Comparative study on the thermal reactivation of spent adsorbents

Abstract

Activated carbons previously used for p-Nitrophenol (PNP) adsorption were subjected to thermal reactivation in order to recover their initial porosity characteristics. Three activating agents were comparatively analysed (air, carbon dioxide and water steam).

Regeneration results improved in the sequence air < CO2 < steam; steam activation almost removed all the adsorbate adsorbed on the carbon, achieving regeneration efficiency values up to 94% for N2 adsorption, and above 100% for PNP adsorption. The activation process did not cause a significant modification of the pore size distribution of the adsorbents, which remained microporous irrespective of the activating agent.

The analysis of gases evolved was consistent with the chemical processes involved in the respective activations. There was a significant difference in the pattern followed by H2 in steam activations compared with CO2 and air. The prominence of water gas and water gas shift reactions were associated to this effect, which was also evident from the increase in CO and CO2 concentration.