Separation of vitamin E from palm fatty acid distillate using silica: II: Kinetics of batch adsorption Original Research Article

The kinetics of vitamin E batch adsorption onto silica was detailed in this study; as functions of initial vitamin E concentration, reaction temperature, agitation rate and silica mass. For all systems, the adsorption occurred rapidly initially and then proceeded gradually to equilibrium in about 5 min. It was found that the fraction of vitamin E adsorbed onto the silica at equilibrium was higher when the initial vitamin E concentration in the solution was lower. However, the reverse was true for the effects of agitation rate and silica mass. Increasing the reaction temperature would result in lower adsorption capacity, suggesting that adsorption of vitamin E onto silica was exothermic in nature. Two main adsorption mechanisms were involved during the vitamin E adsorption, namely external mass transfer and intraparticle diffusion. The external mass transfer coefficient, kf, and rate constant of intraparticle diffusion, kid, were determined for each system. It was noted that increasing the initial vitamin E concentration resulted in a decrease in kf values, but an increase in kid values. Increase in agitation rate facilitated the adsorption processes and therefore increased both kf and kid values. Meanwhile, a higher silica mass gave a lower kid value, indicating that the intraparticle diffusion rate was lower. The activation energies were considered high (−25.45 and −54.13 kJ mol−1 for external mass transfer and intrapartiele diffusion, respectively) suggesting that the adsorption appeared to be a chemosorption rather than low energy physiosorption process.