Kinetics of selective adsorption of impurities from a crude vegetable oil in hexane to activated earths and carbons

In this study, the selective removal of several impurities (chlorophylls an d pheophytins, carotenoids, free fatty acids and oxidation products) from a solution of crude olive residue oil in n-hexane (miscella) by batch adsorp tion to different materials was investigated. The following adsorbents were tested: activated diatomaceous earths, powdered and granulated activated c arbons. For the majority of the adsorbents used, both Freundlich and Langmu ir isotherm models showed a good fit to the adsorption of pigments, free fa tty acids (FFA), conjugated hydroperoxides (HP), and final oxidation produc ts (FOP). Sigmoid profiles were observed for the adsorption of chlorophylls , carotenoids, and FOP to the 20-60 mesh carbon, suggesting the presence of pores in the intermediate range (2-50 nm). The FFA isotherm adsorption to the 8-20 mesh carbon can be explained by a multilayer adsorption phenomenon . On the basis of the estimated values for affinity and separation factors, t he selective adsorption occurred in the following order for every adsorbent tested: chlorophylls and pheophytins>carotenoids>hydroperoxides>final oxid ation products>free fatty acids. The highest adsorption efficiency was obse rved for the powdered activated carbon.