Comparative Adsorption of Phenol, P-Nitrophenol and P-Hydroxybenzoic Acid on Activated Carbon

Adsorption isotherms of phenol, p-nitrophenol and p-hydroxybenzoic acid at three temperatures in the range 1–40° C on activated carbon have been obtained experimentally. Curve fitting to several theoretical equations shows that the Prausnitz equation gives the lowest deviations (1–3%). An inversion of the adsorption capacity of phenol with temperature has been observed, probably as a consequence of the high microporosity of the carbon and the restricted accessibility of phenol to the smaller pores. Adsorption at 40°C is also accompanied by the degradation of phenol by aerobic micro-organisms (ficomicetus-type fungi). Approximate values of the isosteric heats of adsorption of p-nitrophenol have been calculated, being in the range 5.8–6.5 kcal/mol. Differences in the behaviour of the three adsorbates are commented upon in terms of their physicochemical properties.