Batch desorption experiments of vitamin E from silica were carried out to study the effects of reaction temperature and agitation rate on the kinetics and equilibrium of desorption. For all systems, it was found that vitamin E desorbed rapidly in the early stages, followed by a much slower release. The two distinct desorption rates might be due to the heterogeneities of the adsorbing surfaces. A first-order two-component four-parameter model described the desorption kinetics well with a coefficient of determination, R2of >0.97. The rate constants for rapid (krap) and slow (kslow) desorption ranging from 0.51 to 2.23 min-1and from 0.01 to 0.14 min-1, respectively, depending on reaction temperature and agitation rate. It was found that the krapvalue increased with increase in reaction temperature, indicating that desorption of vitamin E from silica was endothermic in nature. The desorption rate also increased with increase in agitation rate. Activation energies for the rapid and slow desorption were 38.64 and 73.08 kJmol-1, respectively. It was found that the desorption isotherm can be fitted by the Fruendlich model. Percentage recovery of vitamin E from silica ranged from 70.36% to 98.74%, depending on the experimental variables. The results from this study provided useful information for achieving high recovery of vitamin E during its separation using an adsorption method. © 2003 Elsevier Ltd. All rights reserved.
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