Two stage thermal regeneration of exhausted activated carbons. Steam gasification of effluents

This work studies the thermal regeneration of p-nitrophenol exhausted activated carbons by a novel method in which two reactors are connected in series in order to minimize the emission of the hazardous adsorbate and other heavy hydrocarbon molecules to the environment. For this task, previous one-stage runs were made, in which the ACs were thermally treated, studying the influence of heating rate and temperature on: (a) the final porosity properties of regenerated ACs, as well as the regeneration efficiency, and (b) the gas profiles (H-2, CO and CO2) evolved during the process. It was found that these compounds were mainly released at high temperatures (above 450 degrees C), corresponding to the removal of the carbon surface functional groups and/or cracking of chemisorbed products. The use of a second reactor gave rise to a significant modification in the gas patterns, in comparison with one step experiments. H-2, CO and CO2 where identified at higher quantities and their emission started at lower temperatures. These results allowed to conclude that the use of this additional gas treatment promotes the steam cracking of the physisorbed p-nitrophenol molecule, which is removed during the first stages of the regeneration process. (c) 2012 Elsevier B.V. All rights reserved.