C. Regeneration efficiency values increased even when the weight of the carbon was reduced; it is thought that new adsorption sites were created by the burning of the carbon.