Application of an effective diffusion model to the adsorption of Aspartame on functionalised divinylbenzene-styrene macroporous resins

The adsorption kinetics of Aspartame on four different divinylbenzene-styrene macroporous resins has been studied in a batch stirred tank at several temperatures. The adsorbents were Amberlite XAD-2 and the following three functionalised resins synthesised by chemical modification of the commercial one: brominated (XAD-2-Br), bromoethylated (XAD-2-CH2-CH2-Br), and chloromethylated (XAD-2-CH2-Cl). With respect to the original Amberlite XAD-2, both the bromoethylated and the chloromethylated resins showed a significant improvement in the adsorption capacity over the whole range of temperature studied. A mathematical model was used to fit the experimental adsorption uptake curves. The model accounted for an effective intraparticle diffusion coefficient whose value was due to two parallel mechanism contributions to the overall intraparticle mass-transfer flux, that is, pore and surface diffusion. The relative contribution of the surface diffusion mechanism decreased as temperature increased in the range 5-25 degreesC for all the systems studied. The different contribution to mass-transfer of both surface and pore diffusion observed in the modified resins was due to the modification of the interaction strength and mechanism between Aspartame and the adsorbent surface and to the modification in the physicochemical characterisation of the adsorbents after the functionalisation process. The chloromethylated resin exhibited the largest enhancement in intraparticle mass-transfer due to surface diffusion amongst all the modified resins. (C) 2003 Elsevier Science Ltd. All rights reserved.