Adsorption isotherm and kinetics modeling of carotene and free fatty acids adsorption from palm oil onto montmorillonite

Adsorption of carotene and free fatty acid from palm oil onto raw and activated montmorillonite clay has been studied. Acid activation lead to the leaching of exchange cations (Ca2+, K+, Na+, Mg2+) and of ferric ions (Fe3+). Acid activated clay has better carotene and free fatty acid adsorption capacities than raw clay. However, leaching of clay with high concentrated acid solution reduced its adsorption efficiency. The amount of carotene adsorbed per gram of adsorbent also increased with temperature, notwithstanding the acid treatment of clay. The kinetics of carotene and free fatty acid were best described by pseudo-second order and intraparticle diffusion models. The activation energies obtained by applying Arrhenius equation to the pseudo-second order kinetic constant were all lower than 24 kJ.mol-1. It was concluded that there are different types of adsorption sites for carotene adsorption as the adsorption isotherms did not fit Langmuir equation, but they fit very well Freundlich and Temkin models. These observations were also valid for free fatty acids adsorption. The small values of Freundlich constant n, and of Temkin constant B, show the loose bonding of carotene and free fatty acids on clay surface. Hence the adsorption of these 2 compounds is a physisorption.