Aqueous thermal desorption as an effective way to regenerate spent activated carbons

• Regeneration of PNP loaded AC by means of aqueous thermal desorption was studied.
• Desorption kinetics was analyzed by applying non-linear Lagergren model.
• Porosity regain results were related to desorption data.
• Temperature only exerted a significant influence on desorption kinetics in the range 140–180 °C.
• Irreversibility of adsorption was confirmed from N2 and PNP adsorption analyses.

This work deals with the regeneration of p-Nitrophenol (PNP) loaded Activated Carbons by means of aqueous thermal desorption.Continuous desorption experiments were performed under different temperature (140–200 °C) and stirring (100–600 rpm) conditions. The study was made with a double point of view; firstly, desorption kinetics was analyzed by applying non-linear Lagergren model. Secondly, the improvements on the textural parameters of the regenerated adsorbents as well as the regeneration efficiency were evaluated.The results obtained revealed that the final amount of PNP desorbed was temperature dependent in the range 140–180 °C, while no improvement was found for higher temperatures, independently of the stirring speed. Likewise, temperature did not exert a marked effect on desorption kinetics.The irreversibility of the adsorption processes was confirmed from N2 and PNP adsorption analyses, although some differences were found. It is worth mentioning that increasing temperature did have a relevant influence on the adsorption regain of the adsorbents, being maximum for 200 °C (N2 and PNP adsorption efficiency values up to 61% and 80%, respectively). This might be attributed to the occurrence of some activating effect induced by water under these conditions. The study of the prevalence of desorption over adsorption for enhanced temperature was complemented by the development of an Arrhenius-based model.

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