Adsorption isotherms of aspartame on commercial and chemically modified divinylbenzene-styrene resins at different temperatures

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) degreesC. 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 degreesC, 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.