Adsorption of phenol and chlorophenols onto granular activated carbon and their desorption by supercritical CO2

BACKGROUND: The adsorption and desorption of phenol, 2-chlorophenol (2-CPh), 4-chlorophenol (4-CPh) and 2,4-dichlorophenol (2,4-DCPh) were carried out using granular activated carbon (GAC) as adsorbent and supercritical CO2 as regenerant. Adsorption studies at three different temperatures were fitted by using two thermodynamic adsorption models, Langmuir and Toth. The GAC regeneration by CO2 at four different pressures and two temperatures was studied and the design basic parameters were found. RESULTS: The Toth model fitted the experimental data better and thermodynamic properties indicated that this adsorption process was spontaneous, feasible and exothermic. Values of standard enthalpy lower than 40 kJ mol(-1) confirmed that adsorption processes were carried out by physical adsorption. It was also observed that the higher the pressure the higher the regeneration efficiency due to the increase in solvent density. CONCLUSION: GAC presented high selectivity for these substituted phenols and the order of adsorption was 2,4-DCPh > 4-CPh > 2CPh > phenol. Supercritical technology was able to regenerate the exhausted GAC, achieving yields comparable with those exhibited by traditional technologies but avoiding additional separation processes. The effective diffusivities of phenols followed the order phenol > 2-CPh congruent to 4-CPh > 2,4-DCPh. (C) 2013 Society of Chemical Industry