Separation of vitamin E from palm fatty acid distillate using silica: I. Equilibrium of batch adsorption

In this study, vitamin E was separated from palm fatty acid distillate by batch adsorption using an orbital shaker. Silica was used as the adsorbent. Equilibrium of the adsorption process as a function of reaction temperature, agitation rate and silica mass on vitamin E adsorption onto silica was investigated over a range of vitamin E concentration. Lower reaction temperature led to higher vitamin E uptake at equilibrium, indicating that the adsorption process in this study was exothermic. Adsorption capacity increased with the rise in agitation rate. However, in this study the maximum adsorption capacity remained unchanged when silica mass was increased. Generally, non-linear regression analysis showed that the Redlich-Peterson and Langmuir isotherm models described the equilibrium data reasonably well (coefficient of determination, R-2 > 0.90 in most cases). The Freundlich model, however, was found to be relatively poor (R-2 < 0.90 in most cases) for explaining the adsorption equilibrium in this study. Thermodynamic parameters of the adsorption further confirmed the exothermic nature of the adsorption process as did the negative heat of enthalpy, accompanied by a negative value of entropy change. The overall Gibbs free energy change during the adsorption process was negative for the experimental range of temperatures, corresponding to spontaneous adsorption. (C) 2003 Elsevier Ltd. All rights reserved.