Adsorption Isotherms of Aspartame on Commercial and Chemically Modified Divinylbenzene−Styrene Resins at Different Temperatures

Abstract

The equilibria of adsorption of aspartame in an aqueous solution on a commercial resin and three chemically modified Amberlite XAD-2 resins were measured at different temperatures within the range (0 to 35) °C. The functional groups, introduced by nucleophilic substitution in the aromatic rings of the divinylbenzene−styrene matrix, were bromine (−Br), bromoethyl (−CH2CH2Br), and chloromethyl (−CH2Cl). All of the isotherms showed a nonlinear and favorable shape with decreasing adsorption capacity as the temperature increased. The chloromethylated resin, and, to a lesser degree, the bromoethylated resin, increased the adsorption capacity for aspartame compared to Amberlite XAD-2. At 35 °C, the chloromethyl resin showed up to a 280% higher saturation capacity than the commercial adsorbent. The experimental equilibrium data were fitted to the Langmuir, Freundlich, Langmuir−Freundlich, Redlich−Peterson, and Toth models. Toth and Langmuir−Freundlich isotherms provided very good fittings for all of the resins over the temperature range studied, whereas the Langmuir and Redlich−Peterson equations were less accurate, although the average errors were, in general, below 10% with respect to the measured values.